A method for preparing lithium manganese iron phosphate

Abstract

The embodiment of the present application provides a method for preparing lithium iron manganese phosphate, which belongs to the field of lithium iron manganese phosphate material manufacturing. The method for preparing lithium iron manganese phosphate includes the following steps: dissolving a lithium source, an iron source, a manganese source and a phosphorus source in water and mixing them to obtain a mixed solution; adjusting the pH of the mixed solution with an acid solution until the pH of the mixed solution is 0 to 1.5; roasting the mixed solution after adjusting the pH to decompose the acid solution to obtain a precursor precipitate; mixing the carbon source and the precursor precipitate to obtain a roasted precursor; and roasting the roasted precursor to obtain lithium iron manganese phosphate. Through this preparation method, it is possible to improve the problems of single raw materials, high preparation cost, high environmental pressure and difficulty in achieving atomic-level mixing of all reaction materials in the preparation of lithium iron manganese phosphate by liquid phase method to a certain extent.

Description

Technical Field

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

[0002] In the prior art, the preparation methods of lithium manganese iron phosphate are mainly divided into two categories: solid phase method and liquid phase method. Among them, the liquid phase method is more suitable for preparing lithium manganese iron phosphate because it can achieve atomic-level mixing of various reaction raw materials. The existing liquid phase methods mainly include sol-gel method, hydrothermal method and co-precipitation method. Among them, the sol-gel method has problems such as relatively single raw materials and high environmental pressure, the hydrothermal method has problems such as large amount of raw materials used in preparation and expensive related equipment, and the co-precipitation method has problems such as difficulty in achieving atomic-level mixing of all reaction materials and high environmental pressure. Since the existing liquid phase method has certain problems in the process of preparing lithium manganese iron phosphate, it is difficult to achieve industrialization of the preparation of lithium manganese iron phosphate using the liquid phase method. Summary of the invention

[0003] The purpose of the present application is to provide a method for preparing lithium manganese iron phosphate, which can to some extent improve the problems of preparing lithium manganese iron phosphate by liquid phase method, such as single raw material, high preparation cost, great environmental pressure and difficulty in achieving atomic-level mixing of all reaction materials.

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

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

[0006] A lithium source, an iron source, a manganese source and a phosphorus source are dissolved in water and mixed to obtain a mixed solution; the pH of the mixed solution is adjusted with an acid solution until the pH of the mixed solution is 0 to 1.5; the mixed solution after the pH adjustment is calcined to decompose the acid solution to obtain a precursor precipitate; a carbon source and the precursor precipitate are mixed to obtain a calcined precursor; and the calcined precursor is calcined to obtain lithium manganese iron phosphate.

[0007] According to the above process, lithium iron manganese phosphate with appropriate ratios of lithium, iron, manganese and phosphorus can be prepared. Among them, the mixed solution includes four elements at the same time, which can achieve atomic-level mixing of the four elements; the pH of the mixed solution is limited to a specific range to effectively reduce the risk of precipitation of the reaction raw materials from the mixed solution, so that the prepared lithium iron manganese phosphate can reach the required target element ratio; the solution is roasted to remove the acid, so that there is no need to carry out related processes such as material cleaning and waste liquid treatment. Compared with the sol-gel method (only nitrate can be used as a reaction raw material, resulting in a single source of raw materials, and the corresponding tail gas generated is flammable and explosive, and difficult to recover, resulting in the problem of greater environmental pressure in this method), the preparation method provided in the embodiment of the present application is not limited to the use of nitrate as a reaction raw material, and other salts containing corresponding elements in the art can be used. Accordingly, it can solve the problems of single preparation raw materials and greater environmental pressure to a certain extent; compared with the hydrothermal method (hydrothermal synthesis is a dissolution and recrystallization process, because phosphate crystals need to be formed under pH conditions close to neutral, it is usually necessary to use three times the amount of lithium source to achieve the pH conditions of the reaction in order to subsequently prepare the same quality of lithium iron manganese phosphate, and And the price of the corresponding high-temperature and high-pressure reactor is also relatively expensive, resulting in a high preparation cost of the method), the preparation method provided in the embodiment of the present application only needs to use one-third of the amount of lithium source used in the hydrothermal method, and does not use a high-temperature and high-pressure reactor, thereby effectively reducing the preparation cost; compared with the coprecipitation method (the one-step method can only achieve atomic-level mixing of ferromanganese or ferromanganese phosphorus, and the atomic-level mixing of the remaining elements requires secondary mixing to achieve, the process is relatively complicated, and the cleaning process of the intermediate will also produce a large amount of wastewater, resulting in greater wastewater treatment pressure and environmental pressure), the preparation method provided in the embodiment of the present application can achieve atomic-level mixing of four elements in only one step without generating a large amount of wastewater, that is, the environmental pressure is also relatively small. Through the joint action of each process, it is possible to improve the problems of single raw materials, high preparation cost, high environmental pressure, and difficulty in achieving atomic-level mixing of all reaction materials in the preparation of lithium manganese iron phosphate by the liquid phase method to a certain extent.

