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

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.