The multi-metal synergetic mechanism of O3-Na0.5Mn0.65Ni0.15Al0.1Mg0.05Co0.05O2 nanoflower for a high-voltage and long-cycle-life cathode material of sodium-ion batteries

With the development of the sodium-ion batteries (SIBs), high rate capability and long cycle life are critical to the application. In this work, a new quinary O3-type MgCo-NaMnNiAlO as a cathode material for SIBs has been synthesized by hydrothermal reaction and solid-state reaction. It can deliver a reversible capacity of 118, 109, 88 and 73 mAh g−1 at a rate from 1 to 10 C. At 1 C, the prepared cathode shows a superior cycle stability under high current density that 82% of the initial rate capacity could be maintained in 1000 cycles with a capacity loss rate of 0.018% in every cycle. During sodiation/desodiation, Mn and Ni were used to provide capacity at low-voltage area and high-voltage area, respectively. What is more, Co ions promote the charge compensations. Furthermore, Al and Mg ions enhance the charge transfer which could play a significant role in stabilizing the structure during Na+ deintercalation/intercalation by means of suppressing O3–P3 phase transition. In addition, Mg doping also can form synergistic effect with Al ion and accelerate Na ion migration rate during circulation under room temperature. The advanced characterization of in situ XRD demonstrates structural changes in Na-ion batteries and promotes an understanding of the structure and properties of five-element O3 materials.