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Old 18-12-2013, 19:52   #3346
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I have read this forum from front to back and have not seen any comments about how to use LiFePO4 house batteries in an "inverter based" boat - A boat where all the current runs through 1 or more inverters whether the current originates from main engine alternators, from a genset, from shore power or from solar/wind. i would be interested in opinions regarding protecting alternators with the inverter or any other experience in this area
Thanks,
Twin Coves
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Old 18-12-2013, 21:39   #3347
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by hellosailor View Post
There's an incredible amount of confusion over HazMat and I think some vendors inflict that on the customer in order to gouge them. Many battery types, especially those that do not use liquid acid electrolyte, do not have to ship as HazMat! The exact terms are carved in stone by the USCode
For large rechargeable lithium ion batteries, it's pretty cut and dry: USPS, UPS, and FedEx all want prominent labeling, special documentation and packaging---and of course---hefty surcharges wherever possible.

It used to be just for domestic air. Now it's ground as well. It's not gouging by the vendors if they jump through all the carriers' required hoops.

I'm torn by those who choose not to. They undersell their competitors by cheating and potentially put carriers at risk---who do have a right to know what they're transporting. OTOH, surcharges are exorbitant for the actual risk.
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Old 18-12-2013, 21:49   #3348
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Welcome hdossett, I'm an RVer too. Comparing Winston to CALB is apples and oranges---design, materials, and operational parameters are different. MaineSail has (or soon will have) both, and I eagerly await his thorough comparison.
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Old 18-12-2013, 22:28   #3349
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Originally Posted by goboatingnow View Post
Note in my previous post , I referred to the freezing of the electrolyte, this is related to ultimate low temperature performance, Here I try and deal with the issues related to sub zero ( c) performance and why it drops off dramatically in commercial cells.
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Originally Posted by goboatingnow View Post

For those of you with an academic bent I would cite

"Research on cathode material of Li-ion battery by yttrium doping,JOURNAL OF RARE EARTHS, Vol. 26, No. 2, Apr. 2008, p. 279 by TIAN Yanwen (田彦文)1, KANG Xiaoxue (康晓雪)1, LIU Liying(刘丽英)2, XU Chaqing (徐茶青)1, QU Tao ()1"

Certainly its clear from that article that Y doping in LiFePo4 in certain amounts improves both initial discharge ability and also cyclic performance was improved. This is because Yttrium doping improves the conductivity of the cell over that of non doped Lifepo4 cathodes .

Low temperature performance of LI cells, is still a matter of considerable scientific debate, but can be summarised as

(a) reduced conductivity of the electrolyte and solid electrolyte interface on the elec- trod surface
(b) limited diffusivity of lithium ions within graphite anode
(c) high polarization of the graphite anode, ( as per (b)
(d) substantially increased charge-transfer resistance on the electrolyte–electrode interfaces

( S.S. Zhang, K. Xu, T.R. Jow, Electrochemical impedance study on the low temperature of Li-ion batteries,US Army Research Laboratory, Adelphi, MD 20783-1197, US, Electrochimica Acta 49 (2004) 1057–1061.)

Of this the primary factor has been to kinetics of Ion transfer at low temperature, and it has been shown that while discharge can occur at increasingly lower temperatures, the equivalent resistance of the cell reaction kinetics, increases with discharge at low termoperatures , making re-charging such cells difficult or even impossible at low temperature.


The key thing here is that Yttrium doping was designed to counter the lower conductivity and improve cyclic performance, in an attempt to recover some of the energy capacity lost in deploying LiFepO4 as a cathodic material. It has little or no effect on temperature.

As is pointed out in the above article, commercial grade LI-ion suffers greatly from low temperatures, a typical 18650 cell, will have less then 5% of original room temperature capacity at -40 degree C ( electrolyte freezing point)


Its furthermore interesting that most of this research work, seems to be in the hands of Asians scientists , working in American research institutions from about 2000-2005, theres nothing new in Yttrium doping , nor is it exclusive to Winston Chung.


