JP5182498B2 - Anode material for non-aqueous electrolyte secondary battery, method for producing the same, lithium ion secondary battery, and electrochemical capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode material for non-aqueous electrolyte secondary battery which has an excellent initial charge and discharge efficiency and cycle characteristics, and is especially effective for a lithium ion secondary battery, to provide a manufacturing method thereof, to provide a lithium ion secondary battery, and to provide an electrochemical capacitor. <P>SOLUTION: The negative electrode material for non-aqueous electrolyte secondary battery is made of silicon oxide particles represented by general formula: SiO<SB>x</SB>(0.5&le;x&lt;1.6), particles having a structure in which crystallites of silicon are dispersed in a silicon-based compound, or whisker-contained particles composed of a mixture of them in which whiskers are formed on the surfaces of them. The non-aqueous electrolyte secondary battery which has a high initial charge and discharge efficiency and superior cycle characteristics can be obtained by using the negative electrode material so obtained as the negative electrode material of the non-aqueous electrolyte secondary battery. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a negative electrode material for a nonaqueous electrolyte secondary battery having excellent initial charge and discharge efficiency and cycle characteristics when used as a negative electrode active material for a nonaqueous electrolyte secondary battery, particularly a lithium ion secondary battery, and its production. The present invention relates to a method, and a lithium ion secondary battery and an electrochemical capacitor.

In recent years, with the remarkable development of portable electronic devices, communication devices, etc., secondary batteries with high energy density are strongly demanded from the viewpoints of economy and downsizing and weight reduction of devices. Conventionally, as a measure for increasing the capacity of this type of secondary battery, for example, a method of using an oxide such as V, Si, B, Zr, or Sn and a composite oxide thereof as a negative electrode material (for example, Patent Document 1: Kaihei 5-174818, Patent Document 2: Japanese Patent Laid-Open No. 6-60867, and a method of applying a melt-quenched metal oxide as a negative electrode material (for example, see Patent Document 3: Japanese Patent Laid-Open No. 10-294112) , A method using silicon oxide as a negative electrode material (for example, see Patent Document 4: Japanese Patent No. 2999741), a method using Si ₂ N ₂ O and Ge ₂ N ₂ O as a negative electrode material (for example, Patent Document 5: 11-102705) and the like are known. In addition, for the purpose of imparting conductivity to the negative electrode material, a method of carbonizing SiO with graphite and then carbonizing (see, for example, Patent Document 6: JP 2000-243396 A), a chemical vapor deposition method on the surface of silicon particles (For example, see Patent Document 7: Japanese Patent Laid-Open No. 2000-215887), and a method for coating a carbon layer on the surface of silicon oxide particles by chemical vapor deposition (for example, Patent Document 8: Japanese Patent Laid-Open No. 2002-2002). 42806) and the like.

  However, in the above conventional method, although the charge / discharge capacity is increased and the energy density is increased, the cycleability is insufficient, or the required characteristics of the market are still insufficient, and are not always satisfactory. However, further improvement in energy density has been desired.

  In particular, in Japanese Patent No. 2997741 (Patent Document 4), silicon oxide is used as a negative electrode material for a lithium ion secondary battery to obtain a high-capacity electrode. There is room for improvement because the irreversible capacity at the time of discharge is large and the cycle performance has not reached the practical level. In addition, regarding the technique for imparting conductivity to the negative electrode material, in Japanese Patent Application Laid-Open No. 2000-243396 (Patent Document 6), since it is a solid-solid fusion, a uniform carbon film is not formed, and conductivity is improved. There is a problem that it is insufficient. Further, in the method disclosed in Japanese Patent Application Laid-Open No. 2000-215887 (Patent Document 7), although a uniform carbon film can be formed, since Si is used as a negative electrode material, expansion / desorption during lithium ion adsorption / desorption is performed. The contraction is too large, and as a result, it cannot be put into practical use, and the cycle performance is lowered. Therefore, a charge amount limit must be provided in order to prevent this, and Japanese Patent Application Laid-Open No. 2002-42806 (Patent Document) In the method of 8), although the improvement of cycleability is confirmed from the fact that the precipitation of fine silicon crystals, the carbon coating structure and the fusion with the base material are insufficient, the cycle number of charge / discharge is repeated. There is a phenomenon in which the capacity gradually decreases and rapidly decreases after a certain number of times, and there is a problem that it is still insufficient for a secondary battery.

