Modulating Salt Dissociation and Solvent Immobilization Through Dipole Interactions in Polymer Electrolytes for Lithium Metal Batteries

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Abstract
Poly(vinylidene fluoride) (VDF)‐based solid polymer electrolytes (SPEs) show great potential for application in solid‐state lithium batteries. However, their poor ion transport capabilities and uncontrolled electrode/electrolyte interfacial reactions induced by residual solvents limit their overall electrochemical performance. To address these challenges, a LiTFSI‐replaced dual‐functional cationic covalent organic framework (COF) is strategically designed, denoted COF‐LiTFSI, as organic fillers into poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVHF)‐based solid polymer electrolyte (SPE) to regulate Li + transport and electrode/electrolyte interface stability. The introduction of dipole interactions between cationic moieties embedded in the COF‐LiTFSI framework and Li salt significantly enhances dissociation, thereby improving Li⁺ transport and lowering the activation energy ( E a ), while the strong dipole interaction between residual N‐methylpyrrolidone (NMP) and the COF‐LiTFSI framework immobilizes the NMP molecule, markedly enhancing the electrochemical stability of the PVHF‐COF‐CPE with a Li metal anode. Consequently, the optimized PVHF‐COF‐CPE achieves a high room temperature ionic conductivity of 0.63 mS cm −1 . Furthermore, the Li/Li, Li/LFP (LiFePO 4 ), and Li/NCM811(LiNi 0.8 Co 0.1 Mn 0.1 O 2 ) cells equipped with PVHF‐COF‐CPE achieve remarkably stable cycling. This work presents a novel strategy to regulate ion transport and interface stability in VDF‐based SPEs by leveraging dipole interactions, enabling high‐performance solid‐state lithium batteries.

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