High-Energy Aqueous Magnesium Hybrid Full Batteries Enabled by Carrier-Hosting Potential Compensation.

Underachieved capacity and low voltage plateau is ubiquitous in conventional aqueous magnesium ion full batteries. Such limitations originate from the electrochemistry and the low carrier-hosting ((de)intercalation) potential of electrode materials. Herein, via a strategy of enhancing the electrochemistry through carrier-hosting potential compensation, high-energy Mg2+ /Na+ hybrid batteries are achieved. A Mg1.5 VCr(PO4 )3 (MVCP) cathode is coupled with FeVO4 (FVO) anode in a new aqueous/organic hybrid electrolyte, giving reliable high-voltage operation. This operation enables more sufficient (de)intercalation of hybrid carriers (Mg2+ /Na+ ), thereby enhancing the reversible capacity remarkably (233.4 mA h g-1 at 0.5 A g-1 , 92.7 Wh kg-1 electrode , that is, ≥1.75-fold higher than those in conventional aqueous electrolytes). The relatively high Na+ -hosting potential of the electrodes compensates for the low Mg2+ -hosting potential and widens/elevates the discharge plateau of the full battery up to 1.50 V. Mechanism study further reveals an unusual phase transformation of FVO to Fe2 V3 and the low-lattice-strain pseudocapacitive (de)intercalation chemistry of MVCP.