JP2016031871A - Positive electrode active material for secondary battery and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for a secondary battery, capable of exhibiting more excellent charge/discharge characteristics, and a method for producing the positive electrode active material for a secondary battery.SOLUTION: A positive electrode active material for a secondary battery comprises a zirconium-containing olivine type silicate compound loaded with graphene and carbon black, the zirconium-containing olivine type silicate compound being represented by the following formula (1): LiFeNiCoMnZrSiO...(1) (in the formula (1), a, b, c and d satisfy a+b+c+d=1-2x, and x represents a number satisfying 0<x<0.5).SELECTED DRAWING: Figure 2

Description

  The present invention relates to a positive electrode active material for a secondary battery capable of obtaining a positive electrode material having a large charge / discharge capacity and a method for producing the same.

  Lithium ion batteries are a type of non-aqueous electrolyte battery and are used in a wide range of fields such as mobile phones, digital cameras, notebook PCs, hybrid cars, and electric cars. 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.

As this positive electrode material, lithium cobaltate (LiCoO ₂ ), lithium manganate (LiMnO ₂ ), lithium iron phosphate (LiFePO ₄ ), lithium iron silicate (Li ₂ FeSiO ₄ ) and the like are known. Among these, LiFePO ₄ and Li ₂ FeSiO ₄ have an olivine structure and are useful as positive electrode materials for high-capacity lithium ion batteries. In particular, so-called olivine-type silicate compounds such as Li ₂ FeSiO ₄ are excellent positive electrodes. It continues to attract attention as a material.

Since such olivine-type silicate compounds have lower electronic conductivity than layered transition metal oxides, the treatment of covering the surface of particles with a conductive substance such as carbon is necessary in order to sufficiently improve charge / discharge characteristics. It has been subjected. For example, Patent Document 1 discloses a method of attaching a large number of carbon particles to the surface of active material particles, and Patent Document 2 discloses a method of pyrolyzing an organic substance mixed with positive electrode material particles. Yes.
On the other hand, if the surface of such positive electrode material particles is simply coated with carbon, there is a possibility that the amount of lithium atoms moving between the inside and outside of the carbon film may be limited, and the improvement of charge / discharge characteristics may be suppressed. In order to improve, Patent Document 3 discloses a method of coating the surface of a carbon nanostructure on positive electrode material particles by plasma decomposition of an organic compound.

Japanese Patent No. 4151210 Japanese Patent No. 5102425 JP 2011-76931 A

  However, in the method using plasma decomposition as described in Patent Document 3, special equipment and technology are required, so that the method described in Patent Documents 1 and 2 is employed while being a simple means. However, it is strongly desired to obtain a positive electrode active material capable of realizing a secondary battery exhibiting excellent charge / discharge characteristics.

  Therefore, the subject of this invention is providing the positive electrode active material for secondary batteries which can express the more superior charging / discharging characteristic, and its manufacturing method.

  Accordingly, the present inventors have made various studies and find that a positive electrode active material for a secondary battery in which two specific conductive materials are supported on a zirconium-containing olivine-type silicate compound exhibits a large charge / discharge capacity. The present inventors have found that a secondary battery can be obtained and completed the present invention.

That is, the present invention has the formula _{(1): Li 2 Fe a} Ni b Co c Mn d Zr x SiO 4 ··· (1)
(In the formula (1), a, b, c and d satisfy a + b + c + d = 1−2x, and x represents a number satisfying 0 <x <0.5)
The positive electrode active material for secondary batteries by which a graphene and carbon black are carry | supported by the zirconium containing olivine type | mold silicate compound represented by these is provided.
In addition, the present invention provides two or more waters selected from graphene oxide, lithium compounds, silicic acid compounds, zirconium compounds, and transition metal (M) salts (M represents Fe, Ni, Co, or Mn) multiple times. The present invention provides a method for producing the positive electrode active material for a secondary battery supporting carbon black after being subjected to a thermal reaction.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to manufacture the positive electrode active material for secondary batteries using a simple means, the charge / discharge capacity which was excellent also in the obtained secondary battery can be expressed.

