PVDF Binder Composition for Low-NMP Electrode Coating
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Solution Overview
Problem
Vinylidene fluoride polymers with low swelling and solubility in N-methyl-2-pyrrolidone (NMP) result in electrode surfaces with reduced smoothness due to sedimentation and excessive volume change during drying, making it difficult to reduce NMP usage and improve productivity.
Innovation Solution
A vinylidene fluoride polymer composition with a melting point of 130°C or higher, having a viscosity ratio of 20 or less when mixed with NMP, and a surfactant with a non-perfluoro group and ionic group to prevent sedimentation, allowing for reduced NMP usage and maintaining electrode surface smoothness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the amount of NMP is reduced to decrease solvent usage and improve productivity, then productivity and cost are improved, but the viscosity of the electrode mixture increases and coatability deteriorates
Solution Approach 1:
The patent changes the physical and chemical parameters of the vinylidene fluoride polymer by controlling its melting point (130°C or higher) and crystallinity. This parameter change allows the polymer to maintain lower viscosity in NMP while reducing the total amount of NMP required, thus improving coatability even with reduced solvent content and enhancing productivity
Solution Approach 2:
The patent creates a composite electrode mixture system combining vinylidene fluoride polymer with specific additional resins (such as polyacrylonitrile, nitrile rubber, or polyvinylidene fluoride with different crystallinity). This composite approach allows optimization of both viscosity and coatability while using reduced NMP amounts, resolving the contradiction between productivity improvement and ease of operation
2Quantity of substance
If the crystallinity of the vinylidene fluoride polymer is increased to reduce swelling and solubility in NMP, then the amount of NMP used is reduced, but the electrode surface smoothness deteriorates
Solution Approach 1:
The patent precisely controls the melting point parameter of the vinylidene fluoride polymer (130°C or higher) and the viscosity ratio parameter (20 or less) to achieve an optimal balance. This parameter optimization allows sufficient reduction in NMP usage while preventing excessive polymer aggregation that would cause surface roughness, thus resolving the contradiction between quantity reduction and precision maintenance
Solution Approach 2:
The patent applies local quality control by specifying that the polymer composition should have heterogeneous structure with controlled crystallinity distribution. This allows different regions of the electrode to have appropriate polymer morphology - sufficient crystallinity to reduce NMP swelling but controlled distribution to maintain surface smoothness, resolving the contradiction between NMP reduction and surface quality
3Strength
If typical PVDF is used as binding agent, then adhesiveness is maintained, but the polymer swells and dissolves in NMP increasing viscosity and reducing productivity
Solution Approach 1:
The patent changes the key parameter of the vinylidene fluoride polymer by specifying a melting point of 130°C or higher, which fundamentally alters the polymer's interaction with NMP. This parameter change reduces swelling and dissolution in NMP, maintaining adhesiveness while significantly reducing drying time and improving productivity
Solution Approach 2:
The patent employs a disposable-like approach by using a specially formulated vinylidene fluoride polymer composition that requires minimal solvent removal. The composition is designed to achieve adequate binding function with reduced NMP content, allowing faster processing and effectively treating the solvent removal step as a minimized necessary operation rather than a lengthy process
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 composition effectively reduces NMP usage, improves productivity, and ensures a smooth electrode surface by preventing excessive swelling and sedimentation, while maintaining adhesiveness and coatability.
Implementation Method 1
the crystallinity of the vinylidene fluoride polymer is increased to reduce the swelling and solubility in NMP
Implementation Method 2
a vinylidene fluoride polymer having a melting point of 130° C. or higher
Implementation Method 3
heating the latex at a temperature, the temperature being: lower than a melting point of the untreated vinylidene fluoride polymer; not lower than the melting point minus 20° C.; and not lower than 100° C., in a state where a surfactant is present in the latex, the surfactant having a non-perfluoro group as a hydrophobic group and an ionic group as a hydrophilic group
Implementation Method 4
heating the latex at a temperature, the temperature being: lower than a melting point of the untreated vinylidene fluoride polymer; not lower than the melting point minus 20° C.; and not lower than 100° C.
Data Source
AI summary
An objective is to provide a vinylidene fluoride polymer composition that is difficult to swell and dissolve in N-methyl-2-pyrrolidone and can form an electrode with a smooth surface. The vinylidene fluoride polymer composition contains a vinylidene fluoride polymer with a melting point of 130° C. or higher. When the vinylidene fluoride polymer composition and N-methyl-2-pyrrolidone are mixed to prepare a vinylidene fluoride polymer dispersion with a content of the vinylidene fluoride polymer of 6 mass %, a ratio of a viscosity of the vinylidene fluoride polymer dispersion at 30° C. to a viscosity of N-methyl-2-pyrrolidone at 30° C. is 20 or less, and when the vinylidene fluoride polymer dispersion is stirred and then allowed to stand for 15 minutes, a rate of change in content of the vinylidene fluoride polymer in an upper 40 volume % area of the vinylidene fluoride polymer dispersion before and after the standing is 2 mass % or less.