Effects of sulfate modification of stoichiometric and lithium-rich LiNiO₂ cathode materials

Lithium nickel oxide, LiNiO₂, has attracted considerable interest as a high energy cathode for next generation lithium-ion batteries. Nevertheless, shortcomings such as significant cycling capacity decay and low stability in ambient atmosphere have hindered its practical application, and consequently most work has focused on the more stable Mn and Co doped analogues Li(Ni,Mn,Co)O₂. Here, we report an investigation of an alternative strategy, sulfate modification, in the LiNiO₂ system. We show that improved performance can be achieved, attributed to the dual effect of a low level of bulk doping and the presence of a self-passivation Li₂SO₄ layer formed beyond the solid solution limit. Ab initio simulations suggest that the behavior is similar to that of other high valent dopants such as W and Mo. These dual effects contribute to the improved air stability and enhanced electrochemical performance for the sulfate modified lithium-rich LiNiO₂, leading to high initial capacities (∼245 mA h g⁻¹ at 25 mA g⁻¹, and ∼205 mA h g⁻¹ at 100 mA g⁻¹) and better capacity retention. Overall, the results show that polyanion modification represents an excellent alternative low-cost strategy to improve the performance of lithium nickel oxide cathode materials.