Memory Effect Discovered In Lithium-Ion Batteries

rwise2112 writes "Lithium-ion batteries have long been thought to be free of the memory effects of other rechargeable batteries. However, this appears to be not the case. Scientists at the Paul Scherrer Institute PSI, together with colleagues from the Toyota Research Laboratories in Japan have now discovered that a widely-used type of lithium-ion battery has a memory effect."

Comments

paywall derp

[SpaceManFlip]

shit's paywalled man, no good for Freedom Internets

Re:paywall derp

[Vanderhoth]

It's ok, No one here needs to read the article anyway. I kid of course ;)

No Shit

[Anonymous Coward]

This has actually been theorized for a long time by people that use Li-On batteries and have to charge them frequently. But they've been told 'nope impossible' by the people who make and research Li-On batteries the whole time. To me this is just like the pharmaceutical industry pushing the next opiate as 'non habit forming' and 'extremely safe' only to have it turn out even more addictive and deadly than the last iteration...time after time.

Re:No Shit

[kelemvor4]

Man ... living in your head must be terrible, in a world so full of daemons and enemies constantly conspiring against you. No wonder you are a bitter AC.

To my knowledge, both his assertions are accurate. One of them is supported by TFA.

Re:No Shit

[thaylin]

Well from the article it is possible to cause it to "forget" the memory so it is understandable why some people see it and others dont see it at the same time.

Re:No Shit

[BitZtream]

No one with any actual understanding of batteries said Li-Ion does not have memory.

What was said is that: From a practical perspective, Li-Ion memory is not an issue to worry about.

The article is basically someone who just did a study to confirm what probably every battery manufacture on the planet knew about Li-Ion at least 15 years ago. Longer I'm sure, I just have no experience before that.

What they did was took something they interpreted incorrectly, and then did a bunch of research to disprove some statement they misheard.

This is roughly like me telling you the surface of the earth is flat when you're building a small house, and then having a bunch of morons who overheard our conversion from 3 tables over do a study to determine that no, infact the Earth isn't flat. Of course its not flat, but from a practical perspective to the man building his home, its flat.

Re:No Shit

[tobia.conforto]

Yes shit. People who "use Li-On[sic] batteries and have to charge them frequently" are simply incurring in an unfortunate characteristic of Li-ion batteries, namely that they have a finite number of recharge cycles, or equivalently, that each recharge cycle diminishes the total charge the battery can hold.*

This has nothing to do with a memory effect.

For comparison, Ni-Cd batteries (as seen for example on power tools) have a strong memory effect, meaning that if you plug them in before they are exhausted, they "remember" the smaller capacity you've used them for, and it takes a number of complete discharge and recharge cycles to restore their full capacity. Of course, all that's needed to fully utilize Ni-Cd is a slightly more expensive charging circuit that fully discharges the battery before switching to recharging, which is why they are widely used in professional applications.

_____________
* Battery-savvy users always keep their mains plugged in on Li-ion devices such as laptops, so that the battery undergoes few recharge cycles and still performs as if it were new when they need it to, even after years of usage. But not after too many years, because Li-ion also have a limited timespan, or equivalently, the total charge they can hold diminishes every second since they leave the factory. Yes, it's a complex world.

Re:No Shit

[ChrisMaple]

Li-ion batteries suck. Their lifespans are considerably reduced if they are either fully charged or fully discharged; ideally they should be kept in the 40%-60% range. Since no charger does that, they are pretty much doomed. Expect your laptop battery to be effectively useless within 3 years of purchase, particularly if it's kept plugged in at all times.

Re:No Shit

[swalve]

If you know it, then the engineers who design battery charging systems in complex devices probably know it too.

Re:No Shit

[russotto]

Li-ion batteries suck. Their lifespans are considerably reduced if they are either fully charged or fully discharged; ideally they should be kept in the 40%-60% range. Since no charger does that, they are pretty much doomed.

