Flexible free-standing MXene-based film electrodes for aqueous zinc ion storage

The explosive development of the Internet of Things (IoT) that connects the physical world with digitally intelligent systems by receiving signals from sensors and actuators embedded in physical objects, urgently requires high-performance power supplies for the sensors and actuators located at the restricted spaces. Among various power supply systems, flexible Zinc-ion energy storage devices have attracted extensive interest due to their cost-effectiveness, high theoretical capacity, superior safety, and environmental friendliness. To achieve flexibility in Zn-ion-based energy storage devices, the design and fabrication of flexible and/or freestanding active electrodes is one of the key issues. MXene as a novel family of two-dimensional (2D) materials shows outstanding integration of metal-like conductivity, abundant active sites, and excellent mechanical properties, which can be promising flexible electrodes for Zn ion storage. This review comprehensively expounds on the progress of reported flexible freestanding MXene-based composite films for different Zn-ion-based energy storage systems including Zn-ion capacitors (ZICs), Zinc-ion batteries (ZIBs), and Zinc-air batteries (ZABs). We also propose the challenges and perspective of improving the electrochemical performance of flexible freestanding MXene-based Zn-ion-based energy storage. This review serves as a guideline to inspire more future endeavors in synthesizing advanced flexible MXene-based electrodes for efficient Zinc ion storage.