2170 cell degradation

2170 cell degradation

Has any one herd what the degradation rate on the 2170 cell is as opposed to the current 18650? Ive read that you can figure on about 3% a year with the 18650 pac but that its not linear and that it drops off slower over time. I know that the 2170 cell is new and that the power density is higher, but have they slowed the degradation rate of the new cell? I ask this because it will influence me as to witch pack to op for when ordering my model 3. I don't want to be looking at changing the pack if after five years the range of the pack is starting to get close to my lower distance minimal.

Noel Kusm | 11 maart 2017

I do not believe that you would be capable of selecting which battery cell to opt for. In either scenario, even if you would be able to select one over the other the 8 year unlimited mile warranty (assuming it too exists for the model 3) would protect you from any significant degradation that may result. Beyond that, I cannot imagine that the newer modeled 2170 cell would have any significant increase in degradation compared to the 18650, but then again I have no background in such an area.

Badbot | 11 maart 2017

the degradation rate on the 2170 will be less than the 18650.
the C rate goes up for higher amp hour rated cells.

Carl Thompson | 11 maart 2017

@Noel Kusm
I don't think that mikdot is talking about choosing the cell technology. I think he is talking about choosing the 70kWh pack vs. the 52kWh, etc.

How much capacity you use also affects degradation rate. If you average using 50% of a larger pack daily then it will degrade slower than if you use 80% of a smaller pack daily.

I plan to just buy the largest battery I can upgrade to for about $10k (not including other options I want). Better to buy more than you'll eventually need than less.


mikdot | 11 maart 2017

I probably should have stated that my commute is 120 miles round trip a day. I have no way of charging at work and no supper chargersbetween home and work at this time. I would have to depend on the battery's range for the full trip. I understand that Tesla has stated that it will have a minimal of 215 miles and I'm pretty sure thats at a 100% charge(not ideal for the life of the battery).
The battery's in the model S do degrade at a rate of appox. 3% a year. That amount has been deemed an acceptable rate and still be under warranty.

At a 80%-90% recommended charge on a 215 mile pac gives you a 172-193 mile range and that's not factoring in for cold weather or running the a/c in the summer or running over 70mph . My concern is after 5-8 years the car wont have enough battery to get the job done.
But if the 2170 cell doesn't degrade like the 18650 that could influence witch pack is large enough to go the distance over time. | 11 maart 2017

The rated miles shown in the cars has a weak correlation with battery cell"degradation" at most. Only Tesla and Panasonic know the true rate of cell degradation and the causative factors: number of cycles?, depth of cycles?, temperature cycling?, random, unwanted chemical byproducts showing up over time?, other? And they aren't talking. Any changes going from the 18650 design to the 2170 have not been revealed. According to J. B. Straubel, they expect a 10-15% improvement in energy density but no words about cell life.

Frank99 | 11 maart 2017

I don't know that I'd worry too much about 100% charging affecting battery life; Tesloop had 6% degradation after 200,000 miles of charging to 100% every day:
https://techcrunch com/2016/09/29/tales-from-a-tesla-model-s-at-200k-miles/

Haggy | 11 maart 2017

I've yet to have degradation at almost 39,000 miles.

PT733 | 12 maart 2017

It might be overkill, but my plan to try to extend calendar life (keeping the car) is:
* Buy the biggest possible battery
* If the battery pack temperature rises much above ambient with use, normally allow it to cool near to 20C before charging?
* Avoid the highest supercharging current, if can wait while charging (to reduce battery temperature rise?)
* Never discharge below 30% or charge above 80%
* For daily short trips, only recharge to 55-60% (charge higher in the hours before starting a long trip)

melinda.v | 12 maart 2017

PT733 - the issue isn't charging above 80% or letting it drop below 30% but letting the battery sit unused With full charge or near empty for an extended amount of time. Like Frank99 pointed out, it can be charged 100% and drained every day without issue (and all using only Superchargers in high temperatures). Desgrdation seems to happen when it's at 100% or discharged and it sits like that not being changed.

PT733 | 12 maart 2017

Re 100% charge: I think I saw a graph that showed with current Li-Ion cell voltages >4 to 4.1 V, sudden capacity collapse could occur after some # of cycles (less cycles life at higher voltage?)
(Sudden drop-off, once the parasitic reactions reduce the surface area of the electrodes?)

The new 2170 might be very good, but there's no harm in not over-stressing the cells, if it's normally easy with how you use the car (I'm guessing, but if you might get 90+% capacity left in 15 years instead of 70%, for a little less standby charge available, it's worth thinking about it, instead of charging at temperature extremes, and leaving the battery charged to max a lot of the time?)

PT733 | 12 maart 2017

melinda.v - yes, I think especially below 20% for a long time may not be good? (we'll see how much the self-discharge will be per day, might be tiny?)

My plan could be called "extreme preventative maintenance"!

PT733 | 12 maart 2017

Although whether charging to max once in a while is needed for balancing, I'm not sure?

Red Sage ca us | 12 maart 2017

Don't worry about it. The car will take care of itself. Chill.

