WO2013042780A1 - 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. 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 arc-melted inside a container formed using a fire-resistant material, in a non-volatile atmosphere or a reducing atmosphere, and a melted product is obtained.

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 secondary battery positive electrode material 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. A raw material preparation step of preparing a raw material preparation, and a melting step of arc melting the raw material preparation in a container formed of a refractory material in an inert atmosphere or a reducing atmosphere to obtain a melt. It is characterized by including.

In the method for producing a secondary battery positive electrode material of the present invention, the inert atmosphere is at least one selected from the group consisting of nitrogen (N ₂ ), helium (He), argon (Ar), and neon (Ne). It is preferable that the gas conditions contain 99% by volume or more of the above inert gas. The reducing atmosphere is formed by adding a reducing gas to at least one inert gas selected from nitrogen (N ₂ ), helium (He), argon (Ar), and neon (Ne). The gas condition is substantially free of oxygen.

It is preferable that the manufacturing method of the positive electrode material for secondary batteries of this invention has a cooling process which cools the said molten material obtained at the said melting process, and obtains a solidified material. 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, “arc melting” means heating and melting by the energy of arc discharge. Heating by arc discharge is also called arc heating.

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 mixture is melted by arc heating, compared with the conventional method using a heating furnace such as an electric furnace, rapid heating is possible with less energy loss and high thermal efficiency, and the melt can be shortened. There are advantages such as being able to be obtained in time and having high mass productivity.

It is sectional drawing which shows the structure of an 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>
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 a compound having an olivine type, pyroxene type, or NASICON type crystal structure, wherein raw materials are prepared. Including a raw material preparation step of preparing a raw material preparation, and a melting step of arc melting the raw material preparation in a container formed of a refractory material in an inert atmosphere or a reducing atmosphere to obtain a melt. Features. 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 is a number depending on the values of d and e, and the valence of M, the valence of X ^{2 and} the valence of Z ^2. Is the value minus.

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 A raw material preparation step (i) for preparing a raw material preparation, and a melting step for obtaining a melt by arc melting the raw material preparation in an inert atmosphere or a reducing atmosphere in a container formed of a refractory material (Ii). 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 Preference is given to at least one selected from the group consisting of acid salts, A or M silicates, A or M borates, A or M aluminates, 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 ₂ , 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 preparation obtained in the raw material preparation step (i) is accommodated in a container formed of a refractory material and generates an arc (hereinafter referred to as an arc electrode or simply an electrode). Installed in an arc melting apparatus (also referred to as an arc melting furnace). Then, in an inert atmosphere or a reducing atmosphere, the raw material composition is arc-heated and melted by arc discharge from the electrodes.

In the present specification, the “refractory material” refers to a material that is excellent in fire resistance and whose composition and physical characteristics do not change at the melting temperature of the raw material formulation. The refractory temperature of the refractory material is preferably 1,000 ° C. or higher. When the fireproof temperature is less than 1,000 ° C., the melt resistance of the container may be significantly lowered.
However, if the refractory temperature of the refractory material is excessively high, the usable constituent materials may be excessively limited. Therefore, the refractory temperature is preferably in the range of 1,200 to 2,000 ° C., A range of 200 to 1,800 ° C. is more preferable. 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 refractory material forming the container include carbon, non-oxide ceramics, and electrocast refractories. In the present specification, “electrocast refractory” is an abbreviation for electromelted cast refractory, and is prepared according to a target component according to a target component and completely melted in an electric furnace. Refractories manufactured by casting into a mold having a predetermined shape are collectively referred to. Here, “refractory” is used in the same meaning as ceramics.

Carbon as the refractory material forming the container is preferable because graphite is inexpensive, easily available, and easy to process. Since such carbon may cause a reduction reaction with an oxide of heavy metal such as iron contained in the raw material preparation at high temperature, it is preferable to adjust the heating and melting temperature.

Non-oxide ceramics include silicon carbide (SiC), zirconium carbide (ZrC), titanium carbide (TiC), silicon nitride (Si ₃ N ₄ ), zirconium nitride (ZrN), titanium nitride (TiN), boron nitride (BN) ), Sialon (eg, Si _6-z Al _z O _z N _8-z , 0 <z ≦ 4.2), zirconium boride (ZrB ₂ ), and titanium boride (TiB ₂ ). There may be mentioned ceramics mainly composed of at least one kind. In the present specification, “mainly” means containing 50% by mass or more of the component.

