WO2016151890A1

WO2016151890A1 - Secondary battery positive electrode active material and method for producing same

Info

Publication number: WO2016151890A1
Application number: PCT/JP2015/076385
Authority: WO
Inventors: 弘樹山下; 智紀初森; 充志中村; 大神　剛章
Original assignee: 太平洋セメント株式会社
Priority date: 2015-03-24
Filing date: 2015-09-17
Publication date: 2016-09-29
Also published as: KR20170129722A; KR102336781B1

Abstract

In order to obtain a high-performance lithium-ion secondary battery or sodium-ion secondary battery, the present invention provides a secondary battery positive electrode active material capable of effectively suppressing water absorption, and a method for producing the same. To be specific, the present invention pertains to a secondary battery positive electrode active material in which a water-insoluble conductive carbon material and a carbon obtained by carbonizing a water-soluble carbon material are supported on an oxide containing at least iron or manganese and represented by formula (A) LiFe_aMn_bM_cPO₄, formula (B) Li₂Fe_dMn_eN_fSiO₄, or formula (C) NaFe_gMn_hQ_iPO₄.

Description

Positive electrode active material for secondary battery and method for producing the same

The present invention relates to a positive electrode active material for a secondary battery in which a water-insoluble conductive carbon material and carbon obtained by carbonizing a water-soluble carbon material are supported on an oxide, and a method for producing the same.

Secondary batteries used in portable electronic devices, hybrid cars, electric cars, and the like have been developed. In particular, lithium ion secondary batteries are widely known as the most excellent secondary batteries that operate near room temperature. Under these circumstances, lithium-containing olivine-type phosphate metal salts such as Li (Fe, Mn) PO ₄ and Li ₂ (Fe, Mn) SiO ₄ are more resource-constrained than lithium transition metal oxides such as LiCoO _2. Therefore, it is possible to exhibit high safety, and therefore, it is an optimum positive electrode material for obtaining a high-output and large-capacity lithium ion secondary battery. However, these compounds have the property that it is difficult to sufficiently increase the conductivity due to the crystal structure, and there is room for improvement in the diffusibility of lithium ions. Has been made.

Furthermore, in lithium ion secondary batteries, which are spreading, it is known that the internal resistance gradually increases when the battery is left for a long time after charging, and the battery performance is deteriorated. This is because the moisture contained in the battery material at the time of manufacture is desorbed from the material during repeated charging and discharging of the battery, and by the chemical reaction between the moisture and the nonaqueous electrolyte LiPF ₆ filling the battery, This is because hydrogen fluoride is generated. It is also known that reducing the water content of the positive electrode active material used in the secondary battery is effective for effectively suppressing such deterioration in battery performance (see Patent Document 1).

Under these circumstances, for example, Patent Document 2 discloses that after the firing treatment of the raw material mixture containing the carbonaceous material precursor, the water content is reduced to a certain value or less by performing pulverization treatment and classification treatment in a dry atmosphere. Technology is disclosed. In Patent Document 3, a predetermined lithium phosphate compound, lithium silicate compound, and the like and a conductive carbon material are mixed by a wet ball mill, and then a mechanochemical treatment is performed so that the conductive carbon material is uniformly applied to the surface. A technique for obtaining a composite oxide deposited is disclosed.

On the other hand, since lithium is a rare valuable material, various studies have been made on sodium ion secondary batteries using sodium instead of lithium ion secondary batteries.
For example, Patent Document 4 discloses a sodium secondary battery active material using marisite-type NaMnPO ₄ , and Patent Document 5 discloses a positive electrode active material containing transition metal sodium phosphate having an olivine structure. Substances are disclosed, and any literature shows that a high-performance sodium ion secondary battery can be obtained.

JP 2013-152911 A JP 2003-292309 A JP 2010-218884 A JP 2008-260666 A JP 2011-34963 A

However, in any of the techniques described in any of the above documents, the surface of the positive electrode active material for secondary batteries is not sufficiently covered with the carbon source, and a part of the surface is exposed, so that moisture adsorption can be suppressed. Therefore, it has been found that it is difficult to obtain a positive electrode active material for a secondary battery having a sufficiently high moisture content and sufficiently high battery properties such as cycle characteristics.

Accordingly, an object of the present invention is to provide a positive electrode active material for a secondary battery that can effectively suppress moisture adsorption and a method for manufacturing the same, in order to obtain a high-performance lithium ion secondary battery or a sodium ion secondary battery. It is to provide.

Therefore, the present inventors have made various studies, and as long as a positive electrode active material for a secondary battery in which conductive carbon powder and carbon obtained by carbonizing a water-soluble carbon material are supported on a specific oxide. Since the carbons derived from a plurality of carbon sources can effectively cover the oxide surface and effectively suppress the adsorption of moisture, lithium ions or sodium ions can effectively carry out electrical conduction. As a substance, it was found to be extremely useful, and the present invention was completed.

That is, the present invention includes at least the following formula (A), (B) or (C) containing iron or manganese:
LiFe _a Mn _b M _c PO ₄ (A)
(In the formula (A), M represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. A, b, and c are 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ c ≦ 0.2, and 2a + 2b + (M valence) × c = 2 and a number satisfying a + b ≠ 0 are shown.)
Li ₂ Fe _d Mn _e N _f SiO ₄ (B)
(In the formula (B), N represents Ni, Co, Al, Zn, V, or Zr. D, e, and f are 0 ≦ d ≦ 1, 0 ≦ e ≦ 1, and 0 ≦ f <1, 2d + 2e +. (The valence of N) × f = 2 is satisfied, and d + e ≠ 0 is satisfied.)
NaFe _g Mn _h Q _i PO ₄ (C)
(In the formula (C), Q represents Mg, Ca, Co, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. G, h, and i are 0 ≦ g ≦. 1, 0 ≦ h ≦ 1, 0 ≦ i <1, and 2g + 2h + (valence of Q) × i = 2 and a number satisfying g + h ≠ 0 are shown.)
A positive electrode active material for a secondary battery is provided in which a water-insoluble conductive carbon material and carbon obtained by carbonizing a water-soluble carbon material are supported on an oxide represented by:

Further, the present invention provides the following formula (A), (B) or (C) containing at least iron or manganese:
LiFe _a Mn _b M _c PO ₄ (A)
(In the formula (A), M represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. A, b, and c are 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ c ≦ 0.2, and 2a + 2b + (M valence) × c = 2 and a number satisfying a + b ≠ 0 are shown.)
Li ₂ Fe _d Mn _e N _f SiO ₄ (B)
(In the formula (B), N represents Ni, Co, Al, Zn, V, or Zr. D, e, and f are 0 ≦ d ≦ 1, 0 ≦ e ≦ 1, and 0 ≦ f <1, 2d + 2e +. (The valence of N) × f = 2 is satisfied, and d + e ≠ 0 is satisfied.)
NaFe _g Mn _h Q _i PO ₄ (C)
(In the formula (C), Q represents Mg, Ca, Co, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. G, h, and i are 0. ≦ g ≦ 1, 0 ≦ h ≦ 1, 0 ≦ i <1, and 2g + 2h + (Q valence) × i = 2 and a number satisfying g + h ≠ 0 are shown.
A method for producing a positive electrode active material for a secondary battery in which a water-insoluble conductive carbon material and carbon obtained by carbonizing a water-soluble carbon material are supported on an oxide represented by:
A step (I) of obtaining an oxide X by subjecting a slurry water containing a lithium compound or sodium compound, a phosphoric acid compound or a silicic acid compound, and a metal salt containing at least an iron compound or a manganese compound to a hydrothermal reaction;
Step (II) in which a water-insoluble conductive carbon material is added to the obtained oxide X and dry-mixed to obtain a composite Y, and a water-soluble carbon material is added to the obtained composite Y and wet-mixed. The manufacturing method of the positive electrode active material for secondary batteries provided with the process (III) to bake is provided.

