KR101381069B1 - Binder for capacitor electrode - Google Patents

Abstract

The present invention exhibits high powder electrode material binding property and adhesiveness with a collecting electrode, and also has excellent wettability to electroconductivity and electrolyte in the state in which the powder electrode material is bound, that is, in the state of the electrode sheet, has high heat resistance, and Chemically stable binders for capacitor electrodes comprising aramid granulated by heat treatment are disclosed.

Adhesion to powder electrode material, adhesion to collector electrode, conductivity in the state of electrode sheet, wettability to electrolyte solution, granulated aramid, binder for capacitor electrode

Description

Binder for Capacitor Electrode {BINDER FOR CAPACITOR ELECTRODE}

The present invention relates to a binder for electrodes useful for forming electrodes of capacitors, such as capacitors and lithium secondary batteries.

As recent advances such as portable communication devices and high-speed information processing devices symbolize, there is a remarkable surprise in miniaturization and high performance of electronic devices. Among them, small-capacity, high-capacity, high-capacity capacitors and batteries that withstand long-term storage have high expectations, and wide application has been achieved, and parts development is rapidly progressing. In order to cope with this, the necessity of technology and quality development is increasing also about the binder which binds an electrode active material in an electrode sheet.

In particular, among the various properties required for the binder, it is recognized that the following five characteristic items are particularly important for the binder for electrodes in a capacitor such as a capacitor and a battery requiring a high withstand voltage, a large capacity, and a large output:

1) high powder electrode material binding and adhesion with collecting electrode,

2) Good conductivity in the state of binding the powder electrode material, that is, the state of the electrode sheet,

3) good wettability of the electrolyte in the state of binding the powder electrode material, that is, the state of the electrode sheet;

4) high heat resistance,

5) Be electrochemically stable.

Conventionally, as binders, PVdF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), SBR (styrene butadiene rubber) latex and the like have been widely used, but these binders have recently been used for capacitors, batteries, and the like for electric vehicles. The high temperature drying of the electrode group which consists of a collector electrode, an electrode, and a separator which the inventors proposed previously as a method for achieving high withstand voltage, a large capacity, a large output, and also these, is mentioned (refer Japanese patent application 2006-073898 specification). It is not always able to cope with enough about. Moreover, PTFE (polytetrafluoroethylene) is difficult to manufacture a thin electrode sheet in practical use, and may be difficult to apply to a large output capacitor and a battery in which a thin electrode is required.

In addition, Japanese Patent Laid-Open No. 2001-345103 uses an organic polymer having a carbonyl group electrochemically active in the main chain or the side chain as part of the negative electrode active material in order to provide a secondary battery negative electrode active material having high charge and discharge efficiency. It is disclosed to use, for example, aramid (aromatic polyamide) as a negative electrode active material and binder for secondary batteries. However, since it is difficult to make powder electrode material binding property, adhesiveness with a collecting electrode, and low electroconductivity in an electrode sheet, desired battery characteristic may not be acquired.

[Disclosure of the Invention]

[Summary of the Invention]

The main object of the present invention is to exhibit high powder electrode material binding property and adhesiveness to the collecting electrode, and also excellent conductivity and wettability to the electrolytic solution in the state in which the powder electrode material is bound, that is, in the state of the electrode sheet, and heat resistance. To provide a high, electrochemically stable binder for capacitor electrodes.

Still another object of the present invention is to provide a capacitor such as a capacitor, a battery, and the like using the binder.

MEANS TO SOLVE THE PROBLEM As a result of earnestly researching in order to achieve the said objective, the present inventors discovered that it was very effective to use the aramid granulated by heat processing as a binder for capacitor electrodes at this time, and came to complete this invention.

In this way, this invention provides the binder for capacitor electrodes containing the aramid granulated by heat processing.

The present invention also provides an electrode sheet produced by mixing a powder electrode material, a binder and a solvent to produce a slurry, and applying the slurry to a collector electrode, wherein the binder is aramid and is subjected to heat treatment after application. .

