Why is moisture measurement critical in lithium-ion battery manufacture? - Part One

Cleanliness is essential to the production process of Lithium-ion batteries, particularly for the anode and cathode coating, which needs to be carried out in two separate clean rooms as the materials cannot be allowed to come into contact with each other. The electrolyte filling must also be performed in a dry environment to prevent the Lithium Hexafluoride reacting with water vapour in the air to form Hydrogen Fluoride. Most manufacturers will carry out the entire assembly process in clean & controlled environments

As a general rule the ambient air in the production environment needs to be drier than -30 °C dew point (or 1.4 %rh at 23 °C).

With many people working on cell manufacturing, the moisture emissions from the personnel must be removed by continually cycling the air from the production environment through rotary dryers.

Parts of the process may take place in a glove box, possibly at near vacuum pressures, where the humidity can be reduced to even lower dew point temperatures, often as low as -65 °C dew point (approx. 3 ppmV, or 0.01 %rh).

What are the best options to measure low humidity environments for battery production?

In these challenging conditions, it’s important to use measurement instrumentation that is both highly sensitive and extremely reliable.

Chilled mirror hygrometers are accurate to ±0.15 °C or better. Because they measure the actual temperature at which condensation forms, they have virtually no drift over time, making them one of the most reliable and practical types of instruments for this application. Measurement ranges vary between models, but for really low humidity levels – below -30 °C dew point – a chilled mirror is the best option.

The chilled mirror hygrometers are used to sample the environmental moisture content at key locations in the manufacturing area. Linking them to a Supervisory Control and Data Acquisition (SCADA) system enables them to directly control the dehumidifiers to maximise energy efficiency. Alarms are essential to provide an immediate indication when the humidity of the room exceeds the specified amount.

Recommended products for monitoring trace humidity in battery production

Michell S8000 RS– best for very dry applications

Michell S8000 – best for dry applications to around -40 °C dew point

Michell Optidew – best for lower specification plants to measure RH or dew point down to -30 °C dew point

Get expert advice for controlling humidity in dry industrial conditions

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