A micro-sized Si–CNT anode for practical application via a one-step, low-cost and green method

Silicon (Si) has been used in Li-ion batteries (LIBs), and considerable progress has been achieved in design and engineering with improved capacity and cycling. However, large-scale application of Si-based anodes is hindered owing to the wide use of toxic raw materials, high manufacturing cost, limited capacity and unpalatable tap density. Herein, we describe a low-cost and green route to solve these problems. Composite Si–carbon nanotube (CNT) spheres were synthesized using a scalable method: rotary spray drying. These spheres were interspersed by many CNTs and wrapped Si nanoparticles (SiNPs) within them. Due to slightly rigid structure of CNTs, many void spaces in spheres could be preserved during the agglomeration of spheres. These voids could accommodate the volume expansion of Si particles and promote a stable integral structure during cycling. Importantly, this micron-grade material could improve the volume density and tap density to achieve high energy density. The prepared material showed promising reversible capacity of 2500 mA h g−1 with retention of 98% during 500 cycles. Ultra-fast discharge–charge (900 mA h g−1 at 20C) was achieved owing to the crosslinking effect between CNTs and SiNPs in these spheres. Moreover, a high-performance Si material was actualized via a simple industrial method rather than a complex synthesis.