Chapter 1243: A film blocking the way

"Lithium, atomic number 3, atomic weight 6.941, is the lightest alkali metal element, and its chemical properties are very active, so it has a certain degree of danger." To illustrate the problem, Wang Jishan casually pulled a piece of white paper and spread it in front of him. Put out a pen and start to explain on the paper while drawing a sketch:
"Let’s briefly introduce the working principle of lithium-ion rechargeable batteries. It mainly relies on the movement of lithium ions between the positive and negative electrodes. During the charging and discharging process, lithium ions are intercalated and deintercalated back and forth between the two electrodes. In this process, when the battery is charged, lithium ions are generated on the positive electrode of the battery, and the generated lithium ions move to the negative electrode through the electrolyte. The graphite of the negative electrode is a layered carbon with many micropores. , The lithium ions reaching the negative electrode are embedded in the micropores of the carbon layer. The more lithium ions are inserted, the higher the charging capacity. Similarly, when the battery is discharged, that is, when we use the battery, it is embedded in the negative carbon layer The lithium ions of the battery are released and move back to the positive electrode. The more lithium ions that return to the positive electrode, the higher the discharge capacity."
Tan Zhenhua looked at this schematic diagram of the battery principle drawn by Wang Jishan later, and couldn't help but secretly praise it-the basic skills of the older generation of scientific researchers are solid, and the drawings they sketched are so neat, meticulous, and watching It is pleasing to the eye. Among the people he has dealt with, Wang Jishan is like this, Chen Yijian is like this, there are many others like this, even his father Tan Ming is like this, this is the skill accumulated by countless hand-drawn drawings, which Like the later generations who use their mobile phones every day, in addition to their own names, I am afraid that they can't even write a serious Chinese character-they are talking about you who are holding your phone and giggling.
"Look at Zhenhua. According to this working principle, we need to add a barrier substance between the positive and negative poles of the battery. This substance has two main functions: first, to isolate the positive and negative plates of the battery cell. To prevent direct contact between the positive and negative plates inside the cell and cause a short circuit; second, to ensure a high ion dialysis rate, that is, to allow ions to move freely between the positive and negative poles."
"Uh, Professor Wang, why do I hear these two requirements a bit contradictory? It seems that it is very troublesome to realize the two main functions you mentioned!"
"The trouble is more than the realization of the two main functions." Wang Jishan continued: "As we said just now, lithium is a very active metal, and the same is true for lithium ions. This causes problems during battery charging and discharging. Some harmful anomalies may occur. The most common and most harmful anomaly is heat. We know that charging and discharging is actually a process of energy input and output, regardless of whether it is energy input or output, its efficiency is not It may be 100%, some of which will be lost. These losses are usually manifested in the form of heat, but the inside of the battery is a closed and narrow space. As the heat continues to accumulate, according to the most basic principle of "thermal expansion and contraction" , The volume of the electrolyte will expand, severely even leading to the vaporization of the electrolyte, the volume will further increase, and the internal pressure will become larger and larger, until the outer wall of the battery can not bear it, so..."
"So I made a "bang" and came up all at once."
"Well, that was the most serious result. The high temperature ignited the covering on the outer surface of the battery. However, in our tests, most of the cases did not become so bad, that is, a bulge on the outside of the battery."
Tan Zhenhua has completely understood the scientific principle of the "Samsung mobile phone explosion" that had caused a stir in his previous life.
"So this film has to have another function-when the heat accumulates to a certain value, it can automatically close the channel for the movement of lithium ions. In this way, the internal movement stops and the charging and discharging process cannot continue. The source of this is cut off, so that extreme situations can be avoided."
Tan Zhenhua scratched his head and said: "Sounds very troublesome, it seems that you need to install a small person who automatically opens the door in the battery to solve this problem."
"The villain doing this job is exhausted, because he must always vigilantly monitor the temperature changes throughout the charging and discharging process and be ready to take measures at any time. This kind of work requires too much concentration, and he may have to ask you Boss Tan needs a high salary."
Wang Jishan also made a rare joke, and then explained:
In fact, it doesn’t have to be so troublesome. Through experiments, we found such a substance, which is the "lithium film" I just mentioned. This polymer material has electronic insulation. , It can ensure the mechanical isolation between the positive and negative electrodes, and at the same time, it has a certain pore size and porosity, ensuring low resistance and high ion conductivity, and has good permeability to lithium ions. At the same time, when the temperature rises When it reaches the threshold, the lithium film will melt, the micropores will be closed and become an insulator, preventing the electrolyte from passing through, thereby achieving the purpose of interrupting the current."
"It sounds really high-tech materials, Professor Wang, listen to you, can our country not produce this kind of material on its own? What are the main difficulties?"
"In fact, this material is not complicated in terms of composition. We have tested it. Both polypropylene PP and polyethylene PE can be used. Their chemical stability is sufficient, but the difficulty is difficult. If you want to apply it to lithium batteries, this layer The membrane must have sufficient mechanical properties, including puncture strength, tensile strength, etc., while the thickness should be as small as possible, dimensional stability and flatness should be good, and the most difficult thing is that the material needs to be made into a microporous membrane structure. The diameter of the micropores is in the micron level, which is very demanding, and the arrangement, distribution, and error of the holes are all required. With our capabilities, it is currently not possible to process this kind of membrane independently. What we are using now is a few from the Japanese The experiments on these materials were produced by Tonen Chemical and Asahi Kasei Industrial Co., Ltd. According to our search, both companies have registered a large number of patented technologies for the production of microporous polymer membranes, and their products are widely used In the molecular sieve equipment, so we are actually facing two difficulties now-blocked by foreign technology and patent barriers."
Tan Zhenhua understood.
In fact, this is the current situation facing China Xia. On the one hand, because of its first-mover advantage, a large number of high-tech achievements and patents are in the hands of Western developed countries. They either simply block China Xia from products to equipment, leading to domestic R&D progress. Slow, like the previous carbon fiber; on the other hand? It also used a large number of patents to restrain the domestic research and development process, so that even if Huaxia broke through the blockade and developed its own technology, it would touch the patent barrier because of the high similarity between these technologies and similar foreign technologies and could not be transformed into real ones. Market products and applications-they either levy high patent licensing fees, such as the practice of Qualcomm in the past of Tan Zhenhua, or use a large number of lawsuits to increase the threshold for customers to use Huaxia products, making it difficult for Huaxia products to go abroad to participate in international market competition This is the "Matthew Effect" in the high-tech field.
But now, what is blocking the commercial application of China's lithium battery industry is such a seemingly thin, transparent film.
Stabbed through it, and a horse Pingchuan is ahead!