Scalable synthesis of porous silicon/carbon microspheres as improved anode materials for Li-ion batteries

We report the scalable synthesis of porous Si/C microspheres (PSCMs) by a spray drying process using carbon black (CB) or graphitized carbon black (GCB) nanoparticles as the primary carbon source, Si nanoparticles as the active additive, and sucrose as the binder, followed by a heat treatment at 900 °C. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption, thermogravimetric analysis, and Raman spectroscopy. It was found that the PSCMs have a particle size range of 5-20 μm, and those composed of GCB and 5 wt% Si nanoparticles (named GCBSi5) display improved electrochemical performance. As can be observed, GCBSi5 delivered a reversible capacity of 483 mA h g^-1 at the current density of 50 mA g^-1 after 100 cycles, which is much higher than that of the commercial graphite microspheres (GMs; 344 mA h g^-1). More importantly, GCBSi5 exhibited excellent rate performance, for example, its capacity is around 435 and 380 mA h g^-1 at the current densities of 500 and 1000 mA g^-1, respectively, which is much higher than those of GMs (200 and 100 mA h g^-1). These enhanced electrochemical properties should correlate with its porous structure that can significantly suppress the aggregation and volume expansion/contraction of the Si nanoparticles and speed up Li ion diffusion. In addition, the introduction of GCB and carbon matrix interconnected with hard carbon derived from sucrose can enhance the electronic conductivity. This work demonstrates the feasibility of the large-scale and low-cost production of Si/C anode composites for Li-ion batteries.