阅读说明：本技术 锂离子二次电池用负极材及其制造方法、锂离子二次电池用负极及锂离子二次电池 (Negative electrode material for lithium ion secondary battery, method for producing same, negative electrode for lithium ion secondary battery, and lithium ion secondary battery ) 是由 伊坂元宏 土屋秀介 星贤匠 佐藤力 须贺启太 于 2018-01-29 设计创作，主要内容包括：一种锂离子二次电池用负极材,其包含满足下述(1)～(3)、(6)和(7)的碳材料。(1)平均粒径(D50)小于或等于22μm。(2)粒径的D90/D10小于或等于2.2。(3)亚麻仁油吸油量小于或等于50mL/100g。(6)圆形度为0.6～0.8且粒径为10μm～20μm的比例大于或等于碳材料整体的5个数％。(7)圆形度小于或等于0.7且粒径小于或等于10μm的比例小于或等于碳材料整体的0.3个数％。(A negative electrode material for a lithium ion secondary battery, comprising a carbon material satisfying the following (1) to (3), (6) and (7). (1) The average particle diameter (D50) is 22 μm or less. (2) The D90/D10 of the particle size is less than or equal to 2.2. (3) Linseed oil absorption of less than or equal to 50mL/100 g. (6) The circularity is 0.6-0.8 and the proportion of the particle diameter is 10-20 μm is more than or equal to 5% of the whole carbon material. (7) The circularity is 0.7 or less and the proportion of particle diameters of 10 μm or less is 0.3% by number or less of the entire carbon material.)

1. A negative electrode material for a lithium ion secondary battery, comprising a carbon material satisfying the following (1) to (3), (6) and (7),

(1) the average particle diameter D50 is less than or equal to 22 μm,

(2) the D90/D10 of the particle size is less than or equal to 2.2,

(3) linseed oil absorption of 50mL/100g or less,

(6) a circularity of 0.6 to 0.8 and a particle diameter of 10 to 20 μm in a proportion of 5 or more to the whole carbon material,

(7) the circularity is 0.7 or less and the proportion of particle diameters of 10 μm or less is 0.3% by number or less of the entire carbon material.

2. A negative electrode material for a lithium ion secondary battery, comprising a carbon material satisfying the following (1), (2), (4), (6) and (7),

(1) the average particle diameter D50 is less than or equal to 22 μm,

(2) the D90/D10 of the particle size is less than or equal to 2.2,

(4) tap density of 1.00g/cm or more³，

(6) A circularity of 0.6 to 0.8 and a particle diameter of 10 to 20 μm in a proportion of 5 or more to the whole carbon material,

(7) the circularity is 0.7 or less and the proportion of particle diameters of 10 μm or less is 0.3% by number or less of the entire carbon material.

3. A negative electrode material for a lithium ion secondary battery, comprising a carbon material satisfying the following (1), (2), (5) to (7),

(1) the average particle diameter D50 is less than or equal to 22 μm,

(2) the D90/D10 of the particle size is less than or equal to 2.2,

(5) when the mixture is stirred in purified water containing a surfactant and then irradiated with ultrasonic waves for 15 minutes by an ultrasonic washing machine, the ratio of D10 after the ultrasonic wave irradiation to D10 before the ultrasonic wave irradiation, that is, D10 after the ultrasonic wave irradiation/D10 before the ultrasonic wave irradiation is 0.90 or more,

(6) a circularity of 0.6 to 0.8 and a particle diameter of 10 to 20 μm in a proportion of 5 or more to the whole carbon material,

(7) the circularity is 0.7 or less and the proportion of particle diameters of 10 μm or less is 0.3% by number or less of the entire carbon material.

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

the carbon material satisfies at least one of the following (4) and (5),

(4) tap density of 1.00g/cm or more³，

(5) When the mixture is stirred in purified water containing a surfactant and then irradiated with ultrasonic waves for 15 minutes by an ultrasonic washing machine, the ratio of D10 after the ultrasonic wave irradiation to D10 before the ultrasonic wave irradiation, that is, D10 after the ultrasonic wave irradiation/D10 before the ultrasonic wave irradiation is 0.90 or more.

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

the carbon material satisfies at least one of the following (3) and (5),

(3) linseed oil absorption of 50mL/100g or less,

(5) when the mixture is stirred in purified water containing a surfactant and then irradiated with ultrasonic waves for 15 minutes by an ultrasonic washing machine, the ratio of D10 after the ultrasonic wave irradiation to D10 before the ultrasonic wave irradiation, that is, D10 after the ultrasonic wave irradiation/D10 before the ultrasonic wave irradiation is 0.90 or more.

6. The negative electrode material for a lithium-ion secondary battery according to claim 3,

the carbon material satisfies at least one of the following (3) and (4),

(3) linseed oil absorption of 50mL/100g or less,

(4) tap density of 1.00g/cm or more³。

7. The negative electrode material for lithium ion secondary batteries according to any one of claims 1 to 6, wherein the average surface distance d is determined by X-ray diffraction₀₀₂Is 0.334 nm-0.338 nm.

8. The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 7, wherein an R value obtained by Raman spectroscopy is 0.1 to 1.0.

9. The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 8,

the carbon material does not have two or more exothermic peaks in a temperature range of 300 ℃ to 1000 ℃ in differential thermal analysis performed in an air stream.

10. The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 9,

the carbon material has a specific surface area of 2m as determined by nitrogen adsorption measurement at 77K²/g～8m²/g。

11. The negative electrode material for a lithium-ion secondary battery according to claim 10,

CO obtained by adsorbing carbon dioxide at 273K of the carbon material₂When the value of the adsorption amount is A and the value of the specific surface area of the carbon material obtained by nitrogen adsorption measurement at 77K is B, CO per unit area calculated from the following expression (a)₂The adsorption capacity was 0.01cm³/m²～0.10cm³/m²，

CO per unit area₂Adsorption capacity (cm)³/m²)＝A(cm³/g)/B(m²/g)···(a)。

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

a carbon material according to any one of claims 1 to 11, which is produced by heat-treating a mixture containing a first carbon material as a core and a precursor of a second carbon material having lower crystallinity than the first carbon material.

13. The method for producing a negative electrode material for a lithium-ion secondary battery according to claim 12,

in the step, the mixture is heat-treated at 950 to 1500 ℃.

14. An anode for a lithium ion secondary battery, comprising: a negative electrode material layer comprising the negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 11, and a current collector.

15. A lithium ion secondary battery comprising: the negative electrode for a lithium-ion secondary battery, the positive electrode, and the electrolyte solution according to claim 14.

Technical Field

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

Background

Lithium ion secondary batteries have been widely used in electronic devices such as notebook personal computers, mobile phones, smart phones, and tablet personal computers, 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 caused by emissions, clean Electric Vehicles (EV) that run only on batteries, Hybrid Electric Vehicles (HEV) that combine a gasoline engine and a battery, and the like have become widespread. In addition, it is recently used for power storage, and its use is gradually expanding in various fields.

