JP5922748B1 - Olivine-type lithium silicate positive electrode active material and method for producing the same - Google Patents

Abstract

An olivine type lithium silicate positive electrode active material for obtaining a lithium ion battery capable of maintaining a high discharge capacity satisfactorily is provided. An olivine lithium silicate compound obtained by subjecting a lithium compound, a silicate compound, and a metal (M) compound to a hydrothermal reaction is converted into a bromoacetonitrile-containing solution or a tetrafluoroborate nitronium tetrachloride-containing acetonitrile solution. An olivine-type lithium silicate positive electrode active material having an amorphous structure, wherein lithium is extracted by dipping in and having the following structure (A): LiaMSiO4 (A). [Selection] Figure 1

Description

  The present invention relates to an olivine-type lithium silicate positive electrode active material having an amorphous structure capable of exhibiting excellent battery characteristics and a method for producing the same.

  A secondary battery such as a lithium ion battery is a kind of non-aqueous electrolyte battery, and is used in a wide range of fields such as a mobile phone, a digital camera, a notebook PC, a hybrid vehicle, and an electric vehicle. Lithium ion batteries mainly use lithium metal oxide as a positive electrode material and a carbon material such as graphite as a negative electrode material.

There are many known positive electrode materials such as lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMnO ₂ ), lithium iron phosphate (LiFePO ₄ ), and lithium iron silicate (Li ₂ FeSiO ₄ ). Yes. Among them, so-called olivine-type lithium silicate compounds such as Li ₂ FeSiO ₄ having an olivine structure are attracting attention as excellent positive electrode materials used for high-capacity lithium ion batteries, and various developments have been made so far. Yes.

  For example, Patent Document 1 discloses a positive electrode active material containing a solid solution compound that is an olivine-type lithium silicate compound containing Co and Mn, and the raw material mixture is solidified through a plurality of firing steps of calcination and main firing. A solid solution compound is obtained by a phase reaction. Further, Patent Document 2 discloses a silicate compound obtained by mixing a raw material, heating and melting it, and then gradually cooling the melt.

JP 2007-335325 A JP 2008-218303 A

However, in the method described in Patent Document 1, not only a long time is required for production, but the resulting compound tends to increase in particle size by firing at a high temperature. In addition, since the compound obtained by the method described in Patent Document 2 is accompanied by crystallization in the cooling process, it tends to cause variation in composition and crystal type and segregation in the crystal, and when pulverizing a massive cooling product. There is a risk that a large amount of distortion is accumulated in the particles.
Therefore, when these compounds are used as a positive electrode active material to obtain a battery, there is a high possibility that the discharge capacity after the second cycle cannot be maintained well even if a high discharge capacity can be shown at the first cycle. There is a need for further improvements.

  Therefore, the subject of this invention is providing the olivine type lithium silicate positive electrode active material for obtaining the lithium ion battery which can maintain high discharge capacity favorably.

  Accordingly, the present inventors have made various studies, and by immersing an olivine-type lithium silicate compound obtained by subjecting a predetermined compound to a hydrothermal reaction in a specific liquid from which lithium can be extracted by a chemical reaction. The olivine type lithium silicate positive electrode active material having an amorphous structure thus obtained has found that a lithium ion battery capable of exhibiting an excellent discharge capacity retention rate can be obtained, and has led to the completion of the present invention. .

That is, the present invention provides an olivine-type lithium silicate compound obtained by subjecting a lithium compound, a silicate compound, and a metal (M) compound to a hydrothermal reaction, a bromoacetonitrile-containing liquid or a tetrafluoroborate nitronium-containing solution. Lithium is extracted by dipping in an acetonitrile solution, and the following formula (A):
Li _a MSiO ₄ (A)
(In the formula, M represents one or more metals selected from Fe, Mn, and Zr, and a represents a number satisfying 0.3 ≦ a ≦ 1.)
The olivine type lithium silicate positive electrode active material having an amorphous structure represented by
In addition, the present invention is obtained in the steps (I) and (I) of obtaining an olivine-type lithium silicate compound by subjecting a lithium compound, a silicate compound, and a metal (M) compound to a hydrothermal reaction. Dipping the olivine-type lithium silicate compound in a bromoacetonitrile-containing solution or a nitronium tetrafluoroborate-containing acetonitrile solution (II)
The manufacturing method of the olivine type lithium silicate positive electrode active material which has the said amorphous structure is provided.