According to the present invention, a predetermined oxide effectively supports a water-insoluble conductive carbon material and carbon obtained by carbonizing a water-soluble carbon material, so that the oxide is partially supported on the oxide surface. Since the oxide is effectively suppressed from being exposed without the presence of carbon, a positive electrode active material for a secondary battery in which the exposed portion on the oxide surface is effectively reduced can be obtained. Therefore, since such a positive electrode active material can effectively suppress the adsorption of moisture, in a lithium ion secondary battery or a sodium ion secondary battery using the positive electrode active material, lithium ions or sodium ions effectively carry electric conduction, and various Excellent battery characteristics such as cycle characteristics can be stably exhibited even in a different use environment.

Hereinafter, the present invention will be described in detail.
The oxide used in the present invention contains at least iron or manganese and has the following formula (A), (B) or (C):
LiFe _a Mn _b M _c PO ₄ (A)
(In the formula (A), M represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. A, b, and c are 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ c ≦ 0.2, and 2a + 2b + (M valence) × c = 2 and a number satisfying a + b ≠ 0 are shown.)
Li ₂ Fe _d Mn _e N _f SiO ₄ (B)
(In the formula (B), N represents Ni, Co, Al, Zn, V, or Zr. D, e, and f are 0 ≦ d ≦ 1, 0 ≦ e ≦ 1, 0 ≦ f <1, and 2d + 2e +. (The valence of N) × f = 2 is satisfied, and d + e ≠ 0 is satisfied.)
NaFe _g Mn _h Q _i PO ₄ (C)
(In the formula (C), Q represents Mg, Ca, Co, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. G, h, and i are 0 ≦ g ≦. 1, 0 ≦ h ≦ 1, 0 ≦ i <1, and 2g + 2h + (valence of Q) × i = 2 and a number satisfying g + h ≠ 0 are shown.)
It is expressed by one of the following formulas.
These oxides all have an olivine structure and contain at least iron or manganese. When the oxide represented by the above formula (A) or (B) is used, a positive electrode active material for a lithium ion battery is obtained, and when the oxide represented by the above formula (C) is used. Provides a positive electrode active material for a sodium ion battery.

The oxide represented by the above formula (A) is an olivine-type transition metal lithium compound containing at least iron (Fe) and manganese (Mn) as so-called transition metals. In the formula (A), M represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd, and is preferably Mg, Zr, Mo, or Co. a is 0 ≦ a ≦ 1, preferably 0.01 ≦ a ≦ 0.99, and more preferably 0.1 ≦ a ≦ 0.9. b is 0 ≦ b ≦ 1, preferably 0.01 ≦ b ≦ 0.99, and more preferably 0.1 ≦ b ≦ 0.9. c satisfies 0 ≦ c ≦ 0.2, and preferably 0 ≦ c ≦ 0.1. These a, b and c are numbers satisfying 2a + 2b + (valence of M) × c = 2 and satisfying a + b ≠ 0. Specific examples of the olivine-type transition metal lithium compound represented by the above formula (A) include LiFe _0.2 Mn _0.8 PO ₄ , LiFe _0.9 Mn _0.1 PO ₄ , LiFe _0.15 Mn _0.75 Mg _0.1 PO ₄ , LiFe _Examples include _0.19 Mn _0.75 Zr _0.03 PO ₄ , and among them, LiFe _0.2 Mn _0.8 PO ₄ is preferable.

The oxide represented by the above formula (B) is a so-called olivine-type transition metal lithium compound containing at least iron (Fe) and manganese (Mn) as transition metals. In the formula (B), N represents Ni, Co, Al, Zn, V, or Zr, and is preferably Co, Al, Zn, V, or Zr. d is 0 ≦ d ≦ 1, preferably 0 ≦ d <1, and more preferably 0.1 ≦ d ≦ 0.6. e is 0 ≦ d ≦ 1, preferably 0 ≦ e <1, and more preferably 0.1 ≦ e ≦ 0.6. f is 0 ≦ f <1, preferably 0 <f <1, and more preferably 0.05 ≦ f ≦ 0.4. These d, e, and f are numbers satisfying 2d + 2e + (N valence) × f = 2 and d + e ≠ 0. Specific examples of the olivine-type transition metal lithium compound represented by the above formula (B) include, for example, Li ₂ Fe _0.45 Mn _0.45 Co _0.1 SiO ₄ , Li ₂ Fe _0.36 Mn _0.54 Al _0.066 SiO ₄ , Li ₂ Fe _0.45 Mn _0.45 Zn _0.1 SiO ₄ , Li ₂ Fe _0.36 Mn _0.54 V _0.066 SiO ₄ , Li ₂ Fe _0.282 Mn _0.658 Zr _0.02 SiO _{4 and the} like can be mentioned, among which Li ₂ Fe _0.282 Mn _0.658 Zr _0.02 SiO ₄ is preferable.

The oxide represented by the formula (C) is an olivine-type transition metal sodium phosphate compound containing iron (Fe) and manganese (Mn) as at least transition metals. In the formula (C), Q represents Mg, Ca, Co, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd, and is preferably Mg, Zr, Mo, or Co. g is 0 ≦ g ≦ 1, and preferably 0 <g ≦ 1. h is 0 ≦ h ≦ 1, and preferably 0.5 ≦ h <1. i is 0 ≦ i <1, preferably 0 ≦ i ≦ 0.5, and more preferably 0 ≦ i ≦ 0.3. These g, h, and i are numbers satisfying 0 ≦ g ≦ 1, 0 ≦ h ≦ 1, and 0 ≦ i <1, 2 + g + 2h + (Q valence) × i = 2 and satisfying g + h ≠ 0. It is. Specific examples of the olivine-type transition metal sodium phosphate compound represented by the above formula (C) include, for example, NaFe _0.2 Mn _0.8 PO ₄ , NaFe _0.9 Mn _0.1 PO ₄ , NaFe _0.15 Mn _0.7 Mg _0.15 PO ₄ , NaFe Examples include _0.19 Mn _0.75 Zr _0.03 PO ₄ , NaFe _0.19 Mn _0.75 Mo _0.03 PO ₄ , NaFe _0.15 Mn _0.7 Co _0.15 PO ₄ , and NaFe _0.2 Mn _0.8 PO ₄ is preferred.

The positive electrode active material for a secondary battery according to the present invention is obtained by carbonizing a water-insoluble conductive carbon material and a water-soluble carbon material on the oxide represented by the above formula (A), (B), or (C). Carbon (carbon derived from a water-soluble carbon material) is supported. That is, a water-insoluble conductive carbon material and a water-soluble carbon material coexist as a carbon source, and the oxide surface is coated without the presence of such carbon while the oxide surface is coated with carbon derived from one carbon source. The carbon derived from the other carbon source is effectively supported on the exposed portion. Therefore, the water-insoluble conductive carbon material and the carbon obtained by carbonizing the water-soluble carbon material are combined and firmly supported on the entire surface of the oxide while effectively suppressing the exposure of the oxide surface. Therefore, moisture adsorption in the positive electrode active material for a secondary battery of the present invention can be effectively prevented.

The water-insoluble conductive carbon material supported on the oxide represented by the above formula (A), (B) or (C) means that the amount dissolved in 100 g of water at 25 ° C. is carbon of the water-insoluble conductive carbon material. A water-insoluble carbon material having an atomic conversion amount of less than 0.4 g, which itself is a conductive carbon source without firing. Examples of the water-insoluble conductive carbon material include one or more selected from graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. Of these, graphite is preferable from the viewpoint of reducing the amount of adsorbed moisture. The graphite may be any of artificial graphite (scaly, massive, earthy, graphene) or natural graphite.

The BET specific surface area of the water-insoluble conductive carbon material that can be used is preferably 1 to 750 m ² / g, more preferably 3 to 500 m ² / g, from the viewpoint of effectively reducing the amount of adsorbed water. Further, from the same viewpoint, the average particle size of the water-insoluble conductive carbon material is preferably 0.5 to 20 μm, more preferably 1.0 to 15 μm.

