WO2012067249A1 - Silicate compound, secondary-battery positive electrode, secondary battery, and manufacturing methods therefor - Google Patents

Abstract

A silicate-compound manufacturing method providing improved control of composition and grain size. In said method, which is a method for manufacturing a silicate compound having a composition represented by formula (B), said silicate compound is manufactured by performing the following steps in order: a step wherein a melt is obtained by heating a feedstock mixture, obtained by controlling a feedstock containing atomic A, atomic M, silicon, and D such that the molar proportions of said atomic A, atomic M, silicon, and D equal the molar proportions indicated by formula (B); a cooling step wherein a solidified material is obtained by cooling the aforementioned melt; a pulverization step wherein a pulverized material is obtained by pulverizing said solidified material; and a heating step wherein the abovementioned silicate compound is obtained by heating said pulverized material. (B) A _e M _b Si _x D_{1− x} O _f2 (In the formula, A represents at least one element selected from a group comprising lithium, sodium, and potassium; M represents at least one element selected from a group comprising iron, manganese, cobalt, and nickel; D represents either aluminum or aluminum and boron; e satisfies 0.8 < e < 2.4; b satisfies 0.7 ≤ b ≤ 1.3; x satisfies 0.3 ≤ x < 1; and f2 represents a number that depends on e, b, x, and the valence (N) of M.)

Description

Silicic acid compound, positive electrode for secondary battery, secondary battery, and production method thereof

The present invention relates to a silicate compound, a positive electrode for a secondary battery, a secondary battery, and a method for producing them.

In recent years, plug-in hybrid vehicles and electric vehicles have been developed from the viewpoint of global CO ₂ emission regulations and energy saving. In addition, in order to realize the concept of a smart city and a smart community, development of a storage battery for power storage is desired. In order to realize these, it is a problem that the secondary battery to be used is increased in capacity, energy, and size while maintaining safety. As the positive electrode material for the next generation lithium ion secondary battery, an olivine type positive electrode material has attracted attention because of advantages in terms of resources, safety, cost, stability, and the like.

As a candidate material for a positive electrode of a secondary battery, an olivine-type silicic acid compound (Li ₂ FeSiO ₄ ) containing two Li in a unit formula and capable of increasing the capacity by a multi-electron reaction has been proposed (non-patent) Reference 1).

Patent Document 1 includes k Li in the unit formula, and [SiO ₄ ], [SO ₄ ], [PO ₄ ], [GeO ₄ ], [VO ₄ ], [AlO ₄ ], [BO]. ₄ ] and the like, and compounds having an orthosilicate structure, which have a wide general formula, have been proposed as electrode materials.

JP 2001-266882 A

Since Li ₂ FeSiO ₄ described in Non-Patent Document 1 is manufactured by a solid-phase reaction, the manufacturing process is complicated and the manufacturing cost increases.

It is Li _1.7 Mn _0.7 Fe _0.3 Si _0.7 P _0.3 O ₄ that is actually disclosed as an electrode material in Patent Document 1 as a compound containing Si. Li ₂ MnSiO ₄ and LiFePO ₄ are mixed and pulverized, sealed in a tube, and heated to produce the solid phase reaction. The solid-phase reaction has a complicated manufacturing process, is expensive to manufacture, is difficult to mass-produce, and composition control is not easy.

The object of the present invention is to control the composition and particle size of silicic acid compounds capable of increasing the capacity per unit mass, more specifically silicic acid-aluminic acid compounds and silicic acid-boric acid-aluminic acid compounds. It is in providing a manufacturing method that is easy to do. The compound is useful as an active material used for a positive electrode for a secondary battery and a positive electrode for a secondary battery. The present invention also provides a positive electrode for a secondary battery having excellent characteristics and reliability and a method for producing the secondary battery.

The present invention is the following [1] to [17].
[1] A method for producing a silicic acid compound having a composition represented by the following formula (B):
_{A e M b Si x D 1} -x O f2 (B)
(In the formula, A is at least one element selected from the group consisting of Li, Na and K. M is at least one element selected from the group consisting of Fe, Mn, Co and Ni, and D is Al, or Al and B. e is 0.8 <e <2.4, b is 0.7 ≦ b ≦ 1.3, x is 0.3 ≦ x <1, f2 is a number depending on the valence N of e, b, x and M.)
A raw material formulation prepared by adjusting a raw material containing the elements A, M, Si, and D so that the molar ratio of the elements A, M, Si, and D is the molar ratio represented by the formula (B) Heating to obtain a melt,
A cooling step of cooling the melt to obtain a solidified product,
A pulverization step of pulverizing the solidified product to obtain a pulverized product, and a heating step of heating the pulverized product to obtain a silicate compound.
Are carried out in this order. A method for producing a silicic acid compound.
[2] A melting step for obtaining a melt having a composition represented by the following formula (A):
A cooling step of cooling the melt to obtain a solidified product,
A pulverization step of pulverizing the solidified product to obtain a pulverized product, and a heating step of heating the pulverized product to obtain a silicate compound having a composition represented by the following formula (B):
Are carried out in this order. [1] The method for producing a silicate compound.
A _e M _b Si _x D _1-x O _f1 (A)
(Wherein A is at least one element selected from the group consisting of Li, Na and K, M is at least one element selected from the group consisting of Fe, Mn, Co and Ni, and D is Al or Al and B, e is 0.8 <e <2.4, b is 0.7 ≦ b ≦ 1.3, x is 0.3 ≦ x <1, f1 is a number that depends on the valence N of e, b, x, and M, and is a number that becomes f2 after the heating step.)
_{A e M b Si x D 1} -x O f2 (B)
(In the formula, A, M, D, e, b and x have the same meanings as described above, but are independent values, and f2 is a number depending on the valence N of e, b, x and M. X) may be 0.3 <x <1.
[3] The melt having the composition represented by the formula (A) is a melt having the composition represented by the following formula (1), and the silicic acid having the composition represented by the formula (B) The method for producing a silicic acid compound according to [2], wherein the compound is a silicic acid-aluminic acid compound having a composition represented by the following formula (2).
A _{1 + x + a} M _b Si _x Al _1-x O _{3 + x + d11} (1)
A _{1 + x + a} M _b Si _x Al _1-x O _{3 + x + d12} (2)
(In the formula, A, M, x and b have the same meaning as described above, a is −0.1 ≦ a ≦ 0.4, and d11 is a number depending on the valence N of a, b and M. There is a number that becomes d12 after the heating step, and d12 is a number that depends on the valence N of a, b, and M. However, in the formulas (1) and (2), a, b, and x are Independent values are shown.)
[4] The melting step includes
The compound containing element A is A carbonate, A bicarbonate, A hydroxide, A silicate, A aluminate, A nitrate, A chloride, A sulfate, At least one selected from the group consisting of A acetate and A oxalate (however, one or more of the one or more may each form a hydrate salt). ,
The compound containing element M is M oxide, M hydroxide, M oxyhydroxide, M silicate, M aluminate, metal M, M chloride, M nitrate, M And at least one selected from the group consisting of an organic salt of M
A compound containing Si is included as at least one selected from the group consisting of silicon oxide, A silicate, M silicate, aluminosilicate, and silicon alkoxide,
A compound containing Al is included as at least one selected from the group consisting of aluminum oxide, aluminum oxyhydroxide, aluminosilicate, aluminum chloride, aluminum nitrate, and aluminum sulfate.
The method for producing a silicic acid compound according to [3], which is a step of heating a raw material formulation to obtain a melt having a composition represented by the formula (1).
[5] The melt having the composition represented by the formula (A) is a melt having the composition represented by the following formula (3), and the silicic acid having the composition represented by the formula (B) The method for producing a silicic acid compound according to [2], wherein the compound is a silicic acid-boric acid-aluminic acid compound having a composition represented by the following formula (4).
A _{1 + x + a} M _b Si _x (B _c Al _1-c ) _1-x O _{3 + x + d21} (3)
A _{1 + x + a} M _b Si _x (B _c Al _1-c ) _1-x O _{3 + x + d22} (4)
Wherein A, M, x and b have the same meaning as described above, a is −0.1 ≦ a ≦ 0.4, c is 0 <c <1, d21 is a, b and It is a number that depends on the valence N of M, and is a number that becomes d22 after the heating step, and d22 is a number that depends on the valence N of a, b, and M. However, the equations (3) and (4 ) A, b, c, and x are independent values.)
[6] The melting step includes
Compound containing element A is A carbonate, A bicarbonate, A hydroxide, A silicate, A borate, A aluminate, A nitrate, A chloride , At least one selected from the group consisting of A sulfate, A acetate, and A oxalate (however, one or more of the one or more may each form a hydrate salt) Included.)
Compound containing element M is M oxide, M hydroxide, M oxyhydroxide, M silicate, M borate, M aluminate, metal M, M chloride And at least one selected from the group consisting of M nitrate, M sulfate and M organic salt,
A compound containing Si is included as at least one selected from the group consisting of silicon oxide, A silicate, M silicate, aluminosilicate, borosilicate, and silicon alkoxide,
A compound containing B is included as at least one selected from the group consisting of boron oxide, boric acid, A borate, M borate, borosilicate and aluminum borate,
A compound containing Al is included as at least one selected from the group consisting of aluminum oxide, aluminum oxyhydroxide, aluminosilicate, aluminum borate, aluminum chloride, aluminum nitrate, and aluminum sulfate.
The method for producing a silicic acid compound according to [5], which is a step of heating a raw material formulation to obtain a melt having a composition represented by the formula (3).
[7] The method for producing a silicate compound according to [1] to [6], wherein the element A is Li.
[8] The method for producing a silicate compound according to [1] to [7], wherein the element M is at least one element selected from the group consisting of Fe and Mn.
[9] The melt having the composition represented by the formula (1) is a melt having the composition represented by the following formula (5A), and the silicic acid having the composition represented by the formula (2) The method for producing a silicic acid compound according to [3], wherein the aluminate compound is a compound containing olivine type crystal particles having a composition represented by the following formula (5).
Li _{1 + x + a} (Fe _y Mn _1-y ) _b Si _x Al _1-x O _{3 + x + d11} (5A)
Li _{1 + x + a} (Fe _y Mn _1-y ) _b Si _x Al _1-x O _{3 + x + d12} (5)
(Wherein, a, b, d11, d12 and x have the same meaning as described above, and y is 0 ≦ y ≦ 1, provided that in formulas (5A) and (5), a, b, x, And y are independent values.)
[10] The melt having the composition represented by the formula (3) is a melt having the composition represented by the following formula (6A), and the silicic acid having the composition represented by the formula (4) The method for producing a silicic acid compound according to [5], wherein the boric acid-aluminic acid compound is a compound containing olivine type crystal particles having a composition represented by the following formula (6):
_{Li 1 + x + a (Fe} y Mn 1-y) b Si x (B c Al 1-c) 1-x O 3 + x + d21 (6A)
Li _{1 + x + a} (Fe _y Mn _1-y ) _b Si _x (B _c Al _1-c ) _1-x O _{3 + x + d22} (6)
(In the formula, a, b, c, d21, d22 and x have the same meaning as described above, and y is 0 ≦ y ≦ 1, provided that in formula (6A) and formula (6), a, b, c, x, and y are independent values.)
[11] The method for producing a silicic acid compound according to [1] to [10], wherein, in the cooling step, the cooling rate is −10 ³ ° C./sec to −10 ¹⁰ ° C./sec.
[12] In the pulverization step, the solidified product includes at least one carbon source selected from the group consisting of an organic compound and carbon powder, and a ratio of a carbon conversion amount (mass) in the carbon source is The method for producing a silicic acid compound according to [1] to [11], wherein the mass is 0.1 to 20% by mass with respect to the total mass of the mass of the solidified product and the carbon conversion amount (mass) in the carbon source.