The performance of the negative electrode material of the lithium ion secondary battery greatly affects the 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 network surfaces of carbon atoms are regularly stacked, and when a negative electrode material for a lithium ion secondary battery is produced, lithium ion insertion and desorption reactions proceed from the end portions of the hexagonal network surfaces, and charging and discharging are performed.

The hexagonal network of amorphous carbon is irregular in lamination or does not have a hexagonal network. Therefore, in the negative electrode material using amorphous carbon, the insertion and desorption reactions of lithium ions proceed over the entire surface of the negative electrode material. Therefore, a lithium ion battery having excellent input/output characteristics can be easily obtained as compared with a case where graphite is used as a negative electrode material (see, for example, patent documents 1 and 2). On the other hand, amorphous carbon has lower crystallinity than graphite and therefore has lower energy density than graphite.

Disclosure of Invention

Problems to be solved by the invention

In view of the above-described characteristics of carbon materials, there has been proposed a negative electrode material in which amorphous carbon and graphite are combined to improve input/output characteristics while maintaining a high energy density, and graphite is coated with amorphous carbon to reduce surface reactivity and improve input/output characteristics while maintaining initial charge/discharge efficiency satisfactorily (see, for example, patent document 3). In lithium ion secondary batteries used in EVs, HEVs and the like, high input/output characteristics are required for charging electric power for regenerative braking and discharging electric power for driving a motor. In addition, automobiles are susceptible to external air temperature, and particularly, lithium ion secondary batteries are exposed to a high temperature state in summer. Therefore, both input/output characteristics and high-temperature storage characteristics are required.

An object of one embodiment of the present invention is to provide a negative electrode material for a lithium ion secondary battery, a method for producing the negative electrode material for a lithium ion secondary battery, and a negative electrode for a lithium ion secondary battery, which are capable of producing a lithium ion secondary battery having excellent input/output characteristics and high-temperature storage characteristics.

Further, an object of one embodiment of the present invention is to provide a lithium ion secondary battery having excellent input/output characteristics and high-temperature storage characteristics.

Means for solving the problems

Examples of a method for improving the input/output characteristics include a method of reducing the particle size of a negative electrode material for a lithium ion secondary battery. However, when the particle size is reduced, the input/output characteristics can be improved, while the high-temperature storage characteristics tend to deteriorate. The present inventors have conducted extensive studies and, as a result, have found a method of achieving both input/output characteristics and high-temperature storage characteristics in this trade-off relationship.

Specific methods for solving the above problems include the following.

< 1 > a negative electrode material for a lithium ion secondary battery, which comprises a carbon material satisfying the following (1) to (3).

(1) The average particle diameter (D50) is 22 μm or less.

(2) The D90/D10 of the particle size is less than or equal to 2.2.

(3) Linseed oil absorption of less than or equal to 50mL/100 g.

< 2 > a negative electrode material for lithium ion secondary batteries, which comprises a carbon material satisfying the following (1), (2) and (4).

(1) The average particle diameter (D50) is 22 μm or less.

(2) The D90/D10 of the particle size is less than or equal to 2.2.

(4) Tap density of 1.00g/cm or more³。

< 3 > a negative electrode material for lithium ion secondary batteries, which comprises a carbon material satisfying the following (1), (2) and (5).

(1) The average particle diameter (D50) is 22 μm or less.

(2) The D90/D10 of the particle size is less than or equal to 2.2.

(5) When the mixture is stirred in purified water containing a surfactant and then irradiated with ultrasonic waves for 15 minutes by an ultrasonic washing machine, the ratio of D10 after the ultrasonic wave irradiation to D10 before the ultrasonic wave irradiation (D10 after the ultrasonic wave irradiation/D10 before the ultrasonic wave irradiation) is 0.90 or more.

< 4 > the negative electrode material for lithium ion secondary batteries according to < 1 >, wherein the carbon material satisfies at least one of the following (4) and (5).

(4) Tap density of 1.00g/cm or more³。

(5) When the mixture is stirred in purified water containing a surfactant and then irradiated with ultrasonic waves for 15 minutes by an ultrasonic washing machine, the ratio of D10 after the ultrasonic wave irradiation to D10 before the ultrasonic wave irradiation (D10 after the ultrasonic wave irradiation/D10 before the ultrasonic wave irradiation) is 0.90 or more.

< 5 > the negative electrode material for lithium ion secondary batteries according to < 2 >, wherein the carbon material satisfies at least one of the following (3) and (5).

(3) Linseed oil absorption of less than or equal to 50mL/100 g.

(5) When the mixture is stirred in purified water containing a surfactant and then irradiated with ultrasonic waves for 15 minutes by an ultrasonic washing machine, the ratio of D10 after the ultrasonic wave irradiation to D10 before the ultrasonic wave irradiation (D10 after the ultrasonic wave irradiation/D10 before the ultrasonic wave irradiation) is 0.90 or more.

< 6 > the negative electrode material for lithium ion secondary batteries < 3 >, wherein the carbon material satisfies at least one of the following (3) and (4).

(3) Linseed oil absorption of less than or equal to 50mL/100 g.

(4) Tap density of 1.00g/cm or more³。

< 7 > the average surface distance d obtained by X-ray diffraction method for the negative electrode material for lithium ion secondary battery according to any one of < 1 > -6 >₀₀₂Is 0.334 nm-0.338 nm.

< 8 > the negative electrode material for a lithium ion secondary battery according to any one of < 1 > to < 7 >, wherein R value obtained by Raman spectroscopic measurement is 0.1 to 1.0.

< 9 > the negative electrode material for a lithium ion secondary battery according to any one of < 1 > to < 8 >, wherein the carbon material does not have two or more heat release peaks in a temperature range of 300 ℃ to 1000 ℃ in a differential thermal analysis performed in an air stream.

< 10 > the negative electrode material for lithium ion secondary battery according to any one of < 1 > to < 9 >, wherein the carbon material has a specific surface area of 2m as determined by nitrogen adsorption measurement at 77K²/g～8m²/g。

< 11 > according to < 10 > for a lithium ion secondary batteryA negative electrode material comprising a carbon material and CO obtained by carbon dioxide adsorption at 273K₂When the value of the adsorption amount is A and the value of the specific surface area of the carbon material obtained by nitrogen adsorption measurement at 77K is B, CO per unit area calculated from the following expression (a)₂The adsorption capacity was 0.01cm³/m²～0.10cm³/m²。

CO per unit area₂Adsorption capacity (cm)³/m²)＝A(cm³/g)/B(m²/g)···(a)

< 12 > the negative electrode material for a lithium ion secondary battery according to any one of < 1 > -11 >, wherein the carbon material satisfies at least one of the following (6) and (7).

