Anhydrous iron phosphate and preparation method thereof and lithium iron phosphate positive electrode material

Abstract

The invention discloses an anhydrous iron phosphate and a preparation method thereof and a lithium iron phosphate positive electrode material, belonging to the technical field of lithium battery materials. The preparation of the anhydrous iron phosphate comprises the following steps: reacting a mixture of a ferrophosphorus solution and an alkaline solution under the conditions of 80-90°C for 20-60min to obtain a reaction solution; cooling the reaction solution to below 50°C within 20min, and then roasting the solid obtained by the reaction. The method is simple and easy to operate, and an anhydrous iron phosphate having a small repose angle and uniform size can be prepared. The anhydrous iron phosphate has excellent fluidity, processing performance and compacted density, which is conducive to improving the processing performance and electrochemical performance of the lithium iron phosphate positive electrode material prepared subsequently.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery materials, and in particular to an anhydrous iron phosphate and a preparation method thereof, and a lithium iron phosphate positive electrode material. Background Art

[0002] The safety of electric vehicles has attracted increasing attention. As the core component of electric vehicles, the power battery, its safety index has directly become a key indicator for people to buy electric vehicles.

[0003] Lithium iron phosphate battery has become one of the most potential power batteries with its high safety and low price. As an important precursor of lithium iron phosphate battery positive electrode material, iron phosphate has a high sintering rate and good low temperature performance in the preparation of lithium iron phosphate, so its corresponding market share is also increasing.

[0004] The performance of iron phosphate directly affects the performance of lithium iron phosphate products. Iron phosphate accounts for about 50% of the cost of lithium iron phosphate. Therefore, the preparation of battery-grade iron phosphate with good performance and economy is the key to lithium iron phosphate batteries.

[0005] Among the performance indicators of iron phosphate, good processability is also an important aspect that affects the application field of iron phosphate. Iron phosphate products with good fluidity have better processability.

[0006] However, at present, the fluidity of iron phosphate products has not received enough attention in the research.

[0007] In view of this, the present invention is proposed. Summary of the invention

[0008] One of the purposes of the present invention is to provide a method for preparing anhydrous ferric phosphate. The method is simple and easy to operate, and can prepare anhydrous ferric phosphate with a small repose angle and uniform size. The anhydrous ferric phosphate has good fluidity, processing performance and compaction density.

[0009] A second object of the present invention is to provide anhydrous ferric phosphate prepared by the above preparation method.

[0010] The third object of the present invention is to provide a lithium iron phosphate positive electrode material prepared from the above-mentioned anhydrous iron phosphate.

[0011] This application can be implemented as follows:

[0012] In a first aspect, the present application provides a method for preparing anhydrous ferric phosphate, which comprises the following steps:

[0013] reacting a mixture of the ferrophosphorus solution and the alkaline solution at 80-90° C. for 20-60 minutes to obtain a reaction solution;

[0014] The reaction solution was cooled to below 50° C. within 20 min, and then the solid obtained by the reaction was calcined.

[0015] In an optional embodiment, the ferrophosphorus solution and the alkaline solution are reacted at a stirring speed of 100-200 r / min.

[0016] In an optional embodiment, the pH value of the mixture of the ferrophosphorus solution and the alkaline solution is 2-3.

[0017] In an alternative embodiment, the reaction is carried out in a tubular reactor.

[0018] In an optional embodiment, a feeding pipe with a jacket structure is connected to the inlet of the tubular reactor.

[0019] In an optional embodiment, the reaction liquid is preheated to 40-50° C. through a feed pipe before entering the tubular reactor for reaction.

[0020] In an optional embodiment, the temperature reduction is performed in a quenching device.

[0021] In an alternative embodiment, the quenching device includes a quenching tank, a quenching tank, or a tubular reaction mixer.

[0022] In an optional embodiment, the temperature is lowered by cooling while discharging.

[0023] In an optional embodiment, the cooling liquid used for cooling is low-temperature pure water or mother liquor washing water remaining after washing in the preparation process of other batches of anhydrous ferric phosphate.

[0024] In an alternative embodiment, the preparation of the ferrophosphorus solution comprises mixing an iron source, a phosphorus source and a strong mineral acid.

[0025] In an optional embodiment, in the ferrophosphorus solution, the molar ratio of iron element to phosphorus element is 0.9-1.3:1.

[0026] In an optional embodiment, the concentration of iron ions in the ferrophosphorus solution is 0.7-1.5 mol / L.

[0027] In an alternative embodiment, the pH value of the ferrophosphorus solution is less than 1.

[0028] In an alternative embodiment, the iron source comprises at least one of iron oxide, iron chloride, and iron nitrate.

[0029] In an alternative embodiment, the phosphorus source includes at least one of phosphoric acid and dihydrogen phosphate.

[0030] In an alternative embodiment, the strong mineral acid comprises at least one of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid.

[0031] In an alternative embodiment, the pH value of the ferrophosphorus solution is adjusted by hydrochloric acid and / or nitric acid.

[0032] In an optional embodiment, the alkaline solution includes at least one of a sodium hydroxide solution and a potassium hydroxide solution.

[0033] In an alternative embodiment, the alkaline solution is a sodium hydroxide solution.

[0034] In an optional embodiment, the concentration of the sodium hydroxide solution is 1-3 mol / L.

[0035] In an optional embodiment, before calcination, the product obtained by the reaction is washed, and the washed solid is dried.

[0036] In an alternative embodiment, the temperature of the washing liquid used for washing does not exceed 60°C.

[0037] In an alternative embodiment, the temperature of the washing liquid used for washing does not exceed 50°C.

[0038] In an optional embodiment, the drying temperature is 100-150° C., and / or the drying time is 30-120 min.

[0039] In an optional embodiment, the calcination temperature is 500-600° C., and / or the calcination time is no more than 3.5 h.

[0040] In a second aspect, the present application provides an anhydrous ferric phosphate, which is prepared by the preparation method of any one of the aforementioned embodiments.

[0041] In an alternative embodiment, the angle of repose of the anhydrous ferric phosphate does not exceed 30°.

