Nanocasting Hierarchical Carbide-Derived Carbons in Nanostructured Opal Assemblies for High-Performance Cathodes in Lithium–Sulfur Batteries

Abstract

Silica nanospheres are used as templates for the generation of carbide-derived carbons with monodisperse spherical mesopores (d=20-40 nm) and microporous walls. The nanocasting approach with a polycarbosilane precursor and subsequent pyrolysis, followed by silica template removal and chlorine treatment, results in carbide-derived carbons DUT-86 (DUT=Dresden University of Technology) with remarkable textural characteristics, monodisperse, spherical mesopores tunable in diameter, and very high pore volumes up to 5.0 cm3 g(-1). Morphology replication allows these nanopores to be arranged in a nanostructured inverse opal-like structure. Specific surface areas are very high (2450 m2 g(-1)) due to the simultaneous presence of micropores. Testing DUT-86 samples as cathode materials in Li-S batteries reveals excellent performance, and tailoring of the pore size allows optimization of cell performance, especially the active center accessibility and sulfur utilization. The outstanding pore volumes allow sulfur loadings of 80 wt %, a value seldom achieved in composite cathodes, and initial capacities of 1165 mAh gsulfur(-1) are reached. After 100 cycle capacities of 860 mAh gsulfur(-1) are retained, rendering DUT-86 a high-performance sulfur host material.

Differences in Electrochemistry between Fibrous SPAN and Fibrous S/C Cathodes Relevant to Cycle Stability and Capacity

“…However, carbonates can react with the dissolved poly(sulfide)s via nucleophilic addition. 28 Consequently, carbonates are usually considered incompatible with classical Li/S batteries based on S 8 . As outlined earlier, the small pores in ACF fibers allow only for the presence of small, amorphous sulfur fragments inside the pores.…”

“…1 This high specific energy density of Li/S batteries results from the high specific capacities of the elemental sulfur cathode with 1672 mA·h·g -1 for the reaction S + 2e -→ S 2-and the lithium metal anode with 3860 mA·h·g -1 for 2Li → 2Li + + 2e -. Nonetheless, Li/S cells also face several challenges such as a low sulfur utilization and low rate capability, which are caused by the insulating character of cyclo-S 8 and its slow redox-kinetics. 2 Another issue is the polysulfide shuttle.…”

Enhanced Cycling Stability of Lithium–Sulfur batteries by Electrostatic-Interaction

“…As for the sulfur electrode modification, there were mainly two approaches to suppress the polysulfide dissolution: physical confinement [16][17][18][19] and chemical interaction trapping through nonvalent bonding [20][21][22][23]. Graphene with excellent conductivity, high surface area, and modifiable surface structure is usually considered to be an appropriate candidate as the host of sulfur active material.…”

Zinc-salt templating of hierarchical porous carbons for low electrolyte high energy lithium-sulfur batteries (LE-LiS)

“…Interestingly, even at a current density of 7.81 mA cm-2 the low voltage plateau (Figure 4 d) is observed, which may indicate the advantage of hierarchical pore systems with high microporosity as well as small mesopores [36,40]. Hence, the zinc salt applied carbothermal reduction process provides the access to an efficient synthesis of a sulfur host material with synergetic properties leading to superior performance in high energy lithium-sulfur battery.…”

“…However, several challenges need to be overcome, such as the extensive expansion and shrinking of the active material [15] as well as the repeated dissolution and deposition of insulating sulfur compounds [16,17]. Therefore, initiated by Nazar et al 2009 [18], a huge number of porous carbons with varying pore structures have been explored as conductive host for the active sulfur species [7,[19][20][21][22][23]. Particularly of importance for high capacity lithium-sulfur batteries is according to investigations of Li et al [24] as well as Liang et al [25] a multimodal pore system with significant differences in pore size especially micro-and mesopores due to the synergistic advantage of both pore systems, which can trigger an improvement of performance under realistic application oriented conditions.…”