Bioelectrochemical Intercalation for Scalable Lithium Recovery

doi:10.21203/rs.3.rs-5160500/v1

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Bioelectrochemical Intercalation for Scalable Lithium Recovery

https://doi.org/10.21203/rs.3.rs-5160500/v1

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The escalating demand for large-scale rechargeable batteries to achieve sustainability goals underscores the urgent need to secure Li metal from diverse sources ^1-3. Intercalation materials offer promise for selective and efficient electrochemical recovery from various sources, but the requirement of electrodes in driving intercalation reactions presents challenges for scale-up ^4-6. Herein, we introduce a biologically driven method for electrochemical Li recovery, utilizing a combination of intercalation nanomaterials and dissimilatory metal-reducing bacteria, specifically Shewanella oneidensis MR-1. This method couples bacterial metabolic hydrocarbon oxidation with Li intercalation into λ-MnO₂, achieving rates and selectivity comparable to electrode-based methods across different Li concentrations. Over 95% of Li was recovered from seawater within hours, with less than 1% co-intercalation of other metal ions. The efficacy of this reaction is maintained across scales by the autonomous formation of microbe/λ-MnO₂ agglomerates, in which extracellular and cell-surface cytochromes facilitate efficient electron transfer. Comprehensive techno-economic and life-cycle analyses for Li₂CO₃ production indicate that our method outperforms conventional evaporative processes, reducing on-site Li source water loss by two orders of magnitude without increasing costs. Our scalable bioelectrochemical approach could enable efficient Li recovery and offer great potential for sustainable resource management and recycling for both research and industrial applications.

Applied & Industrial Microbiology

Rechargeable battery

Extracelular Electron Transfer

Seawater

Brine

techno-economic analysis

life cycle assessment

Li, an essential component of rechargeable batteries ^7,8, is pervasive in nature, yet its distribution exhibits considerable heterogeneity. Historically, the exploitation of high-concentration Li reserves, such as brines and ores, has been the primary focus. However, the escalating global demand for large-scale Li-ion batteries (LIBs) has exposed the constraints of regional availability and the detrimental environmental repercussions associated with conventional evaporative Li recovery from brines and ore refining ^3,9,10. Consequently, there is a burgeoning need to develop environmentally benign Li recovery methods that demonstrate improved energy efficiency and enable the utilization of diverse Li sources ^1–3,10,11. Among the various alternative approaches, electrochemical techniques employing electrode materials for LIBs, such as λ-MnO₂ and FePO₄, demonstrate remarkable ability for rapid and selective Li recovery from sources with a range of concentrations, including low-concentration seawater (Supplementary Table 1) ^5,11–22. However, inherent limitations associated with two-dimensional electrode fabrication, including mass loading of electroactive material and ohmic drop, pose challenges to the scale-up of efficient and sustainable electrochemical Li recovery systems ^1,3–6.

Dissimilatory metal-reducing bacteria are ubiquitous in low-oxygen marine and freshwater environments ^23,24. These bacteria couple anaerobic oxidation of biomass linked to the electrochemical reduction of extracellular electron acceptors via extracellular electron transfer (EET) ^23,25. EET-capable bacteria, such as Shewanella oneidensis MR-1, actively attach to the surface of nano-sized metal oxides to increase the mineral reduction rate ^26–28. Given the remarkable ability of these microbes to reduce metal oxides, EET could be a promising driving force to electrochemically recover Li without using electrodes. To date, EET has primarily been employed for modifying the oxidation state of several transition metals (e.g., Cr, Mn, Fe, and Co) ^29–31, leaving the manipulation of alkali and alkaline-earth metals unexplored. In this study, we examine bioelectrochemical intercalation, wherein dissolved Li ions intercalate into a Li-ion sieve accompanied by electron donation from microbes (Supplementary Fig. 1). Using this approach, we have demonstrated the feasibility of bioelectrochemical Li recovery from artificial Li solutions and real seawater. Furthermore, we have evaluated the biological mechanisms, cost performance, and environmental impact to assess the scalability of our method.

λ-MnO₂ with a spinel structure was chosen from the reported Li-ion sieve materials. λ-MnO₂ has three-dimensional paths for Li diffusion in the lattice (Supplementary Fig. 2), whose size is small enough to prevent the intercalation of other metals that abundantly exist in seawater (e.g., Na⁺, K⁺, and Ca²⁺) ^5,9. In addition, manganese oxides are biocompatible electron acceptors for MR-1 and other EET-capable bacteria ^27,32,33.

