I have visited this subject before, but feel that I should post about it again.
The way Lithium-Ion batteries first became popular, they either had metallic lithium, or graphite as their negative electrode, and lithium-cobalt-oxide as their positive electrode. This stored much energy, but also presented an initial cause for alarm, especially since some of the then-new batteries were prone to catch fire, when over-charged. In response, there existed a trend followed by some companies and manufacturers, to switch to lithium-manganese-oxide, either in the layered or the spinel form, as the next-best positive electrode. ( :2 )
It would seem that the lithium-cobalt-oxide batteries produce 4.2V when fully charged, while the lithium-manganese-oxide batteries only produce 3.7V when fully charged ( :1 ) , and the latter battery-type was deemed ‘safer’.
Additionally, there exists a battery-type which has lithium-iron-phosphate, which is even safer than the 3.7V batteries, and which only produces 3.6V when fully charged. This third family of batteries is used in Segways and some electric cars, where it would be exceptionally unfortunate if the batteries could explode, simply due to a traffic accident – a hypothetical collision.
All the voltages which I’m citing here are relative to a lithium-graphite negative electrode.
What seems to have happened – and I don’t have proof – would be called a ‘trend reversal’. Some manufacturers have switched back to using the lithium-cobalt-oxide batteries, simply because those store more energy.
Why do consumers need to know this? So that they don’t place 3.7V batteries – which are labeled identically to the other type – into 4.2V chargers, and leave them there. That’s all.
I suppose that a valid question which some readers might have would be, ‘What has become of the safety / over-charging issue?’ And my answer would be that most of today’s charging circuits have become ‘smarter’, and less prone actually to over-charging the batteries. The best example of this is the smart-phone. However, if some people buy separate batteries for ‘Vapers’, then those devices have a reputation of ‘no charging intelligence’, i.e., of sometimes over-charging the battery.
The typical behavior of a dumb charger is, to ‘Apply a constant voltage of 4.2V, and when the current which the battery draws falls below a certain amount of current, give an indication that the battery is fully charged. But keep applying 4.2V, even after the LED has changed color.’ The lithium-manganese-oxide batteries will also tolerate such charging voltages for brief periods of time. And the lithium-cobalt-oxide batteries will realize their maximum held charge that way.
The thing not to do, is to keep whichever batteries in their dumb charger for long periods of time, after the LED indicates they are charged.
I also want to add, that this posting is meant to voice an issue, with the low-budget lithium-ion batteries, in the modern era. I understand that high-budget, big-ticket items exist, such as…
(Updated 10/21/2018, 22h55 … )