Surface chlorination-induced electronic structure modulation of Ti3C2 MXene for advanced sodium ion storage

Abstract

With the climate crisis and technological advance, the demand for the development of advanced energy storage device is becoming a major issue worldwide. This study demonstrates that chlorine (Cl) functionalization of MXene via an molten salt method effectively modulates the electronic structure and band gap, thereby significantly enhancing the electrochemical performance of sodium-ion capacitors (SICs). In half-cell tests, Clfunctionalized MXene exhibited a sodium (Na) ion storage capacity of 70.3 mAh g-1 at 0.1 A g-1, approximately three times higher than Fluorine (F) functionalized MXene (24.9 mAh g-1). This improvement is attributed to enhanced electrical conductivity and diffusion-controlled reaction mechanisms. In the practical test (full-cell tests), Cl-MXene//AC SIC achieved an energy density of 121.37 Wh kg-1 at a power density of 767.21 W kg-1, outperforming F-MXene//AC SIC by maintaining higher energy density at lower power densities. The Cl-MXene//AC SIC also exhibited the superior cycle stability retaining 88.56 % of capacitance retention after 20,000 cycles at 1.0 A g-1. These results confirm the potential of surface-modified MXene as a promising electrode material for Na-ion capacitors, offering a pathway for advanced energy storage solutions.