A method for preparing lithium iron phosphate

Abstract

The present application provides a method for preparing lithium iron phosphate, which belongs to the field of nano-scale lithium iron phosphate material manufacturing. The method for preparing lithium iron phosphate includes the following steps: dissolving a divalent iron source, a phosphorus source and a lithium source in water and mixing them to obtain a mixed solution; adjusting the pH of the mixed solution with a pH adjuster until the pH of the mixed solution is 8.5 to 10, and then performing solid-liquid separation on the mixed solution after adjusting the pH to obtain a precursor precipitate; and adding a carbon source to the solution containing the precursor precipitate and mixing, and then drying and roasting in sequence to obtain lithium iron phosphate. The method for preparing lithium iron phosphate can reduce the preparation cost of lithium iron phosphate prepared by coprecipitation to a certain extent.

Description

Technical Field

[0001] The present application relates to the field of nano-scale lithium iron phosphate material manufacturing, and specifically, to a method for preparing lithium iron phosphate. Background Art

[0002] In the prior art, the commonly used preparation methods for nano-scale lithium iron phosphate include solid phase method and liquid phase method. Compared with the solid phase method, the liquid phase method has the advantages of being able to achieve atomic-level mixing of various raw materials, good morphological consistency of the finished lithium iron phosphate, and good particle dispersion, and is more suitable for the preparation of nano-scale lithium iron phosphate. Among them, the coprecipitation method in the liquid phase method does not require the use of a high-temperature and high-pressure autoclave, that is, the calcined precursor of lithium iron phosphate can be prepared at room temperature and pressure, which is more suitable for industrial applications. However, the existing coprecipitation method has the problem of high preparation cost in the process of preparing nano-scale lithium iron phosphate, which limits the application of the coprecipitation method. Summary of the invention

[0003] The purpose of the present application is to provide a method for preparing lithium iron phosphate, which can reduce the preparation cost of lithium iron phosphate prepared by co-precipitation method to a certain extent.

[0004] The embodiment of the present application is implemented as follows:

[0005] The present invention provides a method for preparing lithium iron phosphate, comprising the following steps:

[0006] A divalent iron source, a phosphorus source and a lithium source are dissolved in water and mixed to obtain a mixed solution; the pH of the mixed solution is adjusted by a pH adjuster until the pH of the mixed solution is 8.5-10, and then the mixed solution after the pH adjustment is solid-liquid separated to obtain a precursor precipitate; and a carbon source is added to the solution containing the precursor precipitate and mixed, and then dried and calcined in sequence to obtain lithium iron phosphate.

[0007] In the above technical scheme, after obtaining the mixed solution, a pH adjustment step is added, and the pH of the mixed solution is limited to a specific range. When the amount of lithium source used is equivalent to that of the lithium source used in the solid phase method, the target lithium iron phosphate with a molar ratio of lithium, iron and phosphorus close to 1:1:1 can also be prepared; wherein, the pH of the mixed solution is limited to a specific range because: on the one hand, it can effectively avoid the pH being too low, thereby effectively avoiding the mass proportion of lithium phosphate in the mixed system being too low, that is, effectively avoiding the mass proportion of ferrous phosphate in the mixture being too high (too high a mass proportion of ferrous phosphate will result in more pyrophosphate iron miscellaneous items in the finished lithium iron phosphate, resulting in a large deviation between the molar ratio of lithium, iron and phosphorus in the product and 1:1:1), so as to prepare the target phosphate with a molar ratio of lithium, iron and phosphorus close to 1:1:1 Iron lithium; on the other hand, it can effectively avoid pH being too high (too high pH will cause a large amount of ferrous phosphate to be converted into ferrous hydroxide, which will lead to phosphorus deficiency in the mixed system, and then cause the finished lithium iron phosphate to contain lithium phosphate and ferrous oxide miscellaneous items, resulting in a large deviation between the molar ratio of lithium, iron and phosphorus in the product and 1:1:1), so as to prepare the target lithium iron phosphate with a molar ratio of lithium, iron and phosphorus close to 1:1:1; therefore, compared with the conventional co-precipitation method (there is no pH adjustment step in the corresponding stage, and since various miscellaneous items are easily formed, it is usually necessary to use three times the amount of lithium source in the solid phase method to prepare the target lithium iron phosphate), the preparation method provided in the embodiment of the present application only needs to use about one-third of the lithium source amount of the conventional co-precipitation method, that is, it can reduce the amount of lithium source, thereby reducing the cost of preparing lithium iron phosphate by co-precipitation.

[0008] In some optional embodiments, in the step of adjusting the pH of the mixed solution with a pH adjuster, the pH of the mixed solution is adjusted to 8.8 to 9.8.

[0009] In the above technical scheme, the pH of the mixed solution is limited to a more preferred specific range, so that the molar ratio of ferrous phosphate and lithium phosphate in the mixed system can be closer to 1:1 (the closer the ratio of the two is to 1:1, the less likely it is to produce impurities), that is, the molar ratio of lithium, iron and phosphorus in the prepared precursor precipitate is closer to 1:1:1, and then the target lithium iron phosphate is prepared, in which the molar ratio of lithium, iron and phosphorus is closer to 1:1:1 and the purity is higher (that is, the finished lithium iron phosphate contains less impurities such as iron pyrophosphate, lithium phosphate and ferrous oxide).

