Battery Questions?

Question

What conditions causes a lithium-ion battery to explode?

I know that lithum-ion losing it's charge "extremely" slowly. It also produces charge rather quickly. What would be involved in producing a lithium-ion battery that could hold enough charge to run a vehicle? Without the battery exploding.

Answer 1

Two things are necessary for an explosion of a Lithium ion battery to occur:

1. Excessive heat

2. Poor construction of the container.

Excessive heat may be due to two things:

1. Charging too quickly (the most common cause)

2. Discharging too quickly

The chemical reaction during charging produces heat, as does the self heating due to charging current * internal resistance of the battery (P = I * R).  The battery is also capable of dissipating heat to the ambient, but it has a maximum rate of heat dissipation.  If the internal heat is being produced at a rate faster than the battery can dissipate it, then the temperature will rise; the chemicals inside will expand, and start producing gas if the temperature gets too high.  Pressure inside will build until the case pops.

A cheap case design will make it easier for the case to rupture.  Sometimes batteries have gas vents in them to release pressure, but in Lithium batteries these can be complex and expensive so they aren't always built-in.

Once Lithium hits the air, secondary explosive reactions will occur.

So... what can you do to make Lithium batteries safe?  Build charging circuits and current limiters that monitor the case temperature of the batteries.  If the temperature is rising and getting too close to the danger-zone temperature, then immediately stop charging or discharging the battery (at that high rate).  Perhaps a fan could be turned on by the monitor microprocessor to cool the batteries down.

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Answer 2

In answer to your initial question:

Too much heat.

Lithium is a very flammable and reactive element.  Given enough heat it is liable to combust.  If that combustion takes place in a confined space, say inside the metal container of a battery, then it leads to a pressure explosion.

I don't really understand the remainder of the question.

Battery technology capable of running a vehicle already exists.  (We've had milk-floats for about 40 years).

Ta.

Answer 3

Are you up to the Mccain challenge? I've never experienced an exploding battery before but I would say that keeping the system happy is key.

Don't overheat it otherwise the electrons in the battery will get too excited, which may / may not cause an explosion. Other reasons why an explosion may occur may be a flash charge or discharge causing an unbalanced system. Charging a Li-Ion battery under normal conditions wont cause it to explode so protect it.

A system that will power a car will definitely need controls to monitor the charge on the system and the overall system characteristics to include environmental conditions.

There is excellent battery technology out there that can and do power vehicles including Li-Ion but they are VERY EXPENSIVE.

Below is a link to the Tesla Roadsters battery system for reference. Now that's my dream car :D

Answer 4

The Tesla car runs on  lithium-ion batteries.

http://www.teslamotors.com/

http://en.wikipedia.org/wiki/Tesla_Roads...

Answer 5

The batteries don't "explode" as such, rather they catch fire. The resulting flare may cause secondary damage from such things as case demolition.

The reason they do this is not completely known but it is suspected it is caused by contaminants causing short circuits in the cells. The actual electrolyte is flammable as well as the electrodes. Lithium when burning, will not only combine with Oxygen but also Nitrogen. Lithium fires are difficult to extinguish, requiring special chemicals designed to smother them.

Apart from gross abuse (overcharging, etc) the main combustion problem stems from manufacturing problems.

They also have a low self-discharge rate of approximately 5% per month, compared with over 30% per month in common nickel metal hydride batteries (Low self-discharge NiMH batteries have much lower values, around 1.25% per month; they can still hold 85% of their charge, after one year) and 10% per month in nickel cadmium batteries.

In order to safely use them, just use the correct charging regime. Monitor the temperature and voltage and limit both with shutoff circuitry. There are other safeguards but these will be built into the battery (venting controls, etc.). Don't allow the discharge voltage to go below the minimum recommended by the maker of the battery (usually 3.0v/cell).