Stable Solid Electrolyte Interphase In Situ Formed on Magnesium‐Metal Anode by using a Perfluorinated Alkoxide‐Based All‐Magnesium Salt Electrolyte
Jianhua Xiao, Xinxin Zhang, Haiyan Fan, Yuxing Zhao, Yi Su, Haowen Liu, Xuanzhang Li, Yipeng Su, Hua Yuan, Ting Pan, Qiyuan Lin, Ludi Pan, Yuegang Zhang
Abstract
Abstract Passivation of the Mg anode surface in conventional electrolytes constitutes a critical issue for practical Mg batteries. In this work, a perfluorinated tert‐butoxide magnesium salt, Mg(pftb) 2 , is codissolved with MgCl 2 in tetrahydrofuran (THF) to form an all‐magnesium salt electrolyte. Raman spectroscopy and density function theory calculation confirm that [Mg 2 Cl 3 ·6THF] + [Mg(pftb) 3 ] − is the main electrochemically active species of the electrolyte. The proper lowest unoccupied molecular orbital energy level of the [Mg(pftb) 3 ] − anion enables in situ formation of a stable solid electrolyte interphase (SEI) on Mg anodes. A detailed analysis of the SEI reveals that its stability originates from a dual‐layered organic/inorganic hybrid structure. Mg//Cu and Mg//Mg cells using the electrolyte achieve a high Coulombic efficiency of 99.7% over 3000 cycles, and low overpotentials over ultralong‐cycle lives of 8100, 3000, and 1500 h at current densities of 0.5, 1.0, and 2.0 mA cm −2 , respectively. The robust SEI layer, once formed on a Mg electrode, is also shown highly effective in suppressing side‐reactions in a TFSI − ‐containing electrolyte. A high Coulombic efficiency of 99.5% over 800 cycles is also demonstrated for a Mg//Mo 6 S 8 full cell, showing great promise of the SEI forming electrolyte in future Mg batteries.