Lithium-pol cells

Instead of liquid electrolyte in lithium-pol cells nonflammable solid polymeric electrolyte is used. Polyethylene oxide can be the simplest example of the used polymer. The main problem of these batteries is gradual crystallization of polymeric electrolyte that leads to decrease in accumulator capacity at charge discharge cycles. In addition they differ in small service life and increased requirements to conditions of a charge of accumulators. All this creates serious difficulties for broad commercialization of similar devices.

2020: The Russian scientists found a method how to increase operation of the accumulator in phone up to 70 years

On December 29, 2020 RHTU of D.I. Mendeleyev announced TAdviser that the Russian chemists developed polymeric cathodes for superfast accumulators.

The Russian chemists developed polymeric cathodes for superfast accumulators

Demand for li-ion cells constantly grows, but raw materials for their production are limited, and scientists look for other options of this technology. The Russian researchers from RHTU, Skoltech and IPCP synthesized the cathode materials on the basis of polymers and tested them in lithium two-ionic batteries. They showed that such cathodes can maintain up to 25000 cycles of work and also be loaded for several seconds that exceeds possibilities of li-ion cells for December, 2020. Also using these cathodes the potassium two-ionic accumulators which are not using expensive lithium can be created. Results of work are published in the Energy Technology magazine.

The mankind produces and consumes more and more electricity, and together with it demand for power drives because many devices often work in a standalone mode grows. Li-ion cells can give big power, providing at the same time rather high discharge rates and a charge and also store a lot of energy per unit of the weight. Therefore they are applied as drives of energy not only in electronics and the electric transport, but already and in scales of global power networks. For example, in Australia will build network of huge power drives on the basis of li-ion cells to reserve excesses of the energy made by solar and wind farms.

But if li-ion cells become more, then raw materials for their production will reach a limit sooner or later. For example, cathodes of these batteries often contain cobalt which 60% of production are the share only of one country - DR Congo and therefore if producers want to do even more accumulators the price of cobalt can grow many times over. The similar situation and with lithium - on its production leaves a lot of water that it can become a serious environmental problem. Therefore researchers look for other power drives which on the one hand work by the principle of li-ion cells and save their advantages, and with another use more available raw materials. In work of scientists from the Skolkovo institute of science and technologies, RHTU of D.I. Mendeleyev and IPCP of RAS the post-lithium technology of two-ionic accumulators in which electrochemical processes are involved both anions, and electrolyte cations that many times increases speeds of a charge of batteries in comparison with Li-ion was used. At the same time as cathodes materials on the basis of polymeric aromatic amines which can be synthesized from different organic compounds were tested.

Our group already had works on polymeric cathodes for superfast accumulators with a good capacity which can be loaded and discharged for several seconds, but there was a wish bigger. Among other, earlier we used linear polymers at which each monomeric link forms communications only with two neighbors, and in this work we continued studying of branched polymers at which each link can form communications at least with three other links. They create volume mesh structures which provide faster kinetics of electrode processes. With electrodes from such materials accumulators can be loaded and discharged even quicker. tells the original author of work, the graduate student of Skoltech, Philip Obrezkov.

The standard li-ion cell - it a cell the volume of which is filled with lithium-containing electrolyte and separated by the separator into two parts - in one there is an anode, and in other cathode. In the charged status the majority of atoms of lithium are built in crystal structure of the anode, and at discharge they go out of the anode and via the separator get into the cathode material. Not only cations of electrolyte (i.e. lithium cations), but also anions which are built in participate in two-ionic accumulators with which the Russian scientists worked in electrochemical processes, leave structure of the cathode material. At the expense of it two-ionic accumulators often can quicker be charged, than normal Li-ion.

Besides, in work was one more invention. In some experiments scientists used not lithium-containing electrolytes, but potassium - containing and so potassium two-ionic accumulators for which operation are not necessary expensive lithium received.

Researchers synthesized two branched polymers - one was copolymer of a digidrofenazin and diphenylamine (PDPAPZ), and another - a digidrofenazin and a fenotiazin (PPTZPZ). On their basis made cathodes, and as anodes used metal lithium and potassium - all main characteristics of such prototypes of batteries which are called half-cells, are defined by the cathode part and scientists bring together them quickly to estimate possibilities of the provided cathode materials.

Half-cells with PPTZPZ showed modest performances. PDPAPZ opposite was rather successful material: lithium half-cells with this polymer could be loaded and discharged rather quickly and also showed good stability. They saved to a third of the capacity even after 25 thousand operating cycles - if the normal accumulator in phone had the same stability, then it could be loaded and discharged daily for 70 years. Potassium half-cells on the basis of PDPAPZ showed the good density of energy - 398 W h/kg. For comparison in popular lithium cells this value is 200 – 250 W h/kg, but in this digit the mass of the anode and electrolyte is also considered. Thus, the Russian scientists showed that the developed polymeric cathode materials can be used for creation of lithium and potassium two-ionic accumulators.

2017: Nafen project nanofibres

The project team of Nafen carried out a number of works and tests in 2017-2018 and found out that adding of nanofibres of oxide of aluminum in polyethylene oxide interferes with process of its crystallization, saving polymer in the carrying-out form. Thus nanofibres solve a problem of loss of battery capacity at its long-term use.

Nafen represents nanodimensional fibers of oxide of aluminum. The form, the size and unique properties allow these fibers to interact with different polymeric matrixes, ceramic and metal materials on a nanolevel, introducing additional functionality or improving properties of final materials. The production technology of nanofibres was developed and patented by a project team of Nafen (Tallinn).

'Increase in quantity of cycles of charge/discharge with preserving of stability of operation of the rechargeable battery - a fundamental problem which many work and research teams try to solve. At the moment, we can tell that Nafen has the huge potential for improvement of rechargeable batteries on the basis of lities - polymeric electrolytes", - the Nafen project coordinator Alexey Tretyakov comments.

Tests of the polymeric electrolytic system improved by aluminum oxide nanofibres during 300 cycles of a charge discharge showed obvious superiority over competitive solutions.

'It is quite possible that the polymeric electrolytes which are filled with nanofibres will allow to receive required operational properties for wide circulation of lithium-pol cells in the markets of daily portable devices", - Alexey Tretyakov considers.

Help

Nafen nanofibres are thin nanodimensional fibers with a diameter only 10-20 nanometers and up to 15 centimeters long. They are produced by controlled synthesis of nanostructures of oxide of Al2O3 aluminum on the surface of fusion of aluminum in the presence of special oxidizers. Similar fibers in the nature do not meet and can be received only by an artificial method.

The characteristics of Nafen studied by the Estonian company together with leading universities of the world open ample opportunities for its effective application in the space industry, power industry, fuel industry, metallurgy, chemical industry, machine and aircraft construction, production of construction materials.

Unlike other nanomaterials, Nafen is already made on the trial platform in Tallinn and the company is going to expand production of nanofibres for entry into the markets of large consumers.

The patented production technology of nanofibres can be easily scaled depending on volumes of demand for material that makes Nafen more available to broad application in the most different fields of science and production in comparison with other commercial nanomaterials.

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