JP5744827B2 - Method for producing secondary battery positive electrode active material - Google Patents

Description

  The present invention relates to a method for producing an olivine-type silicate compound for obtaining a secondary battery positive electrode active material capable of realizing a secondary battery having excellent battery properties.

  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.

Examples of the positive electrode material include lithium cobalt oxide (LiCoO ₂ ), lithium manganate (
LiMnO ₂ ), lithium iron phosphate (LiFePO ₄ ), lithium iron silicate (Li ₂ FeS)
Various materials such as iO ₄ ) and lithium iron borate (LiFeBO ₃ ) are known. Among these, LiFePO ₄ , Li ₂ FeSiO ₄ , LiFeBO _{3 and the} like are so-called olivine type lithium compounds having an olivine structure, and in particular, the olivine type silicate compound is extremely useful as a positive electrode material for a high capacity secondary battery. (Patent Documents 1 and 2 and Non-Patent Documents 1 and 2).

JP 2001-266882 A JP 2008-186807 A

Electrochemical and Solid-State Letters 19, 12, A542-A544 (2006) GS Yuasa Technical Report June 2009, Vol. 6, No. 1, p21-26 R. Dominiko et al. Journal of Power Sources 184 (2008), P462-468

A method for producing an olivine-type silicate compound by hydrothermal reaction is a method in which a mixture of a lithium compound, a metal (M) compound and a silicate compound is hydrothermally reacted, and lithium hydroxide is used as the lithium compound. However, since lithium hydroxide is expensive and there is no inexpensive product for industrial use, it is desirable to use lithium carbonate that is inexpensive and easily available. However, the secondary battery employing the olivine-type silicate compound obtained by performing the hydrothermal reaction using lithium carbonate as a lithium source as a positive electrode material is obtained by using the olivine-type silicate compound obtained using lithium hydroxide. It has been found that the discharge capacity is reduced as compared with the secondary battery employed as the positive electrode material.
Therefore, even if it is a case where lithium carbonate is used as a lithium source, the subject of this invention is providing the manufacturing method of the positive electrode active material which shows a high discharge capacity when it is set as a secondary battery.

  Therefore, the present inventors have studied various conditions to produce a positive electrode active material exhibiting a high discharge capacity when using lithium carbonate as a lithium source to form a secondary battery. Then, a certain amount of alkali is reacted, after which a metal (M) compound and a silicate compound are added, and then a hydrothermal reaction is performed, whereby the resulting olivine-type silicate compound particles are made uniform. The present inventors have found that the discharge capacity of the used secondary battery is remarkably improved.

That is, in the present invention, after reacting an acid having an amount of hydrogen ions of 0.9 to 1.1 mol with respect to 1 mol of lithium ions of lithium carbonate, hydroxide ions with respect to 1 mol of lithium ions. A metal M, characterized in that an alkali in an amount of 0.9 to 1.1 mol is reacted, then a metal (M) compound and a silicate compound are added, and the resulting mixture is hydrothermally reacted. The present invention provides a method for producing an olivine-type silicate compound containing (M is Fe, Ni, Co, Al, Zn, Mn, V, or Zr).
The present invention also provides a method for producing a positive electrode active material for a secondary battery, characterized in that carbon is supported on the olivine-type silicate compound obtained by the above method and then fired.
The present invention also provides a method for producing a secondary battery positive electrode active material, characterized in that, in the above production method, a water-insoluble carbon-containing compound is further added to carry out a hydrothermal reaction.
Moreover, this invention provides the secondary battery which has a positive electrode containing the secondary battery positive electrode active material obtained by said manufacturing method.

  The secondary battery positive electrode active material obtained by the production method of the present invention has a high charge / discharge capacity, and is very useful as a positive electrode material for a secondary battery.

The SEM image of the olivine type | mold silicate compound obtained in Example 1 is shown. The SEM image of the olivine type | mold silicate compound obtained by the comparative example 1 is shown. The SEM image of the olivine type | mold silicate compound obtained by the comparative example 2 is shown. The SEM image of the olivine type silicate compound obtained in Reference Example 1 is shown. The X-ray-diffraction figure of the olivine type | mold silicate compound obtained in Example 1 is shown. The X-ray diffraction pattern of the olivine type silicate compound obtained in Comparative Example 1 is shown. The X-ray diffraction pattern of the olivine type silicate compound obtained in Comparative Example 2 is shown. The X-ray diffraction pattern of the olivine type silicate compound obtained in Reference Example 1 is shown. The discharge curve of the secondary battery using the olivine type silicate compound obtained in Example 1, Comparative Example 1, Comparative Example 2, and Reference Example 1 is shown.

