Self-assembling solid cathode enables high-capacity, low-cost Ca-Sb battery

Self-assembling solid cathode enables high-capacity, low-cost Ca-Sb battery | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Physical Sciences - Article Self-assembling solid cathode enables high-capacity, low-cost Ca-Sb battery Hojong Kim, Sanghyeok Im, Peyman Asghari-Rad, Kelly Varnell, Alex Vai, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4356928/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 24 Jul, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract For renewable energy technologies to decarbonize the power grid without compromising its reliability, low-cost grid-scale energy storage with resilient long-term performance is required. Here, we report a new type of high-temperature liquid metal battery (LMB) that achieves unprecedented capacity, low electrode costs, and strong cycling performance by replacing the traditional liquid LMB cathode with one based on solid particles. Through the combination of a liquid calcium (Ca) alloy anode, a cathode based on solid antimony (Sb) particles, and an all-chloride electrolyte, the Ca||Sb (s) system achieved 318% higher discharge capacity per unit mass of the cathode (715 mAh g -1 vs. 171 mAh g -1 ) and 76% lower electrode cost (15.5 $/kWh vs. 65 $/kWh) than the lowest cost LMB chemistry yet published. These Ca||Sb (s) batteries cycled with high Coulombic (>98.4%) and energy efficiencies (79–84%) at C-rates relevant for daily cycling applications. The remarkable increase in specific capacity is due to the self-assembly of Sb into a micro-structured, electronically connected cathode network, which enables nearly complete utilization of Sb. Despite using a solid cathode, the Ca||Sb (s) system retains the characteristic minimal capacity fade of LMBs, with no meaningful degradation observed over ~4000 full depth-of-discharge cycles. Additionally, the liquid Ca alloy anode mitigates the formation of solid Ca dendrites which would be detrimental to stable cycling performance. Physical sciences/Energy science and technology/Energy storage/Batteries Physical sciences/Materials science/Materials for energy and catalysis/Batteries Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction The urgent need to decarbonize the electric grid and integrate renewable energy technologies has created unprecedented growth in the demand for large-capacity energy storage. While storage markets are diverse and need solutions with varying characteristics, a common thread is that the cost of electricity storage must be low enough to displace more carbon-intensive methods of ensuring grid stability, like natural gas peaker plants 1–3 . This cost constraint has thus featured prominently in the recent development of liquid metal batteries (LMBs) made from earth-abundant materials, which display reliable performance and high current capabilities due to fast liquid-liquid kinetics 4–7 . For example, a Li||Sb-Pb( l ) LMB achieved a specific capacity of 171 mAh g -1 and an electrode cost of 65 $/kWh, while successfully demonstrating a long life span with negligible capacity fade at 500 °C 5 . Even as Li-ion battery (LIB) technology has advanced in recent years leading to lower electrode costs (70–250 $/kWh) 8–10 , the low-cost floor of LMB chemistries suggests that they could be a cost-effective contributor to stationary energy storage markets. Even among LMBs, those with calcium-based anodes stand out because low-cost, earth-abundant Ca can be paired with several viable cathode materials 2,4,11,12 . Bradwell, and then Ouchi, et al. first demonstrated the feasibility of Ca-based LMBs using a Ca-Mg||Bi( l ) cell at 550 °C. However, the use of costly Bi metal and the reported low capacity (90 mAh g -1 Bi) resulted in a high energy cost of ~144 $/kWh 6,12 . The Ca||Sb couple has been considered one of the most cost-effective electrode pairs since the inception of the LMB due to the high cell voltage (~1.0 V) and low cost of Ca and Sb metals 12,13 . Unfortunately, the promise of a Ca||Sb cell has not previously been realized due to the constraint of a liquid cathode in traditional LMBs, which necessitates an operating temperature of ~700 °C based on the melting point of Sb ( T m, Sb = 631 °C). Furthermore, the limited solubility of Ca in liquid Sb (~25 at% Ca) results in a low specific capacity (136 mAh g -1 Sb) and a relatively high projected electrode cost of 90 $/kWh 13 . We present a paradigm shift by pairing a Ca-based liquid metal anode with a solid Sb cathode to achieve unprecedented capacity and low energy cost in a LMB. While it might be assumed that the relative slowness of diffusion in a solid electrode could reduce battery performance compared to a liquid electrode, the features observed and described herein for the Ca||Sb (s) system circumvent this logic. This battery operates at ~520 °C in a eutectic CaCl 2 -LiCl electrolyte (35-65 mol%, or 58.5-41.5 wt%, T m = 485 °C) 14 which was chosen to allow direct comparison of cycling performance with prior studies of Ca-based LMBs. Figure 1a displays the discharge potential of an Sb electrode (vs. Ca metal) starting from monolithic Sb under constant current (25 mA), showing that a high, useful potential is maintained to a specific capacity beyond 700 mAh g ‑1 Sb. Post-mortem analysis of Sb electrodes at various stages of discharge indicates that the initial bulk Sb loaded transforms into fine particles with cycling ( Figure 1b ). Chemical analysis of the products at 160 mAh g -1 Sb suggests that the cathode is fragmenting due to volume expansion from the progressive formation of Ca-Sb compounds, including CaSb 2 and Ca 11 Sb 10 . We postulate that the high capacity achieved here is due to the fragmentation of Sb which increases surface area and generates short mass transport pathways which allow operation beyond the typical kinetic limitations of solids. Furthermore, Figure 1c is a scanning electron micrograph (SEM) of the cathode of a Ca||Sb (s) cell stopped in a fully charged state after ~1100 cycles and ~12000 hours of run time. The morphology of the Sb cathode in this state of charge, consisting of a porous network of micron-scale particles, was preserved by repeatedly immersing the electrode in clean water to remove the electrolyte with minimal agitation. As the operating temperature of the battery is an appreciable fraction of the melting point of antimony, there is likely an ongoing balance between cathode particle fragmentation and sintering over the course of cycling that spontaneously produces this interconnected structure. The self-assembly of a networked Sb electrode structure is likely to increase the electronic connectivity of the electrode to help achieve practical high capacity operation. [Figure 1] The equilibrium potential ( E eq ) of a particulate Sb electrode during discharge is displayed in Figure 1d as a function of capacity and mole fraction ( x Ca ). These data are obtained from the steady open-circuit potential achieved following sequential coulometric titration at a constant current (20 mA). The particulate Sb electrode demonstrated a useful specific capacity as high as 738 mAh g -1 Sb by sustaining a high potential ( E eq > 0.87 V) until relatively deep states of discharge ( x Ca = 0.63), far surpassing the solubility-limited capacity of the Ca||Sb( l ) couple even at higher temperatures, i.e., 136 mAh g -1 Sb at 700 °C 13 . The high capacity achieved using particulate Sb electrodes is corroborated by electromotive force (emf) measurements of binary Ca-Sb alloys in two-phase regions, as carried out in previous works using a solid CaF 2 electrolyte 15 and in this work using a eutectic CaCl 2 -LiCl liquid electrolyte ( Figure 1e ), which indicates a thermodynamically limited specific capacity of 733 mAh g -1 Sb (or 62.5 at% Ca in Sb). Despite the close agreement of the specific capacities determined from the measurement of E eq through coulometric titration and the emf of binary Ca-Sb alloys, there is a deviation between E eq and the emf of the binary alloys above 320 mAh g -1 Sb ( Figure 1d ), which can be explained by phase analysis of the electrode as summarized in Figure 2 and discussed further below. [Figure 2] To observe practical cycling performance compared to the emf measurements discussed above and provide larger cathode samples for detailed analysis, a 3-electrode electrochemical cell was constructed for the Ca||Sb (s) system. Figure 2a – 2b displays cycling performance for a particulate Sb electrode held in a stainless steel (SS) crucible subjected to constant currents equivalent