HK1168192B - Planar anode for use in a wet electrolytic capacitor - Google Patents

Description

Flat plate type anode for wet electrolytic capacitor

Technical Field

The invention relates to a flat plate type anode, in particular to a flat plate type anode for a wet electrolytic capacitor.

Background

High voltage electrolytic capacitors are often used as accumulators in many applications, including implantable medical devices. These capacitors are required to have a higher energy density because of the need to minimize the overall size of the implantable device. This is particularly true in implantable cardioverter-defibrillator ("ICD"), also referred to as an implantable defibrillator, because the high voltage capacitor used to deliver the defibrillation pulse occupies one third of the volume of the ICD. ICDs typically employ two electrolytic capacitors in series to achieve the high voltages required for shock delivery.

In order to increase the energy density of the capacitor and thereby reduce its size, one approach is to minimize the volume occupied by the insulating separator paper sheets and the cathode and to maximize the number of anodes. This may be achieved by using a multi-anode stack configuration. The multi-anode stack configuration requires fewer cathode and insulating separator paper sheets than a single anode configuration, thereby allowing for a reduced instrument size. A multi-anode stack includes a plurality of cells including a cathode, an insulating separator sheet of paper, two or more anodes, an insulating separator sheet of paper, and a cathode, with adjacent cells sharing the cathode therebetween. However, in order to charge and discharge the inner anode (furthest from the cathode), charge must flow through the outer anode. With a typical anode, the path through the anode is quite tortuous, resulting in a high equivalent series resistance ("ESR") for the multi-anode structure. Thus, the more anodes that are put together in an anode stack, the higher the ESR. Another way to reduce the size of the instrument is to increase the operating voltage of the capacitor, so that it is possible to use only one electrolytic capacitor. However, the only challenge facing increasing the operating voltage of a capacitor is that high voltages are typically associated with low surface areas, while watchesThe low area reduces the capacitance and also reduces the energy ( ²E = 0.5*CV）。

Regardless of the method specifically adopted, a metal foil (e.g., aluminum foil) is often used in an electrolytic capacitor because of its small size. Since the electrostatic capacitance of the capacitor is proportional to the electrode area thereof, the surface of the metal foil needs to be roughened or chemically converted before the dielectric film is formed to increase the effective area thereof. This roughening step of the metal foil surface is called etching. Etching is generally carried out by a method of immersing in a hydrochloric acid solution (chemical etching) or a method of electrolysis in an aqueous hydrochloric acid solution (electrochemical etching). The capacitance of the electrolytic capacitor depends on the coarsening degree (surface area) of the anode foil and the thickness and dielectric constant of the oxide film. Attempts have been made to use porous sintered pellets (pellets) in wet electrolytic capacitors due to the limited surface area that can be provided by etching the metal foil. For example, tantalum pellets can be formed by pressing a powder under high pressure and sintering at high temperature to form a very strong, dense and highly porous sponge-like structure. The porous structure of the resulting tantalum pellet provides a large internal surface area. However, despite its high surface area, the anodic pellets still have a high ESR and the capacitance is highly sensitive to frequency, especially under the high pressure conditions typically encountered with medical devices. Furthermore, the size of the pellets is usually larger than the anode foil, and it is therefore difficult to use these pellets in applications requiring high volumetric efficiency.

Accordingly, there is a need for an improved electrolytic capacitor for use in implantable medical devices, such as defibrillators.

Disclosure of Invention

In one embodiment of the present invention, a planar anode for a high voltage wet electrolytic capacitor is disclosed. The thickness of the anode is about 5 mm or less and the ratio of the length of the anode to the thickness of the anode is about 5 to about 50. The anode comprises an anodized pellet formed from a pressed sintered powder, wherein the powder comprises a plurality of plate-like particles (particles) having an aspect ratio (aspect ratio) of about 2 to about 100.

In another embodiment of the invention, a method of forming a planar anode for a high voltage wet electrolytic capacitor is disclosed. The method includes pressing a valve metal powder in a direction perpendicular to a longitudinal axis of an anode lead embedded in the powder, wherein the powder comprises a plurality of longitudinally oriented platelet particles. The pressed powder is sintered at a temperature of about 1300 c to about 2000 c to form pellets. The pellets are anodized to form a dielectric layer, wherein the anodized pellets have a thickness of about 5 mm or less.

In another embodiment of the invention, a wet electrolytic capacitor is disclosed that includes a planar anode having a thickness of about 5 mm or less. The ratio of the length of the anode to the thickness of the anode is from about 5 to about 50. The anode comprises an anodized pellet formed from a pressed sintered powder. The capacitor also includes a cathode comprising a metal substrate coated with an electrochemically active material and an aqueous electrolyte connected to the anode and the cathode. The pH of the electrolyte is about 4.5 to about 7.0. The ratio of the voltage at which the capacitor can be charged to the voltage at which the dielectric layer is formed is greater than about 1.

Other features and aspects of the present invention will be described in more detail below.

Drawings

A full and enabling description of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the detailed description, which follows, when taken in conjunction with the accompanying figures and wherein like reference numerals identify identical or similar elements. Wherein:

FIG. 1 is a perspective view of one embodiment of a wet electrolytic capacitor of the present invention;

FIG. 2 is a top view of one embodiment of an anode used in the capacitor of the present invention;

FIG. 3 is a front view of the anode of FIG. 2;

FIG. 4 is a perspective view illustrating assembly of the anode with housing components shown in FIG. 2 to form the capacitor shown in FIG. 1;

FIG. 5 is a schematic illustration of one embodiment of pressing tantalum powder in tablet form into pellets, wherein FIG. 5A illustrates the die prior to compaction and FIG. 5B illustrates the die after compaction;

FIG. 6 shows the specific charge for forming anodes at different sintering temperatures in example 1;

FIG. 7 shows the specific charge for anode formation at different formation voltages in example 1;

FIG. 8 shows the energy densities for anode formation at different sintering temperatures and formation voltages in example 1;

FIG. 9 shows the capacitance of anodes formed at different sintering temperatures and formation voltages in example 2;

FIG. 10 shows the leakage current (at 300 seconds) for anodes formed at different sintering temperatures and formation voltages in example 2; and

fig. 11 shows the leakage current (at 60 seconds) for anodes formed at different sintering temperatures and formation voltages in example 2.

Detailed Description

To those skilled in the art, the following description is provided as exemplary embodiments of the invention and not as a limitation on the scope of the invention, which is embodied in the exemplary constructions.

The present invention relates generally to a relatively thin planar anode for a wet electrolytic capacitor. By combining specific materials and processing techniques, the inventors have surprisingly found that the resulting anode has a high volumetric efficiency and is still capable of operating at high voltages and capacitances, resulting in a capacitor with a high energy density. More specifically, the anode is a pressed pellet formed of a conductive powder comprising a plurality of particles (including an agglomerate of particles). The particles are relatively flat or plate-like sheet-like structures. The inventors have found that this particle morphology can optimize packing density, thereby reducing anode thickness and increasing volumetric efficiency. Such particles may also provide a shorter transport route between the outer and inner surfaces of the anode and provide a highly continuous and dense lead-to-anode connection with higher electrical conductivity. In addition, such particles also contribute to increase the specific charge of the anode when anodic oxidation is performed under higher voltage conditions, thereby increasing the energy density. Such particles may also increase the breakdown voltage (the voltage at which the capacitor fails) and help to reduce the equivalent series resistance ("ESR").

Various embodiments of the capacitor of the present invention will be described in more detail below.

I. Anode

The anode particles are typically formed from a valve metal composition. The specific charge of the composition may vary, for example, from about 2,000 μ F V/g to about 80,000 mF V/g, in some embodiments from about 5,000 μ F V/g to about 40,000 μ F V/g or higher, in some embodiments, from about 10,000 to about 20,000 mF V/g. The valve metal composition comprises a valve metal (i.e., a metal capable of oxidation) or valve metal-based compound such as tantalum, niobium, aluminum, hafnium, titanium and alloys thereof, oxides thereof, nitrides thereof, and the like. For example, the valve metal composition may comprise a conductive oxide of niobium, such as an oxide of niobium having a niobium to oxygen atomic ratio of 1:1.0 ± 1.0, in some embodiments a niobium to oxygen atomic ratio of 1:1.0 ± 0.3, in some embodiments a niobium to oxygen atomic ratio of 1:1.0 ± 0.1, and in some embodiments a niobium to oxygen atomic ratio of 1:1.0 ± 0.05. For example, the oxide of niobium may be NbO_0.7、NbO_1.0、NbO_1.1And NbO₂. The valve metalExamples of oxides are described in U.S. patent No. 6,322,912 to Fife, 6,391,275 to Fife et al, 6,416,730 to Fife et al, 6,527,937 to Fife, 6,576,099 to Kimmel et al, 6,592,740 to Fife et al, 6,639,787 to Kimmel et al, 7,220,397 to Kimmel et al, 2005/0019581 to Schnitter, 2005/0103638 to Schnitter et al, and 2005/0013765 to Thomas et al, which are incorporated herein by reference in their entireties.

