Microwave Hydrothermal Synthesis Of Nickel-cobalt-manganese Ternary Precursors And Their Properties

With the increasing demand for new battery materials,the market expand continually.LiNi_1-x-yCo_xMn_yO₂ material has the advantages of LiNO₂、LiMnO₂ and LiCoO₂.Such as high capacity,large vibration density and high energy density.As seen a new type of cathode material developed in recent years.Ni_1-x-yCo_xMn_y（OH）₂ materials are prepared by traditional co-precipitation method.This three elements（Ni,Co and Mn）are usually precipitated together,and the obtained precursors are mixed with lithium compounds.After calcination,LiNi_1-x-yCo_xMn_yO₂ are prepared.However,this method has some problems such as long crystallization time,uneven temperature and concentration distribution in the reactor.In contrast,the microwave-assisted heating synthesis method has the advantages of short crystallization time,uniform temperature distribution of the solution system,fast heating rate,easy control,energy saving,high efficiency,safety and other advantages,considered as a new green chemical synthesis method.Based on Ni_1-x-yCo_xMn_y（OH）₂ as the precursor of LiNi_1-x-yCo_xMn_yO₂ materials,synthetic precursor by microwave assisted coprecipitation,explore the reaction time,concentration of complexing agent Moore,metal salt solution concentration and p H values of different parameters on the reaction conditions,such as the influence law of the surface morphology and structure of stability of Ni_1-x-yCo_xMn_y（OH）₂.The LiNi_1-x-yCo_xMn_yO₂ materials with uniform morphology and particle size and good phase structure were prepared by lithium doping,pre-sintering and sintering process.The electrochemical properties of the ternary materials were evaluated.The specific contents are as follows:（1）At the microwave power of 1000W,pressure of 0.5Mpa～1MPa,reaction temperature of 150-180℃and reaction time of less than 3 h,Under the microwave digestion apparatus,obtained the homogeneous hexagonal sheet which have β-Ni（OH）2structure,and the microcosmic size of primary particles is 60-100 nm.;（2）According to the microwave synthesis experiment,the following rules are obtained:when the concentration of metal salt solution is too high,the grain nucleation rate in the NiCoMn hydroxide precursor system exceeds the crystal growth rate,and the primary particle morphology is irregular nanometer sheet;When the concentration of the metal salt solution was controlled at 0.1～0.2mol/L,the primary particles were aggregated into secondary particles with similar spherical structure,and the particle size was evenly distributed in the range of 1～20μm.;（3）Using the optimized precursor material,the cathode material was prepared by mixing lithium（Li/M=1.02,1.05,1.08）,pre-sintering（pre-sintering temperature350°C,400°C,450°C,holding for 1 hour）and sintering process（650°C,700°C,holding for 9 hours）.Li/M ratio has little influence on the initial charge-discharge capacity of the material,but has a great influence on the initial discharge capacity,the initial charge-discharge effect and the reappearance property of the material.The I₀₀₃/I₁₀₄=1.64 of the synthesized materials when Li/M=1.05,indicating that the sample has a low degree of Li-Ni mixing.And I₀₀₆+I₁₀₂/I₁₀₁=0.86,indicating that the six-way dense heap structure is orderly;（4）Using the optimized precursor material,the cathode material was prepared by mixing lithium,pre-sintering and sintering process.The Li/M ratio had little effect on the first charge and discharge capacity of the material,but had great effect on the first charge and discharge capacity.When Li/M=1.05,the LiNi_0.6Co_0.2Mn_0.2O₂ has good layered crystal structure and weak cation mixing effect.The maximum discharge capacity can reach 112.73m Ah/g,and the capacity retention rate is 99.72%.After 30cycles at 0.2C,the discharge capacity decreases to 107.38m Ah/g and the capacity retention rate is 99.58%.In this paper,a series of experiments are of significance for the study of microwave assisted synthesis of LiNi_1-x-yCo_xMn_yO₂ materials.