Fiber-Reinforced Ultrathin Solid Polymer Electrolyte for Solid-State Lithium-Metal Batteries

Reducing the thickness of solid polymer electrolytes can help to enhance the energy density for solid-state batteries. However, ultrathin electrolytes still face difficulties in preparation methods, mechanical properties, and interface instability. Herein, a free-standing, scalable, and ultrathin solid polymer electrolyte with a thickness of 10 µm is reported. It is achieved through in situ thermal curing after filling a porous electrospun polyacrylonitrile fiber membrane with poly(ethylene glycol) diacrylate-based electrolyte. Impressively, it contributes to a high ionic conductivity of 8.8 × 10⁻⁴ S cm⁻¹ at room temperature. The membrane can not only provide good mechanical strength but also offer a Li₃N-enriched solid electrolyte interphase, thereby stabilizing the lithium metal anode. The pouch cell pairing the ultrathin electrolyte with Li foil and LiNi_0.8Co_0.1Mn_0.1O₂ cathode of high mass loading can realize a gravimetric/volumetric energy density of 380 Wh kg⁻¹ and 936 Wh L⁻¹. This investigation provides new insights into the potential of fiber-reinforced membranes for high-performance solid-state batteries.