Synergistic effects of composite organic additives on the magnesium-ion battery performance

Magnesium-ion batteries have emerged as a major research focus among multivalent ion batteries owing to their high performance, low cost and dendrite-free characteristics. However, the high reactivity of Mg anodes leads to undesirable side reactions with electrolytes and trace impurities (e.g. H₂O), forming a passivating solid electrolyte interphase that severely limits the reversible deposition and stripping of magnesium. To address this issue, this study introduces o-fluoroaniline as an electrolyte additive. Owing to its preferential coordination, o-fluoroaniline significantly improves the compatibility between magnesium bis(trifluoromethanesulfonyl)imide in 1,2-dimethoxyethane and the Mg anode. This results in a substantial reduction in the deposition overpotential, extended cycle life and a broadened electrochemical window, with the Coulombic efficiency increasing from 20% to 90%. Furthermore, the combined use of o-fluoroaniline and triethyl phosphate in the modified fluoro-phosphate electrolyte (MFPE) produces a synergistic effect that further optimises the Mg²⁺ solvation structure and reduces the desolvation energy barrier. As a result, the cycle life is extended to 500 h with excellent rate performance. Electrodes using the MFPE exhibit a smoother and more uniform surface morphology, along with an expanded electrochemical stability window, demonstrating superior Mg plating stability. The Coulombic efficiency is further improved to 97%. These findings validate a practical electrolyte design strategy that enhances Mg plating stability and efficiency, paving the way for the development of durable, high-performance magnesium-ion batteries for large-scale energy storage.