Optimizing the Electron Density of PVDF-HFP-Based Solid Polymer Electrolyte by Donor-Acceptor COF Toward High-Performance Solid-State Lithium Metal Batteries.

Abstract

Solid-state lithium metal batteries equipped with solid polymer electrolytes (SPEs) are recognized as promising energy storage devices due to their excellent safety and good interfacial contact. However, unstable solid electrolyte interphase (SEI) and sluggish Li⁺ transport kinetics inhibit their practical application. Herein, a bromine-modified covalent organic framework (Br-COF) with donor (D)-acceptor (A) characteristics is designed and incorporated into PVDF-HFP-based SPEs to regulate electron density for promoting Li⁺ migration and high stability LiF-rich SEI formation to solve these problems. The D and A units of Br-COF are confined in particular locations to create independent electron-hole transference channels, achieving rapid electron transfer dynamics, thereby promoting TFSI^- decomposition to obtain high LiF content SEI. Meanwhile, the strong electron-withdrawing Br-group can adsorb the electron from tetra(p-amino-phenyl)porphyrin (TAPP) to create an electron-rich environment, resulting in the regulation of the Li⁺ local coordination environment to facilitate Li⁺ transference. Consequently, Br-COF@PVDF-HFP exhibits high ionic conductivity (9.2 × 10^-4 S cm^-1) and Li⁺ transference number (0.78). Li|Br-COF@PVDF-HFP|Li cells achieve excellent cycling life (3000 h) at 0.1 mA cm^-2, and LFP|Br-COF@PVDF-HFP|Li and NCM90|Br-COF@PVDF-HFP|Li cells can cycle steadily over 2000 cycles and 250 cycles, respectively. This study provides a reference basis for regulating the electron density of PVDF-HFP-based SPEs to enhance the performance of solid-state LMBs.