Along with the water-insoluble conductive carbon material, the water-soluble carbon material supported as carbon carbonized by the oxide represented by the formula (A), (B) or (C) is used in 100 g of water at 25 ° C. Carbon source which dissolves 0.4 g or more, preferably 1.0 g or more, of water-soluble carbon material in terms of carbon atom, and which covers the oxide surface represented by the above formulas (A) to (C) Function as. Examples of the water-soluble carbon material include one or more selected from saccharides, polyols, polyethers, and organic acids. More specifically, for example, monosaccharides such as glucose, fructose, galactose and mannose; disaccharides such as maltose, sucrose and cellobiose; polysaccharides such as starch and dextrin; ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol and butane Examples include polyols and polyethers such as diol, propanediol, polyvinyl alcohol, and glycerin; and organic acids such as citric acid, tartaric acid, and ascorbic acid. Among these, glucose, fructose, sucrose, and dextrin are preferable, and glucose is more preferable from the viewpoint of improving the solubility and dispersibility in a solvent and effectively functioning as a carbon material.

The carbon atom equivalent of the water-insoluble conductive carbon material and the water-soluble carbon material is the positive electrode for the secondary battery of the present invention as the carbon in which the water-insoluble conductive carbon material and the carbonized water-soluble carbon material are supported on the oxide. It will coexist in the active material. The carbon atom equivalent amount of the water-insoluble conductive carbon material and the water-soluble carbon material corresponds to the total supported amount of carbon obtained by carbonizing the water-insoluble conductive carbon material and the water-soluble carbon material. The total amount in the positive electrode active material for batteries is preferably 1.0 to 20.0% by mass, more preferably 2.0 to 17.5% by mass, and still more preferably 3.0 to 15.0%. % By mass. Specifically, the carbon atom equivalent amount of the water-insoluble conductive carbon material and the water-soluble carbon material is preferably the positive electrode active material for a secondary battery in which the oxide is represented by the above formula (A) or (C). 1.0 to 15.0 mass%, more preferably 2.0 to 13.5 mass%, still more preferably 3.0 to 12.0 mass%, and the oxide is represented by the above formula (B). Is preferably 2.0 to 20.0% by mass, more preferably 3.0 to 17.5% by mass, and still more preferably 4.0 to 15%. 0.0% by mass.
Further, the carbon atom equivalent amount of the water-soluble carbon material, that is, the supported amount of carbon obtained by carbonizing the water-soluble carbon material is preferably 0.5 to 17.0 in the positive electrode active material for secondary battery of the present invention. % By mass, more preferably 0.5 to 13.5% by mass, and still more preferably 0.5 to 10.0% by mass. Specifically, the carbon atom equivalent amount of the water-soluble carbon material is preferably 0.5 to 10.0 for the positive electrode active material for a secondary battery in which the oxide is represented by the above formula (A) or (C). A secondary battery in which the oxide is represented by the above formula (B), preferably 0.5 to 9.0 mass%, more preferably 0.5 to 8.0 mass%. In the positive electrode active material for use, it is preferably 0.75 to 17.0% by mass, more preferably 0.75 to 13.5% by mass, and further preferably 0.75 to 10.0% by mass.
The total amount of carbon-atom equivalents of the water-insoluble conductive carbon material and the water-soluble carbon material present in the positive electrode active material for secondary batteries is confirmed as the total carbon amount measured using a carbon / sulfur analyzer. can do. Further, the carbon atom equivalent amount of the water-soluble carbon material can be confirmed by subtracting the addition amount of the water-insoluble conductive carbon material from the total carbon amount measured using a carbon / sulfur analyzer.

The positive electrode active material for a secondary battery according to the present invention efficiently (A), (B) or (C) while the water-insoluble conductive carbon material and the carbon obtained by carbonizing the water-soluble carbon material complement each other. From the viewpoint of supporting the oxide represented by the formula (1), it is preferable that the composite containing the oxide and the water-insoluble conductive carbon material is supported as carbon obtained by carbonizing the water-soluble carbon material. Specifically, it is preferable that a composite formed by supporting a water-insoluble conductive carbon material on an oxide is supported by carbon obtained by carbonizing a water-soluble carbon material.

Specifically, the water-insoluble conductive carbon material is preferably dry-mixed with an oxide obtained by a hydrothermal reaction and supported on the oxide, and is premixed with the oxide. It is more preferable that the mixture is mixed while applying a compressive force and a shearing force and is supported on an oxide. That is, the composite containing the oxide and the water-insoluble conductive carbon material is preferably a dry mixture of the water-insoluble conductive carbon material and an oxide that is a hydrothermal reaction product. In addition, what was carry | supported by the oxide by baking a water-insoluble conductive carbon material is obtained as a composite_body | complex containing an oxide and a water-insoluble conductive carbon material. In addition, during the dry mixing, a water-soluble carbon material may be supplementarily added as necessary, separately from the water-soluble carbon material added during the wet mixing described later. The composite obtained at this time contains a water-soluble carbon material together with an oxide and a water-insoluble conductive carbon material.

A water-soluble carbon material supported as carbonized carbon on a composite containing the oxide and the water-insoluble conductive carbon material is obtained by using the oxide surface of the composite without the presence of the water-insoluble conductive carbon material. From the viewpoint of effectively supporting carbon on the exposed portion, it is preferable that it is supported on an oxide as carbon that is carbonized by being baked after being wet mixed with the composite. . That is, the positive electrode active material for a secondary battery of the present invention is preferably a fired product of a wet mixture of a water-soluble carbon material and a composite containing an oxide and a water-insoluble conductive carbon material. By firing to carbonize this water-soluble carbon material, it is possible to recover the crystallinity of both the oxide and the water-insoluble conductive carbon material, which have been reduced by dry mixing, etc., so the conductivity in the resulting positive electrode active material is effective. Can be increased. The water-soluble carbon material used when wet-mixing may be the same type as the water-soluble carbon material used as an auxiliary when necessary during the dry-mixing, or another type. There may be.

More specifically, the positive electrode active material for a secondary battery of the present invention is a slurry water containing a lithium compound or a sodium compound, a phosphoric acid compound or a silicic acid compound, and a metal salt containing at least an iron compound or a manganese compound. A step (I) of obtaining an oxide X by subjecting to a thermal reaction;
Step (II) in which a water-insoluble conductive carbon material is added to the obtained oxide X and dry-mixed to obtain a composite Y, and a water-soluble carbon material is added to the obtained composite Y and wet-mixed. It is preferably obtained by a production method comprising the step (III) of firing.

Step (I) is a step of obtaining an oxide X by subjecting a slurry water containing a lithium compound or sodium compound, a phosphoric acid compound or a silicic acid compound, and a metal salt containing at least an iron compound or a manganese compound to a hydrothermal reaction. It is.
Examples of the lithium compound or sodium compound that can be used include hydroxides (for example, LiOH.H ₂ O, NaOH), carbonates, sulfates, and acetates. Of these, hydroxide is preferable.
The content of the lithium compound or silicic acid compound in the slurry water is preferably 5 to 50 parts by mass, more preferably 7 to 45 parts by mass with respect to 100 parts by mass of water. More specifically, when a phosphoric acid compound is used in step (I), the content of the lithium compound or sodium compound in the slurry water is preferably 5 to 50 parts by mass with respect to 100 parts by mass of water. The amount is preferably 10 to 45 parts by mass. When a silicate compound is used, the content of the silicate compound in the slurry water is preferably 5 to 40 parts by mass, more preferably 7 to 35 parts by mass with respect to 100 parts by mass of water.

Step (I) is a mixture A containing a lithium compound or a sodium compound from the viewpoint of improving the dispersibility of each component contained in the slurry water and making the obtained positive electrode active material particles finer to improve battery physical properties. ^1, to obtain a mixture a ² was mixed phosphoric acid compound or a silicic acid compound (Ia), to the mixture a ² obtained as well, by adding a metal salt containing at least an iron compound or a manganese compound, and mixed It is preferable to include a step (Ib) of obtaining the oxide X by subjecting the obtained slurry water X to a hydrothermal reaction.

In step (I) or (Ia), prior to mixing the mixture A phosphoric acid compound to ^one or silicic acid compound, preferably it is allowed to stir in advance mixture A ^1. The stirring time of the mixture A ¹ is preferably 1 to 15 minutes, more preferably 3 to 10 minutes. The temperature of the mixture A ¹ is preferably 20 to 90 ° C., more preferably 20 to 70 ° C.