The present invention also provides a capacitor, in particular a capacitor and a battery, using the electrode sheet described above.

The binder of the present invention has high heat resistance, is electrochemically stable aramid, shrinkage stress is applied between the powder electrode materials due to shrinkage of the binder during granulation by heat treatment, and the surface of the powder electrode material. Since the portion covering the film becomes smaller by shrinkage, the contact area between the powder electrode materials increases, and the conductivity in the state of the electrode sheet is remarkably improved. In addition, since the aramid has an amide group in the molecular chain, the binder of the present invention has good wettability with a carbonate-based electrolyte solution having a carboxyl group in the molecule, and because the electrode sheet can be manufactured by a coating method, a thin electrode sheet Can be manufactured, and is suitable for a large output capacitor, a battery, etc., where a thin electrode is required.

BRIEF DESCRIPTION OF THE DRAWINGS It is a micrograph (magnification 3500) of the surface of the coating film (active carbon / aramid = 90 weight% / 10weight%) before the heating of the collector electrode to which the powder electrode material, the aramid, and the solvent mixture slurry were apply | coated.

FIG. 2 is a micrograph (magnification 3500) of the surface of a coating film after heating (350 degreeC) of the collecting electrode shown in FIG.

FIG. 3 is a micrograph (magnification 3500) of the surface of a coating film (active carbon / aramid = 70 wt% / 30 wt%) before heating of a collecting electrode to which a powder electrode material, aramid, and a mixed slurry of a solvent are applied.

4 is a micrograph (magnification 3500) of the surface of the coating film after heating (350 ° C.) of the collecting electrode shown in FIG. 1.

Detailed Description of the Invention

Hereinafter, the present invention will be described in more detail.

Powder electrode material :

The powder electrode material in the present invention comprises a mixture of an electrode active material, a conductive agent added as necessary, and other auxiliary agents.

Electrode Active Material :

The electrode active material used in the present invention is not particularly limited as long as it functions as an electrode of a capacitor and / or a battery. Specifically, in the case of a capacitor, for example, Helmholtz uses an electric double layer discovered in 1879. Carbon-based materials such as activated carbon, foamed carbon, carbon nanotubes, polyacene, nanogate carbon, and the like used in electric double layer capacitors for storing electricity; Metal oxides, conductive polymers, organic radicals, etc. which can utilize the pseudo capacitance accompanying a redox reaction are mentioned, The electrode of a battery can be used for one electrode. Moreover, in the case of a battery, especially a lithium ion secondary battery, lithium metal oxides, such as lithium cobalt, lithium chromate, lithium vanadate, lithium chromate, lithium nickelate, lithium manganate, etc. can be used as a positive electrode, for example. As the negative electrode, for example, natural graphite, artificial graphite, resinous coal, carbides of natural products, carbonaceous materials such as petroleum coke, coal coke, pitch coke, mesocarbon microbeads, metallic lithium and the like can be used.

Challenge

The conductive agent used in the present invention is not particularly limited as long as it has a function of improving the electrical conductivity of the electrode sheet, and examples thereof include carbon blacks such as acetylene black and ketjen black.

Aramid :

The aramid used in the present invention includes a linear polymer compound in which 60% or more of the amide bonds are directly bonded to the aromatic ring, and specifically, for example, polymethaphenylene isophthalamide and its copolymer, polyparaphenyl The lenterephthalamide and its copolymer, poly (paraphenylene) -copoly (3,4-diphenylether) terephthalamide, etc. are mentioned. Although these aramids are industrially manufactured by the well-known interface polymerization method, the solution polymerization method, etc. which are known for itself using isophthalate and metaphenylenediamine, it can obtain as a commercial item, for example, It is limited to these It is not. Among these aramids, in particular, polymethaphenylene isophthalamide is preferably used in view of having properties such as good molding processability, heat adhesiveness, flame retardancy, and heat resistance.

