JP4841814B2 - Non-aqueous secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous secondary battery including a negative electrode having both high capacity and high output.

  In recent years, midnight power storage systems, home-use distributed power storage systems based on solar power generation technology, and power storage systems for electric vehicles have attracted attention from the viewpoint of the effective use of energy aimed at preserving the global environment and conserving resources. Yes.

  Among them, in a combination of a high-efficiency engine and a power storage system (for example, a hybrid electric vehicle) or a combination of a fuel cell and a power storage system (for example, a fuel cell electric vehicle), the engine or the fuel cell operates at maximum efficiency. In order to cope with load-side output fluctuations or energy regeneration, high-power discharge characteristics and / or high-rate charge acceptance characteristics are required in the power storage system.

  Currently, developments such as higher energy density of capacitors (electric double layer capacitors) and higher output of lithium ion batteries are being promoted to meet the above requirements. Lithium ion batteries use a lithium composite oxide such as cobalt, nickel, or manganese as a positive electrode, and a carbon material such as graphite as a negative electrode. As a material applicable as a negative electrode material for a lithium ion battery, graphite and amorphous carbon are generally used, and the shape thereof can take various forms such as a spherical shape, a scale shape, a fibrous shape, and an amorphous particle. In addition, carbon materials having nanostructures such as carbon black and carbon nanotubes, activated carbon having a high specific surface area, and the like are also applicable. In order to increase the output of the lithium ion battery, it is important to improve the lithium ion storage / desorption rate of these materials.

Non-Patent Document 1 discloses that an amorphous material is more advantageous in terms of output as a negative electrode material for high-power lithium ions than graphite-based materials. Non-Patent Document 2 discloses that as the particle size of the active material is smaller, the output is improved from the simulation result regarding the battery output when the particle size of the active material is changed. Patent Document 1 discloses a nonaqueous electrolyte secondary battery using a carbonaceous material containing carbon nanotubes having a diameter of 5 nm to 10 nm as a negative electrode active material. Patent Document 2 discloses a diameter of A lithium secondary battery using a carbon nanotube having a diameter of 10 nm and a length of 0.5 to 5 μm and a carbon nanotube having a diameter of 30 nm and a length of 3 to 10 μm as a negative electrode is disclosed.
Noriko Tanaka et al., Pulse Charge / Discharge Behavior of Negative Carbon Material for High Power Lithium Ion Batteries “Abstracts of the 44th Battery Discussion Meeting”, November 2003, 1D25 p474-475 Takaaki Abe et al., High output of lithium-ion battery “Abstracts of the 43rd Battery Discussion Meeting”, October 2002, 3A12 p218-219 JP 7-14573 A JP 2003-331838 A

  In developing negative electrode materials for high-power lithium-ion batteries, it is important to improve the rate of occlusion / desorption of lithium ions. It is important to reduce the particle size of the negative electrode material or increase the specific surface area. There are two directions. Among the above-mentioned carbon materials, carbon materials having a nanostructure such as carbon black and carbon nanotubes, activated carbon having a high specific surface area, and the like are considered as candidates. However, when these nanostructured materials are used as the negative electrode active material, it has been difficult to obtain a negative electrode having a mixture density, electrode electrical conductivity, high capacity, and high output.

  Therefore, the present invention mainly provides a high-power type lithium ion battery having a negative electrode having density, electrical conductivity, high capacity, and high output by controlling the particle size of the negative electrode active material within a certain range. With a purpose.

The present inventor conducted research while paying attention to the problems of the prior art as described above. As a result, the carbonaceous material having an average particle diameter of 1 μm or less and 0.1 μm or more and a specific surface area by the BET method of less than 500 m ² / g. As a result, the present inventors have found that the above object can be achieved, for example, by using as a main component of the negative electrode.

The nonaqueous secondary battery according to claim 1 has a positive electrode, a negative electrode mainly composed of a material capable of inserting and extracting lithium, and a nonaqueous electrolytic solution in which a lithium salt is dissolved in a nonaqueous solvent. In the non-aqueous secondary battery, the negative electrode is mainly composed of a carbonaceous material having an average particle diameter of 1 μm or less and 0.1 μm or more and a specific surface area by the BET method of less than 20 m ² / g , and the composite material density is 1.0 g / cm. ^{It is characterized by 3} or more and electric conductivity of 1.0 × 10 ⁻² S / cm or more.

    The nonaqueous secondary battery according to claim 2 is characterized in that a 90% particle size in the particle size distribution of the carbonaceous material according to claim 1 is 5 μm or less.

