4.8 V Lithium-rich manganese-based solid-state batteries enabled by high oxidation-tolerance quasi-solid polymer electrolytes

Achieving stable cycling of lithium-rich manganese-based oxide (LRM) cathodes beyond 4.8 V remains a formidable challenge due to severe interfacial degradation between the cathode and the electrolyte. Herein, we design and fabricate a quasi-solid polymer electrolyte with high oxidation tolerance and systematically investigate the interfacial chemistry of LRM cathodes operating at 4.8 V. By incorporating a succinonitrile-based eutectic, the oxidative stability of the electrolyte is extended beyond 5.0 V, while a thin, uniform, and organic-inorganic composite cathode-electrolyte interphase is formed in situ on the LRM surface, effectively mitigating manganese dissolution and cathode structural distortion, as confirmed by extended X-ray absorption fine structure and in situ temperature-dependent X-ray diffraction analyses. As a result, the eutectic-engineered quasi-solid polymer electrolyte enables Li||LRM solid-state batteries to achieve stable cycling over 800 cycles at a cutoff voltage of 4.8 V, with a capacity retention of 88.8 %, offering a promising route toward high-energy-density solid-state Li-metal batteries.