Interlayer Spacing Control of MoS₂ with Covalent Thiol Functionalization: Understanding Structure and Electrochemistry from Experiments and Simulation.

Abstract

Molybdenum disulfide (MoS₂) is an increasingly investigated two-dimensional electrode material for electrochemical energy storage and conversion. Strategies to increase its interlayer spacing are emerging and have been shown to improve ion intercalation capacity and kinetics. This work explores covalent thiol functionalization for controlling MoS₂ interlayer spacing. Using a hydrothermal bottom-up synthesis, dithiolated molecules can be directly incorporated into the MoS₂ lattice to act as pillars. Using a comprehensive combination of experiments and simulation, we investigate the influence of dithiol pillar loading on the emerging structure, pillar-host interactions, and electrochemistry. Our results reveal clustering of pillars at low loading, leading to an inhomogeneous interlayer expansion. At high pillar loading, the formation of defective bonding configurations with excess sulfur is observed. Interlayer expansion leads to an increased electrochemical Li⁺ storage capacity with a maximum of 1.43 Li⁺ per MoS₂. However, dithiols occupy storage sites and impede Li⁺ transport within the interlayer space, leading to unfavorable performance at high pillar loading. This underlines the importance of carefully adjusting the density of nanoconfined pillar molecules within the interlayer space. Overall, the work comprehensively analyzes covalent dithiol functionalization of transition metal dichalcogenide-based electrode materials, offering valuable insights for the design of advanced energy materials.