CN102491302A - Battery-grade anhydrous iron phosphate and preparation method thereof - Google Patents

Abstract

The invention relates to a battery-grade iron phosphate and a preparation method thereof. The battery grade iron phosphate is an orthorhombic battery grade anhydrous iron phosphate. Its preparation method is to use the oxidation precipitation method using air as the oxidant, add the aqueous solution of the mixture of ferrous salt and phosphoric acid or phosphate, add the pH value regulator solution, pass in the air, stir and react to form ammonium, hydroxide It is a crystalline complex with crystal water; it is prepared by solid-liquid separation, washing, drying and roasting. The battery-grade iron phosphate is an ideal raw material for preparing lithium iron phosphate, a cathode material for lithium-ion batteries. The preparation method is suitable for large-scale, economical, stable and reliable production of high-quality battery-grade iron phosphate, has obvious advantages and is of great practical value.

Description

Battery grade anhydrous iron phosphate and preparation method thereof

technical field

The invention belongs to the technical field of energy material preparation, and relates to a battery-grade iron phosphate and a preparation method thereof, in particular to an anhydrous battery-grade iron phosphate and a preparation method thereof. ideal precursor.

Background technique

Lithium-ion batteries are a new generation of green high-energy batteries, which have many advantages such as high voltage, high energy density, good cycle performance, small self-discharge, no memory effect, and wide operating temperature range. They are widely used in mobile phones, notebook computers, and digital cameras. , camcorders, electronic instruments, etc., also have bright application prospects in UPS, electric tools, electric bicycles, electric vehicles, energy storage batteries and other fields. In recent years, the output of lithium-ion batteries has grown rapidly, and the application fields have continued to expand. It has become a high-tech product that is of great significance to the national economy and people's lives in the 21st century.

At present, lithium-ion batteries have become increasingly mature in the field of small batteries for portable electronic products, and their application range is gradually expanding to the fields of medium and large capacity, medium and high power power and energy storage batteries. Cathode materials are an important part of lithium-ion batteries, and their performance largely determines the overall performance of the battery. Cathode material research and performance improvement is one of the cores of lithium-ion battery development. For power and energy storage lithium-ion batteries, the cost, high temperature performance and safety of cathode materials are very important. Lithium-transition metal composite oxide cathode materials that have been applied in the field of small batteries include lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate oxide (LiMn ₂ O ₄ ) and combinations of the above three materials. Derivatives, such as lithium nickel cobalt oxide (LiNi _0.8 Co _0.2 O ₂ ), lithium nickel cobalt manganese oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), etc. cannot meet the requirements yet.

Lithium iron phosphate cathode material with orthorhombic olivine structure has become a research hotspot at home and abroad. The material combines the respective advantages of lithium cobaltate, lithium nickelate, lithium manganate and their derivative positive electrode materials: no precious elements, cheap raw materials, extremely rich resources; stable structure, excellent safety performance, LiFePO ₄ O and P are firmly combined with strong covalent bonds, making it difficult for the material to decompose by oxygen evolution; the high temperature performance and thermal stability are significantly better than other known positive electrode materials; the cycle performance is good; the volume shrinks during charging, and when combined with carbon negative electrode materials Good volume effect; good compatibility with most electrolyte systems, good storage performance; non-toxic, a real green material. Compared with lithium cobaltate, lithium nickelate, lithium manganate and their derivatives, lithium iron phosphate cathode material has outstanding advantages in terms of cost, high temperature performance, and safety, and is expected to become a power and energy storage lithium battery. Ideal cathode material for ion batteries. The industrialization and popular application of lithium iron phosphate cathode materials are of great significance to reduce the cost of lithium-ion batteries, improve battery safety, expand the lithium-ion battery industry, and promote the large-scale and high-power lithium-ion batteries; it will make lithium-ion batteries The application in medium and large capacity UPS, medium and large energy storage batteries, electric tools and electric vehicles has become a reality.

With the gradual depletion of fossil energy, the world is paying more and more attention to the development and utilization of new energy such as solar energy, wind energy, and tidal energy, and regards the research of new energy as a new discipline growth point. In addition to grid-connected power generation, solar energy, wind energy, tidal energy, etc., need to store the generated electric energy in many cases. Only when the problem of electric energy storage is solved, solar energy, wind energy, and tidal energy power generation can be flexibly applied and moved towards large-scale practical application. Therefore, the research on energy storage batteries and their key materials is of great significance for the development and application of new energy.

