Mo-substitution in V₂O₅ tunes the structure towards three-dimensional connectivity and improves Li-ion battery cycling

The development of alternative energy sources is crucial for reducing reliance on fossil fuels, particularly for mobile applications such as personal electronics and transportation. This necessitates the advancement of battery materials based on abundant and inexpensive constituent elements. To achieve this requires investigating materials in a broader compositional and structural design space. Early transition metal oxides, including the intercalation electrode α − V₂O₅, however, the performance of V₂O₅ is hindered by phase transformations during battery cycling that lead to capacity fade and short device lifetimes. This study investigates the modification of V₂O₅ through Mo substitution in a series of the form V 2 − x Mo_xO₅ for x = 0.05, 0.1, 0.2, 0.4, 0.6, and 0.8. X-ray diffraction data reveal progressive structural changes with increasing Mo content, which in turn change the progression of phase transformations during the first discharge. The different product also results in different cycling profile shapes that indicate differences in the charge storage mechanism as a function of Mo content. As a result, samples with higher Mo-substitution, especially V_1.2Mo_0.8O₅, have narrower hysteresis, higher capacity, and improved capacity retention. While there is a limited solubility of Mo in the V₂O₅ structure, with secondary phases and defects at many compositions, we show that Mo substitution alters the cycling behavior of V₂O₅ to deep discharge, which can inform the design of intercalation materials for energy storage applications.