High Conductivity, Lithium Ion Conducting Polymer Electrolyte Based on Hydrocarbon Backbone with Pendent Carbonate

Solid polymer electrolytes (sPE) offer a pathway for safer, less flammable lithium batteries. However, developing a polymer that provides high Li+ mobility as well electrochemical stability remains a challenge, because ion conductive functional units in the polymer main-chain (e.g., polycarbonate and polyether) usually suffer from poor electrochemical stability at high and low potentials. Herein, an sPE with pendent carbonate on a hydrocarbon backbone has been designed and synthesized to overcome conductivity and electrochemical stability problems. This pendant polycarbonate is different from conventional polycarbonate electrolytes because the carbonate moiety is in the sidechain, which mitigates polycarbonate backbone stability problems while still providing high ionic conductivity when used with a plasticizer. Conductivity as high as 1.1 mS cm−1 at 22 °C was obtained. Stable lithium metal plating and stripping using the sPE was observed for 1,200 h and electrochemical stability up to 4.6 V vs Li+/Li has been demonstrated. The low interfacial resistance (<160 ohmcm2 at 22 °C) and reasonable ionic conductivity have enabled acceptable cycling performance in a Li-LiFePO4 battery at 0.98 mA cm−2 for 2,300 cycles.