  According to the olivine-type lithium silicate positive electrode active material of the present invention, in a lithium ion battery obtained by using this, it is possible to effectively suppress a decrease in discharge capacity every time a charge / discharge cycle passes, It is possible to maintain excellent battery characteristics.

The XRD pattern figure of the olivine type lithium silicate positive electrode active material obtained in Example 1 is shown.

Hereinafter, the present invention will be described in detail.
The olivine-type lithium silicate positive electrode active material of the present invention comprises a bromoacetonitrile-containing liquid obtained by subjecting an olivine-type lithium silicate compound obtained by subjecting a lithium compound, a silicate compound, and a metal (M) compound to a hydrothermal reaction. Or lithium is extracted by being immersed in the acetonitrile solution containing nitronium tetrafluoroborate, and the following formula (A):
Li _a MSiO ₄ (A)
(In the formula, M represents one or more metals selected from Fe, Mn, and Zr, and a represents a number satisfying 0.3 ≦ a ≦ 1.)
It has an amorphous structure.

The olivine-type lithium silicate positive electrode active material of the present invention is obtained by first subjecting a lithium compound, a silicate compound, and a metal (M) compound to a hydrothermal reaction (step (I)), and olivine as primary particles. Type lithium silicate compound is used. Specifically, for example, as a metal (M) compound, a metal sulfate represented by MSO ₄ (wherein M represents Fe, Mn, or Zr) or (R) ₂ M (wherein R Represents an organic acid residue, M represents an organic acid metal salt represented by Fe, Mn, or Zr), a basic water containing a lithium compound and a silicic acid compound, and optionally containing an antioxidant. The dispersion is reacted hydrothermally.

Examples of the lithium compound include lithium hydroxide (for example, LiOH.H ₂ O), lithium carbonate (Li ₂ CO ₃ ), lithium sulfate, and lithium acetate, and lithium hydroxide and lithium carbonate are particularly preferable. When metal sulfate (MSO ₄ ) is used as the metal (M) compound, the concentration of the lithium compound in the basic aqueous dispersion is such that the particles of the olivine type lithium silicate cathode active material of the present invention have an appropriate average particle size. From the viewpoint of firmly supporting carbon on such a surface while controlling to 0.30 to 3.00 mol / L, preferably 1.00 to 2.80 mol / L, more preferably 1.50 to 2.80 mol / L. L is more preferable.

The silicic acid compound is not particularly limited as long as it is a reactive silica compound, and amorphous silica and Na ₄ SiO ₄ (for example, Na ₄ SiO ₄ .H ₂ O) are preferable. Of these, the use of Na ₄ SiO ₄ is more preferable because the aqueous dispersion becomes basic. When metal sulfate (MSO ₄ ) is used as the metal (M) compound, the concentration of the silicate compound in the basic aqueous dispersion is controlled so that the particles of the olivine type lithium silicate positive electrode active material have an appropriate average particle size. However, from the viewpoint of firmly supporting carbon on the surface, 0.15 to 1.50 mol / L is preferable, 0.50 to 1.40 mol / L is more preferable, and 0.80 to 1.40 mol / L is preferable. Further preferred.

Furthermore, it is preferable to add an antioxidant to the basic aqueous dispersion from the viewpoint of preventing side reactions. As the antioxidant, hydrosulfite sodium (Na ₂ S ₂ O ₄ ), aqueous ammonia, sodium sulfite and the like can be used. When metal sulfate (MSO ₄ ) is used as the metal (M) compound, the content of the antioxidant in the basic aqueous dispersion increases the generation of an olivine-type lithium silicate compound as primary particles when added in a large amount. Since it suppresses, equimolar amount or less is preferable with respect to metal (M), and 0.5 or less is more preferable by molar ratio with respect to metal (M).

