Tesla Battery Investor Day

[ohmman]

That chart, inasmuch as it means anything or is anything more than an impression, seems to imply that a single tab 21mm charges at the same rate as a tabless 21mm. As diameter increases, it shows that tabbed cells slow down dramatically, while tabless experience much less of an impact relative to their tabbed counterparts.

I can't see any other way to read it, but it might be intended to be visually instructive instead of accurate.

Edit: I think I see what @mongo is saying. That the tabbed chart is slid "down" to align with the tabless chart. I suppose that's a possibility, though I don't much like it.

 

[mongo]

That chart, inasmuch as it means anything or is anything more than an impression, seems to imply that a single tab 21mm charges at the same rate as a tabless 21mm. As diameter increases, it shows that tabbed cells slow down dramatically, while tabless experience much less of an impact relative to their tabbed counterparts.

I can't see any other way to read it, but it might be intended to be visually instructive instead of accurate.

If taken that way, which charges faster, a 15mm tabbed or tabless? How can that be?

I take that chart like a stock return comparison. Place 21mm performance at the same point and extend from there. Doubling diameter on a tabbed cell increaes charge time. Doubling from 21 on a tabless does not.

 

[mongo]

Edit: I think I see what @mongo is saying. That the tabbed chart is slid "down" to align with the tabless chart. I suppose that's a possibility, though I don't much like it.

Exactly. It's for relative change vs diameter, not absolute vs type. It was meant to be illustrative for why you can't make tabbed cells bigger. And then show hiw tabbed are better.

 

[ohmman]

Exactly. It's for relative change vs diameter, not absolute vs type. It was meant to be illustrative for why you can't make tabbed cells bigger. And then show hiw tabbed are better.

Unfortunately, there are a number of conclusions we cannot draw from such a chart, most importantly how a 46mm tabless cell compares to a 21mm tabbed cell. But I suppose time will answer all questions..

 

[mongo]

Unfortunately, there are a number of conclusions we cannot draw from such a chart, most importantly how a 46mm tabless cell compares to a 21mm tabbed cell. But I suppose time will answer all questions..

Yeah, it doesn't tell that.
From the rest of the presentation, there is a 6x power increase for a 5x energy increase, which would seem to imply a potential 20% charge rate increase on a C rate basis.

 

[powertoold]

I would think that if Tesla were able to increase the charging rate on a kilowatt-hour basis, they would have mentioned it during the presentation.

 

[Buckminster]

Alternative thread for specific 4680 chat:
4680 General discussion - Range & $/kWh

 

[JRP3]

I don't see a need for multiple threads on the cell and it's impacts.

 

[67King]

........ they are doing the obvious things that they should do.

One thing that that means is I can finally say that Tesla has broken the mold of decay, destruction, and despair that the old Harvard General Ed teachers hammered starting in the 1940s and 1950s into an entire generation of degenerates that offshored all of USA’s industries and slowed down worldwide innovation, and we are finally waking back up industrially. It helps USA and it helps all the countries that are able to keep up and participate, and we are finally participant in improving the lot of humans again in positive value ways. As with all good quality work performed, we get more out of it than we put in. What this also means is that Tesla will succeed according to the imaginations and work of the younger people, often in excess of the lowered expectations of those older generations. None of this changes physics, but it lets us access and leverage physics to improve us more than the work we put into learning how and doing it.

Thank you. One of the things I love about Tesla. I mentioned him in the context of Henry Ford up above. I really think they are cut from the same cloth. Henry Ford essentially created the production line. The Rouge complext in the early 20th century was the world's best. Integration was so vertical that barges with iron ore would come in from the Rogue River, and cars would go out. There was even a glass factory on site. That is what Musk is doing, now. And as you state, it is 180 degrees from what American companies have been doing for decades, which is all horizontal, oursourcing production, and the "Full Service Supplier" thing even had the engineering leave the companies. Program managers were what were basically hired. So glad to see Tesla doing what it is doing, and I hope others follow suit.