[0008] In some optional embodiments, in the mixed solution, the molar ratio of lithium, iron, manganese and phosphorus is (1-1.04):X:(1-X):(1-1.04), wherein 0<X<1.

[0009] In the above technical solution, the molar ratio of lithium, iron, manganese and phosphorus in the mixed solution is limited to a specific range, so that the prepared lithium manganese iron phosphate can have a more suitable element ratio and purity.

[0010] In some optional implementation schemes, at least one of the following conditions A to D is met:

[0011] A lithium source includes at least one of lithium hydroxide, lithium acetate, lithium carbonate, lithium citrate, lithium nitrate, lithium dihydrogen phosphate, dilithium hydrogen phosphate and lithium phosphate;

[0012] B iron source comprises at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous citrate, ferric sulfate, ferric chloride, ferric nitrate, ferric citrate, iron powder and ferric oxide;

[0013] The manganese source includes at least one of manganous sulfate, manganous chloride, manganous nitrate, manganous citrate, manganous sulfate, manganous chloride and manganous nitrate;

[0014] The D phosphorus source includes at least one of phosphoric acid, lithium dihydrogen phosphate, dilithium hydrogen phosphate and lithium phosphate.

[0015] The technical solution provided in the examples of the present application is applicable to the above-mentioned various lithium sources, iron sources, manganese sources and phosphorus 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.

[0016] In some alternative embodiments, the lithium source and the phosphorus source both include lithium dihydrogen phosphate.

[0017] In the above technical solution, the lithium source and phosphorus source include lithium dihydrogen phosphate at the same time, because lithium dihydrogen phosphate contains two target elements, lithium source and phosphorus source, and the molar ratio of the two is close to 1:1, which can reduce the cost of raw materials compared to using two different reaction raw materials separately. At the same time, when all lithium sources and phosphorus sources are provided by lithium dihydrogen phosphate, the weighing process and calculation process can be reduced once in the batching stage, thereby reducing time consumption and improving batching efficiency.

[0018] In some optional embodiments, the acid solution includes at least one of sulfuric acid, hydrochloric acid and nitric acid.

[0019] The technical solution provided in the embodiments of the present application is applicable to the above-mentioned various acid solution 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, especially compared with the sol-gel method, it can provide more raw material selection options.

[0020] In some optional embodiments, in the mixed solution, the total molar concentration of iron and manganese is ≤1.2 mol / L;

[0021] Optionally, the total molar concentration of iron and manganese elements is 0.6-1.2 mol / L.

[0022] In the above technical scheme, the total molar concentration of iron and manganese in the mixed solution is limited to a specific range in order to effectively reduce the risk of precipitation of the corresponding elements from the mixed solution, thereby making it easier to prepare lithium iron manganese phosphate with a suitable ratio of lithium, iron, manganese and phosphorus and a higher purity.

[0023] Furthermore, the total molar concentration of iron and manganese in the mixed solution is limited to a more preferred range, so that the lithium manganese iron phosphate can have a suitable yield while taking into account the quality of the lithium manganese iron phosphate (when the volume of the reaction container is constant, too low a concentration will result in a lower yield).

[0024] In some optional embodiments, in the step of calcining the mixed solution after adjusting the pH, the treatment temperature is 350 to 900° C. and the treatment time is 10 to 60 seconds.

[0025] In the above technical scheme, the treatment temperature and time in the roasting process are limited to the above ranges respectively, so that the roasting is carried out under appropriate conditions. On the one hand, it can effectively avoid the temperature being too low and the time being too short (the temperature is too low and the time is too short, the acid is not completely decomposed, and there are more residues), so as to achieve a better acid removal effect; on the other hand, it can effectively avoid the temperature being too high and the time being too long (the temperature is too high and the time is too long, the particles in the precursor precipitation are significantly enlarged, resulting in the comprehensive electrical properties of the lithium manganese iron phosphate finally prepared subsequently being reduced), so that the prepared lithium manganese iron phosphate has better comprehensive electrical properties.

[0026] In some alternative embodiments, the carbon source includes at least one of glucose, sucrose, PEG, polyvinyl alcohol, carbon black and graphite.

[0027] The technical solution provided in the examples of the present application is applicable to the above-mentioned various carbon source systems, and is also applicable to organic carbon sources and inorganic carbon sources, 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.

[0028] In some optional embodiments, in the calcined precursor, the mass of the carbon source is 12-16% of the mass of the calcined precursor.

