| Summary: | Sodium-ion batteries (SIBs) have attracted increasing attention for storing renewable clean energy, owing to their cost-effectiveness. Nonetheless, SIBs still remain significant challenges in terms of the availability of suitable anode materials with high capacities and good rate capabilities. Our previous work has developed and verified that Cu<sub>2</sub>S wrapped by nitrogen-doped graphene (i.e., Cu<sub>2</sub>S@NG composite), as an anode in SIBs, could exhibit a superior performance with ultralong cyclability and excellent rate capability, mainly due to the multifunctional roles of NG. However, the Cu<sub>2</sub>S@NG anode still suffers from continuous parasitic reactions at low potentials, causing a rapid performance deterioration. In this study, we investigated the effects of a conformal Al<sub>2</sub>O<sub>3</sub> coating via atomic layer deposition (ALD) on the interfacial stability of the Cu<sub>2</sub>S@NG anode. As a consequence, the ALD-coated Cu<sub>2</sub>S@NG electrode can deliver a high capacity of 374 mAh g<sup>−1</sup> at a current density of 100 mA g<sup>−1</sup> and achieve a capacity retention of ~100% at different rates. This work verified that surface modification via ALD is a viable route for improving SIBs’ performances.
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