Efficient utilization of lignin heterogeneity: Employing a simple approach to modulate the structure-effect relationship of lignin microspheres for its high-quality applications in supercapacitors

Abstract

Lignin, an abundant, sustainable, and cost-effective biomass material, is recognized for its high carbon content, making it an ideal candidate for supercapacitors electrode. However, the inhomogeneity of lignin and the amorphous structure of lignin-derived carbon limit its application in energy storage. To effectively address the aforementioned issues, this study initially fractionated alkali lignin (AL) using a green γ-valerolactone/water system to obtain two fractions (L1 and L2) with distinct molecular weights and phenolic hydroxyl contents. The aim of this initiative was to reduce the heterogeneity of the lignin. Subsequently, three groups of lignin microspheres (LMS-AL, LMS-L1 and LMS-L2) with different morphologies were prepared from AL, L1, and L2 using an industrially proven spray-drying technique. This initiative significantly increased the specific surface area of lignin. Ultimately, lignin microspheres were carbonized to prepare carbon microspheres (LMSC-AL, LMSC-L1 and LMSC-L2) that could be used as supercapacitor electrodes. Notably, LMSC-L1 demonstrated superior electrochemical performance, with a specific capacitance of 200 F g−1 at a current density of 1 A g−1, and retaining 93.34 % capacitance after 15,000 charge/discharge cycles. The excellent electrochemical performance of LMSC-L1 is attributed to its elevated specific surface area (388.1 m2 g−1) and substantial porosity (0.238 cm3 g−1). This study also explored practical application, with LMSC-L1 successfully powering LED lights and calculators. Through this research, we have developed a simple method is proposed to modulate the structure of lignin microspheres by leveraging the heterogeneity of lignin itself. Furthermore, we systematically investigated the structure-effect relationship of lignin microspheres and the electrochemical properties of their carbonized microspheres. This work lays a foundational framework for the efficient utilization of lignin in energy storge applications.