Solid electrolytic capacitor with improved reliability

The present invention if related to an improved electrolytic capacitor and a method of making the improved electrolytic capacitor. The electrolytic capacitor comprises an anode comprising a dielectric layer on the anode. A first mordant layer is on the dielectric wherein the first mordant layer comprises a mordant compound of Formula A: wherein:

BACKGROUND

The present invention is related to an improved method of preparing a solid electrolyte capacitor and an improved capacitor formed thereby. More specifically, the present invention is related to improving reliability and reducing the Anomalous Charging Current (ACC) of a capacitor by incorporating a mordant layer between the dielectric and the conductive polymer layer and between adjacent conductive polymer layers.

Solid electrolyte capacitors have emerged as a major tool in the development of electronic components. Solid electrolytic capacitors, particularly those utilizing valve metal anodes, originally emerged comprising a pressed powder anode with a dielectric on the anode and manganese dioxide as the conductive layer on the dielectric wherein the manganese dioxide functioned as the cathode. The manganese dioxide was replaced by capacitors comprising conductive polymer as the cathode layer due, in part, to their non-burning failure mode. Of these solid electrolytic capacitors comprising polythiophene based conductive polymers have proven to be the most desirable.

However, when the solid electrolytic capacitors comprising polythiophene based conductive polymers are subjected to thorough drying, they exhibit anomalous charge current (ACC) exceeding the theoretical charge current (I (t)), which is calculated as follows: I(t)=C*dv/dt

where C is the capacitance and dV/dt is the voltage ramp. The anomalous charge current (ACC) has the potential to disturb intended circuit function. More details on Anomalous charge current in solid electrolytic capacitors described elsewhere. (Freeman et al, J. Solid State Sci. Technol. 2013, 2, N197-N204, Freeman et al, Appl. Sci. 2021, 11, 5514, and Chacko et al, 9,793,058).

Provided herein is a novel mordanted layer, between the dielectric and conductive polymer layer and between adjacent conductive polymer layers significantly reduces Anomalous charge current (ACC) in solid electrolytic capacitors.

SUMMARY OF THE INVENTION

The present invention is directed to an improved capacitor comprising a mordant layer.

A particular feature of the invention is a mordant layer which reduces the Anomalous Charging Current (ACC) of a capacitor.

Another feature of the invention is the improved reliability of the capacitor with the mordant layer in high temperature and high humidity conditions.

The electrolytic capacitor comprises an anode comprising a dielectric layer on the anode. A mordant layer is between the dielectric and conductive polymer layer and optionally between or within adjacent conductive polymer layers wherein the mordant layer comprises a mixture or reactive product of represented by the mordant compound of Formula A and crosslinker.

An exemplary mordant compound is defined by Formula A:

wherein:
R1and R2is independently selected from H; cation, linear alkyl, cyclic alkyl or substituted alkyl of 1 to 10 carbons;
R3is selected from —CR4R5R6wherein R4represents a hydrogen, an alkyl of 1-20 carbons or an aryl of 6-20 carbons; R4and R5can be taken together to represent a cyclic alkyl or substituted cyclic alkyl or (—CR6OP(O)OR1OR2)n;
R5represents an alkyl of 1-20 carbons or an aryl of 6-20 carbons; R4and R5can be taken together to represent a cyclic alkyl or substituted cyclic alkyl or (—CR6OP(O)OR1OR2)n;
R6represents a hydrogen, an alkyl of 1-20 carbons or an aryl of 6-20 carbons; and
n is an integer from 1 to 20.

These and other advantages, as will be realized, are provided by an electrolytic capacitor. The electrolytic capacitor comprises an anode comprising a dielectric layer on the anode. A first mordant layer is on the dielectric wherein the first mordant layer comprises a mordant compound of Formula A:

wherein:
R1and R2is independently selected from H; cation, linear alkyl, cyclic alkyl or substituted alkyl of 1 to 10 carbons;
R3is selected from —CR4R5R6wherein R4represents a hydrogen, an alkyl of 1-20 carbons or an aryl of 6-20 carbons; R4and R5can be taken together to represent a cyclic alkyl or substituted cyclic alkyl or (—CR6OP(O)OR1OR2)n;
R5represents an alkyl of 1-20 carbons or an aryl of 6-20 carbons; R4and R5can be taken together to represent a cyclic alkyl or substituted cyclic alkyl or (—CR6OP(O)OR1OR2)n;
R6represents a hydrogen, an alkyl of 1-20 carbons or an aryl of 6-20 carbons; and
n is an integer from 1 to 20; and
a crosslinker. A primary conductive polymer layer is on the first mordant layer.