(6) The circularity is 0.6-0.8 and the proportion of the particle diameter is 10-20 μm is more than or equal to 5% of the whole carbon material.

(7) The circularity is 0.7 or less and the proportion of particle diameters of 10 μm or less is 0.3% by number or less of the entire carbon material.

< 13 > the negative electrode material for lithium ion secondary batteries according to < 12 >, wherein the carbon material satisfies the above (6) and (7).

< 14 > a method for producing a negative electrode material for a lithium ion secondary battery, comprising the steps of: a carbon material which is produced by heat-treating a mixture containing a first carbon material serving as a core and a precursor of a second carbon material having lower crystallinity than the first carbon material, wherein the carbon material is any one of < 1 > - < 13 >.

< 15 > the method for producing a negative electrode material for a lithium ion secondary battery according to < 14 >, wherein the mixture is heat-treated at 950 to 1500 ℃ in the step.

< 16 > an anode for a lithium ion secondary battery, comprising: a negative electrode layer containing the negative electrode material for a lithium ion secondary battery described in any one of < 1 > -to < 13 >, and a current collector.

< 17 > a lithium ion secondary battery comprising: < 16 > the negative electrode, positive electrode and electrolyte for lithium ion secondary battery.

ADVANTAGEOUS EFFECTS OF INVENTION

In one embodiment of the present invention, a negative electrode material for a lithium ion secondary battery, a method for producing a negative electrode material for a lithium ion secondary battery, and a negative electrode for a lithium ion secondary battery, which can produce a lithium ion secondary battery having excellent input/output characteristics and high-temperature storage characteristics, can be provided.

Further, according to one embodiment of the present invention, a lithium ion secondary battery having excellent input/output characteristics and high-temperature storage characteristics can be provided.

Drawings

Fig. 1 is a graph showing the relationship between the average particle diameter of the carbon material and the output characteristics in each test.

Fig. 2 is a graph showing the relationship between the carbon coating amount of the carbon material and the output characteristics in each test.

Fig. 3 is a graph showing the relationship between the number of cycles and the discharge capacity maintaining rate in test 2 and test 12.

FIG. 4 is a graph showing the relationship between the output characteristics and the high-temperature storage capacity retention rate in tests 1 to 11 and tests 12 to 17.

Detailed Description

Hereinafter, specific embodiments 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, and the invention is not limited thereto.

In the present disclosure, the term "step" includes a step that is independent from other steps, and also includes a step that can achieve the purpose of the step, even when the step cannot be clearly distinguished from other steps.

In the present disclosure, the numerical range expressed by "to" includes numerical values before and after "to" as a minimum value and a 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 described in the present disclosure, the upper limit or the lower limit of the numerical range may be replaced with the values shown in the respective tests.

In the present disclosure, when a plurality of substances corresponding to each component are present in the negative electrode material neutralizing composition, the content and content of each component in the negative electrode material neutralizing composition means the content and content of the total of the plurality of substances present in the negative electrode material neutralizing composition unless otherwise specified.

In the present disclosure, when a plurality of kinds of particles corresponding to each component are present in the negative electrode material neutralizing composition, the particle diameter of each component in the negative electrode material neutralizing composition is a value for a mixture of the plurality of kinds of particles present in the negative electrode material neutralizing composition unless otherwise specified.

In the present disclosure, the term "layer" includes a layer formed only in a part of a region where the layer is present, in addition to a layer formed in the entire region when the region is observed.

In the present disclosure, the term "stacked" means that layers are stacked, and two or more layers may be combined or two or more layers may be detachable.

< negative electrode material for lithium ion secondary battery >

[ first embodiment ]

The negative electrode material for a lithium-ion secondary battery in the first embodiment of the present invention contains a carbon material satisfying the following (1) to (3).

(1) The average particle diameter (D50) is 22 μm or less.

(2) The D90/D10 of the particle size is less than or equal to 2.2.

(3) Linseed oil absorption of less than or equal to 50mL/100 g.

The negative electrode material for a lithium ion secondary battery satisfies the above (1) to (3), and thus a lithium ion secondary battery having excellent input/output characteristics and high-temperature storage characteristics can be produced.

Further, satisfying the above (1) to (3) tends to improve the tap density of the carbon material. By increasing the tap density of the carbon material, the electrode density when the negative electrode material for a lithium ion secondary battery is applied to the current collector tends to be increased, and the pressing pressure required to obtain a target electrode density of the negative electrode for a lithium ion secondary battery tends to be reduced. By reducing the pressing pressure, the orientation of the carbon material in the transverse direction is reduced, and insertion and release of lithium ions during charge and discharge are facilitated, and as a result, a lithium ion secondary battery having more excellent input/output characteristics tends to be produced.

In a lithium ion secondary battery, since the carbon material repeats expansion and contraction due to charge and discharge, if the adhesion between the carbon material and the current collector is low, the carbon material may peel off from the current collector, thereby reducing the charge and discharge capacity and reducing the cycle characteristics. On the other hand, in the negative electrode material for a lithium ion secondary battery of the present embodiment, the tap density of the carbon material is increased, and thus the adhesion between the carbon material as the negative electrode active material and the current collector tends to be improved. Therefore, by using the negative electrode material for a lithium ion secondary battery of the present embodiment, even when the carbon material repeatedly expands and contracts due to charge and discharge, the adhesion between the carbon material and the current collector can be maintained, and a lithium ion secondary battery having excellent life characteristics such as high-temperature storage characteristics and cycle characteristics tends to be produced.

Further, in the negative electrode material for a lithium ion secondary battery, since the adhesion between the carbon material and the current collector is high, the amount of the binder required for producing the negative electrode can be reduced, and a lithium ion secondary battery having excellent energy density can be produced at low cost.

The structure of the negative electrode material for a lithium-ion secondary battery according to the first embodiment will be described in further detail below.

[ carbon Material ]

The negative electrode material for a lithium-ion secondary battery of the first embodiment (hereinafter, also simply referred to as "negative electrode material") contains a carbon material satisfying the above-described conditions (1) to (3). The content of the carbon material in the negative electrode material is not particularly limited, and is, for example, preferably 50% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass.

The negative electrode material may contain a carbon material other than the carbon materials satisfying the above (1) to (3). Examples of the other carbon material include, but are not particularly limited to, natural graphite such as scale-like, clay-like, and spherical graphite, and graphite such as artificial graphite; amorphous carbon, carbon black, fibrous carbon, nanocarbon, and the like. One kind of other carbon material may be used alone, or two or more kinds may be used in combination. The negative electrode material may contain particles containing an element capable of occluding and releasing lithium ions. The element capable of occluding and releasing lithium ions is not particularly limited, and examples thereof include Si, Sn, Ge, and In.

