 Random news from the Archive Sodium-ion battery
12.03.2015
Chemists have made a sodium-ion battery that works just as well as the lithium-ion battery we are used to.
A few years ago, it was suggested that it is time for humanity to think about an imminent shortage, but not about the oil and gas one, which we are usually afraid of, but about the shortage of an alkali metal - lithium. In our life there are more and more electronic devices and all kinds of gadgets. And all of them, from a mobile phone to an electric car, use electrical energy stored in batteries. Most of these are lithium-ion batteries. Today it is the most common type of rechargeable batteries. And although we are unlikely to see wars over lithium deposits in the near future, its cost may increase. And this means that it is time to think about cheaper batteries that would use other cells. Developers are betting on the closest relative of lithium in the periodic system - sodium, as a much more common and inexpensive metal.
Why can't you just take and replace lithium in a battery with sodium? It's all about atomic size. Although lithium and sodium are very similar in their chemical properties, the sodium atom is significantly larger than the lithium atom. And it turns out to be critical for the operation of the battery. A lithium battery has two electrodes, one made of carbon or graphite and the other made of a metal oxide such as cobalt. Lithium ions serve as a charge carrier between the electrodes, which is why, in fact, they are called lithium-ion batteries. During recharging, lithium ions are released from the metal oxide electrode and move to the second electrode, which is made of carbon.
The size of lithium atoms is such that they can easily be integrated into the structure of the electrode. This process is called intercalation, during which metal ions "squeeze" between the atomic layers of graphite. During discharge, the reverse process occurs - lithium ions leave the graphite electrode and return to the second electrode.
The key point of this electrochemical process is just the incorporation of ions into the electrode. The faster and easier it passes, the greater the instantaneous power can be. If the process is slow, the battery will not be able to provide the current needed to operate the device. This is precisely the difficulty in developing a sodium-ion battery. A carbon electrode is not suitable because sodium ions, due to their size, are extremely reluctant to integrate into the graphite structure.
That's why electrochemists are looking for electrode materials that are suitable for conventional electronics. After all, it is possible to make a battery on sodium ions, and it will work, the whole point is that it will not be as small, capacious and powerful as lithium. But it is power and size that are the most important parameters for mobile devices.
A team of researchers led by Professor Yong Lei from the Technical University of Ilmenau in Germany came up with a material that can be used to make an electrode in a sodium-ion battery, so that it will not be inferior to lithium in terms of power and capacity.
First, the chemists analyzed what properties the electrode material should have in order to ensure the effective introduction of sodium ions. The choice fell on conjugated aromatic compounds of the trans-stilbene class. They have the ability to transfer charge, are stable when charging and discharging the battery, and form intermolecular layers between which sodium can easily be introduced.
Chemists tested how well an electrode made of such a material would work and it turned out that at an average current density of 1 A / g, the capacity would be 160 mAh / g, which is in no way inferior to lithium-ion batteries. The battery also performed well in the endurance test, retaining 70% capacity after 400 charge-discharge cycles. And although the commercial implementation of the project is still far away, the results achieved indicate that sodium-ion batteries have the right to life and can, in principle, replace the already familiar Li-ion batteries.
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