PVDF Binder Composition for Battery Electrode Adhesion
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Solution Overview
Problem
Conventional polyvinylidene fluoride binders used in non-aqueous electrolyte secondary batteries exhibit weak adhesion between electrode active materials and current collectors, leading to reduced discharge capacity over time due to shedding and peeling issues, and existing solutions do not provide a specific mixture formulation or prevent copolymer aggregation on electrode surfaces.
Innovation Solution
A binder composition combining a first vinylidene fluoride polymer with an inherent viscosity of 1.7 dL/g or higher and a second vinylidene fluoride polymer containing (meth)acrylic acid as a monomer unit, blended in a ratio of 75:25 to 25:75 by weight, to enhance adhesion without forming copolymers or aggregates on olivine type lithium compound electrode active materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional polyvinylidene fluoride binder is used, then the electrode structure is simple and easy to manufacture, but the adhesion between electrode active materials and current collector is weak
Solution Approach 1:
The patent applies composite materials by combining two distinct polyvinylidene fluoride binder types: a non-modified PVDF with inherent viscosity of 1.2 dL/g or higher, and a modified PVDF containing carboxyl groups or epoxy groups. This composite binder system achieves superior adhesion strength between electrode active materials and current collector, resolving the contradiction between simple binder composition and strong adhesion.
2Reliability
If polyvinylidene fluoride binder is used, then the manufacturing process is simple, but the electrode active material sheds during use and the electrode mixture layer peels from the current collector
Solution Approach 1:
The patent applies parameter changes by specifying precise inherent viscosity parameters for the non-modified PVDF (1.2 dL/g or higher) and incorporating specific functional groups (carboxyl or epoxy) in the modified PVDF. These parameter specifications ensure reliable electrode stability and prevent shedding and peeling during battery operation, while maintaining a manageable manufacturing process.
3Strength
If copolymer of acrylic acid and vinylidene fluoride is used to improve adhesion, then adhesion is enhanced, but copolymer or aggregate forms on electrode surface reducing battery properties
Solution Approach 1:
The patent extracts and eliminates the harmful copolymerization reaction between acrylic acid and vinylidene fluoride. Instead of using a copolymer system that causes aggregation, the invention separates the functions into two distinct PVDF components: one providing structural integrity (non-modified PVDF with high inherent viscosity) and the other providing adhesion enhancement (modified PVDF with carboxyl or epoxy groups). This extraction of the problematic copolymerization step eliminates aggregate formation while maintaining strong adhesion.
Data Source
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Figure 3A~3B
AI summary
To provide a binder composition having high adhesion, without producing a copolymer or an aggregate of a copolymer and an electrode active material. A binder composition according to the present invention contains: a first vinylidene fluoride polymer with an inherent viscosity of 1.7 dL/g or higher; and a second vinylidene fluoride polymer containing acrylic acid or methacrylic acid as a monomer unit.