JP5460980B2 - Process for producing transition metal phosphate - Google Patents

Description

  The present invention relates to a method for producing a transition metal phosphate that can be doped and dedoped with sodium ions. In detail, it is related with the manufacturing method of the transition metal phosphate useful as an active material for sodium secondary batteries.

  Non-aqueous electrolyte secondary batteries, especially lithium secondary batteries, have been put into practical use and widely used as small power sources for mobile phones and notebook computers. In addition, there is an increasing demand for non-aqueous electrolyte secondary batteries for large power sources such as electric vehicles and distributed power storage.

  However, the lithium used in the lithium secondary battery cannot be said to be abundant in terms of resources, and there is a concern about the depletion of lithium resources in the future. On the other hand, sodium belonging to the same alkali metal is present in abundant resources as compared with lithium, and is one digit cheaper than lithium. Moreover, since sodium has a relatively high standard potential, it is considered that a sodium secondary battery can be a high-capacity secondary battery. Here, as a sodium secondary battery, a positive electrode active material containing sodium is used for the positive electrode, and a secondary battery using metal sodium or a sodium alloy is used for the negative electrode, or a positive electrode active material containing sodium is used for the positive electrode, In addition, a secondary battery using a carbon material or the like for the negative electrode can be used. If a sodium secondary battery can be used instead of the current lithium secondary battery, there is no need to worry about resource depletion. For example, a large battery such as an in-vehicle secondary battery or a distributed power storage secondary battery can be used. Secondary batteries can be produced in large quantities.

  By the way, as a positive electrode active material used for the positive electrode of a sodium secondary battery, for example, in Patent Document 1, a raw material is mixed and fired at 750 ° C. for 8 hours in an argon atmosphere to obtain sodium iron phosphate. , It is disclosed that this is used as a positive electrode active material.

Special table 2004-533706 gazette

  However, in general, although transition metal phosphates have poor conductivity, as disclosed in Patent Document 1, the conventional technique requires heat treatment for a long time at a high temperature, so primary particles grow greatly. As a result, the conductivity of the resulting transition metal phosphate is further reduced. Moreover, it is difficult to obtain a transition metal phosphate having a high crystal purity, and it is difficult to suitably use it as a positive electrode active material for a secondary battery capable of realizing a high capacity. Furthermore, since the firing atmosphere is limited to an inert atmosphere such as argon or nitrogen, a simple synthesis cannot be performed.

  Under such circumstances, an object of the present invention is to provide a transition metal phosphate that can be easily and inexpensively produced a transition metal phosphate suitable as an active material for a sodium secondary battery, particularly a positive electrode active material. It is to provide a manufacturing method.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found a production method that meets the above-mentioned purpose and have reached the present invention.

That is, the present invention relates to the following manufacturing method.
<1> A method for producing a transition metal phosphate including the following steps.
(1) Step of obtaining a liquid material by contacting P source, Na source, M source (where M is one or more transition metal elements) and water (2) separating water from the liquid material Step 2 for obtaining a transition metal phosphate The step (1) is a step in which an aqueous solution containing P and Na is brought into contact with an aqueous solution containing an M compound or an M compound to obtain a liquid material. The manufacturing method of the transition metal phosphate of <1> description.
<3> The method for producing a transition metal phosphate according to <1>, wherein the step (1) is a step of obtaining a liquid by bringing an aqueous solution containing Na and M into contact with an aqueous solution containing P. .
<4> The method for producing a transition metal phosphate according to any one of <1> to <3>, wherein M contains a divalent transition metal element.
<5> The method for producing a transition metal phosphate according to any one of <1> to <4>, wherein M contains at least Fe or Mn.
<6> The method for producing a transition metal phosphate according to <1>, wherein the step (2) includes a step of evaporating water.
<7> The method for producing a transition metal phosphate according to <6>, wherein the water is evaporated by heating.

  According to the production method of the present invention, a transition metal phosphate suitable as an active material for a sodium secondary battery does not require firing at a high temperature for a long time as in the prior art, and also requires an inert atmosphere. Therefore, the present invention is extremely useful industrially because it can be produced easily and inexpensively.

Hereinafter, the present invention will be described in detail.
First, the manufacturing method of this invention concerns on the manufacturing method of the transition metal phosphate containing the following process.
(1) Step of obtaining a liquid material by contacting P source, Na source, M source (where M is one or more transition metal elements) and water (2) separating water from the liquid material , Obtaining a transition metal phosphate

That is, in the present invention, first, (1) at least a P source, a Na source, an M source and water are brought into contact with each other to obtain a liquid material, and then (2) water is separated from the liquid material to make transition. It includes a step of obtaining a metal phosphate.
In the present invention, as each of the P source, the Na source, and the M source, a P compound, a Na compound, and an M compound may be used, or a simple substance of P, Na, and M may be used. In the present invention, the liquid substance may be an aqueous solution in which a solute is completely dissolved, or a solid-liquid mixture containing a solid content precipitated after the dissolution.

