JP2011175767A - Method of manufacturing electrode material, and recovery method of lithium phosphate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an electrode material, capable of efficiently recovering Li salt formed in a manufacturing process of LiFePO<SB>4</SB>as high-purity lithium phosphate, with low manufacturing cost and capable of reducing an environmental load, and to provide a recovery method of lithium phosphate. <P>SOLUTION: The method of manufacturing the electrode material includes: a step of adding an Fe source and a reducing agent to lithium phosphate slurry and to obtain suspension; a step of forming a crude product material which includes LiFePO<SB>4</SB>by making the suspension react under high temperature and high pressure; a step of separating the crude product material into a main product with LiFePO<SB>4</SB>as a principal component and solution; a step of removing an Fe compound by adding, to the solution, first alkaline containing 50 mol% or less of Ca(OH)<SB>2</SB>or CaO; and a step of forming lithium phosphate slurry by further adding a lithium source and a phosphate source so that a composition ratio in the solution (Li:P) is adjusted to 3:1, and by adding a second alkaline. These steps are performed by using the lithium phosphate slurry. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a method for producing an electrode material and a method for recovering lithium phosphate, and in particular, a method for producing an electrode material suitable for use in producing an electrode material represented by LiFePO ₄ and lithium phosphate. It relates to the collection method.

In recent years, lithium batteries, especially lithium-ion batteries, can be reduced in size, weight, and capacity as secondary batteries for portable electronic devices and hybrid vehicles, and have high output and high energy density. Therefore, it is often used.
As a positive electrode active material of this lithium ion battery, various lithium (Li) compounds have been proposed, and among them, a phosphate compound represented by LiFePO ₄ using abundant and inexpensive Fe, It is attracting attention in terms of low toxicity, high safety, and excellent cycle characteristics, and is actively researched for practical use.
As a method for synthesizing this LiFePO _4, a solid phase method has been conventionally known. However, in this solid phase method, since raw materials are mixed and then fired for a long time at a high temperature, the particle size is easily coarsened to 1 μm or more. There was a problem that LiFePO ₄ excellent in monodispersibility could not be synthesized. The coarse particles can be pulverized with a ball mill or the like, but in this case, it is difficult to pulverize to a sufficiently small particle size, and distortion and cracking occur due to the stress applied during pulverization, and the crystallinity also decreases. There is a point. Moreover, since it bakes for a long time at high temperature, there also exists a problem of requiring a lot of energy.

On the other hand, the hydrothermal synthesis method is a method of synthesizing LiFePO ₄ fine particles by heating a raw material at a high pressure in the presence of water. Therefore, LiFePO ₄ is low in temperature and excellent in monodispersibility compared with the solid phase method. _Four fine particles can be obtained.
By the way, when LiFePO ₄ fine particles are synthesized by a hydrothermal synthesis method, when the reaction solution contains acetate ions (CH 3 COO ⁻ ), sulfate ions (SO ₄ ²⁻ ), chlorine ions (Cl ⁻ ), etc., When excessive lithium (Li) is added, single-phase LiFePO ₄ fine particles are obtained, but adding excessive Li leads to an increase in raw material costs, and is not necessarily an inexpensive manufacturing method. Therefore, a method of recovering and reusing lithium (Li) ions remaining in the liquid phase after synthesis, for example, adjusting the pH of a Li salt solution and then adding sodium carbonate (Na ₂ CO ₃ ), etc. A method of recovering as (Li ₂ CO ₃ ) or the like is conceivable, but in this method, lithium carbonate (Li ₂ CO ₃ ) is soluble in water (solubility at 25 ° C .: 0.8 g), so that it remains in the solution. Therefore, there is a problem that lithium ions cannot be completely recovered. Further, in this method, when water is washed for the purpose of removing impurities from the recovered lithium carbonate (Li ₂ CO ₃ ), the lithium carbonate (Li ₂ CO ₃ ) itself gradually dissolves in water, so that it is not always efficient. is not.

Therefore, as a method for increasing the recovery efficiency of lithium ions, for example, an Fe source and a reducing agent are mixed in a lithium phosphate slurry obtained by reacting a Li source and a phosphate source, and then the resulting mixture is subjected to high-temperature and high-pressure conditions. The reaction product is reacted under to obtain a reaction product containing LiFePO ₄ , then the reaction product is separated into a solution containing LiFePO ₄ and unreacted Li, and then the solution containing unreacted Li is purified, and Li A method of obtaining LiLiPO ₄ by reusing lithium phosphate after reacting with phosphoric acid to make lithium phosphate (Patent Document 1), suspension of phosphate containing iron (Fe) A basic lithium source is added to form a precipitated product, which is converted into lithium iron phosphate to form a residual solution containing lithium ions, and a basic phosphate source is added to the residual solution. The method of separating by precipitation of lithium phosphate (Patent Document 2) are proposed.

