KR20170005012A - Electrode, method for producing said electrode, electricity storage device provided with said electrode, and conductive carbon mixture for electricity storage device electrode - Google Patents

Abstract

An electrode for imparting a power storage device having a high energy density and a good cycle life is provided. An electrode for a power storage device of the present invention comprises an electrode active material particle and an active material layer containing a paste-like conductive carbon which is coated on the surface of the electrode active material particle and which is derived from oxidized carbon obtained by oxidizing a carbon raw material having a gap And an electrode. Since the paste-like conductive carbon derived from the oxidation-treated carbon is densely filled not only in the gap portion formed between the active material particles but also inside the hole existing on the surface of the active material particles, thereby increasing the electrode density, The density is improved. In addition, since the conductive carbon in the paste suppresses the dissolution of the active material, the cycle characteristics of the power storage device are improved.

Description

TECHNICAL FIELD [0001] The present invention relates to an electrode, a manufacturing method of the electrode, a storage device having the electrode, and a conductive carbon mixture for a storage device electrode. BACKGROUND OF THE INVENTION 1. Field of the Invention }

The present invention relates to an electrode providing a power storage device having a high energy density and a good cycle life. The present invention also relates to a manufacturing method of the electrode, and a power storage device having the electrode. The present invention also relates to a conductive carbon mixture used in the production of an electrode of a power storage device.

2. Description of the Related Art Power storage devices such as secondary batteries, electric double layer capacitors, redox capacitors, and hybrid capacitors are widely used in power sources for information devices such as cellular phones and notebook computers, motor drive power sources for energy saving vehicles such as electric vehicles and hybrid cars, However, improvement of energy density and cycle life is demanded in order to meet demands for high performance and miniaturization in these power storage devices.

In these storage devices, an electrode active material exhibiting a capacity by a Faraday reaction involving the transfer of electrons to an electrolyte in an electrolyte (including an electrolytic solution) or a non-Faraday reaction involving the transfer of electrons is used for energy storage . 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, or carbon nanotube is usually used. These conductive carbon are used in combination with an active material having a low conductivity to impart conductivity to the composite material. In addition to this, the active material also functions as a matrix for absorbing a change in volume due to the reaction of the active material, It also plays a role of securing a conduction path.

However, the composite material of the active material and the conductive carbon is generally produced by a method of mixing the particles of the active material with the conductive carbon. Since the 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, it is necessary to reduce the amount of conductive carbon per unit volume to increase the amount of active material. Thus, studies have been made to increase the amount of active material per unit volume by approaching the distance between the active material particles by improving the dispersibility of the conductive carbon, or by lowering the structure of the conductive carbon.

For example, Patent Document 1 (Japanese Unexamined Patent Publication (Kokai) No. 2004-134304) discloses a carbon material having an average primary particle diameter of 10 to 100 nm and a small particle diameter (acetylene black in the embodiment) A non-aqueous secondary battery having a positive electrode having a positive electrode active material. The coating material used for preparing the positive electrode may be prepared by dispersing a mixture of the positive electrode active material, the carbon material, the binder and the solvent in a high-speed rotating homogenizer type disperser, a planetary mixer having three or more rotating shafts, A dispersion obtained by dispersing a mixture of the carbon material, the binder and the solvent in a strong shear dispersing device is added to a paste in which a mixture of a positive electrode active material, a binder and a solvent is dispersed, and further dispersed. By using a device having a strong shear force, the carbon material which is difficult to disperse is uniformly dispersed because the particle diameter is small.

In Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2009-35598), a non-aqueous secondary battery comprising a acetylene black having a BET specific surface area of 30 to 90 m 2 / g, a DBP absorption of 50 to 120 mL / A conductive agent for an electrode is disclosed. The mixture of acetylene black and the active material is dispersed in a liquid containing a binder to prepare a slurry, and the slurry is applied to a current collector and dried to form an electrode of the secondary battery. Since the acetylene black having the above characteristics has a lower structure than that of Ketjenblack or conventional acetylene black, the bulk density of the mixture with the active material is improved and the capacity of the battery is improved.

It has also been investigated that the active material and the conductive carbon are uniformly distributed by covering a part or all of the surface of the active material particle with the conductive carbon particles to improve the conductivity between the active materials to prevent the cycle life from being lowered. For example, Patent Document 3 (Japanese Patent Application Laid-Open No. 11-283623) discloses a method of forming a lithium composite oxide base particle such as LiCoO ₂ serving as an active material and a mother particle of a carbon material such as acetylene black A method of coating a part or all of the surface of the mother particle of the composite oxide with the daughter particle of the carbon material by mixing with compression and shear action and a method of using the composite material obtained by this method for the positive electrode of the non- .

Japanese Patent Application Laid-Open No. 2004-134304 Japanese Patent Application Laid-Open No. 2009-35598 Japanese Patent Application Laid-Open No. 11-283623

As a result of investigations made by the inventors of the present invention, it is difficult to efficiently introduce conductive carbon into the active material particles even in the method as in Patent Document 1 or Patent Document 2, It has been difficult to increase the amount of active material per unit volume by approaching the distance. For this reason, there has been a limit in improving the energy density by the positive electrode and / or the negative electrode using the composite material of the active material particles and the conductive carbon. Also, by the method of coating the surface of the active material particles such as Patent Document 3 with carbon particles, there is a limit to the improvement of the energy density and it is also possible to satisfactorily satisfy the cause of the dissolution of the active material in the electrolyte of the non-aqueous secondary battery The cycle life was not obtained.

Therefore, an object of the present invention is to provide an electrode which gives a power storage device having a high energy density and a good cycle life.

As a result of intensive investigations, the present inventors have found that the above object can be achieved by forming an electrode of an electric storage device using an electrode material containing oxidized carbon obtained by subjecting a carbon raw material having voids to oxidation treatment and active material particles Thereby completing the invention.

Therefore, the present invention relates to an electrode for an electric storage device, comprising: electrode active material particles; paste-like particles derived from oxidation-treated carbon obtained by oxidizing a carbon raw material having a void covering the surfaces of the electrode active material particles; ) ≪ / RTI > of conductive carbon. In addition to the voids of the porous carbon powder, the voids include voids in the inner openings of the Ketjen black, voids in the tubes of the carbon nanofibers and the carbon nanotubes, and vacancies between the tubes. The term " paste phase " means a state in which the grain boundary of the carbon primary particles is not confirmed in the SEM photograph taken at a magnification of 25000 times, and the non-particulate irregular carbon is connected.

Oxidation-treated carbon obtained by subjecting a carbon raw material having a void to an oxidation treatment tends to adhere to the surface of the active material particle. Further, the oxidation-treated carbon subjected to the strong oxidizing treatment is characterized in that, when it is subjected to pressure, it is integrally compressed and spreads in the form of a paste and is hardly scattered. Therefore, when the electrode material is obtained by mixing the active material particles with the oxidation-treated carbon subjected to the strong oxidation treatment for the electrodes of the power storage device, the oxidation-treated carbon is adhered to the surface of the active material particles in the course of mixing, Improves acidity. Further, at least a part of the oxidized carbon is spread in the paste by the pressure applied to the oxidized carbon in the course of the mixing so that the surface of the active particle is partially covered. When the active material layer is formed on the collector of the electrode using the electrode material and the pressure is applied to the active material layer, the oxidation-treated carbon in which at least a part is changed into a paste spreads further to cover the surface of the active material particles, As the particles approach each other and the oxidation-treated carbon changed to paste in accordance therewith covers the surface of the active material particles, not only the gap portion formed between the adjacent active material particles but also the holes existing on the surface of the active material particles (Including the gap between the primary particles, which is confirmed in Fig. 2) (see Fig. 2). Therefore, the active material amount per unit volume of the electrode increases, and the electrode density increases. Moreover, the densely packed paste-like oxidation-treated carbon has sufficient conductivity to function as a conductive agent. In addition, the electrode of the present invention may include oxidized carbon which is not changed into a paste.

In a preferred form of the electrode of the present invention, the paste-like conductive carbon derived from the oxidation-treated carbon is present on the surface of the gap portion and / or the electrode active material particle formed between adjacent electrode active material particles with a width of 50 nm or less It also exists inside the hole. Therefore, the coverage of the surface of the active material particles by the conductive carbon on the paste is improved, the conductivity of the entire active material layer is improved, and the electrode density is improved. The " width of the gap portion formed between the electrode active material particles " means the shortest distance between the adjacent active material particles, and " the width of the hole existing on the surface of the electrode active material particles "Quot; is the shortest distance among the distances.

It can be seen that the impregnation of the electrolyte solution into the electrode of the electrical storage device is not inhibited despite the active material layer containing paste-like conductive carbon in which the electrode of the present invention is densely packed. In a preferred form of the electrode of the present invention, when the pore distribution of the active material layer of the electrode is measured by the mercury infusion method, it can be seen that the active material layer has pores having a diameter of 5 to 40 nm. These minute pores are considered to be pores in paste-like conductive carbon mainly derived from oxidation-treated carbon, but are sufficiently large that the electrolyte solution in the electric storage device passes through the conductive carbon in paste to reach the active material particles. Therefore, the paste-like conductive carbon in the electrode has sufficient conductivity and does not inhibit impregnation of the electrolytic solution in the electrical storage device. As a result, the energy density of the power storage device is improved.

It is also believed that the active material layer of the electrode of the present invention is coated with conductive carbon which is densely dispersed in paste form until the inside of the hole existing on the surface of the active material particle is covered with the active material particle. It can be seen that the dissolution of the active material in the electrolyte is suppressed and the cycle characteristics of the power storage device are improved even though the impregnation of the electrolyte solution into the electrodes of the power storage device is not suppressed.

It is preferable that the oxidation-treated carbon providing the conductive carbon on the paste contains a hydrophilic part and the content of the hydrophilic part is 10 mass% or more of the whole oxidized carbon. Here, the " hydrophilic part " 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 subjected to ultrasonic irradiation for 1 minute, and the resulting solution is allowed to stand for 5 hours to precipitate the solid portion. The portion which is not precipitated and dispersed in the aqueous ammonia solution of pH 11 is the " hydrophilic portion ". The content of the hydrophilic part in the whole carbon is determined by the following method. After the precipitation of the solid part, the supernatant is removed and the remainder is dried, and the weight of the solid after drying is measured. Quot; hydrophilic part " in which the weight of the solid after drying is subtracted from the weight of the initial carbon of 0.1 g and is dispersed in an aqueous ammonia solution of pH 11. The weight ratio of the "hydrophilic part" to the initial carbon weight of 0.1 g is the content of the "hydrophilic part" in the carbon.

The proportion of the hydrophilic part in the conductive carbon such as carbon black, natural graphite, and carbon nanotubes used as the conductive agent in the electrode of the conventional power storage device is 5 mass% or less of the total. However, when carbon having a void is used as a raw material and these raw materials are subjected to an oxidation treatment, a hydroxy group, a carboxyl group and an ether bond are introduced to the carbon through oxidation from the surface of the particle, and the conjugated double bond of carbon is oxidized, And the carbon-carbon bond is partially cut off to form a hydrophilic part on the particle surface. When the strength of the oxidation treatment is increased, the proportion of the hydrophilic part in the carbon particles increases, and the hydrophilic part occupies 10% by mass or more of the whole carbon. When subjected to pressure, such oxidation-treated carbon is easily compressed and dispersed in paste, so that most or all of the surface of the active material particles is covered and densified to the inside of the hole existing on the surface of the active material particles . As a result, 80% or more, preferably 90% or more, particularly preferably 95% or more of the surface (outer surface) of the active material particles in the active material layer of the electrode is brought into contact with the densified paste- Is obtained. The covering ratio of the surface of the active material particles with the conductive carbon on the paste is a value calculated from an SEM photograph taken at a magnification of 25000 times the cross section of the active material layer.

