How worried do I need to be about the effect of DC fast charging on battery longevity?

[engnrng]

It's a common knowledge, high capacity Li-ion batteries have a lifetime in 500-1000 range. LG Chem don't publish the numbers though, but they never claimed any miracle either.
I already provided the reference to the study that shows the batteries are dead after just 20 cycles without temperature management: https://news.ucr.edu/articles/2020/03/11/fast-charging-damages-electric-car-batteries
The goal is to achieve a million mile battery, best current numbers I've seen is about 300,000 miles, which is about 1000 full cycles.

Thanks for that @RedStallion. Personally, I have found many times that "common knowledge" is not even close to accurate scientific or engineering knowledge, but in this case, I am not sure. However, I can tell you that our battery pack supplier (cells made by LG) with their Battery Management System and unique cooling have used 2500 to 3000 full charge cycles for calculating design life (staying above 70% of original capacity). That is why I am asking for something specific and traceable. One data point I personally know is a Tesla Model S with over 320,000 miles (included twice weekly trips between Santa Barbara and San Jose, all DCFC) is owned by a P.E. electrical engineer, who measured a 10% degradation over those 320,000+ miles. At the time he gave me that number 2 years ago, he estimated about 1200 full charge cycles. He also mentioned that half of that degradation occurred in the first 2 years, then the rate of degradation tapered down over the next 5 years or so. Would be very interesting to hear other data from long time Tesla owners with lots of miles.

As far as your Riverside article - I wonder how fast their chargers really were. They destroyed a cell after only 25 cycles? I am going to have to read that more closely...

Sponsored

 

[Scarpia]

Typically the battery is considered dead after the capacity drops to 80%.

It's not considered "dead"; it's considered to have a capacity that is 80% of the original capacity. That is far from dead.

 

[RedStallion]

It's not considered "dead"; it's considered to have a capacity that is 80% of the original capacity. That is far from dead.

"For most battery applications, a battery or a battery pack is considered to have reached its end of life when the overall capacity of a battery or a battery pack reaches 80%" - https://onlinelibrary.wiley.com/doi/pdf/10.1002/est2.141

 

[engnrng]

"For most battery applications, a battery or a battery pack is considered to have reached its end of life when the overall capacity of a battery or a battery pack reaches 80%" - https://onlinelibrary.wiley.com/doi/pdf/10.1002/est2.141

Not sure this Wiley online library is a peer reviewed scientific journal. The eight authors seem to be making an argument to establish the value of their work, yet don't provide a citation to support the statement. In addition, they claim that an "industry fast charge technique" resulted in "end of life" after only 25 charge cycles. Their much improved approach increased that to 36 charge cycles. Either their article doesn't fit known behavior, or it does not apply to commercial EV batteries as they claim to. Anyone else want to take a crack at the reference and explain it to me? I remember reading a few years ago of an emergency center (in Norway?) that gathered quite a few used hybrid batteries and created a battery backup system for their emergency response center computers and communications. I think the "end of life" concept may be an opinion based on the application....

 

[stroszek]

I have yet to see a phone without a defective battery after 5 years if you go by that 30% rule.

Huge batteries age better fortunately.

 

[Scarpia]

"For most battery applications, a battery or a battery pack is considered to have reached its end of life when the overall capacity of a battery or a battery pack reaches 80%" - https://onlinelibrary.wiley.com/doi/pdf/10.1002/est2.141

That's just one article, and it doesn't confirm your claim. "For most battery applications" doesn't specify EV Lithium-Ion batteries and would lump in small consumer batteries like AAA's and micro "button" batteries. A set of AA batteries in a flashlight may not provide enough juice at 80% to be useful, but a large Lithium-Ion battery in a car will continue to function, albeit with lower range.

A cursory search revealed dozens of articles that were specific to EV batteries and refuted your statement. Most manufacturers, including Tesla and Ford, guarantee 70% retention of original capacity during the warranty period.

https://www.sciencedirect.com/science/article/pii/S0378775315000841
Highlights:

• EV batteries meet driver needs well beyond 70–80% remaining capacity EOL threshold.
• Even after substantial capacity fade EV batteries accommodate long unexpected trips.
• Energy capacity fade is a more limiting factor governing retirement than power fade.
• EV battery useful life is further extended by enabling charging in more locations.
• Battery retirement metric can be defined instead by when daily driver needs not met.

https://www.batterytechonline.com/testing-and-safety/evaluating-ev-battery-end-life
https://electrek.co/2019/12/14/8-lessons-about-ev-battery-health-from-6300-electric-cars/
https://www.optima-ect.com/news/2021/2/25/what-happens-when-an-ev-battery-reaches-end-of-life
"The consensus from other manufacturers [than Tesla] looking at this question seems to be that a battery is still commercially useful if used carefully down to about 50% SoH."

