Lithium Titanate cells - Page 1
Forum section: electronics / general

author: splin
author_rank: Frequent Contributor
timestamp: July 05, 2019, 01:14:06 am
content: These look extremely promising for many applications for at least three significant characteristics compared to other lithium ion cell types:1) Very long cycle lifetimes - I've seen figures of 10K to 20K or more cycles compared to 500 to 2000 for NMC (and similar) Li-ion and 2K to 5K for LiFePO4. I believe current Li-ion cells are improving in this regard and 5000+ full DOD equivalent cycles may be achievable if the cells are carefully managed. 20K+ cycles is great but what about calendar life? Other Li cells have been stated to have a 10 year calendar life but it is hard to find any real world data to support this, and more recent cell types may be better - or worse - in this respect (I doubt any cordless powr tool or laptop manufacturers are in the least bit interested in long calendar life, especially if it compromises other characteristics). Anybody have any info or thoughts?2) Very high charge/discharge rates with sub 10 minute (or possibly much faster still) charge/discharge times.3) Ability to operate below 0C. My understanding is that Li-ion and LiFePO4 cells must not be charged below 0C because metallic Lithium plating at the anode can occur which will ruin the battery and cause a fire risk. This is quite significant as it means Lithium cells may be usable in low temperature situations such as battery powered equipment for remote, unattended, all year round operation (eg. a remote solar-powered wireless water level meter). Alternatively, much simpler thermal management may be possible for, say, home energy storage systems, avoiding the need for heaters.Does anyone know if the low temperature capabilities extend to charging as well as discharge? I couldn't find any detailed data beyond press-release level info.What about availability? Apart from a few, unknown to me, Chinese brands offering cells or packs, what about more well known manufacturers? How long before there might be ready availability to consumers? Are they likely to get significantly cheaper or are they likely to remain a niche technology for price insensitive applications?

author: splin
author_rank: Frequent Contributor
timestamp: July 05, 2019, 01:24:23 am
content: Forgot to add a link to one of those Chinese suppliers:https://uk.dhgate.com/product/waterproof-lto-60v-30ah-lithium-titanate/448192424.html?f=bm%7cGMC%7cpla%7c1670763299%7c61518981061%7c448192424%7cpla-296557785071%7c103006001%7cGB%7cliuzedong7777%7cc%7c2%7c&utm_source=pla&utm_medium=GMC&utm_campaign=liuzedong7777&utm_term=448192424&gclid=EAIaIQobChMI1KHr182c4wIVS7DtCh1xMg78EAQYBSABEgLIQvD_BwE87.5% positive feedback - think I'll give that one a miss!And another - 40Ah cell @ $28 (ish):https://www.alibaba.com/product-detail/OSN-POWER-deep-cycle-lithium-titanate_60741493433.html

author: Red Squirrel
author_rank: Super Contributor
timestamp: July 05, 2019, 01:41:08 am
content: Sounds interesting. Downside with these type of things, heck even regular lithium ion, is that sourcing them out from a reliable source is hard. Direct from China is always a risk, sometimes it works out, but not always. There's no warranty or anything of that sort. You're lucky to even be able to contact anyone if you have a problem. Insurance definitely won't cover a fire, but that probably goes with anything in this hobby if you're not a certified electrician.

author: splin
author_rank: Frequent Contributor
timestamp: July 05, 2019, 02:53:03 am
content: Quote from: Red Squirrel on July 05, 2019, 01:41:08 amExactly this. Not surprisingly the big names, including Toshiba, Sony, Kokam et al are working on these but that's a far cry from actually making them available to retail customers like us rather than to big customers including car, military etc. manufacturers.I also forgot to mention the main disadvantages of relatively low energy density at 30 to 110Wh/kg compared to 110 to 140Wh/kg for Lithium cobalt cells. And cost and supply probably.Apparantly Lithium Titanate cells are used in the Mitsubishi i-MiEV. I wonder why they aren't shouting that from the rooftops as the advantages are significant and would be a major factor in any decision were I to be looking to buy an EV? Perhaps supply constraints means there's no point as it would create even more unfulfilled demand?

