CN110870114A

CN110870114A - Method for producing negative electrode material for lithium ion secondary battery, and negative electrode material for lithium ion secondary battery

Info

Publication number: CN110870114A
Application number: CN201880045280.4A
Authority: CN
Inventors: 星贤匠; 土屋秀介; 久保田高志
Original assignee: Hitachi Chemical Co Ltd
Current assignee: Lishennoco Co ltd
Priority date: 2017-07-07
Filing date: 2018-07-06
Publication date: 2020-03-06
Anticipated expiration: 2038-07-06
Also published as: CN110870114B; JP7156468B2; JP6981471B2; JP2022153633A; WO2019009422A1; JPWO2019009422A1; JP7371735B2; JP2021180187A

Abstract

The method for producing a negative electrode material for a lithium ion secondary battery comprises the steps of: a step for preparing an activated carbon substance A obtained by subjecting a carbon substance A to a treatment for increasing the BET specific surface area by 2% to 50%; a step of obtaining a mixture by mixing the activated carbonaceous material a and a carbonaceous material precursor that is a source of a carbonaceous material B different from the carbonaceous material a; and a step of obtaining a fired product by heat-treating the mixture.

Description

Method for producing negative electrode material for lithium ion secondary battery, and negative electrode material for lithium ion secondary battery

Technical Field

The present invention relates to a method for producing a negative electrode material for a lithium ion secondary battery, and a negative electrode material for a lithium ion secondary battery.

Background

Lithium ion secondary batteries have been widely used in electronic devices such as notebook Personal Computers (PCs), mobile phones, smart phones, and tablet PCs, by effectively utilizing the characteristics of being small, lightweight, and high in energy density. In recent years, the catalyst is prepared from CO₂Background of environmental problems such as global warming due to emissions, clean Electric Vehicles (EV) that run only on batteries, Hybrid Electric Vehicles (HEV) that combine a gasoline engine and a battery, plug-in hybrid electric vehicles (PHEV), and the like have become widespread, and lithium ion secondary batteries (vehicle-mounted lithium ion secondary batteries) have been used as batteries mounted on EVs, HEVs, PHEVs, and the like. In addition, lithium ion secondary batteries are also used in recent years for power storage, and the use of lithium ion secondary batteries has been expanded in many fields.

The performance of the negative electrode material of the lithium ion secondary battery greatly affects the output characteristics of the lithium ion secondary battery. As a material of a negative electrode material for a lithium ion secondary battery, a carbon material is widely used. The carbon material used for the negative electrode material is roughly classified into graphite and a carbon material (amorphous carbon or the like) having lower crystallinity than graphite. Graphite has a structure in which hexagonal lattice planes of carbon atoms are orderly stacked, and when a negative electrode material for a lithium ion secondary battery is produced, insertion reaction and desorption reaction of lithium ions proceed from the end portions of the hexagonal lattice planes, and charging and discharging are performed.

The hexagonal lattice planes of the amorphous carbon are irregular or have no hexagonal lattice planes. In the case of a negative electrode material using amorphous carbon, an insertion reaction and a desorption reaction of lithium ions are performed on the entire surface of the negative electrode material. Therefore, a lithium ion battery having excellent output characteristics is easily obtained as compared with the case of using graphite as a negative electrode material (for example, see patent documents 1 and 2). On the other hand, amorphous carbon has lower crystallinity than graphite, and therefore has lower energy density than graphite.

Further, patent document 3 proposes improvement of initial efficiency by adjusting the pore volume to a specific range.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 4-370662

Patent document 2: japanese laid-open patent publication No. 5-307956

Patent document 3: international publication No. 2012/090728

Disclosure of Invention

Problems to be solved by the invention

In view of the characteristics of carbon materials, a negative electrode material has been proposed which contains composite particles of graphite coated with amorphous carbon, and which has improved output characteristics by reducing the reactivity of the surface while maintaining a high energy density to maintain good initial charge-discharge efficiency. However, under the background described above, a negative electrode material is required which can further improve the output characteristics of a lithium ion secondary battery. In addition, high-temperature storage characteristics are also required for vehicle-mounted lithium ion secondary batteries such as EVs, HEVs, and PHEVs.

Further, as described in patent document 3, the conventional initial efficiency and micropore capacity have such a long-term relationship, and it is difficult to achieve both of the charging characteristic and the initial efficiency.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing a negative electrode material for a lithium ion secondary battery, which can produce a negative electrode for a lithium ion secondary battery having excellent input characteristics, output characteristics, high-temperature storage characteristics, and initial efficiency.

Means for solving the problems

The present inventors have conducted extensive studies to achieve the above object, and as a result, the present invention has been completed. That is, one embodiment of the present invention includes the following forms.

< 1 > a method for producing a negative electrode material for a lithium ion secondary battery, comprising the steps of:

a step for preparing an activated carbon substance A obtained by subjecting a carbon substance A to a treatment for increasing the BET specific surface area by 2% to 50%;

a step of obtaining a mixture by mixing the activated carbonaceous material a and a carbonaceous material precursor that is a source of a carbonaceous material B different from the carbonaceous material a; and

and a step of obtaining a fired product by heat-treating the mixture.

< 2 > the method for producing a negative electrode material for a lithium ion secondary battery according to < 1 >, wherein the step of obtaining a fired product comprises bringing the BET specific surface area of the fired product to 0.5m²/g～10m²(ii) a step of (i)/g.

< 3 > the method for producing a negative electrode material for a lithium ion secondary battery according to < 1 > or < 2 >, wherein the heat treatment is carried out at a temperature of 700 to 1500 ℃.

< 4 > the method for producing a negative electrode material for a lithium ion secondary battery according to any one of < 1 > to < 3 >, wherein the crystallinity of the carbon substance B is lower than that of the activated carbon substance A.

< 5 > a negative electrode material for lithium ion secondary batteries, which comprises a carbonaceous material AA and a carbonaceous material B different from the carbonaceous material AA,

when the negative electrode material for the lithium ion secondary battery is subjected to heat treatment at 600 ℃ for 30 minutes in an air atmosphere, the ratio of the BET specific surface area after the heat treatment to the BET specific surface area before the heat treatment is greater than or equal to 2.5.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide a negative electrode material for a lithium ion secondary battery excellent in input characteristics, output characteristics, high-temperature storage characteristics, and initial efficiency, and a method for producing a negative electrode material for a lithium ion secondary battery capable of producing the negative electrode material for a lithium ion secondary battery.

Detailed Description

Hereinafter, specific embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps) are not essential unless otherwise explicitly stated. The same applies to values and ranges, without limiting the invention.

In the present disclosure, the word "step" includes a step that is independent from other steps, and if the purpose of the step can be achieved, the step, even if it cannot be clearly distinguished from other steps.

In the present disclosure, the numerical range represented by the term "to" includes the numerical values before and after the term "to" as the minimum value and the maximum value, respectively.

In the numerical ranges recited in the present disclosure, the upper limit or the lower limit recited in one numerical range may be replaced with the upper limit or the lower limit recited in another numerical range recited in a stepwise manner. In the numerical ranges disclosed in the present disclosure, the upper limit or the lower limit of the numerical range may be replaced with the values shown in the examples.

Each ingredient in the present disclosure may contain a plurality of substances corresponding to each ingredient. When a plurality of substances corresponding to each component are present in the negative electrode material or composition, the content or content of each component refers to the content or content of the total of the plurality of substances present in the negative electrode material or composition, unless otherwise specified.

A plurality of particles corresponding to each component may be contained in the present disclosure. When a plurality of particles corresponding to each component are present in the negative electrode material or the composition, the particle diameter of each component is a value indicating a mixture of the plurality of particles present in the negative electrode material or the composition unless otherwise specified.

The word "layer" in the present disclosure includes a case where the layer is formed over the entire region when the region in which the layer is present is observed, and also includes a case where the layer is formed only in a part of the region.

The word "stacked" in the present disclosure means that layers are stacked, and two or more layers may be combined, or two or more layers may be detachable.