Hereinafter, the present invention will be described in detail.
In the method for producing an olivine-type silicate compound of the present invention, lithium carbonate is used as a lithium source, and an acid having an amount of hydrogen ions of 0.9 to 1.1 mol is reacted with 1 mol of lithium ions of lithium carbonate. After that, an alkali having an amount of 0.9 to 1.1 mol of hydroxide ion was reacted with 1 mol of lithium ion, and then a metal (M) compound and a silicate compound were added. The mixture is hydrothermally reacted.

  First, an acid is reacted with lithium carbonate. The amount of acid to be added is set such that the amount of hydrogen ions is 0.9 to 1.1 mol with respect to 1 mol of lithium ions of lithium carbonate. When the acid amount is less than 0.9 mol, the removal of carbonic acid in the lithium carbonate becomes insufficient, which adversely affects the performance of the resulting olivine-type silicate compound (hereinafter also referred to as a synthesized product). On the other hand, when the amount of the acid exceeds 1.1 mol, the carbonic acid in the lithium carbonate is sufficiently removed, but the pH of the mixture is lowered, which adversely affects the performance of the composite. The amount of the acid is preferably such that the amount of hydrogen ions is 0.91 to 1.09 mol, more preferably 0.92 to 1.08 mol, and even more preferably 0.95 to 1.09 mol. The amount is 05 mol.

  The amount of lithium carbonate used is preferably 0.30 to 3.00 mol / l, more preferably 0.50 to 2.00 mol / l in terms of the concentration in the aqueous dispersion during the hydrothermal reaction, and 1.00 to 1. 50 mol / l is more preferable.

  Examples of the acid used include sulfuric acid, nitric acid, hydrochloric acid, boric acid, ascorbic acid, and organic acids having a carboxyl group such as acetic acid, citric acid, and lactic acid. Among these, sulfuric acid, nitric acid, and hydrochloric acid are more preferable.

  The reaction between lithium carbonate and acid is preferably carried out in an aqueous solution. The reaction is preferably performed at 0 ° C. to 60 ° C., more preferably at room temperature, for 10 minutes to 2 hours, and more preferably for 20 minutes to 1 hour.

  Next, an alkali with an amount of 0.9 to 1.1 mol of hydroxide ions is reacted with 1 mol of lithium ions. If the amount of alkali is less than 0.9 mole, the pH of the mixture will drop, adversely affecting the performance of the composite. If the amount of alkali exceeds 1.1 moles, the pH of the mixture will increase, adversely affecting the performance of the composite. A preferable amount of alkali is an amount such that the amount of hydroxide ions is 0.91 to 1.09 mol, more preferably 0.92 to 1.08 mol, and still more preferably 0.95 to 1.05 mol. The amount is 1.05 mol.

  Examples of the alkali used include sodium hydroxide and potassium hydroxide, and among these, sodium hydroxide is more preferable.

  After the alkali addition, the following reaction can be performed, but it is more preferable to stir for 1 minute or more.

  Next, a metal (M) compound and a silicate compound are added, and the resulting mixture is hydrothermally reacted. Here, M is Fe, Ni, Co, Al, Zn, Mn, V, or Zr.

  As the metal (M) compound, an iron compound, a manganese compound, a cobalt compound, a nickel compound, an aluminum compound, a zinc compound, a vanadium compound, or a zirconium compound may be used.

  The iron compound, manganese compound, cobalt compound, nickel compound, and zinc compound may be any divalent iron compound, divalent manganese compound, divalent cobalt compound, divalent nickel compound, or divalent zinc compound. , For example, halides such as iron halide, manganese halide, cobalt halide, nickel halide and zinc halide, sulfates such as iron sulfate, manganese sulfate, cobalt sulfate, nickel sulfate and zinc sulfate, iron oxalate, Examples thereof include organic acid salts such as iron acetate, manganese acetate, cobalt acetate, nickel acetate, and zinc acetate.

  The aluminum compound may be a trivalent compound, and examples thereof include halides such as aluminum halide, metal sulfates such as aluminum sulfate, and metal organic acid salts such as aluminum acetate and aluminum lactate. Examples of vanadium compounds include vanadium halides.

