Polyolefin Separator Pore Control 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 and high dielectric breakdown voltage.
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 and dielectric breakdown voltage decreases
Solution Approach 1:
The patent changes the physical-chemical parameters of the polyolefin resin, specifically controlling the polydispersity index to 2.5-4.2 and regulating pore size distribution (average 20-40 nm, maximum 50 nm or less). These parameter changes enable the separator to maintain its structural integrity and dielectric properties under high-pressure lamination conditions while achieving sufficient binding force.
2Productivity
If processing speed is increased to improve productivity, then manufacturing efficiency is improved, but heat application time is decreased and binding force becomes insufficient
Solution Approach 1:
By optimizing the polydispersity index and pore structure parameters of the polyolefin resin, the separator achieves enhanced mechanical properties that allow for reduced heat application time while maintaining adequate binding force, thus enabling increased processing speed without sacrificing bond quality.
3Strength
If pressure is increased during lamination to ensure binding force, then binding force is improved, but separator thickness is greatly reduced and pore damage increases
Solution Approach 1:
The patent controls the polydispersity index (2.5-4.2) and pore size distribution of the polyolefin resin to optimize the separator's compressive resistance. This enables the separator to withstand high-pressure lamination with minimal thickness reduction and pore damage, maintaining both binding force and manufacturing precision.
4Strength
If polydispersity index is decreased to improve compression resistance, then compression resistance is improved, but processing complexity increases
Solution Approach 1:
The patent identifies an optimal range for polydispersity index (2.5-4.2) that balances compression resistance with manufacturability. Within this range, the separator achieves sufficient compression resistance to withstand lamination pressure while maintaining reasonable processing complexity and avoiding excessive manufacturing difficulties.
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.