MAX Phase Purity Contingent Interlayer Spacing Regulated Ti₃C₂-F MXene Electrodes for Efficient Energy Storage...

This study systematically explores impact of impurity-induced defects in MAX phase on MXene quality and, hence, electrochemical performance. Structural defects in impure MAX phase are transferred to derived MXene and disrupt ion transport pathways by creating non-uniform interlayer spacing, thereby hindering ion diffusion and reducing electrochemical efficiency. Notably, as the purity of Ti₃AlC₂ MAX phase increases from 47% to 99%, the interlayer spacing in MXene expands, significantly enhancing its electrochemical properties. Galvanostatic charge-discharge (GCD) measurements at 1 A g^-1 reveal that the specific capacitance of MXene improves from 121.86 to 680.8 F g^-1 with increasing MAX phase purity. Further enhancement to 918.5 F g^-1 is achieved by incorporating carbon black (CB), which enhances the conductive network between MXene sheets. Symmetric battery-type supercapacitor device assembled with CB@Ti₃C₂-F electrodes exhibits specific capacity of 76.54 mAh g^-1 (@1A g^-1) over 1.65 V potential window, with energy density of 55.58 Wh kg^-1 (@1A g^-1) and power density of 1500.27 kW kg^-1 (@10A g^-1), surpassing previously reported values. Additionally, the device demonstrates excellent cycling stability, retaining 94% of its initial capacitance after 5000 charge-discharge cycles. This study underscores the critical role of MAX phase purity in regulating MXene interlayer spacing, thereby unlocking new opportunities for high-performance hybrid energy storage systems.