[0042] In a third aspect, the present application provides a lithium iron phosphate positive electrode material, whose precursor is the anhydrous iron phosphate of the aforementioned embodiment.

[0043] The beneficial effects of this application include:

[0044] The present application can improve the reaction rate of the substance by reacting the mixture of ferrophosphorus solution and alkaline solution at 80-90°C for 20-60min to quickly generate ferric phosphate, and the above reaction temperature and time are conducive to controlling the crystal morphology in a better state. After the reaction, by rapidly cooling the reaction solution, on the one hand, it is conducive to eliminating the undesirable by-product reaction, and on the other hand, it is conducive to improving the uniformity of the crystal product particles, eliminating the surface stress of the grains, making them tight and not easy to crack, and then it is conducive to obtaining anhydrous ferric phosphate material with excellent fluidity after roasting.

[0045] The main function of the above rapid cooling is to end the reaction process quickly and consistently, effectively stopping the occurrence of unfavorable secondary reactions. The conventional method for preparing ferric phosphate is natural cooling, and the differences in the changes in the environment in which the materials are located increase. Secondary reactions will occur under the action of residual heat, forming random deposits on the surface of the generated materials, causing large differences in the surface of the finished materials, resulting in poor fluidity of the finished products. Rapid cooling ensures the consistency of the material particles after the reaction.

[0046] Furthermore, the cooling liquid is preferably the mother liquor washing water after the solid-liquid separation of the previous batch, which not only improves the surface properties of the product particles, but also saves water. The reason why this method can improve the surface properties of the material is that the mother liquor washing water contains a small amount of tiny crystals, which have a certain repair effect on the small amount of tiny defects on the surface of the crystals after the reaction at a lower temperature when mixed with the product liquid for cooling.

[0047] The preparation method of the anhydrous iron phosphate provided in the present application is simple and easy to operate, and can prepare anhydrous iron phosphate with a small repose angle and uniform size. The anhydrous iron phosphate has excellent fluidity, processing performance and compaction density, which is beneficial to improving the processing performance and electrochemical performance of the subsequently prepared lithium iron phosphate positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0049] Figure 1 The SEM image of anhydrous ferric phosphate provided in Example 3;

[0050] Figure 2 This is a SEM image of anhydrous iron phosphate provided for Comparative Example 1. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0052] The anhydrous iron phosphate and its preparation method and the lithium iron phosphate positive electrode material provided in this application are described in detail below.

[0053] The present application proposes a method for preparing anhydrous ferric phosphate, which comprises the following steps:

[0054] reacting a mixture of the ferrophosphorus solution and the alkaline solution at 80-90° C. for 20-60 minutes to obtain a reaction solution;

[0055] The reaction solution was cooled to below 50° C. within 20 min, and then the solid obtained by the reaction was calcined.

[0056] In the present application, the mixture of the ferrophosphorus solution and the alkaline solution can be obtained by uniformly stirring the ferrophosphorus solution and the alkaline solution in a mixing container, and the pH value of the obtained mixture is 2-3, such as 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3.0, etc., or it can be any other value within the range of 2-3.

[0057] In some optional embodiments, the mixing time of the ferrophosphorus solution and the alkaline solution does not exceed 30 min, such as 30 min, 25 min, 20 min, 15 min, 10 min, 5 min or 2 min, etc., or any other value within the range of not more than 30 min, preferably 5-25 min.

[0058] It should be noted that if the mixing time of the ferrophosphorus solution and the alkaline solution exceeds 30 minutes, precipitation is likely to occur, affecting product quality.

[0059] For reference, the preparation of the above-mentioned ferrophosphorus solution may include: mixing an iron source, a phosphorus source and a strong inorganic acid.

[0060] The iron source may include, but is not limited to, at least one of iron oxide, iron chloride, and iron nitrate. The phosphorus source may include, but is not limited to, at least one of phosphoric acid and dihydrogen phosphate. The strong inorganic acid may include, but is not limited to, at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

[0061] Preferably, in the ferrophosphorus solution, the molar ratio of iron to phosphorus is 0.9-1.3:1, such as 0.9:1, 0.95:1, 1:1, 1.05:1, 1.1:1, 1.15:1, 1.2:1, 1.25:1 or 1.3:1, or any other value within the range of 0.9-1.3:1.

[0062] In the ferrophosphorus solution, the concentration of iron ions can be 0.7-1.5 mol / L, such as 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L or 1.5 mol / L, or any other value within the range of 0.7-1.5 mol / L.

[0063] The pH value of the ferrophosphorus solution is less than 1, and the pH value of the ferrophosphorus solution can be adjusted by hydrochloric acid and / or nitric acid.

[0064] In the present application, the alkaline solution may include at least one of a sodium hydroxide solution and a potassium hydroxide solution, preferably a sodium hydroxide solution.

[0065] For reference, the concentration of the sodium hydroxide solution can be 1-3 mol / L, such as 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L, etc., or any other value within the range of 1-3 mol / L.

[0066] In the present application, the mixed solution of the ferrophosphorus solution and the alkaline solution is preferably reacted in a tubular reactor.

[0067] The present application greatly improves the reaction rate of the above substances by allowing the mixed solution of ferrophosphide solution and alkaline solution to react in a tubular reactor, and can quickly generate ferrophosphate, and the obtained product particles are extremely consistent, with complete and uniform morphology.

[0068] In some preferred embodiments, the inlet of the tubular reactor is connected to a feeding pipe having a jacket structure.

[0069] By adopting the jacket structure, the feed liquid entering the tubular reactor is first preheated by the jacket of the feed pipe (such as preheating to 40-50°C), and then enters the tubular reactor for reaction. This is beneficial to the rapid temperature rise of the reactants after entering the reactor, and reduces the heat loss in the process, which is beneficial to saving energy consumption in the process.

[0070] Correspondingly, the reaction temperature of the ferrophosphorus solution and the alkaline solution can be 80° C., 82° C., 85° C., 88° C. or 90° C., or any other value within the range of 80-90° C. The reaction time can be 20 min., 30 min., 40 min., 50 min. or 60 min., or any other value within the range of 20-60 min.

