Manganese iron phosphate precursor, lithium manganese iron phosphate positive electrode material, preparation method and use

Abstract

The present disclosure belongs to the technical field of lithium batteries, and specifically relates to a manganese iron phosphate precursor, a lithium manganese iron phosphate positive electrode material, a preparation method, and a use. The present disclosure utilizes the feature of iron phosphate precipitation and aluminum phosphate precipitation having similar Ksp, first synthesizing aluminum iron phosphate by means of coprecipitation, and mixing the aluminum iron phosphate evenly, and then using a reaction between aluminum iron phosphate and manganese chloride to prepare a stable manganese iron phosphate precursor; aluminum chloride generated during the reaction can be directly volatilized. The synthesis route provided by the present disclosure can effectively solve the problem of a non-uniform manganese iron phosphate precursor caused by directly coprecipitating manganese phosphate and iron phosphate; the iron-manganese ratio of the prepared manganese iron phosphate precursor is closer to a target value, and the specific capacity and cycle performance of the lithium manganese iron phosphate then prepared using said precursor can be effectively improved. The entire process is simple and easy to operate, with low process costs, and has very good prospects for industrial application.

Description

Manganese iron phosphate precursor, manganese iron phosphate lithium positive electrode material, preparation method and application Technical Field

[0001] The present disclosure belongs to the field of lithium battery technology, and specifically relates to a manganese iron phosphate precursor, a manganese iron phosphate lithium positive electrode material, and a preparation method and application thereof. Background Art

[0002] As lithium-ion batteries become increasingly widely used in society, demands for them are becoming increasingly diverse, such as higher energy density, higher rate capability, and good low-temperature performance. The energy density of lithium-ion batteries depends on the battery materials used. Currently, commonly used cathode materials for lithium-ion batteries include ternary materials (such as lithium nickel cobalt manganese oxide) and lithium iron phosphate. The energy density of lithium iron phosphate batteries is already approaching its theoretical limit, leaving relatively little room for improvement. To further enhance the electrochemical performance of lithium-ion batteries, recent consideration has been given to replacing lithium iron phosphate batteries with lithium manganese phosphate, a polyanion material with the same olivine structure. However, lithium manganese phosphate has lower electronic conductivity and ion diffusion coefficient than lithium iron phosphate, limiting its application at high rates and low temperatures. Furthermore, manganese ions present challenges such as the Jahn-Teller effect and ion dissolution.

[0003] In order to alleviate the above problems, the advantages of lithium iron phosphate and lithium manganese phosphate are combined to form a lithium iron manganese phosphate solid solution (LiMn x Fe 1-x PO4 (where x is the atomic ratio) is a relatively effective approach. Compared to lithium iron phosphate, lithium iron manganese phosphate (LFP) has the same crystal structure. Because it contains manganese ions, the battery's discharge voltage is higher (up to 4.1V), making LFP's energy density approximately 20% higher than that of LFP. Therefore, this solid solution material is expected to replace LFP as the cathode material for the next generation of lithium-ion batteries for large-scale application.

[0004] At present, the method for large-scale production of lithium iron manganese phosphate is mostly a high-temperature solid-phase method: lithium source, manganese source, iron source, phosphorus source and carbon source are mixed in a certain proportion, ball-milled and dried, and then heated to a set temperature in an inert or reducing atmosphere in a muffle furnace. After a period of reaction, lithium iron manganese phosphate material can be obtained. However, this method is difficult to accurately control the ratio of iron and manganese, and it is difficult for transition metals to be evenly distributed in the main structure of the material, which will lead to Mn 3+ The Jahn-Teller effect is serious, which affects the cycle and rate performance of the battery. SP The values ​​differ greatly, and it is difficult to co-precipitate the manganese ferrophosphate precursor in a conventional liquid phase reaction system. Although some scholars have successfully synthesized the manganese ferrophosphate precursor under harsh conditions, the process is complicated and the cost is high, making it difficult to apply to industrial production.

[0005] Therefore, there is an urgent need to develop a simple, easy and low-cost synthesis method, while making the iron-manganese ratio in the prepared lithium manganese iron phosphate closer to the target value, thereby improving the electrochemical performance of high manganese iron phosphate lithium batteries.

[0006] In view of this, the present disclosure is proposed.

[0007] Summary of the Invention

[0008] The purpose of the present disclosure includes providing a manganese iron phosphate precursor, a manganese iron phosphate lithium positive electrode material, and a preparation method and application, aiming to significantly improve the specific capacity and cycle performance of manganese iron phosphate lithium batteries.

[0009] In order to achieve the above-mentioned purpose of the present disclosure, the following technical solutions can be adopted:

[0010] In a first aspect, the solution provided by the present disclosure includes a method for preparing a manganese iron phosphate precursor, comprising: mixing aluminum iron phosphate obtained by a coprecipitation method with manganese chloride and a flux, and reacting them at 185°C-300°C.