We examined Li recovery from LiCl solutions dissolved in phosphate-buffered saline (PBS) at pH 7.4 and at high concentrations of Na⁺ and K⁺. The λ-MnO₂ nanoparticles (Supplementary Fig. 3) and MR-1 were anaerobically incubated with 50 mM LiCl/PBS in the presence of lactate as the electron donor for 24 h at 30°C. The nanoparticles formed sheet-like agglomerates at the bottom of the vial (Fig. 1a). The resuspension of the precipitate yielded 10–50-µm particles (Fig. 1b), which were approximately 100 times larger than those in the initial state (Supplementary Fig. 4). No such agglomerates were seen in the absence of LiCl (insets in Figs. 1a and b). Tunnel-structured MnO₂ polymorphs did not agglomerate even in the presence of LiCl, and the dry weight decreased in relation to that of λ-MnO₂ (Supplementary Fig. 5) with negligible structure change (Supplementary Fig. 6). Contrary to the common knowledge that EET dissolves MnO₂ in aqueous solutions ²⁷, λ-MnO₂ remained in the solid state and agglomerated specifically in the presence of LiCl.

Scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS) was conducted for analysing the agglomerates; the results indicated that microbes with a size of 1–2 µm were attached to the nanoparticles (Figs. 1c and d). The presence of a lower volume of bacteria, along with the nanoparticles, was further confirmed through fluorescence microscopy of DNA-stained MR-1 (Fig. 1e and Supplementary Fig. 7), indicating that MR-1 cells were physically associated with only a minor part of nanoparticles. However, almost all λ-MnO₂ was electrochemically reduced in the precipitate. X-ray diffraction (XRD) peaks shifted clearly without losing their sharpness (Fig. 2a), whereas such a shift was not observed when LiCl was omitted (Supplementary Fig. 8). Furthermore, X-ray absorption near-edge structure (XANES) analysis and inductively coupled plasma optical emission spectroscopy (ICP-OES) results indicated Li intercalation to form Li_1 − xMn₂O₄ (Fig. 2b and Supplementary Fig. 9).

The Li intercalation was associated with microbial respiration. CO₂ production for Li intercalation (Supplementary Fig. 10) indicates an NADH-dependent carbon catabolic pathway coupled with lactate oxidation ³⁴. In the absence of lactate, the XRD peaks did not shift in the presence of MR-1 (Fig. 2c). Although partial reduction occurred even without MR-1 because lactate can act as a mild reductive agent, the peak shift was insufficient, and the peak intensity significantly decreased (Supplementary Fig. 11). This suggests that accelerating the Li intercalation kinetics using MR-1 is critical for maintaining crystallinity during the reaction.

The selectivity of Li intercalation was further confirmed using Li–Mg mixed solutions. Although λ-MnO₂ prevents the intercalation of other alkali metals, this was not the case for Mg²⁺ because its ionic radius is similar to that of Li^{+ 35}. The molar ratio of Li/Mg was 200–1000 times higher in the agglomerates than that in the solution (Fig. 2d). This order is consistent with the difference in diffusion distances estimated from their activation energies (Supplementary Fig. 12). Such slow kinetics of Mg²⁺ diffusion in spinel-oxide materials have also been reported in previous studies on Mg batteries ^36–38. Furthermore, the properties of intermediate states formed by limiting the amount of Li in the reactor (Supplementary Figs. 13–16) are consistent with reported electrochemical charge/discharge of LiMn₂O₄/λ-MnO₂ ^5,39,40. The homogeneous and efficient electrochemical reactions exhibited by our approach closely resemble those observed in electrode-driven systems. This similarity offers a significant advantage for scaling up Li recovery, as our method circumvents the common challenges associated with electrode-based systems, such as mass loading limitations and increased ohmic drop during scale-up ^4–6.