[0029] In the above technical scheme, the mass ratio of the carbon source in the calcined precursor and the calcined precursor is limited within a specific range, so that the two can have an appropriate usage ratio. On the one hand, it can effectively avoid the carbon source mass ratio being too low (the carbon source mass ratio is too low, which will lead to insufficient conductivity of the corresponding product), so that the prepared lithium manganese iron phosphate has better conductivity; on the other hand, it can effectively avoid the carbon source mass ratio being too high (the carbon source mass ratio is too high, which will cause the content of active material components of the lithium manganese iron phosphate in the product to be low, affecting the charging capacity, and an excessively thick carbon coating layer will also cause the corresponding product to have poor particle dispersion), so that the prepared lithium manganese iron phosphate has a higher capacitance and better dispersibility.

[0030] In some optional embodiments, in the step of calcining the calcination precursor, the treatment temperature is 650-750° C. and the treatment time is 4-20 hours.

[0031] In the above technical solution, the processing temperature and processing time are limited within a specific range, so that the roasting process can be carried out under suitable conditions, thereby preparing lithium manganese iron phosphate with relatively excellent quality and comprehensive electrical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] 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.

[0033] Figure 1 A process flow chart of a method for preparing lithium manganese iron phosphate provided in an embodiment of the present application. DETAILED DESCRIPTION

[0034] 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.

[0035] 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”.

[0036] 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".

[0037] In the prior art, the commonly used liquid phase method has certain problems in the process of preparing lithium manganese iron phosphate, which are specifically manifested as follows:

[0038] Sol-gel method: using nitrate as the reaction raw material, removing the solvent by evaporation to obtain a calcined precursor, which is then crushed and sintered to obtain the finished product. Since this method can only use nitrate as the reaction raw material, it has a single source of raw materials, and the corresponding tail gas generated is flammable and explosive, and difficult to recover. This method also causes the problem of greater environmental pressure.

[0039] Hydrothermal method: Usually 3 times the amount of lithium source is needed to adjust the pH to obtain reaction conditions close to neutrality. Only under this pH condition and high temperature and high pressure conditions can lithium iron manganese phosphate be generated through dissolution and recrystallization. In order to prepare lithium iron manganese phosphate that can meet the application requirements in this field, this method requires three times the amount of lithium source as the solid phase method, and the corresponding high temperature and high pressure reactor is also relatively expensive, resulting in a high preparation cost of this method.

[0040] Co-precipitation method: by adjusting the pH, first generate ferromanganese phosphate, oxalate or hydroxide and other precipitation precursors, and then mix the precipitation precursors with the corresponding lithium source and phosphorus source to generate lithium ferromanganese phosphate. In this method, the one-step method can only achieve atomic-level mixing of ferromanganese or ferromanganese phosphorus, and the atomic-level mixing of the remaining elements requires secondary mixing. The process is relatively complicated, and the cleaning process of the intermediates will also produce a large amount of wastewater, resulting in greater wastewater treatment pressure and environmental pressure.

[0041] Since the existing liquid phase method has certain problems in the process of preparing lithium iron manganese phosphate, it is difficult to achieve industrialization in the preparation of lithium iron manganese phosphate using the liquid phase method.

[0042] Based on this, the inventors have creatively discovered that: first, a lithium source, an iron source, a manganese source, and a phosphorus source are dissolved in water to form an atomic-level mixed solution of Li, Fe, Mn, and P, and the pH of the mixed solution is adjusted to a specific range, and then a uniformly mixed precursor precipitate is obtained by a spray roasting method. After the precursor precipitate and the carbon source are evenly mixed, they are roasted under an inert atmosphere to obtain carbon-coated lithium manganese iron phosphate. This can, to a certain extent, improve the problems of preparing lithium manganese iron phosphate by the liquid phase method, such as a single raw material, high preparation cost, high environmental pressure, and difficulty in achieving atomic-level mixing of all reaction materials.

[0043] The following is a detailed description of a method for preparing lithium manganese iron phosphate in an embodiment of the present application.

[0044] The present invention provides a method for preparing lithium manganese iron phosphate, comprising the following steps:

[0045] A lithium source, an iron source, a manganese source and a phosphorus source are dissolved in water and mixed to obtain a mixed solution; the pH of the mixed solution is adjusted with an acid solution until the pH of the mixed solution is 0 to 1.5; the mixed solution after the pH adjustment is calcined to decompose the acid solution to obtain a precursor precipitate; a carbon source and the precursor precipitate are mixed to obtain a calcined precursor; and the calcined precursor is calcined to obtain lithium manganese iron phosphate.

[0046] It should be noted that, as is well known in the art, lithium manganese iron phosphate refers to a qualified product with an appropriate ratio of elements (usually the molar ratio of lithium, iron, manganese and phosphorus is close to 1:1:1) and an appropriate purity (i.e., the content of impurities in the product is low).

[0047] It should be noted that, as is well known in the art, the iron element in lithium manganese iron phosphate is divalent iron, and the manganese element is divalent manganese.

