Lithium manganese iron phosphate precursor, preparation method thereof and lithium manganese iron phosphate

Abstract

The invention provides a preparation method of a lithium manganese iron phosphate precursor, which comprises the following steps: synthesizing ammonium manganese iron phosphate monohydrate by adopting a coprecipitation method, and controlling the pH value of a reaction system to be 5-10 in a coprecipitation reaction process; the preparation method comprises the following steps: grinding ammonium ferromanganese phosphate monohydrate until the particle size D50 of the material is 100-1000nm, and drying; and carrying out low-temperature calcination on the dried material in air to obtain the lithium manganese iron phosphate precursor ferromanganese phosphate glass nano material. According to the method, the nano ferromanganese phosphate glass precursor with uniformly mixed elements on the molecular level, smaller particle size, uniform particle size distribution and controllable proportion of metal to phosphorus is obtained through coprecipitation, ball milling and low-temperature calcination, and the synthesis process is simple to operate, low in equipment requirement, short in reaction time, wide in raw material source, low in cost and suitable for industrial production. The method is suitable for industrial large-scale production.

Description

Technical Field

[0001] The present invention belongs to the field of cathode materials for lithium-ion batteries, and particularly relates to a method for preparing a lithium iron manganese phosphate precursor. Background Art

[0002] Lithium-ion batteries have become an indispensable energy storage device in modern life and are widely used in mobile electronic products, electric vehicles, power tools, and household and industrial energy storage facilities. Among them, the lithium iron phosphate cathode material with an orthorhombic olivine structure has been widely recognized in the market due to its low price, excellent safety performance, and stable cycling performance. However, there are still problems such as low energy density and low conductivity. To solve these existing problems, common measures are as follows: ① To solve the problem of poor conductivity of lithium iron phosphate, the lithium iron phosphate material is nano-sized and carbon-coated to improve the overall conductivity of the lithium iron phosphate / carbon composite material. ② Doping metal elements with higher electrochemical potentials, such as nickel, cobalt, manganese, etc., to increase the overall discharge voltage of the cathode material, thereby increasing the energy density. Among a series of doping elements, manganese stands out due to its relatively low price and high electrochemical potential (4.1V Vs Li + / Li), and manganese-doped lithium iron phosphate has formed a new polyanion material system, lithium iron manganese phosphate.

[0003] At present, the main preparation methods of lithium iron manganese phosphate are hydrothermal method, solid-phase method, and liquid-phase method. The hydrothermal method needs to be carried out in a high-temperature and high-pressure reaction kettle, and the excessive demand for lithium source during the synthesis process is extremely high, making it difficult to carry out large-scale industrial production. The traditional oxide solid-phase method is difficult to ensure the uniform mixing of different elements, and it is also difficult to control the particle size and particle size distribution, thereby affecting the electrochemical performance of the material. The organic salt solid-phase method has weak competitiveness in the market due to the high price of raw materials. The liquid-phase method needs to use nitrates, and toxic nitrogen oxides are released during the sintering process. The recovery and reuse of nitrogen oxides are a major difficulty in the popularization of this technology. In the existing lithium iron phosphate production process, the iron phosphate method has occupied the mainstream, and its main advantages are wide raw material sources and diverse product performance regulation methods. The production route of lithium iron manganese phosphate has been seeking a precursor similar to iron phosphate, which can use water-soluble salts of iron and manganese as raw materials and can easily regulate physicochemical parameters such as the ratio of metal elements, the ratio of metal elements to phosphorus elements, specific surface area, and particle size distribution.

