I see density used fairly loosely by both speakers and readers, and I often wonder who is talking about mass and who is thinking volume.
Can we agree that 2170 is a cost cutting, rather than performance improvement ?
I'm certainly OK with that. After all, it gave rise to the Model 3.
Indeed. And Tesla (Elon) speak always leaves a lot of guessing. Like with the Bolt range comparison, not that I fell for it (this time).
Since this is automotive, I prefer to look at energy deinsity by volume rather than weight. Most mileage is logged on more or level roads, on wheels supporting the weight. In an airplane, I'd look at density by mass as lift comes at such a high price, it's hard enough to be flying at all, let alone for any amount of time. 1% more mass will take rougly 1% more energy to be flown over a given distance, altitude and speed. In a car, space comes at a premium but adding 10 or even 20% of cargo will barely affect consumption at cruise speed.
Unless a big change is effected to the workings of the cell vs the latest generation of 18650's (if that's even what's going into the new 85kWh packs still), I would guess that the 2170's would improve density by weight as well as volume. And the extra 5mm should add capacity (per layer area of floor space) even if the 2 former fail to materialize measurably.
I agree, 2170's are all about cost cutting. Panasonic admits they don't make money on them yet (I presume speaking about the powerwall/pack units and the Model 3 ones built mostly for curing stock). The costs will fall for Tesla and later for Panasonic. It's their cash cow. Others don't have this cheap capacity weapon just yet. How big Panasonic's take it will decide how competitive others may grow to become when their factories are built.
Performance, at least driving, seems to be the least of Tesla's weaknesses. They use such big nuumbers of cells in a pack, that even the slower C rate cells deliver sufficiently for impressive dragstrip runs and fast charging. The slowest ever charging Model S still charged nice and quick in today's market.
Others may achieve similar or better $/kWh, but with unfavorable volume and/or weight density, making big packs cumbersome in a mainstream appeal family car.
Of course Tesla, if the new chemistry was ready too late, could not make Model 3 wait for that. I would have had a contingency plan in place, to do "banker" cells. Just or almost as cheap, just lower density, but nice and reliable. Not enabling the world-shocking range for the longest range Model 3 they may have been planning, but sufficiently good to get the lower cost per kWh in a complete car "on sale today". 85kWh would have made it 350 miles, you know. And it may still if and when they get the new cells properly high density.
We may hope that Tesla has not giving up on the idea of having stunning battery packs, and Elon did report that they explore many new techs being presented to them. Getting a higher density AND faster charging cell to market may be the key to their survival. This is not the moment to quickly lose grip on the pretty high reputation in charge speed. And holding on to 18650 for a day longer than necessary to power S/X would be a public fail. The better cells are needed for S/X, else replacing 18650's will make the cars slower charging. The packs could become 10kWh larger for the same cost and size, but charge speed would barely hold ground until something good and new is introduced.