Lithium-ion energy storage batteries with lithium iron phosphate as the positive electrode material may be a perfect match for solar, wind and tidal power generation systems. Therefore, the research on lithium iron phosphate cathode materials is not only of great value in the field of lithium-ion batteries, but also of great significance to the development and application of new energy technologies such as solar energy, wind energy, and tidal energy.

At present, lithium iron phosphate is the ideal material most likely to be used in power and energy storage lithium-ion batteries on a large scale. Since Professor John B. Goodenough of the United States proposed this material in 1997, extensive and in-depth research has been carried out at home and abroad. People improve the conductivity of the material by coating the surface of the material with conductive carbon, doping the inside with conductive substances, and nanosizing the crystal grains; by optimizing the particle shape, particle size and distribution of the powder, the bulk density of the material is improved. People have developed a variety of preparation processes, some of which have been applied in practice.

To sum up, the current mainstream preparation processes for lithium iron phosphate are the following four or their variants:

1. full wet process

This method is to disperse lithium source, iron source and phosphorus source in water or other solvents, through hydrothermal or solvothermal process, react at relatively low temperature and high pressure to synthesize lithium iron phosphate in one step, and then make it through subsequent treatment . This method has a simple process and can be made into nano-lithium iron phosphate; however, the discharge of waste liquid is large, high-voltage-resistant equipment is required, and industrial scale-up is not easy.

2. Ferrous oxalate process

This method is a classic technique for synthesizing lithium iron phosphate. Ferrous oxalate (FeC ₂ O ₄ 2H ₂ O) is used as iron source, mixed with ammonium dihydrogen phosphate or diammonium hydrogen phosphate, lithium salt, carbon source, pre-decomposed and roasted at high temperature under the protection of reducing or inert atmosphere Made of lithium iron phosphate. A large amount of ammonia gas is generated during the preparation process, which pollutes the environment and corrodes equipment, and the raw material of ferrous oxalate is relatively expensive. This method is currently in heavy use but is not considered a competitive technique.

3. Iron red craft

In this method, iron red (Fe ₂ O ₃ ) is used as iron source, mixed with lithium dihydrogen phosphate (LiH ₂ PO ₄ ) and carbon source through wet grinding, spray-dried, and then subjected to high-temperature carbothermal reduction under the protection of reducing or inert atmosphere. The reaction produces lithium iron phosphate. This method is more environmentally friendly, but the raw material of lithium dihydrogen phosphate is more expensive and unstable. The lithium iron phosphate material prepared by this method usually has general performance and belongs to middle and low-grade products.

4. Iron phosphate process

Iron phosphate (FePO ₄ ) is used as raw material, mixed evenly with lithium carbonate (Li ₂ CO ₃ ) and carbon source, and lithium iron phosphate is produced by high-temperature carbothermal reduction reaction under the protection of reducing or inert atmosphere. The lithium iron phosphate material prepared by this method usually has better performance and is suitable for the preparation of medium and high-end products. The synthesis process is relatively scientific, but its advantages have not been fully utilized, and it is worthy of further study.

According to our analysis, the iron phosphate process has the following advantages:

1. The carbothermal reduction process of iron phosphate (FePO ₄ ), lithium carbonate (Li ₂ CO ₃ ), and carbon sources is similar to the discharge process in batteries: the skeleton of FePO ₄ does not move, ferric iron is reduced to ferrous iron, Li ⁺ inserts into the lattice of FePO ₄ and FePO ₄ becomes LiFePO ₄ . This reaction process is much simpler than the reaction process of the all-wet process, ferrous oxalate process, and iron red process, which makes the ferric phosphate process easier to realize, with more relaxed reaction conditions and stronger controllability.

2. The iron phosphate precursor can be synthesized by wet chemical method, and its composition, structure, and morphology can be precisely regulated; it can be used as the precursor to synthesize lithium iron phosphate, and the precise regulation of the composition, structure, and morphology of the target product can be realized; Most of the technical content of lithium iron phosphate preparation is transferred to the iron phosphate precursor; it can give full play to the advantages of soft chemical synthesis and has a broad space for technological improvement.

At present, the advantages of the iron phosphate process have been gradually recognized by people, and it may develop into a standard process for the preparation of lithium iron phosphate. New technologies for the preparation of high-quality battery-grade iron phosphate have received increasing attention.

