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Tracing the origin of lithium in Li-ion batteries using lithium isotopes

Rechargeable lithium-ion batteries (LIB) play a key role in the energy transition towards clean energy, powering electric vehicles, storing energy on renewable grids, and helping to cut emissions from transportation and energy sectors. Lithium (Li) demand is estimated to increase considerably in the near future, due to the growing need for clean-energy technologies. The corollary is that consumer expectations will also grow in terms of guarantees on the origin of Li and the efforts made to reduce the environmental and social impact potentially associated with its extraction. Today, the LIB-industry supply chain is very complex, making it difficult for end users to ensure that Li comes from environmentally and responsible sources. Using an innovative geochemical approach based on the analysis of Li isotopes of raw and processed materials, we show that Li isotope ‘fingerprints’ are a useful tool for determining the origin of lithium in LIB. This sets the stage for a new method ensuring the certification of Li in LIB.


Lithium, hyped as the “white oil” (petróleo blanco) or the “white gold” of the 21st century, owes its outstanding economic success to its key role in the energy transition 1. Historically, lithium has found wide use in ceramic, glass, steel, and chemical industries, as well as in medicine for treating bipolar disorders. Recently, however, the lithium market has become dominated by Li salts used in rechargeable batteries, which now consume ~65% of all lithium 2.

Lithium-ion battery (LIB) is the term used for a battery composed of multiple electrochemical cells, each of which has a lithium-metal-oxide-based positive electrode (cathode) and a negative electrode (anode, typically graphitic carbon active material), electronically separated by a thin porous plastic film (i.e., separator) which contains the non-aqueous electrolyte solution (general comprising LiPF6 as salt and organic carbonates as solvents), and electronic current collectors (general Cu at the anode and Al at the cathode) that connect the electrochemical cell to an external circuit containing the load to be powered.

LIBs are widely used in portable electronic devices (tablets and mobile phones), and increasingly in cordless electric tools, transportation applications (hybrid and electric vehicles, electric scooters, e-bikes), and stationary power storage for intermittent energy sources (solar or wind). Electrification of transport is becoming a top priority as part of the transition to a low-carbon future, in particular, to meet the targets of the Paris climate agreement of reducing carbon emissions by more than a third by 2030 1. Several recent government initiatives incentivise or even compel car owners to switch to electric: Norway will ban the sale of petrol-powered cars by 2025, while the United Kingdom, Ireland, Germany and the Netherlands plan to do the same by 2030, and France by 2040 3. The recent EU plan for tackling global heating proposes banning new internal-combustion engines by 2035 4. The demand for lithium thus will continue to rise as long as LIBs are the primary power source for electric vehicles (EV). The annual quantity of lithium required should increase by a factor of 44 by 2030 (considering a hypothesis of 0.8 million tons of lithium carbonate in 2030) compared to 2017 production volumes, to satisfy further needs in the mobility sector 5.

Commercial LIB currently uses various cathode compositions including ~5–10% of lithium 6 obtained from lithium salts (lithium carbonate or lithium hydroxide), and different ratios of other metals. The electrolyte, composed of lithium hexafluorophosphate (LiPF6) diluted in solvent (LiPF6/1 mol/L), contains a negligible quantity of lithium compared to the cathode material. High-nickel cathode compounds, in particular lithium-nickel-manganese-cobalt oxide (Li(NiMnCo)O2 or NMC), are the most-used cathode materials today for EV applications and stationary storage 6. First-generation LIB cathodes contained nickel-manganese-cobalt in the proportion of 1:1:1 (often identified in industry jargon as NMC111 or NMC333). In order to increase energy density, the Ni:Mn:Co ratio has gradually shifted from 1:1:1 to 5:3:2 to 6:2:2 to 8:1:1 to reduce the amount of Co required 7. Increasing adoption of higher-nickel cathode compounds has led to greater use of lithium hydroxide, leading to higher-quality cathode materials with a better cycle life and energy density 8. According to earlier studies 6,9. NMC cathodes will represent between 60 and 90% of annual battery demand by 2030, the other battery cathode types being NCA (nickel-cobalt-aluminium) and LFP (lithium-iron-phosphate). In coming years, the main LIB cathode evolution will concern the presence and quantities of cobalt, nickel, manganese, aluminium (NCA batteries) or phosphorus (LFP), but lithium will remain an indispensable component.

From a lithium viewpoint, the LIB manufacturing supply chain is complex and separated into many stages, including mining, extractive and refining metallurgy, cathode active material synthesis, battery-cell manufacturing, and battery-pack assembly, which commonly are completed in different locations and countries.

Most mineral reserves occur in Chile (44%), Australia (22%), Argentina (9%), China (7%), and several other countries accounting for the remaining 18% 10. Lithium resources are primarily divided into three categories 11 : (1) Brine is the main source of lithium with close to 60% of the global identified reserves. Among the brines, salars in the “lithium triangle” of Bolivia, Argentina, Chile, and in Qinghai province and the Tibetan region of China, hold most of the lithium-brine reserves. (2) Hard-rock lithium resources, i.e., lithium-rich pegmatite is the second source by the amount of available lithium. Recent estimates account pegmatites for ~30% of identified lithium reserves. Among the minerals containing lithium in pegmatites, spodumene (LiAlSi2O6) is the primary economic mineral 12. Lithium hard-rock reserves are distributed around the world, the largest spodumene deposits occurring in Australia with major deposits in Canada and China 10. (3) Sediment-hosted deposits (sometimes erroneously generalised as “clay”) are the third source, representing less than 3% of global lithium resources. They consist of hectorite (McDermitt, USA, and Sonora, Mexico) and jadarite (Jadar, Serbia). Producing lithium from this source has so far proven difficult and costly, and hitherto no company has been able to produce commercial quantities from such deposits. In 2020, almost half (47%) of global lithium production came from Australian hard-rock deposits. Other main suppliers were Chile (21%), China (17%), Argentina (7%) and a group of countries including Zimbabwe, USA, Brazil and Portugal (7%) 10.

After mining, the next step in the supply chain is extractive and refining metallurgy, the processing and purification that transforms raw materials into high-purity lithium hydroxide or.carbonate. The world’s lithium-refining capacity is concentrated in China, which supplies over half (53%) of global lithium salts, including most lithium hard-rock production 13. whereas Chile (33%) and Argentina (11%) dominate refined lithium capacity from brine operations 8.

The production of cathode active materials, the manufacturing of battery cells, and the assembly of battery packs as the final product, are the other steps in the LIB supply chain. The lithium-metal oxide for the cathode active material is mostly produced by speciality chemicals companies in China, Japan and South Korea, which deliver 86% of active material 14. China is also a major player in Li-ion cell manufacturing with 66% of global cell production, other suppliers being South Korea and the United States, with 13% each 13. For EVs, manufacturers design battery packs for specific models, and tend to assemble them near the vehicle assembly plant because of the cost of transporting the large and heavy battery packs 15. China is the largest battery producer for EVs, followed by the United States and Germany 5.

The LIB life cycle does not stop there, and supplementary stages can take place. After the use in EVs, LIB life can be extended by repurposing them for less demanding applications, such as energy storage 14. Even if this is not cost-effective today compared to primary resources, the lithium contained in battery cells can be recycled and reused for manufacturing new cathodes.

Another complication in the supply chain of the LIB industry is the fact that every consumer company deals with several suppliers, each of which can deal with multiple sub-suppliers in various countries. For instance, to supply a substantial portion of its lithium needs, the American company Tesla has signed contracts directly with Ganfeng Lithium, a Chinese lithium mining and refining company (see Methods section), which has several subsidiaries involved in the lithium industry in Australia, China, Argentina, Mexico and Ireland 16. The contract gives Tesla assured access to lithium, but in practice, the raw material passes through many other companies and processing steps before it makes it into a car. Panasonic and CATL, which assemble battery cells for Tesla, source cathode active material from various chemicals companies (Sumitomo, BASF Toda, Beijing Easpring, Ecopro, Johnson Matthey) 17. which themselves buy lithium from various refining and mining companies.

Because of this complex supply chain, ensuring that raw materials come from socially and environmentally responsible sources with a low-carbon footprint, is a complicated puzzle for end users. Although the lithium supply chain today is less problematic in terms of social and environmental risks than other battery metals, such as cobalt, lithium can be associated with various environmental and social impacts. With the increasing demand for lithium, the environmental and social impacts of mining tend to increase.

In Argentina, indigenous communities report that lithium operations on their lands threaten their survival and the exercise of their rights 18. In Zimbabwe, where lithium exploitation is currently low (1%) 10. the illicit financial flow has already been identified in the lithium mining sector 19. A recent study 20 on the life-cycle water-scarcity footprint showed that water use associated with lithium-brine mining in Chile and China, mainly through evaporative loss, can create a high risk of natural freshwater scarcity for humans and nature.

According to a comparative Life Cycle Assessment 21 between EV batteries with hard-rock or brine-based lithium, the environmental impact of hard-rock lithium processing, dominated by traditional sulphuric acid processing and melting of the rock, is higher in terms of acidification and global warming potential. A recent study showed that the CO2 equivalent emissions from hard-rock lithium hydroxide production in Australia and refining in China are up to three times higher than those from brine production in Chile and Argentina 22. Another recent study, based on Life-Cycle Analyses of battery-grade lithium salts produced from Chilean brine and from Australian spodumene processed in China, showed that the production of Li salts from brine-based lithium had less life-cycle greenhouse-gas emissions and freshwater consumption than lithium salts from rock-based lithium resources 23.

Major car manufacturers like BMW group, Tesla, and Volvo recently announced that they will increase the transparency of their supply chains for EV batteries, and ensure responsible and sustainable sourcing of raw materials 24,25. Some companies (BASF, Volkswagen, Fairphone) have started a partnership for sustainable lithium mining in Chile 26. Carmakers also explore the usefulness of blockchains for improving the scrutiny of supply chains. A blockchain is the control of chain-of-custody systems, based on the shipping documentation that is included in online databases, to allow real-time raw materials tracking and electronic tagging. However, document-based traceability systems can be falsified, and must be independently controlled and audited to provide credibility 27.

