MoS2—Carbon Materials Composite with Dual Phase of MoS2 and Their Application for Energy Storage System

Graphite and graphene are known to be very good anode materials for lithium ion batteries due to their excellent stability, but have a low theoretical capacity of 372 mAh/g.¹ Electric vehicles and various electronic devices require a battery with a higher capacity than the current capacity, and it is essential to develop an anode material with a higher capacity.² Therefore, anode materials using Si are in the spotlight, but Si has a higher capacity (~4200mAh/g) than conventional graphite materials, but there is a problem of volume expansion when the cycle is performed, so it has a bottleneck in terms of stability.³<br/>Transition metal dichalgogenides (TMD) materials are attracting a lot of attention because of their structural properties, excellent stability, low cost and high storage capacity.⁴ The theoretical capacity of MoS₂, one of the TMD materials, is known to be 670 mAh/g, making it a promising material for a new LIB anode material.⁵ In particular, it is very advantageous to make a single layer of MoS₂ because their layered structure is combined with a weak van der walls force.⁶ It is typically known to have 1T and 2H structures. The 1T phase of MoS₂ has the properties of a conductor and therefore has excellent conductivity as a LIB anode material. 1T structures can be produced when a single layer is made through exfoliation. However, due to its metastable structure, it is easily converted to the 2H phase as the most stable phase.⁷<br/>In this study, a composite of MoS₂ and graphene was prepared by a chemical exfoliation method, and through this, a stable and high-capacity anode material was realized using the high energy storage capacity of MoS₂ and the stability of graphene. In addition, a mixed phase of 1T and 2H structures was generated through the post-treatment process, and it was confirmed that the 1T phase was stably present. Through this, the diffusion of Li⁺ was facilitated by securing wide interface spacing and high conductivity of the 1T structure, and as a result, superior conductivity and high capacity were stably maintained compared to the single-phase material of the 2H structure.<br/><br/>(1) Nishi, Y. Lithium Ion Secondary Batteries; Past 10 Years and the Future. <i>J. Power Sources</i> <b>2001</b>, <i>100</i> (1–2), 101–106.<br/>(2) Armand M., Tarascon -M. J. Building better batteries. <i>Nature</i> <b>2008</b>, <i>451</i>, 652-657.<br/>(3) Casimir, A.; Zhang, H.; Ogoke, O.; Amine, J. C.; Lu, J.; Wu, G. Silicon-Based Anodes for Lithium-Ion Batteries: Effectiveness of Materials Synthesis and Electrode Preparation. <i>Nano Energy</i> <b>2016</b>, <i>27</i>, 359–376.<br/>(4) Choi, W.; Choudhary, N.; Han, G. H.; Park, J.; Akinwande, D.; Lee, Y. H. Recent Development of Two-Dimensional Transition Metal Dichalcogenides and Their Applications. <i>Mater. Today</i> <b>2017</b>, <i>20</i> (3), 116–130.<br/>(5) Stephenson, T.; Li, Z.; Olsen, B.; Mitlin, D. Lithium Ion Battery Applications of Molybdenum Disulfide (MoS2) Nanocomposites. <i>Energy Environ. Sci.</i> <b>2014</b>, <i>7</i> (1), 209–231.<br/>(6) Li, H.; Wu, J. Bin; Ran, F.; Lin, M. L.; Liu, X. L.; Zhao, Y.; Lu, X.; Xiong, Q.; Zhang, J.; Huang, W.; et al. Interfacial Interactions in van Der Waals Heterostructures of MoS2 and Graphene. <i>ACS Nano</i> <b>2017</b>, <i>11</i> (11), 11714–11723.<br/>(7) Lei, Z.; Zhan, J.; Tang, L.; Zhang, Y.; Wang, Y. Recent Development of Metallic (1T) Phase of Molybdenum Disulfide for Energy Conversion and Storage. <i>Adv. Energy Mater.</i> <b>2018</b>, <i>8</i> (19), 1–29.