BACKGROUND OF THE INVENTION

[00013 The present invention is directed to an electrolytic capacitor. Capacitors are electrical devices that stare an electric charge. Electrolytic capacitors are a common form of capacitors and are composed of two or more pairs of electrodes, a liquid electrolyte and a separator such as Kraft paper. Electrolytic capacitors are widely used as parts of electrical circuits in many common electrical devices,

[0002] While widely used, electrolytic capacitors lack suitable performance at extremely high or low temperatures, particularly those experienced in some aerospace applications, la existing electrolytic capacitors, operating at temperatures above 120 degrees C can cause a catastrophic pressure buildup within the capacitor. This is the result of the relatively high vapor pressures of the electrolyte materials used in existing electrolytic capacitors. Although some ionic electrolytic liquids presently used ca resist this pressure build-up at temperatures greater than 120 degrees C ₅ the agglomeration of charges at such temperatures results in no effective charge transfer mechanism between electrodes. Also, existing electrolytic capacitors, when operating at temperatures below 0 degrees often do not have effective charge transfer mechanisms as the colder temperatures have a negative interaction with most electrolyte solvents. Thus, there is a need for better electrolytic capacitors that can operate at both extremely high and low temperatures that are experienced by aerospace applications.

BRI EF DESCRIPTION OF THE INVENTION

[0003] One embodiment of the invention is an electrolytic capacitor having operating temperatures from -50 degrees C to 200 degrees C comprising an anode; a cathode; a Kraft paper separator that is either coated with a polymer coating or where some of the

hemicellulose and cellulose of the Kraft paper has been removed and replaced by the polymer coating, said polymer having a Tg of less than 160 degrees C, a degradation temperature of greater than 200 degree C and a conductivity of 1.0 to . 000 Siemens per centimeter at 20 degrees C; and a non-aqueous liquid electrolyte, said electrolyte having a vapor pressure of less than 2 mm at 20 degrees 0. a boiling point equal to or greater than 200 degrees C, and a melting point equal to or less than -30 degrees C. DETAILED DESCRIPTION OF THE INVENTION

0004] This invention uses a composite approach to the design of the Kraft paper separator and electrolyte within an electrolytic capacitor. By treating the electrolyte and separator as a composite unit, the approach to designing an operational high/low temperature capacitor can be achieved. The proposed composite Kraft separator uses a low vapor pressure non-aqueous solvent as the electrolyte thai remains a liquid from -30 degrees C to 200 degrees C and affords minimal vapor pressure. Suitable non-aqueous solvents include propylene carbonate, di propylene glycol and gamraa-butyrolactone. The Kraft paper separator is either coated with the selected polymer coating chosen for its Tg, degradation and conduction properties or the Kraft paper separator has some of the hemicellulose and cellulose has been removed and replaced by the selected polymer coating chosen for its Tg, degradation and conduction properties.

[0005] Electrolytic capacitors include super capacitors, ultra-capacitors, double layer capacitors, as well as common aluminum and tantalum electrolytic capacitors. Aluminum electrolytic capacitors are commonly constructed from two conducting aluminum foils, one of which is coated with an insulating oxide layer, and a paper spacer soaked in electrolyte. The foil insulated by the oxide layer is the anode while the liquid electrolyte and the second foil acts as the cathode. This stack is then rolled up, fitted with pin connectors and placed in a cylindrical aluminum casing. Aluminum electrolytic capacitors are commonly used when operating voltages are less than 600 Volts.

[0006] The anode used in the present electrolytic capacitors may be made of any suitable material that is used in in electrolytic capacitors. Aluminum is a common anode material It can have either a smooth or rough surface. It can be etched and/or coated with various materials such an insulating oxide layer.

[0007] The cathode used in the present electrolytic capacitors may be made of any suitable material that is used in in electrolytic capacitors. Aluminum is a common anode material. It can have either a smooth or rough surface.

