JP5924925B2 - Positive electrode for secondary battery and secondary battery - Google Patents

Description

  The present invention relates to a positive electrode for a secondary battery and a secondary battery.

  For example, as disclosed in Patent Documents 1 to 9, lithium ion secondary batteries are known. In recent years, a high-capacity lithium ion secondary battery has been demanded, and as a method for increasing the capacity of the lithium ion secondary battery, it has been proposed to increase the thickness of the electrode. By increasing the thickness of the electrode, the volume of the active material in the lithium ion secondary battery can be increased, while the volume of the separator or current collector, that is, the portion not contributing to the reaction in the lithium ion secondary battery is reduced. Therefore, the capacity of the lithium ion secondary battery can be increased.

Japanese Patent Laid-Open No. 11-283629 Japanese Patent No. 2513418 JP 2011-108522 A JP 2004-356078 A JP 2011-108522 A JP 2009-176721 A JP 2009-176720 A JP 2008-270204 A JP 2007-48692 A

  However, as the electrode becomes thicker, the reaction area per unit volume of the electrode (the area of the part in contact with the electrolyte layer) decreases, so that the current density increases even if the rate (C value) during charge and discharge is the same. End up. For this reason, the technology for increasing the thickness of the electrode has a problem in that battery characteristics, particularly high rate discharge characteristics and cycle characteristics are deteriorated. In other words, the capacity of the lithium ion secondary battery could not be increased by simply increasing the thickness of the electrode.

  On the other hand, in the lithium ion secondary batteries disclosed in Patent Documents 1 to 9, a technique of using carbon nanotubes as a positive electrode conductor is disclosed. Thereby, since the electroconductivity between positive electrode active materials improves, a battery characteristic improves. However, this technique alone cannot sufficiently compensate for the deterioration in battery characteristics associated with the thickening of the electrodes.

  The present invention has been made in view of the above problems, and an object of the present invention is for a new and improved secondary battery capable of producing a secondary battery having a higher capacity. The object is to provide a positive electrode and a secondary battery.

  In order to solve the above problems, according to an aspect of the present invention, a composite positive electrode active material including a positive electrode active material, a first fibrous carbon composited on the surface of the positive electrode active material, and a second fiber The mass% of the first fibrous carbon with respect to the mass of the composite positive electrode active material is 0.3 to 2.0 mass%, and includes the first fibrous carbon and the carbon black. The mass% with respect to the total mass of the fibrous carbon and the second fibrous carbon is 20 to 80 mass%, and the mass% with respect to the total mass of the second fibrous carbon and carbon black of the carbon black is 10 to 60 mass%. A positive electrode for a secondary battery is provided.

  According to this aspect, the positive electrode for a secondary battery includes a composite positive electrode active material including a positive electrode active material and a first fibrous carbon composited on the surface of the positive electrode active material, a second fibrous carbon, Carbon black is included, and the ratio of each carbon material is limited to the above range. For this reason, since a strong electroconductive network is formed in the positive electrode for secondary batteries, the quantity of binder required for preparation of the positive electrode for secondary batteries can be reduced significantly. Therefore, high rate discharge characteristics and cycle characteristics are greatly improved. Furthermore, even if the thickness of the positive electrode for a secondary battery is increased, the amount of the binder accompanying the increase in thickness can be significantly reduced, so that fluctuations in high-rate discharge characteristics and cycle characteristics can be kept low.

  Here, the positive electrode active material may be a lithium transition metal oxide.

  According to this viewpoint, a higher capacity can be obtained.

  Further, the first fibrous carbon and the second fibrous carbon are any one selected from the group consisting of vapor grown carbon fiber, carbon nanotube, carbon nanofiber, and a composite of these and carbon black. It may be.

  According to this viewpoint, the conductive network becomes stronger.

  The average fiber diameter of the first fibrous carbon and the second fibrous carbon may be 10 to 150 nm, and the average fiber diameter may be 5 to 30 μm.

  According to this viewpoint, the conductive network becomes stronger.

  Carbon black may consist of any one selected from the group consisting of ketjen black and acetylene black.

