JPWO2014002356A1 - 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 - Google Patents

Abstract

A powder for a negative electrode of a lithium ion secondary battery, comprising a powder of SiOx (0.4 ≦ x ≦ 1.2) having a conductive carbon film on the surface and satisfying 1.5 ≦ B / A ≦ 100. However, A: Specific surface area of the powder for a lithium ion secondary battery negative electrode material calculated on the assumption that the particle is a sphere using a particle size distribution, B: A lithium ion secondary battery negative electrode measured by a one-point method using the BET method It is a specific surface area of the powder for materials, and A is represented by the following formula. A = Σ {ni × (4π (di / 2) 2)} / [ρ × Σ {ni × (4π (di / 2) 3/3)}] where di: for negative electrode material of lithium ion secondary battery The particle size of the powder, ni: the number of particles in the range of particle size di to di + 1 in the particle size distribution, and ρ: the true density of SiO (2.2 g / cm 3). By using this powder for negative electrode material, a lithium ion secondary battery having a large discharge capacity, good cycle characteristics, and withstanding use at a practical level can be obtained.

Description

  The present invention relates to a powder for a negative electrode material that can be used in 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, and the like, 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 illustrating a configuration example of a coin-shaped lithium ion secondary battery. As shown in the figure, 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. Lithium cobaltate (LiCoO ₂ ) and manganese spinel (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 any 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 having a larger effective charge / discharge capacity because it has less degradation such as collapse of the crystal structure and generation of an irreversible material due to insertion and extraction of lithium ions during charge / discharge. Therefore, by using silicon oxide as the negative electrode active material, the capacity is higher than when carbon is used, and the cycle characteristics are better than when a high capacity negative electrode material such as Si or Sn alloy is used. A lithium 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 the powder of silicon oxide 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

  According to the method proposed in Patent Document 1, a uniform conductive carbon film is formed on the conductive silicon composite, and sufficient electrical conductivity can be imparted. However, according to the study by the present inventors, the lithium ion secondary battery using the conductive silicon composite of Patent Document 1 uses silicon dioxide in which silicon microcrystals are dispersed as a negative electrode material. Lithium ion occlusion, expansion and contraction during release increase, and repeated charge / discharge causes problems such as a sudden drop in capacity at a certain point. Further, the discharge capacity and cycle characteristics were not sufficient.

In addition, the present inventors conducted a charge / discharge test on a lithium ion secondary battery using a powder for a negative electrode material in which a conductive carbon film is formed on the surface of a SiO _x (0.4 ≦ x ≦ 1.2) powder. As a result, it was found that the cycle characteristics greatly change depending on the state of the conductive carbon film. Specifically, when the conductive carbon film is rough, the cycle characteristics are inferior to the smooth case, and it is difficult to maintain sufficient performance of the lithium ion secondary battery. This is because when the negative electrode material powder having a rough conductive carbon film occludes lithium ions, the SiO _x powder expands, causing many cracks in the conductive carbon film, and the substantial specific surface area of the negative electrode material powder is reduced. It is thought that the increase is caused and the decomposition of the electrolyte proceeds. When charging / discharging is repeated in this state, the specific surface area of the negative electrode material powder increases every cycle (one charging / discharging), the decomposition of the electrolyte is promoted, the deterioration of the electrolyte progresses, and the cycle characteristics decrease. Will be.

In addition, when forming a conductive carbon film on the surface of a SiO _x powder by CVD, if the growth rate of the conductive carbon film is increased, carbon agglomeration occurs and fine particles are generated instead of the carbon film. There is. When the carbon fine particles are mixed in the negative electrode material powder, the specific surface area of the negative electrode material powder increases, which contributes to deterioration of the electrolyte.

