Hardwood Kraft lignin-derived carbon microfibers with enhanced electrochemical performance

It is of great challenge to prepare lignin-derived carbon microfibers with suitable graphite crystallites due to the volatilization of incorporated polymers. In this work, we proposed a simple method for the construction of graphite crystallites based on the regulation of the hydrogen-bonding interaction between hardwood Kraft lignin (HKL) and poly(m-phenylene isophthalamide) (PMIA). The strong hydrogen-bonding interaction demonstrated by the results of TG, FTIR, XPS, Raman and XRD increased the graphite crystal size and perfected the crystal structure of HKL-based carbon microfibers, which further enhanced the electrochemical performance of HKL/PMIA-based carbon microfibers electrodes, especially for the increase of capacitance and cycle performance and the decrease of charge transfer resistance. The specific capacitance, energy density and power density of P2H2-based (HKL/PMIA = 1:1) carbon microfibers electrode were up to 190.8 F g^-1, 34.4 Wh kg^-1 and 540 W kg^-1 at a current density of 0.5 A g^-1, respectively, which were comparable to or even higher than those of lignin composites-based carbon fibers electrodes. This work reveals the relationship between hydrogen-bonding interaction and crystalline structure, which can be further considered in the preparation of lignin-based carbon fibers electrodes.