Higher energy LiPo pouch cells

[jonescg]

Hi All,

As many of you know I have been building some pretty impressive battery packs using the single cells from Herewin. This company supplies HobbyKing with LiPo cells. My preferred cell for most jobs is the 40C, 5000 mAh cell. The 40 C rating is more like 20 C, and it seems to handle 20 C okay for short bursts.

On paper, the energy density of the 40C LiPo cell is about 145 Wh/kg. The 6 kWh race pack is perfect for our race format, and as a constructed pack complete with BMS, contactors and fuses, it checks in at 53 kg (43 of which is battery). Rather than try for an even lighter battery, I want more kWh for the same mass, offering less heating and more laps.

So I have been shopping around for small format LiPo cells which offer high energy density and acceptable discharge rates. Anything over 170 Wh/kg is a good start, but the C rates are usually rated at 10 C continuous, 15 C burst.

I found these guys:
http://www.firstenergypower.com/product/showproduct.php?lang=en&id=36 (176 Wh/kg)
And they look promising, as do these cells:
http://www.firstenergypower.com/product/showproduct.php?lang=en&id=40 (190 Wh/kg)
which offer even higher energy density. A 1p pack made from 12 Ah cells could be interesting...

A 175 Wh/kg pack would mean I can have 9 kWh for 65 kg. Like our big battery, the weight is going to be much higher up, so it won't handle as nice as the smaller pack.

So has anyone found a ~50 mm wide, ~9 mm thick and ~135 mm long LiPo cell offering high energy density? I would be demanding peaks of 220 A from the pack at full noise.

 

[riba2233]

If you are ok with 10c continuous and 15C burst, have you considered some high power 18650 cells like samsung 25r or lg he2? They are vastly safer and have even higher energy density, 211 wh/kg nominal.. They are also more reliable and will probably last longer.

 

[Hillhater]

Whilst the 18650 would definitely give You a higher capacity pack (9+ kWhr) for a similar weight (~50kg) , it would mean a complete redesign of your pack construction.
You would even have to do a detail assessment to confirm if an 18650 pack would even physically fit in the available pack space.
Conversely , I suspect you have limited your cell choice options with the pack being so closely designed around a very specific cell size !
I'm sure you are well aware of the un reliability of supplier specs for things like C rate.
The "high capacity" (10,& 16 Ahr ) LiPo pouches quoted at 10C are in reality more like 2-4C before they start to heat up.

 

[jonescg]

Well aware of the inflated C-rates, have no fear. I can set the controller to limit the drain on the pack to 200 A if I need to, but just looking for a cell to give me a few extra laps.

18650 cells would never give me the 10C+ rate I need. Not even the best ones. And the only way I could achieve that is with about 27 in parallel - back to where I started with a big heavy pack :lol:

I can make any cell fit, but with compromises. So far the 40C cell has been a real trooper, but a few more Wh/kg would be great. On paper, the 20C 5000 mAh cells (10 mm thick, 42 mm wide and 125 mm long) offer 165 Wh/kg, but because they sag more, you actually get less range than had the pack been built from 40C cells.

 

[liveforphysics]

Well aware of the inflated C-rates, have no fear. I can set the controller to limit the drain on the pack to 200 A if I need to, but just looking for a cell to give me a few extra laps.

18650 cells would never give me the 10C+ rate I need. Not even the best ones. And the only way I could achieve that is with about 27 in parallel - back to where I started with a big heavy pack :lol:

I can make any cell fit, but with compromises. So far the 40C cell has been a real trooper, but a few more Wh/kg would be great. On paper, the 20C 5000 mAh cells (10 mm thick, 42 mm wide and 125 mm long) offer 165 Wh/kg, but because they sag more, you actually get less range than had the pack been built from 40C cells.

There is one cell that might, the VTC5 is pretty amazing, almost like an RC LiPo cell rolled up and stuffed in a can.

 

[Hillhater]

18650 cells would never give me the 10C+ rate I need. Not even the best ones. And the only way I could achieve that is with about 27 in parallel - back to where I started with a big heavy pack :lol:

Sony spec sheets are hard to find, but the Samsung 25R is a good "runner up" example.
20 amps continuous, 100 amp pulse.
Sag is certainly an issue, ...3.18 v average at 10C discharge,....it just depends how it compares to your LiPo .
http://www.endless-sphere.com/forums/download/file.php?id=130053
Theoretically a 6P (15Ahr) pack could give 150a continuous and 200+ A for short periods
The Sonys are reportedly better still.