We propose here an innovative geochemical approach based on analytical fingerprints of lithium isotopes of raw and processed materials, to ensure the traceability of lithium in LIBs. This method helps verify and audit the blockchain, thus ensuring its control. It was developed for the coltan supply chain 28 and, more recently, for native gold from French Guiana 29. Lithium (Li) has two stable isotopes, 6 Li and 7 Li, with relative abundances of 7.6% and 92.4%, respectively. The Li isotope compositions (δ 7 Li) are reported as a classical δ-notation (parts-per-thousand, ‰) with the 7 Li/ 6 Li ratio relative to standard lithium (L-SVEC) 30 : δ 7 Li = [( 7 Li/ 6 Li)sample/( 7 Li/ 6 Li)standard – 1] × 1000. The wide range of Li isotopic compositions in natural samples, between −15‰ and 45‰ 31. provides a strong incentive for using δ 7 Li values as a tool to ensure the traceability of lithium in LIB.

We first discuss the variability of Li isotope compositions between lithium deposits and in coexisting ores. The effects of extractive and refining metallurgy, cathode active materials synthesis and battery manufacturing on the intrinsic signatures of ores are then analysed and discussed. Finally, we discuss how Li isotope compositions can be used for ensuring the traceability and certification of lithium in LIBs.

Results and discussion

The samples and analytical techniques we used are described hereafter under Methods. Figure 1 shows the samples analysed in this study with a known provenance. Supporting information is provided in Supplementary Figs. 1 and 2, Supplementary notes and the data are listed in Supplementary Tables 1 and 2.

Isotope variability between lithium deposits and among coexisting ores

Li isotope compositions of major deposits in China, Chile, Argentina, Bolivia and Australia were taken from previous studies 32,33,34,35,36,37,38,39,40,41 (Fig. 2). Their distribution in natural samples (spodumenes and brines) is shown in Supplementary Fig. 1.

For brines in South American salars in the “lithium triangle” of Bolivia (Salar de Uyuni), Argentina (Salar del Hombre Muerto, Salar de Olaroz, Salar de Ratones, Salar de Centenario, Salar de Pozuelos) and Chile (Salar de Atacama, Salar Grande, Salar de las Parinas, Salar de la Isla, Salar de Pedernales), the interquartile range (IQR) of Li isotope compositions is from 7.9 to 11.3‰ with a median value of 9.8‰ (n = 103) 35,36,37,38,39,40. For brines of the Qaidam Basin in China, the IQR of Li isotope compositions is between 16.1 and 31.4‰ with a median value of 24.3‰ (n = 20) 41. The origin of the lithium in brine is variously explained by low-temperature rock weathering, hydrothermal leaching, or magmatic origin with subsequent evaporation. In such deposits, dissolved lithium is commonly complexed with chloride as a LiCl species 42. General theoretical considerations suggest that the lower coordination states and bond lengths should prefer the heavy isotope 43. At ambient P-T conditions, the four-fold coordination [Li(H2O)4] is the main cluster in aqueous fluids, whereas the coordination of Li in most solids is higher 31,44. Li isotope fractionation in fluid–rock interactions, in particular rock weathering, results in preferential fractionation of the heaviest isotope ( 7 Li) into fluids with a magnitude inversely correlated to temperature 31,45. This behaviour is consistent with low-temperature leaching experiments on tuff, yielding leachate that is 5‰ enriched in 7 Li relative to whole-rock Li 36. over, the Li isotope compositions of brines are also controlled by the incorporation of Li into secondary minerals, such as clays, removing the lightest isotope ( 6 Li) from the solution and enriching water in 7 Li (until 10‰) 31. Thus, the Li isotope compositions of brines result from the mixing of waters derived from various rock reservoirs 46 and from fluid–rock interactions at different temperatures. The enrichment of dissolved Li is consistent with literature data, which showed that δ 7 Li values of South American brines (Bolivia, Argentina, Chile) (7.9 to 11.3‰, n = 103, IQR) and China brines (16.1 to 31.4‰, n = 20, IQR) are generally higher than upper continental crust (UCC) values (0 ± 4‰, 2σ) 31 (Fig. 2). While δ 7 Li values of brines from the Qaidam Basin (China) are marked by strong enrichment (16.1 to 31.4‰, n = 20, IQR) compared to South American “lithium triangle” brines (7.9 to 11.3‰, n = 103, IQR), the variability of δ 7 Li values in the latter brines is considerably greater than their differences (Fig. 2, Fig. S1).

For spodumenes in Australia (Yilgarn and Pilbara cratons) and China (West Kunlun), the IQR of Li isotope compositions is between −0.3 and 6.0‰, a median value of 2.8‰ (n = 20) 32,33,34. The hard-rock deposits, mostly Li-rich granitic pegmatite, are interpreted as the product of fractional crystallisation from a parental granitic melt. Lithium is a major element in various minerals, such as amblygonite, bikitaite, eucryptite, lithiophilite, lithiophosphate, montebrasite, spodumene, and petalite in Li-rich granitic pegmatites. Among them, spodumene is the most exploited on a commercial scale 12. Experiments and ab initio density functional perturbation theory (DFT) calculations, showed that, during pegmatite crystallisation, 6 Li preferentially occupies octahedral sites in spodumene, while 7 Li favours tetrahedral sites in granitic melt 44,47. The ab initio calculations by Liu et al. 48 predicted that Li isotope fractionation in Li-rich minerals has a notable linear correlation with the average Li-O bond lengths and Li coordination numbers; they demonstrated that the δ 7 Li values in minerals formed at the same crystallisation stage from a pegmatite melt in the order petalitelithiophosphatebikitaiteeucryptitemontebrasiteamblygonitelithiophilitespodumene. Therefore, in Li-rich granitic pegmatites, the δ 7 Li values of spodumene are lower than those of petalite. This isotope depletion in spodumene is confirmed by literature data, which showed that δ 7 Li values of spodumene in major deposits in Australia and China are, in contrast to salars, in the same order of magnitude (−0.3 to 6.0‰, n = 20, IQR) as UCC values (0 ± 4‰, 2σ) 31 (Fig. 2). While Li isotope compositions of spodumene from West Kunlun (China) are depleted in heavy isotopes (−1.3 to 1.4‰, n = 8, IQR) compared to Australian spodumene (3.8 and 9‰, n = 12, IQR), the variability of δ 7 Li values within Australian deposits (Yilgarn and Pilbara cratons) is more important than the differences between them.

The Li isotope composition of lithium deposits is linked to the physico-chemical conditions of ore-forming processes and varies within several tens of parts-per-thousand (Fig. 2). The different genesis of (supergene) salars and (magmatic) hard-rock deposits explains why δ 7 Li values of brines are generally higher (7.9 to 11.3‰, n = 103, IQR and 16.1 to 31.4‰, n = 20, IQR) than those of spodumene deposits (−0.3 to 6.0‰, n = 20, IQR). This variation in δ 7 Li values could discriminate a salar from a spodumene origin (see discussion below), but also between deposits of the same type (Australia versus China for hard-rock, South America versus China for salars).

Effects of extractive and refining metallurgy, cathode active materials synthesis, and battery-cell manufacturing

The concentrating, extracting, or processing of the lithium contained in ore deposits will affect their δ 7 Li value. In particular industrial processes, involving chemical transformation with kinetic isotope effects and low-recovery-yield/high-lithium-loss, can induce significant isotope fractionation between industrial and natural samples. The LIB production chain includes several industrial processes: (i) The hard-rock extractive metallurgy process starts with producing a spodumene concentrate, increasing the lithium content by separating undesirable minerals from ore through physical separation (comminution, flotation and magnetic separation) 49. The concentrate is then calcined at 1000 °C, causing the restructuring of α-spodumene to β-spodumene which is readily dissolved in acid 50. The traditional sulphuric acid process was the first to efficiently extract lithium from spodumene in the 1950s (85–90% lithium yield at the time) and was scaled-up shortly after (yield over 90%) 11,12. In this process, the roasted β-spodumene is leached with sulphuric acid and mixed with sodium carbonate to precipitate lithium carbonate. A last step, adding calcium hydroxide, can be used for obtaining lithium hydroxide from lithium carbonate 50. The material used as isotope standard, Li carbonate L-SVEC, was purchased from Lithium Corporation of America (or American Lithium) 30. prepared from Li ore (mostly spodumene) from Foote Mine (Kings Mountain, North Carolina, USA) using traditional extraction with sulphuric acid leaching Grégoire et al. 51 showed that the Foote Mine ore and the derived carbonate have a similar Li isotope signature taking into account analytical uncertainty, indicating that the sulphuric acid process does not cause Li isotope fractionation. As an alternative to the traditional process discussed above, Outotec and Keliber of Finland announced in early 2019 a new process, totally sulphate and acid-free, for producing lithium hydroxide directly from calcined β-spodumene 52. After calcination, two-stage alkaline leaching (pressure- and conversion leaching) produces a hydroxide solution and analcime (NaAlSi2O6.H2O). The overall lithium-leaching extraction yield from concentrate is 84–94% 52. The typical lithium-processing impurities Fe, Al, Ca, Mg and P are then removed from the solution by cation-exchange resins with iminodiacetate or aminophosphonate (ion-exchange purification). Finally, LiOH ⋅ H2O is solidified by pre-concentration and vacuum crystallisation. Figure 3 shows the spodumene concentrate, β-spodumene, analcime and Li hydroxide samples provided by Keliber. In contrast with the American Lithium product, the Finnish samples show strong fractionation between spodumene concentrate and the produced Li hydroxide (Δ 7 Lihydroxide-spodumene concentrate = 5.5‰). Calcination does not cause isotopic fractionation, as spodumene concentrate and β-spodumene have the same lithium isotopic signature (Fig. 3). Concerning the leaching step, we can estimate the Li composition of the product with a Rayleigh model (Supplementary Fig. 2). Using the starting composition of δ 7 Li in ores (1.1‰), the δ 7 Li of the analcime by-product (−0.9‰) and the lithium-leaching extraction yield given by Keliber (84% to 94%), the estimated δ 7 Li values are between 1.3 and 1.5 ‰ for Li in solution (Fig. 3). This shows that leaching does not lead to significant Li isotope fractionation (Δ 7 LiLi-β-concentrate 0.2 to 0.4‰). Concerning ion-exchange purification, strong Li isotope fractionation occurs during ion-exchange chromatography 53. The heavy 7 Li isotope passes more rapidly through the exchange resin than 6 Li, requiring a 100% yield to avoid isotopic fractionation in the eluent during Li chemical preparation 31 (see Methods, hereafter). We carried out laboratory experiments for estimating the fractionation factor between Li and purified Li (eluent) due to purification by cation-exchange resins (see Supplementary note for more details). These experiments showed that even a 95% yield causes strong fractionation between Li and purified Li (Δ 7 Li purified Li-Li 8‰). Concerning the crystallisation process, due to no change in the coordination number between Li in aqueous solution and Li hydroxide monohydrate (both tetrahedrally coordinated sites) 54. this is not expected to result in significant Li isotope fractionation.

