P2-type Na0.67Mn0.72Ni0.14Co0.14O2 with K+ doping as new high rate performance cathode material for sodium-ion batteries

Na0.67-xKxMn0.72Ni0.14Co0.14O2 (x = 0, 0.01, 0.03, 0.05) layered cathodes were prepared as the cathode of sodium-ion batteries by a co-precipitation method. The effects of K+ doping were investigated, as the doping amount of K+ could change the structure and finally influence the electrochemical performances. The appropriate content of K+ could expand the Na+ diffusion channel and improve both the cycleability and rate performance. The Na0.66K0.01Mn0.72Ni0.14Co0.14O2 composite showed enhanced cycle performance with an initial capacity of 141 mAh g−1 and 112 mAh g−1 maintained after 100 cycles at 2.0C rate. Meanwhile, the pristine Na0.67Mn0.72Ni0.14Co0.14O2 (without K+ doping) showed a lower initial capacity of 112 mAh g−1 with 67 mAh g−1 retained after 100 cycles at 2.0C. What's more, the Na0.66K0.01Mn0.72Ni0.14Co0.14O2 sample delivered a high reversible capacity of 88.4 mAh g−1 even at 8.0C, which was much higher than that of Na0.67Mn0.72Ni0.14Co0.14O2 (35 mAh g−1). These results demonstrated that the K+ doping could be a feasible strategy to enhance the performance of layered cathode for sodium ion battery.