The carbon material has an average particle diameter (D50) of 22 [ mu ] m or less. In addition, the average particle diameter (D50) of the carbon material is preferably 17 μm or less, more preferably 15 μm or less, and still more preferably 13 μm or less, from the viewpoint of suppressing the diffusion distance of lithium from the surface of the negative electrode material to the inside thereof from being long, and further improving the input/output characteristics of the lithium ion secondary battery. In addition, the average particle diameter (D50) of the carbon material is preferably not less than 5 μm, more preferably not less than 7 μm, and still more preferably not less than 9 μm, from the viewpoint of easily obtaining a carbon material having an excellent tap density.

The average particle diameter (D50) of the carbon material is a particle diameter at which the cumulative particle diameter reaches 50% when a volume cumulative distribution curve is drawn from the small particle diameter side in the particle diameter distribution of the carbon material. The average particle diameter (D50) can be measured, for example, by dispersing a carbon material in purified water containing a surfactant and using a laser diffraction particle size distribution measuring apparatus (SALD-3000J, manufactured by Shimadzu corporation, for example).

The particle diameter D90/D10 of the carbon material is 2.2 or less. Further, the particle diameter D90/D10 of the carbon material is preferably 2.0 or less, more preferably 1.8 or less, and still more preferably 1.6 or less, from the viewpoint of easily obtaining a carbon material having an excellent tap density and from the viewpoint of suppressing aggregation of carbon materials with each other. The lower limit of the particle diameter D90/D10 of the carbon material is not particularly limited, and may be 1.0 or more, and is preferably 1.3 or more, for example, because the particles are excellent in indirect thixotropy and the input-output characteristics and the cycle characteristics are more excellent.

The particle diameter (D10) of the carbon material is a particle diameter at which the particle diameter reaches a cumulative 10% when a volume cumulative distribution curve is drawn from a small particle diameter side in a particle diameter distribution of the carbon material, and the particle diameter (D90) of the carbon material is a particle diameter at which the particle diameter reaches a cumulative 90% when a volume cumulative distribution curve is drawn from a small particle diameter side in a particle diameter distribution of the carbon material. The particle size (D10) and the particle size (D90) were measured by adding 0.06g of a carbon material and purified water containing 0.2% by mass of a surfactant (trade name: LIPONOL T/15, manufactured by Lion corporation) to a test tube (12 mm. times.120 mm, manufactured by Maruemu, Inc.), stirring the mixture for 20 seconds by a test tube mixer (Pasolina NS-80, manufactured by AS ONE Co., Ltd.), and then using a laser diffraction particle size distribution measuring apparatus (for example, SALD-3000J, manufactured by Shimadzu corporation).

The linseed oil absorption of the carbon material is 50mL/100g or less. In addition, the linseed oil absorption of the carbon material is preferably 48mL/100g or less, more preferably 47mL/100g or less, and still more preferably 45mL/100g or less, from the viewpoint of increasing the tap density of the carbon material and further improving the input/output characteristics and cycle characteristics of the lithium ion secondary battery. The lower limit of the linseed oil absorption of the carbon material is not particularly limited, and may be, for example, 35mL/100g or more, or 40mL/100g or more.

In the present disclosure, the linseed oil absorption of the carbon material can be determined by a method specified in JIS K6217-4:2008 "carbon black for rubber-basic characteristics-part 4: the reagent liquid described in "method for determining oil absorption amount" was measured using linseed oil (manufactured by kanto chemical corporation) without using dibutyl phthalate (DBP). Linseed oil was titrated with a constant-speed burette against the target carbon powder, and the change in viscosity characteristics was measured with a torque detector. The amount of the reagent liquid added per unit mass of the carbon material corresponding to a torque of 70% of the maximum torque generated was defined as linseed oil absorption (mL/100 g). The measurement instrument can be, for example, an absorption amount measuring device available from Asahi, Inc.

The carbon material preferably satisfies the above (1) to (3), and at least one of the following (4) and (5).

(4) Tap density of 1.00g/cm or more³。

(5) After stirring in purified water containing a surfactant, and further irradiating with ultrasonic waves for 15 minutes by an ultrasonic washing machine, the ratio of D10 after ultrasonic irradiation to D10 before ultrasonic irradiation (the same as the particle size (D10) of the carbon material in the above (2)) (D10 after ultrasonic irradiation/D10 before ultrasonic irradiation) was 0.90 or more.

The carbon material satisfies at least one of the above (4) and (5), and thus a lithium ion secondary battery having more excellent input/output characteristics and cycle characteristics can be manufactured.

If detailed description is made, by satisfying the above (4), there is a tendency that the pressing pressure required for obtaining the target electrode density of the negative electrode for a lithium ion secondary battery can be further reduced. This tends to enable the production of a lithium ion secondary battery having more excellent input/output characteristics. Further, satisfying the above (4) tends to enable production of a lithium ion secondary battery having more excellent adhesion between the carbon material and the current collector and more excellent cycle characteristics.

Further, satisfying the above (5) results in a small change rate of D10 of the carbon material before and after ultrasonic irradiation. This further suppresses aggregation of the carbon materials, and tends to further improve the circularity of the carbon materials. As a result, the tap density of the carbon material tends to be excellent, and the input/output characteristics and cycle characteristics of the negative electrode for a lithium ion secondary battery tend to be more excellent.

The tap density of the carbon material is more preferably 1.02g/cm from the viewpoint of more excellent cycle characteristics and energy density of the lithium ion secondary battery³Above, more preferably 1.05g/cm³The above.

The tap density of the carbon material tends to be high when the tap density is within the range satisfying the above (1) to (3), for example, the average particle diameter (D50) of the carbon material is increased, the particle diameter D90/D10 of the carbon material is decreased, the linseed oil absorption of the carbon material is decreased, or the like.

Book of JapaneseIn the above, the tap density of the carbon material is 150cm in capacity³The flat-bottomed test tube with a scale (KRS-406, manufactured by Kyowa Kagaku Co., Ltd.) was charged with 100cm of the sample powder³The above-mentioned flat-bottomed test tube with a scale was closed with a stopper, and the mass and volume of the sample powder after the flat-bottomed test tube with a scale was dropped 250 times from a height of 5cm were determined.

Further, from the viewpoint of further suppressing aggregation of the carbon materials and further improving the circularity of the carbon materials, D10 after ultrasonic irradiation/D10 before ultrasonic irradiation is more preferably equal to or greater than 0.92, and still more preferably equal to or greater than 0.95.

The upper limit of D10 after ultrasonic irradiation/D10 before ultrasonic irradiation is not particularly limited, and may be, for example, 1.0 or less.

The sample used for the measurement of D10 after ultrasonic wave irradiation in (5) above can be obtained as follows.

