Control of crystal size tailors the electrochemical performance of α-V2O5 as a Mg2+ intercalation host

alpha-V2O5 has been extensively explored as a Mg2+ intercalation host with potential as a battery cathode, offering high theoretical capacities and potentials vs. Mg2+/Mg. However, large voltage hysteresis is observed with Mg insertion and extraction, introducing significant and unacceptable round-trip energy losses with cycling. Conventional interpretations suggest that bulk ion transport of Mg2+ within the cathode particles is the major source of this hysteresis. Herein, we demonstrate that nanosizing alpha-V2O5 gives a measurable reduction to voltage hysteresis on the first cycle that substantially raises energy efficiency, indicating that mechanical formatting of the alpha-V2O5 particles contributes to hysteresis. However, no measurable improvement in hysteresis is found in the nanosized alpha-V2O5 in latter cycles despite the much shorter diffusion lengths, suggesting that other factors aside from Mg transport, such as Mg transfer between the electrolyte and electrode, contribute to this hysteresis. This observation is in sharp contrast to the conventional interpretation of Mg electrochemistry. Therefore, this study uncovers critical fundamental underpinning limiting factors in Mg battery electrochemistry, and constitutes a pivotal step towards a high-voltage, high-capacity electrode material suitable for Mg batteries with high energy density.

Automated summary

By nanosizing alpha-V2O5, a reduction in voltage hysteresis and improved energy efficiency is achieved, revealing the contribution of mechanical formatting to hysteresis. However, there is no significant improvement in hysteresis in later cycles, indicating that factors other than Mg transport also play a role. This study uncovers critical limiting factors in Mg battery electrochemistry, paving the way for high-voltage, high-capacity electrode materials for Mg batteries with high energy density.