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Thread: Is charging the 18650 a major event in your life?

  1. #91
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    Default Re: Is charging the 18650 a major event in your life?

    You also need to account for combustion energy, for example, from Barsukov & Qian, p. 94
    ----
    However, one of the side effects of organic electrolytes is that when the temperature exceeds a certain limit depending on battery chemistry, the reaction between the active material and electrolyte releases heat and becomes self-supporting (thermal runaway), which can cause a fire, explosion, or venting of electrolyte. Just how destructive can such an event be? It depends on the amount of energy released. Let's compare the energy of an 18650 Li-ion battery with that of a well-known destructive device, say, a hand grenade filled with TNT. TNT releases energy of 4.1 kJ/g. A Li-ion battery stores 0.250 Wh/g, which corresponds to 0.93 kJ. This is about one-quarter of the TNT energy. But — and this is a big difference with traditional batteries that have a water-based electrolyte — a Li-ion battery has additional energy in its organic electrolyte! In case of combustion, it will also burn. So will polymer separators. As reported in a safety analysis [1], the energy released by the burning of up to 10 g of electrolyte and 1.6-g separators contained in an 18650 cell is 280 kJ. Given the cell weight of 40 g, we get 280/40 = 7 kJ/g of combustion energy. So, taken together, the electric and material burning energy per gram of Li-ion battery is around 8 kJ/g, close to twice that of TNT! Comparing an 18650 cell with a typical hand grenade (U.S. M67, with 180 g of explosive), it takes only five 18650 cells to exceed the hand grenade's energy! A typical notebook battery pack (3 serial/2 parallel, 3s2p) has six cells, so it has more combustion energy than a hand grenade. I trust this will make you pause a moment.

    Fortunately, battery combustion is not nearly as fast as that of explosives ...
    Last edited by Gauss163; 05-23-2015 at 05:49 PM.

  2. #92
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    Default Re: Is charging the 18650 a major event in your life?

    Quote Originally Posted by Gauss163 View Post
    You also need to account for combustion energy, for example, from Barsukov & Qian, p. 94
    Scaremongering, try calculating the equivalent number of hand grenades for a filled gas tank on your car (Gasoline as nearly 10 times the energy density of TNT).
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  3. #93

    Default Re: Is charging the 18650 a major event in your life?

    Quote Originally Posted by Gauss163 View Post
    A typical notebook battery pack (3 serial/2 parallel, 3s2p) has six cells, so it has more combustion energy than a hand grenade.
    Possibly. And probably the same goes for a pound of butter. Your point being?

    Quote Originally Posted by HKJ View Post
    Scaremongering, try calculating the equivalent number of hand grenades for a filled gas tank on your car (Gasoline as nearly 10 times the energy density of TNT).
    +1.

    The destructive effect of a hand grenade (or TNT) comes from the extremely short time in which the energy is released. And shockwave that goes with it (not to mention metal fragments ). NOT so much from the amount of energy (aaaand... if I understand correctly, energy released from explosive detonation is not the same as when the material would be burned).

    The thermal runaway is just a matter of some decomposition process accelerating as temperature rises. Note that decomposition of materials often requires energy input, rather than releasing energy. Compare with boiling water: as you approach 100 oC, water vapor will be produced at increasing rate. But for all water that's boiled off, heat still needs to be added. Boil the water in a pressure vessel, and upon rupture of that vessel result can be spectacular. But if so, to flash-vaporize all water you still need to add enough heat (before vessel ruptures!) to boil off that water.

    And regardless of burn energy: because burning organic compounds requires oxygen, burning can only begin after a cell has vented. Only the material that's vented can burn, what stays inside the cell doesn't. For every weight % that's non-combustible metal or metal salts (a considerable % for most cells, I think), that's less weight % of combustible material. And not all combustible materials burn equally easy...
    Last edited by RetroTechie; 05-24-2015 at 11:00 AM.

  4. #94
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    Default Re: Is charging the 18650 a major event in your life?

    Please read more closely. The text was not written by I. It was excerpted from a (very informative) book written by two leading engineers in TI's battery management systems group. Apparently you missed the final quoted sentence "Fortunately, battery combustion is not nearly as fast as that of explosives ...".

    Their scientific claims appear to be well-founded. Of course it goes without saying that the pertinence of the analysis will depend upon the particular application.

