Inorganic-Coated Battery Separator for Thin High-Adhesion Interfaces
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Solution Overview
Problem
Current separators for electrochemical devices, particularly lithium ion batteries, face challenges with adhesion between the electrode and separator, leading to degradation of cycle life and energy density due to low binding force and increased resistance, especially in flexible aluminum laminate pack casings and during deformation processes.
Innovation Solution
A separator with a porous polymer substrate and an inorganic coating layer containing a combination of polyvinylidene fluoride (PVdF)-based and acrylic polymers, where the acrylic polymer has a low acid value and specific molecular weight, is used, with a higher binder resin content at the electrode adhesive portion to enhance adhesion and ion conductivity, and is manufactured through a humidified phase separation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the content or coating amount of binder resin is increased to improve adhesion, then adhesion between electrode and separator is improved, but the adhesive layer thickness increases causing decreased energy density and increased resistance
Solution Approach 1:
The patent changes the chemical composition parameters of the binder resin by using a copolymer with specific ratios of fluorinated monomer (30-70 mol%) and non-fluorinated monomer (70-30 mol%). This parameter change allows achieving high adhesion with reduced binder resin content, thereby maintaining thin adhesive layer thickness and high energy density while improving interfacial compatibility between PVdF-based resin and inorganic coating layer
Solution Approach 2:
The patent creates a composite binder resin system combining fluorinated polymer (PVdF) and non-fluorinated polymer components in specific ratios. This composite material approach leverages the electrochemical stability of PVdF and the adhesion properties of non-fluorinated polymers, achieving high adhesion strength without increasing overall layer thickness, thus resolving the contradiction between adhesion and energy density
2Strength
If the content or coating amount of binder resin is increased to improve adhesion, then adhesion between electrode and separator is improved, but resistance increases
Solution Approach 1:
The patent optimizes the monomer composition parameters of the binder resin, specifically setting fluorinated monomer content at 30-70 mol% and non-fluorinated monomer at 70-30 mol%. This parameter optimization achieves high adhesion with minimal binder resin content, preventing excessive layer thickness that would increase resistance while maintaining low resistive losses through improved interfacial compatibility
3Quantity of substance
If the thickness of separator is reduced to enhance energy density, then energy density is improved, but adhesion between electrode and separator deteriorates
Solution Approach 1:
The patent changes the chemical parameters of the binder resin by incorporating copolymerization of fluorinated and non-fluorinated monomers in specific ratios. This parameter change enables high adhesion strength even in thin separator structures by improving molecular-level interfacial compatibility, thus achieving high energy density without sacrificing adhesion
Solution Approach 2:
The patent applies local quality enhancement by concentrating the adhesive function at the interface between the binder resin and inorganic coating layer. The copolymer structure creates localized regions of enhanced interfacial compatibility at the binding interface, allowing thin separator design while maintaining high adhesion strength where it is most needed
4Reliability
If a PVdF-based resin is used as binder resin to ensure electrochemical stability, then electrochemical stability is improved, but adhesion to inorganic coating layer is insufficient
Solution Approach 1:
The patent creates a composite binder resin system combining PVdF (fluorinated polymer) with non-fluorinated polymer components in specific ratios (30-70 mol% fluorinated, 70-30 mol% non-fluorinated). This composite structure maintains the electrochemical stability provided by PVdF while the non-fluorinated component enhances adhesion to the inorganic coating layer, resolving the contradiction between stability and adhesion
Solution Approach 2:
The patent applies local quality differentiation within the binder resin structure by having fluorinated segments provide electrochemical stability and non-fluorinated segments provide adhesion functionality. This local functional differentiation allows the single binder resin to simultaneously satisfy both electrochemical stability requirements and adhesion requirements at the interface with inorganic coating layer
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 provides excellent adhesion between the electrode and separator, improving peel strength and heat resistance, reducing separator thickness, and enhancing energy density while maintaining high productivity for mass production.
Implementation Method 1
the binder resin is allowed to migrate toward the surface of the separator through a humidified phase separation process
Data Source
AI summary
A separator including a porous polymer substrate and an inorganic coating layer formed on at least one surface of the porous polymer substrate. The inorganic coating layer includes inorganic particles and a binder resin. The binder resin includes a first binder resin and a second binder resin. The first binder resin comprises a polyvinylidene fluoride (PVdF)-based polymer and the second binder resin comprises an acrylic polymer. The acrylic polymer has an acid value of 1 or less and a glass transition temperature, Tg, of 90° C. to 130° C. In addition, the inorganic coating layer has a high content of binder resin at the top layer portion to provide excellent adhesion between the separator and an electrode.