Examples of the phosphoric acid compound used in the step (I) or (Ia) include orthophosphoric acid (H ₃ PO ₄ , phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, and ammonium hydrogen phosphate. Etc. Of these, phosphoric acid is preferably used, and an aqueous solution having a concentration of 70 to 90% by mass is preferably used. In this step (I) or (Ia), Upon mixing phosphoric acid to the mixture A ^1, preferably dropwise addition of phosphoric acid while stirring the mixture A ^1. By adding phosphoric acid dropwise to the mixture A ¹ and adding small portions little by little, the reaction proceeds well in the mixture A ¹ , and the precursor of the oxide X represented by the above (A) to (C) is contained in the slurry. It is also possible to effectively prevent the oxide precursors from being agglomerated unnecessarily while being uniformly dispersed.

The dropping rate of phosphoric acid into the mixture A ¹ is preferably 15 to 50 mL / min, more preferably 20 to 45 mL / min, and further preferably 28 to 40 mL / min. The stirring time of the mixture A ¹ while dropping phosphoric acid is preferably 0.5 to 24 hours, more preferably 3 to 12 hours. Further, the stirring speed of the mixture A ¹ while dropping phosphoric acid is preferably 200 to 700 rpm, more preferably 250 to 600 rpm, and further preferably 300 to 500 rpm.
Note that when the mixture is stirred for A ^1, preferred to further cool the mixture A in the following ¹ the boiling point temperature. Specifically, cooling to 80 ° C. or lower is preferable, and cooling to 20 to 60 ° C. is more preferable.

The silicic acid compound used in the step (I) or (Ia) is not particularly limited as long as it is a reactive silica compound. Amorphous silica, Na ₄ SiO ₄ (for example, Na ₄ SiO ₄ .H ₂ O) Etc.

The mixture A ² after mixing the phosphoric acid compound or the silicic acid compound preferably contains 2.0 to 4.0 mol of lithium or sodium with respect to 1 mol of phosphoric acid or silicic acid. It is more preferable to contain 1 mol, and the lithium compound or sodium compound and the phosphoric acid compound or silicic acid compound may be used so as to obtain such an amount. More specifically, when a phosphoric acid compound is used in step (I), the mixture A ² after mixing the phosphoric acid compound has 2.7 to 3.3 of lithium or sodium per mol of phosphoric acid. It is preferable to contain 2.8 to 3.1 mol, and when the silicate compound is used in step (I), the mixture A ² after mixing the silicate compound is Lithium is preferably contained in an amount of 2.0 to 4.0 mol, more preferably 2.0 to 3.0, with respect to 1 mol.

By purging the mixture A ² after mixing the phosphoric acid compound or silicic acid compound with nitrogen, the reaction in the mixture A ² is completed, and represented by the above (A) to (C) to produce a precursor of the oxides in the mixture a ^2. When nitrogen is purged, the reaction can proceed in a state where the dissolved oxygen concentration in the mixture A ² is reduced, and the dissolved oxygen concentration in the mixture containing the resulting oxide precursor is also effectively increased. Since it is reduced, oxidation of the iron compound or manganese compound added in the next step can be suppressed. In the mixture A ² , the oxide precursors represented by the above (A) to (C) exist as fine dispersed particles. For example, in the case of the oxide represented by the above formula (A), such an oxide precursor is obtained as trilithium phosphate (Li ₃ PO ₄ ).

The pressure for purging nitrogen is preferably 0.1 to 0.2 MPa, more preferably 0.1 to 0.15 MPa. The temperature of the mixture A ² after mixing the phosphoric acid compound or the silicic acid compound is preferably 20 to 80 ° C., more preferably 20 to 60 ° C. For example, in the case of the oxide represented by the above formula (A), the reaction time is preferably 5 to 60 minutes, more preferably 15 to 45 minutes.
Further, when the purging nitrogen from the viewpoint of advancing satisfactorily reaction, it is preferred to stir the mixture A ² after mixing the phosphoric acid compound or a silicic acid compound. The stirring speed at this time is preferably 200 to 700 rpm, more preferably 250 to 600 rpm.

Further, from the viewpoint of more effectively suppressing oxidation of the oxide precursor on the surface of the dispersed particles and miniaturizing the dispersed particles, dissolved oxygen in the mixture A ² after mixing the phosphoric acid compound or the silicate compound. The concentration is preferably 0.5 mg / L or less, and more preferably 0.2 mg / L or less.

In step (I) or (Ib), an oxide X is obtained by subjecting the obtained oxide precursor and slurry water containing a metal salt containing at least an iron compound or a manganese compound to a hydrothermal reaction. . It is preferable to use the obtained oxide precursor as a mixture and add a metal salt containing at least an iron compound or a manganese compound to the slurry water X. As a result, the oxides represented by the above (A) to (C) can be obtained while simplifying the process, and it is possible to obtain extremely fine particles, which are very useful for secondary batteries. A positive electrode active material can be obtained.

Examples of iron compounds that can be used include iron acetate, iron nitrate, and iron sulfate. These may be used alone or in combination of two or more. Among these, iron sulfate is preferable from the viewpoint of improving battery characteristics.

Examples of manganese compounds that can be used include manganese acetate, manganese nitrate, and manganese sulfate. These may be used alone or in combination of two or more. Among these, manganese sulfate is preferable from the viewpoint of improving battery characteristics.

When both an iron compound and a manganese compound are used as the metal salt, the use molar ratio of these iron compound and manganese compound (iron compound: manganese compound) is preferably 99: 1 to 1:99, more preferably 90. : 10 to 10:90. The total addition amount of these iron compound and manganese compound is preferably 0.99 to 1.01 mol, more preferably 0.995 with respect to 1 mol of Li ₃ PO ₄ contained in the slurry water X. ~ 1.005 mol.

Furthermore, you may use metal (M, N, or Q) salts other than an iron compound and a manganese compound as a metal salt as needed. M, N, and Q in the metal (M, N, or Q) salt have the same meanings as M, N, and Q in the above formulas (A) to (C), and as the metal salt, sulfate, halogen compound, organic Acid salts and hydrates thereof can be used. These may be used alone or in combination of two or more. Among them, it is more preferable to use a sulfate from the viewpoint of improving battery physical properties.
When these metal (M, N, or Q) salts are used, the total amount of iron compound, manganese compound, and metal (M, N, or Q) salt added is phosphoric acid in the mixture obtained in the above step (I). Alternatively, the amount is preferably 0.99 to 1.01 mole, more preferably 0.995 to 1.005 mole relative to 1 mole of silicic acid.

The amount of water used for the hydrothermal reaction is phosphoric acid or silicate ions contained in the slurry water X from the viewpoint of the solubility of the metal salt used, the ease of stirring, the efficiency of synthesis, etc. The amount is preferably 10 to 50 mol, more preferably 12.5 to 45 mol, relative to 1 mol. More specifically, when the ions contained in the slurry water X are phosphate ions, the amount of water used for the hydrothermal reaction is preferably 10 to 30 mol, more preferably 12 .5 to 25 moles. Further, when the ions contained in the slurry water X are silicate ions, the amount of water used for the hydrothermal reaction is preferably 10 to 50 mol, more preferably 12.5 to 45. Is a mole.

In the step (I) or (Ib), the order of adding the iron compound, manganese compound and metal (M, N or Q) salt is not particularly limited. Moreover, while adding these metal salts, you may add antioxidant as needed. As such an antioxidant, sodium sulfite (Na ₂ SO ₃ ), hydrosulfite sodium (Na ₂ S ₂ O ₄ ), aqueous ammonia and the like can be used. From the viewpoint of preventing the formation of the oxides represented by the above formulas (A) to (C) by adding an excessive amount of the antioxidant, an iron compound, a manganese compound, and The amount is preferably 0.01 to 1 mol, more preferably 0.03 to 0.5 mol, relative to a total of 1 mol of the metal (M, N or Q) salt used as necessary.

The content of the oxide precursor in the slurry water X obtained by adding an iron compound, a manganese compound, and a metal (M, N or Q) salt or an antioxidant used as necessary is preferably 10 to It is 50% by mass, more preferably 15 to 45% by mass, and still more preferably 20 to 40% by mass.

