Density functional theory modeling of MnO₂ polymorphs as multivalent cathode materials

Multivalent ion batteries (MVIBs) provide an energy dense alternative to Li-ion batteries (LIBs). While MVIBs are not competitive for use in portable devices, they are a desirable alternative to LIBs for large-scale applications such as grid storage. MnO₂ polymorphs are a popular choice for MVIB cathodes; they offer a high voltage and capacity, as well as structural versatility. Many of the polymorphs are abundant and consequently inexpensive. While several MVIB studies with MnO₂ polymorphs as the cathode material exist, only Mg and Zn were chosen as the primary intercalation agents. Here, we computationally investigate several MnO₂ polymorphs as cathode materials, and the resulting properties upon their intercalation with ions from several multivalent metal anodes (Mg, Ca, Zn, Al), as well as Li for comparison. We use the SCAN functional, to calculate the average voltages for each MnO₂ polymorph upon intercalation with the ions listed above. We also investigate volume change and energy barriers associated with diffusion of those ions in the cathode materials.