Effects of Nb-doping on cycle life, self-discharge and crack resistance of Ni-rich LiNi0.94Co0.02Al0.04O2 cathode for Li-ion batteries

A facile Nb-doping is applied to a high-Ni, low-Co LiNi0.94Co0.02Al0.04O2 cathode material (NCA94). Crystallo-graphic structures, morphologies and electrochemical properties of the pristine and Nb-doped samples are investigated. Nb-doping does not obviously affect the structure and morphology of the material. However, appropriate dose of Nb-doping can suppress the Li+/Ni2+ cation mixing and strengthen the structure, thereby improving cycle life, lowering self-discharge and inhibiting cracking during cycles. The cathode with 0.3 wt% Nb-doping (NCA94-3) exhibits significantly improved structural stability and electrochemical performance. It delivers 172.0 mAh g-1 after 300 charge-discharge (voltage window: 2.8-4.3 V) cycles at 2 C (1 C = 220 mA g-1) with a capacity retention of 88.7 %, whereas the pristine one shows a capacity of only 129.9 mAh g-1 after 300 cycles with a capacity retention of 67.4 % under the same test condition. The self-discharge of the cathode can also be effectively suppressed by Nb-doping. Moreover, after 300 cycles at 2 C, the spherical morphology of NCA94-3 can be maintained well but NCA94-0 cracks obviously.