Preparation method of battery-grade ferromanganese phosphate precursor

Abstract

The invention provides a preparation method and application of a battery-grade ferromanganese phosphate precursor, a ferromanganese salt mixed solution and a phosphorus solution are prepared, the phosphorus solution is slowly dropped into the ferromanganese salt mixed solution by a peristaltic pump at a specific dropping rate, and the mixture is stirred and mixed to form a solution with uniform ferromanganese and phosphorus distribution. The alkaline regulator which can be used as both a precipitator and a complexing agent is added, and because the precipitation coefficients of the manganese ions and the iron ions are different, the selection of the alkaline regulator directly determines the precipitation rate and uniformity of the manganese ions and the iron ions, so that all atoms can be utilized to the maximum extent, and the economic benefit is increased. Adding an oxidizing agent solution, controlling the water bath temperature and the stirring rate, reacting for a period of time to obtain ferromanganese phosphate slurry, and carrying out suction filtration, pulping washing, drying and sintering on the slurry to obtain the ferromanganese phosphate precursor material.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a method for preparing a battery-grade ferromanganese phosphate precursor. Background Art

[0002] With the rapid development of the new energy vehicle industry, lithium-ion batteries have been widely used, and people have put forward higher energy and power density requirements for them. At present, the mainstream positive electrode materials in the market include nickel cobalt manganese oxide (ternary materials) or lithium iron phosphate (phosphate materials). The former has relatively high specific capacity and voltage platform, but its thermal stability is poor, there is a risk of oxygen release, and there are great safety hazards; the latter lithium iron phosphate has an orderly and regular olivine structure, and it started early and has very mature technology development. The core advantage lies in its high structural rigidity, excellent thermal stability, no risk of oxygen release, and outstanding safety performance, but the disadvantage of lithium iron phosphate is its poor low temperature performance and low energy density. Compared with lithium iron phosphate, lithium iron manganese phosphate has an energy density advantage. Under appropriate conditions, its theoretical energy density is 15%-20% higher than that of lithium iron phosphate, which can basically reach the level of ternary battery NCM523, and can provide electric vehicles with a higher range than lithium iron phosphate batteries. And the low temperature performance is remarkable, and the capacity retention rate of lithium iron manganese phosphate can reach about 75% at -20°C.

[0003] The synthesis methods of lithium iron manganese phosphate and lithium iron phosphate are the same, and the main methods in industry are high-temperature solid-phase reaction, hydrothermal synthesis, and co-precipitation. The performance of high-temperature solid-phase products is poor and it is difficult to replace lithium iron phosphate. The performance of hydrothermal products is superior, but the equipment cost is high. If the cost reduction is lower than expected, it may lead to limited practical applications. The co-precipitation method is used to first prepare the iron manganese phosphate precursor product, and then mixed with the lithium source for sintering to prepare a material with good morphology and fine and uniform particles. Therefore, the market has an urgent need for manganese iron phosphate precursor products prepared by co-precipitation. But in fact, unlike lithium iron materials, which have mature iron phosphate as a precursor, lithium iron manganese phosphate materials are in the early stages of development and have no standard precursors. Positive electrode companies need to prepare them themselves, which increases the industry's technical barriers. At present, there are no mature iron manganese phosphate precursors on the market. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing a manganese iron phosphate precursor and its application, which solves the problem in the prior art that the ratio range of manganese to iron in the manganese iron phosphate lithium material is difficult to control, resulting in poor stability and uniformity of the manganese iron phosphate lithium material.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: A method for preparing a ferromanganese phosphate precursor comprises the following steps: S1. A manganese iron salt mixed solution and a phosphorus solution of a certain concentration are prepared in proportion, and the phosphorus solution is slowly dripped into the manganese iron salt mixed solution at a constant rate using a peristaltic pump, and stirred to mix, so as to ensure that the manganese iron ions and the phosphorus element are fully and evenly fused to obtain an initial reaction solution with uniform distribution of manganese iron ions; S2, keeping the initial reaction solution in S1 at room temperature and monitoring the change of its pH value, also using a peristaltic pump to accurately control the dropping rate of the alkaline regulator to better complex the two metal ions, stopping the dropping of the alkaline regulator when the pH value is adjusted to 4-6, and finally adding the oxidant solution and stirring the reaction to obtain a second reaction solution; S3, the second reaction solution in S2 is heated in a water bath for 50-80 o C at 250-450 rpm for 3-10 h. When the pH value stabilizes, the resulting reaction solution is filtered, washed by pulping, dried and heated at 300-600 o C and sintered to obtain ferromanganese phosphate precursor.