JP 2008-66019 A Special table 2008-532910

In general, when LiFePO ₄ is synthesized by a hydrothermal synthesis method, the yield is not 100%. Therefore, when LiFePO ₄ is separated after hydrothermal synthesis, the raw material Fe salt component remains together with lithium carbonate in the filtrate. Will end up. Therefore, in order to recover lithium carbonate from the filtrate, it is essential to separate unreacted Fe salt components contained in the filtrate.
However, in the method of Patent Document 2 described above, the Li salt is recovered without separating the unreacted Fe salt, and therefore, the recovered LiFePO _{4 is} recovered by repeating the process of excess unreacted Fe salt. As a result, unreacted Fe salt is accumulated, and as a result, there is a problem in that reproducibility cannot be obtained in the physical properties of the recovered LiFePO ₄ .
The reason is that the valence of Fe in the unreacted Fe salt is originally divalent, but as the process is repeated, it is changed to trivalent iron oxyhydroxide or iron oxide, resulting in hydrothermal synthesis. This is thought to be because the reaction is inhibited.

Moreover, in the method of Patent Document 1 described above, after separation, unreacted Fe salt can be separated by purifying a solution containing unreacted Li, but when separating the Fe salt, calcium hydroxide is separated. Since (Ca (OH) ₂ ), calcium oxide (CaO), ammonia (NH ₃ ), amine and the like are used, there are the following problems.
(1) When ammonia (NH ₃ ) or amine is used, the pH does not rise easily, and it must be added in a large amount in order to greatly raise the pH, and is practical from the viewpoint of productivity, manufacturing cost, and safety. Poor sex.
(2) Calcium hydroxide (Ca (OH) ₂ ) and calcium oxide (CaO) are common for separating unreacted Fe salts, but LiFePO from which calcium hydroxide and calcium oxide are recovered ₄ remained in the battery ₄ had a problem of adversely affecting the battery characteristics of LiFePO ₄ .

The present invention has been made in order to solve the above problems, and Li salt, which is a by-product generated in the manufacturing process, has been a problem when manufacturing an electrode material represented by LiFePO ₄ . It is an object of the present invention to provide a method for producing an electrode material and a method for collecting lithium phosphate that can be efficiently recovered as high purity lithium phosphate, and that are low in production cost and can reduce environmental burden.

The present inventors have, as a result of intensive studies in order to solve the above problem, a crude product containing LiFePO _4, the main product mainly composed of LiFePO _4, into a solution containing the other product The first alkali containing 50 mol% or less of calcium hydroxide or calcium oxide is added to the solution containing this other product to remove impurities including Fe compounds, and further, the impurities are removed. The Li source and the phosphoric acid source are added to the solution, and the composition ratio (Li: P) in the solution is adjusted to 3: 1, and the second alkali is added to the solution with the adjusted composition ratio Thus, if a lithium phosphate slurry is produced, the lithium phosphate obtained from the solution from which impurities are removed does not contain unreacted Fe salt, is highly pure, has a low manufacturing cost, and is environmentally friendly. The load can be reduced Heading the Rukoto, it has led to the completion of the present invention.

That is, the method for producing an electrode material of the present invention is a method for producing an electrode material represented by LiFePO ₄ , wherein an Fe source and a reducing agent are added to a lithium phosphate slurry obtained by reacting a Li source and a phosphate source. A first step of adding a suspension, a second step of reacting the suspension under high temperature and high pressure conditions to produce a crude product containing LiFePO ₄ , and the crude product, The third step of separating into a main product mainly composed of LiFePO ₄ and a solution containing other products, and 50 mol% or less of calcium hydroxide or calcium oxide in the solution containing the other products A fourth step of adding the first alkali to be contained and removing impurities including the Fe compound; adding a Li source and a phosphoric acid source to the solution from which the impurities have been removed; and a composition ratio ( Li: P) adjusted to 3: 1 A fifth step of generating a lithium phosphate slurry by adding a second alkali to the solution adjusted in composition ratio, and using the lithium phosphate slurry obtained in the fifth step, After the first step, the main product is obtained again.

The first alkali is any one of an alkali metal compound, an alkaline earth metal compound, an alkali metal compound, and an alkaline earth metal compound, and the alkali metal compound is an alkali metal hydroxide, oxide, or carbonate. And one or more selected from the group of these hydrates, and the alkaline earth metal compound is an alkaline earth metal hydroxide, oxide, carbonate or hydrate of these It is preferable that it is 1 type, or 2 or more types selected from the group.
The alkali metal is preferably lithium.
The second alkali is preferably one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, and ammonia.