[13] The method for producing a silicate compound according to [1] to [12], wherein the heating step is performed by heating to 500 to 1,000 ° C.
[14] A silicate compound is obtained by the production method of [1] to [13], and then a positive electrode for a secondary battery is produced using the silicate compound as a positive electrode material for a secondary battery. A method for producing a positive electrode for a secondary battery.
[15] A method for producing a secondary battery, comprising obtaining a positive electrode for a secondary battery by the production method of [14], and then producing a secondary battery using the positive electrode for a secondary battery.
[16] A silicic acid-aluminic acid compound having a composition represented by the following formula (ii):
_{A e M b Si x Al 1} -x O f2 (ii)
(Wherein A is at least one element selected from the group consisting of Li, Na and K, and M is at least one element selected from the group consisting of Fe, Mn, Co and Ni. E is 0.8 <e <2.4, b is 0.7 ≦ b ≦ 1.3, x is 0.3 ≦ x <1, and f2 is the valence of e, b, x and M N is a number that depends on N.) x may be 0.3 <x <1.
[17] A silicic acid-boric acid-aluminic acid compound having a composition represented by the following formula (iv):
_{A e M b Si x (B} c Al 1-c) 1-x O f2 (iv)
(Wherein A is at least one element selected from the group consisting of Li, Na and K, and M is at least one element selected from the group consisting of Fe, Mn, Co and Ni. E is 0.8 <e <2.4, b is 0.7 ≦ b ≦ 1.3, x is 0.3 ≦ x <1, c is 0 <c <1, and f2 is It is a number depending on the valence N of e, b, x and M.) x may be 0.3 <x <1.

The production method of the present invention is useful as an electrode material because it is easy to control the composition, particle size and uniformity of the silicate compound, and can efficiently produce silicate compounds having various compositions. By using the silicate compound of the present invention, a positive electrode material for a secondary battery excellent in characteristics and reliability and a secondary battery can be produced. Furthermore, the present invention provides a silicate compound.

FIG. 4 is a diagram showing X-ray diffraction patterns of silicic acid-boric acid-aluminic acid compounds produced in Examples 1, 2, 3, and 4. FIG. 4 is a diagram showing an X-ray diffraction pattern of silicic acid-boric acid-aluminic acid compounds produced in Examples 5, 6, and 7. FIG. 4 is a diagram showing an X-ray diffraction pattern of silicic acid-boric acid-aluminic acid compounds produced in Examples 14, 15, 16, and 19. FIG. 3 is a diagram showing an X-ray diffraction pattern of silicic acid-boric acid-aluminic acid compounds produced in Examples 31, 32, 33, and 34.

<Method for producing silicic acid compound>
In the method for producing a silicate compound of the present invention, the following melting step (I), cooling step (II), pulverization step (III), and heating step (IV) are performed in this order. In the production method of the present invention, other steps may be performed before, between and after the steps (I) to (IV) as long as each step is not affected.
Melting step (I): a method for producing a silicate compound having a composition represented by the following formula (B):
_{A e M b Si x D 1} -x O f2 (B)
(In the formula, A is at least one element selected from the group consisting of Li, Na and K. M is at least one element selected from the group consisting of Fe, Mn, Co and Ni, and D is Al, or Al and B. e is 0.8 <e <2.4, b is 0.7 ≦ b ≦ 1.3, x is 0.3 ≦ x <1, f2 is a number depending on the valence N of e, b, x and M.)
A raw material formulation prepared by adjusting a raw material containing the elements A, M, Si, and D so that the molar ratio of the elements A, M, Si, and D is the molar ratio represented by the formula (B) Heating to obtain a melt,
Cooling step (II): a step of cooling the melt to obtain a solidified product,
Crushing step (III): crushing the solidified product to obtain a pulverized product, and heating step (IV): heating the pulverized product to obtain a silicate compound having the composition represented by the formula (B). Process.
Said D is Al (aluminum) or Al and B (boron). In the present specification, a compound of formula (B) obtained when D is Al is a silicic acid-aluminic acid compound, and a compound of formula (B) obtained when D is Al and B is silicic acid- Boric acid-aluminic acid compound.
Hereinafter, each step will be specifically described.

[Melting step (I)]
The melting step (I) in the method for producing a silicate compound of the present invention is a step of obtaining a melt having a composition represented by the following formula (A).
A _e M _b Si _x D _1-x O _f1 (A)
(The symbols in the formula have the same meaning as described above.)

In the melting step (I), first, a raw material formulation prepared by adjusting a raw material containing an element source (element A, element M, Si, and D) to have a composition represented by the formula (A) is prepared. It is preferable to do this. When producing a silicic acid-aluminic acid compound, elements A, M, Si, and Al are used as element sources. When producing a silicic acid-boric acid-aluminic acid compound, elements are used as element sources. A raw material containing A, elements M, Si, B, and Al is used.

A in the formula (A) is at least one element selected from the group consisting of Li, Na and K. Since the element 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 silicate compound containing Li increases the capacity per unit volume (mass) of the secondary battery.

The element M in the formula (A) is at least one element selected from the group consisting of Fe, Mn, Co, and Ni. The element M is preferably composed of only one kind or two kinds. In particular, when the silicic acid compound produced by the production method of the present invention is used for a positive electrode material for a secondary battery, it is preferable from the viewpoint of cost that the element M consists of only Fe, only Mn, or Fe and Mn. The valence N of the element M is a numerical value that can change in each step of the production method of the present invention, and is in the range of +2 to +4. The valence N is +2, +8/3 or +3 when the element M is Fe, +2, +3 or +4 when Mn, +2, +8/3 or +3 when Co and +2 or when Ni +4 is preferred. The valence N is more preferably +2 in order to simplify the melting step (I).

In the formula (A), e is in the range of 0.8 <e <2.4, and b is in the range of 0.7 ≦ b ≦ 1.3. By setting e and b in the raw material formulation within the above range, a silicate compound having a target composition can be produced. Moreover, a raw material formulation can be melt | dissolved favorably and a uniform melt is obtained. It is preferable that e is 1.2 ≦ e ≦ 2. In addition, by setting x to 0.3 ≦ x <1, a compound that causes a multi-electron type reaction (reaction that draws more than 1 mol per unit mole) when used as a positive electrode material for a secondary battery is produced. The theoretical electric capacity of the secondary battery can be increased. x may be 0.3 <x <1. x is preferably 0.5 ≦ x <1, and more preferably 0.7 ≦ x <1.

The value of f1 in the formula (A) is a number that depends on the valence N of e, b, and x. Since the valence of the element in the formula can be changed in the subsequent pulverization step (III) and / or the heating step (IV), f1 is adjusted to a value that becomes f2 after the heating step (IV). For example, when the value of f1 increases or decreases due to oxidation / reduction or volatilization of the components in the heating step (IV), it is preferable to set the value in consideration of the increase / decrease. In the production method of the present invention, the value of f1 is preferably 0.9 to 1.2 times the value of f2 of the product described later.

In the formula (A), the melt having a composition when D is Al is a silicic acid-aluminic acid compound having a composition represented by the following formula (i), and represented by the following formula (1). A compound having a composition is preferable, and a compound having a composition represented by the following formula (5A) is particularly preferable.
_{A e M b Si x Al 1} -x O f1 (i)
A _{1 + x + a} M _b Si _x Al _1-x O _{3 + x + d11} (1)
Li _{1 + x + a} (Fe _y Mn _1-y ) _b Si _x Al _1-x O _{3 + x + d11} (5A)

E, b, x and f1 in the formula (i) have the same meaning as in the formula (A). The symbols in formula (1) have the same meaning as described above. The symbols in formula (5A) have the same meaning as described above.
In the case of producing a compound having a composition represented by formula (1) and formula (5A), a and b in the melt are set to −0.1 ≦ a ≦ 0.4 and 0.7 ≦ b ≦ 1. By making it 3, it is possible to produce a silicic acid-aluminic acid compound having the desired composition. Moreover, a raw material formulation can be melt | dissolved favorably and a uniform melt is obtained. In addition, by making x within this range, a silicic acid-aluminic acid compound that causes a multi-electron type reaction (reaction that pulls out more than 1 mol per unit mole) when used as a positive electrode material for a secondary battery is produced. The theoretical electric capacity of the secondary battery can be increased.

Since a and b in the formula (1) and the formula (5A) can easily cause a multi-electron type reaction, −0.1 ≦ a ≦ 0.3, 0.8 ≦ b ≦ 1.3 More preferably. Further, when 0 ≦ a ≦ 0.3 and 1 ≦ b ≦ 1.3, there is an advantage that the effect of increasing the theoretical electric capacity is great within a range in which the structural change of the silicate compound due to charge / discharge does not occur.

The value of f1 in formula (i) is a number that depends on the valence N of e, b, x, and M, and the value of d11 in formula (1) and formula (5A) is a, b, and The number depends on the valence N of M. Since the valence of the element in the formula can change in the subsequent pulverization step (III) and / or heating step (IV), f1 is adjusted to a value that becomes f2 after the heating step (IV), or the heating step (IV) Adjust d11 to a value that will later become d12. For example, when the value of f1 or d11 increases or decreases due to oxidation / reduction or volatilization of the component in the heating step (IV), it is preferable to set the value taking into account the increase / decrease. In the production method of the present invention, it is preferable to set the values of f1 and d11 to 0.9 to 1.2 times the values of f2 and d12 of the product to be described later, respectively.