The process of obtaining a liquid substance by contacting the P source, Na source, M source and water in the step (1) will be described.
In this step, for example, a liquid material is obtained by bringing a P compound, a Na compound, an M compound and water into contact with each other. In this case, a composite compound containing P and Na may be used instead of the P compound and Na compound, or a composite oxide containing P and M may be used instead of the P compound and M compound. Alternatively, a complex oxide containing Na and M may be used instead of the Na compound and the M compound. As complex oxides containing P and Na, NaH ₂ PO ₄ , Na ₂ HPO ₄ , Na ₃ PO _{4 and the} like can be mentioned. As compounds containing M and P, phosphates of M (for example, phosphorus And iron oxide, manganese phosphate, etc.). Among these complex oxides, NaH ₂ PO ₄ is particularly useful.

As the P source, a P compound is usually used, but a simple substance of P such as red phosphorus or black phosphorus can also be used. The P compound is not particularly limited as long as it is a compound containing P, and examples thereof include oxides such as P ₂ O ₅ and P ₄ O ₆ , PCl ₅ , PF ₅ , PBr ₅ , and PI _5. Halides such as, oxyhalides such as POF ₃ , POCl ₃ and POF ₃ , ammonium salts such as (NH ₄ ) ₂ HPO ₄ and (NH ₄ ) H ₂ PO _4, and phosphoric acids such as H ₃ PO ₄ It is done. In the step (1), the P compound is dissolved in water as an aqueous solution (hereinafter also referred to as “P compound aqueous solution”) in that the reactivity with the Na source and / or the M source is improved. It is preferably used.
For example, when an ammonium salt of P is used, the ammonium salt may be dissolved in water to produce a P compound aqueous solution. When the P compound is difficult to dissolve in water, for example, in the case of an oxide, the P compound is dissolved in an acidic aqueous solution such as an organic acid such as hydrochloric acid, sulfuric acid, nitric acid, acetic acid, etc. That's fine. Moreover, you may use 2 or more types together among the above-mentioned water-soluble compound and the compound which is difficult to melt | dissolve. In the step (1), from the viewpoint of obtaining a P compound aqueous solution by a simple method, the P compound is preferably (NH ₄ ) ₂ HPO ₄ and / or (NH ₄ ) H ₂ PO ₄ . (NH ₄ ) ₂ HPO ₄ is particularly preferred in that a high transition metal phosphate can be obtained.

As the Na source, a Na compound is usually used, but Na simple substance (metal Na) can also be used. The Na compound is not particularly limited as long as it is a compound containing Na. Examples of the Na compound include oxides such as Na ₂ O and Na ₂ O ₂ , hydroxides such as NaOH, and halogens such as NaCl and NaF. , Nitrates such as NaNO ₃ , sulfates such as Na ₂ SO ₄ , carbonates such as Na ₂ CO ₃ and NaHCO ₃ , oxalates such as Na ₂ C ₂ O ₄ , acetic acid such as Na (CH ₃ COO) Examples include salt. In the step (1), the Na compound is an aqueous solution obtained by dissolving in water (hereinafter also referred to as “Na compound aqueous solution”) in that the reactivity with the P source and / or the M source is improved. It is preferably used. For example, in the case of using a water-soluble compound such as an oxide, hydroxide, or halide, the compound may be dissolved in water to produce an aqueous Na compound solution. In general, Na compounds are often easily dissolved in water. However, in the case of compounds that are difficult to dissolve, Na compounds can be dissolved in an acidic aqueous solution such as hydrochloric acid, sulfuric acid, nitric acid, acetic acid and other organic acids. What is necessary is just to manufacture compound aqueous solution. Moreover, you may use 2 or more types together among the above-mentioned water-soluble compound and the compound which is difficult to melt | dissolve. In the step (1), from the viewpoint of obtaining an aqueous Na compound solution by a simple method, the Na compound is preferably NaOH and / or NaCl. As described later, the aqueous Na compound solution is preferably alkaline. NaOH is particularly preferred.

  As the M source (where M is a transition metal element), an M compound is usually used, but a simple substance of M (metal M) can also be used. Examples of the transition metal element M include TI, V, Cr, Mn, Fe, Co, NI, and Cu. When the transition metal phosphate obtained by the production method of the present invention is used as a positive electrode active material, M is preferably a divalent transition metal element in that a high-capacity secondary battery can be obtained. Further, it is more preferable that M contains at least Fe or Mn, and it is particularly preferable that M is Fe and / or Mn.

The M compound is not particularly limited as long as it is a compound containing M. Oxides such as MO, MO ₂ , M ₂ O ₃ , MO ₄ , M (OH) ₂ , M (OH) _3, etc. Hydroxides, oxyhydroxides such as MOOH, halides such as MF ₂ , MF ₃ , MCl ₂ , MCl ₃ , MI ₂ , MI ₃ , M (NO ₃ ) ₂ , M (NO ₃ ) _3, etc. Nitrates, sulfates such as M (SO ₄ ), M ₂ (SO ₄ ) ₃ , carbonates such as MCO ₃ , oxalates such as MC ₂ O ₄ , M (CH ₃ COO) ₂ , M (CH ₃ COO ) Acetates such as ₃ , formates such as M (HCOO) ₂ , propionates such as M (C ₂ H ₅ COO) ₂ , malonates such as M (CH ₂ (COO) ₂ ), M (C Succinate such as ₂ H ₄ (COO) ₂ ).
In the step (1), the M compound is an aqueous solution obtained by dissolving in water (hereinafter also referred to as “M compound aqueous solution”) in that the reactivity with the P source and / or Na source is improved. It is preferable. For example, when a water-soluble compound such as a halide, nitrate, sulfate, oxalate, or acetate is used, the compound may be dissolved in water to produce an aqueous M compound solution. When the M compound is difficult to dissolve in water, for example, when the M compound is an oxide, hydroxide, oxyhydroxide, carbonate, etc., organic acids such as hydrochloric acid, sulfuric acid, nitric acid, acetic acid An M compound aqueous solution may be produced by dissolving in an acidic aqueous solution such as Moreover, you may use 2 or more types together among the above-mentioned water-soluble compound and the compound which is difficult to melt | dissolve. In the step (1), the M compound is preferably a halide, and MCl ₂ is particularly preferable from the viewpoint of obtaining an M compound aqueous solution by a simple method.