  The method for recovering lithium phosphate according to the present invention includes adding a first alkali containing 50 mol% or less of calcium hydroxide or calcium oxide to a solution containing Li, and removing impurities containing an Fe compound; A Li source and a phosphoric acid source are added to the solution from which the impurities have been removed, and the composition ratio (Li: P) in the solution is adjusted to 3: 1. And a step of generating a slurry containing lithium phosphate by adding the alkali, and a step of recovering the generated lithium phosphate.

According to the method for producing an electrode material of the present invention, a first step of adding a Fe source and a reducing agent to a lithium phosphate slurry to form a suspension, and reacting the suspension under high-temperature and high-pressure conditions. a third step of separating the second step of the crude product containing LiFePO _4, the crude product, and the main product mainly composed of LiFePO _4, into a solution containing the other product And adding a first alkali containing 50 mol% or less of calcium hydroxide or calcium oxide to the solution containing the other product to remove impurities including Fe compound, and A Li source and a phosphoric acid source are added to the removed solution, the composition ratio (Li: P) in the solution is adjusted to 3: 1, and a second alkali is added to the solution with the adjusted composition ratio. To produce a lithium phosphate slurry In the reaction product after hydrothermal synthesis, the main product is obtained again by performing the first step and thereafter using the lithium phosphate slurry obtained in the fifth step. Unreacted Li contained can be efficiently recovered and reused as high-purity lithium phosphate, and the manufacturing cost is low and the environmental burden is small.

  According to the lithium recovery method of the present invention, a step of adding a first alkali containing 50 mol% or less of calcium hydroxide or calcium oxide to a solution containing Li, and removing impurities containing an Fe compound; A Li source and a phosphoric acid source are added to the solution from which the impurities have been removed, and the composition ratio (Li: P) in the solution is adjusted to 3: 1. Since the step of generating a slurry containing lithium phosphate by adding the alkali of and the step of recovering the generated lithium phosphate, Li contained in the solution as high purity lithium phosphate, It can be collected efficiently, and the manufacturing cost is low and the environmental load is small.

It is a flowchart which shows the manufacturing method of the electrode material of one Embodiment of this invention. It is a figure which shows the high temperature cycling characteristic of Example 1 of this invention, and each comparative example.

The best mode of the electrode material production method, lithium recovery method, positive electrode material and electrode, and battery of the present invention will be described.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

The method for producing an electrode material of the present invention is a method for producing an electrode material represented by LiFePO ₄ , and an Fe source and a reducing agent are added to a lithium phosphate slurry obtained by reacting a Li source and a phosphate source. A first step of making a suspension, a second step of reacting the suspension under high temperature and high pressure conditions to produce a crude product containing LiFePO ₄ , and the crude product, LiFePO ₄ A third step of separating the main product as a main component into a solution containing another product, and a solution containing 50 mol% or less of calcium hydroxide or calcium oxide in the solution containing the other product. A first step of adding an alkali of 1 to generate an impurity containing an Fe compound, and removing the generated impurity; adding a Li source and a phosphoric acid source to the solution from which the impurity has been removed; The composition ratio (Li: P) is 3: And a fifth step of generating a lithium phosphate slurry by adding a second alkali to the solution adjusted in composition ratio, and the phosphoric acid obtained in the fifth step This is a method of performing the first and subsequent steps using lithium slurry to obtain the main product again.

Here, the background to the proposal of the method for producing the electrode material of the present invention will be described.
When the electrode material represented by the above LiFePO ₄ is prepared by a hydrothermal synthesis method in which excess Li is added to a conventional reaction system, for example, the Li source is lithium hydroxide (LiOH) and the Fe source is chlorinated. Ferrous iron (FeCl ₂ ), phosphoric acid source is phosphoric acid (H ₃ PO ₄ ), and when these are added to water, the Fe source is 1, the phosphoric acid source is 1, and the Li source is 1 + x (1 <x ≦ 2) and an excess amount, and the resulting mixture is hydrothermally synthesized, the following reaction occurs.
(1 + x) LiOH + FeCl ₂ + H ₃ PO ₄
→ LiFePO ₄ + xLiCl + (2-x) HCl + (1 + x) H ₂ O

As a result of this reaction, LiFePO ₄ precipitates as a solid and LiCl and HCl remain in solution.
Therefore, when the solution containing the precipitate is washed with pure water, the excess Li component, LiCl, is soluble in water and is recovered as a waste liquid because it is water-soluble. Therefore, in order to reuse Li contained in this waste liquid, it is necessary to remove Cl ions and H ions present in the waste liquid.

