they’d have to use immersion cooling to use the full potential.

I assume 3C is a 20 minute charge?

1 C is defined relative to 1 hour for full discharge and 3 C means a 3x faster discharge rate (full capacity can safely be discharged in 1/3 hour, or you can discharge 3 cells sequentially in an hour). Good lithium cells tend to be above 5C, can reach 10C for peak load or if cooled.

For a large enough battery it doesn’t really matter, but for dense portable ones a lower C rating means you have to discharge from more cells simultaneously to maintain a given output. That makes it more complicated, and you have less headroom to the battery’s maximum Watt output if you need to accelerate a car hard suddenly.

The comment I am responding to is about charge rate, not discharge rate

For most batteries that’s the exact same rate

Sodium ion batteries are asymmetrical, pushing charge current hard can drive the anode negative enough to deposit metallic sodium causing formation of dendrites which destroys the battery. Discharge is not limited by the same mechanism

NMC cells typically operate around 1-2C and LFP cells 1-3C. If you want to achieve 10C then you're probably gonna have to look at LTO cells. All of these are lithium-ion chemistries but they each have different characteristics.

(for context most my knowledge of these cells are from single cell +5000 lumen flashlights :)

And here I was confused why coulombs were being used as a charging rate…

We need to abandon the “use a letter for this unit/property” crap and accept that the alchemists and accountants had it right.

Kind of, yes. But more importantly, it also means it can only push enough power to run at 3c. And that’s probably not for the full charge of the battery.

So a 100 amp hour battery rated at 3c can push out 300 amps. Which also means that if the grid needs a short spike in power, it might be limited.

It shouldn’t be too hard to get a 15c LiPo battery, which could push 5x as much energy at peak demand.

You’d probably kill the battery if you charged it from 0-100 at 15c, but for short bursts of charging and discharging, it should handle it just fine.

The comment I am replying to is discussing charge rate of 3C, not discharge rate

Honestly curious: I’m not a battery or even energy person, but this is interesting.

The charge/discharge efficiencies and rates could just mean we build networks of mixed types? “Trickle” charge/discharge via a slower battery that handles more cycles and is probably way cheaper to build (that’s the premise of Na+, right?), but have those batteries back up a more expensive high-rate bank for when power is needed in a burst? Probably a switching problem at that point, which I imagine we already deal with having solar/hydro/fossil/etc.

A Na+ bank sized to handle regular use and charge a Lithium bank when underused so that one is ready for spikes seems like a way to go.

That is an option. For smaller setup, capacitors are used for high peak demand applications.

Sometimes a mixed setup is just not worth it, cause the peak demand is the important part, so you end up with like 80% LiPo and 20% Na.

But I’m certainly no expert on the economics of infrastructure battery installations.

3C

3x light speed? Carbon?

which could be a pretty big obstacle to grid-scale deployment.

Well, on a grid scale if you’ve got a 100MWh battery and you want to charge it at 3C, then you’re looking to find a spare 300MW out on the grid somewhere for 20 minutes.

That’s not impossible, but you’ll buy that 100MWh a lot cheaper if you’re willing to get it over the course of a few hours. For example, buying power in the middle of the day when there’s excess solar, to then drop it back into the grid in a one hour burst during peak times in the evening for 10 times the price.

That kind of thing is where the battery will make the most profit, so slow charge rates don’t really matter.

i think the big issue is asymmetry. they charge at 3C, but they discharge at 8C. so you need the significantly overbuild.

Ambri had a massive molten salt battery that was cheap for grid storage. They went broke. Sadoway gave a great lecture on how actual solutions are fighting corruption and old money.

This wouldn’t be an obstacle for grid, only for mobile/moving applications.