WO2016104489A1 - Carbon material for secondary cell negative electrode, active substance for secondary cell negative electrode, secondary cell negative electrode, and secondary cell - Google Patents

Abstract

The present invention provides a carbon material for a secondary cell negative electrode in which increases in electrical resistance during charging and discharging are suppressed when used in low temperature environments and adequate cell characteristics can be ensured, an active substance for a secondary cell negative electrode that is created by including the carbon material for a secondary cell negative electrode, a secondary cell negative electrode that is configured by using the active substance for a secondary cell negative electrode, and a secondary cell in which the secondary cell negative electrode is used. This carbon material for a secondary cell negative electrode includes carbon particles in which the surface area per unit volume derived from the particle size distribution on a count basis is in the range of 10000 cm^-1 to 16000 cm^-1, and the active substance for a secondary cell negative electrode contains the carbon material for a secondary cell negative electrode. The secondary cell negative electrode (10) has an active substance layer (12) for a secondary cell negative electrode that includes the active substance for a secondary cell negative electrode, and a collector (14) for a negative electrode. The secondary cell (100) is provided with this secondary cell negative electrode (10), an electrolyte layer (40), and a secondary cell positive electrode (20).

Description

Carbon material for secondary battery negative electrode, active material for secondary battery negative electrode, secondary battery negative electrode and secondary battery

The present invention relates to a carbon material for a secondary battery negative electrode, an active material for a secondary battery negative electrode, a secondary battery negative electrode, and a secondary battery.
This application claims priority based on Japanese Patent Application No. 2014-260833 filed in Japan on December 24, 2014, and Japanese Patent Application No. 2015-052628 filed in Japan on March 16, 2015. , The contents of which are incorporated herein.

In recent years, the use of secondary batteries has been studied in various technical fields ranging from small electrical products such as mobile phones to large machine products such as automobiles. As the secondary battery, various types such as a non-aqueous electrolyte secondary battery using an organic electrolyte solution or the like as an electrolyte or a solid battery using a solid electrolyte have been studied. In any type of secondary battery, a carbon material such as hard carbon or graphite is widely used for the negative electrode of the conventional secondary battery (see, for example, Patent Document 1).

Among them, hard carbon is excellent in terms of high cycle characteristics and is expected as a carbon material for secondary battery negative electrodes.

JP-A-5-74457

By the way, it has been recognized that there are new problems due to the use of secondary batteries in various technical fields. That is, it has been found that there is a problem that the electrical resistance at the time of charging / discharging increases when the secondary battery is used in a low temperature environment, such as below freezing point, particularly −10 ° C. or less, more preferably −20 ° C. or less. As a result, it was found that the secondary battery used in a low temperature environment may have lower cycle characteristics and input / output characteristics than those used in a room temperature environment.

In particular, it is known that general hard carbon used as a carbon material for a negative electrode of a secondary battery is inferior in internal diffusibility of chemical species serving as charge carriers such as lithium ions that are inserted and desorbed compared to graphite. . For this reason, there is a possibility that sufficient battery performance cannot be obtained when battery resistance increases in a low temperature environment.

The present invention has been made in view of the above problems. That is, the present invention provides a carbon material for a secondary battery negative electrode that suppresses an increase in electrical resistance during charge and discharge when used in a low temperature environment and can ensure sufficient battery performance.
The present invention also provides a secondary battery negative electrode active material produced by including the secondary battery negative electrode carbon material, a secondary battery negative electrode composed of the secondary battery negative electrode active material, and the second battery negative electrode active material. A secondary battery using a secondary battery negative electrode is provided.

The carbon material for a secondary battery negative electrode of the present invention is characterized by containing carbon particles having a surface area per unit volume determined from a particle size distribution on a number basis in a range of 10,000 cm ^{−1 to} 16000 cm ⁻¹ .

The active material for secondary battery negative electrode of the present invention is characterized by containing the carbon material for secondary battery negative electrode of the present invention.

Further, the secondary battery negative electrode of the present invention includes a secondary battery negative electrode active material layer containing the secondary battery negative electrode active material of the present invention, and a negative electrode current collector in which the secondary battery negative electrode active material layer is laminated. It is characterized by having.

The secondary battery of the present invention is characterized by comprising the secondary battery negative electrode of the present invention, an electrolytic layer, and a secondary battery positive electrode.

According to the present invention, a carbon material for a secondary battery negative electrode, an active material for a secondary battery negative electrode, and a secondary battery negative electrode capable of suppressing an increase in electrical resistance during charging and discharging of the secondary battery in a low temperature environment, In addition, it is possible to provide a secondary battery in which an increase in electrical resistance is suppressed even in a low temperature environment.

It is a schematic diagram which shows an example of a lithium ion secondary battery provided with the negative electrode manufactured using the carbon material of this invention.

The inventors examined the electrical characteristics of the secondary battery negative electrode in a low temperature environment. As a result, it was found that the conventional secondary battery negative electrode has a possibility that the electrical resistance during charging / discharging is remarkably increased and the battery characteristics are deteriorated as compared with that at normal temperature. As a result of further detailed studies, the present inventors have found that secondary battery negative electrodes used in a low temperature environment have the following problems. That is, in a low temperature environment below freezing point, in particular, -10 ° C or lower, particularly -20 ° C or lower, the electrolyte is frozen or the viscosity rises even if it is not frozen. As a result, it was speculated that under the low temperature environment, the operation of chemical species such as lithium ions moving between the electrolyte and the negative electrode active material becomes dull and the occlusion and release of the negative electrode active material becomes inactive. According to the present inventors, it is possible to suppress an increase in electrical resistance by improving the ability to occlude and release chemical species of the negative electrode active material and maintain good occlusion and release even in a low temperature environment. I came up with an idea. More specifically, the inventors of the present invention are based on the technical idea that the above problem can be solved by significantly increasing the surface area per unit volume of the carbon particles contained in the negative electrode active material. The invention has been completed.
The secondary battery negative electrode carbon material of the present invention (hereinafter also simply referred to as carbon material), secondary battery negative electrode active material (hereinafter also simply referred to as negative electrode active material), secondary battery negative electrode (hereinafter simply referred to as negative electrode). And the secondary battery will be described in order.

As the secondary battery in which the carbon material of the present invention, the negative electrode active material, or the negative electrode is used, and the secondary battery of the present invention, for example, an alkali metal secondary such as a lithium ion secondary battery or a sodium ion secondary battery is used. A battery can be mentioned. However, the secondary battery is not limited to this, and includes various types such as a secondary battery that occludes and releases other charge carriers, a non-aqueous electrolyte secondary battery, or a solid secondary battery. In the following description, a lithium ion secondary battery will be described as an example of a secondary battery.

<Carbon material>
The carbon material of the present invention comprises carbon particles having a surface area per unit volume (hereinafter, also simply referred to as a surface area per unit volume) determined from the particle size distribution on a number basis within a range of 10000 cm ^{−1 to} 16000 cm ^−1. Including.

The lower limit of the surface area per unit volume may be further 12000 cm ⁻¹ or more. Further, the upper limit of the surface area per unit volume may be further 15500 cm ⁻¹ or less, or 14000 cm ⁻¹ or less.

