WO2011138964A1 - (silicic acid)-(phosphoric acid) compound, positive electrode for secondary battery, and process for production of secondary battery - Google Patents

Abstract

Disclosed is a process for producing a (silicic acid)-(phosphoric acid) compound, which enables the production of the (silicic acid)-(phosphoric acid) compound that has excellent battery properties and excellent reliability at low cost and with high efficiency. A (silicic acid)-(phosphoric acid) compound having a chemical composition represented by the following formula: A_xM_ySi_aP_1-aO_z (0.8 < x < 1.2, 0. 8< y < 1.2 and 0.35 ≤ a ≤ 0.95) can be produced by solidifying a molten material by cooling, milling the solidified product, and heating the milled product, wherein the molten material is produced by heating a raw material preparation which comprises at least one atom (A) selected from the group consisting of Li, Na and K, at least one atom (M) selected from the group consisting of Fe, Mn, Co and Ni, Si and P and which contains these atoms in amounts that are expressed in terms of the following oxide contents (mol%): 15% < A₂O < 30%, 35% < MO < 55%, 15% < SiO₂ < 50% and 1% < P₂O₅ < 18%, wherein the A₂O/(0.5SiO₂+P₂O₅) ratio is 0.8 to 1.2 exclusive and the A₂O/0.5MO ratio is 0.8 to 1.2 exclusive.

Description

Silicic acid-phosphoric acid compound, positive electrode for secondary battery, and method for producing secondary battery

The present invention relates to a silicic acid-phosphoric acid compound, a positive electrode for a secondary battery, and a method for producing a secondary battery.

In recent years, lithium ion secondary batteries have been widely used as power sources for portable electronic devices such as mobile phones and laptop computers, and portable power tools. Application of a lithium ion secondary battery as a power source for an electric vehicle is desired, and attempts have been made to increase the capacity of the positive electrode material of the lithium ion secondary battery in order to realize the application to a power source for an electric vehicle.

As a next-generation cathode material for lithium ion secondary batteries, from the viewpoint of resources, safety, cost, stability, etc., olivine-type phosphate compounds represented by olivine-type lithium iron phosphate (LiFePO ₄ ) ( LiMPO ₄ and M are transition metal elements) have attracted attention, and their production methods are being studied.

Patent Document ^{_{1, Li a M 1 (2}} -b) M 2 b Si c P 3-c O 12 (0 ≦ b ≦ 2,0 <c <3, a is selected to balance the formula In addition, a silicon phosphate compound represented by the following formula has been proposed: the number of Li atoms is greater than 0, and M ¹ and M ² are the same or different transition metal elements. It has been suggested that a portion of PO ₄ which is a polyanion is replaced with SiO ₂ .

In Patent Document 2, a mixture containing a transition metal atom M oxide such as Li ₂ O and Fe ₂ O ₃ and P ₂ O ₅ is melted, and the resulting melt is quenched to obtain a precursor glass. After the formation, the precursor glass is baked to deposit LiFePO ₄ crystals, LiMn _x Fe _1-x PO ₄ crystals (0 <x <1), etc., thereby producing a positive electrode material for a secondary battery. It is described to do.

Special table 2002-519836 gazette JP 2009-087933 A

Since the manufacturing method described in Patent Document 1 is manufactured by reacting raw materials, the manufacturing process is complicated and the manufacturing cost increases. Moreover, although manufacture of the silicon phosphate compound is suggested, the example actually manufactured is not described in the Example.
In the production method described in Patent Document 2, it is difficult to control the composition of the silicic acid-phosphoric acid compound particles. Also, be contained _{Nb 2 O 5, V 2 O} 5, SiO 2, Sb 2 O 3 and _Bi 2 _{O 3} or the like for the purpose of improving the vitrification, the molar ratio of _P 2 _{O 5} in terms of oxide Since it has a relatively high glass composition, the upper limit of the heating temperature for melting the raw material is limited to a temperature at which P does not evaporate. For this reason, there existed a problem that manufacturing conditions were restrict | limited.

An object of the present invention is to provide a method that makes it easy to control the composition of a silicic acid-phosphoric acid compound and that is easy to manufacture. According to the method of the present invention, a method for producing a silicic acid-phosphoric acid compound having excellent battery characteristics and reliability at low cost and efficiently can be provided. Furthermore, this invention provides the manufacturing method of the positive electrode for secondary batteries which is excellent in a battery characteristic and reliability, and a secondary battery.

The present invention is the following [1] to [15].

