Flat Battery Separator Joint Design for Stress Control
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Solution Overview
Problem
The existing configuration of flat nonaqueous secondary batteries can lead to bruises on separators and chipping of positive electrode compound layers, causing internal short circuits and reduced capacity, which compromises battery reliability.
Innovation Solution
The battery design incorporates microporous thermoplastic resin separators with a joint formed by welding their peripheries, ensuring a ratio of the shortest distance between the joint's inner end and the positive electrode's thickness is not smaller than 1, and not greater than 2.7, to prevent stress concentration and maintain structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If separators are joined by pressing or hot pressing to form a separator bag, then the manufacturing process is simple, but the corner of the positive electrode compound layer abuts the inner surface of the separator causing bruises or chipping
Solution Approach 1:
The separator is folded back at its end portion before joining, creating a preliminary structural modification that prevents the positive electrode corner from abutting the separator's inner surface during subsequent assembly and operation
Solution Approach 2:
The separator is divided into distinct functional zones: a first portion for joining with the other separator, and a second folded-back portion that creates a protective offset, segmenting the structure to eliminate harmful contact points
2Reliability
If the separator is folded back to prevent electrode contact, then reliability improves, but the manufacturing complexity increases
Solution Approach 1:
The folding back of the separator end portion is performed as a preliminary action during separator preparation, creating a built-in protective feature that prevents electrode contact without requiring additional components or complex assembly steps
Solution Approach 2:
The separator's geometric parameters are modified by folding back the end portion, changing its spatial configuration from a flat structure to a three-dimensional form with offset layers that prevent direct contact with electrode corners
3Strength
If the separator is welded at the periphery to form a joint, then the joint strength should match separator strength, but stress concentration may occur at the joint
Solution Approach 1:
The separator end portion is folded back before the welding process, creating a preliminary structural configuration that distributes stress away from the joint area and prevents stress concentration during subsequent welding and battery operation
Solution Approach 2:
The folded-back separator portion acts as a cushioning element that absorbs and distributes mechanical stress before it can concentrate at the welded joint, protecting the joint from excessive stress during battery assembly and operation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances battery reliability by preventing separator damage and positive electrode compound layer chipping, thus minimizing internal short circuits and maintaining capacity, while ensuring the joint strength matches the separators' strength.
Implementation Method 1
a joint formed by welding together at least a portion of a periphery of the separator
Data Source
AI summary
A flat nonaqueous secondary battery with improved reliability is provided. The flat nonaqueous secondary battery (1) includes an electrode assembly disposed in a space formed by an exterior case (2) and a seal case (3). The electrode assembly includes a plurality of positive electrodes (5) and a plurality of negative electrodes (6) alternately stacked upon each other and a separator (7). The separator (7) has a joint (7c) formed by welding together at least a portion of its periphery. When the separator (7) and the positive electrode (5) are measured along a cross section in their thickness direction, the ratio A/B of the shortest distance A between the end of the joint (7c) of the separator (7) facing the positive electrode (5) and the outer periphery of the positive electrode (5) sandwiched by the separator (7) to the thickness B of the positive electrode (5) is not smaller than 1.