  The zirconium compound may be a tetravalent compound, and examples thereof include organic acid salts such as zirconium halide, zirconium sulfate, zirconium diacetate oxide, zirconium octoate, and zirconium laurate oxide.

  The concentration of the metal (M) compound in the reaction mixture is preferably 0.15 to 1.50 mol / l, more preferably 0.50 to 0.75 mol / l.

The silicic acid compound is not particularly limited as long as it is a reactive silica compound, and amorphous silica, Na ₄ SiO ₄ and Na ₄ SiO ₄ .nH ₂ O (for example, Na ₄ SiO ₄ .H ₂ O) can be used. preferable. Of these, the use of Na ₄ SiO ₄ is more preferable because the reaction mixture becomes basic.
The concentration of the silicate compound is preferably 0.15 to 1.50 mol / l, more preferably 0.50 to 0.75 mol / l.

The obtained mixture is preferably made into a basic aqueous dispersion using water from the viewpoint of the solubility of the silicic acid compound to prevent side reactions. Specifically, the pH of the aqueous dispersion is preferably 12.0 to 14.5. The pH of the aqueous dispersion may be adjusted by adding a base such as sodium hydroxide, but it is preferable to use Na ₄ SiO ₄ as the silicate compound.

  In producing an aqueous dispersion, as a metal (M) compound, for example, when using a metal sulfate, a silicate compound and an antioxidant are added separately from the metal sulfate in terms of suppressing side reactions. It is preferable to prepare in advance a basic aqueous dispersion. In this case, the aqueous dispersion and the metal sulfate are mixed and subjected to a hydrothermal reaction.

  For example, when an organic acid salt is used as the metal (M) compound, it is preferable to prepare a basic aqueous dispersion containing a silicic acid compound and an antioxidant and further containing an organic acid salt. 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.

Examples of the antioxidant include sodium hydrosulfite (Na ₂ S ₂ O ₄ ), aqueous ammonia, sodium sulfite and the like. The content of the antioxidant in the aqueous dispersion is preferably equal to or less than the metal (M), since the formation of the olivine-type silicate compound is suppressed when added in a large amount. More preferably, the molar ratio is 0.5 or less.

  In the present invention, a water-insoluble carbon-containing compound may be added before the mixture is hydrothermally reacted. As a result, the water-insoluble carbon-containing compound serving as the carbon source is uniformly dispersed between the primary particles of the fine olivine-type silicate compound, and then sufficient electrons are formed when the primary particles aggregate to form secondary particles. Conductivity can be ensured and a secondary battery positive electrode active material can be obtained directly.

  The water-insoluble carbon-containing compound means a carbon-containing compound that is insoluble in water (for example, the solubility in water at 25 ° C. is 0.1 g / 100 g or less). Specific examples include cellulose, lignin, chitosan, chitin, carbon nanotubes, graphene, carbon black, graphite, graphite, and synthetic fibers. These may be used alone or in combination of two or more. Especially, it is preferable that it is a compound which has a fibrous form, for example, a cellulose (crystalline cellulose), a carbon nanotube, and a synthetic fiber are mentioned as a preferable water-insoluble carbon containing compound. The amount of the water-insoluble carbon-containing compound added is 0.5 to 20% by mass in terms of carbon atoms contained in the water-insoluble carbon-containing compound in the theoretical amount of the olivine-type silicate compound obtained after the hydrothermal reaction. Is preferably added in an amount of 2 to 15% by mass.

  Further, the water-insoluble carbon-containing compound may be used after being subjected to pretreatment such as fine pulverization with a bead mill or an attritor, or fiberizing treatment.

In adding the water-insoluble carbon-containing compound, it is preferable to make a solution using a solvent from the viewpoint of improving dispersibility. The concentration of the water-insoluble carbon-containing compound in such a solution is preferably 40% by mass or less, more preferably 20% by mass or less.
Examples of the solvent include distilled water, ion-exchanged water, and the like, and it is preferable that the O ₂ concentration in the solution is 0.5 mg / L or less by deoxygenation treatment such as nitrogen aeration. A small amount of a dispersant may be added.
In addition, in order to add the water-insoluble carbon-containing compound, a mixture such as the aqueous dispersion may be added to the solution of the water-insoluble carbon-containing compound, and the solution of the water-insoluble carbon-containing compound is added to the mixture. May be. All of these are mixed and then subjected to a hydrothermal reaction.

