PVDF Separator Adhesion via Low-Melting Copolymer
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Solution Overview
Problem
Conventional separators for non-aqueous secondary batteries require stringent hot-press conditions to achieve adequate adhesion to electrodes, which can damage the porous structure and compromise ion permeability, making it difficult to maintain favorable load characteristics.
Innovation Solution
A separator with an adhesive porous layer containing a polyvinylidene fluoride type resin copolymer having a specific melting point range and molecular weight, along with an inorganic filler, that allows for excellent adhesion and ion permeability even under mild wet heat press conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If wet heat press is carried out at high temperature (90°C or more) and increased pressure to achieve sufficient adhesion, then adhesion between separator and electrode is improved, but the porous structure of the separator is damaged and ion permeability decreases
Solution Approach 1:
The invention changes the chemical composition parameters of the PVDF type resin by incorporating specific copolymer components (HFP content of 3-10 mol% and charge-transfer complexing agent of 1-20 mass%) to reduce the melting point from conventional high values to 145°C or lower. This parameter modification enables the resin to achieve adequate adhesion at lower hot-press temperatures (below 90°C), thereby preventing damage to the porous structure and maintaining ion permeability while still achieving sufficient bonding strength between separator and electrode
Solution Approach 2:
The invention creates a composite material system by combining PVDF type resin with specific copolymer components (hexafluoropropylene) and charge-transfer complexing agents. This composite approach modifies the thermal and adhesive properties of the base resin, enabling it to exhibit both low-temperature processability and high adhesion performance, thus resolving the contradiction between achieving strong bonding and preserving porous structure integrity
2Reliability
If wet heat press is carried out under mild conditions (temperature below 90°C) to preserve porous structure, then ion permeability is maintained, but adhesion between separator and electrode is insufficient
Solution Approach 1:
The invention modifies the chemical composition parameters of the PVDF type resin by incorporating specific copolymer components (HFP content of 3-10 mol% and charge-transfer complexing agent of 1-20 mass%) to reduce the melting point from conventional high values to 145°C or lower. This parameter modification enables the resin to achieve adequate adhesion at lower hot-press temperatures (below 90°C), thereby preventing damage to the porous structure and maintaining ion permeability while still achieving sufficient bonding strength between separator and electrode
Solution Approach 2:
The invention utilizes and preserves the porous structure of the separator by conducting hot-press at lower temperatures that do not collapse the pores. The modified PVDF type resin with reduced melting point provides sufficient adhesion even at these lower temperatures, ensuring that the porous architecture remains intact and ion permeability is maintained while achieving adequate electrode bonding
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 solution enables superior adhesion and ion permeability, enhancing cell strength and battery properties while reducing the risk of gas generation and electrode expansion, suitable for soft pack batteries with aluminum laminated film packages.
Implementation Method 1
When this separator is superimposed and thermally pressed on an electrode with an electrolyte solution included therein (hereinafter, also referred to as 'wet heat press'), the entire of the separator is well adhered to the electrode through the adhesive porous layer
Implementation Method 2
This may decrease ion permeability in a heat-pressed separator
Data Source
AI summary
An embodiment of the present invention provides a separator for a non-aqueous secondary battery, including: a porous substrate; and an adhesive porous layer that is provided on one side or both sides of the porous substrate, and that contains a polyvinylidene fluoride type resin, the polyvinylidene fluoride type resin including copolymer A (polyvinylidene fluoride type resin A) having a melting point of from 130°C to 148°C, and containing, as monomer components, vinylidene fluoride and a monomer represented by Formula (1). R1 to R3: a hydrogen atom, a halogen atom, a carboxyl group or a derivative thereof, or a C1-5 alkyl group; X: a single bond, a C1-5 alkylene group, or a substituted C1-5 alkylene group; Y: a hydrogen atom, a C1-5 alkyl group, or a C1-5 alkyl group that contains at least one hydroxy group.