TWI823900B - Carbonaceous particles, anode material for lithium ion secondary battery, anode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

Carbonaceous particles for an anode for a lithium ion battery, the carbonaceous particles satisfying the following conditions (1) and (2) in a frequency distribution of R value, a peak intensity ratio (G/D) of G band (1580 cm^-1 ) to D band (1360cm^-1 ), of a graphite obtained by Raman mapping: (1) the mode of R value (Rc) is from 0.87 to 0.96; and (2) the R value at 50% in frequency accumulation from the smaller side (R₅₀ ) is from 0.88 to 0.92.

Description

Carbonaceous particles, negative electrode materials for lithium ion secondary batteries, negative electrodes for lithium ion secondary batteries, and lithium ion secondary batteries

The invention relates to a carbonaceous particle, a negative electrode material for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery.

Lithium-ion secondary batteries have higher input/output characteristics than other secondary batteries such as nickel-cadmium batteries, nickel-metal hydride batteries, and lead-acid batteries. Therefore, in recent years, they have been required as power sources for electric vehicles, hybrid electric vehicles, etc. Expectations for power supplies used in high input/output applications are increasing.

Carbon materials commonly used as negative electrode materials (negative electrode active materials) for lithium ion secondary batteries are roughly classified into graphite-based and amorphous carbon-based materials. Graphite has a structure in which hexagonal mesh surfaces of carbon atoms are regularly stacked. Therefore, lithium ions are inserted and removed from the ends of the stacked mesh surfaces to perform charging and discharging. However, the insertion and detachment reaction occurs only at the ends of the hexagonal mesh surface, so there is a limit to the improvement of input/output performance. In addition, since it has high crystallinity and few surface defects, there are problems such as poor affinity with the electrolyte solution and degradation of the life characteristics of the lithium ion secondary battery.

Amorphous carbon has irregular lamination on the hexagonal mesh surface or does not have a mesh structure. Therefore, the insertion and removal reaction of lithium proceeds on the entire surface of the particle, making it easy to obtain a lithium-ion secondary battery with excellent input/output characteristics.

Amorphous carbon used as a negative electrode active material of a lithium ion secondary battery is known to have coke, carbon black, etc. as raw materials (see, for example, Patent Document 1 and Patent Document 2).

[Prior art documents]

[Patent Document]

[Patent Document 1] Japanese Patent Application Publication No. 04-370662

[Patent Document 2] Japanese Patent Application Publication No. 05-307956

As described above, lithium ion secondary batteries using amorphous carbon as a negative electrode material have excellent input/output characteristics, but are not suitable for applications requiring high input/output, such as power supplies for electric vehicles and hybrid electric vehicles. expansion requires further low resistance.

In view of the above situation, the object of the present invention is to provide a carbonaceous particle and a negative electrode material for a lithium ion secondary battery that can produce a low-resistance lithium ion secondary battery, as well as a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery. .

Means for solving the above problems include the following embodiments.

<1> A carbonaceous particle for negative electrode materials of lithium ion secondary batteries, which has a G band (1580cm ^-1 ) and a D band (1360cm) representing graphite obtained by Raman mapping measurement. ^-1 ) The frequency distribution of the R value of the peak intensity ratio (G/D) satisfies the following conditions (1) and (2); (1) The mode (Rc) of the R value is 0.87~0.96; ( 2) The R value (R ₅₀ ) when the cumulative frequency from the side with the smaller R value is 50% is 0.88 to 0.92.

<2> The carbonaceous particles according to <1>, which have a first carbon material as a core, and at least a portion of the surface of the first carbon material that has lower crystallinity than the first carbon material. Second carbon material.

<3> The carbonaceous particles according to <1> or <2>, wherein the crystallite size (Lc) in the c-axis direction is 4.5nm~5.2nm.

<4> The carbonaceous particles according to any one of <1> to <3>, wherein the specific surface area is 2.0m ² /g~5.0m ² /g.

<5> The carbonaceous particles according to any one of <1> to <4>, wherein the average particle diameter (50%D) is 5 μm to 20 μm.

<6> A negative electrode material for lithium ion secondary batteries, which contains the carbonaceous particles according to any one of <1> to <5>.

<7> The negative electrode material for lithium ion secondary batteries according to <6>, which further contains graphite particles.

<8> A negative electrode for lithium ion secondary batteries, which includes the negative electrode material for lithium ion secondary batteries described in <6> or <7>.

