Regarding the safety of EV's and their batteries, there is no real safety advantage between Cylindrical and Prismatic packs. Cylindrical have some minor cooling advantages, but getting the same power density as prismatic packs is difficult. Mechanical strength is important, but the electronic monitoring will react well before any mechanical component has failed. The batteries are monitored (voltage, current, Charge state, State of Health and temperature) on the cell pack level, so even if a single cell shorted, the system will react in microseconds and like any ICE vehicle, the entire power source is also cut as soon as any crash is detected.
As for the driving experience, as mentioned above, it's the torque curve that people notice at first. People are used to an engine needing time to react, especially if they drove a diesel up to then. The motor definitely isn't an ON/OFF situation, it's just like any variable motor control.
I won't comment on the environmental or infrastructure aspect, that's politics not engineering and will be different for every country.
McBryce.
* This information/opinion doesn't come from a report, I've worked in EV and EV Battery development for almost 20 years, including work on the Prius.
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While I obviously don't have your experience with EV PS,
I do understand what you're talking aboot from my own work with telemetry on LiPo batteries and model aviation power systems. The problem here is not the electronic monitoring; it is the concentration of material in a single envelope.
Well, it is the monitoring; in that counting on electronic monitoring to protect you is no excuse for not making the mechanical packaging as safe as possible, and mechanically, prismatic cells are much more material in a single package with a much greater tendency to rupture.
Same reason we
pack dynamite into cylindrical sticks, and we consider a brick of C-4 in a box much more dangerous than an equivalent capacity of dynamite stored appropriately. made dynamite by diluting nitroglycerine with inert material and forming it into cylindrical sticks. The point is to concentrate less of the dangerous material in each cell, thereby reducing the amount of that material likely to be involved in any catastrophe.
Also, the smaller cylindrical shape
of the metal canister makes them much better at maintaining cell integrity under pressure... to the point that we now have cylindrical cells in production for portable computing devices and power tools that do not rupture under short-circuit, but rather bloat slightly and in many cases don't even vent gas before the internal fusible shunt opens up. Prismatic cells do not behave this way.
Cylindrical cells are simply safer because of this in a mobile application, wherein impact-induced puncture and crush damage are not only possible, they are inevitable.
We will see if Tesla's new larger cylindrical cells maintain this tendency; I do have my misgivings. But as they have said in the press releases, it's aboot finding the right balance between inherent safety, energy density, life of the super-pack, and being recyclable.
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Prismatic cells can make pack rebuilding a much less time-consuming affair, greatly increasing the likelihood it will be attempted as a service procedure rather than disposing of the entire super-pack.
IMO this must be a core part of any EV ecology; it certainly does seem that Tesla's packs are made as hard to service as is humanly possible. I realize this is due as much to inherent difficulties of working with the cell type as with the exigencies of mass-production and the desire to make a high-performance pack vs a high-efficiency pack; but I do feel a lot more effort could have been made to facilitate rebuilding on a cell-by-cell level. That is a
fukkin' lot of lithium power to treat even the individual sub-packs as a disposable unit.
As we can see here, the Prius super-pack is much more rebuild-friendly; however there is a lot less energy in this pack than the Tesla pack. Not sure exactly how energy density compares between the two by wet weight/volume tho.
EDIT: Just out of curiosity... did you work with the Prius Ni-MH technology or their Li-Ion tech, or both?mnem
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