Nano-Confinement of Insulating Sulfur in the Cathode Composite of All-Solid-State Li–S Batteries Using Flexible Carbon Materials with Large Pore Volumes

Abstract

Durable nanostructured cathode materials for efficient all-solid-state Li−S batteries were prepared using a conductive single-walled 3D graphene with a large pore volume as the cathode support material. At high loadings of the active material (50−60 wt %), microscale phase segregation was observed with a conventional cathode support material during the charging/discharging processes but this was suppressed by the confinement of insulating sulfur into the mesopores of the elastic and flexible nanoporous graphene with a large pore volume of 5.3 mL g −1 . As such, durable three-phase contact was achieved among the solid electrolyte, insulating sulfur, and the electrically conductive carbon. Consequently, the electrochemical performances of the assembled all-solidstate batteries were significantly improved and feasible under the harsh conditions of operation at 353 K, and improved cycling stability as well as the highest specific capacity of 716 mA h per gram of cathode (4.6 mA h cm −2 , 0.2 C) was achieved with high sulfur loading (50 wt %).

Porous nanographene formation on γ-alumina nanoparticles via transition-metal-free methane activation

“…The vertical axis shows the nominal number of layers of deposited carbon on ANPs calculated by the specic surface area of ANPs. 17 The rate of carbon growth was pseudo-rst order with respect to the partial pressure of CH 4 for both rstand secondlayer depositions (Fig. 1c).…”

“…Especially, CVD on alumina nanoparticles (ANPs) that display high thermal stability 25 as the templates gave nanoporous graphene (NPG) materials from CH 4. [14][15][16][17] The NPGs have a 3D continuous and seamless nanostructure with a large surface area, approaching the ideal value of 2D graphene (2627 m 2 g À1 ). 26 NPGs also have fascinating features including high electrical conductivity, 16 elastic and exible nature, 15,17 and unprecedentedly high electrochemical stability.…”

“…[3][4][5] In contrast, the synthesis of a three-dimensionally and periodically arranged single-walled graphene with a negative curvature has remained a challenge since Mackay and Terrones proposed an ideal 3D minimumsurface graphene structure (Scheme 1) in 1991, 6 despite the recent advances in organic synthesis realizing small molecules with a few heptagons 7,8 or octagons. 9,10 In this regard, chemical vapor deposition (CVD) on templated materials [11][12][13][14][15][16][17][18][19][20][21][22][23][24] is a prominent strategy for realizing 3D minimum-surface graphene. Especially, CVD on alumina nanoparticles (ANPs) that display high thermal stability 25 as the templates gave nanoporous graphene (NPG) materials from CH 4.…”

“…26 NPGs also have fascinating features including high electrical conductivity, 16 elastic and exible nature, 15,17 and unprecedentedly high electrochemical stability. 16,17 The typical synthesis of NPG is performed as follows: a uniform carbon coating via CVD of CH 4 at 900 C on ANPs is followed by the removal of ANPs by chemical washing, and the subsequent high-temperature annealing at temperatures higher than 1600 C under an inert atmosphere to give a single-walled NPG material (Scheme 1 and Fig. S1 †).…”

“…S1 †). [14][15][16][17] It is essential to use stable CH 4 with a high bond dissociation energy (439 kJ mol À1 ) 27,28 as a carbon source, rather than more reactive unsaturated hydrocarbons such as acetylene and propylene, for high-quality graphene formation by suppressing carbon stacking.…”