Flat Battery Separator Orientation for Short-Circuit Suppression
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Solution Overview
Problem
In batteries with a film-shaped separator, when the separator is damaged by an external force, it may not be possible to sufficiently prevent a short circuit between the positive electrode and the negative electrode, as the short direction of the battery and the transverse direction of the separator are the same.
Innovation Solution
A battery design where the electrode assembly has a flat shape, with a separator that has a thickness in the shortest direction and is positioned between the positive and negative electrodes. The separator's tensile strength is minimized in a direction perpendicular to its longest side, and the ratio of the separator's length in this direction to its shortest side is 2.0 or more, ensuring that cracks propagate in a way that prevents short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the separator is oriented with its transverse direction parallel to the short direction of the battery, then the separator can effectively prevent short circuits under normal conditions, but when damaged by external force, it fails to sufficiently prevent short circuits between electrodes
Solution Approach 1:
The patent applies asymmetry by orienting the separator's machine direction (MD) parallel to the long direction of the battery and the transverse direction (TD) parallel to the short direction, creating an asymmetric configuration that optimizes both normal operation and damage resistance. This asymmetric orientation ensures that when external force is applied, cracks propagate along the MD (direction of higher tensile strength) rather than TD, preventing electrode contact
Solution Approach 2:
The patent changes the orientation parameters of the separator relative to the battery geometry. Specifically, it defines the separator's MD || battery long direction and TD || battery short direction, which is a parameter change from conventional orientations. This parameter change ensures that the separator's strength anisotropy works in favor of preventing short circuits under external force
2Device complexity
If the separator is made with standard dimensions and orientation, then the battery structure is simple, but the separator cannot effectively contain crack propagation when damaged
Solution Approach 1:
The patent uses asymmetric orientation of the separator where MD || long direction and TD || short direction, creating an asymmetric configuration that naturally guides crack propagation along the longer dimension. This asymmetric setup provides enhanced damage resistance without adding structural complexity
Solution Approach 2:
The patent leverages the planar geometry of the separator by establishing a clear dimensional relationship: the MD (longer dimension of separator) aligns with the battery's long direction, while TD aligns with the short direction. This dimensional alignment ensures cracks propagate in a controlled manner across the larger surface area, preventing short circuits
Data Source
AI summary
A short circuit between a positive electrode and a negative electrode when a separator is damaged by an external force is suppressed. A battery includes an electrode assembly having a positive electrode, a negative electrode, and a film-shaped separator, the electrode assembly has a flat shape, and when a shortest direction of the electrode assembly is defined as a first direction, the separator has a thickness in at least the first direction, and is provided between the positive electrode and the negative electrode at least in the first direction. When a direction in which a distance between sides of the separator facing each other is minimized in plan view in the first direction is defined as a second direction, and a direction perpendicular to the first direction and the second direction is defined as a third direction, an angle formed between the direction in which the tensile strength of the separator is minimized and the second direction is larger than an angle formed between the direction in which the tensile strength of the separator is minimized and the third direction in plan view in the first direction. In plan view in the first direction, a ratio of a length of the separator in the third direction to a length of the separator in the second direction is 2.0 or more.