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

Abstract

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 μm‐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 μm‐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.

Future Material Developments for Electric Vehicle Battery Cells Answering Growing Demands from an End-User Perspective

“…Indeed, several groups have focused their research on obtaining innovative Si nano-structures to limit the difficulties associated with the volumetric expansion [75,76]. Nevertheless, incorporating micron-sized particles is unequivocally more cost-effective for processing real Li-ion anodes [77]. Furthermore, Si requires fluoroethylene carbonate (FEC) as an additive in the electrolyte to form a stable SEI, which further increases the cost of the cell [71,78].…”

“…Some more realistic research fields attempting the adoption of Si as a regular anode material have been associated with the development of novel binders to minimise the impact of the volumetric expansion [69,79] or the prelithiation of Si-based electrodes to mitigate the capacity losses during the first cycles [75,80,81]. In any case, Si is usually added as an additive, blended with graphite, in the anode formulation [75,77,81] as the aforementioned difficulties associated with its volume change limit its use as the sole active material. In the last years, the development of Si-carbon composites has been widely promoted due to the industrial interest of Si [82][83][84][85].…”

Towards a 3D-resolved model of Si/Graphite composite electrodes from manufacturing simulations

“…Of course, the rheological properties of the slurry without Si nanoparticles must not necessarily have to be similar to the ones of a slurry containing a small addition of Si nanoparticles. In fact, evidence suggests that the rheological properties of graphite/Si slurries differ when using μm-sized and nm-sized Si particles [56]. However, Si in dried electrodes is visible by common microscopy techniques such as Scanning Electron Microscopy (SEM), which allows reproducing its location ad hoc without the need of following their particle evolution from the slurry to the dried electrode.…”

Understanding the processability of graphite blend electrodes with silicon nanoparticles

“…14 The Si size influence has been studied in the slurry rheology with 35% solid content, revealing a higher viscosity for Si nanoparticle-graphite blends (Si Nps/Gr) than Si microparticle-graphite blends (Si µps/Gr). 15 Another helpful technique is to perform frequency sweeps, where the storage (G') and loss (G") modulus can provide hints about the slurry stability and microstructure. However, these slurry studies are reported less frequently.…”