Boosting the capacity of MXene electrodes in neutral aqueous electrolytes

The use of Ti₃C₂T_x (MXene) electrodes for energy storage applications is gaining momentum. Considering the low flammability, high safety, and low cost of neutral aqueous electrolyte solutions, significant efforts have been devoted to the utilization of MXenes in this environment. However, despite the high stability and the excellent rate capability of MXene electrodes in neutral aqueous electrolytes, their capacity remains insufficient, usually below 30 mAh/g. This work aims to benefit from the spontaneous oxidation of MXene materials under ambient conditions to produce TiO₂-coated MXene flakes. By using concentrated lithium chloride solutions, an extended potential window is obtained, allowing reversible insertion of lithium ions into MXene flakes and titanium dioxide nanoparticles. This results in significant capacity enhancement in MXene electrodes (by more than 200%) without impeding the MXene capacitive activity or its mechanical integrity. The prepared electrode presents long-term stability and high rate capability.