First-principles study of electronic properties and lithium ions conduction at graphene/Ni3S2 interface

Abstract

Transition metal sulfides are regarded as one of anode candidate with great promise for lithium-ion batteries because of their relatively large theoretical specific capacity and high conductivity. But the irreversible volume dilation and dissolution of lithium polysulfide during Li⁺ insertion/extraction process limit their coulomb efficiency and cycle stability, and surface coating is suggested as an effective method to tackle these issues. In this study, graphene(G) coated Ni₃S₂ (G@Ni₃S₂) is theoretically constructed and the influence of G coating on electrochemical performance (Li⁺ storage performance) of Ni₃S₂ are revealed by density functional theory (DFT) calculation, the study aimed to reveal the mechanism and performance of G coating on Li⁺ storage performance of Ni₃S₂. Electronic properties and the migration of Li⁺ at the G/Ni₃S₂(110) interface and its transformed G/Li₂S(110) interface during the lithiation/delithiation process are systematically studied by DFT at a micro level. The results indicate that the G coating can enhance the electrical conductivity of Ni₃S₂ and Li₂S surface and facilitate electron transfer during electrochemical process. Internal electric field is formed at the G/Ni₃S₂(110) and G/Li₂S(110) interface, which can facilitate the migration of Li⁺ at the G/Ni₃S₂(110) interface and G/Li₂S(110) interfaces. These results will help researchers to understand the influence of G coating layer on improving Li⁺ storage performance of transition metal sulfide as anode materials of lithium-ions batteries.