In the electrode for power storage device of the present invention, the electrode active material particles in the active material layer are composed of fine particles having an average particle diameter of 0.01 to 2 탆 which can operate as a positive electrode active material or a negative electrode active material, Mu] m and an average particle diameter of not more than 25 mu m. The coarse particles have the function of improving the electrode density by itself and also functioning to rapidly oxidize the oxidized carbon to a paste form during the production of the electrode material and the electrode preferably by pressing the oxidized carbon, Thereby increasing the energy density of the power storage device. Further, by the pressure applied to the active material layer at the time of manufacturing the electrode, the fine particles are oxidized with the oxidized carbon spreading in the paste while pressing the oxidized carbon at least partially pasted, and the gap portion formed between the adjacent coarse particles The electrode density is further increased and the energy density of the power storage device is further improved. The average particle size of the active material particles means a 50% diameter (median diameter) in the measurement of the particle size distribution using the light scattering particle size meter.

In the electrode for an electric storage device of the present invention, it is preferable that the active material layer further contains conductive carbon having higher conductivity than paste conductive carbon derived from other conductive carbon, particularly oxidized carbon. The carbon is coated on the conductive carbon in the form of a paste by the pressure applied to the active material layer at the time of manufacturing the electrode and is filled tightly in the gap portion formed by the adjacent active material particles together with the conductive carbon in the paste to improve the conductivity of the active material layer The energy density of the power storage device is further improved.

In the electrode for power storage device of the present invention, the mass ratio of the electrode active material particles to the conductive carbon in the active material layer is preferably in the range of 95: 5 to 99: 1. When other conductive carbon is contained in addition to the paste-like conductive carbon derived from oxidized carbon, the total amount thereof and the mass ratio of the electrode active material particles are within the above-mentioned range. When the ratio 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 is lowered and the cycle characteristic is lowered. When the ratio of the conductive carbon is larger than the above range, The density is lowered and the energy density of the electrical storage device tends to decrease.

As described above, in the electrode for electric storage device of the present invention,

At least a part of the oxidation-treated carbon is changed into a paste by mixing the carbon raw material having the electrode active material particles and the gap with the oxidized carbon subjected to the oxidation treatment to prepare an electrode material adhered to the surface of the electrode active material particle , And

A step of forming an active material layer on the current collector by the electrode material, applying a pressure to the active material layer,

And the like. Therefore, the present invention also relates to a method for producing the electrode.

When the active material layer contains conductive carbon having higher conductivity than paste conductive carbon derived from other conductive carbon, particularly oxidized carbon,

At least a part of the oxidation-treated carbon is changed into a paste by dry-mixing the oxidation-treated carbon and the other conductive carbon to obtain a conductive carbon mixture attached to the surface of the other conductive carbon; and

Adhering the oxidized carbon that has been at least partially changed into a paste to the surface of the electrode active material particles by dry mixing or wet mixing the conductive carbon mixture and the electrode active material particles

And the like.

Since fine carbon particles are poorly familiar with binders and solvents, when preparing a slurry-type electrode material containing a binder and a solvent, as described above in Patent Document 1 and Patent Document 2, Or dry mixing of electrode active material particles and carbon, followed by wet mixing by adding a binder and a solvent. However, regardless of the mixing method of the mixture and the electrode active material particles, the conductive carbon mixture has a high electrode density Further, an electrode having excellent conductivity is provided. Therefore, the present invention also relates to a conductive carbon mixture for the production of an electrode of a power storage device, which comprises at least a conductive carbon which is at least partially in paste form and which is derived from an oxidized carbon obtained by oxidizing a carbon raw material having a gap, Wherein at least a part of the electrically conductive carbon is pasted on the surface of the other electrically conductive carbon.

The electrode of the present invention provides a power storage device having a high energy density and a good cycle life. Accordingly, the present invention also relates to a battery device having the electrode.

(Effects of the Invention)

In an electrode of the present invention having electrode active material particles and an active material layer containing a paste-like conductive carbon derived from oxidation-treated carbon obtained by oxidizing a carbon raw material having a void covering the surface of the electrode active material particle, Since the paste-like conductive carbon derived from the oxidation-treated carbon is densely filled not only in the gap portion formed between the active material particles but also inside the hole existing on the surface of the active material particles, the amount of active material per unit volume And electrode density increases. Furthermore, the densely packed conductive carbon in the paste has sufficient conductivity to function as a conductive agent, and does not inhibit impregnation of the electrolytic solution in the electrical storage device. As a result, the energy density of the power storage device is improved. It is also believed that the conductive carbon in the paste covers the surface of the active material particles to the inside of the hole existing on the surface of the active material particles in the electrode of the present invention. The dissolution of the active material in the electrolyte solution in the electrical storage device is suppressed, and the cycle characteristics of the electrical storage device are improved.

1 is a graph showing the relationship between the content of the hydrophilic part of the oxidized carbon and the electrode density for the electrodes of the examples and comparative examples.
2 is a SEM photograph of the cross section of the electrode in the embodiment, wherein (A) is a photograph of 1500 times and (B) is a photograph of 25000 times.
3 is an SEM photograph of the cross section of the electrode of the comparative example, wherein (A) is a photograph of 1500 times and (B) is a photograph of 25000 times.
Fig. 4 is a diagram showing the result of measuring the pore distribution by the mercury porosimetry method for the electrodes shown in Figs. 2 and 3. Fig.
5 is a graph showing the rate characteristics of a lithium ion secondary battery having electrodes according to the embodiment or the comparative example.
FIG. 6 is a graph showing the cycle characteristics of the lithium ion secondary battery showing the rate characteristics in FIG.
7 is a graph showing the rate characteristics of a lithium ion secondary battery having electrodes according to the embodiment or the comparative example.
8 is a graph showing the cycle characteristics of the lithium ion secondary battery showing the rate characteristic in FIG.
9 is a graph showing the rate characteristics of a lithium ion secondary battery having electrodes according to the embodiment or the comparative example.
10 is a graph showing the cycle characteristics of the lithium ion secondary battery showing the rate characteristics in FIG.
11 is a SEM photograph of 50000 times of a mixture obtained by dry mixing of oxidized carbon, acetylene black and particles of an active material.
12 is a graph showing the rate characteristics of a lithium ion secondary battery having electrodes according to Examples or Comparative Examples.
13 is a graph showing the cycle characteristics of the lithium ion secondary battery showing the rate characteristics in Fig.
14 is a SEM photograph of 50000 times of a mixture obtained by dry mixing of oxidized carbon or acetylene black and microparticles of an active material.
15 is a SEM photograph of a mixture obtained by dry mixing of oxidized carbon or acetylene black and coarse particles of the active material at 100,000 times.
16 is a SEM photograph of a 50000 times of the conductive carbon mixture.
17 is a TEM photograph of the conductive carbon mixture, (A) is a photograph of 100000 times, and (B) is a photograph of 500000 times.
18 is a SEM photograph of 25000 times of the cross section of an electrode prepared using the conductive carbon mixture.
19 is a graph showing the results of measurement of direct current internal resistance of a lithium ion secondary battery using electrodes of the example or comparative example.

An electrode for a power storage device of the present invention comprises an electrode active material particle and an active material layer containing a paste-like conductive carbon which is coated on the surface of the electrode active material particle and which is derived from oxidized carbon obtained by oxidizing a carbon raw material having a gap . First, the oxidation-treated carbon before being changed into a paste is described, and then the electrode of the present invention and the electrical storage device using the electrode will be described.

(1) Oxidation-treated carbon

In the electrode of the present invention, the oxidized carbon which imparts the paste-like conductive carbon contained in the active material layer may be porous carbon powder, ketjen black, furnace black having voids, carbon nanofiber, and carbon having voids such as carbon nanotubes It is manufactured as raw material. Carbon having a specific surface area of 300 m < 2 > / g or more as measured by the BET method is preferably used because it is likely to be oxidized carbon which is converted into a paste form by oxidation treatment. Particularly, spherical particles such as Ketjen black or furnace black having a void are particularly preferable. It is difficult to obtain an oxidation-treated carbon which is converted into a paste even if oxidation treatment is carried out using solid carbon as a raw material.

For oxidation treatment of the carbon raw material having voids, a known oxidation method can be used without particular limitation. For example, an oxidized carbon can be obtained by treating the carbon raw material in an acid or a hydrogen peroxide solution. As the acid, nitric acid, sulfuric acid mixture, hypochlorous acid aqueous solution and the like can be used. Further, the carbon raw material can be heated in an oxygen-containing atmosphere, steam, or carbon dioxide to obtain an oxidized carbon. Further, the oxidized carbon can be obtained by a plasma treatment, an ultraviolet ray irradiation, a corona discharge treatment, and a glow discharge treatment in an oxygen-containing atmosphere of a carbon raw material.

When a carbon raw material having a void is subjected to an oxidation treatment, it is oxidized from the surface of the particles to introduce a hydroxyl group, a carboxyl group or an ether bond into the carbon, oxidizes the conjugated double bond of the carbon to generate a carbon single bond, The bond is cleaved and a portion having hydrophilicity is generated on the particle surface. The oxidation-treated carbon having such a hydrophilic part easily adheres to the surface of the active material particles and effectively suppresses agglomeration of the active material particles. When the strength of the oxidation treatment is increased, the proportion of the hydrophilic part in the carbon particles is increased, and the oxidation-treated carbon in which the electrode is changed into the paste in the manufacturing process is obtained. The content of the hydrophilic part in the oxidation-treated carbon is preferably 10% by mass or more of the whole oxidized carbon. It is particularly preferable that the content of the hydrophilic part is 12 mass% or more and 30 mass% or less of the whole.

The oxidation-treated carbon containing 10% by mass or more of the total hydrophilic part as a whole,

(a) a step of treating the carbon raw material having voids with an acid,

(b) a step of mixing the acid-treated product with the transition metal compound,

(c) pulverizing the obtained mixture to generate a mechanochemical reaction,

(d) heating the product after the mechanochemical reaction in a non-oxidizing atmosphere, and

(e) a step of removing the transition metal compound and / or the reaction product from the heated product

, And the like.

In the step (a), a carbon raw material having a void, preferably Ketjenblack, is immersed in an acid and allowed to stand. Ultrasonic waves may be irradiated at the time of immersion. As the acid, an acid commonly used for oxidation of carbon such as nitric acid, sulfuric acid mixture, hypochlorous acid aqueous solution and the like 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. Carbon after the acid treatment is thoroughly washed with water and dried, and then mixed with the transition metal compound in the step (b).

Examples of the transition metal compound to be 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, methoxides, ethoxides, An organic metal salt such as a seed, or a mixture thereof. These compounds may be used alone or in combination of two or more. Compounds containing other transition metals may be mixed in a predetermined amount and used. 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 oxidized carbon is used in combination with the active material particles in the production of the electrode of the electrical storage device, the addition of the compound of the element constituting the active material to the carbon raw material can prevent the incorporation of an element that can become an impurity in the active material Therefore, it is desirable.

