JP2000058040A - Positive electrode material for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode material that can provide a secondary battery, having both superior power density and energy density, in a lithium secondary battery whose positive electrode active material is a spinel structured lithium manganese composite oxide. SOLUTION: A positive electrode material of a lithium secondary battery is constituted, by mixing a complex formed by adhering a first conductive material made of carbon material whose specific surface area is not less than 1,000 m2/g to the surface of spinel structured composite oxide containing lithium and manganese with a second conductive material made of carbon material whose specific surface area is larger than 200 m2/g. This ensures satisfactory electron conductivity of positive electrode and the permeability of lithium ions to improve both the characteristics of power density and energy density.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material used for a positive electrode of a lithium secondary battery utilizing occlusion and release of lithium ions, and more specifically, lithium capable of achieving a lithium secondary battery having high power density and high energy density. The present invention relates to a positive electrode material for a secondary battery.

[0002]

2. Description of the Related Art Since lithium secondary batteries have a high energy density, they have been put into practical use and widely used in the fields of information-related equipment and communication equipment with miniaturization of personal computers and mobile phones. In the positive electrode of this lithium ion secondary battery, a composite oxide of lithium and a transition metal such as cobalt, nickel, manganese, and vanadium has been proposed as an active material capable of storing and releasing lithium ions. For reasons such as easy handling, LiCo
The use of O ₂ has become mainstream.

[0003] However, since cobalt is a small resource and expensive, the use of LiCoO ₂ as a positive electrode active material poses a major problem in the future when lithium secondary batteries are used in applications such as electric vehicles and power storage. is there. Therefore, instead of these, use of a lithium manganese composite oxide made of manganese as a raw material, which is abundant in resources and relatively inexpensive, has been studied as a positive electrode active material. Above all, lithium manganese composite oxides having a spinel structure have attracted particular attention because of their high discharge voltage.

In general, a lithium transition metal composite oxide is
The electron conductivity is not sufficient as a material for constituting an electrode of a battery. In particular, the lithium manganese composite oxide having a spinel structure has an electron conductivity about two orders of magnitude lower than that of a positive electrode active material containing cobalt as a main component. To improve the rate,
It is necessary to ensure sufficient electron conductivity of the positive electrode.

Conventionally, in order to ensure the electron conductivity of the positive electrode, a technique of mixing and adding a carbon powder to the positive electrode as a conductive material as disclosed in Japanese Patent Application Laid-Open No. 8-83607, and Japanese Patent Application Laid-Open No. 8-78054. As shown in (1), a technique of mixing and adding a metal powder as a conductive material to a positive electrode has been considered. However, these are merely mixing and adding the conductive material powder to the active material powder. When the electron conductivity of the positive electrode using the spinel structure lithium manganese composite oxide as the positive electrode active material is ensured by such a method, it is effective in terms of improving the power density of the battery due to a decrease in the internal resistance, but it is effective to use the conductive material. Since the amount of addition must be increased, the density of the positive electrode cannot be increased, causing a problem that the energy density of the battery decreases.

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 9-92265, there has been proposed a method of ensuring the electron conductivity of a positive electrode by coating the surface of a positive electrode active material with a carbon material. This method can keep the positive electrode density high and is effective in improving the energy density of the battery.However, when the amount of the conductive material is increased, the film becomes thicker, the lithium ion conductivity is reduced, and the internal resistance is increased. Thus, there is a problem that the power density of the battery decreases.

[0007]

SUMMARY OF THE INVENTION The present invention solves the problems of the above-mentioned conventional method of mixing and adding a conductive material, and the positive electrode active material is lithium, which is a composite oxide containing lithium and manganese having a spinel structure. In a secondary battery, a positive electrode material capable of obtaining a secondary battery excellent in both power density and energy density by appropriately setting a type of a carbon material to be a conductive material and an arrangement relationship in a positive electrode is provided. What you want to do.

