Propylene Random Copolymer Separator for Thermal Shutdown
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Solution Overview
Problem
Existing separators for lithium secondary batteries face challenges in achieving a balance between shutdown properties for thermal safety and mechanical strength, with current solutions either lacking effective shutdown functions due to high melting points or compromising on tensile strength and manufacturing complexity.
Innovation Solution
A microporous monolayer separator made from a propylene random copolymer resin with a melt index of 0.5-10 g/10 minutes and 0.1-8 wt% comonomers, which includes a melt-down blocking layer for enhanced mechanical strength and shutdown properties, is developed using a dry process that avoids the use of organic solvents and simplifies the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a propylene homopolymer is used to prepare a separator via dry process, then the separator has high tensile strength, but it cannot provide effective shutdown function due to high melting point (about 160°C)
Solution Approach 1:
The invention changes the chemical composition parameters by introducing comonomers (ethylene, propylene, or butene) into the polymer structure, creating a random copolymer with controlled comonomer content (0.1-8 wt%). This parameter change reduces the melting point from 160°C to 137°C or lower while maintaining the mechanical strength required for separator application.
Solution Approach 2:
The invention creates a composite polymer material by combining propylene with small amounts of comonomers (ethylene, propylene, or butene) to form a random copolymer. This composite structure integrates the low melting point characteristic of comonomers with the mechanical strength of propylene, achieving both shutdown function and tensile strength.
2Reliability
If a high density polyethylene is used to prepare a porous film via dry process, then shutdown properties are ensured due to low melting point (about 130°C), but mechanical properties such as tensile strength are inferior
Solution Approach 1:
The invention changes the base polymer from high density polyethylene to propylene random copolymer, adjusting the comonomer content to control the melting point within the range of 137°C or lower. This parameter adjustment achieves the desired shutdown temperature while improving mechanical strength compared to pure polyethylene.
3Reliability
If a multilayer separator (polypropylene/polyethylene/polypropylene) is prepared to achieve both shutdown function and high tensile strength, then both properties are improved, but the manufacturing process becomes far too complex and manufacturing cost increases
Solution Approach 1:
The invention merges the functions of multiple layers into a single layer by using propylene random copolymer that inherently provides both the low melting point for shutdown function and the mechanical strength for structural integrity. This eliminates the need for separate polypropylene and polyethylene layers, simplifying the manufacturing process to a single extrusion and stretching operation.
Solution Approach 2:
The propylene random copolymer serves multiple functions simultaneously: it provides the low melting point for shutdown function, maintains high tensile strength for mechanical support, and enables simple single-layer manufacturing. This multi-functional material replaces the need for complex multilayer structures.
4Strength
If a multilayer separator is prepared to achieve both shutdown function and high tensile strength, then both properties are improved, but manufacturing cost becomes much higher
Solution Approach 1:
The invention combines the functions of multiple polymer layers into a single propylene random copolymer layer, eliminating the need for separate extrusion, lamination, and stretching processes for each layer. This merging reduces manufacturing steps, equipment requirements, and operational complexity, leading to lower manufacturing costs while maintaining both strength and shutdown function.
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 propylene random copolymer separator effectively blocks lithium ion migration at elevated temperatures while maintaining high tensile strength and porosity, ensuring thermal safety and mechanical integrity, with a shutdown function activated at 137°C or less, and can be produced with reduced manufacturing costs and complexity.
Implementation Method 1
when a battery is overheated, a function for preventing the battery from being further overheated by shutdown of the holes so as to block the migration of positive lithium ions
Data Source
AI summary
Provided is a microporous separator for a lithium secondary battery having shutdown properties wherein the separator comprises a propylene random copolymer which has a melt index of 0.5-10 g/10 minutes and comprises one or more species of comonomers in the content of 0.1-8 wt %.