Lithium-air accumulator Lithium-air, Li-air

2018: Lithium-air accumulators sustained 700 cycles of a recharge

The American chemists for the first time created the effective lithium-air accumulator which maintains 700 cycles of charging — discharging that is comparable with indicators of modern li-ion cells which work without considerable decrease in capacity from 400 to 1200 cycles. It managed to achieve thanks to a protecting cover on the lithium anode and also specially picked up structures of the cathode and electrolyte in an electrochemical cell, scientists write[1]^[1] to^[2][3].

For increase in efficiency of accumulators scientists try not only to improve the existing schemes of electrochemical cells due to modification of structure and structure of electrodes or electrolyte, but also look for other more profitable oxidation-reduction reactions which happen at charging and accumulator unloading. Lithium-air chemical current sources are considered as one of the most perspective options of replacement to Li-ion batteries most popular now. These batteries are based on reaction of lithium with oxygen with formation of peroxide of lithium of Li2O2, and by theoretical estimates have the specific energy, maximum from the known batteries — about 40 megajoules per kilogram that approximately in 5 times more, than at modern li-ion cells.

The main problem of lithium-air batteries — the complicated work in the conditions of chemical composition of air. Effective lithium - oxygen batteries using pure oxygen already managed to be received, however they cannot be put into practice and have the increased potential of explosion. In case of presence at the gas environment of nitrogen, a carbon dioxide gas and water products of collateral reactions contaminate a surface of electrodes and considerably reduce accumulator operating time, and after 10 — 20 cycles of charging — discharging the battery ceases to work.

For the solution of this problem the group of the American electrochemists under the leadership of Amin Salehi-Khojin from the Illinoyssky university in Chicago offered the new scheme of a lithium-air electrochemical cell which allows to limit intensity of collateral reactions on electrodes and to raise thus time of effective cyclic operation of the accumulator. For this purpose scientists used two approaches. First, the covering on the basis of carbon and a carbonate of lithium was applied on the surface of the lithium anode of the battery. Through such layer pass only lithium ions, thus the anode is protected from influence of the atmosphere. Secondly, as the cathode it was offered to use the nanostructured disulfide of molybdenum which serves as the oxygen recovery reaction catalyst. As electrolyte in the offered architecture of an electrochemical cell served dimethyl sulfoxide mix with ionic liquid on the basis of the tetraftorborat (EMIM-BF4).

For check of cyclic work of the offered scheme of the accumulator researchers made an experiment on a repeated recharge using model gas mix which composition corresponded to composition of air. Except electrochemical measurements, for a research of processes of chemical passivation of electrodes authors of work with the help of microscopy and several spectrometer methods also defined their structure and chemical composition after each 5 cycles.

Microphotographs of a surface of the cathode after the first and 250th discharging (an and c), after the first and 250th charging (b and d). On the right the photo of the discharged cathode received using the translucent electronic microscopy of M. Asadi et al is provided. / Nature, 2018

It turned out that the lithium-air battery made thus maintains not less than 700 cycles of a recharge without noticeable falling of capacity, chemical composition of electrodes at the same time practically does not change. According to authors of work, after each of charging cycles - accumulator unloadings involved remain about 99.97 percent of lithium. Scientists also confirmed efficiency of the offered scheme of the accumulator using numerical calculations with method of the theory of functionality of density, having studied process of a catalysis of reaction of recovery of oxygen at edges of nanoparticles of a disulfide of molybdenum and also the probability of interaction of water and a carbon dioxide gas with the lithium peroxide which is formed in a cell.

Scientists claim that it is actually first effectively working prototype of the lithium-air accumulator which is capable of such long cyclic work. Therefore the offered architecture of an electrochemical cell, according to authors of work — very important step on the way to creation of lithium current sources of new generation with much higher, than at present accumulators, indicators of specific density of energy.

2017: Samsung thought up how to double the capacity of batteries for electric vehicles

According to information of the Japanese Nikkei Asian Review (November, 2017), in Samsung Electronics development of perspective rechargeable batteries for electric vehicles of new generation which charge capacity twice exceeds indicators of li-ion cells popular today is conducted, and approximately for 50%^[4] indicators of new generation of solid-state batteries^[5].

Automobile accumulators of Samsung are based on so-called lithium-air (lithium-air, Li-air) the technology using for generation of current process of oxidation of lithium on the anode and recovery of oxygen on the cathode.

According to information of Nikkei, in case of successful development of batteries of new type of Samsung has every chance to considerably overtake the competitors working in the development area of accumulators for new electric vehicles, mainly, of the companies from Japan and South Korea.

Features of technology

For the first time the lithium-air production technology of rechargeable batteries was offered in the 1970th years, however at that time due to the lack of a complex of necessary technologies of noticeable commercial success it was not succeeded to achieve.

Nevertheless, the interest to lithium - oxygen technology was constantly retained as theoretical specific energy of the lithium-air battery with a work material of Li2O2 is very high: in the charged status it can reach 40.1 MDzh/kg that is already comparable to theoretical specific energy of gasoline (46.8 MDzh/kg).

Li-ion and lithium-air batteries

Interest in lithium-air batteries returned quite recently, in process of development of materials science and modern production technologies. Besides, researches in this area are generously sponsored by the autoindustry today. So, Toyotas Motor already announced plans of the self-produced beginning of solid-state batteries in the middle of the next decade.

Now developers from Samsung managed to achieve the specific capacity of the lithium-air batteries developed by them at the level about 520 W/h per kilogram of battery weight.

The serious break in development managed to achieve due to use of the superthin separator which is a crucial element of construction of such batteries. According to Nikkei, separator thickness in lithium-air accumulators of Samsung is only 20 microns - it is less than 10% of separator thickness in the previous models of batteries. At the expense of it developers managed to increase the specific density of a charge, and, as a result, the general battery capacity at the expense of bigger number of cells per unit of volume.

For comparison of Nikkei gives characteristics of the new electric vehicle Leafot Nissan Motor which battery power is enough for a run on distance about 400 km. The lithium-air battery of Samsung can theoretically provide the similar electric motor with a run from one charge on distance to more than 700 km.

Electric vehicles

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