WO2022039213A1

WO2022039213A1 - Conductive carbon, production method for conductive carbon, and production method for electrode using conductive carbon

Info

Publication number: WO2022039213A1
Application number: PCT/JP2021/030332
Authority: WO
Inventors: 智志久保田; 典之宮本; 大輔堀井
Original assignee: 日本ケミコン株式会社
Priority date: 2020-08-21
Filing date: 2021-08-19
Publication date: 2022-02-24
Also published as: JP2022035839A

Abstract

Provided are: a conductive carbon that makes it possible to achieve a power storage device that has high energy density and improved stability when used at high temperatures; and a production method for the conductive carbon. This conductive carbon spreads like paste when subjected to pressure. The ratio of the peak intensity of an S1 band of a Raman spectrum of the conductive carbon to the peak intensity of an S2 band is 0.85–0.99. The conductive carbon is produced by means of a method that includes an oxidation step for performing an oxidation treatment on a carbon raw material to obtain an oxidized carbon that spreads like paste when subjected to pressure and a crushing step for performing a crushing treatment on the oxidized carbon such that the ratio of the peak intensity of an S1 band of a Raman spectrum of the resulting conductive carbon to the peak intensity of an S2 band is 0.85–0.99.

Description

Conductive carbon, a method for manufacturing this conductive carbon, and a method for manufacturing an electrode using this conductive carbon.

The present invention relates to conductive carbon used for a power storage device having a high energy density and excellent high temperature stability. The present invention also relates to the method for producing the conductive carbon and the method for producing an electrode for a power storage device using the conductive carbon.

Power storage devices such as secondary batteries, electric double-layer capacitors, redox capacitors and hybrid capacitors are used as power supplies for information devices such as mobile phones and laptop computers, motor-driven power supplies for low-emission vehicles such as electric vehicles and hybrid vehicles, and energy regeneration. Although it is a device whose application is widely studied for systems and the like, it is desired to improve the energy density of these power storage devices in order to meet the demands for higher performance and smaller size.

In these energy storage devices, an electrode active material whose capacity is developed by a Faraday reaction involving the transfer of electrons with ions in an electrolyte (including an electrolytic solution) or a non-Faraday reaction without transfer of electrons is used for energy storage. It will be used. And these active materials are generally used in the form of a composite material with a conductive agent. As the conductive agent, conductive carbon such as carbon black, natural graphite, artificial graphite, and carbon nanotubes is usually used. These conductive carbons play a role of imparting conductivity to the composite material when used in combination with an active material having low conductivity, but also act as a matrix for absorbing the volume change accompanying the reaction of the active material. It also plays a role in ensuring an electron conduction path even if the active material is mechanically damaged.

By the way, the composite material of these active materials and conductive carbon is generally manufactured by a method of mixing the particles of the active material and the conductive carbon. Since conductive carbon basically does not contribute to the improvement of the energy density of the power storage device, in order to obtain a power storage device having a high energy density, the amount of conductive carbon per unit volume is decreased and the amount of active material is increased. There is a need. Therefore, studies have been conducted to increase the amount of active material per unit volume by increasing the distance between the active material particles by improving the dispersibility of the conductive carbon or lowering the structure of the conductive carbon. However, it is difficult to efficiently allow the conductive carbon as described above to enter between the active material particles, and therefore it is difficult to increase the amount of active material per unit volume by reducing the distance between the active material particles. Met.

To solve this problem, the applicant has decided to use conductive carbon, which can be obtained by subjecting a carbon raw material to a strong oxidation treatment and has a property of spreading like a paste under pressure, for an electrode of a power storage device. It has been proposed (Patent Documents 1 to 15). Here, the "glue-like" means a state in which the grain boundaries of the carbon primary particles are not recognized in the SEM photograph taken at a magnification of 25,000, and the non-particulate amorphous carbon is connected.

Even if pressure is applied to conductive carbon such as carbon black, natural graphite, and carbon nanotubes used as a conductive agent in the electrodes of conventional power storage devices, the particle shape of carbon is maintained. However, when these conductive carbons are oxidized, they are oxidized from the surface of the particles to introduce hydroxyl groups, carboxyl groups, carbonyl groups, ether bonds, etc. into the carbon, and the conjugated double bonds of the carbon are oxidized. A carbon single bond is formed, and the carbon-carbon bond is partially broken. Further, by increasing the strength of the oxidation treatment, it is possible to obtain conductive carbon having a property of spreading like a paste under pressure.

Conductive carbon, which has the property of spreading like a paste under this pressure, easily adheres to the surface of the electrode active material particles, and when it receives pressure, it is integrally compressed and spreads like a paste, making it difficult for it to fall apart. It has characteristics. Therefore, when a mixture of the conductive carbon and the electrode active material particles is obtained for the electrode of the power storage device, the conductive carbon adheres to the surface of the active material particles and covers the surface in the mixing process, and the active material is covered. Improves particle dispersibility. When the pressure applied to the conductive carbon during the production of the mixture is large, at least a part of the conductive carbon spreads like a paste and the surface of the active material particles is partially covered. Then, when an active material layer is formed on the current collector of the electrode using this mixture and pressure is applied to the active material layer, the conductive carbon further spreads like a paste to cover the surface of the electrode active material particles. The active material particles are densified while covering, and the active material particles approach each other. Along with this, the conductive carbon covers the surface of the active material particles and forms not only the gaps formed between the adjacent active material particles but also the active material particles. It is also extruded and densely filled inside the pores existing on the surface (including the gaps between the primary particles found in the secondary particles). Therefore, the amount of the electrode active material per unit volume of the electrode increases, and the electrode density increases. Further, the densely packed paste-like conductive carbon has sufficient conductivity to function as a conductive agent and does not suppress the impregnation of the electrolytic solution in the power storage device. As a result, the energy density of the power storage device is improved.

For example, Patent Document 6 shows the result of evaluating the content of the hydrophilic portion in the conductive carbon. Here, the "hydrophilic portion" of the conductive carbon has the following meaning. That is, 0.1 g of conductive carbon is added to 20 mL of an aqueous ammonia solution having a pH of 11, and ultrasonic irradiation is performed for 1 minute, and the obtained liquid is left for 5 hours to precipitate a solid phase portion. The portion dispersed in the aqueous ammonia solution having a pH of 11 without precipitating is the "hydrophilic portion". Further, the content of the hydrophilic portion with respect to the entire conductive carbon is determined by the following method. After the solid phase portion is precipitated, the residual portion from which the supernatant has been removed is dried, and the weight of the dried solid is measured. The weight obtained by subtracting the weight of the dried solid from the weight of the first conductive carbon of 0.1 g is the weight of the "hydrophilic portion" dispersed in the aqueous ammonia solution having a pH of 11. The weight ratio of the weight of the "hydrophilic portion" to the weight of the first conductive carbon of 0.1 g is the content of the "hydrophilic portion" in the conductive carbon.