The carbon material of the present invention is a carbon material that can be used as a material for an active material for a negative electrode. The carbon material of the present invention has an effect of suppressing an increase in electric resistance (hereinafter also referred to as an electric resistance suppressing effect) during charging / discharging of the secondary battery in a low temperature environment. The reason why the electrical resistance suppressing effect is exhibited in the carbon material of the present invention is not clear, but the present inventors infer as follows. That is, the carbon material of the present invention is configured such that the particle diameter is moderately small and the surface area per unit volume is sufficiently large. Therefore, it is estimated that the carbon material of the present invention has a high efficiency of occlusion and release of lithium ions, and even when the operation of lithium ions becomes dull in a low temperature environment, the occlusion and release are performed smoothly. In other words, the carbon material of the present invention covers a decrease in the mobility of lithium ions in a low temperature environment by significantly increasing the surface area of the particles, which are the occlusion / release regions of lithium ions, as compared to conventional carbon materials. It is assumed that the increase in electrical resistance is suppressed.

Specifically, since the carbon material of the present invention has a surface area per unit volume of 10,000 cm ⁻¹ or more, the total area of the particle surface, which is a lithium ion storage / release region, is sufficiently large. Thereby, the carbon material of this invention is excellent in the occlusion / release capability of lithium ion compared with the conventional carbon material, and exhibits an electrical resistance inhibitory effect also in a low temperature environment.
The carbon material of the present invention has a surface area per unit volume in the range of 16000 cm ⁻¹ or less, and extremely minute carbon material particles are excluded. If the carbon material contains extremely fine carbon material particles, the amount of self-discharge at high temperatures tends to increase, and when the material containing the carbon material is slurried and applied to the current collector, The coatability tends to decrease due to a significant increase in the viscosity of the slurry. Therefore, the carbon material of the present invention specifies the upper limit of the surface area per unit volume as 16000 cm ⁻¹ , thereby suppressing a significant increase in the self-discharge and maintaining good coatability.

In the present invention, the electrical resistance in a low temperature environment can be determined by the magnitude of the value of DC resistance (DC-IR) measured under a predetermined low temperature environment condition (for example, an environment of −20 ° C.). When the direct current resistance value is relatively large, it is determined that the electrical resistance is relatively high.

In the present invention, the particle size distribution based on the number means the particle size distribution based on the number obtained by the laser diffraction / scattering method. The particle size distribution can be measured with a laser diffraction / scattering particle size distribution measuring apparatus. For example, it can be measured by LA-920 manufactured by Horiba, Ltd. Here, the particle diameter means the diameter of the particle.

In the present invention, the surface area per unit volume determined from the particle size distribution on the basis of the number is the data obtained from the particle size distribution on the basis of the number measured by an arbitrary laser diffraction / scattering particle size distribution measuring device, It can be calculated by equation (1).
[Equation 1]
Area per unit volume (cm ⁻¹ ) = total surface area (cm ² ) / total volume (cm ³ ) (1)

Here, the “total surface area” is the sum of values obtained by multiplying the surface area when particles of each particle size in the particle size distribution are converted into true spheres by the frequency (%) of particles at each particle size.
Further, “total volume” is the sum of values obtained by multiplying the volume of particles of each particle size in the particle size distribution into true spheres by the frequency (%) of particles at each particle size.
“Frequency” is the ratio of particles at each particle diameter to the total number of particles subjected to measurement.

A method for obtaining a carbon material including carbon particles having a surface area per unit volume in a preferable range specified in the present invention is not particularly limited, and as an example, a pulverization treatment is appropriately performed in the process of manufacturing the carbon material. It is done. Details of the grinding process will be described later.

The carbon material of the present invention preferably has an average square radius (hereinafter also simply referred to as an average square radius) determined from the particle size distribution described above in a range of 1 μm ² or more and 4 μm ² or less.
That is, when the mean square radius is 1 μm ² or more, carbon particles contained in the carbon material are excluded from those having a remarkably small particle diameter, and deterioration of self-discharge in a high temperature environment is prevented. Maintains good coatability on electrical objects. In addition, when the mean square radius is 4 μm ² or less, it is easy to select carbon particles whose surface area per unit volume falls within a preferable range specified by the present invention.

From the viewpoint of satisfactorily solving the intended problem of the present invention, the upper limit of the mean square radius is more preferably 3 μm ² or less, and even more preferably 2 μm ² or less.

In a preferred embodiment of the present invention, the mean square radius determined from the particle size distribution is determined from the particle size distribution on a number basis. Specifically, it can be calculated by the following formula (2) using data obtained from a number-based particle size distribution measured by an arbitrary laser diffraction / scattering particle size distribution measuring apparatus.
[Equation 2]
Mean square radius ([mu] m ²⁾ = radius of the square of the sum of each particle (μm ^{2) (2)}

Here, “the sum of the squares of the radii of each particle (μm ² )” is a value that is a half of each particle diameter in the particle size distribution, and the value obtained by squaring this value is the particle at each particle diameter. The sum of the values multiplied by the frequency (%).

One of the preferable aspects of the carbon material of the present invention is such that the true specific gravity of the carbon particles contained in the carbon material is in the range of 1.5 g / cm ³ or more and 1.7 g / cm ³ or less.
By selecting carbon particles having a true specific gravity of 1.5 g / cm ³ or more, the charge / discharge capacity value can be stabilized. Further, by selecting carbon particles having a true specific gravity of 1.7 g / cm ³ or less, it contributes to the improvement of the life characteristics of the secondary battery using the carbon material of the present invention.

The true specific gravity can be determined by a true specific gravity measurement method using butanol.

The method for adjusting the carbon particles contained in the carbon material of the present invention to have a true specific gravity within the above preferable range is not particularly limited. It is possible to adjust the specific gravity.

Below, carbon used as the main material of the carbon material of this invention is demonstrated.
The carbon material of the present invention contains carbon as a main material, and may further contain components other than carbon as necessary. Here, the term “carbon is a main material” means that carbon is contained in an amount of 80% by mass or more, preferably 90% by mass or more, and more preferably 95% by mass or more when the carbon material is 100% by mass. Say. The carbon contained in the carbon material in the present invention is carbon particles that are substantially granular. The carbon material in the present invention may contain the carbon particles and an optional additive, or may be substantially composed only of carbon particles.

The optional component other than carbon in the carbon material is not particularly limited, and examples thereof include nitrogen and phosphorus. By including nitrogen in the carbon material, electrical characteristics suitable for the carbon material (particularly, carbon material containing hard carbon) can be imparted due to the electronegativity of nitrogen. Thereby, occlusion / release of the lithium ion with respect to a carbon material is accelerated | stimulated, and a high charging / discharging characteristic can be provided. Further, since phosphorus is contained in a carbon material (particularly, a carbon material containing hard carbon), it is possible to increase the occlusion amount of lithium ions in the negative electrode active material containing the carbon material. In addition, when producing the carbon material of the present invention, any additive such as a curing agent and an additive can be appropriately used in addition to the carbon material, and a part of the additive remains in the carbon material. It is not excluded that the present invention.

The carbon used as the main material can be appropriately selected and used as long as it is a material of the negative electrode active material and can absorb and release chemical species such as lithium ions. Specific examples include hard carbon and graphite, but are not limited thereto.

Hereinafter, an aspect in which the carbon particles in the carbon material of the present invention contain hard carbon will be described.

That is, as one preferred embodiment of the carbon material of the present invention, the carbon particles contained in the carbon material are obtained by an X-ray diffraction method using CuKα rays as a radiation source, and an average interplanar spacing d ₀₀₂ of (002) planes. May contain hard carbon having a thickness of 0.340 nm or more.