Method for producing negative electrode material for lithium ion secondary battery

The disclosed method for producing a negative electrode material for a lithium ion secondary battery comprises the following steps: a step for preparing an activated carbonaceous material A obtained by subjecting a carbonaceous material A to a treatment for increasing the BET specific surface area by 2% to 50%; a step of mixing the activated carbonaceous material a and a carbonaceous material precursor that is a source of a carbonaceous material B different from the carbonaceous material a to obtain a mixture; and a step of obtaining a fired product by heat-treating the mixture.

The method for producing a negative electrode material for a lithium-ion secondary battery according to the present disclosure may include other steps as necessary.

By using the negative electrode material for a lithium ion secondary battery produced by the method for producing a negative electrode material for a lithium ion secondary battery of the present disclosure, a negative electrode for a lithium ion secondary battery excellent in input characteristics, output characteristics, high-temperature storage characteristics, and initial efficiency can be produced.

Hereinafter, each step included in the method for producing a negative electrode material for a lithium ion secondary battery of the present disclosure, a material used, and the like will be described in detail.

< Process for preparing activated carbon substance A >

In the step of preparing the activated carbonaceous material a, an activated carbonaceous material a is prepared by subjecting the carbonaceous material a to a treatment for increasing the BET specific surface area by 2% to 50%. The treatment for increasing the BET specific surface area of the carbonaceous material a is not particularly limited.

The treatment for increasing the BET specific surface area of the carbonaceous material A includes, for example, the presence of CO₂Gas, water vapor, O₂Heat treatment in an atmosphere of gas or the like, mechanical treatment, or the like. From the viewpoints of controlling the particle diameter of the activated carbonaceous material A, controlling the surface state of the activated carbonaceous material A, and the likePreferably in the presence of O₂The heat treatment is performed in a gas atmosphere (for example, in an air atmosphere).

The suitable treatment temperature varies depending on the gas atmosphere used, the treatment time, and the like. For example, in the case of treatment in an air atmosphere, the heat treatment temperature is preferably 100 to 600 ℃, more preferably 150 to 600 ℃. Within this temperature range, the specific surface area of the activated carbonaceous material a can be increased without burning the carbonaceous material a.

The heat treatment time varies depending on the heat treatment temperature, the type of carbon material, and the like, and is preferably 0.5 to 24 hours, and more preferably 1 to 6 hours. In this time, the specific surface area of the activated carbonaceous material a can be effectively increased. Further, in the presence of O₂When the heat treatment is performed in a gas atmosphere, O is₂The gas content is preferably 1 to 30 vol%. When the amount is within this range, the specific surface area of the activated carbonaceous material a tends to be effectively increased.

The gas atmosphere used was CO₂The heat treatment temperature in the case of a gas atmosphere is preferably 600 to 1000 ℃, and more preferably 700 to 900 ℃. The heat treatment time varies depending on the heat treatment temperature and the type of carbon material, and is preferably 0.5 to 24 hours, and more preferably 1 to 6 hours.

In the present disclosure, nitrogen adsorption at a liquid nitrogen temperature (77K) is measured by a multipoint method and a BET specific surface area is calculated by a BET method.

In the measurement of the BET specific surface area, it is considered that moisture adsorbed on the surface and structure of the sample affects the gas adsorption capacity, and therefore, it is preferable to first perform a pretreatment for removing moisture by heating.

In the pretreatment, for example, a measuring cell (cell) into which 0.05g of a measuring sample is charged is depressurized by a vacuum pump to 10Pa or less, heated at 110 ℃ for 3 hours or more, and then naturally cooled to room temperature (25 ℃) while maintaining the depressurized state. After the pretreatment, the measurement can be performed so that the evaluation temperature is 77K and the evaluation pressure range is less than 1 in terms of relative pressure (equilibrium pressure with respect to saturated vapor pressure).

In the step of preparing the activated carbonaceous material a, the BET specific surface area increase rate of the activated carbonaceous material a with respect to the carbonaceous material a is 2% to 50%, and may be 5% to 50%. If the BET specific surface area increase rate of the activated carbonaceous material a with respect to the carbonaceous material a is less than 2%, the input characteristics tend to be slightly improved. If the BET specific surface area increase rate of the activated carbonaceous material a with respect to the carbonaceous material a exceeds 50%, the initial efficiency and the high-temperature storage characteristics tend to deteriorate.

The carbonaceous material a used in the step of preparing the activated carbonaceous material a is not particularly limited.

Examples of the carbonaceous material a include graphite such as artificial graphite, natural graphite, graphitized mesophase carbon, and graphitized carbon fiber; carbon materials such as low crystalline carbon, amorphous carbon, and mesophase carbon.

The carbonaceous material a preferably contains graphite from the viewpoint of increasing charge/discharge capacity. The shape of the graphite is not particularly limited, and examples thereof include a flake shape, a spherical shape, a block shape, a fibrous shape, and the like. From the viewpoint of obtaining a high tap density, a spherical shape is preferable.

When the carbonaceous material a is spherical natural graphite, the volume average particle diameter (D) of the carbonaceous material a₅₀) Preferably 5 to 30 μm, more preferably 6 to 25 μm, and still more preferably 7 to 20 μm.

When the carbonaceous material a is artificial graphite, the volume average particle diameter (D) of the carbonaceous material a₅₀) Preferably 8 to 40 μm, more preferably 10 to 35 μm, and still more preferably 12 to 30 μm.

When the carbonaceous material A is spherical natural graphite, the BET specific surface area of the carbonaceous material A is preferably 5m²/g～15m²(iv)/g, more preferably 6m²/g～13m²(ii)/g, more preferably 7m²/g～11m²/g。

When the carbonaceous material A is artificial graphite, the BET specific surface area of the carbonaceous material A is preferably 1m²/g～10m²G, more preferably 2m²/g～8m²(ii)/g, more preferably 3m²/g～7m²/g。

When the carbonaceous material A is spherical natural graphite, the BET specific surface area of the activated carbonaceous material A is preferably 5m²/g～23m²(iv)/g, more preferably 6m²/g～20m²(ii)/g, more preferably 7m²/g～15m²/g。

When the carbonaceous material A is artificial graphite, the BET specific surface area of the activated carbonaceous material A is preferably 1m²/g～13m²G, more preferably 2m²/g～12m²(ii)/g, more preferably 3m²/g～10m²/g。

In the method for producing a negative electrode material for a lithium ion secondary battery according to the present disclosure, a commercially available activated carbon substance a can be purchased and prepared.

The artificial graphite may be, for example, graphite particles (hereinafter referred to as "bulk graphite particles") in which a plurality of flat particles are aggregated or bonded so that their orientation planes (main surfaces) are not parallel to each other. Whether or not the bulk graphite particles were included can be confirmed by observation with a Scanning Electron Microscope (SEM).

The flat particles are particles having a shape with a major axis and a minor axis, and are not completely spherical particles. Particles in the shape of, for example, scales, partial blocks, etc. are also included. In the bulk graphite particles, the main surfaces of the plurality of flat particles are not parallel to each other, which means that the surfaces (main surfaces) of the flat graphite particles having the largest cross-sectional area are not aligned in a certain direction.

In addition, in the bulk graphite particles, the flat particles are aggregated or bonded, and the bonding means a state in which the particles are chemically bonded to each other via a carbonaceous material obtained by carbonizing an organic binder such as tar or pitch. The term "aggregate" means a state in which particles are not chemically bonded to each other but retain their shape as an aggregate due to their shape or the like. In the present invention, bonded particles are preferable in terms of mechanical strength.

The number of aggregation or bonding of the flat particles in 1 block-shaped graphite particle is not particularly limited, but is preferably not less than 3, more preferably 5 to 20, and still more preferably 5 to 15.

Method for producing bulk graphite particles

The method for producing the bulk graphite particles is not particularly limited as long as a predetermined structure can be formed. For example, the graphite particles can be obtained by adding 1 to 50 mass% of a graphitization catalyst to the total amount of a graphitizable aggregate or graphite and a graphitizable binder (organic binder), mixing, firing, and then pulverizing. Thus, the graphitization catalyst comes off to form pores, and provides excellent characteristics as bulk graphite particles. The bulk graphite particles can also be adjusted to a desired structure by appropriately selecting a mixing method of graphite or aggregate and a binder, adjustment of a mixing ratio such as an amount of the binder, and pulverization conditions after firing.

