8 - Nano silicon carbon hybrid particles and composites for batteries: Fundamentals, properties and applications

Abstract

Silicon nanoparticles have interesting properties for Li-ion batteries. Today, batteries use graphite (natural or synthetic) as negative electrodes. Graphite has been used as an anode active material since the very beginning of Li-ion batteries but, compared to the positive active materials, its evolution has remained low and is mainly centered on the interface with electrolyte for improved durability at high temperature. Graphite is particularly interesting for its good stability during electrochemical cycling, its low cost, its large availability, and its relatively high capacity (350–375mAh/g based on the LiC6 formation vs. 180–250mAh/g for cathode active materials). Its main drawback is the quasi-absence of improvement perspectives for capacity. Other materials offer potentially much larger capacities, among them silicon and lithium appear to be the most promising with storage capacities of 3579mAh/g (for Li15Si4 phase) and 3860mAh/g, respectively They both have very good capacities, large availabilities (in contrast to germanium for instance), and good technoeconomical potential. This chapter will explain why nanosilicon/carbon hybrids particles have strong interest for Li-ion applications, especially to limit SEI (solid electrolyte interface)-related irreversible capacities. This is made possible by the association of a rather old chemistry (carbon) with silicon particles nanotechnologies to form an active Si/C material. This material meets various well-defined requirements: mainly performances in terms of cycling stability at high capacity values (at least 600 mAh/g), along with cost effectiveness.