<9> A lithium ion secondary battery, which includes the lithium ion secondary battery as described in <8> Use the negative pole of the secondary battery.

According to the present invention, there are provided carbonaceous particles and a negative electrode material for a lithium ion secondary battery that can produce a low-resistance lithium ion secondary battery, as well as a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery.

FIG. 1 is a graph showing the frequency distribution of R values of carbonaceous particles produced in Example 1, Comparative Example 1, and Comparative Example 2.

FIG. 2 is a graph showing a cumulative curve of R values of carbonaceous particles produced in Example 1, Comparative Example 1, and Comparative Example 2.

Hereinafter, modes for implementing the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps, etc.) are not essential unless otherwise expressly stated. The same applies to numerical values and their ranges, which do not limit the present invention.

In this disclosure, the term "step" includes steps other than steps that are independent of other steps, even if they cannot be clearly distinguished from other steps, as long as the purpose of the step is achieved.

In this disclosure, the numerical range represented by "~" includes the numerical values recorded before and after "~" as the minimum value and the maximum value respectively.

Among the numerical ranges recorded in stages in this disclosure, a numerical range is recorded The upper limit or lower limit can also be replaced by the upper limit or lower limit of other numerical ranges recorded in stages. In addition, in the numerical range described in this disclosure, the upper limit value or the lower limit value of the numerical range can also be replaced with the value shown in the embodiment.

In this disclosure, each component may include a variety of consistent substances. When there are multiple substances corresponding to each component in the composition, unless otherwise specified, the content rate or content of each component refers to the total content rate or content of the multiple substances present in the composition.

In this disclosure, a variety of consistent particles may be included in each component. When a plurality of types of particles corresponding to each component are present in the composition, the particle diameter of each component refers to a value for a mixture of the plurality of types of particles present in the composition, unless otherwise specified.

In this disclosure, the terms "layer" or "film" include, when observing a region in which the layer or film exists, not only the case where it is formed in the entire region, but also the case where it is formed in only a part of the region. .

<Carbonaceous particles>

The carbonaceous particles disclosed in the present disclosure are carbonaceous particles used as negative electrode materials for lithium ion secondary batteries. They have a G band (1580 cm ^-1 ) and a D band (1360 cm -1 ) representing graphite obtained by Raman mapping measurement. In the frequency distribution of the R value of the peak intensity ratio (G/D) of ^-1 ), the following conditions (1) and (2) are satisfied.

(1) The mode (Rc) of the R value is 0.87~0.96.

(2) The R value (R ₅₀ ) when the cumulative frequency from the side with the smaller R value is 50% is 0.88 to 0.92.

The inventors and others conducted research, and the results are clear: the use of The lithium ion secondary battery obtained by using the negative electrode material of the carbonaceous particles under conditions (1) and (2) has excellent input/output characteristics and has low resistance.

In the present disclosure, the frequency distribution of R values of carbonaceous particles can be obtained by Raman mapping. The measurement conditions of Raman mapping are as follows: objective lens magnification: 50 times, exposure time: 2 seconds, accumulation count: 4 times, sampling range: 100 μm × 100 μm, and measurement interval: 2 μm. As a measuring device, for example, DXR microlaser Raman from Thermo Fisher Scientific can be used.

From the viewpoint of reducing the resistance of the lithium ion secondary battery, Rc is preferably 0.90 to 0.92.

From the viewpoint of improving battery characteristics such as irreversible capacity, charge and discharge capacity, and cycle life, the interplanar spacing (d002) of the 002 plane of the carbonaceous particles is preferably 0.34 nm to 0.37 nm. If d002 is 0.34 nm or more, good initial charge and discharge efficiency tends to be obtained, and if d002 is 0.37 nm or less, life characteristics and input/output characteristics tend to be excellent.

The inter-plane distance (d002) of the 002 plane of the carbonaceous particles can be determined by XRD (X-ray diffraction) measurement. Specifically, the sample can be irradiated with X-rays (CuKα rays), and the diffraction distribution obtained by measuring the diffracted rays with a goniometer and the diffraction angle that occurs near the diffraction angle 2θ = 24° to 26° can be obtained. The diffraction peak corresponding to the carbon 002 plane is calculated using Bragg's formula.

