JP2008179846A - Method for producing metal powder, metal powder, electrode, and secondary battery using lithium ion - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for easily and securely producing a metal powder which contains a Co-Sn intermetallic compound of high purity obtained by compounding Co and Sn in an objective molar ratio and can improve the characteristics, for instance, of a secondary battery using a lithium ion when being applied to a material composing an electrode of the secondary battery using the lithium ion; the metal powder produced by such a method for producing the metal powder; an electrode obtained by using the metal powder; and the secondary battery using the lithium ion and having excellent service capacity and cycle properties. <P>SOLUTION: This production method comprises the steps of: obtaining a primary powder which contains Co and Sn in the objective molar ratio; and heat-treating the primary powder at 160°C to a temperature lower than 410°C to change a Co-Sn intermetallic compound which has been compounded at a molar ratio other than the objective molar ratio, into the Co-Sn intermetallic compound (CoSn<SB>2</SB>in the figure) which is compounded at the objective molar ratio, and thereby to obtain a secondary powder containing the intermetallic compound of high purity, which has been compounded at the objective molar ratio. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a metal powder, a metal powder, an electrode, and a lithium ion secondary battery.

  In recent years, with the rapid spread of mobile devices, demand for secondary batteries as a power source for mobile devices is increasing. Since the secondary battery can be used repeatedly by being charged, it has an advantage of high cost performance as a power source and low environmental load. Among such secondary batteries, lithium ion secondary batteries are particularly attracting attention because they have excellent features such as high voltage, light weight, and long life.

Conventionally, a carbon-based material is generally used as a material constituting the negative electrode of a lithium ion secondary battery (see, for example, Patent Document 1).
However, with an increase in power consumption of mobile devices and an increase in charge / discharge cycles, further improvements in the discharge capacity and cycle characteristics of lithium ion secondary batteries are expected. Under such circumstances, further improvement of the characteristics of the negative electrode material of the secondary battery is required.

JP 2001-023634 A

  It is an object of the present invention to contain a Co-Sn intermetallic compound formed by combining Co and Sn at a desired molar ratio with high purity, for example, when applied as a material constituting an electrode of a lithium ion secondary battery In addition, a metal powder manufacturing method capable of easily and reliably manufacturing a metal powder capable of improving the characteristics of a lithium ion secondary battery, a metal powder manufactured by such a metal powder manufacturing method, and using such a metal powder are obtained. Another object of the present invention is to provide a lithium ion secondary battery excellent in discharge capacity and cycle characteristics.

The above object is achieved by the following.
The method for producing a metal powder of the present invention includes a first step of melting a raw material containing Co and Sn at a target molar ratio, and pulverizing by an atomizing method to obtain a primary powder;
The primary powder is heated at a temperature of 160 ° C. or higher and lower than 410 ° C., then cooled, and Co— is formed by combining Co and Sn at a molar ratio other than the target molar ratio contained in the primary powder. The Sn intermetallic compound is changed to a Co—Sn intermetallic compound formed by combining Co and Sn at the target molar ratio, and the Co—Sn metal formed by combining Co—Sn at the target molar ratio. And a second step of obtaining a secondary powder in which the intermetallic compound is highly purified.
Accordingly, when a Co—Sn intermetallic compound formed by combining Co and Sn at a target molar ratio is contained with high purity, for example, when applied as a material constituting an electrode of a lithium ion secondary battery, lithium Metal powder that can improve the characteristics of the ion secondary battery can be manufactured easily and reliably.

In the metal powder production method of the present invention, the primary powder preferably has an average particle size of 0.1 to 50 μm.
If the primary powder is sufficiently small as described above, it can be surely heated to the center by a heat treatment described later. As will be described later, a Co—Sn intermetallic compound other than the target is used as the target Co—Sn metal. Interchangeable compounds can be reliably changed. As a result, a metal powder (secondary powder) having a very high content of the target Co—Sn intermetallic compound can be obtained.

In the metal powder manufacturing method of the present invention, in the second step, the heating is preferably performed under conditions such that the primary powder does not cause sintering.
Thereby, it can prevent that a diffusion arises in the interface of primary powder, and these will become an aggregate (block body). In addition, the sintering can prevent the Co—Sn intermetallic compound from being changed into other types of compounds that are not intended, that is, impurities.

In the metal powder manufacturing method of the present invention, it is preferable that the heating is performed in a non-oxidizing atmosphere in the second step.
Thereby, it is possible to reliably prevent the primary powder from being oxidized and generating impurities such as an oxide of a Co—Sn intermetallic compound.
In the method for producing a metal powder of the present invention, the Co—Sn intermetallic compound having the target molar ratio is preferably CoSn ₂ .
Thereby, a metal powder composed mainly of CoSn ₂ is obtained.

In the method for producing metal powder of the present invention, in the second step, the heating time is preferably 10 minutes to 10 hours.
Thereby, heat can be reliably applied to the central part of the primary powder, and the Co—Sn intermetallic compound other than the target can be changed to CoSn ₂ also in the central part.
In the method for producing metal powder of the present invention, in the second step, it is preferable that the cooling from the heating temperature to room temperature is performed at an average cooling rate of 50 to 1000 ° C./hour.
Thereby, the cooling after the heating of the primary powder is optimally performed, and the Co—Sn intermetallic compound other than the target can be more reliably changed to the target Co—Sn intermetallic compound.
In the metal powder manufacturing method of the present invention, in the second step, it is preferable that cooling from the heating temperature to 100 ° C. is performed at an average cooling rate of 300 to 1200 ° C./hour.
Thereby, the cooling after the heating of the primary powder is optimally performed, and the Co—Sn intermetallic compound other than the target can be more reliably changed to the target Co—Sn intermetallic compound.