(ii) The salar extractive metallurgy, i.e. lithium production from brine, depends on its composition, volume and accessibility, as well as on its amenability to local processing 49. At Salar de Atacama (Chile) and Salar de Olaroz (Argentina), the processing flow sheet used by the Rockwood, SQM and Orocobre companies is referred to as the ‘Silver Peak’ method, where it was first developed in Nevada (USA) by Foote Mineral in 1960s 50. Brines are pumped to the surface to be concentrated by solar evaporation in ponds. This concentration causes precipitation of sodium, potassium and magnesium chlorides 50. In addition, at Salar del Hombre Muerto (Argentina), lithium brine is first concentrated by ion absorption onto polycrystalline alumina before solar evaporation 50. However, heavy Li loss is observed due to evaporated brine caught in salts precipitated during evaporation, and the maximum recovery of Li from evaporation is ~80% 55. Concentrated brine is then transferred to processing facilities where reagents are added to remove impurities and to produce lithium compounds via precipitation/crystallisation 50. In the SQM process, the Salar de Atacama brine is drained from the evaporation ponds once lithium concentration in the brine reaches ~6% Li, or the saturation point of lithium chloride, and transported to the Salar del Carmen plant via truck 50. The brines undergo solvent extraction to remove boron, and soda ash is added to precipitate and filter out magnesium carbonate. Then, the concentrated brine is heated and reacted with additional soda ash to precipitate lithium carbonate, which is filtered, washed and dried in a rotary drier 50. As a final step, the Li carbonate can be converted to Li hydroxide by adding calcium hydroxide. For the European market, this last stage takes place at processing plants in Russia 50. The process used by Leverton on Salar de Atacama brines is not described in the literature and Leverton does not disclose its processing information. However, the δ 7 Li values of the carbonate and hydroxide produced by SQM and Leverton from Salar de Atacama brines are close to each other (Δ 7 LiSQM-Leverton 1.0 to 1.4‰), indicating that the metallurgical processes used can be similar. The δ 7 Li value of the carbonate produced in Argentina (7.4‰) is slightly lower than literature data for brines from Salar del Hombre Muerto, Salar de Olaroz, Salar de Ratones and Salar de Pozuelos (7.6 to 11.3‰, n = 58, IQR). The δ 7 Li values of the Li carbonate (11.9 to 13.3‰) and hydroxide (12.7 to 13.7‰) produced by Leverton and SQM from Salar de Atacama brines are slightly higher than those of the Salar de Atacama brines determined in previous studies (9.6 to 11.4‰, n = 36, IQR) (Fig. 3). This difference between natural samples and products may be either due to the fact that the literature data are not representative of brines exploited by salt producers, or to the fact that isotopic fractionation occurs during extraction, in particular during evaporation when Li losses are highest. This point shows the need for working in collaboration with salt producers to evaluate the significance of their products. The conversion of Li carbonate to Li hydroxide does not induce isotopic fractionation since the δ 7 Li values for these products are close for SQM and Leverton samples: Δ 7 Lihydroxide-carbonate 0.4 to 0.8‰ (Fig. 3). Please note that the δ 7 Li values are also close for the Li hydroxide and.carbonate produced by Tianqi Lithium (China) (Fig. 4), reinforcing the hypothesis that the conversion from carbonate to hydroxide does not alter the Li isotope signature.

(iii) The cathode active material synthesis. Producing batteries with a high energy density requires active materials with a high volume density. Coprecipitation synthesis is commonly used for producing dense lithium-layered oxide materials with spherical particles 56. In such a synthesis, a mix of nickel, cobalt, and manganese sulphates in appropriate amounts for producing the targeted NMC, is dissolved in water. This sulphate solution and an ammonium hydroxide solution are pumped together into a stirring tank reactor, with the addition of a sodium hydroxide solution for maintaining the reaction at basic pH. After an ageing period, the resulting precipitate is recovered by filtration. This first synthesis step leads to a mixed-metal hydroxide, which is then mixed with a lithium salt. The resulting powder is calcined at a high temperature to produce the active material (see Methods, hereafter, for more details on NMC622 and NMC811 synthesis). Figure 3 shows the δ 7 Li values for active materials (NMC622 and NMC811) synthetised from Li carbonate and hydroxide (Li01, Li13, Li17, Li18) for this study. Regardless of the type of NMC produced (NMC622 or NMC811) and the precursor used (Li hydroxide or Li carbonate), the δ 7 Li values of the precursor and the product are similar considering analytical uncertainty. Synthesis of active material does not induce significant isotopic fractionation between the lithium salt and the active material.

(iv) The battery-cell manufacturing. A cathode sheet consists of a current collector, typically aluminium foil, on which a fine powder of active material with polyvinylidene difluoride (PVDF) and carbon black is deposited on two sides. The battery-cell assembly consists of alternating anode-, separator- and cathode sheets in a cell pack, filled with electrolyte. As these steps do not involve any chemical transformation of the lithium contained in the active material, they cannot cause any significant isotopic fractionation between the active material and cathode sheet. The Li isotope compositions of different sheets of the same battery cell, whether covered or not by electrolyte, are similar when considering analytical uncertainty (Fig. 3). Such homogeneous composition indicates that a battery can be characterised by a single δ 7 Li value determined by a punctual analysis on a single sheet. The δ 7 Li value of this battery (10.4 ± 0.4‰, 2σ) is in the same value range as Korean LIBs (8.5‰, 2.4‰, 3.1‰, 12.6‰) analysed by a previous study evaluating the impact of anthropogenic input on lithium content in the environment 57.

In conclusion, other than the sulphuric acid process, the extraction and purification processes discussed above tend to increase the δ 7 Li value of the produced salt compared to its initial/natural Li isotope signature. The last, supplementary, step of the lithium transformation chain (conversion of Li carbonate to Li hydroxide) does not introduce isotope fractionation. The other stages of battery manufacture (cathode active material synthesis, battery-cell manufacturing) neither induce significant isotopic fractionation between the lithium salts and the end product, which has a homogenous Li isotope composition.

Assessing the geochemical traceability of lithium

Geochemical traceability is used to try and answer the question “What is the origin of unknown lithium?”, determining the origin (mine site, refining plant) of a material (ore, product) using measurable and quantifiable material properties. For that, materials must have measurable compositions/properties that differ depending on their geological genesis or manufacturing. The Li isotope compositions of lithium deposits are related to the physicochemical conditions of ore-forming processes; differences in their genesis lead to higher δ 7 Li values for brines (7.9 to 11.3‰ and 16.1 to 31.4‰) than for hard-rock deposits (−0.3 to 6.0‰). However, extraction and purification processes, other than the traditional sulphuric acid process, tend to modify the initial/natural signature by increasing the δ 7 Li values by up to 5.5‰. Though such process-related fractionation tends to erase the link of a sample to its geological origin, it can also serve to differentiate lithium salts produced from ores of similar origin, but for which the extraction process may have a different environmental or social impact. For example, this fractionation could discriminate lithium salts produced from spodumene using the traditional sulphuric acid process or using an alternative process without sulphuric acid, such as the Outotec and Keliber process.

Despite the uncertainty related to process-related isotopic enrichment and the lack of data on deposits, we can establish a first estimate of ranges of Li isotopic values for which the probability of the Li salt belonging to either hard-rock-based or brine-based lithium sources is high. This first estimation will be refined as more data are acquired on the different deposits and the various extraction processes. For δ 7 Li values below 6‰ (the third quartile of hard-rock data), the probability is high that the sample was obtained from hard-rock, whereas δ 7 Li values over 11.3‰ (the third quartile of “Li triangle” salars data, the values for the Chinese salar being even higher) indicate a sample probably obtained from brine. However, samples with δ 7 Li values value between 6‰ and 11.3‰ fall in the “unknown origin domain”. Considering samples of known deposits (Fig. 1), the three spodumene concentrates (North American Lithium, Sayona and Keliber) are within the “hard-rock domain” and the four Li salts from Atacama salar brines (Leverton and SQM) fall within the “salar domain” (Fig. 4). The Li hydroxide from Keliber and the Li carbonate from Argentina fall in the “unknown origin domain”. For the other salts, for which only the country of the last refining stage is known, there is a heterogeneity of the Li origin within the same country. For example, samples produced in Russia and the UK come from salars and hard-rock (Fig. 4). The Li carbonate of Ganfeng Lithium, which produces Li salts from Australian and Chinese spodumene concentrates, is in the “hard-rock domain”, while the products of Tianqi Lithium that has a more diversified supply (salar or spodumene), are in the “unknown origin domain”.

As we saw that the synthesis of active material and the manufacturing of battery cells do not induce significant isotopic fractionation, the ranges of Li isotopic values established above can be used as a first estimate for determining the origin of lithium in active materials and battery cathode sheets. The δ 7 Li values for active materials produced by TOB (China) are variable, including for materials produced in the same factory (NMC532 and NMC333) (Fig. 4). Except for the TOB active materials NMC622 (in the “hard-rock domain”) and NMC811 (in the “salar domain”), the other TOB samples and cathode sheets from the Korean battery maker fall in the “unknown origin domain”. These results show that the supply of lithium to the battery industry is based on economic criteria, with no preference for hard-rock- or brine-based lithium.

Though these results show that identifying the origin of an unknown lithium product is a challenging issue, the large diversity of Li isotopic signatures for secondary products demonstrates that δ 7 Li values, like a fingerprint, can be a useful tool for certifying the origin of lithium in LIB.

Towards a methodological approach for certifying a responsible and sustainable lithium supply chain

Our analytical method, based on lithium isotope fingerprints, can help controlling and certifying the origin and trade of lithium production. It is an independent, reliable and tamper-proof approach to auditing the document-based traceability system sought after by end-users (carmakers, consumer electronics companies, etc.), by answering the question: “Does the lithium correspond to its declared origin?”. Traded materials can be analysed to provide additional credibility to document-based traceability systems with due-diligence concepts for raw material supply chains. Implementation of a certification system for lithium will boost the development of a responsible, sustainable and stable supply of raw materials for batteries, guaranteeing the respect and protection of human rights and the conservation of the environment along the value chain. The development of lithium certification is of critical importance, especially in the context of the political will to re-industrialise battery production in Europe or in the US, which are defending sustainable battery manufacturing projects. Such certification would be in accordance with the recent EU regulation for responsible and sustainable sourcing of several other raw materials, such as tin, tantalum, tungsten and gold, and the consumers’ interest in sustainable products. The principle of this analytical method is the same as that used for the traceability of gold and coltan 28,29. which verifies whether the product corresponds to its declared origin by comparing the sample in question with reference samples of known origin stored in a database. As the Li isotopic signature is conserved from lithium salt to the battery, it is possible to develop this control along the value chain.

