Lithium-Ion Transport Environment in Ion-Conducting Glasses
- Release Date
- 07 Apr, 2023
- BL04B2 (High Energy X-ray Diffraction)
[Key achievements]
・Their research achievements will promote the development of ion-conducting glass materials and the understanding of the properties of those materials, providing new guidelines for the development of novel solid electrolyte materials.
・They topologically analyzed the charge clouds of Li ions in Li3PS4 sulfide glass and found that three types of Li-ion environment are present in the glass.
・They successfully applied machine learning to the reverse Monte Carlo (RMC) simulation used for the structural analysis of liquid and amorphous materials.
・They clarified, for the first time, the Li-ion environments in partially crystallized glass structures with improved Li-ion transport properties by combining the results obtained at the world-class, large-scale synchrotron radiation facility in Japan, SPring-8, and the Japan Proton Accelerator Research Complex (J-PARC) with the results obtained using the supercomputer Fugaku.
A joint research group led by the beamline scientists in the Diffraction and Scattering Division, Japan Synchrotron Radiation Research Institute (JASRI), has clarified the lithium (Li)-ion transport environment in Li3PS4 sulfide glass through high-energy X-ray diffraction*1 at the BL04B2 beamline of one of the largest synchrotron radiation facilities in the world, SPring-8*2, and neutron diffraction*3 at BL21 NOVA of the Japan Proton Accelerator Research Complex (J-PARC)*4. Controlling Li-ion transport in glasses at atomic and molecular levels is key to realizing all-solid-state batteries, a promising technology for electric vehicles. Li3PS4 glass is a candidate for a high-performance solid electrolyte. Theoretical studies have suggested that, in Li3PS4 glass, the dynamic coupling between the mobility of Li+ ions and the vibration of PS43- ions results in the transport of Li+ ions through a solid. However, this phenomenon has not been clearly observed in experiments. In this study, the researchers evaluated the valence of Li ions in glass by a topological*5 approach based on Bader analysis*6. They found that three types of Li-ion transport environment are present in Li3PS4 glass and that high-mobility Li ions (Li3-type ions) are likely to exist at relatively long distances of 4.0–5.0Å (angstrom). They also reproduced the experimental data of X-ray, neutron, and electron diffractions through the reverse Monte Carlo (RMC) simulation combined with machine learning*7 using the supercomputer Fugaku*8 and found that Li-ion transport properties are improved in partially crystallized glass structures as a result of the increase in the number of Li3-type ions. Their research achievements will promote the development of ion-conducting glass materials and the understanding of the properties of these materials, providing new guidelines for the development of novel solid electrolyte materials. Their research achievements were reported in the international scientific journal Energy & Environmental Materials published by Wiley on 3 April 2023. The project members supported by the Grant-in-Aid for Scientific Research on Innovative Areas, “Science on Interfacial Ion Dynamics for Solid State Ionics Devices (Interface IONICS)”, worked together to advance this study. 【Publication】 |
Fig. 1: Environment of Li ions evaluated by Bader charge analysis.
a) Charge density of Li ions obtained by Bader analysis of Li2S-P2S5 crystal.
b) Mean valence and variance of Li ions over 1.6 ps.
c) Correlation between mean valence and variance of Li ions in glassy, β-crystal, and γ-crystal phases*9.
d) Distance obtained by Bader analysis.
e) Mean distance and variance between Li-ion position and charge density maxima over 1.6 ps.
f) Correlation between mean distance and variance between Li-ion position and charge density maxima in glassy and crystal phases.
Fig. 2: Classification of Li ions based on results of Bader analysis that enables topological analysis of charge clouds of Li ions.
a) Li1-type: distance between Li-ion position and charge density maxima < 0.045Å.
b) Li2-type: distance = 0.045–0.065Å.
c) Li3-type: distance > 0.065Å.
[Glossary]
*1. X-ray diffraction
X-ray diffraction is an experimental technique used to analyze structures by irradiating a material with X-rays and examining the diffraction patterns specific to the material.
