Study On Carbon/Tin Anode Materials For Sodium Ion Batteries

With the development of society,energy storage is attracting highly increasing attention.Among the energy storage modes,electrochemical energy storage has become the first choice in some fields due to its fast reaction rate and high efficiency.The sodium ion battery possesses more prospects because of its abundant resources and low price of Na element.The history of sodium ion batteries can be traced back to the 1980s,which was invented in the same period with lithium ion batteries.However,due to lack of suitable anode material,sodium ion batteries have never been used on a large scale.In order to settle this issue,this thesis combines the characteristics of high capacity of alloy materials and high stability of carbon materials to prepare tin/carbon composites,and systematically studied the related properties of the materials.Firstly,the structure and morphological characteristics of graphite,soft carbon and hard carbon materials were systematically investigated,and these characteristics were correlated with their electrochemical properties for analysis.By comparing the electrochemical properties of various carbon materials,the advantages and disadvantages of various carbon materials as anode materials for sodium ion batteries are obtained.It is found that the hard carbon materials showed the best sodium-storage performance among the carbon materials studied in this paper.At the current density of 0.04 A g^-1,their specific capacity remained 215 m Ah g^-1 after 100 cycles.Secondly,a"core-shell structure"composite electrode was designed based on electrostatic spinning technique.In the electrode,nano-sized metallic tin particles are obtained by means of carbon thermal reduction heat treatment.After heat treatment,the organic matter transfer carbon,which tightly covers the metallic tin nanoparticles.On the one hand,this structure can avoid the direct contact between the metallic active material and the electrolyte;on the other hand,it can limit the volume change of the active material in the subsequent reaction.The fibers obtained by electrospinning are interlaced to form a good conductive network.Based on the above designs,the"core-shell structure"electrode designed and prepared in this paper effectively improves the electrochemical properties of the electrode.SnCl₂ with PAN,mass ratio of 1:2,carbon thermal reduction temperature 700℃specimen showed the best electrochemical performance in the research and the specific capacity still remained 226 m Ah g^-1 after 100 cycles under the current density of 0.1 A g^-1.Finally,inspired by the building materials,this paper designed and prepared an integrated electrode of"reinforced concrete"structure.The overall structure is constructed by reduced graphene oxide due to its excellent mechanical properties,and the protective layer is constructed by organic matter with high carbon yield which formed the matrix the electrode,that the ion transport channel is constructed by thermal decomposition of organic matter with low carbon yield.The structure was applied to the sodium ion battery and highly improved the comprehensive performance of the electrode.The electrode with starch,heated treatment 2 hours at 320℃,showed the best electrochemical performance,that under the current density of 0.1 A g^-1 loop 100 times still has nearly 200 m Ah g^-1 overall specific capacity.