JP6592156B2 - Negative electrode material for lithium ion secondary battery and method for producing the same, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a negative electrode material for a lithium ion secondary battery and a production method thereof, and also relates to a negative electrode and a lithium ion secondary battery using the negative electrode material for the lithium ion secondary battery.

  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, Sn, or a composite oxide thereof as a negative electrode material (for example, Patent Documents 1 and 2). Reference), a method of applying a melt-quenched metal oxide as a negative electrode material (for example, see Patent Document 3), a method of using silicon oxide as a negative electrode material (for example, see Patent Document 4), and Si ₂ N ₂ O as a negative electrode material And a method using Ge ₂ N ₂ O (see, for example, Patent Document 5) is known.

  Further, for the purpose of imparting conductivity to the negative electrode material, a method of carbonizing SiO after graphite and mechanical alloying (for example, see Patent Document 6), a method of coating a carbon layer on the surface of silicon particles by a chemical vapor deposition method (for example, And Patent Document 7), and a method of coating the surface of silicon oxide particles with a carbon layer by chemical vapor deposition (for example, see Patent Document 8).

  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.

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

  As described above, the conventional negative electrode material still has a problem. In particular, in Patent Document 4, silicon oxide is used as a negative electrode material for a lithium ion secondary battery to obtain a high-capacity electrode. However, as far as the present inventors know, the irreversible capacity at the time of initial charge / discharge is still insufficient. There are problems such as large size and poor cycle performance, and there is room for improvement.

  Further, the technique of imparting conductivity to the negative electrode material also has a problem in Patent Document 6 that a uniform carbon film is not formed because of solid-solid fusion, and the conductivity is insufficient. In the method of Patent Document 8, although improvement in cycle performance is confirmed, the number of cycles of charge / discharge is increased due to insufficient deposition of fine silicon crystals, integration of the carbon coating structure and the base material. As a result, there is a problem that the capacity gradually decreases and then rapidly decreases after a certain number of times, which is still insufficient for a secondary battery.

  This invention is made | formed in view of this problem, and it aims at providing the negative electrode material for lithium ion secondary batteries negative electrodes excellent in cycling characteristics, and its manufacturing method. Another object of the present invention is to provide a negative electrode and a lithium ion secondary battery using such a negative electrode material.

  In order to solve the above problems, the present invention comprises a step of preparing base particles made of a material containing silicon atoms and capable of occluding and releasing lithium ions, and forming a carbon coating on the surface of the base particles In the method for producing a negative electrode material for a lithium ion secondary battery comprising a step of forming coated particles, the substrate particles were measured with a laser diffraction particle size distribution measurement device in a state where the carbon coating was not formed The ratio of particles having a particle size of 1 μm or less in the volume-based distribution was defined as a%, and the ratio of particles having a particle diameter of 1 μm or less in the volume-based distribution measured with a laser diffraction particle size distribution measuring device with respect to the coated particles was defined as b%. In some cases, a method for producing a negative electrode material for a lithium ion secondary battery is provided, wherein the step of forming the carbon film is performed so that a / b ≧ 3.

  Thus, if the negative electrode material is produced by forming a carbon film so that a / b ≧ 3, particles having a particle size of 1 μm or less that existed before the coating with the carbon film (that is, (Fine powder having a relatively small particle diameter) forms secondary particles aggregated with carbon by coating. When the negative electrode is produced from the negative electrode material, the secondary particles fill the gaps of the large particles and contribute to the reduction of the electric resistance of the negative electrode. This leads to an improvement in capacity retention rate when the charge / discharge cycle is repeated.

  In this case, in the step of preparing the base particles, it is preferable to prepare the base particles having the a% of 0.1% to 30%.

  Thus, it becomes easy to form secondary particles when the ratio of particles having a particle size of 1 μm or less in the volume-based distribution is 0.1% or more and 30% or less.

  In the step of preparing the base particles, the base particles may be silicon particles, particles having a composite structure in which silicon fine particles are dispersed in a silicon-based compound, or a general formula SiOx (0.5 ≦ x ≦ 1.6). ), Or a mixture thereof can be prepared.

  The method for producing a negative electrode material of the present invention can be applied to any of the above base particles.

  Moreover, it is preferable that the ratio of the mass of the carbon contained in the coating particle to the mass of the coating particle is 0.5% by mass or more and 40% by mass or less.

  By setting it as such carbon coating amount, sufficient electroconductivity can be provided to a negative electrode material, and charge / discharge capacity can be made high.