[0011] In some embodiments of the present disclosure, the process of preparing a ferromanganese phosphate precursor using aluminum ferrophosphate includes: mixing aluminum ferrophosphate with manganese chloride and a flux, reacting at 185°C-300°C to obtain a dihydrate ferromanganese phosphate precursor, and subjecting the dihydrate ferromanganese phosphate precursor to high-temperature treatment to remove the crystalline water in the dihydrate ferromanganese phosphate precursor.

[0012] In some embodiments of the present disclosure, the flux is a mixture of potassium chloride and sodium chloride.

[0013] In some embodiments of the present disclosure, in the flux, the mass fraction of potassium chloride is 40%-55%, and the mass fraction of sodium chloride is 45%-60%.

[0014] In some embodiments of the present disclosure, the molar ratio of aluminum ferric phosphate to the total amount of flux is 1:(0.4-0.8).

[0015] In some embodiments of the present disclosure, the molar ratio of aluminum ferric phosphate to manganese chloride is 1:(1.5-1.7).

[0016] In some embodiments of the present disclosure, aluminum ferric phosphate is mixed with manganese chloride and a flux, reacted in an inert atmosphere at 250° C.-300° C. for 2 h-6 h, and then washed and dried after cooling to obtain a manganese ferrous phosphate dihydrate precursor.

[0017] In some embodiments of the present disclosure, the high temperature treatment process includes: treating the manganese ferrophosphate dihydrate precursor at 600° C.-700° C. for 1 hour-4 hours.

[0018] In some embodiments of the present disclosure, the high temperature treatment is performed under an inert atmosphere.

[0019] In some embodiments of the present disclosure, the process of preparing the aluminum ferric phosphate includes: adding an iron salt solution, an aluminum salt solution, a phosphoric acid solution, and a precipitant solution into a reactor to carry out a co-precipitation reaction.

[0020] In some embodiments of the present disclosure, by controlling the concentrations and addition rates of the iron salt solution, the aluminum salt solution, and the phosphorus source solution, the molar ratio of iron, aluminum, and phosphorus elements in the reaction system is (0.5-0.8): (0.2-0.5): (1.0-1.1).

[0021] In some embodiments of the present disclosure, the reaction temperature of the coprecipitation reaction is 45° C.-90° C., and the reaction time is 3 h-6 h.

[0022] In some embodiments of the present disclosure, the pH value of the co-precipitation reaction system is adjusted to 2.8-3.5 by controlling the addition rate of the precipitant solution.

[0023] In some embodiments of the present disclosure, the precipitant solution is an aqueous ammonia solution with a concentration of 2 mol / L-6 mol / L.

[0024] In some embodiments of the present disclosure, during the coprecipitation reaction, the rotation speed is controlled to be 100 r / min-400 r / min, and washing and drying are performed after the reaction is completed.

[0025] In some embodiments of the present disclosure, the iron salt is selected from at least one of ferric acetate, ferric carbonate, ferric oxalate, ferric chloride, ferric nitrate, and ferric sulfate.

[0026] In some embodiments of the present disclosure, the aluminum salt is selected from at least one of aluminum nitrate, aluminum sulfate, aluminum chloride, and aluminum carbonate.

[0027] In some embodiments of the present disclosure, the phosphorus source is selected from at least one of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, and ammonium dihydrogen phosphate.

[0028] In a second aspect, the solution provided by the present disclosure also includes a ferromanganese phosphate precursor prepared by the preparation method in the above embodiment.

[0029] In a third aspect, the solution provided by the present disclosure also includes a method for preparing a lithium manganese iron phosphate positive electrode material, comprising: utilizing the manganese iron phosphate precursor in the above embodiment and reacting with a lithium source.

[0030] In some embodiments of the present disclosure, the process comprises: mixing a ferromanganese phosphate precursor, a lithium source, and a carbon source and calcining the mixture; controlling the calcination temperature to be 800° C.-900° C.; and calcining the mixture for 6 h-20 h.

[0031] In some embodiments of the present disclosure, the amount of the ferromanganese phosphate precursor and the lithium source is controlled so that the molar ratio of lithium element to the total amount of ferromanganese is (1.0-1.2):1.

[0032] In some embodiments of the present disclosure, the mass ratio of the amount of the carbon source to the total amount of the manganese ferrophosphate precursor and the lithium source is (5-13):100.

[0033] In some embodiments of the present disclosure, the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, and lithium acetate.

[0034] In some embodiments of the present disclosure, the carbon source is selected from at least one of sucrose, glucose, soluble starch, citric acid, phenolic resin, graphite and carbon black.

[0035] In some embodiments of the present disclosure, calcination is performed under inert atmosphere conditions.

[0036] In a third aspect, the solution provided by the present disclosure also includes a lithium manganese iron phosphate positive electrode material prepared by the preparation method in the above embodiment.

[0037] In a fourth aspect, the solution provided by the present disclosure also includes a positive electrode plate, comprising the lithium manganese iron phosphate positive electrode material in the above embodiment.

[0038] In a fifth aspect, the solution provided by the present disclosure also includes a lithium battery, including the positive electrode plate in the above embodiment.