In the method for producing a metal powder of the present invention, the content of the Co—Sn intermetallic compound having a molar ratio other than the target molar ratio contained in the secondary powder is included in the primary powder as A [wt%]. When the content of the Co—Sn intermetallic compound having a molar ratio other than the intended molar ratio is B [wt%], A / B is preferably 0.1 or less.
As described above, according to the present invention, it is possible to significantly reduce the Co—Sn intermetallic compound other than the purpose corresponding to the impurities for the metal powder. In other words, the present invention is suitably applied particularly when producing metal powder containing a target Co—Sn intermetallic compound with high purity.
In the method for producing a metal powder of the present invention, the content of the Co—Sn intermetallic compound having a molar ratio other than the target molar ratio contained in the secondary powder is preferably 10 wt% or less.
Thus, the metal powder with a small impurity content exhibits the characteristics obtained by the target Co—Sn intermetallic compound more reliably.

The metal powder of the present invention is manufactured by the method for manufacturing a metal powder of the present invention.
Accordingly, when a Co—Sn intermetallic compound formed by combining Co and Sn at a target molar ratio is contained with high purity, for example, when applied as a material constituting an electrode of a lithium ion secondary battery, lithium A metal powder capable of improving the characteristics of the ion secondary battery is obtained.

The electrode of the present invention is characterized by having a portion formed by molding a material containing the metal powder of the present invention.
Thereby, for example, an electrode having excellent characteristics as a negative electrode of a lithium ion secondary battery can be obtained.
The lithium ion secondary battery of the present invention comprises a negative electrode, a positive electrode, and an electrolyte containing lithium ions,
The negative electrode is composed of the electrode of the present invention.
Thereby, the lithium ion secondary battery excellent in discharge capacity and cycling characteristics is obtained.

Hereinafter, the metal powder manufacturing method, metal powder, electrode, and lithium ion secondary battery of the present invention will be described in detail with reference to the accompanying drawings.
The method for producing a metal powder of the present invention comprises a Co—Sn intermetallic compound (hereinafter simply referred to as “target Co-Sn”) formed by combining Co (cobalt) and Sn (tin) at a predetermined (target) molar ratio. This is a method for producing a metal powder comprising “intermetallic compound” as a main component.
This method for producing a metal powder includes a first step of obtaining a primary powder by an atomizing method and a second step of obtaining a secondary powder by subjecting the primary powder to a heat treatment at a predetermined temperature.

Hereinafter, each process will be described sequentially. Hereinafter, a case where the target Co—Sn intermetallic compound is CoSn ₂ will be described as a representative.
[1] First, a melt obtained by mixing and melting Co simple substance and Sn simple substance at a molar ratio of 1: 2 (predetermined molar ratio) is pulverized by an atomizing method to obtain a primary powder (first step).
The melt is obtained by melting a mixture (raw material) obtained by mixing Co and Sn in a melting furnace such as an induction furnace or a gas furnace. The raw material is not particularly limited as long as the molar ratio of Co and Sn is 1: 2.
This melt is pulverized by an atomizing method. Thereby, primary powder 10 'is obtained.

Here, in the atomization method, the molten metal (molten metal) is collided with a jet of a liquid or gaseous spray medium to scatter the molten metal into fine droplets and to take away the heat of the droplets. It is a method of solidifying to obtain a metal powder.
By using this atomizing method, the molten droplets can be rapidly cooled in a short time. For this reason, the time required for the Co atom and the Sn atom in the droplet to take a stable arrangement is not secured, and the droplet has a relatively unstable arrangement of the Co atom and the Sn atom. Solidify in state. As a result, a Co—Sn intermetallic compound that is a structurally relatively unstable compound is mainly produced in the obtained primary powder 10 ′.

At this time, as the Co—Sn intermetallic compound, CoSn ₂ (target Co—Sn metal) formed by combining at a molar ratio (stoichiometric ratio) reflecting the molar ratio of Co and Sn in the melt. In addition to Co-Sn intermetallic compounds such as CoSn, CoSn ₃ , Co ₃ Sn ₂ , that is, Co and Sn are combined in a molar ratio other than the stoichiometric ratio (1: 2). Co-Sn intermetallic compounds (hereinafter collectively referred to as “Co-Sn intermetallic compounds other than the object”) are formed. Thus, primary powder 10 'is comprised with the multiple types of Co-Sn intermetallic compound from which the molar ratio of Co and Sn differs. The primary powder 10 ′ may contain, for example, a Co—Sn intermetallic compound formed by combining Co and Sn at a molar ratio of 0: 1, that is, Sn alone. In this case, this Sn simple substance is also included in the Co—Sn intermetallic compound other than the intended purpose.

Examples of the atomizing method include a liquid atomizing method such as a water atomizing method, a gas atomizing method, and the like depending on the type of the spray medium. Examples of the liquid atomizing method include a high-speed rotating water atomizing method and a rotating liquid atomizing method.
When the water atomizing method is used as the atomizing method, the pressure of the atomized water is not particularly limited, but is preferably about 75 to 120 MPa (750 to 1200 kgf / cm ² ). The temperature of the atomized water is not particularly limited, but is preferably about 1 to 20 ° C.

Moreover, it is preferable that the average particle diameter of primary powder 10 'is about 0.1-50 micrometers, and it is more preferable that it is about 0.1-20 micrometers. If the primary powder 10 ′ is sufficiently small as described above, it can be surely heated to the center by the heat treatment described later, and the Co—Sn intermetallic compound other than the target can be reliably added to CoSn ₂ as described later. Can be changed. As a result, it is possible to obtain a metal powder (secondary powder) 10 having an average particle diameter within the above range and a very high CoSn ₂ content.

[2] Next, the obtained primary powder 10 ′ was heated and then cooled (added), and Co—Sn intermetallic compounds other than the purpose contained in the primary powder 10 ′ were converted into CoSn ₂ (target Co-Sn intermetallic compound) to obtain the metal powder 10 (second step).
This heat treatment can be performed using, for example, the heat treatment apparatus 1 shown in FIG. In the following, for convenience of explanation, the upper side in FIG. 1 is referred to as “upper”, the lower side as “lower”, the left side as “left”, and the right side as “right”.

A heat treatment apparatus 1 shown in FIG. 1 includes a cylindrical furnace body 2 and a belt conveyor (conveying means) 3 that conveys an object to be heat treated into the furnace body 2.
The furnace body 2 is made of various heat-resistant materials, and has a function of keeping the furnace 21 warm and storing the atmospheric gas supplied to the furnace 21.
The interior of the furnace 21 has two internal spaces, a heating zone 22 on the inlet side (left side in FIG. 1) of the furnace body 2 and a cooling zone 23 on the outlet side (right side in FIG. 1) of the furnace body 2. It is divided into zones (areas).

