Zhang Weiran successively graduated from Huazhong University of Science and Technology, Boston University in the United States, and the University of Maryland in the United States for his bachelor's, master's, and doctoral degrees. On the eve of his doctoral graduation, he received a graduation gift: his first-authored paper was published in Nature Energy (IF 56.7).

In his research, he proposed a design principle for a polymer solid-state electrolyte based on high-energy lithium metal batteries.

Lithium metal anodes can greatly increase the energy density of lithium batteries. In recent years, due to being regarded as the target for the next generation of energy storage devices, the achievements in lithium metal batteries have been increasing day by day.

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Among them, the electrolyte is one of the most core parts of the battery. Therefore, the academic community has conducted a large number of studies on this.

Both organic liquid electrolytes and inorganic solid-state electrolytes can be used for lithium metal batteries. However, organic liquid electrolytes may damage safety. Although inorganic solid-state electrolytes can greatly improve the safety of the battery, due to their relatively rigid nature, they can lead to relatively poor contact between the solid-state electrolyte and the solid-state electrode, thereby bringing unstable factors to the solid-solid interface.In comparison, polymer electrolytes have both good interfacial contact and good safety, effectively inheriting the advantages of the aforementioned two types.

However, polymer solid electrolytes still face the following issues: low ionic conductivity, poor lithium anode stability, and severe lithium dendrite growth.

Previously, in a large number of excellent works, ionic conductivity has been greatly improved. However, the issues of lithium anode stability and lithium dendrite growth in polymer electrolytes have always been a concern.

This is a huge challenge for all solid electrolytes because when the anode is unstable and can produce lithium dendrites, these spiky dendrites can easily puncture the electrolyte to reach the cathode, leading to battery short circuits, thermal runaway, and in severe cases, battery combustion and explosion.

A large number of studies have shown that when the concentration of lithium salts in the electrolyte is increased, it will promote the conduction of lithium ions and form a good protective solid electrolyte interface on the lithium metal anode.At the same time, this solid electrolyte interface is also rich in lithium fluoride, which can play a role in suppressing the growth of lithium dendrites.

However, while polymer electrolytes have a high salt content, they also damage the mechanical strength of the polymer.

Based on these understandings, Zhang Weiran and others have proposed a new design for polymer electrolytes, which allows the polymer to produce a solid electrolyte interface (SEI, Solid Electrolyte Interphase) rich in lithium fluoride at the interface between the polymer and lithium metal, thereby improving the stability of the anode and suppressing the growth of lithium dendrites.

In addition, the two polymers that make up the polymer electrolyte: the lithium-conducting polymer and the inert high-strength polymer, can eliminate the interface between the polymers by being miscible with each other, further blocking the growth of lithium dendrites.

After the above design, Zhang Weiran and others have rationally designed and screened a large number of polymers, and finally obtained a locally concentrated solid polymer electrolyte based on miscible polymer blends.This type of polymer electrolyte, while maintaining good mechanical properties, can greatly enhance the stability of the anode and exhibit excellent performance in suppressing lithium dendrites.

It is understood that most polymers have a Coulomb efficiency for lithium anodes between 90-98%, while this team has improved it to over 99%, thereby making a significant breakthrough in the anodic stability of the polymer electrolyte.

Not only that, but this new type of electrolyte also shows extremely high stability on high-voltage cathodes, far exceeding traditional polymer electrolytes. For traditional polymer electrolytes, they are often unable to match cathodes above 4V.

However, this electrolyte can withstand high voltages of 4.5V and can be matched with high-energy NMC811 cathodes.

Since the polymer electrolyte developed this time can match both high-voltage cathodes and high-capacity lithium metal anodes, it is very promising for use in high-energy, long-life solid-state lithium metal batteries.Additionally, it possesses excellent flexibility and, compared to traditional liquid electrolytes, can reduce the risk of leakage and safety hazards, making it highly suitable for portable mobile devices such as smartphones, computers, wearable devices, etc. It is expected to make it possible to reduce the size of the battery, thereby making the devices more lightweight and offering longer battery life.

Taking Apple's Vision Pro as an example, as a head-mounted 3D device, to make the device more lightweight, it uses an external battery, so an external power bank is required when in use, which undoubtedly brings inconvenience to users. The electrolyte in this instance has the potential to solve this problem.

Moreover, they are not only reporting a new electrolyte composition but are also committed to proposing new design concepts, enabling them to be used for screening and designing new polymer electrolytes, which will aid in the development of high-energy batteries.

Working on a doctoral thesis, one benefits from different undergraduate backgrounds.In fact, before this study, Zhang Weiran had no experience in polymer electrolytes, nor did he have much experience with lithium metal batteries.