As the graphitizable aggregate, for example, coke powder, a resin carbide, or the like can be used, and there is no particular limitation as long as it is a graphitizable powder material. Among them, easily graphitizable coke powder such as needle coke is preferable. As the graphite, for example, natural graphite powder, artificial graphite powder, or the like can be used, and there is no particular limitation in the case of a powder. The volume average particle diameter of the aggregate or graphite capable of graphitization is preferably smaller than the volume average particle diameter of the bulk graphite particles, more preferably smaller than or equal to 2/3 of the volume average particle diameter of the bulk graphite particles. The aggregate or graphite that can be graphitized is preferably flat particles.

When the aggregate or graphite capable of graphitization is flat particles, spherical graphite particles such as spherical natural graphite may be used in combination.

The circularity is preferably 0.60 to 0.95, more preferably 0.65 to 0.95, and even more preferably 0.70 to 0.95, from the viewpoint of controlling the particle orientation.

Here, the circularity is a value obtained by dividing a circumference length of a circle calculated from an equivalent circle diameter which is a diameter of a circle having the same area as a projected area of the graphite particles by a circumference length (length of a contour line) measured from a projected image of the graphite particles, and is obtained by the following equation. The circularity is 1.00 when the circle is perfect.

Circularity (circumference of equivalent circle)/(circumference of particle cross-sectional image)

Specifically, the circularity is an average circularity calculated by observing an image magnified 1000 times by a scanning electron microscope, selecting 10 graphite particles arbitrarily, measuring the circularity of each particle, and calculating the arithmetic average of the circularities. The circularity, the perimeter of the equivalent circle, and the perimeter of the projected image of the particle can be obtained by commercially available image analysis software.

As the graphitization catalyst, for example, a graphitization catalyst such as a metal or metalloid such as iron, nickel, titanium, silicon, boron, and a carbide or an oxide thereof can be used. Among them, carbides or oxides of silicon or boron are preferable. The amount of the graphitization catalyst added is preferably in the range of 1 to 50 mass%, more preferably in the range of 5 to 40 mass%, and still more preferably in the range of 5 to 30 mass% with respect to the mass graphite particles obtained. If the amount is 1 mass% or more, the increase in the aspect ratio and the specific surface area of the bulk graphite particles tends to be suppressed, and the growth of graphite crystals tends to be good, while if the amount is 50 mass% or less, uniform mixing tends to be facilitated, and the handling properties tend not to be impaired, and therefore, these are preferable.

The binder (organic binder) is not particularly limited as long as it can be graphitized by firing, and examples thereof include organic materials such as tar, pitch, thermosetting resins, and thermoplastic resins. The binder is added to the flat graphitizable aggregate or graphite preferably in an amount of 5 to 80% by mass, more preferably 10 to 80% by mass, and still more preferably 15 to 80% by mass. By adjusting the amount of the binder to an appropriate amount, the aspect ratio and specific surface area of the produced bulk graphite particles tend to be suppressed from becoming too large.

The method of mixing the graphitizable aggregate or graphite with the binder is not particularly limited, and it is carried out using a kneader or the like, and it is preferable to mix them at a temperature of not less than the softening point of the binder. Specifically, the binder is preferably 50 to 300 ℃ when it is pitch, tar or the like, and preferably 20 to 100 ℃ when it is a thermosetting resin, a thermoplastic resin or the like.

Next, the mixture is fired and graphitized. In addition, the above mixture may be molded into a predetermined shape before the treatment. Further, after molding, the graphite may be pulverized before graphitization, and graphitized after adjusting the particle size. The firing is preferably performed under conditions in which the mixture is hardly oxidized, and examples thereof include a method in which firing is performed in a nitrogen atmosphere, an argon atmosphere, or a vacuum. The temperature for graphitization is preferably 2000 ℃ or higher, more preferably 2500 ℃ or higher, and still more preferably 2800 to 3200 ℃.

By making the temperature of graphitization greater than or equal to 2000 ℃, there is a tendency that the growth of graphite crystals becomes good and the discharge capacity increases. Further, there is a tendency that the added graphitization catalyst can be suppressed from remaining in the produced bulk graphite particles. If the graphitization catalyst remains in the bulk graphite particles, the discharge capacity may be reduced, and therefore it is preferable to suppress the residue. On the other hand, if the temperature for graphitization is 3200 ℃ or less, there is a tendency that sublimation of graphite can be suppressed.

When the particle diameter is not adjusted before graphitization, it is preferable to pulverize the graphitized material obtained by graphitization so that the particle diameter becomes a desired volume average particle diameter. The method for pulverizing the graphitized material is not particularly limited, and known methods such as a jet mill, a vibration mill, a pin mill, and a hammer mill can be used. By the above-described production method, graphite particles in which a plurality of flat particles are aggregated or bonded so that their main surfaces are not parallel, that is, bulk graphite particles can be obtained.

Further, the details of the above-mentioned production method can be referred to Japanese patent No. 3285520 and Japanese patent No. 3325021.

The surfaces of the obtained bulk graphite particles may be coated with low-crystalline carbon.

< Process for obtaining a mixture >

In the step of obtaining the mixture, the activated carbonaceous material a and a carbonaceous material precursor that is a source of a carbonaceous material B different from the carbonaceous material a are mixed.

The carbonaceous material B preferably contains at least one of crystalline carbon and amorphous carbon from the viewpoint of improving input/output characteristics. For example, a carbonaceous material obtained from an organic compound that can be converted into a carbonaceous material by heat treatment (hereinafter, a carbonaceous material precursor that is a source of the carbonaceous material B is also referred to as a precursor of the carbonaceous material B) is preferable. Specific examples of the carbonaceous material B include carbon materials such as low crystalline carbon, amorphous carbon, and mesophase carbon.

The precursor of the carbonaceous material B is not particularly limited, and examples thereof include pitch and organic polymer compounds. Examples of the asphalt include ethylene heavy-oil asphalt, crude oil asphalt, coal tar asphalt, asphalt decomposed asphalt, asphalt produced by thermally decomposing polyvinyl chloride or the like, asphalt produced by polymerizing naphthalene or the like in the presence of a super acid, and the like.

Examples of the organic polymer compound include thermoplastic resins such as polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, and polyvinyl butyral, and natural materials such as starch and cellulose.

When pitch is used as the precursor of the carbonaceous material B, the pitch preferably has a softening point of 70 to 250 ℃, more preferably 75 to 150 ℃, and still more preferably 80 to 120 ℃.

The softening point of the asphalt means a softening point determined by JIS K2425: a value obtained by the method for measuring the softening point of tar pitch (ring and ball method) described in 2006.

The carbon residue ratio of the precursor of the carbonaceous material B is preferably 5 to 80% by mass, more preferably 10 to 70% by mass, and still more preferably 20 to 60% by mass. The method of measuring the carbon residue rate is described below.

The mixture may contain, as necessary, other particulate carbonaceous materials B (carbonaceous particles) in addition to the precursor of the carbonaceous material B. When the mixture contains the precursor of the carbonaceous material B and the carbonaceous particles, the carbonaceous material B formed from the precursor of the carbonaceous material B may be the same as or different from the carbonaceous particles.

The carbonaceous particles used for the other carbonaceous material B are not particularly limited, and examples thereof include particles of acetylene black, oil furnace black, ketjen black, channel black, thermal black, and graphite (amophorous graphite).

In the step of obtaining the mixture, the content of the precursors of the activated carbonaceous material a and the carbonaceous material B in the mixture is not particularly limited. From the viewpoint of input/output characteristics, the content of the precursor of the carbonaceous material B is preferably an amount such that the content of the carbonaceous material B in the total mass of the negative electrode material for a lithium ion secondary battery becomes 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 1% by mass or more. From the viewpoint of suppressing the capacity decrease, the content of the precursor of the carbonaceous material B is preferably an amount such that the content of the carbonaceous material B in the total mass of the negative electrode material for a lithium-ion secondary battery becomes 30% by mass or less, more preferably 20% by mass or less, and still more preferably 10% by mass or less.

