JP6931186B2 - A conductive carbon mixture, an electrode using this mixture, and a power storage device equipped with this electrode. - Google Patents

Description

The present invention relates to a conductive carbon mixture used in the manufacture of electrodes for power storage devices. The present invention also relates to an electrode using the conductive carbon mixture and a power storage device provided with the electrode.

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

In these power 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 electrolyte) or a non-Faraday reaction without transfer of electrons is used for energy storage. It will be used. Then, these electrode 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. However, it also plays a role of securing 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 produced by a method of mixing active material particles and conductive carbon particles. 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. However, there is a problem that it is difficult to efficiently allow the conductive carbon particles to enter between the active material particles, and therefore it is difficult to increase the amount of active material per unit volume by increasing the distance between the active material particles. Was present.

In response to this problem, the applicant has proposed in Patent Document 1 (Japanese Unexamined Patent Publication No. 2016-96125) a conductive carbon mixture for producing an electrode of a power storage device. This conductive carbon mixture is obtained by dry mixing of an oxidation-treated carbon obtained by subjecting a carbon raw material having voids to a strong oxidation treatment and a conductive carbon different from the oxidation-treated carbon. Oxidized carbon that has been subjected to a strong oxidation treatment has the property that at least a part of it changes into a paste when it receives pressure. Oxidation-treated carbon, which is formed into a paste-like state at least in part, adheres to the surface of the other conductive carbon.

The conductive carbon mixture has a good affinity with the electrode active material, and in the process of mixing the conductive carbon mixture and the electrode active material to produce an electrode material for a power storage device, at least a part of the conductive carbon mixture. The paste-like oxidation-treated carbon coats the surface of the electrode active material. Then, when an active material layer is formed on the current collector using this electrode material and a pressure is applied to the active material layer to manufacture an electrode, the pressure further promotes gelatinization of the oxidized carbon. As the coating of the surface of the electrode active material by the gelatinized oxidation-treated carbon further progresses, the particles of the electrode active material in which the gelatinized oxidation-treated carbon and another conductive carbon coated on the gelatinized carbon are close to each other are close to each other. It is extruded and densified. As a result, the content of the electrode active material in the active material layer can be increased, and an electrode having a high electrode density can be obtained. Further, when the power storage device is configured by using the obtained electrodes, the conductive carbon mixture dissolves the electrode active material in the electrolytic solution even though the impregnation of the electrolytic solution in the power storage device into the electrode is not suppressed. It is known to suppress. Therefore, the conductive carbon mixture brings about an improvement in the energy density and cycle life of the power storage device.

Japanese Unexamined Patent Publication No. 2016-96125

The power storage device is always required to further improve the cycle life. Therefore, an object of the present invention is to provide a conductive carbon mixture that further prolongs the cycle life of the power storage device based on the findings of Patent Document 1.

The inventor is a carbon used to evaluate the degree of structural development of a conductive carbon mixture obtained by extensively varying the strength of a dry mixture of oxidized carbon and another conductive carbon. When the dibutyl phthalate oil absorption per 100 g was examined, it was found that the dibutyl phthalate oil absorption per 100 g of the conductive carbon mixture decreased as the dry mixing strength increased. Here, the amount of dibutyl phthalate oil absorbed per 100 g of carbon is a value measured according to JIS K 6217-4. Hereinafter, the amount of dibutyl phthalate oil absorbed by 100 g of carbon measured according to this JIS standard is referred to as "DBP oil absorption amount", and dibutyl phthalate is referred to as "DBP". Further, in the present invention, the "oxidation-treated carbon" refers to carbon obtained by subjecting a conductive carbon raw material to a strong oxidation treatment and having a property that at least a part thereof changes into a paste when pressure is applied. Meaning, "paste-like" means a state in which grain boundaries of carbon primary particles are not recognized in an SEM photograph taken at a magnification of 25,000 times, and non-particulate amorphous carbon is connected. Then, as a result of diligent studies, the inventor shows a value in the range of 70% or less, preferably 40 to 70%, particularly preferably 40 to 65% of the DBP oil absorption amount of the other conductive carbon. The invention was completed by discovering that the cycle life of the power storage device was significantly improved when the power storage device was constructed using the conductive carbon mixture.