[0039] The present disclosure utilizes the similar Ksp characteristics of iron phosphate and aluminum phosphate precipitation to first synthesize uniform iron aluminum phosphate through coprecipitation, and then uses the iron aluminum phosphate, manganese chloride and flux to react to prepare a stable manganese iron phosphate precursor. The aluminum chloride generated during the reaction can be directly volatilized. The synthesis route provided by the present disclosure can effectively solve the problem of uneven manganese iron phosphate precursor caused by directly coprecipitating manganese phosphate and iron phosphate. The iron-manganese ratio of the prepared manganese iron phosphate precursor is closer to the target value. The specific capacity and cycle performance of the manganese iron lithium phosphate further prepared using this precursor can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0041] FIG1 is a process flow chart of a method for preparing a ferromanganese phosphate precursor provided in an embodiment of the present disclosure;

[0042] FIG2 is a process flow chart of a method for preparing a lithium iron manganese phosphate positive electrode material provided in an embodiment of the present disclosure;

[0043] FIG3 is an EDS graph of the precursor prepared in Example 1. DETAILED DESCRIPTION

[0044] The embodiments of the present disclosure will be described in detail below with reference to the examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present disclosure and should not be construed as limiting the scope of the present disclosure. Where specific conditions are not specified in the examples, the experiments were performed under conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.

[0045] The endpoints of the ranges and any values ​​disclosed in this disclosure are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0046] The present disclosure provides a method for preparing a lithium iron manganese phosphate cathode material. As shown in Figure 1, a ferromanganese phosphate precursor is first synthesized using the synthesis route provided in this disclosure. This improved synthesis route allows for greater precursor uniformity and a closer iron-manganese ratio. In conjunction with Figure 2, the lithium iron manganese phosphate cathode material is prepared by reacting the ferromanganese phosphate precursor with a lithium source, significantly improving the specific capacity and cycle performance of the cathode material.

[0047] The specific steps may include:

[0048] S1. Preparation of aluminum iron phosphate

[0049] Aluminum ferric phosphate is prepared by coprecipitation. The specific operation process is not limited. The metallic iron and aluminum can be precipitated in an aqueous solution by controlling the pH value. Taking advantage of the similar Ksp of the precipitates of iron phosphate and aluminum phosphate, aluminum ferric phosphate is first synthesized by coprecipitation to ensure a uniform mixture of the two.

[0050] In some embodiments of the present disclosure, the process for preparing aluminum ferric phosphate includes adding an iron salt solution, an aluminum salt solution, a phosphoric acid solution, and a precipitant solution to a reactor for a co-precipitation reaction. The iron salt solution, the aluminum salt solution, the phosphorus source solution, and the precipitant solution can be added in parallel, or the iron salt solution and the aluminum salt solution can be mixed first and then added to the reactor in parallel with the phosphorus source solution and the precipitant solution to ensure a more uniform reaction.

[0051] In some embodiments of the present disclosure, the iron salt is selected from at least one of ferric acetate, ferric carbonate, ferric oxalate, ferric chloride, ferric nitrate, and ferric sulfate, and may be any one or more of the above; the aluminum salt is selected from at least one of aluminum nitrate, aluminum sulfate, aluminum chloride, and aluminum carbonate, and may be any one or more of the above; and the phosphorus source is selected from at least one of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, and ammonium dihydrogen phosphate, and may be any one or more of the above. In actual operation, the iron salt, aluminum salt, and phosphorus source can be first mixed and dissolved with water, and the iron salt solution and aluminum salt solution can be first added to the reactor, and then the phosphorus source solution and precipitant solution can be added dropwise.

[0052] Furthermore, the type of the precipitant solution is not limited, and can be an ammonia solution, but is not limited thereto. The concentration of the ammonia solution can be 2 mol / L-6 mol / L, such as 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, etc.

[0053] In some embodiments of the present disclosure, by controlling the concentrations and addition rates of the iron salt solution, aluminum salt solution, and phosphorus source solution, the molar ratio of iron, aluminum, and phosphorus elements in the reaction system is adjusted to (0.5-0.8): (0.2-0.5): (1.0-1.1), so that the positive electrode material finally prepared has better electrochemical properties. Specifically, the molar ratio of iron, aluminum and phosphorus elements can be 0.5:0.5:1.0, 0.6:0.4:1.0, 0.7:0.3:1.0, 0.8:0.2:1.0, 0.5:0.5:1.05, 0.6:0.4:1.05, 0.7:0.3:1.05, 0.8:0.2:1.05, 0.5:0.5:1.1, 0.6:0.4:1.1, 0.7:0.3:1.1, 0.8:0.2:1.1, etc.

[0054] In some embodiments of the present disclosure, the coprecipitation reaction temperature is 45°C-90°C, the reaction time is 3-6 hours, and the rotation speed is controlled at 100-400 rpm. Furthermore, the pH value of the coprecipitation reaction system is adjusted to 2.8-3.5 by controlling the addition rate of the precipitant solution. Further control of the coprecipitation reaction conditions ensures sufficient reaction progress, and washing and drying are performed after completion of the reaction to obtain a uniform product.

