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

Abstract

The growth of disordered lithium dendrite and the notorious reaction between Li and electrolyte hamper the practical application of Li metal batteries (LMBs). Herein, an artificial solid electrolyte interphase (ASEI) constructed by a nitro-functionalized covalent organic framework (NO₂-COF) is designed to regulate Li⁺ deposition and stable Li anodes. Strong electron-withdrawing nitro groups can gather the surrounding electrons of connected monomer by the donor-acceptor (D-A) effect, thus regulating the electron structure of the covalent organic framework (COF) and constructing a specific cation-oriented channel. The uniform Li⁺ deposition and inhibition of Li dendrites are achieved under such a high-selective Li⁺ transportation channel and regulated surface electric charge. In addition, the nitro can also be reduced to NO₂⁻ and further react with Li to produce high ionic-conductivity Li₃N and LiN_xO_y during the charging/discharging, which contributes to the migration of Li⁺. As a result, NO₂-COF-modified symmetrical batteries realize an ultra-long cycling life of more than 6000 h under a current density of 5 mA cm⁻² compared to bare Li and TpBD-COF/Li (without nitro). The full cells coupled with LiFePO₄ stably cycle 1000 times with a capacity retention of 91%. Hence, effectively optimizing electron structure by the donor-acceptor (D-A) effect  provides a better platform to elevate the performance of LMB.