to C-rates of C/20–1C (based on a theoretical capacity of 733 mAh g -1 Sb) and corresponding to current densities of 50–1000 mA cm -2 (based on the macroscopic area of the exposed cathode surface). This current density is far greater than that typically demonstrated in room temperature Li-ion batteries (90% of theoretical capacity) at C/20–C/2 rates and was about 400 mAh g ‑1 Sb at the highest 1C rate, demonstrating a far greater specific capacity for Ca||Sb( s ) at 520 °C than the Ca||Sb( l ) couple at 700 °C (<136 mAh g -1 Sb) or advanced LIBs (30 days) and high round-trip coulombic efficiencies (>99.4%) during steady state operation at 90–100% of the theoretical capacity. At practical daily cycle rates (C/8–C/10), the calculated energy efficiency is 79–84%, demonstrating utility for grid-scale energy storage when coupled with intermittent renewable energy technologies. The characterization of cathode products, following 10 cycles with various discharge depths at C/6, reveals the dynamic phase evolution of the Sb( s ) electrode as summarized in Figure 2c . X-ray diffraction (XRD) analysis indicates the formation of [Sb + CaSb 2 ] compounds at 168 mAh g -1 Sb and [CaSb 2 + Ca 11 Sb 10 ] at 312 mAh g -1 Sb, in agreement with the known equilibrium phase behavior of the binary Ca-Sb system 15 . Interestingly, at later stages of discharge, the presence of a ternary LiCaSb compound was evident: [Ca 11 Sb 10 + LiCaSb] at 672 mAh g -1 Sb and [LiCaSb + Ca 2 Sb] at the full depth of discharge (734 mAh g -1 Sb). The formation of the LiCaSb compound implies an electrode reaction in which Ca and Li are co-deposited without an associated decrease in electrode potential, particularly at later stages of discharge (>320 mAh g -1 Sb). The formation of LiCaSb explains the deviation of E eq from the emf of binary Ca-Sb alloys as shown in Figure 1d . [Figure 3] Figure 3a schematically illustrates a Ca | CaCl 2 -LiCl | Sb( s ) battery constructed to demonstrate practical implementation of this system. Pure Ca metal was pre-embedded in an iron foam current collector by wetting the foam in molten Ca. The cycling performance of the Ca||Sb( s ) battery was evaluated at 520 °C using a C/2 current rate, shown in Figure 3b – 3c . The Ca||Sb( s ) battery consistently achieved a high average discharge capacity of 715 mAh g -1 Sb (97% of the theoretical capacity) with no indication of capacity loss over 100 cycles (16 days) with high coulombic (98.4%) and energy (86%) efficiencies. Based on battery performance and the cost of electrode materials, the energy cost and energy density of the Ca||Sb( s ) battery are estimated at 15.5 $/kWh and 620 Wh/kg, outperforming those of prior LMBs (65 $/kWh and 194 Wh/kg) 5,7,18,19 by fully utilizing the low-cost particulate Sb cathode up to the thermodynamic limit. [Figure 4] Historically, the use of Ca metal in molten salt electrolytes has presented unpleasant challenges due to its high reactivity and solubility in molten salts, which typically leads to poor coulombic efficiency (< 82%) and rapid cell degradation 20,21 . Furthermore, cell operation at 520 °C, below the melting point of calcium, introduces the possibility of dendritic growth of solid Ca during charging which may result in a short circuit between electrodes or unstable voltage. We report that the excellent cycling performance and absence of erratic behavior observed for this Ca||Sb( s ) battery can be attributed to spontaneous formation of a Ca-Li alloy at the anode. Figure 4a displays a post-mortem image of a fully charged anode after 100 cycles, showing sound retention of anode materials within the foam current collector. Chemical analysis by ICP-AES in Table 1 confirms that the anode material is a binary Ca-Li (~41 at%, or 11 wt% Li) alloy, corroborated by the presence of both Ca( s ) and Li 2 Ca phases from XRD analysis ( Figure 4b ) and a hypo-eutectic microstructure (L ® L + Ca ® Ca + Li 2 Ca) as observed via SEM ( Figure 4c ) 22 . Notably, the formation of this binary Ca-Li alloy means that the anode is liquid during operation, which eliminates the chance of solid dendrite growth and reduces the chemical reactivity of Ca. Furthermore, the liquid Ca-Li alloy exhibited remarkably low overpotentials (<10 mV) owing to facile liquid-liquid interfacial reactions and rapid mass transport during cycling at various currents (15–150 mA), as displayed in Figure 4d . [Figure 5] As further evidence for the cycling stability achievable with the Ca||Sb( s ) chemistry, Figure 5 shows discharge capacity data from a battery over ~4000 cycles and 9 months. This cell was primarily cycled across its full voltage range (0.6–1.2 V) at a nominal rate of 1C. After an initial set of conditioning cycles, the cell was run under quasi-steady state conditions. Notwithstanding some minor discontinuities in the test data due to an unexpected power outage (partial cool-down), no net capacity fade is observed even after a number of cycles equivalent to over a decade of daily cycling. The increase in steady-state capacity observed after the period of deeper discharge cycles (black square symbol), in which the cell voltage was floated at 0.6 V for 0.5 h in a fully discharged state, further supports the hypothesis that increasing cathode fragmentation increases accessible cell capacity. In conclusion, we demonstrate that the unprecedented high capacity of the Ca||Sb( s ) couple in a molten CaCl 2 -LiCl electrolyte is enabled by spontaneous fragmentation of Sb during cycling, the self-assembly of a porous, electronically conductive cathode network, and the formation of a ternary LiCaSb compound without a corresponding loss in cell voltage. Furthermore, in this electrolyte, the formation of a liquid Ca-Li alloy anode allows for rapid electrode kinetics and stable cycling. While the high fraction of LiCl in the electrolyte, which is considerably more expensive than CaCl 2 and other common chloride salts, provides an opportunity to further reduce system costs by minimizing the use of LiCl, these new findings allowed the successful construction and operation of high-capacity Ca||Sb( s ) batteries with high efficiency, excellent cycle life, and a strong potential to be cost-effective at scale. These results are a foundation for continued development of this system to advance its potential for implementation as an energy storage system as part of a decarbonized electrical grid. Methods Cell Components and Configuration. All cell components were prepared and assembled in an inert Ar-filled glovebox (O 2 99.0%) and CaCl 2 (> 98.0%) in a quartz crucible and pre-melted under the following temperature profile; 8 h at 100°C and 270°C for vacuum-drying of salt, 8 h at 430°C during which time the chamber was purged with Ar gas, and 700°C for 3 h to pre-melt the salt. The pre-melted electrolyte was then crushed into fine powder for electrochemical measurements. Electrode materials were prepared using pure Sb (99.95%) and Ca (99.5%) metals. Monolithic Sb electrodes (Fig. 1 a) were prepared by induction melting (IH15A-2 T, Across International) in a BN crucible (8 mm ID, 12 mm OD, 12 mm height), while particulate Sb electrodes were prepared by grinding Sb with a mortar and pestle before loading into a SS crucible (8 mm ID, 12 mm OD, 12 mm height) covered with SS meshes (100×100). Porous metal structures, such as 95% porosity iron foam, were prepared as an electrode holder for any materials deposited to evaluate the anode performance (Fig. 4 ). The potential of each Sb working electrode (WE) was measured in a 3-electrode cell comprised of a Ca-Bi alloy ( x Ca = 0.40) as the reference electrode (RE) and a Ca-Sb alloy ( x Ca = 0.40) as the counter electrode (CE). The Ca alloy electrodes were fabricated using an arc-melter (MAM-1, Edmund Bühler GmbH). The Ca-Bi RE (2 g) was placed in a BN crucible (8 mm ID, 12 mm OD, 25 mm height) with two capillary holes (1.5 mm) drilled just above the bottom of the crucible and its emf value, 0.801 V vs. Ca( s ) at 520°C 23 was used to report the measured electrode potentials versus Ca(s). The Ca-Sb CE (15 g) was placed in a large surface area BN crucible (21 mm ID, 25 mm OD, 12 mm height). Both RE and CE alloys in BN crucibles were remelted using an induction heater, and tungsten electrical leads were inserted into the alloys while still molten. The components and configuration of the 3-electrode cells used in this study are summarized in Figure S1 and Table S1 . The equilibrium potential of particulate Sb (Fig. 1 d) was determined by the coulometric titration technique. The Sb was discharged using a constant