Lithium Ion Battery Separator Curved End Design
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Solution Overview
Problem
The use of heat-resistant separators in lithium ion secondary batteries can lead to performance deterioration due to damage of the packaging film's inner surface, causing loss of insulating properties and reduced battery capacity, especially when the separator ends come into contact with the metal layer.
Innovation Solution
The battery design incorporates a first heat-resistant separator with a larger end projecting amount and a second separator with a smaller end, where the first separator's end is curved to contact the packaging film's inner surface, reducing pressure and preventing contact with the heat-sealing resin layer, thereby maintaining the insulating properties and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heat-resistant separators are used to prevent internal short-circuiting, then safety is improved, but the separator ends damage the packaging film's inner surface causing loss of insulating properties
Solution Approach 1:
The end of the first separator is formed with a curved portion that curves further inside than a virtual extension plane of the outer surface of the second separator. This curved geometry prevents the separator end from directly contacting and damaging the packaging film's inner surface, while still maintaining the safety function of the heat-resistant separator.
Solution Approach 2:
The curved portion of the first separator acts as an intermediary between the rigid separator material and the packaging film. It provides a transition that reduces contact pressure and prevents direct damage to the packaging film's metal layer, while still allowing the separator to fulfill its safety function.
2Strength
If separator ends contact the packaging film inner surface, then structural support is improved, but insulating properties are lost due to contact with metal layer
Solution Approach 1:
The curved portion at the end of the first separator provides structural support while directing the contact point away from the metal layer of the packaging film. The curvature ensures that the separator end contacts only the heat-sealing resin layer, maintaining insulating properties.
Solution Approach 2:
The separator structure is designed with different geometries at different locations: the main body provides structural support, while the curved portion at the end provides localized contact control to preserve insulating properties by avoiding metal layer contact.
3Reliability
If separator projecting amount is increased to ensure coverage, then safety is improved, but contact pressure with packaging film increases causing damage
Solution Approach 1:
The curved portion distributes the contact pressure over a larger area of the packaging film's heat-sealing resin layer, reducing the pressure intensity at any single point. This allows the separator to maintain its safety function with adequate projecting amount without causing damage.
Solution Approach 2:
The geometry of the separator end is changed from a straight edge to a curved portion, which alters the pressure distribution characteristics. This parameter change allows the separator to exert sufficient pressure for structural support while avoiding concentrated stress that would damage the packaging film.
Data Source
AI summary
A lithium ion secondary battery includes: an electrode multilayer body including a plurality of electrodes stacked with a plurality of separators interposed therebetween; and a package. An end of each of the plurality of separators of the electrode multilayer body housed in the package projects from each of the plurality of electrodes. The plurality of separators includes a first separator, and a second separator which is disposed inside of the first separator and whose projecting amount of an end is smaller than that of the first separator. The end of the first separator is in contact with an inner surface of the packaging film or an inner surface of the separator located outside of the first separator, the end of the first separator is curved further inside than a virtual extension plane of an outer surface of the second separator.