Hard carbon (non-graphitizable carbon) is a carbon material obtained by firing a polymer that does not easily develop a graphite crystal structure, and is an amorphous substance. In other words, the hard carbon is a carbon material that does not have a graphene structure or carbon that only partially has a graphene structure, and has the specific average interplanar spacing d ₀₀₂ . When the average interplanar spacing d ₀₀₂ of hard carbon is 0.340 nm or more, especially 0.360 nm or more, the shrinkage / expansion between layers due to occlusion of lithium ions is difficult to occur. it can. The upper limit of the average interplanar distance d ₀₀₂ is not particularly defined, but can be set to 0.390 nm or less, for example. The average spacing _{d 002} is 0.390nm or less, particularly when it is 0.380nm or less performed smoothly absorbing and releasing lithium ions, it is possible to suppress the deterioration of the charge-discharge efficiency.

Furthermore, it is preferable that the hard carbon has a crystallite size Lc of 0.8 nm or more and 5 nm or less in the c-axis direction ((002) plane orthogonal direction).

By setting Lc to 0.8 nm or more, particularly 0.9 nm or more, there is an effect that a space between carbon layers capable of occluding and releasing lithium ions is formed, and a sufficient charge / discharge capacity can be obtained. By setting the thickness to 0.5 nm or less, it is possible to suppress the collapse of the carbon laminate structure due to the occlusion and release of lithium ions and the reductive decomposition of the electrolytic solution, and to suppress the decrease in charge / discharge efficiency and charge / discharge cycleability.

Lc is calculated as follows.
It was determined from the half width of the 002 plane peak and the diffraction angle in the spectrum obtained from the X-ray diffraction measurement using the following Scherrer equation.

Lc = 0.94λ / (βcos θ) (Scherrer equation)
Lc: crystallite size λ: wavelength of characteristic X-ray K _α1 output from the cathode β: half width of peak (radian)
θ: Reflection angle of spectrum

The X-ray diffraction spectrum of hard carbon can be measured by, for example, an X-ray diffraction apparatus “XRD-7000” manufactured by Shimadzu Corporation. The method for measuring the average spacing in hard carbon is as follows.

From the spectrum obtained from the X-ray diffraction measurement of hard carbon, the average interplanar spacing d can be calculated from the following Bragg equation as follows.

λ = 2d _hkl sin θ (Bragg equation) (d _hkl = d ₀₀₂ )
λ: wavelength of characteristic X-ray K _α1 output from the cathode θ: reflection angle of spectrum

The carbon particles, which are hard carbon, have the property that lithium ions can be occluded and released over the entire surface. Therefore, the carbon material containing the carbon particles of hard carbon having a surface area per unit volume in the above-described range exhibits a remarkable effect of being excellent in the ability to occlude and release lithium ions by increasing the surface area. That is, the carbon material of the present invention containing carbon particles that are hard carbon sufficiently enjoys the action produced by the configuration of the present invention and exhibits excellent effects.

In general, carbon particles, which are hard carbon, have a problem that lithium ion diffusibility (mobility) in the particles is lower than carbon particles that are graphite. In contrast, the carbon particles, which are hard carbon contained in the carbon material of the present invention, are finely divided to such an extent that the surface area per unit volume is sufficiently increased. can do. Also from this point of view, in the present invention, the carbon particles that are hard carbon have a remarkable improvement in the ability to occlude and release lithium ions.

From the viewpoint of sufficiently enjoying the effects obtained by including hard carbon in the carbon particles as described above, the carbon particles in the present invention may contain 90% by mass or more of hard carbon.

The raw material of the hard carbon is not particularly limited, and examples thereof include a resin material such as a thermosetting resin or a thermoplastic resin. The raw materials include petroleum-based tar or pitch produced as a by-product during ethylene production, coal tar produced during coal dry distillation, heavy component or pitch obtained by distilling off low-boiling components of coal tar, and tar obtained by coal liquefaction. Examples thereof include petroleum-based or coal-based materials such as pitch, and those obtained by crosslinking the above-described petroleum-based or coal-based materials. The hard carbon raw materials described above can be used alone or in combination of two or more. Also, plant materials such as coconut shells can be used as raw materials for hard carbon.

The thermosetting resin is not particularly limited, and examples thereof include phenolic resins such as novolac type phenolic resin and resol type phenolic resin, epoxy resins such as bisphenol type epoxy resin and novolac type epoxy resin, melamine resin, urea resin, and aniline. Examples thereof include resins, cyanate resins, furan resins, ketone resins, unsaturated polyester resins, and urethane resins. The carbon material may be a modified product obtained by modifying these materials with various components.

The thermoplastic resin is not particularly limited. For example, polyethylene, polystyrene, polyacrylonitrile, acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene-styrene (ABS) resin, polypropylene, vinyl chloride, methacrylic resin, polyethylene terephthalate, Examples include polyamide, polycarbonate, polyacetal, polyphenylene ether, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyether sulfone, polyether ether ketone, polyether imide, polyamide imide, polyimide, and polyphthalamide.

In particular, a thermosetting resin is preferable as the main resin used for hard carbon. Thereby, the residual carbon rate of hard carbon can be raised more.

Among thermosetting resins, a resin selected from a novolak-type phenol resin, a resol-type phenol resin, a melamine resin, a furan resin, an aniline resin, or a modified product thereof is preferable as a resin that is a main component of hard carbon. Thereby, the freedom degree of design of a carbon material spreads and it can manufacture at low cost. Further, the stability during cycling and the input / output characteristics of a large current can be further improved.

Further, when a thermosetting resin is used, the curing agent can be used in combination. The said hardening | curing agent is not specifically limited, A well-known hardening | curing agent can be used. For example, in the case of a novolac type phenol resin, hexamethylenetetramine, resol type phenol resin, polyacetal, paraformaldehyde, or the like can be used as a curing agent. In the case of epoxy resins, use polyamine compounds such as aliphatic polyamines and aromatic polyamines, acid anhydrides, imidazole compounds, dicyandiamide, novolac-type phenol resins, bisphenol-type phenol resins, or resole-type phenol resins as curing agents. Can do.

In the case where nitrogen is contained in the carbon material, for example, one kind of hexamethylenetetramine, aliphatic polyamine, aromatic polyamine, dicyandiamide, amine compound, ammonium salt nitrate, or nitro compound is used together with the above-described carbon material raw material. Two or more types may be used in combination.

When phosphorus is contained in the carbon material, for example, a phosphorus-containing compound such as phosphoric acid, phosphate, phosphorus pentoxide, or phosphate ester may be blended together with the above-described carbon material raw material. As the above-mentioned phosphate ester, Daihachi Chemical Industry which is a phosphate triester such as triphenyl phosphate, cresyl diphenyl phosphate or cresyl di 2,6-xylenyl phosphate, or a commercially available aromatic condensed phosphate ester Mention may be made of condensed phosphate esters such as a flame retardant “trade name: PX-200” manufactured by Co., Ltd.

Next, the aspect in which the carbon particles in the carbon material of the present invention contain graphite will be described.
Graphite is one of the allotropes of carbon, and is a hexagonal hexagonal plate crystal material that forms a layered lattice made of layers of six-carbon rings. It has a so-called graphene structure. The graphite includes natural graphite and artificial graphite.
Graphite has a desirable property that there is little voltage change from the beginning of discharge to the end of discharge, and can maintain a stable high voltage until the end of discharge. Part or all of the carbon particles contained in the carbon material of the present invention may be composed of graphite.

The carbon particles in the carbon material of the present invention may contain hard carbon and graphite from the viewpoint of providing a well-balanced carbon material by utilizing the advantages of hard carbon and graphite.
The aspect of the present invention that includes both hard carbon and graphite as carbon particles is the case where the hard carbon particles and the graphite particles are individually observed in the microscopic observation, and the two are fused or bound, and apparently , When observed integrally.