The hydrothermal reaction in the step (I) or (Ib) may be 100 ° C. or higher, and preferably 130 to 180 ° C. The hydrothermal reaction is preferably carried out in a pressure-resistant vessel. When the reaction is carried out at 130 to 180 ° C., the pressure at this time is preferably 0.3 to 0.9 MPa, and the reaction is carried out at 140 to 160 ° C. The pressure is preferably 0.3 to 0.6 MPa. The hydrothermal reaction time is preferably 0.1 to 48 hours, more preferably 0.2 to 24 hours.
The obtained oxide X is an oxide represented by the above formulas (A) to (C), which can be isolated by filtration, washing with water, and drying. As the drying means, freeze drying or vacuum drying is used.

The BET specific surface area of the resulting oxide X is preferably 5 to 40 m ² / g, more preferably 5 to 40 m from the viewpoint of efficiently carrying the coexisting carbon and effectively reducing the amount of adsorbed water. 20 m ² / g. When the BET specific surface area of the oxide X is less than 5 m ² / g, the primary particles of the positive electrode active material for the secondary battery become too large, and the battery characteristics may be deteriorated. On the other hand, if the BET specific surface area exceeds 40 m ² / g, the amount of adsorbed moisture of the positive electrode active material for the secondary battery may increase and affect the battery characteristics.

Step (II) is a step of adding the water-insoluble conductive carbon material to the oxide X obtained in step (I) and then dry mixing to obtain the composite Y. In addition to the water-insoluble conductive carbon material, a water-soluble carbon material may be further supplementarily added. In this case, the order of addition is not particularly limited. The amount of the water-insoluble conductive carbon material added is preferably 0.5 to 24.2 parts by mass, more preferably 1.5 to 20.5 parts by mass with respect to 100 parts by mass of the oxide X, for example. The amount is preferably 2.6 to 17.0 parts by mass. Specifically, the addition amount of the water-insoluble conductive carbon material is preferably 0.5 to 17.0 in the case of the positive electrode active material for a secondary battery in which the oxide is represented by the above formula (A) or (C). Secondary battery in which the oxide is represented by the above formula (B), more preferably 1.5 to 14.9 parts by mass, and still more preferably 2.6 to 13.0 parts by mass. The positive electrode active material for use is preferably 1.3 to 23.8 parts by mass, more preferably 2.3 to 20.1 parts by mass, and still more preferably 3.4 to 16.6 parts by mass.
In addition, in the step (II), when the water-insoluble conductive carbon material and the water-soluble carbon material are used in combination, the mass of the addition amount of the water-insoluble conductive carbon material and the carbon atom equivalent amount of the addition amount of the water-soluble carbon material The ratio (water-insoluble conductive carbon material: water-soluble carbon material) is preferably 100: 2 to 3: 100, more preferably 100: 10 to 10: 100.

The dry mixing in the step (II) is preferably mixing by a normal ball mill, and more preferably by a planetary ball mill capable of revolving. Further, the water-insoluble conductive carbon material and the water-soluble carbon material used in combination as necessary are densely and uniformly dispersed on the oxide surface represented by the above formulas (A) to (C) and carbonized. From the viewpoint of effectively supporting the carbon, it is more preferable to mix the composite Y while applying a compressive force and a shearing force to obtain a composite Y ′. The process of mixing while applying a compressive force and a shearing force is preferably performed in a closed container equipped with an impeller. The peripheral speed of the impeller is preferably 25 to 40 m / s, more preferably 27 from the viewpoint of increasing the tap density of the obtained positive electrode active material and reducing the BET specific surface area to effectively reduce the amount of adsorbed water. ~ 40 m / s. The mixing time is preferably 5 to 90 minutes, more preferably 10 to 80 minutes.
The peripheral speed of the impeller means the speed of the outermost end of the rotary stirring blade (impeller), which can be expressed by the following formula (1), and is mixed while applying compressive force and shearing force. The processing time may vary depending on the peripheral speed of the impeller so that it becomes longer as the peripheral speed of the impeller is slower.
Impeller peripheral speed (m / s) =
Impeller radius (m) × 2 × π × rotational speed (rpm) ÷ 60 (1)

In the step (II), the processing time and / or the impeller peripheral speed when performing the mixing process while applying the compressive force and the shearing force need to be appropriately adjusted according to the amount of the composite Y to be charged into the container. There is. 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, and the above formulas (A) to (C The water-insoluble conductive carbon material and the water-soluble carbon material to be used in combination as needed are densely and uniformly dispersed on the oxide surface represented by Combined with the added water-soluble carbon material, a positive electrode active material for a secondary battery that can effectively reduce the amount of adsorbed water can be obtained.
For example, when the mixing process is performed for 6 to 90 minutes in an airtight container equipped with an impeller rotating at a peripheral speed of 25 to 40 m / s, the amount of the composite Y charged into the container is an effective container (airtight equipped with an impeller). Of the containers, a container corresponding to a part capable of accommodating the complex Y) is preferably 0.1 to 0.7 g, more preferably 0.15 to 0.4 g per 1 cm ³ .

Examples of the apparatus equipped with a closed container that can easily perform mixing while applying compressive force and shear force include a high-speed shear mill, a blade-type kneader, and the like. Fine particle composite apparatus Nobilta (manufactured by Hosokawa Micron Corporation) can be suitably used.
As the mixing treatment conditions, the treatment temperature is preferably 5 to 80 ° C., more preferably 10 to 50 ° C. The treatment atmosphere is not particularly limited, but is preferably an inert gas atmosphere or a reducing gas atmosphere.

Step (III) is a step of adding a water-soluble carbon material obtained in step (I), wet mixing, and baking. This effectively suppresses the exposure of the surface of the oxide X represented by the above (A) to (C), while the water-insoluble conductive carbon material and the water-soluble carbon material are carbonized on the oxide X. The formed carbon can be supported firmly together.

The amount of the water-soluble carbon material added in the step (III) is such that carbon obtained by carbonizing the water-soluble carbon material is effectively supported on the surface of the oxide X where no water-insoluble conductive carbon material is present, and sufficient charge is obtained. From the viewpoint of maintaining the discharge capacity, 100 parts by mass of composite Y (or composite Y ′ when the above-described process (II) is further mixed while applying the compressive force and shearing force) On the other hand, it is preferably 1.0 to 55.0 parts by mass, more preferably 1.0 to 40.0 parts by mass, and still more preferably 1.0 to 30.0 parts by mass.

In step (III), it is preferable to add water together with the water-soluble carbon material from the viewpoint of favorably supporting the carbon obtained by carbonizing the water-soluble carbon material on the oxide surface. The amount of water added is preferably 30 to 300 parts by mass, more preferably 50 to 250 parts by mass, and even more preferably 75 to 200 parts by mass with respect to 100 parts by mass of the complex Y (or complex Y ′). Part. When the water-soluble carbon material is supplementarily added in step (II) with this water, the supplementally added water-soluble carbon material supported on the composite Y (or composite Y ′) is dissolved, The same action as the water-soluble carbon material added in (III) can be exhibited.

The wet mixing means in step (III) is not particularly limited, and can be performed by a conventional method. The temperature at the time of mixing after adding the water-soluble carbon material to the composite Y (or the composite Y ′) is preferably 5 to 80 ° C., more preferably 7 to 70 ° C. The resulting mixture is preferably dried before firing. Examples of the drying means include spray drying, vacuum drying, freeze drying and the like.

In step (III), the mixture obtained by the wet mixing is fired. Firing is preferably performed in a reducing atmosphere or an inert atmosphere. The firing temperature is preferably 500 to 800 ° C., more preferably 600 from the viewpoint of improving the conductivity by improving the crystallinity of the water-insoluble conductive carbon material and from the viewpoint of more effectively carbonizing the water-soluble carbon material. It is ˜770 ° C., more preferably 650 to 750 ° C. The firing time is preferably 10 minutes to 3 hours, more preferably 30 minutes to 1.5 hours.

