Preparation method of high-yield ammonium manganese iron phosphate precursor and lithium manganese iron phosphate

Abstract

This invention provides a method for preparing a high-yield ferric ammonium manganese phosphate precursor and lithium iron manganese phosphate. The preparation method includes the following steps: S1, mixing an iron source and a manganese source to prepare a mixed manganese-iron solution as a base liquid; simultaneously pumping phosphorus source I and an ammonia solution at different feed rates to react and obtain a slurry initially containing ferric ammonium manganese phosphate; S2, adding phosphorus source II again to the ferric ammonium manganese phosphate slurry obtained in step S1 for secondary phosphorus replenishment and aging to obtain a slurry containing ferric ammonium manganese phosphate monohydrate precipitate; S3, filtering, pulping, and drying the ferric ammonium manganese phosphate monohydrate slurry obtained in step S2 to obtain the high-yield ferric ammonium manganese phosphate monohydrate powder. This invention achieves an iron-to-phosphorus ratio closer to the theoretical value, reduces the formation of impurity phases, and improves product yield. The preparation method is mild, simple, easy to operate, and requires no special equipment, enabling commercial production.

Description

Technical Field

[0001] This invention belongs to the field of cathode material synthesis technology for lithium-ion batteries, and particularly relates to a method for preparing a high-yield manganese iron ammonium phosphate precursor and lithium manganese iron phosphate. Background Technology

[0002] Lithium iron phosphate (LFP) is a widely used cathode material in power batteries, with a theoretical capacity of up to 170 mAh / g. Compared to other batteries, LFP cathode materials also have advantages such as structural stability, abundant resources, low price, non-toxicity, good thermal stability, and excellent long-cycle performance. However, its energy density is low, and its low-temperature performance and rate performance are poor. Lithium manganese phosphate (LMP) has a similar theoretical specific capacity to LFP, but LMP has a redox potential of 4.1V, which is much higher than LFP's 3.4V. Therefore, theoretically, LMP's energy density is higher than LFP's. Due to the abundance of manganese resources, LMP has become the most promising olivine-structured cathode material after LFP.

[0003] Most of the lithium manganese iron phosphate cathode materials that are currently in mass production are prepared using the high-temperature solid-state method. However, due to the large variety of raw materials, the batch stability of the products is poor, and it is difficult to achieve atomic-level mixing of Fe, Mn, and P in solid-state mixing. Therefore, they only have a certain scale in the small power market.

[0004] Among the many methods for synthesizing lithium manganese iron phosphate precursors, the co-precipitation method is simple, produces homogeneous material mixtures, requires low heat treatment temperatures, easily yields nanoscale particles, and offers controllable morphology. The ferrous method is particularly simple, producing precursors with small particle sizes, making it suitable for large-scale production. However, because Fe and Mn have multiple valence states, the synthesized precursor may be a composite valence product. Furthermore, Mn... 3+ It is prone to disproportionation, therefore it is used to synthesize Fe. x Mn 1-x PO4 is more difficult to prepare. Furthermore, existing methods require the addition of an extra phosphorus source, and currently, excessive primary phosphorus sources are often added, which may lead to low yields. Additionally, due to the aqueous liquid system, impurity phases may precipitate, affecting the molar ratio of Fe to P in the product. In lithium manganese iron phosphate, a significant difference between the iron-phosphorus ratio and the theoretical value can affect the battery's energy density, thus impacting its driving range. Therefore, a high-yield precursor of manganese iron ammonium phosphate needs to be developed. Summary of the Invention

[0005] To address the technical problems in existing lithium manganese iron phosphate precursor synthesis technologies, such as low yield and large deviations from theoretical values ​​of the molar ratio of Fe and P elements, this invention provides a method for preparing a high-yield lithium manganese iron ammonium phosphate precursor and lithium manganese iron phosphate.

[0006] This invention discloses a method for preparing a high-yield ferric ammonium manganese phosphate precursor, the method comprising the following steps:

[0007] S1. Mix the iron source and manganese source to prepare a mixed manganese-iron solution as the base liquid. Simultaneously pump phosphorus source I and ammonia solution at different feed rates to react and obtain a slurry containing manganese-iron ammonium phosphate.

