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Chemical batteries do not seem to have any moving parts, but seem to have a rather short lifetime anyway. Why is this? The only reason I can think of is electrolyte leaking, but I have never noticed a leak of my Li-Ion phone battery and yet I have to replace it at least once a year.

Note, I'm measuring lifetime primarily in cycles of charge/discharge. There are other factors such as temperature and load (or lack thereof for long periods of time).

I'm not only interested in the Li-Ion chemistry. From what I've read, all batteries have a lifetime of charge/discharge cycles, after which they are just no good anymore.

This is apparently one of those rare things that somehow "wears out" quickly despite having no moving parts. The only other thing I know of like that is Flash memory, which wears out because the high voltage needed to write cells degrades them somehow

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    \$\begingroup\$ They do have moving parts, they are just too small to see. \$\endgroup\$
    – Majenko
    Commented Jan 28, 2016 at 1:18
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    \$\begingroup\$ While I'm sure there are a few answers here, or other SE sites, that address battery chemistry, this is a question that is eminently web-searchable. \$\endgroup\$
    – user65586
    Commented Jan 28, 2016 at 1:26
  • \$\begingroup\$ @Majenko I meant moving parts in the general engineering sense, which does not include electrons moving in a current nor ions flowing in a liquid. \$\endgroup\$
    – DrZ214
    Commented Jan 28, 2016 at 1:40
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    \$\begingroup\$ Why do incandescent bulbs have a short lifetime despite having no moving part ? Many things can wear materials : Temperature, acid or alcaline mixtures... \$\endgroup\$
    – Grabul
    Commented Jan 28, 2016 at 1:40
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    \$\begingroup\$ @DrZ214 the moving electrons represent a chemical change of the actual structure of the battery. You are repeatedly reducing and oxidizing one electrode or another. During this process a few things happen - the electrolyte can chemically interact (slowly) with the electrodes and ions, changing its properties as an electrolyte - repeated oxidation and reduction of the electrodes can degrade and corrode them, reducing the potential energy available for electrochemical reactions. The exact mechanism and primary mode of failure depends on the specific battery chemistry \$\endgroup\$
    – crasic
    Commented Jan 28, 2016 at 2:06

2 Answers 2

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It is due to the solid state chemistry. In the most simplistic of descriptions, the surfaces of the anode and cathode will have imperfections. Over time, this will result in some of the ion channels becoming restricted as the ions react with the anode/cathode surface, deforming the structure. As the ions cannot move as freely, capacity will suffer.

http://www.extremetech.com/extreme/183338-scientists-discover-the-reason-that-batteries-lose-capacity-over-time-nanocrystals

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If a Li-Ion battery is charged and discharged frequently, the resulting livetime is short. The number of possible charge/discharge cycles is limited because each cycle causes small internal damages to the cell structure.

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