  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 produced lithium ion secondary batteries using negative electrode material powders having various specific surface areas, and the specific surface area of the negative electrode material powders and the cycle of the lithium ion secondary battery. The relationship with characteristics was examined. As a result, the negative electrode material powder in which the conductive carbon film was formed on the surface of the SiO _x powder had a specific surface area A obtained from the particle size distribution and a specific surface area B measured by the BET method of 1.5 ≦ B / A ≦ When the relationship of 100 was satisfied, it was found that the lithium ion secondary battery using the negative electrode material powder had good cycle characteristics and a large discharge capacity.

  The present invention has been made on the basis of the above findings, and the gist thereof is as follows. (1) to (3) Lithium ion secondary battery negative electrode powder, (4) Lithium ion secondary battery negative electrode And a capacitor negative electrode of the following (5), a lithium ion secondary battery of the following (6), and a capacitor of the following (7).

(1) For a lithium ion secondary battery negative electrode material comprising a powder of SiO _x (0.4 ≦ x ≦ 1.2) having a conductive carbon film on the surface and satisfying the following formula (1) Powder.
1.5 ≦ B / A ≦ 100 (1)
However, A: Specific surface area of the powder for a lithium ion secondary battery negative electrode material calculated on the assumption that the particle is a sphere using a particle size distribution, B: A lithium ion secondary battery negative electrode measured by a one-point method by the BET method It is a specific surface area of the powder for materials, and A is represented by the following formula (2).
_{A = Σ {n i × (} 4π (d i / 2) 2)} / [ρ × Σ {n i × (4π (d i / 2) 3/3)}] ... (2)
Here, _{d i:} a lithium ion secondary battery negative electrode material powder having a particle size, _{n i:} number of particles in the particle size range of _{d i ~d} i _{+ 1} in the particle size distribution, [rho: true density of SiO (2.2 g / cm ³ ).

(2) The powder for a lithium ion secondary battery negative electrode material according to (1), wherein the value of D50 in the particle size distribution satisfies 1 μm ≦ D50 ≦ 50 μm.

(3) The proportion of the conductive carbon film is 3% by mass or less, and the peak derived from the Si crystal does not appear when measured with an X-ray diffractometer. ) Powder for negative electrode material of lithium ion secondary battery.

(4) 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 (3).

(5) A capacitor negative electrode using the lithium ion secondary battery negative electrode powder according to any one of (1) to (3).

(6) A lithium ion secondary battery using the lithium ion secondary battery negative electrode of (4).

(7) A capacitor using the capacitor negative electrode of (5).

In the present invention, _x of SiO _x , particle size distribution of powder for negative electrode material of lithium ion secondary battery, specific surface area (A and B above) and D50 values, and conductive carbon film in the powder for negative electrode material of lithium ion secondary battery Each measuring method of the ratio which occupies will be described later.

As described later, “having a conductive carbon film on the surface” of the SiO _x powder is a result of surface analysis using an X-ray photoelectron spectroscopic analyzer. 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 the results of X-ray diffraction measurement for the powder for a negative electrode material for a lithium ion secondary battery, and FIG. 2 (a) is a diagram when a peak derived from a crystal of Si appears clearly, FIG. FIG. 2B is a diagram when a peak derived from a Si crystal appears, and FIG. 2C is a diagram when a peak derived from a Si crystal does not appear. FIG. 3 is a diagram showing an example of the particle size distribution of the powder for a negative electrode material for a lithium ion secondary battery of the present invention. FIG. 4 is a diagram showing a configuration example of a silicon oxide production apparatus.

1. Powder for Lithium Ion Secondary Battery Negative Electrode Material of the Present Invention The powder for lithium ion secondary battery negative electrode material of the present invention (hereinafter also simply referred to as “powder for negative electrode material”) has SiO _x having a conductive carbon film on the surface. (0.4 ≦ x ≦ 1.2). In the present invention, the reason why the x range of SiO _x is 0.4 ≦ x ≦ 1.2 is that when the value of x is less than 0.4, the lithium ion secondary using the negative electrode material powder of the present invention is used. This is because the battery and capacitor are rapidly deteriorated due to the charge / discharge cycle, and the battery capacity is reduced when it exceeds 1.2. Further, x preferably satisfies 0.8 ≦ x ≦ 1.05.

