Improved formed electrolyte for tantalum solid electrolyte capacitors

Abstract

An improved formed electrolyte suitable for forming an oxide on a valve metal anode and an improved capacitor comprising an oxide formed in the formed electrolyte are provided. The formation electrolyte comprises an inositol derivative defined by Formula (1): wherein each of R1 to R6 is defined.

Description

TECHNICAL FIELD

[0001] The present invention relates to an improved formation (anodization) electrolyte for forming tantalum oxide dielectric on tantalum anode bodies. More particularly, the present invention is directed to a formation electrolyte comprising a compound derived from inositol that significantly improves oxide formation. BACKGROUND

[0002] Solid electrolytic capacitors comprising an oxide formed on a sintered tantalum as an anode and a conductive polymer as a cathode are now widely used throughout the electronics industry, practically every application requiring the use of a capacitive coupling in electronic assemblies. As is well understood by those skilled in the art, tantalum oxide is formed on the tantalum surface, where it serves as a dielectric between the tantalum anode and the conductive polymer cathode. The process of forming tantalum oxide by applying a voltage to the anode in the presence of an electrolyte is known as anodization.

[0003] Dielectric quality is a measure of the electrical performance of a solid electrolytic capacitor. A poor dielectric can result in a faulty part. One factor that leads to electrical performance failure is abnormal charge current (ACC). Parts formed in currently available anodization electrolytes exhibit high ACC, where high ACC is known to be detrimental to electrolytic capacitor quality. This has prompted significant efforts to develop improved formation electrolytes or anodization electrolytes (providing a more stable dielectric) and thus improved solid electrolytic capacitors, particularly with lower ACC.

[0004] Solid electrolytic capacitors using valve metals, particularly tantalum, as an anode, and a conductive polymer as a cathode, show abnormal charge current (ACC) that exceeds the theoretical value {I(t)} calculated as follows: I(t) = C * dv / dt, C being the capacitance and dv / dt the voltage ramp. As described in Y. Freeman and P. Lessner Evolution of Polymer Tantalum Capacitors Appl. Sci. 2021, 11(12), 5514-5521, ACC can interfere with circuit performance, leading to capacitor failure.

[0005] Provided herein is an improved electrolyte that is particularly suitable for forming tantalum oxide on tantalum, where the tantalum oxide is used as an improved dielectric in solid electrolytic capacitors. SUMMARY

[0006] The present invention relates to an improved formation electrolyte that is particularly suitable for forming tantalum oxide on tantalum.

[0007] More particularly, the present invention is directed to a capacitor having improved electrical properties, the capacitor comprising a tantalum anode and a conductive polymer cathode with an improved tantalum pentoxide dielectric between the tantalum anode and the conductive polymer cathode.

[0008] A particular feature of the present invention is the ability to form a dielectric oxide on a tantalum anode without changing manufacturing steps, equipment or procedures.

[0009] As will be appreciated, these advantages and other advantages are provided in a formation electrolyte suitable for forming an oxide on a valve metal anode, the electrolyte comprising an inositol derivative defined by Formula 1 :

[0010]

[0011] wherein:

[0012] R 1 each of R 6 is independently selected from H, a substituted or unsubstituted carbon chain having up to 20 carbon atoms, -PO3R 7 R 8 , -SiR 9 3, -C(O)R 10 ; and

[0013]

[0014] or adjacent groups can together represent -P(O)OH-O-P(O)OH-;

[0015] each R 7 and R 8 is independently selected from H, a cation, a saturated or unsaturated carbon chain having up to 35 carbon atoms, or -CH2CHR 12 CH2R 13 ;

[0016] each R 9 is independently an alkyl group having from 1 to 10 carbon atoms;

[0017] each R 10 is independently an alkyl group having from 1 to 10 carbon atoms;

[0018] each R 11 represents a bond to an oxygen of the inositol derivative of Formula 1 ; and

[0019] R 12 and R 13 are esters terminated with H, a saturated or unsaturated carbon chain having from 1 to 35 carbon atoms.

[0020] Another embodiment provides a method of forming a solid electrolytic capacitor, comprising:

[0021] forming a dielectric oxide on a tantalum anode by the steps of:

[0022] applying a formation electrolyte on the anode, wherein the formation electrolyte comprises an inositol derivative defined by Formula 1 :

[0023]

[0024] wherein:

[0025] R 1 each of R 6 is independently selected from H, a substituted or unsubstituted carbon chain having up to 20 carbon atoms, -PO3R 7 R 8 , -SiR 9 3, -C(O)R 10 ; and

[0026]

[0027] or adjacent groups can together represent -P(O)OH-O-P(O)OH-;

[0028] each R 7 and R 8 is independently selected from H, a cation, a saturated or unsaturated carbon chain having up to 35 carbon atoms, or -CH2CHR 12 CH2R 13 ;

[0029] each R 9 is independently an alkyl group having from 1 to 10 carbon atoms;

[0030] each R 10 is independently an alkyl group having from 1 to 10 carbon atoms;

[0031] each R 11 represents a bond to an oxygen of the inositol derivative of Formula 1 ; and

[0032] R 12 and R 13 are esters terminated with H, a saturated or unsaturated carbon chain having from 1 to 35 carbon atoms; and

[0033] forming a conductive polymer cathode on the dielectric oxide. DETAILED DESCRIPTION

[0034] The present invention relates to an improved solid electrolytic capacitor comprising an improved tantalum oxide dielectric, wherein the performance of the solid electrolytic capacitor, particularly the ACC, is significantly improved over the prior art. More particularly, the present invention relates to an improved formation electrolyte suitable for forming an improved tantalum oxide on a tantalum anode, which results in low wet leakage. Particularly when used with a solid conductive polymer cathode, the capacitor formed with the improved tantalum oxide provides an improved solid electrolytic capacitor.