Aramid granulated by heat treatment :

The aramid granulated by heat treatment can be obtained, for example, by mixing a powdered electrode material, aramid and a solvent to produce a slurry, and applying the slurry to a collector electrode and then heating. The aramid in the coating film is in the shape of a tree as shown in FIG. 1 before heating after application, and when it is heated at 350 ° C. for 2 hours, for example, it becomes granular as shown in FIG. 2. Since aramid shrinks during the granulation process, shrinkage stress acts between the powder electrode materials, and the portion covering the surface of the powder electrode material becomes smaller due to shrinkage, so that the contact area between the powder electrode materials increases. The resistance value of the capacitor decreases due to high conductivity of the electrode sheet, in particular, the aramid formed in this manner has a high binding force, so that the resistance of the capacitor remains low even after impregnation with the electrolyte solution.

Although the usage-amount of an aramid binder in this invention is not specifically limited as long as it granulates by heating, It is usually in the range of 3-15 weight% based on the sum total of aramid and powder electrode material, Especially 5-13 weight% The range of i is preferred. When the amount of the aramid binder used exceeds the above range, granulation is generally difficult to occur, and as shown in FIGS. 3 and 4, the binder covers the powder electrode material even after heating at 350 ° C. for 2 hours, thereby accumulating the capacitor. The function of is significantly lowered.

Although the said heat processing conditions do not have a restriction | limiting in particular as long as the characteristic of a capacitor | capacitor desired is achieved, heat processing is especially preferable at the temperature near the crystallization temperature of aramid because the binding power of aramid is considered to be the highest. For example, when using a polyamide phenylene isophthalamide as aramid, since it may thermally decompose when it exceeds 370 degreeC, heat processing is preferable to carry out at the temperature of 370 degreeC or less, and it is 330-300 in terms of crystallization temperature. It is especially preferable to carry out at the temperature within the range of 365 degreeC. In addition, the timing of heat treatment is not particularly limited as long as it is after application, but once applied, the solvent is dried at a relatively low temperature near the boiling point of the solvent so that foaming due to the dolby of the solvent does not interfere with the characteristics of the capacitor. It is preferable to perform heat processing after removing. As a heating means, the method of thermopressing at high temperature and high pressure between a pair of flat plates or a metal roll is mentioned, for example. The conditions of the thermal pressure can be exemplified in the range of, for example, a temperature of 275 to 365 ° C. and a linear pressure of 50 to 400 kg / cm when using a metal roll, but the present invention is not limited thereto. Only heating can be performed. It is also possible to laminate | stack a some electrode sheet at the time of a hot press, and can also repeat above-mentioned hot press process in multiple times in arbitrary order. It is also possible to assemble a collecting electrode, an electrode, and a separator to form an electrode unit, and then heat treatment.

The electrode unit is not particularly limited as long as the collecting electrode, the electrode, and the separator are assembled, and for example, the collecting electrode, the electrode, the separator, the electrode, and the collecting electrode are superimposed, or the electrode, the collecting electrode, the electrode, the separator, and the electrode. Units can be assembled by overlapping in the order of / collecting electrode / electrode / separator, repeating these superpositions, or further winding up the stacked laminates. In that case, it is also possible to adhere | attach between each member previously with an adhesive agent.

Solvents :

The solvent used in the present invention can be used without particular limitation as long as it can dissolve aramid. Among them, any of the good solvents N, N-dimethylacetamide (DMAC) and N-methyl-2-pyrrolidone (NMP) can be used. One or a mixture thereof is particularly preferred.

Collecting electrode :

The collecting electrode used in the present invention includes a conductive material and is not particularly limited as long as it is stable with respect to the electrode, the solvent, and the electrolyte, and examples thereof include metal thin plates such as aluminum thin plates, platinum thin plates, and copper thin plates.

