Study On Performance Improvement Of Carbon Material For Lithium-ion Battery

Since the commercialization of lithium-ion batteries（LIBs）,which was proposed by SONY in the 1990s.LIBs have become the best choice for consumer electronics,grid energy storage and electric vehicles(including hybrid electric vehicles（HEV）,plug-in hybrid electric vehicles（PHEV）and pure bis widely used in because of low price,low working voltage platform and excellent cycle performance.However,the lithium storage mechanism of graphite leads to low specific capacity（only 372m Ahg-¹）,which severely limits the practical application of LIBs.Therefore,,it is urgent to find the appropriate anode alternative materials to meet the increasing capacity demand and improve the electrochemical properties of lithium.Although the energy and storage sectors have made significant advances,challenges still exist in the performance,function and durability.Researchers are working tirelessly to find possible solutions to deal with it.The cathode materials of silicon-based,tin-based and titanium-based lithium-ion batteries have become hot research areas.Among them,tin and its oxides are promising anode materials because the high theoretical capabilities,rich resources and environmental friendly.Meawhile,tin oxide anode still has some challenging problems,such as low initial Coulomb efficiency（CE）,volume expansion,and agglomeration of tin particles during the discharge/charge cycles.And silicon（Si）is also considered to be the most ideal new-generation cathode material due to the rich content in the crust,low stripping potential（0.5V）and high theoretical specific capacity（4200m Ahg-1）.And the problem which was faced by silicon negative electrode are low conductivity,large volume change（about 300%）and the formation of unstable solid electrolyte interface（SEI）film.These lead to poor rate performance,fast capacity decay and low CE.Therefore,it is crucial to improve the electrochemical properties of the anode materials through rational design.The emergence of carbon-based nanofibers,carbon nanotubes（CNT）,carbon nanoribbons,graphene and other carbon-based nanomaterials has brought the research field into a new stage.Among them,graphene and carbon nanotubes are the most ideal material to solve the problems in energy and storage sectors.Graphene and CNT have been widely studied as negative electrode materials（SIBS）for LIBs.With the evolution of graphene and carbon nanostructures,electrochemical properties and other properties improved as well.As a kind of sp2 hybrid carbon,Graphene can be the excellent buffer material to relieve tin oxide volume expansion because the excellent electrical conductivity,large specific surface area and excellent chemical stability.The synergistic effect of graphene and tin oxide can greatly improve the electrochemical properties.Moreover,lots of studies shown that encapsulating Si in a carbon matrix such as graphene and porous carbon can effectively alleviate the volume expansion of Si and improve the electrical conductivity.CNTs is a new member of the carbon-based material.Researchersfind that one-dimensional CNT have unique hollow nanostructure,which can be perfect materials for the embedding of lithium ions..There for,CNTs have unique application advantages in lithium-ion batteries:First of all,the size of CNTs is in the nanoscale,and the space inside the tube and the interstitial space is also in the nanoscale,so the small size effect of nanomaterials can effectively increase the reactive space of LIBs in chemical power sources;secondly,The specific surface area of CNTs is large,which can increase the reactive sites of LIBs,and as the diameter of the carbon nanotube decreases,it exhibits a valence of non-chemical equilibrium or integer coordination number,and the capacity of lithium storage increases.Finally,CNTs have good electrical conductivity,which increases the free transfer speed of rapid intercalation and deintercalation of lithium ions,leads to the high-power charge and discharge.In this paper,to make full use of the disadvantages of tin oxide anode and silicon anode.we use graphene and carbon nanotubes to form nanocomposite and nanohybrid structure,improve the interaction between materials.wtih the advantages of each material,improve electrochemical performance of tin oxide and silicon composite material.During the process of preparing and studying the composite materials,we came to the following conclusions:With the carbon source of graphene and citric acid,Si@amorphous carbon/graphene（Si@C/G）composites were obtained by high-temperature calcination and self-assembly of electrostatic attraction.The electrostatic attraction of amino and carboxyl groups not only inhibited the agglomeration of Si particles and the accumulation of graphene sheets,but also helped encapsulate the carbon-coated nano Si（Si@C）into graphene.Therefore,the volume expansion and collapse of Si was suppressed during charge and discharge.Meanwhile,Graphene and amorphous carbon prevented Si from being directly exposed to the electrolyte.Furthermore,the three-dimensional（3D）conductive network composed of amorphous carbon and graphene improved the conductivity of Si-based electrodes.Compared with Si electrode,Si@C/G electrode showed good electrochemical performance.The prepared the SnO₂-Mn composite material by mechanical ball milling.The addition of Mn can effectively inhibit the agglomeration of active substances,stabilize its structure,and improve its cycle performance.MWCNT was prepared by CVD method,GO was prepared by improved hummers method.By compounding the two carbon materials with the composite material,the stress caused by the volume change is reduced and the electrical conductivity is improved.The results show that the adjustment performance of one-dimensional MWCNTs for anode materials is better than that of GO encapsulation.Whats more important is that the combination of the two can significantly improve the cycle performance and rate performance of SnO₂-Mn.At a current density of 100 m A/g,SnO₂-Mn/MWCNTs/GO maintained a specific capacity of 683 m Ah/g after 200 cycles,higher than that of SnO₂-Mn/MWCNTs（457 m Ah/g）and SnO₂-Mn/GO（336 m Ah/g）.