In the step (c), the mixture obtained in the step (b) is pulverized to generate a mechanochemical reaction. Examples of the pulverizer for this reaction include, but are not limited to, Leica, a quartz grinder, a ball mill, a bead mill, a rod mill, a roller mill, a stirring mill, a planetary mill, a vibration mill, a hybridizer, have. The pulverization time depends on the amount of the pulverizer used and the amount of carbon to be treated, etc., and is not particularly limited, but is generally in the range of 5 minutes to 3 hours. (d) is performed in a non-oxidizing atmosphere such as a nitrogen atmosphere or an argon atmosphere. The heating temperature and the heating time are appropriately selected depending on the transition metal compound used. In the subsequent step (e), the transition metal compound and / or the reaction product thereof are removed from the product after heating by means such as dissolving in an acid, and the resultant is sufficiently washed and dried to obtain a solution containing 10% Oxidation-treated carbon can be obtained.

In this production method, in the step (c), the transition metal compound functions to accelerate the oxidation of the carbon raw material by the mechanochemical reaction, so that the oxidation of the carbon raw material proceeds rapidly. By this oxidation, an oxidized carbon containing 10% by mass or more of a hydrophilic part as a whole can be obtained.

Oxidation-treated carbon containing 10% by mass or more of a hydrophilic part as a whole is obtained by subjecting a carbon raw material having a void to a strong oxidation treatment, and it is also possible to promote the oxidation of the carbon raw material having a void by a method other than the above- .

The oxidation-treated carbon thus obtained is subjected to a Faraday reaction involving the transfer of electrons to ions in the electrolyte of the electrical storage device, or to the oxidation of electrons in the electrolyte of the electrical storage device, for the production of electrodes of electric storage devices such as secondary batteries, electric double layer capacitors, redox capacitors and hybrid capacitors. And is used in a form mixed with an electrode active material expressing capacity by a non-Faraday reaction which does not involve transferring.

(2)

In the electrode for a power storage device of the present invention,

(A) mixing an electrode active material particle and the oxidized carbon so that at least a part of the oxidized carbon is changed into a paste, thereby preparing an electrode material adhering to the surface of the electrode active material particle; and

(B) a step of forming an active material layer on the collector by the electrode material, and applying a pressure to the active material layer

And the like.

In the step (A), since the oxidation-treated carbon adheres to the surface of the active material particles and covers the surface, aggregation of the active material particles can be suppressed. Further, at least a part of the oxidized carbon is spread in the paste by the pressure applied to the oxidized carbon in the mixing process, so that the surface of the active particle is partially covered.

As the electrode active material used in the step (A), an active material used as a positive electrode active material or a negative electrode active material in a 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 compounds.

Examples of the positive electrode active material of the secondary battery include layered sodium salt LiMO ₂ , layered Li ₂ MnO ₃ -LiMO ₂ solid solution, and spinel LiM ₂ O _{4 wherein} M is Mn, Fe, Co, Ni, ). These specific examples of _{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 . Also, sulfur and _{Li 2 S, TiS 2, MoS} 2, FeS 2, VS 2, Cr 1/2 V 1/2 S 2 and so on of sulfide, NbSe _3, VSe _2, NbSe _3, such as selenide, Cr ₂ O of _{5, Cr 3 O 8, VO} 2, V 3 O 8, V 2 O 5, in addition to oxides of 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 ) _3, and the like.

Of a secondary battery in Examples of the negative electrode active _{material, 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, TiO 2, SnO, Oxides such as SnO ₂ , SiO ₂ , RuO ₂ , WO, WO ₂ and ZnO, metals such as Sn, Si, Al and Zn, complex oxides such as LiVO ₂ , Li ₃ VO ₄ and Li ₄ Ti ₅ O ₁₂ , _{2 . 6 Co 0 .4 N, Ge 3} N 4, Zn 3 N 2, may be mentioned nitrides such as Cu ₃ N.

Examples of the active material in the polarized 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 carbide, polyvinylidene chloride carbide, and microcrystalline carbon. In the hybrid capacitor, the positive electrode active material exemplified for the secondary battery can be used for the positive electrode. In this case, the negative electrode is composed of a polarized electrode using activated carbon or the like. In addition, the negative electrode active material exemplified for the secondary battery can be used for the negative electrode. In this case, the positive electrode is composed of a polarized 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 made of a material such as RuO ₂ and a polarizable material such as activated carbon.

The shape and the particle diameter of the electrode active material particles to be mixed with the oxidized carbon in the step (A) are not limited. However, it is preferable that the average particle diameter of the active material particles is larger than 2 탆 and not larger than 25 탆. This active material particle having a relatively large average particle diameter improves the electrode density by itself and promotes paste formation of the oxidized carbon by the pressing force in the course of mixing with the oxidized carbon. Further, in the step (B) shown below, in the process of applying pressure to the active material layer in the current collector, the active material particles having a relatively large average particle size are preferably pressed The treated carbon is further spread in paste to make it densified. As a result, the electrode density increases and the energy density of the power storage device is improved.

It is also preferable that the active material particles are composed of fine particles having an average particle diameter of 0.01 to 2 占 퐉 and coarse particles having an average particle diameter of more than 2 占 퐉 and not more than 25 占 퐉 which can operate as a polar active material such as fine particles thereof . It is said that particles having a small particle diameter tend to agglomerate. However, since the oxidation-treated carbon adheres to the surface of the coarse particles as well as to the surface of the coarse particles to cover the surface, aggregation of the active material particles can be suppressed, The mixing state can be made uniform. In addition, as described above, the coarse particles promote the vitrification and densification of the paste of the oxidation-treated carbon and increase the electrode density, thereby improving the energy density of the electrical storage device. Further, in the step (B), while the pressure is applied to the active material layer on the current collector, the fine particles are pressed with the oxidation-treated carbon in which at least a part of the fine particles have been changed into a paste, The electrode density is further increased and the energy density of the power storage device is further improved. The coarse particles and the fine particles are preferably selected so as to have a mass ratio of 80:20 to 95: 5, and more preferably 90:10 to 95: 5.

The mass ratio of the electrode active material particles and the oxidized carbon used in the step (A) is preferably in the range of 90:10 to 99.5: 0.5 in mass ratio to obtain the battery device having a high energy density, : 1 is more preferable. If the ratio of the oxidized carbon is less than the above range, the conductivity of the active material layer becomes insufficient, and the covering ratio of the active material particles by the oxidized carbon paste becomes small, and the cycle characteristic tends to be lowered. When the ratio of the oxidized carbon is larger than the above range, the electrode density is lowered and the energy density of the electric storage device tends to decrease.

In the step (A), in addition to the electrode active material particles and the oxidized carbon, at least a part of the oxidized carbon is converted into a paste form by using a conductive carbon, a binder and a solvent for mixing other than the oxidized carbon, So that the electrode material adhering to the surface of the electrode active material particles may be prepared.

By using a solvent, an electrode material in the form of a slurry is obtained.

Examples of the other conductive carbon include carbon black such as ketjen black, acetylene black, furnace black and channel black, fullerene, carbon nanotube, carbon nanofiber, graphene, amorphous carbon, carbon fiber, Natural graphite, artificial graphite, graphitized Ketjen black, mesoporous carbon, vapor-grown carbon fiber, and the like. It is preferable to use conductive carbon having a conductivity higher than that of paste-like conductive carbon derived from oxidation-treated carbon, and it is particularly preferable to use acetylene black. Since the oxidation-treated carbon adheres not only to the surface of the active material particles but also to the surface of the other conductive carbon to cover the surface thereof, aggregation of the other conductive carbon can be suppressed. Further, in the step (B) shown below, in the process of applying pressure to the active material layer in the current collector, the other conductive carbon is closely packed in the gap portion formed by the adjacent particles together with the oxidation- The electrical conductivity of the entire electrode is improved, so that the energy density of the electrical storage device is further improved. The ratio of the oxidized carbon to the other conductive carbon is preferably in the range of 3: 1 to 1: 3 in mass ratio, and more preferably in the range of 2.5: 1.5 to 1.5: 2.5. When another conductive carbon is used, the mass ratio of the total amount of the other conductive carbon and the oxidized carbon to the electrode active material particle is preferably in the range of 10: 90 to 0.5: 99.5, more preferably in the range of 5:95 to 1:99 Is more preferable.

As the binder, known binders such as polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinyl fluoride, and carboxymethyl cellulose are used. The content of the binder is preferably 1 to 30% by mass based on the total amount of the electrode material. If the content is less than 1% by mass, the strength of the active material layer is insufficient. If the content is 30% by mass or more, the discharge capacity of the electrode decreases and the internal resistance becomes excessively large. As the solvent for the mixing, a solvent which does not adversely affect other components in the electrode material such as N-methylpyrrolidone can be used without particular limitation. When each component in the mixture is uniformly mixed, the amount of the solvent is not particularly limited. The binder may be used in a form dissolved in a solvent.

There is no particular limitation on the mixing method of the conductive carbon, the binder and the solvent for mixing other than the electrode active material particles in the step (A), the oxidized carbon, and the oxidized carbon used as needed, and the mixing order.

However, when conductive carbon other than the oxidation-treated carbon is not used, it is preferable that the electrode active material particles and the oxidation-treated carbon are dry-mixed in the step (A). The resultant product is sufficiently kneaded together with a binder and a solvent as required to obtain an electrode material in the form of a slurry. For the dry mixing, a Leica, a quartz grinder, a ball mill, a bead mill, a rod mill, a roller mill, a stirring mill, a planetary mill, a vibrating mill, a hybridizer, a mechanochemical compounding apparatus and a jet mill may be used. Particularly, when mechanochemical treatment is applied to the active material particles and the oxidation-treated carbon, the coverage of the active material particles by oxidation-treated carbon and the uniformity of the coating are improved. The time for dry blending varies depending on the total amount of the active material particles to be mixed and the oxidized carbon and the mixing apparatus to be used, but is generally from 1 to 30 minutes. There is no particular limitation on the method of kneading with the binder and the solvent, and the kneading may be performed by manual mixing using induction, or by using a known mixing device such as a stirrer or a homogenizer. When each component in the electrode material is uniformly mixed, there is no problem even if the mixing time is short.

When the active material particles are composed of fine particles and coarse particles and other conductive carbon is not used, both the fine particles, the coarse particles and the oxidized carbon may be introduced into the mixing device in the step (A) and dry mixed. The product obtained by dry mixing is sufficiently kneaded together with a binder and a solvent as required, whereby an electrode material in the form of a slurry can be obtained. But,

(A1) a step of dry-mixing the oxidation-treated carbon and the fine particles to obtain a preliminary mixture, and

(A2) dry mixing the preliminary mixture with coarse particles

It is preferable to carry out dry mixing. It is preferable to perform the dry mixing by dividing into the step (A1) and the step (A2) because the coarse particles coated with the oxidation-treated carbon and the fine particles are dispersed well and uniformly mixed. In addition, since the product obtained in the step (A2) has a good familiarity with the binder and the solvent, it is possible to easily obtain a slurry-like electrode material in which each component is uniformly mixed. The ratio of the fine particles to the oxidized carbon in the step of obtaining the preliminary mixture is preferably in the range of 70:30 to 90:10 in mass ratio, and more preferably in the range of 75:25 to 85:15.

