WO2012108113A1

WO2012108113A1 - Powder for negative-electrode material of lithium-ion secondary battery, negative-electrode of lithium-ion secondary battery and negative-electrode of capacitor using same, lithium-ion secondary battery, and capacitor

Info

Publication number: WO2012108113A1
Application number: PCT/JP2012/000003
Authority: WO
Inventors: 安田　幸司; 木崎　信吾; 下崎　新二
Original assignee: 株式会社大阪チタニウムテクノロジーズ
Priority date: 2011-02-09
Filing date: 2012-01-04
Publication date: 2012-08-16
Also published as: CN103348513A; KR20130130824A; JP5662485B2; KR101567181B1; JPWO2012108113A1

Abstract

Powder for a negative-electrode material of a lithium-ion secondary battery, which has conductive carbon film formed on the surface of lower silicon-oxide powder, and which is characterized in satisfying a relationship of 0.01 ≤ Fa ≤ 0.4, wherein Fa is the average value of F of 10 particles, F is a coefficient of variation of the thickness of the carbon film and is defined as F = σ/ta, and ta is the average value and σ is the standard deviation of the thickness of the conductive carbon film measured at 24 points of a particle of the lower silicon-oxide powder. The proportion of the conductive carbon film is preferably a mass percent of 0.5% to 10%. The total content of tar constituent measured with a TPD-MS is preferably a mass ppm of 1 ppm to 3500 ppm, and the resistivity is preferably not more than 10,000 Ωcm. The maximum value (P1) of a halo due to SiO_x derived by an XRD measurement, and a peak value (P2) of the strongest line of Si(111) preferably satisfy a relationship of P2/P1 < 0.01. With such a configuration, powder for a negative-electrode material to be used in a lithium-ion secondary battery that has large discharging capacity, good cycling characteristic, and that can withstand practical-level usage, is able to be provided.

Description

Powder for negative electrode material of lithium ion secondary battery, lithium ion secondary battery negative electrode and capacitor negative electrode using the same, lithium ion secondary battery and capacitor

The present invention relates to a powder for a negative electrode material that can be used for a lithium ion secondary battery, has a large discharge capacity, has good cycle characteristics, and can obtain a lithium ion secondary battery that can withstand use at a practical level. The present invention also relates to a lithium ion secondary battery negative electrode and capacitor negative electrode, and a lithium ion secondary battery and capacitor using the negative electrode material powder.

In recent years, with the remarkable development of portable electronic devices, communication devices, etc., there is a strong demand for the development of secondary batteries with high energy density from the viewpoints of economy and miniaturization and weight reduction of the devices. Currently, high energy density secondary batteries include nickel cadmium batteries, nickel metal hydride batteries, lithium ion secondary batteries, and polymer batteries. Among these, lithium ion secondary batteries have a much longer lifespan and higher capacity than nickel cadmium batteries and nickel metal hydride batteries, and thus the demand thereof has shown high growth in the power supply market.

FIG. 1 is a diagram showing a configuration example of a coin-shaped lithium ion secondary battery. As shown in FIG. 1, the lithium ion secondary battery maintains the electrical insulation between the positive electrode 1, the negative electrode 2, the separator 3 impregnated with the electrolyte, and the positive electrode 1 and the negative electrode 2 and seals the battery contents. It consists of a gasket 4. When charging / discharging is performed, lithium ions reciprocate between the positive electrode 1 and the negative electrode 2 through the electrolytic solution of the separator 3.

The positive electrode 1 includes a counter electrode case 1a, a counter electrode current collector 1b, and a counter electrode 1c, and lithium cobaltate (LiCoO ₂ ) and lithium manganate (LiMn ₂ O ₄ ) are mainly used for the counter electrode 1c. The negative electrode 2 is composed of a working electrode case 2a, a working electrode current collector 2b, and a working electrode 2c, and the negative electrode material used for the working electrode 2c is generally an active material capable of occluding and releasing lithium ions (negative electrode active material). And a conductive assistant and a binder.

Conventionally, carbon-based materials have been used as negative electrode active materials for lithium ion secondary batteries. As a new negative electrode active material having a higher capacity of a lithium ion secondary battery than conventional ones, a composite oxide of lithium and boron, a composite oxide of lithium and a transition metal (V, Fe, Cr, Mo, Ni, etc.) Si, Ge, or a compound containing Sn and N and O, Si particles whose surface is coated with a carbon layer by chemical vapor deposition, and the like have been proposed.

However, although all of these negative electrode active materials can improve the charge / discharge capacity and increase the energy density, expansion and contraction at the time of occlusion and release of lithium ions are increased. Therefore, lithium ion secondary batteries using these negative electrode active materials are insufficient in sustainability of discharge capacity (hereinafter referred to as “cycle characteristics”) due to repeated charge and discharge.

On the other hand, it has been attempted to use silicon oxide powder represented by SiO _x (0 <x ≦ 2) such as SiO as the negative electrode active material. Silicon oxide can be a negative electrode active material with a larger effective charge / discharge capacity because it has less degradation such as collapse of the crystal structure and generation of irreversible materials due to insertion and extraction of lithium ions during charge and discharge. Therefore, by using silicon oxide as a negative electrode active material, lithium has a higher capacity than when carbon is used, and has better cycle characteristics than when a high capacity negative electrode material such as Si or Sn alloy is used. An ion secondary battery has been obtained.