In step (1), an aqueous solution containing P and Na and an aqueous solution containing an M compound can be contacted to obtain a liquid material. As an aqueous solution containing P and Na, an arbitrary substance may be selected from simple substances of P and Na, the P compound and the Na compound, and dissolved in water to produce an aqueous solution.
In this case, the aqueous solution containing P and Na may be an aqueous solution formed by bringing a complex compound containing P and Na into contact with water.

In step (1), an aqueous solution containing Na and M and an aqueous solution containing P can be brought into contact with each other to obtain a liquid material. As an aqueous solution containing Na and M, an arbitrary substance may be selected from Na and M alone, the Na compound and the M compound, and dissolved in water to produce an aqueous solution.
In this case, the aqueous solution containing Na and M may be an aqueous solution formed by bringing a complex compound containing Na and M into contact with water.

  Furthermore, in the step (1), the P compound aqueous solution, the Na compound aqueous solution and the M compound aqueous solution can be brought into contact with each other to obtain a liquid material. As the P compound aqueous solution, the Na compound aqueous solution, and the M compound aqueous solution, each required compound may be arbitrarily selected and dissolved in water to produce each compound aqueous solution.

As described above, the P compound, the Na compound, and the M compound are preferably used as an aqueous solution containing each compound, in that a liquid product obtained by uniformly reacting the P compound, the Na compound, and the M compound is obtained. In particular, the M compound is preferably used as an aqueous solution.
Moreover, in the range which does not impair the objective of this invention, you may contain components other than P, Na, M, or water in the said liquid substance.

As specific examples of the step (1), diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ) is used as the P compound, sodium hydroxide (NaOH) is used as the Na compound, and iron (II) chloride tetrahydrate is used as the M compound. A case where a product (FeCl ₂ .4H ₂ O) is used will be described as an example.
For example, sodium iron phosphate represented by NaFePO ₄ , which is one of the preferred compositions, includes sodium hydroxide, iron (II) chloride tetrahydrate, and diammonium hydrogen phosphate in a molar ratio of Na: Fe: P. Weigh each compound so that it has a predetermined ratio, and then completely dissolve each weighed compound in ion-exchanged water to prepare an aqueous solution containing each compound. Then, diammonium hydrogenphosphate aqueous solution and sodium hydroxide are prepared. An aqueous solution is contacted to produce a mixed aqueous solution containing P and Na. Usually, at this time, it is difficult for solids to be present in the mixed aqueous solution. Next, the mixed aqueous solution and the iron (II) chloride aqueous solution are contacted to obtain a liquid material. Usually, at this time, the liquid is a solid-liquid mixture containing a solid. In addition, although a reason is not clear at this time, in order to reduce an impurity phase more when obtaining the said solid-liquid mixture, it is preferable that Na compound aqueous solution is alkaline.

  The order in which each aqueous solution is contacted is not limited to the above, and a sodium hydroxide aqueous solution and an iron (II) chloride aqueous solution are contacted to obtain a mixed aqueous solution containing Na and Fe, and then the phosphoric acid is added to the mixed aqueous solution. A method of obtaining a liquid by contacting an aqueous solution of diammonium hydrogen may be used, or an aqueous solution of diammonium hydrogenphosphate and an aqueous solution of iron (II) chloride may be contacted to obtain a mixed aqueous solution containing P and Fe, and then the mixed aqueous solution Alternatively, a method may be used in which a sodium hydroxide aqueous solution is brought into contact with each other to obtain a liquid.

  In the step of obtaining the mixed aqueous solution and / or liquid, stirring can be performed by any method. Examples of the mixing apparatus include stirring and mixing with a stirrer, stirring and mixing with a stirring blade, a V-type mixer, a W-type mixer, a ribbon mixer, a drum mixer, a ball mill, and the like.

The transition metal phosphate obtained by the production method of the present invention is preferably represented by the following formula (I), and more preferably a positive electrode active material for a sodium secondary battery.
_{Na x M y PO 4 (I} )
(However, in the formula (I), x is in the range of more than 0 and 1.5 or less, y is in the range of 0.8 to 1.2, and M is one or more transition metal elements.)

  In addition, in the formula (I), M preferably contains at least Fe or Mn, and M is particularly preferably Fe and / or Mn in that a high-capacity and inexpensive sodium secondary battery can be obtained.

