In-situ measurement for current distribution in electrochemical cells

Power management systems monitor electrochemical devices, such as fuel cells, batteries, or electrolysers. They work by measuring individual cell voltage across hundreds of cells.

Cells are usually stacked in series and a single measurement of current (or reaction rate) can be used. But, the measured current is not evenly distributed throughout the cells.

At high rates, small areas of an electrode could operate at much higher current density than the rest of the electrode. Standard techniques cannot detect these variations.

Since cells are assembled in stacks and modules, a failure of one of the cells could impact and compromise adjacent cells. Failures may also affect the whole battery module or stack of cells.

Importantly, if one cell started into thermal runaway this could cause catastrophic failure of the whole system due to propagation.

It is possible to measure current distribution within cells in an array of electrodes. This requires breaking down one cell to an array of small cells and logging temperature and current variation in different locations across the array of electrodes. Constructing a cell electrode out of a smaller array of electrodes has limited resolution because of the size of a unit cell and this method is complex and costly.

Technology overview

We have developed an in-situ measurement technique for current distribution in cells.

The technique uses magneto-optical materials that rotate the plane of polarised light in the presence of an applied magnetic field. The amount of rotation observed is
proportional to the field strength where field strength is induced by electrical current.

A direct real-time visualization of current distribution over an entire electrode surface is achieved through coating the back of the electrode with an insulating film incorporating the magneto-optical materials. These materials allow for detection of magnetic field strength with resolution in the range of sub mT and saturation levels 10-100mT or current densities 10s of mA/cm² to A/cm² range.

Succesful testing

The method has been tested successfully on commercial Li Pouch cell 2000 and 4000 mAh.

The sensor was sensitive to 0-2.5mT and could detect current distribution in cells and how it changes over time.

A direct correlation is seen between battery state of health (age) and increase in heterogeneity of current in battery.

Advantages

The technique is agnostic to battery chemistry.

Current research and development is directed at:

1. Developing algorithms to predict battery state of charge and health.
2. Applying the technology to battery packs, fuel cell and electrolyser stacks (i.e. multiples of cells).

Applications

The technology could be applied as a hand held QC device or incorporated into battery management systems.

Opportunity and further information

We are seeking licensing, commercial partners or development partners.

The academic leading the development of this technology is Professor Mohamed Mamlouk.

Contact

For further information, please contact:

• Dr Tim Blackburn, Business Development Manager
• tim.blackburn@newcastle.ac.uk