The electron transfer limited at the bacteria/λ-MnO₂ interface, however, does not fully explain the homogeneous and efficient electrochemical reactions because the amount of MR-1 in the agglomerate was much less than the amount of λ-MnO₂ (Figs. 1d and e). This indicates the biological formation of a long-distance electronic network in the agglomerate with the semiconductive nanoparticles and the extracellular or cell-surface cytochromes ²⁸. To analyse the cellular and material interface formed during agglomeration, we performed electron energy loss spectroscopy (EELS) mapping with scanning transmission electron microscopy (STEM). Subsequent to agglomeration, the Li-containing aggregated material was dispersed by ultrasonication and mounted on a TEM grid. The nanoparticles attached to the cells exhibited no obvious changes in morphology (Fig. 3a), and Mn valency evaluated by EELS decreased from + 4 (initial state) to typically around + 3.5 (after Li intercalation) even if Mn was not directly attached to the cell (Fig. 3b), suggesting the formation of a long-distance electron pathway. Mn was not detected inside the cell through either EELS or EDS (Supplementary Fig. 17), indicating that reduced Mn was not originated from dissolved Mn ions reduced in the cells. EELS and cross-sectional TEM results revealed the presence of a small amount of Mn²⁺ in the vicinity of the microbe (Supplementary Fig. 18), which can likely be attributed to the formation of hydrated Mn phosphate ⁴¹.

Focused ion beam (FIB) milling with cross-sectional SEM–EDS was employed for the direct observation of the cellular morphology inside the agglomerates. Note that the agglomerate was subjected to 3,3′-diaminobenzidine (DAB)-H₂O₂ and OsO₄ staining in advance for labelling redox-active enzymes, including cytochromes ⁴². We selected a small piece with a diameter of 10–20 µm (Supplementary Fig. 19) and subjected it to FIB sputtering to expose a cross-section (Figs. 3c and d). Os was concentrated near microbes but observed with Mn in EDS profiles (Figs. 3e–g and Supplementary Fig. 20). Carbon incorporated in λ-MnO₂ was also detected through EDS; the results suggested the expression of the extracellular and cell-surface cytochromes to physically and electrically support the MR-1–nanoparticle composite. In addition, we observed a nanowire-like structure that potentially facilitates electrical conduction via cytochromes ²³, bridging microbes and nanoparticles (Fig. 3h), and suggesting a possible mechanism for electron transfer in this system. Given that genes for outer-membrane cytochromes (OM c-Cyts) support long-distance electron transport via bridging semiconductive nanoparticles ⁴³, we used gene deletion mutants lacking representative OM c-Cyts (∆mtrC/omcA). In contrast to the wild-type MR-1 (Fig. 3i), little or no reduction of λ-MnO₂ was seen even after 24 h (Fig. 3j). Furthermore, we added riboflavin to increase the rate of direct EET via OM c-Cyts as a bound cofactor ^44,45. The presence of only 2 µM riboflavin accelerated the Li recovery kinetics by more than eight times (Fig. 3k). The estimated rate of Li recovery with 50 mg λ-MnO₂ was approximately 660 µg/h in the presence of riboflavin. In general, cathode materials in LIBs can be charged/discharged within several hours ^5,7. Therefore, once riboflavin enhances the rate of Li intercalation, the Li recovery kinetics is probably limited by the Li-ion diffusion kinetics in λ-MnO₂. Given that the kinetics of our method closely align with such atomic-level phenomena, the comparable Li recovery efficiency to electrode-based technologies is well-justified. These results suggest the primary role of the extracellular and cell-surface cytochromes in Li intercalation and the formation of an electrically conductive network in the agglomerates.

Such microbial interaction is likely induced by the electrochemical properties of λ-MnO₂, given that MR-1 is sensitive to the potential of its extracellular environment ³⁴. Among the MnO₂ polymorphs, λ-MnO₂ exhibits a particularly high potential for Li intercalation (Supplementary Fig. 21) ⁴⁶. Consistent with this, CO₂ production from lactate oxidation was observed in the presence of λ-MnO₂, a process typically triggered when the anode potential is highly positive in a microbial fuel cell system ³⁴. The elevated potential also facilitates electron transfer from MR-1 owing to the high driving force. Moreover, the lithiation of λ-MnO₂ enhances its electronic conductivity by shifting the Fermi level closer to the conduction band ^47,48, potentially further promoting electron transfer within microbial agglomerates ⁴³. Notably, the formation of over-lithiated Li₂Mn₂O₄ was prevented, likely due to the limiting reductive potential of MR-1.

