JP2019036378A - Carbon material for secondary battery negative electrode, active material for secondary battery negative electrode, secondary battery negative electrode, and secondary battery - Google Patents

Abstract

To provide a carbon material for a secondary battery negative electrode capable of securing battery performance excellent in cycle characteristics during charge and discharge even when a secondary battery is used in a low temperature environment.SOLUTION: A carbon material for a secondary battery negative electrode (carbon material CM) includes a carbonaceous material HC in which an average interplanar spacing dof (002) plane determined by X-ray diffraction using CuKα ray as a radiation source is 0.340 nm or more and a carbon black CB with a DBP absorption capacity of 240 mL/100 g or more. An active material for a secondary battery negative electrode includes a carbon material for a secondary battery negative electrode, and the secondary battery negative electrode includes an active material layer for a secondary battery negative electrode containing the above-described active material for the secondary battery negative electrode and a current collector for a negative electrode. The secondary battery includes the above-described secondary battery negative electrode, an electrolyte solution layer, a separator, and a positive electrode.SELECTED DRAWING: Figure 1

Description

  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.

  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 as an electrolyte and a solid battery using a solid electrolyte have been studied. In the secondary battery, charging and discharging are repeated as a chemical species such as lithium ion serving as a charge carrier moves between the positive electrode active material layer and the negative electrode active material layer.

  In such secondary batteries, the negative electrode has an electrode active material layer, and a carbon material is widely used as an electrode active material constituting the electrode active material layer. The electrode active material layer allows the secondary battery to be charged and discharged by occluding chemical species between layers of the carbon material having a layer structure and releasing the chemical species stored from the interlayer.

In Patent Document 1 below, as a negative electrode active material layer in a secondary battery, carbon black satisfying a predetermined condition, a composite metal oxide such as LiFePO ₄ , and a binder resin such as polyvinylidene fluoride are mixed. It is described that it is used.

JP 2014-241279 A

  In recent years, applications of secondary batteries have been expanded, and there is a demand for using them even in a low temperature environment such as below freezing point, particularly −10 ° C. or lower, more noticeably −20 ° C. or lower. However, according to the study by the present inventors, when a secondary battery is used in a low temperature environment, the cycle characteristics at the time of charging and discharging are lower than when used in a room temperature environment, and the secondary battery is repeatedly used. It has been found that it may be difficult to use.

  The present invention has been made in view of the above problems, and provides a carbon material for a secondary battery negative electrode that can ensure battery performance with excellent cycle characteristics during charge and discharge even when the secondary battery is used in a low temperature environment. To do. The present invention also provides an active material for a secondary battery negative electrode produced by including the carbon material for a secondary battery negative electrode, a secondary battery negative electrode configured using the active material for a secondary battery negative electrode, and the secondary battery negative electrode. A secondary battery including a secondary battery negative electrode is provided.

The carbon material for secondary battery negative electrode of the present invention includes a carbonaceous material having a (002) plane average layer spacing d ₀₀₂ of 0.340 nm or more obtained by X-ray diffraction using CuKα rays as a radiation source, and DBP And carbon black having an absorption amount of 240 mL / 100 g or more.

  Moreover, the active material for secondary battery negative electrodes of this invention contains said carbon material for secondary battery negative electrodes.

  Further, the secondary battery negative electrode of the present invention has a secondary battery negative electrode active material layer containing the above-mentioned secondary battery negative electrode active material and the secondary battery negative electrode active material layer laminated on at least a part of the surface. And a negative electrode current collector.

  Moreover, the secondary battery of this invention is equipped with said secondary battery negative electrode, electrolyte solution layer, a separator, and a positive electrode.

  ADVANTAGE OF THE INVENTION According to this invention, the carbon material for secondary battery negative electrodes which can make the cycling characteristics at the time of charging / discharging of a secondary battery favorable in a low temperature environment, the active material for secondary battery negative electrodes, and a secondary battery negative electrode are provided. In addition, a secondary battery having good cycle characteristics during charging and discharging even in a low temperature environment is provided.

It is a schematic diagram explaining the liquid retention mechanism of the electrolyte solution by carbon black. 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.

