Halogenated Ti3C2 MXene as High Capacity Electrode Material for Li-ion Batteries

MXenes have been widely studied for their excellent specific surface area, high conductivity and composition tunability, which have been used as a highly efficient electrode material for lithium-ion batteries (LIBs). However, limited storage capacity and severe lattice expansion caused by Li-ions diffusion restrict the application of MXenes as electrode materials. Here, Ti3C2 MXenes with surface halogenation (fluorination, chlorination and bromination) as representative MXene materials were designed. Effects of surface functionalization on the atomic structures, electronic properties, mechanical properties, and electrochemical performance of Ti3C2T2 (T = F, Cl and Br) anode in LIBs were investigated using first-principles calculations based on density functional theory with van der Waals correction. The results reveal that Ti3C2T2 MXenes exhibit metallic conductivity with improved structural stability and mechanical strength. Compared with Ti3C2F2 and Ti3C2Br2, Ti3C2Cl2 exhibits the large elastic modulus (321.70 and 329.43 N/m along x and y directions, respectively), low diffusion barrier (0.275 eV), high open circuit voltage (0.54 eV), and storage capacity (674.21 mA.h/g) with stoichiometric ratio of Ti3C2Cl2Li6, which renders the enhanced rate performance and endures the repeated lattice expansion and contraction during the charge/discharge process. Moreover, surface chlorination yields expanded interlayer spacing, which can improve Li-ion accessibility and fast charge-discharge rate in Ti3C2Cl2. The research demonstrates that Cl- terminated Ti3C2 is a promising anode material, and provides effective and reversible routes to engineering other MXenes as anode materials for LIBs.