From the viewpoint of improving the irreversible capacity, life characteristics, and charge and discharge capacity of a lithium-ion secondary battery, the carbonaceous particles are preferably made of coke. The type of coke used in the production of carbonaceous particles is not particularly limited, and examples include coal-based coke, petroleum coke Department of coke, etc. Coke is roughly divided into mosaic coke with relatively low crystallinity and needle coke with relatively high crystallinity, and needle coke is more preferred. The coke used for the production of carbonaceous particles may be only one type or two or more types.

The carbonaceous particles may have a first carbon material as a core, and a second carbon material that is present on at least a part of the surface of the first carbon material and has lower crystallinity than the first carbon material. When the carbonaceous particles have a first carbon material as a core and a second carbon material present on at least part of the surface of the first carbon material and having lower crystallinity than the first carbon material, the second carbon material The material may be present on the entire surface of the core or on only a portion of the surface.

In the case where the carbonaceous particles have a first carbon material as a core and a second carbon material that is present on at least part of the surface of the first carbon material and has lower crystallinity than the first carbon material, it can be The first carbon material of the core is made of coke, and the second carbon material present on at least part of the surface of the first carbon material is a material that can be changed into carbonaceous material (precursor of the second carbon material) by heat treatment. Manufactured carbonaceous particles. The precursor of the second carbon material is not particularly limited, and examples thereof include thermoplastic resin, naphthalene, anthracene, phenanthrene, coal tar, tar, asphalt, and the like.

When the carbonaceous particles have a first carbon material as a core and a second carbon material present on at least part of the surface of the first carbon material and having lower crystallinity than the first carbon material, the second carbon material The amount of material is not particularly limited. There is a relationship in which the greater the amount of the second carbon material, the greater the R value, and the smaller the amount of the second carbon material, the smaller the R value. In addition, from the viewpoint of suppressing an increase in the specific surface area, making it difficult to cause side reactions with the electrolyte solution, and obtaining good input/output characteristics, the amount of the second carbon material is preferably not too small. Other On the one hand, from the viewpoint of suppressing the resistance of the second carbon material itself from increasing and deteriorating the input/output characteristics, it is preferable that the amount of the second carbon material is not excessive.

The method for producing carbonaceous particles having a first carbon material as a core and a second carbon material present on at least part of the surface of the first carbon material and having lower crystallinity than the first carbon material is not particularly limited. . For example, it can be produced by the method of producing carbonaceous particles described below.

From the viewpoint of reducing the resistance of the lithium ion secondary battery, the crystallite size (Lc) in the c-axis direction of the carbonaceous particles calculated from the Scherrer formula is preferably 4.5 nm to 5.4 nm. The larger the crystallite size (Lc) in the c-axis direction is, the higher the crystallinity is. Examples of carbonaceous particles having a crystallite size (Lc) in the c-axis direction of 4.5 nm to 5.4 nm include needle coke particles. The crystallite size (Lc) of the carbonaceous particles in the c-axis direction is a value calculated using Scherrer's formula based on the half-width of the diffraction peak of d002 obtained by X-ray diffraction measurement.

The specific surface area of the carbonaceous particles is preferably 2.0m ² /g~5.0m ² /g, more preferably 2.5m ² /g~4.0m ² /g or less, and further preferably 2.7m ² /g~3.3m ² / g. In this disclosure, the specific surface area of the carbonaceous particles is a value obtained by the Brunauer-Emmett-Teller (BET) method (nitrogen adsorption method).

The average particle diameter (50%D) of the carbonaceous particles is preferably 5 μm to 20 μm, more preferably 8 μm to 18 μm, and further preferably 9 μm to 16 μm. When the average particle diameter of the carbonaceous particles is 5 μm or more, the specific surface area does not become too large, and the decrease in the initial charge and discharge efficiency of the lithium ion secondary battery tends to be suppressed. In addition, sufficient contact between particles is ensured, thereby tending to suppress degradation in input/output characteristics. like When the average particle diameter of the carbonaceous particles is 20 μm or less, unevenness occurs on the electrode surface and the occurrence of a battery short circuit tends to be suppressed. In addition, the diffusion distance of Li from the surface to the inside of the particle does not become too long, and the input/output characteristics tend to be maintained favorably.

In this disclosure, the average particle size (50%D) of carbonaceous particles is determined by using laser diffraction. The particle size at which 50% of the volume-based particle size distribution obtained by the scattering method is accumulated from the small diameter side.

