JP2016171057A - Positive electrode active material for secondary battery, and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for a secondary battery, which enables the effective reduction in water content while imparting the property less likely to absorb a water content to a positive electrode active material per se, and a method for manufacturing such a positive electrode active material in order to offer a high-performance lithium ion secondary battery or sodium ion secondary battery.SOLUTION: A positive electrode active material for a secondary battery comprises a composite including at least an oxide including iron or manganese, and expressed by one of the formulas (A) to (C) below, and a cellulose nanofiber-originating carbon, and graphite supported by the composite: LiFeMnMPO(A); LiFeMnNSiO(B); and NaFeMnQPO(C).SELECTED DRAWING: None

Description

  The present invention relates to a positive electrode active material for a secondary battery in which graphite is supported on a composite containing an oxide and carbon derived from cellulose nanofibers, 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.

  For example, in Patent Document 1, an attempt is made to improve the performance of the obtained battery by making primary crystal particles ultrafine particles and shortening the lithium ion diffusion distance in the olivine-type positive electrode active material. In Patent Document 2, a conductive carbonaceous material is uniformly deposited on the particle surface of the positive electrode active material, and a regular electric field distribution is obtained on the particle surface to increase the output of the battery.

By the way, in the lithium ion secondary battery which is spreading widely, a phenomenon is known in which 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. In order to effectively suppress such deterioration of battery performance, it is desirable to reduce the water content of the positive electrode active material used for the secondary battery as much as possible.

  Thus, while it is desired to reduce the water content of the positive electrode active material, for example, in Patent Document 3, after the firing treatment of the raw material mixture containing the carbonaceous material precursor, the pulverization treatment and the classification treatment are dried. A technique for reducing the water content to a certain value or less by performing in an atmosphere is disclosed. In addition, Patent Document 4 considers that an active material obtained using primary particles having an increased specific surface area may be sensitive to deterioration by moist air when the surface is coated with carbon. In addition, a technique is disclosed in which a predetermined raw material is subjected to a synthesis reaction in a dry atmosphere to maintain a humidity level below a certain level during manufacture, storage, and use of a positive electrode material.

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 5 discloses an active material for a sodium secondary battery using marisite-type NaMnPO ₄ , and Patent Document 6 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 2010-251302 A JP 2001-15111 A JP 2003-292309 A Special table 2010-508234 gazette JP 2008-260666 A JP 2011-34963 A

However, since the techniques described in Patent Documents 3 and 4 are intended to perform a drying process for reducing the water content of the positive electrode active material until the battery is processed, until the battery is obtained. In order to effectively prevent the deterioration of the performance of the electronic characteristics, it is still necessary to improve the type and amount of the carbon source to be used.
Further, the sodium ion secondary battery active materials described in Patent Documents 5 and 6 do not sufficiently reduce the water content, and are more useful as an alternative battery for a lithium ion secondary battery. Realization of a secondary battery is desired.

  Therefore, in order to obtain a high-performance lithium ion secondary battery or sodium ion secondary battery, it is an object of the present invention to effectively reduce moisture content while imparting the property of not adsorbing moisture to the positive electrode active material itself. The present invention provides a positive electrode active material for a secondary battery and a method for producing the same.

  Therefore, the present inventors have made various studies, and if it is a positive electrode active material for a secondary battery in which graphite is supported on a composite containing a specific oxide and carbon derived from cellulose nanofibers, it is effective. The present inventors have found that the amount of water is reduced and lithium ions or sodium ions are extremely useful as a positive electrode active material for a secondary battery that can effectively carry electric conduction, and the present invention has been 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, 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 + (Q valence) × i = 2 and a number satisfying g + h ≠ 0 are shown.
The positive electrode active material for secondary batteries formed by carrying | supporting the graphite on the composite_body | complex containing the oxide represented by these, and the carbon derived from a cellulose nanofiber is provided.

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, 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 + (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 graphite is supported on a composite containing an oxide represented by the above and carbon derived from cellulose nanofibers, the oxide and the cellulose nanofibers. Adding a graphite to the composite;
The addition amount of graphite with respect to the carbon atom equivalent amount of cellulose nanofiber is 0.08 to 6 in mass ratio (graphite / cellulose nanofiber), and lithium X or sodium compound and mixture X containing cellulose nanofiber, A step of obtaining a complex X by mixing a phosphoric acid compound or a silicic acid compound (I),
Step (II) of obtaining the composite Y by subjecting the obtained composite X and slurry water Y containing a metal salt containing at least an iron compound or a manganese compound to a hydrothermal reaction.
Step (III) for obtaining composite Z by adding graphite to the obtained composite Y and adding compression force and shearing force, and the obtained composite Z in a reducing atmosphere or an inert atmosphere Firing step (IV)
The manufacturing method of the positive electrode active material for secondary batteries provided with this is provided.

  According to the present invention, it is possible to obtain a positive electrode active material for a secondary battery that firmly supports carbon and graphite derived from cellulose nanofibers without going through a strong drying process, and it is effective in the ability to hardly adsorb moisture. Can be granted. Therefore, in a lithium ion secondary battery or a sodium ion secondary battery using this, lithium ions or sodium ions effectively carry electric conduction, and stably exhibit excellent battery characteristics under various usage environments. Can do.