When silicon oxide powder is used as the negative electrode active material, carbon powder or the like is generally mixed as a conductive aid in order to compensate for the low electrical conductivity of silicon oxide. Thereby, the electrical conductivity of the contact part vicinity of a silicon oxide powder and a conductive support agent is securable. However, electrical conductivity cannot be ensured at a location away from the contact portion, and it is difficult to function as a negative electrode active material.

In order to solve this problem, in Patent Document 1, a carbon film is formed by CVD (chemical vapor deposition) on the surface of particles (conductive silicon composite) having a structure in which silicon microcrystals are dispersed in silicon dioxide. A conductive silicon composite for a nonaqueous electrolyte secondary battery negative electrode material and a method for producing the same have been proposed.

Japanese Patent No. 3952180

Patent Document 1 describes that, according to the method proposed in this document, a uniform conductive carbon film can be formed on silicon oxide particles. However, according to the study by the present inventors, the lithium ion secondary battery using the conductive silicon composite of the same document has problems such as sudden decrease in capacity at a certain point when charging and discharging are repeated. This is probably because silicon dioxide in which microcrystals of silicon are dispersed is used as the negative electrode material, so that lithium ions occlude and expand and contract during discharge. Further, the discharge capacity and cycle characteristics were not sufficient.

In addition, the present inventors have made various studies on silicon oxide, which is considered to be a negative electrode material powder (negative electrode active material) that can increase the capacity of a lithium ion secondary battery. As a result, the decrease in initial efficiency (the value of the ratio of the discharge capacity to the charge capacity at the time of the first charge / discharge (at the time of the first charge / discharge) after the manufacture of the lithium ion secondary battery) is Li ₄ led to think to be due to the formation of SiO _4. In the expression (1), Li ₂₂ Si _{5 in} the first term on the right side is a component responsible for reversible capacity (discharge capacity), and Li ₄ SiO _{4 in} the second term is a component responsible for irreversible capacity. Li ₄ SiO ₄ cannot release lithium ions.
SiO _x + (44−x) / 10Li ⁺ + (44−x) / 10e ⁻
→ (4-x) / 20Li ₂₂ Si ₅ + x / 4Li ₄ SiO ₄ (1)

According to the study by the present inventors, the theoretical characteristic of the lithium ion secondary battery when silicon oxide (SiO _x ) is used as the negative electrode material powder and x = 1 is a reversible capacity of 2007 mAh / g, The initial efficiency was found to be 76%. Conventional lithium ion secondary batteries using silicon oxide as a negative electrode material powder have a reversible capacity of about 1500 mAh / g, so a lithium ion secondary battery using silicon oxide as a negative electrode material powder. It was found that there is still room for improvement in the reversible capacity of the battery.

Furthermore, the present inventors are particularly concerned with silicon oxide having a carbon film that can make the cycle characteristics of lithium ion secondary batteries relatively good among silicon oxide materials used as powders for negative electrode materials. investigated. As a result, under the conditions described in Patent Document 1, using a rotary kiln having a baffle plate on the inner surface of the core tube, using silicon oxide powder having a carbon film formed on the surface using the thermal decomposition reaction of hydrocarbon gas The obtained lithium ion secondary battery was found to have insufficient cycle characteristics.

The present invention has been made in view of this problem, and has a large discharge capacity, good cycle characteristics, and a negative electrode material powder for a lithium ion secondary battery that can withstand use at a practical level, and the negative electrode material. It is an object to provide a lithium ion secondary battery negative electrode and a capacitor negative electrode, and a lithium ion secondary battery and a capacitor using the powder for use.

In order to solve the above problems, the present inventors investigated a silicon oxide powder on which a carbon film was formed under the conditions described in Patent Document 1. Specifically, the silicon oxide powder was observed using a transmission electron microscope. As a result, the method proposed in this document has a certain effect on the homogenization of the carbon film to be formed, but the thickness of the carbon film is the same on the surface on the opposite side even with the same particle. It has been found that it cannot be said that it is sufficiently uniform, for example, it is larger than that.

When a carbon film is formed on the surface of silicon oxide powder using the thermal decomposition reaction of hydrocarbon gas such as methane, it is formed by the part of the particles unless the gas and each particle of silicon oxide powder are in uniform contact with each other. Variations in film thickness. In the method described in Patent Document 1, the thickness of the carbon film formed while stirring the powder with a baffle plate provided on the inner surface of the core tube of the rotary kiln is made uniform. However, since the particles lifted by the baffle plate fall in a lump shape, secondary aggregation of the particles cannot be sufficiently suppressed, and it is assumed that the thickness of the carbon film is not uniform.

The inventors of the present invention have made the inner surface of a quartz core tube made of quartz rough by sandblasting, so that small collapse of the silicon oxide powder occurs frequently when the core tube rotates, and the silicon oxide powder tends to roll. As a result, the thickness of the carbon film formed on the surface of the silicon oxide powder could be made almost uniform. This is because by making the inner surface of the core tube rough, the effect of stirring the silicon oxide powder was enhanced and secondary agglomeration of the particles was sufficiently suppressed, so that the entire surface of each particle was thermally decomposed uniformly. It is assumed that a reaction has occurred.