  When the transition metal phosphate obtained by the production method of the present invention is used as a positive electrode active material, the liquid material preferably contains a conductive material. Examples of the conductive material include carbon materials such as natural graphite, artificial graphite, cokes, and carbon black, and conductive polymer materials. By containing a conductive material in the liquid material, the conductivity of the transition metal phosphate is dramatically improved, and the discharge capacity in the case of a positive electrode for a sodium secondary battery is increased.

  Moreover, in the range which can maintain a high discharge capacity when setting it as a positive electrode for sodium secondary batteries, the substance containing elements other than Na, P, and M is added to the said liquid substance, Na, P in transition metal phosphate, A part of M may be substituted with another element. Here, as other elements, LI, B, C, N, F, Mg, Al, SI, S, Cl, K, Ca, Sc, Zn, Ga, Ge, Rb, Sr, Y, Zr, Nb, Examples of the element include Mo, Tc, Ru, Pd, Rh, Ag, In, Sn, I, Ba, Hf, Ta, W, Ir, and Ln (lanthanoid).

  Further, in the step (1), a step of heating the liquid material may be included, and an effect of promoting the reaction of the P source, the Na source, and the M source may be obtained by heating. It is preferable that the temperature range which heats is 40 degreeC or more and 100 degrees C or less. In addition, it is preferable to heat the liquid while stirring and / or mixing because the reaction promoting effect by heating is increased.

  The atmosphere of the step of heating the liquid is not particularly limited, and includes an oxidizing atmosphere containing oxygen or an air atmosphere, an inert atmosphere containing nitrogen or argon, a reducing atmosphere containing hydrogen, or the like. Can be mentioned. That is, oxygen and nitrogen, oxygen and argon can be mixed as appropriate to adjust the state of the oxidizing atmosphere, or hydrogen and nitrogen, hydrogen and argon can be mixed as appropriate, and the state of the reducing atmosphere can be adjusted. However, a simple atmospheric atmosphere is usually selected.

  Next, process (2) is demonstrated. Step (2) is a step of separating water from the liquid material obtained in step (1). The separation method is not particularly limited, and examples thereof include filtration, centrifugation, and a method of evaporating water. In particular, the step of separating water from the liquid material preferably includes a method of evaporating water, and finally the transition metal phosphoric acid dried by evaporating water by a method such as heating, reduced pressure, or natural drying. A salt can be obtained. In particular, the method of evaporating water by heating is preferable because a homogeneous transition metal phosphate can be easily obtained.

Moreover, you may combine said water separation method. For example, when the liquid is a solid-liquid mixture containing a solid, the transition metal phosphoric acid is obtained by separating the solid from the liquid by filtration, centrifugation, etc., and then evaporating water from the solid to dry it. A salt can be obtained.
Note that the atmosphere in the step of separating water from the liquid is not particularly limited, and is an oxidizing atmosphere containing oxygen, an air atmosphere, an inert atmosphere containing nitrogen or argon, or a reduction containing hydrogen. The atmospheric conditions such as sex atmosphere can be selected arbitrarily. That is, a transition metal phosphate can be easily produced in an air atmosphere.

Hereinafter, a process of removing water from the liquid material by evaporation by heating, which is suitable for separating water from the liquid material (hereinafter sometimes referred to as a heating process) will be described.
From the viewpoint of the evaporation rate of water from the liquid substance and the chemical stability of the resulting transition metal phosphate, the heating temperature range is preferably 50 ° C. or higher and 250 ° C. or lower, more preferably 80 ° C. or higher and 200 ° C. It is below, More preferably, it is 90 to 180 degreeC. Moreover, it can also be made to reach | attain rapidly to the said heating temperature in the range which does not break the container which put the said liquid substance.

  In addition, the transition metal phosphate obtained in the step of separating water from the liquid can be washed by the above filtration, centrifugation, and water evaporation methods. The solvent used for the washing is preferably water, more preferably pure water and / or ion exchange water. A transition metal phosphate from which water-soluble impurities and the like have been removed can be obtained by washing with pure water and / or ion-exchanged water and then drying. A preferable temperature range for the drying is the same as the temperature range for the heating. Moreover, the atmosphere at the time of drying is not specifically limited, It can also carry out by selecting arbitrarily the atmospheric conditions similar to the above-mentioned process (2), and can also carry out in a pressure-reduced atmosphere. Further, washing and drying may be repeated twice or more, and baking may be performed after drying.

  When the transition metal phosphate obtained by the production method of the present invention is used as a positive electrode active material, for example, a positive electrode active material for a sodium secondary battery, the obtained transition metal phosphate can be used as a ball mill, a vibration mill, or a jet mill. Etc. can be pulverized, classified, etc. to adjust the particle size. In addition, the obtained transition metal phosphate and the Na compound aqueous solution may be mixed and further heated, and the obtained transition metal phosphate may be mixed with Na compound or the like as necessary. Firing can also be performed at a temperature of 600 ° C to 1200 ° C. The atmosphere at the time of firing is not particularly limited, and the same atmosphere conditions as in the above step (2) can be arbitrarily selected, but firing in an inert atmosphere or a reducing atmosphere is preferable. . The pulverization and firing may be repeated twice or more, and the obtained transition metal phosphate can be washed or classified as necessary.