[0008]

SUMMARY OF THE INVENTION The inventor of the present invention has made it necessary to improve the geometrical relationship between the active material and the conductive material in the positive electrode in order to achieve both the power density and the energy density of the lithium secondary battery. Focusing on the fact that it is effective to improve the ion permeability of the carbon material used as the conductive material, the inventors of the present invention have come to the following invention after intensive studies.

According to the present invention, there is provided a positive electrode material for a lithium secondary battery, wherein a first conductive material made of a carbon material having a specific surface area of 1000 m ² / g or more is coated on the surface of a composite oxide containing lithium and manganese having a spinel structure. And a second conductive material made of a carbon material having a specific surface area of more than 200 m ² / g.

That is, in the present invention, the electron conductivity of the positive electrode is ensured by using two types of conductive materials having different functions. First
The carbon material serving as the conductive material is a composite oxide containing lithium and manganese having a spinel structure as an active material (hereinafter, referred to as a composite oxide).
(Spinel structure lithium manganese composite oxide) or simply "lithium manganese composite oxide") to form a coating on the particle surface to ensure the static electron conductivity of the positive electrode, The second conductive material is the first conductive material.
It exists so as to bridge between the active material particles to which the conductive material is attached, and secures dynamic electron conductivity such as to respond to a volume change of the positive electrode due to occlusion and release of lithium ions.

Further, in the present invention, the carbon material used as the two kinds of conductive materials is made of a carbon material having a large specific surface area, that is, a porous material, so that not only the electron conductivity of the positive electrode but also the permeability of lithium ions can be improved. Is also to secure. Due to the action of these two types of positive electrode conductive materials, a lithium secondary battery using the present positive electrode material has a power density and energy despite the use of a lithium manganese composite oxide having low electron conductivity as a positive electrode active material. It becomes a lithium secondary battery excellent in both properties such as density.

The specific surface area of the carbon material is measured and calculated by the BET one-point method, which is a measuring method based on the BET adsorption isotherm. Therefore, in the present specification, the specific surface area of the carbon material is defined by the BE unless otherwise specified.
The value is measured and calculated by the T1 point method.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments. The description will be made with respect to a spinel structure lithium manganese composite oxide, a first conductive material, and a second conductive material, which are positive electrode active materials constituting the positive electrode material of the present invention,
Next, a positive electrode is manufactured using the present positive electrode material, and a configuration of a lithium secondary battery using the positive electrode is performed.

<Lithium-manganese composite oxide> In the positive electrode material of the present invention, a composite oxide containing lithium and manganese having a spinel structure is used as a positive electrode active material. Since manganese, which is abundant in resources and relatively inexpensive, is used as a main component and can form a 4V-class lithium secondary battery, it is suitable for secondary batteries for electric vehicles, power storage, and the like. It can be a material.

The lithium manganese composite oxide having a spinel structure is generally represented by the composition formula LiMn ₂ O ₄ , which can be used. However, since the crystal structure is unstable and the cycle characteristics are somewhat difficult, in order to stabilize the crystal structure, a composition formula of Li _{1 + x} Mn _2-x O _{4 in} which manganese is partially substituted by lithium is used. What is done can also be used. However, if the substitution amount x is too large, Mn ³⁺ decreases to maintain electrical neutrality and the battery capacity decreases too much. Therefore, it is preferable to set 0 <x ≦ 0.2. Note that the partial substitution element of manganese is not limited to lithium, but may be Mg, B, Al, Ga, P, Ti, V, C
Substitution can be carried out by one or more of r, Fe, Co, Ni, Cu, or the like, or by lithium and these elements.

The lithium manganese composite oxide uses a powder of fine particles in view of the function as a positive electrode active material of absorbing and releasing lithium ions. The particle size is 0.
It is desirable to be in the range of 5 μm to 20 μm, and it is desirable that the particle size distribution is narrow in order to form a uniform coating of the first conductive material. A conventional method can be used for synthesizing the lithium manganese composite oxide. For example,
Solid-phase reaction method using raw material powder whose particle size distribution is regulated in advance,
A liquid phase method or the like in which the raw materials are once mixed as an aqueous solution and then nucleation and grain growth are performed by appropriate heat treatment can be used.
In the liquid phase method, a method using a citrate complex, which will be described in detail in Examples below, a spray combustion method in which a raw material aqueous solution is emulsified in a combustible liquid and spray combustion is performed, and the like can be used.
Further, the synthesized powder may be pulverized or classified as necessary. The solid phase reaction method is superior in productivity, but the liquid phase method is superior in homogeneity of powder particles.

