JP2014055085A - Phosphate compound, cathode material for second battery, and method for producing second battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an olivine type phosphate compound the electron conductivity and ionic conductivity of which are enhanced and the structure of which is restrained from being changed by a charge/discharge operation.SOLUTION: The method for producing the phosphate compound comprises the steps of: heating and melting a raw materia formulation containing, in terms of oxides, 20-35 mol% of LiO, 20-35 mol% of PO, 35-55 mol% of MnO, FeOequal to or higher than 0 mol% and less than 10 mol%, CoOequal to or higher than 0 mol% and less than 8 mol%, NiO equal to or higher than 0 mol% and less than 15 mol%, and 0.05-10 mol% of at least one selected from the group consisting of MgO, ZnO, CaO, ZrO, and TiOto obtain a molten product; cooling the molten product to obtain a solidified product: crushing the solidified product to obtain a crushed product; and heating the crushed product to obtain particles each containing crystals each having an olivine structure.

Description

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

  In recent years, in the development of electric vehicles, hybrid vehicles, and the like, lithium ion secondary batteries are required to have a significantly higher capacity, higher energy, and larger size while maintaining safety. Further, from the viewpoint of energy problems, development of medium-sized or large-sized stationary storage batteries having high safety and reliability is progressing in order to smooth power supply and demand and to stably supply power in an emergency. Some of these have been put to practical use.

As a positive electrode material used for these batteries, an olivine-type lithium phosphate compound (LiMPO ₄ / M) typified by olivine-type lithium iron phosphate (LiFePO ₄ ) from the viewpoint of resources, safety, cost, stability, and the like. Is a transition metal element), and some have been put into practical use. However, since the olivine type lithium phosphate compound (LiMPO ₄ ) has a higher electrical resistance than the conventional material, the lithium insertion / extraction reaction is slow during the charging / discharging of the lithium ion secondary battery using it as the positive electrode material. As a result, there is a problem that the charge / discharge capacity and energy density of the secondary battery are likely to be lower than theoretical values.

Lithium iron phosphate (LiFePO ₄ ) and lithium manganese phosphate (LiMnPO ₄ ), which are olivine-type lithium phosphate compounds, both have a theoretical discharge capacity of 170 mAh / g. Occlusion and release are theoretically highest and occur at about 3.4 V and 4.0 V, respectively. Therefore, the energy density of LiMnPO ₄ (multiplier of discharge capacity and operating voltage) is larger than that of LiFePO ₄ . In addition, these solid solutions of lithium iron manganese phosphate (LiFe _1-x Mn _x PO ₄ , 0 <x <1) also have a higher average operating voltage and higher energy density as the value of x increases. There is expected. However, the larger the value of x, the more difficult it becomes to develop the theoretical discharge capacity and the theoretical operating voltage (for example, Non-Patent Document 1). Note that lithium cobalt phosphate (LiCoPO ₄ ) and lithium manganese phosphate (LiNiPO ₄ ) are difficult to use from the viewpoint of resources, safety, cost, and the like.

  Various methods for producing these lithium iron phosphates have been proposed. For example, solid phase reaction method, hydrothermal synthesis method, spray pyrolysis method, microwave heating method and the like are known.

In Patent Document 1, in terms of mol%, Li ₂ O is 10 to 50%, Fe ₂ O ₃ is 10 to 40%, P ₂ O ₅ is 20 to 50%, MgO, TiO ₂ , V ₂ O ₅ , At least one selected from MnO ₂ , Co ₃ O ₄ , NiO, Nb ₂ O ₅ , MoO ₃ , WO ₃ and rare earth oxide is mixed at a ratio of 0.5 to 32%, melted and cooled to be a precursor. Lithium secondary battery positive electrode material made of NASICON type, olivine type, spinel type and their solid solutions by manufacturing glass, heat treatment at glass transition temperature or higher, or heating by laser irradiation and its manufacturing method are described The obtained positive electrode material is shown to have high conductivity.

Japanese Unexamined Patent Publication No. 2008-047412

A. Yamada et al., Chemistry of Materials, 18, 804-813 (2006)

  In Non-Patent Document 1, it is considered that the reason why the theoretical discharge capacity and the theoretical operating voltage are difficult to express is that the electron conductivity and the ionic conductivity are low. Furthermore, after the continuous charge / discharge history, good rate characteristics and cycle characteristics have not been obtained, but it is thought to be due to irreversible structural changes.

The method of Patent Document 1 obtains lithium iron manganese phosphate particles having a high MnO ₂ content because the precursor glass contains Fe ₂ O ₃ at least 10 mol% and MnO ₂ at most 32 mol%. I could not. Note that lithium iron manganese phosphate having an Fe ₂ O ₃ content of 10 mol% and an MnO ₂ content of 32 mol% corresponds to approximately LiFe _0.4 Mn _0.6 PO ₄ . In addition, since heat treatment is performed on the molded precursor glass, it is necessary to grind the crystallized product in order to obtain lithium iron phosphate powder, which causes various inconveniences such as a decrease in crystallinity of lithium iron phosphate. Could occur.

  An object of this invention is to provide the manufacturing method of the olivine type | mold phosphate compound by which electronic conductivity and ionic conductivity were improved and the structural change by charging / discharging operation was suppressed. In addition, the present invention provides a positive electrode material for a secondary battery and a secondary battery that exhibit high discharge capacity, are excellent in rate maintenance ratio and discharge capacity maintenance ratio (cycle characteristics), and have improved reliability. Objective.

  The present invention is the following [1] to [10].

[1] 20% or more and 35% or less of Li ₂ O, 20% or more and 35% or less of P ₂ O ₅ , 35% or more and 55% or less of MnO ₂ , Fe ₂ O ₃ 0% to less than 10%, Co ₃ O ₄ to 0% to less than 8%, NiO to 0% to less than 15%, and at least one selected from the group consisting of MgO, ZnO, CaO, ZrO ₂ , and TiO ₂ A raw material formulation containing 0.05% or more and 10% or less, and melting and obtaining a melt,
Cooling the melt to obtain a solidified product;
Pulverizing the solidified product to obtain a pulverized product;
Heating the pulverized product to obtain particles containing crystals containing an olivine structure;
The manufacturing method of the phosphoric acid compound characterized by implementing in this order.

[2] The production method according to [1], wherein the raw material formulation is melted at 1,000 ° C. to 1,400 ° C. in an inert gas or a reducing gas.

[3] The production method according to [1] or [2], wherein the melt is cooled at a cooling rate of 10 ³ to 10 ¹⁰ ° C / second.

[4] The production method according to any one of [1] to [3], wherein the melt is cooled in an inert gas or a reducing gas.

[5] The pulverized product includes the solidified product and at least one carbon source selected from the group consisting of an organic compound and a carbon-based conductive material, and a carbon equivalent amount (mass) in the carbon source is The production according to any one of [1] to [4], which is 0.1 to 20% by mass relative to the total mass of the mass of the solidified product and the carbon equivalent amount (mass) in the carbon source. Method.

[6] The production method according to any one of [1] to [5], wherein the pulverized product is heated at 300 ° C to 900 ° C in an inert gas or a reducing gas.