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 + (Q valence) × 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, for example, 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 LiFe _0.2 Mn _0.8 PO ₄ is particularly 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 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 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 of the present invention is a composite (primary particle) containing an oxide represented by the above formula (A), (B) or (C) and carbon derived from cellulose nanofibers. Graphite is supported. That is, it is obtained by using cellulose nanofibers and graphite as a carbon source, and both carbon obtained by carbonizing cellulose nanofibers contained in the composite and graphite are firmly supported on the oxide. . Cellulose nanofiber is a skeletal component that occupies about 50% of all plant cell walls, and is a lightweight high-strength fiber that can be obtained by defibrating plant fibers constituting such cell walls to nano size, It also has good dispersibility in water. In addition, since the cellulose molecular chain constituting the cellulose nanofiber has a periodic structure formed of carbon, it is carbonized and firmly supported on the oxide, so that it can be obtained in combination with graphite. A useful positive electrode active material that can effectively enhance the discharge characteristics of the battery can be obtained.

  The cellulose nanofiber that can be used is not particularly limited as long as it is obtained by defibrating the plant fiber constituting the plant cell wall to nano size, for example, serish KY-100S (manufactured by Daicel Finechem), etc. Commercial products can be used. The fiber diameter of the cellulose nanofiber is preferably 4 to 500 nm, more preferably 5 to 400 nm, and still more preferably 10 to 300 nm from the viewpoint of firmly supporting the oxide on the oxide.

  The cellulose nanofibers are then carbonized and exist in the positive electrode active material for secondary batteries of the present invention as carbon supported on the oxides derived from cellulose nanofibers. The amount of carbon derived from cellulose nanofibers is preferably 0.5 to 15% by mass, more preferably 0.7 to 10% by mass in the positive electrode active material for secondary battery of the present invention. . More specifically, in the positive electrode active material for secondary batteries in which the oxide is represented by the above formula (A) or (C), preferably 0.5 to 5% by mass in the positive electrode active material for secondary batteries. More preferably, it is 0.7 to 3.5% by mass, and in the positive electrode active material for a secondary battery in which the oxide is represented by the above formula (B), it is preferably 0.5 to 15% by mass. More preferably, it is 1-10 mass%. The atomic conversion amount of carbon derived from cellulose nanofibers present in the positive electrode active material for secondary batteries is obtained by subtracting the amount of graphite added later from the amount of carbon measured using a carbon / sulfur analyzer. Can be confirmed.

  The graphite supported on the oxide represented by the above formula (A), (B) or (C) may be any of artificial graphite (scale-like, massive, earthy, graphene) or natural graphite. .

The BET specific surface area of the graphite 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 moisture. Moreover, from the same viewpoint, the average particle diameter of such graphite is preferably 0.5 to 20 μm, more preferably 1.0 to 15 μm.

Specifically, the composite containing the oxide and carbon derived from cellulose nanofibers includes a lithium compound or a sodium compound, a phosphoric acid compound or a silicic acid compound, and at least an iron compound or a manganese compound, and cellulose nanofibers It is preferable that it is obtained by subjecting the slurry water containing to hydrothermal reaction. That is, the composite is preferably a hydrothermal reaction product of slurry water containing a lithium compound or sodium compound, a phosphoric acid compound or a silicic acid compound, and at least an iron compound or a manganese compound and containing cellulose nanofibers. .
More specifically, the step (I) of obtaining a complex X by mixing a phosphoric acid compound or a silicic acid compound with a mixture X containing a lithium compound or a sodium compound and cellulose nanofibers, and the obtained complex X And a step of obtaining a composite Y by subjecting slurry water Y containing a metal salt containing at least an iron compound or a manganese compound to a hydrothermal reaction (II)
It is preferable that it is obtained by a manufacturing method provided with.

Step (I) is a step of obtaining a composite X by mixing a phosphoric acid compound or a silicic acid compound with a mixture X containing a lithium compound or a sodium compound and cellulose nanofibers.
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 silicate compound in the mixture X 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 mixture X is preferably 5 to 50 parts by mass with respect to 100 parts by mass of water. Preferably it is 10-45 mass parts. Moreover, when a silicic acid compound is used, content of the silicic acid compound in the mixture X becomes like this. Preferably it is 5-40 mass parts with respect to 100 mass parts of water, More preferably, it is 7-35 mass parts.

  The content of cellulose nanofibers in the mixture X is preferably 0.5 to 60 parts by mass, and more preferably 0.8 to 40 parts by mass with respect to 100 parts by mass of water in the mixture X, for example. More specifically, when a phosphoric acid compound is used in step (I), the content of cellulose nanofibers in the mixture X is preferably 0.5 to 20 parts by mass, more preferably 0.8 to 15 parts. Part by mass. Moreover, when a silicic acid compound is used, content of the cellulose nanofiber in the mixture X becomes like this. Preferably it is 0.5-60 mass parts, More preferably, it is 1-40 mass parts.

  Before mixing the phosphoric acid compound or the silicic acid compound with the mixture X, it is preferable to stir the mixture X in advance. The stirring time of the mixture X is preferably 1 to 15 minutes, more preferably 3 to 10 minutes. Moreover, the temperature of the mixture X becomes like this. Preferably it is 20-90 degreeC, More preferably, it is 20-70 degreeC.