In the step of preparing the base particles, the base particles may have a cumulative 50% diameter (D ₅₀ ) in a volume reference distribution measured with a laser diffraction particle size distribution measuring device of the base particles of 0.1 μm. It is preferable to prepare a material having a thickness of 30 μm or less.

  By using such base material particles having a cumulative 50% diameter, it is possible to improve the electrode conductivity without damaging the separator when the negative electrode material is applied for the production of the negative electrode.

In addition, the step of forming the carbon coating is performed such that the cumulative 50% diameter (D ₅₀ ) in the volume reference distribution measured with a laser diffraction particle size distribution measuring device of the coated particles is 1 μm or more and 30 μm or less. Is preferred.

  By setting the cumulative 50% diameter of the coated particles to such a value, it is possible to improve the electrode conductivity without damaging the separator when the negative electrode material is applied for producing the negative electrode.

  In addition, the step of forming the carbon film is performed by chemically vapor-depositing the carbon in the temperature range of 600 to 1200 ° C. in an organic gas atmosphere that can be thermally decomposed to generate carbon. It is preferable.

  By performing carbon coating under such conditions, it is possible to form a good carbon film and to impart appropriate conductivity to the negative electrode material.

  In addition, as a raw material of organic gas that can generate carbon by pyrolysis, methane, ethane, ethylene, acetylene, propane, propylene, butane, butene, pentane, isobutane, hexane, benzene, toluene, xylene, styrene, ethylbenzene, 1 selected from diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, gas light oil obtained in tar distillation process, creosote oil, anthracene oil and naphtha cracked tar oil It is preferable to use more than one species.

  These can be suitably used as the raw material for the organic gas.

  Moreover, this invention provides the negative electrode material for lithium ion secondary batteries manufactured by the manufacturing method of any one of said negative electrode materials for lithium ion secondary batteries.

  The present invention also relates to lithium, which is a coated particle composed of a material containing a silicon atom and comprising a base particle capable of inserting and extracting lithium ions and a carbon coating formed on the surface of the base particle. Proportion of particles having a particle size of 1 μm or less in a volume reference distribution measured with a laser diffraction particle size distribution measuring device with respect to the base particles in a state where the carbon film is not formed in the negative electrode material for an ion secondary battery And a / b ≧ 3, where b is the ratio of particles having a particle size of 1 μm or less in the volume reference distribution measured with a laser diffraction particle size distribution measuring device to the coated particles. There is provided a negative electrode material for a lithium ion secondary battery.

  In the negative electrode material of the present invention, fine particles having a particle size of 1 μm or less that existed before the coating with the carbon coating forms secondary particles aggregated with carbon by the coating. When the negative electrode is produced from the negative electrode material, the secondary particles fill the gaps of the large particles and contribute to the reduction of the electric resistance of the negative electrode. This leads to an improvement in capacity retention rate when the charge / discharge cycle is repeated.

  Moreover, this invention provides the negative electrode for lithium ion secondary batteries using the said negative electrode material for lithium ion secondary batteries.

  Moreover, this invention provides the lithium ion secondary battery characterized by using said negative electrode for lithium ion secondary batteries.

  In the negative electrode for a lithium ion secondary battery using the negative electrode material of the present invention, the presence of the secondary particles contained in the negative electrode material contributes to the reduction of the electric resistance of the negative electrode. This leads to an improvement in capacity retention rate when a charge / discharge cycle of a lithium ion secondary battery using the negative electrode is repeated.

  In the negative electrode material for a lithium ion secondary battery of the present invention, fine particles having a particle size of 1 μm or less that existed before the coating with the carbon coating forms secondary particles aggregated with carbon by the coating. When the negative electrode is produced from the negative electrode material, the secondary particles fill the gaps of the large particles and contribute to the reduction of the electric resistance of the negative electrode. This leads to an improvement in capacity retention rate when the charge / discharge cycle is repeated. In addition, since a material containing silicon atoms is used as the base particle, the negative electrode material of the present invention can have a high capacity. In addition, the manufacturing method is not particularly complicated, is simple, and can sufficiently withstand industrial scale production.

It is a particle size distribution chart of the base particle before performing the carbon coating by CVD in Examples 1 to 3 and Comparative Example 1. 2 is a particle size distribution chart of coated particles in Example 1. FIG. 3 is a particle size distribution chart of coated particles in Example 2. 4 is a particle size distribution chart of coated particles in Example 3. 6 is a particle size distribution chart of coated particles in Example 4. 4 is a particle size distribution chart of coated particles in Comparative Example 1. 6 is a particle size distribution chart of base material particles before performing carbon coating by CVD in Comparative Example 2; 6 is a particle size distribution chart of coated particles in Comparative Example 2.

