Battery Separator Coating With Low Electrolyte Solubility
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Solution Overview
Problem
Vinylidene fluoride polymers used in separator coating compositions for lithium-ion batteries have high solubility in electrolyte solutions, leading to increased electrolyte viscosity, resistance to lithium ion flow, and capacity fading, while also failing to provide adequate adhesion to the separator substrate and electrodes.
Innovation Solution
A coating composition comprising a vinylidene fluoride (VDF)-based polymer with a high fraction of insoluble components in standard polar aprotic solvents, ensuring reduced solubility in electrolyte solutions and improved adhesion to the separator substrate and electrodes, characterized by a high gel fraction and specific crystallinity and insoluble fraction requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a vinylidene fluoride polymer with high solubility in electrolyte solution is used for separator coating, then the coating can be applied and initially adheres to the separator substrate, but the polymer dissolves in the electrolyte leading to increased electrolyte viscosity, increased resistance to lithium ion flow, and capacity fading
Solution Approach 1:
The patent changes the molecular weight parameter of the VDF polymer to greater than 1,000,000 g/mol, which fundamentally alters the polymer's solubility characteristics in electrolyte solutions. This high molecular weight configuration reduces dissolution while maintaining coating applicability and adhesion properties.
2Strength
If a vinylidene fluoride polymer is used to provide adhesion to separator substrate and electrodes, then bonding strength is improved, but the polymer dissolves in electrolyte causing higher electrolyte viscosity and resistance to lithium ion flow
Solution Approach 1:
The patent applies parameter change by setting the molecular weight of the VDF polymer to greater than 1,000,000 g/mol, which reduces the polymer's tendency to dissolve in electrolyte while preserving its adhesive properties. This high molecular weight configuration maintains strong bonding to separator and electrodes without significantly increasing electrolyte viscosity.
3Strength
If a vinylidene fluoride polymer coating is applied to the separator, then lamination strength and interphase homogeneity are improved, but the polymer shows physical swelling in electrolyte leading to volume expansion and potential assembly defects
Solution Approach 1:
The patent changes the molecular weight parameter of the VDF polymer to greater than 1,000,000 g/mol, which reduces physical swelling and volume expansion when exposed to electrolyte. This high molecular weight configuration maintains dimensional stability while preserving lamination strength and interphase homogeneity.
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 reduces the impact on ionic conductivity and enhances long-term battery performance by maintaining adhesion and reducing electrolyte viscosity, thereby improving lamination strength and overall battery performance.
Implementation Method 1
having a gel fraction in a solvent system comprising N,N-dimethylformamide and lithium bromide greater than 60% by weight
Data Source
AI summary
The present invention pertains to a coating composition comprising a vinylidene fluoride polymer aqueous dispersion and to its use for the manufacture of electrochemical cell components, such as separators.