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

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.