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Lithium‐ion battery (LIB) is a dominating power source in the market owing to its high energy density, good cycling stability and environmental benignity. However, technical challenges remain after years' optimization and commercialization, which are detrimental to the expected performance and lifespan of LIBs. For instance, many cathode materials of LIBs suffer from rapid capacity fading and poor high‐rate performance, which are ascribed to self‐aggregation, dissolution and fast increased charge transfer resistances during cycles. In terms of the anode materials, low coulombic efficiency, electrolyte depletion and safety issues are common. In addition, the liquid electrolyte systems trigger safety concerns because flammable and volatile organic solvents are necessary. Recently, carbon dots (CDs) emerge as a sound material to address those challenges of LIBs, and also present promising applications in bioimaging, fluorescence sensing, photo/electro‐catalysis, and electroluminescence. This review will overlook the state‐of‐the‐art advances in the employment of CDs based composites to build cathode/anode materials and electrolytes in LIBs, through tailoring the internal structures and the surface states of electrode materials, and being additives in electrolyte, to improve the performances of the next‐generation LIBs. The major challenges and opportunities in front of CDs in LIBs will be outlined and discussed in detail. [ABSTRACT FROM AUTHOR]

• This protective layer is constructed by TiO 2 nanosheets and N-doped carbon dots. • The TiO 2 layer can immobilize water molecules and prevent the side reactions. • NCDs with abundant functional groups provide the zincophilic nucleation sites. • The Zn-TiO 2 /NCDs||MnO 2 full cells show an excellent reversibility at 2 A/g. Uncontrolled Zn dendrites growth and sustained corrosion originating from severe interfacial reactions are the major shortcomings of Zn metal electrodes in aqueous zinc-ion batteries (ZIBs). In order to overcome these obstacles, we designed a protective coating layer to stabilize the zinc anode and regulate the Zn deposition simultaneously. This hybrid layer (TiO 2 /NCDs) is constructed by mesoporous TiO 2 nanosheets and N-doped carbon dots (NCDs), which is prepared by a solvothermal growth under the control of NCDs. On one hand, the TiO 2 layer immobilize water molecules effectively, preventing them from the parasitic reactions with Zn electrodes. On the other, NCDs with abundant functional groups (–OH, –COOH, –NH 2) provide the zincophilic nucleation sites to endow a small deposition overpotential of 28 mV and guide Zn deposition into a petal structure. Owing to mesoporous protective coating layer, the Zn-TiO 2 /NCDs anode presents a low voltage hysteresis of 48 mV and a prolonged cycling lifespan of 1500 h at 5 mA cm−2 and 2.5 mAh cm−2. Moreover, aqueous ZIBs assembled with the Zn-TiO 2 /NCDs anode and the α-MnO 2 cathode show outstanding reversibility and good cycling stability, whose capacity retention is up to 90% after 1000 cycles. [ABSTRACT FROM AUTHOR]

After incorporation of a few Carbon Dots (CDs), ZnO anodes process thin carbon shells, refined microstructures and special univalent zinc sites, which result in better reactivity, higher corrosion resistance, more effective electron paths to enhance electrochemical performance in high capacity, excellent rate capability and long cycling stability in the Ni-Zn alkaline battery. [Display omitted] • 1. CDs efficiently control morphology of ZnO for sufficient electrochemical reactions. • 2. With the assistance of CDs, ZnO will process conformal carbon shells with few layers. • 3. Univalent zinc sites constructed by CDs play a key role during charging process. The development of high-performance nickel-zinc (Ni-Zn) alkaline batteries is mainly plagued by short life span and poor rate performance of ZnO anode materials. To improve the cycling stability and rate capability of Ni-Zn batteries, carbon dots (CDs) are employed to construct clustered ZnO-CDs nanocomposites, coating ZnO with protective shells of carbon layers and providing electron paths to enhance conductivity of the nanocomposites. Univalent zinc species are found at the interfaces between CDs derivatives and ZnO, which are embedded in the nanoclusters and protected well by carbon coating. Theoretical calculations show univalent zinc species change the electronic structures of ZnO surface, so as to accelerate the charging process of ZnO anode materials. Such ZnO-CDs derived nanocomposites exhibit excellent rate capability (95.3%, 84.7% and 75.0% of capacity retention rate at 2, 5 and 10 A g−1, respectively) and outstanding cycling stability with 92.0% of capacity retention rate after 5000 cycles, which is far better than ZnO based anodes without the protection of CDs (39.1% retention rate from 1 to 10 A g−1 and 71.6% of capacity retention rate after 500 cycles). [ABSTRACT FROM AUTHOR]