WO2015087695A1

WO2015087695A1 - Method for producing electrode material

Info

Publication number: WO2015087695A1
Application number: PCT/JP2014/081058
Authority: WO
Inventors: 優輝東村; 豊浩碓氷; 貴彦井戸
Original assignee: イビデン株式会社
Priority date: 2013-12-11
Filing date: 2014-11-25
Publication date: 2015-06-18
Also published as: JPWO2015087695A1; JP6178431B2

Abstract

This method for producing an electrode material is characterized by comprising: a curing step of adding, to a novolac type phenol resin precursor, an aqueous solution of an alkali metal hydroxide in which an alkali metal hydroxide is dissolved at a quantity that is not more than 8.0 times the weight of the novolac type phenol resin precursor, thereby rendering the novolac type phenol resin precursor basic, and then heating the novolac type phenol resin precursor so as to obtain a cured product of a phenol resin; a carbon powder formation step of pulverizing and firing the cured product of a phenol resin so as to obtain a carbon powder; and a washing step of washing the carbon powder with water and then drying the carbon powder so as to obtain an electrode material.

Description

Method for producing electrode material

The present invention relates to a method for manufacturing an electrode material.

As large-capacity electricity storage devices, lithium ion secondary batteries, electric double layer capacitors, and the like are known.
A lithium ion secondary battery is a secondary battery that performs charging and discharging by moving lithium ions between a positive electrode and a negative electrode. Various electrode materials are used, and lithium cobaltate is often used for the positive electrode and carbon (graphite) is often used for the negative electrode. A positive electrode plate and a negative electrode plate are stacked in layers with a separator in between, and the whole is filled with an organic solvent electrolyte.
On the other hand, when an external voltage is applied to an electric double layer capacitor, the cation and anion in the electrolyte form an electric double layer in a region of a small molecular layer on the surface of the two electrodes, and charge is generated. Accumulated and current flows. It is known that the amount of charge that can be stored that affects the storage capacity is determined by the amount of current from the outside, the amount of ions in the electrolyte, and the surface area of the electrode that stores charges by adsorbing ions.

As such a large-capacity electricity storage device, a carbon material is frequently used. As a carbon material used for such an electricity storage device, “organic resin is at least one of alkaline earth metal compounds selected from the group consisting of oxides, hydroxides, carbonates, and organic acid salts of alkaline earth metals. Patent Document 1 proposes a process for producing activated carbon, which includes a step of mixing with seeds and heating and firing in a non-oxidizing atmosphere. It is disclosed that activated carbon having a specific surface area of 400 to 2000 m ² / g or activated carbon having a mesopore volume of 0.16 mL / g or more can be obtained by such a production method.

JP 2012-82134 A

Electric storage devices such as electric double layer capacitors using the carbon materials described above have been developed for various capacities. There are two measures for the capacity of the electrode material: the storage capacity per weight and the storage capacity per volume. Even if the storage capacity per weight of the electrode material is increased, the storage capacity per volume cannot be increased if the bulk density of the electrode material is low.
In order to increase the power storage capacity per weight and the power storage capacity per volume, it is important to control the pore size. If a large amount of unnecessary large pores or pores are present, the bulk density of the carbon material is lowered, and the storage capacity per volume is reduced.

When the pores are reduced and the specific surface area is reduced, the surface area capable of forming the electric double layer is reduced, and the storage capacity per weight is reduced. For this reason, it is important that there are more fine pores (micropores) related to ions adsorbed and desorbed during power storage.

Moreover, such a subject exists not only in an electric double layer capacitor but also in other power storage devices using the same principle.
In recent years, a lithium ion capacitor combining a lithium ion secondary battery and an electric double layer capacitor has attracted attention. The lithium ion capacitor uses a carbon-based material capable of occluding lithium ions as a negative electrode material while using the principle of a general electric double layer capacitor, and the energy density is improved by adding lithium ions thereto.
The principle of charge and discharge is different between the positive electrode and the negative electrode, and it has a structure in which the negative electrode of the lithium ion secondary battery and the positive electrode of the electric double layer capacitor are combined.

Therefore, the lithium ion capacitor has a large capacity and a high charge / discharge speed. Lithium ion capacitors are highly demanded to have a larger capacity, and the capacity increase of the positive electrode using the principle of the capacitor dominates the storage capacity.

The present invention has been made by paying attention to the above circumstances, and its purpose is to provide an electrode material for a capacitor whose pores are controlled so that the storage capacity per volume and the storage capacity per weight can be increased. It is to provide a manufacturing method.

Another object is to provide a method for producing an electrode material for a positive electrode having a controlled pore so that the storage capacity per volume and the storage capacity per weight of a lithium ion capacitor can be increased. .