Therefore, the present invention first includes a conductive oxidation-treated carbon and a conductive carbon different from the oxidation-treated carbon, and the oxidation-treated carbon covers the surface of the other conductive carbon. , A conductive carbon mixture for producing electrodes of a power storage device, wherein the DBP oil absorption amount of the conductive carbon mixture is 70% or less, preferably 40 to 70% of the DBP oil absorption amount of the other conductive carbon. Particularly preferably in the range of 40-65% with respect to the conductive carbon mixture. In this conductive carbon mixture, it is preferable that at least a part of the oxidized carbon is paste-like.

Due to the pressure received in the process of dry mixing of the oxidation-treated carbon and the other conductive carbon, the other conductive carbon is made finer, and at least a part of the surface of the finer particles is changed into a paste-like oxidation treatment. Although it is coated with carbon, the amount of DBP oil absorbed decreases as the mixing strength is increased by, for example, increasing the frequency of the ball mill used for dry mixing or lengthening the mixing time. This means that as the mixing strength is increased, the amount of DBP oil absorbed decreases due to the miniaturization of the other conductive carbon, and at least a part of the oxidized carbon that has changed to a paste is refined. It is considered that it corresponds to the decrease of the adsorption field of DBP because it covers. Therefore, the DBP oil absorption amount is a value that reflects the coating state of the surface of the other conductive carbon by the oxidation-treated carbon.

Then, the DBP oil absorption amount measured for the conductive carbon mixture obtained by the dry mixing, that is, the conductive carbon mixture in which the oxidation-treated carbon covers the surface of the other conductive carbon, is the other conductivity. It was found that the cycle life of the power storage device was remarkably improved when the amount of DBP oil absorbed by the sex carbon was 70% or less, preferably 40 to 70%, particularly preferably 40 to 65%.

It is preferable that the oxidized carbon in the conductive carbon mixture contains a hydrophilic portion, and the content of the hydrophilic portion is 10% by mass or more of the total amount of the oxidized carbon. Here, the "hydrophilic portion" of carbon has the following meaning. That is, 0.1 g of 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 at pH 11 without precipitating is the “hydrophilic portion”. The content of the hydrophilic portion with respect to the entire 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 solid after drying from the weight of the first carbon of 0.1 g is the weight of the "hydrophilic portion" dispersed in the aqueous ammonia solution at pH 11. The weight ratio of the weight of the "hydrophilic portion" to the weight of the first carbon of 0.1 g is the content of the "hydrophilic portion" in the carbon.

The proportion of hydrophilic portions in conductive carbon such as carbon black, natural graphite, and carbon nanotubes used as conductive agents in the electrodes of conventional power storage devices is 5% by mass or less of the total. However, when the carbon raw material is oxidized, it is oxidized from the surface of the carbon particles, a hydroxy group, a carboxy group or an ether bond is introduced into the carbon, and the conjugated double bond of the carbon is oxidized to form a carbon single bond. , The carbon-carbon bond is partially broken, and a hydrophilic part 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 the hydrophilic portion occupies 10% by mass or more of the total carbon. Then, such an oxidation-treated carbon is preferable because it is integrally compressed when it receives pressure and easily spreads like a paste and is easily densified.

The conductive carbon mixture of the present invention is used in the form of being mixed with an electrode active material for the production of electrodes of a power storage device. In the process of mixing the conductive carbon mixture of the present invention and the electrode active material to obtain an electrode material, gelatinization of the oxidized carbon progresses and the surface of the electrode active material is also coated. Further, in the process of forming an active material layer on the current collector using this electrode material and applying pressure to the active material layer to manufacture an electrode, the pressure further promotes gelatinization of the oxidized carbon. As the surface coating of the electrode active material further progresses, the conductive carbon mixture becomes densified. The conductive carbon mixture of the present invention having a DBP oil absorption amount in the range of 70% or less, preferably 40 to 70%, particularly preferably 40 to 65% of the DBP oil absorption amount of the other conductive carbon described above is an electrode material and an electrode. In the process of manufacturing the electrode active material, the surface of the electrode active material is densified while being particularly well covered, so that the cycle life of the power storage device provided with the obtained electrode is extended. Therefore, the present invention is also an electrode for a power storage device, which has an active material layer containing the electrode active material and the conductive carbon mixture of the present invention, and the oxidation-treated carbon covers the surface of the electrode active material. The present invention relates to an electrode characterized by the above, and further relates to a power storage device provided with the electrode.