They have their problems, but for charge efficiency and energy density, they're way ahead of the rest. They also don't self-discharge to any great extent. They're doing well on power density now too.

Your alternatives are a memory-laden NiMH battery which wastes 30% of its charge and has lousy power and energy density, not to mention a ridiculously high self-discharge rate (except LSD cells which have worse energy density). Or a NiCd which is about the same as NiMH except with better power density and more toxic waste. Let's not even get into lead-acid.

Yes, Li-Ion cells suck, But they're the best we've got.

Re:No Shit

[green1]

Li-ion batteries suck. But they suck ever so slightly less than NiMh batteries, which suck ever so slightly less than NiCd batteries... which makes Li-ion the best of the common technologies available right now.

Battery technology has been improving constantly. That said, it is nowhere near what people want it to be for our increasingly battery dependant lifestyles.

Small effect big consequences

[geoskd]

The question is: how big is the effect. Even a small effect will cause significant distortions in battery metering, but if the effect is large enough, it will cause the batteries not to last any where near as many cycles as originally believed. This could really suck for electric car owners. Any '07 Roadster owners out there care to share how well the batteries are holding up?

-=Geoskd

Re:Small effect big consequences

[jeffmeden]

The question is: how big is the effect. Even a small effect will cause significant distortions in battery metering, but if the effect is large enough, it will cause the batteries not to last any where near as many cycles as originally believed. This could really suck for electric car owners. Any '07 Roadster owners out there care to share how well the batteries are holding up?

-=Geoskd

According to what I could read of TFA without paying $32, the memory effect is actually seen just during discharge, as a function of distorting the voltage vs w/hr capacity. The overall w/hr capacity of the battery is not reduced, but the ability to exactly determine SOC is diminished at mid voltage levels.

I am not a chemist, so input from someone with more insight on the exact study would be appreciated.

Re:Small effect big consequences

[Anonymous Coward]

Pretty accurate. They see a small deflection on what was commonly believed to be a smooth curve near the previous peak charge.voltage. It does not affect the overall charge capacity of the battery over time (what people commonly think about when "memory effect" is used), just the ability of the charge/lifetime remaining software to make accurate estimates.

For all examples shown, a user would be told they have significantly more charge remaining until near that point, then immediately after it would appear their predicted battery life would drop dramatically, and then it would stabilize again. It makes sense that this would be of keen interest to Toyota and other electric vehicle manufacturers.

If their graphs are as accurate, noise-free and reproducible as the figures lead the reader to believe... then the good news is, this effect can probably be accurately modeled and compensated for now that we know it exists. In that respect, it is a significant step forward for Li charge remaining prediction software.

Re:Small effect big consequences

[tibit]

Voltage monitoring should be just one aspect of charge determination. Properly done charge monitoring integrates the electrical charge actually delivered to or taken out of the battery -- as in taking the time integral of the current. The cell voltage should only used together with other indicators (cell temperature!) to determine each cell's health and charge/discharge endpoints (fully charged and fully discharged). The cell voltage should not figure in normal battery "% remaining" indications -- those solely base on the charge taken out of the battery, and the estimation of the 100% charge capacity.

Re:Small effect big consequences

[Anonymous Coward]

The question is: how big is the effect. Even a small effect will cause significant distortions in battery metering,

True, and this is what is seen.

but if the effect is large enough, it will cause the batteries not to last any where near as many cycles as originally believed.

Rubbish. It doesn't diminish the battery's capacity, just changes the q-v characteristic DURING CHARGING. Even if it were a large effect, it's still not going to effect total capacity, or estimating remaining charge by measuring voltage during discharge.