  As a result of examining the electrical characteristics of the secondary battery negative electrode in a low temperature environment, the present inventors have found that the conventional secondary battery negative electrode has an electrolyte supplied to the negative electrode active material at the time of charging as compared to a normal temperature environment. It was speculated that the battery characteristics could be deteriorated due to shortage. That is, in a secondary battery negative electrode used under a freezing temperature, particularly in a low temperature environment of −10 ° C. or lower, particularly −20 ° C. or lower, the viscosity of the electrolytic solution increases and the fluidity decreases, and the negative electrode is supplied to the negative electrode active material. Insufficient amount of electrolyte is produced. For this reason, it is speculated that under low-temperature environments, the operation of chemical species such as lithium ions moving between the electrolyte and the negative electrode active material becomes dull, and the absorption and release of chemical species with respect to the negative electrode active material become inactive. It was. The present inventors have come to the idea that by improving the supply of the electrolyte to the negative electrode active material, it is possible to occlude and release chemical species in a low temperature environment. More specifically, the present inventors blend carbon black having a predetermined characteristic having liquid retention properties with respect to hard carbon in which finer pores are developed than the graphite material. Thus, the present invention has been completed based on the technical idea that the above problem can be solved.

  Hereinafter, a secondary battery negative electrode carbon material (hereinafter also referred to as a carbon material), a secondary battery negative electrode active material (hereinafter also referred to as a negative electrode active material), and a secondary battery according to embodiments of the present invention. A negative electrode (hereinafter sometimes referred to as a negative electrode) and a secondary battery will be described.

The carbon material of the present embodiment is a carbonaceous negative electrode material used for an alkali metal ion secondary battery such as a lithium ion battery or a sodium ion battery. The carbon material of the present embodiment has an average layer surface spacing d ₀₀₂ (hereinafter, sometimes referred to as an average layer surface spacing d ₀₀₂ ) of (002) plane obtained by X-ray diffraction using CuKα rays as a radiation source is 0.340 nm. The carbonaceous material which is the above and carbon black whose DBP absorption amount is 240 mL / 100g or more are included.

  The carbon material 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.

<Carbonaceous material>
First, the carbonaceous material which comprises the carbon material of this embodiment is demonstrated. The d ₀₀₂ of the carbonaceous material obtained by the X-ray diffraction method using CuKα rays as a radiation source is 0.340 nm or more, preferably 0.350 nm or more, and more preferably 0.365 nm or more. When the average layer surface distance d ₀₀₂ is equal to or greater than the above lower limit value, destruction of the crystal structure due to repeated occlusion and release of alkali metal ions such as lithium can be suppressed, and charge / discharge cycle characteristics of the negative electrode can be improved.
The upper limit of the average layer surface distance d ₀₀₂ is not particularly limited, but is 0.400 nm or less, preferably 0.395 nm or less, more preferably 0.390 nm or less. An irreversible capacity in the negative electrode can be suppressed when the average interlayer spacing d ₀₀₂ is not more than the above upper limit value.
A carbonaceous material having such an average layer spacing d ₀₀₂ is generally called hard carbon or non-graphitizable carbon.

  In order to estimate the surface structure of the carbonaceous material, the water content may be measured by the Karl Fischer coulometric titration method as follows. Specifically, the carbonaceous material of the present embodiment is held for 120 hours under conditions of a temperature of 40 ° C. and a relative humidity of 90% RH, and then the carbonaceous material is heated for 1 hour under conditions of a temperature of 130 ° C. and a nitrogen atmosphere. Hold and pre-dry. Next, moisture generated by holding the carbonaceous material after the preliminary drying at 200 ° C. for 30 minutes is measured by the Karl Fischer coulometric titration method. At this time, the amount of water generated from the carbonaceous material after the preliminary drying is preferably 0.20% by mass or less, more preferably 0.15% with respect to 100% by mass of the carbonaceous material after the preliminary drying. The content is not more than mass%, particularly preferably not more than 0.10 mass%. Even when the carbonaceous material according to the present embodiment is stored in the atmosphere for a long period of time when the water content is not more than the above upper limit, deterioration of the carbonaceous material can be further suppressed. Although the minimum of said moisture content is not specifically limited, 0.01 mass% or more is preferable.

The carbonaceous material according to the present embodiment preferably has a crystallite size in the c-axis direction obtained by X-ray diffraction (hereinafter sometimes referred to as Lc ₍₀₀₂₎₎ of 0.8 nm or more and 5 nm or less. Yes, more preferably 3 nm or less, still more preferably 2 nm or less.

The carbonaceous material of the present embodiment preferably has a 50% cumulative particle size D ₅₀ (hereinafter sometimes referred to as an average particle size) in a volume-based cumulative distribution of 1 μm to 50 μm, preferably 2 μm to 30 μm. It is more preferable that Thereby, a high-density negative electrode can be produced.