[0035] The high ACC of the solid electrolytic capacitor is addressed by forming the tantalum oxide on the tantalum anode of the electrolyte comprising the inositol derivative. Without being limited by theory, it is hypothesized that the derivative of inositol is able to bind to the free hydroxyl groups present on the tantalum surface or to the tantalum oxide, thereby stabilizing the interface of the growing dielectric and anode, which facilitates the improved growth of the tantalum oxide.

[0036] The present invention relates to the improved electrical performance of a solid electrolytic capacitor, more particularly, to the abnormal charge current (ACC). The present invention provides a method of forming a dielectric oxide film on a tantalum anode and a method of manufacturing a solid electrolytic capacitor with the dielectric oxide film. The formation of the present invention in the formation electrolyte has free terminal O - ions when ionized in an aqueous solution, forming an improved dielectric oxide layer. Without being limited by theory, it is hypothesized that the geometry of the ions of the formation electrolyte of the present invention anchor to the tantalum surface with free hydroxyl groups. The binding / anchoring of the ions facilitates more electrolyte molecules to enter and effectively form a uniform oxide. Another hypothesis is that a portion of the formation electrolyte of the present invention remains on the surface of the tantalum oxide and forms a stable interface between the dielectric and the conductive polymer at the p-n junction. This facilitates the possible tunneling effect and significantly reduces the abnormal charge current (ACC) of the solid electrolytic capacitor.

[0037] The formation of a stable dielectric interface is critical to have stable electrical performance. The dielectric is formed by anodizing a metal anode in an electrolyte containing the formation electrolyte of the present invention. By selective control of the voltage range, the anodization process results in a dielectric with better electrical performance, which in turn results in an improved ACC of the capacitor, exhibiting a smaller abnormal charge current when charged at a constant voltage switching rate, such as 100 volts / second.

[0038] The inositol derivative is defined by Formula 1.

[0039]

[0040] wherein:

[0041] R 1 to R 6each of R1, R2, R3, R4, R5, and R6 is independently selected from H, a substituted or unsubstituted carbon chain having up to 20 carbon atoms, -PO3R 7 R 8 ; and 9 10 ; and

[0042]

[0043] or adjacent groups can together represent -P(O)OH-O-P(O)OH-;

[0044] each R 7 and R 8 is independently selected from H, a cation, a saturated or unsaturated carbon chain having up to 35 carbon atoms, or -CH2CHR 12 CH2R 13 ;

[0045] each R 9 is independently an alkyl group having from 1 to 10 carbon atoms, preferably having from 1 to 3 carbon atoms, particularly preferably -CH3;

[0046] each R 10 is independently an alkyl group having from 1 to 10 carbon atoms, preferably having from 1 to 3 carbon atoms, particularly preferably -CH3;

[0047] each R 11 represents a bond to an oxygen of the inositol derivative of Formula 1; and R 12 and R 13 are esters terminated with H, a saturated or unsaturated carbon chain having from 1 to 35 carbon atoms.

[0048] In preferred embodiments, at least one of R 1 through R 6 is -PO3R 7 R 8 , at least one of R 7 or R 8 is H, preferably R 7 and R 8 are both H. In more preferred embodiments, at least two of R 1 through R 6 are -PO3R 7 R 8 , at least one of R 7 or R 8 is H, preferably R 7 or R 8 are both -H. In more preferred embodiments, at least three of R 1 through R 6 are -PO3R​7 R 8 , R 7 or R 8 is H, preferably R 7 and R 8 are H. In a more preferred embodiment, at least four of R 1 to R 6 are PO3R 7 R 8 , R 7 or R 8 is -H, preferably R 7 and R 8 are H. In a more preferred embodiment, at least five of R 1 to R 6 are PO3R 7 R 8 , R 7 or R 8 is H, preferably R 7 and R 8 are H. In a more preferred embodiment, each of R 1 to R 6 is PO3R 7 R 8 , R 7 or R 8 is H, preferably R 7 and R 8 are H.

[0049] R 7 and R 8 may be cations, preferably selected from quaternary amines, ammonium; metal cations, saturated or unsaturated carbon chains containing up to 35 carbon atoms, preferably containing 10 to 17 carbon atoms.

[0050] Substituted or unsubstituted carbon chains include alkyl chains and alkene chains, which are linear, branched or cyclic, and can be substituted or unsubstituted. Substitutions include ethers, -OH, carboxylic acids, phosphonic acids, phosphinic acids, esters, amines and amides.

[0051] Particularly preferred inositol derivatives are selected from the group consisting of myo-inositol and its isomers and their respective derivatives, i.e. inositol hexakisphosphate (phytic acid); pentakisphosphate, trisphosphate, diphosphate and their isomers; and inositol monophosphate, inositol trisphosphate, 1-phosphatidylinositol, 1-phosphatidylinositol 3-phosphate; derivatives of ononitol, sequoytol, 1-deoxy-1-(methylamino)-epi-inositol (dombonitol), (1R,2S,3R,4S,5R,6S)-5,6-dimethoxy-1,2,3,4-cyclohexanetetrol (viscumitol), pinicollin, quebrachitol, (1R,2R,3R,4S,5R,6S)-3,6-dimethoxy-1,2,4,5-cyclohexanetetrol (pinpollitol) and L-brahol; myo-inositol 1,3,4,5,6-penta-O-(trimethylsilyl)-, bis(trimethylsilyl)phosphate, phosphatidylinositol 5-phosphate PI(5) bis C8 ammonium salt, phosphatidylinositol 5-phosphate bis C16 (PI(5)P bis C16) sodium salt, 1,2-diacyl-sn-glycero-3-phospho-(1-D-myo-inositol 4,5-bisphosphate), phosphatidylinositol, phosphatidylinositol 3-phosphate, phosphatidylinositol 4-phosphate, phosphatidylinositol 4,5-phosphate, di-myo-inositol-phosphate, ciceritol phosphate, fagopyritol phosphate, glycosyl inositol phosphoryl ceramide, C25,25-Archedityl inositol, ceramide phosphoryl inositol, D-myo-inositol-4-hydrogenphosphoric acid monoammonium salt and phosphatidylinositol phosphate.

