Don't get me wrong, I like the HummerEv, and GM, but neither are perfect. I think its better to be critical of your team so they learn and get better, if people act like everything GM (insert any manufacture) is doing perfect and great, the company does not move forward. for years GM has squandered their position and now Mary Barra talking about GM being a leader in EV is nonsense, nothing could be less true as GM has had to recall every BEV they have made for the last 5 years, and put their customers through a tough time, and its mostly because they did not do enough validation on LG's product, ya, LG the company they are now joined at the hip with in future battery project. I am not sure doing the giant pouch cells that make up the Ultium system are the right way to go, as its really hard to keep pouch cells restrained (they move as they charge and discharge), and the cell has a much greater distance to the center from the cooling plate, which leaves potential for hot spots in individual cells that are hard to detect by the BMS, also once a pouch cell starts to enter a failure or thermal runaway they is no stopping or even slowing it. Bigger and more energetic pouch cells such as used in Ultium could turn out to be a huge mistake for many technical reasons. Cylindrical cells seem easier/ faster to manufacture, cheaper, and safer as they do not fold the layers on top of each other and have a metal can to contain them and keep them dimensionally stable. Cylindrical cell packs like Tesla also have a small fuse on each cell where if the cell overheats the fuse breaks and the cell is offline, hopefully prior to thermal runaway. Tesla pats are also filled with fireproof foam between the cells and in the case that a cell overheats it is able to distribute the heat without a fire (theoretically) The Ultium pack has none of these redundancies and if a Cell gets hot, boom, its gone. Ultium relies on perfectly made cells, which I wonder if is a realistic strategy in mass manufacturing? Obviously LG has struggled with this, having major recalls on the Kona EV' and Bolt EV which cells were made in 2 different plants on 2 different continents. Have you noticed Legacy makers going to pouch cells, start ups doing cylindrical cells? Hmmm, I wonder if it is the lazy engineers at traditional OEM's that cannot figure out how to build packs of small cylindrical cells in scale and cost? Tesla struggled with this for 2 years, and Rivian is struggling with it now, but Tesla solved the problem and has gone on to scale battery packs beyond the rest of the EV market combined. This is a big risk for GM, if they get their wrong, its a serious setback, thats why the fire recently at Milford is a shocking event, clearly a car in test, and that could be a refreshed Bolt, or worse an Ultium pack. Again when cells have no redundancy against bad manufacturing, its risky... How about GM LS/LT engines lifters and valves over the last 5 years, that is a train wreck, and I assure its easier to make perfect lifters than it is to make perfect battery cells. Go read Mary Barra's tweets and all the GM customers reaching out for help with lifter and valve problems in brand new truck and SUV's.
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