According to Patent Document 6, when the strength of the oxidation treatment is increased so that the content of the hydrophilic portion exceeds 8% by mass of the entire conductive carbon, the electrode density of the electrode manufactured by using the obtained conductive carbon is increased. When the content of the hydrophilic portion exceeds 9% by mass of the entire conductive carbon, the electrode density begins to increase rapidly, and when the content of the hydrophilic portion exceeds 10% by mass of the entire conductive carbon, the electrode density begins to increase rapidly. , It has been shown that extremely high electrode densities can be obtained (see Figure 2 of this document). This improvement in electrode density corresponds to the fact that as the strength of the oxidation treatment is increased, the conductive carbon is given the property of spreading like a paste when pressure is applied. Further, a lithium ion secondary battery having a positive electrode containing acetylene black as a conductive carbon and a positive electrode active material and a lithium counter electrode, and conductive carbon obtained by half or all of the acetylene black by the above-mentioned strong oxidation treatment. When the charge / discharge characteristics are evaluated by constructing a lithium ion secondary battery equipped with a positive electrode replaced with the former, it is shown that the latter exhibits better rate characteristics and charge / discharge cycle characteristics than the former (in this document). (See FIGS. 6 to 11, 13, and 14). This improved charge / discharge cycle characteristic is due to the fact that the surface of the electrode active material is covered with the conductive carbon that spreads like a paste, so that the dissolution of the active material in the electrolytic solution is suppressed. (See Table 1 in this document).

Japanese Unexamined Patent Publication No. 2015-079678 JP-A-2015-079680 JP-A-2015-079681 WO2015 / 056759 WO2015 / 056760 WO2015 / 133586 Japanese Unexamined Patent Publication No. 2015-181089 Japanese Unexamined Patent Publication No. 2015-181090 Japanese Unexamined Patent Publication No. 2016-001592 Japanese Unexamined Patent Publication No. 2016-096125 Japanese Unexamined Patent Publication No. 2019-0190114 Japanese Unexamined Patent Publication No. 2019-021420 Japanese Unexamined Patent Publication No. 2019-021421 Japanese Unexamined Patent Publication No. 2019-021427 Japanese Unexamined Patent Publication No. 2019-20866

In the evaluation of the lithium ion secondary battery in Patent Document 6, lithium is used as the counter electrode, but it can be said that this is the evaluation as a half cell. Therefore, although the details will be described later, in order to evaluate the performance as a practical lithium ion secondary battery, a lithium ion secondary battery using a negative electrode containing hard carbon instead of the lithium counter electrode was constructed and left at 60 ° C. When a change in DC internal resistance (hereinafter referred to as "DCIR") was evaluated by conducting a high-temperature standing test, it was found that DCIR increased to more than 2.5 times the initial value after the test (Table). See Comparative Example 1 of 1).

By the way, as described above, recent energy storage devices are required to have high energy density and miniaturization, and stable performance under high temperature use is required so that they can be used even in a highly integrated state. There is. In response to this demand, conductive carbon, which has the property of spreading like a paste under pressure, is excellent in that it provides a storage device having a high energy density, but its stability under high temperature use is further improved. Is desirable.

Therefore, an object of the present invention is to provide conductive carbon and a method for producing the same, which leads to a power storage device having a high energy density and improved stability under high temperature use.

The inventors proceeded with the study based on the conductive carbon having the property of spreading like a paste when subjected to the above-mentioned pressure, which is known to lead to the storage device having a high energy density, and pulverized the conductive carbon into the above-mentioned conductive carbon. The effect of applying the above was investigated. Then, a high-temperature standing test was conducted in which a practical lithium-ion secondary battery including a positive electrode containing pulverized conductive carbon and a positive electrode active material and a negative electrode containing hard carbon was constructed and left at 60 ° C. As a result of evaluating the change in DCIR, it was found that the change in DCIR was once suppressed as the pulverization was strengthened, but the change in DCIR increased again as the pulverization was further strengthened. Therefore, in order to obtain improved stability under high temperature use, it was necessary to select appropriate pulverization conditions.

The inventors then attempted to identify the conductive carbon obtained by applying this moderate pulverization by a Raman spectrum. Non-Patent Document 1 shows an S1 band observed in the Raman spectrum of a graphite structure having high crystallinity near 2700 cm ^-1 , and an S2 band appearing in the vicinity of 2900 cm _-1 when the graphite structure is disturbed (this). See A and B in Figure 3 of the literature). Since it is considered that the crystal structure is disturbed by pulverization, it is expected that the peak intensities of the S1 band and the S2 band of the Raman spectrum can be effectively utilized due to the conductive carbon. FIG. 1 shows Raman using a laser Raman spectrophotometer (excitation light: KTP / 532 laser: wavelength 532 nm) for carbon obtained by pulverizing conductive carbon having the property of spreading like a paste when subjected to pressure. An example of the result of measuring the spectrum is shown. It should be noted that this figure shows a spectrum in which the measured Raman spectrum is subjected to peak smoothing and baseline correction by the simple moving average method, and then converted into relative intensities based on the S2 peak. The stronger the pulverization, the lower the peak intensity _Is1 of the S1 band and the relatively higher the peak intensity _Is2 of the S2 band. Then, as a result of the examination, if the value of the ratio _Is1 / _Is2 of the peak intensity _Is1 of the S1 band to the peak intensity _Is2 of the S2 band is 0.85 to 0.99, the high temperature is improved. It has been found that conductive carbon can be obtained that leads to a storage device with stability in use.

Therefore, the present invention is a conductive carbon to be used as a conductive agent in an electrode of a power storage device.
It has the property of spreading like a paste under pressure, and
The present invention relates to conductive carbon in which the ratio of the peak intensity of the S1 band to the peak intensity of the S2 band in the Raman spectrum of the conductive carbon is in the range of 0.85 to 0.99.