[7] A phosphoric acid compound is obtained by the production method according to [1] to [6], and then a positive electrode material for a secondary battery is obtained using the phosphoric acid compound. Manufacturing method of positive electrode material.

[8] A method for producing a secondary battery, comprising obtaining a positive electrode material for a secondary battery by the production method according to [7], and then obtaining a secondary battery using the positive electrode material for the secondary battery. .

[9] A phosphoric acid compound having a composition represented by the following formula (1).
_{Li 1 + a (Mn 1- (} q + r) Fe q M r) 1-x + b X x PO 4 + c (1)
(Wherein, M is at least one selected from the group consisting of Co and Ni, X is at least one selected from the group consisting of Mg, Zn, Ca, Zr and Ti, a, b, q, r, and x are -0.2≤a≤0.1, -0.2≤b≤0.1, 0≤q≤0.3, 0≤r <0.2, respectively. 0 ≦ (q + r) ≦ 0.35, 0.001 ≦ x ≦ 0.2, and c depends on the valence of Mn, Fe, M, and X, and a, b, q, r, and x And a number that satisfies electrical neutrality.)

[10] A phosphoric acid compound having a composition represented by the following formula (2).
_{Li d (Mn 1-s Fe} s) e X y PO 4 + f (2)
(Wherein X is at least one selected from the group consisting of Mg, Zn, Ca, Zr, and Ti, and d, e, s, and y are 0.95 ≦ d ≦ 1.10, respectively. 0.95 ≦ e ≦ 1.05, 0.03 ≦ s ≦ 0.3, and 0.001 ≦ y ≦ 0.2, and f is the valence of Mn, Fe, and X, and d, Depends on e, s, and y, and is a number that satisfies electrical neutrality.)

  According to the production method of the present invention, it is possible to provide an olivine-type phosphate compound in which electronic conductivity and ionic conductivity are enhanced and structural change due to charge / discharge operation is suppressed. Therefore, it is possible to efficiently produce a positive electrode material and a secondary battery that are excellent in rate maintenance rate and discharge capacity maintenance rate while exhibiting high discharge capacity with good reproducibility.

It is a figure which shows the X-ray-diffraction pattern of the phosphoric acid compound obtained by Example 1, 2, and 3 of the Example. It is a figure which shows the X-ray-diffraction pattern of the phosphoric acid compound obtained by Example 16, 17, and 18 of the Example. It is an electron micrograph of the phosphoric acid compound obtained in Example 1 of an Example.

In the present specification, the olivine-type phosphate compound includes a basic formula Li (M′X) PO ₄ (M ′ is essential to Mn, and includes at least one selected from the group consisting of Fe, Co, and Ni). Often, X is a substance represented by at least one selected from the group consisting of Mg, Zn, Ca, Zr, and Ti. The olivine structure is a crystal structure in which the crystal system is orthorhombic and the space group is represented by Pnma.

  In addition, a crystal including an olivine structure is also referred to as an olivine crystal, and a particle including an 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, 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.

[Phosphate compound]
The phosphoric acid compound of the present invention has a composition represented by the following formula (1).
_{Li 1 + a (Mn 1- (} q + r) Fe q M r) 1-x + b X x PO 4 + c (1)
(Wherein, M is at least one selected from the group consisting of Co and Ni, X is at least one selected from the group consisting of Mg, Zn, Ca, Zr and Ti, a, b, q, r, and x are -0.2≤a≤0.1, -0.2≤b≤0.1, 0≤q≤0.3, 0≤r <0.2, respectively. 0 ≦ (q + r) ≦ 0.35, 0.001 ≦ x ≦ 0.2, and c depends on the valence of Mn, Fe, M, and X, and a, b, q, r, and x And a number that satisfies electrical neutrality.)

  The phosphate compound having the composition represented by the formula (1) is an olivine-type phosphate compound, and when used as a positive electrode material for a secondary battery, exhibits a high discharge capacity while maintaining a rate maintenance rate and a discharge capacity. The rate is high, the reliability is high, and the manufacturing cost is low.

  q and r are 0 ≦ q <0.3, 0 ≦ r <0.2, and 0 ≦ (q + r) ≦ 0.35. When (q + r)> 0.35, it is difficult to obtain a phosphoric acid compound having a high operating voltage when the positive electrode material is used, and the manufacturing cost increases. It is preferable that (q + r) ≦ 0.30. Further, since the discharge capacity can be further increased, (q + r)> 0 is preferable, and (q + r) ≧ 0.03 is more preferable. Further, as the olivine-type phosphoric acid compound, Co and Ni are elements that can increase the voltage but are expensive, and therefore r = 0 is preferable.

  When the atom X is at least one selected from the group consisting of Mg, Zn, Ca, Zr, and Ti, the electron conductivity and ionic conductivity of the phosphate compound are enhanced, and the structural change caused by the charge / discharge operation is suppressed. This is preferable. It is considered that the atom X is structurally present by substituting the Mn position, Fe position, M position, or Li position. As the atom X, Mg, Zn, or Ti is preferable because Mn, Fe, and M have an ionic radius that is relatively equal and considered to be easily substituted.

  It is preferable that x is 0.001 ≦ x ≦ 0.2 because the structure of the phosphoric acid compound is stabilized and the electron conductivity and the ionic conductivity are improved. When x <0.001, the effect of increasing the conductivity is not sufficient, and when x> 0.2, the discharge capacity of the phosphoric acid compound decreases. It is more preferable that 0.002 ≦ x ≦ 0.15. It is particularly preferable that 0.005 ≦ x ≦ 0.1 because it is possible to increase the electron conductivity and ion conductivity while suppressing a decrease in discharge capacity, and to suppress a structural change caused by a charge / discharge operation.

  a and b are −0.2 ≦ a ≦ 0.1 and −0.2 ≦ b ≦ 0.1. When a and b are smaller than −0.2 or larger than 0.1, respectively, it becomes difficult to obtain a phosphate compound. It is more preferable that −0.05 ≦ a ≦ 0.05 and −0.05 ≦ b ≦ 0.05 because the discharge capacity retention rate becomes higher.

  c is a number that satisfies the electrical neutrality depending on the valences of Mn, Fe, M, and X, and a, b, q, r, and x. The valence of Mn, Fe, Co, and Ni in the phosphoric acid compound is preferably +2. Further, the valence of Mg, Zn, and Ca is preferably +2, the valence of Zr is +4, and the valence of Ti is preferably +2, +3, or +4.

As the phosphoric acid compound, a phosphoric acid compound having a composition represented by the following formula (2) is particularly preferable.
_{Li d (Mn 1-s Fe} s) e X y PO 4 + f (2)
(Wherein X is at least one selected from the group consisting of Mg, Zn, Ca, Zr, and Ti, and d, e, s, and y are 0.95 ≦ d ≦ 1.10, respectively. 0.95 ≦ e ≦ 1.05, 0.03 ≦ s ≦ 0.3, and 0.001 ≦ y ≦ 0.2, and f is the valence of Mn, Fe, and X, and d, Depends on e, s, and y, and is a number that satisfies electrical neutrality.)

