Applications of Carbon Dots in Electrochemical Energy Storage

As one kind of carbon nanomaterials, since their discovery at the beginning of the century, carbon dots (CDs) have been attracting extensive attention in sensing, bioimaging, catalysis, organic light-emitting diodes, etc. due to their rich and diverse physical and chemical properties. Although the precise structures of CDs need to be further analyzed and elaborated, it is confirmed that there are many functional groups on the surfaces including amino, hydroxyl, carboxyl and thiol, depending on the precursors and preparation processes used. The crystalline/amorphous conjugated graphite-like sp2 domains and segments inside the CDs provide good electrical conductivity and photoelectric conversion capability. The applications of CDs in electrochemical energy storage have been carried out extensively and become a hot topic in recent years. In this review, the recent progress about the applications of CDs in typical electrochemical energy storage devices including supercapacitors, lithium-ion batteries, sodium-ion batteries and potassium-ion batteries is outlined and summarized. The relationships between material structures and device performances are mainly analyzed. Finally, it is anticipated that the development of CDs can continuously boost the study of high-efficiency energy storage devices profoundly.