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There are many Lithium Ion and Lithium Polymer rechargeable battery related accidents. Are some of these accidents are battery design related? Are some of them misuse of rechargeable batteries.

  • What is the chemical composition of Lithium Ion and Lithium Polymer battery?
  • Why do rechargeable Lithium Ion & Lithium Polymer batteries explode or catch fire?
  • Why cannot the rechargeable battery explosions and catching fire be prevented?

References:

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Disclaimer - I'm not an expert in batteries, but I do some related work with those particular types.

Lithium-ion batteries are a little different from "regular" lead acid batteries in that the Li-ion batteries can provide more power for short periods of time than what their nameplate rating would otherwise indicate. The trade measurement term for this effect is called C-rate. The downside of exceeding a 1C (normal nameplate discharge) rate is that it creates more heat within the battery, wears out the battery faster, and can only safely be done for short periods of time.

So the ability to exceed the regular 1C rate, and the fact that batteries tend to be exposed to a lot of environmental wear from being banged about leads to problems within the internal connections of the battery. This blogpost from The Economist does a good job explaining the thermal cascade that causes the thermal breakdown.

When the battery is charged, lithium ions are driven from the electrolyte into a carbon anode. When the battery is discharged they flow back, creating a balancing flow of electrons in a circuit that powers the device. The trouble comes about if there is a small fault or damage is caused to the extremely thin separators that keep the elements of the battery apart. This can lead to an internal short-circuit and a subsequent build-up of heat. This can trigger what is known as a “thermal runaway” in which the battery overheats and can burst into flame.

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Here is a good resource that has very detailed information about Li-Ion hazards: Lithium-Ion Batteries Hazard and Use Assessment

(Lithium-Ion Batteries Hazard and Use Assessment. Celina Mikolajczak, et al. July 2011. Fire Protection Research Foundation)

I will summarize it below:

  • What is the chemical composition of Lithium Ion and Lithium Polymer battery?

Cathode material varies, most commonly either LiCoO2 or LiFePO4 are used. Anode is usually graphite (carbon) based. The largest fire hazard is the electrolyte: this consists of lithium salts dissolved in an organic solvent.

The organic solvent is comparable to gasoline in flammability. There is some ongoing research to non-flammable electrolytes, but they are not yet in common use, and probably do not work as well as current electrolytes. A non-flammable electrolyte would greatly reduce the fire risk, but the high temperature could still ignite e.g. plastic parts nearby.

  • Why do rechargeable Lithium Ion & Lithium Polymer batteries explode or catch fire?

The batteries store a large amount of energy. If this energy is accidentally released by e.g. short-circuit or physical damage, it will heat up the battery. In addition, when the temperature exceeds about 150°C, the lithium in the battery will start to react chemically and release even more heat, which is called a thermal runaway.

When the electrolyte liquid heats, it will expand, and at some point the pressure exceeds the strength of the battery casing. The batteries are designed with an over-pressure vent, which should allow the electrolyte to leak out relatively slowly. If the vent malfunctions, the only way out is for the battery casing to explode.

No matter how the electrolyte got out, it is flammable and the battery casing is probably very hot at this point. This will often cause the electrolyte to ignite, releasing even more energy and possibly causing other battery cells nearby to overheat also.

  • Why cannot the rechargeable battery explosions and catching fire be prevented?

They are prevented, to a very large extent. Compared to the amount of li-ion batteries currently in use in the world, very few fires occur. Most of the fires that do occur are from low-quality products that do not have the safety systems such as protection circuit and often also overload the batteries.

But ultimately it is similar to "why cannot house fires be prevented". When you have flammable materials and energy in the same place, eventually they'll combine to cause a fire.

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  • $\begingroup$ Apart from 'low-quality' products, Lithium battery fire did occur on products from world top brand name companies, cellphone, laptop and airliner. Engineering is risk-and-benefit analysis and trade off. Use non-Lithium when size/weight allow it, like most vehicle in use as of today. $\endgroup$
    – EEd
    Jun 30 '16 at 8:10
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The chemical inside the battery begins to heat up, which causes the degradation of the separator. The battery can reach a temperature of more than 1000 degree F. At this point flammable electrolytes can ignite or even explode when exposed to oxygen.

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Lithium battery is more "dangerous". It is restricted (Wh limited) as passenger carry-on and banned as cargo, by many airlines.

If you design a new system, do not 'choose to use' Lithium if your product does not require small size/weight per watt hour.

Cellular phone designers and consumers, see size/weight/operating hours are key-to-sale and accept the 'risk'.

Vehicles, can afford bigger battery size/weight, and non-lithium battery are widely used.

The dream-liner switch to Lithium and result was less than smooth. Cellphone and external battery pack catching fire are regular news items, for many years already. Actual failure rate is not 'high', consider the number of battery in use and the risk is considered 'acceptable', by many.

Use Lithium, if you really need. Do not use it when you can afford a bit bigger size/weight in your design.

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