Phosphorus‐Anchored PVDF Polymer‐Regulated Spherulite and Solvation Structure for Long‐Cycling and Safe Solid‐State Lithium‐Ion Batteries

Abstract Polyvinylidene fluoride (PVDF)‐based solid‐state polymer electrolytes always suffer from their intrinsic flammability, limited Li + transfer, and the interfacial degradation induced by high‐activity residual N , N ‐dimethylformamide (DMF) solvent. Herein, a 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide (DOPO)‐anchored PVDF‐based solid‐state electrolyte is synthesized by a two‐step reaction involving PVDF dehydrofluorination and subsequent phosphorus‐hydrogen addition. The covalent immobilization of DOPO on PVDF polymers endows the electrolyte with high flame retardancy while inhibiting phosphorus‐associated reactions with lithium anodes. The alteration in polymer crystallinity and polarity significantly increases the relative permittivity of electrolyte and leads to a densely‐interconnected spherulite network, facilitating the homogeneous Li + distribution and rapid transport. Remarkably, the DOPO‐anchored polymers are involved in Li + solvation at the expense of DMF molecules, which effectively suppresses DMF decomposition on electrode surfaces and promotes formation of a robust anion‐derived solid electrolyte interphase. The resultant polymer electrolyte demonstrates exceptional cycling stability, maintaining over 2500 h in symmetric lithium cell (0.1 mA cm −2 ) and 850 cycles in LiFePO 4 /Li cells (0.5 C) with 94.27% capacity retention. Furthermore, it enables stable operation in high‐voltage LiNi 0.9 Co 0.05 Mn 0.05 O 2 /Li and practical pouch cells, while achieving high safety of batteries under abusive conditions. This work presents an innovative design in PVDF‐based polymer electrolytes for safe and long‐cycling solid‐state lithium‐ion batteries.