Examples of the phosphoric acid compound used in the step (I) include orthophosphoric acid (H ₃ PO ₄ , phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, and ammonium hydrogen phosphate. . Of these, phosphoric acid is preferably used, and is preferably used as an aqueous solution having a concentration of 70 to 90% by mass. In the step (I), when phosphoric acid is mixed with the mixture X, it is preferable to add phosphoric acid dropwise while stirring the mixture X. By adding phosphoric acid dropwise to the mixture X and adding it little by little, the reaction proceeds well in the mixture X, and the complex X is generated while being uniformly dispersed in the slurry. It can also be effectively suppressed.

The dropping rate of phosphoric acid into the mixture X is preferably 15 to 50 mL / min, more preferably 20 to 45 mL / min, and further preferably 28 to 40 mL / min. Moreover, the stirring time of the mixture X while dropping phosphoric acid is preferably 0.5 to 24 hours, and more preferably 3 to 12 hours. Furthermore, the stirring speed of the mixture X while dropping phosphoric acid is preferably 200 to 700 rpm, more preferably 250 to 600 rpm, and further preferably 300 to 500 rpm.
In addition, when stirring the mixture X, it is preferable to further cool below the boiling point temperature of the mixture X. 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) is not particularly limited as long as it is a reactive silica compound, and examples thereof include amorphous silica and Na ₄ SiO ₄ (for example, Na ₄ SiO ₄ .H ₂ O). .

  It is preferable that the mixture X after mixing a phosphoric acid compound or a silicic acid compound contains 2.0-4.0 mol of lithium or sodium with respect to 1 mol of phosphoric acid or silicic acid, and is 2.0-3. 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 X after mixing the phosphoric acid compound is 2.7 to 3.3 mol of lithium or sodium with respect to 1 mol of phosphoric acid. It is preferable to contain 2.8-3.1 mol, and when a silicate compound is used in step (I), the mixture X after mixing the silicate compound is 1 mol of silicate. On the other hand, it is preferable to contain 2.0-4.0 mol of lithium, and it is more preferable to contain 2.0-3.0 mol of lithium.

By purging nitrogen with respect to the mixture X after mixing the phosphoric acid compound or the silicic acid compound, the reaction in the mixture is completed, and the oxides represented by the above (A) to (C) The precursor complex X is formed in the mixture. When nitrogen is purged, the reaction can proceed while the dissolved oxygen concentration in the mixture X is reduced, and the dissolved oxygen concentration in the resulting mixture containing the complex X is also effectively reduced. Therefore, oxidation of the iron compound or manganese compound added in the next step can be suppressed. In the mixture containing the composite X, the precursors of the oxides represented by the above (A) to (C) are present as fine dispersed particles. For example, in the case of the oxide represented by the above formula (A), the composite X is obtained as a composite of trilithium phosphate (Li ₃ PO ₄ ) and cellulose nanofibers.

The pressure for purging nitrogen is preferably 0.1 to 0.2 MPa, more preferably 0.1 to 0.15 MPa. Moreover, the temperature of the mixture X after mixing a phosphoric acid compound or a silicic acid compound becomes like this. Preferably it is 20-80 degreeC, More preferably, it is 20-60 degreeC. 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.
Moreover, when purging nitrogen, it is preferable to stir the mixture X after mixing a phosphoric acid compound or a silicic acid compound from a viewpoint of making reaction progress favorable. 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 the oxidation on the surface of the dispersed particles of the complex X and miniaturizing the dispersed particles, the dissolved oxygen concentration in the mixture X after mixing the phosphoric acid compound or the silicate compound is reduced to 0. 0.5 mg / L or less is preferable, and 0.2 mg / L or less is more preferable.

  In the step (II), the composite X obtained in the step (I) and the slurry water Y containing a metal salt containing at least an iron compound or a manganese compound are subjected to a hydrothermal reaction to obtain the composite Y. It is. The composite X obtained by the step (I) is used as a precursor of the oxide represented by the above (A) to (C) as a mixture, and contains at least an iron compound or a manganese compound. Is preferably used as slurry water Y. Thereby, while simplifying the process, the oxides represented by the above (A) to (C) become extremely fine particles, and the carbon derived from cellulose nanofibers is efficiently converted into the oxide in the subsequent process. It becomes possible to carry | support, and the positive electrode active material for secondary batteries can be obtained very useful.

  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 manganese compound and iron compound (manganese compound: iron compound) is preferably 99: 1 to 1:99, more preferably 90. : 10 to 10:90. The total amount of these iron compounds and manganese compounds is preferably 0.99 to 1.01 moles, more preferably 0.995, with respect to 1 mole of Li ₃ PO ₄ contained in the slurry water Y. ~ 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). Or it is preferably 0.99 to 1.01 mole, and 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 Y from the viewpoint of the solubility of the metal salt used, the ease of stirring, the efficiency of synthesis, etc. Preferably it is 10-50 mol with respect to 1 mol, More preferably, it is 12.5-45 mol. More specifically, when the ions contained in the slurry water Y 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. Moreover, when the ion contained in slurry water Y is a silicate ion, the usage-amount of the water used when attaching | subjecting to a hydrothermal reaction becomes like this. Preferably it is 10-50 mol, More preferably, it is 12.5-45. Is a mole.

In step (II), the order of addition of 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 ), sodium hydrosulfite (Na ₂ S ₂ O ₄ ), aqueous ammonia and the like can be used. From the viewpoint of preventing the generation of oxides represented by the above formulas (A) to (C) from being excessively added, the addition amount of the antioxidant is an iron compound, a manganese compound, and necessary. It is preferably 0.01 to 1 mol, more preferably 0.03 to 0.5 mol, based on 1 mol of the total amount of metal (M, N or Q) salt used depending on the case.

