Starting from a top student and marching towards the sea of ​​stars

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 sufficient, we will have to test the limit of the number of cycles sooner or later."

"Hey, that's the truth, but there will never be enough time to actually start the experiment. If this problem is discovered after a few months, and then detailed research is carried out, I don't know how much time will be wasted."

Thinking of this, Xu Zhou couldn't help feeling helpless.

Even though it seems that his previous experimental ideas were not problematic, Ning Chen was always able to 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 coming back, Xu Zhou asked excitedly:

"Sui Feng, have you finished the test yet?"

"Yes, after I got there, the teacher arranged for me to conduct experiments."

When Sui Feng went, it was just in time for the teacher of the testing center to rest, but because of Xu Zhou's call, the testing center was very quick to help Sui Feng arrange the experiment.

"Well, do you see the reason?"

"Well, it's probably because of the passivation layer formed on the surface of the negative electrode material. For details, let's look at the image of the scanning electron microscope."

As he said that, Sui Feng found out the scanning electron microscope image that had just been completed, 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 sharp 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 to form a passivation layer.

This passivation layer will have some impact on the performance of the electrode material. These impacts are both good and bad. One of the negative impacts is that it will reduce the charge and discharge efficiency of the electrode material, especially the impact on the negative electrode material 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 check 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, but Ning Chen is very familiar with this porous silicon nanomaterial, so he is keenly aware of this change.

"That's right, I also had the same feeling just now. In this way, it is probably because the passivation layer formed on the surface of the negative electrode material has oppressed the porous silicon nanomaterial. This oppressive effect will only slowly reduce the negative electrode. The cycle performance of the material, but as this effect continues to accumulate, it may cause structural damage to the porous silicon nanomaterial."

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

"Yes, the physical properties of porous silicon nanomaterials are still weaker than those of conventional carbon anode materials. Even with the addition of metal substances, this situation has not been completely resolved."

After finding out the reason for the experimental phenomenon, both Ning Chen and Xu Zhou fell into silence, each thinking about a solution to 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 thought of something again, and said to Ning Chen:
"We can try this. On the outer layer of the composite material of silicon and metal, add a thinner layer of carbon structure. This carbon structure can prevent the direct contact between the electrolyte and the porous silicon nanomaterial, while affecting the energy density of the battery. There will be no noticeable impact."

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 intercalation ability, etc., and are very suitable for combining with silicon-based composite materials.Ning Chen couldn't help sighing in his heart, Xu Zhou did have his own unique ideas in the field of materials, and there were many places that Ning Chen could learn from.

In the following time, Xu Zhou and Ning Chen continued to study specific solutions to this problem.

First of all, the experiments on porous nano-silicon-metal anode materials still need to be continued, and they need to find the metal substance that is most suitable for matching with porous silicon.

Secondly, they also need to carry out 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 mesocarbon microspheres.

How thick is the added carbon layer to protect the porous nano-silicon without affecting the capacity of the battery.

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

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

……

As 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 harvested many very valuable experimental phenomena and experimental conclusions.

The improved negative electrode material has significantly improved the battery life, and at the same time, after many charge and discharge cycles, there will be no significant decline 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 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 obtain the 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 unbelievable thing, and the school had confirmed with Ning Chen again and again whether it was really necessary to take so many subjects in one semester.

However, under Ning Chen's constant insistence, 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 start of the exam. It was as easy as watching flowers on horseback.

The final results also proved that Ning Chen really has such achievements.

Not only did each subject pass smoothly, but the scores of most subjects reached full marks or were close to full marks, which amazed the teachers.

This means that Ning Chen completed the double undergraduate degree in materials and mathematics in less than two years.

All that Ning Chen needs to do is to complete the graduation project and graduation defense.

And because Ning Chen has already made excellent results in these two fields, there is no need to do another graduation project, and 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 anode materials for silicon-based lithium batteries 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 a large number of tests, this material shows a high initial reversible capacity, and the reversible capacity is still maintained at a high level after many cycles.

Because of the protective effect of the carbon layer, the porous silicon nanoparticles will not be affected by the electrolyte, and even after 500 cycles, the reversible capacity of the battery has not declined sharply.

Although the addition of metal silver has increased the cost of lithium batteries, it is still within an acceptable range.

Xu Zhou informed Xu Shou of the experimental progress of the experimental group. After Xu Shou learned that the experimental group had made these breakthroughs, he immediately said that he would fly to Shengzhou as soon as possible to learn about the relevant experimental situation.

(End of this chapter)