Lithium-ion Battery Safety: Industry Experts Give Their Points of View

Subscriber Larry Ober, an electronics engineer who has been responsible for designing various products that use lithium batteries, wrote to Undercurrent after reading our warning about lithium-ion battery fires in our October mid-month email.

He says that it is important to distinguish the difference between [pure] lithium batteries and lithium-ion batteries. Lithium-ion batteries are likely the ones used to power your underwater light. In fact, most rechargeable batteries nowadays are lithium-ion. This includes lithium-polymer batteries. He says that "[pure] lithium batteries are only the non-rechargeable ones (for example, the CR123 photo batteries and AA-size lithium non-rechargeable types)."

He cites over-charging, over-loading (by causing to power a bigger wattage than the one for which they were designed), internal short circuits and external heat sources as the culprits of lithium-ion batteries over-heating with a risk of fire. "These batteries can contain a large amount of power, and this power could be a source of re-ignition energy given the proper conditions. Simply, if the battery overheats to the point that it vents its contents, some of the contents are flammable and may ignite due to sparks or just being hot enough."

Lithium-ion batteries can easily reignite after catching fire because they produce so much heat; copious amounts of water should be used to cool off the battery. The FAA recommends the use of carbonated water (soda pop) for dousing lithium-ion battery fires in aircraft cabins, but Ober says the advice ignores the risk of noxious gases so produced. He suggests the use of a dry chemical extinguisher to fight the fire, followed by water to cool. He adds, "Some industry recommendations are really a bit too simplistic to be useful."

Lithium battery fires should not be extinguished with water since lithium burns when in contact with it.

Daniel Emerson from the light manufacturer Light & Motion points out that the diving industry seems only too willing to employ loose lithium-ion cells when other industries do not. "The basic idea behind a battery is to separate two highly reactive materials -- the larger the electrical potential between them, the greater the power density. Lithium-ion batteries are effective because the anode and cathode materials are so volatile when brought together. There are a number of ways a battery membrane can be breached and cause a fire.

"The quality of the membrane, a slip of slightly porous polypropylene separating the reactive materials, is critical. Lax quality control can lead to cells with a slight tear or defect in the thin membrane that can grow as the lights are stressed during repeated charge cycles and cause a failure.

"Impurities in the battery materials, poorly manufactured separator, or damage from an external source that pierces the separator, causing the cell to short, rapidly converting all of the energy in the cell to heat resulting in an exothermic oxidizing reaction, increasing the temperature to hundreds of degrees in a fraction of a second -- causes the neighboring cells to heat up rapidly, making a chain thermal reaction."

So, buy the best lithium-ion batteries you can and take great care with them. A hard knock or rough handling can damage the inner membrane and short out the battery pack, causing a fire.