Crystal and electronic structures, thermodynamic stability, and cathode performance of Li(Ni, Co, M)O2 (M = Cu, Zn)

• The effects of the partial substitution of Cu and Zn of Li(Ni, Co)O2
• Lower structural stability was not preferable for the cathode property.
• A correlation among cycle performance, structure and thermodynamic stability

In this work, we synthesized LiNi0.8Co0.2O2-based materials in which the host transition metals were replaced partially by Cu or Zn, and studied cathode performances, average and local structures, electron density distributions, and thermodynamic stabilities of the specimens. From charge/discharge cycle tests, it was found that the cycle performances of the Cu- and Zn-substituted samples were worse than LiNi0.8Co0.2O2, and the capacity of LiNi0.79Cu0.01Co0.2O2 was the lowest among the investigated samples. Structure analyses by the Rietveld and the maximum entropy methods suggested that the substitutions weakened bond strengths between the transition–metal and oxygen sites. Additionally, it was found that the thermodynamic stability became lower by both the Cu and Zn substitutions. From the results, it can be concluded that there is a correlation among the cycle performance, the structure stability and the thermodynamic stability in the LiNi0.8Co0.2O2-based materials.