The SEM image of the composite_body | complex obtained in Example 1 is shown. The SEM image of the composite_body | complex obtained in Example 1 is shown.

Hereinafter, the present invention will be described in detail.
Positive electrode active material for a secondary battery of the present invention, the following equation _{(1): Li 2 Fe a} Ni b Co c Mn d Zr x SiO 4 ··· (1)
(In the formula (1), a, b, c and d satisfy a + b + c + d = 1−2x, and x represents a number satisfying 0 <x <0.5)
Graphene and carbon black are supported on a zirconium-containing olivine type silicate compound represented by As described above, the positive electrode active material for a secondary battery according to the present invention efficiently contains two kinds of conductive substances different in graphene and carbon black in the gap between the particles of the zirconium-containing olivine silicate compound (1). Since it is arranged and supported, it has very high uniformity and can exhibit excellent battery physical properties.

The zirconium-containing olivine-type silicate compound (zirconium-containing olivine-type silicate compound (1)) used in the present invention has the following formula (1):
Li ₂ Fe _a Ni _b Co _c Mn _d Zr _x SiO ₄ (1)
(In the formula (1), a, b, c and d satisfy a + b + c + d = 1−2x, and x represents a number satisfying 0 <x <0.5)
It is represented by

In the formula (1), x is 0 <x <0.5, and Zr is essential. Moreover, since a, b, c and d are a + b + c + d = 1−2x, at least one of a, b, c and d is not 0, that is, among transition metals of Fe, Ni, Co and Mn. At least one of them is essential. Accordingly, the zirconium-containing olivine silicate compound (1) used in the present invention includes the following embodiments.
Li ₂ Fe _a Zr _x SiO ₄ (1a)
(In Formula (1a), a is a = 1-2x, and x is synonymous with Formula (1)).
Li ₂ Ni _b Zr _x SiO ₄ (1b)
(In formula (1b), b is b = 1-2x, and x is synonymous with formula (1)).
Li ₂ Co _c Zr _x SiO ₄ (1c)
(In formula (1c), c is c = 1−2x, and x is synonymous with formula (1)).
Li ₂ Fe _a Ni _b Zr _x SiO ₄ (1d)
(In formula (1d), a and b are a + b = 1−2x, and x is synonymous with formula (1)).
_{Li 2 Fe a Mn d Zr x} SiO 4 ··· (1e)
(In formula (1e), a and d are a + d = 1−2x, and x is synonymous with formula (1)).

Specific examples of these zirconium-containing olivine type silicate compounds (1) include, for example, Li ₂ Fe _0.96 Zr _0.02 SiO ₄ , Li ₂ Mn _0.9 Zr _0.05 SiO ₄ , Li ₂ Co _0.9 Zr _0.05 SiO ₄ , Li ₂ Fe _0.45 Mn _Examples include _0.45 Zr _0.05 SiO ₄ and Li ₂ Fe _0.64 Mn _0.32 Zr _0.02 SiO ₄ . Among these, from the viewpoint of raw material cost and discharge capacity, it is preferable that a in formula (1) is a compound in which a is not 0, that is, a silicate compound containing at least Fe, specifically, formula (1a) or formula (1e). The silicate compound is more preferable.

  The preferable range of x is 0.001 to 0.1, 0.005 to 0.08 is more preferable, and 0.01 to 0.05 is more preferable from the viewpoint of discharge capacity.

The graphene supported on the zirconium-containing olivine-type silicate compound (1) is a material having a single layer structure in which carbon atoms are SP ² bonded in a honeycomb lattice shape and having excellent conductivity, and graphene oxide is an oxide thereof. is there. Although graphene oxide itself does not have conductivity, graphene can be obtained by reducing it. In addition, graphene is hydrophobic, whereas graphene oxide is hydrophilic because it has a surface functional group, and therefore, it is excellent in handleability through a hydrothermal reaction. Therefore, when obtaining the positive electrode active material for a secondary battery of the present invention, it is preferable to support graphene on the zirconium-containing olivine silicate compound (1) using such graphene oxide.