[0048] In the present application, according to the above process, lithium iron manganese phosphate with suitable ratios of lithium, iron, manganese and phosphorus can be prepared. Among them, the mixed solution includes four elements at the same time, which can achieve atomic-level mixing of the four elements; the pH of the mixed solution is limited to a specific range to effectively reduce the risk of precipitation of the reaction raw materials from the mixed solution, so that the prepared lithium iron manganese phosphate can reach the required target element ratio; the solution is roasted to remove the acid, so that there is no need to carry out related processes such as material cleaning and waste liquid treatment. Compared with the sol-gel method (only nitrate can be used as a reaction raw material, resulting in a single source of raw materials, and the corresponding tail gas generated is flammable and explosive, and difficult to recover, resulting in the problem of greater environmental pressure in this method), the preparation method provided in the embodiment of the present application is not limited to the use of nitrate as a reaction raw material, and other salts containing corresponding elements in the art can be used. Accordingly, it can solve the problems of single preparation raw materials and greater environmental pressure to a certain extent; compared with the hydrothermal method (hydrothermal synthesis is a dissolution and recrystallization process, because phosphate crystals need to be formed under pH conditions close to neutral, it is usually necessary to use three times the amount of lithium source to achieve the pH conditions of the reaction in order to subsequently prepare the same quality of lithium iron manganese phosphate, and And the price of the corresponding high-temperature and high-pressure reactor is also relatively expensive, resulting in a high preparation cost of the method), the preparation method provided in the embodiment of the present application only needs to use one-third of the amount of lithium source used in the hydrothermal method, and does not use a high-temperature and high-pressure reactor, thereby effectively reducing the preparation cost; compared with the coprecipitation method (the one-step method can only achieve atomic-level mixing of ferromanganese or ferromanganese phosphorus, and the atomic-level mixing of the remaining elements requires secondary mixing to achieve, the process is relatively complicated, and the cleaning process of the intermediate will also produce a large amount of wastewater, resulting in greater wastewater treatment pressure and environmental pressure), the preparation method provided in the embodiment of the present application can achieve atomic-level mixing of four elements in only one step without generating a large amount of wastewater, that is, the environmental pressure is also relatively small. Through the joint action of each process, it is possible to improve the problems of single raw materials, high preparation cost, high environmental pressure, and difficulty in achieving atomic-level mixing of all reaction materials in the preparation of lithium manganese iron phosphate by the liquid phase method to a certain extent.

[0049] It should be noted that the method for calcining the mixed solution after adjusting the pH is not limited, and can be set according to conventional selections in the art, for example, it can be spray calcination.

[0050] It is understandable that during the spray roasting process, the spray roasting process can be adjusted in consideration of environmental protection requirements.

[0051] As an example, during the spray roasting process, a step of using water to absorb the corresponding tail gas to prepare the corresponding acid solution is also included.

[0052] In this embodiment, adding a tail gas absorption step can not only meet environmental protection requirements, but also reuse the recovered acid, further reducing the preparation cost.

[0053] It should be noted that the method of mixing the carbon source and the precursor precipitate is not limited and can be set according to conventional selection in the art.

[0054] As an example, a ploughshare mixer is used to mix the carbon source and the precursor precipitate.

[0055] It should be noted that the parameters in the mixing process are not limited and can be set according to conventional selections in the art.

[0056] As an example, in the process of mixing the carbon source and the precursor precipitate using a plowshare mixer, the processing speed is 1000-2000 r / min and the processing time is 30-50 min.

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

[0058] As an example, the step of calcining the calcined precursor is 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 should be noted that the molar ratio of lithium, iron, manganese and phosphorus in the mixed solution is not limited and can be set according to conventional selection in the art.

[0062] As an example, in the mixed solution, the molar ratio of lithium, iron, manganese and phosphorus is (1-1.04):X:(1-X):(1-1.04), wherein 0<X<1.

[0063] It should be noted that the sum of the iron element and the manganese element can be 1. The two elements can be the same, or the iron element or the manganese element can be more.

[0064] In this embodiment, the molar ratio of lithium, iron, manganese and phosphorus in the mixed solution is limited to a specific range, so that the prepared lithium manganese iron phosphate can have a more suitable element ratio and purity.

[0065] It should be noted that the types of lithium source, iron source, manganese source and phosphorus source are not limited and can be set according to conventional selection in the art.

[0066] As an example, at least one of the following conditions A to D is met:

[0067] A lithium source includes at least one of lithium hydroxide, lithium acetate, lithium carbonate, lithium citrate, lithium nitrate, lithium dihydrogen phosphate, lithium hydrogen phosphate and lithium phosphate.

[0068] B. The iron source includes at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous citrate, ferric sulfate, ferric chloride, ferric nitrate, ferric citrate, iron powder and ferric oxide.

