WO2013042778A1 - Production method for positive electrode material for secondary battery - Google Patents

Abstract

Provided is a production method for a secondary battery positive electrode material, whereby a secondary battery positive electrode material having high uniformity of chemical composition and high reliability over the long term can be efficiently produced at low cost.　The method is for producing a secondary battery positive electrode material including an olivine-, augite-, or nasicon-type compound, and has a melting step in which a raw material mixture is housed inside a container formed using a conductive fire-resistant material for at least the inner peripheral section thereof, and the raw material mixture is melted by induction heating of at least the inner peripheral section of the container.

Description

Method for producing positive electrode material for secondary battery

The present invention relates to a method for producing a positive electrode material for a secondary battery.

In recent years, it has an olivine type, pyroxene type, or NASICON type crystal structure as a positive electrode material for next-generation lithium secondary batteries because of its advantages in terms of resources, safety, cost, and performance stability. Compounds are attracting attention. For example, lithium iron phosphate is being developed for practical use.

Also, plug-in hybrid vehicles and electric vehicles are being developed from the viewpoint of carbon dioxide emission regulations and energy saving. In order to realize the popularization of electric vehicles, it is required to increase the capacity and the energy density while maintaining the safety of the secondary battery.

For example, Non-Patent Document 1 discloses an olivine (olivine) silicic acid compound (Li ₂ MSiO ₄ ) containing two Li atoms in one molecule as a secondary battery material capable of increasing the capacity by a multi-electron reaction. , M = Fe, Mn).

As a method for producing the above-mentioned compound having an olivine type, pyroxene type, or NASICON type crystal structure, for example, methods such as a solid phase method and a liquid phase method have been proposed and implemented. Accordingly, there is a demand for further cost reduction of the electrode material.

For example, Non-Patent Document 2 discloses a method of obtaining a positive electrode material for a secondary battery having a predetermined crystal structure by once heating and melting a raw material mixture and then cooling it.
Thus, once the raw material mixture is in a molten state, the positive electrode material for a secondary battery can be manufactured at low cost and in large quantities, and the uniformity of the chemical composition of the obtained positive electrode material can be improved.

For example, Patent Document 1 discloses a method in which a raw material mixture containing a divalent transition metal compound is heated and melted at 1500 ° C. in an argon atmosphere and then rapidly cooled with a single roll to obtain an amorphous transition metal phosphate complex. Is disclosed.

Heat melting of the raw material mixture requires heat treatment at a high temperature, and a container used for heat melting requires characteristics such as heat resistance and corrosion resistance.
For example, in Patent Document 2, a raw material mixture composed of LiFePO ₄ and LiF is placed in a platinum tube, the platinum tube is disposed in a quartz tube, heated by high-frequency induction heating to melt the raw material mixture, and then the melt is cooled. Thus, a method for obtaining an active material composed of a phosphate complex containing a transition metal such as Fe or Mn is disclosed.

Patent Document 3 discloses that after heat-treating raw materials such as Li ₂ CO ₃ , NH ₄ H ₂ PO ₄ , and Fe (II) C ₂ O _{4 in} an alumina crucible with a lid at 300 ° C. in a nitrogen atmosphere. , Melting at 1200 ° C. for 10 minutes in an electric furnace, and then pouring the obtained melt onto an iron plate, pressing and quenching to form a precursor glass, and heat-treating it for a secondary battery A method for obtaining a positive electrode material is disclosed.

Furthermore, in Patent Document 4, a raw material composition containing Li ₂ CO ₃ , Fe (COO) ₂ .2H ₂ O, NH ₄ H ₂ PO _4, etc. is filled in a crucible with a nozzle made of rhodium / platinum alloy. This is heated and melted in an electric furnace equipped with a heating element made of molybdenum silicide, and the obtained melt is dropped on a stainless steel double roller and rapidly cooled, and then (solidified product) is heated. A method for obtaining olivine-type lithium iron phosphate particles is disclosed.

Japanese Unexamined Patent Publication No. 2005-158673 Japanese Unexamined Patent Publication No. 2007-73360 Japanese Unexamined Patent Publication No. 2008-47412 Japanese Unexamined Patent Publication No. 2011-1242

However, the method of Patent Document 2 is not suitable for mass production, and platinum components are mixed from the platinum tube into the internal melt during heating by high-frequency induction, leading to a decrease in product purity and an increase in production costs. There was a fear.

In the method of Patent Document 3, since the corrosion resistance of alumina constituting the crucible is not necessarily high, the crucible wears easily due to erosion of Fe or the like during heating and melting, and the replacement frequency increases. In addition, the alumina component is likely to be mixed into the melt from the crucible, which may cause a decrease in purity. Furthermore, since alumina has a relatively high coefficient of thermal expansion, the crucible may be damaged by a sudden temperature change.

According to the method of Patent Document 4, at high temperatures, the crucible is easily worn out by the formation of platinum and rhodium contained in the crucible and the iron component in the melt, and the platinum and rhodium dissolved from the crucible are melted. It was easy to mix in a liquid, and there existed a possibility of causing the fall of the purity of a product and the increase in manufacturing cost.

Furthermore, in the methods of Patent Documents 3 and 4, since the above-described predetermined raw material mixture is heat-treated by an electric furnace in a state of being contained in a container such as a crucible, the thermal efficiency is poor and the mass productivity is inferior. There was a problem that it was necessary to raise the temperature of the inside, and a sufficient heating rate could not be obtained, resulting in poor production efficiency.

An object of the present invention is to provide a mass-productive method for efficiently producing a positive electrode material for a secondary battery excellent in purity with reduced mixing of components derived from a container used for heating and melting a raw material mixture at low cost. It is to provide.

That is, the method for producing a positive electrode material for a secondary battery according to the present invention is a method for producing a positive electrode material for a secondary battery containing a compound having an olivine type, pyroxene type, or NASICON type crystal structure, wherein the raw materials are prepared. The raw material preparation step of preparing a raw material preparation and the raw material preparation are melted by induction heating at least the inner peripheral portion of the container in a container having at least an inner peripheral portion formed of a conductive refractory material. And a melting step for obtaining a melt.

In the method for producing a positive electrode material for a secondary battery according to the present invention, a melt outlet part having a diameter smaller than that of the container is connected to the bottom part of the container, and the melt outlet part is heated independently of the container. The melt in the container can be led out from the melt lead-out part. The melt outlet part is formed of a conductive refractory material, and the melt outlet part can be heated by induction heating.

The conductive refractory material is preferably carbon or conductive non-oxide ceramics, and the conductive non-oxide ceramics include at least one selected from silicon carbide, zirconium boride, and titanium boride. It is preferable that the ceramic is a main component. Furthermore, it is preferable that the melting step is performed in an inert atmosphere or a reducing atmosphere. In the melting step, the raw material preparation is preferably melted by heating to 1100 ° C. to 1800 ° C.

Furthermore, it is preferable that the manufacturing method of the positive electrode material for secondary batteries of the present invention includes a cooling step of cooling the melt obtained in the melting step to obtain a solidified product. In the cooling step, the melt is preferably cooled at a cooling rate of 1 × 10 ³ ° C./second or more. Moreover, it is preferable to have the crushing process which grind | pulverizes the solidified material obtained at the said cooling process, and obtains a ground material. And in the said grinding | pulverization process, it is preferable to add and grind | pulverize at least 1 sort (s) chosen from the group which consists of an organic compound and a carbonaceous electrically conductive material to the said solidified material. Furthermore, it is preferable to have a heating step of heating the pulverized product obtained in the pulverization step.

As an example of the compound which the positive electrode material for secondary batteries made into the objective of this invention has, the phosphoric acid compound represented by following (1) Formula is mentioned.
AM _1-a X ¹ _a P _1-b Z ¹ _b O _{4 + c} (1)
(In the formula, A represents at least one atom selected from the group consisting of Li, Na, and K, M represents at least one atom selected from the group consisting of Fe, Mn, Co, and Ni; X ¹ represents at least one atom selected from the group consisting of Zr, Ti, Nb, Ta, Mo and W, and Z ¹ represents at least one atom selected from the group consisting of Si, B, Al and V A is 0 ≦ a ≦ 0.2, b is 0 ≦ b ≦ 0.2, c is the numerical value of a and b, and the valence of M, the valence of X ¹ and Z ¹ It depends on the valence of and satisfies the electrical neutrality.)

Moreover, as an example of the other compound which the positive electrode material for secondary batteries made into the objective of this invention has, the silicic acid compound represented by following (2) Formula is mentioned.
A ₂ M _1-d X ² _d Si _1-e Z ² _e O _{4 + f} (2)
(In the formula, A represents at least one atom selected from the group consisting of Li, Na, and K, M represents at least one atom selected from the group consisting of Fe, Mn, Co, and Ni; X ² represents at least one atom selected from the group consisting of Zr, Ti, Nb, Ta, Mo and W, and Z ² represents at least one atom selected from the group consisting of P, B, Al and V D is 0 ≦ d ≦ 0.2, e is 0 ≦ e ≦ 0.2, f is the numerical value of d and e, and the valence of M, the valence of X ² and Z ² It depends on the valence of and satisfies the electrical neutrality.)

In the present specification, the “inner peripheral part” refers to a part that comes into direct contact with the raw material formulation and the melt contained in the container. Specifically, it refers to the inner peripheral portion and inner bottom portion of the side wall of the container.

ADVANTAGE OF THE INVENTION According to this invention, the positive electrode material for secondary batteries excellent in the purity in which mixing of the component derived from the container used for the heat melting of a raw material mixture was reduced can be manufactured efficiently at low cost.
In addition, since the raw material preparation is melted by induction heating at least the inner periphery of the container formed of a conductive refractory material, compared to the conventional method using a heating furnace such as an electric furnace, There are advantages such as low energy loss, high thermal efficiency, rapid heating, the ability to obtain a melt in a short time, and high mass productivity.

It is sectional drawing which shows the structure of an example of the melting apparatus used for embodiment of this invention. It is sectional drawing which shows the structure of another example of the melting apparatus used for embodiment of this invention.