<First Conductive Material> The first conductive material is applied so as to form a film on the surface of the lithium manganese composite oxide particles, and forms a composite with the composite oxide particles. Fine powder of a carbon material is used as the first conductive material. Examples of the carbon material include graphite, carbon black, and acetylene black. In general, any material having electrical conductivity can be used. In the present invention, the material having a specific surface area of 1000 m ² / g or more is used. Is used.
The reason for using a carbon material having a large specific surface area is that the coating formed on the surface of the composite oxide is porous, so that lithium ion permeability is improved, and the energy density of the formed battery can be increased. Because you can.

The carbon material that can be used as the first conductive material is a kind of carbon black, which is obtained by continuously thermally decomposing gaseous or liquid raw materials such as heavy oil and tar in a furnace. Furnace black obtained by the method described above. More specifically, commercially available Ketjen Black (made by Lion: specific surface area 12
00 m ² / g). Since the particle size of the carbon material affects the thickness of the formed film,
As the conductive material, a fine powdery carbon material having a particle diameter of 0.01 μm to 0.1 μm is preferably used.

The attachment of the carbon material as the first conductive material to the surface of the lithium composite oxide is performed by mixing the carbon material powder and the composite oxide powder using a particle composite apparatus subjected to compressive shear stress. This particle compounding device is composed of a rotating drum having a cylindrical inner surface, a fixed arm extending from the central axis of the rotating drum toward the inner peripheral surface of the drum, and a pressure shearing head provided at the tip of the arm.
Both powders are mixed in a rotating drum, and by rotating the rotating drum, compressive shear stress is applied between the inner peripheral surface of the rotating drum and the pressing shear head to cause the carbon material particles to adhere to the surfaces of the composite oxide particles. , To form a complex.

The thickness of the film formed by the first conductive material is limited to 0.2 μm or less, since too large a thickness impairs the conduction of lithium ions to the lithium-manganese composite oxide as an active material. Is preferred. Also from this point of view, the mixing ratio of the lithium manganese composite oxide and the first conductive material constituting the composite is important, and in order to improve both the electronic conductivity and the lithium ion conductivity, the composite is required. (Total of the composite oxide and the first conductive material) is 10
When the content is 0 wt%, the ratio of the first conductive material is 1.5 to 5 w
It is desirable to configure the composite so as to be t%.

Incidentally, Ketjen Black (specific surface area 1)
FIG. 1 shows the data of the electrical resistivity of the composite powder at the compounding ratio when 200 m ² / g) was used as the first conductive material.
FIG. 1 also shows, for comparison, data when furnace black having a specific surface area of 215 m ² / g was used as the first conductive material. The DC electrical resistivity of the composite powder is
2cm diameter powder mixture 1g at a pressure of 280 kg / cm ²
It was calculated from the DC resistance value when compression-pressed into a disk shape of φ and the measured value of the disk thickness. The DC resistance was measured with a digital multimeter (Advantest: TR6846).

From the data shown in FIG. 1, it was confirmed that when the amount of the first conductive material was less than 1.5 wt%, the DC electrical resistivity of the powder significantly increased. At the same blending ratio of the first conductive material, the furnace powder having a specific surface area of 215 m ² / g is more preferable for the composite powder including Ketjen black having a large specific surface area of 1200 m ² / g as the first conductive material. From composite powder composed using black,
It was also confirmed that the electric resistivity was small.