[0008] S2. Add phosphorus source II again to the ferric ammonium manganese phosphate slurry obtained in step S1 for secondary phosphorus replenishment and aging to obtain a slurry containing ferric ammonium manganese phosphate monohydrate precipitate.

[0009] S3. The manganese iron ammonium phosphate monohydrate slurry obtained in step S2 is filtered, pulped, washed and dried to obtain the high-yield manganese iron ammonium phosphate monohydrate powder.

[0010] Furthermore, in step S1, the reaction conditions are: temperature 40-80℃, stirring speed 200-600rpm, phosphorus source I feeding time 0.5-3.0h, and pH value during the reaction process is adjusted by controlling the ammonia water feeding rate to maintain pH at 4.0-6.5.

[0011] Furthermore, the phosphorus source is at least one of phosphoric acid, monoammonium phosphate, diammonium phosphate, and triammonium phosphate; the manganese source is at least one of manganese sulfate, manganese nitrate, manganese acetate, and manganese chloride; and the iron source is at least one of ferrous sulfate, ferrous carbonate, and ferrous chloride.

[0012] Furthermore, in step S1, the concentration of the manganese-iron mixed salt solution is 0.5-2.0 mol / L, wherein the molar ratio of Mn to Fe is 1.3-1.7, and the molar ratio of P to metal (Mn+Fe) in phosphorus source I is 1.00-1.25.

[0013] Furthermore, in step S2, the reaction temperature is 50-90℃, the stirring speed is 100-600rpm, and the total aging time does not exceed 5h.

[0014] Furthermore, in step S2, the concentration of phosphorus source II is 10-15 mol / L, wherein the molar ratio of P to metal (Mn+Fe) in the secondary phosphorus supplement is 0.05-0.25.

[0015] Furthermore, the drying temperature in step S3 is 80-120℃.

[0016] Furthermore, in step S3, the molar ratio of metal element (Mn+Fe) to P element in manganese iron ammonium phosphate monohydrate is 1.0-1.1, and the molar ratio of Fe element to P element is 0.40-0.42.

[0017] The present invention also provides a method for preparing lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate monohydrate with a lithium source and a carbon source, and sintering at 400-800°C under an inert atmosphere.

[0018] The working principle and advantages of this invention are as follows:

[0019] This invention uses a mixed solution of manganese and iron as the base solution. Phosphorus source I and an ammonia solution are added to the acidic base solution to synthesize manganese iron ammonium phosphate. A secondary phosphorus supplementation method is employed to regulate the ratio of metal elements to phosphorus in the product. Simultaneously, the metal ions precipitated as hydroxides are dissolved and then produced as the target product, thereby increasing the proportion of phosphorus in the precursor. This results in an iron-phosphorus ratio closer to the theoretical value and improves the product yield, maintaining it above 95%. The molar ratio of phosphorus to metal elements (Mn+Fe) in the secondary phosphorus supplementation is controlled between 0.05 and 0.25. Within this range, the iron-phosphorus ratio and yield are both advantageous, and the product quality can be adjusted. Below 0.05, the hydroxide precipitate cannot be completely dissolved, resulting in excessive impurities in the product. Above 0.25, the impact on yield and iron-phosphorus ratio is minimal, leading to phosphorus source waste. The slight excess of phosphorus source in the first step is due to the high pH during the reaction. Excess phosphorus source can shift the equilibrium and form more manganese iron ammonium phosphate crystal nuclei, providing more growth sites for particles in the subsequent aging steps. At this point, the particles have already grown, and even if more phosphorus source I is added, it cannot be replenished and will cause uneven particle growth, affecting the quality of the final product.

