Multi-element doped hexagonal sheet Ni/Mn-based layered oxide with ZrO2 surface modification for sodium ion batteries cathode with high capacity and good cycle/air stability

Ni/Mn-based layered oxides have been widely studied for sodium ion battery cathode because of high capacity and simple preparation. However, its application has been restricted owing to unstable structure and poor cycling performance. Herein, the multi-element doped hexagonal sheet Ni/Mn-based layered oxide with ZrO2 surface modification O3-NaNi0.3Mn0.5-xFe0.1Cu0.1ZrxO2@ZrO2 (NFMCZ-x) cathode materials have been successfully synthesize by high temperature calcination method accompanied by ball milling activation. XRD refinement results show Zr4+ substitution of Mn3+ can increase interlayer distance of sodium layer. Benefiting from the synergetic effect of multi-element doping and ZrO2 surface modification, the optimized NFMCZ-0.03 sample exhibits a higher discharge capacity of 178 mAh/g at 0.1C and good capacity retention (77 % after 50 cycles at 2C). Furthermore, NFMCZ-0.03 has an excellent air stability with a capacity retention rate of 86 % during 50 cycles at 1C after being exposed in the air for 20 days. The ex-situ XRD results of NMFC at different charge/discharge voltages show Zr4+ doping can suppress O3 + P3′'–O3′-O3 + P3′' phase transition during charge/discharge process. These results confirm that synergistic effect of multi-doping combined with surface modification can improve electrochemical performance of layered oxides cathodes, which provides a research idea for development of Ni/Mn-based layered oxides cathodes for sodium-ion batteries.