Lignin-Derived Mesoporous Carbon for Sodium-Ion Batteries: Block Copolymer Soft Templating and Carbon Microstructure Analysis

The demand for versatile and sustainable energy materials is on the rise, given the importance of developing novel clean technologies for transition to a net zero economy. Here, we present the synthesis, characterization, and application of lignin-derived ordered mesoporous carbons with various pore sizes (from 5 to approximately 50 nm) as anodes in sodium-ion batteries. We have varied the pore size using self-synthesized PEOn-b-PHA(m) block copolymers with different PEO and PHA chain lengths, applying the "soft templating" approach to introduce isolated spherical pores of 20 to 50 nm in diameters. The pore structure was evaluated by transmission electron microscopy (TEM), nitrogen physisorption, and small-angle X-ray scattering (SAXS). We report the microstructure analysis of such mesoporous lignin-based carbons using Raman spectroscopy and wide-angle X-ray scattering (WAXS). In comparison with nontemplated carbon and carbons templated employing commercial Pluronic F-127 and PIB50-b-PEO45, which created accessible channels and spherical pores up to approximately 10 nm in diameter, the carbon microstructure analysis revealed that templating with all applied polymers significantly impedes graphitization upon thermal treatment. Furthermore, the gained knowledge of similar carbon microstructures regardless of the type of template allowed the investigation of the influence of different pore morphologies in carbon applied as an anode material in sodium-ion batteries, supporting the previous theories in the literature that closed pores are beneficial for sodium storage while providing insights into the importance of pore size.