In the present specification, “compound having an olivine type crystal structure” is also referred to as “olivine type compound”, “compound having a pyroxene type crystal structure” is also referred to as “pyroxene type compound”, and “ "Compound having" is also referred to as "Nashikon-type compound". The “compound having an olivine type, pyroxene type, or NASICON type crystal structure” is also referred to as “compound (α)”.
In the present specification, the phosphoric acid compound having the composition represented by the formula (1) is also referred to as “phosphoric acid compound (1)”, and the silicic acid compound having the composition represented by the formula (2) is referred to as “silicic acid”. Also referred to as “compound (2)”.

<Method for producing positive electrode material for secondary battery>
The method for producing a positive electrode material for a secondary battery according to the present invention is a method for producing a positive electrode material for a secondary battery containing a compound having a crystal structure of olivine type, pyroxene type or NASICON type, wherein the raw material is prepared and the raw material is prepared The raw material preparation step for preparing the composition and the raw material preparation are melted by induction heating at least the inner peripheral part of the container in a container in which at least the inner peripheral part is formed of a conductive refractory material. And a melting step for obtaining a product. The secondary battery positive electrode material according to the present invention is preferably a compound having an olivine type, pyroxene type, or NASICON type crystal structure.

Examples of the olivine type compounds include those represented by the general formula AMPO ₄ , AVOPO ₄ , A ₂ MSiO ₄ , A ₂ VOSiO ₄ , AMBO ₃ , A ₂ MPO ₄ F, or AVOPO ₄ F.
In addition, examples of pyroxene-type compounds include those represented by general formulas AMSi ₂ O ₆ and AVSi ₂ O ₆ . In the present specification, A ₂ MP ₂ O ₇ is also included in the pyroxene-type compound.
Examples of NASICON compounds include those represented by the general formula A ₃ M ₂ (PO ₄ ) ₃ or A ₃ V ₂ (PO ₄ ) ₃ .

In the above general formula, atom A represents an alkali metal atom such as Li, Na, and K, and atom M represents a transition metal atom such as Fe, Mn, Co, and Ni.
In the above general formula, P, Si, B, and V may each be partially substituted with each other, or these may be substituted with atoms such as Al or S.

The olivine-type compound, pyroxene-type compound, and nasicon-type compound described above are selected from the group consisting of Zr, Ti, Nb, Ta, Mo, and W together with atoms A and M, in addition to the compounds represented by the general formula described above. It may contain at least one selected atom.

Of the olivine compounds represented by the general formula described above, the phosphoric acid compound (1) represented by the following formula (1) is preferred as the phosphoric acid compound.
AM _1-a X ¹ _a P _1-b Z ¹ _b O _{4 + c} (1)
Wherein A is at least one atom selected from the group consisting of Li, Na, and K, M is at least one atom selected from the group consisting of Fe, Mn, Co, and Ni, and X ¹ is Zr. , Ti, Nb, Ta, Mo, and W, Z ¹ represents at least one atom selected from the group consisting of Si, B, Al, and V. a is 0. ≦ a ≦ 0.2, b is 0 ≦ b ≦ 0.2, c depends on the numerical values of a and b, and the valence of M, the valence of X ^{1 and} the valence of Z ¹ , It is a number that satisfies the target neutrality.)

When 0 ≦ a ≦ 0.2 and 0 ≦ b ≦ 0.2, the raw material preparation can be satisfactorily melted in the melting step (ii) described later, and a uniform melt can be obtained. In addition, the phosphoric acid compound (1) can be obtained by the heating step (v) described later, and further, the phosphoric acid compound (1) containing an olivine type crystal structure, particularly a phosphoric acid compound (1) comprising only an olivine type crystal structure ) Is preferable.

A is more preferably 0.001 ≦ a ≦ 0.1, and particularly preferably 0.001 ≦ a ≦ 0.05. As for b, 0.001 <= b <= 0.1 is more preferable, and 0.001 <= b <= 0.05 is especially preferable. When a and b are within the above ranges, a phosphoric acid compound (1) showing a multi-electron type reaction (reaction that pulls out more than 1 mol of atoms A per unit mole number) is obtained, and this phosphoric acid compound (1) is obtained. When used as a positive electrode material for a secondary battery, the theoretical electric capacity can be increased.

The value of c in the phosphoric acid compound (1) is a number depending on the numerical values of a and b, and the valence of M, the valence of X ^{1 and} the valence of Z ¹ , from 1/2 of the total positive charge The value obtained by subtracting 4.

Of the olivine compounds represented by the above general formula, as the silicate compound, a silicate compound (2) represented by the following formula (2) is preferred.
A ₂ M _1-d X ² _d Si _1-e Z ² _e O _{4 + f} (2)
Wherein A is at least one atom selected from the group consisting of Li, Na, and K, M is at least one atom selected from the group consisting of Fe, Mn, Co, and Ni, and X ² is Zr. , Ti, Nb, Ta, Mo and W, Z ² represents at least one atom selected from the group consisting of P, B, Al, and V. d represents 0. ≦ d ≦ 0.2, e is 0 ≦ e ≦ 0.2, f depends on the numerical values of d and e, and the valence of M, the valence of X ^{2 and} the valence of Z ² , It is a number that satisfies the target neutrality.)

When 0 ≦ d ≦ 0.2 and 0 ≦ e ≦ 0.2, the raw material preparation can be melted well in the melting step (ii) described later, and a uniform melt can be obtained. In addition, the silicate compound (2) can be obtained by the heating step (v) described later, and further, the silicate compound (2) having an olivine type crystal structure, particularly a silicate compound (2) having only an olivine type crystal structure (2). ) Is preferable.

D is more preferably 0.001 ≦ d ≦ 0.1, and particularly preferably 0.001 ≦ d ≦ 0.05. e is more preferably 0.001 ≦ e ≦ 0.1, and particularly preferably 0.001 ≦ e ≦ 0.05. When d and e are within the above ranges, a silicic acid compound (2) showing a multi-electron type reaction (a reaction of extracting A exceeding 1 mol per mole of unit) is obtained. When used as a positive electrode material for a secondary battery, the theoretical electric capacity can be increased.

The value of f in the composition of the silicate compound (2) is a number that depends on the values of d and e, and the valence of M, the valence of X ^{2 and} the valence of Z ² , and is 1 / The value obtained by subtracting 4 from 2.

In the phosphoric acid compound (1) or the silicic acid compound (2), since the atom A is suitable as a positive electrode material for a secondary battery, it is preferable to make Li essential, and it is particularly preferable to use only Li. The phosphoric acid compound (1) containing Li and the silicic acid compound (2) containing Li increase the capacity per unit volume (mass) of the secondary battery.

In the phosphoric acid compound (1) or the silicic acid compound (2), the atom M is preferably composed of only one kind or two kinds. In particular, it is preferable in terms of cost that the atom M consists of Fe alone, Mn alone, or Fe and Mn.
The valence of atom M in phosphoric acid compound (1) or silicic acid compound (2) is in the range of +2 to +4. The valence of atom M is +2, +8/3, +3 when atom M is Fe, +2, +3, +4 when Mn, +2, +8/3, +3 when Co, +2, when Ni is Ni, +4 is preferred. The valence of atom M is preferably 2 to 2.2, more preferably 2.

In the phosphoric acid compound (1) or the silicic acid compound (2), the atoms X ¹ and X ² are at least one atom selected from the group consisting of Zr, Ti, Nb, Ta, Mo and W. From the viewpoint of performance, Zr, Ti or Nb is preferable, and Zr or Ti is particularly preferable.
The valences of the atoms X ¹ and X ^{2 in} the phosphoric acid compound (1) or the silicic acid compound (2) are basically +4 for Zr, +2 or +4 for Ti, +2 or +5 for Nb, Ta is +2 or +5, Mo is +4 or +6, and W is +4 or +6.

In the phosphoric acid compound (1), the atom Z ¹ is at least one selected from the group consisting of Si, B, Al, and V. From the viewpoint of performance, B or Al is preferable, and B is particularly preferable. In the silicic acid compound (2), the atom Z ² is at least one selected from the group consisting of P, B, Al, and V. From the viewpoint of performance, B or Al is preferable, and B is particularly preferable. In the phosphoric acid compound (1) or the silicic acid compound (2), the valences of the atoms Z ¹ and Z ² are basically +5 for P, +3 for B, +3 for Al, and +3 for V. +3, +4, +5.

In particular, the silicic acid compound (2) is preferable because it can increase the capacity per unit volume (mass) of the secondary battery when used as the positive electrode material for the secondary battery.

A method for producing a positive electrode material for a secondary battery according to the present invention is a method for producing a positive electrode material for a secondary battery containing the compound having the olivine type, pyroxene type, or NASICON type crystal structure described above, and preparing raw materials The raw material preparation step (i) for preparing the raw material preparation, and the melting step (ii) for melting the raw material preparation by induction heating at least the inner peripheral portion of the container. The production method of the present invention preferably further includes a cooling step (iii), a pulverizing step (iv), and a heating step (v). Each step will be specifically described below.

[Raw material preparation step (i)]
In the method for producing a positive electrode material for a secondary battery of the present invention, first, each component source of an olivine type compound, pyroxene type compound, or NASICON type compound is selected and mixed so as to be a melt having a predetermined composition. Prepare the raw material formulation.

Among the starting materials containing the constituent atoms of the olivine type compound, pyroxene type compound, or NASICON type compound, the compound containing atom A includes A carbonate (A ₂ CO ₃ ), A hydrogen carbonate (AHCO ₃ ). , A hydroxide (AOH), A silicate (A ₂ O · 2SiO ₂ , A ₂ O · SiO ₂ , 2A ₂ O · SiO ₂ etc.), A phosphate (A ₃ PO ₄ etc.) ), A borate (A ₃ BO ₃ ), A fluoride (AF), A chloride (ACl), A nitrate (ANO ₃ ), A sulfate (A ₂ SO ₄ ), and At least one selected from the group consisting of an organic acid salt of A (acetate (CH ₃ COOA), oxalate ((COOA) ₂ ), etc.). And may form a Japanese salt). Among these, A ₂ CO ₃ , AHCO ₃ , or AF is more preferable because it is inexpensive and easy to handle.

