It can solve the problem of lithium dendrites in lithium batteries, which proves that this idea and theory are completely problematic.

However, the artificial SEI film made by researcher Yu Zhen did not achieve the desired effect, which aroused Xu Chuan's curiosity and deep thought.

In his speculation, such a question should not arise.

The lithium dendrite problem is part of the lithium evolution problem, and if the lithium dendrite problem can be solved, then the lithium evolution problem should also be solved, or at least partially solved.

However, the test results in his hand told him that the problem of lithium separation had not been solved, and it was even more serious.

This made Xu Chuan a little puzzled.

......

Staring at the test results in his hand, Xu Chuan carefully flipped through them.

According to the array control experiments, the lithium-ion battery with this new artificial SEI film has a higher efficiency of lithium separation at the negative electrode compared with the original lithium-ion battery.

If the coulombic efficiency of the original lithium-ion is in the range of 99.94%~99.96%, then the coulombic efficiency of the lithium battery with the new artificial SEI film is reduced to about 99.91%~99.2%.

Don't look at the proportion of only about 0.03 or 4, but in fact, it has a great impact on the number of charging cycles.

】

"Interesting, what is causing this problem?"

Looking at the tabular data of the control experiment, Xu Chuan touched his chin and thought.

He had never heard of this problem in his previous life, and this new artificial SEI film has also been widely used in all walks of life.

This shows that the problem has been solved.

He believed in his memory, and it was impossible for him to mistake anything about such an important thing, even if he was reborn once, and it would have been many years.

"Is there a problem with the protocol, or is there a problem with the material?"

Staring at the comparison data, Xu Chuan eliminated one guess after another, and finally left the two most likely ideas.

.......

"Senior Brother Fan, please prepare a few sets of materials for me to make this artificial SEI film."

After thinking for a moment and determining what he thought in his heart, Xu Chuan got up and instructed that he was going to do the experiment himself.

After all, the data is long, and there is no deeper understanding of it by yourself.

He had a hunch that this problem might not be very complicated, but if he couldn't find the key node, he wouldn't be able to solve the experiment.

......

SEI thin film refers to a passivation layer covering the surface of the electrode material during the first charge and discharge of the liquid lithium-ion battery, when the electrode material and the electrolyte react at the solid-liquid interface.

This passivation layer is an interface layer with the characteristics of a solid electrolyte, which is an electronic insulator but an excellent conductor of Li+.

The Li+ ions in the electrolyte can be freely embedded and expelled through the passivation layer, so this passivation film is called "solid electrolyte interface film", abbreviated as SEI.

This is where SEI membranes come from.

However, the naturally formed SEI film is not stable, and the spontaneously formed interface quality is poor, and it is difficult to control the deposition state of Li+ ions, which will lead to various problems such as battery short circuit, serious lithium evolution, explosion, fire, and spontaneous combustion.

Therefore, when the battery is manufactured, the researchers have found a way to artificially manufacture an SEI film to replace the natural SEI film, which helps to stabilize lithium electromagnetism, expand the battery capacity, and improve the cycle performance and service life of the electrode.

After decades of development, there are many types of artificial SEI membranes and the materials used are also different.

For example, silicon oxide, methyl acetate, lithium trioxide and so on.

Different anode materials and different electrolytes require different artificial SEI membranes.

So it's a huge, very independent market.

Xu Chuan also saw this.

Because it can bypass patents in other countries or research institutes.

A new type of artificial SEI film, if it can solve the problems of lithium dendrite, lithium precipitation, etc., then it can develop its own unique patent.

And others simply can't ignore it.

After all, the battery capacity used by everyone is about the same, and if the capacity of the new battery is doubled, you don't use it, and others will seize all the market if they use it.

After all, for the same price, someone else's battery life can be doubled, and everyone knows how to choose.

Unless you can develop it yourself.

But this possibility is too small, if it were really that easy, it would have been figured out a long time ago.

......

It took Xu Chuan a few days to make some artificial SEI films and apply them to the new battery for testing experiments.

The test results are like the SEI membranes made by researcher Yu Zhen before, and the lithium dendrite problem has been solved, but the problems of lithium evolution and lithium deposition still exist.