author: Siwastaja
author_rank: Super Contributor
timestamp: July 05, 2019, 07:05:20 am
content: About five years ago, I looked at titanate cells on paper, and based on the experience of others. A few points:- People have had issues with actual life. Cells have started leaking in just a few years. This probably has a lot to do with a fact they are a niche technology, so robust mass quality control is harder to achieve.- Calculate the total cost of ownership properly:For energy storage, $/(kWh*year)For peak power delivery, $/(kW*year)- Consider derating NCA/NMC. There is a lot of evidence available to show tens of thousands of cycles and over a decade of lifetime by operating the cells between, say, 70% and 20%.- If you need power, calculate for power, not capacity. For example, if you need charging power of 100 kW for a 20kWh pack, surely a 20 kWh titanate pack can do it at 5C, but so can a 100kWh NCA pack (at 1C). Even if you didn'tneed100kWh, it may still be the right choice. Now your depth-of-discharge will be only 20% and the lifetime of the NCA pack will likely exceed that of LTO.LTO cells were/are so freaking expensive that whatever I tried to calculate for, an NCA solution would always become cheaper for total cost of ownership. In some cases, the cost would be approximately the same, but the NCA solution would give a bonus of excess capacity.In some cases with very high charge currents, an LTO packcanbe smaller! But do the actual calculation with actual products before assuming this is the case.QuoteThese numbers are way off, they are from 20 years ago! LCO cells are practically phased out as of now. They reached about 190-200Wh/kg ten years ago. Nowadays NCA and NMC cells are mainly used and vary between about 200Wh/kg for old low-cost cells to about 280Wh/kg for the modern cells. This is a huge difference to your quoted numbers!Examples of commercial of-the-shelf cells:Samsung ICR18650-26H, LCO 200Wh/kgSamsung INR18650-29E, old NCA, now available for cheap, 220Wh/kgLG INR18650 MJ1, more modern NCA, but quite affordable, 260Wh/kgBut LTO is marketed primarily for fast charge applications, i.e., very short-term high power storage. So thepower densityis the interesting figure, not the energy density.Ability to charge at cold temperatures is appealing, but this can be mitigated with battery pack insulation and heating solutions. After all, when charging, power for heating is available as well.Do note that the ability to charge LCO/NCA/NMC/LMO/LFP cells at cold temperature is actually not a step function. If you trust the datasheet instruction blindly and charge at, say, +1 degC at full rated current, you are likely to damage the cell and considerably shorten the cycle life. OTOH, even if you went outside of the spec and charged at, say, -1 degC, but did that with a small current (say 1/10th of the rated charge current), you have done no damage at all. IME, you should start linearly derating maximum charge current already from +25 degC, so that it hits zero at about -10 degC. This allows a broader temperature range andstilldoes less damage than the usual step function which allows full charge current at zero degC.For solar/wind storage, LTO is probably completely out of question. AFAIK, most of the time we want to store energy in range ofhours(or even days), notminutes. Ultracaps are good for tens of seconds, LTO for 5-15 minutes, NCA/NMC/LMO/LFP for over 15 minutes, approximately. LTO was marketed for applications like hybrid buses to store a lot of kinetic energy in a short period of time, within a small space. Of course, now it's possible to build aplug-in hybridor a complete EV instead, so larger energy density is needed, and the power density becomes irrelevant at the same time because the large capacity brings the high enough power rating as a side effect.LFP, OTOH, could be a good technology for solar/wind storage, but due to the limited number of manufacturers outside China, and price-fixing in China, it's becoming way too expensive compared to NCA, NMC or LMO, especially as you would want it to becheaper(not more expensive), because it's a energy density tradeoff, so an inferior product spec-wise. Chinese LFP cells have been at the exact same ~$350/kWh for over a decade, while NCA has dropped all the time and now hangs around $170/kWh, half the price of LFP, for small-scale quantities.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 05, 2019, 07:50:22 am
content: Quote from: splin on July 05, 2019, 02:53:03 amThey are not shouting because they only have disadvantages - it's an utter engineering farce, and they are practically out of market.Energy density is,by far, the #1 limiting factor in EVs. Especially was in 2010, but still is. It simply can't be compromised.Others use battery technology with 250 Wh/kg energy density and have no issues whatsoever to provide ranges between 300 to 400 km, while i-MiEV is limited to 100 km range with it's ridiculous 80 Wh/kg battery - the energy density is the same as in the few Ni-MH EVs of the 1990's.Of course, there is no advantage, because the EV charge currents are not limited by the battery, but mostly by infrastructure as of now.We can think about theoretical advantages like putting 16kWh of charge in the pack in just 10 minutes with a 100kW charger, but at the same time, you can put50kWhof charge in a 50-60kWh NCA/NMC pack in just 30 minutes using the same charger. In the first scenario, you need to stop every 100km to charge for 10 minutes (and are completely out of luck if there is any >100km hole in the fast charger network), in the second one, you stop every 350km to charge for 30 minutes. Which one is actually usable?

