JP2019220350A - Negative electrode material for lithium ion battery, negative electrode for lithium ion battery, and lithium ion battery - Google Patents

Abstract

To provide a negative electrode material for a lithium ion battery, excellent in battery performance of large discharge capacity and high charge/discharge efficiency and also suppressed in battery swelling due to charge/discharge.SOLUTION: A negative electrode material for a lithium ion battery contains a complex including crystalline silicon oxide and crystalline silicon. The crystalline silicon oxide contains cristobalite and quartz, and a ratio (Icr/Iqz) of a peak intensity (Icr) in the range of diffraction angle 2θ=21.5±0.5° and a peak intensity (Iqz) in the range of diffraction angle 2θ=26.5±0.5° in powder X-ray diffractometry using a CuKα ray is 3-100.SELECTED DRAWING: None

Description

  The present invention relates to a negative electrode material for a lithium ion battery, a negative electrode for a lithium ion battery, and a lithium ion battery.

  Conventionally, graphite materials such as natural graphite and artificial graphite have been widely used as negative electrode materials for lithium ion batteries.

  However, since the theoretical electric capacity of the graphite material is as small as 372 mAh / g, it is not possible to achieve a high capacity lithium ion battery.

  Negative electrode materials using tin, silicon, and the like are known in order to achieve high capacity lithium ion batteries. From the viewpoint of low cost, practical use of negative electrode materials using silicon is being studied.

  Although the theoretical electric capacity of silicon alone is extremely large at 4400 mAh / g, the volume expansion of the battery when lithium ions are inserted is large, and not only the particles and the electrode film are destroyed but also the charge / discharge cycle is extremely short. However, the function as a lithium ion battery cannot be sufficiently performed.

  Thus, it has been considered to suppress the expansion of the battery by reducing the silicon content to limit the theoretical electric capacity and reducing the crystallite size of silicon. As this means, a method of using a silicon alloy, a silicon oxide or the like as a negative electrode material of a lithium ion battery is known (Patent Document 1, Patent Document 2, etc.).

Japanese Patent No. 3,952,180 Japanese Patent No. 6256346

  The theoretical electric capacity of SiO, which is a silicon oxide described in Patent Documents 1 and 2, is 2000 mAh / g, which is larger than the theoretical electric capacity of a graphite material. However, the charge / discharge efficiency of SiO is 75%, which is lower than the charge / discharge efficiency of graphite material (90 to 95%). However, there is a problem that it is necessary to add an extra positive electrode material in order to increase the temperature.

  Furthermore, in the techniques described in Patent Literature 1 and Patent Literature 2, the expansion of the battery is increased by the insertion of lithium ions, and the destruction of the negative electrode film such as poor conduction between particles occurs. There is a problem that is caused.

  The present invention has been made in view of these problems, and has an excellent battery performance such as a large discharge capacity and a high charge / discharge efficiency, and a lithium battery in which expansion of the battery due to charge / discharge is suppressed. An object is to provide a negative electrode material for a lithium ion battery capable of providing an ion battery.

  The present inventors have conducted intensive studies to achieve the above object, and as a result, used a crystalline silicon dioxide containing a specific component and a negative electrode material for a lithium ion battery containing a composite containing crystalline silicon. By doing so, it has been found that the above-mentioned problem can be achieved. The present invention has been completed by the present inventors by further research.

That is, the present invention provides the following aspects of the invention.
Item 1. Containing a composite comprising crystalline silicon dioxide and crystalline silicon,
The crystalline silicon dioxide contains cristobalite and quartz,
In the powder X-ray diffraction method using CuKα radiation, the intensity (Icr) of the peak existing in the range of diffraction angle 2θ = 21.5 ± 0.5 ° and the diffraction angle 2θ = 26.5 ± 0.5 ° A negative electrode material for a lithium ion battery, wherein the ratio (Icr / Iqz) to the intensity of the existing peak (Iqz) is 3 to 100.
Item 2. In the powder X-ray diffraction method using CuKα radiation, the intensity (Isi) of the peak existing in the range of diffraction angle 2θ = 28.5 ± 0.5 ° and the range of diffraction angle 2θ = 26.5 ± 0.5 ° Item 4. The negative electrode material for a lithium ion battery according to Item 1, wherein the ratio (Isi / Iqz) to the intensity of the existing peak (Iqz) is 3 to 50, and the crystal size of the crystalline silicon is 10 nm or more. .
Item 3. The lithium according to claim 1 or 2, wherein carbon is contained in part or all of the surface of the composite, and the content ratio of the carbon is 5 to 10% by mass with respect to the total mass of the composite. Anode material for ion batteries.
Item 4. The composite is composed of X ₂ SiO ₃ , X ₂ Si ₂ O ₅ and X ₆ Si ₂ O ₇ (where X is at least one element selected from the group consisting of Li, Na and K). It contains at least one alkali metal composite oxide selected from the group consisting of: and the content ratio of the alkali metal composite oxide is 0.1 to 10% by mass relative to the total mass of the composite. The negative electrode material for a lithium ion battery according to any one of items 1 to 3.
Item 5. Any one of the items 1 to 4, which has an average particle diameter of 5 to 20 μm, a nitrogen adsorption BET specific surface area of 1 to 10 m ² / g, and a powder resistance of 1 to 1000 Ω · cm at a packing density of 1.5 g / cm ³ . 2. The negative electrode material for a lithium ion battery according to claim 1.
Item 6. Item 6. A negative electrode for a lithium ion battery, comprising the negative electrode material for a lithium ion battery according to any one of Items 1 to 5, and a current collector.
Item 7. 7. A lithium ion battery comprising a positive electrode, an electrolyte containing lithium ions, and the negative electrode according to item 6.

  Advantageous Effects of Invention According to the present invention, for a lithium-ion battery capable of providing a lithium-ion battery having excellent battery performance such as a large discharge capacity and high charge-discharge efficiency, and in which the expansion of the battery due to charge-discharge is suppressed. A negative electrode material can be provided.

FIG. 1 is a diagram showing the results of analysis of the negative electrode materials for lithium ion batteries and raw material SiO obtained in Example 5 and Comparative Example 2 by powder X-ray diffraction. FIG. 2A is a transmission electron microscope (TEM) photograph of the raw material SiO. FIG. 2B is a TEM photograph of the negative electrode material for a lithium ion battery obtained in Comparative Example 2. FIG. 2C is a TEM photograph of the negative electrode material for a lithium ion battery obtained in Example 5. FIG. 3 is a diagram showing the measurement results of the charge / discharge curves of the lithium ion batteries obtained in Example 5 and Comparative Example 2.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

  In this specification, a numerical range indicated by using “to” indicates a range including numerical values described before and after “to” as a minimum value and a maximum value, respectively.

1. The negative electrode material for a lithium ion battery The negative electrode material for a lithium ion battery of the present invention (hereinafter sometimes abbreviated as “negative electrode material”) contains crystalline silicon dioxide and a composite containing crystalline silicon. Silicon dioxide contains cristobalite and quartz.

  The negative electrode material for a lithium ion battery of the present invention has a peak intensity (Icr) in the range of diffraction angle 2θ = 21.5 ± 0.5 ° in a powder X-ray diffraction method using CuKα ray, and a diffraction angle 2θ = The ratio (Icr / Iqz) to the peak intensity (Iqz) existing in the range of 26.5 ± 0.5 ° is 3 to 100.

  The negative electrode material for a lithium ion battery of the present invention, having these structures, has excellent battery performance such as high discharge capacity and high charge / discharge efficiency, and suppresses expansion of the battery due to charge / discharge. A lithium ion battery can be provided.

  In the negative electrode material of the present invention, Icr means a peak intensity derived from cristobalite within a diffraction angle 2θ = 21.5 ± 0.5 ° in a powder X-ray diffraction method using CuKα radiation.

  In the negative electrode material of the present invention, Iqz means the intensity of a peak derived from quartz in a range of a diffraction angle 2θ = 26.5 ± 0.5 ° in a powder X-ray diffraction method using CuKα radiation.

  In the negative electrode material of the present invention, when the ratio (Icr / Iqz) of the peak intensity (Icr) to the peak intensity (Iqz) is less than 3, amorphous silicon increases in the negative electrode material for a lithium ion battery. Therefore, the charge / discharge efficiency decreases.

  In the negative electrode material of the present invention, when the ratio (Icr / Iqz) of the peak intensity (Icr) to the peak intensity (Iqz) is more than 100, the electrical resistance increases due to an increase in crystalline silicon dioxide. Discharge capacity and charge / discharge efficiency decrease.