 

[pm_dawn]

What about the EIG C020 cells.
Might not have all the power you need, but they come in at 174wh/kg and can do 5c cont and 10c burst (10s)

http://www.eigbattery.com/_eng/designer/skin/02/01_03.asp

here is the data sheet.

View attachment C020.pdf



Regards
/Per

 

[riba2233]

What about the EIG C020 cells.
Might not have all the power you need, but they come in at 174wh/kg and can do 5c cont and 10c burst (10s)

http://www.eigbattery.com/_eng/designer/skin/02/01_03.asp

here is the data sheet.





Regards
/Per

Why, they are even worse then 18650 mentioned in both energy density, power, and cost.


jonescg - you are obviously not aware of potentials of new generation high power 18650 cells, that's too bad. 6p or 8p pack would be enough for your needs, just like hillhater pointed out.

 

[jonescg]

True - I've not been paying much attention to the development of 18650 cells, and I'm sure there's some winners out there. I have about 23 litres to play with. The big pack allows for about 33 litres, but again, it's putting the weight up high where it starts to interfere with hard braking.

The battery dimensions I am working with is four blocks of 100 mm by 155 mm by 380 mm for the 6 kWh pack, and 100 mm by 155 mm by 570 mm for the big pack. The latter being a huge volume for impressive cells, but results in a much higher CoG.

So given this, I can fit a princely total of 295 cells per 175 V (max) block for the big pack (7 in parallel) or 210 cells per block for the small pack (5 in parallel). This gives me a capacity of 10 kWh for the big pack dimensions, and 51 kg worth of cells, or 7.4 kWh and 36 kg worth of cells. As to how these go together and are kept cool is another story, but they're the numbers I'm working with.

I don't fancy spotwelding all these cells, but it's an option at least.

 

[jonescg]

There is one cell that might, the VTC5 is pretty amazing, almost like an RC LiPo cell rolled up and stuffed in a can.

Looks impressive! Shame about the price though - a 7 kWh pack would cost about $25,000

 

[Nuts&Volts]

No idea if these cells actually deliver, but they have great specs. Otherwise I would go with VTC5 cells
http://www.gebattery.com.cn/product/batteryoperatedracingcar.html

 

[liveforphysics]

There is one cell that might, the VTC5 is pretty amazing, almost like an RC LiPo cell rolled up and stuffed in a can.

Looks impressive! Shame about the price though - a 7 kWh pack would cost about $25,000

Ehh, they are sub $0.50/Wh from a good vendor.

 

[cwah]

There is one cell that might, the VTC5 is pretty amazing, almost like an RC LiPo cell rolled up and stuffed in a can.

Looks impressive! Shame about the price though - a 7 kWh pack would cost about $25,000

Ehh, they are sub $0.50/Wh from a good vendor.

Can you help us on seller of authentic one at this price?

 

[riba2233]

VTC5 is currently unavailable, and I think it will be until February. But samsung 25R and lg he2 will also do the job!

 

[liveforphysics]

Can you help us on seller of authentic one at this price?

I personally just request samples from manufactures for cells. If I was going to try to buy them though, I would maybe ask the guy who was selling them in our for sales section. They are well below $1/Wh new from homedepot in Makita packs IIRC.

 

[voicecoils]

True - I've not been paying much attention to the development of 18650 cells, and I'm sure there's some winners out there.
...
I don't fancy spotwelding all these cells, but it's an option at least.

The VTC5 was the 18650 we talked about when you were in Sydney. See the attachment. Would be nice to get a few samples to test for yourself to get beyond the spec sheet.

As for pack building, you could have paralleled groups spotwelded locally into '1S bricks' and then build the pack up from there yourself.

 

[jonescg]

Thanks Abraham,

Yeah, if it's not the C-rate it's the form factor. I'm going through the 6 kWh pack balancing it right now - first time in it's life it's been balanced. It's all still remarkably close. These 40C cells really are pretty good for the money. It's just a shame that cells are like eggs - there's only one egg or two, never one and a half.