  The content of the complex Y in the slurry Y 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 50% by mass. More preferably, it is 15-45 mass%, More preferably, it is 20-40 mass%.

The hydrothermal reaction in process (II) should just be 100 degreeC or more, and 130-180 degreeC is preferable. The hydrothermal reaction is preferably carried out in a pressure vessel, and 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 composite Y is a composite containing the oxides represented by the above formulas (A) to (C) and cellulose nanofibers. After filtration, the composite Y is washed with water and dried to obtain cellulose. It can be isolated as composite particles containing nanofibers. As the drying means, freeze drying or vacuum drying is used.

The BET specific surface area of the obtained composite Y is preferably 5 to 40 m ² / g, more preferably 5 to ²⁰ m ² / g, from the viewpoint of effectively reducing the amount of adsorbed moisture. If the BET specific surface area of the composite Y 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 secondary batteries may increase and affect battery characteristics.

  The positive electrode active material for a secondary battery of the present invention is an active material in which graphite is supported on a composite containing an oxide represented by the above formulas (A) to (C) and carbon derived from cellulose nanofibers. In particular, such a positive electrode active material for a secondary battery includes a step of adding graphite to a composite containing oxides represented by the above formulas (A) to (C) and cellulose nanofibers. After obtaining the composite Y containing the oxide and the cellulose nanofiber through the above steps (I) and (II), graphite is added to the obtained composite Y to add compressive force and shear force. It is preferably obtained by a production method comprising a step (III) of mixing to obtain a composite Z, and a step (IV) of firing the obtained composite Z in a reducing atmosphere or an inert atmosphere. In this way, by performing a mixing process while applying compressive force and shearing force, the composite Y and graphite are uniformly dispersed, while the graphite is deformed or stretched, it is firmly aggregated and the BET specific surface area is obtained. Can be effectively reduced, and in combination with cellulose nanofibers, a positive electrode active material for a secondary battery that can effectively suppress moisture adsorption can be formed as particles.

  Step (III) is a step for adding graphite as a carbon source other than cellulose nanofibers to the composite Y (oxides represented by formulas (A) to (C) + cellulose nanofibers), Specifically, in this step, graphite is added to the composite Y obtained through steps (I) and (II) and mixed while applying compressive force and shearing force to obtain composite Z.

  The amount of graphite added is preferably 0.3 to 5% by mass, more preferably 0.5 to 4% by mass, and still more preferably 0.6% in the positive electrode active material for a secondary battery of the present invention. ˜3 mass%.

  The composite Y and graphite are positive electrode actives for secondary batteries obtained by combining graphite with cellulose nanofibers while efficiently and uniformly covering the surface of the oxide represented by the above formulas (A) to (C). From the viewpoint of effectively reducing the amount of adsorbed moisture of the substance, it is preferably mixed at a mass ratio (composite Y: graphite) 99: 1 to 91: 9, more preferably 98: 2 to 93: 7. Good.

The process of mixing while applying compressive force and shearing force is preferably performed for 5 to 90 minutes, more preferably for 10 to 80 minutes. Such treatment is preferably performed in a closed container equipped with an impeller that rotates at a peripheral speed of 25 to 40 m / s. The peripheral speed of such an impeller is preferably 27 to 40 m / s from the viewpoint of increasing the tap density of the obtained positive electrode active material and effectively reducing the amount of adsorbed moisture by reducing the BET specific surface area.
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)

The treatment time and / or the impeller peripheral speed in the step (III) needs to be adjusted as appropriate according to the amount of the composite Y and graphite to be charged into the container. Then, by operating the container, it becomes possible to perform a process of mixing the impeller and the inner wall of the mixture while applying a compressive force and a shearing force to the mixture. , Graphite particles are densely and uniformly dispersed, and in combination with cellulose nanofibers, composite particles that are positive electrode active materials for secondary batteries that can effectively reduce the amount of adsorbed moisture can be formed.
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 the amount of graphite added to the container is The effective container (a container corresponding to a part capable of accommodating the complex Y and the graphite among the sealed containers including the impeller) is preferably 0.1 to 0.7 g, more preferably 0.15 to 1 cm ^3. 0.4 g.

  In addition, from the viewpoint of improving the uniformity of the obtained positive electrode active material for a secondary battery and improving the efficiency of the process of mixing the composite Y and the graphite, the composite Y and the graphite are put into a sealed container equipped with an impeller. These may be mixed in advance.

Examples of the apparatus provided with a closed container capable of performing the mixing process while applying the compressive force and the shearing force include a high-speed shearing mill, a blade-type kneader, and the like. The nobilta (manufactured by Hosokawa Micron) can be suitably used. By using such an apparatus, it is possible to easily carry out a mixing process while applying a predetermined compressive force and shearing force, and the positive electrode active material for a secondary battery of the present invention can be obtained only by performing such a process. Can do.
As the processing conditions for the mixing, the processing 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 (IV) is a step of firing the composite Z obtained through step (III) in a reducing atmosphere or an inert atmosphere. Through this step (IV), the carbon derived from the cellulose nanofibers is firmly supported on the surface of the oxide represented by the above formulas (A) to (C), and added to the composite Y. Also exist as carbon covering the surface of the oxide represented by the above formulas (A) to (C). Furthermore, since the crystallinity of both the oxide and the graphite, which have been reduced by applying compressive force and shear force, can be recovered by this firing, the conductivity in the obtained positive electrode active material can be effectively increased. .

