As one of the next-generation rechargeable battery technologies beyond the lithium-ion chemistry, the lithium-sulfur chemistry enables the low-cost sulfur cathode to generate a high theoretical capacity of 1,675 mAh g^-1 (10 times higher capacity than those of lithium-ion battery cathode). It further exhibits a high theoretical energy density of 2,600 Wh kg^-1 in lithium-sulfur batteries (2–3 times higher energy density than lithium-ion batteries). However, as reported in recent publications, the development is far from adequate with respect to the high-loading sulfur cathode with high active-material content in building advanced lithium-sulfur batteries with a high energy density. The material challenges result from the use of an insulating sulfur as the active material, which would generate lithium polysulfides that can easily diffuse out from the cathode. The high cathode resistance and fast loss of the active material lead to the poor electrochemical utilization and efficiency of lithium-sulfur battery cathodes. These negative impacts subsequent derive the additional electrochemical challenges. A high amount of conductive and porous substrates is added in the cathode to replace the active material, which results in the limited amount of sulfur in the cathode and further blocks the improvement of designing high-energy-density sulfur cathodes.

To address the above-mentioned issues, the research progresses of high-performance sulfur cathodes aim to design functional host for sulfur cathodes with the use of carbon for high conductivity, polymers for high ionic transfer, porous materials for physical polysulfide retention, polar materials for chemical polysulfide adsorption, catalysts for high reaction kinetics, etc. However, metallic materials that naturally have high conductivity, strong polysulfide adsorption capability, and catalytic conversion ability, are rarely reported. This is because metals have the highest density as compared to the aforementioned host materials, which commonly causes an insufficient amount of active material in the cathode and therefore inhibits the design of metal-sulfur nanocomposite in sulfur cathodes.

To explore the metal/sulfur nanocomposite as a new research trend in sulfur cathodes, we propose a design for a nickel/sulfur nanocomposite as a novel energy-storage material by the electroless nickel plating method, and discuss its applications in lithium–sulfur battery cathodes. The nickel/sulfur energy-storage material possesses metallic nickel on the surface of the insulating sulfur particles as a result of the reduction of nickel ions during autocatalytic plating. By controlling the synthesis and fabrications conditions, the nickel/sulfur energy-storage material attains adjustable high sulfur contents of 60–95 wt% and adjustable high sulfur loadings of 2–10 mg cm⁻² in the resulting cathode. The high-loading cathode with the nickel/sulfur energy-storage material demonstrates high electrochemical utilization and stability, which attains a high areal capacity of 8.2 mA∙h cm⁻², an energy density of 17.3 mW∙h cm⁻², and a stable cyclability for 100 cycles.

Results and Discussion

Here, in our presentation, we discuss our novel method for the fabrication of nickel/sulfur energy-storage material as an advanced composite cathode material for exploring battery electrochemistry and battery engineering. We adopt a modified electroless-plating method to synthesize nickel/sulfur energy-storage materials characterized by adjustable high sulfur contents and promising cathode performance. The plated nickel coating provides the nickel/sulfur energy-storage materials with metallic conductivity and polysulfide adsorption ability, which addresses the two major issues of sulfur cathodes.^[1,2] Therefore, the nickel/sulfur energy-storage material attains high sulfur contents in the cathode and exhibits a high charge-storage capacity of 1,362 mA∙h g⁻¹ and an excellent cyclability for 100 cycles. Moreover, the nickel/sulfur energy-storage material enables high-loading sulfur cathodes with a sulfur loading of 10 mg cm⁻², a high areal capacity of 8.2 mA∙h cm⁻², and an energy density of 17.3 mW∙h cm⁻².

Conclusion

In summary, the summary of our nickel/sulfur energy-storage materials presented in this presentation would demonstrate a light-weight metallic nickel coating technique for fast charge transfer and strong polysulfide retention in the sulfur nanocomposites composite sulfur cathode. Moreover, our systematic analysis of the nickel/sulfur energy-storage materials exhibits their achievements in attaining both high electrochemical designs of high sulfur content and loading as well as possessing high energy density and electrochemical stability.

References

1. C.-S. Cheng, S.-H. Chung, Chem. Eng. J. 2022, 429, 132257.
2. C.-S. Cheng, S.-H. Chung, Batter. Supercaps 2022, 5, e202100323.