Dispelling Battery Chemistry Myths - Link and Summary of Battery Chemistry Technical Insights from Luke Workman's Interview with Electrek.co

[0000]

There is a lot of BS circulating out there, much of it stemming from claims promising great leaps forward on future battery capabilities that are always just around the corner from being available to the consumer market (and eventually to our wheels). It's also often hard to evaluate these claims as most of us don't have an extensive technical background and/or professional experience testing chemistries which results in a lot of confusion and baseless assertions frequently getting thrown around.

I think it's fair to say too that our resident Fire History thread is an ever-present reminder that in rare instances sometimes things can go horribly wrong for some too.

With these concerns in mind, I found Luke Workman's recent interview with Electrek to be particularly enlightening and highly valuable for dispelling a lot of myths people may have adopted often originating from overly enthusiastic tech journalists and the like sloshing around on the inter-webs. The interview starts out a little rough so the link is timestamped to start at 2 mins (segment lasts until about minute 29). They are speaking on ebike batteries, but the insights and advice are equally relevant to EUCs.

Be forewarned, the guy's a scientist, not a polished teleprompter reader (makes it way better IMO) and some of the concepts involved are fairly technical.

 

Some key take-aways:

• Explains a largely unstated risk from riding in winter conditions or freeze/thaw cycles, especially regarding road salt and how this is especially relevant to NY ebike battery fires
• Explains how all battery cells all leak electrolyte to some degree through normal heating and cooling cycles, even being sealed, and the expelled vapor tends to stick/condensate on surfaces with the greatest heat transfer capability (metal) forming bridges over time (numerous heating/cooling cycles) that can eventuate in a voltage potential across the condensate causing electrolysis and thermal runaway
• Explains why IP67 water submersion test is an extremely weak indicator for full product lifecycle battery safety
• No battery standard exists that is useful or meaningful in qualifying whether a battery pack will catch fire over it's lifecycle
• Potted batteries are the key to safe lithium ion battery packs
  • Monolithic polymeric encapsulation removes air barriers eliminating the risk of electrolyte vapor condensate interactions and corrosion completely and helps with even heat transfer between individual cells.
  • Potting with endothermic resins provides an inherent fire-quenching capability to the pack via phase change energy (solid-->liquid). In other words, a well-matched endothermic resin can help both prevent battery fires from occurring as well as negate the necessity for fighting a fire in the first place if an individual cell experiences thermal runaway.
• The fire risk profile from the perspective of liquid ingress and molten salt bridges forming over time is exactly the same whether you're dealing with lithium ion batteries or lithium iron phosphate batteries. The only difference is whether your house burns down because the initial fire starts at 1600 degrees C or 500 degrees C respectively.
  • Anecdotally, his companies professional "post-mortem" evaluations of battery fires has dis proportionally been populated by LiFePO4 batteries as he believes some people are mistakenly assuming lithium iron phosphate are inherently a "safe" chemistry and not taking design of their battery systems for safety as seriously.
• Entertaining (non)disclosure regarding solid state batteries
  • Favors compressed gas over solid electrolyte (solid state) chemistries for extremely safety-relevant chemical realities. Specifically to avoid the possibility of creating explosive poison clouds that cause immediate death even on the scale of even small consumer product batteries, much less PEVs or 4-wheel vehicles, after a mechanical intrusion (puncture).
    • In other words, it seems a fair bet to say solid state batteries are off the menu.
• From a pure physics perspective, large improvements to energy dense batteries are possible with the abundant materials that are readily available - it's a combination of manufacturing challenges and economic feasibility standing in the way of the significant battery improvements we all want.

EUC relevant TL;DW:

So basically, if we want to achieve a collective higher level of safety today and have less EUC fires making the news in the future, we should be asking the EUC manufacturers for all battery packs to come potted (in an endothermic resin).

Edited July 13, 2023 by Vanturion

[Punxatawneyjoe]

1 hour ago, Vanturion said:

Potted batteries are the key to safe lithium ion battery packs

Great video, thanks for finding/sharing this. A lot of great insight. So basically the v13 battery is the only safe one and up here in the north east is a bad place to be riding EUC or any other electric device.

[0000]

10 hours ago, Punxatawneyjoe said:

So basically the v13 battery is the only safe one

Safer maybe, however, I don't think you could claim safe with 100% certainty especially in lieu of some of the information disclosed in the interview. From InMotion's website:

Quote

The battery pack is shielded with stainless steel plates and has an IP67 waterproof rating, making it safer for the riders to use their Challengers in wet conditions

IP67 is a test of water ingress in low-pressure immersion meaning the water surface tension property comes into effect (water tends to stick to itself) which makes it easier to pass this test. IP67 is no way an test of whether you will experience water vapor intrusion (spray coming off 50 mph wheel for example) in real world conditions as Luke pointed out.

The first digit 6 in the IP67 simply means that the Dust Tight: no ingress of dust; this is an airflow test. The second digit 7 is the water submersion test at 1 meter for 30 minutes.

It would be different matter if IP67 was testing a *insert max wheel speed* salt-water slurry spray over the device for 30 minutes and check of water ingress afterwards, but it's not. What the 7 in IP67 says is that you'll (probably) be OK if you pour water on the wheel or submerge it up to 1 meter depth for a while.

Without potting, the ever-present electrolyte leakage at the cell level can occupy the spaces that would otherwise be filled with resin in a safer pack design. This electrolyte bridge formation, if it occurs a high enough rate, over time, can create the hazard where a liquid ingress, salt spray especially, could cause a fire.

Another thing worth pointing out - I assume the stainless steel plates are to protect against mechanical intrusion; however, in the interview Luke highlighted that the electrolyte vapor leakage tends to condensate on metal surfaces, so it's possible that these plates could be a potential hazard by introducing more pathways/surface area for electrolyte bridging to occur. Although the risk would depend on where the plates are located relative to the cells, I'm just throwing that out there as a consideration that may not have been considered by the InMotion design team.

Notice InMotion wisely doesn't claim their packs are safe (perfect safety), simply that they make it safer to ride in wet conditions. It's not an objectively measurable statement beyond the IP67 rating. I'm spending a lot of time on this, but it seems like people, myself included, sometimes see a rating and make a lot of safety assumptions that aren't necessarily based in reality so I apologize for being long-winded here.

10 hours ago, Punxatawneyjoe said:

up here in the north east is a bad place to be riding EUC or any other electric device.

I think it's fair to say most riders prefer fair weather conditions so it's probably also reasonable to say the electrolyte leakage phenomenon probably won't cause problems for the full product (EUC) lifecycle. For those like yourself who may ride in winter conditions, especially in areas that salt, it would probably be wise to exercise increased caution with storing your wheels. At the very least, be aware that you're riding at elevated risk, especially over time.

Besides end-user safety, manufacturers should be producing a robust design that is safe in the full spectrum of riding conditions, including the most adverse. It just makes sense from a future liability point of view to pot all of their battery packs going forward.

Edited July 13, 2023 by Vanturion