JP2018172781A - Lithium powder, negative electrode for lithium ion secondary battery prepared therewith, and lithium ion secondary battery prepared with the negative electrode for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium powder having excellent storage stability in the air, and a negative electrode for lithium ion secondary battery prepared therewith, and a lithium ion secondary battery prepared with the negative electrode for lithium ion secondary battery.SOLUTION: A lithium powder contains a core composed of metallic lithium, and a coating layer that coats the surface of the core. The coating layer contains lithium carbonate. On part of the surface of the lithium carbonate, there is lithium oxide.SELECTED DRAWING: Figure 2

Description

  The present invention relates to lithium powder, a negative electrode for a lithium ion secondary battery using the lithium powder, and a lithium ion secondary battery using the negative electrode for the lithium ion secondary battery.

  Lithium ion secondary batteries are used as a power source for a wide variety of products such as portable electronic devices, power tools, drones, XEVs, stationary power sources, and the like. And with the miniaturization and high functionality of products, further increase in energy density is expected for lithium ion secondary batteries serving as these power sources.

At present, carbon materials such as graphite are often used as negative electrode active materials for lithium ion secondary batteries. However, in order to increase the energy density, in recent years, such as Si, SiO _x , Sn, etc., which have a larger discharge capacity than graphite. Many alloy negative electrode active materials have been studied.

However, graphite, Si, SiO _x , Sn, etc. have irreversible capacity. This is a phenomenon in which lithium ions inserted into the negative electrode active material during charging are trapped in the negative electrode active material and do not desorb from the negative electrode active material during discharge. In order to reduce this irreversible capacity, methods such as increasing the degree of graphitization have been made in graphite. As another method, there is a method of reducing the irreversible capacity by bringing lithium and a negative electrode into contact with each other in advance so that a chemical species causing irreversible capacity and lithium react with each other. And as a form of lithium used for this, there are foil and powder. The foil has a drawback that it is difficult to produce a thin lithium foil, and that the thin lithium foil has a low mechanical strength and thus is easily cut and difficult to use in the production process. On the other hand, lithium powder has an advantage that it easily reacts uniformly with the negative electrode. However, since lithium powder has a larger specific surface area than lithium foil, it has a problem that it is difficult to handle because it reacts with moisture, nitrogen, carbon dioxide, etc. in the use environment.

Patent Document 1 discloses a surface-coated lithium powder containing oxygen and a hydrocarbon containing a lithium compound selected from lithium carbonate, lithium oxide and lithium hydroxide. This structure makes it relatively non-reactive with atmospheric components and can move from one container to another in such surrounding atmosphere without risk of ignition or loss of activity. Have been described. In Patent Document 2, a wax and an inorganic coating are formed on the surface of lithium powder, and the inorganic coating is lithium carbonate, LiF, Li ₃ PO ₄ , SiO ₂ , Li ₄ SiO ₄ , LiAlO ₂ , Li ₂ TiO ₃ , and LiNbO. A lithium powder selected from the group consisting of ₃ is disclosed. Patent Document 3 includes (a) a step of heating a lithium powder above its melting point to obtain a molten lithium metal, (b) a step of dispersing the molten lithium metal, and (c) a lithium phosphate. Contacting the dispersed molten lithium metal with a phosphorus-containing compound to obtain a substantially continuous protective layer on the lithium powder.

Japanese National Patent Publication No. 8-505440 Special table 2010-507197 Special table 2010-535936 gazette

  However, in the techniques described in Patent Documents 1 to 3, the storage stability of lithium powder in the atmosphere is not sufficient.

  Therefore, the present invention has been made to solve the above-described problems, and lithium powder excellent in storage stability in the atmosphere, a negative electrode for a lithium ion secondary battery using the lithium powder, and the negative electrode were used. An object is to provide a lithium ion secondary battery.

  In order to solve the above problems, a lithium powder according to the present invention includes a core made of metallic lithium and a coating layer covering at least a part of the surface of the core, the coating layer containing lithium carbonate, It is a lithium powder in which lithium oxide is present on at least a part of the surface of the lithium carbonate.

  Covering at least a part of the surface of the core in the previous period means covering 50% or more, preferably 80% or more of the surface of the core.

According to the structure concerning this invention, the said lithium powder has the outstanding storage stability in air | atmosphere. The conventional lithium powder has a coating containing lithium carbonate on the surface of the metallic lithium core, whereas the lithium powder of the present application has lithium oxide on at least a part of the lithium carbonate surface on the lithium surface. doing. The effect of the lithium powder of the present application having excellent storage stability is not necessarily clear, but lithium oxide reacts with moisture as shown in the following formula (1) to become lithium hydroxide. Thus, it is thought that there exists an effect which reacts with a water | moisture content and suppresses a water | moisture content permeating | transmitting to lithium of a core. Such a mechanism is considered to improve storage stability in the atmosphere.
_{Li 2 O + H 2 O →} 2LiOH (1)

  The coating layer includes a first coating layer present on at least a part of the core and a second coating layer present on the first coating layer, and the first coating layer contains lithium carbide. More preferably, the second coating layer contains the lithium carbonate.

According to this configuration, the lithium powder has excellent storage stability in the air. Although this effect is not necessarily clear, lithium carbide reacts with moisture as shown in the following chemical formula (2) to become lithium hydroxide. Thus, it is thought that there exists an effect which reacts with a water | moisture content and suppresses a water | moisture content permeating | transmitting to lithium of a core. Such a mechanism is considered to improve storage stability in the atmosphere.
_{Li 2 C 2 + 2H 2 O} → 2LiOH + C 2 H 2 (2)

  More preferably, the second coating layer is a lithium powder containing lithium hydroxide.

  The content of lithium hydroxide in the entire lithium powder is more preferably 0.01% by mass to 1% by mass.

  A lithium powder having a lithium metal content of 80 to 98% by mass in the lithium powder is more preferable.

  According to such a configuration, the lithium powder has an effect of reducing the irreversible capacity by bringing the lithium powder and the negative electrode into contact with each other and causing an electrochemical reaction between the chemical species causing the irreversible capacity and lithium. Cheap.

  Lithium powder having a thickness of the second coating layer of 59 nm to 2060 nm is more preferable.

  According to such a configuration, when the thickness of the coating is in the above range, this coating blocks moisture, carbon dioxide, nitrogen, etc. in the atmosphere, and the reaction between lithium in the core and these is suppressed, which is superior in the atmosphere. Storage characteristics are obtained.

  A lithium powder having a thickness of the first coating layer of 1 nm to 10 nm is more preferable.

  According to such a configuration, when the thickness of the coating is in the above range, this coating blocks moisture, carbon dioxide, nitrogen, etc. in the atmosphere, and the reaction between lithium in the core and these is suppressed, which is superior in the atmosphere. Storage characteristics are obtained.

  The lithium oxide is particles, and lithium powder having a particle diameter of 1 nm to 2000 nm is more preferable.

  According to such a configuration, when the particle size is in the above range, the particles block moisture, carbon dioxide, nitrogen, etc. in the atmosphere, and the reaction between lithium in the core and these is suppressed, which is superior in the atmosphere. Storage characteristics are obtained.

  The lithium oxide is layered, and lithium powder having a thickness of 1 nm to 2000 nm is preferable.

  According to such a configuration, when the thickness of the coating is in the above range, this coating blocks moisture, carbon dioxide, nitrogen, etc. in the atmosphere, and the reaction between lithium in the core and these is suppressed, which is superior in the atmosphere. Storage characteristics are obtained.

  The negative electrode for lithium ion secondary batteries which doped the lithium ion using the said lithium powder is obtained.

  The lithium ion secondary battery provided with the said negative electrode for lithium ion secondary batteries, electrolyte, and a positive electrode is obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium powder excellent in the storage stability in air | atmosphere, the negative electrode for lithium ion secondary batteries using the same, and a lithium ion secondary battery using the same are obtained.

FIG. 1 is a schematic cross-sectional view showing a lithium ion secondary battery according to the present embodiment and a comparative example. FIG. 2 is a flowchart showing a method for producing lithium powder according to the present embodiment and Comparative Example 1.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, the dimensional ratio of drawing is not restricted to the ratio of illustration.

