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Discussion in 'Pyra News' started by EvilDragon, Oct 11, 2018.

  1. Letalis Sonus

    Letalis Sonus Advanced Member

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    Lithium batteries have one of the lowest self-discharge rates, and self-discharging does not mean that they ever reach the level of deep discharge that turns them into short-circuited battery bombs (or actively-damaging levels of discharge in general). The voltage is important, and if you've got nothing that can actively lower it by drawing power from them it will simply stabilize at a certain safe level.

    They are being stored at a certain charge level because it puts them into the chemically most stable state - but other charge levels only accelerate the natural degeneration, it does not actively damage them (in contrast to actively charging or discharging them). I've once got a few unused Thinkpad batteries that were stored without special care as replacement parts, they were being discarded due to switching to a newer series with different batteries. They were still in prime condition after over 5 years, with up to 98% of their original capacity.
     
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  2. levi

    levi Still fresh, damnit!

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    I wonder if you're mixing up lithium primary batteries (CR2032s and things like that) and lithium ion batteries. I have a bunch of old gadgets with lithium ion batteries that I have to periodically recharge because they're discharged more than I'm comfortable with, and most of those are stored outside the device they're designed to power. But even lithium primaries have best before dates.
     
  3. Djoga'Ro

    Djoga'Ro moonstruck

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    For that you'd need no internal Voltage/differing potentials or an ideal battery.
     
  4. Letalis Sonus

    Letalis Sonus Advanced Member

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    I'm explicitly talking about accumulators. I curse the English language for never having gained a widely spread term for rechargeable batteries, for we Germans have one and don't mix them up that easily.

    Modern lithium ion cells are considered to have a self-discharge rate of less than 2% per month at room temperature, which means it takes at least about 4 years for a fully charged battery to drain itself - and a lot more when stored in a cool environment. An increased self-discharge rate is an indicator for a damaged cell.
     
  5. Confuzzled

    Confuzzled Still Fresh

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    The optimal state of charge in which to store a lithium-ion battery is 40%

    Battery University - BU-702: How to Store Batteries: https://batteryuniversity.com/index.php/learn/article/how_to_store_batteries
    Battery University - BU-808: How to Prolong Lithium-based Batteries: https://batteryuniversity.com/index.php/learn/article/how_to_prolong_lithium_based_batteries
    Battery University - BU-802b: What does Elevated Self-discharge Do: https://batteryuniversity.com/index.php/learn/article/elevating_self_discharge
     
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  6. levi

    levi Still fresh, damnit!

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    That makes sense. I have some rather old gadgets that use lithium ion batteries, and I recharge them at most once every 2 years or so. If it could have dropped from 60% to 36% in that time, I personally consider that close enough to the bone to give it a go in the charger. Most of those old devices don't report an accurate percentage though, so that 60% figure is very variable to begin with.
     
  7. WizardStan

    WizardStan Mega GP Mania

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    Interesting. All my investigations suggested an estimated 2-3% loss per year if stored in optimal conditions (about 40% charged, low temperature), with up to 20% loss per year if kept fully charged. (edit: and at room temperature)
    I wonder if that's "average" batteries and there was something special about Thinkpad, or maybe there's a difference between cells and polymer? Or it could've been old data, I did do all that research 4 or 5 years ago now.
     
  8. levi

    levi Still fresh, damnit!

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    Also, Letalis Sonus is talking about original capacities only. Even if your battery is discharging, it hasn't necessarily lost any of its capacity to store charge if you did recharge it.
     
  9. Letalis Sonus

    Letalis Sonus Advanced Member

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    Indeed, they completely discharged themselves during their storage time. The point was that it caused not nearly as much damage as feared - and these are batteries with multiple cells, unlike the single-cell batteries of the Pandora that do not have to suffer from additional stress caused by differences between cells.
     
  10. WizardStan

    WizardStan Mega GP Mania

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    That's exactly what I was talking about as well: even a well stored battery loses it's original capacity which, according to previous research, was at best 2-3% per year. See table two
    Yet Letalis Sonus tells of laptop batteries which only lost 2% after 5 years, so now I'm not sure what to believe.
     