[0020] Compared with existing technologies, this invention has advantages such as simple process and high yield, and is more suitable for large-scale production. Attached Figure Description

[0021] Figure 1 SEM image of the manganese iron ammonium phosphate precursor prepared in Example 1 of this invention;

[0022] Figure 2 SEM image of the manganese iron ammonium phosphate precursor prepared in Example 2 of this invention;

[0023] Figure 3 SEM image of the manganese iron ammonium phosphate precursor prepared in Example 3 of this invention;

[0024] Figure 4 SEM image of the manganese iron ammonium phosphate precursor prepared in Example 4 of this invention;

[0025] Figure 5 This is a SEM image of lithium manganese iron phosphate obtained after sintering in Example 1 of the present invention;

[0026] Figure 6 This is a SEM image of lithium manganese iron phosphate obtained after sintering in Example 2 of the present invention;

[0027] Figure 7 This is a SEM image of lithium manganese iron phosphate obtained after sintering in Example 3 of the present invention;

[0028] Figure 8 SEM image of lithium manganese iron phosphate obtained after sintering in Example 4 of this invention.

[0029] Figure 9 The XRD pattern of the manganese iron ammonium phosphate precursor prepared in Example 2 of this invention;

[0030] Figure 10 The image shows the XRD pattern of lithium manganese iron phosphate obtained after sintering in Example 2 of this invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0032] Example 1

[0033] A method for preparing a high-yield ferric ammonium manganese phosphate precursor, the method comprising the following steps:

[0034] S1. Dissolve 18.9g of ferrous carbonate solid (99.5% purity) and 35.8g of manganese sulfate monohydrate solid (99.5% purity) in pure water to obtain 750ml of mixed metal salt solution as a base liquid. Simultaneously pump in phosphoric acid I and ammonia solution at different feed rates to react and obtain a slurry initially containing manganese iron ammonium phosphate. The reaction conditions are: temperature 50℃, stirring speed 600rpm, phosphoric acid I feed time 0.5h, and pH value is controlled by adjusting the ammonia water feed rate to maintain pH at 4.0. The concentration of the manganese iron mixed salt solution is 0.5mol / L, where the molar ratio of Mn to Fe is 1.30, and the molar ratio of P to metal (Mn+Fe) in phosphoric acid I is 1.00.

[0035] S2. Add phosphoric acid II to the manganese iron ammonium phosphate slurry obtained in step S1 again. The concentration of phosphoric acid II is 10 mol / L. Perform secondary phosphoric acid addition and aging. The molar ratio of P element to metal element (Mn+Fe) in the secondary phosphoric acid addition is 0.05. The reaction temperature is 50℃, the stirring speed is 300 rpm, and the total aging time is 5h to obtain a slurry containing manganese iron ammonium phosphate monohydrate precipitate.

[0036] S3. The manganese ferric ammonium phosphate monohydrate slurry obtained in step S2 is filtered, pulped, washed, and dried at 80°C to obtain the high-yield manganese ferric ammonium phosphate monohydrate powder. Testing showed that the molar ratio of metal element (Mn+Fe) to P element in the prepared manganese ferric ammonium phosphate monohydrate was 1.11, and the molar ratio of Fe element to P element was 0.419.

[0037] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate monohydrate with a lithium source and a carbon source, and sintering at 400°C under an inert atmosphere.

[0038] Example 2

[0039] A method for preparing a high-yield ferric ammonium manganese phosphate precursor, the method comprising the following steps:

[0040] S1. Dissolve 36.2g of ferrous sulfate heptahydrate solid (99.5% purity) and 49.1g of manganese nitrate tetrahydrate solid (99.5% purity) in pure water to obtain 400ml of a mixed metal salt solution as a base liquid. Simultaneously pump in monoammonium phosphate I and ammonia solution at different feed rates to react and obtain a slurry initially containing manganese-iron-ammonium phosphate. The reaction conditions are: temperature 80℃, stirring speed 200rpm, monoammonium phosphate I feed time 1.5h, and pH value is controlled by adjusting the ammonia water feed rate to maintain pH at 6.5. The concentration of the manganese-iron mixed salt solution is 0.8mol / L, where the molar ratio of Mn to Fe is 1.50, and the molar ratio of P to metal (Mn+Fe) in monoammonium phosphate I is 1.25.

