Fibrous Hybrid of Graphene and Sulfur Nanocrystals for High-Performance Lithium–Sulfur Batteries

Abstract

Graphene-sulfur (G-S) hybrid materials with sulfur nanocrystals anchored on interconnected fibrous graphene are obtained by a facile one-pot strategy using a sulfur/carbon disulfide/alcohol mixed solution. The reduction of graphene oxide and the formation/binding of sulfur nanocrystals were integrated. The G-S hybrids exhibit a highly porous network structure constructed by fibrous graphene, many electrically conducting pathways, and easily tunable sulfur content, which can be cut and pressed into pellets to be directly used as lithium-sulfur battery cathodes without using a metal current-collector, binder, and conductive additive. The porous network and sulfur nanocrystals enable rapid ion transport and short Li(+) diffusion distance, the interconnected fibrous graphene provides highly conductive electron transport pathways, and the oxygen-containing (mainly hydroxyl/epoxide) groups show strong binding with polysulfides, preventing their dissolution into the electrolyte based on first-principles calculations. As a result, the G-S hybrids show a high capacity, an excellent high-rate performance, and a long life over 100 cycles. These results demonstrate the great potential of this unique hybrid structure as cathodes for high-performance lithium-sulfur batteries.

Leaf‐Like Graphene‐Oxide‐Wrapped Sulfur for High‐Performance Lithium–Sulfur Battery

“…However, RGO or G does not have the abundant functional groups that can bind sulfur and its discharge products. In addition, similar with previous reports about porous‐carbon/S composites,12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 the sulfur content in the GO/S and RGO/S (or G/S) composites and sulfur loading on the electrode is still low 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44. In addition, some efforts34 have been made to mix high conductivity carbon nanotube (CNT) with GO to improve the conductivity of GO.…”

“…However, one of the most salient problems of GO also arises from the functional groups on the surface that lead to poor electronic conductivity 46. Therefore, the achieved rate performances in most previous reports about GO/S composites are generally below the rate of 2 C (1 C = 1675 mA g −1 ) 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35. On the contrary, reduced GO (RGO) or graphene (G) with higher electronic conductivity was also employed to prepare RGO/S or G/S composites for improving rate performance 36, 37, 38, 39, 40, 41, 42, 43, 44.…”

“…However, the insulating nature of sulfur (S) and its reaction products (i.e., Li 2 S), the large volume expansion from S to Li 2 S, along with the dissolution of lithium polysulfide intermediates (i.e., Li 2 S x , 4 ≤ x ≤ 8) into liquid electrolyte and the consequent shuttling effect between the anode and cathode, makes it generally display poor rate ability, limited cycle life and severe self‐discharge 1, 2, 3, 4, 5, 6, 7. Therefore, a variety of strategies have been pursued to circumvent the sulfur cathode problems, including optimization of organic electrolytes8, 9 and fabrication of sulfur‐conductive polymer composites10, 11 and sulfur–carbon‐based composites 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45. Among these approaches, porous‐carbon/sulfur composites12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 are more attractive because porous carbon can i...…”

“…Very recently, many efforts have been made to develop graphene oxide/sulfur (GO/S) composites cathode for Li–S battery,25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35 because GO consists of a basal plane decorated mostly with epoxide and hydroxyl groups, in addition to carbonyl and carboxyl groups, which are located on the edges. Zhang and co‐workers successfully demonstrated that these functional groups on the surface of GO play an important role for immobilizing the sulfur and its discharge products 25.…”

“…Furthermore, GO network can also accommodates the volume change of the electrode during the Li–S electrochemical reaction. Then, more and more researches have focused on GO/S composites and modified GO/S composites, and further improvements in cyclability of Li–S battery have been achieved by smartly designing GO/S composites in recent years 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35. However, one of the most salient problems of GO also arises from the functional groups on the surface that lead to poor electronic conductivity 46.…”