Synergistic Effect of Lithium Salts with Fillers and Solvents in Composite Electrolytes for Superior Room-Temperature Solid-State Lithium Batteries

To achieve superior solid-state lithium batteries, we have fabricated a flexible composite solid electrolyte (CSE) membrane composed of a poly(vinylidene fluoride) (PVDF) matrix, high-concentration lithium salt (LiTFSI), solvent (DMF), and ceramic filler Li1.3Al0.3Ti1.7(PO4)3 (LATP). A small quantity of polar solvent DMF can not only facilitate the dissociation of LiTFSI but also form lithium-rich complexes [Li(DMF)nTFSI] with Li+, which have the properties of ionic liquids and can improve ionic conductivity. Meanwhile, high-concentration LiTFSI provides a large number of free lithium ions, and TFSI– anions also aggregate to form ion clusters, which pass through the interconnecting network of the filler LATP to form a unique fast conduction channel. Thanks to the synergistic effect between the various components of the LATP-PVDF/Li CSE, the obtained CSE achieves a high ionic conductivity of 2.44 × 10–4 S cm–1 (25 °C), an excellent electrochemical stability window of up to 4.8 V (vs Li+/Li), and desirable self-extinguishing ability. In addition, the CSE exhibits excellent lithium dendrite inhibition ability, which has been verified by periodic lithium stripping/plating tests for more than 3000 h. All of the assembled solid-state LiFePO4||Li, LiCoO2||Li, and LiNi0.6Co0.2Mn0.2O2||Li cells exhibit distinguished rate performance and cycling stability at 30 °C. Furthermore, the LiFePO4||Li solid-state pouch batteries also exhibit excellent flexibility and safety. This investigation demonstrates the importance of the synergistic strategy between the various components of the CSE and opens up ideas for the research and development of high-performance CSEs.