As the compound containing the atom M, oxides of M (FeO, Fe ₃ O ₄ , Fe ₂ O ₃ , MnO, Mn ₂ O ₃ , MnO ₂ , CoO, Co ₃ O ₄ , Co ₂ O ₃ , NiO, etc.) , M oxyhydroxide (MO (OH)), M silicate (MO · SiO ₂ , 2MO · SiO ₂ etc.), M phosphate (M ₃ (PO ₄ ) ₂ etc.), Borate (M ₃ (BO ₃ ) ₂ etc.), M fluoride (MF ₂ etc.), M chloride (MCl ₂ , MCl ₃ etc.), M nitrate (M (NO ₃ ) ₂ , M ( NO ₃ ) ₃ ), M sulfate (MSO ₄ , M ₂ (SO ₄ ) ₃ etc.), M organic acid salt (acetate (M (CH ₃ COO) ₂ ) and oxalate (M (COO ) _2), etc.) and M alkoxide _{(M (OCH} 3) selected from 2, the group consisting of _{M (OC 2} H _{5) 2,} etc.) At least one that is preferable.

In view of availability and cost, at least one compound selected from the group consisting of Fe ₃ O ₄ , Fe ₂ O ₃ , MnO, Mn ₂ O ₃ , MnO ₂ , Co ₃ O ₄ and NiO is more preferable. In particular, as the compound when the atom M is Fe, Fe ₃ O ₄ and / or Fe ₂ O ₃ is preferable, and as the compound when the atom M is Mn, MnO ₂ is preferable. The compound containing atom M may be one type or two or more types.

As the compound containing Si, silicon oxide (SiO ₂ ), silicon alkoxide (Si (OCH ₃ ) ₄ , Si (OC ₂ H ₅ ) _4, etc.), A silicate, or M silicate is preferable. . The compound containing Si may be crystalline or amorphous. Among them, more preferable because SiO ₂ is inexpensive.

As the compound containing P, anhydrous phosphoric acid (P ₂ O ₅ ), ammonium hydrogen phosphate (NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ ), A or M phosphate is preferable.
As the phosphate of A or M, for example, at least one selected from the group consisting of Li ₃ PO ₄ , Fe ₃ (PO ₄ ) ₂ , FePO ₄ and Mn ₃ (PO ₄ ) ₂ is preferable.
The compound containing P may be crystalline or amorphous. Of these, NH ₄ H ₂ PO ₄ is more preferable because it is inexpensive.

Examples of the compound containing atoms X ¹ and X ² (Zr, Ti, Nb, Ta, Mo and W) include oxides of X ¹ and X ² such as ZrO ₂ , TiO ₂ , Nb ₂ O ₅ and Ta ₂ O _5. , MoO ₃ or WO ₃ are preferred.

Compounds containing atoms Z ¹ and Z ² (P, Si, B, Al, and V) include Z ¹ , Z ² oxides (P ₂ O ₅ , B ₂ O _3, etc.), A or M phosphorus Preferred are at least one selected from the group consisting of acid salts, A or M silicates, A or M borates, A or M aluminates, and A or M vanadates.
Among them, when the atoms Z ¹ and Z ² contain P, at least one selected from the group consisting of Li ₃ PO ₄ , Fe ₃ (PO ₄ ) ₂ , FePO ₄ and Mn ₃ (PO ₄ ) ₂ , Si SiO ₂ when contained, B ₂ O ₃ and / or H ₃ BO ₃ when containing B, at least one selected from the group consisting of Al ₂ O ₃ , AlO (OH) and aluminosilicate when containing Al , V is preferable because vanadium oxide (VO, V ₂ O ₃ , VO ₃ , V ₂ O _5, etc.) is inexpensive.

A suitable combination of raw material formulations is Si, where the compound containing atom A is a carbonate or bicarbonate of A, the compound containing atom M is an oxide of M, and the compound containing P is ammonium hydrogen phosphate. This is a combination when the compound to be contained is silicon oxide.

In principle, the composition of the raw material formulation corresponds theoretically to the composition of the melt obtained from the raw material formulation. However, since there are components (such as Li) that are easily lost due to volatilization or the like during the melting process in the raw material preparation, the composition of the obtained melt is based on an oxide standard calculated from the charged amount of each raw material. It may be slightly different from the mol%. In such a case, it is preferable to set the charging amount of each raw material in consideration of the amount lost due to volatilization or the like.

The purity of each raw material in the raw material formulation is not particularly limited. Considering reactivity and physical properties of the positive electrode positive electrode material, the purity excluding hydration water is preferably 99% by mass or more.
As each raw material, it is preferable to use a pulverized raw material. Each raw material may be pulverized and mixed, or may be pulverized after mixing. The pulverization is preferably performed by a dry method or a wet method using a mixer, a ball mill, a jet mill, a planetary mill or the like, and a dry method is preferable because a solvent removal step is unnecessary. The particle diameter of each raw material in the raw material formulation is not limited as long as it does not adversely affect the mixing operation, the filling operation of the mixture into the melting container, the meltability of the mixture, and the like.

[Melting step (ii)]
In the melting step (ii), the raw material composition obtained in the raw material preparation step (i) is put in a container having at least an inner peripheral portion formed of an electrically conductive refractory material, and the electric conductivity constituting at least the inner peripheral portion of the container. Inductively heat the refractory material. Then, the raw material preparation that is in direct contact with the conductive refractory material housed in the container is heated and melted by the heat generated from the conductive refractory material heated by induction.

In the present specification, the “conductive refractory material” means that it has sufficient conductivity to be heated by electromagnetic induction and has excellent fire resistance, appearance, composition and physical properties at the melting temperature of the raw material formulation. A material that does not change. The fireproof temperature of the conductive refractory material is preferably 800 ° C. or higher. When the fireproof temperature is less than 800 ° C., the melt resistance of the container may be significantly lowered.
However, if the fireproof temperature of the conductive refractory material is excessively high, usable constituent materials may be excessively limited. Therefore, the fireproof temperature is preferably in the range of 900 to 2,000 ° C., More preferably, the temperature is in the range of 000 to 1,800 ° C. The refractory temperature means a temperature at which no remarkable change in appearance is observed when the material is heated for 24 hours.

In the present invention, examples of the conductive refractory material forming at least the inner periphery of the container include carbon or conductive non-oxide ceramics.

As the carbon, graphite is preferable because it is inexpensive, easily available, and easy to process. In addition, since there exists a possibility that carbon may carry out a reductive reaction with the oxides of heavy metals, such as iron, contained in a raw material formulation at high temperature, it is preferable to adjust the temperature of induction heating. When carbon is used as the conductive refractory material, a lining layer made of a refractory material other than carbon can be provided. And it is preferable to form a lining layer with electroconductive non-oxide ceramics. That is, it is preferable to use a container having a structure in which inner peripheral portions formed of conductive non-oxide ceramics described later are stacked inside a carbon outer container. According to the container having such a two-layer structure, damage to the container due to reaction with the heavy metal component in the melt can be prevented, and in addition, by induction heating of the conductive non-oxide ceramic constituting the inner peripheral portion. The raw material preparation can be efficiently heated by combining the heat generation and the heat generation by induction heating of carbon constituting the outer container.

Examples of the conductive non-oxide ceramic include ceramics mainly composed of at least one selected from silicon carbide (SiC), zirconium boride (ZrB ₂ ), and titanium boride (TiB ₂ ). In the present specification, “mainly” means containing 50% by mass or more of the component. Among the conductive non-oxide ceramics, a ceramic containing 50 to 98% by mass of zirconium boride is particularly preferable because of its good corrosion resistance.

A container having at least an inner periphery made of carbon or the conductive non-oxide ceramics is not easily eroded by the melt. In addition, as described later, it is preferable to melt the raw material preparation in an inert atmosphere or a reducing atmosphere. However, carbon and the conductive non-oxide ceramics are used in an inert atmosphere or a reducing atmosphere. Therefore, it is suitable as a material constituting a container for melting the raw material formulation. Furthermore, carbon or the conductive non-oxide ceramic is preferable as a constituent material of the container because a fired product obtained by molding a raw material powder, heating and firing is easily available.

As the constituent material of the container other than the inner periphery, a material transparent to the applied electromagnetic wave can be used. The outer peripheral part of the container may be made of alumina ceramics, for example.

The container having at least the inner periphery made of the conductive refractory material is not particularly limited in size and shape, and can be used as a small cylindrical crucible or a large melting tank. In particular, when the container is a large melting tank, the conductive refractory material may be used at least on the inner peripheral portion that comes into contact with the melt, and the non-contact portion with the melt such as the upper structure of the melt tank is made of other materials. It may be configured. Moreover, when using as a small cylindrical crucible, in order to prevent volatilization and evaporation of a raw material preparation or a molten material, it can also melt | dissolve by attaching the lid | cover to the said container.

Hereinafter, the melting apparatus used in the melting step (ii) of the present invention will be described with reference to the drawings.
FIG. 1 shows an example of an apparatus for melting the raw material mixture. The melting apparatus 1 includes a melting container 2 formed of the conductive refractory material, and an induction heating coil 3 disposed so as to surround the outer periphery of the melting container 2. The induction heating coil 3 is arranged so that the direction of the generated magnetic field is parallel to the longitudinal direction of the melting vessel 2.

The shape of the melting container 2 is not particularly limited, and may be a cylindrical shape, for example. Further, not the entire melting container 2 but only the inner peripheral portion can be formed of a conductive refractory material. Furthermore, the conductive refractory material constituting the entire melting container 2 or the inner periphery thereof may not be a single body, but may be a structure in which members divided into a plurality are arranged at a predetermined interval. In such a divided structure, since the induced current flows in each divided part to form a loop, even if a part of the divided part is damaged, the influence is stopped only in that part, Heat generation can be continued. Further, in the case of being configured as a single body, if the size of the melting container 2 is increased, the manufacturing is difficult and the manufacturing cost is high. However, by dividing, the manufacturing is easy and the manufacturing cost can be reduced. In addition, when an insulating member is interposed between the divided parts, there is an advantage that the induced current is less likely to interfere between the parts.