When conductive carbon other than the oxidation-treated carbon is used, the active material particles and the oxidation-treated carbon may be introduced into the mixing apparatus in the step (A), and both conductive carbon and other conductive carbon may be introduced and dry-mixed. The product obtained by dry mixing is sufficiently kneaded together with a binder and a solvent as required to obtain an electrode material in the form of a slurry. But,

(AA1) oxidatively-treated carbon and other conductive carbon, and

(AA2) dry mixing the mixture obtained in the step (AA1) with the active material particles

It is preferable to carry out dry mixing. The mixture obtained in the step (AA1) is a " conductive carbon mixture ". In this step, oxidation-treated carbon is adhered to the surface of the other conductive carbon so that the oxidation of the oxidation-treated carbon partially progresses, and at least a part of the oxidation-treated carbon changed to a paste forms a conductive carbon mixture . Then, the oxidation-treated carbon in which at least a part of the oxidation-treated carbon changed to paste in the step (AA2) is attached to the surface of the electrode active material particles, so that the active material particles coated with the oxidized carbon and other conductive carbon are dispersed well, The electrode material is obtained. Further, since this conductive carbon mixture has good familiarity with the binder and the solvent, in the case of obtaining an electrode material in the form of a slurry, instead of the step (AA2) and the subsequent kneading with the binder and the solvent,

(aa1) wet-mixing the conductive carbon mixture, the active material particles, the binder and the solvent, or

(aa2) wet-mixing the conductive carbon mixture, the binder and the solvent, adding the active material particles and wet-mixing them, or

(aa3) wet mixing the conductive carbon mixture, the active material particles and the solvent, adding a binder and wet mixing,

. It is said that fine carbon particles are difficult to be familiar with a binder and a solvent. However, by using a conductive carbon mixture, an electrode material in which each component is uniformly mixed can be easily obtained regardless of the mixing method of the mixture and the electrode active material particles have. Further, if the conductive carbon mixture is prepared in advance, the subsequent mixing of the active material particles and the binder can be carried out by either wet or dry processes, so that various production lines can be constructed.

When the active material particles are composed of fine particles and coarse particles and other conductive carbon is used, in the step (A), fine particles, coarse particles, oxidation-treated carbon and other conductive carbon are introduced into the mixing apparatus It may be dry mixed. The product obtained by dry mixing is sufficiently kneaded together with a binder and a solvent as required, whereby an electrode material in the form of a slurry can be obtained. But,

(AB1) dry-blending the oxidation-treated carbon with another conductive carbon,

(AB2) dry mixing the microparticles with the mixture obtained in the step (AB1); and

(AB3) Dry mixing of the mixture obtained in the step (AB2) and coarse particles

It is preferable to carry out dry mixing. Also,

(AC1) oxidatively-treated carbon and fine particles,

(AC2) dry mixing the product obtained in the step (AC1) with another conductive carbon, and

(AC3) Dry mixing of the mixture obtained in the step (AC2) and coarse particles

It is also preferable to carry out dry mixing. In these methods, oxidized carbon is attached to the surface of fine particles or other conductive carbon in at least one of (AB1), (AB2), (AC1) and (AC2), and the paste- Thereby, it is possible to obtain a mixture in which oxidation-treated carbon, coarse particles, fine particles and other conductive carbon are dispersed well and uniformly mixed. As described above, the conductive carbon mixture obtained in the step (AB1) has good familiarity with the binder and the solvent. Therefore, when the electrode material in the form of a slurry is obtained, the step (AB2), the step (AB3) Instead of kneading with <

(ab1) wet-mixing the conductive carbon mixture, the fine particles, the coarse particles, the binder and the solvent, or

(ab2) wet-mixing the conductive carbon mixture, the binder and the solvent, adding the fine particles and the coarse particles and wet-mixing them, or

(ab3) wet-mixing the electrically conductive carbon mixture, fine particles, coarse particles and a solvent, adding a binder and wet mixing,

. When the step (A) is carried out by these methods, the ratio of the total amount of the fine particles and the oxidized carbon to the other conductive carbon is set in the range of 70:30 to 90:10 in terms of the mass ratio, preferably 75:25 To 85: 15 by weight based on the total amount of the conductive carbon.

In the step (B), an electrode material obtained in the step (A) is applied on a current collector for constituting a positive electrode or a negative electrode of an electricity storage device to form an active material layer, and after drying the active material layer as required, Pressure is applied by rolling to obtain an electrode. The electrode material obtained in the step (A) may be formed into a predetermined shape and pressed onto the current collector, followed by rolling.

In the step (B), when pressure is added to the active material layer, the oxidation-treated carbon in which at least a part of the oxidation-treated carbon is changed into paste forms further spreads to cover the surface of the active material particles and becomes densified so that the active material particles approach each other, The oxidized carbon covers the surface of the active material particles and is extruded and densely filled not only in the gap portions formed between the adjacent active material particles but also in the holes existing on the surface of the active material particles. Therefore, the active material amount per unit volume of the electrode increases, and the electrode density increases. Moreover, the densely packed paste-like oxidation-treated carbon has sufficient conductivity to function as a conductive agent.

As the current collector for the electrodes of the power storage device, conductive materials such as platinum, gold, nickel, aluminum, titanium, steel, and carbon may be used. The shape of the current collector may be any shape such as film, thin film, plate, net, expanded metal, and cylindrical. When the active material layer is dried, the solvent may be removed by reducing pressure and heating as necessary. The pressure applied to the active material layer by the rolling treatment is generally in the range of 50,000 to 1,000,000 N / cm2, preferably 100,000 to 500,000 N / cm2. There is no particular limitation on the temperature for the rolling treatment, and the treatment may be carried out at room temperature or under heating conditions.

In a preferred form of the electrode of the present invention, the paste-like conductive carbon in the active material layer has a width of 50 nm or less and a void portion formed between adjacent electrode active material particles and / or a hole existing on the surface of the electrode active material particle exist. Therefore, the coverage of the surface of the active material particles by the conductive carbon on the paste is improved, the conductivity of the entire active material layer is improved, and the electrode density is improved. The conductive carbon such as carbon black, natural graphite, or carbon nanotube which is used as a conductive material in the electrode of the conventional power storage device can hardly penetrate into such a narrow gap or hole.

It can be seen that impregnation of the electrolytic solution into the electrode of the electrical storage device is not inhibited although the electrode of the present invention has an active material layer containing paste-like conductive carbon densely packed. In a preferred form of the electrode of the present invention, when the pore distribution of the active material layer of the electrode is measured by the mercury porosimetry, it can be seen that the active material layer has pores having a diameter of 5 to 40 nm. These minute pores are considered to be fine pores in the densified paste-like conductive carbon mainly derived from the oxidation-treated carbon, but are sufficiently large enough for the electrolyte solution in the electric storage device to pass through the conductive carbon in the paste to reach the active material particles. Therefore, the paste-like conductive carbon in the electrode has sufficient conductivity and does not inhibit impregnation of the electrolytic solution in the electrical storage device. As a result, the energy density of the power storage device is improved.

It is also believed that the surface of the active material particles in the active material layer of the electrode of the present invention is covered with the oxide-treated carbon which is densely spread in the paste to the inside of the hole existing on the surface of the active material particles. It can be seen that the dissolution of the active material in the electrolyte solution is suppressed and the cycle characteristics of the power storage device are improved despite the fact that the impregnation of the electrolyte solution into the electrode of the power storage device is not suppressed. In the preferred embodiment of the electrode of the present invention, the dissolution amount of the active material is reduced by about 40% or more as compared with the case where the electrode is composed of a conductive agent such as acetylene black and active material particles. Further, the cycle characteristics of the electrical storage device are greatly improved owing to the drastic suppression of dissolution of the active material.

Particularly, the oxidation-treated carbon having 10% or more of the total hydrophilic part as a whole is compressed and spreads in paste as a whole under pressure, so that most or all of the surface of the active material particles is contained in the holes existing on the surface of the active material particles And it is easy to be densified. As a result, at least 80%, preferably at least 90%, particularly preferably at least 95% of the surface of the active material particles in the active material layer of the electrode is brought into contact with the densified paste-like conductive carbon derived from the oxidation- .

(3) Power 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 electrical storage device includes a pair of electrodes (positive electrode and negative electrode) and an electrolyte disposed therebetween as essential elements, but at least one of the positive electrode and the negative electrode is manufactured by the manufacturing method of the present invention.

In the electrical storage device, the electrolyte disposed between the positive electrode and the negative electrode may be an electrolyte held in the separator, a solid electrolyte, or a gel electrolyte, and the electrolyte used in the conventional electrical storage device may be used without particular limitation. Representative electrolytes are illustrated below. The lithium ion secondary to the battery, ethylene carbonate, propylene carbonate, butylene carbonate, LiPF _6, in a solvent such as dimethyl carbonate, _{LiBF 4, LiCF 3 SO 3,} LiN (CF 3 SO 2) in which electrolyte solution dissolving lithium salt of _2, and Is used in a state of being held by a separator such as a polyolefin fiber nonwoven fabric or a glass fiber nonwoven fabric. In addition, Li ₅ La ₃ Nb ₂ O ₁₂ , Li _{1 . 5} Al _{0 .} Inorganic solid electrolytes such as ₅ Ti _{1 .5} (PO ₄ ) ₃ , Li ₇ La ₃ Zr ₂ O ₁₂ and Li ₇ P ₃ S ₁₁ , polymeric compounds such as lithium salt and polyethylene oxide, polymethacrylate, and polyacrylate An organic solid electrolyte comprising a complex of polyvinylidene fluoride, polyvinylidene fluoride, polyacrylonitrile or the like is also used. For the electric double layer capacitor and the redox capacitor, 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.

When a solid electrolyte or a gel electrolyte is used as the electrolyte between the positive electrode and the negative electrode, a solid electrolyte is added to each of the above-mentioned components in the step (A) for the purpose of securing an ion conductive path in the active material layer The electrode material is prepared.

Example

The present invention will be explained by using the following examples, but the present invention is not limited to the following examples.

(1) Preparation of oxidized carbon and electrode

Example 1

10 g of Ketjenblack (trade name EC300J, product of Ketjen Black International, BET specific surface area 800 m < 2 > / g) was added to 300 ml of 60% nitric acid. Ultrasonic waves were irradiated to the obtained solution for 10 minutes and then filtered to recover Ketjenblack. The recovered Ketjenblack was washed with water three times and dried to obtain an acid-treated Ketjenblack. The acid-treated Ketjen black and _{0.5g, Fe (CH 3 COO) 2} 1.98g and, Li (CH ₃ COO) 0.77g _{and, C 6 H 8 O 7 ·} H 2 O 1.10g and, CH ₃ COOH and 1.32g , by h ₃ PO ₄ 1.31g, and then a solution of 120mL of distilled water by stirring for 1 hour the obtained mixture to a stirrer, and evaporated to dryness in air at 100 ℃ it was collected mixture. Then, the obtained mixture was introduced into a vibrating ball mill and pulverized at 20 Hz for 10 minutes. Heat for 3 minutes for the powder after pulverization at 700 ℃ of nitrogen to obtain a composite LiFePO ₄ is supported on ketjen black.

