low voltage lithium recovery

I'm surprised large lipo cells aren't made with connections for flushing the cells.
I'm just experimenting a bit, it would be good if new electrolyte was readily available. The problems with moisture getting in the cells though is going to make it unlikely any diy kits will come out, its certainly in the reach of serious diy people to do it though.
 
so I repeated my expt with small 220mah cell, this time I took more pics and a couple of vids.
But firstly heres a couple of pics of cobalt oxide lithium cell which I took off the pouch and wrapped it in cellotape about 3 or more years ago. Theres no reaction with the electrolyte, no signs of gassing. So it appears cellotape is compatible with the electrolytes. It appears that way.

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new test:
cell on the left is the one being used, first I pin pricked the cell to let gas out. The cell had zero voltage.
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Cell has tiny tiny internal circuit board.

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next opening the cell with stanley knife blade without damaging internal structure.
9.jpg

cell after removing circuit board, two tabs shown, one thing I found is its almost impossible to remove the pouch plastic, without ripping off a tab.
View attachment 4

Unwrapping the cell:
black area on left is cobalt oxide lithium layer on aluminium ( or manganese oxide not sure), large split across a fold on the aluminium as i opened the cell, they are very thin foils and get weaknesses along the folds.
Through the plastic membrane on right you can see lithium salt or other chemical buildup between the membrane and the graphite/copper sheet visible through membrane.
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Graphite layer on copper, showing lithium salt build up. Graphite layer was in reasonable condition.
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graphite layer showing salt deposits and also along folds the membrane stuck to the graphite, when unravelled some graphite stuck to the membrane.
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next pic shows membrane separator with graphite stuck along fold lines, and also salt deposits stuck to the membrane ( white powder)
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Next pic shows copper/graphite immersed in water, the salt dissolve very quickly, also the graphite layers delaminate from the copper, in large junks, so have to assume the binder used in the graphite in these cells is water soluble. That might lead a problem using water to rejuvenate cells, if the binder used is water soluble the graphite just delaminates, I'm hoping that other cells will use different binders that aren't affected by water.
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a couple of videos:
first one shows copper/graphite being immersed in water, there is gassing reaction occurs (hydrogen), and lithium salts dissolve within a short time.
View attachment P1090454(2).mp4

next vid is just a few seconds after video above, shows the graphite delaminating.
View attachment P1090455.mp4

next video shows membrane being immersed in water, no apparent reaction, its hard to see if any gas produced due to white colour of the membrane, but I couldn't see any. So appears most of the electrolyte is absorbed onto the graphite on copper.
View attachment P1090455.mp4

last video shows the aluminium with coating of cobalt or manganese oxide, there is no reaction and no delaminating. Remains in good condition when immersed in water.
View attachment P1090457.mp4

I would think that rejuvenating a cell it would be preferable not to dismantle the layers of the cell, since the graphite layer is so delicate and easily damaged. Unless its possible to put a new layer of graphite on the copper, there are graphite spray cans that might be suitable, would take alot of experimenting to find out if they work ( i.e. are compatible with electrolytes).
Another issue I"ll can try to solve is to try a different brand cell and see if water causes the graphite to delaminate.
 
Just a couple of bits of info from some reading:
there is an sei layer on both the anode and cathode,
some lipo4 put a very thin layer of carbon on the cathode ( lipo4 layer) to increase conductivity,
the sei layer is extremely thin somewhere in the region of 5 to 20nm,
its made of a mixture of substances that are well documented,
there is some research into using lasers to remove the sei layer in order to reuse the cells ( some good results).

What use this info?
1. you dont want to damage the thin carbon layer on the cathode in lipo4 ( not refering to the thick graphite layer on the anode here)
2. instead of using lasers would simply leaving out the in sun provide enough energy to remove sei layer components?
From reading on the use of lasers it appears to be a very precise science to get correct energy to remove sei layer.

From the cells I've opened up, I think dismantling the cell will disturb the graphite on copper anode, and wont be re-useable, so need to leave the cells intact if thinking of some rejuvenation technique. Though the cathode aluminium side and its metal oxide/po4 layer seems to be very stable and more likely to be undamaged if cell taken apart, so that foil is probably reusable.

