WO2013042777A1

WO2013042777A1 - Production method for positive electrode material for secondary battery

Info

Publication number: WO2013042777A1
Application number: PCT/JP2012/074269
Authority: WO
Inventors: 義久別府
Original assignee: 旭硝子株式会社
Priority date: 2011-09-22
Filing date: 2012-09-21
Publication date: 2013-03-28
Also published as: JPWO2013042777A1

Abstract

Provided is a method for efficiently producing, at low cost, a positive electrode material for a secondary battery having little mixing in of a component derived from a container used for heating and melting a raw material mixture, and having excellent purity. The production method for a secondary battery positive electrode material is a method for producing a secondary battery positive electrode material including a compound having an olivine-, augite-, or nasicon-type crystal structure, and includes: a raw material mixing step in which raw materials are mixed and a raw material mixture is prepared; and a melting step in which the raw material mixture is melted inside a container formed using an electrocast refractory product, 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 a olivine-type 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 a compound having an olivine-type, pyroxene-type, or NASICON-type crystal structure as described above, for example, methods such as a solid phase method and a liquid phase method have been proposed and implemented. With the spread, further cost reduction of the electrode material is required.
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. In Patent Document 3, materials such as Li ₂ CO ₃ , NH ₄ H ₂ PO ₄ , and Fe (II) C ₂ O ₄ are put in an alumina crucible with a lid, melted at 1200 ° C., and then the melt is put on an iron plate. A method for obtaining a precursor glass having a basic composition of LiFePO ₄ by pouring out and pressing and quenching is disclosed. 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 placed in a crucible with a nozzle made of rhodium / platinum alloy at 1300 ° C. A method of obtaining olivine-type lithium iron phosphate particles by heating after melting and then rapidly cooling the melt and then heating after pulverization 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 is a fear. In the method of Patent Document 3, since the corrosion resistance of alumina constituting the crucible is not necessarily high, the crucible is easily worn by erosion of Fe or the like during heating and melting, and the replacement frequency increases. Further, the alumina component is likely to be mixed into the melt from the crucible, and there is a possibility that the purity may be lowered. Furthermore, since alumina has a relatively high coefficient of thermal expansion, the crucible may be damaged due to a rapid temperature change. In Patent Document 4, at high temperatures, the crucible is easily worn out by the formation of an alloy between platinum and rhodium contained in the crucible and the iron component in the melt, and platinum and rhodium dissolved from the crucible are contained in the melt. It may be easily mixed into the product, resulting in a decrease in product purity and an increase in production cost.

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

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. And a raw material preparation step of preparing a raw material preparation, and a melting step of melting the raw material preparation in a container formed of an electroformed refractory to obtain a melt.

The electrocast refractory is preferably at least one selected from the group consisting of an alumina-zirconia-silica electrocast refractory, a high zirconia electrocast refractory, and an alumina electrocast refractory. Further, the melting step is preferably performed at 900 ° C to 1700 ° C.

Furthermore, it is preferable that the method for producing a positive electrode material for a secondary battery of the present invention includes a cooling step of cooling the melt obtained in the melting step to obtain a solidified product. Furthermore, it is preferable to have a heating step of heating the solidified product obtained in the cooling 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 type 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 ^{It is} a number that depends on the valence of ¹ and satisfies 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 type 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 ^{It is} a number that depends on the valence of ² and satisfies electrical neutrality.)

According to the present invention, it is possible to efficiently produce a positive electrode material for a secondary battery that is less contaminated with components derived from a container used for heating and melting the raw material mixture and has excellent purity.

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".
In the present specification, 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 above formula (1) is also referred to as “phosphoric acid compound (1)”, and the silicic acid compound having the composition represented by the above 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. A raw material preparation step of preparing a raw material preparation; and a melting step of melting the raw material preparation in a container formed of an electroformed refractory to obtain a melt. 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 at least selected from Zr, Ti, Nb, Ta, Mo, and W together with the atoms A and M, in addition to the compounds represented by the general formula described above. It may contain one kind of 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, at least one atom selected from the group consisting of 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 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 , Number that satisfies electrical 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 below, 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 (1). ) Is preferable.

