TWI651883B - Anode material for lithium ion secondary battery, method for producing the same, anode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

The present invention provides a negative electrode material for a lithium ion secondary battery negative electrode excellent in cycle characteristics and a method for producing the same.

The present invention relates to a method for producing a negative electrode material for a lithium ion secondary battery, which comprises preparing a substrate particle composed of a material containing a ruthenium atom, and forming a carbon film on the surface of the substrate particle to form a coated particle. In a state in which the carbon film is not formed, the ratio of particles having a particle diameter of 1 μm or less which is measured by a laser diffraction particle size distribution measuring device to the substrate particles is set to a%, and the coated particles are thunder. When the ratio of the particles having a particle diameter of 1 μm or less in the volume-based distribution measured by the diffraction-difference particle size distribution measuring apparatus is b%, the formation of the carbon film is performed so that a/b≧3 is obtained.

Description

Anode material for lithium ion secondary battery, method for producing the same, anode for lithium ion secondary battery, and lithium ion secondary battery

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

In recent years, with the remarkable development of portable electronic devices and communication devices, secondary batteries of high energy density have been strongly expected from the viewpoints of economy and miniaturization and weight reduction of machines.

In the prior art, as a method of increasing the capacity of such a secondary battery, for example, an oxide of V, Si, B, Zr, Sn, or the like and a method of using the composite oxide are known (for example, refer to Patent Document 1). And 2) a method in which a molten and quenched metal oxide is used as a negative electrode material (for example, refer to Patent Document 3), a method in which ruthenium oxide is used for a negative electrode material (for example, refer to Patent Document 4), and Si _{2 is} used for a negative electrode material. N ₂ O and Ge ₂ N ₂ O (for example, refer to Patent Document 5) and the like.

Further, as a purpose of imparting conductivity to the negative electrode material, a method of mechanically alloying SiO with graphite and then performing carbonization treatment (for example) For example, refer to Patent Document 6), a method of coating a carbon layer on a surface of a cerium particle by a chemical vapor deposition method (for example, refer to Patent Document 7), and coating a carbon layer on a surface of cerium oxide particles by chemical vapor deposition. Method (for example, refer to Patent Document 8).

However, in the above-described conventional method, although the charge/discharge capacity is increased and the energy density is increased, the cycle property is insufficient, the required characteristics in the market are not sufficient, and the demand is not necessarily satisfied. Therefore, it is expected that the energy density can be further improved.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 5-174818

[Patent Document 2] Japanese Patent Laid-Open No. Hei 6-60867

[Patent Document 3] Japanese Patent Laid-Open No. Hei 10-294112

[Patent Document 4] Japanese Patent No. 2997741

[Patent Document 5] Japanese Patent Laid-Open No. Hei 11-102705

[Patent Document 6] Japanese Patent Laid-Open Publication No. 2000-243396

[Patent Document 7] Japanese Laid-Open Patent Publication No. 2000-215887

[Patent Document 8] Japanese Patent Laid-Open Publication No. 2002-42806

As mentioned above, there are still problems with the prior negative electrode materials. In particular, in Patent Document 4, cerium oxide is used as a negative electrode material for a lithium ion secondary battery, and a high-capacity electrode can be obtained. However, as far as the inventors know, there is an irreversible capacity at the time of initial charge and discharge. There is still room for improvement, such as large and cyclical problems that do not reach the practical level.

In addition, in the technique of the conductivity of the negative electrode material imparting agent, in Patent Document 6, since the solid and the solid are fused, a uniform carbon film is not formed, and there is a problem that conductivity is insufficient. The method of Patent Document 8 has a problem in that although the cycle property is improved, the fine crystallization of ruthenium, the structure of carbon coating, and the fusion with the substrate are insufficient, and there is a cumulative number of cycles of charge and discharge, and the capacity is gradually reduced. The phenomenon of falling and falling sharply after a certain number of times is not sufficient as a secondary battery.

The present invention has been made in view of the problems, and an object thereof is to provide a negative electrode material for a lithium ion secondary battery negative electrode excellent in cycle characteristics, and a method for producing the same. Further, the present invention has an object of providing a negative electrode using a negative electrode material and a lithium ion secondary battery.

In order to solve the above problems, the present invention provides a method for producing a negative electrode material for a lithium ion secondary battery, which comprises the steps of preparing a substrate particle which is made of a material containing a ruthenium atom and is capable of occluding and releasing lithium ions. A method for producing a negative electrode material for a lithium ion secondary battery in which a carbon film is formed on the surface of the substrate particle to form a coating film, and a laser is formed on the substrate particle in a state where the carbon film is not formed. Diffraction-based particle size distribution measuring device for volume distribution The ratio of the particles having a particle diameter of 1 μm or less is set to a%, and when the ratio of the particles having a particle diameter of 1 μm or less measured by the volume-based distribution measured by the laser diffraction particle size distribution measuring apparatus is b%, In the form of a/b≧3, the step of forming the carbon film is performed.

