Ti-Substituted O3-NaNi<sub>0.5</sub>Mn<sub>0.3</sub>Ti<sub>0.2</sub>O<sub>2</sub> Material with\na Disordered Transition\nMetal Layer and a Stable Structure

O3-type NaNi<sub>0.5</sub>Mn<sub>0.5</sub>O<sub>2</sub> (NNM) is\nvery competitive for sodium-ion batteries (SIBs) due to its high capacity\nand easy production. Nevertheless, the intricate phase transitions\nduring the charging–discharging significantly impede its practical\napplication. This paper proposes a strategy for successfully synthesizing\nNaNi<sub>0.5</sub>Mn<sub>0.3</sub>Ti<sub>0.2</sub>O<sub>2</sub> (NNMT)\nby combining coprecipitation and a high-temperature solid-state method.\nThis method introduces Ti elements while retaining the electrochemically\nactive Ni<sup>2+</sup> content, thus, the NNMT has a high initial\nspecific capacity of 151.4 mAh g<sup>–1</sup> at 1 C. It is\ndemonstrated that introducing Ti<sup>4+</sup> leads to the transition\nmetal layers becoming disordered by ex situ XRD, thus mitigating the\nirreversible phase transition of the material. In addition, Ti<sup>4+</sup> does not have an outer electron, which can reduce electron\ndelocalization in the transition metal layer and improve the material’s\ncyclic stability. The NNMT possesses a capacity retention rate of\n60.66% after 150 cycles, much higher than the initial NNM’s\n18.96%. It also exhibits an excellent discharge capacity of 86.8 mAh\ng<sup>–1</sup> at 5 C. In conclusion, the cycling and rate\nperformance of the Ti-substituted NNMT are greatly improved without\ncapacity loss, which offers innovative concepts for the modification\nmeans of the SIBs layered oxide cathode materials.