JP2016191101A - Stabilized lithium powder, and lithium ion secondary battery obtained by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide stabilized lithium powder which can allow the initial charge/discharge efficiency of a battery, that is obtained by using the stabilized lithium powder, to be improved and to provide a lithium ion secondary battery obtained by using the stabilized lithium powder.SOLUTION: The stabilized lithium powder has a stabilized film on the surface of a metal lithium particle, said film containing an inorganic compound and an organic polymer compound. The inorganic compound is at least one selected from a lithium compound and an inorganic solid electrolyte. The organic polymer compound is a thermoplastic polymer compound.EFFECT: Since the stabilized film contains the inorganic compound and the organic polymer compound, the density of the stabilized film is made lower than that of the stabilized film obtained by using the conventional stabilized lithium powder so that a stabilized lithium particle can be crushed by such a low press pressure that an anode is not damaged and doping of lithium ions can be performed without deteriorating the initial charge/discharge efficiency.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a stabilized lithium powder and a lithium ion secondary battery using the same.

  Lithium ion secondary batteries are widely applied as power sources for portable electronic devices because they are lighter and have a higher capacity than nickel cadmium batteries, nickel metal hydride batteries, and the like. It is also a promising candidate as a power source for use in hybrid vehicles and electric vehicles. With the recent miniaturization and higher functionality of portable electronic devices, further increase in capacity is expected for lithium ion secondary batteries that serve as these power sources.

  The capacity of the lithium ion secondary battery mainly depends on the active material of the electrode. In general, graphite is used as the negative electrode active material, but it is necessary to use a higher capacity negative electrode active material in order to meet the above requirements. Therefore, metallic silicon (Si) having a much larger theoretical capacity (4210 mAh / g) than the theoretical capacity of graphite (372 mAh / g) has attracted attention.

On the other hand, the use of silicon oxide (SiO _x ), which has better cycle characteristics than metal silicon, is also being studied. However, silicon oxide has a larger irreversible capacity than metal silicon. Since the amount of lithium that contributes to charging and discharging is uniquely determined by the amount of lithium in the positive electrode, an increase in irreversible capacity in the negative electrode leads to a decrease in capacity of the entire battery.

  In order to reduce this irreversible capacity, there has been proposed a technique (lithium pre-doping) in which metallic lithium is brought into contact with the negative electrode in advance before starting charging and discharging, and lithium is doped into the negative electrode (for example, see Patent Documents 1 and 2). ). Patent Document 1 discloses a method of doping lithium into the negative electrode by forming a film containing lithium on the negative electrode. Patent Document 2 discloses a method of doping lithium into the negative electrode by incorporating lithium particles in the negative electrode active material layer.

  Lithium used for such doping work is required to have higher safety due to its high reactivity, and the surface of lithium particles is covered with a stable coating in the atmosphere to improve safety and improve handling. Stabilized lithium powder has been proposed (see Patent Document 3).

  Usually, a negative electrode used in a lithium ion secondary battery has a step of forming a layer containing a negative electrode active material on a current collector, and then bringing it into close contact with a press, and this press exposes the lithium metal of the stabilized lithium powder. The dope into the negative electrode proceeds. Therefore, the characteristics required for the stabilized lithium powder are required not only to improve the stability of lithium but also to dope characteristics for producing excellent battery characteristics.

Japanese Patent No. 5196118 JP 2010-160986 A Japanese Patent No. 2699026

  However, even if the stabilized lithium powder described in the above-mentioned patent document is used, the deterioration of the initial charge / discharge efficiency when the battery is made cannot be sufficiently improved. As a result of intensive studies, the present inventors have found that a defect such as a crack occurs in the negative electrode in the step of bringing the stabilized lithium powder into close contact with the press.

  This invention is made | formed in view of the subject which the said prior art has, The lithium ion secondary battery using the stabilized lithium powder which can improve the initial stage charge / discharge efficiency at the time of making a battery, and this The purpose is to provide.

  In order to solve the above-mentioned problems, the stabilized lithium powder of the present invention is characterized by having a stabilizing film containing an inorganic compound and an organic polymer compound on the surface of metallic lithium particles.

According to this, when the stabilizing film is formed of an inorganic compound and an organic polymer compound, the density of the stabilizing film is lower than that of the conventional stabilized lithium powder, so stabilization is achieved with a small press pressure that does not damage the negative electrode. Lithium particles can be crushed, and lithium can be doped without deteriorating initial charge / discharge efficiency.

