Sulfur cells, lithium

Marmorstein D, Yu TH, Striebel KA, McLamon FR, Hou J, Garins EJ (2000) Electrochemical performance of lithium-sulfur cells with three different polymer electrolytes. J Power Sources 89 219-226... 

Another approach is to use a lithium/sulfur cell with nonaqueous electrolyte systems. Rechargeable lithium batteries are being developed for portable power applications such as electric vehicles, partly because of their specific energy ranges 100-150 Wh kg (and... 

High-performance lithium-sulfur cells are being developed for use in off-peak energy storage batteries in electric utility networks. The cells, which operate at 400°C, consist of a lithium electrode, a sulfur or sulfide electrode, and molten LiCl-KCl electrolyte. The chemistry of the lithium electrode is relatively straightforward. However, the electrochemical reactions at the sulfur electrode involve the formation of several intermediate species that are sufficiently soluble in the electrolyte to limit the lifetime and capacity of the cells. Although this effect can be decreased with soluble additives such as arsenic or selenium in the sulfur, a more promising solution appears to be the use of metal sulfides, rather than sulfur, as the active material in the positive electrode. 

The capacity loss of the sulfur electrode can be attributed to sulfur vaporization (the vapor pressure of sulfur at 400°C is 410 torr), migration or dispersion of insoluble sulfur-containing phases from the electrode, solubilization of sulfur-containing species in the electrolyte, and/or inactivation of sulfur within the electrode compartment. Since neither the mechanism of the cell reaction nor the mechanism of sulfur loss was understood, a study of sulfur electrode chemistry and electrochemistry was made. It was expected that information gained from these studies would lead to improved performance and lifetimes of lithium-sulfur cells. 

The first cathodic peak most probably results from the sulfur reduction. This is suggested by the similar results of this investigation and previous electrochemical studies (14) where the initial electroactive species was sulfur and by results from lithium-sulfur cell tests where sulfur is known to form from the electrochemical oxidation of Li2S. 

Use of Additives in Sulfur Electrodes. The use of additives to diminish sulfur loss and, thus, to retain cell capacity, has been investigated at Argonne for several years. Thus far, the most successful cells using sulfur-additive mixtures have incorporated selenium or arsenic as the additive. Cells using these additives have performed much better than those using no additives. However, it appears that these particular additives, at least, do not lower the activity of the sulfur sufficiently for high performance of the lithium-sulfur cell over long periods. 

Reactions of Compounds and Sulfur-Additive Mixtures. When additives and compounds are used to retain sulfur in the positive electrode there are other possible reactions, in addition to the usual electrochemical reactions, that can take place at the positive electrode. These include electrochemical oxidation and reduction of the additive (or compound ) and interaction of the additive with the electrolyte. In addition, there is the possibility of ternary compound formation from a reaction between the discharge product, Li2S, and sulfur compounds. Because the arsenic—sulfur system has undergone the most intensive investigation for use in lithium—sulfur cells, examples of the aforementioned reactions using arsenic are shown below ... 

It was found in these studies that the lithium-sulfur cell system could meet many of the requirements needed to develop a high energy density battery system. Long-term cycling tests showed, however, that... 

Kim S, Jung Y, Park S-J (2007) Effect of imidazolium cation on cycle life characteristics of secondary lithium-sulfur cells using liquid electrolytes. Electrochim Acta 52 2116—2122... 

K. Kumaresan, Y.V. Mkhaylk, R.E. White, A mathematical model for a lithium-sulfur cell , J. Electrochem. Soc., 155, A576-A582,2008. 

Promising strategies regarding this issue were followed recently. Eastwood et al. and Lin et al. have made use of the phase contrast to successfully image a graphite electrode with sub-pm resolution [14] or to understand the dissolution and re-deposition of poly sulfides in lithium sulfur cells [15]. Another approach followed by Zielke et al. was to model structures corresponding to low atomic number elements in combination with FFTXM tomography reconstmctions [55]. 

Mikhaylik YV (2008) Electrol5hes for lithium sulfur cells. US Patent 7,354,680 B2, 8 April 2008... 

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