  Hereinafter, the present invention will be described in detail.

[Anode material for lithium ion secondary battery]
A negative electrode material for a lithium ion secondary battery according to the present invention is made of a material containing silicon atoms, and base particles capable of inserting and extracting lithium ions, and a carbon coating formed on the surface of the base particles. Coated particles consisting of In the negative electrode material of the present invention, the particles before and after the formation of the carbon coating satisfy the following conditions. The ratio of particles having a particle size of 1 μm or less in a volume reference distribution measured with a laser diffraction particle size distribution measuring device with respect to the base material particles in a state where no carbon film is formed is defined as a%. Further, the ratio of particles having a particle diameter of 1 μm or less in the volume reference distribution measured with a laser diffraction particle size distribution measuring device to the coated particles is defined as b%. At this time, the negative electrode material of the present invention satisfies the relationship of a / b ≧ 3.

  The inventors set the distribution of the respective particle sizes of the base particles and the coated particles within a specific range, that is, the particles having the above-mentioned a / b of 3 or more as negative electrode materials for lithium ion secondary batteries ( It has been found that a lithium-ion secondary battery having a high capacity and excellent cycle characteristics can be obtained by using it as an active material), and the present invention has been made.

  As described above, the definition of particle size distribution in the present invention is based on particle size distribution measurement using a laser diffraction method (also referred to as laser diffraction particle size distribution measurement). For example, SALD-3100 manufactured by Shimadzu Corporation can be used as the laser diffraction particle size distribution measuring apparatus. The volume reference distribution measured with a laser diffraction particle size distribution measuring device for specific particles (particle group, powder) is also simply referred to as “volume reference distribution” below. The “ratio of particles having a particle size of 1 μm or less” may be generally referred to as “cumulative 1 μm”.

[Method for producing negative electrode material for lithium ion secondary battery]
The negative electrode material for a lithium ion secondary battery of the present invention can be produced through the following steps. First, base material particles made of a material containing silicon atoms and capable of inserting and extracting lithium ions are prepared (step A). Next, a carbon film is formed on the surface of the substrate particles to form coated particles (step B). At this time, the carbon coating of the base particles is formed so that the above a and b satisfy a / b ≧ 3. This manufacturing method is not particularly complicated, is simple, and can sufficiently withstand industrial scale production.

[Base material particles]
In the present invention, as described above, carbon (coating) is performed on particles (base material particles) made of a material containing silicon atoms and capable of inserting and extracting lithium ions. The substrate particles used in the present invention (that is, the substrate particles prepared in step A) are silicon particles, particles having a composite structure in which silicon fine particles are dispersed in a silicon-based compound, and a general formula SiOx (0.5 ≦ x ≦ The silicon oxide particles represented by 1.6) or a mixture thereof is preferred. The method for producing a negative electrode material of the present invention can be applied to any of the above base particles. By using any of the above as the base particles, a negative electrode material for a lithium ion secondary battery having higher initial charge / discharge efficiency, high capacity, and excellent cycleability can be obtained.

Silicon oxide in the present invention is a general term for amorphous silicon oxide, and silicon oxide before disproportionation is represented by the general formula SiO _x (0.5 ≦ x ≦ 1.6). x is preferably 0.8 ≦ x <1.3, and more preferably 0.8 ≦ x <1.0. This silicon oxide can be obtained, for example, by cooling and precipitating silicon monoxide gas generated by heating a mixture of silicon dioxide and metal silicon.

Particles having a composite structure in which silicon fine particles are dispersed in a silicon-based compound are, for example, a method of firing a mixture of silicon fine particles and a silicon-based compound, or oxidation before disproportionation represented by the general formula SiO _x. It can be obtained by heat-treating silicon particles at a temperature of 400 ° C. or higher, preferably 800 to 1,100 ° C. in an inert non-oxidizing atmosphere such as argon, and performing a disproportionation reaction. In particular, the material obtained by the latter method is suitable because silicon crystallites are uniformly dispersed. By the disproportionation reaction as described above, the size of the silicon nanoparticles can be set to 1 to 100 nm. Note that silicon dioxide in the particles having a structure in which silicon nanoparticles are dispersed in silicon oxide is preferably silicon dioxide. Note that it can be confirmed by transmission electron microscopy that silicon nanoparticles (crystals) are dispersed in amorphous silicon oxide.