0.06g of a carbon material and purified water containing 0.2% by mass of a surfactant (trade name: LIPONOL T/15, manufactured by Lion corporation) were put into a test tube (12 mm. times.120 mm, manufactured by Maruemu, Ltd.), and stirred for 20 seconds by a test tube mixer (Pasolina NS-80, manufactured by AS ONE Co., Ltd.). Then, the test tube was set in an ultrasonic washing machine (U.S. Pat. No. 4,102, manufactured by SND) so as to be inactive, purified water was added to the ultrasonic washing machine to such an extent that the solution in the test tube could be submerged, and ultrasonic waves (high-frequency output 100W and vibration frequency 38kHz) were irradiated for 15 minutes. Thus, a sample for measuring D10 after ultrasonic irradiation was obtained.

In the carbon material, the method of measuring D10 before ultrasonic irradiation and the method of measuring D10 after ultrasonic irradiation are the same as the method of measuring the particle diameter (D10) of the carbon material described above.

The carbon material preferably satisfies the above-described (1) to (3), and at least one of the following (6) and (7), and more preferably satisfies the following (6) and (7).

(6) The circularity is 0.6-0.8 and the proportion of the particle diameter is 10-20 μm is more than or equal to 5% of the whole carbon material.

(7) The circularity is 0.7 or less and the proportion of particle diameters of 10 μm or less is 0.3% by number or less of the entire carbon material.

When the above (6) is satisfied, since the carbon material having a predetermined amount of circularity of 0.6 to 0.8 is present, the contact area between particles tends to be increased, and an electrode having low resistance tends to be obtained. By making it possible to obtain an electrode having low resistance, a lithium ion secondary battery having excellent input/output characteristics tends to be obtained. Further, since the carbon material having a predetermined particle diameter of 10 μm to 20 μm is present, the pressing pressure in the production of the electrode tends to be conducted from the surface of the coated surface to the particles near the current collector in a highly uniform state, and the electrode having excellent uniformity of the electrode density tends to be obtained. Since the uniformity of the electrode density is excellent, a lithium ion secondary battery having excellent input/output characteristics tends to be obtained.

When the above (7) is satisfied, the adhesion between the negative electrode material and the current collector is not easily reduced, and an electrode having excellent adhesion between the negative electrode material and the current collector tends to be obtained. By improving the adhesion between the negative electrode material and the current collector, a lithium ion secondary battery having excellent life characteristics such as input/output characteristics, high-temperature storage characteristics, and cycle characteristics tends to be obtained.

From the viewpoint of balancing the resistance of the electrode and the adhesion between the negative electrode material and the current collector, the ratio of the circularity of 0.6 to 0.8 and the particle diameter of 10 μm to 20 μm is more preferably 5 to 20% by number, and still more preferably 7 to 15% by number of the entire carbon material.

From the viewpoint of improving the adhesion between the negative electrode material and the current collector, the proportion of the circularity of 0.7 or less and the particle diameter of 10 μm or less is more preferably 0.25% by number or less, and still more preferably 0.2% by number or less of the entire carbon material.

In the present disclosure, the ratio between the circularity of the carbon material and the particle diameter in the predetermined range can be measured by a wet flow type particle diameter/shape analyzer. For example, the particle size and circularity of the carbon material are measured by setting the particle size to a range of 0.5 to 200 μm and the circularity to a range of 0.2 to 1.0. From the measurement data, the ratio of the circularity of 0.6 to 0.8 and the particle diameter of 10 to 20 μm and the ratio of the circularity of 0.7 or less and the particle diameter of 10 μm or less were calculated, respectively.

As the measuring instrument, FPIA-3000 (manufactured by Malvern) can be used for the measurement. As a pretreatment for this measurement, 0.06g of a carbon material and purified water containing 0.2% by mass of a surfactant (trade name: LIPONOL T/15, manufactured by Lion corporation) were put into a test tube (12 mm. times.120 mm, manufactured by Maruemu, Inc.), stirred for 20 seconds by a test tube mixer (Pasolina NS-80, manufactured by AS ONE Co., Ltd.), and then stirred for 1 minute by ultrasonic waves. As the ultrasonic washing machine, US102 (high frequency output 100W, vibration frequency 38kHz) manufactured by SND of Kabushiki Kaisha can be used.

The carbon material preferably has an average surface distance d determined by X-ray diffraction₀₀₂Is 0.334 nm-0.338 nm. If mean surface spacing d₀₀₂When the particle size is 0.338nm or less, the lithium ion secondary battery tends to have excellent initial charge/discharge efficiency and energy density.

With respect to the mean surface spacing d₀₀₂The value of (3) is a theoretical value of graphite crystal at 0.3354nm, and the energy density tends to be larger as the value is closer to the theoretical value.

Average surface spacing d for carbon material₀₀₂The diffraction pattern obtained by measuring the diffraction line with a goniometer by irradiating the sample with X-rays (CuK α rays) can be calculated using the bragg formula based on the diffraction peak corresponding to the carbon 002 face appearing in the vicinity of the diffraction angle 2 θ of 24 ° to 27 °.

Average surface distance d of carbon material₀₀₂The value of (b) tends to be small by increasing the temperature of the heat treatment in the production of the negative electrode material, for example. Therefore, the average surface interval d of the carbon material can be controlled by adjusting the temperature of the heat treatment in the production of the negative electrode material₀₀₂。

(R value obtained by Raman spectroscopic measurement)

The carbon material preferably has an R value of 0.1 to 1.0, more preferably 0.2 to 0.8, and further preferably 0.3 to 0.7, as measured by Raman spectroscopy. If the R value is 0.1 or more, the graphite lattice vacancies for insertion and release of lithium ions are sufficiently present, and the lowering 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 can be sufficiently suppressed, and the initial efficiency tends to be suppressed from decreasing.

The above R values are defined as: 1580cm in Raman spectroscopic spectrum obtained in Raman spectroscopic measurement^-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 is usually a peak identified as corresponding to the crystal structure of graphite, and means, for example, at 1530cm^-1～1630cm^-1The observed peak. Furthermore, it is said to be 1360cm^-1The peaks appearing nearby are usually those identified as corresponding to the amorphous structure of carbon, for example at 1300cm^-1～1400cm^-1The observed peak.

In this publication, a laser raman spectrophotometer (model No. NRS-1000, japan spectro corporation) was used to perform raman spectroscopic measurement by irradiating a sample plate, on which a negative electrode material for a lithium ion secondary battery was provided so as to be flat, with argon laser light. The measurement conditions were as follows.

Wavelength of argon laser: 532nm

Wave number resolution: 2.56cm^-1

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

Peak value query: removing background

Specific surface area of carbon material (hereinafter, also referred to as "N") determined by nitrogen adsorption measurement at 77K₂Specific surface area ". ) Preferably 2m²/g～8m²A/g, more preferably 2.5m²/g～7m²(ii)/g, more preferably 3m²/g～6m²(ii) in terms of/g. If N is present₂When the specific surface area is within the above range, a good balance between the input/output characteristics and the initial charge/discharge efficiency of the lithium ion secondary battery tends to be obtained. Specifically, N₂The specific surface area can be determined by the BET method based on the adsorption isotherm obtained by nitrogen adsorption measurement at 77K.