In the method of producing a negative electrode material which is formed by the formation of the carbon film, the particles having a particle diameter of 1 μm or less which are present before the coating with the carbon film are formed (that is, The fine powder having a small particle size is formed by coating to form secondary particles agglomerated with carbon. When the negative electrode is made of a negative electrode material, the secondary particles are buried in the gap between the large particles to contribute to the reduction in the electric resistance of the negative electrode. As a result, the capacitance maintenance ratio at the time of the reverse charge/discharge cycle is improved.

In this case, in the step of preparing the substrate particles, it is preferable that the a% is 0.1% or more and 30% or less as the substrate particles.

In the case where the ratio of the particles having a particle diameter of 1 μm or less in the volume-based distribution is 0.1% or more and 30% or less, the secondary particles are easily formed.

Further, in the step of preparing the substrate particles, as the substrate particles, ruthenium particles, particles having ruthenium particles as a composite structure dispersed in an oxime compound, and a general formula of SiO _x (0.5 ≦ x ≦ 1.6) can be prepared. The cerium oxide particles indicated, or a mixture of these components.

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

In addition, it will contain the mass of the coated particles. The ratio of the mass of carbon to the coated particles is preferably 0.5% by mass or more and 40% by mass or less.

By such a carbon coating amount, sufficient conductivity can be imparted to the negative electrode material, and charge and discharge capacity can be improved.

Further, in the step of preparing the substrate particles, the cumulative 50% diameter (D ₅₀ ) of the volume reference distribution measured by the laser diffraction particle size distribution measuring apparatus of the substrate particles is prepared as the substrate particles. It is preferably 0.1 μm or more and 30 μm or less.

By using the substrate particles having such a cumulative 50% diameter, when the negative electrode material is applied to produce the negative electrode, the separator is not damaged, and the conductivity of the electrode can be made good.

Further, in the step of forming the carbon film, the cumulative 50% diameter (D ₅₀ ) of the volume-based distribution measured by the laser diffraction particle size distribution measuring apparatus for the coated particles is 1 μm or more and 30 μm or less. Come to the ideal.

By setting the cumulative 50% diameter of the coated particles to such a value, when the negative electrode material is applied to produce the negative electrode, the separator is not damaged, and the conductivity of the electrode can be made good.

Further, it is preferable that the carbon film is formed by chemical vapor deposition in a temperature range of 600 to 1200 ° C in an organic gas atmosphere in which carbon atoms can be thermally decomposed in the substrate particles. carried out.

By performing carbon coating under such conditions, a favorable carbon film can be formed, and the conductivity of the negative electrode material can be imparted.

Further, as a raw material of the organic gas which can generate carbon by the above thermal decomposition, methane, ethane, ethylene, acetylene, propane, propylene, butane, butene, pentane, isobutane, hexane, benzene, toluene Light gas obtained by distillation steps of xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, hydrazine, coumarone, pyridine, hydrazine, phenanthrene and tar It is preferable to use one or more of the oil, creosote oil, eucalyptus oil, and naphtha decomposition tar.

These components can be suitably used as a raw material of an organic substance gas.

Moreover, the present invention provides a negative electrode material for a lithium ion secondary battery, which is produced by the method for producing a negative electrode material for a lithium ion secondary battery.

Further, the present invention provides a negative electrode material for a lithium ion secondary battery, which is composed of a material containing a ruthenium atom, a substrate particle capable of occluding and releasing lithium ions, and carbon formed on a surface of the substrate particle. The negative electrode material for a lithium ion secondary battery of the coated particles, which is composed of a film, is characterized in that the carbon film is not formed, and the volume of the base material is measured by a laser diffraction particle size distribution measuring device. The ratio of the particles having a particle diameter of 1 μm or less to be distributed is set to a%, and when the ratio of the particles having a particle diameter of 1 μm or less measured by the volume-based distribution measured by the laser diffraction particle size distribution measuring apparatus is b%. , become a/b≧3.

In the negative electrode material of the present invention, the fine powder having a particle diameter of 1 μm or less which is present before the coating formed of the carbon film is coated The second-order particles agglomerated with carbon are formed. When the negative electrode is made of a negative electrode material, the secondary particles are buried in the gap between the large particles to contribute to the reduction in the electric resistance of the negative electrode. As a result, the capacitance maintenance ratio at the time of the reverse charge/discharge cycle is improved.

Further, the present invention provides a negative electrode for a lithium ion secondary battery, which is characterized by using the above negative electrode material for a lithium ion secondary battery.

Further, the present invention provides a lithium ion secondary battery characterized by using the above negative electrode for a lithium ion secondary battery.