  The measurement of the negative electrode material of the present invention by X-ray diffraction (XRD) using CuKα radiation is performed by the method described in the following examples.

  In the negative electrode material of the present invention, the ratio Icr / Iqz is more preferably from 3.5 to 80, further preferably from 4 to 70, and particularly preferably from 5 to 60.

In the negative electrode material of the present invention, examples of a method for obtaining a composite of silicon dioxide and silicon include the following methods (1) to (3).
(1) A method of uniformly mixing amorphous or crystalline silicon dioxide and amorphous or crystalline silicon to obtain a mixture, and heating the mixture to a temperature at which silicon dioxide in the mixture is melted (2). A method of uniformly mixing amorphous or crystalline silicon dioxide and amorphous or crystalline silicon to obtain a mixture and mechanochemically using a grinding media to impact the mixture (3). A method for obtaining a mixture by uniformly mixing amorphous or crystalline silicon dioxide and amorphous or crystalline silicon, and depositing and collecting an evaporant obtained by heating the mixture in a vacuum.

  In the above methods (1) and (2), the mixing ratio between silicon dioxide and silicon can be arbitrarily adjusted.

The method (3) is based on the oxidation-reduction reaction between silicon dioxide and silicon in heating in vacuum, and the deposited and recovered evaporant is SiO (SiO) regardless of the mixing ratio of silicon dioxide and silicon. ₂ + Si).

  After the composite of silicon dioxide and silicon obtained by the method (1), (2) or (3) is pulverized to adjust the particle size, at least one selected from the group consisting of lithium, sodium and potassium The alkali metal source containing the seed metal is mixed and heated above the melting temperature of the alkali metal source. Thereby, the alkali metal source penetrates into the inside of the composite of silicon dioxide and silicon, and crystallization of silicon dioxide and crystallization of silicon are promoted.

  For the pulverization of the composite of silicon dioxide and silicon, a dry pulverizer such as a hammer mill, a ball mill, or a jet mill, or a wet bead mill can be used.

The alkali metal source is not particularly limited, and a wide range of known alkali metal sources can be used. For example, oxides such as lithium oxide (Li ₂ O), sodium oxide (Na ₂ O), and potassium oxide (K ₂ O); lithium hydroxide (LiOH), sodium hydroxide (NaOH), and potassium hydroxide (KOH) Hydroxides such as lithium carbonate (Li ₂ CO ₃ ), sodium carbonate (Na ₂ CO ₃ ), potassium carbonate (K ₂ CO ₃ ), lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl) , Lithium nitrate (LiNO ₃ ), lithium phosphate (Li ₃ PO ₄ ), lithium sulfate (Li ₂ SO ₄ ), dilithium hydrogen phosphate (Li ₂ HPO ₄ ), lithium dihydrogen phosphate (LiH ₂ PO ₄ ) , Sodium sulfate (Na ₂ SO ₄ ), potassium sulfate (K ₂ SO ₄ ) and other inorganic acid salts of alkali metals; lithium acetate (CH ₃ Organic acid salts of alkali metals such as COOLi), lithium oxalate ((COOLi) ₂ ), sodium acetate (CH ₃ COONa), and potassium acetate (CH ₃ COOK) are preferably used. Among these alkali metal sources, LiOH, Li ₂ CO ₃ , Li ₂ O, Li ₂ SO ₄ , CH ₃ COOLi, NaOH, Na ₂ CO ₃ from the viewpoint of promoting crystallization of silicon dioxide and crystallization of silicon. , Na ₂ O, Na ₂ SO ₄ , CH ₃ COONa, KOH, K ₂ CO ₃ , K ₂ O, K ₂ SO ₄ and CH ₃ COOK are more preferable, and Li ₂ CO ₃ and CH ₃ COOLi are particularly preferable. The above alkali metal sources may be used alone or in combination of two or more.

  The use ratio of the alkali metal source is preferably from 0.1 to 20% by mass, more preferably from 0.2 to 18% by mass, based on the total mass of the mixture of silicon dioxide and silicon and the alkali metal source. The content is more preferably from 0.3 to 16% by mass, and particularly preferably from 0.5 to 15% by mass.

  When the content ratio of the alkali metal source is within such a range, crystallization of silicon dioxide and crystallization of silicon become easy to proceed, and both high charge / discharge efficiency and low expansion can be achieved. Further, when the content ratio of the alkali metal source is within such a range, lithium ions inserted electrochemically are not hindered, so that the discharge capacity increases.

The atmosphere in which the composite of silicon dioxide and silicon whose particle size has been adjusted and the alkali metal source are reacted is preferably an inert atmosphere such as nitrogen or argon from the viewpoint of suppressing oxidation of silicon. By the reaction, X ₂ SiO ₃ , X ₂ Si ₂ O ₅ and X ₆ Si ₂ O ₇ (where X is at least one element selected from the group consisting of Li, Na and K) At least one alkali metal composite oxide selected from the group is produced.

Therefore, in the negative electrode material of the present invention, the composite containing crystalline silicon dioxide and crystalline silicon further includes X ₂ SiO ₃ , X ₂ Si ₂ O _5, and X ₆ Si ₂ O ₇ (where X is , Li, Na, and K), at least one alkali metal composite oxide selected from the group consisting of 0.1% and 0.1% based on the total mass of the composite. 1-10 mass% can be contained.

In the negative electrode material of the present invention, crystalline silicon dioxide and a composite containing crystalline silicon are X ₂ SiO ₃ , X ₂ Si ₂ O ₅ and X ₆ Si ₂ O ₇ (where X is Li, Na and K). At least one element selected from the group consisting of: (a) at least one element selected from the group consisting of: Is preferably 0.1 to 10% by mass based on the total mass of the polymer.

In the negative electrode material of the present invention, crystalline silicon dioxide and a composite containing crystalline silicon are X ₂ SiO ₃ , X ₂ Si ₂ O ₅ and X ₆ Si ₂ O ₇ (where X is Li, Na and K). At least one element selected from the group consisting of the above-mentioned composites, and the content of the alkali metal composite oxide is at least one of the above-mentioned composites. Is more preferably from 0.2 to 9% by mass based on the total mass of the polymer.

In the negative electrode material of the present invention, crystalline silicon dioxide and a composite containing crystalline silicon are X ₂ SiO ₃ , X ₂ Si ₂ O ₅ and X ₆ Si ₂ O ₇ (where X is Li, Na and K). At least one element selected from the group consisting of the above-mentioned composites, and the content of the alkali metal composite oxide is at least one of the above-mentioned composites. Is more preferably 0.25 to 8% by mass based on the total mass of

In the negative electrode material of the present invention, crystalline silicon dioxide and a composite containing crystalline silicon are X ₂ SiO ₃ , X ₂ Si ₂ O ₅ and X ₆ Si ₂ O ₇ (where X is Li, Na and K). At least one element selected from the group consisting of the above-mentioned composites, and the content of the alkali metal composite oxide is at least one of the above-mentioned composites. Is particularly preferably from 0.3 to 7% by mass based on the total mass of the polymer.

  In the negative electrode material of the present invention, the “composite containing crystalline silicon dioxide and crystalline silicon” is preferably a complex composed of only crystalline silicon dioxide and crystalline silicon.

In the negative electrode material of the present invention, “crystalline silicon dioxide and a composite containing crystalline silicon” include crystalline silicon dioxide, crystalline silicon, and X ₂ SiO ₃ , X ₂ Si ₂ O _5, and X ₆ Si ₂ O ₇ (where X is at least one element selected from the group consisting of Li, Na, and K), a composite comprising at least one alkali metal composite oxide selected from the group consisting of preferable. Among the alkali metal composite oxides, at least one lithium composite oxide selected from the group consisting of Li ₂ SiO ₃ , Li ₂ Si ₂ O ₅ and Li ₆ Si ₂ O ₇ is more preferable. It is particularly preferable that the negative electrode material of the present invention contains Li ₂ SiO ₃ , Li ₂ Si ₂ O ₅ and Li ₆ Si ₂ O ₇ as the lithium composite oxide.

  The negative electrode material for a lithium ion battery of the present invention has a peak intensity (Isi) in the range of diffraction angle 2θ = 28.5 ± 0.5 ° in a powder X-ray diffraction method using CuKα ray, and a diffraction angle 2θ = The ratio (Isi / Iqz) to the peak intensity (Iqz) existing in the range of 26.5 ± 0.5 ° is 3 to 50, and the crystal size of the crystalline silicon is 10 nm or more. Is preferred. In this case, the upper limit of the crystal size is preferably 70 nm.