[0010] In some optional embodiments, in the mixed solution, the molar ratio of iron element, phosphorus element and lithium element is 1:(1-1.1):(1-1.5).

[0011] In the above technical scheme, the molar ratio of the three elements in the mixed solution is limited to a specific range, wherein the phosphorus element and the lithium element are slightly excess over the iron element, so that the target lithium iron phosphate with a molar ratio of lithium, iron and phosphorus close to 1:1:1 and appropriate purity can be prepared more easily.

[0012] In some optional embodiments, the molar concentration of iron in the mixed solution is 0.8-1.2 mol / L.

[0013] In the above technical scheme, the molar concentration of the iron element in the mixed solution is limited to a specific range, so that the mixed solution can have an appropriate concentration of iron element. On the one hand, it can effectively reduce the risk of ferrous phosphate precipitating from the mixed solution (ferrous phosphate is easily precipitated when the concentration is too high), so that the molar ratio of ferrous phosphate to lithium phosphate in the mixed system is closer to 1:1. On the other hand, under the condition of a certain volume of the reaction container (too low concentration will result in a lower yield), the preparation of the precursor precipitate can have an appropriate yield.

[0014] In some optional embodiments, at least one of the following conditions is met:

[0015] A divalent iron source includes at least one of ferrous sulfate, ferrous nitrate, ferrous chloride and ferrous citrate;

[0016] B phosphorus source comprises at least one of phosphoric acid, sodium dihydrogen phosphate and ammonium dihydrogen phosphate;

[0017] The C lithium source includes at least one of lithium carbonate, lithium nitrate, lithium hydroxide, lithium acetate and lithium citrate;

[0018] D The pH adjuster includes at least one of sodium hydroxide, potassium hydroxide and ammonia water.

[0019] In the above technical scheme, the divalent iron source, phosphorus source, lithium source and pH adjuster are applicable to more systems and can provide more feasible implementation plans, thereby facilitating the promotion and application of the preparation method provided in the examples of the present application.

[0020] In some alternative embodiments, the carbon source comprises an organic carbon source;

[0021] Optionally, the organic carbon source comprises at least one of glucose, sucrose, citric acid, starch and PEG.

[0022] In the above technical solution, an organic carbon source is used. Compared with an inorganic carbon source, the organic carbon source will decompose and gasify during the heating process, thereby achieving a more uniform coating effect, thereby making the finished lithium iron phosphate have better conductivity.

[0023] Furthermore, the technical solution of the present application is applicable to the above-mentioned various organic carbon source systems, and can provide more feasible implementation plans, thereby facilitating the promotion and application of the preparation method provided in the examples of the present application.

[0024] In some optional embodiments, in the step of dissolving the divalent iron source, the phosphorus source and the lithium source in water and mixing them to obtain a mixed solution, the step includes first dissolving the divalent iron source and the phosphorus source in water and mixing them to obtain a mixed solution intermediate, and then adding the lithium source to the mixed solution intermediate and mixing them to obtain a mixed solution.

[0025] In the above technical solution, the step-by-step dissolution method is adopted. Compared with the one-step method to dissolve and mix the three, the former can make the iron and lithium elements in the mixed solution mix more evenly and have better dispersion.

[0026] In some optional embodiments, the step of first dissolving the divalent iron source and the phosphorus source in water and mixing them to obtain a mixed solution intermediate further includes adding an antioxidant to the water;

[0027] Optionally, the antioxidant comprises ascorbic acid.

[0028] In the above technical solution, adding an antioxidant during the process of dissolving the divalent iron source can effectively reduce the risk of divalent iron being oxidized to trivalent iron, thereby effectively reducing the risk of introducing impurities into the mixed system.

[0029] Furthermore, using ascorbic acid as an antioxidant can effectively reduce the risk of introducing impurities compared to using other antioxidants.

[0030] In some optional embodiments, in the mixed solution intermediate, the molar ratio of iron element to antioxidant is 1:(0.005-0.015).

[0031] In the above technical solution, the molar ratio of the iron element and the antioxidant in the mixed solution intermediate is limited to a specific range, so that the two have a suitable dosage ratio, thereby achieving a better antioxidant effect.

[0032] In some optional embodiments, in the step of calcining, the treatment temperature is 650-780° C., and the treatment time is 4-20 hours.

[0033] In the above technical solution, the treatment temperature and time in the roasting process are limited to specific ranges, respectively, so that the roasting process can be carried out under suitable conditions, thereby preparing finished lithium iron phosphate with good quality and electrical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application 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 paying creative work.

[0035] Figure 1 A process flow chart of a method for preparing lithium iron phosphate provided in an embodiment of the present application. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0037] It should be noted that “and / or” in this application, such as “Feature 1 and / or Feature 2”, refers to the three situations of “Feature 1” alone, “Feature 2” alone, or “Feature 1” plus “Feature 2”.

