WO2016194355A1

WO2016194355A1 - Carbonaceous coated graphite particles for negative-electrode material of lithium-ion secondary cell, negative electrode for lithium-ion secondary cell, and lithium-ion secondary cell

Info

Publication number: WO2016194355A1
Application number: PCT/JP2016/002602
Authority: WO
Inventors: 間所　靖; 江口　邦彦; 哲夫塩出
Original assignee: Ｊｆｅケミカル株式会社
Priority date: 2015-06-01
Filing date: 2016-05-30
Publication date: 2016-12-08

Abstract

Provided is a negative-electrode material with which it is possible to obtain exceptional cell properties when said material is used as the negative-electrode material of a lithium-ion secondary cell. Carbonaceous coated graphite particles for the negative-electrode material of a lithium-ion secondary cell in which a carbonaceous material is provided on at least part of the surfaces of graphite particles that are obtained by anisotropically applying pressure to spheroidal and/or ellipsoidal graphite, wherein the carbonaceous coated graphite particles satisfy conditions (1) through (3) below. (1) The carbonaceous material content is 0.1-3.0 parts by mass per 100 parts by mass of the anisotropically pressurized graphite particles in the carbonaceous coated graphite particles. (2) The pore volume of pores measuring 1.1 µm or less in diameter is 0.100 mL/g or less as measured by a mercury porosimeter, and the ratio of the pore volume of pores measuring 0.54 µm or less in diameter with respect to said pore volume is 80% or greater. (3) The dibutyl phthalate (DBP) oil absorption is 40.0 mL/100 g or less.

Description

Carbonaceous coated graphite particles for lithium ion secondary battery anode material, lithium ion secondary battery anode and lithium ion secondary battery

The present invention relates to a carbon-coated graphite particle for a negative electrode material for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery using the negative electrode.

Lithium ion secondary batteries are widely used in portable electronic devices, and have started to be used in hybrid and electric vehicles. Under such circumstances, lithium ion secondary batteries are required to have higher capacity, faster charge / discharge characteristics, and cycle characteristics.
The lithium ion secondary battery has a negative electrode, a positive electrode, and a non-aqueous electrolyte as main components, and acts as a secondary battery by moving lithium ions between the negative electrode and the positive electrode during a discharging process and a charging process. Currently, graphite is widely used as the negative electrode material. Graphite is roughly classified into natural graphite and artificial graphite. Natural graphite has the advantage of high crystallinity and high capacity, but due to the scale shape, the particles are oriented in one direction within the electrode, resulting in inferior high-speed charge / discharge characteristics and cycle characteristics.

In order to compensate for this, many materials have been proposed in which scaly graphite is processed into a spherical shape and surface-coated. The surface of the spheroidized natural graphite has an exposed edge surface that is highly reactive with the electrolytic solution. The purpose of coating is to seal the edge surface and suppress side reactions. In recent years, there has been a demand for higher energy density of batteries with the increase in size of portable devices, and accordingly, further increase in the density of negative electrodes is also required. However, in the conventional coated natural graphite, the strength of the coating layer is not sufficient, and cracking or cracking occurs in the coating layer due to the increase in density, resulting in a decrease in initial efficiency and cycle characteristics. It was.

On the other hand, Patent Document 1 discloses a method for producing a negative electrode material for a lithium ion secondary battery, characterized in that spheroidized graphite is isotropically pressurized. Patent Document 2 discloses a lithium ion characterized in that a coating layer made of carbide is formed on the surface of pressurized graphite particles obtained by pressurizing natural graphite spheroidized particles and / or natural graphite agglomerated particles. A graphite material for a secondary battery is disclosed.
These are the effects of using high density and highly isotropic graphite particles in the negative electrode material. The gap between the graphite particles is widened at the same negative electrode density, so that the liquid permeability of the electrolyte can be improved. It explains that the crystal structure of graphite is difficult to be oriented even when fabricated, and the liquid permeability of the electrolytic solution is not impaired.
However, even if these methods are used, the effect of improving the battery performance is not yet sufficient.

Japanese Patent No. 4499498 JP 2011-60465 A

The present invention has been made in view of the above circumstances. That is, it aims at providing the negative electrode material which can acquire the outstanding battery characteristic, when it uses for a lithium ion secondary battery negative electrode material. Moreover, it aims at providing the manufacturing method of the negative electrode material, the negative electrode containing the negative electrode material, and the lithium ion secondary battery using the negative electrode. Here, the excellent battery characteristics are high discharge capacity, high initial charge / discharge efficiency, high high-speed charge / discharge characteristics, and excellent cycle characteristics.

The present invention relates to a graphite core material in which spherical or ellipsoidal graphite particles are used as a core material, and the core material is anisotropically pressed, and at least a part of the surface of the core material is coated with carbonaceous material. It is carbonaceous covering graphite particle for lithium ion secondary battery negative electrode materials characterized by being carbonaceous covering graphite particle which has a layer.
The negative electrode of the lithium ion secondary battery is press-molded in the manufacturing process in order to realize the designed electrode density. Usually, a roll press is used for the press molding, and an anisotropic pressure is applied to the negative electrode material constituting the electrode. The present invention has been made paying attention to this point, that is, by subjecting the negative electrode material to anisotropic pressure treatment in advance, deformation of the particles due to press molding at the time of producing the negative electrode, and accompanying it Damage to the coating layer can be suppressed, and high initial charge / discharge efficiency, high-speed charge / discharge characteristics, and cycle characteristics can be maintained even when the electrode density is increased.