What this means, is that for commercial LIfePo4 cells ( with or without doping) both Lithiation and delithiation become very poor at temperatures below zero, primarily due to the kinetics around the Graphite anode. Note that often manufacturers temperature limits , merely mean the battery can be technically used at stated low temperature, ( i.e. the electrolyte will no freeze) , it does NOT mean that in particular the standard charging regime can be applied at sub zero conditions,

IN particular at low temperatures , The battery is easy to "voltage stress " , to simply it looks like a battery of significantly reduced capacity and applying a standard charging regime will over stress the battery and cause irreversible plating of the electrodes. Subsequent attempts can then cause massive oxidisation of the electrolyte and the usual Li issues.

Li technology can be improved with exotic anodes etc and much research is ongoing , but today what we get in commercial cells is not in any way optimised for low temperatures.


Dave

Seriously Dave, you are distorting things here just a tad. you mention not charging below 0degC and electrolyte freezing all together giving the impression that the electrolyte freezes @ 0DegC, but you material you have quoted says it freezes at -40degC, not a temp commonly experienced by most boat people so it does appear that electrolyte freezing isn't every likely to be an issue with a boat house battery.
Next, you mention serious damage if you attempt to recharge below 0 degC
Quote:
"merely mean the battery can be technically used at stated low temperature, ( i.e. the electrolyte will no freeze) , it does NOT mean that in particular the standard charging regime can be applied at sub zero conditions,

IN particular at low temperatures , The battery is easy to "voltage stress " , to simply it looks like a battery of significantly reduced capacity and applying a standard charging regime will over stress the battery and cause irreversible plating of the electrodes. Subsequent attempts can then cause massive oxidisation of the electrolyte and the usual Li issues."

Voltage stress is the issue if you attempt to use standard charging regimes, follow the golden rule of between 2.8v and 3.6v and do not hold a cell at either of these voltages for long periods and "voltage stress" can't happen can it?
It's the same issue with float charging, I have no idea why someone would want to float charge L batteries, but as long as the same rules are adhered to, no damage will result.

It's great to read all you can about these cells, but you need to apply what you have learnt to decipher what the stuff you are reading actually means.
You know what the standard charging regime is, you know from you chart the danger zones for the cell plating to occur, now apply that information to the article you quoted and a whole new lot of information appears.
Too many conclusions are being jumped to, don't assume, apply what you have learned so you learn more.

There seems to be an assumption that these cells loose 2% per mth and this is a linear thing, how do you explain 3 yr old batteries that still have 50% SOC? 2% x 36 mths =... what? If a 100Ah cell looses 2% in the first mth from fully charged it would have lost 2Ah, 2% of 100Ah, so at the end of 1 mth standing the cell would now have 98% capacity. Is the 2% for the next mth calculated from 100Ah or 98Ah? Can you see the assumption had already been made, that 2Ah per mth was lost, therefore after 36mths 72ah would be lost from the battery? So how could there be 50% capacity when the cells were in a box for 36 mths?

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Old 19-12-2013, 00:43   #3350
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I still have the 6 160ah cells I got from Balqon last year, and 8 more 40ah cells,
haven't been used, just been sitting. That would make a 320ah 12v pack.
I would be willing to sell them, as I need a lot more and not getting them from Winston.

I may very well be buying a very large amount of CALB 100ah cells in the next few months and if someone wants to get in on that deal, it will be a bit cheaper than retail.
BTW, HiPower cells are known for short lifetimes..
The only other option I am aware of is Headway and 15ah is largest they make.

PM if interested.
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Old 19-12-2013, 01:38   #3351
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Bob.

This is the Winston sell Sheet from the same link, to the charger you posted.
Quote:

MODEL NO:TS-LFP200AHANominal Capacity :200AHOperating Voltage:2.8V~4.0Vweight:7.3kg±100gDimensions:362×5 5.5×256(mm)Check Full specification>>As factory Thunder-sky change their name to Winston battery. Their products name are change from TS-LFP to WB-LYP. Products are same which you are buying from us. model: "TS-LFP" = "WB-LYP".
Shipment can be issue out on 5-10 days after Payment

Did factory Thunder-sky really change their name to Winston.