In the negative electrode for a lithium ion secondary battery using the negative electrode material of the present invention, the presence of the above-described secondary particles contained in the negative electrode material contributes to a decrease in the electric resistance of the negative electrode. This is an increase in the capacity retention rate when the charge and discharge cycle of the 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 diameter of 1 μm or less which are present before coating with a carbon film are formed by coating to form secondary particles agglomerated with carbon. When the negative electrode is made of a negative electrode material, the secondary particles are buried in the gap between the large particles to contribute to the reduction in the electric resistance of the negative electrode. As a result, the capacitance maintenance ratio at the time of the reverse charge/discharge cycle is improved. Further, since a material containing a ruthenium atom is used as the substrate particles, the negative electrode material of the present invention can be used as a high capacity. In addition, the manufacturing method is not particularly complicated and simple, and can withstand industrial scale production.

[Fig. 1] A particle size distribution map of the substrate particles before the carbon coating of the CVD of Examples 1 to 3 and Comparative Example 1 was carried out.

[Fig. 2] A particle size distribution diagram of the coated particles of Example 1.

[Fig. 3] A particle size distribution diagram of the coated particles of Example 2.

[Fig. 4] A particle size distribution map of the coated particles of Example 3.

[Fig. 5] A particle size distribution map of the coated particles of Example 4.

[Fig. 6] A particle size distribution map of the coated particles of Comparative Example 1.

[Fig. 7] A particle size distribution map of the substrate particles before the carbon coating of the CVD of Comparative Example 2 was carried out.

[Fig. 8] A particle size distribution map of the coated particles of Comparative Example 2.

Hereinafter, the present invention will be described in detail.

[Anode material for lithium ion secondary battery]

The negative electrode material for a lithium ion secondary battery of the present invention is composed of a material containing a ruthenium atom, and is composed of a substrate particle capable of occluding and releasing lithium ions and a carbon film formed on the surface of the substrate particle. Covered particles. Further, the negative electrode material of the present invention is a particle which satisfies the following conditions before and after the formation of the carbon film. In the state in which the carbon film was not formed, the ratio of the particles having a particle diameter of 1 μm or less measured by the laser diffraction particle size distribution measuring device to the substrate particles was set to a%. In addition, The ratio of the particles having a particle diameter of 1 μm or less in the volume-based distribution measured by the laser diffraction particle size distribution measuring apparatus for the coated particles was set to b%. At this time, the negative electrode material of the present invention satisfies the relationship of a/b≧3.

In the inventors' group, the distribution of the respective particle diameters of the substrate particles and the coated particles is set to a specific range, that is, the above a/b is 3 or more particles, and is used as a negative electrode material for a lithium ion secondary battery ( When the active material was used, it was found that a lithium ion secondary battery having high capacity and excellent cycle characteristics was obtained, and the present invention was completed.

As described above, the specification of the particle size distribution of the particles of the present invention is determined based on the particle size distribution using the laser diffraction method (also referred to as laser diffraction type particle size distribution measurement). As the laser diffraction particle size distribution measuring apparatus, for example, SALD-3100 manufactured by Shimadzu Corporation can be used. The volume reference distribution measured by a laser diffraction particle size distribution measuring apparatus for a specific particle (particle group or powder) is also referred to as a "volume reference distribution" hereinafter. In addition, "the ratio of particles having a particle diameter of 1 μm or less" is generally referred to as "accumulation of 1 μm".

[Method of Manufacturing Anode Material for Lithium Ion Secondary Battery]

The negative electrode material for a lithium ion secondary battery of the present invention can be produced by the following steps. First, a substrate particle composed of a material containing germanium atoms and capable of occluding and releasing lithium ions is 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 above a and b form a carbon film of the substrate particles so as to become a/b≧3. This manufacturing method is not particularly complicated and simple, and can withstand Industrial scale production.

[Substrate particles]

In the present invention, as described above, particles composed of a material containing germanium atoms, and particles (substrate particles) capable of occluding and releasing lithium ions are carbon-coated. In the substrate particles used in the present invention (that is, the substrate particles prepared in the step A), the ruthenium particles and the particles having ruthenium are particles of a composite structure dispersed in the lanthanoid compound, and the general formula SiO _x The cerium oxide particles represented by (0.5 ≦ x ≦ 1.6) or a mixture of these components are desirable. The method for producing a negative electrode material of the present invention can also be applied to any of the above substrate particles. When any of the above is used as the substrate particles, a negative electrode material for a lithium ion secondary battery having a higher initial charge and discharge efficiency, a high capacity, and excellent cycle properties can be obtained.