The powder for negative electrode material of the present invention satisfies the following formula (1).
1.5 ≦ B / A ≦ 100 (1)
However, A: specific surface area of the powder for negative electrode material calculated on the assumption that the particles are spherical using particle size distribution, B: specific surface area of the powder for negative electrode material measured by a one-point method by the BET method, A Is represented by the following equation (2).
_{A = Σ {n i × (} 4π (d i / 2) 2)} / [ρ × Σ {n i × (4π (d i / 2) 3/3)}] ... (2)
Here, _{d i:} a negative electrode material for a powder of particle size, _{n i:} number of particles in the particle size range of _{d i ~d} i _{+ 1} in the particle size distribution, [rho: is the true density of SiO (2.2g / cm ³⁾ .

  If the shape of the particles of the negative electrode material powder is a perfect sphere, the value of B / A is 1. The larger the particle shape is, the larger the value is than 1. B / A can be used as an indicator of the surface state of the negative electrode material powder, that is, the state of the conductive carbon film. The closer the B / A value is to 1, the smoother the conductive carbon film is, and the larger the value is, the rougher the film becomes.

  When the present inventors examined, when the value of B / A was 100 or less, it turned out that a lithium ion secondary battery with favorable cycling characteristics is obtained. When the value of B / A is larger than 100, the cycle characteristics of the lithium ion secondary battery are inferior.

As described above, when the negative electrode material powder having a rough conductive carbon film occludes lithium ions, the SiO _x powder expands, causing many cracks in the conductive carbon film, resulting in substantial negative electrode material use. It is thought that the specific surface area of the powder is increased and the decomposition of the electrolyte proceeds. When charging / discharging is repeated in this state, the specific surface area of the negative electrode material powder increases every cycle, the decomposition of the electrolyte is promoted, the deterioration of the electrolytic solution proceeds, and the cycle characteristics are lowered.

  On the other hand, if the value of B / A is 100 or less, since the conductive carbon film is smooth, it is possible to suppress the conductive carbon film from being cracked by charging / discharging, and deterioration or depletion of the electrolyte solution is prevented. It is difficult to proceed and the deterioration of cycle characteristics is suppressed. Therefore, the value of B / A is defined as 100 or less as in the above equation (1).

  Moreover, in order to make the value of B / A smaller than 1.5, it is necessary to extremely reduce the formation rate of the conductive carbon film, and industrial production of the powder for negative electrode material is difficult. For this reason, the value of B / A is defined as 1.5 or more as in the above equation (1).

  In the powder for negative electrode material of the present invention, the value of D50 in the particle size distribution preferably satisfies 1 μm ≦ D50 ≦ 50 μm, and more preferably 3 μm ≦ D50 ≦ 15 μm. This is because when the particle size of the negative electrode material powder is too small, the specific surface area of the entire negative electrode material powder is too large, and thus the reaction between the electrolyte and the negative electrode material powder is excessively promoted in the lithium ion secondary battery. This is because breakdown may occur due to depletion of the electrolyte. In addition, if the particle size of the negative electrode material powder is too large, the separator may be broken and short-circuited in the lithium ion secondary battery.

  In addition, the proportion of the conductive carbon film in the negative electrode material powder (hereinafter referred to as “carbon film ratio”) is 3% by mass or less, and a peak derived from Si crystals appears when measured with an X-ray diffractometer. Preferably not.

The reason why the carbon film rate is preferably 3% by mass or less is that the conductive carbon film also contributes to the charge / discharge capacity of the lithium ion secondary battery, like SiO _x , but the charge / discharge capacity per unit mass is This is because it is smaller than SiO _x .

In addition, when the negative electrode material powder is measured with an X-ray diffractometer, it is preferable that the peak derived from the Si crystal does not appear because the SiO _x in the negative electrode material powder has crystallinity. This is because, when the material is amorphous, expansion due to the penetration of lithium ions is more easily relaxed, and the cycle characteristics of the lithium ion secondary battery are superior.