Or did Sinoply Change the Thunder-sky name to Sinoply????


Lloyd















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Old 19-12-2013, 03:11   #3352
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Quote:
Originally Posted by T1 Terry View Post


Seriously Dave, you are distorting things here just a tad. you mention not charging below 0degC and electrolyte freezing all together giving the impression that the electrolyte freezes @ 0DegC, but you material you have quoted says it freezes at -40degC, not a temp commonly experienced by most boat people so it does appear that electrolyte freezing isn't every likely to be an issue with a boat house battery.
Next, you mention serious damage if you attempt to recharge below 0 degC
Quote:
"merely mean the battery can be technically used at stated low temperature, ( i.e. the electrolyte will no freeze) , it does NOT mean that in particular the standard charging regime can be applied at sub zero conditions,

IN particular at low temperatures , The battery is easy to "voltage stress " , to simply it looks like a battery of significantly reduced capacity and applying a standard charging regime will over stress the battery and cause irreversible plating of the electrodes. Subsequent attempts can then cause massive oxidisation of the electrolyte and the usual Li issues."

Voltage stress is the issue if you attempt to use standard charging regimes, follow the golden rule of between 2.8v and 3.6v and do not hold a cell at either of these voltages for long periods and "voltage stress" can't happen can it?
It's the same issue with float charging, I have no idea why someone would want to float charge L batteries, but as long as the same rules are adhered to, no damage will result.

It's great to read all you can about these cells, but you need to apply what you have learnt to decipher what the stuff you are reading actually means.
You know what the standard charging regime is, you know from you chart the danger zones for the cell plating to occur, now apply that information to the article you quoted and a whole new lot of information appears.
Too many conclusions are being jumped to, don't assume, apply what you have learned so you learn more.

There seems to be an assumption that these cells loose 2% per mth and this is a linear thing, how do you explain 3 yr old batteries that still have 50% SOC? 2% x 36 mths =... what? If a 100Ah cell looses 2% in the first mth from fully charged it would have lost 2Ah, 2% of 100Ah, so at the end of 1 mth standing the cell would now have 98% capacity. Is the 2% for the next mth calculated from 100Ah or 98Ah? Can you see the assumption had already been made, that 2Ah per mth was lost, therefore after 36mths 72ah would be lost from the battery? So how could there be 50% capacity when the cells were in a box for 36 mths?

T1 Terry
Terry. Your post does nothing to contradict what I said , ill summarise it again , personally I have several years experience as a professional designer with Li ( on top of 20 years with Nicd NiMh and others , with several corporate patients to my name) . Including designing many types of chargers. All I was trying to do is give you the science behind this battery technology and dispel some of the myths , especially nonsense about yttrium and low temp for example

Low temperature performance , both charging and discharging falls off rapidly below freezing , that's a fact. ( I've tested it too ) , initially , this is " primarily " due to the fall off in intercalation rates of the graphite anode , which in commercial cells, s usually a cheap coke material.

At below -20 (c) rates dramatically decrease. Again due to various kinetic conductivity issue including intercalation , ion tranport and ion interface issues

Furthermore at below or near freezing in cheap anodes , charging at rates used at room temperature , cause voltage stress , ie the anode cannot accept Li ions at the same rate and dendritic plating begins , which can pierce separators and cause shorts.

For this reason , most commercial Li batteries are rated to freezing and above for charging

Furthermore I do not see any evidence that Winston cells are ANY different

Note that it is quite possible to charge at below freezing , it's just you have to severely modify the charge regime.


Ultimate low temp performance is determined by the freezing point of the electrolyte , nominally around -40 C , and if you got confused by my " article " I'm sorry for the bad layout of the previous piece , it was a bit off the top of the head stuff and re-edited as I added stuff

Hence to summarise , all this applies to all Li commercial cell types

Don't charge at or below freezing , unless you change the charge regime severely

Expect dramatic drops in performance as the temperature falls towards freezing and below ( its one of the reasons Li isn't widely adopted in car starting by the way )


Yttrium is nothing special and wasn't invented by Chung. It's properties have been known for some time , nor does it as you erroneously stated , contribute anything to temperature range . cathode doping is an attempt to improve conductivity, and cycle life . Your comments in regards Winstons temp range specs were just wrong , and show a lack of understanding not only about the basic chemistry , but specifically low temp Li operation


Now terry. I get a right pain when pseudo science is applied , the " my batteries are fine after x years " , unless you have established proper baseline discharge curves and track changes to that , you can't make all real conclusions , I get the same nonsense from guys on boats with 10 year old LA , " nothing wrong with my batteries " then when tested there actually shot and the user just got used to low capacity etc.

