Hard carbon's excellent performance and affordability made it an ideal anode material for sodium-ion batteries. However, hard carbons derived directly from lignin often exhibit poor performance. Optimizing the synthesis process presents a valuable strategy for enhancing performance. In this study, we optimize the synthesis process to minimize costs while integrating green chemistry principles to mitigate environmental impact. Sodium lignosulfonate-formaldehyde resin-derived hard carbon is produced using a simple, low-cost pyrolysis technique involving multiple temperature stages. This process enhances the material's structural stability and electrochemical performance. X-ray diffraction (XRD) and Raman spectroscopy analysis show that higher pyrolysis temperatures lead to a distinct peak, which improves electronic conductivity. In contrast, lower temperatures result in chaotic structural formations. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) image analyses reveal that the resulting material has a porous structure with unique chemical properties. Tested for 200 cycles at a current density of 50 mA g− 1, the materials exhibited specific capacities of 332.24 mAh g− 1, 180.3 mAh g− 1, and 105.6 mAh g− 1, respectively, for LSHC-1400, LSHC-1200, and LSHC-1000. The promising results can be attributed to the unique porous structure and inherent chemical properties of the lignosulfonate precursor, which enhance the transport and storage of sodium ions. This study highlights the critical role of the synthesis method in determining the sodium storage capacity of the carbon anode in sodium-ion batteries, encouraging further exploration and optimization in this area.

Hard carbon anode from sodium lignosulfonate-formaldehyde resin for sodium-ion batteries
    Abstract
    1 Introduction
    2 Experimental section
        2.1 Chemicals and materials
        2.2 Synthesis of lignin-derived hard carbon
        2.3 Materials characterization
        2.4 Electrochemical measurements
    3 Results and discussion
    4 Conclusion
    Acknowledgements 
    References

• Jianyuan Yu(Key Laboratory of Bio‑based Material Science & Technology (Northeast Forestry University), Ministry of Education, Harbin 150040, People’s Republic of China)
• Yanli Ma(Key Laboratory of Bio‑based Material Science & Technology (Northeast Forestry University), Ministry of Education, Harbin 150040, People’s Republic of China)
• Haibo Huang(Key Laboratory of Bio‑based Material Science & Technology (Northeast Forestry University), Ministry of Education, Harbin 150040, People’s Republic of China, College of Materials Science and Engineering, Northeast Forestry University, Harbin 150040, China)
• Ismaila EL Moctar(Key Laboratory of Bio‑based Material Science & Technology (Northeast Forestry University), Ministry of Education, Harbin 150040, People’s Republic of China, College of Materials Science and Engineering, Northeast Forestry University, Harbin 150040, China)
• Shujun Li(Key Laboratory of Bio‑based Material Science & Technology (Northeast Forestry University), Ministry of Education, Harbin 150040, People’s Republic of China, College of Materials Science and Engineering, Northeast Forestry University, Harbin 150040, China) Corresponding author
• Moussa Diawara(Laboratoire de Centre de Calcul de Modélisation et de Simulation (CCMS), DER de Physique de la Faculté des Sciences et Techniques (FST), Université des Sciences des Techniques et des Technologies de Bamako (USTTB), Bamako, Mali)
• Mahamadou Seydou(Université de Paris, ITODYS, CNRS, UMR 7086, 15 rue J‑A de Baïf, 75013 Paris, France)