Preparation of renewable lignin-derived nitrogen-doped carbon nanospheres as anodes for lithium-ion batteries

Abstract

For the common concern that general lignin-based colloidal spheres suffer the weakness of spherical structure destruction during the pyrolysis process, novel uniform lignin-derived nitrogen-doped carbon nanospheres were prepared by direct pyrolysis of lignin-based azo polymer (AL-azo-NO₂) colloidal spheres at 750 °C. In addition, a kind of hard carbon with high graphitization degree was also prepared as a control by direct pyrolysis of alkali lignin (AL). The morphology and structure of the as-obtained carbon materials were investigated by field emission scanning electron microscopy, X-ray diffraction patterns, Raman spectra and elemental analysis. They served as anodes in lithium-ion batteries with the aim to investigate the electrochemical performance. These two kinds of lignin-derived carbon materials exhibited different electrochemical performances due to their various structures and functional groups. The nitrogen-doped carbon nanospheres (C_SAN-750) exhibited a high cyclic stable capacity up to 225 mA h g⁻¹ at a current density of 60 mA g⁻¹ after 50 cycles (C_AL-750, 120 mA h g⁻¹) coupled with high first coulombic efficiency up to 66.4% for C_SAN-3000 with a cyclic capacity of 200 mA h g⁻¹, which is more comparable to that of the C_AL-3000 (53.3%, 199 mA h g⁻¹). This research indicates the great promise of lignin applied in producing hard carbon materials and further energy storage systems.