  Hereinafter, the case where an electrode is an electrode used for a lithium ion secondary battery will be specifically described with reference to FIG. FIG. 1 is a schematic cross-sectional view showing a lithium ion secondary battery 100 according to the present embodiment and a comparative example.

(Lithium ion secondary battery)
The lithium ion secondary battery 100 mainly includes a laminated body 30 and an electrolyte, and includes a case 50 that accommodates the laminated body 30 in a sealed state, and a pair of terminals 60 and 62 connected to the laminated body 30. .

  The laminated body 30 is configured such that a pair of the positive electrode 10 and the negative electrode 20 are opposed to each other with the separator 18 interposed therebetween. The positive electrode 10 is obtained by providing a positive electrode mixture layer 14 on a plate-like (foil-like) positive electrode current collector 12. The negative electrode 20 is obtained by providing a negative electrode mixture layer 24 on a plate-like (foil-like) negative electrode current collector 22. The positive electrode mixture layer 14 and the negative electrode mixture layer 24 are in contact with both sides of the separator 18. Terminals 60 and 62 are connected to the end portions of the positive electrode current collector 12 and the negative electrode current collector 22, respectively, and the end portions of the terminals 60 and 62 extend to the outside of the case 50.

  Hereinafter, the positive electrode 10 and the negative electrode 20 are collectively referred to as an electrode, the positive electrode current collector 12 and the negative electrode current collector 22 are collectively referred to as a current collector, and the positive electrode mixture layer 14 and the negative electrode mixture layer 24 are collectively referred to. It is called a mixture layer.

First, the positive electrode 10 and the negative electrode 20 will be specifically described.
(Positive electrode)
The positive electrode 10 is obtained by providing a positive electrode mixture layer 14 on a plate-like (foil-like) positive electrode current collector 12.
(Positive electrode current collector)
The positive electrode current collector 12 may be an electronically conductive material that resists oxidation during charging and does not corrode easily. For example, a metal foil such as aluminum, stainless steel, or nickel, or a conductive resin foil can be used.
(Positive electrode mixture layer)
The positive electrode mixture layer 14 includes a positive electrode active material, a binder, and a conductive additive.

(Positive electrode active material)
The positive electrode active material is occlusion / release of lithium ions, insertion / desorption (intercalation / deintercalation), or a counter anion of the lithium ions (for example, PF ₆ ⁻ , BF ₄ ⁻ or ClO ₄ ⁻ ). There is no particular limitation as long as the doping and dedoping can proceed reversibly, and a positive electrode active material used in a known lithium ion secondary battery can be used. For example, lithium-containing metal oxide, lithium-containing metal phosphorus oxide, and the like can be given. Examples of the lithium-containing metal oxide include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), and a general formula: LiNi _x Co _y Mn _z O ₂ ( x + y + z = 1), composite metal oxide, lithium vanadium compound (LiVOPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ ), olivine-type LiMPO ₄ (where M represents Co, Ni, Mn or Fe) ) And lithium titanate (Li ₄ Ti ₅ O ₁₂ ).

Further, if the negative electrode is doped with lithium ions in advance, a positive electrode active material not containing lithium can also be used. Non-lithium-containing metal oxides (MnO ₂ , V ₂ O _5, etc.), lithium-free metal sulfides (MoS ₂ , TiS _2, etc.), lithium-free fluorides (FeF ₃ , VF _3, etc.) are also included.

(binder)
In order to adhere the positive electrode active material and the positive electrode active material, the positive electrode active material and the conductive additive, and the positive electrode active material and the current collector, a binder is added to the positive electrode mixture layer. Properties required for the binder include not being dissolved in the electrolytic solution, oxidation resistance, and good adhesion. As a binder used for the positive electrode mixture layer, polyvinylidene fluoride (PVDF) or a copolymer thereof, polytetrafluoroethylene (PTFE), polyamide (PA), polyimide (PI), polyamideimide (PAI), polybenzimidazole (PBI) ), Polyethersulfone (PES), polyacrylic acid (PA) and its copolymer, cross-linked metal ion of polyacrylic acid (PA) and its copolymer, polypropylene (PP) grafted with carboxylic anhydride, or Examples include polyethylene (PE) or a mixture thereof. Among these, PVDF is particularly preferable.

  The binder content in the positive electrode mixture layer 14 is not particularly limited, but is preferably 1% by mass to 15% by mass based on the total mass of the positive electrode active material, the conductive additive, and the binder, More preferably, the content is from 5% by mass to 5% by mass. When the amount of the binder is too small, there is a tendency that a positive electrode having sufficient adhesive strength cannot be formed. On the other hand, when the amount of the binder is too large, a general binder is electrochemically inactive and thus does not contribute to the discharge capacity, and it tends to be difficult to obtain a sufficient volume or mass energy density.

(Conductive aid)
The conductive auxiliary agent is not particularly limited as long as it improves the electronic conductivity of the positive electrode mixture layer 14, and a known conductive auxiliary agent can be used. Examples thereof include carbon materials such as carbon black, carbon nanotubes, and graphene, metal fine powders such as copper, nickel, stainless steel, and iron, conductive oxides such as ITO, and mixtures thereof.

  The content ratio of the conductive additive in the positive electrode mixture layer 14 is not particularly limited, but when adding the conductive additive, it is usually 0.5 based on the total mass of the positive electrode active material, the conductive additive and the binder. It is preferable that it is mass%-20 mass%, and it is more preferable to set it as 1 mass%-5 mass%.

(Negative electrode)
The negative electrode 20 is obtained by providing a negative electrode mixture layer 24 on a plate-like (foil-like) negative electrode current collector 22.
(Negative electrode current collector)
The negative electrode current collector 22 may be any conductive plate material, and for example, a metal foil such as copper, aluminum, nickel, stainless steel, or iron, or a conductive resin foil can be used.
(Negative electrode mixture layer)
The negative electrode mixture layer 24 includes a negative electrode active material, a binder, and a conductive auxiliary agent in an amount as necessary.

(Negative electrode active material)
The negative electrode active material is not particularly limited as long as it can reversibly advance the insertion and extraction of lithium ions and the insertion and desorption of lithium ions. The negative electrode active material used in known lithium ion secondary batteries is used. can do. For example, it combines with natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fiber (MCF), coke, glassy carbon, carbon materials such as organic compound fired bodies, lithium such as Si, SiO _x , Sn, and aluminum. Metals, alloys thereof, composite materials of these metals and carbon materials, oxides such as lithium titanate (Li ₄ Ti ₅ O ₁₂ ), SnO ₂ , and the like. Here, Si and SiO _x are described as Si-based negative electrode active materials.

The shape of the Si-based negative electrode active material is not particularly limited. In the case where the Si-based negative electrode active material is a particle, the average particle size is such that the electrochemical reaction is likely to occur (Li ⁺ is easy to be inserted into and desorbed from Si) and a thin film (thickness of several μm to several tens of μm) In consideration of easiness to make an electrode, the thickness is preferably several nm to 20 to 30 μm. In addition, an average particle diameter is a volume average particle diameter in the particle size distribution measurement by a laser beam diffraction method. The Si-based negative electrode active material may be nanowires or flakes. In the case of nanowires, the average diameter is preferably several nm to 20 to 30 μm, and the average length is preferably several μm to 20 to 30 μm. In the case of a thin piece, the thickness is preferably from several nm to 20 to 30 μm, and the diameter is preferably from several μm to 20 to 30 μm. In addition, the average diameter or average length in this invention is calculated | required from SEM (scanning electron microscope) observation.

Si-based BET method of the negative electrode active material (Brunauer, Emmett, Teller method) specific surface area by, 0.5~100m ² / g is desirable, 1-20 m ² / g is more preferable. When it is smaller than 0.5 m ² / g, an electrochemical reaction (ease of Li ⁺ being easily inserted into and desorbed from Si) hardly occurs, and when it exceeds 100 m ² / g, a Si-based negative electrode active material is converted into an electrode. If the binder is not added more than usual, it becomes difficult to form an electrode, and the capacity and energy per unit volume of the electrode decrease.

  The Si-based negative electrode active material may be crystalline or amorphous. The amorphous Si-based negative electrode active material is produced by a melt span method, a gas atomization method, or the like.

  Si in the Si-based negative electrode active material is an element having an atomic number of 14 and forms an alloy with lithium.