When metal sulfate MSO ₄ (wherein M represents Fe, Mn, or Zr) is used as the metal (M) compound, lithium compound and silica are used separately from the metal sulfate from the viewpoint of suppressing side reactions. It is preferable to prepare in advance a basic aqueous dispersion containing an acid compound. In this case, the basic aqueous dispersion, the metal sulfate and the antioxidant are mixed and subjected to a hydrothermal reaction. In the preparation of the basic aqueous dispersion, the order of addition of the lithium compound and the silicate compound is not particularly limited, and these two components may be simultaneously added to water.

Specific examples of the metal sulfate MSO ₄ include FeSO ₄ , MnSO ₄ , or Zr (SO ₄ ) _2, which may be used alone or in combination of two or more. The amount of metal sulfate (MSO ₄ ) added is from the viewpoint of firmly supporting carbon on the surface of the obtained olivine-type lithium silicate positive electrode active material and maintaining it well while exhibiting excellent discharge capacity in the battery. The total amount of the reaction mixture containing both the basic aqueous dispersion and the metal sulfate is preferably 0.15 to 1.50 mol / L, and preferably 0.50 to 1.40 mol / L. More preferred is an amount of 0.80 to 1.40 mol / L.
In this case, the Li content in the reaction mixture is preferably 2 mol or more with respect to M.

When an organic acid metal salt (R) ₂ M (wherein R represents an organic acid residue and M represents Fe, Mn, or Zr) is used as the metal (M) compound, a lithium compound, silica A basic aqueous dispersion containing an acid compound and an antioxidant and further containing an organic acid metal salt is prepared. In this case, the order of addition of the lithium compound, silicic acid compound, antioxidant and organic acid metal salt is not particularly limited. Moreover, atmospheric conditions may be sufficient. When the organic acid metal salt (R) ₂ M is used as the metal (M) compound, the concentration of the lithium compound in the basic aqueous dispersion (in the total amount of the reaction mixture) is determined by the particles of the olivine type lithium silicate cathode active material. Is controlled to an appropriate average particle diameter, while firmly supporting carbon on such a surface, while maintaining excellent discharge capacity while exhibiting excellent discharge capacity in the battery, 0.30 to 3.00 mol / L is Preferably, 1.00 to 2.80 mol / L is more preferable, and 1.50 to 2.80 mol / L is more preferable. In addition, the content of the silicate compound in the basic aqueous dispersion (in the total amount of the reaction mixture) is preferably 0.15 to 1.50 mol / L, and preferably 0.50 to 1.40 mol / L from the same viewpoint. Is more preferable, and 0.80 to 1.40 mol / L is more preferable. Further, the concentration of the antioxidant in the basic aqueous dispersion (in the total amount of the reaction mixture) suppresses the generation of the olivine-type lithium silicate compound as primary particles when added in a large amount, so that the metal (M) An equimolar amount or less is preferable with respect to the metal (M), and a molar ratio of 0.5 or less is more preferable. Usually, an organic acid salt is a raw material used in a solid phase method, but side reactions can be suppressed by using it in a hydrothermal reaction.
In this case, Li in the reaction mixture is preferably used in a molar ratio of 2 times or more with respect to the metal, and Li: M is more preferably about 2.5: 1 to 3: 1.

The organic acid represented by an organic acid metal salt (R) of ₂ M R, preferably an organic acid having 1 to 20 carbon atoms, more preferably an organic acid having 2 to 12 carbon atoms. More specific organic acids include dicarboxylic acids such as oxalic acid and fumaric acid, hydroxycarboxylic acids such as lactic acid, and fatty acids such as acetic acid. The concentration of the organic acid metal salt (R) ₂ M in the basic aqueous dispersion (in the total amount of the reaction mixture) allows the carbon to be firmly supported on the surface of the obtained olivine type lithium silicate positive electrode active material and is excellent in the battery. From the viewpoint of maintaining a good discharge capacity while maintaining a good discharge capacity, 0.15 to 1.50 mol / L is preferable, 0.5 to 1.40 mol / L is more preferable, and 0.80 to 1.40 mol / L. Is more preferable.

