Ferromanganese phosphate precursor, lithium ferromanganese phosphate positive electrode material, preparation method and application thereof

Abstract

The present disclosure belongs to the field of lithium battery technology, and specifically relates to a ferromanganese phosphate precursor, a lithium iron manganese phosphate positive electrode material, and a preparation method and application. The present disclosure utilizes the similar Ksp characteristics of iron phosphate and aluminum phosphate precipitation, and first synthesizes aluminum iron phosphate by coprecipitation, so that the aluminum iron phosphate is evenly mixed, and then uses aluminum iron phosphate and manganese chloride to react to prepare a stable ferromanganese phosphate precursor, and 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 ferromanganese phosphate precursor caused by directly using manganese phosphate and iron phosphate for coprecipitation. The iron-manganese ratio of the prepared ferromanganese phosphate precursor is closer to the target value, and the specific capacity and cycle performance of the lithium iron manganese phosphate further prepared using the precursor can be effectively improved. The entire process is simple and easy to operate, with low process cost, and has very good prospects for industrial application.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of lithium batteries, and in particular, 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 are used more and more widely in society, people's requirements for batteries are becoming more and more diverse, such as higher energy density, higher rate performance, and good low-temperature performance. The energy density of lithium-ion batteries depends on the battery materials. Currently, the commonly used positive electrode materials for lithium-ion batteries include ternary materials (such as lithium nickel cobalt manganese oxide) and lithium iron phosphate. At present, the energy density of lithium iron phosphate batteries has approached the limit of the theoretical value, and there is relatively little room for improvement. In order to further improve the electrochemical performance of lithium-ion batteries, in recent years, people have considered selecting lithium manganese phosphate, a polyanion material with an olivine structure, to replace lithium iron phosphate batteries. However, the electronic conductivity and ion diffusion coefficient of lithium manganese phosphate are lower than those of lithium iron phosphate, which limits the application of batteries at high rates and low temperatures. At the same time, manganese ions have problems such as 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, x is the atomic ratio) material is a more effective method. Compared with lithium iron phosphate, lithium manganese iron phosphate has the same crystal structure, and because it contains manganese ions, the battery discharge voltage is higher (can be 4.1V), making the energy density of lithium manganese iron phosphate about 20% higher than that of lithium iron phosphate. Therefore, this solid solution material is expected to replace lithium iron phosphate as the next generation of lithium-ion battery positive electrode material for large-scale application.

[0004] At present, the method of mass production of lithium iron manganese phosphate is mostly a high-temperature solid phase method: the raw materials such as 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, it is difficult to accurately control the ratio of iron and manganese in this method, 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 to form ferromanganese phosphate precursor in a conventional liquid phase reaction system. Although some scholars have successfully synthesized ferromanganese phosphate precursors 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. Summary of the invention

[0007] 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 a manganese iron phosphate lithium battery.

[0008] In order to achieve the above-mentioned purpose of the present disclosure, the following technical solutions can be adopted:

[0009] In a first aspect, the solution provided by the present disclosure includes a method for preparing a ferromanganese phosphate precursor, comprising: mixing aluminum ferrophosphate obtained by a coprecipitation method with manganese chloride and a flux, and reacting them at 185°C-300°C.

[0010] 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 crystal water in the dihydrate ferromanganese phosphate precursor.

[0011] In some embodiments of the present disclosure, the flux is a mixture of potassium chloride and sodium chloride.

[0012] 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%.

[0013] 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).

[0014] In some embodiments of the present disclosure, the molar ratio of aluminum iron phosphate to manganese chloride is 1:(1.5-1.7).

[0015] In some embodiments of the present disclosure, aluminum ferric phosphate is mixed with manganese chloride and a flux, reacted for 2h-6h under an inert atmosphere at 250°C-300°C, and washed and dried after cooling to obtain a manganese ferrophosphate dihydrate precursor.

[0016] 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 h-4 h.

[0017] In some embodiments of the present disclosure, the high temperature treatment is performed under an inert atmosphere.

