Aramid Separator Paper Coating for Thin High-Strength Battery Cells
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Solution Overview
Problem
There is a need for a paper with increased tensile strength suitable for use as a separator or insulation in electrochemical cells that can operate at high temperatures and provide flame barrier properties, as existing thin papers often lack adequate strength and performance in these applications.
Innovation Solution
A paper comprising 90 to 99 weight percent aramid fibrous pulp with aramid polymer fibrils of specific dimensions and a 1 to 10 weight percent polyvinylpyrrolidone coating, which enhances tensile strength without compromising porosity or permeability, is developed. The coating is neither chemically nor electrostatically bound to the fibers, and the paper has a thickness of 10 to 40 micrometers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If thin paper is used for electrochemical cell separators, then porosity and permeability are improved, but tensile strength deteriorates
Solution Approach 1:
The patent applies composite materials by combining aramid pulp fibers with polyvinylpyrrolidone (PVP) coating to create a separator that achieves both high porosity and high tensile strength. The PVP coating forms a matrix that binds the aramid fibers together, providing mechanical reinforcement while maintaining the porous structure necessary for electrolyte permeability. This composite approach resolves the contradiction between thin paper porosity and tensile strength.
2Quantity of substance
If paper thickness is reduced for battery applications, then energy density is improved, but mechanical strength and flame barrier properties deteriorate
Solution Approach 1:
The composite structure of aramid pulp reinforced with PVP coating enables the use of thinner paper (10-40 micrometers) while maintaining adequate mechanical strength and flame barrier properties. The PVP matrix provides structural integrity to the thin aramid fiber network, allowing reduced thickness without sacrificing mechanical performance or safety characteristics.
3Quantity of substance
If paper thickness is reduced for battery applications, then energy density is improved, but flame barrier properties deteriorate
Solution Approach 1:
The aramid-PVP composite structure maintains flame barrier properties in thin paper formulations. Aramid fibers inherently provide flame resistance, and the PVP coating enhances this by forming a cohesive matrix that prevents rapid heat transfer and maintains structural integrity at elevated temperatures, enabling thin separators to serve as effective flame barriers.
4Strength
If polyvinylpyrrolidone coating is added to aramid pulp, then tensile strength is improved, but manufacturing complexity increases
Solution Approach 1:
The patent merges the aramid pulp and PVP coating into a single integrated composite material structure. The PVP is applied as a coating that penetrates and binds the aramid fiber network, creating a unified material that achieves high tensile strength without requiring separate reinforcement layers or complex assembly processes. This merging approach simplifies manufacturing compared to using multiple separate components.
Data Source
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Figure 3
AI summary
A paper suitable for use as a separator or thermal or fire insulation for use in or with electrochemical cells, and an electrochemical cell comprising the same, the paper having 90 to 99 weight percent aramid fibrous pulp comprising aramid polymer fibrils and 1 to 10 weight percent polyvinylpyrrolidone present as a coating on the surface of the fibers, the paper having a thickness of 10 to 40 micrometers and a tensile strength of at least 15 megapascals or greater.