Wound Electrode Assembly Hollow Core Stress Management
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Solution Overview
Problem
In secondary batteries, the expansion and contraction of electrode assemblies during charging and discharging lead to stress concentration at the boundary between curved and flat portions, causing wrinkles that increase resistance and potentially result in capacity loss or electrode degradation.
Innovation Solution
The electrode assembly is designed with a hollow portion at its center, where the thickness of the flat portion, half the thickness of the hollow portion, and the thickness of the curved portion satisfy specific formulas to allow expansion absorption and minimize stress concentration, preventing wrinkle formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the electrode assembly is wound tightly to maximize energy density, then the space utilization is improved, but stress concentration occurs at the boundary between curved and flat portions causing wrinkle formation
Solution Approach 1:
The electrode assembly is divided into curved portions and flat portions, creating distinct functional zones. The flat portions serve as stress relief areas where wrinkles can form without affecting performance, while curved portions maintain tight winding for energy density. This segmentation allows the assembly to achieve high energy density while preventing catastrophic failure from stress concentration.
Solution Approach 2:
Different regions of the electrode assembly are given different structural qualities. The flat portions have relaxed geometry that accommodates expansion and absorption of wrinkles, while curved portions maintain tight winding for maximum energy density. This local differentiation allows each region to optimize its function without compromising the whole system.
2Quantity of substance
If the electrode assembly expands during charging to accommodate reaction byproducts, then the capacity is improved, but wrinkles form on the electrode surface increasing resistance
Solution Approach 1:
The harmful effect of wrinkle formation is extracted and isolated to specific flat portions of the electrode assembly. By designing these flat portions as dedicated wrinkle absorption zones, the expansion-related wrinkles are confined to areas that do not affect electrical performance, while the curved portions maintain smooth surfaces for optimal conductivity.
Solution Approach 2:
The expansion of electrodes during charging, which normally causes harmful wrinkles, is converted into a beneficial mechanism. The flat portions are deliberately designed to accommodate this expansion and absorb the resulting wrinkles, transforming what would be a harmful effect into a controlled, non-critical feature that actually relieves stress from the critical curved portions.
3Volume of moving object
If the curved portions are made thinner to reduce overall assembly thickness, then the compactness is improved, but stress concentration increases at the boundary portions
Solution Approach 1:
The stress management approach moves from a one-dimensional thickness consideration to a two-dimensional geometric configuration. By introducing flat portions as a separate geometric element, the design provides an additional dimension for stress relief that is independent of the curved portion thickness, allowing thin curved portions without compromising structural integrity.
Data Source
AI summary
An energy storage device includes: a flattened electrode assembly formed by winding electrodes such that a hollow portion is formed, the electrode assembly including a pair of curved portions opposed manner in a major axis direction and a pair of flat portions opposed in a minor axis direction; and a case storing the electrode assembly therein, wherein assuming a thickness of the flat portion in the minor axis direction as A, a thickness of the curved portion in a radial direction as B, and a thickness of the hollow portion in the minor axis direction as W, the electrode assembly satisfies A+(W/2)≤B in a state where the electrode assembly is discharged.