The positive electrode active material for a secondary battery according to the present invention has the water-insoluble conductive carbon material and the carbon obtained by carbonizing the water-soluble carbon material both supported on the oxide and acting synergistically. The amount of moisture adsorbed in the positive electrode active material for batteries can be effectively reduced. Specifically, the amount of adsorbed moisture of the positive electrode active material for secondary battery of the present invention is the same for the secondary battery in the case of the positive electrode active material for secondary battery in which the oxide is represented by the formula (A) or (C). In the positive electrode active material, it is preferably 850 ppm or less, more preferably 700 ppm or less, and in the positive electrode active material for a secondary battery in which the oxide is represented by the above formula (B), preferably 2900 ppm or less, and more Preferably it is 2500 ppm or less. The amount of adsorbed moisture is such that moisture is adsorbed until equilibrium is reached at a temperature of 20 ° C. and a relative humidity of 50%, the temperature is raised to 150 ° C. and held for 20 minutes, and further raised to a temperature of 250 ° C. Measured as the amount of water volatilized from the start point to the end point, starting from when the temperature rise is resumed from 150 ° C. when held for 20 minutes and ending at the constant temperature state at 250 ° C. It is assumed that the amount of adsorbed moisture of the positive electrode active material for a secondary battery and the amount of moisture volatilized from the start point to the end point are the same, and the measured value of the volatilized moisture amount is This is the amount of moisture adsorbed on the positive electrode active material for the secondary battery.
Thus, since the positive electrode active material for a secondary battery of the present invention hardly adsorbs moisture, the amount of adsorbed moisture can be effectively reduced without requiring strong drying conditions as a production environment, and the resulting lithium In both the ion secondary battery and the sodium ion secondary battery, it is possible to stably exhibit excellent battery characteristics even under various usage environments.
When water is adsorbed until equilibrium is reached at a temperature of 20 ° C. and a relative humidity of 50%, the temperature is raised to 150 ° C. and held for 20 minutes, and further raised to a temperature of 250 ° C. and held for 20 minutes. The amount of water volatilized between the start point and the end point, starting from when the temperature rise is resumed from 150 ° C. and the end point when the constant temperature state at 250 ° C. is completed, is measured using, for example, a Karl Fischer moisture meter Can be measured.

Further, the tap density of the positive electrode active material for a secondary battery of the present invention is preferably 0.5 to 1.6 g / cm ³ , more preferably 0.8 from the viewpoint of effectively reducing the amount of adsorbed moisture. ~ 1.6 g / cm ³ .

Furthermore, the BET specific surface area of the positive electrode active material for a secondary battery of the present invention is preferably 5 to 21 m ² / g, more preferably 7 to 20 m ² / g, from the viewpoint of effectively reducing the amount of adsorbed moisture. It is.

The secondary battery to which the positive electrode for the secondary battery including the positive electrode active material for the secondary battery 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 for the negative electrode, as long as lithium ions or sodium ions can be occluded at the time of charging and can be released at the time of discharging, the material configuration is not particularly limited, and those having a known material configuration can be used. . For example, a carbon material such as lithium metal, sodium metal, graphite, or amorphous carbon. It is preferable to use an electrode formed of an intercalating material capable of electrochemically inserting and extracting lithium ions or sodium ions, 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 or a sodium ion secondary battery. For example, carbonates, halogenated hydrocarbons, ethers, ketones Nitriles, lactones, oxolane compounds and the like can be used.

The type of the supporting salt is not particularly limited, but in the case of a lithium ion secondary battery, an inorganic salt selected from LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , a derivative of the inorganic salt, LiSO ₃ CF ₃ , an organic material selected from LiC (SO ₃ CF ₃ ) ₂ , 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 ) It is preferably at least one of a salt and a derivative of the organic salt. In the case of a sodium ion secondary battery, an inorganic salt selected from NaPF ₆ , NaBF ₄ , NaClO ₄ and NaAsF ₆ , a derivative of the inorganic salt, NaSO ₃ CF ₃ , NaC (SO ₃ CF ₃ ) ₂ and NaN (SO ₃ CF ₃ ) ₂ , NaN (SO ₂ C ₂ F ₅ ) _2, and an organic salt selected from NaN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), and at least one derivative of the organic salt It is preferable.

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.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.

[Example 1-1]
The slurry water was obtained by mixing 4.9 kg of LiOH.H ₂ O and 11.7 kg of water. Next, while maintaining the obtained slurry water at a temperature of 25 ° C. and stirring for 30 minutes at a speed of 400 rpm, 5.09 kg of a 70% phosphoric acid aqueous solution was dropped at 35 mL / min to obtain a mixture A ¹ . . The pH of the mixed slurry was 10.0 and contained 0.33 mol of phosphoric acid with respect to 1 mol of lithium hydroxide.

Next, the resulting mixture A ¹ was purged with nitrogen while stirring at a speed of 400 rpm for 30 minutes to complete the reaction with the mixture A ¹ (dissolved oxygen concentration 0.5 mg / L). Subsequently, 1.63 kg of FeSO ₄ .7H ₂ O and 5.60 kg of MnSO ₄ .H ₂ O are added to 21.7 kg of the mixture A ^{1, and} 0.0468 kg of Na ₂ SO _{3 is} further added, and the speed is 400 rpm. to obtain a mixture a ² are stirred and mixed at. In this case, the added FeSO ₄ · 7H ₂ O and MnSO ₄ · H ₂ O molar ratio of _{_{(FeSO 4 · 7H 2 O:}} MnSO 4 · H 2 O) is 20: was 80.
Next, the mixture A ² was put into a synthesis container installed in a steam heating autoclave. After the addition, the mixture was heated with stirring at 170 ° C. for 1 hour using saturated steam obtained by heating water (dissolved oxygen concentration less than 0.5 mg / L) with a membrane separator. The pressure in the autoclave was 0.8 MPa. The formed crystals were filtered and then washed with water. The washed crystal was vacuum-dried under the conditions of 60 ° C. and 1 Torr to obtain an oxide X ¹ (powder, chemical composition represented by the formula (A): LiFe _0.2 Mn _0.8 PO ₄ ).

100 g of the obtained oxide X ¹ was fractionated, and 4 g of graphite (high-purity graphite powder, manufactured by Nippon Graphite Industry Co., Ltd., BET specific surface area 5 m ² / g, average particle size 6.1 μm, in the active material) (Corresponding to 3.8% by mass in terms of carbon atoms) was mixed by a dry method using a ball mill. The obtained composite Y ¹ was mixed with Nobilta (manufactured by Hosokawa Micron Corporation, NOB130) at 40 m / s (6000 rpm) for 5 minutes to obtain a composite Y ¹ ′ (powder).

10 g of the obtained complex Y ¹ ′ was collected, and 0.25 g of glucose (corresponding to 1.0% by mass in terms of carbon atom in the active material) and 10 mL of water were added to this, and mixed to 80 ° C. in performed 12 hours drying, and calcined at 700 ° C. 11 hours under a reducing atmosphere, the oxide X ¹ to graphite and glucose derived from a cathode active material for a lithium ion secondary battery in which the carbon formed by carrying (LiFe _0.2 Mn _0.8 PO ₄ and carbon amount = 4.8% by mass).

[Example 1-2]
A lithium ion secondary battery was produced in the same manner as in Example 1-1 except that 0.5 g of glucose added to the complex Y ¹ ′ (corresponding to 2.0 mass% in terms of carbon atom in the active material) was used. A positive electrode active material (LiFe _0.2 Mn _0.8 PO ₄ , amount of carbon = 5.8 mass%) was obtained.

[Example 1-3]
A lithium ion secondary battery was produced in the same manner as in Example 1-1, except that 0.75 g of glucose added to the complex Y ¹ ′ (corresponding to 2.9% by mass in terms of carbon atom in the active material) was used. A positive electrode active material (LiFe _0.2 Mn _0.8 PO ₄ , amount of carbon = 6.7% by mass) was obtained.

[Example 1-4]
A lithium ion secondary battery was prepared in the same manner as in Example 1-1, except that 1.25 g of glucose added to the complex Y ¹ ′ (corresponding to 4.8% by mass in terms of carbon atom in the active material) was used. A positive electrode active material (LiFe _0.2 Mn _0.8 PO ₄ , amount of carbon = 8.6% by mass) was obtained.