  Si forms alloys with various elements. The Si alloy according to the present embodiment may be any Si alloy. Elements that make an alloy with Si are Ba, Mg, Al, Ca, Ti, Sn, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, Y, Zr, Nb, Mo, Ba, W, Au etc. are mentioned.

The Si alloy may be an intermetallic compound that forms a compound at a specific ratio with Si, that is, a silicide. Silicide is Mg ₂ Si, Ca ₂ Si, CaSi ₂ Al ₂ , TiSi ₂ , Ti ₅ Si ₃ , VSi ₂ , FeSi ₂ , CoSi ₂ , Nb ₃ Ni ₂ Si, MoSi ₂ , Mo ₃ Si, Mo ₅ Si _3. , Mo ₅ SiB ₂ , and the like.

SiO _x is a fine nano-sized Si cluster dispersed in a SiO ₂ matrix.

Examples of the Si composite material include those in which the surface of Si, Si alloy or SiO _x particles is coated with a conductive material such as a carbon material, Al, Ti, Fe, Ni, Cu, Zn, Ag, or Sn. For example, the surface of the Si particles may be coated with a carbon material with a thickness of several nm, the powder coated with graphite powder having a particle size of several μm, or the carbon nanotubes may be coated.

The coating amount of the carbon material is not particularly limited, but is preferably 0.01 to 30% by mass with respect to the entire particle in which the surface of the Si, Si alloy or SiO _x particle is coated with the carbon material, 20 mass% is more preferable. Sufficient conductivity can be maintained by setting the coating amount of the carbon material to 0.01% by mass or more. As a result, the cycle characteristics when the negative electrode active material for a lithium ion secondary battery is obtained can be improved. On the other hand, when the coating amount of the carbon material exceeds 30% by mass, the ratio of the carbon material to the entire active material increases and the discharge capacity decreases.

The method for coating the surface of Si, Si alloy or SiO _x particles with a conductive material is not particularly limited. For example, a mechanical alloying method, a chemical vapor deposition method, a wet method, or a method in which a polymer is coated on the surface and then pyrolytic carbonization is exemplified.

(Lithium powder)
The lithium powder is produced in a glove box having a low dew point (from −99 ° C.) and a low oxygen concentration (from 1 ppm) circulating argon gas. This glow box is provided with an adsorption tower for adsorbing moisture and oxygen, and the dew point or oxygen concentration in the glove box can be controlled independently. The moisture and oxygen adsorption towers are filled with zeolite that mainly adsorbs moisture and oxygen, respectively. For example, zeolites mainly adsorbing water or oxygen include Zeorum A-3 and SA-600A manufactured by Tosoh Corporation. A stainless steel reaction vessel for producing lithium powder is installed in the glove box, the temperature of the reaction vessel can be controlled, and a stirring blade for stirring the reaction solution inside the reaction vessel is provided. is set up. The reaction vessel has a lid at the top, and a hole through which the column of the stirring blade passes and a supply port for carbon dioxide gas and oxygen gas for forming a coating layer are installed on the lid.

The shape of the lithium powder is not particularly limited, but a substantially spherical shape is preferable from the viewpoint of weighing accuracy and the filling rate of the lithium powder. The average particle diameter is preferably 1 μm to 100 μm from the viewpoints of ease of handling, weighing accuracy, ease of electrochemical reaction (ease of insertion and insertion of Li ⁺ into the negative electrode active material), safety, and the like. 5-50 micrometers is especially preferable.

The average particle diameter of the lithium powder according to the present embodiment is an average particle diameter when observed with an optical microscope or SEM. The average particle diameter is calculated as an equivalent circle diameter. The equivalent circle diameter is a diameter of a circle having an area equal to the projected area of the particle, and is D obtained by the following equation (3). The equivalent circle diameter was measured for 200 lithium powders, and the average value of the 200 particles was taken as the average particle diameter of the lithium powder. For the measurement of the average particle diameter, image analysis software NS2K-Pro manufactured by Nanosystem Corporation was used. In addition, lithium powder reacts with moisture, nitrogen, and carbon dioxide in the atmosphere, and its particle size and form are likely to change. Therefore, when measuring the particle size of lithium powder, lithium powder should not be exposed to the atmosphere.
^{πD 2/4 = S (3} )
Here, S is the area of the lithium powder.

The lithium powder according to this embodiment is effective when used for a negative electrode active material in which lithium ions occluded or inserted in the negative electrode active material during charging have a large amount of lithium ions that are not released or eliminated during discharge. The present invention is particularly effective when Si, Si alloy, SiO _x , Si composite material, tin, tin alloy, or the like is used as the negative electrode active material.

  The lithium powder of the present embodiment includes a core made of metallic lithium and a coating layer covering the surface of the core, the coating layer contains lithium carbonate, and lithium oxide is formed on at least a part of the surface of the lithium carbonate. Is the lithium powder present.

According to this configuration, the lithium powder has excellent storage stability in the air. The conventional lithium powder has a coating containing lithium carbonate on the surface of the metallic lithium core, whereas the lithium powder of the present application has lithium oxide on at least a part of the lithium carbonate surface on the lithium surface. doing. The effect of the lithium powder of the present application having excellent storage stability is not necessarily clear, but lithium oxide reacts with moisture as shown in the following formula (4) to become lithium hydroxide.
Thus, it is thought that there exists an effect which reacts with a water | moisture content and suppresses a water | moisture content permeating | transmitting to lithium of a core. Such a mechanism is considered to improve storage stability in the atmosphere.
_{Li 2 O + H 2 O →} 2LiOH (4)

Lithium powder reacts with moisture, carbon dioxide, nitrogen and the like at room temperature to become lithium hydroxide, lithium carbonate, and lithium nitride, respectively. That is, the lithium metal content in the lithium powder is reduced. Storage stability is measured by thermal analysis, that is, DSC (Differential Scanning Calorimetry), and the lithium metal content in the lithium powder is evaluated for storage stability. Lithium metal has a melting point of 180.54 ° C. and a heat of fusion of 3.00 KJ / mol. The lithium metal content in the lithium powder is calculated by the following formula (5).
Lithium metal content (%) = heat of fusion of sample (KJ) / (mass of sample (g) /6.941 (g / mol) × 3.00 KJ / mol) × 100 (5)
When the lithium powder is stored in a certain humidity control environment, it can be said that the storage stability is excellent if the decrease in the lithium metal content is small. The following formula (6) shows the difference in lithium metal content before and after storage in a wet atmosphere. It can be said that the smaller the difference, the better the storage stability of the lithium powder.
Difference in lithium metal content before and after storage in wet atmosphere (%) = (lithium metal content before storage (%)) − (lithium metal content after storage (%)) (6)

SEM (scanning electron microscope, model: Hitachi Ltd. SU8220) for cross-sectional observation and surface observation of lithium powder, TEM (transmission electron microscope, analytical electron microscope manufactured by JEOL Ltd., model: JEM-2100F (HR) )). Also. Surface analysis was performed using XPS (scanning X-ray photoelectron spectrometer, ULVAC-PHI Co., Ltd., model: PHIQuantera II). By performing cross-sectional observation of the lithium powder with SEM or TEM, the thickness of the lithium carbonate layer, the particle diameter of the lithium oxide particles, or the thickness of the lithium oxide layer can be determined. Further, the presence / absence of lithium hydroxide and the thickness of lithium carbide can be determined by XPS depth direction analysis.

  The coating layer includes a first coating layer present on at least a part of the core and a second coating layer present on the first coating layer, and the first coating layer contains lithium carbide. The second coating layer is preferably lithium powder containing lithium carbonate.

According to this configuration, the lithium powder has excellent storage stability in the air. Although this effect is not necessarily clear, lithium carbide reacts with moisture as shown in the following formula (7) to become lithium hydroxide. Thus, it is thought that there exists an effect which reacts with a water | moisture content and suppresses a water | moisture content permeating | transmitting to lithium of a core. Such a mechanism is considered to improve storage stability in the atmosphere.
_{Li 2 C 2 + 2H 2 O} → 2LiOH + C 2 H 2 (7)

  The second coating layer is preferably lithium powder containing lithium hydroxide.

The content of lithium hydroxide in the entire lithium powder is more preferably 0.01% by mass to 1% by mass.

  Lithium powder having a lithium metal content of 80 to 98% by mass in the lithium powder is preferred.

