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li-ion battery

Discussion in 'Electronic Repair' started by Deodiaus, Oct 29, 2006.

  1. Zak

    Zak Guest


    It may also be caused by high voltage. Increasing voltage by 1/10th of a
    volt stores decidedly more power in the battery, but also makes the life
    a lot shorter. It can be inferred that topping the battery up to full
    charge is bad for it.

    My ancient laptop always charges the battery whenever it has been
    unplugged for a while.

    My new laptop only starts charging whenever there is a real amount of
    discharge. If there is none, the charge light does not come on.

    The cells are now at 4.187 volts, which is slightly below the voltage
    they reach at end of charge. But it is still high, I must say. I'll
    check if it goes down a bit with time.


    Thomas
     
  2. budgie

    budgie Guest

    It is a combination of two factors.

    Heat is the main one - while the laptop is running there is substantial heat
    which reaches the battery bay. Careful design can minimise this, but the
    pressure to jam more functionality into ever thinner (i.e. volumetrically
    smaller) boxes usually negates this effort. Use of external AC/DC power packs
    removes one heat source, but there are many - the CPU and HDD being the main
    two.

    Cell degradation is a function of cell voltage, and maintaining cell voltage at
    the charge termination figure will accelerate its demise. Sensible charging
    regimes ensure that once a pack has reached the charge termination voltage, no
    further attempt is made to charge it until the voltage drops by a noticeable
    amount. For example, using a 4v20 cutoff, charge reinitiation at 3v95 is often
    employed in industrial (non-laptop) applications where the pack remains
    connected to the charger.

    Also the commercial pressures in the laptop market result in the use of
    termination voltages at the high end of the recommended range. Dropping from
    4v20 to 4v10 loses noticeable capacity, but would certainly extend battery pack
    life significantly. To the manufacturer/vendor, that isn't good business. To
    the user who pays the life cycle owning cost, it would be a great decision.
     
  3. budgie

    budgie Guest

    Assuming it is Li-XX, that is not clever at all.
    They are starting to improve things.
    I sincerely wish the user had the choice to lower the charge termination voltage
    from 4v20 to 4v10. I for one would certainly go for the lifetime-vs-endurance
    tradeoff that causes.
     
  4. BillW50

    BillW50 Guest

    [snip]
    You can! Buy or build your own programable charger. I bought one for
    about $125.
     
  5. Actually this is incorrect either. High voltages accelerate reaction
    between electrolyte and anode. That is why charging cells regularly to
    4.1V instead of 4.2V prolongs their cycle life by 30% (this is widely
    used in back-up systems).

    Li-ion is unlike any battery. It does not like either full charge or
    full discharge. It likes to be left alone
    in some intermediate charge state. That is why the cells are shipped in 50%
    state of charge.

    It is not harmful to discharge them to full (it does not cause by itself
    any damage, unlike lead-acid case) as long as you recharge it soon afterwards.
    That is not true, as there is no evidence of any improvement of cycle life
    between cycling from 100 to 20% compared to 100 to 0.
    At the other hand, there is a clear evidence that at high voltages degradation
    is faster.

    What IS harmful is discharging is living battery in discharged state for long
    periods of time, because self-discharge and electronic load will overdischarge
    them into low voltage areas below 3V open circuit voltage (OCV) where
    corrosion of Cu-current collectors can happen.
    Note that "OCV" and voltage under load are different things. If under C/2
    load you stop discharging at 3V, voltage will rapidly relax to 3.5V OCV because
    most of low voltage is caused by IR drop.
    But if you see actual open circuit voltage of 3V, cell is over discharged.

    Regards,
    EVgenij
     
  6. Zak

    Zak Guest

    That was yesterday. Today the voltage has gone down a bit more, to 4.182
    volts. I don't know if that looks like a cell under no load, but I hope so.


    Thomas
     
  7. budgie

    budgie Guest

    I really meant on my laptop collection .....

    (I have designed a commercially successful charger which had selectable
    termination voltage).
     
  8. BillW50

    BillW50 Guest

    [...]
    Do you have any idea that some of us are getting 10 years and more on
    our Li-Ion batteries? It isn't much of a secret, we are just lazy. lol

    I have to tell you that you are on the right track though. I mean you
    are really close. I have not much to disagree with you, but you are not
    there yet. :)
     
  9. Because main reason of usable capacity loss for Li-ions is its impedance
    increase and NOT the loss of available material, you might use the cell
    quite long if your application draws low currents such as below C/5 rate.

    Not charging to full 4.2V and keeping it cold (for example by removing
    it from the laptop when used as PC) can also increase life noticeably.

    Btw Li-ion battery is in mass production for barely more than 10 years (it
    was released in 1990). Initially Sony cells was the only game in town.
    You are telling me that you got your cells in 1996 and they are still alive?
    What is the useable capacity compared to design capacity?

