Cylindrical Electrode Assembly Layout for Shorter Current Paths
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Solution Overview
Problem
Conventional cylindrical secondary batteries face high resistance and heat generation issues due to lengthy current paths, particularly in large form factors, which can lead to ignition risks, especially when used in electric vehicles.
Innovation Solution
The electrode assembly design minimizes the current path by using a current collector with uncoated portions at the top and bottom, welding these to current collector plates, and optimizing the ratio of widthwise to lengthwise current paths to 11 or less, ensuring a DC resistance of 4 mΩ or less and AC resistance of 3 mΩ or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If cell size is increased to increase capacity, then capacity is improved, but current path length increases causing higher resistance and heat generation
Solution Approach 1:
The patent positions electrode tabs at both ends of the electrode along the winding direction, creating a three-dimensional current distribution pattern. This dimensional arrangement allows current to exit from multiple locations simultaneously, effectively reducing the average current path length without changing the electrode area, thus resolving the contradiction between capacity and resistance loss.
Solution Approach 2:
The electrode is divided into multiple current collection points (tabs at both ends) rather than a single collection point. This segmentation of the current collection function allows parallel current paths to form, reducing the overall resistance and heat generation while maintaining the total capacity of the larger cell.
2Quantity of substance
If cell size is increased to increase capacity, then capacity is improved, but heat generation increases leading to ignition risks
Solution Approach 1:
By positioning tabs at both ends of the electrode in the winding direction, the patent creates multiple heat dissipation points distributed along the electrode length. This dimensional arrangement prevents heat concentration in a single location and facilitates better thermal management in large-capacity cells, reducing ignition risks.
Solution Approach 2:
The patent converts the potentially harmful long current paths in large cells into beneficial short paths by strategically positioning tabs at both ends. This transforms the structural characteristic that causes heat generation into a feature that promotes heat dissipation and reduces thermal runaway risks.
3Device complexity
If electrode tabs are positioned at single location, then structure is simple, but current path is lengthy causing high resistance
Solution Approach 1:
The patent segments the current collection function by placing tabs at both ends of the electrode rather than at a single location. This segmentation creates multiple current exit points, forming parallel current paths that reduce resistance and energy loss while adding minimal structural complexity.
4Loss of energy
If current path is minimized for low resistance, then resistance is reduced, but electrode design becomes more complex
Solution Approach 1:
The patent achieves low resistance by utilizing the winding direction dimension to position tabs at both ends of the electrode. This dimensional approach creates short current paths without requiring complex electrode geometries or additional components, simply leveraging the existing three-dimensional wound structure.
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 reduces internal resistance, prevents heat generation, and enhances energy density, making it suitable for high current density applications while maintaining large capacity and output.
Implementation Method 1
a current path ratio L2/L1 is 11 or less when lengths of the widthwise direction current path and the lengthwise direction current path are L1 and L2, respectively
Data Source
AI summary
An electrode assembly includes a core and an outer circumferential surface having a positive electrode, a negative electrode, and a separator interposed therebetween. The positive electrode or the negative electrode includes a current collector having a long side and a short side, the current collector further having an uncoated portion. The uncoated portion includes an electrode tab defined section and at least one electrode tab undefined section not used as an electrode tab. A maximum current path for the at least one electrode tab undefined section includes a widthwise direction current path along the short side of the current collector and a lengthwise direction current path along the long side of the current collector, and a current path ratio L2/L1 is approximately 11 or less and greater than 0 when lengths of the lengthwise direction current path and the widthwise direction current path are L2 and L1, respectively.