| As the progress of human civilization,people get more and more understanding the importance of living in harmony with nature and sustainable development.Because of environment-friendly,high energy density and long service life,The lithium-ion battery has meet the development of human civilization.A lot of national researcher give much more attention to it.Due to these advantages,The layered oxide cathode material has also been identified as one of the most valuable cathode material.First of all,this paper introduces the background,development history and research status of lithium ion batteries.In order to improve the electrochemical properties of the prepared cathode material LiNi0.3C0.2Mn0.5O2,hydrothermal treatment was used for structural modification and titanium dioxide was coated for surface modification.The structure,morphology and electrochemical properties of the materials were characterized by XRD,BET,SEM,TEM,EDS,charge and discharge tests.The hydrothermal method was used to treat the coprecipitated composite hydroxide precursor,And the effects of different hydrothermal temperature and hydrothermal time on the properties of the cathode materials were investigated.The experimental results show that the hydrothermal treatment can make the precursor have the advantage of growing on the(001)crystal face.And when the hydrothermal temperature is 150? and the hydrothermal time is 4 h the discharge capacity is the largest,but the cycling stability is poor.The metal organic frameworks materials(MOFs.MIL-125@Ti)were prepared by solvothermal method.And the effects of different sintering temperatures on the final titanium dioxide phase sintered by the synthesized MIL-125@Ti were studied.It was found that in the presence of butyl titanate as the metal salt,terephthalic acid as the ligand,methanol as the template,dimethyl formamide as the organic solvent,and the metal salt,ligand,solvent and template in the molar ratio of 5:3:90:10,the metal organic frameworks materials(MIL-125@Ti)can be successfully synthesized at a stirring rate of 400 r/min,a reaction holding time of 24 h and a reaction temperature of 150?.When calcining at 380 ?,480 ? and 580 ?,the titanium dioxide will have different phases by using metal organic frameworks material as raw material.The anatase phase will translate into a rutile phase slowly with the increase of temperature which is more pronounced after 500?.The optimum method of coating the cathode material was determined by orthogonal experiment.And the high temperature electrochemical properties of the coated cathode material was tested thought cycle charge and discharge.The results of orthogonal experiments show that the optimum coating process is 150 ? solvent temperature?solvent heat preservation time of 8h?sintering temperature of 380??titanium content of 0.5%.The maximum process factor that affects the capacity retention of the cathode material which has been coated titanium dioxide is the temperature of hydrothermal,followed by the holding time of the hydrothermal and the temperature of the sintered coating,the weakest is the amount of titanium.The advantages of growth in the(110)crystal surface of The coated cathode material disappeared due to hydrothermal treatment.The cyclic stability of the coated cathode material is obviously improved at high temperature,and the cathode material which was treated by hydrothermal is relatively good under 60?. |
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