  According to such a configuration, the lithium powder has an effect of reducing the irreversible capacity by bringing the lithium powder and the negative electrode into contact with each other and causing an electrochemical reaction between the chemical species causing the irreversible capacity and lithium. Cheap.

  A lithium powder having a thickness of the second coating layer of 59 nm to 2060 nm is preferable. The thickness of the second coating layer is the sum of the thickness of the lithium carbonate layer and the particle diameter of the lithium oxide particles, or the sum of the thickness of the lithium carbonate layer and the thickness of the lithium oxide layer.

  Lithium powder having a thickness of the second coating layer of 59 nm to 1165 nm is more preferable.

  According to such a configuration, when the thickness of the coating is in the above range, this coating blocks moisture, carbon dioxide, nitrogen, etc. in the atmosphere, and the reaction between lithium in the core and these is suppressed, which is superior in the atmosphere. Storage characteristics are obtained.

  Moreover, the lithium powder whose thickness of said 1st coating layer is 1 nm-10 nm is preferable.

  According to such a configuration, when the thickness of the first coating layer is in the above range, this coating blocks moisture, carbon dioxide, nitrogen, etc. in the atmosphere, and the reaction between lithium in the core and these is suppressed, Better storage characteristics can be obtained in the atmosphere.

  The lithium oxide is a particle, and a lithium powder having a particle diameter of 1 nm to 2000 nm is preferable.

  The lithium oxide is a particle, and a lithium powder having a particle diameter of 1 nm to 1100 nm is more preferable.

  According to this configuration, when the particle diameter of the lithium oxide particles is in the above range, this coating blocks moisture, carbon dioxide, nitrogen, etc. in the atmosphere, and the reaction between lithium in the core and these is suppressed, and the atmosphere Excellent storage characteristics can be obtained.

  The lithium oxide is layered, and lithium powder having a thickness of 1 nm to 2000 nm is preferable.

  According to this configuration, when the thickness of the lithium oxide layer is in the above range, this coating blocks moisture, carbon dioxide, nitrogen, etc. in the atmosphere, and the reaction between lithium in the core and these is suppressed, Better storage characteristics can be obtained.

  A negative electrode for a lithium ion secondary battery in which lithium ions are doped with the lithium powder is obtained.

  The lithium ion secondary battery provided with the said negative electrode for lithium ion secondary batteries, electrolyte, and a positive electrode is obtained.

  The negative electrode active material used for the negative electrode is as described above.

  The method of doping lithium ions into the negative electrode for a lithium ion secondary battery with the lithium powder is performed as follows. First, lithium powder is supplied on the negative electrode. A normal powder supply method can be used as the supply method. That is, it is possible to crush supply, vibration supply, electrostatic spraying and the like. Secondly, the negative electrode supplied with lithium powder is pressed. This is carried out in order to fix the lithium powder on the negative electrode and to improve the contact between the negative electrode and the lithium powder. Lithium ions are doped to some extent in the negative electrode for lithium ion secondary batteries simply by pressing. The press may or may not be performed. Third, the negative electrode is combined with battery components such as a positive electrode and an electrolyte to produce a battery. By adding the electrolyte, lithium ions are sufficiently doped into the negative electrode for a lithium ion secondary battery.

  The lithium ion secondary battery provided with the said negative electrode for lithium ion secondary batteries, electrolyte, and a positive electrode is obtained.

(binder)
In order to adhere the negative electrode active material and the negative electrode active material, the negative electrode active material and the conductive additive, and the negative electrode active material and the current collector, a binder is added to the negative electrode mixture layer. Properties required for the binder include not being dissolved or extremely swollen in the electrolytic solution, being resistant to reduction, and having good adhesion. As a binder used for the negative electrode mixture layer, polyvinylidene fluoride (PVDF) or a copolymer thereof, polytetrafluoroethylene (PTFE), polyamide (PA), polyimide (PI), polyamideimide (PAI), polybenzimidazole (PBI) ), Styrene butadiene rubber (SBR), carboxymethyl cellulose, polyacrylic acid (PA) and copolymer, cross-linked metal ion of polyacrylic acid (PA) and copolymer, polypropylene grafted with carboxylic anhydride (PP) And polyethylene (PE), or a mixture thereof. Of these, polyamideimide is preferable. Polyimide is added as a precursor polyamic acid, and is heat-treated after electrode formation to become polyimide.

  Although the content rate of the binder in the negative electrode mixture layer 24 is not particularly limited, it is preferably 1% by mass to 15% by mass based on the total mass of the negative electrode active material, the conductive additive, and the binder, and is preferably 3% by mass. More preferably, it is 10 mass%. When the amount of the binder is too small, there is a tendency that a negative electrode having sufficient adhesive strength cannot be formed. Conversely, if the amount of the binder is too large, the binder is generally electrochemically inactive, so that it does not contribute to the discharge capacity, and it tends to be difficult to obtain a sufficient volume or mass energy density. Although the content rate of the conductive support agent in the negative electrode mixture layer 24 is not particularly limited, it is usually preferably 0.5% by mass to 20% by mass with respect to the active material when the conductive auxiliary agent is added. It is more preferable to set it as mass%-12 mass%.

(Conductive aid)
Conductive aids such as carbon materials used in the positive electrode described in paragraph 0039 can also be used in the negative electrode.

  Next, the manufacturing method of the electrodes 10 and 20 concerning this embodiment is demonstrated. The manufacturing method of the electrodes 10 and 20 according to this embodiment includes a step of applying a paint containing an active material, a binder, and a conductive additive on a current collector (hereinafter, also referred to as “application step”), and a collector. And a step of removing the solvent in the paint applied on the electric body (hereinafter, also referred to as “solvent removal step”).

(Coating process)
An application process for applying the paint to the current collectors 12 and 22 will be described. The paint includes an active material, a binder, a conductive aid, and a solvent. The mixing method of the components constituting the coating material such as the active material, the binder, the conductive auxiliary agent and the solvent is not particularly limited, and the mixing order is not particularly limited. For example, first, an active material and a conductive additive are dry-mixed, and a solution containing a binder is added to and mixed with the obtained mixture to prepare a paint. The active material, binder, conductive additive and solvent described above are applied to the current collectors 12 and 22. There is no restriction | limiting in particular as an application | coating method, The method employ | adopted when producing an electrode normally can be used. Examples thereof include a slit die coating method and a doctor blade method.

(Solvent removal step)
Subsequently, the solvent in the paint applied on the current collectors 12 and 22 is removed. The removal method is not particularly limited, and the current collectors 12 and 22 coated with the paint may be dried at, for example, 60 ° C. to 150 ° C. And the electrode in which the mixture layers 14 and 24 were formed in this way can be pressed with a roll press apparatus etc. as needed after that, for example, and it can be made a desired electrode density. The linear pressure of the roll press can be set to 100 to 2000 kgf / cm, for example.

  The electrode concerning this embodiment can be produced through the above process.

  Here, another component of the lithium ion secondary battery 100 using the electrode manufactured as described above will be described.

(Electrolytes)
The electrolyte is contained in the positive electrode mixture layer 14, the negative electrode mixture layer 24, and the separator 18. The electrolyte is not particularly limited. For example, in the present embodiment, an electrolyte solution containing lithium salt (an electrolyte solution using an organic solvent) can be used. As the electrolyte solution, a lithium salt dissolved in a non-aqueous solvent (organic solvent) is preferably used. Examples of the lithium salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₂ F ₅ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN A salt such as (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiN (COC ₂ F ₅ ) ₂ , LiBC ₄ O ₈ can be used. In addition, these salts may be used individually by 1 type, and may use 2 or more types together.

  Examples of the organic solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, fluoroethylene carbonate, difluoroethylene carbonate, diallyl carbonate, 2,5-dioxahexane diacid dimethyl, 2, 5 -Dioxahexane diacid diethyl, furan, 2,5-dimethylfuran, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxane, 1,4-dioxane, dimethoxymethane, dimethoxyethane, 1,2-di Ethoxyethane, diglyme, triglyme, tetraglyme, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, methyl difluoroacetate, ethyl trifluoroacetate Methyl propionate, ethyl propionate, propyl propionate, methyl formate, ethyl formate, ethyl butyrate, isopropyl butyrate, methyl isobutyrate, methyl cyanoacetate, vinyl acetate, γ-butyrolactone, γ-valerolactone, δ-valerolactone, ε -Caprolactone, γ-hexanolactone, γ-undecalactone, trimethyl phosphate, triethyl phosphate, tri-n-propyl phosphate, trioctyl phosphate, triphenyl phosphate, methoxy-nonafluorobutane, ethoxy-nonafluorobutane 1-methoxyheptafluoropropane, 2-trifluoromethyl-3-ethododecoforohexane, methyl nonafluorobutyl ether, ethyl nonafluorobutyl ether and the like are preferable. These may be used alone or in combination of two or more at any ratio.

