Abstract
This application note describes the use of laser diffraction measuring particle size during battery manufacture. The particle size distribution of the materials used within battery electrodes is important in defining battery power and capacity.
Introduction
The market for batteries is rapidly growing. The increased demand for portable electronic devices, including mobile phones and laptops, has required great advances in battery technology in order to provide a light weight, long lasting and stable power source. Battery technology is also being pushed further in electric vehicle applications, which require even more lightweight, high power and fast charging batteries. Both primary (disposable) and secondary (rechargeable) batteries use a wide range of materials in order to achieve the required energy density at a reasonable cost. Within this, an important aspect in the design of the battery is the particle size of the materials used within the electrodes, as this helps define the battery power and capacity. In this application note, we investigated some of the common materials used in battery production, and how the particle size of these can be characterized using the technique of laser diffraction.Particle size requirements
The performance of a battery can be characterized according to the amount of energy that it can store or the amount of power that it can produce. For a particular cell chemistry and battery size, the performance can be optimized for high energy capacity or high power [2]. The power of a battery or its current handling capacity is dependent on the rate of the reaction between the electrodes and electrolyte. This is affected by the particle size distribution of the electrode material, as this defines the available surface area. The maximum battery power can be increased by decreasing the particle size of the electrode material and increasing the surface area.However, the energy storage capacity of a battery is dependent on the volume of electrolyte contained within the cell. As such, there has to be a balance between the space occupied by the electrodes and electrolyte. Reducing the particle size of the electrode material will increase the surface area; however it will also affect the size of the voids between the electrode particles, causing a reduction the overall electrolyte volume and the battery capacity. If these voids become too small then the contact between the electrode surfaces and the electrolyte is also reduced. This may reduce the ionic mobility within the battery, affecting the rate of reaction and reducing the battery's power. As a result, a mixture of coarse and fine particles is often used in the electrodes in order to increase surface area, through the introduction of fines, whilst also controlling the overall packing fraction of the electrode material. This allows good contact between the electrode and the electrolyte [4,5]. The particle size and distribution will also be important during production since it will affect the tap density and compressibility. These are both important parameters in the production of alkaline batteries where the cathode is compressed into shape. The detection of agglomerates will be important, as these may affect the quality of the cathode surface.>> Download the full Application Note as PDF
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