JP7698466B2 - Electrolytic capacitor and method for manufacturing the same - Google Patents

Description

The present invention relates to an electrolytic capacitor and a method for manufacturing an electrolytic capacitor.

Conventionally, quaternized amidinium salt-based electrolytes have been known, and electrolytic capacitors have been proposed that incorporate boric acid and sugar alcohols such as mannitol into the electrolyte to increase the withstand voltage and accommodate rated voltages of 50 to 100 V (Patent Document 1: JP 9-213583 A, Patent Document 2: JP 2011-204949 A, Patent Document 3: WO 2014/051129 A).

Japanese Patent Application Publication No. 9-213583 JP 2011-204949 A WO2014/051129 publication

Electrolytic capacitors using electrolytes are always required to have improved reliability, and in particular to have improved leakage suppression effects. However, the electrolytes in the above patent documents do not adequately meet such demands for high reliability.

The present invention was made in consideration of these circumstances, and aims to provide an electrolytic capacitor that has a higher leakage suppression effect than conventional capacitors, has a low ESR, and can be used at voltages of 50 V or more.

In one embodiment, the above problem is solved by the solution disclosed below.

The electrolytic capacitor of the present invention includes a capacitor element in which an anode foil and a cathode foil are wound with a separator interposed therebetween, and an electrolyte introduced into the capacitor element, the anode foil having a film withstand voltage of 65 V or more, the electrolyte containing 70 to 80 % by weight of γ-butyrolactone, an amidinium phthalate salt constituted by an acid anion and a quaternized cyclic amidinium cation, and constituted by phthalic acid and 1,2,3,4-tetramethylimidazolinium , and triethylamine phthalate which is a first composition constituted by an organic acid and a non-quaternary amine and in which the pKa of a conjugate acid of the non-quaternary amine is 12 or less, the molar ratio of the non-quaternary amine to the quaternized cyclic amidinium cation is 0.2 or more , and the electrolyte containing 5 to 20% by weight of the amidinium phthalate salt and 5% by weight or more of the first composition triethylamine phthalate .

The inventors have found that the use of a specific electrolyte improves leakage resistance and also allows for a low ESR, and have completed the present invention. In other words, according to this configuration, the low resistivity characteristics of the electrolyte containing the quaternized cyclic amidinium salt allow for a low ESR, and the electrolyte containing 5% by weight or more of the first composition provides good leakage resistance, making it possible to use the electrolyte at voltages of 50 V or more. In other words, by using a non-quaternary amine with a small pKa of the conjugate acid, the effect of the quaternized cyclic amidinium salt on leakage resistance is suppressed, and good leakage resistance is obtained. The pKa of the conjugate acid of the non-quaternary amine is 12 or less, preferably the pKa of the conjugate acid of the non-quaternary amine is 11 or less, and more preferably the pKa of the conjugate acid of the non-quaternary amine is 10 or less.

The electrolyte preferably contains 50% by weight or more of gamma-butyrolactone and 2% by weight or more of the quaternized cyclic amidinium salt. This configuration effectively prevents an increase in resistivity in the low temperature range. As an example, the solvent for the electrolyte may be gamma-butyrolactone alone.

The quaternized cyclic amidinium salt preferably has an alkyl group added to all nitrogen atoms constituting the ring among the atoms in the quaternized cyclic amidinium cation. This allows the electrolyte to have a low resistivity. Examples of such cationic components include 1,2,3,4-tetramethylimidazolinium cation, other known quaternized imidazolinium cations, other known quaternized imidazolium cations, etc. One of these may be used alone, or a combination of two or more may be used. In addition, in order to lower the resistivity of the electrolyte and contribute more to the low ESR characteristics of the electrolytic capacitor, the electrolyte may contain 5 [wt %] or more of the quaternized cyclic amidinium salt, or 10 [wt %] or more. On the other hand, the electrolyte preferably has a total value of the proportion of the quaternized cyclic amidinium salt and the proportion of the first composition of 40 [wt %] or less, and more preferably 30 [wt %] or less. This prevents a phenomenon in which a part of the electrolyte components precipitates in a low temperature range.

The molar ratio of the number of moles of the non-quaternary amine to the number of moles of the quaternized cyclic amidinium cation is preferably 0.2 or more. By increasing the molar ratio, the effect of the quaternized cyclic amidinium salt on liquid leakage is suppressed, and good liquid leakage resistance is obtained. The molar ratio is more preferably 0.3 or more. The molar ratio is even more preferably 0.4 or more.