This made Xu Chuan sure that it was not that there was a problem with the experimental procedure, so all that was left was the material.

"Is there a problem with the artificial SEI material?"

Looking at the battery in the laboratory that is undergoing the charge-discharge cycle test, Xu Chuan's eyes seem to be like a perspective, going deep into the lithium battery, and seeing the negative electrode film that is constantly transporting lithium ions.

"No, this artificial SEI membrane is no problem, I have taken it apart and tested the lithium-ion batteries on the market and studied it, and this mature commercial product cannot be defective."

"If this is the case, then the cause of lithium ion problems such as lithium evolution and lithium deposition may be in the electrolyte."

"Maybe there is a problem with the electrolyte, or it may be caused by the mismatch between the electrolyte and the artificial SEI membrane."

In his mind, the information of each item is constantly being analyzed, and with the vision of the next twenty years, Xu Chuan is constantly and quickly investigating the problem.

The option that there was a problem with the artificial SEI material was directly ruled out by him.

That's his strength.

If it is another research institute or laboratory, it will definitely continue to focus on artificial SEI, thinking that it is not perfect, and will try its best to continue to improve. This wastes a lot of time and effort.

But Xu Chuan is different, he is standing on the shoulders of giants and looking forward to the future, and if there are problems in those places, he can directly eliminate them with his prophetic experience.

And other laboratories or research institutes, even if they suspect that there may be a problem with the electrolyte, do not dare to be as sure as he is.

.......

After determining that the problem was not with the artificial SEI film, he quickly found the electrolyte used in the new battery.

The electrolyte of lithium-ion batteries is generally prepared from high-purity organic solvents, electrolyte lithium salts, necessary additives and other raw materials under certain conditions and in a certain proportion.

The electrolyte used in Chuanhai material research is a very common type in the market.

It is mainly composed of cyclic carbonate, ethylene carbonate, lithium difluorooxalate borate and other materials, in addition to some other additives.

Among them, cyclic carbonate is an organic solvent with excellent performance, which can dissolve a variety of polymers and is the most common organic solvent in lithium batteries.

Ethylene carbonate is an indispensable additive, which can significantly improve battery performance when added to the electrolyte.

As for lithium difluoroxalate borate, it is an electrolyte lithium salt, which is used to carry lithium ions.

The three main materials, all fairly common, have their own advantages and disadvantages.

Xu Chuan didn't pay attention to the other rare added materials, and directly locked his eyes on these three main materials.

Large-scale and anomalous lithium evolution reactions and scientific intuition told him that the problem was most likely one of the three materials.

After thinking for a moment, Xu Chuan locked his eyes on ethylene carbonate and lithium difluorooxalate borate.

These two materials are more problematic than cyclic carbonates.

The performance of cyclic carbonate is very stable, and it is an organic solvent used in many lithium-ion batteries on the market, if it has a problem, the coulombic efficiency of lithium batteries is basically increased by less than 99.95%.

However, the current batteries on the market, the coulomb efficiency is basically above 99.95%, so it should be able to be ruled out first.

As for ethylene carbonate and lithium bisoxalate borate, Xu Chuan thought about it and locked the final choice on lithium difluorooxalate borate, a lithium electrolyte.

For the same reason, ethylene carbonate is also a commonly used additive in electrolytes, and it is present in almost every type of lithium-ion battery, and its adaptability is quite wide.

Lithium difluorooxalate borate is different, although many lithium-ion batteries on the market use this electrolyte lithium salt, it has its own drawbacks.

For example, its solubility is poor, and the ionic conductivity is relatively low.

And more importantly, it forms a stable passivation film with the anode material of lithium-ion batteries, which is generally current collector aluminum.

Although it protects the aluminium from electrolyte corrosion, it also interferes with the passage of lithium ions to a certain extent.

Without a doubt, it is the most questionable of the three materials.

......

After determining the goal, Xu Chuan did not continue to waste time and directly started the experiment.

He didn't give the job to anyone else at the institute, but took matters into his own hands.

The test method is very simple, since there is a suspicion that there is a problem with lithium difluorooxalate borate, then directly change to an electrolyte lithium salt.