  The firing temperature is preferably 500 to 800 ° C, more preferably 600 to 770 ° C, and further preferably 650 to 750 ° C, from the viewpoint of effectively carbonizing the cellulose nanofibers. 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 of the present invention thus obtained has a mass ratio (graphite / cellulose nanofiber) between the amount of graphite added and the amount of carbon derived from cellulose nanofibers of 0.08 to 6. Yes, preferably 0.1-4, more preferably 1-3. As a result, the carbon and graphite derived from cellulose nanofibers supported or coated on the surface of the oxide represented by the above formulas (A) to (C) act synergistically, and the positive electrode active for the secondary battery The amount of adsorbed moisture in the substance can be effectively reduced.

The amount of adsorbed water of the positive electrode active material for secondary battery of the present invention is such that the oxide in the positive electrode active material for secondary battery is an oxide whose secondary battery positive electrode active material is represented by the above formula (A) or (C). In the positive electrode active material for a secondary battery in which the oxide is represented by the above formula (B), preferably it is 2500 ppm or less, more preferably 2000 ppm or less. is there. 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 secondary battery and the sodium 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 a Karl Fischer moisture meter, for example. Can be measured.

Moreover, 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 secondary batteries 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 a secondary battery including the positive electrode active material for a secondary battery of the present invention can be applied 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 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 NaN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), and at least one of derivatives 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.

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

[Example 1-1]
12.72 g of LiOH.H ₂ O, 90 mL of water, and 5.10 g of cellulose nanofiber (Serisch KY-100G, manufactured by Daicel Finechem, fiber diameter 4 to 100 nm, abbreviated CNF) were mixed to obtain slurry water. Next, 11.53 g of 85% aqueous phosphoric acid solution was added dropwise at 35 mL / min while stirring the resulting slurry water at a temperature of 25 ° C. for 5 minutes, followed by 12 hours under a nitrogen gas purge at 400 rpm. By stirring at a speed, slurry water X ¹¹ (dissolved oxygen concentration 0.5 mg / L) containing composite X ¹¹ was obtained. The slurry water X ¹¹ contained 2.97 mol of lithium with respect to 1 mol of phosphorus.

Next, the obtained slurry water X ¹¹ 119.4 _g, was added FeSO ₄ · 7H 2 O 4.17g and MnSO ₄ · _5H 2 O 19.29g, were mixed to obtain a slurry water Y ^11. Next, the obtained slurry water Y ¹¹ was put into an autoclave purged with nitrogen gas, and a hydrothermal reaction was performed at 170 ° C. for 1 hour. The pressure in the autoclave was 0.8 MPa. The produced crystal was filtered, and then washed with 12 parts by mass of water with respect to 1 part by mass of the crystal. The washed crystal was freeze-dried at −50 ° C. for 12 hours to give a composite Y ¹¹ (chemical composition of an oxide represented by the formula (A): LiFe _0.2 Mn _0.8 PO ₄ , BET specific surface area 21 m ² / g, average grain 60 nm in diameter and 1.5% by mass of CNF-derived carbon).
98.0 g of the obtained composite Y ¹¹ and graphite (high purity graphite powder, manufactured by Nippon Graphite Industry Co., Ltd., BET specific surface area 5 m ² / g, average particle diameter 6.1 μm) 2.0 g (carbon in the active material) equivalent to 2.0 wt% in terms of atom weight) and premixed to give a mixture Y ^11. The resulting mixture Y ¹¹ particle composite apparatus Nobilta (NOB-130, manufactured by Hosokawa Micron Corporation, power 5.5kw) were charged into a treatment temperature 25 to 35 ° C., the circumferential speed of the impeller 30 m / s, the processing time mixed as 15 minutes, to obtain a composite pre particles Y ^11.
Next, using an electric furnace purged with nitrogen gas, the obtained composite preliminary particles Y ¹¹ were fired at a temperature of 750 ° C. for 90 minutes, and as a composite Z ¹¹ , a positive electrode active material for a lithium ion secondary battery (LiFe _0.2 Mn _0.8 PO ₄ , amount of carbon = 3.5% by mass).

[Example 1-2]
The slurry water X ¹² was obtained in the same manner as the slurry water X ¹¹ obtained in Example 1-1, except that CNF was changed to 1.70 g, and then the same as in the composite Y ¹¹ obtained in Example 1-1. A composite Y ¹² (BET specific surface area 22 m ² / g, average particle size 58 nm, CNF-derived carbon content 0.5 mass%) was obtained. Next, the obtained composite Y ¹² was used, except that 98.0 g of the composite Y ¹² and 2.0 g of graphite (corresponding to 2.0 mass% in terms of carbon atom in the active material) were mixed. In the same manner as in Example 1-1, a positive electrode active material for lithium ion secondary batteries (LiFe _0.2 Mn _0.8 PO ₄ , amount of carbon = 2.5 mass%) was obtained.