Also, experiments were conducted on lithium ion secondary batteries using particles in which the thickness of the carbon film was changed by varying the operating conditions of the rotary kiln. As a result, the higher the uniformity of the thickness of the carbon film, the better the cycle characteristics of the lithium ion secondary battery, and if the coefficient of variation of the thickness of the carbon film is not more than a predetermined value, sufficient cycle characteristics can be obtained. I found out that The coefficient of variation of the thickness of the carbon film will be described later.

When the thickness of the carbon film is uniform, the stress generated in the carbon film as the silicon oxide powder expands during charging and discharging of the lithium ion secondary battery can be alleviated uniformly in all directions. Since the destruction of the film can be suppressed, the cycle characteristics are considered to be good.

The present invention has been made on the basis of the above findings, and the gist thereof is as follows. (1) to (5) Lithium ion secondary battery negative electrode powder, (6) Lithium ion secondary battery negative electrode And a capacitor negative electrode of the following (7), a lithium ion secondary battery of the following (8), and a capacitor of the following (9).

(1) The surface of the lower silicon oxide powder has a conductive carbon film, and the average thickness of the conductive carbon film measured at 24 locations of one particle of the lower silicon oxide powder is ta, When the standard deviation is defined as σ and the variation coefficient F of the thickness of the carbon film is defined as F = σ / ta, the average value Fa of the variation coefficient F of 10 particles is 0.01 ≦ Fa ≦ 0.4. A powder for a negative electrode material for a lithium ion secondary battery, characterized by being satisfied.

(2) The powder for a lithium ion secondary battery negative electrode material according to (1), wherein the proportion of the conductive carbon film is 0.5% by mass or more and 10% by mass or less.

(3) The lithium ion secondary battery negative electrode material according to (1) or (2) above, wherein the total content of tar components measured by TPD-MS is 1 mass ppm or more and 3500 mass ppm or less Powder.

(4) The powder for a negative electrode material for a lithium ion secondary battery according to any one of (1) to (3), wherein the specific resistance is 10,000 Ωcm or less.

(5) The maximum value P1 of halo derived from SiO _x appearing at 2θ = 10 ° to 30 ° and Si appearing at 2θ = 28.4 ± 0.3 ° when measured by XRD using CuK _α- ray The powder for a lithium ion secondary battery negative electrode material according to any one of the above (1) to (4), wherein the relationship of the value P2 of the strongest line peak of (111) satisfies P2 / P1 <0.01 .

(6) A lithium ion secondary battery negative electrode using the powder for a lithium ion secondary battery negative electrode material according to any one of (1) to (5).

(7) A capacitor negative electrode using the lithium ion secondary battery negative electrode powder according to any one of (1) to (5).

(8) A lithium ion secondary battery using the lithium ion secondary battery negative electrode of (6).

(9) A capacitor using the capacitor negative electrode of (7).

In the present invention, the “lower silicon oxide powder” is an SiO _x powder satisfying x ≦ 0.4 ≦ x ≦ 1.2. Each measuring method of _x of SiO _x , the proportion of the conductive carbon film in the negative electrode material powder, and the tar component content will be described later.

As will be described later, “having a conductive carbon film on the surface” of the lower silicon oxide powder is a result of surface analysis using an X-ray photoelectron spectroscopic analyzer. As a result, the Si / C molar ratio value Si / C Is 0.1 or less.

Lithium ion secondary battery negative electrode powder according to the present invention, and lithium ion secondary battery negative electrode or capacitor negative electrode are used to provide lithium having a large discharge capacity and good cycle characteristics, and can be used at a practical level. An ion secondary battery or a capacitor can be obtained. Moreover, the lithium ion secondary battery and capacitor of the present invention have a large discharge capacity and good cycle characteristics.

FIG. 1 is a diagram illustrating a configuration example of a coin-shaped lithium ion secondary battery. FIG. 2 is a diagram showing a method for measuring the thickness of the conductive carbon film. FIG. 3 is a diagram showing a configuration example of a silicon oxide production apparatus.

1. Powder for negative electrode material of lithium ion secondary battery of the present invention The powder for negative electrode material of lithium ion secondary battery of the present invention has a conductive carbon film on the surface of a lower silicon oxide powder, and the thickness of the carbon film of 10 particles. The average value Fa of the variation coefficient F of the thickness satisfies 0.01 ≦ Fa ≦ 0.4.

As described above, the lower silicon oxide powder is a SiO _x powder in which _x satisfies 0.4 ≦ x ≦ 1.2. The reason why x is in this range is that when the value of x is less than 0.4, the lithium ion secondary battery using the negative electrode material powder of the present invention and the capacitor are severely deteriorated due to charge / discharge cycles, and 1.2. This is because the capacity of the battery is reduced when the value exceeds. Further, x preferably satisfies 0.8 ≦ x ≦ 1.05.