Lc ₍₀₀₂₎ is calculated as follows. That is, it can be 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 / (βcosθ) (Scherrer equation)
Where Lc is the size of the crystallite, λ is the wavelength of the characteristic X-ray K _α1 output from the cathode, β is the half width (radian) of the peak, and θ is the reflection angle of the spectrum. The X-ray diffraction spectrum in the carbonaceous material can be measured by an X-ray diffractometer such as XRD-7000 manufactured by Shimadzu Corporation.

The measuring method of said average layer surface spacing in a carbonaceous material (hard carbon) is as follows. That is, from the spectrum calculated | required from the X-ray-diffraction measurement of carbonaceous material (hard carbon), average layer surface space _| interval _d002 is computable as follows from the following Bragg equations.

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

The carbonaceous material of the present embodiment preferably has a specific surface area of 0.5 m ² / g or more and 15 m ² / g or less, preferably 1 m ² / g or more and 8 m ² / g or less, according to the BET three-point method in nitrogen adsorption. Is more preferable. When the specific surface area by the BET three-point method in nitrogen adsorption is not more than the above upper limit value, irreversible reaction between the carbonaceous material and the electrolytic solution can be suppressed. Moreover, when the specific surface area by the BET three-point method in nitrogen adsorption is not less than the above lower limit value, appropriate permeability of the electrolytic solution to the carbonaceous material can be obtained.

  The specific surface area of the carbonaceous material can be calculated as follows. That is, the monolayer adsorption amount Wm is calculated by the following equation (1), the total surface area Total is calculated by the following equation (2), and the specific surface area S is obtained by the following equation (3).

1 / [W · {(Po / P) −1}] = {(C−1) / (Wm · C)} (P / Po) (1 / (Wm · C)) (1)
In the above formula (1), P is the pressure of the gas of the adsorbate in the adsorption equilibrium, Po is the saturated vapor pressure of the adsorbate at the adsorption temperature, W is the adsorption amount at the adsorption equilibrium pressure P, Wm is the monomolecular layer adsorption amount, C is a constant (C = exp {(E1-E2) RT}) regarding the magnitude of the interaction between the solid surface and the adsorbate, E1 is the heat of adsorption (kJ / mol) of the first layer, and E2 is the adsorbate. The heat of liquefaction at the measurement temperature (kJ / mol)].

Total = (Wm · N · Acs) M (2)
In the above formula (2), N is the Avogadro number, M is the molecular weight, and Acs is the adsorption cross section.

S = Total / w (3)
In formula (3), w is a sample weight (g).

  The raw material of the carbonaceous material (hard carbon) of the present embodiment is not particularly limited, and examples thereof include a resin material such as a thermosetting resin or a thermoplastic resin. The above raw materials are obtained by petroleum-based tar or pitch by-produced during ethylene production, coal tar produced during coal dry distillation, heavy components or pitch obtained by distilling off low-boiling components of coal tar, and coal liquefaction. Examples thereof include petroleum-based or coal-based materials such as tar or pitch, and those obtained by crosslinking the aforementioned 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. For example, 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, aniline resin, Examples include cyanate resin, furan resin, ketone resin, unsaturated polyester resin, and urethane resin. The carbon material may be a modified product obtained by modifying these materials with various components.
Moreover, when using a thermosetting resin, the hardening | curing agent can be used together. 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, or paraform 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.

  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, polyamide, Examples include polycarbonate, polyacetal, polyphenylene ether, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyamideimide, polyimide, and polyphthalamide.

  In order to produce a carbonaceous material containing hard carbon, the composition or a cured product of the composition may be carbonized. As conditions for the carbonization treatment, for example, the temperature is raised from room temperature to 1 ° C./hour or more and 200 ° C./hour or less, 800 ° C. or more and 1500 ° C. or less, 0.01 Pa or more and 101 kPa (1 atm) or less, 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.

  In order to obtain the carbonaceous material of the present embodiment, under an inert atmosphere such as nitrogen or helium gas, under a substantially inert atmosphere where a trace amount of oxygen is present in the inert gas, or under a reducing gas atmosphere It is preferable to perform carbonization treatment. By doing in this way, thermal decomposition (oxidative decomposition) of the resin material which is a raw material of a carbonaceous material can be suppressed, and a desired negative electrode material can be obtained.

A pre-carbonization treatment may be performed before the carbonization treatment. As conditions for the pre-carbonization treatment, for example, 200 ° C. or more and 1000 ° C. or less can be performed for 1 hour or more and 10 hours or less. Before the pre-carbonization treatment, the resin composition may be cured.
Although it does not specifically limit as a hardening processing method, For example, it can carry out by the method of giving the heat quantity which can perform hardening reaction to a resin composition, the method of thermosetting, the method of using a thermosetting resin and a hardening | curing agent together. When performing the carbonization treatment or the pre-carbonization treatment, a metal, a pigment, a lubricant, an antistatic agent, an antioxidant, or the like may be added to the resin composition to impart desired characteristics to the negative electrode material.

