Pyrolytic carbons derived from peanut shells and sunflower husk for Lithium Sulfur Batteries

MARÍA LAURA PARA; MARÍA LUZ NIEVA; MARÍA DEL CARMEN ROJAS; ELIZABETH LAURA MOYANO; DANIEL BARRACO; GUILLERMINA LUQUE

Bologna

Congreso; 69th ANNUAL MEETING OF THE INTERNATIONAL SOCIETY OF ELECTROCHEMISTRY; 2018

The Li-S battery technology offers a higher capacity than Li-ion batteries, however, it has some drawbacks such as volume change during cycling and incomplete reduction of S to Li2S, forming polysulphides (PS) known as shuttle effect, which lead to a decrease in coulombic efficiency, in addition to the low conductivity of S. To solve some of these problems, biocarbons obtained from peanut shell and sunflower seed were used as cathodes for Li-S batteries. This novel use of biomaterials adds an important value to the waste of the agricultural industry.The aim of this work is to use pyrolyzed biocarbons as active material for Li-S cathodes, taking advantage of its porous structure, to control the volume change and the shuttle effect. Additionally, two different treatments were tested to improve these active materials.The biocarbons were obtained by means of a pyrolysis of biomaterials in an inert atmosphere, and then were impregnated with sulfur to obtain the active material of the cathodes. Two protocols, acid and basic, were tested to generate different functional groups on the surface and different porous structure. The active materials were characterized with X-ray photoelectron spectroscopy (XPS), adsorption isotherms, thermogravimetric (TGA), adsorption isotherms (BET) and scanning electron microscopy (SEM). The modified biocarbons impregnated with sulfur were mixed with PVDF and carbon Super P in NMP to make slurries that are deposited on aluminum foils to obtain the cathodes. These materials were tested in coin cells, using LiTFSI 1M, LiNO3 0.25 M in 1,2-dimethoxyethane(DME)/1,3-dioxolane (DOL) 1:1 as electrolyte. Electrochemical studies like cycling performance and its potentiodynamic response were analyzed to evaluate the cells behavior.Cells made with these biocarbons have high efficiency and capacity that remains stable throughout 100 charge-discharge cycles. Additionally, the initial specific capacity of discharge is in the order of 800 mA h g-1 for C/16. It was demonstrated that the basic treatment was the one that generated the active material with the best electrochemical response for this type of batteries in both biomasses.