[0041] S2. Add monoammonium phosphate II to the manganese iron ammonium phosphate slurry obtained in step S1. The concentration of monoammonium phosphate II is 15 mol / L. Perform secondary phosphorus supplementation and aging. The molar ratio of P element to metal element (Mn+Fe) in the secondary phosphorus supplementation is 0.15. The reaction temperature is 90℃, the stirring speed is 100 rpm, and the total aging time is 1 h. A slurry containing manganese iron ammonium phosphate monohydrate precipitate is obtained.

[0042] S3. The manganese ferric ammonium phosphate monohydrate slurry obtained in step S2 is filtered, pulped, washed, and dried at 120℃ to obtain the high-yield manganese ferric ammonium phosphate monohydrate powder. Testing showed that the molar ratio of metal element (Mn+Fe) to P element in the prepared manganese ferric ammonium phosphate monohydrate was 1.01, and the molar ratio of Fe element to P element was 0.405.

[0043] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate monohydrate with a lithium source and a carbon source, and sintering at 800°C under an inert atmosphere.

[0044] Example 3

[0045] A method for preparing a high-yield ferric ammonium manganese phosphate precursor, the method comprising the following steps:

[0046] S1. 27.4g of ferrous chloride solid (99.5% purity) and 89.2g of manganese acetate tetrahydrate solid (99.5% purity) were dissolved in pure water to obtain 580ml of a mixed metal salt solution as a base liquid. Diammonium phosphate I and ammonia solution were simultaneously pumped in at different feed rates to obtain a slurry initially containing manganese-ferric ammonium phosphate. The reaction conditions were: temperature 40℃, stirring speed 400rpm, diammonium phosphate I feed time 2.0h, and pH value was maintained at 6.0 by controlling the ammonia water feed rate. The concentration of the manganese-ferric mixed salt solution was 1mol / L, with a molar ratio of Mn to Fe of 1.67, and a molar ratio of P to metal (Mn+Fe) of 1.05 in diammonium phosphate I.

[0047] S2. Add diammonium phosphate II to the manganese iron ammonium phosphate slurry obtained in step S1 again. The concentration of diammonium phosphate II is 12 mol / L. Perform secondary phosphorus supplementation and aging. The molar ratio of P element to metal element (Mn+Fe) in the secondary phosphorus supplementation is 0.25. The reaction temperature is 70℃, the stirring speed is 600 rpm, and the total aging time is 2h. A slurry containing manganese iron ammonium phosphate monohydrate precipitate is obtained.

[0048] S3. The manganese ferric ammonium phosphate monohydrate slurry obtained in step S2 is filtered, pulped, washed, and dried at 100℃ to obtain the high-yield manganese ferric ammonium phosphate monohydrate powder. Testing showed that the molar ratio of metal element (Mn+Fe) to P element in the prepared manganese ferric ammonium phosphate monohydrate was 1.08, and the molar ratio of Fe element to P element was 0.408.

[0049] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate monohydrate with a lithium source and a carbon source, and sintering at 600°C under an inert atmosphere.

[0050] Example 4

[0051] A method for preparing a high-yield ferric ammonium manganese phosphate precursor, the method comprising the following steps:

[0052] S1. Dissolve 64.5g of ferrous sulfate heptahydrate solid (99.5% purity) and 72.7g of manganese chloride tetrahydrate solid (99.5% purity) in pure water to obtain 300ml of mixed metal salt solution as a base liquid. Simultaneously pump in triammonium phosphate I and ammonia solution at different feed rates to obtain a slurry initially containing manganese-ferric ammonium phosphate. The reaction conditions are: temperature 70℃, stirring speed 300rpm, triammonium phosphate I feed time 3.0h, and pH value is controlled by adjusting the ammonia water feed rate to maintain pH at 5.0. The concentration of the manganese-ferric mixed salt solution is 2.0mol / L, with a molar ratio of Mn to Fe of 1.58, and a molar ratio of P to metal (Mn+Fe) of 1.15 in triammonium phosphate I.

[0053] S2. Add triammonium phosphate II to the manganese iron ammonium phosphate slurry obtained in step S1. The concentration of triammonium phosphate II is 13 mol / L. Perform secondary phosphorus supplementation and aging. The molar ratio of P element to metal element (Mn+Fe) in the secondary phosphorus supplementation is 0.10. The reaction temperature is 80℃, the stirring speed is 400 rpm, and the total aging time is 3h. A slurry containing manganese iron ammonium phosphate monohydrate precipitate is obtained.