  In the negative electrode material of the present invention, Isi means a peak intensity derived from silicon within a diffraction angle 2θ = 28.5 ± 0.5 ° in a powder X-ray diffraction method using CuKα radiation.

  When the ratio (Isi / Iqz) of the peak intensity (Isi) to the peak intensity (Iqz) is 3 or more, the amount of silicon capable of reversibly absorbing and desorbing lithium ions increases, so that the discharge capacity is reduced. If the ratio is larger and Isi / Iqz is 50 or less, the amount of silicon dioxide that relaxes the expansion of silicon into which lithium ions have been inserted increases, so that expansion of the battery due to charging and discharging is suppressed.

  The negative electrode material for a lithium ion battery of the present invention has a peak intensity (Isi) in the range of diffraction angle 2θ = 28.5 ± 0.5 ° in a powder X-ray diffraction method using CuKα ray, and a diffraction angle 2θ = The ratio (Isi / Iqz) to the peak intensity (Iqz) existing in the range of 26.5 ± 0.5 ° is 4 to 45, and the crystal size of the crystalline silicon is 15 nm or more and 60 nm or less. More preferably, there is.

  The negative electrode material for a lithium ion battery of the present invention has a peak intensity (Isi) in the range of diffraction angle 2θ = 28.5 ± 0.5 ° in a powder X-ray diffraction method using CuKα ray, and a diffraction angle 2θ = The ratio (Isi / Iqz) to the peak intensity (Iqz) existing in the range of 26.5 ± 0.5 ° is 5 to 40, and the crystal size of the crystalline silicon is 20 nm or more and 55 nm or less. More preferably, it is.

  In the negative electrode material of the present invention, as a method for measuring the crystal size of crystalline silicon, a powder X-ray diffraction method using CuKα ray has a diffraction angle 2θ = 28.5 ± 0.5 ° in the range of Si (111). From the information on the peak of the above formula using Scherrer's formula. In addition, the crystal shape of crystalline silicon in the negative electrode material of the present invention can be confirmed from the TEM image.

  The Scherrer equation is D = Kλ / βcosθ, where D of crystalline silicon means crystal size. In the above formula, β denotes the spread of the diffracted X-ray by the crystallite, θ denotes the diffraction angle, and λ denotes the wavelength of the X-ray source. Further, K in the equation is a Scherrer constant, defined as a volume-weighted average diameter of the spherical crystal grains, and K = 8 / 3π (0.8488).

  In TEM observation, the long and short sides are obtained by image analysis of the regular shading portion of the crystal, and the crystal shape of crystalline silicon can be confirmed from the photographing magnification.

  When the silicon dioxide is non-crystalline, a large amount of lithium ions used for electrochemical reduction are taken in, so that the charge / discharge efficiency is reduced and the expansion is large. Therefore, in the present invention, silicon dioxide is crystalline silicon dioxide in which reduction does not easily progress electrochemically.

  In the negative electrode material of the present invention, the crystalline silicon dioxide contains cristobalite and quartz.

  Cristobalite is formed when amorphous silicon dioxide reacts with an alkali metal source at a high temperature (about 850 ° C. or higher).

  In the negative electrode material of the present invention, the crystalline silicon dioxide is preferably composed mainly of cristobalite and quartz. Here, “mainly composed of cristobalite and quartz” means that the content ratio of cristobalite and quartz constituting crystalline silicon dioxide is 51% by mass or more based on the total mass of crystalline silicon dioxide. .

  In the negative electrode material of the present invention, the crystalline silicon dioxide may further contain trydiymite in addition to cristobalite and quartz. When the crystalline silicon dioxide contains tridymite, the content ratio of tridymite is preferably 1 to 25% by mass based on the total mass of the crystalline silicon dioxide.

  Since cristobalite and tridymite are difficult to separate, tridymite may be inevitably contained in the composite containing crystalline silicon dioxide and crystalline silicon.

  The negative electrode material of the present invention preferably contains crystalline silicon dioxide and crystalline silicon in a ratio of 10:90 to 90:10 (mass ratio).

  More preferably, the negative electrode material of the present invention contains crystalline silicon dioxide and crystalline silicon in a ratio of 80:20 to 50:50 (mass ratio).

  More preferably, the negative electrode material of the present invention contains crystalline silicon dioxide and crystalline silicon in a ratio of 75:25 to 60:40 (mass ratio).

  The negative electrode material of the present invention contains crystalline silicon dioxide and part or all of the surface of the composite containing crystalline silicon, and the content of the carbon is based on the total mass of the composite. It is preferably from 5 to 10% by mass.

  When the negative electrode material of the present invention has such a configuration, the electrical conductivity is increased, so that the lithium ion acceptability is improved. The content ratio of carbon is more preferably 5.5 to 9.5% by mass, and preferably 6 to 9% by mass with respect to the total mass of the composite, from the viewpoint of electric conductivity and reversible capacity. More preferably, it is particularly preferably 6.5 to 8.5% by mass.

  In the negative electrode material of the present invention, any of crystalline carbon and amorphous carbon can be used as the carbon.

The following methods (1) to (4) may be mentioned as methods for forming carbon coating layers by imparting carbon to part or all of the surface of the composite containing crystalline silicon dioxide and crystalline silicon. Among these methods (1) to (4), the methods (3) and (4) are preferable from the viewpoint that conductivity is obtained by uniformly applying carbon to part or all of the surface of the composite.
(1) A ball mill, a vibrating ball mill, by mixing at least one carbon source selected from the group consisting of graphite, glassy carbon, and carbon black with a composite containing crystalline silicon dioxide and crystalline silicon to form a mixture. Of applying carbon to the surface of the composite by a mechanochemical reaction under reduced pressure, vacuum or an inert gas atmosphere using an attritor or mechanofusion (dry mechanochemical method)
(2) After dispersing at least one kind of carbon powder selected from the group consisting of graphite, glassy carbon and carbon black, and a composite containing crystalline silicon dioxide and crystalline silicon in water or an organic solvent, A method in which water or an organic solvent is separated and removed to obtain a solid content, and then the solid content is heat-treated in an inert atmosphere to impart carbon to the surface of the composite (wet composite method)
(3) A method of heat-treating a composite of crystalline silicon dioxide and crystalline silicon in an atmosphere containing a hydrocarbon gas as a carbon source, thereby depositing carbon on the surface of the composite (chemical vapor deposition method).
(4) Pitch as a carbon source and a composite containing crystalline silicon dioxide and crystalline silicon are mixed to form a mixture, and then heat-treated in an inert atmosphere to deposit carbon on the surface of the composite. Method of applying (pitch coating method)

  In the method (2), as the organic solvent, for example, methanol, ethanol, or the like can be used.

  In the method (3), as the hydrocarbon gas, for example, methane, ethane, propane, acetylene, toluene, benzene, xylene, styrene, naphthalene and the like can be used. One of these hydrocarbon gases may be used alone, or two or more thereof may be used in combination.

  In the above methods (1) and (2), the dried powder may be further subjected to a heat treatment under an inert atmosphere. In the methods (1) to (4), the denseness of the carbon coating layer is increased, The heat treatment temperature is preferably 700 ° C. or higher, more preferably 800 ° C. or higher, and even more preferably 900 ° C. or higher, in order to suppress the reactivity with OH. Further, the temperature is preferably 1300 ° C. or lower, more preferably 1200 ° C. or lower, further preferably 1100 ° C. or lower, from the viewpoint of generating silicon crystallites of a desired size.

  In the above methods (1) to (4), the heat treatment time is appropriately selected depending on the type of the carbon source to be used and the amount to be applied, and for example, preferably 1 hour to 10 hours, more preferably 2 hours to 8 hours.

  In the above methods (1) to (4), the heat treatment is preferably performed in an inert atmosphere such as nitrogen or argon. As a device for the heat treatment, a fluidized bed reactor, a rotary furnace, a tunnel furnace, a batch furnace, or the like can be used.

The negative electrode material of the present invention may have an average particle diameter of 5 to 20 μm, a nitrogen adsorption BET specific surface area of 1 to 10 m ² / g, and a powder resistance of 1,000 Ω · cm or less at a packing density of 1.5 g / cm ³ . preferable.

