Chapter 10 - Processing and properties of silicon anode materials

Abstract

Silicon (Si) is a promising anode material for lithium-ion batteries in comparison with current graphite anodes because of its theoretical capacity of ~4200mAh/g, which is 10 times that of graphite (370mAh/g). However, the lithiation of silicon generates an enormous volume expansion of ~400%-associated stresses generated are known to be the primary reason for fracture and failure of the Si anode leading to a significant capacity fade with cycles. To overcome these limitations of silicon anodes, several innovative processing approaches are pursued by researchers to minimize capacity fade. This chapter covers state-of-the-art descriptions of the stress evolution, failure upon lithiation of silicon anodes, and different ways of processing silicon anodes to overcome capacity fade. Several innovative approaches to understanding the failure mechanisms and improve upon capacity fade from our own research are then described more fully. It is shown that the residual stress in single-crystal Si anodes is tensile and increased from 69MPa after 1 cycle to ~291MPa after 50cycles of lithiation and de-lithiation, which led to failure by fracture of the single crystal silicon anode. Two novel approaches of processing silicon anodes and their performances are also described in this chapter from our research in which inexpensive Si powders are processed and tested for performance and displayed excellent capacity retention of 1050mAh/g or 778mAh/g after 200cycles and coulombic efficiency of 99.6%.