A highly ionic transference number eutectogel hybrid electrolytes based on spontaneous coupling inhibitor for solid-state lithium metal batteries

Polymer-based solid electrolytes have been extensively studied for solid-state lithium metal batteries to achieve high energy density and reliable security. But, its practical application is severely limited by low ionic conductivity and slow Li+ transference. Herein, based on the “binary electrolytes” of poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE)) and lithium salt (LiTFSI), a kind of eutectogel hybrid electrolytes (EHEs) with high Li+ transference number was developed via tuning the spontaneous coupling of charge and vacated space generated by Li-cation diffusion utilizing the Li6.4La3Zr1.4Ta0.6O12 (LLZTO) dopant. LLZTO doping promotes the dissociation of lithium salt, increases Li+ carrier density, and boosts ion jumping and the coordination/decoupling reactions of Li+. As a result, the optimized EHEs-10% possess a high Li-transference number of 0.86 and a high Li+ conductivity of 3.2×10−4 S·cm−1 at room temperature. Moreover, the prepared EHEs-10% composite solid electrolyte presents excellent lithiumphilic and compatibility, and can be tested stably for 1,200 h at 0.3 mA·cm−2 with assembled lithium symmetric batteries. Likewise, the EHEs-10% films match well with high-loading LiFePO4 and LiCoO2 cathodes (> 10 mg·cm−2) and exhibit remarkable interface stability. Particularly, the LiFePO4//EHEs-10%//Li and LiCoO2//EHEs-10%//Li cells deliver high rate performance of 118 mA·hg−1 at 1 C and 93.7 mAh·g−1 at 2 C with coulombic efficiency of 99.3% and 98.1%, respectively. This work provides an in-depth understanding and new insights into our design for polymer electrolytes with fast Li+ diffusion.