Preparation And Modification Of Ni-Mn-Al Cathode Materials

In recent years,lithium-ion batteries have been widely used in smart portable electronic products and electric vehicles.The cathode material determines its operating voltage and energy density,and is a hotspot in battery research and development.The high-nickel and cobalt-free cathode materials have attracted widespread attention due to their high energy density and low cost.There are shortcomings such as serious cation mixing,poor high-voltage cycle stability and poor rate performance,so it is necessary to further improve the electrochemical performance of high-nickel and cobalt-free cathode materials.In this paper,high-nickel and cobalt-free material precursors with different morphologies were synthesized by hydrothermal method and solvothermal method,combined with high temperature sintering process to synthesis Li Ni_0.85Mn_0.10Al_0.05O₂ cathode material.The as-synthesized materials were doped by niobium and zirconium to improve their electrochemical properties.（1）The pine cone-like Li Ni_0.85Mn_0.10Al_0.05O₂ cathode material was synthesized by a simple hydrothermal method,and its structure characterization and constant current charge-discharge tests were carried out.The optimum process conditions for synthesizing Li Ni_0.85Mn_0.10Al_0.05O₂were obtained,and the effects of hydrothermal temperature and hydrothermal time on the surface morphology and properties of the material were studied.The cathode material prepared at hydrothermal temperature of 180°C and time of 12 h has the lowest cation mixing degree,the lowest charge transfer impedance,and the best cycle stability.（2）Niobium-doped and zirconium-doped Li Ni_0.85Mn_0.10Al_0.05O₂ cathode materials were synthesized by hydrothermal method,the effects of different doping amounts on the morphology,structure and properties of the materials were studied.The cation mixing degree of the material is further reduced by ion doping,and the ions enter the crystal lattice to support the crystal structure,which significantly improves the cycling stability of the material.The cathode material with Nb doping content of 2%has a capacity of 130.2 m Ah g^-1 after 100cycles at 0.1 C,with a capacity retention rate of 70.9%.The cathode material with Zr doping content of 2%has a capacity retention rate of 68.7%after 100 charge-discharge cycles at 0.1C,which was improved compared with the undoped samples.Therefore,it is indicated that appropriate amount of niobium and zirconium doping are beneficial to improve the electrochemical performance of Li Ni_0.85Mn_0.10Al_0.05O₂ cathode materials.（3）The Ni（HCO₃）₂ precursors with different morphologies were synthesized by solvothermal method,and used as template to synthesis Li Ni_0.85Mn_0.10Al_0.05O₂ cathode material.The cathode material with a larger specific surface area is more easily oxidized during high temperature sintering,so the degree of cation mixing is lower.In addition,the effect of the calcination temperature on the surface morphology and electrochemical performance of the Li Ni_0.85Mn_0.10Al_0.05O₂ cathode material was studied.The cathode material synthesized at 750°C exhibits the best crystallinity,with a first discharge specific capacity as high as 201.5 m Ah g^-1 at 0.1 C rate.And the capacity retention rate after 100 cycles is75.7%.