The cerium oxide of the present invention is a general term for amorphous cerium oxide, and the cerium oxide before disproportionation is represented by a general formula of SiO _x (0.5 ≦ x ≦ 1.6). The x-series 0.8 ≦ x < 1.3 is ideal, and 0.8 ≦ x < 1.0 is preferable. The lanthanum oxide system can be cooled, for example, by heating a cerium oxide gas formed by heating a mixture of cerium oxide and metal cerium. Precipitated.

A particle having a composite structure in which fine particles of cerium are dispersed in a lanthanoid compound, for example, a method of sintering a fine particle of cerium and a lanthanoid compound, or a cerium oxide particle before disproportionation represented by a general formula SiO _x In a non-oxidizing environment inert to argon or the like, heat treatment is carried out at a temperature of 400 ° C or higher and suitably 800 to 1,100 ° C to obtain a disproportionation reaction. In particular, the material obtained by the latter method is suitable because the microcrystals of cerium are uniformly dispersed. The size of the nanoparticle can be set to 1 to 100 nm by the disproportionation reaction as described above. Further, cerium oxide having cerium nanoparticles as particles dispersed in cerium oxide is preferred as cerium oxide. Further, it was confirmed by penetrating electron microscopy that the nanoparticles of yttrium (crystals) were dispersed in amorphous yttrium oxide.

As the substrate particles, the cerium oxide-based material is particularly preferable because the volume expansion ratio at the time of occlusion and release of lithium is low. When the volume expansion ratio of the substrate particles themselves is low, the cycle property is particularly excellent.

The physical properties of the substrate particles used in the present invention can be suitably selected by using the coated particles (composite particles). For example, in the cumulative 50% diameter (D ₅₀ , also referred to as volume average particle diameter) of the volume-based distribution measured by the laser diffraction particle size distribution measuring apparatus, 0.1 μm or more and 30 μm or less can be suitably used. The lower limit of the range is preferably 0.2 μm or more, and more preferably 0.3 μm or more. The upper limit is preferably 20 μm or less, and more preferably 10 μm or less. When the cumulative 50% diameter (D ₅₀ ) is 0.1 μm or more, the BET specific surface area to be described later can be made small enough, and the adverse effect caused by the excessive BET specific surface area is not caused. In addition, when the cumulative 50% diameter (D ₅₀ ) is 30 μm or less, it is easy to apply the negative electrode material during the production of the negative electrode.

The BET specific surface area of the substrate particles used in the present invention is preferably 0.5 m ² /g or more and 100 m ² /g or less, and more preferably 1 m ² /g or more and 20 m ² /g or less. When the BET specific surface area is 0.5 m ² /g or more, the adhesion when the negative electrode material is applied to produce the negative electrode can be made sufficient, and the battery characteristics can be improved. Further, when the BET specific surface area is 100 m ² /g or less, the proportion of cerium oxide produced by natural oxidation of the surface of the particles can be reduced. As a result, since the cerium oxide which does not contribute to the battery reaction can be reduced, it is possible to suppress the battery capacity from being lowered when used as a negative electrode material for a lithium ion secondary battery.

Further, the above "a%" of the substrate particles used in the present invention is preferably 0.1% or more and 30% or less. When the ratio of the particles having a particle diameter of 1 μm or less in the volume-based distribution is 0.1% or more and 30% or less, the above-mentioned secondary particles are easily formed, which contributes to the electric resistance of the negative electrode. reduce.

[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 substrate particles to be coated particles. In order to impart conductivity to the substrate particles, the battery characteristics are improved. In the present invention, it is necessary to form a carbon film on the surface of the substrate particles, but it is also preferable to mix the particles with conductivity such as graphite while performing the carbon coating. As a method of forming a carbon film on the surface of the substrate particles, a method by chemical vapor deposition (CVD) is suitable.

As a method of chemical vapor deposition (CVD), for example, chemical vapor deposition of carbon on a substrate particle in a temperature range of 600 to 1200 ° C in an organic gas atmosphere capable of generating carbon by thermal decomposition is used. method.

This chemical vapor deposition (CVD) is applicable under normal pressure and reduced pressure. As a reduced pressure, it can be reduced by 50 to 30,000 Pa. Press down. Further, an apparatus for forming a carbon film may be a generally known apparatus such as a batch furnace, a rotary kiln, a continuous furnace of a roller kiln, and a fluidized bed. In particular, a rotary kiln that can be continuously vaporized while being stirred can be more efficiently coated with carbon and can improve battery characteristics.

In the formation of a carbon film by chemical vapor deposition, various organic substances such as the following may be mentioned as the carbon source, but the thermal decomposition temperature, the vapor deposition rate, or the vapor deposition may be formed. The characteristics of the carbon film, etc., may vary greatly depending on the substance to be used. The carbon source can be appropriately changed depending on the physical properties of the coated particles for the purpose. A material having a small vapor deposition rate is preferable because it is easy to make the uniformity of the carbon film on the surface sufficient. When the material is decomposed into a low temperature, the growth of the ruthenium crystal in the substrate particles during vapor deposition is suppressed, so that the discharge efficiency or the cycle characteristics can be suppressed.

