With rising greenhouse gas emissions, the urgency of addressing global warming and climate change has intensified, prompting a global shift towards renewable energy. The development of rechargeable batteries is essential for this effort. Lithium-ion batteries (LIBs) are one of the most widely used rechargeable batteries today, being used in cars, smartphones, and even for power storage. However, one major issue with LIBs is the risk of ignition. Commercial LIBs have a carbon-negative electrode with a low working potential. Since carbon operates near lithium metal deposition potential, there is a risk of internal short circuits, especially when the battery is quickly charged.
Alternative materials for LIB-negative electrodes have been thoroughly studied in recent years, with transition metal oxides. Oxide-based materials operate at a slightly higher potential than lithium, reducing the risk of short circuits. Additionally, they have excellent thermal stability, further reducing fire risk. Notably, oxide-based negative electrodes behave as insulators in the fully discharged state, insulating the battery in the event of an accident. Despite these advantages, existing oxide-based electrodes, such as Li4Ti5O12, have a significantly smaller capacity compared to carbon electrodes, which has prompted research into perovskite-related materials. Among these materials, Wadsley–Roth phase oxides, like the TiNb2O7 (TNO), have received considerable attention. However, the atomic structure of TNO remains unknown, essential for understanding and optimizing its negative electrode properties.
To address this gap, a research team from Japan, led by Associate Professor Naoto Kitamura, from the Department of Pure and Applied Chemistry at Tokyo University of Science (TUS), including Mr. Hikari Matsubara, Prof. Chiaki Ishibashi, Prof. Yasushi Idemoto from TUS, Prof. Koji Kimura, Prof. Koichi Hayashi from Nagoya Institute of Technology, Prof. Ippei Obayashi from Okayama University, and Prof. Ken Nakashima from Shimane University, investigated the atomic structure and the effect of network structure on the electrode properties of TNO. Their study was published online in the journal NPG Asia Materials on December 10, 2024. “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,” explains Prof. Kitamura.
They prepared three TNO samples with distinct charge-discharge properties: a pristine version, a ball-milled sample to reduce the particle size, and a heat-treated sample. Then, they collected total scattering data of the samples from quantum beam measurements and used RMC modeling to generate a three-dimensional (3D) atomic structure of the materials using the data. These generated atomic structures reproduced the total scattering data and the Bragg profile data of the real samples, indicating their validity. Further, they conducted topological analysis, based on persistent homology, on the generated 3D structures and thoroughly examined the relationship between the topology of atomic configuration and negative electrode properties in detail.
Their analysis revealed that reducing the particle size by ball milling and subsequent heat treatment, which relaxed the distortion in the network structure, was best for improving charging and discharging capacities. This suggests that network disorder significantly affects negative electrode performance. Moreover, it shows that the topology can be controlled for the best charging/discharging capacities by optimizing the preparation process.
“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,” notes Prof. Kitamura. “TNO can be used in lithium-ion batteries for cars and can contribute to the green growth strategy for achieving carbon neutrality,” he adds, looking towards the future.
These research insights are instrumental in developing next-generation LIBs with improved safety and capacity, paving the way towards a sustainable, renewable energy-powered future.
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Reference
DOI: https://doi.org/10.1038/s41427-024-00581-5
About The Tokyo University of Science
Tokyo University of Science (TUS) is a well-known and respected university, and the largest science-specialized private research university in Japan, with four campuses in central Tokyo and its suburbs and in Hokkaido. Established in 1881, the university has continually contributed to Japan's development in science through inculcating the love for science in researchers, technicians, and educators.
With a mission of “Creating science and technology for the harmonious development of nature, human beings, and society," TUS has undertaken a wide range of research from basic to applied science. TUS has embraced a multidisciplinary approach to research and undertaken intensive study in some of today's most vital fields. TUS is a meritocracy where the best in science is recognized and nurtured. It is the only private university in Japan that has produced a Nobel Prize winner and the only private university in Asia to produce Nobel Prize winners within the natural sciences field.
Website: https://www.tus.ac.jp/en/mediarelations/
About Associate Professor Naoto Kitamura from Tokyo University of Science
Dr. Naoto Kitamura is currently an Associate Professor at the Department of Pure and Applied Chemistry in Tokyo University of Science. Prof. Kitamura obtained his Ph.D. degree from Kyoto University in 2006. He has published over 130 articles which have received over 1,700 citations so far. Prof. Kitamura received the JSPM Award for Innovatory Research in 2016. His research interests include lithium-ion batteries, nanotechnology, and inorganic materials.
Funding information
This research was financially supported by JSPS Grant-in-Aid for Transformative Research Areas (A) “Hyper-Ordered Structures Science” (Grant Nos. 20H05880, 20H05881, and 20H05884) and JSPS KAKENHI (Grant No. 19KK0068).
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