Preparation And Electrochemical Properties Of Cobaltfree Lithium-rich Manganese Cathode Materials

With the fast development of chinese social economy,the modern energy storage system and the field of new energy electric vehicles have put forward higher requirements on energy density and manufacturing cost of energy storage batteries.Therefore,the research and development of energy storage batteries and their key materials with high energy density,high safety and low price have significance and development prospects.Among them,the cobalt-free lithium-rich manganese-based basic-level oxide cathode materials(x Li₂Mn O₃·（1-x）Li Ni_0.5Mn_0.5O₂)have attracted attention due to their relatively high discharge capacity(>250 m Ah·g^-1),lower cost and better safety.However,it has some problems in the charging-discharging cycle process,such as poor cycle stability,fast voltage attenuation,poor multiplier performance and low first coulombic efficiency,which limit the application of commerce.In thesis,the optimized sol-gel preparation and spinel Li₄Mn₅O₁₂ surface modification were used to improve the layered structure stability and cation order of Li_1.2Ni_0.2Mn_0.6O₂,so as to improve the stability of the material charging-discharging cycle.In thesis,the layered structure stability of Li_1.2Ni_0.2Mn_0.6O₂ can be improved by trying the optimized sol-gel method.And it is able to explore the influence of three technological conditions on the preparation of active electrode materials by X-ray Diffraction（XRD）,Scanning Electron Microscope（SEM）,electrochemical performance test and other characterization methods,such as the amount of precursor nitric acid solution,heating rate and calcination temperature.The results showed that under the conditions of 1.5 m L nitric acid solution dosage of precursor,3℃·min^-1 heating rate and900℃calcination temperature,the layered structure of the sample was relatively stable.Thus,the sample had a first coulombic efficiency of 77.10%and a capacity retention rate of 70.51%after 50 cycles,showing good electrochemical performance.At the same time,different contents of spinel Li₄Mn₅O₁₂ and layered heterostructure layer were constructed on the surface of Li_1.2Ni_0.2Mn_0.6O₂ by trying to improve the cation order of the material and optimizing the electrochemical performance of the material:firstly,the moderate modification layer（about 3%）has no obvious influence on the morphology and crystal structure of the sample particles,but increases the relative content of Mn⁴⁺in the crystal structure,which reduces the oxygen loss,thus improving the first coulombic efficiency of the samples to 80.46%.Secondly,the I_（003）/I_（104）value of the samples accumulated with the advance of the modification layer content,indicating that the spinel Li₄Mn₅O₁₂ and layered heterostructure modification layer is helpful to improve the cation order of material.The capacity retention rate of LNMO-3%samples increased to 91.74%after 50 cycles of charging-discharging process.Thirdly,the surface modification layer with spinel Li₄Mn₅O₁₂ as the main component significantly improved the lithium-ion diffusion rate of sample particles and the magnification performance of LNMO-3%samples under high current density.