[0006] Furthermore, the chemical formula of the ferromanganese phosphate precursor is Mn x Fe 1-x PO4, where the value of x is 0.2-0.9, (Mn+Fe): P=0.96-1.02.

[0007] Further, the manganese salt comprises at least one of manganese nitrate, manganese sulfate, manganese carbonate, manganese oxalate, manganese chloride, and manganese acetate. The iron salt comprises at least one of ferrous chloride, ferrous nitrate, ferrous sulfate, and ferrous oxalate. The phosphorus solution solute comprises at least one of diammonium phosphate, phosphoric acid, and monoammonium phosphate. The alkaline regulator comprises at least one of disodium ethylenediaminetetraacetate, urotropine, ammonia water, and ethylenediamine, and the oxidant solution comprises at least one of hydrogen peroxide, potassium permanganate, and nitric acid.

[0008] Furthermore, the concentration of the manganese-iron salt mixed solution is 0.1-2 mol / L, the concentration of the phosphorus solution is 0.2-2 mol / L, the concentration of the alkaline regulator is 15-25%, and the concentration of the oxidant solution is 15-35%.

[0009] Furthermore, the speeds of the phosphorus solution and the alkaline regulator are both precisely controlled by a peristaltic pump, wherein the phosphorus solution dripping acceleration rate is 20-100 rpm / min, and the alkaline regulator dripping acceleration rate is 10-30 rpm / min.

[0010] Furthermore, after the alkaline regulator is added, the pH of the second reaction solution is 4-6.

[0011] Furthermore, the molar ratio of phosphorus to the total molar amount of the manganese source and the iron source is (1-4):1, and the molar ratio of the oxidant to the total molar amount of the manganese source and the iron source is (1-6):1.

[0012] Furthermore, the second reaction solution water bath temperature is 50-80 o C, stirring speed is 250-450rpm, stirring time is 3-10h.

[0013] Furthermore, the sintering temperature of the material after drying is 300-600 o C, sintering time is 1-5h.

[0014] The present invention has the following beneficial effects: 1. The present invention adopts a specific alkaline regulator to control its droplet acceleration rate to effectively precipitate manganese ions and iron ions at the same time, which can solve the problem that the ratio of manganese and iron ions to phosphate ions in the prior art is within an appropriate range.

[0015] 2. The ferromanganese phosphate precursor material prepared by the present invention can ensure that the prepared lithium ferromanganese phosphate material has good electrochemical properties, solves the technical problems of poor stability and uniformity of the lithium ferromanganese phosphate material prepared by the prior art, and is suitable for large-scale mass production. The present invention also provides the application of the ferromanganese phosphate preparation method in lithium ferromanganese phosphate positive electrode materials or lithium ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is a SEM image of ferromanganese phosphate prepared in Example 1 of the present invention; Figure 2 The charge and discharge curve and cycle performance diagram of the lithium manganese iron phosphate positive electrode material prepared from the precursor of Example 1 of the present invention. DETAILED DESCRIPTION

[0016] The embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention.

[0017] Example 1 Prepare a 0.5 mol / L manganese-iron mixed solution at a ratio of Mn / Fe of 6 / 4, and use a peristaltic pump to drop 0.5 mol / L phosphorus solution into the manganese-iron mixed solution at a rate of 50 rpm / min, and stir to ensure that the manganese-iron ions and phosphorus elements are fully and evenly fused to obtain an initial reaction solution with uniform distribution of manganese-iron ions. Use a pH meter to monitor the pH change of the initial reaction solution, and continue to use a peristaltic pump to accurately control the ammonia solution to slowly drop into the initial reaction solution at a rate of 20 rpm / min. When the pH reaches 5.6, stop adding the ammonia solution, and finally add 30% hydrogen peroxide solution. Place in a water bath at 60 o The suspension was filtered, washed by beating, dried and heated at 450 o C sintering, then Mn 0.6 Fe 0.4 PO4 precursor.