Notes regarding this:
1. This effect is shown in LiFePO4, which is commonly marketed as a "safe" chemistry Li-ion. Laptop and mobile phone batteries almost universally use LiCoO, which is not, AFAIK, addressed in this research. The Tesla Roadster also uses either LiCoO or LiMnO (I've seen conflicting reports -- probably because these two have similar electrical characteristics -- and both have much better energy density than LiFePO4), so your plea to Roadster owners seems a little odd...
2. This effect is caused by starting with discharged battery, charging partially (greatest effect for charging ~50%), discharging completely, then recharging completely. During the final (complete) charge process, the voltage starts at baseline (i.e. full-discharge/full-charge cycle, at the same % charging), increases slightly faster than baseline, so that the voltage difference over baseline peaks at 50% (or whatever state you partially charged it to), then increases more slowly than baseline to arrive at the same voltage when fully charged -- so capacity measured while charging will be overestimated. On the subsequent discharge, however, the q-v characteristic conforms to the baseline -- so capacity remaining will be measured accurately when a device is in use.

Re:Small effect big consequences

[wildsurf]

Any '07 Roadster owners out there care to share how well the batteries are holding up?

My '08 Roadster (there are no '07 roadsters) has 33k miles on it, and after 4 1/2 years, its battery capacity has been reduced about 8%. I now get 225 miles on a full charge, down from 244 on day 1. That's even better than Tesla's initial projections, actually.

Re:Small effect big consequences

[swalve]

The only way to know the state of charge is by measuring voltage. Sometimes, batteries fail in that they never manage to get to their "charged up" voltage. Other times, they fail where they appear to top off instantly, and since the voltage is correct, the battery utilities think it is charged. The only way to actually test a battery is to put a known load on it and see how long it takes to hit a certain voltage.

What you experienced was not memory effect, but one or more of the cells failing. Some of them probably would never charge completely up, and the other cells got pushed into over voltage to compensate. If you have cells in series, this is pretty much going to happen sometimes.

Graphs in linked article show minor effect

[WillAffleckUW]

In the source article, I notice it's only about a 4 percent total effect on total charge.

So, while not "no memory effect" it's not as bad as the impacts on the other types of battery storage.

Even storage devices like compressed air (PHES) for wind and solar PV systems have only a 70 percent efficiency, so it's still way better than that.

And that type of battery is....

[DigitAl56K]

LiFePO4.

Cliffhangers in the summary now?

Re:And that type of battery is....

[afidel]

And I wouldn't call LiFePO4 "widely used", it's hardly used at all in the west due to extremely high royalty rates charged by the patent holders. I'd actually love to use LiFePO4 cells for my camping solar setup but the only ones I can find are dodgy Chinese imports with questionable charge controllers.

Re:And that type of battery is....

[Rich0]

I'd actually love to use LiFePO4 cells for my camping solar setup but the only ones I can find are dodgy Chinese imports with questionable charge controllers.

Hey, they could come in handy if you ever run out of tinder and kindling!

Re:And that type of battery is....

[afidel]

I've used the 9V and pot scrubber trick to start a fire when both my lighters failed on a camping trip (I wasn't going far enough away from society to pack the parafin encased bluetips which are my backups when my life depends on fire).

Wrong description

[folderol]

I do wish people would stop calling it a 'memory effect'. It's probably the least descriptive term your could apply.

I don't know about Lithium batteries but NiCad cells exhibit a second plateau which gradually gets more difficult for the charge system to punch through. The usual cure is a couple of heavy charge/discharge cycles.

Don't think I want to try that with Lithium though!

Laptop batteries, anyone?

[toygeek]

I've always wondered why they say that Lithium Ion and Lithium Polymer batteries don't have a memory effect, when even laptop batteries based on those technologies die after several years, and NOT because of charge cycles. I'm talking about the ones that stay plugged in most of their lives, charging. Maybe its the lack of charge cycles that kills them? But to say Lithium batteries have no memory effect has always been ludicrous to me.

Re:Laptop batteries, anyone?