[0018] In some embodiments of the present disclosure, the process of preparing the aluminum iron phosphate includes: 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.

[0019] 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).

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] In some embodiments of the present disclosure, the iron salt is selected from at least one of iron acetate, iron carbonate, iron oxalate, iron chloride, iron nitrate and iron sulfate.

[0025] 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.

[0026] In some embodiments of the present disclosure, the phosphorus source is selected from at least one of phosphoric acid, ammonium phosphate, diammonium phosphate and diammonium phosphate.

[0027] In a second aspect, the solution provided in the present disclosure also includes a ferromanganese phosphate precursor prepared by the preparation method in the above embodiment.

[0028] In a third aspect, the solution provided by the present disclosure also includes a method for preparing a lithium iron manganese phosphate positive electrode material, comprising: utilizing the iron manganese phosphate precursor and a lithium source reaction in the above-mentioned embodiment.

[0029] In some embodiments of the present disclosure, the process comprises: mixing and calcining a ferromanganese phosphate precursor, a lithium source and a carbon source, controlling the calcination temperature to be 800° C.-900° C., and the calcination time to be 6 h-20 h.

[0030] In some embodiments of the present disclosure, the molar ratio of lithium element to the total amount of ferromanganese phosphate is (1.0-1.2):1 by controlling the dosage of ferromanganese phosphate precursor and lithium source.

[0031] In some embodiments of the present disclosure, 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.

[0032] In some embodiments of the present disclosure, the lithium source is selected from at least one of lithium carbonate, lithium hydroxide and lithium acetate.

[0033] 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.

[0034] In some embodiments of the present disclosure, calcination is performed under inert atmosphere conditions.

[0035] 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.

[0036] In a fourth aspect, the solution provided by the present disclosure also includes a positive electrode plate, including the lithium manganese iron phosphate positive electrode material in the above embodiment.

[0037] 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.

[0038] The present disclosure utilizes the similar Ksp characteristics of iron phosphate and aluminum phosphate precipitation, first synthesizes uniform iron aluminum phosphate by coprecipitation, and then uses iron aluminum phosphate, manganese chloride and flux to react to prepare a stable ferromanganese phosphate precursor, and 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 ferromanganese phosphate precursor caused by directly coprecipitating manganese phosphate and iron phosphate, and the iron-manganese ratio of the prepared ferromanganese phosphate precursor is closer to the target value, and the specific capacity and cycle performance of lithium iron manganese phosphate further prepared using the precursor can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, 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 disclosure 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.

[0040] Figure 1 A process flow chart of a method for preparing a ferromanganese phosphate precursor provided in an embodiment of the present disclosure;

[0041] Figure 2 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;

[0042] Figure 3 This is the EDS image of the precursor prepared in Example 1. DETAILED DESCRIPTION

[0043] The embodiments of the present disclosure will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present disclosure and should not be considered to limit the scope of the present disclosure. Where specific conditions are not specified in the examples, they are carried out under conventional conditions or conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be purchased commercially.

[0044] The endpoints and any values ​​of the ranges 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 endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0045] The present disclosure provides a method for preparing a lithium iron manganese phosphate positive electrode material, such as Figure 1 As shown, the ferromanganese phosphate precursor is first synthesized using the synthesis route provided by the present disclosure. Due to the improvement of the synthesis route, the precursor can be more uniform and the iron-manganese ratio is closer to the target value. Figure 2 The preparation of lithium iron manganese phosphate positive electrode material by reacting iron manganese phosphate precursor and lithium source can significantly improve the specific capacity and cycle performance of the positive electrode material.

[0046] The specific steps may include:

[0047] S1. Preparation of aluminum iron phosphate

[0048] Aluminum ferric phosphate is prepared by coprecipitation method. The specific operation process is not limited. Metal iron and aluminum can be precipitated by controlling the pH value in an aqueous solution system. Taking advantage of the similar Ksp characteristics of ferrous phosphate and aluminum phosphate precipitation, aluminum ferric phosphate is first synthesized by coprecipitation method to make the ferrous phosphate and aluminum phosphate evenly mixed.