An example of a quaternary cyclic amidinium salt is a salt of a carboxylic acid anion and a quaternary cyclic amidinium cation. In addition, a salt of an anion of a polycarboxylic acid such as phthalic acid and a quaternary cyclic amidinium cation can be preferably used.

As an example of the organic acid constituting the first composition, carboxylic acids can be given, and in particular, polycarboxylic acids such as phthalic acid, adipic acid, and azelaic acid can be preferably used. One of these may be used alone, or multiple types may be used in combination.

Examples of the non-quaternary amine constituting the first composition include tertiary amines such as triethylamine and ethyldimethylamine. In addition, one of the tertiary amines, secondary amines, and primary amines may be used alone, or a combination of two or more types may be used. It is preferable that the first composition contains a tertiary amine salt. It is preferable that at least one of the non-quaternary amines in the first composition is a tertiary amine.

From the viewpoint of enabling use at higher voltages than conventional products, the anode foil's film withstand voltage may be 80 [V] or more, or 120 [V] or more. Also, from the viewpoint of enabling use at higher voltages, the proportion of quaternized cyclic amidinium salt in the electrolyte may be 20 [wt %] or less, or 15 [wt %] or less. In particular, to enable use at a voltage of 100 [V], the anode foil's film withstand voltage may be 120 [V] or more, and the proportion of quaternized cyclic amidinium salt in the electrolyte may be 15 [wt %] or less.

The method for producing an electrolytic capacitor of the present invention includes a capacitor element in which an anode foil and a cathode foil are wound with a separator interposed therebetween, and an electrolyte introduced into the capacitor element, the anode foil having a film withstand voltage of 65 V or more, the electrolyte containing 70 to 80 % by weight of γ-butyrolactone, and including a phthalic acid amidinium salt composed of an acid anion and a quaternized cyclic amidinium cation and composed of phthalic acid and 1,2,3,4-tetramethylimidazolinium , an organic acid and a non-quaternary amine , and a phthalic acid amidinium salt composed of ... and a second step of adding the first composition, triethylamine phthalate , to the first solution to adjust the molar ratio of the non-quaternary amine to the quaternized cyclic amidinium cation to 0.2 or more, thereby corresponding to a rated voltage of 50 V or more. The electrolytic solution is characterized in that it contains 5 to 20% by weight of the amidinium phthalate salt and 5% by weight or more of the first composition , triethylamine phthalate.

According to this manufacturing method, the concentration of the quaternized cyclic amidinium salt in the first solution can be adjusted to correspond to a rated voltage of 50 V or more, thereby preparing the desired electrolyte solution. The low resistivity characteristic of the electrolyte solution containing the quaternized cyclic amidinium salt allows for a low ESR, while the electrolyte solution containing the first composition provides good leakage resistance.

According to the present invention, the low resistivity characteristic of the electrolyte containing the quaternized cyclic amidinium salt allows for a low ESR, while the electrolyte containing the first composition provides good leakage resistance, allowing use at voltages of 50 V or more. Therefore, an electrolytic capacitor with a low ESR, good leakage resistance, and improved reliability can be realized.

FIG. 1 is a partial cross-sectional side view showing a schematic structure of an electrolytic capacitor according to an embodiment of the present invention. FIG. 2A is a schematic diagram showing the positional relationship between a lead terminal and an anode foil, and between the lead terminal and a cathode foil, and FIG. 2B is a schematic diagram showing the state in which the anode foil, a first separator, a cathode foil, and a second separator are stacked and wound in this order.

The following is a detailed description of an embodiment of the present invention. As shown in Figs. 1, 2A, and 2B, the electrolytic capacitor 1 includes a wound capacitor element 2 into which an electrolytic solution 2e is introduced, lead terminals 5 and 6, a sealing body 3 with two through holes, and a bottomed case 4 for housing the capacitor element 2, with the opening side of the case 4 sealed by the sealing body 3. The sealing body 3 is highly airtight to prevent the intrusion of moisture and the scattering of oxide film repair material, and has a roughly cylindrical shape that matches the inner shape of the case 4. The case 4 is formed by processing a metal such as aluminum, and the sealing body 3 is made of an insulating rubber composition.

The anode foil 2a is made of a valve metal such as aluminum, and its surface is roughened by etching, and then an oxide film is formed by chemical conversion treatment. The cathode foil 2c is made of a valve metal such as aluminum, and its surface is roughened by etching, and then an oxide film is formed by natural oxidation or chemical conversion treatment. A first separator 2d1 or a second separator 2d2 is disposed between the anode foil 2a and the cathode foil 2c. The first separator 2d1 and the second separator 2d2 can be made of paper, nonwoven fabric, etc. containing natural fibers or chemical fibers. Examples of raw materials for natural fibers include wood, Manila hemp, and esparto. Examples of chemical fibers include rayon, and recycled fibers may also be used.