But on the positive side, it seems removal of the sei layer and its components is the key to cell rejuvenation. That layer is extremely thin.
 
no there is no SEI on the cathodic material. as i explained before the SEI is grown on the surface of the anode in order to protect it from the electrolyte. don't know why that doesn't get through to you. that is why they run the freshly created cells through the formation charge. it is the SEI layer that is being formed. it is essential!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
In repsonse to dnum comment above:

no there is no SEI on the cathodic material. as i explained before the SEI is grown on the surface of the anode in order to protect it from the electrolyte. don't know why that doesn't get through to you.

yes thats what I thought too, but some recent reading was some studies on the sei layer on the cathode material,
I was quite surprised to find that its not only on the graphite layer. This is first time I haven't linked the research material to my statements, I'll find some links and put them up on sei layer on cathode side.
 
there is alot of research papers on the cathode sei layer ( the sei layer on the graphite layer is normally what is spoken about but there is also sei layer on cathode, even on the nmetre thin carbon layer on the cathode lipo4 olivine layer) here's one for example:

http://www.researchgate.net/publica...deelectrolyte_interface_in_the_Li-ion_battery

That link is not the paper where I became aware that the cathode also has sei layer ( I didn't save the link), in the paper above they give it a new term
'solid permeable interface' ( spi )
in order to make it distinct from the sei layer on the anode.
I think thats a good idea they have, sei layer for anode/graphite and spi layer for cathode in order to know which side is being referred too.
Sorry that you weren't aware of it, I wasn't either till just recently. Lithiums are complex beasties. Its a constant learning curve for all.
 
One thing i'm not sure has been brought up before, there are two different Internal Resistance measurements can be obtained for a cell, one during charge and one during discharge. The internal resistance is different depending if your charging or discharging. Not sure what it means in terms of the internals of the cell but interesting anyhow.
(And of course there is some difference in IR depending on state of charge of a cell.)
 
this paper goes through calculating IR using various techniques, quite a good read
it also shows values of IR during charge/discharge are different, they also give some explanation
for this. They also go to great lengths to calculate IR using complex methods, but in the end conclude the simple
methods are quite accurate.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3247723/
 
Not sure if I posted this before, but A123 has given details of the electrolytes and salt they use in the cell type batteries
( published 2013), so its quite recent information, they use lipf6 and standard electrolytes ( ec, dmc etc), I'm guessing here but I would expect the 20ahr cells will use same electrolytes also.
Heres a123 data sheet link
http://www.simrad.com/www/01/NOKBG0...A123_System_Safety_Data_Sheet.pdf?OpenElement
 
Another interesting article on a123 20ahr cells.
http://www.osti.gov/scitech/servlets/purl/1060885/
This research paper is done in conjunction with a123, its aimed at improving the drying process for the cathode electrode to reduce time it takes remove water from the cathode.
170deg for 2 mins to remove water is simplified version of what they came up with.

The interesting thing in the paper is it gives the materials used in the cathode( page15):
1. lithium iron phosphate
2. carbon black ( the nanometer thin carbon layer to increase conductivity of the lifepo4 )
3. pvdf binder ( poylvinylidene flouride): that a commonly used binder for both anode and cathode
They give some data on their tests for a123 20ah cells near the end of the paper.
 
Just had a thought:
why do lithiums pouch cells require compression?
I think it relates to the weakness of the cells being the bonding of the graphite layer to the copper, and degradation over time
of the graphite layer. If the cell has compression the graphite layer will tend to remain intact and not detach from the copper,
the graphite layer has to be able to withstand the expansion/contraction of the cell.
If the graphite cracks, a new sei layer forms.
Cells with a metal or plastic casing will have pressure due to the case, when electrolyte is added there is some expansion of the cell. Over time the sei layer can become thicker and thicker, causing higher IR, but it also would give some compression to the layers in the cell. Overcompression can squash the narrow pores in the plastic membrane between electrodes, also increasing IR and reducing ion flow.
 
came across another patent for rejuvenate lithium cells, this one is by Mitsubishi, it is a method for replemish low lithium levels in order to regain capacity, interesting it mentions if too much lithium added to the cell then lithium dendrites can be an issue, it goes into method to determine accurately how much lithium to add to regain a given lost capacity.
http://www.google.com/patents/EP2688134A1?cl=en
 
just a recent taobao search for prices of lipf6 electrolyte, one seller has 500g of lipf6 for approx $40usd,
see link
https://world.taobao.com/item/520373175545.htm?spm=a312a.7700714.0.0.CO07EM#detail
it gives some idea of the value or what price is reasonable if purchasing lipf6 electrolyte.
 
another patent for lithium battery rejuvenation, quite complex not suitable for diy, but interesting, using carbon dioxidej (under very high pressure) to remove components from lithium cell before new electrolyte added. Results seem quite impressive.
https://www.google.com/patents/US8067107
 
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