Glycol-glyme co-solvent electrolytes enable high-capacity and ultrastable VO₂ cathodes in magnesium ion batteries

Abstract

Rechargeable magnesium batteries (RMBs) are regarded as cost-effective candidates for post-lithium-ion batteries. However, the development of RMBs is hindered by the lack of high-capacity cathodes due to the sluggish Mg2+ desolvation at cathode-electrolyte interface and the TFSI--induced surface passivation in the regular Mg(TFSI)<inf>2</inf>/1,2-dimethoxyethane (DME) electrolyte. Herein, we introduced a hydroxyl-rich ethylene glycol (EG) solvent into the ether-based electrolyte to disrupt the unfavorable [Mg(DME)<inf>3</inf>]2+ complexes and build hydrogen bond networks to faciliate Mg ion migration and suppress TFSI- decomposition simutaneously. Consequently, the co-solvent electrolyte demonstrates a high reversible capacity of 258 mAh g−1 for VO<inf>2</inf> cathodes with an extremely low capacity degradation rate of 0.0078 % per cycle over 2000 cycles at 500 mAg−1, which rivals the state-of-the-art cathode performance in Mg ion batteries. Practical application of this new electrolyte is evidenced by the high capacities of above 160 mAh g−1 over 50 cycles for the Mg//VO<inf>2</inf> full cells. This work sets a new frontier for effective electrolytes in RMBs with long life and high energy densities.