In the step of obtaining the mixture, the method for preparing the mixture containing the precursors of the activated carbonaceous material a and the carbonaceous material B is not particularly limited. Examples thereof include a method in which precursors of the activated carbonaceous material a and the carbonaceous material B are mixed in a solvent, and then the solvent is removed (wet mixing); a method of mixing the precursors of the activated carbonaceous material a and the carbonaceous material B in a powder state (powder mixing); and a method of mixing the precursors of the activated carbonaceous material a and the carbonaceous material B while applying mechanical energy (mechanical mixing).

The mixture containing the precursors of the activated carbonaceous material a and the carbonaceous material B is preferably in a composite state. The state of composite refers to a state in which the respective materials are in physical or chemical contact.

< Process for obtaining fired Material >

In the step of obtaining a fired product, the mixture is heat-treated to obtain a fired product.

The heat treatment temperature when the mixture containing the precursors of the activated carbon substance a and the carbon substance B is heat-treated is not particularly limited. For example, the heat treatment is preferably performed at a temperature of 700 to 1500 ℃, more preferably at a temperature of 750 to 1300 ℃, and still more preferably at a temperature of 800 to 1200 ℃. The heat treatment is preferably performed at a temperature of 700 ℃ or higher from the viewpoint of sufficiently carbonizing the precursor of the carbonaceous material B, and at a temperature of 1500 ℃ or lower from the viewpoint of improving the input characteristics. Further, if the heat treatment temperature is within the above range, initial efficiency and input-output characteristics tend to be improved. The heat treatment temperature may be constant from the start to the end of the heat treatment, or may be changed.

The treatment time in the heat treatment of the mixture containing the precursors of the activated carbonaceous material a and the carbonaceous material B may be appropriately varied depending on the kind of the precursor of the carbonaceous material B used. For example, when a coal tar pitch having a softening point of 100 ℃ (+ -20 ℃) is used as the precursor of the carbonaceous material B, the temperature is preferably raised to 400 ℃ at a rate of 10 ℃ per minute or less. The total heat treatment time including the temperature raising process is preferably 2 to 18 hours, more preferably 3 to 15 hours, and further preferably 4 to 12 hours.

The atmosphere in the heat treatment of the mixture containing the precursors of the activated carbon substance a and the carbon substance B is not particularly limited as long as it is an inert gas atmosphere such as nitrogen gas or argon gas, and a nitrogen gas atmosphere is preferred from an industrial viewpoint.

The step of obtaining the calcined product is preferably carried out so that the BET specific surface area of the calcined product becomes 0.5m²/g～10m²A step of more preferably 1 m/g²/g～8m²A step of more preferably 2 m/g²/g～6m²(ii) a step of (i)/g.

The BET specific surface area of the calcined product is a BET specific surface area of a pulverized calcined product described later.

When the treatment temperature is increased during the heat treatment of the mixture, the BET specific surface area of the fired product tends to decrease. When the treatment temperature is lowered in the heat treatment of the mixture, the BET specific surface area of the fired product tends to be increased.

The crystallinity of the carbonaceous material B is preferably lower than that of the activated carbonaceous material a. When the crystallinity of the carbonaceous material B is lower than that of the activated carbonaceous material a, the input characteristics tend to be improved.

The degree of crystallinity of the activated carbonaceous material a and the activated carbonaceous material B can be determined based on the results of observation with a Transmission Electron Microscope (TEM), for example.

The burned product obtained in the step of obtaining a burned product can be pulverized by a chopper (chopper mill), a hammer mill (feather mill), a juicer (juice mixer), or the like. Further, the pulverized fired product may be sieved.

< negative electrode Material for lithium ion Secondary Battery >

Disclosed is a negative electrode material for a lithium ion secondary battery, which contains a carbon material AA and a carbon material B that is different from the carbon material AA, and which has a ratio of the BET specific surface area after the heat treatment to the BET specific surface area before the heat treatment (after heat treatment/before heat treatment) of 2.5 or more when heat-treated at 600 ℃ for 30 minutes in an air atmosphere.

The negative electrode material for a lithium ion secondary battery of the present disclosure may be in a form in which the carbonaceous material B is present on at least a part of the surface of the particles containing the carbonaceous material AA, for example. The presence or absence of the carbonaceous material B on the surface of the particles containing the carbonaceous material AA can be confirmed by transmission electron microscope observation.

The negative electrode material for a lithium-ion secondary battery of the present disclosure can be produced by the production method of the negative electrode material for a lithium-ion secondary battery of the present disclosure. However, the negative electrode material for a lithium ion secondary battery of the present disclosure is not limited to the negative electrode material manufactured by the manufacturing method of the present disclosure.

In the case where the negative electrode material for a lithium ion secondary battery is the negative electrode material produced by the production method of the present disclosure, the particles containing the carbon substance AA are the activated carbon substance a. However, in the negative electrode material for a lithium ion secondary battery of the present disclosure, the particles containing the carbonaceous material AA may not be the particles subjected to the activation treatment.

Examples of the carbonaceous material AA include graphite such as artificial graphite, natural graphite, graphitized mesophase carbon, and graphitized carbon fiber, and carbon materials such as low crystalline carbon, amorphous carbon, and mesophase carbon. Examples of the artificial graphite as the carbonaceous material AA include those described for the carbonaceous material a, and the same applies to preferred embodiments.

The carbonaceous material B may be the one described in the above-mentioned production method, and the same applies to the preferred embodiment.

For example, when the negative electrode material for a lithium ion secondary battery includes particles containing a carbonaceous material AA as a core (for example, an activated carbonaceous material a) and a carbonaceous material B which is present on at least a part of the surface of the particles containing the carbonaceous material AA and has lower crystallinity than the carbonaceous material AA (also referred to as "negative electrode material X for a lithium ion secondary battery"), the types of the carbonaceous material AA and the carbonaceous material B are not particularly limited as long as the conditions that the crystallinity of the carbonaceous material B is lower than the crystallinity of the carbonaceous material AA are satisfied.

In the negative electrode material X for a lithium ion secondary battery, a carbon material B having lower crystallinity than the carbon material AA is present in at least a part of the surface. When the negative electrode material for a lithium ion secondary battery is subjected to a heat treatment (hereinafter, also referred to as "heat treatment X") at 600 ℃ for 30 minutes in an air atmosphere, the carbonaceous material B present on the surface is removed.

That is, if the BET specific surface area is measured after the heat treatment X is performed, the BET specific surface area relating to the surface state of the particle containing the carbonaceous material AA can be obtained. For example, in the case of the negative electrode material for a lithium ion secondary battery produced by the production method of the present disclosure, the BET specific surface area relating to the surface state of the activated carbon substance a can be obtained after the heat treatment X is performed.

The ratio [ (2)/(1) ] of the BET specific surface area (2) of the negative electrode material for a lithium ion secondary battery after the heat treatment X to the BET specific surface area (1) of the negative electrode material for a lithium ion secondary battery before the heat treatment X is performed is 2.5 or more, and from the viewpoint of the input characteristics, is preferably 3.0 or more, more preferably 3.5 or more, and still more preferably 3.8 or more.

From the viewpoint of initial efficiency and high-temperature storage characteristics, the BET specific surface area ratio [ (2)/(1) ] is preferably 6.0 or less, more preferably 5.5 or less, still more preferably 5.3 or less, and particularly preferably 5.0 or less.