For example what exactly is 50 % discharge , how are you determining that , have you graphed and established capacity , have you tracked capacity etc etc. simply pulling 50% out of thin air is simply an irrelevance. What is it 50 % of

My documented experience using LiM/Co and now LIF small cells is in GSM standby , for monitors and sensors, tracking . It's a very very tough case for Li

From the lab results I know

1. Low temp performance is poor in commercial cells , often shockingly so , by low temp I mean below 10 degrees C
2. It is possible to recharge at sub zero if the charger severely reduces the charge regime especially during pre qualification , below -10 it can be at C/100 or even less ( the upper knee appears faster )
3. The cell can be recovered from very low voltage events by low current pre qualification charging , once it's done immediately after the low event , capacity loss does occur , ranging from minor to quantifiable.
Cells are not severely damaged by excursions below the lower " knee" , what damages them is the subsequent uncontrolled re charging. Done properly cell operation can be recovered with little noticeable damage , but not repeatedly so. Li remaining at very low discharge can cause severe degradation
4. Based on my readings , Li degrades around 10% per year no matter what. Degrading occurs faster if the cells are regularly held above 80% soc. ( assuming you know the SOC ) , some cells degrade faster then that. Deep discharges degrade lifetime at a faster rate( GSM is very hard on Li ).

In large format Li batteries its important to realise that many problems are hidden behind the large " nominal capacity ". In my view large format cell manufacturers underplay capacity for a good reason.

So if in your application you start with 400 Ah nominal , testing reveals say 440Ah , and you run very conservatively between say 20-30% and 80% , which is too conservative for small capacity applications by the way, then you may not actually see any negative capacity effects due to float charge , incorrect charging etc , as in effect you have 50% capacity, to get eaten away by these effects, before you see noticeable effects , do you don't see anything. BUT. The effect is occurring .

So yes, based on the scientific research , floating causes problems and results in loss of capacity , whether you can actually notice or measure such capacity loss is another thing entirely.

I do find your condescending attitude ( sorry thats not the correct phrase , i mean more your aloofness) to standard Li research a bit disappointing. Half baked field tests are hardly scientific in any way. Anyone for example will tell you that tests on accelerated Li cycle life shows that 2000 cycles is eminently achievable. But to really qualify that , you have to due proper capacity testing and baseline analysis. Otherwise the results fall into the category of " mine are good , what's the problem dude " .

When you do take the time to evaluate this technology you do find interesting wobbles.

My own setup is quite an extensive lab setup for small format batteries. I also have a 40 ah Winston battery for comparison . Nothing I see suggests that the large formats are IN ANY way different to any other Li packaging.

Capacity masks problems , running tests on 1000Ah batteries is almost useless unless you can stress these batteries and then accurately measure capacity loss, which is quite difficult ( and dangerous too)


There is little I disagree with in this very long thread other then to remember

(A) large format cells operate identically to all other forms of packaging , where there are differences that are immaterial
(b) LiFepo4 has certain specific properties like lots of different Li cathode make-ups, but IT IS still Li -ion not some magical fairy dust. It has ALL the properties of Li ion batteries
(C) charging regime is much more complicated , especially if you want to stay within the operating envelope of the batteries, under all conditions. It is not LA , all excursions outside the envelope , short of physical damage , tend to affect capacity. ( but you may not detect this )
(D) operating life cycle degradation is actually less then standby degradation, especially at high levels of SOC , if you are considering Li in a standby , or near standby application, do a lot of reading before you waste your money. These cells benefit by being used.