The method for producing an electrode material of the present invention for solving the above-described problems is an alkali metal in which an alkali metal hydroxide having a novolac phenol resin precursor dissolved in an amount of 8.0 times or less the weight of the novolac phenol resin precursor is dissolved. After adding an aqueous hydroxide solution and adjusting the novolac phenol resin precursor to basic, a curing step of obtaining a phenol resin cured product by heating the novolac phenol resin precursor;
A carbon powder forming step of pulverizing and firing the phenol resin cured product to obtain a carbon powder;
The carbon powder is washed with water and dried to obtain an electrode material, and
It is characterized by comprising.

In the process of producing a novolak phenol resin that is a thermosetting resin, an aqueous solution of alkali metal hydroxide is added to disperse a large amount of alkali metal ions inside. After that, the novolac phenol resin is pulverized and fired and washed. By washing, alkali metal ions contained therein are removed, and pores having a uniform size are formed.

The electrode material manufacturing method of the present invention can increase the storage capacity per volume and the storage capacity per weight by the following actions, and can provide an electrode material for a capacitor that can easily control pores. .

<Molding action>
Alkali metal hydroxide forms hydrated ions of alkali metal, and serves as a template to form pores close to the size of the ions involved in the electric double layer. Further, when the amount of sodium hydroxide is 8.0 times or less of the weight of the novolak phenol resin precursor, the novolac phenol resin precursor is not diluted too much and the condensation reaction is not easily inhibited. A cured product can be obtained.

<Alkali activation effect>
Since it contains an alkali metal hydroxide, it has a pore forming action due to an alkali activation effect.

<Inhibition of gas generation>
Since a novolak phenol resin precursor having undergone polymerization can be used as a raw material, there are few reaction products in the curing reaction, gas generation can be reduced, and the amount of bubbles that are difficult to control can be reduced. In addition, aldehydes produced by the reaction are consumed as methylol groups added to the aromatic ring of the novolak phenol resin, thereby reducing the generation of gas and reducing the amount of bubbles that are difficult to control.

<Dispersing action of pores>
Since it is an alkali metal hydroxide, it has high solubility and can be dispersed uniformly and fine pores can be formed by hydration ionization.

Furthermore, the following aspect is desirable for the method for producing the electrode material of the present invention.

(1) The novolac phenol resin precursor is a mixture of aldehydes or ketones and a novolac resin.
Furthermore, since a novolak resin having undergone polymerization can be used as a raw material, there are few reaction products, the generation of gas can be reduced, and the amount of bubbles that are difficult to control can be reduced. In addition, since aldehydes or ketones are added to the aromatic ring of the novolak resin by the catalytic action of the base, the novolak resin can be cross-linked and the phenol resin cured product can be obtained efficiently.

(2) The novolac resin is in a B-stage state.
When the novolak resin is in a B-stage state in which a part is gelled, the reaction product can be further reduced by a curing reaction. For this reason, gas generation can be further reduced, and the amount of bubbles difficult to control can be reduced.

(3) The compounding quantity of the said alkali metal hydroxide is 1.0 times or more of the weight of the said novolak-type phenol resin precursor.
When the blending amount of the alkali metal hydroxide is 1.0 times or more of the weight of the novolac phenol resin precursor, more pores can be formed and the specific surface area can be increased. Moreover, when the blending amount of the alkali metal hydroxide is 1.0 times or more of the weight of the novolak phenol resin precursor, it can act as a catalyst for a sufficient amount of base to cure the novolak phenol resin precursor. it can.

(4) The compounding quantity of the said alkali metal hydroxide is 2.0 times or more of the weight of the said novolak-type phenol resin precursor.
When the blending amount of the alkali metal hydroxide is 2.0 times or more of the weight of the novolac phenol resin precursor, more pores can be formed and the specific surface area can be increased. Further, when the blending amount of the alkali metal hydroxide is 2.0 times or more of the weight of the novolak phenol resin precursor, it can act as a catalyst for a sufficient amount of base to cure the novolak phenol resin precursor. it can.

(5) The alkali metal hydroxide is sodium hydroxide.
Sodium hydroxide can be suitably used without being too strong for alkali activation during firing.

(6) The carbon powder forming step includes a pulverizing step of pulverizing the phenol resin cured product to obtain a phenol resin powder, and a pulverizing step of baking the phenol resin powder to obtain a carbon powder.
Since the cured phenol resin can be pulverized in advance to increase the surface area and fired, it can be uniformly carbonized and the variation in pores can be reduced.

(7) The said electrode material manufactured with the manufacturing method of the electrode material of this invention is an electrode material for positive electrodes of a lithium ion capacitor.
In the positive electrode of the lithium ion capacitor, ions that are adsorbed and desorbed at a boundary of 3.0 V with respect to the potential of lithium change. The solvation of lithium ions is involved in the adsorption / desorption at 3.0 V or more, and the solvation of lithium ions at less than 3.0 V. The size of the pores of the electrode material obtained by the method for producing an electrode material of the present invention is close to the size of any ion. For this reason, the electrode material for capacitors which can control easily the pore which can enlarge the electrical storage capacity per volume and the electrical storage capacity per weight can be obtained easily.