The present invention is also the method for producing the conductive carbon of the present invention.
By subjecting the carbon raw material to an oxidation treatment, an oxidation-treated carbon having the property of spreading like a paste under pressure is obtained, an oxidation step, and
The oxidized carbon is pulverized, except that the ratio of the peak intensity of the S1 band to the peak intensity of the S2 band in the Raman spectrum of the obtained conductive carbon is in the range of 0.85 to 0.99. The crushing stage, which is carried out so as to be
The present invention relates to a method for producing conductive carbon, which comprises.

Here, the ratio of the peak intensity of the S1 band to the peak intensity of the S2 band in the Raman spectrum is calculated using the spectrum obtained by performing baseline correction on the measured Raman spectrum. When a noisy Raman spectrum is measured, the ratio of the peak intensity of the S1 band to the peak intensity of the S2 band is calculated after performing peak smoothing and baseline correction on the measured Raman spectrum. It is preferable to do so. By adjusting the ratio of the peak intensity of the S1 band to the peak intensity of the S2 band in the Raman spectrum of the conductive carbon in the range of 0.85 to 0.99, the power storage device obtained by using the conductive carbon Improves stability under high temperature use. The stability of the power storage device under high temperature use is more preferably improved by adjusting the ratio of the peak intensity of the S1 band to the peak intensity of the S2 band in the range of 0.90 to 0.95.

In the conductive carbon of the present invention, when the conductive carbon contains a hydrophilic portion and the content of the hydrophilic portion is 10% by mass or more of the whole conductive carbon, it is paste-like under the pressure of the conductive carbon. It is preferable because the property of spreading carbon fiber becomes remarkable.

By constructing the electrode of the power storage device using the conductive carbon of the present invention, a power storage device having a high energy density and improved stability under high temperature use can be obtained. Therefore, the present invention is also a method for manufacturing an electrode for a power storage device, in which the electrode active material particles and the conductive carbon of the present invention are mixed, and at least a part of the conductive carbon spreads like a paste. An active material layer is formed by a mixing step of obtaining a mixture covering the surface of the electrode active material particles and by applying the mixture on a current collector for the electrode, and the obtained active material layer is obtained. The present invention relates to a method for manufacturing an electrode, which comprises a pressurizing step of applying a pressure to the conductive carbon to further spread the conductive carbon into a paste and densify the conductive carbon.

When the conductivity of the electrode active material contained in the electrode is low and it is desired to improve the conductivity of the electrode, another conductive carbon having a conductivity higher than that of the conductive carbon is used in the mixing step. It is preferable to further mix to obtain a mixture in which at least a part of the conductive carbon spreads like a paste and also covers the surface of the other conductive carbon. In the production of this suitable mixture, the mixing step is a first mixing step of mixing the conductive carbon with another conductive carbon to obtain a conductive carbon mixture, and the conductive carbon mixture. It is preferable to carry out by a method including a second mixing step of mixing the above-mentioned electrode active material particles because the conductivity of the obtained electrode is further improved.

Since the conductive carbon of the present invention has the property of easily adhering to the surface of the active material particles and having the property of being integrally compressed and spreading like a paste when subjected to pressure, the active material particles and the present material are used in the manufacture of electrodes for power storage devices. When pressure is applied to the mixture containing the conductive carbon of the present invention, the pressure causes the conductive carbon of the present invention to spread like a paste and densify while covering the surface of the active material particles, thereby improving the energy density of the power storage device. Brought to you. In addition, the energy storage device provided with the electrode containing the conductive carbon of the present invention exhibits improved stability under high temperature use.

It is a figure which showed the Raman spectrum of the conductive carbon obtained by a strong oxidation treatment.

(A) Conductive carbon and its manufacturing method The conductive carbon for the electrode of the power storage device of the present invention has a property of spreading like a paste under pressure, and the S1 band in the Raman spectrum of the conductive carbon. The ratio of the peak intensity of S2 band to the peak intensity of S2 band is in the range of 0.85 to 0.99. This conductive carbon is subjected to an oxidation step of obtaining an oxidation-treated carbon having a property of spreading like a paste under pressure by subjecting a carbon raw material to an oxidation treatment, and the above-mentioned oxidation-treated carbon is subjected to a pulverization treatment, provided that the pulverization is performed. Manufactured by a method comprising a grinding step carried out so that the ratio of the peak intensity of the S1 band to the peak intensity of the S2 band in the Raman spectrum of the conductive carbon obtained can be in the range of 0.85 to 0.99. Can be done. Hereinafter, each step will be described in detail.

(1) Oxidation stage In the oxidation stage, a relatively strong oxidation treatment is applied to the conductive carbon raw material. The carbon raw materials used include carbon black such as Ketjen black, acetylene black, furnace black, and channel black, fullerene, carbon nanotubes, carbon nanofibers, graphene, amorphous carbon, carbon fibers, natural graphite, artificial graphite, and graphite. Conductive carbon, which is used as a conductive agent for electrodes of conventional power storage devices such as chemical Ketjen black, mesoporous carbon, and vapor phase carbon fiber, can be used without particular limitation, but is easy to oxidize. From this point of view, porous carbon powder, Ketjen black, furnace black with voids, carbon nanofibers and conductive carbon having voids such as carbon nanotubes are preferable, and among them, the specific surface area measured by the BET method is 300 m ² /. Conductive carbon having voids of g or more is preferable, and spherical conductive carbon such as Ketjen black and furnace black having voids is particularly preferable.

For the oxidation treatment of the carbon raw material, a known oxidation method can be used without particular limitation. For example, oxidation-treated carbon can be obtained by treating the carbon raw material in a solution of acid or hydrogen peroxide. As the acid, nitric acid, a mixture of nitric acid and sulfuric acid, an aqueous solution of hypochlorous acid and the like can be used. Further, by heating the carbon raw material in an oxygen-containing atmosphere, steam, or carbon dioxide, oxidation-treated carbon can be obtained. Further, the oxidation-treated carbon can be obtained by mixing the carbon raw material with the alkali metal hydroxide and heating it in an oxygen-containing atmosphere to remove the alkali metal by washing with water or the like. Further, the oxidized carbon can be obtained by plasma treatment in an oxygen-containing atmosphere of the carbon raw material, ultraviolet irradiation, corona discharge treatment and glow discharge treatment, treatment with ozone water or ozone gas, and oxygen bubbling treatment in water.

