Lithium-ion batteries (LIBs) as highly efficient energy storage devices have been utilized as large capacity power sources in various devices. The conventional LIBs rely on intercalation compounds as cathode materials, which have limited specific energy density of 150-200 Wh kg^-1. However, the advent of electric vehicles and other high energy density applications require vast improvement in the energy density of current LIBs, which led to the search for cathode materials based on non-intercalation chemistries. Sulfur cathode is quite attractive for high energy density applications due to its advantages such as high specific theoretical capacity of 1675 mAh g^-1, low cost, natural abundance, and environmental friendliness. Therefore, sulfur is considered as a promising high energy density cathode material for the next generation lithium-ion batteries. However, the poor cycle life of lithium-sulfur (Li-S) batteries due to the critical problems such as large volumetric expansion of sulfur upon lithiation, low ionic and electronic (5×10^-30 S cm^-1) conductivities and dissolution of lithium polysulfide into the electrolyte has been a significant hindrance for their commercialization. Recently, significant efforts have been paid to improve the cycling performance of Li-S batteries by suppressing the dissolution of polysulfide from sulfur active material and preventing the shuttling of lithium polysulfides to the anode side. Moreover, lithium polysulfide leads to serious lithium anode corrosion resulting in low coulombic efficiency. To solve these problems, extensive studies have been carried out by surface coating of cathode active materials with conductive polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPY), and polyaniline (PANI). Surface modification of cathode active materials with conductive polymers is easy and effective way to enhance their electronic conductivity, thermal stability and electrochemical properties. Recently, we demonstrated that the cathode material coated with dual-conductive polymer can exert a significant influence on the cycling performances of lithium-ion batteries [1,2]. In the current work, we report the enhanced cycling performance and high rate performance of sulfur active cathode materials by surface modification with dual-conductive polymeric materials. The presence of protective conductive layer formed on the cathode suppresses the dissolution of lithium polysulfides on the cathode side resulting in more stable cycling characteristics when compared with those of pristine cathode material. Detailed synthesis procedure, characterization of the materials and electrochemical performance will be presented.

References

[1] S. H. Ju, I. –S. Kang, Y. –S. Lee, W. K. Shin, S. Kim, K. Shin, D. -W. Kim, ACS Appl. Mater. Interfaces., 6, 2546-2552 (2014).

[2] Y. -S. Lee, J W. K. Shin, A. G. Kannan, S. M. Koo, D. -W. Kim, ACS Appl. Mater. Interfaces., 7, 13944-13951 (2015).