JP2018006271A - Carbon material for lithium ion secondary battery negative electrode, intermediate thereof, method for manufacturing the same, and negative electrode or battery arranged by use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an amorphous carbon material suitable as a negative electrode active material for a lithium ion secondary battery, which enables the achievement of high diffusibility of lithium ions in a solid because of being small in particle diameter, and which enables the large reduction of side reactions in the surface of an active material by making a specific surface area smaller.SOLUTION: An amorphous carbon material for a lithium ion secondary battery negative electrode is 0.340-0.370 nm in (002) plane interlayer distance (d002), which is calculated from an X-ray diffraction device, 1.90-2.10 g/cmin true specific gravity, 1-10 μm in mean particle diameter, 1.0-6.0 m/g in BET specific surface area, 0.35-1.00 in mean elliptical ratio of major axis vs. minor axis, 0.05-1.00 wt% in ash content, and less than 50-700 wtppm in transition element content. An original coal composition is used to obtain the amorphous material for a lithium ion secondary battery negative electrode, and it comprises green coke powder of 0.01-3.0 wt% in micro intensity, and 1-10 μm in mean particle diameter.SELECTED DRAWING: 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 for hybrid electric vehicles. 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 the 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. In addition, the use of an amorphous carbon material before graphitization as a negative electrode active material as a negative electrode active material, and research and development are progressing. The amorphous carbon material not only has excellent output characteristics, but also has an advantage of not requiring high-temperature treatment at 2000 ° C. or higher because it is obtained by calcining a raw carbon composition such as raw coke.

  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. There is no mention of carbon materials.

  In Patent Document 3, it is shown that a raw coke spherical carbon material having a high sphericity is obtained by spheronization processing that imparts compressive stress and shear stress to raw coke powder. However, in addition to the complexity of the process, the spheroidizing process makes it difficult to spheroidize small particles.

  In Patent Document 4, by applying compressive shear stress to raw coke whose particle size is adjusted by pulverization / classification, an amorphous or graphitic material having a circularity of 0.7 to 0.9 and an average particle diameter of 1 to 30 μm. Obtaining a carbon material is disclosed. However, since this carbon material contains 700-2500 ppm of transition metals, 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 carbon material for a lithium ion secondary battery is disclosed. However, this raw coal composition has poor productivity at the time of pulverization, and it is impossible to achieve the reduction in the particle size necessary for enhancing the output characteristics with good productivity.

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-treated 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 relates to a negative electrode active material for a lithium ion secondary battery in which lithium ions have a high diffusibility in solids due to a small particle size, and side reactions on the active material surface are greatly reduced by reducing a specific surface area. An object of the present invention is to provide a suitable amorphous carbon material. Another object of the present invention is to provide a lithium ion secondary battery negative electrode and a lithium ion secondary battery using the carbon material for a lithium ion secondary battery negative electrode.

  As a result of intensive studies to achieve the above problems, the present inventors have found that the above problems can be solved by controlling the surface area using a small particle size amorphous coke obtained from a specific raw material. The invention has been completed.

That is, in the present invention, 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 , and the average particle diameter is Is 1-10 μm, BET specific surface area is 1.0-6.0 m ² / g, elliptical length-short ratio average is 0.35-1.00, ash content is 0.05-1.00 wt%, and transition element is contained An amorphous carbon material for a negative electrode of a lithium ion secondary battery, characterized in that the amount is less than 50 to 700 wtppm.

  Another aspect of the present invention is a raw material carbon composition used for obtaining the above amorphous material for a negative electrode of a lithium ion secondary battery, having a micro strength of 0.01 to 3.0 wt%, an average particle diameter Consists of raw coke powder of 1 to 10 μm.