In order to remove these ions, phosphoric acid (H ₃ PO ₄ ) is added to the waste liquid to make a strongly acidic solution, and then a neutralizing agent is added to make the solution neutral to alkaline. is reacted with Li ions and PO ₄ ions in the solution, together with the precipitate as _Li 3 PO ₄ of poorly soluble, wash the various components other than _Li 3 PO _4, by separating the Li _Li 3 PO ₄ Can be recovered with high efficiency.
Further, with respect to Li consumed in producing LiFePO ₄ , the balance of Li during synthesis and recovery is obtained by supplementing the waste liquid with a phosphoric acid source such as phosphoric acid (H ₃ PO ₄ ) and a Li source. By matching these, a cycle of synthesis and recovery is formed, and as a result, LiFePO ₄ can be synthesized and recovered more efficiently and at low cost.
The present invention has been made based on the above idea.

Next, the method for manufacturing the electrode material of the present embodiment will be described more specifically based on FIG.
"First step"
First, a Li source and a phosphoric acid source are added to a solvent containing water as a main component, and the Li source and the phosphoric acid source are reacted to generate lithium phosphate (Li ₃ PO ₄ ), and lithium phosphate (Li ₃ PO ₄ ) slurry (SP1).

Examples of the Li source include lithium inorganic acid salts such as lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), lithium chloride (LiCl), and lithium phosphate (Li ₃ PO ₄ ), lithium acetate (LiCH _3). One or more selected from the group of lithium organic acid salts such as (COO) and lithium oxalate ((COOLi) ₂ ), and hydrates thereof are preferably used.
The maximum particle size of this Li source is preferably 500 μm or less. Here, the reason why the maximum particle diameter of the Li source is limited to 500 μm or less is that when the maximum particle diameter exceeds 500 μm, the LiFePO ₄ particles become coarse.

Examples of phosphoric acid sources include phosphoric acid such as orthophosphoric acid (H ₃ PO ₄ ) and metaphosphoric acid (HPO ₃ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), and diammonium hydrogen phosphate ((NH ₄ )). ₂ HPO ₄ ), ammonium phosphate ((NH ₄ ) ₃ PO ₄ ), and one or more selected from the group of these hydrates are preferably used. Among them, orthophosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate are preferable because of their relatively high purity and easy composition control.

The maximum particle size of lithium phosphate (Li ₃ PO ₄ ) in this Li ₃ PO ₄ slurry is preferably 500 μm or less, and more preferably 100 μm or less.
By limiting the maximum particle size of Li ₃ PO ₄ to 500 μm or less, LiFePO ₄ fine particles having a particle size of 0.01 μm (10 nm) to 1 μm can be obtained.

Moreover, as a solvent which has water as a main component, a pure water, a water-alcohol solution, a water-ketone solution, a water-ether solution etc. are mentioned, Among these, a pure water is preferable.
The reason is that water is inexpensive and the physical properties of the solvent such as solubility in each substance can be easily controlled by the operation of temperature and pressure.

Next, an Fe source and a reducing agent are mixed with this Li ₃ PO ₄ slurry to obtain a mixture (SP2).
The Fe source is selected from the group consisting of iron (II) chloride (FeCl ₂ ), iron (II) sulfate (FeSO ₄ ), iron (II) acetate (Fe (CH ₃ COO) ₂ ), and hydrates thereof. One type or two or more types are preferably used.
Examples of the reducing agent include sulfur dioxide (SO ₂ ), sulfurous acid (H ₂ SO ₃ ), sodium sulfite (Na ₂ SO ₃ ), sodium hydrogen sulfite (NaHSO ₃ ), ammonium sulfite ((NH ₄ ) ₂ SO ₃ ), sulfur One or two or more selected from the group of phosphoric acid (H ₂ PHO ₃ ) and ascorbic acid are preferably used.

  The mixing ratio of these Li source, Fe source, and phosphoric acid source is not limited as long as impurities are not generated during hydrothermal synthesis, which will be described later, but the Li source Li ion is 2 mol or more with respect to 1 mol of Fe ion of the Fe source. And 4 mol or less is preferable, More preferably, it is 2.5 mol or more and 3.5 mol or less. Further, the phosphate ion of the phosphate source is preferably 0.9 mol or more and 1.1 mol or less, more preferably 0.98 mol or more and 1.02 mol or less with respect to 1 mol of Fe ion of the Fe source. is there.

  Here, the reason why the number of moles of Li ions relative to 1 mole of Fe ions is limited to the above range is that when Li ions are less than 2 moles, Li involved in the reaction forms a counter ion with the anion contained in the Fe source. This is because there is a problem that the reaction time becomes longer, impurities are generated, particles are coarsened, and the like. On the other hand, if the Li ion is more than 4 mol, the alkalinity of the reaction solution is increased. This is because, since it becomes strong, there is a possibility that problems such as easy generation of impurities may occur.

