WhatParameters
Going outside
Protection board
Datasheet
Structure
Protection
Circuit
Positive end
Can, negative end
Electrode stack
Recoverables
Weak spots
See also
Todo
A dead Tenergy-brand lithium-ion battery
provoked with its content. It is a cylindrical cell, RCR123a sized, containing
650 mAh of energy. A standard lithium cobalt cell.
 cell, outside |  cell, outside |
Stressing the cell outside of the parameters (mainly charging current) is tempting, but will lead to faster degradation of the capacity. For longer times between charges, this is however not much an issue.
In theory, for higher-current pulsed discharge, the protective circuit can be bypassed. This however can introduce significant operational risks, and can dramatically degrade the life.
In theory, the overcurrent protection could be disabled by tying the CS pin (connected via R2) to ground, or adding a resistor between CS and ground to form a divider. This however also strains the battery and if overdone, could lead to a fiery surprise.
The battery consists of the sealed steel can containing the battery itself, the protection circuitry, and the insulating wrapper.
The circuit is located on a round circuitboard, residing over the negative end of the can, on a plastic spacer. The negative side is attached to the can with spot-welded metal strip. The positive side is connected via a thin flat copper wire, laminated in kapton foil.
The outside-accessible negative terminal is located on the opposite side of the circuitboard. The protection is provided by a pair of back-to-back N-MOSFETs.
Caution: The protective wrapper is an integral part of the protection. Without it, the can is exposed and an accidental contact between the positive side and the can can (heh) lead to uncontrolled high-current discharge and overheating. (Which killed this specific cell.) It is easy to damage the plastic foil by using hot-melt adhesive that's too hot, or remelting it with a torch flame too close to the foil. At least ad-hoc replacement with an insulating tape is advised.
 bare cell |  bottom, protection circuit |  bottom, protection circuit |  bottom, protection circuit |
 bottom, protection circuit |  bottom, protection circuit |  bottom, protection circuit |  bottom, protection circuit |
 protection circuitboard, exposed traces |  protection circuitboard, exposed traces |
The protection circuit consists of a handful of parts:
)
The circuitboard perfectly matches the datasheet schematics.
The U2/U3 chips are wired in parallel. Only one, or both, can be populated.
U2/U3 (MOSFET) pinout:
DRAIN - - DRAIN
SRC1 - - SRC2
SRC1 - - SRC2
GATE1 - - GATE2
U1 (control chip) pinout:
dischg enable gate OD - - GND
current sense, charger detect CS - - VCC battery+ via R1,C1
charge enable gate OC - - TD test pin, unused
 schematics from datasheet |
The M1/M2 MOSFETs share the package of U3
The cap on the positive end is crimped in place via an insulating gasket. The narrowing on the can is to provide counterforce for the crimping. The cap contains vent holes for relieving a possible internal overpressure, in an attempt to prevent what the industry calls "rapid spontaneous disassembly".
The top cap is made of two layers, serving as a high-pressure gas relief valve while maintaining hermeticity and preventing electrolyte evaporation. The inside layer also sits on the aluminium(?) contact attached to the positive electrode. The connection between the two is established by mechanical contact and what appears to be a tiny weak spot weld.
The thin flat cable to power the protection chip is attached to the top cap.
 cell top side |  cell top side |  cell top side, crimp opened |  top contact removed |
 positive plate, cathode |  top side spacer, contact plate |  top side spacer, contact plate |  top side spacer, contact plate |
 top side spacer, contact plate | winding partly exposed |
The electrode stack was tightly rolled and even more tightly seated in the can. The can had to be torn away, not unlike some can openers open, well, cans.
After tearing/unrolling most of the sheetmetal, the roll could be pulled out of the remains of the can. There is a thin plastic spacer between the bottom of the can and the roll. A metal strip from the negative electrode is fairly weakly spot-welded to the bottom of the can.
Caution: do the disassembly in a fire-safe area (eg. ceramic bathroom sink). With energy storage devices, an unplanned energy release can never be completely ruled out. Immediately flooding the unruly runaway device with water is a good option to have. This cell had less than two volts and negligible current to give, but better be on the safe side.
 removed can |  bottom spacer, contact |  bottom spacer, contact |  bottom spacer, contact |
 bottom spacer, contact |
The battery consists of two electrodes and a separator, rolled tightly together and soaked with electrolyte.
The positive electrode, the cathode, is made of aluminium foil, coated on both sides with black substance, presumably lithium cobalt oxide.
The negative electrode, the anode, is made of copper foil, coated on both sides (except the outermost portion with no cathode facing it) with black substance, presumably graphite.
The separator, presumably microporous polyolefin membrane, wraps the cathode sheet and is welded on the outer edges, forming a long strip of a bag.
The electrolyte is presumably a lithium hexafluorophosphate dissolved in a mixture of carbonate solvents, likely diethyl carbonate, ethylene carbonate,
and/or propylene carbonate; the somewhat pungent smell would point to the carbonate base.
The stack is tightly rolled and the roll is secured against unrolling with adhesive tape.
The electrode dimension is about 51x3.3 cm. The electrode area, adjusted for the outermost uncoated loop, is (51*3.3+(51-1.6*pi)*3.3=) 320 cm2.
The black goop is prone to flaking off. Beware, cobalt can be harmful to the residents of California.
 electrodes roll |  roll, positive side |  roll, negative side |  roll, negative side |
 roll, beginning unrolling |  roll, beginning unrolling |  unrolling |  unrolling |
 unrolling |  unrolling |  unrolling |  positive contact attachment |
 positive contact attachment |
The cells contain numerous substances and components that can be of potential use.
This applies to pretty much all Li-ion cobalt cells. Could be useful in a zombie apocalypse scenario.
Harvesting Li-polymer pouch cells is much easier, though. No steel can to bother with. The caution about working in a sink to mitigate the risk of the thing going up in flames still applies.
The battery is nice and safe. However, certain specific damage can cause unprotected short between the tip and the can, resulting in uncontrolled discharge and high heating, possibly destruction of the cell. (TODO: destructive tests.)
A puncture or cut can sever the flat wire that goes over the can, and cause a short.
Damage on the insulating sleeve together with a stray metal object can also cause a direct unprotected short.
