Flat Wound Electrode Body with Cylindrical Core for Battery Safety
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Solution Overview
Problem
Lithium ion secondary batteries with flat wound electrode bodies experience short circuits due to inadequate pressure contact between positive and negative electrode sheets and separators in curved portions, leading to thermal contraction and overheating issues.
Innovation Solution
A lithium ion secondary battery design where the central portion is pressed toward the winding axis, generating tensile forces that ensure pressure contact between the positive and negative electrode sheets and separators, preventing thermal contraction and short circuits by using core members with cylindrical surfaces that protrude outward to maintain contact between the sheets and separators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the central portion of the flat wound electrode body is compressed from outside the battery case, then dimensional changes are suppressed, but the degree of strain on the flattened portion becomes lower than on curved portions causing inward bulging
Solution Approach 1:
A cylindrical core member is introduced as an intermediary element inside the electrode body to provide internal support and maintain uniform strain distribution. The core member acts as a mediator between the compressed central portion and the curved portions, preventing inward bulging while maintaining dimensional stability.
Solution Approach 2:
The cylindrical core member provides counter-support to the compressed central portion of the electrode body. By introducing this internal structural element, the patent counteracts the inward bulging force that occurs when the central portion is compressed from outside, thereby maintaining structural integrity.
2Reliability
If a cylindrical winding core is used to press the flattened portion, then the degree of strain is uniformized, but no tensile force is generated in the electrode sheets in the long-side direction causing insufficient pressure contact
Solution Approach 1:
The patent employs a cylindrical core member with a curved surface that contacts the electrode sheets. This curved geometry naturally generates tensile forces in the long-side direction of the electrode sheets when the central portion is compressed, ensuring sufficient pressure contact between the sheets and separators in the curved portions.
Solution Approach 2:
The patent uses a composite structure combining the cylindrical core member with the wound electrode body. This composite design allows the core member to provide both the necessary tensile forces for pressure contact and the structural support for strain uniformity, achieving both objectives simultaneously.
3Reliability
If the separators are not in sufficient pressure contact with the electrode sheets, then thermal contraction causes short circuits, but increasing compression may damage the electrode structure
Solution Approach 1:
The cylindrical core member is positioned inside the electrode body before final compression, establishing preliminary pressure contact between the separators and electrode sheets. This preliminary action ensures that when thermal contraction occurs during overheating, the separators remain in contact with the electrode sheets, preventing short circuits without requiring excessive compression that could damage the electrode 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
The design effectively prevents short circuits during overheating by maintaining pressure contact between the electrode sheets and separators, ensuring reliable battery performance and compact size.
Implementation Method 1
with tensile forces generated, by pressing of the central portion, in a central-portion positive electrode sheet, a central-portion negative electrode sheet, and central-portion separators
Implementation Method 2
the end-portion positive electrode sheet, the end-portion negative electrode sheet, and the end-portion separators are placed in pressure contact with each other and press the outer surface of the core member
Implementation Method 3
the end-portion positive electrode sheet, the end-portion negative electrode sheet, and the end-portion separators are placed in pressure contact with each other and press the outer surface of the core member... preventing thermal contraction and short circuits
Data Source
AI summary
A lithium ion secondary battery includes a flat wound electrode body including a positive electrode sheet and a negative electrode sheet that are wound while interposing therebetween separators into a flat shape, and a battery case. In the flat wound electrode body, a central portion has a more constricted shape than end portions by pressing toward a winding axis in a short-side direction and each end portion includes an end-portion positive electrode sheet, an end-portion negative electrode sheet, and end-portion separators, and a core member arranged more inward than them. With tensile forces generated by pressing of the central portion in a central-portion positive electrode sheet, central-portion negative electrode sheet, and central-portion separators, the end-portion positive electrode sheet, end-portion negative electrode sheet, and end-portion separators are in pressure contact with each other and press the outer surfaces of the core member.