Polyolefin Separator Pore Structure for High-Pressure Lamination
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Solution Overview
Problem
The existing porous film substrates for electrochemical devices, such as secondary batteries, face challenges with deformation and reduced dielectric breakdown voltage under high-pressure lamination conditions, leading to performance issues and defects.
Innovation Solution
A polyolefin separator with a polydispersity index of 2.5 to 4.2, average pore diameter of 20 nm to 40 nm, and maximum pore size of 50 nm or less, manufactured using a wet method with a core part of polyethylene and polypropylene mixture and a polyethylene skin layer, which enhances compression resistance and maintains low thickness change rate during lamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heat and pressure are increased during lamination to improve binding force, then binding force between electrode and separator is improved, but separator deformation increases
Solution Approach 1:
The patent applies parameter changes by optimizing the molecular weight distribution (PDI 2.5-4.2) of the polyolefin resin to achieve optimal mechanical properties that resist deformation under lamination pressure while maintaining adequate binding force
Solution Approach 2:
The patent uses composite materials by creating a multilayer structure with different polyolefin resin compositions in each layer, where the core layer has different properties than the skin layers, allowing the separator to maintain structural integrity and resist deformation during lamination
2Productivity
If processing speed is increased to improve productivity, then manufacturing efficiency is improved, but binding force decreases due to reduced heat application time
Solution Approach 1:
The patent applies parameter changes by optimizing the molecular weight distribution (PDI 2.5-4.2) and pore structure parameters to achieve optimal mechanical properties that enable adequate binding force even with reduced heat application time at higher processing speeds
3Strength
If pressure is increased during lamination to ensure binding force, then binding force is improved, but dielectric breakdown voltage decreases
Solution Approach 1:
The patent uses composite materials with a multilayer structure where the core layer and skin layers have different polyolefin resin compositions, creating a structure that maintains dielectric integrity while withstanding lamination pressure
Solution Approach 2:
The patent applies parameter changes by controlling the pore size distribution (average 20-40 nm, maximum 50 nm or less) and molecular weight distribution to maintain dielectric breakdown voltage while achieving adequate binding force under lamination pressure
4Length of moving object
If thickness is reduced to improve performance, then battery performance is improved, but compression resistance decreases
Solution Approach 1:
The patent uses composite materials with a multilayer structure where the core layer provides mechanical strength and compression resistance while the overall thin structure maintains good battery performance
Solution Approach 2:
The patent applies parameter changes by optimizing the molecular weight distribution (PDI 2.5-4.2) and pore structure parameters to achieve optimal mechanical properties that provide adequate compression resistance even in thin separator structures
Data Source
AI summary
A polyolefin separator for an electrochemical device, the separator having a plurality of pores having an average pore size of 20 nm to 40 nm and a maximum pore size of 50 nm or less and including a polyolefin resin having a polydispersity index (PDI) of in a range of 2.5 to 4.2. The polyolefin separator may have a strain rate of 25% or less as measured when a tensile stress is applied at 60° C. at 15 MPa for 60 seconds, and the polyolefin separator may have a recovery time of 200 seconds or less to reach a recovery rate of 70% as measured after removing a tensile stress applied at 70° C. at 2 MPa for 180 seconds.