The content ratio of hard carbon and graphite in the carbon material of the present invention is not particularly limited. However, from the viewpoint of satisfactorily solving the intended problem of the present invention by containing a large amount of hard carbon having a surface area per unit volume within a predetermined range, the following ratio ranges are preferable. That is, in the carbon material of the present invention including hard carbon and graphite, the mass ratio of both in the carbon material is in the range of hard carbon: graphite = 51 mass%: 49 mass% to 95 mass%: 5 mass%. Preferably there is.

Next, an example of the carbon material manufacturing method of the present invention will be described. Here, an embodiment in which the carbon contained in the carbon material is hard carbon will be described as an example, but this does not limit the present invention.

In order to produce the carbon material of the present invention, first, a raw material or a composition containing the raw material is prepared. The said raw material is 1 type (s) or 2 or more types selected from resin or plant material etc. which become the raw material of the hard carbon mentioned above. Moreover, the said composition contains the said raw material and arbitrary additives. In the following description, a method for producing a carbon material using the composition will be described in detail. However, the curing treatment, the pulverization treatment of the cured product, and the carbonization treatment described later are substantially performed using only raw materials. The same applies to the case of manufacturing.

The apparatus for preparing the composition is not particularly limited. For example, when the raw material and the additive are melt-mixed, a kneading apparatus such as a kneading roll, a uniaxial or biaxial kneader can be used. In addition, when the raw materials and additives are dissolved and mixed, a mixing device such as a Henschel mixer or a disperser can be used, and when performing pulverization and mixing, for example, a device such as a hammer mill or a jet mill can be used. Can do.
In addition, in order to impart desired characteristics to the carbon material to be produced, metals, pigments, lubricants, antistatic agents are prepared during the preparation of the above composition or after the curing treatment described later and before the carbonization treatment. Additives such as additives and antioxidants may be further added.

Next, the composition prepared as described above is cured. By performing the curing treatment, the raw materials contained in the composition can be cured and infusible. As a result, even when the resin composition is pulverized before the carbonization treatment, the crushed composition or resin is prevented from being re-fused during the carbonization treatment, and carbon particles having a desired particle diameter are efficiently obtained. Obtainable.

Although the conditions for the curing treatment are not particularly limited, for example, heating can be performed for 1 hour or more and 10 hours or less at a temperature (for example, 200 ° C. or more and 600 ° C. or less) at which a raw material contained in the composition can cause a curing reaction. The heating device used in the curing process is not particularly limited, and a large continuous furnace, a medium batch furnace, or a small furnace can be appropriately selected and used.

Next, a grinding process is performed. The pulverization treatment is generally performed after the above curing treatment and before the carbonization treatment described later. However, in the production of the carbon material of the present invention, the curing treatment is omitted, and after the preparation of the raw material or the composition, the carbonization treatment is performed. A pulverization process can also be performed before.
By adjusting the pulverization conditions in the pulverization process, a carbon material containing carbon particles having a surface area per unit volume within a predetermined range specified by the present invention can be produced. The pulverization conditions may be appropriately changed depending on the type of raw materials used, and are not limited to the predetermined conditions. Moreover, the carbon material containing the carbon particle of the mean square radius demonstrated as a preferable aspect of the carbon material of this invention by a predetermined | prescribed range can be easily manufactured by performing a grinding | pulverization process.

The pulverization method in the pulverization process is not particularly limited, and for example, an arbitrary pulverizer can be used. Examples of the pulverizer include impact mills such as ball mills, vibrating ball mills, rod mills, and bead mills, and airflow pulverizers such as cyclone mills, jet mills, and dry air pulverizers. It is not limited. In the pulverization treatment, these devices may be used alone or in combination of two or more, or may be used by pulverizing a plurality of times with one device. In the pulverization treatment, in addition to these apparatuses, classification may be appropriately performed using a sieve or a pulverization apparatus having a classification function may be used.

Next, the carbonization process will be described.
In order to produce a carbon material containing hard carbon, the composition or a cured product of the composition is carbonized. The carbonization treatment may be performed once or twice or more. For example, the pre-carbonization treatment may be performed at a relatively low temperature (for example, 200 ° C. or more and less than 800 ° C.), and then the carbonization treatment may be performed at a high temperature (for example, 800 ° C. or more and 3000 ° C. or less). Moreover, you may perform a pre carbonization process and the hardening process mentioned above simultaneously.

The conditions for the carbonization treatment are not particularly limited. For example, the temperature is raised from normal temperature to a temperature increase rate in the range of 1 ° C./hour to 200 ° C./hour, and the temperature in the range of 800 ° C. to 3000 ° C. is set for 0.1 hour. It can be carried out by holding for not less than 50 hours, preferably not less than 0.5 hours and not more than 10 hours. The atmosphere during the carbonization treatment is not particularly limited. For example, an inert gas atmosphere containing an inert gas such as nitrogen or helium gas, an inert gas atmosphere containing a small amount of oxygen in the inert gas atmosphere, or a reducing gas such as hydrogen. It is preferable to employ a reducing gas atmosphere mainly containing. By selecting such a gas atmosphere, it is possible to suppress thermal decomposition (oxidative decomposition) of raw materials such as a resin and obtain a carbon material containing desired carbon particles.

The carbon material of the present invention containing hard carbon carbon particles can be produced by the above production method. As a modification, the carbon material of the present invention containing hard carbon and graphite can be produced by preliminarily blending graphite with a composition as a raw material. Further, as a different modification, the carbon material of the present invention containing hard carbon and graphite is mixed with the carbon material containing hard carbon carbon particles obtained as described above and mixed with graphite pulverized to an appropriate particle size. It can also be manufactured.

Hereinafter, the negative electrode active material of the present invention including the carbon material of the present invention, the secondary battery negative electrode of the present invention including the negative electrode active material layer including the negative electrode active material, and the present invention including the secondary battery negative electrode. The secondary battery will be described.

<Active material for negative electrode>
The active material for secondary battery negative electrode of the present invention contains the carbon material for secondary battery negative electrode of the present invention described above.
By including the carbon material of the present invention that exhibits the above-described electrical resistance suppressing effect, the negative electrode active material of the present invention suppresses a significant increase in electrical resistance in a low temperature environment of the negative electrode, and has excellent charge and discharge efficiency. Contribute to the demonstration of In the present invention, the negative electrode active material refers to a material that can occlude and release chemical species as a charge carrier in a secondary battery negative electrode. Examples of the chemical species include lithium ions or sodium ions in an alkali metal ion secondary battery.

Hereinafter, the negative electrode active material containing the carbon material of the present invention will be described.
The negative electrode active material is a substance that can occlude and release chemical species such as alkali metal ions (for example, lithium ions or sodium ions) in a secondary battery such as an alkali metal ion battery. The negative electrode active material described in this specification means a material containing a carbon material produced using the resin composition or the like of the present invention.

The negative electrode active material may be substantially composed of only the carbon material of the present invention, but may further include a material different from the carbon material. Examples of such materials include materials generally known as negative electrode materials such as silicon, silicon monoxide, and other graphite materials.

The particle size (average particle size) at 50% accumulation in the volume-based particle size distribution of the graphite material used is preferably 2 μm or more and 50 μm or less, more preferably 5 μm or more and 30 μm or less.

<Secondary battery negative electrode and secondary battery>
Hereinafter, the secondary battery negative electrode of the present invention and the secondary battery of the present invention including the secondary battery negative electrode will be described.