Making the aqueous dispersion basic is important in preventing side reactions and dissolving the silicate compound. Specifically, the pH of the basic aqueous dispersion is 12.0 to 13.5 to prevent side reactions (formation of Fe ₃ O ₄ ), solubility of silicate compounds, and progress of the reaction. Is particularly preferable. The pH of the basic aqueous dispersion may be adjusted by adding a base such as sodium hydroxide, but it is particularly preferable to use Na ₄ SiO ₄ as the silicate compound.

  Hydrothermal reaction should just be 100 degreeC or more, 130-200 degreeC is preferable and 140-180 degreeC is more preferable. The hydrothermal reaction is preferably performed in a pressure-resistant vessel, and the pressure when the reaction is performed at 130 to 200 ° C is 0.3 to 1.5 MPa, and the pressure when the reaction is performed at 140 to 180 ° C is 0.4 to 1.0 MPa. The hydrothermal reaction time is preferably 1 to 24 hours, more preferably 3 to 12 hours.

  By the hydrothermal reaction, an olivine type lithium silicate compound is obtained as a primary particle in high yield, and its crystallinity is also high. The average particle diameter of such particles is preferably 10 to 500 nm, more preferably 10 to 100 nm, from the viewpoint of improving the battery characteristics of the lithium ion battery.

  The obtained olivine-type lithium silicate compound (primary particles) can be isolated by filtering after washing and then drying. Examples of the drying means include spray drying, box drying, fluidized bed drying, external heat drying, freeze drying, and vacuum drying. Of these, freeze-drying is preferred. Moreover, when drying, it is preferable to use a slurry prepared in advance using primary particles. The content (solid content concentration) of the olivine-type lithium silicate compound in the slurry is preferably 20 to 60% by mass from the viewpoint of obtaining an olivine-type lithium silicate positive electrode active material capable of favorably supporting carbon on the surface. More preferably, it is 30-50 mass%, More preferably, it is 35-45 mass%.

At this time, a small amount of a dispersant or a thickener may be added to the slurry, and as the dispersant, for example, a polycarboxylic acid type, a polyether type, a polyacrylic acid type, or the like can be used.
As the thickener, for example, a base such as sodium hydroxide, lithium hydroxide or ammonia, or an organic acid such as acetic acid or citric acid can be used.

  The dried product thus obtained may be classified with a separator, cyclone, sieve or the like during or after drying, or may be pulverized with a mortar pin mill, roll mill, crusher or the like.

  The average particle size of the obtained olivine-type lithium silicate compound is preferably 3 to 150 μm, more preferably 3 to 100 μm, and further preferably 5 to 50 μm from the viewpoint of favorably supporting carbon on the surface. is there.

  Next, the obtained olivine-type lithium silicate compound (primary particles) is immersed in a bromoacetonitrile-containing solution or a nitronium tetrafluoroborate-containing acetonitrile solution. The bromoacetonitrile-containing liquid to be used is obtained by using acetonitrile as a solvent and bromine as a solvent, and any liquid containing bromoacetonitrile may be used, and such bromoacetonitrile is ionized in the bromoacetonitrile-containing liquid. It may be present as a salt. Furthermore, in addition to acetonitrile, it may contain a polar solvent miscible with acetonitrile, such as ethanol. For example, the content of bromoacetonitrile in the bromoacetonitrile-containing liquid is preferably 0.001 to 10 mol / L, more preferably 0.01 to 5 mol / L, in terms of bromine atom, in the bromoacetonitrile-containing liquid. More preferably, it is 0.1-3 mol / L.

  The nitronium tetrafluoroborate-containing acetonitrile solution used is obtained by dissolving nitronium tetrafluoroborate in acetonitrile as a solvent. Such nitronium tetrafluoroborate may be ionized in the acetonitrile solution and exist as a salt. You may do it. Further, in addition to acetonitrile, the solvent may contain a polar solvent miscible with acetonitrile, such as ethanol. For example, the content of nitronium tetrafluoroborate in the acetonitrile solution containing nitronium tetrafluoroborate is preferably 0.001 to 10 mol / L in terms of tetrafluoroboric acid in the acetonitrile solution containing nitronium tetrafluoroborate. More preferably, it is 0.01-5 mol / L, More preferably, it is 0.1-3 mol / L.

