JP2015069818A - Coke, electrode active material and battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a battery having high discharge capacity, excellent current charge/discharge characteristics and a high initial efficiency.SOLUTION: In the rectangular visual field of 480 μm×540 μm of a polarization microscopic image obtained by observing an optical texture by means of a polarization microscope, the area of the optical texture is accumulated in the ascending order, when the accumulated area is 60% of the total area of the optical texture, the area of the optical texture is 10-5000 μm, and an anisotropic texture is formed of a flow texture and a fine mosaic texture. An electrode active material, obtained by calcining coke having an area ratio of the flow texture and fine mosaic texture in a range of 40:60-70:30, is used in the negative electrode.

Description

  The present invention relates to coke, an electrode active material, a battery, and the like. More specifically, the present invention relates to coke suitable as an electrode material for a lithium ion secondary battery, a negative electrode active material using coke as a raw material, and a lithium ion secondary battery. The present invention relates to a battery that exhibits good rate characteristics and can be applied to batteries of electric vehicles such as hybrid vehicles and plug-in hybrid vehicles.

  In recent years, expectations for hybrid electric vehicles and plug-in hybrid electric vehicles have increased due to concerns over the shortage of petroleum resources and growing environmental problems. Since lithium ion secondary batteries use materials with high energy density and relatively low toxicity, they are expected to be applied to electric vehicles including hybrid vehicles and plug-in hybrid vehicles.

  A lithium ion secondary battery used in an electric vehicle is particularly required to have high-speed charge / discharge characteristics, and at the same time, high cycle life, high capacity, and high charge / discharge efficiency are required.

  The lithium ion secondary battery includes a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, and the like as constituent materials. Graphite is often used as the negative electrode material. However, although the graphite material has a high capacity, the interlayer is narrow and the interaction between the hexagonal network surface of carbon atoms and lithium is strong, and therefore, it is not suitable for large current charge / discharge. In contrast, soft carbon has a larger interlayer than graphite material and is suitable for large current charge / discharge. Furthermore, soft carbon requires relatively little energy during production, is inexpensive, and is suitable for automobile batteries that require a large amount of electrode material. Soft carbon is obtained by calcining coke and raw coke as raw materials and firing the coke at a relatively low temperature. The following Patent Documents 1 to 4 describe lithium batteries using coke as a negative electrode material.

  Patent Document 1 describes a lithium secondary battery using a carbon material obtained by firing coke as a negative electrode material.

  Patent Document 2 describes a non-aqueous secondary battery using a negative electrode material obtained by performing two-step heat treatment on coke.

  Patent Document 3 describes a lithium ion secondary battery using a negative electrode material obtained by heat-treating a raw material oil composition obtained by coking two kinds of heavy oils.

  Patent Document 4 describes a lithium ion secondary battery in which a raw material charcoal composition obtained by coking a heavy oil composition is heat treated.

Japanese Patent No. 4877568 Japanese Patent No. 3690128 JP 2009-117257 A JP2012-109110A

  In Patent Documents 1 and 2, the heat treatment for producing the carbon material is studied, but sufficient rate characteristics cannot be obtained, so that good large current charge / discharge characteristics cannot be obtained.

  In Patent Documents 3 and 4, although the raw material of the negative electrode material is selected, a sufficient discharge capacity suitable for practical use is not obtained with any of the raw materials.

  Therefore, the negative electrode materials described in Patent Documents 1 to 4 cannot sufficiently improve battery characteristics. In addition, the negative electrode materials described in Patent Documents 1 to 4 cannot provide a battery that can be applied to an electric vehicle.

  Therefore, in the present invention, a coke, an electrode active material, and an electrode active material capable of obtaining a battery having high discharge capacity and large current charge / discharge characteristics, high initial efficiency, and applicable to an electric vehicle or the like. An object is to provide an electrode material containing a substance, an electrode paste, an electrode, and a battery using the electrode active material.

  In order to achieve the above object, the present invention comprises the following aspects.

(1) In a rectangular field of view of 480 μm × 540 μm in a polarizing microscope image obtained by observing an optical structure with a polarizing microscope, areas are accumulated in order from an optical structure having a smaller area, and the cumulative area is 60% of the total area of the optical structure. area of the optical tissue when the area is at 10 [mu] m ² or more 5000 .mu.m ² or less, are anisotropic tissue formed in the flow structure and fine mosaic structure, the area ratio of the flow structure and the fine mosaic tissue Coke that is 40:60 to 70:30.

(2) In a rectangular field of view of 480 μm × 540 μm in a polarizing microscope image obtained by observing an optical structure with a polarizing microscope,
The number of optical structures is counted in order from the optical structure having a small aspect ratio, and the aspect ratio of the optical structure when reaching 60% of the total number of optical structures is 1.5 or more and 6 or less. Coke.

(3) It is a calcined product of coke,
The volume-based average particle diameter by laser diffraction method is 5 μm or more and 30 μm or less,
In the rectangular visual field of 480 μm × 540 μm in the polarizing microscope image obtained by observing the optical structure with the polarizing microscope, the areas are accumulated in order from the optical structure with the smallest area, and the accumulated area becomes 60% of the total area of the optical structure. area of the optical tissue is at 10 [mu] m ² or more 5000 .mu.m ² or less when a anisotropic structure formed by the flow organization and fine mosaic structure, the area ratio of the flow structure and the fine mosaic organization 40:60 An electrode active material having a true density of 1.9 g / cm ^{2 to} 2.17 g / cm ² and a crystallite size in the c-axis direction of hexagonal graphite of 1 nm to 10 nm.

(4) In a rectangular field of view of 480 μm × 540 μm in a polarizing microscope image obtained by observing an optical structure with a polarizing microscope,
The number of optical tissues is counted in order from the optical structure having the smallest aspect ratio, and the aspect ratio of the optical structure when reaching 60% of the total number of optical tissues is 1.5 or more and 6 or less. Electrode active material.

(5) The BET specific surface area is 0.5 m ² / g or more and 5 m ² / g or less, and the interplanar spacing as hexagonal graphite is 0.341 nm or more and 0.346 nm or less as described in (3) or (4) above Electrode active material.

(6) The method for producing an electrode active material according to any one of (3) to (5) above,
Having a step of firing the coke described in (1) or (2) in an inert atmosphere of 950 ° C. or higher and 1500 ° C. or lower,
A method for producing an electrode active material, wherein the coke is pulverized and classified so that the volume-based average particle diameter by laser diffraction method is 5 μm or more and 30 μm or less before or after the firing.

  (7) The petroleum pitch or coal pitch is mixed with the coke so as to be in the range of 0.5% by mass or more and 15.0% by mass or less based on the total mass of the coke and petroleum pitch or coal pitch. The method for producing an electrode active material according to (6), wherein the firing is performed.

  (8) The electrode activity according to (6) or (7), wherein the coke baked after the pulverization and classification, or the coke pulverized and classified after the calcination is further baked in an oxidizing atmosphere of 300 ° C. or higher and 1100 ° C. or lower. A method for producing a substance.

  (9) An electrode material comprising the electrode active material according to any one of (3) to (5) above.

  (10) An electrode paste comprising the electrode active material according to any one of (3) to (5) and a binder.

  (11) An electrode comprising the electrode active material according to any one of (3) to (5) above.

(12) The electrode according to (11), wherein the electrode density is 1 g / cm ² or more and 1.5 g / cm ² or less.

  (13) A battery comprising the electrode according to (11) or (12).

  (14) The battery according to (13), which is a lithium ion secondary battery.

  In the present invention, a battery having high discharge capacity, large current charge / discharge characteristics and initial efficiency can be obtained.

The polarizing microscope photograph (480 micrometers x 540 micrometers) of coke is shown. The polarizing microscope photograph (480 micrometers x 540 micrometers) after baking of the coke shown in FIG. 1 is shown.

Hereinafter, the coke, electrode active material, electrode material, electrode paste, electrode, and battery to which the present invention is applied will be described in detail in the following order. Note that the present invention is not limited to the following detailed description unless otherwise specified.
1. Coke 2. Electrode active material and method for producing the same 3. Electrode material 4. Electrode paste Electrode 6. battery

[1. Coke]
Coke is a raw material for the electrode active material that forms the electrode of the battery. The characteristics of the electrode active material may be influenced by the optical structure such as the isotropic and anisotropic properties of the coke as a raw material and the size of the structure when observed with a polarizing microscope. The electrode active material to which the present invention is applied uses coke having an optical texture area or aspect ratio within a specific range or optical anisotropy as a raw material. The area and aspect ratio of the optical structure of the coke can be calculated by analyzing an image obtained by observing the cross section of the coke with a polarizing microscope.

