Fluorinated Surfactant-Free VDF Copolymer Dispersion for Battery Electrodes
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Solution Overview
Problem
Current aqueous dispersions of vinylidene fluoride (VDF) polymers lack stability and processability for use in electrochemical cell components, particularly in lithium batteries, due to the presence of fluorosurfactants and insufficient molecular weight, which affects cohesion, adhesion, and shelf life.
Innovation Solution
An aqueous dispersion of VDF copolymer with recurring units from VDF and hydrophilic (meth)acrylic monomers, produced through emulsion polymerization in the presence of a persulfate initiator at elevated pressure and temperature without fluorinated surfactants, achieving high molecular weight and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If fluorinated surfactants are used in emulsion polymerization to stabilize VDF dispersion, then colloidal stability is improved, but electrochemical stability deteriorates due to contamination with chemicals interfering with electrochemical reactions
Solution Approach 1:
The invention extracts and eliminates fluorinated surfactants from the emulsion polymerization process. By using alternative stabilizers (ionic or nonionic surfactants without fluorinated groups) and optimizing polymerization conditions (persulfate initiator, temperature 50-90°C, pressure 10-100 bar), the patent achieves colloidal stability without the harmful fluorinated contaminants that interfere with electrochemical reactions.
Solution Approach 2:
The invention introduces alternative intermediary substances to replace fluorinated surfactants. These include ionic surfactants (anionic, cationic, or amphoteric) and nonionic surfactants with specific HLB values (8-18), which mediate the stabilization of VDF copolymer particles during emulsion polymerization without compromising electrochemical stability.
2Strength
If molecular weight of VDF copolymer is increased to improve cohesion and adhesion properties, then mechanical strength is improved, but processability and stability of aqueous dispersion deteriorates
Solution Approach 1:
The invention optimizes multiple parameters simultaneously: molecular weight (Mw 10,000-1,000,000), copolymer composition (VDF 85-99.99 mol%, hydrophilic monomer 0.01-15 mol%), surfactant concentration (0.1-10 wt%), and polymerization conditions (temperature 50-90°C, pressure 10-100 bar). This multi-parameter optimization achieves high molecular weight for strength while maintaining processability through controlled aqueous dispersion properties.
Solution Approach 2:
The invention creates a composite aqueous dispersion system combining VDF copolymer particles with specific molecular weight, hydrophilic monomer units, and non-fluorinated surfactants. This composite structure provides both the high molecular weight needed for cohesion/adhesion and the surfactant-mediated stability for processability.
3Reliability
If high molecular weight VDF copolymer is used to ensure stability and performance, then electrochemical stability is improved, but manufacturing complexity increases due to stringent process requirements
Solution Approach 1:
The invention defines specific parameter ranges that balance electrochemical stability with manufacturing feasibility: molecular weight (10,000-1,000,000), VDF content (85-99.99 mol%), hydrophilic monomer content (0.01-15 mol%), surfactant type (ionic or nonionic without fluorinated groups), and polymerization conditions (50-90°C, 10-100 bar). These optimized parameters ensure electrochemical stability while maintaining reasonable manufacturing complexity.
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 a stable and processable VDF dispersion that ensures adequate shelf-life and optimal performance in electrochemical cell components by maintaining high molecular weight and colloidal stability without fluorinated surfactants, enhancing cohesion and adhesion properties.
Implementation Method 1
produced through emulsion polymerization in the presence of a persulfate initiator at elevated pressure and temperature
Implementation Method 2
emulsion polymerization in the presence of a persulfate initiator
Implementation Method 3
aqueous dispersion of VDF copolymer with recurring units from VDF and hydrophilic (meth)acrylic monomers
Data Source
AI summary
The present invention pertains to a fluorosurfactant free aqueous dispersion of an acrylic-modified vinylidene fluoride polymer, possessing a melt viscosity of at least 30 kPoise, and possessing an amount of end groups of formula —CH2—OH of at least 5 mmol/kg, to a method for its preparation and to its use for the manufacture of electrochemical cell components, such as electrodes and/or composite separators.