Understanding on the Reaction Pathway for Lithium Storage Behavior in Molybdenum Sulfides with Different Sulfur Configuration
Authors: Lee Youn-Ki 
Published: December 2024

Molybdenum disulfide (MoS2) has been considered as promising electrode materials in lithium-ion batteries (LIBs) due to its high theoretical capacity through conversion reactions (MoS2 + 4Li+ + 4e− ↔ Mo + 2Li2S) [1,2]. It is well-known that MoS2 electrode exhibits the intercalation of lithium-ions (167 mAh/g) between layers and the formation of lithium sulfide (669 and 1675 mAh/g) via conversion reaction. Considering these electrochemical reactions, it is speculated that the main capacity in MoS2 electrode originated from lithium sulfide (Li2S) reaction. Thus, research on molybdenum sulfides with higher S (sulfur) content, such as MoSx (2<x<3), MoS3, and MoS4, has been conducted for the development of electrodes with higher capacity [3,4]. Additionally, carbon-based materials are been utilized to overcome the low electrical conductivity and unstable conversion reactions of molybdenum sulfides [5]. However, understanding the precise electrochemical mechanisms of S-rich molybdenum sulfides has challenging due to complex S ligands. Hence, there is a need for a comprehensive understanding of the electrochemical reactions of molybdenum sulfides with various S ligands.
In this study, we demonstrate that the electrochemical reaction pathways of molybdenum sulfides are influenced by different S content and configuration. First, we prepared three-molybdenum sulfides (MoS2, MoS3, and [Mo3S13]2-). From the potentiostatic and galvanostatic measurements, the redox reactions of molybdenum sulfides were distinctly observed in terms of S configuration. Depth X-ray photoelectron spectroscopy (XPS) analysis was performed to elucidate the chemical and structural changes in molybdenum sulfides during the transition reactions. Through these analyses, we confirmed that the activation energy of the redox reaction is significantly influenced by the S ligands, indicating that S-rich molybdenum sulfides have the potential to be applied in both anode and cathode roles within lithium storage systems. Furthermore, we addressed the drawbacks of molybdenum sulfides, such as low electrical conductivity and irreversible reactions, by incorporating carbon composites. Utilizing carbon-molybdenum sulfide composites as both anode and cathode materials exhibited capacities of 962 and 406 mAh/g, respectively, at a current density of 0.1 A/g, along with improved rate-capability and stable lifespan. Therefore, we believe that the analysis of lithium storage mechanisms in molybdenum sulfides and the synthesis of carbon composites will greatly contribute to the development of electrode materials for future batteries.
References
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[2] Wang T, Chen S, Pang H, Xue H, Yu Y. MoS2-Based Nanocomposites for Electrochemical Energy Storage. Adv Sci., 4, 1600289 (2017).
[3] Wang J, Ng SH, Chew SY, Wexler D, Wang GX, Liu HK. Characterization of Nanosize Molybdenum Trisulfide for Lithium Batteries and MoS3 Structure Confirmation via Electrochemistry. Electrochem Solid-State Lett., 10, A204 (2007).
[4] Truong QD, Yin L-C, Hung NT, et al. Anionic redox in a-(Mo3S11)n polymer cathode for all-solid-state Li-ion battery. Electrochim Acta., 332, 135218 (2020).
[5] Li Z, Ottmann A, Sun Q, et al. Hierarchical MoS2–carbon porous nanorods towards atomic interfacial engineering for high-performance lithium storage. J Mater Chem A., 7, 7553 (2019).
Acknowledgement
This research was supported by a grant from the Korea Institue of Machinery and Materials (KIMM) Government-funded Research Program (NK249G).