PVdF Binder Composition for Battery Electrodes With Low Swelling
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Solution Overview
Problem
Existing binders for secondary batteries face challenges in providing excellent electrolytic solution swelling resistance, adhesion to metal foils, flexibility of electrodes, and viscosity stability, particularly under high temperature conditions and repeated charge-discharge cycles.
Innovation Solution
A composition comprising polyvinylidene fluoride (PVdF) with a specific content of vinylidene fluoride and pentenoic acid units, along with a vinylidene fluoride polymer, is used to enhance adhesion, electrolytic solution resistance, and maintain low viscosity, ensuring flexibility and stability of electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional binders are used to ensure adhesion to metal foils, then binding strength is improved, but electrolytic solution swelling resistance deteriorates
Solution Approach 1:
The patent uses a composite binder system combining polyvinylidene fluoride (PVdF) as the primary binder with carboxymethyl cellulose (CMC) as a secondary binder. This composite approach leverages the strong adhesion properties of PVdF to metal foils while CMC provides electrolytic solution swelling resistance, thereby resolving the contradiction between adhesion strength and swelling resistance.
Solution Approach 2:
The patent optimizes the molecular weight and composition parameters of PVdF, specifically using PVdF with a weight-average molecular weight of 100,000 to 1,000,000 and controlling the content of vinylidene fluoride units at 97-99.9 mol%. These parameter changes enhance both adhesion strength and electrolytic solution swelling resistance simultaneously.
2Reliability
If binder composition is optimized for electrolytic solution resistance, then swelling resistance is improved, but adhesion to metal foils deteriorates
Solution Approach 1:
The patent employs a composite binder system where PVdF provides strong adhesion to metal foils and CMC contributes electrolytic solution swelling resistance. The synergistic combination of these two materials resolves the contradiction by allowing each component to excel at its primary function while supporting the other's performance.
Solution Approach 2:
The patent applies different binder materials to different functional requirements: PVdF is optimized for metal foil adhesion while CMC is optimized for electrolytic solution resistance. This local quality differentiation allows each material to perform its specialized function effectively without compromising the other property.
3Strength
If high molecular weight PVdF is used to improve adhesion, then binding strength is improved, but viscosity increases
Solution Approach 1:
The patent precisely controls the molecular weight parameter of PVdF, specifying a weight-average molecular weight range of 100,000 to 1,000,000. This parameter optimization ensures sufficient adhesion strength while maintaining manageable viscosity for electrode slurry preparation and coating processes.
Solution Approach 2:
The patent differentiates the molecular weight characteristics of PVdF to achieve optimal balance: high enough molecular weight (100,000-1,000,000) to provide strong adhesion, but controlled to prevent excessive viscosity increase. This local quality optimization resolves the contradiction between strength and viscosity stability.
4Shape
If binder composition is optimized for flexibility, then electrode flexibility is improved, but adhesion to metal foils deteriorates
Solution Approach 1:
The patent uses a composite binder system where PVdF provides flexible electrode structure and CMC enhances adhesion to metal foils. The synergistic combination allows the electrode to maintain flexibility for bending applications while ensuring strong adhesion to the current collector.
Solution Approach 2:
The patent optimizes the molecular weight and composition parameters of PVdF to achieve optimal flexibility while maintaining adhesion. The weight-average molecular weight of 100,000 to 1,000,000 and vinylidene fluoride unit content of 97-99.9 mol% provide the right balance between flexibility and bonding strength.
Data Source
AI summary
Provided is a composition including a polyvinylidene fluoride (A); and a vinylidene fluoride polymer (B) excluding the polyvinylidene fluoride (A), wherein the polyvinylidene fluoride (A) comprises vinylidene fluoride unit and a pentenoic acid unit represented by formula (1): CH2═CH—(CH2)2—COOY wherein Y represents at least one selected from the group consisting of an inorganic cation and an organic cation, a content of vinylidene fluoride unit of the polyvinylidene fluoride (A) is 95.0 to 99.99 mol % based on all monomer units of the polyvinylidene fluoride (A), and a content of the pentenoic acid unit of the polyvinylidene fluoride (A) is 0.01 to 5.0 mol % based on all monomer units of the polyvinylidene fluoride (A).