Semi‐Chelation Solvation Enables High Interface Compatibilities with both Anode and Cathode in a Bulky Mg[B(HFIP) <sub>4</sub> ] <sub>2</sub> Electrolyte
Chunfeng Chen, Jinlong Chen, Shuangshuang Tan, Zhipeng Gao, Xueting Huang, Ze He, Jia Huang, Rongrui Deng, Fangyu Xiong, Guangsheng Huang, Jingfeng Wang, Lingjie Li, Fusheng Pan
Abstract
Abstract Magnesium fluorinated alkoxyl organoborates (Mg[B‐(OR F ) 4 ] 2 ) electrolytes have received large attention due to the adjusted branched chain, high oxidation stability, and high ion conductivity in rechargeable magnesium batteries (RMBs). However, the most promising Mg[B‐(OCH(CF 3 ) 2 ) 4 ] 2 /1,2‐dimethoxyethane (Mg[B(HFIP) 4 ] 2 /DME) electrolyte still faces the significant challenges of unstable, non‐uniform electrode/electrolyte interphases (SEI/CEI), resulting from the decomposition of strong‐chelation [Mg(DME) 3 ] 2+ ion. Herein, a semi‐chelation solvation structure is designed in Mg[B(HFIP) 4 ] 2 electrolytes by achieving a balance between weak Mg 2+ ‐solvent interactions, ring‐like molecular configurations, and sufficient salt dissociation. The semi‐chelation Mg[B(HFIP) 4 ] 2 electrolyte exhibits lower desolvation energy and processes higher proportions of contact ion pair. The decompositions of semi‐chelation Mg[B(HFIP) 4 ] 2 electrolytes induce the formation of uniform organic–inorganic composite SEI/CEI layers with rich MgB x O y and MgF 2 components. The stable and high‐conductivity SEI/CEI layers enable high interface compatibilities with Mg anode and high‐voltage cathodes. Therefore, Mg anode exhibits a high average coulombic efficiency (99.4%, 500 cycles) and long‐term cycling stability (2000 h). Notably, the high capacity retention (83% after 500 cycles) of Mg||Prussian blue full cell with a discharge platform of 2.1 V can be achieved. This strategy provides a new sight for designing high‐voltage and high‐compatibility boron‐based electrolytes for RMBs.