From the viewpoint of input characteristics and storage characteristics, the BET specific surface area (1) of the negative electrode material for a lithium ion secondary battery before heat treatment X is preferably 0.5m²/g～10m²(ii)/g, more preferably 1m²/g～8m²(ii)/g, more preferably 2m²/g～6m²/g。

The BET specific surface area (2) of the negative electrode material for lithium ion secondary battery after heat treatment X is preferably determined in accordance with the volume average particle diameter (D) of the negative electrode material for lithium ion secondary battery₅₀) And the kind of the same. From the viewpoint of input characteristics, initial efficiency and high-temperature storage characteristics, for example, 1m is preferable²/g～35m²G, more preferably 2m²/g～35m²(iv)/g, more preferably 4m²/g～35m²Per g, particularly preferably 5m²/g～30m²Per g, very preferably 5m²/g～20m²/g。

When the carbonaceous material AA is spherical natural graphite, the BET specific surface area (2) after the heat treatment X is preferably 5m²/g～30m²(iv)/g, more preferably 6m²/g～26m²(ii)/g, more preferably 7m²/g～20m²/g。

In the case where the carbonaceous material AA is an artificial graphite, the BET specific surface area (2) after the heat treatment X is preferably 1m²/g～17m²Per g, more preferably2m²/g～16m²(ii)/g, more preferably 3m²/g～13m²/g。

The content of the carbonaceous material AA (for example, activated carbonaceous material a) and the content of the carbonaceous material B in the negative electrode material for a lithium ion secondary battery are not particularly limited. The content of the carbonaceous material B in the total mass of the negative electrode material for a lithium ion secondary battery is preferably not less than 0.1 mass%, more preferably not less than 0.5 mass%, and still more preferably not less than 1 mass%, from the viewpoint of improving the input/output characteristics. The content of the carbonaceous material B in the total mass of the negative electrode material for a lithium ion secondary battery is preferably 30% by mass or less, more preferably 20% by mass or less, and still more preferably 10% by mass or less, from the viewpoint of suppressing a decrease in capacity. When carbonaceous particles are used in combination with carbonaceous material B as the carbonaceous material B, in addition to carbonaceous material B formed by heat treatment of a precursor of carbonaceous material B, the content of carbonaceous material B refers to the total content of both.

The content of the carbonaceous material B in the negative electrode material for a lithium ion secondary battery can be calculated by multiplying the amount of the precursor of the carbonaceous material B by the carbon residue ratio (mass%) when the content is calculated from the amount of the precursor of the carbonaceous material B. The carbon residue ratio of the precursor of the carbonaceous material B can be calculated from the mass of the precursor of the carbonaceous material B before the heat treatment and the mass of the carbonaceous material B derived from the precursor of the carbonaceous material B after the heat treatment, by performing the heat treatment of the precursor of the carbonaceous material B alone (or in a state of a mixture of the precursor of the carbonaceous material B and the carbonaceous material AA (for example, activated carbonaceous material a) at a predetermined ratio) at a temperature at which the precursor of the carbonaceous material B can become carbonaceous. The mass of the precursor of the carbonaceous material B before the heat treatment and the mass of the carbonaceous material B derived from the precursor of the carbonaceous material B after the heat treatment can be determined by thermogravimetric analysis or the like.

Average surface distance d obtained by X-ray diffraction method in negative electrode material for lithium ion secondary battery₀₀₂Preferably less than or equal to 0.340 nm. If mean surface spacing d₀₀₂Less than or equal to 0.340nm, then lithium ion secondary electricity existsThe initial efficiency and energy density of the cell are both excellent.

With respect to the mean surface spacing d₀₀₂The value of (3) is a theoretical value of graphite crystal, and the closer to this value, the higher the energy density tends to be.

Average surface distance d of negative electrode material for lithium ion secondary battery₀₀₂The diffraction pattern obtained by irradiating a sample as a negative electrode material for a lithium ion secondary battery with X-rays (CuK α rays) and measuring diffraction lines with a goniometer can be calculated from a diffraction peak corresponding to the carbon 002 face appearing in the vicinity of a diffraction angle 2 θ of 24 ° to 27 ° based on the obtained diffraction pattern by using a bragg equation.

There is an average surface distance d of the negative electrode material for a lithium ion secondary battery, for example, by raising the temperature of the heat treatment in producing the negative electrode material for a lithium ion secondary battery₀₀₂The value of (c) tends to be small. Therefore, the average surface distance d of the negative electrode material can be controlled by adjusting the temperature of the heat treatment in producing the negative electrode material for a lithium ion secondary battery₀₀₂。

(R value in Raman Spectroscopy)

The R value of the anode material for a lithium ion secondary battery in Raman spectroscopic measurement is preferably 0.1 to 1.0, more preferably 0.2 to 0.8, and still more preferably 0.3 to 0.7. If the R value is 0.1 or more, the graphite lattice defects used for insertion and desorption of lithium ions are sufficiently present, and the deterioration of the input/output characteristics tends to be suppressed. If the R value is 1.0 or less, the decomposition reaction of the electrolyte solution tends to be sufficiently suppressed, and the decrease in initial efficiency tends to be suppressed.

The R value is defined as 1580cm in Raman spectroscopic spectrum obtained by Raman spectrometry^-1Intensity Ig of the maximum peak in the vicinity of 1360cm^-1Intensity ratio (Id/Ig) of intensity Id of the maximum peak in the vicinity. Here, 1580cm^-1The peak appearing in the vicinity, which is usually identified as a peak corresponding to the crystal structure of graphite, means, for example, at 1530cm^-1～1630cm^-1The observed peak at the site. Besides, 1360cm^-1The peaks appearing nearby are usually identified as being carbon-relatedThe peak corresponding to the amorphous structure is, for example, 1300cm^-1～1400cm^-1The observed peak at the site.

In this publication, a laser raman spectrophotometer (model No. NRS-1000, japan spectro corporation) was used for raman spectroscopy, and measurement was performed by irradiating a sample plate in which a negative electrode material for a lithium ion secondary battery was placed in a flat state with argon laser. The measurement conditions are as follows.

Wavelength of argon laser: 532nm

Wave number resolution: 2.56cm^-1

Measurement range: 1180cm^-1～1730cm^-1

Peak search: background subtraction

Volume average particle diameter (D) of negative electrode material for lithium ion secondary battery₅₀) Preferably 1 to 40 μm, more preferably 3 to 30 μm, and still more preferably 5 to 25 μm.

When the volume average particle diameter of the negative electrode material for a lithium ion secondary battery is 1 μm or more, there is a tendency that a sufficient tap density can be obtained and a good coating property can be obtained when the negative electrode material composition for a lithium ion secondary battery is prepared. On the other hand, if the volume average particle diameter of the negative electrode material for a lithium ion secondary battery is 40 μm or less, the diffusion distance of lithium from the surface of the negative electrode material for a lithium ion secondary battery to the inside tends not to become excessively long, and the input/output characteristics tend to be maintained well.

Volume average particle diameter (D) of negative electrode material for lithium ion secondary battery₅₀) The particle size is a particle size at which 50% of the particle size is accumulated when a volume accumulation distribution curve is drawn from a small diameter side in a particle size distribution of the negative electrode material for a lithium ion secondary battery. Volume average particle diameter (D)₅₀) For example, the negative electrode material for a lithium ion secondary battery can be dispersed in purified water containing a surfactant and measured by a laser diffraction particle size distribution measuring apparatus (for example, SALD-3000J, Shimadzu corporation).

The BET specific surface area of the negative electrode material for a lithium ion secondary battery is preferably 0.5m²/g～10m²Per g, more preferablyIs selected to be 1m²/g～8m²(ii)/g, more preferably 2m²/g～6m²(ii) in terms of/g. If the BET specific surface area is within the above range, there is a tendency that a good balance of input-output characteristics and initial efficiency can be obtained.

The negative electrode material for a lithium ion secondary battery of the present disclosure has excellent high-temperature storage characteristics, and is therefore suitable as a negative electrode material for a large-capacity lithium ion secondary battery used in Electric Vehicles (EV), plug-in hybrid electric vehicles (PHEV), Hybrid Electric Vehicles (HEV), electric tools, electric power storage devices, and the like. In particular, the lithium ion secondary battery is suitable as a negative electrode material for lithium ion secondary batteries used in EVs, PHEVs, HEVs, and the like, which are required to be suitable for various environments.