The carbon-coated graphite particles of the present invention simultaneously satisfy good discharge capacity, initial charge / discharge efficiency, high-speed charge / discharge characteristics, and cycle characteristics as a lithium ion secondary battery negative electrode material. Therefore, the lithium ion secondary battery using the negative electrode material of the present invention satisfies the recent demand for higher energy density of the battery, and is useful for downsizing and higher performance of the mounted device.

FIG. 1 is a cross-sectional view of an evaluation battery for evaluating the battery characteristics of the negative electrode of the present invention.

Hereinafter, the present invention will be described more specifically.
1. Graphite particles (spherical and / or ellipsoidal graphite)
As the raw material for the graphite particles of the present invention, graphite particles having a spherical or ellipsoidal average particle diameter of 1 to 50 μm, preferably an average aspect ratio of 5 or less and an average particle diameter of 5 to 30 μm are used. The average aspect ratio is 2 or less and the average specific surface area is more preferably 10 m ² / g or less, and particularly preferably 8 m ² / g or less.

Commercially available natural graphite particles processed into a spherical or ellipsoidal shape can also be used. In the case of natural graphite having a shape other than spherical or ellipsoidal shape, for example, flaky graphite particles, natural flaky graphite is granulated by mechanical external force to obtain spherical graphite particles. The method of processing into a spherical or ellipsoidal shape is, for example, a method of mixing a plurality of scaly graphites in the presence of a granulating aid such as an adhesive or a resin, without using an adhesive for a plurality of scaly graphites. The method of applying mechanical external force, the combined use of both, etc. are mentioned. However, the most preferable method is to apply a mechanical external force to granulate into a spherical shape without using a granulating aid. The mechanical external force is mechanically pulverizing and granulating, and scaly graphite can be granulated and spheroidized. Examples of the flaky graphite crusher include a pressure kneader, a kneader such as a two-roll mill, a rotating ball mill, a counter jet mill (manufactured by Hosokawa Micron Corporation), a current jet (manufactured by Nisshin Engineering Co., Ltd.), and the like. A grinding device can be used.
Since the pulverized product has an acute-angled surface, the pulverized product may be granulated and used. Examples of granulated spheroidizers for pulverized products include granulators such as GRANUREX (manufactured by Freund Sangyo Co., Ltd.), Newgra Machine (manufactured by Seisin Co., Ltd.), Agromaster (manufactured by Hosokawa Micron Co., Ltd.), and hybridization. Shear compression processing apparatuses such as (manufactured by Nara Machinery Co., Ltd.), mechanomicros (manufactured by Nara Machinery Co., Ltd.), and mechanofusion system (manufactured by Hosokawa Micron Co., Ltd.) can be used.

Lc, which is a measured value of X-ray diffraction of the graphite particles of the present invention, is preferably 40 nm or more, and La is preferably 40 nm or more. Here, Lc is the crystallite size Lc (002) in the c-axis direction of the graphite structure, and La is the crystallite size La (110) in the a-axis direction. d002 is 0.337 nm or less, and the ratio I ₁₃₆₀ / I ₁₅₈₀ (R value) of ₁₃₆₀ cm ⁻¹ peak intensity (I ₁₃₆₀ ) and ₁₅₈₀ cm ⁻¹ peak intensity (I ₁₅₈₀ ) measured by Raman spectroscopy using an argon laser is 0. The full width at half maximum of the 0.06 to 0.30 and 1580 cm ⁻¹ bands is preferably 10 to 60.

[Graphic particles formed by anisotropic pressure]
The graphite particles of the present invention are formed by anisotropically pressing the spherical or ellipsoidal graphite. As a result, the graphite particles of the present invention have an orientation in which the density is high in the anisotropically pressed direction and the density is low in the perpendicular direction.
The graphite particles of the present invention preferably have a pore volume of 500 nm or less as measured by the mercury intrusion method of 0.100 mL / g or less, or a pore volume of 100 to 200 nm as measured by the mercury intrusion method. Is preferably 0.02 mL / g or less. If this range is exceeded, the binder used to produce the negative electrode may permeate into the pores, which may reduce the electrode peel strength.

2. Carbonaceous coated graphite particles The carbonaceous coated graphite particles for a negative electrode material of a lithium ion secondary battery of the present invention have a carbonaceous material on at least a part of the surface of the above-mentioned anisotropically pressed graphite particles. That is, at least a part of the surface of the graphite particles is covered with the carbonaceous material. Although the manufacturing method is not limited, Preferably, at least a part of the surface of the graphite particles is coated with a carbonaceous material by a manufacturing method described later using a carbonaceous precursor as a raw material. Examples of the precursor of the carbonaceous material used include tar pitches and / or resins. Specifically, heavy oils, particularly tar pitches, include coal tar, tar light oil, tar medium oil, tar heavy oil, naphthalene oil, anthracene oil, coal tar pitch, pitch oil, mesophase pitch, oxygen-crosslinked petroleum pitch, heavy Examples include oil. Examples of the resins include thermoplastic resins such as polyvinyl alcohol and polyacrylic acid, and thermosetting resins such as phenol resins and furan resins. It is advantageous in terms of cost if only tar pitches are used without containing resins. Any of the carbonaceous material precursors exemplified above may be used, but the coal tar pitch is particularly preferably 80% by mass or more.