The method of producing the carbonaceous particles of the present disclosure is not particularly limited. For example, it can be produced by a method including heat-treating a mixture containing a precursor of a first carbon material that serves as a core and a second carbon material that has lower crystallinity than the first carbon material.

According to this method, a carbon material having a first carbon material as a core and a second carbon material that is present on at least part of the surface of the first carbon material and has lower crystallinity than the first carbon material can be produced efficiently. Carbonaceous particles.

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

In order to improve the input/output characteristics of the lithium ion secondary battery, the temperature when the mixture is heat-treated is preferably 800°C to 1500°C, more preferably 850°C to 1100°C, and still more preferably 900°C to 1000°C. . The temperature when the mixture is heat-treated may be a fixed temperature from the start to the end of the heat treatment, or may be changed.

The heat-treated mixture may be subjected to processes such as crushing, disintegration, and particle size adjustment if necessary.

In the method, the content of the precursors of the first carbon material and the second carbon material in the mixture before heat treatment is not particularly limited. In order to improve the input/output characteristics of the lithium-ion secondary battery, the content rate of the first carbon material is preferably 85 mass% to 99.9 mass%, more preferably 90 mass% to the total mass of the mixture. 99% by mass, more preferably 95% by mass to 99% by mass. On the other hand, in order to improve the input/output characteristics of the lithium ion secondary battery, the content rate of the precursor of the second carbon material is preferably 0.1 mass % to 15 mass % with respect to the total mass of the mixture, and more preferably Preferably, it is 1 mass % - 10 mass %, More preferably, it is 1 mass % - 5 mass %.

<Anode material for lithium ion secondary batteries>

The negative electrode material for lithium ion secondary batteries of the present disclosure (hereinafter also referred to as negative electrode material) contains the carbonaceous particles.

The negative electrode material of the present disclosure may only include the carbonaceous particles, or may be a combination of carbonaceous particles and other negative electrode materials. For example, by combining carbonaceous particles with graphite particles, the input/output characteristics of the lithium ion secondary battery tend to be further improved compared to the case where only graphite particles are used.

When the negative electrode material of the present disclosure includes carbonaceous particles and graphite particles, the proportion of the carbonaceous particles in the total of the carbonaceous particles and graphite particles is preferably 5% by mass to 50% by mass, and more preferably 10% by mass. %~40% by mass, more preferably 15%~30% by mass.

<Negative electrode for lithium ion secondary batteries>

The negative electrode for a lithium ion secondary battery of the present disclosure (hereinafter also referred to as a negative electrode) contains the above-mentioned negative electrode material. Specific structures of the negative electrode include, for example, a current collector, and a structure of a negative electrode material layer including a negative electrode material arranged on at least one side of the current collector.

The method of producing the negative electrode is not particularly limited. For example, the following methods can be cited: using a mixer, ball mill, super sand mill, pressure kneader and other dispersing devices to knead the negative electrode material and the organic binder together with the solvent to prepare the negative electrode material A method of forming the slurry and coating it on the current collector to form a negative electrode layer; a method of forming the pasty negative electrode material slurry into shapes such as sheets, granules, and integrating it with the current collector.

The organic binder used in preparation of the negative electrode material slurry is not particularly limited. Examples of organic binders include styrene-butadiene copolymer, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylonitrile, Ethylenically unsaturated carboxylic acid esters such as hydroxyethyl methacrylate, acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid and other ethylenically unsaturated carboxylic acids, polyvinylidene fluoride , polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile and other polymer compounds with high ionic conductivity. The content of the organic binder in the negative electrode material slurry is preferably, for example, 1 to 20 mass % of the total of the negative electrode material and organic binder disclosed in the present disclosure.

In this disclosure, "(meth)acrylate" refers to at least one of acrylate and methacrylate, and "(meth)acrylonitrile" refers to at least one of acrylonitrile and methacrylonitrile.

A tackifier for adjusting the viscosity can also be added to the negative electrode material slurry. Examples of thickeners include carboxymethylcellulose, methylcellulose, and hydroxymethylcellulose. Cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid (salt), oxidized starch, phosphorylated starch, casein (casein), etc.

The negative electrode material slurry can also be mixed with conductive auxiliary materials. Examples of conductive auxiliary materials include carbon black, graphite, acetylene black, oxides showing conductivity, nitrides showing conductivity, and the like. The usage amount of the conductive auxiliary material may be, for example, 1% by mass to 15% by mass of the entire negative electrode material (non-volatile components).

