Controllable Construction And Electrochemical Performance Of High-rate Lithium Nickel Manganate Cathode Materials

In recent years,due to its advantages such as high energy density,good circularity and environmental friendliness,lithium-ion battery(LIB)has developed rapidly around the world.Now,it has become the first choice of second batteries,widely applied in portable electronic products,electromobile,hybrid vehicle and large-scale energy storage facilities and other fields,and continues to drive trend of industrial revolution,greatly changing people's way of life.Spinel LiNi_0.5Mn_1.5O₄(LNMO)cathode materials have arisen a lot of attention because of its high discharge specific capacity,high working voltage and high energy density.In this paper,the electrochemical properties of LNMO cathode materials were improved comprehensively from the aspects of constructing the morphology and structure,cationic doping and surface coating.In the first part of this paper,the hollow microsphere with three-dimensional pore channels were synthesized by solvothermal method assisted with soft template(polyoxyethylene,PEO).In this process,PEO,as a soft template,can form a complex with the carbonate precursor,which synthesized during the solvothermal process.At the same time,PEO as a long chain polymer can form a stable dispersion system by using the spatial effects such as winding and bridging,and thus leaded to a homogeneous distribution of carbonate precursor microspheres.During the calcination at high temperature with lithium salt,PEO was decomposed at high temperature,and thus LNMO hollow microspheres with three-dimensional pore channels were obtained.The electrochemical tests results showed that the specific discharge capacity of LNMO-PEO-1g at0.1 C reached at 143.1 mAh�g^-1,and the capacity retention rate was 92.2%after 100 cycles at1C.This strategy can improve the electrochemical activity and electrochemical properties of the LNMO cathode materials.In the second part of the paper,vanadium doped LNMO cathode materials were obtained by adding vanadium salt in solvothermal process.The results of scanning electron microscopy(SEM)showed that the V doped LNMO exhibits a typical octahedral spinel morphology.X-ray powder diffraction(XRD)refinement analysis and X-ray photoelectron spectroscopy(XPS)analysis results showed that the doping of vanadium greatly increased the lattice parameters of LNMO and the content of Mn³⁺in the material.The specific discharge capacity of V-0.04LNMO at rate of 1 C could reach 128.36 mAh�g^-1,while after 100 cycles showed a capacity retention rate of 99.74%.The dope of vanadium significantly improved the rate performance and cycling performance of LNMO.Electrochemical AC impedance spectroscopy(EIS)confirmed that the charge transfer resistance decreased after doping.In the third part of this paper,LNMO microspheres were coated with LiNbO₃(LNO)by wet chemical method.XRD and XPS results revealed that the surface of LNMO is not only coated with a layer of LNO coating,but also formed a rich Mn³⁺region on the surface of LNMO.The rich Mn³⁺region increased the Li⁺ion transport channel and electron transition,which improved the electronic and ionic conductivity of LNMO,and effectively enhanced the multiplier performance of the material.LNO as a coated layer can inhibit the adverse reaction between the electrolyte and LNMO material,prevent the dissolution of Mn ion,and improve the cycling performance of the material.