Secondary Battery Partial Welding Suppresses Internal Short Circuits
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Solution Overview
Problem
Secondary batteries are prone to internal short circuits due to electrode expansion and contraction during charging and discharging, particularly when the innermost area of the electrode end portion is welded to the current collector plate.
Innovation Solution
The electrodes are wound with a separator in between for 9 or more turns, and the first electrode's end portion is partially unwelded, specifically avoiding welding the inner N turns (2 to 8) to reduce stress and restrict electrode movement, thereby reducing the likelihood of piercing the separator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the end portion of the first current collector is welded to the first current collector plate, then electrical connection is improved, but internal short circuits occur due to stress and electrode movement
Solution Approach 1:
The welding is applied selectively to specific regions of the first current collector's end portion. The outer peripheral region is welded to the current collector plate to ensure electrical connection, while the inner region corresponding to inner N turns is left unwelded to reduce stress concentration and prevent electrode piercing, thus resolving the contradiction between electrical connection reliability and internal short circuit prevention
Solution Approach 2:
The end portion of the first current collector is divided into multiple welding regions: an outer peripheral welding region that is welded to the current collector plate, and an inner unwelded region corresponding to inner N turns. This segmentation allows different portions to serve different functions - electrical connection and stress reduction respectively - thereby preventing internal short circuits while maintaining electrical connectivity
2Quantity of substance
If the electrode group is wound for multiple turns, then battery capacity is improved, but stress concentration increases leading to separator piercing
Solution Approach 1:
The welding configuration varies by location along the end portion of the first current collector. The outer peripheral region undergoes welding to provide structural support, while the inner region corresponding to inner N turns remains unwelded to accommodate stress from multiple winding turns, allowing the battery to achieve higher capacity without separator piercing
Solution Approach 2:
By leaving the inner region unwelded before the electrode group undergoes charging and discharging cycles, the design anticipates and cushions against the stress concentration that would otherwise occur at the welded inner turns, preventing separator piercing even when the electrode group is wound for many turns to increase capacity
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 configuration effectively suppresses internal short circuits by alleviating stress on the electrode group, reducing conduction resistance, and preventing electrode contact, thus enhancing battery safety and performance.
Implementation Method 1
a first current collector plate welded to the first electrode
Data Source
Figure 1
Figure 2
AI summary
A disclosed secondary battery 10 includes a first electrode 14b including a first current collector having an elongated sheet shape, a second electrode 14a including a second current collector having an elongated sheet shape, a separator provided between the first electrode 14b and the second electrode 14a, and a first current collector plate 17 welded to the first electrode 14b. The first electrode 14b and the second electrode 14a are wound for 9 or more turns with the separator therebetween to constitute an electrode group 14. An end portion of the first current collector extending in the longitudinal direction thereof protrudes from one of the end surfaces of the electrode group 14. A part of the end portion is welded to the first current collector plate 17, while a region of the end portion that corresponds to inner N turns (N is an integer of 2 or more and 8 or less) is not welded to the first current collector plate 17. In the above configuration, internal short circuits due to charging and discharging can be suppressed.