21 June 2015

LiPo = Li-ionIf you’ve got any kind of gizmo – laptop, tablet, e-book reader, cell phone, MP3 player, cordless screwdriver or drill, etc. – then you’re using lithium-ion batteries all the time.

Lithium-ion batteries, often abbreviated as Li-ion, are extremely common these days.

But what about so-called Lithium Polymer batteries, also called LiPo or Li-poly batteries? Are they really better?

If you believe the marketing folks, yes they are. But, as it turns out, you’ve been fooled just like me!

First, a bit about lithium-ion batteries.

In short, they’re awesome.

Usually, they come in a rigid plastic case. For example, if you have a standard laptop, the battery pack is a big rectangular plastic thing. Inside, there are multiple cells – think AA battery, although the size of your typical lithium-ion cell is a bit bigger.

3.7V, 2600mAh lithium-ion cell
3.7V, 2600mAh lithium-ion cell

Lithium-ion cells have a nominal voltage of 3.7V. You might look at your laptop battery and see that it provides 11.1V. Then you might notice that 3.7 x 3 = 11.1. Thus, your laptop battery is a 3-cell battery. Other laptop batteries have different numbers of cells, but they all work the same.

Typical laptop battery
Typical laptop battery, containing multiple lithium-ion cells

In short, the rigid plastic case contains multiple lithium-ion cells, and usually some electronics for temperature monitoring, and charging.

Lithium-ion batteries must be charged carefully, or they’ll explode and do other fun things. That’s why all Li-ion batteries have either specific fancy chargers or integrated charge-regulating electronics.

First, the batteries are fed with a constant current at a gradually increasing voltage. When the voltage limit per cell is reached, then the charger switches to a constant voltage (11.1V in the example of our 3-cell laptop battery) but with a gradually decreasing current flow. Ta-da! Your battery is charged.

Helpful Tip: Lithium-ion batteries don’t like near-freezing temperatures. If you have a cordless screwdriver, for example, don’t charge the battery in your garage during the winter. Bring the charger and battery inside your house, and charge it where it’s warmer. Most chargers actually will not charge the battery at all if the temperature is too low (5°C / 41°F or lower). Other chargers will charge the battery, but they will use a “low temperature charging mode” that is less effective and not as good for the battery.

Makita quick charger
Makita DC18RC 18V Lithium-Ion Rapid Optimum Charger

Okay, but what about lithium-polymer batteries?

This is where it gets interesting. It turns out that what marketing departments are calling “Lithium-polymer batteries” are actually “Lithium-ion polymer” batteries.

What the heck does that mean?

In short, it means that so-called “lithium-polymer” batteries are almost exactly the same as lithium-ion batteries, but they are instead contained in a flexible polymer casing. It’s basically just a repackaged lithium-ion battery. There is another difference according to batteryuniversity.com:

As far as the user is concerned, lithium polymer is essentially the same as lithium-ion.

Li-polymer is unique in that a micro porous electrolyte replaces the traditional porous separator. Li-polymer offers slightly higher specific energy and can be made thinner than conventional Li-ion, but the manufacturing cost is higher by 10–30 percent.

There is such a thing as a real lithium-polymer battery, which uses a polymer as the electrolyte in the battery instead of other standard liquid electrolytes. This real lithium-polymer battery type is still more or less in the experimental phase. According to BatteryUniversity.com, the true lithium-polymer “plastic battery” never actually went mainstream because of performance issues at room temperature.

“LiPo” battery. Note flexible casing, and the 3.7V rating

Now, you may get longer battery life with your fancy laptop with its “fancy” not-lithium-polymer battery, but that’s primarily due to the flat, flexible format that allows the manufacturer to stuff more battery cells into the machine.

That’s pretty much all there is to it. If you remove the relatively voluminous plastic case with standard lithium-ion cells inside, and you instead stick flat, flexible lithium-ion polymer cells in the same amount of space, you get more power to play with in the same volume – but the basic battery technology itself is the same: lithium-ion. This is what they call “lithium-polymer” these days.

So, if you ever have two choices for purchasing a gizmo, and one has a lithium-ion battery and the other has a lithium-polymer, don’t worry: As far as you’re concerned, it’s all the same thing, but in a different package.

Lithium Polymer vs Lithium-Ion batteries: What’s the deal?
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17 thoughts on “Lithium Polymer vs Lithium-Ion batteries: What’s the deal?

  • 14 January 2016 at 09:35
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    Thanks, that was great information !

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  • 4 April 2016 at 06:08
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    LiPo batteries have been popular for powering remote control aircraft (from before the days that people assumed that they were all “drones”.) LiPo have had the ability to discharge quickly, delivering relatively high power for a short time. Airplanes and helicopters require high power/weight; this is not the same as high energy/weight which is where LiIon really shines. There may be a reduced total capacity of LiPo compared to LiIon.

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    • 4 April 2016 at 11:46
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      Yeah, I do believe sometimes they modify the battery design slightly to allow higher discharge rates without damage. Still, the core technology is not really that different… Kind of like alkaline vs. “ultra” alkalines.

