Optimizing transition metal ion ratio of LiNi0.5+xCo0.2+yMn0.3+zO2 (x+y+z=0) by simplex and normalization combined method

Optimizing the ratio of transition metal (TM) ions is an effective modification strategy to improve the electrochemical properties of LiNi0.5+xCo0.2+yMn0.3+zO2 (x + y + z = 0, and the absolute values of x, y and z are not more than 0.03). In this work, we develope a new method which combines the simplex method with the normalization method of evaluation index (SNEI) to optimize the TM ion ratio of LiNi0.5+xCo0.2+yMn0.3+zO2. This method can significantly improve the optimization efficiency. Only after three times of simplex operation, the optimum component of LiNi0.493Co0.214Mn0.293O2 is obtained. The results show that the electrochemical properties of material have improved significantly through adjustment of the ratio of TM ions slightly, and LiNi0.493Co0.214Mn0.293O2-based cells exhibit long cycle life and good rate capability due to the low degree of Li/Ni mixing and the slow increase of impedance during cycling. Simultaneously, the impact of the intensity of the TM ion ratio on electrochemical performances are studied, and the following trend is observed in decreasing the sensitivity of the evaluation indexes: cycle performance > rate capacity > specific capacity. This newly-developed SNEI method has a wide applicability and great prospects in electrolyte and electrode formulations. (C) 2020 Elsevier Ltd. All rights reserved.