The material and shape of the current collector used in the production of the negative electrode are not particularly limited. For example, a strip formed by forming copper, nickel, titanium, stainless steel, etc. into a foil shape, a perforated foil shape, a mesh shape, etc. can be used. In addition, porous materials such as porous metal (foamed metal), carbon paper, etc. can also be used.

The method of applying the negative electrode material slurry to the current collector is not particularly limited, and examples thereof include: metal mask printing method, electrostatic coating method, dip coating method, spray coating method, roll coating method, and doctor blade method. , gravure coating method, screen printing method, etc. After coating, calendering using a flat plate press, calender roll, etc. can be performed if necessary.

The method of integrating the negative electrode material slurry formed into a sheet shape, granular shape, etc., and the current collector is not particularly limited, and examples thereof include rollers, presses, and combinations thereof.

<Lithium-ion secondary battery>

The lithium ion secondary battery of the present disclosure includes the negative electrode for the lithium ion secondary battery of the present disclosure. Specifically, at least the negative electrode, positive electrode, optional separator, and electrolyte solution of the present disclosure are included.

The positive electrode, like the negative electrode of the present disclosure, may be one in which a positive electrode layer containing a positive electrode material is formed on a current collector. As the current collector, aluminum, titanium, stainless steel can be used Metals or alloys formed into strips such as foil, perforated foil, mesh, etc.

The cathode material contained in the cathode layer is not particularly limited and can be selected from metal compounds, metal oxides, metal sulfides, conductive polymer materials, etc. that can be doped or embedded with lithium ions. Specific examples include: lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), and these complex oxides (LiCo _x Ni _y Mn _z O ₂ , x+y +z=1), lithium manganese spinel (LiMn ₂ O ₄ ), lithium vanadium compound, V ₂ O ₅ , V ₆ O ₁₃ , VO ₂ , MnO ₂ , TiO ₂ , MoV ₂ O ₈ , TiS ₂ , V ₂ S ₅ , VS ₂ , MoS ₂ , MoS ₃ , Cr ₃ O ₈ , Cr ₂ O ₅ , olivine type LiMPO ₄ (M is Co, Ni, Mn or Fe) and other inorganic materials, polyacetylene, poly Conductive polymers such as aniline, polypyrrole, polythiophene, and polyacene, porous carbon, etc. One type of positive electrode material may be used alone, or two or more types may be used in combination.

As the spacer, for example, nonwoven fabrics, cloths, microporous films containing polyolefins such as polyethylene and polypropylene as a main component, or a combination thereof can be used. In addition, when the positive electrode and the negative electrode of the produced lithium ion secondary battery are not in direct contact, there is no need to use a separator.

As the electrolyte solution, a so-called organic electrolyte solution in which an electrolyte is dissolved in a non-aqueous solvent can be used.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , and LiSO ₃ CF ₃ .

Examples of non-aqueous solvents include: ethyl carbonate, propyl carbonate, butyl carbonate, vinyl carbonate, cyclopentanone, cyclobutane, 3-methylcyclobutane, and 2,4-dimethyl Cyclotene, 3-methyl-1,3-oxazolidin-2-one, γ-butyrolactone, dimethyl carbonate, Diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran , 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, mixtures thereof, etc.

The structure of the lithium ion secondary battery is not particularly limited. For example, there is usually a structure in which, with a separator disposed between the positive electrode and the negative electrode, the electrode plate group obtained in the form of a roll or a flat plate-shaped laminate is enclosed in an outer casing, and is used. The electrolyte fills the inside of the exterior body.

The shape of the lithium ion secondary battery is not particularly limited, and examples thereof include paper batteries, button batteries, coin cells, laminated batteries, and cylindrical batteries.

[Example]

Hereinafter, embodiments of the present disclosure will be described in more detail based on examples, but the present disclosure is not limited to these examples.

<Example 1>

Commercially available coke with d002 of 0.346 nm and Lc of 4.6 nm was pulverized using an impact mill with a classifier. To 99 parts by mass of this pulverized product, 1 part by mass of coal tar pitch (softening point: 98° C., residual carbon rate (carbonization rate): 50%) was added to obtain a mixture. Then, the mixture was heated to 900°C at a temperature increase rate of 20°C/hour under nitrogen flow, and maintained at 900°C (calcination treatment temperature) for 1 hour to obtain a heat-treated product. The obtained heat-treated material is crushed using a cutter mill, and then sieved using a 300-mesh sieve to remove coarse powder, thereby obtaining source material. The first carbon material (core) derived from coke, and the carbonaceous particles of the second carbon material derived from coal tar pitch present on at least a part of the surface of the first carbon material.

