JP2018006270A - Graphite carbon material for lithium ion secondary battery negative electrode, method for manufacturing the same, and negative electrode or battery arranged by use thereof - Google Patents

Abstract

Lithium ion secondary battery negative electrode in which lithium ions have high diffusibility in solids due to a small particle size and side reaction on an active material surface is greatly reduced by making the specific surface area relatively small A graphitic carbon material is provided. An (002) plane interlayer distance (d002) calculated from an X-ray diffractometer is 0.340 nm or less, a crystallite diameter Lc (002) is 120 nm or less, a true specific gravity is 2.23 g / cm 3 or more, an average Particle size is less than 1-10 μm, BET specific surface area is 1.0-6.0 m 2 / g, ellipse length-short ratio average is 0.35-1.00, ash content is 0.0005-0.1 wt%, and transition A graphitic carbon material for a negative electrode of a lithium ion secondary battery, wherein the element content is less than 5 to 50 wtppm. [Selection figure] None

Description

  The present invention relates to a carbon material for a negative electrode of a lithium ion secondary battery having both safety, output characteristics and energy density, and a negative electrode and a lithium ion secondary battery using the same. This battery is suitable for a wide range of applications such as a hybrid vehicle such as a plug-in hybrid vehicle, an electric vehicle, and a power tool.

  In modern society supported by electric energy, secondary batteries that can be charged and discharged and can be used repeatedly have become indispensable. In particular, the lithium ion secondary battery not only has excellent features such as a high operating potential, a large battery capacity, and a long cycle life, but also has a low environmental pollution. -Widely used in place of cadmium batteries and nickel metal hydride batteries.

  Lithium ion secondary batteries are mainly used for power sources for small portable electronic devices such as notebook computers and smartphones. In recent years, electric vehicles, motors and gasoline engines have been used to address energy and environmental issues. It is also widely used as a large battery of a hybrid electric vehicle (plug-in hybrid electric vehicle) combined with the above. In addition to this, it is used in combination with generators with variable output, such as solar power generation and wind power generation, to control fluctuation absorption or output to be constant, or to reduce fluctuations and peaks on the demand side. The use as a stationary storage battery for the purpose of shifting has attracted attention, and it is expected that the required characteristics will become higher with increasing demand in various applications related to these energy and environmental problems.

  Examples of the negative electrode active material constituting the negative electrode of the lithium ion secondary battery include carbon materials such as graphite, lithium titanate, silicon, and tin. Carbon materials are generally used from the viewpoint of safety and life. It has been. Among carbon materials, graphite material is an excellent material with high energy density, so it is not only used as a power source for small portable electronic devices but also as a power source for hybrid electric vehicles or for stationary storage batteries. The use of secondary batteries as negative electrode active materials and research and development are progressing.

  The above hybrid electric vehicle is required to have long-term reliability as well as rapid charge and rapid discharge performance. That is, development of a battery that achieves both high input / output and long life is desired.

  Therefore, various lithium secondary battery negative electrode active materials have been proposed in which particles are made small in order to ensure rapid charge / discharge characteristics to increase the diffusibility of lithium ions in the solid and the specific surface area is made small in order to ensure a long life. Yes.

  In Patent Document 1, it is proposed that bulk mesophase graphitized material or carbide having a high degree of spheroidization is used as a negative electrode active material for a lithium ion secondary battery, but a bulk mesophase separation step or the like is required.

  Patent Document 2 discloses a graphite material having an aspect ratio of 1.00 to 1.32 obtained by pulverizing raw coke in which volatile components remain, not calcined coke, and then graphitizing. However, the particles are large and the diffusion in the solid becomes large.

In Patent Document 3, it is shown that a spherical carbon material having a high sphericity is obtained by subjecting raw coke powder to a spheroidizing process that imparts compressive stress and shear stress, followed by carbonization and graphitization. Has been. However, in addition to the complexity of the process, the BET specific surface area is as low as less than 1 m ² / g.

  Patent Document 4 discloses a graphitic carbon material having a circularity of 0.7 to 0.9 and an average particle diameter of 1 to 30 μm by applying a compressive shear stress to raw coke whose particle size is adjusted by pulverization and classification. Has been. However, since this carbon material contains transition metal as much as 100-2500 ppm, it does not satisfy the long-term reliability required for automobile batteries.

  In Patent Document 5, a raw coal composition obtained by coking a heavy oil composition by a delayed coking process, the H / C atomic ratio is 0.30 to 0.50, and the micro strength is 7 to 17 wt%. A raw material carbon composition of a negative electrode graphite material for a lithium ion secondary battery is disclosed. However, there are few descriptions that teach the characteristics that graphite materials should have.

In Patent Document 6, a graphite material with an average particle diameter of 1 to 50 μm and a graphitized material with a quinoline insoluble content of 1 wt% or less is blended in an amount of 2 to 35 wt% with respect to the heavy oil. A method for producing a negative electrode material for a lithium secondary battery, in which raw coke is obtained by delayed coking and then heat treatment and graphitization is disclosed. In this method, the addition of the graphitized material reduces the proportion of the amorphous carbon structure having excellent output characteristics, leading to a decrease in output characteristics.
As described above, any of the methods described in the above documents is not sufficient for obtaining a secondary battery having both high input / output and long life as a lithium secondary battery negative electrode material.

Japanese Patent No. 3126030 JP 2007-172901 A JP 2014-197496 A JP 2014-194852 A Japanese Patent No. 5728475 Japanese Patent No. 4233800

  The present invention provides a lithium ion secondary battery negative electrode in which lithium ions have high diffusibility in solids due to a small particle size, and side reactions on the active material surface are greatly reduced by making the specific surface area relatively small. An object of the present invention is to provide a graphite carbon material for use. Another object of the present invention is to provide a lithium ion secondary battery negative electrode and a lithium ion secondary battery using the graphitic carbon material.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have made the above-mentioned problems by controlling the surface area of the graphitic carbon material with a small particle diameter by using amorphous coke based on a specific raw material. The inventors have found that the present invention can be solved, and have completed the present invention.