The valve metal composition may be formed using various techniques familiar to those skilled in the art. For example, precursor tantalum powders may be reduced to tantalum salts (e.g., potassium fluotantalate (K)) by reducing agents (e.g., hydrogen, sodium, potassium, magnesium, calcium, and the like)₂TaF₇Sodium fluorotantalate (Na)₂TaF₇) Tantalum pentachloride (TaCl)₅) Etc.). The precursor powder may initially comprise granular particles which may then be deformed or flattened by known methods to form a more preferred sheet-like structure. The method for reducing the thickness of the particles comprises subjecting the powder to a mechanical milling process to finely mill the particles. Any milling technique may be employed in the present invention to achieve the desired particle characteristics. For example, the powder may be dispersed in a fluid medium (e.g., ethanol, methanol, fluorinated fluids, etc.) to form a slurry. The slurry is then mixed with a grinding media (e.g., metal balls, such as tantalum) in a mill. The amount of grinding media typically varies depending on the size of the mill, such as from about 100 to about 2000, and in some embodiments, from about 600 to about 1000. The starting powder, fluid medium and grinding medium may be mixed in any proportion. For example, the ratio of starting valve metal powder to grinding media is about 1:5 to about 1: 50. Also, the ratio of the volume of the fluid medium to the combined volume of the initial valve metal powder is about 0.5:1 to about 3:1, and in some embodiments, about 0.5:1 to about2:1, and in some embodiments, from about 0.5:1 to about 1:1. Some examples of mills used in the present invention are described in U.S. Pat. Nos. 5,522,558, 5,232,169, 6,126,097, and 6,145,765, which are incorporated herein by reference in their entirety.

The grinding time may be any predetermined time required to achieve the target specific surface area. For example, the milling time may be from about 30 minutes to about 40 hours, in some embodiments, from about 1 hour to about 20 hours, and in some embodiments, from about 5 hours to about 15 hours. The milling can be carried out at any desired temperature, including room temperature or elevated temperature. After milling, the fluid medium may be separated or removed, for example, by air drying, heating, filtration, evaporation, and the like. For example, the flakes may optionally be subjected to one or more acid leachings to remove metal impurities. Such acid leaching steps are known in the art and any acid may be employed, for example, inorganic acids (e.g., hydrochloric acid, hydrobromic acid, hydrofluoric acid, phosphoric acid, sulfuric acid, nitric acid, and the like), organic acids (e.g., citric acid, tartaric acid, formic acid, oxalic acid, benzoic acid, malonic acid, succinic acid, adipic acid, phthalic acid, and the like), and the like.

Although not required, the powder may be agglomerated using any technique known in the art. These powders may be agglomerated by various means, such as by subjecting them to one or more heat treatments at temperatures of about 700 ℃ to about 1400 ℃, in some embodiments, about 750 ℃ to about 1200 ℃, and in some embodiments, about 800 ℃ to about 1100 ℃. The heat treatment may be performed in an inert atmosphere or a reducing atmosphere. For example, the heat treatment may be performed in an atmosphere containing hydrogen or a hydrogen-releasing compound (e.g., ammonium chloride, calcium hydride, magnesium hydride, etc.) to partially sinter the powder and reduce the impurity content (e.g., fluorine). If desired, agglomeration may also be carried out in the presence of a getter material (magnesium), such as magnesium. After heat treatment, the particles can be passivated by gradual gas filling. Other suitable agglomeration methods are described in U.S. Pat. No. 6,576,038 to Rao, U.S. Pat. No. 6,238,456 to Wolf et al, 5,954,856 to Pathare et al, 5,082,491 to Rerat et al, 4,555,268 to Getz, 4,483,819 to Albrecht, 4,441,927 to Getz et al, and 4,017,302 to Bates et al. The above U.S. patents are incorporated by reference in their entirety.

Other conventional treatments may also be employed in the present invention to improve the properties of the powder. For example, in certain embodiments, the powder may be doped with a sintering retardant in the presence of a dopant, such as an aqueous acid (e.g., phosphoric acid). The amount of dopant depends in part on the surface area of the powder, but generally does not exceed about 200 parts per million ("ppm"). The dopant may be added before, during and/or after any heat treatment step. The powder may also be subjected to one or more deoxidation treatments to improve the ductility of the anode and reduce leakage current. For example, the powder may be exposed to a getter material (e.g., magnesium), as described in U.S. patent No. 4,960,471, which is incorporated by reference herein in its entirety. The amount of getter material is from about 2% to about 6% by weight. The temperature at which deoxygenation is carried out may vary, but is generally from about 700 ℃ to about 1600 ℃, in some embodiments from about 750 ℃ to about 1200 ℃, and in some embodiments, from about 800 ℃ to about 1000 ℃. The total time of the deoxygenation treatment is from about 20 minutes to about 3 hours. The deoxidation is also preferably carried out under an inert atmosphere (e.g. argon). After the deoxidation process is completed, the magnesium or other getter material typically evaporates and deposits form on the cold furnace walls. However, to ensure the scavenging material is removed, the powder may be subjected to one or more acid leaching steps, such as with nitric acid, hydrofluoric acid, and the like. In addition, other suitable methods of forming flakes are described, for example, in U.S. Pat. Nos. 6,348,113, 5,580,367, 5,580,516, 5,448,447, 5,261,942, 5,242,481, 5,211,741, 4,940,490, and 4,441,927, which are incorporated herein by reference in their entirety.

Regardless of the particular method employed, the resulting powder has certain characteristics that enhance its ability to form capacitor anodesAnd (4) point. For example, when employed, the plate-like particles are generally flat. Flatness is generally defined by the "aspect ratio," i.e., the average particle diameter or width of a particle divided by the average thickness ("D/T"). For example, the aspect ratio of the particles is from about 2 to about 100, in some embodiments from about 3 to about 50, and in some embodiments, from about 4 to about 30. The specific surface area of the particles is about 0.5 to about 10.0m²(iv) g, in some embodiments, from about 0.7 to about 5.0 m²(iv) g, in some embodiments, from about 1.0 to about 4.0 m²(ii) in terms of/g. The term "specific surface area" refers to the surface area as measured by physical gas adsorption (B.E.T.) published by Brunauer, Emmet and Teller, journal of the American chemical society, Vol.60, 1938, with the adsorbed gas being nitrogen. Monosorb available from QUANTACHROME Corporation of Syoset, N.Y.^®The specific surface area analyzer performs the test. The analyzer determines the amount of adsorbed nitrogen gas adsorbed on the surface of the solid by sensing changes in the thermal conductivity of a flowing mixture of the adsorbent and an inert carrier gas, such as helium.

The bulk density (also known as Scott (Scott) density) is typically about 0.1 to about 2 grams per cubic centimeter (g/cm)³) And in some embodiments, about 0.2g/cm³To about 1.5 g/cm³And in some embodiments, about 0.4 g/cm³To about 1g/cm³. "bulk density" can be measured using a flow meter funnel and a density cup. More specifically, the sheet sample can be poured into the density cup through a funnel until the sample completely fills the density cup and overflows around the density cup, and then, without shaking, the sample is scraped off with a spatula so that the sample is flush with the rim of the density cup. After leveling, the sample in the density cup was transferred to a balance and the density value was determined to an accuracy of 0.1 g. Such instruments may be available from alcan aluminum corp. of Elizabeth, illinzabeth, new jersey. The particles have an average particle size (e.g., width) of about 0.1 to about 100 microns, in some embodiments about 0.5 to about 70 microns, and in some embodiments, about 1 to about 50 microns.

To facilitate the formation of the anode, certain other components may also be included in the powder. For example, the powder may optionally be mixed with a binder (binder) and/or a lubricant to ensure that the pellets are sufficiently bonded to each other when pressed into an anode body. Suitable binders include, for example, polyvinyl butyral; polyvinyl acetate; polyvinyl alcohol; polyvinylpyrrolidone; cellulose polymers such as carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose and methyl hydroxyethyl cellulose; atactic polypropylene; polyethylene; polyethylene glycol (e.g., Carbowax of dow chemical); polystyrene, poly (butadiene/styrene); polyamides, polyimides and polyacrylamides, high molecular weight polyethers; copolymers of ethylene oxide and propylene oxide; fluoropolymers such as polytetrafluoroethylene, polyvinylidene fluoride, and fluoro-olefin copolymers; acrylic polymers such as sodium polyacrylate, poly (lower alkyl acrylates), poly (lower alkyl methacrylates), and copolymers of lower alkyl acrylates and methacrylates; fatty acids and waxes such as stearic and other soap fatty acids, vegetable waxes, microcrystalline waxes (purified paraffin wax), and the like. The binder is soluble and dispersible in the solvent. Examples of the solvent include water, ethanol and the like. When used, the binder and/or lubricant is present in an amount of about 0.1 to about 8 weight percent based on the total weight. However, it should be understood that the present invention does not require the use of a binder and/or lubricant.