 

[gluu]

The line is normalized relative to the existing 2170 cells. My interpretation is that the larger cells have a little bit slower supercharging times compared to the smaller 2170 cells (see the bottom line slightly slope upwards).

For example, it would take a little longer to charger X kWh of the 4680 vs the same X kWh in 2170 cells.

So, there's no supercharging time benefit with the larger cells (my interpretation).

I read this chart as "it takes about the same amount of time to charge a 2170 vs a 4680." But remember, a 4680 has 5x the energy. This would imply that the cars would charge 5x as fast. If it takes a Model 3 30 minutes to get a full charge on a V3 supercharger, the new time would be 6 minutes!

 

[powertoold]

I read this chart as "it takes about the same amount of time to charge a 2170 vs a 4680." But remember, a 4680 has 5x the energy. This would imply that the cars would charge 5x as fast. If it takes a Model 3 30 minutes to get a full charge on a V3 supercharger, the new time would be 6 minutes!

The chart's Y axis is "Charging time," so it should be interpreted as for the same kWh, there's no charging time benefit vs the smaller cells.

For example, a Model Y 75kWh of 4680s would supercharge a little slower vs a Model Y 75kWh of 2170s.

Charging heat is a physics limitation of li-ion batteries, and Tesla can't beat physics.

 

[mongo]

The chart's Y axis is "Charging time," so it should be interpreted as for the same kWh, there's no charging time benefit vs the smaller cells.

For example, a Model Y 75kWh of 4680s would supercharge a little slower vs a Model Y 75kWh of 2170s.

Charging heat is a physics limitation of li-ion batteries, and Tesla can't beat physics.

The Y axis graph is labled "Supercharge Time Increase"
Both lines start at 0. That does not mean the cells charge instantaneously, nor at the same rate, but only that 21mm is the reference point for each type. From there, the tabless has mininal change in charge time as diameter increases, the tabbed has significant.

The tabbed has a much better electrical and thermal path, so how could it charge at the same rate as tabless at 21mm?

 

[powertoold]

tabbed has a much better electrical and thermal path, so how could it charge at the same rate as tabless at 21mm?

It's a trade off Tesla made. The tabless cell has better thermal path, but they took that advantage and traded it for a larger cell to reduce mfging costs.

You can't have your cake and eat it too in this case. Smaller cells have more surface area for heat dissipation. The fact that Tesla didn't sacrifice much supercharging time while designing a dramatically larger cell is already an achievement.

 

[mongo]

It's a trade off Tesla made. The tabless cell has better thermal path, but they took that advantage and traded it for a larger cell to reduce mfging costs.

You can't have your cake and eat it too in this case. Smaller cells have more surface area for heat dissipation. The fact that Tesla didn't sacrifice much supercharging time while designing a dramatically larger cell is already an achievement.

Yes, larger is slower for both types, but you seem to be saying a 21mm tabless is not able to charge faster than a 21mm tabbed.

Why can't they eat their cake?

Charging heat is a physics limitation of li-ion batteries, and Tesla can't beat physics.

No one is beating physics. They cut the average path length to 1/5 (for a 2170). Ignoring the second order heating due to current, that is a 80% reduction in heat generated. It is also a reduction in thermal resistance.
It's like taking a 500 mm wire and turning it into 10 50 mm wires and connecting them in parallel instead. Physics is happy.

 

[powertoold]

I'm no battery expert, but my general understanding of physics and chemistry tells me the current path isn't the only source of heat generation when it comes to supercharging. But yes, I'm just speculating based on the graph and also based on the fact that Tesla didn't mention any charging speed benefits with their new battery.

Also, you can't use wire physics as an analogy to thermoelectrochemical processes within li-ion batteries.

 

[gluu]

The chart's Y axis is "Charging time," so it should be interpreted as for the same kWh, there's no charging time benefit vs the smaller cells.

For example, a Model Y 75kWh of 4680s would supercharge a little slower vs a Model Y 75kWh of 2170s.

Charging heat is a physics limitation of li-ion batteries, and Tesla can't beat physics.

