Revealing the Distinct Electrochemical Properties of TiSe2 Monolayer and Bulk Counterpart in Li-ion Batteries by First-principles Calculations

Abstract Two-dimensional transition metal dichalcogenides (TMDs) have been intensively studied as electrode materials for lithium-ion batteries. But, most of TMDs are low electronic conductors, and there is lack of research on the distinct electrochemical mechanisms of monolayer and bulk TMDs. In this work, the Li+ storage properties of monolayer and bulk TiSe2 are studied by first-principles calculations based on the density functional theory. Calculations showed that bulk TiSe2 works on the intercalation mechanism, which results in a theoretical capacity of 260 mA·h·g-1 in the voltage window of 1.14-2.09 V. In comparison, monolayer TiSe2 works on the adsorption mechanism which gives a theoretical capacity of 780 mA·h·g-1 in 0.18-1.43 V. A two-stage redox process was revealed for both TiSe2 forms. In the initial stage, Se acted as the main redox species; then both Ti and Se participated in the redox reaction. In addition, the material possesses low Li+ diffusion barriers. Especially, a very small diffusion barrier of 163 meV at high Li+ concentration and 39 meV at low Li+ concentration was obtained for monolayer TiSe2, which provide great potential as a high rate anode material for lithium ion batteries.