In the furnace 21, gas supply pipes 6 that are open at one end at a plurality of locations in the furnace 21 and supply gas to the furnace 21 are provided. Connected to the other end of the gas supply pipe 6 is a gas generating means 7 for generating a gas to be supplied to the furnace 21.
In the heating zone 22, a plurality of heaters 4 are arranged at predetermined intervals along the longitudinal direction of the furnace body 2.

In addition, a temperature regulator 5 that controls the output of the heater 4 and adjusts the temperature in the furnace 21 is provided outside (outer surface) of the furnace body 2. The temperature regulator 5 is configured so that a predetermined temperature gradient can be formed in the furnace 21 by independently controlling the outputs of the plurality of heaters 4 described above.
The cooling zone 23 is provided with a cooling means (not shown) so that the cooling rate of the object to be heat-treated can be adjusted.

A belt conveyor 3 is provided through such a furnace body 2.
The belt conveyor 3 includes a belt part 31 made of a heat-resistant material and a drum part 32 that rotates the belt part 31. The belt unit 31 can be driven at a speed corresponding to the rotation speed by rotating the drum section 32 at a predetermined rotation speed.

In such a heat treatment apparatus 1, the primary powder 10 ′ is passed through the furnace 21 by the belt conveyor 3 to heat-treat the primary powder 10 ′. At this time, by setting the output of the heater 4, the driving speed of the belt portion 31, etc., the heat treatment conditions for the primary powder 10 ′ can be adjusted.
Specifically, first, the primary powder 10 ′ is stored in the tray 8, and the tray 8 is placed on the belt conveyor 3 in this state. Then, the belt conveyor 3 is driven, the primary powder 10 ′ is entered from the entrance side of the furnace body 2, and sequentially passes through the heating zone 22 and the cooling zone 23.
Thereby, the primary powder 10 ′ is heated to a predetermined temperature when passing through the heating zone 22.

  The heating temperature (predetermined temperature) at this time is preferably set so that the primary powder 10 'does not reach sintering. As a result, it is possible to prevent diffusion from occurring at the interface between the primary powders 10 ′ and forming them into aggregates (lumps). In addition, the sintering can prevent the Co—Sn intermetallic compound from being changed into other types of compounds that are not intended, that is, impurities.

Here, in the manufacturing method of the metal powder of this invention, the heating temperature (maximum temperature) of this primary powder 10 'is 160 degreeC or more and less than 410 degreeC. By performing a heat treatment on the primary powder 10 ′ at such a temperature, an appropriate amount of heat is imparted to the Co—Sn intermetallic compound other than the target in the primary powder 10 ′, and Co— The Sn intermetallic compound can be efficiently changed to CoSn ₂ (target Co—Sn intermetallic compound). In addition, it is possible to reliably prevent the generation of impurities, and as a result, the high-purity metal powder 10 which is composed mainly of CoSn ₂ (target Co—Sn intermetallic compound) and has a very small impurity content. Can be obtained.

Further, Sn has a low melting point, and thus may be precipitated (segregated) during heat treatment. However, by performing heat treatment at a relatively low temperature as in the above range, Sn contained in the primary powder 10 ′ is extremely small. Precipitation (segregation) becomes difficult. For this reason, it is possible to reliably prevent variations in composition in the primary powder 10 ′ during the heat treatment. As a result, the metal powder 10 in which CoSn ₂ (target Co—Sn intermetallic compound) is uniformly and uniformly distributed can be obtained. The lithium ion secondary battery including the negative electrode including the metal powder 10 will be described in detail later. Since the electron transfer between the negative electrode and Li ⁺ (lithium ion) is promoted, a high discharge capacity is obtained. As well as having excellent cycle characteristics.

  Furthermore, if the heating temperature of the heat treatment is within the above range, the influence of heat on the furnace (heating device) for performing the heat treatment can be greatly suppressed, and in addition, the energy required for heating and cooling during the heat treatment Time and can be saved. As a result, the life of the furnace can be extended, the running cost can be reduced, and the productivity can be improved. In addition, it is expected that the lifetime of the furnace is extended by about 5% by lowering the heating temperature of the heat treatment by 100 ° C.

Moreover, although the heating temperature of primary powder 10 'shall be 160 degreeC or more and less than 410 degreeC, it is preferable that it is about 200-400 degreeC, and it is more preferable that it is about 250-350 degreeC. By setting the heating temperature within this range, it is possible to more reliably generate impurities while efficiently changing the Co—Sn intermetallic compound other than the target by CoSn ₂ (target Co—Sn intermetallic compound). Can be prevented. In addition, the precipitation (segregation) of Sn can be prevented more reliably, and the thermal effect on the furnace can be further suppressed. As a result, the metal powder 10 that can be used for producing a negative electrode of a high-performance lithium ion secondary battery can be efficiently and inexpensively manufactured.
Further, even when the particle size of the primary powder 10 ′ is small (for example, about 0.1 to 5 μm), it is possible to reliably prevent the particles from being unintentionally sintered by the heat treatment. Moreover, the metal powder 10 excellent in the characteristic (for example, acceptability of Li ^<+> ) as a negative electrode material of a lithium ion secondary battery is obtained with it.

In this case, the heating time varies slightly depending on the heating temperature described above, and is not particularly limited, but is preferably about 10 minutes to 10 hours, more preferably about 30 minutes to 5 hours. Preferably, it is about 1 to 3 hours. Thereby, heat can be reliably applied to the central portion of the primary powder 10 ′, and the Co—Sn intermetallic compound other than the target can be changed to CoSn ₂ also in the central portion. As a result, the content of CoSn _{2 in} the metal powder 10 can be further increased. Even if the heating time is increased beyond the upper limit, further heat treatment cannot be expected.