  According to this viewpoint, the conductive network becomes stronger.

  Moreover, according to the other viewpoint of this invention, a secondary battery characterized by providing said positive electrode for secondary batteries is provided.

  According to this aspect, since the secondary battery includes the above-described positive electrode for secondary battery, battery characteristics, particularly high rate discharge characteristics and cycle characteristics are improved.

  As described above, according to the present invention, since the amount of the binder accompanying the thickening can be greatly reduced, fluctuations in high-rate discharge characteristics and cycle characteristics can be suppressed to a low level. Therefore, the present invention can produce a secondary battery having a higher capacity.

It is sectional drawing which shows the structure of the lithium ion secondary battery which concerns on embodiment of this invention. It is explanatory drawing which shows the outline | summary of the electroconductive network formed with a positive electrode.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<1. Configuration of lithium ion secondary battery>
First, based on FIG.1 and FIG.2, the structure of the lithium ion secondary battery 1 which concerns on this embodiment is demonstrated. The lithium ion secondary battery 1 includes a positive electrode current collector 2, a positive electrode 3, an electrolyte layer 4, a negative electrode 5, and a negative electrode current collector 6.

  The positive electrode current collector 2 is not particularly limited, and is composed of, for example, an aluminum foil. The positive electrode 3 binds the positive electrode active material, the composite positive electrode active material containing the first fibrous carbon compounded on the surface of the positive electrode active material, the second fibrous carbon, and carbon black. And a binder. The second fibrous carbon and carbon black serve as a conductive material for the positive electrode 3. The positive electrode active material is not particularly limited as long as it can reversibly store and release lithium, but is preferably a lithium transition metal oxide. When the positive electrode active material is composed of a lithium transition metal oxide, a higher capacity can be obtained.

Examples of the lithium transition metal oxide include Li · Co based composite oxides such as LiCoO ₂ , Li · Ni · Co · Mn based composite oxides such as LiNi _x Co _y Mn _z O ₂ , and Li · Co such as LiNiO _2. Ni-based composite oxides, LiMn-based composite oxides such as LiMn ₂ O ₄ and the like are conceivable. The positive electrode active material can be used alone or in combination. The positive electrode active material may be a material obtained by subjecting each of the above materials to surface treatment in order to suppress side reactions with the electrolytic solution at high voltage. The average agglomerated particle size of the positive electrode active material particles is preferably 10 to 30 μm from the viewpoints of safety and fillability of the positive electrode active material.

  The first fibrous carbon is any one selected from the group consisting of vapor grown carbon fiber, carbon nanotube, carbon nanofiber, and a composite of these and carbon black. Of these substances, fibrous carbon obtained by combining carbon nanotubes and carbon black is suitable for the first fibrous carbon because it is excellent in dispersibility, conductivity, and entanglement between fibers.

  The average fiber diameter of the first fibrous carbon is preferably 10 to 150 nm, and the average fiber length is preferably 5 to 30 μm. Here, the average fiber diameter is an arithmetic average value of the diameter (outer diameter) of the first fibrous carbon. The average fiber length is an arithmetic average value of the fiber lengths of the first fibrous carbon. The fiber diameter and fiber length of the fibrous carbon can be determined from, for example, an SEM image with a magnification of 2000 to 50000 taken with a field emission scanning electron microscope (JSM-7500F manufactured by JEOL). The same applies to the second fibrous carbon.

  When the average fiber diameter is less than 10 nm or when the average fiber length exceeds 30 μm, the dispersibility of the fibrous carbon at the time of producing the positive electrode is poor and it is difficult to exert a sufficient effect. Further, when the average fiber diameter exceeds 150 nm, or when the average fiber length is less than 5 μm, the conductivity is insufficient and the entanglement between the fibers is insufficient, so that a sufficient effect is hardly exhibited.