  The graphene oxide can exhibit a shape such as a layer shape, a film shape, or a lump shape, but the graphene oxide used in the present invention may have any shape. Such graphene oxide is a method in which raw graphite such as natural graphite is oxidized with potassium permanganate in concentrated sulfuric acid containing sodium nitrate. It can be manufactured by law.

  Examples of the carbon black supported on the zirconium-containing olivine type silicate compound (1) include acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. Among these, acetylene black and ketjen black are preferable from the viewpoint of providing good conductivity in combination with graphene. The average particle size of such carbon black is preferably 5 to 100 nm, more preferably 10 to 50 nm, from the viewpoint of effectively improving the physical properties of the battery obtained. The average particle size means a value measured by a dynamic light scattering particle size analyzer (Nanotrack UPA-EX150, manufactured by Nikkiso Co., Ltd.) after uniformly dispersing the sample with a solvent.

  In the positive electrode active material for secondary battery of the present invention, the total amount of graphene and carbon black supported on the zirconium-containing olivine silicate compound (1) is preferably 5 to 15 mass in the positive electrode active material for secondary battery. %, More preferably 7 to 12% by mass. The amount of graphene is preferably larger than that of carbon black, and the mass ratio of graphene to carbon black (graphene: carbon black) is preferably 51:49 to 80:20, more preferably 55:45 to 70. : 30.

  Specifically, the positive electrode active material for a secondary battery of the present invention includes graphene oxide, a lithium compound, a silicate compound, a zirconium compound, and a transition metal (M) salt (M represents Fe, Ni, Co, or Mn). It is preferable that the positive electrode active material for a secondary battery is obtained by subjecting two or more selected from the above to hydrothermal reaction multiple times to support carbon black.

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 is particularly preferable. As lithium hydroxide, for example, a hydrate such as LiOH.H ₂ O can be used.

The silicic acid compound is not particularly limited as long as it is a reactive silica compound. Tetraethyl orthosilicate, amorphous silica, Na ₄ SiO ₄ or Na ₄ SiO ₄ .nH ₂ O (for example, Na ₄ SiO ₄ .H ₂ O). Of these, tetraethyl orthosilicate is more preferably used from the viewpoint that it can be easily changed to SiO ₂ through hydrolysis.

  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.

As transition metal (M) salt (M represents Fe, Ni, Co or Mn), transition metal sulfate represented by MSO ₄ (wherein M represents Fe, Ni, Co or Mn) or It is preferable to use an organic acid transition metal salt represented by (R) ₂ M (wherein R represents an organic acid residue, and M represents Fe, Ni, Co, or Mn). Examples of the transition metal sulfate MSO ₄ include FeSO ₄ , NiSO ₄ , CoSO _{4, and} MnSO ₄ , and these may be used alone or in combination of two or more. Of these, FeSO ₄ and MnSO ₄ are more preferable.

The organic acid represented by an organic acid transition 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.

More specifically, the positive electrode active material for a secondary battery of the present invention is more specifically a composite X obtained by subjecting slurry water X containing graphene oxide and a silicate compound to a hydrothermal reaction, a lithium compound, a zirconium compound, and Two obtained by supporting carbon black on a composite Y obtained by subjecting slurry water Y containing a transition metal (M) salt (M represents Fe, Ni, Co or Mn) to a hydrothermal reaction. More preferably, it is a positive electrode active material for a secondary battery. That is, slurry water X containing graphene oxide and a silicate compound in advance is subjected to a hydrothermal reaction to obtain a composite X, and then the composite X is mixed with a lithium compound, a zirconium compound, and a transition metal (M) salt. It is preferable to obtain the composite water Y by preparing the slurry water Y to be contained, and subjecting it to a hydrothermal reaction, and then carrying the hydrothermal reaction a plurality of times to carry carbon black.
Hereinafter, the positive electrode active material for a secondary battery of the present invention will be described more specifically as a production method thereof.

