The Effect of Amount of Electrolyte on the Efficiency of Sulphur Utilization in Lithium-Sulphur Cells

Wednesday, May 14, 2014
Grand Foyer, Lobby Level (Hilton Orlando Bonnet Creek)
V. Kolosnitsyn, E. Karaseva, E. Kuzmina, and L. Sheina (Institution of the Russian Academy of Sciences Institute of Organic Chemistry of Ufa Scientific Centre of the Russian Academy of Sciences)
The lithium-sulphur electrochemical system has high value of theoretical specific energy – 2600 Wh/kg. However a real reached specific energy of lithium-sulphur batteries is significantly low against theoretical expected value. So, specific energy of  prototypes of lithum-sulphur cells is in the range of 150-400 Wh/kg, what is only 8-15% of theoretical value of specific energy, while specific energy of lithium-ion batteries reaches about 30-40% of theoretical value [1-2].

The practical specific energy of batteries is determined by a number of factors. The main factors are an efficiency of utilization of active materials of positive and negative electrodes as well as a weight share of accessory components (electrolyte, separator, current collector, cell body etc.) against the total weight of battery. In lithium-ion batteries an efficiency of utilization of active materials of electrodes reaches 90-95% and the weight share of active materials reaches 35-45% against the total weight of battery. In lithium-sulphur batteries a depth of electrochemical reduction of sulphur is usually in the range of 1250-1400 mAh/g(S) what is 75-85% against theoretical value (1675 mAh/g(S)). The weight share of accessory components in lithium-sulphur batteries is significantly greater than in lithium-ion batteries and reaches 70-80%. Electrolyte makes the main contribution into the weight of lithium-sulphur batteries. Usually weight of electrolyte in lithium-sulphur cells is in the range of 40-60% against in lithium-ion – 15-20%.

The difference in functions of electrolyte in lithium-ion and lithium-sulphur batteries is the reason for the difference in amount of electrolyte. Lithium-sulphur batteries can be classified as batteries with a liquid cathode as far as during charge and discharge of them solid-phase active materials – elementary sulphur (S) and lithium sulphide (Li2S) – change into well soluble in electrolytes compounds – lithium polysulphides (Li2Sn):


nS0 + 2Li+ + 2e- →   Li2Sn


nLi2S → Li2Sn +   2(n-1)e- + 2(n-1)Li+

The electrolyte in lithium-sulphur batteries has higher functionality than in lithium-ion batteries. In lithium-ion batteries electrolyte performs the function of ionic conductor. In lithium-sulphur batteries the electrolyte provides an ionic transfer between electrodes as well as dissolves the electroactive components (sulphur and lithium polysulphides). 

The aim of the present work is to determine a minimum amount of electrolyte required for good performance of lithium-sulphur cells.

A study of the electrochemical properties of lithium-sulphur cells was carried out in Swagelok type cell. The sulphur (working) electrodes consisted of 70 wt.% sulphur, 10 wt.% Ketjenblack EC-600JD and 20 wt.% poly(ethylene oxide) (Mw 4x106). The surface capacity of sulphur electrodes was 2 mAh/cm2. Lithium metal foil (99.9%) with the thickness of 80 μm was used as the auxiliary electrode. 1M LiCF3SO3 in sulfolane was used as the electrolyte. Amount of electrolyte into cells was 1.0; 1.5; 2.0; 3.0 and 4.0 mcl/mAh(S). Porous polypropylene Celgard® 3501 was used as the separator. The lithium-sulphur cells were assembled by stacking lithium electrode (d=2.55 cm, area=5.10 cm2), separator (d=2.85 cm, area=6.38 cm2) containing 1M LiCF3SO3 in sulfolane and sulphur electrode (d=2.85 cm, area=6.38 cm2). The charge and discharge performances of the assembled cells were investigated with a PG12-100 potentiostat between 1.5 V and 2.8 V at +30 oC. The charge current density was 0.1 mA/cm2, the discharge current density was 0.2 mA/cm2.

It is shown that the amount of electrolyte effects on the efficiency of sulphur utilization (fig. 1a-1b) and cycle life of lithium-sulphur cells (fig. 1c). For obtaining of acceptable efficiency of sulphur utilization amount of electrolyte in lithium-sulphur cells should be not less than 1.5-2.0 mcl per 1 mAh of sulphur electrode capacity (fig. 1b). The cycle life of lithium-sulphur cells is practically linearly increasing with increasing of amount of electrolyte.


1. 1. Y.V. Mikhaylik and J.R. Akridge, J. Electrochem. Soc., 2004, 151(11), A1969-A1976.

2. M.-Y. Chu, U.S. Patent, US 6,376,123 B1 (2002).