Thin Li1.3Al0.3Ti1.7(PO4)3-based composite solid electrolyte with a reinforced interface of in situ formed poly(1,3-dioxolane) for lithium metal batteries

Composite solid electrolytes (CSEs) exhibit great potential due to their advantages of both sufficient strength and high ionic conductivity. However, their interfacial impendence and thickness hinder potential applications. Herein, a thin CSE with good interface performance is designed through the combination of immersion precipitation and in situ polymerization. By employing a nonsolvent in immersion precipitation, a porous poly(vinylidene fluoride-cohexafluoropropylene) (PVDF-HFP) membrane could be rapidly created. The pores in the membrane could accommodate sufficient well-dispersed inorganic Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) particles. Subsequent in situ polymerized 1,3‑dioxolane (PDOL) further protects LATP from reacting with lithium metal and supplies superior interfacial performance. The CSE has a thickness of ∼ 60 μm, ionic conductivity of 1.57 × 10^-4 S cm^-1, and oxidation stability of 5.3 V. The Li/1.25LATP-CSE/Li symmetric cell has a long cycling performance of 780 h at 0.3 mA cm^-2 for 0.3 mAh cm^-2. The Li/1.25LATP-CSE/LiFePO₄ cell exhibits a discharge capacity of 144.6 mAh/g at 1C and a capacity retention of 97.72 % after 300 cycles. Continuous depletion of lithium salts due to the reconstruction of the solid electrolyte interface (SEI) may be responsible for battery failure. The combination of the fabrication method and failure mechanism gives new insight into designing CSEs.