Preparation And Modification Of Li[Ni_{（0.6+0.2x）}Co_0.2Mn_0.2（1-x）]O₂ Lithium Electrode Cathode Material

In this paper,LiNi_{（0.6+0.2x）}Co_0.2Mn_0.2（1-x）O₂（x=0.1-0.9）was synthesized by hydroxide coprecipitation method and doped research on materials.The effects of ammonia concentration,pH value,reaction temperature,lithium content,calcination temperature and element doping（K,Cu,Al）on the electrochemical properties of the materials were investigated.The morphology,structure and electrochemical performance of the materials were analyzed by SEM,XRD,and other electrochemical tests such as constant current charge and discharge,CV,and EIS.LiNi_{（0.6+0.2x）}Co_0.2Mn_0.2（1-x）O₂（x=0.1-0.9）was synthesized by hydroxide coprecipitation method.The material with the best ratio was determined to be LiNi_0.66Co_0.2Mn_0.14O₂by analyzing the morphology and electrochemical performance of the materials with different element ratios.It was found that the higher the Ni content,the higher capacity,when the Co content is constant.However,due to the similar radii of Ni²⁺and Li⁺,the positions of Li⁺and Ni²⁺may be interchanged,it can cause the collapse of the material structure and reduce the cycle performance and stability of the material.Although the Mn element does not provide capacity during the charge and discharge process,it still plays a role in improving the safety performance of the material in maintaining structural stability.Therefore,the layered LiNi_1-x-yCo_xMn_yO₂lithium ion cathode material can exert its optimal electrochemical performance only when the ratio of the three elements Ni,Co,and Mn is just right.The cathode materials for lithium-ion battery was was synthesized by hydroxide coprecipitation method.Sulfate solution of transition metal ions was used as raw material,Na OH solution was used as precipitant and ammonia or sodium lactate was used as complexing agent.The effects of ammonia concentration（0.8mol/L,1.0mol/L and 1.2mol/L）,pH value（10.5,11.0 and 11.5）,reaction temperature（50 ℃,60 ℃ and 70 ℃）,lithium content（1.01,1.03,1.05 and 1.07）and calcination temperature（750 ℃,800 ℃ and850 ℃）on the electrochemical properties of the materials were investigated,when using ammonia as the complexing agent.It was found that the synthesized LiNi_0.66Co_0.2Mn_0.14O₂at the conditions with ammonia concentration was 1mol/L,pH value was 11 and the hydroxide precursor prepared at a reaction temperature of 60 ℃,it was mixed with an excess of 5%Li₂CO₃ball mill,pre-fired at 450 ℃ for 5 h and calcined at 800 ℃ for 12 h has better electrochemical performance.In the voltage range of 2.7-4.3 V,the first specific discharge capacity of LiNi_0.66Co_0.2Mn_0.14O₂reached 198.8 m Ah/g at 0.1C.The effects of sodium lactate concentration（0.8mol/L,1.0mol/L and 1.2 mol/L）,pH value（10.5,11,11.5and 12）and reaction temperatureon（60 ℃,65 ℃,70 ℃ and 75 ℃）the electrochemical properties of the materials were investigated,when using sodium lactate as the complexing agent.It was found that the synthesized LiNi_0.66Co_0.2Mn_0.14O₂at the conditions with sodium lactate concentration was 1mol/L,pH value was 11.5 and the hydroxide precursor prepared at a reaction temperature of 70 ℃ it was mixed with an excess of 5%Li₂CO₃ball mill,pre-fired at 450 ℃ for 5 h and calcined at 800 ℃ for 12 h has better electrochemical performance.In the voltage range of 2.7-4.3 V,the first specific discharge capacity of LiNi_0.66Co_0.2Mn_0.14O₂reaches 182.8 m Ah/g at 0.1C.Study on the modification of LiNi_0.66Co_0.2Mn_0.14O₂lithium ion cathode materials using single（K）and composite（K,Cu,Al）doping.The effects of different doping amounts on the structure and electrochemical performance of the cathode materials were studied.Studies have shown that replacing Li⁺with K⁺helps to reduce grain size,reduce charge transfer resistance,increase crystallinity and increase interlayer spacing,thereby increasing the lithium ion diffusioncoefficient.The first charge capacity of[Li_0.98K_0.02]Ni_0.66Co_0.20Mn_0.14O₂is about 219.6 m Ah/g,and the first discharge capacity is about 202.0 m Ah/g.Its capacity retention rate of cycling 50 times under 1C was 84.37%.It was found that the doping of an appropriate amount of metal element K improved the cycle and rate performance of the material.In the compound doping,K element can effectively improve the initial discharge specific capacity of the material;the Al element has the greatest influence on the capacity retention rate of the material.The initial charge and discharge specific capacities of[Li_0.99K_0.01](Ni_0.66Co_0.2Mn_0.14)_0.94[Cu_0.03Al_0.03]O₂can reach214.7 m Ah/g and 210.8 m Ah/g and the coulomb efficiency is 98.18%.The capacity retention rate was 87%after 30 cycles at 1C.The research results show that doping metal elements（K,Cu,Al）can reduce the electrochemical impedance of the cathode material and increase the conductivity of the material.This will provide guidance for future research on the modification of doped metal elements in high nickel ternary lithium ion cathode materials.