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Battery Degradation Scientifically Explained

Discussion in 'Model 3: Battery & Charging' started by Zoomit, May 17, 2019.

  1. Zoomit

    Zoomit Active Member

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    The first 20 minutes of this video shows that this guy knows something or two about Li-Ion batteries. The final few minutes are the takeaway's to minimize battery degradation. His conclusions reinforce the credible advice I have seen previously.

    Screen Shot 2019-05-17 at 5.54.15 PM copy.png



    This one video isn't Model 3 specific but his other videos cover Model 3 battery technology and his next video is about V3 Supercharging.
     
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  2. EV-Tech Exp

    EV-Tech Exp Member

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    I'm glad you found my video helpful, and it is nice to see it posted here given the knowledgeable crowd on this forum.

    Feel free to ask me any specific questions on this topic if not addressed by the video.
     
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  3. Zoomit

    Zoomit Active Member

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    Thanks for making the video! I especially liked how you mapped the different causes with their various effects towards the end. It’s so very complicated and that both reinforced the complexity but highlighted the linkages.

    What’s your background—Chemical engineering?
     
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  4. EV-Tech Exp

    EV-Tech Exp Member

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    Thanks, and I hope it can be a useful contribution to the knowledge of the collective.

    I did a PhD in Electrochemical Engineering, and currently work on battery design so battery topics are my specialist topic.
     
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  5. Zoomit

    Zoomit Active Member

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    @EV-Tech Exp What's your assessment of Tesla's continued use of NCA instead of NMC 811. Do you see them staying with NCA for vehicle applications since their battery architecture is focused on relatively small 2170 cells?
     
  6. EV-Tech Exp

    EV-Tech Exp Member

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    Generally high capacity NCA will have both higher energy storage capacity and cycle life stability than NMC 811 right now.

    This begs the obvious question, why are others looking toward NMC811? There are two main reasons:
    • NCA generates more gas than NMC811 as it degrades - within a cylindrical cell, this gas can be managed, however within a large pouch cell, this is problematic, hence NCA is typically not used in pouch cells.

    • High energy NCA has lower thermal stability than NMC811 - passing cell safety tests is a challenge with both chemistries, however the higher volatility of NCA results in it generally only being used in small cells, where the energy content is lower, and can be more carefully managed.
    Ultimately, both chemistries are becoming increasingly similar as NMC tends from NMC111 to NMC9_0.5_0.5 as both are slightly different methods of stabilising Lithium Nickel Oxide. One is not better than the other - what is important is what you have to do in cell design to maintain the desired level of safety whilst continuing to increase energy.

    As both chemistries tend toward cobalt reduction (cost reduction) and increased nickel (increased energy), NMC may become the preferred option if sufficient cycle stability can be achieved as the stabilising aluminium in the NCA does not contribute toward energy storage, however if higher stability can be achieved with NCA, it can be used at higher voltage to extract greater energy from the same capacity thus may see a benefit.

    Tesla's next cell will certainly be interesting!
     
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  7. Zoomit

    Zoomit Active Member

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    How does NCA lack of thermal stability relate to temperature sensitivity during charging? This was a big surprise to me when I started driving my Model 3 from an NMC622 Bolt EV. Max regen and Supercharging power seemed much more sensitive to battery temperature in the Model 3. In addition, the regen limitations went much lower in SoC. Do you think that these effects are due to the <3% Cobalt content in the Tesla batteries?
     
  8. Andrew104

    Andrew104 New Member

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  9. Andrew104

    Andrew104 New Member

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    Thanks for this very informative video, I am not a Tesla owner yet but I hope to be in the very near future. This video will help me take better care of the the battery.
     
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  10. willow_hiller

    willow_hiller Member

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    Finally had a chance to sit down at home and watch this. I'm going to have nightmares about lithium dendrites now!
     
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  11. EV-Tech Exp

    EV-Tech Exp Member

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    When I say thermal stability, I relate this to thermal runaway conditions, thus when I say lower thermal stability, I mean NCA cathodes will enter thermal runaway at a lower temperature, and the rate of heat release will be greater.

    The charging speed will be primarily impacted by cell design (including electrode thickness and porosity), ionic conductivity and anode material - the cathode will have an impact, but a relatively small impact in comparison to these other features.

