A clearer view of change: advanced electron microscopy reveals battery phase shifts

Ishikawa, Japan -- Modern energy technologies are essential for meeting the growing global demand for electricity, driven by rapid industrialization and the global transition toward renewable energy. Among these technologies, rechargeable lithium-ion batteries (LIBs) play a crucial role, powering devices from portable electronics to electric vehicles. To boost their performance and energy density, researchers increasingly rely on high-voltage cathode materials (>4.2 V vs Li/Li⁺), which can deliver more energy per charge cycle. However, operating at such voltages poses challenges: lithium cobalt oxide (LiCoO₂, LCO) cathodes often suffer from structural degradation and the formation of undesired phases that hinder lithium-ion transport. Understanding these phase transformations at the cathode–electrolyte interface is therefore essential for developing longer-lasting, higher-performing LIBs.

To address this challenge, Professor Yoshifumi Oshima from the Japan Advanced Institute of Science and Technology (JAIST), together with Senior Lecturer Kohei Aso from JAIST, Dr. Takuya Masuda from the National Institute for Materials Science, Japan, and Professor Masaaki Hirayama from the Institute of Science Tokyo, developed a novel electron microscopy technique known as cepstral matching analysis (CMA). As Prof. Oshima explains, “This method enables visualization of nanoscale structures with about 1 nm spatial resolution while causing minimal sample damage, a combination previously unattainable with conventional imaging.”

When applied to high-voltage-cycled LCO cathodes, CMA revealed that while the bulk largely retained its layered structure, spinel- and rocksalt-type phases emerged within the top about 3 nm of the electrolyte interface—structures known to contribute to degradation. This study was published in the journal Nano Letters on October 21, 2025.

The researchers combined scanning nanobeam electron diffraction (SNED) with CMA to capture structural information from the diffraction data under an ultralow electron dose (about 3 × 10³ e⁻ nm⁻²), nearly two orders of magnitude lower than that used in conventional methods. This approach reduced beam-induced damage while maintaining a high spatial resolution (about 1 nm). Diffraction patterns collected across epitaxial LCO thin films — chosen for their uniform crystal orientation and minimal mechanical defects — were converted into cepstra and compared with simulated references for layered, spinel, and rocksalt phases. This process minimized artifacts caused by sample tilt, thickness variations, and bending, enabling accurate, low-damage mapping of nanoscale transformations.

CMA identified distinct LCO domains in the epitaxial films. The top 1–3 nm near the electrolyte interface exhibited phase transformations — roughly 1–2 nm of the cathode surface converted to rocksalt-type phases, with spinel-like contrasts appearing on certain facets. Although the bulk structure remained layered, these interfacial transformations hindered lithium-ion transport and contributed to capacity fade.

The SNED–CMA method demonstrated several key advantages. Its low electron dose preserved fragile battery materials. Cepstral transformation further corrected the effects of sample tilt and thickness, improving accuracy and reproducibility. Beyond the immediate findings, Prof. Oshima highlights the method’s wider potential: “This technique can evaluate protective coatings and elemental doping strategies that suppress interfacial structural changes. It is also applicable to next-generation cathode materials, including nickel–manganese–cobalt layered oxides, lithium-rich layered oxides, and all-solid-state batteries, where nanoscale transformations critically impact performance.”

This study marks a significant step forward in low-damage, high-resolution imaging of interfacial phase transformations in energy materials. The insights gained can guide the design of lithium-ion batteries with longer lifespans and higher energy densities, supporting everyday applications such as longer-lasting smartphones and electric vehicles with extended ranges. Moreover, the approach holds promise for studying other devices that depend on ionic conduction and structural stability, including gas sensors, atomic switches, and fuel cells—bridging nanoscale materials science with next-generation energy technologies.

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About Japan Advanced Institute of Science and Technology, Japan

Founded in 1990 in Ishikawa prefecture, the Japan Advanced Institute of Science and Technology (JAIST) was the first independent national graduate university that has its own campus in Japan. Now, after 30 years of steady progress, JAIST has become one of the Japan’s top-ranking universities. JAIST strives to foster capable leaders with a state-of-the-art education system where diversity is key; about 40% of its alumni are international students. The university has a unique style of graduate education based on a carefully designed coursework-oriented curriculum to ensure that its students have a solid foundation on which to carry out cutting-edge research. JAIST also works closely both with local and overseas communities by promoting industry–academia collaborative research.  

About Professor Yoshifumi Oshima from Japan Advanced Institute of Science and Technology, Japan

Professor Yoshifumi Oshima is a Professor at the Japan Advanced Institute of Science and Technology (JAIST), holding a PhD in Science from the Tokyo Institute of Technology. With over 20 years of research experience and more than 130 publications, his work focuses on nanomaterials, surface and interface science, and atomic-scale measurements using advanced microscopy techniques. He currently directs the Nanomaterials and Devices Research Area and the taQumi Quantum Materials Program at JAIST, recognized for pioneering methods to measure atomic-scale mechanical properties in metals.

Funding information

This study was partly supported by JSPS KAKENHI (Grant Nos. JP22K14473, JP25K18108, and JP24H00042); JST GteX Program Japan (Grant Nos. JPMJGX23S5 and JPMJGX23S6); a Grant-in-Aid from the Advanced Low Carbon Technology Research and Development Program (ALCA) of JST; the Joint Research Hub Program of National Institute for Materials Science (NIMS), the Mitani Foundation for Research and Development; the Shibuya Science Culture and Sports Foundation; the Iketani Science and Technology Foundation; the Research Foundation for the Electrotechnology of Chubu (REFEC); the Asahi Glass Foundation, and Japan Advanced Institute of Science and Technology (JAIST) Research Grant (Fundamental Research). This work was performed at the NIMS Battery Research Platform. This work was partly conducted in JAIST supported by the Advanced Research Infrastructure for Materials and Nanotechnology in Japan (ARIM) program of MEXT (JPMXP1222JI0007, JPMXP1223JI0012, and JPMXP1224JI0005).