Mg/Ti doping co-promoted high-performance P2-Na0.67Ni0.28Mg0.05Mn0.62Ti0.05O2 for sodium-ion batteries

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Transition-metal layered oxides (such as P2-Na2/3Ni1/3Mn2/3O2) are suggested as one type of the most potential cathode candidates for sodium ion batteries (SIBs) owing to their high capacity and low cost; however, they suffer from the structural damage and sluggish Na+ kinetics resulting from the undesirable phase transformation of P2−O2 and the Na+/vacancy ordering, respectively. Herein, a Mg/Ti co-doped P2-Na0.67Ni0.28Mg0.05Mn0.62Ti0.05O2 layered oxide is demonstrated as a high-efficiency cathode material for SIBs. The cathode delivers a high reversible capacity of 135.5 mAh g−1, good cycling stability (82.7 mAh g−1 upon 100 cycles at 0.1C), and an attractive energy density of 479.4 Wh Kg−1. Furthermore, the phase transition from the undesirable P2−O2 to the reversible P2−OP4 demonstrated by in situ XRD and the partially suppressed Na+/vacancy ordering as well as the improved electronic and ionic conductivities all give rise to the enhancement. These results show the important role of cationic co-doping in designing and preparing high-efficiency layered oxide cathode materials for SIBs.