Start as a top student and move towards the stars and the sea

Well, I just happened to think of this direction when I was looking at the experimental data. In fact, if the experiment time is enough, we will sooner or later have to conduct the limit test of the number of cycles.

Hey, that's the truth, but when it comes to actually doing experiments, time is never enough. If it takes a few months to discover this problem and conduct detailed 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 could only admit that compared with real geniuses, he still seemed 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 be the teacher's break at the testing center. However, because of Xu Zhou's call, the testing center was very happy to help Sui Feng arrange the experiment.

How's it going? Do 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.

With that said, 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, it is very normal for this kind of passivation layer to form during the charging and discharging process of lithium batteries.

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, which 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.

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 had the same feeling 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 nanomaterial. Normally, this pressure will only slowly reduce the negative electrode However, as this effect continues to accumulate, it may cause structural damage to porous silicon nanomaterials.

After some analysis, Xu Zhou found the possible mechanism for this phenomenon, and Ning Chen agreed with it after hearing this.

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.

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 a thinner carbon structure to the outer layer of the composite material of silicon and metal. This carbon structure can prevent the direct contact between the electrolyte and the porous silicon nanomaterials, while also affecting the energy density of the battery. There will be no significant impact.”

After hearing 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.

The composite of silicon and carbon should be synthesized by what method, etc.

Xu Zhou, Ning Chen and others discussed together for several days before finalizing the experimental plan.

…

As time passed, Xu Zhou, Ning Chen, Sui Feng and others conducted a large number of experiments together. While experiencing countless failures, they also gained many very 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 in more than 30 subjects.

This sounds like an incredible thing. From the beginning, the school repeatedly confirmed with Ning Chen whether it was really necessary to test 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 exam, Ning Chen would complete the answers and hand in the papers in advance about half an hour after the exam started, just like watching a horse fly.

The final result 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.

All Ning Chen had to do was 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 negative electrode 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 satisfactory one is a porous nano-silicon-silver-carbon composite material.

After extensive testing, this material showed a high first reversible capacity, and the reversible capacity remained at a high level after multiple cycles.

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.