(Measurement of d002 and Lc)

The d002 and Lc of the obtained carbonaceous particles were measured using X-ray diffraction measurement. Specifically, a wide-angle X-ray diffraction device of Rigaku Denki Co., Ltd. was used, Cu-Kα rays monochromated by a monochromator were used, and high-purity silicon was used as a standard material. d002 is calculated using Bragg's formula based on the diffraction peak corresponding to the 002 plane that appears near the diffraction angle 2θ=24°~26°. Lc is calculated from the half-width of the diffraction peak of d002 using Scherrer's formula. The results are shown in Table 1.

(Measurement of average particle size)

Using laser diffraction. The average particle diameter (50%D) of the obtained carbonaceous particles was measured using a scattering method. Specifically, a laser diffraction particle size distribution measuring device (SALD-3000J manufactured by Shimadzu Corporation) was used, and a dispersion liquid in which carbonaceous particles and surfactants were dispersed in purified water was placed in the water tank of the device. In the state where ultrasonic waves are applied, the measurement is performed while circulating with a pump. The particle diameter (50%D) when the cumulative volume-based particle size distribution obtained was 50% was defined as the average particle diameter. The results are shown in Table 1.

(Measurement of Rc and R ₅₀ )

The Rc and _R50 of the obtained carbonaceous particles were measured using Raman mapping. Specifically, a Raman mapping device (DXR microlaser Raman from Thermo Fisher Scientific) was used and the magnification of the objective lens: 50 times, the exposure time: 2 seconds, and the cumulative number of times: 4 times, sampling range: 100μm×100μm, measurement interval: 2μm. The peak intensity ratio (G/D) of graphite's G band (1580cm ^-1 ) and D band (1360cm ^-1 ) obtained by measurement was used as the R value, and its mode (Rc) and frequency were calculated. The R value when accumulated to 50% (R ₅₀ ). The results are shown in Table 1.

A graph showing the frequency distribution of the obtained R values is shown in FIG. 1 , and a cumulative curve is shown in FIG. 2 together with the results obtained in Comparative Example 1 and Comparative Example 2 described later.

(Measurement of specific surface area)

The specific surface area (m ² /g) of the obtained carbonaceous particles was determined by the BET method (nitrogen adsorption method) using a specific surface area meter (FlowSorb manufactured by Shimadzu Corporation).

(Measurement of charge and discharge capacity)

For 98% by mass of carbonaceous particles, 1% by mass of carboxymethyl cellulose (CMC) and styrene. Butadiene rubber (SBR) was added at 1% by mass and kneaded to prepare a pasty negative electrode material slurry. This slurry was applied on an electrolytic copper foil with a thickness of 11 μm into a circle with a diameter of 9.5 mm using a mask with a thickness of 200 μm. This was dried at 105°C to prepare a negative electrode for monopolar testing.

Then, the prepared negative electrode, separator, and positive electrode laminated in sequence are placed in a coin battery container, and an electrolyte solution made of ethyl carbonate (EC) and ethyl methyl carbonate is poured into a coin battery container. LiPF ₆ was dissolved in a mixed solvent (EMC) (the volume ratio of EC and EMC is 1:1) so that the concentration becomes 1.0 mol/L. Metal lithium is used as the positive electrode, and a polyethylene microporous film with a thickness of 20 μm is used as the separator.

Using the obtained coin battery, a constant current of 0.1C was passed between the negative electrode and the positive electrode, and charging was performed (making the negative electrode absorb lithium) until the potential of the negative electrode with respect to the positive electrode reached 0.005V (Vvs.Li/Li ⁺ ). Then, charging is performed at a constant voltage of 0.005V until the current decays to 0.01C. Next, a 30-minute pause was set, and then discharge was performed at a constant current of 0.1 C (lithium was released from the negative electrode) until the potential of the negative electrode relative to the positive electrode reached 1.5 V (V vs. Li/Li ⁺ ). This charge and discharge test was performed for one cycle, the charge capacity and discharge capacity in the initial charge and discharge were measured, and the initial charge and discharge efficiency was determined from the obtained values. The results are shown in Table 1.