Li in large capacities, used in low C environments , with very conservative usage and charge limits , tends to produce very good results ( even if its a very inefficient use of the battery ) . Hence in boats the cells are really " dawdling along" and they seem great , especially benchmarked against what are quite appalling LA technology. But that's not really the answer is it, it's not a proper analysis.


In your case you generally have large capacity banks , being used repeatedly , with conservatively set charging regimes , and your questioning why you are getting beyond 1000 cycles or three years. Why would you think you wouldn't. !!! The technology is quite capable of 2000 cycles ( or more ) that's clear from the industry literature. The issues are what degrades lifetime and rate of capacity loss , not simply cycles.

I find it funny , that people looking at 15 year old technology , widely in use, would somehow , feel that the technology can't deliver what is generally claimed. There more then enough experience out there to show that. What is interesting of course is to compare some Chinese manufactures , very wide variation in specs.

What's different , is when you start to push the edges of the envelope , which boaters aren't doing , but say EV and RC modellers are. These are the sites and feedback that are useful, not huge capacity banks in the dessert or something , you learn much more designing say a small capacity Li battery into a demanding GSM monitor application , then you ever will running large banks under non demanding situations.

Simply having an Li installation that works , does not mean you ( one) knows a lot about Li.

Talk to say a laptop charging circuit designer , he knows more about Li issues then any thing here on this forum , that's simply a fact of design criterion. The net is full of specialist talk about the issues.

Ps I provided you and it was you , two articles , from a very extensive set of literature I have , to merely tackle too misleading points you had as I beleive you have the interest in maybe actually reading them.

What's sometime depressing is listening to a kind of fanboy versus detractor argument that occurs here

The detractors point to doom and gloom problems without any scientific knowledge or analysis , the fanboys point to " personal experience " without any scientific or quantitative approach , often using very conservative experiments to draw conclusions

I ask you this , how many here have tested batteries to destruction! .?? How many have good engineering conclusions based on acquired data

Answer these questions
1. What capacity loss from measured maximum has occurred , due to long standing float charge , at various levels of SOC. how have you determined that
2. Have you taken batteries to 0% , have you evaluated the recharge , loss of capacity , changes in internal impedance as a result , hence have you drawn conclusions as to what strategy should be followed in such an event. Do you understand pre qualification charging etc ( Sony didn't )
3. Have you measured the capacity loss by voltage stress at and above the " upper knee" , have you compared cycles at such stress against cycle life.
4. How does capacity and cycle life get affected by dynamic current conditions , especially at multiple C
5. Have you charged to cell destruction, or near destruction, what is your analysis of activity above the upper Knee , how does this affect charger design and safety
6. Have you compared and contrasted your work with established peer review publications. Access to a university online article database is required here of course

Plus many other tests to determine battery characteristics


Then come back and lets talk Li characteristics


Li ion ( in all forms) is a dependable , reliable and rugged technology ,significantly ahead of LA , used in millions of applications every day , used incorrectly is has failure modes that can be an issue. For amateur use , staying right in the middle of the operating envelope is a very good , if inefficient , use of the technology.

Dave
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Old 19-12-2013, 03:53   #3353
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I just realised the length of that post , heres an executive summary


1. Use Li is a predominately above freezing environment preferably above 10 degrees c , degrade capacity accordingly below that and severely so as you progress below freezing.

2. You can only interpret manufacturers specs if you understand the chemistry, see envelope discussion in pt 7

3. Don't use a standard charging regime at below freezing , ( in fact I would add below 5 degrees C for cheap batteries) , basically unless you have a charging regime that's appreciates the Li charging envelopes, just don't do it at all. Operating temp limits do not mean the battery can be used the same over the whole range ( I've avoided high temp discussions). But be aware there are also issues at high ambients

4. Dont buy Li for low capacity standby applications , where extended lifetime is required , AGMs , Gels are better at this. It is not a good technology for essentially standby or backup applications

5. do buy them for high cyclic, high load applications. They like to be used !

6. Do rate them conservatively and apply a conservative charging regime and discharge usage , upper and lower knee voltages have been discussed here to death. In this case especially in fractional C situations they are about the most rugged and useful battery technology you can commercially buy. Do not listen to unscientific doom and gloom, your propane system will blow up the boat before the battery does !