[0018] Example 2 Prepare a 1 mol / L manganese iron mixed solution at a ratio of 5 / 5 for Mn / Fe, and use a peristaltic pump to drop 1 mol / L phosphorus solution into the manganese iron mixed solution at a rate of 50 rpm / min, and stir to ensure that the manganese iron ions and phosphorus elements are fully and evenly fused to obtain an initial reaction solution with uniform distribution of manganese iron ions. Use a pH meter to monitor the pH change of the initial reaction solution, and continue to use a peristaltic pump to accurately control the ammonia solution to slowly drop into the initial reaction solution at a rate of 20 rpm / min. When the pH reaches 5.0, stop adding the ammonia solution, and finally add 30% hydrogen peroxide solution. Place in a water bath at 60 o The suspension was filtered, washed by beating, dried and heated at 450 o C sintering, then Mn 0.5 Fe 0.5 PO4 precursor.

[0019] Example 3 A 0.5 mol / L manganese-iron mixed solution was prepared at a ratio of Mn / Fe of 6 / 4. A 0.5 mol / L phosphorus solution was added to the manganese-iron mixed solution at a rate of 50 rpm / min using a peristaltic pump. The mixture was stirred to ensure that the manganese-iron ions and phosphorus elements were fully and evenly fused to obtain an initial reaction solution with uniform distribution of manganese-iron ions. The pH change of the initial reaction solution was monitored with a pH meter. The peristaltic pump was used to accurately control the urotropine solution to be slowly added to the initial reaction solution at a rate of 20 rpm / min. When the pH reached 5.6, the addition of the urotropine solution was stopped. Finally, a 30% hydrogen peroxide solution was added. The mixture was heated in a water bath at 60 °C. o The suspension was filtered, washed by beating, dried and heated at 450 o C sintering, then Mn 0.6 Fe 0.4 PO4 precursor.

[0020] Example 4 Prepare a 0.5 mol / L manganese iron mixed solution at a ratio of Mn / Fe of 6 / 4, and use a peristaltic pump to drop 0.5 mol / L phosphorus solution into the manganese iron mixed solution at a rate of 50 rpm / min, and stir to ensure that the manganese iron ions and phosphorus elements are fully and evenly fused to obtain an initial reaction solution with uniform distribution of manganese iron ions. Use a pH meter to monitor the pH change of the initial reaction solution, and continue to use a peristaltic pump to accurately control the disodium ethylenediaminetetraacetic acid solution to slowly drop into the initial reaction solution at a rate of 20 rpm / min. When the pH reaches 5.6, stop adding the disodium ethylenediaminetetraacetic acid solution, and finally add 30% hydrogen peroxide solution. Heat the mixture in a water bath for 60 min. oThe suspension was filtered, washed by beating, dried and heated at 450 o C sintering, then Mn 0.6 Fe 0.4 PO4 precursor.

[0021] Comparative Example 1 Prepare a 0.5 mol / L manganese-iron mixed solution at a ratio of Mn / Fe of 6 / 4, and use a peristaltic pump to drop 0.5 mol / L phosphorus solution into the manganese-iron mixed solution at a rate of 50 rpm / min, and stir to ensure that the manganese-iron ions and phosphorus elements are fully and evenly fused to obtain an initial reaction solution with uniform distribution of manganese-iron ions. Use a pH meter to monitor the pH change of the initial reaction solution, and continue to use a peristaltic pump to accurately control the sodium hydroxide solution to slowly drop into the initial reaction solution at a rate of 20 rpm / min. When the pH reaches 5.6, stop adding the sodium hydroxide solution, and finally add 30% hydrogen peroxide solution. Place in a water bath for 60 ℃ and 80 ℃. o The suspension was filtered, washed by beating, dried and heated at 450 o C sintering, then Mn 0.6 Fe 0.4 PO4 precursor.