<Second Conductive Material> The second conductive material is present in the gap between the composite particles in the positive electrode, and ensures a good electron conductivity of the positive electrode, and a lithium-manganese composite oxide. It functions to prevent a decrease in electron conductivity due to a volume change of the positive electrode due to occlusion / release of ions. This second conductive material, like the first conductive material,
Use fine powder of carbon material.

The carbon material includes graphite, carbon black, acetylene black and the like. In general, any material having conductivity can be used. In the present invention, the specific surface area is 200 m ² / g. Is to be used. The reason why a carbon material having a relatively large specific surface area is used is that, similarly to the first conductive material, the permeability of lithium ions in the positive electrode can be increased, and the use of a bulky material allows the second conductive material to be used. This is because the weight used of the material can be reduced, and the energy density of the battery can be improved. The specific surface area of the second conductive material may be as large as about 1300 m ² / g.
Examples of the carbon material that can be used as the second conductive material include furnace black of the same type as the first conductive material.

The second conductive material constitutes a positive electrode material by being mixed with the above-mentioned composite in which the first conductive material is adhered to the surface of the lithium manganese composite oxide. Since the electron conductivity of the positive electrode changes depending on the particle diameter of the carbon material powder serving as the second conductive material and the mixing ratio with the composite, the particle diameter and the mixing ratio with the composite become important. The particle size of the second conductive material is closely related to the particle size of the composite particles and depends on the particle size of the composite, but is 0.01 μm to 0.1 μm.
It is desirable to be within the range. Also, regarding the mixing ratio with the composite, considering that when the mixing ratio of the second conductive material is increased, the electron conductivity of the positive electrode is improved, the active material filling property is reduced and the energy density of the battery is reduced. When the entire positive electrode material (the total of the composite and the second conductive material) is 100 wt%, it is desirable to set the range of 3 wt% to 15 wt%.

Incidentally, the composite material in which the lithium manganese composite oxide and the first conductive material were mixed at a weight ratio of 97.5: 2.5 was used as the second conductive material as the specific surface area of 215 m ² /
g of furnace black (manufactured by Tokai Carbon: TB550)
FIG. 2 shows data on the electrical resistivity of the positive electrode material powder at various mixing ratios when 0) was mixed. FIG. 2 shows a graphite powder having a specific surface area of 34 m ² / g for comparison.
Data for a conductive material is also shown. The DC electrical resistivity of the positive electrode material powder was measured by the same method as the electrical resistance measurement of the composite powder.

From the data shown in FIG. 2, the amount of the second conductive material is 3
It was confirmed that when the content was less than wt%, the DC electrical resistivity of the positive electrode material powder was significantly increased. At the same mixing ratio, the positive electrode material powder using furnace black having a specific surface area of 215 m ² / g as the second conductive material has a specific surface area of 3
It was confirmed that the electrical resistivity was lower than that of the positive electrode material powder using 4 m ² / g of graphite powder as the second conductive material.

<Preparation of Positive Electrode Using This Positive Electrode Material> The positive electrode of a lithium secondary battery is generally prepared by mixing a conductive material and a binder with a positive electrode active material, adding an appropriate amount of a solvent, and kneading the mixture. A mixture is obtained, and this positive electrode mixture is applied to the surface of a current collector made of metal foil, and dried to produce a positive electrode mixture. Since the positive electrode active material and the conductive material are already mixed in the positive electrode material of the present invention, the preparation of the positive electrode may be started from the step of mixing the binder with the positive electrode material.

The binder to be mixed has a role of binding the composite of the lithium manganese composite oxide and the first conductive material and the second conductive material in the positive electrode. As the binder, a fluorinated resin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene can be used. When polyvinylidene fluoride is used as the binder, the mixing ratio is 100% of the total of the positive electrode material and the binder.
It is preferable that the content be 3 wt% to 7 wt% based on wt%.

The solvent added to the mixture of the present positive electrode material and the binder functions to uniformly disperse the composite particles and the second conductive material particles, and at the same time, reduces the viscosity of the obtained paste-like positive electrode mixture. Responsible for adjusting. As a solvent to be added, an organic solvent such as N-methyl-2-pyrrolidone can be used. The amount of addition can be set to an appropriate amount according to the application and drying conditions of the positive electrode mixture. Note that a metal foil such as aluminum can be used for the current collector to which the positive electrode mixture is applied.