The industrial production of iron phosphate has a history of many years. It is usually produced by ferric salt or ferrous salt as raw material, adding phosphoric acid or phosphate to make a mixed solution, and then precipitating with alkaline solution.

For example, ferric nitrate (Fe(NO ₃ ) ₃ ), ferric chloride (FeCl ₃ ), and ferric sulfate (Fe ₂ (SO ₄ ) ₃ ) are used as iron sources, and phosphoric acid (H ₃ PO ₄ ) is used as the iron source. Mix in a certain proportion to make a mixed solution, add sodium hydroxide (NaOH) solution, adjust the temperature and pH value, make Fe ³⁺ and PO ₄ ^3- combine and precipitate, and obtain iron phosphate (FePO ₄ xH ₂ O, x = 2-4).

Or use ferrous ferrous sulfate (FeSO ₄ ) and ferrous chloride (FeCl ₂ ) as the iron source, mix it with phosphoric acid (H ₃ PO ₄ ) in a certain proportion to make a mixed solution, and add an oxidant such as hydrogen peroxide (H ₂ O ₂ ), sodium hypochlorite (NaClO), sodium chlorate (NaClO ₃ ), ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ), etc., to oxidize Fe ²⁺ into Fe ³⁺ , and add sodium hydroxide ( NaOH) solution, adjust the temperature and pH value, make the Fe ³⁺ generated by oxidation combine with PO ₄ ^3- and precipitate, and obtain iron phosphate FePO ₄ ·xH ₂ O (x = 2-4) containing crystal water.

The above methods have common disadvantages:

First, there are by-product salts in the reaction process, such as NaNO ₃ , NaCl, Na ₂ SO ₄ , etc. The by-product salts exist in the mother liquor produced by the reaction, and also exist in large quantities in the washing liquid of the iron phosphate product, and are directly discharged It will seriously pollute the environment, waste liquid treatment will increase the cost, and the by-products are low-value products;

The second is that the ferric phosphate produced contains a certain amount of crystal water, usually two, that is, FePO ₄ 2H ₂ O; the product usually contains a small amount of adsorption water in addition to crystal water; due to the crystal water and adsorption water, iron phosphate The actual composition of lithium iron phosphate is not very certain and reliable, which brings certain difficulties to the precise ingredients in the production of lithium iron phosphate;

In addition, during the long-term storage of products containing crystal water, moisture absorption or weathering may occur, which will cause changes in product components over time, which will adversely affect process stability and product consistency; therefore, FePO ₄ 2H ₂ O It is not suitable to be directly used as a raw material for the production of lithium iron phosphate cathode materials, and generally requires necessary pretreatment.

Moreover, ferrous sulfate (FeSO ₄ ) is commonly used as raw material in the industrial production of FePO ₄ ·2H ₂ O, and the cost is relatively low. However, with the existing technology, a large amount of oxidants such as hydrogen peroxide (H ₂ O ₂ ), sodium hypochlorite (NaClO), sodium chlorate (NaClO ₃ ), ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ), etc. must be consumed to a certain extent increased costs.

In summary, the use of iron phosphate containing crystal water to prepare lithium iron phosphate cathode materials has the disadvantages of high cost, large pollution, and difficulty in precise ingredients in the production process.

Contents of the invention

In order to solve the above-mentioned deficiencies of the existing lithium iron phosphate preparation process using iron phosphate containing crystal water as a raw material, which has high cost, large pollution and difficulty in precise ingredients in the production process, a simple and high-quality production process is proposed. Battery-grade iron phosphate and a method for preparing the battery-grade iron phosphate capable of reducing cost and pollution.

The present invention is achieved through the following schemes:

The battery-grade iron phosphate mentioned above is battery-grade anhydrous iron phosphate with orthorhombic crystal form.

The preparation method of the above-mentioned battery-grade iron phosphate is to adopt the oxidation precipitation method using air as an oxidant, add the aqueous solution of the mixture of ferrous salt and phosphoric acid or phosphate to control the pH value, pass in air, stir, The reaction produces a crystalline complex containing ammonium, hydroxide and crystal water, and then undergoes solid-liquid separation, washing and drying to obtain NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder; the powder The body is roasted in an air atmosphere to decompose and remove ammonium, hydroxide and crystal water to obtain battery-grade anhydrous iron phosphate with orthorhombic crystal form.

