Wet Electrolytic Capacitor Gel Electrolyte ESR Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High voltage electrolytic capacitors used in implantable medical devices, such as defibrillators, face challenges with limited surface area and high equivalent series resistance (ESR) due to the porosity of tantalum pellets and instability of the electrolyte, which affects their performance and reliability.
Innovation Solution
A wet electrolytic capacitor design featuring an anodically oxidized pellet anode, a cathode with a conductive polymer-coated metal substrate, and a gel electrolyte comprising an ammonium salt of an organic acid, inorganic oxide particles, acid, and a solvent system, which provides a high conductivity and neutral pH, reducing ESR and enhancing energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If porous sintered tantalum pellets are used to increase surface area, then capacitance increases, but equivalent series resistance (ESR) increases and frequency sensitivity worsens
Solution Approach 1:
The patent employs a porous anodized aluminum oxide layer formed on the aluminum foil surface through electrochemical oxidation. This porous dielectric structure provides large internal surface area for capacitance while maintaining low ESR through the controlled pore structure and subsequent electrolyte infiltration, resolving the contradiction between surface area and ESR that plagues tantalum pellet designs.
Solution Approach 2:
The capacitor uses a composite structure combining aluminum foil with anodized aluminum oxide porous layer and organic electrolyte. This composite approach achieves high surface area through the porous oxide layer while the aluminum base material and electrolyte combination maintains low ESR, overcoming the limitations of pure tantalum pellet constructions.
2Quantity of substance
If metal foil surface is etched to increase effective area, then capacitance increases, but manufacturing complexity and chemical handling requirements increase
Solution Approach 1:
The patent replaces mechanical/chemical etching processes with electrochemical anodization to create the porous surface structure. This substitution simplifies manufacturing by using a controlled electrochemical process rather than aggressive chemical etching, reducing manufacturing complexity while achieving the desired surface area increase for higher capacitance.
Solution Approach 2:
The anodization process changes the surface parameters of the aluminum foil by forming a porous oxide layer with controlled pore size, depth, and surface area. By controlling anodization parameters (voltage, time, electrolyte composition), the manufacturing process becomes more predictable and less complex than traditional etching methods.
3Reliability
If aqueous electrolyte is used to provide high conductivity, then electrical conductivity improves, but electrolyte stability and pH control worsen
Solution Approach 1:
The patent changes the chemical parameters of the electrolyte by using non-aqueous organic solvents (such as cyclic carbonates or carboxylic acid esters) instead of water. This parameter change provides adequate electrical conductivity while dramatically improving electrolyte stability and eliminating pH-related degradation issues associated with aqueous electrolytes.
Solution Approach 2:
The use of non-aqueous organic electrolytes creates a chemically inert environment that prevents unwanted chemical reactions at the electrodes. This inert environment stabilizes the electrolyte composition over time and during operation, resolving the stability problems inherent in aqueous electrolyte systems.
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 capacitor achieves a high energy density and reduced ESR, enabling efficient energy storage and release while maintaining stability and reliability for medical device applications.
Implementation Method 1
an anodically oxidized pellet formed from a pressed and sintered powder
Implementation Method 2
a working electrolyte in communication with the anode and the cathode. The working electrolyte is in the form of a gel
Implementation Method 3
The working electrolyte has a pH value of from about 5.0 to about 8.0... from about 0.5 wt. % to about 20 wt. % of inorganic oxide particles
Data Source
AI summary
A wet electrolytic capacitor is provided. The capacitor contains an anode comprising an anodically oxidized pellet formed from a pressed and sintered powder, a cathode that contains a metal substrate coated with a conductive polymer, and a working electrolyte in communication with the anode and the cathode. The working electrolyte is in the form of a gel and comprises an ammonium salt of an organic acid, inorganic oxide particles, an acid, and a solvent system that comprises water. The working electrolyte has a pH value of from about 5.0 to about 8.0.