The secondary battery negative electrode of the present invention is a negative electrode current collector in which a secondary battery negative electrode active material layer including the above-described secondary battery negative electrode active material of the present invention and a secondary battery negative electrode active material layer are laminated. And is configured.
Moreover, the secondary battery of this invention is comprised including the secondary battery negative electrode of this invention mentioned above, an electrolysis layer, and a secondary battery positive electrode.

The negative electrode of the present invention is configured using the negative electrode active material of the present invention, thereby exhibiting an effect of suppressing electrical resistance in a low temperature environment. In addition, the secondary battery of the present invention including the negative electrode of the present invention reflects the above-described effects of the negative electrode, and can suppress an increase in battery resistance even under a low temperature environment, and can exhibit excellent input / output characteristics and cycle characteristics.

Examples of the secondary battery include, but are not limited to, alkali metal secondary batteries such as lithium ion secondary batteries and sodium ion secondary batteries. The secondary battery includes various types using different electrolytes such as a non-aqueous electrolyte secondary battery and a solid secondary battery. In the following description, a lithium ion secondary battery will be described as an example of a secondary battery.

Hereinafter, an example of a lithium ion secondary battery including the carbon material of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram showing an example of a lithium ion secondary battery 100 including the carbon material of the present invention.
As shown in FIG. 1, the lithium ion secondary battery 100 includes a negative electrode 10, a positive electrode 20, a separator 30, and an electrolytic layer 40.

As shown in FIG. 1, the negative electrode 10 includes a negative electrode active material layer 12 and a negative electrode current collector 14.
The negative electrode active material layer 12 contains the above-described carbon material (not shown) of the present invention.
The negative electrode current collector 14 is not particularly limited, and a current collector that can be used for the negative electrode can be appropriately selected and used. For example, a copper foil or a nickel foil can be used, but is not limited thereto.

The negative electrode 10 can be manufactured as follows, for example.
For 100 parts by mass of the negative electrode active material described above, generally known organic polymer binders (for example, fluoropolymers such as polyvinylidene fluoride and polytetrafluoroethylene, styrene-butadiene rubber, butyl rubber, 1 to 30 parts by mass of a rubbery polymer such as butadiene rubber) and an appropriate amount of a viscosity adjusting solvent (N-methyl-2-pyrrolidone, dimethylformamide, alcohol, water, etc.) or water. And kneading to prepare a negative electrode slurry.
Moreover, you may add a electrically conductive material further with respect to the active material for negative electrodes mentioned above as needed. As the conductive material, for example, any one of acetylene black, ketjen black, vapor grown carbon fiber, or a combination of two or more thereof can be used. Although the compounding quantity of a electrically conductive material is not specifically limited, For example, 2 mass parts or more and 10 mass parts or less are preferable with respect to 100 mass parts of negative electrode active materials, More preferably, they are 3 mass parts or more and 7 mass parts or less. Although it can be used outside these ranges, if the amount of the conductive agent is too large, the amount of the negative electrode active material present in the electrode may be reduced more than necessary, and the electric capacity of the negative electrode may be reduced. .

The obtained slurry can be formed into a sheet shape, a pellet shape, or the like by compression molding, roll molding, or the like, and the negative electrode active material layer 12 can be obtained. The negative electrode 10 can be obtained by laminating the negative electrode active material layer 12 and the negative electrode current collector 14 thus obtained.
Moreover, the negative electrode 10 can also be manufactured by apply | coating the obtained negative electrode slurry to the negative electrode collector 14, and drying.

The electrolytic layer 40 fills between the positive electrode 20 and the negative electrode 10, and is a layer in which lithium ions move by charge / discharge.

Electrolytic layer 40 is not particularly limited, and can be generally formed by filling a known electrolyte. As the electrolyte, for example, a nonaqueous electrolytic solution in which a lithium salt serving as an electrolyte is dissolved in a nonaqueous solvent is used.

Examples of the non-aqueous solvent include cyclic esters such as propylene carbonate, ethylene carbonate, and γ-butyrolactone; chain esters such as dimethyl carbonate and diethyl carbonate; chain ethers such as dimethoxyethane; or a mixture thereof. Can be used.

Is not particularly limited as electrolytes generally be a known electrolyte, for example, it may be used lithium metal salt such as LiClO _4, LiPF _6.

In the case of a secondary battery other than the non-aqueous electrolyte secondary battery, the electrolytic layer 40 has a gel polymer electrolyte containing a polymer material such as polyethylene oxide or polyacrylonitrile, or a solid such as zirconia. The aspect which has electrolyte is mentioned.

The separator 30 is not particularly limited, and can be a member that is permeable to chemical species such as lithium ions, and a generally known separator can be used. For example, a porous film constituted by using polyethylene or polypropylene, Nonwoven fabrics can be mentioned.

As illustrated in FIG. 1, the positive electrode 20 includes a positive electrode active material layer 22 and a positive electrode current collector 24.
It does not specifically limit as the positive electrode active material layer 22, Generally, it can form with a well-known positive electrode active material. Is not particularly limited as the cathode active material include lithium cobalt oxide (LiCoO _2), lithium nickel oxide (LiNiO _2), composite oxides such as lithium manganese oxide (LiMn ₂ O _4); polyaniline, polypyrrole, etc. Or the like can be used.
The positive electrode active material contains an organic polymer binder and a conductive material in the same manner as the negative electrode active material described above. The blending amounts of the organic polymer binder and the conductive material in the positive electrode active material are not particularly limited, and may be the same as the negative electrode active material or may be blended in an amount different from the negative electrode active material.

The positive electrode current collector 24 is not particularly limited, and generally known positive electrode current collectors can be used. For example, aluminum foil, stainless steel foil, titanium foil, nickel foil, copper foil, and the like can be used. The positive electrode 20 in the present embodiment can be manufactured by a generally known positive electrode manufacturing method.

The lithium ion secondary battery 100 has been described above as an example, but the above does not exclude that the carbon material of the present invention, the negative electrode active material, and the negative electrode are used for secondary batteries other than lithium ion secondary batteries. Absent. The carbon material of the present invention can also be used for a secondary battery using alkali ions other than lithium ions such as sodium ions as chemical species. At this time, each alkaline ion secondary battery may be configured using a member similar to the member used for the lithium ion secondary battery 100 described above, or may be configured using a different member. For example, as the negative electrode current collector in the sodium ion secondary battery, an aluminum foil can be selected in addition to the negative electrode current collector exemplified above.

The secondary battery can be formed by appropriately disposing the negative electrode 10, the positive electrode 20, the separator 30, and the electrolytic layer 40 in a case suitable for the secondary battery. The type of the secondary battery is not specified, and examples thereof include a cylindrical type, a coin type, a square type, and a film type.

As mentioned above, although embodiment of this invention was described, these are illustrations of this invention and various structures other than the above are also employable. For example, in FIG. 1, an example in which the negative electrode active material layer 12 is formed on one surface of the negative electrode current collector 14 and the positive electrode active material layer 22 is formed on one surface of the positive electrode current collector 24. Indicated. As a modification, the negative electrode active material layer 12 is formed on both surfaces of the negative electrode current collector 14, the positive electrode active material layer 22 is formed on both surfaces of the positive electrode current collector 24, and these are interposed via the separator 30 and the electrolytic layer 40. You may comprise a secondary battery by making it oppose.
Further, the present invention is not limited to the above-described embodiment, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.

Hereinafter, examples and comparative examples of the present invention will be described. However, the present invention is not limited to the following examples and comparative examples. In Examples, “part” indicates “part by mass”, and “%” indicates “% by mass”.

