Improving lithium–sulfur battery performance via a carbon-coating layer derived from the hydrothermal carbonization of glucose

Abstract

Sulfur possesses a high specific capacity as a rechargeable lithium battery cathode. However, the commercial applications of sulfur cathodes are limited by the poor electronic/ionic conductivity of elemental sulfur and polysulfides, volume expansion of sulfur during the discharge process, and the high solubility of long-chain lithium polysulfides (Li₂S_n, 4 ≤ n ≤ 8). Herein, we design a core–shell structure composed of active carbon (AC) and an amorphous carbon-coating layer to encapsulate the sulfur in the carbon matrix. The carbon-coating layer obtained from the hydrothermal carbonization of glucose can effectively entrap the polysulfides. Furthermore, the composite matrix provides a conducting framework serving as an electrochemical reaction chamber for the sulfur cathode. After wrapping AC–S with an amorphous carbon layer, the obtained composite cathode can effectively confine the polysulfides and buffer the volume change. Consequently, the resulting composite cathode possesses a high specific capacity, good rate capability, and stable cycling performance. At 0.2 A g⁻¹ current density, the as-prepared carbon-coated AC–S composite cathode shows a high specific discharge capacity of 1103 mA h g⁻¹. At a current density of 0.8 A g⁻¹ and 1.6 A g⁻¹, the composite cathode exhibits 75% capacity retention over 150 cycles. The Coulombic efficiency of the cell remains at approximately 95%.