Crosslinked Separator Porosity Control for Lithium Ion Battery Capacity
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Solution Overview
Problem
Lithium ion secondary batteries experience a decrease in initial capacity due to unevenness in the size of the separator, which is caused by thermal shrinkage during manufacturing, leading to a surplus region with lower porosity that affects lithium ion conduction and battery performance.
Innovation Solution
A lithium ion secondary battery with a crosslinked separator structure, where the separator is thermally cut to create a high-porosity region opposite to the electrodes and a low-porosity surplus region not opposite to the electrodes, ensuring the separator's size is larger than the electrodes and minimizing shrinkage-induced unevenness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the separator is formed to be sufficiently large relative to the positive electrode and negative electrode to prevent short-circuiting, then the reliability of the battery is improved, but the initial capacity of the battery decreases due to electrolyte solution migration to the surplus region
Solution Approach 1:
The separator is designed with different porosity in different regions: the opposite region has higher porosity to maintain lithium ion conduction, while the surplus region has lower porosity to prevent electrolyte solution migration. This local differentiation resolves the contradiction by allowing the separator to simultaneously prevent short-circuiting (reliability) and minimize capacity loss (quantity of substance).
Solution Approach 2:
The separator is divided into functionally distinct regions: an opposite region facing the electrodes with high porosity for ion transport, and a surplus region extending beyond the electrodes with low porosity to contain electrolyte. This segmentation allows each region to optimize its function, preventing electrolyte migration while maintaining battery capacity.
2Quantity of substance
If the porosity of the surplus region is reduced to prevent electrolyte solution migration, then the initial capacity is maintained, but the manufacturing precision becomes more difficult to control due to thermal shrinkage unevenness
Solution Approach 1:
The separator structure is designed in advance with the understanding that thermal shrinkage will occur during battery assembly. The surplus region is intentionally created with lower porosity before thermal cutting, and the thermal shrinkage is controlled to be minimal (1-10%) through crosslinking treatment. This preliminary design accounts for the shrinkage and ensures consistent porosity distribution despite manufacturing variations.
Solution Approach 2:
The porosity of the surplus region is controlled within a specific range (0-50%) through material selection and processing parameters. By adjusting the porosity parameter of the surplus region material and controlling thermal shrinkage to 1-10%, the invention achieves both capacity retention and manufacturing feasibility, resolving the precision control difficulty.
3Reliability
If thermal cutting is used to create the surplus region with lower porosity, then the electrolyte solution migration is prevented, but the size unevenness of the separator increases due to thermal shrinkage
Solution Approach 1:
The thermal shrinkage rate is controlled within a specific range (1-10%) by adjusting the porosity parameter of the surplus region and the crosslinking degree of the separator material. This parameter control ensures that while thermal cutting creates the necessary low-porosity surplus region for electrolyte containment, the resulting size unevenness remains minimal and does not compromise battery performance.
Solution Approach 2:
The separator is constructed as a composite structure with different material properties in different regions. The opposite region uses high-porosity material for ion conduction, while the surplus region uses low-porosity material (0-50% porosity) that undergoes controlled thermal shrinkage (1-10%). This composite approach allows thermal cutting to create the desired shape while minimizing size unevenness.
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 suppresses the decrease in initial capacity and prevents electrolyte solution migration, maintaining high battery capacity over time by reducing size unevenness and porosity differences.
Implementation Method 1
a separator with a crosslinked structure, extending along the first direction and provided between the positive electrode and the negative electrode
Implementation Method 2
the surplus region has lower porosity than the opposite region
Data Source
AI summary
A lithium ion secondary battery according to an embodiment of the present disclosure includes: a positive electrode extending along a first direction; a negative electrode extending along the first direction and disposed opposite to the positive electrode along a second direction orthogonal to the first direction; and a separator with a crosslinked structure, extending along the first direction and provided between the positive electrode and the negative electrode. The separator includes an opposite region opposite to the positive electrode and the negative electrode along the second direction, and a surplus region not opposite to the positive electrode and/or the negative electrode along the second direction, and the surplus region has lower porosity than the opposite region.