Intercalation and delamination behavior of Ti3C2Tx and MnO2/Ti3C2Tx/RGO flexible fibers with high volumetric capacitance†
The intercalation and delamination processes of Ti3C2Tx are systematically investigated by using alkylammonium hydroxides (TAAOH) with different chain lengths. TAA+ cations have a key function for the intercalation reaction of Ti3C2Tx nanosheets, and the basal spacing and the crystal phase of TAA+-intercalated Ti3C2Tx 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 Ti3C2Tx and the drying conditions. Moreover, the intercalation process is very rapid and it can be carried out by just 4 h treatment. TAA+-intercalated Ti3C2Tx can be delaminated into Ti3C2Tx nanosheets by hand shaking or repeated washing. By introducing a graphene oxide nanosheet suspension into the Ti3C2Tx nanosheet suspension, Ti3C2Tx/RGO fibers are firstly prepared by a wet-spinning method followed by reducing Ti3C2Tx/GO fibers in HI/CH3COOH solution. Then the Ti3C2Tx/RGO fiber is soaked in KMnO4 solution with different concentrations at room temperature, and a MnO2/Ti3C2Tx/RGO ternary hybrid fiber with good flexibility and capacitance is prepared. The MnO2/Ti3C2Tx/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/Ti3C2Tx/RGO//MnO2/Ti3C2Tx/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 Ti3C2Tx-based fibers for new wearable energy storage devices with good energy density and flexibility.