author: MagicSmoker
author_rank: Super Contributor
timestamp: July 05, 2019, 10:38:39 am
content: Yeah, Lithium Titanate is a proverbial solution in search of a problem these days. A case could be made for using it in cordless power tools, but not much else.But charging an EV that has a 60kWh to 100kWh battery at 5C? That would require >400A service at 480VAC/3ph. just for the charger, and in the US most electric utilities employ "demand billing" for 3ph. service, in which you are charged for the peak power you use, rather than (just) the total kWh. That could get mighty expensive mighty quick.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 05, 2019, 03:00:41 pm
content: Quote from: MagicSmoker on July 05, 2019, 10:38:39 amAnd people won't need it. Tesla's supercharging rates are satisfactory (have a 30-minute stop every 350-400km!), maybe someone would want 30% more, but they don't need to be increased by 3x or 4x. Tesla's battery capacity is also satisfactory, someone might again want a tiny bit more but they are already there.Only thing left is to reduce the price, weight and size even further, all of which are really problematic for LTO or LFP or any other "alternative" compromise chemistry to achieve. Energy density is still #1.And with high energy density, likely comes lower price (unless special expensive materials are needed) - now the bulk of the li-ion price comes from the relatively low-cost materials. Tesla probably pays approx. $100/kWh (if not less) for the cells, and they are approx. 270Wh/kg, so they are paying approx $27/kg for the average bulk of cell, and this price includes all work, non-recurring costs etc.! But it's mostly materials, a lot of it is graphite, copper, aluminium, nickel, cobalt... No high-cost materials, only low and maybe medium cost, even just the copper and graphite prices are hurting them already.So they need to reduce the bulk weight to save in cost as well. So as long as higher energy density doesn't require some plutonium space rock material, increasing it further is the key to all problems. The winner uses the highest energy density cells possible, and those who think about makinganycompromise there, will lose. For example, LTO or LFP are way inferior in almost every metric, and remain that way because of the low amount of sales, low amount of R&D, and high unit costs. And even if they somehow managed to get a $10 billion investment on NRE, the material weight alone makes these low-energy-density technologies costly, and this can't be solved.

author: john61ct
author_rank: Regular Contributor
timestamp: July 05, 2019, 03:59:02 pm
content: Quote from: Siwastaja on July 05, 2019, 07:05:20 amNot caring what they're marketed for, just actual performance, I do not understand this at all.Yes, I want to store energy for many hours, even days, bank size 5-20kWh.Neither energy density nor power density are important to this use case.Cost per kWh **per year** over a few decades is more important than initial acquisition cost, so besidessafety (low likelihood of thermal runaway),longevity is the critical factor, both cycle count and calendar life.So why would LTO be less suited for "long-term" storage?Self-discharge rate afaict would be relevant, but you don't mention that.