  The phosphoric acid compound having the composition represented by the formula (2) is low in production cost, and when used as a positive electrode material for a secondary battery, electrochemical characteristics such as discharge capacity, discharge capacity maintenance rate, rate maintenance rate, etc. It is preferable in order to exhibit good properties in a balanced manner.

  When the phosphoric acid compound of the present invention is used as a positive electrode material for a secondary battery, the positive electrode material for a secondary battery preferably contains a conductive material. The conductive material is derived from at least one carbon source selected from the group consisting of organic compounds and carbon-based conductive materials. The conductive material is preferably present on the surface of the phosphoric acid compound particles or the interparticle interface. The content of the conductive material is preferably 0.1 to 20% by mass, more preferably 0.1 to 10% by mass, and more preferably 2 to 10% by mass with respect to the total mass of the phosphoric acid compound and the conductive material. Is particularly preferred.

  It is particularly preferable that the phosphoric acid compound particles include olivine type crystal particles and consist only of olivine type crystal particles. The crystal particles include both primary particles and secondary particles. When secondary particles are present in the obtained phosphoric acid compound, they may be crushed and pulverized in such a range that the primary particles are not destroyed.

  The average particle diameter of the phosphoric acid compound particles is preferably 10 nm to 10 μm, particularly preferably 10 nm to 1 μm, in terms of volume median diameter. By making the average particle diameter within this range, the conductivity of the phosphoric acid compound becomes higher. The average particle size can be measured with a laser diffraction / scattering particle size measuring device.

The specific surface area of the phosphate compound particles is preferably 0.2~200m ² / g, more preferably 1~200m ² / g, more preferably 3 to 50 m ² / g. By making a specific surface area into this range, the electroconductivity of a phosphoric acid compound becomes high. The specific surface area can be measured with a specific surface area measuring apparatus using a nitrogen adsorption method. The average particle size and specific surface area of the phosphoric acid compound are the average particle size and specific surface area when the phosphoric acid compound does not contain a conductive material.

The average particle diameter of the phosphoric acid compound particles coated with the conductive material 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 phosphoric acid compound becomes higher. The specific surface area of the phosphoric acid compound is preferably 0.2~200m ² / g, more preferably ^{1~200m 2 / g, 5~50m 2 /} g is particularly preferred. By making a specific surface area into this range, the electroconductivity of a phosphoric acid compound becomes high.

[Method for producing phosphate compound]
The manufacturing method of the phosphoric acid compound of this invention implements each process of the following melting processes (I)-heating process (IV) in this order. Other steps may be performed before, between and after the melting step (I) to the heating step (IV) as long as each step is not affected.

Melting step (I): 20% to 35% Li ₂ O, 35% to 55% MnO ₂ , 0% to less than 10% Fe ₂ O ₃ , P ₂ O ₅ is 20% to 35%, Co ₃ O ₄ is 0% to less than 8%, NiO is 0% to less than 15%, and selected from the group consisting of MgO, ZnO, CaO, ZrO ₂ , and TiO _2. A step of heating and melting a raw material formulation containing at least one of 0.05% or more and 10% or less to obtain a melt;
Cooling step (II): a step of cooling the melt to obtain a solidified product,
Pulverization step (III): a step of pulverizing the solidified product to obtain a pulverized product;
Heating step (IV): A step of heating the pulverized product to obtain particles containing crystals containing an olivine structure.

(Melting step (I))
In the melting step (I), the raw material containing each atomic source (Li, Mn, P, Fe, Co, Ni, Mg, Zn, Ca, Zr, Ti) was adjusted to have a composition in the above range. Prepare the formulation.

  The raw material formulation having the composition in the above range can be completely melted and the melt has an appropriate viscosity, and can be easily processed in the subsequent cooling step.

Li ₂ O is a main component of the phosphoric acid compound, and the Li ₂ O content is 20% to 35%, preferably 23% to 33%. When it is less than 20% or more than 35%, it becomes difficult to obtain a phosphoric acid compound even when the obtained pulverized product is heated.

P ₂ O _{5 is} also a main component of the phosphate compound, and the P ₂ O ₅ content is 20% or more and 35% or less, preferably 23% or more and 30% or less. When it is less than 20% or more than 35%, it becomes difficult to obtain a phosphoric acid compound even when the obtained pulverized product is heated.

MnO _{2 is} also a main component of the phosphoric acid compound, and the content of MnO ₂ is 35% or more and 55% or less, preferably 37% or more and 52% or less. This range is preferable because a material having a high operating voltage is easily obtained when the positive electrode material is used. If it is less than 35%, it is difficult to obtain a material having a high operating voltage. On the other hand, when the content is more than 55%, it becomes difficult to obtain a phosphoric acid compound even if the obtained pulverized product is heated.

Fe ₂ O ₃ is an optional component of the phosphate compound, and the content thereof is 0% or more and less than 10%. When the amount falls within this range, a melt having an appropriate viscosity can be obtained. If it is 10% or more, it is difficult to obtain a material having a high operating voltage. Further, if it exceeds 0%, the discharge capacity can be further increased, which is more preferable.

Co ₃ O ₄ is an optional component of the phosphate compound. When the content of Co ₃ O ₄ is 0% or more and less than 8%, a material having a high operating voltage is easily obtained when a positive electrode material is used. If it is 8% or more, it becomes difficult to obtain a uniform melt.

  NiO is an optional component of the phosphate compound. When the content of NiO is 0% or more and less than 15%, a material having a high operating voltage is easily obtained when a positive electrode material is used. When it is 15% or more, it becomes difficult to obtain a uniform melt.

Among them, when Co ₃ O ₄ and NiO are 0% and Fe ₂ O ₃ is 8.5% or less, the electrochemical properties such as discharge capacity, discharge capacity maintenance rate, rate maintenance rate, etc. are well balanced. It is more preferable because it exhibits excellent characteristics.

Co ₃ O ₄ and NiO are each 0%, and Fe ₂ O ₃ is preferably 8.5% or less.

At least one selected from the group consisting of MgO, ZnO, CaO, ZrO ₂ , and TiO ₂ is an essential component and acts to increase the electronic conductivity and ionic conductivity of the phosphate compound. In addition, there is an effect of suppressing structural changes due to charge / discharge operations. Furthermore, it has the effect of widening the melting range of the melt. The content of MgO, ZnO, CaO, ZrO ₂ , and TiO ₂ is 0.05% or more and 10% or less, preferably 0.1% or more and 7% or less, with the total amount of these components. When the content is less than 0.05%, the above-described effect is difficult to occur, whereas when the content is more than 10%, melting becomes difficult.

When the content of MgO, ZnO, CaO, ZrO ₂ , and TiO _{2 in} the melt is in the above range, the x and y ranges of the phosphoric acid compound of the above formula (1) can be satisfied.

  The valence of Mn, Fe, Co, and Ni in the melt is preferably in the range of +2 to +4. For Fe, +2, +8/3, or +3, for Mn, +2, +3, or +4, for Co, +2, +8/3, or +3, and for Ni, +2 or +4 is preferable. The valence of these elements in the obtained phosphoric acid compound is preferably +2.0 to +2.5, more preferably +2.0 to +2.2, and particularly preferably +2.