When the carbon raw material, preferably the carbon raw material having voids described above, is oxidized, it is oxidized from the surface of the carbon particles, a hydroxyl group, a carboxyl group or an ether bond is introduced into the carbon, and the conjugated double bond of the carbon is oxidized. Then, a carbon single bond is formed, the carbon-carbon bond is partially broken, and a highly hydrophilic portion is formed on the particle surface. Then, as the strength of the oxidation treatment is increased, the proportion of the hydrophilic portion in the carbon particles increases, and it is possible to obtain the oxidation-treated carbon having the property of spreading like a paste under pressure. The content of the hydrophilic portion in the oxidized carbon is preferably 10% by mass or more of the total amount of the oxidized carbon. When such oxidized carbon is subjected to pressure, it is integrally compressed and easily spreads like a paste and is easily densified.

Oxidized carbon containing 10% by mass or more of the total hydrophilic part is
(A1) A step of treating a carbon raw material having voids with an acid,
(B1) Step of mixing the product after acid treatment with the transition metal compound,
(C1) A step of pulverizing the obtained mixture to cause a mechanochemical reaction.
(D1) A step of heating the product after the mechanochemical reaction in a non-oxidizing atmosphere, and
(E1) It can be suitably obtained by the first production method including the step of removing the transition metal compound and / or the reaction product thereof from the product after heating.

In the step (a1), the carbon raw material having voids is immersed in an acid and left to stand. Ultrasonic waves may be applied during this immersion. As the acid, an acid usually used for oxidation treatment of carbon such as nitric acid, a mixture of nitric acid and sulfuric acid, and an aqueous solution of hypochlorous acid can be used. The soaking time depends on the concentration of the acid and the amount of the carbon raw material to be treated, but is generally in the range of 5 minutes to 5 hours. The carbon after the acid treatment is thoroughly washed with water, dried, and then mixed with the transition metal compound in the step (b1).

Examples of the transition metal compound added to the carbon raw material in the step (b1) include halides of transition metals, nitrates, sulfates, and inorganic metal salts such as carbonates, formates, acetates, oxalates, methoxydos, ethoxydos, and iso. Organic metal salts such as propoxide or mixtures thereof can be used. These compounds may be used alone or in combination of two or more. Compounds containing different transition metals may be mixed and used in predetermined amounts. Further, a compound other than the transition metal compound, for example, an alkali metal compound may be added together as long as the reaction is not adversely affected. Since the conductive carbon of the present invention is used by being mixed with active material particles in the production of electrodes of a power storage device, when a compound of an element constituting the active material is added to a carbon raw material, an impurity is added to the active material. It is preferable because it can prevent the mixing of potential elements.

In the step (c1), the mixture obtained in the step (b1) is pulverized to cause a mechanochemical reaction. Examples of crushers for this reaction include raikais, ball mills, bead mills, rod mills, roller mills, stirring mills, planetary mills, vibration mills, hybridizers, mechanochemical compounding devices and jet mills. The crushing time depends on the crusher used, the amount of carbon to be processed, and the like, and is not strictly limited, but is generally in the range of 5 minutes to 3 hours. The step (d1) is performed in a non-oxidizing atmosphere such as a nitrogen atmosphere and an argon atmosphere. The heating temperature and heating time are appropriately selected depending on the transition metal compound used. In the subsequent step (e1), the transition metal compound and / or its reaction product is removed from the heated product by means such as dissolving it with an acid, and then thoroughly washed and dried to remove the oxidized carbon. Obtainable.

In the first production method, in the step (c1), the transition metal compound acts to promote the oxidation of the carbon raw material by the mechanochemical reaction, and the oxidation of the carbon raw material proceeds rapidly. By this oxidation, an oxidation-treated carbon containing a hydrophilic portion of 10% by mass or more of the total conductive carbon can be obtained.

Oxidized carbon containing more than 10% by weight of the total hydrophilic part also
(A2) A step of mixing a carbon raw material having voids and a transition metal compound,
(B2) A step of heating the obtained mixture in an oxidizing atmosphere, and
(C2) It can also be preferably obtained by a second production method including a step of removing the transition metal compound and / or a reaction product thereof from the product after heating.

As the transition metal compound added to the carbon raw material in the step (a2), inorganic metal salts such as halides, nitrates, sulfates and carbonates of transition metals, formates, acetates, oxalates, methoxydos, ethoxydos and iso Organic metal salts such as propoxide or mixtures thereof can be used. These compounds may be used alone or in combination of two or more. Compounds containing different metals may be mixed and used in predetermined amounts. Further, a compound other than the transition metal compound, for example, an alkali metal compound may be added together as long as the reaction is not adversely affected. Since this conductive carbon is used by being mixed with active material particles in the production of electrodes of a power storage device, an element that can become an impurity with respect to the active material when a compound of an element constituting the active material is added to the carbon raw material. It is preferable because it can prevent the mixing of the compound.

The step (b2) is carried out in an oxygen-containing atmosphere, for example, in air, and is carried out at a temperature at which carbon partially disappears but does not completely disappear, preferably at a temperature of 200 to 350 ° C. In the subsequent step (c2), the transition metal compound and / or its reaction product is removed from the heated product by means such as dissolving it with an acid, and then thoroughly washed and dried to remove the oxidized carbon. Obtainable.

In the second production method, the transition metal compound acts as a catalyst for oxidizing the carbon raw material in the heating step in the oxidizing atmosphere, and the oxidation of the carbon raw material proceeds rapidly. By this oxidation, an oxidation-treated carbon containing a hydrophilic portion of 10% by mass or more of the total conductive carbon can be obtained.

A suitable oxidation-treated carbon containing a hydrophilic portion of 10% by mass or more of the whole is obtained by subjecting the carbon raw material to a strong oxidation treatment, and the carbon raw material can be obtained by a method other than the first production method and the second production method. It is also possible to promote oxidation.

(2) Crushing Step The conductive carbon of the present invention can be obtained by subjecting the oxidation-treated carbon to a crushing treatment in the crushing step. The pulverization treatment is carried out so that the ratio of the peak intensity of the S1 band to the peak intensity of the S2 band in the Raman spectrum of the obtained conductive carbon is in the range of 0.85 to 0.99. By adjusting the ratio of the peak intensity of the S1 band to the peak intensity of the S2 band in the range of 0.90 to 0.95, the stability under high temperature use is more preferably improved.