[0069] The manganese source includes at least one of manganous sulfate, manganous chloride, manganous nitrate, manganous citrate, manganous sulfate, manganous chloride and manganous nitrate.

[0070] The D phosphorus source includes at least one of phosphoric acid, lithium dihydrogen phosphate, dilithium hydrogen phosphate and lithium phosphate.

[0071] In this embodiment, the technical solution provided in the embodiment of the present application is applicable to the above-mentioned multiple lithium sources, iron sources, manganese sources and phosphorus source systems, and can provide more feasible implementation plans, thereby facilitating the promotion and application of the preparation method provided in the embodiment of the present application.

[0072] It is understandable that, under the condition of meeting the reaction requirements, the fewer types of raw materials need to be prepared, the less time is spent in the preparation stage, and at the same time, the cost of raw materials is also lower. Based on this, the types of reaction raw materials can be adjusted.

[0073] As an example, the lithium source and the phosphorus source both include lithium dihydrogen phosphate.

[0074] It should be noted that in the embodiments of the present application, all lithium sources and phosphorus sources can be provided by lithium dihydrogen phosphate; of course, a part of the lithium source and phosphorus source can also be provided by lithium dihydrogen phosphate, and the remaining lithium source and phosphorus source can be provided simultaneously or separately by other salts.

[0075] In this embodiment, the lithium source and the phosphorus source include lithium dihydrogen phosphate at the same time, because lithium dihydrogen phosphate contains two target elements, lithium source and phosphorus source, and the molar ratio of the two is close to 1:1, which can reduce the cost of raw materials compared to using two different reaction raw materials separately. At the same time, when all lithium sources and phosphorus sources are provided by lithium dihydrogen phosphate, the weighing process and calculation process can be reduced once in the batching stage, thereby reducing time consumption and improving batching efficiency.

[0076] It should be noted that the type of acid solution is not limited and can be set according to conventional selection in the art.

[0077] As an example, the acid solution includes at least one of sulfuric acid, hydrochloric acid and nitric acid.

[0078] In this embodiment, the technical solution provided in the embodiment of the present application is applicable to the above-mentioned multiple acid liquid systems, and can provide more feasible implementation plans, thereby facilitating the promotion and application of the preparation method provided in the embodiment of the present application, especially compared with the sol-gel method, it can provide more raw material selection options.

[0079] It should be noted that the total molar concentration of the iron element and the manganese element in the mixed solution is not limited and can be set according to conventional selection in the art.

[0080] As an example, in the mixed solution, the total molar concentration of iron and manganese elements is ≤1.2 mol / L.

[0081] Optionally, the total molar concentration of iron and manganese elements is 0.6 to 1.2 mol / L, for example, but not limited to, the total molar concentration is any one of 0.6 mol / L, 0.7 mol / L, 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.

[0082] In this embodiment, the total molar concentration of iron and manganese in the mixed solution is limited to a specific range in order to effectively reduce the risk of precipitation of the corresponding elements from the mixed solution, thereby making it easier to prepare lithium iron manganese phosphate with a suitable ratio of lithium, iron, manganese and phosphorus and a higher purity.

[0083] Furthermore, the total molar concentration of iron and manganese in the mixed solution is limited to a more preferred range, so that the lithium manganese iron phosphate can have a suitable yield while taking into account the quality of the lithium manganese iron phosphate (when the volume of the reaction container is constant, too low a concentration will result in a lower yield).

[0084] It should be noted that, during the process of calcining the mixed solution, the treatment temperature and time are not limited and can be set according to conventional selections in the art.

[0085] As an example, in the step of calcining the mixed solution after adjusting the pH, the treatment temperature is 350-900°C, for example but not limited to the treatment temperature of any one of 350°C, 400°C, 500°C, 600°C, 700°C, 800°C and 900°C or a range between any two of them; the treatment time is 10-60s, for example but not limited to the treatment time of any one of 10s, 20s, 30s, 40s, 50s and 60s or a range between any two of them.

[0086] In this embodiment, the treatment temperature and time during the calcination process are respectively limited to the above ranges in order to carry out the calcination under appropriate conditions. On the one hand, it can effectively avoid the temperature being too low and the time being too short (the temperature is too low and the time is too short, the acid is not completely decomposed and there are more residues), so as to achieve a better acid removal effect; on the other hand, it can effectively avoid the temperature being too high and the time being too long (the temperature is too high and the time is too long, the particles in the precursor precipitate are significantly enlarged, resulting in a decrease in the comprehensive electrical properties of the lithium manganese iron phosphate finally prepared later), so that the prepared lithium manganese iron phosphate has better comprehensive electrical properties.

[0087] It should be noted that the type of carbon source is not limited and can be set according to routine selection in the art.

[0088] As an example, the carbon source includes at least one of glucose, sucrose, PEG, polyvinyl alcohol, carbon black and graphite.