"Second step"
This mixture is reacted under high temperature and high pressure conditions (hydrothermal synthesis) to obtain a reaction product containing LiFePO ₄ (SP3).
The high temperature and high pressure conditions may be in the range of the temperature, pressure and time at which LiFePO ₄ is produced. In particular, in order to obtain LiFePO ₄ particles having an average particle diameter of 1 μm or less, the reaction temperature is 120 ° C. ° C or lower is preferable, and 150 ° C or higher and 220 ° C or lower is more preferable. Further, the pressure during the reaction is preferably 0.2 MPa or more, and more preferably 0.4 MPa or more. The reaction time depends on the reaction temperature, but is preferably 1 hour to 24 hours, more preferably 3 hours to 12 hours.

"Third process"
The reaction product containing LiFePO ₄ is washed with pure water, and the reaction product obtained by filtration or the like is separated into LiFePO ₄ and a Li-containing waste liquid (solution containing unreacted Li) (SP4).
The separated LiFePO ₄ is dried at 40 ° C. or higher for 3 hours or more using a drier or the like, and then pulverized or the like, so that the average particle size is 0.01 μm or more and 1 μm or less, preferably 0.02 μm or more. and the following LiFePO ₄ particles 0.5 [mu] m (SP5).

"Fourth process"
An alkali A (first alkali) containing 50 mol% or less of calcium hydroxide (Ca (OH) ₂ ) or calcium oxide (CaO) is added to the separated Li-containing waste liquid, and Fe contained in the waste liquid Impurities such as components and PO ₄ components are removed (SP6). Impurities such as Fe component and PO ₄ component removed here are discarded.

The alkali A is preferably an alkali metal compound, an alkaline earth metal compound, an alkali metal compound, or an alkaline earth metal compound and soluble on the acidic side.
The alkali metal compound is preferably one or more selected from the group of alkali metal hydroxides, oxides, carbonates and hydrates thereof, and the alkaline earth metal compound is an alkaline earth compound. One or more selected from the group of metal hydroxides, oxides, carbonates and hydrates thereof are preferred. These alkali metal compounds and alkaline earth metal compounds may be used alone or in combination of two or more.

Examples of the alkali metal compound and alkaline earth metal compound include lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), potassium hydroxide (KOH), sodium hydroxide (NaOH), and barium hydroxide (Ba (OH) ₂ ) and the like, and among these, lithium hydroxide (LiOH) and lithium carbonate (Li ₂ CO ₃ ), which are lithium compounds, are particularly preferable. These alkali metal compounds may be used alone or in combination of two or more.

Considering that it is better not to leave calcium hydroxide (Ca (OH) ₂ ) or calcium oxide (CaO) in the recovered LiFePO ₄ when removing the Fe component, calcium hydroxide (Ca (OH) ₂ It is preferable to use alkali A other than calcium oxide (CaO). Depending on the type of anion of the Fe component, either alkali hydroxide (Ca (OH) ₂ ) or calcium oxide (CaO) may be included in alkali A. In some cases, it is more efficient to include one or both.

For example, when the alkali A used is a mixture of lithium hydroxide (LiOH) and calcium hydroxide (Ca (OH) ₂ ), the molar ratio Ca / Li is preferably 0 <Ca / Li ≦ 1. More preferably, 0 <Ca / Li ≦ 0.3, and further preferably 0 <Ca / Li ≦ 0.05.
This Li-containing waste liquid becomes a purified Li-containing solution (solution from which impurities have been removed) by removing impurities such as Fe component and PO ₄ component (SP7).

"Fifth process"
A phosphoric acid source is added to this Li-containing solution to obtain a Li- and PO ₄ -containing solution (SP8). As the addition amount of the phosphoric acid source, it is preferable to add a phosphoric acid source in an equimolar amount with respect to the phosphoric acid source in the first step.
As the phosphoric acid source, as in the first step, phosphoric acid such as orthophosphoric acid (H ₃ PO ₄ ), metaphosphoric acid (HPO ₃ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), hydrogen phosphate One or more selected from the group of diammonium ((NH ₄ ) ₂ HPO ₄ ), ammonium phosphate ((NH ₄ ) ₃ PO ₄ ), and hydrates thereof are preferably used.
Here, the reason why an equimolar amount of phosphoric acid source is added to the Li-containing solution is that LiFePO ₄ having a stoichiometric composition is obtained in a subsequent step.

Next, a Li source is added to the Li and PO ₄ containing solution so that the composition ratio (Li: P) of Li and P in the solution is 3: 1, and further, an alkali B (second alkali) is added. ) Is added.
The alkali B is preferably an alkali that hardly generates impurities during neutralization, that is, all the impurities that are generated are readily soluble in water and can be easily separated from lithium phosphate when washed with water. One or more selected from the group consisting of sodium hydroxide (NaOH), potassium hydroxide (KOH) and ammonia (NH ₃ ) are preferred.
Thereby, a solution containing lithium phosphate (Li ₃ PO ₄ ) is generated (SP9). Next, the solution containing Li ₃ PO ₄ is allowed to stand to precipitate Li ₃ PO ₄ in the solution.