CO obtained by adsorbing carbon dioxide of a carbon material at 273K₂Amount of adsorption (hereinafter, also referred to as "CO")₂Adsorption amount ". ) Is set to be A, the above-mentioned N₂When the value of the specific surface area is B, CO per unit area calculated from the following expression (a)₂The adsorption capacity is preferably 0.01cm³/m²～0.10cm³/m²More preferably 0.03cm³/m²～0.08cm³/m²More preferably 0.04cm³/m²～0.06cm³/m². When the amount is within the above range, the input/output characteristics and the high-temperature storage characteristics (or the initial charge/discharge efficiency) of the lithium ion secondary battery tend to be well balanced. Further, if CO per unit area₂The adsorption capacity is less than or equal to 0.10cm³/m²There is a tendency that irreversible capacity due to a side reaction with the electrolyte decreases, and a decrease in initial efficiency can be suppressed. In addition, CO₂The adsorption capacity was measured at a measurement temperature of 273K and a relative pressure P/P₀＝3.0×10^-2(P is equilibrium pressure, P₀26142mmHg (3.49 MPa)).

CO per unit area₂Adsorption capacity (cm)³/m²)＝A(cm³/g)/B(m²/g)···(a)

In the differential thermal analysis (DTA analysis) performed in an air stream, the carbon material preferably does not have two or more exothermic peaks in a temperature range of 300 to 1000 ℃. This tends to further improve the input/output characteristics and high-temperature storage characteristics of the lithium ion secondary battery.

The carbon material having no two or more exothermic peaks means that it has no discernible exothermic peaks, that is, it has no discernible exothermic peaks or 1 discernible exothermic peak in the temperature range of 300 to 1000 ℃. Here, the term "having a plurality of identifiable exothermic peaks" means having a plurality of exothermic peaks having a peak value at least 5 ℃ or more apart.

In the present disclosure, differential thermal analysis (DTA analysis) can be performed using a differential thermogravimetric simultaneous measurement apparatus (for example, EXSTAR TG/DTA6200 manufactured by Seiko Instruments co., ltd.). Specifically, the presence or absence of an exothermic peak of DTA at 300 to 1000 ℃ was confirmed by measuring the temperature at a rate of 2.5 ℃/min while passing dry air at 300 mL/min with α -alumina as a reference.

The carbon material is not particularly limited, and examples thereof include graphite, low crystalline carbon, amorphous carbon, and mesophase carbon. Examples of the graphite include artificial graphite, natural graphite, graphitized mesophase carbon, graphitized carbon fiber, and the like. The carbon material is preferably spherical graphite particles, and more preferably spherical artificial graphite, spherical natural graphite, or the like, from the viewpoint of excellent charge/discharge capacity and excellent tap density of the lithium ion secondary battery.

Further, by using spherical graphite particles, aggregation of graphite particles can be suppressed, and when the graphite particles are coated with a carbon material having lower crystallinity (for example, amorphous carbon), the graphite particles can be appropriately coated. Further, when the negative electrode material composition is produced using the carbon material which is aggregated at the time of coating, exposure of the region not coated with the carbon material can be suppressed when the aggregation of the carbon material is released by stirring. As a result, when a lithium ion secondary battery is manufactured, the decomposition reaction of the electrolytic solution at the surface of the carbon material tends to be suppressed, and the decrease in the primary efficiency tends to be suppressed.

The carbon material contained in the negative electrode material may be one kind alone or two or more kinds.

The carbon material may include a first carbon material as a core and a second carbon material that is present on at least a part of a surface of the first carbon material and has lower crystallinity than the first carbon material. The first carbon material and the second carbon material are not particularly limited as long as they satisfy the condition that the crystallinity of the second carbon material is lower than that of the first carbon material, and can be appropriately selected from the above-mentioned examples of carbon materials, for example. The first carbon material and the second carbon material may be one or two or more kinds, respectively.

The presence of the second carbon material on the surface of the first carbon material can be confirmed by transmission electron microscope observation.

The second carbon material preferably contains at least one of crystalline carbon and amorphous carbon in order to improve the input/output characteristics of the lithium ion secondary battery. Specifically, at least one selected from the group consisting of carbonaceous substances obtained from organic compounds (hereinafter, also referred to as precursors of the second carbon material) that can become carbonaceous by heat treatment and carbonaceous particles is preferable.

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

The carbonaceous particles used as the second carbon material are not particularly limited, and examples thereof include particles such as acetylene black, oil furnace black, ketjen black, channel black, thermal black, and soil graphite.

In the case where the carbon material includes the first carbon material and the second carbon material, the ratio of the amounts of the first carbon material and the second carbon material in the carbon material is not particularly limited. The amount of the second carbon material in the total mass of the carbon materials is preferably 0.1 to 15 mass%, more preferably 1 to 10 mass%, and still more preferably 1 to 5 mass%, in terms of improving the input/output characteristics of the lithium ion secondary battery.

Regarding the amount of the second carbon material in the carbon material, in the case of calculation from the amount of the precursor of the second carbon material, it can be calculated by multiplying the amount of the precursor of the second carbon material by the residual carbon ratio (mass%). The carbon residual ratio of the precursor of the second carbon material can be calculated by performing heat treatment on the precursor of the second carbon material alone (or in a state of a mixture of the precursor of the second carbon material and the first carbon material in a predetermined ratio) at a temperature at which the precursor of the second carbon material can become carbonaceous, based on the mass of the precursor of the second carbon material before heat treatment and the mass of the carbonaceous substance derived from the precursor of the second carbon material after heat treatment, by thermogravimetric analysis or the like.

Next, negative electrode materials for lithium ion secondary batteries in the second and third embodiments of the present invention will be described. The carbon material used in the second and third embodiments, the average particle size (D50) of the carbon material, the D90/D10 of the particle size, the linseed oil absorption, the tap density, the D10 after the ultrasonic irradiation/the D10 before the ultrasonic irradiation, and the average surface distance D₀₀₂R value, N₂Specific surface area and CO₂The preferred numerical range of the amount of adsorption, the measurement method, and the like are the same as those in the first embodiment, and therefore, the description thereof is omitted.

In addition, as the carbon material used in the second embodiment and the third embodiment, it is preferable that the carbon material does not have two or more exothermic peaks in a temperature range of 300 to 1000 ℃ in a differential thermal analysis (DTA analysis) performed in an air stream, as in the first embodiment. The carbon material used in the second and third embodiments may be the carbon material specifically described in the first embodiment.