Yet another embodiment is provided in a method of forming an electrolytic capacitor comprising:

forming an anode;

forming a dielectric on the anode;

forming a first mordant layer on the dielectric wherein the first mordant layer comprises a mordant compound of Formula A:

wherein:
R1and R2is independently selected from H; cation, linear alkyl, cyclic alkyl or substituted alkyl of 1 to 10 carbons;
R3is selected from —CR4R5R6wherein R4represents a hydrogen, an alkyl of 1-20 carbons or an aryl of 6-20 carbons; R4and R5can be taken together to represent a cyclic alkyl or substituted cyclic alkyl or (—CR6OP(O)OR1OR2)n;
R5represents an alkyl of 1-20 carbons or an aryl of 6-20 carbons; R4and R5can be taken together to represent a cyclic alkyl or substituted cyclic alkyl or (—CR6OP(O)OR1OR2)n;
R6represents a hydrogen, an alkyl of 1-20 carbons or an aryl of 6-20 carbons; and
n is an integer from 1 to 20; and
a crosslinker; and
a primary conductive polymer layer on said first mordant layer.

DESCRIPTION

The present invention is related to an improved electrolytic capacitor which exhibits significantly lower Anomalous Charging Current (ACC). More specifically, the present invention is related to an electrolytic capacitor comprising a mordant between the dielectric and conductive polymer layer and optionally between or within adjacently conductive polymer layers wherein the mordant layer significantly reduces Anomalous Charging Current (ACC) of capacitor.

The invention will be described with reference to the figures which are an integral, but non-limiting, part of the specification provided for clarity of the invention.

An embodiment of the invention will be described with reference toFIG.1. InFIG.1, an inventive capacitor,10, is illustrated schematically in cross-sectional view. The capacitor comprises an anode,12, which is preferable a porous monolith formed by pressing a powder. An anode wire,14, extends from the anode. The anode wire can be embedded in the powder prior to pressing, which is preferred, or the anode wire can be attached to the surface of the anode after pressing such as by welding. A dielectric,16, is formed on the surface of the anode. While illustrated as a layer of consistent thickness the actual dielectric layer is on the interstitial surfaces of the porous monolith. A first mordant layer,21, overlies the dielectric and is between the dielectric and primary conductive polymer layer,18, wherein the primary conductive polymer layer,18, is on the mordant layer and preferably extends into the interstitial surfaces of the monolith to increase the surface area of conductive polymer coating on the dielectric. While illustrated as a single layer, for the purposes of discussion, the primary conductive polymer layer is typically applied from multiple applications. A second mordant layer,20, is optionally formed on or in the primary conductive layer wherein the mordant layer comprises a mordant compound of Formula A, described herein below, and a crosslinker. A secondary conductive polymer layer,22, is formed on the mordant layer or on the primary conductive polymer layer. An adhesion layer,24, is optionally but preferably formed on the secondary conductive polymer layer. The adhesion layer allows electrical attachment of a cathode lead,26, to the secondary conductive polymer layer such as by soldering or by a conductive adhesive. It is known in the art that attachment of a lead to a conductive polymer layer is difficult and an adhesion layer is typically used to allow good physical and electrical contact between the secondary conductive polymer layer and cathode lead. An anode lead,28, is in electrical contact with the anode wire. An optional but preferred electrically insulating resin,30, encases all but the bottom portion of the cathode lead and anode lead.

An embodiment of the invention of the invention is illustrated schematically inFIG.3. InFIG.3, the anode,12, has a dielectric,16, thereon wherein the dielectric forms on the interstitial surfaces of the anode. A first mordant layer,21, is on the dielectric and preferably the mordant layer extends into the interstitial surfaces of the anode to form a coating on the dielectric. A primary conductive polymer layer,18, forms a coating on the first mordant layer,21. In an embodiment, coated on the primary conductive polymer layer are alternating layers of mordant,201-20n, and secondary conductive polymer layers,221-22nwith the number, n, of alternating layers of mordant and secondary conductive polymer layer being at least one, and preferably at least two, to no more than 20.