The resulting powder is then compacted to form pellets using any conventional powder compaction equipment. For example, the press die may be a single station press comprising one die and one or more punches. Alternatively, an anvil die using only a single die and a single lower punch may also be used. There are several basic types of single station presses, such as cam presses, toggle presses/toggle presses and eccentric presses/crank presses with different production capacities, which may be, for example, single-action, double-action, floating-bed presses, movable-bed presses, opposed-ram presses, screw presses, impact presses, hot-pressing presses, impression presses or finishing presses. The powder may be compacted around the anode lead. The leads are typically made of any conductive material, such as tantalum, niobium, aluminum, hafnium, titanium, and the like, and their conductive oxides and/or nitrides.

For example, referring to FIG. 5, one exemplary embodiment of compacting the powder into a flat anode shape using a press die 110 will now be described in more detail. In this particular embodiment, the die 110 includes a die 119 having a first die portion 121 and a second die portion 123. Of course, mold 119 may also be formed from a single part rather than multiple parts. However, in FIG. 5, the first mold portion 121 defines inner walls 121a and 121b and the second mold portion defines inner walls 123a and 123 b. The inner walls 121a and 123a are substantially perpendicular to the inner walls 121b and 123b, respectively. First mold portion 121 and second mold portion 123 also define opposing surfaces 115 and 117. In use, the surfaces 115 and 117 are positioned adjacent to each other such that the inner walls 121b and 123b are substantially aligned to form the mold cavity 120 having a flat D-shaped configuration. It should be noted that although a single mold cavity is shown in fig. 5, multiple mold cavities may be used. As shown in fig. 5A, a quantity of powder 126 is added to the mold cavity 120 with the anode lead 113 embedded in the powder. Although the anode lead 113 is shown as a cylindrical shape in the present embodiment, it should be understood that the anode lead 113 may take any other shape. In addition, the anode lead 113 may be pressed and/or sintered after being connected (e.g., welded) to the anode.

In any event, as shown in FIG. 5B, after filling, the mold cavity 120 is closed by the upper punch 122. It should be understood that other punches (e.g., lower punch) may also be used. The direction of pressure application can improve the performance of the resulting capacitor. For example, as shown by the directional arrows in fig. 5B, the direction of the force applied by punch 122 is substantially perpendicular to the longitudinal axis "a" of lead 113. That is, the force applied is about 60 to about 120, preferably about 90, relative to the "A" axis. In this manner, the lead 113 is embedded in the powder 126 so that it may slide into the space between adjacent flakes. The vertical pressing technique described above results in pellets containing particles (e.g., flakes) oriented generally toward the longitudinal axis of the wire 113 (see also, the "y" direction in fig. 2). 3). This forces the particles into intimate contact with the wire, forming a strong wire-powder connection.

After compaction, the pellets may be heated at a temperature (e.g., about 150 ℃ to about 500 ℃) under vacuum for several minutes to remove any binder/lubricant. Alternatively, the beads may be contacted with an aqueous solution to remove the binder/lubricant, as described in U.S. patent No. 6,197,252 to Bishop et al, which is incorporated herein by reference in its entirety.

The pellets are then sintered to form a porous monolith. The inventors have found that certain sintering conditions lead to an increase in the specific charge of the resulting anode and increase the breakdown voltage of the resulting capacitor. More specifically, the pellets are typically sintered at a temperature of about 1300 ℃ to about 2000 ℃, in some embodiments about 1400 ℃ to about 1800 ℃, in some embodiments about 1500 ℃ to about 1700 ℃, for a time period of about 5 minutes to about 100 minutes, and in some embodiments, about 30 minutes to about 60 minutes. If desired, sintering may be carried out in an atmosphere that limits the transfer of oxygen atoms to the anode. For example, sintering may be performed in a reducing atmosphere, such as in vacuum, inert gas, hydrogen, and the like. The pressure of the reducing atmosphere is about 10 torr to about 2000 torr, in some embodiments, about 100 torr to about 1000 torr, and in some embodiments, about 100 torr to about 930 torr. Mixtures of hydrogen and other gases (e.g., argon or nitrogen) may also be used. When used, the platelet particles are better able to withstand the high sintering temperatures and longer sintering times typically employed in forming anodes, and result in porous sintered anode bodies having lower shrinkage and larger specific surface areas.

After sintering, the pellets shrink due to the growth of metallurgical bonds (metallurgical bonds) between the particles (e.g., sheets). Since shrinkage generally increases the density of the pellets, the desired target density can still be achieved with a lower compaction density ("green"). For example, the target density of the sintered pellets is typically about 7.5 to about 8 g/cm³. Due to the shrinkage phenomenon, the pellets do not need to be pressed to such a high density, but to a density of less than about 7.5g/cm³And in some embodiments, from about 6 to about 7.5g/cm³. Furthermore, the ability to use lower green densities can result in significant cost savings and improved machining efficiency. It should be understood that the compaction density of the entire pellet is not always uniform, particularly when compacted in a direction perpendicular to the longitudinal axis of the wire. In other words, the material amount is divided by the volume of the pressed pellet to obtain the pressed density. The volume of the pellet is proportional to the pressed length perpendicular to the longitudinal axis of the wire. The density is inversely proportional to the press length. Thus, in practice the pressed length is shorter near the leads than elsewhere in the pellet. Also, the pressing density is greater in the vicinity of the lead. For example, the pressed density of the pellets in the vicinity of the leads is typically at least about 10% higher, and in some embodiments, at least about 20% higher, than the pressed density of the pellets elsewhere.

Due to the thin nature of the plate-like anode, it is sometimes necessary to control the manner in which the anode lead is inserted to limit the amount of pressure applied during manufacture which can cause the lead to pull out of the anode. For example, in one embodiment, at least a portion of the lead within the anode is bent at an angle with respect to the longitudinal axis of the lead. This "bowing" reduces the ease with which the lead can be pulled out in the longitudinal direction after anode pressing and sintering. For example, referring to fig. 2-3, one embodiment of an anode 200 including an anode lead 220 is shown. The anode lead includes a first portion 221 that extends in a longitudinal direction (the "y" direction) from the anode 200. Within the anode body, lead 220 also includes a second portion 222 bent at an "α" angle relative to first portion 221. Angle "a" is typically about 40 ° to about 120 °, in some embodiments, about 60 ° to about 110 °, and in some embodiments, about 80 ° to about 100 ° (e.g., about 90 °). Such a curved structure can be implemented in various ways. For example, in one embodiment, the die is partially filled with flakes and then a "pre-bent" anode lead is inserted into the die. The compression mold is then filled with powder and the entire assembly is pressed into pellets.

In addition to its geometry, the extent to which the anode lead is inserted into the anode can be controlled to help minimize the likelihood of being pulled out during manufacture. That is, the deeper the lead is inserted, the less easily the lead is pulled out of the anode. Of course, too deep a lead insertion can alter the uniformity of the pressed density, affecting the electrical performance of the resulting anode. In this regard, the inventors have discovered that the ratio of the length of the anode of the inserted lead to the length of the entire anode is generally about 0.1 to about 0.6, and in some embodiments, about 0.2 to about 0.5. For example, in FIG. 2, the length "L₁"denotes the length of the anode 200 into which the anode lead is inserted, and" L "denotes the entire length of the anode 200. In some cases, the length "L" of the anode 200 is about 1 mm to about 80 mm, in some embodiments, about 10 mm to about 60 mm, and in some embodiments, about 20 mm to about 50 mm. Likewise, length "L₁"has a length of about 1 mm to about 40 mm, in some embodiments about 2 mm to about 20 mm, and in some embodiments, about 5 mm to about 15 mm. The width "W" of the anode is about 0.05 mm to about 40 mm, in some embodiments about 0.5 mm to about 25 mm, and in some embodiments, about 2 mm to about 10 mm.

As described above, the thickness of the plate anode is small to improve the electrical performance and volumetric efficiency of the resulting capacitor. For example, in fig. 3, the thickness of anode 200 is represented by dimension "H". Generally, the thickness of the anode is about 5 mm or less, in some embodiments, about 0.05 mm to about 4 mm, and in some embodiments, about 0.1 to about 3.5 mm. The ratio of anode length to anode thickness is about 5 to about 50, in some embodiments about 6 to about 30, and in some embodiments, about 7 to about 20. Although shown in fig. 2 as being "D" shaped, it should be understood that the anode may be any desired shape, such as square, rectangular, circular, oval, triangular, etc. Polygons with more than four (4) sides (e.g., hexagons, octagons, heptagons, pentagons, etc.) are particularly desirable because of their relatively large surface area.