The method for producing a positive electrode active material for a secondary battery according to the present invention comprises graphene oxide, a lithium compound, a silicate compound, a zirconium compound, and a transition metal (M) salt (M represents Fe, Ni, Co, or Mn). This is a method of supporting carbon black after subjecting two or more selected types to hydrothermal reaction a plurality of times, and the positive electrode active material for a secondary battery of the present invention is obtained by such a method as described above. Is preferred. More specifically, according to the method for producing a positive electrode active material for a secondary battery of the invention, different types of conductive substances of graphene and carbon black are provided in the gaps between the particles of the zirconium-containing olivine silicate compound (1). From the viewpoint of efficiently arranging and supporting the slurry, the step (I) of obtaining the composite X by subjecting the slurry water X containing graphene oxide and the silicate compound to a hydrothermal reaction,
The obtained composite X, a lithium compound, a zirconium compound, and a transition metal (M) salt (M represents Fe, Ni, Co or M) are subjected to a hydrothermal reaction to subject the composite Y to a hydrothermal reaction. Step (II) for obtaining carbon black and step (III) for supporting carbon black on the obtained composite Y
It is more preferable to contain.

  The slurry water X used in step (I) preferably contains graphene oxide and a silicate compound, and further contains an organic solvent in addition to water. Such organic solvents include ethanol, ethylene glycol, and glycerin. Of these, ethanol is preferable. The amount of the organic solvent is preferably 5 to 50% by mass and more preferably 10 to 30% by mass in the total amount of water and organic solvent contained in the slurry water X.

  The total amount of graphene oxide and silicic acid compound in the slurry water X is preferably 5 to 30 parts by mass, more preferably 7 to 15 parts by mass with respect to 100 parts by mass of water. The mass ratio of graphene oxide to silicate compound (graphene oxide: silicate compound) is preferably 1: 3 to 1:12, more preferably 1: 6 to 1:12.

In the step (I), by subjecting the slurry water X to a hydrothermal reaction, the SiO ₂ particles derived from the silicate compound can be efficiently and firmly attached to the surface of the graphene oxide. The temperature of the hydrothermal reaction is preferably 130 to 200 ° C, more preferably 140 to 170 ° C, from the viewpoint of satisfactorily attaching SiO ₂ particles to the surface of graphene oxide. Moreover, hydrothermal reaction time becomes like this. Preferably it is 1 to 12 hours, More preferably, it is 3 to 9 hours. The pressure during the reaction is preferably 0.2 to 1.5 MPa, more preferably 0.3 to 0.7 MPa.

Next, in step (II), a slurry containing the composite X obtained in step (I), a lithium compound, a zirconium compound, and a transition metal (M) salt (M represents Fe, Ni, Co, or M). Water Y is subjected to a hydrothermal reaction to obtain complex Y. The complex X is preferably used while containing the water and the organic solvent used in the step (I). The slurry water Y preferably further contains sodium hydroxide from the viewpoint of effectively suppressing the generation of impurities.
When using sodium hydroxide in the step (II), specifically, the total amount of the lithium compound and sodium hydroxide in the slurry water Y is preferably 8 to 40 parts by mass with respect to 100 parts by mass of water. Preferably it is 8-38 mass parts, More preferably, it is 8-36 mass parts. The molar ratio of lithium to sodium (Li: Na) is preferably 1: 2 to 1: 6, more preferably 1: 2 to 1: 4. Furthermore, the molar ratio of the silicic acid compound and sodium hydroxide in the slurry water Y is preferably 1: 3 to 1: 6, more preferably 1: 3 to 1: 5.

  When lithium hydroxide is used as the lithium compound, the amount of lithium hydroxide in the total amount is a value converted to the amount of lithium hydroxide (LiOH). Further, in terms of stoichiometry, the amount of lithium hydroxide as a Li source is 1.5 to 5 based on the total molar amount of the zirconium compound and the transition metal (M) salt in the zirconium-containing olivine-type silicate compound (1). It is preferably 4 times, and more preferably 2 to 3.5 times.

  The slurry water Y is preferably finally adjusted to pH 9 to 13.5, more preferably adjusted to pH 9.5 to 13. Thereby, the growth of by-products and particles can be effectively suppressed. At this time, a known pH adjuster may be used as necessary.

