Not enough power for mobile phones?They found a new way to "extend life" to the battery

The following article comes from WeChat public account: Global Science, author Global Science

Picture source: pixabay

I don't know how long your mobile phone is charged with electricity once. Some scientists are also paying attention to the same thing -the life of lithium -ion batteries. However, they used higher precision imaging technology and machine learning methods to "see" the damage of the battery electrode particles, and found a special feature -the characteristics of these particles' group behavior may be the key to design and manufacture long -life batteries Essence

Written article | Wang Yibo

Audit | Erqi

You may notice that once the phone is filled to a certain amount of power (such as 80%), it takes a longer time to fully fill it. The same is true for mobile phones that support fast charging. This is actually because charging the mobile phone is not to directly "throw" as much voltage and current into the battery as possible. In fact, the charging of mobile phone lithium -ion batteries is usually composed of two stages: constant current charging and constant voltage charging.

Under normal circumstances, when a mobile phone without a power starts charging, a constant current charging will be performed first. At this time, the battery voltage will soar, but the increase in battery capacity (which can be understood as charged power) is slightly lagging. This stage is a critical period that fast charging mobile phones can use, because once the peak voltage is reached (the setting threshold), the mobile phone will enter the constant voltage charging phase. At this time, the voltage will no longer change, the current will decrease, and the rate of battery capacity will slow down, that is, the battery charging speed will slow down in the second stage.

More importantly, long -term high voltage is actually "pressurizing" mobile phone batteries, which will cause electrode damage and decreased battery life. Therefore, the second -stage constant voltage charging, or if the battery is fully charged, may help extend the battery life. In fact, the battery management software system of most mobile phones can do this "silently". Take Apple mobile phones as an example. Starting from the iOS 13 system, there is an option called "Optimized Battery Charging" in the battery settings. This setting allows the mobile phone to charge about 80%, and it temporarily stops, so as to avoid letting the mobile phone enter the "high -voltage area area "".

Battery health setting diagram. (Photo at 5.30)

One question is: If you can maintain your mobile phone battery from now on, can it keep "alive"? We may have experienced such a scene: After the new mobile phone is fully charged, it can be used for 1 day. If it is enough for half a day, then after 2 years or more, you must not go out without a charging treasure.

In fact, even if you are used carefully, mobile phone batteries will always be "dead" one day. Our ordinary people can only try to maintain the battery as much as possible in daily life, and scientists who are dedicated to battery research have not been idle, and they are also worried about the life of lithium -ion batteries.

The bottleneck of lithium ion battery

2019 is the "highlight" of the lithium -ion battery business. The Nobel Prize in the Nobel Prize in that year was awarded three scientists and engineers with outstanding contributions to the invention and development of lithium ion batteries. M. Stanley Whittingham, John B. Goodnough, and Akira Yoshino.

Among them, Professor Guridov's contribution was that he proposed a lithium ion battery cathode material -layered six -square compound cobaltate in around 1980. Until now, the mobile phones in our pocket are equipped with some cathode materials evolved from this material, such as replacing cobalt elements with nickel and manganese, or mixed with nickel, manganese, iron, magnesium, aluminum, etc. In lithium cobaltate. However, their structures are layered structures and have a common feature: the ability to store and release lithium ions, so that lithium ions are embedded and dected between the cathode layer and the layer, and ideal are ideal. Will not destroy the basic structure of cathode materials.

Lithium ion battery schematic diagram. (Picture source: nobelprize.com)

Similarly, the battery anode should also have the same ability: In 1983, Dr. Richard Yazami confirmed that graphite with layered structures can be embedded and dehydrated with lithium ions, which has become an excellent anode candidate. However, in order to further improve the performance of lithium ion batteries, scientists are still looking for and trying new anode materials, such as silicon anode and lithium metal anode.

Although the research of cathode materials has been relatively mature, the optimization of anode materials and the related research of liquid electrolytes with solid electrolytes instead of dangerous liquid electrolytes have fallen into difficulties. Therefore, it can be said that the development of lithium -ion batteries has entered a bottleneck period.

However, there are some scientists thinking about another question: Can it be able to "squeeze" some electrical energy on the basis of existing materials?

Recently, researchers from the American SLAC National Accelerator Lab, Purdue University, Virginia University of Technology, and the European Synchronous Radiation Laboratory (ESRF) jointly published a study in Science Magazine to develop long -life lithium -ion batteries in Science. In terms of key issues, these scientists have to find answers from "why batteries are inactivated".

"Reduce" a piece of electrode to particles

One thing to explain is that when the lithium -ion battery is charged, the cathode material will store the lithium ions stored in advance, passing through electrolytes, diaphragms, transmitted to theode, and stored between the anode layer. During discharge, the transmission process of lithium ions will reverse, that is, from theode to cathode. In the process of continuous entry and exit of lithium ions, Ideally, the electrode structure will not be destroyed, but this is not the case. This is also a key cause of the battery's gradual loss. Speaking of electrodes, what will appear in your mind? One electrode board? After all, in our textbooks, the electrode is an "board" inserted into the electrolyte. But in fact, the electrodes are stacked from layers of millions of electrode particles. This may be well understood. When lithium ion comes in or out, it will inevitably collide with the electrode particles or other interactions, so that the electrode particles will crack. After repeated charging discharge, the electrode particles will also lose electrochemical activity.