[0089] In this embodiment, the technical solution provided in the embodiment of the present application is applicable to the above-mentioned multiple carbon source systems, and is also applicable to organic carbon sources and inorganic carbon sources, and can provide more feasible implementation plans, thereby facilitating the promotion and application of the preparation method provided in the embodiment of the present application.

[0090] It can be understood that a suitable amount of carbon coating can make the prepared lithium manganese iron phosphate have better comprehensive electrical properties.

[0091] As an example, in the calcined precursor, the mass of the carbon source is 12-16% of the mass of the calcined precursor, for example but not limited to any one of 12%, 13%, 14%, 15% and 16% or a range between any two of them.

[0092] In this embodiment, the mass ratio of the carbon source in the calcined precursor and the calcined precursor is limited within a specific range, so that the two can have an appropriate usage ratio. On the one hand, it can effectively avoid the carbon source mass ratio being too low (too low carbon source mass ratio will lead to insufficient conductivity of the corresponding product), so that the prepared lithium manganese iron phosphate has better conductivity; on the other hand, it can effectively avoid the carbon source mass ratio being too high (too high carbon source mass ratio will lead to low content of active material components of lithium manganese iron phosphate in the product, affecting the charging capacity, and an excessively thick carbon coating layer will also cause poor particle dispersion of the corresponding product), so that the prepared lithium manganese iron phosphate has higher capacitance and better dispersibility.

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

[0094] As an example, in the step of calcining the calcination precursor, the processing temperature is 650-750°C, for example but not limited to the processing temperature of any one of 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C and 750°C, or a range between any two of them; the processing time is 4-20h, for example but not limited to the processing time of any one of 4h, 8h, 10h, 12h, 14h, 16h, 18h and 20h, or a range between any two of them.

[0095] In this embodiment, the processing temperature and the processing time are limited to a specific range, so that the roasting process can be carried out under suitable conditions, thereby preparing lithium manganese iron phosphate with relatively excellent quality and comprehensive electrical properties.

[0096] It should be noted that the processes and steps not specifically described or limited in the preparation process of lithium manganese iron phosphate are not limited and can be set according to conventional selections in the art.

[0097] As an example, after the step of preparing lithium manganese iron phosphate, the step of crushing the lithium manganese 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, lithium manganese iron phosphate is crushed by a gas crusher, and the crushing pressure is 0.4Mpa to 0.6Mpa.

[0100] In this embodiment, the gas crushing method can prepare lithium manganese 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 manganese iron phosphate is shown as follows: Figure 1 shown.

[0102] The features and performance of the present application are further described in detail below in conjunction with the embodiments.

[0103] Example 1

[0104] The present invention provides a method for preparing lithium manganese iron phosphate, comprising the following steps:

[0105] Ferrous sulfate, manganous sulfate and lithium dihydrogen phosphate were dissolved in deionized water at a molar ratio of 0.4:0.6:1 and stirred to obtain a mixed solution, wherein the total molar concentration of iron and manganese elements in the mixed solution was 1.0 mol / L; sulfuric acid was used to adjust the pH of the mixed solution until the pH of the mixed solution was 1.5, and then the mixed solution after the pH adjustment was transferred to a spray roasting furnace for roasting to decompose the sulfuric acid to obtain a precursor precipitate, wherein the treatment temperature was 350°C, the treatment time was 60s, and deionized water was used. Water absorbs the roasting tail gas and obtains sulfuric acid; glucose monohydrate and the precursor precipitate are mixed by a plowshare mixer to obtain a roasting precursor, wherein the mass of glucose monohydrate is 12% of the mass of the precursor precipitate, the rotation speed is 1500r / min, and the processing time is 45min; the roasting precursor is roasted in a nitrogen atmosphere to obtain lithium iron manganese phosphate, wherein the processing temperature is 650°C and the processing time is 10h; the lithium iron manganese phosphate is crushed by a jet mill to obtain lithium iron manganese phosphate particles, wherein the crushing pressure is 0.5Mpa.

[0106] Example 2

[0107] The embodiment of the present application provides a method for preparing lithium manganese iron phosphate, which differs from Example 1 only in that the mixed solution after adjusting the pH is transferred to a spray calcining furnace for calcining to decompose sulfuric acid to obtain a precursor precipitate, wherein the treatment temperature is 900°C.

[0108] Example 3

[0109] The embodiment of the present application provides a method for preparing lithium manganese iron phosphate, which differs from Example 1 only in that the mixed solution after adjusting the pH is transferred to a spray calcining furnace for calcining to decompose the sulfuric acid to obtain a precursor precipitate, wherein the treatment temperature is 250°C.

[0110] Example 4

[0111] The embodiment of the present application provides a method for preparing lithium manganese iron phosphate, which differs from Example 1 only in that the mixed solution after adjusting the pH is transferred to a spray roasting furnace for roasting to decompose sulfuric acid to obtain a precursor precipitate, wherein the processing temperature is 1200°C.

