Effects of Various Elements Doping on LiNi0.6Co0.2Mn0.2O2 Layered Materials for Lithium-Ion Batteries

Ni-rich LiNi0.6Co0.2Mn0.2O2 (NCM622) and doped LiNi0.6-x Co0.2Mn0.2M x (M = Cr, Cu, Fe, Sn, and Zn) are synthesized and investigated for lithium-ion batteries. The doping effects on morphology, crystal structure, and electrochemical performance are evaluated. These results suggest that introducing elements of Cu, Sn, and Zn is favorable for the structural integrity because the cation mixing of Li+/Ni2+ is reduced. Extended cycle life is obtained for these Cu- and Sn-doped electrodes. When operated at the cutoff voltage of 4.4 V, about 86% and 99% of the initial capacity can be maintained within 200 cycles for LiNi0.59Co0.2Mn0.2Cu0.01O2 and LiNi0.59Co0.2Mn0.2Sn0.01O2, respectively. Possible factors for capacity decay involving structural properties, polarization degree, and impedance increment are discussed. Meanwhile, Cu looks promising as a novel dopant for layered NCM622 cathode materials with improved structures and properties, in which the optimized doping amount is also discussed in detail.