There are a few possible interpretations, I see no reason to conclude that it is for the same kWh. The Y-axis is the relative amount of time to charge the cell, with the baseline being a 2170. If they meant "time to fully charge a cell", then my interpretation would be correct. If they meant "time to charge a cell to X kWh" then your interpretation would be correct. It's common in battery parlance to discuss C-rates which makes me think that the Y-axis is "time to fully charge a cell" rather than to some target kWh. (1C = rate to fully discharge/charge a cell in 1 hour)

 

[byeLT4]

Love the discussion you guys are having. I really wanted to propose these theories but my mind keeps going back and forth on what the chart represents. Kind of like those pics that show two combined images and while you are looking at one it is clear that its a duck, then look again, no.. That's a rabbit

 

[mongo]

I'm no battery expert, but my general understanding of physics and chemistry tells me the current path isn't the only source of heat generation when it comes to supercharging. But yes, I'm just speculating based on the graph and also based on the fact that Tesla didn't mention any charging speed benefits with their new battery.

Also, you can't use wire physics as an analogy to thermoelectrochemical processes within li-ion batteries.

Sure, resistive losses are not the only heating factor, but they are a factor (that increase as the square of current). The electrodes are wires (very thin and wide wires), so one can use that analogy when discussing the resistive heating effects. Reducing that effect reduces the heat generated. Thus, if the cell charge rate over a supercharge session was thermally limited (as you mentioned), then it will increase the overall charge speed (note that peak charge rate is partly lithium ion transport limited, but also resistence limited).

To claim the 21mm tabless charges at the same rate as the 21mm tabbed means that none of the changes in chemistry, manufacturing, and packaging provide any improvement. The energy density increased 5x (kWh), and the power density increased 6x (kW). Would that not imply a 20% increase in current handling (both at a charge and discharge level)?

As to not mentioning this impact more directly, they also did not mention they have had cells in vehicles since May, so omission is not an indicator of anything.
Also, there is the complication that V3 superchargers max out at 250kW (per Tesla). Tesla V3 Supercharger Test: We Find Out Exactly How Fast It Really Is
Model 3 already hits 250kW charging. So no cell changes will impact that peak number on current equipmemt (nor is the new taper likely determined). However, the new cells can reduce the taper in the ways:
1. Less heat generation (shorter electrical path)
2. Better heat rejection (direct electrode to can interface)
3. More uniform voltage

To expand in #3: a critcal parameter in charging is the voltage potential applied to the two electrodes. If this is too high, you get litium plating which permanently reduces capacity. V=IR, so as we move further down the electrodes from the tab, the voltage drops and so does the charge rate. However, the max voltage is limited by the higest voltage in the cell (at the tab junction). Thus, as charge progresses, the cell charges from the tabs outward. Reducing voltage drop increases the rate at which the total cell can charge without violating the voltage or amp/mm^2 current loading.

 

[powertoold]

To claim the 21mm tabless charges at the same rate as the 21mm tabbed means that none of the changes in chemistry, manufacturing, and packaging provide any improvement.

That's not what I'm claiming. It's likely Tesla just dumbed down that graph for us. Much of the battery day presentation was dumbed down. For me, the point of that graph was to say that charging time isn't improved, but it would have been a lot worse if they simply increased the cell diameter.

 

[mongo]

That's not what I'm claiming. It's likely Tesla just dumbed down that graph for us. Much of the battery day presentation was dumbed down. For me, the point of that graph was to say that charging time isn't improved, but it would have been a lot worse if they simply increased the cell diameter.

And herein lies part of the disagreement. IMO, it had nothing to do with charge time of one versus the other. Just think of it as two sets of data on the same graph. The point of the graph was to show that increasing the diameter of a tabbed cell really hurts charging time, whereas increasing the diameter of the tabless does not. The previous slide showed larger cells are cheaper per kWh, and this was to address the logical next question, "So why not just make the cells bigger?"

Larger cells are cheaper
-So why not make the cell bigger?
Because it hurts charging time (shows first line)
-Oh
But the new cells are mostly diameter invariant (shows second like)
-Yay!


Anywho, we've probably killed this topic, will be interesting to see the new vehicle taper.