<Carbon black>
The carbon black which comprises the carbon material of this embodiment with said carbonaceous material (hard carbon) is demonstrated. The carbon black of the present embodiment is considered to play a role of holding an electrolytic solution as well as lowering electric resistance as a conductive auxiliary. Although the principle is not necessarily clear, as schematically shown in FIG. 1, the carbon black CB has a three-dimensional network structure, and it is considered that the electrolyte ES is taken in and retained therein. The carbon material CM is composed of a carbonaceous material HC and carbon black CB. In the carbon material CM, the carbon black CB is dispersed and compounded around the carbonaceous material HC, so that an electrolyte such as lithium ion (Li ⁺ ) existing around the carbon black CB is contained in the secondary battery. At the time of charging, it is considered that the carbonaceous material HC takes in the carbon black CB having a large liquid retention amount. For this reason, it is considered that the decrease of the electrolyte concentration on the surface of the carbonaceous material HC during charging is suppressed even at a low temperature.

  The DBP absorption amount of the carbon black of the present embodiment is 240 mL / 100 g or more, preferably 300 mL / 100 g or more. The DBP absorption amount of carbon black can be determined by measuring the oil absorption amount under the conditions for the non-compressed sample according to JIS K 6217-4. The carbon black sample is measured as 20 g. It has been clarified by the present inventors that the carbon black has a DBP absorption amount equal to or higher than the above lower limit value, so that stable conductive performance is imparted to the carbonaceous material.

The average particle diameter of the primary particles of carbon black is preferably 25 nm or less, and more preferably 20 nm or less. The average particle diameter of the primary particles of carbon black is measured using an image photographed with a transmission electron microscope (TEM) at a magnification of, for example, 10,000 times, and a large number (for example, 100) of primary particles are measured. It can be determined as an average value of the particle diameter. And the average particle diameter of the primary particle of carbon black is preferably 2.5% or less, and more preferably 1% or less, of the particle diameter D ₅₀ (average particle diameter) of the carbonaceous material described above.
By setting the carbon black CB to a value not more than the upper limit, the carbon black CB having a sufficiently small diameter forms a fine network structure with respect to the carbonaceous material HC and takes in the electrolyte ES well. It is thought that it is dispersed and adhered to the surface (see FIG. 1).

The bulk density of carbon black is preferably 0.04 or less, and more preferably 0.03 g / cm ³ or less. The bulk density of carbon black can be measured according to JIS K 6219.

  The volatile content of carbon black is preferably 0.20% or less. The ratio of volatile components of carbon black can be measured in accordance with JIS K 6221. When the volatile component contained in the carbon black is not more than the above upper limit value, the generation of gas is suppressed in the drying process when the negative electrode is produced, and a negative electrode with a smooth surface is obtained. Generation of gas due to a typical reaction is reduced, and deterioration of battery performance is suppressed.

  Examples of the carbon black of the present embodiment include thermal black, furnace black, lamp black, channel black, acetylene black and the like. As an example, a method for producing carbon black can be produced by incompletely burning acetylene gas and oxygen gas. If necessary, other gases may be added to cause incomplete combustion.

  The mixing ratio of the carbonaceous material and carbon black in the carbon material of the present embodiment is not particularly limited, but the mass of the carbonaceous material is 100 and the mass of the carbon black is 0.1 or more, preferably 1 or more. The same mass can be 5 or less, preferably 3 or less. By setting it as the said range, the low temperature cycling characteristic in a secondary battery becomes favorable so that it may mention later.

  The carbonaceous material (hard carbon) is preferably prepared by performing firing and pulverization in advance and then mixing with carbon black. In mixing, a kneading apparatus such as a kneading roll, a rotating / revolving mixer, a uniaxial or biaxial kneader can be used.

  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.

  The active material for secondary battery negative electrodes of this embodiment contains the carbon material (carbon material) for secondary battery negative electrodes mentioned above. By containing the carbon material described above, the negative electrode active material of the present embodiment exhibits excellent cycle characteristics under the low temperature environment of the negative electrode. The negative electrode active material refers to a material capable of occluding and releasing chemical species that serve as charge carriers in the secondary battery negative electrode. Examples of the chemical species include lithium ions or sodium ions in an alkali metal ion secondary battery. The negative electrode active material may be substantially composed of only the carbon material of the present embodiment, 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.