As described above, the melting container 2 around which the induction heating coil 3 is provided outside is housed in a jacket (exterior housing) 4 formed of a metal material such as stainless steel or a fireproof material such as ceramics. The jacket 4 has an openable / closable part (for example, a lid part) (not shown) for carrying in and taking out the melting container 2. A raw material supply pipe 6 for supplying the raw material mixture 5 into the melting container 2 is connected to the upper portion of the jacket 4. Further, on the side of the jacket 4, a gas introduction pipe 7 for introducing an inert gas or a reducing gas, which will be described later, into the jacket 4, and a gas discharge pipe 8 for discharging the gas in the jacket 4 to the outside. Are attached to each. The jacket 4 is preferably hermetically sealed except for the attachment parts of the raw material supply pipe 6, the gas introduction pipe 7 and the gas discharge pipe 8.

In order to perform the melting step (ii) in the present invention using such a melting apparatus 1, first, the raw material mixture 5 is introduced into the melting container 2 accommodated in the jacket 4 through the raw material supply pipe 6. Supply. Then, an alternating current is supplied to the induction heating coil 3 to inductively heat the conductive refractory material constituting at least the inner peripheral portion of the melting vessel 2. And the raw material formulation 5 accommodated in the melting container 2 is heated and melted by the heat generated by the induction heating.

The frequency of the alternating current supplied to the induction heating coil 3 is preferably 1 kHz to 5 GHz, for example.

The heating temperature of the raw material formulation 5 is preferably 1100 ° C. to 1800 ° C. Here, the heating temperature refers to the temperature of the melt itself and can be measured with a thermocouple or a pyrometer. Heating the raw material formulation 5 to a temperature of 1100 ° C. to 1800 ° C. is preferable because the olivine type, pyroxene type, or NASICON type compound raw material formulation 5 is melted to obtain a melt having a uniform composition. Here, “melting” means that each raw material melts and becomes transparent with the naked eye. When the heating temperature is 1100 ° C. or higher, melting is facilitated, and when it is 1800 ° C. or lower, the raw material formulation 5 is difficult to volatilize.
The heating temperature of the raw material formulation 5 is more preferably 1200 ° C to 1600 ° C. By performing heating at a temperature of 1200 ° C. or higher, melting can be performed more easily. Further, by heating at a temperature of 1600 ° C. or lower, the wear of the conductive refractory material due to heating is further suppressed.

The heating time can be appropriately set in consideration of the melting method, the melting scale, the molten metal uniformity, etc., but is preferably 0.2 to 24 hours, particularly preferably 0.5 to 2 hours. If the heating time is 0.2 hours or more, the uniformity of the melt is sufficient, and if it is 24 hours or less, the raw material formulation 5 is difficult to volatilize. In the melting step (ii), stirring may be performed to increase the uniformity of the melt. Further, the melt may be clarified at a temperature lower than the maximum temperature during melting until the next cooling step (iii) is performed. Furthermore, the raw material may be charged once or a plurality of times.

The melting step (ii) in the present invention can be performed in the atmosphere, but an inert gas or a reducing gas is introduced into the jacket 4 from the gas introduction pipe 7 and is performed in an inert atmosphere or a reducing atmosphere. It is preferable to perform melting. In particular, when producing an olivine type compound or a part of pyroxene type compound, it is preferable that the element M in the melt is in a low oxidation number state (for example, Fe ²⁺ when M = Fe). In order to suppress wear due to oxidation of the melting vessel, the melting step (ii) is performed in an inert atmosphere or a reducing atmosphere. The melt is preferably more reductive, but even if it is more oxidative, it can be reduced (for example, change from M ³⁺ to M ²⁺ ) in the heating step (iv) described later.

As the melting conditions, conditions suitable for the size and type of the container can be selected. The pressure may be carried out under any conditions of normal pressure, pressurization, and reduced pressure (0.9 × 10 ⁵ Pa or less). Moreover, after filling the raw material formulation 5 into the melting vessel 2, it can be replaced by introducing an inert gas or a reducing gas before heating.

Here, the inert atmosphere is a gas condition containing 99% by volume or more of at least one inert gas selected from nitrogen (N ₂ ) and a rare gas such as helium (He) and argon (Ar). Say.
Further, the reducing atmosphere refers to a gas condition in which a reducing gas is added to the above-described inert gas and substantially does not contain oxygen. Examples of the reducing gas include hydrogen (H ₂ ), carbon monoxide (CO), and ammonia (NH ₃ ). The amount of the reducing gas added to the inert gas is preferably 0.1% by volume or more, more preferably 1 to 10% by volume of the reducing gas in the total gas. The oxygen content is preferably 1% by volume or less in the gas, and more preferably 0.1% by volume or less.

Thus, by the induction heating of the melting container 2, the melt heated and melted in the melting container 2 is taken out and cooled in the next cooling step (iii). When the melting apparatus 1 shown in FIG. 1 is used, after the melting container 2 containing the melt is taken out from the jacket 4, the melting container 2 is tilted so that the melt flows out from the opening such as the upper end. Then, the discharged melt is supplied to a cooling and solidifying device described later.

In the melting step (ii) of the present invention carried out using such a melting apparatus 1, at least the inner periphery of the melting vessel 2 containing the raw material mixture 5 is formed of a conductive refractory material, and this conductive Since the raw material mixture 5 in direct contact with the conductive refractory material is heated and melted by induction heating of the refractory refractory material, the melting container is housed in a heating furnace such as an electric furnace and heated. Compared with energy loss, heat efficiency is high. In addition, the heating rate is high, rapid heating is possible, and mass productivity is high.

Furthermore, in the melting step (ii) of the present invention, convection occurs in the melt due to the interaction between the magnetic field generated by the induction heating coil 3 and the induced current in the melt, and this convection causes a melt having a uniform composition. can get. Therefore, it is not necessary to perform external stirring.

Moreover, since at least the inner peripheral portion of the melting container 2 containing the raw material mixture 5 is formed of an electrically conductive refractory material having excellent fire resistance, it can be used at a high temperature, and the raw material mixture 5 can be melted. It is difficult for the melting container 2 to be worn at a temperature. Furthermore, since the melting container 2 is not easily eroded by the raw material formulation 5, the components constituting the melting container 2 are difficult to mix in the melt.

Next, another example of the melting apparatus used in the melting step (ii) of the present invention will be described.
The melting apparatus 1 shown in FIG. 2 has, as a melting container, a melting space in which the horizontal opening cross section gradually decreases from the middle in the vertical direction downward, and at least the inner periphery is formed of the conductive refractory material. It has a molten part 2a. Then, a melt outlet part is connected to the melting part 2a. That is, a melt outlet pipe 2b having a diameter smaller than that of the melting section 2a is connected to the bottom of the melting section 2a so as to communicate with the melting space, and a melt outlet section is formed by the melt outlet pipe 2b. ing. The position to which the melt outlet pipe 2b is connected may be the bottom part or the side part of the melt part 2a, but is preferably connected vertically downward to the bottom part of the melt part 2a from the viewpoint of the lead property of the melt. .
In addition, the melt outlet tube 2b can be formed of an electrically conductive refractory material at least on the inner periphery as in the molten portion 2a, but the entire melt outlet tube 2b is preferably formed of an electrically conductive refractory material. .

In addition, an induction heating coil (hereinafter, referred to as a first induction heating coil) 3a for heating the melting part is disposed outside the melting part 2a so as to surround the melting part 2a in the circumferential direction. In addition, an induction heating coil (hereinafter, referred to as a second induction heating coil) 3b for heating the melt outlet tube is disposed outside the melt outlet tube 2b so as to surround the outer periphery thereof.

Further, the melted part 2a around which the first induction heating coil 3a is provided outside is housed in a jacket 4 formed of a fireproof material such as a metal material or ceramics. And the through-hole is provided in the bottom part of the jacket 4, The lower part of the melt outlet pipe 2b is arrange | positioned outside through this through-hole. In addition, a cooling mechanism (not shown) such as a cooling gas jetting mechanism is disposed in the vicinity of the opened lower end of the melt outlet pipe 2b, and the cooling gas is introduced by a method such as introducing a cooling gas. The melt outlet pipe 2b is cooled. In addition, it is preferable to seal the clearance gap of the through-hole by which the melt | dissolution lead-out tube 2b was penetrated by methods, such as filling with a refractory material, for example.

As the conductive refractory material for forming at least the inner peripheral portion of the melting portion 2a and the melt outlet tube 2b, carbon or conductive non-oxide ceramic described as a constituent material of the melting vessel 2 in the melting apparatus 1 shown in FIG. Can be mentioned. The melting part 2a and the melt outlet pipe 2b may be formed of different materials, but are preferably formed of the same material because they are easy to manufacture.

The first induction heating coil 3a for induction heating the melting part 2a and the second induction heating coil 3b for induction heating the melt outlet pipe 2b can be connected to different power sources and controlled independently. preferable.

2, reference numeral 9 indicates a cooling and solidifying apparatus used in a cooling step described later, and reference numeral 10 indicates a solidified product obtained by the cooling and solidifying apparatus 9. As the cooling and solidifying device 9, as will be described later, a twin roller rotating at a high speed or a rotating single roller, or a device configured to press a melt on a cooled carbon plate or metal plate to obtain a solidified product, etc. Is used. In the melting apparatus 1 shown in FIG. 2, since the other part is comprised similarly to the melting apparatus 1 shown in FIG. 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

In order to perform the melting step (ii) using the melting apparatus 1 shown in FIG. 2, first, the raw material mixture 5 is supplied to the melting part 2 a housed in the jacket 4 using the raw material supply pipe 6. . Here, before supplying the raw material preparation 5, the solidified product (plug 11) of the melt having the same composition as that of the raw material preparation 5 is placed inside the melt outlet pipe 2b (for example, a connecting portion with the melting part 2a). It is preferable to close the melt outlet pipe 2b by prepacking at least a part of the melt.

