Carbon materials with controlled porosity for sodium-ion batteries – CARAMBAR

The CARAMBAR project aims to elaborate hard carbons for the preparation of negative electrodes for sodium-ion batteries. Hard carbons are extensively studied for this application: they are disordered materials, simply obtained by available precursors such as sugars, some polymers or biomass. Their structure allows a sorption of sodium which is well adapted for battery running, even if precise interactions mechanisms between sodium ions and hard carbons are still controversial. In order to get a high capacity and a good cyclability, hard carbone have to exhibit both a low specific surface area, and an important proportion of closed porosity. These features are obtained after high temperature treatments (around 1500°C), which implies a high energetic cost. The CARAMBAR project proposes an alternative to these high temperature treatments thanks to the elaboration of hard carbons by pressurized pyrolysis, pressure being an experimental parameter which is rarely studied in the literature. Our first results show that even at moderate temperatures, an increase of pressure of only a few bars allows a drastic decrease of the specific surface area, and the closure of some pores. The electrochemical behavior is then improved. The CARAMBAR project is then focused on a deeper exploration of this promising elaboration route, through a multi-scale characterization of the as-obtained hard carbons, and a careful electrochemical study based on several techniques. For this last point, a post-doctoral researcher will join the project team which is more specialized in the carbon science. The goals of this project are a deep understanding of the mechanisms operating during the pressurized pyrolysis, as well as a thorough study of the interactions between sodium and hard carbons. This will lead to the elaboration of high-performance hard carbons with a lower energetic cost.