In the carbonaceous coated graphite particles of the present invention, the content of the carbonaceous material is 0.1 to 3.0 parts by mass with respect to 100 parts by mass of the graphite particles in the carbonaceous coated graphite particles. When the content of the carbonaceous material is less than 0.1 parts by mass, it is difficult to completely cover the active graphite edge surface, and the initial charge / discharge efficiency may be lowered. On the other hand, when it exceeds 3.0 parts by mass, the proportion of the carbon material having a relatively low discharge capacity is too high, and the discharge capacity of the carbonaceous coated graphite particles is reduced. In addition, if the ratio of the raw materials (thermosetting resins and tar pitches) for forming the carbonaceous material is large, the particles are easily fused in the coating process and the subsequent heat treatment process, and the carbon obtained finally. The carbonaceous material layer of the carbon-coated graphite particles may be cracked or peeled off, resulting in a decrease in initial charge / discharge efficiency. The content of the carbonaceous material is 0.3 to 3.0 parts by mass, more preferably 1.0 to 3.0 parts by mass with respect to 100 parts by mass of the graphite particles in the carbonaceous coated graphite particles. preferable. The content of the carbonaceous material may be in the above range as an average of the entire carbonaceous coated graphite particles. It is not necessary that all the individual particles are within the above range, and some particles outside the above range may be included.

The carbon-coated graphite particles of the present invention have a pore volume of not more than 0.100 mL / g and a pore diameter of not more than 0.54 μm with respect to the pore volume, as measured with a mercury porosimeter. The ratio of the pore volume is 80% or more. When the pore volume with a pore diameter of 1.1 μm or less exceeds 0.100 mL / g, the binder used in the production of the negative electrode penetrates into the pores, and the electrode peel strength decreases, resulting in cycle characteristics. May decrease. In addition, even when the ratio of the pore volume with a pore diameter of 0.54 μm or less to the pore volume is less than 80%, the binder used in the production of the negative electrode also penetrates into the pores, and the sufficient electrode The peel strength cannot be obtained, and the cycle characteristics may be deteriorated.
The carbon-coated graphite particles of the present invention preferably have a pore volume of 1.1 μm or less as measured with a mercury porosimeter of 0.090 mL / g or less, and more preferably 0.085 mL / g or less. preferable.
In the carbon-coated graphite particles of the present invention, the ratio of the pore volume having a pore diameter of 0.54 μm or less to the pore volume (pore volume having a pore diameter of 1.1 μm or less) is preferably 81% or more, More preferably, it is 82% or more.

The carbon-coated graphite particles of the present invention have a dibutyl phthalate (DBP) oil absorption of 40.0 mL / 100 g or less. When this numerical value is exceeded, the binder used in the production of the negative electrode penetrates into the pores, so that the electrode peel strength is lowered and the cycle characteristics may be lowered.
The graphitic particles of the present invention preferably have a dibutyl phthalate (DBP) oil absorption of 38.0 mL / 100 g or less, more preferably 37.0 mL / 100 g or less.

The average particle size of the carbon-coated graphite particles as the final product is preferably in the range of 1 to 50 μm, and more preferably in the range of 5 to 30 μm. The specific surface area measured by the BET method is preferably 6.0 m ² / g or less, and more preferably 4.0 m ² / g or less.
The carbon-coated graphite particles had a ratio I ₁₃₆₀ / I ₁₅₈₀ (R value) of ₁₃₆₀ cm ⁻¹ peak intensity (I ₁₃₆₀ ) and ₁₅₈₀ cm ⁻¹ peak intensity (I ₁₅₈₀ ) measured by Raman spectroscopy using an argon laser. ) Is larger than the R value of graphite and is preferably 0.05 to 0.80.

3. Method for producing carbon-coated graphite particles (pressurizing step)
The method for producing the carbonaceous coated graphite particles of the present invention is not limited, but preferably, the above-mentioned spherical and / or ellipsoidal graphite is first subjected to anisotropic pressure treatment. Anisotropic pressurization means applying a pressure in a specific direction, not an isotropic pressurization. Isotropic pressurization is, for example, a method of isotropic pressurization using a pressurizing medium such as gas or liquid. In Comparative Examples 2 and 3 described later, a cold isostatic press was used.
The anisotropic pressurization is preferably pressurization from one direction or two directions. The method of anisotropic pressurization is not particularly limited, and examples thereof include a mold press, a roll press, and extrusion molding. The applied pressure and the anisotropic direction are not limited, but are performed to the extent corresponding to the applied pressure in the negative electrode forming step when the carbonaceous coated graphite particles are used for the negative electrode material of the lithium ion secondary battery and the anisotropic pressure direction. Is preferred. With respect to the applied pressure, for example, a mold having an internal volume of 2000 to 3000 cm ³ is filled at a height of 5 to 10 cm and pressurized at a pressure of 40 to 300 MPa.

If there is sticking in the pressure treatment, a crushing step may be introduced after the pressure treatment, if necessary. During the pressure treatment, carbonaceous or graphite fibers, carbonaceous precursor materials such as amorphous hard carbon, organic materials, inorganic materials, and metal materials may or may not be added. When added, the combination of the pressurizing direction and the non-pressurizing direction becomes complicated, so that the pressurization result becomes closer to isotropic pressurization. When not added, the pressing result becomes simpler and the difference in orientation between the pressing direction and the non-pressing direction becomes larger than when other materials are added during the pressing process.

[Mixing process]
The obtained pressure-treated product is mixed with a carbonaceous precursor. A mixing process will not be specifically limited if it can mix uniformly, A well-known mixing method can be used. Preferably, solid graphite particles and a solid or semi-solid (including viscous liquid) carbonaceous precursor are mixed. Heavy oil is solid at room temperature.
When a liquid carbonaceous precursor such as tar light oil or tar medium oil is mixed as a solvent, it is preferable to volatilize the solvent in advance at a temperature of about 200 ° C. or lower to perform the next firing step. The raw materials are mixed so that the mixing ratio is 0.1 to 3.0 parts by mass of the carbonaceous material with respect to 100 parts by mass of the graphite particles as the final product. You may perform mixing with the temperature rising process for the heating process mentioned later. The heating and mixing method is not particularly limited, and examples thereof include a biaxial kneader having a heating mechanism such as a heater and a heat medium. During the mixing process, carbonaceous or graphite fibers, carbonaceous precursor materials such as amorphous hard carbon, organic materials, inorganic materials, and metal materials may be added. The mixing step may be performed simultaneously with the baking step described later or may be performed after mixing.

