Sn-Doping and Li2SnO3 Nano-Coating Layer Co-Modified LiNi0.5Co0.2Mn0.3O2 with Improved Cycle Stability at 4.6 V Cut-off Voltage

Abstract

Nickel-rich layered LiNi1−x−yCoxMnyO2 (LiMO2) is widely investigated as a promising cathode material for advanced lithium-ion batteries used in electric vehicles, and a much higher energy density in higher cut-off voltage is emergent for long driving range. However, during extensive cycling when charged to higher voltage, the battery exhibits severe capacity fading and obvious structural collapse, which leads to poor cycle stability. Herein, Sn-doping and in situ formed Li2SnO3 nano-coating layer co-modified spherical-like LiNi0.5Co0.2Mn0.3O2 samples were successfully prepared using a facile molten salt method and demonstrated excellent cyclic properties and high-rate capabilities. The transition metal site was expected to be substituted by Sn in this study. The original crystal structures of the layered materials were influenced by Sn-doping. Sn not only entered into the crystal lattice of LiNi0.5Co0.2Mn0.3O2, but also formed Li+-conductive Li2SnO3 on the surface. Sn-doping and Li2SnO3 coating layer co-modification are helpful to optimize the ratio of Ni2+ and Ni3+, and to improve the conductivity of the cathode. The reversible capacity and rate capability of the cathode are improved by Sn-modification. The 3 mol% Sn-modified LiNi0.5Co0.2Mn0.3O2 sample maintained the reversible capacity of 146.8 mAh g−1 at 5C, corresponding to 75.8% of its low-rate capacity (0.1C, 193.7mAh g−1) and kept the reversible capacity of 157.3 mAh g−1 with 88.4% capacity retention after 100 charge and discharge cycles at 1C rate between 2.7 and 4.6 V, showing the improved electrochemical property.