What is the difference between Lipo and lifepo4?

This was asked in the new FAQ section.

Not sure I can fully answer it but for starters I will attempt a short FAQ type answer.

Lifepo4 and Lipo are both lithium chemistries, so technically they are both lithium polymer batteries. The difference is in the type of anodes and cathodes and the metals used inside. The naming conventions don't always make perfect sense since it's been constantly evolving. Both kinds can be killed by overdischarging, and both kinds have pretty light weight. Some types are in round cans, that add weight and volume to a large pack.

Lifepo4 is lithium iorn phosphate.

It charges to somewhere around 3.7v. My pingbattery for example comes off the charger at 3.75v per cell. Discharging below 2.0 v is said to kill a cell. It has a pretty flat discharge curve that makes a battery meter hard to use. For most of the discharge, voltage will remain about the same, followed by a steep drop when nearly discharged. It is a "safer" chemistry with less chance of going into a thermal runaway when overcharged. Discharge rates vary. 1c discharge rate 18650 cells are common, as are 2c pouch cells. Other manufacturers like heaway and psi are said to be 5c or more. A123 makes the highest discharge rate lifepo4 I've heard of, and often has the highest price. When assembled into a bike size battery pack, lifepo4 is often equipped with a battery management system. The BMS will shut off the battery if overdischarged, and works with the charger to balance the pack. Because it's regarded as "safe" you can buy a ready to use lifepo4 pack for an E- bike or scooter.

Lipo, commonly refers to lithium cobalt batteries.

For the purpose of this definition, I am refering to the batteries commonly used in radio control helicopters, rc planes, trucks, etc. It charges to 4.2v. Discharging below 3.0v may not kill the cell, but it is said that once discharged below that voltage the cell may become dangerous to charge. It is said that overcharging above 4.3v may also make the cell dangerous to charge. The discharge curve is not as flat as lifepo4. This means you can monitor the voltage of lipo and have a better idea of the % of discharge just by knowing the voltage at that moment. It is said to be a more dangerous chemistry, because if you have abused the cell with overcharge or overdischarge that cell could overheat while charging, puff up, vent toxic chemicals, or even catch fire. Discharge rates vary. 15 c is considered a low c rate for lipo. 50c and above is avalialbe now. This makes a very small and light, but very powerful pack possible with this chemistry. Lipo is considered to be the lightest weight per watthour chemistry. There have been recent developments in this chemistry that have improved c rates, and seems to have greatly improved it's safety to use. Many still report puffing cells and venting, but not fires. Lipo STILL SHOULD BE CHARGED IN A SAFE PLACE. Don't charge lipo, or any battery for that matter, sitting on carpet, cardboard, wood, next to the drapes, etc. It is still recomended that the charging process be monitored, and done in a fire resistant area. Because of the risk of disaster when charging, lipo is not very often avalialbe in a ready to use pack for an Ebike or scooter. To use lipo, you have to assemble a battery yourself, and you are on your own to select a suitable charging method. Because of the "less safe" charging, the bms for charging is typically built into the charger. For discharge the less flat discharge curve means many run with out a low voltage cut off, and simply stop when they see voltage dropping to the level they have decided to stop at. Low voltage warning devices are also common.

Well, so much for short. Start ripping it guys, I have to have some glaring mistakes in there.

small correction..

lifepo4 can be safely discharged all the way to 2.0v

Lipo should be kept above 3.0v

LiFePO4 and Lipo are both "lithium ion" Batteries - lithium ions are used as charge carriers within the batteries (Charge: from Cathode, through electrolyte, to Anode. Discharge: the reverse; anod -> electrolyte -> cathode).

generally a more or less liquid electrolyte is used (compare to the acid in an old fashion car starter battery) between a lithium-metal-cathode and a graphite anode.

charging is done by applying an electric potential over the battery causing the lithium-ions to flow over and place themselves between the 2-dimensional sheets in the graphite anode.

"Lipo-batteries" is short for "Lithium polymer batteries" due to the fact that they use POLYMERS as electrolytes.
hence:
A "lithium (Li) iron (Fe) phosphate (PO4)"-battery can therefore also be a "lipo" battery when a polymer electrolyte is used.

Depending on the metal added to the lithium in the cathode, different battery properties can be achieved - Iron and phosphate for example makes the battery much safer at the cost of weight and electric potential (lower cell voltage).
Different electrolytes also change the properties (eg. polymers allow for pouch cells and often better (power) performance).
lastly, also the anode can influence the performance; eg titanate is much more robust than graphite (carbon), but is also more expensive and heavy...

I am charging LiPo with the Lithium-Ion setting (LiIo) which ends at 4.1V per cell, and I am using 3.65V per cell as my LVC in the hopes of extending battery life, rather than trying to squeeze the maximum miles from each charge. (some charge up to 4.2V, and discharge down to 3.0V per cell).

