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 application 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 its implementation with high voltage cathodes for high-energy-density ASSLBs. Effective interfacial engineering between high voltage cathodes and SPEs 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, atomic layer deposition (ALD) coating on the electrode instead of active material particles realizes a unique method to protect the cathode/SPE interface. As a successful example, a thin ALD-derived lithium tantalate coating on the high-voltage LiCoO2 electrode demonstrated good compatibility with PEO-based SPEs, significantly enhancing the cycling performance of the ASSLBs. The inner mechanism is attributed to the fact that the protection of the conductive carbon/SPE interface helps reduce the electrochemical oxidation of PEO-based SPEs. This work shall give new insights for the interfacial engineering of high voltage cathodes and solid polymer electrolytes.