In Situ Electrochemical Synthesis of MXenes without Acid/Alkali Usage in/for an Aqueous Zinc Ion Battery

The traditional method to fabricate a MXene based energy storage device starts from etching MAX phase particles with dangerous acid/alkali etchants to MXenes, followed by device assembly. This is a multistep protocol and is not environmentally friendly. Herein, an all-in-one protocol is proposed to integrate synthesis and battery fabrication of MXene. By choosing a special F-rich electrolyte, MAX V₂AlC is directly exfoliated inside a battery and the obtained V₂CT_X MXene is in situ used to achieve an excellent battery performance. This is a one-step process with all reactions inside the cell, avoiding any contamination to external environments. Through the lifetime, the device experiences three stages of exfoliation, electrode oxidation, and redox of V₂O₅. While the electrode is changing, the device can always be used as a battery and the performance is continuously enhanced. The resulting aqueous zinc ion battery achieves outstanding cycling stability (4000 cycles) and rate performance (97.5 mAh g⁻¹ at 64 A g⁻¹), distinct from all reported aqueous MXene-based counterparts with pseudo-capacitive properties, and outperforming most vanadium-based zinc ion batteries with high capacity. This work sheds light on the green synthesis of MXenes, provides an all-in-one protocol for MXene devices, and extends MXenes’ application in the aqueous energy storage field.