Bimodal Conductive Polymer Capacitor for ESR Stability
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Solution Overview
Problem
Solid electrolytic capacitors with conductive polymer cathodes face challenges in achieving effective coverage of edges and corners, leading to high DC leakage current and reliability issues in humid environments, and suffer from increased Equivalent Series Resistance (ESR) due to mechanical weakening under thermomechanical stresses.
Innovation Solution
A conductive polymer dispersion with a bimodal size distribution of conductive polymer:polyanion complex particles is applied, featuring first particles with an average diameter of 1 micron to 10 microns and second particles with an average diameter of 1 nm to 600 nm, enhancing corner and edge coverage and interfacial adhesion through high shear mixing or other post-processing techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If solid particles of conductive polymer are added to conductive polymer:polyanion dispersion to improve edge and corner coverage, then coverage is improved, but dispersion stability deteriorates and viscosity increases significantly
Solution Approach 1:
The patent changes the particle size parameter of the conductive polymer particles from large solid particles (0.7-20 μm) to nanoscale particles (1-100 nm). This parameter change allows the particles to remain dispersed in the polyanion solution without settling, while still providing effective coverage of edges and corners due to their small size and ability to penetrate into crevices.
Solution Approach 2:
The patent applies different particle sizes to different functional requirements: nanoscale particles (1-100 nm) are used specifically for edge and corner coverage where penetration is needed, while the bulk of the dispersion maintains its stability. This local application of appropriate particle size resolves the contradiction between coverage and stability.
2Manufacturing precision
If solid particles are added to conductive polymer dispersion to improve coverage, then coverage is improved, but ESR increases due to brittle outer film and flaking
Solution Approach 1:
The patent changes the particle size from micrometer scale to nanometer scale (1-100 nm). This size reduction prevents the particles from making the polymeric outer film brittle, as the nanoscale particles can be integrated into the film structure without creating stress concentration points that would cause flaking and increased ESR.
Solution Approach 2:
The patent creates a composite material system where conductive polymer particles are dispersed within a polyanion matrix. This composite structure allows the particles to provide coverage while the polyanion matrix maintains film integrity and prevents flaking, thus maintaining low ESR.
3Ease of manufacture
If uniform particle size dispersion is used, then processing is simpler, but edge and corner coverage is insufficient
Solution Approach 1:
The patent uses a narrow particle size distribution (1-100 nm) rather than a broad distribution or larger particles. This controlled parameter range provides sufficient coverage of edges and corners due to the small size, while keeping the dispersion homogeneous and easy to process without requiring complex multi-size blending procedures.
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
This approach results in improved ESR stability and reduced leakage current, achieving less than 100% ESR shift and 0.1 CV leakage after 1000 hours at 85°C and 85% relative humidity, significantly enhancing the reliability of solid electrolytic capacitors.
Implementation Method 1
enhancing corner and edge coverage and interfacial adhesion through high shear mixing or other post-processing techniques
Implementation Method 2
forming a conductive polymer layer on the anodized anode wherein the conductive polymer layer comprises first particles comprising conductive polymer and polyanion and second particles comprising the conductive polymer and the polyanion
Data Source
AI summary
A capacitor comprising an anode foil; and a conductive polymer layer on the anode foil. The conductive polymer layer comprises first particles comprising conductive polymer and polyanion and second particles comprising the conductive polymer and the polyanion wherein the first particles have an average particle diameter of at least 1 micron to no more than 10 microns. The second particles have an average particle diameter of at least 1 nm to no more than 600 nm.