Chapter 103 This is our ideal anode material
“Well, I just happened to think of this direction when I was looking at the experimental data. In fact, if the experimental time is enough, we will also have to perform the number of cycles sooner or later. "It's the ultimate limit test."
"Hey, this is the truth, but when it comes to actual experiments, there will never be enough time to find out this problem in detail. Research, I don’t know how much time will be wasted.”
Thinking of this, Xu Zhou couldn’t help but feel helpless.
Even now it seems that there is no problem with his previous experimental ideas, but Ning Chen can always find the key experimental ideas more keenly than himself.
Xu Zhou always felt that Ning Chen seemed to have some special abilities, but as a staunch materialist, Xu Zhou knew that this was not a scientific idea.
Xu Zhou can only admit that compared with real geniuses, he still seems a bit ordinary.
While Ning Chen and Xu Zhou were discussing these issues, Sui Feng had already returned to the laboratory with the samples.
Seeing Sui Feng come back, Xu Zhou asked excitedly:
"Sui Feng, have you finished the test?"
"Yes, after I got there, the teacher arranged for me to conduct experiments."
When Sui Feng went there, it happened to coincide with the teacher's break in the testing center. However, because of Xu Zhou's call, the testing center still Very readily helped Sui Feng arrange the experiment.
"How about it, can you see the reason?"
"Well, it's probably because of the passivation layer formed on the surface of the negative electrode material. Let's look at the scanning electron microscope image for details."
As he said that, Sui Feng found the scanning electron microscope image he had just finished and showed it to Ning Chen and Xu Zhou.
Seeing the scanning electron microscope image, Ning Chen and Xu Zhou also saw what the material in the image was.
“Yes, it is indeed the passivation layer on the surface of the negative electrode material. But why does this have such a drastic impact on the cycle capacity of lithium batteries?”
In fact, when charging and discharging lithium batteries, It is very normal for this passivation layer to form during the process.
Because the electrolyte will continuously react with the electrode material, the substances generated by these reactions will slowly accumulate near the electrode material, forming a passivation layer.
This passivation layer will have some effects on the performance of the electrode material. These effects are good and bad. One of the negative effects is that it will reduce the charge and discharge efficiency of the electrode material, especially the negative electrode material. The impact is more obvious.
However, this effect is often relatively slow and will not cause a cliff-like impact on the performance of lithium batteries.
At this time, Ning Chen suddenly thought of something and continued to look at the scanning electron microscope images made by Sui Feng.
"No...the volume of porous silicon nanomaterials seems to have changed significantly compared to before. Perhaps this is the root cause of this phenomenon."
Thinking of this , Ning Chen said:
"Teacher Xu, look at the image here. Do you feel that the volume of the porous silicon nanomaterial here seems to have changed somewhat?"
In fact, judging from the accuracy of the image, this change is not easy to detect. It's just that Ning Chen is very familiar with this porous silicon nanomaterial, so he is keenly aware of this change.
"Yes, I felt the same way just now. In this way, it is probably because the passivation layer generated on the surface of the negative electrode material exerts a compressive effect on the porous silicon nanomaterials. This compressive effect is normal It will only slowly reduce the cycle performance of the anode material, but as this effect continues to accumulate, it may cause structural damage to the porous silicon nanomaterials.”
After some analysis, Xu Zhou found out. After hearing this, Ning Chen agreed with the possible mechanism of this phenomenon.
“Yes, the physical properties of porous silicon nanomaterials are still more fragile than conventional carbon anode materials. Even if metal substances are added, this situation has not been completely solved.”< br>
After finding the cause of the experimental phenomenon, Ning Chen and Xu Zhou fell into silence, each thinking about ways to solve the problem.
Sui Feng was waiting on the side. Anyway, Sui Feng also knew that problems of this level were definitely not something he could solve.
At this time, Xu Zhou seemed to have another idea and said to Ning Chen:
“We can try this. Add another layer to the outer layer of the composite material of silicon and metal. Thin carbon structure. This carbon structure can prevent direct contact between the electrolyte and the porous silicon nanomaterials, and will not have a significant impact on the energy density of the battery."