  In the stabilized lithium powder of the present invention, it is preferable that the inorganic compound further contains at least one selected from a lithium compound or an inorganic solid electrolyte.

In the stabilized lithium powder of the present invention, it is preferable that the lithium compound further contains at least one selected from Li ₂ O, Li ₂ CO ₃ , and LiOH.

  In the stabilized lithium powder of the present invention, the organic polymer compound is preferably a thermoplastic polymer compound.

  In the stabilized lithium powder of the present invention, the thermoplastic polymer compound further includes polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyacetal, It is preferable to include at least one selected from the group consisting of polyacrylic acid, polymethyl acrylate, polyamide, polyimide, and polyamideimide.

  In the stabilized lithium powder of the present invention, the mass part ratio of the inorganic compound and the organic polymer compound in the stabilization film is preferably 50:50 to 95: 5.

The stabilized lithium powder of the present invention preferably further has a particle size ratio of 0.2 or less. Here, when the average ferret diameter of the stabilized lithium powder is FD1, and the average ferret diameter of the inorganic compound is FD2, the particle size ratio is defined by the following formula 1. The ferret diameter is defined by the length of the long side of the rectangle that circumscribes the observation image.
Formula 1: Particle size ratio = FD2 / FD1

  In the stabilized lithium powder of the present invention, the area ratio occupied by the organic polymer compound in the cross section of the stabilizing film is preferably 5% or more and 50% or less.

  In the stabilized lithium powder of the present invention, it is preferable that the stabilizing film ratio of the stabilizing film to the entire stabilized lithium powder is 1% by mass or more and 10% by mass or less.

  In this way, by including an organic polymer compound in the stabilization film, the stabilization film has a lower density than the stabilized lithium powder made of inorganic compounds only, and is stabilized easily. Lithium powder can be obtained. Furthermore, the use of this stabilized lithium powder can improve the initial charge / discharge efficiency of the lithium ion secondary battery.

  ADVANTAGE OF THE INVENTION According to this invention, the stabilized lithium powder which can improve the initial stage charge / discharge efficiency at the time of making a battery, and a lithium ion secondary battery using the same can be provided.

It is a schematic cross section of the stabilized lithium powder of this embodiment. It is a schematic cross section of the lithium ion secondary battery of this embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined.

<Stabilized lithium powder>
The stabilized lithium powder of this embodiment is characterized by having a stabilizing film containing an inorganic compound and an organic polymer compound on the surface of metallic lithium particles.

Examples of the inorganic compound include lithium compounds and inorganic solid electrolytes, and examples of the lithium compound include Li ₂ O, Li ₂ CO ₃ , and LiOH.

The inorganic solid electrolyte is preferably a solid electrolyte of an oxide, sulfide, nitride, or phosphate compound of at least one element selected from the group consisting of Ti, Al, La, Zr, Ge, and Si. For example, β-alumina, ZrO _x , LaO _x , TiO _x , GeO _x , LiZnGeO (LISICON), LiAlTiPO ₄ (LATP), LiLaZrO (LLZ), LiPO ₄ N (LiPON), Li ₂ O—Si ₂ O, Li ₂ S—Ge ₂ S, Li ₂ S—P ₂ S _{5 and the} like.

  The organic polymer compound is preferably a thermoplastic polymer compound, for example, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, Examples thereof include polyvinyl alcohol, polyacetal, polyacrylic acid, polymethyl acrylate, polyamide, polyimide, polyamideimide and the like.

  The mass part ratio of the inorganic compound to the organic polymer compound is preferably 50:50 to 95: 5, and preferably 80:20 to 95: 5, from the viewpoint of the density of the stabilization film and storage stability. More preferred.

  In addition, the particle size ratio (FD2 / FD1) of the stabilized lithium powder is preferably 0.2 or less, and more preferably 0.1 or less, in order to facilitate crushing of the stabilized film.

The FD1 of the stabilized lithium powder is preferably FD1 ≦ 53 μm in order to facilitate crushing of the stabilized film.

  Furthermore, the area ratio occupied by the organic polymer compound in the cross section of the stabilization film is preferably 5% or more and 50% or less from the viewpoint of the density and storage stability of the stabilization film, and is preferably 5% or more and 20% or less. It is more preferable that

  According to these, compared with the stabilization film of the stabilized lithium powder of the prior art, the above-mentioned stabilization film has a low density and is easily crushed, so that it can be doped with lithium without damaging the negative electrode. Is possible. The use of the negative electrode doped with lithium using the stabilized lithium powder improves the initial charge / discharge efficiency of the lithium ion secondary battery.