Another aspect of the present invention is a lithium ion secondary battery negative electrode containing the amorphous carbon material for a lithium ion secondary battery negative electrode as an essential component, and further using these lithium ion secondary battery negative electrodes. Next battery.
In this case, the lithium secondary battery preferably has a 0.2 second direct current resistance (DCR _0.2 ) of less than 20Ω during discharge 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 obtained by coking a coal-based or petroleum-based heavy oil composition having a quinoline insoluble content adjusted to a range of 10 to 30 wt% by a delayed coking process to obtain a raw coke. Is made into a raw material carbon composition having an average particle diameter of 1 to 10 μm, and the raw material carbon composition is heat-treated at 900 ° C. to 1500 ° C. The amorphous carbon for a lithium ion secondary battery negative electrode It is a manufacturing method of material.

  The amorphous carbon material for a negative electrode of a lithium ion secondary battery according to the present invention is a lithium ion secondary battery that is excellent in rapid chargeability, long life, and long-term reliability by being used as a negative electrode active material for a secondary battery. A battery can be obtained.

2 is a SEM photograph of the amorphous carbon material for negative electrode of Example 1. 4 is a SEM photograph of the negative electrode amorphous carbon material of Comparative Example 1.

  The amorphous carbon material for a negative electrode of a lithium ion secondary battery of the present invention (hereinafter referred to as an amorphous carbon material for a negative electrode) is preferably obtained by heat treating raw coke having a micro strength of 0.01 to 3.0 wt%. Obtained.

  The raw coke is excellent when 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 amorphous carbon material for a negative electrode of the present invention, 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 is preferable from the viewpoint of life characteristics.

  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 calcined coke further heat-treated are amorphous coke, and unlike needle coke in which coarse carbon crystals are aligned in one direction, fine carbon crystals are densely and randomly arranged. When used as the negative electrode active material of a lithium ion secondary battery, it can be expected to diffuse lithium quickly into the negative electrode active material due to the small carbon crystal, and it does not have the cleavage property like needle coke. Small rounded fine particles can be easily obtained only by a grinding operation.

  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, about 900 to 1500 ° C. is further added. 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, it is preferable that it is 1.0-10 wt%, and, as for the quantity of the volatile matter of raw coke, 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 the grindability, and in order to obtain the amorphous 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 keep the particle size control during pulverization and keep the quality constant. If it exceeds 3.0 wt%, the particle diameter becomes coarse and the elliptical equivalent length-to-short ratio decreases. In addition, problems such as an increase in manufacturing cost due to a decrease in grinding efficiency occur. The preferred microstrength is 0.05 to 1.0 wt%, more preferably 0.10 to 0.50 wt%. This microintensity 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.

  As described above, raw coke, which is the amorphous carbon material precursor of the present invention, has good pulverization properties. Therefore, if compressive shear stress is applied too much, the particles are excessively pulverized to obtain a desired particle size. Therefore, it is necessary to appropriately adjust the compressive shear stress. On the other hand, an appropriate volatile component is present 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. If the average particle size is in the above range, fine powders of less than 1 μm and coarse particles of more than 10 μm may be included, but the proportions of fine powder of 0.5 μm or less and coarse particles of 20 μm or more are both 10 vol% or less. It is preferable that

  The raw coke after pulverization is heat-treated to be an amorphous carbon material for a negative electrode. For this heat treatment, a method of calcining at a maximum attained temperature of 800 ° C. to 1500 ° C. in a low oxygen atmosphere is suitable. The calcination temperature is preferably in the range of 900 ° C to 1500 ° C, more preferably 1000 ° C to 1400 ° C. The heat treatment removes moisture and volatile components from the raw coke and converts hydrocarbons remaining as polymer components into coke, thereby promoting crystal growth. For this calcination treatment, equipment such as a lead hammer furnace, shuttle furnace, tunnel furnace, rotary kiln, roller hearth kiln, or microwave capable of mass heat treatment can be used, but is not particularly limited thereto. Further, the calcining treatment may be either a continuous type or a batch type.