[0054] S3. The manganese ferric ammonium phosphate monohydrate slurry obtained in step S2 is filtered, pulped, washed, and dried at 90°C to obtain the high-yield manganese ferric ammonium phosphate monohydrate powder. Testing showed that the molar ratio of metal element (Mn+Fe) to P element in the prepared manganese ferric ammonium phosphate monohydrate was 1.05, and the molar ratio of Fe element to P element was 0.412.

[0055] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate monohydrate with a lithium source and a carbon source, and sintering at 700°C under an inert atmosphere.

[0056] Comparative Example 1

[0057] A method for preparing a precursor of manganese iron ammonium phosphate, the method comprising the following steps:

[0058] S1. Dissolve 36.2g of ferrous sulfate heptahydrate solid (99.5% purity) and 49.1g of manganese nitrate tetrahydrate solid (99.5% purity) in pure water to obtain 400ml of a mixed metal salt solution as a base liquid. Simultaneously pump in monoammonium phosphate I and ammonia solution at different feed rates to obtain a slurry initially containing manganese-iron-ammonium phosphate. The reaction conditions are: temperature 80℃, stirring speed 200rpm, monoammonium phosphate I feed time 1.5h, and pH value is controlled by adjusting the ammonia water feed rate to maintain pH at 6.5. The concentration of the manganese-iron mixed salt solution is 0.8mol / L, with a molar ratio of Mn to Fe of 1.5, and a molar ratio of P to metal (Mn+Fe) of 1.25 in monoammonium phosphate I.

[0059] S2. The reaction temperature is raised to 90℃, the stirring speed is 100rpm, and the total aging time is 1h to obtain a slurry containing manganese iron ammonium phosphate monohydrate precipitate.

[0060] S3. The manganese ferric ammonium phosphate monohydrate slurry obtained in step S2 is filtered, pulped, washed, and dried at 120℃ to obtain the high-yield manganese ferric ammonium phosphate monohydrate powder. Testing showed that the molar ratio of metal element (Mn+Fe) to P element in the prepared manganese ferric ammonium phosphate monohydrate was 1.18, and the molar ratio of Fe element to P element was 0.526.

[0061] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate monohydrate with a lithium source and a carbon source, and sintering at 800°C under an inert atmosphere.

[0062] Comparative Example 2

[0063] A method for preparing a precursor of manganese iron ammonium phosphate, the method comprising the following steps:

[0064] S1. Dissolve 36.2g of ferrous sulfate heptahydrate solid (99.5% purity) and 49.1g of manganese nitrate tetrahydrate solid (99.5% purity) in pure water to obtain 400ml of a mixed metal salt solution as a base liquid. Simultaneously pump in monoammonium phosphate I and ammonia solution at different feed rates to obtain a slurry initially containing manganese-iron-ammonium phosphate. The reaction conditions are: temperature 80℃, stirring speed 200rpm, monoammonium phosphate I feed time 1.5h, and pH value is controlled by adjusting the ammonia water feed rate to maintain pH at 6.5. The concentration of the manganese-iron mixed salt solution is 0.8mol / L, with a molar ratio of Mn to Fe of 1.5, and a molar ratio of P to metal (Mn+Fe) of 1.25 in monoammonium phosphate I.

[0065] S2. Add monoammonium phosphate II to the manganese iron ammonium phosphate slurry obtained in step S1. The concentration of monoammonium phosphate II is 15 mol / L. Perform secondary phosphorus supplementation and aging. The molar ratio of P element to metal element (Mn+Fe) in the secondary phosphorus supplementation is 0.03. The reaction temperature is 90℃, the stirring speed is 100 rpm, and the total aging time is 1 h. A slurry containing manganese iron ammonium phosphate monohydrate precipitate is obtained.