The initial charge and discharge efficiency is calculated in the form of discharge capacity (Ah/kg)/charge capacity (Ah/kg) × 100 (%).

(Measurement of DC resistance value)

98% by mass of carbonaceous particles were added so that CMC was 1% by mass and SBR was 1% by mass, and the mixture was kneaded to prepare a pasty negative electrode material slurry. This slurry was applied to an electrolytic copper foil with a thickness of 11 μm using a coater so that the coating amount per unit area was 4.5 mg/cm ² . Thereafter, the mixture was dried at 105° C., and further compressed and molded using a roller press so that the density of the mixed material was 1.05 g/cm ³ to produce a negative electrode.

Then, the negative electrode, the separator, and the positive electrode (Li metal) were laminated in this order and placed in a coin battery container. A coin battery type lithium ion secondary battery was produced by injecting 3 ml of an electrolyte solution composed of ethyl ethylene carbonate (EC) and ethyl methyl carbonate (EMC) ( LiPF ₆ was dissolved in a mixed solvent (the volume ratio of EC and EMC is 1:1) so that the concentration becomes 1.0 mol/L.

The DC resistance (DCR) was measured using the produced lithium ion secondary battery. Specifically, first, charging was performed at a constant current of 0.2C and a constant voltage of 0V in a 25° C. environment until the current value reached 0.02C, and then, discharge was performed at a constant current of 0.2C until a voltage value of 1.5V was reached.

After charging and discharging under the above conditions, charging was performed with a constant current of 0.2 C to achieve a state of charge (SOC) of 50%. Thereafter, constant current discharge was performed at 1 C for 1 minute, then at 3 C for 1 minute, and then at 5 C for 1 minute. Based on the above test, find the difference (ΔV) between the voltage value when the SOC is 50% and the voltage value after 10 seconds of discharge at each current value. The current value is plotted on the horizontal axis and ΔV is plotted on the vertical axis. The slope of the graph is set to the DC resistance (25°C DCR) value (Ω) at 25°C. The results are shown in Table 1.

The lithium ion secondary battery was placed in a constant temperature bath set at 25°C, and one cycle of charge and discharge was performed under the following conditions.

Charging: CC/CV 0.2C 0V 0.02C Cut

Discharge: CC 0.2C 1.5V Cut

Then, constant current charging was performed with a current value of 0.2C until the SOC reached 50%. Thereafter, it was placed in a thermostat set at -30°C, and constant current discharge was performed at 0.1C for 1 minute, then constant current discharge was performed at 0.3C for 1 minute, and then constant current discharge was performed at 0.5C for 1 minute. Discharge. Furthermore, find the SOC as The difference (△V) between the voltage value at 50% and the voltage value after 10 seconds of discharge at each current value (ΔV), plotting the current value on the horizontal axis and △V on the vertical axis, the slope of the graph is -30℃ DC resistance (-30℃ DCR) value (Ω). The results are shown in Table 1.

<Example 2>

Carbonaceous particles were obtained in the same manner as in Example 1, except that commercially available coke with d002 of 0.346 nm and Lc of 5.2 nm was pulverized using an impact mill with a classifier. The carbonaceous particles were measured in the same manner as in Example 1. In addition, a lithium ion secondary battery was produced using the carbonaceous particles, and the same measurement as in Example 1 was performed. The results are shown in Table 1.

<Example 3>

Carbonaceous particles were obtained in the same manner as in Example 1, except that commercially available coke with d002 of 0.347 nm and Lc of 5.4 nm was pulverized using an impact mill with a classifier. The carbonaceous particles were measured in the same manner as in Example 1. In addition, a lithium ion secondary battery was produced using the carbonaceous particles, and the same measurement as in Example 1 was performed. The results are shown in Table 1.

<Example 4>

Carbonaceous particles were obtained in the same manner as in Example 1, except that commercially available coke with d002 of 0.345 nm and Lc of 4.7 nm was pulverized using an impact mill with a classifier. The carbonaceous particles were measured in the same manner as in Example 1. In addition, a lithium ion secondary battery was produced using the carbonaceous particles, and the same measurement as in Example 1 was performed. The results are shown in Table 1.