JP-A-5-174818 JP-A-6-60867 JP 10-294112 A Japanese Patent No. 2999741 JP-A-11-102705 JP 2000-243396 A JP 2000-215887 A JP 2002-42806 A Japanese Patent No. 3952180

  The present invention has been made in view of the above circumstances, and has good initial charge / discharge efficiency and cycle characteristics, and in particular, a negative electrode material for a non-aqueous electrolyte secondary battery effective as a lithium ion secondary battery, and a method for producing the same, and An object is to provide a lithium ion secondary battery and an electrochemical capacitor.

  As a result of various studies to achieve the above object, the present inventors have found that whisker silicon oxide in which whiskers are formed on the surface of silicon oxide particles or particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound. It has been found that by using the particles as the negative electrode material, even if the charge and discharge cycles are repeated, the current collecting property is not impaired by the whisker, and the battery characteristics are remarkably improved.

  That is, as a result of evaluating battery characteristics of particles obtained under various conditions during the examination process, the present inventors confirmed that there are differences in characteristics depending on the materials. Therefore, as a result of analysis of the obtained various materials, it is possible to obtain a negative electrode material for a nonaqueous electrolyte secondary battery with good characteristics by using a material having whiskers in particles as a negative electrode material, and The manufacturing method was discovered.

Accordingly, the present invention provides the following negative electrode material for a non-aqueous electrolyte secondary battery, a method for producing the same, a lithium ion secondary battery, and an electrochemical capacitor.
[1]. Silicon oxide particles represented by the general formula SiO _x (0.5 ≦ x <1.6), particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound, or a mixture of these particles are formed on the surface of silicon oxide. A negative electrode material for a non-aqueous electrolyte secondary battery comprising a structure in which fine crystals of silicon are dispersed in a silicon-based compound, or whisker-containing particles in which whiskers made of a mixture thereof are formed.
[2]. The negative electrode material for a nonaqueous electrolyte secondary battery according to [1], wherein the whisker-containing particles are particles whose surfaces are coated with a carbon film.
[3]. Silicon oxide particles represented by the general formula SiO _x (0.5 ≦ x <1.6), particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound, or mixed particles thereof are reduced in pressure to 30000 Pa or less. The method for producing a negative electrode material for a nonaqueous electrolyte secondary battery according to [1], wherein the heat treatment is performed at 900 to 1300 ° C.
[4]. Silicon oxide particles represented by the general formula SiO _x (0.5 ≦ x <1.6), particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound, or mixed particles thereof are reduced in pressure to 30000 Pa or less. The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 2, wherein the heat treatment is performed at 900 to 1300 ° C in an organic gas that is thermally decomposed at a heat treatment temperature of 900 to 1300 ° C to generate carbon. Manufacturing method.
[5]. A lithium ion secondary battery comprising the negative electrode material for a nonaqueous electrolyte secondary battery according to [1] or [2] .
[6]. An electrochemical capacitor comprising the negative electrode material for a non-aqueous electrolyte secondary battery according to [1] or [2] .

  By using the negative electrode material obtained in the present invention as a negative electrode material for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery having high initial charge / discharge efficiency and excellent cycleability can be obtained.

The negative electrode material for a non-aqueous electrolyte secondary battery of the present invention has a structure in which silicon oxide particles represented by the general formula SiO _x (0.5 ≦ x <1.6) and silicon microcrystals are dispersed in a silicon compound. It is made of whisker-containing particles in which whiskers are formed on the surface of the particles having the above or mixed particles thereof.

