Two-Dimensional MoS2 Nanosheets Derived from Cathodic Exfoliation for Lithium Storage Applications

Abstract

The preparation of 2H-phase MoS2 thin nanosheets by electrochemical delamination remains a challenge, despite numerous efforts in this direction. In this work, by choosing appropriate intercalating cations for cathodic delamination, the insertion process was facilitated, leading to a higher degree of exfoliation while maintaining the original 2H-phase of the starting bulk MoS2 material. Specifically, trimethylalkylammonium cations were tested as electrolytes, outperforming their bulkier tetraalkylammonium counterparts, which have been the focus of past studies. The performance of novel electrochemically derived 2H-phase MoS2 nanosheets as electrode material for electrochemical energy storage in lithium-ion batteries was investigated. The lower thickness and thus higher flexibility of cathodically exfoliated MoS2 promoted better electrochemical performance compared to liquid-phase and ultrasonically assisted exfoliated MoS2, both in terms of capacity (447 vs. 371 mA·h·g−1 at 0.2 A·g−1) and rate capability (30% vs. 8% capacity retained when the current density was increased from 0.2 A·g−1 to 5 A·g−1), as well as cycle life (44% vs. 17% capacity retention at 0.2 A·g−1 after 580 cycles). Overall, the present work provides a convenient route for obtaining MoS2 thin nanosheets for their advantageous use as anode material for lithium storage.