  As the base particle, a silicon oxide-based material is particularly preferable because it has a low volume expansion coefficient during insertion and extraction of lithium. When the volume expansion coefficient of the base particle itself is low, the cycle property is particularly good.

The physical properties of the base particles used in the present invention can be appropriately selected depending on the target coated particles (composite particles). For example, it is preferable to use a material whose cumulative 50% diameter (D ₅₀ , also referred to as volume average particle diameter) in a volume reference distribution measured with a laser diffraction particle size distribution measuring apparatus is 0.1 μm or more and 30 μm or less. it can. The lower limit of this range is more preferably 0.2 μm or more, and further preferably 0.3 μm or more. The upper limit is more preferably 20 μm or less, and further preferably 10 μm or less. If the cumulative 50% diameter (D ₅₀ ) is 0.1 μm or more, the BET specific surface area described later can be made sufficiently small, and no adverse effect due to the excessively large BET specific surface area is exerted. Further, if the cumulative 50% diameter (D ₅₀ ) is 30 μm or less, it becomes easy to apply a negative electrode material or the like when producing the negative electrode.

BET specific surface area of the substrate particles used in the present invention is preferably from 0.5 m ² / g or more 100 m ² / g or less, ^{1 m} 2 / g or more ^{20 m} 2 / g or less is more preferable. When the BET specific surface area is 0.5 m ² / g or more, the adhesiveness when the negative electrode material is applied to produce the negative electrode can be made sufficient, and the battery characteristics can be improved. Moreover, if the BET specific surface area is 100 m ² / g or less, the ratio of silicon dioxide due to natural oxidation of the particle surface can be reduced. As a result, since silicon dioxide that does not contribute to the battery reaction can be reduced, a decrease in battery capacity can be suppressed when used as a negative electrode material for a lithium ion secondary battery.

  Further, the “a%” of the base particles used in the present invention is preferably 0.1% or more and 30% or less. By making the base particles have a ratio of particles having a particle size of 1 μm or less in a volume-based distribution of 0.1% or more and 30% or less, the secondary particles described above can be easily formed, and the electric resistance in the negative electrode is reduced. Contribute to.

[Method of forming carbon film]
In the present invention, as described above, in Step B, a carbon film is formed on the surface of the base material particles to form coated particles. This is for imparting conductivity to the base particles and improving battery characteristics. In the present invention, it is essential to form a carbon film on the surface of the substrate particles, but this carbon coating may be performed and mixed with conductive particles such as graphite. As a method for forming a carbon film on the surface of the substrate particles, a method performed by chemical vapor deposition (CVD) is suitable.

  As a method of chemical vapor deposition (CVD), for example, a method of performing chemical vapor deposition of carbon in a temperature range of 600 to 1200 ° C. in an organic gas atmosphere that can be pyrolyzed to generate carbon with respect to base particles. Is mentioned.

  This chemical vapor deposition (CVD) can be applied at both normal pressure and reduced pressure. Examples of reduced pressure include reduced pressure of 50 to 30,000 Pa. Moreover, generally known apparatuses, such as a batch furnace, a continuous kiln, such as a rotary kiln and a roller hearth kiln, and a fluidized bed, can be used for the apparatus used for the formation process of a carbon film. In particular, a rotary kiln capable of continuously performing vapor deposition while stirring can efficiently coat carbon more uniformly, and can improve battery characteristics.

  The formation of a carbon film by chemical vapor deposition includes the following various organic substances as the carbon source. The thermal decomposition temperature, vapor deposition rate, and the characteristics of the carbon film formed after vapor deposition largely depend on the substance used. May be different. The carbon source can be appropriately changed according to the physical properties of the target coated particles. A substance having a low vapor deposition rate is preferred because it tends to make the surface carbon film uniform enough. On the other hand, if the substance is decomposed at a low temperature, the growth of silicon crystals in the base material particles during vapor deposition is suppressed, so that it is possible to suppress a decrease in discharge efficiency and cycle characteristics.

  As raw materials of organic gas that can generate carbon by pyrolysis, methane, ethane, ethylene, acetylene, propane, propylene, butane, butene, pentane, isobutane, hexane, benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene Phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, gas light oil obtained in the tar distillation step, creosote oil, anthracene oil, and naphtha cracked tar oil. These can be used singly or in appropriate combination of two or more.

