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.
】
"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.
To be continued...