Insulating Collector Cover Layer for Wound Battery Curvature
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries with flat wound electrode bodies face issues of positive electrode active material peeling off, leading to potential short circuits due to large curvature at semi-cylindrical portions, and heat shrinkage causing contact between collector and active material layers, resulting in unwanted electrical contact and heat generation.
Innovation Solution
A collector cover layer with electrical insulation properties, such as resin or ceramic, is applied to cover the innermost semi-cylindrical facing collector portions, preventing peeling fragments from moving and reducing heat shrinkage by maintaining separator integrity between collector and active material layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If the positive electrode plate is bent into a semi-cylindrical shape to form a flat wound electrode body, then the battery achieves a compact flat shape, but the large curvature at semi-cylindrical portions causes the positive electrode active material layer to peel off
Solution Approach 1:
An insulating layer is formed on the positive electrode collector foil at the semi-cylindrical portions before winding, in advance preventing the peeling problem that would occur after assembly. This preliminary protective measure addresses the adhesion issue caused by curvature stress.
Solution Approach 2:
An insulating layer acts as an intermediary substance between the positive electrode collector foil and the positive electrode active material layer at the semi-cylindrical portions. This intermediate layer prevents direct contact and peeling while maintaining the structural integrity required for the flat wound configuration.
2Strength
If insulating layer is applied to collector portions to prevent peeling, then active material layer adhesion is improved, but manufacturing complexity increases due to additional coating steps
Solution Approach 1:
The insulating layer is applied selectively only at the semi-cylindrical portions of the positive electrode collector foil, not uniformly across the entire collector. This localized application reduces material usage and simplifies the manufacturing process compared to full-surface coating, while still addressing the peeling problem at the critical curved regions.
3Stability of the object's composition
If the separator is retained by pressing force at flat portions, then heat shrinkage is prevented, but the innermost semi-cylindrical portions experience large heat shrinkage due to lack of pressing force
Solution Approach 1:
The insulating layer serves as an additional intermediary element between the positive electrode collector foil and the separator at the innermost semi-cylindrical portions. This extra insulating barrier compensates for the lack of pressing force by providing mechanical support and preventing separator shrinkage and contact between electrodes in the high-heat curvature regions.
4Strength
If collector portions are reinforced with insulating resin to prevent deformation, then structural stability is improved, but electrical insulation properties may be compromised if the insulating layer is too thin
Solution Approach 1:
The solution uses a composite structure combining the positive electrode collector foil with an insulating layer formed at the semi-cylindrical portions. This composite construction provides both the structural reinforcement needed to prevent deformation and the electrical insulation required to maintain reliability, with the insulating layer thickness optimized to balance mechanical and electrical requirements.
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
Prevents short circuits and heat-induced contact between collector and active material layers, enhancing the reliability of nonaqueous electrolyte secondary batteries by ensuring electrical insulation and maintaining separator integrity, thus preventing unwanted electrical contact and heat generation.
Implementation Method 1
a collector cover layer having electrical insulation properties and covering a part in the longitudinal direction of the positive electrode collector portion
Implementation Method 2
an elongated separator, the positive electrode plate and the negative electrode plate being overlapped upon one another via the separator
Data Source
AI summary
Disclosed is a nonaqueous electrolyte secondary battery which comprises a flat wound electrode body wherein a positive electrode plate, which comprises a positive electrode collector foil and a positive electrode active material layer, and a negative electrode plate, which comprises a negative electrode collector foil and a negative electrode active material layer, are wound up with a separator being interposed therebetween. The positive electrode plate has a collector cover layer that has electrical insulation properties and covers at least a part of a facing collector portion in the longitudinal direction in a positive electrode collector portion. The collector cover layer covers at least an innermost semi-cylindrical facing collector portion which forms the innermost part of the facing collector portion and has a half-cylindrical shape.