  About the coating amount of a carbon film, it is preferable that the ratio of the mass of the carbon contained in this coating particle with respect to the mass of a coating particle shall be 0.5 mass% or more and 40 mass% or less. As for this ratio, 1.0-30 mass% is more preferable. Although it depends on the particles to be coated, by setting the carbon coating amount to 0.5% by mass or more, it is possible to maintain substantially sufficient conductivity, and the cycle characteristics when used as a negative electrode of a nonaqueous electrolyte secondary battery. Can be reliably achieved. In addition, if the carbon coating amount is 40% by mass or less, the effect of imparting conductivity by the carbon coating can be obtained, and a decrease in charge / discharge capacity due to an increase in the proportion of carbon in the negative electrode material can be suppressed. Can do.

[Particle size distribution and particle size range of anode material]
As described above, the negative electrode material of the present invention satisfies the relationship of a / b ≧ 3 in terms of particle size. Particles (fine powder) having a particle size of 1 μm or less in the volume-based distribution of the base material particles in a state where no carbon coating is formed form secondary particles aggregated with carbon by the coating. When the negative electrode is produced from the negative electrode material, the secondary particles fill the gaps of the large particles and contribute to the reduction of the electric resistance of the negative electrode (electrode). This leads to an improvement in capacity retention rate when the charge / discharge cycle is repeated.

The carbon coating is preferably formed so that the 50% cumulative diameter (D ₅₀ ) in the volume reference distribution measured with a laser diffraction particle size distribution measuring device of the coated particles is 1 μm or more and 30 μm or less. Thereby, when apply | coating a negative electrode material in order to produce a negative electrode, the electroconductivity of an electrode can be made favorable, without damaging a separator.

  In the present invention, in order to make the base material particles have a specific particle size distribution and particle size range, it can be appropriately adjusted by treatment such as pulverization and classification. Moreover, in order to make the coated particles on which the carbon coating is formed have a specific particle size distribution and particle size range, it can be appropriately adjusted depending on the coating amount. The coating amount of the carbon coating depends on conditions such as the carbon source gas used for CVD, the heat treatment temperature, and the heat treatment time, in addition to the physical properties of the base particles. The relationship between the coating conditions and the coating amount can be easily determined experimentally.

  A known apparatus can be used for pulverizing the particles. For example, the apparatus illustrated below can be used. First, a ball mill and a medium agitation mill are exemplified in which a pulverizing medium such as a ball or a bead is moved and an object is pulverized using an impact force, a frictional force, or a compressive force. Moreover, the roller mill which grind | pulverizes using the compressive force by a roller is illustrated. In addition, a jet mill is exemplified in which the object to be crushed collides with the lining material at high speed or particles collide with each other, and pulverization is performed by the impact force of the impact. Further, examples include a hammer mill, a pin mill, and a disk mill that pulverize a material to be crushed by using an impact force generated by rotation of a rotor having a hammer, blade, pin, and the like fixed thereto. Moreover, the colloid mill using a shear force is illustrated. Further, a high-pressure wet-opposing collision type disperser “Ultimizer” is exemplified. For pulverization, both wet and dry processes can be used.

  Furthermore, in order to adjust the particle size distribution after pulverization, dry classification, wet classification, sieving classification, or the like can be used. In the dry classification, an air stream is mainly used, and dispersion, separation (separation of fine particles and coarse particles), collection (separation of solid and gas), and discharge are sequentially or simultaneously performed. Also, pre-treatment (adjustment of moisture, dispersibility, humidity, etc.) before classification so as not to reduce classification efficiency due to interference between particles, particle shape, turbulence of air flow, velocity distribution, static electricity, etc. ) Or adjusting the moisture and oxygen concentration of the airflow used. In addition, in a dry type such as a cyclone in which a classifier is integrated, pulverization and classification are performed at a time, and a desired particle size distribution can be obtained.

  In the present invention, the above coated particles are used for a negative electrode material (active material) for a lithium ion secondary battery. Using the negative electrode material for a lithium ion secondary battery obtained in the present invention, a negative electrode is prepared, and lithium An ion secondary battery can be manufactured.

[Negative electrode]
When producing a negative electrode using the said negative electrode material for lithium ion secondary batteries, conductive agents, such as carbon and graphite, can be added further. 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 configured battery may be used. Specifically, metal particles such as Al, Ti, Fe, Ni, Cu, Zn, Ag, Sn, Si, metal fibers, natural graphite, artificial graphite, various coke particles, mesophase carbon, vapor grown carbon fiber, pitch Graphite such as carbon-based carbon fiber, PAN-based carbon fiber, and various resin fired bodies can be used.

  Examples of the method for preparing the negative electrode (molded body) include the following methods.