  A specific method for combining the positive electrode active material and the first fibrous carbon is not particularly limited, and a known method is arbitrarily applied. For example, the compounding is performed by a dry mechanochemical method. As a dry mechanochemical method, for example, a method of uniformly applying an impact force, a shearing force, and a compressive force to individual particles of a raw material mixed powder can be considered. Compounding by a dry mechanochemical method is performed by, for example, Nobilta (manufactured by Hosokawa Micron Corporation). The compounding may be performed by a wet method such as a spray coating method or a forced loading method.

  By such a composite, the first fibrous carbon is firmly bonded to the surface of the positive electrode active material. Therefore, higher conductivity can be obtained than when the first fibrous carbon and the positive electrode active material are simply mixed.

  The second fibrous carbon is the same as the first fibrous carbon. That is, the second fibrous carbon is any one selected from the group consisting of vapor grown carbon fiber, carbon nanotube, carbon nanofiber, and a composite of these and carbon black. Of these substances, fibrous carbon obtained by combining carbon nanotubes and carbon black is suitable for the second fibrous carbon because it is excellent in dispersibility, conductivity, and entanglement between fibers. The compounding may be performed by the same method as the compounded positive electrode active material described later.

  The average fiber diameter of the second fibrous carbon is preferably 10 to 150 nm and the average fiber length is preferably 5 to 30 μm. The carbon black is composed of any one selected from the group consisting of ketjen black and acetylene black.

  The mass% of each carbon material in the positive electrode 3 is set as follows. That is, the mass% with respect to the mass of the composite cathode active material of the first fibrous carbon is 0.3 to 2.0 mass%. The mass% of the second fibrous carbon with respect to the total mass of the first fibrous carbon and the second fibrous carbon is 20 to 80 mass%. The mass% with respect to the total mass of the conductive material of carbon black (that is, the second fibrous carbon and carbon black) is 10 to 60 mass%.

  FIG. 2A is an explanatory diagram showing the positive electrode 3 in an enlarged manner. FIGS. 2B and 2C are explanatory views showing the areas A and B in FIG. 2A in an enlarged manner, respectively. As shown in FIGS. 2A to 2C, when the mass% of each carbon material in the positive electrode 3 has the above value, the composite positive electrode active material 100, the second fibrous carbon 110, and carbon black 120 can form a conductive network by being strongly entangled with each other. For example, the conductive network is formed between the positive electrode active materials 101 and between the positive electrode active material 101 and the positive electrode current collector 2. The composite positive electrode active material 100 includes a positive electrode active material 101 and a first fibrous carbon 102. This conductive network is firmly held even when the lithium ion secondary battery 1 is repeatedly charged and discharged. Therefore, the amount of the binder in the positive electrode 3 can be greatly reduced.

  A binder is not specifically limited, A well-known structure is applied arbitrarily. For example, the binder may include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), styrene butadiene rubber (SBR), and the like, modified products and derivatives thereof, and co-polymers including acrylonitrile. A polymer, a polyacrylic acid derivative, or the like can be used.

  The electrolyte layer 4, the negative electrode 5, and the negative electrode current collector 6 are not particularly limited, and known configurations are arbitrarily applied. For example, the electrolyte layer 4 includes a solvent and an electrolyte. The solvent may be any solvent that can dissolve the lithium salt, but an organic solvent having a large aprotic dielectric constant is particularly preferable. The electrolyte layer 4 may include a separator.

  Examples of such an organic solvent include 4-fluoro-1,3-dioxolan-2-one, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, γ-valerolactone, methyl acetate, methyl propionate, ethyl propionate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropironitrile, succinonitrile, trimethyl phosphate, triethyl phosphate, ethylene sulfide, etc. Can be mentioned. These solvents can be used alone or in an appropriate mixture.

As the electrolyte, lithium salts that generate stable anions, for example, lithium perchlorate, lithium borofluoride, lithium hexachloroantimonate, lithium hexafluorophosphate (LiPF ₆ ), and the like are suitable. The separator is composed of a synthetic fiber or glass fiber nonwoven fabric, a woven fabric, a polyolefin-based porous membrane, a polytetrafluoroethylene nonwoven fabric, or the like.