In the active material layer of the electrode, the ratio of the electrode active material to the conductive carbon mixture is not strictly limited, but the conductive carbon mixture covers the surface of the electrode active material particularly well and conducts to the active material layer. The amount of the electrode active material in the active material layer can be increased because the property is imparted and the material is densified. Increasing the amount of electrode active material leads to an improvement in the energy density of the power storage device. The ratio of the electrode active material to the conductive carbon mixture is preferably in the range of 95: 5 to 99.5: 0.5 and in the range of 97: 3 to 99.5: 0.5 in terms of mass ratio. Is particularly preferable. If the proportion of the conductive carbon mixture is less than the above range, the conductivity of the active material layer is insufficient, and the coverage of the active material by the conductive carbon mixture tends to decrease, resulting in a decrease in cycle characteristics.

DBP oil absorption in a conductive carbon mixture containing conductive oxidation-treated carbon and conductive carbon different from the oxidation-treated carbon, and the oxidation-treated carbon covers the surface of the other conductive carbon. The conductive carbon mixture of the present invention, which has a DBP oil absorption of 70% or less of the DBP oil absorption of the other conductive carbon, densifies the surface of the electrode active material while particularly well covering the surface of the electrode material and the electrode in the process of manufacturing the electrode. Therefore, the cycle life of the power storage device provided with the obtained electrodes is extended.

(1) Conductive Carbon Mixture The conductive carbon mixture for producing the electrode of the power storage device of the present invention contains an oxidation-treated carbon having conductivity and a conductive carbon different from the oxidation-treated carbon. The oxidation-treated carbon coats the surface of the other conductive carbon. Preferably, at least a part of the oxidized carbon is paste-like. The DBP oil absorption amount of this conductive carbon mixture is 70% or less, preferably 40 to 70%, particularly preferably 40 to 65% of the DBP oil absorption amount of the other conductive carbon.

Oxidized carbon, which at least partly changes into a paste in the process of mixing with the other conductive carbon, can be obtained by subjecting the conductive carbon raw material to a relatively strong oxidation treatment. The carbon raw material used is not particularly limited, but from the viewpoint of easiness of oxidation, carbon having voids such as porous carbon powder, Ketjen black, furnace black having voids, carbon nanofibers and carbon nanotubes can be used. It is preferable, and carbon having voids having a specific surface area of 300 m ^{2 / g or more measured by the BET method is preferable.} Of these, spherical particles such as Ketjen black and furnace black having voids are 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 oxidized 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 subjected to an oxidation treatment, it is oxidized from the surface of the carbon particles, a hydroxy group, a carboxy 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. The oxidized carbon having such a hydrophilic portion easily adheres to the surface of the other conductive carbon, and effectively suppresses the aggregation of the other conductive carbon. Then, as the strength of the oxidation treatment is increased, the proportion of the hydrophilic portion in the carbon particles increases, and at least a part of the oxidation-treated carbon that changes into a paste in the process of mixing with the other conductive carbon can be obtained. .. 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. It is particularly preferable that the content of the hydrophilic portion is 12% by mass or more and 30% by mass or less of the whole.

Oxidized carbon containing 10% by mass or more of the total hydrophilic part is
(A) A step of treating a carbon raw material having voids with an acid,
(B) Step of mixing the product after acid treatment with the transition metal compound,
(C) A step of crushing the obtained mixture to cause a mechanochemical reaction.
(D) A step of heating the product after the mechanochemical reaction in a non-oxidizing atmosphere, and
(E) It can be preferably obtained by a production method including a step of removing the transition metal compound and / or its reaction product from the product after heating.

In the step (a), a carbon raw material having voids, preferably Ketjen black, 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 immersion 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 step (b).

Examples of the transition metal compound added to the carbon raw material in the step (b) include 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 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. Oxidized carbon is used by being mixed with the electrode active material in the manufacture of electrodes for power storage devices. Therefore, when a compound of an element constituting the electrode active material is added to the carbon raw material, it becomes an impurity with respect to the electrode active material. It is preferable because it can prevent the mixing of possible elements.

In the step (c), the mixture obtained in the step (b) is crushed to cause a mechanochemical reaction. 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 in this step. Examples of crushers for this reaction include raikai machines, millstone grinders, ball mills, bead mills, rod mills, roller mills, stirring mills, planetary mills, vibration mills, hybridizers, mechanochemical compounding devices and jet mills. be able to. 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 (d) is performed in a non-oxidizing atmosphere such as a nitrogen atmosphere or an argon atmosphere. The heating temperature and heating time are appropriately selected according to the transition metal compound used. In the subsequent step (e), the transition metal compound and / or its reaction product is removed from the heated product by means such as dissolution with an acid, and then thoroughly washed and dried. Through these steps, it is possible to obtain an oxidized carbon containing a hydrophilic portion of 10% by mass or more, preferably 12% by mass or more and 30% by mass or less of the whole.

