Ultrathin Solid Composite Electrolyte Based on Li_6.4La₃Zr_1.4Ta_0.6O₁₂/PVDF-HFP/LiTFSI/Succinonitrile for High-Performance Solid-State Lithium Metal Batteries

Solid composite electrolytes (SCEs) are regarded as an effective solution to ensure safety and enhance the energy density of lithium-based batteries. This work reports an ultrathin SCE membrane (∼ 15 μm) based on Li6.4La3Zr1.4Ta0.6O12/PVDF-HFP/LiTFSI/succinonitrile; it not only possesses good ionic conductivity (6.53 × 10–4 S cm–1 with a little amount of liquid electrolyte) at 30 °C and a satisfactory lithium ion transfer number (0.55 without electrolyte), but also exhibits excellent thermal and mechanical properties. A symmetric cell with SCE succinonitrile-10% (SN-10%) can be continuously cycled without short circuit at 0.2 mA cm–2 for about 340 h. Moreover, a high reversible discharge capacity of 150.2 mAh g–1 at 0.5 C was maintained by the cell (LiFePO4/SCE SN-10%/Li) after 269 cycles at room temperature. Notably, a capacity of about 100 mAh g–1 at 5 C was also obtained. This work might guide the improvement of future solid-state lithium/sodium metal batteries and lithium–sulfur batteries, even for wearable flexible batteries.