  The valence of Mg, Zn, and Ca in the melt is preferably +2, the valence of Zr is +4, and the valence of Ti is preferably +2, +3, or +4.

As the compound containing Li in the raw material preparation, lithium carbonate (Li ₂ CO ₃ ), lithium hydrogen carbonate (LiHCO ₃ ), lithium hydroxide (LiOH), and lithium phosphate (Li ₃ PO ₄ , (LiPO ₃ ) _n It is preferable to use at least one selected from the group consisting of These make it easier to obtain the desired phosphate compound. In addition, lithium chloride (LiCl), lithium nitrate (LiNO ₃ ), lithium sulfate (Li ₂ SO ₄ ), and organic acid salts such as lithium acetate (CH ₃ COOLi) and lithium oxalate ((COOLi) ₂ ) are used. (However, a part or all of the at least one kind may each form a hydrated salt.) Among these, Li ₂ CO ₃ and LiHCO ₃ are particularly preferable because they are inexpensive and easy to handle.

As the compound containing P in the raw material preparation, phosphorus oxide (P ₂ O ₅ ), ammonium phosphate (hydrogen) ((NH ₄ ) ₃ PO ₄ , (NH ₄ ) ₂ HPO ₄ , NH ₄ H ₂ PO ₄ ) It is preferable to use at least one selected from the group consisting of lithium phosphate (Li ₃ PO ₄ , (LiPO ₃ ) _n ), and phosphates of Mn, Fe, Co, and Ni. These make it easier to obtain the desired phosphate compound. Further, phosphoric acid (H ₃ PO ₄ ), phosphorous acid (H ₃ PO ₃ ), and hypophosphorous acid (H ₃ PO ₂ ) may be used. When each of the above compounds contains water of crystallization, the water-containing compound is included. Of these, ammonium dihydrogen phosphate ((NH ₄ ) H ₂ PO ₄ ) and lithium phosphate (Li ₃ PO ₄ , LiPO ₄ ) are preferable from the viewpoint of ease of handling and availability.

As a compound containing Mn in the raw material preparation, manganese oxide (MnO, Mn ₂ O ₃ , Mn ₃ O ₄ ), manganese hydroxide (Mn (OH) _2, etc.), manganese oxyhydroxide (MnO (OH) ₂ ) And at least one selected from the group consisting of manganese phosphate (Mn ₃ (PO ₄ ) ₂ , Mn ₂ P ₂ O _7, etc.). These make it easier to obtain the desired phosphate compound. Further, manganese chloride (MnCl ₂ etc.), manganese nitrate (Mn (NO ₃ ) ₂ etc.), manganese sulfate (MnSO ₄ etc.), Mn alkoxide (Mn (OCH ₃ ) ₂ , Mn (OC ₂ H ₅ ) ₂ etc. ), And organic acid salts such as manganese acetate (Mn (CH ₃ COO) ₂ ) and manganese oxalate (Mn (COO) ₂ ). When each of the above compounds contains water of crystallization, the water-containing compound is included. Among these, MnO ₂ and MnO are particularly preferable from the viewpoint of availability and cost.

As the compound containing Fe, Co, and Ni in the raw material preparation, oxides (FeO, Fe ₃ O ₄ , Fe ₂ O ₃ , CoO, Co ₃ O ₄ , Co ₂ O ₃ , NiO), oxyhydroxides (FeO (OH) etc.), phosphate (Fe ₃ (PO ₄ ) ₃ , Fe ₃ PO ₄ etc.), chloride (FeCl ₂ , FeCl ₃ etc.), nitrate (Fe (NO ₃ ) ₂ etc.), sulfuric acid Salt (FeSO ₄ , Fe ₂ (SO ₄ ) ₃ etc.), Fe alkoxide (Fe (OCH ₃ ) ₂ , Fe (OC ₂ H ₅ ) ₂ etc.), and Fe acetate salt (Fe (CH ₃ COO) ₂ And at least one selected from the group consisting of organic acid salts such as iron oxalate (Fe (COO) ₂ ). Among these, at least one compound selected from the group consisting of Fe ₃ O ₄ , Fe ₂ O ₃ , Co ₃ O ₄ and NiO is more preferable from the viewpoint of availability and cost.

Examples of the compound containing Mg, Zn, Ca, Zr, and Ti in the raw material preparation include oxides (MgO, ZnO, CaO, ZrO ₂ , TiO ₂ ), hydroxides (Mg (OH) ₂ , Zn (OH) _{2 , Ca (OH) 2, Zr} (OH) 4, Ca (OH) 2), carbonate _{(MgCO 3, ZnCO 3, CaCO} 3), phosphate _(Mg 3 _{(PO 4) 2,} etc.), chlorides ( MgCl ₂ etc.), nitrates (Mg (NO ₃ ) ₂ etc.), sulfates (MgSO ₄ etc.), and organic salts such as acetates (Mg (CH ₃ COO) ₂ ) and oxalates (Mg (COO) ₂ ) At least one selected from the group consisting of acid salts is preferred. Among these, MgO, ZnO, CaCO ₃ , ZrO ₂ , and TiO ₂ are particularly preferable because they are inexpensive and easy to handle.

  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 the raw material mixture, there is a component that is easily lost due to volatilization or the like during the melting process, for example, a component such as P. May differ slightly from mol%.

  The purity of each raw material is not particularly limited as long as it does not deteriorate the desired characteristics, but the purity excluding hydration water is preferably 99% or more, more preferably 99.9% or more. .

  The particle size of each raw material is not particularly limited as long as it is within a range in which a uniform melt can be obtained by melting. Each raw material is preferably melted after being mixed dry or wet using a mixing / pulverizing means such as a mixer, ball mill, planetary mill or the like.

  In the melting step (I), the raw material mixture obtained by the above method is then heated to melt. It is preferable to put the raw material preparation in a container or the like, and heat and melt it using a heating furnace. Examples of the container include alumina, carbon, silicon carbide, zirconium boride, titanium boride, boron nitride, carbon, platinum, platinum alloy containing rhodium, refractory bricks, and reduction. A container made of a material such as a material (for example, graphite) can be used. In order to prevent volatilization and evaporation in the heating furnace, the container is preferably fitted with a lid. 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) can be carried out in air, in an inert gas, or in a reducing gas. When carried out in an inert gas or a reducing gas, the valences of Mn, Fe, Co, and Ni can be maintained in a state close to +2 or +2, and a desired phosphate compound can be easily obtained, which is preferable. When melted in the air, it is preferable to perform reduction (for example, change from M ³⁺ to M ²⁺ ) in the subsequent heating step (IV).