The value of y in the formula (5A) is preferably 0 ≦ y ≦ 1, and particularly preferably 0 <y <1. The molar ratio of Fe to Mn is preferably 20 to 80:80 to 20, and particularly preferably 25 to 75:75 to 25.

In the formula (A), the melt having a composition when D is Al and B is a silicic acid-boric acid-aluminic acid compound having a composition represented by the following formula (iii), A compound having a composition represented by 3) is preferred, and a compound having a composition represented by the following formula (6A) is particularly preferred.
_{A e M b Si x (B} c Al 1-c) 1-x O f1 (iii)
A _{1 + x + a} M _b Si _x (B _c Al _1-c ) _1-x O _{3 + x + d21} (3)
_{Li 1 + x + a (Fe} y Mn 1-y) b Si x (B c Al 1-c) 1-x O 3 + x + d21 (6A)

E, b, x and f1 in formula (iii) have the same meaning as in formula (A). The symbols in formula (3) have the same meaning as described above. The symbols in formula (6A) have the same meaning as described above.
The preferable ranges of a and b in Formula (3) and Formula (6A) are the same as the preferable ranges of a and b in Formula (1). c is preferably 0 <c <1.

The value of f1 in formula (iii) is a number that depends on the valence N of e, b, x, and M, and the value of d21 in formula (3) and formula (6A) is a, b, and The number depends on the valence N of M. Since the valence of the element in the formula can change in the subsequent pulverization step (III) and / or heating step (IV), f1 is adjusted to a value that becomes f2 after the heating step (IV), or the heating step (IV) Adjust d21 to a value that will later become d22. For example, when the value of f1 or d21 increases or decreases due to oxidation / reduction or volatilization of the component in the heating step (IV), it is preferable to set the value taking into account the increase / decrease. In the production method of the present invention, it is preferable that the values of f1 and d21 are 0.9 to 1.2 times the values of f2 and d22 of the product to be described later, respectively.

The value of y in the formula (6A) is preferably 0 ≦ y ≦ 1, and particularly preferably 0 <y <1. The molar ratio of Fe to Mn is preferably 20 to 80:80 to 20, and particularly preferably 25 to 75:75 to 25.

In the present invention, melting in the melting step (I) can be facilitated by setting the composition of the raw material formulation to a specific range.

(Raw material formulation: Compound containing element A)
The compound containing element A in the raw material formulation includes A carbonate (A ₂ CO ₃ ), A hydrogen carbonate (AHCO ₃ ), A hydroxide (AOH), and A silicate (A ₂ O · 2SiO ₂ , A ₂ O · SiO ₂ , 2A ₂ O · SiO _2, etc., A borate (A ₂ O · B ₂ O ₃ , A ₂ O · 2B ₂ O ₃ , A ₂ O · 4B) ₂ O ₃ etc.), A aluminate (AAlO ₂ etc.), A nitrate (ANO ₃ ), A chloride (ACl), A sulfate (A ₂ SO ₄ ), A acetate (CH ₃ COOA) and at least one selected from the group consisting of organic acid salts such as oxalate ((COOA) ₂ ). The element A is preferably Li. Furthermore, these compounds may be hydrates. Of these, carbonates and bicarbonates of A are more preferred because they are inexpensive and easy to handle.

(Raw material formulation: Compound containing element M)
As the compound containing the element M in the raw material preparation, 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 hydroxide (M (OH) ₂ , M (OH) ₃ ), M oxyhydroxide (MO (OH)), M silicate (MSiO ₃ , M ₂ SiO ₄₎ Etc.), M borate (MBO ₃ , M ₂ B ₂ O ₅ etc.), M aluminate (MO · Al ₂ O ₃ etc.), metal M, M chloride (MCl ₂ , MCl ₃ ) , M nitrate (M (NO ₃ ) ₂ , M (NO ₃ ) ₃ ), M sulfate (MSO ₄ , M ₂ (SO ₄ ) ₃ ), M acetate (M (CH ₃ COO) ₂ ) And at least one selected from the group consisting of organic acid salts such as oxalate (M (COO) ₂ ). Good. The compound containing the element M is at least 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 because of availability and cost. One type is more preferable. In particular, when the element M is Fe and Mn, at least one selected from the group consisting of Fe ₃ O ₄ , Fe ₂ O ₃ and MnO ₂ is particularly preferable. Fe ₃ O ₄ , Fe ₂ O ₃ and MnO ₂ may be used alone or in combination of two or more.

(Raw material preparation: Compound containing Si (silicon))
As the compound containing Si in the raw material preparation, silicon oxide (SiO ₂ ), A silicate, M silicate, borosilicate (for example, B ₂ O ₃ .nSiO ₂ (0.5 <n <20 ), _and, a 2 O, may contain MO.), an aluminosilicate (e.g. _{Al 2 O 3 .nSiO 2 (0.5} <n <20), a 2 O, may contain MO. And at least one selected from the group consisting of silicon alkoxides (Si (OCH ₃ ) ₄ , Si (OC ₂ H ₅ ) _{4 and the} like). Among these, silicon oxide is more preferable because it is inexpensive. The compound containing Si may be crystalline or amorphous.

(Raw material formulation: Compound containing B (boron))
Compounds containing B in the raw material formulation include boron oxide (B ₂ O ₃ ), boric acid (H ₃ BO ₃ ), A borate, M borate, borosilicate, aluminum borate, and the like At least one selected from the group consisting of is preferable, and at least one selected from the group consisting of boron oxide and boric acid is particularly preferable because it is inexpensive.

(Raw material formulation: Compound containing Al (aluminum))
As the compound containing Al in the raw material formulation, aluminum oxide (Al ₂ O ₃ ), aluminum oxyhydroxide (including AlO (OH), aluminum oxyhydroxide salt), A aluminate, M aluminate At least one selected from the group consisting of aluminosilicate, aluminum borate, aluminum chloride, aluminum nitrate and aluminum sulfate is preferred. Among these, at least one selected from the group consisting of aluminum oxide, aluminum oxyhydroxide, and aluminosilicate is particularly preferable because it is inexpensive.

(Preferred combination of raw material formulations)
The raw material preparation used in the production of the silicic acid-aluminic acid compound includes a combination of A carbonate or bicarbonate; M oxide or M oxyhydroxide; silicon oxide; aluminum oxide or aluminum oxyhydroxide; Is preferred.
Furthermore, as the raw material formulation, a combination of Li ₂ CO ₃ or LiHCO ₃ ; one or more compounds selected from the group consisting of Fe ₃ O ₄ , Fe ₂ O ₃ and MnO ₂ ; SiO ₂ ; Al ₂ O ₃ ; Particularly preferred.

The raw material preparation used in the method for producing a silicic acid-boric acid-aluminic acid compound includes A carbonate or bicarbonate; M oxide or M oxyhydroxide; silicon oxide; boron oxide or boric acid; A combination of aluminum oxide or aluminum oxyhydroxide is preferred.
Furthermore, as a raw material formulation, Li ₂ CO ₃ or LiHCO ₃ ; one or more compounds selected from the group consisting of Fe ₃ O ₄ , Fe ₂ O ₃ and MnO ₂ ; SiO ₂ ; B ₂ O ₃ ; Al ₂ O ₃ ; is particularly preferred.

The composition of the raw material formulation should in principle correspond to the composition of the melt. However, in the raw material preparation, when a component (for example, Li, B, etc.) that is easily lost due to volatilization or the like is present in the melting step (I), the composition of the obtained melt is the composition of the raw material preparation. May be different. In such a case, it is preferable to appropriately change the composition of the raw material formulation in consideration of the amount lost due to volatilization or the like.

The purity of each raw material included in the raw material preparation is not particularly limited. Considering reactivity, characteristics of the positive electrode material for secondary batteries, and the like, the purity excluding hydrated water is preferably 99% by mass or more.

(Conditions for melting step (I))
The melting step (I) is preferably carried out by heating and melting the raw material formulation. Prior to melting, each raw material or raw material preparation is preferably pulverized and / or mixed dry or wet using a mixer, ball mill, jet mill, planetary mill or the like. The particle size of each raw material in the raw material preparation is not limited as long as it does not adversely affect the mixing operation, the filling operation of the raw material preparation into the melting container, the meltability of the raw material preparation, and the like.

Next, the raw material preparation is preferably put in a container or the like, heated using a heating furnace, and melted. The container is preferably made of alumina, carbon, silicon carbide, zirconium boride, titanium boride, boron nitride, carbon, platinum, or a platinum alloy containing rhodium. A container made of a refractory-based brick and a reducing material (eg, graphite) can also be employed. In order to prevent volatilization and evaporation in the heating furnace, it is preferable to attach a lid to the container and melt it. The heating furnace is preferably a resistance heating furnace, a high frequency induction furnace, or a plasma arc furnace. The resistance heating furnace is preferably an electric furnace provided with a heating element made of an alloy such as a nichrome alloy, silicon carbide, or molybdenum silicide.

The melting step (I) is preferably carried out in air, in an inert gas or in a reducing gas. Melting conditions can be changed as appropriate depending on conditions such as the type of container or heating furnace and the heating method such as a heat source. The pressure may be any of normal pressure, pressurization, and reduced pressure (0.9 × 10 ⁵ Pa or less). The melting conditions are preferably reducing conditions. Oxidizing conditions may be used. When melted under oxidizing conditions, it is preferable to perform reduction (for example, change from M ³⁺ to M ²⁺ ) in the heating step (IV).
The inert gas is a gas containing 99% by volume or more of at least one inert gas selected from the group consisting of nitrogen gas (N ₂ ) and rare gases such as helium gas (He) and argon gas (Ar). Say. The reducing gas refers to a gas that is substantially free of oxygen by adding a reducing gas to the above inert gas. Examples of the reducing gas include hydrogen gas (H ₂ ), carbon monoxide gas (CO), and ammonia gas (NH ₃ ). The amount of the reducing gas in the inert gas is preferably 0.1% by volume or more, and particularly preferably 1 to 10% by volume of the reducing gas contained in the total gas volume. The content of oxygen in the inert gas is preferably 1% by volume or less, particularly preferably 0.1% by volume or less, based on the total gas volume.

