The Research Methods Of The TiO₂-SiO₂ Nanocomposites As Anode Materials For Li-ion Batteries

From the micro batteries for the small electronic device to the power source of the huge electro-car,lithium ion battery is getting wider application.By analyzing the current situation of the development of lithium ion batteries we get the information,lithium ion batteries is still the main growth point of the secondary battery market in the next few years.The improvement of the performance of lithium ion battery mainly depends on the embedded energy density of lithium electrode materials and the improvement of cycle life.In the aspect of the Anode materials in lithium ion batteries,graphite carbon material,due to its good cycle stability,ideal platform of current charge and discharge and the highest cost performance,is still the future of best choice for a period of lithium ion battery cathode materials.But the carbon material's charge and discharge specific capacity is low?the theorical data of the lithium storage capacity is 372 mAh/g?,specific storage volume also has no advantage,it's difficult to meet the requirement of battery with high capacity to the electric and hybrid electric vehicles.Thus developing the new type lithium ion battery cathode material which has high capacity,high charge-discharge efficiency,long cycle life is extremely urgency.In the study of new type of,carbon anode materials,The metal such as Si,Al,Sn,Ag,etc which can alloy with Li and their alloys materials,use it to get the negative pole,the reversible intercalated-li is much greater than the amount of graphite,and their charge and discharge potential is usually a little higher than carbon material,thus it can reduce or avoid the lithium metal electrode surface precipitation when large current charging,and has better security and reliability.In these systems,the Si-base material,with the highest theoretical intercalated-li capacity?4200 mAh/g,which is far higher than other all of the anode materials?is getting more and more notable.If Si-base electrode can reach practical degree,it will greatly broaden the application scope of lithium-ion batteries.However,Si-base material,under the condition of high level to take off the intercalated-li,exist heavily volume effect,here are serious cause in the cycle stability of the electrode.In view of the silicon volumetric efficiency,making the recombination between silicon and the carrier which is flexible and has stable performance,buffer the volume change of silicon,it will be effective ways to improve the stability of the silicon materials.It has been successfully applied in lithium ion battery materials of titanium dioxide which get relatively flexible structure.It is a good conductor of lithium ions and electrons,having a certain capacity of lithium and its chemical properties of stability,high working voltage,good security itself.if the titanium and silicon can realize effective compound,can effectively buffer the silicon embedded lithium off volume change,make volume change of whole electrode under control in a reasonable scope,improve the cycle stability while maintaining the high capacity,Based on the analysis above,this paper determine the silicon/titanium composite material as the main research object.Optimizing the structure of material design and preparation method s,inspect some preparation methods of silica/titanium composites and modification methods,a nd use various means to study the preparation of the structure and electrochemical performance of silicon/titanium composites,in order to promote further research and practical application o f this materials and provide some beneficial exploration to the lithium off mechanism of this m aterials.This paper using the method of hydrolysis and diol preparation of adding different proportions of TiO₂-SiO₂ nanocomposites,and the metal doping modification of composite materials,is a highly efficient method of preparation of nanocomposites.By X-ray diffraction?XRD?,scanning electron microscope?SEM?,specific surface area?BET?,and pore size distribution analysis of nanometer TiO₂-SiO₂ had been used to characterize the microstructure of the composite material.Results show that the degree of crystallization is not perfect,but the preparation of the composite material for structure of anatase titanium dioxide,and may generate silica is embedded in the lattice of TiO₂.The composite materials prepared by each two methods can both be formed cladding,the composite state can be divided into two kinds,one is Mosaic structure which SiO₂ particles show block or flake dispersed in Ti O₂,the other is a single grain structure of cladding which SiO₂ form for Ti O₂ particles.Alcoholysis method,the composites than the hydrolysis method,composite material is greater than surface area,up to 387.9634 m²/g.And the pore of the sample get by alcoholysis method is smaller than the sample get by hydrolysis method,pore diameter distribution set in 4.5 to 5.5 nm,it can deduce that the crystal configuration of the sample get by alcoholysis methods more dense,and its nano series is smaller.At the same time,the product pore diameter of the hydrolysis often set in10-20 nm in diameter,specific surface area is smaller than the samples of alcoholysis,but it still reached 240.9349 m²/g.By electrochemical performance tests showed that the nanometer TiO₂-SiO₂ composite material has good specific capacity.The materials prepared by Alcohol solution preparation,its first time discharge specific capacity reach 558.2 mAh/g,after a 100-cycle its capacity maintain in 49.6 mAh/g,and the sample,prepared by alcohol hydrolysis and mingle with Ni,which its ratio of titanium and silica is 1:1,its initial discharge specific capacity reach 808.7mAh/g,after a 100-cycle its capacity maintain in 68.6 mAh/g,proving that with metal Ni modified effectively the materials'electrical conductive ability has been improved greatly.And hydrolysis method showed better in charge-discharge performance,the sample prepared under the hydrolysis conditions which titanium silicon material is of 1:1 ratio,its first time discharge specific capacity reach 987.4 mAh/g,it is equivalent to the intercalated-li coefficient of 2.95,and after a 100-cycle,its capacity maintain in 76.1 mAh/g.