By forming a conductive carbon film on the lower silicon oxide powder, which is an insulator, the discharge capacity of a lithium ion secondary battery using this lower silicon oxide powder as a negative electrode material powder can be improved. Further, the closer the thickness of the conductive carbon film is, the better the cycle characteristics of the lithium ion secondary battery are, and the average value Fa of the coefficient of variation F of the thickness of the conductive carbon film (hereinafter referred to as “average coefficient of variation”). If it is also 0.4) or less, sufficient cycle characteristics can be obtained. The average variation coefficient is an index of the uniformity of the thickness of the conductive carbon film, and the smaller the value, the closer the thickness of the conductive carbon film is. When the particles of the lower silicon oxide powder are obtained by crushing and are indefinite, it is difficult to make the average coefficient of variation smaller than 0.01. From the above, the powder for a lithium ion secondary battery negative electrode material of the present invention satisfies the average variation coefficient Fa of 0.01 ≦ Fa ≦ 0.4. The average variation coefficient Fa preferably satisfies 0.01 ≦ Fa ≦ 0.2. A method for calculating the average coefficient of variation will be described later.

In the powder for a lithium ion secondary battery negative electrode material of the present invention, the proportion of the conductive carbon film (hereinafter referred to as “carbon film ratio”) is preferably 0.5 mass% or more and 10 mass% or less. This is due to the following reason.

The carbon film also contributes to the charge / discharge capacity of the lithium ion secondary battery as in the case of lower silicon oxide, but its charge / discharge capacity per unit mass is smaller than that of lower silicon oxide. Therefore, the carbon film rate of the negative electrode material powder is preferably 10% by mass or less from the viewpoint of securing the charge / discharge capacity of the lithium ion secondary battery. On the other hand, if the carbon film ratio is less than 0.5% by mass, the effect of imparting conductivity by the conductive carbon film cannot be obtained, and the lithium ion secondary battery using the negative electrode material powder is difficult to function as a battery. . The carbon film rate is more preferably 0.5% by mass or more and 2.5% by mass or less.

In the lithium ion secondary battery negative electrode powder of the present invention, the total content of the tar component is preferably 1 mass ppm or more and 3500 mass ppm or less. The tar component is generated when the conductive carbon film is formed, as will be described later. When the total content of the tar components is more than 3500 mass ppm, the resistance to expansion and contraction of the negative electrode accompanying charge / discharge of the lithium ion secondary battery is poor, and the cycle characteristics are poor. On the other hand, when it is 3500 ppm by mass or less, a lithium ion secondary battery having good initial efficiency and cycle characteristics can be obtained, and the cycle characteristics are particularly good. At 2000 mass ppm or less, initial efficiency and cycle characteristics are further improved. Further, the total content of the tar component is set to 1 mass ppm or less because the time for vacuum treatment of the negative electrode material powder for the lithium ion secondary battery becomes longer and the manufacturing cost is increased. From these things, it is more preferable that the total content of the tar component is 40 mass ppm or more and 2000 mass ppm or less.

The specific resistance of the powder for a lithium ion secondary battery negative electrode material of the present invention is preferably 10,000 Ωcm or less. This is because when the specific resistance is larger than 10,000 Ωcm, it is difficult to act as an electrode active material of the lithium ion secondary battery. The smaller the specific resistance, the better the electric conduction and the better the electrode active material of the lithium ion secondary battery, so there is no need to provide a lower limit.

The powder for a lithium ion secondary battery negative electrode material of the present invention has a maximum halo P1 derived from SiO _x that appears at 10 ° ≦ 2θ ≦ 30 ° and 2θ = 2θ = when measured by XRD using CuK _α rays. It is preferable that the value P2 of the strongest peak of Si (111) appearing at 28.4 ± 0.3 ° satisfies P2 / P1 <0.01, that is, amorphous. Compared to the case where the lower silicon oxide powder in the negative electrode material powder is amorphous, the expansion due to the intrusion of lithium ions is easier to relax, and the cycle characteristics of the lithium ion secondary battery are reduced. It is because it is excellent in.

It is preferable that the powder for a lithium ion secondary battery negative electrode material of the present invention satisfies 1 μm ≦ D50 ≦ 10 μm in the particle size distribution. Dn (0 <n ≦ 100) is the particle size when the cumulative frequency from the smaller particle size reaches n%. When D50 <1 μm, bubbles are likely to be generated during the production of the slurry, and thus the adhesion between the electrode substrate and the negative electrode is weakened. On the other hand, when 10 μm <D50, the roughness of the negative electrode surface increases, and in this case also, the adhesion between the electrode substrate and the negative electrode is weakened. It is more preferable that D50 satisfies 3 μm ≦ D50 ≦ 10 μm.

The powder for a negative electrode material for a lithium ion secondary battery of the present invention preferably has a specific surface area measured by the BET method of 3.0 m ² / g or less. If the specific surface area is larger than 3.0 m ² / g, the surface area becomes considerably large, so the ratio of the SEI film (Solid Electrolyte Interface, irreversible capacity component) formed on the particle surface increases, and the lithium ion secondary battery Capacity may be reduced.

2. Analysis method 2-1. Method of calculating coefficient of variation The coefficient of variation of the thickness of the conductive carbon film of the negative electrode powder for lithium ion secondary batteries is calculated by the following method.

