Electrochemical performance of LiNi_0.5Mn_0.5O₂ as cathode material for lithium-ion batteries prepared by oxalate co-precipitation method

The oxalate co-precipitation method was used to synthesize LiNi_0.5Mn_0.5O₂. The effects of pH on the structure, morphology, and electrochemical performance of LiNi_0.5Mn_0.5O₂ were investigated. The crystal structures and surface morphologies of the oxalate precursor and LiNi_0.5Mn_0.5O₂ obtained at pH=4.0, 5.5, 7.0, 8.5 were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. The electrochemical performance of LiNi_0.5Mn_0.5O₂ was evaluated by galvanostatic charge/discharge tests. Results show that the LiNi_0.5Mn_0.5O₂ obtained at pH=7.0 has a smaller particle size, more uniform distribution, better layered characteristics and a smaller degree of cation mixing. Electrochemical tests confirmed that the sample obtained at pH=7.0 had the best electrochemical performance. At 0.1C rate, its discharge capacity reached 185 mAh·g^-1 at the first cycle and remained over 160 mAh·g^-1 after the 20th cycle. X-ray photoelectron spectroscopy (XPS) results indicated that the oxidation states of Ni and Mn in the LiNi_0.5Mn_0.5O₂ obtained at pH=7.0 were +2 and +4, respectively.