[0049] In some embodiments of the present disclosure, the process of preparing aluminum iron phosphate includes: adding an iron salt solution, an aluminum salt solution, a phosphoric acid solution and a precipitant solution into a reactor for a coprecipitation 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, so that the reaction proceeds more uniformly.

[0050] In some embodiments of the present disclosure, the iron salt is selected from at least one of iron acetate, iron carbonate, iron oxalate, iron chloride, iron nitrate and iron 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; the phosphorus source is selected from at least one of phosphoric acid, ammonium phosphate, diammonium phosphate and diammonium phosphate, and may be any one or more of the above. In actual operation, the iron salt, aluminum salt and phosphorus source can be mixed and dissolved with water respectively, the iron salt solution and the aluminum salt solution are first added to the reactor, and then the phosphorus source solution and the precipitant solution are added dropwise.

[0051] Furthermore, the type of the precipitant solution is not limited, and may be an aqueous ammonia solution, but is not limited thereto. The concentration of the aqueous ammonia solution may 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.

[0052] In some embodiments of the present disclosure, by controlling the concentration and addition rate 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), so that the finally prepared positive electrode material 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.

[0053] In some embodiments of the present disclosure, the reaction temperature of the coprecipitation reaction is 45°C-90°C, the reaction time is 3h-6h, and the rotation speed is controlled to be 100r / min-400r / min; at the same time, the pH value of the coprecipitation reaction system is 2.8-3.5 by controlling the addition rate of the precipitant solution. By further controlling the reaction conditions of the coprecipitation, the reaction is fully carried out, and washing and drying are performed after the reaction is completed to obtain a uniform product.

[0054] 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.

[0055] S2. Preparation of ferromanganese phosphate precursor

[0056] Aluminum iron phosphate is reacted with manganese chloride to prepare a ferromanganese phosphate precursor, and a stable ferromanganese phosphate precursor is prepared by reacting aluminum iron phosphate and manganese chloride. The aluminum chloride generated during the reaction can be directly volatilized.

[0057] It should be noted that if manganese phosphate and iron phosphate are directly used for co-precipitation, it will lead to the problem of uneven manganese iron phosphate precursor. 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. The specific capacity and cycle performance of lithium manganese iron phosphate further prepared using the precursor can be effectively improved.

[0058] 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 crystal water in the dihydrate ferromanganese phosphate precursor to obtain the ferromanganese phosphate precursor. The addition of the flux can reduce the eutectic point, so that the reaction can be carried out at a lower temperature, and a relatively stable ferromanganese phosphate precursor is formed after low-temperature heat treatment.

[0059] Specifically, the reaction temperature for preparing the manganese ferrophosphate dihydrate precursor can be 185° C., 200° C., 250° C., 300° C., etc.

[0060] In some embodiments of the present disclosure, the flux is a mixture of potassium chloride and sodium chloride, and the use of a mixture of potassium chloride and sodium chloride can effectively reduce the reaction temperature. Further, in the flux, the mass fraction of potassium chloride is 40%-55%, such as 40%, 45%, 50%, 55%, etc., 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%.

[0061] 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 cathode 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.

[0062] 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 flux, reacted for 2h-6h under an inert atmosphere (such as nitrogen, argon, etc.) at 250°C-300°C, and washed and dried after cooling to obtain the manganese ferrophosphate dihydrate precursor. Specifically, the reaction time can be 2h, 3h, 4h, 5h, 6h, etc.

[0063] 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 1h-4h under an inert atmosphere (such as nitrogen, argon, etc.) to fully remove the crystal water in the precursor. Specifically, the treatment temperature can be 600°C, 650°C, 700°C, etc., and the treatment time can be 1h, 2h, 3h, 4h, etc.

[0064] S3. Preparation of lithium manganese iron phosphate positive electrode material

[0065] The manganese iron phosphate precursor prepared in S2 is reacted with a lithium source to prepare a manganese iron phosphate lithium positive electrode material.