The preparation method of described battery grade iron phosphate, its concrete steps are as follows:

a. Prepare a mixed aqueous solution of ferrous salt and phosphoric acid or phosphate;

b, prepare pH value adjuster solution;

c. Continuously input the above prepared ferrous salt and phosphoric acid or phosphate mixed aqueous solution and the pH regulator solution into the reactor with stirring respectively, and input them into the reactor with a certain flow rate through the air compressor Air; through a constant temperature water bath, control and adjust the temperature of the reaction liquid in the reactor and keep it constant within the range of 40-98 ° C; constant flow of the mixed aqueous solution of ferrous salt and phosphoric acid or phosphate and air, control and adjust the reaction liquid in the reactor The pH value is 0.5-7.5 and kept constant; after the addition is completed, continue to stir and age and continue to introduce air to oxidize to form a crystalline complex NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O;

d. Transfer the material obtained in the previous step into a solid-liquid separator for solid-liquid separation, and wash the solid product obtained by the solid-liquid separation with deionized water until the SO ₄ ^2- in the washing water cannot be detected with BaCl ₂ solution, or use AgNO ₃ solution until no Cl ^- in the washing water can be detected; the washed product is dried in an oven at 80-120°C for 2-10 hours to obtain NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder ;

e. Calcining NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder in an air atmosphere at 500-700°C for 2-24 hours to decompose and remove ammonium, hydroxide and crystal water to obtain Orthorhombic battery grade anhydrous iron phosphate.

The method for preparing battery-grade iron phosphate, wherein: the ferrous salt is at least one of ferrous sulfate and ferrous chloride. The ferrous sulfate is prepared by reacting sulfuric acid and metallic iron. The ferrous chloride is prepared by reacting hydrochloric acid and metallic iron.

The method for preparing battery-grade iron phosphate, wherein: the phosphate is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate and ammonium phosphate.

The method for preparing battery-grade iron phosphate, wherein: the concentration of iron in the mixed aqueous solution of the ferrous salt and phosphoric acid or phosphate is 0.2-2 mol/liter, and the molar ratio of phosphorus to iron in the aqueous solution is 0.95-1.05 : 1.

The method for preparing battery-grade iron phosphate, wherein: the pH regulator is at least one of ammonia water, urea, hexamethylenetetramine, ammonium carbonate and ammonium bicarbonate.

Beneficial effect:

The invention prepares high-quality battery-grade anhydrous ferric phosphate by using cheap ferrous salts of ferrous sulfate and ferrous chloride as raw materials, and the mother liquor and washing liquid produced only contain ammonium salt, which can be directly used in agricultural and forestry production as nitrogen fertilizer. Will not pollute the environment, no need for waste liquid treatment;

The preparation process uses air as the oxidant, without consuming additional oxidant, which can significantly save costs;

The prepared product is anhydrous iron phosphate that does not contain crystal water and adsorbed water, has an orthorhombic crystal form, high crystallinity and reactivity, reliable composition, stable and storage-resistant, and is an ideal raw material for the preparation of lithium iron phosphate, which is conducive to improving the process stability and product consistency;

The preparation method is suitable for large-scale, economical, stable and reliable production of high-quality battery-grade iron phosphate, has obvious advantages and is of great practical value.

Detailed ways

The battery-grade iron phosphate of the present invention is an orthorhombic battery-grade anhydrous iron phosphate. The battery-grade anhydrous iron phosphate is an ideal raw material for preparing lithium iron phosphate cathode materials.

The method for preparing battery-grade iron phosphate is to adopt the method of oxidative precipitation with oxygen as a catalyst. First, ferrous salt, phosphoric acid or phosphate are mixed in proportion to form a mixture aqueous solution, and then a pH regulator solution is added, and at the same time, the Air is used as an oxidant, and the ^temperature and pH _of the ^mixture are controlled under stirring, and a crystalline complex (NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O); after solid-liquid separation, washing and drying, NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder was obtained; in air atmosphere Calcining NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder at a certain temperature for a certain period of time, decomposing and removing ammonium, hydroxide and crystal water, and obtaining high-quality battery grade with orthorhombic crystal form Anhydrous iron phosphate (FePO ₄ ).

