Regulating the Electron Structure of Covalent Organic Frameworks by Strong Electron-Withdrawing Nitro to Construct Specific Li~+ Oriented Channel

摘要

The growth of disordered lithium dendrite and the notorious reaction betweenLi and electrolyte hamper the practical application of Li metal batteries(LMBs). Herein, an artificial solid electrolyte interphase (ASEI) constructed bya nitro-functionalized covalent organic framework (NO_2-COF) is designed toregulate Li~+ deposition and stable Li anodes. Strong electron-withdrawingnitro groups can gather the surrounding electrons of connected monomer bythe donor-acceptor (D-A) effect, thus regulating the electron structure of thecovalent organic framework (COF) and constructing a specific cation-orientedchannel. The uniform Li~+ deposition and inhibition of Li dendrites areachieved under such a high-selective Li~+ transportation channel andregulated surface electric charge. In addition, the nitro can also be reduced toNO_2~? and further react with Li to produce high ionic-conductivity Li_3N andLiN_xO_y during the charging/discharging, which contributes to the migrationof Li~+. As a result, NO_2-COF-modified symmetrical batteries realize anultra-long cycling life of more than 6000 h under a current density of 5 mAcm~（?2） compared to bare Li and TpBD-COF/Li (without nitro). The full cellscoupled with LiFePO_4 stably cycle 1000 times with a capacity retention of91%. Hence, effectively optimizing electron structure by the donor-acceptor(D-A) effect provides a better platform to elevate the performance of LMB.