Electricity: electrical systems and devices – Electrolytic systems or devices – Liquid electrolytic capacitor
Reexamination Certificate
2002-06-13
2003-02-18
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Liquid electrolytic capacitor
C361S504000, C252S062200
Reexamination Certificate
active
06522524
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to an electrolyte gel for use in electrolytic capacitors and to an electrolytic capacitor impregnated with the electrolyte gel of the present invention for use in an implantable cardioverter defibrillator (ICD).
2. Related Art
Compact, high voltage capacitors are utilized as energy storage reservoirs in many applications, including implantable medical devices. These capacitors are required to have a high energy density since it is desirable to minimize the overall size of the implanted device. This is particularly true of an Implantable Cardioverter Defibrillator (ICD), also referred to as an implantable defibrillator, since the high voltage capacitors used to deliver the defibrillation pulse can occupy as much as one third of the ICD volume.
Implantable Cardioverter Defibrillators, such as those disclosed in U.S. Pat. No. 5,131,388, incorporated herein by reference, typically use two electrolytic capacitors in series to achieve the desired high voltage for shock delivery. For example, an implantable cardioverter defibrillator may utilize two 350 to 400 volt electrolytic capacitors in series to achieve a voltage of 700 to 800 volts.
Electrolytic capacitors are used in ICDs because they have the most nearly ideal properties in terms of size, reliability and ability to withstand relatively high voltage. Conventionally, such electrolytic capacitors include an etched aluminum foil anode, an aluminum foil or film cathode, and an interposed kraft paper or fabric gauze separator impregnated with a solvent-based liquid electrolyte. While aluminum is the preferred metal for the anode plates, other metals such as tantalum, magnesium, titanium, niobium, zirconium and zinc may be used. A typical solvent-based liquid electrolyte may be a mixture of a weak acid and a salt of a weak acid, preferably a salt of the weak acid employed, in a polyhydroxy alcohol solvent. The electrolytic or ion-producing component of the electrolyte is the salt that is dissolved in the solvent. The entire laminate is rolled up into the form of a substantially cylindrical body, or wound roll, that is held together with adhesive tape and is encased, with the aid of suitable insulation, in an aluminum tube or canister. Connections to the anode and the cathode are made via tabs. Alternative flat constructions for aluminum electrolytic capacitors are also known, comprising a planar, layered, stack structure of electrode materials with separators interposed therebetween, such as those disclosed in the above-mentioned U.S. Pat. No. 5,131,388.
In an implantable cardioverter device, one concern is leakage of electrolyte from the electrolytic capacitors within the finished device. Gas buildup within a capacitor may result in leakage of the electrolyte from the capacitor, even if the capacitor is in a sealed system. The build up of gas in a capacitor can be caused by the thermal decomposition of the electrolyte, the chemical reaction of the cathode with the fill electrolyte and/or the cathodic reduction produced by the leakage current through the capacitor during manufacture and use. It is known in the art to use a cathode depolarizer to prevent the production of hydrogen gas. Picric acid has been used in low voltage applications and nitroaromatic compounds and materials such as sorbic acid, have been used in high voltage applications, as disclosed in U.S. Pat. Nos. 5,175,674 and 5,687,057. However, there remains a need in the art for an electrolyte that when impregnated into an electrolytic capacitor has reduced leakage, while maintaining a conductivity that is reasonable for use in an electrolytic capacitor.
SUMMARY OF THE INVENTION
The present invention is directed to a gelled electrolyte that when impregnated into an electrolytic capacitor, reduces the leakage of electrolyte from in between the foils and provides very reasonable conductivity with a breakdown voltage enhancement, and to an electrolytic capacitor impregnated with the gelled electrolyte of the present invention for use in an implantable cardioverter defibrillator (ICD). The electrolyte according to the present invention is an electrolyte gel that is generated by the addition of a gelling agent, preferably D-mannitol, to a conventional electrolyte. An amount of D-mannitol is added to the electrolyte to reach a final weight percent of 8-15% by weight of the total electrolyte mixture. Typically, the amount of D-mannitol necessary for gel formation also provides a boost of about 50 volts to the breakdown voltage of the electrolyte in a finished capacitor. The desired state for a gelled electrolyte is that it will remain in the gelled state at 37° C., the approximate operating temperature for an ICD, and is liquefied at a higher temperature for impregnation.
A preferred electrolyte for use with the present invention is composed of a two solvent mixture of ethylene glycol and a polar organic cosolvent, such as a polar solvent selected from the group of N-methylformamide (NMF), 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, di(ethylene glycol), di(ethylene glycol) butyl ether, di(ethylene glycol) ethyl ether, propylene glycol, dimethylsulfoxide, acetonitrile, and propylene carbonate. Other combinations of mixed polar solvents can also be employed to obtain the desired results. Dissolved in this mixture is an aliphatic dicarboxylic acid, preferably of carbon chain length from eight to thirteen (C
8
to C
13
), such as suberic, azelaic, sebacic, undecanedioic, dodecanedioic, or brassylic acid, as the ionogen. Smaller dicarboxylic acids can be used in low voltage applications. In addition, other acids such as boric acid and hypophosphorous acid can be optionally added to enhance the initial conductivity and/or final breakdown voltage. In order to achieve the necessary electrolyte conductivity, an amine, such as ammonia, dimethylamine, trimethylamine, diethylamine, triethylamine, ethanolamine, diethanolamine, triethanolamine and diisopropylethylamine, is added to adjust the electrolyte pH to within a range of about 6.0 to about 10.0. Additionally, a cathode depolarizer, or degassing agent, from the group of nitro-substituted aromatic compounds (nitroaromatics), including nitrobenzene, nitrotoluene, nitrophenol, nitroacetophenone, nitrobenzyl alcohol, and nitroanisole, can be added to reduce the amount of gas produced during capacitor life. The water content of the initial electrolyte can vary from about 1% to about 8% by weight, as determined by Karl Fischer titration. The electrolyte may be further neutralized with anhydrous ammonia to achieve a pH of about 5.5 to about 8.5, preferably about 6.5 to about 7.5.
A representative electrolyte composition according to the present invention is:
72.9% by weight ethylene glycol;
17.3% by weight n-methylformamide;
6.0% by weight azelaic acid;
1.0% by weight boric acid;
1.0% by weight 2-nitroacetophenone;
1.6% by weight ammonium hydroxide (28-30% w/w); and
0.2% by weight anhydrous ammonia.
The gelled electrolyte according to the present invention, when impregnated in an electrolytic capacitor, will not leak and will provide very reasonable conductivity with a breakdown voltage enhancement.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to a gelled electrolyte for use in electrolytic capacitors and to an electrolytic capacitor impregnated with the gelled electrolyte of the present invention for use in an ICD. In particular, the gelled electrolyte according to the present invention, when impregnated in an electrolytic capacitor, will not leak and will provide very reasonable conductivity with a breakdown voltage enhancement.
Preferred embodiments of the present invention are now described. While specific configurations and arrangements are discussed, it should be understood that this is done for illustrative purposes only. A person skilled in the relevant art will recognize that other configurations and arrangements can be used without departing from the spirit and scope of the invention. It will be apparent to
Dapo Roland Francis
Feger Christopher
Dinkins Anthony
Mitchell Steven M.
Pacesetter Inc.
LandOfFree
Conductive electrolyte gel for high voltage electrolytic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Conductive electrolyte gel for high voltage electrolytic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Conductive electrolyte gel for high voltage electrolytic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3152810