Study On Preparation And Modification Of Nickel Cobalt Manganese Cathode Material

Lithium ion battery Li Ni_xCo_yMn_（1-x-y）O₂has the advantages of high discharge capacity,good rate performance and low toxicity.Among them,Li(Ni_0.5Co_0.2Mn_0.3)O₂ cathode material is widely concerned because of its good comprehensive performance,and Li(Ni_0.9Co_0.05Mn_0.05)O₂is the future development trend due to its high capacity cost and environmental advantages.However,these nickel-cobalt-manganese ternary cathode materials are faced with the problems of Li/Ni mixed discharge,voltage attenuation during charging and discharging,and a series of phase transitions resulting in structural damage,resulting in rapid capacity decay.In response to these problems,the ion doping method is adopted to carry out modification research,as follows:（1）Two cathode materials,Li(Ni_0.5Co_0.2Mn_0.3)O₂ and Li(Ni_0.9Co_0.05Mn_0.05)O₂,were prepared by ball milling combined with drying spray method.The results show that under the condition of calcination in oxygen atmosphere,both materials have lower Li/Ni mixed arrangement and more stable structure,and their electrochemical performance is more prominent.（2）The Li(Ni_0.5Co_0.2Mn_0.3)_1-xZn_xO₂（NCMZ）cathode materials are prepared by high temperature solid-state reaction.XRD,XPS and other structural and element tests show that Zn²⁺entered into the lattice structure and replaced the transition metals.Electrochemical tests show Zn doping can improve discharge capacity and cycling retention of Li(Ni_0.5Co_0.2Mn_0.3)O₂（NCMZ0）by reducing polarization and voltage attenuation.The capacity of Li(Ni_0.5Co_0.2Mn_0.3)_0.95Zn_0.05O₂（NCMZ0.5）at 5C（1C=160m Ah/g）can reach 125.9m Ah/g,much higher than that of NCM（98m Ah/g）.Under high-cutoff voltage（4.5V）,the capacity retention of NCMZ0.5 increased by 18.4%compared to NCM at 1C after 100 cycles.The electrochemical properties of NCM/graphite full battery have also been greatly improved by Zn doping.（3）The Li_1-x(Ni_0.9Co_0.05Mn_0.05)Mg_xO₂（MNCM）cathode materials are prepared by ball milling-drying spray method.XRD and XPS proved that Mg²⁺occupied the Li layer,reduced Li/Ni mixture and inhibited phase transition,which stabilized the structure of Li(Ni_0.9Co_0.05Mn_0.05)O₂（MNCM0）.Mg doping can improve capacity and cycling stability by reducing voltage attention at high rate.The Li_0.99(Ni_0.9Co_0.05Mn_0.05)Mg_0.01O₂（MNCM1）cathode shows an excellent discharge capacity of 164 m Ah/g,and the corresponding cycle retention is 89%at 5C（1C=200 m Ah/g）after 150 cycles,much higher than NCM90（144.5m Ah/g and 50.1%）.The results of EIS show that Mg doping can effectively improve the lithium ion diffusion coefficient and reduce the impedance generated during the cycles.In addition,the cycle performance of NCM/graphite full battery is also significantly improved with the help of Mg doping.After 150 cycles,SEM of electrode materials shows that MNCM1 retained more secondary spherical particles,which proved that Mg doping can improve the structural stability of materials during cycles.