According to the method for producing an electrode material of the present invention, it is possible to provide an electrode material for a capacitor that can easily control pores capable of increasing the storage capacity per volume and the storage capacity per weight.

It is a measurement result of the adsorption isotherm using nitrogen adsorption of an example and a comparative example. It is the graph which converted the measurement result of the adsorption isotherm into the pore diameter distribution which makes a horizontal axis the pore diameter by HK method.

In the method for producing an electrode material of the present invention, an alkali metal hydroxide aqueous solution in which an alkali metal hydroxide of 8.0 times or less the weight of the novolac phenol resin precursor is dissolved in a novolac phenol resin precursor is added, After adjusting the novolac phenol resin precursor to basic, a curing step of obtaining a phenol resin cured product by heating the novolac phenol resin precursor;
A carbon powder forming step of pulverizing and firing the phenol resin cured product to obtain a carbon powder;
The carbon powder is washed with water and dried to obtain an electrode material, and
It is characterized by comprising.

According to the method for producing an electrode material of the present invention, it is possible to increase the storage capacity per volume and the storage capacity per weight by the following actions, and to provide an electrode material for a capacitor in which pores can be easily controlled. Can do.

<Molding action>
Alkali metal hydroxide forms hydrated ions of alkali metal, and serves as a template to form pores close to the size of the ions involved in the electric double layer. Further, when the amount of sodium hydroxide is 8.0 times or less of the weight of the novolak phenol resin precursor, the novolac phenol resin precursor is not diluted too much and the condensation reaction is not easily inhibited. A cured product can be obtained. The blending amount of the alkali metal hydroxide indicates a ratio of only the solute contained in the aqueous solution of the alkali metal hydroxide, and the amount of water is not limited.

<Inhibition of gas generation>
Since a novolak phenol resin precursor having undergone polymerization can be used as a raw material, there are few reaction products in the curing reaction, gas generation can be reduced, and the amount of bubbles that are difficult to control can be reduced. In addition, aldehyde generated by the reaction is consumed as a methylol group added to the aromatic ring of the novolak phenol resin, thereby reducing gas generation and reducing the amount of bubbles that are difficult to control.

The method for producing the electrode material of the present invention uses a novolac phenol resin precursor. The novolac phenol resin precursor is not particularly limited as long as it is an uncured novolac phenol resin precursor.

There are novolak phenol resin and resol phenol resin in phenol resin.

The novolak phenol resin is obtained from the monomer through a two-step reaction. In the first-stage reaction, an aldehyde or a ketone is added to phenol or a phenol monomer, and condensed using an acid as a catalyst to obtain a novolak resin. Next, in the second stage reaction, a novolac phenol resin is obtained by curing by adding a crosslinking agent such as hexamine and crosslinking the novolak resin.

Since the novolac resin does not have a large amount of methylol groups, the crosslinking reaction does not proceed at the first stage and is a thermoplastic resin. In general, this novolak resin is further cured by adding a crosslinking agent to form a novolak phenol resin.

Examples of the reaction of synthesizing a novolac resin by condensing phenol and formaldehyde in the formulas (1) to (3). This reaction proceeds similarly even if phenols are used instead of phenol. This reaction proceeds in the same manner even when aldehydes or ketones are used instead of formaldehyde. In the formula (1), formaldehyde is added to phenol using an acid as a catalyst to introduce a methylol group. In the right side of the formula (1), the position to which the methylol group is added is not specifically described, but the methylol group is added to the o-position or p-position of the phenol. As shown in the formula (2), the phenol (monomethylol body) to which the methylol group is added immediately bonds with the phenol to form a dimer. A methylol group is further added to the dimer aromatic ring obtained by the formula (2) as shown in the formula (1), and a phenol is immediately bonded to form a trimer as shown in the formula (2). . Since the reaction rate of the formula (1) is slower than the reaction rate of the formula (2), the polymerization proceeds linearly as in the formula (3), and a thermoplastic novolak resin is obtained.

On the other hand, a resol type phenol resin which is another kind of phenol resin is also obtained from the monomer through a two-step reaction. In the first stage reaction, an aldehyde or a ketone is added to phenol or a phenol monomer, and a methylol group or the like is added to an aromatic ring using a base as a catalyst to obtain a methylol body. Next, the methylol body is cured by a second-stage reaction to form a resol-based phenol resin. In the first-stage reaction, when a methylol group is added to the monomer, depending on the number of methylol groups added to the monomer, one added is a monomethylol body, two added is a dimethylol body, 3 The added one is called a trimethylol body. A methylol group is added at the o-position or p-position. As the addition reaction using a base as a catalyst proceeds, the reaction proceeds from a monomethylol body to a dimethylol body and a trimethylol body. In the second stage reaction, the methylol body can be bonded and cured by adding heat or acid.

