JP4739326B2 - Integrated separator for electrolytic capacitors - Google Patents

Description

The present invention relates to electrolytic capacitors and their manufacture.

In order to prevent direct mechanical and electrical contact between the plates of the electrolytic capacitor, their structure generally includes a porous element, which allows movement of current carriers through the plates while simultaneously separating them. This element is therefore manufactured from an insulating material and when placed in the electrolyte medium, it must be sufficiently stable mechanically, thermally and chemically. It must also not contaminate this medium and must not significantly increase the equivalent series (electrical) resistance (ESR) of the capacitor. Traditionally, special types of paper or coatings have been used in the form of thin and very thin layers to provide reliable electrical properties over a wide range of temperatures. According to the nominal voltage rating, the typical thickness of the paper separator is in the range of 25-200 microns, while the fabric separator is characterized by a thickness of 110-120 microns and a minimum thickness of 40 microns. Yes. Typical thicknesses for paper separators are about 50-60 microns for low voltage capacitors and 160-200 microns for high voltage capacitors. The dimensionless coefficient of permeability φ of the paper separator is about 25-30, which is close to 10 for the cloth type separator. A very thin type of paper separator is about 12-13 microns in thickness. The contribution of the thickness of a conventional separator can be large, for example up to 40% of the capacitor volume. Obviously, the thinner the separator, the smaller the equivalent series resistance (ESR) value of the capacitor.

In order to compare the different types of separators and their contribution to ESR values, it is reasonable to multiply their thickness by their permeability factor. This product H = d · φ has a dimension of length, which corresponds to the interelectrode distance without the separator and has the same resistivity as the applied electrolyte. Thus, this equivalent thickness H of typical industrially manufactured separators is generally not less than 1-2 mm. The value of parameter H is particularly important for aluminum electrolytic capacitors because of the low value of the specific conductivity of the electrolyte. Our interest is to reduce this value as much as possible because the ESR value is proportional to H. Unfortunately, further reduction in the thickness of conventional separators is not possible due to the critical loss of mechanical strength. Another serious problem is the possibility of electrolyte contamination by chlorine and metal ions (cations) such as Ca, Mg or Na. This type of contamination causes defects that can have a detrimental effect on the capacitor properties, such as, for example, unstable conductivity of the electrolyte solution and accelerated corrosion. Paper and fabric separators significantly reduce the thermal conductivity of electrolytic capacitors, and this effect clearly reduces the maximum load on the capacitor.

Many attempts have been made to reduce the specific volume of electrolytic capacitors by coating the separator directly onto the surface of the capacitor electrode. In order to obtain a continuous film of the desired thickness on the electrode surface, a phenolic resin adhesive in solution containing submicron powders (eg chromium oxide, boric acid and titanium oxide) has been proposed. Another method for producing the separator layer has also been proposed on the basis of insulating powders (alumina or silica) whose adhesion to the electrode surface is fusible, for example by application of ammonium perborate. Also, vacuum deposition of silicon dioxide (or silicate) has been proposed to obtain separator coatings with desirable properties.

An alternative method of pyrolysis of metal salts with porous refractory oxides to form a separator layer was disclosed in British Patent No. 1092741. The central idea of this method is the thermal decomposition of aluminum nitrate, including subsequent deposition of alumina on colloidal silica powder, and then sintering to create a strong bond to the electrode surface during electrode foil annealing. Is done. The thickness of the separator film is recommended to exceed 10 μm in order to avoid a short circuit between the electrodes. However, it was found that this coating produced substantial losses in specific capacity, up to 40-50% of the initial value. Further, it is assumed that a loss with a high specific capacity is accompanied by a corresponding increase in the ESR value.

Conventional methods, such as those listed above, suffer from the similar disadvantages of volume reduction, poor adhesion and low porosity and permeability of these coatings. The last effect is explained by the point-like structure, especially due to the etching of the electrode foil, which can be easily closed (ie interrupted) by the outer insulation coating, and thus the current along the foil surface Prevent carrier movement. Another situation is realized, especially for trench-like porous structures in an integral separator, when the current has access to a larger part of the electrode surface and is propagated into the porous wire. It may be. Therefore, one should be aware of the negative consequences that can occur due to changes in the porous structure.