[0066] In some embodiments of the present disclosure, the process comprises: mixing and calcining a ferromanganese phosphate precursor, a lithium source and a carbon source, controlling the calcination temperature to be 800°C-900°C, and the calcination time to be 6h-20h. Lithium is added to the ferromanganese phosphate precursor and a carbon source is added for high temperature calcination to obtain a lithium ferromanganese phosphate positive electrode material, and the carbon source is carbonized and coated on the surface of the lithium ferromanganese phosphate to further stabilize the crystal structure of the lithium ferromanganese phosphate.

[0067] 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.

[0068] In some embodiments of the present disclosure, 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, and the mass ratio of the dosage of the carbon source to the total amount of the ferromanganese phosphate precursor and the lithium source is (5-13): 100. By further controlling the dosage ratio of the raw materials, the reaction is more complete and the carbon coating amount is more appropriate, which is conducive to further improving the cycle performance of the positive electrode material.

[0069] 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.

[0070] 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.

[0071] In some embodiments of the present disclosure, calcination is performed under an inert atmosphere. The type of the inert atmosphere is not limited and may be nitrogen, argon, or the like.

[0072] It should be added that the method for preparing 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, and can greatly reduce energy consumption, reduce synthesis cost and simplify the production process.

[0073] The disclosed embodiment also provides 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.

[0074] The embodiment of the present disclosure also provides a positive electrode sheet, including the above-mentioned lithium iron manganese phosphate positive electrode material, which can be prepared by conventional preparation methods, such as forming a positive electrode slurry with the lithium iron manganese phosphate positive electrode material and a conductive agent, a dispersant, a binder, etc., and applying the positive electrode slurry on the positive electrode collector to form a coating after drying. Due to the improved performance of the positive electrode material, the electrochemical performance of the prepared positive electrode sheet is also improved.

[0075] The disclosed embodiment also provides a lithium battery, including the above-mentioned positive electrode plate, and may also include a negative electrode plate, an electrolyte, a separator, etc. to form a complete lithium battery. Due to the improvement of the performance of the positive electrode material, the lithium battery has better electrochemical performance.

[0076] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0077] Example 1

[0078] 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:

[0079] (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 co-precipitation reactor in parallel under stirring for co-precipitation reaction, and the flow rates of the ferric sulfate aqueous solution, the aluminum sulfate aqueous solution, and the phosphoric acid aqueous solution were controlled to be 120 mL / min. 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. and the stirring rate was 200 r / min. After reacting for 4 hours, the mixture was washed with deionized water and dried at 80° C. for 6 hours to obtain aluminum iron phosphate.

[0080] (2) The aluminum iron phosphate, manganese chloride and flux in step (1) are mixed uniformly at 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, washed with deionized water after cooling with the furnace, and dried at a temperature of 100°C for 4 hours to obtain a dihydrate manganese iron phosphate precursor. The flux is a mixture of 50% by mass potassium chloride and 50% by mass sodium chloride. In a nitrogen atmosphere, the dihydrate manganese iron phosphate precursor is kept warm at a temperature of 650°C for 3 hours to remove the crystal water of the dihydrate manganese iron phosphate precursor to obtain a manganese iron phosphate precursor.

[0081] (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, then cool to room temperature to obtain lithium ferromanganese phosphate positive electrode material.

[0082] The EDS image of the precursor prepared in Example 1 is as follows Figure 3 As shown, it can be seen from the EDS diagram 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.

[0083] Example 2

[0084] 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:

[0085] (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 to a co-precipitation reactor in parallel under stirring for co-precipitation 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. The pH of the reaction solution was adjusted to 2.8±0.2 by controlling the addition rate of ammonia water. The reaction temperature was 90° C. and the stirring speed was 400 r / min. After reacting for 3 hours, the mixture was washed with deionized water and dried at 80° C. for 6 hours to obtain aluminum ferric phosphate.

[0086] (2) The aluminum iron phosphate, manganese chloride and flux in step (1) are mixed uniformly at 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, washed with deionized water after cooling with the furnace, and dried at 100°C for 4 hours to obtain a dihydrate manganese iron phosphate precursor. The flux is a mixture of 55% by mass potassium chloride and 45% by mass sodium chloride. In a nitrogen atmosphere, the dihydrate manganese iron phosphate precursor is kept warm at 700°C for 1 hour to remove the crystal water of the dihydrate manganese iron phosphate precursor to obtain a manganese iron phosphate precursor.