FIG. 2 is a diagram showing the results of X-ray diffraction measurement of the negative electrode material powder. X-ray diffraction measurement using CuK _alpha rays was performed on the negative electrode material powders with different production conditions, and the results shown in FIG. When X-ray diffraction measurement is performed on Si crystal powder using CuK _α- ray, a peak appears at 2θ = 28.4 ° ± 0.3 °. The figure (a) is a figure when the peak derived from the crystal of Si appears clearly, the figure (b) is the figure when the peak derived from the crystal of Si appears, and the figure (c) is the figure of Si. It is a figure when the peak derived from a crystal | crystallization does not appear. In the negative electrode material powder of the present invention, it is preferable that no peak derived from Si crystals appears as shown in FIG.

2. Analysis method 2-1. 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 negative electrode material powder, for example, O content and Si content measured by the following measurement method It can be calculated using the rate.

2-2. Method for Measuring O Content The O content in the negative electrode material powder is quantitatively evaluated by analyzing 10 mg of a sample by an inert gas melting / infrared absorption method using an oxygen concentration analyzer (Leco, TC436). Calculated from the O content in the prepared sample.

2-3. Method for Measuring Si Content The Si content in the negative electrode material powder is determined by adding nitric acid and hydrofluoric acid to the sample to dissolve the sample, and analyzing the resulting solution with an ICP emission spectrometer (manufactured by Shimadzu Corporation). It calculates from Si content in the sample evaluated quantitatively by doing.

2-4. Method for Evaluating Formation State of Conductive Carbon Film In the negative electrode powder of the present invention, “having a conductive carbon film on the surface of the lower silicon oxide powder” means X-ray using AlK _α- ray (1486.6 eV). When the surface analysis of the lower silicon oxide powder that has been subjected to the conductive carbon film formation treatment is performed with a photoelectron spectrometer (XPS), the molar ratio value Si / C of Si and C is 0.1 or less. Say something. The XPS measurement conditions are as shown in Table 1. In order to sufficiently impart electric conductivity to the negative electrode material powder, 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.

2-5. Method for Measuring Particle Size Distribution and Specific Surface Area of Powder for Lithium Ion Secondary Battery Negative Electrode Material FIG. 3 is a diagram showing an example of the particle size distribution of the powder for negative electrode material of the present invention. In the same figure, the frequency for each section of the particle size of the powder and the value of the accumulated part are shown. The particle size distribution was measured under the conditions shown in Table 2 using a laser diffraction particle size distribution measuring apparatus.

The measurement range of the particle diameter d in this measurement was 0.02 μm to 2000 μm, and a section obtained by dividing the measurement range into 85 equal parts by logarithmic equal division was defined as one section. For example, the first interval is in the range of particle size d ₀ (0.02 μm) to d ₁ (0.022 μm), the second interval is greater than particle size d _{1 and} less than d ₂ (0.026 μm), The 85 section was larger than the particle size d ₈₄ (1754.6 μm) and not more than d ₈₅ (2000 μm).

That is, in the formula (2) shown below, i is an integer that satisfies 1 ≦ i ≦ 85. In the following formula (2), the particles included in each section (range of particle diameters d _{i to} d _{i + 1} ) are regarded as spheres having a particle diameter d _i and the number n _i of particles in each section is used for the negative electrode material powder. The total specific surface area was calculated. In the case of the particle size distribution shown in FIG. 3, the value of A was 1.8169 m ² / g.
_{A = Σ {n i × (} 4π (d i / 2) 2)} / [ρ × Σ {n i × (4π (d i / 2) 3/3)}] ... (2)
Here, _{d i:} a negative electrode material for a powder of particle size, _{n i:} number of particles in the particle size range of _{d i ~d} i _{+ 1} in the particle size distribution, [rho: is the true density of SiO (2.2g / cm ³⁾ .

