A new generation of energy storage electrode materials constructed from carbon dots

Carbon dots (CDs), an emerging class of carbon materials, hold a promising future in a broad variety of engineering fields owing to their high diversity in structure, composition and properties. Recently, their potential applications have spanned from bio-imaging, fluorescent probing and catalysis, to energy storage fields, in particular as materials in the key components of electrochemical energy storage devices. The state-of-the-art research work has revealed that CD-based or modified electrodes exhibit profound improvement in all key functions, such as coulombic efficiency, cycling life, enlarging capacity, etc., in comparison to traditional electrodes. The improvement in all these properties can be realized by introducing a small quantity of CDs to the traditional electrode systems. A comparative optimization in this regard, however, requires incorporation of more carbon nanotubes (CNTs) or graphene or other carbon-based materials, indicating that CD-incorporated electrode materials would maintain their energy density more efficiently. This review will summarize the progress to date in the design and preparation of CD-incorporated energy storage devices, including supercapacitors, Li/Na/K-ion batteries, Li–S batteries, metal–air batteries and flow batteries, and elaborate on the influence of these unique structures and rich properties of CDs on the electrochemical performance of the resulting electrodes and devices. Consequently, the specific functions and the novel working mechanisms of CD-modified electrodes for energy storage units will be discussed, aiming at providing new insights for guidance for design and manufacturing of the next generation of electrode materials for high-performance energy storage.