Polypropylene Battery Laminate Adhesive for High Temperature
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Solution Overview
Problem
Polypropylene adhesives lack sufficient adhesive force to metals under high temperature conditions, particularly in applications like lithium ion batteries where safety is a concern due to the melting point of polyethylene separators near 120°C, leading to a need for enhanced thermal stability and adhesion.
Innovation Solution
A laminate for batteries comprising a polypropylene adhesive layer with a specific composition of 40-94% propylene copolymer, 3-30% butene-containing copolymer, and 3-30% ethylene-α-olefin copolymer, ensuring high adhesiveness to metal substrates both at normal and elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polypropylene is used as adhesive material, then flexibility and adhesive force at normal temperature are improved, but adhesive force under high temperature deteriorates
Solution Approach 1:
The patent uses a composite adhesive layer combining polypropylene (40-94 wt%) with ethylene-vinyl alcohol copolymer (3-30 wt%) and ethylene-α-olefin copolymer (3-30 wt%). This composite structure leverages the flexibility and normal-temperature adhesion of polypropylene while the polar EVOH component provides high-temperature stability and enhanced adhesion to polar substrates, resolving the contradiction between normal-temperature performance and heat resistance.
Solution Approach 2:
The patent modifies the chemical composition parameters of the adhesive layer by incorporating specific ratios of copolymers with different properties. The EVOH content (3-30 wt%) is optimized to provide polar character for high-temperature adhesion while maintaining overall flexibility, and the ethylene-α-olefin copolymer content (3-30 wt%) is controlled to balance crystallinity and flexibility, enabling the adhesive to maintain performance across a wide temperature range.
2Strength
If polypropylene is modified with unsaturated carboxylic acid to improve adhesiveness to polar materials, then adhesive force is improved, but flexibility deteriorates
Solution Approach 1:
Instead of modifying polypropylene with unsaturated carboxylic acid (which would reduce flexibility), the patent uses a composite approach where unmodified polypropylene provides flexibility and the separate EVOH component provides polar adhesion. This composite strategy achieves both goals without the trade-off inherent in chemical modification.
Solution Approach 2:
The EVOH copolymer acts as an intermediary substance that bridges the nonpolar polypropylene and polar substrates. The EVOH's dual character (polymer backbone from polyolefin plus polar vinyl alcohol groups) allows it to adhere to both nonpolar and polar surfaces, enabling strong adhesion to polar materials without requiring modification of the polypropylene itself.
3Reliability
If additional safety systems are added to prevent temperature increase beyond heat-resistant temperature, then safety is improved, but device complexity increases
Solution Approach 1:
The adhesive layer is designed to inherently maintain adhesion at high temperatures through its composite composition, particularly the EVOH component's thermal stability and polar character. This self-service approach allows the adhesive to protect the battery assembly at elevated temperatures without requiring external monitoring or control systems, thereby improving safety while avoiding increased complexity.
Solution Approach 2:
The patent incorporates thermal cushioning by selecting copolymers with appropriate melting points and thermal properties. The ethylene-α-olefin copolymer with controlled crystallinity and the EVOH component provide thermal stability that cushions against temperature increases, maintaining adhesive performance near 120°C and beyond without requiring additional safety intervention systems.
Data Source
AI summary
A laminate for a battery with a polypropylene adhesive layer and a metal substrate layer: (1) the adhesive includes 40-94 wt % of a propylene copolymer (A), 3-30 wt % of a butene-containing copolymer (B), 3-30 wt % of an ethylene-α-olefin copolymer (C) ((A), (B), and (C) is 100 wt %), (2) the copolymer (A) has a melting point of 130° C. or more measured with a differential scanning calorimeter, and a total proportion of a structural unit derived from ethylene is 4-25 mol % relative to 100 mol % of a total structural units forming all the copolymers (A) contained in the adhesive, (3) the copolymer (B) includes less than 1 mol % of a structural unit derived from ethylene, and has a melting point of 100° C. or less measured with a differential scanning calorimeter, and (4) the copolymer (C) includes 50-99 mol % of a structural unit derived from ethylene.