In the paste-like positive electrode mixture, the composite particles, the second conductive material particles, and the binder need to be kneaded and dispersed sufficiently and uniformly in order to ensure good battery performance. . Therefore, the kneading and dispersing step is desirably performed using a stirrer having rotating blades, a ball mill, a medium stirring mill, or the like. The method of applying the positive electrode mixture to the current collector surface is not particularly limited, but it is preferable to use a coater-type coating machine that can continuously apply and dry the positive electrode mixture on the belt-shaped current collector. It is convenient. Since the positive electrode mixture has a relatively high viscosity, it is preferable to adopt a coating method such as a comma coat, a squeeze coat, and a lip coat in the coating section of the coating machine. Among them, application roll, backup roll,
The reverse comma roll system using three comma rolls is excellent in that a uniform coating thickness can be obtained and the viscosity can be easily changed. The coating thickness of the positive electrode mixture can be arbitrarily set in the range of 100 μm to 300 μm according to the use of the battery. In order to increase the density of the positive electrode after coating and drying the positive electrode mixture to form a positive electrode, pressing after drying is effective in increasing the energy density of the battery.

<Structure of Lithium Secondary Battery> A lithium secondary battery mainly includes a positive electrode and a negative electrode, a separator, and a non-aqueous electrolyte. Since the above-mentioned thing may be used for the positive electrode, other components except the positive electrode will be described here. In addition, about a component except a positive electrode, a well-known thing can be used in general, The following is an example and is not limited to this.

The negative electrode is composed of lithium metal, a lithium compound,
Although a lithium alloy or the like can be used, there is a problem that dendrite is precipitated due to repetition of charge and discharge. Therefore, it is preferable to use a carbon material as the negative electrode active material instead of these. When a carbon material is used as the negative electrode active material, the negative electrode is prepared by mixing a binder with the carbon material, adding an appropriate solvent as needed, and forming a paste-like negative electrode mixture into a metal foil like the positive electrode. It is formed by coating and drying on the surface of a current collector made of aluminum and then increasing the negative electrode density by pressing. As the carbon material, a fired organic compound such as graphite or phenol resin, or a powdered material such as coke can be used.

Similar to the positive electrode, a fluorine-containing resin such as polyvinylidene fluoride or the like can be used as a binder, and an organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent. Instead of these materials, Composite binder of one or more cellulose ether-based substances selected from the group of methylcellulose, carboxymethylcellulose and the like as a binder and a synthetic rubber-based latex adhesive such as styrene-butadiene rubber latex and carboxy-modified styrene-butadiene rubber latex And water can be used as a solvent.

The separator sandwiched between the positive electrode and the negative electrode separates the positive electrode from the negative electrode and holds the electrolyte, and a microporous membrane such as polyethylene or polypropylene can be used. The non-aqueous electrolyte is a solution in which an electrolyte is dissolved in an organic solvent.Examples of the organic solvent include aprotic organic solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, acetonitrile, and dimethoxyethane. , Tetrahydrofuran, dioxolan, methylene chloride, or a mixture of two or more thereof. Also, as the electrolyte to be dissolved,
LiI, LiClO ₄ , LiAsF ₆ , LiBF ₄ , Li
Lithium salts such as PF ₆ can be used.

The lithium secondary battery constituted as described above can have various shapes such as a cylindrical type, a stacked type, a coin type and the like. Regardless of the shape used, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body, and a current collecting lead extends from the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal that lead to the outside. Etc., and sealed in a battery case together with the non-aqueous electrolyte to complete it.

