Interfacial engineering enables stable cycling of high voltage Li-rich cathodes in PEO-based all-solid-state batteries

Poly(ethylene oxide)-based solid polymer electrolytes (PEO-SPEs) are regarded as promising alternatives to liquid electrolyte in batteries due to their improved safety and good compatibility with lithium-metal anode. However, the decomposition of PEO matrix at high voltage that leads to capacity degradation, hindering its further deployment in high-voltage all-solid-state lithium-metal batteries (ASSLMBs). Herein, we studied the failure mechanism of PEO-SPEs with high-capacity Li-rich layered cathode and reported a strategy of using an Al2O3 coating to improve electrochemical performance. The anion redox of Li1.2Ni0.13Co0.13Mn0.54O2 (LR114) generates reactive oxygen species, causing the terminal hydrogen of PEO to dissociate into H+, which combines with TFSI– to form HTFSI. HTFSI initiates the further autocatalytic decomposition of PEO, which induces the dissolution of transition metals and formation of the spinel-like phase on the surface of LR114. By integrating Al2O3 protective layer on cathodes, it adsorbs the TFSI–/FSI– anions preferentially, leading to the formation of a LiF-rich cathode-electrolyte interphase (CEI), which in turn inhibits the decomposition of PEO. The obtained Li-In|PEO|Al2O3@LR114 ASSLMBs exhibit better cycling performance with a capacity retention of 93.5% after 100 cycles at 0.2 C. This study demonstrates the potential of interfacial engineering to control the chemical composition of electrode-electrolyte interphase in high-voltage ASSLMBs.