  The mass ratio of the olivine-type lithium silicate compound and the bromoacetonitrile-containing liquid as primary particles (olivine-type lithium silicate compound: bromoacetonitrile-containing liquid) or the olivine-type lithium silicate compound and tetra The mass ratio of the nitronium fluoroborate-containing acetonitrile solution (olivine-type lithium silicate compound: nitronium tetrafluoroborate-containing acetonitrile solution) is preferably 1: 2 to 1: 300, more preferably 1: 5 to 1: 1. 200.

  The temperature of the bromoacetonitrile-containing liquid or the nitronium tetrafluoroborate-containing acetonitrile solution at the time of immersion is preferably 5 to 50 ° C, more preferably 10 to 40 ° C. Moreover, the time to immerse becomes like this. Preferably it is 1-48 hours, More preferably, it is 6-36 hours.

  It is preferable to stir the olivine-type lithium silicate compound in the bromoacetonitrile-containing liquid or the nitronium tetrafluoroborate-containing acetonitrile solution. For the stirring, an apparatus such as IKA vane stirrer EUROSTAR20 digital can be used, and the stirring speed is preferably 50 to 1500 rpm, more preferably 100 to 1000 rpm.

  The obtained olivine-type lithium silicate positive electrode active material can be isolated by filtering after washing and then drying. For the cleaning, acetonitrile is preferably used. Specifically, 5 to 50 parts by mass of acetonitrile is preferably used with respect to 1 part by mass of the olivine type lithium silicate positive electrode active material. As a drying means, the same method as the above olivine type lithium silicate compound can be used, and freeze drying is particularly preferable.

The olivine-type lithium silicate positive electrode active material of the present invention obtained by immersing the olivine-type lithium silicate compound in a bromoacetonitrile-containing liquid or a nitronium tetrafluoroborate-containing acetonitrile solution is obtained by extracting lithium, (A):
Li _a MSiO ₄ (A)
(In the formula, M represents one or more metals selected from Fe, Mn, and Zr, and a represents a number satisfying 0.3 ≦ a ≦ 1.)
It is represented by Specifically, for example, the following aspects are included.
Li ₂ Fe _b Zr _c SiO ₄ (A1)
(In formula (A1), b is b = 1-2c, and c is 0 <c <0.5)
Li ₂ Fe _d Mn _1-d SiO ₄ (A2)
(In formula (A2), d is 0 ≦ d ≦ 1)
Li ₂ Fe _e Mn _f Zr _g SiO ₄ (A3)
(In the formula (A3), e and f are e + f = 1−2 g, and g is 0 <g <0.5)
Especially, the olivine type lithium silicate positive electrode active material represented by Formula (A3) is preferable from the viewpoint of maintaining excellent battery characteristics.

  The average particle diameter of the particles of the olivine type lithium silicate positive electrode active material of the present invention is preferably 1 to 100 μm, more preferably 5 to 50 μm. The tap density is preferably 0.5 g / mL or more, more preferably 0.7 g / mL or more.

  Note that the olivine-type lithium silicate positive electrode active material has an amorphous structure, for example, as shown in FIG. 1, which can be confirmed by an XRD pattern diagram. The proportion of lithium extracted effectively can be determined from the chemical composition formula, and preferably 60% based on the lithium present in the olivine-type lithium silicate compound (primary particles) obtained immediately after the hydrothermal reaction. It is above, More preferably, it is 65 to 85%.

  Then, it is preferable to carry | support carbon on the surface of the particle | grains of the olivine type lithium silicate positive electrode active material obtained by process (II) (process (III)). By doing in this way, the electron conduction area (electron conduction path) of an olivine type lithium silicate positive electrode active material will increase, and sufficient battery conductivity can be ensured and the outstanding battery characteristic can be exhibited. .

  As the treatment for supporting carbon, for example, a conductive carbon material is used as a carbon source, a slurry containing the obtained olivine-type lithium silicate positive electrode active material and a conductive carbon material is prepared, and fired after granulation Is mentioned. The slurry may appropriately contain an organic binder and an inorganic binder. By performing such treatment, a carbon thin film can be formed on the surface of the particles of the olivine type lithium silicate positive electrode active material, and more excellent battery characteristics can be exhibited.