  In the stabilized lithium powder, the proportion of the stabilized film is preferably 1% by mass or more and 10% by mass or less from the viewpoint of doping efficiency.

(Method for producing stabilized lithium powder)
Next, the manufacturing method of the stabilized lithium powder of this invention is demonstrated. First, a lithium ingot is introduced into a hydrocarbon oil, heated to a temperature higher than the melting point of lithium, this molten lithium-hydrocarbon oil mixture is stirred for a sufficient time to form a dispersion, and then cooled to form a metallic lithium. Make particles.

  The lithium metal used as a raw material for producing the stabilized lithium powder of the present invention is not particularly limited as long as it is lithium in a range that does not hinder the use of the lithium ion secondary battery, and is square, granular, powdery, Metallic lithium such as foil can be used.

  Various hydrocarbon oils can be used as the hydrocarbon oil necessary for producing the stabilized lithium powder of the present invention. As used herein, hydrocarbon oils include various oily liquids consisting primarily of hydrocarbon mixtures, including mineral oils, i.e., liquid products of mineral origin with viscosity limitations recognized as oils, and therefore Including but not limited to petroleum, shale oil, paraffin oil and the like. Typical hydrocarbon oils are, for example, liquid paraffin manufactured by Sanko Chemical Co., Ltd., S type, industrial type, trade names of MORESCO: Moresco White P-40, P-55, P-60, P-70 , P-80, P-100, P-120, P-150, P-200, P-260, P-350P, High Call M series (High Call M-52, High Call M-72, High Call M, manufactured by Kaneda) -172, High Coal M-352, K Series (High Coal K-140N, High Coal K-160, High Coal K-230, High Coal K-290, High Coal K-350, and High Coal E-7. Not limited to these, any purified hydrocarbon solvent boiling above the melting point of lithium or sodium metal can be used.

  From the viewpoint of uniform dispersibility after melting, the hydrocarbon oil is preferably 1 to 30 parts by mass, more preferably 2 to 15 parts by mass when the lithium ingot is 1 part by mass.

  The temperature required to produce the stabilized lithium powder of the present invention is preferably equal to or higher than the temperature at which lithium metal melts. Specifically, it is 190 degreeC-250 degreeC, Preferably it is 195 degreeC-240 degreeC, More preferably, it is 200 degreeC-220 degreeC. If the temperature is too low, lithium is solidified, making it difficult to produce lithium powder. If the temperature is too high, vaporization may occur depending on the type of hydrocarbon oil, making it difficult to handle in production.

  The stirring ability necessary to produce the stabilized lithium powder of the present invention depends on the container size and the amount of treatment, but there is no need to limit the stirring device as long as the stirring method can obtain a desired particle size. It is possible to make fine particles with various agitators and dispersers.

  Thereafter, an inorganic compound is added to the metal lithium particles, and dry pulverization is performed by a pulverizer to obtain a stabilized lithium powder precursor in which the metal lithium particles are coated with the inorganic compound.

  Although it does not specifically limit as said inorganic compound, For example, a lithium compound and an inorganic solid electrolyte can be used. Further, the particle size ratio of the stabilized lithium powder can be controlled by changing the particle size of the inorganic compound.

  Examples of the pulverizer include an attritor device, a planetary ball mill, a vibration mill, a conical mill, and a tube mill. In dry pulverization with a ball mill, basically, particles such as steel balls collide with each other in a pulverizer, and the particles are crushed, alloyed, or amorphized. Particles are aggregated and adhered by impact action to form composite particles.

  Thereafter, the stabilized lithium powder precursor is dispersed in an organic solvent in which a high molecular organic compound is dissolved, heated and dried to remove the organic solvent, thereby forming a stabilized film containing an inorganic compound and an organic high molecular compound. The provided stabilized lithium powder was obtained.

  The heat drying is not particularly limited as long as the organic solvent evaporates. For example, when methyl ethyl ketone is used as the organic solvent, it can be dried at 100 ° C.

<Lithium-doped negative electrode>
(Method for producing lithium-doped negative electrode)
The lithium-doped negative electrode is obtained by doping the above-described stabilized lithium powder into the negative electrode at the time of preparing the negative electrode, and then completing the lithium ion secondary battery to obtain a lithium ion secondary battery with improved initial charge / discharge efficiency. The negative electrode 20 can be produced by forming a negative electrode active material layer 24 on a negative electrode current collector 22 as described later.