  In addition, the value of D50 in the particle size distribution is a particle size at which the integrated value from the smaller particle size in the particle size distribution reaches 50%. In the case of the particle size distribution shown in FIG. 3, the value of D50 was 6.4626 μm.

2-6. Method for Measuring Specific Surface Area of Lithium Ion Secondary Battery Negative Electrode Powder by BET Method The specific surface area of the lower silicon oxide powder on which the conductive carbon film is formed can be measured by the following BET method. 0.5 g of sample is put in a glass cell and dried under reduced pressure at 200 ° C. for about 5 hours. And a specific surface area is computed from the nitrogen gas adsorption isotherm in the liquid nitrogen temperature (-196 degreeC) measured about this sample. The measurement conditions are as shown in Table 3.

2-7. Carbon film ratio measurement method The carbon film ratio is quantified by analyzing the CO ₂ gas by the oxygen gas flow combustion-infrared absorption method using the mass of the powder for the negative electrode material and a carbon concentration analyzer (CS400, manufactured by Leco). Calculated from the result of the evaluated carbon content. The crucible is a ceramic crucible, the auxiliary combustor is copper, and the analysis time is 40 seconds.

3. 3. Method for producing powder for negative electrode material of lithium ion secondary battery of the present invention 3-1. Method for Producing SiO _x Powder FIG. 4 is a diagram illustrating 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 configured by 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 SiO generated by sublimation in the raw material chamber 6.

  A vacuum device (not shown) for discharging 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.

When producing the SiO _x by using the manufacturing apparatus shown in FIG. 4, the Si powder and SiO ₂ powder were blended at a predetermined ratio as the raw material, mixing, mixing granulation raw material 9 was granulated and dried using. 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 sublimation rises from the raw material chamber 6 and enters the precipitation chamber 7, vapor-deposits on the surrounding precipitation base 11, and precipitates as SiO precipitates 12. Then, remove the SiO deposit 12 from deposition substrate 11, by grinding using a ball mill or the like, SiO _x powder. The reason why the powder is expressed as SiO _x is that the value of x varies from 1 due to the formation of an oxide film on the surface of the powder after the SiO precipitate 12 is pulverized.

The grinding conditions will be specifically described below. As the SiO precipitates 12, those having a ratra value of 10.0 W% or less in a lump state before pulverization are used. The ratra value is a value used for evaluating the wear resistance of the green compact, and is a value represented by a weight reduction rate before and after a test in which the green compact is repeatedly rotated and dropped in a cage. The measurement method of ratra value is the standard “JPMA” of Japan Powder Metallurgy Association (JPMA).
It is set as the value measured by the method described in "P11-1992 Metal Rattle Value Measuring Method".

The lump-like SiO precipitate 12 is pulverized in an air atmosphere with a humidity of 60% or less to form a SiO _x powder, and then pressure is maintained at a pressure of 10 Pa to 1000 Pa and a temperature of 200 ° C. to 400 ° C. for a certain period of time. Apply heat treatment. Since this pressure heat treatment is performed before the formation of the conductive carbon film, it is hereinafter also referred to as “pre-drying”. The pre-dried SiO _x powder is put in a rotary kiln described later in a state where it is housed in a sealed container and is not in contact with the atmosphere.

3-2. Adjustment method of particle size When adjusting the particle size of the SiO _x powder obtained by pulverizing the massive SiO precipitates 12, for example, the following method can be employed. The SiO _x powder is immersed in a beaker containing water so that the water depth becomes 10 cm, and ultrasonic vibration is applied by an ultrasonic cleaner. Thereafter, natural sedimentation is performed, the fine water remaining in the aqueous layer is removed by discarding the supernatant water, and only the settled powder is recovered. By adjusting the settling time of the grinding time and SiO _x powder SiO _x precipitate to adjust the particle size of the SiO _x powder, it can be a value of D50 with a predetermined range.

