Understanding the Phase Evolution and Charging Mechanism in Dual Cation Cathodes

Multivalent batteries offer potential advantages over lithium-ion batteries but face challenges due to limited ionic mobility in solid-state cathodes. Recent investigations have demonstrated that incorporating multivalent cations, particularly calcium ions (Ca 2+ ), into monovalent cathodes such as NaSICON and R-3m NaV 2 (PO 4 ) 3 , results in improved capacity retention. This study investigates the phase evolution and charging mechanism in these dual cation cathodes by using a cluster expansion and charge-neutral Monte Carlo simulation in a Ca-Na-V 2 (PO 4 ) 3 system. Our results found that during the discharge with either Ca or Na ions, phase transitions occurs when the oxidation state of the transition metal changes, in particular between Na 1 V 2 (PO 4 ) 3 - Na 3 V 2 (PO 4 ) 3 and Na 1 V 2 (PO 4 ) 3 - Ca 1 V 2 (PO 4 ) 3 . This behavior suggests that the charging pathway of Na/Ca ions can be altered by varying the Ca/Na chemical potential. Figure 1