I opened a lithuim battery salvaged from my old laptop battery pack. I checked million times that it is 0V and it was by the time i was opening it. For some reason i would love to know, it is now MAGICALLY charged up to 3.99V and that scared me so i left it aside keeping it cool. It has no protection circuit. So is oxygen reacting with Lithium metal and creating such voltage? Or is it really charged?
Update:
I'm charging the battery that was spot welded in parallel to the battery #1. Just for tests and observing its temp. The battery #2 also holds 0V (which also assures that bettery #1 was definitely 0V) so if it stays like that I'll open it and see if it suddenly charges as well up to 4V and what is the reason. Also I sealed up bat#1 Here's bat#2: 
I did a 100R load on the battery #1 and here's the data:
-T=0 3.96V
-T=10 min 3.91V
-T=20 min 3.91V
-T=30 min 3.90V
-T=1 hr 3.87V
-T=1 hr 30 min 3.86V
-T=2 hr 3.84V
-T=4 hr 3.78V
-T=6 hr 30 min 3.72V
-T=9 hr 3.67V
-T=11 hr 30 min 3.61V
It took a long time so i stopped at 3.6V 
Graphed by T. Stewart using data above Using Ic=CdV/dt \$C=V/R*dt/dV~\$ with units \$~= [F]=[V/Ω*[s/V]]\$ for R=at 10k load 11h
Next test 100 Ohm load to 3.0V (faster test) taking two measurements; with load and without. This will measure C2 and ESR. Voltage readings were unstable at first ( double layer effect) but averaging 20 F rising to 40 Farads.
Note that a fresh 18650 cell ranges from 5000 Farads to 10kF so this dead battery will have much higher ESR and C1 <1% of it's initial capacity (unknown).
However it still useful for Volatile Memory backup.
Momentary short circuit current will also measure ESR.
Answer
There is a protection current interrupt device under the positive terminal. Inside, the battery is still charged. See the structure in this article.
No comments:
Post a Comment