  130-250 degreeC is preferable and the temperature at the time of attaching | subjecting to a hydrothermal reaction has more preferable 150-200 degreeC. The hydrothermal reaction is preferably performed in a pressure vessel. When the reaction is performed at 130 to 250 ° C, the pressure at this time is 0.3 to 4.0 MPa, and the pressure when the reaction is performed at 150 to 200 ° C is 0. 5 to 1.6 MPa. The hydrothermal reaction time is preferably 0.5 to 24 hours, and more preferably 3 to 12 hours.

  The preparation of the mixed solution and the hydrothermal reaction are preferably performed under non-oxygen conditions, for example, in a nitrogen atmosphere.

By the hydrothermal reaction, an olivine-type silicate compound is obtained in high yield, and its crystallinity is also high.
After the hydrothermal reaction, the produced olivine-type silicate compound is collected by filtration and washed to obtain primary particles. Washing is preferably carried out with water using a filtration device having a cake washing function.
Here, the particle size of the obtained primary particles is preferably as small as possible. The average particle size of the primary particles of the particles obtained by the present invention is preferably less than 200 nm.

Then, drying is performed. As the drying means, a box-type dryer, freeze-drying, vacuum drying, fluidized bed dryer, or spray-type dryer (spray dryer) can be used.
About the obtained dried material, you may crush using a mortar, a pin mill, a roll mill, a crusher, etc.

Examples of the olivine type silicate compound to be obtained include the following.
Li ₂ Fe _x Mn _y Co _z SiO ₄ (1)
(In the formula, x, y, and z represent numbers satisfying 0 ≦ x <1, 0 ≦ y <1, 0 <z <1, x + y + z = 1, and x + y ≠ 0.)
_{Li a1 Fe x Mn y Al z} SiO 4 ··· (2)
(Where, a1, x, y and z represent numbers satisfying 1 <a1 ≦ 2, 0 ≦ x <1, 0 ≦ y <1, 0 <z <1, a1 + 2x + 2y + 3z = 4 and x + y ≠ 0. .)
_{Li a2 Fe x Mn y V z} SiO 4 ··· (3)
(Wherein a2, x, y and z are 1 <a2 ≦ 2, 0 ≦ x <1, 0 ≦ y <1, 0 <z <1, a2 + 2x + 2y + (2-5) z = 4, and x + y ≠ Indicates a number satisfying 0.)
Li ₂ Fe _x Mn _y Zn _z SiO ₄ (4)
(In the formula, x, y, and z represent numbers satisfying 0 ≦ x <1, 0 ≦ y <1, 0 <z <1, x + y + z = 1, and x + y ≠ 0.)
Li ₂ Fe _a3 Ni _b Co _c Mn _d Zr _x1 SiO ₄ (5)
(Wherein a3, b, c and d satisfy a3 + b + c + d = 1−2 × 1 and x1 represents a number satisfying 0 <x1 <0.5)

The olivine type silicate compound may contain F or the like by doping. For example, when F is doped, the following compounds are obtained.
Li ₂ M ¹ SiO _4-x2 F _2x2 (6)
(In the formula, M ¹ represents one or more selected from Fe, Mn, Co and Ni, and x2 represents a number satisfying 0 <x2 ≦ 4.)

  Thereafter, carbon is supported on primary particles or secondary particles of the obtained olivine-type silicate compound. By doing in this way, the electron conduction area (electron conduction path) of an olivine type silicate compound will increase, and more sufficient electronic conductivity can be ensured.

  Examples of the treatment for supporting carbon include a treatment in which a slurry containing the obtained olivine-type silicate compound and a conductive carbon material is prepared and fired after granulation. 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 secondary particles formed from primary particles, and electron conductivity can be further enhanced.

  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.

  The amount of the conductive carbon material used in the process of preparing the slurry and firing after granulation is based on 100 parts by mass of the olivine-type silicate compound in the slurry from the viewpoint of good charge / discharge capacity and economy. An amount of 0.5 to 20 parts by mass in terms of carbon atoms is preferable, and an amount of 2 to 10 parts by mass is more preferable.

  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 silicate compound 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 secondary particles having a desired particle diameter can be obtained, but it is preferably by spray drying, and most preferably by spray drying by a spray drying method. . The average particle size of the secondary particles obtained after the granulation treatment is preferably 1 μm to 500 μm, and more preferably 20 μm to 50 μm.
The obtained secondary particles can then be used as a secondary battery positive electrode active material by firing.