By doing in this way, it can prevent that the raw material preparation 5 is discharged from the melt outlet pipe 2b during a heating process. As the plug 11 made of a melt-solidified product of the raw material mixture, a stay-solidified product formed in the melt-derived tube 2b in the melt-derived step described later can also be used. That is, when heating to the melt outlet tube 2b is stopped in the melt outlet step, the melt obtained in the melting part 2a is solidified in the melt outlet tube 2b to form a solidified product having a plug function. Sometimes. By using this solidified material as it is, the outflow of the melt from the melt outlet pipe 2b can be closed.

Next, without supplying current to the second induction heating coil 3b, current is supplied only to the first induction heating coil 3a, and the conductive refractory material constituting at least the inner periphery of the melting portion 2a is induction heated. To do. And by this induction heating, the raw material preparation 5 accommodated in the melting part 2a is heated and melted. At this time, in order to prevent the plug 11 made of the melted and solidified product of the raw material mixture 5 from being melted, the inside of the melt outlet tube 2b is introduced by a method such as introducing a cooling gas from the lower end of the melt outlet tube 2b. Is preferably cooled.

About the heating temperature, heating time, heating atmosphere, etc. of the raw material formulation 5, it is the same as that of the case where a melting process (ii) is performed using the melting apparatus shown in FIG.
In this way, the first induction heating coil 3a induction heats the melting part 2a to heat and melt the raw material mixture 5 accommodated in the melting part 2a, and then the second induction heating coil 3b is also supplied with current. Then, the melt outlet pipe 2b is induction-heated. Since the plug 11 is melted and dropped by the induction heating of the melt outlet pipe 2b and the blockage of the melt outlet pipe 2b is released, the melt in the melted part 2a quickly passes through the melt outlet pipe 2b. Derived externally.

Even when such a melting apparatus 1 is used, energy loss is reduced as compared with the conventional method of storing and heating in a heating furnace such as an electric furnace as in the case of using the melting apparatus 1 shown in FIG. It has low heat efficiency and high heating speed, enabling rapid heating and high mass productivity.
In addition, since the melted part 2a and the melt outlet pipe 2b are not easily eroded by the raw material mixture 5, the components constituting the melted part 2a and the like are hardly mixed in the melt.

Furthermore, the cooling process (iii) is continuously performed from the melting process (ii) by supplying the melt derived from the melt discharge pipe 2b as it is to a cooling solidification device 9 (for example, a twin roll) described later. Can do. Further, as described above, when the inside of the melt outlet pipe 2b is cooled by a method such as interrupting the power supply to the second induction heating coil 3b and introducing a cooling gas into the melt outlet pipe 2b, Due to the temperature drop, the melt is solidified in the melt outlet pipe 2b to form a solidified product having a plug function. By closing the melt outlet tube 2b again with the solidified material thus formed, it is possible to prevent the melt from flowing out, and thus the steps from melting to cooling and solidification can be performed intermittently.

It should be noted that the melt outlet tube 2b can be heated not by induction heating as described above but by energization heating. That is, the melt discharge pipe is formed of the conductive refractory material or metal material, and current is supplied from the electrodes respectively disposed at the upper and lower ends thereof to form the melt discharge pipe. It is also possible to heat the inside of the melt outlet pipe by causing the material to generate heat. Further, when the melt outlet tube 2b is electrically heated, the same effect as that obtained when induction heating can be achieved.

[Cooling step (iii)]
In the cooling step (iii), the melt obtained in the melting step (ii) is cooled to around room temperature (20 to 25 ° C.) to obtain a solidified product.

The solidified product is preferably an amorphous material, but a part of the solidified product may be a crystallized product. When the solidified product contains an amorphous material, the next pulverization step (iv) can be easily performed, and the composition and particle size of the resulting compound can be easily controlled. In the case where the solidified product contains a crystallized product, the crystallized product becomes a crystal nucleus in the heating step (v) described later, and it is easy to crystallize. The amount of crystallized material in the solidified product is preferably 0 to 30% by mass with respect to the total mass of the solidified product. When a large amount of crystallized material is contained, it becomes difficult to obtain a granular or flaky solidified material. Moreover, the wear of the cooling device is accelerated, and the burden of the subsequent pulverization step (iv) is increased.

The cooling of the melt is preferably performed in the air, under an inert atmosphere, or under a reducing atmosphere because the equipment is simple. Preferred conditions for the inert atmosphere and the reducing atmosphere are the same as those described in the melting step (ii).

The cooling rate is preferably more than 1 × 10 ³ ℃ / sec from 1000 ° C. to 50 ° C., more 1 × 10 ⁴ ℃ / sec is particularly preferable. When the cooling rate is 1 × 10 ³ ° C./second or more, an amorphous material is easily obtained. The higher the cooling rate, the easier it is to obtain an amorphous material, but considering the production equipment and mass productivity, the cooling rate is preferably 1 × 10 ¹⁰ ° C./second or less, and 1 × 10 ⁸ ° C./second from the practical point of view. Particularly preferred is seconds or less.

Cooling methods include, for example, a method in which a melt is dropped between twin rollers rotating at high speed to obtain a flake-like solidified product, and a flake-like or plate-like solidified product by dropping the melt on a rotating single roller , A method of obtaining a lump solidified product by pressing a melt on a cooled carbon plate or a metal plate, a method of obtaining a lump solidified product by spraying the melt in air or water in small particles, Is preferably adopted.
Among these, a cooling method using twin rollers is more preferable because the cooling rate is high and a large amount of processing can be performed. As the double roller, it is preferable to use one made of metal, carbon or ceramic.

As described above, after the melting step (ii), by rapidly cooling the melt at a cooling rate of 1 × 10 ³ ° C./second or more, the resulting solidified product tends to be amorphous, and the chemical composition of the solidified product This is preferable because uniformity is improved.
The so-called rapid cooling treatment at a cooling rate of 1 × 10 ³ ° C./second or more may be carried out as it is with respect to the melt flowed out from the container formed of the conductive refractory material, and melted in the container. The melt may be once cooled at a normal rate and then remelted.

The solidified product is preferably flaky or fibrous. In the case of flakes, the average thickness is preferably 200 μm or less, and more preferably 100 μm or less. The average diameter of the surface perpendicular to the flake thickness direction is not particularly limited. In the case of a fibrous form, the average diameter is preferably 50 μm or less, and more preferably 30 μm or less.
When the average thickness or the average diameter is not more than the upper limit value, the burden of the subsequent pulverization step (iv) can be reduced, and the crystallization efficiency in the heating step (v) can be increased. The average thickness of the flaky solidified product can be measured with a caliper or a micrometer. Further, the average diameter of the fibrous solidified product can be measured by the above method or observation with a microscope.

[Crushing step (iv)]
After the cooling step (iii), it is preferable to perform a pulverization step (iv) in which the obtained solidified product is pulverized to obtain a pulverized product.

Since the solidified product obtained in the cooling step (iii) usually contains a large amount of an amorphous material or consists of an amorphous material, there is an advantage that it can be easily pulverized. Further, there is an advantage that the apparatus used for pulverization can be pulverized without imposing a burden and the particle diameter can be easily controlled.
For example, when a positive electrode material is obtained by a solid phase reaction, pulverization is performed after firing. In this case, residual stress may be generated by pulverization and battery characteristics may be deteriorated. In contrast, by performing the pulverization step (iv) before the heating step (v) described later, the residual stress generated by the pulverization can be reduced or removed by the heat treatment.

In the pulverization step (iv), at least one selected from the group consisting of an organic compound and a carbon-based conductive material may be added as a carbon source.
Since the organic compound and / or the carbon-based conductive material functions as a conductive material after the heating step (v) described later, the conductivity of the positive electrode material for secondary batteries can be increased. Further, by adding an organic compound and / or a carbon-based conductive material, oxidation in the pulverization step (iv) and the heating step (v) can be prevented, and further reduction can be promoted.

When the carbon source is added in the pulverization step (iv), the solidified product and the carbon source are mixed and then pulverized, the solidified product and the carbon source are pulverized and mixed, or the solidified product is added. A step of adding a carbon source after pulverization is preferred. In addition, when a carbon source is only an organic compound, it can mix with a solidified material, without grind | pulverizing.

Since the compound (α) obtained in the heating step (v) of the next step is an insulator, it is preferable to increase the electrical conductivity for use as a positive electrode material for a secondary battery.
When a carbon-based conductive material is used as the carbon source, the carbon-based conductive material serves as conductive carbon and covers at least a part of the surface of the compound (α). Further, when an organic compound is used, at least a part of the organic compound is carbonized by performing the heating step (v) of the next step, and at least a part of the surface of the compound (α) is formed as conductive carbon. Cover. Since the conductive carbon functions as a conductive material for the compound (α), the electrical conductivity of the positive electrode material for a secondary battery can be increased.

The organic compound as the carbon source is preferably a compound that undergoes a thermal decomposition reaction when heated in an inert atmosphere or a reducing atmosphere, and oxygen and hydrogen are released and carbonized. The organic compound is at least one selected from the group consisting of saccharides, amino acids, peptides, aldehydes, ketones, carboxylic acids, terpenes, heterocyclic amines, fatty acids and aliphatic acyclic polymers having functional groups. Species are preferred.

The carbon conductive material as the carbon source is preferably at least one selected from the group consisting of carbon black, graphite, acetylene black, carbon fiber, and amorphous carbon. As the amorphous carbon, those in which the CO bond peak and CH bond peak causing the decrease in the conductivity of the positive electrode material are not substantially detected in the FTIR analysis are preferable.

The ratio of the mass of the carbon source is such that the carbon equivalent (mass) in the carbon source is 0.1 to 20 with respect to the total mass of the mass of the solidified product and the carbon equivalent (mass) in the carbon source. An amount of mass% is preferable, and an amount of 2 to 10 mass% is more preferable.
When the organic compound and the carbon-based conductive material are used in combination, the total amount is adjusted so as to fall within the above range. By making the amount of carbon 0.1% by mass or more, the conductivity of the positive electrode material for a secondary battery made of the compound (α) can be sufficiently increased. Moreover, electroconductivity can fully be improved, keeping the characteristic as a positive electrode material for secondary batteries high by making carbon amount 20 mass% or less.