That is, according to the present invention, the interlayer distance calculated from the X-ray diffractometer is 0.340 m or less, the crystallite diameter Lc (002) is 120 nm or less, the true specific gravity is 2.23 g / cm ³ or more, and the average particle diameter is 1 to 10 μm, BET specific surface area of 1.0 to 6.0 m ² / g, ellipse length / short ratio average of 0.35 to 1.00, ash content of 0.0005 to 0.1 wt% or less, and transition element content of A graphitic carbon material for a negative electrode of a lithium ion secondary battery, characterized by being less than 5 to 50 wtppm.

The graphitic carbon material for a negative electrode of the lithium ion secondary battery has an interlayer distance (d002) of (002) plane calculated from an X-ray diffraction apparatus of 0.340 to 0.370 nm and a true specific gravity of 1.90 to 2. 10 g / cm ³ , average particle size of less than 1 to 10 μm, BET specific surface area of 1.0 to 6.0 m ² / g, ellipse length / short ratio average of 0.30 to 1.00, ash content of 0.05 to It is preferably obtained by graphitizing an amorphous carbon material having a 1.00 wt% and transition element content of less than 50 to 700 wtppm.

  Another aspect of the present invention is a lithium ion secondary battery negative electrode comprising the above graphitic carbon material for a lithium ion secondary battery negative electrode as an essential component, and further a lithium ion secondary battery using these lithium ion secondary battery negative electrodes It is a battery.

The lithium ion secondary battery preferably has a 0.2 second direct current resistance (DCR _0.2 ) of 22Ω or less during discharge.

The DCR _0.2 is represented by the following formula.
DCR _0.2 = ΔE / ΔI
here,
ΔE: Voltage after 5C rate 0.2 seconds -1C rate Voltage after 0.2 seconds ΔI; 5C rate current -1C rate current

  Furthermore, the present invention provides a raw coke by coking a coal or petroleum heavy oil composition having a quinoline insoluble content adjusted to a range of 10 to 30 wt% by a delayed coking process, and obtaining the obtained coke. The raw material carbon composition having an average particle diameter of 1 to 10 μm is pulverized, and then the raw material carbon composition is calcined at 800 ° C. to 1500 ° C. to obtain an amorphous carbon material. The method for producing a graphitic carbon material for a negative electrode of a lithium ion secondary battery, wherein the carbon material is graphitized at 2500 ° C to 3200 ° C.

  The graphite carbon material for a negative electrode of a lithium ion secondary battery of the present invention is excellent in rapid chargeability while having a high discharge capacity, which is a characteristic of a graphite material, by using it as a negative electrode active material of a secondary battery. A lithium ion secondary battery having a long life and excellent long-term reliability can be obtained.

The graphitic carbon material for a negative electrode of a lithium ion secondary battery of the present invention (hereinafter also referred to as a graphite carbon material or a graphitic carbon material for a negative electrode) is advantageously graphitized amorphous carbon material having the following characteristics. Obtained. This amorphous carbon material has an (002) plane interlayer distance (d002) of 0.340 to 0.370 nm, a true specific gravity of 1.90 to 2.10 g / cm ³ , an average calculated from an X-ray diffractometer. A particle size of less than 1-10 μm, a BET specific surface area of 1.0-6.0 m ² / g, an elliptical length-short ratio average of 0.30-1.00, an ash content of 0.05-1.00 wt%, and The transition element content is satisfied to be less than 50 to 700 wtppm.

  The amorphous carbon material is preferably obtained by calcining the following raw coke at 800 ° C. to 1500 ° C. This raw coke satisfies a micro strength of 0.01 to 3.0 wt% and an average particle size of less than 1 to 10 μm.

  The raw coke is excellent in that it is obtained by coking a coal-based or petroleum-based heavy oil (hereinafter also referred to as heavy oil) whose quinoline insoluble content (QI) is adjusted to a range of 10 to 30 wt%. .

Examples of the heavy oil include coal-based heavy oil such as coal tar, tar-based heavy oil, and tar pitch, and petroleum-based heavy oil such as petroleum-based pitch, asphalt, heavy oil, and heavy crude oil. In this heavy oil, the quinoline insoluble content (QI) is preferably adjusted to 10 to 30 wt%, and by controlling the QI within this range, mesophase development is inhibited during coking, and carbon crystal growth Is suppressed, and a good amorphous structure appears. If the amount of QI is too small, the amorphous structure does not appear, and if it is excessive, the crystal growth of carbon is excessively inhibited, resulting in non-graphitizable carbon. When the QI amount is adjusted within the above range, the crystal growth of carbon is moderately inhibited, so that a homogeneous amorphous structure can be expressed. In addition, the true density of the carbon material can be sufficiently increased and the energy density of the negative electrode can be increased. It can also be increased. The QI may be adjusted by blending a heavy oil containing a large amount of QI and a heavy oil having a low QI, or by adjusting only the QI component to a heavy oil having a low QI. Also good. For example, when the QI in the heavy oil is small, the separated QI can be added to the heavy oil by the de-QI treatment.
In order to obtain the raw coke or amorphous carbon material, it is preferable to use a heavy coal oil. Petroleum heavy oil has a high sulfur content, which reacts with lithium (Li) when used as an amorphous carbon material for a negative electrode of a lithium ion secondary battery, and causes a decrease in life characteristics. On the other hand, coal-based heavy oil has a low sulfur content, and it is preferable to use coal-based heavy oil from the viewpoint of life characteristics.
Further, the above QI changes the mesophase structure of raw coke and calcined coke and contains a large amount of ash and transition elements, which is considered to have a good effect on the characteristics of the graphitic carbon material.

  For heavy oil coking, for example, using a coking equipment such as a delayed coker, the maximum ultimate temperature is about 400 ° C. to 700 ° C. for about 24 hours, and the heat cracking / polycondensation reaction is advanced to produce raw coke. It is suitable to carry out by the delayed coking method.

