“Polymer-in-ceramic” based poly(Ɛ-caprolactone)/ceramic composite electrolyte for all-solid-state batteries

Inspired by the concept of “polymer-in-ceramic”, a composite poly(Ɛ-caprolactone) (PCL)/ceramic containing LiTFSI is prepared and investigated as a solid electrolyte for all-solid-state batteries. The composite with the optimum concentration of 45 wt% LiTFSI and 75 wt% Li1.5Al0.5Ge1.5(PO4)3 (LAGP, NASICON-type structure) exhibits a high ionic conductivity (σi= 0.17 mS cm−1) at 30 °C, a transference number of 0.30, and is stable up to 5.0 V. The composite electrolyte is a flexible and self-standing membrane. Solid-state LiFePO4//Li batteries with this composite electrolyte demonstrate excellent cycling stability with high discharge capacity of 157 mA h g−1, high capacity retention of 96% and coulombic efficiency of 98.5% after 130 cycles at 30 °C and 0.1 C rate. These electrochemical properties are better than other PCL-based all-solid-lithium batteries, and validate the concept of “polymer-in-ceramic” by avoiding the drawback of lower conductivity in prior “polymer-in-ceramic” electrolyte at high concentration of the ceramic.