Next, the solution in which Li ₃ PO ₄ is precipitated is washed with pure water, and then this solution is separated into Li ₃ PO ₄ and waste liquid by using filtration or the like (SP10). The waste liquid separated here is subjected to a predetermined treatment to be cleaned and discharged.
Li ₃ PO ₄ thus separated has a very low content of Fe components, Ca components, and the like, which are impurities. Therefore, this Li ₃ PO ₄ is dispersed in pure water to obtain a lithium phosphate (Li ₃ PO ₄ ) slurry (SP1).

Thus, by repeating the first step to the fifth step, Li that has a very low content of impurities such as Fe component and Ca component without discarding excess Li discharged as waste liquid. It can be recovered and reused as ₃ PO ₄ , reducing the cost of Li and obtaining LiFePO ₄ at a low cost.

When the particle size of Li ₃ PO ₄ is desired to be 500 μm or less, it can be achieved by grinding the produced Li ₃ PO ₄ by a wet method such as a ball mill or a dry method such as a pin mill. When the Li source and the phosphoric acid source are added to the solvent in the process, the Li source is made into a fine powder of 500 μm or less, preferably 100 μm or less, and the fine powder Li source and the phosphoric acid source are allowed to react with each other. Li ₃ PO ₄ fine particles having a diameter of 500 μm or less can be obtained.

The electrode material thus obtained is an electrode material represented by LiFePO ₄ , and this electrode material is suitable as a positive electrode positive electrode material when applied to a lithium battery, particularly a lithium ion battery. Used.

The average particle size of LiFePO ₄ is preferably 0.01 μm or more and 1 μm or less, and more preferably 0.02 μm or more and 0.5 μm or less. Here, if the average particle size is less than 0.01 μm, the particles may be destroyed due to structural changes accompanying Li insertion / desorption, and when this material is used as a positive electrode active material, the specific surface area is Since it becomes large, a large amount of bonding agent is required. As a result, there is a possibility that problems such as a significant decrease in the packing density of the positive electrode and a significant decrease in electrical conductivity occur. On the other hand, if the average particle diameter exceeds 1 μm, the internal resistance of the positive electrode active material increases, and the movement of Li ions is delayed, which may cause problems such as a decrease in utilization rate.
In order to enable higher output, particles of 0.5 μm or less that have a small influence on the internal resistance of the positive electrode active material are preferable.

For the amount of Ca remaining in the LiFePO ₄ it must be a quantity that does not adversely affect the battery characteristics of the LiFePO _4, considering this, the following are preferred 400 ppm, more preferably 200ppm or less, more preferably 100ppm or less It is.
Incidentally, when the amount of Ca remaining in LiFePO ₄ is more than 400 ppm, the battery characteristics of LiFePO _4, in particular high-temperature cycle characteristics are remarkably deteriorated, so the life of the battery is possible to greatly reduce, undesirable.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely by Examples 1-6 and a comparative example, this invention is not limited by these Examples.

A. Preparation of powder sample [Example 1]
(First step)
Lithium hydroxide (LiOH) 3 mol and orthophosphoric acid (H ₃ PO ₄ ) 1 mol were added to 1 L of pure water and stirred to obtain a lithium phosphate slurry.
Next, 1 mol of iron (II) chloride (FeCl ₂ ) is added to the lithium phosphate slurry, 0.01 mol of sulfurous acid (H ₂ SO ₃ ) is further added as a reducing agent, and water is added to make the total amount 2 L. It was set as the liquid A-1. The concentration of this raw material liquid A-1 when converted to LiFePO ₄ was 0.5 mol / L.

(Second step)
Subsequently, this raw material liquid A-1 was put into a pressure-resistant sealed container, heated in a sealed state at 170 ° C. for 6 hours, and hydrothermally synthesized.
(Third step)
Subsequently, the obtained reaction liquid was taken out from the pressure-resistant airtight container, washed with 6 L of pure water, filtered, and separated into powder and filtrate. Thereafter, this powder was dried to obtain Sample B-1.

(Fourth process)
Next, a small amount of lithium hydroxide (LiOH) was added to the filtrate to precipitate a precipitate. Next, the precipitate was removed from the filtrate to obtain a Li-containing solution.
(Fifth step)
Next, orthophosphoric acid (H ₃ PO ₄ ) 2/3 mol was added to this Li-containing solution and stirred, and then 2 mol of aqueous ammonia (NH ₄ OH) was added to obtain a white precipitate.
This white precipitate was washed with 2 L of pure water and then dried to obtain a white sample C-1.