  The raw coke preferably has an optically isotropic structure uniformly dispersed in the cross-sectional observation image of the polarizing microscope. When raw coke takes an optically isotropic structure, it becomes possible to obtain a fine powder with a small aspect ratio during pulverization. Such raw coke and an amorphous carbon material (also referred to as calcined coke) obtained by further heat treatment are amorphous coke, which is different from needle coke in which coarse carbon crystals are aligned in one direction. Is dense and randomly arranged.

The raw coke is taken out in a lump from the coking equipment, and is used after being pulverized using a pulverizer such as an atomizer used industrially.
Generally, raw coke obtained with a delayed coker has insufficient crystal growth of carbon and still contains moisture and volatile components. Therefore, in order to remove these volatile components, after that, further about 900 to 1500 ° C. A calcination treatment by temperature is generally performed. However, the calcined coke obtained by performing the calcining treatment grows carbon crystals and develops anisotropy. Therefore, when the calcined coke is pulverized into a powder, it becomes a particle powder having a large aspect ratio. Therefore, it is preferable to grind or classify to a predetermined particle size in the state of raw coke in which volatile matter still remains, not in the state of calcined coke. In addition, as a volatile matter of raw coke, it is preferable that it is 1.0-10 wt%, and it is more preferable that it is 3.0-7.0 wt%. If the volatile content is less than 1.0 wt%, fine powder is generated during pulverization, and the classification yield decreases. On the other hand, if it exceeds 10 wt%, a large amount of volatile matter is generated during firing, which is not preferable from the viewpoint of firing yield.

  There is a correlation between the growth state of carbon crystals and grindability, and in order to obtain the graphitic carbon material for negative electrode of the present invention, the micro strength of raw coke is in the range of 0.01 to 3.0 wt%. If the microstrength is less than 0.01 wt%, it is impossible to maintain the qualitative quality of the particle size control at the time of pulverization, and it is impossible to keep the quality constant. In addition to a decrease in the number of particles, there is a problem such as an increase in production cost due to a decrease in pulverization efficiency. The preferred microstrength is 0.05 to 1.0 wt%, more preferably 0.10 to 0.50 wt%. The micro strength is known from Patent Document 5 and the like, and this micro strength is measured under the conditions described in the examples described later. The microintensity can be adjusted by changing the coking conditions. For example, the microintensity decreases as the QI amount increases.

  The raw coke after pulverization may be further subjected to spheronization treatment or surface coating in order to control the shape and BET specific surface area. Amorphous raw coke is random in structure, and the grain boundary size is dense and free of anisotropy. The sphericity of the particles can be easily improved by the treatment. Examples of the spheroidizing method include a method of mixing in the presence of a binder pitch that can be a raw coke raw material, a method of imparting mechanical external force to the raw coke, and a method of using these methods in combination. Among these methods, a method of granulating by applying a mechanical external force without using a binder component is particularly preferable because a fine powder can be easily obtained. Examples of the apparatus used for these include Nobilta, Mechanofusion (manufactured by Hosokawa Micron), Hybridization System (manufactured by Nara Machinery Co., Ltd.), Mechano Hybrid, Composit (manufactured by Nippon Coke Industries, Ltd.), and the like.

  As mentioned above, since the above-mentioned raw coke has good pulverization properties, if compressive shear stress is applied too much, the particles will be excessively pulverized and the desired particle size cannot be obtained. There is a need to. On the other hand, an appropriate volatile component exists as a plasticizer, so that it has deformation processability, and it is not necessary to excessively apply a strong external force such as compressive shear stress. As an indication of the processing time, the upper limit is about 120 minutes, and the processing temperature is preferably less than 300 ° C. from the viewpoint of productivity. In this way, crushed particles of raw coke can be shaped, the ellipse length / shortness ratio can be made closer to 1.00, and the BET specific surface area can be adjusted to a smaller value.

The particle size of the raw coke after pulverization or the particle size after performing the spheroidizing treatment or surface coating is set in a range such that the average particle size (D ₅₀ ) after heat treatment is 1 to 10 μm. Therefore, the particle size of the raw coke after grinding 1~10μm an average particle size _{(D 50),} preferably in that the 2-7 [mu] m. The measurement conditions for the average particle diameter follow the method described in the examples. Further, if the average particle size is within the above range, fine particles of less than 1.0 μm and coarse particles of 10.0 μm or more may be included, but fine particles of less than 0.5 μm and coarse particles of 20.0 μm or more. The content of the grains is preferably less than 10 vol%.

The raw coal composition obtained by pulverizing raw coke as described above has a BET specific surface area of 1.0 to 6.0 m ² / g, an average particle size (D ₅₀ ) of 1 to 10 μm, and an elliptical length. It is preferably processed into rounded fine particles having an average ratio of 0.30 to 1.00.

  The amorphous carbon material can be obtained by calcining raw coke pulverized material, which is the raw carbon composition, at a maximum temperature of 800 ° C. to 1500 ° C. in a low oxygen atmosphere. The calcination temperature is preferably in the range of 900 ° C to 1500 ° C, more preferably 1000 ° C to 1400 ° C. The calcining process removes moisture and volatile components from raw coke, converts hydrocarbons remaining as polymer components into coke, and promotes crystal growth. , Shuttle furnaces, tunnel furnaces, rotary kilns, roller hearth kilns, microwaves, and the like, but are not particularly limited to these equipments. Further, the calcining treatment may be either a continuous type or a batch type.

  The calcined coke obtained by the calcining treatment is particularly excellent as an amorphous carbon material as an intermediate of the graphitic carbon material for negative electrode of the present invention. The calcined coke or amorphous carbon material preferably has the following characteristics.

