Structural Evolution and Phase Coexistence in Mg-Intercalated V₂O₅ Revealed by Advanced Electron Microscopy

The transition to next-generation energy storage requires rechargeable batteries with higher energy density and improved stability. While lithium-ion systems dominate the market, concerns over cost, safety, and resource availability motivate exploration of alternatives. Magnesium-based batteries offer advantages such as natural abundance, low cost, safer Mg metal anodes, and higher volumetric energy density via multivalent charge transfer. Transition metal oxides can reversibly host Mg²⁺ ions, but intercalation often induces irreversible structural rearrangements, causing capacity and voltage fade. Understanding these transformations is thus crucial for designing stable Mg-ion cathodes.

In this work, we combine pair distribution function (PDF) analysis with aberration-corrected scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) to track phase evolution in Mg-intercalated V₂O₅ cycled at 110 °C. PDF refinements reveal two coexisting phases distinct from the δ and ε polymorphs, providing improved structural models of intermediate states. Atomic-resolution imaging and diffraction mapping show nanoscale phase coexistence within individual particles, while spectroscopy reveals surface transformations that deviate from bulk behavior, offering new insights into Mg intercalation in V₂O₅.