There are many products that can replace it, whether it is lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate and other materials in the conventional inorganic electrolyte lithium salt; Or lithium bisoxalate borate, lithium bisfluorosulfonimide and other materials in the organic electrolyte lithium salt can be replaced.

It doesn't take much time to make some rudimentary lab batteries.

In less than six hours, Xu Chuan completed the overall experiment, not only replacing the electrolyte lithium salt material, but also completing the preliminary test of the new battery.

However, the result made Xu Chuan frown.

After the replacement of the electrolyte lithium salt material, the problem of lithium evolution and lithium deposition is still not solved.

"The problem isn't with lithium salts?"

Looking at the preliminary test results, Xu Chuan was a little surprised.

According to his analysis, the probability of lithium salt problems is as high as more than 80%, but the experimental results show that the problem does not occur in lithium salts.

If it's not lithium salts, what went wrong?

Organic solvent? Or additives?

It is very troublesome to check one by one, there are many added materials in the electrolyte, and the adaptability of each material to other materials must be considered.

For a laboratory like the Kawakai Materials Research Institute, which had almost no previous battery R&D experience, there was no previous empirical data to refer to, so it can be said that it had to start all over again.

After thinking about it, Xu Chuan rearranged the work in his hand.

For the follow-up test of the electrolyte lithium salt, he handed it over to others in the laboratory.

After all, there are still omissions in one or two experiments, and repeated experiments many times can determine whether there is a problem with the electrolyte lithium salt.

As for himself, he has conducted research on ethylene carbonate, a commonly used additive.

Although no problem was found in the electrolyte lithium salt, Xu Chuan still believes that the key to the problem of lithium evolution and lithium deposition is in the electrolyte. And it will definitely be on the three main materials.

For the study of ethylene carbonate, like the electrolyte lithium salt, he cleanly chose to directly replace the material.

It is the fastest and most effective way to simply detect the problem and judge whether there is a problem with the corresponding material, regardless of the suitability or anything.

Although material research and development is a matter of chance, experience and mathematical analysis can help R&D personnel make relatively correct choices, greatly reducing R&D time and investment costs.

After replacing the ethylene carbonate with another 'odorant carbonate' with a similar effect, Xu Chuan re-tested the battery.

The test, which had little hope, surprised him with the results.

After replacing the ethylene carbonate, the rate of lithium evolution and lithium deposition of lithium-ion batteries has been greatly improved.

When using ethylene carbonate as an additive to improve battery performance, the highest coulombic efficiency of the new battery is only about 99.93%.

After replacing it with odorized carbonate, the coulombic efficiency of the new battery has increased to about 99.98%.

An increase of 0.05 percentage points, which is enough to increase the number of charging and discharging cycles by 300 to 400 times.

But there are also disadvantages, after replacing ethylene carbonate, the performance of lithium batteries has decreased a lot.

For example, the charging speed has been reduced by nearly 18 percent, and the activation performance of the electrolyte has also been reduced a lot.

However, compared to the problem of lithium separation, these are acceptable.

.......

"Is the problem with ethylene carbonate? It's hard to believe. ”

Looking at the test results, Xu Chuan was surprised again.

If he remembers correctly, ethylene carbonate is an additive that will be used in future lithium-ion batteries, lithium-metal batteries, and even lithium-sulfur batteries.

Because compared with other additives, ethylene carbonate improves the performance of lithium battery batteries quite high, and other additives cannot be compared at all.

That's why he didn't think much about it.

But now, the results of the experiment clearly told him that the main culprit for lithium evolution and lithium deposition was ethylene carbonate.

"It's hard to believe."

Staring at the test results, Xu Chuan fell into deep thought again.

It should have been a very happy thing to solve the problem of lithium separation, but he had doubts about it.

In the future, when the research institute in the United States solved the problem of lithium dendrite, it must have encountered this problem, but they still chose ethylene carbonate as an additive.

Why is that?

Ethylene carbonate as an additive can indeed improve the performance of lithium batteries, but if it is the main culprit of lithium dendrites, then it should be replaced.

Why didn't that institute do that?

For this question, Xu Chuan was a little puzzled.

..........