[Baking process]
The resulting mixture is fired at 700-2200 ° C. The method for the baking treatment is not particularly limited, but baking is preferably performed while stirring, and the use of a rotary kiln is preferable because homogeneous baking can be performed. As long as the final temperature reaches the firing temperature, the heat treatment may be performed in a plurality of stages. The atmosphere may be oxidizing or non-oxidizing, and both may be used properly at each stage. Examples of the non-oxidizing atmosphere include argon, helium, and nitrogen. The firing time is preferably 5 minutes to 30 hours. Further, the temperature profile at the time of temperature rise and firing can take various forms such as a linear temperature rise and a stepwise temperature rise in which the temperature is held at a constant interval.
The method for producing carbonaceous coated graphite particles of the present invention preferably does not include a pulverization step after firing. Further, different types of graphite materials may be attached, embedded, or combined before firing. Carbonaceous or graphite fibers, carbonaceous precursor materials such as amorphous hard carbon, organic materials, inorganic materials, and metal materials may be attached to, embedded in, or combined with the graphite particles of the core material.

4). Negative electrode The present invention is also a negative electrode for a lithium ion secondary battery containing the above-mentioned carbonaceous coated graphite particles, and a lithium ion secondary battery using the negative electrode.
The negative electrode for a lithium ion secondary battery of the present invention is produced according to a normal negative electrode molding method, but is not limited as long as it is a method capable of obtaining a chemically and electrochemically stable negative electrode. In producing the negative electrode, it is preferable to use a negative electrode mixture prepared in advance by adding a binder to the carbonaceous coated graphite particles of the present invention. As the binder, those showing chemical and electrochemical stability with respect to the electrolyte are preferable. For example, fluorine-based resin powders such as polytetrafluoroethylene and polyvinylidene fluoride, and resin powders such as polyethylene and polyvinyl alcohol Carboxymethyl cellulose and the like are used. These can also be used together. The binder is usually used at a ratio of about 1 to 20% by mass in the total amount (dry basis) of the negative electrode mixture. Therefore, the carbonaceous coated graphite particles of the present invention are usually used at a ratio of 99 to 80% by mass (dry basis).

More specifically, first, the negative electrode material of the present invention is adjusted to a desired particle size by classification or the like, and a mixture obtained by mixing with a binder is dispersed in a solvent to prepare a negative electrode mixture in a paste form. That is, a slurry obtained by mixing the negative electrode material of the present invention and a binder with a solvent such as water, isopropyl alcohol, N-methylpyrrolidone, dimethylformamide, and the like, using a known stirrer, mixer, kneader, kneader, etc. Use to stir and mix to prepare paste. When the paste is applied to one or both sides of the current collector and dried, a negative electrode in which the negative electrode mixture layer is uniformly and firmly bonded is obtained. The film thickness of the negative electrode mixture layer is 10 to 200 μm, preferably 20 to 100 μm.

Since the negative electrode produced from the negative electrode mixture containing carbonaceous coated graphite particles of the present invention is anisotropically pressurized in the state of graphite particles, the negative electrode is prepared after forming the negative electrode mixture layer. Even when press molding is not performed, the electrode density can be made relatively high.
The negative electrode of the present invention can also be produced by dry-mixing the negative electrode material of the present invention and resin powders such as polyethylene and polyvinyl alcohol and hot pressing in a mold.
When the negative electrode mixture layer is formed and then pressure bonding such as pressurization is performed, the adhesive strength between the negative electrode mixture layer and the current collector can be further increased.
The shape of the current collector used for producing the negative electrode is not particularly limited, but may be a foil shape, a mesh shape, a net shape such as expanded metal, or the like. The material for the current collector is preferably copper, stainless steel, nickel or the like. The thickness of the current collector is preferably about 5 to 20 μm in the case of a foil.
It should be noted that the negative electrode of the present invention can be included even if different types of graphite materials, carbonaceous materials such as amorphous hard carbon, organic substances, metals, metal compounds, and the like are mixed within a range that does not impair the object of the present invention. Alternatively, it may be coated or laminated.

Since the negative electrode produced from the negative electrode mixture containing carbonaceous coated graphite particles of the present invention is anisotropically pressurized in the state of graphite particles, the negative electrode is prepared after forming the negative electrode mixture layer. This suppresses the deformation of the particles due to press pressurization and damage to the coating layer, and maintains high initial charge / discharge efficiency, high-speed charge / discharge characteristics, and cycle characteristics even when the electrode density is high. .

[Positive electrode]
The positive electrode used in the lithium secondary battery of the present invention is formed, for example, by applying a positive electrode mixture comprising a positive electrode material, a binder and a conductive agent to the surface of the current collector. The positive electrode material (positive electrode active material) is preferably selected from materials that can occlude / release a sufficient amount of lithium, and lithium such as lithium-containing transition metal oxides, transition metal chalcogenides, vanadium oxides, and lithium compounds thereof. Containing compound, general formula M _X Mo ₆ S _8-Y (wherein M is at least one transition metal element, X is a value in the range of 0 ≦ X ≦ 4, Y is 0 ≦ Y ≦ 1) Chevrel phase compounds, activated carbon, activated carbon fibers and the like.