The concrete steps of the preparation method of above-mentioned battery grade iron phosphate are as follows:

a. Prepare a mixed aqueous solution of a certain concentration of ferrous salt and phosphoric acid or phosphate;

b. Prepare a certain concentration of pH regulator solution;

c. Continuously input the above prepared ferrous salt and phosphoric acid or phosphate mixed aqueous solution and the pH regulator solution into the reactor with stirring respectively, and input them into the reactor with a certain flow rate through the air compressor Air; through a constant temperature water bath, control and adjust the temperature of the reaction liquid in the reactor and keep it constant within the range of 40-98 ° C; constant flow of the mixed aqueous solution of ferrous salt and phosphoric acid or phosphate and air, control and adjust the reaction liquid in the reactor The pH value is 0.5-7.5 and kept constant; after the addition is completed, continue to stir and age and continue to introduce air to oxidize to form a crystalline complex NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O;

d. Transfer the material obtained in the previous step into a solid-liquid separator for solid-liquid separation, and wash the solid product obtained by the solid-liquid separation with deionized water until the SO ₄ ^2- in the washing water cannot be detected with BaCl ₂ solution, or use AgNO ₃ solution until no Cl ^- in the washing water can be detected; the washed product is dried in an oven at 80-120°C for 2-10 hours to obtain NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder ;

e. Calcining NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder in an air atmosphere at 500-700°C for 2-24 hours to decompose and remove ammonium, hydroxide and crystal water to obtain Orthorhombic battery grade anhydrous iron phosphate.

The present invention is further described in detail below in conjunction with embodiment:

Example 1

Prepare ferrous sulfate and phosphoric acid mixed aqueous solution, wherein ferrous sulfate concentration is 1.5 mol/liter, phosphoric acid concentration is 1.5 mol/liter;

Preparation concentration is the ammonia solution of 5.0 mol/liter as pH regulator;

Add 2 liters of deionized water to the reaction kettle with a volume of 7 liters, stir vigorously, and pass constant temperature water into the jacket of the reaction kettle to control the water temperature in the reaction kettle to 70°C;

Through the air compressor, import air into the reactor as the oxidant with a flow rate of 5 liters/minute;

Ferrous sulfate and phosphoric acid mixed aqueous solution, ammonia solution are respectively continuously input in the reactor with pump, the flow of controlling ferrous sulfate and phosphoric acid mixed aqueous solution is 20 milliliters/minute, regulates the flow of ammonia solution, controls the flow rate of reaction solution in the reactor. The pH value is 6.00±0.05;

Through a constant temperature water bath, control and adjust the temperature of the reaction liquid in the reactor and keep it within the range of 69-71°C;

Add 2 liters of mixed aqueous solution of ferrous sulfate and phosphoric acid to the reaction kettle, stop feeding, continue to stir and age for 10 hours, and at the same time continue to feed air; during the aging process, the temperature of the reaction solution should always be kept within the range of 69-71 °C , and timely add ammonia solution to control the pH value of the reaction solution in the reactor to 6.00±0.05;

After aging, discharge the materials in the reactor, use a centrifuge for solid-liquid separation, and wash the solid product obtained by solid-liquid separation with deionized water at 60°C until no SO _{4 2} in the washing water can be detected with BaCl ^{2 -} up to;

drying the washed product in an oven at 105°C for 4 hours to obtain NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder;

Put the NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder in a corundum crucible, and bake it in an air atmosphere muffle furnace at 580°C for 4 hours to decompose and remove ammonium, hydroxide and crystal water to obtain Orthorhombic battery grade anhydrous iron phosphate.

The ammonia gas produced by roasting and decomposition can be absorbed by sulfuric acid to generate ammonium sulfate; the mother liquor and washing liquid after centrifugation only contain ammonium sulfate; the two batches of ammonium sulfate solution can be directly used as nitrogen fertilizer after adjusting the pH value to neutral with ammonia solution.