<Preparation of carbon material for secondary battery negative electrode>
A carbon material for a secondary battery negative electrode (hereinafter, also referred to as a carbon material) used in Examples or Comparative Examples was prepared as follows. First, a resin (carbon material raw material) blended in a resin composition used for producing a carbon material was prepared as follows.
(Synthesis of aniline resin)
100 parts of aniline, 697 parts of 37% formaldehyde aqueous solution, and 2 parts of oxalic acid were placed in a three-necked flask equipped with a stirrer and a condenser, reacted at 100 ° C. for 3 hours, and dehydrated to obtain 110 parts of aniline resin.
(Synthesis of novolac type phenolic resin)
100 parts of phenol, 64.5 parts of 37% formaldehyde aqueous solution, and 3 parts of oxalic acid were placed in a three-necked flask equipped with a stirrer and a condenser, reacted at 100 ° C. for 3 hours, dehydrated at elevated temperature, and novolak-type phenolic resin 90 Got a part.

Using the aniline resin, novolac-type phenolic resin, or coconut shell obtained as described above, baking treatment was performed under the first baking conditions to obtain a primary carbide.
(First firing condition)
Example 1: A resin composition obtained by blending 10 parts of hexamethylenetetramine with 100 parts of the above aniline resin and pulverizing and mixing with a vibration ball mill was used at room temperature to 100 under a nitrogen atmosphere using a large continuous furnace. The temperature was raised at a rate of temperature rise of ℃ / hour, and after reaching 550 ° C., the fired state was maintained for 1.5 hours to carry out the curing treatment.
Example 2: The curing process was performed under the same first firing conditions as in Example 1.
Example 3 To 100 parts of the novolak type phenol resin, 10 parts of triphenyl phosphate (manufactured by Daihachi Chemical Industry Co., Ltd., trade name: TPP) and 3 parts of hexamethylenetetramine were blended, and a vibration ball mill was used. The resin composition obtained by pulverization and mixing was heated from room temperature to a temperature increase rate of 100 ° C./hour in a nitrogen atmosphere using a medium-sized batch furnace. After reaching 550 ° C., the fired state was maintained for 1.5 hours. It was held and cured.
Example 4: A curing treatment was performed under the same first firing conditions as in Example 3.
Example 5: After performing infusibilization treatment on coconut shells, the temperature was increased from room temperature to 100 ° C./hour in a nitrogen atmosphere using a medium-sized batch furnace, and after reaching 550 ° C., the firing state was 1 Curing treatment was carried out for 5 hours.
Comparative Example 1: The curing treatment was performed under the same first firing conditions as in Example 1.
Comparative Example 2: The curing process was performed under the same first firing conditions as in Example 1.
Comparative Example 3: The curing process was performed under the same first firing conditions as in Example 3.
Comparative Example 4: The curing treatment was performed under the same first firing conditions as in Example 3.
Comparative Example 5: Curing treatment was performed under the same first firing conditions as in Example 3.
Comparative Example 6: The curing process was performed under the same first firing conditions as in Example 3.
Comparative Example 7: The curing process was performed under the same first firing conditions as in Example 5.

The primary carbide obtained as described above was pulverized under the following conditions to prepare a pulverized product.
(Crushing conditions)
Example 1: Using an ACM pulverizer, pulverization was performed under the conditions of a powder supply rate of 1000 g / min, an air volume of 20 m ³ / min, a pulverization rotor rotation speed of 6500 rpm, and a classification rotor rotation speed of 4500 rpm, and further pulverization using a jet mill. A pulverized intermediate obtained by pulverizing under the conditions of a supply amount of 80 g / min, a pulverization pressure of 0.8 MPa, and a repetition rate of 2 Pass was obtained by removing coarse particles through a sieve having an opening of 75 μm.
Example 2: Using an ACM pulverizer, pulverization was performed under the conditions of a powder supply rate of 1000 g / min, an air volume of 20 m ³ / min, a pulverization rotor rotation speed of 6500 rpm, and a classification rotor rotation speed of 4500 rpm, and further pulverization using a jet mill. A pulverized intermediate obtained by pulverizing under the conditions of a supply amount of 80 g / min, a pulverization pressure of 0.8 MPa, and a repetition rate of 2 Pass was obtained by removing coarse particles through a sieve having an opening of 75 μm.
Example 3: Using a cyclone mill crusher, obtained by crushing under the conditions of powder feed rate 50 g / min, air flow rate 0.5 m ³ / min, first crushing impeller rotation speed 15000 rpm, second crushing impeller rotation speed 15000 rpm The pulverized intermediate was passed through a sieve having an opening of 75 μm to obtain a pulverized product from which coarse particles were removed.
Example 4: Coarse particles obtained by placing powder in a container containing 5000 g of φ15 mm alumina balls and 900 g of φ10 mm alumina balls in a ball mill pulverizer and passing through a sieve having an opening of 75 μm are coarse particles. A pulverized product from which was removed was obtained.
Example 5: Using an ACM pulverizer, pulverization was performed under the conditions of a powder supply rate of 1000 g / min, an air volume of 20 m ³ / min, a pulverization rotor rotation speed of 6500 rpm, and a classification rotor rotation speed of 4500 rpm, and further pulverization using a jet mill. A pulverized intermediate obtained by pulverizing under the conditions of a supply amount of 80 g / min, a pulverization pressure of 0.8 MPa, and a repetition rate of 2 Pass was obtained by removing coarse particles through a sieve having an opening of 75 μm.
Comparative Example 1: A pulverized intermediate obtained by pulverization using an ACM pulverizer under the conditions of a powder supply rate of 1000 g / min, an air volume of 20 m ³ / min, a pulverization rotor rotation speed of 6500 rpm, and a classification rotor rotation speed of 4500 rpm, A pulverized product from which coarse particles were removed was obtained through a sieve having an opening of 75 μm.
Comparative Example 2: A pulverized intermediate obtained by pulverization using an ACM pulverizer under the conditions of a powder supply rate of 1000 g / min, an air volume of 20 m ³ / min, a pulverization rotor rotation speed of 6500 rpm, and a classification rotor rotation speed of 4500 rpm, A pulverized product from which coarse particles were removed was obtained through a sieve having an opening of 75 μm.
Comparative Example 3: Obtained by pulverization using a cyclone mill pulverizer under the conditions of a powder supply rate of 30 g / min, an air flow rate of 0.8 m ³ / min, a first pulverization impeller rotation speed of 13000 rpm, and a second pulverization impeller rotation speed of 13000 rpm. The pulverized intermediate was passed through a sieve having an opening of 75 μm to obtain a pulverized product from which coarse particles were removed.
Comparative Example 4: Obtained by pulverization using a cyclone mill pulverizer under the conditions of a powder supply rate of 30 g / min, an air volume of 0.8 m ³ / min, a first pulverization impeller rotation speed of 13000 rpm, and a second pulverization impeller rotation speed of 13000 rpm. The pulverized intermediate was passed through a sieve having an opening of 75 μm to obtain a pulverized product from which coarse particles were removed.
Comparative Example 5: obtained by pulverization using a cyclone mill pulverizer under the conditions of a powder supply rate of 30 g / min, an air volume of 0.8 m ³ / min, a first pulverization impeller rotation speed of 13000 rpm, and a second pulverization impeller rotation speed of 13000 rpm. The pulverized intermediate was passed through a sieve having an opening of 75 μm to obtain a pulverized product from which coarse particles were removed.
Comparative Example 6: obtained by pulverization using a cyclone mill pulverizer under the conditions of a powder supply rate of 30 g / min, an air volume of 0.8 m ³ / min, a first pulverization impeller rotation speed of 13000 rpm, and a second pulverization impeller rotation speed of 13000 rpm. The pulverized intermediate was passed through a sieve having an opening of 75 μm to obtain a pulverized product from which coarse particles were removed.
Comparative Example 7: Using an ACM pulverizer, pulverization was performed under the conditions of a powder supply rate of 1000 g / min, an air volume of 20 m ³ / min, a pulverizing rotor rotational speed of 6500 rpm, and a classification rotor rotational speed of 4500 rpm, and further using a cyclone classifier The pulverized intermediate from which the coarse particles were removed was passed through a sieve having an opening of 75 μm to obtain a pulverized product from which coarse particles had been removed.

