4680

[Frankenblob]

The new 4680 batteries, will they still be 3.2v or 3.7v with 2.2ish amps?

I know Elon said 6x the power but he did not say 6x the STORAGE capacity (i.e 100 amps does not become 600 amps).

Any info or insight?

 

[ajdelange]

A battery doesn't have a voltage. It has a voltage range. When fully charged the voltage is high and when fully discharged it is low. "Fully charged" and "fully discharged" voltages are somewhat arbitrarily chosen by the manufacturer. A battery that is "fully charged" can be charged further but this will result in damage to it. Similarly, a fully discharged battery still has charge in it but if that charge is taken it will be damaged. Thus the manufacturer chooses the definitions of empty and full to trade the maximum range you can get against battery longevity. The new batteries will be based on Lithium and so will use voltages in the 3 - 4 volt range. Will the range be the same as in the current cars? Probably slightly different.

When it comes to current batteries are not rated by the current they can supply but by the amount of charge they hold. Thus a battery that requires 2 amperes of current flowing into it over a 2 hour period to raise its voltage from the "empty" voltage to the "full" voltage is rated as having capacity 4 Ampere-hours. As the new cells have volume many times that of the current cells their capacities will be many times that of the current cells.

There is a limitation, of course, on how fast you want to charge or discharge a cell. A 2 ampere-hour battery discharged at 1 ampere is said to be charging at 0.5C. Discharges at 2 amperes that 1C etc. As C for the newer cells will be many times more than it is for the current ones a given rate, such as 2C, will correspond to a much higher current.

 

[Luke42]

I know Elon said 6x the power but he did not say 6x the STORAGE capacity (i.e 100 amps does not become 600 amps).

Some Electrical Physics Pedantry

I think you're conflating amps (A) an amp-hours (Ah). I've made this mistake before, and I spot these kinds of mistakes in blog posts about green energy and electric vehicles all the time. If this is you, you're in good company -- but the numbers will make a lot more sense if you're conscientious about this distinction.

Amps (A) is the amount of continuous electrical current the battery can produce during an instant in time. This is analogous to the torque produced by an ICE engine -- it's only part of the story about how power is applied to move objects, but it's often a very important part of the story.

Amp-hours (Ah) is the battery's storage capacity. This is analogous to the size of the gas tank on an ICE engine. Again, just one part of the power-delivery story -- but it is often important too.

A Little Bit About Batteries

Battery performance is physically constrained by both amps (A) and amp-hours (Ah). However, consumer-oriented batteries are often marketed without complete information (often A or Ah will be omitted) which drives me absolutely crazy. ("YOU CALL THIS A DATASHEET!?? I'll show you a datasheet!") Though, to be fair, the A and Ah ratings often interact with each other, and the ratings can be influenced by external factors (like temperature) -- so a single scaler number will often fail to really explain how a particular battery behaves. Still, describing this sort of thing is what datasheets are for.

Back to Tesla

I understood Musk's comments to mean that the amp-rating (A) of the battery increased dramatically, due to the increased surface area and more direct connections provided by the tabless connections within the battery cell can.

My other take-away was that the amp-hour (Ah) rating of the 4680 battery only increased because the battery is physically larger and can be packed into the vehicle more efficiently. It's possible that there are capacity (Ah) increases from other sources (improved chemistry, tighter packing within the cell), but these improvements are not as dramatic as the increase in the available current flow (A).

In other words, the tabless 4680s can discharge (and recharge) the cell much more quickly than a regular lithium-ion battery, but are largely similar in other respects. This is the C rating that ajdelange referred to. (He provided a good explanation for a numerate engineering audience; I'm trying to explain the same idea in the most accessible way possible.)

Most of the other gains that Tesla claims seem to come from the fact that they can pack the 4680 cells into the car more efficiently. In other words, they can fit more battery cells into the car, and it takes less heavy metal to support the battery (and the rest of the car.) This makes the car less expensive and increases the range. This is how you "simplify and add lightness".

The Big Picture

Overall, this looks like some fine engineering -- and exactly the kind of thing you'd hope to see as EVs transform from a niche technology into a fully mature mainstream technology.