The development of functional carbon materials using waste biomass as raw materials is one of the research hotspots of lithium-sulfur batteries in recent years. In this work, used a natural high-quality carbon source—coffee grounds, which contain more than 58% carbon and less than 1% ash. Honeycomb-like S and N dual-doped graded porous carbon (SNHPC) was successfully prepared by hydrothermal carbonization and chemical activation, and the amount of thiourea used in the activation process was investigated. The prepared SNHPC showed excellent electrochemical energy storage characteristics. For example, SNHPC-2 has a large pore volume (1.85 cm3·g− 1), a high mesoporous ratio (36.76%), and a synergistic effect (S, N interaction). As the cathode material of lithium-sulfur batteries, SNHPC-2/S (sulfur content is 71.61%) has the highest specific capacity. Its initial discharge-specific capacity at 0.2 C is 1106.7 mAh·g−1, and its discharge-specific capacity after 200 cycles is still as high as 636.5 mAh·g−1.

Coffee grounds derived sulfur and nitrogen dual-doped porous carbon for the cathode material of lithium-sulfur batteries
    Abstract
    1 Introduction
    2 Experiment
        2.1 Synthesis of carbon materials
        2.2 Preparation of sulfur-carbon composites
        2.3 Characterization
            2.3.1 Physical characterization
            2.3.2 Electrochemical characterization
    3 Results and discussion
        3.1 Physicochemical characterization of the HPC, SNHPC-n, HPCS, and SNHPC-nS
        3.2 Electrochemical performance of the HPCS and SNHPC-nS
    4 Conclusion
    Acknowledgements 
    References

• Yating Wen(School of Chemical Engineering, Zhengzhou University, Zhengzhou 450001, China)
• Xiaobin Wang(School of Chemical Engineering, Zhengzhou University, Zhengzhou 450001, China)
• Jingyi Huang(School of Chemical Engineering, Zhengzhou University, Zhengzhou 450001, China)
• Yu Li(School of Chemical Engineering, Zhengzhou University, Zhengzhou 450001, China)
• Tao Li(School of Chemical Engineering, Zhengzhou University, Zhengzhou 450001, China)
• Baozeng Ren(School of Chemical Engineering, Zhengzhou University, Zhengzhou 450001, China)