[Example 1-3]
The slurry water X ¹³ was obtained in the same manner as the slurry water X ¹¹ obtained in Example 1-1, except that CNF was 3.40 g, and then the same as in the composite Y ¹¹ obtained in Example 1-1. A composite Y ¹³ (BET specific surface area 21 m ² / g, average particle size 55 nm, CNF-derived carbon content 1.0 mass%) was obtained. Subsequently, the obtained composite Y ¹³ was used, except that 98.0 g of the composite Y ¹³ and 2.0 g of graphite (corresponding to 2.0 mass% in terms of carbon atom in the active material) were mixed. In the same manner as in Example 1-1, a positive electrode active material for lithium ion secondary battery (LiFe _0.2 Mn _0.8 PO ₄ , amount of carbon = 3.0 mass%) was obtained.

[Example 1-4]
Using a complex Y ¹¹ obtained in Example 1-1, such conjugates Y ¹¹ 98.0 g and scale graphite (Ito Graphite Industries Co., BET specific surface area 13.2 m ² / g, average particle size 8 .6 μm) A positive electrode active material for lithium ion secondary batteries (LiFe) in the same manner as in Example 1-1 except that 2.0 g (corresponding to 2.0 mass% in terms of carbon atom in the active material) was mixed. _0.2 Mn _0.8 PO ₄ , amount of carbon = 3.5% by mass).

[Example 1-5]
Using a complex Y ¹¹ obtained in Example 1-1, (equivalent to 0.5 wt% in terms of carbon atoms content in the active material in) such conjugates Y ¹¹ 99.5 g of graphite 0.5g and the mixture In the same manner as in Example 1-1, a positive electrode active material for a lithium ion secondary battery (LiFe _0.2 Mn _0.8 PO ₄ , amount of carbon = 2.0% by mass) was obtained in the same manner as in Example 1-1.

[Example 1-6]
Using a complex Y ¹¹ obtained in Example 1-1, (equivalent to 3.0 wt% in terms of carbon atoms content in the active material in) such conjugates Y ¹¹ 97.0 g of graphite 3.0g and the mixture In the same manner as in Example 1-1, a positive electrode active material for a lithium ion secondary battery (LiFe _0.2 Mn _0.8 PO ₄ , the amount of carbon = 4.5 mass%) was obtained.

[Example 1-7]
Example using a slurry water X ¹¹ obtained in 1-1, to such slurry water _{^{X 11 FeSO 4 · 7H 2 O}} 5.00g and MnSO ₄ · _5H 2 other _{O 19.29g, MgSO 4 · 7H 2} O Complex Y ¹⁷ (chemical composition of oxide represented by formula (A): LiFe _0.18 Mn _0.80 Mg _0.02 PO ₄ , BET specific surface area 21 m ^{2 in the same} manner as Example 1-1 except that 0.50 g was added. / G, average particle size 56 nm).
Subsequently, the composite Y ¹⁷ thus obtained was used, except that 98.0 g of the composite Y ¹⁷ and 2.0 g of graphite (corresponding to 2.0 mass% in terms of carbon atom in the active material) were mixed. In the same manner as in Example 1-1, a positive electrode active material for lithium ion secondary battery (LiFe _0.18 Mn _0.80 Mg _0.02 PO ₄ , amount of carbon = 3.5 mass%) was obtained.

[Example 1-8]
Example using a slurry water X ¹¹ obtained in 1-1, to such slurry water X ¹¹ FeSO ₄ · _7H 2 O5.00g and MnSO ₄ · _5H 2 other _{O19.29g, Zr (SO 4) 2} · 4H ₂ Except that 0.36 g of O was added, the composite Y ¹⁸ (chemical composition of the oxide represented by the formula (A): LiFe _0.18 Mn _0.80 Zr _0.01 PO ₄ , BET specific surface area of 21 m was the same as in Example 1-1. ² / g, average particle diameter 60 nm, CNF-derived carbon content 1.5% by mass).
Next, the obtained composite Y ¹⁸ was used, except that 98.0 g of the composite Y ¹⁸ and 2.0 g of graphite (corresponding to 2.0% by mass in terms of carbon atom in the active material) were mixed. In the same manner as in Example 1-1, a positive electrode active material for lithium ion secondary battery (LiFe _0.18 Mn _0.80 Zr _0.01 PO ₄ , amount of carbon = 3.5 mass%) was obtained.

[Comparative Example 1-1]
Except that Example with complex Y ¹¹ obtained in 1-1, was not added carbon source other than the cellulose nanofibers of graphite in such conjugates Y ^11, the lithium ion in the same manner as in Example 1-1 A positive electrode active material for a secondary battery (LiFe _0.2 Mn _0.8 PO ₄ , amount of carbon = 1.5 mass%) was obtained.

[Comparative Example 1-2]
Using a complex Y ¹¹ obtained in Example 1-1, such conjugates Y ¹¹ 98.0 g of Ketjen black (Lion Co., Ltd., BET specific surface area 800 m ² / g, an average particle diameter of 30.0) A positive electrode active material for lithium ion secondary battery (LiFe _0.2 Mn _{0.8) in the same} manner as in Example 1-1 except that 2.0 g (corresponding to 2.0 mass% in terms of carbon atom in the active material) was mixed. PO ₄ , amount of carbon = 3.5% by mass).