The anode may also include a dielectric layer formed by anodizing (anodizing) the sintered anode such that the dielectric layer is formed on and/or within the anode. For example, a tantalum (Ta) anode may be anodized to tantalum pentoxide (Ta)₂O₅). Generally, anodization begins by applying a solution to the anode, such as by dipping the anode into an electrolyte. Aqueous solvents (e.g., water) and/or non-aqueous solvents (e.g., ethylene glycol) may be employed. In order to enhance the ion conductivity, a compound that can be dissociated in a solvent to form ions may be used. Examples of such compounds include, for example, acids, as described in the electrolyte section below. For example, the acid (e.g., phosphoric acid) may be present in the anodizing solution in an amount of about 0.01wt% to about 5 wt%, in some embodiments about 0.05 wt% to about 0.8 wt%, and in some embodiments, about 0.1wt% to about 0.5 wt%. Mixtures of acids may also be employed if desired.

A current is passed through the anodizing solution to form a dielectric layer. The forming voltage value determines the thickness of the dielectric layer. For example, the power supply is initially established in a constant current mode until the desired voltage is reached. The power supply can then be switched to a constant potential mode to ensure that the desired dielectric layer thickness is formed over the entire surface of the anode. Of course, other methods known to those skilled in the art, such as pulsed or step potentiostatic methods, may be used. The voltage of anodization is typically high to make a capacitor capable of operating in a higher voltage range. That is, the voltage is typically about 100 volts to about 300 volts, in some embodiments about 150 volts to about 250 volts, and in some embodiments, about 170 volts to about 220 volts. The temperature of the anodizing solution is about 10 c to about 200 c, in some embodiments about 20 c to about 60 c, and in some embodiments, about 30 c to about 40 c (e.g., 37 c). The resulting dielectric layer may be formed on the surface of the anode or within the anode hole. When used, the specific nature of the powder may cause the resulting anode to have a higher specific charge, even at the higher formation voltages employed in the present invention. For example, within the ranges shown above, the specific charge of the anode may still be up to about 2,000 μ F V/g to about 20,000 mF V/g, in some embodiments, about 5,000 μ F V/g to 15,000 μ F V/g or higher, and in some embodiments, about 8,000-.

II. cathode

In addition to the anode, a cathode, which can be constructed using any technique, is also used in the capacitor. In one embodiment, the cathode comprises a metal substrate, which may comprise any metal, such as tantalum, niobium, aluminum, nickel, hafnium, titanium, copper, silver, steel (e.g., stainless steel), alloys thereof (e.g., conductive oxides), composites thereof (e.g., metal coated with conductive oxides), and the like. Titanium and tantalum and their alloys are particularly suitable for use in the present invention. The geometry of the substrate may generally vary, as is well known to those skilled in the art, and may be in the form of, for example, containers, cans, foils, sheets, screens, and nets. In one embodiment, for example, the metal substrate forms a generally cylindrical housing. However, it should be understood that the present invention may take any geometric configuration, such as D-shaped, rectangular, triangular, prismatic, etc. The housing optionally includes a cover over the anode and electrolyte, which may be made of the same or different material as the housing.

The substrate may be roughened to increase its surface area and to increase the extent to which the electrochemically active material can adhere thereto. For example, in one embodiment, the metal substrate surface is chemically etched, such as by applying a solution of a corrosive substance (e.g., hydrochloric acid) to the surface. The surface may also be electrochemically etched, such as by applying a voltage to a solution of corrosive material, which is then electrolyzed. The voltage is raised sufficiently high to produce a "spark" at the substrate surface, which is believed to produce a local surface temperature high enough to corrode the substrate. This method is described in greater detail in Dreisig et al, U.S. patent application publication No. 2010/0142124, which is incorporated herein by reference in its entirety. In addition to chemical or electrochemical roughening methods, mechanical roughening may also be employed. For example, in one embodiment, the surface of the metal substrate is grit blasted by blasting a blast of abrasive material (e.g., sand) against at least a portion of the substrate.

The cathode substrate may also be coated with an electrochemically active material to inhibit corrosion and also act as a thermal barrier layer when the voltage is increased. Generally, any known electrochemically active material may be used. One suitable material is a conductive polymer, such as those pi-conjugated and electrically conductive after oxidation or reduction (e.g., conductivity of at least about 1 μ S-cm after oxidation)^-1) The conductive polymer of (1). Examples of such pi-conjugated conductive polymers include, for example, polyheterocycles (e.g., polypyrrole, polythiophene, polyaniline, etc.); polyacetylene; poly-p-phenylene; polyphenolates, and the like.

Substituted polythiophenes are particularly suitable for use as the electrochemically active material of the present invention. Without being bound by theory, it is believed that charging the capacitor to a higher voltage (e.g., beyond the formation voltage) will force ions of the electrolyte into the coating comprising such substituted polythiophenes. This causes the conductive polymer to "swell" (swell) and retain ions near the surface, thereby increasing the charge density. Since the polymer is generally amorphous and non-crystalline, it may also dissipate and/or absorb heat associated with high voltages. We also believe that, upon discharge, the substituted polythiophene "relaxes" allowing ions in the electrolyte to leave the coating. By this swelling and relaxation mechanism, the charge density near the metal substrate can be increased without the need for chemical reaction with the electrolyte. Thus, mechanical strength and good electrical properties are provided without the need for conventional conductive coatings, such as those prepared using activated carbon or metal oxides (e.g., ruthenium oxide). In fact, excellent results can be obtained with the coating as the main material of the metal substrate. That is, the coating comprises at least about 90 wt% of the material on the metal substrate, in some embodiments at least about 92wt%, and in some embodiments, at least about 95 wt%. However, it should be understood that other conductive coatings may be used in some embodiments of the invention.

In a particular embodiment, the substituted polythiophene has a repeating unit of formula (i), formula (ii) or formula (i) and formula (ii):

wherein the content of the first and second substances,

a is optional C₁- C₅Olefinic substituents (e.g., methylene, vinyl, n-propenyl, n-butenyl, n-pentenyl, and the like);

r is linear or branched optional C₁- C₁₈Alkyl substituents (e.g., methyl, ethyl, n-or isopropyl, n-butyl, isobutyl, sec-or tert-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1-ethylpropyl, 1-dimethylpropyl, 1, 2-dimethylpropyl, 2-dimethylpropyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-hexadecyl, n-octadecyl, etc.); optionally C₅- C₁₂Cycloalkyl substituents (e.g., cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, etc.); optionally C₆- C₁₄Aryl substituents (e.g., phenyl, naphthyl, and the like); optionally C₇-C₁₈Aralkyl substituents (e.g., benzyl, o, m, p-tolyl, 2,3-, 2,4-, 2,5-, 2,6, 3,4-, 3, 5-xylyl, trimethylphenyl, and the like); optionally C₁-C₄A hydroxyalkyl substituent or a hydroxy substituent; and

x is an integer from 0 to 8, in some embodiments from 0 to 2, and in some embodiments, x is 0. Examples of substituents for "a" or "R" include, for example, alkyl, cycloalkyl, aryl, aralkyl, alkoxy, halo, ether, thioether, disulfide, sulfoxide, sulfone, sulfonate, amino, aldehyde, ketone, carboxylate, carboxylic acid, carbonate, carboxylate, cyano, alkylsilane, and alkoxysilyl, carboxamide groups and the like.

The total number of repeating units of formula (I) or formula (II) or formulae (I) and (II) is generally from 2 to 2000, and in some embodiments from 2 to 100.

Particularly suitable substituted polythiophene derivatives are those in which "A" is optionally C₂- C₃A derivative of an olefinic substituent and x is 0 or 1. In one embodiment, the substituted polythiophene is poly (3, 4-ethylenedioxythiophene) ("PEDT") having repeating units of formula (II) wherein "A" is CH₂-CH₂And "x" is 0. The monomers used to form such polymers may vary as desired. For example, particularly suitable monomers are substituted 3, 4-alkylenedioxythiophenes of the general formulae (III), (IV) or of the general formulae (III) and (IV):

wherein A, R and X are as defined above.

Examples of such monomers include, for example, optionally substituted 3, 4-vinyldioxythiophene. An example of a commercially suitable 3, 4-alkylenedioxythiophene is the product sold under the name Clevios M by H.C. Starck GmbH. Derivatives of these monomers, such as dimers or trimers of the above monomers, may also be employed. Higher molecular weight derivatives, such as tetramers, pentamers, etc. of the monomer precursors are suitable for use in the present invention. The derivatives may be composed of the same or different monomer units, and may be used in pure form as well as in a mixture with another derivative and/or monomer. The oxidized or reduced state of these monomer precursors may also be used.

