Interface stability between cathode and electrolyte is closely related to the interface resistance and electrochemical performance of all-solid-state lithium ion batteries (LIBs). However, the significant interface issues between cathode and all-solid-state polymer electrolyte have been researched rarely. Here, we demonstrate that severe interface decomposition reactions occur continually and deteriorate the cycling life of high voltage LiCoO2/cellulose-supported poly(ethylene oxide) (PEO)-lithium difluoro(oxalato) borate (LiDFOB)/Li battery between 2.5 and 4.45 V vs. Li/Li+. To improve the interface stability between LiCoO2 and PEO-LiDFOB electrolyte, we modify the LiCoO2 surface by a thin layer of high ionic conducting and electrochemical oxidation resistant poly(ethyl cyanoacrylate) (PECA) through in-situ polymerization method. The PECA coating layer significantly suppresses the continuous decomposition of lithium difluoro(oxalato) borate (LiDFOB) salt in PEO electrolyte. As a result, the PECA-coated LiCoO2/PEO-LiDFOB/Li battery shows decreased interface resistance and enhanced cycling stability. This work will enlighten the understanding of interface stability and enrich the modification strategy between cathode and polymer electrolyte as well as boost the further development of all-solid-state LIBs. (c) 2017 The Electrochemical Society. All rights reserved.