Abstract
Herein, a series of novel disulfide polymers were synthesized by using the raw materials of diallyl-o-phthalate, tung oil, peanut oil, and styrene. Four kinds of products: Poly (sulfur-diallyl-o-phthalate) copolymer, poly (sulfur-tung oil) copolymer, poly (sulfur-peanut oil) copolymer, and poly (sulfur-styrene-peanut oil) terpolymer were characterized, and their solubility was studied and compared. Among the four kinds of disulfide polymers, poly (sulfur-styrene-peanut oil) terpolymer had the best solubility in an organic solvent, and it was chosen to be the active cathode material in Li-S battery. Subsequently, two different conductive additives—conductive carbon black and graphene were separately blended with this terpolymer to prepare two battery systems. The electrochemical performances of the two batteries were compared and analyzed. The result showed that the initial specific capacity of poly (sulfur-styrene-peanut oil) terpolymer (blended with conductive carbon black) battery was 935.88 mAh/g, with the capacity retention rate about 43.5%. Comparingly, the initial specific capacity of poly (sulfur-styrene-peanut oil) terpolymer (blended with graphene) battery was 1008.35 mAh/g, with the capacity retention rate around 60.59%. Therefore, the battery system of poly (sulfur-styrene-peanut oil) terpolymer with graphene showed a more stable cycle performance and better rate performance. This optimized system had a simple and environmental-friendly synthesis procedure, which showed a great application value in constructing cathode materials for the Li-S battery.
Highlights
Compared with the present cathode materials, sulfur has a higher specific capacity (1675 mAh/g), and the theoretical energy density of lithium-sulfur (Li-S) battery is as high as 2600 wh/kg, which is 3–5 times larger than other traditional lithium-ion batteries [1]
According to the dissolution test, poly(S-Sty-P) terpolymer had the best solubility among the disulfide polymers and it was completely soluble in the tetrahydrofuran solution
The electrochemical impedance spectroscopy (EIS) of the cathode materials was measured in the ARBIN electrochemical workstation at the frequency range from 105 to 102 Hz and all cells were charged to 3 V before the electrochemical spectroscopy (EIS) test
Summary
Compared with the present cathode materials, sulfur has a higher specific capacity (1675 mAh/g), and the theoretical energy density of lithium-sulfur (Li-S) battery is as high as 2600 wh/kg, which is 3–5 times larger than other traditional lithium-ion batteries [1]. The inverse vulcanization [7,8,9,10] method was invented to prepare polymers with high sulfur content In this process, molten sulfur was directly copolymerized with vinyl monomers, which increased the branching of sulfur chains, and produced polysulfide rings. Swapnil et al [16] prepared the phenol benzoxazine monomer-sulfur random copolymer at 185 ◦ C and found that the curing temperature decreased from 242 to 185 ◦ C When this copolymer was used as cathode material, the specific capacity of the battery kept at. The poly (sulfur-styrene-peanut oil) terpolymer showed the best solubility and electrode processability: It was viscous, and it can be completely soluble in the tetrahydrofuran solution at room temperature It was utilized both as an active substance of the cathode material and as a binder in Li-S batteries. The optimized battery system proved that the monomer without benzene ring can react with molten sulfur and can be successfully utilized as the cathode material in Li-S battery
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