High Strength Separator Paper for Electrochemical Cells
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Solution Overview
Problem
Existing separator papers for electrochemical cells lack adequate tensile strength and suffer from porosity and uniformity issues, making them unsuitable for high-performance applications, particularly at high temperatures.
Innovation Solution
A paper comprising 95 to 100 weight percent fibrils and 0 to 5 weight percent aramid fibrids, with fibrils made from a polymer blend of 80 to 96 weight percent polyparaphenylene terephthalamide and 4 to 20 weight percent polyvinylpyrrolidone, having a thickness of 10 to 40 micrometers and a tensile strength of at least 15 megapascals, which addresses strength, porosity, and uniformity challenges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the paper is made very thin to meet separator requirements, then the thickness requirement is satisfied, but the tensile strength becomes inadequate
Solution Approach 1:
The patent uses a composite fibrous structure combining aramid fibers (providing strength) with cellulose fibers (filling voids), creating a multi-material system that achieves both thinness and adequate tensile strength. The composite nature allows the paper to be thin while maintaining mechanical integrity through the synergistic combination of different fiber types.
2Strength
If larger diameter fibrous material is incorporated to provide strength, then the tensile strength is improved, but porosity and uniformity problems occur
Solution Approach 1:
The patent applies local quality by having different fiber types occupy different spatial roles: aramid fibers are distributed to provide localized strength reinforcement, while cellulose fibers fill the interstices between larger aramid fibers. This spatial differentiation of fiber functions creates uniformity in the overall structure while maintaining localized strength where needed.
3Strength
If larger diameter fibrous material is incorporated to provide strength, then the tensile strength is improved, but pin holes and porosity increase
Solution Approach 1:
The patent converts the potential harm of large fiber diameter (which creates voids and pin holes) into a benefit by using the larger aramid fibers as the primary strength-providing component, then filling the resulting voids with smaller cellulose fibers. This transforms the harmful porosity into a structured composite architecture where the smaller fibers beneficially occupy the spaces between larger fibers, reducing pin hole formation while maintaining strength.
Data Source
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AI summary
A paper suitable for use as a separator paper in electrochemical cells and an electrochemical cell comprising same, the paper comprising as the sole fibrous components (95) to (100) weight percent fibrils and (0) to (5) weight percent aramid fibrids and having a thickness of (10) to (40) micrometers and a tensile strength of at least (15) megapascals or greater, the fibrils comprising a polymer blend of (80) to (96) weight percent polyparaphenylene terephthalamide and (4) to (20) weight percent of polyvinylpyrrolidone; the fibrils having a diameter of (10) to (2000) nanometers, a length of (0.2) to (3) millimeters, a surface area of (3) to (40) square meters/gram, and a Canadian Standard Freeness of (0) to (10) milliliters.