New Sulfur-CNF-composites to Boost Performance of Lithium Sulfur Batteries

TAGS:  Nanotechnologies     New Energy Solutions    

The researchers from Toyohashi University of Technology have found that cathode composites made by combining a sulfur active material and carbon nanofiber (CNF) developed using an electrostatic assembly method shows high discharge capacity equivalent to the theoretical capacity of sulfur and maintained high capacity after repeated charge-discharge cycles.

All-solid-state lithium sulfur batteries using sulfur-CNF composites and electrochemically stable Li₂S-P₂S₅-LiI solid electrolytes synthesized by liquid phase process showed better results.

Low-cost Sulfur-carbon Composite

It is required that a sulfur active material and a carbon material are appropriately combined for making high-performance all-solid-state lithium sulfur batteries.

Conventionally, sulfur-carbon composites were synthesized by mechanical mixing, liquid mixing using a special organic solvent and complicated methods, in which sulfur is combined with a porous carbon material with a high specific surface area.

However, there were few reports that all-solid-state lithium sulfur batteries showed high capacity almost equivalent to the theoretical capacity of sulfur and high cycle stability.

Therefore, researchers focused on making a sulfur-carbon composite using a low-cost and simple electrostatic adsorption method which can uniformly combine nanomaterials. It was confirmed that sulfur at the sulfur-carbon composite synthesized by electrostatic adsorption method was accumulated on carbon nanofiber in the form of sheets.

Besides, researchers constructed all-solid-state lithium sulfur batteries and found that sulfur was fully utilized as an active material. The other merit is that this sulfur-carbon composite can be produced by lower cost than conventional processes.

Electrostatic Adsorption Method

In the electrostatic adsorption method, larger mother particles and smaller particles are electrostatically adsorbed by adjusting surface charges of the particles using polyelectrolytes in order to induce an electrostatic interaction. Although design of a variety of ceramic composites by the electrostatic adsorption were already reported, the adjustment of the surface charges of sulfur is difficult. However, our research group succeeded in the charge adjustment by using chemical reactions, in which Na₂S and S reacted in ion-exchanged water to form aqueous soluble Na₂S₃. Therefore, this study achieved a new chemical process by applying the basic principle of electrostatic adsorption.

This method is a low-cost and relatively simple method for preparing sulfur-carbon composites, so it is suitable for mass production. All-solid-state lithium-sulfur batteries using a sulfur active material will be put to practical use by this method. Besides, it is expected the exponential improvement in the energy density of electric vehicles, large-sized power source batteries for household and business use.

Source: Toyohashi University of Technology