[0055] Specifically, the reaction temperature of the coprecipitation reaction can be 45°C, 50°C, 60°C, 70°C, 80°C, 90°C, etc.; the reaction time can be 3h, 4h, 5h, 6h, etc.; the controlled rotation speed can be 100r / min, 200r / min, 300r / min, 400r / min, etc.; the pH value of the coprecipitation reaction system can be 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, etc.

[0056] S2. Preparation of ferromanganese phosphate precursor

[0057] Aluminum ferrophosphate is reacted with manganese chloride to prepare a ferromanganese phosphate precursor, and a stable ferromanganese phosphate precursor is prepared by reacting aluminum ferrophosphate and manganese chloride. The aluminum chloride generated during the reaction can be directly volatilized.

[0058] It should be noted that if manganese phosphate and iron phosphate are directly co-precipitated, the problem of uneven manganese iron phosphate precursor will occur. The synthesis route provided by the present invention can effectively avoid the above problem. The iron-manganese ratio of the prepared manganese iron phosphate precursor is closer to the target value, and the specific capacity and cycle performance of the manganese iron lithium phosphate further prepared using the precursor can be effectively improved.

[0059] In some embodiments of the present disclosure, the process of preparing a ferromanganese phosphate precursor using aluminum ferrophosphate includes: mixing aluminum ferrophosphate with manganese chloride and a flux, reacting at 185°C to 300°C to obtain a ferromanganese phosphate dihydrate precursor, and subjecting the ferromanganese phosphate dihydrate precursor to a high-temperature treatment to remove water of crystallization from the ferromanganese phosphate dihydrate precursor to obtain the ferromanganese phosphate precursor. The addition of the flux can lower the eutectic point, allowing the reaction to proceed at a lower temperature, and forming a relatively stable ferromanganese phosphate precursor after the low-temperature heat treatment.

[0060] Specifically, the reaction temperature for preparing the manganese ferrophosphate dihydrate precursor can be 185° C., 200° C., 250° C., 300° C., etc.

[0061] In some embodiments of the present disclosure, the flux is a mixture of potassium chloride and sodium chloride. Using a mixture of potassium chloride and sodium chloride can effectively reduce the reaction temperature. Furthermore, in the flux, the mass fraction of potassium chloride is 40%-55%, such as 40%, 45%, 50%, 55%, etc., and the mass fraction of sodium chloride is 45%-60%, such as 45%, 50%, 55%, 60%, etc., and the total amount of potassium chloride and sodium chloride is 100%.

[0062] In some embodiments of the present disclosure, the molar ratio of aluminum iron phosphate to the total amount of flux is 1: (0.4-0.8), and the molar ratio of aluminum iron phosphate to manganese chloride is 1: (1.5-1.7). By further controlling the amount of raw materials, the uniformity of the prepared precursor is improved, thereby improving the electrochemical performance of the positive electrode material finally prepared. Specifically, the molar ratio of aluminum iron phosphate to the total amount of flux can be 1: 0.4, 1: 0.5, 1: 0.6, 1: 0.7, 1: 0.8, etc., and the molar ratio of aluminum iron phosphate to the manganese element in manganese chloride can be 1: 1.5, 1: 1.6, 1: 1.7, etc.

[0063] In the process of synthesizing the manganese ferrophosphate dihydrate precursor, the specific operation process can be as follows: aluminum ferrophosphate is mixed with manganese chloride and a flux, reacted under an inert atmosphere (such as nitrogen, argon, etc.) at 250°C-300°C for 2h-6h, and then washed and dried after cooling to obtain the manganese ferrophosphate dihydrate precursor. Specifically, the reaction time can be 2h, 3h, 4h, 5h, 6h, etc.

[0064] In some embodiments of the present disclosure, the high-temperature treatment process includes treating the manganese ferrophosphate dihydrate precursor at 600°C to 700°C for 1 to 4 hours under an inert atmosphere (such as nitrogen, argon, etc.) to fully remove the crystallized water in the precursor. Specifically, the treatment temperature can be 600°C, 650°C, 700°C, etc., and the treatment time can be 1 hour, 2 hours, 3 hours, 4 hours, etc.

[0065] S3. Preparation of lithium manganese iron phosphate positive electrode material

[0066] The manganese iron phosphate precursor prepared in S2 is reacted with a lithium source to prepare a manganese iron phosphate lithium positive electrode material.

[0067] In some embodiments of the present disclosure, a ferromanganese phosphate precursor, a lithium source, and a carbon source are mixed and calcined at a temperature of 800°C to 900°C for 6 to 20 hours. The ferromanganese phosphate precursor is doped with lithium and a carbon source and calcined at high temperature to produce a lithium ferromanganese phosphate cathode material. The carbon source is carbonized and coated on the surface of the lithium ferromanganese phosphate, further stabilizing the crystal structure of the lithium ferromanganese phosphate.