author: MagicSmoker
author_rank: Super Contributor
timestamp: July 05, 2019, 06:07:22 pm
content: Quote from: john61ct on July 05, 2019, 03:59:02 pmLFP is still the safest of the li-ion chemistries, AFAIK, has an excellent cycle life (~3000 cycles at 80% depth of discharge), and a near zero self-discharge rate (but that isn't unusual for li-ion).As Siwastaja has already mentioned, however, there isn't as much competition or innovation going on in LFP compared to the other chemistries that are most popular in phones, laptops and EVs, so price and capacity haven't improved much since they were first released, oh, about 10-15 years ago.

author: john61ct
author_rank: Regular Contributor
timestamp: July 05, 2019, 07:02:07 pm
content: Yes, but I do see LTO as a potential alternative, where LFP was previously the only option.Apparently just as safe, and even longer lifespan. Cold charging would be icing on the cake.Just trying to figure out the rationale behind that whole "suitability for storing energy over a longer period".Don't care about innovation in a chemistry, and as long as longevity promises are realized, higher initial acquisition cost is mostly irrelevant here.10-15 years is about how long I would wait for a new chemistry to prove itself in use anyway.

author: MagicSmoker
author_rank: Super Contributor
timestamp: July 05, 2019, 07:47:17 pm
content: Quote from: john61ct on July 05, 2019, 07:02:07 pmOn paper, this would appear to be the case, but I have personal experience with LFP so can wholeheartedly recommend it, especially if you also need to slot a new battery into an old lead-acid application (generally, 4 LFP cells in series is equivalent to a 12V lead-acid battery and can even use the same charger [Is this ideal? No, but it works well enough and isn't unsafe]).Quote from: john61ct on July 05, 2019, 07:02:07 pmI interpreted that comment as more of an economic indictment, rather than a technological one. LTO has about the lowest terminal voltage of all the li-ion chemistries (maybe LiS is lower; can't remember) so energy density is relatively poorer, which typically means a higher overall materials cost for a given amount of energy stored unless the materials are that much cheaper, and they aren't for LTO.

author: john61ct
author_rank: Regular Contributor
timestamp: July 05, 2019, 08:02:20 pm
content: Yes, I've been working with LFP for some time myself.As I stated, for my use cases, energy/power density and acquisition costs are not major concerns, nor are generalities about market trends.I just had a specific question, addressed to Siwastaja, and am happy to just wait for them to respond in case there is a substantive factor involved there I'm not yet aware of.Thanks for responding though.

author: nctnico
author_rank: Super Contributor
timestamp: July 05, 2019, 08:39:48 pm
content: Quote from: john61ct on July 05, 2019, 03:59:02 pmI agree. Only for electric cars weight and low self discharge are important. For (grid) energy storage the TCO (total cost of ownership) is what matters. Energy density by itself not so much.

author: john61ct
author_rank: Regular Contributor
timestamp: July 05, 2019, 11:35:21 pm
content: Well actually all vehicles, including flying models and eBikes

author: nctnico
author_rank: Super Contributor
timestamp: July 05, 2019, 11:42:20 pm
content: Quote from: john61ct on July 05, 2019, 11:35:21 pmNot so much. It depends on the size. Compare a car and a bicycle for example. A regular bicycle can carry many times it's own weight. A regular car can carry half it's weight if you are lucky. It doesn't matter much if a battery pack for a bicycle weighs 5kg or 10kg (except for convenience when taking it on and off the cicycle).

author: john61ct
author_rank: Regular Contributor
timestamp: July 06, 2019, 12:02:12 am
content: Well depends of course, in hill country and when pedaling every ounce counts.