The non-aqueous secondary battery according to claim 3 is the non-aqueous secondary battery according to claim 1 or 2 , wherein the carbonaceous material as the main component of the negative electrode has an average fiber diameter of 0.05 μm or more and 1 μm or less. It is characterized by pulverizing a fibrous carbon material.

The non-aqueous secondary battery according to claim 4 is the non-aqueous secondary battery according to any one of claims 1 to 3 , wherein the hydrogen / carbon atomic ratio of the carbonaceous material which is the main component of the negative electrode is the same. It is characterized by being less than 0.05.

The nonaqueous secondary battery according to claim 5 is characterized in that the thickness of the negative electrode mixture is 20 μm or more in the nonaqueous secondary battery according to any one of claims 1 to 4 .

According to the configuration of the first to fifth aspects, a non-aqueous secondary battery having a high energy density and a high output can be obtained.

As described above, the non-aqueous secondary battery of the present invention includes a positive electrode, a negative electrode mainly composed of a material capable of inserting and extracting lithium, and a non-aqueous electrolyte solution in which a lithium salt is dissolved in a non-aqueous solvent. In the water-based secondary battery, the negative electrode is mainly composed of a carbonaceous material having an average particle diameter of 1 μm or less and 0.1 μm or more and a specific surface area by the BET method of less than 500 m ² / g, and the composite material density is 1.0 g / cm ^3. In addition, the electrical conductivity is 1.0 × 10 ⁻² S / cm or more.
Therefore, there is an effect that a non-aqueous secondary battery having a high energy density and a high output exceeding 10 C can be provided.

  One embodiment of the present invention will be described as follows.

The non-aqueous secondary battery of the present invention includes a positive electrode, a negative electrode mainly composed of a material capable of inserting and extracting lithium, and a non-aqueous secondary electrolyte in which a lithium salt is dissolved in a non-aqueous solvent. In the battery, the negative electrode is mainly composed of a carbonaceous material having an average particle size of 1 μm or less and 0.1 μm or more, and a specific surface area by the BET method of less than 500 m ² / g, and the composite material density is 1.0 g / cm ³ or more, and The electrical conductivity is 1.0 × 10 ⁻² S / cm or more. The negative electrode mainly composed of a material capable of occluding and releasing lithium in the present invention is mainly composed of a carbonaceous material such as graphite and amorphous carbon material, and the type and shape thereof are not particularly limited, When the number of hydrogen / carbon atoms is less than 0.05, lithium is preferably occluded / released. These carbonaceous materials have an average particle size of 1 μm or less and 0.1 μm or more, and this value can be measured with a commercially available laser diffraction particle size distribution analyzer. When the average particle size of the carbonaceous material of the present invention exceeds 1 μm, sufficient output cannot be obtained, and when it is less than 0.1 μm, it is difficult to form into an electrode or the composite density is low even if it can be formed into an electrode. It is difficult to obtain a density of 1.0 g / cm ³ or more, which is a constituent requirement of the present invention. In order to obtain a sufficient output density, it is desirable that the 90% particle size in the particle size distribution of the carbonaceous material be 5 μm or less. The specific surface area in the BET method of the carbonaceous material in the present invention is less than 500 m ² / g, preferably less than 100 m ² / g, more preferably less than 20 m ² / g. It is not preferable because it becomes low or lithium cannot be occluded / released efficiently.

The composite density of the negative electrode of the nonaqueous secondary battery of the present invention is 1.0 g / cm ³ or more. When the composite material density is less than 1.0 g / cm ³ , the energy density is lowered in a non-aqueous secondary battery using this negative electrode, which is not preferable. Further, the negative electrode of the present invention has an electric conductivity of 1.0 × 10 ⁻² S / cm or more, and when the electric conductivity is 1.0 × 10 ⁻² S / cm or less, a non-aqueous system using this negative electrode A sufficient output cannot be obtained in the secondary battery.

The shape of the carbonaceous material in the present invention is not particularly limited, and is appropriately selected from spherical, fibrous, amorphous particles, and the like, for example, a particle size distribution having an average particle size of 1 μm or less and 0.1 μm or more. It is also possible to obtain a carbonaceous material having an average fiber diameter of 0.05 μm to 1 μm by pulverization. Examples of the fibrous carbonaceous material having an average fiber diameter of 0.05 μm or more and 1 μm or less include vapor grown carbon fiber (VGCF). When such an extremely fine fibrous carbonaceous material is used, secondary aggregates entangled with fibers tend to be generated, and it is difficult to increase the electrode density. However, the 90% particle size in the particle size distribution should be 5 μm or less. Thus, a negative electrode having a composite material density of 1.0 g / cm ³ or more can be easily obtained.