1 g of the obtained composite was added to 100 ml of a hydrochloric acid aqueous solution having a concentration of 30%, and LiFePO ₄ in the composite was dissolved while ultrasonically irradiating the resulting solution for 15 minutes. The resulting solid was filtered, washed with water and dried. A part of the solid after drying was heated to 900 DEG C in air by TG analysis, and the weight loss was measured. The steps of dissolving, filtering, washing and drying LiFePO ₄ with the hydrochloric acid aqueous solution described above were repeated until it was confirmed that the weight loss was 100%, that is, LiFePO ₄ remained, whereby LiFePO ₄ -free oxidation- .

Then, 0.1 g of the oxidized carbon obtained was added to 20 mL of an aqueous ammonia solution having a pH of 11, and ultrasonic irradiation was performed for 1 minute. The resulting solution was allowed to stand for 5 hours to precipitate the solid phase portion. After precipitation of the solid phase portion, the remaining portion from which the supernatant liquid was removed was dried, and the weight of the solid after drying was measured. The weight ratio of the solid after drying to the weight of 0.1 g of the weight of the first oxidized carbon of the weight obtained by subtracting 0.1 g of the weight of the first oxidized carbon from the weight of the solid after the drying was regarded as the content of the "hydrophilic portion" in the oxidized carbon.

A mixed solution obtained by introducing Fe (CH ₃ COO) ₂ , Li (CH ₃ COO), C ₆ H ₈ O ₇ .H ₂ O, CH ₃ COOH and H ₃ PO ₄ into distilled water was added to a 1 After stirring for a time, the mixture was evaporated to dryness at 100 ° C in the air, and then heated in nitrogen at 700 ° C for 3 minutes to obtain fine particles of LiFePO _{4 having} a primary particle diameter of 100 nm (average particle size of 100 nm). Then, coarse particles of a commercially available LiFePO ₄ (1 primary particle size 0.5 ~ 1㎛, 2 primary particle size 2 ~ 3㎛, 2.5㎛ average particle diameter) and, fine particles thus obtained and, the oxidation-treated carbon of 90: 9: 1 To obtain an electrode material. Further, a total of 5% by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone are added and sufficiently kneaded to form a slurry, and this slurry is applied on an aluminum foil Dried, and rolled to obtain an electrode. The electrode density was calculated from the measured value of the volume and weight of the active material layer on the aluminum foil in this electrode.

Example 2

0.5 g of acid-treated ketchen black, 1.98 g of Fe (CH ₃ COO) ₂ , 0.77 g of Li (CH ₃ COO) and 1.10 g of C ₆ H ₈ O ₇ .H ₂ O 1.8 g of acid-treated ketchen black, 0.5 g of Fe (CH ₃ COO) _{2 and} 0.5 g of Li (CH ₃ COO) ₂ were added to a portion to be mixed with 1.32 g of CH ₃ COOH, 1.31 g of H ₃ PO ₄ and 120 mL of distilled water, And 0.28 g of C ₆ H ₈ O ₇ .H ₂ O, 0.33 g of CH ₃ COOH, 0.33 g of H ₃ PO ₄ and 250 mL of distilled water were mixed in the order of Example 1 Repeat the order.

Example 3

10 g of Ketjenblack used in Example 1 was added to 300 ml of 40% nitric acid, and ultrasonic waves were irradiated to the obtained solution for 10 minutes, followed by filtration to recover Ketjenblack. The recovered Ketjenblack was washed with water three times and dried to obtain acid treated Ketjenblack. The procedure of Example 2 was repeated except that 1.8 g of the acid-treated ketchen black was used instead of 1.8 g of the acid-treated ketchen black used in Example 2.

Comparative Example 1

10 g of Ketjenblack used in Example 1 was added to 300 ml of 60% nitric acid, and ultrasonic waves were irradiated to the obtained solution for 1 hour, followed by filtration to recover Ketjenblack. The recovered Ketjenblack was washed with water three times and dried to obtain acid treated Ketjenblack. The acid-treated Ketjen black was heated in nitrogen at 700 占 폚 for 3 minutes. The content of the hydrophilic part was measured in the same manner as in the procedure of Example 1 for the obtained oxidized carbon. Using the oxidation-treated carbon thus obtained, LiFePO ₄ -containing electrodes were prepared in the same manner as in the procedure of Example 1, and the electrode densities were calculated.

Comparative Example 2

10 g of Ketjenblack used in Example 1 was added to 300 ml of 30% nitric acid, ultrasonic waves were irradiated to the obtained solution for 10 minutes, and the Ketjenblack was recovered by filtration. The recovered Ketjenblack was washed with water three times and dried to obtain an acid-treated Ketjenblack. Subsequently, the mixture was heated in nitrogen at 700 DEG C for 3 minutes without pulverization by a vibrating ball mill. The content of the hydrophilic part was measured in the same manner as in the procedure of Example 1 for the obtained oxidized carbon. Using the oxidation-treated carbon thus obtained, LiFePO ₄ -containing electrodes were prepared in the same manner as in the procedure of Example 1, and the electrode densities were calculated.

Comparative Example 3

In order to confirm the contribution of the hydrophilic part to the electrode density, 40 mg of the oxidized carbon obtained in Example 1 was added to 40 mL of pure water, and ultrasonic irradiation was conducted for 30 minutes to disperse the carbon in purified water, and the dispersion was allowed to stand for 30 minutes The supernatant was removed, and the remaining portion was dried to obtain a solid. With respect to this solid, the content of the hydrophilic part was measured in the same manner as in the procedure of Example 1. [ Using the solid obtained, LiFePO ₄ -containing electrodes were prepared in the same manner as in Example 1, and the electrode densities were calculated.

Comparative Example 4

With respect to the ketjen black raw material used in Example 1, the content of the hydrophilic portion was measured in the same manner as in the procedure of Example 1. Using this ketchen black raw material, an electrode containing LiFePO ₄ was prepared in the same manner as in the procedure of Example 1, and the electrode density was calculated.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the relationship between the hydrophilic partial content of carbon in Examples 1 to 3 and Comparative Examples 1 to 4 and the electrode densities of the electrodes of Examples 1 to 3 and Comparative Examples 1 to 4; Fig. As is apparent from Fig. 1, when the content of the hydrophilic part exceeds 8 mass% of the entire oxidized carbon, the electrode density starts to increase. When the content exceeds 9 mass%, the electrode density starts to increase sharply, When the content exceeds 10 mass% of the entire oxidation-treated carbon, it is found that a high electrode density of 2.6 g / cc or more can be obtained. As is clear from the comparison between the results of Example 1 and Comparative Example 3, it was found that the contribution of the hydrophilic portion of the oxidized carbon to the improvement of the electrode density was large. As a result of the observation by the SEM photograph, it was confirmed that when the content of the hydrophilic part of the oxidation-treated carbon was increased and the electrode density began to increase sharply, the oxidation of the oxidation-treated carbon rapidly proceeded.

(2) Evaluation as a lithium ion secondary battery

(i) Active material: LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2} O ₂

Example 4

Li ₂ CO ₃ , Ni (CH ₃ COO) ₂ , Mn (CH ₃ COO) ₂ and Co (CH ₃ COO) ₂ were introduced into distilled water and the obtained mixed solution was stirred with a stirrer for 1 hour, The mixture was mixed with a ball mill and heated in air at 800 ° C for 10 minutes to obtain LiNi _0.5 Mn _0.3 Co _0.2 O ₂ fine particles having an average particle diameter of 0.5 μm. The fine particles and the oxidized carbon obtained in Example 1 were mixed at a mass ratio of 90:10 to obtain a preliminary mixture. Then, 86 parts by weight of a commercially available LiNi _{0. 5} Mn _{0 . 3} Co _{0 . 2} O ₂ of the coarse particles (average particle diameter 5㎛) and 9 parts by mass of the premix, and 2 parts by mass of acetylene black (primary particle size 40㎚) were mixed, and further 3 parts by mass of polyvinylidene fluoride with an appropriate amount of N-methylpyrrolidone was added thereto and sufficiently kneaded to form a slurry. The slurry was coated on an aluminum foil and dried, followed by rolling to obtain a positive electrode for a lithium ion secondary battery. The electrode density was calculated from the measured values of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 4.00 g / cc. Using the obtained positive electrode, a 1: 1 solution of 1M LiPF ₆ in ethylene carbonate / diethyl carbonate was used as an electrolytic solution to prepare a lithium ion secondary battery in which the counter electrode was lithium. The charge and discharge characteristics of the obtained battery were evaluated under a condition of a wide range of current density.

Example 5

94 parts by weight of a 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 oxidized carbon obtained in Example 1, and 2 parts by mass of acetylene black (primary particle diameter: 40 nm) were mixed and 2 parts by mass of polyvinyl fluoride Lidene and an appropriate amount of N-methylpyrrolidone were added and sufficiently kneaded to form a slurry. This slurry was coated on an aluminum foil, dried and subjected to a rolling treatment to obtain a positive electrode for a lithium ion secondary battery. The electrode density was calculated from the measured values of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 3.81 g / cc. Using the obtained positive electrode, a 1: 1 solution of 1M LiPF ₆ in ethylene carbonate / diethyl carbonate was used as an electrolytic solution to prepare a lithium ion secondary battery in which the counter electrode was lithium. The charge and discharge characteristics of the obtained battery were evaluated under a condition of a wide range of current density.

Comparative Example 5

94 parts by weight of a commercially available LiNi _{0. 5} Mn _{0 . 3} Co _{0 . 2} O ₂ particles (average particle diameter: 5 μm) and 4 parts by mass of acetylene black (primary particle diameter: 40 nm) were mixed, and 2 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone were added And the slurry was kneaded to form a slurry. The slurry was coated on an aluminum foil and dried, followed by rolling to obtain a positive electrode for a lithium ion secondary battery. The electrode density was calculated from the measured values of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The electrode density value was 3.40 g / cc. Using the obtained positive electrode, a 1: 1 solution of 1M LiPF ₆ in ethylene carbonate / diethyl carbonate was used as an electrolytic solution to prepare a lithium ion secondary battery in which the counter electrode was lithium. The charge and discharge characteristics of the obtained battery were evaluated under a condition of a wide range of current density.

Fig. 2 is a SEM photograph of a cross section of the positive electrode of the lithium ion secondary battery of Example 5, and Fig. 3 is an SEM photograph of the cross section of the positive electrode of the lithium ion secondary battery of Comparative Example 5. In each drawing, (A) is a photograph of 1500 times, and (B) is a photograph of 25000 times. Although the thickness of the active material layer is shown by t in Figs. 2A and 3A, the lithium ion 2 of Example 5 It can be seen that the active material layer in the secondary battery is thinner than the active material layer in the lithium ion secondary battery of Comparative Example 5. [ 2 (A) and 3 (A), it can be seen that in the active material layer of the lithium ion secondary battery of Example 5, the active material particles approach each other and the total area of the active material layer in the image The ratio of the area occupied by the carbon is small. Further, as can be understood from FIG. 2B and FIG. 3B, the shapes of the carbon in both cases are significantly different. In the active material layer (FIG. 3 (B)) of the lithium ion secondary battery of Comparative Example 5, the grain boundaries of the carbon (acetylene black) primary particles are clear and the active material particles and the carbon particles Large bubbles exist in the vicinity of the interface, particularly in the vicinity of the hole formed on the surface of the active material particles. In the active material layer (FIG. 2B) of the lithium ion secondary battery of Example 5, The grain boundary is not confirmed and the carbon is in the form of paste and the carbon on the paste penetrates into the deep portion of the hole (gap between the primary particles) having a width of 50 nm or less of the active material particle, . It is also found that at least 90% of the surface of the active material particles is in contact with the paste-like carbon. It was found that the difference in the shape of the carbon resulted in an increase in the electrode density in the positive electrode of the lithium ion secondary battery of Example 5 and Comparative Example 5.

