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

Abstract

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.