  Although it does not specifically limit as a positive electrode in this invention, For example, lithium composite cobalt oxide, lithium composite nickel oxide, lithium composite manganese oxide, or these mixtures, Furthermore, it is different in these composite oxides. A system to which one or more metal elements are added can be used, and materials such as a conductive polymer and activated carbon can be used.

  When forming the negative electrode used for the non-aqueous secondary battery of the present invention, a conductive material and a binder are used as necessary. The type of the binder is not particularly limited, and examples thereof include fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, and polyolefins such as fluorine rubber, SBR, acrylic resin, polyethylene, and polypropylene. . The amount of the binder is not particularly limited. For example, the binder amount is preferably about 1 to 30% of the weight of the carbonaceous material capable of inserting and extracting lithium of the present invention. The type of the conductive material is not particularly limited, and examples thereof include carbon black and acetylene black. The amount of the conductive material is not particularly limited, and for example, it is usually preferable to set the ratio to about 1 to 20% of the weight of the carbonaceous material capable of inserting and extracting lithium of the present invention. Moreover, the negative electrode used for the non-aqueous secondary battery of this invention can be manufactured using general electrode forming methods, such as application | coating shaping | molding, press molding, and roll shaping | molding.

  The negative electrode used in the non-aqueous secondary battery of the present invention can be formed on a current collector, or an electrode formed in a sheet shape can be bonded to the current collector or bonded via a conductive layer. The material of the current collector is not particularly limited, and copper, iron, stainless steel and the like can be used. Furthermore, a structure in which an electrode can be formed on a metal foil or in a gap between metals, for example, an expanded metal, a mesh material, or the like can be used as a current collector.

The non-aqueous secondary battery of the present invention uses a non-aqueous electrolyte solution in which a lithium salt is dissolved in a non-aqueous solvent. As the non-aqueous electrolyte solution used in the present invention, a non-aqueous electrolyte solution containing a lithium salt can be used. According to the use conditions such as the type of the positive electrode material, the property of the negative electrode material, the charging voltage, etc. It is determined. Examples of the non-aqueous electrolyte containing a lithium salt include lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethoxyethane, γ-butyrolactone, acetic acid. What was melt | dissolved in the organic solvent which consists of 1 type, or 2 or more types, such as methyl and methyl formate, can be used. The concentration of the electrolytic solution is not particularly limited, but generally about 0.5 to 2 mol / l is practical. As a matter of course, it is preferable to use an electrolytic solution having a water content of 100 ppm or less.

    The shape of the non-aqueous secondary battery of the present invention is not particularly limited, and can be appropriately determined according to the purpose, such as a coin type, a cylindrical type, a square type, a film type, and the like.

  Hereinafter, examples will be shown to further clarify the features of the present invention, but the present invention is not limited to the examples.

(1) A commercially available graphitized vapor-grown carbon fiber (VGCF: fiber diameter, 0.15 μm) is pulverized by a ball mill to obtain a powder (carbonaceous material) having an average particle diameter of 0.69 μm and a 90% particle diameter of 3.5 μm. Obtained. The specific surface area of the powder according to the BET method was 8 m ² / g. By mixing 85 parts by weight of the obtained powder with 15 parts by weight of acetylene black as a conductive material and 10 parts by weight of polyvinylidene fluoride as a binder in N-methylpyrrolidone, and coating and drying on a copper foil having a thickness of 18 μm. The composite material layer was molded and pressed to obtain a negative electrode. The thickness of the composite layer was 23 μm, and the composite density was 1.2 g / cm ³ . The electrical conductivity of the electrode was 1.5 × 10 ⁻² S / cm.
(2) LiPF ₆ dissolved at a concentration of 1 mol / l in a solvent in which ethylene carbonate and diethyl carbonate are mixed at a weight ratio of 3: 7 as an electrolyte, using lithium as a reference electrode and a counter electrode as the negative electrode. Was used to assemble an electrochemical cell.
(3) The carbonaceous material is charged with constant current at a current of 60 mA up to 0.01 V with respect to the lithium potential and then applied with a constant voltage (0.01 V) for 8 hours. 1 g was discharged to 2.0 V at a current of 60 mA. The capacity at this time was 290 mAh / g based on the weight of the carbonaceous material. Subsequently, in order to confirm the output characteristics, after charging in the same manner as described above, 1 g of carbonaceous material was discharged at 6000 mA. The capacity at this time was 275 mAh / g based on the weight of the carbonaceous material.
[Comparative Example 1]

