Reversible Redistribution in Ag-Si Electrodes for Stable Anode-Free All-Solid-State Batteries

Abstract

Anode-free all-solid-state batteries (AFASSBs) have emerged as promising candidates for next-generation energy storage systems due to their high safety and potential for exceptionally high gravimetric and volumetric energy densities. However, achieving long-term cycling stability remains a critical challenge because of nonuniform Li plating/stripping. A dual-component, bifunctional interfacial coating at the current collector/solid electrolyte interface, incorporating both a protective layer and seed sites, is considered critical for uniform Li plating and formation of a stable interface. Nevertheless, how the dual-component redistribution changes during cycling remains poorly understood, and design guidelines for effectively harnessing this phenomenon are still lacking. Here, we employ a gradient cosputtering approach to produce dual-element coated current collectors in which Ag serves as a Li-affinitive nucleation seed and Si functions as an ion-conducting protective interlayer. Compositional gradients enabled a systematic study of composition-dependent behaviors, and ex-situ analyses revealed that a lower Si fraction in the protective layer promotes a “reversible redistribution”, where Si repeatedly migrate during cycling, preventing crack formation over prolonged cycling. The optimized Ag with 1 mol % Si electrode achieved stable cycling even at room temperature. This bifunctional interfacial design provides valuable mechanistic insights and practical guidelines for engineering dual-component electrode architectures for stable, high-energy-density AFASSBs.