The interlayer distance (d002) of the (002) plane calculated from the X-ray diffractometer is 0.340 to 0.370 nm, preferably 0.340 to 0.350 nm.
The true specific gravity is 1.90 to 2.10 g / cm ³ , preferably 2.00 to 2.10 g / cm ³ .
The average particle size is less than 1-10 μm, preferably 2-8 μm.
The BET specific surface area is 1.0 to 6.0 m ² / g, preferably 1.0 to 5.0 m ² / g.
The ellipse length-short ratio average is 0.30 to 1.00, preferably 0.40 to 0.70.
Ash content is 0.05 to 1.00 wt%, preferably 0.20 to 0.80 wt%.
The transition element content is 50 to less than 700 wtppm, preferably 100 to 500 wtppm.

The ash includes oxides of Si, Ca, Al, and the like, and the transition element is Fe. The ash contains a large amount of metal elements, but these adversely affect the battery performance when the secondary battery is made. Therefore, if it is excessive, the long-term reliability of the secondary battery may be impaired. If the content of the transition element is higher than the above, there may be a problem of battery safety.
The presence of a large amount of ash and transition elements is not desired, but the presence of a small amount within the above range is rather desirable. In other words, ash and transition elements inhibit the anisotropy of particles by inhibiting the growth of carbon crystals, and have the effect of controlling the desired ellipse length to short ratio, so ash and transition elements in the above range are included. It is preferable.

  The raw coke pulverized product as the raw coal composition is subjected to a calcining treatment and subsequently graphitized. Graphitization can be performed at a temperature of 2500 ° C. to 3200 ° C. in a non-oxidizing atmosphere. At this time, a silicon-containing compound or a boron-containing compound may be used as a graphitization catalyst, or phosphorus or a phosphorus compound may be added. Further, after the graphitization, surface oxidation by high-temperature treatment in an air atmosphere can be separately performed.

The graphitic carbon material for negative electrode of the present invention can be obtained through the above method. This graphite carbon material for negative electrode has an (002) plane interlayer distance (d002) of 0.340 nm or less, a crystallite diameter Lc (002) of 120 nm or less, and a true specific gravity of 2 calculated from an X-ray diffractometer. 0.23 g / cm ³ or more, average particle diameter of 1 to 10 μm, BET specific surface area of 1.0 to 6.0 m ² / g, elliptical length / short ratio average of 0.30 to 1.00, ash content of 0.1 wt % Or less, and the transition element content is less than 50 wtppm.
The average particle size and axial length ratio of the graphitic carbon material for the negative electrode inherits the properties of the raw carbon composition before graphitization or the amorphous carbon material as an intermediate, but some changes Arise. In addition, since the crystal structure and the surface state change, and components that volatilize at high temperatures decrease, the specific surface area, transition element content, and the like also change as is generally known.

The BET specific surface area of the graphitic carbon material for negative electrode of the present invention is 1.0 to 6.0 m ² / g, preferably 1.0 to 5.0 m ² / g, and 1.0 to 4. More preferably, it is 5 m ² / g. By making the BET specific surface area in the above range, the reactivity with the electrolytic solution can be suppressed, the occurrence of side reactions during use can be reduced, and the lithium ion reactivity can be improved to obtain a charge / discharge rate. Can do. Furthermore, since the BET specific surface area also affects the speed of the surface reaction when lithium ions enter and exit the carbon structure, by subjecting the raw coke pulverized product to surface coating or spheronization to an appropriate value within the above range, It is good to control so that it may become in a more preferable range.

The graphitic carbon material for negative electrode of the present invention has an average particle diameter (D ₅₀ ) of 1.0 to less than 10.0 μm, desirably in the range of 2 to 8 μm, and more preferably 2 to 5 μm. preferable. When the average particle size is within the above range, when used as a negative electrode active material of a lithium ion secondary battery, diffusion of lithium ions into the active material is performed more rapidly than conventional graphite materials, and rapid chargeability and Li precipitation resistance is improved. When the average particle size is less than 1 μm, the side reaction on the surface increases due to the BET specific surface area becoming too large. If it is 10 μm or more, the BET specific surface area becomes too small, so that the reactivity of lithium ions is lowered, and the charge / discharge rate is slowed.
In addition, the measurement conditions of an average particle diameter follow the method as described in an Example. Further, if the average particle size is within the above range, fine particles of less than 1.0 μm and coarse particles of 10.0 μm or more may be included, but fine particles of less than 0.5 μm and coarse particles of 20.0 μm or more. The content of the grains is preferably less than 10 vol%.

Here, the diffusibility of lithium ions into the negative electrode active material (in-solid diffusibility) refers to the movement speed of lithium ions in the particles, and the use of a negative electrode active material having high diffusivity in the solid. Thus, the insertion and removal of lithium ions can be easily performed, so that the input / output characteristics and the Li deposition resistance of the secondary battery are improved.
In addition, regarding the carbon material for the negative electrode of the lithium ion secondary battery, in particular, the diffusion of lithium ions into the active material (diffusion in the solid) in the negative electrode active material particle itself, the output characteristic evaluation by the single particle of the negative electrode active material, the carbon material Can be evaluated by measuring direct current resistance (DCR) during a short time (for example, 0.2 seconds) of a secondary battery having a negative electrode as the negative electrode. In the former, the higher the output characteristics, the more the latter In, the smaller the resistance calculated from the DCR measurement, the better the solid internal diffusibility.

The graphitic carbon material for negative electrode of the present invention is graphitized so that the interlayer distance (d002) between 002 faces of carbon crystals is 0.340 nm or less and the true specific gravity is 2.23 g / cm ³ or more. . The crystallite diameter Lc (002) of the 002 plane that serves as an index of the size of the carbon crystal is 120 nm or less, preferably 100 nm or less, and more preferably 95 nm or less. By using raw coke having an amorphous structure for the raw coal composition, the graphite carbon material for negative electrode of the present invention has an internal structure consisting of innumerable fine graphite crystals, and therefore rounded fine particles. However, it is possible to obtain a graphitic carbon material for a negative electrode of a lithium ion secondary battery having both high capacity density, which is a characteristic of graphite, and high internal diffusion rate of lithium ions.