The conductive carbon mixture of the present invention can be obtained by dry-mixing the obtained oxidation-treated carbon and a conductive carbon different from the oxidation-treated carbon.

As another conductive carbon mixed with the oxidation-treated carbon, the conductive carbon used for the electrode of the conventional power storage device can be used without particular limitation, and examples thereof include Ketjen Black. Carbon black such as acetylene black, channel black, furnace black, thermal black, fullerene, carbon nanotubes, carbon nanofibers, amorphous carbon, carbon fiber, natural graphite, artificial graphite, graphitized Ketjen black, mesoporous carbon, vapor phase method Carbon fiber can be mentioned. These may be used alone or in combination of two or more. It is preferable to use conductive carbon having higher conductivity than the oxidized carbon which is at least partially paste-like, and it is particularly preferable to use acetylene black.

The ratio of the oxidized carbon to the other conductive carbon is preferably in the range of 3: 1 to 1: 3, preferably in the range of 2.5: 1.5 to 1.5: 2.5 in terms of mass ratio. More preferred. For dry mixing, raikai, millstone grinders, 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 dry mixing time varies depending on the total amount of the oxidized carbon and the other conductive carbon to be mixed and the mixing device used, but is generally between 10 minutes and 1 hour.

In the process of dry mixing, at least a part of the oxidized carbon is changed into a paste to coat the surface of the other conductive carbon, so that the aggregation of the other conductive carbon can be suppressed. Then, when the DBP oil absorption amount of the conductive carbon mixture after the dry mixing is measured, the higher the mixing strength in the dry mixing, in other words, at least a part of the surface of the other conductive carbon made of paste-like oxidized carbon. As the coating progresses, the amount of DBP oil absorbed decreases. The DBP oil absorption of the conductive carbon mixture of the present invention is 70% or less, preferably 40 to 70%, particularly preferably 40 to 65% of the DBP oil absorption of the other conductive carbon. The dry mixing conditions for adjustment can be determined by a simple preliminary experiment. In the process of manufacturing the electrode material and the electrode shown below, the conductive carbon mixture of the present invention is densified while covering the surface of the electrode active material particularly well. Life is extended. When the dry mixing strength of the oxidized carbon and the other conductive carbon is increased until the DBP oil absorption of the conductive carbon mixture is less than 40% of the DBP oil absorption of the other conductive carbon, the conductive carbon mixture is mixed. Although the cycle life of the power storage device is longer than when an insufficient dry mixing strength is adopted such that the DBP oil absorption amount exceeds 70% of the DBP oil absorption amount of another conductive carbon, the DBP of the conductive carbon mixture is extended. Compared with the case where a suitable dry mixing strength in which the oil absorption amount is in the range of 40 to 70% of the DBP oil absorption amount of another conductive carbon is adopted, the cycle life of the power storage device tends to be shortened. At present, the reason is not clear.

(2) Electrodes The conductive carbon mixture of the present invention is used for the production of electrodes for power storage devices such as secondary batteries, electric double layer capacitors, redox capacitors and hybrid capacitors. It is used in the form of being mixed with an electrode active material that develops a capacitance by a Faraday reaction involving transfer or a non-Faraday reaction without transfer of electrons.

As the electrode active material used in combination with the conductive carbon mixture of the present invention, the active material used as the positive electrode active material or the negative electrode active material in the conventional power storage device can be used without particular limitation. These active materials may be a single compound or a mixture of two or more kinds of compounds.

Examples of the positive electrode active material of the secondary battery include, first, 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 Examples include _{Ni 1/2} O _4. In addition, sulfur and _{sulfides such as Li 2} S, 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 In addition to 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 include composite oxides such as _3.

Examples of the negative electrode active material of the secondary battery 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 polarization electrode of the electric double layer capacitor include carbon materials such as activated carbon having a large specific surface area, carbon nanofibers, carbon nanotubes, phenol 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 polarizing material such as activated carbon.