In the method for producing an electrode material of the present invention, a novolac phenol resin precursor is used. As described above, the novolac phenol resin and the resol phenol resin are synthesized by a two-step reaction. Comparing the molecular weights of the first and second stage intermediate products, the novolac phenolic resin capable of causing the polycondensation reaction in the first stage is larger. For this reason, the amount of by-products generated in the second-stage reaction can be reduced in the novolac phenol resin, and the generation of pores or bubbles that are the basis of pores can be reduced.

The size of bubbles generated with the second-stage reaction varies depending on pressure, temperature, the number of moles of by-products contained in one bubble, and the like. For this reason, it is difficult to control the size of the bubbles. In the novolac phenol resin, the molecular weight of the intermediate product is large, so it is possible to reduce the generation of bubbles whose size is difficult to control. Therefore, the size of the pores or pores of the electrode material obtained by firing the phenol resin It is possible to reduce the influence of bubbles on the surface.

Moreover, the manufacturing method of the electrode material of this invention has the hardening process which performs hardening reaction by adding the aqueous solution of an alkali metal hydroxide to a novolak-type phenol resin precursor, and making it basic. This reaction is shown in Formula (5). By making it basic, a methylol group can be added to a position where an aromatic ring of phenol or phenols contained in the novolak phenol resin precursor is vacant. Further, by applying heat, the methylol groups undergo dehydration condensation and can be cured. The position to which the methylol group is added is the o-position or the p-position, and is added to a vacant position.

Alkali metal hydroxide ionizes when dissolved in water and is separated into alkali metal ions and OH ⁻ . Alkali metal ions do not exist alone, but combine with several water molecules to form a hydrated structure. Ions bound to water molecules are called hydrated ions, and are larger than single alkali metal ions.

The radius of alkali metal hydrated ions is 0.3 to 0.4 nm, which is close to the size of ions involved in the electric double layer. For this reason, ionized alkali metal hydrate ions serve as a template to form pores, and the surface area involved in the electric double layer can be efficiently increased.

Therefore, in the method for producing an electrode material of the present invention, an alkali metal hydroxide acts as a basic catalyst for adding a methylol group to a novolac resin and acts as a template by becoming a hydrated ion of an alkali metal. And has two-sided actions.

In the method for producing an electrode material of the present invention, heat is applied to a novolak resin to which a methylol group is added, so that methylol groups are bonded to each other by the catalytic action of a base. This reaction is a cross-linking reaction, and the novolak resin is gelled and becomes a thermosetting resin and is cured. The curing method is not particularly limited, but it is desirable to heat and cure. The heating temperature is not particularly limited, but is 70 to 300 ° C. The heating time is not particularly limited. For example, 3 minutes to 20 hours. The higher the temperature, the faster the curing reaction is completed.

The electrode material manufacturing method of the present invention is characterized by using an alkali metal hydroxide. The alkali metal hydroxide is a strong base and has a strong action as a catalyst, and also has higher water solubility than an alkaline earth metal, and more alkali metal ions can be dispersed in an aqueous solution. For this reason, the effect | action as a basic catalyst which adds a methylol group and the effect | action from which the hydrated ion of an alkali metal becomes a template can be strengthened.

The novolak phenol resin precursor of the present invention is not particularly limited. As the novolac phenol resin precursor, a mixture of aldehydes or ketones and phenols can be used. Alternatively, a mixture of aldehydes or ketones and a novolac resin may be used.

Examples of phenols include, but are not limited to, those having phenolic-OH such as phenol, cresol, xylenol, p-alkylphenol, p-phenylphenol, chlorophenol, bisphenol A, phenolsulfonic acid, resorcin and the like.

Aldehydes are organic compounds having a structure in which one hydrogen atom is substituted on the carbonyl carbon in the molecule. Ketones are a compound in which two alkyl groups are substituted on the carbonyl carbon in the molecule. It is an organic compound. Examples of aldehydes include, but are not limited to, formaldehyde, acetaldehyde, propionaldehyde, acrolein, benzaldehyde, cinnamaldehyde, and perylaldehyde. Although it does not specifically limit as ketones, Acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl amyl ketone, cyclohexanone, isophorone etc. are mentioned.

Phenols are condensed with aldehydes or ketones in the presence of an acid catalyst to form a novolak resin. Novolak resins are generally condensation products of phenolic compounds with aldehydes or ketones or their derivatives such as ketal or hemiketal functional groups.

It is preferable that the novolak-type phenol resin precursor of the manufacturing method of the electrode material of this invention is a mixture of aldehydes or ketones, and a novolak resin.
Furthermore, since a novolak resin having undergone polymerization can be used as a raw material, there are few reaction products, the generation of gas can be reduced, and the amount of bubbles that are difficult to control can be reduced. In addition, since aldehydes or ketones are added to the aromatic ring of the novolak resin by the catalytic action of the base, the novolak resin can be cross-linked, and a novolac phenol resin cured product can be obtained efficiently.