  Examples of the conductive carbon material include glucose, polyvinyl alcohol, carboxymethyl cellulose, and carbon black.

Examples of the binder include glucose, polyvinyl alcohol and carboxymethyl cellulose which can also be used as a conductive carbon material, as well as fructose, polyethylene glycol, saccharose, starch, dextrin, citric acid and the like.
Among these, glucose, polyvinyl alcohol, and carboxymethyl cellulose are preferable, and glucose is more preferable because it functions as a carbon source by adjusting the amount used and can also be used as a conductive carbon material.

  Examples of the inorganic binder include scaly silica (silicon dioxide), silica-titania, silicon glass, colloidal silica, silica sol, and alumina sol.

  From the viewpoint of good charge / discharge capacity and economy, the amount of the conductive carbon material used in the process of preparing the slurry and firing after granulation is the particle of the olivine type lithium silicate positive electrode active material in the slurry. It is preferably 0.5 to 20 parts by mass and more preferably 2 to 10 parts by mass with respect to 100 parts by mass.

  Moreover, you may use water or an organic solvent as a solvent, and water is preferable from an economical viewpoint. The content (slurry concentration) of the olivine-type lithium silicate positive electrode active material and the conductive carbon material in the slurry is preferably 30 to 60% by mass, and more preferably 45 to 55% by mass. The slurry viscosity at 25 ° C. is preferably 3 to 3000 m · Pa, more preferably 10 to 100 m · Pa. Furthermore, the pH of the slurry is preferably adjusted to 10.5 to 11.2.

The granulation treatment is not particularly limited as long as an olivine type lithium silicate positive electrode active material having a desired particle diameter can be obtained, but is preferably by spray drying, especially by spray drying by a spray drying method. Things are optimal. The average particle size of the particles obtained after the granulation treatment is preferably 1 μm to 500 μm, and more preferably 20 μm to 50 μm.
The obtained particles are preferably fired from the viewpoint of firmly supporting carbon on the surface.

  In addition to the above granulation treatment, as a treatment for supporting carbon on the surface of the particles, for example, a method of pulverizing / compositing / mixing a mixture containing an olivine type lithium silicate cathode active material and a conductive carbon material is used May be. By performing such treatment, particles in which the positive electrode active material and the conductive carbon material are combined can be formed, and the conductivity can be further increased.

  Examples of the conductive carbon material used in the pulverization treatment include the same conductive carbon materials that can be used in the granulation treatment. Of these, carbon black is preferable, and acetylene black and ketjen black are more preferable. The addition amount of the conductive carbon material in the pulverization treatment is 0.5 to 20 parts by mass in terms of carbon atoms with respect to 100 parts by mass of the olivine type lithium silicate positive electrode active material from the viewpoint of good discharge capacity and economy. It is preferable that it is 2 to 10 parts by mass.

  The mixture containing the olivine-type lithium silicate positive electrode active material and the conductive carbon material is pulverized / composited / mixed in a dry manner. At this time, a small amount of diethylene glycol, ethanol or the like may be added as an auxiliary agent.

  As an apparatus for pulverizing / combining / mixing, an ordinary ball mill may be used, but a planetary ball mill (manufactured by Fritsch) capable of rotating and revolving is preferred, and nobilta (manufactured by Hosokawa Micron), multipurpose mixer (manufactured by Nippon Coke Industries, Ltd.). ), Or a hybridizer (manufactured by Nara Machinery Co., Ltd.), etc., as long as it can perform a mechanochemical action / combination treatment on an object to be processed.

  Examples of the container of the device used in the planetary ball mill include steel, stainless steel, and nylon, and the inner wall includes alumina brick, magnetic material, natural silica, rubber, urethane, and the like. As the ball, alumina sphere, natural silica, iron ball, zirconia ball or the like is used. The size of the ball is preferably 0.1 mm to 20 mm, more preferably 0.5 mm to 5 mm. It is preferable that the filling amount of the ball is a ratio in which the filling volume of the ball occupies 5 to 50% with respect to the internal volume of the mill to be used.

