Charging/Discharging Dynamics in Two-Dimensional Titanium Carbide (MXene) Slit Nanopore: Insights from molecular dynamic study

Abstract

While most theoretical studies on slit nanopore electrodes are limited in their static properties, understanding the dynamic charge storage is crucial for promoting their electrochemical performance in the field of energy storage systems. In this article, the charging/discharging dynamics in MXene (Ti3C2(OH)2) electrode featuring intrinsic slit nanopore with room temperature ionic liquid are investigated by molecular dynamic simulation. The galvanostatic cycling is modeled to help to understand the dynamic charge storage mechanism. The simulation results show that the electrolyte ions spontaneously wet the Ti3C2(OH)2 slit nanopore in the absence of external potential, even at 0.7nm layer distance pore case. An intriguing electroneutrality breakdown and faster diffusion property is observed inside the nanopore. During charge/discharge process, the charge storage takes place by a fast counter-ion insertion and counter-ion/co-ion exchange. Besides, the spatial distribution of ions and the orientation of the cation dipoles inside the pore vary cyclically alone with the charge/discharge process, which helps to screen the external electric potential. Having elucidated the charge mechanism, we investigate the layer distance factor and show that the ions exhibit more significantly acceleration and more ordered dipole orientation inside the narrower pore. This will help Ti3C2(OH)2 electrode with narrower pore exhibit better power performance.