  Further, an additive may be further added to the electrolyte. Examples of the additive include those that produce a good SEI (Solid Electrolyte Interface) on the surface of the negative electrode active material, those that produce a good SEI on the surface of the positive electrode active material, and those that are effective in preventing overcharge. Specifically, acetonitrile, propionitrile, succinonitrile, glutaronitrile, adiponitrile, pimeonitrile, suberonitrile, sebaconitrile, cyclohexylbenzene, fluorocyclohexylbenzene compound (1-fluoro-2-cyclohexylbenzene, 1-fluoro-3- Cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene), tert-butylbenzene, tert-amylbenzene, 1-fluoro-4-tert-butylbenzene, biphenyl, terphenyl (o-, m-, p-isomer), Diphenyl ether, fluorobenzene, difluorobenzene (o-, m-, p-isomer), anisole, 2,4-difluoroanisole, terphenyl partially hydride (1,2-dicyclohexylbenzene, 2 Phenylbicyclohexyl, 1,2-diphenylcyclohexane, o-cyclohexylbiphenyl), methyl isocyanate, ethyl isocyanate, butyl isocyanate, phenyl isocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 1,4-phenylene diisocyanate, 2- Isocyanatoethyl acrylate and 2-isocyanatoethyl methacrylate, 2-propynylmethyl carbonate, 2-propynyl acetate, 2-propynyl formate, 2-propynyl methacrylate, 2-propynyl methanesulfonate, 2-propynyl vinyl sulfonate, 2, -(Methanesulfonyloxy) propionic acid 2-propynyl, di (2-propynyl) oxalate, methyl 2-pro Pinyl oxalate, ethyl 2-propynyl oxalate, di (2-propynyl) glutarate, 2-butyne-1,4-diyldimethanesulfonate, 2-butyne-1,4-diyl diformate, 2,4- Hexadiyne-1,6-diyldimethanesulfonate, 1,3-propane sultone, 1,3-butane sultone, 2,4-butane sultone, 1,4-butane sultone, 1,3-propene sultone, 2,2-dioxide-1 , 2-oxathiolan-4-yl acetate, 5,5-dimethyl-1,2-oxathiolan-4-one 2,2-dioxide, etc., ethylene sulfite, hexahydrobenzo [1,3,2] dioxathiolane- 2-oxide (also called 1,2-cyclohexanediol cyclic sulfite), 5-vinyl Such as cyclic sulfites such as hexahydro-1,3,2-benzodioxathiol-2-oxide, butane-2,3-diyldimethanesulfonate, butane-1,4-diyldimethanesulfonate, methylenemethanedisulfonate, etc. Sulfonic acid ester, divinyl sulfone, 1,2-bis (vinylsulfonyl) ethane, bis (2-vinylsulfonylethyl) ether, 1,3-propane sultone, 1,3-butane sultone, 1,4-butane sultone, 2,4 -Butane sultone, 1,3-propene sultone, 2,2-dioxide-1,2-oxathiolan-4-yl acetate, 5,5-dimethyl-1,2-oxathiolan-4-one 2,2-dioxide, methylene methane Disulfonate, ethylene sulfite, and 4- (methylsulfonylmethyl) ) -1,3,2-dioxathiolane 2-oxide, butane-2,3-diyldimethanesulfonate, butane-1,4-diyldimethanesulfonate, dimethylmethane disulfonate, pentafluorophenylmethanesulfonate, divinylsulfone, And bis (2-vinylsulfonylethyl) ether, trimethyl phosphate, tributyl phosphate, and trioctyl phosphate, tris (2,2,2-trifluoroethyl) phosphate, bis (2,2,2-triphosphate) Fluoroethyl) methyl, bis (2,2,2-trifluoroethyl) ethyl phosphate, bis (2,2,2-trifluoroethyl) phosphate, 2,2-difluoroethyl phosphate, bis (2,2,2) 2-trifluoroethyl) 2,2,3,3-tetrafluoropropyl, bis (2,2-diflurate) phosphate Roethyl) 2,2,2-trifluoroethyl, bis (2,2,3,3-tetrafluoropropyl) phosphate 2,2,2-trifluoroethyl, phosphoric acid (2,2,2-trifluoroethyl) ) (2,2,3,3-tetrafluoropropyl) methyl, tris (1,1,1,3,3,3-hexafluoropropan-2-yl) phosphate, methyl methylenebisphosphonate, ethyl methylenebisphosphonate , Methyl ethylene bisphosphonate, ethyl ethylene bisphosphonate, methyl butylene bisphosphonate, ethyl butylene bisphosphonate, methyl 2- (dimethylphosphoryl) acetate, ethyl 2- (dimethylphosphoryl) acetate, methyl 2- (diethylphosphoryl) acetate, ethyl 2 -(Diethylphosphoryl) acetate, 2-propynyl 2- Dimethylphosphoryl) acetate, 2-propynyl 2- (diethylphosphoryl) acetate, methyl 2- (dimethoxyphosphoryl) acetate, ethyl 2- (dimethoxyphosphoryl) acetate, methyl 2- (diethoxyphosphoryl) acetate, ethyl 2- (diethoxy) Phosphoryl) acetate, 2-propynyl 2- (dimethoxyphosphoryl) acetate, 2-propynyl 2- (diethoxyphosphoryl) acetate, methyl pyrophosphate, ethyl pyrophosphate, acetic anhydride, propionic anhydride, or succinic anhydride, maleic anhydride 2-allyl succinic anhydride, glutaric anhydride, itaconic anhydride, 3-sulfo-propionic anhydride, methoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, phenoxype Examples include interfluorocyclotriphosphazene and ethoxyheptafluorocyclotetraphosphazene.

  In the present embodiment, the electrolyte may be a gel electrolyte obtained by adding a gelling agent in addition to the liquid. Further, instead of the electrolyte solution, a solid electrolyte (a solid polymer electrolyte or an electrolyte made of an ion conductive inorganic material) may be contained.

(Separator)
The separator 18 is an electrically insulating microporous film, for example, a single layer microporous film or a laminated microporous film made of polyethylene, polypropylene or other polyolefin, or a dry method or a wet method of the polymer mixture film. Examples thereof include a microporous membrane prepared by a method, or a nonwoven fabric made of at least one constituent material selected from the group consisting of cellulose, polyester, polyethylene, or polypropylene. Moreover, the microporous film which consists of glass fibers may be sufficient.

  A heat-resistant layer may be formed on one side or both sides of the separator. The heat-resistant layer is composed of inorganic particles such as alumina and a binder. As the binder, the binders described in paragraphs 0035 and 0073 can be used.

(Exterior body)
The exterior body 50 seals the laminated body 30 and the electrolyte solution therein. The outer package 50 is not particularly limited as long as it can prevent leakage of the electrolytic solution to the outside and entry of moisture and the like into the electrochemical device 100 from the outside. For example, as the outer package 50, as shown in FIG. 1, a metal laminate film in which a metal foil 52 is coated with a polymer film 54 from both sides can be used. As the metal foil 52, for example, an aluminum foil or a stainless steel foil can be used. The outer polymer film 54 is preferably a polymer having a high melting point such as polyethylene terephthalate (PET) or polyamide, and the inner polymer film 54 is preferably made of polyethylene (PE) or polypropylene (PP).

(Terminal)
The terminals 60 and 62 are made of a conductive material such as aluminum or nickel.

  Then, the terminals 60 and 62 are respectively welded to the positive electrode current collector 12 and the negative electrode current collector 22 by a known method, and a separator is provided between the positive electrode mixture layer 14 of the positive electrode 10 and the negative electrode mixture layer 24 of the negative electrode 20. 18 may be inserted into the outer package 50 together with the electrolyte, and the opening of the outer package 50 may be heat-sealed.