[ second embodiment ]

The negative electrode material for a lithium ion secondary battery in the second embodiment of the present invention contains a carbon material satisfying the following (1), (2), and (4).

(1) The average particle diameter (D50) is 22 μm or less.

(2) The D90/D10 of the particle size is less than or equal to 2.2.

(4) Tap density of 1.00g/cm or more³。

The negative electrode material for a lithium ion secondary battery satisfies the above (1), (2), and (4), and thus a lithium ion secondary battery having excellent input/output characteristics and high-temperature storage characteristics can be manufactured.

If the details are described, the lithium ion secondary battery having excellent input/output characteristics tends to be manufactured by satisfying the above (1).

Further, satisfying (2) above makes it easy to obtain a carbon material having an excellent tap density, and a carbon material satisfying (4) above is easily obtained. By satisfying the above (4), the tap density of the carbon material becomes high, the electrode density when the negative electrode material for a lithium ion secondary battery is applied to the current collector is increased, and the pressing pressure required for obtaining the target electrode density of the negative electrode for a lithium ion secondary battery tends to be reduced. By lowering the pressing pressure, the orientation of the carbon material in the transverse direction is lowered, and insertion and release of lithium ions during charge and discharge are facilitated, and as a result, a lithium ion secondary battery having more excellent input/output characteristics tends to be produced.

In a lithium ion secondary battery, since the carbon material repeats expansion and contraction due to charge and discharge, if the adhesion between the carbon material and the current collector is low, the carbon material may peel off from the current collector, thereby reducing the charge and discharge capacity and reducing the cycle characteristics. On the other hand, in the negative electrode material for a lithium ion secondary battery of the present embodiment, the tap density of the carbon material is increased, and thus the adhesion between the carbon material as the negative electrode active material and the current collector tends to be improved. Therefore, by using the negative electrode material for a lithium ion secondary battery of the present embodiment, even when the carbon material repeatedly expands and contracts due to charge and discharge, the adhesion between the carbon material and the current collector can be maintained, and a lithium ion secondary battery having excellent cycle characteristics tends to be produced.

Further, in the negative electrode material for a lithium ion secondary battery, since the adhesion between the carbon material and the current collector is high, the amount of the binder required for producing the negative electrode can be reduced, and a lithium ion secondary battery having excellent energy density can be produced at low cost.

The carbon material preferably satisfies the above (1), (2), and (4), and at least one of the following (3) and (5).

(3) Linseed oil absorption of less than or equal to 50mL/100 g.

(5) After stirring in purified water containing a surfactant, and further irradiating with ultrasonic waves for 15 minutes by an ultrasonic washing machine, the ratio of D10 after ultrasonic irradiation to D10 before ultrasonic irradiation (the same as the particle size (D10) of the carbon material in the above (2)) (D10 after ultrasonic irradiation/D10 before ultrasonic irradiation) was 0.90 or more.

By satisfying at least one of (3) and (5) above with a carbon material, a lithium ion secondary battery having more excellent input/output characteristics and cycle characteristics can be manufactured.

The carbon material preferably satisfies the above (1), (2), and (4), and at least one of the following (6) and (7), more preferably satisfies the following (6) and (7).

(6) The circularity is 0.6-0.8 and the proportion of the particle diameter is 10-20 μm is more than or equal to 5% of the whole carbon material.

(7) The circularity is 0.7 or less and the proportion of particle diameters of 10 μm or less is 0.3% by number or less of the entire carbon material.

By satisfying the above (6) with a carbon material, a lithium ion secondary battery having excellent input/output characteristics tends to be obtained.

When the carbon material satisfies the above (7), a lithium ion secondary battery having excellent input/output characteristics, high-temperature storage characteristics, cycle characteristics, and other life characteristics tends to be obtained.

[ third embodiment ]

A negative electrode material for a lithium-ion secondary battery in a third embodiment of the present invention contains a carbon material satisfying the following (1), (2), and (5).

(1) The average particle diameter (D50) is 22 μm or less.

(2) The D90/D10 of the particle size is less than or equal to 2.2.

(5) After stirring in purified water containing a surfactant, and further irradiating with ultrasonic waves for 15 minutes by an ultrasonic washing machine, the ratio of D10 after ultrasonic irradiation to D10 before ultrasonic irradiation (the same as the particle size (D10) of the carbon material in the above (2)) (D10 after ultrasonic irradiation/D10 before ultrasonic irradiation) was 0.90 or more.

By satisfying the above (1), (2) and (5) with the negative electrode material for a lithium ion secondary battery, a lithium ion secondary battery having excellent input/output characteristics and cycle characteristics can be produced.

If the details are described, the lithium ion secondary battery having excellent high-temperature storage characteristics tends to be produced by satisfying the above (1).

Further, by satisfying the above (2) and (5), aggregation of the carbon materials is further suppressed, circularity of the carbon materials is further improved, and tap density of the carbon materials tends to be improved. The increase in tap density of the carbon material increases the electrode density when the negative electrode material for a lithium ion secondary battery is applied to the current collector, and tends to reduce the pressing pressure required to obtain a target electrode density of the negative electrode for a lithium ion secondary battery. By reducing the pressing pressure, the orientation of the carbon material in the transverse direction is reduced, and insertion and release of lithium ions during charge and discharge are facilitated, and as a result, a lithium ion secondary battery having more excellent input/output characteristics tends to be produced.

In a lithium ion secondary battery, since the carbon material repeats expansion and contraction due to charge and discharge, if the adhesion between the carbon material and the current collector is low, the carbon material may peel off from the current collector, thereby reducing the charge and discharge capacity and reducing the cycle characteristics. On the other hand, in the negative electrode material for a lithium ion secondary battery of the present embodiment, the tap density of the carbon material is increased, and thus the adhesion between the carbon material as the negative electrode active material and the current collector tends to be improved. Therefore, by using the negative electrode material for a lithium ion secondary battery of the present embodiment, even when the carbon material repeatedly expands and contracts due to charge and discharge, the adhesion between the carbon material and the current collector can be maintained, and a lithium ion secondary battery having excellent cycle characteristics tends to be produced.

Further, in the negative electrode material for a lithium ion secondary battery, since the adhesion between the carbon material and the current collector is high, the amount of the binder required for producing the negative electrode can be reduced, and a lithium ion secondary battery having excellent energy density can be produced at low cost.

The carbon material preferably satisfies the above (1), (2), and (5), and at least one of the following (3) and (4).

(3) Linseed oil absorption of less than or equal to 50mL/100 g.

(4) Tap density of 1.00g/cm or more³。

By satisfying at least one of the above (3) and (4) with a carbon material, a lithium ion secondary battery having more excellent input/output characteristics and cycle characteristics can be manufactured.

The carbon material preferably satisfies the above (1), (2), and (5), and at least one of the following (6) and (7), more preferably satisfies the following (6) and (7).