[0008] The Kraft paper separator used herein is either coated with a polymer coating or where some of the hemicellulose and cellulose of the Kraft paper has been removed and replaced by the polymer coating. Kraft paper is made from wood pulp wherein most of the ligoin is removed during chemical pulping. Lignin removal allows for the formation of hydrogen bonds between the cellulose (and hemicellulose) in the paper fibers. The resulting product is a paper with high tensile strength. In the case where the Kraft paper is coated with the polymer, any suitable Kraft paper commonly used in electrolytic capacitors can be used herein. I n the case where some of the hemiceliulose and cellulose of the Kraft paper has been removed and replaced by the polymer coating, the starting Kraft paper can a! so be any suitable Kraft paper commonly used in electrolytic capacitors. The removal of some of the hemiceliulose and cellulose from the Kraft paper can be accomplished by soaking the paper in an aqueous solution of sodium hydroxide.

[0009] The polymers used in either case must have certain physical properties. Fo some embodiments, they have a Tg of less than 160 degrees C, a degradation temperature of greater than 300 degree C and a conductivity of 10 to 1000 Siemens per centimeter at 20 degrees C. For other embodiments, they have a Tg of less than 150 degrees C, a degradation temperature of greater than 220 degree C and a conductivity of 20 to 500 Siemens per centimeter at 20 degrees C. For still other embodiments, they have a Tg of less than 140 degrees C, a degradation temperature of greater than 250 degree C and a conductivity of 30 to 500 Siemens per centimeter at 20 degrees C.

[0010 j Suitable polymers fo least some of these embodiments include copolymers of poly (3.4-ethyletie dioxythiophene) and poly(styre»e sulfonate) (also known as PEDOT:PSS). These mixtures have glass transition temperatures (Tg) of around 100 degrees C; degradation temperatures of at least 260 degrees C and conductivities of 100 to 1 00 Siemens per centimeter at 20 degrees C. These mixtures can be any suitable weight ratio of the PEDOT to The PSS. In some embodiments, the weiuht ratio of PEDOT to PSS can be from 9: 1 to 1:9.

[0 1 1] Other suitable polymers are polypyrroles. These polymers have glass

transition, temperatures (Tg) of around 140-160 degrees C; degradation temperatures of at least 300 degrees C and conductivities of 10 to 50 Siemens per centimeter at 20 degrees C.

[0012] The amount of polymer added to the Kraft paper in either ca se may be any amount that is suitable to produce a working electrolytic capacitor. For some embodiments, that amount may be an. amount from 10% to 100% by weight of the Kraft paper in the electrolytic capacitor.

[0013] The polymer may be combined with the Kraft paper by any suitable technique. For example, any suitable coating technique such as spin coating, and brush coating or vacuum infiltration may be used.

[0014] Additionally, there may also be additives included within the polymer film to alter the conductivity. Additives may include types of carbon powder such as graphitic film to adjust the conductivity. Additives may include types of carbon powder such as graphitic carbon, amorphous carbon and turbostratic carbon; metal powders such as copper or iron; and metal oxide powders that include but are not limited to tin (II) oxide, titanium oxide and zinc oxide,

[00 ! 5] The non-aqueous liquid electrolyte, used herein has a vapor pressure of less than 2 mm at 20 degrees C a boiling point equal to or greater than 200 degrees C, and a melting point equal to or less than -30 degrees C. Any non-aqueous solvent that meets that combination of physical properties may be used. Examples of such propylene carbonate ( vapor pressure of 0.13 at 20 degrees C, boiling point of 241 degrees C and melting point of - 55 degrees C); gamma-butyro lactone (vapor pressure of 1.5 at 20 degrees C, boiling point of 230 degrees C and melting point of -44 degrees C); and dipropyiene glycol (vapor pressure of 0.04 at 20 degrees C, boiling point of 220 degrees C and melting point of -78 degrees C). In addition, these electrolytes are non-corrosive to aluminum.

[0016] One embodiment is directed to aluminum electrolytic capacitor having a structure wherein an anode foil and a cathode foil are wound together or laminated with a Kraft paper separator as defined above placed between the wound foils. The anode foil is an etched foil consisting of a val ve action metal such as aluminum and has a chemical oxide film formed on that etched foil, and the cathode foil is an etched foil also made of a valve action metal such as aluminum. The capacitor is impregnated with the electrolyte solution as defined above, and is housed into a sealed tubular metal case made of aluminum.