[Maximum Prophet]

With any battery technology, it's almost never the "Memory Effect", but simple overcharging. If your laptop batteries are always hot just sitting there when the laptop is plugged into the mains, they won't last as long as ones that are properly charged and left alone until they are needed for discharge. With cheap cordless drills and other tools, simple putting a timer on the charger will greatly increase the number of cycles you can get out of the batteries.

Re:Laptop batteries, anyone?

[Anonymous Coward]

"
Batteries should be stored in a cool location. Keeping a battery in your notebook for long periods of time when running off of AC subject it to high temperatures and a shortened lifespan.
"
Nope, that's not the reason.

Typically, a new laptop owner does the following.
Buy new laptop
Install battery (if it's not already)
Place on desk.
Plug in to AC power.
Use for 5 years or less, and never move it from that spot.

In other words, the battery is NEVER used.
I've seen it personally with the last 3 business laptops I've had (hp, lenovo, dell) as well as the past four personal laptops i've sold to people. Those that actually use the battery down to zero at least once a month? Batteries last forever.
Batteries never actually used, but the laptop runs on AC power with the battery sitting there doing nothing? 100% of them will not hold a charge of any kind after 12 months of this "non-use".

Back in the 90's, there was Windows (3.11, wfw, NT, win95, win98) software available to exercise the battery while it was plugged into AC power. Such software allowed even ni-cad's to last for years without developing "memory" or losing run time. It allowed you to schedule a full discharge of the laptop battery weekly or monthly. Such software was also available for UPS's at the time. (Remember those UPS's that actually would run a computer for hours instead of minutes, yeah, those ones)

Since then, all such software has disappeared, and what do we have? Completely useless batteries in both laptops and UPS's, in under a year.

It's the same trend as printers and power tools. Consumables must cost more than the original unit and/or fail every year, minimum. Inkjet cartridges? Check! Power drill batteries? Check! Color laser printer toner? Check! Laptop batteries? Check!
When things in the PAST are worse than things in the PRESENT, and they perform the same task, it's not the advancement of technology that is to blame.
It's sociopath-run businesses wanting to turn everything into a service with an annual fee. Go-go-gadget free market consumerism!

My personal experience with laptop batteries has been that if they are fully/completely discharged to zero at least once a month, they last forever, regardless of all other usage patterns, elevation, humidity, temperature, make, model, or cell count.

Re:Laptop batteries, anyone?

[Ecuador]

I don't see how plugged-in laptop batteries dieing has anything to do with a memory effect. Lithium-Ion batteries when stored lose capacity depending on how much they are charged and how high the temperature is. At the relatively high temperatures of a laptop and kept at near 100% charge they can lose as much as 40% capacity per year. This is a known fact and has nothing to do with what is called memory-effect. The summary talks about a specific (and not widely used as I understand it) kind of Lithium battery which has a memory effect (in addition I assume to the effect I described that kills Li-Ion batteries).
If you want to make sure your Li-Ion batteries won't go bad, when you don't use charge (or discharge) them to 40% capacity and put them far from heat.

Re:Laptop batteries, anyone?

[Firethorn]

Okay, first up let's define memory effect: Memory effect is NOT a battery dying. Memory effect is the tendency for a battery to stop charging/discharging at a set level if you regularly fail to completely charge/discharge it. It develops a 'memory', and thus falsely acts as though it's fully charged or discharged before it actually is.

While this can ruin a battery, a number of techniques have been developed to rehabilitate such batteries to restore full function.

However, batteries don't just wear from charge/discharge cycles. They age over time as well. Alkaline and Lithium primary cells are especially resistant to this, but until very recently LiIon rechargeable cells were very, very vulnerable to this, losing 10% or more of total capacity just sitting on a shelf in a cool warehouse at 70% charge(the ideal situation for them).

Sitting in a hot laptop being kept at 100% is much worse than ideal, you could be losing 30% or more per year in that scenario.

Re:Laptop batteries, anyone?

