Mg-rich disordered rocksalt oxide cathodes for Mg-ion batteries

The discovery of new transition metal (TM) oxide cathodes which can act as intercalation hosts for Mg²⁺ ions is critical for the development of high energy density Mg-ion batteries. 

In Li-ion batteries, disordered rocksalts with sufficiently high Li⁺ charge carrier ion concentration, (ie Li:TM>1.1) can support fast Li⁺ diffusion and therefore deliver high capacities (~300 mA h g^-1) and rate performance.  

In the paper 'Mg-rich disordered rocksalt oxide cathodes for Mg-ion batteries' published in Journal of Materials Chemistry A, the authors investigated a range of simple Mg-rich disordered rocksalt cathodes, Mg₂TMO₃ (TM=Mn, Ni, Co), which possess similar charge carrier ion concentrations and similar ratios between the ion size and interstitial tetrahedron height to Li-rich disordered rocksalts.  Even with high carbon loadings and elevated cycling temperatures and reduced particle and crystallite size, however, no significant Mg²⁺ deintercalation was observed, indicating that conventional design rules established for Li-rich DRS cannot be simply translated to Mg-rich systems.  

Despite the lack of activity in Mg-rich oxides, the authors demonstrate that Mg²⁺ intercalation into close-packed cubic disordered rocksalts (such as Li_2-xMnO₂F(x=1)), is possible, opening potential routes to activating Mg-rich systems.