Abstract
This study explores the impact of introducing vacancy in the transition metal layer of rationally designed Na(0.6)[Ni(0.3)Ru(0.3)Mn(0.4)]O(2) (NRM) cathode material. The incorporation of Ru, Ni, and vacancy enhances the structural stability during extensive cycling, increases the operation voltage, and induces a capacity increase while also activating oxygen redox, respectively, in Na(0.7)[Ni(0.2)V(Ni0.1)Ru(0.3)Mn(0.4)]O(2) (V-NRM) compound. Various analytical techniques including transmission electron microscopy, X-ray absorption near edge spectroscopy, operando X-ray diffraction, and operando differential electrochemical mass spectrometry are employed to assess changes in the average oxidation states and structural distortions. The results demonstrate that V-NRM exhibits higher capacity than NRM and maintains a moderate capacity retention of 81% after 100 cycles. Furthermore, the formation of additional lone-pair electrons in the O 2p orbital enables V-NRM to utilize more capacity from the oxygen redox validated by density functional calculation, leading to a widened dominance of the OP4 phase without releasing O(2) gas. These findings offer valuable insights for the design of advanced high-capacity cathode materials with improved performance and sustainability in sodium-ion batteries.