Battery Degradation Scientifically Explained

[AlanSubie4Life]

I don’t really want to futz with it day to day. For most days I wont drive enough for it to even matter, but if I drive up to Reno and end up driving around all day and then back home I don’t want to have to worry about it either.

So assume you don’t care about the longevity of the battery, you have a Performance, and you drive like an idiot. (i.e. hard pulls from every light, 15 over on the freeway, etc...) What would you charge it to?

I read somewhere that Tesla recommends 90%. Is that right? How much practical range will that get you in a performance?

Last reply in this thread on this topic: 90% is fine. You will get approximately Range (miles) = 279rmi * (230Wh/rmi) / (Displayed Wh/mi). Realistically that works out to no more than about 230 miles. Adding another 10% is unlikely to matter in most situations.

 

[Dan203]

Last reply in this thread on this topic: 90% is fine. You will get approximately Range (miles) = 279rmi * (230Wh/rmi) / (Displayed Wh/mi). Realistically that works out to no more than about 230 miles. Adding another 10% is unlikely to matter in most situations.

Thank you. Sorry it was a bit off topic, but all the battery experts seemed to be in this thread.

 

[darth_vad3r]

Slightly more on-topic ... I paid closer attention to regen limiting last night, and arriving home after a 30-minute drive in 24, 23C outside temperature, with battery at 60% (started at 70%) I still had a few regen dots displaying full-time. Not enough to affect the feel ... but it makes me wonder how long it takes to warm up the battery after I discharged 10% of its capacity, half or more at freeway speeds, I would have expected it to be sufficiently warmed up enough to accept a regen charge without risking damage to the battery.

 

[mechrock]

Slightly more on-topic ... I paid closer attention to regen limiting last night, and arriving home after a 30-minute drive in 24, 23C outside temperature, with battery at 60% (started at 70%) I still had a few regen dots displaying full-time. Not enough to affect the feel ... but it makes me wonder how long it takes to warm up the battery after I discharged 10% of its capacity, half or more at freeway speeds, I would have expected it to be sufficiently warmed up enough to accept a regen charge without risking damage to the battery.

I was surprised how long it took to warm up to have full regen last winter. I went to visit a friend so the car sat outside ~30f, -1C. Drove it up into town a few hundred feet elevation, 20 mile round trip. Car sat another hour again, then I drove back home 100 miles down and then back up the mountain. It took 1 hour + of 60 miles of 50-60mph driving to get 3/4 regen and then 5 miles of 6% grade uphill 65mph driving to finish warming up the battery for full regen.

 

[BrandX]

So assume you don’t care about the longevity of the battery, you have a Performance, and you drive like an idiot. (i.e. hard pulls from every light, 15 over on the freeway, etc...)

That’s SOP, not idiotic.

 

[darth_vad3r]

That's right in terms of capability, however it is a lot of additional complexity and cost for the capability you receive...

Combined systems will be coming in the future, but they'll be battery/battery combinations rather than battery/supercapacitor....

Seems that an ICE car is already using a form of supercapacitor on the roads ... not even a hybrid, just a good ol' fashioned ICE ...

Mazda are using what they call a "low-resistance, high-capacity electric double layer capacitor (EDLC)" in their i-ELOOP technology:
MAZDA: Brake Energy Regeneration System | Environmental Technology

I think future Teslas will incorporate capacitors in some form ... they can be used both to make regenerative braking more efficient (less limitations so you can use it more of the time) AND save the battery from degradation from the extra charge/discharge cyles.

In addition to this they can add a quick-charge component to the Supercharging network where they zap your capacitor full to the max super fast and slowly use that up. In this case, part of preconditioning on the way to the Supercharger would be to discharge the capacitor completely by using that energy to charge the battery.

These could be various levels of technology. The 2170's of today will be the future's hard drives for backing storage of energy not used primarily for braking and acceleration ... the more expensive, but less capacity level 2 capacitors will handle most of that, and the even more expensive, but even less capacity level 1 capacitors will handle the most bursty portions.