  Further, the secondary battery negative electrode of the present embodiment has at least the surface of the secondary battery negative electrode active material layer including the secondary battery negative electrode active material of the present embodiment described above and the secondary battery negative electrode active material layer. And a negative electrode current collector disposed in the portion. In addition, the secondary battery of the present embodiment includes the above-described secondary battery negative electrode, an electrolyte layer, and a secondary battery positive electrode. The secondary battery including the negative electrode of the present embodiment reflects the above effect of the negative electrode active material, and exhibits excellent cycle characteristics even in a low temperature environment.

  Examples of the secondary battery include, but are not limited to, an alkali metal secondary battery such as a lithium ion secondary battery or a sodium ion secondary battery. 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.

  Below, an example of the lithium ion secondary battery containing the carbon material of this embodiment is demonstrated using FIG. FIG. 2 is a schematic diagram showing an example of a lithium ion secondary battery 100 including the carbon material of the present embodiment. The lithium ion secondary battery 100 includes a negative electrode 10, a positive electrode 20, a separator 30, and an electrolyte solution layer 40.

  As shown in FIG. 2, 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 is laminated and disposed on at least part of the surface of the negative electrode current collector 14. The negative electrode active material layer 12 contains the carbon material described above. 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.

The negative electrode 10 can be manufactured as follows, for example.
A known organic polymer binder and an appropriate amount of a viscosity adjusting solvent or water are added to the negative electrode active material and kneaded to prepare a negative electrode slurry. 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 electrolyte 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. The electrolyte solution layer 40 can be configured 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. As the electrolyte, a known substance can be used. For example, a lithium metal salt such as LiClO ₄ or LiPF ₆ can be used.

  In the case of a secondary battery other than the non-aqueous electrolyte secondary battery, the electrolyte layer 40 has an aspect having a gel polymer electrolyte containing a polymer material such as polyethylene oxide or polyacrylonitrile, or zirconia. The aspect which has a solid 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 known separator can be used. For example, a porous film, a nonwoven fabric, or the like configured using polyethylene or polypropylene is used. Can be mentioned.

As illustrated in FIG. 2, the positive electrode 20 includes a positive electrode active material layer 22 and a positive electrode current collector 24.
The positive electrode active material layer 22 can be formed of a known positive electrode active material. Examples of the positive electrode active material include lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), and ternary Li (Ni _1/3 Mn _1/3). A composite oxide such as Co _1/3 ) O ₂ ; a conductive polymer such as polyaniline and polypyrrole; and 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.

  As the positive electrode current collector 24, a known positive electrode current collector can be used. For example, an aluminum foil, a stainless steel foil, a titanium foil, a nickel foil, a copper foil, or the like can be used.

  Although the lithium ion secondary battery 100 has been described above as an example, the carbon material of the present embodiment can also be used for a secondary battery using alkali ions other than lithium ions as chemical species such as sodium ions.

<Discharge capacity>
The carbonaceous material of the present embodiment is preferable in the first cycle of the charge / discharge cycle when the secondary battery produced under the conditions described below is charged / discharged at the low temperature cycle characteristics evaluation described below. Is 30 mAh / g or more, more preferably 35 mAh / g or more. In the present specification, “mAh / g” indicates a capacity per 1 g of the positive electrode active material. The discharge capacity at the 50th cycle of the charge / discharge cycle is preferably 24 mAh / g or more, more preferably 28 mAh / g or more, and further preferably 32 mAh. The maintenance rate of the discharge capacity at the 50th cycle relative to the discharge capacity at the 1st cycle of the charge / discharge cycle is preferably 80% or more, more preferably 83% or more, and still more preferably 90% or more.

  Examples of the present invention and comparative examples will be described below. 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 carbonaceous material (hard carbon)>
Using a phenol resin PR-55321B (manufactured by Sumitomo Bakelite Co., Ltd.), which is a thermosetting resin, as a raw material, a carbonaceous material was obtained by performing treatment in the order of the following steps (a) to (f).

