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

Abstract

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 Mg<inf>1.5</inf>VCr(PO<inf>4</inf>)<inf>3</inf> (MVCP) cathode is coupled with FeVO<inf>4</inf> (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<inf>electrode</inf>, 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 Fe<inf>2</inf>V<inf>3</inf> and the low-lattice-strain pseudocapacitive (de)intercalation chemistry of MVCP.