[0071] It should be noted that if the reaction temperature exceeds 90°C or the reaction time exceeds 60 minutes, not only will the uniformity of the grains be reduced, but also the purity of the finished product will be affected. If the reaction temperature is lower than 80°C or the reaction time is shorter than 20 minutes, the reaction will be incomplete.

[0072] Preferably, the reaction process is assisted by stirring, and the stirring speed can be controlled to be 100-200 r / min, such as 100 r / min, 120 r / min, 150 r / min, 180 r / min or 200 r / min, or any other value within the range of 100-200 r / min.

[0073] By stirring during the reaction, the reaction can be made more uniform.

[0074] After the reaction is completed, the obtained reaction solution is cooled to terminate the reaction.

[0075] In the present application, the temperature reduction is carried out in a quenching device.

[0076] For reference, the quenching device may be a quenching tank, a quenching tank or a tubular reaction mixer, and preferably a tubular reaction mixer.

[0077] The temperature of the feed liquid can be quickly reduced to below 50°C by means of cold water heat exchange, such as cooling to 45°C, 40°C, 35°C, 30°C, 25°C, 20°C, 15°C, 10°C or 5°C.

[0078] The above-mentioned cooling process is controlled to be completed within 20 minutes (such as 20 minutes, 18 minutes, 15 minutes, 12 minutes, 10 minutes, 8 minutes or 5 minutes, etc.) to ensure that the product has good fluidity.

[0079] The present application rapidly cools the reaction liquid, which is beneficial to eliminating adverse by-product reactions on the one hand, and improving the uniformity of the crystallized product particles on the other hand, eliminating the surface stress of the grains, making them tight and not easy to crack, and further facilitating obtaining anhydrous ferric phosphate material with excellent fluidity after roasting.

[0080] Preferably, the above-mentioned cooling is carried out by cooling while discharging the material.

[0081] The cooling liquid used for cooling can be low-temperature pure water, or it can be the mother liquor remaining after washing in the preparation process of other batches of anhydrous ferric phosphate, preferably it is the mother liquor washing water remaining after washing in the preparation process of other batches of anhydrous ferric phosphate.

[0082] It should be noted that the cooling liquid uses the mother liquor washing water left after washing in the preparation process of other batches of anhydrous ferric phosphate, which not only improves the surface properties of the product particles, but also saves water. The reason for improving the surface properties of the product particles is that the mother liquor washing water contains a small amount of tiny crystals, which have a certain repair effect on the tiny defects that may exist on the surface of the crystals after the reaction during the process of mixing with the product liquid and cooling.

[0083] Furthermore, before calcination, the product obtained by the reaction is washed, and the washed solid is dried.

[0084] The temperature of the washing liquid used for washing does not exceed 60°C, such as 60°C, 55°C, 50°C, 45°C, 40°C, 35°C, 30°C, 25°C, 20°C, 15°C, 10°C or 5°C, etc., and is preferably not more than 50°C.

[0085] The above washing process can be carried out in a filter press. After washing, the filter cake is dried and the filtrate can be used as mother liquor washing water for cooling other batches of anhydrous ferric phosphate preparation process.

[0086] In the present application, the drying temperature can be 100-150°C, such as 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C or 150°C, etc., or it can be any other value within the range of 100-150°C.

[0087] The drying time may be 30-120 min, such as 30 min, 50 min, 80 min, 100 min or 120 min, etc., or any other value within the range of 30-120 min.

[0088] By drying, a dihydrate iron phosphate product having excellent fluidity can be obtained.

[0089] Further, the obtained ferric phosphate dihydrate product is roasted.

[0090] For reference, the calcination temperature may be 500-600°C, such as 500°C, 520°C, 550°C, 580°C or 600°C, etc., or any other value within the range of 500-600°C.

[0091] The calcination time does not exceed 3.5 h, for example, it can be 3.5 h, 3 h, 2.5 h, 2 h, 1.5 h, 1 h or 0.5 h.

[0092] By roasting, anhydrous ferric phosphate products with excellent fluidity can be obtained.

[0093] Correspondingly, the present application also provides an anhydrous ferric phosphate, which is prepared by the above preparation method.

[0094] The repose angle of the obtained anhydrous ferric phosphate does not exceed 30°, such as 30°, 29°, 28°, 27°, 26° or 25°, etc., and may also be other values ​​not exceeding 30°.

[0095] The above-mentioned repose angle is an important indicator of material fluidity. Generally speaking, the smaller the repose angle, the smaller the friction and the better the fluidity. Specifically, the repose angle is also called the angle of repose, which is the minimum angle between the inclined plane and the horizontal surface when the object placed on it is in a critical state of sliding down the inclined plane (that is, as the inclination angle increases, the object on the inclined plane will slide more easily; when the object reaches the state of starting to slide, the angle of the critical state is called the repose angle).

[0096] As mentioned above, the anhydrous ferric phosphate provided in the present application not only has a small repose angle and uniform crystal particle size, but also has good fluidity, processing performance and compaction density.

[0097] In addition, the present application also provides a lithium iron phosphate positive electrode material, whose precursor is the above-mentioned anhydrous iron phosphate.

[0098] The lithium iron phosphate positive electrode material has better processing performance and electrochemical performance.

[0099] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0100] Example 1

[0101] This embodiment provides an anhydrous ferric phosphate, which is prepared by the following method:

[0102] Step 1: Prepare a ferrophosphorus solution using iron oxide, phosphoric acid and nitric acid.

[0103] The molar ratio of iron element to phosphorus element in the ferrophosphorus solution is 1.0:1, the iron ion concentration is 0.8 mol / L, and the pH value of the ferrophosphorus solution is 0.7.

[0104] Step 2: Prepare a sodium hydroxide solution with a concentration of 1.1 mol / L.

[0105] Step 3: First, add the ferrophosphorus solution prepared in step 1 to the reactor, then add the sodium hydroxide solution prepared in step 2, mix and stir evenly to make the pH value of the mixed solution 2.2, and the mixing time is 20 minutes. Then, the mixed solution is preheated to 45°C through a feed pipe with a jacket structure and then enters the tubular reactor for reaction, and the reaction temperature is controlled to 85°C, the reaction time is controlled to 30 minutes, and the stirring rate is 100r / min.

