Mechanically Strong Active‐Site‐Enriched Polymer Composite Solid Electrolytes toward Superior Room‐Temperature Performance in Lithium Batteries

Abstract Solid‐state electrolytes (SSEs) are promising for lithium batteries with higher safety, cycling stability, and energy density. Among the various SSEs, solid polymer electrolytes (SPEs) are a highly preferred choice due to their high thermal stability, thin design, and good formability. However, polymer electrolytes have low ionic conductivity, for example, polyethylene oxide (PEO), one of the most dominant polyelectrolyte materials, has a low ionic conductivity at room temperature due to its high crystallinity. Theoretically, increasing the ionic active sites by decreasing its crystallinity is an effective strategy, but this may lead to its inability to form films or poor mechanical strength. In this work, the crystallinity of PEO is reduced by introducing succinonitrile (SN), and solution blow‐spun polyacrylonitrile (PAN) fiber film is employed as the skeleton of the SPE to provide good mechanical strength. PEO‐LiTFSI‐SN/PAN SPEs have a tensile strength of at least 4.5 MPa. To provide more Li+ active sites, PEO‐LiTFSI‐SN/MXene@PAN composite SPEs are fabricated by doping the PAN fibers with MXene rich in functional groups. The specific capacity of the LFP|PEO‐LiTFSI‐SN/MXene@PAN|Li button cell reaches 134.8 mAh g−1 in the first cycle, and the capacity retention rate of 100 cycles is 75.8% at 0.5 C at room temperature.