[0037]

EXAMPLE A lithium manganese composite oxide was prepared as an active material, and a specific surface area of 1200 m ² /
g Ketjen Black as a first conductive material,
A positive electrode material was prepared by mixing furnace black having a specific surface area of 215 m ² / g as the second conductive material, and a lithium secondary battery was actually manufactured using the positive electrode material. The lithium secondary battery of the embodiment was prepared by changing the mixing ratio of the first conductive material and the mixing ratio of the second conductive material in various ways, and the positive electrode material and the second conductive material without the first conductive material were mixed. Using a positive electrode material that has not been used as a lithium secondary battery of a comparative example, charge and discharge tests were performed on these secondary batteries, the power density and energy volume density of each were determined, and the positive electrode material of the present invention was obtained. The superiority of the lithium secondary battery used was confirmed. Hereinafter, configurations and manufacturing methods of the lithium secondary batteries of Examples and Comparative Examples, a charge / discharge test, and results thereof will be described.

EXAMPLE 1 1.5 wt% of a first conductive material was applied to the surface of a lithium manganese composite oxide as a positive electrode active material.
This is a lithium secondary battery using a positive electrode material in which a second conductive material is mixed with 5% by weight (when the positive electrode material is 100% by weight) to the attached composite (when the composite is 100% by weight).

First, a lithium manganese composite oxide having a spinel structure as a positive electrode active material was synthesized. The synthesis was performed by a liquid phase method using a citric acid complex. First, a 2.6M aqueous lithium acetate solution, a 1.3M aqueous manganese acetate solution, and a 1.6M aqueous citric acid solution were prepared, and the molar ratio of lithium ion, manganese ion, and citrate ion was 1.03: 1. .97: 1.83.
This mixed solution was heated to 200 ° C. under reduced pressure in a rotary evaporator to be dehydrated to obtain a precursor. Next, this precursor was placed in an alumina crucible and calcined at 400 ° C. for 4 hours in an air atmosphere. Heating rate is 100 ° C / H
r, the temperature drop rate was 100 ° C./Hr. This was crushed, press-formed, fired at 800 ° C. for 12 hours in an oxygen atmosphere, and crushed again to obtain a powdery lithium manganese composite oxide.

The particle size distribution of the produced lithium composite oxide was measured by a laser diffraction method.
It was confirmed that the powder had a narrow particle size distribution with a maximum particle size of 5 μm and a median particle size of 1 μm. The specific surface area is B
When the specific surface area was measured by the ET one-point method, it was 4 m ² /
g. Further, from observation with a scanning electron microscope (SEM), it was confirmed that the primary particles had little aggregation and did not form secondary particles.

A specific surface area of 1200 m ² / g as a first conductive material was formed on the particle surface of the lithium manganese composite oxide powder.
Ketchen Black (Lion: ECP600J
D: average particle size of 0.03 μm) to form a film. The formation of the film by this adhesion is performed with an inner diameter of 200 m.
The measurement was carried out using a particle composite apparatus (AM20-F, manufactured by Hosokawa Micron) having a rotating drum of m and an arm having a length of 70 mm in the axial direction and subjected to compressive shear stress. By mixing the composite oxide powder and Ketjen black in a rotating drum so that the weight ratio becomes 98.5: 1.5, and rotating the rotating drum at a rotation speed of 1800 rpm and a rotation time of 60 minutes, A powdery composite in which a coating of the first conductive material was formed on the surface of the active material was produced.

The resulting composite powder was mixed with furnace black having a specific surface area of 215 m ² / g (manufactured by Tokai Carbon: TB5500: average particle diameter 0.05 μm) as a second conductive material to obtain a positive electrode material of the present invention. Was. The mixing ratio of the furnace black was 5 wt% when the total of the composite and the furnace black was 100 wt%. Mixing is
This was performed for 5 minutes using a mixer (manufactured by Sanyo: SM-V32).

To the prepared positive electrode material, an N-methyl-2-pyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) was used as a binder at 3 wt% in terms of the amount of PVDF (the total of the positive electrode material and PVDF was 100 wt%). Case) In addition, the mixture was further kneaded in vacuum while adding NMP until an appropriate viscosity was obtained, to obtain a paste-like positive electrode mixture. Next, this positive electrode mixture was applied to both surfaces of a 20 μm-thick aluminum foil current collector with a coater and dried. Then, a roll press was performed to form the positive electrode mixture under pressure such that the layer of the positive electrode mixture had a thickness of 80 μm per side, thereby completing a positive electrode. The size of the positive electrode was 54 mm in width and 45 cm in length.