    Regards,
    Yevgen
     
  10. BillW50

    BillW50 Guest

    Yes I do have Li-ion batteries this old. They are cell phone batteries
    though. And I don't use them anymore. But I still charge them up about
    once a year. I haven't checked their capacity in a few years. But I do
    know they did have 50% or better still left just a year or two ago.

    My Palm IIIc Li-Ion battery lasted 5 years. And I just replaced it. And
    the last 6 months of its life, I had it on the charger 24/7 (it's
    automatic and will kickoff and on when needed). And I believe this is
    what killed it. Yet the charger only charges it up to 4.10 volts. And
    you can't turn these things off. It runs for about 2 weeks in standby or
    about 12 hours up and running. And I run it down to only 50% before I
    recharge it.

    I have very good luck only draining Li-Ion batteries down to about 40 to
    50% and then recharging them. Either by use, or by self discharge.

    I have 4 six year old laptop batteries. Two were left in the machines
    being charged and hardly ever used. They died just over two years. The
    other two had some experience being left in on charge for a few months.
    The one that spent the most time on charge is down 40% of capacity. The
    other one which rarely ever spent time in the charger only has lost 20%.

    The weird thing is, with cell phones... keeping them on the charger
    seems to make them last long. But for Palms and laptops, avoiding the
    charger seems to be best.
     
  11. We have a 7200 Wh (yes, really, 1008 2.0Ah 18650 cells) Li-ion battery
    that I have been maintaining since 2002. It is for an occasional use
    project. I cycle it and balance the cells once a year, and then leave
    it at 50% state of charge. So far it has held close to its original
    capacity at the C/20 rate.

    Some of the other batteries we use have shown increases in impedance in
    just a couple of years. In one case we had a pair of units,
    manufactured at the same time and operated by the same outfit, returned
    for evaluation after 2 years of use; one unit had like-new batteries,
    the other showed 20% loss of capacity due to increased impedance, and
    both units had similar numbers of battery cycles (according to the
    internal counter). I think, but don't know, that the higher impedance
    unit had been stored at full charge, and or at elevated temperature.

    --
    NOTE: to reply, remove all punctuation from email name field

    Ned Forrester 508-289-2226
    Applied Ocean Physics and Engineering Dept.
    Oceanographic Systems Lab http://adcp.whoi.edu/
    Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
     
  12. Dan_Musicant

    Dan_Musicant Guest

    :BillW50 wrote:
    :
    :> I agree Larry. Although laptop Li-Ion batteries seem to act differently.
    :> Tons of people have learned for you leave them in the charger 24/7 (in
    :> the laptop under AC power), the battery is usually worthless in about 2
    :> years (even though you never used it). Brand doesn't matter.
    :>
    :> But if you leave them out of the laptop and just recharge them about
    :> once every 6 months, they can last 10 years or more. Some of us have
    :> theories why this happens. And most of us believe it is do to the fact
    :> that laptops usually get pretty hot and slowly destroys them.
    :
    :
    :It may also be caused by high voltage. Increasing voltage by 1/10th of a
    :volt stores decidedly more power in the battery, but also makes the life
    :a lot shorter. It can be inferred that topping the battery up to full
    :charge is bad for it.
    :
    :My ancient laptop always charges the battery whenever it has been
    :unplugged for a while.
    :
    :My new laptop only starts charging whenever there is a real amount of
    :discharge. If there is none, the charge light does not come on.
    :
    :The cells are now at 4.187 volts, which is slightly below the voltage
    :they reach at end of charge. But it is still high, I must say. I'll
    :check if it goes down a bit with time.
    :
    :
    :Thomas

    Li-on batteries degrade more quickly when fully charged. I try not to
    fully charge mine, therefore. If I do fully charge them, I try to take a
    little charge off quickly.

    I believe the self degradation of these batteries is lowest at around a
    40% charge, and if you don't intend to use them for a while, refrigerate
    them at this charge level. That's the way I store my video camera
    batteries, since I use them very occasionally.

    Even if you take the best care of them, they won't last indefinitely. I
    figure if you get 3+ years out of one, you are doing well. Typical usage
    I believe is maybe 2 years.

    I learned this stuff by checking out the newsgroup:

    sci.chem.electrochem.battery

    Do www.groups.google.com search on this newsgroup and li-on and battery
    life, etc.

    Dan
     
  13. BillW50

    BillW50 Guest

    Why is it that people who claims to have knowledge about care for Li-Ion
    batteries also claim of keeping them alive for only 3 years, while
    others ignore this care and feeding and are getting 10 years and
    counting with ours?
     