7. Never forget these are not lead acid batteries , either use the conservative numbers or clearly understand the operating envelope and its affects on discharge and recharge. If you wish to be ( or are ) anywhere near the edges of the envelope , understand precisely the issues and effects. Proceed accordingly

8. Use LVC HVC BMS balancing systems, standard chargers etc ,etc , BUT understand their function and limitations , do not install an Li system without understanding what everything does and it's failure consequences. Li isn't idiot proof

9. Follow MaineSails build examples !

Dave
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Old 19-12-2013, 20:04   #3354
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Interesting Dave, would you use testing information gained when using cylindrical cells that are known to give a high discharge rate for short periods yet have little capacity, to determine the suitability of all types of lithium ferrous batteries for house power supply use?
You claim to know a lot about lithium ferrous batteries, what are the differences in construction between cylindrical cells and prismatic cells? Do you believe they are both equally as suitable for use in high rate discharging and low rate discharging over a long period? Which type of cell contruction has a better cycle life?

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Old 20-12-2013, 04:54   #3355
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Interesting Dave, would you use testing information gained when using cylindrical cells that are known to give a high discharge rate for short periods yet have little capacity, to determine the suitability of all types of lithium ferrous batteries for house power supply use?
You claim to know a lot about lithium ferrous batteries, what are the differences in construction between cylindrical cells and prismatic cells? Do you believe they are both equally as suitable for use in high rate discharging and low rate discharging over a long period? Which type of cell contruction has a better cycle life?

T1 Terry
Actually I never claimed to "know a lot", I have been using and characterising LiFepo4 cells for use in applications in the last two years, with more activity recently.

Im not sure what you mean by packaging differences

Large format batteries are simply repackaged "pouch or prismatic" Li cells. compared with cylindric cells, they offer slightly higher energy density and more flexible packaging, but need to be encased, protected and constrained to contain the mechanical issues and the bulging etc, over cylindric cells, which are heavier and more mechanically robust at the cost of a slightly inferior weight energy trade off.

Hence large format cells are merely repackaged parallel prismatic pouches each a Life cell.

I can point you to a large body of explanations that look at differences between the cell construction. But prismatics & pouches generally have better heat dispersion, better conductivity due to the tab design and are easier to interconnect to form large cells. ( Though interesting Telsa has remained with the 18650 cylindric cell).


Leaving aside heat conductivity and some interconnect benefits , lifecycle and discharge ability are generally unrelated to packaging. prismatics & pouches with good Tab design are generally better at high discharge applications merely because of mechanical issues. I see no real difference in cycle life.

certainly leaving aside mechanical issues, both types can make good battery banks suitable for either high or low discharge ( it also depends on what you mean)

I do see much more variety in the quality of manufacture between cylindric cells, ranging from some almost terrible quality and construction to very good accurately characterised cells. in the large prismatic pouch formats , I do have a few pouches to evaluate, because I am considering a prismatic pouch for a new design , but I can't really comment on the CALB, SImoply, Winston, Thundersky as I haven't seen enough of them to comment on manufacturing quality. The big issue with pouches is to protect the cell from physical damage and to contain the cell in relation to bulging.


As to construction specifics, prismatics/pouches as generally flat wound cells, , with top exit tabs, generally copper and aluminium . a number of these are paralleled to get the desired capacity.

I think its important to remember and I feel some people forget , that Winston batteries etc, are just numbers of standard Lifepo4 prismatic pouches ( i.e. without a sealing pouch bag) interconnected.

Cycle life, discharge etc are all related to cathode composition , anode quality, electrolytic composition and general construction quality. I see no specific function of the packaging in determining any of that . for example cylindric 18650 format cells exhibit about 1800-2000 W/kg and 4400 W/L of energy storage density , while prismatic pouches typically provide about 2400-2800 W/Kg and about 4700 W/L of energy density, not a huge difference.