[Example 1-5]
Oxide X ² (powder, represented by formula (A)) was prepared in the same manner as in Example 1-1, except that FeSO ₄ · 7H ₂ O was 7.34 kg and MnSO ₄ · H ₂ O was 0.7 kg. After obtaining LiFe _0.9 Mn _0.1 PO ₄ ), 4 g of graphite (corresponding to 3.8% by mass in terms of carbon atom in the active material) was mixed to obtain composite Y ² and composite Y ² ′. Next, 0.25 g of glucose (corresponding to 1.0% by mass in terms of carbon atom in the active material) is added, and the lithium ion secondary battery in which graphite and carbon derived from glucose are supported is obtained. A positive electrode active material (LiFe _0.9 Mn _0.1 PO ₄ , amount of carbon = 4.8% by mass) was obtained.

[Comparative Example 1-1]
A positive electrode active material for a lithium ion secondary battery (LiFe _0.9 Mn _0.1 PO ₄ , amount of carbon = 3.8% by mass) in the same manner as in Example 1-5, except that glucose was not added to the complex Y ² ′. )

[Example 2-1]
3.75 L of ultrapure water was mixed with 0.428 kg of LiOH.H ₂ O and 1.40 kg of Na ₄ SiO ₄ .nH ₂ O to obtain slurry water. To this slurry water, 0.39 kg of FeSO ₄ .7H ₂ O, 0.79 kg of MnSO ₄ .5H ₂ O, and 0.053 kg of Zr (SO ₄ ) ₂ .4H ₂ O were added and mixed. Subsequently, the obtained mixed liquid was put into an autoclave, and a hydrothermal reaction was performed 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 crystals were freeze-dried at −50 ° C. for 12 hours to obtain oxide X ³ (powder, chemical composition represented by formula (B): Li ₂ Fe _0.28 Mn _0.66 Zr _0.03 SiO ₄ ).

213.9 g of the obtained oxide X ³ was fractionated and mixed with 16.1 g of graphite (corresponding to 7.0% by mass in terms of carbon atom in the active material) by a ball mill in a dry manner. The obtained composite Y ³ was mixed with Nobilta (manufactured by Hosokawa Micron Corporation, NOB130) at 40 m / s (6000 rpm) for 5 minutes to obtain a composite Y ³ ′ (powder). 5 g of the obtained complex Y ³ ′ was fractionated, and 0.125 g of glucose (corresponding to 1.0% by mass in terms of carbon atom in the active material) and 10 mL of water were added to this, and mixed to 80 ° C. For 12 hours, calcined at 650 ° C. for 1 hour in a reducing atmosphere, and positive electrode active material for lithium ion secondary battery (Li ₂ Fe) in which graphite and carbon derived from glucose are supported on oxide X ³ _0.28 Mn _0.66 Zr _0.03 SiO ₄ , amount of carbon = 8.0% by mass).

[Example 2-2]
A lithium ion secondary battery was produced in the same manner as in Example 2-1, except that the amount of glucose added to the complex Y ³ ′ was 0.25 g (corresponding to 2.0 mass% in terms of carbon atom in the active material). A positive electrode active material (Li ₂ Fe _0.28 Mn _0.66 Zr _0.03 SiO ₄ , amount of carbon = 9.0% by mass) was obtained.

[Example 2-3]
A lithium ion secondary battery was produced in the same manner as in Example 2-1, except that 0.375 g of glucose added to the complex Y ³ ′ (corresponding to 2.9% by mass in terms of carbon atoms in the active material) was used. A positive electrode active material (Li ₂ Fe _0.28 Mn _0.66 Zr _0.03 SiO ₄ , amount of carbon = 9.9% by mass) was obtained.

[Example 2-4]
A lithium ion secondary battery was prepared in the same manner as in Example 2-1, except that 0.875 g of glucose added to the complex Y ³ ′ (corresponding to 6.8% by mass in terms of carbon atom in the active material) was used. A positive electrode active material (Li ₂ Fe _0.28 Mn _0.66 Zr _0.03 SiO ₄ , amount of carbon = 13.8% by mass) was obtained.

[Comparative Example 2-1]
A positive electrode active material for lithium ion secondary battery (Li ₂ Fe _0.28 Mn _0.66 Zr _0.03 SiO ₄ , amount of carbon = 7) in the same manner as in Example 2-1, except that glucose was not added to the composite Y ³ ′. 0.0 mass%) was obtained.

[Example 3-1]
A solution was obtained by mixing 0.60 kg of NaOH and 9.0 L of water. Next, the obtained solution is stirred for 5 minutes while maintaining the temperature at 25 ° C., and 0.577 kg of 85% phosphoric acid aqueous solution is dropped at 35 mL / min, followed by stirring at a speed of 400 rpm for 12 hours. Thus, a slurry containing the mixture A ⁴ was obtained. Such a slurry contained 3.00 moles of sodium per mole of phosphorus. The obtained slurry was purged with nitrogen gas to adjust the dissolved oxygen concentration to 0.5 mg / L, then 0.139 kg of FeSO ₄ .7H ₂ O, 0.964 kg of MnSO ₄ .5H ₂ O, MgSO _4. 0.124 kg of 7H ₂ O was added. Subsequently, the obtained liquid mixture was thrown into the autoclave purged with nitrogen gas, and the hydrothermal reaction was performed at 200 degreeC for 3 hours. The pressure in the autoclave was 1.4 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 crystals were freeze-dried at −50 ° C. for 12 hours to obtain oxide X ⁴ (powder, chemical composition represented by formula (C): NaFe _0.1 Mn _0.8 Mg _0.1 PO ₄ ).

153.6 g of the obtained oxide X ⁴ was fractionated and mixed with 6.4 g of graphite (corresponding to 4% by mass in terms of carbon atom in the active material) by a dry method using a ball mill. The obtained composite Y ⁴ was mixed with Nobilta (manufactured by Hosokawa Micron Corporation, NOB130) at 40 m / s (6000 rpm) for 5 minutes to obtain a composite Y ⁴ ′ (powder). 5 g of the obtained complex Y ⁴ ′ was fractionated, and 0.125 g of glucose (corresponding to 1.0% by mass in terms of carbon atom in the active material) and 10 mL of water were added to this, and mixed to 80 ° C. For 12 hours, calcined at 700 ° C. for 1 hour in a reducing atmosphere, and positive electrode active material for sodium ion secondary battery (NaFe _0.1 Mn) in which graphite and glucose-derived carbon are supported on oxide X ⁴ _0.8 Mg _0.1 PO ₄ , amount of carbon = 5.0% by mass).

[Example 3-2]
Sodium ion secondary battery in the same manner as in Example 3-1, except that 0.25 g of glucose added to complex Y ⁴ ′ (corresponding to 2.0% by mass in terms of carbon atom in the active material) was used A positive electrode active material (NaFe _0.1 Mn _0.8 Mg _0.1 PO ₄ , amount of carbon = 6.0% by mass) was obtained.

[Example 3-3]
A sodium ion secondary battery was prepared in the same manner as in Example 3-1, except that 0.375 g of glucose added to the complex Y ⁴ ′ (corresponding to 2.9% by mass in terms of carbon atom in the active material) was used. A positive electrode active material (NaFe _0.1 Mn _0.8 Mg _0.1 PO ₄ , amount of carbon = 6.9% by mass) was obtained.

[Example 3-4]
A sodium ion secondary battery was prepared in the same manner as in Example 3-1, except that the glucose added to the complex Y ⁴ ′ was 0.92 g (corresponding to 6.8% by mass in terms of carbon atoms in the active material). A positive electrode active material (NaFe _0.1 Mn _0.8 Mg _0.1 PO ₄ , amount of carbon = 10.8% by mass) was obtained.

[Comparative Example 3-1]
A positive electrode active material for sodium ion secondary battery (NaFe _0.1 Mn _0.8 Mg _0.1 PO ₄ , amount of carbon = 4.0) in the same manner as in Example 3-1, except that glucose was not added to the complex Y ⁴ ′. Mass%).

