Recently, sodium-ion batteries have been intensively studied as an alternative to lithium-ion batteries because of the abundance of sodium and its ability, for example, to answer to smart grid energy storage applications. Among all anode materials, carbonaceous materials have shown promising results, particularly hard carbons owing to their high capacity and low insertion voltage (vs. Na + /Na). However, these materials often suffer from their high cost and low initial coulombic efficiency. In this paper, we investigate an easy route of hard carbon synthesis from low-cost pitch precursor. A pre-treatment under a controlled atmosphere can hinder the graphitization of the pitch upon pyrolysis and induce an amorphous-like microstructure with high

The demand for efficient and cheap electrochemical storage devices is very high today. Naion batteries are emerging as a promising alternative to Li-ion batteries for large-scale applications, due to the much larger abundance of sodium. Among the different negative electrode materials allowing Na insertion at low potentials, hard carbons are the materials with the best electrochemical performances reported so far. Here we investigate the synthesis of hard carbons from tannins, an abundant and cheap bio-sourced carbon precursor made of polyphenolic molecules. We show that by a well-controlled synthesis method and hightemperature pyrolysis (1600°C), a hard carbon with developed ultra-microporosity is obtained. This hard carbon delivers a reversible capacity of 306 mAh g -1 at C/20 with a firstcycle coulombic efficiency of 87 %. To our knowledge, these electrochemical performances are among the best ever reported in the literature for biomass-derived hard carbons.

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