The vanadium oxide is represented by V ₂ O ₅ , V ₆ O ₁₃ , V ₂ O ₄ , or V ₃ O ₈ .
The lithium-containing transition metal oxide is a composite oxide of lithium and a transition metal, and may be a solid solution of lithium and two or more transition metals. The composite oxide may be used alone or in combination of two or more.

Specifically, the lithium-containing transition metal oxide is LiM ¹ _1-X M ² _X O ₂ (wherein M ¹ and M ² are at least one transition metal element, and X is in the range of 0 ≦ X ≦ 1. LiM ¹ _1-Y M ² _Y O ₄ (wherein M ¹ and M ² are at least one transition metal element, and Y is a value in the range of 0 ≦ Y ≦ 1). Indicated.
The transition metal elements represented by M ¹ and M ² are Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, In, Sn, etc., preferably Co, Fe, Mn, Ti, Cr , V, Al, etc. Preferable specific examples include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiNi _0.9 Co _0.1 O ₂ , LiNi _0.5 Co _0.5 O ₂ and the like.
Examples of the lithium-containing transition metal oxide include lithium, transition metal oxides, hydroxides, salts, and the like as starting materials, and these starting materials are mixed in accordance with the composition of the desired metal oxide, and are mixed under an oxygen atmosphere. It can be obtained by firing at a temperature of ˜1000 ° C.

The positive electrode active material may be used alone or in combination of two or more. For example, a carbon salt such as lithium carbonate can be added to the positive electrode. Moreover, when forming a positive electrode, conventionally well-known various additives, such as a electrically conductive agent and a binder, can be used suitably.

[Production of positive electrode]
The positive electrode is produced by applying a positive electrode mixture comprising the positive electrode material, a binder, and a conductive agent for imparting conductivity to the positive electrode on both sides of the current collector to form a positive electrode mixture layer. As the binder, the same one as that used for producing the negative electrode can be used. As the conductive agent, known materials such as graphitized materials and carbon black are used.
The shape of the current collector is not particularly limited, but a foil shape or a mesh shape such as a mesh or expanded metal is used. The material of the current collector is aluminum, stainless steel, nickel or the like. The thickness is preferably 10 to 40 μm.
Similarly to the negative electrode, the positive electrode mixture may be formed in a paste by dispersing the positive electrode mixture in a solvent, and the paste-like positive electrode mixture may be applied to a current collector and dried to form a positive electrode mixture layer. After forming the agent layer, pressure bonding such as press pressing may be further performed. As a result, the positive electrode mixture layer is uniformly and firmly bonded to the current collector.

[Non-aqueous electrolyte]
The non-aqueous electrolyte used in the lithium ion secondary battery of the present invention, an electrolyte salt used in the conventional non-aqueous _{_{electrolyte, LiPF 6, LiBF 4, LiAsF}} 6, LiClO 4, LiB (C 6 H 5 ), LiCl, LiBr, LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ CH ₂ OSO ₂ ) ₂ , LiN (CF ₃ CF _{_{_{2 OSO 2) 2, LiN (}}} HCF 2 CF 2 CH 2 OSO 2) 2, LiN ((CF 3) 2 CHOSO 2) 2, LiB [{C 6 H 3 (CF 3) 2}] 4, LiAlCl 4, Lithium salts such as LiSiF ₆ can be used. From the viewpoint of oxidation stability, LiPF ₆ and LiBF ₄ are particularly preferable.
The electrolyte salt concentration in the electrolytic solution is preferably from 0.1 to 5.0 mol / L, more preferably from 0.5 to 3.0 mol / L.
The non-aqueous electrolyte may be a liquid non-aqueous electrolyte or a polymer electrolyte such as a solid electrolyte or a gel electrolyte. In the former case, the non-aqueous electrolyte battery is configured as a so-called lithium ion secondary battery, and in the latter case, the non-aqueous electrolyte battery is configured as a polymer electrolyte battery such as a polymer solid electrolyte or a polymer gel electrolyte battery. .

Solvents for preparing the non-aqueous electrolyte include carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate, 1,1- or 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, ethers such as anisole and diethyl ether, thioethers such as sulfolane and methylsulfolane, acetonitrile, chloronitrile, propionitrile, etc. Nitrile, trimethyl borate, tetramethyl silicate, nitromethane, dimethylformamide, N-methylpyrrolidone, ethyl acetate, trimethyl orthoformate, nitrobenzene, benzoyl chloride Benzoyl bromide, tetrahydrothiophene, dimethyl sulfoxide, 3-methyl-2-oxazolidone, ethylene glycol, aprotic organic solvents such as dimethyl sulfite may be used.

Generally, when a graphite negative electrode material is used, a system that does not contain propylene carbonate (PC) is used as the electrolytic solution. PC is not preferable because it tends to cause a decomposition reaction on the graphite surface, increases the internal pressure of the battery due to gas generation, and reduces the battery characteristics because a large amount of decomposition reaction products (SEI coating) are generated on the negative electrode material. It is said that. In the carbon-coated graphite particles of the present invention, spherical and / or ellipsoidal graphite is anisotropically pressurized and further coated with carbon, so the reactivity between the surface of the carbon-coated graphite particles and propylene carbonate is low. Even if propylene carbonate is contained in the electrolyte, the battery characteristics when used as a negative electrode material for a lithium ion secondary battery are comparable.

