Encapsulation of Cu2S with a nitrogen-doped carbon boosts Na+ storage with a reversible Na2S conversion reaction

The high reversibility of a conversion-anode material enables high reversible capacity and maintains its cyclability. In this work, we report copper sulfide microspheres encapsulated by nitrogen-doped carbon (Cu 2 S@NC) prepared via a conventional polyol process and demonstrate their potential use as anode materials for sodium-ion batteries. Nitrogen-doped carbon stimulates a reversible conversion reaction of Cu 2 S + Na ↔ Na 2 S + Cu while corroborating the phase stability, leading to excellent Na + storage properties of the Cu 2 S@NC. Thus, the Cu 2 S@NC anode demonstrates an excellent cyclability of 284.99 mA/h/g at a higher current at 5000 mA/g. Operando X-ray diffraction and density functional theory calculations are combined to verify the electrochemical Na + storage mechanism of the Cu 2 S@NC.