[0052] The chemical conversion electrolyte can further include an additive selected from the group consisting of metal salts, organic acid salts, inorganic acid salts, organic acids, inorganic acids, organic metal compounds, inorganic solvents, organic solvents, cross-linking agents, surfactants, buffers, and the like.

[0053] The metal salts, inorganic acid salts, and organic acid salts included in the chemical conversion electrolyte can include halides, nitrides, sulfides, amides, nitrates, sulfates, phosphates, carbonates, chromates, chlorates, perchlorates, oxides, oxychlorides, peroxides, carboxylates, amides, and esters.

[0054] The organic acids and inorganic acids included in the chemical conversion electrolyte can include carboxylic acids, phosphonic acids, phosphinic acids, pyrophosphoric acids, phosphoric acids, phthalic acids, maleic acids, malonic acids, and trimesic acids, and the like.

[0055] Organometallic compounds contained in the formation electrolyte can include organosilanes, organoboranes, carbonyls, phosphines, cross-linking agents, surfactants, and buffers.

[0056] Solvents contained in the formation electrolyte can be selected from water, alcohols, ethylene glycol, polyethylene glycol, tetraethylene glycol dimethyl ether, propylene glycol, ethylene glycol ethers, and alkanolamines.

[0057] The solid electrolytic capacitor includes an anode, a cathode, and a dielectric oxide between the anode and the cathode. The anode is a sintered, porous tantalum metal that is anodized to form the dielectric oxide. The dielectric oxide layer is covered by a solid electrolyte, preferably a conductive polymer, that acts as the cathode. The dielectric oxide is formed by subjecting the anode to a voltage in the presence of the formation electrolyte of the present invention, in a process known in the art as anodization.

[0058] The solid electrolytic capacitor includes an anode, a cathode, and a dielectric oxide between the anode and the cathode. The anode is a sintered, porous tantalum metal that is anodized to form the dielectric oxide. The dielectric oxide layer is covered by a solid electrolyte, preferably a conductive polymer, that acts as the cathode. The dielectric oxide is formed by subjecting the anode to a voltage in the presence of the formation electrolyte of the present invention, in a process known in the art as anodization.

[0059] After the anode is formed (anodization), the dielectric thereon can be cleaned. In one embodiment, the anode with the dielectric thereon is not cleaned, which allows residual formation electrolyte to remain anchored to the surface, which facilitates bonding to the cathode layer.

[0060] A formation temperature of about 60 °C to 125 °C is suitable for demonstration of the present invention. More preferably, an anodization temperature of about 75 °C to 90 °C is suitable for demonstration of the present invention.

[0061] Abnormal charge current (ACC) refers to the ideal current (I 理想 ) in milliamps (mA) used to charge the capacitor. I 理想 = 1000 x C (dv / dt), C is the capacitance in farads, and dv / dt is the rate of change of voltage, typically about 100 V / S. Thus, the actual charge current remains constant or is greater than the ideal charge current (I 理想 ). I 实际 / I 理想 = 1 or greater.

[0062] The structure of the solid electrolytic capacitor is well known to those skilled in the art and need not be further elaborated herein.

[0063] The electrically conductive polymer is preferably selected from each of polyaniline, polypyrrole and polythiophene, which can be substituted. A particularly preferred polymer comprises a conjugated group having the structure of Formula 2:

[0064]

[0065] wherein:

[0066] R 1 and R 2 independently represent a linear or branched C1-C 16 alkyl or C2-C 18 alkoxyalkyl; or is C3-C8cycloalkyl, phenyl or benzyl, which is unsubstituted or substituted by C1-C6alkyl, C1-C6alkoxy, halogen or OR 3 ; or R 1 and R 2 together are a linear C1-C6alkylene, a 5-, 6- or 7-membered heterocyclic ring structure containing two oxygen elements, 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. R 3 preferably represents hydrogen, a linear or branched C1-C 16 alkyl or C2-C 18 alkoxyalkyl; or is C3-C8cycloalkyl, phenyl or benzyl, which is unsubstituted or substituted by C1-C6alkyl;

[0067] X is S, N or O, most preferably X is S;

[0068] R 1 and R 2 of Formula 2 are preferably selected to prevent polymerisation in the beta-position of the ring, as only alpha-position polymerisation is most preferably allowed to occur; more preferably R 1 and R 2 are not hydrogen, more preferably R 1 and R 2 are alpha-directors, ether bonds are more preferred than alkyl bonds; most preferably R 1 and R 2 are small, to avoid steric interference.

[0069] In a particularly preferred embodiment, R 1 and R 2 of Formula 1 together represent -O-(CHR 4 ) n -O-, wherein:

[0070] n is an integer from 1 to 5, most preferably 2;

[0071] R 4 is independently selected from hydrogen, linear or branched C1 to C 18 alkyl, C5 to C 12 cycloalkyl, C6 to C 14 aryl, C7 to C 18 aralkyl or C1 to C4 hydroxyalkyl, optionally substituted with a functional group selected from carboxylic acid, hydroxyl, amine, substituted amine, olefin, acrylate, thiol, alkyne, azide, sulfate, sulfonate, sulfonic acid, imide, amide, epoxy, anhydride, silane and phosphate ester; or R 4 is selected from -(CHR 5 ) a -R 16 , -O(CHR 5 ) a R 16 , -CH2O(CHR 5 ) a R 16 , -CH2O(CH2CHR 5 O) a R 16 , or

[0072] R 4 is a functional group selected from hydroxyl, carboxyl, amine, epoxy, amide, imide, anhydride, hydroxymethyl, olefin, thiol, alkyne, azide, sulfonic acid, benzene sulfonic acid sulfate, SO3M, anhydride, silane, acrylate and phosphate ester;

[0073] R 5 is H or an alkyl chain containing 1 to 5 carbon atoms, optionally substituted with a functional group selected from carboxylic acid, hydroxyl, amine, olefin, thiol, alkyne, azide, epoxy, acrylate and anhydride;

[0074] R 16 is H or SO3M or an alkyl chain containing 1 to 5 carbon atoms, optionally substituted with a functional group selected from carboxylic acid, hydroxyl, amine, substituted amine, olefin, thiol, alkyne, azide, amide, imide, sulfate, SO3M, amide, epoxy, anhydride, silane, acrylate and phosphate ester;

[0075] a is an integer from 0 to 10; and

[0076] M is H or a cation preferably selected from ammonia, sodium or potassium.