Among these non-oxide ceramics, when the ceramic is mainly composed of at least one selected from the group consisting of silicon carbide, silicon nitride, sialon, zirconium boride, and titanium boride, it is an inert atmosphere or reduced. It is preferable because it can be used in an atmosphere. Further, ceramics containing 50 to 98% by mass of zirconium boride have a dense structure, and even when a raw material preparation containing a heavy metal element at a high rate is melted, these components are difficult to enter, and the contents It is difficult to cause problems such as leakage.
Furthermore, carbon and the non-oxide ceramic are preferable because a fired product obtained by molding and heating the raw material powder is easily available.

Electrocast refractories include alumina-silica electrocast refractories, alumina electrocast refractories, alumina-zirconia-silica electrocast refractories, and high zirconia electrocast refractories. Among these, alumina-zirconia-silica electrocast refractories, high zirconia electrocast refractories, or alumina electrocast refractories are preferably used from the viewpoint of easy availability and high corrosion resistance.

The alumina-zirconia-silica electrocast refractory is an electrocast refractory having a structure in which a matrix surrounds corundum, baderite, or eutectic thereof. The content of the matrix glass phase in the alumina-zirconia-silica electrocast refractory is preferably 20% by mass or less, and more preferably 16% by mass or less.

As the chemical composition, when the entire alumina-zirconia-silica electrocast refractory containing the matrix glass phase is 100% by mass in terms of oxide, Al is 45 to 55% by mass in terms of Al ₂ O ₃ , Zr Is preferably 35 to 45% by mass in terms of ZrO ₂ , Si is 10 to 16% by mass in terms of SiO ₂ , and Na is 1 to 2% by mass in terms of Na ₂ O.

Examples of the alumina-zirconia-silica electrocast refractories include ZB-1681 (trade name of AGC Ceramics), ZB-1711 (trade name of AGC Ceramics), SCIMOS CS-3 (trade name of Saint-Gobain tee M), SCIMOS CS-5 (Saint-Gobain tee product name).

A high zirconia electrocast refractory is an electrocast refractory having a zirconia (ZrO ₂ ) content of 90% by mass or more, and has, for example, a structure in which a small amount of matrix glass phase surrounds a bedrite crystal phase. Are preferably used. The high zirconia electrocast refractory preferably has a matrix glass phase content of 4 to 12% by mass, and more preferably 4 to 7% by mass.

As the chemical composition of the high zirconia electrocast refractory, when the entire high zirconia electrocast refractory including the matrix glass phase is 100% by mass in terms of oxide, Zr is 90 to 97 in terms of mass% in terms of ZrO _2. %, Si containing 3 to 5% in terms of SiO ₂ , Na containing 0.1 to 2% in terms of Na ₂ O, and Al containing 0.5 to 2.5% in terms of Al ₂ O ₃ are preferred. It contains more than 92 to 97% in terms of ZrO ₂ , Si to 3 to 4% in terms of SiO ₂ , Na to 0.2 to 1% in terms of Na ₂ O, and Al to 1 to 2% in terms of Al ₂ O ₃ preferable.
Further, B may be contained in an amount of 0.1 to 0.5% in terms of B ₂ O ₃ , and P may be contained in an amount of 0.1 to 0.5% in terms of P ₂ O ₃ .

Examples of the high zirconia electrocast refractories include ZB-X950 (AGC Ceramics company name) and SCIMOS Z (Saint Govin T.M company name).

Alumina electrocast refractories are electrocast refractories with a total content of α-alumina and β-alumina of 95% by mass or more, depending on the ratio of α-alumina and β-alumina contained in the electrocast refractories. , Α-alumina electrocast refractory, α, β-alumina electrocast refractory or β-alumina electrocast refractory.

Among these, α, β-alumina electrocast refractories are easy to obtain, have sufficient strength, and have a dense structure, so that they can be suitably used as containers for heating and melting.

In the alumina electrocast refractory, the content of the matrix glass phase is preferably 10% by mass or less, and preferably 2% by mass or less.

