Interfacial engineering of perfluoroalkyl functionalized covalent organic framework achieved ultra-long cycled and dendrite-free lithium anodes
Yongxin Yang, Conghui Zhang, Zhiyuan Mei, Yongjiang Sun, Qi An, Qi Jing, Genfu Zhao, Hong Guo
Abstract
The finite lithium-ion utilization, short cycling life, and lower capacity retention caused by irreversible dendrite growth become the maximum dilemma in lithium metal batteries’ (LMBs’) commercialization. Herein, a perfluoroalkyl-functionalized covalent organic framework (COF-F6) equipped with high stability and supernal proton conduction is introduced as an artificial solid electrolyte interface to stable the lithium metal anode. Benefiting from the strong electron-withdrawing effect of perfluoroalkyl, Li + will be freed more by the competition of electronegative fluorine (F) and bis(trifluoromethanesulphonyl)imide anion (TFSI − ). The dissociation of LiTFSI and process of Li + desolvation are easier to achieve. In addition, high electronegative fluorine can also regulate local electron-cloud density to induce the fast immigration of Li + . All the above roles contribute to improving the Li + transfer number (0.7) and achieving the goal of inhibiting Li dendrite. As a result, the perfluoroalkyl COF-F6 modified LMB presents outstanding cycling stability. The symmetric batteries accomplish an overlong life-span of more than 5000 h with a lower hysteresis voltage (11 mV) at 5 mA·cm −2 . Also, no dendrites are observed when using an in-situ optical microscope to learn the process of Li deposition. Therefore, this dendrite-free protection tactic holds broad prospects for the practical application of Li metal anodes.