  As described above, the lithium powder, the negative electrode for the lithium ion secondary battery using the lithium powder, and the preferred embodiment of the lithium ion secondary battery using the lithium powder have been described in detail. However, the invention is limited to the embodiment. It is not something.

  For example, the negative electrode can also be used for electrochemical elements other than lithium ion secondary batteries. For example, it can be used for the negative electrode of a lithium ion capacitor. These electrochemical elements can be used for applications such as mobile phones (including smart phones), notebook personal computers, digital cameras, power tools, vehicles, and stationary power sources.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example. The production conditions of the lithium powder in each Example and Comparative Example are summarized in Table 1, and the properties of the lithium powder and the storage stability in the air are summarized in Table 2, respectively.

<Preparation of lithium powder>
Lithium powder was produced by the following method and evaluated.

Example 1
The lithium powder was produced in a glove box having a dew point of -99 ° C and an oxygen concentration of 0.01 ppm in which argon gas was circulated. 6 L of liquid paraffin and 200 g of lithium ingot were put into a stainless steel container installed in the glow box, and the stainless steel lid with a stirring blade was covered. The stainless steel container was heated with a heater, and liquid paraffin was heated to 185 ° C. to dissolve lithium. That is, the reaction solution temperature is 185 ° C. Next, the stirring blade was rotated at 10,000 rpm and held for 15 minutes. Subsequently, while rotating at 10,000 rpm, carbon dioxide gas was first supplied at an addition rate of 155 cm ³ / min for 240 seconds, and then oxygen gas was supplied at an addition rate of 1 cm ³ / min for 60 seconds. The carbon dioxide gas addition rate of 155 cm ³ / min is a rate at which the volume of carbon dioxide gas is supplied per minute in the standard state, that is, converted to 0 ° C. and 1 atm. The amount of carbon dioxide gas added at that time is 155 cm ³ / min × 4 min = 620 cm ³ . The same applies to oxygen gas. Thereafter, the rotation of the stirring blade was stopped, the reaction solution was cooled to 50 ° C., and filtered through a filter (pore size 2 μm). The lithium powder remaining on the filter was washed with hexane to remove liquid paraffin from the lithium powder. Lithium powder was transferred from the filter to a glass bottle and further sealed with an aluminum laminate bag.

<Lithium powder surface, cross-sectional observation, surface analysis, particle size measurement and thermal analysis>
The core was lithium, and the lithium surface was coated with a lithium carbonate film (thickness: 58 nm), and a film containing lithium oxide particles (particle diameter: 1 nm) was present on the lithium carbonate surface. The lithium metal content was 90% by mass. The average particle size was 25 μm. These results are summarized in Table 2.

<Storage stability of lithium powder>
A desiccator was placed in a dry room (temperature: 23 ° C., dew point −50 ° C.), and 500 cm ³ of a saturated cesium fluoride aqueous solution was placed in the desiccator. Due to the vapor pressure of the aqueous solution, the relative humidity in the desiccator was 3.8% (this state is hereinafter referred to as a humid atmosphere). A stainless steel bat was placed on the eye plate in the desiccator, 1 g of lithium powder was weighed there, and the desiccator was covered and left for 3 hours. When this lithium powder was subjected to thermal analysis, the lithium metal content was 88% by mass. Therefore, the difference in lithium metal content before and after storage in a wet atmosphere (lithium metal content before storage in a wet atmosphere−lithium metal content after storage in a wet atmosphere) was as small as 2% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

(Example 2)
In the following examples and comparative examples, the dew point, carbon dioxide supply amount, oxygen gas supply amount and reaction solution temperature were controlled as shown in Table 1, and lithium powder was produced in the same manner as in Example 1. did. In this example, everything was performed in the same manner as in Example 1 except that oxygen gas was supplied for 60 seconds at an addition rate of 12 cm ³ / min. The finished lithium powder has a lithium core as in Example 1 and a lithium carbonate coating (thickness 60 nm) on the surface of lithium, and lithium oxide particles (particle diameter 10 nm) on the surface of lithium carbonate. There was a coating to contain. The lithium metal content was 92% by mass and the average particle size was 22 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 2% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

(Example 3)
The same procedure as in Example 1 was performed except that oxygen gas was supplied at an addition rate of 55 cm ³ / min for 60 seconds. The resulting lithium powder has a lithium core as in Example 1 and a lithium carbonate coating (thickness 63 nm) on the lithium surface, and lithium oxide particles (particle diameter 115 nm) on the lithium carbonate surface. There was a coating to contain. The lithium metal content was 90% by mass and the average particle size was 26 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 2% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

Example 4
The same procedure as in Example 1 was performed except that oxygen gas was supplied at an addition rate of 400 cm ³ / min for 60 seconds. As in Example 1, the finished lithium powder has a lithium core and a lithium carbonate coating (thickness: 62 nm) on the surface of lithium, and lithium oxide particles (particle diameter: 530 nm) on the lithium carbonate surface. There was a coating to contain. The lithium metal content was 89% by mass and the average particle size was 25 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 3% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

(Example 5)
All operations were performed in the same manner as in Example 1 except that oxygen gas was supplied at an addition rate of 700 cm ³ / min for 60 seconds. The resulting lithium powder has a lithium core as in Example 1 and a lithium carbonate coating (thickness 65 nm) on the lithium surface, and lithium oxide particles (particle size 1100 nm) on the lithium carbonate surface. There was a coating to contain. The lithium metal content was 88% by mass and the average particle size was 26 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 2% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

(Example 6)
All operations were performed in the same manner as in Example 1 except that oxygen gas was supplied at an addition rate of 1300 cm ³ / min for 60 seconds. The resulting lithium powder has a lithium core as in Example 1 and a lithium carbonate coating (thickness 60 nm) on the surface of lithium, and lithium oxide particles (particle diameter 2000 nm) on the surface of lithium carbonate. There was a coating to contain. The lithium metal content was 87% by mass and the average particle size was 28 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 1% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

(Example 7)
All were performed in the same manner as in Example 1 except that oxygen gas was supplied at an addition rate of 400 cm ³ / min for 60 seconds and the reaction solution temperature was 200 ° C. The resulting lithium powder has a lithium core as in Example 1, a lithium carbide coating (thickness 1 nm) on the surface of lithium, and a lithium carbonate coating (thickness 62 nm) on the surface of lithium carbide. A film containing lithium oxide particles (particle diameter 500 nm) was present on the surface of lithium. The lithium metal content was 90% by mass and the average particle size was 22 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 2% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

(Example 8)
All were performed in the same manner as in Example 1 except that oxygen gas was supplied at an addition rate of 400 cm ³ / min for 60 seconds and the reaction solution temperature was 210 ° C. The resulting lithium powder has a lithium core as in Example 1, a lithium carbide coating (thickness 3 nm) on the surface of lithium, and a lithium carbonate coating (thickness 60 nm) on the surface of lithium carbide. A film containing lithium oxide particles (particle size 510 nm) was present on the surface of lithium. The lithium metal content was 92% by mass and the average particle size was 23 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 3% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

Example 9
All were performed in the same manner as in Example 1 except that oxygen gas was supplied at an addition rate of 400 cm ³ / min for 60 seconds and the reaction solution temperature was 220 ° C. The resulting lithium powder has a lithium core as in Example 1, a lithium carbide coating (thickness 6 nm) on the lithium surface, and a lithium carbonate coating (thickness 61 nm) on the lithium carbide surface. A film containing lithium oxide particles (particle size: 520 nm) was present on the surface of lithium. The lithium metal content was 91% by mass and the average particle size was 21 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 2% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

(Example 10)
All were performed in the same manner as in Example 1 except that oxygen gas was supplied at an addition rate of 400 cm ³ / min for 60 seconds and the reaction solution temperature was 230 ° C. The resulting lithium powder has a core of lithium as in Example 1, a lithium carbide coating (thickness 8 nm) on the surface of lithium, and a lithium carbonate coating (thickness 63 nm) on the surface of lithium carbide. A film containing lithium oxide particles (particle diameter 480 nm) was present on the surface of lithium. The lithium metal content was 90% by mass and the average particle size was 26 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 2% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

