Molecular‐Grafting‐Induced Anion Immobilization in Polymer Electrolytes for High‐Transference‐Number and Dendrite‐Free Solid‐State Lithium Batteries

Solid polymer electrolytes (SPEs) are pivotal to developing safe, high‐energy‐density lithium metal batteries, yet their commercialization is hindered by low ionic conductivity and inadequate suppression of lithium dendrite growth. This work tackles these challenges through a molecular grafting strategy that functionalizes a poly(vinylidene fluoride‐ co ‐trifluorochloroethylene) (PVDF‐CTFE) backbone with lithium phenylsulfonate groups, yielding a novel copolymer, PVDF‐BSFE, with enhanced ion transport properties and interfacial stability. The grafted phenylsulfonate units facilitate lithium‐ion dissociation via their strong electron‐withdrawing effect and restrict anion migration through steric hindrance, significantly increasing the lithium‐ion transference number to 0.67, far exceeding that of conventional SPEs (0.16–0.5). The PVDF‐BSFE electrolyte demonstrates a room‐temperature ionic conductivity of 0.91 × 10 −3 S cm −1 , representing a 184% improvement over unmodified PVDF counterparts. When deployed in symmetric Li||Li cells, the grafted PVDF‐BSFE electrolyte enables stable cycling for over 450 h with minimal voltage fluctuation (< 0.15 V) at 0.1 mA cm −2 , illustrating exceptional dendrite suppression capability. Furthermore, Li/LiFePO 4 cells with PVDF‐BSFE exhibit high capacity retention (> 81% after 200 cycles) and remarkable rate performance. This work establishes a generalizable molecular design principle, that leverages functional group grafting to simultaneously enhance ion transport and interfacial stability, paving the way for a scalable path toward advanced solid‐state batteries.