Two New Low-Expansion Li-Ion Cathode Materials with Promising Multi-Property Performance

We have identified CrOF₄ and NbFe₃(PO₄)₆ as candidate cathodes with density functional theory (DFT) calculations which suggest a useful balance of low chemical expansion and gravimetric energy density. Low chemical expansion is a likely requirement for high cycle batteries and the employment of solid electrolytes. CrOF₄ and NbFe₃(PO₄)₆ have predicted average voltages of 5.1 and 4.0 V and chemical expansion less than 3% and 1% within the stoichiometric range of 0 to 1 Li per formula unit, respectively, significantly outperforming commonly used cathode materials. While practical energy densities can be challenging to estimate with DFT calculations, DFT suggests that these exhibit gravimetric capacity densities in excess of 200 and 100 Ah/kg and gravimetric energy density in excess of 1020 and 400 Wh/kg, respectively, depending on irreversible processes during cycling. These were identified by screening approximately 38,000 compounds using statistical models trained on available data and physically motivated descriptors. We also assessed ease of synthesizablity in our selection of these materials, and will provide an update on efforts of experimental validation.