―Ultra-thin working electrodes enable direct, real-time visualization of electrochemical reactions inside pressed and closed batteries.―
Researchers) Research Institute of Electrochemical Energy, KITTA Mitsunori, Senior Researcher, SANO Hikaru, Chief Senior Researcher, MAEYOSHI Yuta, Senior Researcher
Researchers at AIST have successfully developed a method for non-destructive visual inspection of the interior of a battery while it is in operation.
Batteries consist of three components: a positive electrode, a negative electrode, and a separator. The two electrodes are metal plates or foils that typically do not transmit visible light. In other words, since the interior of the battery is enclosed by materials that do not transmit visible light, it is impossible to see inside the battery directly with the naked eye without disassembling it. However, understanding “what happens inside a battery during operation” is crucial for developing high-performance and safe rechargeable batteries. For example, lithium metal rechargeable batteries are expected to be among the candidates for next-generation high-energy-density batteries, and observing the behavior of lithium metal precipitation and dissolution inside these batteries helps us understand their operating mechanism.
The technology developed in this study was made possible by making one of the electrodes thin enough to allow visible light to pass through. It is about 10 nanometers thick. This is about one ten-thousandth the thickness of a sheet of copy paper. Applying such a thin copper film to the electrodes of a lithium metal secondary battery made it possible to see through the electrodes into the battery’s interior. We used this technology to visually inspect the interior of a lithium metal secondary battery under development and discovered that gas generated by the electrolyte’s decomposition during charging accumulates at the interface between the electrode and the separator containing the electrolyte. This significantly affects the battery’s charge-discharge performance. Furthermore, we confirmed the uneven deposition of lithium metal on the electrode surface and successfully visualized the factors causing short circuits between electrodes. These findings are expected to contribute to the advancement in technologies that suppress the degradation of next-generation high-energy-density batteries, such as lithium metal batteries.
Details of this research were published online in “Electrochemistry Communications” on March 5, 2026.
The global demand for smaller, more powerful, and safer rechargeable (secondary) batteries is growing, and research and development in this area is advancing worldwide. Currently, lithium-ion batteries are widely used in mobile power banks and electric vehicles. However, “lithium metal secondary batteries”, which can store even more energy, are attracting attention as the next-generation secondary batteries. There is a strong desire to make them practical. These batteries utilize the repeated precipitation and dissolution of lithium metal at the negative electrode. However, if these reactions occur unevenly during this cycle, it can cause battery degradation or short circuits, leading to reduced cycle life and the risk of thermal runaway. Therefore, a thorough understanding of the mechanisms of lithium metal deposition and dissolution within the battery is essential for improving cycle stability, safety, reliability, and durability. This understanding is considered indispensable for the practical application of lithium metal secondary batteries.
Journal：Electrochemistry Communications
Title of paper：Direct operand visualization of Li-metal plating and stripping inside pressed, closed battery cells using optically transmitting ultra-thin electrode
Authors：Mitsunori Kitta*, Hikaru Sano and Yuta Maeyoshi*
DOI：https://doi.org/10.1016/j.elecom.2026.108142