[0068] Specifically, the calcination temperature can be 800° C., 850° C., 900° C., etc., and the calcination time can be 6 h, 8 h, 10 h, 15 h, 20 h, etc.

[0069] In some embodiments of the present disclosure, the amounts of the ferromanganese phosphate precursor and the lithium source are controlled to achieve a molar ratio of lithium to the total amount of ferromanganese of (1.0-1.2):1, and a mass ratio of the carbon source to the total amount of the ferromanganese phosphate precursor and the lithium source of (5-13):100. Further controlling the ratio of the raw materials allows for a more complete reaction and a more appropriate amount of carbon coating, which helps further improve the cycling performance of the positive electrode material.

[0070] Specifically, by controlling the amount of ferromanganese phosphate precursor and lithium source, the molar ratio of lithium element to the total amount of ferromanganese can be 1.0:1, 1.1:1, 1.2:1, etc.; the mass ratio of the amount of carbon source to the total amount of ferromanganese phosphate precursor and lithium source can be 5:100, 8:100, 10:100, 13:100, etc.

[0071] In some embodiments of the present disclosure, the lithium source is selected from at least one of lithium carbonate, lithium hydroxide and lithium acetate, and may be any one or more of the above; the carbon source is selected from at least one of sucrose, glucose, soluble starch, citric acid, phenolic resin, graphite and carbon black, and may be any one or more of the above.

[0072] In some embodiments of the present disclosure, calcination is performed under an inert atmosphere. The type of inert atmosphere is not limited and may be nitrogen, argon, or the like.

[0073] It should be added that the preparation method of the lithium manganese iron phosphate positive electrode material provided in the embodiment of the present disclosure avoids the shortcomings of the traditional process such as high process cost and relatively complex process, can greatly reduce energy consumption, reduce synthesis cost and simplify the production process.

[0074] The disclosed embodiments also provide a lithium iron manganese phosphate positive electrode material, which is prepared by the above-mentioned preparation method, and can obtain lithium iron manganese phosphate with a target iron-manganese ratio, and can also improve the compaction density and energy density.

[0075] The present disclosure also provides a positive electrode sheet comprising the aforementioned lithium iron manganese phosphate positive electrode material. Conventional methods can be used to prepare the positive electrode sheet, such as by combining the lithium iron manganese phosphate positive electrode material with a conductive agent, a dispersant, a binder, and the like to form a positive electrode slurry, applying the positive electrode slurry to a positive electrode current collector, and drying the resulting coating. Due to the improved performance of the positive electrode material, the electrochemical performance of the resulting positive electrode sheet is also improved.

[0076] The present disclosure also provides a lithium battery comprising the aforementioned positive electrode sheet, and further comprising a negative electrode sheet, an electrolyte, a separator, etc., to form a complete lithium battery. Due to the improved performance of the positive electrode material, the lithium battery has even better electrochemical performance.

[0077] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0078] Example 1

[0079] This embodiment provides a method for preparing a manganese iron phosphate precursor and a manganese iron phosphate lithium positive electrode material, comprising the following steps:

[0080] (1) 0.5 mol / L ferric sulfate aqueous solution, 0.5 mol / L aluminum sulfate aqueous solution, 1 mol / L phosphoric acid aqueous solution, and 4 mol / L ammonia aqueous solution were prepared respectively, and the four solutions were added into a coprecipitation reactor in parallel under stirring for coprecipitation reaction, and the flow rates of ferric sulfate aqueous solution, aluminum sulfate aqueous solution, and phosphoric acid aqueous solution were controlled to be 120 mL / min. By controlling the addition rate of ammonia water, the pH of the reaction solution was adjusted to 3.1±0.2, the reaction temperature was 70°C, the stirring speed was 200 r / min, and after reacting for 4 hours, the mixture was washed with deionized water and dried at 80°C for 6 hours to obtain aluminum ferric phosphate.

[0081] (2) The aluminum ferric phosphate, manganese chloride and flux in step (1) are mixed uniformly in a molar ratio of 1:1.6:0.6, placed in a muffle furnace, introduced with nitrogen, and kept warm at a temperature of 250°C for 4 hours. After cooling with the furnace, the mixture is washed with deionized water and dried at a temperature of 100°C for 4 hours to obtain a dihydrated manganese ferrophosphate precursor. The flux is a mixture of 50% by mass of potassium chloride and 50% by mass of sodium chloride. Under a nitrogen atmosphere, the dihydrated manganese ferrophosphate precursor is kept warm at a temperature of 650°C for 3 hours to remove the crystallization water of the dihydrated manganese ferrophosphate precursor to obtain a manganese ferrophosphate precursor.

[0082] (3) Weigh lithium carbonate and the ferromanganese phosphate precursor in step (2), mix them evenly in a molar ratio of lithium source to ferromanganese phosphate precursor of 1.2:1, add 7wt% of sucrose (i.e., the mass ratio of sucrose to the total amount of lithium source and ferromanganese phosphate precursor is 7:100), heat to 850°C in a nitrogen atmosphere and calcine for 10h, and then cool to room temperature to obtain lithium ferromanganese phosphate positive electrode material.