The recovered SiO _x powder is dried in an oven at 130 ° C. for 24 hours or more under atmospheric pressure. Thereafter, it is crushed in an agate mortar, dried again under the same conditions, and further subjected to the above prior drying.

Adjustment of the particle size of the SiO _x powder is not limited to sedimentation separation, but can also be performed by air classification or the like.

3-3. Method for Forming Conductive Carbon Film The conductive carbon film is formed on the surface of the pre-dried SiO _x powder by CVD or the like. Specifically, a rotary kiln is used as an apparatus, and a mixed gas of a hydrocarbon gas and an inert gas is used as a gas. The growth rate of the film is relatively slow and is set to 0.1 nm / h or more and 10 nm / h or less. By setting the growth rate of the film within this range, it is possible to suppress the generation of carbon fine particles due to aggregation. The film growth rate can be controlled by the gas flow rate.

By applying a pre-dried SiO _x powder, since aggregation of SiO _x powder by moisture is suppressed, thereby improving the uniformity of the conductive carbon coating. Moreover, a smooth conductive carbon film can be formed by slowing the growth rate. By having both pre-drying before putting into the rotary kiln and the slow growth rate of the conductive carbon film, it is possible to obtain a negative electrode material powder satisfying B / A of 1.5 ≦ B / A ≦ 100. .

As the hydrocarbon gas that is a carbon source, methane, ethane, propane, acetylene, or the like can be used. Of these, propane (C ₃ H ₈ ) is most desirable. As the mixed gas, for example, argon can be used. The content of the hydrocarbon gas in the mixed gas is 2% or more and 50% or less, preferably 20% or more and 40% or less in volume%.

  The forming temperature of the conductive carbon film is 600 ° C. or higher and 900 ° C. or lower, and preferably 700 ° C. or higher and 750 ° C. or lower. The formation processing temperature is adjusted by a heater provided in the rotary kiln.

4). 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, ie, the working electrode 2c which comprises the negative electrode of the lithium ion secondary battery of this invention, is comprised using the powder for negative electrode materials of this invention. Specifically, the negative electrode material powder of the present invention, which is an active material, other active materials, a conductive additive, and a binder can be used. The ratio of the powder for negative electrode materials of this invention with respect to the sum total of the structural material except a binder among the structural materials in a negative electrode material shall be 20 mass% or more. It is not always necessary to add an active material other than the negative electrode material powder of the present invention. As the conductive additive, 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 negative electrode material of the present invention and the lithium ion secondary battery negative electrode, it has a large discharge capacity, good cycle characteristics, and can be used at a practical level. obtain.

  Moreover, the powder for negative electrode materials of this invention and a negative electrode using the same are applicable also to a capacitor.

  In order to confirm the effect of the present invention, the following tests using a lithium ion secondary battery were performed and the results were 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. Si powder and SiO ₂ powder were mixed, and mixed, granulated and dried mixed granulation raw materials were used as raw materials, and SiO was deposited on the deposition substrate using the apparatus shown in FIG. The SiO precipitate was pulverized using an alumina ball mill to obtain a powder having D50 = 10 μm. This powder had an O / Simol ratio (x value of SiO _x ) of 1.02.

A conductive carbon film was formed on the surface of the SiO _x powder to obtain a powder for a lithium ion secondary battery negative electrode material. For the formation of the conductive carbon film, a rotary kiln was used as the apparatus, a mixed gas of propane and argon was used as the gas, and the processing temperature was 700 ° C. The carbon film rate was 2.5%.

As shown in Table 4, the value of B / A was changed depending on whether or not pre-drying was performed on the SiO _x powder and setting the growth rate of the conductive carbon film. In Invention Examples 1 to 4, B / A satisfied 1.5 ≦ B / A ≦ 100. In Comparative Examples 1 to 5, B / A did not satisfy 1.5 ≦ B / A ≦ 100. The pre-drying condition was to heat to 200 ° C. for 3 hours in a vacuum. As can be seen from Table 4, if the carbon film formation rate is the same, the B / A value is smaller when the SiO _x powder is pre-dried, and the carbon film formation rate is smaller if the pre-drying conditions are the same. The value of B / A was small.

