Asymmetric SO<sub>3</sub>CF<sub>3</sub><sup>−</sup>‐Grafted Boron‐Center Anion Enables Boron‐Containing Interphase for High‐Performance Rechargeable Mg Batteries
Xueting Huang, Shuangshuang Tan, Jinlong Chen, Ziwei Que, Rongrui Deng, Juncai Long, Fangyu Xiong, Guangsheng Huang, Xiaoyuan Zhou, Lingjie Li, Jingfeng Wang, Liqiang Mai, Fusheng Pan
Abstract
Abstract Mg(SO 3 CF 3 ) 2 (Mg(OTf) 2 ) is a simple and cost‐effective magnesium salt, which can promote the future applications of rechargeable magnesium batteries (RMBs). However, the simple Mg(OTf) 2 /ether electrolytes suffer from poor electrochemical properties due to the low solubility of Mg(OTf) 2 and the serious decomposition passivation of the [Mg 2+ ‐OTf − ] ion pair on Mg. Herein, the OTf − anion is successfully grafted on low‐cost fluoride boronic esters (B(OC x H y F 2x‐y+1 ) 3 ) to obtain the asymmetric and weak‐coordination boron‐center [B(OC x H y F 2x‐y+1 ) 3 OTf] − anion in ether electrolytes. The ‐OCH 2 CF 3 (TFE) groups in B(TFE) 3 effectively realize the charge delocalization of the OTf − and B‐O plane, restraining the independent decomposition of the [Mg 2+ ‐OTf − ] ion pair. The co‐decomposition of the asymmetric [B(TFE) 3 OTf] − induces the formation of the B‐containing organic/inorganic interphase, thus achieving a reversible Mg plating/stripping. After the further solubilization reaction, the obtained electrolyte exhibits a high average coulombic efficiency of 98.13% and long‐term cycling stability (1000 h). Notably, the long cycling life (capacity retention of 90.2% after 600 cycles at 1 C) and high‐rate capacity (43.0 mAh g −1 at 5 C) of the Mg/Mo 6 S 8 full cell demonstrate a favorable electrolyte/cathode compatibility. This work brings new insights to design the new‐type and low‐cost Mg‐salts and high‐performance electrolytes for commercial RMBs.