Silicon carbon void structures as anode material for advanced lithium-ion and lithium-sulfur batteries

Due to its high theoretical gravimetric capacity (3590 Ah kg-1 Li15Si4) and its low working potential, silicon is an attractive candidate to at least partially substitute the graphite anode material in state of the art lithium-ion batteries in order to achieve higher energy densities [1]. Additionally, the cycle life of lithium-sulfur batteries mainly suffers from the instable lithium anode. Lithiated silicon could be a more stable alternative preventing dendrite formation and electrolyte decomposition for that next generation battery cell type [2]. During the lithiation process of silicon a large undesirable volume expansion occurs generally known from other lithium alloys [1]. This volume expansion/contraction leads to the degradation of the entire anode and fast capacity fading. Nanostructured silicon carbon composites with free volume between the silicon core and the carbon shell could potentially compensate the volume change and ensure a stabile SEI at the surface of the carbon shell preventing electrolyte consumption during cycling. According to the recently published references, these void structures are mainly generated using silica templates which deliver a precise control of the void structure, but need to be removed by toxic hydrofluoric acid and laborious washing steps [3]. In this work an easily scalable process without this step is presented in order to gain a free volume between silicon and the carbon shell. The void structure results from the removal of a sacrificial template layer on the surface of commercially available silicon particles during the carbonization of the silicon carbon composite within a concerted process.