Chapter 237 The key to solving the problem of lithium dendrites
It can solve the problem of lithium dendrites in lithium batteries, proving that this idea and theory is completely without problems.
However, the artificial SEI film produced by researcher Yu Zhen did not achieve the desired effect, which aroused Xu Chuan's curiosity and deep thought.
In his speculation, this kind of problem should not arise.
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 on hand told him that the lithium precipitation problem had not been solved, and had even become more serious.
This made Xu Chuan a little puzzled.
...
Staring at the test results in his hand, Xu Chuan began to read through them carefully.
Judging from a series of control experiments, the lithium-ion battery using this new artificial SEI film has a higher efficiency of lithium precipitation from 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 using the new artificial SEI film is reduced to about 99.91% to 99.2%.
Although it only accounts for about 0.03 to 4%, in fact, it has a great impact on the number of charging cycles.
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"Interesting, what exactly caused 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. 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 trusted his memory very much. For such important things, even if he was reborn once and many years had passed, he would not be able to remember anything wrong.
"Is there something wrong with the experimental procedure, or is there something wrong with the materials?"
Staring at the comparative data, Xu Chuan eliminated guesses one by one, and finally left two most likely ideas.
.......
"Senior Brother Fan, please prepare a few sets of materials for making this kind of artificial sei film for me."
After thinking for a moment and confirming his thoughts, Xu Chuan stood up and ordered that he was going to do the experiment himself.
After all, I only read a lot of data, and I don’t have a deeper understanding by doing it myself.
He had a hunch that this problem might not be very complicated, but if the key nodes could not be found, no matter how experiments he tried, he would not be able to solve it.
...
SEI film refers to 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, forming a passivation layer covering the surface of the electrode material.
This passivation layer is an interface layer that has the characteristics of a solid electrolyte. It is an electronic insulator but an excellent conductor of li.
Li ions in the electrolyte can freely insert and detach through the passivation layer, so this passivation film is called "solid electrolyte interface film", the English word solid electrolyte interface, abbreviation sei.
This is the origin of sei membrane.
However, the naturally formed SEI film is not stable, and the quality of the spontaneously formed interface is poor, making it difficult to control the deposition state of li ions, which can lead to battery short circuit, serious lithium deposition, explosion, fire, spontaneous combustion and other problems.
Therefore, when manufacturing batteries, researchers tried to artificially create a SEI film to replace the natural SEI film to stabilize lithium electromagnetism, expand battery capacity, and improve the cycle performance and service life of electrodes.
After decades of development, there are currently many types of artificial SEI membranes, and the materials used are also different.
For example, silicone oxide, methyl acetate, dilithium trioxide, etc.
Different negative electrode materials and different electrolytes require different artificial SEI membranes.
So this is a very large and independent market.
Xu Chuan was also right about this.
Because it can bypass patents from 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 its own unique patent.
And others simply cannot ignore it.
After all, the batteries currently used by everyone have the same capacity. If the capacity of the new battery is doubled, if you don't use it, others will seize all the market.
After all, for the same price, other people’s battery life can be doubled, so everyone knows how to choose.
Unless you can develop it yourself.
But the possibility of this is too small. If it were that easy, it would have been done long ago.
...
After spending a few days, Xu Chuan personally made some artificial SEI films and applied them to new batteries to conduct test experiments.
The test results are the same as the previous SEI film made by researcher Yu Zhen. The problem of lithium dendrites has been solved, but the problems of lithium precipitation and lithium deposition still exist.
This allowed Xu Chuan to confirm that there was no problem with the experimental procedures, and all that was left were the materials.
"Is there something wrong with the artificial sei material?"
Looking at the batteries undergoing charge and discharge cycle tests in the laboratory, Xu Chuan's gaze seemed to be like a perspective, looking deep into the lithium battery and seeing the negative electrode film that was constantly transporting lithium ions.
"No, there is nothing wrong with this artificial SEI film. I have dismantled and tested lithium-ion batteries on the market and studied them. This mature commercial product cannot be defective."
"If this is the case, then the cause of problems such as lithium precipitation and lithium deposition in lithium ions may occur in the electrolyte."
"Perhaps 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, pieces of information were constantly being analyzed. Using the perspective of the next twenty years, Xu Chuan was constantly investigating problems quickly.
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 artificial SEI, thinking it was imperfect, and would try their best to continue improving it. This would waste a lot of time and energy.
This chapter is not over yet, please click on the next page to continue reading! But Xu Chuan is different. He is standing on the shoulders of giants and looking forward to the future. Where there are problems, he can directly eliminate them with his prophetic experience.
Other laboratories or research institutes, even if they suspected that there might be a problem with the electrolyte, did not dare to be as sure as he was.
.......
After determining 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 in a certain proportion under certain conditions.
