Reaction Pathways and Electrochemistry of Various Alloy Anodes in Solid-State Batteries

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Foil-based alloy anodes are a promising negative electrode design for solid-state batteries (SSBs), as they enable high energy density through their dense structure. The scalability and ease of manufacturing of metal foils further positions foil-based alloy anodes as an attractive option for incorporation into next-generation batteries, alongside porous silicon composites or lithium metal anodes. Prior investigations have been carried out to understand the electrochemical behavior of foil-based alloy anodes within liquid-electrolyte lithium-ion batteries1, but there remains a gap in understanding the reaction pathways and microstructural evolution of these anodes in solid-state environments, particularly across broad range of different alloy materials. Here, the electrochemical alloying/dealloying behavior and reversibility of 12 distinct foil-based alloy anodes are investigated and compared within SSBs. Solid-state half cells featuring different foil-based alloy anodes showed a wide range of initial Coulombic efficiency (CE) values, varying from ~99 to ~20%. Observations using cryogenic focused-ion-beam scanning electron microscopy uncovered different evolution of the reaction fronts in different materials during dealloying. The results suggest that diffusional lithium trapping within the foils cause irreversibility (initial CE <80%), which is driven by the formation of the low conductivity delithiated phase that prevents transport from the lithiated phase to the solid-state electrolyte (SSE). Contact loss at the SSE interface may also play a role. The initial CE surpassing 99% of indium results from divergent microstructural evolution, which is clearly different from other materials. Further investigation into the behavior of alloy anodes in half cells with liquid electrolyte as well as SSB full cells, performed under identical stack pressure as that of solid-state half cells (8 MPa), offers additional understanding of how lithium trapping affects electrochemical performance. Our results establish mechanistic insights into the behavior of alloy anodes in solid-state environments, which could be important for next-generation SSBs. Heligman, B. T. et al. Elemental Foil Anodes for Lithium-Ion Batteries. ACS Energy Lett. 6, 2666–2672 (2021).