The value of a is more preferably 0.001 ≦ a ≦ 0.1, and particularly preferably 0.001 ≦ a ≦ 0.05. The value of b is more preferably 0.001 ≦ b ≦ 0.1, and particularly preferably 0.001 ≦ b ≦ 0.05. 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-type compounds represented by the above general formula, the silicate compound (2) represented by the following formula (2) is preferred as the silicate compound.
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.

The value of d is more preferably 0.001 ≦ d ≦ 0.1, and particularly preferably 0.001 ≦ d ≦ 0.05. The value of 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 in a container formed of an electroformed refractory to obtain a melt. 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 ) and M alkoxides (M (OCH ₃ ) ₂ , M (OC ₂ H ₅ ) ₂ etc.) At least one is preferred.
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 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 is preferred.
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 the raw material formulations is a carbonate or hydrogen carbonate in which the compound containing atom A is A, an oxide of M in compound containing atom M, an ammonium hydrogen phosphate or a phosphate in which compound P is contained In this case, it is a combination when the compound containing Si 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)]
Next, the raw material preparation obtained in the raw material preparation step (i) is placed in a container formed of an electroformed refractory, and this is heated to perform a melting step (ii) for melting the raw material preparation in the container.

In the present specification, the electroformed refractory is an abbreviation for electrofused cast refractory, and a selected raw material is prepared in accordance with a target component and completely melted in an electric furnace. It is a generic term for refractories produced by casting in a mold and solidifying by slow cooling. In this specification, the refractory is used in the same meaning as ceramics.

Examples of the 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.

An alumina-zirconia-silica electrocast refractory is an electrocast refractory having a structure in which matrix glass surrounds corundum, baderite, or eutectic thereof.

In the alumina-zirconia-silica electrocast refractory, the content of the matrix glass phase 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 a structure in which a small amount of a matrix glass phase surrounds a bedrite crystal phase, for example. Preferably used.

In the high zirconia electrocast refractory, the content of the matrix glass phase is preferably 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 refractory include ZB-X950 (AGC Ceramics company trade name) and SCIMOS Z (Saint Govin T. M trade 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 (trade name of AGC Ceramics), SCIMOS M (trade name of Saint-Gobain tee M), Jaguar M (trade name of Societe Europian de Prodéy Leflectaire), β-alumina Examples of cast refractories include MB-U (trade name of 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 α-alumina, baderite, or eutectic thereof, and matrix glass surrounding these crystals. Even when a raw material composition containing a heavy metal element at a high rate is melted, it is preferable because these components are difficult to enter and problems such as leakage of contents are unlikely to occur.

Also, in the production of a phosphoric acid compound having a relatively low melting temperature, it is preferable to melt the raw material formulation in a container formed of a high zirconia electroformed refractory with little contamination from the refractory.

The fireproof temperature of the electroformed refractory used for the container is preferably 1000 ° C. or higher. When the fireproof temperature of the electroformed refractory is less than 1000 ° C., the melt resistance of the container used for melting may be significantly reduced. However, when the fireproof temperature of the electroformed refractory becomes excessively high, usable constituent materials may be excessively limited. Therefore, the refractory temperature of the electroformed refractory is preferably in the range of 1,000 to 2,000 ° C., more preferably in the range of 1,200 to 1,800 ° C. In addition, the refractory temperature of the electrocast refractory means a temperature at which no remarkable change in appearance is observed when the electrocast refractory is heated for 24 hours.

The surface roughness (Rmax) of the electroformed refractory is preferably 0.035 to 5 mm. If the surface roughness (Rmax) of the electroformed refractory exceeds 5 mm, the container may be easily eroded by heavy metal elements such as Fe and Mn in the melt. The surface roughness (Rmax) of the electroformed refractory is more preferably 0.04 to 3 mm, and more preferably 0.05 to 1 mm.
The surface roughness (Rmax) of the electrocast refractory can be measured using a contact-type surface roughness meter.

The porosity of the electroformed refractory is preferably 0.1 to 5%. An electrocast refractory having a porosity of less than 0.1% is actually difficult to manufacture. On the other hand, if the porosity of the electroformed refractory exceeds 5%, heavy metal elements such as Fe and Mn contained in the melt are likely to enter the refractory, and sufficient corrosion resistance cannot be obtained. There is a possibility that leakage of the molten material is likely to occur.
In addition, the porosity of this electrocast refractory can be measured using a specific gravity method.