current of 20 mA for 30 min in each titration step, followed by an open-circuit potential measurement for 2 h to allow for stabilization of the Sb electrode ( Figure S2 ). For emf measurements of binary Ca-Sb alloys (Fig. 1 e), arc-melted alloys ( x Ca = 0.54–0.65) were equilibrated by annealing at 650°C for 72 h after which the equilibrium phases were confirmed by X-ray diffraction (XRD) ( Figure S3 ). The annealed Ca-Sb alloys were placed in BN crucibles with the same dimension as the RE crucible described above, before their potentials were measured with respect to the Ca-Bi RE at 520°C for 10 h. In the two-electrode Ca||Sb( s ) battery cell of Fig. 3 , the Ca anode was fabricated by immersing iron foam (95% porosity) in molten Ca while the particulate Sb cathode was prepared in a SS crucible with a SS mesh (40×40) spot welded to the top. Both electrodes were then assembled in a SS crucible with an interelectrode distance of 0.5 cm. Once assembled, pre-melted electrolyte powder (120 g) was poured into the crucible. Detailed descriptions of cell components are summarized in Table S2 . The Ca | CaCl 2 -LiCl | Sb( s ) battery was placed in an air-tight SS test chamber under an argon atmosphere and cyclically discharged and charged at 520°C. Electrochemical measurements were carried out using a potentiostat (Interface 5000E, Gamry Instruments) and cell temperature was monitored using a data acquisition system (NI 9211, National Instruments). For the characterization of cycle life data (Fig. 5 ), a two-electrode Ca||Sb (s ) battery cell was prepared and cycled using an Arbin Instruments battery tester for both electrochemical control and data logging. This cell consisted of a SS housing sealed with welds and a brazed ceramic to ensure electrical isolation between the positive and negative terminals. Internally, the liquid anode was held within a stack of SS meshes (35 mesh) with a macroscopic area of ~ 19.7 cm 2 . The cathode was contained in a SS crucible with an opening of equal area covered with SS mesh (80×700 Dutch weave). The electrode holding components were assembled facing each other in a prismatic configuration at a nominal interelectrode spacing of 1.3 cm. Molten salt electrolyte was then poured into the housing around the electrode assemblies as a liquid and allowed to freeze before the cell was sealed. Further construction details for this cell are summarized in Table S2. Characterization/Analysis. Upon completion of electrochemical measurements, the electrodes were raised above the electrolyte and the cell was cooled to room temperature. Each electrode was separated from the cell assembly, immersed in dimethyl sulfoxide (99.9%) for 3 days to remove the entrained salt layer, mounted in epoxy resin, and cross sectioned for post-mortem characterization. For characterization of Sb electrodes in a fully charged state (Fig. 1 c), multiple changes of deionized water were used over several days to remove salt and reveal the electrode morphology. One half of the cross sectioned electrode was polished for microstructural characterization using scanning electron microscopy (SEM, FEI Quanta 200) coupled with energy dispersive spectroscopy (EDS). The second half of the electrode was used for structural analysis by XRD (PANalytical Empyrean, Cu K α -radiation) or chemical analysis by inductively coupled plasma-atomic emission spectroscopy (ICP-AES, Thermo iCAP 7400) after removing the electrode materials from the current collectors/holders. The electrode materials cost per unit energy, C , was calculated using \(C={\sum }_{i}{P}_{i}{m}_{i}/{E}_{D}\) , where \({P}_{i}\) is the commodity bulk price of each electrode material in $ /kg, \({m}_{i}\) is the mass in g, and \({E}_{D}\) is the average discharge energy in kWh. A detailed cost calculation for the Ca||Sb( s ) battery is presented in Table S3 based on electrochemical performance (Fig. 3 ). This approach for electrode cost calculation is consistent with the previously reported values for various LMB cells and the estimated values are compared in Table S4 . Declarations Acknowledgements This work was supported by Ambri Incorporated. The authors also wish to acknowledge Prof. Donald Sadoway for his mentorship, support, and leadership in advancing the research and development of Liquid Metal Batteries. Author contributions. Sanghyeok Im : Conceptualization, Methodology, Investigation, Writing–original draft, Visualization. Peyman Asghari-Rad : Methodology, Visualization, Writing – review & editing. Kelly Elizabeth Varnell : Methodology, Investigation, Writing – review & editing. Alex T. Vai : Validation, Writing – review & editing. Jianyi Cui : Validation, Writing – review & editing. Rachael Howland : Methodology development. David Bradwell : Validation, Writing – review & editing, Project administration. Hojong Kim : Writing – review & editing, Project administration, Supervision. References Gür TM (2018) Review of electrical energy storage technologies, materials and systems: Challenges and prospects for large-scale grid storage. Energy Environ Sci 11:2696–2767 Vesborg PCK, Jaramillo TF (2012) Addressing the terawatt challenge: Scalability in the supply of chemical elements for renewable energy. RSC Adv 2:7933–7947 Dunn B, Kamath H, Tarascon JM (2011) Electrical energy storage for the grid: A battery of choices. Sci (80-) 334:928–935 Kim H et al (2013) Liquid metal batteries: Past, present, and future. Chem Rev 113:2075–2099 Wang K et al (2014) Lithium-antimony-lead liquid metal battery for grid-level energy storage. Nature 514:348–350 Ouchi T, Kim H, Spatocco BL, Sadoway DR (2016) Calcium-based multi-element chemistry for grid-scale electrochemical energy storage. Nat Commun 7:1–5 Bradwell DJ, Kim H, Sirk AHC, Sadoway DR (2012) Magnesium-antimony liquid metal battery for stationary energy storage. J Am Chem Soc 134:1895–1897 Wentker M, Greenwood M, Leker J (2019) A bottom-up approach to lithium-ion battery cost modeling with a focus on cathode active materials. Energies 12:1–18 Mauler L, Duffner F, Zeier WG, Leker J (2021) Battery cost forecasting: A review of methods and results with an outlook to 2050. Energy Environ Sci 14:4712–4739 Mineral commodity summaries (2023) Mineral Commodity Summaries 210 https://pubs.usgs.gov/publication/mcs2023 (2023) 10.3133/mcs2023 Calcium Commodity Price (2023) https://www.intratec.us/chemical-markets/calcium-price Bradwell DJ (2005) Technical and Economic Feasibility of a High-Temperature Self-Assembling Battery. Massachusetts Institute of Technology Ouchi T, Kim H, Ning X, Sadoway DR (2014) Calcium-Antimony Alloys as Electrodes for Liquid Metal Batteries. J Electrochem Soc 161:A1898–A1904 Mahendran KH, Nagaraj S, Sridharan R, Gnanasekaran T (2001) Differential scanning calorimetric studies on the phase diagram of the binary LiCl–CaCl 2 system. J Alloys Compd 325:78–83 Poizeau S, Kim H, Newhouse JM, Spatocco BL, Sadoway DR (2012) Determination and modeling of the thermodynamic properties of liquid calcium-antimony alloys. Electrochim Acta 76:8–15 Li H (2019) Practical Evaluation of Li-Ion Batteries. Joule 3:911–914 Yan S et al (2021) Utilizing in situ alloying reaction to achieve the self-healing, high energy density and cost-effective Li||Sb liquid metal battery. J Power Sources 514:1–7 Ning X et al (2015) Self-healing Li-Bi liquid metal battery for grid-scale energy storage. J Power Sources 275:370–376 Li H et al (2016) Liquid Metal Electrodes for Energy Storage Batteries. Adv Energy Mater 6:1–19 Takeda O, Uda T, Okabe TH Chapter 2.9 - Rare Earth, Titanium Group Metals, and Reactive Metals Production. in (ed. Seetharaman, S. B. T.-T. on P. M.) 995–1069 (Elsevier, 2014). https://doi.org/10.1016/B978-0-08-096988-6.00019-5 Sharma RA (1970) Solubilities of calcium in liquid calcium chloride in equilibrium with calcium-copper alloys. J Phys Chem 74:3896–3900 Bale CW, Pelton AD (1987) The Ca – Li (Calcium-Lithium) system. J Phase Equilib 8:125–127 Kim H et al (2012) Thermodynamic properties of calcium-bismuth alloys determined by emf measurements. Electrochim Acta 60:154–162 Tables Table 1 . ICP-AES chemical composition analysis of the fully charged anode after 100 charge/discharge cycles ( Figure 3 ). Sample Concentration Ca Li Sb Cr Fe Ni (at %) (ppm) #1 57.7 41.3 0.9 246 570 1,332 #2 57.8 41.5 0.6 216 403 2,091 Additional Declarations There is NO Competing Interest. Supplementary Files CaSbbatterySupplementalData.docx Supplemental Information Cite Share Download PDF Status: Published Journal Publication published 24 Jul, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4356928","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Physical Sciences - Article","associatedPublications":[],"authors":[{"id":301943672,"identity":"c4b9cd1d-8d1f-48f0-913c-6f7f787b66a8","order_by":0,"name":"Hojong 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09:05:57","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1178940,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ee,\u003c/strong\u003e Emf measurements of binary Ca-Sb alloys (54–65 at% Ca) in a liquid CaCl\u003csub\u003e2\u003c/sub\u003e-LiCl electrolyte.