Another related method is Russian L. First developed by Godes, he developed a porous layer of aluminum hydroxide (by mixing aluminum salts) on the cathode and anode foils, 6-60 volts in an electrolyte containing group II cations (cations). It was proposed to form the electrode by electrochemical treatment. This can be done, for example, in a water-soluble sulfur or oxalic acid solution, and also in an acidic mixture. It has been found that saturation of the porous layer with the working electrolyte tends to enhance the overall conductivity of the membrane. It is recommended that the thickness of each layer (covering the cathode and anode) be 5-6 microns. Unfortunately, the considerable thickness of the barrier film formed under the separator during this process causes a significant reduction in capacity. In addition, the low mechanical strength of the coating, the high loss rate and the contamination of the working electrolyte, which can be attributed to the slightly soluble aluminum salts, inevitably occur inside the porous layer, and this process is intended for industrial Make it inappropriate. This method is closely related to the electrochemical etching of the anode foil used as a technique for surface area expansion. Other methods of electrode manufacture, such as the vacuum deposition technique of the present invention, open the possibility of avoiding the use of paper separators, and sticky separators, especially when this technique has been previously applied to coat the electrode surface It is considered more promising as an environmentally friendly technology for depositing films.

One object of the present invention is to create new technologies and overcome the problems associated with prior art separators. Other objects of the present invention will become clear from the following description.

Accordingly, in one aspect, the present invention provides an anode having an insulating film on its surface, a cathode, an electrolyte in contact with the anode and the cathode surface, and at least one electrode selected from the anode and the cathode as an integrated anode-cathode separator. At least one valve metal oxide layer integrated with at least one surface of the substrate, wherein the average thickness of the integral valve metal oxide separator layer on either or each of the anode and cathode is less than 10 microns. An electrolytic capacitor is provided.

Optionally, the capacitor can be characterized by the lack of any non-integrated anode-cathode separator.

The anode and cathode can each (independently) consist essentially of a valve metal, and the insulating film can consist essentially of a valve metal oxide. Currently preferred valve metals and valve metal oxides are aluminum and alumina, respectively. Preferably, the integral valve metal oxide separator layer is present only on the cathode.

In certain embodiments, the cathode comprises at least one layer of a mixture of valve metal and valve metal oxide deposited thereon prior to deposition of the integral valve metal oxide separator layer.

In another aspect, the present invention provides a process for the manufacture of the electrolytic capacitor of the present invention, which comprises at least one electrode selected from an anode and a cathode is valve oxidized with a predetermined thickness of less than 10 microns. Subjecting the valve metal to vapor deposition in the presence of oxygen under conditions such that the valve metal oxide is deposited on at least one surface of the at least one electrode until a physical layer is obtained.

In a preferred method of carrying out this process, the cathode is subjected to at least one of a mixture of valve metal and valve metal oxide thereon prior to deposition of the valve metal oxide having a predetermined thickness as defined above. Subjected to layer deposition. It is particularly preferred that the vapor deposition of the mixture and the vapor deposition of the valve metal oxide with a predetermined thickness are carried out continuously without intermediate exhaust in the same equipment.

In yet another aspect, the present invention provides a cathode for use in the electrolytic capacitor of the present invention, which comprises a substantially flat substrate (eg, a valve metal foil such as an Al foil) and essentially this A first layer comprising a mixture of valve metal and valve metal oxide deposited on at least one side of a flat substrate, and comprising a valve metal oxide deposited on the first layer and having a thickness of less than 10 microns A further layer. The cathode of the present invention comprises subjecting a substrate to the deposition of at least one layer of a mixture of a valve metal and a valve metal oxide, and then a valve metal oxide having a predetermined thickness as defined above. It can be made by subjecting it to vapor deposition. Preferably, the two deposition steps are carried out continuously in the same equipment without intermediate evacuation.

The electrolyte used in the inventive capacitor can be solid or liquid and can be organic or inorganic.

Reference is made to our previous U.S. patent entitled "Method for Forming High Surface Area Foil Electrodes" for exemplary details regarding the deposition of a mixture of valve metal and valve metal oxide on a substrate. No. 6,287,673. The entire contents of US Pat. No. 6,287,673 are hereby incorporated by reference.