(Current collector for negative electrode)
The negative electrode current collector 22 may be a conductive plate material, and for example, a metal thin plate (metal foil) such as copper, nickel, an alloy thereof, or stainless steel can be used.

(Negative electrode active material layer)
The negative electrode active material layer 24 is mainly composed of a negative electrode active material, a negative electrode binder, and an amount of a negative electrode conductive additive as required.

(Negative electrode active material)
The negative electrode active material preferably has a large irreversible capacity, and examples thereof include metal silicon (Si) and silicon oxide (SiO _x ).

(Binder for negative electrode)
The negative electrode binder bonds the negative electrode active materials and the current collector 22 together with the negative electrode active materials. The binder is not particularly limited as long as the above-described bonding is possible, and examples thereof include fluorine resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). In addition to the above, for example, cellulose, styrene / butadiene rubber, ethylene / propylene rubber, polyimide resin, polyamideimide resin, or the like may be used as the binder. Alternatively, an electron conductive conductive polymer or an ion conductive conductive polymer may be used as the binder. Examples of the electron conductive conductive polymer include polyacetylene. In this case, since the binder also exhibits the function of the conductive assistant particles, it is not necessary to add the conductive assistant. As the ion-conductive conductive polymer, for example, those having ion conductivity such as lithium ion can be used. For example, polymer compounds (polyether-based polymer compounds such as polyethylene oxide and polypropylene oxide) , Polyphosphazene, etc.) and a lithium salt such as LiClO ₄ , LiBF ₄ , LiPF ₆ , or an alkali metal salt mainly composed of lithium, and the like. Examples of the polymerization initiator used for the combination include a photopolymerization initiator or a thermal polymerization initiator that is compatible with the above-described monomer.

  The content of the binder in the negative electrode active material layer 24 is not particularly limited, but when added, it is preferably 0.5 to 5% by mass with respect to the mass of the positive electrode active material.

(Conductive aid for negative electrode)
The conductive aid for the negative electrode is not particularly limited as long as it improves the conductivity of the negative electrode active material layer 24, and a known conductive aid can be used. Examples thereof include carbon-based materials such as graphite and carbon black, metal fine powders such as copper, nickel, stainless steel, and iron, a mixture of carbon materials and metal fine powders, and conductive oxides such as ITO.
(Method for producing negative electrode)
The dispersion liquid in which the above stabilized lithium powder is dispersed in a solvent is applied on the negative electrode active material layer formed on the negative electrode current collector, and dried and then pressed to dope lithium into the negative electrode active material. Progresses to complete the negative electrode doped with lithium.

  As the solvent for the dispersion, those having a high vapor pressure are preferable, and examples thereof include normal heptane, normal hexane, and methyl ethyl ketone.

  The pressing method is not particularly limited, and a known method such as a hand press or a roller press can be used.

<Lithium ion secondary battery>
FIG. 2 shows a schematic cross-sectional view of the lithium ion secondary battery of the present embodiment.

  The lithium ion secondary battery 100 can be manufactured by manufacturing the lithium-doped negative electrode 20, the positive electrode 10, and the separator 18 impregnated with the electrolyte as shown in FIG. 2 as described above. Here, the positive electrode 10 can be produced by forming the positive electrode active material layer 14 on the positive electrode current collector 12. In the drawings, reference numerals 60 and 62 denote a positive electrode and a negative electrode, respectively.

<Positive electrode>
(Current collector for positive electrode)
The positive electrode current collector 12 may be a conductive plate material, and for example, a metal thin plate (metal foil) such as aluminum, an alloy thereof, or stainless steel can be used.

(Positive electrode active material layer)
The positive electrode active material layer 14 is mainly composed of a positive electrode active material, a positive electrode binder, and a necessary amount of positive electrode conductive additive.

(Positive electrode active material)
Examples of the positive electrode active material include occlusion and release of lithium ions, desorption and insertion (intercalation) of lithium ions, or doping and dedoping of lithium ions and counter anions (for example, PF6 ⁻ ) of the lithium ions. If it can be made to advance reversibly, it will not specifically limit, A well-known electrode active material can be used. For example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganese spinel (LiMn ₂ O ₄ ), and the general formula: LiNi _x Co _y Mn _z MaO ₂ (x + y + z + a = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ a ≦ 1, and M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, and Cr) Oxide, lithium vanadium compound (LiV ₂ O ₅ ), olivine type LiMPO ₄ (where M is one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr, or VO) shown), and composite metal oxides of lithium titanate _{(Li 4 Ti 5 O 12)} , LiNi x Co y Al z O 2 (0.9 <x + y + z <1.1) , etc.