The heating temperature in the melting step (I) is preferably 1,300 to 1,600 ° C., particularly preferably 1,400 to 1,550 ° C. Here, melting means that each raw material is melted and is in a transparent state visually. When the heating temperature is equal to or higher than the lower limit value in the above range, melting becomes easy, and when the heating temperature is equal to or lower than the upper limit value in the above range, the raw material is hardly volatilized. The heating time is preferably 0.2 to 2 hours, particularly preferably 0.5 to 2 hours. By setting the time, the homogeneity of the melt is sufficient and the raw material is not easily volatilized.
In the melting step (I), stirring may be performed to increase the uniformity of the melt. Further, the melt may be clarified at a temperature lower than the heating temperature until the next cooling step (II) is performed. Furthermore, the melt obtained in the melting step (I) may be subjected to another step before the cooling step (II) as long as it does not adversely affect the next cooling step (II).

[Cooling step (II)]
The cooling step (II) is a step of cooling the melt obtained in the melting step (I) to near room temperature to obtain a solidified product. The solidified product is preferably an amorphous material. However, a part of the solidified product may be a crystallized product. When the solidified product contains an amorphous material, the next pulverization step (III) can be easily performed, and the composition and particle size of the compound can be easily controlled. Furthermore, in the heating step (IV), there is an advantage that the product can be prevented from being agglomerated and the particle size of the product 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 (IV), which is a subsequent step, and it is easy to crystallize. The amount of crystallized product 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 (III) is increased.

The cooling step (II) is preferably carried out by a method of cooling in air, in an inert gas, or in a reducing gas because the equipment is simple. The cooling rate of the melt is preferably not less than -1 × 10 ³ ℃ / sec, -1 × 10 ⁴ ℃ / sec or more is particularly preferable. In the present specification, a temperature change per unit time (ie, cooling rate) in the case of cooling is indicated by a negative value, and a temperature change per unit time in case of heating (ie, the heating rate) is indicated by a positive value. When the cooling rate is higher than this value, an amorphous material is easily obtained. The upper limit of the cooling rate is preferably about −1 × 10 ¹⁰ ° C./second from the viewpoint of manufacturing equipment and mass productivity, and is particularly preferably −1 × 10 ⁸ ° C./second from the viewpoint of practicality. The cooling rate of the melt is particularly preferably from -10 ³ ° C / second to -10 ¹⁰ ° C / second from 1000 ° C to 50 ° C.

As another method of carrying out the cooling step (II), a melt is dropped between twin rollers rotating at high speed to obtain a flake-like solidified product, and a melt is dropped onto a rotating single roller to form a flake. Or the method of sweeping a plate-shaped solidified material, or the method of pressing a molten material on the cooled carbon plate or metal plate and obtaining a block-shaped solidified material is preferable. 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 a cooling method, there is also a method in which the melt is directly poured into water, but this method has the disadvantage that it is difficult to control, it is difficult to obtain an amorphous material, the solidified product becomes a lump, and a lot of labor is required for grinding is there. As a cooling method, there is also a method in which a melt is directly charged into liquid nitrogen, and the cooling rate can be made faster than in the case of water, but there are problems similar to the method using water and the cost is high.

The solidified product obtained in the cooling step (II) is preferably flaky or fibrous. The flaky solidified product preferably has an average thickness of 200 μm or less, particularly preferably 100 μm or less. The average diameter of the plane perpendicular to the average thickness as the flaky solidified product is not particularly limited. The fibrous solidified product preferably has an average diameter of 50 μm or less, particularly preferably 30 μm or less. When the average thickness or the average diameter is less than or equal to the upper limit value, it is possible to reduce the labor of the subsequent pulverization step (III) and increase the crystallization efficiency. The average thickness and average diameter can be measured with a caliper or a micrometer. The average diameter can also be measured by microscopic observation.
The solidified product obtained in the cooling step (II) may be subjected to other steps before the pulverization step (III) as long as the pulverization step (III) is not adversely affected.

[Crushing step (III)]
The pulverization step (III) is a step of pulverizing the solidified product obtained in the cooling step (II) to obtain a pulverized product. Since the solidified product usually contains a large amount of amorphous material or consists of an amorphous material, there is an advantage that it is easy to grind. In addition, there is an advantage that pulverization can be performed without imposing a burden on an apparatus used for pulverization and the particle size can be easily controlled. On the other hand, in the conventional solid phase reaction, pulverization is performed after the heating step (IV), but the present inventor has noticed that there is a problem that residual stress is generated by pulverization and battery characteristics are deteriorated. Therefore, the manufacturing method of the present invention employs a method of pulverizing before the heating step (IV) and reducing or removing the generated residual stress in the subsequent heating step (IV).

The pulverization is preferably performed using a jaw crusher, a hammer mill, a ball mill, a jet mill, a planetary mill or the like. The method of pulverization may be either dry or wet. Before the pulverization step (III), it is preferable that the solidified product be struck by hand or a hammer to make it finer, because the burden of the pulverization step (III) is reduced. When the pulverization is performed in a wet manner, it is preferable to carry out the heating step (IV) after removing the dispersion medium by sedimentation, filtration, drying under reduced pressure, heat drying and the like. However, when there are few dispersion media, especially when the ratio of the mass of the solid content to the mass of the pulverized product is 30% or more, the heating step (IV) may be performed with the pulverized product containing the dispersion medium as it is.

Since the silicic acid compound in the present invention is an insulating material, when used as a positive electrode material for a secondary battery, it is preferable to include a conductive material in the solidified product. Moreover, when using as a positive electrode material for secondary batteries, it is preferable that it is a fine particle form. The average particle diameter of the pulverized product is preferably 10 nm to 10 μm, and particularly preferably 10 nm to 5 μm, in terms of volume-based median diameter. The particle size can be measured by a sedimentation method or a laser diffraction / scattering particle size measuring device. When the particle size of the pulverized product is small, the reduction reaction is promoted, and the heating temperature and time in the heating step (IV) can be reduced, which is preferable. By setting the average particle size of the pulverized product within the above range, the workability of the pulverization step (III) and the heating step (IV) is improved, and the average particle size of the product of the heating step (IV) can be easily controlled. There is.

The conductive material is preferably at least one carbon source selected from the group consisting of organic compounds and carbon powder. The amount of at least one carbon source selected from the group consisting of an organic compound and carbon powder is such that the carbon equivalent amount (mass) in the carbon source is the mass of the solidified product and the carbon equivalent amount (mass in the carbon source). ) In an amount of 0.1 to 20% by mass, particularly preferably 2 to 10% by mass. By setting the amount of carbon in the above range, the conductivity as the positive electrode material for secondary batteries can be sufficiently increased.
The organic compound and / or carbon powder contained in the solidified product prevents oxidation in the pulverization step (III) and heating step (IV), and further promotes reduction. Further, the organic compound is pyrolyzed in the heating step (IV) to become a carbide, and the carbon powder remains after the heating step (IV) and functions as a conductive material. Therefore, the conductivity of the positive electrode material for secondary batteries can be increased.

The organic compound is preferably at least one selected from the group consisting of saccharides, amino acids, peptides, aldehydes, ketones, glycols, polyvinyl alcohol, celluloses, and fatty acids, and saccharides, glycols, or polyvinyl alcohol. Is particularly preferred. Examples of the saccharide include monosaccharides such as glucose, fructose, and galactose, oligosaccharides such as sucrose, maltose, cellobiose, and trehalose, invert sugar, polysaccharides such as dextrin, amylose, amylopectin, and cellulose, and ascorbic acid. It is done. Examples of amino acids include amino acids such as alanine and glycine. Peptides include low molecular weight peptides having a molecular weight of 1,000 or less.
As the carbon powder, carbon black, graphite, acetylene black and the like are preferable. The carbon powder may be fibrous carbon or plate-like carbon.

In the pulverization step (III), when the solidified product is pulverized by including an organic compound or carbon powder, there is an advantage that the step of mixing the conductive material can be omitted after the heating step (IV). Moreover, the organic compound and carbon powder can suppress the grain growth of the solidified product. In the pulverization step (III) when the organic compound is included in the solidified product, wet pulverization is preferably employed in order to uniformly disperse the pulverized product on the surface. As a dispersion medium for pulverization, water or an organic solvent such as ethanol, isopropyl alcohol, acetone, hexane, or toluene can be used. Of these, water is preferable because it is inexpensive. A dry method is preferable for the pulverization step (III) when the solidified product contains carbon powder.
Furthermore, the pulverized product obtained in the pulverization step (III) may be subjected to another step before the heating step (IV) as long as it does not adversely affect the next heating step (IV).

[Heating step (IV)]
The heating step (IV) is a step of heating the pulverized product obtained in the pulverizing step (III). In the heating step (IV), a silicic acid compound having a composition represented by the following formula (B) is obtained.
_{A e M b Si x D 1} -x O f2 (B)
(The symbols in the formula have the same meaning as described above, but indicate values independent of the values in the formula (A).)

The value of f2 in the formula (B) is generally represented by f2 = 0.5 (e + bN + x + 3). f2 is preferably 3 ≦ f2 ≦ 5, particularly preferably 3 ≦ f2 ≦ 4. Preferred ranges of e, b, and x in the formula (B) are the same as those in the formula (A).

When the production method of the present invention is carried out using a melt having a composition represented by the formula (i) in which D is Al as the compound having the composition represented by the formula (A), the formula (B A silicic acid-aluminic acid compound having a composition represented by the following formula (ii) is obtained as a silicon compound having a composition represented by formula (ii).
_{A e M b Si x Al 1} -x O f2 (ii)
(In the formula, A, M, e, b and x have the same meaning as described above, but are independent of the values in formula (i). F2 represents the valence N of e, b, x and M. Depends on the number.)
The preferred range of e, b and x in formula (ii) is the same as the preferred range in formula (i).
Element A is Li, Element M is Fe only, or Fe and Mn, e is 0.8 <e <2.4, b is 0.7 ≦ b ≦ 1.3, x is 0.3 ≦ x <1, A compound in which f2 is 3 ≦ f2 ≦ 5 is particularly preferable. x may be 0.3 <x <1.

In particular, when the production method of the present invention is carried out using a melt having a composition represented by formula (1), which is a preferred embodiment of a melt having a composition represented by formula (i), formula (ii) As a silicon compound having a composition represented by (2), a silicic acid-aluminic acid compound having a composition represented by the following formula (2) is obtained.
A _{1 + x + a} M _b Si _x Al _1-x O _{3 + x + d12} (2)
(In the formula, A, M, a, b and x have the same meaning as described above, but are independent of the values in formula (1). D12 depends on the valence N of a, b and M. Number.)

