Secondary Battery Electrode Winding for Short Circuit Prevention
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Solution Overview
Problem
Lithium ion batteries face issues with internal short circuits during high rate discharge due to deformation of electrodes, which reduces battery life and causes welding failures.
Innovation Solution
A secondary battery design where strip-shaped positive and negative electrodes with active material non-covered portions are stacked and wound with a separator, with specific dimensions and overlapping configurations to prevent internal short circuits and ensure high initial capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the number of idling windings of separator is increased to improve deformation resistance, then cycle life is improved, but device complexity increases
Solution Approach 1:
The separator is divided into multiple discrete windings (first idling winding, second idling winding, etc.) with specific functions. The first idling winding prevents short circuits at the inner peripheral portion, while subsequent windings provide deformation resistance. This segmentation allows each layer to be optimized for its specific function rather than requiring a uniformly complex structure throughout.
Solution Approach 2:
The idling windings are placed at predetermined positions before electrode assembly completion. The first idling winding is positioned at the inner peripheral portion where short circuits are most likely to occur, and subsequent windings are placed at specific intervals. This preliminary placement prevents deformation and short circuits before they can occur during charging/discharging cycles.
2Duration of action of stationary object
If inert material is wound together with separator to improve deformation resistance, then cycle life is improved, but manufacturing precision requirements increase
Solution Approach 1:
Instead of uniformly increasing separator thickness or adding inert material throughout, the invention places idling windings only at specific locations where they are most needed - the inner peripheral portion and at predetermined intervals. This local application of deformation resistance features maintains overall manufacturing simplicity while effectively preventing short circuits at critical locations.
3Reliability
If active material non-covered portion is made longer to prevent internal short circuit, then reliability is improved, but initial capacity decreases
Solution Approach 1:
The separator structure is segmented into multiple functional zones: the first idling winding at the inner peripheral portion provides short circuit prevention with minimal length, while subsequent windings are placed at predetermined intervals. This segmentation allows the non-covered portion to be sufficiently long for reliability without excessive length that would reduce capacity, as the multi-zone approach provides distributed protection.
Solution Approach 2:
The idling windings act as intermediary protective elements between the active material non-covered portions of positive and negative electrodes. These windings provide the necessary separation and deformation resistance without requiring the non-covered portions themselves to be excessively long, thus maintaining both reliability and capacity.
Data Source
AI summary
Disclosed is a secondary battery in which a positive electrode active material non-covered portion is joined to a positive electrode current collector plate at one end portion of an electrode winding body, a negative electrode active material non-covered portion is joined to a negative electrode current collector plate at the other end portion of the electrode winding body, the electrode winding body has a flat surface formed by bending at least the positive electrode active material non-covered portion toward a central axis of the wound structure and overlapping each other, a groove formed in the flat surface, and an inner peripheral portion located inside innermost peripheries of a positive electrode and a negative electrode and including only a separator.