Binary metal co-substituted P2-type Na0.67Mn0.7Cu0.15Ni0.15O2 microspheres as robust cathode for high-power sodium ion battery

Abstract Developing suitable cathode materials is essential to promote the development of sodium ion batteries (SIBs). In this work, Ni, Cu co-substituted P2-type Na0.67Mn0.7Cu0.15Ni0.15O2 microspheres are designed and synthesized through high temperature solid reaction using MnO2 template. Compared with pristine Na0.67MnO2, or monometal substituted Na0.67Mn0.7Ni0.3O2 and Na0.67Mn0.7Cu0.3O2, this binary metal co-substituted Na0.67Mn0.7Cu0.15Ni0.15O2 microsphere shows markedly enhanced electrochemical performance as cathode material for SIBs, especially for long-term cycling stability and high rate capability. For the rate capability measurements, when the current increases from 50 mA g-1 to high current of 2000 mA g-1 (40-folds increase), the capacity retention can be kept for 65.0%. And for the long-term cycling performance within 1000 cycles, a capacity of 74.1 mAh g-1 can be maintained in the voltage range of 2.0-4.0 V at high current of 1000 mA g-1, corresponding to a capacity retention of 88.1%. The impressive cycling stability and rate capability should be attributed to the stable microsphere structure and synergistic effect of electrochemical active Ni, Cu co-existence in P2 phase lattice. Coupled with presodiation MoSe2/P-C anode and assembled into full cells, the specific capacities are almost matched with those in half-cells, delivering a considerable energy density of 200 Wh Kg-1.