Lithium-ion batteries: How do they work?

in StemSocial2 months ago
Greetings dear friends of Hive.

Today the most common way to communicate, the cell phone, or to work anywhere, the laptop, are possible only thanks to the existence of this electrochemical device that supplies them with energy; so let's talk a little about the essential characteristics of this important type of battery.

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Our mobile equipment is powered by Li-ion batteries. Source: @emiliomoron.

In the field of rechargeable batteries, one of the batteries that has received the most attention is undoubtedly the lithium-ion batteries or Li-ion as it is usually abbreviated; and thanks to properties such as lightness, high energy capacity and low memory effect have allowed the design of compact batteries, of various shapes and above all, with high performance, which have adapted very well to the requirements of the consumer electronics industry. Their use has become popular in equipment such as cell phones, tablets and laptops. Since its appearance, this device has received strong investments in research and development with the purpose of increasing its duration, reducing its weight and decreasing its manufacturing cost among other aspects, being the main interested parties the great figures of the cell phones and electric vehicles market.

So, despite having a few years in the market, the expectations for this type of batteries are still huge, and we are still betting on its evolution to continue delivering energy to our mobile devices and even electric cars.


Electric vehicle charging battery. Source: pixabay.com.

Lithium-ion battery

As we already know, a battery is a device capable of producing and storing electrical energy through a series of chemical reactions called oxidation-reduction reactions; by means of which a transfer of electrons between chemical species is established.

Lithium-ion batteries are a type of rechargeable battery that uses a lithium salt as electrolyte to provide the ions necessary for the chemical reaction to take place between the cathode and the anode[1]. Basically, the oxidation capacity of lithium is exploited to induce a flow of electrons from the anode to the cathode of the cell.

Lithium is a metal with a low reduction potential, -3.05 V, which means that it is one of the chemical elements that very easily receives electrons, remaining as a positively charged ion (Li+), which is why batteries are called lithium-ion batteries.

A common lithium-ion battery can deliver 3.6-3.7 V, its energy density can range from 250-730 W.h/Kg, with charge cycles ranging from 400 to 1200[1].

How do they work?

As in an electrochemical cell, these batteries are composed of an anode (where oxidation occurs), a cathode (where reduction occurs) and an electrolyte. The flow of electrons is produced by the oxidation of the lithium present in the anode, while the reduction of the material it is made of occurs. The cathode is generally made of a compound called lithium cobalt oxide (LiCoO2) although in newer batteries it is lithium iron phosphate (LiFePO4). The general chemical reaction that occurs can be described as follows:

imagen.png
The operation of this type of battery is based on a process called Lithium ion (Li+) insertion-de-insertion. In general, the process is described as follows:
imagen.png

The process occurs in the solid state between two insertion compounds that form the electrodes, where one acts as a host (M) and the other as a host (A). And M reacts by occupying vacant sites in the structure of A, which is usually a crystalline solid[2].

During discharge, at the anode lithium is oxidized, and lithium ions move through the electrolyte to the cathode, where reduction of the host species and insertion of the host species occurs. The total reaction will be:

imagen.png
So, when we use the battery, lithium ions at the anode flow to the cathode through the electrolyte, electrons separated from the lithium also flow, but through the external circuit, which powers a mobile device or a vehicle.

liion ingles.jpg
Schematic diagram of the operation of a lithium-ion battery. Source: @emiliomoron.

The most common lithium ion batteries have a cobalt oxide cathode and an anode of a graphite-like material, arranged in a laminar fashion with sites that can accommodate the ions, which will travel back and forth depending on the charge or discharge cycle.

The laminar arrangement of the electrodes allows these batteries to be thinner and lighter compared to Ni-Cd batteries.

liion ingles2.jpg
Representation of the electrode arrangement in a cell phone battery. Source: @emiliomoron.

A bit of history

Lithium is a metal that has a strong tendency to give up its outermost electron, and to produce electricity we need precisely substances that have this ability, so the idea of using it to build a battery has long been considered.

But this apparent advantage was also a curse. Since lithium gives up its electron so easily that it is able to give it up even to the air, which makes it a very unstable metal that oxidizes quickly, so the arrival of a battery with lithium took a long time.