(Binder for positive electrode)
There is no limitation in particular as a binder for positive electrodes, The thing similar to the binder for negative electrodes described above can be used.

(Conductive aid for positive electrode)
There is no limitation in particular as a conductive support agent for positive electrodes, The thing similar to the conductive support agent for negative electrodes described above can be used.

<Electrolyte>
The electrolyte is contained in the positive electrode active material layer 14, the negative electrode active material layer 24, and the separator 18. The electrolyte is not particularly limited, and for example, in the present embodiment, an electrolytic solution containing a lithium salt can be used.

  It is preferable to use an organic solvent that can be operated at a high voltage as the electrolytic solution, for example, an aprotic high dielectric constant solvent such as ethylene carbonate or propylene carbonate, or an acetate ester such as dimethyl carbonate or ethyl methyl carbonate. Or aprotic low-viscosity solvents such as propionates. Furthermore, it is desirable to use these aprotic high dielectric constant solvents and aprotic low viscosity solvents in combination at an appropriate mixing ratio.

Further, an ionic liquid using imidazolium, ammonium, and pyridinium type cations may be used as the organic solvent. The counter anion is not particularly limited, and examples thereof include BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ^{− and the} like, and they may be used by mixing with the above-mentioned organic solvent.

It does not specifically limit as said lithium salt, The lithium salt used as an electrolyte of a lithium ion secondary battery can be used. For example, inorganic acid anion salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiFSI, and LiBOB, organic acid anion salts such as LiCF ₃ SO ₃ , (CF ₃ SO ₂ ) ₂ NLi, and the like can be used.

  Furthermore, the concentration of the lithium salt is preferably 0.5 to 2.0 M from the viewpoint of electrical conductivity. The conductivity of the electrolyte at 25 ° C. is preferably 0.01 S / m or more, and is adjusted by the type of lithium salt or its concentration.

  When the electrolyte is a solid electrolyte or gel electrolyte, poly (vinylidene fluoride) or the like can be contained as a polymer material.

Furthermore, you may add various additives in the electrolyte solution of this embodiment as needed. Examples of additives include vinylene carbonate and methyl vinylene carbonate for the purpose of improving cycle life, biphenyl and alkyl biphenyl for the purpose of preventing overcharge, various carbonate compounds for the purpose of deoxidation and dehydration, Carboxylic anhydride, various nitrogen-containing and sulfur-containing compounds can be mentioned.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  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.

[Example 1]
(Production of stabilized lithium powder)
A stainless steel resin flask reactor was charged with 100 g of lithium ingot from Kanto Chemical Co. and Carnation hydrocarbon oil from Witco, and the inside of the vessel was replaced with dry argon. The reactor was then heated to 200 ° C. to melt the lithium. The mixture was stirred at high speed for 5 minutes in the molten state. After cooling this to room temperature, the obtained powder was washed with hexane to obtain metallic lithium particles.

To 95 parts by mass of the metal lithium particles obtained by the above method, Li ₂ O4 part by mass of FD2 of 4.8 μm is added as an inorganic compound, and rotated for 2 minutes at a rotational speed of 300 rpm / min with a ball mill under an argon atmosphere. A stabilized lithium powder precursor was obtained.

  99 parts by mass of the stabilized lithium powder precursor obtained by the above method, 1 part by mass of polystyrene as the organic polymer compound, and 200 parts by mass of methyl ethyl ketone as the solvent were mixed, and stirred for 10 hours at a rotation speed of 300 rpm / min with an overhead stirrer. Thereafter, the mixture was dried at 100 ° C. for 10 hours to obtain stabilized lithium powder.

(Preparation of negative electrode doped with lithium)
83 parts by mass of silicon oxide (SiO _x ), 2 parts by mass of acetylene black, 15 parts by mass of polyamideimide, and 100 parts by mass of N-methylpyrrolidone were mixed to prepare a slurry for forming a negative electrode active material layer. The slurry was applied to one surface of a copper foil having a thickness of 14 μm as a current collector so that the amount of the negative electrode active material applied was 2.0 mg / cm ² and dried at 100 ° C. to thereby form the negative electrode active material layer. Formed. Then, the negative electrode whose thickness of a negative electrode active material layer is 22 micrometers was obtained by pressure-molding with a roller press, and heat-processing in a vacuum at 350 degreeC for 3 hours.

