Preparation And Modification Of Single Crystal High Nickel Ternary Cathode Materials LiNi_0.8Co_0.1Mn_0.1O₂

Ni-rich layered oxide cathodes with Ni content above 80%have great potential in lithium-ion batteries due to their high capacity and low cost.However,stability issues,poor cycling performance,and severe structural defects limit their development.In order to solve these problems,this paper adopts a synergistic modification strategy of Mg²⁺doping and V₂O₅ coating to synthesize single-crystal Li_0.98Ni_0.83Co_0.11Mn_0.06Mg_0.02O₂@V₂O₅ composite material.The structure,morphology and valence states of surface constituent elements were characterized by XRD,SEM,TEM,XPS and the electrochemical test system and electrochemical workstation were used to test the materials such as cyclic voltammetry and impedance.1.Single-crystal NCM811 cathode materials was successfully synthesized by flux assist and high-temperature calcination.By continuously adjusting the calcination temperature,lithium salt ratio and calcination atmosphere,the synthesized single-crystal NCM811 material have uniform particle size,smooth surface and a stable layered structure.The first cycle discharge specific capacity is 181.7 mAh g^-1at the current density of 1 C(1 C=200 mA g^-1),and the capacity retention rate is 76.9%after 100 cycles.At the current density of 5 C,the discharge specific capacity is 106.9m Ah g^-1.2.Based on the synthesized single-crystal NCM811 material,Mg²⁺doping method was used to study the modification of the material.The Rietveld refinement results confirmed that with increasing Mg doping amount,the lattice parameters of a and c increased.The material with doping content of 2wt%Mg²⁺have the best electrochemical performance.The first-cycle discharge specific capacity of Li_0.98Ni_0.83Co_0.11Mn_0.06Mg_0.02O₂material at 1 C is 173.7 mAh g^-1,and the capacity retention rate is 86.5%after 100 cycles.At 5 C,the discharge specific capacity is 136.2 mAh g^-1.The cycling and rate performance of the NCM811 material improved after Mg doping modification.The voltage difference between the oxidation and reduction peaks of the material in the CV curve is 0.13 V,and the sample modified by Mg²⁺doping shows good reaction reversibility.3.Finally,the V₂O₅coating modification is used to modify the surface of Li_0.98Ni_0.83Co_0.11Mn_0.06Mg_0.02O₂ material by solvent-thermal method.It is found that when the V₂O₅ coating content is 2wt%,the crystal surface of the material is evenly coated with a layer of about 9 nm.At 1 C,the first discharge specific capacity of Li_0.98Ni_0.83Co_0.11Mn_0.06Mg_0.02O₂@V₂O₅ composite material is 177.3 mAh g^-1,the discharge specific capacity is 158.0 mAh g^-1after 100 cycles,and the capacity retention rate is 89.1%.The discharge specific capacity is 143.8 mAhg^-1at 5 C.The Li⁺diffusion coefficient of Li_0.98Ni_0.83Co_0.11Mn_0.06Mg_0.02O₂@V₂O₅material is calculated to be 9.62×10^-15cm²s^-1,higher than that of NCM811 and Li_0.98Ni_0.83Co_0.11Mn_0.06Mg_0.02O₂materials.The synergistic effect of single crystal structure,Mg²⁺doping and V₂O₅coating makes the composite material have a stable structure,fast lithium ion diffusion,and surface/interface electrochemical reaction kinetics,as well as excellent pseudocapacitive charge storage capacity,significantly improving the cycling performance and rate performance of NCM811 material.