As described above, since the active material layer in Example 5 is thinner than the active material layer in Comparative Example 5, it can be seen that the material filling rate in the active material layer of Example 5 is large, but the following formula To confirm the material filling rate. The theoretical electrode density is an electrode density assuming that the voids in the active material layer are 0%.

Material filling rate (%) = electrode density x 100 / theoretical electrode density (I)

Theoretical electrode density (g / cc)

  = 100 / a / X + b / Y + (100-a-b) / Z}

  a: mass% of the active material with respect to the entire active material layer

  b: mass% of carbon with respect to the entire active material layer

  100-a-b: mass% of polyvinylidene fluoride relative to the whole active material layer

  X: true density of active material Y: true density of carbon black

  Z: true density of polyvinylidene fluoride

As a result, the material filling ratio of the active material layer in Example 5 was 86.8%, and the filling ratio of the active material layer in Comparative Example 5 was 79.1%. In the electrode including the paste-like conductive carbon derived from the oxidation- 7.7% improvement in filling rate was confirmed.

Fig. 4 shows the results of measurement of pore distribution by the mercury porosimetry for the active material layer in Example 5 and the active material layer in Comparative Example 5. Fig. In the active material layer in Comparative Example 5, pores having a diameter of less than 20 nm are hardly present, and most of the pores are pores showing a peak at a diameter of about 30 nm, a diameter of about 40 nm, and a diameter of about 150 nm. The pores showing a peak at a diameter of about 150 nm are mainly pores originating from active material particles and the pores showing a peak at a diameter of about 30 nm and a diameter of about 40 nm are considered to be mainly pores found among the particles of acetylene black. On the other hand, in the active material layer in Example 5, pores of a diameter of about 100 nm or more in the pores of the active material layer in Comparative Example 5 decreased, and pores having a diameter in the range of 5 to 40 nm . It is considered that the pores of the diameter of about 100 nm or less are reduced because the pores of the active material particles are covered with the conductive carbon in the paste. The pores having a diameter of 5 to 40 nm are considered to be fine pores in the paste-like conductive carbon mainly derived from oxidation-treated carbon. However, when the electrolyte in the electric storage device passes through the conductive carbon in the paste to reach the active particles to be. Therefore, it was judged that the paste-like conductive carbon in the electrode did not inhibit impregnation of the electrolytic solution in the electrical storage device.

5 is a graph showing the relationship between the rate and the discharge capacity per volume of the positive electrode active material layer for the lithium ion secondary battery of Example 4, Example 5, and Comparative Example 5. Fig. The lithium ion secondary battery of Example 5 exhibited an increased capacity as compared with the lithium ion secondary battery of Comparative Example 5, and the lithium ion secondary battery of Example 4 exhibited a larger capacity than that of the lithium ion secondary battery of Example 5 Respectively. That is, as the electrode density of the positive electrode increases, the discharge capacity per volume also increases. In addition, these secondary batteries exhibited substantially the same rate characteristics. From this, it was also confirmed that the paste-like conductive carbon derived from the oxidation-treated carbon contained in the active material layer of the secondary battery of Examples 4 and 5 had sufficient conductivity to function as a conductive agent, The impregnation of the electrolytic solution in the battery is not suppressed. Although the positive electrode of the secondary battery of Example 4 and the positive electrode of the secondary battery of Example 5 exhibited higher electrode densities than those of the latter in spite of the fact that the active material layer and the carbon content of the active material layer were approximately the same, In the active material layer in the positive electrode of the secondary battery of Example 4, the fine particles were extruded into the gap portion formed between the adjacent coarse particles together with the oxidized carbon subjected to the paste-making while pressing the oxidized carbon obtained in Example 1 It was thought to be charged.

Charging and discharging of lithium ion secondary batteries of Example 5 and Comparative Example 5 were repeated at a charging and discharging rate of 60C and 0.5C under the condition of 4.6 to 3.0V. Fig. 6 shows the results of the obtained cycle characteristics. It can be seen that the secondary battery of Example 5 has better cycle characteristics than the secondary battery of Comparative Example 5. [ As can be understood from a comparison between Fig. 2 and Fig. 3, almost all of the surface of the active material particles in the active material layer in the former is covered with the dense paste-like carbon until reaching the deep part of the hole in the surface of the active material particle. It is thought that the dense paste-like carbon suppresses deterioration of the active material.

(ii) the active material: LiCoO ₂

Example 6

Li ₂ CO ₃ , Co (CH ₃ COO) ₂ and C ₆ H ₈ O ₇ .H ₂ O were introduced into distilled water, and the obtained mixed solution was stirred for 1 hour with a stirrer. Then, And then heated in air at 800 ° C for 10 minutes to obtain LiCoO ₂ fine particles having an average particle diameter of 0.5 μm. The fine particles and the oxidized carbon obtained in Example 1 were mixed at a mass ratio of 90:10 to obtain a preliminary mixture. Subsequently, 86 parts by mass of commercially available coarse particles of LiCoO ₂ (average particle size of 10 μm), 9 parts by mass of the above premix and 2 parts by mass of acetylene black (primary particle diameter of 40 nm) were mixed to obtain 3 parts by mass of poly Vinylidene fluoride and an appropriate amount of N-methylpyrrolidone were added and sufficiently kneaded to form a slurry. The slurry was coated on an aluminum foil and dried, followed by rolling to obtain a positive electrode for a lithium ion secondary battery. The electrode density was calculated from the measured values of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 4.25 g / cc. Using the obtained positive electrode, a 1: 1 solution of 1M LiPF ₆ in ethylene carbonate / diethyl carbonate was used as an electrolytic solution to prepare a lithium ion secondary battery in which the counter electrode was lithium. The charge and discharge characteristics of the obtained battery were evaluated under a condition of a wide range of current density.

Example 7

94 parts by mass of commercially available LiCoO ₂ particles (average particle diameter 10 μm), 2 parts by mass of the oxidized carbon obtained in Example 1, and 2 parts by mass of acetylene black (primary particle diameter: 40 nm) And a suitable amount of N-methylpyrrolidone was added thereto and sufficiently kneaded to form a slurry. This slurry was coated on an aluminum foil and dried, and then subjected to rolling to obtain a positive electrode for a lithium ion secondary battery . The electrode density was calculated from the measured values of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 4.05 g / cc. Using the obtained positive electrode, a 1: 1 solution of 1M LiPF ₆ in ethylene carbonate / diethyl carbonate was used as an electrolytic solution to prepare a lithium ion secondary battery in which the counter electrode was lithium. The charge and discharge characteristics of the obtained battery were evaluated under a condition of a wide range of current density.

Comparative Example 6

94 parts by mass of commercially available LiCoO ₂ particles (average particle diameter 10 μm) and 4 parts by mass of acetylene black (primary particle diameter 40 nm) were mixed, and 2 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone And the mixture was sufficiently kneaded to form a slurry. The slurry was coated on an aluminum foil and dried, followed by rolling to obtain a positive electrode for a lithium ion secondary battery. The electrode density was calculated from the measured values of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 3.60 g / cc. Using the obtained positive electrode, a 1: 1 solution of 1M LiPF ₆ in ethylene carbonate / diethyl carbonate was used as an electrolytic solution to prepare a lithium ion secondary battery in which the counter electrode was lithium. The charge and discharge characteristics of the obtained battery were evaluated under a condition of a wide range of current density.

With respect to the active material layer in Example 7 and the active material layer in Comparative Example 6, the material filling rate was confirmed by using the above-mentioned formulas (I) and (II). As a result, the material filling rate of the active material layer in Example 7 was 85.6%, and the material filling ratio of the active material layer in Comparative Example 6 was 79.1%. In the electrode including the paste-like conductive carbon derived from the oxidation- 6.5% improvement in filling rate was confirmed.

7 is a graph showing the relationship between the rate and the discharge capacity per volume of the positive electrode active material layer for the lithium ion secondary battery of Example 6, Example 7, and Comparative Example 6. Fig. Similar to the result shown in Fig. 5, the discharge capacity also increases with the increase in electrode density, and it is found that substantially the same rate characteristics are obtained. Charging and discharging of the lithium ion secondary batteries of Example 7 and Comparative Example 6 were repeated at a charging / discharging rate of 60 ° C and 0.5C under the condition of 4.3 to 3.0 V. 8 shows the results of the obtained cycle characteristics. 6, it can be seen that the secondary battery of Example 7 has better cycle characteristics than the secondary battery of Comparative Example 6.

(iii) Active material: Li _{1 . 2} Mn _{0 . 56} Ni _{0 . 17} Co _{0 . 07} O ₂

Example 8

Li (CH ₃ COO) 1.66g _{and, Mn (CH 3 COO) 2} · 4H 2 O 2.75g _{and, Ni (CH 3 COO) 2} · 4H 2 O 0.85g _{and, Co (CH 3 COO) 2} · 4H 2 O and 200 mL of distilled water were mixed, and the solvent was removed using this separator, and the mixture was collected. Subsequently, the collected mixture was introduced into a vibrating ball mill and pulverized at 15 Hz for 10 minutes to obtain a uniform mixture. 1 hours heating the mixture after the pulverization at 900 ℃ in air, and less than or equal to the average particle diameter 1㎛ excess lithium solid solutions Li _{1. 2} Mn _{0 . 56} Ni _{0 . 17} Co _{0 . 0.0} > ₀₂ < / _RTI > 91 parts by mass of the crystal grains and 4 parts by mass of the oxidized carbon obtained in Example 1 were mixed and 5 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone were added and sufficiently kneaded to obtain a slurry The slurry was coated on an aluminum foil and dried, followed by rolling to obtain a positive electrode for a lithium ion secondary battery. The electrode density was calculated from the measured values of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The electrode density value was 3.15 g / cc. Using the obtained positive electrode, a 1: 1 solution of 1M LiPF6 in ethylene carbonate / diethyl carbonate was used as an electrolytic solution to prepare a lithium ion secondary battery in which the counter electrode was lithium. The charge and discharge characteristics of the obtained battery were evaluated under a condition of a wide range of current density.

Comparative Example 7

91 parts by mass of Li _{1 . 2} Mn _{0 . 56} Ni _{0 . 17} Co _{0 . 07} O ₂ particles and 4 parts by mass of acetylene black (primary particle diameter: 40 nm) were mixed, and 5 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone were added and sufficiently kneaded to form a slurry , The slurry was coated on an aluminum foil, dried and then subjected to a rolling treatment to obtain a positive electrode for a lithium ion secondary battery. The electrode density was calculated from the measured values of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 2.95 g / cc. Using the obtained positive electrode, a 1: 1 solution of 1M LiPF ₆ in ethylene carbonate / diethyl carbonate was used as an electrolytic solution to prepare a lithium ion secondary battery in which the counter electrode was lithium. The charge and discharge characteristics of the obtained battery were evaluated under a condition of a wide range of current density.