The preferable range of a, b, and x in Formula (2) is the same as the preferable range in Formula (1).
The value of f2 in the formula (ii) is generally represented by f2 = 0.5 (e + bN + x + 3). f2 is preferably 3 ≦ f2 ≦ 5, particularly preferably 3 ≦ f2 ≦ 4.
The value of d12 in formula (2) is, for example, d12 = 0 if a = 0, b = 1, and N = + 2, and is generally expressed as d12 = 0.5 (a + bN−2). d12 is preferably −0.2 ≦ d12 ≦ 1.2, particularly preferably 0 ≦ d12 ≦ 0.5. The valence of N is preferably +2.

When the production method of the present invention is carried out using a melt having a composition represented by the formula (iii) in which D is Al and B as the compound having the composition represented by the formula (A), the formula As the silicon compound having the composition represented by (B), a silicic acid-boric acid-aluminic acid compound having a composition represented by the following formula (iv) is obtained.
_{A e M b Si x (B} c Al 1-c) 1-x O f2 (iv)
(In the formula, A, M, e, b, c and x have the same meaning as described above, but are independent of the values in formula (iii). F2 is the valence of e, b, x and M. The number depends on N.)
The preferred range of e, b, x and c in formula (iv) is the same as the preferred range in formula (iii).
Element A is Li, Element M is Fe only, or Fe and Mn, e is 0.8 <e <2.4, b is 0.7 ≦ b ≦ 1.3, x is 0.3 ≦ x <1, A compound in which c is 0 <c <1 and f2 is 3 ≦ f2 ≦ 5 is particularly preferable. x may be 0.3 <x <1.

In particular, when the production method of the present invention is carried out using a melt having a composition represented by formula (3), which is a preferred embodiment of a melt having a composition represented by formula (iii), the formula (B As a silicon compound having a composition represented by (4), a silicic acid-boric acid-aluminic acid compound having a composition represented by the following formula (4) is obtained.
A _{1 + x + a} M _b Si _x (B _c Al _1-c ) _1-x O _{3 + x + d22} (4)
(In the formula, A, M, a, b, c and x have the same meaning as described above, but are independent of the values in formula (3). D22 represents the valence N of a, b and M. Depends on the number.)

The preferred range of a, b, x and c in formula (4) is the same as the preferred range in formula (3).
The value of f2 in the formula (iv) is generally represented by f2 = 0.5 (e + bN + x + 3). f2 is preferably 3 ≦ f2 ≦ 5, particularly preferably 3 ≦ f2 ≦ 4.
The value of d22 in the formula (4) is, for example, d22 = 0 when a = 0, b = 1, and N = + 2, and is generally expressed as d22 = 0.5 (a + bN−2). d22 is preferably −0.2 ≦ d22 ≦ 1.2, particularly preferably 0 ≦ d22 ≦ 0.5. The valence of N is preferably +2.
In the formula (2), the silicon compound having a composition when D is Al is particularly preferably a compound having a composition represented by the following formula (5).
Li _{1 + x + a} (Fe _y Mn _1-y ) _b Si _x Al _1-x O _{3 + x + d12} (5)
(Wherein, a, b, d12 and x have the same meaning as described above, and y is 0 ≦ y ≦ 1.)
The value of y in the formula (5) is preferably 0 ≦ y ≦ 1, and particularly preferably 0 <y <1. The molar ratio of Fe to Mn is preferably 20 to 80:80 to 20, more preferably 25 to 75:75 to 25, and particularly preferably 40 to 60:60 to 40.
In the formula (4), the silicon compound having a composition when D is Al and B is particularly preferably a compound having a composition represented by the following formula (6).
Li _{1 + x + a} (Fe _y Mn _1-y ) _b Si _x (B _c Al _1-c ) _1-x O _{3 + x + d22} (6)
(Wherein a, b, c, d22 and x have the same meaning as described above, and y is 0 ≦ y ≦ 1.)
The value of y in the formula (6) is preferably 0 ≦ y ≦ 1, and particularly preferably 0 <y <1. The molar ratio of Fe to Mn is preferably 20 to 80:80 to 20, more preferably 25 to 75:75 to 25, and particularly preferably 40 to 60:60 to 40.

The product of the heating step (IV) is preferably crystal particles, and more preferably olivine type crystal particles. In the heating step (IV) in the present invention, the pulverized material is heated, so that the relaxation of the residual stress is promoted. In addition, since the formation of crystal nuclei and grain growth are performed by heating, the composition, grain size, and distribution thereof are easily controlled.

Furthermore, the heating step (IV) in the case where the organic compound and / or carbon powder is included in the solidified product in the pulverizing step (III) causes the conductive material to be bonded to the surface of the product, preferably the crystal grains of the product. It can be a process. The organic compound is thermally decomposed in the heating step (IV) and becomes a carbide to function as a conductive material.

The heating temperature in the heating step (IV) is preferably 500 to 1,000 ° C. When the heating temperature is 500 ° C. or higher, crystals are easily generated. When the heating temperature is 1,000 ° C. or less, melting of the pulverized product can be prevented. The heating temperature is more preferably 600 to 900 ° C. When the heating temperature is used, crystal particles having appropriate crystallinity, particle diameter, particle size distribution, and the like are easily obtained, and olivine-type crystal particles are preferably obtained.
When the pulverization step (III) is performed in a wet manner, the heating step (IV) can be a step of removing the dispersion medium when the heating step (IV) is performed while the dispersion medium is included.

The heating in the heating step (IV) may be performed at a constant temperature after raising the temperature at once, or may be performed by changing the temperature in multiple stages. Since the particle diameter to be generated tends to increase as the heating temperature increases, the heating temperature is preferably set according to the desired particle diameter. The heating time (holding time depending on the heating temperature) is preferably 1 to 72 hours in consideration of a desired particle size. Heating is preferably carried out in a box furnace, tunnel kiln furnace, roller hearth furnace, rotary kiln furnace, microwave heating furnace or the like using electricity, oil, gas or the like as an energy source.

Similar to the heating in the melting step (I), the heating step (IV) can be carried out in air, in an inert gas or in a reducing gas, and is preferably carried out in an inert gas or in a reducing gas. The conditions in the inert gas and the reducing gas are the same as those in the melting step (I). The heating step (IV) may be carried out by reducing the pressure in an inert gas or a reducing gas (0.9 × 10 ⁵ Pa or less). In addition, when heating is performed by charging a container containing a reducing agent (eg, graphite) and pulverized material in a heating furnace, reduction of M in the pulverized material (eg, change from M ³⁺ to M ²⁺⁾ . ) Can be promoted.

In the present invention, after the heating step (IV), 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. Further, the cooling may be left to cool to room temperature. The cooling is preferably allowed to cool to room temperature. Cooling is preferably performed in an inert gas or a reducing gas.

<Silic acid compound>
The silicic acid compound obtained by the production method of the present invention is a novel compound useful as a positive electrode material for secondary batteries.

In particular, the silicic acid-aluminic acid compound having the composition represented by the formula (2) and the silicic acid-boric acid-aluminic acid compound having the composition represented by the formula (4) have an element A atom number of 1 Since it is 2 or more, it becomes a multi-electron type, and the capacity per unit mass becomes large when used for a positive electrode for a secondary battery.

That is, in the silicic acid-aluminic acid compound having the composition represented by the formula (2), when the element A is Li, more than one and not more than two per unit ([SiO ₄ ] + [AlO ₄ ]) tetrahedron Since the compound has a structure containing Li, the number of Li atoms can be 1.2 or more. Furthermore, according to the production method of the present invention, it is possible to obtain a silicic acid-aluminic acid compound in which [SiO ₄ ] tetrahedron, [AlO ₄ ] tetrahedron and [LiO ₄ ] tetrahedron are uniformly distributed.

When the element A is Li, the silicic acid-boric acid-aluminic acid compound having the composition represented by the formula (4) has a unit ([SiO ₄ ] + [BO ₄ ] + [AlO ₄ ]) tetrahedron. Since it is a compound having a structure containing more than one and not more than two Li, the number of atoms of Li can be increased to 1.2 or more. Further, according to the production method of the present invention, [SiO ₄ ] tetrahedron, [BO ₄ ] tetrahedron, [AlO ₄ ] tetrahedron and [LiO ₄ ] tetrahedron are uniformly distributed silicic acid-boric acid-aluminic acid A compound can be obtained.

The silicate compound in the present invention preferably contains olivine type crystal particles. The crystal particles include both primary particles and secondary particles. When secondary particles are present in the product, they may be crushed and pulverized as long as the primary particles are not destroyed.

The silicate compound produced by the production method of the present invention preferably contains olivine type crystal particles, and is preferably olivine type crystal particles. The olivine type crystal particle is a material that exhibits a multi-electron type theoretical electric capacity.

In the production method of the present invention, when an organic compound and / or carbon powder is included in the solidified product, carbon derived from the organic compound or carbon powder is uniformly and strongly used as a conductive material on the surface of the silicic acid compound. Can be combined. The silicic acid compound to which the conductive material is bonded can be used as it is for a positive electrode material for a secondary battery.

When the silicic acid-aluminic acid compound having the composition represented by the formula (2) or the silicic acid-boric acid-aluminic acid compound having the composition represented by the formula (4) is a crystal, it is a solid solution crystal or a eutectic crystal. Preferably there is. In particular, when x in the formula (2) or the formula (4) is 0.8 ≦ x <1, it tends to be a solid solution crystal. The reason is considered that a part of Si is substituted with Al or Al and B by the reaction represented by the following formula (7) to form a solid solution crystal.
xA ₂ MSiO ₄ + (1-x) AM (B, Al) O ₃
→ A _{1 + x} M [Si _x (B, Al) _1-x ] O _{3 + x} (7)
(In the formula, A and M have the same meanings as described above, x is 0.8 ≦ x <1, and [] represents a solid solution. B may not be included.)

Since the solid solution crystal has a stable crystal structure as compared with a crystal composed of only Si, Li ions easily move in the crystal. Therefore, a high capacity can be obtained and the electrical conductivity can be increased, and the charge / discharge cycleability can be improved when used as a positive electrode material for a secondary battery.

When the silicic acid compound in the present invention is a solid solution crystal or contains a solid solution crystal, the crystal is a solid solution crystal in which a part of Si is substituted with Al or Al and B, and an olivine type crystal. Particles are preferred.
When a silicate compound that is a solid solution crystal is used as a positive electrode material for a secondary battery, Li ions easily move in the crystal, resulting in a high capacity and an increase in electrical conductivity. Therefore, when used as a positive electrode material for a secondary battery, a theoretical capacity is easily obtained, and it is considered that the charge / discharge cycleability is improved.

