First-principles calculations for the adsorption of lithium sulfide by zinc oxide

Abstract

Context

Lithium‒sulfur batteries (LSBs) are regarded as next-generation energy storage technologies owing to their high energy density; however, their practical application is constrained by the shuttle effect of lithium polysulfides (LiPSs), which leads to capacity degradation and safety concerns. This work focuses on the adsorption mechanism of Li₂S on ZnO and investigates the microscopic mechanism by which ZnO suppresses the shuttle effect through first-principles calculations. The results demonstrate that the adsorption energy of a Li₂S molecule on the ZnO (100) facet is negative (−1.67 eV), which is thermodynamically more favorable than that on the (111) facet (1.73 eV). The Li–O ionic bonds and S–Zn covalent bonds formed between the (111) facet and the Li₂S molecule exhibit stronger coupling than those on the (100) facet, resulting in stronger overall interfacial electronic interactions. Nevertheless, the deformation magnitude of the Li–S bond on the (111) facet (9%–14%) exceeds that on the (100) facet (less than 5%). The (100) facet achieves energetically superior stable adsorption through weak bonding and low deformation, whereas the (111) facet, despite stronger bonding, has a deformation energy that surpasses the energy released by bond formation, rendering it a thermodynamically metastable configuration. Evidently, ZnO strongly adsorbs Li₂S—the final product of the shuttle effect—thereby suppressing the shuttle effect to a certain extent.

Methods

In this study, first-principles calculations were performed via the Materials Studio software via density functional theory (DFT) via the generalized gradient approximation (GGA) with the PBE functional and the GGA-PBE + U approach. Ultrasoft pseudopotentials were employed to balance computational efficiency and accuracy. Crystal models of zinc oxide (ZnO) and Li₂S were constructed via the CASTEP code. The nonpolar (100) facet and polar (111) facet of ZnO were selected for Li₂S molecule adsorption, followed by structural optimization. The adsorption energy, electronic band structure, partial density of states (PDOS), charge density, Mulliken charge population, and chemical bond lengths were subsequently calculated.