  In the step (II), the slurry water Y is subjected to a hydrothermal reaction. The hydrothermal temperature should just be 100 degreeC or more, Preferably it is 130-250 degreeC, More preferably, it is 140-230 degreeC. For example, when using a steam heating type autoclave, it is only necessary to seal in an autoclave and heat with steam. When the reaction is performed at 130 to 250 ° C, the pressure becomes 0.3 to 1.5 MPa, and 140 to 230 ° C. When the reaction is performed at 0.4 to 1 MPa. The reaction time is preferably 10 minutes to 24 hours, more preferably 1 to 12 hours.

  After completion of the hydrothermal reaction, the produced complex Y is preferably collected by filtration, and then washed from the viewpoint of effectively removing impurities. Washing is preferably performed with water using a filtration device having a cake washing function. The obtained crystals are dried if necessary. Examples of the drying means include spray drying, vacuum drying, freeze drying and the like.

  Subsequently, in the step (III), carbon black is supported on the obtained composite Y. This makes it possible to efficiently dispose carbon black on the surface of the zirconium-containing olivine-type silicate compound (1) to which no conductive substance has yet adhered, or on the gaps between the particles of the compound (1).

  Specifically, the step (III) is preferably a step of mixing the composite Y obtained in the step (II) and carbon black and then mixing them while applying a compressive force and a shearing force. As a result, the composite Y and the carbon black are firmly agglomerated while being uniformly dispersed, and these conductive materials can be efficiently disposed in combination with the graphene, thereby obtaining a positive electrode active material with further reduced electric resistance. be able to. The mass ratio of graphene oxide to carbon black (graphene oxide: carbon black) in the composite Y is preferably 51:49 to 70:30, more preferably 55:45 to 70:30.

The process of mixing while applying a compressive force and a shearing force is preferably carried out in a closed container equipped with an impeller that rotates at a peripheral speed of 25 to 40 m / s. The peripheral speed of the impeller is preferably 27 to 35 m / s from the viewpoint of improving the battery physical properties by increasing the tap density of the obtained positive electrode active material. In addition, the peripheral speed of an impeller means the speed of the outermost edge part of a rotary stirring blade (impeller), and can be represented by following formula (I).
Impeller peripheral speed (m / s) =
Impeller radius (m) × 2 × π × rotational speed (rpm) ÷ 60 (I)
The time for performing the mixing process while applying compressive force and shearing force may vary depending on the peripheral speed of the impeller so that the slower the peripheral speed of the impeller, the more preferably it is 5 to 90 minutes. Preferably it is 10 to 60 minutes.

The impeller peripheral speed and / or processing time in the process of mixing while applying a compressive force and a shearing force need to be adjusted as appropriate according to the amount of the composite Y and carbon black charged into the container. Then, by operating the container, it is possible to perform a process of mixing the mixture while applying a compressive force and a shearing force between the impeller and the inner wall of the container. In addition, a positive electrode active material in which carbon black is densely and uniformly dispersed can be obtained.
For example, when the mixing process is performed for 5 to 90 minutes in an airtight container equipped with an impeller rotating at a peripheral speed of 25 to 40 m / s, the total amount of the composite Y and carbon black charged into the container is an effective container ( Among sealed containers equipped with an impeller, a container corresponding to a part capable of accommodating the composite Y and carbon black) is preferably 0.1 to 0.7 g, more preferably 0.15 to 0.4 g, per 1 cm ^3. It is.

  After the step (III), the positive electrode active material is preferably obtained by firing. Thereby, graphene oxide can be reduced and converted into graphene, and the zirconium-containing olivine-type silicate compound (1) can firmly support carbon black together with graphene. Such firing is preferably performed under an inert gas atmosphere or under reducing conditions, and the firing temperature is preferably 700 ° C. or lower, more preferably 300 to 600 ° C., and the firing time is preferably 10 minutes to 3 hours, more preferably 0.5 to 1.5 hours.