When x in formula (2) or formula (4) is 0.3 ≦ x <0.8, it tends to be a eutectic. The eutectic silicic acid compounds are A ₂ MSiO ₄ olivine type crystal, AM (B, Al) O ₃ olivine type crystal, and A _{1 + z} MSi _z (B, Al) _1-z O _{3 + z} (z is 0 < z <1.0.) A crystal body in which a group of olivine crystals coexists.
As the eutectic in the present invention, an olivine type crystal having a composition represented by the formula Li _{1 + z} MSi _z (B, Al) _1-z O _{3 + z} olivine type crystal is essential, and further Li ₂ MSiO ₄ olivine type crystal. , LiM (B, Al) O ₃ olivine type crystals, and Li _{1 + z} MSi _z (B, Al) _1-z O _{3 + z} (z is 0.2 <z <0.8) olivine type crystals A eutectic of a silicic acid compound containing an olivine crystal selected from (may or may not contain B in the crystal) is particularly preferred. (B, Al) is Al or Al and B.

The eutectic of the silicic acid compound is considered to be generated by the reaction represented by the following formula (8).
(1-x) A ₂ MSiO ₄ + xAM (B, Al) O ₃ → (1-xw ₁ ) A ₂ MSiO ₄ + (xw ₂ ) AM (B, Al) O ₃ + wA _{2− z} MSi _z (B, Al) _1-z O _{3 + Z} (8)
(Wherein x and z are 0.3 ≦ x <0.8 and 0.2 <z <0.8, w ₁ , w ₂ and w are each a number from 0 to 1, and w ₁ + w ₂ = w. B may not be included.)

It is preferable that the silicic acid compound of the present invention is a eutectic because the electric conductivity tends to increase. The reason is that the eutectic has a plurality of crystal structures, and crystallites having different electric conductivities are formed. Therefore, when a potential is applied, a potential difference occurs between the crystallites, and the primary particles This is probably because the electrical conductivity of the device itself increases. In addition, a structure having a grain boundary is formed between the crystallites in the primary particle, and this grain boundary is extremely thin as compared with that in the primary particle, which is considered to be because the electrical conductivity of the primary particle itself is increased.
The silicic acid compound of the present invention is particularly preferably an eutectic because it is easy to obtain high electric conductivity and charge / discharge cycleability is improved.

When applied to a positive electrode for a secondary battery, the silicate compound of the present invention is preferably a solid solution crystal from the viewpoint of having a high capacity and easily obtaining good cycle characteristics, and easily obtaining high electrical conductivity. From this point, eutectic is particularly preferable.

The average particle diameter of the silicate compound of the present invention is preferably an average particle diameter of 10 nm to 10 μm, more preferably 10 nm to 6 μm, and particularly preferably 10 nm to 2 μm in terms of volume median diameter. The lower limit value may be 100 nm. By making the average particle diameter within this range, the conductivity becomes higher. The average particle diameter can be determined by, for example, observation with an electron microscope or measurement with a laser diffraction particle size distribution meter.
The specific surface area of the silicate compound is preferably 0.2 ~ 200m ² / g, preferably ^{0.5 ~ 200m 2 / g, 1} ~ 200m 2 / g is particularly preferred. The upper limit value may be 100 m ² / g or 10 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 silicic acid compound of the present invention is a compound having a composition represented by formula (ii) or a compound having a composition represented by formula (iv), and the compound is preferably an olivine type crystal. Examples of compounds include the compounds listed in Table 3 below.

<Positive electrode for secondary battery and method for producing secondary battery>
The silicic acid compound obtained by the production method of the present invention is useful as a positive electrode material for a secondary battery. Therefore, the positive electrode for secondary batteries and a secondary battery can be manufactured using this silicate compound.
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 silicate compound obtained by the manufacturing method of the present invention. For example, if necessary, the silicic acid compound of the present invention is added to a known binder (polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, Obtained by mixing with polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, etc.) and, if necessary, known conductive materials (acetylene black, carbon, graphite, natural graphite, artificial graphite, needle coke, etc.). The mixed powder may be pressure-formed on a support made of stainless steel or filled in a metal container. Further, for example, the mixed powder is mixed with an organic solvent (N-methylpyrrolidone, toluene, cyclohexane, dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran. And the like, and a slurry obtained by mixing with a metal substrate such as aluminum, nickel, stainless steel, or copper can also be employed.

The secondary battery can employ a configuration in a known secondary battery using the positive electrode for a secondary battery obtained by the production method of the present invention 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 a carbon material, an alkali metal material, and an alkaline earth metal material is preferably used. As the electrolytic solution, a non-aqueous electrolytic solution is preferable. That is, as the 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.
[Examples 1 to 13]
The composition of the melt is Li ₂ O, Na ₂ O, FeO, MnO, CoO, NiO, SiO ₂ , and Al ₂ O ₃ equivalent (unit: mol%), so that the ratios shown in Table 1 are obtained, respectively. Lithium carbonate (Li ₂ CO ₃ ), sodium carbonate (Na ₂ CO ₃ ), triiron tetroxide (Fe ₃ O ₄ ), manganese dioxide (MnO ₂ ), tricobalt tetroxide (Co ₃ O ₄ ), nickel oxide ( NiO), silicon dioxide (SiO ₂ ), and aluminum oxide (Al ₂ O ₃ ) were weighed, mixed and pulverized in a dry process to obtain a raw material formulation.

Each raw material formulation was filled in a platinum alloy crucible containing 20% by mass of rhodium. Next, the crucible was placed in an electric furnace (manufactured by Motoyama, apparatus name: NH-3035) having 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 and heated at 1,400 to 1,500 ° C. for 0.5 hour. Each melt was obtained after confirming that it became transparent visually. The composition formula of the obtained melt is shown in the right column of Table 1.

(Cooling process)
The melt in the crucible obtained in the melting step was cooled at −1 × 10 ⁵ ° C./second by passing through a twin roller having a diameter of about 15 cm rotating at 400 revolutions per minute to obtain a flaky solidified product. .
(Crushing process)
The flake solidified product obtained in the cooling step was lightly kneaded and finely ground, and then coarsely pulverized using a pestle and mortar. Further, the coarsely pulverized solidified product was pulverized in a dry manner using a planetary mill using zirconia balls as a pulverizing medium to obtain a pulverized product. When the particle diameter of the pulverized product of Example 1 and Example 4 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 2.1 μm. (Example 1) and 2.5 μm (Example 4).

(Heating process)
The pulverized material obtained in the pulverization step is placed in 3% by volume H ₂ —Ar gas, and heated for 8 hours at four temperature conditions of 600 ° C., 700 ° C., 800 ° C. and 900 ° C. for each example, Silica-aluminate compound particles were precipitated by cooling at a rate of −200 ° C./hour. Among each Example, X-ray diffraction, particle size distribution, and composition analysis were performed about the particle | grains obtained by implementing a heating process at 700 degreeC.

(X-ray diffraction)
The mineral phase of the obtained silicate compound particles was examined using an X-ray diffractometer (manufactured by Rigaku Corporation, apparatus name: RINT TTRIII). The particles obtained in Examples 1 to 13 are all orthorhombic olivine type Li ₂ MSiO ₄ (K. Zaghib et al., Journal of Power Sources, 160, 1381-1386, 2006 and R. Dominko et al. , Electrochemistry Communications, 8, 217-222 (2006)). From the results, it was confirmed that the silicate compound particles were crystals and a solid solution crystal in which a part of Si of the A ₂ MSiO ₄ crystal was substituted with Al.
The X-ray diffraction patterns of the crystals obtained in Examples 1, 2, 3, and 4 are respectively shown in (a), (b), (c), and (d) of FIG. 7, the X-ray diffraction patterns of the respective crystals obtained by heating at 800 ° C. are shown in FIG. 2 (a), (b), and (c), respectively.

(Particle size distribution)
The particle size distribution of the silicic acid-aluminic acid compound obtained in Example 1 was measured with a laser diffraction / scattering particle size distribution analyzer (manufactured by Horiba, Ltd., apparatus name: LA-920). The median diameter in terms of volume was 2.3 μm. Furthermore, when the specific surface area was measured with a specific surface area measuring device (manufactured by Shimadzu Corporation, device name: ASAP2020), it was 1.4 m ² / g.

[Examples 14 to 30]
Carbonic acid so that the composition of the melt is Li ₂ O, FeO, MnO, CoO, SiO ₂ , B ₂ O ₃ , and Al ₂ O ₃ equivalent (unit: mol%), and the ratio shown in Table 2 respectively. Lithium (Li ₂ CO ₃ ), triiron tetroxide (Fe ₃ O ₄ ), manganese dioxide (MnO ₂ ), tricobalt tetroxide (Co ₃ O ₄ ), silicon dioxide (SiO ₂ ), boron oxide (B ₂ O ₃ ) and aluminum oxide (Al ₂ O ₃ ) were weighed to obtain a raw material formulation. These were mixed and pulverized, melted, cooled and solidified, pulverized, and heated in the same manner as in Example 1 to precipitate silicate compound particles. The particles obtained by carrying out the heating step at 700 ° C. were subjected to X-ray diffraction, particle size distribution and composition analysis. The composition formula of the obtained melt is shown in the right column of Table 2.

(X-ray diffraction)
When the mineral phase of the obtained silicic acid compound particles was examined using an X-ray diffractometer, the particles obtained in Examples 14 to 19 and Examples 22 to 30 were all orthorhombic olivine type Li _2. A diffraction pattern similar to MSiO ₄ was exhibited. From the results, it was confirmed that the silicate compound particles were crystals and a solid solution crystal in which a part of Si of the A ₂ MSiO ₄ crystal was substituted with B and Al. The particles obtained in Examples 20 and 21 were A ₂ MSiO ₄ olivine type crystal, AM (B, Al) O ₃ olivine type crystal, and A _{1 + z} MSi _z (B, Al) _1-z O _{3 + z} olivine type. A diffraction pattern considered to be a eutectic including a crystal is shown, and an A ₂ MSiO ₄ olivine type crystal, an AM (B, Al) O ₃ olivine type crystal, and an A _{1 + z} MSi _z (B, Al) _1-z O _{3 + z} olivine type are shown. It was confirmed that a eutectic containing crystals was obtained.
The X-ray diffraction patterns of the crystals obtained in Examples 14, 15, 16, and 19 are shown in (a), (b), (c), and (d) of FIG.

(Particle size distribution)
The particle size distribution of the silicic acid compound obtained in Example 14 was measured with a laser diffraction / scattering particle size distribution analyzer (manufactured by Horiba, Ltd., apparatus name: LA-920). The median diameter in terms of volume was 1.9 μm. there were. Furthermore, when the specific surface area was measured with a specific surface area measurement device (manufactured by Shimadzu Corporation, device name: ASAP2020), it was 1.5 m ² / g.

