b is for batteries

Batteries, and the chargers for them, are everywhere. They are available in a wide range of specifications using a variety of chemistries. The characteristics of the battery are determined by the particle size of the electrolyte powder, or slurry, and the surface roughness of the electrodes, which is determined by the particle size of its coating. By controlling the surface area, through particle size, a battery can be optimised for high capacity or high power.

The capacity of a battery is the amount of electrical charge it can deliver at the specified voltage. The capacity depends on the quantity of electrolyte material contained within the battery. Batteries are most commonly manufactured to certain standard shapes, which will dictate the volume available. However by controlling the electrolyte particle size, it is possible to pack more material inside the battery case by filling the interstitial spaces:

particle size distribution packing fraction

Large particles also have the advantage of being able to store more charge, so the arrangement in figure 1b is often preferred.

Unfortunately the power of the battery, or its ability to discharge current, is determined by the reaction between the electrodes and the electrolyte, and is therefore controlled by the surface area of the particles. In this case, it is desirable to reduce the particle size and so increase the surface area. So there is a trade-off in battery design between capacity and power (figure 2).

capacity, power and volume in a battery

In this example, the particle sizes of three different electrolyte materials were measured by laser diffraction. In this case, all three samples contain similar proportions of fine and coarse particles, in order to achieve a high packing fraction as in figure 1b. However the coarse particle sizes vary, enabling the designer to fine-tune the battery properties for high power (EMD 1), as a mid-range battery (EMD 2) and for high capacity (EMD 3) (figure 3).

electrolyte particle size distribution

These samples were provided as slurries, which were dispersed into liquids for measurement in the Mastersizer laser diffraction particle size analyzer. The wide dynamic range of the Mastersizer enables both the coarse and fine particle fractions to be characterized in one single measurement.

Batteries, and the chargers for them, are everywhere and we’ve seen here how batteries are examples of systems regulated by particle size. We’ve also seen that we can easily measure the particle size in the slurries by laser diffraction and that the results can be used to optimise the battery for either high power or high capacity.

For a more detailed description of the particle size analysis of battery materials, please see our documents:

Characterisation of Battery Materials using Laser Diffraction

Charging Ahead – Sizing particles for better batteries

The Influence of Particle Shape on the Characteristics of Coating Films for Battery Electrodes

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