Rapid charge lithium-iron batteries - practicable?

[coops]

How fast might it be practicable to recharge Lithium-iron (LiFe) batteries?

I read that they can be charged much faster than most batteries are right now (e.g. with 10-20A chargers, 2-3A being the 'norm' now, so charging at least 5-6 times faster & allowing top-up charges in minutes, not hours?), and that would make ebikes more useable by vastly reducing 'downtime' during recharges aswell as facilitate longer rides or touring by reducing the need (and hence extra weight and now substantial cost) of a second battery, and help to maximise the number of charge cycles before battery ageing might reduce performance (although thats less of an issue if LiFe lives up to claims of many years useful life).

Is there a downside or difficulty to this though, such as bulkier, heavier chargers, wasted energy & overheating issues due to less efficient, higher currents, and how detrimental might it be to the battery lifetime?

I realise its still early days for LiFe batteries and as such there are still many uncertainties, but if they do prove reliable for ebikes it'd be good to be informed of their capabilities, so I'd like to know what's possible, if possible .

Of course, if LiFe isn't the next big thing & anyone has more up-to-date information then I'd like to hear about that too!

Stuart.

 

[Jeremy]

It depends very much on the individual cell construction. For example, the pouch type LiFePO4 cells can be safely charged at about the 1C rate. Cylindrical cells and the larger prismatic ones seem to generally have a higher charge rate, perhaps around 2C to 5C.

It's certainly possible to charge a LiFePO4 pack in around an hour; it might well be OK to charge a pack built from A123, eMoli, Headway, LiFeBATT or Thundersky cells in as little as 10 to 15 minutes or so with some care.

I'm sure the only reason that fast chargers aren't more readily available is due to the cost of the chargers. 2A to 5A chargers are very cheap, but 20A to 50A chargers are very expensive.

Jeremy

 

[Tiberius]

I have also heard that the bulk of the charge can be done quickly, but the topping off of the last 10% or so is much slower. How true this is, how much it varies between different manufacturers, I don't know. It may even be a question of trade-off between safety and complexity of the charging control circuitry, but it certainly sounds plausible.

What that would mean is that if you kept between, say, 20% and 80% of the batteries limits, you could have very fast charge and discharge rates with the right cells. Getting the bulk of the charge in in 5 to 10 minutes might not be out of the question.

Nick

 

[coops]

Thanks for your replies guys.

Seems it can be done then, how fast depending somewhat on the cell type. I hope the price of faster chargers comes down if LiFePO4 takes off - I'm encouraged by the availability now of higher capacity & discharge cells e.g. 12-13Ah 6C, but to be able to top-up charge a 36V 13Ah (or more) pack in about 15-20mins during a stop for refreshment (every 20-30 miles or so)would be the icing on the cake for longer rides & touring!

Stuart.

 

[giguana]

15-20 mins would be like a super capacitor. even mobile phones that are designed to charge fast take 1 hour...

i have heard that they charge fine at double speed i.e. 0.3C so a 20ah battery could be durable with a 5amp charger charging in 4 hours, but i dont know about 0.5-0.6C. maybe ask battery tech forum at endless sphere

 

[coops]

It was being reminded about the potentially very fast charging of LiFePO4 while reading that forum, and learning of the apparent availability now of the hardware to achieve it (thanks Miles! ) for ebikes, which prompted me to ask here about its viability.

20A chargers for certain LiFePO4 batteries are apparently being offered, which will charge 10Ah batteries from empty to 90% full in 30mins, and presumably even less for quick refill charges (fine for current lithium batteries) to maintain the charge level between around 20-80%, as Nick said .

There is increased optimism about better performance in ebikes from some new lithium batteries and I'm eager to see if a substantial reduction in the time needed to recharge might also be achieved .

Stuart.

 

[joab]

Have a look here:
Charging lithium-ion batteries

it says:
"There is only one way to charge lithium-based batteries. The so-called 'miracle chargers', which claim to restore and prolong batteries, do not exist for lithium chemistries. Neither does super-fast charging apply. Manufacturers of lithium-ion cells have very strict guidelines in charge procedures and the pack should be charged as per the manufacturers "typical" charge technique."

Jo

 

[giguana]

hmmm lifepo4 miracle charger...

any used a chargebug hb1212 ?....while searching for a highpower a123 pack charger, i have found this at Home

 

[Jeremy]

Whereas I usually respect the information from the Battery University website, in this case they haven't yet caught up with the technology. They even give a charging voltage which is way too high for the new LiFePO4 chemistry being discussed here. Float charge voltage for LiFePO4 is 3.65 to 3.7V, not 4.2V. LiFePO4 terminal voltage off charge is also lower, 3.2 to 3.3V, rather than 3.7V.

What they say is perfectly true for ordinary Lithium Ion batteries, using 1st and 2nd generation electrode materials. It isn't quite right for Lithium IRON Phosphate cells though, as these are capable of very high charge and discharge rates.

A good example of the fast charge rates that can be used is the latest prototype hybrid packs that use these cells. Hybrids (and pure EVs) can gain a worthwhile performance improvement by using regenerative braking. This does, however, create challenges for the battery, as it has to be able to absorb charging currents that are well into the many tens, or even hundreds, of amps.

Luckily LiFePO4 is able to do this almost as well as NiMH, due to it's ability to tolerate higher charge rates than other Lithium Ion chemistries.

Jeremy

 

[Tiberius]

I did the calculations on regenerative braking recently. Whether it is worthwhile on a bike all depends on the nature of the journey.

What works is steep rolling hills, going up one side and then letting it down on the brakes on the other.

