PVdF Binder Composition for Flexible, Swelling-Resistant Electrodes
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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, and flexibility, leading to issues such as increased resistance and discharge capacity loss during high-temperature storage and repeated charging/discharging.
Innovation Solution
A polyvinylidene fluoride (PVdF) binder is developed with a specific composition of vinylidene fluoride and pentenoic acid units, adjusted within certain molecular weight and content ranges, to enhance electrolytic solution swelling resistance, adhesion, and flexibility, forming electrodes with improved adhesion to metal foils and maintaining discharge capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If binder composition is optimized for adhesion, then binding strength improves, but electrolytic solution swelling resistance deteriorates
Solution Approach 1:
The invention creates a composite binder system where PVdF provides the electrolytic solution swelling resistance while the incorporated polyacrylic acid or polymethacrylic acid provides the adhesion strength. The synergistic combination allows both properties to be enhanced rather than traded off against each other.
Solution Approach 2:
The functional component (polyacrylic acid or polymethacrylic acid) is distributed at specific locations within the binder matrix at controlled concentrations (1-20 mass%), providing localized adhesion functionality while the majority PVdF matrix maintains electrolytic solution swelling resistance.
2Strength
If high molecular weight binder is used, then adhesion improves, but electrode flexibility deteriorates
Solution Approach 1:
The copolymer composition combines high molecular weight PVdF for adhesion with controlled amounts of functional component polymers, creating a composite material that maintains flexibility while providing strong adhesion. The functional component acts as a plasticizer and flexibility enhancer within the rigid PVdF matrix.
Solution Approach 2:
The invention controls the molecular weight and compositional ratio parameters to optimize the balance between adhesion and flexibility. By adjusting the content of the functional component within specific ranges and controlling the overall molecular weight distribution, the electrode achieves both strong adhesion and required flexibility.
Data Source
AI summary
Provided is a polyvinylidene fluoride comprising: vinylidene fluoride unit; and a pentenoic acid unit represented by formula (1): CH2=CH-(CH)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 is 95.0 to 99.99 mol% based on all monomer units of the polyvinylidene fluoride, and a content of the pentenoic acid unit is 0.01 to 5.0 mol% based on all monomer units of the polyvinylidene fluoride.