Sustainable and scalable fabrication of high-performance hard carbon anode for Na-ion battery

Sustainable and green manufacturing of hard carbon (HC) material in a low-cost way is the key issue in promoting its industrial applications in Na-ion batteries (SIB). Nowadays, most synthesis ways to prepare HC need the help of chemical reagents to improve its Na-ion storage performance. Herein, we firstly developed a completely green biological fermentation technology to prepare HCs on a large scale using cheap and renewable carbon sources of various biomass starch. Pre-treatment by bio-fermentation can effectively modify the carbon precursor for facile pyrolysis to fabricate starch-based HCs, and make its internal microstructure with larger interlayer spacing, more disordered structure and abundant closed micropores. Finally, a case of cornstarch based hard carbon exhibits a high reversible capacity of 335 mA h g-1 at a current density of 30 mA h g-1 and high rate performance with a reversible capacity of 140.6 mA h g-1 even at a high current of 5 A g-1 as well as long cycling stability. In-situ Raman spectra, ex-situ SAXS and ex-situ XPS tests during discharge and charge process reveal the pore filling mechanism of quasi-metallic Na in hard carbon anode. Such a "bread-making" strategy is a facile and scalable route to fabricate various starch-based hard carbons with improved performance, demonstrating a very practically promising application for industrial manufacture.