(Example 11)
All were performed in the same manner as in Example 1 except that oxygen gas was supplied at an addition rate of 400 cm ³ / min for 60 seconds and the reaction solution temperature was 240 ° C. The resulting lithium powder has a lithium core as in Example 1, a lithium carbide coating (thickness 9 nm) on the lithium surface, and a lithium carbonate coating (thickness 65 nm) on the lithium carbide surface. A film containing lithium oxide particles (particle diameter 500 nm) was present on the surface of lithium. The lithium metal content was 89% by mass and the average particle size was 25 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 3% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

(Example 12)
Except that the dew point was -65 ° C, the reaction solution temperature was 210 ° C, carbon dioxide gas was first supplied at an addition rate of 155 cm ³ / min for 550 seconds, and then oxygen gas was supplied at an addition rate of 400 cm ³ / min for 60 seconds. All were performed in the same manner as in Example 1. The resulting lithium powder has a lithium core as in Example 1, a lithium carbide coating (thickness 3 nm) on the surface of lithium, and a lithium carbonate coating (thickness 230 nm) on the surface of lithium carbide. A coating containing lithium particles (particle diameter 510 nm) and lithium hydroxide was present. The lithium metal content was 89% by mass and the average particle size was 23 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 2% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

(Example 13)
Except that the dew point was -65 ° C, the reaction solution temperature was 210 ° C, carbon dioxide gas was first supplied for 453 seconds at an addition rate of 155 cm ³ / min, and then oxygen gas was supplied for 60 seconds at an addition rate of 400 cm ³ / min. All were performed in the same manner as in Example 1. The resulting lithium powder has a lithium core as in Example 1, a lithium carbide coating (thickness 2 nm) on the surface of lithium, and a lithium carbonate coating (thickness 170 nm) on the surface of lithium carbide. A coating containing lithium particles (particle diameter 490 nm) and lithium hydroxide was present. The lithium metal content was 90% by mass and the average particle size was 22 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 3% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

(Example 14)
Except that the dew point was -65 ° C, the reaction solution temperature was 210 ° C, carbon dioxide gas was first supplied at an addition rate of 155 cm ³ / min for 348 seconds, and then oxygen gas was supplied at an addition rate of 400 cm ³ / min for 60 seconds. All were performed in the same manner as in Example 1. The finished lithium powder has a core of lithium as in Example 1, a lithium carbide coating (thickness 1 nm) on the surface of lithium, and a lithium carbonate coating (thickness 110 nm) on the surface of lithium carbide. There was a coating containing lithium particles (particle size 520 nm) and lithium hydroxide. The lithium metal content was 91% by mass and the average particle size was 25 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 2% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

(Example 15)
The dew point was -65 ° C, the reaction solution temperature was 210 ° C, carbon dioxide gas was first supplied for 240 seconds at an addition rate of 155 cm ³ / min, and then oxygen gas was supplied for 60 seconds at an addition rate of 400 cm ³ / min. All were performed in the same manner as in Example 1. The resulting lithium powder has a core of lithium as in Example 1, a lithium carbide coating (thickness 3 nm) on the surface of lithium, and a lithium carbonate coating (thickness 60 nm) on the surface of lithium carbide. A coating containing lithium particles (particle diameter 540 nm) and lithium hydroxide was present. The lithium metal content was 96% by mass and the average particle size was 21 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 3% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

(Example 16)
The dew point is -65 ° C, the reaction solution temperature is 210 ° C, carbon dioxide gas is first supplied for 120 seconds at an addition rate of 155 cm ³ / min, and then oxygen gas is supplied for 60 seconds at an addition rate of 400 cm ³ / min. All were performed in the same manner as in Example 1. The resulting lithium powder has a lithium core as in Example 1, a lithium carbide coating (thickness 3 nm) on the surface of lithium, and a lithium carbonate coating (thickness 30 nm) on the surface of lithium carbide. A coating containing lithium particles (particle diameter 500 nm) and lithium hydroxide was present. The lithium metal content was 97% by mass and the average particle size was 23 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 2% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

(Example 17)
Except that the dew point was -65 ° C, the reaction solution temperature was 210 ° C, carbon dioxide gas was first supplied at an addition rate of 155 cm ³ / min for 60 seconds, and then oxygen gas was supplied at an addition rate of 400 cm ³ / min for 60 seconds. All were performed in the same manner as in Example 1. The finished lithium powder has a core of lithium as in Example 1, a lithium carbide coating (thickness 2 nm) on the surface of lithium, and a lithium carbonate coating (thickness 10 nm) on the surface of lithium carbide. A coating containing lithium particles (particle diameter 490 nm) and lithium hydroxide was present. The lithium metal content was 98% by mass and the average particle size was 27 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as small as 1% by mass. Thus, even when stored in a humid atmosphere, the decrease in lithium metal content was small. Therefore, the lithium powder of this example has excellent storage characteristics in the air.

(Comparative Example 1)
The same procedure as in Example 1 was performed except that oxygen gas was not supplied. The finished lithium powder had a lithium core and a lithium carbonate coating (thickness 60 nm) on the surface of lithium. The lithium metal content was 90% by mass and the average particle size was 26 μm. The difference in lithium metal content before and after storage in a wet atmosphere was as large as 12% by mass. Thus, the lithium metal content decreased greatly when stored in a humid atmosphere. Therefore, the lithium powder of this comparative example did not have excellent storage characteristics in the atmosphere.

(Comparative Example 2)
The same procedure as in Example 1 was performed except that oxygen gas was first supplied for 60 seconds at an addition rate of 55 cm ³ / min, and then carbon dioxide gas was supplied for 240 seconds at an addition rate of 155 cm ³ / min. The finished lithium powder has a core of lithium and a lithium oxide coating (thickness 115 nm) on the surface of lithium, and a coating containing lithium carbonate particles (particle diameter 61 nm) is present on the lithium oxide surface. It was. The lithium metal content was 91% by mass and the average particle size was 25 μm. The difference in lithium metal content before and after storage in a humid atmosphere was as large as 11% by mass. Thus, the lithium metal content decreased greatly when stored in a humid atmosphere. Therefore, the lithium powder of this comparative example did not have excellent storage characteristics in the atmosphere.

(Example 18)
<Production of negative electrode>
Stirrers that weigh SiO _x , carbon black (manufactured by Denki Kagaku Kogyo Co., Ltd., DAB50), and 15% by weight aqueous solution of polyacrylic acid binder in 10 g, 0.231 g, and 7.584 g resin containers, respectively. A negative electrode paint was prepared by mixing with a product of Keyence Co., Ltd. (trade name: hybrid mixer). This negative electrode paint was applied to a copper foil (width 99 mm, thickness 10 μm) as a current collector by a doctor blade method, followed by drying at 110 ° C. to prepare a negative electrode having a negative electrode mixture layer on one side. The copper current collector was provided with a portion to which no paint was applied in order to weld the external lead terminal. Similarly, a negative electrode paint was applied to the other surface to prepare a negative electrode having a negative electrode mixture layer on both surfaces. This negative electrode was heat-treated at 150 ° C. for 20 hours in a vacuum atmosphere. Next, this negative electrode was pressed with a roll press so as to have a predetermined density.

<Measurement of irreversible capacity of negative electrode>
The negative electrode mixture on one side of the negative electrode prepared in paragraph (0124) was removed, and punched into a predetermined shape provided with a portion where the external lead electrode could be welded. Moreover, the copper foil which affixes lithium foil was prepared, and it punched in the predetermined shape which provided the part which can weld an external extraction electrode. The negative electrode, separator (polyethylene microporous film), lithium foil (thickness 100 μm) and the copper foil were prepared and laminated in this order. Note that the negative electrode mixture of the negative electrode and the lithium foil were opposed to each other with a separator interposed therebetween. Each of the negative electrode and the copper foil was ultrasonically welded with a nickel foil (width 4 mm, length 40 mm, thickness 100 μm) as an external lead terminal. In order to improve the sealing performance between the external terminal and the exterior body, a polypropylene film grafted with maleic anhydride was wrapped around this external lead terminal and thermally bonded. A battery outer package enclosing a battery element in which a negative electrode, a separator, a lithium foil, and a copper foil are laminated is made of an aluminum laminate material. The structure is made of polyethylene terephthalate (thickness 12 μm) / aluminum (thickness 40 μm) / polypropylene (thickness). 50 μm) was prepared. At this time, the bag was made so that the polypropylene was inside. The battery element was inserted into the outer package, an appropriate amount of electrolyte was added, and the outer package was vacuum sealed to produce a so-called half cell. The electrolyte is dissolved in a mixed solvent of fluoroethylene carbonate (abbreviated as FEC) and diethyl carbonate (abbreviated as DEC) (FEC: DEC = 30: 70 vol%) so that LiPF6 is 1 M (remark: M = moldm ⁻³ ). What was made to use was used. The half cell was charged to 5 mV at a current of 0.05 C and subsequently discharged to 2 V. The charge / discharge capacity at this time is referred to as the charge capacity of the first cycle and the discharge capacity of the first cycle. And the irreversible capacity | capacitance was calculated | required by the following Formula (8).
Irreversible capacity (mAh) = first cycle charge capacity (mAh) −first cycle discharge capacity (mAh)
(8)
Here, the C (sea) rate notation will be described. nC (mA) is a current that can charge and discharge the nominal capacity (mAh) at 1 / n (h). For example, in the case of a battery with a nominal capacity of 70 mAh, the current of 0.05 C is 3.5 mA (calculation formula 70 × 0.05 = 3.5).

