Rounded Pouch Battery Cup Geometry to Prevent Edge Cracks
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Solution Overview
Problem
Pouch-type secondary batteries face issues with cracks and whitening during molding due to stress concentration at edges and corners during the press processing of thin pouch films, leading to reduced durability and increased defect rates.
Innovation Solution
The design includes a pouch-type battery case with rounded punch edges, thickness edges, and corners, where the curvature radii of these features differ, and the corners have a variable curvature radius with a central portion greater than the peripheral portion, dispersing stress and preventing cracks and whitening during molding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If drawing molding is performed on a thin pouch film by applying pressure with a punch, then the cup part is formed and the battery case is manufactured, but stress concentrates at edges and corners causing cracks and whitening
Solution Approach 1:
The invention applies curvature to the punch edges and corners during the molding process. Specifically, the punch is designed with rounded edges having a curvature radius of 0.1mm to 1.0mm and rounded corners with a curvature radius of 0.5mm to 2.0mm. This curvature prevents stress concentration at sharp edges and corners during drawing molding, eliminating cracks and whitening while maintaining manufacturability of the battery case
Solution Approach 2:
The invention applies different curvature radii to different locations on the punch based on local stress requirements. The punch edges have a smaller curvature radius (0.1mm to 1.0mm) while the corners have a larger curvature radius (0.5mm to 2.0mm), as corners experience higher stress concentration. This localized differentiation optimizes stress distribution across the pouch film during molding
2Shape
If the pouch film is elongated during press processing, then the cup part shape is formed, but stress concentration at edges and corners causes cracks and whitening
Solution Approach 1:
The invention modifies the punch geometry to include rounded edges and corners with specific curvature radii. The rounded punch edges (0.1mm to 1.0mm radius) and rounded corners (0.5mm to 2.0mm radius) ensure uniform stress distribution during film elongation, preventing defects while achieving the required cup part shape with high manufacturing precision
3Device complexity
If a sharp-edged punch is used for molding, then the manufacturing process is simple, but cracks and whitening occur due to stress concentration
Solution Approach 1:
The invention modifies the punch design by adding curvature to edges and corners. The punch includes rounded edges with a curvature radius of 0.1mm to 1.0mm and rounded corners with a curvature radius of 0.5mm to 2.0mm. This relatively simple geometric modification significantly improves battery case durability by preventing stress concentration and resulting defects, without substantially increasing device complexity
Data Source
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AI summary
A pouch-type secondary battery according to an embodiment of the present invention for solving the above problems includes a cup part configured to accommodate an electrode assembly formed by stacking electrodes and separators, wherein the cup part includes: a bottom portion configured to form a bottom; an outer wall configured to form a side surface and meet the bottom portion; a punch edge configured to connect the bottom portion to the outer wall; a thickness edge configured to connect two adjacent outer walls to each other; and a corner formed by connecting the two adjacent punch edges to the thickness edge, wherein at least one of the punch edges is rounded, at least one of the thickness edge is rounded, at least one of the corner is rounded and has a curvature radius different from that of each of the punch edge and the thickness edge.