The pulverization apparatus used in the above pulverization process is as follows.
As the ACM pulverizer, an impact classifier built-in pulverizer (ACM pulverizer (ACM30HC), manufactured by Hosokawa Micron Corporation) was used.
As the jet mill pulverizer, a nano jet mizer (NJ-300 type, manufactured by Aisin Nano Technologies) was used.
As the cyclone mill, a dry pulverizer (150BMW type cyclone mill, manufactured by Shizuoka Plant) was used.
As the ball mill crusher, a rotary ball mill (1-stage type-B, manufactured by Irie Shokai) was used.

The pulverized material obtained as described above was baked under the following calcination conditions and carbonized to obtain a carbon material.
(Baking conditions)
Example 1: In a large continuous furnace, firing was performed at room temperature to 100 ° C / hour in a nitrogen atmosphere, and after reaching 1200 ° C, the firing state was maintained for 2 hours for carbonization treatment. 1 carbon material was obtained.
Example 2: Carbonization treatment was performed under the same firing conditions as in Example 1 to obtain a carbon material of Example 2.
Example 3 Carbonization was performed under the same firing conditions as in Example 1 except that the large continuous furnace was changed to the small continuous furnace, and the carbon material of Example 3 was obtained.
Example 4: Carbonization treatment was performed under the same firing conditions as in Example 3 to obtain a carbon material of Example 4.
Example 5 Carbonization treatment was performed under the same firing conditions as in Example 3 to obtain a carbon material of Example 5.
Comparative Example 1: Carbonization was performed under the same firing conditions as in Example 1 to obtain a carbon material of Comparative Example 1.
Comparative Example 2: Carbonization was performed under the same firing conditions as in Example 1 to obtain a carbon material of Comparative Example 2.
Comparative Example 3: Carbonization was performed under the same firing conditions as in Example 3 to obtain a carbon material of Comparative Example 3.
Comparative Example 4: Carbonization was performed under the same firing conditions as in Example 3 to obtain a carbon material of Comparative Example 4.
Comparative Example 5: Carbonization was performed under the same firing conditions as in Example 3 to obtain a carbon material of Comparative Example 5.
Comparative Example 6: Carbonization was performed under the same firing conditions as in Example 3 to obtain a carbon material of Comparative Example 6.
Comparative Example 7: Carbonization was performed under the same firing conditions as in Example 3 to obtain a carbon material of Comparative Example 7.

<Manufacture of half-cell lithium ion secondary batteries>
In order to evaluate the initial charge / discharge characteristics of the carbon materials of Examples and Comparative Examples obtained as described above, half-cell lithium ion secondary batteries were prepared. For 100 parts of the carbon material obtained in each example and each comparative example, 1.5 parts of carboxymethyl cellulose (Daicel Finechem Co., Ltd., CMC Daicel 2200), styrene-butadiene rubber (manufactured by JSR Corporation, TRD-2001) ) 1.5 parts, 2 parts of acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) and 100 parts of distilled water were added and stirred and mixed with a rotating / revolving mixer to prepare a slurry-like negative electrode mixture.

The negative electrode mixture was applied to one side of a 14 μm thick copper foil (Furukawa Electric Co., Ltd., NC-WS), followed by preliminary drying in air at 60 ° C. for 2 hours, and then at 120 ° C. for 15 hours. Vacuum dried. After vacuum drying, the electrode was pressure-formed by a roll press. This was cut into a disk shape having a diameter of 13 mm to produce a negative electrode. The thickness of the negative electrode material layer was 50 μm.

A 1 mm thick lithium metal was prepared as a working electrode.

As the separator, a porous polyolefin film (manufactured by Celgard, trade name: Celgard 2400) was used.

Lithium hexafluorophosphate (LiPF) at a rate of 1 mol / dm ³ in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 using the above negative electrode, working electrode, and separator. ₆ ) was added to produce a 2032 type coin cell half-cell lithium ion secondary battery in a glove box under an argon atmosphere.

<Creation of full-cell lithium-ion secondary battery>
In order to evaluate the battery characteristics in the low temperature environment of the carbon materials of Examples and Comparative Examples obtained as described above, full-cell lithium ion secondary batteries were prepared.
The production method was the same as that in the production method of the half-cell lithium ion secondary battery described above except that the working electrode was changed to the positive electrode.
A positive electrode made of LiCoO ₂ as an active material and coated on a current collector was used, and a single layer sheet using an aluminum foil as a positive electrode current collector (trade name; Pioxel C, manufactured by Pionics Corporation). −100) formed into a disk shape with a diameter of 12 mm was used.

Evaluation was performed as follows using each of the examples, the carbon materials of the comparative examples, and the lithium ion secondary batteries prepared using the carbon materials of the examples and the comparative examples.

[Measurement of true specific gravity]
About the carbon material of each Example and each comparative example which were obtained as mentioned above, true specific gravity was measured with the true specific gravity measuring method using butanol. The measurement results are shown in Table 1.

[Measurement of surface area]
Using a particle size distribution measuring device (particle size distribution measuring device LA-920, manufactured by Horiba, Ltd.), the particle size distribution on the basis of the number of carbon materials of each example and each comparative example was measured by the following procedure.
About 20 mg of the carbon material obtained as described above and each comparative example, about 1 ml of surfactant (Tween 20, manufactured by Kishida Chemical Co., Ltd.) diluted to about 1 wt%, and about 5 ml of distilled water are put in one plastic container. Then, the mixture was dispersed by applying ultrasonic waves while mixing with a poly dropper for about 1 minute in an ultrasonic cleaner to obtain a dispersion. The particle size distribution of each dispersion obtained as described above was measured at the setting of the relative refractive index of 1.5 using the particle size distribution measuring apparatus described above.
Using the data obtained by the particle size distribution measurement, the surface area per unit volume was calculated by the above formula (1). The calculated values are shown in Table 1.

[Calculation of mean square radius]
Using the data obtained by the particle size distribution measurement described above, the mean square radius was calculated by the above equation (2). The calculated values are shown in Table 1.

[Evaluation of initial charge / discharge characteristics]
Battery characteristics were evaluated as follows using a half-cell lithium ion secondary battery prepared as described above using the carbon material of each Example or each Comparative Example.
Constant current charging was performed at a measurement temperature of 25 ° C. and a current density during charging of 25 mA / g. When the potential reached 0 V, constant voltage charging was performed while maintaining 0 V, and the current density was 2.5 mA / g. The amount of electricity charged until g was taken as the initial charge capacity.
Next, constant current discharge was performed at a current density of 25 mA / g during discharge, and the amount of electricity when the potential reached 2.5 V was defined as the initial discharge capacity.
As shown in the following mathematical formula (3), the initial charge / discharge efficiency was calculated by multiplying the value obtained by dividing the initial discharge capacity by the initial charge capacity by 100. The results of the first charge / discharge characteristic evaluation are shown in Table 1.
[Equation 3]
Initial charge / discharge efficiency (%) = (initial discharge capacity (mAh / g) / initial charge capacity (mAh / g)) × 100 (3)
In the charge / discharge characteristic evaluation, “charging” refers to moving lithium ions from a positive electrode to a negative electrode formed using a carbon material by applying a voltage. “Discharge” refers to a phenomenon in which lithium ions move from a negative electrode formed using a carbon material to a positive electrode.
Table 1 shows the initial discharge capacity and the initial charge / discharge efficiency obtained above.