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFragmentation of solid Sb and resulting high capacity.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea,\u003c/strong\u003e Discharge potential of monolithic Sb electrodes in a 3-electrode cell discharged to 160, 320, 480, 660, and 731 mAh g\u003csup\u003e-1 \u003c/sup\u003eSb, respectively, using constant current (25 mA) in CaCl\u003csub\u003e2\u003c/sub\u003e-LiCl electrolyte at 520 °C.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eb,\u003c/strong\u003e Optical cross-section images of monolithic Sb electrodes at each state of discharge targeted in \u003cstrong\u003eFigure\u003c/strong\u003e \u003cstrong\u003e1a,\u003c/strong\u003e and electron microscopy images at 160 and 660 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb showing the fragmentation of Sb with the formation of Ca-Sb compounds based on EDS point analysis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ec, \u003c/strong\u003eSEM images of the desalted Sb cathode in a fully charged state after ~1100 discharge/charge cycles, primarily at a rate of C/5 between 0.6 and 1.3 V, showing a porous, networked structure consisting of micron-scale cathode particles.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ed,\u003c/strong\u003e Equilibrium potential of particulate Sb (square symbols) as a function of specific capacity via coulometric titration, compared to the emf of binary Ca-Sb alloys (solid lines) using a liquid CaCl\u003csub\u003e2\u003c/sub\u003e-LiCl electrolyte (red) in this work or a solid CaF\u003csub\u003e2\u003c/sub\u003e electrolyte (blue)\u003csup\u003e15\u003c/sup\u003e in previous works.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-4356928/v1/fcd2cf1c3aca7e24b9ab8912.png"},{"id":57405016,"identity":"035ab813-6783-49ad-82a4-99e8cee608f3","added_by":"auto","created_at":"2024-05-30 09:05:58","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":872304,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectrochemical performance and characterization of the particulate Sb electrode.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e, Potentials for a particulate Sb electrode in a SS holder in a 3-electrode cell with a eutectic CaCl\u003csub\u003e2\u003c/sub\u003e-LiCl electrolyte at 520 °C during charging/discharging cycles at various C-rates (25–500 mA), in comparison with the equilibrium potential (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eeq\u003c/sub\u003e) determined in \u003cstrong\u003eFigure 1d\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eb\u003c/strong\u003e, Specific charge/discharge capacity, coulombic efficiency, and energy efficiency as a function of cycle number at various C-rates for an Sb electrode.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ec\u003c/strong\u003e, SEM images, EDS analysis, and XRD patterns of Sb electrodes after 10 discharge/charge cycles to each respective state of discharge under a constant current rate of C/6.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-4356928/v1/0e539224246ad6c5bb24db9f.png"},{"id":57405018,"identity":"ccbf9888-eb30-4df6-b115-8ebc92904d87","added_by":"auto","created_at":"2024-05-30 09:05:58","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":670463,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDemonstration and performance of a Ca | CaCl\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e-LiCl | Sb(\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003es\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e) battery.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e, Schematic of a Ca||Sb(\u003cem\u003es\u003c/em\u003e) battery with optical and elemental X-ray mapping images of the initial configuration for Ca anode and Sb cathode.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eb\u003c/strong\u003e, Representative cell voltage profiles for 100 charge/discharge cycles operated at a rate of C/2 (250 mA) at 520 °C.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ec, \u003c/strong\u003eSpecific charge/discharge capacity, coulombic efficiency, and energy efficiency as a function of cycle number.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-4356928/v1/648dd5feb2b542ef37f49da6.png"},{"id":57405021,"identity":"fa54d94e-c357-4ee1-9bb1-ea162a655971","added_by":"auto","created_at":"2024-05-30 09:06:01","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":857973,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePostmortem characterization and kinetics of the liquid Ca alloy anode.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e, Optical images showing the absence of dendrite formation on the fully charged anode after 100 charge/discharge cycles (\u003cstrong\u003eFigure 3\u003c/strong\u003e) after the salt layer was removed via soaking in dimethyl sulfoxide (left) and after cross-sectioning (right).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eb, \u003c/strong\u003eXRD patterns of the anode indicating the presence of a Ca-Li alloy identified as the Li\u003csub\u003e2\u003c/sub\u003eCa phase.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ec, \u003c/strong\u003eSEM image and Ca element EDS mapping of the anode, indicating hypo-eutectic reaction\u003csup\u003e22\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ed,\u003c/strong\u003e Overpotentials at the liquid Ca alloy in a 3-electrode cell during charging/discharging cycles at various current rates (15–150 mA).\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-4356928/v1/75ac80d10b2a4776504e0b58.png"},{"id":57405017,"identity":"18a225ae-ff80-4f73-b1d3-3423fa9ab3a6","added_by":"auto","created_at":"2024-05-30 09:05:58","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":25503,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eLong-term cycles of a Ca | CaCl\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e-LiCl | Sb(\u003c/strong\u003e\u003cem\u003e\u003cstrong\u003es\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e) battery. \u003c/strong\u003eDischarge capacity of a battery operated over 4000 discharge-charge cycles between 0.6 and 1.2 V at a nominal rate of 1C (4 A, ~200 mA cm\u003csup\u003e-2\u003c/sup\u003e) over ~9 months. Data represented with a black symbol indicates the discharge capacity obtained with the addition of a constant voltage float of 0.6 V for 0.5 h in a state of full discharge, which resulted in a steady increased capacity in the following cycles.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-4356928/v1/eeaa869b97d0c36f970c51ba.png"},{"id":87555596,"identity":"6588ce27-bcdb-4cad-84bb-e56d1a0ff28b","added_by":"auto","created_at":"2025-07-25 07:06:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4940399,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4356928/v1/099d083f-0208-4214-a80c-fdb6db55d59f.pdf"},{"id":57405019,"identity":"70176761-7fc1-438a-8a97-aec95eff6270","added_by":"auto","created_at":"2024-05-30 09:05:59","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":257127,"visible":true,"origin":"","legend":"Supplemental Information","description":"","filename":"CaSbbatterySupplementalData.docx","url":"https://assets-eu.researchsquare.com/files/rs-4356928/v1/c5759b7055065d88ef0ca0eb.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Self-assembling solid cathode enables high-capacity, low-cost Ca-Sb battery","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe urgent need to decarbonize the electric grid and integrate renewable energy technologies has created unprecedented growth in the demand for large-capacity energy storage. While storage markets are diverse and need solutions with varying characteristics, a common thread is that the cost of electricity storage must be low enough to displace more carbon-intensive methods of ensuring grid stability, like natural gas peaker plants\u003csup\u003e1\u0026ndash;3\u003c/sup\u003e. This cost constraint has thus featured prominently in the recent development of liquid metal batteries (LMBs) made from earth-abundant materials, which display reliable performance and high current capabilities due to fast liquid-liquid kinetics\u003csup\u003e4\u0026ndash;7\u003c/sup\u003e. For example, a Li||Sb-Pb(\u003cem\u003el\u003c/em\u003e) LMB achieved a specific capacity of 171 mAh g\u003csup\u003e-1\u003c/sup\u003e and an electrode cost of 65 $/kWh, while successfully demonstrating a long life span with negligible capacity fade at 500 \u0026deg;C\u003csup\u003e5\u003c/sup\u003e. Even as Li-ion battery (LIB) technology has advanced in recent years leading to lower electrode costs (70\u0026ndash;250 $/kWh)\u003csup\u003e8\u0026ndash;10\u003c/sup\u003e, the low-cost floor of LMB chemistries suggests that they could be a cost-effective contributor to stationary energy storage markets.