Adopting such an approach will require guidelines for collecting reliable data on sample provenance, and for a reference database with comprehensive and up-to-date data on Li products available on the market. To this end, reference samples must be collected of raw and processed materials from locations worked by one or several companies for a certain period of time, such as a year. In particular, it must be verified whether samples produced by the same company from the same deposit are more closely related to each other than samples produced by another company from a different deposit. This approach is only possible if robust data on within-deposit variations are available; moreover, the database must be active, as new orebodies of deposit are exploited, new extraction sites are open, and new mining/refining companies enter the market. The limitation of this approach will be the overlaps in the data of Li products from different locations or salt producers. A specific statistical data evaluation strategy is needed for evaluating matches between unknown and reference samples from mine sites or processing plants declared as the origin of the unknown sample.

Beyond this study, further challenges for developing lithium certification will consist in enlarging the database and assessing the applicability of this approach to non-conventional Li sources (e.g., geothermal waters, clay minerals) to support the future development of the global lithium supply chain.


Sample description

Three spodumene concentrates from mining companies in Finland (Keliber Oy) and Canada (North American Lithium, Sayona Québec) were sampled. Keliber also provided processed products: β-spodumene, analcime (NaAlSi2O6·H2O) and lithium hydroxide monohydrate (LiOH. H2O).

Keliber Oy (Keliber) operates spodumene deposits located in Central Ostrobothnia province (Finland) 50. and produces battery-grade lithium hydroxide in its chemical plant

North American Lithium operates an open-pit mine in La Corne (Abitibi, Québec, Canada) and plans the opening of a lithium carbonate plant

Sayona Québec (Sayona) is a subsidiary of Sayona Mining, an emerging lithium miner with projects in Québec and Western Australia. It further owns the Authier Lithium Project in Québec for the development of an open-pit spodumene mine

We also analysed eight samples of lithium carbonate (Li2CO3) and ten samples of lithium hydroxide monohydrate (LiOH. H2O) of battery-grade purity (Li 99.5%) coming from various chemical companies (Alfa Aeser, Acros Organics, Fluka, Sigma Aldrich, Fisher Chemical, Leverton), and from mining/refining companies that manufacture cathode active material. In particular, we analysed Li salts from three of the world’s top five producers of lithium chemicals (SQM, Ganfeng, and Tianqi) 8. We assumed that the lithium carbonate produced by Alfa Aeser in Argentina (Li 11) was made from Argentinian salars.

Leverton-Clarke (Leverton) operates a processing plant in Basingstoke, Hampshire, UK; they produce lithium hydroxide and battery-grade carbonate from Salar de Atacama brine (personal communication).

Sociedad Quimica y Minera (SQM) extracts lithium brine from the Salar de Atacama in northern Chile. It is the world’s largest producer of lithium carbonate and a major producer of lithium hydroxide. SQM operates a lithium carbonate and.hydroxide plant at the Salar del Carmen facilities at La Negra, near Antofagasta 50. Lithium carbonate, supplied by SQM, is also transformed at processing facilities in Russia to lithium hydroxide, which is redistributed mainly in the European market 50.

Jiangxi Ganfeng Lithium (Ganfeng Lithium) operates a spodumene mine in China (Ningdu) and has a 50% equity ownership in the Mt. Marion lithium mine in Western Australia 50. as well as exclusive supply agreements with Pilbara Minerals (Pilgangoora and Altura projects) in Australia Ganfeng Lithium operates a number of subsidiaries, undertaking lithium exploration in Ireland, Canada, Australia, Mexico and Argentina, lithium processing in China, and marketing of lithium products in the Chinese and international markets 50.

Sichuan Tianqi Lithium Industries (Tianqi Lithium) is a state-owned Chinese enterprise operating multiple lithium operations and projects, mainly in China and Australia. It holds a 51% share in the Greenbushes Mine of Western Australia 50. is the largest producer of lithium mineral concentrates, and exploits the brines of Zhabuye Salt Lake on the Tibetan Plateau (China) 58. Two Li-processing plants are operated by subsidiaries of Tianqi Lithium in China, in Sichuan and Jiangsu provinces. They produce lithium chemicals from Li products imported from a diversified supply base (salar or spodumene origins) 50.

Xiamen TOB New Energy Technology (TOB) is a Chinese company specialised in lithium-ion battery research and manufacturing. It provides equipment, materials and comprehensive battery production-line solutions for international companies and research institutions (BMW, Daimler-Benz, A123, SKC, MIT, IIT, etc.), and produces cathode active materials, four of which (NMC333, NMC532, NMC622 and NMC811) were sampled. Samples NMC333 and NMC532 were produced in factory A, whereas NMC622 and NMC811 were each produced in two other factories (B and C).

For this study, we synthetised two types of active materials (NMC622 and NMC811) from lithium carbonate (Li13, Li18) and.hydroxide (Li01, Li17) at CEA LITEN (Commissariat à l’Energie Atomique et aux énergies alternatives Laboratoire d’Innovation pour les Technologies des Energies nouvelles et les Nanomatériaux). Layered lithium-oxide material was synthesised by coprecipitation using commercial sulphate reactants from Sigma Aldrich. In a standard synthesis, three different solutions, containing all reactants, were prepared. The transition metal-ion solution was obtained by dissolving NiSO4·6H2O (127.4 g for NMC622, 169.9 g for NMC811), MnSO4·H2O (27.3 g for NMC622, 13.7 g for NMC811) and CoSO4·7H2O (45.4 g for NMC622, 22.7 g for NMC811) in 400 g water. The ammonium hydroxide solution was produced by mixing 150 g NH4OH (28% from Sigma Aldrich) in 233 g water, and the sodium hydroxide solution resulted from dissolving 81.6 g NaOH (from Sigma Aldrich) in 400 g water. The transition metal-ion solution and the ammonium hydroxide solution were pumped directly into the reactor, the pH being kept at 11 during synthesis through controlled injection of the hydroxide solution. After the introduction of the reactive solutions, the mixture was aged for 3 hours in the reactor, before recovery by filtration of nickel-manganese-cobalt hydroxides [Ni0.6Mn0.2Co0.2(OH)2 or Ni0.8Mn0.1Co0.1(OH)2]. The product was washed several times with hot water in order to remove residual sodium and sulphate species, and finally, the hydroxide was dried overnight in an oven at 80 °C. To obtain the final NMC material, the hydroxide was intimately mixed with excess (3.3%) lithium salt and the mixture was fired at 850 °C for 24 h under air for producing NMC622, and at 925 °C for 12 h under oxygen for producing NMC811.

A large prismatic “automotive-grade” battery cell (30 × 9 cm) from South Korea with an NMC532 cathode, containing 52 cathode sheets and 53 anode sheets, was sampled as well.

Reagents and materials

All plastic and Teflon equipment for this study was acid-cleaned before use. All acids were purified by sub-boiling distillation before use. The water was distilled “Milli-Q” water with a resistivity of 18.2 MΩ cm (Millipore®). Cation-exchange resin AG 50 W − X12 (200–400 mesh) and hydrogen from BioRad® were used for Li purification.

Sample preparation

The “automotive-grade” battery cell was opened in the EDF-LME (Électricité de France-Laboratoire des Matériels Electriques) RD laboratory, after complete discharge for safety reasons. Four cathode sheets (A, B, C, D) were selected to provide representative samples of the cell. Sheets A and B were rinsed with “Milli-Q” to remove any electrolyte residues, whereas sheets C and D were left untouched.

The samples were then further prepared in the BRGM (Bureau de Recherches Géologiques et Minières) laboratory. Several 3-cm-wide strips were cut from each sheet at different places with a ceramic chisel, and the front (A1, B1, C1, D1, A7, B3) or rear (A8, B6, C6, D6) faces were carefully scratched off with a ceramic lancet to avoid damaging the collector, composed of aluminium foil. About 200 mg of cathode active materials were calcined at 550 °C and dissolved in concentrated acids (HNO3, HClO4, HF, HCl) on a hot plate in the cleanroom. About 200 mg of spodumene concentrate and analcime were dissolved in concentrated acid using the same protocol. After drying, the residue was diluted in 0.5 M HNO3. About 200 mg of lithium carbonate and.hydroxide were also dissolved in 0.5 M HNO3.

Lithium isotope analysis

Li concentrations were measured using an X Series II ICP-MS (Thermo Fisher Scientific) in the BRGM laboratory. A sample volume of ~100 ng Li was dried on a hot plate in the cleanroom. For cathode active materials, the residue was dissolved in a mixture of 0.2 M HCl. Lithium was separated from matrix elements using an AG 50 W − X12 resin (200–400 mesh) 59. before drying and re-dissolving in 0.5 M HNO3. To avoid isotope fractionation of Li due to chemical purification, the Li recovery from this protocol was checked by analysing one aliquot before and after chemical separation by ICP-MS: recoveries were consistently close to 100%. The other samples were directly dried and re-dissolved in 0.5 M HNO3. Total procedural blanks were measured to verify the cleaning procedure; such blanks are generally less than 30 pg, representing 0.03% of the lithium mass analysed.

Lithium isotope compositions were measured at a concentration of 50 μg/L with a Thermo Fisher Scientific Neptune MC-ICP-MS—upgraded to ‘Neptune Plus’—in the BRGM laboratory, following the procedure developed before 59. The Li-isotope composition of each sample was expressed in δ-notation relative to the mean value of the bracketing Li standard (L-SVEC): δ 7 Li = [( 7 Li/ 6 Li)sample/( 7 Li/ 6 Li)standard – 1] × 1000. The quality of Li-isotope analyses was controlled by regular measurements of “in-house” standards, whose long-term reproducibility is 0.5‰ (2σ). The external reproducibility (2σ) reported in the various figures and tables was typically ±0.4‰, calculated by measuring the same sample multiple times over the many analytical sessions.

Data availability

All data generated or analysed during this study are included in the Supplementary Information.


