Flat Wound Battery Electrode Assembly for Inner-Curve 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 curved portions is greatest, and existing solutions like insulating tape application are difficult to scale for mass production and lead to non-uniform battery reactions.
Innovation Solution
The battery design includes at least two layers of the second electrode plate disposed on the inner side of the curved portion of the first electrode plate at the innermost circumference, reducing curvature and stress, and maintaining separator thickness to prevent insulation breakdown and internal short circuits while minimizing energy density reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the separator is increased to prevent insulation breakdown and internal short circuit, then reliability is improved, but energy density decreases
Solution Approach 1:
The patent applies different separator thicknesses at different locations: the separator is thicker at the innermost circumference of the curved portion where stress is highest and curvature is greatest, and thinner in other areas. This local differentiation prevents insulation breakdown at critical locations while maintaining overall energy density.
Solution Approach 2:
The separator is divided into multiple regions with different thickness characteristics. The curved portion at the innermost circumference has increased thickness compared to the flat portion, creating segmented thickness distribution that addresses local stress concentrations without uniformly reducing energy density.
2Reliability
If an insulating tape is attached to the 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 extracts the insulating function from a separate tape component and integrates it directly into the separator structure. The separator itself is designed with increased thickness at the curved portion, eliminating the need for separate insulating tape attachment and simplifying manufacturing while maintaining reliability.
Solution Approach 2:
The insulating function previously provided by a separate tape is merged with the separator structure. The separator serves both its primary function of ion transport and the secondary function of providing mechanical support and insulation at the curved portion, reducing component count and manufacturing steps.
3Reliability
If an insulating tape is attached to the curved portion to prevent internal short circuit, then reliability is improved, but non-uniform battery reaction occurs leading to localized current concentration
Solution Approach 1:
The separator thickness is locally increased only at the innermost circumference of the curved portion where stress concentration occurs, rather than applying a uniform tape across the entire curved surface. This localized approach prevents internal short circuits at critical points while maintaining uniform battery reaction areas.
Data Source
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.