Key Takeaways & Executive Findings
- •• N and S co-doped coal-based hard carbon (NSPC1200) was synthesized via two-step carbonization and molten salt template method, achieving high sodium storage capacity of 314.2 mAh g−1 at 20 mA g−1. • Two-step carbonization effectively adjusts carbon microcrystal structure and expands interlayer spacing, enhancing Na+ intercalation. • N and S co-doping regulates electronic structure, providing more active sites for sodium storage. • NaCl template constructs porous structure, improving electrode-electrolyte contact and ion/electron transport, leading to excellent cycling stability (224.4 mAh g−1 after 200 cycles).
Abstract
Hard carbon, known for its abundant resources, stable structure and high safety, has emerged as the most popular anode material for sodium-ion batteries (SIBs). Among various sources, coal-derived hard carbon has attracted extensive attention. In this work, N and S co-doped coal-based carbon material (NSPC1200) was synthesized through a combination of two-step carbonization process and heteroatom doping using long-flame coal as a carbon source, thiourea as a nitrogen and sulfur source, and NaCl as a template. The two-step carbonization process played a crucial role in adjusting the structure of carbon microcrystals and expanding the interlayer spacing. The N and S co-doping regulated the electronic structure of carbon materials, endowing more active sites. Additionally, the introduction of NaCl as a template contributed to the construction of pore structure, which facilitates better contact between electrodes and electrolytes, enabling more efficient transport of Na+ and electrons. Under the synergistic effect, NSPC1200 exhibited exceptional sodium storage capacity, reaching 314.2 mAh g−1 at 20 mA g−1. Furthermore, NSPC1200 demonstrated commendable cycling stability, maintaining a capacity of 224.4 mAh g−1 even after 200 cycles. This work successfully achieves the strategic tuning of the microstructure of coal-based carbon materials, ultimately obtaining hard carbon anode with excellent electrochemical performance.
1. Introduction
Lithium-ion batteries (LIBs) stand as the most widely used secondary batteries in energy storage systems. However, limited resources of Li and its challenging extraction processes have constrained further developments in LIBs. Sodium, on the other hand, is not only abundantly available and inexpensive but also shows similar chemical properties to lithium, making sodium ion batteries (SIBs) stand out as a vital supplement or potential substitute for LIBs in research and industrialization[1–3]. However, the development and application of electrodes in SIBs are in the early stages. Graphite is usually used as the LIBs anode, but it is not suitable for SIBs due to the larger ionic radius of sodium[4–5]. Therefore, finding suitable electrode materials is crucial for the future development of SIBs.
Researchers have explored various anode materials for SIBs, each accompanied by its set of challenges. Common alloying reaction anode materials, such as Na-P[6], Na-Ge[7] and Na-Sb[8], exhibit high specific capacity. However, these materials undergo volume expansion during the intercalation and de-intercalation processes of Na+, resulting in faster specific capacity decay and reduced cycling performance. Carbon materials based on intercalation reaction, such as graphene, hard and soft carbon, are significantly advantageous considering their low cost, high stability and other aspects[9–10]. Therefore, carbon materials continue to be the mainstream choice for anodes in SIBs. Among them, coal and its by-products present a wide range of options and high carbon content, making them promising precursors for hard carbon anodes.
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NIU Hui-zhu, WANG Hai-hua, SUN Li-yu, YANG Chen-rong, WANG Yu, CAO Rui, YANG Cun-guo, WANG Jie, SHU Ke-wei (2025). N, S co-doped coal-based hard carbon prepared by two-step carbonization and a molten salt template method for sodium storage. SinoTechIntel Verified Research. https://doi.org/10.1016/S1872-5805(NCM2024-39-02-08)
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
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Frequently Asked Questions
What is the significance of N and S co-doping in coal-based hard carbon for sodium storage?
N and S co-doping regulates the electronic structure of carbon materials, creating more active sites for sodium ion adsorption and improving the overall electrochemical performance.
How does the two-step carbonization process affect the structure of coal-based hard carbon?
The two-step carbonization process plays a crucial role in adjusting the structure of carbon microcrystals and expanding the interlayer spacing, which facilitates sodium ion intercalation and enhances storage capacity.
What role does NaCl template play in the synthesis of NSPC1200?
NaCl acts as a template to construct a porous structure in the carbon material, which improves electrode-electrolyte contact and enables more efficient transport of Na+ and electrons, contributing to better rate performance and cycling stability.
What are the key electrochemical performance metrics of NSPC1200?
NSPC1200 exhibits a high sodium storage capacity of 314.2 mAh g−1 at a current density of 20 mA g−1 and maintains a capacity of 224.4 mAh g−1 after 200 cycles, demonstrating excellent cycling stability.
Why is coal considered a promising precursor for hard carbon anodes in sodium-ion batteries?
Coal is abundant, low-cost, and has a high carbon content, making it an attractive precursor for hard carbon. The resulting coal-based hard carbon shows stable structure and high safety, which are essential for practical sodium-ion battery applications.
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