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Lithium Polymer Batteries

lithium polymer batteries1


How safe are lithium polymer batteries (Li-Po)? First, let's talk about lithium ion batteries and their bad habits.

Lithium is really nice for batteries, because of lithium's energy density; it packs a lot of wallop per pound. But it has its drawbacks, doesn't it? I think everyone's seen the videos of flaming laptops ; ) The plot of the "flaming laptop" videos is always about the same - someone wanting to demonstrate the dangerous nature of lithium batteries puts a cheap laptop on the grill (or fires a bullet into it, like in the video link above) and waits.

After it heats up, the battery starts to smoke...and the tension builds.

Pretty soon, a hissing spark shoots through the casing of the laptop, and then all hell breaks loose.

Does it actually explode? Well, not in any Hollywood-worthy sense of the word "explosion", but it certainly does burst into flame, which is alarming enough - and then the fire seems to spread from one end of the long, flat battery to the other.

lithium polymer batteries 3 Looks bad, but it's simply the nature of lithium. When lithium ion batteries are insulted - whether that insult comes from being barbecued, short-circuited, overcharged, pounded, dropped, or punctured with a nail - they tend to react strongly. First, the insulted cell begins to heat up, and as it does, the lithium chemical reaction begins to run faster and faster (as chemical reactions want to do when you add heat), which produces more heat and insults the surrounding cells, sending the chemical reaction running still faster...

...and pretty soon the whole battery pack is spewing flames.

This troubling characteristic of lithium-ion batteries is aptly named "thermal runaway".

So what do lithium polymer batteries have to do with lithium ion batteries?

lithium polymer batteries 4 A Li-Po battery uses similar chemistry to lithium-ion, but instead of the lithium salts being dissolved in a liquid solvent, they are trapped in a solid, dry plastic-like film - the polymer. This has two advantages - one, being trapped in a structure keeps the lithium ions from responding so strongly to puncture and other physical insults; and two, because that film makes up much of the support structure for the battery, it means the battery casing can be very flexible (they look more like foil pouches than batteries) and the battery design can be very flexible (thin as a credit card? No problem!).

How much do lithium polymer batteries cost?

money You already know lithium-ion batteries are expensive compared to the other battery chemistries like NiCd, NiMH, or lead-acid, right? Well, the good news is that li-pos are a little less expensive than their lithium-ion cousins, because manufacturing costs are lower. It will cost you more than 10K to put lithium polymer batteries in your electric car.

The bad news...they don't last as long (in terms of cycle life) as lithium-ion batteries, but you can expect 800 cycles out of your li-po batteries before they need to be replaced.

Where do you get a lithium polymer battery?