Studies have shown that an addition of small amounts of silver or copper to the cathode can have a significant effect on cycle life, equally research has been undertaken thats shows modifications in the composition of the electrolyte can aid cycle life , for example adding vinylene carbonate to the electrolyte has shown that cycle life is improved for batteries operating at high ambients( circa 55 degrees C) , research has shown that adding Titantium to the cathode, can improve cycle life at higher C rates , its a trade off of price, performance and target product market segmentation.

Pouches of course have a significant factor in that they can be made in quite large cell sizes with 20Ah being common and pouches available upto 40Ah, wheres the form factor of small cylindric cells limits typical outputs to 800 to 1500 mAh, hence requiring more external interconnects to achieve higher densities


Dave
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Old 20-12-2013, 05:30   #3356
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

I should point out that there are a number of prismatic formats about as well, include stacked or "jelly" wound electrodes. Since Ive not cut open a Winston cell !!!, going in pictures it seems to be parallel prismatic pouches of some type.

for those of you that would like more technical but understandable information Ive found Sonys manual on this technology always useful ( note its aimed at LiCo/Mn cells but most applies to LiFe)

http://www.sony.com.cn/products/ed/battery/download.pdf



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Old 20-12-2013, 06:05   #3357
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Quote:
would you use testing information gained when using cylindrical cells that are known to give a high discharge rate for short periods yet have little capacity, to determine the suitability of all types of lithium ferrous batteries for house power supply use?

Just to deal with this question, The answer is yes and no. The characterisation of low capacity cells , i.e. 800 to 1500mAh, is not particularly different to large pouch or prismatic cells. I also now have a couple of large Ah pouches and these seem no different.

This is what I was saying before , actually characterising a big prismatic cell, is quite hard because of the energies involved , no more then doing so with a large Li pouch. However nothing suggests that the underlying performance of the Li chemistry is any different based on the construction methodologies deployed. Therefore its as valid as anything method.

What I can do is stress a 18650 cell much easier and safer then I can a 40Ah prismatic . Thats not to say the results are a "carbon copy" , but I don't see any evidence that there is any difference, other then due to slight variations in Cathode, anode, electrolyte composition and general material and build quality. This variation exists across all types of Li cell constructions. So I will see variability in 18650 cells , both across the ( supposedly ) same composition but different quality ( and tech claims) and across the variants of Li cathode chemistry.


SO that confusions suggest the results scale without significant divergence, stressing a 1000mAh cell , is similar to stressing a 100Ah set of cells. ( except in one there a bit of warping, in the other I could melt the desk.)

It would be nice to have the money and a protected lab !! to engage in full scale characterisation of large format cells, ( and thereis some research on this ) . But I see nothing to suggest that Large prismatics are in any way substantively different ( in electrical characteristics) from any other form of construction.


This was part of my "fairy dust" comment, somehow, people seem to think that say a winston, CALB, Sinoply battery in Lifepo4 is some different animal to other LI-ion, including even that it is different to say a 18650format Lifepo4. while there are documented differences where the cathode material is modified, I see no documentation to suggest there is any noticeable difference due to physical construction. There is of course some minor changes due to differences in heat dissipation. internal impedance due to physical routing etc, , ion transport due to layout and size , etc, but nothing to change the characteristsations enough to bother .


An lifepo4 cell is just that , irrespective of construction.
Dave
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Old 20-12-2013, 06:09   #3358
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

Dave,
Prismatic cells do not have cylindrical cells inside. I think it's time you cut open a cylindrical cell and a prismatic cell so you can see just how different their construction is, they are worlds apart in their construction method and plating thickness (not the carrier plates, the actual active material coated on the plates)and information relating to one type does not cross over to the other, they are each designed and built for a different purpose.
Just like lead acid starting batteries and flooded deep cycle batteries, the same components in their make up, but they are not the same and are not suitable for swapping from one type of service to the other.
I too am an engineer, but an Automotive Mechanical Engineer, so my training and experience is all hands on so it required actually spending a large amount of my own money to sort fact from fiction, what related to what type of cell construction and what didn't relate to LiFeP04 at all.
There is an enormous amount of information on the web, unfortunately a lot of it is the result of people jumping to conclusions or interpreting results to verify some idea that they had before they started the test. Results are too easily twisted if the correct mind set is not adopted before the testing begins. All to often an answer is followed by a test to prove it, not the other way around.

