Kokam batteries

Post by **photomac** » Thu, 11 Feb 2010, 02:13

To rival A123 batteries there's the Kokam (now Dow-Kokam) nano lithium batteries offering a 36kWH bank recharge in 7mins. These appear to be the supplier for Energetique's evMe.
Currently their web site
http://www.kokam.com/english/product/battery_main.html
shows 70Ahand 100Ah forms - but I do not think they are nano tech.

ProEV's Subaru Impreza used Kokam to beat petrol heads - shoulder to shoulder - in a circuit race.

100Ah Cells   Ah/litre   Ah/kg | Height   Width   Depth | Weight
Thundersky     46       31.25 |   220      145     68 mm | 3.2kg
      Kokam       83          37   |   455      325     8.1mm | 2.7kg

Anybody had experience with the 70Ah or 100Ah - Supplier in Oz? Pricing?

Post by **lithbattboss** » Thu, 11 Feb 2010, 02:29

I think you will find they are Lithium Polymer and a potential fire hazard.
I saw one of the cells at a presentation night where Phil Coop from Energetique (evMe) brought one for display.
I questioned him about the safety of the cell and he was clearly not willing to confirm they are as safe as LiFePO4 such as A123 etc. In fact he seemed decidedly uncomfortable when I brought the subject up.

I don't doubt that they are a high performance cell being Li-Po. I only doubt their safety and thus whether they are suitable for use in an EV.

If you can find a detailed data sheet for the cells please let me know. I would be very interested to see the specifications.

Post by **Gow864** » Thu, 11 Feb 2010, 03:36

Here's their catalog. Here

Post by **zeva** » Thu, 11 Feb 2010, 03:52

Hard to beat LiPos for energy density, but I share lithbattboss's reservations about using them in EVs due to the somewhat unstable nature of Lithium Cobalt chemistry! LiFePO4 chemistry is much more robust.

As for pricing, I looked into Kokams some time ago and found them to be literally several times more expensive than ThunderSky (per amp-hour), which pretty much prices them out of the market except for racing applications, in my estimation.

Post by **lithbattboss** » Thu, 11 Feb 2010, 04:25

I agree with Zeva's comments entirely. Great energy density but at the expense of safety it is just not worth it.

I will have a look at the catalog in more detail shortly but a quick look shows that the Kokam cells are definitely more hazardous than LiFePO4. There is certainly none of the shipping approval information (IATA transport information is a good guide to safety) I was hoping to see as with LiFePO4 cells.

Post by **cell_man** » Thu, 11 Feb 2010, 12:01

I believe they are rated 5C constant and 10C peak. Those figures above don't account for the higher voltage compared to LiFePO4 so the power density cannot be compared by just the Ah. Any idea of their cost? Would be interesting to know. They seem to have been the cell to use in race EV. The Agni bike uses them as do most of the race EVs AFAIK, for now

Post by **Tritium_James** » Thu, 11 Feb 2010, 13:21

They're about twice the price of TS cells per Wh, and just slightly more per Wh than the LiFeTech cells...

But *much* lower internal impedance than TS, so an equivalent capacity pack can put out 2 or 3 times the power. Their other downside is lower cycle life, it's around 1000-1500 cycles, so under half the LiFePO4 chemistries.

Post by **photomac** » Tue, 16 Feb 2010, 02:20

Thanks all!
Sufficient caution there. I missed the detail of them being the cobalt form. Not nano? It's looking like TS or SE then based on reputation and specs and value. Just noticed a 'Headway' brand thread too.

Post by **Johny** » Tue, 16 Feb 2010, 14:34

I'm doing a car load of Headways. About a 12kW/hr pack in all. It should be on the road in the next few months so we'll see how they shape up.

Post by **hipo_ev** » Mon, 22 Feb 2010, 20:53

It might pay to wait a little bit before purchasing your headways. I just read a post on the EVDL mailing list showing rusted Headway cells. Basically the end of each cell has rusted after being stored.

His blog is HERE if you want to have a read.

Post by **Johny** » Mon, 22 Feb 2010, 21:32

Too late - I already have them. They are stored in air-conditioned comfort here at work. I'll take the point though. As I have to open every pack I will investigate the pro-cons of securing some silica gel pouches in the almost-sealed packs. Since mine will be in almost constant use as soon as they are installed in the vehicle I am hopeful that I won't have any rust issues. Checking with a magnet and my eyes, I surmise that the positive terminal is chrome plated steel.

Like my old car, chrome rusts pretty easily but there are safeguards you can apply.

Of more concern is that I did the same magnet trick on the connection plates in the pack. They are also very magnetic - steel again. Not sure what they are coated with...

Post by **hipo_ev** » Mon, 22 Feb 2010, 22:02

Might be worth spraying each end with CRC battery terminal protector or similar product (vaso at a min) just to be safe

Post by **Johny** » Mon, 22 Feb 2010, 22:25

I agree. I've taken the top and bottom off one of my packs and there is no sign yet. Over the years I have pretty much written off CRC and WD40 as requiring too many repetitions to be that useful. I'll look at a spray wax I think. If you can seal out the humidity they should be OK. Also, his packs looked like they were wrapped, not in a case. Mine are in an ABS case that will not be at all hard to make totally water proof. A couple of pouches of silica gel per pack and the heat of the BMS each night may well make this a non-event when they are in real use.
Disturbing nonetheless. Thanks for the heads up.

Post by **lithbattboss** » Tue, 23 Feb 2010, 00:53

Johny wrote: Over the years I have pretty much written off CRC and WD40 as requiring too many repetitions to be that useful. I'll look at a spray wax I think. If you can seal out the humidity they should be OK.

CRC, WD40 and similar lubricant sprays are a waste of time since they dry out after a short time and all their corosion properties are then lost.

The best (proper) stuff to use on battery terminals to provide long term protection from rust/corrosion is a special silicone manufactured by Dow Corning. This is Dow Corning 4 which is the consistency of a thin grease. I have used it for many years during my time in both the aerospace and UPS industries. It is what we use to prevent corrosion on battery terminals which are subjected to harsh environments such as extremely high humidity. It is a high grade electrical insulating grease
which is made in the USA and conforms to military specification MIL-S-8660B

It is quite expensive and I have several large tubs of it (more than I will need in a lifetime). I would be happy to provide anyone who needs only a small amount at the bargain price of only $5 per 100gms plus postage. You would need to put it in your own jar or container since I would send it in a plastic clip lock bag.
PM me if anyone wants some-

Info is here-
http://www.ellsworth.com/display/produc ... ab=vendors

Post by **Squiggles** » Tue, 23 Feb 2010, 01:44

You will find that lanolin based products do a very good job at corrosion prevention as well. If you look around you might even find an Australian made brand...now there is a novel idea!

Post by **Johny** » Tue, 23 Feb 2010, 02:31

hipo_ev wrote: Might be worth spraying each end with CRC battery terminal protector or similar product (vaso at a min) just to be safe

I just read your post again more carefully - not just CRC. I like the sound of what I read about it and to be useful it really has to be spray can as I have so many to do. Thanks again hipo.