Suppressing the P2-O2 phase transition of P2-type Ni/Mn-based layered oxide by synergistic effect of Zn/Ti co-doping for advanced sodium-ion batteries

P2-type Ni/Mn-based layered oxides are regarded to be promising cathode materials for advanced sodium-ion batteries (SIBs) owing to their rapid sodium ion diffusion kinetics, high working voltage, and high theoretical capacity. However, P2-type Ni/Mn-based layered oxides are prone to phase transition during charging and discharging processes, resulting in serious capacity fading. Here, introduction of Zn and Ti into transition-metal layers of P2-type layered Na0.66Ni0.33Mn0.67O2 can effectively inhibit P2-O2 phase transition at high voltage, leading to the improved cycling endurance. When being used as cathode materials for SIBs, Na0.66Ni0.27Zn0.06Mn0.61Ti0.06O2 (NNZMT) can deliver a discharge specific capacity of 106.6 mAh g(-1), with 95.17% capacity retention after the 100th cycle at 100 mA g(-1) within 2.1-4.3 V, which are much higher than those (58.4 mAh g(-1) and 45.2%) of Zn/Ti-undoped Na0.66Ni0.33Mn0.67O2 (NNM). Besides, NNZMT displays a much better rate capability compared to the NNM sample. The full cell, based on P2-type layered NNZMT as cathode material and hard carbon as anode material, can provide an initial discharge specific capacity of 94.1 mAh g(-1), with a capacity retention of 75.6% after 100 cycles at 100 mA g(-1) within 1.0-4.2 V. This research work confirms that low-lost Zn/Ti co-doping strategy is an effective approach for designing and preparing cathode materials for advanced SIBs.