New Ultra-High Cycle Stable Accordion-Like High Entropy MXene with Improving Energy Storage Performance of Supercapacitors

2D transition metal carbides, nitrides, and carbonitrides (MXenes) are widely used in energy-related fields, however, the instability of MXenes limits their application in supercapacitors. Currently, one of the main scientific challenges is how to modify MXenes to enhance their electrochemical performance. Compared to mono-transition-metal MXenes (MTMs), the large surface combined with multiple transition metals makes high entropy MXenes (HE-MXenes) more appealing in energy storage. Here, a HE-MAX phase, (TiVNbMoW)3AlC2, and a corresponding accordion-like HE-MXene are successfully synthesized by selective removal of Al from the HE-MAX in aqueous hydrofluoric acid (HF). The addition of W allows the high-entropy MAX (HE-MAX) to reach greater lattice distortion than (TiVNbMo)3AlC2. It also successfully resolves the problem of inadequate configurational entropy in the M layer and expands the range of M layer. The accordion-like HE-MXene with open microstructure and high crystallinity provides multi-channels for rapid ionic charge diffusion during interlayer ion insertion/extraction. Owing to these designs, the capacity retention rate is 98.7% after 10 000 cycles at 5 A g-1, demonstrating high stability throughout the charge-discharge cycling both in acidic and alkaline. The synthesis of HE-MXene enriches the selection for energy applications and greatly increases the compositional variety of the MXene family.