[0106] Step 4: The method of discharging and cooling is adopted. After the reaction liquid leaves the reactor, it quickly enters the quenching tank, and cold water is added to quickly reduce the temperature of the liquid to 45°C (cooling time is 10 minutes). The cold water is the mother liquor washing water after washing in the preparation process of the previous batch of anhydrous ferric phosphate.

[0107] Step 5: The cooled liquid in the quench tank is washed by a filter press, and the washing water temperature is controlled to be 35° C. After washing, the obtained filter cake is dried at 120° C. for 100 minutes to obtain a dihydrate ferric phosphate product with excellent fluidity.

[0108] Step 6: calcine the dihydrate ferric phosphate product obtained in step 5 at 550° C. for 2.5 h to obtain an anhydrous ferric phosphate product with excellent fluidity.

[0109] Example 2

[0110] This embodiment provides an anhydrous ferric phosphate, which is prepared by the following method:

[0111] Step 1: Prepare a ferrophosphorus solution using ferric nitrate, phosphoric acid and hydrochloric acid.

[0112] The molar ratio of iron element to phosphorus element in the ferrophosphorus solution is 1.1:1, the iron ion concentration is 0.7 mol / L, and the pH value of the ferrophosphorus solution is less than 1.

[0113] Step 2: Prepare a sodium hydroxide solution with a concentration of 1.0 mol / L.

[0114] Step 3: First, add the ferrophosphorus solution prepared in step 1 to the reactor, then add the sodium hydroxide solution prepared in step 2, mix and stir evenly to make the pH value of the mixed solution 2.3, and the mixing time is 25 minutes. Then, the mixed solution is preheated to 40°C through a feed pipe with a jacket structure and then enters the tubular reactor for reaction, and the reaction temperature is controlled to 85°C, the reaction time is controlled to 20 minutes, and the stirring rate is 120r / min.

[0115] Step 4: The method of discharging and cooling is adopted. After the reaction liquid leaves the reactor, it quickly enters the quenching tank, and cold water is added to quickly reduce the temperature of the liquid to 43°C (cooling time is 15 minutes). The cold water is the mother liquor washing water after washing in the preparation process of the previous batch of anhydrous ferric phosphate.

[0116] Step 5: The cooled liquid in the quench tank is washed by a filter press, and the washing water temperature is controlled to be 45° C. After washing, the obtained filter cake is dried at 120° C. for 100 minutes to obtain a dihydrate ferric phosphate product with excellent fluidity.

[0117] Step 6: calcine the dihydrate ferric phosphate product obtained in step 5 at 550° C. for 2.5 h to obtain an anhydrous ferric phosphate product with excellent fluidity.

[0118] Example 3

[0119] This embodiment provides an anhydrous ferric phosphate, which is prepared by the following method:

[0120] Step 1: Prepare a ferrophosphorus solution using ferric chloride, phosphoric acid and nitric acid.

[0121] The molar ratio of iron element to phosphorus element in the ferrophosphorus solution is 1.0:1, the iron ion concentration is 0.9 mol / L, and the pH value of the ferrophosphorus solution is less than 1.

[0122] Step 2: Prepare a sodium hydroxide solution with a concentration of 1.0 mol / L.

[0123] Step 3: First, add the ferrophosphorus solution prepared in step 1 to the reactor, then add the sodium hydroxide solution prepared in step 2, mix and stir evenly to make the pH value of the mixed solution 2.7, and the mixing time is 10 minutes. Then, the mixed solution is preheated to 42°C through a feed pipe with a jacket structure and then enters the tubular reactor for reaction, and the reaction temperature is controlled to 85°C, the reaction time is controlled to 20 minutes, and the stirring rate is 120r / min.

[0124] Step 4: The method of discharging and cooling is adopted. After the reaction liquid leaves the reactor, it quickly enters the quenching tank, and cold water is added to quickly reduce the temperature of the liquid to 41°C (cooling time is 12 minutes). The cold water is the mother liquor washing water after washing in the preparation process of the previous batch of anhydrous ferric phosphate.

[0125] Step 5: The cooled liquid in the quench tank is washed by a filter press, and the washing water temperature is controlled to be 40°C. After washing, the obtained filter cake is dried at 120°C for 100 minutes to obtain a dihydrate ferric phosphate product with excellent fluidity.

[0126] Step 6: calcine the dihydrate ferric phosphate product obtained in step 5 at 550° C. for 2.5 h to obtain an anhydrous ferric phosphate product with excellent fluidity.

[0127] Example 4

[0128] This embodiment provides an anhydrous ferric phosphate, which is prepared by the following method:

[0129] Step 1: Prepare a ferrophosphorus solution using ferric oxide, sodium dihydrogen phosphate and nitric acid.

[0130] The molar ratio of iron element to phosphorus element in the ferrophosphorus solution is 0.9:1, the iron ion concentration is 0.7 mol / L, and the pH value of the ferrophosphorus solution is 0.5.

[0131] Step 2: Prepare a 2 mol / L sodium hydroxide solution.

[0132] Step 3: First, add the ferrophosphorus solution prepared in step 1 to the reactor, then add the sodium hydroxide solution prepared in step 2, mix and stir evenly to make the pH value of the mixed solution 2, and the mixing time is 20 minutes. Then, the mixed solution is preheated to 46°C through a feed pipe with a jacket structure and then enters the tubular reactor for reaction, and the reaction temperature is controlled to 80°C, the reaction time is controlled to 60 minutes, and the stirring rate is 110r / min.

[0133] Step 4: The method of discharging and cooling is adopted. After the reaction liquid leaves the reactor, it quickly enters the quenching tank, and cold water is added to quickly reduce the temperature of the liquid to 45°C. The cooling time is 15 minutes. The cold water is low-temperature pure water.

