Stable Cycling of a Scalable Graphene-Encapsulated Nanocomposite for Lithium–Sulfur Batteries

Abstract

We report the synthesis of a low-cost carbon/sulfur nanocomposite using Ketjen black (KBC) as the carbon framework, encapsulated by thin graphene sheets using a simple process that relies on binding a functionalized KBC/S nanoparticle surface with graphene oxide (GO), which is reduced in situ. A slight excess of GO is employed to create a second layer of graphene wrapping around the KBC/S. This g-KBC/S sulfur cathode exhibits excellent cyclability over 200 cycles where the average stabilized fade rate is only 0.026% or 1.1 mAh g(-1) per cycle. This excellent performance is primarily attributed to the wrapped, internally porous architecture. The large pore volume, small pore diameter, and uniform nanoparticle size of the mesoporous KBC array provides an ideal frame for the fabrication of a homogeneous C/S composite, whereas the graphene/GO sheets serve as an external chemical and physical barrier that inhibits polysulfide diffusion.

Core@shell sulfur@polypyrrole nanoparticles sandwiched in graphene sheets as cathode for lithium–sulfur batteries

“…5(d), which also implies the partial reduction of GO in the S@PPy/GS composite [40]. The above analyses indicate that the graphene coating on the S@PPy nanoparticles could suppress lithium polysulfides through the effect of oxygen-containing functional groups, improving the utilization of active materials and enhancing the cycle life of Li-S batteries [35,36].…”

“…Furthermore, a faint signal of oxygen element was also probed, indicating that GO was partially reduced by hydrazine hydrate, and some residual oxygen-containing functional groups on the graphene sheets still remain in the S@PPy/GS composite [35]. These functional groups are reported to be critical for long cycling life by immobilizing sulfur and effectively restricting the dissolution of Li polysulfides [35,36].…”

“…(3) The S@PPy nanoparticles are tightly wrapped by the graphene sheets to form a three-dimensional conductive network, which will provide an effi- cient and fast transport of lithium ions and electronic transfer within the electrode. What's more, due to the residual oxygen-containing functional groups on the surface of GS, polysulphides anions can be further alleviated in the cathode [35,36], diminishing the shuttle reaction and mass loss of the active materials during cycles. Hence, the S@PPy/GS electrode exhibits good cycling stability and rate performance.…”

Critical Link between Materials Chemistry and Cell-Level Design for High Energy Density and Low Cost Lithium-Sulfur Transportation Battery

“…It is apparent in Figure 3 that pack-level specific energy and energy density decreases significantly at low specific capacities. Initial specific capacities of 1000 mAh/g and higher are achievable in the literature, 8,9,[12][13][14][15][16][17][18]20,21,31 however retaining this capacity is still one of the biggest challenges as the highest retained capacity reported was 740 mAh/g after 1500 cycles. 18 The electrolyte to sulfur ratio in the cathode (E/S) is one of the most critical parameters playing a key role in capacity retention.…”

Facile assembly of partly graphene-enveloped sulfur composites in double-solvent for lithium–sulfur batteries

“…Various carbonaceous materials, such as meso/micro-porous carbon [10][11][12][13], carbon nanotube [14,15], carbon nanofiber [16,17], and hollow carbon sphere [18,19], have been ultilized to enhance electrical conductivity of sulfur and trap soluble polysulfide intermediates. Among these carbonaceous materials, graphene is a single layer or a few layers of graphitic carbon conductor with excellent properties, such as high surface area and high electronic conductivity; these properties make graphene a viable carbon matrix to anchor active materials for lithium-sulfur batteries [20][21][22][23].…”