Batteries and Battery Separators

Batteries and separators

The porous nature of various elements in the structure of a battery has a crucial effect on its performance and is the subject of much material characterisation work using PMI instruments. Materials used to separate the cells in a battery are of particular concern, but so too are a number of other key components.

Battery separators need to be tested and analysed in relation to, for example, the rate at which they take up cathode and anode gases or liquids, and the rate at which ions of different sizes pass through or are retained. Raw materials such as zinc dioxide and manganese dioxide, which are part of the cell composition, also need to characterised.

Capillary flow porometry is the main technique used in this analysis, although a variety of supporting methods are combined to yield comprehensive data. A porometer will measure the pore size of the separator material’s through-pores, which have an important bearing on its behaviour and its transport properties. By determining pore throat size, it is possible to make predictions on retention and – in turn – its effect on how the battery performs.

There is much more to a separator material’s porosity than its dead-end pores, as the characteristics of all of its pores can have an effect – as can the shape and surface structure of the separator. A porometer cannot answer every question, so PMI employs other instruments, including its mercury intrusion porosimeter and its BET sorptometer, to complete the picture. Total pore volume, surface area and chemisorption are among the factors to be determined.

Analysis of the powdered materials found in cells includes measuring surface area, pore size and shape, as these affect reactivity. Again the mercury intrusion porosimeter and BET sorptometer have important roles to play.

PMI’s development of instruments to help in this industry sector continues at a rapid pace. For example, in recent years the minimum pore size that can be measured, for through-pores, has come down from 33 nm to 13.5 nm.

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