  In addition to the above granulation process, as a process for supporting carbon, for example, a method of pulverizing / combining / mixing a mixture containing an olivine-type silicate compound and a conductive carbon material may be used. By performing such treatment, secondary particles in which the primary particles of the precursor 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 preferably 0.5 to 20 parts by mass in terms of carbon atom with respect to 100 parts by mass of the primary particles of the olivine silicate compound from the viewpoint of good discharge capacity and economy. Furthermore, 2-10 mass parts is preferable.

  The mixture containing the olivine-type silicate compound 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, a normal 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 Kogyo Co., 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.

  Firing of the secondary particles subjected to the treatment for supporting carbon as described above is preferably performed at 500 to 800 ° C. for 10 minutes to 24 hours, more preferably at 600 to 700 ° C. in an inert gas atmosphere or under reducing conditions. It is preferable to carry out for 0.5 to 3 hours. By this treatment, a positive electrode active material that is secondary particles in which carbon is further firmly supported on the surface of the olivine-type silicate compound 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 average particle diameter of the obtained secondary particles 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.

  The obtained secondary battery positive electrode active material is excellent in terms of charge / discharge capacity, and a very useful secondary battery can be obtained. The secondary battery to which the secondary battery positive electrode active material obtained by the production method of the present invention can be applied may be a lithium ion secondary battery, as long as it has a positive electrode, a negative electrode, an electrolyte, and a separator as essential components. There is no particular limitation.

  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 sort of.

  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]
Lithium carbonate 3.7 g (50 mmol), sulfuric acid 5.2 g (50 mmol) and water 80 g were stirred at room temperature for 30 minutes. To this was added 8.3 g (100 mmol) of a 50% aqueous sodium hydroxide solution. Furthermore, 2Na ₂ O.SiO ₂ .nH ₂ O 14.0 g, FeSO ₄ .7H ₂ O 8.9 g, MnSO ₄ .5H ₂ O 3.8 g, and Zr (SO ₄ ) ₂ .4H ₂ O 0.4 g Was added. The obtained aqueous dispersion was subjected to a hydrothermal reaction at 150 ° C. and 0.5 MPa for 12 hours. The reaction product was filtered, washed and lyophilized. Then H ₂ / Ar = 3% under reducing conditions, then baked 1 hour at 600 ° C., to give 8.4g of the olivine-type silicate compounds of _{Li 2 Fe 0.643 Mn 0.317 Zr 0.02} SiO 4.
The average particle diameter of the obtained primary particles was 100 nm. FIG. 1 shows an SEM image of the obtained primary particles, and FIG. 5 shows an X-ray diffraction diagram.

  To 100 g of the obtained primary particles, 22.5 g of glucose (60% aqueous solution) and 100 g of ultrapure water were added and dispersed for 3 minutes with a homogenizer to prepare a slurry. The content of primary particles of the obtained slurry was 46% by mass, the viscosity at 20 ° C. as measured with a digital viscometer was 100 mPa · s, and the pH was 10.70.

Subsequently, the obtained slurry was granulated using a spray drying apparatus (micro mist dryer equipped with a four-fluid nozzle: manufactured by Fujisaki Electric Co., Ltd.) under the following conditions, and then fired at 600 ° C. for 1 hr in a reducing atmosphere.
Air pressure: 0.6 MPa
Air flow rate: 50LN / min
Hot air volume: 1.0 m ³ / min
Inlet temperature: 180 ° C
Exhaust temperature: 100 ° C
Slurry flow rate: 60 g / min

[Comparative Example 1]
Li ₂ Fe _0.64 Mn _0.32 Zr _0.02 SiO ₄ primary particles were obtained in the same manner as in Example 1 except that the amount of the 50% NaOH aqueous solution added was 2.1 g (25 mmol). Further, carbon support was performed in the same manner as in Example 1 to obtain secondary particles.
The average particle diameter of the obtained primary particles was 300 nm. The SEM image of the obtained primary particles is shown in FIG. 2, and the X-ray diffraction diagram is shown in FIG.

[Comparative Example 2]
Except that the addition amount of sulfuric acid was 1.3 g (12.5 mmol), the same operation as in Example 1 was performed to obtain primary particles of Li ₂ Fe _0.64 Mn _0.32 Zr _0.02 SiO ₄ . Further, carbon support was performed in the same manner as in Example 1 to obtain secondary particles.
The average particle diameter of the obtained primary particles was 350 nm. FIG. 3 shows an SEM image of the obtained primary particles, and FIG. 7 shows an X-ray diffraction diagram.