The negative electrode 5 includes a negative electrode active material and a binder. The negative electrode active material is not particularly limited as long as it can reversibly store and release lithium, and a known configuration is arbitrarily applied. For example, as the negative electrode active material, carbon materials such as natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fiber (MCF), cokes, glassy carbon, organic compound fired bodies, lithium such as Al, Si, Sn, etc. A metal that can be combined with Si, a compound of Sn, a compound of Sn, Li ₄ Ti ₅ O ₁₂ , and the like. Examples of the Si compound or the Sn compound include Si oxide and Sn oxide. In addition to Si or Sn, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, and bismuth. In addition, constituent elements such as antimony and chromium may be included. The compound of Si and the compound of Sn may be combined with carbon or the like.

  As the binder, the same binder as that of the positive electrode 2 can be used. The negative electrode current collector 6 is made of, for example, copper, nickel, stainless steel, or the like.

<2. Manufacturing method of lithium ion secondary battery>
The manufacturing method of the lithium ion secondary battery 1 is not specifically limited, A well-known method is arbitrarily applied. For example, the positive electrode 3 and the negative electrode 5 are manufactured by preparing a slurry containing the material of each electrode, applying the slurry onto a current collector, drying the slurry, and rolling the dried laminate. The electrolyte layer 4 is produced by impregnating a separator with an electrolytic solution.

<3. Examples and Comparative Examples>
Next, examples of the present embodiment and comparative examples will be described. The lithium ion secondary battery which concerns on Examples 1-11 and Comparative Examples 1-9 was manufactured by changing the kind and mass of each material which comprise a lithium ion secondary battery, and performing each following process.

(Preparation of positive electrode)
A composite positive electrode active material is obtained by dry-compositing Li · Co-based composite oxide (LiCoO ₂ ) having an average particle size of 16 μm and first fibrous carbon with Nobilta NOB-130 (manufactured by Hosokawa Micron Corporation). It was. The load power at this time was 1.5 kW, and the compounding process was performed for 10 minutes. Here, the average particle size of the lithium cobalt composite oxide is a value obtained by arithmetically averaging the particle size (diameter) when each particle is regarded as a sphere, that is, a so-called sphere equivalent diameter. The average particle size was measured by a laser diffraction / scattering particle size analyzer MT3000 (manufactured by Microtrac).

  The obtained composite positive electrode active material, second fibrous carbon and ketjen black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are mixed at a predetermined ratio, and further a solvent. A slurry was prepared by adding an appropriate amount of N-methylpyrrolidone (NMP) solution and mixing. In addition, the binder was mixed in the range of 0.3 to 2.0 mass% with respect to the total weight of the mixture excluding NMP.

Next, the prepared slurry was applied to one surface of a 15 μm-thick positive electrode current collector made of an aluminum foil by a doctor blade method so that the coating mass after drying was 40 mg / cm ² . Then, NMP was volatilized by making it dry in the thermostat kept at 80 degreeC, exhausting NMP vapor | steam. The dried sheet was rolled to a thickness of 125 μm using a roll press and further vacuum dried at 100 ° C. to obtain a positive electrode.

(Preparation of negative electrode)
Mass ratio of negative electrode active material, binder and thickener to graphite as negative electrode active material, styrene butadiene rubber (SBR) as binder and carboxymethylcellulose (CMC) aqueous solution as thickener Was prepared to be 98: 1: 1. Next, a negative electrode slurry was prepared by kneading them.

Next, this negative electrode slurry is applied to one side of a negative electrode current collector made of copper foil and having a thickness of 10 μm so that the applied mass after drying is 19 mg / cm ^2, and is dried in a constant temperature bath maintained at 80 ° C. As a result, water was volatilized. The dried sheet was rolled to a thickness of 119 μm using a roll press, and further vacuum dried at 100 ° C. to obtain a negative electrode.

(Preparation of electrolyte)
A LiPF ₆ solution was prepared by dissolving LiPF ₆ at 1 mol / liter in a solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 3: 7. Subsequently, 1 part by weight of vinylene carbonate was mixed with 100 parts by weight of the LiPF ₆ solution to prepare an electrolytic solution.

