As
@svetz said, I do have some of these cells in my system. My first bank of them has now been running for 14 months. Cycling about 40% of their capacity every day. Full charge was just shy of 90% and running them down to about 50% each night. That original pack is made from the LG GM 2017 Vista 2.1 version cells. They were brand new, never cycled in a car. The GM plant evidently rejected them because the robot was not able to fit them into the car. Most likely the bolt holes didn't line up. They are an NMC chemistry which is safer than many Cobalt type cells, but can obviously still burn. They are not as safe as LFP type cells, but they hold more energy for their size and weight, and can also accept much high charge and discharge currents. The cells are rated for continuous charge at up to 1C and discharge to 3C. So fully charge in 1 hour, and discharge in just 20 minutes. Think about that for a bit. This is how the Chevy Bolt can accelerate to 60 in under 7 seconds on a 60 KWH battery. Tesla pushes their NMC cells to 5C, or full to dead in just 12 minutes.
In my use, I am charging the cells at far less than 0.1C rate, keeping the cell voltage under 4.1 volts (now down to just 4.05 volts or 82% charged) and my maximum draw so far has only been to 80 amps, which calculated back to 0.22C discharge rate. At these low current rates, the cells are running stone cold. There is no temp rise over the concrete floor of my garage. I have temp monitoring, and a smoke detector. If anything goes wrong, it is one plug, and roll the steel cabinet out of the garage. I am keeping a close on on them, but I am not worried about them.
I have now added another bank of Chevy Bolt cells. The second bank has now been online just over 2 weeks. There are 2020 cells labeled Gen 2.2 that came out of a car that was totaled with very low mileage. When I added the second bank, I lowered the full charge voltage down from the 4.10 to 4.05 volts to reduce the stress, and I also raised the low side cut off as well. My total current is a little higher, but that makes the current per bank only about 60% of what it was before. I am only cycling 30% of the cells capacity now, and the currents are even lower. At the state of charge and the currents I am using, I am not worried about the fire risk.
GM and LG have been studying the problem, and it seems they may have finally found the root cause. The first flaw is when the cells are being made, the separator sheet in 1 cell out of hundreds might have a fold in it. If it happens in only one place in a cell, it should not cause a problem. But it just cause a high spot that puts more pressure on the separators in the other layers of the cell. They do not think that this alone would cause a problem as there is a foam pad between each pair of cells to give some room for the cells to swell. But they also identified an assembly problem where the robot spot welding the cell tabs to the bus bars was evidently using too much force. This seems to have caused a few cells to end up with a small tear in the cell tab. The Chevy Bolt battery pack uses groups of 3 cells in parallel. With one of the cells having a ton tab, it will cause the group of three to not properly share the current load. The two with intact tabs carry more current, and that can cause them to swell more, and the one with the tear has higher resistance, so it will be heated from that and also cause some swelling. Combine this with a cell that has a folded separator, and the extra room for the cell to swell can be used up and the anode and cathode can get forced through the separator and cause a short. The odds of the problems stacking onto a single cell are quite slim, and I know none of my cells have any tears in the tabs. Add to that my cells never get even the slightest bit warm. Again, not worried.
The original Tesla battery design is not as energy dense. Their battery pack is much larger and heavier for a given amount of stored energy. They are using many small cells in parallel. The Bolt Design is just 3 cells in parallel, but each cell is 60 amp hours. Tesla's newer battery designs are moving to fewer but larger cells as the packaging becomes more efficient. But they are still going with metal cased cylindrical cells. Both systems use a liquid cooling system to help manage the cell temperature. In the Tesla, they have a flattened tube weaving between and contacting the case of each cell. In the Chevy Bolt design, there is an aluminum plate runner between each pair of cells, and then folding over 90 degrees above and below the cells. On the bottom side, these aluminum plates are resting on the cooling plates with the coolant flowing under the cells. A huge amount of the cells surface are is in contact with the aluminum cooling plates. Cell temperature in normal use has not been a problem with either design.
Any type of battery can become dangerous. The fact there may be a flaw inside some of my cells did make me a little nervous at first, but I am closely following the news from GM and LG and taking precautions. My brother and his wife both own Chevy Bolts, and they really like them. They are actually running a much higher risk than I am . Even with both of my battery banks, I am still at just 36 KWH of battery. With their 2 cars, they now have 120 KWH of these cells. For now they have the reduced charging limit, and they have not been using fast charging. Under the latest recall, it seems they are going to change the entire battery pack in early models, and they will open and inspect the newer models and only replace bricks that have an issue. They have not said how this will be determined though. If it is just looking for torn tabs, then I know mine are safe from that.