(6) The circularity is 0.6-0.8 and the proportion of the particle diameter is 10-20 μm is more than or equal to 5% of the whole carbon material.

(7) The circularity is 0.7 or less and the proportion of particle diameters of 10 μm or less is 0.3% by number or less of the entire carbon material.

By satisfying the above (6) with a carbon material, a lithium ion secondary battery having excellent input/output characteristics tends to be obtained.

When the carbon material satisfies the above (7), a lithium ion secondary battery having excellent input/output characteristics, high-temperature storage characteristics, cycle characteristics, and other life characteristics tends to be obtained.

The method for producing the negative electrode material of the present disclosure is not particularly limited. In order to efficiently produce a negative electrode material that satisfies the above conditions, when a carbon material is produced using the first carbon material and the second carbon material precursor, it is preferable to produce the negative electrode material by the following method for producing a negative electrode material.

Method for producing negative electrode material for lithium ion secondary battery

A method for producing a negative electrode material for a lithium-ion secondary battery according to one embodiment of the present invention includes: a carbon material is produced by heat-treating a mixture containing a first carbon material as a core and a precursor of a second carbon material having lower crystallinity than the first carbon material.

According to the method, the negative electrode material can be efficiently produced.

In the above method, details and preferred embodiments of the first carbon material, the precursor of the second carbon material, and the carbon material are the same as those described in the above item of the negative electrode material for a lithium ion secondary battery.

The temperature at which the mixture is heat-treated is preferably 950 to 1500 ℃, more preferably 1000 to 1300 ℃, and still more preferably 1050 to 1250 ℃ in order to improve the input/output characteristics of the lithium ion secondary battery. The temperature at which the mixture is heat-treated may be constant from the start to the end of the heat treatment or may be varied.

In the above method, the content of the precursors of the first carbon material and the second carbon material in the mixture before the heat treatment is not particularly limited. From the viewpoint of improving the input/output characteristics of the lithium ion secondary battery, the content of the first carbon material is preferably 85 to 99.9 mass%, more preferably 90 to 99 mass%, and still more preferably 95 to 99 mass%, based on the total mass of the mixture. On the other hand, the content of the precursor of the second carbon material is preferably 0.1 to 15% by mass, more preferably 1 to 10% by mass, and still more preferably 1 to 5% by mass, based on the total mass of the mixture, from the viewpoint of improving the input/output characteristics of the lithium ion secondary battery.

< 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 and the current collector.

For example, a negative electrode for a lithium ion secondary battery can be produced by kneading a negative electrode material and a binder together with a solvent to prepare a slurry-like negative electrode material composition, applying the slurry-like negative electrode material composition onto a current collector to form a negative electrode material layer, or by forming the negative electrode material composition 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, a super sand mill, or a pressure kneader.

The binder used for preparing the negative electrode material composition is not particularly limited. Examples of the binder include polymers of ethylenically unsaturated carboxylic acid esters such as styrene-butadiene copolymer, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, acrylonitrile, methacrylonitrile, hydroxyethyl acrylate, and hydroxyethyl methacrylate; polymers of ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid; and high-molecular compounds having high ionic conductivity such as polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, and polyacrylonitrile. In the case where the negative electrode material composition contains a binder, the amount thereof is not particularly limited. The content of the binder may be, for example, 0.5 to 20 parts by mass with respect to 100 parts by mass of the total of the negative electrode material and the binder.

The solvent is not particularly limited as long as it can dissolve or disperse the binder. Specific examples thereof include organic solvents such as N-methyl-2-pyrrolidone, N-dimethylacetamide, N-dimethylformamide, and γ -butyrolactone. The amount of the solvent used is not particularly limited as long as the negative electrode material composition can be formed into a desired state such as a paste. The amount of the solvent used is, for example, preferably 60 parts by mass or more and less than 150 parts by mass with respect to 100 parts by mass of the negative electrode material.

The negative electrode material composition may include a thickener. Examples of the thickener include carboxymethyl cellulose or a salt thereof, methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid or a salt thereof, alginic acid or a salt thereof, oxidized starch, phosphorylated starch, and casein. In the case where the negative electrode material composition contains a thickener, the amount thereof is not particularly limited. The content of the thickener may be, for example, 0.1 to 5 parts by mass with respect to 100 parts by mass of the negative electrode material.

The negative electrode material composition may include a conductive auxiliary material. Examples of the conductive auxiliary material include carbon materials such as natural graphite, artificial graphite, and carbon black (acetylene black, thermal black, furnace black, and the like), oxides exhibiting conductivity, and nitrides exhibiting conductivity. In the case where the negative electrode material composition contains the conductive auxiliary material, the amount thereof is not particularly limited. The content of the conductive auxiliary material may be, for example, 0.5 to 15 parts by mass with respect to 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) or carbon paper can be used as the current collector.

When the negative electrode material composition 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 is applied to the current collector, the solvent contained in the negative electrode material composition is removed by drying. Drying can be performed using, for example, a hot air dryer, an infrared dryer, or a combination of these apparatuses. Rolling treatment may be performed as necessary. The rolling treatment can be performed by a flat press, a roll, or the like.

When the negative electrode material composition molded into a sheet, a pellet, or the like is integrated with the current collector to form the negative electrode material layer, the method of integration is not particularly limited. For example, it can be carried out by a roll, a flat press, or a combination of these methods. The pressure at the time of integration is preferably, for example, 1MPa to 200 MPa.

< lithium ion secondary battery >

The lithium ion secondary battery of the present disclosure includes the negative electrode for a lithium ion secondary battery (hereinafter, also simply referred to as "negative electrode") of the present disclosure, a positive electrode, and an electrolytic 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 made of a metal or an alloy such as aluminum, titanium, or stainless steel in a foil shape, an open-pore foil shape, a mesh shape, or the like can be used.

The positive electrode material used for forming the positive electrode material layer is not particularly limited. For example, lithium ions can be generatedDoped or intercalated metal compounds (metal oxides, metal sulfides, etc.) and conductive polymer materials. 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 LiMPO₄Lithium-containing compounds such as (M: Co, Ni, Mn, Fe), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, polyacene, and porous carbon. The positive electrode material may be one kind alone or two or more kinds.

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 one kind alone or two 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, ethylmethyl carbonate, methylpropyl carbonateEsters, 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 nonaqueous solvent may be one kind alone or two or more kinds.

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, if necessary, a separator disposed between the positive electrode and the negative electrode 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 nonwoven fabric, a cloth, a microporous film made of a resin, or a combination thereof 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, in the case where the positive electrode and the negative electrode are not in direct contact, the separator may not be used.

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 rectangular type battery.

The lithium ion secondary battery of the present disclosure is excellent in output characteristics, and therefore is suitable as a large-capacity lithium ion secondary battery used in electric vehicles, power 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.