The pulverization is preferably performed using a cutter mill, jaw crusher, hammer mill, ball mill, jet mill, planetary mill or the like. Moreover, pulverization can be efficiently advanced by using various methods stepwise depending on the particle diameter. For example, preliminarily pulverizing with a cutter mill and then pulverizing with a planetary mill or ball mill is preferable because the time required for pulverization can be shortened. From the viewpoint of productivity, it is particularly preferable to use a ball mill. As the grinding media, it is preferable to use zirconia balls, alumina balls, glass balls or the like. In particular, zirconia balls are preferable because they have a low wear rate and can suppress the mixing of impurities.

The diameter of the grinding media is preferably 0.1 to 30 mm. After pulverization is performed in multiple stages and pulverization is performed with a large pulverization medium, the pulverization medium and the pulverized product may be separated and pulverized using a smaller pulverization medium. With this method, the remaining of unground particles can be suppressed.
The pulverization container is not particularly limited, but the pulverization efficiency is good when the pulverization medium and the solidified material are placed in the container up to 30 to 80% of the container volume. When a ball mill is used, the pulverization time is preferably 6 to 360 hours, more preferably 6 to 120 hours, and particularly preferably 12 to 96 hours. If the pulverization time is 6 hours or more, the pulverization can be sufficiently advanced, and if it is 360 hours or less, excessive pulverization can be suppressed.

The pulverization may be performed either dry or wet, but is preferably performed in a wet manner from the viewpoint that the particle size of the pulverized product can be reduced. Moreover, when adding a carbon source at the grinding | pulverization process (iv), it is preferable to carry out by a wet point also from the point which can mix a solidified material and a carbon source uniformly. That is, the pulverization step (iv) is preferably performed using a solvent (pulverization solvent). When the grinding solvent is filled up to 30 to 80% of the container volume with the grinding media contained, the grinding efficiency is improved. When the pulverization step (iv) is performed in a wet manner, it is preferable to carry out the heating step (v) after removing the pulverization solvent by sedimentation, filtration, drying under reduced pressure, drying by heating, or the like. However, when the ratio of the solid content with respect to the grinding solvent is 30% or more, the pulverized product containing the grinding solvent may be used in the heating step (v).

As the pulverization solvent, a solvent having an appropriate polarity that is difficult to dissolve the solidified product and is compatible with the carbon source, and does not significantly increase the viscosity when mixed with the solidified product and the carbon source is preferable. Water is preferable from the viewpoint of cost and safety. On the other hand, when a problem such as elution of the solidified product occurs, an organic solvent is preferable. Examples of the organic solvent include ethanol, isopropyl alcohol, acetone, hexane, toluene and the like. The grinding solvent is more preferably at least one selected from the group consisting of water, acetone and isopropyl alcohol, and acetone is particularly preferred.

The amount of the grinding solvent used is preferably such that the total concentration of the solidified product and the carbon source is 1 to 80%, particularly preferably 10 to 40%. Productivity can be improved by making the usage-amount of a grinding | pulverization solvent into 1% or more. Moreover, mixing and grinding | pulverization of a solidified material and a carbon source can be advanced efficiently because the usage-amount of a grinding | pulverization solvent shall be 80% or less.

The average particle size of the pulverized product is preferably 10 nm to 10 μm, particularly preferably 10 nm to 5 μm in terms of volume-based median diameter, from the viewpoint of obtaining higher conductivity when applied to a positive electrode material for a secondary battery. When the average particle size is 10 nm or more, when the heating step (v) is performed, the particles of the compound (α) do not sinter and the particle size does not become too large. When the average particle size is 10 μm or less, it is easy to obtain a secondary battery positive electrode material exhibiting high conductivity, and it becomes easy to realize a higher capacity and a higher energy density. However, if a lot of very fine particles having a particle size of less than 10 nm are contained, the sintering aid acts when the heating step (v) is performed, and the average particle size after heating is increased.
In the present specification, the average particle size is obtained mainly by a laser diffraction / scattering particle size measuring device (trade name: LA-950, manufactured by Horiba, Ltd.). When measurement is difficult, a sedimentation method or a flow image analyzer can be used.

[Heating step (v)]
After the pulverization step (iv), the obtained pulverized product is heated in an inert atmosphere or a reducing atmosphere to synthesize a compound (α) having a predetermined composition from the pulverized product of the solidified product. Preferably it is done.
The heating step (v) preferably includes relaxation of stress generated by pulverization, crystal nucleation of the pulverized product, and grain growth. By performing such a heating step (v) after the pulverization step (iv) described above, it is possible to obtain a positive electrode material for a secondary battery in which crystals are grown while reducing or removing residual stress due to pulverization.

In the heating step (v), for example, it is preferable to obtain particles of the phosphoric acid compound (1) or particles of the silicic acid compound (2), and crystal particles of the phosphoric acid compound (1) or the silicic acid compound (2) are obtained. It is more preferable to obtain, and it is particularly preferable to obtain crystal particles of the phosphoric acid compound (1) having an olivine type crystal structure or crystal particles of the silicate compound (2) having an olivine type crystal structure.
It is preferable that the obtained compound does not contain an amorphous substance. When the compound does not contain an amorphous substance, a halo pattern is not detected by X-ray diffraction.

The organic compound or carbon-based conductive substance adhering to the surface of the pulverized product in the pulverization step (iv) is bonded to the surface of the compound (α), preferably its crystal particles, generated in the heating step (v), and functions as a conductive material. To do. The organic compound is thermally decomposed in the heating step (v), and at least a part thereof becomes a carbide to function as a conductive material. When the pulverization step (iv) is performed in a wet manner, the dispersion medium may be removed simultaneously with heating.

The heating temperature for synthesizing the compound (α) is preferably 400 to 1,000 ° C., particularly preferably 500 to 900 ° C. When the heating temperature is 400 ° C. or higher, a reaction is likely to occur, and when it is 1,000 ° C. or lower, the pulverized product is difficult to melt and the crystal system and particle diameter are easily controlled. Further, at the heating temperature, it becomes easy to obtain a compound (α) having an appropriate crystallinity, particle size, particle size distribution, etc., preferably its crystal particles, more preferably olivine type crystal particles. The heating is not limited to being held at a constant temperature, and may be performed by setting the holding temperature in multiple stages. As the heating temperature is increased, the particle diameter of the generated particles tends to increase. Therefore, it is preferable to set the heating temperature according to a desired particle diameter.

The heating time (holding time depending on the heating temperature) is preferably 1 to 72 hours in consideration of the desired particle size. Heating is preferably performed in a box furnace, tunnel kiln, roller hearth kiln, rotary kiln, microwave heating furnace, or the like that uses electricity, oil, gas, or the like as a heat source.

The heating step (v) is preferably performed in the air, in an inert atmosphere, or in a reducing atmosphere. Preferred conditions for the inert atmosphere and the reducing atmosphere are the same as those described in the melting step (ii). The atmospheric pressure may be any of normal pressure, pressurization, and reduced pressure (0.9 × 10 ⁵ Pa or less).
Moreover, you may charge the container which put the reducing agent (for example, graphite) in the heating furnace. If the heating step (v) is performed in an inert atmosphere or a reducing atmosphere, reduction of M ions in the pulverized product (for example, change from M ³⁺ to M ²⁺ ) can be promoted.

After heating, it is usually cooled to room temperature. The cooling rate in the cooling is preferably 30 ° C./hour to 300 ° C./hour. By setting the cooling rate within this range, distortion due to heating can be removed, and when the product is a crystal, the target product can be obtained while maintaining the crystal structure. The cooling is preferably allowed to cool to room temperature. Cooling is preferably performed in an inert atmosphere or a reducing atmosphere.

Carbon source can be added in the heating step (v). In this case, the pulverized product obtained in the pulverization step (iv) (preferably a pulverized product containing no carbon source) is heated to obtain the compound (α), and then the compound (α) and the carbon source are obtained. It is preferable to adopt a production method in which a pulverized product containing the following is obtained and then the pulverized product is heated.

The compound (α) having a predetermined composition as a positive electrode material for a secondary battery is manufactured through the melting, cooling, pulverization, and heating steps described above. The compound (α) preferably contains crystal particles and is preferably an olivine type. With such a composition and crystal system, as described above, a multi-electron type material having a theoretical electric capacity can be obtained.

Particularly, a silicate compound is preferable because it can increase the capacity per unit volume (mass) of the secondary battery when used as a positive electrode material for a secondary battery. The silicate compound is preferably an olivine type, and the olivine type silicate compound is suitable as a positive electrode material for a secondary battery. A phosphoric acid compound is preferable when used as a positive electrode material for a secondary battery because the reliability of the performance of the secondary battery can be increased. The phosphate compound is preferably an olivine type, and the olivine type phosphate compound is suitable as a positive electrode material for a secondary battery.

The specific surface area of the positive electrode material for a secondary battery obtained by the present invention is preferably 0.2 m ² / g to 200 m ² / g, more preferably 1 m ² / g to 100 m ² / g. By setting the specific surface area within this range, the conductivity is increased. The specific surface area can be measured by, for example, a specific surface area measuring apparatus using a nitrogen adsorption method.

In addition, the average particle diameter of the crystal particles of the positive electrode material for secondary batteries is preferably 10 nm to 10 μm, more preferably 10 nm to 2 μm, in terms of volume median diameter in order to increase the conductivity of the particles. The average particle diameter of the positive electrode material for a secondary battery obtained by the present invention is preferably 10 nm to 10 μm in terms of volume median diameter even if it contains not only crystal particles but also amorphous particles. More preferably, it is ˜2 μm.

According to the present invention, a raw material preparation of an olivine type compound, pyroxene type compound, or NASICON type compound is induction-heated in a container having at least an inner peripheral portion formed of the conductive refractory material. Compared to the conventional method in which a melting vessel is housed in a heating furnace such as an electric furnace and heat melting is performed, heat efficiency is high, rapid heating is possible, and mass productivity is high. . In the melting step (ii), a production amount of 10 kg or more, preferably 100 kg or more per batch can be realized.
In addition, the container can be prevented from being eroded by heavy metal elements such as Fe and Mn contained in the melt, and the container used for heating and melting can be prevented from being worn. Therefore, the frequency of maintenance is reduced and the manufacturing cost of the positive electrode material for the secondary battery is reduced. Can be reduced. Furthermore, it can suppress that the component derived from a container mixes in the melt in the said container, and can obtain the positive electrode material for secondary batteries excellent in purity.