Examples of the raw material of the organic gas which can generate carbon by thermal decomposition include methane, ethane, ethylene, acetylene, propane, propylene, butane, butene, pentane, isobutane, hexane, benzene, and toluene. Gas light oil obtained by distillation steps of xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, hydrazine, coumarone, pyridine, hydrazine, phenanthrene and tar , creosote oil, eucalyptus oil and naphtha decomposition tar. These may be used singly or in combination of two or more.

The amount of the carbon film to be coated is preferably 0.5% by mass or more and 40% by mass or less based on the mass of the coated particles. This ratio is 1.0~30 The amount % is ideal. In addition, the amount of carbon coating is 0.5% by mass or more, and substantially sufficient conductivity can be maintained, and the cycle property as a negative electrode of a nonaqueous electrolyte secondary battery can be reliably achieved. In addition, when the carbon coating amount is 40% by mass or less, the effect of imparting conductivity by carbon coating can be obtained, and the decrease in the charge/discharge capacity due to the increase in the proportion of carbon in the negative electrode material can be suppressed. .

[Particle size distribution and particle size range of negative electrode material]

The negative electrode material of the present invention is as described above, and the particle size is defined as a relationship satisfying a/b≧3. Particles (fine powder) having a particle diameter of 1 μm or less in a volume-based distribution of the substrate particles in a state in which no carbon coating is formed are formed by coating to form secondary particles agglomerated with carbon. When the negative electrode is made of a negative electrode material, the secondary particles are buried in the gap between the large particles to contribute to a decrease in the electric resistance of the negative electrode (electrode). As a result, the capacitance maintenance ratio at the time of the reverse charge/discharge cycle is improved.

In addition, it is preferable that the carbon film is formed so that the cumulative 50% diameter (D ₅₀ ) of the volume-based distribution measured by the laser diffraction particle size distribution measuring apparatus of the coated particles is 1 μm or more and 30 μm or less. Therefore, when the negative electrode material is applied to produce the negative electrode, the separator is not damaged, and the conductivity of the electrode can be made good.

In the present invention, in order to set the substrate particle to a specific particle size distribution and particle size range, it can be suitably adjusted by treatment such as pulverization or classification. Further, in order to set the particle size distribution and the particle size range of the coated particles on which the carbon film is formed, it is possible to apply the coating amount or the like. Should be adjusted. The coating amount of the carbon film depends on the physical properties of the substrate particles, and also depends on the carbon source gas used for CVD, the heat treatment temperature, the heat treatment time, and the like. The relationship between the conditions at the time of coating and the amount of coating can be easily obtained experimentally.

For the pulverization of the particles, a generally known device can be used. For example, it can be used for the device exemplified below. First, a ball mill or a media agitating mill that pulverizes a crushed medium such as a ball or a bead and pulverizes the scraped material by an impact force, a frictional force, or a compressive force generated by the kinetic energy can be exemplified. Further, a roll mill that pulverizes by a compressive force generated by a roll can be exemplified. Further, a jet mill that pulverizes the scraped material at a high speed against the lining material or causes the particles to collide with each other and is pulverized by the impact force of the impact can be exemplified. In addition, a hammer mill, a column pulverizer, and a disc pulverizer that pulverize the scraped object by an impact force by a rotation of a rotor such as a hammer, a blade, or a pin are fixed. Further, a colloid mill using shearing force can be exemplified. Further, a high pressure wet type collision type disperser "Ultimaizer" can be exemplified. The pulverizing system can be used in both wet and dry forms.

Moreover, in order to defragment the particle size distribution, dry classification, wet classification, and screening classification may be used. Dry grading is mainly carried out by using air flow, dispersion or separation (separation of fine particles and coarse particles), collection (separation of solid and gas), and discharge. Further, in order to prevent the classification efficiency from being lowered by the interference of the particles, the shape of the particles, the disturbance of the flow of the gas flow, the velocity distribution, and the influence of static electricity, the pretreatment (water, dispersibility, humidity, etc.) is performed before the classification. Adjust) and adjust the moisture or oxygen concentration of the airflow used. Further, in a form in which the cyclone or the like is dry and integrated with the classifier, it is possible to simultaneously pulverize and classify, and to achieve a desired particle size distribution.

In the present invention, the negative electrode material (active material) for a lithium ion secondary battery can be used, and a negative electrode material for a lithium ion secondary battery obtained by the present invention can be used to produce a negative electrode, thereby producing a lithium ion secondary battery.

