Preparation Of NCM622 Cathode Material By Coprecipitation Method And Study On Co-doping Of Na And Br

LiNixCoyMn1-x-yO2 cathode material has been extensively studied due to its high specific capacity,environmentally friendly,low cost and good safety performance,and is considered to be one of the substitutes for LiCoO2 cathode material.Among them,LiNi0.6Co0.2Mn0.2O2 cathode material can provide higher capacity due to the high content of Ni element,and meet the needs of higher capacity of lithium ion battery,and become one of the most promising lithium ion cathode materials.However,this material still has many drawbacks such as poor cycle stability,poor rate performance and serious cation mixing.In view of the above problems,the precursor of Ni0.6Co0.2Mh0.2(OH)2 was prepared by co-precipitation method,the effects of different synthesis conditions on the morphology and particle size distribution of the precursors were investigated.Based on this,the prepared precursor was calcined into LiNi0.6Co0.2Mn0.2O2 cathode material,and the effects of calcination temperature and preparation conditions on the structure and properties of LiNi0.6Co0.2Mn0.2O2 cathode material were investigated.Finally,the co-doping of Na+ and Br-is used to improve the crystal structure of the material and improve the stability and electrochemical performance of the material.The specific content is as follows:Ni0.6Co0.2Mn0.2(OH)precursor was successfully synthesized by coprecipitation method with sodium hydroxide as precipitant and ammonia as complexing agent.The effects of different pH values,different ammonia concentrations,different feed rates and different feed times on the morphology and particle size distribution of the precursors were investigated.The results show that at pH=111,the ammonia concentration is 0.5 mol/L,the feed rate is 0.28 ml/min,and the feed time is 3h,the primary particles of the precursor are needle-like,the secondary particles aggregated by primary particle stacking are closer to the spheroidal shape.The precursor synthesized by co-precipitation method was mixed with a excess of 5%LiOH·H2O,and calcined at 450? for 5 h to study the effects of different calcination temperatures on the structural properties of the materials.XRD showed that the samples synthesized at different temperatures of 820?,850? and 880? had a layered structure of a single phase.Through refinement,it was proved that Ni2+ had the lowest occupancy rate in the Li position at 850?,indicating that it had the best cation order.The material synthesized at 850? has the highest initial discharge capacity of 193.6 mAh/g and a capacity of 149.6 mAh/g at 5 C rate.LiNi0.6Co0.2Mn0.2O2 cathode material was synthesized by solid phase reaction at 850? using the prepared hydroxide precursor.XRD showed that all of the samples had a layered structure of ?-NaFeO2.Through the refinement and calculation of the lithium layer spacing,the results showed that the material had the smallest cation mixing and maximum lithium layer spacing under the conditions of pH=11,0.5mol/L of ammonia concentration,0.28 ml/min of feed rate and 3 h of feed time.The electrochemical performance showed that the material with this condition had the highest first discharge capacity of 208.7 mAh/g at rate of 0.1 C,corresponding to the coulombic efficiency of 88.21%,and the highest discharge capacity of 165 mAh/g at 5 C rate,showing the best electrochemical performance.The LiNi0.6Co0.2Mn0.2O2 cathode material was co-doped with Na+and Br-,which were characterized by XRD and refinement,the co-doping of Na+ and Br-did not change the lamellar phase of the material,and the sample of doping 1%had minimal Li/Ni mixing.The electrochemical performance showed that the first discharge capacity of the sample with a doping amount of 1%was higher,which was 213 mAh/g at 0.1 C rate.After cycling 50 times at 1 C rate,the voltage decay is the smallest and the capacity retention rate is 86.0%,morever,the capacity at 5 C rate is up to 178.2 mAh/g,which is much higher than the undoped sample.