Polyethylene Composite Membrane Bonding Lithium Ion Battery
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Solution Overview
Problem
Existing polyolefin microporous membranes for lithium ion batteries lack sufficient mechanical strength, thermal stability, and bonding capability with electrode pieces, leading to inadequate cycle life and safety, particularly at high temperatures.
Innovation Solution
A polyethylene-based composite microporous membrane with crystalline high-density polyethylene as the base material, modified with 10-25 wt.% of polyisobutylene or ethylene-propylene methylene copolymer, using an aliphatic dibasic acid ester as a high-temperature compatilizer and asymmetric cooling for phase separation, resulting in a membrane with enhanced tensile strength, thermal contraction control, and improved bonding with electrode pieces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyolefin microporous membrane is used for lithium ion batteries, then high voltage oxidation resistance and stability are achieved, but mechanical strength and bonding capability with electrode pieces are insufficient
Solution Approach 1:
The patent uses composite materials by combining polyethylene base material with rubber modifiers (polyisobutylene or ethylene-propylene methylene copolymer) to create a microporous membrane that simultaneously achieves high mechanical strength, thermal stability, and bonding capability while maintaining the oxidation resistance and stability of polyolefin materials
Solution Approach 2:
The patent changes the physical and chemical parameters of the membrane by controlling the amorphous content through rubber modification and processing conditions, enabling the membrane to exhibit thermal bonding capability at specific temperature ranges while maintaining mechanical strength and bonding properties
2Strength
If thermoplastic polyolefin elastomers are blended into polyolefin matrix to improve transverse rupture resistance, then mechanical property increases, but porosity formation capability decreases
Solution Approach 1:
The patent optimizes the proportion of thermoplastic polyolefin elastomers to 10-25 wt.% and controls processing parameters including stretching temperature (110-120°C), stretching ratio, and cooling rate to simultaneously achieve high transverse rupture resistance and proper porosity formation in the microporous membrane
Solution Approach 2:
The patent creates local quality differences by controlling the distribution and concentration of rubber modifiers in different regions of the polyolefin matrix, enabling simultaneous improvement of mechanical strength and porosity formation through localized structural optimization
3Strength
If hot stretching process is employed to strengthen PE membrane, then transverse tensile strength improves, but thermal shrinkage increases
Solution Approach 1:
The patent controls the hot stretching temperature within 110-120°C and adjusts the stretching ratio and cooling rate to achieve optimal balance between transverse tensile strength and thermal shrinkage, preventing excessive thermal shrinkage while maintaining mechanical strength
Solution Approach 2:
The patent incorporates rubber modifiers before hot stretching to provide cushioning effect that reduces thermal shrinkage during subsequent heating processes, allowing the membrane to maintain dimensional stability while achieving high transverse tensile strength through hot stretching
4Strength
If PVDF-HFP copolymer microporous physical gel membrane is used, then bonding capability with electrode pieces improves, but pore size becomes too large
Solution Approach 1:
The patent controls the pore size parameters by adjusting rubber content (10-25 wt.%), processing temperature (110-120°C), and stretching conditions to achieve optimal pore dimensions that provide both sufficient bonding capability with electrode pieces and appropriate pore size for battery performance
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 high tensile strength, low thermal shrinkage, and strong bonding with electrodes, ensuring improved safety and cycle life of lithium ion batteries, with a peel strength exceeding 0.03 N/20 mm and thermal contraction less than 10% at 130°C, while maintaining low internal resistance and porosity.
Implementation Method 1
using an aliphatic dibasic acid ester as a high-temperature compatilizer and asymmetric cooling for phase separation
Implementation Method 2
thermal contraction less than 10% at 130°C
Data Source
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AI summary
The present invention relates to a microporous membrane of polyethylene-based composite material with adhesion under hot pressing, which utilises ethylene-propylene rubber and polyisobutene rubber with medium molecular weights to modify high density polyethylene with a high degree of crystallisation, and utilises an ester of an aliphatic dicarboxylic acid with a flash point higher than 210°C as the process solvent and pore-forming agent for the membrane, to obtain the membrane with the property of adhesion under hot pressing; the membrane is hot-pressed with a positive electrode sheet so these adhere together, and the heat shrinkage of the membrane is inhibited thereby; the composite material membrane has high strength, resistance to high temperature, and can be used in lithium ion power batteries with a high degree of safety and a long cycle life.