-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
-
On today's TMC Podcast, we ask the question "What is the Tesla Cybercab?". Join us on YouTube live at 1PM and participate in the chat.
Don't assume it's linear. I remember reading somewhere that this type of chemistry drops a few percent quickly, then levels out for a very long time. (I'm sure the source is on this forum...)
Indeed. My recollection is "assume it's very non-linear." There have been forum discussions in the past that the future storage capability of a used 85 kWh @ 60 kWh should exceed that of a new 60 kWh. Unless I'm misremembering...
I'm confused. I mean, people already mentioned it was non-linear, but even if it was linear 3% after 12.5K miles would predict exactly 30% after 125K miles. I've always understood degradation to be much more related to mileage (i.e. number of complete recharge cycles) than time.
Johan
Ex got M3 in the divorce, waiting for EU Model Y!
... unless you drive very little, in that case ageing becomes the factor that drives degradation. And the effect of ageing v.s. cycling is not a summation but more "either or" whichever effect is greater (for most practical purposes it will be cycling).
I see this thread is a bit old, but perhaps I can add my own thoughts and there will be more discussion. I find the battery talk interesting, so I'm sorry I missed out here. My understanding is the Li-Ion technology has a reverse logarithmic curve so that loss of capacity is slow at first and then fast toward the end. That would make it looking something like #2 in the OP. A good resource is found here. Essentially, the resource says that:
1. The curve is a reverse logarithm.
2. The overall rate of degradation is related to temperature at which the battery is operated at and levels of charge/discharge.
Tesla can't do much to address #1, but does address #2 through the use temperature management systems and charge level control. That said, the maximum number of cycles that even a well-designed, well regulated Li-Ion battery can achieve is about 1,000. If we assume that a cycle is performed on the Tesla every 300 miles, then the car should be able to achieve 300,000 miles without a problem. Unfortunately, this is not how most people operate their cars nor is it a practical way to operate the car. Most people "top off" and do other things that greatly increase partial cycling, which can extend the life of the battery substantially. Under such conditions it seems that after 100,000 miles, the battery will have about 85% capacity. So, from 300 mi, the Model S will drop to about 255.
Unfortunately, the number of variables (depth of discharge, rate of charge, operating temperature, etc., etc.) makes it impossible to predict what the average battery will do. What should be clear is that the Tesla will show a wide range of behaviors, just like an ICE car does. Take care of it, and it should perform well at 5-8 years out. Neglect the battery and abuse the car and you can expect it to crap out in only a few years time. In other words, there is still maintenance to be done in the sense that you need to be conscientious of how you use the car, check to ensure it is charging and discharging appropriately, and so forth. In the end, the batteries in the Model S are off the shelf and so should be expected to perform similarly as they do in other devices (with differences between management schemes taken into account of course).
1. The curve is a reverse logarithm.
2. The overall rate of degradation is related to temperature at which the battery is operated at and levels of charge/discharge.
Tesla can't do much to address #1, but does address #2 through the use temperature management systems and charge level control. That said, the maximum number of cycles that even a well-designed, well regulated Li-Ion battery can achieve is about 1,000. If we assume that a cycle is performed on the Tesla every 300 miles, then the car should be able to achieve 300,000 miles without a problem. Unfortunately, this is not how most people operate their cars nor is it a practical way to operate the car. Most people "top off" and do other things that greatly increase partial cycling, which can extend the life of the battery substantially. Under such conditions it seems that after 100,000 miles, the battery will have about 85% capacity. So, from 300 mi, the Model S will drop to about 255.
Unfortunately, the number of variables (depth of discharge, rate of charge, operating temperature, etc., etc.) makes it impossible to predict what the average battery will do. What should be clear is that the Tesla will show a wide range of behaviors, just like an ICE car does. Take care of it, and it should perform well at 5-8 years out. Neglect the battery and abuse the car and you can expect it to crap out in only a few years time. In other words, there is still maintenance to be done in the sense that you need to be conscientious of how you use the car, check to ensure it is charging and discharging appropriately, and so forth. In the end, the batteries in the Model S are off the shelf and so should be expected to perform similarly as they do in other devices (with differences between management schemes taken into account of course).
I missed this thread before. Hmmm..
Here is a paper written by some Panasonic engineers that tested some cells that are not the same, but use roughly the same chemistry:
http://bit.ly/1ajpkr2
Note the 2nd graph - at 2C charge/discharge, even at 50 degrees C, that chemistry lasted through 3,000 cycles with degradation about 15%. They achieved this by limiting the voltage range to between 3.6 and 4.05 V, which is precisely how Tesla's BMS protects the pack. Note that this is using 2C charging, which would be 160 kW on the Model S 85 kWh pack. At the moment, Tesla only charges at 120 kW for the first 2/3's SoC and then tapers.
Here is a paper written by some Panasonic engineers that tested some cells that are not the same, but use roughly the same chemistry:
http://bit.ly/1ajpkr2
Note the 2nd graph - at 2C charge/discharge, even at 50 degrees C, that chemistry lasted through 3,000 cycles with degradation about 15%. They achieved this by limiting the voltage range to between 3.6 and 4.05 V, which is precisely how Tesla's BMS protects the pack. Note that this is using 2C charging, which would be 160 kW on the Model S 85 kWh pack. At the moment, Tesla only charges at 120 kW for the first 2/3's SoC and then tapers.
omgwtfbyobbq
Active Member
According to the NREL, capacity loss is the greater of calendar life losses that are determined by average storage temperatures or cycle life losses, that are determined by depth of discharge. It should be fairly straightforward to dump this info into a calculator/site, like Leaf owners have.
http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/45048.pdf
Those results (page 18) are positive, although I imagine someone who routinely used 80+% of the pack might have less than 70% capacity left after 10 years.