  Moreover, this graphite carbon material for negative electrodes has an average of the ellipse length-short ratio of 0.35 to 1.00, preferably 0.40 to 0.95, and more preferably 0.40 to 0.70. . The average of the ellipse length / short ratio is obtained by observing the particle cross section of the amorphous carbon material by a method such as SEM to obtain the ellipse-equivalent minor axis length (La) and the ellipse-equivalent major axis length (Lb). The / (Lb) ratio is calculated, this is performed for several tens of particles, and the average value is obtained. Specifically, the particle image observed by a method such as SEM can be analyzed using image analysis software (WinROOF: manufactured by Mitani Corporation). When this numerical value is within the above range, the carbon material particles become nearly spherical, and therefore the non-surface area of the fine particles can be reduced.

Furthermore, the graphite carbon material for negative electrode has an ash content of 0.0005 to 0.1 wt%, preferably 0.001 to 0.01 wt%. The transition element content is less than 5 to 50 wtppm, preferably 5 to 15 wtppm.
Since metal elements contained in ash and ash, especially transition elements such as Fe, may adversely affect battery performance when used as a secondary battery, the presence of a large amount is not desired. The presence of a small amount within the range is rather desirable to realize the internal structure and shape of the graphite material of the present invention.
In other words, when the ash and transition elements are excessive, when the amorphous carbon material is graphitized, it inhibits the arrangement of the carbon crystals and causes defects in the crystals, so that the lithium ions occluded in the negative electrode active material As a result, the amount that cannot be used due to trapping increases, the irreversible capacity increases, and the initial efficiency of the battery decreases. On the other hand, if the amount is too small, the carbon crystal size (Lc) becomes too large, so there is a problem that the ellipse equivalent length-to-short ratio cannot be controlled to a desired value, and ash and transition elements in the above range are included. Is required.

The negative electrode for a lithium ion secondary battery according to the present invention has a negative electrode active material formed by laminating a negative electrode active material using the graphitic carbon material for a negative electrode on a current collector such as a copper foil, and a binder or the like mixed therewith. Is obtained. This layer is referred to as a negative electrode active material layer.
In addition, the graphite carbon material for negative electrodes can also be made into the negative electrode active material which has the characteristic of both by using a mixture with another negative electrode active material as a negative electrode active material. The compounding ratio (weight ratio) in this case is 10: 1 to 1:10, preferably 10: 1 to 10: 5. Other negative electrode active materials include artificial graphite, spheroidized natural graphite, mesocarbon microbeads or graphitized products thereof with different particle sizes, amorphous carbon materials, low crystalline carbon materials (graphitizable carbon, non-graphitizable carbon) ), Silicon and its alloys.

The negative electrode active material layer is formed by preparing a slurry of the negative electrode active material and a binder using a solvent (for example, N-methylpyrrolidone, dimethylformamide, water, alcohol, etc.) and applying the slurry onto a current collector. , Drying, and then compacting under predetermined conditions. The thickness of the negative electrode active material layer obtained after consolidation is usually 30 to 150 μm. More specifically, for example, the negative electrode active material and the binder are dispersed in a solvent at a mass ratio of 93: 7 to 99: 2 (negative electrode active material: binder) and kneaded to obtain a slurry. By applying this slurry onto a copper foil having a predetermined thickness, drying the solvent under a drying condition of 60 to 150 ° C., and then compacting, an electrode (negative electrode) having a negative electrode active material layer can be obtained.
The binder is generally made of a fluorine resin powder such as polyvinylidene fluoride or a water-soluble binder such as polyimide resin, styrene butadiene rubber, carboxymethyl cellulose, but is not limited thereto.

As a positive electrode used in the lithium ion secondary battery of the present invention, a current collector obtained by slurrying a positive electrode active material, a binder, a conductive material and the like with an organic solvent or water, as in a normal secondary battery. It is used after being applied to and dried to form a sheet. The positive electrode active material contains a transition metal and lithium and is preferably a material containing one kind of transition metal and lithium. Examples thereof include a lithium transition metal composite oxide and a lithium-containing transition metal phosphate compound. These may be used in combination. As the transition metal of the lithium transition metal composite oxide, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, copper and the like are preferable. Specific examples of the lithium transition metal composite oxide include lithium cobalt composite oxide such as LiCoO ₂ , lithium nickel composite oxide such as LiNiO ₂ , and lithium manganese composite oxide such as LiMnO ₂ , LiMn ₂ O ₄ , and Li ₂ MnO _3. , Some of the transition metal atoms that are the main components of these lithium transition metal composite oxides are aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, magnesium, gallium, zirconium, etc. The thing substituted with the metal etc. are mentioned. Specific examples of the substituted ones include, for example, LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.80 Co _0.17 Al _0.03 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn _1.8 Al _0.2 O ₄ , LiMn _1.5 Ni _0.5 O ₄ or the like. Further, as the transition metal of the lithium-containing transition metal phosphate compound, vanadium, titanium, manganese, iron, cobalt, nickel and the like are preferable. Specific examples thereof include iron phosphates such as LiFePO ₄ , LiCoPO _{4 and the} like. Cobalt phosphates, some of the transition metal atoms that are the main components of these lithium transition metal phosphate compounds are aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, magnesium, gallium, zirconium And those substituted with other metals such as niobium.

  The binder for the positive electrode and the solvent for forming the slurry may be the same as those used for the negative electrode. The amount of the binder used for the positive electrode is preferably 0.001 to 20 parts by mass, more preferably 0.01 to 10 parts by mass, and most preferably 0.02 to 8 parts by mass with respect to 100 parts by mass of the positive electrode active material. preferable. 30-300 mass parts is preferable with respect to 100 mass parts of positive electrode active materials, and, as for the usage-amount of the solvent of a positive electrode, 50-200 mass parts is still more preferable.

  Examples of the conductive material for the positive electrode include graphite fine particles, carbon black such as acetylene black and ketjen black, amorphous carbon fine particles such as needle coke, and carbon nanofibers, but are not limited thereto. 0.01-20 mass parts is preferable with respect to 100 mass parts of positive electrode active materials, and, as for the usage-amount of the electrically conductive material of a positive electrode, 0.1-10 mass parts is still more preferable. In addition, as a current collector for the positive electrode, aluminum, stainless steel, nickel-plated steel, or the like is usually used.