Example 2

Prepare ferrous chloride, phosphoric acid, ammonium phosphate mixed aqueous solution, wherein ferrous chloride concentration is 1.0 mol/liter, phosphoric acid concentration is 0.75 mol/liter, ammonium phosphate concentration is 0.25 mol/liter;

Preparation concentration is the hexamethylenetetramine solution of 1.5 mol/liter as pH regulator;

Add 1 liter of deionized water to the reactor with a volume of 7 liters in advance, stir vigorously, and pass constant temperature water into the jacket of the reactor, and control the water temperature in the reactor to 95°C;

Through the air compressor, import air into the reactor as the oxidant with a flow rate of 5 liters/minute;

With ferrous chloride, phosphoric acid, ammonium phosphate mixed aqueous solution, hexamethylenetetramine solution is continuously input in the reactor respectively with pump, and the flow of controlling ferrous chloride, phosphoric acid, ammonium phosphate mixed aqueous solution is 20 milliliters/minute, Adjust the flow rate of the hexamethylenetetramine solution, and control the pH value of the reaction solution in the reactor to 1.60±0.05; control and adjust the temperature of the reaction solution in the reactor through a constant temperature water bath and keep it within the range of 94-96°C;

Add 2 liters of mixed aqueous solution of ferrous chloride, phosphoric acid and ammonium phosphate to the reactor, then stop feeding, continue to stir and age for 5 hours, and continue to feed air at the same time; during the aging process, the temperature of the reaction solution should always be kept at 94- Within the range of 96°C, and timely add hexamethylenetetramine solution to control the pH value of the reaction solution in the reactor to 1.60±0.05;

After aging, the materials in the reactor were discharged, the solid-liquid separation was carried out with ^a centrifuge, and the solid product obtained from the solid-liquid separation was washed with deionized water at 60°C until the Cl- in the washing water could not be detected with the AgNO ₃ solution until;

drying the washed product in an oven at 80°C for 4 hours to obtain NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder;

Put the NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder in a corundum crucible, bake it in an air atmosphere muffle furnace at 700°C for 2 hours, decompose and remove ammonium, hydroxide and crystal water, and obtain Orthorhombic battery grade anhydrous iron phosphate.

The ammonia gas produced by roasting and decomposition can be absorbed by hydrochloric acid to generate ammonium chloride; the mother liquor and washing liquid after centrifugation only contain ammonium chloride; the two batches of ammonium chloride solution can be directly used as Nitrogen fertilizer use.

Example 3

Prepare ferrous sulfate, phosphoric acid, diammonium hydrogen phosphate mixed aqueous solution, wherein the ferrous sulfate concentration is 1.0 mol/liter, the phosphoric acid concentration is 0.5 mol/liter, and the diammonium hydrogen phosphate concentration is 0.5 mol/liter;

Preparation concentration is the aqueous ammonia solution of 4.0 mol/liter as pH regulator;

Add 1 liter of deionized water to a reactor with a volume of 7 liters, stir vigorously, and pass constant temperature water into the jacket of the reactor to control the water temperature in the reactor to 45°C;

Through the air compressor, import air into the reactor as the oxidant with a flow rate of 5 liters/minute;

The ferrous sulfate, phosphoric acid, diammonium hydrogen phosphate mixed aqueous solution and ammonia solution are respectively continuously input into the reaction kettle with a pump, and the flow rate of the ferrous sulfate, phosphoric acid, diammonium hydrogen phosphate mixed aqueous solution is controlled to be 20 ml/min, and the ammonia solution is adjusted. The flow rate is to control the pH value of the reaction solution in the reactor to 2.30±0.05; through a constant temperature water bath, control and adjust the temperature of the reaction solution in the reactor and keep it within the range of 44-46°C; add 2 liters of ferrous sulfate, After phosphoric acid and diammonium hydrogen phosphate mixed aqueous solution, stop feeding;

Pass high-temperature constant-temperature water into the jacket of the reaction kettle, raise the temperature of the materials in the reaction kettle, control the temperature of the materials in the reaction kettle within the range of 94-96°C, continue to stir and age for 10 hours, and continue to feed air at the same time;

After aging, discharge the materials in the reactor, use a centrifuge for solid-liquid separation, and wash the solid product obtained by solid-liquid separation with deionized water at 60°C until no SO _{4 2} in the washing water can be detected with BaCl ^{2 -} up to;

The washed product was dried in an oven at 120°C for 4 hours to obtain NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder;

Put the NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder in a corundum crucible, bake it in an air atmosphere muffle furnace at 500°C for 24 hours, decompose and remove ammonium, hydroxide and crystal water, and obtain Orthorhombic high quality battery grade anhydrous iron phosphate.

The ammonia gas produced by roasting and decomposition can be absorbed by sulfuric acid to generate ammonium sulfate; the mother liquor and washing liquid after centrifugation only contain ammonium sulfate; the two batches of ammonium sulfate solution can be directly used as nitrogen fertilizer after adjusting the pH value to neutral with ammonia solution.