[1] including at least one atom A selected from the group consisting of Li, Na and K, at least one atom M selected from the group consisting of Fe, Mn, Co and Ni, and Si and P (However, at least one selected from the group consisting of atom A, atom M, Si, and P is included as an oxide.) The oxide equivalent amount of each atom when it becomes a melt (unit: Mol%)
15% <A ₂ O <30%,
35% <MO <55%,
15% <SiO ₂ <50%,
1% <P ₂ O ₅ <18%,
0.8 <A ₂ O / (0.5SiO ₂ + P ₂ O ₅ ) <1.2,
0.8 <A ₂ O / 0.5MO <1.2,
Heating the raw material formulation to obtain a melt,
Cooling the melt to obtain a solidified product,
A step of pulverizing the solidified product to obtain a pulverized product, and a heating step of heating the pulverized product to obtain a silicic acid-phosphoric acid compound having a composition represented by the following formula (1):
A process for producing a silicic acid-phosphoric acid compound, comprising:
_{A x M y Si a P 1} -a O z (1)
(In the formula, A and M are the same kind of atoms as described above, and x, y and a are 0.8 <x <1.2, 0.8 <y <1.2, 0.35 ≦ a ≦ 0.95, and z is a number depending on the valence N of x, y, a and M.)
[2] At least one atom A selected from the group consisting of Li, Na and K, at least one atom M selected from the group consisting of Fe, Mn, Co and Ni, and Si and P (provided that And at least one selected from the group consisting of A, atoms M, Si and P is included as an oxide.), And an oxide equivalent amount (unit: Mol%)
15% <A ₂ O <30%,
35% <MO <55%,
15% <SiO ₂ <50%,
1% <P ₂ O ₅ <18%,
0.8 <A ₂ O / (0.5SiO ₂ + P ₂ O ₅ ) <1.2,
0.8 <A ₂ O / 0.5MO <1.2,
Obtaining a melt that is a step of cooling the melt to obtain a solidified product,
Pulverizing the solidified product to obtain a pulverized product, and heating the pulverized product to obtain a silicic acid-phosphoric acid compound having a composition represented by the following formula (1):
A method for producing a silicic acid-phosphoric acid compound comprising:
_{A x M y Si a P 1} -a O z (1)
(In the formula, A and M are the same kind of atoms as described above, and x, y and a are 0.8 <x <1.2, 0.8 <y <1.2, 0.35 ≦ a ≦ 0.95, and z is a number depending on the valence N of x, y, a and M.)
[3] The atom A contained in the raw material preparation is A carbonate, A bicarbonate, A hydroxide, A phosphate and hydrogen phosphate, A nitrate, A chloride. At least one selected from the group consisting of a product, sulfate of A, acetate of A, and oxalate of A (provided that a part or all of the one or more forms a hydrate salt, respectively) May be included),
Atom M is selected from the group consisting of M oxide, M oxyhydroxide, M metal, M phosphate, M chloride, M nitrate, M sulfate, and M organic salt Included as at least one
Si is a silicate of A selected from the group consisting of silicon oxide, A ₂ SiO ₃ and A ₄ SiO ₄ (where A is the same kind of atom as described above), and MSiO ₃ and M ₂ SiO ₄ M silicate selected from the group consisting of (wherein M is the same kind of atom as described above), and included as at least one selected from the group consisting of:
P is at least one selected from the group consisting of phosphorus oxide, ammonium phosphate, ammonium hydrogen phosphate, phosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, A phosphate, and M phosphate A method for producing a silicic acid-phosphoric acid compound of [1] or [2], which is contained as a seed.
[4] The method for producing a silicic acid-phosphoric acid compound of [1] to [3], wherein the atom A is Li.
[5] The method for producing a silicic acid-phosphoric acid compound of [1] to [4], wherein the atom M is at least one selected from the group consisting of Fe and Mn.
[6] The silicic acid-phosphoric acid compound having the composition represented by the formula (1) is a crystal particle of a compound having the composition represented by the following formula (2): [1] to [3] A method for producing a silicic acid-phosphoric acid compound.
Li _x (Fe _b Mn _1-b ) _y Si _a P _1-a O _z (2)
(In the formula, x, y, z and a are respectively the same numerical values as above, and b is 0 ≦ b ≦ 1.)
[7] The silicic acid-phosphate compound of [6], wherein the crystal grains of the compound having the composition represented by the formula (2) are the crystal grains of the compound having the composition represented by the following formula (3) Manufacturing method.
_{LiFe b Mn 1-b Si a} P 1-a O z (3)
(In the formula, z, a and b are the same numerical values as described above.)
[8] In the pulverization step, the solidified product includes at least one carbon source selected from the group consisting of an organic compound and a carbon-based conductive active material, and the amount of the carbon source is determined based on the amount of the solidified product and carbon. The silicic acid-phosphoric acid of [1] to [7], wherein the ratio of the carbon conversion amount (mass) to the total mass with the carbon conversion amount (mass) in the source is 0.1 to 20% by mass A method for producing a compound.
[9] The method for producing a silicic acid-phosphate compound according to [1] to [8], wherein in the step of obtaining the solidified product, a cooling rate is −10 ³ ° C./second to −10 ¹⁰ ° C./second.
[10] The method for producing a silicic acid-phosphoric acid compound according to any one of [1] to [9], wherein the solidified product is a solid compound containing an amorphous part.
[11] The production of the silicic acid-phosphoric acid compound of [1] to [10], wherein the step of obtaining the silicic acid-phosphoric acid compound is performed in an inert gas or a reducing gas at 500 ° C. to 1,000 ° C. Method.

[12] A silicic acid-phosphoric acid compound having a composition represented by the following formula (1):
_{A x M y Si a P 1} -a O z (1)
Wherein A is at least one atom selected from the group consisting of Li, Na and K, M is at least one atom selected from the group consisting of Fe, Mn, Co and Ni, and x, y and a is 0.8 <x <1.2, 0.8 <y <1.2, 0.35 ≦ a ≦ 0.95, and z is the valence N of x, y, a, and M. Depends on the number.)

[13] The conductive carbonaceous layer may be 0.1 to 20% by mass of the silicic acid-phosphoric acid compound particles based on the total mass of the silicic acid-phosphoric acid compound and the conductive carbonaceous layer. The silicic acid-phosphoric acid compound according to [12], which is contained on the surface of the particle or the interparticle interface.
[14] Obtaining a silicic acid-phosphoric acid compound by the production method of [1] to [11], and producing a secondary battery positive electrode using the silicic acid-phosphoric acid compound as a positive electrode material for a secondary battery. The manufacturing method of the positive electrode for secondary batteries characterized by these.

[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.

The method for producing a silicic acid-phosphoric acid compound of the present invention provides a method for efficiently producing a silicic acid-phosphoric acid compound using an inexpensive raw material and a simple technique. In the production method of the present invention, since the composition of the silicic acid-phosphoric acid compound is easily controlled, a silicic acid-phosphoric acid compound having a desired composition can be produced efficiently. Therefore, by using the silicic acid-phosphoric acid compound obtained by the present invention, a positive electrode for secondary batteries and a secondary battery excellent in battery characteristics and reliability can be produced.
The present invention also provides a silicic acid-phosphoric acid compound that is excellent in battery characteristics and reliability.

FIG. 3 is a diagram showing an X-ray diffraction pattern of silicic acid-phosphoric acid compound particles produced in Examples 1, 3 and 6. FIG. 4 is a view showing an X-ray diffraction pattern of silicic acid-phosphoric acid compound particles produced in Examples 13 and 14.

In the following description, A represents at least one atom selected from the group consisting of Li, Na and K. A represents an atom of the above three alkali metal elements. A may consist of a combination of two or more atoms. M represents at least one atom selected from the group consisting of Fe, Mn, Co and Ni. M represents an atom of the above four transition metal elements. M may consist of a combination of two or more atoms. In addition, chemical formulas, such as Formula (1), Formula (2), Formula (3), represent an average composition.
A crystal having an olivine structure is hereinafter referred to as an olivine crystal, and a particle containing the olivine crystal is also referred to as an olivine crystal particle. The olivine-type crystal particle may partially include a crystal structure other than the olivine-type crystal structure, or may partially include an amorphous structure. It is preferable that substantially all of the olivine type crystal particles are made of olivine type crystals.

[Method for producing silicic acid-phosphoric acid compound]
In the method for producing a silicic acid-phosphoric acid compound of the present invention, the following step (1), step (2), step (3), and step (4) are performed in this order. Other steps may be performed before, between and after the steps (1) to (4) as long as each step is not affected.
Step (1): at least one atom A selected from the group consisting of Li, Na and K; at least one atom M selected from the group consisting of Fe, Mn, Co and Ni; The oxide equivalent amount (unit: mol%) of the content of each atom when it becomes a product is 15% <A ₂ O <30%, 35% <MO <55%, 15% <SiO ₂ <50% 1% <P ₂ O ₅ <18%, 0.8 <A ₂ O / (0.5SiO ₂ + P ₂ O ₅ ) <1.2, 0.8 <A ₂ O / 0.5MO <1 .2. Heating the raw material formulation to obtain a melt,
Step (2): a step of cooling the melt to obtain a solidified product,
Step (3): pulverizing the solidified product to obtain a pulverized product,
Step (4): A step of heating the pulverized product to obtain a silicic acid-phosphoric acid compound having a composition represented by the formula (1).