Moreover, the electrolyte solution containing electrolyte and a non-aqueous electrolyte solution is normally satisfy | filled between the said positive electrode and a negative electrode. As the electrolyte, conventionally known electrolytes can be used. For example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiB (CF ₃ SO ₃ ) ₄ , LiB (C ₂ O ₄ ) ₂ , LiBF ₂ (C ₂ O ₄ ), LiSbF ₆ , LiSiF ₅ , LiAlF ₄ , LiSCN, LiClO ₄ , LiClO, LiF, LiBr, Examples include LiI, LiAlF ₄ , LiAlCl ₄ , and derivatives thereof. Among these, the group consisting of LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiCF ₃ SO ₃ derivatives and LiC (CF ₃ SO ₂ ) ₃ derivatives. It is preferable to use at least one selected from the group consisting of excellent electrical characteristics.

  Examples of the non-aqueous electrolyte include propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,1-dimethoxyethane, 1,2-dimethoxyethane, 1,2- Diethoxyethane, γ-butyrolactan, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, anisole, diethyl ether, sulfolane, methylsulfolane, acetonitrile, chloronitrile, propionitrile, Trimethyl borate, tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethylorthoformate, nitrobenzene, chloride Nzoiru, benzoyl bromide, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, sulfite, a single solvent or a mixture of two or more solvents thereof such as dimethyl sulfite may be used.

  In the lithium ion secondary battery of the present invention, it is preferable to use a separation membrane between the positive electrode and the negative electrode. As the separation membrane, a commonly used polymer microporous film can be used without any particular limitation. Examples of the film include polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polytetrafluoroethylene, polysulfone, polyethersulfone, polycarbonate, polyamide, polyimide, polyethylene oxide and polypropylene oxide. Films composed of ethers, various celluloses such as carboxymethylcellulose and hydroxypropylcellulose, polymer compounds mainly composed of poly (meth) acrylic acid and various esters thereof, derivatives thereof, copolymers and mixtures thereof. Etc. These films may be used alone, or may be used as a multilayer film by superimposing these films. Furthermore, various additives may be used for these films, and the kind and content thereof are not particularly limited. Among these films, a film made of polyethylene, polypropylene, polyvinylidene fluoride, or polysulfone is preferably used for the lithium ion secondary battery of the present invention.

  These films are microporous so that the electrolyte can penetrate and ions can easily pass therethrough. This method of microporosity includes a phase separation method in which a solution of a polymer compound and a solvent is formed while microphase separation is performed, and the solvent is extracted and removed to make it porous, and a molten polymer compound is extruded at a high draft. After forming the film, heat treatment is performed, the crystals are arranged in one direction, and further, a stretching method for forming a gap between the crystals by stretching to achieve porosity, and the like is appropriately selected depending on the film to be used.

  The lithium ion secondary battery of the present invention can be obtained by using the negative electrode and the positive electrode thus manufactured. The lithium ion secondary battery of this invention is arrange | positioned so that a separation membrane may exist between an above-described negative electrode and a positive electrode, and electrolyte solution containing a normal electrolyte and a non-aqueous electrolyte solution is satisfy | filled. The lithium ion secondary battery of the present invention is not particularly limited in its shape, and can have various shapes such as a coin shape, a cylindrical shape, and a square shape.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example and a comparative example, this invention is not limited at all of the following examples.

As raw coke, coal-based heavy oil was used, and raw coke A to C obtained by delayed coking at 500 ° C. for 24 hours were used. The amount of quinoline insoluble (QI) in the heavy coal oil used in the production of raw coke A to C is as follows.
・ Raw coke A; QI is 10wt%
・ Raw coke B: QI is 30wt%
・ Raw coke C: QI is 0wt%

  The measurement of micro strength of raw coke E. Measurement was performed based on the method of Brayden. Put 2g of 20-30 mesh sample and 12 steel balls of diameter 5/16 inch (7.9mm) in a steel cylinder (inner diameter 25.4mm, length 304.8mm) and put it in the center of the cylinder in the longitudinal direction. Rotate 800 cylinders at 25 rpm so that the longitudinal direction of the cylinder is parallel to the vertical direction by the attached rotating shaft and reverse the top and bottom, then screen with 48 mesh, and calculate the percentage of the mass on the sieve relative to the sample as a percentage did.

The micro strengths of the raw cokes A to C were as follows.
・ Raw coke A; 0.30wt%
・ Raw coke B: 0.14wt%
・ Raw coke C: 9.98 wt%

Production Example 1
Raw coke A was coarsely pulverized with an Orient mill (manufactured by Seishin Enterprise Co., Ltd.) and then finely pulverized with a jet mill (STJ-200; manufactured by the same company) to obtain an average particle diameter (D ₅₀ ) of 5.5 μm. This was heat-treated in a roller hearth kiln under a nitrogen atmosphere at a maximum temperature of 1300 ° C. for 1 hour to obtain an amorphous carbon material 1.

Production Example 2
Raw coke A was coarsely pulverized with an orient mill and then finely pulverized with a jet mill to obtain an average particle size of 2.5 μm. This was heat-treated in a roller hearth kiln under a nitrogen atmosphere at a maximum temperature of 1300 ° C. for 1 hour to obtain an amorphous carbon material 2.

Production Example 3
Raw coke B was coarsely pulverized with an orient mill and then finely pulverized with a jet mill to obtain an average particle size of 5.4 μm. This was heat-treated in a roller hearth kiln under a nitrogen atmosphere at a maximum temperature of 1300 ° C. for 1 hour to obtain an amorphous carbon material 3.

Production Example 4
Raw coke A was coarsely pulverized with an orient mill and then finely pulverized with a jet mill to obtain an average particle size of 5.5 μm. Then, the spheronization process was performed in the composite (made by Nippon Coke). This was heat-treated in a roller hearth kiln under a nitrogen atmosphere at a maximum temperature of 1300 ° C. for 1 hour to obtain an amorphous carbon material 4.

