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How to distinguish between Lithium-ion and Lithium Polymer cell

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What is and how to distinguish between Lithium-ion and Lithium Polymer cell?

What is  'grey soft pouch' cell that are universally found on modern cellular phone or other 'small size' devices (instead of 16500 big cylinderical cell) ?   

We need 50 to 100mAh and light weight.

Many thanks

There is no such a thing as "lithium polymer" cell. It's a marketing term used to describe pouch cells. The chemistry itself is similar to other form factors. The "polymer" refers to the plastic used in the outer packaging (it's aluminum-plastic sandwich pouch).

In 18650 cell, the internals are wrapped like a swiss roll, then pushed into metal cylinder. In a pouch cell, they have a "roll" with sharper edges, vacuum packaged into the plastic-aluminum pouch.

Most professionals prefer to say "pouch cell" instead of "polymer".

In 1990's, there were hopes in developing polymerized, solid electrolyte. This was the initial use of "lithium polymer". They never materialized commercially, but the term was reused by marketing after that.

One issue with pouch cells is that they need external mechanical protection. If you puncture a charged cell it could easily go up in flames. The metal-cased cylindrical cells are much more robust and harder to damage.

Note that there are also rectangular (hard) metal-cased cells, although they tend to be less common.

In the pics first one with wide metal tabs is a raw cell, without any over-voltage, under-voltage, over-current or thermal fuse protection.

The second one, with wires, has an internal PCB with a protection circuit on it, for the above situations.  Same for the mobile phones batteries, they came with a protection PCB embedded in the metal or plastic enclosure of the battery.

If you see the contacts are like wide metal sheet tabs, that's usually a raw cell, easy to damage or to set on fire.  Never use raw cells to directly power your circuit.  Similar for the round 18650 (or other sizes, 18x650 is the diameter x length), some have internal protection (made to be used by the end users), others are raw cells meant to replace dead batteries in battery-packs that have their own BMS (battery management system, like e.g. in laptop batteries, hand-tool drills, battery vacuum cleaners, etc.).

You must have a dedicated circuit to supervise rechargeable Li based batteries, because when discharged too much, Li recheargeables form internal metallic bridges (unrecoverable damage), and when overcharged they catch fire.  Same if the current is too high (either during charging, or during discharging) or when a short-circuit happens.


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