  When the average particle diameter is in the range of 5 to 20 μm, the effect of uniformly dispersing the negative electrode particles in the negative electrode film and suppressing expansion is increased, and the life of the charge / discharge cycle can be extended.

When the nitrogen adsorption BET specific surface area is 1 m ² / g or more, the resistance of lithium ion insertion / removal decreases, and the input / output characteristics of the lithium ion battery improve. Further, when the nitrogen-adsorbed BET specific surface area is 10 m ² / g or less, the amount of decomposition of the electrolyte or the solvent on the surface of the active material is reduced, and the initial charge / discharge efficiency of the lithium ion battery is improved.

When the powder resistance at a packing density of 1.5 g / cm ³ is 1 to 1000 Ω · cm, the input / output characteristics of the lithium ion battery are improved because the electron transfer resistance is reduced due to the reduction in electric resistance.

Particles composed only of a carbon material such as graphite have a powder resistance of 0.005 to 0.1 Ω · cm at a packing density of 1.5 g / cm ³ . On the other hand, in the case of a mixture of silicon dioxide and silicon used in an insulating or semiconductor region, it is difficult to obtain a powder resistance of less than 0.1 Ω · cm by carbon coating, and a good conductivity is obtained. Therefore, the powder resistance at a packing density of 1.5 g / cm ³ is particularly preferably 1 Ω · cm.

The negative electrode material of the present invention has an average particle diameter of 7 to 18 μm, a nitrogen adsorption BET specific surface area of 2 to 8 m ² / g, and a powder resistance at a packing density of 1.5 g / cm ³ of 1 to 600 Ω · cm or less. Is more preferable.

  The negative electrode material of the present invention may contain other additives as long as the effects of the present invention are not impaired. Other additives include, for example, artificial graphite, natural graphite, their carbon-coated products, non-graphitizable carbon, and the like.

2. Negative Electrode for Lithium Ion Battery The negative electrode for a lithium ion battery of the present invention (hereinafter sometimes abbreviated as “negative electrode”) includes the above negative electrode material and a current collector.

  The negative electrode of the present invention has a current collector and a negative electrode film material layer including the negative electrode material provided on the current collector.

  The negative electrode of the present invention is, for example, a coating solution obtained by mixing the above negative electrode material, a binder, a solvent such as a solvent or water, and, if necessary, a thickener, a conductive auxiliary, and a conventionally known carbon-based negative electrode material. It is obtained by preparing and applying (coating) this coating solution to the current collector, drying the solvent, and press-molding to form a negative electrode film. Generally, the mixture is kneaded with a binder, a solvent, and the like, and formed into a shape such as a sheet or a pellet.

  As the material of the current collector for the negative electrode, for example, it is preferable to use a metal material such as copper, nickel, stainless steel, aluminum, chromium, silver, and an alloy thereof from the viewpoint of electrochemical stability. Among these, copper is preferred from the viewpoint of ease of processing and cost.

  In the negative electrode of the present invention, it is more preferable that the current collector mainly contains copper. Here, “mainly composed of copper” means that the content ratio of copper constituting the current collector is 51% by mass or more based on the total mass of the current collector.

  As the binder, for example, an organic compound such as polyvinylidene fluoride, polypropylene, polyethylene, polyimide, or polyamideimide; or an aqueous compound such as styrene butadiene rubber (SBR) emulsion can be used. When using an aqueous binder such as an SBR emulsion, a thickener such as carboxymethyl cellulose (CMC) can be used.

  The content of the binder is 3 to 15 parts by mass when the above-mentioned organic compound is used, based on 100 parts by mass of the anode material, from the viewpoint of improving the strength, battery capacity, and conductivity of the anode. Is preferred.

  The content of the binder is from 1 to 10 parts by mass when the above-mentioned aqueous binder is used with respect to 100 parts by mass of the anode material, from the viewpoint of improving the strength, battery capacity and conductivity of the anode. Preferably, there is.

3. Lithium-ion battery The lithium-ion battery of the present invention includes a positive electrode, an electrolyte containing lithium ions, and the negative electrode.

  As a method for manufacturing a lithium ion battery, for example, first, a positive electrode and the negative electrode are arranged to face each other with a separator interposed therebetween, and they are wound. The obtained spiral wound group is inserted into a battery can, and a tab terminal previously welded to the negative electrode current collector is welded to the bottom of the battery can. An electrolyte containing an electrolyte is injected into the obtained battery can, and a tab terminal previously welded to the current collector of the positive electrode is welded to a battery cover, and the cover is connected to the battery can through an insulating gasket. A lithium ion battery is obtained by placing it on the upper part and caulking and sealing the portion where the lid and the battery can are in contact.

  Examples of the shape of the lithium ion battery include a cylindrical shape, a square shape, and a button shape.

  The positive electrode can be obtained by forming a positive electrode film on the surface of the current collector in the same manner as the negative electrode. As the current collector in the positive electrode, the same as the current collector described in the negative electrode can be used.

Materials used for the positive electrode of the lithium ion battery of the present invention (hereinafter sometimes abbreviated as “positive electrode material”) include, for example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), ternary nickel aluminum (LiNiCoAlO ₂ ) and the like.

  As the separator, for example, a porous film such as polypropylene (PP), polyethylene, polyamide, polyimide, polyester, and polyphenylene sulfide can be used.

  The electrolyte containing the electrolyte is not particularly limited, and a known material can be used. For example, a lithium ion battery can be manufactured by using a solution in which an electrolyte is dissolved in an organic solvent as an electrolyte.

As the electrolyte, for _example, can be used _{LiPF 6, LiClO 4, LiBF 4} , LiClF 4, LiAsF 6, LiSbF 6, LiAlO 4, LiAlCl 4, LiCl, lithium salt that produces a hard anion solvated such LiI . Among them, LiPF ₆ is preferable from the viewpoint of permittivity and safety.

  Examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), butylene carbonate (BC), and γ-butyrolactone (GBL). , 1,2-dimethoxyethane (DME), tetrahydrofuran (THF) and the like can be used. These organic solvents may be used alone or as a mixed solvent of two or more. Among these, it is preferable to dissolve EC with DMC, DEC, and MEC and add vinylene carbonate (VC) or fluoroethylene carbonate (FEC) as a SEI film forming material from the viewpoints of dielectric constant and low-temperature operability.

  Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to only these.

(Example 1)
<Preparation of negative electrode material for lithium ion battery>
A planetary ball mill (Fritsch, P-5) obtained by mixing 60 g of silicon dioxide powder (Wako Pure Chemical Industries, special grade reagent) and 28 g of silicon powder (Wako Pure Chemical Industries, special grade reagent) and replacing with nitrogen. After the mechanochemical treatment for 10 hours, the mixture was sized with a 400-mesh test sieve to obtain a mixture of silicon dioxide and silicon having an average particle size of 5 μm. 0.5 g (0.5% by mass) of lithium carbonate (manufactured by Wako Pure Chemical Industries, Ltd., special grade) as an alkali metal source was mixed with 99.5 g of the mixture, and calcined at 1000 ° C. for 2 hours in a nitrogen atmosphere. By doing so, a complex was obtained. To 45 g of the obtained composite, 5 g (carbon content: 10% by mass) of natural graphite having an average particle size of 10 μm was added, and dry-mixed for 10 minutes in a vacuum atmosphere using a planetary ball mill (Fritsch, P-5). Thereafter, the composite was loaded with carbon (dry mechanochemical method) by performing a heat treatment at 1000 ° C. for 2 hours in a nitrogen atmosphere, and the negative electrode material for a lithium ion battery of Example 1 (hereinafter referred to as Example 1). (Referred to as a negative electrode material).

<Measurement method of average particle size>
The negative electrode material of Example 1 (about 0.01 mg) was placed in an aqueous solution of about 0.01% by mass of a surfactant (trade name: Tween 20, manufactured by Kanto Chemical Co., Ltd.), and a vibration stirrer (trade name, manufactured by Shimadzu Corporation, trade name: SALD-MS23). The resulting dispersion was placed in a sample water tank of a laser diffraction type particle size distribution measuring device (manufactured by Shimadzu Corporation, SALD2300), circulated by a pump while applying ultrasonic waves, and measured by a laser diffraction type particle size distribution measuring device. The volume cumulative 50% particle size (D50%) of the obtained particle size distribution was defined as the average particle size. Table 2 shows the measurement results of the average particle diameter of the negative electrode material of Example 1. Hereinafter, in Examples and Comparative Examples, measurement of the average particle diameter of the negative electrode material for a lithium ion battery was performed in the same manner.

