Enhanced Cycling Performance of High-Voltage Solid-State Lithium Batteries via In Situ Cathode–Electrolyte Interface Construction

The [solvent-Li⁺] complex in poly(vinylidene fluoride) (PVDF)-based polymer electrolytes enables fast ion conduction but also makes it difficult to be compatible with high-voltage cathodes. Here, we demonstrate that the residual amount of solvent significantly affects the ion transport properties and interfacial stability of the electrolyte. In LiNi_xCo_yMn_zO₂/Li batteries, a nonuniform and unstable double-layer CEI is formed due to the decomposition of desolvated NMP molecules and lithium salts, resulting in aggravated polarization and rapid capacity decay. Thus, lithium difluorophosphate (LDFP) is introduced as a sacrificial additive into the composite cathode to construct in situ a robust protective CEI layer. Computational and experimental results indicate that its strong adsorption on the NCM surface helps to form a uniform inorganic-rich interface and passivate the catalytic sites of NCM, thereby achieving stable long-term cycling of solid-state batteries.