Robust Micron-sized Silicon Secondary Particles Anchored by Polyimide as High-capacity High-stability Li-ion Battery Anode.

Silicon is an attractive high capacity anode material for lithium-ion battery. With the help of nanostructures, cycle performance of silicon anode has improved significantly in the past couple of years. However, three major shortcomings associated with nanostructures still need to be addressed, namely their high surface area, low tap density and poor scalability. Herein, we present a facile and practical method to produce micron-sized Si secondary particle cluster (SiSPC) with high tap density and low surface area from bulk Si by high energy ball-milling. By coupling SiSPC with a mechanically robust polyimide binder, more than 95% of the initial capacity is retained after 500 cycles at 3500 mA g (1 C rate). Reversibility of electrode thickness change is confirmed by in-situ dilatometry. In addition, the polyimide binder suppresses surface reaction of the particles with electrolyte, resulting in a high coulombic efficiency of 99.7%. Excellent cycle performance is obtained even for thick electrodes with an areal capacity of 3.57 mAh cm, similar to those in commercial lithium-ion batteries. The presented Si electrode system has a high volumetric capacity of 598 mAh cm, which is higher than that of commercial graphite anode materials.