Engineering the Conductive Carbon/PEO Interface to Stabilize Solid Polymer Electrolytes for All-Solid-State High Voltage LiCoO2 Batteries
All-solid-state lithium batteries (ASSLBs) are promising energy storage devices for applications in electric transportation and large-scale energy storage systems. Polyethylene oxide (PEO)-based solid polymer electrolytes (SPEs) are attractive solid-state electrolytes for ASSLBs due to their high ionic conductivity, light weight, and low cost. However, the low electrochemical oxidation potential window of PEO seriously restricts their implementation with high voltage cathodes for high-energy-density ASSLBs. Effective interfacial engineering between high voltage cathodes and SPE can be a solution. Most of the reported conventional cathode protection approaches have been focused on building coating layers on active material particles, which, however, can be insufficient because the conductive carbon is able to accelerate the decomposition of SPEs. In this work, ALD coating on electrode instead of active material particles realizes a unique method to protect cathode and SPE interface. As a successful example, a thin lithium tantalate coating on high-voltage LiCoO2 electrode by atomic layer deposition demonstrated good compatibility with PEO-based SPEs, significantly enhancing the cycling performance of the ASSLBs. The inner mechanism is attributed to that the protection of conductive carbon/SPE interface helps to reduce the electrochemical oxidation of PEO-based SPE. This work shall give new insights for the interfacial engineering of high voltage cathode and solid polymer electrolytes.