The thickness of the conductive carbon film of the negative electrode material for a lithium ion secondary battery is measured using a transmission electron microscope (Transmission Electron Microscope; TEM). In order to facilitate the measurement of the thickness of the film, the observation sample is deposited with a metal layer of several nm on the powder of the sample to be observed, mixed with bisphenol A type epoxy resin, and dried for 12 hours or more. Make it. The prepared observation sample is processed by a focused ion beam (FIB) method to produce an observation region having a width of 10 μm and a depth of 10 μm. In the observation region, the entire particle can be completely observed, and includes at least one powder for a negative electrode material of a lithium ion secondary battery that is processed to a thickness of 100 nm by the FIB method and has a long diameter of 2 μm or more after processing. This is the pass area. Of the particles of the negative electrode powder for the lithium ion secondary battery in the pass region, the particles with the largest major axis are the observation targets. Table 1 shows the apparatus used for the FIB method, and the TEM used and the observation conditions using the TEM.

FIG. 2 is a diagram showing a method for measuring the thickness of the conductive carbon film. As shown in the figure, the midpoint of the major axis of the observed particle is defined as a center 21a, and straight lines passing through the center are drawn every 15 ° from the major axis. The thickness of the carbon film 22 at the intersection between each straight line and the surface of the silicon oxide powder 21 is measured. The thickness of the carbon film 22 is the shortest distance from the intersection of each straight line and the surface of the silicon oxide powder 21 to the surface of the carbon film 22.

The thickness t of the carbon film 22 is measured for each straight line, and the average value ta and the standard deviation σ of the total 24 measured values are calculated. Using the average value ta and the standard deviation σ, the variation coefficient F of the thickness of the carbon film 22 of the particle is defined as F = σ / ta.

The calculation of such a coefficient of variation F is performed for 10 acceptable regions, and the carbon of the powder for a lithium ion secondary battery negative electrode material using the average coefficient of variation Fa, which is an average value of the coefficient of variation F of 10 particles, as a sample. It is used as an index of film thickness uniformity.

2-2. Calculation method of x of SiO _x x of SiO _x is a molar ratio (O / Si) of O content and Si content in the powder for a negative electrode of a lithium ion secondary battery, for example, O measured by the following measurement method It can calculate using a content rate and Si content rate.

2-3. Measuring method of O content O content in powder for lithium ion secondary battery negative electrode material was analyzed by 10% of sample by inert gas melting / infrared absorption method using oxygen concentration analyzer (Leco, TC436). It is calculated from the O content in the sample quantitatively evaluated.

2-4. Method for Measuring Si Content The Si content in the negative electrode powder for lithium ion secondary batteries was determined by adding nitric acid and hydrofluoric acid to the sample to dissolve the sample, and then adding the resulting solution to an ICP emission spectrometer (Shimadzu Corporation). It is calculated from the Si content in the sample quantitatively evaluated by analyzing the product.

2-5. Method for Evaluating State of Formation of Conductive Carbon Film In the powder for a negative electrode material for a lithium ion secondary battery of the present invention, “having a conductive carbon film on the surface of a lower silicon oxide powder” means AlK _α ray (1486.6 eV). When the surface analysis of the lower silicon oxide powder subjected to the conductive carbon film formation treatment was performed with an X-ray photoelectron spectroscopic analyzer (XPS) using Si, the molar ratio value Si / C of Si / C was It means 0.1 or less. The XPS measurement conditions are as shown in Table 2. In order to sufficiently impart electric conductivity to the powder for a negative electrode material for a lithium ion secondary battery, the Si / C is preferably 0.05 or less, and more preferably 0.02 or less. “Si / C is 0.02 or less” is a state in which most of the surface of the lower silicon oxide powder is covered with C and Si is hardly exposed.

2-6. Carbon film ratio measurement method The carbon film ratio is determined by measuring the mass of the powder for the negative electrode material of the lithium ion secondary battery and the CO ₂ gas by an oxygen gas flow combustion-infrared absorption method using a carbon concentration analyzer (Leco, CS400). It is calculated from the result of carbon amount quantitatively evaluated by analysis. The crucible is a ceramic crucible, the auxiliary combustor is copper, and the analysis time is 40 seconds.

2-7. Method of measuring content of tar component by TPD-MS The amount of residual tar component of the negative electrode material powder for lithium ion secondary batteries is determined by the following TPD-MS (Temperature Programmed Desorption-Mass Spectroscopy). Can be measured. A 50 mg sample is placed in a silica cell and heated from room temperature to 1000 ° C. at a rate of 10 K / min in a 50 mL / min helium gas flow. The generated gas is analyzed with a mass spectrometer (manufactured by Shimadzu Corporation, GC / MS QP5050A).

The tar component is a high molecular weight component such as an aromatic hydrocarbon generated when a hydrocarbon or organic gas is thermally decomposed. In the present invention, the total amount of components having molecular weights of 57, 106, 178, 202, 252 and 276 is defined as the residual tar component amount (see Table 5 described later). Representative chemical species of each molecular weight are 106 for xylene, 178 for phenanthrene and anthracene, 202 for pyrene, 252 for perylene and benzopyrene, and 276 for pentacene and picene.