(Production of battery)
The positive electrode and the negative electrode produced by the above method were cut into a predetermined size, and a current collecting tab was attached to a metal foil as a current collector. Next, a separator having a thickness of 25 μm made of a polyolefin microporous film (ND525 (manufactured by Asahi Kasei E-Materials Co., Ltd.)) was sandwiched between the positive electrode and the negative electrode to obtain a flat electrode body. This flat electrode body is inserted into a laminate container composed of a laminate of PET (polyethylene terephthalate) and aluminum, and after the current collecting tab protrudes outside from the opening, the sealing portion of the exterior body Was sealed. Next, the electrolyte solution was injected from the opening of the exterior body, and then the opening was sealed to prepare a battery.

  The battery produced as described above was charged at a constant current and a constant voltage with an upper limit voltage of 4.35 V and 0.2 C under a room temperature environment, followed by 5 cycles of a 0.2 C constant current discharge up to a lower limit voltage of 3.0 V. Was fully activated and subjected to each evaluation.

(Discharge capacity measurement)
After performing constant current / constant voltage charging at 0.5 C to an upper limit voltage of 4.35 V in a room temperature environment, 0.2 C discharge capacity was measured by performing 0.2 C constant current discharge to a lower limit voltage of 3.0 V. Next, 0.5 C constant current constant voltage charging was performed up to the upper limit voltage of 4.35 V, and then 1 C constant current discharging was performed up to the lower limit voltage of 3.0 V, thereby measuring the 1 C discharge capacity.

(Measurement of cycle characteristics)
Perform 300 cycles of constant current and constant voltage charge with upper limit voltage of 4.35V and 0.5C under room temperature environment and 1C constant current discharge to lower limit voltage of 3.0V and maintain discharge capacity at 300th cycle relative to discharge capacity at 1st cycle The rate was determined as cycle characteristics.

(Evaluation of the amount of binder necessary for holding the positive electrode sheet)
The amount of binder necessary to hold the positive electrode on the positive electrode current collector was derived by measuring 180 ° peel strength between the obtained positive electrode and the positive electrode current collector. The peel strength measurement was performed as follows.

(Positive electrode peel strength measurement)
An adhesive tape was applied to the positive electrode side, and a 180 ° peel test was conducted. The peel speed was 100 mm / min. The same test was performed twice, and the arithmetic average value of the obtained values was taken as the measured value.

  Table 1 shows the type, mass%, and measurement results of the carbon material for each example and comparative example.

In Table 1, VGCF is a graphitized vapor-grown carbon fiber having an average fiber diameter of 150 nm and an average fiber length of 15 μm. CNT-A is a specific surface area of carbon nanotubes and acetylene black having an average fiber diameter of 60 nm and an average fiber length of 7 μm. Is mechanochemically compounded so as to be 70 m ² / g. Here, the specific surface area was measured by NOVA4200e (manufactured by Quantachrome). CNT-B is a carbon nanotube having an average fiber diameter of 11 nm and an average fiber length of 10 μm. The binder amount, 0.2C discharge capacity, and 1C discharge capacity necessary for holding the positive electrode sheet are all relative values with the value of Comparative Example 1 being 100.

  As shown in Table 1, in Examples 1 to 11, the high rate discharge characteristics (1C discharge capacity) and the cycle characteristics are particularly improved as compared with Comparative Examples 1 to 9. The following can be considered as this reason.

  That is, in Examples 1-11, since the ratio of each carbon material is limited to the said range, the 1st fibrous carbon in a composite positive electrode active material and a 2nd fibrous carbon are intertwined intricately. As a result, a strong conductive network is formed. That is, the first fibrous carbon and the second fibrous carbon exhibit a binder-like function.

  On the other hand, in Comparative Examples 1 to 9, the fibrous carbon is simply mixed, only the active material obtained by compounding the fibrous carbon is used, or the amount of each fibrous carbon and carbon black is within the specified range. Since it is outside, the conductive network is not formed, or the bonding force in the conductive network is weaker than those in Examples 1 to 11. Therefore, in Examples 1-11, since the quantity of a binder is reduced significantly, it is thought that a high rate discharge characteristic and cycling characteristics improve.

