One reason they went with Panasonic. They rely on their world class manufacturing consistency to get them cells that will only show a defect one in 10 million . They did pioneer the six sigma process, which Motorola then developed.flathill wrote:The reason cells catch on fire is when one of them starts to fail but doesn't blow the cell level fuse. In some situations the cells with internal shorts continues to work but gets hotter and hotter and goes into thermal runaway, all while the cell level fuse never blows. This is the hardest failure mode to catch without false positives. Telsa has a dead man or crowbar switch on their pack that will blow the fuses and interrupt the short on purpose to protect against this type of failures, but it can still happen, which is why preventing cell to cell propagation is critical if you want to park the car in your garage with a house full of people sleeping.
But anytime the cell is over ~35C degradation is accelerated. Tesla keeps the cells in a tight 15-35C window to ensure long life. Not possible without active temp control. It is very easy for a cell to reach 35C in room temp whether charging or discharging. Stupid finicky batteries with liquid electrolyte.
NCA cells can get away from you obviously if you have seen any Tesla's on fire AFTER A CRASH. Note there has never been a Tesla that caught fire just sitting there or charging like some other EV's. That would be game over for Tesla. This doesn't mean every cell is perfect, it just means any single cell failures have not been publicized because the car just said seek service and the battery pack got replaced. You wouldn't even smell smoke if one cell in a Telsa pack caught fire. The pressure would not be enough to blow the vent seals.
How about 5000 100% DOD cycles with zero fire risk? No active cooling or heating required. Lower energy density on a cell level but much higher on a complete pack level.
The hummingbird is back now that the Germans realize they have to compete and not bury this tech:
http://www.kolibri-ag.com/en/kolibri-po ... the-market
Making 5,000,000,000 of the same cell helps too. People think that larger cells means less cells to fail. That's not looking at the big picture. Larger cells also means MUCH less manufacturing volume = WAY more defects and variance cell to cell.
More volume = more consistency.