Polyimide gel polymer electrolyte-nanoencapsulated LiCoO_2 cathode materials for high-voltage Li-ion batteries

摘要

We demonstrate a novel and facile approach to surface modification of high-voltage charged LiCoO_2, which is based on encapsulating LiCoO_2 by a polyimide (PI) gel polymer electrolyte layer. The PI is introduced onto the LiCoO_2 by thermally curing 4-component (pyromellitic dianhydride/biphenyl dianhydride/phenylenediamine/oxydianiline) polyamic acid. The PI nanoencapsulating layer features the high surface coverage, nanometer thickness, and facile ion transport. These unique characteristics are expected to enable the PI coating layer to effectively suppress the undesirable interfacial reaction of the LiCoO_2 with liquid electrolyte, which plays a key role in noticeably improving the 4.4 V cycle performance and mitigating the vigorous exothermic reaction between the charged LiCoO_2 and liquid electrolyte.