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Old 20-12-2013, 06:34   #3359
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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Dave,
Prismatic cells do not have cylindrical cells inside. I think it's time you cut open a cylindrical cell and a prismatic cell so you can see just how different their construction is, they are worlds apart in their construction method and plating thickness (not the carrier plates, the actual active material coated on the plates)and information relating to one type does not cross over to the other, they are each designed and built for a different purpose.


I never said prismatics were composed of cylindric cells. I said "Large format batteries are simply repackaged "pouch or prismatic" Li cells. compared with cylindric cells"

ie prismatic cells are a derivative of pouch cells,


Quote:
he actual active material coated on the plates)and information relating to one type does not cross over to the other, they are each designed and built for a different purpose.

explain to me the difference, there is a fundamental mis-understanding in your comparison as you use LA terminology in the context of LI,

so explain what you mean " by they are worlds apart in their construction method and plating thickness (not the carrier plates, the actual active material coated on the plates)"

just what plates do you mean. are you talking about the cathode, anode, separator, electrolyte (aqueous or non aqueous)

How large prismatics in LI are put together is very fundamentally different from large La cells, because of manufacturing issues and the need to physically have the Cathode and anode separated by tiny distances, Most prismatics are in essence a series of parallel cells.

While there are obviously differences between small cylindric cells and larger pouches, no more then there are differences between a 10Ah LA cell and a 100 Ah LA cell ( note cell not battery), But it is wrong to takes specific issues like plate thickness which derive from LA thinking and translate it directly into Li. The fundamental chemical reaction is totally totally different.

For example ion diffusion time is a big factor in Li conductivity, hence instantaneous current response. So to make a good Li cell that does not sag, cathode and to some extent electrolyte composition play a big part ( because Li diffusion is slow) , intercalation ( lithiation) of the graphite anode is comparatively fast but very very temperature dependant.


Hence building the equivalent of a "deep cycle" LI battery which in itself is a nonsense term when applied to Li, concerns completely different compromises then in a LA battery


I am beginning to see that you seem to equate LI technology to perhaps a more familiar LA technology , Nothing could be father from the truth. there is no comparison , primarily because Li technology simply doesn't create or store electricity in the same way.

Quote:
Just like lead acid starting batteries and flooded deep cycle batteries, the same components in their make up, but they are not the same and are not suitable for swapping from one type of service to the other.
Utter rubbish when applied to Li, we have deep cycle and starter batteries ( which are really only visions of the same thing) however Li is easily capable of doing both due to the fundamental differences in chemistry. Other factors are much more important in Li ( when looking at starting for example), cold temperature response, ( again a function of Li anode make-up) , not LA factors like plate thickness , or more correctly plate mechanical durability etc.

way way different processes at work in LI Terry way way different issues then come to play

Quote:
There is an enormous amount of information on the web, unfortunately a lot of it is the result of people jumping to conclusions or interpreting results to verify some idea that they had before they started the test.
The only research and information I generally rely on is academic research and high quality commercial information. The rest I take with a grain of salt. I provide you with links to journals like material science. you think this is "twisted results"

You have yet to actually contribute any opposing views, argued scientifically, to any of my statements, and in reality are misreading my posts or critising my English grammar.

Simply charging and discharging cells in the field is not a good set of tests quite frankly

Disagreeing with me , means actually saying what you know, not simply telling me I'm wrong.

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Old 20-12-2013, 07:36   #3360
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Re: LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks

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All to often an answer is followed by a test to prove it, not the other way around.
That process, correctly applied,is a bedrock of scientific research. Testing in the absence of a formulated hypothesis , just results in a confusion of uncorrelated data .

All testing tends to work against an expected reponse, norm to theoretical behaviour

Quote:
Results are too easily twisted if the correct mind set is not adopted
and

Quote:
nterpreting results to verify some idea that they had before they started the test
fine , but stop just saying "things are wrong" outline the examples you mean above.
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