Fortunately, in addition to his study of materials science during his graduate studies, he also had a background in chemistry from his undergraduate studies. Therefore, he learned about batteries and electrolytes from his seniors in the group, and occasionally discussed polymer chemistry with his teachers and classmates from his undergraduate days.

Because of this, he had a good sensitivity to different chemical structures and properties, which helped him quickly screen many polymer combinations. After that, he made a lot of attempts on these combinations and summarized the advantages and disadvantages of each combination.

Through this, he gradually found that the two polymers must be mixed. When the two polymers are not mixed, the electrochemical properties will show a huge gap.

In addition, Zhang Weiran also made a lot of attempts on different lithium salts and different solvent media.For liquid electrolytes, dissolving salts in a solvent can quickly prepare the electrolyte, and a large number of batteries can be quickly assembled for testing. However, for polymer solid-state electrolytes, they have to go through complex processes such as dissolution, casting, and demolding.

Additionally, the survival rate of polymer solid-state batteries is also far lower than that of liquid electrolyte batteries. At first, Zhang Weiran was not proficient enough. Every time a batch of batteries was made, half might "die" on the spot. After the test was over, another half would "die" the next day.

In this way, the cycle went on and on, and a week passed in a flash, which was also a great test of his patience.

"But when the right ingredients and design principles were finally found, I was really happy for myself," he said.

Finally, the related paper was published in Nature Energy with the title "Single-phase local-high-concentration solid polymer electrolytes for lithium-metal batteries" [1].Zhang Weiran is the first author, Professor Wang Chunsheng from the University of Maryland and Professor Srinivasa R. Raghavan, as well as Professor Anh T. Ngo from the Argonne National Laboratory in the United States, serve as the co-corresponding authors.

"With the mentor coming to the lab seven days a week, it's hard not to work hard."

It is also reported that the aqueous electrolyte was the most famous direction of Professor Wang Chunsheng's research group a few years ago. When Zhang Weiran first arrived here, he also chose this direction by reputation.

Later, due to the limitations of aqueous electrolytes, he became interested in lithium metal and high-voltage cathodes, and thus did some work. On another day, he was assigned to be responsible for the silicon anode project, so he carried out research on the electrolyte for the silicon anode and its calendar life.

During this period, he and his mentor tried to extract new knowledge from the concept of liquid electrolytes in lithium metal batteries, which led to the proposal of the current concept of polymer electrolytes.Later on, Zhang Weiran was never able to realize the idea about a certain liquid electrolyte, so he tried to combine it with the insights of solid-state electrolytes, and in the end, he also achieved good results.

Along the way, from the initial liquid electrolyte, it seems that Zhang Weiran's personal research direction has overall begun to focus on all-solid-state electrolytes.

He said: "Thanks to the experience in these five years, I have a certain understanding and attempt of different directions of the battery. Although in the process of constantly changing the topic, some work was not completed in time and wasted some time, it also improved my cognition and the breadth of my insights, which makes me not limited to a certain place, and these directions will also inspire each other."

He continued: "So I often say that Teacher Wang is my Bole, if in other places, a student like me who wants to try everything, may have been educated long ago."

In Zhang Weiran's eyes, the mentor Wang Chunsheng is not only a doctoral supervisor but also a "teacher" who educates people. He is very eager for students to inherit his thoughts and way of thinking from him, so he always spares no effort to guide students.In addition, the team's paper output is very high. Regarding this, Zhang Weiran said that this is mainly due to the following three points:

Firstly, the mentor Wang Chunsheng's thinking has always been at the forefront of scientific research. He has a clear understanding of the vast majority of directions in the field of batteries and encourages students to focus on researching more challenging directions. Therefore, the goals of the research group are very clear.

Secondly, the mentor Wang Chunsheng is not easily influenced by others' opinions. When dealing with every new work in the field, he thinks about what views this work has proposed, what views it has proved, what views he agrees with, and what views he disagrees with.

Moreover, he has always required students to do the same. Under his long-term influence, the research efficiency of the research group has naturally been greatly improved.

Thirdly, Zhang Weiran said: "The most important thing is that Teacher Wang himself is a very hardworking person. When your mentor comes to the laboratory seven days a week, it is difficult for you not to work hard."Next, Zhang Weiran and his colleagues will attempt to scale up the production of this polymer electrolyte and test its capabilities in large batteries.

In addition, the research group is also focusing on the study of inorganic solid-state electrolytes. Only by making inorganic solid-state electrolytes thinner can they achieve real-world applications. Therefore, they also hope to combine polymers with inorganic solid-state electrolytes.

At the same time, AI is also very important for the development of electrolytes. Taking this work as an example, after determining the main logic for designing the polymer electrolyte, if AI can quickly screen potential polymers based on requirements, it can reduce human trials or narrow the scope of trials.

Therefore, the team is currently also collaborating with Professor Jay Lee from the Industrial AI Center at the University of Maryland to develop electrolytes using AI.