[0083] The EDS graph of the precursor prepared in Example 1 is shown in FIG3 . It can be seen from the EDS graph that the manganese and iron elements are evenly distributed in the prepared precursor, and the atomic percentage contents of manganese, iron, phosphorus, and oxygen in the precursor are 20.83%, 19.10%, 19.61%, and 40.46%, respectively.

[0084] Example 2

[0085] This embodiment provides a method for preparing a manganese iron phosphate precursor and a manganese iron phosphate lithium positive electrode material, comprising the following steps:

[0086] (1) 0.6 mol / L ferric nitrate aqueous solution, 0.4 mol / L aluminum nitrate aqueous solution, 1.1 mol / L ammonium dihydrogen phosphate aqueous solution, and 2 mol / L ammonia aqueous solution were prepared respectively, and the four solutions were added into a coprecipitation reactor in parallel under stirring for coprecipitation reaction, and the flow rates of ferric sulfate aqueous solution, aluminum sulfate aqueous solution, and phosphoric acid aqueous solution were controlled to be 120 mL / min. By controlling the addition rate of ammonia aqueous solution, the pH of the reaction solution was adjusted to 2.8 ± 0.2, the reaction temperature was 90 ° C, the stirring speed was 400 r / min, and after reacting for 3 hours, the solution was washed with deionized water and dried at 80 ° C for 6 hours to obtain aluminum ferric phosphate.

[0087] (2) The aluminum ferric phosphate, manganese chloride and flux in step (1) are mixed uniformly in a molar ratio of 1:1.7:0.8, placed in a muffle furnace, introduced with nitrogen, and kept warm at 300°C for 2 hours. After cooling with the furnace, the mixture is washed with deionized water and dried at 100°C for 4 hours to obtain a dihydrated manganese ferrophosphate precursor. The flux is a mixture of 55% by mass of potassium chloride and 45% by mass of sodium chloride. Under a nitrogen atmosphere, the dihydrated manganese ferrophosphate precursor is kept warm at 700°C for 1 hour to remove the crystal water of the dihydrated manganese ferrophosphate precursor to obtain a manganese ferrophosphate precursor.

[0088] (4) Weigh lithium carbonate and the manganese iron phosphate precursor in step (3), mix them evenly in a molar ratio of lithium source to manganese iron phosphate precursor of 1.2:1, add 13 wt% of sucrose, heat to 900 ° C in a nitrogen atmosphere and calcine for 6 h, and then cool to room temperature to obtain a lithium manganese iron phosphate positive electrode material.

[0089] Example 3

[0090] This embodiment provides a method for preparing a manganese iron phosphate precursor and a manganese iron phosphate lithium positive electrode material, comprising the following steps:

[0091] (1) 0.8 mol / L ferric sulfate aqueous solution, 0.2 mol / L aluminum sulfate aqueous solution, 1.1 mol / L phosphoric acid aqueous solution, and 6 mol / L ammonia aqueous solution were prepared respectively, and the four solutions were added to a coprecipitation reactor in parallel under stirring for coprecipitation reaction, and the flow rates of the ferric sulfate aqueous solution, aluminum sulfate aqueous solution, and phosphoric acid aqueous solution were controlled to be 120 mL / min. By controlling the addition rate of ammonia water, the pH of the reaction solution was adjusted to 3.5±0.2, the reaction temperature was 45°C, the stirring speed was 100 r / min, and after reacting for 6 hours, the mixture was washed with deionized water and dried at 80°C for 6 hours to obtain aluminum ferric phosphate.

[0092] (2) The aluminum ferric phosphate, manganese chloride and flux in step (1) are mixed uniformly in a molar ratio of 1:1.5:0.4, placed in a muffle furnace, introduced with nitrogen, and kept warm at 185°C for 6 hours. After cooling with the furnace, the mixture is washed with deionized water and dried at 100°C for 4 hours to obtain a dihydrated manganese ferrophosphate precursor. The flux is a mixture of 40% by mass of potassium chloride and 60% by mass of sodium chloride. Under a nitrogen atmosphere, the dihydrated manganese ferrophosphate precursor is kept warm at 600°C for 4 hours to remove the crystallization water of the dihydrated manganese ferrophosphate precursor to obtain a manganese ferrophosphate precursor.

[0093] (3) Weigh lithium carbonate and the manganese iron phosphate precursor in step (2), mix them evenly in a molar ratio of lithium source to manganese iron phosphate precursor of 1:1, add 5wt% of sucrose, heat to 800°C in a nitrogen atmosphere and calcine for 20h, and then cool to room temperature to obtain a lithium manganese iron phosphate positive electrode material.

[0094] Example 4

[0095] The only difference from Example 1 is that the cosolvent in step (2) is replaced by sodium chloride.

[0096] Example 5

[0097] The only difference from Example 1 is that the reaction temperature in step (2) is 400°C.