In the present invention, the novolak resin refers to those having a weight average molecular weight of 1000 or more, and those less than that are, for example, oligomers or monomers.

The method for producing an electrode material of the present invention includes a carbon powder forming step of pulverizing and firing a phenol resin cured product.

The carbon powder forming step includes a pulverization step and a firing step. The order of the pulverization step and the baking step is not particularly limited, but it is desirable that there is a baking step after the pulverization step. In this case, it consists of a pulverizing step of pulverizing the phenol resin cured product to obtain a phenol resin powder, and a pulverizing step of baking the phenol resin powder to obtain a carbon powder. In this case, the cured phenol resin can be pulverized in advance and fired after increasing the surface area, so that it can be uniformly carbonized and the variation in pores can be reduced.

The average particle diameter (diameter) of the pulverizer used in the pulverization step of the production method of the electrode material of the present invention and the phenol resin powder obtained is not particularly limited. As the pulverizer, for example, a pin mill, a ball mill, a jet mill, a hammer mill, a bead mill, a roller mill and the like can be used, and the pulverizer is not particularly limited.

The firing pattern in the firing step of the method for producing an electrode material of the present invention is not particularly limited. For example, the temperature is raised at a constant rate, and after reaching the maximum temperature, it is allowed to cool gradually. The firing temperature (maximum temperature) is, for example, 600 to 2000 ° C., and the heating rate is, for example, 0.1 to 100 ° C./min.

In the firing step, a carbide containing alkali metal ions is obtained by firing while containing alkali metal hydrate ions. At this time, the hydrated ions of the alkali metal are dehydrated by the action of heat and become hydroxides, carbonates, and the like.

In addition, since the carbide of the phenol resin powder is heated together with the alkali metal hydroxide at this time, an alkali activation reaction in which carbon is consumed by the reaction between the alkali metal hydroxide and carbon also occurs at the same time, and the surface area of the carbon material It works to increase.

The alkali activation reaction follows, for example, the following reaction formula.
2KOH → K ₂ O + H ₂ O (6)
C _n + K ₂ O → C _n−1 + 2K + CO ↑ (7)
C _n + H ₂ O → C _n−1 + CO ↑ + H ₂ (8)
CO + H ₂ O → CO ₂ ↑ + H ₂ ↑ (9)
CO ₂ + K ₂ O → K ₂ CO ₃ (10)

K ₂ O + H ₂ O generated by the formula (6) oxidizes carbon as shown by the formula (7) and the formula (8). This reaction occurs in the vicinity of the alkali metal oxide and acts to widen one pore filled with alkali metal ions. Further, CO ₂ produced by the formula (9) deactivates K ₂ O to prevent the pores from becoming too large, and the expansion of the pore size stops.

The average particle diameter (diameter) of the carbon powder is preferably 0.1 to 50 μm, for example. The average particle diameter can be measured by a laser diffraction particle size distribution diameter.

In the pulverization step, the surface area is increased by finely pulverizing so that the alkali metal hydroxide incorporated in the interior is at or near the surface of the particles.

In the method for producing an electrode material of the present invention, the electrode material is obtained by a washing step in which the carbon powder is washed with water and then dried.
In the washing step, the alkali metal ions are removed by washing with water, and pores corresponding to the hydrated ions of the alkali metal can be formed.

It is preferable that the novolak resin of the manufacturing method of the electrode material of this invention exists in the state of B stage.
When the novolak resin is in a B-stage state in which a part is gelled, the reaction product can be further reduced by a curing reaction. For this reason, gas generation can be further reduced, and the amount of bubbles difficult to control can be reduced.

Thermosetting resins are classified into A stage, B stage, and C stage in order from the raw material to complete curing, and the reaction proceeds in the order of A, B, and C.

The A stage is an initial state of the thermosetting resin production reaction, and is completely dissolved in a solvent and melts when heated.

The B stage is an intermediate state of curing of the thermosetting resin and dissolves in a solvent and softens when heated, but does not completely melt or dissolve. That is, it is a state in which a part is gelled.

The C stage is the final state of curing of the thermosetting resin, is insoluble and infusible, and the completely cured thermosetting resin is in this state.

The A stage and the B stage are uncured stages, and the novolac phenol resin precursor of the present invention is in any one of these states.

The blending amount of the alkali metal hydroxide in the method for producing an electrode material of the present invention is preferably 1.0 times or more the weight of the novolac phenol resin precursor.

The blending amount of the alkali metal hydroxide indicates a ratio of only the solute contained in the aqueous solution of the alkali metal hydroxide, and the amount of water is not limited.

When the blending amount of the alkali metal hydroxide is 1.0 times or more of the weight of the novolac phenol resin precursor, more pores can be formed and the specific surface area can be increased. Moreover, when the blending amount of the alkali metal hydroxide is 1.0 times or more of the weight of the novolak phenol resin precursor, it can act as a catalyst for a sufficient amount of base to cure the novolak phenol resin precursor. it can.

