Why should lithium air battery technology inhibit side effects?

In fact, in recent years, the battery main power comes from the industry's rapid expansion power battery demand of the industry, so the battery technology development, technology in the process of practical application is often the most need to consider is the need of power battery, and at this point, the lithium battery empty even at low magnification are great polarization will inevitably lead to very not ideal energy efficiency and the ratio of performance, this also is in the field of power battery for practical important obstacle to overcome.

Lithium-air battery is a very potential high capacity battery technology, the use of lithium metal and oxygen reversible reaction, the theoretical upper limit of the energy density of 11000 Wh/kg, far more than the pool is the actual energy density of 200 + Wh/kg, that result in the academia and industry, is widely considered to be a battery in the field of reverse technology in the future.But empty lithium battery research in the industry there has been a lot of question, many people think that lithium air batteries defined (oxygen) should be called lithium complex, reaction mechanism, the polarization low efficiency, poor cycle life, is not the future (power battery demand as the driving force for the important industry) on development direction of the battery industry.Of course in this process, the researchers work efforts, to produce a lot of achievements, to in-depth discussion in the direction of the future.

Recently scientists in the United States and reached a breakthrough in the study of lithium air batteries, in the journal NATURE, success can be made in class air atmosphere circulation over 700 batteries, good solved before many system can only react with pure oxygen, circle life is very poor, often a few dozen times), in the field of scientific research level have made great progress.In this, the author will introduce in this paper, the research progress of content, and put forward the empty lithium battery technology industrialization practical prospect in the future.

1 empty, lithium battery technology concept discussion, inhibit the importance of the adverse event

One big advantage of empty lithium battery technology is 11000 wh/kg of theoretical maximum density is almost equivalent to that of fossil fuels.However, the data is only a the most optimistic estimate method.

In the preparation of the reaction, if you don't calculate the quality of O2, think its inexhaustible, from the air, of course, can be pure lithium energy change values in the response to directly calculate the ideal value of 11500 wh/kg (below).However, the calculation is actually not rigorous: 1) the reaction system of specific energy calculation should not be thrown in addition to the quality of the reaction gas, if the quality of computing into the O2, the energy density of reaction system will soon reduced to 3500 wh/kg;2) lithium will actually complicated with almost all of the components in the air of irreversible reaction, which is one of the bottleneck of the lithium battery empty system technology.

1.png

The calculation of theoretical energy density of lithium air batteries (not including the quality of the oxygen), from JeffDahn report "ElectricallyRechargeableMetal - airBatteriesComparedtoAdvancedLithium - ionBatteries".

So actually, lithium air batteries (Li - air) strict definition is lithium battery oxygen (O2) Li -, and inhibition of lithium complex reaction with other components in the air, in fact, lithium air batteries one of the most important first to solve the basic problem.

2, the solution in this paper

Solution is: in CO2 atmosphere, repeated on lithium anode electrochemical charge cycle, make its surface generated Li2CO3 / C composite coating.Researchers use the SEM, EELS, XPS for the layer of dense morphology, chemical state, element had been used to characterize the existence situation, confirmed that the formation of the layer.Then on the protective layerLithium electricityDo the test, they found that even in the deep circulation of lithium all ran out strippingtest (0.5 mA/cm2), it can implement weekly cycle of lithium/material 99.97% retention capacity, the data is far higher than other research achievements in the industry.

3, the whole cell reaction, the life situation and protective layer preparation process optimization

With MoS2 anode, cathode, the protective layer of lithium EMIM - BF4 / DMSO (25% / 75%) made the whole battery electrolyte, and the class in the human has the air atmosphere.Reaction began to occur in the first week 2.92 V, and Li2O2 formation was very close to the potential of 2.96 V, illustrates the main reaction is good, in 3.75 V when the specific capacity of 500 mah/g.Circular polarization voltage difference of the first week of 0.88 V, 50 weeks of 1.3 V, 1.62 V after 550 weeks.In response to 700 weeks later, the battery can still work;In contrast, without the protection of lithium air batteries can only cycle around 10 times have failed.For the thickness of the protective layer selection, in this paper, the author thinks: too thin protective layer can cause the electrolyte decomposition, thick protective layer and leads to the charge transfer of electric potential and side effects, so you need to optimize.After experiment, found that 10 times cycle preparation of protective layer thickness is most appropriate.

[editor1526204293436412.png]

Has a protective layer of cells first weeks to 550 weeks of charge-discharge curve B10 time advance preparation of protective layer of the sample can achieve optimal circulation loop performance

[editor1526204293582278.png]

Lithium empty oxygen, lithium battery with cyclic polarization voltage changes

4, all kinds of characterization methods for the side effects of inhibition

Further, the author adopted the RAMAN study circle on the surface of the anode after discharge, found that only need Li2O2 reaction, no other impurities, and the Li2O2 in the electrolyte also showed good stability.The author also combines the NMR method, further show that the system is not common in the air caused by CO2, H2O, more complex reaction.Finally the author also combined with the calculation method of DFT, illustrates the protective layer can effectively prevent the N2, O2 diffusion to lithium metal anode (restrain side effects), but for the lithium ion diffusion to the anode reaction (need).Also use ABINITIO algorithm shows the water molecules and the reaction of Li2O2 is difficult in the thermodynamics, reaction with CO2 need multiple clusters composed of CO2, and that under the condition of low CO2 concentration in the air is difficult to achieve.

5, summary

By the visible on, this paper gives a detailed analysis of characterization methods, illustrates the method for lithium battery empty side effects of protective growth inhibition and the improvement of cycle life has obvious effect.The two problems are troubling lithium air batteries at the heart of the challenge, so the paper work has made important breakthrough in the field of basic research, so to speak.

The page contains the contents of the machine translation.