The synthesis and application of two-dimensional materials (2DMs) have ever-increasingly evolved over time since the first isolation of graphene in 2004. The most notable applications include electrochemical energy storage in the form of batteries and supercapacitors. At present there is an intense focus on expanding the family of numerous new 2DMs, such as MXene, phosphorene, metal oxides, transition metal dichalcogenides, etc., and their composites or heterostructures to provide synergistic effects as active materials. However, 2DMs are not restricted to only active materials for electrodes. Their roles have become increasingly important as other components of batteries and supercapacitors. For instance, boron nitride nanosheets have demonstrated remarkable potential as a separator in supercapacitors while graphene nanosheets can act as excellent current collectors as well as conducting additives for lithium ion batteries, and also serve as the hosts of sulfur and lithium metal, the interlayer on the side of sulfur cathode, and interfacial layer for lithium sulfur batteries. So far, 2DMs have provided a large number of intriguing options for designing different devices. Consequently, we have organized this special issue of 2D Energy Materials to highlight their uniqueness and importance, their state-of-the-art advances and breakthrough innovations, discuss their key challenges and perspectives that still need to be overcome, and guide the future directions of research through the topical review and research articles.

This special issue of 2D Energy Materials covers the cutting-edge, extremely timely, and wide impact research results and breakthrough solutions in the fantastic field of 2DMs for energy storage and conversion devices, with a particular focus on (i) precise fabrication of graphene & other 2DMs, such as MXene, boron, phosphorene, metal oxides, MoS2, and polymer nanosheets; (ii) elaborated assembly of 2D hybrid nanosheets, 2D heterostructures & 3D nanosheet-based architectures; (iii) fundamental investigations of nanosheet-based electrodes and related energy storage devices with in-situ/ex-situ characterizations and theoretical simulation; (iv) fundamental and applied aspects of nanosheet-based Li and other ion (Na, K+, Mg2+, Al3+, Zn2+) batteries, Li-metal, Li-S, Metal (Li+, Zn2+)-O2, & solid-state batteries; (v) electrical double layer capacitors, pseudocapacitors, hybrid capacitors, dielectric capacitors, 1D & 2D flexible energy storage devices; and (vi) other new energy-related applications, such as redox flow batteries, Li-CO2, & seawater desalination.