Flat Wound Electrode Assembly for Capacity Retention Under Expansion
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Solution Overview
Problem
Conventional energy storage devices with flat wound-type electrode assemblies experience a decrease in discharge capacity due to electrode expansion, particularly at curved surface portions, leading to reduced conductivity and capacity retention ratios during charge-discharge cycles.
Innovation Solution
The energy storage device incorporates a flat wound-type electrode assembly with a fibrous conductive agent in the active material layer, adhering to the formulas (R/D)A≥2X and A/D≥0.2, which ensures that the fibrous conductive agent extends to maintain conductivity even as the curved surface expands, preventing further expansion and enhancing capacity retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the electrode assembly is wound into a flat shape and housed in a case, then the device structure is compact and stable, but the curved surface portions of the electrode assembly are not in contact with the case and are prone to expansion during charge-discharge cycles
Solution Approach 1:
The invention applies different functional requirements to different regions of the electrode assembly. The flat portions are designed to be in contact with the case for structural stability, while the curved surface portions are designed with specific geometric parameters (R/D ratio and surface roughness A/D ratio) to maintain conductivity and prevent expansion. This local differentiation allows each region to optimize its function without compromising the other.
Solution Approach 2:
The invention changes the geometric parameters of the curved surface portions, specifically controlling the ratio of the radius of curvature R to the average particle size D (R/D ≥ 2X) and the surface roughness A to the average particle size D (A/D ≥ 0.2). These parameter changes ensure that the curved portions maintain adequate conductivity and resist expansion during charge-discharge cycles, thereby improving capacity retention.
2Duration of action of moving object
If the electrode expands due to repeated charge-discharge, then the active material particles separate from each other, but this separation decreases the conductivity of the active material layer and discharge capacity
Solution Approach 1:
The invention controls the surface roughness A and the radius of curvature R of the active material layer to satisfy specific ratios (A/D ≥ 0.2 and R/D ≥ 2X). These parameter changes create a surface structure that maintains adequate contact between active material particles even during expansion, thereby preserving conductivity throughout the charge-discharge cycle life.
Solution Approach 2:
The invention designs the curved surface portions with predetermined geometric parameters before the electrode undergoes charge-discharge cycles. This pre-design cushions against the harmful effects of expansion by ensuring that the particle arrangement and surface topology are optimized to maintain conductivity pathways even when expansion occurs during operation.
3Adaptability or versatility
If the curved surface portion of the electrode assembly is not in contact with the case, then it is free to expand, but this expansion causes a decrease in capacity
Solution Approach 1:
The invention transforms the unrestricted expansion problem into a controlled geometric parameter optimization problem. By setting specific values for the radius of curvature R and surface roughness A (with ratios R/D ≥ 2X and A/D ≥ 0.2), the invention allows the curved surface portions to expand freely while maintaining adequate particle contact and conductivity, thus preserving capacity.
Solution Approach 2:
The invention applies different design strategies to different regions: flat portions are constrained by case contact for stability, while curved surface portions are designed with specific geometric qualities (controlled R and A values) that enable them to accommodate expansion while maintaining functionality. This local quality differentiation resolves the contradiction between expansion freedom and capacity retention.
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
This design maintains high conductivity and capacity retention ratios by suppressing electrode expansion, thereby improving the performance of the energy storage device.
Implementation Method 1
at least one of the positive electrode and the negative electrode includes an active material layer containing active material particles and a fibrous conductive agent
Data Source
AI summary
One aspect of the present invention is an energy storage device satisfying the following formula 1, in which a flat electrode assembly obtained by winding a positive electrode and a negative electrode with a separator interposed therebetween and having two curved surface portions facing each other, and a case that houses the electrode assembly, and at least one of the positive electrode and the negative electrode includes an active material layer containing active material particles and a fibrous conductive agent. In the formula 1, X is a distance from a distal end of one of the curved surface portions to the inner surface of the case facing the distal end of the curved surface portion as viewed in the winding axis direction of the electrode assembly. R is a length of a periphery of the one curved surface portion as viewed in the winding axis direction of the electrode assembly. D is an average particle size D50 of the active material particles. A is a surface roughness Ra of the active material layer.(R/D)A≥2X 1