Solid Polymer Electrolyte Reinforced with a Li1.3Al0.3Ti1.7(PO4)3-Coated Separator for All-Solid-State Lithium Batteries

Poly(ethylene oxide) (PEO)-based solid-state lithium batteries (SSLBs), accompanied by potential high energy density and reliable safety, have attracted wide attention. However, PEO-based solid-state electrolytes (SSEs) are hard to scale up due to their low oxidation stability, low ionic conductivity at room temperature, and relatively poor mechanical properties. Here, a PEO-based ceramic-polymer (PCP) composite SSE is designed. The porous Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP)-coated polyethylene (PE) separator is filled with PEO/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) solution, which possesses both a robust mechanical property and processable flexibility. The results show the PCP membrane effectively suppresses the growth of lithium (Li) dendrites identified by a flat Li deposition. It is attributed to the robustness of the PCP membrane itself and the formation of a mixed ionic/electronic conducting interphase (MCI) intertwined with a solid electrolyte interface (SEI) between the PCP membrane and the Li anode. The MCI-SEI intertwined mixed phase facilitates the homogeneous Li deposition and enhances the cycle stability of the electrolyte/anode interface. Hence, the PCP membrane effectively prevents short-circuiting and shows a good cycling stability of more than 2000 h in a Li/PCP/Li symmetric cell with a current density of 0.2 mA cm^-2 at 60 °C. Moreover, the Li/PCP/LiFePO₄ all-solid-state battery shows a stable cycling performance with 160 mAh g^-1 at 0.2C after 200 cycles at 60 °C. The results show the purposed PCP membrane based on a LATP-coated PE separator is easy to be fabricated and could be practical for many applications.