[0038] In addition, in the description of the present application, unless otherwise specified, the meaning of "multiple" in "one or more" refers to two or more; the range of "value a ~ value b" includes the two end values ​​"a" and "b", and the "unit" in "value a ~ value b + unit of measurement" represents the "unit of measurement" of both "value a" and "value b".

[0039] In the prior art, in the process of preparing nano-scale lithium iron phosphate by co-precipitation, the corresponding precursor precipitate is a mixture of ferrous phosphate and lithium phosphate. In order to finally prepare the target lithium iron phosphate with a molar ratio of lithium, iron and phosphorus close to 1:1:1 and suitable purity, it is necessary to ensure that the molar ratio of ferrous phosphate and lithium phosphate is as close to 1:1 as possible. At present, three times the amount of lithium source used in the solid phase method is usually used to participate in the reaction to achieve this. In addition, the commonly used lithium source in the co-precipitation method is lithium hydroxide, which is also relatively expensive, resulting in the problem of high preparation cost of lithium iron phosphate using the existing co-precipitation method.

[0040] Based on this, the inventors have discovered that by optimizing the existing co-precipitation preparation process, that is, adding a pH adjustment step after obtaining a mixed solution of lithium, iron and phosphorus and adjusting the pH of the mixed solution to a specific range, under the condition that the amount of lithium source used is equivalent to that in the solid phase method, the target lithium iron phosphate with a molar ratio of lithium, iron and phosphorus close to 1:1:1 and appropriate purity can be prepared.

[0041] The following is a detailed description of a method for preparing lithium iron phosphate according to an embodiment of the present application.

[0042] The present invention provides a method for preparing lithium iron phosphate, comprising the following steps:

[0043] A divalent iron source, a phosphorus source and a lithium source are dissolved in water and mixed to obtain a mixed solution; the pH of the mixed solution is adjusted by a pH adjuster until the pH of the mixed solution is 8.5-10, and then the mixed solution after the pH adjustment is solid-liquid separated to obtain a precursor precipitate; and a carbon source is added to the solution containing the precursor precipitate and mixed, and then dried and calcined in sequence to obtain lithium iron phosphate.

[0044] It should be noted that in this field, in order to meet application requirements, lithium iron phosphate generally refers to a high-quality product with a molar ratio of lithium, iron and phosphorus close to 1:1:1 and appropriate purity, rather than a low-quality product with a large difference in the molar ratio of the three and a lower purity.

[0045] It should be noted that, as is well known in the art, the iron in lithium iron phosphate refers to ferrous ions derived from a divalent iron source.

[0046] It should be noted that the method of "mixing" is not limited and can be set according to conventional selections in the art, for example, it can be stirring mixing or shaking mixing.

[0047] It should be noted that the method of "solid-liquid separation" is not limited and can be set according to conventional selections in the art, for example, it can be centrifugal separation or filtration separation.

[0048] It should be noted that in the art, "precursor solution" generally refers to an aqueous solution containing a precursor precipitate, and its specific solid-liquid volume ratio is not limited and can be set according to conventional selections in the art as long as it can dissolve the added precursor precipitate and carbon source.

[0049] In the present application, after obtaining the mixed solution, a pH adjustment step is added, and the pH of the mixed solution is limited to a specific range. When the amount of lithium source used is equivalent to that of the lithium source used in the solid phase method, the target lithium iron phosphate with a molar ratio of lithium, iron and phosphorus close to 1:1:1 can also be prepared; wherein the pH of the mixed solution is limited to a specific range because: on the one hand, it can effectively avoid the pH being too low, thereby effectively avoiding the mass proportion of lithium phosphate in the mixed system being too low, that is, effectively avoiding the mass proportion of ferrous phosphate in the mixture being too high (too high a mass proportion of ferrous phosphate will result in more pyrophosphate iron miscellaneous items in the finished lithium iron phosphate, resulting in a large deviation between the molar ratio of lithium, iron and phosphorus in the product and 1:1:1), so as to prepare the target iron phosphate with a molar ratio of lithium, iron and phosphorus close to 1:1:1 Lithium; on the other hand, it can effectively avoid pH being too high (too high pH will cause a large amount of ferrous phosphate to be converted into ferrous hydroxide, which will lead to phosphorus deficiency in the mixed system, and then cause the finished lithium iron phosphate to contain lithium phosphate and ferrous oxide miscellaneous items, resulting in a large deviation between the molar ratio of lithium, iron and phosphorus in the product and 1:1:1), so as to prepare the target lithium iron phosphate with a molar ratio of lithium, iron and phosphorus close to 1:1:1; therefore, compared with the conventional co-precipitation method (there is no pH adjustment step in the corresponding stage, and since various miscellaneous items are easily formed, it is usually necessary to use three times the amount of lithium source in the solid phase method to prepare the target lithium iron phosphate), the preparation method provided in the embodiment of the present application only needs to use about one-third of the lithium source amount of the conventional co-precipitation method, that is, it can reduce the amount of lithium source, thereby reducing the cost of preparing lithium iron phosphate by co-precipitation.

