Deciphering Polarity Effects of Polymer to Regulate Li ⁺ Ionic Environment in Solid Polymer Electrolytes for Solid‐State Lithium Batteries

ABSTRACT Poly(vinylidene fluoride) (PVDF)‐based solid polymer electrolytes (SPEs) containing residual solvents are promising candidates for solid‐state batteries due to their high ionic conductivity, which arises from enhanced lithium salt dissociation and conformational regulation of the polymer matrix. However, the role of the polymer matrix has been confined to facilitating bulk conduction of Li ⁺ , while the influence of polymer polarity on the behavior of residual solvents and their impact on electrode/SPE interfacial chemistry remains insufficiently understood. Here, we introduce the concept of an ionic environment, which extends the conventional solvation structure model by incorporating the role of polymer polarity in governing Li ⁺ coordination. Atomic‐scale simulations and experimental characterizations reveal that, compared with PVDF, the highly polar P(VDF–TrFE) establishes an ionic environment where residual DMF and FSI ⁻ strongly interact with the polymer, facilitating the desolvation of Li ⁺ from DMF and FSI ⁻ . In addition, the higher binding affinity of P(VDF–TrFE) toward DMF promotes a more uniform residual DMF distribution within the SPE and mitigates its decomposition, which in turn enhances the electrochemical performance and interfacial stability of solid‐state cells. By elucidating the previously underappreciated effects of polymer polarity, this work provides guiding principles for the rational design of advanced SPEs.