[0087] (4) Weigh lithium carbonate and the ferromanganese phosphate precursor in step (3), mix them evenly in a molar ratio of lithium source to ferromanganese 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 ferromanganese phosphate positive electrode material.

[0088] Example 3

[0089] 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:

[0090] (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 into a co-precipitation reactor in parallel under stirring for co-precipitation reaction, and the flow rates of the ferric sulfate aqueous solution, the aluminum sulfate aqueous solution, and the phosphoric acid aqueous solution were all controlled to be 120 mL / min. The pH value of the reaction solution was adjusted to 3.5±0.2 by controlling the addition rate of ammonia water, the reaction temperature was 45° C., the stirring rate 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 iron phosphate.

[0091] (2) The aluminum iron phosphate, manganese chloride and flux in step (1) are mixed uniformly at a molar ratio of 1:1.5:0.4, placed in a muffle furnace, introduced with nitrogen, kept warm at 185°C for 6 hours, washed with deionized water after cooling with the furnace, and dried at 100°C for 4 hours to obtain a dihydrate manganese iron phosphate precursor. The flux is a mixture of 40% by mass potassium chloride and 60% by mass sodium chloride. In a nitrogen atmosphere, the dihydrate manganese iron phosphate precursor is kept warm at 600°C for 4 hours to remove the crystal water of the dihydrate manganese iron phosphate precursor to obtain a manganese iron phosphate precursor.

[0092] (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 1:1, add 5 wt % of sucrose, heat to 800 ° C in a nitrogen atmosphere and calcine for 20 h, and then cool to room temperature to obtain a lithium ferromanganese phosphate positive electrode material.

[0093] Example 4

[0094] The only difference from Example 1 is that the co-solvent in step (2) is replaced by sodium chloride.

[0095] Example 5

[0096] The only difference from Example 1 is that the reaction temperature in step (2) is 400°C.

[0097] Comparative Example 1

[0098] This comparative example provides a method for preparing a lithium manganese iron phosphate positive electrode material, comprising the following steps:

[0099] (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 co-precipitation reactor in parallel under stirring for co-precipitation 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. and the stirring speed was 200 r / min. 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.

[0100] (2) Weigh lithium carbonate and the ferromanganese phosphate precursor in step (1), mix them evenly in a molar ratio of lithium source to ferromanganese phosphate precursor of 1.2:1, add 7wt% of sucrose, heat to 850°C in a nitrogen atmosphere and calcine for 10h, then cool to room temperature to obtain a lithium ferromanganese phosphate positive electrode material.

[0101] Comparative Example 2

[0102] This comparative example provides a method for preparing a lithium manganese iron phosphate positive electrode material, comprising the following steps:

[0103] Using lithium carbonate, ferric sulfate, manganese nitrate and ammonium phosphate as raw materials, the raw materials are 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 is added as a carbon source. According to the high-temperature solid-phase synthesis route, the mixture is calcined at 850°C for 20 hours under nitrogen atmosphere protection to obtain lithium manganese iron phosphate positive electrode material, and the molar ratio of iron and manganese elements in the product is 1:1.

[0104] Comparative Example 3

[0105] The only difference from Example 1 is that no flux is added in step (2).

[0106] Comparative Example 4

[0107] The only difference from Example 1 is that the reaction temperature in step (2) is 170°C.

[0108] Test Example 1

[0109] The performance of the lithium manganese iron phosphate positive electrode materials prepared in the test examples and comparative examples is shown in Table 1.

