Great Country Academician

It can solve the problem of lithium dendrites in lithium batteries, which proves that this line of thinking and theory is completely correct.

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

In his speculation, this kind of problem should not arise.

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

However, the test results in his hand told him that the problem of lithium analysis has not been solved, and it has even become more serious.

This made Xu Chuan a little puzzled.

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

Judging from the array control experiments, the lithium-ion battery using this new type of artificial SEI film has a higher efficiency of lithium-ion separation at the negative electrode than the original lithium-ion battery.

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

Although it only accounts for about 0.03 or 4, in fact, it has a great impact on the number of charging cycles.

"Interesting, what exactly is causing this problem?"

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

He had never heard of this problem in his previous life, and this new type of 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 own memory. For such an important thing, even if he was reborn once, it would take many years, and he would not be able to remember anything wrong.

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

Staring at the comparison data, Xu Chuan ruled out guesses one by one, and finally left two most likely ideas.

"Brother Fan, please prepare some sets of materials for making this artificial SEI film."

After thinking for a while and confirming his thoughts, Xu Chuan got up and ordered that he was going to do an experiment by himself.

After all, if you look at more data, you don't have a deeper understanding by doing it yourself.

He has a hunch that this problem may not be very complicated, but if the key nodes cannot be found, no experiment will be done.

SEI film refers to a passivation layer covering the surface of the electrode material formed by the reaction between the electrode material and the electrolyte at the solid-liquid phase interface during the first charging and discharging process of the liquid lithium-ion battery.

This passivation layer is an interfacial layer that has the characteristics of a solid electrolyte, an electronic insulator but an excellent conductor of Li+.

Li+ ions in the electrolyte can be freely inserted and extracted through the passivation layer, so this passivation film is called "solid electrolyte interface film", the English word solid electrolyte interface, abbreviated as SEI.

This is the origin of the SEI film.

However, the naturally formed SEI film is not stable, and the quality of the spontaneously formed interface 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, severe lithium precipitation, explosion, fire, and spontaneous combustion.

Therefore, when the battery was manufactured, the researchers tried to artificially manufacture a kind of SEI film, which was used to replace the natural SEI film, to help stabilize the lithium electromagnetic, 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 films, and the materials used are also different.

Such as silicon oxide, methyl acetate, lithium trioxide and so on.

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

So this is a very large and very independent market.

This is exactly what Xu Chuan was aiming for.

Because it can bypass the patents of other countries or research institutes.

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

And no one else can ignore it.

After all, the capacity of batteries used by everyone is similar at present, and if the capacity of the new battery is doubled, if you don’t use it, others will seize all the market if it is used.

After all, for the same price, the battery life of others 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 done long ago.

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

The test results are the same as the previous SEI film made by Yu Zhen. The problem of lithium dendrites has been solved, but the problems of lithium analysis and lithium deposition still exist.

This allowed Xu Chuan to confirm that it was not a problem with the experimental procedures, so the only thing left was the materials.

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

Looking at the battery that was undergoing charge-discharge cycle test in the laboratory, Xu Chuan's eyes seemed to penetrate into the lithium battery as if through perspective, and he saw the negative electrode film that was continuously transporting lithium ions.

"No, this artificial SEI film is fine. I have disassembled and inspected lithium-ion batteries on the market, and this mature commercial product cannot be defective."

"If this is the case, then the cause of lithium ion precipitation and lithium deposition may be in the electrolyte."

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

In his mind, each piece of information was constantly being analyzed, using the perspective of the next twenty years, Xu Chuan was constantly and quickly troubleshooting the problem.

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

This is his advantage.

If it is other research institutes or laboratories, they will definitely continue to focus on the artificial SEI, thinking that it is not perfect, and will try their best to continue to improve it. Thus wasting a lot of time and energy.

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

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

After confirming that the problem was not caused by the artificial SEI film, he quickly found the electrolyte used in this 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 solution used by Chuanhai Materials Research Institute 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 additive materials.

Among them, cyclic carbonate is an organic solvent with excellent performance, which can dissolve various 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 difluorooxalate borate, it is an electrolyte lithium salt for carrying lithium ions.

The three main materials, all fairly common stuff, 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.

The large-scale and abnormal lithium analysis reaction and scientific intuition told him that the problem is likely to be in one of these three materials.

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

These two materials are more prone to problems 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 there is a problem with it, the Coulombic efficiency of lithium batteries will basically increase by less than 99.95%.

However, the coulombic efficiency of batteries currently on the market is basically above 99.95%, so it should be ruled out first.

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

For the same reason, ethylene carbonate is also a commonly used additive in the electrolyte. It exists in almost every type of lithium-ion battery and has a wide range of adaptability.

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

Such as its poor solubility, relatively low ionic conductivity and other issues.

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

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

It is without a doubt the most questionable of the three materials.

Having determined the goal, Xu Chuan didn't waste any more time and started the experiment directly.

He didn't hand over the job to other people in the institute, but did it himself.

The test method is very simple. Since it is suspected that there is a problem with lithium difluorooxalate borate, then directly change to another electrolyte lithium salt.

There are many products that can replace it, whether it is lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate and other materials in conventional inorganic electrolyte lithium salts; or lithium bisoxalate borate, bisdifluoro Materials such as lithium sulfonyl imide can be substituted.

It won't take long to make some crude 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 testing of the new battery.

However, the result made Xu Chuan frown.

After replacing the electrolyte lithium salt material, the problems of lithium analysis and lithium deposition are still not resolved.

"The problem is not lithium salt?"

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

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

If it's not lithium salt, what's wrong?

Organic solvents? Or additives?

It is very troublesome to check one by one. There are many additive materials in the electrolyte, and the change of each material must consider the compatibility with other materials.

For a laboratory like the Chuanhai Materials Research Institute, which has almost no previous experience in battery research and development, there is no previous experience data to refer to, and it can be said that it has to start from scratch.

After thinking about it, Xu Chuan re-arranged the work in hand.

For subsequent tests on the lithium salt of the electrolyte, he passed it on to others in the lab.

After all, there are still omissions in one or two experiments. Only by repeating the experiment many times can it be determined whether there is any problem with the electrolyte lithium salt.

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

Although no problem has been found from the electrolyte lithium salt, Xu Chuan still believes that the key to the problem of lithium analysis and lithium deposition lies in the electrolyte. And it will definitely be on the three main materials.

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

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

Although material research and development is a matter of luck, experience and mathematical analysis can help developers make relatively correct choices, greatly reducing research and development time and cost.

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

The test that he didn't hold much hope for originally surprised him greatly.

After replacing ethylene carbonate, the lithium ion battery's lithium analysis and lithium deposition speed have 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 ethanocarbonate, the Coulombic efficiency of the new battery increased to about 99.98%.

An increase of 0.05 percentage points 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 dropped a lot.

For example, the charging speed has decreased by nearly 18%, and the activation performance of the electrolyte has also decreased a lot.

However, compared with the solution to the lithium analysis problem, these are acceptable.

"It's ethylene carbonate that's the problem? It's unbelievable."

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

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

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

This is also the reason why he didn't think much about the problem.

But now, the experimental results clearly told him that the culprit of lithium precipitation 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 be a very happy thing to solve the problem of lithium analysis, but he has doubts about it.

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

why is that?

As an additive, ethylene carbonate can indeed improve the performance of lithium batteries, but if it is the culprit causing the lithium dendrite problem, then it should be replaced anyway.

Why didn't that institute do this?

Xu Chuan was a little confused about this question.