The process for forming the electrolytic capacitor will be described with reference toFIG.2. InFIG.2the process for forming an electrolytic capacitor is represented in a flow chart. An anode is prepared at40. The anode can be a foil or the anode can be prepared by pressing a powder. A pressed powder anode preferably comprises an anode wire extending therefrom. The anode is preferably sintered, particularly if a powder of niobium or tantalum is used as the anode powder. A dielectric is formed on the anode at42. The method of forming the dielectric is not limiting with typical methods known to those of skill in the art suitable for demonstration of the invention. A mordant layer is formed on the dielectric at43. A primary conductive polymer layer is formed on the mordant layer at44. The primary conductive polymer layer is formed by in-situ polymerization or by the application of a pre-formed conductive polymer from a polymer solution or slurry. In-situ polymerization is well known to those of skill in the art to include polymerization of a monomer in the presence of the surface upon which the polymer is formed. In this instance the surface is the dielectric. The pre-formed conductive polymer suitable for use in forming the primary layer has a particle size of less than 20 nm and preferably below 1 nm, which is considered non-detectable, at which point the pre-formed conductive polymer is referred to as a soluble polymer. The primary conductive polymer layer is typically formed by multiple applications of the in-situ formed layer or conductive polymer solution or slurry. A mordant layer is formed on the primary conductive polymer layer at46. The first mordant layer and second mordant layer are formed by applying a solution independently comprising a mordant compound, defined by Formula A, and a crosslinker, followed by drying. The first mordant layer and optional second mordant layer may comprise the same compound defined by Formula A or they may be different. The solvent for the first mordant layer application is not particularly limiting with water being exemplary for demonstration of the invention. The second mordant layer may be formed from a single application of solution or sequential applications. A secondary conductive polymer layer is formed on the mordant layer at48. The secondary conductive polymer layer is preferably formed by applying a slurry comprising a conductive polymer wherein the conductive polymer has an average particle size of at least 50 nm to no more than 200 nm. The secondary conductive polymer layer is preferable formed from multiple applications of slurry. The sequential formation of the second mordant layer and secondary conductive polymer layer is repeated n times until the desired number of alternating layers is achieved. An adhesive layer is preferably formed on the terminal secondary conductive polymer layer at50wherein the adhesive layer preferable comprises at least one carbon containing layer and at least one metal containing layer as known in the art. The capacitor is finished at52wherein finishing typically includes the attachment of cathode external terminations, anode external terminations and resin encapsulation. Testing and any electrical or physical treatment may also be included as part of the finishing step.

Each secondary conductive polymer layer may comprise multiple sublayers with a primer layer therebetween. Primer layers are known in the art to comprise a crosslinker or a weak ionic acid between adjacent conductive polymer sub-layers to improve inter-layer adhesion. Primer layers suitable for demonstration of the invention are taught in U.S. Pat. Nos. 8,882,856; 9,761,347; 9,761,378; 10,109,428 and 10,643,796 each of which is incorporated herein by reference. Particularly preferable primers are amine salts selected from an amine and a weak acid.

A particularly preferred anode material is a metal and a particularly preferred metal is a valve metal or a conductive oxide of a valve metal. Particularly preferred anodes comprise a material selected from the group consisting of niobium, aluminum, tantalum and NbO. Tantalum is the most preferred anode material. While not limited thereto, the advantages of the invention are most easily appreciated with high charge density powders such as above 50,000 CV/g. Below about 50,000 CV/g the issues related to power cycling are not as prevalent and therefore the advantages offered by the invention are not as readily realized. As the powder charge density increases the advantages of the invention are more readily apparent. Particularly preferred powders have a charge density above 100,000 CV/g, preferably above 200,000 CV/g and even more preferably above about 250,000 CV/g up to about 350,000 CV/g.

The anode wire is either embedded in or attached to the anode with a preference for an embedded anode wire. The material of construction for the anode wire is not particularly limited, however, it is preferable that the anode wire be the same material as the anode for manufacturing conveniences.

The dielectric, and method of forming the dielectric is not particularly limited herein. A particularly preferred dielectric is an oxide of the anode due to manufacturing considerations.