  14. Dan_Musicant

    Dan_Musicant Guest

    ::>
    :>> BillW50 wrote:
    :>>
    :>>> I agree Larry. Although laptop Li-Ion batteries seem to act
    :>>> differently. Tons of people have learned for you leave them in the
    :>>> charger 24/7 (in the laptop under AC power), the battery is usually
    :>>> worthless in about 2 years (even though you never used it). Brand
    :>>> doesn't matter.
    :>>>
    :>>> But if you leave them out of the laptop and just recharge them about
    :>>> once every 6 months, they can last 10 years or more. Some of us have
    :>>> theories why this happens. And most of us believe it is do to the
    :>>> fact that laptops usually get pretty hot and slowly destroys them.
    :>>
    :>>
    :>> It may also be caused by high voltage. Increasing voltage by 1/10th
    :>> of a volt stores decidedly more power in the battery, but also makes
    :>> the life a lot shorter. It can be inferred that topping the battery
    :>> up to full charge is bad for it.
    :>>
    :>> My ancient laptop always charges the battery whenever it has been
    :>> unplugged for a while.
    :>>
    :>> My new laptop only starts charging whenever there is a real amount of
    :>> discharge. If there is none, the charge light does not come on.
    :>>
    :>> The cells are now at 4.187 volts, which is slightly below the voltage
    :>> they reach at end of charge. But it is still high, I must say. I'll
    :>> check if it goes down a bit with time.
    :>>
    :>> Thomas
    :>
    :> Li-on batteries degrade more quickly when fully charged. I try not to
    :> fully charge mine, therefore. If I do fully charge them, I try to
    :> take a little charge off quickly.
    :>
    :> I believe the self degradation of these batteries is lowest at around
    :> a 40% charge, and if you don't intend to use them for a while,
    :> refrigerate them at this charge level. That's the way I store my
    :> video camera batteries, since I use them very occasionally.
    :>
    :> Even if you take the best care of them, they won't last indefinitely.
    :> I figure if you get 3+ years out of one, you are doing well. Typical
    :> usage I believe is maybe 2 years.
    :>
    :> I learned this stuff by checking out the newsgroup:
    :>
    :> sci.chem.electrochem.battery
    :>
    :> Do www.groups.google.com search on this newsgroup and li-on and
    :> battery life, etc.
    :>
    :> Dan
    :
    :Why is it that people who claims to have knowledge about care for Li-Ion
    :batteries also claim of keeping them alive for only 3 years, while
    :eek:thers ignore this care and feeding and are getting 10 years and
    :counting with ours?

    Hey, I wouldn't know. In fact I've never lost a li-ion battery. I've
    simply read posts trying to find out the score. I've certainly had my
    problems with Ni-Cad batteries, so I figure it's certainly worth the
    trouble to read posts from people who seem to know what they are talking
    about and learn from them.

    Why don't you answer your question for me. I certainly can't. You
    evidently have some ideas.

    Dan
     
  15. Probably because applications are different. Li-ion batteries lose very
    little active material, however their effective DC-impedance increases a
    lot with aging, typically 70% in 100 cycles.

    Therefore:
    1) For low rate applications (C/5 rate and below) Li-ion can live very long,
    as such applications don't care about impedance
    2) For high rate applications (above C/5 rate) I*R drop is going to kill
    useable energy, therefore impedance increase cuts useable run-time
    dramatically.

    Battery is not going to "die" (like have no voltage on it or leak), but
    it will be just useless for high-rate applications, device will die
    right after turn-on.

    You keep talking about 10 years. Let's get a little meat here,
    so we talk numbers and not just heating air:
    - what rate of discharge (in C-rate) you have in your device?
    - how much run-time (in %) you get in your device as compared
    with new-battery run time?

    Regards,
    Yevgen
     
  16. PeteS

    PeteS Guest

    Duh. Battery life depends probably more on load cycling than any other
    single thing.

    Li-ion batteries lose very
    Hmm. I don't know what you are using, but my products have Li+ in them
    and at well over 100 cycles they are still well above 95% rated
    capacity. (That's from randomly removed and tested devices,
    incidentally)
    Hmm again. Sure they do, but the degree of caring is different.

    Pure BS. I have three separate applications where I use Li+ cells. In
    one, the average current is about C under full load. I have tested
    numerous units repetitively including charge cycles. After 200 cycles
    they are still at greater than 95% original capacity.
    I will agree that high load currents will limit the time a load may be
    active especially at the end of the discharge curve, however; but not
    by that much

    I noted some comments earlier in this thread; A Li+ with a terminal
    potential of 3V is at nominal discharge, and it is perfectly safe to
    discharge them to this point provided you charge them again within,
    say, 96 hours.
    True of any battery that is low; NiCads had this issue, NiMH had this
    issue.

    More specifically, how much real energy is available.

    Cheers

    PeteS
     
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