Maximizing the ion accessibility and high mechanical strength in nanoscale ion channel MXene electrodes for high-capacity zinc-ion energy storage

Two-dimensional transition-metal carbides (MXenes) have superhydrophilic surfaces and superior metal conductivity, making them competitive in the field of electrochemical energy storage. However, MXenes with layered structures are easily stackable, which reduces the ion accessibility and transport paths, thus limiting their electrochemical performance. To fully exploit the advantages of MXenes in electrochemical energy storage, this study reports the etching of large-sized MXene into nanosheets with nanoscale ion channels via a chemical oxidation method. While the resulting ion-channel MXene electrodes retain the excellent mechanical strength and electrical conductivity of large-sized MXene nanosheets, they can effectively shorten the ion transport distance and improve the overall electrochemical activity. The fabricated self-healing MXene-based zinc-ion microcapacitor exhibits a high areal specific capacitance (532.8 mF cm−2) at the current density of 2 mA cm−2, a low self-discharge rate (4.4 mV h−1), and high energy density of 145.1 μWh cm−2 at the power density of 2800 μW cm−2. The proposed nanoscale ion channel structure provides an alternative strategy for constructing high-performance electrochemical energy storage electrodes, and has great application prospects in the fields of electrochemical energy storage and flexible electronics.