Application Of Sb @ C Composite Material As Anode Material For Lithium Battery

With the development of science and technology,more and more electronic devices were used,and accordingly to match these devices high-performance powers are neededpeople use electronic devices,such as high capacity,high power,and foldable.Lithium ion batteris have been used in our life for many years.However,the graphite as an anode material cannot meet requirements for higher performance batteries due to its relatively low theoretical capacity(372m Ahg^-1).People have been working hard to explore new high-performance anode materials,such as other type carbon materials,alloys,metal oxides and so on.Among these new materials,antimony is one of the intensively researched anode materials for metal ion batteries because of its higher theoretical capacity and relatively low cost.However,during the charging and discharging process,the material undergoes a serious volume expansion/contraction with the insertion/extraction of lithium ions,which leads to serious capacity decay and poor cycle performance,and reduces the performances of the battery.In order to resolve the problem of poor cycle performance caused by the volume expansion/contraction,several kinds of materials have been developed,such as Sb₂S₃/graphene composite,rod-shaped Sb/C composite materials,Sb/C nano-composite fibers and so on.At present,a general method is to synthesize antimony-based carbon composite materials based on the advantages of graphite in lithium-ion batteries.In this paper,a simple method was used to prepare the precursor of Sb@C composite materials with structure of metal-organic frameworks(MOFs).On the basis of controlling the morphology of the Sb@C precursor,a carbon shell from resorcinol-formaldehyde(RF)by a soft templateand Sb@C composite materials sintered under different high temperature were investigated to improve the electrochemical performances of the anode materials.(1)First,the morphology of precursors for Sb@C composite was studied by a sedimentation method using dimethylimidazole and antimony trichloride as raw materials.And then the factors that affect the morphology of the precursor were explored by a series of orthogonal experiments.It was found that the molar ratio is the key to change morphology of precursors.When the molar ratio of dimethylimidazole and Sb Cl₃ was between 1-8.5,the nanoscale flake was formed and the strip was then formed with increasing the molar ratio of dimethylimidazole and Sb Cl₃to the range of25.8-8.6.Notely the grain size of stips varies differently.The cone shapes were formed while molar ratios reaches to the range of 34.5 and 13.Secondly,based on the results of the precursors'morphology,the parameters for synthesis of Sb@C composites were studied with a flake-like precursor.Sb@C composites can be obtained by heat treatment at 400,500,600,700?under Ar and H₂ mixed atmosphere.The experimental results show that the sample Sb@C composite obtained at 500?presents a well crystallinity and good electrochemical performances.At a current density of 0.1 C,the as-obtained product shows a specific discharge capacity of 1194.6 m Ah g^-1 for the first discharge.The specific discharge capacity after 100 charge/discharge cycles is 788.3 m Ah g^-1 higher than those of products obtained at 400,600 and 700?of 751.4,316.8,and 400.9 m Ah g^-1,respectively.(2)Based on the exploration of the precursor morphology in the previous chapter,the precursors of nanoparticle morphology were used as raw materials to explore the key factors of affecting the preparation and performance of Sb@C composite materials.The precursor with nanoparticle morphology was coated with carbon,and a series of Sb@C composite were prepared by changing the heat treatment temperature.It was found that Sb@C composite obtained at 400?shows a discharge specific capacity of 690.6m Ahg^-1 after 100 cycles at 0.1C.It also shows an excellent rate performances,higher than other composites obtained at 500,600,and 700?.(3)During the researches of above two chapters,it was found that the electrode preparation process has a greater impact on battery performances,so in this chapter we further explored the technical parameters to improve the electrochemical performances of Sb@C composite.Taking the composite material obtained from the flake precursor in Chapter 1 as the object,technical parameters of electrode preparation were optimized under different conditions through different active materials,conductive agents,molar ratios,and thicknesses of carbon.It found that the best cycling performance of the samples is the flake precursor after RF coating,with carbon nano-tubes(CNTs)of 3%and heat treatment at 400?.For the initial specific discharge capacity shows 1232.6m Ah g^-1.After 100 cycles,the specific discharge capacity is still 836.3m Ahg^-1.In this paper,the precursor preparation of the Sb@C composite was explored.Results show that the flake precursor had the best performance when the carbon coating amount was double,the addition of 3%CNTs and sintering temperature at400?.The first discharge capacity was 1232.6m Ah g^-1,and the specific discharge capacity after 83 cycles was 836.3m Ah g^-1,which was superior to those of the samples prepared by other morphological precursors.The results of exploration on electrode preparation show that the material has the best electrochemical performances with sintering temperature at 400?and 3%CNT as the conductive agent.The research results of this paper provide a reference to the preparation method and manufacturing process for the application of Sb@C composite materials in lithium ion batteries.However,there are still many problems to be resolved for the high-performance composite materials,which are needed future researches,such as the control of the thickness of the Sb@C coating layer,the ion implantation mechanism during charge and discharge.