Revisit Carbon/Sulfur Composite for Li-S Batteries

Abstract

To correlate the carbon properties, e.g. surface area and porous structure, with the electrochemical behaviors of carbon/sulfur (C/S) composite cathodes for lithium-sulfur (Li-S) batteries, four different carbon frameworks including Ketjen Black (KB, high surface area and porous), Graphene (high surface area and nonporous), Acetylene Black (AB, low surface area and nonporous) and Hollow Carbon Nano Sphere (HCNS, low surface area and porous) are employed to immobilize sulfur (80 wt%). It has been revealed that high surface area of carbon improves the utilization rate of active sulfur and decreases the real current density during the electrochemical reactions. Accordingly, increased reversible capacities and reduced polarization are observed for high surface area carbon hosts such as KB/S and graphene/S composites. The porous structure of KB or HCNS matrix promotes the long-term cycling stability of C/S composites but only at relatively low rate (0.2 C). Once the current density increases, the pore effect completely disappears and all Li-S batteries show similar trend of capacity degradation regardless of the different carbon hosts used in the cathodes. The reason has been assigned to the formation of reduced amount of irreversible Li2S on the cathode as well as shortened time for polysulfides to transport toward lithium anode at elevated current densities. This work provides valuable information for predictive selection on carbon materials to construct C/S composite for practical applications from the electrochemical point of view.

Molecular-confinement of polysulfides within mesoscale electrodes for the practical application of lithium sulfur batteries

“…However, the columbic efficiency of NPC-80S is high at 96% with decent capacity retention of 83% over 100 cycles. The large surface area and high pore [30]. The lower plateau at 2.1V revealed the semisolid phase Li 2 S 4 further reduction to solid phase low-order Li 2 S 2 , even Li 2 S. The polarization potential between charge-discharge curves in NPC-MWCNT-80S was significantly reduced to 206mV comparing to that in NC-80S and MWCNT-80S electrode, which was 220mV and 340mV, respectively ( Figure 4d).…”

“…To investigate the difference, disodium magnesium EDTA hydrate was directly pyrolyzed to obtain NPC carbon. Sulfur was loading by a wet-dry method reported previously [30,31]. CS 2 solution containing 10wt% sulfur was added into the prepared carbon, followed by sonication for 15min to form homogeneous slurry.…”

Trimethylsilyl Chloride-Modified Li Anode for Enhanced Performance of Li–S Cells

“…26 The third problem arises from the reduction of the poflysulfides by Li metal to form an insoluble and insulating Li 2 S 2 and/or a Li 2 S film on its surface, which can block Li + diffusion and deteriorate the cell performance. [27][28] In addition, a large amount of heat will be released when the Li metal reacts with the electrolytes, which can pose risks of overheating. 29 Many in-situ/ex-situ attempts, such as reactive organic/inorganic additives, [30][31][32] Li alloy, [33][34] polymer coatings, [35][36] sputtered solid electrolytes, 37 have been applied to passivate Li metal.…”

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

“…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. Although other porous carbons shown similar performance [21,[41][42][43][44], the sulfur loading is low and, moreover, more importantly the amount of electrolyte is far away from industrially applied conditions. The latter is crucial to achieve energy densities beyond state of the art lithium ion batteries [26,27].…”