author: splin
author_rank: Frequent Contributor
timestamp: July 06, 2019, 02:13:27 am
content: I use the abreviation LCO (probably incorrectly) for Lithium Cobalt based cells, including NMC, as compared to LFP and LTO.Quote from: Siwastaja on July 05, 2019, 07:05:20 amDissapointing, but most new technologies have issues in the early days - hopefully they will have been resolved by now - at least by the major manufacturers.QuoteI found some data on Toshiba ScIB LTO cells:https://www.scib.jp/en/index.htm20,000 full DOD cycle life (to 30% loss of capacity), operation down to -30C, 93Wh/kg, 202Wh/l and significantly, 10 year calendar life. I don't know how conservative that is but to achieve 20,000 cycles in 10 years requires 5.5 full cycles per day! That isn't going to happen in any normal solar power storage system so the long cycle life is likely irrelevant.In fact few systems are going to cycle even once per day on average - especially PV systems sized to provide enough storage for a day or two in winter. I'd be surprised if many systems would see 300 cycles/year so assuming all lithium types have a similar calendar life then any battery capable of 3000 cycles will have a similar lifetime.Calendar life might exceed 10 years for many lithium types but I've not managed to find anything to support that - probably because Li-ion cells haven't been around long enough in these types of applications (but it would be interesting to know if there is any data from old, but lightly used laptops). 15 years or longer may be possible in colder climes in which case 4,500 cycles would be required. This may be achieved by some batteries but older LFP cells were specced at 2000 cycles @ 70% and LCO types were specced at less than 1000 cycles (as far as I can remember).As you say, longer cycle lifes can be achieved by partial cycling, so comparing lifetime energy throughput cost needs to account for the reduced usable capacity so restriciting LCO DOD to 70% usable requires 43% more capacity compared to 100% for LTO.Another cost factor is the assembled battery cost given that LFP and LTO are available in much larger cell capacities than LCO. Also, many large format LFP systems don't use or require an expensive (and often unreliable) BMS - just the occasional top or bottom balancing is performed. This may also be the case for LTO if reasonably high capacity cells can be obtained. I doubt that many 18650 or 26650 based large batteries are used without a BMS, partly because of the safety issues.Another very important cost factor is the reliability of a complete storage system - if some or all cells are damaged prematurely due to accidental overcharge or discharge, the economics case comes unstuck. Many lead acid systems die early because it so easy to make a mistake, or have a failure of a charger or the like, and if non-trivial it only needs to happen once. Lithium batteries are simpler to manage but BMSs seem to have got a terrible reputation for destroying batteries - it would be interesting to see any reliable statistics. It's possible that LFP or LTO batteries without a BMS may be much more reliable than LCO + BMS.Thermal management can't be ignored either. If you live in an area with sub zero winters you will have to provide heating for LCO and LFP but probably not for LTO or lead acid. I personnaly wouldn't have a problem installing an LFP or LTO battery in a garage attached to my house where it would be relatively easy to keep the battery above 0C. But definately not a large LCO battery unless suplied by a reputable supplier such as Tesla, Samsung etc, but then the cost is going to be far beyond the cost of the cells. So if home built, additional cost for an external housing plus heaters.Still might not make LTO cost competitive but I'm not sure it's as clear cut as you claim.QuoteLimiting DOD to 50% doubles the cost.QuoteYes, that's the nub of the problem. If you can't get them at a sensible price then all the other factors are irrelevant. I wouldn't buy unknown Chinese brands of LTO any more than I would want '*fire' LCO cells - there may be high quality Chinese cells available but if I can't find them and be sure of their quality they are effectively unvailable. Toshiba, who require registration to download a datasheet, are almost certainly not interested in selling to me and I expect there won't be any distributers either.QuoteMea culpa! It was late and I was lazy and didn't look far for some numbers - I knew that would come back to bite me! Like many numbers on the internet they weren't reliable. But, as others have responded, for many storage applications specific energy is not very important other than how it affects cost.QuoteAgreed; it's not easy (for me!) to think of suitable applications other than regenerative braking in hybrid vehicles which don't have room for large batteries.QuoteNot for low powered (eg. IOT) applications - a 1W solar panel isn't going to supply anywhere near enough energy to heat a cell in winter @ -20C, but enough to transmit a sensor reading every 10 minutes or so. LTO seems to be a very good alternative to Ni-Cad (NiMh aren't especiallly rugged and lead acid don't have very long lifetimes).QuoteThat sounds very reasonable and plausible but I don't see how you could design a commercial product based on that given the safety implications. Do you have any links to any research or supporting data? I'm sure you're right which would be fine for a few home built gizmos but if I wanted to sell them I'd need more substantial evidence - if only for insurance purposes.QuoteYes, I've observed, and been surprised by the total lack of movement in LFP pricing over the last 10 years. I wonder if the recent interest in home energy storage might attract more competition?Could you provide some links to cells at $170/kWh as I can't find them (with a superficial search at least)?

