Theoretical Exploration Of MXene/graphene Heterostructures As Potential Electrodes For Ion Batteries

Two-dimensional?2D?early transition-metal carbides and/or nitrides,known as MXenes,have received extensive research interest because of their excellent mechanical and electronic properties.Many researchers focus on MXenes as ion batteries due to their outstanding electrical conductivity,high ion storage capability,and large specific surface area.Nevertheless,restacking of MXene layers is inevitable during electrode preparation,significantly hindering the ion transport and electrolyte infiltration.Moreover,the stretchability of MXenes combined with a strong anisotropy of the mechanical properties severely hampers the fabrication of flexible electrodes.Recently,MXene/graphene heterostructures have been successfully fabricated and demonstrated to exhibit excellent performance as electrodes for ion batteries.However,research on the mechanisms behind these encouraging experimental properties is still at an early stage.Herein,we use first-principles calculations to systematically study the electrochemical properties of MXene/graphene heterostructures,choosing Ti₂CX₂?X=F,O,and OH?as representative MXenes.Our calculations show that the presence of graphene not only avoids the restacking of MXene layers but also enhances the electrical conductivity,ion adsorption strength?while maintaining a high ion mobility?,and mechanical stiffness.These favorable attributes collectively lead to the excellent performance of MXene/graphene electrodes observed experimentally.The Ti₂CO₂/graphene heterostructure is proposed to be the most promising candidate among the studied materials.Furthermore,it is found that twisting does not critically affect the electronic properties and ion intercalation/diffusion behavior of the heterostructures.The developed comprehensive understanding is of significance also for the future rational design of high-performance MXene-based electrodes.