Synthesis And Properties Of The Lithium Battery Cathode Material Sulfur Polymer

With the extensive use of portable devices, high energy and high performance cathode materials are commanded. Therefore, cathode material with high specific capacity is the key factor to develop high energy density lithium batteries. Organic disulfides afford energy storage by reversible two-electron redox reaction of the disulfide bond, namely, -S-S-+2e 2-SH. Among them, 2, 5-dimercapto-1, 3, 4-thiadiazole is regarded as one of the most well known organic disulfide due to its high theoretical charge density, high potential vs lithium metal, and high stability to cycling and temperature. However, there are still some weak points in the application for batteries, such as chemical reverse but kinetic slow and low current capability, etc. In this work, two organodisulfides 3-thienylmethyl disulfide and benzyl disulfide were successfully and easily synthesized by Hydrocarbylation Reaction of thiourea with high production, while their polymer/copolymers were successfully synthesized by electrochemical polymerization and chemical oxidation. Moreover, the electrochemical behavior and the CE reaction mechanisms of the organodisulfides were studied. It is to deduce their kinetic equations and analysis their kinetic parameters by using the classical electrochemical equation on condition that electrochemical reaction is the rate determining step. Therefore the corresponding electrochemical reaction mechanisms and electrode kinetic equations can be determined basis for the kinetic parameters which were measured by rotating disk electrode technique and static leaching test. The electrochemical properties of -S-S- bonds redox behavior in the organodisulfides were investigated in Acetonitrile (CH3CN)/ 0.1 mol/L Tetrabutylammonium Hexafluorophosphate ([Bu4N] [PF6]) solution. The separation of the anodic and the cathodic peak potentials for poly 3-thienylmethyl disulfide is 180 mV. The poly 3-thienylmethyl disulfide there is an excellent electrochemical reversibility. Moreover, it is found that the different state of micro structure (π-electron action) is the primary cause of the deactivation and reactivation of poly 3-thienylmethyl disulfide on glass carbon electrode.The copolymerization of 3-thienylmethyl disulfide and benzyl disulfide was investigated. Copolymer of them, especially TcB1:4, was easier electropolymerized to form a stable and higher conductive structure at a lower potential on Pt, Au or GC electrode. TcB1:4 and TcB4:1, especially the former, exhibited better conductivities than those of pure poly 3-thienylmethyl disulfide and poly benzyl disulfide. Moreover, TcB1:4 can reach a highest value, namely, 7.51×10-6 S/cm. The cyclic voltammogram of copolymer gave current-potential curve with larger areas than that of homopolymer and copolymers show better kinetic reversibility. The copolymer showed that it is capable of supplying more power, energy and better performances than homopolymer itself. Copolymer could be used as cathode material for lithium secondary battery because of their functional group could not be destroyed before 80 oC. In scanning electron micrography, the copolymers, except TcB4:1, showed larger compacter structure. The charge and discharge test shows TcB4:1 has the best performances. The results of the copolymer systems show that they have a high potential as cathode materials for lithium batteries.