2-8. Specific Resistance Measurement Method The specific resistance ρ (Ωcm) of the powder for a negative electrode material for a lithium ion secondary battery is calculated using the following equation (2).
ρ = R × A / L (2)
Here, R: electrical resistance (Ω) of the sample, A: bottom area (cm ² ) of the sample, and L: thickness (cm) of the sample.
The electrical resistance of the sample can be measured, for example, by a two-terminal method using a digital multimeter (VOAC7513, manufactured by Iwatatsu Measurement Co., Ltd.). In this case, the sample was filled with 0.20 g of the sample in a powder resistance measurement jig (jig part: stainless steel with an inner diameter of 20 mm, frame part: made of polytetrafluoroethylene), and pressurized at 20 kgf / cm ² for 60 seconds. The thickness of the molded sample is measured with a micrometer.

2-9. Method for Measuring D50 in Particle Size Distribution D50 can be measured using a laser diffraction particle size distribution measuring device. The measurement conditions are as shown in Table 3. A 2 g sample is placed in the apparatus, and 2 g / L sodium hexametaphosphate is added as a dispersant. The measurement range is 0.02 μm to 2000 μm, and the weight distribution is measured. D50 is the particle size when the cumulative frequency from the smaller particle size reaches 50%.

3. Method for Producing Lower Silicon Oxide Powder FIG. 3 is a diagram showing a configuration example of a silicon oxide production apparatus. This apparatus includes a vacuum chamber 5, a raw material chamber 6 disposed in the vacuum chamber 5, and a deposition chamber 7 disposed on the upper portion of the raw material chamber 6.

The raw material chamber 6 is formed of a cylindrical body, and a cylindrical raw material container 8 and a heating source 10 surrounding the raw material container 8 are disposed at the center thereof. As the heating source 10, for example, an electric heater can be used.

The deposition chamber 7 is composed of a cylindrical body arranged so that its axis coincides with the raw material container 8. A deposition base 11 made of stainless steel is provided on the inner peripheral surface of the deposition chamber 7 for vapor deposition of gaseous silicon oxide generated by sublimation in the raw material chamber 6.

A vacuum device (not shown) for discharging the atmospheric gas is connected to the vacuum chamber 5 that accommodates the raw material chamber 6 and the deposition chamber 7, and the gas is discharged in the direction of arrow A.

In the case of producing lower silicon oxide using the production apparatus shown in FIG. 3, a mixed granulated raw material 9 in which silicon powder and silicon dioxide powder are blended at a predetermined ratio as a raw material, mixed, granulated and dried is used. The mixed granulated raw material 9 is filled in the raw material container 8 and heated (heated by a heating source 10) in an inert gas atmosphere or vacuum to generate (sublimate) SiO. Gaseous SiO generated by the sublimation rises from the raw material chamber 6 and enters the deposition chamber 7, is vapor-deposited on the surrounding deposition base 11, and is deposited as lower silicon oxide 12. Thereafter, the lower silicon oxide 12 deposited from the deposition base 11 is removed and pulverized using a ball mill or the like to obtain a lower silicon oxide powder.

4). Method for Forming Conductive Carbon Film The conductive carbon film is formed on the surface of the lower silicon oxide powder having the adjusted particle size by CVD or the like. Specifically, a rotary kiln is used as an apparatus, and a hydrocarbon gas as a carbon source or a mixed gas of an organic substance-containing gas and an inert gas is used as a gas.

The rotary kiln can be made by using sandblasting with the inner surface of a quartz core tube made of quartz roughened. The roughness of the inner surface of the core tube is the maximum height (Rz) specified in JIS B0601: 2001, and is preferably 40 μm or more. This is because when the Rz is less than 40 μm, the lower silicon oxide powder hardly rolls even when the core tube rotates, and the thickness of the conductive carbon film is difficult to be uniform.

However, when organic substances other than hydrocarbons are used as the carbon source, components other than C and H such as O and N react with silicon oxide to generate SiO ₂ and Si ₃ N _4. The amount of Si that can contribute is reduced, and the capacity of the lithium ion secondary battery is reduced. Therefore, hydrocarbon gas consisting only of C and H is preferable as the carbon source. When a hydrocarbon gas is used as the carbon source, an aromatic composed of only C and H is generated as a tar component, and components having molecular weights of 57, 106, 178, 202, 252 and 276 are the main components.

The forming temperature of the conductive carbon film is 700 ° C. or higher and 750 ° C. or lower. Moreover, although processing time is set between 20 minutes or more and 120 minutes or less according to the gas flow rate and the thickness of the conductive carbon film to form, it is so preferable that it is short. This treatment condition is a range in which a conductive carbon film having low crystallinity can be obtained. Moreover, it is also the range in which the production | generation of SiC in the interface vicinity of the surface of a lower silicon oxide powder and a carbon film is suppressed.

According to the inventors' investigation, it is known that the conductive carbon film has better cycle characteristics of the lithium ion secondary battery when the crystallinity is lower. This is considered to be due to the fact that the higher the crystallinity of the conductive carbon film, the lower the lithium ion acceptance rate and the lower the ability to relax the expansion and contraction of silicon oxide. Further, SiC is generated near the interface between the surface of the lower silicon oxide powder and the carbon film when the heating temperature is excessively high. Since generation of SiC reduces the amount of Si that can contribute to the capacity of the battery, it is preferable to suppress generation of SiC.

