Rational Design of Robust Si/C Microspheres for High-Tap-Density Anode Materials

Si has been recognized as a next-generation anode alternative to graphite for high-energy-density lithium-ion batteries. However, the most intractable problem of previous Si-based anodes is the relatively low compressive strength of particles because of excess voids and porous structures, thus leading to poor structural integrity and electrochemical performance under high pressure of the rolling procedure in practical application. Therefore, a rational design of robust Si/C microspheres with a compact nano/microstructure is an effective strategy to address the above-mentioned issues. In this ingenious structure, Si nanoparticles are homogeneously dispersed and anchored on flake graphite and then the composites self-assemble into microspheres via polycondensation and surface tension of pitch under high temperature and high pressure. Benefitting from this innovative approach and rational design, the obtained robust Si/C microspheres not only present high compressive property and high tap density (1.0 g cm^–3) but also demonstrate high initial Coulombic efficiency (90.5%) and cycling stability with areal capacity (4 mA h cm^–2) under a compaction density of 1.3 g cm^–3. Furthermore, the full cell assembled with LiNi_0.8Co_0.1Mn_0.1O₂ and the resultant Si/C microsphere anode also displays good cycling performance and rate capabilities. Owing to these aspects, the proposed rational design of encapsulating Si nanoparticles in high-tap-density microspheres could be extended to load other nanomaterials for advanced batteries.