Recent progress in solution assembly of 2D materials for wearable energy storage applications

Wearable energy storage devices are desirable to boost the rapid development of flexible and stretchable electronics. Two-dimensional (2D) materials, e.g., graphene, transition metal dichalcogenides and oxides, and MXenes, have attracted intensive attention for flexible energy storage applications because of their ultrathin 2D structures, high surface-to-volume ratio, and unique physical/chemical properties. To achieve commercialization of 2D material-based wearable energy storage devices (2DM-WESDs), scalable and cost-efficient manufacturing is a critical challenge. Among existing manufacturing technologies, solution-based assembly strategies show strong potential to achieve low-cost and scalable production. A timely review of the recent progress in solution-based assembly strategies and the resultant 2DM-WESDs will be meaningful to guide the future development of 2DM-WESDs. In this review, first, a brief introduction of exfoliation and solution preparation of 2D material species from bulk materials is discussed. Then, the solution-based assembly strategies are summarized, and the advantages and disadvantages of each method are compared. After that, two major categories of 2DM-WESDs, supercapacitor and battery, are discussed, emphasizing their state-of-the-art energy storage performances and flexibilities. Finally, insights and perspectives on current challenges and future opportunities regarding the solution assembly of 2DM-WESDs are discussed.