The atmosphere in the furnace 21 during the heat treatment is preferably a non-oxidizing atmosphere. Thereby, it is possible to reliably prevent the primary powder 10 ′ from being oxidized and generating impurities such as an oxide of a Co—Sn intermetallic compound.
Examples of the non-oxidizing atmosphere include an inert atmosphere such as argon, helium, and nitrogen, and a reducing atmosphere such as hydrogen and carbon monoxide.
Furthermore, such a non-oxidizing atmosphere is preferably in a dry state (having as little water vapor content as possible). Thereby, the oxidation of primary powder 10 'by the influence of the water vapor | steam (water | moisture content) which exists in atmosphere can be prevented.

The primary powder 10 ′ heated in the heating zone 22 as described above subsequently passes through the cooling zone 23. At this time, the primary powder 10 'is cooled.
When the atmospheric gas is introduced into the cooling zone 23, the cooling rate of the primary powder 10 ′ can be adjusted by changing the flow rate of the atmospheric gas. The cooling rate can also be adjusted by the driving speed of the belt conveyor 3.
Here, as a result of repeated studies by the present inventors, in order to surely change the Co—Sn intermetallic compound other than the objective to the target Co—Sn intermetallic compound, after the heating of the primary powder 10 ′ ( In particular, it has been found that the cooling rate immediately after heating is important.

As a result of further studies by the inventor, it has been found that cooling is preferably performed under the following conditions.
I: Cooling from the heating temperature (maximum temperature) to room temperature is preferably performed at an average cooling rate of about 50 to 1000 ° C./hour, more preferably about 75 to 500 ° C./hour. In addition, although it may cool by making an average cooling rate slower than the said lower limit, there exists a possibility that production efficiency may fall remarkably.

II: Cooling from the heating temperature to 100 ° C. is preferably performed at an average cooling rate of about 300 to 1200 ° C./hour, more preferably about 400 to 1000 ° C./hour.
In addition, it is preferable that these conditions satisfy at least one, and it is more preferable to satisfy both. Thus, cooling after completion of the heating of the primary powder 10 'is best carried out, it is possible to more reliably change the CoSn intermetallic compound other than the target to the CoSn _2. As a result, the content of CoSn ₂ in the metal powder 10 is particularly high.
As described above, the metal powder 10 composed mainly of CoSn ₂ can be obtained.

  In addition, the content of the Co—Sn intermetallic compound other than the purpose contained in this is A [wt%], and the content of the Co—Sn intermetallic compound other than the purpose contained in the primary powder 10 ′ is B [ wt%], A / B is preferably 0.1 or less, and more preferably 0.05 or less. Thus, according to the present invention, the Co—Sn intermetallic compound other than the purpose corresponding to the impurities for the metal powder 10 can be significantly reduced to the above range. In other words, the present invention is suitably applied particularly to the production of the metal powder 10 containing the target Co—Sn intermetallic compound with high purity.

Specifically, the content (A [wt%]) of the Co—Sn intermetallic compound other than the purpose in the metal powder 10 is preferably 10 wt% or less, and more preferably 1 wt% or less. Thus, the metal powder 10 with a small impurity content exhibits the characteristics obtained by the target Co—Sn intermetallic compound more reliably.
The metal powder 10 thus obtained can be applied to, for example, electrodes, wirings, etc., but is particularly preferably applied to electrodes (negative electrodes) for lithium ion secondary batteries.

Hereinafter, the lithium ion secondary battery will be described.
Here, in the lithium ion secondary battery, Li ⁺ (lithium ions) move between the positive electrode and the negative electrode, and Li ⁺ is introduced (doped) into the electrode, or conversely, Li ⁺ is desorbed (desorbed) from the electrode. The battery is charged and discharged by causing an electron flow (current) in an external circuit connected to the positive electrode and the negative electrode by doping.

FIG. 2 is a schematic view (longitudinal sectional view) showing an embodiment of the lithium ion secondary battery of the present invention.
A lithium ion secondary battery (lithium ion secondary battery of the present invention) 100 shown in FIG. 2 has a so-called coin-type configuration, and includes a disk-shaped negative electrode (electrode of the present invention) 120, It has a disk-shaped positive electrode 140 facing each other with the separator 130 interposed therebetween.

Further, the negative electrode 120, the separator 130, and the positive electrode 140 are accommodated in the negative electrode can 150 and the positive electrode can 160. The negative electrode can 150 is electrically connected to the negative electrode 120, and the positive electrode can 160 is electrically connected to the positive electrode 140. Electric energy generated between the negative electrode 120 and the positive electrode 140 is externally passed through the negative electrode can 150 and the positive electrode can 160. It can be taken out.
Further, the connecting portion between the negative electrode can 150 and the positive electrode can 160 is filled with an insulating gasket 170 to seal the negative electrode can 150 and the positive electrode can 160.
The space defined by the negative electrode can 150, the positive electrode can 160, and the insulating gasket 170 is filled with an electrolyte (not shown).

Hereinafter, each part will be described sequentially.
The negative electrode 120 includes a negative electrode current collector 121 and a negative electrode active material layer 122 provided in contact with the negative electrode current collector 121.
Among these, the negative electrode current collector 121 has, for example, a foil shape or a net shape.
Examples of the constituent material of the negative electrode current collector 121 include Cu (copper), Ni (nickel), Ti (titanium), Al (aluminum), stainless steel, and permalloy.
The average thickness of the negative electrode current collector 121 is preferably about 0.03 to 0.3 μm, more preferably about 0.05 to 0.2 μm.
On the other hand, the negative electrode active material layer 122 is formed by molding a material containing the metal powder 10 of the present invention into a disc shape (electrode shape).

As described above, the metal powder 10 is composed mainly of a Co—Sn intermetallic compound formed by combining Co and Sn at a predetermined molar ratio. By including the metal powder 10 in the negative electrode active material layer 122, the reaction amount and reaction density (energy density) with Li ⁺ by the Co—Sn intermetallic compound are improved, and as a result, the negative electrode active material layer 122 is formed. The provided negative electrode 120 has excellent characteristics as a negative electrode of a lithium ion secondary battery.
In addition, the lithium ion secondary battery 100 of the present invention includes the negative electrode 120 as described above. Thereby, the lithium ion secondary battery 100 has high discharge capacity and excellent cycle characteristics.

