Wet Electrolytic Capacitor High-Temperature Sealing
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Solution Overview
Problem
Wet electrolytic capacitors face issues with leakage due to gas buildup and corrosion of hermetic seals, leading to poor equivalent series resistance (ESR) stability, especially in high-temperature environments.
Innovation Solution
A wet electrolytic capacitor design featuring a metal substrate with an electrochemically active material, an anodically oxidized sintered porous anode, and a high-temperature elastomeric barrier seal, which maintains ESR stability and prevents leakage, with a dielectric layer thickness controlled between 10 nanometers to 500 nanometers to minimize reactivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hermetic seal is used to prevent liquid electrolyte leakage, then sealing reliability is improved, but the hermetic seal itself becomes corroded by the liquid electrolyte
Solution Approach 1:
The patent introduces a liquid seal as an intermediary barrier between the liquid electrolyte and the hermetic seal. This liquid seal prevents direct contact between the corrosive electrolyte and the hermetic seal material, thereby protecting the hermetic seal from corrosion while maintaining sealing effectiveness.
Solution Approach 2:
The sealing system is divided into two distinct components: a hermetic seal for gas tightness and a liquid seal for chemical barrier protection. This segmentation allows each component to perform its specialized function - the hermetic seal provides mechanical gas tightness while the liquid seal provides chemical corrosion protection.
2Device complexity
If conventional non-hermetic polymeric seals are used, then device complexity is reduced, but gas pressure buildup causes leaks around the seals
Solution Approach 1:
The patent employs a composite sealing approach combining hermetic seal materials (providing mechanical strength and gas tightness) with liquid seal materials (providing chemical resistance and pressure tolerance). This composite structure achieves both low complexity and high reliability by leveraging the complementary properties of different materials.
3Temperature
If the capacitor operates at high temperatures, then performance in commercial applications is improved, but ESR stability deteriorates
Solution Approach 1:
The patent modifies the liquid seal composition and physical parameters to maintain stability at elevated temperatures. By adjusting the chemical composition and physical properties of the liquid seal, it remains effective as a barrier and maintains ESR stability even when operating at high temperatures typical of commercial applications.
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 ESR of 3,000 milliohms or less at 200°C, maintaining stability for extended periods, and the high-temperature elastomeric seal ensures mechanical stability and prevents vapor leakage, enhancing overall performance.
Implementation Method 1
These tantalum slugs first undergo an electrochemical oxidation that forms an oxide layer coating acting as dielectric over the entire external and internal surfaces of the tantalum body
Implementation Method 2
an anode formed from an anodically oxidized sintered porous body
Implementation Method 3
a fluid working electrolyte that is in electrical contact with the anode and the electrochemically active material
Data Source
AI summary
A wet electrolytic capacitor that contains an anode formed from an anodically oxidized sintered porous body and a fluidic working electrolyte is provided. The casing contains a metal substrate coated an electrochemically-active material. Through a unique and controlled combination of features relating to the capacitor configuration and sealing assembly, the present inventor has discovered that good electrical properties (e.g., ESR stability) can be achieved at relatively high temperatures. One unique feature of the wet electrolytic capacitor that can help achieve such good ESR stability is the presence of a dielectric layer on the metal substrate of the cathode within a controlled thickness range. In other embodiments, a sealing assembly may be employed that contains a hermetic seal (e.g., glass-to-metal seal) and an elastomeric barrier seal formed from a high-temperature elastomeric material.