[0134] Step 5: The cooled liquid in the quench tank is washed by a filter press, and the washing water temperature is controlled to be 40°C. After washing, the obtained filter cake is dried at 100°C for 150 minutes to obtain a dihydrate ferric phosphate product with excellent fluidity.

[0135] Step 6: calcine the dihydrate ferric phosphate product obtained in step 5 at 500° C. for 3 h to obtain an anhydrous ferric phosphate product with excellent fluidity.

[0136] Example 5

[0137] This embodiment provides an anhydrous ferric phosphate, which is prepared by the following method:

[0138] Step 1: Prepare a ferrophosphorus solution using iron oxide, phosphoric acid and nitric acid.

[0139] The molar ratio of iron element to phosphorus element in the ferrophosphorus solution is 1.3:1, the iron ion concentration is 1.5 mol / L, and the pH value of the ferrophosphorus solution is 0.8.

[0140] Step 2: Prepare a 3 mol / L sodium hydroxide solution.

[0141] Step 3: First, add the ferrophosphorus solution prepared in step 1 to the reactor, then add the sodium hydroxide solution prepared in step 2, mix and stir evenly to make the pH value of the mixed solution 3, and the mixing time is 25 minutes. Then, the mixed solution is preheated to 47°C through a feed pipe with a jacket structure and then enters the tubular reactor for reaction, and the reaction temperature is controlled to 90°C, the reaction time is controlled to 20 minutes, and the stirring rate is 120r / min.

[0142] Step 4: The method of discharging and cooling is adopted. After the reaction liquid leaves the reactor, it quickly enters the quenching tank, and cold water is added to quickly reduce the temperature of the liquid to 40°C. The cooling time is 10 minutes. The cold water is the mother liquor washing water after washing in the preparation process of the previous batch of anhydrous ferric phosphate.

[0143] Step 5: The cooled liquid in the quench tank is washed by a filter press, and the washing water temperature is controlled to be 50° C. After washing, the obtained filter cake is dried at 150° C. for 30 minutes to obtain a dihydrate ferric phosphate product with excellent fluidity.

[0144] Step 6: calcine the dihydrate ferric phosphate product obtained in step 5 at 600° C. for 3.5 h to obtain an anhydrous ferric phosphate product with excellent fluidity.

[0145] Example 6

[0146] This embodiment provides an anhydrous ferric phosphate, which is prepared by the following method:

[0147] Step 1: Prepare a ferrophosphorus solution using iron oxide, phosphoric acid and nitric acid.

[0148] The molar ratio of iron element to phosphorus element in the ferrophosphorus solution is 1.0:1, the iron ion concentration is 0.8 mol / L, and the pH value of the ferrophosphorus solution is 0.7.

[0149] Step 2: Prepare a sodium hydroxide solution with a concentration of 1.1 mol / L.

[0150] Step 3: First, add the ferrophosphorus solution prepared in step 1 to the reactor, then add the sodium hydroxide solution prepared in step 2, mix and stir evenly to make the pH value of the mixed solution 2.2, and the mixing time is 20 minutes. Then, the mixed solution is preheated to 45°C through a feed pipe with a jacket structure and then enters the tubular reactor for reaction, and the reaction temperature is controlled to 85°C, the reaction time is controlled to 30 minutes, and the stirring rate is 100r / min.

[0151] Step 4: The method of discharging and cooling is adopted. After the reaction liquid leaves the reactor, it quickly enters the quenching tank, and cold water is added to quickly reduce the temperature of the liquid to 45°C (cooling time is 10 minutes). The cold water is low-temperature pure water.

[0152] Step 5: The cooled liquid in the quench tank is washed by a filter press, and the washing water temperature is controlled to be 35° C. After washing, the obtained filter cake is dried at 120° C. for 100 minutes to obtain a dihydrate ferric phosphate product with excellent fluidity.

[0153] Step 6: calcine the dihydrate ferric phosphate product obtained in step 5 at 550° C. for 2.5 h to obtain an anhydrous ferric phosphate product with excellent fluidity.

[0154] That is, the difference between this embodiment and embodiment 1 is that low-temperature pure water is used instead of mother liquor washing water as the cooling liquid in the rapid cooling process.

[0155] Comparative Example 1

[0156] This comparative example provides an anhydrous ferric phosphate, which is prepared by the following method:

[0157] Step 1: Prepare a feed solution using ferrous sulfate, pure water and phosphoric acid.

[0158] The molar ratio of iron to phosphorus in the above-mentioned liquid is 1:1, and an excess of 20wt% hydrogen peroxide is added to oxidize it and then added to the reactor to make the iron concentration of the liquid 0.6mol / L;

[0159] Step 2: Add 1 mol / L diammonium phosphate solution into the reactor and adjust the pH of the solution to 3.5;

[0160] Step 3: Heat the reactor to 90°C and keep it warm for 1 hour;

[0161] Step 4: After natural cooling, the solid and liquid are separated, and the precipitate is washed with pure water to obtain a filter cake;

[0162] Step 5: drying the filter cake at 105° C. for 2 h, and crushing it to obtain ferric phosphate dihydrate product;

[0163] Step 6: After calcining at 550°C in a muffle furnace for 2 h, the product iron phosphate is obtained.

[0164] Comparative Example 2

[0165] This comparative example provides an anhydrous ferric phosphate, which is prepared by the following method:

[0166] Step 1: Prepare a feed solution using ferric chloride, pure water and phosphoric acid.

[0167] The molar ratio of iron to phosphorus in the above-mentioned liquid is 1:1. After adding an excess of 20wt% hydrogen peroxide for oxidation, the iron concentration of the liquid is 0.8mol / L.

[0168] Step 2: Add 1 mol / L diammonium phosphate solution to the above-mentioned feed solution to adjust the solution pH to 3.5;

[0169] Step 3: Add into a tubular reactor and react at 95°C;

[0170] Step 4: After natural cooling, the solid and liquid are separated, and the precipitate is washed with pure water to obtain a filter cake;

[0171] Step 5: drying the filter cake at 105° C. for 2 h, and crushing it to obtain ferric phosphate dihydrate product;

[0172] Step 6: After calcining at 550°C in a muffle furnace for 2 h, the product iron phosphate is obtained.

