Chapter 238 The Key to Solving the Lithium Dendrite Problem

It can solve the problem of lithium dendrites in lithium batteries, proving that this idea and theory are completely fine.

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

In his speculation, this problem should not occur.

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

However, the test results in hand told him that the lithium precipitation problem has not been solved, and it is even more serious.

This made Xu Chuan puzzled.

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

From the array control experiment, the lithium-ion battery using this new artificial SEI film has a higher efficiency of negative electrode lithium precipitation than the original lithium-ion battery.

If the original lithium ion coulomb efficiency is in the range of 99.94%~99.96%, then the lithium battery using the new artificial SEI film has a coulomb efficiency reduced to about 99.91%~99.2%.

Although it only accounts for about 0.03 or 0.4, it actually has a great impact on the number of charging cycles.

"Interesting, what exactly caused this problem?"

Looking at the table 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 this problem has been solved.

He believes in his memory very much. For such an important thing, even if he has been reborn once, it has been many years, and it is impossible to remember anything wrong.

"Is there a problem with the experimental steps, or is there a problem with the materials?"

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

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

After thinking for a moment and confirming his idea, Xu Chuan stood up and ordered that he was going to do the experiment himself.

After all, the more data you look at, the deeper your understanding will be.

He has a hunch that this problem may not be very complicated, but if you can't find the key node, you won't be able to solve it no matter how you experiment.

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 interface during the first charge and discharge process of the liquid lithium-ion battery.

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

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

This is the origin of the SEI film.

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

Therefore, when manufacturing batteries, researchers tried to artificially create a SEI film to replace the natural SEI film, which helps to stabilize lithium electromagnetism, expand 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.

For example, silicon oxide, methyl acetate, lithium trioxide, etc.

Different negative electrode materials and different electrolytes require different artificial SEI membranes.

So this is a huge and independent market.

Xu Chuan is also targeting this point.

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

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

And others can't ignore it at all.

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

After all, for the same price, others can double their battery life, and everyone knows how to choose.

Unless you can develop it yourself.

But this possibility is too small. If it is that easy, it would have been done long ago.

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

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

This confirmed that it was not the experimental steps that were problematic, so the only thing left was the materials.

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

Looking at the battery undergoing charge and discharge cycle tests in the laboratory, Xu Chuan's eyes seemed to be as if he had a perspective, penetrating deep into the lithium battery and seeing the negative electrode film that was constantly transporting lithium ions.

"No, this artificial SEI film is fine. I have disassembled and tested lithium-ion batteries on the market and studied them. This mature commercial product cannot have defects."

"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, maybe it is caused by the mismatch between the electrolyte and the artificial SEI film."

In his mind, one piece of information after another was constantly being analyzed. With the vision of the next twenty years, Xu Chuan was constantly and quickly troubleshooting the problem.

He directly ruled out the option that there was a problem with the artificial SEI material.

This is his advantage.

If it were other research institutes or laboratories, they would definitely continue to focus on the artificial SEI, thinking that it was imperfect and would try every means to continue to improve it. Thus wasting a lot of time and energy.

But Xu Chuan is different. He is standing on the shoulders of giants to look to the future. If there are problems in those places, he can directly rule them out with his prophetic experience.

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 made of high-purity organic solvents, electrolyte lithium salts, necessary additives and other raw materials, prepared under certain conditions and in a certain proportion.

The electrolyte used by Chuanhai Materials Research Institute is a very common type on 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.

And ethylene carbonate is an indispensable additive. It can significantly improve battery performance when added to the electrolyte.

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

The three main materials are quite common things, with their own advantages and disadvantages.

Xu Chuan ignored other rare additives and directly locked his eyes on these three main materials.

The large-scale and abnormal lithium precipitation reaction and scientific intuition told him that the problem was most likely in one of these three materials.

After thinking for a while, Xu Chuan locked 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. It is an organic solvent used in many lithium-ion batteries on the market. If it has problems, the coulomb efficiency of lithium batteries will basically not be increased to more than 99.95%.

However, the coulomb efficiency of batteries on the market is basically above 99.95%, so it should be excluded first.

As for ethylene carbonate and lithium bis(oxalate borate), Xu Chuan thought about it and locked the final choice on lithium electrolytes such as lithium difluorooxalate borate.

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

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

For example, it has poor solubility and relatively low ionic conductivity.

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

Although it can protect the negative electrode current collector aluminum from corrosion by the electrolyte, it will also interfere with the passage of lithium ions to a certain extent.

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

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

He did not hand over the work 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, just change it 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 bis oxalate borate, bis difluorosulfonyl imide and other materials in organic electrolyte lithium salts.

It doesn't take long to make some simple laboratory 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 replacing the electrolyte lithium salt material, the problem of lithium precipitation and lithium deposition was still not solved.

"The problem is not with the lithium salt?"

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

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

If it is not lithium salt, then what is wrong?

Organic solvent? Or additives?

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

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

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

For the subsequent testing of electrolyte lithium salt, he handed it over to other people in the laboratory.

After all, one or two experiments still have omissions, and repeated experiments can determine whether there is a problem with electrolyte lithium salt.

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

Although no problems were found in the electrolyte lithium salt, Xu Chuan still believed that the key to the lithium precipitation and deposition problems was in the electrolyte. And it must be in the three main materials.

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

The fastest and most effective way is to simply detect the problem and judge whether the corresponding material has any problems without considering compatibility.

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

After replacing ethylene carbonate with another "stinky carbonate" with similar effects, Xu Chuan retested the battery.

The test results, which did not hold much hope, surprised him greatly.

After replacing ethylene carbonate, the lithium precipitation and lithium deposition rates of lithium-ion batteries have been greatly improved.

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

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

An increase of 0.05 percentage points is enough to increase the number of charge and discharge cycles by 300 to 400 times.

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

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

However, compared with the solution of the lithium precipitation problem, these are acceptable.

"The problem is actually with ethylene carbonate? This is really hard to believe."

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

If he remembered 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 has a very high improvement in the performance of lithium batteries, and other additives cannot be compared at all.

This is 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 is ethylene carbonate.

"It's really hard to believe."

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

Solving the lithium precipitation problem should have been a very happy thing, but he doubted it.

When the US research institute 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 this?

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

Why didn't the research institute do this?

Xu Chuan was a little confused about this question.