Phase engineering of MoS$_2$ monolayers: A pathway to enhanced lithium-polysulfide battery performance

Abstract

This study explores the potential of MoS$_2$ polymorphs, specifically the semiconducting 2H phase and the metallic 1T$^\prime$ phase, as anchoring materials to enhance the electrochemical performance of lithium-sulfur (Li--S) batteries. Using density functional theory calculations, we show that 1T$^\prime$-MoS$_2$ exhibits stronger Li--S interactions, greater charge transfer, and enhanced catalytic activity compared to its 2H counterpart, effectively suppressing polysulfide dissolution and facilitating redox reactions. The reversible 2H$\leftrightarrow$1T$^\prime$ transition offers a tunable design space for balancing conductivity and structural stability. These findings position hybrid MoS$_2$ architectures as promising platforms for next-generation Li--S batteries with improved energy density, cycling stability, and rate capability.

Figures (7)

• Figure 1: Schematic representation of various lithium sulfide (Li$_m$S$_n$) clusters and monolayer MoS$_2$ structures. The top panel illustrates the geometries of the Li$_m$S$_n$ molecules studied, while the bottom panel depicts the 2H-MoS$_2$ (left) and 1T$^\prime$-MoS$_2$ (right) phases. For the MoS$_2$ monolayers, both top (view along the c-axis) and side (view along the b-axis) perspectives are presented. The shaded regions in the bottom panel indicate the supercells under investigation. Lithium (Li) is shown in blue, molybdenum (Mo) in purple, and sulfur (S) in yellow.
• Figure 2: Li$_m$S$_n$ adsorption properties on MoS$_2$ monolayers. Panel (a) shows the adsorption energy ($E_{\text{ads}}$) for the 2H and 1T$^\prime$ phases, panel (b) shows the charge transfer ($\Delta Q$) from the Li$_m$S$_n$ molecules to the MoS$_2$ monolayer (positive values indicate charge transfer to MoS$_2$), and panel (c) illustrates the vertical distance ($h$) between the molecules and the surface. Blue squares represent the 2H-MoS$_2$ phase, and red circles represent the 1T$^\prime$-MoS$_2$ phase.
• Figure 3: The density of states (DOS) of 2H-MoS$_2$ with adsorbed Li$_m$S$_n$ molecules, compared with the pristine 2H-MoS$_2$ DOS. Different panels correspond to the DOS for 2H-MoS$_2$ with Li$_m$S$_n$ molecules: S$_8$ in (a), Li$_2$S in (b), Li$_2$S$_2$ in (c), Li$_2$S$_4$ in (d), Li$_2$S$_6$ in (e), and Li$_2$S$_8$ in (f), respectively. Blue lines represent the DOS of the 2H-MoS$_2$ system with an adsorbed molecule, while the pristine DOS is shown as a shaded background for comparison.
• Figure 4: The density of states (DOS) of 1T$^\prime$-MoS$_2$ with adsorbed Li$_m$S$_n$ molecules, compared with the pristine 1T$^\prime$-MoS$_2$ DOS (shaded region). The panel distribution and labeling are the same as in Fig. \ref{['Fig:2Hdos']}.
• Figure 5: NEB calculation for the Li$_2$S$_4$ delithiation process on 2H- and 1T$^\prime$-MoS$_2$ surfaces. The external markers indicate the energies of metastable configurations along the reaction pathway. Blue lines represent the 2H phase, and red lines represent the 1T$^\prime$ phase. Energies are given in electron volts (eV) relative to the reactants (energy of isolated molecule plus pristine surface).