EDIT: To change 'capacitor' to 'supercapacitor' in first line, according to this EDLC is one type of supercapacitor:
Supercapacitor - Wikipedia

 

[321filip]

Interesting research suggesting that high nickel NCA batteries shouldn't be used in a top 60% SOC for longevity

https://pubs.acs.org/doi/full/10.1021/acsenergylett.9b00733

 

[Jedi2155]

Interesting research suggesting that high nickel NCA batteries shouldn't be used in a top 60% SOC for longevity

https://pubs.acs.org/doi/full/10.1021/acsenergylett.9b00733

That is extremely interesting. Basically its WAY better to be 0-60% than 100% to 40%. A question that keeps popping up is what is 0% Voc, and what is 100% Voc? They're stating 2.7v and 4.3v, while this post implies 0% is ~2.8v and 100% <4.2v.

I'm also wondering what the NCA makeup of our exact Model 3 2170 cells are (I've only heard 8:1:1 ratio). They mentioned the S/X cells use NCA84 in their 18650 cells.

This is more about mechanical stress with really high nickel concentrations

And with NCA80 / NCA88

 

[KenC]

That is extremely interesting. Basically its WAY better to be 0-60% than 100% to 40%. A question that keeps popping up is what is 0% Voc, and what is 100% Voc? They're stating 2.7v and 4.3v, while this post implies 0% is ~2.8v and 100% <4.2v.

I'm also wondering what the NCA makeup of our exact Model 3 2170 cells are (I've only heard 8:1:1 ratio). They mentioned the S/X cells use NCA84 in their 18650 cells.

This is more about mechanical stress with really high nickel concentrations

And with NCA80 / NCA88

So what should we be doing? Use the battery from 60% to 10%? Avoid the area above 60% for daily driving?

 

[earthwormjim]

So what should we be doing? Use the battery from 60% to 10%? Avoid the area above 60% for daily driving?

That's what the paper concluded for Ni ratios above 0.8. Stress cracks occur above 60%, and the cracks penetrate all the way from the inner core of the cathode to the exterior. By not heavily discharging, the cathodes remain under strain too, so the cracks never close and they spread.

Stress cracks occur when charged to 60% too, but do not reach the outer core. By nearly fully discharging the cells, the strain created on the cathodes is relieved, so the stress cracks do not accumulate. Not only that, but discharging seems to close up the micro-cracks too.

What I can gather, is that charging above 60% permanently damages the cells, cracks propagate from the inner core to the outer exterior, which allows electrolyte to enter the inner core, poisoning the cathode. If you discharge to a low level, that at least closes up the cracks, but you still have some electrolyte inside of the cathode now.

If you don't charge above 60%, you still get some cracking, but it never reaches the outer surface of the cathode, so no electrolyte poisoning occurs, yet. If you never discharged to a low level, these cracks would accumulate over time, and presumably reach the outer surface of the cathode, but discharging to a low level closes the cracks up by relieving strain.

The NCA95 particles charged to 4.0 V contained a large number of microcracks that nearly traversed the entire particle but terminated before reaching the particle surface (Figure 2a). In comparison, the NCA95 cathode particles that were fully charged to 4.3 V contained numerous microcracks propagated through the entire particle to the surface, facilitating electrolyte penetration into the particle interior. These microcracks partially fractured the secondary particle into several smaller segments (Figure 2c). However, surprisingly, when the NCA95 cathode was fully discharged to 2.7 V, the microcracks generated from charging to either 4.0 V (lower DOD of 60%) or 4.3 V (DOD of 100%) closed back and hardly any microcracks were observed in the discharged state (Figure 2b,d). The reason for the crack closure is likely due to the expansion of the primary grains upon lithiation which fills the cracks.

 

[Jedi2155]

An important thing to consider that the issue is only pronounced as the Nickel content increases. We don't know what level of Nickel tesla uses in the 2170's, but we do know that the 18650's in the S/X is NCA84 which where Tesla may already be aware of this potential failure mode and optimized for maximum capacity vs. potential damage risk.

