The key to solving the lithium dendrite problem falls on a common additive in the electrolyte.

This answer was a bit unexpected.

After all, the industry and the battery industry have always focused on solving the problem of lithium dendrites in artificial SEI films or electrolytes.

In the opinion of most experts or researchers, these two materials are the key.

If he hadn't come back with twenty years of vision and experience, Xu Chuan wouldn't have directly locked his eyes on the electrolyte.

As the saying goes, the more neglected a place is, the more deadly it is likely to breed.

Vinyl carbonate, which is added to almost all lithium-ion batteries, is a great improvement for lithium batteries.

However, it may also be the culprit responsible for the lithium dendrites problem.

......

After replacing the additives in the electrolyte, Xu Chuan conducted a variety of tests on the new batteries in his hands, and also manufactured several new batteries at the same time, using different additive materials to verify the previous judgment.

The final experimental and test results show that different kinds of additives can indeed affect the working properties of the new artificial SEI film.

Among them, ethylene carbonate, alkyl phosphate and other materials are particularly serious.

The organic phosphide and organic fluoride additives are relatively light, and the best fluoroalkyl phosphate can even achieve a coulomb efficiency of 99.98%.

This data is enough to increase the number of charging and discharging cycles of lithium batteries to more than four thousands of times.

This is more than double the current standard charge and discharge times of 500 times for lithium batteries.

But at the same time, after replacing ethylene carbonate, the performance of lithium batteries, from battery capacity, to charging, discharge speed, to the activation performance of the electrolyte has been significantly reduced.

Among them, the fluoroalkyl phosphate with the best coulombic efficiency is directly reduced by about 25% in charge and discharge efficiency.

And the lower the outside temperature, the greater the interference of the charge-discharge efficiency, and when the temperature is too high, the instability of the electrolyte will increase.

If the temperature is too high, the battery will bulge and expand.

Although there are no problems such as spontaneous combustion and explosion in the current test, Xu Chuan knows that with the increase of time and the number of tests, if fluoroalkyl phosphate is used instead of ethylene carbonate, these problems will appear.

He doesn't want the battery he developed to be comparable to a certain star company.

Batteries that can explode and spontaneously combust at any time, no matter how high the capacity is, it is useless, and the safety performance will not pass the test at all.

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Finding an additive that can replace ethyl carbonate has become the current focus of Chuanhai Materials Research Institute.

Yu Zhen and Ye Zan have temporarily stopped the research and development of artificial SEI films and electrolytes and entered this work.

In the laboratory, including those doctoral students and master's students, who have the ability to conduct battery experiments alone, Xu Chuan also arranged experiments in pairs.

Compared to formal researchers, these people still lack a lot of ability.

However, it is basically not too bad to be able to read to the stage of doctoral students.

These people can be cultivated as the team of the Chuanhai Materials Research Institute, and Xu Chuan will not be stingy with his resources and money.

And for these PhD and Master's students, there is nothing more gratifying.

After all, only with experiments can there be data, only with results, only with graduation, and only with qualifications......

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"Boss, this is the result of the experiments of the various groups of people these days."

In the laboratory, Fan Pengyue handed the information in his hand to Xu Chuan, and at the same time made some simple statements: "According to your requirements, seven groups of personnel in the laboratory conducted experiments on a total of 14 different ethylene carbonate substitutes. ”

"In the results of the experiment, the two best materials were fluoroethylene carbonate and trimethylsilane sulfite."

"These two materials can be matched to a large extent with the current artificial SEI film, and the calculated coulombic efficiency after replacement is 99.645% and 99.721%, respectively."

"But correspondingly, these two materials also have their own disadvantages when replaced."

"For example, fluoroethylene carbonate has been replaced with a decrease in charge and discharge efficiency....... and so on. ”

"The amount of experimental data is relatively small, and we can only make a preliminary reference, after all, we don't have enough time to do complete experiments and tests."

"In addition, some safety tests are not ......."

In the laboratory, Xu Chuan took over the experimental data from Fan Pengyue's hands, and listened to his brief description while looking at the information in his hand.