<Positive electrode for secondary battery and method for producing secondary battery>
By using the secondary battery positive electrode material obtained by the production method of the present invention, a secondary battery positive electrode and a secondary battery can be produced. Examples of the secondary battery include a metal lithium secondary battery, a lithium ion secondary battery, and a lithium polymer secondary battery, and a lithium ion secondary battery is preferable. The battery shape is not limited, and various shapes and sizes such as a cylindrical shape, a square shape, and a coin shape can be appropriately employed.

The positive electrode for a secondary battery can be manufactured according to a known electrode manufacturing method using the positive electrode material for a secondary battery obtained by the manufacturing method of the present invention. For example, a positive electrode material for a secondary battery obtained according to the present invention may be prepared by using a known binder (polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile-butadiene as required. After mixing with rubber, fluoro rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, etc., further known organic solvents (N-methylpyrrolidone, toluene, cyclohexane, dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate) , Methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.) to form a slurry, and a known current collector (aluminum, By a method such as coating to the metal foil or the like) of stainless steel, it can be produced.

As the structure of the secondary battery, a structure in a known secondary battery can be adopted except that the positive electrode material for a secondary battery obtained by the production method of the present invention is used as an electrode. The same applies to separators, battery cases, and the like. As the negative electrode, a known negative electrode active material can be used as the active material, and at least one selected from the group consisting of carbon materials, alkali metal materials, and alkaline earth metal materials is preferably used. As the electrolytic solution, a non-aqueous electrolytic solution is preferable. That is, as the secondary battery using the positive electrode material for a secondary battery obtained by the production method of the present invention, a nonaqueous electrolyte lithium ion secondary battery is preferable.

The present invention will be specifically described with reference to examples, but the present invention is not limited to the following examples.

<Example 1>
(Raw material preparation step (i))
The composition of the melt is 25.0 mol%, 50.0 mol%, and 25.0 mol% in terms of Li ₂ O, FeO, and P ₂ O ₅ (unit: mol%), respectively. , Lithium carbonate (Li ₂ CO ₃ ), triiron tetroxide (Fe ₃ O ₄ ), and ammonium hydrogen phosphate (NH ₄ H ₂ PO ₄ ) are weighed, mixed and pulverized dry to obtain a raw material formulation It was.

(Melting step (ii))
The obtained raw material formulation was heated and melted as shown below using a melting apparatus. That is, first, the raw material mixture was filled into a cylindrical crucible made of graphite and having an outer diameter of 50 mm, an inner diameter of 40 mm, and a height of 100 mm. Next, this crucible was loaded inside a copper induction coil (made by Keddy Corporation) having an inner diameter of 70 mm, which was installed in a stainless steel lidded outer container (jacket) having a volume of 50 L. Then, while flowing N ₂ gas at a flow rate of 10 L / min in the outer container, an alternating current of 5 kHz was passed through the induction heating coil to inductively heat the crucible. The temperature in the crucible was raised at a rate of 20 ° C./minute, and when it reached 1250 ° C., this temperature was maintained for 10 minutes. Thus, the raw material formulation in the crucible was heated and melted to obtain a melt.

(Cooling step (iii))
The crucible was removed from the outer container, and the melt obtained in the melting step (ii) was poured out onto a stainless steel plate cooled with water. Then, another stainless steel plate was put on the melt that had flowed out and pressed to obtain a solidified product. The cooling rate is considered to be 1 × 10 ³ ° C./second or more because the temperature of the solidified product has decreased to about 50 ° C. after pressing.

(Crushing step (iv))
The obtained solidified product was coarsely pulverized using a pestle and a mortar. Further, the solidified product after coarse pulverization was pulverized in acetone using a planetary mill (manufactured by Ito Seisakusho, device name: LP-4) using zirconia balls as pulverization media to obtain a pulverized product. The average particle diameter of the obtained pulverized product was 0.22 μm in terms of volume-based median diameter.

(Heating step (v))
The pulverized product obtained in the pulverization step (iv) is heated at 700 ° C. for 8 hours in an Ar gas atmosphere containing 3% by volume of H ₂ gas using an electric furnace (manufactured by Motoyama, model name: SKM-3035). Then, the mixture was cooled to room temperature to precipitate lithium iron phosphate particles.

The mineral phase of the obtained lithium iron phosphate particles was measured using an X-ray diffraction apparatus (manufactured by Rigaku Corporation, apparatus name: RINT TTRIII). From the diffraction pattern, it was confirmed that the obtained lithium iron phosphate particles were orthorhombic olivine type LiFePO ₄ . Moreover, it was 25 m < ² > / g when the specific surface area was measured using the specific surface area measuring apparatus (The Shimadzu Corp. make, apparatus name: ASAP2020). Furthermore, when the average particle diameter of the obtained lithium iron phosphate particles was measured using a laser diffraction / scattering particle size analyzer (Horiba, Ltd., apparatus name: LA-950), the volume-converted median diameter was 0. .23 μm.
In addition, when the crucible after taking out and cooling a melt was cut | disconnected and the amount of erosion was measured with the flux line, it was 0.2 mm or less.

<Example 2>
Carbonic acid so that the composition of the melt is 33.3 mol%, 33.3 mol%, and 33.3 mol% in terms of Li ₂ O, FeO, and SiO ₂ (unit: mol%), respectively. Lithium (Li ₂ CO ₃ ), triiron tetroxide (Fe ₃ O ₄ ), and silicon dioxide (SiO ₂ ) were weighed and mixed dry to obtain a raw material formulation.

Next, the obtained raw material mixture was melted in the same manner as in Example 1 except that the temperature in the crucible was held at 1450 ° C. for 30 minutes using the same melting apparatus as in Example 1, to obtain a melt. Next, in the same manner as in Example 1, the cooling step (iii) and the pulverization step (iv) were sequentially performed to obtain a pulverized product.

Next, the pulverized product obtained in the pulverization step (iv) was heated in the same manner as in Example 1 to precipitate lithium iron silicate particles. When the mineral phase of the obtained lithium iron silicate particles was measured, it was confirmed to be orthorhombic olivine type Li ₂ FeSiO ₄ . Moreover, it was 23 m < ² > / g when the specific surface area was measured. Furthermore, when the average particle diameter of the lithium iron silicate particles was measured, the median diameter in terms of volume was 0.45 μm.
After the melt was taken out and cooled, the crucible was cut, and the amount of erosion was measured with a flux line.

<Example 3>
The composition of the _{melt, Li 2 O, Fe 2 O} 3, and SiO ₂ in terms of the amount (unit: mol%), respectively, 16.7 mol%, 16.7 mol%, and become as 66.7 mol% Lithium carbonate (Li ₂ CO ₃ ), diiron trioxide (Fe ₂ O ₃ ), and silicon dioxide (SiO ₂ ) were weighed, mixed and pulverized in a dry process to obtain a raw material formulation.

The obtained raw material mixture was heated and melted as shown below using a melting apparatus. That is, first, the raw material formulation was filled in a crucible made of silicon carbide having an inner diameter of 35 mm and a height of 60 mm fitted and arranged inside a graphite crucible having an outer diameter of 50 mm, an inner diameter of 40 mm, and a height of 100 mm. Next, this double-structured crucible was loaded inside a copper induction heating coil (made by Kydeky Corp.) having an inner diameter of 70 mm installed in a stainless steel lid with a volume of 50 L. Then, induction heating was performed in the same manner as in Example 2, and the raw material formulation was melted by holding the inside of the silicon carbide crucible at 1450 ° C. for 30 minutes to obtain a melt.

Then, in the same manner as in Example 1, the cooling step (iii) and the pulverization step (iv) were sequentially performed to obtain a pulverized product.

Next, the pulverized product obtained in the pulverization step (iv) was heated in the same manner as in Example 1 to precipitate lithium iron silicate particles. When the mineral phase of the obtained lithium iron silicate particles was measured, it was confirmed to be monoclinic pyroxene-type LiFeSi ₂ O ₆ . Moreover, it was 23 m < ² > / g when the specific surface area was measured. Furthermore, when the average particle diameter of the lithium iron silicate particles was measured, the median diameter in terms of volume was 0.38 μm.
The silicon carbide crucible after the melt was taken out and cooled was cut, and the amount of erosion measured with a flux line was 0.2 mm or less.

<Example 4>
The composition of the _{melt, Li 2 O, Fe 2 O} 3, and _P 2 _{O 5} equivalent amount (unit: mol%), respectively, 37.5 mol%, and 25.0 mol%, and 37.5 mol% Lithium carbonate (Li ₂ CO ₃ ), diiron trioxide (Fe ₂ O ₃ ), and ammonium hydrogen phosphate (NH ₄ H ₂ PO ₄ ) are weighed, mixed and pulverized in a dry manner I got a thing.

The obtained raw material composition was filled in a silicon carbide crucible installed inside a graphite crucible in the same manner as in Example 3, and the inside of the crucible was held at 1200 ° C. for 10 minutes, as in Example 3. The same heating was performed to obtain a melt.

Then, in the same manner as in Example 1, the cooling step (iii) and the pulverization step (iv) were sequentially performed to obtain a pulverized product.

Next, the obtained pulverized product was heated in the atmosphere at 650 ° C. for 8 hours using the same electric furnace as in Example 1, and then cooled to room temperature to precipitate lithium iron phosphate particles.

When the mineral phase of the obtained lithium iron phosphate particles was measured, it was confirmed to be monoclinic NASICON type Li ₃ Fe ₂ (PO ₄ ) ₃ . Moreover, it was 31 m < ² > / g when the specific surface area was measured. Furthermore, when the average particle diameter of the lithium iron phosphate particles was measured, the median diameter in terms of volume was 0.35 μm.
The silicon carbide crucible after the melt was taken out and cooled was cut, and the amount of erosion measured with a flux line was 0.2 mm or less.

