Research On Synthesis And Electrochemical Properties Of LiNi_1/2Mn_1/2O₂ Layered As Cathode Material

LiCoO2 has become the main cathode in commercial lithium-ion batteries based on its merit of high capacity, excellent reversibility and discharge rate. Because of the high cost and toxicity of LiCoO2, researchers have been searching for alternative materials. The researchers made extensively study on LiNiO2 and LiMnO2 as LiCoO2 alternatives. Although there has been a lot of progress in making those materials in many aspects, they still possess various problems for practical application. Recently, the solid solution materials mainly containing Ni and Mn, which was proved to be superior to the LiNiO2 and LiMnO2, had become an important research aspect in cathode material field.In this work, layered LiMn1/2Ni1/2O2 was selected as research object and was studied on its synthesis and modification in detail. Use the sol-gel mehod and co-precipitation method synthesized the LiMn1/2Ni1/2O2. Because the material synthesized by co-precipitation had batter properties, the synthesis technics of co-precipitation was mainly studied. A new method which adopted H2O2 oxiding the co-precipitated mixture was studied. We got the stoichiometric precursor by oxiding Mn2+ to Mn4+ with H2O2. By X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscope (SEM), Thermogravimetery and differential thermal analysis (TG-DTA), Cyclic voltammetry (CV) and Electrochemical impedance spectroscope (EIS) measurement, studied the effects of ultrasonic disposal, reaction time and temperature, cooling patterns on structure and electrochemical properties, optimized the synthesis technics. Furthermore, the material was modified by Al doping.The results of experiment show that the LiMn1/2Ni1/2O2 sample, which was synthesized with H2O2 oxiding the precursor, by LiOH as lithium source, by Li:M(Ni and Mn) = 1.05:1, calcined at 900℃for 9 hours, quenched at room temperature quickly, has best electrochemical properties. LiMn1/2Ni1/2O2 exhibits a high reversible capacity of 145 mAh·g-1 at a discharge rate 0.5C in the voltage range of 2.8 ~ 4.6V, after 40th cycle, the capacity maintained at 140 mAh·g-1. The discharge capacity was 104.62 mAh·g-1 with 1.5C discharge rate. XRD and SEM...