[0173] Comparative Example 3

[0174] This comparative example provides an anhydrous ferric phosphate, which is prepared by the following method:

[0175] Step 1: prepare a feed solution using iron oxide, pure water and phosphoric acid.

[0176] The molar ratio of iron to phosphorus in the above-mentioned liquid is 1:1. After adding an excess of 20wt% hydrogen peroxide for oxidation, the iron concentration of the liquid is 0.7mol / L.

[0177] Step 2: Add 1 mol / L diammonium phosphate solution to the above-mentioned feed solution to adjust the solution pH to 3.2;

[0178] Step 3: Add to the tubular reactor, control the reaction temperature to evenly rise to 95°C for reaction, and continue the reaction for 1 hour after the feed liquid reaches 95°C;

[0179] Step 4: After the reaction is completed, cold water is added to the quenching tank to quickly cool to 45°C, and then solid-liquid separation is performed, and the precipitate is washed with pure water to obtain a filter cake;

[0180] Step 5: drying the filter cake at 105° C. for 2 h, and crushing it to obtain ferric phosphate dihydrate product;

[0181] Step 6: After calcining at 550°C in a muffle furnace for 2 h, the product iron phosphate is obtained.

[0182] Comparative Example 4

[0183] This comparative example provides an anhydrous ferric phosphate, which is prepared by the following method:

[0184] Step 1: Prepare a ferrophosphorus solution using ferric chloride, phosphoric acid and nitric acid.

[0185] The molar ratio of iron element to phosphorus element in the ferrophosphorus solution is 1.0:1, the iron ion concentration is 0.9 mol / L, and the pH value of the ferrophosphorus solution is less than 1.

[0186] Step 2: Prepare a sodium hydroxide solution with a concentration of 1.0 mol / L.

[0187] Step 3: First, add the ferrophosphorus solution prepared in step 1 to the reactor, then add the sodium hydroxide solution prepared in step 2, mix and stir evenly to make the pH value of the mixed solution 2.7, and the mixing time is 10 minutes. Then, the mixed solution is preheated to 42°C through a feed pipe with a jacket structure and then enters the tubular reactor for reaction, and the reaction temperature is controlled to be 100°C, the reaction time is controlled to be 20 minutes, and the stirring rate is 120r / min.

[0188] Step 4: The method of discharging and cooling is adopted. After the reaction liquid leaves the reactor, it quickly enters the quenching tank, and cold water is added to quickly reduce the temperature of the liquid to 41°C (cooling time is 12 minutes). The cold water is the mother liquor washing water after washing in the preparation process of the previous batch of anhydrous ferric phosphate.

[0189] Step 5: The cooled liquid in the quench tank is washed by a filter press, and the washing water temperature is controlled to be 40°C. After washing, the obtained filter cake is dried at 120°C for 100 minutes to obtain a dihydrate ferric phosphate product with excellent fluidity.

[0190] Step 6: calcine the dihydrate ferric phosphate product obtained in step 5 at 550° C. for 2.5 h to obtain an anhydrous ferric phosphate product with excellent fluidity.

[0191] That is, the difference between this comparative example and Example 3 is that the reaction temperature of the mixed solution of the ferrophosphorus solution and the alkaline solution in the tubular reactor is 100°C.

[0192] Comparative Example 5

[0193] Step 1: Prepare a ferrophosphorus solution using ferric chloride, phosphoric acid and nitric acid.

[0194] The molar ratio of iron element to phosphorus element in the ferrophosphorus solution is 1.0:1, the iron ion concentration is 0.9 mol / L, and the pH value of the ferrophosphorus solution is less than 1.

[0195] Step 2: Prepare a sodium hydroxide solution with a concentration of 1.0 mol / L.

[0196] Step 3: First, add the ferrophosphorus solution prepared in step 1 to the reactor, then add the sodium hydroxide solution prepared in step 2, mix and stir evenly to make the pH value of the mixed solution 2.7, and the mixing time is 10 minutes. Then, the mixed solution is preheated to 42°C through a feed pipe with a jacket structure and then enters the tubular reactor for reaction, and the reaction temperature is controlled to 85°C, the reaction time is controlled to 80 minutes, and the stirring rate is 120r / min.

[0197] Step 4: The method of discharging and cooling is adopted. After the reaction liquid leaves the reactor, it quickly enters the quenching tank, and cold water is added to quickly reduce the temperature of the liquid to 41°C (cooling time is 12 minutes). The cold water is the mother liquor washing water after washing in the preparation process of the previous batch of anhydrous ferric phosphate.

[0198] Step 5: The cooled liquid in the quench tank is washed by a filter press, and the washing water temperature is controlled to be 40°C. After washing, the obtained filter cake is dried at 120°C for 100 minutes to obtain a dihydrate ferric phosphate product with excellent fluidity.

[0199] Step 6: calcine the dihydrate ferric phosphate product obtained in step 5 at 550° C. for 2.5 h to obtain an anhydrous ferric phosphate product with excellent fluidity.

[0200] That is, the difference between this comparative example and Example 3 is that the reaction time of the mixed solution of the ferrophosphorus solution and the alkaline solution in the tubular reactor is 80 minutes.

[0201] Comparative Example 6

[0202] This comparative example provides an anhydrous ferric phosphate, which is prepared by the following method:

[0203] Step 1: Prepare a ferrophosphorus solution using ferric chloride, phosphoric acid and nitric acid.

[0204] The molar ratio of iron element to phosphorus element in the ferrophosphorus solution is 1.0:1, the iron ion concentration is 0.9 mol / L, and the pH value of the ferrophosphorus solution is less than 1.

[0205] Step 2: Prepare a sodium hydroxide solution with a concentration of 1.0 mol / L.

[0206] Step 3: First, add the ferrophosphorus solution prepared in step 1 to the reactor, then add the sodium hydroxide solution prepared in step 2, mix and stir evenly to make the pH value of the mixed solution 2.7, and the mixing time is 10 minutes. Then, the mixed solution is preheated to 42°C through a feed pipe with a jacket structure and then enters the tubular reactor for reaction, and the reaction temperature is controlled to 85°C, the reaction time is controlled to 20 minutes, and the stirring rate is 120r / min.