As the chemical composition of the alumina electrocast refractory, when the entire alumina electrocast refractory including the matrix glass phase is 100% by mass in terms of oxide, Al is 93 to 99 in terms of mass% in terms of Al ₂ O _3. 0.5%, Si containing 0.1 to 1.0% in terms of SiO ₂ , Na containing 0.2 to 6.5% in terms of Na ₂ O, Al being preferably 94.5 in terms of Al ₂ O ₃ More preferably, it contains ˜99%, Si contains 0.1 to 1.0% in terms of SiO ₂ , and Na contains 0.2 to 5% in terms of Na ₂ O.

Specific examples of alumina electrocast refractories include α-alumina electrocast refractories, MB-A (trade name of AGC Ceramics), SCIMOS A (trade name of Saint-Gobain T.M), α, β-alumina As electroformed refractories, MB-G (product name of AGC Ceramics), SCIMOS M (product name of Saint-Gobain T.M.), Jaguar M (product name of Societe Europian de Prodéy Leflectre), β-alumina Examples of electroformed refractories include MB-U (manufactured by AGC Ceramics), SCIMOS H (trade name of Saint-Gobain tee M), and Jaguar H (trade name of Societe Europian de Produy Leflectre).

Among these electrocast refractories, alumina-zirconia-silica electrocast refractories have a dense structure composed of a eutectic of α-alumina and badelite and matrix glass surrounding these crystals, Even when a raw material composition containing a heavy metal element at a high rate is melted, these components are difficult to enter, and it is difficult to cause problems such as leakage of contents, which is preferable. In particular, in the production of a phosphate compound having a relatively low melting temperature, it is preferable to arc-melt the raw material formulation in a container formed of a high zirconia electroformed refractory that has low contamination from the refractory.

A container formed of carbon, non-oxide ceramics or electrocast refractory is not easily eroded by the melt of the raw material mixture. In addition, as will be described later, melting of the raw material preparation by arc heating is performed in an inert atmosphere or a reducing atmosphere. However, the above-described carbon, non-oxide ceramics, or electrocast refractory is in an inert atmosphere or reduced. Therefore, it is suitable as a container material in the melting step (ii).

The size and shape of the container formed of such a refractory material are not particularly limited, and can be a small cylindrical crucible or a large melting tank. In particular, when the container is a large melting tank, the refractory material may be used at least in the inner peripheral portion that comes into contact with the melt. May be. Moreover, when using as a small cylindrical crucible, in order to prevent volatilization and evaporation of a raw material formulation or a molten material, it can melt | dissolve by attaching the lid | cover to the said container.

For the arc heating in the melting step (ii) of the present invention, either a direct arc heating method or an indirect arc heating method can be used. The direct arc heating method is a method in which the object to be heated is heated as an arc medium, and the indirect arc heating method is a method in which the heat of the arc is transmitted to the object to be heated by radiation, conduction, or convection. . In any heating method, it is preferable that the electrode has a structure capable of moving up and down.

In the melting step (ii) of the present invention, a graphite electrode, an iridium electrode, or the like can be used as the arc electrode. Use of a graphite electrode is preferred because it is easy to process and inexpensive. The number of electrodes may be one or more. When a plurality of electrodes are used, the heating of the raw material mixture can be made uniform, and the temperature distribution of the melt can be made uniform.

The power source used for arc heating may be a DC power source or an AC power source, or a single-phase power source or a three-phase power source. In particular, by using multiple arc electrodes and using a three-phase AC power supply, the arc is stabilized and an arc is generated not only between the electrode and the melt but also between the electrodes to increase heating efficiency. Can be improved.

In the present invention, melting of the raw material mixture in the container by arc heating is performed in an inert atmosphere or a reducing atmosphere. Here, the inert atmosphere is a gas containing 99% by volume or more of at least one inert gas selected from the group consisting of nitrogen (N ₂ ), helium (He), argon (Ar), and neon (Ne). Say conditions. 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 (hereinafter referred to as reducing gas) include hydrogen (H ₂ ), carbon monoxide (CO), ammonia (NH ₃ ), and the like. 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, more preferably 0.1% by volume or less in the total gas.