(First step)
Next, 115.8 g of the white sample C-1 was put into 0.5 L of pure water and stirred to obtain a lithium phosphate slurry.
Next, iron chloride (II) (FeCl ₂ ) is added to the lithium phosphate slurry, and sulfurous acid (H ₂ SO ₃ ) is further added as a reducing agent, and a raw material liquid having the same composition as the above raw material liquid A-1 A-2 was produced.

(Second step)
Subsequently, this raw material liquid A-2 was put into a pressure-resistant airtight container, heated in a sealed state at 170 ° C. for 6 hours, and hydrothermally synthesized.
(3rd step)
Next, the obtained reaction solution was washed with 6 L of pure water and then filtered to separate into a powder and a filtrate. Thereafter, this powder was dried to obtain Sample B-2.

(4th step)
Next, a small amount of lithium hydroxide was added to the above filtrate to precipitate a precipitate. Next, the precipitate was removed from the filtrate to obtain a Li-containing solution.
(5th step)
Next, orthophosphoric acid (H ₃ PO ₄ ) was added to the Li-containing solution and stirred, and then aqueous ammonia (NH ₄ OH) was added to obtain a white precipitate.
The white precipitate was washed with pure water and then dried to obtain a white sample C-2.

[Example 2]
Sample B-2 of Example 2 and a white sample according to Example 1 except that lithium carbonate (Li ₂ CO ₃ ) was used instead of lithium hydroxide (LiOH) in the fourth step of Example 1 C-2 was obtained.

[Example 3]
Sample B-2 in Example 3 and white sample C- in accordance with Example 1 except that sodium hydroxide (NaOH) was used instead of lithium hydroxide (LiOH) in the fourth step of Example 1. 2 was obtained.

[Example 4]
Sample B-2 and white sample C- of Example 4 were prepared in the same manner as in Example 1 except that potassium hydroxide (KOH) was used in place of lithium hydroxide (LiOH) in the fourth step of Example 1. 2 was obtained.

[Example 5]
In the fourth step of Example 1, lithium hydroxide (LiOH) and calcium hydroxide (Ca (OH) ₂ ) were replaced by LiOH: Ca (OH) ₂ = 75: 25 (moles) instead of lithium hydroxide (LiOH). The sample B-2 and the white sample C-2 of Example 5 were obtained in the same manner as in Example 1 except that the mixed alkali was mixed so that

[Example 6]
In the fourth step of Example 1, lithium hydroxide (LiOH) and calcium hydroxide (Ca (OH) ₂ ) were replaced by LiOH: Ca (OH) ₂ = 50: 50 (moles) instead of lithium hydroxide (LiOH). The sample B-2 and the white sample C-2 of Example 6 were obtained in the same manner as in Example 1 except that the mixed alkali was mixed so that

[Comparative example]
Sample B-2 of the comparative example and white color according to Example 1 except that calcium hydroxide (Ca (OH) ₂ ) was used instead of lithium hydroxide (LiOH) in the fourth step of Example 1. Sample C-2 was obtained.

[Evaluation of powder sample]
(Crystal phase identification and composition analysis)
The crystal phases of Samples B-2 and White Sample C-2 of Examples 1 to 6 and Comparative Example were identified by a powder method using an X-ray diffractometer.
Moreover, the analysis of the impurities of Samples B-2 and White Sample C-2 of Examples 1 to 6 and Comparative Example was performed by ICP analysis.
The results of identification of these crystal phases and measurement of impurities are shown in Tables 1 and 2.
In Table 1, as an example of a sample that is not recycled, Sample B-1 obtained by hydrothermal synthesis in the third step of Example 1 is given as a reference example.

(Measurement of specific surface area)
The specific surface area of Sample B-2 in each of Examples 1 to 6 and Comparative Example was measured by the BET method.
These measurement results are shown in Table 1.

(Li recovery rate)
The Li recovery rate from the filtrate of each of the white samples C-2 of Examples 1 to 6 and Comparative Example was calculated.
Table 2 shows the calculation results.

B. Preparation and evaluation of lithium ion secondary battery [carbon coating treatment]
Each sample B-2 obtained in Examples 1 to 6 and Comparative Example was added to 5 g of polyethylene glycol and 150 g of pure water with respect to 150 g in terms of solid content, and 12 mm by a ball mill using 5 mm diameter zirconia beads as media. A uniform slurry was prepared by carrying out time grinding and dispersion treatment.
Next, the slurry was sprayed into an air atmosphere at 180 ° C. and dried to obtain a granulated body having an average particle size of about 6 μm. This granulated body was fired at 750 ° C. for 1 hour under an inert atmosphere to prepare positive electrode active materials for lithium ion batteries of Examples 1 to 6 and Comparative Example.