Example 4

Prepare ferrous sulfate and ammonium dihydrogen phosphate mixed aqueous solution, wherein the concentration of ferrous sulfate is 1.5 mol/liter, and the concentration of ammonium dihydrogen phosphate is 1.5 mol/liter;

Prepare a urea solution with a concentration of 2.5 mol/liter as a pH regulator;

Add 2 liters of deionized water in advance to a reactor with a volume of 7 liters, stir vigorously, and pass constant temperature water into the jacket of the reactor to control the water temperature in the reactor to 90°C. Through the air compressor, import air into the reactor as the oxidant with a flow rate of 5 liters/minute;

The mixed aqueous solution of ferrous sulfate and ammonium dihydrogen phosphate and the urea solution are respectively continuously input into the reactor with a pump, and the flow rate of the mixed aqueous solution of ferrous sulfate and ammonium dihydrogen phosphate is controlled to be 20 ml/min, and the flow rate of the urea solution is adjusted to control The pH value of the reaction liquid in the reaction kettle is 5.00±0.05; through a constant temperature water bath, the temperature of the reaction liquid in the reaction kettle is controlled and maintained within the range of 89-91°C;

Add 2 liters of mixed aqueous solution of ferrous sulfate and ammonium dihydrogen phosphate to the reaction kettle, stop feeding, continue to stir and age for 8 hours, and at the same time continue to feed air; during the aging process, the temperature of the reaction solution should always be kept at 89-91 ℃ range, and timely add urea solution to control the pH value of the reaction solution in the reactor to 5.00±0.05;

After aging, discharge the materials in the reactor, use a centrifuge for solid-liquid separation, wash the solid product obtained by solid-liquid separation with deionized water at 60°C, until no SO ₄ in the washing water can be detected with BaCl ₂ solution ^2- so far;

drying the washed product in an oven at 105°C for 4 hours to obtain NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder;

Put the NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder in a corundum crucible, and bake it in an air atmosphere muffle furnace at 600°C for 6 hours to decompose and remove ammonium, hydroxide and crystal water to obtain Orthorhombic battery grade anhydrous iron phosphate.

The ammonia gas produced by roasting and decomposition can be absorbed by sulfuric acid to generate ammonium sulfate; the mother liquor and washing liquid after centrifugation only contain ammonium sulfate; the two batches of ammonium sulfate solution can be directly used as nitrogen fertilizer after adjusting the pH value to neutral with ammonia solution.

Example 5

Ferrous chloride was used to replace ferrous sulfate in Example 1, and battery-grade anhydrous ferric phosphate was prepared under the same process conditions. The difference is: wash the solid product obtained by solid-liquid separation with deionized water at 60°C until no Cl ^- in the washing water can be detected with AgNO ₃ solution. The ammonia gas produced by roasting and decomposition can be absorbed by hydrochloric acid to generate ammonium chloride; the mother liquor and washing liquid after centrifugation only contain ammonium chloride; the two batches of ammonium chloride solution can be directly used as Nitrogen fertilizer use. Other conditions are with embodiment 1.

Example 6

Ferrous sulfate was used to replace ferrous chloride in Example 2, and battery-grade anhydrous ferric phosphate was prepared under the same process conditions. The difference is that the solid product obtained by solid-liquid separation is washed with deionized water at 60° C. until no SO ₄ ^2- in the washing water can be detected with BaCl ₂ . The ammonia gas produced by roasting and decomposition can be absorbed by sulfuric acid to generate ammonium sulfate; the mother liquor and washing liquid after centrifugation only contain ammonium sulfate; the two batches of ammonium sulfate solution can be directly used as nitrogen fertilizer after adjusting the pH value to neutral with ammonia solution. Other conditions are with embodiment 2.

Example 7

Embodiment 1 directly uses ferrous sulfate as raw material. Under heating state, in the sulfuric acid solution that concentration is 4M, add excessive metal iron, filter after sufficient reaction, make ferrous sulfate solution, replace the ferrous sulfate in embodiment 1, prepare ferrous sulfate and phosphoric acid mixed aqueous solution, High-quality battery-grade anhydrous iron phosphate was prepared by the same process conditions as in Example 1.