The high redox potential of λ-MnO₂ for Li intercalation is sustained even in low-concentration Li environments, such as seawater (Supplementary Fig. 22). Seawater mining is attracting growing attention since the Li content in seawater (about 25 µM) is orders of magnitude higher than that in most freshwater systems (on the order of 0.01 µM) ^11,22. However, the concentration of Li in seawater is still low enough to make its recovery challenging ⁹. We, therefore, next examined the feasibility of bioelectrochemical Li recovery from real seawater collected from Oarai, located on the east seaside of Japan. λ-MnO₂ (5 mg) and MR-1 were placed in a bottle filled with lactate-spiked seawater (50 mL), and the Li concentration of the supernatant liquid was evaluated through ICP mass spectroscopy (ICP-MS) in the absence of riboflavin. As shown in Figs. 4a and b, Li was recovered from seawater within several hours, consistent with PBS-based experiment without riboflavin, and inserted Li was stably stored even after the microbial activity had settled (Supplementary Fig. 23). The molar ratios of Li/M (M = Na, Mg, K, Ca) electrochemically intercalated into the material were all greater than 100 (Supplementary Tables 2 and 3). In contrast, λ-MnO₂ itself, without microbial reduction, was not effective because of the absence of the electrochemical driving force (inset in Fig. 4b). The small variation in the reaction rate was dependent on the seawater sample, suggesting that transient substrates, such as flavins, in seawater affect the rate of EET. Indeed, the Li recovery rate was enhanced approximately two times by spiking 2 µM riboflavin (Supplementary Fig. 24). We also confirmed the reproducible Li recovery performance when using different seawater batches, volumes, and/or the mixing ratios of seawater/λ-MnO₂ (Fig. 4c). Self-agglomeration was observed even at a higher seawater/λ-MnO₂ ratio (Fig. 4d). These results further support the scalability of our method utilizing the autonomous formation of the agglomerates.

Remarkably, our proposed method achieved the Li recovery efficiency comparable to, and even displaying superior selectivity than, the electrode-based processes for seawater treatment, all without the need for electrodes or electrochemical equipment ¹¹ (Fig. 4a). Also, ion-exchange materials ²⁰ and the electrical pumping method that uses a solid-state electrolyte membrane ²² used for Li recovery necessitate time-consuming purification stages, highlighting the benefits of our efficient and straightforward bioelectrochemical approach for Li recovery.

To further evaluate the advantages of our method, we conducted comprehensive techno-economic analysis (TEA) and life-cycle assessment (LCA), which revealed that our approach could significantly outperform conventional evaporative processes. Considering that electrogenic bacterial strains capable of reducing MnO₂ under brine-level salinity conditions have been isolated ⁴⁹, we used data from LiCl/PBS solution experiments to estimate the potential for Li₂CO₃ production from brine sources. Developed Li recovery process (Fig. 5a) involved oxidizing Li_1 − xMn₂O₄ with Na₂S₂O₈ to obtain a Li-containing solution while regenerating λ-MnO₂ (Supplementary Fig. 25), with only a 0.001% Mn loss (Supplementary Fig. 26). The Li-containing solution underwent Mn²⁺ removal, volume reduction, and Li₂CO₃ precipitation with the addition of Na₂CO₃, resulted in the purity of ∼98% (Supplementary Fig. 27), followed by filtration, washing, and drying. The estimated production cost of our method is 5.97 USD/kg Li₂CO₃ (Fig. 5b), comparable to the evaporation method for brines ^50,51, and below the industrial Li₂CO₃ market price (Supplementary Table 4). Moreover, our production rate is orders of magnitude faster than that of the evaporation method, highlighting the efficiency and scalability of our approach.

Our LCA indicated a water consumption of 0.39 m³eq/kg Li₂CO₃ (Fig. 5c), representing brine water loss being reduced by 97–99% compared to currently used methods ⁵², thus highlighting the potential of our technology to alleviate local water conflicts ^3,9,10. The climate change impact was calculated at 16.8 kg CO₂eq/kg Li₂CO₃ (Fig. 5d), higher than currently used methods ⁵², primarily due to the use of Na₂S₂O₈ in the Li₂CO₃ precipitation process. Na₂S₂O₈ is also a significant factor in the overall cost (Supplementary Fig. 28) and water consumption. Development of more cost-effective Li leaching methods would further improve the sustainability of our approach. Importantly, given the cost, water, and CO₂ contribution from Li intercalation rate is much smaller than the input of chemicals, the advantages of our method remain even if microbial Li intercalation turns out to be slower in brine. We have now built a prototype of an anaerobic culture bottle with a cation-exchange membrane, and successfully demonstrated the collection of Li from outside the membrane (Supplementary Fig. 29). Installing such a membrane to separate the microbial reactor and environmental water source serves as an example of a scalable method that can be implemented with further minimizing environmental impact ^3,53.

