Insights Into the Interfacial Degradation of High-Voltage All-Solid-State Lithium Batteries

Poly(ethylene oxide)(PEO)-based solid polymer electrolyte(SPE)is considered as a promising solid-state electrolyte for all-solid-state lithium batteries(ASSLBs).Nevertheless,the poor interfacial stability with high-voltage cathode materials(e.g.,LiCoO_(2))restricts its application in high energy density solid-state batteries.Herein,high-voltage stable Li_(3)AlF_(6) protective layer is coated on the surface of LiCoO_(2) particle to improve the performance and investigate the failure mechanism of PEO-based ASSLBs.The phase transition unveils that chemical redox reaction occurs between the highly reactive LiCoO_(2) surface and PEO-based SPE,resulting in structure collapse of LiCoO_(2),hence the poor cycle performance of PEO-based ASSLBs with LiCoO_(2) at charging voltage of 4.2 V vs Li/Li+.By sharp contrast,no obvious structure change can be found at the surface of Li_(3)AlF_(6)-coated LiCoO_(2),and the original layered phase was well retained.When the charging voltage reaches up to 4.5 V vs Li/Li+,the intensive electrochemical decomposition of PEO-based SPE occurs,leading to the constant increase of cell impedance and directly causing the poor performance.This work not only provides important supplement to the failure mechanism of PEO-based batter-ies with LiCoO_(2),but also presents a universal strategy to retain structure stability of cathode-electrolyte interface in high-voltage ASSLBs.