Production Example 5
Raw coke C was heat treated in a rotary kiln at a maximum temperature of 1300 ° C. for 3 hours, then coarsely pulverized in an orient mill and finely pulverized in a jet mill to an average particle size of 2.2 μm. This was heat-treated in a roller hearth kiln under a nitrogen atmosphere at a maximum temperature of 1300 ° C. for 1 hour to obtain an amorphous carbon material 5.

Production Example 6
Raw coke C was coarsely pulverized with an orient mill and then finely pulverized with a jet mill to obtain an average particle size of 4.0 μm. This was heat-treated in a roller hearth kiln under a nitrogen atmosphere at a maximum temperature of 1300 ° C. for 1 hour to obtain an amorphous carbon material 6.

Production Example 7
Raw coke C was heat-treated in a rotary kiln at a maximum temperature of 1300 ° C. for 3 hours, then coarsely pulverized by an orientation mill and finely pulverized by a jet mill to obtain an average particle size of 10.3 μm. This was heat-treated with a roller hearth kiln under a nitrogen atmosphere at a maximum temperature of 1300 ° C. for 1 hour to obtain an amorphous carbon material 7.

Production Example 8
Raw coke C was roughly crushed with an orient mill and then finely pulverized with a jet mill to obtain an average particle size of 10.4 μm. This was heat-treated with a roller hearth kiln under a nitrogen atmosphere at a maximum temperature of 1300 ° C. for 1 hour to obtain an amorphous carbon material 8.

Example 1
Amorphous carbon material 1 obtained in Production Example 1 is filled in a carbon crucible, and held at 2800 ° C. for 1 hour in an Ar gas atmosphere in a carbon furnace (manufactured by Noritake Co., Ltd.). Carbon material 1 was obtained.

Examples 2-4
In place of the amorphous carbon material 1, the amorphous carbon material 2, 3 or 4 obtained in Production Examples 2 to 4 was used, except that the graphite carbon material 2 for negative electrode, 3 or 4 was obtained.

Comparative Examples 1-4
In place of the amorphous carbon material 1, the graphite carbon materials 5 to 8 for negative electrode were prepared in the same manner as in Example 1 except that the amorphous carbon materials 5 to 8 obtained in Production Examples 5 to 8 were used. Obtained.

Examples and Comparative Examples (Production Examples of Negative Electrode and Secondary Battery)
47.75 parts by mass of the graphite carbon materials 1 to 8 for negative electrodes obtained in Examples 1 to 4 and Comparative Examples 1 to 4 as negative electrode active materials, 0.50 parts by mass of acetylene black as a conductive material, and binder As a thickener, 1.0 part by mass of styrene butadiene rubber (TRD2001 manufactured by JSR) and 0.75 part by mass of carboxymethyl cellulose (MAC500LC manufactured by Nippon Paper Chemical Co., Ltd.) as a thickener are mixed, and the mixture is dispersed in 50.00 parts by mass of water. To form a slurry. This slurry is applied to a negative electrode current collector made of copper, applied with a GAP of 80 μm using a fully automatic applicator, preliminarily dried at 70 ° C. for 6 minutes, and then dried in a hot air oven at 120 ° C. for 2 minutes. of 3.1 mg / cm ^2, to obtain a negative electrode discharge capacity 1.2 mAh / cm ^2. Then, it compacted with the linear pressure of 300 kg / cm with the roll press machine, the electrode was pierced with the hand punch made from Nogami Giken of 15 mm diameter, and the negative electrode was produced.

  In a glove box in an argon gas atmosphere, a metal lithium foil having a thickness of 0.5 mm (manufactured by Honjo Metal Co., Ltd.) was cut to 15.5 mmφ to form a positive electrode.

As the electrolyte solution, a solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent composed of 30% by volume of ethylene carbonate, 40% by volume of ethyl methyl carbonate, and 30% by volume of dimethyl carbonate was used.

  A microporous film made of polypropylene with a thickness of 25 μm punched into 18 mmφ was immersed in the electrolyte solution for 10 seconds and placed between the negative electrode and the positive electrode in a coin cell (CR 2032) so that the active material layer faces each other. . Next, the coin cell was hermetically sealed with a caulking device (manufactured by Hosen Co., Ltd.), a lithium ion secondary battery was produced, and various measurements and evaluations were performed. The results are shown in Tables 1 and 2.

  Unless otherwise specified, various measurements and evaluations are as follows.

  The (002) plane interlayer distance (d002) is X-ray diffractometer (Rigaku Corporation, RINT-TTRIII, X-ray tube: CuKα, tube current: 300 mA, tube voltage: 50 kV), and high purity silicon is standard. The substance was measured by the Gakushin method.

  The true specific gravity was measured by a liquid phase replacement method (pycnometer method). Specifically, powder of negative electrode graphitic carbon material is put into a pycnometer (manufactured by Beetrex), distilled water is added, and air and solvent liquid on the powder surface are replaced by vacuum deaeration to obtain an accurate powder mass And the true specific gravity value was calculated by calculating the volume.

The average particle size (D ₅₀ ) was measured using an apparatus LA-920 (manufactured by HORIBA), and the dispersion medium was water + activator (manufactured by Lion, trade name Mama Lemon). As a reference for the abundance ratio of the particles, the volume distribution was measured using a laser diffraction / scattering method, and the value of the cumulative 50 volume% diameter was defined as the average particle diameter (D ₅₀ ).

  The BET specific surface area was obtained by vacuum drying the particles at 200 ° C. for 3 hours, measuring nitrogen adsorption by a multipoint method using BELSORP-miniII (manufactured by Nippon Bell Co., Ltd.), and calculating according to the BET method.