 

[RedStallion]

That's just one article, and it doesn't confirm your claim. "For most battery applications" doesn't specify EV Lithium-Ion batteries and would lump in small consumer batteries like AAA's and micro "button" batteries. A set of AA batteries in a flashlight may not provide enough juice at 80% to be useful, but a large Lithium-Ion battery in a car will continue to function, albeit with lower range.

You can find measurements in the article that you were so quick to dismiss. It's not only capacity drops, it's the resistance that is also growing. So despite of the fact you may still use the battery at 50% capacity, the growth in resistance would make it dismal experience. How would like if the car 0-60 dropped twice, or fast charging dropped under 50kW in addition to half of the original range? Would you still insist the battery is usable? 80% is a very reasonable cutoff, nobody would like driving such car anyway.

 

[Mach-Lee]

You can find measurements in the article that you were so quick to dismiss. It's not only capacity drops, it's the resistance that is also growing. So despite of the fact you may still use the battery at 50% capacity, the growth in resistance would make it dismal experience. How would like if the car 0-60 dropped twice, or fast charging dropped under 50kW in addition to half of the original range? Would you still insist the battery is usable? 80% is a very reasonable cutoff, nobody would like driving such car anyway.

Agree, it's non-linear because the internal resistance becomes significant. When my laptop battery degraded 75% capacity (after only 700 cycles) it was driving me nuts because anything more than just simple web browsing would drain it in a hurry. The SoC meter was all over the place due to the internal resistance. If it was an electric car it would have significantly degraded acceleration and top speed in addition to poor range. Replaced the battery and it was an astonishing improvement.

If you only need the car to go 0-60 mph in 15 seconds (slow) you could live with a battery less than 70%, but the car wouldn't be any fun anymore. Pure utilitarian driving only.

On devices I've had with cycle counters, I really haven't seen a lithium battery get past more than 1000-1100 cycles without considering it absolute unusable junk. Sometimes they only make it to 500 cycles. Time will tell how the car does but 1000 is the accepted industry standard unless proven otherwise in a specific application. Apple still considers 1000 cycles end-of-life in their products, and that hasn't increased in 12 years!

Personally I think it's a real tragedy the warranty threshold is only 70% instead of 80%, or even 75%. I think most people will get frustrated with the performance long before it gets down to 70%. Personally I would sell the car before it got to 80% or 1000 cycles unless future data changes my mind about cycle life.

1000 cycles in a Mach ER would be 220-270k miles, which should be plenty of life for most people. But if that's cut in half due to fast charging (110-140k miles) then some people might be disappointed if they keep the car a long time or if its market value plummets.

 

[Scarpia]

You can find measurements in the article that you were so quick to dismiss. It's not only capacity drops, it's the resistance that is also growing. So despite of the fact you may still use the battery at 50% capacity, the growth in resistance would make it dismal experience. How would like if the car 0-60 dropped twice, or fast charging dropped under 50kW in addition to half of the original range? Would you still insist the battery is usable? 80% is a very reasonable cutoff, nobody would like driving such car anyway.

I challenged your original assertion that "Typically the battery is considered dead after the capacity drops to 80%." You furnished one article stating that, while I pointed to just a few of many that say differently.

That is not a generally accepted viewpoint regarding Lithium-Ion batteries used in EVs. The typical warranty is 70% retention. Manufacturers are conservative in granting warranties, and the fact that they will warrant 70% is significant.

Another factor is that EV batteries are huge and, although they share some characteristics with smaller devices such as phone batteries, there are vast differences in how the batteries perform. The battery technology is not at all equivalent.

 

[RedStallion]

I challenged your original assertion that "Typically the battery is considered dead after the capacity drops to 80%." You furnished one article stating that, while I pointed to just a few of many that say differently.

You think you can challenge a scientific research paper with opinions in some articles? It's not even close.

 

[engnrng]

You think you can challenge a scientific research paper with opinions in some articles? It's not even close.

You see, you have not cited a "scientific research paper". Apparently, @RedStallion you are choosing to ignore both of my posts as well. When you can present science that has been peer reviewed in an industry accepted journal rather than one self-published by some students who managed to kill batteries in only 25 cycles, please do.

Sponsored