The demand for energy storage with higher energy density is increasing day by day and intensive researches are being carried out. Many researches have been concentrated on the anode of lithium-ion battery with high energy density. However, the practically usable anode electrode material is very limited for a number of reasons. And commercial cathode still has low capacity, the effect of full-cell configuration using a high capacity anode is insignificant, which is an obstacle to the development of the entire energy storage device. The newly proposed conversion type cathode has a storage capacity of 10 times that of the existing intercalate cathode. Sulfur is an interesting cathode material due to its high theoretical capacity of 1,673 mAh / g, large quantities, very low cost and low toxicity. Theoretically, S-based cathodes are configured full cell battery with a Si or lithium metal anode can achieve four or five times the theoretical specific energy of a commercial C-LiCoO2 system. Despite the theoretical capacity of the sulfur, the practical steps mentioned above could not be reached because of insulating properties and large volume expansion of sulfur, and dissolution of the intermediate reaction product in the electrolyte results in the poor lifetime.
In this study, we use a polymer with a channel to enclose sulfur particles to prevent volume expansion and dissolution, and try to approach to impart mass transfer capability through hybridization with conductive graphene. The polymer with a channel is synthesized through a low-temperature heat treatment based on the difference of the vaporization temperature according to the degree of polymerization of the polymer. Through the channel, the lithium ion and the electron to be delivered to the sulfur contained in the polymer. All of the synthesis processes attempted in this study are scalable and very easy to mass-produce.
The polymer used in this study is an aliphatic rubbery synthetic polymer and has a vaporization temperature of 60 ° C or less when it is in a monomer state. However, the vaporization temperature rises sharply according to the degree of polymerization, and when it is completely cured, it has a vaporization and decomposition temperature of 300 degrees or more. But in this work, the polymer in the hybrids mostly had a very low degree of polymerization in the MALDI-TOF analysis of the synthesized whole hybrids. This is because of the polymerization reaction, which originated from sulfur, terminated very quickly and the reaction was complete when the polymer met the sulfur and graphene particles. Due to the very low degree of polymerization of the polymer, the polymer can be vaporized at temperatures below 90 degrees, which results in many pores and channels on the surface and inside of the polymer from low-temperature heat treatment. Such a pore-forming polymer has superior mass transfer characteristics and high lifetime performance while offsetting the disadvantages of sulfur.