Surface engineering with ammonium niobium oxalate: a multifunctional strategy to enhance electrochemical performance and thermal stability of Ni-rich cathode materials at 4.5 V cutoff potential

ABSTRACT Ni-rich layered oxides with high energy density and low costs are among the most promising candidate cathode materials for the next-generation lithium-ion batteries. However, the intrinsic issues of lithium residuals on particle surface and structural degradation with cycling deteriorate the electrochemical performance and cause safety issues. In this work, a facile and scalable Nb-modification strategy is proposed to remove the surface lithium residuals and in situ form Li-ion conductive LiNbO3 on Ni-rich LiNi0.6Co0.2Mn0.2O2 (NCM622) particle surface with small amount of Nb diffusing into surface lattice and doping at Li sites. The surface Nb-modification is performed with water soluble ammonium niobium oxalate by a wet chemistry route. The reconstructed LiNbO3-coated/Nb-doped hybrid surface structure of NCM622 enables a unique combination of significantly improved cycling stability, superior rate performance and excellent thermal stability. This developed strategy can be applied to modulate the surface chemistry of other Li-containing materials.