Enhanced Properties of Sulfur-Infiltrated Carbon Sphere with Conductive Polymer Coating for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) battery is promising energy system with a high theoretical energy density (2500 Wh kg^-1), which is ~7 times larger than those of the current LIBs (~387 Wh kg^-1) utilizing the unparalleled theoretical capacity of sulfur (1675 mAh g^-1). Sulfur as a cathode material also has other advantages such as non-toxicity, low cost, and abundance of raw materials.For all its virtues, several challenges such as an insulating nature of sulfur (conductivity ~10^-30), a large volume expansion by up to 80 % upon full lithiation and a severe capacity fading during cycling still remained unsolved. Sulfur, unlike the insertion based electrode, suffers a serious of structural and morphological changes during cycling with the formation of high-order lithium polysulfides (Li₂S_n, 2<n≤8) and low-order lithium polysulfides (Li₂S₂ and Li₂S), which are insulators. Besides, the high-order lithium polysulfides are soluble in current liquid electrolyte at the early stage of discharging. The dissolution of high-order polysulfides results in the so-called shuttling effects.Those problems should be addressed for utilization of lithium-sulfur battery in consumer electronics.

In this present investigation, we developed sulfur infiltrated hollow carbon sphere with conductive polymer layer. The numerous small pores in carbon sphere were formed by evaporation of inner materials without damages of outer carbon layer. The conductive polymer layer (PEDOT) coated on the surface of carbon sphere could improve in the trapping of polysulfides and play a role in buffer layers against the volume changes of sulfur. The electrode design could improve the electrical performance with resolving the aforementioned issues.