Here, the inert gas refers to a gas containing 99% by volume or more of at least one gas selected from rare gases such as helium (He) and argon (Ar) and nitrogen (N ₂ ) gas. The reducing gas is a gas having a reducing property such as hydrogen (H ₂ ), carbon monoxide (CO), or ammonia (NH ₃ ) in the above-described inert gas, and the content is 0.1% by volume or more. More preferably, the gas is present in an amount of 1 to 10% by volume, and the oxygen (O ₂ ) content is 1% by volume or less, more preferably 0.1% by volume or less. However, when gas is generated during decomposition or melting of the raw material, the atmosphere does not have to be satisfied during the period. Furthermore, the raw material mixture may be melted in an atmosphere (0.8 × 10 ⁵ Pa or less) in which an inert atmosphere or a reducing atmosphere is reduced.

  The heating temperature for melting is preferably 1,000 to 1,400 ° C, particularly preferably 1,200 to 1,350 ° C. Here, melting means that each raw material is melted and is in a transparent state visually. When the heating 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 heating time is preferably 0.2 to 2 hours, particularly preferably 0.5 to 2 hours. When the heating time is not less than the lower limit of the above range, the uniformity of the melt is sufficient, and when it is not more than the upper limit, the raw material is hardly volatilized. Moreover, you may stir in order to raise the uniformity of a melt. Further, the melt may be clarified at a temperature lower than the melting temperature until the next cooling step (II) is performed.

(Cooling step (II))
The cooling step (II) is a step of cooling the melt obtained in the melting step (I) to near room temperature (20 to 25 ° C.) to obtain a solidified product. The solidified product is preferably an amorphous material, but a part of the solidified product may be a crystallized product. The amount of the 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. 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 phosphoric acid compound can be easily controlled. When an olivine-type phosphate compound is produced by crystallizing an amorphous substance, the reaction time can be shortened compared to the case of synthesizing a compound from a plurality of powders by a solid-phase reaction. Uniformity of composition, structure, etc. can be improved.

  The cooling of the melt can be carried out in air, in an inert gas or in a reducing gas. When carried out in an inert gas or a reducing gas, the facilities are simple and oxidation of Mn, Fe, Co, and Ni can be prevented or suppressed. In the case of rapid cooling in an open system, it is preferable that the atmosphere around the contact portion between the material to be cooled (melt) and the cooling medium (for example, a twin roller) is an inert atmosphere or a reducing atmosphere.

The cooling rate of the melt is preferably 1 × 10 ³ ° C./second or more, and more preferably 1 × 10 ⁴ ° C./second or more. 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 1 × 10 ³ ° C./sec to 1 × 10 ¹⁰ ° C./sec.

  As a method for cooling the melt, a method in which the melt is dropped between twin rollers rotating at a high speed, a method in which the melt is dropped on a rotating single roller to cool, a carbon plate that has cooled the melt, A method of cooling by pressing on a metal plate is preferred. 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 such as stainless steel, carbon or ceramic.

  The solidified product obtained in the cooling step (II) 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 plane perpendicular to the flaky average thickness 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. When the average thickness or average diameter is not more than the upper limit of the above range, the burden on the pulverization step (III) can be reduced, and the crystallization efficiency in the heating step (IV) can be increased. 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.

(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 can be easily pulverized. Further, 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, but there is a problem that residual stress is generated by pulverization and battery characteristics and the like are deteriorated. In the production method of the present invention, since the pulverization step (III) is performed before the heating step (IV), the residual stress generated in the pulverization step (III) can be reduced or removed in the heating step (IV).

  The pulverization is preferably performed using a cutter mill, jaw crusher, hammer mill, ball mill, jet mill, planetary mill or the like. Moreover, pulverization can be efficiently advanced by using each method stepwise depending on the particle diameter. For example, it is preferable to preliminarily make it fine with a hand massage or a hammer because the burden of the pulverization process is reduced. Further, after preliminary pulverization with a cutter mill, pulverization with a planetary mill or ball mill is preferable because the time required for pulverization can be shortened. From the viewpoint of productivity, it is particularly preferable to use a ball mill.

  As the grinding media, it is preferable to use zirconia balls, alumina balls, silicon nitride balls, silicon carbide balls, glass balls, or the like. In particular, zirconia balls have a low wear rate and can suppress the mixing of impurities. The diameter of the grinding media is preferably 0.1 to 30 mm. After pulverization is performed in multiple stages and pulverization is performed with a large pulverization medium, the pulverization medium and the pulverized product may be separated and pulverized using a smaller pulverization medium. With this method, the remaining of unground particles can be suppressed.

  The pulverization container is not particularly limited, but the pulverization efficiency is good when the pulverization medium and the solidified material are placed in the container up to 30 to 80% of the container capacity. When using a ball mill, the grinding time is preferably 6 to 360 hours, more preferably 6 to 120 hours, and particularly preferably 12 to 96 hours. If the pulverization time is not less than the lower limit of the above range, the pulverization can be sufficiently advanced, and if it is not more than the upper limit, excessive pulverization can be suppressed.

  The pulverization may be performed either dry or wet, but is preferably performed wet from the viewpoint of pulverization particle size. As a solvent used for pulverization (hereinafter also referred to as pulverization solvent), water or an organic solvent such as ethanol, isopropyl alcohol, acetone, hexane, or toluene can be used. Water is preferable from the viewpoint of cost and safety. On the other hand, when a problem such as elution of the solidified product occurs in the polar solvent, the organic solvent is preferable. When the pulverization solvent is filled up to 30 to 80% by volume of the container capacity in a state where the solidified product and the pulverization medium are contained, the pulverization efficiency is improved. When the pulverization is performed by a wet process, it is preferable to carry out the heating step (IV) after removing the pulverization solvent by sedimentation, filtration, drying under reduced pressure, drying by heating, or the like. However, when the pulverizing solvent is small, particularly when the ratio of the mass of the solid content to the mass of the pulverized product is 30% or more, the pulverized product containing the pulverizing solvent may be used for the heating step (IV). .

  The average particle diameter of the pulverized product is preferably 10 nm to 10 μm, more preferably 10 nm to 5 μm, in terms of volume-based median diameter. When the average particle size is not less than the lower limit of the above range, the pulverized products are not sintered together in the heating step (IV) and the particle size does not become too large. Heating temperature and time in heating process (IV) can be reduced as it is below the upper limit of the said range, and the particle size of the phosphoric acid compound obtained can be made small. The average particle size is measured with a laser diffraction / scattering particle size measuring device.

  Since the phosphoric acid compound of the present invention is an insulating material, when used as a positive electrode material for a secondary battery, it is preferable to coat at least a part of the surface of the phosphoric acid compound with a conductive material. In the pulverization step (III), it is preferable to include at least one carbon source selected from the group consisting of an organic compound and a carbon-based conductive material. As the carbon source, it is particularly preferable to use an organic compound and a carbon-based conductive material in combination. By using in combination, the distribution of the carbon-based conductive material in the phosphoric acid compound becomes uniform, and the contact area with the organic compound and its thermal decomposition product (carbide) increases. By these, the electroconductivity of the positive electrode material for secondary batteries using a phosphoric acid compound can be improved.