[Silicon oxide particles]
In the present invention, silicon oxide is a general term for amorphous silicon oxides obtained by cooling and precipitating silicon monoxide gas generated by heating a mixture of silicon dioxide and metal silicon. Means a material represented by the general formula SiO _x (0.5 ≦ x <1.6). x is preferably 0.8 ≦ x <1.6, and more preferably 0.8 ≦ x <1.3.

The silicon oxide is further pulverized into silicon oxide particles. The physical properties of the silicon oxide particles are not particularly limited, but the average particle size is a volume average value D ₅₀ according to the laser diffraction scattering type particle size distribution measurement method (that is, the particle size (median when the cumulative volume becomes 50%) (Diameter) is preferably from 0.01 to ₅₀ μm, more preferably from 0.1 to 10 μm, and if D ₅₀ is smaller than 0.01 μm, purity decreases due to the effect of surface oxidation, and the negative electrode material for a non-aqueous electrolyte secondary battery is used. If used, the charge / discharge capacity may decrease, the bulk density may decrease, and the charge / discharge capacity per unit volume may decrease, whereas if it exceeds 50 μm, it may cause a short circuit through the negative electrode film. there are. Further, BET specific surface area is preferably not less than 0.1 m ² / g, more preferably 0.2 m ² / g or more, preferably 30 m ² / g or less as the upper limit, more preferably 20 m ² / g or more It is.

[Particles having a structure in which silicon microcrystals are dispersed in a silicon compound]
In the particles having a structure in which silicon microcrystals are dispersed in a silicon compound (silicon composite powder), the silicon compound is preferably inactive, and silicon dioxide, silicon nitride, silicon carbide, and silicon oxynitride are preferable. .

The particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound preferably have the following properties.
i. In X-ray diffraction (Cu-Kα) using copper as the counter-cathode, a diffraction peak attributed to Si (111) centered around 2θ = 28.4 ° is observed, and based on the broadening of the diffraction line The particle diameter of the silicon crystal determined by the Scherrer equation is preferably 1 to 500 nm, more preferably 2 to 200 nm, and still more preferably 2 to 20 nm. If the size of the silicon fine particles is smaller than 1 nm, the charge / discharge capacity may be reduced. Conversely, if the silicon fine particle is larger than 500 nm, the expansion / contraction during charge / discharge increases, and the cycle performance may decrease. The size of the silicon fine particles can be measured by a transmission electron micrograph.
ii. In solid-state NMR ( ²⁹ Si-DDMAS) measurement, there is a peak characteristic of Si diamond crystals in the vicinity of −84 ppm, along with a broad silicon dioxide peak whose spectrum is centered around −110 ppm. This spectrum is completely different from ordinary silicon oxide (SiO _x : x = 1.0 + α), and the structure itself is clearly different. Further, it is confirmed by transmission electron microscope that silicon crystals are dispersed in amorphous silicon dioxide.

  The amount of silicon microcrystals (Si) dispersed in particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound is preferably 2 to 36% by mass, and more preferably 10 to 30% by mass. If the amount of dispersed silicon is less than 2% by mass, the charge / discharge capacity may be reduced, and conversely if it exceeds 36% by mass, the cycle performance may be reduced.

Particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound have an average particle diameter of a volume average value D ₅₀ (that is, a particle diameter at a cumulative volume of 50% (according to a laser diffraction scattering particle size distribution measurement method) The production method is not particularly limited as long as the median diameter is 0.01 to 50 μm. For example, it is represented by the general formula SiO _x (0.5 ≦ x <1.6). The silicon oxide powder can be obtained by subjecting it to a disproportionation by subjecting it to a heat treatment in the temperature range of 900 to 1400 ° C. in an inert gas atmosphere.