[The Wannabe King]

High battery temperature and a high state of charge is a killer combination for Li-ion batteries. This is exactly what happens in a laptop that is plugged in and running. An electric car, on the other hand, usually avoids this. My Nissan Leaf charges to 80 % SOC, unless I explicitly ask it for a full charge, and even then it will not allow the batteries to reach the real 100% SOC. (Just like the batteries aren't really empty at 0 % SOC.) The advice is not to leave the batteries at full charge for more than a few days, and preferably only a few hours. The Leaf does not have active cooling (but the Model S has) which is not a problem in most climates. The batteries are still cooler than the laptop batteries that are stacked next to the CPU, at least in my laptop. The exception here is Arizona, as some Leaf owners have been unfortunate enough to discover. No problems after 21 000 km in Norway, though... there is still snow on the lawn!

Re:Laptop batteries, anyone?

[tibit]

The problem with most batteries is that the designs are cheap and the cells are not individually controlled with bypass switches. Then you have a pack with just one bad cell and the whole pack is "bad". All the rechargeable battery pack failures I've seen were of this kind: one weak cell with all the others having lots of life in them. The bad cell issue is self-exacerbating: as soon as a cell has higher internal resistance than the others, it will always get overcharged and over-discharged, accelerating the deterioration that leads to further raise of internal resistance.

Re:Laptop batteries, anyone?

[tibit]

With modern charge controllers, there is no overcharging of any sort -- a charged battery pack is not being charged anymore, that's it. Only after it self-discharges a bit -- enough so that it's detectable -- will it be topped up. The problem you have of course is that the battery pack is still treated as a whole and while charge controllers in mobile device battery packs will detect voltage on individual cells, still very few have the electronic bypass switches needed for cell charge equalization and cell bypass. Never mind that most power supplies are not designed to properly work with a battery that has a dead cell in it -- even if it's entirely technically feasible.

Re:GODDAMNIT DURACELL

[Vicarius]

http://en.wikipedia.org/wiki/Duracell_Bunny

The Duracell Bunny campaign was launched in 1973 and predates the Energizer Bunny, which was created in 1989.

Ping Battery

[Slashdot Parent]

I'd actually love to use LiFePO4 cells for my camping solar setup but the only ones I can find are dodgy Chinese imports with questionable charge controllers.

I can't really vouch for their quality because I am far from a battery expert, but Ping Battery is very highly respected among DIY electric bicycling enthusiasts.

Definitely place them in your category of "dodgy Chinese imports", but anyway they're considered to be very reliable among that particular category!

Re:No shit Sherlock

[Immerman]

Degradation with time and usage != memory effect. Memory effect is a specific kind of degradation due to partial charging or discharging. For example if you recharged a NiCd battery that was only down to 50% charge you would immediately and permanently reduce it's total capacity, hence the tendency of those "in the know" to drain the batteries completely before recharging them.

Discombobulating multiple issues

[WaffleMonster]

First of all of LiFePO4 are not commonly used in any of our portable gadgets.

Second memory effects we are seeing in our gear are illusions based on memory effects in the electronics that help figure out capacity. Deep cycling lion batteries works to clear these effects as what you are actually doing is resetting the "gas gauge" to synchronize with reality of the battery.

Memory free batteries don't exist

[BitZtream]

And I expect never will. All batteries have various flavors of memory. The only question is, does the memory effect cause enough of a problem to make it worth addressing the issue to extend battery life.

You worry about memory in a NiCad because the process that causes the memory is easily reversible (partially), and the battery itself is still functional.

If the memory effect of Li-Ion only effects ... say 1% of the total capacity before the rest of the chemical processes break down and cause the battery to 'wear out' than it has memory, but from a practical perspective the memory is irrelevant.

There are all sorts of batteries that would appear 'memory less' at first glance, but thats only cause they are so shitty in other ways that you don't get to the point of noticing the processes that cause memory to start happening.

Until a battery is 100% energy efficient, its going to have memory, so never.