Red phosphorus confined in hierarchical hollow surface-modified Co9S8 for enhanced sodium storage

Abstract

Phosphorus-based materials can be used to construct promising anodes for sodium-ion batteries (SIBs) due to their high theoretical capacity (2596 mA h g⁻¹) and safe working potential. However, their disadvantages are severe volume changes as well as poor electronic conductivity (10⁻¹⁴ S cm⁻¹), resulting in fast capacity decay during cycling. To find solutions to the aforementioned issues, in this work, self-assembled nanosheets were used to synthesize hierarchical hollow spherical Co₉S₈. The unique hierarchical hollow spherical structures provide more active sites, which accommodate the volume change and effectively improve the conductivity. Amorphous red P was encapsulated in the hierarchical hollow spherical Co₉S₈ and formed a P@Co₉S₈ anode. Moreover, the introduction of red P via an evaporation–condensation method led to the effective surface modification of Co₉S₈ and thus further improved the conductivity of the hollow P@Co₉S₈ hybrid anode. The unique structure of SIBs assembled with the P@Co₉S₈ anode alleviated volume change and enabled fast electron transport, and excellent cycling stability and outstanding rate capability were exhibited, retaining a high discharge capacity of 551.7 mA h g⁻¹ after 1000 cycles at 1 A g⁻¹ and maintaining coulombic efficiencies greater than 98.2%. Furthermore, the sodium-ion storage mechanism of P@Co₉S₈ was dynamically investigated, providing a new perspective for determining the electrochemical cycling behavior.