\u003c/p\u003e\n\u003cp\u003eEven among LMBs, those with calcium-based anodes stand out because low-cost, earth-abundant Ca can be paired with several viable cathode materials\u003csup\u003e2,4,11,12\u003c/sup\u003e. Bradwell, and then Ouchi, et al. first demonstrated the feasibility of Ca-based LMBs using a Ca-Mg||Bi(\u003cem\u003el\u003c/em\u003e) cell at 550 \u0026deg;C. However, the use of costly Bi metal and the reported low capacity (90 mAh g\u003csup\u003e-1\u003c/sup\u003e Bi) resulted in a high energy cost of ~144 $/kWh\u003csup\u003e6,12\u003c/sup\u003e. The Ca||Sb couple has been considered one of the most cost-effective electrode pairs since the inception of the LMB due to the high cell voltage (~1.0 V) and low cost of Ca and Sb metals\u003csup\u003e12,13\u003c/sup\u003e. Unfortunately, the promise of a Ca||Sb cell has not previously been realized due to the constraint of a liquid cathode in traditional LMBs, which necessitates an operating temperature of ~700 \u0026deg;C based on the melting point of Sb (\u003cem\u003eT\u003c/em\u003e\u003csub\u003em, Sb\u003c/sub\u003e = 631 \u0026deg;C). Furthermore, the limited solubility of Ca in liquid Sb (~25 at% Ca) results in a low specific capacity (136 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb) and a relatively high projected electrode cost of 90 $/kWh\u003csup\u003e13\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eWe present a paradigm shift by pairing a Ca-based liquid metal anode with a solid Sb cathode to achieve unprecedented capacity and low energy cost in a LMB.\u0026nbsp;While it might be assumed that the relative slowness of diffusion in a solid electrode could reduce battery performance compared to a liquid electrode, the features observed and described herein for the Ca||Sb\u003cem\u003e(s)\u003c/em\u003e system circumvent this logic. This\u0026nbsp;battery operates at ~520 \u0026deg;C in a eutectic CaCl\u003csub\u003e2\u003c/sub\u003e-LiCl electrolyte (35-65 mol%, or 58.5-41.5 wt%, \u003cem\u003eT\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e = 485 \u0026deg;C)\u003csup\u003e14\u003c/sup\u003e which was chosen to allow direct comparison of cycling performance with prior studies of Ca-based LMBs. \u003cstrong\u003eFigure 1a\u003c/strong\u003e displays the discharge potential of an Sb electrode (vs. Ca metal) starting from monolithic Sb under constant current (25 mA), showing that a high, useful potential is maintained to a specific capacity beyond 700 mAh g\u003csup\u003e‑1\u003c/sup\u003e Sb. Post-mortem analysis of Sb electrodes at various stages of discharge indicates that the initial bulk Sb loaded transforms into fine particles with cycling (\u003cstrong\u003eFigure 1b\u003c/strong\u003e). Chemical analysis of the products at 160 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb suggests that the cathode is fragmenting due to volume expansion from the progressive formation of Ca-Sb compounds, including CaSb\u003csub\u003e2\u003c/sub\u003e and Ca\u003csub\u003e11\u003c/sub\u003eSb\u003csub\u003e10\u003c/sub\u003e. We postulate that the high capacity achieved here is due to the fragmentation of Sb which increases surface area and generates short mass transport pathways which allow operation beyond the typical kinetic limitations of solids.\u003c/p\u003e\n\u003cp\u003eFurthermore, \u003cstrong\u003eFigure 1c\u003c/strong\u003e is a scanning electron micrograph (SEM) of the cathode of a Ca||Sb\u003cem\u003e(s)\u003c/em\u003e cell stopped in a fully charged state after ~1100 cycles and ~12000 hours of run time. The morphology of the Sb cathode in this state of charge, consisting of a porous network of micron-scale particles, was preserved by repeatedly immersing the electrode in clean water to remove the electrolyte with minimal agitation. As the operating temperature of the battery is an appreciable fraction of the melting point of antimony, there is likely an ongoing balance between cathode particle fragmentation and sintering over the course of cycling that spontaneously produces this interconnected structure. The self-assembly of a networked Sb electrode structure is likely to increase the electronic connectivity of the electrode to help achieve practical high capacity operation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e[Figure 1]\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe equilibrium potential (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eeq\u003c/sub\u003e) of a particulate Sb electrode during discharge is displayed in \u003cstrong\u003eFigure 1d\u003c/strong\u003e as a function of capacity and mole fraction (\u003cem\u003ex\u003c/em\u003e\u003csub\u003eCa\u003c/sub\u003e). These data are obtained from the steady open-circuit potential achieved following sequential coulometric titration at a constant current (20 mA). The particulate Sb electrode demonstrated a useful specific capacity as high as 738 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb by sustaining a high potential (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eeq\u003c/sub\u003e \u0026gt; 0.87 V) until relatively deep states of discharge (\u003cem\u003ex\u003c/em\u003e\u003csub\u003eCa\u003c/sub\u003e = 0.63), far surpassing the solubility-limited capacity of the Ca||Sb(\u003cem\u003el\u003c/em\u003e) couple even at higher temperatures, i.e., 136 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb at 700 \u0026deg;C\u003csup\u003e13\u003c/sup\u003e. The high capacity achieved using particulate Sb electrodes is corroborated by electromotive force (emf) measurements of binary Ca-Sb alloys in two-phase regions, as carried out in previous works using a solid CaF\u003csub\u003e2\u003c/sub\u003e electrolyte\u003csup\u003e15\u003c/sup\u003e and in this work using a eutectic CaCl\u003csub\u003e2\u003c/sub\u003e-LiCl liquid electrolyte (\u003cstrong\u003eFigure 1e\u003c/strong\u003e), which indicates a thermodynamically limited specific capacity of 733 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb (or 62.5 at% Ca in Sb). Despite the close agreement of the specific capacities determined from the measurement of \u003cem\u003eE\u003c/em\u003e\u003csub\u003eeq\u003c/sub\u003e through coulometric titration and the emf of binary Ca-Sb alloys, there is a deviation between \u003cem\u003eE\u003c/em\u003e\u003csub\u003eeq\u003c/sub\u003e and the emf of the binary alloys above 320 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb (\u003cstrong\u003eFigure 1d\u003c/strong\u003e), which can be explained by phase analysis of the electrode as summarized in \u003cstrong\u003eFigure 2\u0026nbsp;\u003c/strong\u003eand discussed further below.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e[Figure 2]\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo observe practical cycling performance compared to the emf measurements discussed above and provide larger cathode samples for detailed analysis, a 3-electrode electrochemical cell was constructed for the Ca||Sb\u003cem\u003e(s)\u003c/em\u003e system. \u003cstrong\u003eFigure 2a\u003c/strong\u003e\u0026ndash;\u003cstrong\u003e2b\u003c/strong\u003e displays cycling performance for a particulate Sb electrode held in a stainless steel (SS) crucible subjected to constant currents equivalent to C-rates of C/20\u0026ndash;1C (based on a theoretical capacity of 733 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb) and corresponding to current densities of 50\u0026ndash;1000 mA cm\u003csup\u003e-2\u0026nbsp;\u003c/sup\u003e(based on the macroscopic area of the exposed cathode surface). This current density is far greater than that typically demonstrated in room temperature Li-ion batteries (\u0026lt;10 mA cm\u003csup\u003e-2\u003c/sup\u003e)\u003csup\u003e16\u003c/sup\u003e, consistent with the generally facile kinetics in LMBs. The achieved discharge capacity was more than 659 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb (\u0026gt;90% of theoretical capacity) at C/20\u0026ndash;C/2 rates and was about 400 mAh g\u003csup\u003e‑1\u003c/sup\u003e Sb at the highest 1C rate, demonstrating a far greater specific capacity for Ca||Sb(\u003cem\u003es\u003c/em\u003e) at 520 \u0026deg;C than the Ca||Sb(\u003cem\u003el\u003c/em\u003e) couple at 700 \u0026deg;C (\u0026lt;136 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb) or advanced LIBs (\u0026lt;250 mAh g\u003csup\u003e‑1\u003c/sup\u003e)\u003csup\u003e13,17\u003c/sup\u003e. The Sb electrode performance in this cell was reliable with negligible capacity loss over 50 cycles (\u0026gt;30 days) and high round-trip coulombic efficiencies (\u0026gt;99.4%) during steady state operation at 90\u0026ndash;100% of the theoretical capacity. At practical daily cycle rates (C/8\u0026ndash;C/10), the calculated energy efficiency is 79\u0026ndash;84%, demonstrating utility for grid-scale energy storage when coupled with intermittent renewable energy technologies.