*2. Large synchrotron radiation facility, SPring-8
SPring-8, owned by RIKEN, is a large synchrotron radiation facility that delivers one of the most powerful synchrotron radiations in the world. It is located in Harima Science Garden City, Hyogo Prefecture, Japan. JASRI supports users of this facility. The name “SPring-8” is derived from “Super Photon ring-8 GeV”. The research conducted at SPring-8 covers a wide range of fields including nanotechnology, biotechnology, and industrial applications.
*3. Neutron diffraction
Neutron diffraction is a measurement technique used to investigate the solid and liquid materials from the diffraction of neutron beams. In X-ray diffraction, X-rays are scattered by electrons. On the other hand, in neutron diffraction, atomic nuclei are involved in the scattering. This is why neutron diffraction is suitable for obtaining information about light elements that are difficult to detect with X-rays, such as hydrogen and lithium. In this study, the positions of Li in Li3PS4 were determined by neutron diffraction.
*4. Japan Proton Accelerator Research Complex (J-PARC)
J-PARC is an experimental facility complex located at Tokai Village, Ibaraki Prefecture, operated as a joint project between the High Energy Accelerator Research Organization (KEK) and the Japan Atomic Energy Agency (JAEA). J-PARC provides experiment opportunities for cutting-edge studies in wide areas, including academic areas such as elementary particle physics, nuclear physics, solid-state physics, chemistry, materials science, and biology, and industrial applications. The Materials and Life Science Experimental Facility (a J-PARC facility) houses some of the world’s most powerful muon and neutron beams used by researchers around the world.
*5. Topological analysis
Topological analysis uses topology, which is an area of mathematics in which the abstract nature of figures and the features of space are studied.
*6. Bader analysis
Bader analysis is a technique for analyzing the topology of electron density and was proposed by Dr. Richard F. W. Bader. Electron density (or charge density) can be classified by dividing space with a plane on which the gradient of electron density passing through the plane is zero.
*7. Reverse Monte Carlo (RMC) simulation combined with machine learning
Reverse Monte Carlo (RMC) simulation is a technique used to obtain a structural model by moving atoms randomly to reproduce the experimental data of X-ray and neutron diffractions. Atoms are placed in a cubic cell so that they have the density of the target material. An attempt has been made to improve this technique by using the potential energy instead of moving atoms randomly. However, the accuracy of simulation is low when the empirical potential energy is used. A high accuracy is achieved by using the nonempirical potential energy; however, the computational cost is high. To address this problem, the research group developed a new technique that combines the first-principles potential energy calculated nonempirically with machine learning. The computational cost is markedly reduced with this new technique. The first author of the group’s paper, Dr. Hiroki Yamada, visited Dr. L. Pusztai in Hungary from October to December 2021 under the International Labo Exchange Program, which is supported by the Grant-in-Aid for Scientific Research on Innovative Areas, “Science on Interfacial Ion Dynamics for Solid State Ionics Devices (Interface IONICS)”, and implemented this technique through discussion and development.
*8. Supercomputer Fugaku
Fugaku is a computer developed by RIKEN as a successor of the supercomputer K. Its trial use under the Program for Promoting Research on the Supercomputer Fugaku started in April 2020. It was made available for public use on 9 March 2021. Fugaku retained the top spot on the major high-performance computer rankings, TOP500 and HPL-AI, for four consecutive terms up to November 2021. It also retained the top spot on HPCG and Graph500 for six consecutive terms up to November 2022. Fugaku boasts world-class computing performance. Visit the website of the RIKEN Center for Computational Science (https://www.r-ccs.riken.jp/en/fugaku) for more information about Fugaku.
*9. Phase
A phase is a state of matter characterized by homogeneity within an area separated from other matter by a distinguishable boundary. A solid is also called a “solid phase”, a liquid is also called a “liquid phase”, and a gas is also called a “gas phase”. The different states in each phase are further classified as α-, β-, and γ-phases.
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