Revealing the correlation between the mechanical properties of sulfide solid-state electrolyte and the microstructure evolution of composite alloy-anode

Abstract

Alloy-based anodes such as Sn exhibit substantial volumetric changes during lithiation and delithiation, posing critical challenges to cycle stability in all-solid-state batteries (ASSBs). ASSBs have attracted significant attention due to their enhanced safety and potential to utilize lithium metal anodes, offering superior energy densities compared to conventional liquid electrolyte-based lithium-ion batteries. However, mechanical stresses arising from volume changes during battery operation remain major obstacles to their practical implementation. In this study, we systematically explore the relationship between mechanical properties, porosity evolution, and cycling performance in Sn–sulfide electrolyte (SE) composite anodes, using three distinct sulfide electrolytes: Large-SE (large particles, D₅₀ = 11.82 μm), Small-SE (small particles, D₅₀ = 1.03 μm), and Fine-SE (fine particles, D₅₀ = 0.87 μm). Initial microstructural characterization via XCT imaging reveals a paradoxical result: the LSE composite shows localized large pores yet lower measured porosity, while the DSE composite demonstrates uniform and fine pore distribution but higher apparent porosity. Electrochemical analysis shows superior cycling stability and lower irreversible capacity for the LSE composite, despite its higher macro-porosity, suggesting that localized large pores effectively buffer volumetric stresses, maintaining robust interfacial stability. Conversely, DSE composites exhibit significant chemical degradation and increased irreversible capacity due to uniformly distributed micro-scale voids, leading to accelerated interfacial damage and mechanical degradation. Operando stress measurements highlight that the magnitude of pressure change alone does not directly correlate with cycling stability; rather, stress buffering capability and interfacial integrity critically influence long-term performance. This study emphasizes the importance of pore structure distribution and stress-buffering mechanisms in ASSBs, providing critical insights for designing mechanically resilient, high-performance solid-state composite electrodes. These findings pave the way toward realizing stable, high-energy-density ASSBs by carefully controlling electrode microstructure and electrolyte interface characteristics.