Disassembly of UltraFire 9900mAh 18650 battery


I recently reviewed this battery, it did not live up to its specifications, capacity was significantly below rated capacity, but how do manufacturers make this type of very cheap battery? One solution I have seen is to rewrap old batteries, but this cell was too consistent in capacity for that.


The final look at the cell. The PCB mentioned on the cell was nowhere to be found.


And it is open, without any heat, smoke or flames (If the cutter short the battery it will get hot).

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The roll do not fill the battery, that is some of the explanation for the low capacity. I included another cell for comparison.
This do also explain the low weight of the cell.


Wrapper, can, roll, and top.

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Lets take a closer look at the top, below the white washer is the vent holes. The button top is not welded on, it is part of the top, this means this battery is produced with button top.

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The plus pole is isolated from the can with a soft plastic spacer.


Remaining part of can removed.


Top removed from plastic spacer.

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The underside of the plus pole has a metal foil that works as an over pressure vent, i.e. it is supposed to break if the pressure in the cell gets to high.
I did have some problems breaking it with a screwdriver and needed pliers to fold it out. I wonder what will break first on high pressure, the can or the seal? Below the seal the vents and the backside of the button top can be seen.
There is no trace of a PTC (Over temperature protection and indirectly over current protection), it is supposed to be placed between the pressure vent foil and the external positive connection.

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lets take a closer look at the battery roll.


I rolled it up and placed it down for photos and then it started smoking. The paper (My photo background) sheet behind the copper foil was brown/black due to heat.

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Here is one more look at the layers:
Positive electrode (Cathode) is Lithium Cobalt Dioxide coating on aluminium
Negative electrode (Anode) is Lithium Carbon (graphite) on copper
The two layers of separator is a plastic foil with microscopic holes in it, when in the battery there was also some organic solvent.
The length of the anode was around 32 to 33cm.


This cell is manufacturer to be a cheap low capacity cell, to make it as cheap as possible the safety is not very good.
I have a suspicion that they use the old Lithium Cobalt construction (This is the most dangerous LiIon type).


Review of UltraFire SZ18650 9900mAh (Yellow)

Disassembly of cheap 18650 battery
Disassembly of some UltraFire batteries

Is my battery protected

How is a protected LiIon battery constructed