The particle shape and particle size of the electrode active material are not limited, but the average particle size of the active material is preferably larger than 2 μm and 25 μm or less. This active material having a relatively large average particle size improves the electrode density by itself, and in the process of manufacturing the electrode material and the electrode, the pressing force causes at least a part of the conductive carbon mixture to be present. Promotes paste-like and densification of paste-like oxidation-treated carbon. Further, the active material is composed of 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 poles as the fine particles. It may be configured. It is said that particles with a small particle size tend to aggregate, but at least a part of the conductive carbon mixture has paste-like oxidation-treated carbon adhering not only to the surface of coarse particles but also to the surface of fine particles on the surface. Therefore, the aggregation of the active material can be suppressed, and the mixed state of the active material and the conductive carbon mixture can be made uniform.

The mass ratio of the electrode active material to be mixed and the conductive carbon mixture is not particularly limited, but in order to obtain a power storage device having a high energy density, the mass ratio is 90: 10 to 99.5: 0.5. It is preferably in the range of. The conductive carbon mixture of the present invention having a DBP oil absorption amount in the range of 70% or less, preferably 40 to 70%, particularly preferably 40 to 65% of the DBP oil absorption amount of the other conductive carbon described above is an electrode material and an electrode. In the process of manufacturing, the surface of the electrode active material is densified while covering it particularly well, so that the amount of the electrode active material can be further increased, and the ratio of the electrode active material to the conductive carbon mixture is 95 in terms of mass ratio. It is preferably in the range of: 5 to 99.5: 0.5, and particularly preferably in the range of 97: 3 to 99.5: 0.5. If the proportion of the conductive carbon mixture is less than the above range, the conductivity of the active material layer is insufficient, and the coverage of the active material by the conductive carbon mixture tends to decrease, resulting in a decrease in cycle life.

By mixing the conductive carbon mixture of the present invention and the electrode active material together with a binder and a solvent, an electrode material in the form of a slurry used for producing an electrode can be obtained.

As the binder, known binders such as polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinyl fluoride, and carboxymethyl cellulose are used. The binder content is preferably 1 to 30% by mass with respect to the total amount of the electrode 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. As the solvent, a solvent that does not adversely affect other components in the electrode material such as N-methylpyrrolidone, dimethylformamide, tetrahydrofuran, isopropyl alcohol, and water can be used without particular limitation. The binder can be used in the form of being dissolved in a solvent. The amount of the solvent used is not particularly limited as long as it does not interfere with the formation of the active material layer of the electrode shown below.

The electrode material in the form of a slurry can be produced by a method in which the conductive carbon mixture of the present invention and the electrode active material are dry-mixed, and then the obtained mixture is mixed with a binder and a solvent. In the process of dry mixing of the conductive carbon mixture and the electrode active material, at least a part of the conductive carbon mixture is paste-like, and the oxidized carbon further spreads like a paste to cover the surface of the electrode active material. For dry mixing, raikai, millstone grinders, 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 dry mixing time varies depending on the total amount of the conductive carbon mixture and the electrode active material to be mixed and the mixing device used, but is generally between 10 minutes and 1 hour. The mixing method in the subsequent wet mixing with the binder and the solvent is not particularly limited, and may be performed by hand mixing using a mortar, or may be performed using a known mixing device such as a stirrer or a homogenizer. The time of wet mixing also varies depending on the amount of material to be mixed and the mixing device used, but is generally between 10 minutes and 1 hour.

Further, since the conductive carbon mixture of the present invention is compatible with the binder and the solvent, a method of wet-mixing the conductive carbon mixture, the electrode active material, the binder and the solvent may be adopted instead of the above method. Alternatively, a method may be adopted in which the conductive carbon mixture, the binder and the solvent are wet-mixed, and then the electrode active material is added and wet-mixed, or the conductive carbon mixture, the electrode active material and the solvent are wet-mixed. A method of mixing and then adding a binder and wet mixing may be adopted. Also in these wet mixing, the mixing method is not particularly limited, and the mixing time is appropriately selected according to the mixing device and the mixing amount. It is said that the fine carbon particles are difficult to be compatible with the binder and the solvent, but by using the conductive carbon mixture, it is possible to easily obtain an electrode material in which each component is uniformly mixed regardless of the mixing method.

Next, an electrode material in the form of a slurry is applied onto a current collector for forming a positive electrode or a negative electrode of a power storage device to form an active material layer, and if necessary, the active material layer is dried and then the active material. An electrode is obtained by applying pressure to the layer by rolling treatment. The obtained electrode material may be formed into a predetermined shape, crimped onto a current collector, and then rolled.