When the non-aqueous electrolyte is a polymer electrolyte such as a polymer solid electrolyte or a polymer gel electrolyte, it is preferable to use a polymer gelled with a plasticizer (non-aqueous electrolyte) as a matrix. Examples of the polymer constituting the matrix include ether-based polymer compounds such as polyethylene oxide and crosslinked products thereof, polymethacrylate-based polymer compounds, polyacrylate-based polymer compounds, polyvinylidene fluoride, and vinylidene fluoride-hexafluoropropylene. It is particularly preferable to use a fluorine-based polymer compound such as a copolymer.
The polymer solid electrolyte or polymer gel electrolyte is mixed with a plasticizer, and as the plasticizer, the electrolyte salt and the non-aqueous solvent can be used. In the case of a polymer gel electrolyte, the concentration of the electrolyte salt in the non-aqueous electrolyte as a plasticizer is preferably 0.1 to 5.0 mol / L, and more preferably 0.5 to 2.0 mol / L.

The method for producing the polymer solid electrolyte is not particularly limited. For example, a method of mixing a polymer compound constituting a matrix, a lithium salt, and a nonaqueous solvent (plasticizer) and heating to melt the polymer compound, an organic solvent A method in which a polymer compound, a lithium salt, and a non-aqueous solvent (plasticizer) are dissolved in, and an organic solvent for mixing is evaporated, a polymerizable monomer, a lithium salt, and a non-aqueous solvent (plasticizer) are mixed, and the mixture is mixed Examples thereof include a method of polymerizing a polymerizable monomer by irradiating an ultraviolet ray, an electron beam, a molecular beam or the like to obtain a polymer.
Here, the proportion of the non-aqueous solvent (plasticizer) in the solid electrolyte is preferably 10 to 90% by mass, more preferably 30 to 80% by mass. If it is less than 10% by mass, the electrical conductivity will be low, and if it exceeds 90% by mass, the mechanical strength will be weak and film formation will be difficult.

[Separator]
In the lithium ion secondary battery of the present invention, a separator can also be used. Although the material of a separator is not specifically limited, For example, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, etc. can be used. As a material for the separator, a microporous membrane made of synthetic resin is suitable. Among them, a polyolefin microporous membrane is suitable in terms of thickness, membrane strength, and membrane resistance. Specifically, polyethylene and polypropylene microporous membranes, or microporous membranes composed of these are suitable.

[Manufacture of lithium ion secondary batteries]
The lithium ion secondary battery of the present invention is configured by laminating the negative electrode, the positive electrode, and the nonaqueous electrolyte having the above-described configuration in the order of, for example, the negative electrode, the nonaqueous electrolyte, and the positive electrode, and accommodating the laminate in the battery exterior material. The Further, a non-aqueous electrolyte may be disposed outside the negative electrode and the positive electrode.
In addition, the structure of the lithium ion secondary battery of the present invention is not particularly limited, and the shape and form thereof are not particularly limited, and are cylindrical, depending on the application, mounted equipment, required charge / discharge capacity, and the like. , Square shape, coin shape, button shape, and the like. In order to obtain a sealed nonaqueous electrolyte battery with higher safety, it is preferable to use a battery equipped with means for detecting an increase in the internal pressure of the battery and shutting off the current when an abnormality such as overcharging occurs.
In the case where the lithium ion secondary battery is a polymer solid electrolyte battery or a polymer gel electrolyte battery, a structure in which the lithium ion secondary battery is enclosed in a laminate film may be used.

EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited to these Examples. In the following Examples and Comparative Examples, as shown in FIG. 1, a current collector (negative electrode) 7b having a negative electrode mixture 2 of the present invention attached to at least a part of its surface and a counter electrode (positive electrode) 4 made of lithium foil. A button-type secondary battery for single electrode evaluation composed of An actual battery can be produced according to a known method based on the concept of the present invention.
Each physical property in this specification is measured by the following method.
1) Average particle size (μm): The particle size at which the cumulative frequency of the particle size distribution measured with a laser diffraction particle size distribution meter is 50% by volume percentage.
2) Carbonaceous ratio (%): A carbonaceous precursor raw material (including a plurality of types) is provided with the same thermal history as the carbonaceous coated graphite particles to prepare a carbonaceous carbide. The residual coal rate of the raw material was obtained. The ratio of carbonaceous matter in the carbonaceous coated graphite particles was calculated in terms of the residual carbon ratio obtained.
3) Pore volume (mL / g): Measured by mercury porosimetry to determine the relationship between the pore diameter and the pore volume, and calculated the total pore volume with a pore diameter of 1.1 μm or less and 0.54 μm or less. .
4) DBP oil absorption (mL / 100 g): According to JIS K6217, 40 g of measurement material was added, and measurement was performed until the maximum value of torque was confirmed under the conditions of a dropping speed of 4 mL / min and a rotation speed of 125 rpm. The amount of oil dropped when the torque was 70% of the maximum torque in the range from the start of measurement to the maximum torque was calculated per 100 g of material.

(Example 1)
[Production of carbon-coated graphite particles as negative electrode material]
Natural graphite particles processed into a spherical shape with an average particle diameter of 15 μm were anisotropically pressurized at 50 MPa using a mold press. After pulverizing this so that the average particle diameter is 15 μm, the tar-in-oil solution of coal tar pitch (residual carbon ratio 50%) becomes 2.0 parts by mass with respect to 100 parts by mass. And heated to 150 ° C. with a biaxial kneader and mixed for 60 minutes. The obtained mixture was heat-treated at 1300 ° C. for 3 hours under a flow of nitrogen 2 L / min using a tubular furnace to obtain a final product.
[Preparation of negative electrode mixture paste]
98 parts by mass of the negative electrode material, 1 part by mass of carboxymethyl cellulose as a binder, and 1 part by mass of styrene-butadiene rubber were placed in water and stirred to prepare a negative electrode mixture paste.
[Production of working electrode (negative electrode)]
The negative electrode mixture paste is applied to a copper foil with a uniform thickness, the solvent is volatilized at 90 ° C. in a vacuum, and the negative electrode mixture layer is pressed by a roll press so that the electrode density is 1.70 g / cm ³ . It was adjusted. The copper foil and the negative electrode mixture layer were punched into a cylindrical shape having a diameter of 15.5 mm to prepare a working electrode (negative electrode) composed of a current collector and a negative electrode mixture adhered to the current collector.
[Production of counter electrode (positive electrode)]
A lithium metal foil is pressed against a nickel net and punched into a circular shape with a diameter of 15.5 mm. A current collector made of nickel net and a counter electrode made of a lithium metal foil (thickness 0.5 mm) in close contact with the current collector ( Positive electrode) was prepared.
[Electrolyte, separator]
LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate 33 vol% -methyl ethyl carbonate 67 vol% to prepare a non-aqueous electrolyte. The obtained nonaqueous electrolytic solution was impregnated into a polypropylene porous body (thickness 20 μm) to produce a separator impregnated with the electrolytic solution.