The container formed of the electroformed refractory is not particularly limited in size and shape, and can be used as a small cylindrical crucible or a large melting tank. In the case of a large melting tank, the electroformed refractory may be used at least in a contact portion with the melt, and a non-contact portion with the melt, such as the upper structure of the melt tank, may be composed of other materials. . 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 is preferable to heat-melt by attaching a lid to the container.

Although it does not specifically limit as a heat source of a heating furnace, Electricity, oil, gas, etc., or these combinations can be used. It is preferable to burn with a burner using oil or gas. The burner is preferably placed at the top of the melt tank.

The raw material mixture is preferably melted at a heating temperature of 900 to 1700 ° C. This is because a melt having a uniform composition can be obtained from a raw material preparation of a positive electrode material for a secondary battery containing an olivine type compound, pyroxene type compound, or NASICON type compound. 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. When the heating temperature is 900 ° C. or higher, melting is facilitated, and when it is 1700 ° C. or lower, the raw material is hardly volatilized.
Since melting can be performed more easily, melting is more preferably performed at a heating temperature of 1000 ° C. or higher. Moreover, since wear of the electroformed refractory due to heating is suppressed, melting is more preferably performed at a heating temperature of 1500 ° C. or less.

The heating time can be appropriately set in consideration of the melting method, the melting scale, the uniformity of the molten metal, etc., but is preferably 0.2 to 24 hours, particularly preferably 0.5 to 2 hours. When the heating time is 0.5 hours or more, the uniformity of the melt is sufficient, and when it is 2 hours or less, the raw material 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. The raw material may be charged once or a plurality of times.

The melting step (ii) is preferably performed in the air, in an inert atmosphere, or in a reducing atmosphere. In particular, in the olivine type compound, it is preferable that the element M in the melt of the raw material preparation is in a low oxidation number state (for example, Fe ^{2+ in} the case of M = Fe). It is preferable to carry out in an atmosphere, an inert atmosphere, or a reducing atmosphere. On the other hand, the pyroxene type or NASICON type compound containing the atom V does not require any particular control.
Conditions suitable for the heating method such as the type of container and heating furnace and heat source can be selected as the melting conditions. The pressure may be carried out under any conditions of normal pressure, pressurization, and reduced pressure (0.9 × 10 ⁵ Pa or less). Furthermore, you may charge the container which put the reducing agent (for example, graphite) in the heating furnace. It is preferred that the melt is more reductive, but even if it is more oxidative, it can be reduced (for example changing from M ³⁺ to M ²⁺ ) in the subsequent heating step (v).

Here, the inert atmosphere is a gas condition including 99% by volume or more of at least one inert gas selected from the group consisting of noble gases such as nitrogen (N ₂ ), helium (He), and argon (Ar). Say something.
The reducing atmosphere means that the above-described inert gas is a gas condition that contains a gas having a reducing property and does not substantially contain oxygen. Examples of the reducing gas include hydrogen (H ₂ ), carbon monoxide (CO), and ammonia (NH ₃ ). The amount of the reducing gas in 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.

The melting step (ii) may be performed batchwise or continuously.

Although the reduction treatment of the element M can be performed in this step, the reduction treatment can be performed by performing the heat treatment in the subsequent step. It does not have to be performed in the process.

[Cooling step (iii)]
After the melting step (ii), it is preferable to perform a cooling step (iii) in which the obtained melt 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 faster the cooling rate, the easier it is to obtain an amorphous material. However, in consideration of production equipment and mass productivity, it is preferably 1 × 10 ¹⁰ ° C./second or less, and from the point of practical use, it is 1 × 10 ⁸ ° C./second or less. Particularly preferred.

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 metal plate, a method of obtaining a lump solidified product by spraying the melt into air or water in small particles It is preferable to adopt. 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 of the container formed of the electroformed refractory, and the melt melted in the container The product 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.

The solidified product obtained in the cooling step (iii) usually has an advantage of being easily pulverized because it contains a lot of amorphous material or consists of an amorphous material. 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 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 the secondary battery can be increased. Further, by adding an organic compound 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.
The organic compound and the carbon-based conductive material are adjusted so that the total amount thereof falls within the above range when used in combination. 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 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 (v). It is preferable to carry out.
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 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.
In particular, 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.