In the production method of the present invention, since it can be melted in a wide composition range by forming a melt having the above composition in step (1), the following step (2), step (3), and step (4) are performed. As a result, a silicic acid-phosphoric acid compound having a desired composition represented by the formula (1) can be obtained. Accordingly, it is possible to produce a silicic acid-phosphoric acid compound having a composition not described in Patent Document 1.

In the production method of the present invention, since the composition has a relatively low molar ratio of P ₂ O _{5 in} terms of oxide, the material cost can be reduced. Moreover, since the upper limit of the heating temperature at the time of melting a raw material formulation rises, a melting temperature range can be expanded and it becomes easy to manufacture.
Hereinafter, each step will be specifically described.

(Process (1))
In the step (1), first, at least one atom A selected from the group consisting of Li, Na and K, at least one atom M selected from the group consisting of Fe, Mn, Co and Ni, Si and (Wherein at least one selected from the group consisting of atom A, atom M, Si and P is included as an oxide), and an oxide having a content of each atom when it becomes a melt The conversion amount (unit: mol%) is 15% <A ₂ O <30%, 35% <MO <55%, 15% <SiO ₂ <50%, 1% <P ₂ O ₅ <18%, A raw material formulation having 0.8 <A ₂ O / (0.5SiO ₂ + P ₂ O ₅ ) <1.2 and 0.8 <A ₂ O / 0.5MO <1.2 is obtained. Subsequently, the raw material formulation is heated to obtain a melt. Before the raw material preparation is heated, it may be mixed, pulverized and heated to obtain a melt. Alternatively, the raw material preparation may be manufactured after each raw material has been pulverized in advance. The raw material mixture is mixed and pulverized using a ball mill, a jet mill, a planetary mill or the like in a dry or wet manner. A dry method is preferable in that it is not necessary to remove the dispersion medium.

If the melt has a composition satisfying 15% <A ₂ O <30%, 35% <MO <55%, 15% <SiO ₂ <50%, and 1% <P ₂ O ₅ <18% This is preferable because the product can be easily melted. When A ₂ O is 15% or less, MO is 55% or more, SiO ₂ is 15% or less, or P ₂ O ₅ is 1% or less, it is difficult to melt the raw material preparation. On the other hand, when A ₂ O is 30% or more, MO is 35% or less, SiO ₂ is 50% or more, or P ₂ O ₅ is 18% or more, it is difficult to obtain the target silicic acid-phosphate compound. It becomes. In addition, it melt | dissolves here means that a raw material formulation melt | dissolves and it will be in a transparent state visually.

The melt further has a composition satisfying 18% <A ₂ O <25%, 40% <MO <50%, 17% <SiO ₂ <38%, and 1% <P ₂ O ₅ <18%. The desired silicic acid-phosphoric acid compound can be obtained, which is particularly preferable.

Further, when the composition satisfies 0.8 <A ₂ O / (0.5SiO ₂ + P ₂ O ₅ ) <1.2 and 0.8 <A ₂ O / 0.5MO <1.2, the formula (1 It is preferable because a silicic acid-phosphoric acid compound having a composition represented by

The melt is not limited to those consisting only of atoms A, atoms M, silicon (Si), phosphorus (P), and oxygen (O), but from Ti, V, B, Al, Ca, Cu, Mg, and Zn. It may contain at least one atom X selected from the group consisting of By containing the atom X, the raw material preparation can be easily melted. The content of atoms X (the total amount in the case of a plurality of atoms) is 0.1 to 5% in terms of oxide content (unit: mol%) of the content of each atom when it becomes a melt. preferable.

In the raw material formulation, atoms A, atoms M, Si and P are converted into oxides (unit: mol%) of the content of each atom when it becomes a melt, and 15% <A ₂ O <30% 35% <MO <55%, 15% <SiO ₂ <50%, 1% <P ₂ O ₅ <18%, 0.8 <A ₂ O / (0.5SiO ₂ + P ₂ O ₅ ) < The raw materials are selected and mixed so that a melt satisfying 1.2, 0.8 <A ₂ O / 0.5MO <1.2 is obtained. The raw material is a compound containing atom A, a compound containing atom M, a compound containing Si, a compound containing P, or a compound containing atom X as necessary.

<Compound containing atom A>
A may be at least one atom selected from the group consisting of Li, Na and K. However, since it is suitable as a positive electrode material for a secondary battery, it is preferable to make Li essential. It is particularly preferred. The silicic acid-phosphoric acid compound containing Li can increase the capacity per unit volume (mass) of the secondary battery.

Compounds containing an atom A include A carbonate (A ₂ CO ₃ ), A bicarbonate (AHCO ₃ ), A hydroxide (AOH), A phosphate and hydrogen phosphate (A _t H _3−t PO ₄ , 0 <t ≦ 3), A nitrate (ANO ₃ ), A chloride (ACl), A sulfate (A ₂ SO ₄ ), A acetate (CH ₃ COOA) ) And A oxalate ((COOA) ₂ ), and at least one selected from the group consisting of (COOA) ₂ ) (however, these compounds may each form a hydrate salt). Among these, A ₂ CO ₃ or AHCO ₃ is particularly preferable because it is inexpensive and easy to handle.

<Compound containing atom M>
M may be at least one atom selected from the group consisting of Fe, Mn, Co and Ni. In the case where the silicic acid-phosphoric acid compound is applied to the positive electrode material for secondary batteries, it is preferable to use at least one atom selected from the group consisting of Fe and Mn as M from the viewpoint of cost. Fe is particularly preferable because the theoretical capacity of the positive electrode material for a secondary battery is easily developed. From the viewpoint of increasing the operating voltage, at least one atom selected from the group consisting of Co and Ni is preferable.

As the compound containing the atom M, oxides of M (FeO, Fe ₃ O ₄ , Fe ₂ O ₃ , MnO, Mn ₂ O ₃ , MnO ₂ , CoO, Co ₃ O ₄ , Co ₂ O ₃ , NiO), Oxyhydroxide (MO (OH)) of element M, metal M, M phosphate (M ₃ (PO ₄ ) ₂ , MPO ₄ ), M chloride, M nitrate, M sulfate, M At least one selected from the group consisting of organic salts and the like is preferred. Among these, Fe ₃ O ₄ , Fe ₂ O ₃ , MnO ₂ , Co ₃ O ₄ or NiO is more preferable because it is inexpensive and easy to handle. Fe ₃ O ₄ , Fe ₂ O ₃ or MnO ₂ is particularly preferred.

<Compound containing Si>
As the compound containing Si, silicate of A selected from the group consisting of silicon oxide (SiO ₂ ), A ₂ SiO ₃ and A ₄ SiO ₄ (where A is the same kind of atom as described above), And at least one selected from the group consisting of M silicates selected from the group consisting of MSiO ₃ and M ₂ SiO ₄ (wherein M is the same type of atom as described above). Of these, SiO ₂ is particularly preferable from the viewpoint of inexpensiveness. Note that the compound containing Si may be crystalline or amorphous.