In general, in one aspect, the present invention provides an improved design for a valve metal electrolytic capacitor. This type of capacitor includes an anode plate having an insulating film on its surface, a cathode plate, and an electrolyte in contact with the anode and cathode surfaces. The capacitor of the present invention is further characterized by the presence of a porous valve metal oxide coating on at least one outer surface of the electrode, preferably on the cathode plate.

In accordance with another aspect of the invention, in a method for manufacturing a capacitor comprising an electrolyte in contact with an insulating valve metal oxide coating, preferably an anode foil and a cathode foil having an aluminum oxide layer on at least one surface thereof. An improvement is provided, which comprises the step of vacuum deposition of a porous valve metal (eg aluminum) oxide coating on at least one surface of the cathode. In certain embodiments, the method comprises a deposition rate in the range of about 120-620 liters / second, preferably 400-500 liters / second, and a pressure in the range of about 1-2 mTorr, preferably 1.0-1.4 mTorr. Pure oxygen atmosphere, or an O ₂ / Ar gas mixture with an oxygen partial pressure close to 1 mTorr and an argon partial pressure 1.3-2.3 mTorr, preferably 1.7-2 mTorr, and about 200-350 ° C., preferably 250 It can be carried out at substrate temperatures in the range of −300 ° C.

One advantage of the present invention is a reduction in overall thickness (diameter) and weight of a product capacitor including an anode foil, a separator body and a cathode foil with a dielectric layer compared to a conventional capacitor.

Another advantage of the present invention is the reduction in the ESR value achieved with a thinner separator body. Yet another advantage of the present invention is the improved purity of the electrolyte composition, particularly the reduced amount of chloride ions compared to standard capacitors. Yet another advantage of the present invention is the excellent mechanical strength, flexibility and hardness of the formed separator layer. Another advantage is the improved thermal conductivity of the wound capacitor body across its axis. This last effect becomes more apparent when comparing the corresponding values of thermal conductivity of 0.13 watt / m ² / ° K for paper and 3.35 watt / m ² / ° K for alumina (for example). .

Further advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the detailed description of the invention herein.

For definition, a valve metal is a metal that, when oxidized, allows current to pass through if used as a cathode, but opposes current flow when used as an anode. Examples of valve metals include magnesium, thorium, cadmium, tungsten, tin, iron, silver, silicon, tantalum, titanium, aluminum, zirconium and niobium.

The monolithic separator can be applied to coat capacitor cathode (and anode) foils of different origins and to coat both foils at the same time. However, due to consideration of the total capacitor thickness and especially the thickness of the anode foil (and formation, ie electrochemical treatment of the anode), it is generally more reasonable to limit its deposition to the cathode only, and therefore However, it is preferable. This inevitable treatment of the anode foil can generally change the structure of the alumina separator (if deposited on the anode), thus causing an undesirable change in its properties. Although there is the potential to overcome this difficulty by alumina separator deposition following this type of processing, it unfortunately complicates the technique of making anode foils. Furthermore, it is more convenient for operation to spread a method for treating the foil relatively more uniformly.

Two types of alumina oxide separators have been tested and illustrated as follows, and thus
(1) Vacuum deposition of alumina as an outer porous coating on an aluminum foil substrate.
This type of alumina separator is intended for experimental investigation of its parameters and optimization of VD measures.
(2) Vacuum deposition of alumina as the outer porous coating on the primary aluminum / aluminum oxide VD coating on the aluminum foil substrate, intended as a method to increase the surface area.

Both above-mentioned types of alumina coatings are obtained by vacuum deposition of pure aluminum in a reactive atmosphere of pure oxygen or a gas mixture containing oxygen for the purpose of fully oxidizing the aluminum deposited during the deposition process. It was. The 32/64 micron thick foil substrate band was either fixed in a vaporized aluminum source or moved at a uniform speed. The rate of aluminum condensation (evaporation), the total gas pressure in the vacuum chamber, and the foil velocity (if movable foils are used) are deposited as alumina coating thicknesses in the range of 0.3-7 μm, also as a porous layered structure. Applied to provide alumina.

An embodiment of the present invention is illustrated in FIG. The electrode having an integral separator comprises an aluminum foil 1 and, therefore, a layer 2 made of aluminum and alumina and a layer 3 made of alumina are provided on both side surfaces thereof. The thickness of each of layers 2 and 3 is preferably less than 10 microns.

