VDF Polymer Dispersion Stabilization Without Fluorinated Surfactants
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Solution Overview
Problem
There is a shortfall in the stability and shelf life of aqueous dispersions of vinylidene fluoride (VDF)-based polymers for lithium battery applications, which also face challenges in processability and contamination issues due to the presence of fluorinated surfactants.
Innovation Solution
A method involving adjusting the pH of the aqueous dispersion to a value higher than 6.5 and adding a non-ionic surfactant with a primary alcohol group to stabilize the VDF-based polymer dispersion, ensuring stability against coagulation and preventing contamination from fluoride ions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If fluorinated surfactants are used to stabilize aqueous dispersions of VDF-based polymers, then stability against coagulation is improved, but contamination with fluoride ions occurs which interferes with electrochemical reactions
Solution Approach 1:
The invention extracts and eliminates fluorinated surfactants from the stabilization process entirely. Instead, it uses non-fluorinated alternatives (such as carboxylic acids, phenolic compounds, or their salts) that provide the necessary steric and/or electrostatic stabilization without introducing harmful fluoride ion contamination into the electrochemical system.
Solution Approach 2:
The invention introduces non-fluorinated surfactants as intermediary substances that perform the stabilization function previously fulfilled by fluorinated surfactants. These intermediaries (carboxylic acids, phenolic compounds, or their salts) adsorb onto polymer particle surfaces providing steric and/or electrostatic repulsion without the harmful side effects of fluorinated compounds.
2Duration of action of stationary object
If the aqueous dispersion is stabilized using conventional methods, then shelf life is extended, but processability and stability during formulation deteriorate
Solution Approach 1:
The invention changes the chemical parameters of the stabilization system by switching from fluorinated surfactants to non-fluorinated alternatives with different molecular structures and interaction mechanisms. This parameter change enables the dispersion to maintain stability during storage while improving processability during formulation, as the new surfactants provide appropriate surface charge and steric hindrance without the drawbacks of conventional fluorinated compounds.
3Reliability
If fluorinated surfactants are used to ensure adequate stability, then reliability of the dispersion is improved, but harmful chemical interference in electrochemical reactions increases
Solution Approach 1:
The invention converts the potential harm of using any surfactant (which could interfere with electrochemical reactions) into a benefit by selecting non-fluorinated surfactants that not only provide necessary stabilization but are also electrochemically inert. The carboxylic acids, phenolic compounds, or their salts used as surfactants do not interfere with lithium ion insertion/extraction or other electrochemical processes, thus turning the stabilization requirement into an opportunity to eliminate harmful chemical interference.
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 method provides a stable and processable aqueous dispersion suitable for electrochemical applications, avoiding contaminants and ensuring adequate shelf life without the need for fluorinated surfactants.
Implementation Method 1
adding a non-ionic surfactant with a primary alcohol group to stabilize the VDF-based polymer dispersion
Implementation Method 2
The non-ionic surfactant comprises a hydrogenated linear alkyl chain comprising from 6 to 15 carbon atoms and a (poly)alkoxylated group comprising 2 or 3 carbon atoms
Implementation Method 3
contacting said dispersion with at least one base so as to provide a VDF-based (semi)crystalline polymer aqueous dispersion having a pH equal to or higher than 6.5 and lower than 9.0
Implementation Method 4
adjusting the pH of the aqueous dispersion to a value higher than 6.5
Implementation Method 5
contacting said dispersion with at least one base so as to provide a VDF-based (semi)crystalline polymer aqueous dispersion having a pH equal to or higher than 6.5 and lower than 9.0
Data Source
AI summary
The present invention relates to a method for stabilizing aqueous dispersions, notably of polymers based on vinylidene fluoride (VDF), and to the use of the stabilized aqueous dispersion thus obtained in electrochemical applications.