What is the "crucifix" of solid-state battery performance degradation? "Artificial Intelligence Microscope" to find out

Produced by: Science Popularization China

Author: Wang Chunyang (Institute of Metal Research, Chinese Academy of Sciences)

Producer: China Science Expo

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All-solid-state lithium batteries are regarded as the next generation battery technology that surpasses traditional liquid lithium-ion batteries due to their high safety and high energy density. However, so far, the instability of the interface formed by the contact between the positive electrode material (the carrier for storing lithium ions) and the solid electrolyte (the transport medium for lithium ions) has always been a bottleneck restricting the performance and service life of all-solid-state batteries.

Lithium-ion battery

(Photo source: veer photo gallery)

Recently, a research team from the Institute of Metal Research, Chinese Academy of Sciences, and the University of California, Irvine, used artificial intelligence (AI)-assisted transmission electron microscopy (TEM) technology to clarify the structural degradation mechanism of the cathode/electrolyte interface at the atomic scale, revealing the mystery behind the performance degradation of all-solid-state lithium batteries.

What is an all-solid-state lithium battery?

All-solid-state lithium battery is a battery technology that uses solid electrolytes instead of traditional liquid electrolytes. Due to its higher safety, higher energy density and wider operating temperature range, it is currently considered to be a research hotspot and major breakthrough direction for the next generation of lithium battery technology.

Nowadays, the biggest problem encountered by all-solid-state lithium batteries is the electrochemical instability between the electrode and the electrolyte, which is the "culprit" for the rapid decline in battery performance. This instability affects the structure of the layered oxide cathode material and becomes the biggest obstacle to the stable performance of all-solid-state lithium batteries. In-depth research on the material structure degradation mechanism caused by interface instability in all-solid-state batteries is expected to provide important theoretical guidance for the development of high-performance all-solid-state batteries.

How to look at the structure of battery materials?

If you want to develop advanced materials, you must first have a deep understanding of the structure of the materials. The Transmission Electron Microscope (TEM) is a "weapon" for observing the internal structure of materials. It can observe materials at the atomic scale with a resolution of up to 0.05 nanometers, which is equivalent to one millionth of the diameter of a hair! In material science research, TEM is one of the most important means of material characterization in the world today. The Institute of Metal Research of the Chinese Academy of Sciences in Shenyang is one of the earliest units in my country to carry out electron microscopy research (the founder of this direction is Mr. Guo Kexin, a famous electron microscopist and crystallographer in my country). As the cradle of electron microscopy talent training in my country, the Institute of Metal Research has more than ten transmission electron microscopes of various types (worth hundreds of millions of yuan), and has a deep foundation and a strong scientific research team in the electron microscopy research of materials.

Schematic diagram of the basic structure of a transmission electron microscope

(Image source: Chinese Academy of Sciences)

Transmission electron microscope of the Institute of Metal Research, Chinese Academy of Sciences

(Image source: provided by the author)

What role does AI play?

The structural complexity of battery materials and their inability to withstand electron beam irradiation pose a huge challenge to material scientists in understanding their phase transitions and structural evolution at the atomic scale. However, the research team did not give up. With the advantages of artificial intelligence in image processing and analysis, they creatively used convolutional neural networks to develop new methods for atom recognition, segmentation, and high-precision positioning, achieving atomic-level high-precision imaging and analysis of the crystal structure, defects, and complex phase interfaces of layered oxide cathode materials.

Concept image: AI transmission electron microscopy reveals the atomic structure of cathode materials

(Image source: provided by the author)

Through AI-assisted TEM technology, the research team successfully revealed the atomic-scale structural degradation mechanism of all-solid-state lithium-ion layered oxide cathode materials. They found that there are three main "culprits" for the performance degradation of layered oxide cathode materials in all-solid-state batteries.

The first is lattice oxygen loss, that is, the positive electrode material will lose its main component element - oxygen during the electrochemical reaction, causing the structural framework of the material to be destroyed; the second is "lattice fragmentation", that is, the crystal structure on the surface of the material is broken under the action of stress, resulting in a significant decrease in the material's ability to transport lithium ions; the third is lattice shear phase transition, which is a phenomenon of rearrangement of the internal structure of the material caused by the delithiation process (that is, lithium ions are removed from the positive electrode material during battery charging), causing the material to transform from the initial crystal structure to another harmful crystal structure.

Fine atomic configuration analysis of shear phase interface structure in layered oxide cathodes

(Image source: provided by the author)

Surface “lattice fragmentation” of layered oxides induced by interfacial electrochemical reactions

(Image source: provided by the author)

This research result reveals the structural degradation mechanism of layered oxide cathode materials in all-solid-state lithium batteries, expands the phase change degradation theory of layered oxide cathodes, and provides important theoretical guidance for the optimization design of cathode materials and cathode/electrolyte interfaces for all-solid-state batteries. In addition, it also provides a new perspective for understanding the interfacial behavior in all-solid-state batteries and points out the direction for the development of high-performance all-solid-state lithium batteries. At the same time, this research also fully highlights the important role of advanced electron microscopy characterization technology in solving core scientific problems in the energy field.

Wang Chunyang and his "partner" transmission electron microscope

(Image source: provided by the author)

Conclusion

Through artificial intelligence-assisted TEM technology, the team successfully revealed the failure mechanism of all-solid-state lithium battery positive electrode materials at the atomic scale. These new insights provide a scientific basis and important theoretical guidance for optimizing the design of existing materials.

In the future, the team will continue to conduct basic research on the core scientific issues in the structure-performance relationship of all-solid-state lithium battery materials. They will leverage the team's expertise in electron microscopy research and material science research, and continue to break through existing technical bottlenecks by "discovering new knowledge, developing new methods, and creating new materials", contributing to the optimization design of all-solid-state batteries and the development of new materials.