  First, a paste-like mixture prepared by kneading a solvent such as N-methylpyrrolidone or water with the above-described negative electrode material, if necessary, a conductive agent, and other additives such as a binder such as a polyimide resin. And This mixture is applied to the sheet of the current collector. 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 of this invention is a lithium ion secondary battery using said negative electrode for lithium ion secondary batteries. In addition to the negative electrode, at least a positive electrode and a lithium ion conductive nonaqueous electrolyte are included. The lithium ion secondary battery of the present invention is characterized in that it comprises a negative electrode using the negative electrode material composed of the above coated particles, and other positive electrode, electrolyte, separator, and other materials and battery shapes are used. There is no particular limitation. As described above, the negative electrode material of the present invention has good battery characteristics (charge / discharge capacity and cycle characteristics) when used as a negative electrode material for a lithium ion secondary battery, and is particularly excellent in cycle durability. .

As the positive electrode active material, it is possible to use known materials such as oxides of transition metals such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , V ₂ O ₅ , MnO ₂ , TiS ₂ , MoS ₂ , lithium, and chalcogen compounds. it can.

  As the electrolyte, for example, a non-aqueous solution containing a lithium salt such as lithium hexafluorophosphate and lithium perchlorate is used. As the non-aqueous solvent, one or a combination of two or more of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethoxyethane, γ-butyrolactone, 2-methyltetrahydrofuran and the like are used. 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 more concretely, this invention is not restrict | limited to the following Example.

[Example 1]
SiOx (x = 1.0) coarsely crushed by a jaw crusher (Maekawa Kogyo) was pulverized for 80 minutes by a ball mill (Makino) using alumina balls having a diameter of 10 mm as a medium. These particles were used as substrate particles (Step A). When this base material particle was measured with a laser diffraction particle size distribution analyzer (SALD-3100, Shimadzu Corporation) under a refractive index of 3.90-0.01i, the D ₅₀ (cumulative 50% diameter) in the volume-based distribution was 4. 0.6 μm and cumulative 1 μm (ratio of particles having a particle diameter of 1 μm or less) were 14.8% (that is, a = 14.8). A particle size distribution chart of the base particles is shown in FIG.

  100 g of this substrate particle was laid on a tray so that the thickness of the powder layer was 10 mm, and charged into a batch type heating furnace. Then, the pressure in the furnace was increased to 1,000 ° C. at a temperature increase rate of 200 ° C./hr while the pressure in the furnace was reduced by an oil rotary vacuum pump. After reaching 1,000 ° C., methane was passed through the furnace at 0.3 L / min, and carbon coating treatment was performed for 10 hours (step B). After stopping methane, the temperature in the furnace was lowered and cooled to obtain 106 g of black particles.

The obtained black particles were conductive particles having a carbon coating amount of 4.8% by mass with respect to the black particles. Further, the particle size distribution of the particles were measured in the same manner as described above, _{D 50} in the volume-based distribution 5.3 .mu.m, (the ratio of the particle size 1μm or less of the particles) Cumulative 1μm is 2.6% (i.e., b = 2. 6). A particle size distribution chart of the coated particles is shown in FIG.

<Battery evaluation>
Next, battery evaluation using the obtained coated particles as a negative electrode active material was performed by the following method. First, 45% by mass of the obtained negative electrode material, 45% by mass of artificial graphite (average particle size 10 μm), and 10% by mass of polyimide were mixed, and N-methylpyrrolidone was further added to form a slurry. This slurry was applied to a copper foil having a thickness of 12 μm, dried at 80 ° C. for 1 hour, then subjected to pressure molding by a roller press, and the electrode was vacuum-dried at 350 ° C. for 1 hour. Then, it punched out to 2 cm < ² > and set it as the negative electrode.

  In order to evaluate the charge / discharge characteristics of the obtained negative electrode, a lithium foil was used for the counter electrode, and lithium hexafluorophosphate was mixed with ethylene carbonate and diethyl carbonate in a 1/1 (volume ratio) mixture 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 is allowed to stand at room temperature overnight, and then charged with a secondary battery charge / discharge tester (manufactured by Nagano Co., Ltd.) until the voltage of the test cell reaches 0 V at 0.5 mA / cm ^2. After reaching 0V, the battery was charged by decreasing the current so as to keep the cell voltage at 0V. The charging was terminated when the current value fell below 40 μA / cm ² . The discharge was performed at a constant current of 0.5 mA / cm ² , and the discharge was terminated when the cell voltage reached 1.4 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. The results are shown in Table 1. It was confirmed that the lithium-ion secondary battery had a high capacity with an initial discharge capacity of 1781 mAh / g, a cycle retention rate of 94% after 50 cycles, and excellent cycle performance.