[0050] It is understandable that, considering the cleanliness and purity of the precursor precipitate, the precursor precipitate may be washed after being obtained and before the carbon source is added.

[0051] It should be noted that the specific cleaning process is not limited and can be set according to conventional selections in the art.

[0052] It is understandable that the criterion for determining whether the cleaning is complete is not limited and can be set according to conventional selection in the art. For example, taking ferrous sulfate as the ferrous iron source as an example, cleaning is performed until the S content in the filter cake is less than 2000 ppm.

[0053] It is understandable that the coating amount of the carbon source is related to the conductivity of the finished lithium iron phosphate. Taking the conductivity of the finished lithium iron phosphate into consideration, the usage ratio of the carbon source to the iron element can be adjusted.

[0054] As an example, in the step of adding the carbon source to the solution containing the precursor precipitate and mixing, the molar mass ratio of the carbon source and the iron element is (4-10):100, for example but not limited to the molar mass ratio of any one of 4:100, 6:100, 8:100 and 10:100 or a range between any two of them.

[0055] It should be noted that the method of "drying" is not limited and can be set according to conventional selections in the art, for example, it can be dried in an oven.

[0056] It is understandable that the criterion for determining the end of drying is not limited and can be set according to conventional selections in the art, such as drying until the moisture content of the precursor precipitate after carbon coating is less than 2%.

[0057] It is understandable that the external environment may interfere with the preparation process of lithium iron phosphate. Considering the quality of the prepared lithium iron phosphate, the preparation process can be adjusted.

[0058] As an example, the pH adjustment step, the washing step, the carbon coating step, the drying step and the calcining step are all performed under an inert atmosphere.

[0059] It should be noted that the type of inert atmosphere is not limited and can be set according to conventional selection in the art.

[0060] As an example, the inert atmosphere includes at least one of nitrogen and argon.

[0061] It can be understood that the closer the molar ratio of ferrous phosphate and lithium phosphate in the mixed system is to 1:1, the less likely it is to produce impurities during the preparation process. Considering the molar ratio of the three elements in the finished lithium iron phosphate and the product purity, the pH of the mixed solution can be further adjusted.

[0062] As an example, in the step of adjusting the pH of the mixed solution using a pH adjuster, the pH of the mixed solution is adjusted until it is 8.8-9.8, for example but not limited to any one of pH 8.8, 9.0, 9.2, 9.4, 9.6 and 9.8 or a range between any two of them.

[0063] In this embodiment, the pH of the mixed solution is limited to a more preferred specific range, so that the molar ratio of ferrous phosphate and lithium phosphate in the mixed system can be closer to 1:1 (the closer the ratio of the two is to 1:1, the less likely it is to produce impurities), that is, the molar ratio of lithium, iron and phosphorus in the prepared precursor precipitate is closer to 1:1:1, and the target lithium iron phosphate is prepared, wherein the molar ratio of lithium, iron and phosphorus is closer to 1:1:1 and the purity is higher (i.e., the finished lithium iron phosphate contains less impurities such as iron pyrophosphate, lithium phosphate and ferrous oxide).

[0064] It should be noted that the molar ratio of the three elements in the mixed solution is not limited and can be set according to conventional selection in the art.

[0065] As an example, in the mixed solution, the molar ratio of iron, phosphorus and lithium is 1:(1-1.1):(1-1.5), for example, but not limited to, the molar ratio is any one of 1:1:1, 1:1.1:1.1, 1:1.1:1.2, 1:1.1:1.3, 1:1.1:1.4 and 1:1.1:1.5 or a range between any two of them.

[0066] In this embodiment, the molar ratio of the three elements in the mixed solution is limited to a specific range, wherein the phosphorus element and the lithium element are slightly excessive compared to the iron element, so that the target lithium iron phosphate with a molar ratio of lithium, iron and phosphorus close to 1:1:1 and suitable purity can be more easily prepared.

[0067] It should be noted that the molar concentration of the iron element in the mixed solution is not limited and can be set according to conventional selection in the art.

[0068] As an example, in the mixed solution, the molar concentration of iron element is 0.8-1.2 mol / L, for example but not limited to any one of 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L and 1.2 mol / L or a range between any two of them.

[0069] In this embodiment, the molar concentration of the iron element in the mixed solution is limited to a specific range, so that the mixed solution can have an appropriate concentration of iron element. On the one hand, it can effectively reduce the risk of ferrous phosphate precipitating from the mixed solution (ferrous phosphate is easily precipitated when the concentration is too high), so that the molar ratio of ferrous phosphate to lithium phosphate in the mixed system is closer to 1:1. On the other hand, under the condition of a certain volume of the reaction container (too low concentration will result in a lower yield), the preparation of the precursor precipitate can have an appropriate yield.

[0070] It should be noted that the types of the ferrous iron source, phosphorus source, lithium source and pH adjuster are not limited and can be set according to conventional selection in the art.

[0071] As an example, at least one of the following conditions is met:

[0072] A divalent iron source includes at least one of ferrous sulfate, ferrous nitrate, ferrous chloride and ferrous citrate.