  5. #95
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    Default Re: Is charging the 18650 a major event in your life?

    Quote Originally Posted by Gauss163 View Post
    Please read more closely. The text was not written by I. It was excerpted from a (very informative) book written by two leading engineers in TI's battery management systems group. Apparently you missed the final quoted sentence "Fortunately, battery combustion is not nearly as fast as that of explosives ...".

    Their scientific claims appear to be well-founded. Of course it goes without saying that the pertinence of the analysis will depend upon the particular application.
    It does not change the fact that it is scaremongering, they could just as easily compare the battery pack to a small cup of gasoline, but that would not sound nearly as dangerous.
    My website with battery and charger information: lygte-info.
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    Compare 18650 LiIon batteries or smaller (RCR123, 16340, 14500, 10450) LiIon batteries.

  6. #96
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    Default Re: Is charging the 18650 a major event in your life?

    The authors are attempting to convey to the intended audience (designers of (li-ion) battery systems) a rough idea of the amount of combustion energy in a typical 18650 cell. Presumably they are being a bit hyperbolic in order to encourage such designers that safety matters deserve serious consideration.

    The link I gave goes to the exact page in Google Books. One can browse further to get a better idea of the context.

    Please don't confuse my personal view on such matters with those of authors that I quote. I suspect that my view is a bit less conservative than the TI engineers, and probably slightly more conservative than the average CPF member.

    I think it is important that readers are exposed to healthy balance of scientific literature, so that they have at hand the facts to perform their own risk analyses (a highly subjective decision process).

  7. #97
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    Default Re: Is charging the 18650 a major event in your life?

    Quote Originally Posted by HKJ View Post
    Scaremongering, try calculating the equivalent number of hand grenades for a filled gas tank on your car (Gasoline as nearly 10 times the energy density of TNT).
    Holy sh*t. I think I see a Tesla in my future. :-)

    On the other hand, I'm not as worried now about carrying those hand grenades in my trunk. LOL
    Last edited by magellan; 05-25-2015 at 06:43 AM.
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  8. #98
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    Default Re: Is charging the 18650 a major event in your life?

    Quote Originally Posted by HKJ View Post
    It does not change the fact that it is scaremongering, they could just as easily compare the battery pack to a small cup of gasoline, but that would not sound nearly as dangerous.
    You are missing the point. The book is targeted at readers designing li-ion battery systems (e.g. laptop batteries) that may be used by many millions of users. It is essential that such designers have a good idea of just how dangerous such battery packs can become should they reach thermal runaway. This is not something that many designers would typically have strong intuition about from working with older battery technology.

    Generally the risk analyses performed by such designers will be far more conservative than those we may perform for hobby apps (e.g. we are generally far more educated about safety matters than the general public). Nonetheless, the data used in these professional analyses can prove useful for anyone making safety decisions for hobby applications.

  9. #99

    Default Re: Is charging the 18650 a major event in your life?

    Charged my first 18650, wasnt even depleted and took 4 hours.

  10. #100

    Default Re: Is charging the 18650 a major event in your life?

    I've learned a bit since I last posted in this thread. I should say that floating them at 4.2v is not good for the cells but due to the very low wattages is not particularly dangerous. Most cells recommend a termination current in their datasheet. In many cases it is significantly higher than what my Nitecore d4 charger terminates on (and my i4 overcharges cells relative to the d4).
    I've pretty much moved on from buying LCO and NCA cells to NMC and LMC (LCO/LMO hybrids) for added safety and not having to deal with protection. The LGH2 is my current go-to cell. If I'm going far into the woods I will take NCAs for specific power (less cells and each weighs a bit less) for everything but high drain lamps.

    Mike
    Last edited by Arizona_Mike; 04-16-2017 at 12:06 PM.

  11. #101

    Default Re: Is charging the 18650 a major event in your life?

    For me, charging 18650 batteries is about as exciting as charging a phone, but a lot less frequent.

    I get more worked up about charging AAA Eneloops, wondering if my cheap charger is doing right by them or not, occasionally feeling the battery to see if it's getting warm or not, wondering if they were discharged enough before they went on the charger, wondering if the charge terminated properly or not.
    Last edited by eh4; 04-16-2017 at 12:36 AM.
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