[negative electrode]

When a negative electrode is produced using the negative electrode material for a lithium ion secondary battery, a conductive agent such as carbon or graphite may be further added. In this case, the type of the conductive agent is not particularly limited, and the battery to be formed may be a material that does not cause decomposition or deterioration of electron conductivity. Specifically, metal particles or metal fibers of Al, Ti, Fe, Ni, Cu, Zn, Ag, Sn, Si, or the like, or natural graphite, artificial graphite, various coke particles, mesophase carbon, vapor deposited carbon fiber, or the like may be used. Graphite such as pitch-based carbon fiber, PAN-based carbon fiber, and various resin sintered bodies.

The method of preparing the negative electrode (molded body) is exemplified by the following method.

First, a solvent such as N-methylpyrrolidone or water is kneaded in the above-mentioned negative electrode material and other additives such as a conductive agent and a binder such as a polyimide resin, and the paste is formed. Mixture. This mixture was applied to a sheet of a current collector. In this case, as a material for the current collector copper foil, nickel foil, or the like, which is generally used as a current collector of the negative electrode, the thickness and surface treatment can be used without particular limitation. Still, forming the mixture The method for forming the sheet form is not particularly limited, and a generally known method can be used.

[Lithium ion secondary battery]

The lithium ion secondary battery of the present invention is a lithium ion secondary battery using the above-described negative electrode for a lithium ion secondary battery. A non-aqueous electrolyte having at least a positive electrode and lithium ion conductivity in addition to the negative electrode. The lithium ion secondary battery of the present invention is characterized in that it is formed of a negative electrode using a negative electrode material composed of the coated particles, and a material such as a positive electrode, an electrolyte, a separator, and a battery shape. A general person can be used, and it is not particularly limited. As described above, the negative electrode material of the present invention is excellent in battery characteristics (charge and 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, generally known ones of oxides of transition metals such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , V ₂ O ₅ , MnO ₂ , TiS ₂ , and MoS ₂ , lithium, and chalcogen compounds can be used.

As the electrolyte, for example, a nonaqueous solution containing a lithium salt such as lithium hexafluorophosphate or lithium perchlorate can be used. As the non-aqueous solvent, one or a combination of two or more of propylene carbonate, ethyl carbonate, diethyl carbonate, dimethoxyethane, γ-butyrolactone, and 2-methyltetrahydrofuran can be used. . Further, various other nonaqueous electrolytes or solid electrolytes may be used.

[Examples]

Hereinafter, the present invention will be more specifically described by showing examples and test examples, but the present invention is not limited to the examples described below.

[Example 1]

An alumina ball having a diameter of 10 mm was pulverized by a ball mill (manufactured by MAKINO) for 80 minutes using SiO _x (x = 1.0) crushed by a jaw crusher (manufactured by Hosei Industry Co., Ltd.) as a medium. This particle was used as a substrate particle (step A). When the substrate particles were measured by a laser diffraction particle size distribution measuring apparatus (Shimadzu Corporation SALD-3100) under the conditions of a refractive index of 3.90 to 0.01 μ, the D ₅₀ (accumulated 50% diameter) in the volume-based distribution was 4.6 μm. The cumulative 1 μm (ratio of particles having a particle diameter of 1 μm or less) was 14.8% (that is, a=14.8). The particle size distribution map of the substrate particles is shown in Fig. 1.

100 g of the substrate particles were placed on a tray so that the thickness of the powder layer became 10 mm, and the mixture was placed in a batch type heating furnace. Then, the inside of the furnace was decompressed with an oil rotary vacuum pump while the temperature in the furnace was raised to 1,000 ° C at a heating rate of 200 ° C / hr. Then, after reaching 1,000 ° C, methane was ventilated at 0.3 L/min in a furnace, and carbon coating treatment was carried out for 10 hours (step B). After the methane was stopped, the inside of the furnace was cooled 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, when the particle size distribution of the particles was measured in the same manner as described above, the D ₅₀ of the volume-based distribution was 5.3 μm, and the cumulative 1 μm (the ratio of the particles having a particle diameter of 1 μm or less) was 2.6% (that is, b = 2.6). . The particle size distribution map of the coated particles is shown in Fig. 2.

<Battery evaluation>

Next, the obtained coated particles were used as a negative electrode active material by the following method to carry out battery evaluation. First, 45 mass% of the obtained negative electrode material, 45 mass% of artificial graphite (average particle diameter: 10 micrometer), 10 mass% of polyimine, and N-methyl pyrrolidone are further added as a slurry. This slurry was applied to a copper foil having a thickness of 12 μm, dried at 80 ° C for 1 hour, and then the electrode was pressed by rolling, and the electrode was vacuum dried at 350 ° C for 1 hour. Then punched to 2 cm ² as a negative electrode.

