Cylindrical Battery Separator Structure for Inner-Core Electrolyte Retention
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Solution Overview
Problem
High-capacity lithium ion secondary batteries with small-sized cylindrical designs face challenges in maintaining electrolyte solution retention, leading to decreased charge-discharge cycle characteristics, especially during quick charging due to the large curvature of the inner peripheral electrode group.
Innovation Solution
A cylindrical secondary battery design featuring a wound electrode group with a separator having an inner non-contact region that is at least 5% of its length, ensuring sufficient electrolyte solution retention on the inner peripheral side by preventing mix layer contact, thus enhancing cycle characteristics during quick charge cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the battery size is reduced to create compact power supplies, then the battery dimensions are improved, but the curvature of the inner peripheral side of the electrode group increases, causing decreased electrolyte solution retentivity and worsened charge-discharge cycle characteristics
Solution Approach 1:
The separator is designed with a non-contact region specifically at the inner peripheral side where both surfaces are not in contact with electrode mix layers. This local structural modification addresses the specific problem of electrolyte solution retentivity at the inner peripheral side without affecting other parts of the battery, enabling compact battery design while maintaining reliable charge-discharge cycle characteristics during quick charge operations
2Reliability
If the inner non-contact region of the separator is increased to improve electrolyte solution retentivity, then the charge-discharge cycle characteristics are improved, but the amount of separator material increases and the battery volume increases
Solution Approach 1:
The non-contact region is localized specifically at the inner peripheral side of the separator rather than increasing the overall separator dimensions. This targeted approach provides sufficient electrolyte solution retentivity (5% or more of separator length) while minimizing the impact on total battery volume, resolving the contradiction between reliability improvement and volume control
Data Source
AI summary
An aspect of the present invention relates to a cylindrical secondary battery including a bottomed cylindrical battery case having an opening, an electrode group, an electrolyte solution, the electrode group and the electrolyte solution being housed in the battery case, and a sealing member blocking the opening of the battery case. The electrode group includes a positive electrode, a negative electrode, and a separator placed between the positive electrode and the negative electrode and is formed by winding the positive electrode and the negative electrode with the separator therebetween. The negative electrode includes a negative electrode current collector and a negative electrode mix layer formed on at least one principal surface of the negative electrode current collector. The positive electrode includes a positive electrode current collector and a positive electrode mix layer formed on at least one principal surface of the positive electrode current collector. The separator includes an inner non-contact region which is located on the inner peripheral side of the electrode group and which has both surfaces that are in contact with none of the negative electrode mix layer and the positive electrode mix layer. The length of the inner non-contact region is 5% or more of the length of the separator in a winding direction of the electrode group. According to the present invention, a compact cylindrical battery with particularly excellent charge-discharge cycle characteristics in association with quick charge can be provided.