Great Country Academician

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

The answer is somewhat unexpected.

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

In the eyes 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 would not have directly locked his eyes on the electrolyte.

As the saying goes, the easier it is to be ignored, the more deadly things are likely to grow.

Ethylene carbonate, a material that is added to almost all lithium-ion batteries, has greatly improved lithium batteries.

Only, it may also be the culprit for the lithium dendrite problem.

After replacing the additives in the electrolyte, Xu Chuan conducted various tests on the new battery in his hand, and also manufactured several new batteries simultaneously, using different additive materials to verify the previous judgment.

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

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

The organophosphide and organic fluoride additives are relatively light, and the fluoroalkyl phosphate with the best performance can even achieve a Coulombic efficiency of 99.98%.

This data is enough to increase the number of charge and discharge cycles of lithium batteries to more than four digits and thousands of times.

Compared with the current standard charging and discharging times of 500 times for lithium batteries, this is more than doubled.

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

Among them, the fluoroalkyl phosphate with the best Coulombic efficiency directly reduces the charge and discharge efficiency by about 25%.

And the lower the external temperature, the greater the disturbance to the charging and discharging efficiency, but when the temperature is too high, the instability of the electrolyte will increase accordingly.

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

Although there have been 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.

A battery that can explode and spontaneously ignite at any time, no matter how high the capacity is, it is useless, and the safety performance cannot pass the test at all.

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

The research and development of artificial SEI thin film and electrolyte in the hands of Yu Zhen and Ye Zan have temporarily stopped and entered this work.

In the laboratory, including those doctoral students and master's students who are capable of conducting battery experiments alone, Xu Chuan also arranged experiments in pairs.

Compared with formal researchers, the abilities of these people are still lacking a lot.

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

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

And for these Ph.D. and master's students, nothing could be more exciting than that.

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

"Boss, these are the experimental results of the various groups of people these days."

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

"Among the experimental results, the two best materials are fluoroethylene carbonate and trimethylsilyl sulfite."

"These two materials can match the current artificial SEI film to a large extent, and the calculated Coulombic efficiencies after replacement are 99.645% and 99.721% respectively."

"But corresponding to this, these two materials also have their own shortcomings after being replaced."

"For example, after the replacement of fluoroethylene carbonate, the charge and discharge efficiency decreased. And other problems."

"The amount of data in these experiments is relatively small, and it can only be used as a preliminary reference. After all, we don't have enough time to do complete experiments and tests."

"In addition, some security tests were not done."

In the laboratory, Xu Chuan took over the experimental data of these days from Fan Pengyue, and while listening to his brief introduction, he flipped through the materials in his hand.

Since it was discovered in early November that ethylene carbonate is the main cause of lithium dendrites and lithium precipitation, Chuanhai Materials Research Institute has been conducting experiments on it.

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

Of course, the experiments and tests these days are not perfect and not very formal.

Issues such as the compatibility between materials, battery safety performance testing, etc. are not considered.

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

Xu Chuan wanted to settle this problem before going to Sweden to receive the award on December 10th.

After finishing it, go to receive a Nobel Prize. After returning from Europe, the test of the two protective materials on the nuclear energy beta radiation energy conversion project is almost completed.

In this way, he can devote his main energy to nuclear energy projects after the Nobel Prize.

But judging from the current progress, this wish may be difficult to realize.

At present, none of the more than a dozen additives tested is very suitable, and basically all have problems of one kind or another.

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

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

Flipping through the test report in his hand, Xu Chuan came up with another way to solve the problem.

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

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

Suddenly, another term appeared in Xu Chuan's mind.

"Plan to be scrapped!"

The so-called planned obsolescence 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.

First appeared on the light bulb.

During Christmas 1924, Osram, Philips, General Electric and other companies gathered in Geneva to form a monopoly group called "Phoebus", with the purpose of controlling the life of light bulbs to about 1000 hours (while the life of light bulbs at that time could reach 2500 hours)

In 1942, the U.S. government took the "Phoebus" group to court and sued the other party's actions. Although the agreement was terminated in name, these companies did not pay any compensation.

More importantly, the alliance proposed to control the life of ordinary light bulbs, and it has continued. So far, the life of most light bulbs is only 1,000 hours.