For crushing, a raikai device, a stone mill type grinder, a ball mill, a bead mill, a rod mill, a roller mill, a stirring mill, a planetary mill, a vibration mill, a hybridizer, a mechanochemical compounding device and a jet mill can be used. The pulverization time varies depending on the amount of the oxidized carbon to be pulverized and the mixing device used, but is generally between 10 minutes and 1 hour.

(B) Method for manufacturing an electrode The conductive carbon of the present invention is an electrode active material whose capacity is developed by a Faraday reaction involving the transfer of electrons with ions in the electrolyte of a power storage device or a non-Faraday reaction without transfer of electrons. In mixed form with particles, it is used for electrodes of power storage devices such as secondary batteries, electric double layer capacitors, redox capacitors and hybrid capacitors. The power storage device includes a pair of electrodes (positive electrode, negative electrode) and an electrolyte arranged between them as essential elements, and at least one of the positive electrode and the negative electrode contains the conductive carbon of the present invention and the electrode active material particles. Manufactured using the inclusion mixture.

The electrolyte arranged between the positive electrode and the negative electrode in the power storage device may be an electrolytic solution held in the separator, a solid electrolyte, or a gel-like electrolyte, and may be a conventional power storage device. The electrolyte used in the above can be used without particular limitation. The following is an example of a typical electrolyte. For a lithium ion secondary battery, a lithium salt such as LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , or LiN (CF ₃ SO ₂ ) ₂ is added to a solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, or dimethyl carbonate. The dissolved electrolytic solution is used in a state of being held by a separator such as a polyolefin fiber non-woven fabric or a glass fiber non-woven fabric. In addition, inorganic solid electrolytes such as Li ₅ La ₃ Nb ₂ O ₁₂ , Li _1.5 Al _0.5 Ti _1.5 (PO ₄ ) ₃ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₇ P ₃ S ₁₁ and the like. , An organic solid electrolyte composed of a composite of a lithium salt and a polymer compound such as polyethylene oxide, polymethacrylate, and polyacrylate, and a gel-like electrolyte in which an electrolytic solution is absorbed by polyvinylidene fluoride, polyacrylonitrile, or the like are also used. For electric double layer capacitors and redox capacitors, an electrolytic solution in which a quaternary ammonium salt such as (C ₂ H ₅ ) ₄ NBF ₄ is dissolved in a solvent such as acrylonitrile or propylene carbonate is used. For the hybrid capacitor, an electrolytic solution in which a lithium salt is dissolved in propylene carbonate or the like or an electrolytic solution in which a quaternary ammonium salt is dissolved in propylene carbonate or the like is used.

The positive electrode or the negative electrode of the energy storage device using the conductive carbon of the present invention is generally prepared by mixing the electrode active material particles and the conductive carbon of the present invention together with a solvent in which a binder is dissolved, if necessary. By a mixing step of obtaining a mixture in which at least a part of the conductive carbon spreads like a paste and covers the surface of the electrode active material particles, and by applying the mixture onto a current collector for the electrodes. It is produced by a method including a pressurizing step of forming an active material layer and applying pressure to the obtained active material layer to further spread the conductive carbon into a paste and densify it. When a solid electrolyte or a gel-like electrolyte is used as the electrolyte between the positive electrode and the negative electrode, an ion conduction path in the active material layer is secured in the mixture containing the conductive carbon of the present invention and the electrode active material particles. A solid electrolyte is added for the purpose of the above, and if necessary, these are sufficiently kneaded with a solvent in which the binder is dissolved, and the obtained mixture is used to form an active material layer on the current collector. As the current collector, a conductive material such as platinum, gold, nickel, aluminum, titanium, steel, or carbon can be used. As the shape of the current collector, any shape such as a film shape, a foil shape, a plate shape, a net shape, an expanded metal shape, and a cylindrical shape can be adopted.

In the above mixing step, the conductive carbon of the present invention adheres to the surface of the active material particles and covers the surface, so that aggregation of the active material particles can be suppressed. Further, when the pressure applied to the conductive carbon of the present invention is large in the above mixing step, at least a part of the conductive carbon spreads like a paste and the surface of the active material particles is partially covered. Further, due to the pressure applied to the active material layer in the pressurizing step, the conductive carbon of the present invention further spreads like a paste and becomes densified while covering the surface of the active material particles, and the active material particles approach each other to this. Along with this, the conductive carbon of the present invention covers the surface of the active material particles and is extruded not only into the gaps formed between the adjacent active material particles but also into the pores existing on the surface of the active material particles. Is filled with. Therefore, the amount of active material per unit volume in the electrode increases, and the electrode density increases. Further, the densely packed paste-like conductive carbon has sufficient conductivity to function as a conductive agent and does not suppress the impregnation of the electrolytic solution in the power storage device. As a result, the energy density of the power storage device is improved.

As the positive electrode active material and the negative electrode active material mixed with the conductive carbon of the present invention in the above mixing step, the electrode active material used in the conventional power storage device can be used without particular limitation. The active substance may be a single compound or a mixture of two or more kinds of compounds.

Examples of positive electrode active materials for secondary batteries include layered rock salt type LiMO ₂ , layered Li ₂ MnO ₃ -LiMO ₂ solid solution, and spinel type LiM ₂ O ₄ (M in the formula is Mn, Fe, Co, Ni or a combination thereof). Specific examples of these include LiCoO ₂ , LiNiO ₂ , LiNi _4/5 Co _1/5 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _1/2 Mn _1/2 O. ₂ , LiFeO ₂ , LiMnO ₂ , Li ₂ MnO ₃ -LiCoO _2, Li ₂ MnO ₃ -LiNiO ₂ , Li ₂ MnO ₃ -LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , Li ₂ MnO ₃ -LiNi _1/2 Mn _1/2 O ₂ , Li ₂ MnO ₃ -LiNi _1/2 Mn _1/2 O ₂ -LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , LiMn _3/2 Ni _1/2 O ₄ can be mentioned. In addition, sulfur and sulfides such as Li 2S, TiS ₂ , MoS ₂ , FeS ₂ , VS ₂ , Cr _1/2 V _1/2 S ₂ and sulphides such as NbSe ₃ , _VSe ₂ and NbSe ₃ , Cr ₂ Oxides such as O ₅ , Cr ₃ O ₈ , VO ₂ , V ₃ O ₈ , V ₂ O ₅ , V ₆ O ₁₃ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiVOPO ₄ , LiV ₃ O ₅ , LiV ₃ O ₈ , MoV ₂ O ₈ , Li ₂ FeSiO ₄ , Li ₂ MnSiO ₄ , LiFePO ₄ , LiFe _1/2 Mn _1/2 PO ₄ , LiMnPO ₄ , Li ₃ V ₂ (PO ₄ ) Examples thereof include composite oxides such as ₃ .

