Study of the electrical conductivity of biobased carbonaceous powder materials under moderate pressure for the application as electrode materials in energy storage technologies

Abstract

This study focusses on the assessment of the electrical conductivity (EC) of biobased electrode materials for the application in energy storage devices and presents a simple and reproducible method to measure the EC of carbonaceous powders under moderate pressure (10–50 N). Based on the pyrolysis of corncob at three different temperatures (600, 800, and 900°C) and further treatments of the biochar obtained at 600°C, 11 different carbonaceous powder materials were produced including biochars, activated carbons, and composites. Composite materials were obtained by adding either metal oxide (RuO 2 or Fe 3 O 4 ) in different proportions or additives which are commonly used in electrode production (5 wt% binder and 15 wt% conductive additive). Furthermore, one physically activated commercial AC based on peat with a known EC of 33 S/m was treated with additives and used as a reference. For all materials, an increase of applied pressure resulted in higher EC values due to closer particle contact. The comparison of two methods (with and without preload) showed that a prepelletization of the samples is not necessary to obtain reliable results. By analyzing the obtained EC values while taking mechanical and physicochemical properties into account, it could be shown that a high carbonization temperature and high specific surface area favor the increase of EC. Furthermore, certain proportions of metal oxides lead to an improvement of EC (40 wt% RuO 2 , 10 wt% Fe 3 O 4 ), while the treatment with additives leads to a decrease of EC. The EC values among all samples varied between 0.8 S/m (biochar) and 408 S/m (AC/RuO 2 composite) at the highest pressure level (637 kPa). Thus, promising biobased electrode materials for environmentally friendly energy storage technologies are presented with the aim of contributing to the establishment of a biobased resource and product platform for bioeconomy.