Ultrafast charging of ionic liquid-Ti₂CT₂ MXene supercapacitors: a first-principles study

MXenes could be ideal electrode materials for supercapacitors (SCs) because of their favorable metallic conductivity and high specific surface area. Meanwhile, the potential window of ionic liquid (IL) electrolytes could reach up to 3 V, and the combination of MXene electrodes with ILs represents a promising class of interfaces for electrochemical energy storage and related applications; however, the microscopic structure and interaction mechanisms at MXene-IL interfaces remain insufficiently understood. In this work, first-principles simulations were employed to systematically investigate the adsorption behavior and interfacial structure of a series of imidazolium-based ILs on Ti₂CT₂ MXenes with different terminations. The differences in the adsorption of ILs on the MXenes indicate that the adsorption of ILs is primarily governed by the interaction between the imidazolium cation and the MXene surface, while the influence of anion chemistry is comparatively secondary. The adsorption behavior of [Emim]⁺ on MXenes was investigated. It was found that the diffusion barrier of [Emim]⁺ on the MXene surface was extremely low, indicating that it could exhibit good charging and discharging behavior in energy storage devices. In addition, the arrangement of [Emim]⁺ cations at different coverages on the MXene surface was investigated. The configuration of the [Emim]⁺ cation changed from a "flat structure" to a "stand structure" as the surface coverage increased, and the interfacial stability of MXenes with multiple [Emim]⁺ was studied via ab initio molecular dynamics simulations. This work investigated the adsorption structure, diffusion behavior, configuration transformation and charge storage ability of [Emim]⁺ cations at the MXene-IL interfaces. It provides insights into the microstructure of the MXene-IL interfaces at the atomic level, which would be helpful for the development of MXene-IL SCs and other energy storage devices.