<Compound containing P>
As the compound containing P, phosphorus oxide (P ₂ O ₅ ), ammonium phosphate ((NH ₄ ) ₃ PO ₄ ), ammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ , NH ₄ H ₂ PO ₄ ), Phosphoric acid (H ₃ PO ₄ ), polyphosphoric acid (H _{(n + 2)} P _n O _{(3n + 1)} ), phosphorous acid (H ₃ PO ₃ ), hypophosphorous acid (H ₃ PO ₂ ), A phosphate And at least one selected from the group consisting of M phosphates and the like. Among these, NH ₄ H ₂ PO ₄ , (NH ₄ ) ₂ HPO ₄ , A phosphate or P ₂ O ₅ is particularly preferable because it is inexpensive and easy to handle.

A suitable combination of a compound containing atom A as a raw material formulation, a compound containing atom M, a compound containing Si, and a compound containing P is:
Compounds containing atom A are A carbonate (A ₂ CO ₃ ), bicarbonate (AHCO ₃ ), A hydroxide (AOH), A phosphate and hydrogen phosphate (A _t H _{3 -T} PO ₄ , 0 <t ≦ 3), 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 oxalates of A (however, these compounds may each form a hydrate salt);
A compound containing an atom M is an oxide 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), M Oxyhydroxide (MO (OH)), metal M, M phosphate (M ₃ (PO ₄ ) ₂ , MPO ₄ ), M chloride, M nitrate, M sulfate, and M At least one selected from the group consisting of organic salts,
A compound containing Si is a silicate of A selected from the group consisting of silicon oxide (SiO ₂ ), A ₂ SiO ₃ and A ₄ SiO ₄ (wherein A is the same kind of atom as described above), and And at least one selected from the group consisting of M silicates selected from the group consisting of MSiO ₃ and M ₂ SiO ₄ (wherein M is the same type of atom as described above), and
Compounds containing P are phosphorous oxide (P ₂ O ₅ ), ammonium phosphate ((NH ₄ ) ₃ PO ₄ ), ammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ , NH ₄ H ₂ PO ₄ ), phosphorus Acid (H ₃ PO ₄ ), polyphosphoric acid (H _{(n + 2)} P _n O _{(3n + 1)} ), phosphorous acid (H ₃ PO ₃ ), hypophosphorous acid (H ₃ PO ₂ ), and A phosphate And a combination which is at least one selected from the group consisting of M phosphates.
More preferably,
The compound containing atom A is a carbonate of A (A ₂ CO ₃ ) or a bicarbonate (AHCO ₃ );
The compound containing the atom M is an oxide 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) or M Oxyhydroxide (MO (OH)) of
The compound containing Si is silicon oxide (SiO ₂ ),
The combination in which the compound containing P is ammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ , NH ₄ H ₂ PO ₄ ).

In principle, the composition of the raw material formulation corresponds theoretically to the composition of the melt obtained from the raw material formulation. However, in this raw material formulation, there are components that are easily lost due to volatilization etc. during melting, such as Li, P, etc., so the composition of the resulting melt is determined by each element calculated from the amount of each raw material charged. May be slightly different from the oxide equivalent amount (unit: mol%).

Although the purity of the raw material in a raw material formulation is not specifically limited, The range which does not reduce a desired characteristic is preferable. The purity excluding the water of hydration is preferably 99% or more, particularly preferably 99.9% or more. Further, the particle size of the raw material is not particularly limited as long as it is within a range in which a uniform melt can be obtained by melting.

The container used for heating is preferably made of alumina, carbon, silicon carbide, zirconium boride, titanium boride, boron nitride, platinum or platinum containing rhodium, but refractory bricks should be used. You can also. Furthermore, it is preferable to attach a lid to the container in order to prevent volatilization and evaporation.

Heating is preferably performed using a resistance heating furnace, a high frequency induction furnace or a plasma arc furnace. The electric resistance furnace is particularly preferably an electric furnace provided with a heating element made of a metal such as a nichrome alloy, silicon carbide, or molybdenum silicide.

<Melting conditions>
The temperature at which the raw material mixture is heated and melted is preferably 1,250 ° C. to 1,550 ° C., particularly preferably 1,350 ° C. to 1,500 ° C. When the melting temperature is not less than the lower limit of the above range, melting becomes easy, and when it is not more than the upper limit, the raw material is hardly volatilized.
The time for heating and melting the raw material preparation is preferably 0.2 to 2 hours, particularly preferably 0.5 to 2 hours. If the melting time is not less than the lower limit of the above range, the uniformity of the melt will be sufficient, and if it is not more than the upper limit, the raw material components will not easily evaporate.

(Process (2))
In step (2), the melt obtained in step (1) is rapidly cooled to around room temperature (20 to 25 ° C.) to obtain a solidified product. The solidified product preferably contains an amorphous part. By including the amorphous part, it is softer than the crystalline part and thus easily pulverized, and the material diffusion in the amorphous part is fast, so that the reactivity can be increased. It becomes easy to control the composition of the silicic acid-phosphoric acid compound. Furthermore, in the post-process (4), the product can be prevented from being agglomerated, and the particle size of the product can be easily controlled. The amorphous part is preferably 80 to 100% by mass of the solidified product. It is preferable for the amorphous part to be in this range because the solidified product is easily pulverized and the reactivity is increased. When a large amount of crystalline part is contained, it becomes difficult to obtain a granular or flaky solidified product. Further, the wear of the cooling device is remarkably accelerated, and the burden of the subsequent step (3) is increased.

The cooling of the melt is preferably performed in an inert gas or a reducing gas because the equipment is simple. According to this cooling method, an amorphous substance can be obtained more easily.
The cooling rate 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 −1 × 10 ⁸ ° C./second is particularly preferable from the viewpoint of practicality.

As a method for cooling the melt, a method in which the melt is dropped between twin rollers rotating at high speed, a method in which the melt is dropped on a single rotating roller, and cooling is performed, or a carbon plate on which the melt is cooled. Alternatively, a method of cooling by pressing on a metal plate is preferable. Among these, a cooling method using twin rollers is particularly 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. In addition, a fiber-like solidified material can be obtained by winding a fiber-like solidified material (long fiber) continuously from the melt with a drum that rotates at high speed, or by using a spinner that rotates at high speed and has pores on the side walls. You may use the method of obtaining (short fiber). If these apparatuses are used, the melt is effectively cooled, and a solidified product having a high purity and a uniform chemical composition can be obtained.
In addition, as a cooling method, there is also a method in which the melt is directly poured into water, but this method is difficult to control, it is difficult to obtain an amorphous material, the solidified product becomes a lump, and the disadvantage of requiring a lot of labor for grinding There is. As a cooling method, there is also a method in which a melt is directly added to 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 is preferably flaky or fibrous.
In the case of flakes, the average thickness is preferably 200 μm or less, particularly preferably 100 μm or less. The average diameter of the surface perpendicular to the average thickness in the case of flakes is not particularly limited. In the case of a fibrous form, the average diameter is preferably 50 μm or less, particularly preferably 30 μm or less. By setting the average thickness and the average diameter to be equal to or less than the above upper limit values, it is possible to reduce the time and labor of the subsequent step (3) 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.

