Yeah, I’m starting to cycle back around on myself. Back in ’12 I posted about this site, The Electropaedia, which is pretty much an astounding resource on batteries, energy, technology… you could hang out there for days. Battery University is another one, but honestly, I think there’s more detail here.
The site provides a comprehensive knowledge base about energy supply and battery technologies, battery applications, chargers and ancillary equipment.
It contains over 140 web pages of information and explanations, many of which are the equivalent of several A4 pages long.
It also contains a History of Technology (with a special mention of batteries of course)
Here’s the page on Battery Testing, once again.
silliness posts about RC lipo reminded me of a great page he has there, about “Lithium Battery” failure modes. In it, he talks about “Lithium Ion”, a pretty generic term, but it’s incredibly helpful in understanding the fairly narrow parameters for running lithium chemistry and what happens at a chemical level when they’re exceeded. “Violated”. “Surpassed”? You get the idea. I think it’s fairly safe to say that out of the small window you see in that graphic, RC lipo holds an even smaller space within it.
Here’s a sample, but don’t deprive yourself of a visit to the site:
If the charging voltage is increased beyond the recommended upper cell voltage, typically 4.2 Volts, excessive current flows giving rise to two problems.
- Lithium Plating
With excessive currents the Lithium ions can not be accommodated quickly enough between the intercalation layers of the anode and Lithium ions accumulate on the surface of the anode where they are deposited as metallic Lithium. This is known as Lithium plating. The the consequence is a reduction in the free Lithium ions and hence an irreversible capacity loss and since the plating is not necessarily homogeneous, but dendritic in form, it can ultimately result in a short circuit between the electrodes. Lithium plating can also be caused by low temperature operation. See below.
Excessive current also causes increased Joule heating of the cell, accompanied by an increase in temperature. See next section below.
- Under-voltage / Over-discharge
Rechargeable Lithium cells suffer from under-voltage as well as over-voltage. Allowing the cell voltage to fall below about 2 Volts by over-discharging or storage for extended periods results in progressive breakdown of the electrode materials.
First the anode copper current collector is dissolved into the electrolyte. This increases the self discharge rate of the cell however, as the voltage is increased again above 2 volts, the copper ions which are dispersed throughout the electrolyte are precipitated as metallic copper wherever they happen to be, not necessarily back on the current collector foil. This is a dangerous situation which can ultimately cause a short circuit between the electrodes.
Keeping the cells for prolonged periods at voltages below 2 Volts results in the gradual breakdown of the cathode over many cycles with the release of Oxygen by the Lithium Cobalt Oxide and Lithium Manganese Oxide cathodes and a consequent permanent capacity loss. With Lithium Iron Phosphate cells this can happen over a few cycles .