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe characterization of cathode products, following 10 cycles with various discharge depths at C/6, reveals the dynamic phase evolution of the Sb(\u003cem\u003es\u003c/em\u003e) electrode as summarized in \u003cstrong\u003eFigure 2c\u003c/strong\u003e. X-ray diffraction (XRD) analysis indicates the formation of [Sb + CaSb\u003csub\u003e2\u003c/sub\u003e] compounds at 168 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb and [CaSb\u003csub\u003e2\u003c/sub\u003e + Ca\u003csub\u003e11\u003c/sub\u003eSb\u003csub\u003e10\u003c/sub\u003e] at 312 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb, in agreement with the known equilibrium phase behavior of the binary Ca-Sb system\u003csup\u003e15\u003c/sup\u003e. Interestingly, at later stages of discharge, the presence of a ternary LiCaSb compound was evident: [Ca\u003csub\u003e11\u003c/sub\u003eSb\u003csub\u003e10\u003c/sub\u003e + LiCaSb] at 672 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb and [LiCaSb + Ca\u003csub\u003e2\u003c/sub\u003eSb] at the full depth of discharge (734 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb). The formation of the LiCaSb compound implies an electrode reaction in which Ca and Li are co-deposited without an associated decrease in electrode potential, particularly at later stages of discharge (\u0026gt;320 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb). The formation of LiCaSb explains the deviation of \u003cem\u003eE\u003c/em\u003e\u003csub\u003eeq\u003c/sub\u003e from the emf of binary Ca-Sb alloys as shown in \u003cstrong\u003eFigure 1d\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e[Figure 3]\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFigure 3a\u0026nbsp;\u003c/strong\u003eschematically illustrates a Ca | CaCl\u003csub\u003e2\u003c/sub\u003e-LiCl | Sb(\u003cem\u003es\u003c/em\u003e) battery constructed to demonstrate practical implementation of this system. Pure Ca metal was pre-embedded in an iron foam current collector by wetting the foam in molten Ca. The cycling performance of the Ca||Sb(\u003cem\u003es\u003c/em\u003e) battery was evaluated at 520 \u0026deg;C using a C/2 current rate, shown in \u003cstrong\u003eFigure 3b\u003c/strong\u003e\u0026ndash;\u003cstrong\u003e3c\u003c/strong\u003e. The Ca||Sb(\u003cem\u003es\u003c/em\u003e) battery consistently achieved a high average discharge capacity of 715 mAh g\u003csup\u003e-1\u003c/sup\u003e Sb (97% of the theoretical capacity) with no indication of capacity loss over 100 cycles (16 days) with high coulombic (98.4%) and energy (86%) efficiencies. Based on battery performance and the cost of electrode materials, the\u0026nbsp;energy cost and energy density of the Ca||Sb(\u003cem\u003es\u003c/em\u003e) battery are estimated at 15.5 $/kWh and 620 Wh/kg, outperforming those of prior LMBs (65 $/kWh\u0026nbsp;and 194 Wh/kg)\u003csup\u003e5,7,18,19\u003c/sup\u003e by fully utilizing the low-cost particulate Sb cathode up to the thermodynamic limit.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e[Figure 4]\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHistorically, the use of Ca metal in molten salt electrolytes has presented unpleasant challenges due to its high reactivity and solubility in molten salts, which typically leads to poor coulombic efficiency (\u0026lt; 82%) and rapid cell degradation\u003csup\u003e20,21\u003c/sup\u003e. Furthermore, cell operation at 520 \u0026deg;C, below the melting point of calcium, introduces the possibility of dendritic growth of solid Ca during charging which may result in a short circuit between electrodes or unstable voltage. We report that the excellent cycling performance and absence of erratic behavior observed for this Ca||Sb(\u003cem\u003es\u003c/em\u003e) battery can be attributed to spontaneous formation of a Ca-Li alloy at the anode. \u003cstrong\u003eFigure 4a\u003c/strong\u003e displays a post-mortem image of a fully charged anode after 100 cycles, showing sound retention of anode materials within the foam current collector. Chemical analysis by ICP-AES in \u003cstrong\u003eTable 1\u003c/strong\u003e confirms that the anode material is a binary Ca-Li (~41 at%, or 11 wt% Li) alloy, corroborated by the presence of both Ca(\u003cem\u003es\u003c/em\u003e) and Li\u003csub\u003e2\u003c/sub\u003eCa phases from XRD analysis (\u003cstrong\u003eFigure 4b\u003c/strong\u003e) and a hypo-eutectic microstructure (L\u0026nbsp;\u0026reg;\u0026nbsp;L + Ca\u0026nbsp;\u0026reg;\u0026nbsp;Ca + Li\u003csub\u003e2\u003c/sub\u003eCa) as observed via SEM (\u003cstrong\u003eFigure 4c\u003c/strong\u003e)\u003csup\u003e22\u003c/sup\u003e. Notably, the formation of this binary Ca-Li alloy means that the anode is liquid during operation, which eliminates the chance of solid dendrite growth and reduces the chemical reactivity of Ca. Furthermore, the liquid Ca-Li alloy exhibited remarkably low overpotentials (\u0026lt;10 mV) owing to facile liquid-liquid interfacial reactions and rapid mass transport during cycling at various currents (15\u0026ndash;150 mA), as displayed in \u003cstrong\u003eFigure 4d\u003c/strong\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e[Figure 5]\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAs further evidence for the cycling stability achievable with the Ca||Sb(\u003cem\u003es\u003c/em\u003e) chemistry, \u003cstrong\u003eFigure 5\u003c/strong\u003e shows discharge capacity data from a battery over ~4000 cycles and 9 months. This cell was primarily cycled across its full voltage range (0.6\u0026ndash;1.2 V) at a nominal rate of 1C. After an initial set of conditioning cycles, the cell was run under quasi-steady state conditions. Notwithstanding some minor discontinuities in the test data due to an unexpected power outage (partial cool-down), no net capacity fade is observed even after a number of cycles equivalent to over a decade of daily cycling. The increase in steady-state capacity observed after the period of deeper discharge cycles (black square symbol), in which the cell voltage was floated at 0.6 V for 0.5 h in a fully discharged state, further supports the hypothesis that increasing cathode fragmentation increases accessible cell capacity.\u003c/p\u003e\n\u003cp\u003eIn conclusion, we demonstrate that the unprecedented high capacity of the Ca||Sb(\u003cem\u003es\u003c/em\u003e) couple in a molten CaCl\u003csub\u003e2\u003c/sub\u003e-LiCl electrolyte is enabled by spontaneous fragmentation of Sb during cycling, the self-assembly of a porous, electronically conductive cathode network, and the formation of a ternary LiCaSb compound without a corresponding loss in cell voltage. Furthermore, in this electrolyte, the formation of a liquid Ca-Li alloy anode allows for rapid electrode kinetics and stable cycling. While the high fraction of LiCl in the electrolyte, which is considerably more expensive than CaCl\u003csub\u003e2\u003c/sub\u003e and other common chloride salts, provides an opportunity to further reduce system costs by minimizing the use of LiCl, these new findings allowed the successful construction and operation of high-capacity Ca||Sb(\u003cem\u003es\u003c/em\u003e) batteries with high efficiency, excellent cycle life, and a strong potential to be cost-effective at scale. These results are a foundation for continued development of this system to advance its potential for implementation as an energy storage system as part of a decarbonized electrical grid.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e \u003cb\u003eCell Components and Configuration.