From theory to practice: Optimizing Mg2+ ratios in spinel MgV2O4 for elevated performance cathode in aqueous zinc-ion batteries

In aqueous zinc ion batteries (AZIBs) research, spinel-structured materials are posited as potential cathodes. However, the intrinsic spinel configuration faces impediments, largely due to enhanced electrostatic interactions of hosted Zn2+, resulting in notable diffusion energy barriers and hindered kinetics. From prior work on inverse spinel Mg2VO4, we discerned benefits of ion-exchange techniques enhancing Zn2+ transport. Building on this, our study refines Mg2+ concentration in MgV2O4 (MgVO), targeting a confluence of capacity and cycle durability. Employing Density Functional Theory (DFT) and Ab Initio Molecular Dynamics (AIMD) simulations, our findings corroborate that Mg2+ concentration-optimized MgVO manifests improved Zn2+ diffusion, elevated electrical conductance, and diminished diffusion energy barriers. Subsequently, through sol-gel synthesis of MgVO, we observe a nuanced equilibrium between cycling endurance and capacity contingent on Mg2+ ratios. Intriguingly, an Mg:V ratio of 1.25:2 (MgVO-1.25) showcases optimal electrochemical performance, recording an initial capacity of 300 mAh g-1 at 0.1 A g-1. At an aggressive 20 A g-1, it demonstrates enduring capacity retention of 91.4 % across 5000 cycles. This optimized MgVO cathode feasibility is further epitomized in flexible quasi-solidstate AZIBs, efficiently energizing varied electronic setups. Collectively, our findings delineate a blueprint for advancing AZIBs cathode materials, accentuating Zn2+ diffusion and capacity enrichment.