[0112] Example 5

[0113] The embodiment of the present application provides a method for preparing lithium manganese iron phosphate, which is different from the embodiment 1 only in that the mass of glucose monohydrate is 16% of the mass of the precursor precipitate.

[0114] Example 6

[0115] The embodiment of the present application provides a method for preparing lithium manganese iron phosphate, which is different from the embodiment 1 only in that the mass of glucose monohydrate is 10% of the mass of the precursor precipitate.

[0116] Example 7

[0117] The embodiment of the present application provides a method for preparing lithium manganese iron phosphate, which is different from the embodiment 1 only in that the mass of glucose monohydrate is 18% of the mass of the precursor precipitate.

[0118] Example 8

[0119] The embodiment of the present application provides a method for preparing lithium manganese iron phosphate, which differs from Embodiment 1 only in that: the calcination precursor is calcined in a nitrogen atmosphere to obtain lithium manganese iron phosphate, wherein the processing temperature is 750°C.

[0120] Example 9

[0121] The embodiment of the present application provides a method for preparing lithium manganese iron phosphate, which differs from Embodiment 1 only in that: the calcination precursor is calcined in a nitrogen atmosphere to obtain lithium manganese iron phosphate, wherein the processing temperature is 550°C.

[0122] Example 10

[0123] The embodiment of the present application provides a method for preparing lithium manganese iron phosphate, which differs from Embodiment 1 only in that: a calcined precursor is calcined in a nitrogen atmosphere to obtain lithium manganese iron phosphate, wherein the processing temperature is 800°C.

[0124] Embodiment 11

[0125] The embodiment of the present application provides a method for preparing lithium manganese iron phosphate, which differs from Embodiment 1 only in that sulfuric acid is replaced by hydrochloric acid.

[0126] Example 12

[0127] The embodiment of the present application provides a method for preparing lithium manganese iron phosphate, which differs from Embodiment 1 only in that glucose monohydrate is replaced by sucrose.

[0128] It should be noted that the yield of lithium manganese iron phosphate produced by the preparation method provided in the examples of the present application is substantially consistent with that of the conventional hydrothermal method.

[0129] Comparative Example 1

[0130] The comparative example of the present application provides a method for preparing lithium manganese iron phosphate, which differs from Example 1 only in that the pH of the mixed solution is adjusted by using sulfuric acid until the pH of the mixed solution is 2.

[0131] Test Example 1

[0132] Performance test of lithium manganese iron phosphate

[0133] Test method:

[0134] Lithium manganese iron phosphate was prepared according to the preparation methods of Examples 1 to 12 and Comparative Example 1, and then numbered respectively. Electrodes were prepared from lithium manganese iron phosphate (LMFP) with different numbers according to the ratio of LMFP: SP: PVDF = 90:5:5, and further assembled into 2032 batteries. The charge and discharge specific capacity and discharge efficiency of the battery were tested at room temperature (25°C) at a current density of 0.1C, and the test voltage range was 2.5-3.8V.

[0135] Table 1 Performance test results

[0136] Sample name Charge capacity (mAh / g) Discharge specific capacity (mAh / g) Discharge efficiency (%) Example 1 159.3 155.2 97.4 Example 2 160.1 156.2 97.6 Example 3 158.9 153.2 96.4 Example 4 157.4 151.2 96.1 Example 5 160.3 157.2 98.1 Example 6 159.1 154.8 97.3 Example 7 157.2 155.5 97.5 Example 8 160.4 155.7 97.6 Example 9 158.9 155.1 97.2 Example 10 155.3 150.2 96.7 Embodiment 11 159.4 155.7 97.7 Example 12 159.2 155.3 97.6 Comparative Example 1 157.2 152.4 96.9

[0137] Referring to Table 1, it can be seen from the test results of Example 1 and Comparative Example 1 that when the pH of the mixed solution is higher than the upper limit range of pH provided in the embodiments of the present application, due to the problems analyzed from the reaction raw material part, the comprehensive electrical properties of the finally prepared lithium manganese iron phosphate are poor.

[0138] It can be seen from the test results of Example 1 and Example 3 that when the lower limit of the treatment temperature of the spray roasting is lower than the lower limit of the temperature provided in the embodiments of the present application, due to the residual acid solution, S element remains in the product, which in turn leads to the poor comprehensive electrical properties of the finally prepared lithium manganese iron phosphate.

[0139] It can be seen from the test results of Example 2 and Example 4 that when the upper limit of the treatment temperature of the spray roasting is higher than the upper limit of the temperature provided in the embodiments of the present application, the size of the precursor particles is significantly increased, resulting in poor comprehensive electrical properties of the finally prepared lithium manganese iron phosphate.