<Measurement of adsorbed water content>
The adsorbed moisture content of each positive electrode active material obtained in Examples 1-1 to 3-4 and Comparative Examples 1-1 to 3-1 was measured according to the following method.
About the positive electrode active material (composite particle), after allowing it to stand for 1 day in an environment of a temperature of 20 ° C. and a relative humidity of 50% and adsorbing moisture until reaching equilibrium, raising the temperature to 150 ° C. and holding for 20 minutes, Furthermore, when the temperature is raised to 250 ° C. and held for 20 minutes, the start point is when the temperature rise is resumed from 150 ° C., and the end point is when the constant temperature state at 250 ° C. is completed. The amount of water volatilized in the water was measured with a Karl Fischer moisture meter (MKC-610, manufactured by Kyoto Electronics Industry Co., Ltd.) and determined as the amount of water adsorbed on the positive electrode active material.
The results are shown in Table 1.

<< Evaluation of charge / discharge characteristics using secondary battery >>
Using the positive electrode active materials obtained in Examples 1-1 to 3-4 and Comparative Examples 1-1 to 3-1, positive electrodes of lithium ion secondary batteries or sodium ion secondary batteries were produced. Specifically, the obtained positive electrode active material, ketjen black, and polyvinylidene fluoride were mixed at a mixing ratio of 75: 20: 5, and N-methyl-2-pyrrolidone was added thereto and kneaded sufficiently. A positive electrode slurry was prepared. 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 secondary battery was constructed using the positive electrode. A lithium foil punched to φ15 mm was used for the negative electrode. For the electrolyte, LiPF ₆ (in the case of a lithium ion secondary battery) or NaPF ₆ (in the case of a sodium ion secondary battery) is added to a mixed solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 1: 1. Those dissolved at a concentration of 1 mol / L were 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 having a dew point of −50 ° C. or lower to produce a coin-type secondary battery (CR-2032).

A charge / discharge test was performed using the manufactured secondary battery. In the case of a lithium ion battery, the charging condition is a constant current and constant voltage charge with a current of 1 CA (330 mA / g) and a voltage of 4.5 V, the discharge condition is 1 CA (330 mA / g), and a constant current discharge with a final voltage of 1.5 V. As a result, the discharge capacity at 1 CA was obtained. In the case of a sodium ion battery, the charging conditions are a constant current and constant voltage charging with a current of 1 CA (154 mA / g) and a voltage of 4.5 V, the discharging conditions are a constant current discharge of 1 CA (154 mA / g) and a final voltage of 2.0 V. As a result, the discharge capacity at 1 CA was obtained. Furthermore, 50 cycle repetition tests were performed under the same charge / discharge conditions, and the capacity retention rate (%) was determined by the following formula (2). All charge / discharge tests were performed at 30 ° C.
Capacity retention (%) = (discharge capacity after 50 cycles) / (discharge capacity after 1 cycle) × 100 (2)
The results are shown in Table 2.

From the above results, it can be seen that the positive electrode active material of the example can surely reduce the amount of adsorbed moisture as compared with the positive electrode active material of the comparative example, and can also exhibit excellent performance in the obtained battery.

Claims

The following formula (A), (B) or (C) containing at least iron or manganese:
LiFe a Mn b M c PO 4 (A)
(In the formula (A), M represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. A, b, and c are 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ c ≦ 0.2, and 2a + 2b + (M valence) × c = 2 and a number satisfying a + b ≠ 0 are shown.)
Li 2 Fe d Mn e N f SiO 4 (B)
(In the formula (B), N represents Ni, Co, Al, Zn, V, or Zr. D, e, and f are 0 ≦ d ≦ 1, 0 ≦ e ≦ 1, and 0 ≦ f <1, 2d + 2e +. (The valence of N) × f = 2 is satisfied, and d + e ≠ 0 is satisfied.)
NaFe g Mn h Q i PO 4 (C)
(In the formula (C), Q represents Mg, Ca, Co, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. G, h, and i are 0. ≦ g ≦ 1, 0 ≦ h ≦ 1, 0 ≦ i <1, and 2g + 2h + (Q valence) × i = 2 and a number satisfying g + h ≠ 0 are shown.
A positive electrode active material for a secondary battery, in which a water-insoluble conductive carbon material and carbon obtained by carbonizing a water-soluble carbon material are supported on an oxide represented by:
The positive electrode active material for a secondary battery according to claim 1, wherein carbon obtained by carbonizing a water-soluble carbon material is supported on a composite including an oxide and a water-insoluble conductive carbon material.
The positive electrode active material for a secondary battery according to claim 1 or 2, wherein the water-insoluble conductive carbon material and the water-soluble carbon material have a total carbon atom conversion amount of 1.0 to 20.0 mass%.
The positive electrode active material for a secondary battery according to any one of claims 1 to 3, wherein the water-soluble carbon material is one or more selected from saccharides, polyols, polyethers, and organic acids.
The positive electrode active material for a secondary battery according to any one of claims 1 to 4, wherein the water-insoluble conductive carbon material is graphite.
The composite according to any one of claims 2 to 5, wherein the composite is supported on an oxide by dry mixing with a water-insoluble conductive carbon material and an oxide obtained by a hydrothermal reaction. Positive electrode active material for secondary battery.
The positive electrode active material for a secondary battery according to claim 6, wherein the dry mixing is a mixture in which an oxide and a water-insoluble conductive carbon material are premixed and then mixed while applying compressive force and shearing force.
The water-soluble carbon material according to any one of claims 2 to 7, wherein the water-soluble carbon material is supported on the oxide as carbon that is carbonized by being wet-mixed with the composite containing the oxide and then calcined. Positive electrode active material for secondary battery.
The following formula (A), (B) or (C) containing at least iron or manganese:
LiFe a Mn b M c PO 4 (A)
(In the formula (A), M represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. A, b, and c are 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ c ≦ 0.2, and 2a + 2b + (M valence) × c = 2 and a number satisfying a + b ≠ 0 are shown.)
Li 2 Fe d Mn e N f SiO 4 (B)
(In the formula (B), N represents Ni, Co, Al, Zn, V, or Zr. D, e, and f are 0 ≦ d ≦ 1, 0 ≦ e ≦ 1, and 0 ≦ f <1, 2d + 2e +. (The valence of N) × f = 2 is satisfied, and d + e ≠ 0 is satisfied.)
NaFe g Mn h Q i PO 4 (C)
(In the formula (C), Q represents Mg, Ca, Co, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd. G, h, and i are 0. ≦ g ≦ 1, 0 ≦ h ≦ 1, 0 ≦ i <1, and 2g + 2h + (Q valence) × i = 2 and a number satisfying g + h ≠ 0 are shown.
A method for producing a positive electrode active material for a secondary battery in which a water-insoluble conductive carbon material and carbon obtained by carbonizing a water-soluble carbon material are supported on an oxide represented by:
A step (I) of obtaining an oxide X by subjecting a slurry water containing a lithium compound or sodium compound, a phosphoric acid compound or a silicic acid compound, and a metal salt containing at least an iron compound or a manganese compound to a hydrothermal reaction;
Step (II) in which a water-insoluble conductive carbon material is added to the obtained oxide X and dry-mixed to obtain a composite Y, and a water-soluble carbon material is added to the obtained composite Y and wet-mixed. The manufacturing method of the positive electrode active material for secondary batteries provided with the process (III) baked.
The method for producing a positive electrode active material for a secondary battery according to claim 9, wherein the water-soluble carbon material is one or more selected from saccharides, polyols, polyethers, and organic acids.
The method for producing a positive electrode active material for a secondary battery according to claim 9 or 10, wherein the water-insoluble conductive carbon material is graphite.
The method for producing a positive electrode active material for a secondary battery according to any one of claims 9 to 11, wherein a water-soluble carbon material is added together with the water-insoluble conductive carbon material in the step (II).
The secondary battery according to any one of claims 9 to 12, wherein the amount of the water-soluble carbon material added in step (III) is 1.0 to 55.0 parts by mass with respect to 100 parts by mass of the composite Y. A method for producing a positive electrode active material.
14. The dry mixing in step (II) is a mixture in which an oxide and a water-insoluble conductive carbon material are premixed and then mixed while applying compressive force and shearing force. The manufacturing method of the positive electrode active material for secondary batteries of description.