9 is a graph showing the relationship between the rate and the discharge capacity per volume of the positive electrode active material layer for the lithium ion secondary battery of Example 8 and Comparative Example 7. Fig. Similar to the results shown in Fig. 5, it can be seen that as the electrode density increases, the discharge capacity also increases and substantially the same rate characteristics are obtained. Charging and discharging of the lithium ion secondary batteries of Example 8 and Comparative Example 7 were repeated at a charge / discharge rate of 25 C and 0.5 C under the condition of 4.8 to 2.5 V. Fig. 10 shows the results of the obtained cycle characteristics. 6, it can be seen that the secondary battery of Example 8 has a cycle characteristic superior to that of Comparative Example 7.

(iv) Change in oxidation-treated carbon

Example 9

10 g of furnace black (average particle diameter 20 nm, BET specific surface area 1400 m < 2 > / g) having voids was added to 300 mL of 60% nitric acid. Ultrasonic waves were irradiated to the obtained solution for 10 minutes and then filtered to recover furnace black. The recovered furnace black was washed with water three times and dried to obtain an acid-treated furnace black. The acid treated furnace black and _{0.5g, Fe (CH 3 COO) 2} 1.98g and, Li (CH ₃ COO) 0.77g _{and, C 6 H 8 O 7 ·} H 2 O 1.10g and, CH ₃ COOH and 1.32g , by h ₃ PO ₄ 1.31g, and then a solution of 120mL of distilled water by stirring for 1 hour the obtained mixture to a stirrer, and evaporated to dryness in air at 100 ℃ it was collected mixture. Then, the obtained mixture was introduced into a vibrating ball mill and pulverized at 20 Hz for 10 minutes. The powder after the pulverization was heated in nitrogen at 700 캜 for 3 minutes to obtain a composite in which LiFePO ₄ was supported on furnace black.

1 g of the obtained composite was added to 100 mL of a hydrochloric acid aqueous solution having a concentration of 30%, and LiFePO ₄ in the composite was dissolved while ultrasonically irradiating the resultant solution for 15 minutes. The resulting solid was filtered, washed with water and dried. A part of the solid after drying was heated to 900 DEG C in air by TG analysis, and the weight loss was measured. The steps of dissolving, filtering, washing and drying LiFePO ₄ with the hydrochloric acid aqueous solution described above were repeated until it was confirmed that the weight loss was 100%, that is, LiFePO ₄ remained, whereby LiFePO ₄ -free oxidation- .

Then, 0.1 g of the oxidized carbon obtained was added to 20 mL of an aqueous ammonia solution having a pH of 11, and ultrasonic irradiation was performed for 1 minute. The resulting solution was allowed to stand for 5 hours to precipitate the solid phase portion. After precipitation of the solid phase portion, the remaining portion from which the supernatant liquid was removed was dried, and the weight of the solid after drying was measured. The weight ratio of the solid after drying to the weight of 0.1 g of the weight of the first oxidized carbon of the weight obtained by subtracting 0.1 g of the weight of the first oxidized carbon from the weight of the solid after the drying was regarded as the content of the "hydrophilic portion" in the oxidized carbon. The oxidation-treated carbon contained 13% of the hydrophilic part. In addition, the hydrophilic portion in the furnace black having voids used as the raw material is only 2%.

94 parts by weight of a commercially available LiNi _{0. 5} Mn _{0 . 3} Co _{0 . 2} O ₂ particles (average particle diameter: 5 μm), 2 parts by mass of the obtained oxidized carbon and 2 parts by mass of acetylene black (primary particle diameter: 40 nm) were mixed. Fig. 11 shows SEM photographs of the obtained mixture at 50000 times. The surface of the particles is partially covered with the paste, so that the outline can not be clearly grasped. However, the paste product is spreading while covering the surface of the particles by the pressure of the mixing, which is obtained by oxidizing the furnace black raw material . It is also seen that acetylene black having a primary particle diameter of 40 nm is well dispersed. In general, it is said that fine particles tend to flocculate, but aggregation of fine particles is effectively suppressed by oxidation-treated carbon.

Subsequently, 2 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone were added to the resulting mixture and sufficiently kneaded to form a slurry. The slurry was coated on an aluminum foil, dried, and then subjected to rolling to obtain lithium Thereby obtaining a positive electrode for an ion secondary battery. The electrode density was calculated from the measured values of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The electrode density value was 3.80 g / cc. Using the obtained positive electrode, a 1: 1 solution of 1M LiPF ₆ in ethylene carbonate / diethyl carbonate was used as an electrolytic solution to prepare a lithium ion secondary battery in which the counter electrode was lithium. The charge and discharge characteristics of the obtained battery were evaluated under a condition of a wide range of current density. Charging and discharging of the obtained battery were repeated at a charging / discharging rate of 4.6 to 3.0 V under conditions of a charging / discharging rate of 60C and 0.5C.

In Example 9 and Comparative Example 5, the same conditions were the same except for the type of carbon for the positive electrode. In Example 9, the oxidized carbon obtained from the furnace black raw material having voids and acetylene black were used. In Comparative Example 5 Only acetylene black was used. The electrode density of the positive electrode in Comparative Example 5 was 3.40 g / cc, and the electrode density was significantly improved by the use of the oxidation-treated carbon. In Example 9 and Example 5, the oxidation-treated carbon obtained from the ketjen black raw material was used in Example 5, while the other conditions were the same except for the type of the oxidized carbon used for the positive electrode. In Example 9, Oxidized carbon obtained from the raw material was used. The electrode density of the positive electrode in Example 5 was 3.81 g / cc, and almost the same electrode density was obtained irrespective of the difference in raw materials in the oxidized carbon.

12 shows the relationship between the rate for the lithium ion secondary battery of Example 9 and Comparative Example 5 and the discharge capacity per volume of the positive electrode active material layer, and FIG. 13 shows the relationship between the rate for the lithium ion secondary battery of Example 9 and Comparative Example 5 The results of the cycle characteristics are shown. It can be seen from Fig. 12 that as the electrode density increases, the discharge capacity also increases, and substantially the same rate characteristics are obtained. The rate characteristics of the secondary battery of Example 5 in Fig. 5 and the rate characteristics of the secondary battery of Example 9 in Fig. 12 are compared with each other, It can be seen that almost the same rate characteristics can be obtained. It can be seen from Fig. 13 that the secondary battery of Example 9 has better cycle characteristics than the secondary battery of Comparative Example 5. The cycle characteristics of the secondary battery of Example 5 shown in Fig. 6 and the cycle characteristics of the secondary battery of Example 9 shown in Fig. 13 were compared with each other. As a result, It can be seen that almost the same cycle characteristics can be obtained.

(3) Solubility of active material

As described above, excellent cycle characteristics can be obtained in the lithium ion secondary battery having the electrode of the present invention because substantially all of the surface of the active material particles is covered with the paste-like carbon, and the carbon on the paste is deteriorated . In order to confirm this, the solubility of the active material was investigated.

Each of the oxidized carbon and acetylene black obtained in Example 1 was mixed with LiFePO ₄ particles having an average particle diameter of 0.22 μm, LiCoO ₂ particles having an average particle diameter of 0.26 μm, and LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2} O ₂ particles at a mass ratio of 5:95. Further, 5% by mass of polyvinylidene fluoride as a whole and an appropriate amount of N-methylpyrrolidone were added and sufficiently kneaded to form a slurry, Dried, and rolled to obtain an electrode. A coin-type battery was prepared using this electrode and an electrolyte in which 1,000 ppm of water was added to a 1: 1 solution of 1M LiPF ₆ in ethylene carbonate / diethyl carbonate. In this test, fine particles having a large specific surface area were used for the purpose of increasing the area of the active material in contact with the electrolytic solution. Furthermore, since 1000 ppm of water is liable to dissolve the active material as the amount of water increases, it is added for the purpose of acceleration test. The battery was allowed to stand at 60 占 폚 for one week and then decomposed. An electrolyte was sampled and the amount of metal dissolved in the electrolyte was analyzed by an ICP emission spectrometer. Table 1 shows the results obtained.

As is apparent from Table 1, the paste-like conductive carbon derived from the oxidation-treated carbon obtained in Example 1 remarkably suppressed the dissolution of the active material into the electrolyte as compared with acetylene black. This is because the oxidation-treated carbon obtained in Example 1 effectively covers aggregation of the fine particles even though the active material has fine particles having an average particle size of 0.22 to 0.32 占 퐉 and covers the entire surface of the active material particles do.

(4) Mixed state of oxidation-treated carbon and active material

In order to confirm the mixed state of the active material and carbon, the following experiment was conducted.

(i) mixing of fine particles and carbon

Each of the oxidized carbon and acetylene black obtained in Example 1 was treated with LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2} O ₂ fine particles at a mass ratio of 20:80, and dry mixing was carried out. 14 shows an SEM photograph at a magnification of 50000 times. In the case of using acetylene black as the carbon, it can be seen that the fine particles are aggregated in spite of the same mixing conditions as in the case of using the oxidation-treated carbon obtained in Example 1. Thus, it can be seen that the oxidation-treated carbon obtained in Example 1 effectively suppressed aggregation of the fine particles.

(ii) mixing of coarse particles and carbon

Each of the oxidized carbon and acetylene black obtained in Example 1 was treated with LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2} O ₂ coarse particles at a mass ratio of 4:96, and dry mixing was carried out. 15 shows an SEM photograph of a magnification of 100000 times. When acetylene black was used as the carbon, coarse particles and acetylene black exist separately. However, in the case of using the oxidized carbon obtained in Example 1, the coarse particles are covered with the paste, and the outline of the coarse particles is clearly It can be seen that it is not grasped. This paste product was spread with the oxidation-treated carbon obtained in Example 1 covering the surface of the coarse particles by the pressure of mixing. The oxidation treatment carbon obtained in Example 1 spreads in a paste state by covering the surface of the active material particles with the rolling material at the time of electrode formation to densify the active material particles so that the active material particles approach each other, It is supposed that the active material per unit volume of electrode is increased and electrode density is increased since it is extruded and densely filled in the gap portion formed between adjacent active material particles while covering the surface of active material particles.

(5) Use of conductive carbon mixture

(i) Active material: LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2} O ₂

Example 10

The oxidation-treated carbon obtained in Example 1 and acetylene black (primary particle size: 40 nm) were introduced into a ball mill at a mass ratio of 1: 1 and dry mixed to obtain a conductive carbon mixture. Fig. 16 shows a SEM photograph of the obtained conductive carbon mixture, and Fig. 17 shows a TEM photograph. 16 is a photograph of 50000 times, FIG. 17 (A) is a photograph of 100000 times, and FIG. 17 (B) is a photograph of 500000 times. In the SEM photograph of Fig. 16, it can be seen that the carbon on the surface is present on the surface because the outline of the carbon particles can not be clearly grasped. It can also be seen from the TEM photograph of FIG. 17 that the conductive carbon mixture is composed of the granular material and the layered material on the surface of the granular material. The broken line in (B) of Fig. 17 shows the surface of the granular material. The granular material is acetylene black particles, and the layered product is a layer formed by adhering the acetylene black particles to the surface of the acetylene black particles with the oxidation-treated carbon collapsing. From FIG. 17 (B), it can be seen that the layered product is composed of a paste-like portion to which a non-particulate amorphous carbon is connected and a fibrous or needle-like portion.

