In this study, nanoarchitectured polyimide (PI) gel polymer electrolyte (GPE)-coated lithium cobalt oxide (LiCoO2) cathode materials are fabricated and their application to high-voltage lithium-ion batteries is explored. Distinctive features of the PI coating layer are the highly-continuous surface coverage with nanometer thickness (∼5nm) and also the facile ion transport via the nanoscale layer. Based on the physicochemical characterization of the PI coating layer, its influence on the cell performance and thermal stability of high-voltage charged LiCoO2 is investigated as a function of charge cut-off voltage (herein, 4.4, 4.5, and 4.6V). The anomalous nanoarchitectured PI coating layer, which behaves as an ion-conductive protection barrier to mitigate the undesired side reactions predominantly occurring onto the charged LiCoO2 surface, plays a viable role in improving the cell performance and alleviating the interfacial exothermic reaction between the delithiated LiCoO2 and liquid electrolyte. Notably, these advantageous effects of the PI-coated LiCoO2 become more pronounced as the charge cut-off voltage is increased, where liquid electrolyte is highly vulnerable to electrochemical decomposition.