The amorphous carbon material for negative electrodes of the present invention can be obtained by the method as described above.
The amorphous carbon material for a negative electrode of the present invention has an (002) plane interlayer distance (d002) 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 1 to 10 μm, BET specific surface area, ellipse length / short ratio average 0.35 to 1.00, ash content 0.05 to 1.00 wt%, and transition element content 50 to 50 Satisfying less than 700 wtppm. And it is good that it is a rounded fine particle.

This amorphous carbon material for negative electrode has a BET specific surface area of 1.0 to 6.0 m ² / g, preferably 1.0 to 5.0 m ² / g, more preferably 1.5 to 4.5 m. ² / g.
The BET specific surface area is determined by the shape after pulverization due to the crystal state of raw coke and the particle size distribution, but can be changed by this condition when spheroidizing treatment or surface coating is performed after pulverization. By controlling the BET specific surface area within the above range, the reactivity with the electrolytic solution can be suppressed and the occurrence of side reactions during use can be reduced, and the lithium ion reactivity can be improved to achieve a desired charge / discharge rate. Can be obtained. Since the BET specific surface area affects the speed of surface reaction when lithium ions enter and exit the carbon structure, it is preferable to control the BET specific surface area within the above range.
The control of the BET specific surface area is preferably performed by spheronization or surface coating after the raw coke is pulverized as described above.

  The amorphous carbon material for negative electrode of the present invention is characterized in that the BET specific surface area is very small with respect to the average particle diameter, but in order to further reduce the BET specific surface area, a carbonaceous film is formed on the particle surface. A surface coat may be formed. The carbonaceous film can be formed by a dry method or a wet method using pitch, an organic polymer compound or the like, a CVD method using an aromatic hydrocarbon gas, etc., but a thin film is formed uniformly over the entire circumference of the particle. A CVD method that can be used is preferable.

  Further, this amorphous carbon material for negative electrode has the above-mentioned interlayer distance (d002) of 0.340 to 0.370 nm, preferably 0.340 to 0.350 nm. If this value is less than 0.340 nm, the acceptability of lithium ions, which is a feature of the amorphous carbon material, is lowered. If it exceeds 0.370 nm, the crystal growth of carbon does not sufficiently proceed, so that carbon defects are generated. The amount of inactive lithium ions that are not lost but are occluded by carbon defects during charging increases.

  Moreover, this amorphous | non-crystalline carbon material for negative electrodes has an average of the said ellipse length-short ratio of 0.35-1.00. 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 short axis length (La) and the ellipse-equivalent major axis length (Lb). ) / (Lb) ratio is calculated, this is performed for several tens or more 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. For this reason, the ellipse length / short ratio average is preferably 0.40 to 0.95, and more preferably 0.45 to 0.90.

Further, the amorphous carbon material for negative electrode has an average particle diameter (D ₅₀ ) in the range of 1 to 10 μm, desirably 2 to 8 μm, and more preferably 2 to 5 μm. 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 carried out quickly in combination with the amorphous structure, and rapid chargeability and Li precipitation are achieved. 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 exceeds 10 μm, the BET specific surface area becomes too small, so that the reactivity of lithium ions is lowered and the charge / discharge rate is slowed. If the average particle size is in the above range, fine powders of less than 1 μm and coarse particles of more than 10 μm may be included, but the proportions of fine powder of 0.5 μm or less and coarse particles of 20 μm or more are both 10 vol% or less. It is preferable that

Here, the diffusibility of lithium ions into the negative electrode active material (in-solid diffusibility) refers to the lithium ion migration speed inside the particles. Since the movement of ions in the active material is performed quickly, 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 using 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 amorphous carbon material for negative electrode has an ash content of 0.05 to 1.00 wt%, preferably 0.1 to 1.00 wt%, more preferably 0.2 to 0.70 wt%. It is. Ash contains a lot of metal elements, but these adversely affect the battery performance when used as a secondary battery. If it exceeds 1.00 wt%, the long-term reliability of the secondary battery may be impaired. is there.