      Reply
  • 11 May 2016 at 06:34
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    I ran over my Dewalt drill battery with the mower and discovered it had a supercapacitor on top. Youtube shows a similar battery/capacitor config and called it a hybrid battery assembly. What if you made a capacitor bank in parallel with the lipo batteries?

    Reply
  • 11 May 2016 at 06:41
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    Start-Run capacitors are common in a/c window units.

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  • 24 May 2016 at 15:11
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    @Scottie
    Higher current capability is natural due to the physical difference between a tubular LiIon battery and a flat LiPo battery. In a cylindrical battery, the battery is a long pair of sheets that is rolled up into a cylindrical cell. Therefore, all of the current flows in that single sheet.
    The LiPo batteries are parallel sheets tied together by common electrodes at each end, so each layer that makes up the thickness has its own connection. Basically you have a high number of parallel cells so they can have a high discharge current – at least as far as the conductive sheets are concerned. That is ignoring the impact of the elctrolyte.

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  • 7 June 2016 at 02:54
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    Thsnk you for your explanation.it really help me to understand more.

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  • 19 August 2016 at 12:27
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    @BobZ
    You are correct this THE main feature of Lipo. Current draw from Lithium ion is only about one tenth.

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  • 19 August 2016 at 15:03
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    For something like an RC car, high current capacity in a short time is certainly a benefit (without blowing up the battery). You can get more power output over a shorter time. But for a laptop, for example? Not so much.

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  • 15 October 2016 at 16:48
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    I donno, my PS3’s Li-Po battery doesn’t JUST give it a longer battery life, it lasts without a charge for DAYS a few WEEKS actually. I mean all the controller’s actions are only accurately, quickly inputting commands via me clicking buttons, but still that is a LOT of potential. I am pretty loyal to Li-Po.

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  • 4 November 2016 at 07:30
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    It is great useful explanation,especially while charging battery behaviors of current and voltage explanation is very nice…

    Thank you very much..

    Reply
  • 23 November 2016 at 16:03
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    @Da Bruh

    The reason your PS3 controller battery lasts so long is not because of the battery chemistry, it’s because the current draw is tiny.

    If that same battery was used to power a more power-hungry device like a cellphone, you would probably find it lasted less than a day.

    I don’t remember the exact capacity, but I remember that when I replaced the battery in my PS3 controller it was pretty small.

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  • 4 February 2017 at 16:31
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    I was surprised to see no mention of the major benefit of real lithium polymer—that it’s not a major fire hazard. It blows my mind that so many products are out and about, particularly cars, using LiIon technology and their owners don’t know this at all. I was unaware of the seriousness of the problem until airlines stopped shipping them on passenger flights, etc.

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  • 5 February 2017 at 02:02
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    I understand that lithium ion batteries containing liquid electrolytes are prone to bursting into flame, where the polymer batteries containing no liquid will not. Is that the case? Also, the polymer batteries carry much more power density.

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  • 5 February 2017 at 09:11
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    Thamks for a great article. It would be great for the author to comment on the previous 2 comments about fire hazards of the Lithium Vs Li-Polymer subject.

    Reply
  • 5 February 2017 at 13:39
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    LiPo batteries are definitely still a fire hazard in certain cases/circumstances. Li-ion may be more likely to “explode violently” due to their rigid shell, but LiPo can still vent gas, swell up, produce lots of heat, and potentially ignite flammable material nearby. The gel electrolyte in LiPos doesn’t make them fireproof.

    Of course, explodification is normally due to some manufacturing defect, a failure in the charging circuit, etc. Improperly charge any Li battery, and you can get a nice kaboom. And the safety measures incorporated into the battery itself must ALSO fail…

    When you hear about exploding cell phones and the like, that’s an epic failure on multiple levels. Even the batteries themselves have safety features to prevent this very thing.

    IMO, considering the number of Li-ion and LiPo batteries in use today, they’re pretty darn safe overall.

    As for power density, LiPo has a slightly higher specific energy (energy per unit mass), but the amount of power you can pull out of it over a given period of time depends on the battery design.

    I have 2 LiPo batteries in front of me. One is small, 11.1V, 2.2Ah, 40C. The other is big, heavy, 22.2V, 10Ah, and 30C. I can pull tons of power from the larger battery, but its lower temp rating means I don’t want to go TOO nuts – or use it in the desert. 😉 Some batteries have very high temp ratings, and are designed for high discharge rates.

    But then, that’s not much different than, say, a lead-acid battery for a car. Bigger usually means more power, but the design of the battery internally can also make a difference in terms of “cold-cranking amps”, max continuous current load, overall battery life, and even self-discharge rate.

    Your best bet when sizing a LiPo or Li-ion battery is the same as with any other battery: If I’m powering my 100W LED light cannon, then the 22.V 10Ah battery is okay as long as it’s not too hot. At 22.2V x 10Ah, I could get 220W for 1 hour by really pushing it. But instead I only need 100W for 2.2 hours (much safer, as I’m only pulling 4.5A out of a potential 10A). In reality, the 100W LED is only about 94W, and the other circuits consume a few watts, so it only uses about 96W, which is 4.3A out of 10A.

    Perfectly safe – unless the battery is defective or my charger goes nuts on me!

    Reply

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