Compositions – Electrolytes for electrical devices
Reexamination Certificate
2001-03-19
2003-05-13
Koslow, C. Melissa (Department: 1755)
Compositions
Electrolytes for electrical devices
C361S506000, C361S504000, C607S005000, C429S326000, C429S339000, C429S341000, C429S343000
Reexamination Certificate
active
06562255
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a conductive electrolyte for high voltage electrolytic capacitors and to an electrolytic capacitor impregnated with the electrolyte 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.
There are numerous commercially available compositions of electrolyte for use in electrolytic capacitors that can confirm to reasonable specifications, as long as the operating voltage of the capacitor remains at 400 volts or lower. However, once this limit is exceeded, the choices become somewhat more limited. Many high voltage electrolytes employ the use of very long chain dicarboxylic acids and large bases to achieve the necessary breakdown voltages, however, the resultant electrolytes have very low conductivities (≦1 mS/cm). For example, U.S. Pat. No. 4,860,169 to Dapo discloses an electrolytic capacitor for use in operation at voltages above 500 volts, produced by employing an electrolyte containing a straight chain saturated aliphatic dicarboxylic acid in which the carboxylic moieties are separated by at least 14 carbon atoms. In particular, an electrolyte for use in electrolytic capacitors is disclosed consisting essentially of a solution of a straight chain saturated aliphatic dicarboxylic acid in which the carboxylics are separated by at least 14 carbon atoms in a mixture of at least one polar organic solvent and at least water in an amount of from 4-30% by weight of the organic solvent or a borate in an amount of 2-5% by weight of the organic solvent.
Therefore, what is needed in the art is an electrolyte that provides acceptable breakdown characteristics with reasonable conductivity when impregnated in an electrolytic capacitor operating above 400 volts.
SUMMARY OF THE INVENTION
The present invention is directed to a conductive electrolyte for use in high voltage electrolytic capacitors and to an electrolytic capacitor impregnated with the electrolyte of the present invention for use in an implantable cardioverter defibrillator (ICD). The electrolyte according to the present invention is composed of a two solvent mixture of ethylene glycol and di(ethylene glycol); a combination of boric acid with an aliphatic dicarboxylic acid of carbon chain length from eight to thirteen, such as suberic, azelaic, sebacic, undecanedioic, dodecanedioic, or brassylic acid; a very long chain dicarboxylic acid, where the acid moieties are separated by 34 carbons (referred to as “dimer acid”); and a nitro-substituted aromatic compound as a degassing agent, such as 3-nitroacetophenone or 2-nitroanisole. This electrolyte is then titrated with a light amine such as ammonia, diethylamine, dimethylamine, trimethylamine, or triethylamine. A representative composition according to the present invention that displays the desired properties is: 64.1% by weight ethylene glycol, 27.5% by weight di(ethylene glycol), 1.8% by weight dimer acid, 3.4% by weight azelaic acid, 0.9% by weight boric acid, 0.9% by weight 3-Nitroacetophenone, and 1.4% by weight ammonium hydroxide (28-30% w/w).
The electrolyte according to the present invention, when impregnated in an electrolytic capacitor, provides an acceptable breakdown voltage while having a reasonable bulk conductivity. This is accomplished by combining the superior conductivity characteristics of an eight to thirteen carbon chain dicarboxylic acid, with the high breakdown strength characteristics of a very long chain dicarboxylic acid, where the acid moieties are separated by 34 carbons. This electrolyte, when impregnated within a capacitor constructed of appropriate foils and paper spacers, should provide a part with a working voltage of at least 500 volts, while having a bulk conductivity of approximately 3 mS/cm.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is directed to a conductive electrolyte for use in high voltage electrolytic capacitors and to an electrolytic capacitor impregnated with the electrolyte of the present invention for use in an ICD. In particular, the electrolyte according to the present invention, when impregnated in an electrolytic capacitor, provides an acceptable breakdown voltage while having a reasonable bulk conductivity. The electrolyte according to the present invention may be used in a capacitor operating above 400 VDC.
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 a person skilled in the relevant art that this invention can also be employed in a variety of other devices and applications.
The electrolyte according to the present invention is composed of a two solvent mixture of ethylene glycol and di(ethylene glycol); a combination of boric acid with an aliphatic dicarboxylic acid of carbon chain length from eight to thirteen, such as suberic, azelaic, sebacic, undecanedioic, dodecanedioic, or brassylic acid; a very long chain dicarboxylic acid, where the acid moieties are separated by 34 carbons, such as dimer acid; and a nitro-substituted aromatic compound as a degassing agent, such as 3-nitroacetophenone or 2-nitroanisole. This electrolyte is then titrated with a light amine such as ammonia, diethylamine, dimethylamine, trimethylamine, or triethylamine. A representative composition according to the present invention that displays the desired properties is: 64.1% by weight ethylene glycol, 27.5% by weight di(ethylene glycol), 1.8% by weight dimer acid, 3.4%
Koslow C. Melissa
Mitchell Steven M.
Pacesetter Inc.
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