Pre-oxidation of Lignin Precursors for Hard Carbon Anode with Boosted Lithium-Ion Storage Capacity

Lignin-derived hard carbon (HC) has great potential as energy storage materials. However, it is difficult to obtain desired electrochemical performances by direct carbonization of lignin. Herein, we demonstrate a pre-oxidation strategy to enhance the reversible capacity of hard carbon with lignin as precursor. The pre-oxidation mechanism and its influence on the microstructures of the resulted hard carbon are systematically studied. Based on in-situ FT-IR and C-13 NMR spectrum, etc., it is confirmed that three dominant configurations of oxygen-containing functional groups are formed during the process, and the content of the desired carbonyl groups (C=O) reaches a maximum value at a pre-oxidation temperature of 200 degrees C. Meanwhile, the alkyl groups are transformed into peroxides or alcohols, contributing to intermolecular cross-linkage within lignin. As a result, the obtained material with highly random orientation nanotexture gives a much larger d(002) and abundant porous structure. Benefiting from these structural merits, the optimized lignin-derived hard carbon enables excellent Li-ion storage performance with a reversible capacity of 584 mA h g(-1) at 50 mA g(-1). This work provides insights into the rational design of high-performance hard carbon anodes for Li-ion batteries and beyond. (C) 2021 Elsevier Ltd. All rights reserved.