How To Repair Broken LiFePO4 Battery Cell Terminal

[ThermallyFrigid]

I have a 16 cell, 50v LiFePO4 battery pack and one of the tabs broke off yesterday. It is the Positive Pack Tab on number 1 cell.
The Tab itself is aluminum so I cannot solder to it.

What they did at the factory was took a small piece of what looks like copper/Nickel/tim sheet metal (.3mm) and wrapped it around the tab and then clamped it down tight so it would make good contact and have good conductivity and allow soldering the wires to it.

I have ordered a piece of 65% Copper/19%Nickel/17%Tin sheet metal that is .4mm thick and planned to wrap it around the remaining 1/4 inch of protruding battery tab then clamp it as tight as I can with vice grips and hope for the best.

In not sure but the factory may have used some kind of micro spot welds to hold the fold over piece onto the aluminum tab.  Not sure.

Has anyone ever had to do this and can recommend a "best" way to repair this tab?

Thanks

[thm_w]

Its possible to solder to aluminum with the right flux or prep. The crimping method may work but how much current are we talking about here?

I would assume the original tab was spot welded or soldered. Isn't that solder shown in your photo?

https://forum.allaboutcircuits.com/threads/3-7v-li-ion-battery-tabs-can-thin-aluminum-or-copper-be-used-with-spot-welding.147160/
https://hackaday.com/2022/03/06/how-to-solder-to-aluminum-easily/

[ThermallyFrigid]

This was very helpful.  Thanks.

Here is a photo of the broken off tab for anyone interested.
It appears to have been spot welded with a special spot welder and that makes sense because it is on a 50v battery that can transfer up to 100Amps and a soldered connection might let go under load.
Then again, if that tab reached solder melting point during use the cell would probably be in trouble anyway.
I have a spot welder but not one that can do multiple spots at the same time like the factory.   I may try clamping it, then applying one of two spot welds to hold it in place.

I'd bet the type spot welder the factory used to attach this metal clamp on piece to the aluminum tab costs more than a Bugatti.

It's all iffy.  It may be that I have to replace that cell.   $400 battery so that's a shame if I can't get a replacement cell or fix this one.

[ThermallyFrigid]

The damage occurred through normal use.  It is an e-bike battery 20Ah 50v and the tabs on these batteries can endure some vibration and forces during bike riding.  It is out of warranty.

The vice grips were only for compressing the new wrap around steel tab securely to the old tab.
(If you assumed they would be a permanent addition to the battery Not the case I can assure you)

My idea was to use a spot welder to then secure the wrap around steel tab to the aluminum tab.
Great care must be taken not to overheat the cell itself so it is a tricky proposition.
The ideal solution is likely out of reach of consumers and available only to larger battery manufacturing firms.

Another potential solution here is to use a mini screw type copper 1 inch vice clamp that could be tightly screwed onto the existing remaining tab stub.  Then the wires could easily be soldered to that.
That is one of the options I am considering since it's the least risky and permanent as well.  It has two, 3/32 copper/Nickel alloy bars with M3 screws at each end and tightens securely on the tab stub.
Once tightened in place it is as permanent as spot welding and conducts as well as or better than the original tab.

Of course, one also has to always be aware that an arc of considerable amperage is nearby if a mistake is made unless the cell is first removed from the pack.

That leaves one to be very creative or replace the cell.....or buy an entirely new battery as mentioned previously.

[abdulbadii]

buying, using induction heat solderer should be worth it
as it'll be useful, being used repetitively in most metal repairing works
though not sure if Aluminum is applicable on induction heat

[abdulbadii]

If your goal is to melt and light the battery on fire, sure. They are way too slow for this task.

elaborate a proving argument ?

[Nusa]

The original battery tab was likely ultrasonic welded, not spot welded. It's a cheap process in manufacturing, but the equipment is too expensive for most individuals.

[abdulbadii]

If your goal is to melt and light the battery on fire, sure. They are way too slow for this task.

elaborate a proving argument ?

Inductive heating happens over seconds. Spot welding happens over milliseconds.

a proving argument ?

said 'battery on fire'
what it has something with: inductive heating happens over seconds

[ThermallyFrigid]

So I was able to repair the tab.

What I did on this one is bought the Aluminum soldering kit suggested by thm_w (THANKS !!)

I cut a 1 inch by 1 inch piece of sheet metal as described earlier (copper, Nickel, Tin)

Then, using the aluminum soldering kit and my soldering experience (quite a bit), I plated the remaining tab from the battery with the aluminum solder.  It did well.
Then I plated the small metal square with the same solder.

Then I sandwiched the tab inside the folded over new metal tab and clamped it tight.

Next I used regular 60/40 solder to wick into the gap and using a high mass soldering iron was able to get the solder to wick into the joint.
Each time I soldered I immediately cooled the tab as to minimize heat getting to the battery itself.

It all seems to be good so far.   Saved a $400 LiFePO4 battery pack.
I was prepared to replace the once cell if necessary.

this particular LiFePO4 50v pack is going in my Dodge Caravan RV to power my EQK 24v 2000btu AC unit

Thanks for the help everyone.
I like Happy Endings.