Interfaces Silicon-Based Electrodes / Solid Electrolyte for High Energy Density Lithium-Ion Batteries

The development of all-solid-state batteries (ASSBs) is a promising route to enhance the energy density and safety of next-generation energy storage systems [1]. Silicon, with its exceptionally high theoretical capacity (~3579 mAh/g), represents a promising alternative to conventional graphite at the negative electrode. However, its large volume change during (de)lithiation [2] and poor interfacial stability with solid electrolytes [3] remain major challenges that hinder practical implementation. This work presents a systematic study of the combined influence of interface architecture and particle size on the electrochemical performance and interfacial stability of Si-based anodes for ASSBs. Two distinct interface configurations were investigated: 2D interfaces, formed by a thin silicon electrode pressed onto dense solid electrolytes, allowing low interfacial passivation. 3D composite interfaces, where Si particles are embedded within a solid electrolyte together with an electronic conductor additive, promoting improved ionic transport and mechanical compliance. The silicon particle size, varied from ~100 nm to 5 µm, was found to strongly affect interfacial contact, stress distribution, and degradation mechanisms. These electrodes were characterised in half cell configuration vs. Li-In metal counter electrode using a sulphide-based solid electrolyte (Li 6 PS 5 Cl), by electrochemical (EIS, ICA, galvanostatic cycling) and structural analyses (FIB-SEM, XPS). These analyses revealed the formation of thin passivation layers at the electrolyte/electrode interface in 2D architectures, due to chemical reactivity, however capacity fading is mainly governed by mechanical stress accumulation and electrode cracking. In contrast, 3D composites mitigate mechanical degradation but are more prone to electrochemical interfacial passivation. These results emphasize the critical role of interface design and particle size in governing the performance and durability of silicon-based ASSBs, providing key insights for the development of stable, high-capacity solid-state anodes.