[0140] It can be seen from the test results of Example 1 and Example 5 that, within the limited range provided in the embodiments of the present application, appropriately increasing the content of the carbon source can increase the comprehensive electrical properties of the prepared lithium manganese iron phosphate.

[0141] It can be seen from the test results of Example 1 and Example 6 that when the lower limit of the quality of the carbon source is lower than the lower limit of the carbon source provided in the examples of the present application, the comprehensive electrical properties of the lithium manganese iron phosphate finally prepared are poor due to the reduction in conductivity.

[0142] It can be seen from the test results of Example 1 and Example 7 that when the upper limit of the mass of the carbon source is higher than the upper limit of the carbon source provided in the embodiments of the present application, the charging capacity of the lithium manganese iron phosphate finally prepared is poor due to the high mass proportion of the carbon source.

[0143] It can be seen from the test results of Example 1 and Example 9 that when the lower limit of the calcination treatment temperature is lower than the lower limit of the temperature provided in the examples of the present application, the comprehensive electrical properties of the finally prepared lithium manganese iron phosphate are poor due to the decrease in the crystallinity of the material.

[0144] It can be seen from the test results of Example 8 and Example 10 that when the upper limit of the calcination treatment temperature is higher than the upper limit of the temperature provided in the embodiments of the present application, the comprehensive electrical properties of the finally prepared lithium manganese iron phosphate are poor due to the significant increase in material size and the generation of miscellaneous substances.

[0145] It can be seen from the test results of Example 1 and Examples 11 to 12 that, within the selection range provided in the examples of the present application, by replacing some of the reaction raw materials, the comprehensive electrical properties of the prepared lithium manganese iron phosphate are basically the same, indicating that the preparation method provided in the examples of the present application is applicable to a variety of systems.

[0146] 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 manganese iron phosphate, characterized in that: The following steps are involved: Dissolving a lithium source, an iron source, a manganese source and a phosphorus source in water and mixing them to obtain a mixed solution; In the mixed solution, the molar ratio of lithium, iron, manganese and phosphorus is (1-1.04):X:(1-X):(1-1.04), wherein 0<X<1; Using an acid solution to adjust the pH of the mixed solution until the pH of the mixed solution is 0 to 1.5; calcining the mixed solution after adjusting the pH to decompose the acid solution and obtain a precursor precipitate; mixing the carbon source and the precursor precipitate to obtain a calcined precursor; and The calcined precursor is calcined to obtain lithium manganese iron phosphate.

2. The method for preparing lithium iron manganese phosphate according to claim 1, characterized in that: Satisfy at least one of the following conditions A to D: A said lithium source comprises at least one of lithium hydroxide, lithium acetate, lithium carbonate, lithium citrate, lithium nitrate, lithium dihydrogen phosphate, dilithium hydrogen phosphate and lithium phosphate; B. The iron source comprises at least one of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous citrate, ferric sulfate, ferric chloride, ferric nitrate, ferric citrate, iron powder and ferric oxide; C. The manganese source comprises at least one of manganous sulfate, manganous chloride, manganous nitrate, manganous citrate, manganous sulfate, manganous chloride and manganous nitrate; D. The phosphorus source includes at least one of phosphoric acid, lithium dihydrogen phosphate, dilithium hydrogen phosphate and lithium phosphate.

3. The method for preparing lithium manganese iron phosphate according to claim 2, characterized in that: The lithium source and the phosphorus source both include lithium dihydrogen phosphate.

4. The method for preparing lithium manganese iron phosphate according to any one of claims 1 to 3, characterized in that: The acid solution includes at least one of sulfuric acid, hydrochloric acid and nitric acid.

5. The method for preparing lithium manganese iron phosphate according to any one of claims 1 to 3, characterized in that: In the mixed solution, the total molar concentration of iron and manganese elements is ≤1.2 mol / L.

6. The method for preparing lithium manganese iron phosphate according to claim 5, characterized in that: The total molar concentration of the iron element and the manganese element is 0.6-1.2 mol / L.

7. The method for preparing lithium manganese iron phosphate according to any one of claims 1 to 3, characterized in that: In the step of calcining the mixed solution after adjusting the pH, the treatment temperature is 350-900° C. and the treatment time is 10-60 seconds.

8. The method for preparing lithium manganese iron phosphate according to any one of claims 1 to 3, characterized in that: The carbon source includes at least one of glucose, sucrose, PEG, polyvinyl alcohol, carbon black and graphite.

9. The method for preparing lithium manganese iron phosphate according to claim 8, characterized in that: In the calcined precursor, the mass of the carbon source is 12-16% of the mass of the calcined precursor.

10. The method for preparing lithium manganese iron phosphate according to claim 1, characterized in that: In the step of calcining the calcination precursor, the treatment temperature is 650-750° C. and the treatment time is 4-20 hours.

Images