The blending amount of the alkali metal hydroxide in the method for producing an electrode material of the present invention is more preferably 2.0 times or more of the weight of the novolac phenol resin precursor.
When the blending amount of the alkali metal hydroxide is 2.0 times or more of the weight of the novolac phenol resin precursor, more pores can be formed and the specific surface area can be increased. Further, when the blending amount of the alkali metal hydroxide is 2.0 times or more of the weight of the novolak phenol resin precursor, it can act as a catalyst for a sufficient amount of base to cure the novolak phenol resin precursor. it can.

Examples of the alkali metal hydroxide in the method for producing an electrode material of the present invention include lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide.
Of these, sodium hydroxide is preferable.

Sodium hydroxide is not too strong for alkali activation during firing and can be suitably used.

The ratio of the novolak phenol resin precursor in the mixed solution of the aqueous solution of sodium hydroxide and the novolak phenol resin precursor in the method for producing the electrode material of the present invention (ratio of the novolak phenol resin precursor in the total amount) is 4 It is preferably 5% by weight or more. When the ratio of the novolac phenol resin precursor is 4.5% by weight or more, the novolac phenol resin precursor is not excessively dispersed. If the novolak phenolic resin precursor is too dispersed, the condensation reaction between other molecules is difficult to occur when the novolak resin is cured, and it is difficult to condense between the methylol groups of one molecule and gel. . That is, the molecules of one novolac resin are condensed into a lump and gelation is difficult to proceed.

The electrode material is a positive electrode material for a lithium ion capacitor.
In the positive electrode of the lithium ion capacitor, ions that are adsorbed and desorbed at a boundary of 3.0 V with respect to the potential of lithium change. The solvation of lithium ions is involved in the adsorption / desorption at 3.0 V or more, and the solvation of lithium ions at less than 3.0 V. The size of the pores of the electrode material obtained by the production method of the present invention is close to the size of any ions. For this reason, the electrode material for capacitors which can control easily the pore which can enlarge the electrical storage capacity per volume and the electrical storage capacity per weight can be obtained easily. For example, when using LiPF ₆ as an electrolyte and an electrolyte solution having a concentration of 1 mol / L of ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) = 3: 1: 4 as a nonaqueous solvent, 3.0 V is used. The anion that adsorbs and desorbs at the above potential is PF ₆ ⁻ , and its diameter is 0.51 nm. Lithium ions adsorbed and desorbed at a potential of 3.0 V or less are solvent-bonded to form a solvate and have a diameter of 0.82 nm. In addition, even when other solvents or water solvents are used, the size of the anion is the same in the electricity storage device in which lithium ions are involved. Alkali activation effect is further added to the mold that forms the solvation of alkali metal ions, and when used as a lithium ion capacitor, the size of the anion and lithium solvation is the same as the size of the pores, and the storage capacity per volume is efficiently In addition, an electrode material having a large storage capacity per weight can be manufactured.

Examples according to the comparative example and the method for producing the electrode material of the present invention will be described below.
Examples and Comparative Examples were carried out according to the following process.

<Curing process>
In advance, an alkali metal hydroxide is dissolved in water to obtain an aqueous solution of the alkali metal hydroxide. Next, an aqueous solution of an alkali metal hydroxide and a novolac phenol resin precursor are mixed. In Comparative Example 1, water was used in place of the alkali metal hydroxide aqueous solution.

In this example and comparative example, sodium hydroxide was used as the alkali metal hydroxide, and Tamanol 7509 (registered trademark, Arakawa Chemical Industries, Ltd.) manufactured by Arakawa Chemical Industries was used as the novolac phenol resin precursor. Tamanol 7509 is a bisphenol-A-formaldehyde resin. Tamanol 7509 is a novolak resin in which monomer bisphenol-A is partially polymerized with formaldehyde. The content of formaldehyde in Tamanol 7509 analyzed separately was 62 μg / g.

Specifically, sodium hydroxide was dissolved in water, Tamanool 7509 was added, and the mixture was stirred for 30 minutes using a stirrer in a 200 ml beaker. In addition, the compounding quantity of Tamanol 7509 at this time is 5g, and the quantity of sodium hydroxide and water changes for every Example and a comparative example, and it describes in Table 1.

Next, the mixed solution was poured into a fluororesin container and heated in an inert oven in a nitrogen atmosphere. As a heating condition, a temperature rising pattern was used in which the temperature was raised at a constant rate and the temperature was maintained when the curing temperature was reached. The heating rate was 1 ° C./min, the curing temperature was 170 ° C., and the holding time was 30 minutes. Excess water is evaporated by this operation, and the phenolic resin cured product is left as a solid.