(A) 510 g of thermosetting resin was allowed to stand in a heat treatment furnace. Thereafter, without reducing gas replacement, inert gas replacement, reducing gas flow, and inert gas flow, the temperature was raised from room temperature to 500 ° C. at 100 ° C./hour.
(B) Next, reducing gas replacement, inert gas replacement, reducing gas flow, and inert gas flow were not performed, and after degreasing at 500 ° C. for 2 hours, cooling was performed.
(C) The obtained powder was finely pulverized with a vibration ball mill.
(D) Thereafter, 204 g of the obtained powder was allowed to stand in a heat treatment furnace. Subsequently, the temperature was raised from room temperature to 1200 ° C. at 100 ° C./hour under inert gas (nitrogen) substitution and circulation.
(E) Under an inert gas (nitrogen) flow, it was kept at 1200 ° C. for 8 hours and carbonized.
(F) Under natural gas (nitrogen) circulation, the mixture was naturally cooled to 600 ° C., and then cooled from 600 ° C. to 100 ° C. at 100 ° C./hour.
The carbonaceous material (hard carbon) prepared by the above production method was measured for the average layer surface spacing d ₀₀₂ , Lc ₍₀₀₂₎ , the average particle size D ₅₀ and the specific surface area by the BET three-point method in nitrogen adsorption. The results are shown in Table 1 below.

<Preparation of carbon black>
(Sample 1)
Acetylene gas is mixed at 12 m ³ / hour, oxygen gas is 9 m ³ / hour, and hydrogen gas is mixed at 0.5 m ³ / hour. At the top of the carbon black production furnace (furnace length 5 m, furnace diameter 0.5 m) The carbon black concerning sample 1 was manufactured by spraying from the installed nozzle and utilizing thermal decomposition and combustion reaction of acetylene. The average particle size of the primary particles of the carbon black of Sample 1 is increased by 150% using a transmission electron microscope (TEM) without changing the aspect ratio of the 10000 times photograph, and becomes the maximum at the diameter of 100 particles. The value was measured and the average value was obtained. The average particle diameter of primary particles of the carbon black of Sample 1 was 18 nm. The specific surface area of sample 1 is a relative pressure p / p ⁰ = 0.30 ± 0.04 using nitrogen as an adsorption gas by a BET one-point method using a nitrogen adsorption specific surface area meter (Macsorb 1201 manufactured by Mountec Co., Ltd.). It was 370 m ² / g when measured under conditions. Moreover, the volatile content measured according to JIS K 6217-4 was 0.18%.

(Sample 2)
After carbon black according to Sample 1 is used as a raw material, water is contained for 0.5 hour in a constant temperature and humidity device under conditions of a temperature of 25 ° C. and a humidity of 80%, and then placed in an electric furnace heated to 750 ° C. While maintaining the pressure in the furnace at 0.1 kPa, air was introduced at 25 L / hour and oxidation treatment was performed for 1 hour to obtain carbon black according to sample 2. The average particle size of the carbon black primary particles of Sample 2 was 18 nm, the specific surface area was 863 m ² / g, and the volatile content was 1.10%.

(Sample 3)
As the carbon black of Sample 3, Denka Black FS-35, which is acetylene black manufactured by Denka Corporation (Electrochemical Industry Co., Ltd.), was used. The carbon black of Sample 3 was a press product obtained by pressing the following powder product, and the average particle size of the primary particles was 23 nm and the specific surface area was 133 m ² / g.

(Sample 4)
As the carbon black of Sample 4, Denka Black AB, which is acetylene black manufactured by Denka Corporation (Electrochemical Industry Co., Ltd.), was used. The carbon black of Comparative Example 1 was a powdery product as produced in the cracking furnace, and the primary particles had an average particle size of 35 nm and a specific surface area of 68 m ² / g.

100 parts of hard carbon, 3 parts of carboxymethylcellulose (manufactured by Daicel Finechem Co., Ltd., CMC Daicel 2200), 1.5 parts of styrene-butadiene rubber (manufactured by JSR Corporation, TRD-2001), carbon black (sample 1) 2 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 (Sample 1).
Moreover, it replaced with the sample 1 instead of the sample 1 and mix | blended the said sample 2 and the sample 4, respectively, and prepared the negative electrode mixture (sample 4) from the slurry-like negative electrode mixture (sample 2).
Furthermore, a slurry-like negative electrode mixture (sample 5) prepared without blending carbon black was obtained. The ratio of the mass of the carbon black to the hard carbon is shown as the carbon blending ratio in Table 1 below.

<Creation of full-cell lithium-ion secondary battery>
The negative electrode mixture (Sample 1 to Sample 5) is applied to one side of a 14 μm thick copper foil (Furukawa Electric Co., Ltd., NC-WS), and then pre-dried in air at 60 ° C. for 2 hours. Next, it was vacuum-dried at 120 ° C. for 15 hours. 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 single layer using an aluminum foil as a positive electrode current collector using Li (Ni _1/3 Mn _1/3 Co _1/3 ) O ₂ as an active material and applied on a current collector A sheet formed into a disk shape having a diameter of 12 mm was used.
As the separator, a polyolefin porous 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 ) to which a 2032 type coin cell full cell lithium ion secondary battery was manufactured in a glove box under an argon atmosphere.