    Limitations in performance could relate to low cobalt content, as this will reduce structural stability under energy cycling, but I doubt it is the primary factor in making charge rates more temperature sensitive.
     
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  12. Zoomit

    Zoomit Active Member

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    #12 Zoomit, May 19, 2019
    Last edited: May 19, 2019
    @EV-Tech Exp I have another question about the recommendations in your video. You mention 15% and 90% SoC as boundaries to avoid use beyond. I understand those are approximate values and are a function of ambient temperature as well as battery design/chemistry. But there's a fairly large variation in indicated SoC as a percentage of absolute SoC. The e-tron, EQC and e-Golf only allow 86-88% of the battery to be usable, whereas Teslas are closer to 96% or higher. Were you thinking of indicated or absolute SoC in your 15 and 90% recommendations?

    I know the fall off is not linear. It's a bathtub curve where the extremes are much worse for the battery than slightly off the extremes. So a secondary question is how sensitive are batteries to levels just inside of those boundaries? This graph is *JUST MY INTUITION* for battery storage stress bathtub curves. To ask the question differently, how would adjust these lines for a generic EV battery?

    20190519, Battery stress bathtub.png
     
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  13. Silicon Desert

    Silicon Desert Active Member

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    Speaking as an electronic engineer with some knowledge of battery chemistry, that is a great video. I learned more than I thought. Oh and I didn't realize Aluminum was a 5 syllable word :D Ha, just kidding. The English is certainly better than mine.
    I'd love to see a video explaining what happens (and why) these batteries become such an explosive fireball when compromised.
    Thanks for a fabulous presentation.
     
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  14. Silicon Desert

    Silicon Desert Active Member

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    Lord yes. Just when I was thinking that degradation of dendrites in my nerve cells might be a future cause of worry...…. this comes along :eek::D
     
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  15. Leafdriver333

    Leafdriver333 Somewhat Active Member

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    According to the graph, 15-75% seems better than 20~90%.
    I have been charging to 85% every 4 days.
    I am changing it to 75% from now on.
    And for longer trips I will only charge to 93%, especially in summer months.
     
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  16. Zoomit

    Zoomit Active Member

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    Remember, I just made that graph up and hope @EV-Tech Exp can reply and help correct it. I charge to 85-90% daily.
     
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  17. willow_hiller

    willow_hiller Member

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    No matter where the flat part of the curve lies, there will always be decreasing marginal returns to keeping your vehicle at a lower maximum SOC, right?

    Huge longevity gains by charging to 90% daily as opposed to 100% daily, and presumably some longevity gains by charging to 80% daily, but not nearly as much.

    And I assume it will also be heavily dependent on one's daily routine. If you can keep your battery at 80%, that's great, but if that SOC would cause you to Supercharge more often, I have to guess that more frequent supercharging would offset any longevity gains from maintaining that lower SOC.

    I'm taking our SR+ for our first short road-trip in August, and we essentially have a choice between charging to 100% or supercharging along the route. Given all that's been shared so far, I'm pretty sure that briefly touching 100% is healthier for the battery than any supercharging.
     
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  18. Zoomit

    Zoomit Active Member

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    I agree with all this.
    Yes, an occasional charge up to 100% before leaving should not be a concern and will help battery calibration and leveling. Then again a single trip with a Supercharging session is definitely not a concern either. It’s when you tally thousands of sessions that it might matter.
     
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  19. willow_hiller

    willow_hiller Member

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    @EV-Tech Exp for a battery lay-person like myself, does the current research on lithium ion battery degradation show any sort of priority or ranking in the severity of damage caused by the various mechanisms?

    Would you be able to say something like "In the degraded batteries we've studied, we think the leading cause of degradation has been...X" or "If you're looking to increase the life of your battery with the fewest possible lifestyle changes, the one thing you can change that has the most impact would be...Y"?
     
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  20. DirtyT3sla

    DirtyT3sla Member

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    Great thread with tons of great info. I have added the video to my watch later and will watch it later today. I plan on making a video about what degradation I've seen so far on my TM3 (1% or less after 12k miles) and I may reference this video. I will already be referencing the one from Professor Jeff Dahn.
     
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