[0098] Comparative Example 1

[0099] This comparative example provides a method for preparing a lithium manganese iron phosphate positive electrode material, comprising the following steps:

[0100] (1) 0.5 mol / L ferric sulfate aqueous solution, 0.5 mol / L manganese sulfate aqueous solution, 1 mol / L phosphoric acid aqueous solution, and 4 mol / L ammonia aqueous solution were prepared respectively, and the four solutions were added to a coprecipitation reactor in parallel under stirring for coprecipitation reaction. The ratio of metal salts Fe and Mn was maintained at 1:1 by controlling the flow rate. The pH of the reaction solution was adjusted to 3.1±0.2 by controlling the addition rate of ammonia water. The reaction temperature was 70°C, the stirring speed was 200 r / min, and after reacting for 4 hours, the mixture was washed with deionized water and dried at 80°C for 6 hours to obtain a manganese iron phosphate precursor.

[0101] (2) Weigh lithium carbonate and the manganese iron phosphate precursor in step (1), mix them evenly in a molar ratio of lithium source to manganese iron phosphate precursor of 1.2:1, add 7wt% of sucrose, heat to 850°C in a nitrogen atmosphere and calcine for 10h, and then cool to room temperature to obtain a lithium manganese iron phosphate positive electrode material.

[0102] Comparative Example 2

[0103] This comparative example provides a method for preparing a lithium manganese iron phosphate positive electrode material, comprising the following steps:

[0104] Lithium carbonate, ferric sulfate, manganese nitrate and ammonium phosphate were used as raw materials. The raw materials were weighed according to the stoichiometric ratio of lithium, iron, manganese and phosphorus of 1.2:0.5:0.5:1. After mixing evenly, 7% sucrose was added as a carbon source. According to the high-temperature solid-phase synthesis route, the materials were calcined at 850°C for 20 hours under nitrogen atmosphere to obtain lithium manganese iron phosphate positive electrode material. The molar ratio of iron and manganese elements in the product was 1:1.

[0105] Comparative Example 3

[0106] The only difference from Example 1 is that no flux is added in step (2).

[0107] Comparative Example 4

[0108] The only difference from Example 1 is that the reaction temperature in step (2) is 170°C.

[0109] Test Example 1

[0110] The performance of the lithium manganese iron phosphate positive electrode materials prepared in the test examples and comparative examples are shown in Table 1.

[0111] Testing Method: The lithium manganese iron phosphate cathode material obtained in the Examples and Comparative Examples was mixed with acetylene black as a conductive agent and PVDF as a binder in a mass ratio of 8:1:1. A certain amount of the organic solvent NMP was added, stirred, and coated onto aluminum foil to form a positive electrode sheet. A metallic lithium sheet was used as the negative electrode; the separator was a Celgard 2400 polypropylene porous membrane; the electrolyte consisted of a solution of EC, DMC, and EMC in a mass ratio of 1:1:1, with LiPF6 as the solute at a LiPF6 concentration of 1.0 mol / L. 2023 button-type cells were assembled in a glove box. The batteries were subjected to charge and discharge cycle performance testing, measuring the 0.1C and 1C discharge capacities within a cutoff voltage range of 2.2 to 4.3 V. The electrochemical performance results are shown in Table 1.

[0112] Table 1 Basic properties of lithium manganese iron phosphate materials

[0113] Examples 1-7 are lithium manganese iron phosphate prepared by the present invention, and comparative examples 1-2 are lithium manganese iron phosphate prepared by conventional methods. From the data, it can be seen that the lithium manganese iron phosphate positive electrode material disclosed in the present invention has a high compaction density, and its application in lithium-ion batteries can significantly increase the specific capacity of lithium-ion batteries and improve the cycle performance of lithium-ion batteries. Industrial Applicability

[0114] This disclosure utilizes the similar Ksp properties of ferric phosphate and aluminum phosphate precipitations to first synthesize aluminum ferric phosphate via a coprecipitation method, achieving a uniform mixing of the two. The aluminum ferric phosphate is then reacted with manganese chloride to produce a stable ferromanganese phosphate precursor. The aluminum chloride generated during the reaction can be directly volatilized. The lithium ferromanganese phosphate cathode material is obtained by doping the lithium ferromanganese phosphate precursor with lithium and adding a carbon source, followed by high-temperature calcination. This method offers the advantages of low process cost and ease of implementation, making it suitable for industrial applications.

Claims

1. A method for preparing a ferromanganese phosphate precursor, characterized in that: include: The aluminum iron phosphate obtained by the coprecipitation method is mixed with manganese chloride and a flux and reacted at 185°C-300°C.

2. The preparation method according to claim 1, characterized in that: The process of preparing the ferromanganese phosphate precursor using the aluminum ferrophosphate includes: mixing the aluminum ferrophosphate with manganese chloride and a flux, reacting at 185°C-300°C to obtain a dihydrate ferromanganese phosphate precursor, and subjecting the dihydrate ferromanganese phosphate precursor to high-temperature treatment to remove the crystal water in the dihydrate ferromanganese phosphate precursor.