Moreover, about the content rate of a transition element, it is 50-700 wtppm, Preferably it is 50-600 wtppm, More preferably, it is 50-500 wtppm. If the content of the transition element is higher than the above, there may be a problem of battery safety.
The ash includes Si, Ca, Al oxides, and the transition element is Fe. 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. That is, since ash and transition elements have the effect of suppressing particle anisotropy by inhibiting the growth of carbon crystals and controlling the desired ellipse length to short ratio, 0.05 to 1.00 wt% ash and It is preferable that a transition element of 50 to 700 wtppm or more is contained.

Moreover, this amorphous carbon material for negative electrodes has a true specific gravity of 1.90 to 2.10 g / cm ³ , preferably 2.00 to 2.10 g / cm ³ . When the true specific gravity exceeds 2.105 g / cm ³ , some kind of crystallization or graphitization has progressed as a carbon material, so that the output characteristics that are characteristic of an amorphous carbon material are reduced, and 1.90 g. If it is less than / cm ³ , the life characteristics deteriorate.

The negative electrode for a lithium ion secondary battery of the present invention has a layered negative electrode active material obtained by using the above amorphous carbon material for negative electrode as a negative electrode active material on a current collector such as a copper foil, and mixing a binder or the like with the negative electrode active material. It is obtained by forming. This layer is referred to as a negative electrode active material layer.
In addition, the amorphous carbon material for negative electrodes of this invention can also be used as a 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. In this case, the blending ratio (amorphous carbon material for negative electrode of the present invention: other negative electrode active material) is in the range of 10: 1 to 1:10, preferably 10: 1 to 10: 5 by weight. Other negative electrode active materials include artificial graphite, spheroidized natural graphite, mesocarbon microbeads or graphitized products thereof, graphitic carbon materials, low crystalline carbon materials (graphitizable carbon, non-graphitizable carbon) having different particle sizes Examples include 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 placing the slurry on the current collector. It is performed by coating, 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 was 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. That is, in a steel cylinder (inner diameter: 25.4 mm, length: 304.8 mm), a 20 g to 30 mesh sample and 12 steel balls having a diameter of 5/16 inch (7.9 mm) are placed in the center of the cylinder in the longitudinal direction. After rotating the cylinder at 800 rpm at 25 rpm so that the longitudinal direction of the cylinder is parallel to the vertical direction and rotating up and down by the rotation axis attached to the part, it is sieved with 48 mesh, and the ratio of the mass on the sieve to the sample is Calculated as a percentage.

The micro strength of each raw coke was as follows.
・ Raw coke A; 0.30wt%
・ Raw coke B: 0.14wt%
・ Raw coke C: 9.98 wt%

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 at a maximum temperature of 1300 ° C. for 1 hour in a roller hearth kiln under a nitrogen atmosphere to obtain an amorphous carbon material for a negative electrode.

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 at a maximum temperature of 1300 ° C. for 1 hour in a roller hearth kiln under a nitrogen atmosphere to obtain an amorphous carbon material for a negative electrode.

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 at a maximum temperature of 1300 ° C. for 1 hour in a roller hearth kiln under a nitrogen atmosphere to obtain an amorphous carbon material for a negative electrode.

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 at a maximum temperature of 1300 ° C. for 1 hour in a roller hearth kiln under a nitrogen atmosphere to obtain an amorphous carbon material for a negative electrode.

Comparative Example 1
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 at a maximum temperature of 1300 ° C. for 1 hour in a roller hearth kiln under a nitrogen atmosphere to obtain an amorphous carbon material for a negative electrode.

Comparative Example 2
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 at a maximum temperature of 1300 ° C. for 1 hour in a roller hearth kiln under a nitrogen atmosphere to obtain an amorphous carbon material for a negative electrode.

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

Comparative Example 4
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 at a maximum temperature of 1300 ° C. for 1 hour in a roller hearth kiln under a nitrogen atmosphere to obtain an amorphous carbon material for a negative electrode.