<Method of measuring carbon content>
The carbon content of the negative electrode material of Example 1 was measured by resistance furnace heating combustion-infrared analysis. Resistance furnace heating combustion-Infrared analysis method is an analysis method in which a measurement sample is heated and burned in an oxygen stream in a furnace, carbon and sulfur in the sample are converted into CO ₂ and SO ₂ respectively, and quantified by an infrared absorption method. It is. The measuring device, measuring conditions, etc. are as follows. Table 2 shows the measurement results of the carbon amount of the negative electrode material of Example 1. Hereinafter, in Examples and Comparative Examples, the measurement of the carbon content of the negative electrode material for a lithium ion battery was performed in the same manner.
-Apparatus: Carbon sulfur concentration meter (SC832DR, manufactured by LECO)
Infrared detector (product name: CO ₂ infrared detector, manufactured by LECO)
・ Firing temperature: 1350 ° C
・ Measurement sample: about 0.1g
・ Analysis time: about 2 minutes ・ Standard sample: CaCO ₃

<X-ray powder diffraction method using CuKα radiation>
The negative electrode material of Example 1 was analyzed by powder X-ray diffraction (XRD). Specifically, using a powder X-ray diffractometer (Rigaku Corporation, RINT-TTRIII), a measurement sample (about 1 g) was placed on a sample stage, and X-ray diffraction measurement was performed under the following conditions.
・ Radiation source: CuKα ray ・ Tube voltage: 50 kV
-Tube current: 300 mA
・ Step width: 0.02 °
・ Measurement speed: 10 sec / step
・ Measurement angle range (2θ): 10 to 90 °

  Based on the obtained X-ray diffraction pattern, the intensity of the observed peak was determined. That is, in the X-ray diffraction pattern obtained by setting the X axis as an angle (2θ [°]) and the Y axis as intensity (cps [counts per second]), the value of the Y coordinate of the peak of each peak is represented by the value of each peak. Was determined as the strength. Table 2 shows the measurement results of “Icr / Iqz” and “Isi / Iqz” of the negative electrode material of Example 1. Hereinafter, in Examples and Comparative Examples, the powder X-ray diffraction method using CuKα radiation of the negative electrode material for lithium ion batteries was performed in the same manner.

<Calculation method of silicon crystal size>
From the X-ray diffraction pattern obtained by the powder X-ray diffraction, the crystallite size (silicon crystal size) of Si in the negative electrode material of Example 1 was determined from the peak attributed to Si (111) by the following Scherrer's formula. Calculated. Table 2 shows the calculation results. Hereinafter, in Examples and Comparative Examples, the measurement method of the silicon crystal size of the negative electrode material for a lithium ion battery was performed in the same manner.
Scherrer's equation: D = Kλ / βcosθ
β = [(Bexp) ² − (Bi) ² ] ^1/2
D: crystallite size (nm)
K: Scherrer constant (8 / 3π)
λ: Cu-Kα ray wavelength (0.154056 nm)
θ: peak angle of Si (111) Bexp: half width of Si (111) Bi: half width of NIST SRM 640e (Si standard sample)

<Method for calculating content ratio of Li ₂ SiO ₃ , Li ₂ Si ₂ O ₅ and Li ₆ Si ₂ O ₇ >
The X-ray diffraction pattern obtained by the above powder X-ray diffraction was processed by a RIR (Reference Intensity Ratio) method using integrated powder X-ray analysis software (Rigaku Corporation: PDXL), and the negative electrode of Example 1 was treated. The content ratio of Li ₂ SiO ₃ , Li ₂ Si ₂ O ₅ and Li ₆ Si ₂ O _{7 in} the material was calculated. Table 2 shows the calculation results. Hereinafter, in Examples 2 to 7 and Comparative Example 3, the method of measuring the content ratio of Li ₂ SiO ₃ , Li ₂ Si ₂ O ₅ and Li ₆ Si ₂ O _{7 in} the negative electrode material for a lithium ion battery was performed in the same manner. .

<Method of measuring powder resistance>
The powder resistance of the negative electrode material of Example 1 was measured using a powder resistance meter (trade name: PD-51, manufactured by Mitsubishi Chemical Analytic Inc.). Specifically, the negative electrode material (approximately 1 g) of Example 1 as a measurement sample was put in a measurement container and pressurized at 4 kN, 6 kN, 8 kN, 10 kN, 12 kN, 16 kN, 18 kN, and 20 kN, and each pressurization was performed. The value of the powder resistance was measured by a four-probe method using a lorester, and the thickness of the powder in the container was measured with a caliper attached to the main body. From the powder resistance at each pressurization and the packing density of the powder, the powder resistance at a packing density of 1.5 g / cm ³ was determined. Table 2 shows the results. Hereinafter, in Examples and Comparative Examples, the method of measuring the powder resistance at a packing density of 1.5 g / cm ³ of the negative electrode material for a lithium ion battery was performed in the same manner.

<Method for measuring nitrogen adsorption BET specific surface area>
The nitrogen adsorption BET specific surface area of the negative electrode material of Example 1 was measured based on the nitrogen adsorption ability. As a nitrogen adsorption measurement device, a specific surface area meter (Macsorb HM1210, manufactured by Mountech Co., Ltd.) was used, and the negative electrode material of Example 1 (about 0.5 g) as a measurement sample was vacuum-heated at 350 ° C. 77K) using a nitrogen gas BET adsorption method. Table 2 shows the measurement results. Hereinafter, in Examples and Comparative Examples, the measurement method of the nitrogen-adsorbed BET specific surface area of the negative electrode material for a lithium ion battery was performed in the same manner.

<Preparation of negative electrode for lithium ion battery>
5% by mass of the powder of the negative electrode material of Example 1 and 95% by mass of natural graphite having a median particle diameter of 15 μm (BD15-097, manufactured by Aoshima Kuroyu Co., Ltd.) as a carbon-based negative electrode material were mixed. Thereafter, 1% by mass of carboxymethylcellulose (CMC # 2200, manufactured by Daicel Chemical Industries, Ltd.) as a thickener and 1% by mass of styrene butadiene rubber emulsion as a binder were added and kneaded to prepare a uniform slurry. The obtained slurry was applied on a 10 μm-thick rolled copper foil (manufactured by Nippon Foil Co., Ltd.) using a blade coater, and the blade gap was adjusted to adjust the application amount to 7.5 mg / cm ² . Thereafter, a curing treatment was performed by drying in the air with hot air at 120 ° C. for 10 minutes to obtain a negative electrode for a lithium ion battery.

<Production of lithium ion battery>
The negative electrode for a lithium ion battery prepared by the above method was punched into φ13 mm, and the negative electrode and a positive electrode (2.2 mAh / cm ² ) in which a LiNiCoAl active material was formed on an aluminum foil were sandwiched between PP separators in a 2016 type coin cell. It was wound facing up and loaded into a cylindrical can. Thereafter, EC (ethylene carbonate) / DEC (diethyl carbonate) / DMC (dimethyl carbonate) (1: 1: 1 volume ratio) containing 1 mol / L LiPF ₆ as an electrolytic solution and VC (vinylene carbonate) (1 vol%) ) Was injected into the cylindrical can, and the upper lid was sealed to produce a lithium ion battery.

(Evaluation of lithium ion battery)
<Discharge capacity, charge / discharge efficiency, expansion rate>
The lithium ion battery produced by the above method was charged in a constant temperature bath at 25 ° C. at a constant current of 0.5 mA / cm ² until the voltage reached 0.01 V, and further charged at a constant voltage of 0.01 V at a current of 0.05 mA. / Cm ² until the current reached. The electric capacity after charging was defined as the charging capacity in the first cycle. Thereafter, the battery was discharged to a voltage of 1.5 V at a constant current of 0.5 mA / cm ² . The electric capacity after the discharge was defined as the discharge capacity in the first cycle. The value obtained by dividing the discharge capacity at the first cycle by the charge capacity at the first cycle was defined as the charge / discharge efficiency.

  The thickness of the electrode film before charging / discharging (thickness of the battery) is set to 100, the lithium ion battery is disassembled in a charged state, and the thickness of the electrode film is measured with a micrometer (trade name: MDC-25SX, manufactured by Mitutoyo Corporation). The expansion ratio was calculated as [(thickness of electrode film in charged state / thickness of electrode film before charge / discharge) × 100] (%). Table 2 shows the measurement results of the discharge capacity of the lithium ion battery obtained in Example 1, and the calculation results of the charge / discharge efficiency and the expansion rate.

