Study On Synthesis And Electrochemical Properties Of Lithium-manganese-nickel Oxides Cathode

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 extensive 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 LiNi_1/2Mn_1/2O₂ powders are successfully synthesized by a co-precipitation, their preparation and properties are deeply and systematically explored by means of XRD,SEM,TG/DSC,CV,XPS and so on. Effects on the structure and properties of samples are studied from Li resources, different performs, LiOH/M(OH)₂ molar ratio, cooling pattern, calcining heat condition, the best synthesis technics are optimized. The results got from the experiments show that the samples of LiNi_1/2Mn_1/2O₂ which were sintered at 800℃from LiOH:M(OH)₂= 1.05:1, pressing pellets, quenching pattern are best. LiNi_1/2Mn_1/2O₂ exhibited a discharge capacity of 145.6mAh/g in the voltage range of 2.8-4.6V and at a specific current of 20mA/g.Considering the disadvantages of co-precipition process to synthesis of LiCo_1/3Ni_1/3Mn_1/3O₂, we applied sol-gel method to prepare Li[Ni_(1-x)/2Co_xMn_(1-x)/2]O₂ (0＜x≤1/2) series. The structure and electrochemical properties have been investigated, all the compounds haveα-NaFeO₂ type structure and have a spherical or ellipse shape, its particles are uniform and in the size range of 100-500nm. Electrochemical measurements show that all the samples perform good electrochemical properties when cycled in the voltage range of 2.9-4.6V and at a specific current of 20mA/g, exhibiting higher capacity than non-doping cobalt LiNi_1/2Mn_1/2O₂. The first discharge capacities of all the samples synthesized in the temperature range 600℃～1000℃are higher than 200mAh/g, and the discharge capacity remains higher than 170mAh/g after 50 times cycling. The material shows good performance at different charge/discharge rate.