Post-Crosslinked Rubber-Plastic Composite Diaphragm for Li-Ion Battery Safety
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Solution Overview
Problem
Current polyolefin microporous membranes for lithium ion batteries lack sufficient strength, toughness, thermal stability, and compressible elasticity, leading to inadequate safety and cycle life, especially at high temperatures, and existing solutions face challenges with production costs and consistency.
Innovation Solution
A nano microporous membrane with a post-crosslinked rubber-plastic composite material, featuring a high rubber content in one layer and a polyolefin main body in another, utilizing a co-extruded process with thermally induced phase separation and electron beam irradiation to achieve uniform distribution and high elasticity, while maintaining low production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thermoplastic polyolefin elastomers are blended into polyolefin matrix to improve transverse rupture resistance, then transverse rupture resistance is improved, but the capability of pore-formation through stretching is influenced and proper porosity cannot be obtained
Solution Approach 1:
The patent changes the chemical state of the rubber from thermoplastic to post-crosslinked vulcanized rubber. This parameter change allows the rubber to maintain its reinforcing effect on transverse rupture resistance while eliminating the interference with pore-formation during stretching, as the crosslinked rubber particles remain stable and do not disrupt the crystallization and stretching processes needed for proper porosity.
Solution Approach 2:
The patent creates a composite material system combining polyolefin matrix with post-crosslinked vulcanized rubber particles. This composite approach allows the rubber to provide reinforcement for transverse rupture resistance while the crosslinked structure prevents interference with the pore-formation mechanism, simultaneously achieving both improved strength and proper porosity.
2Reliability
If PE layer with shutdown temperature of 135-145°C is used in PP/PE/PP composite membrane, then high temperature shutdown capacity is achieved, but thermal shrinkage and membrane rupture occur at temperatures above 130°C
Solution Approach 1:
The patent creates a composite membrane structure combining PP microporous layers with a PE shut-down layer containing post-crosslinked vulcanized rubber. The crosslinked rubber particles in the PE layer reinforce the matrix, preventing thermal shrinkage and membrane rupture at high temperatures while maintaining the shutdown capacity at 135-145°C.
Solution Approach 2:
The patent changes the thermal stability parameter of the PE layer by incorporating post-crosslinked vulcanized rubber. This parameter change raises the thermal decomposition temperature and improves the dimensional stability of the PE layer at high temperatures, preventing thermal shrinkage and rupture while preserving the shutdown function.
3Adaptability or versatility
If compressible elasticity is increased in the thickness direction, then stress absorbency is improved, but transverse tensile strength may be compromised
Solution Approach 1:
The patent applies local quality by distributing post-crosslinked vulcanized rubber particles specifically in the PE shut-down layer. This localized reinforcement provides compressible elasticity and stress absorbency in the thickness direction where needed, while the overall membrane structure maintains transverse tensile strength through the PP layers and controlled porosity.
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 exhibits enhanced tensile strength, thermal shutdown properties, and compressible elasticity, ensuring improved safety and reliability, with a Gurley value indicating optimal porosity and pore size, and demonstrating extended cycle life and resistance to thermal shrinkage.
Implementation Method 1
the heated and evenly blended high temperature melt is quickly solidified on the surface of the cooling roller, and the phase separation occurs in the process of the temperature drop
Implementation Method 2
The resulting lamina is stretched and strengthened using biaxial stretch step by step or synchronous biaxial stretch
Implementation Method 3
The high temperature compatibilizer is extracted from a semi-finished product membrane using a volatile cleaning solvent
Implementation Method 4
a microporous membrane having nano-sized pores communicating with each other is obtained after second hot stretching strengthening, hot-setting, and cooling
Data Source
AI summary
The present invention relates to a composite nano microporous diaphragm for use in lithium ion cells using polyolefin modified with post-crosslinked rubber and manufacturing method thereof. The microporous diaphragm at least comprises a nano microporous diaphragm A layer with a chemical gel content of more than 20%, the microscopic structure thereof is designed to be the rubber material that has been evenly dispersed and has subjected to a post-crosslinking treatment in polyolefin nano microfiber matrix, forming a nano microporous diaphragm of rubber-plastic composite. The nano microporous diaphragm with high strength, thermal cutoff, high temperature resistance, as well as good liquid absorption and swelling and compression elasticity can be applied to lithium ion power cells with high safety and long cycling life.