Intercalation and delamination behavior of Ti3C2Tx and MnO2/Ti3C2Tx/RGO flexible fibers with high volumetric capacitance

Abstract

The intercalation and delamination processes of Ti₃C₂T_x are systematically investigated by using alkylammonium hydroxides (TAAOH) with different chain lengths. TAA⁺ cations have a key function for the intercalation reaction of Ti₃C₂T_x nanosheets, and the basal spacing and the crystal phase of TAA⁺-intercalated Ti₃C₂T_x at different stages are closely related to the size of the intercalated TAA⁺ ions, and they are hardly changed with the addition of molar equivalents of TAAOH per mole of Ti₃C₂T_x and the drying conditions. Moreover, the intercalation process is very rapid and it can be carried out by just 4 h treatment. TAA⁺-intercalated Ti₃C₂T_x can be delaminated into Ti₃C₂T_x nanosheets by hand shaking or repeated washing. By introducing a graphene oxide nanosheet suspension into the Ti₃C₂T_x nanosheet suspension, Ti₃C₂T_x/RGO fibers are firstly prepared by a wet-spinning method followed by reducing Ti₃C₂T_x/GO fibers in HI/CH₃COOH solution. Then the Ti₃C₂T_x/RGO fiber is soaked in KMnO₄ solution with different concentrations at room temperature, and a MnO₂/Ti₃C₂T_x/RGO ternary hybrid fiber with good flexibility and capacitance is prepared. The MnO₂/Ti₃C₂T_x/RGO ternary hybrid fiber electrode shows the largest volumetric capacitance of 851 F cm⁻³ in 1 M Na₂SO₄ electrolyte and good flexibility. By twisting two of these fiber electrodes together, an all-solid-state symmetric MnO₂/Ti₃C₂T_x/RGO//MnO₂/Ti₃C₂T_x/RGO fiber supercapacitor with PVA–LiCl gel electrolyte is assembled. It not only exhibits a volumetric capacitance of 24 F cm⁻³ and superior cycle stability of 92% after 10 000 cycles, but also shows outstanding flexibility and mechanical properties in which the volumetric capacitance has no obvious change after bending the supercapacitor at 90° 1000 times. Furthermore, the assembled symmetric supercapacitor shows the maximum volumetric energy density of 2.13 mW h cm⁻³ at a volumetric power density of 8.16 mW cm⁻³. This work will open a new application field of Ti₃C₂T_x-based fibers for new wearable energy storage devices with good energy density and flexibility.