[0077] The electrically conductive polymer can be either a water-soluble compound or a water-dispersible compound. Examples of such π-conjugated electrically conductive polymers include polypyrrole or polythiophene. Particularly preferred electrically conductive polymers include poly(3,4-ethylenedioxythiophene), poly(4-(2,3-dihydrothieno[3,4-b][l,4]dioxin-2-yl)methoxy)-l-butane-sulfonic acid / sulfonate), poly(4-(2,3-dihydrothieno[3,4-b][l,4]dioxin-2-yl)methoxy)-l-propane-sulfonic acid / sulfonate), poly(4-(2,3-dihydrothieno[3,4-b][l,4]dioxin-2-yl)methoxy)-l-methyl-l-propane-sulfonic acid / sulfonate), poly(4-(2,3-dihydrothieno[3,4-b][l,4]dioxin-2-yl)methoxy alcohol, poly(N-methylpyrrole), poly(3-methylpyrrole), poly(3-octylpyrrole), poly(3-decylpyrrole), poly(3-dodecylpyrrole), poly(3,4-dimethylpyrrole), poly(3,4-dibutylpyrrole), poly(3-carboxypryrrole), poly(3-methyl-4-carboxypryrrole), poly(3-methyl-4-carboxyethylpryrrole), poly(3-methyl-4-carboxybutylpryrrole), poly(3-hydroxypyrride), poly(3-methoxypyrride), polythiophene, poly(3-methylthiophene), poly(3-hexylthiophene), poly(3-heptylthiophene), poly(3-octylthiophene), poly(3-decylthiophene), poly(3-dodecylthiophene), poly(3-octadecylthiophene), poly(3-bromothiophene), poly(3,4-dimethylthiophene), poly(3,4-dibutylthiophene), poly(3-hydroxythiophene), poly(3-methoxythiophene), poly(3-ethoxythiophene), poly(3-butoxythiophene), poly(3-hexyloxythiophene), poly(3-heptoxythiophene), poly(3-octyloxythiophene), poly(3-decyloxythiophene), poly(3-dodecyloxythiophene), poly(3-octadecyloxythiophene), poly(3,4-dihydroxythiophene), poly(3,4-dimethoxythiophene), poly(3,4-ethylenedioxythiophene), poly(3,4-propylenedioxythiophene), poly(3,4-butylenedioxythiophene), poly(3-carboxythiophene), poly(3-methyl-4-carboxythiophene), poly(3-methyl-4-carboxyethylthiophene), poly(3-methyl-4-carboxybutylthiophene), polyaniline, poly(2-methylaniline), poly(3-isobutylaniline), poly(2-anilinesulfonate), poly(3-anilinesulfonate), and the like.

[0078] Co-polymers consisting of at least two different co-monomers are contemplated. The co-polymer comprises at least one polymerized monomer selected from the group consisting of poly-pyrrole, poly-thiophene, poly(4-(2,3-dihydrothieno[3,4-b][l,4]dioxin-2-yl)methoxy)-l-butane-sulfonic acid / sulfonate), poly(4-(2,3-dihydrothieno[3,4-b][l,4]dioxin-2-yl)methoxy)-l-methyl-l-propane-sulfonic acid / sulfonate), poly(N-methyl pyrrole), poly(3-methyl thiophene), poly(3-methoxy thiophene), and poly(3,4-ethylenedioxythiophene).

[0079] A particularly preferred conductive polymer is poly-3,4-polyethylenedioxythiophene (PEDOT).

[0080] The conductive polymer layer can be formed on the dielectric by any technique commonly used in the art. The conductive polymer can be formed into a slurry and deposited onto the surface. Alternatively, the conductive polymer can be added as a monomer and polymerized in situ as is known in the art.

[0081] In the art, it is known to add additional layers to the cathode to facilitate soldering the cathode to a lead frame or circuit. Carbon-containing layers and metal-containing layers are known and well documented in the art and need not be further discussed herein.

[0082] Organofunctional silanes and organic compounds having more than one cross-linking group, especially more than one epoxy group, are particularly suitable for use in combination with the electrolyte of the present invention. The electrolyte can comprise the organofunctional silane and the organic compound having more than one cross-linking group as an additive in combination with the inositol derivative. After the dielectric oxide is formed, the anode having the dielectric thereon can be cleaned. In one embodiment, the anode having the dielectric thereon is not cleaned, which allows the presence of residual organofunctional silane and the organic compound having more than one cross-linking group as well as the inositol derivative during the formation of the cathode.

[0083] Exemplary organofunctional silanes are defined by the formula:

[0084] XR1Si(R3) 3-n (R2) n ,

[0085] where X is an organofunctional group such as amino, epoxy, anhydride, hydroxyl, mercapto, sulfonate, carboxylate, phosphonate, halogen, vinyl, methacryloxy, ester, alkyl, etc.; R1is an aryl or alkyl (CH2) m where m can be 0 to 14; R2is individually a hydrolyzable functional group such as alkoxy, acyloxy, halogen, amine or hydrolysis product thereof; R3is individually an alkyl functional group containing 1 to 6 carbon atoms; and n is 1 to 3.

[0086] The organofunctional silane can also be dipodal, defined by the formula:

[0087] Y(Si(R3) 3-n (R2)n)2

[0088] where Y is any organic group containing a reactive or non-reactive functional group, such as an alkyl group, an aryl group, a sulfide, or melamine; R3, R2, and n are defined above. The organofunctional silane can also be a multifunctional silane or a polymeric silane, such as a polybutadiene-modified silane or a polyamine-modified silane, among others.