In the melting step (ii) of the present invention, in order to make the inside of the container an inert atmosphere or a reducing atmosphere, the inert gas or a mixed gas obtained by adding the reducing gas to the inert gas is placed in the container. To introduce. The inert gas introduced in this manner is converted into plasma by arc discharge from the electrode and a plasma arc is generated, so that a high temperature can be obtained efficiently and stably. Note that the arc melting furnace may have a sealed structure in which gas does not leak so that the introduced gas is stably converted into plasma.

Hereinafter, an arc melting apparatus used in the melting step (ii) of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view schematically showing an arc melting apparatus used in an embodiment of the present invention. The arc melting apparatus 1 includes a melting container 2 made of the above-described refractory material, and a jacket (exterior housing) 3 with a lid for storing the melting container 2. The jacket 3 is preferably attached with a cooling mechanism (not shown) such as a water-cooled tube.

The melting vessel 2 is composed of a furnace wall portion 2 a and a furnace bottom portion 2 b, and a graphite electrode 4 that is an arc electrode is installed in the melting vessel 2. In the upper part of the jacket 3, a raw material supply pipe 6 for supplying the raw material mixture 5 into the melting container 2 and an inert gas such as nitrogen (N ₂ ) and argon (Ar) are introduced into the jacket 3. The gas introduction pipe 7 and the gas exhaust pipe 8 for exhausting the gas in the jacket 3 to the outside are respectively connected. Further, a melt outlet pipe 9 is provided through the furnace wall 2 a and the jacket 3 of the melting container 2. Further, the arc melting apparatus 1 has a structure that can be tilted, and is configured such that the melt obtained in the melting vessel 2 can be directly led out from the melt outlet pipe 9 to the cooling and solidifying apparatus 10.

In addition, in FIG. 1, the code | symbol 12 shows the solidified material obtained by the cooling solidification apparatus 10, and the code | symbol 11 shows the solidified material collection | recovery apparatus which collect | recovers the solidified material 12. FIG. As the cooling and solidifying device 10, 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 order to perform the melting step (ii) in the present invention using such an arc melting apparatus 1, first, the raw material mixture 5 is supplied into the melting container 2 through the raw material supply pipe 6. Then, a voltage is applied to the graphite electrode 4 while an inert gas such as nitrogen (N ₂ ) or argon (Ar) is blown into the melting container 2 from the gas introduction tube 7 to cause arc discharge. And the raw material preparation 5 in the melting container 2 is rapidly heated and melted by the plasma arc discharge of the inert gas.

The number of graphite electrodes 4 that are arc electrodes is one in FIG. The graphite electrode 4 is installed in the center part of the melting container 2, for example. The graphite electrode 4 may be installed so as to move up and down in accordance with the change in the molten metal surface position. Moreover, when installing the several graphite electrode 4, you may install so that an electrode space | interval may be changed. That is, in the initial stage of melting, the graphite electrode 4 is brought into contact with the raw material preparation 5 and melted by contact arc discharge. After a melt is generated to some extent, the graphite electrode 4 is gradually raised and the electrode interval is widened. Then, it is completely melted by plasma arc discharge of the blown inert gas. In this way, a melt with few impurities can be obtained.

Such arc discharge is performed at an output of 100 kVA to 200 kVA, for example. The raw material mixture is rapidly heated and melted to a high temperature of 1,100 ° C. to 1,800 ° C. by arc discharge accompanied by plasma formation of gas between the graphite electrode 4 and the raw material composition 5 or between the graphite electrodes 4. The Then, by rapidly raising the temperature in this way, the raw material mixture 5 having a predetermined composition corresponding to the olivine type compound, pyroxene type compound, or NASICON type compound is melted almost simultaneously even in the raw material mixture having different melting points. Therefore, a melt having a uniform composition can be obtained. When the heating temperature is 1,100 ° C. or higher, melting becomes easy, and when it is 1,800 ° C. or lower, the raw material is difficult to volatilize. The heating temperature is more preferably 1,200 ° C. to 1,600 ° C. Here, the heating temperature refers to the temperature of the melt itself and can be measured with a thermocouple or a pyrometer. Melting means that each raw material melts and becomes transparent with the naked eye.

The heating time can be appropriately set in consideration of the type of raw material, the melting scale, the homogeneity of the melt, etc., but is preferably 0.5 to 4 hours, particularly preferably 1 to 2 hours. When the heating time is 0.5 hours or more, the uniformity of the melt is sufficient, and when it is 4 hours or less, the raw material is difficult to volatilize.

