LifePO4 Lifespan (not cycle life)

[natterjak]

Hi all,

Does anyone have any data on the lifespan of LiFePO4 batteries, by which I mean the retained capacity over time? Many manufacturers publish cycle life data showing that 2000 cycles, etc. are achieveable, but I'm specifically interested in the effect of time on the capacity.

For example, if I only cycle my battery once a week, a 2000 cycle lifespan to 85% capacity will in theory last until 2046. I wouldn't mind betting though that capacity is lost year by year.

Does anyone have either manufactuer's data, theoretical predictions or real world experience?

TIA.

 

[fechter]

I don't think we really know, but I've seen 10 years mentioned as a lifespan (assuming cells are never allowed outside of the allowable voltage range).

 

[Battboy]

LiFeBATT guarantees its cells for 2000 deep discharge/charge cycles before a 10% degradation of overall capacity may occur. Past the 2,000 cycle threshold, the cells still don't need replacement, but the user will notice a 10% reduction in battery capacity after a full charge. For an electric vehicle, a driver might see a 10% reduction in distance traveled as the battery pack ages beyond 2,000 cycles.

The definition of 2,000 deep discharge cycles for LiFePO4 chemistry is 72% - 98% depletion before recharge. Shallow discharge/recharge cycles will prolong battery pack life, extending it beyond 5,000 cycles with little loss in overall capacity, up to 10,000 cycles before degradation of overall battery capacity starts exceeding 10%. Shallow cycles are defined as less than 72% discharge and can be maintained by always allowing more than 28% of the battery pack capacity to remain undischarged when reconnecting the battery pack charger.

At 2,000 deep discharge/charge cycles, averaging 1 cycle per day would allow for 5.5 years of use before a noticeable loss of capacity. 10,000 shallow discharge/charge cycles would last around 13+ years.

Don Harmon

 

[mcstar]

I think what Don is trying to say is that as of yet, there are no known age related processes that degrade the cell's capacity over time outside of the charge/discharge cycles. This is based on the knowledge we have at this time. The chemistry has proven stable in all testing that has been done to this point and does not noticeably degrade over time.

Other chemistries, like lead acid and Nickel based batteries, are all known to have limited shelf life's due to specific chemical processes that degrade them over time. For instance, sulfur builds up on the plates of lead acid that acts to increase its internal resistance. The Nickel based batteries grow crystals that eventually lead to their demise. As of yet, none has identified specific chemical processes that age LiFePO4 due to shelf life. This is due to the matrix of carbon atoms that serve to act as a fence of sorts around the Lithium. This "fence" restricts the movement of the cathode material and prevents it from degrading. Of course the oldest of these batteries is only what 2years old? Basically, we haven't had them long enough for us to know for sure, but the chemistry seems stable in all testing that's been done and in the lab experiments that were done to create it.

 

[swbluto]

Interesting. I did notice, though, that Aleee's performance lifepo4 has a calendar life of 1 year as per manufacturer specifications. While I guess whatever chemical process involved may not be inherent to LiFePO4(Maybe they have some other additive involved?), I'd be inclined to say there's probably an aging process to LiFePO4. Previous lithium chemistries in general have an aging process, though I guess LiFePO4 might be special due its unique chemical structure, and it seems that a123systems predict their cell's calendar life are upwards of 15 years or so and the "chief scientist"(The guy that developed the a123 cell chemistry) has been working with the chemistry for roughly 6-10 years, so he'd probably start to see some aging-related processes by now.

 

[Battboy]

Interesting. I did notice, though, that Aleee's performance lifepo4 has a calendar life of 1 year as per manufacturer specifications. While I guess whatever chemical process involved may not be inherent to LiFePO4(Maybe they have some other additive involved?), I'd be inclined to say there's probably an aging process to LiFePO4. Previous lithium chemistries in general have an aging process, though I guess LiFePO4 might be special due its unique chemical structure, and it seems that a123systems predict their cell's calendar life are upwards of 15 years or so and the "chief scientist"(The guy that developed the a123 cell chemistry) has been working with the chemistry for roughly 6-10 years, so he'd probably start to see some aging-related processes by now.

