Graphene/Single-Walled Carbon Nanotube Hybrids: One-Step Catalytic Growth and Applications for High-Rate Li–S Batteries

Abstract

The theoretically proposed graphene/single-walled carbon nanotube (G/SWCNT) hybrids by placing SWCNTs among graphene planes through covalent C-C bonding are expected to have extraordinary physical properties and promising engineering applications. However, the G/CNT hybrids that have been fabricated differ greatly from the proposed G/SWCNT hybrids because either the covalent C-C bonding is not well constructed or only multiwalled CNTs/carbon nanofibers rather than SWCNTs are available in the hybrids. Herein, a novel G/SWCNT hybrid was successfully fabricated by a facile catalytic growth on layered double hydroxide (LDH) at a high temperature over 950 °C. The thermally stable Fe nanoparticles and the uniform structure of the calcined LDH flakes are essential for the simultaneously catalytic deposition of SWCNTs and graphene. The SWCNTs and the CVD-grown graphene, as well as the robust connection between the SWCNTs and graphene, facilitated the construction of a high electrical conductive pathway. The internal spaces between the two stacked graphene layers and among SWCNTs offer room for sulfur storage. Therefore, the as obtained G/SWCNT-S cathode exhibited excellent performance in Li-S batteries with a capacity as high as 650 mAh g(-1) after 100 cycles even at a high current rate of 5 C. Such a novel G/SWCNT hybrid can serve not only as a prototype to shed light on the chemical principle of G/CNT synthesis but also as a platform for their further applications in the area of nanocomposites, heterogeneous catalysis, drug delivery, electrochemical energy storage, and so on.

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.…”

“…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.…”

“…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.…”

Sulfur–Graphene Nanostructured Cathodes via Ball-Milling for High-Performance Lithium–Sulfur Batteries

“…To overcome the above-mentioned obstacles, carbon based materials with various hierarchical structures, including meso-/micro-porous carbons [6][7][8][9][10][11] , hollow carbon spheres [12][13][14] , carbon nanotubes/nanofibers [15][16][17][18][19] , graphene derivatives [20][21][22][23][24][25][26][27][28][29][30] , and flexible carbon membranes 31 6 C with a low decay rate of 0.039% per cycle over 1500 cycles) 25 , a sulfur-graphene composite with ~ 63.6 wt% sulfur uniformly coated on graphene through reduction of GO and concomitant sulfurization (440 mAh g -1 after 500 cycles at 0.75 C) 22 , and polyvinylpyrrolidone (PVP)-encapsulated hollow S nanospheres (i.e., S@PVP nanospheres) from the reaction of Na2S2O3 and…”