  The obtained positive electrode active material is excellent in terms of discharge capacity, and is useful as a positive electrode material for a secondary battery. The average particle size of the positive electrode active material is preferably 10 to 300 nm, and more preferably 20 to 200 nm. The secondary battery to which the positive electrode active material of the present invention can be applied may be a lithium ion secondary battery, and is not particularly limited as long as it has a positive electrode, a negative electrode, an electrolytic solution, and a separator as 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 secondary battery. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolanes, A 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]
Mixing 0.30 g of graphene oxide, 2.61 g of tetraethyl orthosilicate, 5.0 g of ethanol, and 32.5 mL of water, prepared by the Hammers method using a pulverized product of natural graphite (SP-270, manufactured by Nippon Graphite Co., Ltd.) Slurry water X was prepared.
The obtained slurry water X was put into an autoclave and subjected to a hydrothermal reaction at 150 ° C. for 10 hours under a pressure of 0.7 MPa to obtain a mixed solution containing the produced complex X.
An SEM image of the complex X is shown in FIG.

Then, it uses the resulting mixture after the hydrothermal reaction, LiOH · H ₂ O 1.05g in such _{mixture, Zr (SO 4) 2 ·} 4H 2 O 0.13g, MnSO 4 · 5H 2 O 2. 55 g of FeSO ₄ .7H ₂ O 0.33 g and NaOH 2.0 g were added and mixed to obtain slurry water Y having a pH of 13. In such slurry water, the total amount of lithium hydroxide and sodium hydroxide with respect to 100 parts by mass of water is 9 parts by mass, the molar ratio (Li: Na) is 1: 2, and tetraethyl orthosilicate and sodium hydroxide The molar ratio was 1: 4. Furthermore, the amount of lithium hydroxide as a Li source based on the total molar amount of the zirconium compound and the transition metal (M) salt was doubled.
The obtained slurry water Y was put into an autoclave, and a hydrothermal reaction was performed at 150 ° C. for 12 hours under a pressure of 0.7 MPa to produce a composite Y. The produced complex Y was filtered, washed with water in an amount such that the mass ratio (crystal: water) was 1:12, and then lyophilized at −50 ° C. for 12 hours.
The SEM image of the composite Y is shown in FIG.

Subsequently, carbon black (carbon ECP, manufactured by Lion Corporation) was added to the obtained composite Y in an amount of 15% by mass in the total amount of the composite Y and carbon black, and a mixture was obtained. The obtained mixture was put into a fine particle composite apparatus Nobilta (NOB-MINI, manufactured by Hosokawa Micron Corporation, power 0.75 kW), the processing temperature was set to 25 to 35 ° C., the impeller peripheral speed was 39 m / s, and the processing time was 20 Mixing as a minute, composite particles before firing were obtained.
Next, using an electric furnace purged with nitrogen gas, the obtained composite particles before firing were fired at a temperature of 700 ° C. for 1 hour, and the composite particles after firing (Li ₂ Fe _0.09 Mn _0.85 Zr _0.03 SiO ₄ / C, average particle size 50 nm). The total amount of graphene and carbon black supported in the obtained composite particles after firing is 12% by mass, and the mass ratio of graphene to carbon black (graphene: carbon black) is 58.3: 41. .7.

[Comparative Example 1]
LiOH.H ₂ O 1.05 g, Zr (SO ₄ ) ₂ .4H ₂ O 0.13 g, MnSO ₄ .5H ₂ O 2.55 g, FeSO ₄ .7H ₂ O 0.33 g, Na ₄ SiO ₄ .nH ₂ 3.49 g of O and 9.4 mL of water were mixed to prepare slurry water Z.
The obtained slurry water Z was put into an autoclave and subjected to a hydrothermal reaction at 150 ° C. for 12 hours under a pressure of 0.7 MPa to produce a composite. The formed complex was filtered, washed with water in an amount such that the mass ratio (crystal: water) was 1:12, and then lyophilized at −50 ° C. for 12 hours.
Next, carbon black was added to and mixed with the obtained composite in the same manner as in Example 1 to obtain a mixture, and then fired in the same manner to obtain composite particles (Li ₂ Fe _0.09 Mn after firing). _0.85 Zr _0.03 SiO ₄ / C, average particle size 50 nm). The total amount of carbon black supported in the obtained composite particles after firing was 12% by mass.