<Carbon powder formation process-grinding process>
Next, the obtained phenolic resin cured product was pulverized by a planetary ball mill. The planetary ball mill was a 500 ml zirconia container, and 10 20 mm zirconia balls were used and pulverized for 6 minutes at 200 rpm three times. By pulverizing, a phenol resin powder was obtained.

<Carbon powder formation process-firing process>
The obtained phenol resin powder was fired in a firing furnace in a nitrogen atmosphere to obtain carbon powder. As a heating condition, a temperature rising pattern was used in which the temperature was raised at a constant rate and the temperature was maintained when the firing temperature was reached. The heating rate was 1 ° C./min, the firing temperature was 800 ° C., and the holding time was 120 minutes. By firing, a carbon powder was obtained.

<Washing process>
The obtained carbon powder was pulverized in a mortar, transferred to a beaker containing 100 ml of water, stirred for 1 hour using a stirrer, filtered, and water was removed. Next, 100 ml of water was added, neutralized with hydrochloric acid, stirred for 1 hour using a stirrer, and filtered to remove water. Further, the carbon powder was dried with a dryer at 110 ° C. for 1 hour.

<Performance evaluation>
For the performance evaluation, the specific surface area and pore volume of the obtained electrode materials of Examples and Comparative Examples were measured.

Table 1 is a table summarizing the conditions and results regarding the composition, yield, and results of the curing steps of Examples 1 to 5 and Comparative Examples 1 and 2.

In Table 1, “resin precursor” refers to “novolac phenol resin precursor”, and “resin” refers to “cured phenol resin”.

In Table 1,
A is blending amount of novolac phenol resin precursor B is blending amount of water as solvent C is blending amount of sodium hydroxide D is sum of blending amounts: D = A + B + C
E is blending amount other than solvent: E = A + C
F is the ratio of the novolak phenol resin precursor in the total blending amount: F = A / D
G is the concentration of sodium hydroxide aqueous solution (wt%): G = C / (B + C)
H is the ratio of sodium hydroxide to the novolac phenolic resin precursor (times): H = C / A
I shows the quantity of the obtained phenol resin hardened | cured material.

“Presence / absence of precipitate” indicates the presence / absence of precipitation after mixing the novolak phenol resin precursor and the aqueous sodium hydroxide solution.
“Curing” is indicated by “O” when cured after the curing process, “X” when not cured, and “△” when cured but not completely cured (partial curing). Yes.

From the results in Table 1, the results of the curing reaction are examined while considering the blending amount E other than the solvent, the obtained phenolic resin cured product and the yield I of sodium hydroxide, and the presence or absence of the curing reaction.

Table 2 relates to Examples 1 to 5 and Comparative Examples 1 and 2, pulverizing the phenol resin cured product obtained in the curing step, firing the obtained phenol resin powder, and washing the obtained carbon powder It is the table | surface which put together the conditions regarding a mixing | blending in a washing | cleaning process, a yield, a result, and a result.

In Table 2,
J is the blending amount of the phenol resin powder. K is a calculated value obtained by removing NaOH from the blending amount of the phenol resin powder:
K = J × (1-C / I)
L is the weight of the carbon powder after firing M is the weight of the electrode material after cleaning N is the carbonization yield of the cured phenol resin: N = M / K
It is.

Table 3 shows the measurement results of the performance evaluation of Examples 1 to 5, Comparative Examples 1 and 2, and Comparative Example 3.
O represents a specific surface area.
P to R are pore volumes measured for each range of pore radii.

The measurement of the specific surface area was performed in advance by using BELPREP-vacII manufactured by Nippon Bell Co., Ltd. for 2H at 200 ° C. and using BELSORP-miniII manufactured by Nippon Bell Co., Ltd. FIG. 1 shows the results of an adsorption isotherm using nitrogen adsorption. The specific surface area in Table 3 was calculated using the BET method.

In particular,
Measurement method: constant volume gas adsorption method Adsorbed gas: N ₂
Adsorption temperature: 77K (-196.15 ° C)
Pressure range: 0 to 0.9995 (relative to the saturated vapor pressure of nitrogen at the adsorption temperature)
Cell size: approx. 1.8 cm ³
It is.

The pore volume was calculated from the data of the measurement results of the specific surface area using the HK method (Horvath, Kawazoe method). (Figure 2, Table 3)
FIG. 1 shows the amount of gas adsorption when adsorbed gas molecules (N ₂ ) at a certain pressure p are adsorbed on the solid surface, and p / p ₀ (relative value: p ₀ is the saturated vapor pressure of nitrogen at the adsorption temperature). Showing the relationship.

FIG. 2 shows that when the pore diameter is dp and the pore volume is Vp, the horizontal axis is the value of dp, and the vertical axis is dVp / ddp, that is, the pore volume Vp is differentiated by the pore diameter dp. It is a graph which is a value.