This work was financially supported by BRGM ( Traçabilité batteries. PEX batteries ), and EDF Lab (TREE and LME Departments, PEM Project). Some state-of-the-art elements come from the SURFER project, financed by the French Environment Energy ministry (ADEME, grant number 1605C0025). The authors wish to thank companies (Keliber, SQM, North American Lithium, Sayona Québec, Leverton) and universities (UQAT, Tianjin University) for providing samples. Thanks are also due to the batteries-traceability team project (BRGM and EDF Lab) for helpful discussions. Special thanks to colleagues from BRGM’s Water, Environment, Analysis and Processes Division. H.M. Kluijver edited the final English version of this paper.

Author information

Authors and Affiliations

  • BRGM, F-45060, Orléans, France Anne-Marie Desaulty, Daniel Monfort Climent, Gaétan Lefebvre, Sébastien Perret Catherine Guerrot
  • EDF, EDF RD, 77818, t sur Loing, France Antonella Cristiano-Tassi Anthony Urban
  • Université Grenoble-Alpes, CEALITEN, 38054, Grenoble, Cedex 9, France David Peralta

Battery Yates

Compared to other batteries in the region, Battery Yates held relatively small, 3-inch diameter Rapid fire rifles, used to protect the bay entrance. In the event of a foreign attack, its guns could fire up to 30 shots per minute at fast moving enemy torpedo boats. During World War II, the guns protected an anti-submarine net that spanned the entrance to the bay.

Lime Point

In the mid-1800s, the US Army wanted to build a fort to match Fort Point on the north end of the San Francisco Bay. This was to be at Lime Point, and it was to be built roughly where the north tower of the Golden Gate Bridge stands today. In order to build upon the rock outcropping that stood separate from Marin, the plans called for heavy blasting to level the surface of the rock. This proved too difficult and the plans were abandoned. The army decided to forgo their brick fort defense designs altogether, in favor of a more modern defense: a network of batteries.

The Great White Fleet

On May 6th, 1908, some 200,000 people came out to the hills of the Marin Headlands to watch as the Great White Fleet pulled into the San Francisco Bay. A showy display of military strength, the fleet was something akin to the Blue Angels of today. The US naval battle fleet stopped here on its circumnavigation of the globe on the orders of President Theodore Roosevelt, to demonstrate American military might.

Mission Blue Butterflies

Mission blues are just little guys. Adults are about the size of a quarter, and larvae are so small that they’re rarely seen. These little beauties look a little different depending on if they’re guys or gals. Females have brown and some blue coloration on the upper side of their wings. Males are light blue. Both have dark edges around their wings. The underside of their wings are off-white with two rows of irregularly shaped black spots.

Mission blues require a host plant and nectar in coastal grassland habitat to survive. The host plants utilized by the Mission blue are several varieties of lupine. Nectar plants include various composites that grow in association with the lupines.

Their sensitivity to habitat and diet in addition to human impact on their environment has made mission blues endangered. Remaining populations are found in only a few locations around the San Francisco Bay Area, the Marin Headlands, Skyline Ridge in San Mateo County and San Bruno Mountain.

Ants and Butterflies: A Dynamic Duo

Mission blue larvae produce a sugary solution that’s super-irresistible to native ant species. Because of their uncontrollable sweet tooth’s, the ants voluntarily tend to the larvae in return for feeding off their sweetness. While in their care, the ants protect the larvae from predators.

Monarch Butterflies

Monarchs are famous nomads. Every fall, a new generation of travelers are born. Like one big, happy family, they migrate from areas as far north as the East Coast of Canada several million strong, all the way to central Mexico. It may take five or six generations for the butterflies to return all the way to their summer homes. They’re the only butterflies that make such a massive journey, up to 3,000 miles.

The monarchs that migrate here to overwinter in the mild Pacific Coast temperatures come from west of the Rocky Mountains and generally have a less arduous journey. They’re extremely recognizable with their orange and black wing patterns and sometimes congregate in large groups, mainly on the branches of eucalyptus trees at Fort Baker and other spots along the California coast.

The 11 Best Outdoor Solar Lights of 2023, Tested and Reviewed

Jenica Currie is an expert content manager, producer, writer, and editor with over a decade of experience cultivating online communities.

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Outdoor lights using solar energy are the perfect landscape lighting solution. They tend to be budget-friendly and easy to install, and you can place them exactly where you want them because they don’t require plug-in power sources. But it’s important to consider the placement and purpose of outdoor solar lights, says Sheva Knopfler, Co-Founder and Creative Director of, a well-known online retailer of all kinds of lights and lightbulbs. How much brightness do you need? she recommends asking yourself. Does the light need to be direct or spread out? The height of your solar lights is also important. Will they be a tripping hazard? Are you able to install them into your pavement or garden?

Over the course of several days, we tested 27 different solar lights at our Lab in Des Moines, Iowa, including path lights, spotlights, lanterns, wall-mounted, and string lights. After assembling and charging them in sunlight for the time specified by the manufacturer’s instructions, we evaluated their assembly, brightness, features, design, value, and durability. And then we went beyond: We froze them, read under them, and dropped golf balls on their solar panels. We even video-recorded them overnight to make sure they truly stayed on from dusk until dawn! To test wall-mounted lights, we tested and installed 18 options in our own homes.

open, close, batteries, included

Best Overall

AloftSun Solar Motion Sensor Outdoor Lights

  • Highest waterproof rating
  • Three easy-to-use modes
  • Bright enough to read by
  • Two installation methods

Our top pick, AloftSun Motion Sensor Solar Landscape Spotlights, withstood all of our durability tests, are easy to use, and are bright enough to read by! These spotlights can detect motion from as much as 33 feet away, depending on the setting. The three modes that operate from dusk until dawn—dim light/high light when motion is detected; no light/high light when motion is detected; or medium light/constantly on—give you options to suit your lighting needs and are simple to use. (It did, however, take us a few minutes at first to figure out how to trigger them.) Easy to put together (just two pieces), this two-pack of lights can either be staked into the ground (the method we tested) or mounted onto a wall with the included hardware.

We were impressed at how these lights held up during our durability tests. Since the manufacturer claims these lights have the highest waterproof rating and are frost-resistant, we sprinkled water on them, then froze them for over an hour. After each test, the lights still worked just as well as before! We also dropped a golf ball on their solar light panel from a distance of 6 feet, and they still held up.

These spotlights feature 30 LED light chips, which help illuminate your pathway or yard easily, stand up to the elements, and are noted by the manufacturer to have a 40,000-hour lifespan. However, they are not particularly stylish. And they are more cool-toned (6500K) than we’d prefer for a home. However, if you are looking for durable, bright lights with useful features, you can’t go wrong with this pick.

Price at time of publish: 33

Dimensions: ‎11.81 x 5.43 x 4.33 inches | Lumens: Not listed | Power Source: Solar panel and 2200 mAh rechargeable battery | Charging time: 1-2 days first use, up to 8 hours on cloudy days | Operating time: 6-12 hours depending on setting | Lights in sets: 2 | Weather Resistance Rating: IP68 | Color Temperature: 6500K

Best Budget

Home Zone Security Solar Wall Lantern 2-Pack

If you are looking for wall-mountable lantern-style lights, this option from Home Zone is the perfect choice. You get a two-pack of preassembled lanterns that include wall brackets and screws (no tools included). We love how versatile this set is—you can place them on a table, on a garden hook, mount them to the wall, or carry them around by their handles when you need extra light. Plus, they come with a 1-year warranty.

Made of stainless steel and glass, these lights stood up to our durability testing, with no damage to the glass or solar panels. They are bright and cheery for an entryway but not as bright as other options we tested—we couldn’t read under them. With a simple, automatic dusk-to-dawn operation, these lights are simple to use but have no other features. They also need two AA batteries to operate, which eventually need replacing. However, we love their farmhouse-style, affordable price, and the ability to have wall-mountable lights without needing electricity.

Price at time of publish: 45

Dimensions: ‎8.66 x 6.3 x 10.04 inches | Lumens: 10 each | Power Source: Solar powered and two AA batteries ( included) | Charging Time: 8 hours | Operating time: Not listed | Lights in Set: 2 | Weather Resistance Rating: Not listed | Color Temperature: 3000K

Best Path Light

Better Homes Gardens Ellis Transitional Pathway Light

  • Light shines 360 degrees
  • Tall, durable stake
  • Displays a sunburst pattern on the ground
  • Affordable

Sometimes, one simple path light is all you need to make your entryway shine. The Better Homes Gardens Ellis Solar Powered Black Metal and Glass LED Path Light is a nice addition to any entryway or outdoor space, and you may even be tempted to buy two! With a tall stake, and a globe that completely illuminates the surrounding area, this affordably priced solar light emits a nice, warm yellow glow (Better Homes Gardens is owned by The Spruce’s parent company, Dotdash Meredith). (When setting up, remember to pull the tab off the battery on top.) While testing, we appreciated the sunburst pattern the light displayed on the ground. We also found it bright enough to read by, although we did expect it to be even brighter, considering the size of the bulb.

open, close, batteries, included

This product capably withstood our durability testing—water, freezing, and dropping a golf ball on the glass didn’t affect the light fixture or the quality of the light. This path light lacks motion sensor capabilities or other features aside from an on/off switch. But when switched on, the unit stayed lighted from dusk until dawn, which, during our summer testing, was 9:13 to 5:27 a.m. CDT.

Price at time of publish: 14

Dimensions: 6.69 x 6.69 x 21.40 Inches | Lumens: 20 | Power Source: Solar powered | Charging Time: Not listed | Operating time: Not listed | Lights in Set: 1 | Weather Resistance Rating: Not listed | Color Temperature: Not listed

Best Set

Hampton Bay Solar Landscape Path Lights

  • Great value for pack size
  • Durable and bright
  • Stylish design
  • 2-year warranty

Solar path lights allow you to illuminate a walkway or driveway without having to worry about having outdoor electricity or extension cords. Aside from being stylish and durable, this 10-pack from Hampton Bay is a great value, especially if you have a longer area to illuminate. We loved the “sparkly effect” these lights display on the ground, as well as their unique crackle look on the glass. Our concern that this would affect the brightness of the light was unfounded—it was still so bright, you could read directly under them!

We also found these lights to be as durable as they were aesthetically pleasing, holding up well during watering, freezing, and being impacted with a golf ball. Made of aluminum, glass, and plastic, they stand 18 inches tall and have only three pieces to assemble, which we found to be easy. Like many of these solar lights, they feature dusk-to-dawn operation and stayed lit for 8 hours (after an 8-hour charge). They offer no other settings or special features and only come in packs of 10. However, if you are looking for a great set of path lights, this option stands out.