[Reference Example 1]
LiOH.H ₂ O 4.2 g, 2Na ₂ O.SiO ₂ .nH ₂ O 14.0 g and 60 g of water were mixed, and this was mixed with FeSO ₄ .7H ₂ O 8.8 g and MnSO ₄ .5H ₂ O 3.8 g. Then, 0.4 g of Zr (SO ₄ ) ₂ .4H ₂ O was added to prepare an aqueous dispersion. This aqueous dispersion was subjected to a hydrothermal reaction under the same conditions as in Example 1 and then treated in the same manner to obtain primary particles of Li ₂ Fe _0.64 Mn _0.32 Zr _0.02 SiO ₄ . Further, carbon support was performed in the same manner as in Example 1 to obtain secondary particles.
The average particle diameter of the obtained primary particles was 100 nm. FIG. 4 shows an SEM image of the obtained primary particles, and FIG. 8 shows an X-ray diffraction pattern.

[Test Example 1]
Using the fired products obtained in Example 1, Comparative Examples 1 and 2 and Reference Example 1, a positive electrode of a lithium ion secondary battery was produced. The fired product obtained in Example 1, Comparative Examples 1 and 2 and Reference Example 1, Ketjen Black (conductive agent), and polyvinylidene fluoride (binder) were mixed at a weight ratio of 75:15:10. N-methyl-2-pyrrolidone was added thereto and kneaded sufficiently 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 secondary battery (CR-2032).

  Charging / discharging at a constant current density was performed for 4 cycles using the manufactured lithium ion secondary battery. The charging conditions at this time were constant current and constant voltage charging with a current of 0.1 CA (33 mA / g) and a voltage of 4.5 V, and the discharging conditions were constant current discharging with a current of 0.1 CA and a final voltage of 1.5 V. All temperatures were 30 ° C. The discharge curve of the battery constructed with the positive electrode material obtained in Example 1, Comparative Examples 1-2 and Reference Example 1 is shown in FIG. The discharge capacity is shown in Table 1.

  As is clear from FIG. 1 and Table 1, the secondary battery employing the olivine type silicate compound obtained by the method of the present invention using sodium carbonate is the same as the olivine type silicate compound obtained using lithium hydroxide. Discharge capacity. On the other hand, the secondary using the olivine type silicate compound obtained by the method of Comparative Example 1 in which the amount of sodium hydroxide is less than 0.9 mol and Comparative Example 2 in which the amount of sulfuric acid is less than 0.9 mol. The discharge capacity of the battery was low.

Claims (6)

After stirring and reacting sulfuric acid in an amount of 0.9 to 1.1 mol of hydrogen ion in an aqueous solution for 10 minutes to 2 hours with respect to 1 mol of lithium ion of lithium carbonate, to 1 mol of lithium ion Then, sodium hydroxide in an amount of 0.9 to 1.1 mol of hydroxide ions is reacted, then a metal (M) compound and a silicate compound are added, and the resulting mixture is heated to a temperature of 130 to 200 ° C. And a hydrothermal reaction at a pressure of 0.5 to 1.6 MPa, and a method for producing an olivine-type silicate compound containing metal M (M is Fe, Ni, Co, Al, Zn, Mn, V, or Zr) . The method for producing an olivine-type silicate compound according to claim 1, wherein sulfuric acid is reacted at 0 ° C to 60 ° C. The method for producing an olivine-type silicate compound according to claim 1 or 2, wherein the pH of the mixture obtained by adding the metal (M) compound and the silicate compound is 12.0 to 14.5. . The olivine-type silicate compound has the following formula (5):
Li ₂ Fe _a3 Ni _b Co _c Mn _d Zr _x1 SiO _Four ... (5)
(Wherein a3, b, c and d satisfy a3 + b + c + d = 1−2 × 1 and x1 represents a number satisfying 0 <x1 <0.5)
It is represented by these, The manufacturing method of the olivine type | mold silicate compound of any one of Claims 1-3 characterized by the above-mentioned. And carbon-supported in olivine-type silicate compounds obtained by the method according to any one of claims 1 to 4 and then and firing method of the secondary battery positive electrode active material. The manufacturing method of claim 1-4, further characterized by performing the addition to hydrothermal reaction of water-insoluble carbon-containing compound, method of manufacturing a secondary battery positive electrode active material.