(1) Area and aspect ratio of optical structure Coke accumulates the area in order from an optical structure with a small area in a rectangular field of view of 480 μm × 540 μm in a polarizing microscope image obtained by observing the optical structure with a polarizing microscope, the area of the optical tissue when the cumulative area of 60% of the area of the total area of the optical tissues (hereinafter also referred to as Da (60).) is at 10 [mu] m ² or more 5000 .mu.m ² or less, preferably 10 [mu] m ² or more 2000 .mu.m ² Or less, more preferably 20 μm ² or more and 1000 μm ² or less. If Da (60) is in the range of 10 [mu] m ² or more 5000 .mu.m ² or less, in the case of using such a coke as a raw material of the electrode active material, the discharge capacity, large current load characteristics, the three balance of cycle characteristics Can be taken.

  In addition, the coke counts the number of optical tissues in order from the optical structure having the smallest aspect ratio, and the aspect ratio of the optical structure when it reaches 60% of the total number of optical tissues (hereinafter also referred to as ARb (60)). Is preferably 1.5 or more and 6 or less. When ARb (60) is 1.5 or more and 6 or less, when such coke is used as a raw material for the electrode active material, three balances of discharge capacity, current load characteristics, and cycle characteristics can be achieved. .

  Here, the optical structure when it reaches 60% of the total number of optical tissues is determined by (total number of optical tissues in a rectangular field of view of 480 μm × 540 μm in the polarization microscope image) × (60/100). Optical organization. For example, when the total number of optical textures is 200, the aspect ratio of the 120th optical texture counted from the smallest optical texture is 1.5 or more and 6 or less.

(2) Anisotropy of optical texture The shape and physical characteristics of coke differ depending on the type. Coke preferably has a flow structure and anisotropy when the optical structure is observed. Here, the optical structure of the coke is determined by the image obtained by polarizing microscope observation, the aspect ratio: the aspect ratio of the particles: the maximum length Dmax / the maximum length vertical length DNmax (Dmax: the maximum at two points on the contour of the particle image) Length; DNmax: When an image is sandwiched between two straight lines parallel to the maximum length, the shortest length that connects the two straight lines vertically is 2.5 or more. A fine mosaic structure is one that is greater than 1 and less than 2.5. When coke is used as a raw material for the negative electrode active material, relatively high initial efficiency can be obtained by using coke having a flow structure, and relatively low initial efficiency and high discharge capacity can be obtained by using coke having a fine mosaic structure. Is obtained.

  Therefore, in order to balance the desired initial efficiency and discharge capacity, it is preferable to appropriately control the ratio of the flow texture to the fine mosaic texture. In particular, the ratio of the flow structure to the fine mosaic structure is preferably 40:60 to 70:30. A ratio of 40:60 or more is preferable because the initial efficiency of the battery is increased, and a ratio of 70:30 or less is preferable because the discharge capacity is increased. If there are too many fine mosaic structures, the initial efficiency of the battery will be low.

  As the coke, for example, petroleum coke and coal coke are preferable. Petroleum-based coke and coal-based coke can be obtained, for example, by heat-treating petroleum-based heavy oil or coal-based heavy oil at a pressure of 2 MPa or less and a temperature of 400 ° C. or more and 600 ° C. or less for 3 hours or more. In petroleum coke and coal coke, Da (60), the flow ratio of the anisotropic structure and the area ratio of the fine mosaic structure, and ARb (60) satisfy the respective ranges described above. In addition, the manufacturing method of coke is not limited to this, If Da (60), the area ratio of the flow structure of an anisotropic structure and a fine mosaic structure, ARb (60) satisfy | fills each range mentioned above, it will be other It may be a manufacturing method or manufacturing conditions.

(3) Observation with a polarizing microscope The cross section of coke which becomes an observation object region observed with a polarizing microscope is prepared by preparing a sample as follows.
[Sample preparation for polarizing microscope observation]
First, in the first step, a double-sided tape is attached to the bottom of a plastic sample container having an internal volume of 30 cm ³ , and about 2 cups of spatula (about 2 g) are placed on the observation sample. The next step is a cold embedding resin (trade name: cold embedding resin # 105, manufacturing company: Japan Composite Co., Ltd., sales company: Marumoto Struers Co., Ltd.) and a curing agent (trade name: curing agent (M Agent), manufacturing company: Nippon Oil & Fat Co., Ltd., sales company: Marumoto Struers Co., Ltd.) and knead for 30 seconds. In the next step, the obtained mixture (about 5 ml) is slowly poured into a sample container until the height is about 1 cm, and allowed to stand for 1 day to solidify. In the next step, the solidified sample is taken out and the double-sided tape is peeled off. In the final step, the surface to be measured of the sample is polished using a polishing plate rotating type polishing machine.

  Polishing is performed such that the polishing surface of the sample is pressed against the rotating surface of the polishing plate. The rotational speed of the polishing plate is, for example, 1000 rpm. For polishing, the counts of the polishing plates were changed in the order of # 500, # 1000, # 2000, and finally alumina (trade name: Baikalox type 0.3CR, particle size 0.3 μm, manufacturer: manufactured by Baikowski) Polishing using a sales company: Baikowski Japan). As the above-described cold embedding resin, curing agent, and alumina, known cold embedding resins, curing agents, and alumina used for polishing can also be used.

  And the observation of the sample cross section which grind | polished fixes a sample with a clay on a preparation, and observes with a polarizing microscope (OLYMPAS company make, brand name: BX51).

  The adjustment of the coke cross section is not limited to the above-described method, and the coke is embedded in the cold embedding resin as it is, and the polishing surface of the coke taken out from the cold embedding resin is subjected to polishing such as mirror polishing. You may do it. This method is suitable when coke is obtained as a mass having a size of several centimeters. In this method, since the coke is only embedded in the cold embedding resin and polished, the sample can be easily manufactured.

[Method of analyzing polarized light microscope image]
Next, a method for analyzing a polarization microscope image will be described. The sample produced as described above is observed with a polarizing microscope. Observation is performed at 200 times, for example. What was observed with a polarizing microscope is an image taken by connecting an OLYMPUS CAMEDIA C-5050 ZOOM digital camera to the polarizing microscope with an attachment. The shutter time is 1.6 seconds. Of the photographic data, an image of 1200 × 1600 pixels is set as an analysis target. This is equivalent to considering a field of view of 480 μm × 540 μm. The image analysis uses ImageJ (manufactured by the National Institutes of Health) to determine the color of the blue portion, yellow portion, red portion, and black portion. The parameters defining each color of ImageJ are as shown in Table 1 below.

  Then, statistical processing for the detected optical tissue is performed using an external macro. The black part, that is, the part corresponding to the resin part instead of the optical structure is excluded from the statistical object. For each optical structure of blue, yellow, and red, the area and aspect ratio of each optical structure are calculated. Da (60) and ARb (60) are calculated from the area and aspect ratio of the obtained optical structure.

[2. Electrode active material and method for producing the same]
The electrode active material can be obtained by using coke having the above-described properties as a raw material, preferably at least one of petroleum coke and coal coke and firing the coke. That is, the electrode active material is soft carbon which is a fired product of coke. The electrode active material has a volume-based average particle diameter (D50) by laser diffraction of 5 μm or more and 30 μm or less. Furthermore, the electrode active material accumulates the area in order from the optical structure with the smallest area in the rectangular field of view of 480 μm × 540 μm in the polarizing microscope image obtained by observing the optical structure with the polarizing microscope, and the accumulated area is the total area of the optical structure. and the area of the optical tissue when the 60% of the area of 10 [mu] m ² or more 5000 .mu.m ² below, a flow structure and fine mosaic structure with at forming anisotropic tissue, area of the flow organization and fine mosaic structure The ratio is 40:60 to 70:30. The electrode active material has a true density of 1.9 g / cm ² or more and 2.17 g / cm ² or less, and a crystallite size in the c-axis direction as hexagonal graphite of 1 nm or more and 10 nm or less. Furthermore, the electrode active material is optical when the number of optical tissues is counted in order from the optical structure having a small aspect ratio in a rectangular field of view of 480 μm × 540 μm in the polarizing microscope image, and reaches 60% of the total number of optical tissues. It is preferable that the aspect ratio of the tissue is 1.5 or more and 6 or less. Since Da (60) and ARb (60) are the same as Da (60) and ARb (60) of coke, detailed description is omitted.