< negative electrode for lithium ion secondary battery >

The disclosed negative electrode for a lithium ion secondary battery comprises: a negative electrode material layer containing the negative electrode material for a lithium ion secondary battery of the present disclosure, and a current collector. The negative electrode for a lithium ion secondary battery may contain other components as needed, in addition to the negative electrode material layer containing the negative electrode material for a lithium ion secondary battery of the present disclosure and the current collector.

The negative electrode for a lithium ion secondary battery can be produced, for example, by kneading a negative electrode material for a lithium ion secondary battery and a binder together with a solvent to prepare a slurry-like negative electrode material composition for a lithium ion secondary battery, applying the slurry-like negative electrode material composition to a current collector to form a negative electrode material layer, or by molding the negative electrode material composition for a lithium ion secondary battery into a sheet-like or granular shape and integrating the sheet-like or granular shape with the current collector. The kneading can be carried out using a dispersing apparatus such as a mixer, a ball mill, an attritor, and a pressure kneader.

The binder used for preparing the negative electrode material composition for a lithium ion secondary battery is not particularly limited. Examples of the binder include ethylenically unsaturated carboxylic acid esters such as styrene-butadiene copolymer (SBR), methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, hydroxyethyl acrylate and hydroxyethyl methacrylate, homopolymers or copolymers of ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid and maleic acid, and high-molecular-conductivity polymer compounds such as polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile and polymethacrylonitrile. In the case where the negative electrode material composition for a lithium ion secondary battery contains a binder, the content of the binder is not particularly limited. For example, the amount of the binder may be 0.5 to 20 parts by mass based on 100 parts by mass of the total of the negative electrode material for a lithium ion secondary battery and the binder.

The negative electrode material composition for a lithium ion secondary battery may include a thickener. As the thickener, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid or a salt thereof, oxidized starch, phosphorylated starch, casein, or the like can be used. In the case where the negative electrode material composition for a lithium ion secondary battery contains a thickener, the content of the thickener is not particularly limited. For example, the amount of the negative electrode material for a lithium ion secondary battery may be 0.1 to 5 parts by mass per 100 parts by mass of the negative electrode material.

The negative electrode material composition for a lithium ion secondary battery may include a conductive auxiliary material. Examples of the conductive auxiliary material include carbon materials such as carbon black, graphite, and acetylene black, inorganic compounds such as oxides exhibiting conductivity, and nitrides exhibiting conductivity, and the like. In the case where the anode material composition for a lithium ion secondary battery contains a conductive auxiliary material, the content of the conductive auxiliary material is not particularly limited. For example, the amount of the negative electrode material for a lithium ion secondary battery may be 0.5 to 15 parts by mass per 100 parts by mass of the negative electrode material.

The material of the current collector is not particularly limited, and can be selected from aluminum, copper, nickel, titanium, stainless steel, and the like. The state of the current collector is not particularly limited, and can be selected from foil, perforated foil, mesh, and the like. In addition, a porous material such as porous metal (foamed metal), carbon paper, or the like can also be used as the current collector.

When the negative electrode material composition for a lithium ion secondary battery is applied to a current collector to form a negative electrode material layer, the method is not particularly limited, and known methods such as a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, a doctor blade method, a comma coating method, a gravure coating method, and a screen printing method can be used. After the negative electrode material composition for a lithium ion secondary battery is applied to a current collector, the solvent contained in the negative electrode material composition for a lithium ion secondary battery is removed by drying. For example, drying can be performed using a hot air dryer, an infrared dryer, or a combination of these apparatuses. The anode material layer may be subjected to rolling treatment as needed. The rolling treatment can be performed by a method such as a flat press or a roll.

When the negative electrode material composition for a lithium ion secondary battery molded into a sheet, a pellet or the like is integrated with a current collector to form a negative electrode material layer, the method of integration is not particularly limited. For example, it can be carried out by means of rollers, flat presses or a combination of these units. The pressure at which the negative electrode material composition for a lithium ion secondary battery is integrated with the current collector is, for example, preferably about 1MPa to 200 MPa.

The anode density of the anode material layer is not particularly limited. For example, it is preferably 1.1g/cm³～1.8g/cm³More preferably 1.2g/cm³～1.7g/cm³More preferably 1.3g/cm³～1.6g/cm³. By making the density of the negative electrode greater than or equal to 1.1g/cm³So that there is a tendency that an increase in resistance is suppressed and capacity is increased, by making the density 1.8g/cm or less³Thus, the degradation of the input-output characteristics and the cycle characteristics tends to be suppressed.

< lithium ion secondary battery >

The lithium ion secondary battery of the present disclosure includes a negative electrode for a lithium ion secondary battery, a positive electrode, and an electrolyte solution.

The positive electrode can be obtained by forming a positive electrode material layer on a current collector in the same manner as the method for producing the negative electrode. As the current collector, a current collector obtained by forming a metal or an alloy such as aluminum, titanium, or stainless steel into a foil shape, an open-pore foil shape, a mesh shape, or the like can be used.

The positive electrode material used to form the positive electrode material layer is not particularly limited. As positive electrode materialExamples thereof include metal compounds (metal oxides, metal sulfides, etc.) and conductive polymer materials capable of doping or intercalating lithium ions. More specifically, lithium cobaltate (LiCoO) may be mentioned₂) Lithium nickelate (LiNiO)₂) Lithium manganate (LiMnO)₂) And a composite oxide thereof (LiCo)_xNi_yMn_zO₂X + y + z ═ 1), composite oxide containing additive element M' (LiCo)_aNi_bMn_cM’_dO₂And a + b + c + d is 1, M': al, Mg, Ti, Zr or Ge), spinel type lithium manganese oxide (LiMn)₂O₄) Lithium vanadium compound, V₂O₅、V₆O₁₃、VO₂、MnO₂、TiO₂、MoV₂O₈、TiS₂、V₂S₅、VS₂、MoS₂、MoS₃、Cr₃O₈、Cr₂O₅Olivine type LiMPO₄Metal compounds such as (M: Co, Ni, Mn, Fe), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, and porous carbon. The number of the positive electrode materials may be 1 or 2 or more.

The electrolyte solution is not particularly limited, and for example, an electrolyte solution (so-called organic electrolyte solution) in which a lithium salt as an electrolyte is dissolved in a nonaqueous solvent can be used.

As the lithium salt, LiClO is mentioned₄、LiPF₆、LiAsF₆、LiBF₄、LiSO₃CF₃And the like. The lithium salt may be 1 kind alone or 2 or more kinds.

Examples of the nonaqueous solvent include ethylene carbonate, fluoroethylene carbonate, ethylene chlorocarbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, cyclohexylbenzene, sulfolane, propane sultone, 3-methylsulfolane, 2, 4-dimethylsulfolane, 3-methyl-1, 3-

Oxazolidin-2-one, gamma-butyrolactone, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, methyl ethyl acetate, methyl ethyl carbonate, ethyl acetate, ethyl,Methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1, 2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1, 3-dioxolane, methyl acetate, ethyl acetate, trimethyl phosphate, triethyl phosphate, and the like. The number of the nonaqueous solvents may be 1 or 2 or more.

The states of the positive electrode and the negative electrode in the lithium ion secondary battery are not particularly limited. For example, the positive electrode, the negative electrode, and a separator disposed between the positive electrode and the negative electrode as needed may be wound in a spiral shape, or they may be stacked in a flat plate shape.

The separator is not particularly limited, and for example, a resin nonwoven fabric, a woven fabric (cloth), a microporous film, or a separator obtained by combining these materials can be used. Examples of the resin include resins containing polyolefins such as polyethylene and polypropylene as a main component. In the structure of the lithium ion secondary battery, the separator may not be used when the positive electrode and the negative electrode are not in direct contact with each other.

The shape of the lithium ion secondary battery is not particularly limited. Examples thereof include a laminate type battery, a paper type battery, a button type battery, a coin type battery, a laminate type battery, a cylindrical type battery and a prismatic type battery.