On the other hand, the positive electrode 140 includes a positive electrode current collector 141 and a positive electrode active material layer 142 provided in contact with the positive electrode current collector 141.
Among these, the positive electrode current collector 141 has, for example, a foil shape or a net shape.
As a constituent material of the positive electrode current collector 141, a material similar to that of the negative electrode current collector 121 can be used.

On the other hand, the positive electrode active material layer 142 is preferably made of a metal compound material or a conductive polymer material that can be doped or dedoped with Li ⁺ . Specifically, examples of the metal compound material include CoS ₂ , MoS ₂ , TiS ₂ , FeS ₂ , NbSe ₂ , V ₂ O ₅ , LiCoO ₂ , LiSnO ₂ , LiNiO ₂ , LiMnO ₂ , LiMnO ₄ , LiMn _2. O ₄ etc. are mentioned. Examples of the conductive polymer material include polyacetylene and polyaniline.

The separator 130 is interposed between the negative electrode 120 and the positive electrode 140, allows Li ⁺ to pass therethrough, and prevents a short circuit therebetween. The separator 130 also has a function of holding the liquid electrolyte when the electrolyte is in a liquid state. As will be described in detail later, when the electrolyte is solid or gel, the separator 130 can be omitted.
Such a separator 130 is composed of a porous film. Then, Li ⁺ can be passed through the pores in the porous membrane.
In addition, the separator 130 can be composed of a single layer or a laminate of two or more layers.

  The constituent material of each layer includes, for example, olefin resin such as polyethylene and polypropylene, fluorine resin, styrene resin such as polystyrene, ABS resin, vinyl chloride resin, vinyl acetate resin, acrylic resin, polyamide resin, acetal resin, polycarbonate resin These can be used, and one or more of these can be used in combination.

In the case of a laminated body, layers having different constituent materials may be laminated.
The thickness of the separator 130 is preferably about 5 to 70 μm, and more preferably about 10 to 50 μm.
In addition, the size of the minute holes provided in the separator 130 is preferably about 0.01 to 3 μm in inner diameter, more preferably about 0.1 to 2 μm in inner diameter.

The electrolyte contains a Li ^+, is intended to conduct the Li ⁺ between the negative electrode 120 and positive electrode 140.
The electrolyte may be liquid, solid or gel.
When the electrolyte is liquid, the electrolyte is composed of various lithium salt electrolyte salts and an organic solvent.
Examples of the lithium salt include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiAsF ₆ , LiCl, LiBr, LiB (C ₆ H ₆ ), LiSn (SO ₂ CF ₃ ), Li (CF ₃ SO ₂ ). _{2 N,} include such LiC ₄ F 9 SO _3, can be used singly or in combination of two or more thereof.

  On the other hand, as the organic solvent, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethoxymethane, diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, 1,3- Dioxolane, methyl formate, methyl acetate, methyl propionate and the like can be mentioned, and one or more of these can be used in combination.

When the electrolyte is solid, the electrolyte is composed of the above-described electrolyte salt and a polymer having an ethylene oxide bond. Specific examples of the polymer include polyethylene oxide resins.
Moreover, when electrolyte is a gel form, electrolyte is comprised with the above-mentioned electrolyte salt and gel-like polymer. Examples of the gel polymer include polyethylene oxide, polyacrylonitrile, poly (vinylidene fluoride), polymethyl methacrylate and the like, and these can be used alone or in combination. In addition, you may add an organic solvent etc. to a gel-like polymer as needed.

The negative electrode can 150 is a container that houses the negative electrode 120 and prevents leakage of electrolyte and the like. Further, it is electrically joined to the negative electrode 120 and has a function as an external electrode.
The negative electrode can 150 is preferably made of a material having high electrical conductivity and high resistance to an electrolyte.
On the other hand, like the negative electrode can 150, the positive electrode can 160 is a container that houses the positive electrode 140 and prevents leakage of the electrolyte. Further, it is electrically connected to the positive electrode 140 and has a function as an external electrode.

The positive electrode can 160 is preferably made of the same material as the negative electrode can 150.
The insulating gasket 170 is provided at a connection portion between the negative electrode can 150 and the positive electrode can 160 and has a function of sealing the lithium ion secondary battery 100. Such an insulating gasket 170 can prevent electrolyte leakage and the like.
Such a lithium ion secondary battery of the present invention has a high discharge capacity and excellent cycle characteristics.

Such a lithium ion secondary battery 100 is manufactured as follows, for example.
[A] First, the negative electrode 120 is manufactured.
[A-1] The metal powder 10, the conductive agent, the binder, and the diluent are kneaded to prepare a paste-like negative electrode mixture (material for electrode formation).
Examples of the conductive agent include acetylene black (AB), graphite, ketjen black, and the like, and one or more of these can be used in combination.

Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-propylene-diene copolymer (EPDM), and the like. One or more of these may be used. They can be used in combination.
Examples of the diluent include N-methylpyrrolidone, N, N′-dimethylformamide, N, N′-dimethylacetamide, toluene, methyl ethyl ketone, water and the like, and one or more of these are combined. Can be used.

The mixing ratio of the metal powder 10, the conductive agent and the binder in the negative electrode mixture is preferably about 10 to 15: 4 to 9: 1 to 4 by weight.
Moreover, the mixing ratio of the diluent in the negative electrode mixture is not particularly limited, and may be appropriately set according to the viscosity of the negative electrode mixture.
The kneading method is not particularly limited, and examples thereof include a method using various kneaders such as a stirrer, a ball mill, and a pressure kneader.

[A-2] Next, the obtained negative electrode mixture is applied onto one surface of the negative electrode current collector 121 and dried.
Here, as the negative electrode current collector 121, a belt-shaped (tape-shaped) member made of the constituent material of the negative electrode current collector 121 described above is suitable. By using such a negative electrode current collector 121, work efficiency in the production of the negative electrode 120 is improved.
The method for applying the negative electrode mixture on one surface of the negative electrode current collector 121 is not particularly limited, but includes dipping method, dripping, doctor blade method, spin coating method, brush coating, spray coating method, roll coating. Examples include various coating methods such as a method, various printing methods such as a metal mask printing method and a screen printing method.

