Abstract
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 Li1.5Al0.5Ti1.5(PO4)3 (LATP) and a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) gel containing a highly concentrated electrolyte of Li[N(SO2CF3)2] (LiTFSA)/sulfolane using a solution casting method. We successfully demonstrated the operation of Li/LiCoO2 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 6Li magic-angle spinning NMR measurements for LATP treated with the 6LiTFSA/sulfolane electrolyte suggested that the Li+-ion exchange occurred at the interface between LATP and 6LiTFSA/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·cm2 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.
Highlights
Li-ion-conducting inorganic solid electrolytes (SEs) have been widely investigated because of their high thermal stability and single-ion conducting properties.[1−3] Recently, sulfide-based SEs have shown high ionic conductivity on the order of 10−3− 10−2 S cm−1 at room temperature, comparable to that of conventional liquid electrolytes, and a Li-ion cell with a sulfidebased SE has been demonstrated to exhibit high rate performance in a wide temperature range.[4]
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
The large interfacial resistance caused the less contribution of LATP particles to the Li-ion conduction in the composite electrolyte
Summary
Li-ion-conducting inorganic solid electrolytes (SEs) have been widely investigated because of their high thermal stability and single-ion conducting properties.[1−3] Recently, sulfide-based SEs have shown high ionic conductivity on the order of 10−3− 10−2 S cm−1 at room temperature, comparable to that of conventional liquid electrolytes, and a Li-ion cell with a sulfidebased SE has been demonstrated to exhibit high rate performance in a wide temperature range.[4]. We previously reported that sulfolanebased highly concentrated Li salt electrolytes exhibit high tLi+ (0.6−0.8) and that Li batteries can be operated at a current density of ∼2 mA cm−2, regardless of the relatively low ionic conductivity (0.3−0.5 mS cm−1) at room temperature.[31,32] In this work, we applied composite electrolytes to Li/LiCoO2 cells. LiTFSA and SL were mixed in a 1:2 molar ratio in an Ar-filled glovebox to prepare a highly concentrated liquid electrolyte. This liquid electrolyte is hereinafter abbreviated as [Li(SL)2][TFSA]. The weight ratio of PVDF−HFP/[Li(SL)2][TFSA] was 30:70 This polymer solution was mixed with the LATP powder, vigorously stirred for 2 h, poured into a glass dish, and dried to obtain a composite membrane. Galvanostatic charge−discharge measurements were performed using an automatic charge−discharge instrument (HJ1001SD8, Hokuto Denko) at 60 °C
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