Controllable construction of core–shell CuCo2S4@polypyrrole nanocomposites as advanced anode materials for high-performance sodium ion half/full batteries

Abstract

It is important to design and fabricate novel anode materials with stable structure and high capacity for sodium ion batteries (SIBs). Herein, core–shell CuCo₂S₄@polypyrrole (CS-CuCo₂S₄@PPy) nanocomposites were prepared by a facile solvothermal reaction and subsequent in situ chemical oxidation polymerization. The CS-CuCo₂S₄@PPy nanocomposites show superior electrochemical performance for half SIBs with a high reversible capacity (551.2 mA h g⁻¹ at 0.1 A g⁻¹ after 200 cycles), excellent rate capability (370.7 mA h g⁻¹ at 2 A g⁻¹), and ultra-long cycling stability (324.9 mA h g⁻¹ at 2 A g⁻¹ after 2000 cycles). In addition, the kinetic analysis reveals that 74.6% of charge contribution is from capacitive-controlled capacity. The Na₃V₂(PO₄)₃‖CS-CuCo₂S₄@PPy full cell further illustrates its practical application with a high capacity of 243.6 mA h g⁻¹ at 0.5 A g⁻¹ after 150 cycles. The competitive electrochemical performances of CS-CuCo₂S₄@PPy can be attributed to the core–shell structure and the synergistic effect of CuCo₂S₄ and PPy. The ternary spinel CuCo₂S₄ can offer rich valence constituent and active sites to achieve high capacity. The PPy layer cannot only improve the electrical conductivity but also buffer the volume variation to protect CuCo₂S₄ spheres from pulverization during the charge/discharge processes. This work provides a facile method to prepare conductive polymer-coated transition metal sulfide nanocomposites with stable core–shell architectures, confirming their potential application in the energy storage and conversion field.