[0022] Comparative Example 2 Prepare a 0.5 mol / L manganese-iron mixed solution at a ratio of Mn / Fe of 6 / 4, and use a peristaltic pump to drop 0.5 mol / L phosphorus solution into the manganese-iron mixed solution at a rate of 50 rpm / min, and stir to ensure that the manganese-iron ions and phosphorus elements are fully and evenly fused to obtain an initial reaction solution with uniform distribution of manganese-iron ions. Use a pH meter to monitor the pH change of the initial reaction solution, and continue to use a peristaltic pump to accurately control the ammonia solution to slowly drop into the initial reaction solution at a rate of 20 rpm / min. When the pH reaches 3, stop adding the ammonia solution, and finally add 30% hydrogen peroxide solution. Place in a water bath at 60 o The suspension was filtered, washed by beating, dried and heated at 450 o C sintering, then Mn 0.6 Fe 0.4 PO4 precursor.

[0023] Comparative Example 3 Prepare a 1 mol / L manganese-iron mixed solution at a ratio of 5 / 5 for Mn / Fe, and use a peristaltic pump to drop 1 mol / L phosphorus solution into the manganese-iron mixed solution at a rate of 50 rpm / min, and stir to ensure that the manganese-iron ions and phosphorus elements are fully and evenly fused to obtain an initial reaction solution with uniform distribution of manganese-iron ions. Use a pH meter to monitor the pH change of the initial reaction solution, and continue to use a peristaltic pump to accurately control the ammonia solution to slowly drop into the initial reaction solution at a rate of 20 rpm / min. When the pH reaches 3, stop adding the ammonia solution, and finally add 30% hydrogen peroxide solution. Place in a water bath at 60 o The suspension was filtered, washed by beating, dried and heated at 450 o C sintering, then Mn 0.5 Fe 0.5 PO4 precursor. The content of the ferromanganese phosphate products obtained in Examples 1-4 and Comparative Examples 1-3 was tested, and the test results are shown in Table 1. The detection method refers to "TCIAPS0029-2023 Lithium Iron Manganese Phosphate Positive Electrode Material for Lithium Ion Batteries".

[0024] Table 1

[0025] Example 5 Phosphorus solution drop acceleration rate is 20-100 rpm / min Based on Example 1, the difference lies in the dropping rate of phosphoric acid. The rest is the same as Example 1. The content detection results are shown in Table 2.

[0026] Table 2

[0027] Example 6 The dropping rate of the alkaline regulator is 10-30 rpm / min Based on Example 1, the difference lies in the dropping rate of the alkaline regulator. Others are the same as Example 1. The content detection results are shown in Table 3.

[0028] Table 3

[0029] Test example According to the molar ratio (Fe+Mn): Li: carbon source = 1: 1.02: 0.2, the ferromanganese phosphate precursors obtained in Examples 1-4 and Comparative Examples 1-3 were ball-milled and mixed with lithium carbonate and glucose, and calcined at 650 ° C for 10 hours under a nitrogen atmosphere to obtain a lithium ferromanganese phosphate positive electrode material. Then, the mass ratio of lithium ferromanganese phosphate: acetylene black: PVDF = 8: 1: 1 was mixed, and the organic solvent NMP was added, and after stirring, it was coated on aluminum foil and dried to form a positive electrode sheet, and the negative electrode used a metal lithium sheet; the diaphragm used a polypropylene porous membrane; and the 2023 button half-cell was assembled in a glove box. The battery was tested for charge and discharge cycle performance, and the 0.1C and 1C discharge specific capacities were tested within the cut-off voltage range of 2.5 to 4.5V; the electrochemical performance test results are shown in Table 4, and the test refers to "TCIAPS0029-2023 Lithium Iron Manganese Phosphate Positive Electrode Material for Lithium Ion Batteries".