[Comparative Example 2]
A slurry water X was prepared in the same manner as in Example 1 except that no graphene oxide was used, and a hydrothermal reaction was performed to obtain a mixed solution containing the complex X. Next, in the same manner as in Example 1, after obtaining the slurry water Y, the carbon black was mixed and mixed with Nobilta, fired and fired composite particles (Li ₂ Fe _0.09 Mn _0.85 Zr _0.03 SiO ₄ / C, average particle size 50 nm).

[Test Example 1]
Using the fired composite particles obtained in Example 1 and Comparative Examples 1 and 2, a positive electrode of a lithium ion secondary battery was produced. Specifically, the composite particles after firing obtained in Example 1 and Comparative Examples 1-2, ketjen black (conductive agent), and polyvinylidene fluoride (binding agent) in a weight ratio of 75:15:10 are used. The mixture was mixed at a blending ratio, and 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).

One cycle of charge and discharge at a constant current density was performed using the manufactured lithium ion battery. The charging conditions at this time were constant current and constant voltage charging with a current of 0.1 CA (33.3 mA / g) and a voltage of 4.5 V, and the discharging conditions were constant current discharging with a current of 0.6 CA and a final voltage of 1.5 V. All temperatures were 30 ° C.
The results are shown in Table 1.

  From the results in Table 1, it can be seen that the lithium ion battery using the positive electrode active material for the secondary battery of the present invention has battery characteristics superior to those of the comparative example.

Claims (10)

Following formula _{(1): Li 2 Fe a} Ni b Co c Mn d Zr x SiO 4 ··· (1)
(In the formula (1), a, b, c and d satisfy a + b + c + d = 1−2x, and x represents a number satisfying 0 <x <0.5)
The positive electrode active material for secondary batteries by which a graphene and carbon black are carry | supported by the zirconium containing olivine type | mold silicate compound represented by these.   The positive electrode active material for a secondary battery according to claim 1, wherein a in the formula (1) is not 0.   The positive electrode active material for a secondary battery according to claim 1 or 2, wherein the total amount of graphene and carbon black is 5 to 15% by mass.   Two or more kinds selected from graphene oxide, lithium compound, silicate compound, zirconium compound, and transition metal (M) salt (M represents Fe, Ni, Co, or Mn) are subjected to hydrothermal reaction multiple times. The positive electrode active material for a secondary battery according to any one of claims 1 to 3, obtained by supporting carbon black.   Complex X obtained by subjecting slurry water X containing graphene oxide and silicic acid compound to hydrothermal reaction, lithium compound, zirconium compound, and transition metal (M) salt (M is Fe, Ni, Co or Mn. The positive electrode active for secondary batteries of any one of Claims 1-4 obtained by carrying | supporting carbon black on the composite Y obtained by attaching | subjecting the slurry water Y containing this to hydrothermal reaction material.   The positive electrode active material for a secondary battery according to any one of claims 1 to 5, wherein the silicate compound is tetraethyl orthosilicate.   After subjecting two or more kinds selected from graphene oxide, lithium compound, silicic acid compound, zirconium compound, and transition metal (M) salt (M represents Fe, Ni, Co or Mn) to hydrothermal reaction multiple times The manufacturing method of the positive electrode active material for secondary batteries of any one of Claims 1-6 which carry | supports carbon black. A step (I) of obtaining a composite X by subjecting a slurry water X containing graphene oxide and a silicate compound to a hydrothermal reaction;
The obtained composite X, a lithium compound, a zirconium compound, and a transition metal (M) salt (M represents Fe, Ni, Co or M) are subjected to a hydrothermal reaction to subject the composite Y to a hydrothermal reaction. Step (II) for obtaining carbon black and step (III) for supporting carbon black on the obtained composite Y
The manufacturing method of the positive electrode active material for secondary batteries of Claim 7 containing this.   The step (III) is a step of mixing the obtained composite Y and carbon black and then mixing them while applying a compressive force and a shearing force. The positive electrode active material for a secondary battery according to claim 7 or 8 Production method.   The method for producing a positive electrode active material for a secondary battery according to any one of claims 7 to 9, wherein the silicate compound is tetraethyl orthosilicate.