Then, in order to evaluate the charge and discharge characteristics of the obtained negative electrode, a lithium foil was used for the counter electrode, and 1/1 (volume ratio) of lithium hexafluorophosphate to ethyl carbonate and diethyl carbonate was used as the nonaqueous electrolyte. A nonaqueous electrolyte solution in which the mixed solution was dissolved at a concentration of 1 mole/L, and a lithium ion secondary battery for evaluation of a polyethylene microporous film having a thickness of 30 μm was used as the separator.

After the prepared lithium ion secondary battery was allowed to stand at room temperature for one night, a secondary battery charge and discharge tester (manufactured by NAGANO Co., Ltd.) was used until the voltage of the test cell reached 0 V and charged at a constant current of 0.5 mA/cm ² . After reaching 0V, the current is reduced and the battery is charged so that the cell voltage is maintained at 0V. Then, the charging is ended when the current value is lower than 40 μA/cm ² . Then, 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 and discharge test was repeated, and a charge and 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 initial discharge capacity was 1781 mAh/g, the cycle retention rate after 50 cycles was 94%, and the lithium ion secondary battery excellent in cycle property was obtained.

[Embodiment 2]

100 g of the SiO _x (x = 1.0) pulverized product (base material particle) similar to that of Example 1 was placed in a batch type heating furnace in the same manner as in Example 1. Then, the inside of the furnace was decompressed with an oil rotary vacuum pump while the temperature was raised to 1,100 ° C at a heating rate of 200 ° C / hr. Then, after reaching 1,100 ° C, methane was ventilated at 0.3 L/min in a furnace for 16 hours of carbon coating treatment. After the methane is stopped, the furnace is cooled 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. This particle size D ₅₀ of the distribution system 5.8μm, cumulative 1 m (ratio of particle diameter of 1 m or less) 0.3% (i.e., b = 0.3). The particle size distribution map of the coated particles is shown in Fig. 3.

[Example 3]

The SiO _x (x = 1.0) pulverized product (substrate particles) which was the same as in Example 1 was heated to 1000 ° C in a kiln at a temperature of 1 °, and the inside of the kiln was supplied with 2 kg / hr from the inlet side. From the outlet side, methane was diluted with nitrogen to 16% by volume. The number of revolutions of the kiln was set to 1 rpm. Six hours after the start of the introduction, the conductive particles having a coating amount of 3.5% by mass were obtained from the outlet side. This particle size D ₅₀ of the distribution system 5.2μm, cumulative 1 m (ratio of particle diameter of 1 m or less) of 3.7% (i.e., b = 3.7). The particle size distribution map of the coated particles is shown in Fig. 4.

[Example 4]

The SiO _x (x = 1.0) pulverized product (substrate particles) which was the same as in Example 1 was heated to 1000 ° C in a kiln at a temperature of 1 °, and the kiln was supplied at a rate of 2.8 kg / from the inlet side. Hr, ventilated from the outlet side with methane diluted to 16 vol% with nitrogen. The number of revolutions of the kiln was set to 1 rpm. Six hours after the start of the introduction, the conductive particles having a coating amount of 2.6% by mass were obtained from the outlet side. This particle size D ₅₀ of the distribution system 4.4μm, cumulative 1 m (ratio of particle diameter of 1 m or less) 4.9% (i.e., b = 4.9). The particle size distribution map of the coated particles is shown in Fig. 5.

[Comparative Example 1]

100 g of the SiO _x (x = 1.0) pulverized product (base material particle) similar to that of Example 1 was placed in a batch type heating furnace in the same manner. Then, the inside of the furnace was decompressed with an oil rotary vacuum pump while the temperature in the furnace was raised to 1,000 ° C at a heating rate of 200 ° C / hr. After reaching 1,000 ° C, methane was ventilated at 0.1 L/min in a furnace for 2 hours of carbon coating treatment. After the methane was stopped, the inside of the furnace was cooled 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 based on the black particles. This particle size D ₅₀ of the distribution system 4.8μm, cumulative 1 m (ratio of particle diameter of 1 m or less) was 11.4% (i.e., b = 11.4). The particle size distribution map of the coated particles is shown in Fig. 6.

[Comparative Example 2]

The SiO _x (x=1.0) pulverized product which was the same as in Example 1 was classified by a gas flow classifier (TC-15 manufactured by Nissin Engineering Co., Ltd.) under the conditions of an air volume of 2.5 Nm ³ /min and a rotor rotation number of 10,000 rpm. The D ₅₀ of the particles on the coarse powder side recovered under the classifier was 6.1 μm, and the cumulative 1 μm (the ratio of the particles having a particle diameter of 1 μm or less) was 1.0% (that is, a = 1.0). This powder was used as the substrate particles of Comparative Example 2 (particles to be carbon-coated). The particle size distribution map of this substrate particle is shown in Fig. 7. The carbon coating treatment was carried out in the same manner as in Example 1 on the substrate particles. The obtained particle-based carbon coating amount was 4.2% by mass, D ₅₀ was 6.2 μm, and the cumulative 1 μm (ratio of particles having a particle diameter of 1 μm or less) was 0.7% (that is, b=0.7). The particle size distribution map of the coated particles is shown in Fig. 8.