\u003c/b\u003e All cell components were prepared and assembled in an inert Ar-filled glovebox (O\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.5 ppm). Eutectic CaCl\u003csub\u003e2\u003c/sub\u003e-LiCl (35\u0026ndash;65 mol%) electrolyte was prepared by mixing appropriate weights of anhydrous LiCl (\u0026gt;\u0026thinsp;99.0%) and CaCl\u003csub\u003e2\u003c/sub\u003e (\u0026gt;\u0026thinsp;98.0%) in a quartz crucible and pre-melted under the following temperature profile; 8 h at 100\u0026deg;C and 270\u0026deg;C for vacuum-drying of salt, 8 h at 430\u0026deg;C during which time the chamber was purged with Ar gas, and 700\u0026deg;C for 3 h to pre-melt the salt. The pre-melted electrolyte was then crushed into fine powder for electrochemical measurements.\u003c/p\u003e \u003cp\u003eElectrode materials were prepared using pure Sb (99.95%) and Ca (99.5%) metals. Monolithic Sb electrodes (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea) were prepared by induction melting (IH15A-2 T, Across International) in a BN crucible (8 mm ID, 12 mm OD, 12 mm height), while particulate Sb electrodes were prepared by grinding Sb with a mortar and pestle before loading into a SS crucible (8 mm ID, 12 mm OD, 12 mm height) covered with SS meshes (100\u0026times;100). Porous metal structures, such as 95% porosity iron foam, were prepared as an electrode holder for any materials deposited to evaluate the anode performance (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe potential of each Sb working electrode (WE) was measured in a 3-electrode cell comprised of a Ca-Bi alloy (\u003cem\u003ex\u003c/em\u003e\u003csub\u003eCa\u003c/sub\u003e = 0.40) as the reference electrode (RE) and a Ca-Sb alloy (\u003cem\u003ex\u003c/em\u003e\u003csub\u003eCa\u003c/sub\u003e = 0.40) as the counter electrode (CE). The Ca alloy electrodes were fabricated using an arc-melter (MAM-1, Edmund B\u0026uuml;hler GmbH). The Ca-Bi RE (2 g) was placed in a BN crucible (8 mm ID, 12 mm OD, 25 mm height) with two capillary holes (1.5 mm) drilled just above the bottom of the crucible and its emf value, 0.801 V vs. Ca(\u003cem\u003es\u003c/em\u003e) at 520\u0026deg;C\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e was used to report the measured electrode potentials versus Ca(s). The Ca-Sb CE (15 g) was placed in a large surface area BN crucible (21 mm ID, 25 mm OD, 12 mm height). Both RE and CE alloys in BN crucibles were remelted using an induction heater, and tungsten electrical leads were inserted into the alloys while still molten. The components and configuration of the 3-electrode cells used in this study are summarized in \u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e and \u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e.\u003c/p\u003e \u003cp\u003eThe equilibrium potential of particulate Sb (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed) was determined by the coulometric titration technique. The Sb was discharged using a constant current of 20 mA for 30 min in each titration step, followed by an open-circuit potential measurement for 2 h to allow for stabilization of the Sb electrode (\u003cb\u003eFigure S2\u003c/b\u003e). For emf measurements of binary Ca-Sb alloys (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee), arc-melted alloys (\u003cem\u003ex\u003c/em\u003e\u003csub\u003eCa\u003c/sub\u003e = 0.54\u0026ndash;0.65) were equilibrated by annealing at 650\u0026deg;C for 72 h after which the equilibrium phases were confirmed by X-ray diffraction (XRD) (\u003cb\u003eFigure S3\u003c/b\u003e). The annealed Ca-Sb alloys were placed in BN crucibles with the same dimension as the RE crucible described above, before their potentials were measured with respect to the Ca-Bi RE at 520\u0026deg;C for 10 h.\u003c/p\u003e \u003cp\u003eIn the two-electrode Ca||Sb(\u003cem\u003es\u003c/em\u003e) battery cell of Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the Ca anode was fabricated by immersing iron foam (95% porosity) in molten Ca while the particulate Sb cathode was prepared in a SS crucible with a SS mesh (40\u0026times;40) spot welded to the top. Both electrodes were then assembled in a SS crucible with an interelectrode distance of 0.5 cm. Once assembled, pre-melted electrolyte powder (120 g) was poured into the crucible. Detailed descriptions of cell components are summarized in \u003cb\u003eTable S2\u003c/b\u003e. The Ca | CaCl\u003csub\u003e2\u003c/sub\u003e-LiCl | Sb(\u003cem\u003es\u003c/em\u003e) battery was placed in an air-tight SS test chamber under an argon atmosphere and cyclically discharged and charged at 520\u0026deg;C. Electrochemical measurements were carried out using a potentiostat (Interface 5000E, Gamry Instruments) and cell temperature was monitored using a data acquisition system (NI 9211, National Instruments).\u003c/p\u003e \u003cp\u003eFor the characterization of cycle life data (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), a two-electrode Ca||Sb\u003cem\u003e(s\u003c/em\u003e) battery cell was prepared and cycled using an Arbin Instruments battery tester for both electrochemical control and data logging. This cell consisted of a SS housing sealed with welds and a brazed ceramic to ensure electrical isolation between the positive and negative terminals. Internally, the liquid anode was held within a stack of SS meshes (35 mesh) with a macroscopic area of ~\u0026thinsp;19.7 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. The cathode was contained in a SS crucible with an opening of equal area covered with SS mesh (80\u0026times;700 Dutch weave). The electrode holding components were assembled facing each other in a prismatic configuration at a nominal interelectrode spacing of 1.3 cm. Molten salt electrolyte was then poured into the housing around the electrode assemblies as a liquid and allowed to freeze before the cell was sealed. Further construction details for this cell are summarized in \u003cb\u003eTable S2.\u003c/b\u003e\u003c/p\u003e \u003cp\u003e \u003cb\u003eCharacterization/Analysis.\u003c/b\u003e Upon completion of electrochemical measurements, the electrodes were raised above the electrolyte and the cell was cooled to room temperature. Each electrode was separated from the cell assembly, immersed in dimethyl sulfoxide (99.9%) for 3 days to remove the entrained salt layer, mounted in epoxy resin, and cross sectioned for post-mortem characterization. For characterization of Sb electrodes in a fully charged state (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec), multiple changes of deionized water were used over several days to remove salt and reveal the electrode morphology. One half of the cross sectioned electrode was polished for microstructural characterization using scanning electron microscopy (SEM, FEI Quanta 200) coupled with energy dispersive spectroscopy (EDS). The second half of the electrode was used for structural analysis by XRD (PANalytical Empyrean, Cu K\u003cem\u003eα\u003c/em\u003e-radiation) or chemical analysis by inductively coupled plasma-atomic emission spectroscopy (ICP-AES, Thermo iCAP 7400) after removing the electrode materials from the current collectors/holders.\u003c/p\u003e \u003cp\u003eThe electrode materials cost per unit energy, \u003cem\u003eC\u003c/em\u003e, was calculated using \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e \\(C={\\sum }_{i}{P}_{i}{m}_{i}/{E}_{D}\\) \u003c/span\u003e \u003c/span\u003e, where \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e \\({P}_{i}\\) \u003c/span\u003e \u003c/span\u003e is the commodity bulk price of each electrode material in \u003cspan\u003e$\u003c/span\u003e/kg, \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e \\({m}_{i}\\) \u003c/span\u003e \u003c/span\u003e is the mass in g, and \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e \\({E}_{D}\\) \u003c/span\u003e \u003c/span\u003e is the average discharge energy in kWh. A detailed cost calculation for the Ca||Sb(\u003cem\u003es\u003c/em\u003e) battery is presented in \u003cb\u003eTable S3\u003c/b\u003e based on electrochemical performance (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). This approach for electrode cost calculation is consistent with the previously reported values for various LMB cells and the estimated values are compared in \u003cb\u003eTable S4\u003c/b\u003e.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by Ambri Incorporated. The authors also wish to acknowledge Prof. Donald Sadoway for his mentorship, support, and leadership in advancing the research and development of Liquid Metal Batteries.