Lithium battery is a part of electronic devices. They are essential to have your next monitoring unit working without being tied to a power supply. The cell can be harvest and reuse from old electronics such as your old laptop battery. However, lithium battery discharge a bust of high current. If the positive and negative is shorted, the battery can discharge a high amount of energy leading to heating up the connect wire. If the wire was not burnt and melted away or the protection valve not tripped. Next, the heat built up inside the battery will lead to short circuit inside battery. We don't want what happen next if a close space because the fire will start and only stop after the energy inside battery is fully disipited through head. Have a look at the video below.
Short story is the lithium battery can store energy, and if we are not manage them carefully, the energy stored will uncontrollly release at us or anything that in close proximity to the burning battery cell.
A simple example. Supposed we have an old battery with a capacity of 1000mAh. A-1000mAh means the battery can discharge 1000mA in 1h. Similar to a 9Ah lead battery, which can dischage 1A in 9h.
If you watch the video above, short circuit discharge lasted about 10 seconds before the energy is run out, which means the average discharge current is about 1Ah/(10s/3600s/h) = 360A. The power dissipation is I2V ~ 1V*360(A)*360(A) ~ 130 kW. One volt is taken ambiguously for a shorted-circuit battery. An iron is rated at 2kW. A condo has a energy consumption rate peaks around 10kW for comparison.
But fear not, lithium battery is small, not expensive, can be reuse easily. There is no acid liquid. If the circuit has fuse or current protection in place, it is safe to use. It can power a small monitoring device to run your bike or even your car.
In this writing, I will provide some hand-on experience working with used lithium battery, mostly a popular 18650 cell. The post will conver how to harvest, how to know a good battery, and how to discharge them properly. Most useful information are photos taken during my journey with lithium cells.
First, let have a look at what a 18650 battery looks like. 18650 means a cylinder cell (0) with a diameter of 18mm and a height of 65mm.
Don't try to open and tear down lithium cells. Uncontrolled discharge from the battery could cause severe burn, fire and odor. Make sure the battery is fully discharged (no energy in the cell). Use a multimeter to read the voltage. For safe, the voltage should be zero.
It may look simple outside, the engineering put in place is amazing. The cell is a airtight tin can which a thermal protection using bi-metal strip. Energy (or electron) is stored in between layers of rolls of copper layer, a layer of to retain and discharge electron (black), and an isolation layer (white).