Microporous Polyolefin Membrane Strain Absorption
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Solution Overview
Problem
Conventional microporous polyolefin membranes used in high packing density or alloy negative electrode batteries face issues such as reduced permeability, electrode swelling leading to fold formation, and potential internal short circuits due to poor strain absorption and electrical insulation, which degrade battery performance and safety.
Innovation Solution
A microporous polyolefin membrane with specific properties, including porosity of 45% to 85%, maximum pore diameter of 0.1 μm to 0.23 μm, longitudinal elastic modulus of 400 MPa to 2000 MPa, and a ratio of longitudinal to transverse elastic modulus of 1.5 to 9, is developed to enhance strain absorption and maintain ion permeability and electrical insulation performance even after compression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional microporous polyolefin membranes are used in batteries with high packing density or alloy negative electrodes, then the membrane provides basic separation function, but the membrane is crushed during compression, resulting in reduced permeability to lithium ions
Solution Approach 1:
The patent applies parameter changes by optimizing the gel fraction of the polyolefin resin within a specific range (30-80%) to achieve the desired balance between compression resistance and permeability retention. By controlling the gel fraction parameter, the membrane structure is tuned to provide both mechanical strength during compression and adequate ion permeability after compression.
Solution Approach 2:
The patent uses composite materials by combining polyolefin resin with specific gel fraction characteristics and controlling the pore structure through stretching processes. The membrane comprises a composite structure of polymer matrix and porous network that provides both mechanical integrity and ion transport pathways.
2Reliability
If conventional microporous polyolefin membranes are used in batteries with high packing density or alloy negative electrodes, then the membrane provides basic separation function, but the membrane fails to absorb strain, causing fold development and battery swelling
Solution Approach 1:
The patent applies parameter changes by optimizing the gel fraction within 30-80% and controlling the pore diameter (0.03-1 μm) and porosity (30-80%) to achieve optimal strain absorption capability while maintaining structural stability. The specific parameter ranges enable the membrane to deform elastically during electrode swelling and recover, preventing fold development.
Solution Approach 2:
The patent implements beforehand cushioning by designing the membrane with adequate gel fraction and pore structure that anticipates and absorbs the strain from electrode swelling before it causes damage. The membrane structure is pre-configured to accommodate volume changes, acting as a cushion that prevents fold formation and battery swelling.
3Reliability
If conventional microporous polyolefin membranes are used in batteries with high packing density or alloy negative electrodes, then the membrane provides basic separation function, but the membrane fails to maintain electrical insulation, causing internal short circuits
Solution Approach 1:
The patent applies parameter changes by controlling the pore diameter within 0.03-1 μm and porosity within 30-80% to ensure adequate electrical insulation while maintaining ion permeability. The optimized pore structure provides sufficient insulation barriers to prevent electron transport (avoiding short circuits) while allowing lithium ion transport through the pores.
Solution Approach 2:
The patent applies local quality by creating a heterogeneous pore structure where different regions of the membrane have optimized characteristics for their specific functions: smaller pores provide electrical insulation, while interconnected larger pores facilitate ion transport. The gel fraction distribution also varies locally to provide both insulation and mechanical strength.
4Reliability
If the membrane porosity is increased to improve ion permeability, then the permeability to lithium ions improves, but the mechanical strength and compression resistance decrease
Solution Approach 1:
The patent resolves this contradiction by optimizing multiple parameters simultaneously: porosity (30-80%), pore diameter (0.03-1 μm), and gel fraction (30-80%). By adjusting these parameters within specific ranges, the membrane achieves adequate ion permeability while maintaining sufficient mechanical strength through the gel fraction-controlled polymer network.
Solution Approach 2:
The patent uses composite materials by creating a dual-phase structure where the gel fraction forms a continuous polymer matrix providing mechanical strength, while the porous network provides ion transport pathways. This composite architecture allows simultaneous optimization of both permeability and strength.
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
The membrane effectively absorbs strain during compression, maintaining high permeability and electrical insulation, thereby improving battery cycle performance and safety by preventing internal short circuits and swelling.
Implementation Method 1
a microporous polyolefin membrane which easily absorbs the strain produced when the membrane undergoes compression
Implementation Method 2
retains excellent permeability and excellent electrical insulation performance even after compression
Data Source
AI summary
The present invention provides a microporous polyolefin membrane having a porosity of 45% to 85% wherein the microporous polyolefin membrane easily absorbs the strain produced when the membrane undergoes compression, and retains excellent permeability and excellent electrical insulation performance even after compression by setting the maximum pore diameter at 0.1 μm to 0.23 μm, the MD elastic modulus at 400 to 2,000 MPa, and the ratio MD elastic modulus/TD elastic modulus at 1.5 to 9.