The enhancement of cyclability of Ni‐rich LiNi 0 . 9 Co 0 . 05−x Mn 0 . 05 Zn x cathode materials by the substitution of Zn for Co

Abstract

In the development of LiNixCoyMnzO2 (NCM) cathode active materials in lithium-ion batteries (LIBs) for electric vehicles, it is widely accepted that Ni-rich and Co-free NCM is the best candidate for the promotion of electric vehicle deployment. Inspired by the fact that Zn is an element that can be incorporated in regenerated NCM in the LIB recycling, Zn is doped into NCM from an impurity level in the leachate from spent LIBs to a level where Co is completely replaced by Zn. LiNi0.9Co0.05Mn0.05O2 (NCM955), LiNi0.9Co0.0495Mn0.05Zn0.0005O2 (NCMZ-0.05), LiNi0.9Co0.045Mn0.05Zn0.005O2 (NCMZ-0.5), and LiNi0.9Mn0.05Zn0.05O2 (NMZ955) are synthesized by a co-precipitation method. It is confirmed that Zn, which has a similar radius to Li+ and Ni2+, is incorporated into both Li and transition metal layers. An optimum cation mixing on the Zn-doped NCM surface and the expanded NCM lattice due to Zn doping lead to improved cyclability and rate capability. For example, the optimized NCMZ-0.5 exhibits enhanced capacity retention of 91.7% compared to NCM955 (69.8%) after 80 cycles. The cyclability improvement of Zn-doped NCM is ascribed to better reversibility as well as lower overvoltage than NCM955. In particular, NMZ955 displays outstanding capacity retention in cycling tests with a wide voltage range, which implies that Co-free NMZ has a competitive edge in cyclability compared to NCM. This work not only elucidates the positive effect of Zn doping in regenerated NCM, but also further provides a practical approach to designing a Co-free Ni-rich cathode for higher energy density.