Core–shell structures of Cu2O constructed by carbon quantum dots as high-performance zinc-ion battery cathodes

The practical capacity of conversion-type Cu-based materials is low and the structural instability usually results in poor capacity retention and rate performance. Carbon quantum dots (CDs) composites are an effective way to overcome the above-mentioned shortcomings. Herein, a core–shell architecture self-assembled by CDs and Cu2O was well engineered. Such a unique construction efficiently integrates the advantages of CDs and the functional cladding interface. The constrain effect of the CDs shell effectively limits the collapse of the structure and the dissolution of active substances in Cu2O, and improves the phase transformation reaction and reaction kinetics of the composite. Theoretical calculations show that CDs reduce the ion diffusion energy barrier and improve the electrical conductivity of Cu2O. In particular, the optimized Cu2O-CDs-20 provides a high capacity of 425 mA h g−1 at 0.1 A g−1 (only 260 mA h g−1 for pure Cu2O) as the cathode for aqueous zinc ion batteries (AZIBs) and shows superior cycling stability and rate performance. The excellent performance of the composite should be contributed to the CDs modification and the conversion-type zinc storage mechanism of Cu2O as confirmed by in situ XRD, in situ Raman spectroscopy and electrochemical characterizations.