[0030] Table 4

[0031] As can be seen from Table 2, the electrochemical performance results of the positive electrode materials of lithium iron manganese phosphate synthesized in Comparative Examples 1-3 and Examples 1-4 are quite different. This is because when the precursor preparation conditions are changed, the ratio of manganese to iron in the precursor of the iron manganese phosphate is unbalanced, resulting in poor stability and reduced performance of the synthesized lithium iron manganese phosphate positive electrode material. However, the manganese, iron and phosphorus of the iron manganese phosphate precursors of Examples 1-4 are mixed uniformly in proportion, and the corresponding lithium iron manganese phosphate positive electrode material prepared has excellent performance, high discharge specific capacity, and excellent cycle performance.

[0032] The above-mentioned embodiments are only preferred technical solutions of the present invention and should not be regarded as limitations of the present invention. The embodiments and features in the embodiments of the present application can be arbitrarily combined with each other without conflict. The protection scope of the present invention shall be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A method for preparing a battery-grade ferromanganese phosphate precursor, characterized in that: The following steps are involved: S1, dropping the phosphorus solution into the manganese and iron salt mixed solution, stirring and mixing, to obtain an initial reaction solution with uniform distribution of manganese and iron ions; S2, adding an alkaline regulator to the initial reaction solution, and finally adding an oxidant solution and stirring the reaction to obtain a second reaction solution; S3, stirring the second reaction liquid in S2 in a water bath, filtering, pulping, washing, drying and sintering the obtained reaction liquid to obtain a ferromanganese phosphate precursor.

2. The method for preparing a battery-grade ferromanganese phosphate precursor according to claim 1, characterized in that: In step S1, the manganese salt comprises at least one of manganese nitrate, manganese sulfate, manganese carbonate, manganese oxalate, manganese chloride, and manganese acetate; The iron salt comprises at least one of ferrous chloride, ferrous nitrate, ferrous sulfate and ferrous oxalate; The phosphorus solution solute comprises at least one of diammonium phosphate, phosphoric acid and monoammonium phosphate.

3. The method for preparing a battery-grade ferromanganese phosphate precursor according to claim 1, characterized in that: In step S2, the alkaline regulator comprises at least one of disodium ethylenediaminetetraacetate, urotropine, ammonia water, and ethylenediamine; The oxidant solution includes at least one of hydrogen peroxide, potassium permanganate, nitric acid, sodium hypochlorite and potassium hypochlorite.

4. The method for preparing a battery-grade ferromanganese phosphate precursor according to claim 1, characterized in that: The chemical formula of the synthesized manganese iron phosphate precursor is Mn x Fe 1-x PO4, where the value of x is 0.2-0.9, (Mn+Fe): P=0.96-1.

02.

5. The method for preparing a battery-grade ferromanganese phosphate precursor according to claim 1, characterized in that: The concentration of the manganese-iron salt mixed solution is 0.1-2 mol / L, the concentration of the phosphorus solution is 0.2-2 mol / L, the concentration of the alkaline regulator is 15-25%, and the concentration of the oxidant solution is 15-35%.

6. The method for preparing a battery-grade ferromanganese phosphate precursor according to claim 1, characterized in that: In steps S1 and S2, the speeds of the phosphorus solution and the alkaline regulator are both controlled by peristaltic pumps, wherein the phosphorus solution dripping rate is 20-100 rpm / min, and the alkaline regulator dripping rate is 10-30 rpm / min.

7. The method for preparing a battery-grade ferromanganese phosphate precursor according to claim 1, characterized in that: In step S2, the alkaline regulator adjusts the pH to 4-6.

8. A method for preparing a battery-grade ferromanganese phosphate precursor as claimed in claim 1, characterized in that: The molar ratio of phosphorus to the total molar amount of the manganese source and the iron source is (1-4):1, and the molar ratio of the oxidant to the total molar amount of the manganese source and the iron source is (1-6):

1.

9. A method for preparing a battery-grade ferromanganese phosphate precursor as claimed in claim 1, characterized in that: In step S3, the stirring condition of the second reaction liquid is a water bath temperature of 50-80 o C, stirring speed is 250-450rpm, stirring time is 3-10h.

10. A method for preparing a battery-grade ferromanganese phosphate precursor as claimed in claim 1, characterized in that: In step S3, the sintering temperature of the material after drying is 300-600 o C, sintering time is 1-5h.

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