??! Magnetic field on 18650 lithium-ion batteries improves them!?

[Logic11]

I was looking at MHD (Magneto HydroDynamic) drives, so it occurred to me to look at what effect a magnetic field had on batteries.
True as nuts; it improves them!

(Full Paper)

Study on the influence of magnetic field on the performance of lithium-ion batteries:​

"...The charge–discharge performance with imposing magnetic field is better than that without imposing magnetic field. The discharge capacity, charge capacity discharge energy and charge energy increase obviously, and they all increase with magnetic induction intensity...

https://www.sciencedirect.com/science/article/pii/S2352484722003420

So basically + N; - S to improves them.
I have no practical idea how strong an X Tesla field is or how big and heavy a magnet/s is required to get a noticeable effect but doubt lugging a magnet and cell sandwich around is worth it?
Perhaps thin coin shaped magnets of the right diameter is a great way to stick all those button cells together in a series cylinder..?

This may help for charging and stationary batteries however?
Perhaps simply aligning your charging pack with the earths magnetic field will help a smidge? Cant hurt.

Or; align your bike's cells horizontally and only ever ride North. Don't come back!

 

[Diggs]

My induction heater (strong magnetic field) would fit an 18650 perfectly but I'm assuming that's not what they meant.... chuckles..

(It does make me want to do a field experiment though.)

 

[Logic11]

I took a closer look at this:

"...discharge capacity is found to be 2.46 Ah when the battery is not placed in the magnetic field...
When the magnetic induction intensity increases to 39.50 mT, the discharge capacity is 2.89 Ah, which increases by 17.48%..."

I assume mT is micro Tesla (1000 mT per T)
These 18mm diameter (same as 18650 batteries) are 234 mT!

18mm x 3mm 45/64in x 1/8in N52 Discs Rare Earth Neodymium Magnet 18x3mm

Pull Force: 10.71 LBDimensions: 18mm diameter x 3mm thickness, (0.709in x 0.118in) approx. 45/64in x 1/8inMaterial Features: Neodymium (chemical symbol Nd) is element 60 on the periodic table. It is a rare earth metal and forms one of the Lanthanides series. When added to Ir

jc-magnetics.com

Cell weight = 45g
Magnet (x2) weight =20.4g
So 45% weight increase for ???% capacity increase at 234mT?

So this is more interesting than I thought! How often is it easy to get a 17% improvement nowadays!?
They talk of an increase in both power and energy density.
It looks worthwhile for stationary charging and constant speed vehicles?
Maybe even during acceleration..?

 

[scianiac]

I also did some math when I saw this but I think you got some things wrong there, mT should be millitesla not micro that would be uT. And that is the field strength inside the whole cell, the magnet strength listed on magnets is the surface strength so once you put some either side of a cell the field is vastly weaker. Using some 3/4in by 1/16 in neo magnets from KJ magnetics I found one on either side of the cell would make an average field in the cell of 137uT and far weaker in the middle, so nowhere even near the strength used in the paper. That did not factor in how the construction of the battery would effect things but it may make it worse or better idk but probably enough to get where we need to be. So that seems to indicate the magnets would need to be quite large.

I considered maybe using lots of smaller magnets inbetween the cells but kinda hard to fight the inverse sqaure law.

 

[Logic11]

I also did some math when I saw this but I think you got some things wrong there, mT should be millitesla not micro that would be uT. And that is the field strength inside the whole cell, the magnet strength listed on magnets is the surface strength so once you put some either side of a cell the field is vastly weaker. Using some 3/4in by 1/16 in neo magnets from KJ magnetics I found one on either side of the cell would make an average field in the cell of 137uT and far weaker in the middle, so nowhere even near the strength used in the paper. That did not factor in how the construction of the battery would effect things but it may make it worse or better idk but probably enough to get where we need to be. So that seems to indicate the magnets would need to be quite large.

I considered maybe using lots of smaller magnets inbetween the cells but kinda hard to fight the inverse sqaure law.

Thx scianiac

Umm...
m is milli. 1000 milli T (mT) in 1 Tesla (in this case)
u is micro. 1 000 000 micro T (uT) in 1Tesla

Metric (SI) Prefixes

As of August 16, 2023 the physics.nist.gov historic SI Units site has permanently retired.

www.nist.gov

And 10 000 Gauss per Tesla
So 2340 Gauss per (linked) magnet = 0.234T = 234mT
My maths is correct as far as I can tell..?

I just had a look and the outer cylinder is A3 Steel.

What’s inside an 18650 cell? And why its important

There has been a boom in ebike builders making their own battery packs out of the popular 18650-format cells (18mm diameter, 65mm long), and I want to share what I’ve found out about the guts…

www.electricbike.com

No info on thickness or what A3 means.

But yes; the field will concentrate in it some and has to be taken into consideration.
Also the para? or dia? magnetic copper aluminum graphite 'jelly role'.
So ye; the maths would get pretty complicated and likely go well over my head.

I would say testing a cell with 2 off the shelf magnets to see if there was a measurable difference would be more productive.
Did you perhaps do any?

 

[scianiac]

Yes your math is correct, I just pointed out the units because later in the post I used the correct units and then my numbers would be confusing. The real issue is that magnets are rated as surface field strength so even a few mm away the strength has decreased greatly at the inverse square law. But yeah you can see why I stopped at a rough approximation and didn't try and estimate how the metal can, and cell internals would effect things.

I was actually thinking about doing a test, might do that if I have some time.

 

[belllfador]

In this case para and dia are not for consideration. Only the steel can will disturb a bit the magnetic field. Using FEA I manage to calculate what will be field density inside of the 18650 cell:


And if we put NdFe magnets D20 H10 mm:


Personally I don't believe in significant M field influence, but probably will use my 20x20 magnet in the next capacity check.