Hear Xu Zhou's plan. , Ning Chen couldn’t help but nodded vigorously.
Carbon materials have the advantages of good electrical conductivity, small volume change, and appropriate lithium insertion ability, and are very suitable for combination with silicon-based composite materials. Ning Chen couldn't help but sigh in his heart, Xuzhou did have his own unique ideas in the field of materials, and there were many places worth learning from Ning Chen.
In the following time, Xu Zhou and Ning Chen continued to study specific solutions to this problem.
First of all, experiments on porous nano-silicon-metal anode materials need to continue. They need to find the metal substance that is most suitable for matching with porous silicon.
Secondly, they also need to conduct a lot of experimental work on the idea of adding a carbon layer to the outer layer of the material.
For example, whether to choose to add graphite, carbon nanotubes, or mesophase carbon microspheres.
How thick should the added carbon layer be so that it can protect the porous nano-silicon without affecting the battery capacity.
How to synthesize silicon and carbon composites, etc.
Xu Zhou, Ning Chen and others discussed it for several days before finalizing the experimental plan.
......
Time passed day by day. Xu Zhou, Ning Chen, Sui Feng and others conducted a large number of experiments together. While experiencing countless failures, they also gained a lot of extraordinary results. Valuable experimental phenomena and experimental conclusions.
The improved negative electrode material has significantly improved the battery life. At the same time, after experiencing multiple charge and discharge cycles, there will no longer be a significant decrease in reversible capacity.
During this period, Ning Chen also completed the proof of the second stage of Qiu Chengtong's conjecture, compiled it into a paper, and submitted it again to the Journal of the American Mathematical Society.
At this point in the proof work, Ning Chen also knew that he was only one step away from completely solving Qiu Chengtong's conjecture.
At the end of the semester, in order to get her undergraduate degree certificate and graduation certificate earlier, Ning Chen completed the final exams of more than 30 subjects in a row.
This sounds like an incredible thing. From the beginning, the school also repeatedly confirmed with Ning Chen whether it really needed to take so many subjects in one semester.
However, with Ning Chen's constant persistence, the school agreed to Ning Chen's request.
In fact, this is nothing to Ning Chen, because he has already learned the knowledge of many exam subjects, and Ning Chen does not need to invest too much energy in it.
For each subject's exam, Ning Chen would complete the answers and hand in the paper in advance about half an hour after the exam started, just like watching a horse fly.
The final results also proved that Ning Chen really had such achievements.
Not only did every subject pass smoothly, but the scores in most subjects reached full marks or were close to full marks, which amazed the teachers.
This means that Ning Chen completed his undergraduate double major in materials and mathematics in less than two years.
The only thing left for Ning Chen to do is to complete his graduation project and graduation defense.
And because Ning Chen has already made outstanding achievements in these two fields, there is no need for another graduation project. The graduation defense is just a formality.
......
After the winter vacation began, Ning Chen did not go home immediately. Instead, he stayed at school temporarily and continued experiments on silicon-based anode materials.
The current experiment has entered the final stage. After continuous testing, we have found several silicon-based lithium battery anode materials that have the potential to enter the application stage.
Among them, the most satisfying one is a porous nano silicon-silver-carbon composite material.
After extensive testing, this material has shown a high first reversible capacity, and after multiple cycles, the reversible capacity remains at a high level.
Because of the protective effect of the carbon layer, the porous silicon nanoparticles will not be affected by the electrolyte. Even after 500 cycles, the reversible capacity of the battery has not declined sharply.
Although the addition of metallic silver increases the cost of lithium batteries, it is still within an acceptable range.
Xu Zhou informed Xu Shou about the experimental progress of the experimental team. After Xu Shou learned that the experimental team had made these breakthroughs, he immediately said that he would fly to Shengzhou as soon as possible to learn about the relevant experimental conditions.
(End of this chapter)