Previous Lithium chemitries have a significant "cap fade" problem which kind of makes the calendar - aging process moot. It's the extremely long cycle life that LiFePO4 is capable of offering that even makes calendar - aging remotely relevant. The whole field is moving fast so that by next year there will be newly developed cells with even better specs. which means most of the future cells will be "freshly minted". I doubt calendar - life really has a big effect on LiFePO4 - at least not for a few more years as these cells will go into service within very short periods of being plucked off the new production lines.

Don Harmon

 

[dogman dan]

One cycle a week does make the payback time a long way off natter. Do you particularly need lifepo4? Like for more range like I do? If not, maybe you would be much better served by sla's. One the other hand, one cycle a week sounds like toy, or entertainment budget to me, so who cares what fun costs? I have heard the time lifespan of lifepo4 claimed to be 5 years, but not with any credible data to back up the statement. So take 5 years of cycles, say 40 a year, and you have about 250 cycles. If your pack costs $750 that's about 3 bucks a ride, so ask yourself if it's worth that. Bear in mind too, that 3 bucks won't buy squat in another couple years. Consider anything after 5 years to be freebie

In my case , I could see 1000 cycles in three years, and my free riding will begin next summer if I don't upgrade. Actually I'll be happy enough if I use the battery a year and a half, since I am getting so much riding out of it. Once it degrades a small ammount, I won't make it all the way home. Uphill all the way.

 

[Reid Welch]

Q: will LiFePo4 suffer shelf-life span if kept at full charge whilst stored?

That is, is it relatively immune to the bad effect of, say, full charge kept constantly on a Lithium-cobalt cell?

Is it OK to keep the LiFePo4 cell at full voltage during storage? Or will that reduce its shelf life?

 

[dogman dan]

See the "store for the winter" thread. It won't matter to me Rubbing it in as hard as I can. We'll finally see consistent freezing mornings by christmas. We do get snow, though, at least every other year it will even stick to the ground! 100 miles further north and it's a different story, 1000 feet higher.

 

[Battboy]

Q: will LiFePo4 suffer shelf-life span if kept at full charge whilst stored? NO.

That is, is it relatively immune to the bad effect of, say, full charge kept constantly on a Lithium-cobalt cell? YES.

Is it OK to keep the LiFePo4 cell at full voltage during storage? Or will that reduce its shelf life?

YES / NO.

Don Harmon

 

[mcstar]

Q: will LiFePo4 suffer shelf-life span if kept at full charge whilst stored?

That is, is it relatively immune to the bad effect of, say, full charge kept constantly on a Lithium-cobalt cell?

Is it OK to keep the LiFePo4 cell at full voltage during storage? Or will that reduce its shelf life?

This is a good question as well. I usually leave my battery about 1/2 discharged over the weekends and charge it Monday night to be ready for the morning. The idea being that higher voltage potentials == higher stress on the cathode. During the week I put on about 10 cycles, so I just plug in the charger as soon as I'm done riding. With this mixed charging schedule I figure I'm putting the minimum amount of stress on the pack. I'm sure that the different constructions of cells will each last differently based on their quality. I've got about 300 cycles on my BMI pack now and still get > 10Ah from the 10Ah rated pack. The pack has about 30%-50% more capacity than I actually use on each cycle, so I'm sure it will last many years. At this rate it will be about 10years before I have 5000cycles on it, and even then I still should have > 80% capacity. Of course I'll let everyone on this forum know if thing don't work out as planned

 

[D-Man]

I think these batteries will always be changing just like computers. Always a new model coming out. The older models filter down to people with less money which is good. People like change. They think they're buying the latest and greatest thing. Battery companies make more money also.

 

[dogman dan]

True enough! I expect I'll want more speed, more range, etc, and be getting new fast motor, and new high discharge battery to go with it, before I reach 1000 cycles in two more years. Cool that the old pack will be able to sit around waiting for me to need it as a spare. Or I could pass it on to a needy friend.

 

[magudaman]

I have had my a123 packs for around 2 and half years now and keep them fully charged. Lets say I cycle them on average around 4 times a week (some times more sometimes less) which would equals over 500 cycles. My recent battery tests gave an average of 2.04 ah and the initial back tests in 2006 gave 2.12 ah average, so I lost around 5% so far. If I can keep this up I should be able to reach 2000 cycles in another 6 years and will be just reaching the 80% mark by that time. So far they are my longest lasting EV component...heck my longest last EV thing all together.