The average particle diameter of the crystal particles of the positive electrode material for a secondary battery 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, the raw material mixture of an olivine type compound, pyroxene type compound, or NASICON type compound containing heavy metal elements such as iron and manganese is heated and melted in a container made of electroformed refractory. Therefore, erosion due to heavy metal elements such as Fe and Mn contained in the melt can be suppressed, and wear of containers used for heat melting can be prevented, reducing the frequency of maintenance and reducing the manufacturing cost of the positive electrode material for secondary batteries. can do. Moreover, 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.
In the present invention, when a large melting tank is used in the melting step (ii), it is possible to produce 1 kg / batch or more in the batch type and 1 t / day or more in the continuous type.

<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 description.

<Example 1>
(Raw material preparation step (i))
Composition _Li 2 O melt, FeO, and _P 2 _{O 5} equivalent amount (unit: mol%) in each 25.0 mol%, 50.0 mol%, and so that 25.0 mol% , 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 in a dry process, Obtained.

(Melting step (ii))
The raw material mixture was filled in a crucible made of alumina-zirconia-silica electrocast refractory (AGC Ceramics, trade name: ZB-1711, porosity 0.3%) having an inner diameter of 20 mm and a height of 40 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 1,250 ° C. for 0.5 hours, and heated to obtain a melt.

(Cooling step (iii))
The molten material in the crucible obtained in the melting step (ii) is cooled to room temperature at 1 × 10 ⁵ ° C./second by passing through a stainless steel double roller having a diameter of about 15 cm rotating at 400 revolutions per minute. A solidified product was obtained.

(Crushing step (iv))
The obtained flaky solidified product was lightly crushed by hand and then coarsely pulverized using a pestle and mortar. Furthermore, using a planetary mill (product name: LP-4, manufactured by Ito Seisakusho Co., Ltd.) using 500 g of zirconia balls as grinding media, the coarsely ground solidified product is 250 rpm for 4 hours with acetone as a solvent. A pulverized product was obtained by wet pulverization. The average particle diameter of the obtained pulverized product was 0.15 μm in terms of volume-based median diameter.

(Heating step (v))
The pulverized product obtained in the pulverization step (iv) was 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, apparatus 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 28 m < ² > / g when the specific surface area of the obtained lithium iron phosphate particle was measured with the specific surface area measuring apparatus (Shimadzu Corporation make, apparatus name: ASAP2020). Further, when the average particle size of the obtained lithium iron phosphate particles was measured using a laser diffraction / scattering particle size analyzer (manufactured by Horiba, Ltd., apparatus name: LA-950), the median diameter in terms of volume was It was 0.18 μm.
The crucible after the cooling step (iii) was not deformed in appearance. Moreover, when the crucible was cut and the amount of erosion was measured, it was about 50 μm. The amount of erosion is indicated by the maximum erosion depth (μm) measured with the flux line.

<Example 2>
(Corrosion resistance test)
In the same manner as in Example 1, the raw material preparation step (i), the melting step (ii), and the cooling step (iii) were performed, and the obtained solidified product was coated with alumina-zirconia having an inner diameter of 20 mm and a height of 40 mm. -A crucible made of siliceous electroformed refractory (manufactured by AGC Ceramics, trade name: ZB-1711) was filled.
Next, the crucible containing the solidified material 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 increased at a rate of 300 ° C./hour, and after reaching 1,300 ° C., the temperature was maintained and heated for 48 hours. After the heat treatment, the cooled crucible was cut and the amount of erosion was measured.

<Example 3>
Composition _Li 2 O melt, FeO, and SiO ₂ in terms of the amount (unit: mol%) in each 14.3 mol%, so that 28.6 mol%, and 57.1 mol%, carbonate Lithium (Li ₂ CO ₃ ), triiron tetroxide (Fe ₂ O ₃ ), and silicon dioxide (SiO ₂ ) were weighed, mixed and pulverized in a dry process to obtain a raw material preparation (raw material preparation step (i) ).