In this study, we have demonstrated a scalable bioelectrochemical method for Li recovery, where S. oneidensis MR-1 bacteria autonomously create efficient electron transfer pathways in MR-1/λ-MnO₂ agglomerates, driving Li intercalation with efficacy and selectivity comparable to conventional electrode-based systems. Unlike conventional methods, which are limited by the surface area of electrodes, our approach leverages self-organized agglomeration in a homogeneous system, enabling scalability without the need for electrodes. This method can also be coupled to microbial metabolic anoxic oxidation of biomass ²⁵, offering a low-carbon alternative for large-scale Li recovery ^10,4. As electron-donating bacteria flourish under various pH and salinity conditions ^24,49, our approach has broad applicability for diverse Li recovery and recycling scenarios. Future research should focus on improving the economic and environmental costs associated with oxidants used in Li leaching. For instance, the ability of dissimilatory metal-reducing bacteria to both donate and extract electrons from solids ^54–56 suggests the possibility of combining microbial Li recovery with biomass-based oxidants and microbial electron uptake to further enhance sustainability. The autonomous formation of MR-1/λ-MnO₂ agglomerates driven by Li intercalation introduces a novel mechanism that could improve the efficiency of metal reduction ^25,26,28. Exploring how Li intercalation activates this bacterial phenotype could provide critical insights for future innovations. Ultimately, bioelectrochemical intercalation could facilitate efficient handling of alkali and alkaline-earth metals under ambient conditions, opening the way for innovative metal handling and electrochemical tuning of intercalation materials ⁵⁷.

Acknowledgements

This research was supported by NIMS Joint Research Hub Program (QN3510) and by JSPS KAKENHI (Grant numbers 22H02265, and 20K22460) and JST, PRESTO grant number JPMJPR19H1, Japan. XRD, SEM–EDS, FIB–SEM–EDS, and STEM–EELS analyses were carried out at the NIMS Battery Research Platform. ICP-MS/OES analysis was performed at Materials Analysis Station, NIMS, and at Analytical Research Core for Advanced Materials, Institute for Materials Research, Tohoku University. The authors thank Dr. Takashi Fujikawa, Dr. Fuyuki Sakamoto, and Dr. Akio Iwanade for their technical help with the materials synthesis and ICP-MS/OES analysis. We also thank Prof. Tetsu Ichitsubo (Tohoku University) for fruitful discussions.

Authors Contributions

K.S. and A.O. conceived the idea of this study. A.O. supervised the project. K.S. and D.M.P. conducted materials synthesis and characterization. K.S., D.M.P., and X.L. performed Li recovery from the PBS solutions. K.S. and X.L. prepared the materials for cross-sectional SEM and TEM observations. D.M.P. carried out fluorescence spectroscopy, Li recovery from seawater, and establishing the Li₂CO₃ production process. D.M.P., H.Y.T, and Y.K. performed TEA and LCA. K.S., D.M.P., and A.O. wrote the first draft, and all authors participated in the manuscript revision.

Competing interest declaration

K.S., D.M.P., and A.O. filed a patent application for the bioelectrochemical Li recovery method.

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Synthesis

λ-MnO₂ was prepared from LiMn₂O₄ using an acid-leaching process ⁵⁸. LiMn₂O₄ particles (0.3 g) were placed in a glass bottle, filled with 0.4 M HCl aqueous solution (30 mL), and stirred for 24 h at room temperature. The obtained material was filtered and washed several times with pure water, followed by vacuum drying for 10 h at 100 °C. The synthesised λ-MnO₂ powder was stored in a desiccator until used in Li recovery experiments. LiMn₂O₄ was synthesised using a solution combustion method ^59,60, as briefly described below. LiNO₃ (Wako Chemicals, 98%), Mn(NO₃)₂·6H₂O (Wako Chemicals, 98%), and citric acid (Wako Chemicals, 98%) were dissolved in water. The temperature of the solution was carefully increased to evaporate the liquid until a gel was formed. Subsequently, the gel was ignited by a sudden increase in the temperature. Heat treatment was also performed for 4 h at 700 °C in an air atmosphere to increase the crystallinity and decrease the impurity phase. VESTA ⁶¹ was used to visualise the crystal structures of the oxides and the Li diffusion paths.