  The pulverization step (III) is preferably a step of obtaining a pulverized product of a solidified product and a carbon source. The pulverization step (III) includes a step of pulverizing after mixing the solidified product and the carbon source, a step of mixing after pulverizing the solidified product and the carbon source, and a step of adding the carbon source after pulverizing the solidified product. It is more preferable that

  The ratio of the mass of the carbon source is such that the carbon conversion amount (mass) in the carbon source is 0.1 to 20 with respect to the total mass of the mass of the solidified product and the carbon conversion amount (mass) in the carbon source. An amount of mass% is preferred, an amount of 0.1-10 mass% is more preferred, and an amount of 2-10 mass% is particularly preferred. By setting the amount of the carbon source to be equal to or higher than the lower limit of the above range, the electrical conductivity can be sufficiently increased when the phosphoric acid compound is used as a positive electrode material for a secondary battery. When the thickness of the conductive material covering the phosphoric acid compound does not become too thick by setting it to the upper limit value or less of the above range, a positive electrode for a secondary battery is produced using a phosphoric acid compound. The electrolyte can be sufficiently distributed to the material.

  When the organic compound is included in the solidified product, the pulverization step (III) is preferably performed by a wet method in order to uniformly disperse the pulverized product surface. The pulverization step (III) when the solidified material contains only the carbon-based conductive material may be dry.

  Organic compounds as carbon sources include glucose, sucrose, glucose-fructose invert sugar, caramel, paraffin, starch, pregelatinized starch, carboxymethylcellulose, ethylcellulose, camphor, melamine, stearic acid, oleic acid, linoleic acid, ascorbic acid More preferably, at least one selected from the group consisting of polyethylene glycol, polyvinyl alcohol, polyacrylic acid, and phenolic resin, glucose, sucrose, ethyl cellulose, camphor, melamine, stearic acid, ascorbic acid, polyethylene glycol, polyvinyl alcohol, and Particularly preferred is at least one selected from the group consisting of polyacrylic acid.

  The carbon-based conductive material as the carbon source is preferably at least one selected from the group consisting of carbon black, graphite, acetylene black, carbon fiber, and amorphous carbon. As the amorphous carbon, those in which a C—O bond peak or a C—H bond peak causing a decrease in conductivity of the positive electrode material is not substantially detected in the FT-IR analysis are preferable.

(Heating step (IV))
The heating step (IV) is a step in which the pulverized product obtained in the pulverization step (III) is heated to obtain a phosphate compound containing crystals containing an olivine structure. The obtained phosphoric acid compound is preferably particulate. Moreover, it is preferable that a phosphoric acid compound does not contain an amorphous substance. The fact that the phosphoric acid compound does not contain an amorphous substance can be confirmed by the fact that no halo pattern is detected by X-ray diffraction.

  In the heating step (IV), since the pulverized product is heated, the relaxation of the residual stress generated by the pulverization is promoted. Further, since crystal nuclei are generated and grains are grown by heating, it is easy to control the composition, grain size and distribution of the phosphate compound.

  The heating temperature is preferably 300 to 900 ° C, more preferably 500 to 900 ° C, and particularly preferably 550 to 800 ° C. When the heating temperature is 300 ° C. or higher, a carbonization reaction is likely to occur, and a phosphoric acid compound crystal is likely to be generated. When the heating temperature is 900 ° C. or lower, the pulverized product is hardly melted, and the crystal system and the particle diameter are easily controlled. In the case of the heating temperature, phosphoric acid compound particles having olivine type crystals having appropriate crystallinity, particle diameter, particle size distribution and the like are easily obtained. Moreover, it is easy to obtain phosphate compound particles in which the conductive material is uniformly bonded to the surface of the particles.

  The heating is not limited to being held at a constant temperature, and may be performed by setting the holding temperature in multiple stages. When 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 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 performed in a box furnace, tunnel kiln furnace, roller hearth furnace, rotary kiln furnace or the like.

Heating is preferably performed in air, an inert gas, or a reducing gas, and particularly preferably performed in an inert gas or a reducing gas. The conditions of the inert gas and the reducing gas are the same as those in the melting step (I). In addition, the gas atmosphere can be adjusted by introducing methane gas or acetylene gas into the furnace. The pressure may be any of normal pressure, pressurization (1.1 × 10 ⁵ Pa or more), and reduced pressure (0.9 × 10 ⁵ Pa or less). In addition, when a container containing a reducing agent (for example, graphite) and pulverized material is loaded in a heating furnace, reduction of M in the pulverized material (for example, change from M ³⁺ to M ²⁺ ) is promoted. can do. Thereby, a phosphoric acid compound can be obtained with good reproducibility.

  After the heating step (IV), it is usually cooled to room temperature. The cooling rate is preferably 30 to 300 ° C./hour. By setting the cooling rate within this range, distortion due to heating can be removed. 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. The cooling is preferably performed from 300 to 900 ° C. in the heating step (IV) to room temperature at a cooling rate of 30 to 300 ° C./hour.

  After obtaining the phosphoric acid compound in the heating step (IV), a pulverized product of the phosphoric acid compound and a carbon source may be obtained, and then the pulverized product may be heated in an inert gas or a reducing gas. .

  In the production method of the present invention, when at least one carbon source selected from the group consisting of an organic compound and a carbon-based conductive material is included, a conductive material derived from the carbon source is uniformly formed on the surface of the phosphate compound particles. And can be firmly bonded. The phosphoric acid compound particles to which the conductive material is bonded can be used as a positive electrode material for a secondary battery as it is. When an organic compound is used as the carbon source, the organic compound is carbonized in the heating step (IV), and the carbide covers at least a part of the surface of the phosphate compound as a conductive material. When a carbon-based conductive material is used as the carbon source, the material covers at least a part of the surface of the phosphate compound as a conductive material. Further, when both are used as the carbon source, the carbide derived from the organic compound and the carbon-based conductive material cover at least a part of the surface of the phosphate compound to form a conductive material network.

[Positive electrode for secondary battery and method for producing secondary battery]
A positive electrode for a secondary battery and a secondary battery can be produced using the phosphoric acid compound obtained by the production method of the present invention as a positive electrode material for a secondary battery. 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 of the present invention can be manufactured according to a known electrode manufacturing method except that the phosphoric acid compound of the present invention is used. For example, if necessary, the phosphoric acid compound of the present invention may be a known binder (polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, (Polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, etc.) and further mixed with a known conductive material (acetylene black, carbon, graphite, natural graphite, artificial graphite, needle coke, etc.) if necessary, and further known Organic solvents (N-methylpyrrolidone, toluene, cyclohexane, dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropyl alcohol) Emissions, ethylene oxide, was slurried with tetrahydrofuran), by a method such as coating the known current collector (aluminum or stainless steel metal foil and the like), can be produced.

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

  Although an example is given and explained concretely, the present invention is not limited to the following explanation. Examples 1-28 and Examples 41-48 are Examples, Examples 31-34, and Examples 51 and 52 are comparative examples.