In Examples 1 to 4 and Comparative Examples 1 to 2, the amount of the novolak phenol resin precursor and the amount of water were the same, and the test was performed by changing the amount of sodium hydroxide. Comparative Example 1 does not contain sodium hydroxide, and Examples 1 to 5 contain sodium hydroxide. The amount of sodium hydroxide is increased so as to be approximately a geometric series in the order of Examples 1 to 4 and Comparative Example 2.

In Comparative Example 1 containing no sodium hydroxide, the yield I was significantly less than the blended amount of the novolac phenol resin resin precursor and sodium hydroxide, and the product was not cured. This is presumably because formaldehyde could not be added to the novolak resin, and the crosslinking reaction due to the methylol group did not occur. For this reason, it is presumed that low molecular weight components such as formaldehyde contained in the novolac phenol resin resin precursor are volatilized by heating and the weight is reduced (I <E). In addition, the novolak phenol resin precursor before curing was not completely melted in water.

In Examples 1 to 4 and Comparative Example 2 containing sodium hydroxide, the yield I is higher than the blending amount of the novolac phenol resin resin precursor and sodium hydroxide (I <E).
This is considered to be due to the effects of formaldehyde being added to the novolac resin, the low molecular weight component being taken into the phenolic resin cured product, and the sodium ions forming a hydrate.

In Example 4 and Comparative Example 2, although the electrode material was obtained, it was in a partially cured state that was not completely cured, and the carbonization yield was low. (In Comparative Example 2, a sufficient sample could not be obtained and measured.) This was because the novolak phenol resin precursor was too diluted with sodium hydroxide and could not form bonds with other molecules. It is presumed that crosslinking did not progress. However, in Example 4, the specific surface area is larger than in Examples 1 to 3, and the pore volume in any region of PQR in Table 3 is at a high level. For this reason, when the amount of sodium hydroxide is increased, the carbonization yield has a maximum value and starts to decrease, but the performance of the obtained electrode material may be at a high level even if the carbonization yield is low. confirmed.

Next, Example 5 in which the amount of sodium hydroxide is the same as Example 3 and the amount of water to be diluted is reduced will be described while comparing Example 3 and Example 5. In Example 3, the blending amount of water is 80.89 g, whereas in Example 5, it is 37.9 g. For this reason, the ratio of the novolak phenol resin precursor to the blending amount is 4.7% in Example 3 and 7.9% in Example 5. Each level has a high specific surface area, and the pore volume in any region of PQR in Table 3 is at a high level. The carbonization yield N is greatly improved in Example 5 in which the blending amount of water during blending is reduced.
Further, in Example 4 in which the ratio of the novolak phenol resin precursor to the blending amount was 4.0% and in Comparative Example 2 in which 2.8%, complete curing could not be achieved.

From these results, when the ratio F of the novolak phenol resin precursor to the blending amount is 4.5% or more, the novolac phenol resin precursor can be cured and a sufficient carbonization yield can be obtained. Was confirmed.
Comparative Example 3 shows the specific surface area of an electrode material made of general activated carbon activated with alkali. The electrode materials of Examples 1 to 5 had performance equivalent to or higher than that of Comparative Example 3 in specific surface area. According to the method for producing an electrode material of the present invention, it is easy to control the size of the pores, and for a capacitor with controlled pores so that the storage capacity per volume and the storage capacity per weight can be increased. It was confirmed that a method for producing the electrode material can be provided.

Claims

An alkali metal hydroxide aqueous solution in which an alkali metal hydroxide of 8.0 times or less the weight of the novolak phenol resin precursor is dissolved is added to the novolak phenol resin precursor, and the novolac phenol resin precursor is made basic. After adjusting to, a curing step of obtaining a phenol resin cured product by heating the novolac phenol resin precursor,
A carbon powder forming step of pulverizing and firing the phenol resin cured product to obtain a carbon powder;
The carbon powder is washed with water and dried to obtain an electrode material, and
A process for producing an electrode material comprising:
The novolac phenolic resin precursor is
Aldehydes or ketones,
Novolac resin,
The method for producing an electrode material according to claim 1, wherein the electrode material is a mixture of
3. The method for producing an electrode material according to claim 2, wherein the novolac resin is in a B-stage state.
The electrode material production according to any one of claims 1 to 3, wherein the amount of the alkali metal hydroxide is 1.0 or more times the weight of the novolac phenol resin precursor. Method.
The method for producing an electrode material according to claim 4, wherein the blending amount of the alkali metal hydroxide is at least 2.0 times the weight of the novolac phenol resin precursor.
The method for producing an electrode material according to any one of claims 1 to 5, wherein the alkali metal hydroxide is sodium hydroxide.
The carbon powder forming step includes
Crushing the phenol resin cured product to obtain a phenol resin powder; and
Crushing the phenol resin powder to obtain a carbon powder,
The method for producing an electrode material according to any one of claims 1 to 6, wherein:
8. A method for producing an electrode material, wherein the electrode material produced by the method for producing an electrode material according to claim 1 is an electrode material for a positive electrode of a lithium ion capacitor.