Tunnel-structured MnO₂ was synthesised by the following procedure. 0.8 g KMnO₄ (Yoneyama Yakuhin Kougyo, >99%) was dissolved in 20 mL water at 90 °C, and 10 M NaOH (Wako Chemicals, 97%) aqueous solution was added to neutralise it. Subsequently, another solution of 1.5 g MnCl₂·4H₂O (Wako Chemicals, 99%) dissolved in 7.5 mL water was added to the prepared solution to obtain a precipitate. The dispersion was stirred for 1 h at 90 °C, followed by rinsing it with water and drying at 80 °C overnight. The prepared material was then ground to obtain a finer powder.

Bacterial preparation

Wild-type Shewanella oneidensis MR-1 and mutant strain lacking MtrC and OmcA (∆mtrC/omcA) were grown aerobically in a Luria-Bertani (LB) medium (10 g/L tryptone, 5 g/L yeast extract, and 10 g/L NaCl) at 30 °C overnight. The deletion mutant strain was constructed as previously described ⁶². Then, the culture was centrifuged at 6000 rpm for 10 min, and the LB medium was replaced with PBS (8 g/L NaCl, 0.2 g/L KCl, 0.24 g/L KH₂PO₄, and 1.44 g/L Na₂HPO₄; pH 7.4). After removing the LB medium, the concentration of bacteria was adjusted to the given optical density (OD) value at 600 nm prior to use in the Li recovery experiments.

Bioelectrochemical Li recovery

A PBS-based LiCl solution and real seawater were used for the Li recovery experiments. LiCl (Wako Chemicals, 99%) and lactate (Wako Chemicals, sodium L-lactate solution, 70%) were dissolved in PBS and left overnight to obtain homogeneous solutions. MgCl₂ (Wako Chemicals, 97%) was also dissolved to examine the performance of the Li–Mg mixed solutions. Seawater samples were taken from Oarai in Ibaraki, which is on the east side of Japan. Unless otherwise noted, Oarai seawater with 50 mM lactate was used for the Li recovery experiments. The seawater was passed through 0.2 µm filters to remove contaminated cells prior to use.

The Li-containing solution and λ-MnO₂ nanoparticles were placed in a glass bottle, and dissolved oxygen was eliminated by N₂ bubbling. The typical amount of λ-MnO₂ used for the experiments with 50 mL PBS solution was 50 mg. Subsequently, microbes were injected into the reactor, and the mixture was shaken at 30 °C in an incubator. The obtained agglomerates could be easily separated from the supernatant liquid because they were attached to the bottom of the reactor. The agglomerates were dispersed in water by ultrasonication and were washed by treatment with 2% Triton X-100 (Sigma-Aldrich) for 15 min. The process of centrifugation and replacement with pure water was repeated five times to purify the material. Vacuum drying at 100 °C for 18 h was performed to completely remove the water. The washing process was skipped for the dry-weight measurements. The Li concentrations before and after Li recovery were analysed through ICP-MS/OES at the Materials Analysis Station, NIMS, and at the Analytical Research Core for Advanced Materials, Institute for Materials Research, Tohoku University. An ion chromatography system (Shimazu) was employed to determine the amounts of lactate and acetate. CO₂ gas generated from lactate metabolisms was measured by a Gas chromatography-mass spectrometry (Agilent 7000D) coupled with a HP-PLOT/Q column (30 m length, 0.32 mm diameter, and 20 µm film thickness).

As for the prototype with a cation-exchange membrane, an anaerobic culture bottle containing 50 mL PBS solution with 50 mM lactate, MR-1 (OD 0.3), and 50 mg MnO₂ was prepared with N₂ bubbling. Inside a glovebox chamber filled with N₂, the mixture in the culture bottle was transferred to a 50 mL glass bottle. The bottle was then sealed with a cation-exchange membrane (ASTOM, CXP-S). After removal from the glovebox chamber, the bottle was dipped upside-down in a beaker containing 400 mL PBS solution with 10 mM and 50 mM LiCl. The whole apparatus was stood for 24 h at 30 °C.