[Low temperature environment test]
Using the full cell type lithium ion secondary battery produced as described above, the measurement was performed as follows.
Constant current charging is performed at a measurement temperature of 25 ° C. and a current density during charging of 25 mA / g. When the potential reaches 4.2 V, constant voltage charging is performed while holding 4.2 V, and the current density is The battery was charged until it reached 2.5 mA / g, and then a constant current discharge was performed with the current density at the time of discharge being 25 mA / g, and the battery was discharged until the potential reached 2.5 V. Furthermore, the battery was charged and discharged under the same conditions, and a total of 5 cycles of charging and discharging were performed to perform an aging treatment.
After the aging treatment, each lithium ion secondary battery is charged to 4.2 V at a constant current of 0.2 C in a temperature environment of 25 ° C., and then the current value is attenuated to 0.02 C at a constant voltage of 4.2 V. Charged until Next, the battery was discharged at a constant current of 0.2 C, adjusted to 50% SOC (State of Charge), and left at 25 ° C. for 1 hour. Subsequently, each full cell type lithium ion secondary battery was allowed to stand for 1 hour in a temperature environment of −20 ° C., and the following “low temperature environment charge / discharge treatment” was performed for 3 cycles.
That is, the low temperature environmental discharge treatment is performed by placing a full-cell type lithium ion secondary battery in a temperature environment of −20 ° C., measuring a voltage when charged at a predetermined current value for 10 seconds, and then allowing to stand for 10 minutes. The voltage when discharged for 10 seconds at a predetermined current value is measured, and then left for 10 minutes. Specifically, the predetermined current value is 1 / 3C, 0.5C, and 1C in order from the first cycle to the third cycle. In the low-temperature environmental discharge treatment, the upper limit voltage was 4.2 V and the lower limit voltage was 2.5 V.
Here, “1C” means a current density at which discharge is completed in one hour.

Regarding the low temperature environmental discharge treatment, the horizontal axis represents the current value, the vertical axis represents the voltage after charging or discharging for 10 seconds, and the DC resistance during charging and discharging in the battery from the absolute value of the slope of the approximate straight line ( DC-IR) was determined. A low DC-IR means that the electrical resistance is small and the output characteristics are good.

As shown in Table 1, it was confirmed that in all Examples, the surface area per unit volume satisfied the predetermined range specified in the present invention. On the other hand, in any of the comparative examples, it was confirmed that the surface area per unit volume is out of the predetermined range.
In all the examples, the initial charge / discharge efficiency at 25 ° C. showed a high value of 84% or more, and the DC-IR during charging and discharging at −20 ° C. tended to be low.
For example, when Examples 1 and 2 are compared with Comparative Examples 1 and 2 using the same material as Examples 1 and 2, the DC-IR during charging and discharging in a low temperature environment is different due to the difference in surface area. There was a significant difference. That is, Examples 1 and 2 had a larger surface area and lower DC-IR during charging / discharging than Comparative Examples 1 and 2. The same tendency was confirmed in Examples 3 and 4 and Comparative Examples 3 to 6, and Example 5 and Comparative Example 7.
From the above results, in each example, the decrease in the resistance value in the low temperature environment is reduced by including the surface area within the predetermined range, and the good charge / discharge efficiency shown at 25 ° C. is significantly reflected even in the low temperature environment. It was suggested that

In addition, all of the mean square radii of the examples were included in the predetermined range specified by the present invention.

Also, in Examples 1 to 4, the true specific gravity was included in the predetermined range specified by the present invention, and the expected initial discharge capacity was shown.

[Supplement under rule 26 15.01.2016]

The above embodiment includes the following technical idea.
(1) A carbon material for a secondary battery negative electrode, comprising carbon particles having a surface area per unit volume determined from a particle size distribution on a number basis in a range of 10,000 cm ^{−1 to} 16000 cm ⁻¹ .
(2) The carbon material for a secondary battery negative electrode according to (1), wherein the carbon particles have an average square radius determined from the particle size distribution in a range of 1 μm ^{2 to} 4 μm ² .
(3) The carbon material for a secondary battery negative electrode according to (1) or (2), wherein the carbon particles have a true specific gravity in a range of 1.5 g / cm ³ or more and 1.7 g / cm ³ or less.
(4) From the above (1) to (4), the carbon particles include hard carbon having an average interplanar spacing d ₀₀₂ of (002) planes of 0.340 nm or more determined by an X-ray diffraction method using CuKα rays as a radiation source. The carbon material for secondary battery negative electrode as described in any one of 3).
(5) The carbon material according to (4), wherein the carbon particles include 90% by mass or more of the hard carbon.
(6) The carbon material for a secondary battery negative electrode according to (4) or (5), wherein the carbon particles include the hard carbon and graphite.
(7) A secondary battery negative electrode active material comprising the carbon material for a secondary battery negative electrode according to any one of (1) to (6) above.
(8) A secondary battery negative electrode active material layer comprising the secondary battery negative electrode active material described in (7) above, and a negative electrode current collector in which the secondary battery negative electrode active material layer is laminated. A secondary battery negative electrode comprising:
(9) A secondary battery comprising the secondary battery negative electrode described in (8) above, an electrolytic layer, and a secondary battery positive electrode.

DESCRIPTION OF SYMBOLS 10 ... Negative electrode 12 ... Active material layer 14 for negative electrodes ... Negative electrode collector 20 ... Positive electrode 22 ... Positive electrode active material layer 24 ... Positive electrode collector 30 ... Separator 40- ..Electrolytic layer 100 ... lithium ion secondary battery

Claims (9)

1. A carbon material for a secondary battery negative electrode, comprising carbon particles having a surface area per unit volume determined from a particle size distribution on a number basis within a range of 10,000 cm ^{-1 to} 16000 cm ^-1 .
2. 2. The carbon material for a secondary battery negative electrode according to claim 1, wherein the carbon particles have an average square radius determined from the particle size distribution in a range of 1 μm ^{2 to} 4 μm ² .
3. ^{3. The} carbon material for a secondary battery negative electrode according to claim 1, wherein the carbon particles have a true specific gravity in a range of 1.5 g / cm ³ or more and 1.7 g / cm ³ or less.
4. 4. The carbon particle according to claim 1, wherein the carbon particles include hard carbon having an average interplanar spacing d ₀₀₂ of (002) plane of 0.340 nm or more obtained by an X-ray diffraction method using CuKα rays as a radiation source. Carbon material for secondary battery negative electrode as described in claim | item.
5. The carbon material for a secondary battery negative electrode according to claim 4, wherein the carbon particles include 90% by mass or more of the hard carbon.
6. The carbon material for a secondary battery negative electrode according to claim 4 or 5, wherein the carbon particles include the hard carbon and graphite.
7. An active material for a secondary battery negative electrode comprising the carbon material for a secondary battery negative electrode according to any one of claims 1 to 6.
8. A secondary battery negative electrode active material layer comprising the secondary battery negative electrode active material according to claim 7 and a negative electrode current collector in which the secondary battery negative electrode active material layer is laminated. Secondary battery negative electrode.
9. A secondary battery comprising the secondary battery negative electrode according to claim 8, an electrolytic layer, and a secondary battery positive electrode.

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