The melting step (ii) was performed at 1380 ° C. using the same crucible made of alumina-zirconia-silica electrocast refractory as in Example 1, and the heating step (v) was performed in an air atmosphere. In the same manner as in Example 1, the melting step (ii), the cooling step (iii), the pulverization step (iv), and the heating step (v) were performed to deposit lithium iron silicate particles. When the mineral phase of the obtained lithium iron silicate particles was measured using an X-ray diffractometer, it was confirmed that the particles were orthorhombic pyroxene-type LiFeSi ₂ O ₆ . Moreover, it was 27 m < ² > / g when the specific surface area of the lithium iron silicate particle | grains was measured. Furthermore, when the average particle diameter of the lithium iron silicate particles was measured, the median diameter in terms of volume was 0.067 μm.
The crucible after the cooling step (iii) was not deformed in appearance. Moreover, when the crucible was cut and the amount of erosion was measured, it was about 100 μm.

<Example 4>
Composition _Li 2 O melt, FeO, and _P 2 _{O 5} equivalent amount (unit: mol%) in each 37.5 mol%, 25.0 mol%, and so that 37.5 mol% , Lithium carbonate (Li ₂ CO ₃ ), ferric trioxide (Fe ₂ O ₃ ), and ammonium hydrogen phosphate (NH ₄ H ₂ PO ₄ ) are weighed, mixed and pulverized in a dry process, Obtained (raw material preparation step (i)).

The raw material mixture was filled in a crucible made of high zirconia electrocast refractory (AGC Ceramics, trade name: ZB-X950, porosity 0.2%) having an inner diameter of 20 mm and a height of 40 mm. The melting step (ii) was performed in the same manner as in Example 1 except that the raw material formulation was melted at 1,200 ° C. in the air. Moreover, it carried out similarly to Example 1, and performed the cooling process (iii) and the grinding | pulverization process (iv), and obtained the ground material.
The pulverized product obtained in the pulverization step (iv) was heated in the atmosphere at 650 ° C. for 8 hours using an electric furnace (manufactured by Motoyama, apparatus name: SK-3035F), then cooled to room temperature, and then iron phosphate Lithium particles were precipitated (heating step (v)).
When the mineral phase of the obtained lithium iron phosphate particles was measured, it was confirmed that the obtained lithium iron phosphate particles were monoclinic Nasicon type Li ₃ Fe ₂ (PO ₄ ) ₃ . Moreover, when the specific surface area of the obtained lithium iron phosphate particle was measured, the specific surface area was 25 m ² / g. Furthermore, when the average particle diameter of the lithium iron phosphate particles was measured, the median diameter in terms of volume was 0.23 μm.
The crucible after the cooling step (iii) was not deformed in appearance. Moreover, when the crucible was cut | disconnected and the amount of erosion was measured, it was 50 micrometers or less.

<Comparative Example 1>
A raw material preparation having the same composition as in Example 1 is filled in a crucible made of platinum alloy (internal volume 100 mL) containing 20% by mass of rhodium, and in the same manner as in Example 1, the raw material preparation step (i), the melting step (Ii) The cooling step (iii) was performed to obtain a solidified product.
Subsequently, the Pt content and the 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.
The lithium iron phosphate particles obtained in Examples 1 and 4 and the lithium iron silicate particles obtained in Example 3 were measured for the Pt content and Rh content in the same manner as described above. It was 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 temperature was raised under the same conditions as in Example 1, and reached 1,250 ° C., then held for 2 hours and heated to perform the melting step (ii). Thereafter, the temperature was lowered at a rate of 300 ° C./hour and cooled to room temperature.
When the crucible after the cooling step (iii) was visually observed, cracks were generated on the surface of the crucible. Moreover, when a part of crucible was cut and the amount of erosion was measured, it was 600 μm.

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.
The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2011-207025 filed on September 22, 2011 are incorporated herein as the disclosure of the specification of the present invention. Is.

Claims

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 method for producing a positive electrode material for a secondary battery, comprising: melting a raw material preparation in a container formed of an electroformed refractory to obtain a melt.
2. The electrocast refractory is at least one selected from the group consisting of an alumina-zirconia-silica electrocast refractory, a high zirconia electrocast refractory, and an alumina electrocast refractory. A method for producing a positive electrode material for a secondary battery.
The method for producing a positive electrode material for a secondary battery according to claim 1 or 2, wherein the melting step is performed at 900 ° C to 1700 ° C.
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. 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.
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.
The method for producing a positive electrode material for a secondary battery according to claim 6, 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.
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.
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 type 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 It is a number that depends on the valence of 1 and satisfies electrical neutrality.)
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 type 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 It is a number that depends on the valence of 2 and satisfies electrical neutrality.)