Enabling Efficient Ion Transport and Stable Interfaces of PEO-Based Solid Electrolytes via an I2/COF Charge-Transfer Complex

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Insufficient Li+ transport kinetics and poor interfacial stability hinder the practical application of polyethylene oxide (PEO)-based solid-state electrolytes (SSEs) in all-solid-state lithium metal batteries. In this work, we propose iodine-induced charge transfer of a covalent organic framework (COF) as an effective strategy to achieve fast ion transport and a stable SSE/Li interface. First, the electron-deficient COF skeleton in the I2/COF charge-transfer complex anchors TFSI- anions through enhanced electrostatic interactions, thereby promoting the dissociation of lithium salt to release free Li+. Second, the electron deficiency of COF strengthens its dipole-dipole interactions with PEO, leading to suppressed PEO crystallization and enhanced COF/PEO compatibility. Third, the electron-deficient COF tailors the Li+ coordination environment via weakening the affinity of PEO and COF toward Li+. Consequently, the I2/COF charge-transfer complex accelerates Li+ transport kinetics in PEO-based composite SSEs. Furthermore, the confinement effect of COF toward I2 via charge transfer effectively inhibits the aggressive lithium anode corrosion by I2, resulting in the controlled growth of a stable, robust, and conductive solid electrolyte interface (SEI) rich in LiF and LiI. Thus, the I2/COF charge-transfer complex enables excellent rate capability and cycling stability of the resulting COF/PEO-based composite SSE, maintaining a capacity retention of 88.58% after 1000 cycles at 2 C. This work offers a promising strategy for designing COF/PEO-based composite SSEs for next-generation all-solid-state lithium metal batteries.