The primary conductive layer comprises a conductive polymer. The primary conductive layer is formed by in-situ polymerization of a monomer or the primary conductive layer is formed as a coating of pre-polymerized conductive polymer comprising a small average particle size, below about 20 nm, and more preferably, a soluble conductive polymer.

An in-situ formed conductive polymer is hypothesized to more effectively enter the interstitial portions of the porous anodized anode thereby forming an improved capacitor.

A soluble conductive polymer is a conductive polymer that completely dissolves in a solvent or solvent mixture without detectable particles with below about 1 nm being considered below typical particle size detection limits.

The solvent for the soluble conductive polymer can be water, organic solvents, or mixtures of water with miscible solvents such as alcohol and non-hydroxy polar solvents such as dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), etc.

A soluble conductive polymer is believed to impregnate the pores of anodes as effectively as conductive polymers formed by in-situ methods and better than conductive polymer dispersion with detectable particles. Neither in-situ conductive polymer nor soluble conductive polymer contains polyanion dopants such as polystyrene sulfonic acid. In many cases, soluble conductive polymers contain self-doping functionalities.

The mordant layer comprises a mordant compound of Formula A and a crosslinker wherein Formula A is defined by;

wherein:
R1and R2is independently selected from H; cation, linear alkyl, cyclic alkyl or substituted alkyl of 1 to 10 carbons;
R3is selected from —CR4R5R6wherein R4represents a hydrogen, an alkyl of 1-20 carbons or an aryl of 6-20 carbons; R4and R5can be taken together to represent a cyclic alkyl or substituted cyclic alkyl or (—CR6OP(O)OR1OR2)n;
R5represents an alkyl of 1-20 carbons or an aryl of 6-20 carbons; R4and R5can be taken together to represent a cyclic alkyl or substituted cyclic alkyl or (—CR6OP(O)OR1OR2)n;
R6represents a hydrogen, an alkyl of 1-20 carbons or an aryl of 6-20 carbons;
n is an integer from 1 to 20.

A preferred embodiment of the mordant compound is represented by:

wherein:
each of R13-R18is independently selected from H; —PO(OH)2and —POOR19;
each of R7-R12is independently a H or each of R7-R12may be taken with one adjacent group to represent an alkene; and
each R19is independently H, alkyl or substituted alkyl of 1 to 10 carbons;
with the proviso that at least one of R13-R18is —PO(OH)2.

The crosslinker comprises one or more functional groups selected from carboxylic, hydroxyl, amine, epoxy, anhydride, isocyanate, imide, amide, carboxyl, carboxylic anhydride, silane, oxazoline, (meth)acrylates, vinyls, maleates, maleimides, itaconates, allyl alcohol esters, dicyclo-pentadiene-based unsaturations, unsaturated C12-C22fatty esters or amides, carboxylic acid salts, quaternary ammonium salts, polyester, polyurethane, polyamide, polyamine, polyimide, silicone polyester, hydroxyl functional silicone, hydroxyethyl cellulose, polyvinyl alcohol, phenolic, epoxy, butyral, copolymers of these or mixture of these multifunctional polymers such as epoxy/amine, epoxy/anhydride, isocyanate/amine, isocyanate/alcohol, unsaturated polyesters, vinyl esters, unsaturated polyester and vinyl ester blends, unsaturated polyester/urethane hybrid resins, polyurethane-ureas, reactive dicyclopentadiene resins or reactive polyamides. The oligomer or polymer with multifunctional or multiple reactive groups preferably includes at least one carboxylic acid group and at least one hydroxyl function group. A particularly preferred oligomer or polymer with multifunctional reactive groups is a polyester containing carboxylic and hydroxyl functionality. In addition to oligomers or polymers, inorganic particles with surface functional groups.

Particularly preferred organometallic compounds selected from organofunctional silane, titanate and so forth.

Organofunctional silanes and organic compounds with more than one crosslinking group, especially more than one epoxy group, are particularly suitable for use as crosslinkers for the instant invention especially when used in combination.

An exemplary organofunctional silane is defined by the formula:
XR1Si(R3)3-n(R2)n
wherein X is an organic functional group such as amino, epoxy, anhydride, hydroxy, mercapto, sulfonate, carboxylate, phosphonate, halogen, vinyl, methacryloxy, ester, alkyl, etc; R1is an aryl or alkyl (CH2)mwherein m can be 0 to 14; R2is individually a hydrolysable functional group such as alkoxy, acyloxy, halogen, amine or their hydrolyzed product; R3is individually an alkyl functional group of 1-6 carbons; n is 1 to 3.

