Batteries are ubiquitous in modern life and our reliance on them has never been greater. Therefore, ensuring optimum battery performance through manufacturing control is of increasing significance. In previous application notes we have discussed the importance of controlling the size of particles used in the manufacture of battery materials [1] and the impact of carbon microstructure in graphite electrodes on battery performance [2]. Shape is also an important factor to consider and control, as irregular shaped particles not only reduce packing density, but they can lead to the formation of a high viscosity electrode slurry. In this third application note on batteries, we consider the role of size and shape on the viscosity of the electrode slurry
Electrode composition
The typical structure of a battery electrode is given in Figure 1. The electrode is usually fabricated by applying a slurry of particles in suspension onto a metal foil.
The slurry in question is composed of electrode particles (anode or cathode), small carbon particles to aid conduction, and binder material (composed of solvent and polymer) to hold the structure together. The concentration of particles in the slurry is high, representing between 20-40 % of the total by weight. Consequently, the particle properties have a significant impact on the physical properties of the resultant slurry.
Particle properties and slurry viscosity
The viscosity, dispersibility, concentration and compactability of the slurry are important parameters in determining how effective the slurry will be during application. A high viscosity slurry causes difficulties in the coating process , and poor dispersibility results in low film uniformity; the concentration and compactability of the slurry controls the film density. Uniformity of the coating thickness and the layer density are important to ensure control over the ion transfer rate and life time (recharge cycle time) of the battery, while controlling the layer thickness enables a smaller battery to be produced.
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