Price at time of publish: 114

Dimensions: ‎18.1 x 4.92 x 4.92 inches | Lumens: 10 | Power Source: Solar | Charging Time: 10-12 hours | Operating time: 8 hours | Lights in Set: 10 | Weather Resistance Rating: IPX4 | Color Temperature: 3000K

Best Spotlight

Vont LED Outdoor Solar Lights

  • Durable and waterproof
  • Two placement options
  • Can pivot 120 degrees
  • Lifetime warranty

If you need to illuminate a large space or specific focal point and don’t want to worry about wires or electricity, solar spotlights are a great option. The Vont LED Outdoor Solar Lights are easy to put together and install, with sturdy stakes to put in the ground or with the included screws to mount on the wall. You can even pivot them up to 120 degrees, so they can point in the exact direction you need.

The manufacturer lists these spotlights as being weather resistant, and they back this claim with a lifetime warranty. Despite what we put them through, we noticed no changes in their brightness or anything else. Although these lights turn on automatically at night, they don’t offer any other lighting features besides two brightness settings. However, if you are looking for bright spotlights that can withstand the elements, these should be your go-to.

Price at time of publish: 40

Dimensions: ‎5.5 x 4.2 x 12.2 inches | Lumens: 100 | Power Source: Solar, Built-in 2000 mAh 18650 lithium battery | Charging Time: Not listed | Operating time: Up to 12 hours | Lights in Set: 2 | Weather Resistance Rating: IPX7 | Color Temperature: 6500K

Best String Lights

Brightech Ambiance Pro Solar Non-Hanging String Lights

  • Stylish design
  • Versatile placement
  • Durable, with shatterproof plastic bulbs
  • Simple installation
  • Can’t connect multiple strings
  • Lights aren’t as bright or stay on as long as other lights we tested

Illuminate your outdoor space with pretty string lights like this set from Brightech. This set is 27 feet long, with no electricity required. Just stake the solar panel in the ground or clip it to a balcony or other surface and place the lights where you want them! These shatterproof plastic Edison-style bulbs not only look stylish but are durable as well, holding up well during our tests. Though the solar panel moved a bit when we hit it with a golf ball, it showed no damage. They have a 1,000-hour charge lifespan (around 2.5 years, according to the manufacturer) and are backed by a full 2-year warranty.

We loved the “moody lighting” these lights emitted but noted they were bright enough to read by only when the lights were gathered together and not strung out. Also, these did not stay lit as long as the others we tested (6 hours total). If you are mostly using them for decor or entertaining purposes, this shouldn’t be an issue. And although you can’t connect multiple strands together (as we hoped!), there is a 48-foot strand available if you have the space.

Price at time of publish: 48

Dimensions: 27 feet long | Lumens: Not listed | Power Source: Solar | Charging Time: 6 hours | Operating time: Up to 6 hours fully charged | Lights in Set: 1 string | Weather Resistance Rating: Not listed | Color Temperature: 3000K

Best Decorative

Brightown LED Solar Powered Fairy Lights

For an affordable lighting option that adds ambiance to your outdoor space, we recommend the 33-foot-long Brightown Outdoor Solar string lights. Available in seven colors (we tested white), these fairy lights survived all of our durability tests and were easy to install, with only two stakes needed for the solar panels. And because they are solar-powered, you don’t need electricity for them to work, unlike many other outdoor string lights. We would have liked them, however, to provide more light to read by.

We especially appreciate the eight lighting modes, including combination, waves, sequential, slow glow, chasing/flash, slow fade, twinkle/flash, and steady-on, so you can choose fun options for gatherings or holidays. After turning on automatically at night, these lights have an up to 10-hour runtime, but inexplicably, they did turn off for 60-second increments during our overnight testing. Also, you have to be sure to place the solar light panels where they can get light, which may limit placement options a bit. However, this two-pack is a great budget option, especially if you are looking for string lights or want to add a fun element to your outdoor decor.

Price at time of publish: 23

Dimensions: ‎33 feet long | Lumens: Not listed | Power Source: Solar powered, 800mAh high capacity rechargeable batteries | Charging Time: Not listed | Operating time: 8-10 hours after fully charged | Lights in Set: 2 sets of string lights | Weather Resistance Rating: IP65 | Color Temperature: 2700K

Best for Post

Kemeco Solar Post Light

  • Bright, beautiful light
  • Stylish design
  • Two placement options
  • Easy to assemble and install

A light post can add a stylish, vintage look to your decor while illuminating your entryway. And with the Kemeco Solar Post Light Fixture, you have many more options on where to add it to your outdoor space, with no electricity or wires needed. You can mount this light to a post (not included) or to its included mounting base and place it just about anywhere. We tested both installation methods—at our lab, we assembled the light to the mounting base and placed it on a step, and during our at-home test, we assembled and installed the light on an existing round pole. We also noted that screws and a bracket were included for both a round or square pole, which isn’t listed on the manufacturer’s product description.

In both settings, we found the light easy to put together with just two pieces. While using the mounting base, however, we found it a bit top-heavy. If you choose to use the mounting base, we recommend also using the mounting bracket to screw it securely to a step to correct any concern over top-heaviness. We found both methods easy to install, and once set up, we loved how this aluminum light fixture’s lantern style and ripple glass added a nice glow. Despite the ripple glass, the light shines so brightly that we could even read around it while testing. While it’s certainly still bright, this light isn’t bright enough to be a security spotlight.

We noted that the only feature, aside from its solar capabilities, is an on/off switch. Our lab testing also revealed some conflicting results. On the one hand, the frosted glass shattered during our golf ball test; on the other, the solar panels still worked. The manufacturer claims the product is weatherproof and wasn’t damaged when we poured water directly above it in the lab. We also haven’t noticed any issues with the light being damaged by storms so far in our real-world testing.

Price at time of publish: 100

Dimensions: 8.8 x 8.8 x 18.1 including 5.5-inch mounting base | Lumens: 130-145 | Power Source: Solar with 3 x 1.2v 2300mAh Ni-MH rechargeable batteries | Charging Time: At least 8 hours | Operating time: 6-8 hours | Lights in Set: 1 fixture and mounting base | Weather Resistance Rating: Not listed | Color Temperature: 3000K

Best Motion-Sensor

Linkind StarRay Solar Spotlights

  • Two motion detection modes
  • Bright for large spaces and pathways
  • Simple, all-in-one design
  • Can wall mount or stake in ground

Solar-powered lights with motion sensors allow you to add lighting when and where you need it. The Linkind StarRay LED Solar Motion Sensor Landscape Spotlights have two modes to suit your needs. You can choose to have them turn on for 25 seconds when motion is detected or to operate constantly at half light and only brighten for 10 seconds when motion is detected. (We noted that on the second mode, the difference between half-light and full-light was hardly detectable, although both modes are bright enough that we could read under them.) Although they are powered during the day, these lights do not automatically turn on at dusk unless you select one of those modes.

Aside from their motion sensor feature, we also love their versatility and streamlined design. You can stake them in the ground or mount them on a wall with the included hardware. The light and solar panel are on the same unit and can be pivoted up to 90 degrees vertically (180 degrees horizontally), so you can angle the light exactly where you want it to shine. Also, we found that these lights withstood our water and golf ball tests without sustaining damage. But when frozen, they strobed three times before turning off.

The price for the Linkind StarRay LED seems a little high for a single light, but we found it works as described and feels sturdy. We recommend it either for landscape lighting or for lighting pathways and security.

Price at time of publish: 33

Dimensions: ‎11.4 x 6.26 x 3.94 inches | Lumens: Not listed | Power Source: Solar powered, ‎lithium Ion battery | Charging Time: Not listed | Operating time: 6-12 hours | Lights in Set: 2 | Weather Resistance Rating: IP67 | Color Temperature: 6500K

Best Hanging

Derynome Solar Lantern Outdoor Lights with Wall Mount Kit

  • Small footprint
  • Easy to install
  • On and off switch
  • Durable and stylish

Wall-mounted lights can help you save space, but they can be a little intimidating and time-consuming to install. Plus, there could be many reasons you can’t install them in the location you want to, including lack of sunlight or surface space. Requiring a small footprint for the hanging bracket, the Derynome Solar Lantern Outdoor Lights give you all of the benefits of wall-mounted lights with little effort—you will need a drill and to make sure the holes are level, but only two screws are needed.

We installed both of these lights at one of our homes (one on an enclosed side porch and the other on a front porch post) in less than 15 minutes, not including the time it took to locate a drill. Once the brackets were installed, it only took seconds to hang the lantern on the hook. Keep in mind, though, that the lantern feels sturdy and durable but is lightweight (just over 3 pounds) and can swing around on the hook—make sure you hang it at a height that is accessible for when you need to remove it. We did note after rainy and windy weather (although not extreme), the lantern never blew off. The on/off switch is located inside the lantern, but it was easy to twist the lantern to access it. When on, the lantern will go on and off automatically (dusk until dawn).

The bracket extends 5 inches from the wall, so even with a small overhang, the solar panel is more likely to get sun. In fact, we installed them under a little overhang, and they were still able to get the sunlight they needed to remain lit overnight. But since they are so easy to install, if you find you need a sunnier spot, it’s relatively easy to rehang. Although a little brighter, this pick is very similar in style, price, weight, and durability to our lab-tested, Best Budget option, the Home Zone Solar Wall Lanterns. However, the Derynome Solar Lantern Outdoor Lights have an on/off switch and are available in three different colors (black, white, and bronze). We also like that the battery lasts longer. If you are looking for a lantern you can place on a table though, the Home Zone pick is the better choice, with a wider base.

Price at time of publish: 50

Dimensions: ‎11 x 6 x 6 inches | Lumens: 15 each | Power Source: Solar powered and Lithium Ion battery (included) | Charging Time: 6 hours | Operating time: 8 hours | Lights in Set: 2 | Weather Resistance Rating: IP65 | Color Temperature: 3000

Best Smart

Ring Solar Floodlight

  • Plenty of settings controlled via app
  • Easy to set up
  • Large solar panel
  • Works with Alexa

The Ring Smart Lighting Solar Floodlight is a great way to upgrade your existing floodlight and tap into the benefits of Smart home features. We did just that in one of our homes: We removed a traditional motion sensor light (keeping the existing plate) and quickly installed this Ring Smart Light, utilizing the easy-to-follow, illustrated directions (which are also helpful if you are installing a light for the first time). Keep in mind, you will also need to buy and install the Ring Bridge to utilize all of the Smart features (if you don’t have it already), although it was easy to plug in, install the app, and set up.