I normally bulk-charge my pack (without balancing the individual cell charges), and I plan to individually balance-charge each brick once every ten charges or so.

good stuff guys, thanks !.. i will quote and copy the bits into the FAQ shortly.. !!..

Ypedal said:

small correction..

lifepo4 can be safely discharged all the way to 2.0v

Lipo should be kept above 3.0v

Click to expand...

Agreed, but highly misleading imo. It's a lot more complicated than that. At 3.0V lifepo4 will be close to 100% discharge under low amp use. Even at very high amp use, 2.5V is pretty much empty. Going below 3.0V for normal ebike use is pretty much worthless, even though you can.

For lipo, I'd put that at about 3.4V-3.5V. Yes, you can go lower, just like with lifepo4, but you won't get much more out of it under ebike use before possibly damaging a cell.

Other than the technical differences, the main difference I see is that lipo is smaller, lighter, and more powerful than lifepo4, while lifepo4 is easier to manage safely and has a longer life cycle.

Over the last few years, lithium battery technology has undergone lots of changes, and is still maturing. I think you'll see newer technologies in the near future that will obsolete both lipo and lifepo4, so pick your poison. I chose lipo because it's cheaper with more than adequate power output in a smaller, lighter pack that I can carry between two fingers at 3.5lbs and less than 6x4x2 inches.

We are mixing two things here a little. It is hard to be clear because common terminology is not precise and often mis-used.

Two Chemistries:

• Lithium Cobalt (oxide) LiCoO2
• Lithium Iron Phosphate LiFePO4

And two Electrolytes

• Liquid (cylindrical) (electrolyte in organic solvent)
• Polymer (pouch) (electrolyte in solid polymer)

Both chemistries and both electrolytes can be combined to give Four batteries, all of which we commonly see:

• Lithium Cobalt Liquid Electrolyte - usually called Lithium Ion or LiCo - 18650 laptop cylindrical cells are an example
  
• Lithium Cobalt Polymer Electrolyte - usually called LiPo - in a pouch - RC batteries are the most common example, also many PDA and smartphones
  
• Lithium Iron Liquid Electrolyte - called Lithium Iron or LiFePO4 - A123M1 cells are an example, typically cylindrical, also Headway, et al
  
• Lithium Iron Polymer Electrolyte - called Lithium Iron pouch batteries - Ping is an example, also A123 makes a pouch battery

Changes made per Ypedal suggestion. Shoulda looked up stuff more before. I was confusing some kill a cell numbers and usable capacity numbers. Interesting post Alan B. I'd still like to see my post shortened and simplified. But it's not a very short or simple subject.

The big difference for us is the per cell voltage with lipo typically at 3.7V nominal (though apparently the new nanotech lipos are closer to 4V) and Lifepo4 at 3.2 or 3.3V nominal. This accounts for the big difference in energy density, since the higher voltage means more energy for the same amp-hours.

Another significant difference is size. The commonly used RC lipo packs are incredibly small rectangles, because there's no wasted air space. Another 3.7V cell some of us use is the Sony US18650V found in Makita 3ah powertool packs. These cells, also called konions, are cylindrical 18650's (18mm dia by 65mm length), and while they have a slightly higher energy density by weight than than the RC lipos, packs of these cells are much larger since a rectangle packed with cylinders is 22% air between the cells.

The discharge curves are also quite different, and the lipo cells have a greater slope in the curve. Lifepo4 cells drop more quickly in voltage at very beginning, and then it stays quite flat with most of the capacity discharged over the small range of 3.2V-3.0V per cell. At the end of discharge they again drop quickly. What this means is that with a lipo pack, once you become familiar with your pack, you can use pack voltage as a fuel gauge. With lifepo4 you really can't rely on voltage to know where you stand, and need a more sophisticated device like at Cycle Analyst to know how much energy you've used to know how much you have left. That's arguably better, but what happens if you don't know your exact status of charge when you start the ride?

The other big difference is cycle life. Lifepo4s are proving to live up to their expected life of 2000 cycles or more. The newer lipo are apparently able to exceed 1000 cycles, but only if they are used conservatively. Lifepo4's may go out to the many 1000's of cycles if run conservatively. In fact, there was one A123 test that showed >90% capacity at 100,000 cycles with a 50% DOD and moderate discharge rates. It's pretty safe to assume as long as you avoid mishaps to prematurely kill cells, that lifepo4 will last at least twice as long. If you're looking at batteries from an economic standpoint, you can't ignore this.

I adopted the viewpoint that batteries are pretty rapidly advancing in quality and power, while prices are decreasing significantly, so I don't want to get tied down with an expensive pack now when I believe within a year and a half to 3 years, much better batteries will be available for cheaper that are smaller, lighter, more powerful and longer lasting. This approach served me well over the past 2.5 years, when I bought used Makita packs to build the cheapest and easiest to use packs that are still going pretty strong. At the time lipo and lifepo4 cells were going for well over $1/wh, but my Konions only cost me about $.50/wh. Recently I paid $.26/wh for some quality lipo packs that are far better than the best lipo available 2 years ago.