[Comparative Example 1-3]
Except for using no CNF, after obtaining the slurry water X ^c13 in the same manner as the slurry water X ¹¹ obtained in Example 1-1, the complex in the same manner as in the complex Y ¹¹ obtained in Example 1-1 Y ^c13 (chemical composition of oxide represented by formula (A): LiFe _0.2 Mn _0.8 PO ₄ , BET specific surface area 21 m ² / g, average particle diameter 60 nm, CNF-derived carbon content 0.0 mass%) is obtained. It was. Subsequently, the obtained primary particles Y ^c13 were used, ^{except that} 98.0 g of the composite Y c13 and 2.0 g of graphite (corresponding to 2.0 mass% in terms of carbon atom in the active material) were mixed. In the same manner as in Example 1-1, a positive electrode active material for lithium ion secondary battery (LiFe _0.2 Mn _0.8 PO ₄ , amount of carbon = 2.0 mass%) was obtained.

[Comparative Example 1-4]
Using a slurry water X ¹¹ obtained in Example 1-1, according except for adding only FeSO ₄ · _7H 2 O 27.80g slurried water X ^11, composite Y ¹⁴ in the same manner as in Example 1-1 (Chemical composition of oxide represented by formula (A): LiFePO ₄ , BET specific surface area 19 m ² / g, average particle size 85 nm, CNF-derived carbon content 1.5 mass%).
Next, 98.0 g of the composite Y ¹⁴ and 2.0 g of Ketjen Black (corresponding to 2.0% by mass in terms of carbon atom in the active material) were mixed using the obtained composite Y ¹⁴ In the same manner as in Example 1-1, a positive electrode active material for lithium ion secondary battery (LiFePO ₄ , amount of carbon = 3.5% by mass) was obtained.

[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 X ²¹ . Next, the obtained slurry X ²¹ was purged with nitrogen gas to adjust the dissolved oxygen concentration to 0.5 mg / L, and then added to this slurry water X ²¹ with 1.49 kg of CNF, FeSO ₄ .7H ₂ O 0. .39 kg, MnSO ₄ .5H ₂ O 0.79 kg, and Zr (SO ₄ ) ₂ .4H ₂ O 0.053 kg were added and mixed to obtain slurry water Y ²¹ . Next, the obtained slurry water Y ²¹ was put into an autoclave purged with nitrogen gas, 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 crystal was freeze-dried at −50 ° C. for 12 hours to give a composite Y ²¹ (powder, chemical composition represented by the formula (B): Li ₂ Fe _0.28 Mn _0.66 Zr _0.03 SiO ₄ , carbon amount derived from CNF. 0% by mass) was obtained.

98.0 g of the obtained composite Y ²¹ was fractionated and mixed with 2.0 g of graphite (corresponding to 2.0 mass% in terms of carbon atom in the active material) by a dry method using a ball mill to obtain a mixture Y ²¹ It was. The resulting mixture Y ²¹ was mixed with Nobilta (NOB-130, manufactured by Hosokawa Micron Corporation, power 5.5 kw) at an impeller peripheral speed of 30 m / s for 15 minutes to give composite preliminary particles Y ²¹ . Obtained. The resulting complex pre particles Y ^21, and then calcined 1 hour at 650 ° C. under a reducing atmosphere, the positive electrode active material for a lithium ion secondary battery as a complex _{^{Z 21 (Li 2 Fe 0.28 Mn}} 0.66 Zr 0.03 SiO 4, Carbon amount = 9.0% by mass).

[Example 2-2]
Using a complex Y ²¹ obtained in Example 2-1, (equivalent to 3.0 wt% in terms of carbon atoms content in the active material in) such conjugates Y ²¹ 97.0 g of graphite 3.0g and the mixture In the same manner as in Example 2-1, a positive electrode active material for a lithium ion secondary battery (Li ₂ Fe _0.28 Mn _0.66 Zr _0.03 SiO ₄ , amount of carbon = 10.0 mass%) was obtained.

[Comparative Example 2-1]
Except that Example with complex Y ²¹ obtained in 2-1, was not added carbon source other than the cellulose nanofibers of graphite in such conjugates Y ^21, the lithium ion in the same manner as in Example 2-1 A positive electrode active material for a secondary battery (LiFe _0.2 Mn _0.8 PO ₄ , amount of carbon = 7.0% by mass) was obtained.

[Example 3-1]
0.60 kg of NaOH, 9.0 L of water, and 0.51 kg of CNF were mixed to obtain slurry water. Next, 0.577 kg of 85% phosphoric acid aqueous solution is dropped at 35 mL / min while stirring the obtained slurry water for 5 minutes while maintaining the temperature at 25 ° C., followed by stirring at a speed of 400 rpm for 12 hours. by obtain a slurry X ³¹ containing a complex X ^31. The slurry X ³¹ contained 3.00 mol of sodium per mol of phosphorus. Next, the obtained slurry X ³¹ was purged with nitrogen gas to adjust the dissolved oxygen concentration to 0.5 mg / L, and then FeSO ₄ · 7H ₂ O 0.139 kg, MnSO ₄ · 5H ₂ O 0.964 kg. , 0.124 kg of MgSO ₄ .7H ₂ O was added and mixed to obtain slurry water Y ³¹ . Next, the obtained slurry water Y ³¹ was put into an autoclave purged with nitrogen gas, and a hydrothermal reaction was performed at 200 ° C. 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 crystal was freeze-dried at −50 ° C. for 12 hours to give composite Y ³¹ (powder, chemical composition represented by the formula (C): NaFe _0.1 Mn _0.8 Mg _0.1 PO ₄ , CNF-derived carbon content 1.5 mass %).

