Cycling Behavior of Silicon-Containing Graphite Electrodes, Part A: Effect of the Lithiation Protocol

Silicon (Si) is a promising additive for enhancing the specific charge of graphite negative electrodes in Li-ion batteries. However, Si alloying with lithium leads to an extreme volume expansion and in turn to rapid performance decline. Here we present how controlling the lithiation depth affects the performance of graphite/Si electrodes when different lithiation cutoff potentials are applied. The relationship between Si particle size and cutoff potential was investigated to clarify the interdependence of these two parameters and their impact on the performance of Si containing graphite electrodes. For Si with a particle size of 30-50 nm, Li15Si4 is only formed for the potential cutoff of 5 mV vs Li+/Li, whereas using a higher cutoff of 50 mV has no impact on the performance. For larger Si nanoparticles, 70-130 nm in size, Li15Si4 is already formed at 50 mV. However, in these larger particles only 70% of the Si initially participates in the lithiation, independent of the cutoff potential (5 or 50 mV), and the performance fades rapidly. For the highest tested cutoff potential of 120 mV, the contribution of larger Si particles to the specific charge of the electrodes was negligible, but for the smaller particles a stable and still significant Si specific charge was obtained.