That's when the plan was scrapped.

Then, over time, this agreement gradually spread to other products.

For example, batteries and chips in mobile computers; ink cartridges in printers; key buttons of various electrical equipment, etc.

This thing now has the ability to plan to be scrapped, that is, after a period of use, it will be damaged due to various reasons.

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

Therefore, in order to introduce new products and expand their own interests, manufacturers will inevitably choose to eliminate old products in the market, because new products face 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 in the number of charge and discharge cycles, the lithium precipitation of the negative electrode will become more serious, which will naturally lead to battery damage.

It is only necessary to control the impact of ethylene carbonate on lithium-ion batteries, and it can be said that the natural plan is scrapped.

This may be the reason why ethylene carbonate will cause lithium analysis problems, but it still exists in future lithium batteries?

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

If his guess just now is correct, then the solution to this problem is nothing more than controlling the content of ethylene carbonate or using another additive.

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

Simply verify the method in mind, the method used is very simple, just reduce the content of ethylene carbonate in the electrolyte directly.

For the first experiment, he reduced the ethylene carbonate content in the electrolyte by 20 percent, made a new lithium-ion battery, and retested it.

One-fifth of the amount is enough to ensure that if the content of ethylene carbonate really affects the lithium deposition in the negative electrode, it will definitely be reflected in the data, and it will be in a larger arc.

The test results are just as he guessed. After reducing the content of ethylene carbonate in the electrolyte by 20%, the problem of lithium deposition at the negative electrode of the lithium battery has been greatly improved, and the Coulombic efficiency of the battery has changed from about 99.91% before. Increased to 99.95%.

The coulombic efficiency of 99.95% is enough to ensure that a battery can still maintain more than 80% of its capacity after completing 500 charge-discharge cycles.

This has reached the standard of lithium-ion batteries used in the market today.

"The hearts of capitalists are indeed black."

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

Although it was just 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 precipitation problems in lithium-ion batteries, and this additive is still used in large quantities in lithium-ion batteries.

It's not that a more suitable material cannot be found, but because it is the most suitable.

A certain content of ethylene carbonate can increase the performance of lithium batteries and at the same time automatically execute the planned scrapping work to make way for the next generation of products and earn a lot of silver taels.

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

The average selling price of a battery is between 150 and 300 yuan. After deducting all costs, it can bring at least 50 to 150 yuan in net profit.

If one 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, one person can own mobile phones, computers, electric vehicles, and other electrical appliances that 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.

Anyone who comes to this huge profit will be tempted.

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

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

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

But for consumers, this is a very cheating thing.

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

After confirming that reducing the content of ethylene carbonate can improve the coulombic efficiency of the battery, Xu Chuan began to arrange other researchers in the laboratory to conduct more detailed tests on the battery in hand according to the standard test of lithium batteries.

Battery testing is a rather tedious and lengthy process.

It takes a lot of time from electrical tests such as overcharge, overdischarge, external short circuit, forced discharge, etc., to mechanical tests such as extrusion, acupuncture, impact, vibration, and drop.

Not to mention other things, the charge and discharge test alone needs to be done at least 500 times.

The IEC stipulates that the standard cycle life test of lithium batteries is: after the battery is placed at 0.2C to 3.0V/piece, it is charged to 4.2V at 1C constant current and constant voltage, and the cut-off current is 20MA. One cycle) After 500 cycles, the capacity should be more than 60% of the initial capacity.

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

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

As for himself, there were other arrangements.

He needs to find a material that can reduce the lithium-evolution effect of ethylene carbonate.

From the previous experimental results, the content of ethylene carbonate is directly related to the lithium precipitation of the negative electrode. Experiments have shown that the more ethylene carbonate is added to the electrolyte, the faster the lithium precipitation rate generated by the negative electrode will be.

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

This is what Xu Chuan does not want to see.

So it is also very important to find another additive and control it.

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

Perhaps the Chuanhai Materials Research Institute can test out the required additives bit by bit, but it may take as long as a few months or a year or two. For Xu Chuan, this is too slow.

He is going to use his mathematical ability to complete the calculation of this additive!

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