The average particle diameter (volume average value D ₅₀ ) of the silicon oxide powder is preferably 0.01 μm or more, more preferably 0.1 μm or more, and further preferably 0.5 μm or more. Although an upper limit is not specifically limited, 50 micrometers or less are preferable and 30 micrometers or less are more preferable. BET specific surface area is preferably not less than 0.1 m ² / g, preferably at least 0.2 m ² / g, is not particularly limited but preferably is 30 m ² / g or less, 20 m ² / g or less is more preferable. The range of x is 0.5 ≦ x <1.6, preferably 0.8 ≦ x <1.3, and more preferably 0.8 ≦ x ≦ 1.2. If the average particle diameter and the BET specific surface area of the silicon oxide powder are outside the above ranges, particles having a structure in which silicon microcrystals having a desired average particle diameter and a BET specific surface area are dispersed in a silicon-based compound may not be obtained. It is difficult to produce a SiO _x powder having an _x value of less than 0.5, and those having an x value of 1.6 or more are treated with heat treatment and subjected to a disproportionation reaction. The ratio of ₂ is large, and when used as a lithium ion secondary battery, the charge / discharge capacity may be reduced.

  On the other hand, in disproportionation of silicon oxide, if the heat treatment temperature is lower than 900 ° C., disproportionation does not proceed at all or it takes an extremely long time to form fine silicon cells (silicon microcrystals), which is efficient. On the other hand, if the temperature is higher than 1400 ° C., the structure of the silicon dioxide portion is advanced and the lithium ion traffic is hindered, so that the function as the lithium ion secondary battery may be deteriorated. 1000-1300 degreeC is preferable and the heat processing temperature has more preferable 1100-1250 degreeC. The treatment time (disproportionation time) can be appropriately selected in the range of 10 minutes to 20 hours, particularly 30 minutes to 12 hours, depending on the disproportionation treatment temperature. For example, at a treatment temperature of 1100 ° C. Gives particles (silicon composite powder) having a desired physical property and having a structure in which silicon microcrystals are dispersed in a silicon-based compound in about 5 hours.

The disproportionation treatment may be performed using a reaction apparatus having a heating mechanism in an inert gas atmosphere, and is not particularly limited, and can be performed by a continuous process or a batch process. Specifically, a fluidized bed reactor, A rotary furnace, a vertical moving bed reactor, a tunnel furnace, a batch furnace, a rotary kiln, or the like can be appropriately selected according to the purpose. In this case, as the (treatment) gas, an inert gas alone or a mixed gas thereof such as Ar, He, H ₂ , N ₂ or the like can be used.

[Whisker-containing particles]
The whisker-containing particles of the present invention include silicon oxide particles represented by the general formula SiO _x (0.5 ≦ x <1.6), particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound, or these Whisker is formed on the surface of the mixed particles.

In addition, the applicant of the present invention in Patent No. 3952180,
“In X-ray diffraction, a diffraction peak attributed to Si (111) is observed, and the silicon crystal size determined by the Scherrer method based on the half width of the diffraction line is 1 to 500 nm. A conductive silicon composite for a negative electrode material for a non-aqueous electrolyte secondary battery, wherein the surface of particles having a structure in which microcrystals of the above are dispersed in a silicon compound is coated with carbon. "
This is usually produced by disproportionating silicon oxide with organic gas and / or steam at a temperature of 900 to 1400 ° C. and under normal pressure (atmospheric pressure). Thus, since the whisker of the present invention is not formed, it is different from the whisker-containing particle of the present invention.

  The whisker is composed of silicon oxide, a structure in which microcrystals of silicon are dispersed in a silicon-based compound, or a mixture thereof, and the length is preferably 0.01 to 30 μm, and more preferably 0.1 to 10 μm. If it is shorter than 0.01 μm, the contribution to improving the current collecting property may be insufficient, and if it is longer than 30 μm, it may be broken during electrode production. The thickness of the whisker is preferably 0.001 to 1 μm, and more preferably 0.01 to 0.1 μm. If it is thinner than 0.001 μm, the strength may be insufficient, and if it is thicker than 1 μm, the effect as a whisker may not be exhibited. 0.001-10 mass% is preferable, the presence ratio of the whisker with respect to a silicon oxide particle is more preferable, 0.01-5 mass% is more preferable, and 0.1-1 mass% is further more preferable. If the amount is less than 0.001% by mass, the existence effect may be insufficient. If the amount is more than 10% by mass, electrode preparation may be difficult.

