Separator Low Porosity Regions Suppress Curling
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Solution Overview
Problem
Lithium secondary batteries face issues with curling due to differences in extension and contraction between separator sheets and filler layers, leading to production defects and nonuniform pressure distribution, which affects battery performance.
Innovation Solution
A nonaqueous electrolyte secondary battery design featuring a filler layer with an inorganic filler and binder on one side of the separator sheet, with a low porosity region near the ends to minimize curling, achieved by compression or filling pores, ensuring uniform extension and contraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a filler layer is disposed on only one side of a separator sheet, then heat shrinkage of the separator sheet is prevented, but the separator sheet curls up due to differences in extension/contraction between the separator sheet and the filler layer
Solution Approach 1:
The patent applies local quality by creating a low porosity region at specific locations (ends in the winding direction) of the separator sheet. This localized modification allows the separator sheet to have different properties in different regions: the low porosity region provides extension/contraction resistance to prevent curling, while the rest of the separator sheet maintains its original porosity for heat shrinkage prevention and ion transport.
2Shape
If the separator sheet is pressed into a flat shape, then the wound electrode assembly is flattened, but the curl region is crimped and a height difference is formed at the peripheral surfaces
Solution Approach 1:
The patent applies preliminary anti-action by pre-forming low porosity regions at the ends of the separator sheet in the winding direction before the winding and flattening processes. These pre-formed regions resist extension and contraction, preventing curl formation during winding and eliminating the need for aggressive pressing that would cause crimping and height differences.
3Shape
If a low porosity region is formed by compression, then curling is suppressed, but the porosity of the separator sheet is reduced
Solution Approach 1:
The patent applies local quality by forming low porosity regions only at specific locations (the ends in the winding direction) rather than uniformly across the entire separator sheet. This localized approach suppresses curling where it occurs most while preserving the porosity and ion transport capabilities of the main body of the separator sheet.
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 suppresses curling, enhances insertability, and maintains uniform pressure distribution, resulting in improved cycle characteristics and battery performance.
Implementation Method 1
The separator sheet has a low porosity region, which has a porosity lower than at a location outside this region, in a region leaving a prescribed width from the winding start end and/or from the winding finish end of the sheet toward the center of the sheet
Data Source
AI summary
The nonaqueous electrolyte secondary battery 100 according to the present invention is provided with a wound electrode assembly in which a positive electrode sheet and a negative electrode sheet are wound, with a porous separator sheet 30 interposed therebetween. A filler layer 40 comprising an inorganic filler and a binder is formed on one side of the separator sheet 30. The filler layer 40 is continuously provided from the winding start end 38A to the winding finish end 38B of the separator sheet 30 in the winding direction of this sheet. The separator sheet 30 has low porosity regions 36A, 36B, which have a lower porosity than a location 35 outside these regions, in regions having prescribed width WA, WB from the winding start end 38A and/or the winding finish end 38B of the sheet toward the center of the sheet.