  An electrode active material is contained in the electrode material of a battery as a substance which receives and discharge | releases lithium ion, for example. The electrode active material is suitable for a negative electrode active material of a lithium battery. When the negative electrode active material is contained in the negative electrode material, a negative electrode having high discharge capacity, large current charge / discharge characteristics, and initial efficiency can be formed. The electrode active material preferably further has a specific average particle diameter, a BET specific surface area, a face spacing as hexagonal graphite, and a crystallite size in the c-axis direction.

(1) Average particle diameter, BET specific surface area, interplanar spacing, crystallite size Volume-based average particle diameter (D50) (hereinafter also referred to simply as average particle diameter) by laser diffraction method is 5 μm or more and 30 μm or less. Is preferred. When the average particle size is in the range of 5 μm or more and 30 μm or less, the electrode density can be increased, and the lithium diffusion into the negative electrode active material does not take time, and high-speed charging can be performed. The average particle diameter can be measured with a laser diffraction type master sizer.

The BET specific surface area is preferably 0.5 m ² / g or more and 5 m ² / g or less. When the BET specific surface area is in the range of 0.5 m ² / g or more and 5 m ² / g or less, it is not necessary to use an excessive amount of binder, and a contact area with the electrolytic solution can be ensured. When the BET specific surface area is within this range, lithium ions can be smoothly inserted and desorbed, the reaction resistance of the battery can be reduced, the capacity can be increased, and high-speed charging can be performed. The strength of the electrode can be set to a desired strength by adjusting the BET specific surface area of the electrode active material. The BET specific surface area can be measured by a general method for measuring the amount of adsorption / desorption of gas per unit mass.

  The interplanar spacing d (002) as hexagonal graphite is preferably 0.341 nm or more and 0.346 nm or less. When the inter-surface distance d (002) is 0.341 nm or more and 0.346 nm or less, large current charge / discharge can be realized. More preferably, the interplanar spacing d (002) is in the range of 0.342 nm to 0.3455 nm. When the interplanar spacing d (002) is 0.342 nm or more and 0.3455 nm or less, the energy density can be increased. More preferably, the interplanar spacing d (002) is in the range of 0.343 nm to 0.345 nm. When the interplanar spacing d (002) is 0.343 nm or more and 0.345 nm or less, the discharge capacity and the initial efficiency can be balanced.

  The surface interval d (002) can be measured by a wide angle X-ray diffraction method. The interplanar spacing d (002) corresponds to the carbon 002 plane that appears near the diffraction angle 2θ = 24 to 26 ° from the diffraction profile obtained by irradiating the sample with X-rays (CuKα rays) and measuring the diffraction lines with a goniometer. It can be calculated from the diffraction peak using the Bragg equation.

  The crystallite size Lc (002) in the c-axis direction as the hexagonal graphite is preferably 1 nm or more and 10 nm or less. When the crystallite size Lc (002) is 1 nm or more and 10 nm or less, excellent large current charge / discharge characteristics can be realized. The crystallite size Lc (002) is more preferably 2 nm or more and 7 nm or less. When the crystallite size Lc (002) is 2 nm or more and 7 nm or less, the energy density can be further increased. More preferably, the crystallite size Lc (002) is 3 nm or more and 5 nm or less. When the crystallite size Lc (002) is 3 nm or more and 5 nm or less, it is possible to balance the initial efficiency and the discharge capacity.

  The crystallite size Lc (002) can be measured by a wide angle X-ray diffraction method. The crystallite size Lc (002) is a carbon (002) plane that appears at a diffraction angle 2θ = 24 to 26 ° from a diffraction profile obtained by irradiating a sample with X-rays (CuKα rays) and measuring diffraction lines with a goniometer. Can be calculated using the Scherrer equation.

  The adjustment of the interplanar spacing d (002) and the crystallite size Lc (002) is adjusted to the above-mentioned range by appropriately adjusting the temperature (950 ° C. to 1500 ° C.) at the time of firing the raw coke, for example. Can do.

The true density is preferably in the range of 1.9 g / cm ³ or more and 2.17 g / cm ³ or less. When the true density is 1.9 g / cm ³ or more and 2.17 g / cm ³ or less, the energy density per volume of the electrode can be increased. The true density is more preferably 1.95 g / cm ³ or more and 2.17 g / cm ³ or less. When the true density is 1.95 g / cm ³ or more and 2.17 g / cm ³ or less, the proportion of lithium ions occluded in the electrode active material that remains without being desorbed during discharge decreases. More preferably, the true density is 2 g / cm ³ or more and 2.15 g / cm ³ or less. When the true density is 2 g / cm ³ or more and 2.15 g / cm ³ or less, it is possible to suppress a problem that the capacity that can be charged with a large current rapidly decreases.

  The true density can be measured by a gas phase substitution method. In the gas phase substitution method, the true density is calculated from the volume of helium gas in a constant volume in an environment maintained at a constant temperature. As an apparatus for the gas phase substitution method, for example, a Whale Trap pycnometer 1000 manufactured by Yuasa Ionics can be used.

The electrode active material as described above, consists of soft carbon, Da (60) is at 10 [mu] m ² or more 5000 .mu.m ² or less, the area ratio of the flow organization and fine mosaic organization 40: 60-70: 30 anisotropy The structure has a true density of not less than 1.9 g / cm ^{2 and not} more than 2.17 g / cm ² , and a crystallite size in the c-axis direction as hexagonal graphite is not less than 1 nm and not more than 10 nm. The large current charge / discharge characteristics and the initial efficiency can be improved, and the balance between these can be improved. Therefore, the electrode active material can be charged and discharged at high speed, and the cycle characteristics can be improved. By using such an electrode active material as a negative electrode active material instead of a conventional graphite material, it is possible to exhibit good battery characteristics even when applied to batteries of electric vehicles as well as dry batteries and the like. it can.

Method for manufacturing method the electrode active material (2) electrode active material, Da (60) satisfies 10 [mu] m ² or more 5000 .mu.m ² or less, are anisotropic tissue formed in the flow structure and fine mosaic structure, flow The area ratio of the structure to the fine mosaic structure is 40:60 to 70:30, the true density is 1.9 g / cm ² or more and 2.17 g / cm ² or less, and crystallites in the c-axis direction as hexagonal graphite Although it will not specifically limit if size becomes 1 nm or more and 10 nm or less, The manufacturing method demonstrated below can be manufactured efficiently.

  The method for producing an electrode active material includes a baking step of baking coke, and includes a pulverization step of pulverizing coke and a classification step of classifying coke after pulverization before or after the baking step. Furthermore, in order to adjust the specific surface area of the electrode active material, if necessary, it further has a coating step of mixing pitch with coke and coating the pitch on the surface of coke and an oxidation step of oxidizing coke. May be.

Hereinafter, each step will be described.
(Crushing process)
In the pulverization step, coke having the above-described properties, for example, at least one of petroleum coke and coal coke is pulverized by a pulverizer. For the pulverization, a known jet mill, hammer mill, roller mill, pin mill, vibration mill or the like can be used. The pulverization is performed so that the average particle size (D50) of the coke is 5 μm or more and 30 μm or less.

(Classification process)
In the classification step, the particle size distribution is adjusted by using airflow classification or a sieve.

  The pulverization and classification steps are preferably performed before the calcination step because pulverization after the calcination step may significantly increase the specific surface area of the electrode active material.

(Baking process)
In the firing step, coke such as petroleum coke and coal coke having the above-described properties in an inert atmosphere is fired at a temperature of 950 ° C to 1500 ° C. In the firing step, coke is oxidized if a large amount of oxygen is mixed in the heat treatment furnace, so that the heat treatment is performed in an inert atmosphere to prevent oxidation. An inert gas such as argon is used to create an inert atmosphere in the heat treatment furnace.

In the firing step, the coke having the above-described properties is fired at a relatively low temperature of 950 ° C. or more and 1500 ° C. or less, whereby soft carbon having the properties described above can be obtained. The resulting soft carbon, Da (60) is at 10 [mu] m ² or more 5000 .mu.m ² or less, are anisotropic tissue formed in the flow structure and fine mosaic structure, the area ratio of the flow organization and fine mosaic organization 40 : 60-70: 30. Further, the soft carbon has an ARb (60) of 1.5 or more and 6 or less. That is, soft carbon includes coke, including Da (60) contained in the raw material coke, an anisotropic structure having an area ratio of flow structure to fine mosaic structure of 40:60 to 70:30, and ARb (60). Is almost the same.

  FIG. 1 shows a polarizing microscope photograph of coke before firing, and FIG. 2 shows a polarizing microscope photograph of soft carbon obtained by firing the coke shown in FIG. 1 at 1300 ° C. In the photographs of FIGS. 1 and 2, the gray portion is the optical structure, and the black portion is the resin. As shown in FIGS. 1 and 2, it can be seen that the optical structures are almost the same before and after firing. The micrographs of FIGS. 1 and 2 were taken by the same method as the above-described observation and analysis method of coke with a polarizing microscope.