5. Vacuum treatment method of lower silicon oxide powder with conductive carbon film formed The lower silicon oxide powder with conductive carbon film formed under vacuum at a temperature of 600 ° C. or higher and 750 ° C. or lower for 10 minutes or longer and 1 hour or shorter Apply vacuum treatment to hold. The vacuum treatment is performed in a state where the lower silicon oxide powder is housed in a vacuum chamber, and the internal pressure of the vacuum chamber is maintained at 1 Pa or less using an oil diffusion pump. This internal pressure is measured using a Pirani gauge.

The tar component generated during the formation of the carbon film can be volatilized and removed from the carbon film by vacuum treatment. Moreover, when the heating holding temperature is in the above range, the generation of SiC in the vicinity of the interface between the silicon oxide and the carbon film is suppressed.

6). Configuration of Lithium Ion Secondary Battery A configuration example of a coin-shaped lithium ion secondary battery using the powder for a lithium ion secondary battery negative electrode material and the lithium ion secondary battery negative electrode of the present invention is described with reference to FIG. explain. The basic configuration of the lithium ion secondary battery shown in FIG.

The negative electrode material used for the negative electrode 2, that is, the working electrode 2c constituting the negative electrode of the lithium ion secondary battery of the present invention is configured using the powder for negative electrode material of the lithium ion secondary battery of the present invention. Specifically, it can be comprised with the powder for lithium ion secondary battery negative electrode materials of this invention which is an active material, another active material, a conductive support agent, and a binder. Of the constituent materials in the negative electrode material, the ratio of the powder for the negative electrode material of the lithium ion secondary battery of the present invention to the total of the constituent materials excluding the binder is 20% by mass or more. It is not always necessary to add an active material other than the powder for a negative electrode material of the lithium ion secondary battery of the present invention. As the conductive assistant, for example, acetylene black or carbon black can be used, and as the binder, for example, polyacrylic acid (PAA) or polyvinylidene fluoride can be used.

Since the lithium ion secondary battery of the present invention uses the above-described powder for a lithium ion secondary battery negative electrode material and a lithium ion secondary battery negative electrode of the present invention, the discharge capacity is large, the cycle characteristics are good, and the practical level. Can withstand use in

The powder for negative electrode material of the present invention and the negative electrode using the same can also be applied to capacitors.

In order to confirm the effect of the present invention, the following test using a lithium ion secondary battery was performed, and the result was evaluated.

1. Test conditions 1-1. Configuration of Lithium Ion Secondary Battery The configuration of the lithium ion secondary battery was the coin shape shown in FIG.

First, the negative electrode 2 will be described. Silicon powder and silicon dioxide powder were blended at a predetermined ratio, and mixed, granulated and dried mixed granulation raw materials were used as raw materials, and lower silicon oxide was deposited on the deposition substrate using the apparatus shown in FIG. . The deposited lower silicon oxide was pulverized for 24 hours using an alumina ball mill to obtain a powder having a D50 of 4.8 μm and a BET specific surface area of 2.73 m ² / g. This lower silicon oxide (SiO _x ) powder satisfied x = 1.

A conductive carbon film was formed on the surface of the lower silicon oxide powder to obtain a negative electrode material powder for a lithium ion secondary battery. For the formation of the carbon film, a rotary kiln was used as the apparatus, a mixed gas of propane and Ar was used as the gas, and the processing temperature was 700 ° C. The average coefficient of variation and the carbon film ratio were as shown in Table 4 and Table 5.

In test numbers 1 to 4 shown in Table 4, the value of the average coefficient of variation was changed by changing the roughness (Rz) of the inner surface of the core tube. The value of Rz was controlled by the particle size of the sand used for sandblasting. Test Nos. 1 to 3 are examples of the present invention, and the average coefficient of variation satisfied the provisions of the present invention. Test No. 4 was a comparative example, and the value of the average variation coefficient was larger than the specified range of the present invention.

In Test Nos. 5 and 6 shown in Table 5, a vacuum treatment was performed after forming a conductive carbon film. The holding temperature of the vacuum treatment was 750 ° C., the holding time was as shown in the table, and the internal pressure of the vacuum chamber was kept at 1 Pa or less using an oil diffusion pump.

A slurry is prepared by adding n-methylpyrrolidone to a mixture of 65% by mass of the negative electrode material powder for lithium ion secondary battery, 10% by mass of acetylene black, and 25% by mass of PAA. This slurry was applied to a copper foil having a thickness of 20 μm, dried in an atmosphere at 120 ° C. for 30 minutes, and then punched out to a size with an area of 1 cm ^{2 on} one side to obtain a negative electrode 2.

The counter electrode 1c was a lithium foil. As the electrolyte, LiPF ₆ (lithium phosphorous hexafluoride) was dissolved in a mixed solution in which EC (ethylene carbonate) and DEC (diethyl carbonate) had a volume ratio of 1: 1 so as to have a ratio of 1 mol / liter. It was set as the solution. As the separator, a polyethylene porous film having a thickness of 30 μm was used.