<Example 5>
A raw material formulation having the same composition as that of Example 1 was heated and melted as shown below using the melting apparatus shown in FIG. In this melting apparatus, a graphite nozzle portion (melt discharge) having an outer diameter of 15 mm, an inner diameter of 5 mm, and a length of 10 mm is formed at the bottom of a melting portion made of graphite having an outer diameter of 50 mm, an inner diameter of 40 mm, and a height of 100 mm. Tube). Further, a copper induction coil having an inner diameter of 70 mm (manufactured by Keddy Corp.), which is the first induction heating coil, is provided outside the melting portion, and a copper induction coil having an inner diameter of 25 mm, which is the second induction heating coil, is provided outside the nozzle portion. Each of them was made by KDDY Corporation. Further, the melting part, the nozzle part, and the first and second induction heating coils are housed in a stainless steel lidded outer container (jacket) having a volume of 50 L and a through-hole having a diameter of 20 mm at the bottom part. It installed so that a lower end part might extend outside from the through-hole of an exterior container.

The raw material mixture was filled in the melting part of the melting apparatus having such a structure. Here, the nozzle part was previously filled with a plug prepared by melting and solidifying the same composition as the raw material formulation filled in the melting part. Then, while flowing N ₂ gas at a flow rate of 10 L / min in the melting part, an alternating current of 5 kHz was passed through the first induction heating coil installed outside the melting part to inductively heat the melting part. The temperature in the melting part was increased at a rate of 20 ° C./min. When the temperature reached 1250 ° C., this temperature was maintained for 10 minutes to melt the raw material formulation in the melting part. During this heating, N ₂ gas was introduced at a flow rate of ₂ L / min from the lower end opening of the nozzle portion to cool the inside of the nozzle portion.

Next, the introduction of N ₂ gas into the nozzle part is stopped, and an AC current of 8 kHz is supplied to the second induction heating coil installed outside the nozzle part while continuing to energize the first induction heating coil. did. In this way, the nozzle part was induction-heated to melt the plug made of the above-mentioned melted and solidified material mixture, and the nozzle part was closed. And the molten material which flowed down through the nozzle part was dripped at the stainless steel double roller (the outer diameter of 10 cm, the rotation speed of 200 rpm) installed under the nozzle part, and it cooled rapidly, and the solidified material was obtained. The cooling rate was about 1 × 10 ⁴ ° C./second.

Next, in the same manner as in Example 1, the pulverization step (iv) and the heating step (v) were sequentially performed to precipitate lithium iron phosphate particles.

When the mineral phase of the obtained lithium iron phosphate particles was measured, it was confirmed to be orthorhombic olivine-type LiFePO ₄ . Moreover, it was 32 m < ² > / g when the specific surface area was measured. Furthermore, when the average particle diameter of the lithium iron phosphate particles was measured, the median diameter in terms of volume was 0.30 μm.

<Comparative Example 1>
A raw material composition having the same composition as that of Example 1 was filled in a platinum alloy crucible containing 20% by mass of rhodium (with an internal volume of 100 mL), and then the crucible was equipped with a heating element made of molybdenum silicide. It was put in a furnace (manufactured by Motoyama, apparatus name: NH-3035). While flowing N ₂ gas at a rate of ₂ L / min in the electric furnace, the temperature was increased at a rate of 300 ° C./hour, held at 1250 ° C. for 0.5 hours, and heated to obtain a melt. The melt was cooled to room temperature at 1 × 10 ⁵ ° C./second by passing through a stainless steel twin roller having a diameter of about 15 cm rotating at 400 revolutions per minute to obtain a flaky solidified product.

Next, the Pt content and Rh content in the obtained solidified product were quantified as follows. That is, the solidified product was decomposed with HF-HClO ₄ and then redissolved with HCl, and the Pt content and Rh content in the solution were measured by ICP emission spectroscopy. As a result, the Pt content in the solidified product was 9.6 μg / g, and the Rh content was 23 μg / g.
For the solidified product obtained in Example 1, the Pt content and Rh content were measured in the same manner as described above, and both were 0.1 μg / g or less.

<Comparative example 2>
A raw material formulation having the same composition as in Example 1 was filled in an alumina sintered crucible (made by Nikkato, trade name: SSA-S) with an outer diameter of 46 mm and a height of 53 mm. Next, the crucible was placed in an electric furnace (manufactured by Motoyama, apparatus name: NH-3035) equipped with a heating element made of molybdenum silicide. While flowing N ₂ gas at a rate of ₂ L / min in the electric furnace, the temperature was raised at a rate of 300 ° C./hour, held at 1450 ° C. for 0.5 hours, and heated to obtain a melt. The melt was cooled to room temperature at 5 ° C./min without rapid cooling. When the crucible after the heating and cooling treatment was visually observed, a crack was generated on the surface of the crucible. Moreover, it was 900 micrometers when a part of crucible was cut | disconnected and the amount of erosion was measured.

ADVANTAGE OF THE INVENTION According to this invention, the positive electrode material for secondary batteries excellent in purity can be manufactured efficiently at low cost.
It should be noted that the entire content of the specification, claims, drawings and abstract of Japanese Patent Application No. 2011-207026 filed on September 22, 2011 is cited here as the disclosure of the specification of the present invention. Incorporated.

DESCRIPTION OF SYMBOLS 1 ... Melting apparatus, 2 ... Melting container, 2a ... Melting part, 2b ... Melt outlet pipe, 3 ... Induction heating coil, 3a ... 1st induction heating coil, 3b ... 2nd induction heating coil, 4 ... Jacket, DESCRIPTION OF SYMBOLS 5 ... Raw material preparation, 6 ... Raw material supply pipe, 7 ... Gas introduction pipe, 8 ... Gas discharge pipe, 9 ... Cooling solidification apparatus, 10 ... Solidified material. 11: A plug made of a melt-solidified material mixture.

Claims (14)

1. A method for producing a positive electrode material for a secondary battery comprising a compound having an olivine type, pyroxene type, or NASICON type crystal structure,
   Raw material preparation step of preparing raw material preparation by preparing raw materials,
   A melting step of melting the raw material formulation by inductively heating at least the inner periphery of the container in a container having at least an inner periphery formed of a conductive refractory material;
   The manufacturing method of the positive electrode material for secondary batteries characterized by including.
2. A melt outlet part having a smaller diameter than the container is connected to the bottom of the container, and the melt outlet part is heated independently of the container, whereby the melt in the container is removed from the melt outlet part. The manufacturing method of the positive electrode material for secondary batteries of Claim 1 made to derive.
3. The method for producing a positive electrode material for a secondary battery according to claim 2, wherein the melt lead-out part is formed of a conductive refractory material, and the melt lead-out part is heated by induction heating.
4. The method for producing a positive electrode material for a secondary battery according to any one of claims 1 to 3, wherein the conductive refractory material is carbon or conductive non-oxide ceramics.
5. 5. The positive electrode material for a secondary battery according to claim 4, wherein the conductive non-oxide ceramic is a ceramic mainly composed of at least one selected from the group consisting of silicon carbide, zirconium boride, and titanium boride. Production method.
6. The method for producing a positive electrode material for a secondary battery according to any one of claims 1 to 5, wherein the melting step is performed in an inert atmosphere or a reducing atmosphere.
7. The method for producing a positive electrode material for a secondary battery according to any one of claims 1 to 6, wherein in the melting step, the raw material preparation is heated to 1100 ° C to 1800 ° C to melt.
8. The method for producing a positive electrode material for a secondary battery according to any one of claims 1 to 7, further comprising a cooling step of cooling the melt obtained in the melting step to obtain a solidified product.
9. The method for producing a positive electrode material for a secondary battery according to claim 8, wherein in the cooling step, the melt is cooled at a cooling rate of 1 × 10 ³ ° C./second or more.
10. The method for producing a positive electrode material for a secondary battery according to claim 8 or 9, further comprising a pulverization step of pulverizing the solidified product obtained in the cooling step to obtain a pulverized product.
11. The method for producing a positive electrode material for a secondary battery according to claim 10, wherein in the pulverizing step, at least one selected from the group consisting of an organic compound and a carbon-based conductive material is added to the solidified product and pulverized.
12. The manufacturing method of the positive electrode material for secondary batteries of Claim 10 or 11 which has a heating process which heats the ground material obtained at the said grinding | pulverization process.
13. The method for producing a positive electrode material for a secondary battery according to any one of claims 1 to 12, wherein the positive electrode material for a secondary battery contains a phosphoric acid compound represented by the following formula (1).
    AM _1-a X ¹ _a P _1-b Z ¹ _b O _{4 + c} (1)
    (In the formula, A represents at least one atom selected from the group consisting of Li, Na, and K, M represents at least one atom selected from the group consisting of Fe, Mn, Co, and Ni; X ¹ represents at least one atom selected from the group consisting of Zr, Ti, Nb, Ta, Mo and W, and Z ¹ represents at least one atom selected from the group consisting of Si, B, Al and V A is 0 ≦ a ≦ 0.2, b is 0 ≦ b ≦ 0.2, c is the numerical value of a and b, and the valence of M, the valence of X ¹ and Z ¹ It depends on the valence of and satisfies the electrical neutrality.)
14. The method for producing a positive electrode material for a secondary battery according to any one of claims 1 to 12, wherein the positive electrode material for a secondary battery contains a silicate compound represented by the following formula (2).
    A ₂ M _1-d X ² _d Si _1-e Z ² _e O _{4 + f} (2)
    (In the formula, A represents at least one atom selected from the group consisting of Li, Na, and K, M represents at least one atom selected from the group consisting of Fe, Mn, Co, and Ni; X ² represents at least one atom selected from the group consisting of Zr, Ti, Nb, Ta, Mo and W, and Z ² represents at least one atom selected from the group consisting of P, B, Al and V D is 0 ≦ d ≦ 0.2, e is 0 ≦ e ≦ 0.2, f is the numerical value of d and e, and the valence of M, the valence of X ² and Z ² It depends on the valence of and satisfies the electrical neutrality.)

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