When the firing temperature is 950 ° C. or more and 1500 ° C. or less, a high discharge capacity can be obtained, and the balance between the initial efficiency and the discharge capacity can be improved. Moreover, by firing within this temperature range, an electrode active material having a true density of 1.9 g / cm ² or more and 2.17 g / cm ² or less can be obtained. The firing temperature is more preferably 1000 ° C. or higher and 1400 ° C. or lower. When the firing temperature is 1000 ° C. or higher and 1400 ° C. or lower, a higher discharge capacity can be obtained. More preferably, it is 1100 ° C. or higher and 1300 ° C. or lower. When the firing temperature is 1100 ° C. or higher and 1300 ° C. or lower, the balance between the initial efficiency and the discharge capacity can be improved.

(Coating process)
The coating step is performed, for example, after pulverizing and classifying coke such as petroleum-based coke and coal-based coke before calcination and after pulverization and classification. In the coating process, for example, in order to reduce the BET specific surface area of the electrode active material, petroleum-based or coal-based pitch having an average particle size of 0.01 μm or more and 25 μm or less is mixed with pulverized and classified coke, and 900 ° C. or more and 1500 ° C. or less. Heat treatment is performed for 3 hours in a nitrogen atmosphere. The addition amount of the pitch is preferably 0.5% or more and 15% or less of the total mass of the coke and the petroleum-based or coal-based pitch. When the added amount of pitch is 0.5% or more and 15% or less, high initial efficiency can be obtained. Moreover, the addition amount of pitch is more preferably 0.5% or more and 10% or less of the total mass. When the added amount of pitch is 0.5% or more and 10% or less, coke aggregation can be suppressed. Further, the addition amount of the pitch is more preferably 0.5% or more and 5% or less of the total mass. When the added amount of pitch is 0.5% or more and 5% or less, the balance between the initial efficiency and the large current charge / discharge characteristics can be improved.

(Oxidation process)
In the oxidation step, coke baked after pulverization and classification, or coke pulverized and classified after calcination is oxidized in an oxidizing atmosphere of 300 ° C. or higher and 1100 ° C. or lower. The oxidizing atmosphere only needs to contain an oxidizing gas such as oxygen, and may be air. In the oxidation step, for example, in order to increase the specific surface area of the electrode active material, an oxidation treatment is performed for 1 hour in an oxidizing atmosphere. The oxidation temperature is 300 ° C. or higher and 1100 ° C. or lower. When the oxidation temperature is in the range of 300 ° C. or higher and 1100 ° C. or lower, the specific surface area of the electrode active material can be improved, and the coke can be prevented from being excessively oxidized. Moreover, it is more preferable if oxidation temperature is 500 degreeC or more and 1000 degrees C or less. When the oxidation temperature is in the range of 500 ° C. or higher and 1000 ° C. or lower, high initial efficiency can be maintained. More preferably, the oxidation temperature is 700 ° C. or higher and 900 ° C. or lower. When the oxidation temperature is in the range of 700 ° C. to 900 ° C., the balance between the initial efficiency and the large current charge / discharge characteristics can be improved.

In the method for producing an electrode active material as described above, an electrode active material made of soft carbon can be obtained by calcining the coke before or after pulverization, classification, or after classification at 950 ° C. or more and 1500 ° C. or less. In the manufacturing method of the electrode active material, Da (60) is at 10 [mu] m ² or more 5000 .mu.m ² or less, a formed in the flow structure and fine mosaic structure anisotropic structure, the area ratio of the flow organization and fine mosaic structure By using coke with 40:60 to 70:30 as a raw material, the obtained soft carbon can be obtained with the same optical structure, and high discharge capacity, large current charge / discharge characteristics and initial efficiency can be obtained. In addition, it is possible to produce an electrode active material having a good balance between these. Therefore, in this method for producing an electrode active material, an electrode active material that can be charged and discharged at high speed, has high cycle characteristics, and can be applied to a battery such as an electric vehicle can be obtained.

[3. Electrode material]
The electrode material includes the above-described electrode active material. When the electrode material is used particularly as a negative electrode active material for a negative electrode, high discharge capacity, large current charge / discharge characteristics and initial efficiency can be obtained, and cycle characteristics can be improved.

  The electrode material can be used, for example, as an electrode material that includes the above-described negative electrode active material and forms the negative electrode of a lithium-based battery.

  In addition to the electrode active material, the electrode material may further contain a conductive auxiliary agent in order to obtain a lithium-based battery excellent in large current charge / discharge characteristics. As the conductive assistant, known carbon-based materials such as acetylene black, furnace black, ketjen black, artificial graphite fine powder, and carbon fiber can be used.

  The content of the conductive auxiliary agent is preferably 0.5% by mass or more and 20% by mass or less, and more preferably 0.5% by mass or more and 10% by mass or less with respect to the entire electrode material. In the case of adding a conductive additive to the negative electrode material, if the conductive auxiliary agent content is 0.5% by mass or more, the effect of maintaining the negative electrode conductivity can be satisfactorily exhibited, and electrode characteristics such as cycle life can be obtained. Can be suppressed. If it is 20 mass% or less, the fall of the current density of a negative electrode, the coating property of the coating liquid for negative electrode formation at the time of negative electrode preparation, etc. can be suppressed.

[4. Electrode paste]
(1) Electrode paste The electrode paste contains an electrode material containing an electrode active material and a binder. The electrode paste is obtained by kneading an electrode material and a binder. For kneading, a known kneading apparatus such as a ribbon mixer, a screw kneader, a Spartan rewinder, a ladyge mixer, a planetary mixer, a universal mixer, or the like can be used. The electrode paste can be formed into a sheet shape, a pellet shape, or the like.

  There is no restriction | limiting in particular as a binder, It can select from a conventionally well-known material suitably as a binder used for the negative electrode of a lithium battery. Examples of the binder include fluorine-containing polymers such as polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, and vinylidene fluoride-tetrafluoroethylene copolymer. Examples thereof include molecular polymers and styrene-butadiene copolymer rubber (SBR).

  The binder content is appropriately determined depending on the type of binder. For example, in the case of using PVDF, from the viewpoint of maintaining good conductivity and sufficiently exhibiting the function as a binder, the negative electrode active material, that is, 0.5 part by mass or more and 20 parts by mass with respect to 100 parts by mass of the electrode material. The range of 1 part by mass or less is preferable, and the range of 1 part by mass or more and 10 parts by mass or less is more preferable. When SBR is used, the range of 0.5 to 5 parts by mass with respect to 100 parts by mass of the electrode material is preferable from the viewpoint of maintaining good conductivity and sufficiently exhibiting the function as a binder. A range of 0.5 parts by mass or more and 3 parts by mass or less is more preferable.

(2) Method for Producing Electrode Paste Electrode paste is obtained by kneading an electrode active material or a solution or dispersion containing a binder and a binder and a solvent as necessary. It is done. The electrode paste serves as an electrode-forming coating solution when forming an electrode.

  There is no restriction | limiting in particular as a solvent used for preparation of a solution or a dispersion liquid, and a dispersion medium, From the solvent conventionally used for formation of the electrode in a lithium battery, 1 type, or 2 or more types can be selected. Examples of the solvent include N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone, dimethylformamide, dimethylacetamide, N, N-dimethylaminopropylamine, tetrahydrofuran and the like. In particular, when polyvinylidene fluoride (PVDF) is used as the binder, it is preferable to use N-methyl-2-pyrrolidone as the solvent.

  In addition to the solvent and the dispersant, a solvent may be further added to the electrode paste in order to impart fluidity. As the solvent for imparting fluidity, the same solvents as those described above can be used, and water can also be used.

  On the other hand, when SBR is used as a binder, a solution containing SBR can be prepared using N-methyl-2-pyrrolidone or water as a solvent. When water is used as a solvent, in order to impart viscosity to the resulting slurry, an aqueous thickener solution is introduced into the kneader before the aqueous SBR dispersion is introduced into the kneader. It is preferable to mix an electrode material in advance with the thickener aqueous solution.

  As the thickener, for example, polyethylene glycols, celluloses, polyacrylamides, poly N-vinyl amides, poly N-vinyl pyrrolidones and the like can be used. Among these, polyethylene glycols and celluloses such as carboxymethyl cellulose (CMC) are preferable, and carboxymethyl cellulose (CMC) having a high affinity for styrene butadiene (SBR) is particularly preferable. There are sodium salt type and ammonium salt type in CMC, and any of them can be used.

