Electrode assembly, cylindrical battery, and battery pack and vehicle including the same
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Solution Overview
Problem
Conventional cylindrical batteries face issues such as high resistance, heat generation, internal short circuits, and poor electrolyte impregnation due to the design of the uncoated portions and electrode tabs, which become significant problems when scaling up for use in electric vehicles.
Innovation Solution
The electrode assembly features a segmental structure for the uncoated portions, optimized separator positioning, and the use of single or pseudo-single particle positive electrode active materials, along with a silicon-containing negative electrode, to improve current collection efficiency, reduce resistance, and enhance thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a strip-shaped electrode tab is used to connect the uncoated portion of the positive and negative electrodes, then the battery structure is simple and easy to manufacture, but the current collection efficiency is poor due to large resistance and heat generation
Solution Approach 1:
The uncoated portion of the electrode is divided into multiple segments along the winding direction, with each segment having a separate current collector. This segmentation distributes the current collection points, reducing the current density at each point and thereby reducing resistance and heat generation, while improving overall current collection efficiency
Solution Approach 2:
Different regions of the electrode are designed with different properties: the coated portions contain active materials for electrochemical reactions, while the uncoated segments are specifically designed for current collection with high electrical conductivity materials, optimizing both electrochemical performance and electrical connection
2Reliability
If the uncoated portion is bent to improve current collection, then the current collection efficiency improves, but internal short circuits may occur due to improper positioning
Solution Approach 1:
An insulation layer is introduced as an intermediary between the uncoated portion and the separator. This insulation layer prevents direct contact between the uncoated portion and the separator, eliminating the risk of internal short circuits while allowing the uncoated portion to be bent for improved current collection efficiency
Solution Approach 2:
The insulation layer is positioned in advance between the uncoated portion and the separator to prevent potential short circuits before they can occur, providing a safety buffer that allows the electrode structure to be optimized for current collection without compromising safety
3Reliability
If the separator is positioned close to the uncoated portion to prevent short circuits, then safety improves, but electrolyte impregnation becomes poor
Solution Approach 1:
The insulation layer serves as a mediator that maintains an optimal distance between the separator and the uncoated portion. This distance is sufficient to prevent short circuits but not so large as to hinder electrolyte impregnation, as the insulation layer itself can be permeated by electrolyte
Solution Approach 2:
The insulation layer is designed with porous structure that allows electrolyte to penetrate through it, enabling the electrolyte to reach the uncoated portion and current collectors for effective impregnation while maintaining the safety distance from the separator
4Reliability
If the uncoated portion is made long to improve current collection, then current collection efficiency improves, but the battery volume increases reducing energy density
Solution Approach 1:
The uncoated portion is segmented into multiple sections along the winding direction, with each segment having its own current collector. This allows the current collection function to be distributed throughout the electrode length, improving current collection efficiency without requiring a single long uncoated portion that would increase battery volume
Solution Approach 2:
Instead of extending the uncoated portion in one dimension (length), the current collection is optimized by adding multiple collection points along the winding direction, effectively utilizing the third dimension (radial direction) to improve current collection without increasing overall battery volume
Data Source
AI summary
An electrode assembly having a first electrode, a second electrode, and a separator interposed therebetween are wound, and the first electrode includes an insulation layer that covers a boundary of an uncoated portion and a coated portion along a winding direction of the electrode assembly. A plurality of segments are bent along a radial direction of the electrode assembly to define a bent surface. When a line parallel with the winding direction and passing through a point having a smallest height of the first uncoated portion of the first electrode at lower ends of the plurality of cutting lines with respect to the first coated portion of the first electrode is a datum line, a separation distance between one end of the separator and the datum line along the winding axis is 1.5 mm or less.