Scientists observe the damage of the electrode particles in the charging cycle through synchronous radiation X -ray imaging technology. (Photo source: yang yang/eSRF)

However, most of the previous studies have focused on the characteristics of a single particle, such as the size and appearance of the particles, but rarely have research on group behaviors that pay attention to granules. However, no particles are an islands, and how the granular network will change with charging. It is also very important.

Granules group behavior

In fact, this research team composed of multiple units published two studies in 2019. They "see" thousands of lithium -ion batteries damage to lithium ion batteries through synchronous radiation X -rays, and calculating simulation and machine learning. Electrical particles. It is important that they find that the electrode particles are not invalid at the same time, and the particles in some positions will be lost faster. For example, compared with particles closer to the electrode, particles closer to the battery diaphragm will be excessively "used", and the electrochemical activity will be lost faster. Moreover, this "non -uniform loss" phenomenon is even more serious under thicker electrodes and fast charge conditions.

Seeing this, we may not know why this non -uniform attracts their attention. However, in 2021, the team published an article in the magazine of Nature · Materials Studies saying that different electrode particles were different in charging and discharge. Earlier, scientists have always believed that lithium ions will flow or flow from all electrode particles at the same time at the same time and almost the same speed. However, this team found that during charging, some particles could immediately release lithium ions, but at the same time, some particles were almost "working". Researchers said that this "non -uniform" behavior will put too much pressure on some "employees" of the electrode, thereby reducing their life. Moreover, in many cycles, these diligent particles "employees" have always been the main work of work, and the particles that are not working hard at the beginning have not improved.

In this new study published in Science recently, this team once again discovered the importance of "uniformity". This time, they put their attention on the cathode material of the lithium -ion battery, and used a composite cathode -rich cathode -from multi -layer lithium nickel -manganese cobalt oxides (NMC) particles, as well as conductive carbon and adhesion The agent is combined, and the active particles are wrapped in conductive carbon. After synchronizing the radiation X -ray fault scanning imaging, calculating simulation, and computer vision technology, they have studied the charging and discharge cycle (10 and 50 times) under multiple fast charge conditions (5C). Change of the characteristics of particles.

A computer vision algorithm developed by this research team can distinguish the particles based on the characteristics of particle size, appearance and damage. (Picture source: Liu Yijin of the American SLAC National Accelerator Lab)

According to Professor Zhao Kejie of Purdue University (one of the communications authors of this research), these cathode particles are like people. At the beginning, everyone took their own way, and then met their companions, so they walked together. Therefore, "we not only need to study the electrochemical behavior of a single particle, but also understand the performance of these particles in the group."

In the end, the researchers identified more than 2,000 cathode particles through computer vision, and then calculated simulation to obtain individual characteristics such as the size, appearance and surface roughness of each particle, and obtained more group characteristics, such as these particles, such as these particles. How to contact each other and their appearance differences.

By analyzing these characteristics, they discovered a very special change trend: after 10 charging and discharge cycles, the most critical factor that determined whether particles were damaged and ineffective are the individual characteristics of the particles, such as the surface area of ​​the particles and whether it was spherical. However, after 50 charging and discharge cycles, the most critical factor is whether these particles have similar granules, granular arrangements, and appearances.

After 10 charging and discharge cycles, the key role is the individual characteristics of cathode particles; however, after 50 charging and discharge cycles, it is a particle behavior. (Picture source: Doi: 10.1126/Science.abm8962))

We can see that as the charging loop is performed, or after using the mobile phone for a longer time (such as 1 year), it is the interaction between the electrode particles that determine the life of the lithium ion battery. This is very important for scientists and engineers, because they can develop related technologies and control the group behavior of controlling particles by designing and manufacturing battery electrodes, so as to "squeeze" some electricity. Liu Yijin of the American SLAC National Accelerator Lab (one of the communications authors of this research) proposes: "You can use magnetic fields or electric fields to control the arrangement between particles." 1) said that their laboratory is currently redesigned battery electrodes in order to create electrode structures that support fast charging and long life.

Cover source: pixabay

Reference link:

https://www.science.org/doi/10.1126/sclence.abm8962

https://vtx.vt.edu/articles/2022/04/sclence-Feng_lin_LICHARGE_LIFESPAN_TESTING.HTML

https://onlineelibrary.wiley.com/doi/10.1002/aenm.201900674

https://www.sciencedirect.com/science/article/abs/pii/s0022509619303126?via%3DIHUB

https://www.nature.com/articleS/S41563-021-00936-1

https://www.cnet.com/tech/mobile/does-fast-Affect-battery-life-6-Phone-battery-AnSwered/

https://batteryniversity.com/article/bu- 409-charging- Lithium- ION

This article is authorized to reprint from WeChat public account: Global Science Author: Global Science

Reprinted content only represents the author's point of view

It does not represent the high energy office of the Chinese Academy of Sciences

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