author: john61ct
author_rank: Regular Contributor
timestamp: July 06, 2019, 02:31:43 am
content: Quote from: splin on July 06, 2019, 02:13:27 amWell I can see why, but yes that does lead to a lot of confusion.> I found some data on Toshiba ScIB LTO cells:https://www.scib.jp/en/index.htmYes so far those seem to be the ones I'd trust.> Calendar life might exceed 10 years for many lithium types but I've not managed to find anything to support thatI know many many LFP owners well past 7-8 years now, most cycling daily with **zero** capacity loss.I'd be very surprised if **calendar** life wasn't well over a century isolated from loads and otherwise in ideal conditions.The vendor specs are grossly conservative, and assume high dis/charge rates and pushing into the voltage shoulders at both ends.> I doubt that many 18650 or 26650 based large batteries are used without a BMS, partly because of the safety issues.No problem with LFP, long as you monitor and periodically test them properly.> It's possible that LFP or LTO batteries without a BMS may be much more reliable than LCO + BMS.That may be overstating things, but then most owners can't be bothered with manual monitoring much less periodically testing them.> Yes, I've observed, and been surprised by the total lack of movement in LFP pricing over the last 10 years.The greater the interest, the more support for high pricing.I've never had any expectation of LFP prices declining, just grateful they haven't been doubling every year.

author: SiliconWizard
author_rank: Super Contributor
timestamp: July 06, 2019, 02:52:03 pm
content: LTO batteries of small capacity have been commercially available for a few years already:https://www.batteryspace.com/Lithium-Titanate-Battery.aspxThey have an impressive max discharge rate and number of charging cycles, but their energy density is not impressive. I haven't gotten around to testing them but I might one of these days. As of now, I'm under the impression that LiFePo4 are a better overall option.

author: ebclr
author_rank: Super Contributor
timestamp: July 06, 2019, 05:15:47 pm
content: https://item.taobao.com/item.htm?spm=a230r.1.14.14.774f6473e6nl4Q&id=588988487668&ns=1&abbucket=1#detail

author: Nauris
author_rank: Regular Contributor
timestamp: July 08, 2019, 02:25:16 pm
content: Quote from: splin on July 06, 2019, 02:13:27 amI tested old HP laptop from the scrap metal dumpster, battery date: 08/2008 cells made in Korea 55 Wh, so 11 years old. Runs 3 hours with that battery, capacity is about 45 Wh. Means 80% of original capacity, not bad. But I have no clue what kind of useage it has had.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 08, 2019, 04:22:23 pm
content: Quote from: splin on July 06, 2019, 02:13:27 amNissan Leaf modules (LiMn) are about $200/kWh in small quantities, bulk orders significantly less.

author: splin
author_rank: Frequent Contributor
timestamp: July 10, 2019, 02:28:33 am
content: Quote from: NiHaoMike on July 08, 2019, 04:22:23 pmYou mean used cells? So $200/kWh of capacity when new? Where can you buy them in bulk?

author: splin
author_rank: Frequent Contributor
timestamp: July 10, 2019, 02:31:48 am
content: Quote from: Nauris on July 08, 2019, 02:25:16 pmAn interesting data-point - thanks. So it looks like the calendar life could easily be well in excess of 10 years, especially as that battery must have had at least some use and thus spent some of its cycle life - unless you happened to get lucky and found an exceptionally good example.