The negative electrode facing the positive electrode was prepared as follows. Spheroidal graphite (manufactured by Osaka Gas Chemicals: MCMB: average particle size 25 μm) was used as the negative electrode active material, and PVDF was used as a binder at a ratio of 5 wt% (when the total of the spherical graphite and PVDF was 100 wt%). The mixture was mixed, an appropriate amount of NMP was added, and the mixture was kneaded similarly to the positive electrode to obtain a paste-like negative electrode mixture. This negative electrode mixture was coated with a coater to a thickness of 10 μm.
Was coated on both sides of a copper foil current collector and dried. Then, perform roll pressing to make the layer of the negative electrode mixture 100 μm per side.
To form a negative electrode. The size of the negative electrode was 56 mm in width and 50 cm in length.

A thickness of 25 μm between the positive electrode and the negative electrode
Was sandwiched with a polyethylene separator (manufactured by Tonen Tarpis Co., Ltd.) and wound using a winding machine to form a roll-shaped electrode body. Then, this electrode body was made 18 mm in diameter and 65
mm, and inserted into a 18650 type battery can, and a non-aqueous electrolyte was injected to impregnate the electrodes and the separator. The non-aqueous electrolyte is prepared by mixing a solvent mixture of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 1 with L
The iPF ₆ was used dissolved at a concentration of 1M. Finally, the battery was sealed with a top cap to complete a lithium secondary battery. This lithium secondary battery was used as the secondary battery of Example 1.

Example 2 2.5 wt% of a first conductive material on the surface of a lithium manganese composite oxide as a positive electrode active material
This is a lithium secondary battery using a positive electrode material in which a second conductive material is mixed with 3% by weight (when the positive electrode material is set to 100% by weight) to the attached composite (when the composite is 100% by weight). Except for the mixing ratio of the first conductive material and the mixing ratio of the second conductive material, the materials used for manufacturing the battery, the manufacturing method, the configuration of the battery, and the like are the same as those of the secondary battery of Example 1.

Example 3 A second conductive material was attached to the surface of a lithium manganese composite oxide as a positive electrode active material by 3 wt% (assuming that the composite was 100 wt%).
3 wt% of conductive material (when the cathode material is 100 wt%)
This is a lithium secondary battery using a mixed positive electrode material.
Excluding the mixing ratio of the first conductive material and the mixing ratio of the second conductive material,
The materials used for manufacturing the battery, the manufacturing method, the configuration of the battery, and the like are the same as those of the secondary batteries of Embodiments 1 and 2.

<Comparative Example 1> No second conductive material was mixed
A positive electrode material was produced, and a positive electrode produced using the positive electrode material.
This is a lithium secondary battery constituted by using the above. Above implementation
As in the case of the example, the surface of the lithium manganese composite oxide
The specific surface area is 1200 m as the first conductive material. ^Two/ G
3% by weight of chain black (100% by weight of composite)
To form a composite,
A binder and solvent are added to the composite and kneaded to produce a positive electrode mixture.
The positive electrode mixture is applied to a current collector and dried to form a positive electrode.
Was prepared. Other materials and methods used to manufacture batteries
The method and the configuration of the battery are the same as those of the secondary battery of the above embodiment.
It is like.

<Comparative Example 2> A positive electrode material in which the first conductive material was not adhered to the surface of the lithium manganese composite oxide was prepared, and a lithium secondary battery constituted using a positive electrode prepared using this positive electrode material was used. is there. A specific surface area of 215 m ² / g as the second conductive material was added to the lithium manganese composite oxide powder.
Furnace black of 7 wt% (100% of cathode material)
(in the case of wt%) to prepare a positive electrode material. Then, a binder and a solvent were added to the positive electrode material and kneaded in the same manner as in the above example to prepare a positive electrode mixture. The positive electrode mixture was applied to a current collector and dried to prepare a positive electrode. The other materials used for manufacturing the battery, the manufacturing method, the configuration of the battery, and the like are the same as those of the secondary battery of the above embodiment.

