Porous microspherical silicon composite anode material for lithium ion battery

• Porous Si/CNT/C microspheres are obtained via spray drying and carbonization.
• The favorable composite structure leads to excellent cycling stability and rate performance.
• Introduction of copper into the microspheres significantly enhances the mechanical stability and cycle performance.

Nano/micro-structured Si/CNT/C and Si-Cu/CNT/C microspheres are prepared by two simple steps of spray drying and carbonization, which are efficient and easy to scale up. In the Si/CNT/C composites, silicon particles (about 50–200 nm) are covered by a layer of carbon formed by pyrolysis of phenol-formaldenhyde resin (PF), which, in turn, connects with the three-dimensional multiwall carbon nanotubes (MWCNTs) conductive network. Numerous open pores, which could buffer volume expansion of silicon and improve the electrode kinetics, are engendered in the microspheres due to the rapid evaporation of solvent and unfoldment of flexible MWCNTs. Moreover, introduction of small amount of copper (5 wt.%) into the microspheres as Cu3Si phase reinforces the mechanical stability and improves the electronic conductivity. The favorable Si/CNT/C composite structure leads to significantly improved cycling stability and rate performance (ca. 1250 mA h g−1 at 5 A g−1) compared to pristine Si particles. Addition of copper further enhances the capacity retention to 91.2% after 80 cycles.

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