What sounds like it should work but is much more difficult is stopping at junctions. The current into the battery gets large because it all happens in a second or less. And of course on a bike, you can save as much energy by shutting off the power early and coasting up to the halt as you can with regenerative braking.

The emergency stop situation is worse. Then the current peak can be far too large for the battery.

Nick

 

[coops]

Thanks joab and giguana, but why 'miracle charger' giguana?! (ok, they make it look impressive, but I hope it works under normal conditions too! ).

Miles posted a link for a 20A 'BMI' (Battery Manufacturers International, Taiwan?) charger in this thread on 2nd page - there's not much information about high current chargers but thats why I'm asking. [Link to ebay page removed].

joab: thanks for the link but is that page up-to-date (created April 2003; last edited March 2006) and comprehensive for all current Li battery chemistries? For instance, many lithium cells are lower voltage now, below 4V at full charge e.g. 3.65V, so it seems to need updating? If you look online for A123 for example, one of the earliest examples of 'lithium nano-phosphate' batteries, you'll find that even several years ago it was said they could be almost fully charged in 15-30mins or less. - oops, I see Jeremy beat me to it!

Stuart.

 

[jac]

toshiba are saying they have a new battery of 24 volt and 4.2ah which will charge to 90 percent in 5 minutes it is desinged for transport uses

jim

 

[Tiberius]

toshiba are saying they have a new battery of 24 volt and 4.2ah which will charge to 90 percent in 5 minutes it is desinged for transport uses

jim

Not unbelievable. Some of the newer LiFePO4 cells are quoted as 30C discharge rate, so accepting 10C or more charge should not be out of the question.

10C peak doesn't mean fully charged in 6 minutes, unless you can do 10C all the way through. But 90% is in 5 minutes is getting plausible.

Nick

 

[Tiberius]

... some more information about the batteries, mention of "7-10A regular" & "10-20A rapid" chargers available & who BMI are on this slightly controversial but information-packed ebay battery page.

Stuart.

Hi Stuart,

There is an overlap between the discussion here and one on endless-sphere.com

You will recognise one of the names referred to on that ebay page.

Nick

 

[flecc]

toshiba are saying they have a new battery of 24 volt and 4.2ah which will charge to 90 percent in 5 minutes it is desinged for transport uses

jim

Most of Toshiba's research in this direction has been for cars which charge in minutes at "fuel" stations, and it's been with lithium polymer batteries. No precise details, but there's never been a mention of LiFePO4.
.

 

[coops]

Yes, those proposed lipo Toshiba 'SciB' cells, and the bias towards fast-charge car battery research as opposed to high energy-density batteries for bikes, have had several mentions, including:

Advances in battery technology
Battery Advances, the Myth and the Reality
Ebay LiFePO4 batteries

Having re-read some of that, I suppose energy density is the priority for practical range & battery weight for bikes, but with research having been directed to cars as said, and bikes managing say 30-40 miles per charge even on the moderate/low energy-density batteries available to us, is fast charging at such intervals an acceptable compromise for longer range trips, or is there a more practical solution on the horizon?! (preferably without buying/carrying extra batteries... )

Most importantly, does anyone know if this is this viable now, or at least very likely & very soon!! I'm not trying to be speculative; its more about can-it or can't-it be done .

Nick: Thanks, I was aware of a connection/overlap with 1 or 2 threads on endless sphere, but none specifically about this topic, so I didn't consider this thread as duplication of whats there. Also I posted the ebay page for information only: I didn't think the 'named' person would mind me posting the link, but I will certainly amend my posts if they cause any problem .

Stuart.

 

[Jeremy]

I agree about regen on bikes, Nick, I don't think it's really worth the extra complexity. It works well as the weight of the vehicle goes up though; the Prius gets about 8% of it's expended energy back from regenerative braking. It gets around the low speed problem by using electronically operated brakes, so that it uses regeneration down to about 5mph, then uses conventional brakes from 5mph to a standstill.

I hadn't realised that the anti-Chinese eBay seller had decided to publish his lengthy reply to my simple question (which I note he chose not to publish) on eBay. In fact I'm mildly annoyed that he chose to publish his rant, with the implication that I had asked him detailed questions, or been highly critical of him (although it's fair to say that I find his slagging off of other products a bit OTT). To set the record straight, I didn't make a reference to most of the stuff he replied to, I simply asked him if the cells were made by BMI in Taiwan. He is quite clearly on a mission to rubbish all suppliers except his own, which is a good enough reason for me to never consider buying from him.

He's wrong anyway, as many Thundersky and Li Ping customers will attest. I've no doubt that the A123 and other Phostec powder based battery manufacturers make good cells, but it's a proven fact that there are other companies that make good cells too.

Jeremy

 

[coops]

Sorry Jeremy, it was unwise of me to post that link - now removed in the interest of fair play & trade. I agree that the negative sales pitch could use modifying, and that includes posting a reply without the original question, on a selling page, which could mislead others.

Oops, I made things a bit messy now -

Nick: would you mind editing your post to remove the link/quote from there, thanks then I'll amend my last post accordingly & Jeremy can change his if he wants, or will that make it more messy? Oh dear... some days...

Stuart.

 

[Jeremy]

Stuart,

Please don't worry about it, as it's obviously been up on eBay for some time anyway. I'm certainly not at all bothered by any mention on here, in fact I'm grateful that these posts brought this chaps comments to my notice.

Jeremy

 

[coops]

Ok, thanks Jeremy - I'll leave the link removed though now for the reasons I said . I also honestly thought you were aware of his reply on that page: well you are now! No bad intention from me I assure you, just a bad decision! & thanks for your understanding.

Stuart.