A dispersion obtained by dispersing 100 parts by mass of the above stabilized lithium powder in 100 parts by mass of methyl ethyl ketone on the negative electrode obtained by the above method is applied so that the coating amount of the stabilized lithium powder becomes 0.5 mg / cm ^2. And dried at 100 ° C. Then, it pressurized by the force of 30 kN with the hand press, and lithium was doped to the negative electrode, and the negative electrode doped with lithium was obtained.

(Production of evaluation lithium-ion secondary battery)
The negative electrode doped with lithium prepared above, the counter electrode obtained by attaching a lithium metal foil to a copper foil as a counter electrode, and a separator made of a polyethylene microporous film sandwiched between them, and put in an aluminum laminate pack, this aluminum laminate pack After injecting 1M LiPF ₆ solution (solvent: ethylene carbonate / diethyl carbonate = 3/7 (volume ratio)) as an electrolytic solution, vacuum sealing was performed to produce a lithium ion secondary battery for evaluation.

<Measurement of particle size ratio>
The above methods inorganic compounds used in stabilized lithium powder and said prepared in the (Li 2 _O), was determined by observing the particles with an optical microscope. The obtained observation image was binarized, and the particle diameter was determined by image analysis. Here, the ferret diameter is defined by the length of the long side of the rectangle circumscribing the observation image.

  The above image analysis was performed on at least 500 particles, the average ferret diameter FD1 of the stabilized lithium powder and the average ferret diameter FD2 of the inorganic compound were measured, and the particle size ratio was determined.

<Measurement of area ratio>
Particles were observed using an optical microscope for an arbitrary cross section passing through the central portion of the stabilized lithium powder produced by the above method. The obtained observation image was binarized so that the inorganic compound and the organic polymer compound in the stabilization film were clearly distinguished, each area was obtained by image analysis, and the area ratio was measured. Here, when the area occupied by the inorganic compound is S1, and the area occupied by the organic compound is S2, the area ratio is defined by the following formula 2.
Formula 2: Area ratio (%) = {S2 / (S1 + S2)} × 100

<Measurement of Stabilized Film Ratio>
1 g of the stabilized lithium powder produced by the above method was sprayed on one surface of a copper foil having a thickness of 14 μm, and pressed and pressed by a hand press with a force of 20 kN. The copper foil is used as a negative electrode, a new copper foil is used as a positive electrode, and a separator made of a polyethylene microporous film is sandwiched between them and placed in an aluminum laminate pack. In this aluminum laminate pack, a 1M LiPF ₆ solution ( After injecting the solvent: ethylene carbonate / diethyl carbonate = 3/7 (volume ratio)), the mixture was vacuum-sealed to prepare a lithium ion secondary battery for measuring the stabilized film ratio.

About the lithium ion secondary battery for measuring the stabilized film ratio manufactured by the above method, the secondary battery charge / discharge test apparatus was used, and the voltage range was 0.005 V to 2.5 V, and discharge was performed at a current value of 100 mA. . When the discharge capacity C (mAh) obtained here is divided by the theoretical capacity 3861 mAh / g of metallic lithium, the mass w of metallic lithium in the stabilized lithium powder is obtained as shown in Equation 3.
Formula 3: w = C (mAh) / 3861 (mAh / g)
w is a value obtained by decreasing the mass W of the stabilized lithium powder by the mass of the stabilizing film that does not contribute to charge / discharge. Therefore, the difference between W and w becomes the mass of the stabilization film, and the ratio of the stabilization film is expressed by Equation 4 from this.
Formula 4: Stabilized film ratio (% by mass) = (W (g) −w (g)) / W (g) × 100
Since the stabilized lithium powder used is 1 g, the stabilized film ratio can be finally obtained from Equation 5.
Formula 5: Stabilized film ratio (% by mass) = (1−C / 3861) × 100

<Measurement of initial charge / discharge efficiency>
About the lithium ion secondary battery for evaluation produced by the above method, using a secondary battery charge / discharge test apparatus, the voltage range is 0.005 V to 2.5 V, and the current at 0.05 C is 1C = 1600 mA / h. Charging / discharging was performed with the value. This determined the initial discharge capacity. The higher the initial discharge capacity, the lower the irreversible capacity, which means that excellent doping efficiency is obtained. The initial charge / discharge efficiency is shown in Table 1 as a comparative value when the result of Comparative Example 1 using a stabilized lithium powder having a stabilized coating of only an inorganic compound, which is a prior art, is 100%.