[0066] S3. The manganese ferric ammonium phosphate monohydrate slurry obtained in step S2 is filtered, pulped, washed, and dried at 120℃ to obtain the high-yield manganese ferric ammonium phosphate monohydrate powder. Testing showed that the molar ratio of metal element (Mn+Fe) to P element in the prepared manganese ferric ammonium phosphate monohydrate was 1.15, and the molar ratio of Fe element to P element was 0.517.

[0067] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate monohydrate with a lithium source and a carbon source, and sintering at 800°C under an inert atmosphere.

[0068] Comparative Example 3

[0069] A method for preparing a precursor of manganese iron ammonium phosphate, the method comprising the following steps:

[0070] S1. Dissolve 36.2g of ferrous sulfate heptahydrate solid (99.5% purity) and 49.1g of manganese nitrate tetrahydrate solid (99.5% purity) in pure water to obtain 400ml of a mixed metal salt solution as a base liquid. Simultaneously pump in monoammonium phosphate I and ammonia solution at different feed rates to obtain a slurry initially containing manganese-iron-ammonium phosphate. The reaction conditions are: temperature 80℃, stirring speed 200rpm, monoammonium phosphate I feed time 1.5h, and pH value is controlled by adjusting the ammonia water feed rate to maintain pH at 6.5. The concentration of the manganese-iron mixed salt solution is 0.8mol / L, with a molar ratio of Mn to Fe of 1.5, and a molar ratio of P to metal (Mn+Fe) of 1.25 in monoammonium phosphate I.

[0071] S2. Add monoammonium phosphate II to the manganese iron ammonium phosphate slurry obtained in step S1. The concentration of monoammonium phosphate II is 15 mol / L. Perform secondary phosphorus supplementation and aging. The molar ratio of P element to metal element (Mn+Fe) in the secondary phosphorus supplementation is 0.30. The reaction temperature is 90℃, the stirring speed is 100 rpm, and the total aging time is 1 h. A slurry containing manganese iron ammonium phosphate monohydrate precipitate is obtained.

[0072] S3. The manganese ferric ammonium phosphate monohydrate slurry obtained in step S2 is filtered, pulped, washed, and dried at 120℃ to obtain the high-yield manganese ferric ammonium phosphate monohydrate powder. Testing showed that the molar ratio of metal element (Mn+Fe) to P element in the prepared manganese ferric ammonium phosphate monohydrate was 1.00, and the molar ratio of Fe element to P element was 0.404.

[0073] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate monohydrate with a lithium source and a carbon source, and sintering at 800°C under an inert atmosphere.

[0074] Comparative Example 4

[0075] A method for preparing a precursor of manganese iron ammonium phosphate, the method comprising the following steps:

[0076] S1. Dissolve 36.2g of ferrous sulfate heptahydrate solid (99.5% purity) and 49.1g of manganese nitrate tetrahydrate solid (99.5% purity) in pure water to obtain 400ml of a mixed metal salt solution as a base liquid. Simultaneously pump in monoammonium phosphate I and ammonia solution at different feed rates to react and obtain a slurry initially containing manganese-iron-ammonium phosphate. The reaction conditions are: temperature 80℃, stirring speed 200rpm, monoammonium phosphate I feed time 1.5h, and pH value is controlled by adjusting the ammonia water feed rate to maintain pH at 6.5. The concentration of the manganese-iron mixed salt solution is 0.8mol / L, where the molar ratio of Mn to Fe is 1.5, and the molar ratio of P to metal (Mn+Fe) in monoammonium phosphate I is 0.9.

[0077] S2. Add monoammonium phosphate II to the manganese iron ammonium phosphate slurry obtained in step S1. The concentration of monoammonium phosphate II is 15 mol / L. Perform secondary phosphorus supplementation and aging. The molar ratio of P element to metal element (Mn+Fe) in the secondary phosphorus supplementation is 0.15. The reaction temperature is 90℃, the stirring speed is 100 rpm, and the total aging time is 1 h. A slurry containing manganese iron ammonium phosphate monohydrate precipitate is obtained.

[0078] S3. The manganese ferric ammonium phosphate monohydrate slurry obtained in step S2 is filtered, pulped, washed, and dried at 120℃ to obtain the high-yield manganese ferric ammonium phosphate monohydrate powder. Testing showed that the molar ratio of metal element (Mn+Fe) to P element in the prepared manganese ferric ammonium phosphate monohydrate was 1.10, and the molar ratio of Fe element to P element was 0.472.