As the current collector for the electrodes of the power storage device, 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. The active material layer may be dried by reducing the pressure and heating as necessary to remove the solvent. The pressure applied to the active material layer by the rolling process is generally in the range of ^{50,000 to 1,000,000 N / cm 2} , preferably 100,000 to 500,000 N / cm ^2. Further, the temperature of the rolling process is not particularly limited, and the process may be performed at room temperature or under heating conditions.

When pressure is applied to the active material layer on the current collector, at least a part of the conductive carbon mixture is paste-like, and the oxidized carbon further spreads like a paste, covering the surface of the active material particles and becoming dense. The active material particles approach each other, and the oxidized carbon that has changed into a paste form covers the surface of the active material particles and is formed between the adjacent active material particles as well as the active material particles. The inside of the hole existing on the surface of the above is also extruded together with the above-mentioned other conductive carbon and is densely filled. Therefore, the amount of active material per unit volume of the electrode increases, and the electrode density increases. Further, the densely packed conductive carbon mixture has sufficient conductivity to function as a conductive agent and suppresses the dissolution of the electrode active material in the electrolytic solution.

(3) Storage device The electrode of the present invention is used for an electrode of a power storage device such as a secondary battery, an electric double layer capacitor, a redox capacitor and a hybrid capacitor. 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 is the electrode of the present invention.

The electrolyte arranged between the positive electrode and the negative electrode in the power storage device may be an electrolyte solution held in the separator, a solid electrolyte, or a gel-like electrolyte, and is a conventional power storage device. The electrolyte used in the above can be used without particular limitation. A typical electrolyte is illustrated below. 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 etc.} , 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.

However, when a solid electrolyte or a gel-like electrolyte is used as the electrolyte between the positive electrode and the negative electrode, each of the above-described configurations is described in the electrode material preparation step for the purpose of ensuring an ion conduction path in the active material layer. Prepare by adding solid electrolyte to the elements.

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

Example 1
To 300 mL of 60% nitric acid, 10 g of Ketjen Black (trade name EC300J, manufactured by Ketjen Black International, BET specific surface area 800 m ² / g) was added, and the obtained liquid was irradiated with ultrasonic waves for 10 minutes and then filtered. Ketjen Black was recovered. The recovered Ketjen black was washed with water three times and dried to obtain an acid-treated Ketjen black. And acid treatment Ketjenblack _0.5g, and _{Fe (CH 3 COO) 2 1.98g} , and Li (CH 3 COO) _0.77g, and _{C 6 H 8 O 7 · H} 2 O1.10g, CH 3 1.32 g of COOH, 1.31 g of H ₃ PO ₄ and 120 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 pulverized at 20 hz for 10 minutes. The pulverized powder was heated in nitrogen at 700 ° C. for 3 minutes to obtain a composite in which _{LiFePO 4 was supported on Ketjen black.}

1 g of the obtained complex was added to 100 mL of a 30% hydrochloric acid aqueous solution, LiFePO ₄ in the complex was dissolved while irradiating the obtained solution with ultrasonic waves for 15 minutes, the remaining solid was 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 with water 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 had been 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 taken as the content of the "hydrophilic portion" in the oxidized carbon. bottom. The content of the hydrophilic moiety was 15.2% by mass.

The obtained oxidized carbon and acetylene black (DBP oil absorption: 207 mL / 100 g) were introduced into a vibrating ball mill device at a mass ratio of 1: 1 and dry-mixed at 10 hz for 20 minutes to obtain a conductive carbon mixture. rice field. The amount of DBP oil absorbed was measured for this mixture.

2 parts by mass of the obtained conductive carbon mixture, 2 parts by mass of vinylidene fluoride, an appropriate amount of N-methylslurrydone, and 96 parts by mass of commercially available LiNi _1/3 Mn _1/3 Co _1/3 O ₂ Particles (average particle size 5 μm) are wet-mixed to form a slurry, and the obtained slurry is applied onto an aluminum foil and dried, and then rolled to obtain a positive electrode for a lithium ion secondary battery. rice field. Further, 93 parts by mass of graphite, 1 part by mass of acetylene black, 6 parts by mass of polyvinylidene fluoride, and an appropriate amount of N-methylpyrrolidone were wet-mixed to form a slurry, and the obtained slurry was placed on a copper foil. After being applied to and dried, it was rolled to obtain a negative electrode for a lithium ion secondary battery. The capacity of the positive electrode and the capacity of the negative electrode were adjusted so that the capacity ratio was 1: 1.2. Using the positive electrode and the negative electrode, a lithium ion secondary battery was prepared using a solution obtained by adding 1% by mass of vinylene carbonate to a 1: 1 solution of ethylene carbonate / dimethyl carbonate of _{1M LiPF 6 as an electrolytic solution.} The obtained battery was repeatedly charged and discharged in the range of 4.2 to 3.0 V under the conditions of a charge / discharge rate of 25 ° C. and 1 C, and the capacity retention rate after 200 cycles of experience was determined.