  11. Letalis Sonus

    Letalis Sonus Advanced Member

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    Maybe their data is simply out of date (or even not old enough), the comments go back the first commercially used lithium cobalt dioxide battery already appeared in '91. Even if these are still the most popular for mobile devices, a lot about them has changed in all these years, such as the structure of the electrodes - that has to have a significant influence on the storage capacity degeneration. Maybe it even makes a difference if these cells are cylindrical or flat pouch ones.

    These advancement at least had a significant influence on the self-discharge rate: In '99 it was still as high as 8% per month, a more recent source I found even claimed that nowadays 0.5-1% would be typical.
     
  12. rv6502-2

    rv6502-2 Still Fresh

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    What they tend to do is a bit sneaky: they give the total mAh capacity from maximum charge to maximum discharge.

    But give the capacity degradation numbers over the years according to a partial charge/discharge cycle. Say: only charge to 80% only discharge to 60% "2% loss after 5 year."

    Both are true statements (not false advertising), just not at the same time.

    Some tablets have a battery preservation mode where they'll only do 80%-60% charge cycles so you can minimise the battery wear when you're at home then turn this off before a long trip and get the full 100%-0% range.
     
  13. WizardStan

    WizardStan Mega GP Mania

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    Who is "they"? There's no marketing here, this is a pretty legitimate knowledge site, and it's not the only one; I don't think they're trying to sell anything except their book.
     
  14. Letalis Sonus

    Letalis Sonus Advanced Member

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    We're talking about storage degradation, not usage degradation. There is no charge/discharge level trickery involved, it is all about not touching them at all.
     
  15. lukey

    lukey Rare Species

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    Good, So we all agree that Pyra should ship sooner :)
     
  16. levi

    levi Still fresh, damnit!

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    Yes, once it's done. And not before.
     
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  17. Xcl4m4t10n

    Xcl4m4t10n Very Active Member

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    So... Yeas, Pyra project. And?
     
  18. Bosbeetle

    Bosbeetle Terminally lost

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    I wonder if the evildragon has seen some nice materials, at the material convention thingy.
     
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  19. netlinker

    netlinker Still Fresh

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    Regarding lithium batteries, there are several reasons for degradation:
    1. Reaction of the electrolyte with the electrode materials
    2. Mechanical stress of the electrodes due to deformation during charge/discharge
    3. Secondary reactions at the electrodes caused by too high overpotential in the diffusion zone of the battery (if I'm not mistaken ... lecture was some time ago ...)

    1. Is a temporal thing ... the longer you store your battery, the higher the voltage and the higher the storage temperature, the bigger the degradation ... basic laws of chemical reactions.

    2. Is a DOD (depth of discharge) thing. The electrodes expand and shrink when they accumulate/release the lithium ions from the carbon matrix of a electrode. Therefore it is a purely physical effect. This mechanical stress breaks the structure of the electrodes on microscopic level. The surface area is shrinking and blockages for ion travel build up as fragments block the otherwise very rough structure of the electrode. Less surface area means higher current density and therefore higher resistance of the cell and higher overpotential at the electrodes. This very important during charging and leads to 3.
    So ... the lower the cycle depth, the lesser the wear of the battery. If one charges his phone rather often (NOT FASTCHARGE ...) and uses only lets say 20% of the capacity, the battery will last a lot longer. If those 20% are between 40 and 60 and not 80 and 100 it will last even longer (see 1.). Thats also why TLP for lenovo laptops has an adjustable charge value in % (I set mine to 80%).

    3. If the charging current is to high for the current impedance of the cell, you have a lot of voltage drop at the electrodes. The voltage is therefore a lot higher as the current equilibrium of the cell and the energy is high enough to start secondary reactions. Namely this is lithium plating of the electrode. If this occurs, the cell will be dead after several cycles as elementary lithium is very reactive and must never exist in the cell.
    Therefore it is important to charge a lithium battery at moderate rates and elevated temperatures (35°C to increase ion mobility and decrease overpotential), especially if they get old and have lots of cycles.
    (Cars even have a battery preheat with alternating current to heat the battery prior to charging, which is especially important during winter)

    I hope this brings some light in the understanding of the voodoo lithium battery thingy and battery management ;).
    If anybody wants to know more I'll have to look it up in my university books.
     
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