Construction of high-performance sodium ion hybrid capacitors based on MXene surface modulation and electrolyte matching.

Abstract

Sodium-ion hybrid capacitors have garnered significant attention due to their high power and energy densities, as well as the abundance of sodium reserves. However, the mismatch between anode and cathode dynamics is the biggest barrier to improving their performance. To address this issue, we propose a strategy for the preparation of porous MXene by hydrogen peroxide (H2O2)-controlled etching to solve the capacity degradation and ion diffusion limitation, which are caused by van der Waals forces between MXene nanosheets. This approach facilitates the realization of three-dimensional ion channels with both vertical and horizontal pathways, significantly enhancing the availability of active sites and improving the ion diffusion rate. By adjusting the amount of oxidant, porous MXene (P-MXene-2) with an optimal pore size range was obtained. The assembled half-cell has a capacity of 180 mAh g-1 at a rate of 0.05 A g-1. Furthermore, by combining a porous carbon cathode with porous MXene and electrolyte screening, a SIHC with a high energy density of 110.6 Wh kg-1 at 1000 W kg-1 and 71.1 Wh kg-1 at 20 kW kg-1 was successfully constructed. This study provides useful insights into the design and preparation of porous MXene electrodes and their energy storage applications.