Lithium Superionic Conductive Nanofiber-Reinforcing High-Performance Polymer Electrolytes for Solid-State Batteries

Although composite solid-state electrolytes (CSEs) are considered promising ionic conductors for high-energy lithium metal batteries, their unsatisfactory ionic conductivity, low mechanical strength, poor thermal stability, and narrow voltage window limit their practical applications. We have prepared a new lithium superionic conductor (Li-HA-F) with an ultralong nanofiber structure and ultrahigh room-temperature ionic conductivity (12.6 mS cm^-1). When it is directly coupled with a typical poly(ethylene oxide)-based solid electrolyte, the Li-HA-F nanofibers endow the resulting CSE with high ionic conductivity (4.0 × 10^-4 S cm^-1 at 30 °C), large Li⁺ transference number (0.66), and wide voltage window (5.2 V). Detailed experiments and theoretical calculations reveal that Li-HA-F supplies continuous dual-conductive pathways and results in stable LiF-rich interfaces, leading to its excellent performance. Moreover, the Li-HA-F nanofiber-reinforced CSE exhibits good heat/flame resistance and flexibility, with a high breaking strength (9.66 MPa). As a result, the Li/Li half cells fabricated with the Li-HA-F CSE exhibit good stability over 2000 h with a high critical current density of 1.4 mA cm^-2. Furthermore, the LiFePO₄/Li-HA-F CSE/Li and LiNi_0.8Co_0.1Mn_0.1O₂/Li-HA-F CSE/Li solid-state batteries deliver high reversible capacities over a wide temperature range with a good cycling performance.