My experience is slightly different than Johns, but not a lot:

Konions and Makita packs are yet another chemistry, lithium manganese. I have not seen this chemistry in pouch form, only cylindrical cells. The energy density is lower than Lithium Cobalt Oxide, but higher than Lithium Iron Phosphate. The voltage is more similar to Lithium Cobalt and the current delivery is higher, more like Lithium Iron. So they are great for portable tools and electric bikes. The manufacturers of these cells have controlled them more tightly so availability is poor and this has reduced their use in e-bikes. I use some in high powered flashlights and while they are not as good as A123 in current delivery they deliver higher voltage which is helpful in keeping the number of cells (length of flashlight) down.

People talk about lifepo4 being a LOT heavier and physically larger than lipo. This is true of round cells, with the weight of the can, and the air space. Actually, the weights are not so different when considering a pouch cell lifepo4 and a lipo of the same AH and voltage. But the HUGE difference is that you may be able to run a lot smaller ah when using lipo, while with the typical 2c discharge rate of lifepo4 pouch cells, you should be carrying 15 ah or more of it. Then you are looking at 15 pounds of lifepo4 in many cases. Depending on your needs, 15 pounds may be really heavy, or really light.

But, lipo is still quite a bit smaller and a little bit lighter per ah. So it's really a good choice for a superlight bike, or for simply fitting more ah of battery onto a particular bike frame.

How about adding general charge/discharge curves of the respective Li chemistries at .5c / 1c / 2c / 5c?

I know that would be helpful to a lot of people.

Sanyo, 2.5Ah UR18650F ('laptop cell')

Gravimetric and volumetric wise lipo has a ~25% lead on lifepo4 - BUT who here would recommend discharging to 100% DOD and charging to 100% SOC with lipo on a daily use bike? Most people chop the top 10% and bottom 20% off their charge/discharge schedules. Thus, for a day to day bike designed for long term use you could say lipo has 5% less energy density than lifepo4.

However, while lifepo4 tolerates deep discharges much, much better, no one recommends riding to full discharge with a lifepo4 pack anyways. I've never gone below 90% DOD charge with my pack, and I suspect (or hope) that's common. Even further you could go to say that the common advice here is to get TWICE the capacity you think you'll need. In the case where you have a properly sized battery pack so that you very rarely go beneath 75% DOD, lipos energy density retains it's 25% lead.

Of course my desires in a bike is practical/transportation. For those who ride on weekends, cycle life probably isn't an issue, so just disregard all that above.

It's not black and white for sure. Compare a ping battery to a pack made out of zippy/turnigy 15/20C batteries.. you will see that the lipo is about 20% smaller and lighter per watt hour.

I am a weekend / seasonal ebike rider so i chose lipo, hands down. I will exceed it's calendar life before i exceed it's cycle life.

I take 5% off the top and ~7.5% off the bottom of my lipo cycles. If you wanted lifepo4 to last a seriously long time, you'd do the same.

But lifepo4 is generally rated at 3 times the cycles that RC lipo is.
And lifepo4 won't burst into flames if abused.

Pick your poison, no such thing as a perfect battery as of writing

neptronix said:

It's not black and white for sure. Compare a ping battery to a pack made out of zippy/turnigy 15/20C batteries.. you will see that the lipo is about 20% smaller and lighter per watt hour.

I am a weekend / seasonal ebike rider so i chose lipo, hands down. I will exceed it's calendar life before i exceed it's cycle life.

I take 5% off the top and ~7.5% off the bottom of my lipo cycles. If you wanted lifepo4 to last a seriously long time, you'd do the same.

But lifepo4 is generally rated at 3 times the cycles that RC lipo is.
And lifepo4 won't burst into flames if abused.

Pick your poison, no such thing as a perfect battery as of writing

Click to expand...

HA! I remember these reports last winter when I first launched into the world of eBikes. Fire reports made me avoid Lipo then, but my off-road bike has me taking another peek. LiFePO4 is what opened the eBike door for me. Already trolling for used packs to experiment on.

This is great intel, guys. I'm studying all the battery threads and just had to stop here and say "Thanks!" for all you do.
~don

Excellent charge and discharge videos of GBS and A123 cells on youtube.
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http://www.youtube.com/watch?v=VxZF8J7wrww
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http://www.youtube.com/watch?v=RYOZUteqNEg
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Here are the discharge and charge curves for 8s GBS cells. The A123 Amp20 cells were almost exactly the same voltages. Many people have signatures here that state "Lithium cells- never charge above x, never discharge below y" but these are incorrect for the newer LiFePo4 cells. You will ruin your Amp20 cells in short order if you charge them above 4v. There is really no added power to be had above 3.6v . It's time to change those signatures.

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HVC was 3.55v . The curve is already straight up at 3.425. No sense going beyond that unless you need the low current areas of the curve for balancing.
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