Cylindrical Electric Vehicle Battery... Optimal Electrode Design Found

As global electric vehicle companies adopt cylindrical batteries, securing cylindrical battery super-gap technology has emerged as an important issue. Research results showing that problems such as lithium metal precipitation can be alleviated simply by designing electrodes that take into account the curvature of the battery are drawing attention.



Professor Kyung-Min Jeong's team from the Department of Energy and Chemical Engineering at Ulsan National Institute of Science and Technology (UNIST) has clarified the effect of the curvature of cylindrical battery electrodes on electrochemical performance and presented an optimized electrode design that takes this into account.



A cylindrical battery is a battery that is stacked in order with a separator inserted between the cathode and anode and then rolled up. If the cathode, separator, anode, and separator are considered as one set, there are usually 20 to 60 sets rolled up in one cylindrical battery cell for an electric vehicle.



The capacity ratio between the cathode and anode varies depending on whether the facing surface of the reference electrode in the curved electrode of a cylindrical lithium-ion battery is concave or convex. [Photo = UNIST]



The research team began this study by reporting that the contact area between the negative and positive electrodes may change due to the curvature characteristics of the cylindrical battery, which may cause the capacity ratio of the negative and positive electrodes to deviate from the ideal design value.



In general, when designing a battery, the negative electrode capacity is designed to be larger than the positive electrode capacity to prevent lithium metal precipitation and enable fast charging.



After fabricating an experimental curved single-plate cell that simulated various curvature conditions and comparing it with a commercial 21700 cylindrical battery, they confirmed that the capacity ratio of the electrode varied depending on the location of the electrode.



In the central area with a large curvature, the risk of lithium metal precipitation increased significantly when charging at low temperatures or high voltages. Lithium metal precipitation causes short circuits. In addition, this curvature sensitivity was greater in large-capacity, high-nickel cathode materials.



To solve this problem, the research team proposed a design strategy that adjusts the thickness of each side of the electrode. This is the principle of compensating for the capacity ratio change caused by the change in the contact area ratio between the negative and positive electrodes by adjusting the thickness of the electrode.



First author Researcher Jeon Byeong-jin explained, "We found that electrode curvature is an important design variable in cylindrical battery design," adding, "It is significant in that we need an advanced research approach that considers electrode curvature as well as material characteristics for battery performance and stability."



Professor Jeong Gyeong-min said, "This study confirmed the importance of an approach that links battery form factor with design and process technology," adding, "In order to secure an edge in the intense global competition, it is difficult to do research only aimed at improving the capacity of the material itself."



This study (title: Unveiling the Impact of Electrode Curvature on N/P Ratio Variations in Cylindrical Lithium-ion Batteries) was published online in Energy Storage Materials, an international academic journal in the energy field, on the 20th of last month.





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