Triethyl Phosphate Enables Regulated Solvation Structure and Robust Anode Interphase in Dual-Salt Mg(OTf)2-MgCl2 Electrolytes for Rechargeable Magnesium Batteries

Abstract

Rechargeable magnesium batteries are promising next-generation energy storage systems owing to the low cost and high natural abundance of magnesium. However, their practical application is critically impeded by the parasitic decomposition of conventional electrolytes at the Mg anode, leading to the formation of a passivation layer, high desolvation barriers, and poor cycling stability. Herein, triethyl phosphate (TEP) is introduced as a cosolvent into the Mg(OTf)₂ + MgCl₂-DME electrolyte to regulate solvation structures and interfacial chemistry. Comprehensive spectroscopic and electrochemical analyses reveal that TEP facilitates salt dissociation and reconstructs the Mg²⁺ solvation structure, thereby reducing the desolvation barrier and promoting ion transport. Meanwhile, TEP contributes to the formation of a stable and robust solid electrolyte interphase on the Mg anode, effectively suppressing side reactions and enabling uniform Mg deposition. The Mg||Mg symmetric cell exhibits stable cycling for over 3500 h with an overpotential below 0.2 V at 0.1 mA cm^–2 and 0.05 mAh cm^–2. The Mg||Mo asymmetric cell delivers a Coulombic efficiency of 99.4% after 3000 h at 0.5 mA cm^–2 and 0.25 mAh cm^–2. Furthermore, the Mg||α-MnO₂ full cell maintains a discharge capacity of 176.9 mAh g^–1 after 350 cycles at 0.1 C. This work provides a solvation-regulation strategy for designing high-performance Mg electrolytes.