Poly(4‐styrene sulfonic acid) to Disperse Graphene for Applications in Lithium‐Sulfur Batteries

Abstract

The use of poly(4‐styrene sulfonic acid) (PSSA) to effectively disperse graphene in an aqueous sulfur (S) cathode slurry is proposed, and the cell performance of the resulting Li−S battery is investigated and compared to that of the battery prepared by adding as‐received graphene. The addition of PSSA improves not only the dispersion of the as‐received graphene, but also the homogeneity of the constituents in the S cathode slurry; accordingly, better electronic and ionic conductivities are obtained. The electrical impedance of the cell constructed using the S cathode with the as‐received graphene is greatly reduced from 142.0 to 14.6 Ω when PSSA is added during the preparation of the cathode. Moreover, the addition of the PSSA‐dispersed graphene to the S cathode significantly improves the capacity, cycle life, and coulombic efficiency during the charge‐discharge process, since PSSA increases the contact between the dispersed graphene and the insulated S powder.

Facile Synthesis of Hierarchical Sulfur Composites for Lithium–Sulfur Batteries

“…Figure 8(b) compares the coulombic efficiency (CE) of the four cells. According to previous reports in the literature, [23,53] cells suffer from high polarization when the carbon at the surface of the cathode is covered by Li 2 S 2 /Li 2 S during discharge; this polarization will decrease as the Li 2 S 2 and Li 2 S are oxidized to soluble PS during charging, and the presence of the potential barrier just demonstrates a polarization-reduction phenomenon. The S/CB, S@C aggl , and S@C disp cells showed initial CE values of 89 %, 81 %, and 100 %, respectively, and the CEs of the former two cells increased gradually to near-constant values of 92 % and 97 % after several cycles.…”

“…Besides, a potential barrier associated with the deposition of insulating Li 2 S 2 /Li 2 S on the carbon surface was observed at the beginning of the charging process of the four cells. According to previous reports in the literature, [23,53] cells suffer from high polarization when the carbon at the surface of the cathode is covered by Li 2 S 2 /Li 2 S during discharge; this polarization will decrease as the Li 2 S 2 and Li 2 S are oxidized to soluble PS during charging, and the presence of the potential barrier just demonstrates a polarization-reduction phenomenon. In other words, a larger potential barrier indicates an initially higher polarization and a greater amount of Li 2 S 2 /Li 2 S on the carbon surface of the "discharged" cathode.…”

“…However, S also presents a number of challenges that have to be overcome, such as its low electrical conductivity (5 × 10-30 S cm À 1 ), [15] the shuttle effect caused by easy dissolution of the intermediates (high-order polysulfide (PS) species) generated during discharge, [16][17][18][19][20] and the high volume expansion (80 %). [23][24][25][26][27][28][29][30][31][32][33][34] One frequently adopted method is to produce a composite of S and a carbonaceous material. In addition, volume expansion of S can occur during its discharge/lithiation process, which may cause high mechanical stress that damages the cathode.…”

“…[21] The shuttle effect, relating to the dissolution of high-order PS species that are produced as electrochemical intermediates in a polar electrolyte and the followed migration to the lithium anode due to the concentration gradient, results in a continual loss of the active S material from the cathode and thus the eventual decay of the capacity. Carbonaceous materials, including graphene, [23][24][25] graphite, [26] carbon fibers, [27] carbon nanotubes, [28][29][30][31] and carbon nanoparticles, [34] have long been reported to efficiently improve electronic conductivity of S; additionally, the carbon defects were reported to be helpful in inhibiting the PS dissolution and the shuttle effect. [21] The poor electrical conductivity of S, which is also one of pressing issues for the commercialization of LiÀ S batteries, not only results in low capacity and energy density in the batteries, but also causes a high ohmic potential drop that leads to rapid cell fading.…”

“…[23][24][25][26][27][28][29][30][31][32][33][34] One frequently adopted method is to produce a composite of S and a carbonaceous material. Carbonaceous materials, including graphene, [23][24][25] graphite, [26] carbon fibers, [27] carbon nanotubes, [28][29][30][31] and carbon nanoparticles, [34] have long been reported to efficiently improve electronic conductivity of S; additionally, the carbon defects were reported to be helpful in inhibiting the PS dissolution and the shuttle effect. [35,36] In this investigation, a feasible method for easy fabrication of core-shell structured composites of S and carbon nanopowder (nano-CB) is proposed, in which the structural geometry and particle size of the synthesized composites can be adjusted.…”