  Mixing using a planetary ball mill is performed, for example, under conditions of revolution of 50 to 800 rpm and rotation of 100 to 1,600 rpm, preferably 5 minutes to 24 hours, more preferably 0.5 to 6 hours, and further preferably 1 to 3 hours.

  After the treatment of supporting carbon on the surfaces of the particles of the olivine type lithium silicate positive electrode active material as described above, preferably under an inert gas atmosphere or under reducing conditions, preferably at 500 to 800 ° C. for 10 minutes to 24 hours. More preferably, baking is performed at 600 to 700 ° C. for 0.5 to 3 hours. By this treatment, particles in which carbon is further firmly supported on the surface of the positive electrode active material particles can be obtained. The apparatus used for firing is not particularly limited as long as the firing atmosphere and temperature can be adjusted, and any of a batch system, a continuous system, and a heating system (indirect or direct) can be used. . Examples of such an apparatus include tubular electric furnaces such as an external heat kiln and a roller hearth.

  The lithium ion battery to which the positive electrode for a lithium ion battery containing the olivine type lithium silicate positive electrode active material of the present invention can be applied is not particularly limited as long as the positive electrode, the negative electrode, the electrolytic solution, and the separator are essential components.

  Here, as long as lithium ions can be occluded at the time of charging and released at the time of discharging, the material structure is not particularly limited, and a known material structure can be used. For example, a carbon material such as lithium metal, graphite, or amorphous carbon. It is preferable to use an electrode formed of an intercalating material capable of electrochemically inserting and extracting lithium, particularly a carbon material.

  The electrolytic solution is obtained by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent that is usually used for an electrolyte solution of a lithium ion secondary battery. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones An oxolane compound or the like can be used.

The type of the supporting salt is not particularly limited, but an inorganic salt selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , a derivative of the inorganic salt, LiSO ₃ CF ₃ , LiC (SO ₃ CF ₃ ) ₂ and LiN (SO ₃ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ and LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), and organic salt derivatives It is preferable that it is at least 1 type of these.

  The separator plays a role of electrically insulating the positive electrode and the negative electrode and holding the electrolytic solution. For example, a porous synthetic resin film, particularly a polyolefin polymer (polyethylene, polypropylene) porous film may be used.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

[Example 1]
37.5 mL of ultrapure water was added to and mixed with 4.20 g of LiOH.H ₂ O and 13.98 g of Na ₄ SiO ₄ .nH ₂ O. To this aqueous dispersion, 3.92 g of FeSO ₄ .7H ₂ O, 7.93 g of MnSO ₄ .5H ₂ O, and 0.53 g of Zr (SO ₄ ) ₂ .4H ₂ O were added and mixed (pH = about 13). ).
The obtained mixed solution was put into an autoclave and subjected to a hydrothermal reaction at 150 ° C. for 12 hours. The pressure in the autoclave was 0.4 MPa. The produced crystal was filtered, and then washed with 12 parts by mass of water with respect to 1 part by mass of the crystal. The washed crystal was freeze-dried at −50 ° C. for 12 hours to obtain an olivine type lithium silicate compound (Li ₂ Fe _0.28 Mn _0.66 Zr _0.03 SiO ₄ , average particle size: 40 nm).

1.0 g of the obtained olivine-type lithium silicate compound was immersed in 100 ml of a bromoacetonitrile-containing liquid (bromoacetonitrile content: 0.3 mol / L in terms of bromine atom) at 25 ° C. for 24 hours while stirring at 200 rpm. Then, it was washed with 12 parts by mass of acetonitrile with respect to 1 part by mass of crystals. The washed crystals are freeze-dried at −50 ° C. for 12 hours, and lithium is extracted to obtain an olivine type lithium silicate positive electrode active material (Li _0.5 Fe _0.28 Mn _0.66 Zr _0.03 SiO ₄ , average particle size: 50 nm, hydrothermal reaction Immediately after that, the proportion of lithium extracted based on lithium present in the olivine-type lithium silicate compound obtained was 75%).
As will be described later, the composition of the positive electrode active material is calculated from the charge capacity of a coin-type lithium ion secondary battery manufactured using the positive electrode active material, and the lithium is also effective according to the XRD pattern diagram shown in FIG. It was confirmed that it was extracted.