[Example 2]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were produced using the same method as in Example 1 except that Li ₂ CO ₃ was used as the inorganic compound.

[Example 3]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were produced using the same method as in Example 1 except that LiOH was used as the inorganic compound.

[Example 4]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were prepared in the same manner as in Example 1 except that polyethylene was used as the organic polymer compound.

[Example 5]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were produced using the same method as in Example 1 except that polypropylene was used as the organic polymer compound.

[Example 6]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were prepared in the same manner as in Example 1 except that polyvinyl chloride was used as the organic polymer compound.

[Example 7]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were produced in the same manner as in Example 1 except that polyvinylidene chloride was used as the organic polymer compound.

[Example 8]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were prepared in the same manner as in Example 1 except that polyvinyl fluoride was used as the organic polymer compound.

[Example 9]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were produced in the same manner as in Example 1 except that polyvinylidene fluoride was used as the organic polymer compound.

[Example 10]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were prepared in the same manner as in Example 1 except that polytetrafluoroethylene was used as the organic polymer compound.

[Example 11]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were prepared in the same manner as in Example 1 except that polyvinyl alcohol was used as the organic polymer compound.

[Example 12]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were produced in the same manner as in Example 1 except that polyacetal was used as the organic polymer compound.

[Example 13]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were prepared in the same manner as in Example 1 except that polyacrylic acid was used as the organic polymer compound.

[Example 14]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were produced using the same method as in Example 1 except that polymethyl acrylate was used as the organic polymer compound.

[Example 15]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were prepared in the same manner as in Example 1 except that polyamide was used as the organic polymer compound.

[Example 16]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were prepared in the same manner as in Example 1 except that polyimide was used as the organic polymer compound.

[Example 17]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were prepared in the same manner as in Example 1 except that polyamideimide was used as the organic polymer compound.

[Example 18]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were used in the same manner as in Example 1 except that 2.5 parts by mass of Li ₂ O as an inorganic compound and 2.5 parts by mass of polystyrene as an organic polymer compound were used. Produced.

[Example 19]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were used in the same manner as in Example 1 except that 3.5 parts by mass of Li ₂ O as an inorganic compound and 1.5 parts by mass of polystyrene as an organic polymer compound were used. Produced.

[Example 20]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were used in the same manner as in Example 1 except that 4.75 parts by mass of Li ₂ O as an inorganic compound and 0.25 parts by mass of polystyrene as an organic polymer compound were used. Produced.

[Example 21]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were prepared in the same manner as in Example 1 except that 5 parts by mass of polystyrene was used as the organic polymer compound.

[Examples 22 to 24]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were prepared in the same manner as in Example 1 except that LiO ₂ having an FD2 of 6.5 μm to 13.1 μm was used as the inorganic compound.

[Example 25]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were produced using the same method as in Example 1 except that 90 parts by mass of metallic lithium particles and 9 parts by mass of Li ₂ O as an inorganic compound were used.

[Example 26]
Evaluation as stabilized lithium powder using the same method as in Example 1 except that 88 parts by mass of metallic lithium particles, 9.6 parts by mass of Li ₂ O as an inorganic compound, and 2.4 parts by mass of polystyrene as an organic polymer compound were used. A lithium ion secondary battery was prepared.

[Example 27]
Evaluation as stabilized lithium powder using the same method as in Example 1 except that 99 parts by mass of metallic lithium particles, 0.8 part by mass of Li ₂ O as an inorganic compound, and 0.2 parts by mass of polystyrene as an organic polymer compound were used. A lithium ion secondary battery was prepared.

[Example 28]
Stabilized lithium powder using the same method as in Example 1 except that 99.5 parts by mass of metallic lithium particles, 0.4 part by mass of Li ₂ O as an inorganic compound, and 0.1 part by mass of polystyrene as an organic polymer compound were used. A lithium ion secondary battery for evaluation was prepared.

[Example 29]
A stabilized lithium powder and a lithium ion secondary battery for evaluation were prepared using the same method as in Example 1 except that LATP was used as the inorganic compound.

  Table 1 shows the results of various tests described in Example 1 performed on the evaluation lithium ion secondary batteries of Examples 2 to 29. In Examples 1 to 3, high charge / discharge efficiency of 140% or more was shown with respect to Comparative Example 1 regardless of the type of inorganic compound, and in Examples 4 to 17 regardless of the type of organic polymer compound. As shown in Examples 1 to 17, the inorganic: organic polymer mass part ratio is 80:20, the particle size ratio is 0.1 or less, the area ratio is 20% or less, and the stabilization film ratio is 10% or less. In the case where the above condition is satisfied, all showed high charge / discharge efficiency of 140% or more with respect to Comparative Example 1.

