Sulfur-Infiltrated Graphene-Based Layered Porous Carbon Cathodes for High-Performance Lithium–Sulfur Batteries

Abstract

Because of advantages such as excellent electronic conductivity, high theoretical specific surface area, and good mechanical flexibility, graphene is receiving increasing attention as an additive to improve the conductivity of sulfur cathodes in lithium-sulfur (Li-S) batteries. However, graphene is not an effective substrate material to confine the polysulfides in cathodes and stable the cycling. Here, we designed and synthesized a graphene-based layered porous carbon material for the impregnation of sulfur as cathode for Li-S battery. In this composite, a thin layer of porous carbon uniformly covers both surfaces of the graphene and sulfur is highly dispersed in its pores. The high specific surface area and pore volume of the porous carbon layers not only can achieve a high sulfur loading in highly dispersed amorphous state, but also can act as polysulfide reservoirs to alleviate the shuttle effect. When used as the cathode material in Li-S batteries, with the help of the thin porous carbon layers, the as-prepared materials demonstrate a better electrochemical performance and cycle stability compared with those of graphene/sulfur composites.

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

“…All the capacity retention and capacity degradation are calculated from the third cycle after achieving stabilized capacity. The achieved cycling ability in Figure 5c,d is much better than that of most previous reports 8, 9, 10, 11, 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, 48. Only very recently, Cui and co‐workers51 successfully demonstrated that the TiO 2 /S yolk–shell composites can be cycled over 1000 times with a capacity decay of 0.033% per cycle.…”

“…Even after cycling for 600 cycles, the battery still gives a specific areal capacity of 1.6 mAh cm −2 . However, the specific areal capacity in most previous reports13, 16, 20, 21, 23, 26, 28, 30, 39, 40, 43, 45, 51 is lower than 2 mAh g −1 due to the low sulfur loading in the electrodes (see Table S1 in the Supporting Information and corresponding discussion). Moreover, some previous superior cycling performances over 500 cycles20, 43, 45, 51 are achieved by low sulfur loading, which is usually lower than 1 mg cm −2 (Table S1, Supporting Information), while in our present work, the electrode with 2.7 mg cm −2 sulfur loading can still run over 600 cycles.…”

“…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...…”

“…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, RGO or G does not have the abundant functional groups that can bind sulfur and its discharge products.…”

“…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.…”