Electrochemical performance and structural stability of layered Li–Ni–Co–Mn oxide cathode materials in different voltage ranges

Abstract In this study, layered Li–Ni–Co–Mn oxide (LiNi1-x-yCoxMnyO2) cathode materials with different transition metal compositions (LiNi1/3Co1/3Mn1/3O2, LiNi0.5Co0.2Mn0.3O2, and LiNi0.8Co0.1Mn0.1O2) are synthesized by a simple mixing process and solid-state reaction at a high temperature. The samples show a typical hexagonal α–NaFeO2 structure with a single phase and predominantly spherical morphology with a homogeneous particle size distribution. The electrochemical properties of the samples are investigated in different voltage ranges by galvanostatic charge/discharge tests. The results reveal that the capacity increases with increasing the charging cutoff voltage by 0.1 V for all the samples. In addition, the LiNi1/3Co1/3Mn1/3O2, LiNi0.5Co0.2Mn0.3O2 and LiNi0.8Co0.1Mn0.1O2 samples deliver initial discharge capacities of 161.0, 170.8, and 202.3 mAh g−1, respectively, at a 0.1 C rate with the voltage ranging from 3.0 to 4.3 V, which increase by 23.4%, 18.8%, and 8.2%, respectively, with the increase in the charging cutoff voltage from 4.3 to 4.6 V. Furthermore, compared with LiCoO2, the samples exhibit a relatively superior cycling performance with an increase of the charging cutoff voltage. Cyclic voltammetry tests reveal that the redox process at approximately 4.5–4.6 V corresponds to Co3+/Co4+, and that at approximately 3.6–3.8 V corresponds to Ni2+/Ni4+. X-ray diffraction measurements confirm the reversible phase transition and excellent structural stability of the LiNi1-x-yCoxMnyO2 materials against prolonged cycling.