The technology developed by the Warwick Manufacturig Group (WMG) works as part a battery’s normal operation and has been tested on standard commercially available automotive battery cells. If a battery becomes over heated it risks severe damage to the electrolyte, breaking down to form gases than are both flammable and cause significant pressure build up. Overcharging of the anode can lead to lithium electroplating that forms metallic dendrites that can cause internal short circuits and fires.
The WMG researchers developed miniature reference electrodes and Fibre Bragg Gratings (FBG) threaded through a bespoke strain protection layer. An outer skin of fluorinated ethylene propylene (FEP) was applied over the fibre, adding chemical protection from the corrosive electrolyte. The result is a sensor with direct contact with all the key parts of the battery and withstand electrical, chemical and mechanical stress inflicted during the batteries operation while still enabling precise temperature and potential readings.
“This method gave us a novel instrumentation design for use on commercial 18650 cells that minimises the adverse and previously unavoidable alterations to the cell geometry," said WMG Associate Professor Dr Rohit Bhagat. "The device included an in-situ reference electrode coupled with an optical fibre temperature sensor. We are confident that similar techniques can also be developed for use in pouch cells.”
The data from the sensor is much more precise than external sensing and this has been used to show that commercially available lithium batteries available today could be charged at least five times faster than the current recommended maximum rates of charge.