"The core of this work is to explore the attenuation mechanism of metal lithium anode at high surface capacity, and try to propose solutions from the perspective of lithium anode carrier material design to achieve high-energy density lithium metal batteries."

"The core of this work lies in exploring the attenuation mechanism of metal lithium anode at high surface capacity, and trying to propose solutions from the perspective of lithium anode carrier material design to achieve high-energy density lithium metal batteries." Regarding the paper recently published in the sub-job Science, the team of Professor Wang Dawei of the School of Chemical Engineering of the University of New South Wales, Australia, said.

Figure | Professor Wang Dawei (Source: Wang Dawei)

lays a solid "foundation" for the " lithium metal battery " building

lithium metal battery is a complex system. If you want it to be put into practical application, it is necessary to solve problems including positive electrode material component regulation and structural design, negative electrode structure design, electrolyte regulation, positive and negative electrode capacity matching, and battery management system. This work mainly focuses on the design of negative electrode structure in complex lithium metal systems.

is like building a building. What the research team can do is to try to lay the foundation of this part of the research part as firmly as possible. It will take many efforts in the future to finally witness the completion of the building. Compared with the current commercial lithium-ion battery,

, as a lithium metal battery with a new high-energy density battery system, it has higher energy storage potential and is expected to make the standby time of portable electronic devices such as mobile phones and computers longer, and the electric vehicle has a longer range.

In addition, in the field of effective storage and conversion of renewable energy such as wind energy and solar energy with periodic and gap characteristics, high-energy lithium metal battery systems also have great application prospects.

Specifically, this work has conducted research and discussion on the new high-energy density battery system of lithium metal batteries.

In recent years, the rapid development of mobile electronic devices, electric vehicles and smart grids has put forward increasingly high requirements for battery energy density.

Currently, the energy density of commercial lithium-ion batteries has approached the theoretical limit. Even so, it is still difficult to meet the rapidly growing market demand.

Therefore, the research and development of the next generation of high-energy density battery system is of great significance. For lithium metal batteries, it uses metal lithium as the negative electrode, and its theoretical specific capacity is as high as 3860 mAh g–1, which is more than ten times that of the graphite negative electrode (372 mAh g–1) for commercial lithium-ion batteries. Therefore, lithium metal batteries are expected to achieve a significant increase in energy density, and have also received widespread attention from scholars from all over the world in recent years.

However, the practical application of metal lithium negative electrode is hindered by problems such as poor cycle life. This is mainly due to the high chemical and electrochemical reaction activity of lithium metal itself, which causes continuous and uncontrollable side reactions with the electrolyte, resulting in the continuous irreversible consumption of the active metal lithium and the electrolyte, and the generation of an unstable solid electrolyte interface, which ultimately leads to battery damage.

It is worth noting that when the metal lithium negative electrode has a high surface capacity, the above problems will be further amplified, that is, the cycle life of the high-capacity metal lithium negative electrode will be further shortened.

and the higher surface capacity is a prerequisite for realizing high-energy-density batteries. Although the metal lithium anode has the advantage of high specific capacity, a higher specific capacity may not necessarily lead to higher surface capacity.

Studies have shown that the surface capacity of lithium metal batteries needs to reach 4 mAh cm–2 to achieve energy density higher than 350 Wh kg–1 , thereby meeting the practical application needs of next-generation batteries.

Therefore, how to ensure the stable cycle life of the metal lithium negative electrode at a higher surface capacity is one of the key points and difficulties in the practical process of lithium metal batteries.

The core of Wang Dawei's research team launched this research is to explore the attenuation mechanism of metal lithium anode at high surface capacity, and try to propose solutions from the perspective of lithium anode carrier material design. During

, he and his team first conducted quantitative analysis of the attenuation process of metal lithium anode at different surface capacity, thus discovering some rules, and proposed a quantitative description factor based on this, thereby correlating the cycle life of high-surface capacity lithium anode with the structural characteristics of lithium anode carrier material.

Through further comparison and analysis, it proposed a cross-scale design principle of lithium anode carrier material to achieve a lithium anode with high surface capacity and long cycle life.