The lithium ion secondary battery of the present disclosure has excellent output characteristics, and is therefore suitable as a large-capacity lithium ion secondary battery used in electric vehicles, electric tools, power storage devices, and the like. In particular, the lithium ion secondary battery is suitable for use in Electric Vehicles (EV), Hybrid Electric Vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and the like, which require charging and discharging under a large current in order to improve acceleration performance and brake regeneration performance.

Examples

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples.

< example 1 >

(1) Production of negative electrode Material

100g of spherical natural graphite (volume average particle diameter: 10 μm) as the carbonaceous material A was placed in an alumina crucible having a volume of 2.25L, and allowed to stand at a constant temperature of 500 ℃ for 3 hours in an air atmosphere.

100 parts by mass of the obtained activated carbonaceous material a and 10 parts by mass of coal tar pitch (softening point: 98 ℃, char yield: 50 mass%) as a precursor of the carbonaceous material B were powder-mixed to obtain a mixture. Next, the mixture is heat-treated to produce a fired product in which the carbonaceous material B adheres to the surface of the activated carbonaceous material a. The heat treatment was carried out by raising the temperature from 25 ℃ to 1000 ℃ at a rate of 200 ℃/hr under a nitrogen stream and holding the temperature at 1000 ℃ for 1 hour. The fired material having the carbonaceous material B adhered to the surface of the activated carbonaceous material a was pulverized by a chopper, and sieved with a 300-mesh sieve, and the undersize fraction was used as a negative electrode material (negative electrode material) for a lithium ion secondary battery.

The BET specific surface area of the carbonaceous material a, the BET specific surface area of the activated carbonaceous material a, and the volume average particle diameter (D) of the negative electrode material were measured by the methods shown below₅₀) And BET specific surface area of the anode material. Further, based on the BET specific surface area of the carbonaceous material a and the BET specific surface area of the activated carbonaceous material a, the BET specific surface area increase rate of the activated carbonaceous material a relative to the carbonaceous material a [ (BET specific surface area of the activated carbonaceous material a-BET specific surface area of the carbonaceous material a)/BET specific surface area of the carbonaceous material a) × 100 (%) ] is calculated. The results are shown in table 1.

[ measurement of BET specific surface area ]

The BET specific surface area was calculated by the BET method by measuring nitrogen adsorption at a liquid nitrogen temperature (77K) by a multipoint method using a specific surface area/pore distribution measuring apparatus (FlowSorb II 2300, manufactured by east-sea physic corporation).

[ volume average particle diameter (D)₅₀) Measurement of (2)]

A sample was dispersed in purified water together with a surfactant to obtain a dispersion, and the dispersion was charged into a sample water tank of a laser diffraction particle size distribution measuring apparatus (SALD-3000J, Shimadzu corporation). Subsequently, the dispersion was circulated by a pump while applying ultrasonic waves theretoThe volume cumulative 50% particle diameter of the obtained particle size distribution was defined as the volume average particle diameter (D)₅₀)。

(2) Production of lithium ion secondary battery

An aqueous solution of CMC (carboxymethyl cellulose, segrogen WS-C, first industrial pharmaceutical co., ltd.) as a thickener (CMC concentration: 2 mass%) was added to 98 parts by mass of the negative electrode material so that the amount of the solid component of CMC became 1 part by mass, and kneaded for 10 minutes. Subsequently, purified water was added in portions so that the total solid content concentration of the negative electrode material and CMC became 45 mass% to 60 mass%, and kneading was performed for 10 minutes. Next, an aqueous dispersion of SBR (styrene-butadiene copolymer, BM400-B, japan regen corporation) (SBR concentration: 40 mass%) as a binder was added so that the solid content of the SBR became 1 part by mass, and mixed for 10 minutes to prepare a paste-like negative electrode material composition (negative electrode material composition) for a lithium ion secondary battery. Then, the coating amount per unit area was adjusted to 10.0mg/cm²The negative electrode material composition was coated on an electrolytic copper foil having a thickness of 11 μm to form a negative electrode material layer. Then, the anode density was adjusted to 1.5g/cm by a manual press³. The electrolytic copper foil on which the negative electrode material layer was formed was punched out into a disk shape having a diameter of 14mm, to prepare a sample electrode (negative electrode).

The prepared sample electrode (negative electrode), separator, and counter electrode (positive electrode) were sequentially placed in a coin-type battery container, and an electrolyte was injected to prepare a coin-type lithium ion secondary battery. As the electrolyte, a mixed solvent of Ethylene Carbonate (EC) and Ethyl Methyl Carbonate (EMC) (EC/EMC volume ratio of 3:7) in which LiPF is dissolved at a concentration of 1.0mol/L was used₆The electrolyte of (1). As the positive electrode, LiNi was used_1/3Mn_1/3Co_1/3O₂. The initial negative electrode capacity/initial positive electrode capacity was designed to be 1.2.

As the separator, a polyethylene microporous membrane having a thickness of 20 μm was used. The fabricated lithium ion secondary battery was charged to 4.2V at a current value CC corresponding to 0.2CA, and then CV-charged to a level corresponding to 0.02 CA. Then, the discharge was stopped for 30 minutes, and the discharge was stopped for 30 minutes at a current value of 2.7V corresponding to 0.2 CA. The series of steps was initialized by repeating 3 cycles with 1 cycle. Using the initialized lithium ion secondary battery, evaluation of initial efficiency, input characteristics, output characteristics, and high-temperature storage characteristics was performed by the following methods. The obtained results are shown in table 1.

[ evaluation of initial efficiency ]

(1) Charging was carried out at a constant current of 0.2CA up to 0V (vs. Li/Li)⁺) Then, constant voltage charging was performed at 0V until the current value became 0.02 CA. The capacity at this time is set as the initial charging capacity.

(2) After 30 minutes of off-time, discharge was carried out at a constant current of 0.2CA until 1.5V (vs. Li/Li)⁺). The capacity at this time was set as the initial discharge capacity.

(3) Based on the charge-discharge capacities obtained in the above (1) and (2), the initial efficiency was obtained using the following (formula 1).

Initial efficiency (%) (initial discharge capacity (mAh)/initial charge capacity (mAh)) × 100 … (formula 1)

[ evaluation of output characteristics ]

(1) Charging was carried out at a constant current of 0.2CA up to 0V (vs. Li/Li)⁺) Then, constant voltage charging was performed at 0V until the current value became 0.02 CA.

(2) After 30 minutes of off-time, discharge was carried out at a constant current of 0.2CA until 1.5V (vs. Li/Li)⁺)。

(3) The discharge capacity at this time was defined as "discharge capacity 1" (mAh) by repeating the steps (1) and (2).

(4) After 30 minutes of rest time, charge was carried out at a constant current of 0.2CA until 0V (vs. Li/Li)⁺) Then, constant voltage charging was performed at 0V until the current value became 0.02 CA.

(5) After 30 minutes of off-time, discharge was carried out at a constant current of 3CA until 1.5V (vs. Li/Li)⁺) The discharge capacity at this time was defined as "discharge capacity 2" (mAh).

(6) Based on the discharge capacities obtained in (3) and (5), the output characteristics were obtained using the following (formula 2).

Output characteristics (%) (discharge capacity 2 (mAh)/discharge capacity 1(mAh)) × 100 … (formula 2)

[ evaluation of input characteristics ]

(1) Charging was performed at a constant current of 0.2CA until 4.2V, and then constant voltage charging was performed at 4.2V until the current value became 0.02 CA. The charge capacity at this time was "charge capacity 1" (mAh).

(2) After 30 minutes of off time, discharge was carried out at a constant current of 0.2CA until 2.7V.

(3) After a 30 minute off time, charging was carried out at a constant current of 3CA up to 4.2V. The charge capacity at this time was "charge capacity 2" (mAh).

(4) Based on the discharge capacities obtained in (1) and (3), the input characteristics were obtained using the following (formula 3).

Input characteristics (%) (charge capacity 2 (mAh)/charge capacity 1(mAh)) × 100 … (formula 3)

[ evaluation of high temperature storage Properties ]

(3) After 30 minutes of rest time, charge was carried out at a constant current of 0.2CA until 0V (vs. Li/Li)⁺). The charge capacity (mAh) at this time was measured.