(Process (3))
Step (3) is a step of pulverizing the solidified product obtained in step (2) to obtain a pulverized product. The solidified product may contain at least one carbon source selected from the group consisting of an organic compound and a carbon-based conductive active material. The solidified product may be pulverized after containing the carbon source. Alternatively, the solidified product may be pulverized in advance and then mixed with the carbon source. The solidified product and the carbon source may be pulverized in advance. You may mix. The carbon source has an action of preventing oxidation and promoting reduction in the steps (3) and (4). Since the carbon source is mixed with the solidified product and pulverized to uniformly coat the surface of the solidified product or exists at the interface between the solidified products, a silicic acid-phosphate compound was used as the positive electrode material of the secondary battery. In some cases, the conductive material can be a positive electrode material.

The mixing / pulverization is preferably performed by a dry or wet method using a ball mill, a jaw crusher, a jet mill, a planetary mill or the like. In particular, when a carbon source is included, it is preferable to pulverize in a wet manner in order to uniformly disperse the carbon source on the surface of the pulverized product. In particular, when the carbon source is an organic compound, wet pulverization using a dispersion medium capable of dissolving the organic compound is preferable.

As a dispersion medium for wet pulverization, water or an organic solvent such as ethanol, isopropyl alcohol, acetone, hexane, or toluene can be used. Water is particularly preferred because of its low cost. In addition, when mixing and pulverization are performed in a wet manner, the subsequent step (4) is preferably performed after the dispersion medium is removed by sedimentation, filtration, drying under reduced pressure, drying by heating, and the like.

The average particle diameter of the pulverized product is preferably 1 nm to 100 μm, more preferably 10 nm to 10 μm, and particularly preferably 10 nm to 1 μm in terms of volume median diameter in order to increase conductivity when applied to a positive electrode material for a secondary battery. preferable. It is preferable that the average particle size is not less than the lower limit of the above range, because the pulverized products are not sintered together in the subsequent step (4) and the particle size is not too large. Moreover, since it is less than the upper limit of the said range, the heating temperature and time of the following process (4) can be reduced, it is preferable.

<Organic compounds>
As the organic compound, at least one selected from the group consisting of saccharides, amino acids, peptides, aldehydes and ketones is preferable, and saccharides, amino acids and peptides are particularly preferable. Examples of sugars include monosaccharides such as glucose, fructose, and galactose; oligosaccharides such as sucrose, maltose, cellobiose, and trehalose; polysaccharides such as invert sugar, dextrin, amylose, amylopectin, and cellulose; and similar substances such as ascorbic acid. Can be mentioned. Monosaccharides and oligosaccharides are preferred because of their strong reducing properties.
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. Furthermore, organic compounds having a reducing functional group such as an aldehyde group or a ketone group are also included.
As the organic compound, specifically, glucose, sucrose, glucose-fructose invert sugar, caramel, starch, pregelatinized starch, carboxymethylcellulose and the like are preferable.

<Carbon-based conductive active material>
As the carbon-based conductive active material, carbon black, graphite, acetylene black, carbon fiber, amorphous carbon and the like are preferable. By including the carbon-based conductive active material at the time of mixing and pulverizing the solidified product, it is not necessary to separately provide a step of mixing the carbon-based conductive active material after producing the silicic acid-phosphate compound in step (4). . Furthermore, by including the carbon-based conductive active material together with the organic compound when the formulation is pulverized, the distribution of the carbon-based conductive active material in the silicic acid-phosphate compound powder becomes uniform, and the organic compound or its thermal decomposition The contact area with the object (carbide) increases. This makes it possible to increase the binding force of the carbon-based conductive active material to the silicic acid-phosphoric acid compound.

The amount of the carbon source is preferably such that the ratio of the carbon equivalent (mass) to the total mass of the solidified product and the carbon equivalent (mass) in the carbon source is 0.1 to 20% by mass. An amount of mass% is particularly preferred. By setting the carbon source to be equal to or higher than the lower limit of the above range, it is possible to sufficiently increase the conductivity when the silicic acid-phosphoric acid compound is used as a positive electrode material for a secondary battery. By setting it to the upper limit of the above range or less, when the silicic acid-phosphoric acid compound is used as the positive electrode material for the secondary battery, the characteristics as the positive electrode material for the secondary battery can be kept high.

(Process (4))
Step (4) is a step of obtaining a silicic acid-phosphoric acid compound having a composition represented by formula (1), preferably crystal grains thereof.

Step (4) preferably includes crystal nucleation and grain growth of the pulverized product. Further, when at least one selected from the group consisting of an organic compound and a carbon-based conductive active material is included in the previous pulverization step, the resulting silicic acid-phosphoric acid compound, preferably on the surface of the crystal particles. It is preferably a step of bonding at least one selected from an organic compound, a carbon-based conductive active material, and a reactant thereof. When the step (3) is performed by a wet method, the dispersion medium may be removed at the same time as the heating and firing.

In the formula (1), x, y and a satisfy 0.8 <x <1.2, 0.8 <y <1.2 and 0.35 ≦ a ≦ 0.95, and N = + 2 In the case where the silicic acid-phosphoric acid compound particles are applied to the positive electrode material for a secondary battery, good characteristics are exhibited, which is preferable. The value of z is 3.75 when x = 1, y = 1, N = + 2, and a = 0.5.
In the formula (1), in order to improve the performance, a part of 0.3 to 15 mol% of the atom M may be substituted with an element having a valence of +2 or +3. For example, Ti, V, B, Al, Ca, Cu, Mg, and Zn are mentioned.

Further, it is preferable that the silicic acid-phosphoric acid compound particles represented by the formula (1) are a compound having a composition represented by the formula (2) and are crystalline particles because they can be manufactured at low cost.
Li _x (Fe _b Mn _1-b ) _y Si _a P _1-a O _z (2)
(In the formula, x, y, z and a are respectively the same numerical values as above, and b is 0 ≦ b ≦ 1.)

Furthermore, since the silicic acid-phosphoric acid compound particles represented by the above formula (2) are compounds having the composition represented by the formula (3), a material that exhibits good characteristics can be produced at low cost. Particularly preferred.
_{LiFe b Mn 1-b Si a} P 1-a O z (3)
(In the formula, z, a and b are respectively the same numerical values as described above.)

In the formula (1), A is +1 valence, M is +2 valence, Si is +4 valence, and P is +5 valence, which is a stable valence. Therefore, Z = {x + 2y + 4a + 5 (1-a )} / 2.

<Heating conditions>
Step (4) is preferably performed in an inert gas or a reducing gas.
The pressure may be normal pressure, increased pressure (1.1 × 10 ⁵ Pa or more), and reduced pressure (0.9 × 10 ⁵ Pa or less). Further, when the container containing the reducing agent (for example, graphite) and the pulverized material is loaded in the heating furnace, reduction of M ions in the pulverized material (for example, change from M ³⁺ to M ²⁺ ). Can be promoted. Thereby, a silicic acid-phosphoric acid compound having a composition represented by the formula (1) can be obtained with good reproducibility.

