Power density W/kg vs Energy density Wh/kg ratio in battery cells

V

Victor Österlund

New Member
I have tried to hoover the net for an answer, but cannot seem to find it.
There is alot of discussion on EV battery technologies on mass energy density Wh/kg vs volume energy density Wh/L ratio, which is also very important (limited amount of space on an EV) as for example Tesla M3 is now going for the cheaper safer and easier produced LFP which has a lower Wh/L than the

But what I'm wondering now about is the W/kg to Wh/kg ratio.
Is this somehow determined by the battery cell technology, what the ratio is, and one has found the most "efficient"?
For example, in the 2170 the ratio is around 1000W/kg vs 250Wh/kg. or 4:1.

How are these two related? Can you decrease power output to increase energy density?
Or is the pay-off so small?
As an example, if you decrease power density by 50%, you only get 5% higher energy density, and then the loss in power is just too high for the small gain in energy density (by for example changing the ratio of components in the battery).

Hope someone here has more insight to open this up for me. Thanks! :)
 
We are learning new battery chemistries, packaging, production, and operational scenarios almost daily. Some of them appear to be 'dead ends' (i.e. press releases are notorious.) Not trying to be difficult but power and energy density are just the tip of a much larger battery problem.

Is there a specific application you have in mind?

Bob Wilson
 
I'm just thinking of the reason why for example Tesla are making quite powerful cars (batteries) which are not really needed.
Can you increase on energy density (A LOT) if you do a cut-back on power?

I mean a battery with 350Wh/kg / 500W/kg would be much more interesting for me.
Doing a 300kg battery pack would give 105KWh of capacity and 150kW, which be more than enough power for the most people.

But for some reason there seems to be more power than capacity in mind. I mean who needs a pick-up doing 0-60 in 3.5sec? if you could do it in 7sec and increase range with for example 40%?
Or is it just that it's technically impossible to do what I am describing?
 
Ok, I have a better idea of what you are after:
  • Lower weight - use a higher energy and power density battery ... see Chevy Bolt
  • Moderate weight - use a lower energy and power density battery and efficient EV ... see Tesla Model 3 Std Rng Plus
  • Higher weight - use moderate energy and power density battery and less efficient EV ... see all but Lucid EVs
Does this match your interest?

If so, I'll cite the EPA sources and we'll have a common set of facts and data to discuss. Works for you?

Bob Wilson
 
Victor Österlund said:
Can you increase on energy density (A LOT) if you do a cut-back on power?


But for some reason there seems to be more power than capacity in mind. I mean who needs a pick-up doing 0-60 in 3.5sec? if you could do it in 7sec and increase range with for example 40%?
Or is it just that it's technically impossible to do what I am describing?
Click to expand...

It's not just battery chemistry dictating output; the topology of the motor is more the limiting factor with regards to the power drain.

The currently available AC induction motors are specified for longer service life (few moving parts) at the expense of efficiency.

There are some breathtaking advancements in pulsed power supplies, but they're finicky and the sort of thing mass market car buyers will not accept.

https://www.motioncontroltips.com/m...he-world-uses-brushless-motors-in-drivetrain/
 
We are probably Several Battery Generations away from the Solid State Battery in a 10 year package of not busting apart. So an answer is you just limp along with your battery constantly on a Charger of you buy a gas vehicle/Hybrid. Maybe the Fiat/Chrysler design hybrid Etorque with a Larger / better battery will get us to the Solid State Battery someday ! I tend to want to leave the motor inside the Transmission be. It would seem the real problem with the modern Lithium battery is the 30,000 gallons of water needed to put the fire out over 12 hours if in a bad wreck. Let alone the EPA involvements !
 
Source: https://insideevs.com/news/557527/tesla-model3-lfp-charging-recommendations/

Tesla is recommending owners of the new Model 3 RWD base model equipped with lithium iron phosphate (LFP) battery cells to charge to 100% on a regular basis.
. . .​

I'm patient with newer or different battery chemistries and systems. My 2019 Model 3 Std Rng Plus battery has its characteristics so I operate the car to minimize the weaker aspects. For example, I only charge to 100% for the first drive of the day. Daily I charge to 68% which provides more than enough charge for chores.

Rather than wish or wait for perfection, use 'good enough' and operate the car to minimize bad things happening.

Bob Wilson
 
GM is the EV leader:
us-president-joe-biden-test-driving-the-2022-gmc-hummer-ev-pickup.jpg

Happily I own TSLA stock.

Bob Wilson
 
Last edited:
Jim Matthews said:
Stop spamming this website with last year's smear campaign.
Click to expand...
I agree but after 12 years of Prius ownership, the Prius trolls would not give up but you could wear them down. The troll rantings 'sharpened' our responses. The Prius trolls sold more Prius as we rapidly deflated their FUD. Eventually, they get bored of the cut-and-paste-and-smackdown and wander off.

Bob Wilson
 
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