Since the discovery of ethylene carbonate in early November, which is the main cause of lithium dendrites and lithium precipitation problems, the Chuanhai Institute of Materials has been continuously experimenting with it.

Although the time was very short, only about 20 days, with a target and enough manpower and equipment, it was enough for them to experiment with a lot of new materials.

Of course, these days' experiments and tests are not very perfect, nor are they very formal.

Issues such as the compatibility between materials and the safety performance test of batteries are not considered.

However, compared to these problems, it is more important to find an additive that can replace ethylene carbonate, and as for other things, it can be slowly improved later.

Xu Chuan wants to solve this problem before he goes to Sweden to receive the award on December 10.

After getting it, I went to get a Nobel Prize, and when I came back from Europe, the test of the two protective materials on the side of the nuclear β radiation energy gathering and conversion project was almost completed.

In this way, he can devote his main energy to the nuclear energy project in the post-Nobel Prize time.

It's just that judging from the current progress, this wish is probably difficult to achieve.

Of the more than a dozen additives tested, none of them are very suitable at present, and they basically have such and such problems.

If lithium dendrites and lithium precipitation are put aside, ethylene carbonate is really the best of all additives.

"Maybe you can dilute the concentration of ethylene carbonate? Or maybe find a material to neutralize it? ”

Looking at the test report in his hand, another way to solve the problem came to Xu Chuan's mind.

Ethylene carbonate will still be active in the future lithium battery in the future, and it will definitely have its role.

"If we can find a solution to the problem of lithium separation caused by ethylene carbonate, maybe ethylene carbonate has another role."

Suddenly, another term came to Xu Chuan's mind.

"Planned to be scrapped!"

The so-called planned scrapping refers to a strategy in industry.

That is, the product supplier deliberately designs a limited service life for the product, so that the product will be scrapped after a certain period of time.

It first appeared on light bulbs.

During Christmas 1924, Osram, Philips, General Electric and other companies gathered in Geneva to form a monopoly called "Phoebus", with the aim of controlling the life of the light bulb to about 1,000 hours (when the light bulb life could reach 2,500 hours)

In 1942, the government took the "Phoebus" group to court, accusing the other party of its actions, and although the agreement was nominally terminated, the companies did not pay any compensation.

What's more, this alliance proposed the life control of ordinary light bulbs, which has been continued, and so far, the life of most light bulbs is only 1000 hours.

This was the planned scrapping at that time.

Then, over time, this convention spread to other products.

For example, batteries and chips in mobile phones and computers; ink cartridges in printers; Key keys for various electrical equipment, etc.

Nowadays, this thing has the ability to be scrapped in a planned way, that is, after a period of use, it will be damaged for various reasons.

For manufacturers of these things, if a product can be used in the hands of users for a long time, then after the new product is launched, the number of people who buy it will decrease.

Therefore, in order to introduce new products and expand their own interests, manufacturers will inevitably choose to eliminate the old products in the market, because new products are facing competition from old products to a certain extent.

In lithium-ion batteries, the presence of ethylene carbonate can improve the performance of lithium batteries on the one hand, and on the other hand, with the increase of the number of charge-discharge cycles, the lithium evolution of the negative electrode will become more and more serious, which will naturally lead to battery damage.

The impact of ethylene carbonate on lithium-ion batteries that only needs to be controlled can be said to be a natural plan to be scrapped.

This may be the reason why ethylene carbonate will bring the problem of lithium separation, but it will still exist in lithium batteries in the future, right?

Xu Chuan probably figured out where to start to solve the problem of lithium evolution.

If his guess is correct, then the solution to this problem is nothing more than to control the content of ethylene carbonate or use another additive.

......

After confirming the conjecture in his mind, Xu Chuan immediately started to re-conduct the experiment.

The method used is very simple, and it is enough to directly reduce the content of ethylene carbonate in the electrolyte.

In the first experiment, he reduced the amount of ethylene carbonate in the electrolyte by 20 percent, built a new lithium-ion battery, and retested it.

One-fifth of the amount is enough to ensure that if the content of ethylene carbonate affects the lithium evolution of the anode, it can definitely be reflected in the data, and it is in a large radian.

