Exchanging the active specie, Li⁺ in Li-ion batteries by multivalent, abundant and cheap cations, such as Mg²⁺, are projected to boost the energy density and lower the cost per kilo-watt-hour significantly, making the Mg-ion battery technology a promising candidate for one of the battery technologies of the future.^1,2

The increase in energy density is i.a. a result of the divalent Mg²⁺ carrying twice as much charge as the monovalent Li⁺.^1,2 However, the higher charge also poses a problem as it significantly increases the charge density of the ion, which results in stronger interactions with the host lattice of the electrodes and hampers facile ion transport. Therefore, development of novel electrode materials for effective Mg-ion storage is a vital step for the realization of this battery technology.³

In this study, we have synthesized series of vanadium oxides with varying chemical composition and varying nanotopologies, e.g. nanosheets, xerogels and nanotubes. The mechanism for Mg-intercalation and deintercalation is studied by electroanalysis, impedance spectroscopy and through operando synchrotron powder X-ray diffraction measured during battery operation. These results show e.g. that Mg-intercalation in multivalled V₇O₁₆-nanotubes occurs within the space between the individual vanadium oxide layers building the walls of the nanotubes while the underlying V₇O₁₆ frameworks constructing the walls are affected only to a minor degree by the intercalation. Our investigation provides new insights into the size requirements of the channels/layers in the host frameworks that will allow for efficient Mg-ion storage.

Reference:   

1. R. van Noorden, Nature 2014, 507, 26
2. Pellion Technologies, “Moving Beyond Lithium with Low-Cost, High-Energy, Rechargeable Magnesium Batteries”, Pellion White Paper, September 2011
3. P. Saha, M. K. Datta, O. I. Velikokhatnyi, A. Manivannan, D. Alman, P. N. Kumta, Progress in Materials Science 2014, 66, 1.