Research On Synthesis And Mg/Ti Doping Modification Of Nickel-Rich Ternary LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Material

With the reduction of non-renewable resource reserves and the increasingly prominent environmental problems,lithium-ion batteries with significant advantages such as high operating voltage,high specific capacity,and environmental friendliness are widely used in the field of energy and transportation.The rapid development of electric vehicles has also put forward requirements for the energy density of batteries.The Nickel-rich ternary cathode material Lithium nickel cobalt manganate/aluminate oxide（NCM/NCA）for lithium ion has become research mainstream today.However,with the increase of nickel content,the synthesis difficulty of the material increases,and the structural stability also decreases significantly,which is an urgent problem to be solved at present.This work takes the high-nickel ternary cathode material LiNi_0.8Co_0.1Mn_0.1O₂（NCM811）as the research object,and explores the effect and law of the synthesis conditions on the properties of the material.The results show that the calcination temperature,calcination time and lithium content have obvious effects on the crystallinity and structural stability of the material.Under the synthesis conditions of calcination temperature of 845℃,calcination time of 20 h,and lithium content of 1:1.03,the first discharge specific capacity of the material was 186.3 m Ah g^-1at a current density of 0.1 C,and the Coulombic efficiency was 83.2%.The specific capacities before and after 100 discharges were 184.6 and 161.9 m Ah g^-1at a current density of 0.2 C,respectively,the cycle retention rate was 87.7%.After the current density of 5 C returned to 0.1 C,the capacity retention rate was 90.2%compared with the initial 0.1 C.The synthesized NCM811 material is doped with Mg²⁺.When Mg²⁺is incorporated into the bulk phase of the NCM material,the interlayer spacing of lithium will be expanded,the c-axis parameter and the unit cell volume V will increase,and the degree of Li⁺/Ni²⁺mixing will decrease,thereby stabilizing the material structure.The first discharge specific capacity of the modified material is 180.1 m Ah g^-1at 0.1 C rate,and the first discharge specific capacity of the material is177.4 m Ah g^-1at 0.2 C rate.After 100 cycles,the capacity retention rate is as high as 92.4%.The Ti⁴⁺doping of the synthesized NCM811 material can suppress the structural collapse of the material at a higher rate due to the strong Ti-O bond energy.The modified material has a first discharge specific capacity of 198.1 m Ah g^-1at 0.1 C rate.The first discharge specific capacity of the material at 1 C rate is 164.0 m Ah g^-1.After 100 cycles,the capacity retention rate is as high as92.9%.After returning to the initial 0.1 C rate after a large rate of 5 C,the recovery rate of the material is as high as 96.1%.In order to improve the long-term cycle stability and structural stability of NCM811,the materials were modified by Mg²⁺-Ti⁴⁺doping,in order to cooperate with the dual effect of Mg²⁺to reduce the mixture of Li⁺/Ni²⁺and Ti⁴⁺to enhance the bond strength between transition metals and oxygen（M-O）.The results showed that the modification significantly improved the electrochemical performance of the material:the first discharge specific capacity was 186.4 m Ah g^-1at 0.1 C current density,and the Coulombic efficiency was 89.5%.The discharge specific capacity before and after 100 cycles at 0.2 C current density were respectively are 182.5 and 164.3m Ah g^-1,and the retention rate is 90.0%.The lithium ion diffusion rate is significantly improved at1 C current density,from 1.84×10^-14cm~2s^-1to 4.62×10^-13cm~2s^-1,The discharge specific capacities before and after 100 cycles are 175.4 and 149.6 m Ah g^-1,respectively,and the retention rate is85.3%.There is still a discharge specific capacity of 117.5 m Ah g^-1at 5 C high current density.Compared with 0.1 C,the capacity retention rate is 94.8%.