  Furthermore, with the transition metal phosphate obtained by the production method of the present invention as a core material, on the surface of the particles (core material), B, Al, Mg, Ga, In, SI, Ge, Sn, Nb, Surface treatment such as deposition of a compound containing one or more elements selected from Ta, W, Mo, and transition metal elements may be performed. Among the above elements, one or more selected from B, Al, Mg, Mn, Fe, Co, NI, Nb, Ta, W, and Mo are preferable, and Al is more preferable from the viewpoint of operability. Examples of the compound include organic acid salts such as oxides, hydroxides, oxyhydroxides, carbonates, nitrates, and acetates of the above elements, or mixtures thereof. Of these, oxides, hydroxides, oxyhydroxides, carbonates or mixtures thereof are preferred. Of these, alumina is more preferable.

  The above-mentioned transition metal phosphate can be used as an active material for a secondary battery such as a positive electrode active material for a sodium secondary battery by leaving it untreated or performing a surface treatment such as deposition.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these. Unless otherwise specified, powder X-ray diffraction measurement, particle size distribution measurement, BET specific surface area measurement and SEM observation of transition metal phosphates were performed by the following methods. The coin-type battery for charge / discharge test was produced by the following method.

(1) Powder X-ray diffraction measurement of transition metal phosphate As a powder X-ray diffraction apparatus, a powder X-ray diffraction measurement apparatus RINT2500TTR manufactured by Rigaku Corporation was used under the following conditions.
X-ray: CuKα
Voltage-current: 40 kV-140 mA
Measurement angle range: 2θ = 10-80 °
Step: 0.02 °
Scanning speed: 4 ° / min Divergent slit width: (DS) 1 °
Scattering slit width: (SS) 1 °
Light receiving slit width: (RS) 0.3 mm

(2) Particle size distribution measurement of transition metal phosphate It measured using the master sizer 2000 by Malvern as a laser diffraction scattering method particle size distribution measuring apparatus. As the dispersion medium, an aqueous 0.2 wt% sodium hexametaphosphate solution was used. As the measured value D50, the value of the particle size viewed from the fine particle side when 50% accumulated in the volume-based cumulative particle size distribution was used.

(3) Measurement of BET specific surface area of transition metal phosphate 1 g of transition metal phosphate powder was dried at 150 ° C. for 15 minutes in a nitrogen stream, and then measured using a Micrometrix Flowsorb II2300.

(4) SEM observation of transition metal phosphate As a scanning electron microscope observation apparatus, JSM-5500 made by JEOL Datum Co., Ltd. was used, and observation was performed under the condition of an acceleration voltage of 20 kV. For the aspect ratio (a / b) of the particles, the major axis a and minor axis b of 50 particles arbitrarily extracted from the obtained SEM observation photograph were measured, and the average value thereof was adopted.

(5) Production of coin-type battery for charge / discharge test Positive electrode active material powder, which will be described later as an example, acetylene black (hereinafter, also referred to as AB, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, and a binder SUS that becomes a positive electrode mixture by mixing and kneading PTFE (manufactured by Daikin Industries, Ltd.) so that the positive electrode active material: AB: PTFE is 75: 20: 5 in a weight ratio. The positive electrode mixture was applied to a mesh (# 100, 10 mmφ) and vacuum-dried at 150 ° C. for 8 hours to obtain a positive electrode. The weight of the obtained positive electrode was measured, the weight of the SUS mesh was subtracted from the weight of the positive electrode, the weight of the positive electrode mixture was calculated, and the weight of the positive electrode active material powder was calculated from the weight ratio of the positive electrode mixture. A solution obtained by dissolving NaClO ₄ in propylene carbonate (hereinafter sometimes referred to as PC) as an electrolyte so as to be 1 mol / liter (hereinafter sometimes referred to as NaClO ₄ / PC). Using a polyethylene porous membrane as a separator and metallic sodium as a negative electrode, a coin-type battery (R2032) was produced by combining these.

Using the above coin-type battery, a charge / discharge test was performed under the conditions shown below while maintaining at 25 ° C.
(Cell structure) Bipolar type Positive electrode: Electrode containing positive electrode active material Negative electrode: Electrode made of metallic sodium
Electrolyte: 1M NaClO ₄ / PC
(Charge / discharge conditions)
Voltage range: 1.5-4.2V
Charging rate: 0.05C rate (speed to fully charge in 20 hours)
Discharge rate: 0.05C rate (rate of complete discharge in 20 hours)

Example 1
(A) Synthesis of transition metal phosphate powder S ₁ Sodium hydroxide (NaOH); 1.8 g, diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ); 2.7 g, iron (II) chloride tetrahydrate Japanese (FeCl ₂ .4H ₂ O); 2.0 g was weighed and each weighed compound was placed in a glass 100 ml beaker. Next, 33 g of ion-exchanged water was added to the beaker and dissolved completely with stirring to prepare each compound aqueous solution. Next, while adding an aqueous sodium hydroxide solution and an aqueous diammonium hydrogen phosphate solution and stirring well, the iron (II) chloride tetrahydrate aqueous solution is further added thereto to obtain a solid-liquid mixture containing solids. It was. The obtained solid-liquid mixture was put into an eggplant-shaped flask, and then the eggplant-shaped flask was heated in an oil bath set at 170 ° C. to obtain a dry solid product in which water was evaporated. Next, the dryness article was collected, washed with water, filtered to give a transition metal phosphate powder S ₁ and then dried.