(Example 2)
In the same manner as in Example 1, a mixture of silicon dioxide and silicon having an average particle diameter of 5 μm was obtained, and 1 g (1% by mass) of lithium carbonate was mixed with the mixture as an alkali metal source. For 2 hours. The obtained composite, 3.5 g of natural graphite having an average particle diameter of 10 μm, 100 g of water, and 0.2 g of CMC (Daicel # 1120) as a surfactant were wet-mixed for 10 hours in a ball mill. The treated dispersion was frozen and water was removed with a freeze dryer. After being crushed in a mortar and sieved with a 200 mesh, the composite was loaded with carbon by performing a heat treatment at 950 ° C. for 4 hours under a nitrogen atmosphere to obtain a negative electrode material for a lithium ion battery (hereinafter, Example 2). Of the negative electrode material).

  The negative electrode material of Example 2 was evaluated in the same manner as in Example 1. Using the negative electrode material of Example 2, a negative electrode for a lithium ion battery was manufactured in the same manner as in Example 1. Further, using the prepared negative electrode for a lithium ion battery, a lithium ion battery was prepared and evaluated in the same manner as in Example 1. Table 2 shows the evaluation results.

(Example 3)
In the same manner as in Example 1, a mixture of silicon dioxide and silicon having an average particle diameter of 5 μm was obtained, and 3 g (3% by mass) of lithium carbonate was mixed with the mixture as an alkali metal source. For 2 hours. An acetylene gas is flowed through the obtained composite using argon gas as a carrier, and a chemical vapor deposition (CVD) treatment is performed at a heat treatment temperature of 750 ° C., whereby carbon is loaded on the composite and a lithium ion battery is provided. A negative electrode material for use (hereinafter, referred to as a negative electrode material of Example 3) was produced.

  The negative electrode material of Example 3 was evaluated in the same manner as in Example 1. Using the negative electrode material of Example 3, a negative electrode for a lithium ion battery was produced in the same manner as in Example 1. Further, using the prepared negative electrode for a lithium ion battery, a lithium ion battery was prepared and evaluated in the same manner as in Example 1. Table 2 shows the evaluation results.

(Example 4)
In the same manner as in Example 1, a mixture of silicon dioxide and silicon having an average particle diameter of 5 μm was obtained, and 10 g (10% by mass) of lithium carbonate was mixed with the mixture as an alkali metal source. For 2 hours. The obtained composite is subjected to a CVD treatment in the same manner as in Example 3, whereby carbon is supported on the composite, and a negative electrode material for a lithium ion battery (hereinafter, referred to as a negative electrode material of Example 4) is obtained. Produced.

  The negative electrode material of Example 4 was evaluated in the same manner as in Example 1. Using the negative electrode material of Example 4, a negative electrode for a lithium ion battery was produced in the same manner as in Example 1. Further, using the prepared negative electrode for a lithium ion battery, a lithium ion battery was prepared and evaluated in the same manner as in Example 1. Table 2 shows the evaluation results.

(Comparative Example 1)
In the same manner as in Example 1, a mixture of silicon dioxide and silicon having an average particle diameter of 5 μm was obtained, and the mixture was subjected to a baking treatment at 1000 ° C. for 2 hours in a nitrogen atmosphere. The obtained composite is subjected to a chemical vapor deposition (CVD) process using an argon gas as a carrier and an acetylene gas as a carbon source at a heat treatment temperature of 750 ° C. to carry carbon on the composite, A negative electrode material for a lithium ion battery (hereinafter, referred to as a negative electrode material of Comparative Example 1) was produced.

  The negative electrode material of Comparative Example 1 was evaluated in the same manner as in Example 1. Using the negative electrode material of Comparative Example 1, a negative electrode for a lithium ion battery was produced in the same manner as in Example 1. Further, using the prepared negative electrode for a lithium ion battery, a lithium ion battery was prepared and evaluated in the same manner as in Example 1. Table 2 shows the evaluation results. In Comparative Example 1, since the alkali metal source was not used, “Temperature and calcination time of the calcination treatment with the alkali metal source” was described as “−” in Table 1.

(Example 5)
<Preparation of negative electrode material for lithium ion battery>
SiO is a V-type mixer (manufactured by Tsutsui Rikagaku Kiki Co., Ltd., trade name: VM-2 type) prepared by mixing 300 g of silicon dioxide powder (manufactured by Wako Pure Chemical Industries, first grade) and 300 g of silicon powder (reagent, Wako Pure Chemical Industries). ) And heated in a vacuum atmosphere at 1100 ° C. for 10 hours to deposit and deposit the evaporated SiO to obtain a deposit of SiO. This deposit was pulverized to an average particle diameter of 5 μm with a jet mill (trade name: Cojet System α-mkV, manufactured by Seishin Enterprise Co., Ltd.) to obtain a pulverized product. Thereafter, 5 g (5 mass%) of lithium acetate (manufactured by Wako Pure Chemical Industries, Ltd.) as an alkali metal source was mixed with 95 g of the pulverized material, and the mixture was calcined at 800 ° C. for 1 hour in a nitrogen atmosphere. The complex was obtained. 100 g of the obtained composite and 10 g of coal-based pitch (softening point: 250 ° C.) having a residual carbon ratio of 70% were mixed with a V-type mixer (trade name: VM-2, manufactured by Tsutsui Physical and Chemical Instruments) to obtain a mixture. Obtained. This mixture was subjected to a heat treatment at 1000 ° C. for 2 hours in a nitrogen atmosphere, whereby carbon was supported on the composite, and a negative electrode material for a lithium ion battery was produced (hereinafter, referred to as a negative electrode material of Example 5). . The negative electrode material of Example 5 was evaluated in the same manner as in Example 1. Table 4 shows the evaluation results.

<Preparation of negative electrode for lithium ion battery>
5% by mass of the powder of the negative electrode material of Example 5 and 95% by mass of natural graphite having a median particle size of 15 μm (BD15-097, manufactured by Aoshima Kuroyu Co., Ltd.) as a carbon-based negative electrode material were mixed. Thereafter, 1% by mass of carboxymethylcellulose (CMC # 2200, manufactured by Daicel Chemical Industries, Ltd.) as a thickener and 1% by mass of styrene butadiene rubber emulsion (SBR emulsion) as a binder are added and kneaded to produce a uniform slurry. did. The obtained slurry was applied on a rolled copper foil (manufactured by Nippon Foil Co., Ltd.) having a thickness of 10 μm with a blade coater, and the blade gap was adjusted to adjust the application amount to 7.5 mg / cm ² . Thereafter, a curing treatment was performed by drying in the air with hot air at 120 ° C. for 10 minutes to obtain a negative electrode for a lithium ion battery.

<Production of lithium ion battery>
The negative electrode for a lithium ion battery prepared in Example 5 was punched into φ13 mm, and the negative electrode and a positive electrode (2.2 mAh / cm ² ) having a LiNiCoAl active material formed on an aluminum foil were sandwiched with a PP separator in a 2016 type coin cell. And wound into a cylindrical can. Thereafter, EC (ethylene carbonate) / DEC (diethyl carbonate) / MEC (methyl ethyl carbonate) (1: 1: 1 volume ratio) containing 1 mol / L LiPF ₆ as an electrolytic solution and VC (vinylene carbonate) (1 volume) %) Was injected into the cylindrical can, and the upper lid was sealed to produce a lithium ion battery.

(Evaluation of lithium ion battery)
<Discharge capacity, charge / discharge efficiency, expansion rate>
The lithium ion battery produced by the above method was evaluated in the same manner as in Example 1. Table 4 shows the results.

(Example 6)
A negative electrode material for a lithium ion battery (hereinafter, referred to as a negative electrode material of Example 6) was produced in the same manner as in Example 5, except that the addition amount of lithium acetate was changed to 10 g (10% by mass).

  The negative electrode material of Example 6 was evaluated in the same manner as in Example 1. Using the negative electrode material of Example 6, a negative electrode for a lithium ion battery was produced in the same manner as in Example 5. Further, using the prepared negative electrode for a lithium ion battery, a lithium ion battery was prepared and evaluated in the same manner as in Example 5. Table 4 shows the evaluation results.

(Example 7)
A negative electrode material for a lithium ion battery (hereinafter, referred to as a negative electrode material of Example 7) was produced in the same manner as in Example 5, except that the addition amount of lithium acetate was changed to 15 g (15% by mass).

