Self-assembled CdS quantum dots in carbon nanotubes: induced polysulfide trapping and redox kinetics enhancement for improved lithium–sulfur battery performance

Abstract

Lithium–sulfur batteries appear to hold promise as next-generation energy storage systems owing to their theoretical energy density that is five times higher than commercial Li ion batteries. However, the insulating nature of sulfur/lithium sulfides and the severe polysulfide shuttle reaction between the Li anode and sulfur cathode can hinder their practical applications. Herein, we demonstrate the rational design and construction of CdS quantum dots uniformly attached to carbon nanotubes for sulfur infiltration, these structures were subsequently used as a high-performance sulfur cathode in lithium–sulfur batteries. This special architecture exhibits a high polysulfide adsorption and confinement while allowing fast electron and Li ion transfer. In addition, the synergic catalytic effect of the cadmium and the introduced heteroatoms favor the enhancement of the reaction kinetics. As a result, this carbon nanotubes/CdS quantum dots/S composite greatly improves the rate and cycle performance of lithium–sulfur batteries. The specific capacity decreases slowly from 1237.8 mA h g⁻¹ at 0.2C to 918.1 mA h g⁻¹ at 2.0C, showing an excellent rate performance and a good capacity retention of 820.6 mA h g⁻¹ at 0.5C for over 150 cycles with a coulombic efficiency of over 98.0%. The inclusion of the CdS quantum dots suppresses the shuttle effect and enhances the redox kinetics, thereby leading to the high utilization of sulfur, and thus providing new avenues for the design of advanced cathode materials for high-performance lithium–sulfur batteries.