Aluminum Electrolytic Capacitor Electrolyte with Azelaic Acid
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Solution Overview
Problem
Aluminum electrolytic capacitors face challenges with high impedance and reduced service life due to the reaction of water and carboxylic acid anions with the aluminum oxide film, leading to aluminum dissolution and hydrogen gas generation, which is exacerbated at high temperatures, and existing solutions like phosphoric acid addition do not adequately inhibit these reactions.
Innovation Solution
The use of an electrolytic solution containing azelaic acid or azelaic acid salt, combined with a phosphorus oxoacid ion-generating compound and a chelating agent to form a phosphorus oxoacid ion and aluminum chelate complex, which inhibits aluminum dissolution and hydrogen gas generation by forming protective layers on the electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If water content in the electrolytic solution is increased to lower specific resistance, then conductivity is improved, but electrode foil deteriorates and service life is reduced
Solution Approach 1:
Phosphate ions are introduced as an intermediary substance that mediates between water and aluminum. The phosphate ions form protective complexes with aluminum ions, preventing direct reaction between water and aluminum metal, thus enabling high water content electrolytes to maintain both conductivity and service life
Solution Approach 2:
The chemical composition parameters of the electrolyte are changed by adding phosphate ions and controlling the balance between water, carboxylic acid, and phosphate content. This parameter optimization allows the electrolyte to achieve low specific resistance while maintaining electrode stability through the protective effect of phosphate ions
2Duration of action of stationary object
If phosphoric acid is added to prevent electrode foil deterioration, then service life is extended, but phosphate ions form insoluble compounds that attach to electrode foil and disappear from solution
Solution Approach 1:
The solution creates different local chemical environments: phosphate ions concentrate at the electrode surface forming protective films, while maintaining adequate concentration in the bulk electrolyte. This local quality differentiation allows phosphate ions to serve both protective and conductive functions
Solution Approach 2:
Phosphate ions are added in advance to the electrolyte formulation at optimized concentrations. This preliminary action ensures that phosphate ions are already present to form protective complexes before aluminum dissolution occurs, preventing electrode deterioration while maintaining sufficient phosphate ion availability
3Reliability
If excessive phosphoric acid is added, then electrode protection is enhanced, but aluminum oxide film dissolves and leakage current increases
Solution Approach 1:
The pH and phosphate concentration parameters are precisely controlled within optimal ranges. By adjusting these parameters, the electrolyte achieves sufficient electrode protection without excessive phosphate ion concentration that would cause aluminum oxide film dissolution and increased leakage current
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 solution significantly reduces impedance and extends the service life of aluminum electrolytic capacitors, particularly at high temperatures, by preventing aluminum oxide film dissolution and maintaining adequate phosphorus oxoacid ion levels in the electrolyte.
Implementation Method 1
a chelating agent which can coordinate with aluminum to form an aqueous aluminum chelate complex
Implementation Method 2
form protective layers on the electrodes
Implementation Method 3
a solvent containing water, electrolytes selected from the group consisting of a carboxylic acid and a carboxylic salt
Data Source
Figure 1~2
AI summary
Disclosed are an aluminum electrolytic capacitor having low impedance properties and a long service life, and an electrolytic solution which enables to give such capacitor. The electrolytic solution contains a solvent containing water, a phosphorus oxoacid ion-generating compound which can generate a phosphorus oxoacid ion in an aqueous solution, and a chelating agent which can coordinate with aluminum to form an aqueous aluminum chelate complex. The electrolytic solution further contains a compound selected from the group consisting of azelaic acid and an azelaic acid salt, and a compound selected from the group consisting of formic acid, a formic acid salt, adipic acid, an adipic acid salt, glutaric acid and a glutaric acid salt. The content of azelaic acid and/or the azelaic acid salt is at least 0.03 moles per kg of the solvent. When the electrolytic solution is used in an electrolytic capacitor which utilizes an anode having an aluminum oxide film containing phosphorus in an amount of 30 to 150 mg per unit CV product in terms of phosphoric acid, the service life of the capacitor is remarkably prolonged.