| With the popularity of electric vehicles,the energy density of lithium-ion batteries(LIBs)has become an important constraint to develop electric vehicles.In order to meet the increasing demand for range,the research work in the last few years has focused on further increasing the energy density of LIBs.As the main component of lithium-ion battery,the cathode materials have play a significant role on the energy density and cost of the battery.The Ni-rich material Li Ni0.83Co0.11Mn0.06O2(Ni83)is an important member of the ternary cathode system that is moving towards industrialization with high specific capacity and energy density,and has certain cost advantages.However,the problems such as interfacial instability and structural degradation during long cycle times limit its mass production applications.Based on the above problems,this work takes Ni83 as the object of study and uses structural simulations and experimental verification to optimize the design of Ni83 materials to improve the overall performance of Ni-rich materials.The main tasks include:(1)The Ni83 cathode material was prepared by the high temperature solid phase method under different heating rates,Li/TM ratios and sintering temperatures,and the differences in material structure and electrical properties were analysed and optimum process parameters were derived.The crystallinity of the synthesised material and the degree of Li/Ni mixing were analysed by X-ray diffraction and the particle morphology of the material was observed by scanning electron microscopy.Using the optimum process parameters,the Ni83 cathode material discharged 195 m Ah·g-1 at a multiplicity of 0.1 C.The capacity retention after 60 cycles was up to 97.3%,and the corresponding differential capacity curve indicated good phase change reversibility.(2)The crystal models of Ce4+,Zr4+ and Ti4+ ion-doped Ni83 were constructed by Materials Studio(MS)software,respectively.Based on Density Functional Theory(DFT)calculations to investigate the effects of different elemental doping on the electronic structure and electrical properties of Ni83 materials.It’s found that the Zr4+ doped Ni83(NCM-Zr)material has a small band gap width(0.40 e V),indicating that the material conductivity can be significantly improved.Guided by the results of simulation calculations,different ion-doped Ni83 materials were synthesized by solid-phase reactions.The results show that the Zr4+ doped Ni83 material has a high lithium-ion conductivity and stable capacity play.The amount of doping was further optimised to obtain an optimum Zr4+ doping of 1 wt%.An appropriate amount of Zr4+ introduction can inhibit Li/Ni mixing and promote Li+ transport.The modified Ni83 material provides a capacity of 121.9m Ah·g-1 after 200 cycles at 1 C and still has a reversible capacity of 128.9 m Ah·g-1 at 10 C.(3)On the basis of the Zr doping model,the crystal models of Ni83 adsorbed on the surfaces of Zr O2,Mg O and Ce O2 were established by MS,respectively.Comparative analysis of the differences in energy bands and density of states through simulations leads to the conclusion that the Ce O2 adsorption NCM-Zr model can effectively reduce the electron migration energy barrier and increase the surface conductivity.The calculation results were used as a guide to cover the surface of NCM-Zr material with different oxides by wet chemical method.It is shown that Ce O2 coating can indeed increase the diffusion rate of lithium ions on the surface of the material,which is consistent with the results of the simulations.It’s further found that Ce O2 induces spinel phase production in the sub-surface layer of NCM-Zr@Ce materials,providing more channels for lithium-ion migration.Under the synergistic modification mechanism of internal Zr doping and surface Ce O2 coating of the NCM material,the prepared NCM-Zr@Ce material can still exert a capacity of 138.5m Ah·g-1 and a retention rate of 78.5% after 200 cycles at 1 C,with a reversible capacity of up to 144.5 m Ah·g-1 at 10 C. |
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