[0089] Examples of organofunctional silanes include 3-glycidoxypropyltrimethoxysilane, 3- aminopropyltriethoxysilane, aminopropylsilanetriol, (triethoxysilyl)propyl succinic anhydride, 3- mercaptopropyltrimethoxysilane, vinyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3- trihydroxysilyl-l-propane sulfonic acid, octyltriethoxysilane, bis(triethoxysilyl)octane, and the like. The examples are illustrative of the present application and are not to be considered limiting. Examples of organofunctional silanes include 3-glycidoxypropyltrimethoxysilane, 3- aminopropyltriethoxysilane, aminopropylsilanetriol, (triethoxysilyl)propyl succinic anhydride, 3- mercaptopropyltrimethoxysilane, vinyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3- trihydroxysilyl-l-propane sulfonic acid, octyltriethoxysilane, bis(triethoxysilyl)octane, and the like. The examples are illustrative of the present application and are not to be considered limiting.

[0090] A particularly preferred organofunctional silane is a glycidoxy silane defined by the formula:

[0091]

[0092] where R1is an alkyl group containing 1 to 14 carbon atoms, more preferably selected from the group consisting of methyl, ethyl, and propyl; and each R2is independently an alkyl group or a substituted alkyl group containing 1 to 6 carbons.

[0093] A particularly preferred glycidoxy silane is 3-glycidoxypropyltrimethoxysilane, defined by the formula:

[0094]

[0095] For convenience, it is referred to herein as "Silane A".

[0096] Particularly suitable organometallics are neoalkoxy titanates having the following groups: titanium IV 2,2(bis 2-propenyl)butyl, tris neo caprylato-O; titanium IV 2,2(bis 2-propenyl)butyl, tris(dodecyl)benzenesulfonato-O; titanium IV 2,2(bis 2-propenyl)butyl, tris(dioctyl)phosphato-O; titanium IV 2,2(bis 2-propenyl)butyl, tris(dioctyl)pyrophosphato-O; titanium IV 2,2(bis 2-propenyl)butyl, tris(2-ethylenediamino)ethanolate; and titanium IV 2,2(bis 2-propenyl)butyl, tris(3-amino)phenoxy, are representative neoalkoxy titanates and derivatives thereof.

[0097] Crosslinkers having at least two epoxy groups are referred to herein as epoxy crosslinking compounds and are defined by the formula:

[0098]

[0099] wherein X is an alkyl or substituted alkyl group containing from 0 to 14 carbon atoms, preferably from 0 to 6 carbon atoms; an aryl or substituted aryl group, an acetylene or substituted acetylene group, a polyacetylene or substituted polyacetylene group having from 2 to 20 acetylene groups, or a combination thereof. Particularly preferred substituents are epoxy groups.

[0100] Examples of epoxy crosslinking compounds having more than one epoxy group include ethylene glycol diglycidyl ether (EGDGE), propylene glycol diglycidyl ether (PGDGE), 1,4-butanediol diglycidyl ether (BDDGE), pentanediol diglycidyl ether, hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, resorcinol diglycidyl ether, glycerol diglycidyl ether (GDGE), glycerol polyglycidyl ether, diglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol diglycidyl ether (sorbitol-DGE), sorbitol polyglycidyl ether, polyethylene glycol diglycidyl ether (PEGDGE), polypropylene glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, di(2,3-epoxypropyl) ether, 1,3-butadiene diepoxide, 1,5-hexadiene diepoxide, 1,2,7,8-diepoxyoctane, 1,2,5,6-diepoxycyclooctane, 4-vinylcyclohexene diepoxide, bisphenol A diglycidyl ether, maleimide-epoxy compounds, and the like.

[0101] Examples

[0102] Wet capacitance and wet leakage were measured by LCR meter in 25 wt% phosphoric acid in water at a test frequency of 120 Hz and a test voltage of 70% of the forming voltage. For wet leakage, the components were tested after a charge time of 120 seconds and a DC bias voltage of 2 V. ACC (abnormal charge current) was measured at the end of the production process. The finished parts were mounted on a circuit board and measured at 0°C and 80% Vr, expressed as times theoretical value (xTLV).

[0103] Comparative Example: A tantalum anode (330 microfarad, 16 V rated voltage) was prepared by sintering tantalum powder. First, the anode was anodized in a control electrolyte {about (2 wt% to 5 wt%) phosphoric acid, (50 wt% to 70 wt%) ethylene glycol, and water, with a resistivity of about (100 to 370) ohm-cm, measured at 80°C} at 35 V and 80°C to form a dielectric oxide on the tantalum anode (first anodization). The anode was rinsed, heat treated at 450°C for 30 minutes, and re-anodized in the original electrolyte. Wet leakage after the first anodization is shown in Table 1. The anode was then coated with a conductive polymer as a cathode, followed by a carbon and silver coating. The component was assembled and molded into a surface mount finished capacitor using known techniques. ACC was measured on the mounted component at 0°C and reported as current (mA) at 12.8 V {80% of the rated voltage (Vr)}. Capacitance and equivalent series resistance (ESR) of the finished part, as well as ACC, are also reported in Table 1.

[0104] Inventive Example 1 : A series of solid electrolytic capacitors were prepared in a similar manner as in Comparative Example 1 using 300 microfarad components, rated voltage of 16 V, with the exception that the electrolyte was an aqueous solution of (5 wt% to 10 wt%) inositol-6-phosphate with a resistivity of (7 to 15) ohm-cm at 80°C. Wet leakage after the first anodization, capacitance and ESR of the final component, as well as ACC, are reported as current (mA) at 12.8 V (80% of Vr) as shown in Table 1.

[0105] Inventive Example 2: A series of solid electrolytic capacitors were prepared in a similar manner as in Inventive Example 1 using 300 microfarad components, rated voltage of 16 V, with the exception that the anodization electrolyte was an aqueous solution of a mixture of (5 wt% to 10 wt%) inositol-6-phosphate and epoxysilane (1 : 1) with a resistivity of (9 to 17) ohm-cm at 80°C. Wet leakage after the first anodization, capacitance and ESR of the final component, as well as ACC, are reported as current (mA) at 12.8 V (80% of Vr) as shown in Table 1.