[0017 Set forth below are some embodiments of the electrolytic capacitor.

[0018] Embodiment 1 : An electrolytic capacitor comprising an anode; a cathode; a Kraft paper separator that is either coated with a polymer coating or where some of the hetntcelluJose and cellulose of the Kraft paper has bee removed and. replaced by the polymer coating, said polymer having a Tg of less than 1.60 degrees C, a degradation tempera ture of greater than 200 degree C and a conductivity of 10 to 1000 Siemens per centimeter at 20 degrees C; and a non-aqueous liquid electrolyte, said electrolyte having a vapor pressure of less than 2 mm at 20 degrees C, a boiling point equal to or greater than 200 degrees C, and a melting point equal to or less than -30 degrees C.

[0019] Embodiment s: The electrolytic capacitor of Embodiment 1 wherein the anode, the cathode, a paper separator, and electrolytic are contained in a metal container.

[0020] Embodiment 3: The electrolytic capacitor of Embodiment 2 wherein metal container is an aluminum container.

[0021] Embodiment 4: The electrolytic capacitor of any of Embodiments I to 3 wherein the paper separator is Kraft paper coated with the polymer. [0022] Embodiment 5: The electrolytic capacitor any of Embodiments 1 to 4 wherein the polymer has a Tg of less than 150 degrees C, a degradation temperature of greater than 220 degree C and a conductivity of 20 to 500 Siemens per centimeter at 20 degrees C.

[0023] Embodiment 6: The electrolytic capacitor any of Embodiments 1 to 5 wherein the polymer has a Tg of les than 140 degrees C, a degradatio temperature of greater than 250 degree C and a conductivity of 30 to 500 Siemens per centimeter at 20 degrees C.

[0024] Embodiment 7; The electrolytic capacitor any of Embodiments 1 to 6 wherein the polymer is copolymer of poly (3,4-ethySene dioxythiophene) and poly(s£yrene sulfonate).

[0025] Embodiment 8: The electrolytic capacitor any of Embodiments 1 to 6 wherein the polymer is poly pyrrole.

[0026] Embodiment 9: The electrolytic capacitor any of Embodiments i to 8 wherein the electrolyte has a vapor pressure of less than 1.5 mm at 20 degrees C, a boiling point equal to or greater than 220 degrees C, and a melting point equal to or less than -40 degrees C.

[0027] Embodiment 10: The electrolytic capacito any of Embodiments I to 9 wherein the electrolyte is propylene carbonate.

[0028] Embodiment I ! : The electrolytic capacitor any of Embodiments 1 to 9 wherein the electrolyte Is dipropylene glycol.

[0029] Embodiment 12: The electrolytic capacitor any of Embodiments 1 to 9 wherein the electrolyte is ganima-butyro lactone.

[0030] Embodiment 13: The electrolytic capacitor any of Embodiments 1 to 12 wherein the polymer additionally contains at least one carbon powder, at least one metal powder at least one metal oxide powder or mixtures thereof.

[0031] All ranges disc losed herein are inclusi ve of the endpotnts, and die endpoims are independently combinabl with each other (e.g., ranges of "up to 25 wt.%, or, more specifically, 5 wt.% to 20 wt.%", is inclusive of the endpoints and all intermediate values of the ranges of "5 wt.% to 25 wt.%," etc.). "Combination" is inclusive of blends., mixtures, alloys, reaction products, and the like. Furthermore, the terms "first," "second," and the like, herein do not denote any order, quantity, or importance, but rather are used to denote one element from another. The terms "a" and "an" and "the" herein do not denote a limitation of quantity, and are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The suffix "($)" as used herein is intended to incl ude both die singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the filni(s) includes one or more films). Reference throughout the specification to "one embodiment", "another embodiment", "an embodiment", and so forth, means that a particular element (e.g., feature., structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the variou embodiments.

[0032] While the invention has been described in detail in connection: with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to mcorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention.

Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described

embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.