How to glue a battery pack

[Technological]

I'm building a 20S9P battery pack using 21700 cells for a kick scooter.
It's going to be a high power pack. I'm targeting 400 A current output for the pack. I'll be using pure copper connections between all cells to achieve that.
The cells are going to be Molicel P42A which are cable of 45 amps each, 9 in parallel.
The pack layout is going to be flat 20 x 9 with cells standing vertical.
There is no room for using cell holders in a kick scooter deck so I need to find a different way of holding the pack together.
Considering the high current output the pack should be optimized for thermal management too.
I know that a lot of people are using hot glue for gluing the pack together. I think that it's not a good option for a high power pack. The hot glue is not good at conducting heat at all.

The glue should be thermally conductive to spread heat across neighbor cells to prevent hot spots at high power. It should also facilitate conduction of heat outwards.

I searched through the forum but I didn't find a thread discussing gluing of battery packs.

Please share your experience, thoughts about gluing battery packs!

Do you know any thermally conductive glue which is good for using in battery packs?

 

[fechter]

The best thing is to completely pot the pack with thermally conductive potting compound. There are some topics around that discuss this, but I couldn't make a recommendation. On packs I built, I used silicone RTV. Fairly thermally conductive and can withstand very high temps without failing. Another approach is to use cell holder blocks, but I haven't seen them for 21700 size cells. These also add space between the cells.

At 400A, things could get hot. That's going to be one hell of a kick scooter.

 

[amberwolf]

There are a number of posts and threads that deal with potting batteries, which is what you're probably wanting to do (rather than just applying an adhesive (glue) to the contact-areas of cells).

The search is a bit difficult to get what you want out of ATM, so this link is not as easy to find the specific threads as it could be, but the first hit is the most recent by PaulD on potting compounds intended to help absorb heat to mitigate thermal runaway. Not the same as what you want, but a starting point.

Search results for query: potting* batter*

endless-sphere.com

 

[Tony01]

400 amps on a 37ah molicel pack isn’t going to happen. Those cells might do that on full charge but you’ll find yourself sagging into LVC most of the time. Build it for 30 amps peak or lower your power requirements. I’d be surprised if you can even put that kind of power down with the little scooter tires.

 

[Technological]

I don't think that potting the entire battery pack is a good idea.
I think that having some open gaps between cells would allow for air circulation. It would help to dissipate heat. The adhesive between cells should be appllied only to contacting surfaces without filling all of the gaps.
Thick mass of glue or any other compound in the gaps would have bad thermal conductivity. So it's not worth filling gaps.
I think it's more beneficial to have air circulating and carrying heat away.
The main goals for an adhesive are providing structural integrity of the pack and carrying heat between adjacent cells.

I researched RTV silicones but have yet to find a thermally conductive one.

 

[fechter]

Silicone is inherently a pretty good thermal conductor. They make heat sink insulators out of it. In a very thin film, the thermal resistance will be quite low. Unless you have a fan or some way to circulate the air, the air gaps between cells won't help much with heat dissipation. Heat can escape the cells from the ends much better than from the sides, so if one end of the cells is glued to the case, the heat has somewhere to go.

 

[PaPaSteve]

Thermally Conductive - Epoxies Etc.

epoxies.com

 

[goatman]

you can try some vhb tape
Vortecks uses it in his builds

 

[Technological]

I just want to share my research on thermally conductive adhesives for gluing battery packs.

DOWSIL™ TC-2030 Adhesive, DOWSIL™ TC-2035 Adhesive - Silicone adhesive delivering superior thermal management for standard and advanced automotive PCB system modules
DOWSIL™ TC-4605 - Thermally Conductive Encapsulant (Silicone Elastomer)

LOCTITE® EA 9497™ is a medium viscosity, two component, room temperature curing epoxy adhisive

I ended up using Loctite. It is a very good strong epoxy. It bonds very well to battery cells. I totally recommend it.

 

[Chalo]

Putting a battery pack makes it disposable/unrepairable. Of course in this case, it's apparently for a 30hp disposable kick scooter for a rider who considers himself disposable as well.

I've repaired and repurposed enough packs and modules that I think turning them into irretrievable garbage is a mistake.

 

[nicobie]

Anybody that's building a 30hp kick scooter isn't worried about $.

 

[Technological]

Chalo​

It's possible to disassemble the pack by braking the heatshrink tubes of the battery cells.
New PVC heatshrink tube can be applied to the cells and they can be reused.

Another story is removing spot welds. I tried to brake the welds but the negative terminal of the battery deformed. So I think spot welding battery cells already makes them irretrievable.

 

[harrisonpatm]

Another story is removing spot welds. I tried to brake the welds but the negative terminal of the battery deformed. So I think spot welding battery cells already makes them irretrievable.

Every single one of the 1008 recycled 18650 cells on my house's powerwall was retrieved from a spot welded pack, with little to no deformation. Significantly easier to repurpose than a potted pack.

 

[Chalo]

Anybody that's building a 30hp kick scooter isn't worried about $.

Or about cobalt, nickel, lithium and good stewardship, evidently.

I mean, it doesn't rise to the level of car-driver selfish indifference and gluttony, but there are definitely things we should all be more careful about wasting for specious reasons.

If for whatever reason I wanted to stick cells together, I'd go for hot glue, neutral cure silicone, or VHB tape. Any one of these things could damage the cell wrappers, but doesn't pose the same difficulty in disassembling the pack for repairs or reconfiguration, compared to potting.