[0079] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate monohydrate with a lithium source and a carbon source, and sintering at 800°C under an inert atmosphere.

[0080] Comparative Example 5

[0081] A method for preparing a precursor of manganese iron ammonium phosphate, the method comprising the following steps:

[0082] S1. Dissolve 36.2g of ferrous sulfate heptahydrate solid (99.5% purity) and 49.1g of manganese nitrate tetrahydrate solid (99.5% purity) in pure water to obtain 400ml of a mixed metal salt solution as a base liquid. Simultaneously pump in monoammonium phosphate I and ammonia solution at different feed rates to obtain a slurry initially containing manganese-iron-ammonium phosphate. The reaction conditions are: temperature 80℃, stirring speed 200rpm, monoammonium phosphate I feed time 1.5h, and pH value is controlled by adjusting the ammonia water feed rate to maintain pH at 6.5. The concentration of the manganese-iron mixed salt solution is 0.8mol / L, with a molar ratio of Mn to Fe of 1.5, and a molar ratio of P to metal (Mn+Fe) of 1.3 in monoammonium phosphate I.

[0083] S2. Add monoammonium phosphate II to the manganese iron ammonium phosphate slurry obtained in step S1. The concentration of monoammonium phosphate II is 15 mol / L. Perform secondary phosphorus supplementation and aging. The molar ratio of P element to metal element (Mn+Fe) in the secondary phosphorus supplementation is 0.15. The reaction temperature is 90℃, the stirring speed is 100 rpm, and the total aging time is 1 h. A slurry containing manganese iron ammonium phosphate monohydrate precipitate is obtained.

[0084] S3. The manganese ferric ammonium phosphate monohydrate slurry obtained in step S2 is filtered, pulped, washed, and dried at 120℃ to obtain the high-yield manganese ferric ammonium phosphate monohydrate powder. Testing showed that the molar ratio of metal element (Mn+Fe) to P element in the prepared manganese ferric ammonium phosphate monohydrate was 1.03, and the molar ratio of Fe element to P element was 0.407.

[0085] A lithium manganese iron phosphate, wherein the lithium manganese iron phosphate is prepared by mixing the above-mentioned iron manganese ammonium phosphate monohydrate with a lithium source and a carbon source, and sintering at 800°C under an inert atmosphere.

[0086] Comparative Examples 1-5 are all based on Example 2. Comparative Example 1 involves a single addition of the phosphorus source; Comparative Example 2 involves a smaller amount of phosphorus source added (the molar ratio of P to metal (Mn+Fe) in the secondary phosphorus supplement is 0.03); Comparative Example 3 involves a larger amount of phosphorus source added (the molar ratio of P to metal (Mn+Fe) in the secondary phosphorus supplement is 0.3); Comparative Example 4 involves a smaller amount of phosphorus source added initially (the molar ratio of P to metal (Mn+Fe) in phosphorus source I is 0.9); and Comparative Example 5 involves a larger amount of phosphorus source added initially (the molar ratio of P to metal (Mn+Fe) in phosphorus source I is 1.3).

[0087] The yield and Fe:P ratio of the manganese ferric ammonium phosphate precursor prepared in Example 1 were compared with those prepared by conventional methods and primary phosphorus supplementation methods in Comparative Examples 1-5. The results are shown in Table 1.

[0088] Table 1 Comparison of the effects of the secondary phosphorus supplementation proposed in this invention and the traditional primary phosphorus source.

