Designing silicon based anode for lithium-ion batteries

Abstract

Lithium-ion batteries (LIBs) are the most widely used energy storage devices at present, especially in portable electronic devices. However, to satisfy the requirement of electric vehicles and other applications like grid storage, the current commercial graphite based anodes are limited by their theoretical capacity of 372mAh/g. Among a variety of alternative to replace graphite, silicon is a promising anode material because of its high theoretical capacity of 4200mAh/g. However, the capacity of these anodes fade quickly after few initial cycles of operation because of stresses induced by large volume expansion of the silicon during lithiation, which primarily results in fracture of particles. To overcome this issue, several strategies have been employed, for example, reducing the size of silicon and making composite with other materials. But often these methods are difficult to achieve a stable and reversible capacity after many cycles and are not cost effective. In this study, an innovative method is used for realizing a high reversible capacity anode based on silicon by negating the effect of volume expansion, based on low cost metallurgical grade polycrystalline silicon powder. In this approach, first the silicon nanowires are created by metal assisted chemical etching and then a rapid freezing of the solution containing superconductive carbon particles and etched silicon particles in furfuryl alcohol is carried out. In the next step, the mixture is pyrolyzed for getting conformal coating of carbon on the etched silicon particles. The coating together with the highly conducting phase of carbon not only improves the conductivity of the electrode (both the connection between the active particles and with the current collector) but also provides the flexibility for managing the volume expansion during lithiation. The resultant material exhibited a reversible specific capacity of more than 1200mAh/g after 50 cycles with a coulombic efficiency of 99.6%.