Some observed progress in Lithium-Ion Batteries.

I have posted before about Lithium-Ion batteries. My relatively new Samsung Galaxy S9 Smart-Phone possesses one, and seems to have better battery performance overall, than my old Galaxy S6 did. Also, both these phones had a sensor chip which measures battery voltage. I use an Android app called GSam Battery Monitor Pro, to get occasional glimpses of what my battery is doing, and without such a hardware chip, the app would not be able to provide meaningful information. On my Galaxy S9 phone, the battery has a voltage of ~4.2V once fully charged, and I’m assuming that to plug the phone in just keeps it connected to a constant voltage source…

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On my previous, Galaxy S6, when fully charged, the battery had a voltage of ‘only’ ~3.7V. And so one strategy which Samsung could be using to increase battery life, would simply be to charge the same battery technology to a higher voltage. However, usually, doing so would only result in the battery catching fire. And so, some improvement in the actual design of the battery had to take place, so that it could be kept charged to 4.2V, and not suffer any immediate damage.

Dirk

 

What is a Lithium-Ion, Polymer Battery?

I’ve posted quite a few times now, about Lithium-Ion Batteries, without ever answering the question of how Lithium-Ion Polymer Batteries differ. And I think that I should write a posting about that subject, which this time around, will contain no links to other articles.

My previous postings assumed that standard, lithium-ion batteries are being examined, which were not of the polymer variety, but those postings did mention plenty of possible electrode materials. Well, batteries are not solely defined by their electrode materials, but are sometimes defined as much, by the choice of electrolyte which Engineers put their trust in.

In a standard, lithium-ion battery, most of the time, the electrolyte needs to be kept under pressure, in order to be liquid. In fact, this means that the standard battery variety also has a pressurized container around it, from which its electrodes are insulated electrically, but that adds bulk. The electrolytes in question are not Brønsted acids, as was once the case with lead – lead oxide batteries, but are very flammable.

In a polymer-variety battery, the electrolyte is the polymer, but the same assortment of electrode materials is still available. The favorite composition for the positive electrode seems to be lithium-iron-phosphate. Because the electrolyte is the polymer, it counts as a solid, which does not need to be kept under pressure, and through which lithium ions effuse, even though this solid is also flexible. As soon as this option presents itself, it creates advantages on two fronts:

  1. Energy-to-mass ratio,
  2. Safety.

(Updated 10/25/2018, 13h25 : )

Continue reading What is a Lithium-Ion, Polymer Battery?

An Observation about Modern Lithium-Ion Batteries

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.

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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 … )

Continue reading An Observation about Modern Lithium-Ion Batteries

Measurement of 18650 Batteries and Conclusion

I have now received my “9900mAh, 3.7V” batteries, and their bundled “4.2V” charger, which I first wrote about in this earlier posting. After receiving a full charge, their measured voltage while still inserted was 4.215V , immediately after removed at no load 4.195V , and after standing for 30 minutes, at no load, 4.138V . When new they require approximately 4h + 5min to charge.

I have to conclude that these batteries do not contain any series-connected, internal, over-voltage-protection chip. They seem to be based on the Layered Lithium-Manganese-Oxide: Li2MnO3 . They differ from the “3400mAh, 3.7V” variety, in that the other kind are based on the Spinel Lithium-Manganese-Oxide: LiMn2O4 .

I must only use this charger, with the batteries it shipped with.

Continue reading Measurement of 18650 Batteries and Conclusion