As with other solar lights, you need to ensure that the solar panel on this Smart outdoor light gets enough sunlight to fully charge each day. Since the Ring Smart Floodlight has a solar panel that hangs on a long cord, you have more options on where you can install the light. The solar panel is large and matches the color of the floodlight. Since this light is available in both black and white finishes, we found the white finish helped the solar panel to blend into the siding of a home. You can also choose to recharge the battery separately using the USB cord.

After setting up the app, you will be impressed with the abundance of features you can use with this Smart home product. Not only can you turn the light on and off via the app, but you can also schedule when the light will be activated, adjust motion sensitivity, adjust the brightness, and more. We found all of these features to be very useful but do wish the light was as bright as the previous floodlight installed at one of our homes (although we did appreciate the warmness of this Ring light). It was bright enough to serve its purpose as a floodlight and think this floodlight is the ideal choice for homeowners who already have multiple Smart devices integrated in their home. This light can also work with other Ring devices and lights through the Ring app.

Price at time of publish: 140

Dimensions: 5.51 x 10.43 x 4.68 inches | Lumens: Up to 1200 (adjustable) | Power Source: Solar power, battery pack with USB cord to recharge | Charging Time: Not listed | Operating time: Not listed | Lights in Set: 1 | Weather Resistance Rating: IP66 | Color Temperature: 3500


Durable and versatile, the AloftSun Motion Sensor Solar Landscape Spotlights are our top pick with three easy-to-use lighting modes and two installation methods, so you can have bright light when and where you need it. We also love the Home Zone Solar Wall Lanterns, 2-Pack, a stylish and affordable way to brighten up your doorway without worrying about electricity. Easy to mount on the wall, this set is built to withstand the elements and features an on/off switch.

Other Options We Tested

Ring Solar Pathlight: This path light was one of the brighter models we tested, but we struggled to get it to connect to the Ring Bridge, which is required for Smart capabilities. This struggle left us frustrated, but we will note that this light survived both our water and golf ball drop tests. For the price, we think you can easily purchase a pack of solar lights without the Smart features, if they’re not a must on your buying list. Aogist Solar Ground Lights: While there wasn’t anything particularly wrong with this set of lights, they just didn’t impress us as much compared to other designs. Frankly, we found them a bit boring, and we question their durability against a work boot or a bike tire. They did survive and function after our water, freeze, and golf ball drop tests, but we still think there are better sets available that will last multiple seasons. Beau Jardin 4-Pack Solar Pathway Lights: With the number of rave reviews online, we had high hopes for this pathway light set. The ground spikes on these lights felt loose, and our suspicions were confirmed when we attempted to remove the lights from styrofoam after our water tests. They are also very dim, so we were not able to read with the amount of light they put out.

How We Tested The Outdoor Solar Lights

We researched popular outdoor solar lights of various styles and selected 27 to test in our Lab in Des Moines, Iowa. We installed 18 wall-mounted solar lights in our own homes. We evaluated each on a wide and thorough array of attributes that included ease of assembly and installation, feature set, brightness, durability, and value. After putting them together, we let all the lights charge in full sunlight for the time specified in their instructions. We then took each to a dark room to run through all of their features, including any motion sensors and lighting modes and noted how easy it was to cycle through those. (If the lights didn’t turn on automatically, we searched for an accessible and functioning on/off switch.) For lights with motion sensors, we exited the room, waited 2 minutes, then re-entered, and we noted whether the lights turned on without any prompting. Then, we evaluated each light’s brightness by attempting to read a book under it. Next, for the lights we tested in our lab, we wanted to see how each product withstood the elements, including rain, hail, and winter’s subfreezing temperatures. To simulate rain, we sprinkled water on them from a watering can; hail took the form of a golf ball, dropped from 6 feet above the fixture and 4 feet above the solar panel. Then, we froze each light for an hour. After each test, we noted any changes and checked to see that all the features were still working. For lights we used in our homes, we noted how the lights have faired against any inclement weather over a period of one month (so far). After our lab tests, we took the lights outside and evaluated how easy they were to install, when applicable. After making sure the lights were on the appropriate setting (dusk-to-dawn mode, turned on, or left alone if automatic), we set up a video camera and recorded each overnight. We then reviewed the recording, noting when each light turned on and off and any anomalies.

What to Look For in Outdoor Solar Lights


Outdoor solar lights fall into three general types based on their light output: motion-activated, dusk-to-dawn, and timer-controlled. Because of solar cell size and battery capacity, the gathered solar energy is a limited resource, so consider when you want the lights to shine and for how long. Timer-controlled solar lights give you the most control since you can specify the time they turn on and for how long. Dusk-to-dawn solar lights use sensors to automatically illuminate when daylight dwindles and should have the lights remain on until sunrise. In regions with more limited sun, especially during winter, dusk-to-dawn lights may have trouble storing enough solar energy to stay bright for an extended period each night. Motion-activated lights turn on when triggered by movement and conserve solar energy reserves, such as the AloftSun Motion Sensor Solar Landscape Spotlights, our best overall pick for its bright lighting, three modes, and two installation methods. This style is often used for floodlights or for specific lighting needs, such as outside your back door. Our best Smart pick, the Ring Smart Lighting Solar Floodlight, offers all of the benefits of a Smart home device, including being able to set the lighting schedule, adjust the brightness, and adjust the motion detection settings, all from an app.


Where you want to use solar lights determines how you install them. Some outdoor solar lights mount like traditional light fixtures, using screws. For path lighting, solar lights with stakes are quick and easy to install—just push them into the ground, and you’re ready to go. Brick lights are great for illuminating gardens and pathways, as they can be installed into pavement or dirt, says Sheva Knopfler, Co-Founder and Creative Director of, a well-known online lighting retailer. Another option that is typically easy to install is solar-powered string lights. These typically have a solar panel that needs to be placed where it can receive a good amount of sun daily. For example, the Brightech Solar LED String Lights, our favorite tested string lights, can provide ambiance to your outdoor space all year long. Wall lights, which are similar to string lights in effect, are also an option some retailers offer. Wall lights are great for general lighting around the perimeter of your space, Knopfler adds.


Lumens determine brightness: from 5 lumens for landscaping ambiance to 350 lumens or more for a strong spotlight or floodlight. Your needs depend on your desired location and application. During testing, we noted that not all products listed their lumen ratings on the package. Keep in mind that different retailers will offer different solar brightness options, which are all designed for different purposes. Depending on size, color, and placement in relation to the sun, most of our solar lights could produce up to 20 lumens, Knopler says. These lights are meant to be layered, so you can customize your brightness by placing them closer or further away from each other.

Typically, outdoor solar lights contain several key components, including solar cells, rechargeable batteries, photoresistors, and lightbulbs. During the day, solar cells convert the sun’s rays into electricity, which the batteries store. At night, photoresistors detect the absence of ambient light and switch on the units. The light stays on until the batteries run out or the photoresistors detect light in the morning.

Solar lights placed in bright, direct light collect more energy in their batteries, which means your light stays on longer. For best results, place your solar light in a location that gets several hours of direct sunlight. However, solar lights still work in indirect light or on cloudy days—they just won’t collect as much energy and may not stay on as long.

To install solar lights, follow the product instructions. Some lights are designed to be mounted to the wall using screws, while others have stakes that you stick in the ground. For the best results, arrange your product’s solar panel in a way that it gets several hours of sunlight throughout the day.

To get the best results from your outdoor solar lights, place them where they get 6 to 8 hours of direct sunlight. If they’re designed to be wall-mounted, consider placing them up high, so they’re closer to the sun. Ensure that your lights aren’t in an inconvenient location, like in the path of your lawn mower, blocking a window, or encased in shadow.

In general, batteries in outdoor solar lights last 3 to 4 years before needing replacement. Some manufacturers sell replacement batteries, while others require you to buy an entirely new fixture. You can help increase your solar lights’ life span by cleaning the panels regularly and protecting them from harsh winter weather. LED lights can last up to 10 years, so if your solar lights are properly cared for and protected from extreme elements, they could last a decade, Knopfler adds.

Why Trust The Spruce?

Jenica Currie is the Associate Commerce Editor for outdoor, gardening, and home improvement at The Spruce. She has tested dozens of products at home and in the Lab, including artificial Christmas trees, clothing racks, bean bag chairs, fans, and vacuums. She spends her weekends gardening and working on other projects to improve the outdoor space around her home (including adding path lights along her driveway!). For this article, she used our test results and researched dozens of top-rated outdoor solar lights to compile this list of the best available options. She also personally installed and is testing the Derynome Solar Lantern Outdoor Lights on her front porch.

Emma Phelps, an Updates Writer for The Spruce, provided research assistance for this article. She reached out to Sheva Knopfler, the Co-Founder and Creative Director of, to learn more about best practices for choosing, installing, and caring for solar lights.

What Is The Spruce Approved?

Here at The Spruce, we want to ensure we fully stand behind every product we recommend and that when we say something is the best, we mean it. You might have noticed The Spruce Approved badge next to the products on this list. Every product with this badge has been rigorously tested in person and carefully selected by our expert team of lab testers and editors. In most cases, we buy all these products ourselves, though occasionally, we get samples provided to us directly by companies. No matter how we procure products, they all go through the same tests and must meet the same strict criteria to make the best-of cut.

The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

Your Next Car May Be Built With Ocean Rocks. Scientists Can’t Agree If That’s Good

Polymetallic nodules coat fields of the ocean floor and are rich in critical minerals needed to make batteries for electric vehicles.

NOAA Office of Ocean Exploration and Research

Sprawling fields of rocks about the size of your fist coat the Pacific seabed. Below miles of ocean, these nodules burst with copper, nickel, manganese and cobalt, all key to building batteries for electric vehicles.

As the global push for electric transportation grows, these metals have converted a remote underwater plain into a battleground over the hard decisions required to address climate change. A nascent industry of deep sea mining is growing to harvest these rocks. The industry’s first commercial mining applications may be filed in as little as two years despite incomplete regulations and unsettled science about mining’s effects.