Examples of the method for drying the applied negative electrode mixture include various drying methods using a hot plate, vacuum drying, N ₂ or air blow, oven, and the like, and one or more of these are combined. Can be used. Further, two or more of these may be sequentially performed.
As drying temperature in the case of drying, about 50-200 degreeC is preferable and about 80-170 degreeC is more preferable. Thereby, it can dry reliably, preventing that the metal powder 10 in a negative mix is oxidized.

Moreover, as drying time in the case of drying, 0.5 hour or more is preferable and 2 hours or more are more preferable. Thereby, a negative mix can be dried reliably.
Further, in the case of drying using a hot plate, N ₂ or air blow, it is preferable to dry until the vapor generated from the negative electrode mixture disappears in the drying process. Thereby, necessary and sufficient drying can be performed easily.

[A-3] Next, the dried negative electrode mixture is pressurized (hot pressed) while being heated. Thereby, a green compact of the negative electrode mixture is obtained on the negative electrode current collector 121.
For the pressurization, for example, a press device or the like can be used.
In the case of using a press device, the negative electrode current collector 121 to which the negative electrode mixture is applied is mounted on a mold of the press device, and the negative electrode material mixture is pressed onto the negative electrode current collector 121 by applying pressure while heating.
At this time, the heating temperature is preferably about 50 to 200 ° C. Thereby, the binder in a negative electrode mixture melts moderately, and the shape retention of the green compact obtained improves.
The load during hot pressing is preferably about 20 to 100 tons, and the pressing time is preferably about 5 to 60 seconds.

[A-4] Next, the obtained green compact is dried.
As the method for drying the green compact, the above-mentioned various drying methods can be used, and it is particularly preferable to use vacuum drying.
At this time, the drying conditions can be the same as described above.
[A-5] Next, the dried green compact is punched into a predetermined shape (for example, a disk shape or the like) together with the negative electrode current collector 121. Thereby, the negative electrode 120 is obtained.
For the punching, for example, a punching (punch) processing machine or the like can be used.
Subsequently, the punched green compact is further dried.
As the drying method at this time, the above-mentioned various drying methods can be used.
The drying conditions can be the same as described above.

[B] Next, the positive electrode 140 is manufactured.
The positive electrode 140 can be manufactured in the same manner as the manufacturing method of the negative electrode 120 in the step [A].
[C] Next, the negative electrode 120 is accommodated in the negative electrode can 150, and the positive electrode 140 is accommodated in the positive electrode can 160.
In addition, it is preferable to perform all the processes after this process in clean environment, such as the inside of a glove box or a clean room. Thereby, mixing of the foreign material in a lithium ion secondary battery can be suppressed.

[D] Next, the negative electrode can 150 and the positive electrode can 160 are stacked so that the separator 130 is interposed between the negative electrode 120 and the positive electrode 140, and the inside of the space formed by the negative electrode can 150 and the positive electrode can 160. Inject and fill electrolyte.
[E] Next, the connecting portion between the negative electrode can 150 and the positive electrode can 160 is sealed with the insulating gasket 170.
The lithium ion secondary battery 100 is manufactured through the above steps.

As mentioned above, although the manufacturing method of the metal powder of this invention, the metal powder, the electrode, and the lithium ion secondary battery were demonstrated based on suitable embodiment, this invention is not limited to this.
For example, in the above embodiment, the finally obtained metal powder 10 is mainly composed of a Co—Sn intermetallic compound (CoSn ₂ ) formed by combining Co and Sn at a molar ratio of 1: 2. Although the case has been described as a representative, it goes without saying that the same applies when the molar ratio is a molar ratio other than 1: 2 (eg, 1: 1, 1: 3, 3: 2). In that case, it can respond by changing various conditions of heat processing suitably.

Moreover, in the manufacturing method of a metal powder, arbitrary processes can also be added as needed.
For example, after obtaining the secondary powder in the second step, the secondary powder after the predetermined treatment may be used as the final metal powder by the step of performing the predetermined treatment.
Moreover, although the said embodiment demonstrated the case where the heat processing apparatus 1 was a continuous furnace, as a heat processing apparatus 1, a batch furnace, a vacuum furnace, etc. may be sufficient.
In the above embodiment, the coin-type lithium ion secondary battery has been described. However, the present invention is not limited to this, and the shape of the lithium ion secondary battery may be a cylindrical type, a square type, a button type, a film exterior type, or the like. There may be.

1. Production of metal powder and lithium ion secondary battery (Example 1)
[1] First, Co and Sn were weighed so as to have a weight ratio of 2: 8 (a molar ratio of 1: 2) to obtain a mixed raw material, which was melted in a gas furnace to obtain a melt.
[2] Next, the obtained melt was pulverized by a water atomization method to obtain a primary powder having an average particle size of 10 μm.

About the obtained primary powder, the crystal structure analysis by the X ray diffraction method was performed. In the X-ray diffraction spectrum obtained by the analysis, a peak due to a Co—Sn intermetallic compound such as CoSn ₃ or Co ₃ Sn ₂ or a single metal such as Sn was observed (see FIG. 3).
Moreover, when the result of the X-ray diffraction was quantitatively analyzed, the content of Co—Sn intermetallic compounds other than CoSn ₂ contained in the primary powder (hereinafter abbreviated and referred to as “content B”). Was 85%.

[3] Next, the obtained primary powder was heat-treated using the heat treatment apparatus 1 shown in FIG. 1 under the following heat treatment conditions. Thereby, metal powder was obtained.
<Heat treatment conditions>
・ Heating temperature (maximum temperature): 200 ° C
-Heating time: 1 hour-Furnace atmosphere: Argon gas-Average cooling rate to room temperature: 100 ° C / hour-Average cooling rate to 100 ° C: 450 ° C / hour For the obtained metal powder, X-ray diffraction method Crystal structure analysis was performed. In the X-ray diffraction spectrum obtained by the analysis, a peak due to CoSn ₂ was observed.