  The whisker-containing particles are preferably provided with conductivity by coating the surfaces of the particles, whiskers, or both with a carbon film. The carbon coating amount is not particularly limited, but is preferably 0.3 to 40% by mass, and more preferably 0.5 to 30% by mass with respect to the silicon oxide particles. If the carbon coating amount is less than 0.3% by mass, the conductivity may not be maintained, and as a result, when the negative electrode material for a non-aqueous electrolyte secondary battery is used, the cycle performance may be reduced. Conversely, even if the carbon coating amount is more than 40% by mass, not only the improvement of the effect is seen, but also the proportion of carbon in the negative electrode material increases, and when used as a negative electrode material for a non-aqueous electrolyte secondary battery, The discharge capacity may be reduced.

The average particle diameter of the whisker-containing particles is preferably 0.01 to ₅₀ μm, and more preferably 0.1 to 10 μm, in the volume average value D ₅₀ by the laser diffraction / scattering particle size distribution measurement method.

Examples of the method for obtaining the whisker-containing particles of the present invention include a structure in which silicon oxide particles represented by the general formula SiO _x (0.5 ≦ x <1.6) and silicon microcrystals are dispersed in a silicon compound. The method which heat-processes the particle | grains which have or these mixed particles at 900-1300 degreeC under the reduced pressure of 30000 Pa or less, Preferably 1-20000 Pa, Preferably it is 950-1100 degreeC. When the pressure is higher than 30000 Pa, it becomes difficult to generate whiskers. When the processing temperature is lower than 900 ° C., the amount of whisker generated is reduced. When the processing temperature is higher than 1300 ° C., the structuring of the silicon dioxide portion progresses and lithium ions come and go. Since it will be inhibited, the function as a negative electrode material for lithium ion secondary batteries may be reduced. The treatment time is appropriately selected depending on the desired whisker production amount, treatment temperature, treatment pressure, etc. Usually, about 1 to 10 hours, particularly about 2 to 5 hours is economically efficient. This manufacturing method is simple and can sufficiently withstand industrial scale production. When silicon oxide particles represented by the general formula SiO _x (0.5 ≦ x <1.6) are heat-treated at 30000 Pa or less and 900 to 1300 ° C., silicon microcrystals are dispersed in the silicon-based compound. Particles having a structure may be formed.

  When the surface of the whisker-containing particles is coated with a carbon film, a chemical vapor deposition method is preferable, and it is also possible to efficiently carry out by introducing an organic gas into the reactor during the heat treatment for forming the whisker.

  As an organic substance used as a raw material for generating an organic gas in the present invention, a substance that can be pyrolyzed at the above heat treatment temperature to generate carbon (graphite) is selected, particularly in a non-acidic atmosphere. For example, methane, ethane, A single or mixture of hydrocarbons such as ethylene, acetylene, propane, butane, butene, pentane, isobutane, hexane, benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone , Pyridine, anthracene, phenanthrene, and the like, and monocyclic to tricyclic aromatic hydrocarbons or a mixture thereof. In addition, gas gas oil, creosote oil, anthracene oil, and naphtha cracked tar oil obtained in the tar distillation step can be used alone or as a mixture.

[Negative electrode material for non-aqueous electrolyte secondary battery]
This invention uses the said whisker containing particle | grain for the negative electrode material for nonaqueous electrolyte secondary batteries, and is a negative electrode material for nonaqueous electrolyte secondary batteries which consists of whisker containing particles. Using the nonaqueous electrolyte secondary battery negative electrode material obtained in the present invention, a negative electrode can be produced to produce a lithium ion secondary battery.