Bearing in mind that the perfect anode for a battery would have to be lithium, it remained then to describe the perfect cathode to use it. The first lithium battery was developed in the 1970s, it had a titanium sulfide cathode that was able to accommodate the ions coming from a metallic lithium anode; in this battery LiPF6 dissolved in propylene carbonate was used as electrolyte, which gave protection to the lithium from water and air, providing stability, thus achieving for the first time 2.5 V with this type of battery[3]. The first commercial lithium battery was an evolution of this, which marked the beginning of the race to develop better lithium batteries.

The problem with these batteries is that when heated they could explode, it was found that with each charge and discharge cycle lithium dendrites were formed that penetrated the electrolyte barrier and reached the cathode, causing a short circuit.

In 1985 the problem was solved, Akira Yoshino found a solution by trying a different anode, he used a compound called lithium cobalt oxide (LiCoO2), which is more stable as it has a much higher reduction potential, making it unnecessary to use pure metallic lithium. This dramatically increased the safety of the batteries and scaled up their production to an industrial level[1].

In 1991, thanks to the collaboration between Sony and the Japanese corporation Asai Kasei, the first commercial lithium-ion battery was launched onto the market, which used a lithium cobalt oxide anode and a coke cathode; years earlier, Asai Kasei had demonstrated that petroleum coke was a very efficient way of accommodating lithium ions[3].

Today, even more efficient lithium batteries are being manufactured, thanks to the fact that in 2004 a group at MIT replaced cobalt-lithium oxide with lithium iron phosphate (LiFePO4), making them cheaper to produce, since cobalt is a very expensive and scarce metal, and also increasing their performance.

In 2015, Tesla Motors presented its two famous energy storage systems, the Powerwall/Powerback batteries for the storage of electrical energy from renewable sources, such as solar or wind power.


Tesla's rechargeable battery for domestic use. Source: Wikimedia commnos.

In 2019 the development of lithium batteries achieved the Novel Prize in Chemistry, shared between the British M. Stanley Whittingham who led the research on the intercalation of lithium ions into metal disulfides in the 1970s, the German John Goodenough, who proposed the solution of the cobalt-lithium oxide cathode to prevent the battery from exploding, and the Japanese Akira Yoshino, who working for the Asahi Kasei Corporation proposed the use of the coke anode.

Applications

As we have already mentioned, the sector with the highest demand for lithium-ion batteries is the market of cell phones and computers, without doubt the development of these devices has been thanks to the evolution and efficiency of this type of batteries, and thanks to the fact that they can be accommodated in different geometries. For these applications we can find them as seen in the following image.

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Cell phone battery models. Source: @emiliomoron.

One of the most attractive markets for this type of batteries are the energy storage systems, being a sector of strong growth the batteries for electric vehicles. For this application, multiple cells are grouped into several units to supply the energy necessary for the vehicle to operate with sufficient autonomy. In the following image we can see the arrangement of a battery for an electric vehicle.


Cut in the chassis of a Nissan electric vehicle to show part of the battery arrangement. Source: Wikipedia.com.

Conclusion

Lithium-ion batteries are today one of the most demanded batteries in the market of electronic devices of great consumption, such as cell phones, and are of those that have a huge increase in demand for their application in electric cars, thanks to their performance and efficiency; which has been achieved with the selection of the appropriate anode for one of the most easily oxidizable metals of the periodic table.

In these batteries we can observe how the redox processes have allowed an efficient way to store energy, the chemical equations described allow us to socialize the operation of this type of battery, being a good resource for the didactic explanation of the electrochemical processes that take place.


Well friends, this is the end of this post, I hope you found the information presented interesting. Thank you very much for reading, see you next time.


References

  1. Wikipedia.com. Batería de ion litio
  2. Hamel, J. (2011). Celdas, pilas y baterías de ion-litio, una alternativa para… Journal Boliviano de Ciencias, volumen 8, número 22, pag. 40-47.
  3. Cuaderno de cultura científica. Así funcionan las baterías de litio.
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