Enhancing ion storage and transport in Ti3C2Tz MXene via a “sacrificial cations” strategy

Abstract

MXenes have gained significant attention in supercapacitors (SCs) due to their high electronic conductivity and tunable surface terminations. However, challenges arise during etching such as interlayer restacking and the presence of inactive –F terminations that impede the full utilization of their intrinsic capabilities. To tackle these issues, we propose a “sacrificial cation” strategy involving electrochemistry-driven cation intercalation (ECI) and calcination. Specifically, alkylammonium cations with different chain lengths are intercalated into the interlayers of Ti₃C₂T_z MXene by ECI, and then these intercalated cations are removed by pyrolysis at 400 °C. This approach aims to augment interlayer spacing and introduce a substantial number of –O surface terminations, thereby enhancing capacitance contributions. The resulting dodecyl-trimethylammonium cation intercalated Ti₃C₂T_z after calcination (T-C8-C) presents high volumetric capacitances of 1737.6 F cm⁻³ at 1 A g⁻¹. T-C8-C, when integrated with nitrogen-doped activated carbon (NAC) into an asymmetric SC, achieves outstanding volumetric energy density (56.7 W h L⁻¹ at 0.15 kW L⁻¹), high power densities at elevated energy densities (30.1 kW L⁻¹ at 36.7 W h L⁻¹), and remarkable lifespan (96.2% retention after 30 000 cycles at 10 A g⁻¹). This strategy provides valuable insights for developing high-performance 2D materials in energy storage through interlayer spacing adjustment and surface modification.