Frank99 | 12 maart 2017

Don't use the collected wisdom of RC guys to decide how to manage the battery pack in your car. There have been a lot of changes in pack chemistry as well as pack charging since much of that wisdom was collected. You also don't have all the information you need to decide what to do - for example, what cell voltage does 100% charge correspond with? What cell voltage does 0% charge correspond with? I'm pretty sure that neither one corresponds with what you might expect.

Tesla has a recommendation for day-to-day charging when you don't need to maximize range in the owners manual. Tesla has also said "a plugged-in Tesla is a happy Tesla". My recommendation is to follow those two recommendations, and stop stressing about battery life. All the information we have says battery degradation just isn't much of a problem. See:

Carl Thompson | 12 maart 2017

"PT733 - the issue isn't charging above 80% or letting it drop below 30% but letting the battery sit unused With full charge or near empty for an extended amount of time. Like Frank99 pointed out, it can be charged 100% and drained every day without issue (and all using only Superchargers in high temperatures). Desgrdation seems to happen when it's at 100% or discharged and it sits like that not being changed."

I have not heard of these issues with EV batteries. Are you sure of this information? Do you know from where it comes?


Carl Thompson | 12 maart 2017

"* Never discharge below 30% or charge above 80%
* For daily short trips, only recharge to 55-60% "

If you do that then you lose the actual benefit from the battery capacity for which you will have paid a lot of money. What's the point of getting a Tesla with long range if you are going to limit yourself to the utility you'd get from an old Leaf?

Buy the biggest battery you can afford and just go ahead and use it. If after 10-12 years and 150k miles your battery has degraded 10% - 20% and you feel you need to replace it then fine. By then Li Ion battery production will be at least 30 times greater than it is today (maybe 100 or more times greater) and you should be able to replace that battery for about the cost of a new gas engine or less. In other words it's not worth the loss of use and satisfaction to baby your battery like that.

Just use it.


david.jones24 | 12 maart 2017

+ 1000 Carl

EaglesPDX | 13 maart 2017

It is a real concern in EV's as Tesla Raodster current battery replacement is $29,000. Roadster is hitting eight years. The idea to get biggest battery you can afford is good advice. The tech issue with li-ion batteries is avoid full cycles, full discharge and recharge. The life of the batteries is finite measured by full dischrage/recharge cycles. These typically won't occur with regular usage.

andy.connor.e | 13 maart 2017

Temperature of cells during charge/discharge also contributes significantly to degradation. In otherwords, frequent supercharging and frequent "flooring it" causes higher cell temperature.

Although, i would not focus too much on the Roadster Mr. Eagles. Didnt they discontinue it? I dont believe the Roadster was meant to be produced forever, more or less to just get them started.

Frank99 | 13 maart 2017

The Roadster is kind of a unique case; it used actual 18650 Laptop cells whose chemistry isn't optimized for EV use. Even so, it only has about a 15% degradation over 100,000 miles.
And the battery pack that pigeon is discussing is a factory Roadster 3.0 upgrade - which includes a 70 KWH pack to upgrade the stock 53 KWH pack, an aero kit to reduce Cd, replacement low-rolling-resistance tires, and includes labor.

Haggy | 14 maart 2017

The Roadster was made in small quantities and battery packs need to be built by hand. They are expensive and the primary reason for upgrading them is that the new packs provide a lot more range. It has nothing to do with needing new batteries after eight years. The original range was less than it is for new batteries.

The cars take care of the charging. When you use a supercharger, the charging tapers substantially for the final 10%. The thermal management system will not overheat the battery. You aren't looking at a $10 cell phone charger.

What has been said about not letting the car sit with a low charge or with a 100% charge for extended periods is accurate in the sense that there hasn't been accelerated degradation shown when people don't do that. It doesn't mean there will be accelerated degradation when people do that, but there are too many hypothetical scenarios for Tesla to make a definitive statement, so they make recommendations based on what they know will be safe.

I've charged to 100% but don't do it unless I'm on a trip, and I don't leave the car at 100%. I drive right after charging. I've gone down to about 5-6% on a few occasions, literally plugging in to charge as soon as I arrived somewhere that low. After 2.5 years and 39,000 miles, I'm seeing the same range as when the car was new, down to the mile.

That doesn't mean that if I had left it at 100% for a few hours at a time I would have damaged the battery, nor does it mean that had I waited until the next morning to charge when it was very low, it would have made a difference. I don't know, and I don't have to know because I had no reason to do anything different. I do know that if I charged to 100% every day and left the car plugged in and sitting in the garage for months on end, it wouldn't be a good idea. Likewise, if I left the car sitting with 10 miles of range for a month, I might brick the battery. There's likely some point between occasionally leaving the car at 100% for 10 hours and doing it for months on end where a difference crops up. Not doing it unless you have to means you don't have to worry about where that point is.

Tesla says that regular charging to 90% is safe. I do that daily. I could probably go higher without hurting my battery, but 90% is so many times what I might drive in a single day that there would be no point. I charge to 100% before long trips. Otherwise, I don't.