[Example 2]
The same SiOx (x = 1.0) pulverized product (base particle) as in Example 1 was charged in a batch heating furnace in the same manner as in Example 1. Then, the pressure in the furnace was increased to 1,100 ° C. at a temperature increase rate of 200 ° C./hr while the pressure in the furnace was reduced by an oil rotary vacuum pump. After reaching 1,100 ° C., methane was passed through the furnace at 0.3 L / min, and carbon coating treatment was performed for 16 hours. After stopping methane, the temperature in the furnace was lowered and cooled.

The obtained black particles were conductive particles having a carbon coating amount of 21.3% by mass with respect to the black particles. As for the particle size distribution of these particles, D ₅₀ was 5.8 μm, and the cumulative 1 μm (ratio of particles having a particle size of 1 μm or less) was 0.3% (that is, b = 0.3). A particle size distribution chart of the coated particles is shown in FIG.

[Example 3]
The same SiOx (x = 1.0) pulverized product (substrate particles) as in Example 1 was supplied at 2 kg / hr from the inlet side to the rotary kiln that was inclined at 1 ° and the temperature inside the kiln was raised to 1000 ° C. Methane diluted with nitrogen was vented to 16% by volume from the outlet side. The rotation speed of the kiln was 1 rpm. Six hours after the start of charging, conductive particles having a coating amount of 3.5% by mass were obtained from the outlet side. The particle size distribution of the particles _{D 50} is 5.2 .mu.m, (the ratio of the particle size 1μm or less of the particles) accumulated 1μm was 3.7% (i.e., b = 3.7). A particle size distribution chart of the coated particles is shown in FIG.

[Example 4]
The same SiOx (x = 1.0) pulverized product (base particles) as in Example 1 was supplied at 2.8 kg / hr from the inlet side to a rotary kiln that was inclined at 1 ° and the temperature inside the kiln was raised to 1000 ° C. Then, methane diluted with nitrogen to 16% by volume was vented from the outlet side. The rotation speed of the kiln was 1 rpm. Six hours after the start of charging, conductive particles having a coating amount of 2.6% by mass were obtained from the outlet side. The particle size distribution of the particles _{D 50} of 4.4 [mu] m, (the proportion of the particle size 1μm or less of the particles) accumulated 1μm was 4.9% (i.e., b = 4.9). A particle size distribution chart of the coated particles is shown in FIG.

[Comparative Example 1]
100 g of the same SiOx (x = 1.0) pulverized product (substrate particles) as in Example 1 was charged into a batch-type heating furnace. Then, the pressure in the furnace was increased to 1,000 ° C. at a temperature increase rate of 200 ° C./hr while the pressure in the furnace was reduced by an oil rotary vacuum pump. After reaching 1,000 ° C., methane was passed through the furnace at a rate of 0.1 L / min, and a carbon coating treatment was performed for 2 hours. After the methane was stopped, the temperature in the furnace was lowered and cooled to obtain 127 g of black particles.

The obtained black particles were conductive particles having a carbon coating amount of 0.3% by mass with respect to the black particles. The particle size distribution of the particles _{D 50} is 4.8 .mu.m, (ratio of particle diameter 1μm or less of the particles) Cumulative 1μm was 11.4% (i.e., b = 11.4). A particle size distribution chart of the coated particles is shown in FIG.

[Comparative Example 2]
The same SiOx (x = 1.0) pulverized product as in Example 1 was subjected to a flow rate classifier (TC-15 manufactured by Nisshin Engineering Co., Ltd.) with an air volume of 2.5 Nm ³ / min and a rotor rotational speed of 10,000 rpm. Classification with. The D ₅₀ of the coarse particles recovered under the classifier was 6.1 μm, and the cumulative 1 μm (ratio of particles having a particle size of 1 μm or less) was 1.0% (that is, a = 1.0). This powder was used as base material particles (particles to be subjected to carbon coating) in Comparative Example 2. A particle size distribution chart of the substrate particles is shown in FIG. The base particles were subjected to a carbon coating treatment in the same manner as in Example 1. The resulting particles a carbon coating amount 4.2 _{wt%, D 50} is 6.2 .mu.m, (the ratio of the particle size 1μm or less of the particles) accumulated 1μm was 0.7% (i.e., b = 0.7) . A particle size distribution chart of the coated particles is shown in FIG.