(B) Various Evaluations of Transition Metal Phosphate Powder S _{1 When} X-ray diffraction measurement was performed on the powder S ₁ , it was found to be single-phase orthorhombic NaFePO ₄ (malisite) (FIG. 1). ). The measured particle size distribution and the BET specific surface area of the powder S _1, D50 is 1.3 .mu.m, the BET specific surface area was 20 m ² / g. Further, SEM observation of the powder S ₁ revealed that the average value of the aspect ratio a / b was 9 when the major axis of the particles was a and the minor axis was b, including rod-shaped particles (FIG. 2). . Next, to prepare a coin battery using Powder S ₁ as the positive electrode active material was subjected to a charge and discharge test, it is confirmed that can be charged and discharged, the discharge capacity of 5th cycle was 78 mAh / g.

Example 2
(A) Synthesis of transition metal phosphate powder S ₂ A solid product is separated by filtration instead of a dry product obtained by evaporating water to obtain a separated product, except that the separated product is washed, filtered and dried. to obtain a transition metal phosphate powder S ₂ in the same manner as in example 1.

(B) Various Evaluations of Transition Metal Phosphate Powder S _{2 When} X-ray diffraction measurement was performed on the powder S ₂ , it was found to be a single-phase orthorhombic NaFePO ₄ (FIG. 1). The measured particle size distribution and the BET specific surface area of the powder S _2, D50 is 1.8 .mu.m, the BET specific surface area was 36m ² / g. Further, when SEM observation of the powder S ₂ was performed, the average value of the aspect ratio a / b was 5 when the major axis of the particle was a and the minor axis was b, including rod-shaped particles (FIG. 3). . Next, to prepare a coin battery using Powder S ₂ as the positive electrode active material was subjected to a charge and discharge test, it is confirmed that can be charged and discharged, the discharge capacity at the fifth cycle was 80mAh / g.

Example 3
(A) Synthesis of transition metal phosphate powder S ₃ Except that acetylene black as a conductive material was added to the solid-liquid mixture by 10% by weight with respect to the obtained transition metal phosphate, and the mixture was stirred and mixed. example obtain a transition metal phosphate powder S ₃ in the same manner as 1.

(B) Various Evaluations of Transition Metal Phosphate Powder S _{3 When} X-ray diffraction measurement was performed on the powder S ₃ , it was found to be single-phase orthorhombic NaFePO ₄ (FIG. 1). The measured particle size distribution and the BET specific surface area of the powder S _3, D50 is 2.6 [mu] m, BET specific surface area was 32m ² / g. Furthermore, it was subjected to SEM observation of the powder S _3, comprises a rod-like particles, that acetylene black was uniformly attached was verified on each particle (Fig. 4). The average aspect ratio a / b was 7 when the major axis of the particles was a and the minor axis was b. Next, to prepare a coin battery using Powder S ₃ as the positive electrode active material was subjected to a charge and discharge test, it is confirmed that can be charged and discharged, the discharge capacity at the fifth cycle was 85mAh / g.

Example 4
(A) Synthesis of transition metal phosphate powder S ₄ Diammonium hydrogen phosphate; phosphoric acid (H ₃ PO ₄ ) aqueous solution (phosphoric acid concentration 85 wt%, specific gravity 1.69) instead of 2.7 g; 2 mL except for using, to obtain a transition metal phosphate powder S ₄ in the same manner as in example 3.

(B) Various Evaluations of Transition Metal Phosphate Powder S _{4 When} X-ray diffraction measurement was performed on the powder S ₄ , it was found to be a single-phase orthorhombic NaFePO ₄ (FIG. 1). The measured particle size distribution and the BET specific surface area of the powder S _4, D50 is 0.35 .mu.m, BET specific surface area was 18m ² / g. Furthermore, was subjected to SEM observation of the powder S _4, comprises a rod-like particles, it was confirmed that the acetylene black was uniformly deposited on the particles (FIG. 5). The average value of the aspect ratio a / b was 6 when the major axis of the particles was a and the minor axis was b. Next, to prepare a coin battery using Powder S ₄ as the positive electrode active material was subjected to a charge and discharge test, it is confirmed that can be charged and discharged, the discharge capacity of 5th cycle was 75 mAh / g.

Example 5
(A) Synthesis of transition metal phosphate powder S ₅ Sodium hydroxide (NaOH); 3.5 g, manganese (II) chloride tetrahydrate (MnCl ₂ .4H ₂ O); 3.1 g, phosphoric acid (H ₃ PO ₄ ) aqueous solution (phosphoric acid concentration 85% by weight, specific gravity 1.69); 2 mL was weighed, and each weighed compound was placed in a glass 100 mL beaker. Next, 33 g of ion-exchanged water was added to the beaker and dissolved completely with stirring to prepare each compound aqueous solution. Next, an aqueous sodium hydroxide solution and an aqueous manganese (II) chloride tetrahydrate solution were added and stirred well, and the phosphoric acid aqueous solution was further added thereto to obtain a solid-liquid mixture containing solids. The obtained solid-liquid mixture was put into an eggplant-shaped flask, and then the eggplant-shaped flask was heated in an oil bath set at 170 ° C. and evaporated to dryness until water evaporated to obtain a dried product. Next, the dryness products were collected, washed with water, filtered to give a transition metal phosphate powder S ₅ and then dried.

