PVDF Separator Adhesive Layer for Battery Electrode Bonding
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Solution Overview
Problem
Non-aqueous secondary batteries, such as lithium ion batteries, face challenges with adhesion between electrodes and separators, particularly in larger formats, leading to reduced battery capacity, deteriorated charge-discharge characteristics, and stability issues due to external impacts and expansion. Existing methods like wet heat press can decompose electrolytes, causing gas production and lowering cycle characteristics.
Innovation Solution
A separator with an adhesive porous layer containing a combination of polyvinylidene fluoride type resins A and B, with specific molecular weight ranges and hexafluoropropylene monomer unit proportions, is used to enhance adhesion through either wet or dry heat press methods, maintaining adhesion and dimensional stability while preventing electrolyte decomposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a separator with adhesive porous layer containing polyvinylidene fluoride type resin is used to improve adhesion between electrode and separator, then adhesion is improved, but ion permeability may be reduced
Solution Approach 1:
The separator is designed with different layers having different properties: the base porous substrate provides ion permeability while the adhesive porous layer provides adhesion. This local differentiation allows each layer to optimize its function without compromising the other.
Solution Approach 2:
The separator combines polyvinylidene fluoride type resin (providing adhesion) with porous substrate material (providing ion permeability) into a composite structure. This composite approach allows simultaneous achievement of adhesion and ion permeability that cannot be obtained with single materials.
2Use of energy by moving object
If the battery area is increased for electric power storage or electric vehicles, then energy density is improved, but adhesion between electrode and separator deteriorates
Solution Approach 1:
The adhesive porous layer parameters are optimized including resin composition (polyvinylidene fluoride type resin with specific fluorine content), layer thickness (1-10 μm), and porosity (30-80%). These parameter adjustments ensure adequate adhesion even in large-area batteries where mechanical stress and thermal expansion differences are more pronounced.
3Strength
If wet heat press method is used to enhance adhesion, then adhesion is improved, but electrolyte decomposition occurs causing gas production and reduced cycle characteristics
Solution Approach 1:
The invention replaces the chemical/wet heat press process with a dry heat press method. By using dry heat press at controlled temperatures (80-150°C), adhesion is achieved through thermal activation of the polyvinylidene fluoride type resin without causing electrolyte decomposition, thus eliminating gas production and maintaining cycle characteristics.
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 separator achieves excellent adhesion to electrodes, maintaining cycle characteristics and dimensional stability, even in larger formats, by using a combination of polyvinylidene fluoride type resins with specific molecular weights and hexafluoropropylene monomer unit proportions, and prevents electrolyte decomposition during heat press processes.
Implementation Method 1
a separator having an adhesive porous layer containing a polyvinylidene fluoride type resin on a polyolefin microporous film... When this separator is superimposed and thermally pressed on an electrode with an electrolyte solution included therein, it is well adhered to the electrode through the adhesive porous layer
Implementation Method 2
When this separator is superimposed and thermally pressed on an electrode... it is well adhered to the electrode through the adhesive porous layer
Implementation Method 3
the porous structure and thickness of an adhesive porous layer, from the viewpoint of compatibility between adhesiveness to an electrode and ion permeability
Data Source
AI summary
There is provided a separator for a non-aqueous secondary battery, containing a porous substrate, and an adhesive porous layer that is provided on one side or both sides of the porous substrate, in which the adhesive porous layer contains a polyvinylidene fluoride type resin A including a vinylidene fluoride monomer unit and a hexafluoropropylene monomer unit, and a polyvinylidene fluoride type resin B including a vinylidene fluoride monomer unit and a hexafluoropropylene monomer unit, a proportion of the hexafluoropropylene monomer unit in the polyvinylidene fluoride type resin A is more than 1.5 mol % and 5 mol % or less with respect to a total amount of the vinylidene fluoride monomer unit and the hexafluoropropylene monomer unit of the polyvinylidene fluoride type resin A, a proportion of the hexafluoropropylene monomer unit in the polyvinylidene fluoride type resin B is more than 5 mol % and 15 mol % or less with respect to a total amount of the vinylidene fluoride monomer unit and the hexafluoropropylene monomer unit of the polyvinylidene fluoride type resin B, and a weighted average of a weight-average molecular weight of the polyvinylidene fluoride type resin A and a weight-average molecular weight of the polyvinylidene fluoride type resin B is from 600,000 to 2,000,000.