  The kneading machine is not particularly limited, and examples thereof include a planetary mixer, a defoaming kneader, a ball mill, a paint shaker, a vibration shear, and a Redige mixer.

  For example, when using a PVDF solution or an SBR solution containing N-methyl-2-pyrrolidone as a solvent, an electrode active material or a mixture of an electrode active material and a conductive assistant, a PVDF solution or an SBR solution, In some cases, NMP is preferably kneaded as a further solvent to prepare a negative electrode-forming coating solution comprising the resulting slurry.

  When an aqueous SBR dispersion using water as a solvent is used, a mixed aqueous solution is prepared by first mixing an electrode active material or a mixture of an electrode active material and a conductive additive with an aqueous solution of a thickener in a kneader. . Next, in the kneader, the mixed aqueous solution, the SBR aqueous dispersion, and, in some cases, further solvent water are kneaded to prepare a negative electrode-forming coating solution comprising a slurry.

  The amount of the solvent charged into the kneader is a viscosity suitable for applying the obtained negative electrode forming coating solution to the current collector, for example, 23 ° C., preferably 1,000 mPa · s or more and 10,000 mPa · s or less. More preferably, it is preferably selected so as to be 2,000 mPa · s or more and 5,000 mPa · s or less.

[5. electrode]
An electrode consists of a molded object of electrode paste, for example, a negative electrode of a lithium battery. The electrode is obtained, for example, by applying an electrode paste on a current collector, drying, and pressure forming.

  Examples of the current collector include foils such as aluminum, nickel, copper, and stainless steel, and meshes. The coating thickness of the electrode paste is usually 50 μm or more and 200 μm or less. If the coating thickness is too thick, the electrode may not be accommodated in a standardized battery container. The method for applying the electrode paste is not particularly limited, and is, for example, a doctor blade or a bar coater method.

Examples of the pressure molding method include molding methods such as roll pressing and press pressing. The pressure is preferably about 1 t / cm ² or more and 3 t / cm ² or less. In a battery, the battery capacity per volume usually increases as the electrode density of the electrode increases. However, when the electrode density is increased too much, the cycle characteristics usually deteriorate. When the electrode paste containing the electrode active material described above is used, even if the electrode density is increased, the deterioration of the cycle characteristics is small, so that an electrode having a high electrode density can be obtained. Therefore, the electrode to which the present invention is applied has a high capacity because the electrode density can be increased, and has excellent cycle characteristics.

When the electrode paste containing the electrode active material described above is used, the maximum value of the electrode density of the electrode is usually 1.3 to 1.5 g / cm ³ . Specifically, the electrode density is preferably in the range of 1 g / cm ^{3 to} 1.5 g / cm ³ . When the electrode density is in the range of 1 g / cm ^{3 to} 1.5 g / cm ³ , excellent large current charge / discharge characteristics can be obtained. The electrode density is more preferably in the range of 1.1 g / cm ³ or more and 1.4 g / cm ³ or less. When the electrode density is in the range of 1.1 g / cm ³ or more and 1.4 g / cm ³ or less, the energy density can be increased. The electrode density is more preferably in the range of 1.2 g / cm ³ or more and 1.3 g / cm ³ or less. When the electrode density is in the range of 1.2 g / cm ³ or more and 1.3 g / cm ³ or less, excellent cycle characteristics can be obtained. This electrode is suitable for a negative electrode of a battery, particularly a negative electrode of a lithium secondary battery.

  Since the electrode contains the electrode active material having the specific properties described above, the discharge capacity, the large current charge / discharge characteristics and the initial efficiency of the battery can be improved, and the balance between them can be achieved. Can be improved. Further, the electrode has a high energy density, can be charged / discharged at high speed, and can improve cycle characteristics. Therefore, by using the electrode in place of the negative electrode using a conventional graphite material, it is possible to exhibit good battery characteristics even when applied to a battery of an electric vehicle as well as a dry battery or the like.

(Method for manufacturing electrode)
The electrode is obtained by applying an electrode-forming coating solution to a current collector, drying, and then pressure-molding.

  As the current collector, conventionally known materials such as aluminum, nickel, titanium and alloys thereof, stainless steel, platinum, and carbon sheets can be used. The method for applying the electrode-forming coating solution onto the current collector is not particularly limited, and a conventionally known method such as a method using a doctor blade or a bar coater can be employed. The electrode sheet obtained by coating in this manner is dried by a known method, and then formed into a desired thickness and density by a known method such as a roll press or a pressure press to obtain an electrode. It is done.

[6. battery]
The battery is, for example, a primary battery or a secondary battery provided with the above-described electrode active material, preferably a negative electrode containing a negative electrode active material. For example, it is a lithium battery, and is a lithium ion secondary battery or a lithium polymer battery.

(1) Battery, Secondary Battery As a battery to which the present invention is applied, a lithium ion secondary battery will be described as an example. A lithium ion secondary battery has a structure in which a positive electrode and a negative electrode are immersed in an electrolytic solution.

(Negative electrode)
The negative electrode containing the negative electrode active material described above is used as the negative electrode.

(Positive electrode)
A known material can be used for the positive electrode as the positive electrode active material. For example, a lithium-containing transition metal oxide can be used, and an oxide mainly containing at least one transition metal element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Mo, and W and lithium. A compound having a molar ratio of transition metal element to lithium of 0.3 to 2.2 is preferable.

Moreover, the general formula _Li x _M y _P z _{O 4} olivine lithium metal phosphate represented by (0 <x <2,0 <y <1.5,0.9 <z <1.1, M is one of Mg, Ca, Fe, Mn, Ni, Co, Zn, Ge, Cu, Cr, Ti, Sr, Ba, Sc, Y, Al, Ga, In, Si, B, or a rare earth element. Or two or more) can be used.

  Note that the positive electrode active material may contain Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, or the like in a range of less than 30 mol% with respect to the transition metal present. Good.

The average particle size of the positive electrode active material is not particularly limited, but is preferably 0.1 μm or more and 50 μm or less. The volume of particles of 0.5 μm or more and 30 μm or less is preferably 95% or more. More preferably, the volume occupied by a particle group having a particle size of 3 μm or less is 18% or less of the total volume, and the volume occupied by a particle group of 15 μm or more and 25 μm or less is 18% or less of the total volume. The specific surface area is not particularly limited, but is preferably 0.01 m ² / g or more ^{50 m} 2 / g or less by the BET method, and particularly preferably 0.2 m ² / g or more 1.0 m ² / g or less. Further, the pH of the supernatant when 5 g of the positive electrode active material is dissolved in 100 ml of distilled water is preferably 7 or more and 12 or less.

(Nonaqueous electrolyte)
As the non-aqueous electrolyte solution, a non-aqueous solvent containing a lithium salt as a solute can be used. Examples of the lithium salt include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCl, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , and LiN (CF ₃ SO ₂ ) _2. . These lithium salts may be used individually by 1 type, and may be used in combination of 2 or more type. The concentration of the lithium salt is preferably from 0.1 mol / L to 5.0 mol / L, more preferably from 0.5 mol / L to 3.0 mol / L.

  Non-aqueous solvents include diethyl ether, dibutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, ethylene glycol phenyl ether, 1 Ether, such as 1,2-dimethoxyethane; formamide, N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylformamide, N-methylacetamide, N, N-dimethylacetamide, N-ethyl Acetamide, N, N-diethylacetamide, N, N-dimethylpropionamide, Amides such as oxamethyl phosphorylamide; sulfur-containing compounds such as dimethyl sulfoxide and sulfolane; dialkyl ketones such as methyl ethyl ketone and methyl isobutyl ketone; cyclic ethers such as ethylene oxide, propylene oxide, tetrahydrofuran, 2-methoxytetrahydrofuran and 1,3-dioxolane; Carbonates such as ethylene carbonate and propylene carbonate; γ-butyrolactone; N-methylpyrrolidone; solutions of organic solvents such as acetonitrile and nitromethane are preferred.

  Among these, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate are more preferable. These solvents may be used alone or in a combination of two or more.

(Polymer solid electrolyte)
The polymer solid electrolyte contains a polymer compound that forms a matrix, a lithium salt, and, if necessary, a plasticizer. Examples of the polymer compound include polyalkylene oxide derivatives such as polyethylene oxide and polypropylene oxide and polymers containing the derivatives, polyvinylidene fluoride, polyhexafluoropropylene, polycarbonate, phosphate ester polymers, polyalkylamines, polyacrylonitrile, poly Derivatives such as (meth) acrylic acid esters, polyphosphazenes, polyurethanes, polyamides, polyesters, polysiloxanes, polymers containing the derivatives, and the like can be given.