It has been found according to one embodiment of the present invention that the primary (preliminary) deposited sub-layered structure has a strong influence on the properties of the subsequently deposited alumina separator layer. In particular, it has been clarified that the porosity of the outer alumina separator layer depends on the unevenness of the inner lower layer. In this regard, when alumina was deposited on a planar aluminum foil surface, the degree of permeation porosity was low, and very low, especially for relatively thick alumina coatings. Better results were obtained for the VD process type (2) when a suitable porous sublayer of mixed Al / Al ₂ O ₃ was provided.

All specimens are intended to measure dry surface conductivity, mechanical stiffness, adhesion quality and electrical properties such as specific capacity, Q factor values and the stability of these parameters under conventional test procedures. It was examined. The value of the conventional product shown here as the Q factor (or sample quality) is Q = ω · C · R = 2π · f · C · R, where f is the measurement frequency (assumed to be equal to 120 Hz). , C and R are capacitance and series resistance values, measured against a measuring electrolytic layer by a Thorby Thunder device precision LCR-bridge. The degree of permeation porosity was assessed by its specific capacity and its effect on the Q factor. Comparison with the same reference sample without the alumina separator coating was the primary method and was applied to estimate the impact of the secondary coating.

All samples of cathode foil, coated on both sides of the integral alumina separator layer, were tested with a digital MultiLog ™ 710 apparatus to verify the insulation properties of the outer alumina layer. It was found that all the dry specimens under consideration have reliable insulation properties with surface resistance exceeding the upper limit of 50 megohms of the device, on both sides of the foil and with the polarity of the applied voltage.

The mechanical properties of the manufactured samples were investigated according to conventional requirements to confirm the adhesion of the upper alumina coating to the lower lower layer and the total coating adhesion to the foil substrate body. All of the samples were found to have good adhesion satisfying standard requirements, including adhesive tape test and bending test. The influence of the alumina layer on the electrical properties (specific capacity, Q factor) of the sample was measured. In the case of Example (2), it was found that the average specific capacity (relative to the vacuum deposition conditions described below) decreased as the thickness of the alumina layer increased. In particular, if the thickness of the alumina layer is 2.5 μm, the volume specific capacity of the sample is close to 178 μF / μm / cm ² compared to 225 μF / μm / cm ² without the alumina layer (reference sample). Furthermore, this ratio is almost maintained after electrochemical treatment (so-called passivation) of both samples (see Examples 1-4). As can be seen by the following calculation, the evaluation gives an approximate 10% capacity drop for an alumina layer thickness of 1 micron.
100% * (225-178) /0.5 (225 + 178) /2.5=100%*47/201.5/2.5=9.33%.

The finite value of the electrolyte resistance in the porous channel of the alumina layer caused an increase in Q factor, i.e. a decrease in sample quality. Further, in the case of the sample area S = 5 cm ² , a gradual increase in the resistance of the sample δR = 0.02 ohm was revealed per 1 μm of the alumina layer thickness D (sep).

If the specific resistance (p (el) = 12.7 Ohms · cm) of the electrolyte for measurement is known, then the value of the H parameter for a given sample can be calculated by the following equation.
H = 2 · δR · S · D (sep) / p (el) = 2 · 0.02 Ohms / μm · 5 · D (μm) /12.7·10 (−4) = 157 · D [μ]
If the thickness of the alumina separator is D = 1.6 μm, then H (D) = 0.25 mm. Therefore, compared to a conventional separator, a much smaller value of the H parameter is obtained in the present invention.

The cathode foil specimens were subjected to electrochemical treatment (passivation) in order to provide chemical long-term stability of the primary Al / Al ₂ O ₃ black coating in the electrolyte medium. Passivation exhibits a low voltage formation of the primary (inner) coating at room temperature. The prepared cathode foil samples were then tested by two accelerated aging procedures. In the first procedure, the sample was boiled in pure deionized water for 60 minutes, after which the electrical parameters were verified. In the second procedure, the sample was immersed in a special electrolyte for a specified time to mimic the operating mode. The electrolyte composition, referred to below as “paste”, is as follows.
51% deionized water
Ethylene glycol 34%
Ammonium adipate 13%
Ammonium phosphate 1%
D-Gluconic acid 1%
The electrolyte composition E-II used for processing the sample after deposition has the following components.
1000ml deionized water
Boric acid 30 grams / liter ammonium adipate 30 grams / liter ammonium dihydrogen phosphate 1.5 grams / liter ammonium 5-borate 0.5 grams / liter

