Technology Dive: Formation
If you enjoy this newsletter please give us a share and subscribe! For business inquiries, please reach out!
I have recently been exploring battery formation cycling in manufacturing through reading papers and interviews with industry/factory professionals and thought it would be useful to share some cleaned-up notes.
What is formation?
Once batteries are assembled in a factory into their final form, cells go through a formation and ageing process. There are several steps in the process, and each company/factory has its own flavour of doing it (different C-rates, different temperatures, different # cycles, different voltages, etc) depending on what cells they’re making, and is very difficult to get this trade secret.
It starts from charging cells to a low voltage (e.g. 1.5V) to protect the copper from corrosion, and then a rest session for electrolyte wetting.
The cells are charged/discharged at a very low C-rate (e.g. C/20) to ensure a stable SEI layer is formed.
After or during formation cycles, there could be steps at an elevated temperature too for further electrolyte wetting and SEI stabilization.
Cells are degassed before finally being sealed for shipment.
The point of the formation step is to form the first charge/discharge cycles so they’re ready to go. The formation step is also used as quality control when you would find out if any cells are faulty if they:
Don’t show the expected capacity during the first few cycles, perhaps to any defects throughout any of the previous manufacturing processes
Have unexpected dimensional changes/swelling
The problem
Time. The whole process can last on the order of 20 hours (maybe less) to 3 weeks. This makes it a bottleneck sometimes. Other times, it isn’t since the bottleneck is already baked into the process.
Capital. There are significant costs in terms of floor space, equipment, and energy to process. There is some labour too, but can be quite hands-off as many processes are automated depending on the factory.
Costs. Nelson et al. estimated it costs ~32% of the entire manufacturing process. In terms of electricity usage, it uses a small amount <1% of total energy costs per cell. In an industry where margins are thin, any amount of cost savings is attractive especially when manufacturing volumes are large.