An ultrafast, stable and highly reversible nickel magnesium vanadate cathode for magnesium ion batteries

Abstract

Rechargeable magnesium batteries are one among the strongest candidates over lithium ion batteries with abundance, cost effective and less environmental hazard. However, limitations including slow Mg2+ ion kinetics in the electrode-electrolyte interface and formation of passivating layers on the surface of magnesium metal anode affecting the rechargeable behavior of a cathode. Herein, hydrothermally synthesized NiMg2(VO4)2 nanomaterial used as cathode. The oxidation and reduction properties of Mg and V facilitates the diffusion pathway for Mg2+ and Li+ ions. Additionally, the employment of activated carbon cloth as anode diminishes the strong ionic interactions between Mg2+ ions and crystal lattice, enabling the faster diffusion of Mg2+ ions. All the electrochemical investigations are carried out at room temperature in the potential window of 1.23 V to 3.83 V against Mg/Mg2+. At a lower current density of 100 mA g−1, the specific discharge capacity have been 220 mAh g−1 for the 2nd cycle and retention of 97.1 % over 25 cycles. The specific capacity increases with more Mg2+ involvement in the reaction. At the highest current rate of 5000 mA g−1 the capacity retention is 96.8 % after 1000 cycles. Calculated energy density for a low current density is 556 Wh kg−1. The presence of multivalent V ions in the cathode reduces volume expansion, assisting charge redistribution to maintain electroneutrality. The dynamic valence property of. Vanadium ions (V2+/V5+) assist the intercalation of Mg2+ ions into the crystal lattice of cathode and possibly contribute to the highly stable and reversible discharge capacity over cycles. These findings provide a new perspective on NiMg2(VO4)2 as cathode material for magnesium ion batteries.