3. The preparation method according to claim 2, characterized in that: The flux is a mixture of potassium chloride and sodium chloride.

4. The preparation method according to claim 3, characterized in that: In the flux, the mass fraction of potassium chloride is 40%-55%, and the mass fraction of sodium chloride is 45%-60%.

5. The preparation method according to any one of claims 2 to 4, characterized in that: The molar ratio of the aluminum iron phosphate to the total amount of the flux is 1: (0.4-0.8).

6. The preparation method according to any one of claims 2 to 5, characterized in that: The molar ratio of the aluminum iron phosphate to the manganese chloride is 1:(1.5-1.7).

7. The preparation method according to any one of claims 2 to 6, characterized in that: The aluminum iron phosphate is mixed with the manganese chloride and the flux, and reacted for 2h-6h under an inert atmosphere at 250° C.-300° C., and then washed and dried after cooling to obtain the manganese iron phosphate dihydrate precursor.

8. The preparation method according to any one of claims 2 to 7, characterized in that: The high temperature treatment process includes: treating the manganese ferrophosphate dihydrate precursor at 600° C.-700° C. for 1 h-4 h.

9. The preparation method according to claim 8, characterized in that: The high temperature treatment is performed under an inert atmosphere.

10. The preparation method according to any one of claims 1 to 9, characterized in that: The process of preparing the aluminum iron phosphate comprises: adding an iron salt solution, an aluminum salt solution, a phosphoric acid solution and a precipitant solution into a reactor for a co-precipitation reaction.

11. The preparation method according to claim 10, characterized in that: By controlling the concentrations and addition rates of the iron salt solution, the aluminum salt solution and the phosphorus source solution, the molar ratio of iron, aluminum and phosphorus elements in the reaction system is (0.5-0.8): (0.2-0.5): (1.0-1.1).

12. The preparation method according to claim 10 or 11, characterized in that: The reaction temperature of the coprecipitation reaction is 45° C.-90° C., and the reaction time is 3 h-6 h.

13. The preparation method according to any one of claims 10 to 12, characterized in that: By controlling the adding rate of the precipitant solution, the pH value of the coprecipitation reaction system is adjusted to 2.8-3.

5.

14. The preparation method according to claim 13, characterized in that: The precipitant solution is an aqueous ammonia solution with a concentration of 2 mol / L-6 mol / L.

15. The preparation method according to any one of claims 10 to 14, characterized in that: During the coprecipitation reaction, the rotation speed is controlled to be 100 r / min-400 r / min, and washing and drying are performed after the reaction is completed.

16. The preparation method according to any one of claims 10 to 15, characterized in that: The iron salt is selected from at least one of ferric acetate, ferric carbonate, ferric oxalate, ferric chloride, ferric nitrate and ferric sulfate.

17. The preparation method according to any one of claims 10 to 16, characterized in that: The aluminum salt is selected from at least one of aluminum nitrate, aluminum sulfate, aluminum chloride and aluminum carbonate.

18. The preparation method according to any one of claims 10 to 17, characterized in that: The phosphorus source is selected from at least one of phosphoric acid, ammonium phosphate, diammonium phosphate and diammonium phosphate.

19. A ferromanganese phosphate precursor, characterized in that: It is prepared by the preparation method described in any one of claims 1 to 18.

20. A method for preparing a lithium manganese iron phosphate positive electrode material, characterized in that: include: The ferromanganese phosphate precursor of claim 19 is reacted with a lithium source.

21. The preparation method according to claim 20, characterized in that: include: The ferromanganese phosphate precursor, lithium source and carbon source are mixed and calcined, and the calcination temperature is controlled to be 800° C.-900° C. and the calcination time is 6 h-20 h.

22. The preparation method according to claim 20 or 21, characterized in that: By controlling the dosage of the ferromanganese phosphate precursor and the lithium source, the molar ratio of lithium element to the total amount of ferromanganese is (1.0-1.2):

1.

23. The preparation method according to claim 21 or 22, characterized in that: The mass ratio of the amount of the carbon source to the total amount of the ferromanganese phosphate precursor and the lithium source is (5-13):

100.

24. The preparation method according to any one of claims 20 to 23, characterized in that: The lithium source is selected from at least one of lithium carbonate, lithium hydroxide and lithium acetate.

25. The preparation method according to any one of claims 21 to 24, characterized in that: The carbon source is selected from at least one of sucrose, glucose, soluble starch, citric acid, phenolic resin, graphite and carbon black.

26. The preparation method according to any one of claims 21 to 25, characterized in that: Calcination is carried out under inert atmosphere.

27. A lithium manganese iron phosphate positive electrode material, characterized in that: It is prepared by the preparation method described in any one of claims 20-26.

28. A positive electrode plate, characterized in that: Including the lithium manganese iron phosphate positive electrode material described in claim 27.

29. A lithium battery, characterized in that: Includes the positive electrode sheet as described in claim 28.

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