As described above, arc melting of the raw material mixture 5 in the present invention is performed while blowing an inert gas such as nitrogen (N ₂ ) or argon (Ar) from the gas introduction pipe 7 into the melting vessel 2, and is inert. Performed under atmosphere.

Thus, the melt obtained by melting the raw material mixture 5 in the melting vessel 2 is led out from the melt outlet tube 9 by tilting the arc melting device 1. Then, it is supplied to a cooling and solidifying device 10 such as a single roller or double roller, which will be described later, and cooled to recover the solidified product 12.

Thus, in the melting step (ii) of the present invention, since the raw material mixture 5 accommodated in the melting vessel 2 is heated and melted by plasma arc discharge, the melt can be obtained in a short time. Suitable for mass production. In addition, compared with a conventional method in which the melting container is housed in a heating furnace such as an electric furnace and heated, the energy loss is small and the thermal efficiency is high. Furthermore, since rapid heating is possible and a high temperature can be obtained in a short time, it is possible to obtain a melt having a uniform composition by melting the raw material mixture in a short time. Furthermore, since it is possible to obtain a higher temperature by heating by arc discharge, various raw material formulations can be easily melted, and the composition range of the resulting melt is widened.

[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 from the temperature of the melt to 50 ° C. is preferably more than 1 × 10 ³ ℃ / sec, 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 into 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 obtained solidified product tends to be an amorphous material, 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 performed as it is on the melt flowed out from the container formed of the refractory material, and the melt melted in the container May be performed on the remelted material once cooled at a normal rate. Alternatively, the melt melted in the container may be continuously transferred to another container, heated to re-homogenize the components, and cooled.

The solidified product is preferably flaky, massive 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 lump, the average diameter is preferably 50 μm or less, and more preferably 30 μm or less. 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. In addition, 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.
In addition, for example, when a positive electrode material is obtained by a solid phase reaction, pulverization is performed after firing. In that 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 a 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 pulverized. After that, it is preferable to add the carbon source. 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 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 this 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.). If this 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. When 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 above-described melting, cooling, pulverization, and heating steps. 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.

Further, the average particle diameter of the 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 formulation of an olivine type compound, pyroxene type compound, or NASICON type compound is heated and melted by arc discharge in a container formed of a refractory material and in an inert atmosphere or a reducing atmosphere. Therefore, compared with the conventional method of heating and melting in a heating furnace such as an electric furnace, the thermal efficiency is high, rapid heating is possible, and mass productivity is high. A production amount of 10 kg or more per batch can be realized in the melting step (ii).
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 ) were weighed and mixed dry to obtain a raw material formulation.

(Melting step (ii))
The obtained raw material mixture is filled in a crucible made of a high zirconia electroformed refractory (AGC Ceramics, product name ZB-X950) having an inner diameter of 40 mm and a depth of 40 mm mounted on a stainless steel water cooling device. Then, using an arc generator (manufactured by Pressure Motion), a plasma arc was generated while flowing Ar gas at 1 L / min using carbon as an electrode. Then, the raw material formulation in the crucible was heated to about 1250 ° C. in about 10 minutes by arc discharge, and then held at 1250 ° C. for 3 minutes to be completely melted.

(Cooling step (iii))
After stopping the arc discharge, the melt obtained in the melting step (ii) was poured into a stainless steel double roller (outer diameter 10 cm, rotation speed 200 rpm) and rapidly cooled to obtain a solidified product. The cooling rate was about 1 × 10 ⁴ ° C./second.

(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. When the average particle diameter of the obtained pulverized product was measured using a laser diffraction / scattering particle size analyzer (manufactured by Horiba, Ltd., apparatus name: LA-950), the volume-based median diameter was 0.40 μm. .

(Heating step (v))
The finely pulverized product obtained in the pulverization step (iv) was used for 8 hours at 700 ° C. in an Ar gas atmosphere containing 3% by volume of H ₂ gas using an electric furnace (manufactured by Motoyama, model name: SKM-3035). Heated and then 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 23 m < ² > / g when the specific surface area was measured using the specific surface area measuring apparatus (The Shimadzu Corp. make, apparatus name: ASAP2020). Further, when the average particle diameter of the lithium iron phosphate particles was measured using a laser diffraction / scattering particle size analyzer (manufactured by Horiba, Ltd., apparatus name: LA-950), the volume-converted median diameter was 0.42 μm. there were.
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 0.6 mm.