  The SEM photograph of the amorphous carbon material for negative electrode of Example 1 is shown in FIG. 1, and the SEM photograph of the amorphous carbon material for negative electrode of Comparative Example 1 is shown in FIG. In addition, the cross-sectional shape of the amorphous carbon material of Examples 2-4 was similar to FIG. 1, and the cross-sectional shape of the amorphous carbon material of Comparative Examples 2-4 was similar to FIG.

Examples and Comparative Examples (Production Examples of Negative Electrode and Secondary Battery)
Amorphous carbon materials for negative electrodes obtained in Examples 1 to 4 and Comparative Examples 1 to 4 as negative electrode active materials (the carbon materials obtained by heat treating raw coke C are all needle-like coke. ) 47.75 parts by mass, acetylene black 0.50 parts by mass as a conductive material, 1.0 part by mass of styrene butadiene rubber (TRD2001 manufactured by JSR) as a binder, and carboxymethyl cellulose (manufactured by Nippon Paper Chemicals Co., Ltd.) as a thickener. MAC500LC) 0.75 parts by mass was mixed, and the mixture was 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, coated with GAP of 100 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. A negative electrode of 4.3 mg / cm ² was obtained. 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 obtained by dissolving LiPF ₆ 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.
Table 1 shows the characteristics of the amorphous carbon material for the negative electrode and the evaluation results of the lithium ion secondary battery.

  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 amorphous 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 diameter (D ₅₀ ) was measured using an apparatus LA-920 (manufactured by HORIBA) and water + activator (manufactured by Lion Corporation, trade name Mama Lemon) as a dispersion medium. 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-to-short ratio average is amorphous at a magnification of 500 to 1000 using a scanning electron microscope (FE-SEM S4700, manufactured by Hitachi High-Tech) using an electrode cross-section by CP (Cross-section Polisher) method. Carbon 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 amorphous carbon material and the graphitic carbon material are specified, it is possible to measure the ellipse equivalent length average of each particle.

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

  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 fluorescent X-ray 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 was measured by charging the lithium metal electrode at a constant current of 30 mA / cm ^{2 at} a constant current density of 23 mA / cm ² until the Li ⁺ / Li equilibrium potential of the lithium metal electrode was 0 and the negative electrode potential was changed from 1.5V to 0V. Then, constant potential charging is performed at 0V 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 85.0% or more as good and less than 85.0% as normal or defective.
Charging / discharging efficiency (%) = 100 × D1 / C1

Lithium in-solid diffusion evaluation was performed 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 was 50% was calculated.
2) After charging at a constant current rate of 1 C until the voltage of the coin cell reaches 0.25 V, which is a negative electrode potential indicating that the charging rate of the cell is 50%, the constant potential is further maintained at 0.25 V for 90 minutes. Charge the battery.
3) The coin cell subjected to the above charging operation is further 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, a 0.2 second direct current resistance (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 seconds-Voltage 1C rate after 0.2 seconds ΔI; 5C rate current -1C rate current Evaluation criteria were DCR _0.2 of less than 20Ω as good and 20Ω or more as normal or defective.

Claims (6)

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 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 0.05 to 1.00 wt%, and transition element content of less than 50 to 700 wtppm An amorphous carbon material for a negative electrode of a lithium ion secondary battery.   A raw material carbon composition used for obtaining an amorphous material for a negative electrode of a lithium ion secondary battery according to claim 1, wherein the micro strength is 0.01 to 3.0 wt%, and the average particle size is 1 to A raw material charcoal composition comprising a raw coke powder of 10 μm.   A lithium ion secondary battery negative electrode comprising the amorphous carbon material for a lithium ion secondary battery negative electrode according to claim 1 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 ) at the time of discharging represented by the following formula is less than 20Ω.
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 2. The amorphous carbon material for a lithium ion secondary battery negative electrode according to claim 1, wherein the raw carbon composition has a diameter of 1 to 10 μm and is heat-treated at 900 to 1500 ° C. 3. Manufacturing method.

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