Highly crystalline vinylene-linked covalent organic frameworks enhanced solid polycarbonate electrolyte for dendrite-free solid lithium metal batteries

The development of solid-state electrolytes (SSEs) with high ionic conductivity, outstanding electrochemical window, and promising mechanical strength is a key factor in realizing the commercialization of high energy density solid-state lithium metal batteries (LMBs). Covalent organic frameworks (COFs) are a functional crystalline material with highly customizable molecular networks and one-dimensional channel structures, thus showing great potential applications in SSEs. Herein, we design flexible COF-poly(vinyl ethylene carbonate) (PVEC) (abbreviated as COF-PVEC) composite electrolyte films with excellent ionic conductivity and high mechanical strength, enabling dendrite-free and long-term running solid-state LMBs. Owing to the lithium-philic triazine and carbon-carbon double bonds groups in the COF skeleton, the obtained flexible COF-PVEC shows high ionic conductivity up to 1.11 × 10−4 S·cm−1 at 40 °C, and enlarged electrochemical window up to 4.6 V (vs. Li+/Li) compared with pure PVEC electrolyte. At the same time, the lithium dendrites are efficiently inhibited after discharge-charging cycles, due to the improved Young's modulus (150 MPa) and ordered channels of COF. Using the various features of COF-PVEC, we assembled a solid-state full battery with LiFePO4 cathode, which showed superior rate capacity (151.8, 146.2, 139.2, 128.1, 113.7, and 100.8 mAh·g−1 at 0.1, 0.2, 0.5, 1, 1.5, and 2 C, respectively) and excellent long-term cycling stability (over 400 cycles at 1 C). We believe that the COF-based composite electrolyte can become one of the most promising high-performance SSEs for solid-state LMBs.