  The full cell type lithium ion secondary batteries prepared from the negative electrode mixture (sample 1) using the negative electrode mixture (sample 3) are referred to as the full cell secondary batteries of Examples 1 to 3, respectively, and the negative electrode mixture (sample 4). ) And a negative electrode mixture (sample 5) are referred to as full cell secondary batteries of Comparative Example 1 and Comparative Example 2, respectively.

  Evaluation was performed as follows using the full-cell secondary batteries of Examples and Comparative Examples obtained as described above.

[Low temperature environment test]
First, pretreatment was performed. In the pretreatment, each lithium ion secondary battery is charged to 4.2 V with 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 with a constant voltage of 4.2 V. The battery was charged and rested for 5 minutes. Next, the battery was discharged at a constant current of 0.2 C to 2.5 V and rested for 5 minutes. Such charging / discharging was performed 5 cycles. Here, “1C” means a current density at which discharge is completed in one hour.
Following the pretreatment, the following charge / discharge cycles were performed at least 50 cycles. As the charge / discharge cycle, each full cell type lithium ion secondary battery is charged to 4.2 V at a constant current of 1 C in a temperature environment of minus 20 ° C., and then charged at a constant voltage until the current reaches 0.1 C. 5 Then, the battery was discharged at a constant current of 1 C to 2.5 V and then rested for 5 minutes. In addition, when performing the low-temperature cycle characteristic evaluation of the pre-processed lithium ion secondary battery, it is good to perform the following charge / discharge cycles, without performing said pre-process further.

  As the low temperature cycle characteristic evaluation, the maintenance rate (%) of the discharge capacity at the 50th cycle with respect to the discharge capacity at the first cycle of the charge / discharge cycle was calculated as the low temperature life characteristic. The results are shown in Table 1. Table 1 shows the full-cell lithium ion secondary batteries according to Examples 1 to 3 and Comparative Examples 1 and 2 in the first cycle, the tenth cycle, and the 50th cycle of the charge / discharge cycle of the pretreatment in the low-temperature environment test. The discharge capacity is shown. In Table 1, in addition to the discharge capacity [mAh / g] at each cycle, the ratio [%] of the discharge capacity at the 10th cycle and the 50th cycle when the discharge capacity at the first cycle is taken as 100% is also shown. it's shown.

From the results shown in Table 1, in the full-cell lithium ion secondary batteries according to Examples 1 to 3 in which carbon black having an average particle size of 25 nm or less was added to hard carbon, discharge at the 50th cycle relative to the discharge capacity at the 1st cycle It was found that the capacity maintenance rate exceeded 80% in all cases. On the other hand, in the full cell type lithium ion secondary batteries according to Comparative Example 1 and Comparative Example 2, the above-mentioned maintenance rate was less than 80, specifically, 65% or less. In particular, with respect to Example 1 and Example 2 in which the average particle diameter of carbon black is 20 nm or less and the specific surface area is 300 m ² / g or more, the discharge capacity at the 10th cycle is substantially equal to the discharge capacity at the 50th cycle. Therefore, it is predicted that a sufficient discharge capacity can be maintained even if charging and discharging are repeated a number of times exceeding 50 cycles in a low temperature environment. In particular, regarding Example 1, a surprising result was obtained in which the discharge capacities at the first, tenth and fifty cycles were substantially equal to each other. On the other hand, regarding Comparative Examples 1 and 2, a significant decrease in the discharge capacity was confirmed from the 1st cycle to the 10th cycle and from the 10th cycle to the 50th cycle.
From the above results, according to the carbon material, the negative electrode active material, the secondary battery negative electrode, and the secondary battery according to Examples 1 to 3 of the present invention, the cycle characteristics during charging and discharging are well maintained even in a severe low temperature environment. I found it possible.

  The present invention is not limited to the above-described embodiment, and includes various modifications and improvements as long as the object of the present invention is achieved.

