Quasi-Ionic Liquid Enabling Single-Phase Poly(vinylidene fluoride)-Based Polymer Electrolytes for Solid-State LiNi0.6 Co0.2 Mn0.2 O2 ||Li Batteries with Rigid-Flexible Coupling Interphase.

Poly(vinylidene fluoride)-based polymer electrolytes are being intensely investigated for solid-state lithium metal batteries. However, phase separation and porous structures are still pronounced issues in traditional preparing procedure. Herein, a bottom-to-up strategy is employed to design single-phase and densified polymer electrolytes via incorporating quasi-ionic liquid with poly(vinylidene fluoride-co-hexafluoropropylene). Due to strong ion/dipole-dipole interaction, the optimized polymer electrolyte delivers high room-temperature ionic conductivity of 1.55 × 10-3 S cm-1 , superior thermal and oxidation stability of 4.97 V, excellent stretchability of over 1500% and toughness of 43 MJ cm-3 as well as desirable self-extinguishing ability. Furthermore, the superb compatibility toward Li anode enables over 3000 h cycling of Li plating/stripping and ≈98% Coulombic efficiency in Li||Cu test at 0.1 mA cm-2 . In particular, lithium metal battery Li||LiNi0.6 Co0.2 Mn0.2 O2 exhibits a room-temperature discharge retention rate of 96% after 500 cycles under a rate of 0.1 C, which is associated with the rigid-flexible coupling electrodes/electrolytes interphase. This investigation demonstrates the potential application of quasi-ionic liquid/polymer electrolytes in safe lithium metal batteries.