[Examples 1-22, 31-33]
(Melting step (I))
The composition of the melt is Li ₂ O, P ₂ O ₅ , MnO ₂ , Fe ₂ O ₃ , Co ₃ O ₄ , NiO, MgO, ZnO, CaO, ZrO ₂ , and TiO ₂ equivalent (unit: mol%) , Lithium carbonate (Li ₂ CO ₃ ), ammonium hydrogen phosphate (NH ₄ H ₂ PO ₄ ), manganese dioxide (MnO ₂ ), triiron tetroxide (Fe ₃ O ₄₎ ), Tricobalt tetroxide (Co ₃ O ₄ ), nickel oxide (NiO), magnesium oxide (MgO), zinc oxide (ZnO), calcium carbonate (CaCO ₃ ), zirconium oxide (ZrO ₂ ), and titanium oxide ( TiO ₂ ) was weighed, mixed and pulverized by a dry method to obtain a raw material formulation.

The obtained raw material mixture 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 Co., Ltd., apparatus name: NH-3035) having a heating element made of molybdenum silicide. The electric furnace was heated at a rate of + 300 ° C./hour and heated at 1,250 to 1,320 ° C. for 0.5 hours while flowing N ₂ gas at a flow rate of ₂ L / min. After confirming that it became transparent visually, a melt was obtained.

(Cooling step (II))
The melt in the crucible obtained in the melting step (I) is passed through a stainless steel double roller having a diameter of about 15 cm rotating at 400 revolutions per minute to cool the melt to room temperature at 1 × 10 ⁵ ° C./sec. A solidified product was obtained. The obtained solidified product was a glassy substance.

(Crushing step (III))
The flaky solidified product obtained in the cooling step (II) was lightly kneaded and finely ground, and then coarsely pulverized using a cutter mill. Furthermore, this was pulverized wet with a ball mill using zirconia balls as a pulverizing medium and dried to obtain a finely pulverized product. The pulverization was performed stepwise using a ball having a diameter of 5 mm and then a ball having a diameter of 2 mm. Ethanol was used as a grinding solvent.

  Glucose, sucrose, and carbon black are added to the finely pulverized product, and the mass ratio of the finely pulverized product, the carbon equivalent of glucose, the carbon equivalent of sucrose, and the carbon equivalent of carbon black is 89: 3: 5: 3. Then, a small amount of pure water was added and mixed. The pulverized material mixed with the carbon source was dried and then subjected to the subsequent heating step (IV).

(Heating step (IV))
The pulverized material obtained by mixing a carbon source, an electric furnace (manufactured Motoyama Co., Ltd., device name: SKM-3035) using a _{H 2} gas at 3 _vol% H 2 -N ₂ gas and heated for 8 hours at 600 ° C. Then, the mixture was cooled to room temperature to precipitate phosphate compound particles.

[Examples 23 and 24]
Lithium carbonate (Li ₂ CO ₃ ), ammonium hydrogen phosphate (NH ₄ H ₂ PO ₄ ), manganese dioxide (MnO ₂ ), dioxide trioxide so that the composition of the melt is the same as in Examples 1 and 16, respectively. Iron (Fe ₂ O ₃ ) and zirconium oxide (ZrO ₂ ) were weighed, mixed and pulverized by a dry method to obtain a raw material formulation. The obtained raw material formulation was melted in the same manner as in Example 1 to obtain a melt.

  Otherwise in the same manner as in Example 1, phosphoric acid compound particles were obtained.

[Examples 25 and 26]
Lithium carbonate (Li ₂ CO ₃ ), ammonium hydrogen phosphate (NH ₄ H ₂ PO ₄ ), manganese oxalate (Mn (COO) ₂ ) so that the composition of the melt is the same as in Example 1 and Example 12, respectively. , Iron oxalate (Fe (COO) ₂ ), magnesium oxide (MgO) and titanium oxide (TiO ₂ ) were weighed, mixed and pulverized in a dry process to obtain a raw material formulation.

  Otherwise in the same manner as in Example 1, phosphoric acid compound particles were obtained.

[Examples 27 and 28]
In the same manner as in Examples 1 and 12, melting and cooling were performed. The flaky solidified product obtained in the cooling step (II) was lightly crushed by hand and then coarsely pulverized using a cutter mill to obtain a coarsely pulverized product. The coarsely pulverized product and ethyl cellulose were mixed so that the mass ratio of the coarsely pulverized product and the amount of carbon in the ethyl cellulose was 9: 1. Using acetone as a grinding solvent, fine grinding was performed using a ball mill. After the finely pulverized product was dried, it was subjected to the subsequent heating step (IV) to obtain phosphate compound particles.

[Example 34]
The melt was prepared and melted in the same manner as in Example 1 so that the composition of the melt was Li ₂ O, P ₂ O ₅ , MnO ₂ , and MgO equivalent (unit: mol%) and the ratio shown in Table 1. However, a uniform melt could not be obtained.

(Measurement of X-ray diffraction)
The mineral phase of the obtained phosphoric acid compound particles was examined using an X-ray diffraction apparatus (manufactured by Rigaku Corporation, apparatus name: RINT TTRIII). The phosphoric acid compound particles obtained in Examples 1 to 28 were all confirmed to be olivine-type crystal particles in which the crystal system is orthorhombic and the space group is considered to be Pnma. An oxide of Mg, Zn, Ca, Zr, and Ti, a composite compound of at least one of these with Li, and a composite compound of at least one of these with P were not identified. The X-ray diffraction patterns of the phosphoric acid compound particles obtained in Examples 1 to 3 are shown in FIG. 1 (a), (b), and (c), respectively. The X-ray diffraction patterns of the phosphoric acid compound particles obtained in Examples 16 to 18 are shown in (a), (b), and (c) of FIG. 2, respectively.

(Morphological observation)
The form of the phosphoric acid compound particles obtained in Example 1 was observed with a scanning electron microscope (manufactured by Hitachi, Ltd., apparatus name: SU6600). FIG. 3 shows an image obtained by observation.

(Measurement of particle size distribution and specific surface area)
The particle size distribution of the phosphoric acid compound particles obtained in Examples 1 to 3 was measured with a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba, Ltd., device name: LA-920). The volume-converted median diameters were 0.34 μm (Example 1), 0.36 μm (Example 2), and 0.34 μm (Example 3), respectively.

Furthermore, when the specific surface area was measured with a specific surface area measuring device (manufactured by Shimadzu Corporation, device name: ASAP2020), 29 m ² / g (Example 1), 28 m ² / g (Example 2), and 31 m ² / g, respectively. (Example 3).

(Composition analysis)
The chemical composition of the obtained phosphoric acid compound particles was measured. First, organic substances on the particle surface were removed by oxidation with 4 mol / L H ₂ O ₂ , and then a 6.0 mol / L HCl solution was added and decomposed at 80 ° C. Li in the decomposition solution was quantified using an atomic absorption photometer (manufactured by Hitachi High-Technologies Corporation, apparatus name: Z-2310). Further, P, Mn, Fe, Co, Ni, Mg, Zn, Ca, Zr, and Ti in the decomposition solution are obtained by using an inductively coupled emission spectroscopic analyzer (manufactured by Seiko Instruments Inc., apparatus name: SPS3100). Quantified. From the quantitative values of Li, P, Mn, Fe, Co, Ni, Mg, Zn, Ca, Zr, and Ti, Li ₂ O, P ₂ O ₅ , MnO, FeO, CoO, NiO, MgO, ZnO, CaO, The amounts of ZrO ₂ and TiO ₂ were calculated respectively. Table 2 shows quantitative values of chemical compositions of the phosphoric acid compound particles obtained in Examples 1 to 28 and Examples 31 to 33.