As mentioned above, thiophene monomers can be oxidizedChemical polymerization is carried out in the presence of a catalyst. The oxidation catalyst typically comprises a transition metal cation, such as iron (III), copper (II), chromium (VI), cerium (IV), manganese (VII), ruthenium (III), and the like. A dopant may also be used to provide excess charge to the conducting polymer and stabilize the conductivity of the polymer. The dopant generally comprises an inorganic or organic anion, such as a sulfonate ion. In certain embodiments, the oxidation catalyst used in the precursor solution includes a cation (e.g., a transition metal) and an anion (e.g., a sulfonic acid) to provide both catalytic and doping functions. For example, the oxidation catalyst can be a transition metal salt comprising an iron (III) cation, such as an iron (III) halide (e.g., FeCl)₃) Or iron (III) salts of other mineral acids, e.g. Fe (ClO)₄）₃Or Fe₂（SO₄）₃And Iron (III) salts of organic acids and of inorganic acids containing organic radicals. Examples of iron (III) salts of inorganic acids having organic groups include, for example, C₁- C₂₀Iron (iii) salts of sulfuric monoesters of alkanols (e.g., iron (iii) lauryl sulfate). Also, examples of the iron (III) salt of an organic acid include, for example, C₁- C₂₀Iron (iii) alkylsulfonate (e.g., methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, butanesulfonic acid, or dodecylsulfonic acid); an iron (iii) salt of an aliphatic perfluorosulfonic acid (such as trifluoromethanesulfonic acid, perfluorobutanesulfonic acid, or perfluorooctanesulfonic acid); aliphatic C₁- C₂₀Iron (III) carboxylates (e.g., 2-ethylhexylcarboxylic acid); an iron (iii) salt of an aliphatic perfluorocarboxylic acid (such as trifluoroacetic acid or perfluorooctanoic acid); optionally is covered with C₁- C₂₀An iron (iii) salt of an alkyl-substituted aromatic sulfonic acid (e.g., benzenesulfonic acid, o-toluenesulfonic acid, p-toluenesulfonic acid, or dodecylbenzenesulfonic acid); and iron (iii) cycloalkanesulfonate salts (e.g., camphorsulfonic acid), and the like. Mixtures of the above-mentioned iron (III) salts can also be used. Iron (III) p-toluenesulfonate and iron (III) o-toluenesulfonate, and mixtures thereof, are particularly suitable for the present invention. A commercially suitable iron (III) o-toluenesulfonate salt is sold under the name Clevios C by H.C. Starck GmbHAnd (5) producing the product.

Various methods can be used to form the conductive coating on the metal substrate. In one embodiment, the oxidizing agent and the monomer precursor are either sequentially coated or coated together, allowing the polymerization reaction to proceed in situ on the part. Suitable coating techniques for forming a conductive polymer coating include screen printing, dipping, electrophoretic coating, spraying, and the like. For example, the monomer may be initially mixed with the oxidation catalyst to form a precursor solution. Once the mixture is formed, it can be coated onto a metal substrate and then allowed to polymerize, thereby forming a conductive coating on the surface. Alternatively, the oxidation catalyst and the monomer may be sequentially coated. For example, in one embodiment, the oxidation catalyst may be dissolved in an organic solvent (e.g., butanol) and then applied as an impregnation solution. Then, the substrate is dried to remove the solvent on the substrate. Then, the substrate is dipped into a solution containing the monomer.

Depending on the oxidant used and the desired reaction time, the polymerization is carried out at a temperature of from about-10 ℃ to about 250 ℃, and in some embodiments, from about 0 ℃ to about 200 ℃. Suitable polymerization processes, such as those described above, are described in more detail in U.S. patent publication No. 2008/232037 to Biler. In addition, other methods of applying such conductive coatings are described in U.S. Pat. No. 5,457,862 to Sakata et al, U.S. Pat. No. 5,729,428 to Sakata et al, and U.S. Pat. No. 5,812,367 to Kudoh et al, which are incorporated herein by reference in their entirety.

In addition to in situ coating, the conductive coating may also be applied to the substrate in the form of a dispersion of conductive polymer particles. Although the particle size may vary, it is generally desirable that the particle size be smaller to increase the surface area that adheres to the anode part. For example, the particles may have an average particle size of about 1 nm to about 500 nm, in some embodiments about 5 nm to about 400 nm, and in some embodiments, about 10 nm to about 300 nm. D of the particles₉₀Value (particle size less than or equal to D)₉₀Particles of valueVolume 90% of the total volume of all solid particles) is about 15 microns or less, in some embodiments about 10 microns or less, and in some embodiments, about 1 nm to about 8 microns. The diameter of the particles can be determined by well-known methods, such as ultracentrifugation, laser diffraction, and the like.

The independent counter ions are adopted to neutralize the positive charges carried by the substituted polythiophene, so that the conductive polymer can be promoted to form a particle shape. In some cases, the polymer may have positive and negative charges in the structural unit, the positive charge being on the backbone and the negative charge being selectively on an "R" substituent, such as a sulfonate or carboxylate group. The positive charge of the backbone may be partially or fully neutralized by the optional presence of anionic groups on the "R" substituent. Viewed as a whole, in these cases, the polythiophene can be cationic, neutral or even anionic. However, because the polythiophene backbone is positively charged, they are all considered cationic polythiophenes.

The counter ion may be a monomeric anion or a polymeric anion. The polymeric anion can be, for example, a polycarboxylic acid (e.g., polyacrylic acid, polymethacrylic acid, polymaleic acid, etc.) anion; polysulfonic acid (e.g., polystyrene sulfonic acid ("PSS"), polyvinylsulfonic acid, etc.) anions. The acid may also be a copolymer, such as copolymers of vinyl carboxylic and vinyl sulfonic acids with other polymerizable monomers, such as acrylates and styrene. Likewise, suitable monomeric anions include, for example, C₁- C₂₀Alkyl sulfonic acid (e.g., dodecyl sulfonic acid) anions; aliphatic perfluorosulfonic acid (such as trifluoromethanesulfonic acid, perfluorobutanesulfonic acid, or perfluorooctanesulfonic acid) anion; aliphatic C₁- C₂₀Carboxylic acid (2-ethylhexyl carboxylic acid) anion; aliphatic perfluorocarboxylic acid (such as trifluoroacetic acid or perfluorooctanoic acid) anions; optionally is covered with C₁- C₂₀Alkyl-substituted aromatic sulfonic acid (e.g., benzenesulfonic acid, o-toluenesulfonic acid, p-toluenesulfonic acid, or dodecylbenzenesulfonic acid) anion; cycloalkanesulfonic acids (e.g. camphorsulfonic acid or tetrafluoroborate, hexafluorophosphate, perchlorate, hexafluoroantimonate)Arsenate or hexachloroantimonate) anions, and the like. Particularly suitable counterions are polymeric anions such as polycarboxylic acids or polysulfonic acids (e.g., polystyrene sulfonic acid ("PSS")). The molecular weight of such polymeric anions is generally about 1,000-2,000,000, and in some embodiments, about 2,000-500,000.

When used, the weight ratio of such counterions to substituted polythiophenes in a given coating is generally from about 0.5:1 to about 50:1, in some embodiments from about 1:1 to about 30:1, and in some embodiments, from about 2:1 to about 20: 1. The weight of the substituted polythiophene mentioned in the above weight ratio refers to the weight of the monomer fraction used (assuming complete conversion of the monomer during polymerization).

The dispersion may also include one or more binders to further enhance the adhesion of the polymeric layer and also to improve the stability of the particles within the dispersion. The binder may be organic, such as polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl chloride, polyvinyl acetate, polyvinyl butyrate, polyacrylates, polyacrylamides, polymethacrylates, polymethacrylamides, polyacrylonitrile, styrene/acrylates, vinyl acetate/acrylates and ethylene/vinyl acetate copolymers, polybutadiene, polyisoprene, polystyrene, polyethers, polyesters, polycarbonates, polyurethanes, polyamides, polyimides, polysulfones, melamine-formaldehyde resins, epoxy resins, silicone resins or cellulose. Crosslinkers may also be employed to enhance the adhesive ability of the binder. Such crosslinking agents include, for example, melamine compounds, blocked isocyanates or functional silanes, such as 3-glycidoxypropyltrialkylsilane, tetraethoxysilane and tetraethoxysilane hydrolysates or crosslinkable polymers, such as polyurethanes, polyacrylates or polyolefins, and subsequent crosslinking. Other components, such as dispersing agents (e.g., water), surface active substances, etc., may also be included in the dispersion, as is well known in the art.

If desired, one or more of the coating steps described above may be repeated until the desired coating thickness is achieved. In some embodiments, only a relatively thin layer of coating is formed at a time. The total target thickness of the coating is generally dependent on the desired performance of the capacitor. Generally, the resulting conductive polymer coating has a thickness of about 0.2 microns ("μm") -50 μm, in some embodiments about 0.5 μm-20 μm, and in some embodiments about 1 μm-5 μm. It should be understood that the coating thickness need not be the same at all locations on the metal substrate. However, the average thickness of the coating on the substrate is generally within the above-described range.

