Micro versus Nano: Impact of Particle Size on the Flow Characteristics of Silicon Anode Slurries

Silicon is interesting for use as a negative electrode material in Li-ion batteries due to its extremely high gravimetric capacity compared with today's state-of-the-art material, graphite. However, during cycling the Si particles suffer from large volume changes, leading to particle cracking, electrolyte decompositions, and electrode disintegration. Although utilizing nm-sized particles can mitigate some of these issues, it would instead be more cost-effective to incorporate mu m-sized silicon particles in the anode. Herein, it is shown that the size of the Si particles not only influences the electrode cycling properties but also has a decisive impact on the processing characteristics during electrode preparation. In water-based slurries and suspensions containing mu m-Si and nm-Si particles, the smaller particles consistently give higher viscosities and more pronounced viscoelastic properties, particularly at low shear rates. This difference is observed even when the Si particles are present as a minor component in blends with graphite. It is found that the viscosity follows the particle volume fraction divided by the particle radius, suggesting that it is dependent on the surface area concentration of the Si particles.