The capacity fading mechanism and improvement of cycling stability in MoS2-based anode materials for lithium-ion batteries

Abstract

Two-dimensional (2D) layered MoS₂ nanosheets possess great potential as anode materials for lithium ion batteries (LIBs), but they still suffer from poor cycling performance. Improving the cycling stability of electrode materials depends on a deep understanding of their dynamic structural evolution and reaction kinetics in the lithiation process. Herein, thermodynamic phase diagrams and the lithiation dynamics of MoS₂-based nanostructures with the intercalation of lithium ions are studied by using first-principles calculations and ab initio molecular dynamics simulations. Our results demonstrate that the continuous intercalation of Li ions induces structural destruction of 2H phase MoS₂ nanosheets in the discharge process that follows a layer-by-layer dissociation mechanism. Meanwhile, the intercalation of Li ions leads to a structural transition of MoS₂ nanosheets from the 2H to the 1T phase due to the ultralow transition barriers (∼0.1 eV). We find that the phase transition can slow down the dissociation of MoS₂ nanosheets during lithiation. The result can be applied to explain extensive experimental observation of the fast capacity fading of MoS₂-based anode materials between the first and the subsequent discharges. To suppress the dissociation of MoS₂ nanosheets in the lithiation process, we propose a strategy by constructing a sandwich-like graphene/MoS₂/graphene structure that indicates high chemical stability, superior conductivity, and high Li-ion mobility in the charge/discharge process, implying the possibility to induce an improvement in the anode cycling performance. This work opens a new route to rational design layered transition-metal disulfide (TMD) anode materials for LIBs with superior cycling stability and electrochemical performance.