Potassium Ion-Assisted Self-Assembled MXene-K-CNT Composite as High-Quality Sulfur-Loaded Hosts for Lithium-Sulfur Batteries.

ABSTRACT

We successfully synthesized hybrid MXene-K-CNT composites composed of alkalized two-dimensional (2D) metal carbide and carbon nanotubes (CNTs), which were employed as host materials for lithium-sulfur (Li-S) battery cathodes. The unique three-dimensional (3D) intercalated structure through electrostatic interactions by K+ ions in conjunction with the scaffolding effect provided by CNTs effectively inhibited the self-stacking of MXene nanosheets, resulting in an enhanced specific surface area (SSA) and ion transport capability. Moreover, the addition of CNTs and in situ-grown TiO2 considerably improved the conductivity of the cathode material. K+ ion etching created a more hierarchical porous structure in MXene, which further enhanced the SSA. The 3D framework effectively confined S embedded between nanosheet layers and suppressed volume changes of the cathode composite during charging/discharging processes. This combination of CNTs and alkalized nanosheets functioned as a physical and chemical dual adsorption system for lithium polysulfides (LiPSs). When subjected to a high current at 1.0C, S@MXene-K-0.5CNT with S-loaded of 1.2 mg cm-2 had an initial capacity of 919.6 mAh g-1 and capacity decay rate of merely 0.052% per cycle after 1000 cycles. Moreover, S@MXene-K-0.5CNT maintained good cycling stability even at a high current of up to 5.0C. These impressive results highlight the potential of alkalized 2D MXene nanosheets intercalated with CNTs as highly promising cathode materials for Li-S batteries. The study findings also have prospects for the development of next-generation Li-S batteries with high energy density and prolonged lifespans.