Examples of negative electrode active materials for secondary batteries are Fe ₂ O ₃ , MnO, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , CoO, Co ₃ O ₄ , NiO, Ni ₂ O ₃ , TiO, and TIO ₂ . , SnO, SnO ₂ , SiO ₂ , RuO ₂ , WO, WO ₂ , ZnO and other oxides, Sn, Si, Al, Zn and other metals, LiVO ₂ , Li ₃ VO ₄ , Li ₄ Ti ₅ O ₁₂ and the like. Examples thereof include composite oxides and nitrides such as Li _2.6 Co _0.4 N, Ge ₃ N ₄ , Zn ₃ N ₂ and Cu ₃ N.

Examples of the active material in the polarizable electrode of the electric double layer capacitor include carbon materials such as activated carbon having a large specific surface area, carbon nanofibers, carbon nanotubes, phenolic resin carbides, polyvinylidene chloride carbides, and microcrystalline carbon. In the hybrid capacitor, the positive electrode active material exemplified for the secondary battery can be used for the positive electrode, and in this case, the negative electrode is composed of a polar electrode using activated carbon or the like. Further, the negative electrode active material exemplified for the secondary battery can be used for the negative electrode, and in this case, the positive electrode is composed of a polarizable electrode using activated carbon or the like. Examples of the positive electrode active material of the redox capacitor include metal oxides such as RuO ₂ , MnO ₂ , and NiO, and the negative electrode is composed of an active material such as RuO ₂ and a polarizable material such as activated carbon.

The shape and particle size of the active material particles are not limited, but the average particle size is preferably larger than 2 μm and 25 μm or less. The active material particles having such a relatively large particle size improve the electrode density by themselves, and in the mixing step, the pressing force of the active material particles promotes the gelatinization of the conductive carbon. Further, in the process of applying pressure to the active material layer on the current collector in the electrode manufacturing, the active material particles having such a relatively large particle size further press the conductive carbon which is at least partially pasty. Then, the conductive carbon is further spread like a paste to be densified. As a result, the electrode density is further increased, and the energy density of the power storage device is further improved.

Further, the active material particles include fine particles having an average particle size of 0.01 to 2 μm, and coarse particles having an average particle size of 25 μm or less, which is larger than 2 μm and can operate as an active material having the same pole as the fine particles. It is preferably composed of. In the mixing step, the conductive carbon of the present invention adheres not only to the surface of the fine particles but also to the surface of the coarse particles to cover the surface, so that aggregation of the active material particles can be suppressed, and the active material particles and the conductivity can be suppressed. The mixed state with carbon can be made uniform. Further, as described above, the coarse particles promote the gelatinization and densification of the conductive carbon of the present invention, increase the electrode density, and improve the energy density of the energy storage device. Further, due to the pressure applied to the active material layer formed on the current collector by the rolling process in the electrode production, the fine particles press the conductive carbon of the present invention together with the conductive carbon spread like a paste. Since the gaps formed between the adjacent coarse particles are extruded and filled, the electrode density is further increased, and the energy density of the energy storage device is further improved.

When the conductivity of the electrode active material contained in the electrode is low and it is desired to improve the conductivity of the electrode, another conductive carbon having a conductivity higher than that of the conductive carbon is used in the mixing step. It is preferable to further mix to obtain a mixture in which at least a part of the conductive carbon spreads like a paste and also covers the surface of the other conductive carbon. Other conductive carbons mentioned above include carbon blacks such as Ketjen black, acetylene black, furnace black, and channel black, which are used for electrodes of conventional power storage devices, fullerene, carbon nanotubes, carbon nanofibers, and graphene. Examples thereof include amorphous carbon, carbon fiber, natural graphite, artificial graphite, graphitized Ketjen black, mesoporous carbon, and vapor phase carbon fiber. The mass ratio of the conductive carbon to the other conductive carbon is generally in the range of 3: 1 to 1: 3.

In this embodiment, in the mixing step, at least a part of the conductive carbon of the present invention spreads like a paste and adheres not only to the surface of the electrode active material but also to the surface of the other conductive carbon described above to cover the surface. It is possible to suppress the aggregation of the other conductive carbon. Further, due to the pressure applied to the active material layer formed on the current collector in the pressurizing step, the other conductive carbon is formed by adjacent active material particles together with the conductive carbon of the present invention spread like a paste. Since the gaps are densely filled and the conductivity of the entire electrode is improved, the energy density of the power storage device is further improved.

In the production of a suitable mixture containing the other conductive carbon, the mixing step is the first mixing step of mixing the conductive carbon with the other conductive carbon to obtain a conductive carbon mixture. Further, it is preferable to carry out by a method including a second mixing step of mixing the conductive carbon mixture and the electrode active material particles because the conductivity of the electrode obtained after the pressurizing step is further improved.

The mixing method for carrying out the mixing step is not particularly limited, and a known mixing method can be used, but the active material particles, the conductive carbon of the present invention, and another conductive material used in combination as necessary are used. It is preferred to mix the carbon by dry mixing and then, if necessary, with a solvent in which the binder is dissolved. For dry mixing, lyca, ball mills, bead mills, rod mills, roller mills, stirring mills, planetary mills, vibration mills, hybridizers, mechanochemical compounding devices and jet mills can be used. The ratio of the active material particles to the total of the conductive carbon of the present invention or another conductive carbon used in combination with the conductive carbon of the present invention as needed is to obtain a power storage device having a high energy density. The mass ratio is preferably in the range of 90:10 to 99.5: 0.5, more preferably in the range of 95: 5 to 99: 1. If the proportion of the conductive carbon is less than the above range, the conductivity of the active material layer is insufficient, and the coverage of the active material particles by the conductive carbon tends to decrease. Further, when the ratio of the conductive carbon is larger than the above range, the electrode density tends to decrease, and the energy density of the power storage device tends to decrease.