The conductive polymer coating can optionally heal. Healing may be performed after each application of the conductive polymer layer or after the entire conductive polymer coating is applied. In some embodiments, the conductive polymer may be healed by immersing the metal substrate in an electrolyte solution, and then applying a constant voltage to the solution until the current is reduced to a preselected level. This healing can be accomplished in multiple steps, if desired. For example, the electrolyte solution may be a dilute solution of the monomer, catalyst and dopant in an alcohol solvent (e.g., ethanol). The coating may also be cleaned, if desired, to remove various by-products, excess reagents, etc.

III working electrolyte (workgelectrrolyte)

The capacitor of the present invention may also use a working electrolyte that is an electrochemically active material that provides a connecting path between the anode and cathode. The working electrolyte is typically in liquid form, such as a solution (e.g., aqueous or non-aqueous), dispersion, colloid, or the like. If desired, the anode is impregnated with an electrolyte (not shown) prior to placement inside the housing. The electrolyte can also be added to the capacitor at a later stage of production. Various suitable electrolytes are described in U.S. patent nos. 5,369,547 and 6,594,140 to Evans et al, which are incorporated herein by reference in their entirety.

In general, the electrolyte is ionically conductive, as measured using any known conductivity meter (e.g., Oakton Con Series 11) at a temperature of 25 deg.C, and has an ionic conductivity of about 0.5 to about 100 milliSiemens per centimeter ("mS/cm"), in some embodiments about 1 to about 80 mS/cm, in some embodiments about 5 mS/cm to about 60mS/cm, and in some embodiments, about 10 to about 40 mS/cm. It is believed that, in the ranges mentioned above, the ionic conductivity of the electrolyte extends the electric field into the electrolyte for a length (debye length) sufficient to cause significant charge separation. This extends the potential energy of the dielectric to the electrolyte, and therefore the resulting capacitor stores a higher potential energy than predicted from the dielectric thickness. In other words, the capacitor chargeable voltage exceeds the formation voltage of the dielectric. The ratio of the capacitor chargeable voltage to the formation voltage is, for example, greater than about 1, in some embodiments, from about 1 to about 2, and in some embodiments, from about 1.1 to about 1.5. For example, the capacitor chargeable voltage may be about 120 volts to about 320 volts, in some embodiments about 180 volts to about 280 volts, and in some embodiments, about 200 volts to about 240 volts.

By selecting a range of ionic compounds (e.g., acids, bases, salts, etc.) within a certain concentration range, the desired ionic conductivity can be achieved. In one particular embodiment, the weak organic acid salt is effective in achieving the desired electrolyte conductivity. The cation of the salt may comprise a monoatomic cation, such as an alkali metal (e.g., Li)⁺、Na⁺、K⁺、Rb⁺Or Cs⁺) Alkaline earth metals (e.g. Be)²⁺、Mg²⁺、Ca²⁺、Sr²⁺Or Ba²⁺) Transition metal (e.g., Ag)⁺、Fe²⁺、Fe³⁺Etc.) and polyatomic cations, such as NH₄ ⁺. Monovalent ammonium (NH)₄ ⁺) Sodium, sodium (Na)⁺) Potassium (K)⁺) Lithium (Li)⁺) Are particularly suitable cations for the present invention. The organic acid used to form the anion of the salt is a "weak acid" in the sense that it has a typical first acid dissociation constant (measured at 25 ℃.) ( _a1pK) From about 0 to about 11, and in some embodiments, isFrom about 1 to about 10, and in some embodiments, from about 2 to about 10. Any suitable weak organic acid may be used in the present invention, such as carboxylic acids, e.g., acrylic acid, methacrylic acid, malonic acid, succinic acid, salicylic acid, sulfosalicylic acid, adipic acid, maleic acid, malic acid, oleic acid, gallic acid, tartaric acids (e.g., d-tartaric acid, meso-tartaric acid, etc.), citric acid, formic acid, acetic acid, glycolic acid, oxalic acid, propionic acid, phthalic acid, isophthalic acid, glutaric acid, gluconic acid, lactic acid, aspartic acid, glutamic acid, itaconic acid, trifluoroacetic acid, barbituric acid, cinnamic acid, benzoic acid, 4-hydroxybenzoic acid, aminobenzoic acid, and the like; and mixtures of the above acids, and the like. Polybasic acids (e.g., dibasic, tribasic, etc.) are particularly desirable for use in salt formation, such as adipic acid (adipate) _a1pKThe content of the carbon dioxide is 4.43, _a2pKis 5.41), a-tartaric acid ( _a1pKIs 2.98 and _a2pK4.34), meso-tartaric acid ( _a1pKIs 3.22 and _a2pKis 4.82), oxalic acid: ( _a1pKIs 1.23 and _a2pKis 4.19), lactic acid: ( _a1pKThe content of the carbon black is 3.13, _a2pKis 4.76 and _a3pK6.40), etc.

The actual amount used may vary depending on the particular salt used, its solubility in the solvent used for the electrolyte, and the other components present, such weak organic acid salts being present in the electrolyte in an amount of about 0.1 to about 25 weight percent, in some embodiments about 0.2 to about 20 weight percent, in some embodiments about 0.3 to about 15 weight percent, and in some embodiments about 0.5 to about 5 weight percent.

The electrolyte is typically an aqueous solution comprising an aqueous phase solvent, such as water (e.g., deionized water). For example, the electrolyte may contain water (e.g., deionized water) in an amount of about 20wt% to about 95 wt%, in some embodiments about 30 wt% to about 90 wt%, and in some embodiments, about 40wt% to about 85 wt%. A second solvent may also be used to form a solvent mixture. Suitable second solvents may include, for example, glycols (e.g., ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, hexylene glycol, polyethylene glycol, ethoxydiglycol, dipropylene glycol, and the like); glycol ethers (e.g., methyl glycol ether, ethyl glycol ether, isopropyl glycol ether, etc.); alcohols (e.g., methanol, ethanol, n-propanol, isopropanol, and butanol); ketones (e.g., acetone, methyl ethyl ketone, and methyl isobutyl ketone); esters (e.g., ethyl acetate, butyl acetate, diethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate, ethylene carbonate, propylene carbonate, etc.); amides (e.g., dimethylformamide, dimethylacetamide, dimethyloctyl/decyl fatty acid amide, and N-alkylpyrrolidone); sulfoxides or sulfones (e.g., dimethyl sulfoxide (DMSO) and sulfolane), and the like. Such solvent mixtures typically contain from about 40wt% to about 80 wt% water, in some embodiments from about 50 wt% to about 75 wt% water, in some embodiments from about 55 wt% to about 70 wt% water, and the second solvent content is from about 20wt% to about 60 wt%, in some examples from about 25 wt% to about 50 wt%, and in some embodiments, from about 30 wt% to about 45 wt%. For example, the second solvent may comprise from about 5 wt% to about 45 wt%, in some embodiments from about 10 wt% to about 40wt%, and in some embodiments, from about 15 wt% to about 35 wt% of the electrolyte.

If desired, the electrolyte may be relatively neutral, having a pH of about 4.5 to about 7.0, in some embodiments about 5.0 to about 6.5, and in some embodiments, about 5.5 to about 6.0. In addition, such pH values may enhance the ability of hydrogen ions present in the aqueous electrolyte to interact with the cathode material, achieving maximum capacitance, and thereby increasing energy density. To help achieve the desired pH, one or more pH adjusting agents (e.g., acids, bases, etc.) may be used. In one embodiment, an acid is used to reduce the pH to the desired range. Suitable acids include, for example, inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, polyphosphoric acid, boric acid, and the like; organic acids including carboxylic acids such as acrylic acid, methacrylic acid, malonic acid, succinic acid, salicylic acid, sulfosalicylic acid, adipic acid, maleic acid, malic acid, oleic acid, gallic acid, tartaric acid, citric acid, formic acid, acetic acid, glycolic acid, oxalic acid, propionic acid, phthalic acid, isophthalic acid, glutaric acid, gluconic acid, lactic acid, aspartic acid, glutamic acid, itaconic acid, trifluoroacetic acid, barbituric acid, cinnamic acid, benzoic acid, 4-hydroxybenzoic acid, aminobenzoic acid, and the like; sulfonic acids such as methanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid, trifluoromethanesulfonic acid, styrenesulfonic acid, naphthalenedisulfonic acid, hydroxybenzenesulfonic acid, and the like; high molecular acids, such as poly (acrylic acid) or poly (methacrylic acid) and copolymers thereof (e.g., maleic acid-acrylic acid copolymer, sulfonic acid-acrylic acid copolymer, styrene-acrylic acid copolymer), carrageenan, carboxymethyl cellulose, alginic acid, and the like. Although the total concentration of the pH adjusting agents may vary, they comprise from about 0.01wt% to about 10 wt%, in some embodiments from about 0.05 wt% to about 5 wt%, and in some embodiments, from about 0.1wt% to about 2wt% of the electrolyte.