The ellipse-equivalent length / short ratio average is obtained by preparing a cross section of an electrode by CP (Cross-section Polisher) method and using a scanning electron microscope (FE-SEM S4700 manufactured by Hitachi High-Tech) at a magnification of 500 to 1000 times for graphite for negative electrode. A carbonaceous material was observed. The number of particles observed was 300 or more. The measurement of the ellipse-equivalent length-to-short ratio of the particles was analyzed using image analysis software (WinRooF: manufactured by Mitani Corporation), and an average value (arithmetic average value) was calculated for each.
Even after the electrodes are formed, if the particles of the graphitic carbon material are specified, it is possible to measure the ellipse equivalent length / short ratio average of each particle.

  About the measurement of ash content, it measured according to JIS M8812: 2006 coals and cokes-industrial analysis method.

  For the measurement of the amount of transition elements, a tablet having a diameter of about 30 mm is prepared for each sample using a PE binder, and a scanning X-ray fluorescence analyzer is used under the conditions of spectral crystal LiF, tube rhodium, tube voltage 50 kV, and current 35 mA. The elemental composition was measured using (Rigaku ZSX Primus II).

The charge / discharge efficiency is measured in a constant temperature room at 23 ° C. with a constant current density of 30 mA / cm ² , and the Li ⁺ / Li equilibrium potential of the lithium metal electrode is set to 0, and the negative electrode potential is changed from 1.5V to 0V. Thereafter, it is charged at a constant potential for 90 minutes. After resting for 30 minutes, discharge was performed from 0 V to 1.5 V at a constant current of 30 mA / cm ² . The charge / discharge efficiency is the ratio of the initial discharge capacity (D1) to the initial charge capacity (C1), and is expressed by the following equation. The charge / discharge efficiency was 90.0% or higher as excellent and less than 90.0% as normal or defective.
Charging / discharging efficiency (%) = 100 × D1 / C1

Lithium diffusion in the solid was evaluated by measuring the direct current resistance (DCR) during discharge using the lithium ion secondary batteries (coin cells) of Examples and Comparative Examples according to the following procedure.
1) The charge / discharge operation is repeated one more time on the coin cell in which the charge / discharge efficiency is measured under the same conditions, and the 1C rate current value, 5C rate current value, and charge are determined from the measured charge capacity. The negative electrode potential at which the rate is 50% is calculated.
2) After charging at a constant current rate of 1C up to 0.14V, where the voltage of the coin cell is a negative potential indicating that the charging rate of the cell is 50%, and then charging at a constant voltage of 90 minutes at 0.14V .
3) The coin cell subjected to the above charging operation is subjected to 1 C constant current discharge for 0.2 seconds, and the cell voltage at this time (cell voltage after 1 C rate 0.2 seconds) is measured.
4) Discharge all the cells once.
5) Perform the above operation 2) once more on the discharged coin cell.
6) The above operation 3) is carried out at a 5C current value, and the cell voltage at this time (cell voltage after 5C rate 0.2 seconds) is measured.
Then, from the battery voltages at the respective constant currents thus measured, 0.2 sec DCR (DCR _0.2 ) serving as an index of the diffusion rate of Li in the solid was obtained from the following equation. The reason for setting the time to 0.2 seconds is to measure the DC resistance change based on the diffusion in the solid.
DCR _0.2 = ΔE / ΔI
here,
ΔE: Voltage after 5C rate 0.2 second -1C rate Voltage after 0.2 second ΔI; 5C rate current -1C rate current DCR _0.2 is excellent when it is 22.0Ω or less Defective.

  The characteristics of the amorphous carbon materials 1 to 8 obtained in Production Examples 1 to 8 are shown in Table 1, and the characteristics of the graphitic carbon materials 1 to 8 for negative electrodes obtained in Examples 1 to 4 and Comparative Examples 1 to 4 are shown. Table 2 shows the characteristics and the evaluation results of the lithium ion secondary battery obtained therefrom.

Claims (6)

The (002) plane interlayer distance (d002) calculated from the X-ray diffractometer is 0.340 nm or less, the crystallite diameter Lc (002) is 120 nm or less, the true specific gravity is 2.23 g / cm ³ or more, and the average particle size is 1 to less than 10 μm, BET specific surface area of 1.0 to 6.0 m ² / g, ellipse length / short ratio average of 0.35 to 1.00, ash content of 0.0005 to 0.1 wt%, and transition element content A graphitic carbon material for a negative electrode of a lithium ion secondary battery, characterized in that the amount is less than 5 to 50 wtppm. The (002) plane interlayer distance (d002) calculated from the X-ray diffractometer is 0.340 to 0.370 nm, the true specific gravity is 1.90 to 2.10 g / cm ³ , the average particle size is less than 1 to 10 μm, BET specific surface area is 1.0-6.0 m ² / g, elliptical length-short ratio average is 0.30-1.00, ash content is 0.05-1.00 wt%, and transition element content is 50-700 wtppm. 2. The graphitic carbon material for a negative electrode of a lithium ion secondary battery according to claim 1, which is obtained by graphitizing an amorphous carbon material of less than   A lithium ion secondary battery negative electrode comprising the graphite carbon material for a lithium ion secondary battery negative electrode according to claim 1 or 2 as an essential component.   A lithium ion secondary battery using the lithium ion secondary battery negative electrode according to claim 3. The lithium ion secondary battery according to claim 4, wherein a 0.2 second direct current resistance (DCR _0.2 ) during discharge represented by the following formula is 22Ω or less.
DCR _0.2 = ΔE / ΔI
here,
ΔE: Voltage after 5C rate 0.2 seconds -1C rate Voltage after 0.2 seconds ΔI; 5C rate current -1C rate current Coal or petroleum heavy oil composition with quinoline insoluble content adjusted to a range of 10 to 30 wt% is coked by a delayed coking process to obtain raw coke, and the obtained raw coke is pulverized to obtain an average particle size The raw carbon composition is calcined at 800 ° C. to 1500 ° C. to obtain an amorphous carbon material, and the amorphous carbon material is obtained at 2500 ° C. to 3200. The method for producing a graphitic carbon material for a negative electrode of a lithium ion secondary battery according to claim 1, wherein the graphitization treatment is performed at a temperature of 0 ° C.