  The negative electrode material of Example 7 was evaluated in the same manner as in Example 1. Using the negative electrode material of Example 7, a negative electrode for a lithium ion battery was produced in the same manner as in Example 5. Further, using the prepared negative electrode for a lithium ion battery, a lithium ion battery was prepared and evaluated in the same manner as in Example 5. Table 4 shows the evaluation results.

(Comparative Example 2)
In the same manner as in Example 5, SiO was obtained by mixing 300 g of silicon dioxide powder (Wako Pure Chemical Industries, first grade reagent) and 300 g of silicon powder (Wako Pure Chemical Industries, reagent) with a V-type mixer (Tsutsui Chemical Chemical Instruments Co., Ltd.). (Trade name: VM-2 type), and heated at 1100 ° C. for 10 hours in a vacuum atmosphere to deposit and deposit evaporated SiO to obtain a deposit of SiO. This deposit was pulverized to an average particle diameter of 5 μm with a jet mill (trade name: Cojet System α-mkV, manufactured by Seishin Enterprise Co., Ltd.) to obtain a pulverized product. A mixture obtained by mixing 100 g of the obtained pulverized product and 10 g of coal-based pitch having a residual carbon ratio of 70% (softening temperature: 250 ° C.) with a V-type mixer (trade name: VM-2, manufactured by Tsutsui Chemical Chemical Instruments). Got. This mixture is heat-treated at 1000 ° C. for 2 hours in a nitrogen atmosphere, and further subjected to a chemical vapor deposition method (CVD) using acetylene gas as a carbon source to carry carbon on the composite, thereby obtaining a negative electrode for a lithium ion battery. A material (hereinafter, referred to as a negative electrode material of Comparative Example 2) was produced.

The negative electrode material of Comparative Example 2 was evaluated in the same manner as in Example 1. Using the negative electrode material of Comparative Example 2, a negative electrode for a lithium ion battery was produced in the same manner as in Example 5. Further, using the prepared negative electrode for a lithium ion battery, a lithium ion battery was prepared and evaluated in the same manner as in Example 5. Table 4 shows the evaluation results. In Comparative Example 2, since the alkali metal source was not used, “Temperature and firing time of the calcination treatment with the alkali metal source” was described as “−” in Table 3. In Comparative Example 2, the “content ratio of Li ₂ SiO ₃ , Li ₂ Si ₂ O ₅ and Li ₆ Si ₂ O ₇ ” was described as “not detected” in Table 4 because no alkali metal source was used.

(Comparative Example 3)
A negative electrode material for a lithium ion battery (hereinafter, referred to as a negative electrode material of Comparative Example 3) was produced in the same manner as in Example 5, except that the addition amount of lithium acetate was changed to 20 g (20% by mass).

  The negative electrode material of Comparative Example 3 was evaluated in the same manner as in Example 1. Using the negative electrode material of Comparative Example 3, a negative electrode for a lithium ion battery was produced in the same manner as in Example 5. Further, using the prepared negative electrode for a lithium ion battery, a lithium ion battery was prepared and evaluated in the same manner as in Example 5. Table 4 shows the evaluation results.

(Example 8)
In the same manner as in Example 5, SiO was obtained by mixing 300 g of silicon dioxide powder (Wako Pure Chemical Industries, first grade reagent) and 300 g of silicon powder (Wako Pure Chemical Industries, reagent) with a V-type mixer (Tsutsui Chemical Chemical Instruments Co., Ltd.). (Trade name: VM-2 type), and heated at 1100 ° C. for 10 hours in a vacuum atmosphere to deposit and deposit evaporated SiO to obtain a deposit of SiO. This deposit was pulverized to an average particle diameter of 5 μm with a jet mill (trade name: Cojet System α-mkV, manufactured by Seishin Enterprise Co., Ltd.) to obtain a pulverized product. Thereafter, 5 g (5% by mass) of lithium carbonate (manufactured by Wako Pure Chemical Industries, Ltd., special grade) as an alkali metal source was mixed with 95 g of the pulverized material, and calcined at 1050 ° C. for 1 hour in a nitrogen atmosphere. The complex was obtained. 100 g of the obtained composite and 10 g of coal-based pitch (softening point: 250 ° C.) having a residual carbon ratio of 70% were mixed with a V-type mixer (trade name: VM-2, manufactured by Tsutsui Physical and Chemical Instruments) to obtain a mixture. Obtained. This mixture was subjected to a heat treatment at 1050 ° C. for 2 hours in a nitrogen atmosphere to carry carbon on the composite, thereby producing a negative electrode material for a lithium ion battery (hereinafter, referred to as a negative electrode material of Example 8). .

The negative electrode material of Example 8 was evaluated in the same manner as in Example 1. Using the negative electrode material of Example 8, a negative electrode for a lithium ion battery was produced in the same manner as in Example 1. Further, using the prepared negative electrode for a lithium ion battery, a lithium ion battery was prepared and evaluated in the same manner as in Example 1. Table 6 shows the evaluation results. The “content ratio (% by mass) of X ₂ SiO ₃ , X ₂ Si ₂ O _5, and X ₆ Si ₂ O ₇ ” in Example 8 in Table 6 means “Li ₂ SiO ₃ , Li ₂ Si ₂ O ₅ and Li ₆ Si ₂ O ₇ content ratio (% by mass) ”.

(Example 9)
A negative electrode material for a lithium ion battery (hereinafter, referred to as a negative electrode material of Example 9) was produced in the same manner as in Example 8, except that lithium carbonate was changed to sodium carbonate as an alkali metal source.

The negative electrode material of Example 9 was evaluated in the same manner as in Example 1. A negative electrode for a lithium ion battery was produced in the same manner as in Example 1 except that the negative electrode material of Example 9 was used. Further, using the prepared negative electrode for a lithium ion battery, a lithium ion battery was prepared and evaluated in the same manner as in Example 1. Table 6 shows the evaluation results. The “content ratio (% by mass) of X ₂ SiO ₃ , X ₂ Si ₂ O _5, and X ₆ Si ₂ O ₇ ” in Example 9 in Table 6 means “Na ₂ SiO ₃ , Na ₂ Si ₂ O ₅ and Na ₆ Si ₂ O ₇ content ratio (% by mass) ”.

<Method for calculating content ratio of Na ₂ SiO ₃ , Na ₂ Si ₂ O ₅ and Na ₆ Si ₂ O ₇ >
The negative electrode material of Example 9 was analyzed by XRD under the same conditions as in Example 1. The X-ray diffraction pattern obtained by XRD was processed by a RIR (Reference Intensity Ratio: reference intensity ratio) method using integrated powder X-ray analysis software (PDXL, manufactured by Rigaku Corporation), and Na ₂ in the negative electrode material of Example 9 was used. The content ratios of SiO ₃ , Na ₂ Si ₂ O ₅ and Na ₆ Si ₂ O ₇ were calculated.

(Example 10)
A negative electrode material for a lithium ion battery (hereinafter, referred to as a negative electrode material of Example 10) was produced in the same manner as in Example 8, except that lithium carbonate was changed to potassium carbonate as the alkali metal source.

The negative electrode material of Example 10 was evaluated in the same manner as in Example 1. Using the negative electrode material of Example 10, a negative electrode for a lithium ion battery was produced in the same manner as in Example 1. Further, using the prepared negative electrode for a lithium ion battery, a lithium ion battery was prepared and evaluated in the same manner as in Example 1. Table 6 shows the evaluation results. The “content ratios (% by mass) of X ₂ SiO ₃ , X ₂ Si ₂ O _5, and X ₆ Si ₂ O ₇ ” in Example 10 in Table 6 are “K ₂ SiO ₃ , K ₂ Si ₂ O ₅ and K ₆ Si ₂ O ₇ content ratio (% by mass) ”.

<Method for calculating the content ratio of K ₂ SiO ₃ , K ₂ Si ₂ O ₅ and K ₆ Si ₂ O ₇ >
The negative electrode material of Example 10 was analyzed by XRD under the same conditions as in Example 1. The X-ray diffraction pattern obtained by XRD was processed by RIR (Reference Intensity Ratio: reference intensity ratio) method using integrated powder X-ray analysis software (PDXL, manufactured by Rigaku Corporation), and K ₂ in the negative electrode material of Example 10 was used. The content ratios of SiO ₃ , K ₂ Si ₂ O ₅ and K ₆ Si ₂ O ₇ were calculated.

