An Aqueous Electrolyte Rechargeable Li-Ion/Polysulfide Battery

Technological and societal demands for higher capacity energy storage as well as cost effective options provide impetus for the exploration of alternate electrochemical energy storage systems. Over the past 20 years, lithium ion batteries (LIBs) played a crucial role in the development of such energy storage technologies. Although great improvements have been accomplished, and while active research for further developments continues, current lithium-ion technologies provide a limited gravimetric energy density.  

More drastic approaches can be accomplished by the earth abundant sulfur to reach high energy and low cost battery system. For instance, non-aqueous lithium-sulfur (Li-S) batteries offer a five-fold increase in energy density compared with present Li-ion technologies^1,2. Li-S battery configuration represents a valuable option as it can provide low equivalent weight, high capacity (1672 mAh/g), low cost and environmentally benign factors. All these characteristics cannot be accomplished with current Li-ion technology. However, the Li-S battery technology faces several drawbacks leading to a poor cycle life which prevents its practical realization until recently. Besides the insulating nature of sulfur which necessities to have a close contact with conductive matrix, namely porous carbon, another big challenge in Li-S batteries is the formation of non-soluble and insulating least sulfur reduction specie (Li₂S). Upon several cycling, Li₂S precipitates on the composite matrix as nonconductive slabs resulting poor electrical contact^3,4. Recently, dissolved polysulfide (so called catholyte) rather than sulfur impregnated composites has been used to further eliminate the formation of Li₂S within the porous structure and leads to superior performance to the conventional Li–S cell³. Even though such an improvement holds great promises, the SEI layer formed on Li and the resulting effects are not fully understood. Thus, to find an environmental and economic manner for a high rate energy storage devices are still challenging issues. In this respect, we propose to use an aqueous electrolyte rechargeable polysulfide battery system in combination with the commercial lithium battery electrode materials whose performances in aqueous media are already known for a long time⁵.  

The redox reaction of aqueous polysulfide is different from the organic electrolyte and forms HS^- which is soluble in water and can be reversibly cycled (Eq. 1). The high capacity and rates are the result of the anomalously high solubility of polysulfide salts in water contrary to non-aqueous electrolytes in which Li₂S are not soluble.

S + H₂O + 2e^- ↔ HS^- + OH^-  E_o= -0.51 V vs SHE           (Eq. 1)

The use of aqueous polysulfide electrolytes were suggested by Licth et al^6,7 and co-workers more than 20 years ago either in batteries or in photoelectrochemical solar cells. Since then the topic was almost not touched until a very recent patent filed by Visco et al⁸providing the use of aqueous electrolyte Li-S batteries which requires using a high cost Li-ion conductive glass membrane as Li anode protective layer.

Therefore, herein, we will show to use of Li-ion/polysulfide cell configuration targeting to eliminate the expensive membrane for a cheap, sustainable and high power storage device. A survey of different electrolyte additives able to trigger polysulfide chemical reactions in aqueous electrolyte will be presented together with the different Li-ion cathode performances leading to a full cell configuration. A comparative study with a classical Li-S battery system will be discussed. The common fast capacity decay phenomenon in a classical Li-S cell was not observed with such Li-ion/polysulfide system resulting superior cycling performances over 100 cycles (Fig. 1). Then, those findings applied to a redox flow battery configuration to achieve higher capacities and cheaper options to the current high temperature (300-350 ^oC) Na/S, vanadium flow or soluble lead acid flow batteries.

 

References

1- Ji, Lee, Nazar, Nature Materials, 8, 2009, 500

2- Demir-Cakan, Morcrette, Nouar, Davoisne, Devic, Gonbeau, Dominko, Serre, Ferey, Tarascon, JACS, 2011, 133, 16154

3- Demir-Cakan, Morcrette, Gangulibabu, Guéguen, Dedryvère, Tarascon, 2013, Energy Environ. Sci., 6, 176

4- Demir-Cakan, Morcrette, Tarascon, submitted

5- Li, McKinnon, Dahn, J. Electrochem. Soc. 1994, 141, 2310

6- Peramunage, Licht, Science, 1993, 261, 1029

7- Licht, Hodes, Manassen, Inorg. Chem. 1986, 25, 2486

8- Visco et al, US Patent, US 2013/0122334