Preparation And Synergistic Modification Of Doping And Coating Of Ni-rich Ternary Cathode Material LiNi_0.8Co_0.1Mn_0.1O₂

Nickel-rich ternary material LiNi_0.8Co_0.1Mn_0.1O₂（NCM811）has the advantages of high specific capacity of Ni,high stability of Co,and high safety of Mn.It is a new type of lithium-ion battery cathode material with great development prospects.However,it has some problems of its own that need to be improved to be more suitable for the future development of the lithium-ion battery industry.In this thesis,NCM811 pure-phase anode materials with ellipsoidal rod shape and microspherical shape were synthesized by surfactant-assisted hydrothermal method.In the process of synthesizing ellipsoidal rod-shaped NCM811,the molar ratio of urea to transition metal ions was adjusted and the optimum reaction condition was determined at a molar ratio of 2:1;in the process of synthesizing microspherical-shaped NCM811,the addition amount of surfactant polyethylene glycol was adjusted and the optimum reaction condition was determined at 10%.Finally,two different morphologies of the respective optimal samples were selected to investigate the electrochemical properties,and the results showed that the initial discharge specific capacity of the microspherical-shaped sample at 0.1 C was 195.3m Ah/g under 2.8～4.3 V,which was about 5 m Ah/g higher than that of the ellipsoidal rod-shaped sample of 190.4 m Ah/g.After 100 cycles,the capacity retention rate of the ellipsoidal rod-shaped sample was only 71.4%,while the microspherical-shaped sample reached 75.5%.Therefore,the microspherical-shaped NCM811 pure phase cathode material is more promising.Based on the above studies,the following modification research works were carried out on the basis of pure phase materials of NCM811 in microspherical shape.Firstly,Na⁺-doped NCM811 cathode materials were synthesized by solid-phase grinding and calcination methods,and the results showed that 3%Na⁺doping was the best.Next,on the basis of 3%Na⁺doping,the AlF₃ coating modification study was carried out to investigate the effects of Na⁺doping and AlF₃ coating synergistic modification on the electrochemical properties of NCM811cathode materials.During the electrochemical performance analysis,it was found that the Na⁺-doped and simultaneously AlF₃-coated sample exhibited the highest initial discharge specific capacity and cycling stability compared with the pure phase,single Na⁺-doped,and single AlF₃-coated samples.It had an initial discharge specific capacity of 202.6 m Ah/g and a capacity retention of 86.8%after 100 cycles at a current density of 0.1 C in the voltage range of 2.8～4.3 V,which was 11.3%higher than that of the original sample.LiV₂O₄-covered and simultaneously V⁴⁺-doped NCM811 cathode materials were successfully synthesized by the wet chemical method and annealing treatment to investigate the effects of LiV₂O₄-coating and V⁴⁺-doping on the electrochemical performance of NCM811 cathode materials.The results showed that the best electrochemical performance was obtained when the LiV₂O₄ coating amount was set to 0.6 wt%,and its initial discharge specific capacity reached 203.5 m Ah/g at 2.8～4.3 V after 100 cycles at 0.1 C,with a retention rate of 87.6%,which was 12.1%higher compared with 75.5%of the original sample.When the rate was increased to 5 C,the capacity of the original sample plummeted to only about100 m Ah/g,but the discharge capacity of the sample with 0.6 wt%of coating was still 140.9m Ah/g.The experiments confirmed that this synergistic modification of coating and doping provides a new idea for enhancing the electrochemical performance of Ni-rich ternary materials for lithium-ion batteries.