Electrode Sheet :

The electrode sheet in this invention can be manufactured by manufacturing the slurry which mixed the powder electrode material, an aramid binder, and a solvent, for example, apply | coating this slurry to a collector electrode, and heat-processing. Specifically, for example, it can be produced as follows:

1) Slurry Manufacturing Process:

Aramid is dissolved in a solvent to prepare an aramid solution. A homogeneous slurry is prepared by mixing and stirring this solution and powder electrode material.

2) Thick Sheet Manufacturing Process:

The slurry is applied to one or both sides of the collecting electrode by using a slurry coating device such as a doctor knife, and, for example, is passed through a continuous drying furnace, or dried and solidified in a stationary drying furnace. Manufacture. Although the inside of the range of the boiling point +/- 5 degreeC of a solvent of the drying temperature at that time is preferable, it is not limited to this.

3) Press process:

The density and mechanical strength of the sheet can be improved by, for example, hot pressing at high temperature and high pressure between a pair of flat plates or between a metal roll. It is preferable that the electrode sheet after press satisfy | fills the range shown by following formula (1).

0.25 <D × (1 / D-We / De-Wc / Dc-Wb / Db) <0.75

Wherein,

D is the density of the electrode sheet excluding the collecting electrode,

We is the weight fraction of the electrode active material,

De is the abundance of the electrode active material,

Wc is the weight fraction of the conductive agent,

Dc is in the middle of the conductive agent,

Wb is the weight fraction of the binder,

Db is an abundance of binder.

When D x (1 / D-We / De-Wc / Dc-Wb / Db) is 0.75 or more, the electrode sheet is not sufficiently densified, and it is difficult to obtain a sufficient capacity as a capacitor and a battery. On the contrary, when D x (1 / D-We / De-Wc / Dc-Wb / Db) is 0.25 or less, it is difficult for the electrode sheet to become too dense to obtain sufficient output as a battery.

Hereinafter, the present invention will be described more specifically by way of examples. In addition, these Examples are only illustrations and do not limit the content of this invention at all.

Reference Example 1 (Manufacture of Electrode Sheet)

1) Slurry Manufacturing Process:

Polymetaphenyleneisophthalamide (1.38 in true specific gravity) was dissolved in NMP to prepare a metaaramid solution.

A homogeneous slurry was prepared by mixing and stirring the solution, activated charcoal (RP-20, manufactured by Kuraray Chemical Co., Ltd.), and Ketjen Black. The compounding ratio was adjusted so that the weight ratio of activated carbon: ketjen black: polymethaphenylene isophthalamide = 85: 5:10 after NMP evaporated.

2) electrode sheet manufacturing process:

The slurry obtained above was applied to one side of an aluminum foil collector electrode (conductively added with a phenolic resin in advance) using a doctor knife, dried (100 ° C. for 20 minutes, atmospheric pressure, and atmospheric atmosphere), and then pressed and dried ( Temperature 170 degreeC, the pressure of 1 torr or less, 10 hours), and obtained the electrode sheet of 93 micrometers in thickness.

Reference Example 2 (Manufacture of Electrode Unit)

According to the description of the Example of Unexamined-Japanese-Patent No. 2005-307360, the separator (mean weight 24.4 g / m <^2> , thickness 46 micrometers, density 0.53 g / cm <^3> ) containing m-aramid and p-aramid was prepared, The electrode unit was sandwiched between the electrode sheets of a pair of stationary electrodes.

Example 1

The electrode unit prepared in Reference Example 2 was heat-treated at a temperature of 350 ° C. (pressure 1 torr or lower, 12 hours), dried in a dry atmosphere, and inserted into an aluminum laminate enclosure. Subsequently, the three sides of the exterior were sealed, and 1.5 M of TEMABF ₄ / PC (a solution of triethylmethylammonium tetrafluoroborate dissolved in propylene carbonate) was injected as an electrolyte solution, and the resultant was impregnated under reduced pressure to carry out the rest of the exterior. The surface was sealed under reduced pressure, and the capacitor of the structure shown in following Table 1 was manufactured.

