Synthesis of Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ by sol–gel method and its electrochemical properties as cathode materials for lithium-ion batteries

Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ was synthesized by sol–gel method at 700, 800, 900 and 1000 °C, respectively, characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and measured as the cathode materials for lithium-ion batteries (LIBs). After their performances have been compared, 800 °C was considered as the optimum synthesis temperature for Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ as the cathode materials for LIBs. When charge–discharged at 20 mA g⁻¹ in a voltage window of 2.0–4.8 V, the Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ synthesized at 800 °C (LMNCO-800) showed charge and discharge capacities of 376.2 and 276.3 mAh g⁻¹, respectively, with irreversible capacity of 99.9 mAh g⁻¹ and Coulombic efficiency of 73.4%, in the first charge–discharge cycle. The discharge capacity was 239.0 mAh g⁻¹ in the 50th charge–discharge cycle, with capacity retention of 86.6%. The LMNCO-800 also showed superior high-rate performances. When cycled at the rates of 0.5, 1, 2 and 5 C rate (1 C = 200 mA g⁻¹), the discharge capacities of the Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ can reach 241, 171, 150 and 110 mAh g⁻¹, respectively. When characterized with high-resolution transmission electron microscopy (TEM), nanodomains with two different structures can be found in LMNCO-800, with some nanodomains showing monoclinic Li₂MnO₃ structure and the other nanodomains showing hexagonal LiMO₂ structure.