The Preparation And Sodium Storage Performance Of Pitch-based Tin/Carbon Composites

Large-scale energy storage system is an effective method to solve the intermittent problem of clean energy such as solar and wind energy.Compared with lithium ion batteries,sodium ion batteries exhibit the advantage of price due to the abundance of sodium resource.With the research on cathode materials becoming mature,the development of anode materials matching the properties is the key to the commercial application of sodium ion batteries.The large diameter of sodium ion hinders the intercalation process of sodium storage in traditional carbon materials,while the large volume expansion greatly reduces the cycle life of metal materials.Among numerous anode materials,metal-carbon composites have the advantages of high capacity and high cycle stability,showing great potentiality.It is possible to achieve the even dispersion of metal by utilizing the carbonaceous matrix with carboxyl and hydroxyl groups on the surface.In this paper,Sn O₂ and SnS with high theoretical capacity were combined with a new type of asphalt-based carbon material in aqueous solution,respectively,and the electrochemical properties of the composites were studied.Amphiphilic carbonaceous material（ACM）with abundant oxygen-containing functional groups was prepared from medium-temperature coal tar pitch by mixed acid oxidation.The composition and structure of ACM were analyzed by means of elemental analysis,FTIR,XRD and SEM.Then,Sn O₂-ACM composites were prepared by hydrothermal method using ACM as carbon source and Sn Cl₄·5H₂O as tin source,and the influence of the raw material ratio and heat treatment temperature on the composition was explored.The existence of C-O-Sn chemical bond was confirmed by comparing the electron binding energies of Sn and O elements in the XPS spectra of Sn O₂ and Sn O₂-C-2.Based on the electrochemical test of the composites with different Sn O₂ contents,Sn O₂-C-2 exhibits the most outstanding performance that the first charge specific capacity is 311.8 m Ah·g^-1 at the current density of 0.1 A·g^-1 and the capacity retention rate is 66.7%at 0.5 A·g^-1 after 1000 cycles.When the Sn source is changed to Sn Cl₂·2H₂O,the content of C-O-Sn bond decreases and the electrochemical performance of the composite obviously becomes worse because of the partial reduction of nitro group in ACM.The electronic conductivity and cycling stability of Sn O₂-C-2 could be improved by the introduction of the right amount of GO as the coating layer.The capacity retention rate of GO-Sn O₂-C-2-5%reached 91.8%after 200 cycles.The introduction of ACM carbon layer has no significant effect on ion transport,but can effectively improve the cycle life and electron conductivity of Sn O₂-r GO material.The charge transfer resistance of Sn O₂-r GO material decreases from 387.9Ωto 217.2Ω.The sulfur source determines the structure of SnS-C-2composites that the unique flower-like carbon layer appears when the sulfur source is L-cysteine.Among the composites with different SnS contents,SnS-C-2 is the best in electrochemical performance.The heat treatment temperature has an important effect on the composition of composites,and the temperature above 700℃causes a large amount of SnS loss.