Flat Wound Battery Electrode Layout for Inner Bend Short Prevention
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries with flat wound electrode assemblies face issues of reduced energy density and internal short circuits due to curvature-induced stress and separator breakdown at the innermost circumference, where the curvature of the electrode plates is greatest, and existing solutions like attaching insulating tape are difficult to implement in mass production and can lead to non-uniform battery reactions.
Innovation Solution
The battery design includes a configuration where at least two layers of the second electrode plate are disposed on the inner side of the curved portion of the first electrode plate at the innermost circumference, reducing curvature and stress, and minimizing the impact on energy density by strategically locating the winding start ends of the plates and using an appropriate thickness of the separator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the separator is increased to prevent breakdown voltage decrease and internal short circuit, then reliability is improved, but energy density decreases
Solution Approach 1:
The patent applies different separator thicknesses at different locations: a first separator thickness at the innermost circumference of curved portions where stress is highest, and a second, smaller separator thickness at the flat portion. This local differentiation maintains reliability at critical stress points while preserving energy density in less critical areas.
Solution Approach 2:
The separator is divided into multiple sections with different thicknesses based on the structural requirements of different battery components. The separator includes a first section with greater thickness for the curved portions and a second section with smaller thickness for the flat portion, allowing optimized performance across different regions.
2Reliability
If insulating tape is attached to curved portion to prevent peel-off and internal short circuit, then reliability is improved, but manufacturing complexity increases and energy density decreases
Solution Approach 1:
The patent removes the insulating tape component entirely and replaces it with a structurally integrated separator design. The varied thickness separator provides both insulation and mechanical support functions that previously required separate insulating tape layers, simplifying the overall structure and manufacturing process.
Solution Approach 2:
The separator performs multiple functions: electrical insulation, mechanical support to prevent peel-off, and stress distribution. By designing the separator with varied thickness, it simultaneously provides enhanced protection at curved portions while maintaining overall structural integrity, replacing what would otherwise require multiple separate components.
3Reliability
If insulating tape is attached to curved portion to prevent internal short circuit, then reliability is improved, but battery reaction uniformity worsens due to non-uniform reaction area
Solution Approach 1:
The patent removes the insulating tape that created non-uniform reaction areas and replaces it with a varied thickness separator that maintains uniform electrode contact. The separator's thickness variation is designed to provide protection without creating dead zones or non-reactive areas on the electrode surfaces.
Solution Approach 2:
The separator's local thickness variation is optimized to provide mechanical support and insulation where needed while maintaining proper electrode separation and contact elsewhere. This ensures uniform battery reaction across the entire electrode surface while still preventing internal short circuits at critical curved portions.
Data Source
Figure 1(a)~1(b)
Figure 2~4
AI summary
A decrease in energy density of a battery is suppressed, and the occurrence of internal short circuit between a positive plate and a negative plate located at the innermost circumference of a curved portion of a flat electrode assembly, where the curvature of the curved portion is greatest, is suppressed. In a nonaqueous electrolyte secondary battery including a flat wound electrode assembly (14), the electrode assembly (14) has a pair of curved portions (20A, 20B) located at either end and a flat portion (21) located between the pair of curved portions. In at least one of the curved portions, at least two layers of a second electrode plate are disposed on an inner side of a curved portion of a first electrode plate located at an innermost circumference.