Comparative Example 1

The capacitor of the structure shown in Table 1 was manufactured by the method similar to Example 1 except having set the temperature of the heat processing of the electrode unit manufactured in the reference example 2 to 150 degreeC. In this case, the heat treatment was performed for drying the activated carbon electrode, and the heating temperature received by the binder after coating was 170 ° C in the electrode sheet manufacturing step.

<Characteristic evaluation>

Initial characteristics, rate characteristics, and low temperature characteristics of the capacitor were measured by the following method.

1) Initial charge and discharge characteristics

As the initial characteristics, the resistance was calculated by performing charge and discharge measurements and impedance measurements at an initial rate of 1C. Measurement conditions are as follows.

Initial capacity measurement (25 ℃)

Charge: CCCV 3.0 mA (1C), 2.8 V-2 hours (*)

Discharge: CC 3.0 mA (1C), 0.01 V (**)

(*) CCCV: constant current constant voltage, (**) CC: constant current

Impedance Measurement (25 ℃)

Measuring state: discharge

Measuring frequency: 20000 Hz to 0.1 Hz

Amplitude (ΔE): 10 mV

2) low temperature characteristics

As the low-temperature characteristics at -30 ° C, charge and discharge measurements and impedance measurements at 1C rate were performed to calculate resistance. Measurement conditions are as follows.

Capacity measurement (-30 degrees Celsius)

Charge: CCCV 3.0 mA (1C), 2.8 V-2 hours (*)

Discharge: CC 3.0 mA (1C), 0.01 V (**)

(*) CCCV: constant current constant voltage, (**) CC: constant current

Impedance Measurement (-30 ℃)

Measuring state: discharge

Measuring frequency: 20000 Hz to 0.1 Hz

Amplitude (ΔE): 10 mV

These results are as showing in Table 2.

As apparent from Table 2, the resistance of the capacitor of Example 1 according to the present invention was lower than that of the capacitor of Comparative Example 1, showing good results, and it was confirmed that the capacitor functions sufficiently as a capacitor.

This is because shrinkage stress acts between the powder electrode materials due to shrinkage of the binder during granulation due to heating at a temperature of 350 ° C., and the portion covering the surface of the powder electrode material becomes smaller due to shrinkage. This is considered to be due to the increase in the contact area between the powder electrode materials.

Claims (15)

A binder for capacitor electrodes comprising aramid granulated by heat treatment. An electrode sheet produced by mixing a powder electrode material, a binder, and a solvent to produce a slurry, and applying the slurry to a collecting electrode, wherein the binder is aramid and is subjected to heat treatment after application to granulate the binder. The electrode sheet according to claim 2, wherein the slurry contains 3 to 15% by weight of aramid based on the sum of the aramid and the powder electrode material. The binder according to claim 1, wherein the heat treatment is performed at a temperature near the crystallization temperature of the aramid. The binder according to claim 1, wherein the aramid is polymetaphenyleneisophthalamide. The binder according to claim 5, wherein the heat treatment is performed at a temperature within the range of 330 to 365 ° C. The binder according to claim 1, wherein the heat treatment is performed by hot pressing between a pair of flat plates or between a metal roll. The electrode sheet according to claim 2, wherein the solvent is N, N-dimethylacetamide, N-methyl-2-pyrrolidone (NMP) or a mixture thereof. The capacitor using the electrode sheet of Claim 2. delete The battery using the electrode sheet of Claim 2. The electrode sheet according to claim 2, wherein the heat treatment is performed at a temperature near the crystallization temperature of the aramid. The electrode sheet according to claim 2, wherein the aramid is polymetaphenylene isophthalamide. The electrode sheet according to claim 13, wherein the heat treatment is performed at a temperature within the range of 330 to 365 ° C. The electrode sheet according to claim 2, wherein the heat treatment is performed by hot pressing between a pair of flat plates or between a metal roll.

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