Characterisation

XRD was performed using an X-ray diffractometer (Rigaku, SmartLab) with Cu-Kα radiation at the NIMS Battery Research Platform, and Rietveld analysis was carried out using the RIETAN-FP program ⁶³ to evaluate the lattice constant. The particle size of the synthesised material was evaluated using a nanoparticle tracking analyser (Particle Metrix, ZetaView), in which the sample was prepared by dispersing λ-MnO₂ nanoparticles in water by ultrasonication. SEM–EDS (JEOL, JSM-7800F) of the agglomerate of MR-1 and nanoparticles was performed at the NIMS Battery Research Platform after a dehydration process. Briefly, the material was immersed in 10% glutaraldehyde overnight, and the supernatant liquid was gradually changed to higher concentrations of ethanol. 100% ethanol was then replaced with tert-butyl alcohol, and the material was freeze-dried overnight, followed by Pt coating to increase conductivity.

Bright-field and fluorescence images were obtained using an inverted microscope (Leica DMi8, Leica) combined with a microcamera (Leica, Leica DFC9000). An agglomerate in the culture vial, after decanting to remove the supernatant, was resuspended by pipetting with 5 mL of pure water. To obtain fluorescence microscopy images of DNA-stained MR-1 cells, 2 μL of the resuspended agglomerate was mixed with 2 μL of 4′,6-diamidino-2-phenylindole (DAPI, 0.5 μg/mL) on a microscope slide. The microscope slide was kept in the dark at 4 °C for 3 min before microscopy. A DAPI filter was used to obtain fluorescence microscopy images.

XANES spectra were obtained at BL-12C, Photon Factory, Japan, where boron nitride (Mitsuwa Chemicals, 99.5%) was used to dilute the materials for XANES analysis. STEM–EELS (JEOL, JEM-ARM200F) of a composite of MR-1 and nanoparticles was conducted at the NIMS Battery Research Platform. The original sample was the same as that used for SEM–EDS, but it was dispersed in ethanol to be loaded onto a TEM grid. The EELS mapping profile showing the valence state of Mn was obtained by fitting the result at each point with those of MnO (Mn²⁺) and MnO₂ (Mn⁴⁺) as the reference materials. Cross-sections of the agglomerates were characterised by FIB–SEM–EDS (Hitachi, SMF2000), which was subjected to DAB-H₂O₂ and OsO₄ staining before the analysis. Cross-sectional TEM (JEOL, JEM-1400Plus) was performed using Tokai Electron Microscopy (Nagoya, Japan) for a resin-embedded sample sectioned with an ultramicrotome (Leica, Ultracut UCT).

Techno-economic and life-cycle analyses

The environmental performance of the bioelectrochemical Li intercalation was evaluated based on the cradle-to-gate LCA of battery-grade Li₂CO₃ ⁶⁴ for ease of comparison with current manufacturing ^65,66. We defined the system boundary as shown in Supplementary Fig. 30. An extended Li₂CO₃ precipitation was included based on our experiments. The Li extraction site was modelled on Salar de Atacama. Within the system, λ-MnO₂ (host material) and water used for Li_1-xMn₂O₄ washing and Li concentration were assumed to be recyclable. The life cycle inventory was detailed in Supplementary Tables 5–15.

We modelled water consumption and climate change impact to represent environmental performance of the technology. The background inventory, e.g., environmental loads of general chemical production and electricity generation, was adopted from ecoinvent 3.10, a commercial LCA database. The water consumption was categorized into in-situ water, brine’s water, and ex-situ water, to distinguish water stress with geography consideration. The climate change impact was characterized by the greenhouse gases’ global warming potential over 100 years ⁶⁷; the contribution was breakdown into Li intercalation or concentration and Li₂CO₃ precipitation, to differentiate the contribution of this study.

TEA was conducted based on the modelled system same as LCA, which assumed a factory producing 70,000-ton Li₂CO₃ per year and operating throughout the year (Supplementary Table 15). The cost of Li₂CO₃ production was calculated based on the annual operation expenditures, including raw materials, utilities, operation and maintenance, overhead, tax and insurance, general expenses, and asset depreciation. The price of raw materials was referred from online wholesale markets in China and the utility cost was based on the Chilean’s electricity rate. We estimated the rest of operation and maintenance cost and the capital expenditures, represented as asset depreciation, based on an up-flow anaerobic sludge blanket (UASB) facility ⁶⁸. The UASB facility was assumed to resemble the Li intercalation facility designed in this study.

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The authors declare potential competing interests as follows: K.S., D.M.P., and A.O. filed a patent application for the bioelectrochemical Li recovery method.

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Bioelectrochemical Intercalation for Scalable Lithium Recovery

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