(Comparative Example 4)
A negative electrode material for a lithium ion battery (hereinafter, referred to as a negative electrode material of Comparative Example 4) was produced in the same manner as in Example 8, except that calcium carbonate was used as an alkaline earth metal source instead of lithium carbonate.

The negative electrode material of Comparative Example 4 was evaluated in the same manner as in Example 1. Using the negative electrode material of Comparative Example 4, a negative electrode for a lithium ion battery was produced in the same manner as in Example 1. Further, using the prepared negative electrode for a lithium ion battery, a lithium ion battery was prepared and evaluated in the same manner as in Example 1. Table 6 shows the evaluation results. In Comparative Example 4, the content of X ₂ SiO ₃ , X ₂ Si ₂ O ₅ and X ₆ Si ₂ O ₇ was not detected in Table 6 because an alkaline earth metal source was used instead of the alkali metal source. ".

  Hereinafter, FIG. 1 will be described. FIG. 1 shows the results of the analysis of the negative electrode materials for lithium ion batteries obtained in Example 5 and Comparative Example 2 by the powder X-ray diffraction method using CuKα radiation and the analysis of the raw material SiO by the powder X-ray diffraction method using CuKα radiation. It is a figure showing a result.

  As described in Example 5 and Comparative Example 2, the raw material SiO was mixed with silicon dioxide and silicon, and was vaporized as SiO by heating in a vacuum to precipitate and deposit, and pulverized to an average particle diameter of 5 μm by a jet mill. No heat treatment was performed after the deposition. Therefore, the raw material SiO showed a broad peak derived from amorphous silicon dioxide at a diffraction angle 2θ of around 17 to 26 ° in a powder X-ray diffraction method using CuKα radiation.

  The raw material SiO showed a small peak derived from quartz at a diffraction angle of 2θ = 26.5 ° and a small peak derived from silicon Si (111) at a diffraction angle of 2θ = 28.5 °.

When the raw material SiO is heated at about 1000 ° C. in an inert atmosphere, a peak derived from Si (111) at a diffraction angle 2θ of about 28.5 ° and a Si (220) derived at a diffraction angle 2θ of about 47.0 ° are obtained. A peak and a peak derived from Si (311) near the diffraction angle 2θ = 56.0 ° grow, and separation from SiO _2, that is, a so-called disproportionation reaction occurs.

  In FIG. 1, the broad peak derived from amorphous silicon dioxide at a diffraction angle of 2θ = 17 to 26 ° is higher in intensity than the raw material SiO by heating, but has not yet reached a clear crystallization.

  Further, in FIG. 1, a small peak derived from quartz near the diffraction angle 2θ = 26.5 ° had almost the same intensity as the raw material SiO.

  After the disproportionation reaction occurs, by performing carbon coating by a chemical vapor deposition method using a hydrocarbon gas, or by heating a carbon source such as pitch and raw material SiO at about 1000 ° C. to perform carbon coating. And SiO / C with low powder resistance can be obtained.

  The peak derived from quartz near the diffraction angle 2θ = 26.5 ° of the negative electrode material obtained in Example 5 shows almost the same intensity as the peak derived from quartz near the diffraction angle 2θ = 26.5 ° of the raw material SiO. Was.

  The negative electrode material obtained in Example 5 showed sharp peaks derived from cristobalite at diffraction angles 2θ = around 21.5 ° and around 36.0 °. These peaks also overlap with the tridymite peak.

  Further, the negative electrode material obtained in Example 5 has sharp peaks derived from silicon near diffraction angles 2θ = 28.5 °, 47.5 ° and 56.0 °, and 2θ = 68.0, 76.5 and 88. A peak derived from silicon was shown around 0.0 °. Thus, by heating the alkali metal source and the amorphous silicon oxide, crystallization of silicon dioxide and crystallization of silicon can be advanced.

  Hereinafter, (A) to (C) of FIG. 2 will be described. FIG. 2A is a transmission electron microscope (TEM) photograph of the raw material SiO. FIG. 2B is a TEM photograph of the negative electrode material for a lithium ion battery obtained in Comparative Example 2. FIG. 2C is a TEM photograph of the negative electrode material for a lithium ion battery obtained in Example 5.

  Since the raw material SiO is in a state where amorphous silicon dioxide and amorphous silicon are mixed, the silicon diffraction contrast caused by the crystal lattice was not seen, and the crystal size of silicon could not be clearly confirmed ( FIG. 2 (A)).

  In the negative electrode material obtained in Comparative Example 2, the raw material SiO (average particle size: 5 μm) was mixed with coal-based pitch, and heated at 1000 ° C. in a nitrogen atmosphere for 2 hours, whereby the silicon diffraction contrast due to the crystal lattice was observed. (FIG. 2B). The long side and the short side of the silicon crystal were each about 5 nm (FIG. 2B). From the X-ray diffraction pattern obtained by powder X-ray diffraction, it was confirmed that the silicon crystal reflects the result calculated based on Scherrer's formula.

  In the negative electrode material obtained in Example 5, an alkali metal source was added to the raw material SiO (average particle diameter: 5 μm), heated at 800 ° C. for 1 hour in a nitrogen atmosphere, and further mixed with coal-based pitch at 1000 ° C. for 2 hours. By heating for a time, a silicon diffraction contrast due to the crystal lattice was confirmed (FIG. 2C).

  Clear diffraction contrast of the crystal-grown silicon was confirmed. The long side of the silicon crystal was about 40 nm, and the short side of the silicon crystal was about 25 nm (FIG. 2C). From the X-ray diffraction pattern obtained by powder X-ray diffraction, it was confirmed that the silicon crystal reflects the result calculated based on Scherrer's formula.

  Hereinafter, FIG. 3 will be described. FIG. 3 is a diagram showing the measurement results of the charge / discharge curves of the lithium ion batteries obtained in Example 5 and Comparative Example 2.

  The lithium ion battery using the negative electrode material obtained in Comparative Example 2 had a large overvoltage during charging, a charge capacity of 460 mAh / g, a discharge capacity of 405 mAh / g, and a charge / discharge efficiency of 88.0%.

In the lithium ion battery using the negative electrode material obtained in Example 5, the overvoltage was low during charging, and a plateau derived from crystalline silicon was observed around 0.5 V (vs. Li ⁺ / Li) during discharging. . The charge capacity was 435 mAh / g, the discharge capacity was 396 mAh / g, and the charge / discharge efficiency was 91.0%.

Claims (7)

Containing a composite comprising crystalline silicon dioxide and crystalline silicon,
The crystalline silicon dioxide contains cristobalite and quartz,
In the powder X-ray diffraction method using CuKα radiation, the intensity (Icr) of the peak existing in the range of diffraction angle 2θ = 21.5 ± 0.5 ° and the diffraction angle 2θ = 26.5 ± 0.5 ° A negative electrode material for a lithium ion battery, wherein the ratio (Icr / Iqz) to the intensity of the existing peak (Iqz) is 3 to 100. In the powder X-ray diffraction method using CuKα radiation, the intensity (Isi) of the peak existing in the range of diffraction angle 2θ = 28.5 ± 0.5 ° and the range of diffraction angle 2θ = 26.5 ± 0.5 ° The negative electrode for a lithium ion battery according to claim 1, wherein the ratio (Isi / Iqz) to the intensity (Iqz) of the existing peak is 3 to 50, and the crystal size of the crystalline silicon is 10 nm or more. material. 3. The composite according to claim 1, wherein the composite contains carbon on a part or all of a surface thereof, and a content ratio of the carbon is 5 to 10 mass% with respect to a total mass of the composite. 4. Negative electrode material for lithium ion batteries. The composite is composed of X ₂ SiO ₃ , X ₂ Si ₂ O ₅ and X ₆ Si ₂ O ₇ (where X is at least one element selected from the group consisting of Li, Na and K). It contains at least one alkali metal composite oxide selected from the group consisting of: and the content ratio of the alkali metal composite oxide is 0.1 to 10% by mass relative to the total mass of the composite. The negative electrode material for a lithium ion battery according to claim 1. The powder resistance is 1 to 1000 Ω · cm at an average particle diameter of 5 to 20 μm, a nitrogen adsorption BET specific surface area of 1 to 10 m ² / g, and a packing density of 1.5 g / cm ³ . The negative electrode material for a lithium ion battery according to claim 1.   A negative electrode for a lithium ion battery, comprising: the negative electrode material for a lithium ion battery according to claim 1; and a current collector.   A lithium ion battery comprising a positive electrode, an electrolyte containing lithium ions, and the negative electrode according to claim 6.