98.0 g of the obtained composite Y ³¹ was fractionated and mixed with 2.0 g of graphite (corresponding to 2.0 mass% in terms of carbon atom in the active material) by a dry method using a ball mill to obtain a mixture Y ³¹ . It was. The resulting mixture Y ³¹ was mixed with Nobilta (NOB-130, manufactured by Hosokawa Micron Corporation, power 5.5 kw) at an impeller peripheral speed of 30 m / s for 15 minutes to give composite preliminary particles Y ³¹ . Obtained.
Next, using an electric furnace purged with nitrogen gas, the obtained composite preparatory particles Y ³¹ were fired at a temperature of 700 ° C. for 1 hour to obtain a positive electrode active material for sodium ion secondary batteries (NaFe _0.1 Mn _0.8 Mg _0.1 PO ₄ and the amount of carbon = 3.5% by mass).

[Example 3-2]
Using the complex Y ³¹ obtained in Example 3-1, 97.0 g of the complex Y ³¹ and 3.0 g of graphite (corresponding to 3.0% by mass in terms of carbon atom in the active material) were mixed. In the same manner as in Example 3-1, a positive electrode active material for a sodium ion secondary battery (NaFe _0.1 Mn _0.8 Mg _0.1 PO ₄ , amount of carbon = 4.5 mass%) was obtained.

[Comparative Example 3-1]
Using the composite Y ³¹ obtained in Example 3-1, 99.9 g of the composite Y ³¹ and 0.1 g of ketjen black (corresponding to 0.1% by mass in terms of carbon atom in the active material) A positive electrode active material for a sodium ion secondary battery (NaFe _0.1 Mn _0.8 Mg _0.1 PO ₄ , the amount of carbon = 1.6% by mass) was obtained in the same manner as in Example 3-1.

[Comparative Example 3-2]
Except that Example with complex Y ³¹ obtained in 3-1, was not added carbon source other than the cellulose nanofibers of graphite in such conjugates Y ^31, sodium in the same manner as in Example 3-1 Ion A positive electrode active material for secondary battery (NaFe _0.1 Mn _0.8 Mg _0.1 PO ₄ , amount of carbon = 1.5% by mass) was obtained.

<Measurement of adsorbed water content>
The adsorbed moisture content of each positive electrode active material obtained in Examples 1-1 to 3-2 and Comparative Examples 1-1 to 3-2 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 finished. The amount of water that volatilized was measured with a Karl Fischer moisture meter (MKC-610, manufactured by Kyoto Electronics Industry Co., Ltd.) and determined as the amount of moisture adsorbed in the positive electrode active material.
The results are shown in Tables 1-3.

<< Evaluation of charge / discharge characteristics using secondary battery >>
Using the positive electrode active materials obtained in Examples 1-1 to 3-2 and Comparative Examples 1-1 to 3-2, 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 weight ratio of 90: 3: 7, 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. In the electrolyte solution, LiPF ₆ (in the case of a lithium ion secondary battery) or NaPF ₆ (in the case of a sodium ion secondary battery) is mixed in 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 with 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 2 cycles) × 100 (2)
The results are shown in Tables 1-3.

  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 (8)

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 graphite is supported on a composite containing an oxide represented by formula (II) and carbon derived from cellulose nanofibers.   The positive electrode active material for a secondary battery according to claim 1, wherein the amount of carbon derived from cellulose nanofibers is 0.5 to 15% by mass.   The positive electrode active material for a secondary battery according to claim 1 or 2, wherein the graphite has an average particle size of 0.5 to 20 µm.   A composite containing an oxide and carbon derived from cellulose nanofibers includes a lithium compound or sodium compound, a phosphoric acid compound or silicic acid compound, and at least an iron compound or a manganese compound, and slurry water containing cellulose nanofibers, The positive electrode active material for a secondary battery according to any one of claims 1 to 3, which is a hydrothermal reaction product. 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 graphite is supported on a composite containing an oxide represented by the above and carbon derived from cellulose nanofibers, the oxide and the cellulose nanofibers. Adding a graphite to the composite;
The addition amount of graphite with respect to the carbon atom equivalent amount of cellulose nanofiber is 0.08 to 6 in mass ratio (graphite / cellulose nanofiber), and lithium X or sodium compound and mixture X containing cellulose nanofiber, A step of obtaining a complex X by mixing a phosphoric acid compound or a silicic acid compound (I),
Step (II) of obtaining the composite Y by subjecting the obtained composite X and slurry water Y containing a metal salt containing at least an iron compound or a manganese compound to a hydrothermal reaction.
Step (III) for obtaining composite Z by adding graphite to the obtained composite Y and adding compression force and shearing force, and the obtained composite Z in a reducing atmosphere or an inert atmosphere Firing step (IV)
A method for producing a positive electrode active material for a secondary battery.   The method for producing a positive electrode active material for a secondary battery according to claim 5, wherein the mixing time in the step (III) while applying the compressive force and shear force is 5 to 90 minutes.   The method for producing a positive electrode active material for a secondary battery according to claim 5 or 6, wherein the amount of graphite added in step (III) is 0.3 to 5 mass%.   The process of mixing while applying a compressive force and a shearing force in the step (III) is a process performed in a closed container provided with an impeller rotating at a peripheral speed of 25 to 40 m / s. The manufacturing method of the positive electrode active material for secondary batteries as described in an item.