Post-synthetic Covalent Organic Framework to Improve the Performance of Solid-State Li<sup>+</sup> Electrolytes
Jing Zhang, Derong Luo, Hong Xiao, Huizi Zhao, Bing Ding, Hui Dou, Xiaogang Zhang
Abstract
As a new class of crystalline materials, covalent organic frameworks (COFs) have long-range ordered channels and feasibility to functionalize. The well-arranged pores make it possible to contain and transport ions. Here, we designed a novel functionalized anionic COF-SS-Li by a post-synthetic method utilizing the Povarov reaction of BDTA-COF, anchoring −SO 3 – groups to the COF backbone and converting the imine linkage to a more stable quinoline unit. The grafted −SO 3 – groups and directional channels can promote the lithium-ion transport through a hopping mechanism. As a solid-state lithium-ion electrolyte, COF-SS-Li exhibits the conductivities of 9.63 × 10 –5 S cm –1 at 20 °C and 1.28 × 10 –4 S cm –1 at 40 °C and a wide electrochemical window of 4.85 V. The assembled Li|COF-SS-Li|Li symmetric cell can cycle stably for 600 h at 0.1 mA cm –2 . Also, the Li|COF-SS-Li|LiFePO 4 cell delivers an initial capacity of 117 mAh g –1 at 0.1 A g –1 and retains a capacity rate of 56.7% after 500 cycles. The research enriches the solid-state electrolytes for lithium-ion batteries.