(B) Various Evaluations of Transition Metal Phosphate Powder S _{5 When} X-ray diffraction measurement was performed on the powder S ₅ , it was found to be single-phase orthorhombic NaMnPO ₄ (FIG. 6). The measured particle size distribution and the BET specific surface area of the powder S _5, D50 is 1.67 .mu.m, BET specific surface area was 4.0 m ² / g. Furthermore, was subjected to SEM observation of the powder S _5, spherical particles were confirmed (Fig. 7). Next, to prepare a coin battery using Powder S ₅ as the positive electrode active material was subjected to a charge and discharge test, it was confirmed that the charge and discharge.

Comparative Example 1
(A) Synthesis of comparative powder R _{1 As} raw materials, ferric trioxide (Fe ₂ O ₃ ); 3.2 g, sodium carbonate (Na ₂ CO ₃ ); 2.1 g, diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ); 5.1 g was weighed, and each raw material was sufficiently pulverized and mixed with a ball mill to obtain a raw material mixture. Next, the raw material mixture was filled in an alumina boat, and in an electric furnace, a comparative powder R ₁ was obtained by holding and firing at a temperature of 750 ° C. for 8 hours while supplying nitrogen gas at 5 liters / minute.

(B) Various evaluations of the comparative powder R _{1 When} X-ray diffraction measurement was performed on the powder R ₁ , the main phase was monoclinic Na ₃ Fe ₂ (PO ₄ ) ₃ , and the single phase NaFePO ₄ was It was not obtained (FIG. 8). The measured particle size distribution and the BET specific surface area of the powder R _1, D50 is 14 [mu] m, BET specific surface area was 0.10 m ² / g. Furthermore, it was subjected to SEM observation powder R _1, particle shape was irregular shape (FIG. 9). Next, a coin-type battery was prepared using the powder R ₁ as a positive electrode active material and a charge / discharge test was performed. As a result, it was confirmed that charge / discharge was possible, but the discharge capacity at the fifth cycle was as low as 1 mAh / g. .

Comparative Example 2
(A) Synthesis of Comparative Powder R ₂ Iron oxalate dihydrate (FeC ₂ O ₄ .2H ₂ O): 5.1 g, sodium carbonate (Na ₂ CO ₃ ); 1.5 g, diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ); 3.8 g was weighed, and each raw material was sufficiently pulverized and mixed with a ball mill to obtain a raw material mixture. Next, the raw material mixture was filled in an alumina boat, in an electric furnace, a nitrogen gas with 5 liters / min aeration maintained at a temperature of 750 ° C. 24 hours to obtain Comparative Powder R ₂ by firing.

(B) Various evaluations of the comparative powder R _{2 When} X-ray diffraction measurement was performed on the powder R ₂ , the main phase was monoclinic Fe ₂ O ₃ and no single-phase NaFePO ₄ was obtained ( FIG. 8). The measured particle size distribution and the BET specific surface area of the powder R _2, D50 is 30 [mu] m, BET specific surface area was 0.26 m ² / g. Further, SEM observation of the powder R ₂ revealed that the particle shape was indefinite (FIG. 10). Next, a coin-type battery was prepared using the powder R ₂ as a positive electrode active material, and a charge / discharge test was performed. I could not.

Comparative Example 3
(A) except that the temperature during the synthesis calcination of Comparative Powder R ₃ to 800 ° C., in the same manner as in Comparative Example 2 to obtain a comparative powder R _3.

(B) Various evaluations of comparative powder R _{3 When} X-ray diffraction measurement was performed on powder R ₃ , the main phase was rhombohedral Fe ₂ O ₃ , and single-phase NaFePO ₄ was not obtained (see FIG. 8). The measured particle size distribution and the BET specific surface area of the powder R _3, D50 is 17 .mu.m, BET specific surface area was 0.47 m ² / g. Furthermore, it was subjected to SEM observation of the powder R _3, particle shape was irregular shape (FIG. 11). Next, to prepare a coin battery using Powder R ₃ as the positive electrode active material was subjected to a charge and discharge test, 1 discharge capacity cycle is as low as 1 mAh / g, it is charged and discharged up to the fifth cycle I could not.

Production Example 1 (Production of laminated porous film)
(1) Production of coating liquid After 272.7 g of calcium chloride was dissolved in 4200 g of N-methylpyrrolidone (NMP), 132.9 g of paraphenylenediamine was added and completely dissolved. To the obtained solution, 243.3 g of terephthalic acid dichloride was gradually added and polymerized to obtain para-aramid, which was further diluted with NMP to obtain a para-aramid solution (A) having a concentration of 2.0% by weight. To 100 g of the obtained para-aramid solution, 2 g of alumina powder (a) (Nippon Aerosil Co., Ltd., Alumina C, average particle size 0.02 μm) and 2 g of alumina powder (b) (Sumitomo Chemical Co., Ltd. Sumiko Random, AA03, average particles) 4 g in total as a filler is added and mixed, treated three times with a nanomizer, filtered through a 1000 mesh wire net, and degassed under reduced pressure to produce a slurry coating solution (B) did. The weight of alumina powder (filler) with respect to the total weight of para-aramid and alumina powder is 67% by weight.