[0106] Invention Example 3: In this example, a series of solid electrolytic capacitors were prepared in a similar manner as in Invention Example 1 using 300 microfarad parts rated at 16V, except that ethylene glycol (EG) was added to the electrolyte. Myo-inositol-6-phosphate (5 to 10 wt%) was added to an aqueous solution of ethylene glycol (50 to 70 wt%) having a resistivity of (75-100) ohm-cm at 80°C. The wet leakage after the first anodization, capacitance and ESR of the final parts were also reported along with the ACC, as the current (mA) at 12.8V (80% of Vr) as shown in Table 1.

[0107] Invention Example 4: In this example, a series of solid electrolytic capacitors were prepared in a similar manner as in Invention Example 2 using 300 microfarad parts rated at 16V, except that the polymer also contained the same electrolyte as used in Invention Example 2 along with a conductive polymer. The wet leakage after the first anodization, capacitance and ESR of the final parts were also reported along with the ACC, as the current (mA) at 12.8V (80% of Vr) as shown in Table 1.

[0108] Invention Example 5: In this example, a series of solid electrolytic capacitors were prepared in a similar manner as in Invention Example 1 using 300 microfarad parts rated at 16V, except that the electrolyte contained an aqueous solution of myo-inositol (1 to 6 wt%) and phosphoric acid (1 to 6 wt%) having a resistivity of about (10 to 30) ohm-cm. The wet leakage after the first anodization, capacitance and ESR of the final parts were also reported along with the ACC, as the current (mA) at 12.8V (80% of Vr) as shown in Table 1.

[0109] Table 1

[0110]

[0111] The Invention Examples demonstrate the ability to form capacitors using the inventive formulated electrolyte with an abnormal charge current less than 4 times the theoretical value. This is not obtainable in the art.

[0112] The Invention has been described with reference to the preferred embodiments, but is not limited thereto. Additional embodiments will be recognized by one skilled in the art upon reading the attached claims and description of the Invention.

Claims

1. A formation electrolyte suitable for forming an oxide on a valve metal anode, the formation electrolyte comprising an inositol derivative defined by formula 1: in: R 1 to R 6 each are independently selected from H, a substituted or unsubstituted carbon chain containing up to 20 carbon atoms, -PO3R 7 R 8 , -SiR 9 3, -C(O)R 10 ; and Or adjacent groups may together represent -P(O)OH-OP(O)OH-; each R 7 and R 8 are independently selected from H, a cation, a saturated or unsaturated carbon chain containing up to 35 carbon atoms, or -CH2CHR 12 CH2R 13 ; Each R 9 are all independently an alkyl group containing 1 to 10 carbon atoms; Each R 10 are all independently an alkyl group containing 1 to 10 carbon atoms; each R 11 represents a bond of an oxygen of the inositol derivative of Formula 1; and R 12 and R 13 are esters terminated with H, saturated or unsaturated carbon chains containing 1 to 35 carbon atoms.

2. The formation electrolyte suitable for forming an oxide on a tantalum anode according to claim 1, wherein R 1 at least one of R 6 at least one of R 7 R 8 at least one of R 7 or R 8 is -H.

3. A formation electrolyte suitable for forming an oxide on a tantalum anode according to claim 2, wherein R 7 and R 8 are each -H.

4. The formation electrolyte suitable for forming an oxide on a tantalum anode according to claim 2, wherein R 1 at least two of R 6 to R 7 are -PO3R 8 .

5. The formation electrolyte suitable for forming oxides on tantalum anodes according to claim 4, wherein R 1 at least three of R 6 are -PO3R 7 R 8 .

6. The formation electrolyte suitable for forming an oxide on a tantalum anode according to claim 5, wherein R 1 at least four of R 6 to R 7 R 8 .

7. A formation electrolyte suitable for forming an oxide on a tantalum anode according to claim 6, wherein R 1 to at least five of R 6 are -PO3R 7 R 8 .

8. A formation electrolyte suitable for forming an oxide on a tantalum anode according to claim 7, wherein R 1 each of R 6 to R 7 is -PO3R 8 .

9. The formation electrolyte suitable for forming an oxide on a tantalum anode according to claim 8, R 7 and each of R 8 is -H.

10. The formation electrolyte suitable for forming an oxide on a tantalum anode according to claim 1, wherein R 7 or at least one of R 8 is a cation.

11. A formation electrolyte suitable for forming an oxide on a tantalum anode according to claim 10, wherein the cation is selected from quaternary amines and saturated or unsaturated carbon chains containing up to 35 carbon atoms.

12. The formation electrolyte suitable for forming an oxide on a tantalum anode according to claim 1, wherein each R 9 is independently an alkyl group containing from 1 to 3 carbon atoms.

13. A formation electrolyte suitable for forming an oxide on a tantalum anode according to claim 12, wherein each R 9 is -CH3.

14. The formation electrolyte suitable for forming an oxide on a tantalum anode according to claim 1, wherein each R 10 is independently an alkyl group containing from 1 to 3 carbon atoms.

15. A formation electrolyte suitable for forming an oxide on a tantalum anode according to claim 14, wherein each R 10 is -CH3.