[0110] Test method: The lithium manganese iron phosphate positive electrode material obtained in the embodiment and the comparative example, acetylene black as a conductive agent, PVDF as a binder, are mixed at a mass ratio of 8:1:1, and a certain amount of organic solvent NMP is added, and the mixture is coated on an aluminum foil after stirring to form a positive electrode sheet. A metal lithium sheet is used as the negative electrode; the diaphragm is a Celgard2400 polypropylene porous membrane; the solvent in the electrolyte is a solution composed of EC, DMC and EMC in a mass ratio of 1:1:1, the solute is LiPF6, and the concentration of LiPF6 is 1.0 mol / L; a 2023 button cell is assembled in a glove box. The battery is tested for charge and discharge cycle performance, and the 0.1C and 1C discharge specific capacities are tested within the cut-off voltage range of 2.2 to 4.3V; the electrochemical performance test results are shown in Table 1.

[0111] Table 1 Basic properties of lithium manganese iron phosphate materials

[0112]

[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. It can be seen from the data that the lithium manganese iron phosphate positive electrode material of 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.

[0114] Industrial Applicability

[0115] The present invention utilizes the similar Ksp characteristics of iron phosphate and aluminum phosphate precipitation, synthesizes aluminum ferrous phosphate by coprecipitation, mixes aluminum ferrous phosphate evenly, and then uses aluminum ferrous phosphate and manganese chloride to react to prepare a stable iron manganese phosphate precursor. The aluminum chloride generated during the reaction can be directly volatilized. The lithium iron manganese phosphate positive electrode material is obtained by doping lithium in the lithium iron manganese phosphate precursor and adding a carbon source for high-temperature calcination. It has the advantages of low process cost and simple and easy process, and is suitable for industrial application.

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; The flux is a mixture of potassium chloride and sodium chloride, wherein the mass fraction of potassium chloride is 40%-55% and the mass fraction of sodium chloride is 45%-60%.

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 molar ratio of the aluminum iron phosphate to the total amount of the flux is 1: (0.4-0.8).

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

5. The preparation method according to claim 2, 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.

6. The preparation method according to claim 2, 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.

7. The preparation method according to claim 6, characterized in that: The high temperature treatment is performed under an inert atmosphere.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The process of preparing the aluminum iron phosphate comprises: adding an iron salt solution, an aluminum salt solution, a phosphorus source solution and a precipitant solution into a reactor for a co-precipitation reaction.

9. The preparation method according to claim 8, 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).

10. The preparation method according to claim 8, characterized in that: The reaction temperature of the coprecipitation reaction is 45°C-90°C, and the reaction time is 3h-6h.

11. The preparation method according to claim 8, 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.

12. The preparation method according to claim 11, characterized in that: The precipitant solution is an aqueous ammonia solution with a concentration of 2 mol / L-6 mol / L.

13. The preparation method according to claim 8, 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.

14. The preparation method according to claim 8, 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.

15. The preparation method according to claim 8, characterized in that: The aluminum salt is selected from at least one of aluminum nitrate, aluminum sulfate, aluminum chloride and aluminum carbonate.

16. The preparation method according to claim 8, characterized in that: The phosphorus source in the phosphorus source solution is selected from at least one of phosphoric acid, ammonium phosphate and diammonium phosphate.

17. A ferromanganese phosphate precursor, characterized in that: It is prepared by the preparation method described in any one of claims 1 to 16.

18. A method for preparing a lithium manganese iron phosphate positive electrode material, characterized in that: include: The ferromanganese phosphate precursor according to claim 17 is reacted with a lithium source.

19. The preparation method according to claim 18, 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.

20. The preparation method according to claim 18, 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.

21. The preparation method according to claim 19, 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.

22. The preparation method according to claim 18, characterized in that: The lithium source is selected from at least one of lithium carbonate, lithium hydroxide and lithium acetate.

23. The preparation method according to claim 19, 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.

24. The preparation method according to claim 19, characterized in that: Calcination is carried out under inert atmosphere.

25. A lithium manganese iron phosphate positive electrode material, characterized in that: It is prepared by the preparation method described in any one of claims 18 to 24.

26. A positive electrode plate, characterized in that: Including the lithium manganese iron phosphate positive electrode material described in claim 25.

27. A lithium battery, characterized in that: Includes the positive electrode sheet as described in claim 26.

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