The electrolyte may also contain other components that help improve the electrical performance of the capacitor. For example, depolarizers may be used in the electrolyte to help suppress the generation of hydrogen gas at the cathode of the electrolytic capacitor, which can cause the capacitor to swell and ultimately cause failure. Where a depolarizer is used, the amount of depolarizer in the electrolyte is about 1 to 500 ppm, in some embodiments about 10 to 200 ppm, and in some embodiments about 20 to 150 ppm. Suitable depolarizers include nitroaromatic compounds such as 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2-nitrobenzoic acid, 3-nitrobenzoic acid, 4-nitrobenzoic acid, 2-nitroacetophenone, 3-nitroacetophenone, 4-nitroacetophenone, 2-nitroanisole, 3-nitroanisole, 4-nitroanisole, 2-nitrobenzaldehyde, 3-nitrobenzaldehyde, 4-nitrobenzaldehyde, 2-nitrobenzyl alcohol, 3-nitrobenzyl alcohol, 4-nitrobenzyl alcohol, 2-nitrophthalic acid, 3-nitrophthalic acid, 4-nitrophthalic acid, and the like. Nitroaromatic depolarizers particularly suitable for use in the present invention are nitrobenzoic acids substituted with one or more alkyl groups (e.g., methyl, ethyl, propyl, butyl, etc.) and the anhydrides or salts thereof. Specific examples of such alkyl-substituted nitrobenzoic acid compounds include, for example, 2-methyl-3-nitrobenzoic acid; 2-methyl-6-nitrobenzoic acid; 3-methyl-2-nitrobenzoic acid; 3-methyl-4-nitrobenzoic acid; 3-methyl-6-nitrobenzoic acid; 4-methyl-3-nitrobenzoic acid; and anhydrides or salts thereof.

The particular manner in which these components are mixed into the capacitor is not critical and can be accomplished in a variety of ways. However, in most embodiments, the anode is located within the housing. For example, referring to fig. 1 and 4, one embodiment of a capacitor 10 including the anode 200 of fig. 2-3 is shown. Although only one anode is shown, it should be understood that multiple anodes (e.g., an anode stack) may be employed, as described in U.S. Pat. No. 7,483,260 to Ziarniak et al. In the illustrated embodiment, the anode 200 may be located within a housing 12 comprised of a first housing member 14 and a second housing member 16. The first housing member 14 has a side wall 18 connected to a surrounding side wall 20, the side wall 20 extending to an edge 22. The second housing member 16 is plate-like and includes a second face wall 24 with a peripheral edge 26. The housing members 14 and 16 may be hermetically sealed by welding (e.g., laser welding) the overlapping edges 22 and 26 in contact with each other. The housing elements 14 and/or 16 may be similar to the substrates described above and may have a layer of electrochemically-active material (not shown) deposited on an inner surface thereof. Alternatively, a separate metal substrate may be placed adjacent housing element 14 and/or 16, the substrate being coated with the electrochemically-active material.

Although not shown, one or more separators may be used to help isolate the anode from the electrochemically-active material. Examples suitable for such purposes include, for example, porous polymeric materials (e.g., polypropylene, polyethylene, etc.), porous inorganic materials (e.g., glass fiber mats, porous glass sandpaper, etc.), ion exchange resin materials, and the like. Specific examples include ionic perfluorosulfonic acid polymer membranes (e.g., Nafion. of e.i. DuPont de Nemeours & co.), sulfonated fluorocarbon polymer membranes, Polybenzimidazole (PBI) membranes, and Polyetheretherketone (PEEK) membranes. Although direct contact between the anode and cathode can be avoided, the separator still allows ionic current from the electrolyte to flow to each electrode.

A feedthrough (feedthru) 30 that electrically isolates the anode lead 200 from the case 12 may also be used. The feedthrough 30 extends from within the housing 12 to outside the housing. A hole 34 may also be provided in the peripheral side wall 20 of the housing element 14 through which the feedthrough 30 passes. For example, feedthrough 30 may be a glass-to-metal seal ("GTMS") comprising a ferrule (not shown) with a cylindrical bore of constant internal diameter. Accordingly, an insulating glass may provide a hermetic seal between the internal bore and the anode lead 200 passing through the internal bore.

After assembly and sealing (e.g., welding), electrolyte may be added through the charging port. The capacitor may be placed in a vacuum chamber so that the feed port extends into the electrolyte tank to complete electrolyte feeding. When the vacuum chamber is evacuated, the pressure within the capacitor is reduced. When the vacuum is released, the pressure within the capacitor is re-equalized and electrolyte is drawn into the capacitor through the feed port.

The capacitor of the present invention exhibits excellent electrical properties regardless of the specific structure. For example, the capacitor has a high volumetric efficiency, e.g., a volumetric efficiency of about 50,000 μ F V/cm, measured at a frequency of 120Hz and room temperature (e.g., 25 ℃)³To about 300,000 muF V/cm³In some embodiments, about 60,000 μ F V/cm³About 200,000 μ F V/cm³In some embodiments, about 80,000 μ F V/cm³To about 150,000 muF V/cm³. The volumetric efficiency is obtained by multiplying the component's forming voltage by its capacitance and then dividing the resulting product by the component volume. For example, the capacitance of the component is 520 μ F, the resulting voltage is 175 volts, and the product of the two is 91,000 μ F V. If the volume occupied by the component is about 0.8 cm³The volume efficiency is about 113,750 μ F V/cm³。

Capacitors also have a higher energy density, making them suitable for high pulse applications. Energy density is generally according to the formula E =1/2 CV²Where C is the capacitance in farads (F) and V is the capacitor operating voltage in volts (V). For example, the capacitance can be measured using a capacitance meter (e.g., Keithley 3330 precision LCZ meter, Kelvin lead, 2 volt bias and 1 volt signal) at a frequency of 10-120 Hz (e.g., 120 Hz) and at a temperature of 25 deg.CThe measurement was carried out. For example, the energy density of the capacitor is about 2.0 joules per cubic centimeter (J/cm)³) Or greater, and in some embodiments about 3.0J/cm³And in some embodiments, about 3.5J/cm³-about 10.0J/cm³And in some embodiments, from about 4.0 to about 8.0J/cm³. Also, the capacitance is about 1 millifarad per square centimeter ("mF/cm)²") or greater, and in some embodiments about 2mF/cm²Or greater, and in some embodiments, about 5 to about 50 mF/cm²And in some embodiments about 8-20 mF/cm²。

The capacitor also has a relatively high "breakdown voltage" (the voltage at which the capacitor fails), such as about 180 volts or more, in some embodiments about 200 volts or more, and in some embodiments, about 210 to about 260 volts.

Equivalent series resistance ("ESR") -the extent to which a capacitor acts as a resistance when charged and discharged in an electronic circuit-is less than about 15,000 milliohms, in some embodiments less than about 10,000 milliohms, in some embodiments less than about 5,000 milliohms, and in some embodiments, between about 1 milliohm and about 4500 milliohms when measured at a frequency of 120Hz, bias voltage of 2 volts, and signal voltage of 1 volt. In addition, leakage current, which generally refers to current flowing from one conductor to a nearby conductor through an insulator, can also be kept at a relatively low level. For example, the value of the standard leakage current of the capacitor of the invention is in some embodiments about less than 1 μ a/μ F V, in some embodiments about less than 0.5 μ a/μ F V, in some embodiments about less than 0.1 μ a/μ F V, wherein μ a is microampere and μ F V is the product of the capacitance and the rated voltage. The Leakage current is measured using a Leakage current tester (e.g., MC 190 Leakage test from mantracourt electronics, ltd., uk) at a temperature of 25 c, a certain rated voltage, and after charging for about 60-300 seconds. The above ESR and standard leakage current can be maintained even after aging at high temperature for a long time. For example, these values may be maintained at a temperature of about 100 ℃ to 250 ℃, in some embodiments, about 100 ℃ to 200 ℃ (e.g., 100 ℃, 125 ℃, 150 ℃, 175 ℃, or 200 ℃), for about 100 hours or more, in some embodiments for 300 hours to 2500 hours, and in some embodiments for 400 hours to 1500 hours (e.g., 500 hours, 600 hours, 700 hours, 800 hours, 900 hours, 1000 hours, 1100 hours, or 1200 hours).

