Reviewed by Lexie CornerDec 10 2024
Researchers from Tokyo University of Science, led by Associate Professor Naoto Kitamura, investigated the atomic structure of TiNb2O7 and found that optimizing network topology is key to improving the performance of lithium-ion batteries (LIBs). They also explored how the network structure affects the electrode properties of TNO. Their findings were published in the journal NPG Asia Materials.
As greenhouse gas emissions continue to rise, the need to address climate change and global warming has become more urgent. This has driven a global shift towards renewable energy, which relies on the development of rechargeable batteries.
LIBs are widely used in applications such as automobiles, smartphones, and power storage devices. However, the risk of ignition remains a significant issue with LIBs.
The carbon-negative electrode in commercial LIBs has a low working potential, which can lead to internal short circuits, especially during rapid charging, as carbon operates near the lithium metal deposition potential.
Transition metal oxides have been extensively researched as alternative materials for LIB-negative electrodes. These oxide-based materials offer a slightly higher potential than lithium, reducing the risk of short circuits. They also have outstanding thermal stability, which further reduces the risk of fire. When fully discharged, oxide-based negative electrodes act as insulators, protecting the battery from damage.
Despite their benefits, research into perovskite-related materials has been driven by the fact that current oxide-based electrodes, such as Li4Ti5O12, have a substantially lower capacity than carbon electrodes. Wadsley-Roth phase oxides, such as TiNb2O7 (TNO), have gained significant interest among these substances. The atomic structure of TNO, which is crucial for understanding and improving its performance as a negative electrode, is still unknown.
The team included Mr. Hikari Matsubara, Professor Chiaki Ishibashi, Professor Yasushi Idemoto from TUS, Professor Koji Kimura, Professor Koichi Hayashi from Nagoya Institute of Technology, Professor Ippei Obayashi from Okayama University, and Professor Ken Nakashima from Shimane University.
The network structure of TNO forms lithium-ion conduction pathways and has a significant influence on the properties of negative electrodes. However, elucidating such network structures by conventional crystal structure analysis techniques is difficult. In this study, we performed reverse Monte Carlo (RMC) modeling using quantum beam data and topological analysis based on persistent homology to explain the factors that affect the negative-electrode properties.
Naoto Kitamura, Associate Professor, Tokyo University of Science
Three TNO samples with different charge-discharge characteristics were prepared: a pristine sample, one that had been heat-treated, and one that had been ball-milled to reduce the particle size.
The team then used RMC modeling to generate a three-dimensional (3D) atomic structure of the materials based on total scattering data obtained from quantum beam measurements. The validity of these atomic structures was confirmed by their ability to reproduce the Bragg profile and total scattering data of the actual samples.
Additionally, they performed topological analysis on the generated 3D structures using persistent homology and examined the relationship between the negative electrode properties and the atomic configuration topology.
Their analysis indicated that the best way to improve charging and discharging capacities was to reduce the particle size through ball milling, followed by heat treatment, which helped relieve distortion in the network structure.
This suggests that the performance of the negative electrode is strongly influenced by network disorder. It also shows that by refining the preparation process, the topology can be optimized for better charging and discharging capacities.
For the first time, we could prove that the combination of intermediate-range structure and topology analyses is a promising way of developing a guideline for improving electrode properties. TNO can be used in lithium-ion batteries for cars and can contribute to the green growth strategy for achieving carbon neutrality.
Naoto Kitamura, Associate Professor, Tokyo University of Science
These research findings are crucial for creating next-generation LIBs with increased capacity and safety, which will contribute to a future driven by renewable energy sources.
Journal Reference:
Kitamura, N., et al. (2024) Relationship between network topology and negative electrode properties in Wadsley–Roth phase TiNb2O7. NPG Asia Materials. doi.org/10.1038/s41427-024-00581-5.