I've tried asking ownership about what precisely they consider to be excessive losses given different conditions (charge and discharge rates, average temps, etc...), and I've gotten nothing back, which doesn't inspire a whole lot of confidence.
Based on what Roadster and S owners have said, my guess is Tesla they will replace individual bricks if they loose capacity faster than the rest of the pack, but if you're one of the unlucky few percent of owners that have uniform capacity loss, you're probably SOL, even if there are ten other owners in the same situation (commute, temps, etc...) that have much less capacity loss than you do.
http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/45048.pdf
Those results (page 18) are positive, although I imagine someone who routinely used 80+% of the pack might have less than 70% capacity left after 10 years.
I've tried asking ownership about what precisely they consider to be excessive losses given different conditions (charge and discharge rates, average temps, etc...), and I've gotten nothing back, which doesn't inspire a whole lot of confidence.
Based on what Roadster and S owners have said, my guess is Tesla they will replace individual bricks if they loose capacity faster than the rest of the pack, but if you're one of the unlucky few percent of owners that have uniform capacity loss, you're probably SOL, even if there are ten other owners in the same situation (commute, temps, etc...) that have much less capacity loss than you do.
stopcrazypp
Well-Known Member
They aren't going to provide any hard numbers, because they know owners will hold them to those numbers immediately after they provide it (as we have seen in previous posts about other issues). I doubt they will provide any hard numbers unless they decide to provide a degradation warranty instead of a defect based one (no need given the demand, and despite some owners complaining about degradation, the rate is still not enough for alarm, unlike the Leaf's case, which had cars under 70% capacity and a handful approaching).
VIDEO
Here is the explanation of "Why do Li-ion Batteries die? And how to improve the situation?"
http://www.youtube.com/watch?v=pxP0Cu00sZs
Quite long video, but it gets more and more interesting.
And: You get the answer for "What does the battery degradation curve look like?"
Here is the explanation of "Why do Li-ion Batteries die? And how to improve the situation?"
http://www.youtube.com/watch?v=pxP0Cu00sZs
Quite long video, but it gets more and more interesting.
And: You get the answer for "What does the battery degradation curve look like?"
djp
Model 3 Performance
Fantastic video Saftwerk! This deserves its own thread - I'll post in the video forum.
Why do Li-ion Batteries die? And how to improve the situation?
Last edited:
Electrolyte composition may be different in the "A" and "B" packs of the Model S
Amazing! This explains why model S owners are seeing minimal degradation in their batteries (assuming their packs are balanced). This research group tested Tesla's battery chemistry with different electrolytes and found different degradations. The types of electrolytes and electrolyte combinations make a huge difference in cycle life even in the same chemistry. Wow!
It makes me wonder if the "A" and "B" battery packs only differ by their electrolyte composition. One of the members of the group which made these discoveries of combining electrolytes to increase cycle life started working for Tesla right around the time the Tesla started changing the packs in the Model S. Interesting.
Amazing! This explains why model S owners are seeing minimal degradation in their batteries (assuming their packs are balanced). This research group tested Tesla's battery chemistry with different electrolytes and found different degradations. The types of electrolytes and electrolyte combinations make a huge difference in cycle life even in the same chemistry. Wow!
It makes me wonder if the "A" and "B" battery packs only differ by their electrolyte composition. One of the members of the group which made these discoveries of combining electrolytes to increase cycle life started working for Tesla right around the time the Tesla started changing the packs in the Model S. Interesting.
OK...this is over an hour long. I truly thought I would watch a few minutes and get the gist of it. I watched the whole thing...TWICE! I am not a science guy, or an electrical engineer, or a chemist, (hence TWICE, and even then...) but I think this ought to be required watching for anyone interested in battery life. (And that should include the vast majority of Tesla owners I would think.)
omgwtfbyobbq
Active Member
That's probably likely, but it's a big reservation I have when purchasing a new MS. The fact that other manufacturers like Mitsubishi provide a warranty (10yr/100k/70% capacity I think) with a much smaller pack that isn't liquid cooled may speak to some lack of confidence on Tesla's part.
The Nissan fiasco was just ridiculous btw...
Lawyers nightmare: When 9th Circuit Chief Judge Kozinski is class objector | Alison Frankel
I'd suggest:
1. Battery swap is practical for commercial use where the cost of vehicle downtime is high.
2. Tesla is still in the beta stage for battery swap.
3. If battery swap is the only source of income for a company, it's not practical due to the capital layout. As an "advertising expense" and being revenue neutral (or close) it can be an advantage.
In addition, so few people use it, battery swaps are basically a money pit.
From this report: "The difference in capacity loss is significantly smaller than the overall loss of capacity".
Considering these tests were done with a LEAF that has no battery cooling and done in hot climate, I'm pretty confident that Supercharging with active liquid cooling has very little effect on battery degradation on the Model S.
Similar threads