(1) The same commercially available graphitized vapor grown carbon fiber (VGCF: fiber diameter, 0.15 μm) as in Example 1 was mixed with 10 parts by weight of polyvinylidene fluoride as a binder in N-methylpyrrolidone, A composite layer was formed by coating and drying on a 18 μm thick copper foil, and a negative electrode was obtained by pressing. The graphitized vapor-grown carbon fibers used had an average particle size of 2.2 μm and a 90% particle size of 9.5 μm. The thickness of the mixture layer of the obtained negative electrode was 17 μm, and the mixture density was 0.75 g / cm ³ . The electrical conductivity of the electrode was 1.2 × 10 ⁻² S / cm.
(2) LiPF ₆ dissolved at a concentration of 1 mol / l in a solvent in which ethylene carbonate and diethyl carbonate are mixed at a weight ratio of 3: 7 as an electrolyte, using lithium as a reference electrode and a counter electrode as the negative electrode. Was used to assemble an electrochemical cell.
(3) The carbonaceous material is charged with constant current at a current of 60 mA to 1 V with respect to lithium potential to 0.01 V and then applied with constant voltage (0.01 V) for 8 hours. 1 g was discharged to 2.0 V at a current of 60 mA. The capacity at this time was 230 mAh / g based on the weight of the carbonaceous material. Subsequently, in order to confirm the output characteristics, after charging in the same manner as described above, 1 g of carbonaceous material was discharged at 6000 mA. The capacity at this time was 200 mAh / g based on the weight of the carbonaceous material.
[Comparative Example 2]

(1) Commercially graphitized vapor-grown carbon fiber (VGCF: fiber diameter, 0.15 μm) is pulverized with a ball mill to obtain a powder (carbonaceous material) having an average particle diameter of 0.88 μm and a 90% particle diameter of 2.5 μm. Obtained. The specific surface area of the powder according to the BET method was 48 m ² / g. 100 parts by weight of the obtained powder is mixed with 10 parts by weight of polyvinylidene fluoride as a binder in N-methylpyrrolidone, and the mixture layer is formed on a copper foil having a thickness of 18 μm and dried, and then pressed. Thus, a negative electrode was obtained. The thickness of the composite layer was 22 μm, and the composite density was 1.1 g / cm ³ . The electrical conductivity of the electrode was 6 × 10 ⁻³ S / cm.
(2) LiPF ₆ dissolved at a concentration of 1 mol / l in a solvent in which ethylene carbonate and diethyl carbonate are mixed at a weight ratio of 3: 7 as an electrolyte, using lithium as a reference electrode and a counter electrode as the negative electrode. Was used to assemble an electrochemical cell.
(3) The carbonaceous material is charged with constant current at a current of 60 mA to 1 V with respect to lithium potential to 0.01 V and then applied with constant voltage (0.01 V) for 8 hours. 1 g was discharged to 2.0 V at a current of 60 mA. The capacity at this time was 248 mAh / g based on the weight of the carbonaceous material. Subsequently, in order to confirm the output characteristics, after charging in the same manner as described above, 1 g of carbonaceous material was discharged at 6000 mA. The capacity at this time was 171 mAh / g based on the weight of the carbonaceous material.

Examples of the use of the non-aqueous secondary battery of the present invention include use as an output power storage device such as a hybrid electric vehicle and a fuel cell electric vehicle. In particular, the present non-aqueous secondary battery can achieve both high energy density and high output, which have been the subject of the prior art, and contributes to reducing the size and weight of the output power storage device.

Claims (5)

In a non-aqueous secondary battery having a positive electrode, a negative electrode mainly composed of a material capable of inserting and extracting lithium, and a non-aqueous electrolyte solution in which a lithium salt is dissolved in a non-aqueous solvent, the negative electrode has an average particle size 1 μm or less 0.1 μm or more, a carbonaceous material having a BET method specific surface area of less than 20 m ² / g as a main component, a composite material density of 1.0 g / cm ³ or more, and an electric conductivity of 1.0 A non-aqueous secondary battery characterized by being 10 ⁻² S / cm or more.   The nonaqueous secondary battery according to claim 1, wherein a 90% particle diameter in a particle size distribution of the carbonaceous material is 5 μm or less. 3. The non-aqueous secondary battery according to claim 1, wherein the carbonaceous material is obtained by pulverizing a fibrous carbon material having an average fiber diameter of 0.05 μm to 1 μm. The nonaqueous secondary battery according to any one of claims 1 to 3 , wherein the carbonaceous material has a hydrogen / carbon atomic ratio of less than 0.05. The nonaqueous secondary battery according to any one of claims 1 to 4 , wherein the negative electrode composite material has a thickness of 20 µm or more.