I've been gone a while, but is there now any easy way of getting Lifebatt batteries? When I was around last I gave up on them when that whole group buy thing went sour.

 

[ZapPat]

LiFeBATT guarantees its cells for 2000 deep discharge/charge cycles before a 10% degradation of overall capacity may occur. Past the 2,000 cycle threshold, the cells still don't need replacement, but the user will notice a 10% reduction in battery capacity after a full charge. For an electric vehicle, a driver might see a 10% reduction in distance traveled as the battery pack ages beyond 2,000 cycles.

The definition of 2,000 deep discharge cycles for LiFePO4 chemistry is 72% - 98% depletion before recharge. Shallow discharge/recharge cycles will prolong battery pack life, extending it beyond 5,000 cycles with little loss in overall capacity, up to 10,000 cycles before degradation of overall battery capacity starts exceeding 10%. Shallow cycles are defined as less than 72% discharge and can be maintained by always allowing more than 28% of the battery pack capacity to remain undischarged when reconnecting the battery pack charger.

At 2,000 deep discharge/charge cycles, averaging 1 cycle per day would allow for 5.5 years of use before a noticeable loss of capacity. 10,000 shallow discharge/charge cycles would last around 13+ years.

Don Harmon

I guess Don isn't around to banter with anymore, but I must point out that his statements above are more opmitistic that what is written in the sandia labs report (for "shallow" cycles), and also more optimistic than his own provided deep discharge test results too. I could pull out the actual numbers to prove this. Unless my memory is totaly shot, which might also be possible! I don't aim to blast him specificaly, but I don't like any kind of salesmen that subtlely make their numbers look better than they really are.

 

[safe]

I usually leave my battery about 1/2 discharged over the weekends and charge it Monday night to be ready for the morning. The idea being that higher voltage potentials == higher stress on the cathode.

This is the correct answer if the work at GM's Chevy Volt is valid.

Assuming the company doesn't go bankrupt before they even get the chance to launch the product, what they are going with is this idea of keeping the battery in between the 20%-80% charge level all the time. Apparently either full charge or empty charge causes wear on LiFePO4.

We don't know yet what is the long term shelf life of LiFePO4 because the chemistry is too new, but it's likely that keeping a middle level charge when in storage is the key to getting the most of what is possible. It's probably as long as NiCads which can last for 10 years.

SLA likes a full charge all the time.
NiCad seems to not care much, but don't overcharge.
LiFePO4 needs a middle charge for storage and avoid either extremes.

 

[dogman dan]

By using the snot out of em, 2 cycles a day when I ride to work, my pack spends very little time sitting around at full charge. All I will need is shelf life of about 2 years. Good advice though, for those who ride only on weekends, or are storing for the winter now.

 

[ZapPat]

This is the correct answer if the work at GM's Chevy Volt is valid.
Assuming the company doesn't go bankrupt before they even get the chance to launch the product, what they are going with is this idea of keeping the battery in between the 20%-80% charge level all the time. Apparently either full charge or empty charge causes wear on LiFePO4.
We don't know yet what is the long term shelf life of LiFePO4 because the chemistry is too new, but it's likely that keeping a middle level charge when in storage is the key to getting the most of what is possible. It's probably as long as NiCads which can last for 10 years.
SLA likes a full charge all the time.
NiCad seems to not care much, but don't overcharge.
LiFePO4 needs a middle charge for storage and avoid either extremes.

This contradicts Don's answer, but I would tend to trust this conclusion also. However, I have not yet seen any real long-term tests done to prove either theory (from Don/lifebatt nor from GM). It would be a quite easy test to do, but to really see any differences it would still take one or two years to do the tests. Using hotter storage conditions might help us here though, making any degradation happen faster.

 

[safe]

It's possible that the GM Volt team runs their product development in the same dysfunctional way as the rest of the overall company and then maybe we could suspect that they were stupid.

But assuming the Chevy Volt people AREN'T making a mistake then the fact they chose to use the 20%-80% range of capacity to extend the life of their LiFePO4 should tell us something.

My guess is that NiCads represent the most stable battery we've known so far... they can last 10 years or more... if the LiFePO4s last as long as NiCads we would think:

"Yeah, okay, that sounds about right."

