Superior electrochemical performance of O3-type NaNi0.5-xMn0.3Ti0.2ZrxO2 cathode material for sodium-ion batteries from Ti and Zr substitution of the transition metals

Due to the low cost and abundance of sodium, sodium-ion batteries (SIBs) show great potential as energy storage devices. As far as the current research is concerned, cathode materials are still the bottleneck for boosting the performance of SIBs. O3-type layered NaNi0.5Mn0.5O2 is considered as an important cathode material of SIBs, but its irreversible phase transition, poor stability in air, and sluggish kinetics usually lead to reduced capacity, poor rate performance and high cost for material storage, which largely limit the large-scale application. Herein, a remarkable O3-type layered material NaNi0.5-xMn0.3Ti0.2ZrxO2 (NaNMTZ, x = 0.02, 0.05), with stable phase structure has been synthesized by the solid-phase method. The partial substitution of electrochemical inactive Ti/Zr brings about higher electronic delocalization and entropy of mixing leading to enhanced structural stability. In addition, the enlarged interlayer spacing and good conductivity contribute to better rate capability. The micro-nano structure leads to faster Na+ diffusion rates and shorter diffusion paths for both ions and electrons. Therefore, NaNi0.45Mn0.3Ti0.2Zr0.05O2 exhibits an initial reversible capacity of 141.4 mAh g−1 with a coulombic efficiency of 98.8% and remarkable capacity retention of 70% after 200 cycles at 0.05C, presenting better electrochemistry performance than the conventional NaNi0.5Mn0.5O2. This study provides a new angle to design high capacity cathode materials with high rate capability and cycling stability through crystal lattice modulation.