Transport Properties of Flexible Composite Electrolytes Composed of Li1.5Al0.5Ti1.5(PO4)3 and a Poly(vinylidene fluoride-co-hexafluoropropylene) Gel Containing a Highly Concentrated Li[N(SO2CF3)2]/Sulfolane Electrolyte

Flexible solid-state electrolyte membranes are beneficial for feasible construction of solid-state batteries. In this study, a flexible composite electrolyte was prepared by combining a Li + -ion-conducting solid electrolyte Li 1.5 Al 0.5 Ti 1.5 (PO 4 ) 3 (LATP) and a poly(vinylidene fluoride -co -hexafluoropropylene) (PVDF-HFP) gel containing a highly concentrated electrolyte of Li[N(SO 2 CF 3 ) 2 ] (LiTFSA)/sulfolane using a solution casting method. We successfully demonstrated the operation of Li/LiCoO 2 cells with the composite electrolyte; however, the rate capability of the cell degraded with increasing LATP content. We investigated the Li-ion transport properties of the composite electrolyte and found that the gel formed a continuous phase in the composite electrolyte and Li-ion conduction mainly occurred in the gel phase. Solid-state 6 Li magic-angle spinning NMR measurements for LATP treated with the 6 LiTFSA/sulfolane electrolyte suggested that the Li + -ion exchange occurred at the interface between LATP and 6 LiTFSA/sulfolane. However, the kinetics of Li + transfer at the interface between LATP and the PVDF-HFP gel was relatively slow. The interfacial resistance of LATP/gel was evaluated to be 67 Ω·cm 2 at 30 °C, and the activation energy for interfacial Li + transfer was 39 kJ mol -1 . The large interfacial resistance caused the less contribution of LATP particles to the Li-ion conduction in the composite electrolyte.