<Charge / Discharge Test> A charge / discharge test was performed for each of the lithium secondary batteries of the above-mentioned Examples and Comparative Examples. In the charge / discharge test, the battery was charged at a constant current and a constant voltage of 486 mA to 4.2 V for 5 hours, and then was discharged at a constant current of 486 mA to 3.0 V. Wh). The volume of the battery is 0.016 in a battery can with a diameter of 18 mm and a length of 65 mm.
The volume energy density (Wh / l) of the battery was set to a value obtained by dividing the battery energy by 0.0165 l.

The power density was determined as follows. That is, a state in which 20% of the battery capacity was discharged after charging at 486 mA to 4.2 V for 5 hours at a constant current and at a constant voltage was set as an initial state, and 10 seconds after discharging at each current of 1 A, 3 A, and 5 A. The voltage was measured. The current value corresponding to 3.0 V was extrapolated from a relational expression obtained by linearly approximating the current-voltage relationship. The value obtained by multiplying this current value by 3 V was defined as the power (W) of the battery, and this value was divided by the total weight of the battery to obtain the power density (W / kg).

The results are shown in Table 1 below and FIG.

[0053]

[Table 1] From this result, it was confirmed that the secondary battery of Comparative Example 1, which did not use the second conductive material, exhibited a low value of the power density despite having a high value of the volume energy density. On the contrary, it can be confirmed that the secondary battery of Comparative Example 2 to which the first conductive material is not attached shows only a low value of the volume energy density despite the high value of the power density. Was. On the other hand, the secondary batteries of Examples 1, 2, and 3 manufactured using the positive electrode material of the present invention show high values in both the volume energy density and the power density. Was confirmed. Therefore, this result demonstrates that the positive electrode material of the present invention is a positive electrode material that can constitute a lithium secondary battery excellent in both volume energy density and power density.

[0054]

According to the present invention, a positive electrode active material of a lithium manganese composite oxide having a spinel structure and a positive electrode material for a lithium secondary battery comprising a positive electrode conductive material of a carbon material are used. , One of which is arranged on the surface of the active material particles and the other is arranged in the gap between the active material particles. By using a carbon material having a large specific surface area for each conductive material, it is intended to secure the electron conductivity and the lithium ion permeability of the positive electrode using the present positive electrode material. By the action of the positive electrode conductive material, a lithium secondary battery using the present positive electrode material can be a lithium secondary battery excellent in both characteristics of power density and energy density.

[Brief description of the drawings]

FIG. 1 is a diagram showing the electrical resistivity of a composite powder with respect to the mixing ratio of a first conductive material.

FIG. 2 is a view showing the electrical resistivity of a positive electrode material powder with respect to the mixing ratio of a second conductive material.

FIG. 3 is a diagram showing a relationship between volume energy density and power density of lithium secondary batteries of Examples and Comparative Examples.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takahiko Homma 41 Toyota Chuo R & D Co., Ltd., No. 41, Nagachute-cho, Nagakute-cho, Aichi, Japan. No. 1 In Denso Co., Ltd. (72) Inventor Hisao Hisashi Kojima 1-1-1 Showa-cho, Kariya-shi, Aichi F-term in Denso Co., Ltd. 5H003 AA01 AA02 BA03 BB05 BB15 BC05 BC06 BD05 5H014 AA02 BB06 BB08 CC01 EE07 EE10 HH06

Claims (1)

[Claims] A composite in which a first conductive material made of a carbon material having a specific surface area of 1000 m ² / g or more is attached to the surface of a composite oxide containing lithium and manganese having a spinel structure; A positive electrode material for a lithium secondary battery, characterized by being mixed with a second conductive material made of a carbon material exceeding 200 m ² / g.