Demystifying Semi-Solid-State Batteries: Insights from X-Ray Photoemission Spectroscopy and Electrical Abuse Tests

This study investigates four semi-solid-state battery cell types by using X-ray photoemission spectroscopy to characterize fresh cathodes from unabused cells according to their electrolyte systems and interphase strategies. Their safety behaviour is then evaluated through external short-circuit (ESC) and overcharge tests conducted in accordance with the IEC 62660-2:2018 and IEC 62660-3:2022 standards, respectively. The ESC test reveals the differences in short-circuit tolerance, as cells with a polymer-based electrolyte transition most rapidly to hazardous failure, with the most severe visible effects compared to the cells with a Li3PS4 (LPS) coating interphase strategy. Additionally, the overcharge test produces more severe outcomes than ESC once the IEC voltage threshold is exceeded. The criterion .> +0.1 V s−1 after the voltage plateau may serve as an electrical precursor for voltage failure, providing an indication of abnormal cell behaviour prior to separator hard short-circuiting in cases where failure subsequently occurred. Under liquid wetting conditions, the resulting interfacial chemistry depends on the interaction between the liquid phase, the host material, and the additives present. FTIR gas-phase analysis indicates that ESC behaviour is dominated by localized Joule heating, wetting-agent evaporation, swelling, and venting, whereas overcharge conditions promote structural deformation, oxygen release, fire, and explosion.