(Composition analysis)
The chemical composition of the obtained silicic acid compound particles was measured. First, the particles were heated and decomposed at 120 ° C. with a 2.5 mol / L KOH solution, and the decomposition solution was dried under hydrochloric acid acidity. Next, after filtration as a hydrochloric acid acidic solution, a filtrate and a residue were obtained. The amounts of Si, B, Al, Fe, Mn, Co and Ni in the filtrate were quantified using an inductively coupled emission spectroscopic analyzer (manufactured by Seiko Instruments Inc., apparatus name: SPS3100). The amounts of Li and Na in the filtrate were quantified using an atomic absorption photometer (manufactured by Hitachi High-Technologies Corporation, apparatus name: Z-2310). From the quantitative values of Si, B, Al, Fe, Mn, Co, Ni, Li and Na, SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , FeO, MnO, CoO, NiO, Li ₂ O and Na ₂ O The amount of each was calculated. Further, the residue was incinerated and then decomposed with hydrofluoric acid-sulfuric acid, and the weight loss due to this treatment was changed to SiO ₂ . The total amount of SiO ₂ was the sum of the amount calculated from the weight loss and the amount of SiO ₂ in the filtrate. Table 3 shows quantitative values of the chemical compositions of the silicate compound particles obtained in Examples 1 to 10 and Examples 14 to 21.

[Examples 31 to 37]
The coarsely pulverized product obtained by melting, cooling, and coarsely pulverizing in Examples 1 to 4 and Examples 14 to 16 and carbon black were 9: 1 in mass ratio of the pulverized product and the amount of carbon in the carbon black. Each was mixed and ground using a planetary mill in the same manner as in Example 1. The carbon-containing pulverized product in each example was heated in Ar gas at two temperatures of 700 ° C. and 800 ° C. for 8 hours and cooled at a rate of −200 ° C./hour to obtain silicate compound particles. The X-ray diffraction pattern of the obtained silicate compound almost coincided with that of olivine type lithium iron silicate.

In Examples 31, 32, 33, and 34, X-ray diffraction patterns of silicic acid compounds obtained by heating at 700 ° C. are shown in FIGS. 4 (a), (b), (c), and (d), respectively. Show. In Examples 31 and 34, the mixture was heated at 700 ° C. for 8 hours and cooled at a rate of −200 ° C./hour, and the carbon content of the obtained silicate compound particles was determined by a carbon analyzer (manufactured by Horiba, Ltd., device name: EMIA-920V) were 9.8% by mass (Example 31) and 9.7% by mass (Example 34), respectively. Moreover, when the specific surface area was measured, they were 28 m ² / g (Example 31) and 32 m ² / g (Example 34), respectively.

[Examples 38 to 41]
The coarsely pulverized product obtained by melting, quenching, and coarsely pulverizing in Examples 1, 2, 14, and 15, the carbon black and the sucrose aqueous solution, the C content in the pulverized product and carbon black, and the C content in sucrose. The mixture was mixed so that the mass ratio with respect to the content was 0.90: 0.05: 0.05, and pulverized and heated in the same manner as in Example 31 to obtain silicate compound particles. The X-ray diffraction pattern of the obtained silicate compound was the same as that of the olivine type lithium iron silicate as in Examples 31, 32, 35 and 36. In Examples 38 and 41, the carbon content of the silicate compound particles obtained by heating at 700 ° C. for 8 hours was measured with a carbon analyzer (manufactured by Horiba, apparatus name: EMIA-920V). They were 7 mass% (Example 38) and 7.4 mass% (Example 41). Moreover, when the specific surface area was measured, they were 48 m ² / g (Example 38) and 46 m ² / g (Example 41), respectively.

[Reference Example 1]
The composition of the melt is 38.5%, 38.5%, 7.7% and 15.4% in terms of Li ₂ O, FeO, SiO ₂ and Al ₂ O ₃ (unit: mol%). Lithium carbonate (Li ₂ CO ₃ ), triiron tetroxide (Fe ₃ O ₄ ), silicon dioxide (SiO ₂ ) and aluminum oxide (Al ₂ O ₃ ) were weighed, mixed and pulverized in a dry manner. A raw material formulation was obtained. The raw material formulation was melted in the same manner as in Example 1, but could not be melted. The composition of the raw material formulation corresponds to a = 0.8, b = 1, and x = 0.8 in the formula (1) of the present invention.

[Reference Example 2]
The composition of the melt is 32.3%, 48.4%, 6.5%, 3% in terms of Li ₂ O, FeO, SiO ₂ , B ₂ O ₃ , and Al ₂ O ₃ (unit: mol%). Lithium carbonate (Li ₂ CO ₃ ), triiron tetroxide (Fe ₃ O ₄ ), silicon dioxide (SiO ₂ ), boron oxide (B ₂ O ₃ ), oxidation to be 0.2% and 9.7% Aluminum (Al ₂ O ₃ ) was weighed, mixed and pulverized in a dry manner to obtain a raw material formulation. The raw material formulation was melted in the same manner as in Example 1, but could not be melted. The composition of the raw material formulation corresponds to a = 0, b = 2, c = 0.5, and x = 0.2 in the formula (3) of the present invention.

[Reference Example 3]
The composition of the melt is 32.8%, 34.5%, 31.0%, and 1.7% in terms of Li ₂ O, FeO, and SiO ₂ , and Al ₂ O ₃ (unit: mol%). Lithium carbonate (Li ₂ CO ₃ ), triiron tetroxide (Fe ₃ O ₄ ), silicon dioxide (SiO ₂ ) and aluminum oxide (Al ₂ O ₃ ) are weighed so that A raw material formulation was obtained. In the same manner as in Example 1, the raw material formulation was melted at 1,450 ° C. and then cooled at a cooling rate of −300 ° C./hour to obtain a crystallized product. When the mineral phase of the obtained crystallized product was identified using XRD, it was a coarse crystal mainly composed of Li ₂ SiO ₃ and Fe ₃ O ₄ . That is, after melting, cooling was performed at a slow cooling rate to obtain a crystallized product, and when the pulverization step and heating step in the present invention were not performed, the target compound could not be obtained.

[Reference Example 4]
The composition of the melt is Li ₂ O, FeO, and SiO ₂ , B ₂ O ₃ , and Al ₂ O ₃ equivalent (unit: mol%), 32.8%, 34.5%, 31.0%, Lithium carbonate (Li ₂ CO ₃ ), triiron tetroxide (Fe ₃ O ₄ ), silicon dioxide (SiO ₂ ), boron oxide (B ₂ O ₃ ) so as to be 0.85% and 0.85% And aluminum oxide (Al ₂ O ₃ ) was weighed, mixed and pulverized by a dry method, and a raw material formulation was obtained. In the same manner as in Example 1, the raw material formulation was melted at 1,450 ° C. and then cooled at a cooling rate of −300 ° C./hour to obtain a crystallized product. When the mineral phase of the obtained crystallized product was identified, it was a coarse crystal mainly composed of Li ₂ SiO ₃ and Fe ₃ O ₄ . That is, after melting, cooling was performed at a slow cooling rate to obtain a crystallized product, and when the pulverization step and heating step in the present invention were not performed, the target compound could not be obtained.

[Examples 42 to 46: Production of positive electrode for Li ion secondary battery and battery for evaluation]
In Examples 1, 2, 9, 14, and 15, silicic acid compound particles obtained by heating at 700 ° C. for 8 hours and cooling at a rate of −200 ° C./hour and an aqueous sucrose solution, The sucrose was mixed and ground so that the mass ratio with respect to the C content was 0.90: 0.10. The active material, polyvinylidene fluoride resin (binder) and acetylene black (conductive material) are weighed so that the mass ratio is 85: 5: 10, and in N-methylpyrrolidone (solvent). A slurry was prepared by mixing until uniform. Next, the slurry was applied to an aluminum foil having a thickness of 30 μm with a bar coater. After drying this at 120 degreeC in the air and removing a solvent, after consolidating the coating layer with the roll press, it cut out to the strip shape of width 10mm * length 40mm.

The coating layer was peeled off leaving a 10 × 10 mm tip of strip-shaped aluminum foil, which was used as an electrode. The coating thickness of the obtained electrode after roll pressing was 20 μm. The obtained electrode was vacuum-dried at 150 ° C., then carried into a glove box filled with purified argon gas, and opposed to a counter electrode made by pressure bonding a lithium foil to a nickel mesh with a porous polyethylene film separator, Both sides were fixed with a polyethylene plate.

Put the counter electrode in a polyethylene beaker and inject a non-aqueous electrolyte solution of lithium hexafluorophosphate dissolved in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (1: 1 volume ratio) at a concentration of 1 mol / L. Was impregnated. The electrode after impregnation with the electrolytic solution was taken out from the beaker, put in an aluminum laminate film bag, the lead wire part was taken out and sealed to form a half battery. The characteristics of this half-cell were measured as follows.

(Charge / discharge characteristic evaluation of positive electrode for Li ion secondary battery)
The obtained half-cell was placed in a constant temperature bath at 60 ° C. and connected to a constant current charge / discharge tester (manufactured by Hokuto Denko Co., Ltd., device name: HJ201B) to conduct a charge / discharge test. The current density was charged / discharged with the current value per mass of the electrode active material (the mass excluding the conductive material and the binder) being 16 mA / g. The end-of-charge potential was 4.2 V with respect to the Li counter electrode, and discharge was started immediately after reaching the end-of-voltage. The end-of-discharge voltage was 1.5 V with respect to the Li counter electrode. This charge / discharge cycle was repeated 5 times. The discharge capacities at the fifth cycle were 151 mAh / g (Example 42), 153 mAh / g (Example 43), 235 mAh / g (Example 44), 160 mAh / g (Example 45), and 155 mAh / g (implemented), respectively. Example 46).

[Examples 47 to 48]
Using the silicate compound particles obtained in Examples 38 and 40 as an active material, the active material, polyvinylidene fluoride resin (binder), and acetylene black (conductive material) in a mass ratio of 90: 5: 5 An electrode was produced in the same manner as in Example 42 except that the weight was measured so that the charge / discharge characteristics were evaluated in the same manner as in Example 42. The discharge capacities at the fifth cycle were 154 mAh / g (Example 47) and 161 mAh / g (Example 48), respectively.