(4) The battery of (3) was left at 60 ℃ for 5 days.

(5) Discharge was carried out at a constant current of 0.2CA up to 1.5V (vs. Li/Li)⁺). The discharge capacity (mAh) at this time was measured.

(6) Based on the charge capacity obtained from (3) and the discharge capacity obtained from (5), the high-temperature storage characteristics were obtained using the following (formula 4).

High temperature storage property (%) (discharge capacity (mAh)/charge capacity (mAh)) × 100 … (formula 4)

< example 2 >

Evaluation was performed in the same manner as in example 1, except that the heat treatment temperature (activation treatment temperature) of the carbonaceous material a was set to 300 ℃. The obtained results are shown in table 1.

< example 3 >

Evaluation was performed in the same manner as in example 1, except that the heat treatment temperature (activation treatment temperature) of the carbonaceous material a was set to 400 ℃. The obtained results are shown in table 1.

< example 4 >

Evaluation was performed in the same manner as in example 1, except that the heat treatment temperature (activation treatment temperature) of the carbonaceous material a was set to 600 ℃. The obtained results are shown in table 1.

< example 5 >

Except that the atmosphere for treating the carbonaceous material A is CO₂Evaluation was performed in the same manner as in example 1 except that the treatment temperature (activation treatment temperature) was changed to 900 ℃. The obtained results are shown in table 1.

< example 6 >

Evaluation was carried out in the same manner as in example 1 except that spherical natural graphite (volume average particle diameter: 16 μm) was used as the carbonaceous material A. The obtained results are shown in table 1.

< example 7 >

Evaluation was carried out in the same manner as in example 1 except that spherical natural graphite (volume average particle diameter: 20 μm) was used as the carbonaceous material A. The obtained results are shown in table 1.

< example 8 >

50 parts by mass of coke powder having an average particle size of 8 μm, 20 parts by mass of tar pitch, 20 parts by mass of silicon carbide, and 10 parts by mass of spherical natural graphite (circularity 0.92) having an average particle size of 20 μm were mixed and stirred at 100 ℃ for 1 hour to obtain a mixture. Subsequently, the mixture was pulverized to have an average particle diameter of 18 μm, and the resultant pulverized powder was put into a mold and molded into a rectangular parallelepiped. The obtained rectangular parallelepiped was heat-treated at 1000 ℃ in a nitrogen atmosphere, and then fired at 2800 ℃ to graphitize a graphitizable component. The obtained graphite molded body was pulverized to an average particle diameter of 18 μm to prepare graphite particles. The obtained graphite particles contained graphite particles in which a plurality of flat particles were aggregated or bonded so that the orientation planes (main surfaces) were not parallel, as a result of observation by SEM. 100g of the obtained graphite particles were charged into an alumina crucible having a volume of 2.25L, and the mixture was allowed to stand at a fixed temperature of 500 ℃ for 3 hours in an air atmosphere. The BET specific surface area of the obtained carbonaceous material a (activated carbonaceous material a) was measured.

100 parts by mass of the activated carbonaceous material a and 2 parts by mass of coal tar pitch (softening point: 98 ℃, char yield: 50 mass%) as a precursor of the carbonaceous material B were powder-mixed to obtain a mixture. Next, the mixture is heat-treated to produce a fired product in which the carbonaceous material B adheres to the surface of the activated carbonaceous material a. The heat treatment was carried out by raising the temperature from 25 ℃ to 1000 ℃ at a rate of 200 ℃/hr under a nitrogen stream and holding the temperature at 1000 ℃ for 1 hour. The fired material having the carbonaceous material B adhered to the surface of the activated carbonaceous material a was pulverized by a chopper, and sieved with a 300-mesh sieve, and the undersize fraction was used as a negative electrode material (negative electrode material) for a lithium ion secondary battery.

Using the obtained negative electrode material, evaluation was performed in the same manner as in example 1. The obtained results are shown in table 1.

< example 9 >

40 parts by mass of coke powder having an average particle size of 8 μm, 25 parts by mass of tar pitch, 5 parts by mass of silicon carbide having an average particle size of 48 μm, and 20 parts by mass of coal tar were mixed and stirred at 200 ℃ for 1 hour. Next, the graphite particles were fired at 2800 ℃ in a nitrogen atmosphere and then pulverized to prepare graphite particles having an average particle diameter of 20 μm. The obtained graphite particles were observed by SEM and included graphite particles in which a plurality of flat particles were aggregated or bonded so that their orientation planes (main surfaces) were not parallel to each other. 100g of the obtained graphite particles were charged into an alumina crucible having a volume of 2.25L, and the mixture was allowed to stand at a fixed temperature of 500 ℃ for 3 hours in an air atmosphere. The BET specific surface area of the obtained carbonaceous material a (activated carbonaceous material a) was measured.

Using the obtained activated carbon material a, a negative electrode material (negative electrode material) for a lithium ion secondary battery was obtained in the same manner as in example 8.

< example 10 >

Evaluation was performed in the same manner as in example 1 except that the carbonaceous material a was heated to 700 ℃ in a nitrogen atmosphere, and then a gas obtained by flowing nitrogen gas into 80 ℃ water at a flow rate of 100cc/min was blown in for 3 hours. The obtained results are shown in table 1.

< comparative example 1 >

Evaluation was performed in the same manner as in example 1, except that the carbonaceous material a was not subjected to the heat treatment (activation treatment). The obtained results are shown in table 1.

< comparative example 2 >

Evaluation was performed in the same manner as in example 1, except that the carbonaceous material a was heat-treated in a nitrogen atmosphere. The obtained results are shown in table 1.

< comparative example 3 >

Evaluation was performed in the same manner as in example 1, except that the carbonaceous material a was heat-treated at 200 ℃. The obtained results are shown in table 1.

< comparative example 4 >

Evaluation was performed in the same manner as in example 1, except that the carbonaceous material a was heat-treated at 800 ℃. The obtained results are shown in table 1.

[ Table 1]

As shown in the results of table 1, it is understood that the lithium ion secondary battery produced using the negative electrode material of the example is superior to the lithium ion secondary battery produced using the negative electrode material of the comparative example in one of the input characteristic, the output characteristic, the high-temperature storage characteristic, and the initial efficiency, and exhibits characteristics equivalent to those of the comparative example for the other items.

The negative electrode materials of examples 1, 6 to 8 and comparative examples 1 and 4 were subjected to heat treatment X at 600 ℃ for 30 minutes in an air atmosphere. The BET specific surface area (2) of the negative electrode material after the heat treatment X was measured by the method described above. The ratio [ (2)/(1) ] of the BET specific surface area (2) after the heat treatment X to the BET specific surface area (1) before the heat treatment X was calculated. The results are shown in table 2.

[ Table 2]

Claims

1. A method for producing a negative electrode material for a lithium ion secondary battery, comprising the steps of:

and a step of obtaining a fired product by heat-treating the mixture.

2. The method for producing a negative electrode material for a lithium-ion secondary battery according to claim 1,

the step of obtaining a calcined product is to set the BET specific surface area of the calcined product to 0.5m²/g～10m²(ii) a step of (i)/g.

3. The method for producing a negative electrode material for a lithium-ion secondary battery according to claim 1 or 2, wherein the heat treatment is performed at a temperature of 700 ℃ to 1500 ℃.

4. The method for producing a negative electrode material for a lithium-ion secondary battery according to any one of claims 1 to 3, wherein the crystallinity of the carbon substance B is lower than the crystallinity of the activated carbon substance A.

5. A negative electrode material for a lithium ion secondary battery, comprising a carbonaceous material AA and a carbonaceous material B different from the carbonaceous material AA,

when the negative electrode material for a lithium ion secondary battery is subjected to heat treatment at 600 ℃ for 30 minutes in an air atmosphere, the ratio of the BET specific surface area after the heat treatment to the BET specific surface area before the heat treatment is 2.5 or more.