(2) Production and Evaluation of Laminated Porous Film As a porous film that can be shut down, a polyethylene porous film (film thickness 12 μm, air permeability 140 seconds / 100 cc, average pore diameter 0.1 μm, porosity 50%) Was used. The polyethylene porous film was fixed on a PET film having a thickness of 100 μm, and the slurry-like coating liquid (B) was applied onto the porous film by a bar coater manufactured by Tester Sangyo Co., Ltd. While the coated porous film on the PET film is integrated, it is immersed in water which is a poor solvent to deposit a para-aramid porous layer (heat resistant porous layer), and then the solvent is dried to obtain a heat resistant porous layer. And a porous film 1 made of polyethylene were laminated. The thickness of the laminated porous film 1 was 16 μm, and the thickness of the para-aramid porous layer (heat resistant porous layer) was 4 μm. The laminated porous film 1 had an air permeability of 180 seconds / 100 cc and a porosity of 50%. When the cross section of the heat-resistant layer in the laminated porous film 1 was observed with a scanning electron microscope (SEM), relatively small pores of about 0.03 μm to 0.06 μm and relatively large fines of about 0.1 μm to 1 μm. It was found to have pores. The laminated porous film was evaluated by the following method.

Evaluation of laminated porous film (A) Thickness measurement The thickness of the laminated porous film and the thickness of the polyethylene porous film were measured in accordance with JIS standards (K7130-1992). Moreover, as the thickness of the heat-resistant layer, a value obtained by subtracting the thickness of the polyethylene porous film from the thickness of the laminated porous film was used.
(B) Measurement of air permeability by Gurley method The air permeability of the laminated porous film was measured with a digital timer type Gurley type densometer manufactured by Yasuda Seiki Seisakusho, based on JIS P8117.
(C) Porosity A sample of the obtained laminated porous film was cut into a square having a side length of 10 cm, and the weight W (g) and the thickness D (cm) were measured. The weight of each layer in the sample (WI (g)) was determined, and the volume of each layer was determined from WI and the true specific gravity (true specific gravity I (g / cm ³ )) of the material of each layer, The porosity (volume%) was obtained from the following formula.
Porosity (volume%) = 100 × {1− (W1 / true specific gravity 1 + W2 / true specific gravity 2 + ·· + Wn / true specific gravity n) / (10 × 10 × D)}

  In each of the above examples, when the laminated porous film obtained in Production Example 1 is used as a separator, a sodium secondary battery capable of further increasing the thermal membrane breaking temperature can be obtained.

  According to the production method of the present invention, a transition metal phosphate suitable as an active material for a sodium secondary battery can be produced by a simple and inexpensive production method, and comprises the transition metal phosphate. Since the sodium secondary battery using the electrode has a high capacity, it can be used not only for small applications such as portable electronic devices, but also for various applications such as medium and large applications such as hybrid vehicles and power storage. Furthermore, since abundant sodium as a resource is contained in the active material and a cheaper non-aqueous electrolyte secondary battery can be manufactured, the present invention is extremely useful industrially.

It is a figure which shows the powder X-ray-diffraction analysis result in Examples 1-4. 2 is a view showing an SEM observation photograph in Example 1. FIG. 6 is a view showing an SEM observation photograph in Example 2. FIG. 6 is a view showing an SEM observation photograph in Example 3. FIG. 6 is a view showing an SEM observation photograph in Example 4. FIG. FIG. 6 is a graph showing the result of powder X-ray diffraction analysis in Example 5. 6 is a view showing an SEM observation photograph in Example 5. FIG. It is a figure which shows the powder X-ray-diffraction analysis result in Comparative Examples 1-3. 6 is a view showing an SEM observation photograph in Comparative Example 1. FIG. 6 is a view showing an SEM observation photograph in Comparative Example 2. FIG. 10 is a view showing an SEM observation photograph in Comparative Example 3. FIG.

Claims (7)

A method for producing a transition metal phosphate having an orthorhombic crystal structure and represented by formula (I), comprising:
(1) Step of obtaining a liquid material by contacting P source, Na source, M source (where M is one or more transition metal elements) and water (2) separating water from the liquid material , Obtaining a transition metal phosphate

_{Na x M y PO 4 (I} )
(However, in the formula (I), x is in the range of more than 0 and 1.5 or less, y is in the range of 0.8 to 1.2, and M is Fe and / or Mn.)   The method for producing a transition metal phosphate according to claim 1, wherein the step (1) is a step of obtaining a liquid by bringing an aqueous solution containing P and Na into contact with an M compound or an aqueous solution containing an M compound. .   2. The method for producing a transition metal phosphate according to claim 1, wherein the step (1) is a step of obtaining a liquid by bringing an aqueous solution containing Na and M into contact with an aqueous solution containing P. The method for producing a transition metal phosphate according to any one of claims 1 to 3, wherein each of x and y in the transition metal phosphate represented by the formula (I) has a value of 1.   The method for producing a transition metal phosphate according to claim 1, wherein M is Fe or Mn. The method for producing a transition metal phosphate according to claim 1, wherein the step (2) includes a step of evaporating water.   The method for producing a transition metal phosphate according to claim 6, wherein the water is evaporated by heating.