16. The formation electrolyte for forming an oxide on a tantalum anode according to claim 1, wherein the inositol derivative is selected from the group consisting of inositol and its isomers and their respective derivatives, namely, inositol hexaphosphate (phytic acid); pentaphosphate, triphosphate, diphosphate and their isomers; and inositol monophosphate, inositol tripyrophosphate, 1-phosphatidylinositol, 1-phosphatidylinositol 3-phosphate; derivatives of hononiol, tetrol, 1-deoxy-1-(methylamino)-epi-inositol, (1R,2S,3R,4S,5R,6S)-5,6-dimethoxy-1,2,3,4-cyclohexane tetraol, pinitol, quebrachol, (1R,2R,3R,4S,5R,6S)-3,6-dimethoxy-1,2,4,5-cyclohexane tetraol and L-quebrachol; inositol 1,3 ,4,5,6-penta-O-(trimethylsilyl)-, bis(trimethylsilyl) phosphate, phosphatidylinositol 5-phosphate PI(5) bis C8 ammonium salt, phosphatidylinositol 5-phosphate bis C16 (PI(5)P bis C16) sodium salt, 1,2-diacyl-sn-glycerotriyl-3-phospho-(1-D-inositol 4,5-bisphosphate), phosphatidylinositol, phosphatidylinositol 3-phosphate, phosphatidylinositol 4-phosphate, phosphatidylinositol 4,5-phosphate, diinositol phosphate, chickpea sugar alcohol phosphate, buckwheat alcohol phosphate, glycosyl inositol phosphoceramide, C25,25-Archeditylinositol, ceramide phosphoinositol, D-inositol-4-hydrogen phosphate monoammonium salt and phosphatidylinositol phosphate, and D-inositol-4-hydrogen phosphate; monoammonium salt.

17. A formation electrolyte suitable for forming an oxide on a valve metal anode according to claim 1, wherein the formation electrolyte further comprises an additive selected from the group consisting of metal salts, organic acid salts, inorganic acid salts, organic acids, inorganic acids, organometallic compounds, inorganic solvents, organic solvents, crosslinking agents, surfactants and buffers.

18. A formation electrolyte suitable for forming an oxide on a valve metal anode according to claim 17, wherein the metal salts, inorganic acid salts and organic acid salts include halides, nitrides, sulfides, amides, nitrates, sulfates, phosphates, carbonates, chromates, chlorates, perchlorates, oxides, oxychlorides, peroxides, carboxylates, amides and esters.

19. The formation electrolyte suitable for forming an oxide on a valve metal anode according to claim 17, wherein the organic acid and the inorganic acid include carboxylic acid, phosphonic acid, phosphinic acid, phosphoric acid, phthalic acid, maleic acid, malonic acid and trimesic acid.

20. The formation electrolyte suitable for forming oxides on valve metal anodes according to claim 17, wherein the organometallic compound comprises organosilane, organoborane, carbonyl, phosphine, crosslinker, surfactant, and buffer.

21. The formation electrolyte suitable for forming oxides on valve metal anodes according to claim 17, wherein the formation electrolyte further comprises at least one solvent selected from water, alcohol, ethylene glycol, polyethylene glycol, tetraethylene glycol dimethyl ether, propylene glycol, glycol ether, and alkanolamine.

22. A method of forming a solid electrolytic capacitor comprising: forming a dielectric oxide on a tantalum anode by: applying a formation electrolyte on the anode, wherein the formation electrolyte comprises an inositol derivative defined by Formula 1: wherein: R 1 each of R 6 is independently selected from H, a substituted or unsubstituted carbon chain having up to 20 carbon atoms, -PO3R 7 R 8 , -SiR 9 3, -C(O)R 10 ; and or adjacent groups can together represent -P(O)OH-O-P(O)OH-; each R is independently selected from H, a cation, a saturated or unsaturated carbon chain having up to 35 carbon atoms, or -CH2CHR 7 and R 8 are each independently selected from H, a cation, a saturated or unsaturated carbon chain having up to 35 carbon atoms, or -CH2CHR 12 CH2R 13 ; Each R 9 are all independently an alkyl group containing 1 to 10 carbon atoms; Each R 10 are all independently an alkyl group containing 1 to 10 carbon atoms; each R 11 represents a bond of an oxygen of the inositol derivative of Formula 1; and R 12 and R 13 is an ester terminated with H, a saturated or unsaturated carbon chain containing 1 to 35 carbon atoms; and forming a conductive polymer cathode on the dielectric oxide.

23. The method of forming a solid electrolytic capacitor of claim 22, wherein R 1 at least one of R 6 at least one of R 7 at least one of R 8 at least one of R 7 or R 8 is -H.

24. The method of forming a solid electrolytic capacitor of claim 23, wherein R 7 and R 8 are each -H.

25. The method of forming a solid electrolytic capacitor of claim 23, wherein R 1 at least two of R 6 to R 7 R 8 .

26. The method of forming a solid electrolytic capacitor of claim 25, wherein R 1 at least three of R 6 to R 7 R 8 .

27. The method of forming a solid electrolytic capacitor of claim 25, wherein R 1 to at least four of R 6 are -PO3R 7 R 8 .

28. The method of forming a solid electrolytic capacitor of claim 27, wherein R 1 to at least five of R 6 are -PO3R 7 R 8 .

29. The method of forming a solid electrolytic capacitor of claim 27, wherein R 1 each of R 6 to R 7 is -PO3R 8 .

30. The method of forming a solid electrolytic capacitor of claim 29, wherein each of R 7 and R 8 is -H.

31. The method of forming a solid electrolytic capacitor of claim 22 wherein R 7 or at least one of R 8 is a cation.

32. The method of forming a solid electrolytic capacitor according to claim 22, wherein the cation is selected from quaternary amine and saturated or unsaturated carbon chain containing up to 35 carbon atoms.

33. The method of forming a solid electrolytic capacitor of claim 22 wherein each R 9 is independently an alkyl group containing from 1 to 3 carbon atoms.

34. The method of forming a solid electrolytic capacitor of claim 33 wherein each R 9 is -CH3.

35. The method of forming a solid electrolytic capacitor of claim 22 wherein each R 10 is independently an alkyl group containing from 1 to 3 carbon atoms.