[Production of evaluation battery]
A button-type secondary battery shown in FIG. 1 was prepared as an evaluation battery.
The exterior cup 1 and the exterior can 3 were sealed by interposing an insulating gasket 6 at the peripheral portion thereof and caulking both peripheral portions. A copper current collector 7 a made of nickel net, a cylindrical counter electrode (positive electrode) 4 made of lithium foil, a separator 5 impregnated with an electrolytic solution, and a negative electrode mixture 2 are attached to the inside of the outer can 3 in that order. This is a battery system in which a current collector (negative electrode) 7b made of foil is laminated.
In the evaluation battery, the separator 5 impregnated with the electrolytic solution was laminated between the current collector 7b and the counter electrode 4 in close contact with the current collector 7a, and then the current collector 7b was placed in the outer cup 1 4 is accommodated in the outer can 3, the outer cup 1 and the outer can 3 are combined, and further, an insulating gasket 6 is interposed between the outer peripheral portion of the outer cup 1 and the outer can 3, and both peripheral portions are caulked and sealed. And produced. The charge / discharge characteristics were measured by the following method. The results are shown in Table 1.
[Charge / discharge test]
After constant current charging of 0.9 mA until the circuit voltage reaches 1 mV, switching to constant voltage charging is performed when the circuit voltage reaches 1 mV, and further, the charging capacity (unit: : MAh / g). Then, it rested for 10 minutes. Next, constant current discharge was performed at a current value of 0.9 mA until the circuit voltage reached 1.5 V, and the discharge capacity (unit: mAh / g) was determined from the amount of electricity supplied during this period. This was the first cycle. Next, charging and discharging were performed in the same manner as in the first cycle, with the charging current being 1C and the discharging current being 2C. The current values of 1C and 2C were calculated from the discharge capacity of the first cycle and the active material weight of the negative electrode.
The initial charge / discharge efficiency was calculated from the following equation (1).
Initial charge / discharge efficiency (%) = 100 × ((first cycle charge capacity−first cycle discharge capacity) / first cycle discharge capacity) (1)
Moreover, 1C charge rate was computed from following Formula (2).
1C charge rate (%) = 100 × (charge capacity of CC portion at 1C current value / discharge capacity of first cycle) (2)
The 2C discharge rate was calculated from the following equation (3).
2C discharge rate (%) = 100 × (discharge capacity at 2C current value / discharge capacity of first cycle) (3)
The cycle characteristics were measured as follows. After constant current charging at 1 C current value until the circuit voltage reached 1 mV, switching to constant voltage charging was continued until the current value reached 20 μA, and then rested for 10 minutes. Next, constant current discharge was performed at a current value of 2C until the circuit voltage reached 1.5V. This charge / discharge was repeated 50 times, and the cycle characteristics were calculated from the obtained discharge capacity using the following equation (4).
Cycle characteristics (%) = 100 × (50th cycle discharge capacity / first cycle discharge capacity) (4)
In this test, the process of occluding lithium ions in the negative electrode material was charged, and the process of detaching lithium ions from the negative electrode material was discharge.

(Example 2)
In Example 1, evaluation was performed in the same manner as in Example 1 except that the electrode density at the time of battery performance evaluation was 1.75 g / cm ³ . The evaluation results are shown in Table 1.

(Example 3)
In Example 1, except that the carbonaceous coating amount was changed to the amount shown in Table 1, carbonaceous coated graphite particles were produced in the same manner as in Example 1, and evaluation batteries were produced and evaluated in the same manner as in Example 1. did.

Example 4
In Example 1, carbonaceous coated graphite particles were produced in the same manner as in Example 1 except that the pressure during the pressure treatment was 100 MPa, and the electrode density was evaluated as 1.70 g / cm ³ . The evaluation results are shown in Table 1.

(Example 5)
In Example 1, carbonaceous coated graphite particles were produced in the same manner as in Example 1 except that the pressure during the pressure treatment was 150 MPa, and the electrode density was evaluated as 1.70 g / cm ³ . The evaluation results are shown in Table 1.

(Example 6)
Evaluation was made in the same manner as in Example 1 except that the carbonaceous coating amount was changed to the amount shown in Table 1 in Example 1. The evaluation results are shown in Table 1.

(Comparative Example 1)
In Example 1, carbonaceous coated graphite particles were produced in the same manner as in Example 1 except that no pressure treatment was performed, and an evaluation battery was produced and evaluated in the same manner as in Example 1.

(Comparative Example 2)
In Example 1, a coated natural graphite material was produced in the same manner as in Example 1 except that 50 MPa was isotropically pressurized using a cold isostatic press as the method of pressure treatment. An evaluation battery was prepared and evaluated.