Industry proponents say deep sea mining is more environmentally friendly than land-based mining, making it the best option in the face of looming mineral shortages for electric vehicles and a tight timeline to decarbonize transit. Marine and climate scientists counter that there’s scant data on the deep sea to gauge potential consequences for oceanic biodiversity and carbon sequestration, and that it would take decades of study to get a holistic assessment.

Because of such serious uncertainties, conservation groups, hundreds of scientists and some battery-reliant manufacturers are calling for a moratorium on deep sea mining. In March, BMW and Volvo Group, along with Samsung and Google, pledged to abstain from sourcing deep sea minerals.

It’s a sustainability paradox, says Kris Van Nijen, managing director of Global Sea Mineral Resources, a deep sea mining contractor for Belgium. On the one hand, we have a whole world demanding we deal with climate change. [but] there is not one solution that does not impact biodiversity that actually helps to mitigate climate change, because, in the end, we have to do something and we have to make choices.

The world does not have decades to decide how to handle climate change. And, when it comes to regulating deep sea mining, the international community may have even less time.

In June, the 8-square-mile, Pacific island nation of Nauru took the first step in launching the industry. It announced plans to submit an application for commercial extraction as early as 2023 to the International Seabed Authority, the organization overseeing deep sea mining. Such an application will be judged against whatever the deep sea mining rules are at that time — finalized or otherwise.

It’s a concerning move, says Andrew Friedman, who oversees the Pew Charitable Trusts’ deep sea mining project. We’re taking what was intended to be a deliberative, consensus-based process to regulate an untested industry in a part of the world that remains largely unexplored, and we’re compressing it somewhat arbitrarily into a two-year window. It’s raising a lot of questions about what’s going to happen next.

A sediment plume (above in the foreground) created by deep sea mining vehicles unfurls over a field of deep sea polymetallic nodules. Scientists are researching and developing models to determine how far this sediment will spread across the seafloor. NOAA/DeepCCZ expedition hide caption

Getting critical metals is complicated

Metals to make clean energy batteries can be extracted from the land, sea or recycling. Advocates for marine mining say harvesting ocean minerals would be safer for workers than traditional mining and would have a lower carbon footprint by avoiding deforestation. A traditional land mining project for lithium has already sparked controversy in Nevada because of alleged environmental degradation. Cobalt mining in the Democratic Republic of Congo has long faced accusations of child labor abuses.

If your nickel comes from [a traditional terrestrial mine in] Indonesia, you are guaranteed that your atmospheric carbon emissions will be many times higher than if your nickel was coming from nodules, DeepGreen, Nauru’s Canadian-based contractor, tells NPR. The company points to a peer-reviewed paper in the Journal of Cleaner Production, which it commissioned, that found nodules put 94 percent less sequestered carbon at risk and disrupt sequestration by 88 percent less than terrestrial ores. Just like with land mining, DeepGreen says, permits should be decided on a project-by-project basis.

Mineral production on land is also concentrated in certain countries, giving them outsize power over extraction and distribution. than 75% of lithium and rare-earth elements come from Australia, China and Congo, which also holds more than 70% of the world’s cobalt.

Researchers deploy a hose off the coast of San Diego to study how discharged mining sediment would move in the ocean. John Freidah hide caption

By contrast, the international waters of the deep sea are home to trillions of mineral-rich nodules. The nodule fields between Hawaii and Mexico known as the Clarion-Clipperton Fracture Zone — about the size of the United States — are estimated to contain six times more cobalt and three times more nickel than land reserves.

Environmentalists argue the best option is to forgo all mining and gather critical materials instead through electronics recycling. But reports by the World Bank and the International Energy Agency conclude recycling alone will not address the world’s clean energy mineral needs. By 2050, global demand for minerals such as cobalt and nickel will shoot up nearly 500%, the World Bank predicts.

Recycling can have a major role, probably, after the 2030s, says Tae-Yoon Kim, an energy analyst for the International Energy Agency and an author of its recent report, when technology has improved and spent clean energy batteries are ready to be recycled.

Until then, experts say, a steady flow of freshly mined minerals will be key to decarbonizing transportation. Shortages could drive up the price of electric vehicles or hamper production, slowing their adoption.

The deep sea holds more than critical minerals

Among the different kinds of deep sea mineral deposits, those that draw the most commercial interest are metal-rich nodules. Though the nodules were discovered more than a century ago, attempts at commercial extraction started only in the 1970s.

The International Seabed Authority was created in 1994 to oversee mining in the high seas. While continuing to draft the Mining Code, or the rules of international seabed mining, it has already issued at least 29 exploratory permits to allow nations and their contractors to search for nodules, test mining equipment and conduct environmental analyses. Sixteen of the permits are for harvesting polymetallic nodules in the Clarion-Clipperton Fracture Zone. The organization did not respond to repeated interview requests for this story.


Unlike the lifeless barrens most people expect the deep sea to be, the remote ocean floors are a biodiverse and complex ecosystem. The intensive logistics to reach the deep sea thwart most research. It’s only in the last several decades that scientists have begun to piece this picture together.

Interest in deep sea mining is now drawing industrial and academic dollars, broadening our understanding of this plain. DeepGreen has spent millions of dollars since 2012 to study its leases’ environmental baseline and [ways to] mitigate impacts of nodule collection on the marine environment, it told NPR via email.

Citing an impending merger in which DeepGreen will become The Metals Co., the corporation declined to comment on whether the science of deep sea mining will be settled by 2023, when the Nauru-sponsored mining application is likely to be submitted to the International Seabed Authority.

Other companies also seek a picture of what the deep sea environment is right now. The mining company GSR, which anticipates starting commercial extraction by 2030, is collaborating with an independent European Union scientific consortium, MiningImpact, to assess its leases. MiningImpact periodically monitors the deep sea environment and GSR’s mining tests. In April, MiningImpact collected data during field tests of GSR’s second vehicle prototype. But this data will not be fully analyzed for several years.

DeepGreen CEO Gerard Barron and the company’s chief ocean scientist, Greg Stone, then-Nauru President Baron Waqa and International Seabed Authority Secretary-General Michael Lodge speak with the crew of the Maersk, an international shipping container company, in San Diego in 2018 while the Maersk Launcher undertakes a DeepGreen research mission. Sandy Huffaker/AP for DeepGreen Resources hide caption

Could mining affect the ocean’s storage of carbon dioxide?

As the world’s largest carbon sink, the ocean has absorbed a substantial portion of our greenhouse gas emissions, with rising water temperatures and acidification to show for it.

Ocean carbon moves from the surface down into the seabed. Most of this occurs in the relatively shallow continental shelves where plentiful light and animals push carbon down the water column. A small portion makes its way down to the deep seabed. How exactly mining could affect this deep sea carbon is unclear, scientists say, and depends, in part, on exactly how mining technology functions.

If carbon-packed sediment that’s dislodged by mining stays near the seabed, it is unlikely to contribute to atmospheric carbon levels on a meaningful time scale, says Trisha Atwood, an associate professor of watershed sciences at Utah State University. Atwood is co-author of a recent study that discovered bottom trawling releases as much carbon dioxide annually as global aviation.

Once you get below 2,000 meters, carbon cycling slows down a lot, Atwood says. While deep sea mining might expose carbon. there’s a pretty big time lag between when microbes would turn that into CO2, and when that CO2 is likely to hit the atmosphere, potentially thousands of years.

Still, Atwood is one of the nearly 500 scientists who called in June for a deep sea mining moratorium. Even if that carbon isn’t coming out into the atmosphere, we are weakening the oceans’ capacity to take up more CO2, she says.

But it’s uncertain if mining sediment will remain at the bottom of the ocean. Both GSR’s and DeepGreen’s mining vehicles use seawater to displace several centimeters of sediment and nodules so they can be sucked into the vehicle, which separates muck from rocks. The nodules are then raised to the surface for processing while the sediment is returned to the seafloor. Early tests indicate the sediment plumes generated by their activities disperse several kilometers across the seabed but do not rise significantly. Scientists recently developed a model to estimate how plumes will move around in the water to inform regulations and affect estimates.

Keeping the sediment close to the seabed is relatively expensive, says Matthias Haeckel, who oversees MiningImpact. It requires additional technology to re-cool the sediment so it stays dense and does not rise in the water column. Mining operators looking to save money could decide to release the sediment at or near the surface.

There are currently no provisions in the Mining Code that regulate the height at which sediment can be released in the water column, according to Pew’s Friedman.

Hoovering up deep ocean mud may also affect microbes living in the seabed that consume carbon dioxide. These microbes absorb so-called natural carbon dioxide, or carbon that was not emitted by people but from ongoing organic and inorganic processes instead. The bacteria could be responsible for up to 10% of background natural carbon absorbed by the ocean annually.

Scientists do not know if disturbing the microbes through mining would alter the ocean’s ability to capture and hold carbon long term. What is evident is that this bacteria recover slowly from disturbances. Researchers dragged small plows in the Peru Basin in 1989 to simulate small-scale mining. Decades later, the sites remain scarred, and they house decreased microbial activity.

The microbial community does take a long time to recover following simulated mining disturbance, says Andrew Sweetman, a deep sea ecologist at Heriot-Watt University, who discovered carbon-consuming bacteria in the Clarion-Clipperton Fracture Zone in 2018. So if these processes are important and are taking up CO2, then it’s possible that mining may impact those processes to a large extent.

Deep sea mining companies say the amount of seabed that could be disturbed is inconsequential to carbon levels. Even if nodule collection severely disrupted the carbon-cycling in mining areas, writes sustainability researcher Daina Paulikas in the Cleaner Production paper, harvesting enough rocks to build 1 billion electric vehicles would disturb only 0.2% of the ocean’s deep sea bacteria.

Down the road, DeepGreen anticipates pivoting from oceanic mining to recycling minerals in support of a circular economy. Several U.S. port cities are under consideration as potential sites for future recycling plants.

Energy Secretary Jennifer Granholm said in June that the Biden administration wants to see the supply for clean energy minerals met through responsible mining that respects the environment.

A June report from the White House on potential supply chain shortages notes that significant quantities of strategic and critical materials may be found on the seabed, but the industry to extract these resources remains nascent, given both technical challenges of mining in the marine environment and the potential for significant environmental harm.

In the end, experts say, mining the deep sea will likely come down to a value judgment.

The carbon impact of deep sea mining is probably not going to be huge, Heriot-Watt’s Sweetman says, but I would say, at what point does a small number become significant?

Correction Sept. 7, 2021

A previous version of this story incorrectly said Global Sea Mineral Resources is a contractor for Belgium and Germany. It is only a contractor for Belgium.

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