Elsevier

Journal of Power Sources

Volume 211, 1 August 2012, Pages 169-172
Journal of Power Sources

Short communication
A proof-of-concept lithium/sulfur liquid battery with exceptionally high capacity density

https://doi.org/10.1016/j.jpowsour.2012.04.006Get rights and content

Abstract

In this communication, we disclose a proof-of-concept lithium/sulfur liquid battery that has exceptionally high capacity density. In such a battery, the cathode consists of a highly porous carbon cloth (CC) as the cathode current collector and a porous sulfur paper as the source of active material. In the first discharge, sulfur is reduced on the CC surface into high order lithium polysulfide (PS), which dissolves into liquid electrolyte and serves as the catholyte of the so-called “Li/S liquid battery”. By adopting a LiNO3-contained electrolyte to protect Li anode, the Li/S liquid cell is shown to cycle reversibly between 1.7 V and 2.8 V with an initial capacity of 778 mAh g−1 S, corresponding to a capacity density of 10.1 mAh cm−2 CC, which could be the highest capacity density among the rechargeable Li/S batteries reported ever. This work reveals that the high capacity density Li/S batteries can be made through a “Li/S liquid cell” by employing a highly porous carbon electrode to accommodate the insoluble sulfur reduction products (Li2S2/Li2S) with appropriate protection of the Li anode.

Highlights

► A Li/S liquid cell with two-layer structural cathode is proposed for high capacity density. ► Initial mixing state of sulfur and carbon in cathode is not important for a Li/S liquid cell. ► High surface area carbon and solvent with high polysulfide solubility favor cell performance. ► Effective improvement on Li/S cell should be on the Li anode, instead of the cathode.

Section snippets

Experimental

Carbon cloth (CC, E-Tek, V2.02) and activated carbon cloth (ACC, Maxwell Tech.) were punched into small circular disks with an area of 1.27 cm2 and used as the cathode current collector. Using phase inversion method [25], porous sulfur paper consisting of 90 wt.% sulfur and 10 wt.% binder was prepared by a general procedure as follows: Calculated amount of sulfur powder (>99.5%, Aldrich) was added to a 5 wt.% solution of Kynar FlexTM 2801, a poly(vinylidene fluoride-co-hexafluoropropylene)

Results and discussion

Fig. 1 shows the images of a highly porous sulfur paper made by the phase inversion method. Similar to those observed from the pure Kynar polymer membrane, the sulfur paper has relatively dense surface and highly porous body [25]. As an indication of the highly porous structure, the sulfur paper immediately gets wetted and swollen upon contact with any liquid electrolytes. Except for the high porosity, the sulfur paper is neither electronically conductive nor ionically conductive.

Fig. 2 shows a

Conclusions

This work demonstrates that the rechargeable Li/S liquid cells having exceptionally high capacity density can be made by starting with a high sulfur loading cathode. Initial mixing state of the sulfur and carbon in the cathode is not important as the PS active species eventually dissolve into liquid electrolyte. For a cell with sufficient amount of sulfur, its capacity is determined by the porosity of carbon electrode and the dissolution capability of PS in liquid electrolyte while the cycle

Acknowledgments

The authors would like to thank Dr. R.Z. Jiang of the fuel cell team for supplying carbon cloth.

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