  Those having an oxyalkylene, urethane, or carbonate structure such as polyalkylene oxide, polyurethane, or polycarbonate in the molecule are preferable because they have good compatibility with various polar solvents and good electrochemical stability. From the viewpoint of stability, those having a fluorocarbon group such as polyvinylidene fluoride or polyhexafluoropropylene in the molecule are also preferred. These oxyalkylene, urethane, carbonate, and fluorocarbon groups may be contained in the same polymer. The repeating number of these groups should just be the range of 1-1000 respectively, and the range of 5-100 is preferable.

  As the lithium salt, the same lithium salt used for the non-aqueous electrolyte can be used. The content of the lithium salt is preferably 1 mol / kg or more and 10 mol / kg or less, and more preferably 1 mol / kg or more and 5 mol / kg or less. Moreover, as a plasticizer, the non-aqueous solvent used for a non-aqueous electrolyte solution can be used.

(2) Battery Manufacturing Method The lithium ion secondary battery and the lithium polymer battery can be manufactured by the following representative manufacturing methods, but are not limited thereto.

  First, a positive electrode sheet having a positive electrode active material layer formed on a current collector is prepared by a conventionally known method. Moreover, the negative electrode sheet in which the negative electrode active material layer is formed on the current collector is manufactured by the above-described negative electrode manufacturing method including the negative electrode active material.

  Next, the produced positive electrode sheet and negative electrode sheet are processed into a desired shape, combined and laminated to form a positive electrode sheet / separator / negative electrode sheet, and an electrode body is produced so that the positive electrode and the negative electrode do not touch each other. Then, the electrode body is housed in a coin type, square type, cylindrical type, sheet type container or the like. If there is a possibility that the electrode or separator has adsorbed moisture or oxygen when laminating the electrode or housing the electrode body, it remains in an inert atmosphere with reduced pressure and / or low dew point (-50 ° C or lower). After drying again, move to an inert atmosphere with a low dew point.

  Next, a lithium ion secondary battery or a lithium polymer battery can be produced by injecting a nonaqueous electrolytic solution or a polymer solid electrolyte, attaching a lid, and sealing the container.

  A well-known separator can be used as the separator, but a porous microporous film made of polyethylene or polypropylene is preferable from the viewpoint of being thin and having high strength. The porosity is preferably higher from the viewpoint of ionic conduction, but if it is too high, it causes a decrease in strength and a short circuit between the positive electrode and the negative electrode. Therefore, the porosity is usually 30% or more and 90% or less, preferably 50% or more and 80% or less. Further, the thickness of the separator is preferably thin from the viewpoint of ion conduction and battery capacity, but if it is too thin, it causes a decrease in strength and a short circuit between the positive electrode and the negative electrode. Therefore, the thickness is usually 5 μm or more and 100 μm or less, preferably 5 μm or more and 50 μm or less. The microporous film can be used in combination of two or more kinds or other separators such as a nonwoven fabric.

  The lithium ion secondary battery or lithium polymer battery as described above can obtain high discharge capacity, large current charge / discharge characteristics, and initial efficiency because the electrode active material having the above-mentioned specific properties is contained in the electrode. It is possible to further balance these. Furthermore, the lithium ion secondary battery or the lithium polymer battery has a high energy density, can be charged / discharged at high speed, and has excellent cycle characteristics. Therefore, a lithium ion secondary battery or a lithium polymer battery can be used in place of a battery using a negative electrode using a conventional graphite material and applied to a battery of an electric vehicle as well as a dry battery. Demonstrates good battery characteristics.

  The lithium ion secondary battery or lithium polymer battery as described above can be used for electronic devices, tools, automobiles, and the like. For example, it can be suitably used in a power source of a mobile phone, a mobile electronic device such as a PDA (Personal Digital Assistants), an electric tool, a large machine, a hybrid electric vehicle (HEV), and an electric vehicle. Moreover, it can also be used as a battery for electric power storage by combining with a wind power generator or a solar power generator.

  Specific examples of the present invention will be described below. However, the present invention is not limited to the following examples.

First, the evaluation methods of the average particle diameter, true density, BET specific surface area, and battery evaluation method of the negative electrode active materials used in Examples and Comparative Examples will be described.
[1] Average particle diameter The average particle diameter (D50) was determined from a value of 50% by measuring the particle size distribution using a laser diffraction scattering particle size distribution measuring device Micro Trunk HRA (manufactured by Nikkiso Co., Ltd.).

[2] True density The true density was measured by a gas phase substitution method using helium gas with an ultra pycnometer 10001 manufactured by Yuasa Ionics Co., Ltd.

[3] BET specific surface area The BET specific surface area was measured by a BET method using nitrogen gas in NOVA2200e manufactured by Yuasa Ionics Co., Ltd.

[4] Battery Production Method and Evaluation Method (1) Negative Electrode To 100 g of the negative electrode active material of each Example and Comparative Example, 1.5 g of carboxymethyl cellulose (CMC) as a thickener and water were appropriately added to adjust the viscosity. 3.8 g of an aqueous solution in which styrene-butadiene (SBR) fine particles with a solid content ratio of 40% were dispersed was added and stirred and mixed to prepare a slurry dispersion having sufficient fluidity. Next, the prepared dispersion was applied onto a copper foil having a thickness of 20 μm using a doctor blade so as to be uniform at a thickness of 150 μm, dried on a hot plate, and then dried at 70 ° C. for 12 hours in a vacuum dryer. It was. And after drying, it pressure-molded with the roll press, the density was adjusted, and the negative electrode for battery evaluation was obtained. The coating amount of the negative electrode was 6 mg / cm ² , and the electrode density was 1.2 g / cc.

(2) Positive electrode 90 g of Li ₃ Ni _1/3 Mn _1/3 Co _1/3 as a positive electrode active material, 5 g of carbon black (manufactured by TIMCAL) as a conductive additive, and 5 g of polyvinylidene fluoride (PVDF) as a binder The mixture was stirred and mixed with N-methyl-pyrrolidone as appropriate to prepare a slurry dispersion.

Next, the prepared dispersion is applied on a 20 μm thick aluminum foil using a roll coater so as to be uniform at a thickness of 150 μm, dried on a hot plate, and then dried at 90 ° C. for 12 hours in a vacuum dryer. I let you. And after drying, it pressure-molded with the roll press, the density was adjusted, and the positive electrode for battery evaluation was obtained. The coating amount of the positive electrode was 10 mg / cm ² , and the electrode density was 3.0 g / cc.

(3) Electrolyte solution As a nonaqueous solvent, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 3: 7, and 1.0 mol of lithium hexafluorophosphate (LiPF ₆ ) is used as an electrolyte salt. / L dissolved was used as an electrolytic solution.

(4) Battery production:
[Bipolar cell]
First, a negative electrode and a positive electrode piece having an area of 20 cm ² were obtained by punching out the negative electrode and the positive electrode. An Al tab was attached to the Al foil of the positive electrode piece, and an Ni tab was attached to the Cu foil of the negative electrode piece. Next, the polypropylene microporous film was sandwiched between the negative electrode piece and the positive electrode piece, and packed in an aluminum laminate in that state. Next, an electrolytic solution was poured into the aluminum laminate. Thereafter, the opening was sealed by thermal fusion to obtain a battery for evaluation (design capacity 25 mAh).

[Counter electrode lithium cell]
The counter electrode lithium cell is laminated with a polypropylene microporous film (Polypore Corporation, Cellguard 2400) sandwiched between a produced negative electrode and a metal lithium foil punched out to 16 mmφ in a polypropylene screwed lid cell (inner diameter of about 18 mm). Then, an electrolyte solution was added to prepare.

(5) Initial efficiency and discharge capacity Evaluation was conducted using a counter electrode lithium cell. Charging is performed by CC (constant current: constant current) charging (hereinafter also referred to as CC mode) at 0.2 mA from the rest potential to 0.002V. Next, it switches to CV (constant voltage: constant voltage) charging (hereinafter also referred to as CV mode) at 0.002 V, and is stopped when the current value drops to 25.4 μA.

  Discharging is performed at 0.2 mA in CC mode with an upper limit voltage of 1.5V. The test is performed in a thermostat set to 25 ° C. At this time, the capacity at the first discharge was defined as the discharge capacity. The ratio of the amount of electricity at the time of initial charge / discharge, that is, the result of expressing the amount of discharged electricity / the amount of charged electricity as a percentage was defined as the initial efficiency.