I heard from a Tesla employee at the Gigafactory is that you want to minimize charging to 100% as much as possible. I heard from a secondary source that you'd want to minimize going to 100% as often as possible because you're basically "stretching" the battery each time thus the crack formations. With low concentrations of nickel, the cathode is more stretchable but with higher concentrations it tends to get brittle and crack. The amount of crack formation is a tiny bit each time but the more often you do it it adds up.

The NCA88 relationship shows that the capacity lost is a function of merely going to 100% because the 100-40% and 100-0% have very similar capacity loss rates. Regardless of how long you stay at 100%, just merely getting there introduces stress.

At NCA80, the stress is negligible and the 60-0 case had no loss at all.

 

[Dr. J]

I don't know much, so please correct me:

"Currently, Li[Ni0.8Co0.15Al0.05]O2 and Li[Ni0.6Co0.2Mn0.2]O2 cathodes are adapted for EVs (Tesla Model 3 and GM Bolt) that have a driving range of 380 km for a single charge, which is still short of the recommended threshold. "

Isn't the bold formula for the battery in Model S and X, not the Model 3?
Isn't the Model 3 battery still Ni0.8? (8:1:1 ratio)
So isn't this paper irrelevant to batteries with 80% nickel or less?

 

[321filip]

I don't know much, so please correct me:

"Currently, Li[Ni0.8Co0.15Al0.05]O2 and Li[Ni0.6Co0.2Mn0.2]O2 cathodes are adapted for EVs (Tesla Model 3 and GM Bolt) that have a driving range of 380 km for a single charge, which is still short of the recommended threshold. "

Isn't the bold formula for the battery in Model S and X, not the Model 3?
Isn't the Model 3 battery still Ni0.8? (8:1:1 ratio)
So isn't this paper irrelevant to batteries with 80% nickel or less?

I think they mixed models up but even for Ni0.8 the above still applies just not as much (graph for NCA80)

This article suggest that Model 3 uses NCA84 and model S NCA80

• makes an NCA-80,15,5 cathode powder, which is 9.2% cobalt by weight, for use in the 18650 cells that Panasonic manufactures in Japan for Tesla’s Models S and X; and
• makes an NCA-84,12,4 cathode powder, which is 7.3% cobalt by weight, for use in the 2170 cells that Panasonic manufactures in Nevada for Tesla’s Model 3.

Tesla’s Cobalt Blues; Growth Fallacies And Supply Chain Risque Majeure

It makes sense as Model 3 batteries density is higher and cobalt content is lower than in Model S

 

[derotam]

I think they mixed models up but even for Ni0.8 the above still applies just not as much (graph for NCA80)

This article suggest that Model 3 uses NCA84 and model S NCA80

• makes an NCA-80,15,5 cathode powder, which is 9.2% cobalt by weight, for use in the 18650 cells that Panasonic manufactures in Japan for Tesla’s Models S and X; and
• makes an NCA-84,12,4 cathode powder, which is 7.3% cobalt by weight, for use in the 2170 cells that Panasonic manufactures in Nevada for Tesla’s Model 3.

Tesla’s Cobalt Blues; Growth Fallacies And Supply Chain Risque Majeure

It makes sense as Model 3 batteries density is higher and cobalt content is lower than in Model S

A better reference would be from the May 2018 Tesla Shareholder letter as referenced https://electrek.co/2018/05/03/tesla-model-3-battery-cells-rare-data-energy-density-cobalt/

This mentions the 2170 cells being the 8:1:1 ratio.
https://electrek.co/2018/05/03/tesla-model-3-battery-cells-rare-data-energy-density-cobalt/

 

[Dr. J]

A better reference would be from the May 2018 Tesla Shareholder letter as referenced Tesla releases rare details about Model 3's battery cells, claims highest energy density and less cobalt - Electrek

This mentions the 2170 cells being the 8:1:1 ratio.