1-2. Charge / Discharge Test Conditions For the charge / discharge test, a secondary battery charge / discharge test apparatus (manufactured by Nagano Corporation) was used. Charging was performed at a constant current of 1 mA until the voltage between both electrodes of the lithium ion secondary battery reached 0 V, and after the voltage reached 0 V, charging was performed while maintaining 0 V. Thereafter, charging was terminated when the current value fell below 20 μA. The discharge was performed at a constant current of 1 mA until the voltage between both electrodes of the lithium ion secondary battery reached 1.5V. The above charge / discharge test was performed 10 cycles.

2. Test Results A charge / discharge test was performed on the lithium ion secondary battery manufactured under the above conditions, and evaluation was performed using the cycle capacity maintenance rate as an index. Moreover, the carbon film rate was also measured about the powder for lithium ion secondary battery negative electrode materials. For

test numbers

1, 7 and 8, the total content of tar components was also measured. These values are shown in Table 4 and Table 5 together with the test conditions. The cycle capacity retention rate is a value obtained by dividing the discharge capacity at the 10th cycle by the initial discharge capacity, and the larger the value, the better the cycle characteristics.

2-1. Influence of Average Fluctuation Coefficient Based on the test results shown in Table 4, the influence of the average fluctuation coefficient value will be described. In all of the test numbers 1 to 4, the carbon coverage was within the range preferable in the present invention.

In test number 4, the value of the average variation coefficient was larger than the specified range of the present invention, and the initial discharge capacity was as small as 71.2%.

On the other hand, in the test numbers 1 to 3, the value of the average variation coefficient was within the range defined by the present invention, and the initial discharge capacity was an excellent value of 88.1% or more.

2-2. Influence of the total content of tar components Based on the test results shown in Table 5, the influence of the total content of tar components will be described. In each of Test Nos. 5 and 6, the specific surface area, the carbon coverage, and the thickness of the carbon film were within the ranges preferred in the present invention. Table 5 also shows test number 1 as a comparison target.

As shown in Table 5, in Test Nos. 5 and 6 in which the value of the average variation coefficient was equal to that of Test No. 1, the tar component was removed, and the total content of the tar component was adjusted to 3500 mass ppm or less for the first time. The discharge capacity was even better. From the results shown in Table 5, it can be seen that the longer the vacuum treatment time, the lower the total content of tar components and the larger the initial discharge capacity.

Also, it was confirmed that any of the lithium ion secondary batteries of test numbers 1 to 6 had a sufficient carbon coverage and an excellent discharge capacity.

Lithium ion secondary battery negative electrode powder according to the present invention, and lithium ion secondary battery negative electrode or capacitor negative electrode are used to provide lithium having a large discharge capacity and good cycle characteristics, and can be used at a practical level. An ion secondary battery or a capacitor can be obtained. Moreover, the lithium ion secondary battery and capacitor of the present invention have a large discharge capacity and good cycle characteristics. Therefore, the present invention is a useful technique in the field of secondary batteries and capacitors.

1: positive electrode, 1a: counter electrode case, 1b: counter electrode current collector, 1c: counter electrode,
2: negative electrode, 2a: working electrode case, 2b: working electrode current collector,
2c: working electrode, 3: separator, 4: gasket
5: Vacuum chamber, 6: Raw material chamber, 7: Deposition chamber, 8: Raw material container,
9: mixed granulation raw material, 10: heating source, 11: precipitation base,
12: Lower silicon oxide, 21: Silicon oxide powder,
21a: center of silicon oxide powder, 22: carbon film

Claims

Having a conductive carbon film on the surface of the lower silicon oxide powder;
The average value of the thickness of the conductive carbon film measured at 24 points of one particle of the lower silicon oxide powder is ta, the standard deviation is σ, and the variation coefficient F of the thickness of the carbon film is F = When defined as σ / ta, the average value Fa of the coefficient of variation F of 10 particles satisfies 0.01 ≦ Fa ≦ 0.4.
2. The powder for a negative electrode material for a lithium ion secondary battery according to claim 1, wherein the proportion of the conductive carbon film is 0.5% by mass or more and 10% by mass or less.
3. The powder for a negative electrode material for a lithium ion secondary battery according to claim 1, wherein the total content of the tar components measured by TPD-MS is 1 mass ppm or more and 3500 mass ppm or less.
The powder for a negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the specific resistance is 10,000 Ωcm or less.
When measured with an X-ray diffractometer using CuK α- ray, the maximum value P1 of halo derived from SiO x appearing at 2θ = 10 ° to 30 ° and Si appearing at 2θ = 28.4 ± 0.3 ° The powder for a negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the relationship of the value P2 of the strongest peak of (111) satisfies P2 / P1 <0.01.
A lithium ion secondary battery negative electrode using the powder for a lithium ion secondary battery negative electrode material according to any one of claims 1 to 5.
A capacitor negative electrode using the powder for a negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 5.
A lithium ion secondary battery using the lithium ion secondary battery negative electrode according to claim 6.
A capacitor using the capacitor negative electrode according to claim 7.