36. The method of forming a solid electrolytic capacitor of claim 35 wherein each R 10 is -CH3.

37. The method of forming a solid electrolytic capacitor according to claim 22, wherein the inositol derivative is selected from inositol and its isomers and their respective derivatives, namely inositol hexakisphosphate (phytic acid); pentakisphosphate, triphosphate, diphosphate, and their isomers; and inositol monophosphate, inositol trisphosphate, 1 -phosphatidylinositol, 1 -phosphatidylinositol 3-phosphate; anaurol, erythrodiol, 1 -deoxy- 1 -(methylamino)-epi-inositol, (1R,2S,3R,4S,5R,6S)-5,6-dimethoxy-1,2,3,4-cyclohexanetetrol, pinostrobin, quebrachitol, (1R,2R,3R,4S,5R,6S)-3,6-dimethoxy-1,2,4,5-cyclohexanetetrol, and L-quebrachitol derivatives; inositol 1,3,4,5,6-penta-O-(trimethylsilyl)-, bis(trimethylsilyl)phosphate, phosphatidylinositol 5-phosphate PI(5) bis C8 ammonium salt, phosphatidylinositol 5-phosphate bis C16 (PI(5)P bis C16) sodium salt, 1,2-diacyl-sn-glycero-3-phospho-(1 -D-inositol 4,5-bisphosphate), phosphatidylinositol, phosphatidylinositol 3-phosphate, phosphatidylinositol 4-phosphate, phosphatidylinositol 4,5-phosphate, diinositol phosphate, ciceritol phosphate, fagaronol phosphate, glycosyl inositol phosphoryl ceramide, C25,25-Archeditylinositol, ceramide phosphoinositol, D-inositol-4-hydrogenphosphoric acid monoammonium salt, and phosphatidylinositol phosphate.

38. The method of forming a solid electrolytic capacitor according to claim 22, wherein the formation electrolyte comprises an additive selected from metal salt, organic acid salt, inorganic acid salt, organic acid, inorganic acid, organometallic compound, inorganic solvent, organic solvent, crosslinker, surfactant, and buffer.

39. The method of forming a solid electrolytic capacitor of claim 38, wherein the metal salt, inorganic acid salt, and organic acid salt comprise halides, nitrides, sulfides, amides, nitrates, sulfates, phosphates, carbonates, chromates, chlorates, perchlorates, oxides, oxychlorides, peroxides, carboxylates, amides, and esters.

40. The method of forming a solid electrolytic capacitor of claim 38, wherein the organic and inorganic acids comprise carboxylic acids, phosphonic acids, phosphinic acids, phosphoric acids, phthalic acids, maleic acids, malonic acids, and trimesic acids.

41. The method of forming a solid electrolytic capacitor of claim 38, wherein the organometallic compound comprises organosilanes, organoboranes, carbonyls, phosphines, crosslinking agents, surfactants, and buffers.

42. The method of forming a solid electrolytic capacitor of claim 22, wherein the formation electrolyte further comprises at least one solvent selected from water, alcohols, ethylene glycol, polyethylene glycol, tetraethylene glycol dimethyl ether, propylene glycol, glycol ethers, and alkanolamines.

43. The method of forming a solid electrolytic capacitor of claim 22, wherein the electrically conductive polymer is selected from the group consisting of poly(3,4- ethylenedioxythiophene), poly(4-(2,3-dihydrothieno[3,4-b][l,4]dioxin-2-yl)methoxy)- 1 -butane-sulfonic acid / sulfonate), poly(4-(2,3-dihydrothieno[3,4-b][l,4]dioxin-2-yl)methoxy)- 1 -propane-sulfonic acid / sulfonate), poly(4-(2,3-dihydrothieno[3,4-b][l,4]dioxin-2-yl)methoxy)- 1 -methyl- 1 -propane-sulfonic acid / sulfonate), poly(4-(2,3-dihydrothieno[3,4-b][l,4]dioxin-2-yl)methoxy alcohol, poly(N-methylpyrrole), poly(3-methylpyrrole), poly(3-octylpyrrole), poly(3-decylpyrrole), poly(3-dodecylpyrrole), poly(3,4-dimethylpyrrole), poly(3,4-dibutylpyrrole), poly(3-carboxy pyrrole), poly(3-methyl-4-carboxy pyrrole), poly(3-methyl-4-carboxyethyl pyrrole), poly(3-methyl-4-carboxybutyl pyrrole), poly(3-hydroxypyrrole), poly(3-methoxypyrrole), polythiophene, poly(3-methylthiophene), poly(3-hexylthiophene), poly(3-heptylthiophene), poly(3-octylthiophene), poly(3-decylthiophene), poly(3-dodecylthiophene), poly(3-octadecylthiophene), poly(3-bromothiophene), poly(3,4-dimethylthiophene), poly(3,4-dibutylthiophene), poly(3-hydroxythiophene), poly(3-methoxythiophene), poly(3-ethoxythiophene), poly(3-butoxythiophene), poly(3-hexyloxythiophene), poly(3-heptoxythiophene), poly(3-octyloxythiophene), poly(3-decyloxythiophene), poly(3-dodecyloxythiophene), poly(3-octadecyloxythiophene), poly(3,4-dihydroxythiophene), poly(3,4-dimethoxythiophene), poly(3,4-ethylenedioxythiophene), poly(3,4-propylenedioxythiophene), poly(3,4-butylenedioxythiophene), poly(3-carboxythiophene), poly(3-methyl-4-carboxythiophene), poly(3-methyl-4-carboxyethylthiophene), poly(3-methyl-4-carboxybutylthiophene), polyaniline, poly(2-methylaniline), poly(3-isobutylaniline), poly(2-anilinesulfonate), poly(3-anilinesulfonate).

44. The method of forming a solid electrolytic capacitor of claim 22, wherein the dielectric is not washed prior to the forming the electrically conductive polymer cathode.

45. A capacitor comprising an anode prepared by anodizing a pressed valve metal powder in the electrolytic solution of claim 22.

46. The capacitor of claim 45, wherein the electrically conductive polymer layer comprises an inner polymer layer and an outer polymer layer, the inner and outer polymers comprising a pre-polymerized electrically conductive polymer.

47. The capacitor of claim 45, wherein the abnormal charge current of the capacitor is less than 4 times the theoretical value.

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