(6) Large current load test A test was conducted using a bipolar cell. In the test, the bipolar cell was charged at 5 mA in the CC-CV mode with an upper limit voltage of 4.15 V and a cut-off current value of 1.25 mA, and then discharged at 125 mA (= 5 C) in the CC mode at the lower limit voltage of 2.8 V. Based on the 2C discharge capacity (0.2C = 5 mA), the ratio of the discharge capacities at 1C, 5C, and 10C was calculated.

  In addition, the bipolar cell was discharged at 5 mA in CC mode with a lower limit voltage of 2.8 V, and then charged with 125 mA (= 5 C) in CC mode with an upper limit voltage of 4.15 V, and 0.2 C charge capacity (0.2 C = 5 mAh) was obtained. As a reference, the ratio of charge capacities at 1C, 5C, and 10C was calculated.

(7) Electrode density Test electrodes were prepared as follows. First, in the first step, the electrode paste was applied onto a high-purity copper foil to a thickness of 150 μm using a doctor blade, and vacuum-dried at 70 ° C. for 12 hours. In the next step, the dried product is punched to 15 mmφ, the punched electrode is sandwiched between super steel press plates, and the press pressure is 1 × 10 2 N / mm ² (1 × 103 kg / cm ³ ) with respect to the electrode. Pressed. About the obtained electrode, the electrode density was computed from electrode mass and electrode thickness.

[Examples and Comparative Examples]
In the following examples and comparative examples, one raw material was selected from three types of cokes A, B, and C to prepare a negative electrode active material. Each coke was produced as follows.

(Coke A)
First, in the first step, Iranian crude oil (API30, wax content 2%, sulfur content 0.7%) is subjected to atmospheric distillation, and a sufficient amount of molybdenum nickel catalyst is used for the heavy fraction, Reaction with hydrogen at 280 ° C. and 40 atm. In the next step, the solid content of the catalyst and the like was centrifuged until the obtained oil became transparent to obtain a viscous liquid. In the next step, this oil was put into a small delayed coking process. The drum inlet temperature was 550 ° C., and the drum internal pressure was 600 kPa (6 kgf / cm ² ), and this state was maintained for 10 hours. And finally, water cooling was performed to obtain a black lump.

(Coke B)
First, in the first step, crude oil produced in Liaoning Province, China (API28, wax content 17%, sulfur content 0.66%) is distilled at atmospheric pressure to provide a sufficient amount of Y-type zeolite catalyst for heavy distillate. Was used for fluidized bed catalytic cracking at 510 ° C. and normal pressure. In the next step, solids such as the catalyst were centrifuged until the obtained oil became transparent to obtain a decant oil. In the next step, this oil was put into a small delayed coking process. The drum inlet temperature was 505 ° C., and the drum internal pressure was 600 kPa (6 kgf / cm ² ), and this state was maintained for 10 hours. And finally, water cooling was performed to obtain a black lump.

(Coke C)
The raw material was a residue obtained by atmospheric distillation of Mexican crude. The components of the raw material are a specific gravity of 0.7 ° API, an asphaltene content of 15% by mass, a resin content of 14% by mass, and a sulfur content of 5.3% by mass. This raw material was put into a small delayed coking process. At this time, the heater outlet temperature before the coke drum was 560 ° C., and the drum internal pressure was 207 kPa (2 kgf / cm ² ). Then, unlike usual, coke is in a state of being granulated into particles having a particle size of about 3 to 8 mm. This was cooled and removed from the coking drum.

  The cross section of each coke was observed with a polarizing microscope, and the area ratio of Da (60), ARb (60), flow structure and mosaic structure was calculated. The observation method using the polarizing microscope and the analysis method of the optical structure are the same as the observation method and analysis method of the cross section of the coke described above.

First, in the first step, a double-sided tape was affixed to the bottom of a plastic sample container having an internal volume of 30 cm ³ , and about 2 cups of spatula (about 2 g) was placed on the coke. The next step is a cold embedding resin (trade name: cold embedding resin # 105, manufacturing company: Japan Composite Co., Ltd., sales company: Marumoto Struers Co., Ltd.) and a curing agent (trade name: curing agent (M Agent), manufacturing company: Nippon Oil & Fat Co., Ltd., sales company: Marumoto Struers Co., Ltd.) and kneaded for 30 seconds. In the next step, the obtained mixture (about 5 ml) was slowly poured into a sample container until the height became about 1 cm, and allowed to stand for 1 day to solidify. In the next step, the solidified sample was taken out and the double-sided tape was peeled off. In the last step, the surface to be measured of the sample was polished using a polishing plate rotating type polishing machine.

  Polishing was performed by setting the rotational speed of the polishing plate to 1000 rpm and pressing the polishing surface of the sample against the polishing plate. For polishing, the counts of the polishing plates were changed in the order of # 500, # 1000, # 2000, and finally alumina (trade name: Baikalox type 0.3CR, particle size 0.3 μm, manufacturer: manufactured by Baikowski) , A sales company: Baikowski Japan).

  Next, the cross section of the polished sample was observed by fixing the sample with a clay on a preparation and observing with a polarizing microscope (trade name: BX51, manufactured by OLYMPAS).

  Observation was performed at 200 times, and a cross section of the sample was photographed with a CAMEDIA C-5050 ZOOM digital camera manufactured by OLYMPUS connected to a polarizing microscope. The shutter time was 1.6 seconds. A rectangular field of view of 480 μm × 540 μm was analyzed from the photographed data. For image analysis, ImageJ (manufactured by National Institutes of Health) was used to determine the color of the blue, yellow, red, and black portions. The area and aspect ratio of each optical structure were calculated for each of the blue, yellow, and red optical structures. Then, Da (60) and ARb (60) were calculated from the area and aspect ratio of the obtained optical structure.

Table 2 below shows the observation results of coke A, B, and C.

<Example 1>
In Example 1, the coke A was pulverized and classified so as to have an average particle size of 24 μm, and then heat-treated in a nitrogen atmosphere at 1300 ° C. for 3 hours to prepare a negative electrode active material. Table 3 below shows the BET specific surface area, particle size distribution, (002) plane spacing (d002), C-axis crystallite size (Lc (002)), and true density of this negative electrode active material.

  Next, carboxymethyl cellulose (CMC) is mixed with this negative electrode active material, water is additionally mixed and kneaded, and the styrene-butadiene copolymer rubber (SBR) becomes 1.5 mass% in the total solid. In addition, a coating liquid for forming a negative electrode was prepared. This negative electrode forming coating solution was applied onto a copper foil and dried to prepare a negative electrode of a lithium ion secondary battery. In Example 1, battery evaluation was performed using this negative electrode. The evaluation results are shown in Tables 3 and 4.

<Example 2>
In Example 2, the coke B was pulverized and classified so as to have an average particle diameter of 21 μm, and then heat-treated at 1300 ° C. in a nitrogen atmosphere for 3 hours to prepare a negative electrode active material. Table 3 shows the BET specific surface area, particle size distribution, (002) plane spacing (d002), C-axis crystallite size (Lc (002)), and true density of this negative electrode active material.

  Next, using this negative electrode active material, a negative electrode was produced in the same manner as in Example 1, and battery evaluation was performed using this negative electrode. The evaluation results are shown in Tables 3 and 4.

<Example 3>
In Example 3, the coke A was pulverized and classified so that the average particle size was 24 μm, and the average particle size was 7.0 μm and substantially 30 μm or more so as to be 2% by mass with respect to the whole. An anisotropic petroleum pitch (softening point: 230 ° C., residual carbon ratio: 73%) containing no particles was dry-mixed at 2000 rpm for 20 minutes with a rotating and rotating mixer to obtain a mixture.

  Next, this mixture was heat-treated at 1300 ° C. in a nitrogen atmosphere for 3 hours to prepare a negative electrode active material. Table 3 shows the BET specific surface area, particle size distribution, (002) plane spacing (d002), C-axis crystallite size (Lc (002)), and true density of this negative electrode active material.

  Next, using this negative electrode active material, a negative electrode was produced in the same manner as in Example 1, and battery evaluation was performed using this negative electrode. The evaluation results are shown in Tables 3 and 4.

<Example 4>
In Example 4, a negative electrode active material was produced in the same manner as in Example 2 except that the negative electrode active material obtained in Example 2 was oxidized at 700 ° C. in an air atmosphere for 1 hour. Table 3 shows the BET specific surface area, particle size distribution, (002) plane spacing (d002), C-axis crystallite size (Lc (002)), and true density of this negative electrode active material.

  Next, using this negative electrode active material, a negative electrode was produced in the same manner as in Example 1, and battery evaluation was performed using this negative electrode. The evaluation results are shown in Tables 3 and 4.