The organofunctional silane can also be dipodal, define by the formula:
Y(Si(R3)3-n(R2)n)2
wherein Y is any organic moiety that contains reactive or nonreactive functional groups, such as alkyl, aryl, sulfide or melamine; R3, R2and n are defined above. The organofunctional silane can also be multi-functional or polymeric silanes, such as silane modified polybutadiene, or silane modified polyamine, etc.

Examples of organofunctional silane include 3-glycidoxypropyltrimethoxysilane, 3-aminopropytriethoxysilane, aminopropylsilanetriol, (triethoxysilyl)propylsuccinic anhydride, 3-mercaptopropyltrimethoxysilane, vinyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-trihydroxysilyl-1-propane sulfonic acid, octyltriethyoxysilane, bis(triethoxysilyl)octane, etc. The examples are used to illustrate the invention and should not be regarded as conclusive Examples of organofunctional silane include 3-glycidoxypropyltrimethoxysilane, 3-aminopropytriethoxysilane, aminopropylsilanetriol, (triethoxysilyl)propylsuccinic anhydride, 3-mercaptopropyltrimethoxysilane, vinyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-trihydroxysilyl-1-propane sulfonic acid, octyltriethyoxysilane, bis(triethoxysilyl)octane, etc. The examples are used to illustrate the invention and should not be regarded as conclusive.

A particularly preferred organofunctional silane is glycidyl silane defined by the formula:

wherein R1is an alkyl of 1 to 14 carbons and more preferably selected from methyl ethyl and propyl; and each R2is independently an alkyl or substituted alkyl of 1 to 6 carbons.

A particularly preferred glycidyl silane is 3-glycidoxypropyltrimethoxysilane defined by the formula:

which is referred to herein as “Silane A” for convenience.

A crosslinker with at least two epoxy groups is referred to herein as an epoxy crosslinking compound and is defined by the formula:

wherein the X is an alkyl or substituted alkyl of 0-14 carbons, preferably 0-6 carbons; an aryl or substituted aryl, an ethylene ether or substituted ethylene ether, polyethylene ether or substituted polyethylene ether with 2-20 ethylene ether groups or combinations thereof. A particularly preferred substitute is an epoxy group.

A preferred epoxy crosslinking compound is glycidyl ether, defined by the formula:

wherein R3is an alkyl or substituted alkyl of 1-14 carbons, preferably 2-6 carbons; an ethylene ether or polyethylene ether with 2-20 ethylene ether groups; an alkyl substituted with a group selected from hydroxy, or

or —(CH2OH)xCH2OH wherein X is 1 to 14.

Particularly preferred glycidyl ethers are represented by:

where n is an integer of 1 to 220;
PEGDGE: polyethylene glycol diglycidyl ether

Mixtures of the crosslinkers may be used.

The secondary conductive polymer layers are formed from a slurry comprising a prepolymerized polymer of polythiophene and optionally a dopant such as a styrene sulfonic acid or polymer comprising styrene sulfonic acid groups. The preferred polymerization method uses a stator screen which provides a uniform droplet size resulting in average polymer particle sizes of at least about 50 nm to no more than about 200 nm, more preferably 150 nm and even more preferably below about 100 nm.

The preferred polythiophene monomer for polymerization is shown as polymerized in Formula B:

wherein:
R14and R52independently represent linear or branched C1-C16alkyl, C2-C18alkoxyalkyl C3-C8cycloalkyl, phenyl or benzyl which are unsubstituted or substituted by C1-C6alkyl, C1-C6alkoxy, halogen or OR17; or
R14and R15, taken together, are linear C1-C6alkylene which is unsubstituted or substituted by C1-C6alkyl, C1-C6alkoxy, halogen, C3-C8cycloalkyl, phenyl, benzyl, C1-C4alkylphenyl, C1-C4alkoxyphenyl, halophenyl, C1-C4alkylbenzyl, C1-C4alkoxybenzyl or halobenzyl, 5-, 6-, or 7-membered heterocyclic structure containing two oxygen elements. R17represents hydrogen, linear or branched C1-C16alkyl or C2-C18alkoxyalkyl, C3-C8cycloalkyl, phenyl or benzyl which are unsubstituted or substituted by C1-C6alkyl;
X is S;
n represents that the compound of Formula B is a polymer with a range of molecular weights; in general n is an integer of 2 to a number sufficient to reach an average molecular weight of about 500,000.