例５−８

The non-limiting examples of experimental data below illustrate the main features of the present invention.
Example 1-4

Example 5-8

These values of capacity loss are perfectly acceptable in electrolytic capacitor manufacturing, since this capacity loss can be easily compensated by a slight increase in the thickness of the aluminum (Al / Al ₂ O ₃ ) type coating. . For example, if a typical cathode foil has a specific capacity of 1000 μF / cm ² , the thickness of the conductive coating is equal to 4.5 μm. In the case of using additional separators, this coating thickness increases up to 5.6 μm. The total thickness change for a double coated cathode foil is therefore equal to 2.2 μm. Obviously, this increase in thickness does not significantly impair the outer shape of the capacitor.

Although the present invention has been described with reference to specific embodiments, including the presently preferred manner of practicing the present invention, there are numerous modifications and substitutions of the systems and techniques described above that fall within the scope of the invention. Those skilled in the art will appreciate that.

1 is a cross-sectional view of an electrode having an integrated separator according to one embodiment of the present invention.

Claims (13)

An anode having an insulating film on its surface, a cathode, an electrolyte in contact with the anode and the cathode surface, and at least one surface of at least one electrode selected from the anode and the cathode as an integral anode-cathode separator; At least one valve metal oxide layer integrated, and the average thickness of the integrated valve metal oxide separator layer on either or each of the anode or cathode is less than 10 microns. Electrolytic capacitor characterized by. The following four features:
The anode is made of a valve metal, and the insulating film is made of a valve metal oxide ;
The cathode is made of a valve metal ;
The valve metal is aluminum, and the valve metal oxide is alumina;
Lack of any non-integrated anode-cathode separator,
The electrolytic capacitor of claim 1, further characterized by at least one of: The electrolytic capacitor according to claim 2, wherein the integrated metal oxide separator layer exists only on the cathode. The said cathode comprises at least one layer of a mixture of valve metals and a valve metal oxide deposited thereon prior to the deposition of said integral valve metal oxide separator layer. 3. The electrolytic capacitor according to 3. At least one electrode selected from the anode and the cathode is 10 microns of the valve oxide layer under conditions such that a valve metal oxide is deposited on at least one surface of the at least one electrode. The process for the production of an electrolytic capacitor according to claim 1, comprising subjecting the deposition of the valve metal in the presence of oxygen until a predetermined thickness of less than is obtained. The following four features:
The anode is made of a valve metal, and the insulating film is made of a valve metal oxide ;
The cathode is made of a valve metal ;
The valve metal is aluminum, and the valve metal oxide is alumina;
Lack of any non-integrated anode-cathode separator,
The process of claim 5 further characterized by at least one of: The process of claim 6 wherein the integral valve metal oxide separator layer is deposited only on the cathode. The cathode is subjected to deposition of a minimum layer of a mixture of valve metal and valve metal oxide thereon prior to deposition of the valve metal oxide having the predetermined thickness. Item 8. The process according to Item 7. 9. The process of claim 8, wherein the deposition of the mixture and the deposition of the valve metal oxide having the predetermined thickness are performed continuously in the same equipment without intermediate evacuation. A flat substrate, a first layer of a mixture of valve metal and valve metal oxide deposited on at least one side of the flat substrate, and a thickness of less than 10 microns deposited on the first layer The cathode used in the electrolytic capacitor of claim 4, further comprising a further valve metal oxide layer. 11. The cathode according to claim 10, wherein the valve metal is aluminum, and the valve metal oxide is alumina. The substrate is subjected to vapor deposition of a minimum layer of a mixture of valve metal and valve metal oxide thereon and then subjected to vapor deposition of a valve metal oxide having the predetermined thickness. A process for the manufacture of a cathode according to claim 10. The following features:
The deposition of the mixture and the deposition of the valve metal oxide having the predetermined thickness are carried out continuously in the same equipment without intermediate exhaust;
The valve metal is aluminum, and the valve metal oxide is alumina;
The process of claim 12, further characterized by at least one of:

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