  Battery evaluation was performed in the same manner as in Example 1 for the particles obtained in Examples 2 to 4 and Comparative Examples 1 and 2.

Table 1 shows a list of the particle sizes and battery characteristics of Examples 1 to 4 and Comparative Examples 1 and 2.

  It was confirmed that the negative electrode materials of Examples 1 to 4 were lithium ion secondary batteries that were clearly superior in battery characteristics as compared with the negative electrode materials of Comparative Examples 1 and 2.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

Claims (9)

Preparing base particles made of a material containing silicon atoms and capable of inserting and extracting lithium ions;
In the method for producing a negative electrode material for a lithium ion secondary battery, comprising a step of forming a carbon film on the surface of the base particle to form a coated particle,
In the step of preparing the substrate particles, by adjusting the processing conditions of pulverization and classification, particles having a particle size of 1 μm or less in a volume reference distribution measured with a laser diffraction particle size distribution measuring device with respect to the substrate particles The ratio is a%, and the base particles are silicon particles, particles having a composite structure in which silicon fine particles are dispersed in a silicon-based compound, oxidation represented by the general formula SiOx (0.5 ≦ x ≦ 1.6) In the step of preparing silicon particles or a mixture thereof and forming the carbon coating, the coating amount after the carbon coating is formed is adjusted by adjusting the coating amount of the carbon coating. A carbon film is formed so that a / b ≧ 3 when the ratio of particles having a particle diameter of 1 μm or less in a volume reference distribution measured by a diffraction particle size distribution analyzer is b%, and the carbon The step of forming the coating is performed such that a cumulative 50% diameter (D ₅₀ ) in a volume reference distribution measured with a laser diffraction particle size distribution measuring device of the coated particles is 1 μm or more and 30 μm or less. A method for producing a negative electrode material for a lithium ion secondary battery.   2. The lithium ion secondary battery according to claim 1, wherein in the step of preparing the base particle, the base particle is prepared such that the a% is 0.1% or more and 30% or less. Manufacturing method of negative electrode material.   3. The lithium ion according to claim 1, wherein a ratio of a mass of carbon contained in the coated particle to a mass of the coated particle is 0.5% by mass or more and 40% by mass or less. A method for producing a negative electrode material for a secondary battery. In the step of preparing the base material particles, the base material particles have a cumulative 50% diameter (D ₅₀ ) in a volume reference distribution measured by a laser diffraction particle size distribution measuring device of the base material particles of 0.1 μm or more and 30 μm. The method for producing a negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the following is prepared.   The step of forming the carbon coating is performed by chemically vapor-depositing carbon in a temperature range of 600 to 1200 ° C. in an organic gas atmosphere that can be pyrolyzed to generate carbon with respect to the substrate particles. The manufacturing method of the negative electrode material for lithium ion secondary batteries of any one of Claim 1 to 4 characterized by the above-mentioned.   As raw materials for organic gases that can generate carbon by pyrolysis, methane, ethane, ethylene, acetylene, propane, propylene, butane, butene, pentane, isobutane, hexane, benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, One or more selected from naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, gas light oil obtained in tar distillation process, creosote oil, anthracene oil and naphtha cracked tar oil The method for producing a negative electrode material for a lithium ion secondary battery according to claim 5, wherein: Base material particles made of a material containing silicon atoms and capable of occluding and releasing lithium ions;
A negative electrode material for a lithium ion secondary battery, which is a coated particle comprising a carbon coating formed on the surface of the substrate particle,
The ratio of particles having a particle size of 1 μm or less in a volume-based distribution measured with a laser diffraction particle size distribution analyzer is a%,
The substrate particles are silicon particles, particles having a composite structure in which silicon fine particles are dispersed in a silicon compound, silicon oxide particles represented by the general formula SiOx (0.5 ≦ x ≦ 1.6), or these A mixture of
The ratio of particles having a particle diameter of 1 μm or less in the volume-based distribution measured with a laser diffraction particle size distribution analyzer is b%,
The cumulative 50% diameter (D ₅₀ ) in a volume-based distribution measured with a laser diffraction particle size distribution analyzer of the coated particles is 1 μm or more and 30 μm or less,
A negative electrode material for a lithium ion secondary battery, wherein a / b ≧ 3.   A negative electrode for a lithium ion secondary battery, wherein the negative electrode material for a lithium ion secondary battery according to claim 7 is used.   A lithium ion secondary battery using the negative electrode for a lithium ion secondary battery according to claim 8.

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