This sentence from the shareholder letter is ambiguous:

"The cobalt content of our Nickel-Cobalt-Aluminum cathode chemistry is already lower than next-generation cathodes that will be made by other cell producers with a Nickel-Manganese-Cobalt ratio of 8:1:1."

Does it mean Tesla's NCA cathode is 8:1:1, or does it mean the other cell producers' nextgen NMC ratio is 8:1:1? Based on the other evidence, I think it's the latter.

Edit: I can't fathom why this basic information is so elusive.

 

[Jedi2155]

Trade secrets i guess. Its not that other manufacturers cant find it out its just expensive to reverse engineer the secret.

Kinda like a secret ingredients even if its not the whole recipe.

 

[321filip]

This sentence from the shareholder letter is ambiguous:

"The cobalt content of our Nickel-Cobalt-Aluminum cathode chemistry is already lower than next-generation cathodes that will be made by other cell producers with a Nickel-Manganese-Cobalt ratio of 8:1:1."

Does it mean Tesla's NCA cathode is 8:1:1, or does it mean the other cell producers' nextgen NMC ratio is 8:1:1? Based on the other evidence, I think it's the latter.

Edit: I can't fathom why this basic information is so elusive.

NMC 8:1:1 will be used in Chinese model 3 AFAIK


"Now a different report from tech news publication ‘the Elec’ in Korea, where LG Chem is based, states that the battery manufacturer started to “mass produce batteries for Tesla’s Model 3 electric vehicles from its Nanjing plant in China” last week.

According to the report, Tesla will now be getting NCM battery cells from LG:

“LG Chem convinced Tesla to switch to NCM811 batteries based on the longer driving distances per charge. It also hinted that it may be able to begin mass producing NCMA batteries, which is even higher in nickel, beginning in 2022 to apply to EVs.”"

 

[Dr. J]

NMC 8:1:1 will be used in Chinese model 3 AFAIK


"Now a different report from tech news publication ‘the Elec’ in Korea, where LG Chem is based, states that the battery manufacturer started to “mass produce batteries for Tesla’s Model 3 electric vehicles from its Nanjing plant in China” last week.

According to the report, Tesla will now be getting NCM battery cells from LG:

“LG Chem convinced Tesla to switch to NCM811 batteries based on the longer driving distances per charge. It also hinted that it may be able to begin mass producing NCMA batteries, which is even higher in nickel, beginning in 2022 to apply to EVs.”"

Interesting article:

"The US-based EV maker will be using LG Chem’ 21700 type batteries using NCM811 that boast a nickel proportion of 80% or more." (emphasis added)

"Until now, Tesla has been supplied by Japan’s Panasonic, which uses NCA, which is another type of high nickel cathode material."

So the "even higher" nickel content in the NCMA battery is on top of the 80% or more nickel proportion in the NCM811. I've never heard of NCM811--M is for manganese. Here are some references:

2019 PREVIEW: NCM811 batteries 'not likely' to be used in electric vehicles in 2019 | Metal Bulletin.com

NCM 811 Lithium-Ion Cells Quickly Increase In Market Share

NCM 90: successor of NCM 811 battery cells - PushEVs

 

[Renzo]

So if we drive a model S... Am I to understand then the best practice is to charge to 60 percent... And drain to as close to 0 as safely possible (say 5%) before recharging back up to 60 percent? Any idea if that would also help undo any degradation that's happened after 6 years of charging to 90 percent?

 

[321filip]

So if we drive a model S... Am I to understand then the best practice is to charge to 60 percent... And drain to as close to 0 as safely possible (say 5%) before recharging back up to 60 percent? Any idea if that would also help undo any degradation that's happened after 6 years of charging to 90 percent?

I would say if you use 70% a day, charge to 80%. That way average daily SOC will be around 40% if you use 30% charge to 50% (can't set less). The worst you could do is to charge to 90% every day while you use only 10% (battery average SOC 85% all the time).
But having Model S it's not that critical as the cathode chemistry is more resistant to high level of charge (still better to charge less, though).