Based on this principle, the team designed and prepared a defective graphene array with a three-dimensional hyperbranched structure and used it as a metal lithium anode carrier to achieve stable cycles at face capacity higher than 6 mAh cm–2 .

In general, this work is committed to solving the problem of short cycle life of high-face capacity metal lithium anode. From the perspective of basic scientific research on exploring the attenuation mechanism of metal lithium anode, the cycle life of lithium anode and its carrier material structure design are correlated through a quantitative description factor, thus providing a theoretical basis for the design of lithium metal batteries with high-face capacity and long cycle life.

Recently, the relevant paper was published on Science Advanceds Science Advanceds .

Figure | Related papers (Source: Science Advanceds)

Professor Wang Dawei serves as the corresponding author of , and his team member Dr. Fang Ruopian serves as the first author. The latter said that other issues at hand are expected to end in two years and there may be plans to return to work later.

Figure | Dr. Fang Ruopian (Source: Fang Ruopian)

will explore the lithium metal battery system based on high-capacity ternary positive electrode material

The team said that this work spans the entire time period for its research on lithium metal battery system. In early 2019, researchers began the project of lithium metal batteries.

In order to gain an in-depth understanding of this system, it made some preliminary explorations on the electrochemical behavior of metal lithium negative electrodes, and gained some qualitative understanding and understanding, but no in-depth quantitative analysis was conducted at that time.

Since 2020, it has made some attempts to design lithium negative electrode carrier materials. Through continuous comparative tests, the research team has already had a preliminary understanding of the design ideas of lithium negative electrode carrier materials that can achieve both high surface capacity and long cycle life.

However, these understandings are more based on experience. For example, the first draft of the paper is written entirely from the perspective of material design. "But after writing, I always feel that something is missing, and I feel that our views are not convincing enough. We hope to find some theoretical basis for our material design ideas, not just experience-based attempts," the team said.

2020 to 2021, during the epidemic, the laboratory continued to be closed for at least several months and at most six months. The experiment was forced to stop and the paper was revised halfway. Dr. Fang found that there was less data, but he could not make up for it in time.

"It was during the time when I couldn't supplement the new data, that I began to sort out some early data. At that time, we certainly didn't expect that part of the data could still be used like this. But it was during the process of 'forced' sorting of early data that I suddenly discovered the subtle connection between them and the paper we were preparing," she said.

By carefully and in-depth analysis of the earliest batch of electrochemical data and comparing it with multiple systems that have been tried before, the research team discovered some unique small rules that are usually ignored, and based on this, it proposed a quantitative description factor to correlate the circulation performance of lithium negative electrodes with material design ideas.

"This naturally provides a theoretical basis for our material design ideas. So we drew a lot of the first draft paper, added some data including the earliest initial exploration in 2019, and added some corresponding tests to obtain the prototype of our last published paper. At the same time, this is also a process of improving our understanding and concrete understanding of the lithium metal battery system." The researchers said.

For the same data, you can analyze it from different angles and draw conclusions from different angles. Therefore, there is no need to set limits for data, nor for our thinking. Sometimes, you may get unexpected surprises by stopping and thinking more deeply.

(Source: Science Advanceds)

Since the research subject of this work is a high-face capacity metal lithium negative electrode. At the end of the study, the characterization part of the whole battery was lithium ferrous phosphate as the positive electrode material and ether solvent as the electrolyte solvent to confirm the feasibility of the composite lithium anode structure proposed by the team in the whole battery system.

(Source: Science Advanceds)

However, the specific capacity and voltage of lithium iron phosphate itself are slightly lower than that of ternary positive electrode materials such as nickel cobalt lithium manganate and nickel cobalt lithium aluminum aluminate.

Therefore, in order to maximize the advantages of lithium metal batteries as a high-energy battery system, the team will next explore a lithium metal battery system based on ternary positive electrode materials. At the same time, the electrolyte system also needs to be optimized accordingly to meet the needs of high-voltage positive electrodes.

Reference:

1.Fang, R., Han, Z., Li, J., Yu, Z., Pan, J., Cheong, S., ... & Wang, D. W. (2022). Rationalized design of hyperbranched trans-scale graphene arrays for enduring high-energy lithium metal batteries. Science Advances, 8(34), edc9961.