As shown in FIG. 2B, the capacitor element 2 is formed by stacking and winding the anode foil 2a with an oxide film formed thereon, the first separator 2d1, the cathode foil 2c, and the second separator 2d2 in that order. The capacitor element 2 is then impregnated with the electrolyte 2e.

As an example, electrolyte solution 2e contains γ-butyrolactone as an organic solvent, a quaternized cyclic amidinium salt composed of an equimolar acid anion and a quaternized cyclic amidinium cation in a ratio of 5% by weight to 25% by weight, and 5% by weight or more of a first composition consisting of one or more organic acids and one or more non-quaternary amines, with a configuration in which a portion of the γ-butyrolactone in a reference electrolyte solution that does not contain the first composition is replaced with the first composition.

Next, examples of electrolytes A1, A2, B, C1, C2, D1, and D2 will be described below.

[Electrolyte Example A1]
It contains 80% by weight of γ-butyrolactone and 20% by weight of a quaternized cyclic amidinium salt in which an acid anion and a quaternized cyclic amidinium cation are composed in equimolar amounts. The quaternized cyclic amidinium salt is a salt of phthalic acid and 1,2,3,4-tetramethylimidazolinium. It does not contain the first composition. It does not contain boric acid. It does not contain sugar alcohols.

[Electrolyte Example A2]
It contains 85% by weight of gamma-butyrolactone, 5% by weight of a quaternized cyclic amidinium salt in which an acid anion and a quaternized cyclic amidinium cation are formed in equimolar amounts, 4% by weight of boric acid, and 6% by weight of mannitol. The quaternized cyclic amidinium salt is a salt of phthalic acid and 1,2,3,4-tetramethylimidazolinium. The first composition is not included.

[Electrolyte Example B]
It contains 73% by weight of gamma-butyrolactone, 20% by weight of a quaternized cyclic amidinium salt in which an acid anion and a quaternized cyclic amidinium cation are composed in equimolar amounts, 3% by weight of boric acid, and 4% by weight of mannitol. The quaternized cyclic amidinium salt is a salt of phthalic acid and 1,2,3,4-tetramethylimidazolinium. The first composition is not included.

[Electrolyte Example C1]
The electrolyte solution C1 contains 70% by weight of γ-butyrolactone, 20% by weight of a quaternized cyclic amidinium salt in which an acid anion and a quaternized cyclic amidinium cation are equimolar, and 10% by weight of a first composition in which adipic acid and triethylamine are mixed in a weight ratio of 8:2. The quaternized cyclic amidinium salt is a salt of phthalic acid and 1,2,3,4-tetramethylimidazolinium. The electrolyte solution C1 is configured such that the electrolyte solution A1 is used as a reference electrolyte solution, and a portion of the γ-butyrolactone in the reference electrolyte solution is replaced with the first composition in the same weight ratio, thereby making the specific resistance about 1.6 times that of the reference electrolyte solution. An example electrolyte C1 was prepared by preparing a first solution containing γ-butyrolactone and a quaternized cyclic amidinium salt, and then adding adipic acid and triethylamine constituting a first composition to the first solution.

[Electrolyte Example C2]
The electrolyte solution C2 contains 70% by weight of γ-butyrolactone, 20% by weight of a quaternized cyclic amidinium salt in which an acid anion and a quaternized cyclic amidinium cation are equimolar, and 10% by weight of a first composition in which azelaic acid and triethylamine are mixed in a weight ratio of 8.5:1.5. The quaternized cyclic amidinium salt is a salt of phthalic acid and 1,2,3,4-tetramethylimidazolinium. The electrolyte solution C2 is configured such that the electrolyte solution A1 is used as a reference electrolyte solution, and a portion of the γ-butyrolactone in the reference electrolyte solution is replaced with the first composition in the same weight ratio, thereby making the specific resistance about 1.6 times that of the reference electrolyte solution. An example electrolyte C2 was prepared by preparing a first solution containing γ-butyrolactone and a quaternized cyclic amidinium salt, and then adding azelaic acid and triethylamine, which constitute a first composition, to the first solution.