Binders to be mixed with the active material particles, the conductive carbon of the present invention and other conductive carbons used in combination as needed include polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, and polyhood. Known binders such as vinyl fluoride and carboxymethyl cellulose are used. The binder content is preferably 1 to 30% by mass with respect to the total amount of the mixed material. If it is 1% by mass or less, the strength of the active material layer is not sufficient, and if it is 30% by mass or more, inconveniences such as a decrease in the discharge capacity of the electrode and an excessive internal resistance occur. The solvent to be mixed with the active material particles, the conductive carbon of the present invention and another conductive carbon used in combination as necessary is not particularly limited to a solvent that does not adversely affect other materials such as N-methylpyrrolidone. Can be used.

The present invention will be described with reference to the following examples, but the present invention is not limited to the following examples.

Comparative Example 1
10 g of Ketjen Black (trade name EC300J, manufactured by Ketjen Black International Co., Ltd.) was added to 300 mL of 40% nitric acid, and the obtained liquid was irradiated with ultrasonic waves for 10 minutes and then filtered to recover Ketjen Black. The recovered Ketjen black was washed with water three times and dried to obtain an acid-treated Ketjen black. 1.8 g of this acid-treated Ketjen Black, ₂ 0.5 g of Fe (CH ₃ COO), 0.19 g of Li (CH ₃ COO), C ₆ H ₈ O ₇ · H ₂ O 0.28 g, and CH ₃ 0.33 g of COOH, 0.33 g of H ₃ PO ₄ and 250 mL of distilled water were mixed, and the obtained mixture was stirred with a stirrer for 1 hour and then evaporated to dryness in air at 100 ° C. to collect the mixture. .. Then, the obtained mixture was introduced into a vibrating ball mill device, and pulverization was performed at 20 hz for 10 minutes. The pulverized powder was heated in nitrogen at 700 ° C. for 3 minutes to obtain a complex in which LiFePO ₄ was supported on Ketjen black.

1 g of the obtained complex is added to 100 mL of a 30% hydrochloric acid aqueous solution, LiFePO ₄ in the complex is dissolved while irradiating the obtained solution with ultrasonic waves for 15 minutes, the remaining solid is filtered, and washed with water. And dried. A part of the dried solid was heated to 900 ° C. in air by TG analysis, and the weight loss was measured. The steps of dissolution, filtration, washing and drying of LiFePO ₄ with the above-mentioned aqueous hydrochloric acid solution were repeated until it was confirmed that the weight loss was 100%, that is, LiFePO ₄ did not remain, to obtain LiFePO ₄ -free oxidized carbon. ..

Next, 0.1 g of the obtained oxidized carbon was added to 20 mL of an aqueous ammonia solution having a pH of 11, and ultrasonic irradiation was performed for 1 minute. The obtained liquid was left to stand for 5 hours to precipitate the solid phase portion. After the solid phase was precipitated, the residue from which the supernatant was removed was dried, and the weight of the dried solid was measured. The weight ratio of the weight of the dried solid minus the weight of the first oxidized carbon of 0.1 g to the weight of the first oxidized carbon of 0.1 g is the content of the "hydrophilic moiety" in the oxidized carbon. did. The content of the hydrophilic portion was 10.2% of the total oxidized carbon.

Further, the Raman spectrum of the obtained oxidation-treated carbon was measured using a laser Raman spectrophotometer (NRS-5500 manufactured by JASCO Corporation, excitation light: KTP / 532 laser: wavelength 532 nm). Then, the measured Raman spectrum is smoothed and baseline corrected by the simple moving average method using the analysis software (spectrum manager) attached to the spectrophotometer, and the S1 band is obtained from the obtained spectrum. The ratio _Is1 / _Is2 of the peak intensity _Is1 to the peak intensity _Is2 of the S2 band was calculated.

Further, an appropriate amount for 96 parts by mass of commercially available LiNi _0.5 Mn _0.3 Co _0.2 O ₂ particles (average particle size 5 μm), 2 parts by mass of the above-mentioned oxidized carbon, and 2 parts by mass of polyvinylidene fluoride. N-Methylpyrrolidone was added and sufficiently kneaded to form a slurry. This slurry was applied onto an aluminum foil and dried, and then pressurized three times under the condition of 1.5 t / cm to obtain a positive electrode for a lithium ion secondary battery.

Further, 93 parts by mass of hard carbon, 1 part by mass of acetylene black, and 6 parts by mass of polyvinylidene fluoride were added with an appropriate amount of N-methylpyrrolidone and sufficiently kneaded to form a slurry. This slurry was applied onto a copper foil, dried, and then pressurized to obtain a negative electrode for a lithium ion secondary battery having an electrode density of 1.0 g / cc. The ratio of the positive electrode capacity to the negative electrode capacity was 1: 1.2.

After vacuum-drying the obtained positive electrode and negative electrode at 100 ° C. for 12 hours, a lithium ion secondary battery was prepared using a 1 M LiPF ₆ ethylene carbonate / dimethyl carbonate / propylene carbonate 1: 1: 1 solution as an electrolytic solution. ..

The obtained battery was subjected to a high temperature standing test. First, the obtained battery is charged until the SOC (remaining capacity (Ah) / full charge capacity (Ah) x 100) reaches 50%, and then discharged with a constant current for 10 seconds to obtain the initial DCIR from the voltage drop. Calculated. Next, the battery is charged to 4 V, left in a constant temperature bath at 60 ° C. for 2 weeks, then the battery is taken out from the constant temperature bath, charged until the SOC reaches 50%, and then discharged at a constant current for 10 seconds from the voltage drop. The DCIR after leaving was calculated. Then, the resistance increase rate of the DCIR after being left to stand from the initial DCIR was calculated as a measure of the high temperature holding stability.

Example 1
The LiFePO ₄ -free oxidation-treated carbon obtained in Comparative Example 1 was introduced into a vibrating ball mill device and pulverized for 20 minutes under the condition of 10 Hz. The obtained pulverized conductive carbon was used in place of the oxidized carbon of Comparative Example 1 to prepare a lithium ion secondary battery in the same procedure as in Comparative Example 1, and the obtained battery was prepared in the same procedure as in Comparative Example 1. A high temperature standing test was performed.

