First-principles calculations of the Ti-doping effects on layered NaNiO2 cathode materials for advanced Na-ion batteries

The NaNiO₂ structure is a promising cathode material for sodium ion batteries due to its reasonably high capacity (～120 mAh/g), environmental friendliness and the low cost of required raw materials. First-principles calculations have been carried out to study the Ti ions doped NaNi_1-xTi_xO₂ (x = 0, 0.037, 0.056, 0.083 and 0.167) phases. Results show that Ti doping can lead to a higher average intercalation voltage and improved electronic conductivity. The optimized NaNi_0.917Ti_0.083O₂ sample can effectively suppress the volume change of the unit cell by 4% upon full desodiation and an increased ion mobility was found in this sample by nudged elastic band calculation. We suggest that the NaNi_0.917Ti_0.083O₂ cathode could be a promising candidate for Na-ion batteries.