  In addition, when producing a negative electrode using the said negative electrode material for nonaqueous electrolyte secondary batteries, electrically conductive agents, such as carbon and graphite, can be added. Also in this case, the kind of the conductive agent is not particularly limited, and any electronic conductive material that does not cause decomposition or alteration in the constituted battery may be used. Specifically, Al, Ti, Fe, Ni, Cu, Metal powder such as Zn, Ag, Sn, Si, metal fiber or natural graphite, artificial graphite, various coke powders, mesophase carbon, vapor grown carbon fiber, pitch carbon fiber, PAN carbon fiber, various resin fired bodies Such graphite can be used.

  Examples of the method for preparing the negative electrode (molded body) include the following methods. A paste-like mixture is prepared by kneading the whisker-containing particles, if necessary, a conductive agent and other additives such as a binder with a solvent such as N-methylpyrrolidone or water. Apply to current collector sheet. In this case, as the current collector, any material that is usually used as a negative electrode current collector, such as a copper foil or a nickel foil, can be used without any particular limitation on thickness and surface treatment. In addition, the shaping | molding method which shape | molds a mixture into a sheet form is not specifically limited, A well-known method can be used.

[Lithium ion secondary battery]
The lithium ion secondary battery is characterized in that the negative electrode material is used, and other materials such as the positive electrode, the negative electrode, the electrolyte, and the separator, and the battery shape and the like can be known, and are not particularly limited. For example, as the positive electrode active material, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , V ₂ O ₅ , MnO ₂ , TiS ₂ , MoS _{2 and} other transition metal oxides, lithium, chalcogen compounds, and the like are used. As the electrolyte, for example, a non-aqueous solution containing a lithium salt such as lithium hexafluorophosphate and lithium perchlorate is used. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethoxyethane, γ-butyrolactone, One type or a combination of two or more types such as 2-methyltetrahydrofuran is used. Various other non-aqueous electrolytes and solid electrolytes can also be used.

[Electrochemical capacitor]
In the case of obtaining an electrochemical capacitor, the electrochemical capacitor is characterized in that the negative electrode material is used, and other materials such as an electrolyte and a separator and a capacitor shape are not limited. For example, non-aqueous solutions containing lithium salts such as lithium hexafluorophosphate, lithium perchlorate, lithium borofluoride, lithium hexafluoroarsenate, etc. are used as the electrolyte, and propylene carbonate, ethylene carbonate, dimethyl carbonate are used as the non-aqueous solvent. , Diethyl carbonate, dimethoxyethane, γ-butyrolactone, 2-methyltetrahydrofuran and the like. Various other non-aqueous electrolytes and solid electrolytes can also be used.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not limited to the following Example.

[Example 1]
200 g of silicon oxide powder represented by the general formula SiO _x (x = 1.02) having an average particle diameter of 5.0 μm was charged into a batch type heating furnace. Thereafter, while reducing the pressure to 100 Pa or less with an oil rotary vacuum pump, the temperature was raised to 1100 ° C. at a temperature rising rate of 300 ° C./hr, held for 5 hours, and then naturally cooled to room temperature. The obtained powder had an average particle size = 5.3 μm. When confirmed by TEM, it was a particle having a structure in which silicon microcrystals were dispersed in a silicon-based compound. When confirmed by a scanning electron microscope (SEM), whiskers were confirmed over the entire field of view (see FIG. 1). The length of the whisker was 0.5 to 5 μm, the thickness of the whisker was 0.05 to 0.3 μm, and the ratio of the whisker to the silicon oxide particles was 0.1 to 0.3% by mass. .

<Battery characteristics>
In order to confirm the usefulness of the negative electrode material, the battery characteristics were evaluated by the following method.
85 parts by mass of the obtained powder, 5 parts by mass of Denka Black (carbon) manufactured by Denki Kagaku Kogyo, and 10 parts by mass of polyimide were mixed, and further N-methylpyrrolidone was added to form a slurry. This slurry was formed into a copper foil having a thickness of 20 μm. After coating and drying at 80 ° C. for 1 hour, the electrode was pressure-molded by a roller press, and this electrode was vacuum-dried at 350 ° C. for 1 hour, and then punched out to 2 cm ² to obtain a negative electrode.