Example 2
The LiFePO ₄ -free oxidation-treated carbon obtained in Comparative Example 1 was introduced into a vibrating ball mill apparatus and pulverized for 20 minutes under the condition of 15 Hz. The obtained pulverized conductive carbon was used in place of the oxidized carbon of Comparative Example 1 to prepare a lithium ion secondary battery in the same procedure as in Comparative Example 1, and the obtained battery was prepared in the same procedure as in Comparative Example 1. A high temperature standing test was performed.

Example 3
The LiFePO ₄ -free oxidation-treated carbon obtained in Comparative Example 1 was introduced into a vibrating ball mill device and pulverized for 30 minutes under the condition of 15 Hz. The obtained pulverized conductive carbon was used in place of the oxidized carbon of Comparative Example 1 to prepare a lithium ion secondary battery in the same procedure as in Comparative Example 1, and the obtained battery was prepared in the same procedure as in Comparative Example 1. A high temperature standing test was performed.

Example 4
The LiFePO ₄ -free oxidation-treated carbon obtained in Comparative Example 1 was introduced into a vibrating ball mill device and pulverized for 60 minutes under the condition of 20 Hz. The obtained pulverized conductive carbon was used in place of the oxidized carbon of Comparative Example 1 to prepare a lithium ion secondary battery in the same procedure as in Comparative Example 1, and the obtained battery was prepared in the same procedure as in Comparative Example 1. A high temperature standing test was performed.

Example 5
The LiFePO ₄ -free oxidation-treated carbon obtained in Comparative Example 1 was introduced into a vibrating ball mill device and pulverized for 20 minutes under the condition of 30 Hz. The obtained pulverized conductive carbon was used in place of the oxidized carbon of Comparative Example 1 to prepare a lithium ion secondary battery in the same procedure as in Comparative Example 1, and the obtained battery was prepared in the same procedure as in Comparative Example 1. A high temperature standing test was performed.

Comparative Example 2
The LiFePO ₄ -free oxidation-treated carbon obtained in Comparative Example 1 was introduced into a vibrating ball mill apparatus and pulverized for 60 minutes under the condition of 30 Hz. The obtained pulverized conductive carbon was used in place of the oxidized carbon of Comparative Example 1 to prepare a lithium ion secondary battery in the same procedure as in Comparative Example 1, and the obtained battery was prepared in the same procedure as in Comparative Example 1. A high temperature standing test was performed.

In Table 1, for Examples 1 to 5 and Comparative Examples 1 and 2, the ratio of the peak intensity _Is1 of the S1 band to the peak intensity _Is2 of the S2 band obtained from the Raman spectrum of the conductive carbon is _Is1 / _Is2 . , The resistance increase rate calculated in the high temperature standing test of the lithium ion secondary battery is shown together.

As can be clearly seen from Table 1, after the oxidation-treated carbon of Comparative Example 1 was pulverized, a practical lithium-ion secondary battery was constructed using the obtained conductive carbon, and a high-temperature standing test was performed. However, it was found that when the strength of the pulverization treatment was increased, the resistance increase rate in the high temperature standing test, which had once decreased, started to increase again. Therefore, in order to obtain a power storage device having a high energy density and improved stability under high temperature use, the ratio I of the peak intensity _Is1 of the S1 band to the peak intensity _Is2 of the S2 band in the Raman spectrum. It is necessary to grind the oxidized carbon so that _s1 / _Is2 is in the range of 0.85 to 0.99. Further, in order to obtain the stability of the power storage device under higher temperature use, the ratio of the peak intensity _Is1 of the S1 band to the peak intensity _Is2 of the S2 band in the Raman spectrum is _0.90 to _Is2 . It is important to grind the oxidized carbon so that it is in the range of 0.95.

By using the conductive carbon of the present invention, a power storage device having a high energy density and improved stability under high temperature use can be obtained.

Claims

Conductive carbon that should be used as a conductive agent in the electrodes of power storage devices.
It has the property of spreading like a paste under pressure, and
The conductive carbon is characterized in that the ratio of the peak intensity of the S1 band to the peak intensity of the S2 band in the Raman spectrum of the conductive carbon is in the range of 0.85 to 0.99.
The conductive carbon according to claim 1, wherein the ratio of the peak intensity of the S1 band to the peak intensity of the S2 band in the Raman spectrum of the conductive carbon is in the range of 0.90 to 0.95.
The conductive carbon contains a hydrophilic portion and contains
The conductive carbon according to claim 1 or 2, wherein the content of the hydrophilic portion is 10% by mass or more of the total conductive carbon.
The method for producing conductive carbon according to claim 1.
By subjecting the carbon raw material to an oxidation treatment, an oxidation-treated carbon having the property of spreading like a paste under pressure is obtained, an oxidation step, and
The oxidized carbon is pulverized, except that the ratio of the peak intensity of the S1 band to the peak intensity of the S2 band in the Raman spectrum of the obtained conductive carbon is in the range of 0.85 to 0.99. The crushing stage, which is carried out so as to be
A method for producing conductive carbon, which comprises.
Claimed in the above-mentioned pulverization step, the pulverization treatment is carried out so that the ratio of the peak intensity of the S1 band to the peak intensity of the S2 band in the Raman spectrum of the obtained conductive carbon is in the range of 0.90 to 0.95. 4. The method for producing conductive carbon according to 4.
The conductive carbon according to claim 4 or 5, wherein in the oxidation step, the oxidation treatment is carried out so that the content of the hydrophilic portion in the obtained oxidation-treated carbon is 10% by mass or more of the total oxidation-treated carbon. Production method.
It is a method of manufacturing electrodes for power storage devices.
The electrode active material particles and the conductive carbon according to any one of claims 1 to 3 are mixed, and at least a part of the conductive carbon spreads like a paste to cover the surface of the electrode active material particles. To obtain the mixture, the mixing process, and
An active material layer is formed by applying the mixture onto a current collector for the electrodes, and pressure is applied to the obtained active material layer to further spread and densify the conductive carbon in a paste-like manner. A method for manufacturing an electrode, which comprises a pressurizing step.
In the mixing step, another conductive carbon having a conductivity higher than that of the conductive carbon is further mixed, and at least a part of the conductive carbon spreads like a paste on the surface of the other conductive carbon. The method for producing an electrode according to claim 7, wherein the mixture is also coated with the above-mentioned material.
The mixing step
A first mixing step of mixing the conductive carbon with the other conductive carbon to obtain a conductive carbon mixture, and
The method for manufacturing an electrode according to claim 8, further comprising a second mixing step of mixing the conductive carbon mixture and the electrode active material particles.