N-methylpyrrolidone is added to a mixture containing 65% by mass of the negative electrode material powder, 10% by mass of acetylene black, and 25% by mass of PAA to prepare a slurry. 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 was lithium foil. The electrolyte is a solution in which LiPF ₆ (lithium hexafluorophosphate) is dissolved at a ratio of 1 mol / L in a mixed solution of EC (ethylene carbonate) and DEC (diethyl carbonate) in a volume ratio of 1: 1. It was. 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 Co., Ltd.) 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 100 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 initial discharge capacity and the cycle maintenance rate after 100 cycles as indexes. These values are shown in Table 4 together with the test conditions. The cycle maintenance ratio is a value (%) of the ratio of the charge / discharge capacity at the 100th cycle to the charge / discharge capacity at the first cycle. Comprehensive evaluation is ◎ (excellent) when the initial discharge capacity is 1900 mAh / g or more and the cycle maintenance ratio is 85% or more, and ○ (good) when the initial discharge capacity is 1700 mAh / g or more and the cycle maintenance ratio is 80% or more. ), And the case where the initial discharge capacity was less than 1700 mAh / g or the cycle maintenance rate was less than 80% was evaluated as x (impossible).

  As can be seen from Table 4, the smaller the B / A value, the larger the initial discharge capacity and the cycle retention rate. In addition, in the comparative examples where B / A did not satisfy 1.5 ≦ B / A ≦ 100, the overall evaluation was x, and in all of the satisfied examples of the present invention, the overall evaluation was ○ or ◎. . Among the inventive examples, in particular, in inventive examples 3 and 4 in which the value of B / A was 30 or less, the initial discharge capacity was 1952 mAh / g or more and the cycle maintenance ratio was 88.7% or more, which was an excellent value. Yes, overall evaluation was ◎.

  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: Precipitation chamber, 8: Raw material container, 9: Mixed granulated raw material,
10: Heat source, 11: Precipitation substrate, 12: SiO precipitate

Claims (7)

A powder for a negative electrode material for a lithium ion secondary battery comprising a powder of SiO _x (0.4 ≦ x ≦ 1.2) having a conductive carbon film on the surface and satisfying the following formula (1).
1.5 ≦ B / A ≦ 100 (1)
However, A: Specific surface area of the powder for a lithium ion secondary battery negative electrode material calculated on the assumption that the particle is a sphere using a particle size distribution, B: A lithium ion secondary battery negative electrode measured by a one-point method by the BET method It is a specific surface area of the powder for materials, and A is represented by the following formula (2).
_{A = Σ {n i × (} 4π (d i / 2) 2)} / [ρ × Σ {n i × (4π (d i / 2) 3/3)}] ... (2)
Here, _{d i:} a lithium ion secondary battery negative electrode material powder having a particle size, _{n i:} number of particles in the particle size range of _{d i ~d} i _{+ 1} in the particle size distribution, [rho: true density of SiO (2.2 g / cm ³ ).   2. The powder for a negative electrode material for a lithium ion secondary battery according to claim 1, wherein a value of D50 in the particle size distribution satisfies 1 μm ≦ D50 ≦ 50 μm.   3. The lithium ion according to claim 1, wherein the proportion of the conductive carbon film is 3% by mass or less and a peak derived from a Si crystal does not appear when measured with an X-ray diffractometer. Powder for secondary battery negative electrode material.   The lithium ion secondary battery negative electrode using the powder for lithium ion secondary battery negative electrode materials in any one of Claims 1-3.   The capacitor negative electrode using the powder for lithium ion secondary battery negative electrode materials in any one of Claims 1-3.   The lithium ion secondary battery using the lithium ion secondary battery negative electrode of Claim 4.   A capacitor using the capacitor negative electrode according to claim 5.

Images