Influencing Factors on Li‐ion Conductivity and Interfacial Stability of Solid Polymer Electrolytes, Exampled by Polycarbonates, Polyoxalates and Polymalonates

Abstract

AbstractThe application of solid polymer electrolytes (SPEs) in all‐solid‐state(ASS) batteries is hindered by lower Li+‐conductivity and narrower electrochemical window. Here, three families of ester‐based F‐modified SPEs of poly‐carbonate (PCE), poly‐oxalate (POE) and poly‐malonate (PME) were investigated. The Li+‐conductivity of these SPEs prepared from pentanediol are all higher than the counterparts made of butanediol, owing to the enhanced asymmetry and flexibility. Because of stronger chelating coordination with Li+, the Li+‐conductivity of PME and POE is around 10 and 5 times of PCE. The trifluoroacetyl‐units are observed more effective than −O−CH2−CF2−CF2−CH2−O− during the in situ passivation of Li‐metal. Using trifluoroacetyl terminated POE and PCE as SPE, the interfaces with Li‐metal and high‐voltage‐cathode are stabilized simultaneously, endowing stable cycling of ASS Li/LiNi0.6Co0.2Mn0.2O2(NCM622) cells. Owing to an enol isomerization of malonate, the cycling stability of Li/PME/NCM622 is deteriorated, which is recovered with the introduce of dimethyl‐group in malonate and the suppression of enol isomerization. The coordinating capability with Li+, molecular asymmetry and existing modes of elemental F, are all critical for the molecular design of SPEs.