Example 8

Embodiment 2 directly uses ferrous chloride as raw material. Add excessive metallic iron in the hydrochloric acid solution that concentration is 4M, filter after sufficient reaction, make ferrous chloride solution, replace ferrous chloride in embodiment 2, prepare ferrous chloride, phosphoric acid, ammonium phosphate mixed aqueous solution , according to the same process conditions as in Example 2 to prepare high-quality battery-grade anhydrous iron phosphate.

Example 9

The 2.5 mol/liter urea solution in Example 4 was replaced by 2.5 mol/liter ammonium carbonate solution, and high-quality battery-grade anhydrous iron phosphate was prepared according to the same process conditions as in Example 4.

Example 10

The 2.5 mol/liter urea solution in Example 4 was replaced by 5 mol/liter ammonium bicarbonate solution, and high-quality battery-grade anhydrous iron phosphate was prepared according to the same process conditions as in Example 4.

Claims (9)

1. A battery grade iron phosphate, characterized in that: the battery grade iron phosphate is an orthorhombic battery grade anhydrous iron phosphate. 2. The preparation method of battery grade ferric phosphate as claimed in claim 1, is characterized in that: described preparation method is to adopt the oxidation precipitation method that takes air as oxidant, the mixture aqueous solution of ferrous salt and phosphoric acid or phosphate is added The pH value regulator solution controls the pH value, introduces air, stirs, and reacts to form a crystalline complex containing ammonium, hydroxide, and crystal water, and then undergoes solid-liquid separation, washing, and drying to obtain NH ₄ Fe ₂ (OH )(PO ₄ ) ₂ ·2H ₂ O powder; the powder is roasted in the air atmosphere to decompose and remove ammonium, hydroxide and crystal water to obtain battery-grade anhydrous iron phosphate with orthorhombic crystal form. 3. the preparation method of battery grade iron phosphate according to claim 2, its concrete steps are as follows: a. Prepare a mixed aqueous solution of ferrous salt and phosphoric acid or phosphate; b, prepare pH value adjuster solution; c. Continuously input the above prepared ferrous salt and phosphoric acid or phosphate mixed aqueous solution and the pH regulator solution into the reactor with stirring respectively, and input them into the reactor with a certain flow rate through the air compressor Air; through a constant temperature water bath, control and adjust the temperature of the reaction liquid in the reactor and keep it constant within the range of 40-98 ° C; constant flow of the mixed aqueous solution of ferrous salt and phosphoric acid or phosphate and air, control and adjust the reaction liquid in the reactor The pH value is 0.5-7.5 and kept constant; after the addition is completed, continue to stir and age and continue to introduce air to oxidize to form a crystalline complex NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O; d. Transfer the material obtained in the previous step into a solid-liquid separator for solid-liquid separation, and wash the solid product obtained by the solid-liquid separation with deionized water until the SO ₄ ^2- in the washing water cannot be detected with BaCl ₂ solution, or use AgNO ₃ solution until no Cl ^- in the washing water can be detected; the washed product is dried in an oven at 80-120°C for 2-10 hours to obtain NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder ; e. Calcining NH ₄ Fe ₂ (OH)(PO ₄ ) ₂ ·2H ₂ O powder in an air atmosphere at 500-700°C for 2-24 hours to decompose and remove ammonium, hydroxide and crystal water to obtain Orthorhombic battery grade anhydrous iron phosphate. 4. The method for preparing battery-grade iron phosphate according to claim 2 or 3, characterized in that: the ferrous salt is at least one of ferrous sulfate and ferrous chloride. 5. The preparation method of battery-grade iron phosphate according to claim 4, characterized in that: said ferrous sulfate is prepared by reacting sulfuric acid and metallic iron. 6. The method for preparing battery-grade ferric phosphate according to claim 4, characterized in that: the ferrous chloride is prepared by reacting hydrochloric acid and metallic iron. 7. The method for preparing battery-grade iron phosphate according to claim 2 or 3, characterized in that: the phosphate is at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate and ammonium phosphate. 8. The preparation method of battery-grade iron phosphate according to claim 2 or 3, characterized in that: the concentration of iron in the mixed aqueous solution of the ferrous salt and phosphoric acid or phosphate is 0.2-2 mol/liter, and in the aqueous solution The molar ratio of phosphorus to iron is 0.95-1.05:1. 9. The preparation method of battery grade iron phosphate according to claim 2 or 3, characterized in that: the pH regulator is at least one of ammonia, urea, hexamethylenetetramine, ammonium carbonate and ammonium bicarbonate A sort of.