[0073] The B phosphorus source includes at least one of phosphoric acid, sodium dihydrogen phosphate and ammonium dihydrogen phosphate.

[0074] The C lithium source includes at least one of lithium carbonate, lithium nitrate, lithium hydroxide, lithium acetate and lithium citrate.

[0075] D The pH adjuster includes at least one of sodium hydroxide, potassium hydroxide and ammonia water.

[0076] In this embodiment, the divalent iron source, phosphorus source, lithium source and pH adjuster are all applicable to more systems and can provide more feasible implementation plans, thereby facilitating the promotion and application of the preparation method provided in the embodiments of the present application.

[0077] It should be noted that the type of carbon source is not limited and can be set according to routine selection in the art.

[0078] As an example, the carbon source includes an organic carbon source.

[0079] Optionally, the organic carbon source comprises at least one of glucose, sucrose, citric acid, starch and PEG.

[0080] In this embodiment, an organic carbon source is used. Compared with an inorganic carbon source, the organic carbon source will decompose and gasify during the heating process, thereby achieving a more uniform coating effect, thereby making the finished lithium iron phosphate have better conductivity.

[0081] Furthermore, the technical solution of the present application is applicable to the above-mentioned various organic carbon source systems, and can provide more feasible implementation plans, thereby facilitating the promotion and application of the preparation method provided in the examples of the present application.

[0082] It is understandable that the preparation process of the mixed solution may be adjusted in consideration of the mixing uniformity and dispersibility of the various elements in the mixed solution.

[0083] As an example, in the step of dissolving a divalent iron source, a phosphorus source and a lithium source in water and mixing them to obtain a mixed solution, the divalent iron source and the phosphorus source are first dissolved in water and mixed to obtain a mixed solution intermediate, and then the lithium source is added to the mixed solution intermediate and mixed to obtain a mixed solution.

[0084] In this embodiment, a step-by-step dissolution method is adopted. Compared with a one-step method for dissolving and mixing the three, the former can make the iron element and the lithium element in the mixed solution mix more evenly and have better dispersion.

[0085] It is understandable that divalent iron is easily oxidized to trivalent iron in the air. In order to reduce the risk of introducing impurities into the mixed system, the corresponding process can be adjusted.

[0086] As an example, in the step of first dissolving the divalent iron source and the phosphorus source in water and mixing them to obtain a mixed solution intermediate, an antioxidant is also added to the water.

[0087] Optionally, the antioxidant comprises ascorbic acid.

[0088] In this embodiment, adding an antioxidant during the process of dissolving the ferrous iron source can effectively reduce the risk of ferrous iron being oxidized to ferric iron, thereby effectively reducing the risk of introducing impurities into the mixed system.

[0089] Furthermore, using ascorbic acid as an antioxidant can effectively reduce the risk of introducing impurities compared to using other antioxidants.

[0090] It is understandable that the antioxidant effect is related to the dosage ratio of iron and antioxidants. In order to achieve a better antioxidant effect, the dosage ratio of the two can be adjusted.

[0091] As an example, in the mixed solution intermediate, the molar ratio of iron element and antioxidant is 1:(0.005-0.015), for example but not limited to the molar ratio of any one of 1:0.005, 1:0.008, 1:0.01, 1:0.012, 1:0.014 and 1:0.015 or a range between any two of them.

[0092] In this embodiment, the molar ratio of the iron element and the antioxidant in the mixed solution intermediate is limited to a specific range, so that the two have a suitable dosage ratio, thereby achieving a better antioxidant effect.

[0093] It should be noted that the treatment temperature and time during the calcination process are not limited and can be set according to conventional practices in the art.

[0094] As an example, in the roasting step, the processing temperature is 650-780°C, for example but not limited to the temperature of any one of 650°C, 680°C, 700°C, 720°C, 740°C, 760°C and 780°C or the range between any two of them; the processing time is 4-20h, for example but not limited to the time of any one of 4h, 8h, 10h, 12h, 14h, 16h, 18h and 20h or the range between any two of them.

[0095] In this embodiment, the treatment temperature and time during the calcination process are limited to specific ranges, respectively, so that the calcination process can be carried out under suitable conditions, thereby preparing a finished lithium iron phosphate with good quality and electrical properties.

[0096] It should be noted that, in the preparation process of lithium iron phosphate, any process or step not specifically described or limited is not limited and can be set according to conventional selection in the art.

[0097] As an example, after the step of preparing lithium iron phosphate, the step of crushing the lithium iron phosphate is also included.

[0098] It should be noted that the crushing method is not limited and can be set according to conventional selections in the art.

[0099] As an example, a gas crusher is used to crush lithium iron phosphate, and the crushing pressure is 0.3Mpa to 0.5Mpa.

[0100] In this embodiment, the gas crushing method can prepare lithium iron phosphate particles with good particle size uniformity, wherein the crushing pressure is limited to a specific range, and the prepared particle size can better meet the requirements of subsequent processes.

[0101] As an example, the process flow chart of the preparation method of lithium iron phosphate is shown as follows: Figure 1 shown.

