A process for grading used lithium-ion batteries from electric vehicles in less than 15 minutes has been developed by researchers in the UK using packs from vehicle OEM Nissan.
The process of embedding algorithms to grade second-life batteries was developed by WMG, University of Warwick, alongside electronics firm Ametek. WMG is due to make a technical publication in a few months, and a patent has been applied for the algorithm.
The team was able to grade 50 used Nissan LEAF battery modules in quarter of an hour rather than three hours the process normally takes.
Researchers used Electrochemical Impedance Spectroscopy (EIS) to determine module state of health (SOH). Modules with a SOH of more than 65% are used in energy storage applications, lower SOH and the modules are placed in other specific applications (spare parts). Those without sufficient SOH are recycled.
For example the Generation 1 Nissan LEAF has a new battery capacity of 24kWh. So if the used battery has a capacity of 17 kWh, the SOH is 70%
David Greenwood, professor, Advanced Propulsion Systems WMG, The University of Warwick, told BEST: “In essence, we use an electrochemical impedance spectrograph of the full module, and derive some factors from that which can be compared to a known “ageing” pattern.
“We have done extensive testing to confirm that this short test, taking under three minutes, is accurate to within a few percent of the figure obtained from full charge and discharge tests lasting several hours.
“This yields two key figures, both expressed as a percentage – a state of health for capacity (what proportion of the module original capacity remains accessible) and a state of health for power (what proportion of the original module power is still accessible). Different second life applications value these two features differently – so even a module with poor energy capacity could still be useful for applications which need short bursts of power.”
The process developed in WMG was successfully transferred to a pilot second-life facility, where 1MWh of second-life energy storage was deployed last year.
Nissan hopes to be able to re-use the vast majority of packs assembled in EVs in Europe using the grading process tested at the second-life pilot facility.
Andrew Williams, Ametek advanced measurement technology business unit manager, said the algorithm was developed with assistance from Ametek EIS analyzers.
Professor David Greenwood from WMG, University of Warwick, said: “Opening up a second life for batteries improves both the environmental and the economic value we draw from those resources before they need recycling.”
If successful, the project aims to open the UK”s first facility for grading and sorting end-of-life battery packs.