...at least that's my thinking.

I just wouldn't believe that LiFePO4 has infinite life.

10 years is still a long time.

-----------------------------------

Probably the main thing to remember is that if you want to store your LiFePo4 battery over the winter that you should not worry about keeping it fully charged. Just let the natural self discharge lower the charge level and by the time spring comes you can recharge and go for a ride. Just don't constantly charge LiFePO4 if you don't need to. (so don't leave it on a trickle charger or anything like that for a winter of storage)

 

[Battboy]

Don Harmon [/quote]
I guess Don isn't around to banter with anymore, but I must point out that his statements above are more opmitistic that what is written in the sandia labs report (for "shallow" cycles), and also more optimistic than his own provided deep discharge test results too. I could pull out the actual numbers to prove this. Unless my memory is totaly shot, which might also be possible! I don't aim to blast him specificaly, but I don't like any kind of salesmen that subtlely make their numbers look better than they really are.[/quote]

We have tested our cell’s to 3,600 cycles at 100% depth of discharge. These
cells are still operating within specification, at 84% of original capacity. Sandia
National Laboratories, New Mexico, USA, have independently tested our cells
using PSOC hybrid scenario (10% DOD) to 8,394 cycles, estimating a usable
cell life in excess of 20,000 cycles using this PSOC model.

Don Harmon

 

[safe]

LifePO4 Lifespan (not cycle life)

...this was the topic of this thread.

What we are still unsure about is the lifespan... the internal deterioration that takes place naturally. Reduced wear from cycle life that takes place within a short period of time does not mean that if the battery just sat there that it wouldn't eventually decay. Cycle life is not lifespan or "shelf life".

For example:

NiCads are very durable and have been around for long enough to know that they can sit in storage for years with little noticable decay. If you use them all the time then the cycles will start to subtract from the capacity and you might be able to wear them out in a couple of years. But if you did absolutely nothing... just let them sit around... they still decay anyway, just very slowly.

So by this thinking one would guess that since NiCads have such a known stable chemistry and last a long time that LiFePO4 should do equally well or even slightly better. Heck, maybe the shelf life will turn out to be 20 years for all we know. Only time will give us an answer. (and things like heat testing might not give linear results, so it's hard to guess if such a test is reliable)

 

[mpalka]

My LiFePo4 15Ah/36V last for 6 years.

I belong to users who care for their accus. I started with 15Ah and ended with capacity 6Ah. (90km range at beginning - very light use on flat/small hills , 35km range at the end- heavy use, few steep hills). Ended with faster voltage drop during full discharge currents. Battery was used aproximately 100 full cycles. 50% was real full cycle - aprox 10km before BMS would switch it off and rest was Equiped by quality battery management circuit, everytime fast charged (5A), everytime stored at full charge, used at ebike in temperatures 20-35Celsius, packed in alubox. Battery is still usable affter 6 years but I would recommend it for flat /small hills surface and short rides.

Battery was marketed as 1000 cycles capable. Now seller told me that its life is also limited by 4-5yrs.

 

[dogman dan]

Old thread. Since then I wore out two ping lifepo4. One lasted 3 years, the other 3.5 years. I have heard of longer, like 5 years. I don't know anybody using typical lifepo4 much longer than that.

However, the real A123 packs, the ones made in 2009 or 10? I think some are still using them. Which shows you a lot, about how much more a really high quality cell matters than chemistry.

 

[999zip999]

Dogman that must be me. Victpower A123 20 ah midwest group buy. Mine about 4 yrs old to but probably another 4 years on that. A123 20ah 24s 948 cycles of use as a daily rider.Ageless. yes heavy yes big. Bulk charge keeping balance charging 12s at a time 16amp each 12s. Use at 85 amps high regen burst I think it wakes them up. I have big alumiun blocks between rabs.

 

[mrbill]

On my old Valence batteries I saw about 5-13% reduction in capacity over 8 years, cycles <200. The batteries with the 13% loss had been cycled about 2-3x as many as the batteries with the 5% loss, but each had fewer than 200 cycles. I stored them at full-charge most of the time.

An old battery made up of PSI cells retained about 90% of their rated capacity over 7 years with a similar number of cycles.