[Reference Examples 5 and 6]
Using the pulverized material obtained in Reference Examples 3 and 4 as an active material, an electrode was produced in the same manner as in Example 42, and the charge / discharge characteristics were evaluated in the same manner as in Example 42. The discharge capacities at the first cycle were 5 mAh / g (Reference Example 5) and 7 mAh / g (Reference Example 6), respectively.

The method for producing a silicic acid compound of the present invention is useful because the composition of the silicic acid compound can be easily controlled and produced. The obtained silicic acid compound is useful for a positive electrode material for a secondary battery and further for a secondary battery. A secondary battery using the silicate-phosphate compound of the present invention as a positive electrode material is useful as a secondary battery mounted in a plug-in hybrid vehicle or an electric vehicle, and as a storage battery for storing power.
The entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2010-259360 filed on November 19, 2010 are cited herein as disclosure of the specification of the present invention. Incorporated.

Claims (17)

1. A method for producing a silicic acid compound having a composition represented by the following formula (B):
   _{A e M b Si x D 1} -x O f2 (B)
   (In the formula, A is at least one element selected from the group consisting of Li, Na and K. M is at least one element selected from the group consisting of Fe, Mn, Co and Ni, and D is Al, or Al and B. e is 0.8 <e <2.4, b is 0.7 ≦ b ≦ 1.3, x is 0.3 ≦ x <1, f2 is a number depending on the valence N of e, b, x and M.)
   A raw material formulation prepared by adjusting a raw material containing the elements A, M, Si, and D so that the molar ratio of the elements A, M, Si, and D is the molar ratio represented by the formula (B) Heating to obtain a melt,
   A cooling step of cooling the melt to obtain a solidified product,
   A pulverization step of pulverizing the solidified product to obtain a pulverized product, and a heating step of heating the pulverized product to obtain a silicate compound.
   Are carried out in this order. A method for producing a silicic acid compound.
2. A melting step for obtaining a melt having a composition represented by the following formula (A):
   A cooling step of cooling the melt to obtain a solidified product,
   A pulverization step of pulverizing the solidified product to obtain a pulverized product, and a heating step of heating the pulverized product to obtain a silicate compound having a composition represented by the following formula (B):
   The manufacturing method of the silicic acid compound of Claim 1 which implements in this order.
   A _e M _b Si _x D _1-x O _f1 (A)
   (In the formula, A is at least one element selected from the group consisting of Li, Na and K. M is at least one element selected from the group consisting of Fe, Mn, Co and Ni, and D is Al, or Al and B. e is 0.8 <e <2.4, b is 0.7 ≦ b ≦ 1.3, x is 0.3 ≦ x <1, f1 is a number that depends on the valence N of e, b, x, and M, and is a number that becomes f2 after the heating step.)
   _{A e M b Si x D 1} -x O f2 (B)
   (In the formula, A, M, D, e, b and x have the same meanings as described above, but are independent values, and f2 is a number depending on the valence N of e, b, x and M. .)
3. The melt having the composition represented by the formula (A) is a melt having the composition represented by the following formula (1), and the silicate compound having the composition represented by the formula (B) is: The method for producing a silicic acid compound according to claim 2, wherein the silicic acid-aluminic acid compound has a composition represented by the following formula (2).
   A _{1 + x + a} M _b Si _x Al _1-x O _{3 + x + d11} (1)
   A _{1 + x + a} M _b Si _x Al _1-x O _{3 + x + d12} (2)
   (In the formula, A, M, x and b have the same meaning as described above, a is −0.1 ≦ a ≦ 0.4, and d11 is a number depending on the valence N of a, b and M. There is a number that becomes d12 after the heating step, and d12 is a number that depends on the valence N of a, b, and M. However, in the formulas (1) and (2), a, b, and x are Independent values are shown.)
4. The melting step is
   The compound containing element A is A carbonate, A bicarbonate, A hydroxide, A silicate, A aluminate, A nitrate, A chloride, A sulfate, At least one selected from the group consisting of A acetate and A oxalate (however, one or more of the one or more may each form a hydrate salt). ,
   The compound containing element M is M oxide, M hydroxide, M oxyhydroxide, M silicate, M aluminate, metal M, M chloride, M nitrate, M And at least one selected from the group consisting of an organic salt of M
   A compound containing Si is included as at least one selected from the group consisting of silicon oxide, A silicate, M silicate, aluminosilicate, and silicon alkoxide,
   A compound containing Al is included as at least one selected from the group consisting of aluminum oxide, aluminum oxyhydroxide, aluminosilicate, aluminum chloride, aluminum nitrate, and aluminum sulfate.
   The manufacturing method of the silicic acid compound of Claim 3 which is a process of heating a raw material formulation and obtaining the melt which has a composition represented by said Formula (1).
5. The melt having the composition represented by the formula (A) is a melt having the composition represented by the following formula (3), and the silicic acid compound having the composition represented by the formula (B) is: The method for producing a silicic acid compound according to claim 2, which is a silicic acid-boric acid-aluminic acid compound having a composition represented by the following formula (4).
   A _{1 + x + a} M _b Si _x (B _c Al _1-c ) _1-x O _{3 + x + d21} (3)
   A _{1 + x + a} M _b Si _x (B _c Al _1-c ) _1-x O _{3 + x + d22} (4)
   Wherein A, M, x and b have the same meaning as described above, a is −0.1 ≦ a ≦ 0.4, c is 0 <c <1, d21 is a, b and It is a number that depends on the valence N of M, and is a number that becomes d22 after the heating step, and d22 is a number that depends on the valence N of a, b, and M. However, the equations (3) and (4 ) A, b, c, and x are independent values.)
6. The melting step is
   Compound containing element A is A carbonate, A bicarbonate, A hydroxide, A silicate, A borate, A aluminate, A nitrate, A chloride , At least one selected from the group consisting of A sulfate, A acetate, and A oxalate (however, one or more of the one or more may each form a hydrate salt) Included.)
   Compound containing element M is M oxide, M hydroxide, M oxyhydroxide, M silicate, M borate, M aluminate, metal M, M chloride And at least one selected from the group consisting of M nitrate, M sulfate and M organic salt,
   A compound containing Si is included as at least one selected from the group consisting of silicon oxide, A silicate, M silicate, borosilicate, aluminosilicate, and silicon alkoxide,
   A compound containing B is included as at least one selected from the group consisting of boron oxide, boric acid, A borate, M borate, borosilicate and aluminum borate,
   A compound containing Al is included as at least one selected from the group consisting of aluminum oxide, aluminum oxyhydroxide, aluminosilicate, aluminum borate, aluminum chloride, aluminum nitrate, and aluminum sulfate.
   The manufacturing method of the silicic acid compound of Claim 5 which is a process of heating a raw material formulation and obtaining the melt which has a composition represented by said Formula (3).
7. The method for producing a silicate compound according to any one of claims 1 to 6, wherein the element A is Li.
8. The method for producing a silicate compound according to any one of claims 1 to 7, wherein the element M is at least one element selected from the group consisting of Fe and Mn.
9. The melt having the composition represented by the formula (1) is a melt having the composition represented by the following formula (5A), and the silicic acid-aluminic acid having the composition represented by the formula (2) The manufacturing method of the silicic acid compound of Claim 3 whose compound is a compound containing the olivine type | mold crystal particle which has a composition represented by the following Formula (5).
   Li _{1 + x + a} (Fe _y Mn _1-y ) _b Si _x Al _1-x O _{3 + x + d11} (5A)
   Li _{1 + x + a} (Fe _y Mn _1-y ) _b Si _x Al _1-x O _{3 + x + d12} (5)
   (Wherein, a, b, d11, d12 and x have the same meaning as described above, and y is 0 ≦ y ≦ 1, provided that in formulas (5A) and (5), a, b, x, And y are independent values.)
10. The melt having the composition represented by the formula (3) is a melt having the composition represented by the following formula (6A), and the silicic acid-boric acid having the composition represented by the formula (4) The method for producing a silicate compound according to claim 5, wherein the aluminate compound is a compound containing olivine type crystal particles having a composition represented by the following formula (6).
    _{Li 1 + x + a (Fe} y Mn 1-y) b Si x (B c Al 1-c) 1-x O 3 + x + d21 (6A)
    Li _{1 + x + a} (Fe _y Mn _1-y ) _b Si _x (B _c Al _1-c ) _1-x O _{3 + x + d22} (6)
    (In the formula, a, b, c, d21, d22 and x have the same meaning as described above, and y is 0 ≦ y ≦ 1, provided that in formula (6A) and formula (6), a, b, c, x, and y are independent values.)
11. The method for producing a silicate compound according to any one of claims 1 to 10, wherein in the cooling step, a cooling rate is set to -10 ³ ° C / second to -10 ¹⁰ ° C / second.
12. In the pulverization step, the solidified product contains at least one carbon source selected from the group consisting of an organic compound and a carbon powder, and a ratio of a carbon conversion amount (mass) in the carbon source is a solidified product. The production of a silicate compound according to any one of claims 1 to 11, which is 0.1 to 20% by mass with respect to the total mass of the mass of the carbon and the carbon equivalent amount (mass) in the carbon source. Method.
13. The method for producing a silicate compound according to any one of claims 1 to 12, wherein the heating step is performed by heating to 500 to 1,000 ° C.
14. A silicate compound is obtained by the production method according to any one of claims 1 to 13, and then the silicate compound is used as a cathode material for a secondary battery to produce a cathode for a secondary battery. A method for producing a positive electrode for a secondary battery.
15. A method for producing a secondary battery, comprising: obtaining a positive electrode for a secondary battery by the production method according to claim 14, and then producing a secondary battery using the positive electrode for the secondary battery.
16. A silicic acid-aluminic acid compound having a composition represented by the following formula (ii):
    _{A e M b Si x Al 1} -x O f2 (ii)
    (Wherein A is at least one element selected from the group consisting of Li, Na and K, and M is at least one element selected from the group consisting of Fe, Mn, Co and Ni. E is 0.8 <e <2.4, b is 0.7 ≦ b ≦ 1.3, x is 0.3 ≦ x <1, and f2 is the valence of e, b, x and M The number depends on N.)
17. A silicic acid-boric acid-aluminic acid compound having a composition represented by the following formula (iv):
    _{A e M b Si x (B} c Al 1-c) 1-x O f2 (iv)
    (Wherein A is at least one element selected from the group consisting of Li, Na and K, and M is at least one element selected from the group consisting of Fe, Mn, Co and Ni. E is 0.8 <e <2.4, b is 0.7 ≦ b ≦ 1.3, x is 0.3 ≦ x <1, c is 0 <c <1, and f2 is (The number depends on the valence N of e, b, x and M.)

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