<Example 5>

Carbonaceous particles were obtained in the same manner as in Example 1, except that commercially available coke with d002 of 0.346 nm and Lc of 5.1 nm was pulverized using an impact mill with a classifier. The carbonaceous particles were measured in the same manner as in Example 1. In addition, a lithium ion secondary battery was produced using the carbonaceous particles, and the same measurement as in Example 1 was performed. The results are shown in Table 1.

<Comparative example 1>

Carbonaceous particles were obtained in the same manner as in Example 1, except that commercially available coke with d002 of 0.347 nm and Lc of 5.2 nm was pulverized using an impact mill with a classifier. The carbonaceous particles were measured in the same manner as in Example 1. In addition, a lithium ion secondary battery was produced using the carbonaceous particles, and the same measurement as in Example 1 was performed. The results are shown in Table 1.

<Comparative example 2>

Carbonaceous particles were obtained in the same manner as in Example 1, except that commercially available coke with d002 of 0.347 nm and Lc of 3.5 nm was pulverized using an impact mill with a classifier. The carbonaceous particles were measured in the same manner as in Example 1. In addition, a lithium ion secondary battery was produced using the carbonaceous particles, and the same measurement as in Example 1 was performed. The results are shown in Table 1.

<Comparative Example 3>

Carbonaceous particles were obtained in the same manner as in Example 1, except that commercially available coke with d002 of 0.346 nm and Lc of 5.7 nm was pulverized using an impact mill with a classifier. The carbonaceous particles were measured in the same manner as in Example 1. In addition, a lithium ion secondary battery was produced using the carbonaceous particles, and the same process as in Example 1 was carried out. Same assay. The results are shown in Table 1.

<Comparative Example 4>

Carbonaceous particles were obtained in the same manner as in Example 1, except that commercially available coke with d002 of 0.346 nm and Lc of 4.7 nm was pulverized using an impact mill with a classifier. The carbonaceous particles were measured in the same manner as in Example 1. In addition, a lithium ion secondary battery was produced using the carbonaceous particles, and the same measurement as in Example 1 was performed. The results are shown in Table 1.

As shown in Table 1, it was found that the lithium ion secondary battery produced using the carbonaceous particles of the Example in which Rc obtained by Raman mapping was in the range of 0.87 to 0.96 and R ₅₀ was in the range of 0.88 to 0.92 was relatively good. For the lithium ion secondary battery produced using the carbonaceous particles of the comparative example in which at least one of Rc and _R50 is outside the above range, the DC resistance value is small, especially at low temperature (-30°C), the DC resistance The value of the resistor is significantly smaller.

From the above results, it is known that by using the carbonaceous particles of the present disclosure as negative electrode materials, and low-resistance lithium-ion secondary batteries can be obtained.

All documents, patent applications, and technical specifications described in this specification are incorporated by reference into this specification to the same extent as if each individual document, patent application, or technical specification was specifically and individually indicated to be incorporated by reference. middle.

Claims (8)

Carbonaceous particles for negative electrode materials of lithium ion secondary batteries, which have a first carbon material as a core and at least a part of the surface of the first carbon material that is lower in crystallinity than the first carbon material. The second carbon material satisfies the following condition (1) in the frequency distribution of the R value representing the peak intensity ratio G/D of the G band and the D band of graphite obtained by Raman mapping measurement. and condition (2); (1) the mode of the R value is 0.87~0.96; (2) the R value when the cumulative frequency from the side with the smaller R value is 50% is 0.88~0.92. For the carbonaceous particles described in item 1 of the patent application, the crystallite size in the c-axis direction is 4.5nm~5.2nm, and the crystallite size in the c-axis direction is obtained by X-ray diffraction measurement. The half-maximum width of the diffraction peak of d002 is calculated using Scherrer's formula. For example, the carbonaceous particles described in item 1 or 2 of the patent application scope have a specific surface area of 2.0m ² /g~5.0m ² /g. The carbonaceous particles described in item 1 or 2 of the patent application scope have an average particle size of 5 μm to 20 μm. A negative electrode material for lithium ion secondary batteries, which contains the carbonaceous particles described in any one of items 1 to 4 of the patent application scope. The negative electrode material for lithium ion secondary batteries described in claim 5 of the patent application further contains graphite particles. A negative electrode for lithium ion secondary batteries, which includes the negative electrode material for lithium ion secondary batteries described in item 5 or 6 of the patent application scope. A lithium ion secondary battery, which includes the negative electrode for lithium ion secondary batteries described in item 7 of the patent application scope.