[0089]

[0090]

[0091] As can be seen from the test data in Table 1, compared with the traditional one-time addition of phosphorus source, the two-time phosphorus supplementation process in this invention can dissolve the metal ions precipitated in the form of hydroxide and then produce them in the form of the target product. This is beneficial to increase the proportion of P element in the precursor, thereby better controlling the Fe:P ratio and maintaining a high yield. In this preparation method, the amount of the first phosphorus source added and the amount of the second phosphorus source added have a direct and important impact on the reaction. The molar ratio of P element to metal element (Mn+Fe) in the second phosphorus supplementation is controlled between 0.05 and 0.25. Within this range, the iron-phosphorus ratio and yield are both advantageous, and the quality of the product can be adjusted. Below 0.05, the hydroxide precipitate cannot be completely dissolved, and the product has too much impurity content. Above 0.25, it has little impact on the yield and iron-phosphorus ratio, resulting in waste of phosphorus source. The initial phosphorus source amount should be controlled at a molar ratio of P to metal (Mn+Fe) of 1-1.25. If the initial phosphorus source amount is too low, the metal ions cannot combine with the phosphate ions, and the theoretical ratio cannot be achieved. If the initial phosphorus source amount is too high, the phosphorus source will exist in a form other than orthophosphate ions, which will produce impurities.

[0092] In summary, this invention, through a secondary phosphorus supplementation process, better controls the Fe:P ratio and maintains a high yield. It boasts advantages such as a simple process and high yield, making it more suitable for large-scale production and possessing significant market potential.

[0093] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-yield ferric ammonium manganese phosphate precursor, the method comprising the following steps: S1. Mix the iron source and manganese source to prepare a mixed manganese-iron solution as the base liquid. Simultaneously pump phosphorus source I and ammonia solution at different feed rates to react and obtain a slurry containing manganese-iron ammonium phosphate. S2. Add phosphorus source II to the ferric ammonium manganese phosphate slurry obtained in step S1 again for secondary phosphorus replenishment and aging to obtain a slurry containing ferric ammonium manganese phosphate monohydrate precipitate. S3. The slurry of manganese iron ammonium hydrate precipitate obtained in step S2 is filtered, pulped, washed and dried to obtain the manganese iron ammonium hydrate powder. In step S1, the concentration of the manganese-iron mixed solution is 0.5-2.0 mol / L, wherein the molar ratio of Mn to Fe is 1.3-1.7, and the molar ratio of P to Mn+Fe in phosphorus source I is 1.00-1.

25. In step S2, the concentration of phosphorus source II is 10-15 mol / L, and the molar ratio of P to Mn+Fe in the secondary phosphorus supplement is 0.05-0.

25.

2. The method for preparing the high-yield ferric ammonium manganese phosphate precursor according to claim 1, characterized in that, In step S1, the reaction conditions are: temperature 40-80 ℃, stirring speed 200-600 rpm, phosphorus source I feeding time 0.5-3 h, and pH value during the reaction process is adjusted by controlling the ammonia water feeding rate to maintain pH at 4.0-6.

5.

3. The method for preparing the high-yield ferric ammonium manganese phosphate precursor according to claim 1, characterized in that, The phosphorus source is at least one of phosphoric acid, monoammonium phosphate, diammonium phosphate, and triammonium phosphate; the manganese source is at least one of manganese sulfate, manganese nitrate, manganese acetate, and manganese chloride; and the iron source is at least one of ferrous sulfate, ferrous carbonate, and ferrous chloride.

4. The method for preparing the high-yield ferric ammonium manganese phosphate precursor according to claim 1, characterized in that, In step S2, the reaction temperature is 50-90 ℃, the stirring speed is 100-600 rpm, and the total aging time does not exceed 5 h.

5. The method for preparing the high-yield ferric ammonium manganese phosphate precursor according to claim 1, characterized in that, The drying temperature in step S3 is 80-120 ℃.

6. The method for preparing the high-yield ferric ammonium manganese phosphate precursor according to claim 1, characterized in that, In step S3, the molar ratio of metal elements Mn+Fe to P in the slurry of manganese iron ammonium phosphate monohydrate precipitate is 1.0-1.1, and the molar ratio of Fe to P is 0.40-0.

42.

7. A method for preparing lithium manganese iron phosphate, characterized in that, The lithium manganese iron phosphate is prepared by mixing manganese iron ammonium phosphate monohydrate powder prepared by the preparation method of manganese iron ammonium phosphate precursor according to any one of claims 1 to 6 with a lithium source and a carbon source, and sintering at 400-800 °C under an inert atmosphere.

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