Inorganic solids for dual magnesium and sodium battery electrodes

Despite the success of lithium-ion batteries, recognized through the award of the 2019 Nobel Prize in Chemistry, the forecast of a wide application of these systems to avoid the use of fossil fuels and their effect on global warming has raised doubts about their safety, sustainability, and performance. To make a post-lithium era possible, other reducing metals are investigated. While sodium shows certain analogies with lithium, some advantages with respect to its abundance and availability or the lack of Al alloy that could substantially reduce production costs make sodium-ion batteries a good alternative, particularly for stationary applications. On the other hand, other abundant multivalent elements such as Mg can provide even higher energy densities. The possibility of using dual ions can be a strategy to get the best of each element in a synergistic battery system. Dual Na+/Mg2+ systems have been considered a potential option by different researchers. In this review, we shall discuss different results on dual-metal-ion systems studied in our laboratory, particularly vanadium oxides and phosphates and layered manganese oxides.