Zinc-substituted P2-type Na0.67Ni0.23Zn0.1Mn0.67O2 cathode with improved rate capability and cyclic stability for sodium-ion storage at high voltage

P2-type layered transition metal oxides are considered one of the ideal cathode materials for sodium ion batteries because of its high working voltage and excellent theoretical specific capacity. P2-Na 0.67 Ni 0.33 Mn 0.67 O 2 electrodes deliver a theoretical specific capacity of 173 mAh g -1 , which is dependent on Ni 2+ /Ni 3+ /Ni 4+ charge compensation. High operating voltage leads to higher specific capacity and energy density , which are better adapted to practical development needs, but at the same time it causes the material to undergo a destructive P2-O2 phase transition, which greatly affect cycle stability and Na + diffusion kinetics. In this study, we propose Zn 2+ doping and spherical morphology modification strategy. The spherical morphology not only reduces the distance of Na + diffusion and improves the rate performance, but also the spherical structure can alleviate the volume change during Na + intercalation/extraction. Furthermore, the doping of Zn 2+ changes the valence distribution of Mn, suppressing the phase transition at high voltage and further improving the cycling stability. At a high cut-off voltage of 4.4 V, the cathode material with Zn 2+ doping and spherical shaped possesses an average operating voltage of up to 3.6 V and exhibits 90% capacity retention after 30 cycles (compared to only 56% for the pristine material). Above that, the rate performance is also greatly improved, with the modified material contributing an excellent specific capacity of 95 mAh g -1 , even at a high current density of 5 C (1 C = 170 mA g -1 ).