[Electrolyte Example D1]
It contains 80% by weight of γ-butyrolactone, 5% by weight of a quaternized cyclic amidinium salt composed of equimolar acid anion and quaternized cyclic amidinium cation, 4% by weight of boric acid, 6% by weight of mannitol, and 5% by weight of a first composition composed of equimolar phthalic acid and triethylamine. The quaternized cyclic amidinium salt is a salt of phthalic acid and 1,2,3,4-tetramethylimidazolinium. Electrolyte solution example D1 was prepared by using electrolyte solution example A2 as a reference electrolyte solution, and replacing a portion of the γ-butyrolactone in the reference electrolyte solution with the same weight ratio of the first composition to make the resistivity about 0.9 times that of the reference electrolyte solution, and by preparing a first solution containing γ-butyrolactone and a quaternized cyclic amidinium salt, and then adding phthalic acid and triethylamine constituting the first composition to the first solution.

[Electrolyte Example D2]
The electrolyte solution D2 contains 75% by weight of γ-butyrolactone, 5% by weight of a quaternized cyclic amidinium salt composed of an equimolar acid anion and a quaternized cyclic amidinium cation, 4% by weight of boric acid, 6% by weight of mannitol, and 10% by weight of a first composition composed of equimolar phthalic acid and triethylamine. The quaternized cyclic amidinium salt is a salt of phthalic acid and 1,2,3,4-tetramethylimidazolinium. The electrolyte solution D2 is configured such that the electrolyte solution A2 is used as a reference electrolyte solution, and a part of the γ-butyrolactone in the reference electrolyte solution is replaced with the first composition in the same weight ratio, thereby making the specific resistance about 1.1 times that of the reference electrolyte solution. An example electrolyte D2 was prepared by preparing a first solution containing γ-butyrolactone and a quaternized cyclic amidinium salt, and then adding phthalic acid and triethylamine constituting a first composition to the first solution.

Next, examples of capacitor elements E to H are described below.

[Capacitor element example E]
The anode foil 2a and the cathode foil 2c are made of aluminum, and the first separator 2d1 and the second separator 2d2 contain rayon at 60% by weight or more. The anode foil has a membrane withstand voltage of 65 V or more. The anode foil 2a has a thickness of 90 μm, the cathode foil 2c has a thickness of 50 μm, the first separator 2d1 has a thickness of 50 μm, and the second separator 2d2 has a thickness of 50 μm. The total thickness of the anode foil 2a, the first separator 2d1, the cathode foil 2c, and the second separator 2d2 is 240 μm.

[Capacitor element example F]
The anode foil 2a and the cathode foil 2c are made of aluminum, and the first separator 2d1 and the second separator 2d2 contain rayon at 60% by weight or more. The anode foil has a membrane withstand voltage of 65 V or more. The anode foil 2a has a thickness of 70 μm, the cathode foil 2c has a thickness of 50 μm, the first separator 2d1 has a thickness of 40 μm, and the second separator 2d2 has a thickness of 40 μm. The total thickness of the anode foil 2a, the first separator 2d1, the cathode foil 2c, and the second separator 2d2 is 200 μm.

[Capacitor element example G]
The anode foil 2a and the cathode foil 2c are made of aluminum, and the first separator 2d1 and the second separator 2d2 contain 60% or more by weight of rayon. The anode foil has a membrane withstand voltage of 65 V or more. The anode foil 2a has a thickness of 65 μm, the cathode foil 2c has a thickness of 40 μm, the first separator 2d1 has a thickness of 40 μm, and the second separator 2d2 has a thickness of 40 μm. The total thickness of the anode foil 2a, the first separator 2d1, the cathode foil 2c, and the second separator 2d2 is 185 μm.

[Capacitor element example H]
The anode foil 2a and the cathode foil 2c are made of aluminum, and the first separator 2d1 and the second separator 2d2 contain rayon at 60% by weight or more. The anode foil has a membrane withstand voltage of 120 V or more. The anode foil 2a has a thickness of 70 μm, the cathode foil 2c has a thickness of 50 μm, the first separator 2d1 has a thickness of 40 μm, and the second separator 2d2 has a thickness of 40 μm. The total thickness of the anode foil 2a, the first separator 2d1, the cathode foil 2c, and the second separator 2d2 is 200 μm.

Next, electrolytic solution examples A1, B, C1, and C2 were combined with capacitor element examples E to G to produce 10 electrolytic capacitors each with a rated voltage of 50 [V] and a capacitance of 33 [μF]. The ESR was then measured at a temperature of 25 [°C] and a frequency of 100 [kHz] to calculate the average value, after which the capacitors were placed in a thermo-hygrostat at a temperature of 85 [°C] and a humidity of 85 [% RH] and subjected to a load test of 1,000 [hours] in which a rated voltage of 50 [V] was applied, and the presence or absence of leakage after the test was confirmed. The performance evaluation results are shown in Table 1 below.