[Comparative Example 1]
The lithium ion secondary for evaluation of Comparative Example 1 was evaluated in the same manner as in Example 1 except that stabilized lithium powder (trade name: SLMP) having a stabilized coating composed only of an inorganic compound of FMC was used as the stabilized lithium particles. When the battery was produced and the various tests described in Example 1 were performed, as shown in Table 1, results inferior to those of the Examples were obtained. This is because defects such as cracks were generated in the negative electrode in the step of bringing the stabilized lithium powder into close contact with the press because the film was formed only from the inorganic compound.

[Comparative Example 2]
According to the method of Example 1, using Li ₂ O5 parts by mass as an inorganic compound, using the obtained stabilized lithium precursor, a stabilized lithium powder and a lithium ion secondary battery for evaluation were prepared. As shown in Table 1, results inferior to those of the examples were obtained. This is because, as in Comparative Example 1, since the film was formed only with the inorganic compound, defects such as cracks were generated in the negative electrode in the step of bringing the stabilized lithium powder into close contact with the press.

[Comparative Example 3]
In the method of Example 1, a stabilized lithium powder and an evaluation lithium ion secondary battery were prepared by directly coating a stabilized lithium precursor with 10 parts by mass of polystyrene as an organic polymer compound without using an inorganic compound. When various tests described in Example 1 were performed, results inferior to those of the Examples were obtained as shown in Table 1. The stabilization film formed only with organic polymer compounds easily allows moisture and oxygen to pass through, and the metal lithium inside the stabilized lithium powder has reacted with moisture and oxygen during the doping process. This is because the proportion of metallic lithium occupied decreases and sufficient doping to the negative electrode has not progressed.

  By using the negative electrode doped with the stabilized lithium powder of the present invention, a lithium ion secondary battery with improved initial charge / discharge efficiency can be provided.

DESCRIPTION OF SYMBOLS 1 ... Metallic lithium, 2 ... Inorganic compound, 3 ... Organic polymer compound, 4 ... Stabilization film, 10 ... Positive electrode, 12 ... Positive electrode collector, 14 ... Positive electrode active material layer, 18 ... Separator, 20 ... Negative electrode, 22 DESCRIPTION OF SYMBOLS ... Negative electrode collector, 24 ... Negative electrode active material layer, 30 ... Laminated body, 50 ... Case, 60, 62 ... Lead, 100 ... Lithium ion secondary battery.

Claims (10)

  Stabilized lithium powder having a stabilized film containing an inorganic compound and an organic polymer compound on the surface of metallic lithium particles.   The stabilized lithium powder according to claim 1, wherein the inorganic compound contains at least one selected from a lithium compound or an inorganic solid electrolyte. The stabilized lithium powder according to claim 2, wherein the lithium compound contains at least one selected from Li ₂ O, Li ₂ CO ₃ , and LiOH.   The stabilized lithium powder according to any one of claims 1 to 3, wherein the organic polymer compound is a thermoplastic polymer compound.   The thermoplastic polymer compound is polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyacetal, polyacrylic acid, polymethyl acrylate, polyamide 5. The stabilized lithium powder according to claim 4, comprising at least one selected from the group consisting of polyimide, polyamideimide and polyamideimide.   The stabilized lithium according to any one of claims 1 to 5, wherein a mass part ratio of the inorganic compound and the organic polymer compound in the stabilization film is 50:50 to 95: 5. powder. The stabilized lithium powder according to any one of claims 1 to 6, wherein a particle size ratio of the stabilized lithium powder is 0.2 or less. However, when the average ferret diameter of the stabilized lithium powder is FD1, and the average ferret diameter of the inorganic compound is FD2, the particle size ratio is defined by the following formula 1.
Formula 1: Particle size ratio = FD2 / FD1   The stabilized lithium powder according to any one of claims 1 to 7, wherein an area ratio occupied by the organic polymer compound in a cross section of the stabilizing film is 5% or more and 50% or less.   The stabilization film according to any one of claims 1 to 8, wherein the stabilization film ratio of the stabilization film to the entire stabilized lithium powder is 1 mass% or more and 10 mass% or less. Lithium powder. A lithium ion secondary battery comprising a negative electrode doped with the stabilized lithium powder according to any one of claims 1 to 9, a positive electrode, and an electrolyte.

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