[4] Next, the obtained metal powder, acetylene black (conductive agent) and polyvinylidene fluoride (binder) were mixed at a weight ratio of 8: 8: 1 to obtain a mixture. Subsequently, this mixture and N-methylpyrrolidone (diluent) were kneaded. As a result, a paste-like negative electrode mixture was obtained.
[5] Next, the obtained negative electrode mixture was applied onto a copper foil tape (negative electrode current collector) having an average thickness of 0.08 mm, and dried in two portions under the following drying conditions.

<Drying conditions>
・ The first time ・ Drying method: Hot plate ・ Drying temperature: 100 degrees Celsius
・ Drying time: 2 hours ・ Second time ・ Drying method: Vacuum drying ・ Drying temperature: 100 ° C.
・ Drying time: 3 hours

[6] Next, the dried negative electrode mixture was hot-pressed by a press device under the following pressing conditions. Thereby, the green compact of the negative electrode mixture was obtained on the copper foil tape.
<Press conditions>
・ Temperature: 130 ℃
・ Load: 80 tons ・ Pressurization time: 20 seconds

[7] Next, the obtained green compact was dried under the following drying conditions.
<Drying conditions>
-Drying method: vacuum drying-Drying temperature: 160 ° C
・ Drying time: 15 hours

[8] Next, the dried green compact was punched into a disk shape having an outer diameter of 13 mm with a punching machine together with the copper foil tape. The punched green compact was dried under the following drying conditions. This obtained the negative electrode.
<Drying conditions>
-Drying method: vacuum drying-Drying temperature: 100 ° C
・ Drying time: 3 hours

[9] Next, a positive electrode was obtained in the same manner as the negative electrode, using LiCoO ₂ (positive electrode active material) and an aluminum foil tape (positive electrode current collector).
[10] Next, the obtained negative electrode was accommodated in the negative electrode can, and the positive electrode was accommodated in the positive electrode can. Subsequently, the negative electrode can and the positive electrode can are stacked so that the negative electrode and the positive electrode face each other with a polypropylene porous film (separator) interposed therebetween, and the following is shown in the space formed by the negative electrode can and the positive electrode can. Liquid electrolyte was injected and filled. And the connection part of a negative electrode can and a positive electrode can was sealed with the insulating gasket, and the lithium ion secondary battery was obtained.
<Electrolyte>
Electrolyte salt: LiPF ₆
・ Solvent: Ethylene carbonate + dimethyl carbonate

(Example 2)
A metal powder was obtained in the same manner as in Example 1 except that the heating temperature in the heat treatment was changed to 300 ° C., and a negative electrode and a lithium ion secondary battery were obtained using this metal powder.
(Example 3)
A metal powder was obtained in the same manner as in Example 1 except that the heating temperature in the heat treatment was changed to 400 ° C., and a negative electrode and a lithium ion secondary battery were obtained using this metal powder.
Example 4
In the step [2] of Example 1, the metal powder was obtained in the same manner as in Example 1 except that the metal atom having an average particle diameter of 2 μm was obtained by changing the water atomization conditions. A negative electrode and a lithium ion secondary battery were obtained using the powder.

(Comparative Example 1)
A metal powder was obtained in the same manner as in Example 1 except that the heat treatment was omitted and the primary powder obtained by the atomization method was used as it was as a metal powder. Using this metal powder, a negative electrode and a lithium ion secondary battery were obtained. Got.
(Comparative Example 2)
A metal powder was obtained in the same manner as in Example 1 except that the heating temperature in the heat treatment was changed to 150 ° C., and a negative electrode and a lithium ion secondary battery were obtained using this metal powder.

(Comparative Example 3)
A metal powder was obtained in the same manner as in Example 1 except that the heating temperature in the heat treatment was changed to 550 ° C., and a negative electrode and a lithium ion secondary battery were obtained using this metal powder.
(Comparative Example 4)
While changing the heating temperature in the heat treatment to 550 ° C. and changing the water atomization conditions, a metal powder having an average particle diameter of 2 μm was obtained in the same manner as in Example 1 to obtain a metal powder, Using this metal powder, a negative electrode and a lithium ion secondary battery were obtained.

2. Evaluation 2.1 Evaluation of metal powder The crystal structure analysis by the X-ray diffraction method was performed about the metal powder obtained by each Example and each comparative example, respectively. Subsequently, quantitative analysis was performed on the obtained analysis results, and the contents of components (metal simple substance and intermetallic compound) contained in the metal powder were measured. Then, the content of Co—Sn intermetallic compounds other than CoSn ₂ contained in the metal powder (hereinafter referred to as “content A”) was evaluated.

Hereinafter, as representatives, X-ray diffraction spectra obtained by conducting crystal structure analysis on the metal powders obtained in Examples 2 and 3 and Comparative Examples 1 and 2 are shown in FIGS.
FIG. 3 is an X-ray diffraction spectrum obtained by subjecting the primary powder to no heat treatment (Comparative Example 1), that is, a crystal structure analysis of the primary powder. In this spectrum, peaks due to intermetallic compounds other than CoSn ₂ or simple metals were observed.

4 and 5 are X-ray diffraction spectra obtained by conducting crystal structure analysis on the metal powders obtained in Examples 2 and 3. FIG. In each spectrum, a peak due to CoSn ₂ was observed. From this, it was confirmed that the metal powder obtained in Examples 2 and 3 has CoSn ₂ as a main component.
Note that the portion indicated by arrow A in FIG. 5, not observed in FIG. 4, the peak of an impurity believed to be due CoSn ₃ was observed. Therefore, it seems that CoSn ₃ is slightly mixed in the metal powder obtained in Example 3.
On the other hand, in the metal powder obtained in Comparative Example 2, as shown in FIG. 6, X-ray diffraction spectra having dominant peaks due to intermetallic compounds other than CoSn ₂ or simple metals were obtained. From this, it was confirmed that the metal powder obtained in Comparative Example 2 contained almost no CoSn ₂ .

2.2 Evaluation of Lithium Ion Secondary Battery For the lithium ion secondary batteries obtained in each of the examples and comparative examples, a charge / discharge test is performed as follows to evaluate the characteristics of the lithium ion secondary battery. did.
[1] First, each lithium ion secondary battery was charged with a charging voltage of 5 mV and a charging current of 1 mA, and the charging was terminated when the current decreased to 20 μA.