Example 2
Example 1 was repeated except that the dry mixing condition by the vibrating ball mill device for obtaining the conductive carbon mixture in Example 1 was changed from the condition of 20 minutes at 10 hz to the condition of 10 minutes at 20 hz. ..

Example 3
Example 1 was repeated except that the dry mixing condition by the vibrating ball mill device for obtaining the conductive carbon mixture in Example 1 was changed from the condition of 20 minutes at 10 hz to the condition of 20 minutes at 20 hz. ..

Example 4
Example 1 was repeated except that the dry mixing condition by the vibrating ball mill device for obtaining the conductive carbon mixture in Example 1 was changed from the condition of 20 minutes at 10 hz to the condition of 30 minutes at 20 hz. ..

Example 5
Example 1 was repeated except that the dry mixing condition by the vibrating ball mill device for obtaining the conductive carbon mixture in Example 1 was changed from the condition of 20 minutes at 10 hz to the condition of 20 minutes at 30 hz. ..

Example 6
Example 1 was repeated except that the dry mixing condition by the vibrating ball mill device for obtaining the conductive carbon mixture in Example 1 was changed from the condition of 20 minutes at 10 hz to the condition of 30 minutes at 30 hz. ..

Comparative Example Except that the dry mixing condition by the vibrating ball mill device for obtaining the conductive carbon mixture in Example 1 was changed from the condition of 20 minutes at 10 hz to the condition of 10 minutes at 10 hz, Example 1 was used. Repeated.

Table 1 shows the DBP oil absorption amount of the conductive carbon mixture and the lithium ion secondary battery of Examples 1 to 6 and the comparative example, and the DBP oil absorption amount of the conductive carbon mixture with respect to the DBP oil absorption amount (207 mL / 100 g) of acetylene black. The ratio and the capacity retention rate after 200 cycles of experience are shown together.

As is clear from Table 1, a high capacity retention rate of the lithium ion secondary battery can be obtained by using the conductive carbon mixture of Examples 1 to 6 in which the DBP oil absorption amount is 70% or less of the DBP oil absorption amount of acetylene black. Therefore, a longer cycle life of the lithium ion secondary battery was achieved.

By using the conductive carbon mixture of the present invention, a power storage device having a good cycle life can be obtained.

Claims (6)

Oxidized carbon with conductivity and
Conductive carbon different from the oxidized carbon,
A conductive carbon mixture for the manufacture of electrodes for power storage devices, wherein the oxidized carbon comprises the surface of the other conductive carbon.
Dibutyl phthalate oil absorption amount per 100g of the conductive carbon mixture, Ri 70% der following dibutyl phthalate oil absorption amount per 100g of the another conductive carbon,
A conductive carbon mixture characterized in that at least a part of the oxidized carbon is paste-like. The conductive carbon mixture according to claim 1 , wherein the oxidized carbon contains a hydrophilic portion, and the content of the hydrophilic portion is 10% by mass or more of the total amount of the oxidized carbon. The conductivity according to claim 1 or 2 , wherein the dibutyl phthalate oil absorption per 100 g of the conductive carbon mixture is in the range of 40 to 70% of the dibutyl phthalate oil absorption per 100 g of the other conductive carbon. Sex carbon mixture. Electrodes for power storage devices
Electrode active material and
The conductive carbon mixture according to any one of claims 1 to 3 and
An electrode having an active material layer containing the above-mentioned electrode, wherein the oxidation-treated carbon covers the surface of the electrode active material. The electrode according to claim 4 , wherein the ratio of the electrode active material to the conductive carbon mixture is in the range of 97: 3 to 99.5: 0.5 in terms of mass ratio. A power storage device comprising the electrode according to claim 4 or 5.