Fiber‐Reinforced Composite Polymer Electrolytes for Solid‐State Lithium Batteries

Abstract Solid‐state composite polymer electrolytes (CPEs) have attracted much attention due to their flexibility and low interfacial impedance. Researchers have been improving their ionic conductivity at room temperature, ionic transference number, and (electro)chemical stability. Here, a fiber‐reinforced CPE is prepared by infusing polyethylene oxide (PEO) and Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) electrolytes onto polyacrylonitrile (PAN) nanofiber networks. The introduction of both inorganic ceramic filler LLZTO and plasticizer succinonitrile (SN) reduces the crystallinity of PEO, increases the solubility of lithium salts, and further improves ionic transport kinetics. The ionic conductivity of CPE is 2.57 × 10⁻⁴ S cm⁻¹ at 30 °C and the lithium‐ion transference number is 0.6. Meanwhile, the high content of LLZTO (60 wt.%) brings a better capability to suppress lithium dendrites, and thus lithium symmetrical cells based on this CPE can be stably cycled for up to 500 h. In addition, the PAN fiber network endows CPE with high mechanical strength and high oxidation resistivity, and accordingly an electrochemical stability window as high as 4.7 V. Both LiFePO₄/CPE/Li and LiNi_1/3Co_1/3Mn_1/3O₂/CPE/Li cells can be operated at 30 °C for 100 cycles. This work provides a promising strategy for the preparation of thin CPEs for solid‐state lithium metal batteries.