[0207] Step 4: The method of discharging and cooling is adopted. After the reaction liquid leaves the reactor, it enters the cooling pool and pure water is added to reduce the temperature of the liquid to 41°C in 35 minutes.

[0208] Step 5: The cooled liquid in the quench tank is washed by a filter press, and the washing water temperature is controlled to be 40°C. After washing, the obtained filter cake is dried at 120°C for 100 minutes to obtain a dihydrate ferric phosphate product with excellent fluidity.

[0209] Step 6: calcine the dihydrate ferric phosphate product obtained in step 5 at 550° C. for 2.5 h to obtain an anhydrous ferric phosphate product with excellent fluidity.

[0210] That is, the difference between this comparative example and Example 3 is that the cooling time corresponding to the cooling process is 30 minutes.

[0211] Comparative Example 7

[0212] This comparative example provides an anhydrous ferric phosphate, which is prepared by the following method:

[0213] Step 1: Prepare a ferrophosphorus solution using ferric chloride, phosphoric acid and nitric acid.

[0214] The molar ratio of iron element to phosphorus element in the ferrophosphorus solution is 1.0:1, the iron ion concentration is 0.9 mol / L, and the pH value of the ferrophosphorus solution is less than 1.

[0215] Step 2: Prepare a sodium hydroxide solution with a concentration of 1.0 mol / L.

[0216] Step 3: First, add the ferrophosphorus solution prepared in step 1 to the reactor, then add the sodium hydroxide solution prepared in step 2, mix and stir evenly to make the pH value of the mixed solution 2.7, and the mixing time is 10 minutes. Then, the mixed solution is preheated to 42°C through a feed pipe with a jacket structure and then enters the tubular reactor for reaction, and the reaction temperature is controlled to 85°C, the reaction time is controlled to 20 minutes, and the stirring rate is 120r / min.

[0217] Step 4: The method of discharging and cooling is adopted. After the reaction liquid leaves the reactor, it quickly enters the cooling pool, and pure water is added to quickly reduce the temperature of the liquid to 70°C within 12 minutes.

[0218] Step 5: The cooled liquid in the quench tank is washed by a filter press, and the washing water temperature is controlled to be 40°C. After washing, the obtained filter cake is dried at 120°C for 100 minutes to obtain a dihydrate ferric phosphate product with excellent fluidity.

[0219] Step 6: calcine the dihydrate ferric phosphate product obtained in step 5 at 550° C. for 2.5 h to obtain an anhydrous ferric phosphate product with excellent fluidity.

[0220] That is, the difference between this comparative example and Example 3 is that the reaction liquid is cooled to 70°C.

[0221] Comparative Example 8

[0222] This comparative example provides an anhydrous ferric phosphate, which is prepared by the following method:

[0223] Step 1: Prepare a ferrophosphorus solution using ferric chloride, phosphoric acid and nitric acid.

[0224] The molar ratio of iron element to phosphorus element in the ferrophosphorus solution is 1.0:1, the iron ion concentration is 0.9 mol / L, and the pH value of the ferrophosphorus solution is less than 1.

[0225] Step 2: Prepare a sodium hydroxide solution with a concentration of 1.0 mol / L.

[0226] Step 3: First add the ferrophosphorus solution prepared in step 1 to the reactor, then add the sodium hydroxide solution prepared in step 2, mix and stir evenly until the pH value of the mixed solution is 2.7, and the mixing time is 10 minutes. Then heat the reactor, control the reaction temperature to 85°C, control the reaction time to 50 minutes, and the stirring rate to 120r / min.

[0227] Step 4: The method of discharging and cooling is adopted. After the reaction liquid leaves the reactor, it quickly enters the quenching tank, and cold water is added to quickly reduce the temperature of the liquid to 41°C (cooling time is 12 minutes). The cold water is the mother liquor washing water after washing in the preparation process of the previous batch of anhydrous ferric phosphate.

[0228] Step 5: The cooled liquid in the quench tank is washed by a filter press, and the washing water temperature is controlled to be 40°C. After washing, the obtained filter cake is dried at 120°C for 100 minutes to obtain a dihydrate ferric phosphate product with excellent fluidity.

[0229] Step 6: calcine the dihydrate ferric phosphate product obtained in step 5 at 550° C. for 2.5 h to obtain an anhydrous ferric phosphate product with excellent fluidity.

[0230] That is, the difference between this comparative example and Example 3 is that the reaction is directly carried out in a mixing tank without involving a tubular reactor.

[0231] Test example

[0232] ①. The morphology of the anhydrous ferric phosphate obtained in Example 3 and Comparative Example 1 was observed. The scanning electron microscope images of the two were as follows: Figure 1 and Figure 2 shown.

[0233] Depend on Figure 1 and Figure 2 It can be seen that the anhydrous ferric phosphate particles obtained in Example 3 are uniform in size and have a complete and uniform morphology; the anhydrous ferric phosphate obtained in Comparative Example 1 has more agglomerates and poor consistency in particle size.

[0234] ②. According to the molar ratio of each element in the chemical formula of Li:Fe:glucose = 1:1:1, the iron phosphate obtained in Example 1-5 and Comparative Example 1-8 was added to deionized water with glucose and lithium carbonate respectively, and fully mixed and stirred in a mixing tank. After spray drying, the mixture was calcined at 650°C in an inert atmosphere for 8 hours and crushed to obtain lithium iron phosphate positive electrode material.

[0235] Using the lithium iron phosphate material obtained in the embodiment and the comparative example, acetylene black as a conductive agent, PVDF as a binder, the active material, the conductive agent and the binder are weighed in a ratio of 92:4:4, and a certain amount of organic solvent NMP is added, and the mixture is coated on an aluminum foil after stirring to form a positive electrode sheet. A metal lithium sheet is used as the negative electrode, and a button battery is made in a glove box filled with argon gas and the electrochemical properties of the button battery are tested.