(Comparative Example 3)
In Comparative Example 2, the evaluation was performed in the same manner as in Comparative Example 2 except that the electrode density during battery performance evaluation was 1.75 g / cm ³ . The evaluation results are shown in Table 1.

(Comparative Example 4)
Except that the carbonaceous coating amount was changed to the amount shown in Table 1 in Example 1, carbonaceous coated graphite particles were produced in the same manner as in Example 1, and evaluation batteries were produced and evaluated in the same manner as in Example 1. .

(Comparative Example 5)
Except that the carbonaceous coating amount was changed to the amount shown in Table 1 in Example 1, carbonaceous coated graphite particles were produced in the same manner as in Example 1, and evaluation batteries were produced and evaluated in the same manner as in Example 1. .

(Comparative Example 6)
In Example 1, it evaluated similarly to Example 1 except the pressure at the time of a pressurizing process being 10 Mpa. The evaluation results are shown in Table 1.

(Comparative Example 7)
In Example 1, it evaluated similarly to Example 1 except the pressure at the time of a pressurizing process being 10 Mpa, and making a carbonaceous coating amount into 3.0 mass parts. The evaluation results are shown in Table 1.

(Comparative Example 8)
In Example 1, it evaluated similarly to Example 1 except the pressure at the time of a pressurizing process being 30 Mpa, and making a carbonaceous coating amount into 3.0 mass parts. The evaluation results are shown in Table 1.

(Comparative Example 9)
In Example 1, it evaluated similarly to Example 1 except the pressure at the time of a pressurizing process being 10 Mpa, and making a carbonaceous coating amount into 0.15 mass part. The evaluation results are shown in Table 1.

Examples 1 to 6 in which the graphite particles formed by anisotropic pressure satisfy the following (1) to (3) have good discharge capacity, initial charge / discharge efficiency, high-speed charge / discharge characteristics, and cycle characteristics. . As is clear from the comparison between Examples 1 and 2, this characteristic is maintained even when the electrode density is increased.
(1) The content of the carbonaceous material is 0.1 to 3.0 parts by mass with respect to 100 parts by mass of the graphite particles formed by anisotropic pressure in the carbonaceous coated graphite particles.
(2) The pore volume with a pore diameter of 1.1 μm or less measured with a mercury porosimeter is 0.100 mL / g or less, and the ratio of the pore volume with a pore diameter of 0.54 μm or less to the pore volume is 80% or more .
(3) Dibutyl phthalate (DBP) oil absorption is 40.0 mL / 100 g or less.
On the other hand, Comparative Example 1 in which the graphite particles are not pressure-treated, Comparative Examples 2 and 3 in which the isotropic pressure treatment is performed, Comparative Example 4 in which the coating amount of the carbonaceous material is less than 0.1%, carbon Comparative Example 5 in which the covering amount of the porous material exceeds 3%, the pore volume with a pore diameter of 1.1 μm or less exceeds 0.100 mL / g, and the ratio of the pore volume with a pore diameter of 0.54 μm or less to the pore volume is Comparative Example 6 having a DBP oil absorption of less than 80% and a DBP oil absorption of more than 40.0 mL / 100 g, Comparative Example 7 having a pore volume of 1.1 μm or less and a pore volume of more than 0.1 mL / g, and a pore diameter of 1.1 μm or less Comparative Example 8 in which the ratio of the pore volume with a pore diameter of 0.54 μm or less to the pore volume is less than 80%, the pore volume with a pore diameter of 1.1 μm or less exceeds 0.100 mL / g, and the DBP oil absorption is 40 Comparative Example 9 of more than 0.0 mL / 100 g has high discharge capacity, high initial charge / discharge efficiency, high high-speed charge / discharge It could not be achieved sex and excellent cycle characteristics at the same time. In Comparative Examples 2 and 3 subjected to isotropic pressure treatment, when the electrode density was further increased, it was confirmed that the initial charge / discharge efficiency, high-speed charge / discharge characteristics, and cycle characteristics were lowered.

The negative electrode material composed of carbonaceous coated graphite particles of the present invention is a negative electrode material having good discharge capacity, initial charge / discharge efficiency, fast charge / discharge characteristics, and cycle characteristics as a negative electrode material for a lithium ion secondary battery. Taking advantage of these characteristics, it can be used for negative electrodes of high-performance lithium ion secondary batteries ranging from small to large.

DESCRIPTION OF SYMBOLS 1 Exterior cup 2 Negative electrode mixture 3 Exterior can 4 Counter electrode 5 Electrolyte solution impregnation separator 6

Insulation gasket

7a, 7b Current collector 10 Aluminum plate 12 Double-sided tape 15 Negative electrode material 17 Arrow direction

Claims

Carbonaceous coated graphite particles having a carbonaceous material on at least a part of the surface of graphite particles obtained by anisotropically pressing spherical and / or ellipsoidal graphite, wherein the carbonaceous coated graphite particles are Graphite particles for a lithium ion secondary battery negative electrode material satisfying the following (1) to (3).
(1) The content of the carbonaceous material is 0.1 to 3.0 parts by mass with respect to 100 parts by mass of the graphite particles formed by anisotropic pressure in the carbonaceous coated graphite particles.
(2) The pore volume with a pore diameter of 1.1 μm or less measured with a mercury porosimeter is 0.100 mL / g or less, and the ratio of the pore volume with a pore diameter of 0.54 μm or less to the pore volume is 80% or more .
(3) Dibutyl phthalate (DBP) oil absorption is 40.0 mL / 100 g or less.
A lithium ion secondary battery negative electrode comprising the graphite particles for a lithium ion secondary battery negative electrode material according to claim 1.
A lithium ion secondary battery having the lithium ion secondary battery negative electrode according to claim 2.