With respect to the particles obtained in Examples 2 to 4 and Comparative Examples 1 and 2, battery evaluation was performed in the same manner as in Example 1.

Tables 1 of the particle sizes and battery characteristics of Examples 1 to 4 and Comparative Examples 1 and 2 are shown in Table 1.

In the negative electrode materials of Examples 1 to 4, lithium ion secondary batteries having excellent battery characteristics as compared with the negative electrode materials of Comparative Examples 1 and 2 were confirmed.

Further, the present invention is not limited to the above embodiment. The above-described embodiments are exemplified, and any ones having substantially the same effects as those of the technical scope described in the patent application of the present invention are included in the technical scope of the present invention.

Claims (12)

A method for producing a negative electrode material for a lithium ion secondary battery, comprising: preparing a substrate particle containing a ruthenium atom, absorbing and releasing lithium ion, and forming carbon on a surface of the substrate particle The step of forming the coated particles as a coating film is characterized in that, in the state in which the carbon film is not formed, the particle diameter distribution of the substrate particles measured by the laser diffraction particle size distribution measuring device is 1 μm or less. The ratio of the particles is set to a%, and when the ratio of the particles having a particle diameter of 1 μm or less in the volume-based distribution measured by the laser diffraction particle size distribution measuring apparatus is b%, the ratio of the particles is a/b≧. In the manner of 3, the step of forming the carbon film is performed. The method for producing a negative electrode material for a lithium ion secondary battery according to claim 1, wherein the step of preparing the substrate particles is such that the a% is 0.1% or more and 30% or less as the substrate particles. The method for producing a negative electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein, in the step of preparing the substrate particles, ruthenium particles and fine particles having ruthenium are prepared as the base material particles A particle having a composite structure of a compound, cerium oxide particles represented by a general formula of SiO _x (0.5 ≦ x ≦ 1.6), or a mixture of these components. The method for producing a negative electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the ratio of the mass of carbon contained in the coated particles to the mass of the coated particles is 0.5% by mass or more and 40% by mass %the following. The method for producing a negative electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein, in the step of preparing the substrate particles, a particle size of the substrate particles in a laser diffraction method is prepared as the substrate particles The cumulative 50% diameter (D ₅₀ ) of the volume reference distribution measured by the distribution measuring device is 0.1 μm or more and 30 μm or less. The method for producing a negative electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the step of forming the carbon film is performed on a volume basis measured by a laser diffraction particle size distribution measuring device for the coated particles The cumulative 50% diameter (D ₅₀ ) of the distribution is performed in a manner of 1 μm or more and 30 μm or less. The method for producing a negative electrode material for a lithium ion secondary battery according to claim 1 or 2, wherein the step of forming the carbon film is performed, and an organic gas atmosphere capable of generating carbon by thermal decomposition of the substrate particles is obtained. The carbon is chemically vapor deposited at a temperature ranging from 600 to 1200 °C. The method for producing a negative electrode material for a lithium ion secondary battery according to claim 7, wherein the raw material of the organic gas capable of generating carbon by the thermal decomposition is methane, ethane, ethylene, acetylene, propane, propylene or butane. , butene, pentane, isobutane, hexane, benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, hydrazine, fragrant One or more selected from the group consisting of gas light oil, creosote oil, eucalyptus oil, and naphtha decomposition tar obtained by the benzene ketone, pyridine, hydrazine, phenanthrene, and tar distillation steps are used. A negative electrode material for a lithium ion secondary battery, which is produced by the method for producing a negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 8. A negative electrode material for a lithium ion secondary battery, which is composed of a material containing a ruthenium atom, a substrate particle capable of occluding and releasing lithium ions, and a carbon film formed on the surface of the substrate particle. The coated particles are characterized in that, in a state in which the carbon film is not formed, the ratio of the particles having a particle diameter of 1 μm or less measured by a volume measurement basis measured by a laser diffraction particle size distribution measuring device of the substrate particles is a. % is a/b≧3 when the ratio of particles having a particle diameter of 1 μm or less in the volume-based distribution measured by the laser diffraction particle size distribution measuring apparatus is b%. A negative electrode for a lithium ion secondary battery, which is characterized by using the negative electrode material for a lithium ion secondary battery of claim 9 or 10. A lithium ion secondary battery characterized by using the negative electrode for a lithium ion secondary battery of claim 11.