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSanghyeok Im\u003c/strong\u003e: Conceptualization, Methodology, Investigation, Writing\u0026ndash;original draft, Visualization.\u0026nbsp;\u003cstrong\u003ePeyman Asghari-Rad\u003c/strong\u003e: Methodology, Visualization, Writing \u0026ndash; review \u0026amp; editing.\u0026nbsp;\u003cstrong\u003eKelly Elizabeth Varnell\u003c/strong\u003e: Methodology, Investigation, Writing \u0026ndash; review \u0026amp; editing.\u0026nbsp;\u003cstrong\u003eAlex T. Vai\u003c/strong\u003e: Validation, Writing \u0026ndash; review \u0026amp; editing. \u003cstrong\u003eJianyi Cui\u003c/strong\u003e: Validation, Writing \u0026ndash; review \u0026amp; editing.\u003cstrong\u003e\u0026nbsp;Rachael Howland\u003c/strong\u003e:\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eMethodology development.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eDavid Bradwell\u003c/strong\u003e: Validation, Writing \u0026ndash; review \u0026amp; editing, Project administration. \u003cstrong\u003eHojong Kim\u003c/strong\u003e: Writing \u0026ndash; review \u0026amp; editing, Project administration, Supervision.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eG\u0026uuml;r TM (2018) Review of electrical energy storage technologies, materials and systems: Challenges and prospects for large-scale grid storage. 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Joule 3:911\u0026ndash;914\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYan S et al (2021) Utilizing in situ alloying reaction to achieve the self-healing, high energy density and cost-effective Li||Sb liquid metal battery. J Power Sources 514:1\u0026ndash;7\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNing X et al (2015) Self-healing Li-Bi liquid metal battery for grid-scale energy storage. J Power Sources 275:370\u0026ndash;376\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi H et al (2016) Liquid Metal Electrodes for Energy Storage Batteries. Adv Energy Mater 6:1\u0026ndash;19\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTakeda O, Uda T, Okabe TH Chapter 2.9 - Rare Earth, Titanium Group Metals, and Reactive Metals Production. in (ed. Seetharaman, S. B. T.-T. on P. M.) 995\u0026ndash;1069 (Elsevier, 2014). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/B978-0-08-096988-6.00019-5\u003c/span\u003e\u003cspan address=\"10.1016/B978-0-08-096988-6.00019-5\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSharma RA (1970) Solubilities of calcium in liquid calcium chloride in equilibrium with calcium-copper alloys. J Phys Chem 74:3896\u0026ndash;3900\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBale CW, Pelton AD (1987) The Ca\u0026thinsp;\u0026ndash;\u0026thinsp;Li (Calcium-Lithium) system. J Phase Equilib 8:125\u0026ndash;127\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKim H et al (2012) Thermodynamic properties of calcium-bismuth alloys determined by emf measurements. Electrochim Acta 60:154\u0026ndash;162\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e1\u003c/strong\u003e. ICP-AES chemical composition analysis of the fully charged anode after 100 charge/discharge cycles (\u003cstrong\u003eFigure 3\u003c/strong\u003e).\u0026nbsp;\u003c/p\u003e\n\u003cdiv\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.08831908831909%\" rowspan=\"3\" valign=\"top\"\u003e\n \u003cp\u003eSample\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"80.91168091168092%\" colspan=\"6\" valign=\"top\"\u003e\n \u003cp\u003eConcentration\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.197183098591548%\"\u003e\n \u003cp\u003eCa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.197183098591548%\"\u003e\n \u003cp\u003eLi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.197183098591548%\"\u003e\n \u003cp\u003eSb\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.197183098591548%\"\u003e\n \u003cp\u003eCr\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.197183098591548%\"\u003e\n \u003cp\u003eFe\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.014084507042252%\"\u003e\n \u003cp\u003eNi\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"48.59154929577465%\" colspan=\"3\"\u003e\n \u003cp\u003e(at %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"51.40845070422535%\" colspan=\"3\"\u003e\n \u003cp\u003e(ppm)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.08831908831909%\"\u003e\n \u003cp\u003e#1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.105413105413106%\"\u003e\n \u003cp\u003e57.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.105413105413106%\"\u003e\n \u003cp\u003e41.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.105413105413106%\"\u003e\n \u003cp\u003e0.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.105413105413106%\"\u003e\n \u003cp\u003e246\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.105413105413106%\"\u003e\n \u003cp\u003e570\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.384615384615385%\"\u003e\n \u003cp\u003e1,332\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"19.08831908831909%\"\u003e\n \u003cp\u003e#2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.105413105413106%\"\u003e\n \u003cp\u003e57.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.105413105413106%\"\u003e\n \u003cp\u003e41.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.105413105413106%\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.105413105413106%\"\u003e\n \u003cp\u003e216\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.105413105413106%\"\u003e\n \u003cp\u003e403\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.384615384615385%\"\u003e\n \u003cp\u003e2,091\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4356928/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4356928/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFor renewable energy technologies to decarbonize the power grid without compromising its reliability, low-cost grid-scale energy storage with resilient long-term performance is required. Here, we report a new type of high-temperature liquid metal battery (LMB) that achieves unprecedented capacity, low electrode costs, and strong cycling performance by replacing the traditional liquid LMB cathode with one based on solid particles. Through the combination of a liquid calcium (Ca) alloy anode, a cathode based on solid antimony (Sb) particles, and an all-chloride electrolyte, the Ca||Sb\u003cem\u003e(s)\u003c/em\u003e system achieved 318% higher discharge capacity per unit mass of the cathode (715 mAh g\u003csup\u003e-1\u003c/sup\u003e vs. 171 mAh g\u003csup\u003e-1\u003c/sup\u003e) and 76% lower electrode cost (15.5 $/kWh vs. 65 $/kWh) than the lowest cost LMB chemistry yet published. These Ca||Sb\u003cem\u003e(s)\u003c/em\u003e batteries cycled with high Coulombic (\u0026gt;98.4%) and energy efficiencies (79–84%) at C-rates relevant for daily cycling applications. The remarkable increase in specific capacity is due to the self-assembly of Sb into a micro-structured, electronically connected cathode network, which enables nearly complete utilization of Sb. Despite using a solid cathode, the Ca||Sb\u003cem\u003e(s)\u003c/em\u003e system retains the characteristic minimal capacity fade of LMBs, with no meaningful degradation observed over ~4000 full depth-of-discharge cycles. Additionally, the liquid Ca alloy anode mitigates the formation of solid Ca dendrites which would be detrimental to stable cycling performance.\u003c/p\u003e","manuscriptTitle":"Self-assembling solid cathode enables high-capacity, low-cost Ca-Sb battery","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-30 09:05:52","doi":"10.21203/rs.3.rs-4356928/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"5cb27f1c-4597-4a9a-afaf-724481c6fe27","owner":[],"postedDate":"May 30th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":31855737,"name":"Physical sciences/Energy science and technology/Energy storage/Batteries"},{"id":31855738,"name":"Physical sciences/Materials science/Materials for energy and catalysis/Batteries"}],"tags":[],"updatedAt":"2025-07-25T07:06:48+00:00","versionOfRecord":{"articleIdentity":"rs-4356928","link":"https://doi.org/10.1038/s41467-025-62080-7","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2025-07-24 04:00:00","publishedOnDateReadable":"July 24th, 2025"},"versionCreatedAt":"2024-05-30 09:05:52","video":"","vorDoi":"10.1038/s41467-025-62080-7","vorDoiUrl":"https://doi.org/10.1038/s41467-025-62080-7","workflowStages":[]},"version":"v1","identity":"rs-4356928","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4356928","identity":"rs-4356928","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}