The electrolytic capacitors of the present invention may be used in a variety of applications, including, but not limited to, medical devices, such as implantable defibrillators, pacemakers, cardioverters, neurostimulators, drug delivery devices, and the like; automotive applications; military applications, such as radar systems; consumer electronics such as radios, televisions, and the like. For example, in one embodiment, the capacitor may be used in an implantable medical device to provide high voltage therapy (e.g., about 500 volts to about 850 volts, or, if desired, about 600 to about 900 volts) to a patient. The apparatus may comprise a fully sealed and biologically inert container or housing. One or more leads are used to electrically connect the device to the patient's heart intravenously. Cardiac electrodes are provided to sense cardiac activity and/or to provide voltage to the heart. At least a portion of the lead (e.g., the lead tip) is provided adjacent to, or in contact with, one or more ventricles and atrium of the heart. The instrument also includes a capacitor bank, which typically includes two or more capacitors connected in series and connected to a battery internal or external to the instrument to provide power to the capacitor bank. Partly because of the higher conductivity, the capacitor of the present invention has excellent electrical properties, and is therefore suitable for use in capacitor banks for implantable medical devices.

The invention will be better understood from the following examples.

Examples of the invention 1

Electrical performance of anodes formed with NH175 nodular tantalum powder (h.c. Starck), TU4D nodular/flaky tantalum powder (Cabot Corp.), and C255 flaky tantalum powder (Cabot Corp.) were tested. More specifically, each powder type was mixed with 0.5% PEG lubricantThe sample was pressed to a density of 6.5 g/cm³. NH175 powder has a lower scott density and therefore the pellet length must be shortened. After lubricant removal, each powder sample was vacuum sintered in a suspended crucible at 1550 ℃, 1600 ℃, 1650 ℃ and 1700 ℃ for 40 minutes. After sintering, the pellets were placed at a temperature of 85 ℃ and a conductivity of 1.3 mS/cm containing 50% ethylene glycol/water and H₃PO₄Is subjected to anodic oxidation in the solution of (1). The formation current density of each sample was 45 mA/g. Formation voltages of 175 volts, 200 volts and 225 volts were tested.

Then, the capacity of the resulting anode in an aqueous electrolyte containing sulfuric acid (5M) (measured at 120Hz at room temperature) was measured. Then, the specific charge (CV/g) of each type of powder at different sintering temperatures (1550 ℃, 1600 ℃, 1650 ℃, and 1700 ℃) and formation voltages (175V, 200V, and 225V) was measured. The results are shown in FIGS. 6-7. As shown, C-255 flakes can achieve relatively high specific charges at different sintering temperatures and forming voltages. Using the resulting capacitance values and assuming an operating voltage of 212 volts, the energy density (E = 0.5 CV) was also calculated²). The results are shown in FIG. 8. As shown, the specific charge (CV/g) of TU4D powder was lower, significantly reducing its energy density. In contrast, the energy density of C255 flakes is highest.

The breakdown voltage was tested for two units each consisting of a combination of powder, sintering temperature and formation voltage according to the following method. The 300 volt, 1.5A power supply is set to the lowest current value and the highest voltage value. Without the series resistor, one cell at a time is measured. The test was performed in a neutral electrolyte at room temperature. When a low constant current is applied, a voltage rise is recorded. Finally, when the leakage current reaches the current set limit, the voltage stops rising. This transition is not abrupt, but in any event, the "breakdown voltage" is roughly defined as the point at which the voltage rise levels off significantly. More detailed results are listed in table 1.

Examples of the invention 2

This example demonstrates that capacitors of the present invention can be formed. First, both ends of the tantalum wire cut in advance are bent. The bent wire is placed in the bottom groove of the mold half. The mold cavity was then filled with C255 flake tantalum powder (Cabot Corp.) and polyethylene glycol lubricant (0.5%). Pressing the two sides of the powder by a hydraulic press to a density of 7.5g/cm³Thirty-two (32) anode samples were made. After lubricant removal, sixteen (16) samples were vacuum sintered in a suspended crucible at 1600 ℃ for 40 minutes, and an additional sixteen (16) samples were vacuum sintered in a suspended crucible at 1650 ℃ for 40 minutes. After sintering, all samples were placed at a temperature of 85 ℃ with a conductivity of 1.3 mS/cm containing 50% ethylene glycol/water and H₃PO₄Is subjected to anodic oxidation in the solution of (1). The formation current density of each sample was 45 mA/g and the soaking time was 90 minutes. Forming voltages of 200 volts and 225 volts were used. After the first formation, the oxide was annealed at 380 ℃ for 60 minutes. Then, a second formation was carried out at the same voltage for 15 minutes. The resulting anode was D-shaped, with a length "L" of about 37 mm, a width "W" of about 20 mm and a thickness "H" of about 2.1 mm (fig. 2-3).

Once formed, the capacitance ("Cap") and leakage current ("DCL") were measured in a neutral electrolyte at room temperature. The capacitance was measured from a 150 volt discharge through a 10,000 ohm resistor. The leakage current was measured using a 1,000 ohm resistor in series, charged to 212 volts and the voltage drop across the capacitor was calculated. The results are shown in FIGS. 9-11.

These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention. Additionally, it should be understood that aspects of the various embodiments may be substituted in whole or in part. Furthermore, those skilled in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in such appended claims.

Claims (25)

1. A method of forming a planar anode for a high voltage wet electrolytic capacitor, the method comprising:

pressing an electrically conductive valve metal powder in a direction perpendicular to the longitudinal axis of an anode lead embedded in the powder, wherein the powder comprises a plurality of flaky particles having an aspect ratio of 2 to 100 oriented in the longitudinal direction;

sintering the pressed powder at a temperature of 1300 ℃ to 2000 ℃ to form pellets; and

anodizing the pellets to form a dielectric layer, wherein the anodized pellets have a thickness and a length from 20 mm to 50 mm, and wherein a ratio of the length of the anode to the thickness of the anode is 7 to 20.

2. The method of claim 1, wherein the pressed powder is sintered at a temperature of 1500 ℃ to 1700 ℃.

3. The method of claim 1, wherein the compressed density is 6 to 7.5g/cm³。

4. The method of claim 1, wherein the pellet is anodized at a formation voltage of 150 volts to 250 volts.

5. A wet electrolytic capacitor comprising:

a planar anode having a thickness and a length of from 20 mm to 50 mm, wherein the ratio of the length of the anode to the thickness of the anode is from 7 to 20, the anode comprising anodized pellets formed from pressed sintered conductive powder, wherein the powder is formed from a plurality of plate-like particles having an aspect ratio of from 2 to 100;

a cathode including a metal substrate coated with an electrochemically active material; and

an aqueous electrolyte connected to the anode and the cathode, wherein the electrolyte has a pH of 4.5 to 7.0 and the ratio of the charging voltage of the capacitor to the formation voltage of the dielectric layer is greater than 1.

6. The wet electrolytic capacitor as claimed in claim 5, wherein the powder is formed of a plurality of flaky particles having an aspect ratio of 4 to 30.

7. The wet electrolytic capacitor as claimed in claim 5, wherein the anode is D-shaped.

8. The wet electrolytic capacitor of claim 5 wherein the metal substrate comprises titanium.

9. The wet electrolytic capacitor of claim 5 wherein the electrochemically-active material comprises a conductive polymer.

10. The wet electrolytic capacitor of claim 9 wherein the conductive polymer is a substituted polythiophene.

11. The wet electrolytic capacitor of claim 10 wherein the substituted polythiophene is poly (3, 4-ethylenedioxythiophene).

12. The wet electrolytic capacitor as claimed in claim 5, wherein the pH is 5.0 to 6.5.

13. The wet electrolytic capacitor of claim 5 wherein the capacitor comprises only a single anode.

14. The wet electrolytic capacitor as claimed in claim 5, wherein the voltage at which the capacitor can be charged is 180 to 280 volts.

15. The wet electrolytic capacitor of claim 5 wherein the volumetric efficiency of the capacitor is 80,000 μ F V/cm measured at a frequency of 120Hz and a temperature of 25 ℃³To 150,000. mu.F V/cm³。

16. The wet electrolytic capacitor according to claim 5, wherein the energy density of the capacitor measured at a frequency of 120Hz and a temperature of 25 ℃ is 3.5J/cm³To 10.0J/cm³。

17. The wet electrolytic capacitor as claimed in claim 5, wherein a breakdown voltage of the capacitor is 200 volts or more.

18. The wet electrolytic capacitor of claim 5 wherein the capacitor has an equivalent series resistance of 1 to 4,500 milliohms measured at a frequency of 120 Hz.

19. An implantable medical device comprising the electrolytic capacitor of claim 5.

20. The wet electrolytic capacitor as claimed in claim 5, wherein the bulk density of the powder is 0.1g/cm³To 2g/cm³。

21. The method of claim 1, wherein the particles have an average particle size of from 0.1 microns to 100 microns.

22. The method of claim 1, wherein the specific surface area of the particles is 0.5 to 10.0m²/g。

23. The method of claim 1, wherein the bulk density of the powder is 0.1g/cm³To 2g/cm³。

24. The wet electrolytic capacitor as claimed in claim 5, wherein the average particle diameter of the particles is 0.1 to 100 microns.

25. The wet electrolytic capacitor as claimed in claim 5, wherein the specific surface area of the particles is 0.5 to 10.0m²/g。