Confine sulfur in double-hollow carbon sphere integrated with carbon nanotubes for advanced lithium–sulfur batteries

Abstract

The lithium–sulfur (Li–S) batteries are promising because of the high energy density, low cost, and natural abundance of sulfur material. Li–S batteries have suffered from severe capacity fading and poor cyclability, resulting in low sulfur utilization. Herein, S-DHCS/CNTs are synthesized by integration of a double-hollow carbon sphere (DHCS) with carbon nanotubes (CNTs), and the addition of sulfur in DHCS by melt impregnations. The proposed S-DHCS/CNTs can effectively confine sulfur and physically suppress the diffusion of polysulfides within the double-hollow structures. CNTs act as a conductive agent. S-DHCS/CNTs maintain the volume variations and accommodate high sulfur content 73 wt%. The designed S-DHCS/CNTs electrode with high sulfur loading (3.3 mg cm−2) and high areal capacity (5.6 mAh mg cm−2) shows a high initial specific capacity of 1709 mAh g−1 and maintains a reversible capacity of 730 mAh g−1 after 48 cycles at 0.2 C with high coulombic efficiency (100%). This work offers a fascinating strategy to design carbon-based material for high-performance lithium–sulfur batteries.

Sulfur Encapsulation into Carbon Nanospheres as an Effective Technique to Limit Sulfide Dissolution and Extend the Cycle Life of Lithium–Sulfur Batteries

“…Kim et al confined sulfur in carbon micropores and demonstrated 36% retention of capacity after 250 cycles [26]. Walle et al trapped sulfur in double hollow spheres to achieve 57% retention at a 0.2 C rate and 48 cycles [9]. Some of these findings are summarized in Table 1: During discharge, solid sulfur (S8) is reduced into a lithium polysulfide after dissolution in the electrolyte, which is reflected in a stepwise voltage discharge profile analogous to what is shown in Figure 3B (cycle 2).…”

“…Several methods have been proposed to curb the transfer of resistive sulfide species to the anode or their dissolution into the electrolyte: engineering of the carbon surface with functional groups to chemically anchor the polysulfides to the carbon pores [1]; employing catalytic transition metal nitrides, sulfide, or oxides to increase the efficiency of the chain reaction [2,3]; or physical entrapment of sulfur into conductive matrices [4,5] to limit the deposition of resistive lithium sulfides at the anode. Previous efforts have shown that capacity degradation of the lithium-sulfur system stems from the higher discharge plateau [6], since that is where nonrecoverable products of the redox reaction involving long Energies 2024, 17, 2168 2 of 10 chain polysulfide are formed; therefore, efforts to create carbon-sulfur nanocomposites and the confinement of sulfur would cull the full reduction in polysulfide chain products, as wrapped sulfur sites would act as sites with limited lithium reactivity [7][8][9]. Additionally, encapsulation of recrystallized sulfur aims to circumvent drawbacks in the conventional methods of carbon-sulfur integration, namely, the limited effectiveness of the ball milling technique and the energy cost associated with the melt method [7].…”

“…Various methods have been employed for the synthesis of carbonaceous nanomaterials such as Chemical Vapor Deposition (CVD) [8] and polymer pyrolysis. Walle et al [9] used the melt method to confine sulfur in double hollow nanospheres (S-DHCS) integrated into carbon nanotubes (CNTs). The diameter of these S-DHCS/CNTs ranged from 20 to 200 nm and demonstrated decent electrochemical performance in a lithium-sulfur system of 730 mAh/g after 48 cycles at 0.2 C. The authors attributed the superior functioning to the successful confinement of sulfur into the carbonaceous vessel, which minimized both the polysulfide dissolution reaction and the volumetric growth of sulfur during cycling [9].…”

“…Walle et al [9] used the melt method to confine sulfur in double hollow nanospheres (S-DHCS) integrated into carbon nanotubes (CNTs). The diameter of these S-DHCS/CNTs ranged from 20 to 200 nm and demonstrated decent electrochemical performance in a lithium-sulfur system of 730 mAh/g after 48 cycles at 0.2 C. The authors attributed the superior functioning to the successful confinement of sulfur into the carbonaceous vessel, which minimized both the polysulfide dissolution reaction and the volumetric growth of sulfur during cycling [9]. Other efforts concentrated on hosting sulfur in carbonaceous structures formed through the carbonization of polyacrylonitrile (PAN) to obtain SPAN electrodes with excellent electrochemical performance.…”

“…et al confined sulfur in carbon micropores and demonstrated 36% retention of capacity after 250 cycles[26]. Walle et al trapped sulfur in double hollow spheres to achieve 57% retention at a 0.2 C rate and 48 cycles[9]. Some of these findings are summarized in A concise summary of previous efforts on cathode designs for Li-S electrodes.…”