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 difluoroxalate borate and other materials, in addition to some other additive materials.
Among them, cyclic carbonate is an organic solvent with excellent performance and can dissolve a variety of polymers. It is the most common organic solvent in lithium batteries.
Ethylene carbonate is an indispensable additive, and its addition to the electrolyte can significantly improve battery performance.
As for lithium difluoroxalate borate, it is an electrolyte lithium salt used to carry lithium ions.
The three main materials are all quite common and have their own advantages and disadvantages.
Xu Chuan ignored the other rare additive materials and directly focused on these three main materials.
The large-scale and abnormal lithium evolution reaction and scientific intuition told him that the problem most likely lies in one of these three materials.
After thinking for a moment, Xu Chuan focused on ethylene carbonate and lithium difluoroxalate 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 by many lithium-ion batteries currently on the market. If there is a problem with it, the Coulombic efficiency of the lithium battery will basically not increase to more than 99.95%.
However, the Coulombic efficiency of batteries currently on the market is basically above 99.95%, so it should be eliminated first.
As for ethylene carbonate and lithium bisoxaloborate, Xu Chuan thought about it and settled on the lithium electrolyte of lithium difluoroxaloborate.
For the same reason, ethylene carbonate is also a commonly used additive in electrolytes. It is present in almost every type of lithium-ion battery and has a wide range of adaptability.
Lithium difluoroxalate borate is different. Although many lithium-ion batteries on the market use this electrolyte lithium salt, it has its own shortcomings.
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 current collector aluminum.
Although it can protect the negative electrode current collector aluminum from electrolyte corrosion, it will also interfere 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 waste any more time and started the experiment directly.
Rather than leaving the job to others at the institute, he took matters into his own hands.
The test method is very simple. Since it is suspected that there is a problem with lithium difluoroxalate borate, just change the electrolyte lithium salt directly.
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 bisoxaloborate, bisdifluoride in organic electrolyte lithium salts.
Materials such as lithium sulfonylimide can be substituted.
Making some crude laboratory batteries won't take long.
In less than six hours, Xu Chuan completed the overall experiment, not only replacing the electrolyte lithium salt material, but also completing preliminary testing of the new battery.
However, the result made Xu Chuan frown.
After replacing the electrolyte lithium salt material, the problems of lithium precipitation and lithium deposition are still not solved.
"The problem is not the 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 over 80%, but experimental results show that the problem does not occur with lithium salts.
If it's not lithium, what's wrong?
Organic solvent? Or additive?
It is very troublesome to check one by one. There are many additive materials in the electrolyte, and every change of material must consider its compatibility with other materials.
For a laboratory like Chuanhai Institute of Materials, which has almost no experience in battery research and development before, 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 rearranged the work at hand.
For subsequent testing of the electrolyte lithium salt, he handed it over to others in the laboratory.
After all, there are still some omissions in one or two experiments. Only by repeating the experiment many times can we determine whether there is any problem with the electrolyte lithium salt.
As for himself, he conducted research on ethylene carbonate, a commonly used additive.
Although no problem has been found in the electrolyte lithium salt, Xu Chuan still believes that the key to the problem of lithium precipitation and lithium deposition lies in the electrolyte. And it must be in the three main materials.
For the research on ethylene carbonate, just like the electrolyte lithium salt, he neatly chose to directly replace the material.
It is a simple detection problem to determine whether there is any problem with the corresponding material, without considering the adaptability. This is the fastest and most effective way.
Although material research and development is a matter of luck, experience and mathematical analysis can help researchers make relatively correct choices and greatly reduce research and development time and costs.
After replacing ethylene carbonate with another 'odorized carbonate' with similar effects, Xu Chuan re-tested the battery.
The test result, which he didn't have much hope for, surprised him greatly.
After replacing ethylene carbonate, the lithium evolution and lithium deposition rate of lithium-ion batteries 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%.
This chapter is not over yet, please click on the next page to continue reading! After replacing it with odorant carbonate, 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 charge and discharge cycles by 300 to 400 times.
But there are also disadvantages. After replacing ethylene carbonate, the performance of the lithium battery dropped 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 problem of lithium precipitation, these are acceptable.
.......
"The problem is ethylene carbonate? It's unbelievable."
Looking at the test results, Xu Chuan was surprised again.
If he remembered correctly, the additive ethylene carbonate will be used in future lithium-ion batteries, lithium metal batteries, and even lithium-sulfur batteries.
Because compared to other additives, ethylene carbonate can improve the performance of lithium batteries very much, and other additives are simply incomparable.
This is also the reason why he didn't think much about the problem that would arise here.
But now, the experimental results clearly told him that the culprit causing 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 had doubts about it.
When the American research institute solves the problem of lithium dendrites in the future, they will definitely encounter this problem, but they still choose 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 at all costs.