  Subsequently, 8.4 g of the obtained olivine type lithium silicate positive electrode active material, 2.3 g of glucose (corresponding to 10 parts by mass as carbon amount with respect to 100 parts by mass of olivine type lithium silicate compound (primary particles)), and water 10 mL. Crushed and mixed with a planetary ball mill (medium 1 mmΦ) at 400 rpm for 1 hour, calcined at 650 ° C. for 1 hour in an argon hydrogen atmosphere (hydrogen concentration 3%), and the surface of the particles of the olivine type lithium silicate cathode active material The carbon was uniformly coated.

A positive electrode of a lithium ion secondary battery was produced using the olivine type lithium silicate positive electrode active material having carbon coated on the particle surface. Specifically, the obtained olivine-type lithium silicate positive electrode active material, ketjen black, and polyvinylidene fluoride were mixed at a weight ratio of 75:15:10, and N-methyl-2-pyrrolidone was added thereto. Were sufficiently kneaded to prepare a positive electrode slurry. The positive electrode slurry was applied to a current collector made of an aluminum foil having a thickness of 20 μm using a coating machine, and vacuum dried at 80 ° C. for 12 hours. Thereafter, it was punched into a disk shape of φ14 mm and pressed at 16 MPa for 2 minutes using a hand press to obtain a positive electrode.
Next, a coin-type lithium ion secondary battery was constructed using the positive electrode. A lithium foil punched to φ15 mm was used for the negative electrode. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 1 was used. As the separator, a known one such as a polymer porous film such as polypropylene was used. These battery components were assembled and housed in a conventional manner in an atmosphere with a dew point of −50 ° C. or lower to produce a coin-type lithium ion secondary battery (CR-2032).

[Example 2]
Similar to Example 1 except that a nitronium tetrafluoroborate-containing acetonitrile solution (nitronium tetrafluoroborate acetonitrile content: 0.3 mol / L in terms of tetrafluoroboric acid) was used instead of the bromoacetonitrile-containing solution. Thus, a coin-type lithium ion secondary battery (CR-2032) was produced.

[Comparative Example 1]
A coin-type lithium ion secondary battery (CR) was obtained in the same manner as in Example 1 except that the olivine-type lithium silicate compound obtained in Example 1 was used as a positive electrode active material without being immersed in a bromoacetonitrile-containing liquid. -2032) was produced.

<Evaluation of battery characteristics>
Using the batteries obtained in Example 1 and Comparative Example 1, constant current and constant voltage charging at a voltage of 4.3 で was performed at a current of 0.1 CA (33 mA / g), and a final voltage of 1.5 で at a current of 0.1 CA. The constant current discharge was performed. Based on the discharge capacity at the first cycle, the capacity retention rate (%) was obtained for the discharge capacity at the second to fourth cycles. In addition, all the temperatures of this test were performed at 30 degreeC.
The results are shown in Table 1.

  From the above results, since the olivine-type lithium silicate positive electrode active material used in the examples has an amorphous structure in which lithium is satisfactorily extracted, in the obtained lithium secondary battery, the first cycle It can be seen that the discharge capacity is high and the capacity retention rate after the second cycle is also high.

Claims (2)

Step (I) of obtaining an olivine-type lithium silicate compound by subjecting a lithium compound, a silicate compound, and a metal (M) compound to a hydrothermal reaction, and an olivine-type lithium silicate obtained in step (I) Step of immersing compound in bromoacetonitrile-containing solution or nitronium tetrafluoroborate-containing acetonitrile solution (II)
Comprising the following formula (A):
Li _a MSiO ₄ (A)
(In the formula, M represents one or more metals selected from Fe, Mn, and Zr, and a represents a number satisfying 0.3 ≦ a ≦ 1.)
The manufacturing method of the olivine type lithium silicate positive electrode active material which has an amorphous structure represented by these . Further comprising the step step of supporting the carbon on the surface of the resulting olivine type lithium silicate compound (II) (III), olivine-type lithium silicate positive electrode active material having an amorphous structure according to claim 1 Manufacturing method.

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