Micropores of pure nanographite spheres for long cycle life and high-rate lithium–sulfur batteries

Abstract

An effective way to prevent shuttling of polysulfides is the key to obtaining long cycle life lithium–sulfur batteries. In this paper, an effective and novel structure of pure hollow nanographite with micropores (∼8 Å) was successfully synthesized, and high-rate and long cycle life lithium–sulfur batteries were obtained. Ni²⁺ acts as a catalyst to promote the growth of super absorbent polymers into graphite carbon shells at lower temperatures. Then, after etching the internal Ni with acid, hollow nanographite spheres are obtained and there are some micropores inside graphite carbon shells. The number of micropores can be controlled by the amount of Ni in the precursor. The existence of micropores facilitates the infiltration of sulfur in the molten state and limits the shuttling of polysulfide during charging and discharging. Therefore, the structure is apt to package sulfur by better restricting the shuttle of polysulfides, which can promote the cycle performance of the S@HNG. The fast kinetics of the graphite carbon shells can increase the rate capability. Specifically, when using S@HNG as a cathode in lithium–sulfur batteries, the specific capacity can still remain at 658 mA h g⁻¹ under a current density of 1C after 1000 cycles. In addition, the phenomenon of self-discharge of lithium–sulfur batteries is also greatly alleviated.