Subsequently, 4 parts by mass of the obtained conductive carbon mixture, 2 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone were wet-mixed to obtain a commercially available LiNi _0.5 Mn _0.3 Co _0.2 O ₂ particle ( Average particle diameter 5 mu m) was added and wet-mixed to form a slurry. The slurry was coated on an aluminum foil and dried, followed by rolling to obtain a positive electrode for a lithium ion secondary battery. The electrode density was calculated from the measured values of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 3.81 g / cc. Using the obtained positive electrode, a 1: 1 solution of 1M LiPF ₆ in ethylene carbonate / diethyl carbonate was used as an electrolytic solution to prepare a lithium ion secondary battery in which the counter electrode was lithium. The obtained battery was subjected to measurement of a discharge curve in a range of 4.5 to 3.0 V under the condition of 25 DEG C and a discharge rate of 0.5C, and the DC internal resistance (DCIR) was calculated from the voltage drop.

Example 11

Carried out with 4 parts by mass of conductive carbon mixture portion obtained in Example 10, 94 parts by weight of a commercially available LiNi _{0. 5} Mn _{0 . 3} Co _{0 . 2} O ₂ particles (average particle diameter: 5 μm) were dry-mixed, and then 2 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone were wet-mixed to form a slurry. The slurry was coated on an aluminum foil and dried, followed by rolling to obtain a positive electrode for a lithium ion secondary battery. The electrode density was calculated from the measured values of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The electrode density value was 3.80 g / cc. Using the obtained positive electrode, a lithium ion secondary battery was prepared in the same manner as in Example 10, and the obtained battery was subjected to DCIR calculation.

The active material layer of the positive electrode in Example 10 and Example 11 has the same composition as the active material layer of the positive electrode in Example 5, but the order of mixing of the respective components in the process of preparing the electrode material is different. Fig. 18 shows a SEM photograph of a 25000 times magnification of the cross section of the positive electrode of Example 10. Fig. The SEM photograph of FIG. 18 is similar to the SEM photograph of the cross section of the positive electrode in Example 5 shown in FIG. 2 (B). That is, the grain boundary of the carbon primary particles is not confirmed, the carbon is paste-like, and the carbon on the paste penetrates into the deep portion of the hole (interval between primary particles) of the active material particle with a width of 50 nm or less, Are rarely present. In addition, 90% or more of the surface of the active material particles is in contact with the paste-like carbon. Since the fine carbon particles are poorly familiar with the binder and the solvent, when preparing an electrode material in the form of a slurry containing a binder and a solvent, after the electrode active material particles and carbon are dry-mixed as in the process of Example 5, It is common to add a solvent to perform wet mixing. However, since the electrode densities of the positive electrodes of Examples 10, 11, and 5 are almost the same and the observation results of SEM photographs are similar, the conductive carbon mixture is mixed with the binder And that it is good in familiarity with a solvent and provides an electrode exhibiting the same high electrode density even when wet-mixed with active material particles in the presence of a binder and a solvent.

DCI was measured for the lithium ion secondary battery of Example 5 and the lithium ion secondary battery of Comparative Example 5 using only acetylene black as the carbon in the same procedure as that of Example 10, 10 and the DCIR in the lithium ion secondary battery of Example 11 were compared with each other. The results are shown in Fig. The DCIR of the secondary battery of Example 5 is significantly lower than that of the secondary battery of Comparative Example 5, and it can be seen that remarkable reduction of DCIR is achieved by using the electrode of the present invention. Further, the DCIR of the secondary batteries of Examples 10 and 11 is lower than that of the DCIR of the secondary battery of Example 5, so that the conductive carbon mixture has conductivity It can be seen that this excellent positive electrode is provided.

(ii) the active material: LiCoO ₂

Example 12

4 parts by mass of the conductive carbon mixture obtained in Example 10, 2 parts by mass of polyvinylidene fluoride and an appropriate amount of N-methylpyrrolidone were wet-mixed and 94 parts by mass of commercially available LiCoO ₂ particles (average particle diameter 10 Mu m) was added and wet-mixed to form a slurry. The slurry was coated on an aluminum foil and dried, followed by rolling to obtain a positive electrode for a lithium ion secondary battery. The electrode density was calculated from the measured values of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 4.05 g / cc.

Example 13

4 parts by mass of the conductive carbon mixture obtained in Example 10 and 94 parts by mass of commercially available LiCoO ₂ particles (average particle size of 10 μm) were dry-mixed and then 2 parts by mass of polyvinylidene fluoride and an appropriate amount of N- Rawlidon was wet-mixed to form a slurry. The slurry was coated on an aluminum foil and dried, followed by rolling to obtain a positive electrode for a lithium ion secondary battery. The electrode density was calculated from the measured values of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 4.05 g / cc.

The active material layer of the positive electrode in Example 12 and Example 13 has the same composition as the active material layer of the positive electrode in Example 7, but the order of mixing of the respective components in the process of preparing the electrode material is different. Since the electrode densities in the positive electrodes of Examples 12, 13 and 7 are the same, the conductive carbon mixture is good in familiarity with the binder and the solvent, and is wet-mixed with the active material particles in the presence of a binder and a solvent. Thereby providing an electrode showing density.

(iii) Change of carbon mixed with oxidation-treated carbon

Example 14

The oxidized carbon obtained in Example 1 and a vapor grown carbon fiber (average fiber diameter: 150 nm, average fiber length: 3.9 μm) were introduced into a ball mill at a mass ratio of 1: 1 and dry mixed to obtain a conductive carbon mixture. Then, the wet mixture 4 parts by weight, 2 parts by weight of polyvinylidene fluoride and, N- methyl pyrrolidone, a suitable amount of the resulting conductive carbon mixture, and further 94 parts by weight of a commercially available LiNi _{0. 5} Mn _{0 . 3} Co _{0 . 2} O ₂ particles (average particle diameter: 5 탆) were added and wet-mixed to form a slurry. The slurry was coated on an aluminum foil and dried, followed by rolling to obtain a positive electrode for a lithium ion secondary battery. The electrode density was calculated from the measured values of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The electrode density value was 3.66 g / cc.

Comparative Example 8

Example 14 using the vapor-grown carbon fiber according to 4 parts by weight, 2 parts by weight of polyvinylidene fluoride and, N- methyl pyrrolidone wet-mixed, and further 94 parts by weight of commercially available suitable amount of LiNi _{0. 5} Mn _{0 . 3} Co _{0 . 2} O ₂ particles (average particle diameter: 5 탆) were added and wet-mixed to form a slurry. The slurry was coated on an aluminum foil and dried, followed by rolling to obtain a positive electrode for a lithium ion secondary battery. The electrode density was calculated from the measured values of the volume and weight of the active material layer on the aluminum foil in this positive electrode. The value of the electrode density was 3.36 g / cc.

From the comparison between Example 14 and Comparative Example 8, it can be seen that the use of the conductive carbon mixture containing the oxidation-treated carbon obtained in Example 1 significantly improves the electrode density.

Example 15

The procedure of Example 14 was repeated except that graphene (length in the plane direction: 2 mu m, length in the direction of the cross section: nm) was used instead of vapor-grown carbon fiber. The value of the electrode density was 3.69 g / cc.

Comparative Example 9

The procedure of Comparative Example 8 was repeated except that graphene used in Example 15 was used instead of vapor-grown carbon fiber. The electrode density value was 3.45 g / cc.

From the comparison between Example 15 and Comparative Example 9, it can be seen that the use of the conductive carbon mixture containing the oxidation-treated carbon obtained in Example 1 significantly improves the electrode density.

Example 16

The procedure of Example 14 was repeated except that furnace black (average particle diameter 35 nm) was used instead of vapor-grown carbon fiber. The value of the electrode density was 3.76 g / cc.

Comparative Example 10

The procedure of Comparative Example 8 was repeated except that the furnace black used in Example 16 was used in place of the vapor-grown carbon fiber. The value of the electrode density was 3.42 g / cc.

From the comparison between Example 16 and Comparative Example 10, it can be seen that the use of the conductive carbon mixture containing the oxidation-treated carbon obtained in Example 1 significantly improves the electrode density.

Example 17

The procedure of Example 14 was repeated except that graphite (average particle size of 6 mu m) was used instead of vapor-grown carbon fibers. The electrode density value was 3.81 g / cc

Comparative Example 11

The procedure of Comparative Example 8 was repeated except that graphite used in Example 17 was used instead of vapor-grown carbon fibers. The value of the electrode density was 3.48 g / cc.

From the comparison between Example 17 and Comparative Example 11, it can be seen that the use of the conductive carbon mixture containing the oxidation-treated carbon obtained in Example 1 significantly improves the electrode density.

≪ Industrial Availability >

By using the electrode of the present invention, a battery device having a high energy density is obtained.

Claims (12)

An electrode for a power storage device,
Electrode active material particles,
And an active material layer containing paste-like conductive carbon derived from oxidation-treated carbon obtained by oxidizing a carbon raw material having a void covering the surface of the electrode active material particle. The method according to claim 1,
Wherein the conductive carbon on the paste is also present in the gap existing in the gap portion formed between adjacent electrode active material particles and / or on the surface of the electrode active material particle, the width being 50 nm or less. 3. The method according to claim 1 or 2,
Wherein the active material layer has pores having a diameter of 5 to 40 nm. 4. The method according to any one of claims 1 to 3,
Wherein the oxidation-treated carbon comprises a hydrophilic part, and the content of the hydrophilic part is 10 mass% or more of the entire oxidation-treated carbon. 5. The method according to any one of claims 1 to 4,
Wherein at least 80% of the surface of the electrode active material particles is in contact with the conductive carbon on the paste. 6. The method according to any one of claims 1 to 5,
Wherein the electrode active material particles are fine particles having an average particle diameter of 0.01 to 2 탆 which can operate as a positive electrode active material or a negative electrode active material and coarse particles having an average particle diameter of greater than 2 탆 and not greater than 25 탆, The electrode is composed of particles. 7. The method according to any one of claims 1 to 6,
Wherein the active material layer further comprises another conductive carbon, and the surface of the conductive carbon is covered with the conductive carbon on the paste. 8. The method according to any one of claims 1 to 7,
Wherein the mass ratio of the electrode active material particles to the conductive carbon in the active material layer is in the range of 95: 5 to 99: 1. 9. A method of manufacturing an electrode according to any one of claims 1 to 8,
At least a part of the oxidation-treated carbon is changed into a paste by mixing the carbon raw material having the electrode active material particles and the gap with the oxidized carbon subjected to the oxidation treatment to prepare an electrode material adhered to the surface of the electrode active material particle , And
And a pressing step of forming an active material layer on the current collector by the electrode material and applying pressure to the active material layer. 10. The method of claim 9,
Wherein the electrode material further comprises another conductive carbon,
In the preparation step,
At least a part of the oxidation-treated carbon is changed into a paste by dry-mixing the oxidation-treated carbon and the other conductive carbon to obtain a conductive carbon mixture attached to the surface of the other conductive carbon; and
And adhering the oxidized carbon, which has been at least partially changed into a paste, to the surface of the electrode active material particles by dry mixing or wet mixing the conductive carbon mixture with the electrode active material particles. 1. A conductive carbon mixture for the production of an electrode of a power storage device,
At least a part of which is a paste-like conductive carbon derived from oxidation-treated carbon obtained by oxidizing a carbon raw material having a void,
Wherein at least a portion of the electrically conductive carbon is pasted on the surface of the other electrically conductive carbon. An electrical storage device comprising the electrode according to any one of claims 1 to 8.

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