Porous Copper Sulfide Microflowers Grown In Situ on Commercial Copper Foils as Advanced Binder‐Free Electrodes with High Rate and Long Cycle Life for Sodium‐Ion Batteries

Abstract Copper sulfide (CuS) is considered as a promising sodium storage anode with its high theoretical capacity (558 mAh g −1 ), low cost and environmental friendliness. However, the development of applicable CuS anodes with high rate and long life is still greatly hindered by the sluggish electronic/ionic transport kinetics and huge volume change during repeated charge/discharge processes. In this work, a scalable and binder‐free 3D porous CuS microflower (CuS‐b) electrode was prepared via a simple method with in situ sulfur engraving on commercial copper foil. The as‐prepared CuS‐b delivers a high reversible capacity of 543 mAh g −1 , excellent rate capability of 413 mAh g −1 at 60 A g −1 and remarkable long‐term cycling stability of 98.2 % capacity retention over 3600 cycles. The 3D self‐supporting porous structure can increase ionic transfer kinetics and provides enough space to buffer the volume expansion/contraction during repeated cycling, resulting in excellent Na storage performances. More importantly, the synthesis path is simple and efficient, which provides new insights for the design and development of high‐performance redox‐active electrodes for large‐scale energy storage applications.