Mechanistic comparison of lithiation–delithiation in indium versus tin foil anodes for all-solid-state batteries

Abstract

All-solid-state batteries employing inorganic solid electrolytes are expected to enable higher-rate operation, longer lifetime, and a wider operating-temperature window than conventional liquid-electrolyte lithium-ion batteries. To realize these advantages, high-capacity alloy anodes are attractive alternatives to graphite; however, the lithiation/delithiation mechanisms and their compatibility with inorganic solid electrolytes remain insufficiently understood. Here, we investigate mechanically compliant metallic alloy foil anodes of indium and tin, two adjacent elements in the periodic table (theoretical volumetric capacities >2000 mAh cm⁻³) paired with an argyrodite-type Li₆PS₅Cl solid electrolyte in half cells. Indium exhibits a coulombic efficiency of ∼99%, whereas tin exhibits a much lower coulombic efficiency. Electrochemical measurements combined with X-ray diffraction indicate that indium undergoes reversible crystalline phase transitions over a wide state-of-charge range, yielding distinct potential plateaus. In contrast, tin shows plateau behavior associated with crystalline phase transitions at early lithiation, followed by a gradual potential decrease accompanied by amorphization at higher lithiation levels. These findings clarify distinct reaction pathways of mechanically compliant alloy anodes in all-solid-state batteries, reveal a crystallographic origin of the markedly different reversibility between In and Sn, and provide guidance for selecting alloy/solid-electrolyte pairings toward high-rate and durable cells.