High-Voltage Aqueous Mg-Ion Batteries Enabled by Solvation Structure Reorganization

Herein, an eco-friendly and high safety aqueous Mg-ion electrolyte (AME) with a wide electrochemical stability window (ESW) approximate to 3.7 V, containing polyethylene glycol (PEG) and low-concentration salt (0.8 m Mg(TFSI)(2)), is proposed by solvation structure reorganization of AME. The PEG agent significantly alters the Mg2+ solvation and hydrogen bonds network of AMEs and forms the direct coordination of Mg2+ and TFSI-, thus enhancing the physicochemical and electrochemical properties of electrolytes. As an exemplary material, V2O5 nanowires are tested in this new AME and exhibit initial high discharge/charge capacity of 359/326 mAh g(-1) and high capacity retention of 80% after 100 cycles. The high crystalline alpha-V2O5 shows two 2-phase transition processes with the formation of epsilon-Mg0.6V2O5 and Mg-rich MgxV2O5 (x approximate to 1.0) during the first discharge. Mg-rich MgxV2O5 (x approximate to 1.0) phase formed through electrochemical Mg-ion intercalation at room temperature is for the first time observed via XRD. Meanwhile, the cathode electrolyte interphase (CEI) in aqueous Mg-ion batteries is revealed for the first time. MgF2 originating from the decomposition of TFSI- is identified as the dominant component. This work offers a new approach for designing high-safety, low-cost, eco-friendly, and large ESW electrolytes for practical and novel aqueous multivalent batteries.