As he suspected, after reducing the ethylene carbonate content in the electrolyte by 20 percent, the problem of lithium separation at the anode of lithium batteries has been greatly improved, and the coulombic efficiency of the battery has increased from about 99.91% to 99.95%.

The 99.95% coulomb efficiency is enough to ensure that a battery still maintains more than 80% capacity after completing 500 charging and discharging cycles.

This is up to the standard for lithium-ion batteries used on the market today.

"The hearts of capitalists are really black."

Looking at the results of the preliminary test, Xu Chuan shook his head.

Although it was only a simple test, it was enough for him to be sure that the problem was here.

It is no wonder that ethylene carbonate is one of the causes of lithium dendrites and lithium evolution problems in lithium-ion batteries, and this additive is still used in large quantities in lithium batteries.

It's not that you can't find a more suitable material, but because it's the most suitable.

Ethylene carbonate at a certain level can increase the performance of lithium batteries while automatically executing planned scrapping work, making way for the next generation of products, and earning a lot more silver taels.

Take mobile phones as an example, the lifespan of a mobile phone battery is about one to three years.

The average selling price of a battery is about 15 to 300 yuan, excluding the cost of all aspects, it can bring at least 50 to 150 yuan of net profit.

If a billion people use mobile phones, that's a net profit of 50 billion to 150 billion.

In fact, the consumption of batteries in countries around the world is far greater than the corresponding number of people, after all, a person can have a mobile phone, a computer, an electric car, and other electrical appliances that need to use batteries at the same time.

It is no wonder that after the lithium dendrite problem is solved in the future, ethylene carbonate is still widely used in mobile phone batteries.

This huge profit is tempted by whoever comes.

Of course, the performance of ethylene carbonate itself is also excellent enough, and it is more suitable for this new artificial SEI film than other additives, and it can bring greater performance improvement.

The better the battery, the more people will buy it, even if it's more expensive.

And such an 'almost perfect' additive, no battery manufacturer will not love.

But for consumers, this is a very bad thing.

After all, the increase in consumer spending is real, but it could have been avoided.

......

After determining that reducing the ethylene carbonate content would improve the coulombic efficiency of the battery, Xu Chuan began to arrange for other researchers in the lab to begin more detailed tests on the batteries in their hands according to the standard of lithium batteries.

Battery testing is a tedious and lengthy process.

From electrical tests such as overcharge, over-discharge, external short circuit, forced discharge, etc., to mechanical tests such as extrusion, acupuncture, shock, vibration, drop, etc..... It takes a lot of time.

Not to mention the rest, just the charge and discharge test, you need to do at least 500 times.

IEC stipulates that the standard cycle life test of lithium batteries is: after the battery is put to 3.0V/branch at 0.2C, the battery is charged to 4.2V with 1C constant current and constant voltage, the cut-off current is 20mA, and after being put aside for 1 hour, it is discharged to 3.0V (one cycle) at 0.2C (one cycle) and the capacity should be more than 60% of the initial capacity after repeated cycles for 500 times.

In other words, even if the charge and discharge test is carried out day and night for 20 hours, it will take at least 20 days to a month.

However, compared to the huge benefits that lithium batteries can bring, these are nothing at all.

As for himself, there are other arrangements.

He needed to find a material that would reduce the lithium evolution of ethylene carbonate.

According to the results of previous experiments, the content of ethylene carbonate is directly related to the lithium evolution of the anode. Experiments have shown that the more ethylene carbonate is added to the electrolyte, the faster the lithium evolution will be generated from the anode.

Reducing the content of ethylene carbonate can indeed weaken the generation rate of lithium precipitation, but it will also cause the overall performance of the battery to decline to a certain extent.

This is what Xu Chuan does not want to see.

So it's also important to find an alternative additive and control it.

Xu Chuan did not hand over this job to the Chuanhai Materials Research Institute.

Maybe the Chuanhai Materials Research Institute can experiment with the required additives little by little, but the time required may be as long as a few months or a year or two, which is too slow for Xu Chuan.

He's going to use his mathematical skills to complete the calculation of this additive!

I haven't studied math for a while, and I don't know if my math ability has regressed.

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