O-benzyl Disulfide Polymer Synthesis And Electrochemical Performance Studies

Polyorganodisulfides are a new stored energy materials, having high energy density, low toxin, environmental protection et al. Its theoretical specific energy can reach 1500~3000 Wh/kg, matching with the lithium metal's(3861 Wh/kg). So poly organodisulfides are taken for an ideal cathode material of lithium batteries. But the redox of poly organodisulfides are too slow and the reversibility aren't ideal, which prevent it to using as the positive material for lithium battery most seriously. In this article, two polyorganodisulfides were synthesized successfully, the S-S bonds of which were linked with the polymers directly, in order to improve the electrochemical properties of poly organodisulfides.Two organodisulfides(Dithieno[3,2-d:2',3'-f][1,2]dithiocin and 1, 4-dihydro- 2,3-benzodithiin ) were synthesized via nucleophilic substitution reaction of halide and thiourea. Its composition and structure were characterized via EA, HNMR, MS, IR and Rama, which indicated that the molecular structure were consistent with the predesign's. Poly(1, 4-dihydro-2,3-benzodithiin)(PDBD) was synthesized by FeCl3 as oxidant. With the same synthetic method, the copolymer CO-PDBDT) of 1, 4-dihydro -2,3-benzodithiin and thiophene(2:1 in mole) was synthesized successfully.The electrochemical properties of DBD, PDBD and CO-PDBDT were invest- -tigated by cyclic voltammetry. 0.1 mol·L-1 DBD of NMP solution, containing electrolyte LiClO4 (0.1 mol·L-1), showed a reductive peak(recombined S-S bonds) at -2.6 V and a oxidative peak(combined S-S bonds) at 0.58 V on the GC working electrode, the separate peak was 3.2 V. But the same DBD solution showed the redox and separate peaks at -1.9 V, -0.65 V and 1.3 V respectively on the Pt working electrode, which manifested that the DBD can show very good reversibility. In the 0.02 g PDBD of NMP(5mL) solution, containing 0.1 mol·L-1 LiClO4, the S-S bonds were reduced(recombined S-S bonds, diselectropolymerization) at -0.14 V and were oxidized(combined S-S bonds, electropolymerization) at 0.24 V on the Pt working electrode, the separate peak was 0.38 V. Moreover, in the same concentration of CO-PDBDT and LiClO4 solution of NMP, the CV showed redox peaks and separate peak at -0.088 V, 0.25 V and 0.34 V respectively on the same working electrode. According to these experimental results, the order of the three organosulfide reversibility can be showed as follows: DBD﹤PDBD﹤CO-PDBDT. This order indicated that the main chain of conducting polymer can electrocatalyze the redox reaction of S-S bonds. In other words, the conductive polymer can act as electrocatalyst to improve the process of released and stored energy of S-S bonds.The thermal analysis results showed the decomposition temperature of S-S bonds of DBD, PDBD and CO-PDBDT at 166℃, 143℃and 144℃respectively. These results manifested that the conductive polymers affected the thermostability of S-S bonds faintly and the three organosulfides can be used as the positive material of lithium batteries at moom temperature. According to cyclic voltammetry and thermostability of three organosulfides, its have using value in the cathode materials of lithium batteries.