The heating temperature is preferably 500 to 1,000 ° C, particularly preferably 600 to 900 ° C. When the heating temperature is 1,000 ° C. or less, the pulverized product is difficult to melt and the crystal diameter and particle diameter can be easily controlled. In addition, when the heating temperature is within the above range, a silicic acid-phosphoric acid compound having an appropriate crystallinity, particle size, particle size distribution, and the like, preferably crystal particles thereof can be easily obtained.

Step (4) may be performed at a constant temperature or by changing the temperature in multiple stages. As the heating temperature is increased, the particle diameter of the generated particles tends to increase. Therefore, it is preferable to set the heating temperature according to a desired particle diameter.
The heating time (holding time depending on the heating temperature) is preferably 1 to 72 hours in consideration of a desired particle size.

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-described 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, more preferably 1 to 10% by volume of the reducing gas in the total gas volume. The oxygen content is preferably 1% by volume or less, and particularly preferably 0.1% by volume or less in the gas volume.

After the heating in step (4) is completed, 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 crystalline particles, the target product can be obtained while maintaining the crystal structure. There is also an advantage that cooling can be performed without using a cooling means. The cooling may be left to cool to room temperature. Cooling is preferably performed in an inert gas or a reducing gas.

The organic compound or carbon-based conductive active material adhering to the surface of the pulverized product in the step (3) can bind to the particle surface of the silicic acid-phosphate compound generated in the step (4) and function as a conductive material. The organic compound is thermally decomposed in the step (4), and at least a part of the organic compound becomes a carbide to function as a conductive material. The thermal decomposition of the organic compound is preferably performed at 400 ° C. or lower, and the carbonization is preferably performed at 600 ° C. or lower. When pyrolysis is performed at 600 ° C. or lower, in addition to carbonization of the carbon-based conductive active material, the volume change associated with the pyrolysis reaction can be reduced, so that the carbide and the carbon-based conductive active material can be used as a conductive carbonaceous layer. It can bond uniformly and firmly to the surface of the acid-phosphate compound particles or the interface between the silicic acid-phosphate compound particles.
The particles of silicic acid-phosphoric acid compound further contain a conductive carbonaceous layer, and 0.1 to 20% by mass with respect to the total mass of the silicic acid-phosphoric acid compound and the conductive carbonaceous layer. The conductive carbonaceous layer is preferably contained on the surface of the particles or at the interface between the particles, and particularly preferably 2 to 10% by mass.

Through the steps (1) to (4) described above, a silicic acid-phosphate compound having a composition represented by the formula (1) is produced. The silicic acid-phosphoric acid compound is preferably a particle, more preferably a crystal particle, and particularly preferably an olivine type crystal particle.

The particles include both primary particles and secondary particles. In addition, when a carbon source is included in the solidified product, a conductive material based on an organic compound or a carbon-based conductive active material is uniformly and firmly formed on the surface simultaneously with the formation of crystal particles of a silicic acid-phosphoric acid compound. Combined materials can be produced. This powder material is suitable for a positive electrode material for a secondary battery. When secondary particles are present in the obtained silicic acid-phosphate compound particles and the powder material containing the same, they may be crushed and pulverized to the extent that the primary particles are not destroyed.
The crystal particles preferably have an orthorhombic crystal system and do not include crystals composed of cristobalite and phosphoric acid M.

The average particle size of the silicic acid-phosphoric acid compound particles of the present invention is preferably 10 nm to 10 μm, particularly preferably 10 nm to 2 μm, in terms of volume median diameter. By making the average particle diameter within this range, the conductivity of the powder of silicic acid-phosphoric acid compound particles 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. Silicate - specific surface area of the powder consisting of phosphoric acid compound is preferably ^{0.2 ~ 200m 2 / g, 1} ~ 200m 2 / g is particularly preferred. By setting the specific surface area within this range, the conductivity of the powder made of silicic acid-phosphoric acid compound is increased. The specific surface area can be measured by, for example, a specific surface area measuring apparatus using a nitrogen adsorption method. The crystal particles are preferably composed only of primary particles.

Since the method for producing a silicic acid-phosphoric acid compound of the present invention is excellent in manufacturability and composition controllability of the silicic acid-phosphoric acid compound, an olivine-type silicic acid-phosphoric acid compound can be produced at low cost and efficiently. it can. In particular, the manufacturability of the silicic acid-phosphoric acid compound crystal particles can be enhanced. Further, it is possible to obtain silicic acid-phosphoric acid compound crystal particles having excellent chemical composition and uniform particle diameter and high crystallinity.

[Method for producing positive electrode for secondary battery]
A positive electrode for a secondary battery can be produced using the silicic acid-phosphate compound obtained by the production method of the present invention as a positive electrode material for a secondary battery.
When the silicic acid-phosphoric acid compound of the present invention is used as a positive electrode material for a secondary battery, when the atom M is, for example, Fe and / or Mn, these divalent / trivalent redox reactions are utilized for charging and discharging, Works.

The crystalline particles of silicic acid-phosphoric acid compound obtained by the production method of the present invention have high crystallinity, and therefore, when applied to a positive electrode material for a secondary battery, suppresses functional deterioration during repeated use. Can do. Therefore, it is possible to provide a secondary battery positive electrode excellent in battery characteristics and reliability at low cost.

The positive electrode for a secondary battery of the present invention can be manufactured according to a known electrode manufacturing method except that the silicic acid-phosphoric acid compound obtained by the manufacturing method of the present invention is used. For example, a silicic acid-phosphoric acid compound powder may be added to a known binder (polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluorine if necessary. After mixing with rubber, 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 thus obtained may be press-molded 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.

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

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

According to the secondary battery manufacturing method of the present invention, by applying the secondary battery positive electrode obtained by the secondary battery positive electrode manufacturing method of the present invention to the secondary battery positive electrode, characteristics and reliability can be improved. An excellent secondary battery can be obtained.

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 14]
(Process (1))
Lithium carbonate (Li ₂ CO ₃ ), so that the composition of the melt is a Li ₂ O, FeO, MnO, SiO ₂ and P ₂ O ₅ conversion amount (unit: mol%), and the ratio shown in Table 1 respectively. Triiron tetroxide (Fe ₃ O ₄ ), manganese dioxide (MnO ₂ ), silicon dioxide (SiO ₂ ), and ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) were weighed, mixed and pulverized in a dry process. A raw material formulation was obtained.

The obtained raw material mixture was filled in a platinum crucible containing 20% by mass of rhodium. Next, the crucible was placed in an electric furnace (model name: NH-3035, manufactured by Motoyama) equipped with a heating element made of molybdenum silicide. The electric furnace was heated at a rate of 300 ° C./hour and heated at 1,350 to 1,450 ° C. for 0.5 hour while flowing N ₂ gas at a flow rate of 1 L / min. Each melt was obtained after confirming that it became transparent visually.