R14and R15of Formula B are preferably chosen to prohibit polymerization at the β-site of the ring as it is most preferred that only α-site polymerization be allowed to proceed. It is more preferred that R14and R15are not hydrogen and more preferably, R14and R15are α-directors with ether linkages being preferable over alkyl linkages. It is most preferred that the R14and R15are small to avoid steric interferences.

A particularly preferred polymer is 3,4-polyethylene dioxythiophene (PEDOT) which is prepared from monomeric 3,4-ethylene dioxythiophene (EDOT).

Particularly suitable polymers or co-polymers are selected from the group consisting of poly(4-(2,3-dihydrothieno-[3,4-b][1,4]dioxin-2-yl)methoxy)-1-butane-sulphonic acid, salt), poly(4-(2,3-dihydrothieno-[3,4-b][1,4]dioxin-2-yl)methoxy)-1-methyl-1-propane-sulphonic acid, salt), poly(N-methylpyrrole), poly(3-methylthiophene), poly(3-methoxythiophene), and poly(3,4-ethylenedioxythiophene).

The insulating resin is not particularly limited herein with any non-electrically conducting compatible resin being suitable for demonstration of the invention. If the electrolytic capacitor is embedded or encased the resin optional.

Comparative Example 1

A series of tantalum anodes (330 microfarads, 16V rated voltage) were prepared. The tantalum was anodized to form a dielectric on the tantalum anode. The primary conductive polymer were formed by dipping the anode in the oxidizer Iron Tosylate followed by dipping in EDOT monomer drying and washing. This process was repeated a few times to build PEDOT film inside the anode pores. A conductive polymer dispersion containing epoxy and silane compounds was applied to form a secondary conductive polymer layer. After drying, alternating layers of an amine salt and the secondary conductive polymer dispersion was applied and repeated 4-5 more times. The anodes with the conductive polymer layers were washed and dried, followed by sequential coating of a graphite layer and a silver layer to produce a solid electrolytic capacitor. Parts were assembled and packaged. Capacitance and ESR was measured on packaged parts.

A series of solid electrolytic capacitors were prepared in similar manner to that in comparative example 1 except that a solution comprising phytic acid silane was applied between primary conductive polymer and secondary conductive polymer.

A series of solid electrolytic capacitors were prepared in similar manner to that in Comparative Example 1 except that a solution comprising phytic acid and silane was applied between dielectric and primary conductive polymer and optionally washed with methanol or water.

A series of solid electrolytic capacitors were prepared in similar manner to that in Comparative Example 1 except that a solution comprising phytic acid and silane was applied between dielectric and primary conductive polymer and over each layer of primary conductive polymer and optionally washed with methanol or water.

Comparative Example 2

A series of solid electrolytic capacitors were prepared in similar manner to that in Comparative Example 1 except that 470 microfarads, 16V tantalum anodes were used.

A series of solid electrolytic capacitors were prepared in similar manner to that in Comparative Example 2 except that a solution comprising phytic acid and silane was applied over each layer of primary conductive polymer and optionally washed with methanol or water.

A series of solid electrolytic capacitors were prepared in similar manner to that in Comparative Example 2 except that a solution comprising phytic acid and silane was applied between dielectric and primary conductive polymer and over each layer of primary conductive polymer and optionally washed with methanol or water.

TABLE 2Anomalous Charging Current(ACC) (xTheoretical Value)Comparative Example 233.0Example 47.65Example 52.31
As shown in Table 1 and Table 2, examples containing mordant layer shows reduced anomalous charging current.

TABLE 460° C./90% RH load humidity testESRLeakageTime (h)% changeCurrent (uA)Comparative0044.6Example 15008.385.661,00015.1026.06Example 3006.725000.346.61,0001.7624.43
As shown in Table 3 and Table 4, examples containing mordant layer shows improved ESR and leakage reliability in high temperature and high humidity conditions at rated voltage which is 55% of formation voltage.

The invention has been described with reference to preferred embodiments without limit thereto. One of skill in the art would realize additional embodiments which are described and set forth in the claims appended hereto.