The above embodiment includes the following technical idea.
(1) A carbonaceous material having an average layer 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, and a DBP absorption amount of 240 mL / 100 g or more. Carbon material for secondary battery negative electrode containing carbon black.
(2) The carbonaceous material is a carbon material for a secondary battery negative electrode according to (1), wherein the 50% cumulative particle size D ₅₀ in the volume-based cumulative distribution is 1 μm or more and 50 μm or less.
(3) The carbonaceous material according to (1) or (2), wherein the carbon material has a specific surface area of 1 m ² / g or more and 15 m ² / g or less according to a BET three-point method in nitrogen adsorption.
(4) The carbon material for a secondary battery negative electrode according to any one of (1) to (3), wherein an average particle diameter of primary particles of the carbon black is 25 nm or less.
(5) A carbon material for a secondary battery negative electrode used for a secondary battery negative electrode, wherein the low-temperature life characteristic shown in the following low-temperature cycle characteristic evaluation is 80% or more, and any one of (1) to (4) Carbon material for secondary battery negative electrode;
The low temperature cycle characteristic evaluation is
A secondary battery negative electrode containing the carbon material for a secondary battery negative electrode, a positive electrode using Li (Ni _1/3 Mn _1/3 Co _1/3 ) O ₂ as an active material, and an electrolyte solution containing a dissolved electrolyte, A lithium ion secondary battery comprising a separator,
After charging to 4.2V with a constant current of 1C in a temperature environment of minus 20 ° C, the battery is charged for a constant voltage until the current reaches 0.1C, and rests for 5 minutes, and then 2.5V with a constant current of 1C. A charge / discharge cycle in which discharge is performed and paused for 5 minutes is repeated, and a maintenance ratio of the discharge capacity at the 50th cycle to the discharge capacity at the first cycle of the charge / discharge cycle is calculated as the low-temperature life characteristic.
(6) A secondary battery negative electrode active material containing the carbon material for secondary battery negative electrode according to any one of (1) to (5) above.
(7) A secondary battery negative electrode active material layer including the secondary battery negative electrode active material of (6) above, and a negative electrode current collector in which the secondary battery negative electrode active material layer is disposed at least on a part of the surface And a secondary battery negative electrode.
(8) A secondary battery comprising the secondary battery negative electrode, electrolyte layer, separator and positive electrode of (7) above.

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 Electrolyte layer 100 Lithium ion secondary battery CB Carbon black CM Carbon material ES Electrolyte HC Carbonaceous material

Claims (8)

A carbonaceous material having an average layer spacing d _{002 of} (002) planes of 0.340 nm or more determined by X-ray diffraction using CuKα rays as a radiation source, and carbon black having a DBP absorption of 240 mL / 100 g or more, The carbon material for secondary battery negative electrodes containing these. 2. The carbon material for a secondary battery negative electrode according to claim 1, wherein the carbonaceous material has a 50% cumulative particle size D ₅₀ in a cumulative distribution on a volume basis of 1 μm or more and 50 μm or less. 3. The carbon material for a secondary battery negative electrode according to claim 1, wherein the carbonaceous material has a specific surface area of 0.5 m ² / g or more and 15 m ² / g or less by a BET three-point method in nitrogen adsorption.   The carbon material for a secondary battery negative electrode according to any one of claims 1 to 3, wherein an average particle diameter of primary particles of the carbon black is 25 nm or less. The secondary battery according to any one of claims 1 to 4, wherein the carbon material for a secondary battery negative electrode used for a secondary battery negative electrode has a low-temperature life characteristic of 80% or more shown in the following low-temperature cycle characteristic evaluation. Carbon material for battery negative electrode;
The low temperature cycle characteristic evaluation is
A secondary battery negative electrode containing the carbon material for a secondary battery negative electrode, a positive electrode using Li (Ni _1/3 Mn _1/3 Co _1/3 ) O ₂ as an active material, and an electrolyte solution containing a dissolved electrolyte, A lithium ion secondary battery comprising a separator,
After charging to 4.2V with a constant current of 1C in a temperature environment of minus 20 ° C, the battery is charged for a constant voltage until the current reaches 0.1C, and rests for 5 minutes, and then 2.5V with a constant current of 1C. A charge / discharge cycle in which discharge is performed and paused for 5 minutes is repeated, and a maintenance ratio of the discharge capacity at the 50th cycle to the discharge capacity at the first cycle of the charge / discharge cycle is calculated as the low-temperature life characteristic.   The active material for secondary battery negative electrodes containing the carbon material for secondary battery negative electrodes as described in any one of Claims 1-5.   A secondary battery negative electrode active material layer comprising the secondary battery negative electrode active material according to claim 6, and a negative electrode current collector in which the secondary battery negative electrode active material layer is disposed at least on a part of the surface thereof. A secondary battery negative electrode.   A secondary battery comprising the secondary battery negative electrode according to claim 7, an electrolyte layer, a separator, and a positive electrode.

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