Study On The Preparation And Modification Of Nickel-rich Cathode Materials For Lithium Ion Batteries

Compared with the currently commercialized materials layered Li Co O₂,olivert-type Li Fe PO₄,spinel type Li Mn₂O₄and other cathode materials,nickel-rich cathode materials LiNi_1-xM_xO₂（M=Co,Mn,Al,x≤0.4）are considered to have a very broad application prospect in the field of energy storage of electric vehicles due to their higher specific capacity.However,with the increase of nickel content,the nickel-rich cathode materials show some fatal defects such as poor cyclic stability in the process of charging and discharging.Therefore,in this paper,nickel-rich cathode materials of lithium ion batteries were taken as the object,the synthetic process conditions were investigated,and Sb³⁺doping,Ti⁴⁺and Al³⁺double doping were adopted to improve the cyclic stability of the materials.Nickel-rich precursor Ni_0.9Co_0.05Mn_0.05（OH）₂was synthesized from mixed salt and mixed alkali solution at a certain temperature by co-precipitation method.Then the precursor was mechanically mixed with lithium and sintered in high temperature solid phase in oxygen-rich atmosphere to obtain nickel rich cathode material LiNi_0.9Co_0.05Mn_0.05O₂.Through the use of X-ray diffraction（XRD）,scanning electron microscopy（SEM）,charge-discharge performance test and cyclic voltammetry curve（CV）and other common analysis test methods,the effects of pH value and ammonia concentration on the morphology,structure and electrochemical properties of nickel-rich cathode materials were studied..And the optimum conditions for the synthesis of Ni_0.9Co_0.05Mn_0.05（OH）₂were investigated.The final experimental results showed that when the pH value of solution reaction was 11.5 and the concentration of ammonia was2mol/L,the synthesized LiNi_0.9Co_0.05Mn_0.05O₂cathode material had the best electrochemical performance.In the voltage range of 2.5～4.3V,under the charge and discharge ratio of 0.2C,the initial discharge capacity of the material is 198m Ah·g^-1,and the discharge capacity after the cycle of 50 weeks is 173.9m Ah·g^-1,and the capacity retention rate is 87.3%.In order to improve the cyclic stability of LiNi_0.9Co_0.05Mn_0.05O₂materials,Sb³⁺doping,Ti⁴⁺and Al³⁺double doping were studied.The results show that the Sb³⁺doped material with the doping amount of 1.25%has better cyclic stability and rate performance,and the first specific discharge capacity of the material with the doping amount of 1.25%is 196.58m Ah·g^-1,and the capacity retention rate is 95.1%.By exploring the influence of Ti⁴⁺,Al³⁺and Ti⁴⁺\Al³⁺double doping on the electrochemical performance of the material,it was finally determined that both Ti⁴⁺and Al³⁺could improve the cyclic performance of the material.When Ti⁴⁺and Al³⁺double doping,the electrochemical performance of the material was the best.the first discharge capacity of the material is 199.13m Ah·g^-1,and the capacity loss rate of the material in 50 weeks was 0.38%.