<Example 5>
In Example 5, a negative electrode active material was produced in the same manner as in Example 4 except that the oxidation treatment temperature was 1000 ° C. Table 3 shows the BET specific surface area, particle size distribution, (002) plane spacing (d002), C-axis crystallite size (Lc (002)), and true density of this negative electrode active material.

  Next, using this negative electrode active material, a negative electrode was produced in the same manner as in Example 1, and battery evaluation was performed using this negative electrode. The evaluation results are shown in Tables 3 and 4.

<Example 6>
In Example 6, a negative electrode active material was produced in the same manner as in Example 2 except that coke B was pulverized and classified so that the average particle diameter was 21 μm. Table 3 shows the BET specific surface area, particle size distribution, (002) plane spacing (d002), C-axis crystallite size (Lc (002)), and true density of this negative electrode active material.

  Next, using this negative electrode active material, a negative electrode was produced in the same manner as in Example 1, and battery evaluation was performed using this negative electrode. The evaluation results are shown in Tables 3 and 4.

<Example 7>
In Example 7, a negative electrode active material was produced in the same manner as in Example 2 except that heat treatment was performed at 1100 ° C. in a nitrogen atmosphere for 3 hours. Table 3 shows the BET specific surface area, particle size distribution, (002) plane spacing (d002), C-axis crystallite size (Lc (002)), and true density of this negative electrode active material.

  Next, using this negative electrode active material, a negative electrode was produced in the same manner as in Example 1, and battery evaluation was performed using this negative electrode. The evaluation results are shown in Tables 3 and 4.

<Example 8>
In Example 8, coke B was heat-treated at 1300 ° C. in a nitrogen atmosphere for 3 hours, and then pulverized and classified so that the average particle size was 22 μm to prepare a negative electrode active material. Table 3 shows the BET specific surface area, particle size distribution, (002) plane spacing (d002), C-axis crystallite size (Lc (002)), and true density of this negative electrode active material.

  Next, using this negative electrode active material, a negative electrode was produced in the same manner as in Example 1, and battery evaluation was performed using this negative electrode. The evaluation results are shown in Tables 3 and 4.

  In the above Examples 1-8, the discharge capacity and the initial efficiency were high, and the large current charge / discharge characteristics were also excellent. In addition, the three balances of discharge capacity, initial efficiency, and large current charge / discharge characteristics were good. Therefore, it can be seen from the results shown in Examples 1 to 8 that a battery having excellent battery characteristics can be obtained by using the negative electrode active material to which the present invention is applied.

<Comparative Example 1>
In Comparative Example 1, coke C was pulverized and classified to an average particle size of 20 μm, and then heat-treated at 1300 ° C. in a nitrogen atmosphere for 3 hours to prepare a negative electrode active material. Table 3 shows the BET specific surface area, particle size distribution, (002) plane spacing (d002), C-axis crystallite size (Lc (002)), and true density of this negative electrode active material.

  Next, using this negative electrode active material, a negative electrode was produced in the same manner as in Example 1, and battery evaluation was performed using this negative electrode. The evaluation results are shown in Tables 3 and 4.

  In Comparative Example 1, the discharge capacity was higher than in Examples 1 to 6 and 8, but the initial efficiency was remarkably lowered and the large current charge / discharge characteristics were also lowered.

<Comparative Example 2>
In Comparative Example 2, a negative electrode active material was prepared in the same manner as in Example 1 except that heat treatment was performed at 2000 ° C. in a nitrogen atmosphere for 3 hours. Table 3 shows the BET specific surface area, particle size distribution, (002) plane spacing (d002), C-axis crystallite size (Lc (002)), and true density of this negative electrode active material.

  Next, using this negative electrode active material, a negative electrode was produced in the same manner as in Example 1, and battery evaluation was performed using this negative electrode. The evaluation results are shown in Tables 3 and 4.

  In Comparative Example 2, the initial efficiency was higher than those in Examples 1 to 8, but the discharge capacity was significantly reduced and the large current charge / discharge characteristics were also reduced.

<Comparative Example 3>
In Comparative Example 3, a negative electrode active material was produced in the same manner as in Example 2 except that heat treatment was performed at 900 ° C. in a nitrogen atmosphere for 3 hours. Table 3 shows the BET specific surface area, particle size distribution, (002) plane spacing (d002), C-axis crystallite size (Lc (002)), and true density of this negative electrode active material.

  Next, using this negative electrode active material, a negative electrode was produced in the same manner as in Example 1, and battery evaluation was performed using this negative electrode. The evaluation results are shown in Tables 3 and 4.

  In Comparative Example 3, the discharge capacity was higher than in Examples 1 to 8, but the initial efficiency was significantly reduced, and the large current charge / discharge characteristics were also reduced.

Therefore, in Comparative Examples 1 to 3, all of the discharge capacity, initial efficiency, and large current charge / discharge characteristics could not be improved, and the three balances were poor. Therefore, it can be seen that the negative electrode active materials of Comparative Examples 1 to 3 cannot provide excellent batteries as in the examples.

Claims (14)

In the rectangular visual field of 480 μm × 540 μm in the polarizing microscope image obtained by observing the optical structure with the polarizing microscope, the areas are accumulated in order from the optical structure with the smallest area, and the accumulated area becomes 60% of the total area of the optical structure. area of the optical tissue is at 10 [mu] m ² or more 5000 .mu.m ² or less when a anisotropic structure formed by the flow organization and fine mosaic structure, the area ratio of the flow structure and the fine mosaic organization 40:60 Coke that is ~ 70: 30. In a rectangular field of view of 480 μm × 540 μm in a polarizing microscope image obtained by observing an optical structure with a polarizing microscope,
2. The coke according to claim 1, wherein the optical tissue has an aspect ratio of 1.5 or more and 6 or less when the number of optical structures is counted in order from the optical structure having the smallest aspect ratio and reaches 60% of the total number of optical structures. . It is a fired product of coke,
The volume-based average particle diameter by laser diffraction method is 5 μm or more and 30 μm or less,
In the rectangular visual field of 480 μm × 540 μm in the polarizing microscope image obtained by observing the optical structure with the polarizing microscope, the areas are accumulated in order from the optical structure with the smallest area, and the accumulated area becomes 60% of the total area of the optical structure. area of the optical tissue is at 10 [mu] m ² or more 5000 .mu.m ² or less when a anisotropic structure formed by the flow organization and fine mosaic structure, the area ratio of the flow structure and the fine mosaic organization 40:60 An electrode active material having a true density of 1.9 g / cm ^{2 to} 2.17 g / cm ² and a crystallite size in the c-axis direction of hexagonal graphite of 1 nm to 10 nm. In a rectangular field of view of 480 μm × 540 μm in a polarizing microscope image obtained by observing an optical structure with a polarizing microscope,
4. The electrode according to claim 3, wherein the number of the optical tissues is counted in order from the optical structure having the smallest aspect ratio, and the aspect ratio of the optical tissues when reaching 60% of the total number of the optical tissues is 1.5 or more and 6 or less. Active material. The electrode active material according to claim 3 or 4, wherein the BET specific surface area is 0.5 m ² / g or more and 5 m ² / g or less, and the interplanar spacing as hexagonal graphite is 0.341 nm or more and 0.346 nm or less. . It is a manufacturing method of the electrode active material given in any 1 paragraph of Claims 3 thru / or 5,
Having a step of firing the coke according to claim 1 or 2 in an inert atmosphere of 950 ° C to 1500 ° C,
A method for producing an electrode active material, wherein the coke is pulverized and classified so that the volume-based average particle diameter by laser diffraction method is 5 μm or more and 30 μm or less before or after the firing.   The coke is mixed with the petroleum pitch or coal pitch so as to be in the range of 0.5% by mass or more and 15.0% by mass or less based on the total mass of the combined coke and petroleum pitch or coal pitch. The method for producing an electrode active material according to claim 6.   The method for producing an electrode active material according to claim 6 or 7, wherein the coke baked after the pulverization and classification, or the coke pulverized and classified after the calcination is further baked in an oxidizing atmosphere of 300 ° C or higher and 1100 ° C or lower. .   An electrode material comprising the electrode active material according to any one of claims 3 to 5.   An electrode paste comprising the electrode active material according to claim 3 and a binder.   An electrode comprising the electrode active material according to any one of claims 3 to 5. The electrode according to claim 11, wherein the electrode density is 1 g / cm ² or more and 1.5 g / cm ² or less.   A battery comprising the electrode according to claim 11.   The battery according to claim 13, which is a lithium ion secondary battery.