[0102] It should be noted that the preparation method provided in the embodiment of the present application is not only applicable to the preparation of lithium iron phosphate, but also applicable to the preparation of lithium manganese iron phosphate and the preparation of doped lithium iron phosphate, wherein the type of doping element is not limited, for example, the doping element includes at least one of Ti, V, Nb, Sn, Zr and Co.

[0103] The features and performance of the present application are further described in detail below in conjunction with the embodiments.

[0104] Example 1

[0105] The present invention provides a method for preparing lithium iron phosphate, comprising the following steps:

[0106] Ferrous sulfate, phosphoric acid and ascorbic acid are dissolved in water and stirred to obtain a mixed solution intermediate, wherein the molar ratio of iron element, phosphorus element and antioxidant in the mixed solution intermediate is 1:1:0.01, and the molar concentration of iron element is 1 mol / L; lithium hydroxide is added to the mixed solution intermediate and stirred to obtain a mixed solution, wherein the molar ratio of iron element to lithium element in the mixed solution is 1:1.

[0107] Under a nitrogen atmosphere, sodium hydroxide solution was added to the mixed solution until the pH of the mixed solution was 8.8, and the mixed solution after adjusting the pH was filtered to obtain a precursor precipitate; under a nitrogen atmosphere, the precursor precipitate was washed and filtered with deionized water until the content of S element in the filter cake was 2000ppm.

[0108] Under a nitrogen atmosphere, glucose is added to the aqueous solution prepared by the cleaned precursor precipitate and stirred to obtain a solution containing a carbon-coated precursor, wherein the molar mass ratio of glucose to iron element is 5:100; under a nitrogen atmosphere, the solution of the carbon-coated precursor is placed in an oven for drying until the water content in the precipitate of the carbon-coated precursor is 2%; the dried carbon-coated precursor is placed in a roller furnace and calcined under an argon atmosphere to obtain lithium iron phosphate, wherein the treatment temperature is 720°C and the treatment time is 8 hours.

[0109] The lithium iron phosphate is crushed by a jet mill to obtain lithium iron phosphate particles, wherein the crushing pressure is 0.4 MPa.

[0110] Example 2

[0111] The present invention provides a method for preparing lithium iron phosphate, comprising the following steps:

[0112] Ferrous sulfate, phosphoric acid and ascorbic acid are dissolved in water and stirred to obtain a mixed solution intermediate, wherein the molar ratio of iron element, phosphorus element and antioxidant in the mixed solution intermediate is 1:1:0.005, and the molar concentration of iron element is 0.8 mol / L; lithium hydroxide is added to the mixed solution intermediate and stirred to obtain a mixed solution, wherein the molar ratio of iron element to lithium element in the mixed solution is 1:1.

[0113] Under a nitrogen atmosphere, sodium hydroxide solution was added to the mixed solution until the pH of the mixed solution was 8.5, and the mixed solution after adjusting the pH was filtered to obtain a precursor precipitate; under a nitrogen atmosphere, the precursor precipitate was washed and filtered with deionized water until the content of S element in the filter cake was 2000ppm.

[0114] Under a nitrogen atmosphere, glucose is added to an aqueous solution prepared by precipitating the cleaned precursor and stirred to obtain a solution containing a carbon-coated precursor, wherein the molar mass ratio of glucose to iron is 4:100; under a nitrogen atmosphere, the solution of the carbon-coated precursor is placed in an oven for drying until the water content in the precipitate of the carbon-coated precursor is 2%; the dried carbon-coated precursor is placed in a roller furnace and calcined under an argon atmosphere to obtain lithium iron phosphate, wherein the treatment temperature is 650°C and the treatment time is 20 hours.

[0115] The lithium iron phosphate is crushed by a jet mill to obtain lithium iron phosphate particles, wherein the crushing pressure is 0.4 MPa.

[0116] Example 3

[0117] The present invention provides a method for preparing lithium iron phosphate, comprising the following steps:

[0118] Ferrous sulfate, phosphoric acid and ascorbic acid are dissolved in water and stirred to obtain a mixed solution intermediate, wherein the molar ratio of iron element, phosphorus element and antioxidant in the mixed solution intermediate is 1:1.1:0.015, and the molar concentration of iron element is 1.2 mol / L; lithium hydroxide is added to the mixed solution intermediate and stirred to obtain a mixed solution, wherein the molar ratio of iron element to lithium element in the mixed solution is 1:1.5.

[0119] Under a nitrogen atmosphere, sodium hydroxide solution was added to the mixed solution until the pH of the mixed solution was 10, and the mixed solution after adjusting the pH was filtered to obtain a precursor precipitate; under a nitrogen atmosphere, the precursor precipitate was washed and filtered with deionized water until the content of S element in the filter cake was 2000ppm.

[0120] Under a nitrogen atmosphere, glucose is added to the aqueous solution prepared by the cleaned precursor precipitate and stirred to obtain a solution containing a carbon-coated precursor, wherein the molar mass ratio of glucose to iron element is 10:100; under a nitrogen atmosphere, the solution of the carbon-coated precursor is placed in an oven for drying until the water content in the precipitate of the carbon-coated precursor is 2%; the dried carbon-coated precursor is placed in a roller furnace and calcined under an argon atmosphere to obtain lithium iron phosphate, wherein the treatment temperature is 780°C and the treatment time is 4 hours.