(Process (2))
Next, the melt is cooled at −1 × 10 ⁵ ° C./sec by passing the melt in the crucible through a stainless steel double roller having a diameter of about 15 cm and rotating at 400 revolutions per minute to obtain a flaky solidified product. It was. The obtained solidified product was a glassy substance. The thickness of the flaky solidified material obtained in each example was measured with a micrometer and found to be 50 to 150 μm.

(Process (3))
The obtained flaky solidified product was lightly kneaded and coarsely pulverized, and then coarsely pulverized using a pestle and mortar. Further, the pulverization medium was made into balls made of zirconia and mixed and pulverized by a dry method using a planetary mill to obtain a pulverized product. When the particle diameter of the pulverized product of Example 1 was measured using a laser diffraction / scattering particle size distribution measuring apparatus (manufactured by Horiba, Ltd., apparatus name: LA-950), the volume-converted median diameter was 1.7 μm. there were.

(Process (4))
By heating the pulverized materials of Examples 1 to 14 after sieving in 3% by volume of H ₂ —Ar gas at 700 ° C. for 8 hours, silicate-phosphorus having a composition represented by formula (1), respectively. Acid compound particles were obtained. Further, in each example, each pulverized product was heated at 600 ° C. for 8 hours and heated at 800 ° C. for 8 hours in 3% by volume H ₂ —Ar gas. Silica-phosphate compound particles having a composition represented by the same formula (1) as in the case of × 8 hours of heating were obtained. The average particle diameter of the silicic acid-phosphoric acid compound particles obtained by heating at 700 ° C. was 4.4 μm in terms of volume median diameter. Furthermore, it was 1.4 m < ² > / g when the specific surface area was measured with the specific surface area measuring apparatus (Shimadzu Corporation make, apparatus name: ASAP2020).

(Composition analysis)
The chemical composition of the resulting silicic acid-phosphoric acid compound particles was measured. First, silicic acid-phosphoric acid compound particles were decomposed by heating and sealing with a 2.5 mol / L NaOH solution at 120 ° C., and the decomposed solution was dried to dryness under hydrochloric acid acidity and filtered again as hydrochloric acid acidic solution. A residue was obtained. Fe, Mn, Si, and P in the filtrate use an inductively coupled emission spectroscopic analyzer (manufactured by Seiko Instruments Inc., apparatus name: SPS3100), and Li in the filtrate uses an atomic absorption photometer (manufactured by Hitachi High-Technologies Corporation, apparatus name). : Z-2310). From the measured Fe, Mn, Si, P and Li contents, FeO, MnO, SiO ₂ , P ₂ O ₅ and Li ₂ O were calculated. Further, the residue was ashed and then decomposed with hydrofluoric acid-sulfuric acid, and the weight loss due to this treatment was defined as the SiO ₂ content. The total SiO ₂ content was the total of this value and the SiO ₂ content identified by the inductively coupled emission spectrometer. Table 2 shows the chemical composition of the particles obtained from these quantitative values of the silicic acid-phosphate compound particles obtained by heating at 800 ° C. for 8 hours in Examples 1 to 14.

(X-ray diffraction)
The mineral phase of the obtained silicic acid-phosphate compound particles was examined using an X-ray diffraction apparatus (manufactured by Rigaku Corporation, apparatus name: RINT TTRIII). As a result, all the particles of Examples 1 to 14 consisted of crystals considered to be orthorhombic, and cristobalite, iron phosphate and manganese phosphate were not identified. For reference, X-ray diffraction patterns of silicic acid-phosphoric acid compound particles obtained in Examples 1, 3, 6, 13 and 14 by heating at 800 ° C. for 8 hours are shown in FIGS. And c), and a) and b) of FIG. 2, respectively.

[Example 15]
With respect to the flaky solidified product obtained in Example 3, carbon black and glucose (aqueous solution) are mixed so that the mass ratio of the solidified product, carbon black and glucose is 90: 2.5: 2.5. Added to. Next, using a ball made of zirconia, it was pulverized in a dry manner to obtain a pulverized product.

The obtained pulverized product was heated at 800 ° C. for 8 hours in Ar gas in the same manner as in Example 3. The chemical composition of the obtained particles was measured in the same manner as in Example 3. As a result, the chemical composition was Li _0.99 Fe _0.98 Si _0.63 P _0.37 O _3.66 . Furthermore, when the carbon content of the obtained particles was measured using a carbon analyzer (manufactured by Horiba, Ltd., apparatus name: EMIA-920A), it was 2.8% based on the C mass. Moreover, the average particle diameter of the obtained particle | grains was 1.4 micrometers in median diameter of volume conversion.

[Example 16]
(Manufacture of positive electrode for Li ion secondary battery and evaluation battery)
The carbon-containing particles obtained in Example 15 were used as active materials, and these, polyvinylidene fluoride resin as a binder, and acetylene black as a conductive material were weighed so as to have a mass ratio of 85: 5: 10. Then, N-methylpyrrolidone was mixed well as a solvent to prepare a slurry. Next, the slurry was applied to an aluminum foil having a thickness of 30 μm with a bar coater. The solvent was removed by drying at 120 ° C. in the air, and then the coating layer was consolidated by a roll press and cut into strips each having a width of 10 mm and a length of 40 mm.

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 in which lithium foil was pressure-bonded to a nickel mesh with a porous polyethylene film separator, Both sides were fixed with a polyethylene plate.

The counter electrode was put in a polyethylene beaker, and a nonaqueous electrolyte solution in which lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (1: 1 volume ratio) at a concentration of 1 mol / L was injected. Fully 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 these half cells 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 25 ° 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 85 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 set to 2.0 V based on the Li counter electrode. This charge / discharge cycle was repeated 10 cycles. The discharge capacity at the fifth cycle of the half cell using the active material of Example 15 was 128 mAh / g. Further, the charge / discharge cycle was repeated 10 cycles in the same manner at 60 ° C. The discharge capacity at the fifth cycle was 148 mAh / g.

[Comparative Example 1]
Lithium carbonate (5%, 60%, 30%, 5%) in terms of Li ₂ O, FeO, SiO ₂ and P ₂ O ₅ equivalent amounts (unit: mol%), respectively, Li ₂ CO ₃ ), triiron tetroxide (Fe ₃ O ₄ ), silicon dioxide (SiO ₂ ), and ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) are weighed, mixed and pulverized in a dry process, A raw material formulation was obtained. Although it melted at 1,450 ° C. in the same manner as in Example 1, a complete melt could not be obtained.

In Examples 1 to 15, a silicic acid-phosphoric acid compound having a desired composition could be produced efficiently. Further, it was confirmed in Example 16 that the produced silicic acid-phosphoric acid compound had excellent characteristics as a positive electrode material for a secondary battery and further as a secondary battery.

