First-principles Study Of Doping Modification Of Nickel-rich Cathode Materials For Lithium-ion Batteries

The nickel-rich ternary cathode material has the advantages of high energy density and low cost,but it has some problems such as poor thermal stability and cycle stability In view of the unknown microcosmic mechanism of elements in the doping modification process of nickel-rich ternary cathode materials,Li Ni_0.6Co_0.2Mn_0.2O₂（NCM622）and Li Ni_0.8Co_0.1Mn_0.1O₂（NCM811）are taken as the research objects,and the first-principles calculation method is adopted to study the effect of high nickel ternary cathode materials The influence of co-ion doping on its thermal stability and cyclic stability,and from the cell volume change ion bond length electronic structure Li/Ni interposition defects and Bader charge and other properties to explain the micro mechanism of doping modification,providing theoretical support for the doping modification of high nickel terpolymer cathode materials main work.The main work and conclusions of this paper are as follows:（1）Two theoretical calculation models of metal cation(Mg²⁺,Zr⁴⁺,W⁶⁺)doping at NCM622 transition metal site and alkali metal Na⁺doping at Li site were established.The doping occupying situation of metal cation at NCM622 transition metal site was determined by DFT+U calculation.The results show that W⁶⁺doping can form stronger W-O covalent bonds in and around the lattice to inhibit the volume change,and Na⁺、Mg²⁺can promote the Li⁺diffusion by broadening the Li+diffusion channel.Bader charge calculation results show that ion doping can reduce the charge of O lattice of delithium/li-embedded phase,thus improving its thermal stability,and the mechanism of action is analyzed from the perspective of electronic structure.（2）To solve the problem of stability deterioration caused by increasing Ni content in ternary cathode materials（NCM811）,a calculation model of Al³⁺,V³⁺and Ti⁴⁺doped NCM811 was constructed.The results show that the thermal stability of NCM811 anode material during the process of lithium insertion is an important reason for the deterioration of its cyclic stability.Ion doping can reduce the possibility of Li⁺/Ni²⁺mixing by reducing the ratio of Ni²⁺/Ni³⁺content.A^l3+and Ti⁴⁺doping can inhibit the escape of O₂by reducing the Bader charge of lattice O,thus improving the thermal stability of the materials.（3）The theoretical calculation model of W,F and W@F co-doped NCM811 was established,and the effects of W,F and W@F co-doped NCM811 materials on their thermal stability and cyclic stability were studied.The mechanism of synergistic cation and anion co-doping on NCM811 materials was studied by comparison.W@F co-doping can use the advantages of W doping to reduce volume change and F doping to inhibit Li/Ni interposition,so that the doped materials can obtain good cyclic stability and thermal stability.