[2] Next, it was left for 2 minutes in the state of the step [1].
[3] Next, discharge was performed at a current of 0.05 mA, and the discharge was terminated when the voltage dropped 1.2 V from the initial voltage.
[4] The steps [1] to [3] were repeated, and 50 charge / discharge tests were performed.
As a result of the charge / discharge test as described above, it was revealed that each of the lithium ion secondary batteries obtained in each example had a higher discharge capacity than each comparative example.

Also, the ratio of the 20th discharge capacity to the initial discharge capacity is defined as the discharge capacity (initial discharge capacity) C ₁ [mAh / g] in the _first charge / discharge cycle and the 20th discharge capacity C ₂₀ [mAh / g]. C ₂₀ / C _{1 was} compared with the lithium ion secondary batteries obtained in the respective examples and comparative examples.
The evaluation results of 2.1 and 2.2 are shown in Table 1.

As is clear from the evaluation results of 2.1 in Table 1, the content A of each example showed a low value of 5% or less. This content A was 0.1 or less as a ratio (A / B) to the content B (85%). This indicates that the heat treatment reduced Co—Sn intermetallic compounds other than CoSn ₂ , that is, impurities to 1/10 or less.
In particular, the content A of Examples 2 and 3 was as low as less than 1%, and high-purity CoSn ₂ was obtained.

Further, as is clear from the evaluation result of 2.2 in Table 1, in the lithium ion secondary batteries obtained in the respective examples, C ₂₀ / C ₁ (percentage) has a relatively high value of 87 to 98%. Indicated. This indicates that the reduction in discharge capacity is suppressed even after 20 cycles, and the cycle characteristics of these lithium ion secondary batteries are excellent.
In particular, among the examples, the lithium ion secondary battery obtained in Example 2 had a high C ₂₀ / C ₁ (percentage) of 98%, indicating that the cycle characteristics were particularly excellent.
On the other hand, in each comparative example, C ₂₀ / C ₁ (percentage) showed a low value of less than 80%. This indicates that the cycle characteristics of the lithium ion secondary batteries obtained in the respective comparative examples are insufficient.
In addition, some of the metal powder obtained in Comparative Example 4 was sintered.

It is the schematic (longitudinal sectional view) which shows the structure of the heat processing apparatus used for the manufacturing method of the metal powder of this invention. It is the schematic (longitudinal sectional view) which shows each embodiment of the electrode and lithium ion secondary battery of this invention. 3 is an X-ray diffraction spectrum obtained from the metal powder (primary powder) obtained in Comparative Example 1. 3 is an X-ray diffraction spectrum obtained from the metal powder obtained in Example 2. 3 is an X-ray diffraction spectrum obtained from the metal powder obtained in Example 3. 3 is an X-ray diffraction spectrum obtained from the metal powder obtained in Comparative Example 2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Heat processing apparatus 2 ... Furnace body 21 ... Furnace 22 ... Heating zone 23 ... Cooling zone 3 ... Belt conveyor 31 ... Belt part 32 ... Drum part 4 ... Heater 5 ... Temperature controller 6 ... Gas supply pipe 7 ... Gas generating means 8 ... Tray 10 ... Metal powder (secondary powder) 10 '... Primary powder 100 ... Lithium ion secondary battery 120 ... Negative electrode 121 ... Negative electrode current collector Body 122 ... Negative electrode active material layer 130 ... Separator 140 ... Positive electrode 141 ... Positive electrode current collector 142 ... Positive electrode active material layer 150 ... Negative electrode can 160 ... Positive electrode can 170 ... Insulation gasket

Claims (13)

A first step of melting a raw material containing Co and Sn at a target molar ratio and pulverizing by an atomizing method to obtain a primary powder;
The primary powder is heated at a temperature of 160 ° C. or higher and lower than 410 ° C., then cooled, and Co— is formed by combining Co and Sn at a molar ratio other than the target molar ratio contained in the primary powder. The Sn intermetallic compound is changed to a Co—Sn intermetallic compound formed by combining Co and Sn at the target molar ratio, and the Co—Sn metal formed by combining Co—Sn at the target molar ratio. And a second step of obtaining a secondary powder in which the intermetallic compound is highly purified.   The said primary powder is a manufacturing method of the metal powder of Claim 1 whose average particle diameter is 0.1-50 micrometers.   The method for producing a metal powder according to claim 1 or 2, wherein in the second step, the heating is performed under a condition such that the primary powder does not reach sintering.   The method for producing metal powder according to any one of claims 1 to 3, wherein in the second step, the heating is performed in a non-oxidizing atmosphere. CoSn intermetallic compound in a molar ratio of said object, method for producing a metal powder according to any one of claims 1 to 4 is CoSn _2.   The method for producing a metal powder according to claim 5 or 6, wherein, in the second step, the heating time is 10 minutes to 10 hours.   The method for producing a metal powder according to any one of claims 1 to 6, wherein in the second step, cooling from the heating temperature to room temperature is performed at an average cooling rate of 50 to 1000 ° C / hour.   The method for producing metal powder according to any one of claims 1 to 7, wherein in the second step, cooling from the heating temperature to 100 ° C is performed at an average cooling rate of 300 to 1200 ° C / hour.   The content ratio of the Co—Sn intermetallic compound having a molar ratio other than the target molar ratio included in the secondary powder is A [wt%], and the molar ratio other than the target molar ratio is included in the primary powder. The method for producing a metal powder according to any one of claims 1 to 8, wherein A / B is 0.1 or less when the content of the Co-Sn intermetallic compound is B [wt%].   The method for producing a metal powder according to any one of claims 1 to 9, wherein the content of the Co-Sn intermetallic compound having a molar ratio other than the target molar ratio contained in the secondary powder is 10 wt% or less. .   A metal powder produced by the method for producing a metal powder according to claim 1.   It has a part formed by shape | molding the material containing the metal powder of Claim 11, The electrode characterized by the above-mentioned. A negative electrode, a positive electrode, and an electrolyte containing lithium ions,
A lithium ion secondary battery comprising the electrode according to claim 12 as the negative electrode.

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