  As described above, the positive electrode 3 of the present embodiment includes the positive electrode active material, the composite positive electrode active material containing the first fibrous carbon composited on the surface of the positive electrode active material, the second fibrous carbon, and the carbon black. The ratio of each carbon material is limited to the above range. For this reason, since a strong conductive network is formed in the positive electrode, the amount of the binder necessary for producing the positive electrode can be greatly reduced. Therefore, high rate discharge characteristics and cycle characteristics are greatly improved. Furthermore, even if the positive electrode 3 is made thicker, the amount of the binder accompanying the thickening can be greatly reduced, so that fluctuations in high-rate discharge characteristics and cycle characteristics can be kept low. Therefore, this embodiment can produce a secondary battery with a higher capacity.

  Further, the first fibrous carbon and the second fibrous carbon are any one selected from the group consisting of vapor-grown carbon fibers, carbon nanotubes, carbon nanofibers, and composites of these with carbon black. Therefore, the conductive network becomes stronger.

  Furthermore, since the average fiber diameter of the first fibrous carbon and the second fibrous carbon is 10 to 150 nm and the average fiber diameter is 5 to 30 μm, the conductive network becomes stronger.

  Furthermore, since carbon black consists of any one selected from the group consisting of ketjen black and acetylene black, the conductive network becomes stronger.

  Furthermore, since the lithium ion secondary battery 1 includes the positive electrode 3, it has excellent high rate discharge characteristics and cycle characteristics.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

For example, the present invention also applies to a circular, elliptical, or polygonal secondary battery having a winding structure, or a secondary battery having other shapes such as folding and stacking a plurality of positive and negative electrodes. Can be applied to. In addition, the present invention can be similarly applied to secondary batteries having other shapes such as a coin shape, a button shape, a square shape, or a laminate film shape.
Moreover, although the case where electrolyte solution was used as an electrolyte was demonstrated in the said embodiment and Example, you may make it use the gel electrolyte which hold | maintained electrolyte solution to holding bodies, such as a polymer compound. Examples of such a polymer compound include polyacrylonitrile, polyvinylidene fluoride, copolymers of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, and polyphosphazene. , Polysiloxane, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene or polycarbonate. In particular, polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene, or polyethylene oxide is preferable from the viewpoint of electrochemical stability.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 2 Positive electrode collector 3 Positive electrode 4 Electrolyte layer 5 Negative electrode 6 Negative electrode collector

Claims (6)

A composite positive electrode active material including a positive electrode active material and a first fibrous carbon composited on the surface of the positive electrode active material; a second fibrous carbon; and carbon black.
The mass% of the first fibrous carbon with respect to the mass of the composite positive electrode active material is 0.3 to 2.0 mass%,
The mass% of the second fibrous carbon with respect to the total mass of the first fibrous carbon and the second fibrous carbon is 20 to 80 mass%,
The positive electrode for a secondary battery, wherein a mass% of the carbon black with respect to a total mass of the second fibrous carbon and the carbon black is 10 to 60 mass%.   The positive electrode for a secondary battery according to claim 1, wherein the positive electrode active material is a lithium transition metal oxide.   The first fibrous carbon and the second fibrous carbon may be any one selected from the group consisting of vapor grown carbon fiber, carbon nanotube, carbon nanofiber, and a composite of these and carbon black. The positive electrode for a secondary battery according to claim 1, wherein the positive electrode is for a secondary battery. The average fiber diameter of said 1st fibrous carbon and 2nd fibrous carbon is 10-150 nm, and average fiber length is 5-30 micrometers, The any one of Claims 1-3 characterized by the above-mentioned. A positive electrode for a secondary battery as described in 1.   5. The positive electrode for a secondary battery according to claim 1, wherein the carbon black is one selected from the group consisting of ketjen black and acetylene black.   A secondary battery comprising the positive electrode for a secondary battery according to claim 1.

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