(Measurement of carbon content)
The carbon content of the obtained phosphoric acid compound particles was measured with a carbon analyzer (manufactured by Horiba, Ltd., apparatus name: EMIA-920V). Table 2 shows the carbon contents of the phosphoric acid compound particles obtained in Examples 1 to 28 and Examples 31 to 33.

[Examples 41 to 48, Examples 51 to 52: Production Examples of Positive Electrode for Li-ion Secondary Battery and Evaluation Battery]
Phosphoric acid compound particles (active material), polyvinylidene fluoride resin (binder) and acetylene black (conductive material) obtained in Examples 1, 2, 5, 11, 16, 18, 23, 25, 31, and 32 Were weighed so as to have a mass ratio of 80: 8: 12 and mixed in N-methylpyrrolidone (solvent) until uniform to prepare a slurry. Next, the slurry was applied to an aluminum foil having a thickness of 20 μm with a doctor blade. 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 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. and then carried into a glove box filled with purified argon gas. The electrode was opposed to a counter electrode obtained by pressure bonding a lithium foil to a nickel mesh through a separator made of porous polyethylene film, and both sides were sandwiched and fixed by a polyethylene plate to obtain a counter electrode.

  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 counter electrode after impregnation with the electrolytic solution was taken out from the beaker, placed in an aluminum laminate film bag, the lead wire portion was taken out and sealed to form a half-cell. The characteristics of this half-cell were measured as follows.

(Evaluation of electrochemical properties 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 perform an initial 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 15 mA / g (equivalent to 0.088 C). The end-of-charge voltage was 4.5 V based on 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. Table 3 shows the initial discharge capacity values obtained in Examples 41 to 48 and Examples 51 and 52.

  Next, the rate maintenance rate was measured. The current density during charging was 15 mA / g, and the current density during discharging was 15 mA / g, 37.5 mA / g, 150 mA / g, 300 mA / g, 600 mA / g, and 1200 mA / g. Moreover, the charge end voltage was set to 4.5 V with respect to the Li counter electrode, and discharge was started immediately after reaching the end voltage. The end-of-discharge voltage was 1.5 V with respect to the Li counter electrode. A value obtained by dividing the discharge capacity value at 600 mA / g by the discharge capacity value at 15 mA / g was defined as a rate maintenance rate. The rate maintenance rates obtained in Examples 41 to 48 and Examples 51 and 52 are shown in Table 3.

  Furthermore, the discharge capacity retention rate was measured. The current densities during charging and charging were 150 mA / g and 37.5 mA / g, respectively, and the charge end potential and discharge end voltage were 4.5 V and 1.5 V, respectively, based on the Li counter electrode. This charging / discharging was repeated 20 times. The ratio of the 20th discharge capacity value to the 1st discharge capacity value was defined as the discharge capacity retention rate. The discharge capacity retention rates obtained in Examples 41 to 48 and Examples 51 and 52 are shown in Table 3.

It has been found that the phosphoric acid compound of the present invention exhibits excellent electrochemical properties, particularly rate maintenance rate and discharge capacity maintenance rate. That is, it was confirmed that the phosphoric acid compound of the present invention can be used as a positive electrode material for a secondary battery, and a positive electrode for a secondary battery having good electrochemical properties can be obtained efficiently.

  The phosphoric acid compound of the present invention is useful when applied to a positive electrode material for a secondary battery and further to a secondary battery. The method for producing a phosphate compound of the present invention is useful because a phosphate compound having excellent electrochemical properties can be produced inexpensively and efficiently.

Claims (10)

In terms of oxide-based mol%, Li ₂ O is 20% to 35%, P ₂ O ₅ is 20% to 35%, MnO ₂ is 35% to 55%, and Fe ₂ O ₃ is 0% or more. Less than 10%, Co ₃ O ₄ is 0% or more and less than 8%, NiO is 0% or more and less than 15%, and at least one selected from the group consisting of MgO, ZnO, CaO, ZrO ₂ and TiO ₂ is 0.00. A step of heating and melting the raw material formulation containing 05% or more and 10% or less to obtain a melt;
Cooling the melt to obtain a solidified product;
Pulverizing the solidified product to obtain a pulverized product;
Heating the pulverized product to obtain particles containing crystals containing an olivine structure;
The manufacturing method of the phosphoric acid compound characterized by implementing in this order.   The manufacturing method according to claim 1, wherein the raw material formulation is melted at 1,000 ° C. to 1,400 ° C. in an inert gas or a reducing gas. The manufacturing method according to claim 1 or 2, wherein the melt is cooled at a cooling rate of 10 ³ to 10 ¹⁰ ° C / second.   The manufacturing method according to any one of claims 1 to 3, wherein the melt is cooled in an inert gas or a reducing gas.   The pulverized product includes the solidified product and at least one carbon source selected from the group consisting of an organic compound and a carbon-based conductive material, and a carbon equivalent amount (mass) in the carbon source is the amount of the solidified product. The manufacturing method as described in any one of Claims 1-4 which is 0.1-20 mass% with respect to the total mass of mass and the carbon conversion amount (mass) in this carbon source.   The manufacturing method as described in any one of Claims 1-5 which heats the said pulverized material at 300 to 900 degreeC in inert gas or reducing gas.   A method for producing a positive electrode material for a secondary battery, wherein a phosphoric acid compound is obtained by the production method according to claim 1 and then a positive electrode material for a secondary battery is obtained using the phosphoric acid compound. .   A method for producing a secondary battery, comprising: obtaining a positive electrode material for a secondary battery by the production method according to claim 7, and then obtaining a secondary battery using the positive electrode material for the secondary battery. A phosphoric acid compound having a composition represented by the following formula (1).
_{Li 1 + a (Mn 1- (} q + r) Fe q M r) 1-x + b X x PO 4 + c (1)
(Wherein, M is at least one selected from the group consisting of Co and Ni, X is at least one selected from the group consisting of Mg, Zn, Ca, Zr and Ti, a, b, q, r, and x are -0.2≤a≤0.1, -0.2≤b≤0.1, 0≤q≤0.3, 0≤r <0.2, respectively. 0 ≦ (q + r) ≦ 0.35, 0.001 ≦ x ≦ 0.2, and c depends on the valence of Mn, Fe, M, and X, and a, b, q, r, and x And a number that satisfies electrical neutrality.) A phosphoric acid compound having a composition represented by the following formula (2).
_{Li d (Mn 1-s Fe} s) e X y PO 4 + f (2)
(Wherein X is at least one selected from the group consisting of Mg, Zn, Ca, Zr, and Ti, and d, e, s, and y are 0.95 ≦ d ≦ 1.10, respectively. 0.95 ≦ e ≦ 1.05, 0.03 ≦ s ≦ 0.3, and 0.001 ≦ y ≦ 0.2, and f is the valence of Mn, Fe, and X, and d, Depends on e, s, and y, and is a number that satisfies electrical neutrality.)

Images