<Preparation of pre-doped negative electrode>
Lithium powder produced in Example 1 was sprayed on both sides of the negative electrode prepared in paragraph (0124), and then pressed with a hand press at 20 kN to fix the lithium powder to the negative electrode. This negative electrode is called a pre-doped negative electrode. For the amount of lithium powder sprayed per unit area, a mass corresponding to the irreversible capacity per unit area of one side of the negative electrode was sprayed. The amount of application was determined by the following formula (9).
Application rate (g / cm ² ) × 3862 mAh / g × lithium metal content before storage (%) / 100
= Irreversible capacity (mAh / cm ² ) (9)

<Preparation of positive electrode>
LiNi _0.8 Co ₀ . 85 g of ₁₅ Al _0.05 O ₂ , 5 g of carbon black (manufactured by Denki Kagaku Kogyo Co., Ltd., DAB50), 5 g of graphite (manufactured by Timcal Co., Ltd., trade name: KS-6), and polyvinylidene fluoride as a binder 50 g of (PVDF) solution (manufactured by Kureha Chemical Industry Co., Ltd., trade name: KF7305, NMP solution containing 5% by mass of PVDF) was weighed in a resin container and mixed with a hybrid mixer to prepare a positive electrode paint. This positive electrode paint was applied to an aluminum foil (thickness 20 μm) as a current collector by a doctor blade method and then dried at 110 ° C. to produce a positive electrode having a positive electrode mixture layer on one side. The aluminum current collector was provided with a portion to which the positive electrode paint was not applied in order to weld the external lead terminal. Similarly, a positive electrode paint was applied to one side to produce a positive electrode having a positive electrode mixture layer on both sides. Next, this positive electrode was pressed with a roll press so as to have a predetermined density.

<Production of battery>
A pre-doped negative electrode prepared in paragraph (0126), a positive electrode prepared in paragraph (0127), and a separator (polyethylene microporous film) were prepared and cut into predetermined dimensions. Subsequently, the positive electrode, the separator, and the pre-doped negative electrode were laminated in this order. The laminate was fixed with tape so that the positive electrode, the separator, and the negative electrode were not displaced. An aluminum foil (width 4 mm, length 40 mm, thickness 100 μm) and nickel foil (width 4 mm, length 40 mm, thickness 100 μm) were ultrasonically welded to the positive electrode and the negative electrode, respectively, as external lead terminals. In order to improve the sealing performance between the external terminal and the exterior body, a polypropylene film grafted with maleic anhydride was wrapped around this external lead terminal and thermally bonded. The battery outer package enclosing the battery element in which the positive electrode, the negative electrode, and the separator are laminated is made of an aluminum laminate material, and the structure is polyethylene terephthalate (thickness 12 μm) / aluminum (thickness 40 μm) / polypropylene (thickness 50 μm). I prepared something. At this time, the bag was made so that the polypropylene was inside. The battery element is inserted into the outer package, and LiPF ₆ is dissolved in the electrolyte (a mixed solvent of FEC and DEC (FEC: DEC = 30: 70 vol%) to 1M (remark M = moldm ⁻³ )). (Ii) was added in an appropriate amount, and the outer package was vacuum-sealed to produce a lithium ion secondary battery.

(Battery test method)
Evaluation of the lithium ion secondary battery produced in the paragraph (0128) was carried out by a charge / discharge cycle test. The charge / discharge test was performed in a constant temperature bath at 25 ° C. The charge / discharge cycle test conditions were as follows. In the first cycle, the battery was charged at 0.05 C for 3 hours, and then charged at C to 0.2 V at 0.2 C. Discharge was discharged to 3.0V at 0.2C. After the second cycle, the CCCV charge was performed up to 4.2V at 0.5C and discharged to 3.0V at 1C. The CCCV charging is a charging method in which charging is first performed to a predetermined voltage with a predetermined constant current, and charging is performed until the voltage is attenuated to a predetermined current after reaching the predetermined voltage. In the current charge / discharge cycle test, the predetermined current was set to 0.05C. This charge / discharge cycle test was repeated up to 500 cycles.

  Table 3 shows capacity retention ratios obtained by standardizing the discharge capacity after 500 cycles, assuming that the discharge capacity of the first cycle is 100. The example shows a higher capacity retention rate than the comparative example. This is considered to be due to the storage stability of lithium powder in the atmosphere. Lithium powder having excellent storage stability in the air can sufficiently cause a chemical reaction between a chemical species causing irreversible capacity and lithium. However, it is considered that the lithium powder that is not excellent in storage stability cannot sufficiently cause the electrochemical reaction between the chemical species causing the irreversible capacity and lithium.

(Examples 19 to 34 and Comparative Examples 3 to 4)
Examples 19 to 34 and Comparative Example 3 were the same as Example 18, except that the lithium powder dispersed in the negative electrode mixture layer was the lithium powder obtained in Examples 2 to 17 and Comparative Examples 1 and 2. The lithium ion secondary battery of -4 was produced and the charge / discharge cycle test was done.

備考：ＮＤは検出されずの意味。

Note: ND means not detected.

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

  According to the present invention, a lithium powder excellent in storage stability in the air, a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery excellent in cycle characteristics using the lithium powder can be obtained. This is suitably used as a power source for portable electronic devices, and is also used as an electric vehicle, a household battery, and an industrial storage battery.

DESCRIPTION OF SYMBOLS 10 ... Positive electrode, 12 ... Positive electrode collector, 14 ... Positive electrode active material layer, 18 ... Separator, 20 ... Negative electrode, 22 ... Negative electrode current collector, 24 ... Negative electrode active material layer, 30 ... Laminated body, 50 ... Outer body, 62 ... Positive electrode terminal, 60 ... Negative electrode terminal, 100 ... Lithium ion secondary battery

Claims (10)

  A core made of metallic lithium; and a coating layer covering at least a part of the surface of the core, the coating layer containing lithium carbonate, and lithium oxide is present on at least a part of the surface of the lithium carbonate. Lithium powder.   The coating layer includes a first coating layer present on at least a part of the previous core and a second coating layer present on the surface of the first coating layer, the first coating layer being lithium carbide. The lithium powder according to claim 1, wherein the second coating layer contains lithium carbonate.   The lithium powder according to claim 2, wherein the second coating layer contains lithium hydroxide.   The lithium powder according to any one of claims 1 to 3, wherein a lithium content in the lithium powder is 80 to 98 mass%.   The lithium powder according to any one of claims 2 to 4, wherein a thickness of the second coating layer is 59 nm to 2060 nm.   The lithium powder according to claim 2, wherein the first coating layer has a thickness of 1 nm to 10 nm.   The lithium powder according to claim 1, wherein the lithium oxide is a particle, and the particle diameter of the particle is 1 nm to 2000 nm.   The lithium powder according to claim 1, wherein the lithium oxide is layered, and the thickness of the layer is 1 nm to 2000 nm.   The negative electrode for lithium ion secondary batteries which doped the lithium ion using the lithium powder of any one of Claims 1-8. The lithium ion secondary battery provided with the negative electrode for lithium ion secondary batteries of Claim 9, an electrolyte, and a positive electrode.

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