Electrochemical Behaviors and Doping Rules of NaRhO2 Cathode Materials for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have great advantages for energy storage and conversion due to their low cost and large storage capacity. Currently, NaRhO2 is used as an electrode material for sodium-ion batteries. Doping first- and second-row transition metals has been carried out to comprehensively assess NaRhO2 as a cathode material. The geometric and electronic structures and electrochemical and doping behaviors of NaRhO2 cathode materials for SIBs have been investigated using density functional theory calculations. The results show that the bond lengths of Rh-O in NaRhO2 decrease during sodium deintercalation. The band gap of NaRhO2 with sodium extraction gradually reduces. The density of states of NaxRhO2 shows that the interaction between the Rh-4d and O-2p orbitals increases and the orbitals shift toward the right. The average intercalation voltage of NaxRhO2 cathode material increased from 2.7 to 3.9 eV. After doping with first- and second-row transition metal elements from Sc to Zn and Y to Cd, the changes in the band gaps of the doped NaRhO2 materials exhibit a W-type rule. In contrast, their magnetic moments show a reverse W-type rule. These findings on the pristine and doped NaRhO2 can provide theoretical guidance for the preparation of novel electrode materials suitable for sodium-ion batteries.