 

[TheBeastie]

True - I've not been paying much attention to the development of 18650 cells, and I'm sure there's some winners out there.
...
I don't fancy spotwelding all these cells, but it's an option at least.

The VTC5 was the 18650 we talked about when you were in Sydney. See the attachment. Would be nice to get a few samples to test for yourself to get beyond the spec sheet.

As for pack building, you could have paralleled groups spotwelded locally into '1S bricks' and then build the pack up from there yourself.

Good pdf doc info there. Interesting how a lot of these new 18650s are being tested with cut off down to 2.5volts, this is unheard of voltage levels in lipo cells.
I built a pack with Samsungs 29E which I am happy with but thats because I dont need heavy discharge.
I recon the best bang for buck in terms of good C rate and capacity is the Samsung 25R, as far as I know the VTC5 has been going up in price since its release because all the nicotine addicted vaper-modders are going crazy for them like a horde of zombies after fresh meat.

As far as I can tell the 25R is just as good and almost half the price.
I am now secretly looking forward to Teslas new 22700 cell standard as it doesn't appear the big reputable 18650 cell makers like Samsung,Sony,Panasonic don't seem going down the 26650 path. I can imagine them copying Teslas 22700 cell size.

 

[liveforphysics]

I am now secretly looking forward to Teslas new 22700 cell standard as it doesn't appear the big reputable 18650 cell makers like Samsung,Sony,Panasonic don't seem going down the 26650 path. I can imagine them copying Teslas 22700 cell size.

Going just 2mm larger radius and 5mm longer could only be for one reason, to package substantially more energy in the existing battery pack size/volume so things remain backwards compatible with everything.

 

[flathill]

That would be brillant if true and I have been thinking along the same lines after reading their patents. All the spacing they currently use for the liquid tempetrue cooling tubing could be used if they only cooled one end of the cell with enought room left over for safety. New Tesla patents show they might move both the negative and postive terminals to one side of the can and mount the other side of the can to a giant temp controlled baseplate. Direct thermal contact. The busbar could also be cooled/heated. I think the new gigafactory cell is just going to be NCA cells with a silicone anode so maybe around 6ah

18650 volume 16530 mm^3
22700 volume 26600 mm^3
So 1.6x more volume

We know current si anode 18650 cells are hitting 4ah
So 4 time 1.6 is 6.4ah
lets call it 6 to be conservative
The current model s cell is 3.3 ah
6/3.3 is 1.8
1.8 times 85kwh pack = 153kwh pack for next gen model s

This means the top of the line second gen model s pack with gigafactory cells will have around 540 miles of range at 65mph. The second gen model s chassis itself will be much lighter so the added weight of a larger and heavier pack will be a wash. First gen model s cars will be able to be upgraded with the second gen pack. The second gen battery case will also be lighter so in the end the extra pounds (raw cell mass) wont be a big deal

Once solid states cells come out that elimate the fire risk a third gen pack could be built in the same size battery case. This would need zero cell spacing. This means we are going to see TODAYS Model S vehicles upgraded with more than 1000 miles of range at 65mph but it would be heavy. Normal cars will still have lighter/smaller packs for better performance. You only swap in a 1000 mile pack for road trips

Did you see the quick swap station is open right now in beta? Takes 3 min now with the new shields but they are confident they can get it down to under a minute

 

[crossbreak]

175V and 200A sound like 35kW to me? At 10kWh that is 3.5C. Think the Samsung INR 25R will do a good job. IMO 5C is the most one should do to this cell in a larger pack where cooling becomes an issue

 

[Hillhater]

175 volt ?
Where did you get that from ?
....Jonescg runs a slightly higher voltage than that ! :wink:

 

[jonescg]

175 volt ?
Where did you get that from ?
....Jonescg runs a slightly higher voltage than that ! :wink:

Each quarter of my pack is 175 V max I'd build them as modules of 42s5p if using 18650s.

In any case, I have a large volume to work with, so any cell can be made to fit. It's just a matter of positioning that weight where I want it.

 

[jonescg]

No idea if these cells actually deliver, but they have great specs. Otherwise I would go with VTC5 cells
http://www.gebattery.com.cn/product/batteryoperatedracingcar.html

They do look good Kyle! No mention of C-rates though. Hope to know more soon.

 

[Rodney64]

If you like ill drop my pack off and you can have a look at how its built Chris.