Enhancement of Structural, Electrochemical, and Thermal Properties of High-Energy Density Ni-Rich LiNi0.85Co0.1Mn0.05O2 Cathode Materials for Li-Ion Batteries by Niobium Doping.

Ni-rich layered oxide LiNi1 - x - yCoxMnyO2 (1 - x - y > 0.5) materials are favorable cathode materials in advanced Li-ion batteries for electromobility applications because of their high initial discharge capacity. However, they suffer from poor cycling stability because of the formation of cracks in their particles during operation. Here, we present improved structural stability, electrochemical performance, and thermal durability of LiNi0.85Co0.1Mn0.05O2(NCM85). The Nb-doped cathode material, Li(Ni0.85Co0.1Mn0.05)0.997Nb0.003O2, has enhanced cycling stability at different temperatures, outstanding capacity retention, improved performance at high discharge rates, and a better thermal stability compared to the undoped cathode material. The high electrochemical performance of the doped material is directly related to the structural stability of the cathode particles. We further propose that Nb-doping in NCM85 improves material stability because of partial reduction of the amount of Jahn-Teller active Ni3+ ions and formation of strong bonds between the dopant and the oxygen ions, based on density functional theory calculations. Structural studies of the cycled cathodes reveal that doping with niobium suppresses the formation of cracks during cycling, which are abundant in the undoped cycled material particles. The Nb-doped NCM85 cathode material also displayed superior thermal characteristics. The coherence between the improved electrochemical, structural, and thermal properties of the doped material is discussed and emphasized.