Carbonization of polysaccharides in FeCl3/BmimCl ionic liquids: Breaking the capacity barrier of carbon negative electrodes in lithium ion batteries

International audiencePolysaccharide-derived carbonaceous materials were prepared using an ionothermal carbonization approach in iron-containing ionic liquids (i.e. mixtures of 1-butyl-3-methylimidazolium chloride, BmimCl, and iron(III) chloride, FeCl3). The as-prepared ionochars were subsequently pyrolyzed to yield carbon materials. These carbons were thoroughly characterized and investigated as negative electrodes for Li-ion batteries. The use of four polysaccharides (i.e. starch, chitosan, pectin and alginic acid) and three different FeCl3/BmimCl ratios allowed obtaining a set of porous carbons with different textural properties (specific surface area and pore volume) and nitrogen contents. Besides, the amount of residual iron within the carbonaceous framework was adjusted through a washing step before pyrolysis, which provided an additional control over the degree of graphitization. The best electrochemical performance in battery was obtained for the carbons prepared from chitosan (i.e., the carbon displaying the highest nitrogen content) and pre-treated in the ionic liquid with the lowest FeCl3/BmimCl ratio (i.e., 0.5, which yielded carbons with higher pore volumes). This work further highlights the versatility offered by the ionothermal approach towards textural, structural and electrochemical properties of the as-prepared carbon materials