  Here, in order to evaluate the charge / discharge characteristics of the obtained negative electrode, a lithium foil was used as a counter electrode, and lithium hexafluoride was mixed with 1/1 (volume ratio) of ethylene carbonate and diethyl carbonate as a non-aqueous electrolyte. A lithium ion secondary battery for evaluation using a non-aqueous electrolyte solution dissolved at a concentration of 1 mol / L and a polyethylene microporous film having a thickness of 30 μm as a separator was prepared.

The prepared lithium ion secondary battery was allowed to stand at room temperature overnight, and then charged with a secondary battery charge / discharge tester (manufactured by Nagano Co., Ltd.) until the test cell voltage reached 0 V at 0.5 mA / cm ² . Charging was performed at a constant current, and after reaching 0V, charging was performed by decreasing the current so as to keep the cell voltage at 0V. Then, charging was terminated when the current value fell below 40 μA / cm ² . Discharging was performed at a constant current of 0.5 mA / cm ² , and discharging was terminated when the cell voltage exceeded 2.0 V, and the discharge capacity was determined.

  The above charge / discharge test was repeated, and a charge / discharge test after 50 cycles of the lithium ion secondary battery for evaluation was performed. As a result, the initial charge capacity is 1844 mAh / g, the initial discharge capacity is 1475 mAh / g, the initial charge / discharge efficiency is 80%, the discharge capacity at the 50th cycle is 1342 mAh / g, the cycle retention after 50 cycles is 91%, and the high capacity. It was confirmed that the lithium ion secondary battery was excellent in initial charge / discharge efficiency and cycleability.

[Comparative Example 1]
A battery was prepared by obtaining a powder in the same manner as in Example 1 except that the silicon oxide powder represented by the general formula SiO _x (x = 1.02) used in Example 1 was used as it was without heat treatment. When the powder was confirmed with a scanning electron microscope (SEM), whiskers were not confirmed (see FIG. 2).

  As a result of the same evaluation for this battery, the initial charge / discharge capacity was 1846 mAh / g, the initial discharge capacity was 1403 mAh / g, the initial charge / discharge efficiency was 76%, the 50th cycle discharge capacity was 1221 mAh / g, and after 50 cycles. It was a lithium ion secondary battery having a cycle retention of 87% and inferior initial charge / discharge efficiency and cycleability compared to Example 1.

The SEM photograph of the electroconductive powder in Example 1 is shown. The SEM photograph of the electroconductive powder in the comparative example 1 is shown.

Claims (6)

Silicon oxide particles represented by the general formula SiO _x (0.5 ≦ x <1.6), particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound, or a mixture of these particles are formed on the surface of silicon oxide. A negative electrode material for a non-aqueous electrolyte secondary battery comprising a structure in which fine crystals of silicon are dispersed in a silicon-based compound, or whisker-containing particles in which whiskers made of a mixture thereof are formed. The negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the whisker-containing particles are particles whose surfaces are coated with a carbon film. Silicon oxide particles represented by the general formula SiO _x (0.5 ≦ x <1.6), particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound, or mixed particles thereof are reduced in pressure to 30000 Pa or less. The method for producing a negative electrode material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the heat treatment is performed at 900 to 1300 ° C. General formula SiO _x The silicon oxide particles represented by (0.5 ≦ x <1.6), the particles having a structure in which silicon microcrystals are dispersed in a silicon-based compound, or a mixed particle of these particles is 900 to 30,000 Pa under reduced pressure of 30000 Pa or less. The method for producing a negative electrode material for a non-aqueous electrolyte secondary battery according to claim 2, wherein heat treatment is performed at 900 to 1300 ° C in an organic gas that is thermally decomposed at a heat treatment temperature of 1300 ° C to generate carbon. Claim 1 or a lithium ion secondary battery comprising the negative electrode material for non-aqueous electrolyte secondary battery 2 according. Claim 1 or electrochemical capacitors which comprises a negative electrode material for non-aqueous electrolyte secondary battery 2 according.