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2017-06-10

LITHIUM-ION BATTERY: WHAT IS AND HOW IT WORKS



What is a lithium-ion battery

Lithium-ion batteries are rechargeable batteries. Compared to traditional not rechargeable lithium batteries, rechargeable lithium batteries use an interpolated lithium material rather than the metallic one.
A battery is a device based on a chemical process happening in a small metal container: if we connect the two extremities of the battery to something like a torch al reaction starts and the chemicals elements, which are contained in the battery, break and new chemicals are produced.
These new chemicals elements are ions, some positive charged particles and electrons, which are negatively charged particles. Both these particles move and turn chemical energy into electric power, which allows the torch to light.
While in traditional batteries chemical reactions can happen only once,in only one direction, and batteries can’t be recharged, lithium-ion batteries are rechargeable because the chemical reactions are in fact reversible.
During the discharge process, lithium ions go one way and the battery loses power; while instead, during the charging process, lithium ions go in the other direction and the battery receives power.
These chemical processes can repeat several times in both directions and for it is this reason that a lithium-ion battery can live a few years.

How does a lithium-ion battery work

As any other type of battery, a lithium-ion battery is made of some cells, which are power-generating compartments.
Each cell has three different parts:
  • a positive electrode;
  • a negative electrode;
  • an electrolyte, which is a chemical, placed between the positive electrode and the negative one.
When a lithium-ion battery is charging, some lithium ions move from the positive electrode, through the electrolyte, to the negative electrode and remain there. In this way, the produced energy is stored.
When the battery is discharging, the lithium ions come back from the negative electrode, through the electrolyte, to the positive electrode, producing electricity. In both cases, electrons move in the opposite direction to the ions around the external circuit.
These movements are interconnected so if one of them stops, so does the other one. It means that if the battery, for instance, is fully discharged, both the flows of ions and electrons stop and you have not powered at all.
The battery will be fully charged when there are no more ions flowing; it will be fully discharged when all ions have come back from the negative to the positive electrode.

How to charge lithium-ion battery

One of the main advantages of li-ion batteries is that they don’t suffer from a problem known as “memory effect”.
Traditional batteries, as nickel ones, had this problem. They “remembered” the last charge when they were recharged, and then returned only that last part of stored energy. It was actually hard to recharge them unless they were fully discharged first.
As li-ion batteries don’t suffer this problem, they can be recharged even if they are not fully discharged, without produce any negative effect on their health.

Charging a lithium-ion battery for the first time

When we purchase a new smartphone or laptop with a rechargeable lithium-ion battery, we don’t know how long the battery has been inserted, so the first time we need to fully charge it, before starting to use the device.
Most people think it is necessary to charge the battery many hours. It is not true: 5 or 6 hours will be enough, when you recharge your battery for the first time.
After that, it is recommended to have 2 or 4 charge and full discharge cycles (a device could be considered out of power when it reaches about 20% of charge).
Later, you can use your battery even with partial charge cycles.

What is the life of a lithium-ion battery

Lithium-ion battery life is typically measured according to the number of full charge-discharge cycles it can sustain, before to lose significant capacity.
On average, lifetime is made of 1000 complete cycles, even if the majority of devices rarely perform well after 500 cycles.
This means that batteries of smartphones or other electronic devices, intended for daily use, are expected to usually last about two or three years.
It is important to know that a battery’s life starts when it is produced. This means that a battery “lives” even when it sits on a shop shelf unused.
So, if you are purchasing a new battery pack, make sure it is really new and be suspicious of old or already used batteries.

Best way to charge lithium ion battery and to preserve its life

Even though battery life is more or less predetermined, there are some things you can do to preserve your battery life and to allow it to last longer.
Because of its inner chemical reaction, battery works harder under 20% and above 80% of charge: we suggest you keep your battery always between these two gaps of charge.
However, a good practice is to have it completely discharged every 20-30 partial charge cycles, meaning when the tablet or mobile phone gives a low battery warning, about 20%, as we mentioned before, and then to recharge it.
As a general principle, we can say that you should never make a full charge cycle after another, but it is always suitable to alternate partial charging cycles with full charge ones.
Moreover, it is not good for battery life to leave it constantly plugged in (this is very frequent for laptops, for instance) because it will perform better if it is often discharged and recharged.

Applications of lithium ion battery

Li-ion batteries have a lot of applications, beyond mobile phones and laptops. From medical equipment to luxury yachts, this kind of batteries are today almost everywhere and can both facilitate our daily activities or provide emergency support, accordingly.
Among the top applications of lithium-ion battery, there is the emergency power backup or UPS which protects you from instability or energy loss.
It offers you an instant energy to power the equipment, you are using, which is connected to: this is very important for critical equipment, such as computers and medical gear.
Another important application is the electric vehicle. However, to make these vehicles a real alternative to traditional ones, it is necessary for their batteries to charge and discharge very fast.
Researchers are still at work to recharge batteries faster and to improve them.
A possibility seems to be connected to nanotechnologies: some researchers at the University of Illinois are actually studying the possibility to charge a lithium-ion battery to 90% in two minutes, thanks to the cathode produced from a 3D nanostructure.

Why some li-ion batteries may explode

You have probably heard about some cases of lithium-ion batteries exploding in the news lately.
It is possible this happened because one of the main problems connected to lithium-ion batteries is that, sometimes, they can overcharge or overheat and this can, in extremely rare circumstances, lead to their thermal runaway.
The thermal runaway is a chemical process generated when a battery produces heat and it causes additional reactions which produce more heat and so on until the device explodes.
Another problem is that technologies in our electronics improve very fast and they require new kinds of batteries to be correctly powered, but the progress in batteries capacity is proving to be slow: this technological gap may cause some problems and it is not easy to fix.
Moreover, the li-ion battery chemical composition can have some dangerous effects in case of manufacturing anomalies or damage affecting its integrity.
The inner electrolyte is made of a highly flammable liquid and if this liquid is exposed or the electrolyte integrity is compromised, because of physical damage for example, the battery can burn and explode.

Measuring battery state of charge is important to prevent explosions

To regulate how to charge and discharge li-ion batteries in order to prevent overcharging and their “thermal runaway”, it is actually important to measure the battery state of charge.
For this reason, unlike simpler batteries, all lithium-ion batteries have today an inner electronic controller.
As we explained before, the thermal runaway is not the only cause of battery explosion.
Batteries can actually explode because of their technology and chemical composition. That is why some of them continue to explode despite the inner electronic controller.

High capacity lithium ion battery to prevent its explosion

To prevent problems connected to the accidental battery explosion, the aim is really to develop a new battery technology which is cost-effective, efficient, with non-volatile electrolyte material and no explosive risks.
Researchers at Tufts University are studying a possible solution.
They created a durable plastic electrolyte material to produce very thin batteries (they are barely as thick as a couple of playing cards) which could even be cut into fractions without exploding.
Moreover, this battery would offer twice the capacity of the current technologies.
Researchers are still working on these technology and these batteries are not ready for the market yet. However we can be confident that this will happen in the near future.