Spot Welding Copper Strips to 18650 Battery Cells

Batteries, Chargers, and Battery Management Systems.
TrotterBob   1 W

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Post by TrotterBob » May 08 2021 10:29pm

So what happens to .25mm copper busbars after a few months when the copper starts to corrode? Does it lose any conductivity?

garolittle   1 kW

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Post by garolittle » May 09 2021 2:01am

TrotterBob wrote:
May 08 2021 10:29pm
So what happens to .25mm copper busbars after a few months when the copper starts to corrode? Does it lose any conductivity?
No

john61ct   100 GW

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Post by john61ct » May 09 2021 4:41am

Depends on the environment and degree of exposure.

Tin plating, "tinning" copper is certainly required for long term integrity in coastal areas with salt fog atmospheres

unless the case is very well sealed.

Of course rising resistance may not be a big problem over just a few years, if the conductivity was overkill for that use case anyway.

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ridethelightning   1 MW

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Post by ridethelightning » May 09 2021 5:36am

anyone able to recommend a good source of tin for plating copper?
id like to try it as i suspect it may work better than nickel when it comes to welding

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spinningmagnets   100 GW

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Post by spinningmagnets » May 09 2021 9:03am

The shells of 18650/21700 cells are typically a steel core with nickel-plating for corrosion resistance.

The cathode positive nipple on "some" Tesla 21700's are aluminum with no nickel-plating. Tesla uses ultrasonic vibrations to friction-weld aluminum fuse-wire to the cell.

NullValue   1 µW

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Post by NullValue » May 12 2021 7:24pm

So...I was thinking about the core task to be performed in making the parallel and series connections.

And it's not welding, soldering or any particular technology.

It's making a low resistance, chemically stable, vibration resistant connection by whatever means works.

So I thought of a couple alternatives:

1> Flip it - from what I understand (my welder is due for delivery today) while welding copper to nickel is a challenge, welding nickel to copper is trivial.

So if you're using cell holders, and your arrangement is symmetrical or mostly symmetrical, you could lay out your nickel parallel strips using the empty holders as a template, then lay your copper series strips with a slot or notch cut out, and weld the copper to the nickel.

Once the sheet is welded up, assemble the cells in the holders, flip the sheet and lay it on top and weld through the holes/notches, welding the nickel to the cell tops.

I see no reason this would not work, but it obviously is cumbersome, and potentially increases risk of a mishap when laying down the sheet across a large pack.

2> attach both parallel and series connections with a high conductivity adhesive. Silver is much more conductive than nickel, so a silver based epoxy adhesive would provide strong, low r connections without welding or soldering.

It would actually be better than soldering, as solder is a piss poor conductor (which explains why people get mediocre results from overlaying a bus with solder.)

There are a wide number of such adhesives available.

Downside - they are expensive, and have a limited working time. you would have to be organized so that you don't waste it.
It also has limited shelf life. And you have to be careful what you select. There are formulations that are thermally conductive, but not particularly electrically conductive, which are packaged and sold right alongside the electrically conductive formulations.

https://www.amazon.com/Conductive-Adhes ... AndDetails

3> There is no 3.
Well, there is, but it's still germinating.

I was planning on putting together a 280 cell pack, but batteryhookup now has the spim08hp pouch cells cells broken out so it doesn't add $250 to ship them, so I cancelled my order for 18650's and I'm going pouch cells instead.

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Post by john61ct » May 13 2021 12:43am


NullValue wrote: 3> There is no 3
There are dozens of threads with discussion on all that.

The third option is mechanical pressure, as with magnets, poron foam "springs" etc

For this specific thread only one strategy is on topic.

Start your own thread for general discussion comparing others if you aren't able to find other existing ones to resurrect.

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Post by garolittle » May 13 2021 7:12am

NullValue wrote:
May 12 2021 7:24pm

I was planning on putting together a 280 cell pack, but batteryhookup now has the spim08hp pouch cells cells broken out so it doesn't add $250 to ship them, so I cancelled my order for 18650's and I'm going pouch cells instead.
Advantages of pouch cells … Easier assembly. Disadvantage… Lower energy density than 18650 (usually).

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flippy   100 MW

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Post by flippy » May 13 2021 7:28am

garolittle wrote:
May 13 2021 7:12am
Advantages of pouch cells … Easier assembly. Disadvantage… Lower energy density than 18650 (usually).
and they blow up.

if that is an advantage or not depends on who you ask here, some people actually think that puffing pouches is actually a good thing.... :confused:
The bitterness of low quality remains long after the sweetness of low price is forgotten

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spinningmagnets   100 GW

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Post by spinningmagnets » May 16 2021 11:57am

Discussion of compressing flat pouch cells has been moved to its own thread, found here:

"Compression of pouch cells, info/data"
https://www.endless-sphere.com/forums/v ... 4&t=111797

"Index of flat pouch cell connection methods"
viewtopic.php?f=14&t=111704

BigBlock   10 mW

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Post by BigBlock » Jun 14 2021 10:57am

dont' know if it has been discussed yet, but I found an interesting system that looks to avoid soldering the copper bus bar on the cell

Image

john61ct   100 GW

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Post by john61ct » Jun 14 2021 11:45am

Hopefully using more than just two connection points.

The copper making the cell contact is much more reliable, the nickel just helping with the spotweld process.

Propulsion use cases inflict lots of shock/vibration, you don't want points of higher resistance causing hot spots current bottlenecks

Scottyc   1 µW

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Post by Scottyc » Jun 16 2021 4:17pm

BigBlock wrote:dont' know if it has been discussed yet, but I found an interesting system that looks to avoid soldering the copper bus bar on the cell

Image
Where did you find them?


Sent from my iPhone using Tapatalk

TrotterBob   1 W

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Post by TrotterBob » Jun 16 2021 7:29pm

spinningmagnets wrote:
May 16 2021 11:57am
Discussion of compressing flat pouch cells has been moved to its own thread, found here:

"Compression of pouch cells, info/data"
Spot Welding Copper Strips to 18650 Battery Cells
Getting a 404'ed from that link. Compression of pouch cells, info/data thread here:

viewtopic.php?f=14&t=111797

BigBlock   10 mW

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Re: Spot Welding Copper Strips to 18650 Battery Cells

Post by BigBlock » Jun 17 2021 7:34am

Scottyc wrote:
Jun 16 2021 4:17pm
BigBlock wrote:dont' know if it has been discussed yet, but I found an interesting system that looks to avoid soldering the copper bus bar on the cell

Image
Where did you find them?


Sent from my iPhone using Tapatalk
found the picture on Ali

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