<Example 2>
After melting the raw material formulation having the same composition as that of Example 1 in the same process as the melting process (ii) of Example 1, the obtained melt was directly put into tap water (temperature 15 ° C.) in a stainless steel container. It was charged and cooled to obtain a solidified product. The cooling rate was estimated at about 200 ° C./second.

Next, the solidified material was collected and dried, and then the pulverization step (iv) and (v) heating step were performed in the same manner as in Example 1 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 25 m < ² > / g when the specific surface area was measured. Furthermore, when the average particle diameter of the particles was measured, the median diameter in terms of volume was 0.36 μm.

<Example 3>
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, mixed and pulverized in a dry process to obtain a raw material formulation.

Subsequently, the obtained raw material formulation is melted in the same step as the melting step (ii) of Example 1, and then the cooling step (iii), the pulverizing step (iv) and the heating step in the same manner as in Example 1. (V) was performed in order to deposit 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 16 m < ² > / g when the specific surface area was measured. Furthermore, when the average particle diameter of the crystal particles was measured, the median diameter in terms of volume was 0.67 μm.

<Comparative example>
A raw material formulation having the same composition as in Example 3 was filled into an alumina sintered crucible (made by Nikkato, trade name: SSA-S) with a lid and 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 circulating N ₂ gas at a rate of ₂ L / min in the electric furnace, the temperature was raised at a rate of 5 ° C./min, 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. When the crucible after the heating and cooling treatment was visually observed, cracks were generated on the surface of the crucible, and a solid product with high purity was not obtained.

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 contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2011-2007028 filed on September 22, 2011 are cited herein as disclosure of the specification of the present invention. Incorporated.

DESCRIPTION OF SYMBOLS 1 ... Arc melting apparatus, 2 ... Melting container, 2a ... Furnace wall part, 2b ... Furnace bottom part, 3 ... Jacket, 4 ... Graphite electrode, 5 ... Raw material preparation, 6 ... Raw material supply pipe, 7 ... Gas introduction pipe, 8 DESCRIPTION OF SYMBOLS ... Gas discharge pipe, 9 ... Melt discharge pipe | tube, 10 ... Cooling solidification apparatus, 11 ... Solidified substance recovery apparatus, 12 ... Solidified substance.

Claims (10)

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 arc melting the raw material formulation in a container formed of a refractory material under an inert atmosphere or a reducing atmosphere to obtain a melt;
   The manufacturing method of the positive electrode material for secondary batteries characterized by including.
2. The inert atmosphere is a gas condition containing 99% by volume or more of at least one inert gas selected from the group consisting of nitrogen (N ₂ ), helium (He), argon (Ar), and neon (Ne). The manufacturing method of the positive electrode material for secondary batteries of Claim 1.
3. The reducing atmosphere is obtained by adding a reducing gas to at least one inert gas selected from the group consisting of nitrogen (N ₂ ), helium (He), argon (Ar), and neon (Ne). The method for producing a positive electrode material for a secondary battery according to claim 1, wherein the gas condition is substantially free of oxygen.
4. The method for producing a positive electrode material for a secondary battery according to any one of claims 1 to 3, further comprising a cooling step of cooling the melt obtained in the melting step to obtain a solidified product.
5. 5. The method for producing a positive electrode material for a secondary battery according to claim 4, wherein, in the cooling step, the melt is cooled at a cooling rate of 1 × 10 ³ ° C./second or more.
6. The method for producing a positive electrode material for a secondary battery according to claim 4 or 5, further comprising a pulverization step of pulverizing the solidified product obtained in the cooling step to obtain a pulverized product.
7. The method for producing a positive electrode material for a secondary battery according to claim 6, wherein, in the pulverization 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.
8. The manufacturing method of the positive electrode material for secondary batteries of Claim 6 or 7 which has a heating process which heats the ground material obtained at the said grinding | pulverization process.
9. The method for producing a positive electrode material for a secondary battery according to any one of claims 1 to 8, 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.)
10. The method for producing a positive electrode material for a secondary battery according to any one of claims 1 to 8, 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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