[0121] The lithium iron phosphate is crushed by a jet mill to obtain lithium iron phosphate particles, wherein the crushing pressure is 0.4 MPa.

[0122] Example 4

[0123] The embodiment of the present application provides a method for preparing lithium iron phosphate, which differs from Embodiment 1 only in that: under a nitrogen atmosphere, a sodium hydroxide solution is added to the mixed solution until the pH of the mixed solution is 8.5.

[0124] Example 5

[0125] The embodiment of the present application provides a method for preparing lithium iron phosphate, which differs from Embodiment 1 only in that: under a nitrogen atmosphere, a sodium hydroxide solution is added to a mixed solution until the pH of the mixed solution is 10.

[0126] Example 6

[0127] The embodiment of the present application provides a method for preparing lithium iron phosphate, which differs from Embodiment 1 only in that: under a nitrogen atmosphere, a sodium hydroxide solution is added to the mixed solution until the pH of the mixed solution is 9.8.

[0128] Example 7

[0129] The embodiment of the present application provides a method for preparing lithium iron phosphate, which differs from Example 1 only in that: ferrous sulfate and phosphoric acid are dissolved in water and stirred to obtain a mixed solution intermediate, wherein the molar ratio of iron element to phosphorus element in the mixed solution intermediate is 1:1, and the molar concentration of the iron element is 1 mol / L.

[0130] Example 8

[0131] The embodiment of the present application provides a method for preparing lithium iron phosphate, which differs from Example 1 only in that: under a nitrogen atmosphere, glucose is added to the aqueous solution prepared by the cleaned precursor precipitation and stirred to obtain a solution containing a carbon-coated precursor, wherein the molar mass ratio of glucose to iron element is 9:100.

[0132] Example 9

[0133] The embodiment of the present application provides a method for preparing lithium iron phosphate, which differs from Embodiment 1 only in that lithium hydroxide is added to a mixed solution intermediate and stirred to obtain a mixed solution, wherein the molar ratio of iron element to lithium element in the mixed solution is 1:1.2.

[0134] Example 10

[0135] The embodiment of the present application provides a method for preparing lithium iron phosphate, which differs from Embodiment 1 only in that the molar concentration of the iron element is 1.5 mol / L.

[0136] Embodiment 11

[0137] The embodiment of the present application provides a method for preparing lithium iron phosphate, which differs from Example 1 only in that the dried carbon-coated precursor is placed in a roller furnace and calcined under an argon atmosphere to obtain lithium iron phosphate, wherein the treatment temperature is 820° C. and the treatment time is 4 hours.

[0138] Example 12

[0139] The embodiment of the present application provides a method for preparing lithium iron phosphate, which differs from Example 1 only in that the dried carbon-coated precursor is placed in a roller furnace and calcined under an argon atmosphere to obtain lithium iron phosphate, wherein the treatment temperature is 600°C and the treatment time is 20 hours.

[0140] Comparative Example 1

[0141] The comparative example of the present application provides a method for preparing lithium iron phosphate, which differs from Example 1 only in that lithium hydroxide is added to a mixed solution intermediate and stirred to obtain a mixed solution, wherein the molar ratio of iron element to lithium element in the mixed solution is 1:3, and no pH adjustment related steps are performed, that is, lithium iron phosphate is prepared according to a conventional co-precipitation method.

[0142] Comparative Example 2

[0143] The comparative example of the present application provides a method for preparing lithium iron phosphate, which differs from Example 1 only in that: under a nitrogen atmosphere, a sodium hydroxide solution is added to the mixed solution until the pH of the mixed solution is 7.5.

[0144] Comparative Example 3

[0145] The comparative example of the present application provides a method for preparing lithium iron phosphate, which differs from Example 1 only in that: under a nitrogen atmosphere, a sodium hydroxide solution is added to the mixed solution until the pH of the mixed solution is 10.5.

[0146] Test Example 1

[0147] Lithium iron phosphate performance test

[0148] Test method:

[0149] Lithium iron phosphate was prepared according to the preparation methods of Examples 1 to 12 and Comparative Examples 1 to 3, and then numbered respectively. Electrodes were prepared from lithium iron phosphate (LFP) with different numbers according to the ratio of LFP:SP:PVDF=90:5:5, and further assembled into 2032 batteries. The battery was then tested at room temperature (25°C) for charge and discharge specific capacity and discharge efficiency at a current density of 0.1C, and the test voltage range was 2.5-3.8V.

[0150] Table 1 Performance test results

[0151]

[0152]

[0153] It should be noted that the yield of lithium iron phosphate in the preparation method provided in the embodiment of the present application is basically the same as that in the conventional co-precipitation method, that is, lithium iron phosphate with a comparable output is prepared at the same yield.

[0154] It should be noted that when the amount of carbon source added is constant, it is normal for the carbon content in the product to fluctuate.

