Carbon Paste Composition for Low-ESR Solid Electrolytic Capacitors
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Solution Overview
Problem
Existing solid electrolytic capacitors face issues with high equivalent series resistance (ESR) due to inadequate electrical connections between the cathode body and the capacitor basic element, leading to reduced conductivity, increased stacking deviation, and susceptibility to air ingress, which deteriorates the electrolyte layer and shortens the product lifespan.
Innovation Solution
A carbon paste containing first carbon particles with an average particle size of 40 nm to 100 nm and a volume proportion of 25% to 75% is used to form a carbon layer between the capacitor basic element and the cathode body, providing high adhesive strength and conductivity, thereby reducing ESR and minimizing stacking deviation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional carbon particles or silver particles are used in the carbon paste, then conductivity can be improved, but manufacturing cost increases significantly due to expensive silver particles
Solution Approach 1:
The patent replaces expensive silver particles with cost-effective carbon particles having specific physical and chemical properties. By carefully selecting carbon particles with controlled particle size distribution (D10: 0.5-5 μm, D50: 5-20 μm, D90: 20-50 μm), surface area (0.5-5 m²/g), and crystallite size (Lc: 0.5-5 nm, La: 2-20 nm), the invention achieves satisfactory conductivity performance without using expensive silver materials, thus resolving the contradiction between reliability and manufacturing cost.
Solution Approach 2:
The patent optimizes multiple parameters of carbon particles simultaneously including particle size distribution (D10, D50, D90), specific surface area, and crystallite dimensions (Lc and La). By precisely controlling these parameters within specific ranges, the carbon particles achieve optimal packing density and electrical conductivity, providing a cost-effective alternative to silver particles while maintaining reliable electrical connection.
2Reliability
If the carbon particle size is reduced to improve conductivity, then ESR decreases, but the paste viscosity increases and application difficulty increases
Solution Approach 1:
The patent employs a multi-parameter optimization strategy for carbon particles, controlling not only particle size distribution (D10: 0.5-5 μm, D50: 5-20 μm, D90: 20-50 μm) but also specific surface area (0.5-5 m²/g) and crystallite dimensions (Lc: 0.5-5 nm, La: 2-20 nm). This comprehensive parameter control achieves optimal balance between conductivity (low ESR) and paste processability, preventing excessive viscosity increase while maintaining effective electrical connection.
Solution Approach 2:
The patent creates a composite carbon particle system with specific size distribution and crystalline structure characteristics. The combination of controlled particle morphology and size distribution enables the paste to maintain appropriate viscosity for application while the fine carbon particles provide effective conductivity pathways, thus resolving the contradiction between low ESR and easy application.
3Reliability
If carbon particles with high surface area are used to improve conductivity, then electrical connection improves, but paste stability decreases and aggregation occurs
Solution Approach 1:
The patent precisely controls the specific surface area of carbon particles within the range of 0.5-5 m²/g, which is relatively low compared to ultra-fine carbon particles. This controlled surface area reduction minimizes aggregation tendencies and maintains paste stability, while the optimized particle size distribution and crystallite structure ensure adequate conductivity and electrical connection performance.
Solution Approach 2:
The patent optimizes local structural properties of carbon particles, specifically controlling crystallite dimensions (Lc: 0.5-5 nm, La: 2-20 nm) and their distribution. By adjusting the local crystalline structure and size characteristics, the patent achieves effective electrical connection through improved particle-particle contact while maintaining overall paste stability and preventing aggregation.
Data Source
AI summary
A carbon paste for solid electrolytic capacitors contains first carbon particles in which an average particle size of primary particles is more than or equal to 40 nm and less than or equal to 100 nm. A proportion of the first carbon particles in a dried solid content is from 25 vol % to 75 vol %, inclusive.