The method for producing a silicic acid-phosphoric acid compound of the present invention is useful because the composition of the silicic acid-phosphoric acid compound can be easily controlled and produced. The obtained silicic acid-phosphoric acid compound is useful when applied to a positive electrode material for a secondary battery and further to a secondary battery.
The entire content of the specification, claims, drawings and abstract of Japanese Patent Application No. 2010-106762 filed on May 6, 2010 is cited here as the disclosure of the specification of the present invention. Incorporated.

Claims (15)

1. Including at least one atom A selected from the group consisting of Li, Na and K, at least one atom M selected from the group consisting of Fe, Mn, Co and Ni, and Si and P (wherein At least one selected from the group consisting of atom A, atom M, Si and P is included as an oxide.), Oxide equivalent amount (unit: mol%) of the content of each atom when it becomes a melt But,
   15% <A ₂ O <30%,
   35% <MO <55%,
   15% <SiO ₂ <50%,
   1% <P ₂ O ₅ <18%,
   0.8 <A ₂ O / (0.5SiO ₂ + P ₂ O ₅ ) <1.2,
   0.8 <A ₂ O / 0.5MO <1.2,
   Heating the raw material formulation to obtain a melt,
   Cooling the melt to obtain a solidified product,
   Pulverizing the solidified product to obtain a pulverized product, and heating the pulverized product to obtain a silicic acid-phosphoric acid compound having a composition represented by the following formula (1):
   A process for producing a silicic acid-phosphoric acid compound, comprising:
   _{A x M y Si a P 1} -a O z (1)
   (In the formula, A and M are the same kind of atoms as described above, and x, y, and a are 0.8 <x <1.2, 0.8 <y <1.2, 0.35, respectively. ≦ a ≦ 0.95, and z is a number depending on the valence N of x, y, a and M.)
2. At least one atom A selected from the group consisting of Li, Na and K; at least one atom M selected from the group consisting of Fe, Mn, Co and Ni; and Si and P (provided that atom A, atom And at least one selected from the group consisting of M, Si, and P is included as an oxide.), And an oxide equivalent amount (unit: mol%) of the content of each atom But,
   15% <A ₂ O <30%,
   35% <MO <55%,
   15% <SiO ₂ <50%,
   1% <P ₂ O ₅ <18%,
   0.8 <A ₂ O / (0.5SiO ₂ + P ₂ O ₅ ) <1.2,
   0.8 <A ₂ O / 0.5MO <1.2,
   Obtaining a melt which is
   Cooling the melt to obtain a solidified product,
   Pulverizing the solidified product to obtain a pulverized product, and heating the pulverized product to obtain a silicic acid-phosphoric acid compound having a composition represented by the following formula (1):
   A method for producing a silicic acid-phosphoric acid compound comprising:
   _{A x M y Si a P 1} -a O z (1)
   (In the formula, A and M are the same kind of atoms as described above, and x, y and a are 0.8 <x <1.2, 0.8 <y <1.2, 0.35 ≦ a ≦ 0.95, and z is a number depending on the valence N of x, y, a and M.)
3. Atoms A contained in the raw material formulation are A carbonate, A bicarbonate, A hydroxide, A phosphate and hydrogen phosphate, A nitrate, A chloride, A And at least one selected from the group consisting of A sulfate, A acetate, and A oxalate (however, these compounds may each form a hydrate salt),
   Atom M is selected from the group consisting of M oxide, M oxyhydroxide, M metal, M phosphate, M chloride, M nitrate, M sulfate, and M organic salt Included as at least one
   Si is a silicate of A selected from the group consisting of silicon oxide, A ₂ SiO ₃ and A ₄ SiO ₄ (where A is the same kind of atom as described above), and MSiO ₃ and M ₂ SiO ₄ M silicate selected from the group consisting of (wherein M is the same kind of atom as described above), and included as at least one selected from the group consisting of:
   P is at least one selected from the group consisting of phosphorus oxide, ammonium phosphate, ammonium hydrogen phosphate, phosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, A phosphate, and M phosphate The method for producing a silicic acid-phosphate compound according to claim 1 or 2, which is contained as a seed.
4. The method for producing a silicic acid-phosphate compound according to any one of claims 1 to 3, wherein the atom A is Li.
5. The method for producing a silicic acid-phosphate compound according to any one of claims 1 to 4, wherein the atom M is at least one selected from the group consisting of Fe and Mn.
6. The silicic acid-phosphoric acid compound having a composition represented by the formula (1) is a crystal particle of a compound having a composition represented by the following formula (2): A process for producing the silicic acid-phosphoric acid compound as described.
   Li _x (Fe _b Mn _1-b ) _y Si _a P _1-a O _z (2)
   (In the formula, x, y, z and a are respectively the same numerical values as above, and b is 0 ≦ b ≦ 1.)
7. The crystal particle of the compound having the composition represented by the formula (2) is a crystal particle of a compound having the composition represented by the following formula (3): Production method.
   _{LiFe b Mn 1-b Si a} P 1-a O z (3)
   (In the formula, z, a and b are respectively the same numerical values as described above.)
8. In the step of obtaining the pulverized product, the solidified product includes at least one carbon source selected from the group consisting of an organic compound and a carbon-based conductive active material, and the amount of the carbon source is determined based on the amount of the solidified product and carbon. The amount according to any one of claims 1 to 7, wherein the ratio of the carbon equivalent (mass) to the total mass with the carbon equivalent (mass) in the source is 0.1 to 20% by mass. A method for producing a silicic acid-phosphoric acid compound.
9. The method for producing a silicic acid-phosphate compound according to any one of claims 1 to 8, wherein in the step of obtaining the solidified product, a cooling rate is from -10 ³ ° C / second to -10 ¹⁰ ° C / second. .
10. The method for producing a silicic acid-phosphoric acid compound according to any one of claims 1 to 9, wherein the solidified product is a solid compound containing an amorphous part.
11. The silicic acid-phosphoric acid compound according to any one of claims 1 to 10, wherein the step of obtaining the silicic acid-phosphoric acid compound is performed in an inert gas or a reducing gas at 500 ° C to 1,000 ° C. Manufacturing method.
12. A silicic acid-phosphoric acid compound having a composition represented by the following formula (1):
    _{A x M y Si a P 1} -a O z (1)
    Wherein A is at least one atom selected from the group consisting of Li, Na and K, M is at least one atom selected from the group consisting of Fe, Mn, Co and Ni, and x, y and a is 0.8 <x <1.2, 0.8 <y <1.2, 0.35 ≦ a ≦ 0.95, and z is the valence N of x, y, a, and M. Depends on the number.)
13. The particles of the silicic acid-phosphoric acid compound comprise 0.1 to 20% by mass of the conductive carbonaceous layer based on the total mass of the silicic acid-phosphoric acid compound and the conductive carbonaceous layer. The silicic acid-phosphoric acid compound according to claim 12, which is contained on the surface or the interparticle interface.
14. A silicic acid-phosphoric acid compound is obtained by the production method according to any one of claims 1 to 11, and then the silicic acid-phosphoric acid compound is used as a positive electrode material for a secondary battery. The manufacturing method of the positive electrode for secondary batteries characterized by manufacturing a positive electrode for batteries.
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.

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