[0236] The electrochemical performance test results are shown in Table 1.

[0237] Table 1 Electrochemical performance results

[0238] 0.1C discharge capacity (mAh / g) 1C discharge capacity (mAh / g) Example 1 165.3 149.4 Example 2 164.6 149.3 Example 3 166.4 149.6 Example 4 166.2 149.4 Experimental Example 5 165.4 148.9 Experimental Example 6 164.3 148.2 Comparative Example 1 150.3 140.2 Comparative Example 2 152.1 142.1 Comparative Example 3 150.4 140.6 Comparative Example 4 149.6 139.2 Comparative Example 5 145.7 136.3 Comparative Example 6 151.3 140.1 Comparative Example 7 147.2 137.3 Comparative Example 8 150.2 141.1

[0239] It can be seen from Table 1 that the batteries corresponding to Examples 1-6 are higher than the batteries corresponding to Comparative Examples 1-8 in terms of both 0.1C discharge capacity and 1C discharge capacity, indicating that the anhydrous iron phosphate provided in the embodiments of the present application is more conducive to the preparation of lithium iron phosphate positive electrode materials with better electrochemical properties.

[0240] By comparing Example 1 with Example 6, it can be concluded that using the mother liquor washing water after the above batch solid-liquid separation as the coolant during the rapid cooling process can be more conducive to preparing the lithium iron phosphate positive electrode material with better electrochemical performance than using low-temperature pure water as the coolant.

[0241] ③. The repose angles of the products obtained from Examples 1-3 and Comparative Examples 1-3 were tested by injection method, and the results are as follows: the repose angles of the products obtained from Examples 1-3 were 28°, 28.5°, and 27.5°, respectively; the repose angles of the products obtained from Comparative Examples 1-3 were 34°, 36°, and 35°, respectively, and the morphology changed greatly. Its poor processability is also one of the reasons that affect its electrical performance. This shows that the product provided in the embodiment of the present application has good fluidity, is very beneficial to industrial processing and use, and is also beneficial to the electrical performance of its product precursor.

[0242] In summary, the preparation method of anhydrous iron phosphate provided in the present application is simple and easy to operate, and can prepare anhydrous iron phosphate with a small repose angle and uniform size. The anhydrous iron phosphate has excellent fluidity, processing performance and compaction density, which is beneficial to improving the processing performance and electrochemical properties of the subsequently prepared lithium iron phosphate positive electrode material.

[0243] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing anhydrous ferric phosphate, characterized in that: The following steps are involved: reacting a mixture of the ferrophosphorus solution and the alkaline solution at 80-90° C. for 20-60 minutes to obtain a reaction solution; The reaction is carried out in a tubular reactor; The reaction solution is cooled to below 50°C within 20 minutes, and then the solid obtained by the reaction is roasted; the cooling is carried out in a quenching device; The cooling is carried out by discharging and cooling at the same time; the cooling liquid used for cooling is low-temperature pure water or mother liquor washing water left after washing in the preparation process of other batches of anhydrous ferric phosphate; The preparation of the ferrophosphorus solution comprises: mixing an iron source, a phosphorus source and a strong inorganic acid.

2. The preparation method according to claim 1, characterized in that: The ferrophosphorus solution and the alkaline solution react at a stirring speed of 100-200 r / min.

3. The preparation method according to claim 1, characterized in that: The pH value of the mixed solution of the ferrophosphorus solution and the alkaline solution is 2-3.

4. The preparation method according to claim 1, characterized in that: The inlet of the tubular reactor is connected with a feeding pipe with a jacket structure.

5. The preparation method according to claim 1, characterized in that: The reaction liquid is preheated to 40-50°C through a feed pipe and then enters the tubular reactor for reaction.

6. The preparation method according to claim 1, characterized in that: The quenching device comprises a quenching tank or a quenching tank.

7. The preparation method according to claim 1, characterized in that: In the ferrophosphorus solution, the molar ratio of iron element to phosphorus element is 0.9-1.3:

1.

8. The preparation method according to claim 1, characterized in that: In the ferrophosphorus solution, the concentration of iron ions is 0.7-1.5 mol / L.

9. The preparation method according to claim 1, characterized in that: The pH value of the ferrophosphorus solution is less than 1.

10. The preparation method according to claim 1, characterized in that: The iron source includes at least one of iron oxide, iron chloride and iron nitrate.

11. The preparation method according to claim 1, characterized in that: The phosphorus source includes at least one of phosphoric acid and dihydrogen phosphate.

12. The preparation method according to claim 1, characterized in that: The strong inorganic acid includes at least one of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid.

13. The preparation method according to claim 9, characterized in that: The pH value of the ferrophosphorus solution is adjusted by hydrochloric acid and / or nitric acid.

14. The preparation method according to claim 1, characterized in that: The alkaline solution includes at least one of a sodium hydroxide solution and a potassium hydroxide solution.

15. The preparation method according to claim 14, characterized in that: The alkaline solution is a sodium hydroxide solution.

16. The preparation method according to claim 14, characterized in that: The concentration of the sodium hydroxide solution is 1-3 mol / L.

17. The preparation method according to claim 1, characterized in that: Before calcination, the product obtained by the reaction is washed, and the washed solid is dried.

18. The preparation method according to claim 17, characterized in that: The temperature of the washing liquid used for washing does not exceed 60°C; the drying temperature is 100-150°C, and the drying time is 30-120 minutes.

19. The preparation method according to claim 17, characterized in that: The temperature of the washing liquid used for washing does not exceed 50°C.

20. The preparation method according to claim 1, characterized in that: The calcination temperature is 500-600°C and the calcination time does not exceed 3.5h.

21. Anhydrous ferric phosphate, characterized in that: Prepared by the preparation method according to any one of claims 1 to 20.

22. The anhydrous ferric phosphate according to claim 21, characterized in that The repose angle of the anhydrous ferric phosphate is no more than 30°.

23. A lithium iron phosphate positive electrode material, characterized in that: The precursor of the lithium iron phosphate positive electrode material is the anhydrous iron phosphate as described in claim 21 or 22.

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