Quick question:
Are the sizes of 18650 and 20700 batteries encoded in their type number? I.e., is 18, 650, 20, and 700 some type of measurements?
Next thing:
I've been thinking once Tesla starts making their own batteries, they can redesign the batteries from the ground up, chemistry, format, battery pack, etc.: they can design the actual cell internals for best cooling, integrating the cooling directly into the cells themselves, making one big battery pack that has the least extraneous parts, the most efficient use of space for purpose (i.e., as densely packed as possible for proper electrochemical, thermo, safety and structural function), etc.. Once this approach is taken, then things like the cylinder of the cell can be eliminated and replaced with a more purpose-built container that integrates the proper functions needed for a car battery. I don't know what this all entails; i.e., what redundancies can be added on purpose for better integrity or performance, what redundancies can be reduced on purpose because they actually cause more problems than they solve, etc., but even those two last concepts are not the proper way to do a from-scratch purpose-built design. In essence, I wonder, and assume, that there are huge efficiencies for building an actively thermally controlled car battery with the form factor needed by Tesla from scratch, without having to integrate off-the-shelf battery sizes and packaging (e.g., 18650, cylinder, etc.). In this case, opening a Tesla battery pack in the future won't be a situation of saying "oh, I recognize what they put in there!". It would be much more unique.
All this doesn't mean they have to sacrifice modularity, redundancy, resiliency, etc.. Far from it: those things should be designed into it. But I think it doesn't have to be in a particular off the shelf format like it is currently.
For instance: is cylindrical the best shape? Should they be able to expand in some direction (such as up), and if so, should that happen within their own packaging or outside of it? Could their packaging be oversized to handle this situation? And if so, does the packaging have to be so small that so much metal is used on tiny little 18650-sized cells? Could chemistry monitoring and balancing integration be done for every region of battery in a more fine tuned way? Can the cooling liquid be allowed to flow more closely to the chemicals? Can the electrolytic chemicals flow through the cooling system?
I don't know a single thing about the actual chemistry (I'm not a chemist).