The Obstacle Course on the Path to Repurposing Used EVBs — Part II: Battery Grading

  1. Status quo: how batteries are tested today
  2. What is UL 1974 and what are some of its limitations?
  3. ReJoule’s recommendations for a faster battery grading process
Electric truck battery pack made of lithium iron phosphate (LFP)

The status quo: how batteries are tested today

After you disassemble from packs to modules, you have to sort the modules. You may be able to buy them pre-sorted (ReJoule can help with that!) If not, you start by looking for signs of physical damage or leakage.

What about UL 1974?

UL 1974 is a standard to evaluate the performance of used batteries, but is not yet widely adopted. It includes a procedure to examine and sort batteries and various tests to assign a grade to a used battery, as well as recommendations for how to repackage the used batteries. The test procedures include physical inspection, battery management system (BMS) operation checks, historical data gathering, open circuit voltage (OCV) testing, capacity testing, direct current internal resistance (DCIR) testing, and self-discharge testing. Assuming zero down time, we estimate it would take 40+ hours to complete a UL1974 test per used battery.

ReJoule’s recommendations for a rapid battery grading process

ReJoule’s fast grading technology expands on a proven fast battery testing technique, electrochemical impedance spectroscopy (EIS). These tests measure a battery’s Impedance, a crucial battery health metric that can be used to model a battery’s true health and remaining useful life (RUL).

  • 2% accuracy in 5 minutes test (> 70x faster than status quo)
  • 4% accuracy in 30 seconds test
Our early results on a capacity prediction model based on EIS. The diagonal line shows where 100% accuracy would be. This data is based on the LFP truck modules.
The chart shows the ACI of a cell as its capacity degrades during accelerated aging. Data shown is for NMC 18650 cells. This data was generated using funds from NSF Phase I award.

Next steps

We will expand the screening process to different battery types (chemistries and form factors) so we can continue to refine this process. Form factors include modules and packs as well as cylindrical and pouch cell types. Our cofounder and CEO, Steven is a UL 1974 standards technical panel member and will work with UL on advancing the standard to make it more accessible and viable.

  1. Direct labor: this is the time an operator spends to disassemble, inspect, and test the batteries.
  2. Non-recurring engineering (NRE): there is no one-size-fits-all for batteries so each new battery design requires a bit of engineering to set it up. The more batteries are tested, the lower this cost becomes on a cost per unit basis.
  3. Equipment cost: for high voltage EV batteries, this equipment is easily $50K or more. We allocate a small percentage of that cost to this case study. Same as with the NRE, the cost per unit goes down the more units you test.
  4. Overhead costs: this includes rent (the space the batteries as a percent of your total facility), utilities, and any custom cables or parts. For instance, you may need to buy specific software to be able to perform a BMS check.

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