[Production of lithium ion secondary battery]
About the said positive electrode active material for lithium ion batteries, the following processes were performed and the lithium ion secondary battery of Examples 1-6 and each comparative example was produced.
First, 90 parts by mass of the positive electrode active material, 5 parts by mass of acetylene black as a conductive auxiliary agent, 5 parts by mass of polyvinylidene fluoride (PVDF) as a binder, and N-methyl-2-pyrrolidinone (NMP) as a solvent were mixed. .
Next, these were kneaded using a three-roll mill to produce a positive electrode active material paste.

Next, this positive electrode active material paste was applied onto an aluminum current collector foil having a thickness of 30 μm, and then dried under reduced pressure at 100 ° C. to produce a positive electrode having a thickness of 60 μm.
Next, this positive electrode was punched into a 2 cm ² disk shape, dried under reduced pressure, and then a lithium ion secondary battery was produced using a stainless steel 2016 type coin cell in a dry argon atmosphere.
Here, metallic lithium is used as a negative electrode, a porous polypropylene film is used as a separator, and 1 mol of LiPF ₆ is mixed into an electrolytic solution in a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) 1: 1. The resulting mixture was used.

[Evaluation of lithium ion secondary battery]
Evaluation of the lithium ion secondary battery of each of Examples 1 to 6 and Comparative Example was performed by a battery charge / discharge test and a high temperature cycle test. The test method is as follows.
(Battery charge / discharge test)
The cut-off voltage was set to 2.0 V to 4.0 V, and the initial discharge capacity was measured by charging at 0.1 C and discharging at 0.1 C.

(High temperature cycle test)
A charge / discharge test was performed under the following conditions using the lithium ion secondary batteries of Examples 1 to 6 and Comparative Example, except that a natural graphite negative electrode sheet (manufactured by Hosen Co., Ltd.) was used for the negative electrode.
Cut-off voltage: 2.0V to 4.0V
Measurement temperature: 60 ° C
From the 1st cycle to the 3rd cycle: 0.2C discharge after 0.2C charge From the 4th cycle to the 600th cycle: 1C discharge after 1C charge In addition, the percentage of the capacity of the nth cycle to the capacity of the 4th cycle is maintained. Rate.
The test results are shown in Table 3, and the high-temperature cycle characteristics of Example 1 and Comparative Example are shown in FIG. In FIG. 2, A shows the high-temperature cycle characteristics of Example 1, and B shows the high-temperature cycle characteristics of the comparative example.
In Table 3, a lithium ion secondary battery obtained using Sample B-1 of Example 1 is given as a reference example as an example of a sample that is not recycled.

Claims (5)

A method for producing an electrode material represented by LiFePO ₄ ,
A first step of adding a Fe source and a reducing agent to a lithium phosphate slurry obtained by reacting a Li source and a phosphate source to form a suspension;
A second step of reacting the suspension under high temperature and high pressure conditions to produce a crude product containing LiFePO ₄ ;
A third step of separating the crude product into a main product mainly composed of LiFePO ₄ and a solution containing other products;
A fourth step of adding a first alkali containing 50 mol% or less of calcium hydroxide or calcium oxide to the solution containing the other product, and removing impurities including the Fe compound;
A Li source and a phosphoric acid source are added to the solution from which the impurities are removed, and the composition ratio (Li: P) in the solution is adjusted to 3: 1. And adding a second alkali to produce a lithium phosphate slurry,
A method for producing an electrode material, characterized in that the main product is obtained again by performing the first and subsequent steps using the lithium phosphate slurry obtained in the fifth step. The first alkali is any one of an alkali metal compound, an alkaline earth metal compound, an alkali metal compound, and an alkaline earth metal compound,
The alkali metal compound is one or more selected from the group of alkali metal hydroxides, oxides, carbonates and hydrates thereof,
2. The alkaline earth metal compound is one or more selected from the group consisting of hydroxides, oxides, carbonates and hydrates of alkaline earth metals. The manufacturing method of the electrode material of description.   The method for producing an electrode material according to claim 2, wherein the alkali metal is lithium.   The electrode material according to any one of claims 1 to 3, wherein the second alkali is one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, and ammonia. Production method. Adding a first alkali containing 50 mol% or less of calcium hydroxide or calcium oxide to a solution containing Li, and removing impurities containing an Fe compound;
A Li source and a phosphoric acid source are added to the solution from which the impurities are removed, and the composition ratio (Li: P) in the solution is adjusted to 3: 1. Adding an alkali of 2 to produce a slurry containing lithium phosphate;
Recovering the produced lithium phosphate;
A method for recovering lithium phosphate, comprising:

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