[0155] Referring to Table 1, it can be seen from the test results of Example 1 and Comparative Example 1 that the co-precipitation method provided in the embodiment of the present application for preparing lithium iron phosphate, compared with the conventional co-precipitation method, can prepare lithium iron phosphate with equivalent electrical properties while using only one-third of the lithium source amount of the conventional co-precipitation method.

[0156] It can be seen from the test results of Examples 1 to 3 that lithium iron phosphate with relatively excellent electrical properties can be prepared by preparing lithium iron phosphate within the parameter ranges defined in the examples of the present application.

[0157] It can be seen from the test results of Example 1 and Examples 4 to 6 that limiting the pH of the mixed solution to a more preferred range (i.e., 8.8 to 9.8) results in lithium iron phosphate having better electrical properties than limiting the pH of the mixed solution to a preferred range (i.e., 8.5 to 10).

[0158] It can be seen from the performance test results of Example 1 and Example 7 that when an antioxidant is used in the process of dissolving the secondary iron source, the corresponding lithium iron phosphate has better electrical properties than when no antioxidant is used.

[0159] It can be seen from the performance test results of Example 1 and Example 8 that, within the dosage range specified in the embodiments of the present application, appropriately increasing the dosage of the carbon source is helpful to improve the electrical properties of the corresponding lithium iron phosphate.

[0160] It can be seen from the performance test results of Examples 1 and 9 that, within the dosage range specified in the embodiments of the present application, appropriately increasing the dosage of the lithium source is helpful to improve the electrical properties of the corresponding lithium iron phosphate.

[0161] It can be seen from the performance test results of Example 1 and Example 10 that the molar concentration of the iron element in the mixed solution is too high. Compared with limiting the molar concentration of the iron element in the mixed solution to the range specified in the embodiments of the present application, the latter corresponds to better electrical properties of lithium iron phosphate.

[0162] It can be seen from the performance test results of Example 1 and Example 11 / 12 that limiting the treatment temperature and time during the roasting process to a specific range provided in the embodiments of the present application, compared to not being within the set range, the corresponding lithium iron phosphate of the former has better electrical properties.

[0163] It can be seen from the performance test results of Example 1 and Comparative Examples 2 / 3 that when the pH of the mixed solution is limited to the specific range provided in the embodiments of the present application, the lithium iron phosphate corresponding to the former has better electrical properties than when the pH is not within the set range.

[0164] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

Claims

1. A method for preparing lithium iron phosphate, It is characterized in that The following steps are involved: Dissolving a divalent iron source, a phosphorus source and a lithium source in water and mixing them to obtain a mixed solution; The pH of the mixed solution is adjusted by using a pH adjusting agent until the pH of the mixed solution is 8.8-9.8, and then the mixed solution after the pH adjustment is subjected to solid-liquid separation to obtain a precursor precipitate; as well as Adding a carbon source to a solution containing the precursor precipitate and mixing, and sequentially drying and calcining to obtain lithium iron phosphate; In the mixed solution, the molar ratio of iron element, phosphorus element and lithium element is 1:1:(1-1.2); In the mixed solution, the molar concentration of the iron element is 0.8-1.2 mol / L.

2. The method for preparing lithium iron phosphate according to claim 1, It is characterized in that Satisfy at least one of the following conditions A to D: A. The divalent iron source comprises at least one of ferrous sulfate, ferrous nitrate, ferrous chloride and ferrous citrate; B. The phosphorus source comprises at least one of phosphoric acid, sodium dihydrogen phosphate and ammonium dihydrogen phosphate; C. The lithium source comprises at least one of lithium carbonate, lithium nitrate, lithium hydroxide, lithium acetate and lithium citrate; D. The pH adjuster includes at least one of sodium hydroxide, potassium hydroxide and ammonia water.

3. The method for preparing lithium iron phosphate according to claim 1, It is characterized in that The carbon source includes an organic carbon source.

4. The method for preparing lithium iron phosphate according to claim 3, It is characterized in that The organic carbon source includes at least one of glucose, sucrose, citric acid, starch and PEG.

5. The method for preparing lithium iron phosphate according to claim 1, It is characterized in that The step of dissolving the divalent iron source, the phosphorus source and the lithium source in water and mixing them to obtain a mixed solution comprises: Firstly, the divalent iron source and the phosphorus source are dissolved in the water and mixed to obtain a mixed solution intermediate, and then the lithium source is added to the mixed solution intermediate and mixed to obtain the mixed solution.

6. The method for preparing lithium iron phosphate according to claim 5, It is characterized in that The step of first dissolving the divalent iron source and the phosphorus source in the water and mixing them to obtain a mixed solution intermediate further includes adding an antioxidant to the water.

7. The method for preparing lithium iron phosphate according to claim 6, It is characterized in that The antioxidant includes ascorbic acid.

8. The method for preparing lithium iron phosphate according to claim 6, It is characterized in that In the mixed solution intermediate, the molar ratio of the iron element to the antioxidant is 1: (0.005-0.015).

9. The method for preparing lithium iron phosphate according to claim 1, It is characterized in that In the calcining step, the treatment temperature is 650-780° C. and the treatment time is 4-20 h.

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