In-Situ Growth of Mn O Nanoparticles on Nitrogen-Doped Carbon Dots-Derived Carbon Skeleton as Cathode Materials for Aqueous Zinc Ion Batteries.

Mn O is a promising cathode material for aqueous zinc ion batteries (ZIBs) which is a new type of low cost, eco-friendly, high security energy storage system, while those previously reported electrochemical capacities of Mn O are far from its theoretical value. In this work, Mn O nanoparticles and nitrogen-doped carbon dots (NCDs) are synthesized together through an in-situ hydrothermal route, and then calcined to be a nanocomposite in which Mn O nanoparticles are anchored on a nitrogen-doped carbon skeleton (designated as Mn O /NCDs). Although the carbon content is only 3.9 wt.% in the Mn O /NCDs, the NCDs-derived carbon skeleton provides an electrically conductive network and a stable structure. Such a special nanocomposite has a large specific surface area, plenty of active sites, excellent hydrophilicity and good electronic conductivity. Owing to these structural merits, the Mn O /NCDs electrode exhibits a preeminent specific capacity of 443.6 mAh g and 123.3 mAh g at current densities of 0.1 and 1.5 A g in ZIBs, respectively, which are far beyond the bare Mn O nanoparticles synthesized under the similar condition. The electrochemical measurement results prove that carbon dots, as a new type of carbon nanomaterials, have strong ability to modify and improve the performance of existing electrode materials, which may push these electrode materials forward to practical applications.