Two-dimensional (2D) nanomaterials are gaining attention for energy storage applications on account of their exceptional characteristics and versatility. This chapter offers an overview of latest research on 2D nanomaterials in energy storage device applications, focusing on the various synthesis methods and electrochemical behavior. It also examines the recent progress in the development of flexible, free-standing supercapacitors utilizing 2D materials. 2D materials gained significant interest on account of their large surface area, making them suitable candidate for energy storage applications. The extensive need for energy generation applications substantially enhances the advanced research in the synthesis of 2D nanomaterials specifically from the discovery of graphene. Key factors in designing high-performance energy storage devices include electronic conductivity, available intercalation sites, and cycling stability. The chapter emphasizes the properties of 2D materials and provides description of electrodes based on 2D heterostructured materials that demonstrate unique efficiency, resulting in improved electrochemical performance.