According to Table 1, leakage occurred in all of Reference Examples 1 to 3 using electrolyte examples A1 and B. In addition, in Reference Example 1 using electrolyte example A1, the withstand voltage of the electrolyte was insufficient, and the yield rate in the specified aging process in which a voltage equal to or higher than the rated voltage was applied was lower than in the other examples. In contrast, leakage did not occur in any of Examples 1 to 6 using electrolyte examples C1 and C2. Furthermore, the yield rate in the specified aging process in which a voltage equal to or higher than the rated voltage was also good, and it was confirmed that good leakage resistance and sufficient withstand voltage characteristics can be obtained by using electrolyte 2e containing the first composition. In particular, it was confirmed that the use of capacitor element example F or capacitor element example G results in a lower ESR than the configuration using capacitor element example E, and that the use of capacitor element example G results in an even lower ESR than the configuration using capacitor element example F.

Next, electrolytic solution examples A2, D1, and D2 were combined with capacitor element example H to produce 10 electrolytic capacitors each with a rated voltage of 100 [V] and a capacitance of 22 [μF]. The ESR was then measured at a temperature of 25 [°C] and a frequency of 100 [kHz] to calculate the average value, and the capacitors were then placed in a thermo-hygrostat at a temperature of 85 [°C] and a humidity of 85 [% RH] to carry out a load test for 5,000 [hours] in which a rated voltage of 100 [V] was applied, and the presence or absence of leakage after the test was confirmed. The performance evaluation results are shown in Table 2 below.

According to Table 2, leakage occurred in Reference Example 4, which used electrolyte example A2. In contrast, no leakage occurred in Examples 7 to 8, which used electrolyte examples D1 and D2, confirming that good leakage resistance was achieved by electrolyte solution 2e containing the first composition. In particular, it was confirmed that good low ESR was achieved by using capacitor element example H. Therefore, the effect of improving leakage resistance by electrolyte solution 2e containing the first composition is remarkable.

The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the scope of the present invention.

1 Electrolytic capacitor 2 Capacitor element 2a Anode foil 2c Cathode foil 2e Electrolyte 3 Sealing body 4 Case 5 Lead terminal 6 Lead terminal

Claims (2)

1. An electrolytic capacitor comprising: a capacitor element in which an anode foil and a cathode foil are wound with a separator interposed therebetween; and an electrolyte introduced into the capacitor element, the anode foil having a film withstand voltage of 65 V or more, the electrolyte containing 70 to 80 % by weight of gamma-butyrolactone, a phthalic acid amidinium salt constituted by an acid anion and a quaternized cyclic amidinium cation, and constituted by phthalic acid and 1,2,3,4-tetramethylimidazolinium , and triethylamine phthalate as a first composition constituted by an organic acid and a non-quaternary amine and in which the pKa of a conjugate acid of the non-quaternary amine is 12 or less, a molar ratio of the non-quaternary amine to the quaternized cyclic amidinium cation is 0.2 or more, and the electrolyte containing 5 to 20% by weight of the phthalic acid amidinium salt and 5% by weight or more of the first composition triethylamine phthalate . The present invention relates to a capacitor element including an anode foil and a cathode foil wound with a separator therebetween, and an electrolyte introduced into the capacitor element, the anode foil having a withstand voltage of 65 V or more, the electrolyte containing 70 to 80 % by weight of γ-butyrolactone, and including an acid anion and a quaternized cyclic amidinium cation , a phthalic acid amidinium salt including phthalic acid and 1,2,3,4-tetramethylimidazolinium , an organic acid, and a non-quaternary amine , the pKa value of a conjugate acid of the non-quaternary amine being greater than or equal to 1. 1. A method for producing an electrolytic capacitor containing triethylamine phthalate as a first composition having a molecular weight of 12 or less, the method comprising: a first step of preparing a first solution containing the amidinium phthalate salt in an organic solvent; and a second step of adding the triethylamine phthalate as the first composition to the first solution to adjust the molar ratio of the non-quaternary amine to the quaternized cyclic amidinium cation to 0.2 or more, corresponding to a rated voltage of 50 V or more , the electrolytic solution containing 5 to 20% by weight of the amidinium phthalate salt and 5% by weight or more of the first composition, triethylamine phthalate.

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