[0004] Similar to the synthesis of iron phosphate, some studies have prepared ammonium iron manganese phosphate as a precursor of lithium iron manganese phosphate by co-precipitation method. The synthesis process is generally to mix FeSO 4 、MnSO 4 、NH 4 H 2 PO4 It is dissolved in water to prepare a metal ion and phosphate solution. However, the existing preparation methods of ammonium iron manganese phosphate materials are difficult to balance material morphology control, production efficiency, and cost, etc. Moreover, when ammonium iron manganese phosphate is used to prepare lithium iron manganese phosphate, the contained ammonium ions will be discharged during the sintering process, which not only has a certain corrosive effect on the sintering equipment, increases the ammonia treatment cost, but also results in more impurities and lower capacity in the finally sintered lithium iron manganese phosphate. Some synthetic methods in the prior art carry out reactions in organic solutions, and cost and environmental protection issues have caused great difficulties for their large-scale industrial production. Summary of the Invention

[0005] Aiming at the above technical problems, the purpose of the present invention is to provide a lithium iron manganese phosphate precursor, its preparation method, and lithium iron manganese phosphate.

[0006] To achieve the above purpose, the present invention proposes the following solutions: The present invention provides a preparation method of a lithium iron manganese phosphate precursor, including: (1) Synthesize ammonium iron manganese phosphate monohydrate by the coprecipitation method. During the coprecipitation reaction process, control the pH value of the reaction system to be 5-10; (2) Grind the ammonium iron manganese phosphate monohydrate until the material particle size D50 is 100-1000 nm, and then dry it; (3) Calcinate the dried material at low temperature in air to obtain a manganese iron phosphate glass nanomaterial.

[0007] Preferably, in step (3), the calcination temperature of the low temperature is 400-500 °C; the time of the low-temperature calcination is 1-8 h.

[0008] Preferably, in step (2), the drying is spray drying.

[0009] Preferably, in step (2), the grinding is sand grinding; before grinding, it further includes the step of adding ammonium phosphate salt to ammonium iron manganese phosphate monohydrate; the ammonium phosphate salt is one or more of ammonium dihydrogen phosphate, ammonium phosphate, and ammonium hydrogen phosphate; the addition amount of the ammonium phosphate salt is 0-8% of the mass of ammonium iron manganese phosphate monohydrate.

[0010] Preferably, in step (1), the synthesis of ammonium iron manganese phosphate monohydrate by the coprecipitation method includes: S1. Prepare a mixed salt solution A of manganese salt and iron salt; prepare a solution B of ammonium dihydrogen phosphate and ammonia water; prepare a reaction kettle bottom liquid; S2. Introduce the mixed salt solution A and the solution B into the reaction kettle bottom liquid and flow them in, and use ammonia water to adjust the pH value of the reaction system to be 5-10, and carry out a coprecipitation reaction; S3. After the coprecipitation reaction is completed, through aging and solid-liquid separation, ammonium iron manganese phosphate monohydrate is obtained.

[0011] Preferably, in the mixed salt solution A, the total concentration of metal ions is 0.5 to 2 mol / L.

[0012] Preferably, in the solution B, the concentration of ammonium dihydrogen phosphate is 0.5 to 2 mol / L, and the concentration of ammonia water is 0.5 to 2 mol / L.

[0013] Preferably, the bottom liquid of the reaction kettle is an aqueous solution mixture of ammonia water and ammonium dihydrogen phosphate; in the bottom liquid of the reaction kettle, the concentration of ammonium dihydrogen phosphate is 0.5 to 2 mol / L, and the concentration of ammonia water is 0.5 to 2 mol / L.

[0014] Preferably, the temperature of the coprecipitation reaction is room temperature to 80 °C.

[0015] As a general inventive concept, the present invention also provides a lithium iron manganese phosphate precursor prepared by the foregoing preparation method.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The synthesis process of the lithium iron manganese phosphate precursor of the present invention is simple in operation, low in equipment requirements, short in reaction time, wide in raw material sources and low in cost, and is suitable for large-scale industrial production. This method obtains a nano manganese iron phosphate glass precursor with uniform mixing of elements at the molecular level, small particle size and uniform particle size distribution through coprecipitation, ball milling and low-temperature calcination. At the same time, since it is an amorphous phase, it has a higher chemical potential energy and a simple phase formation during the subsequent sintering process with lithium carbonate. Compared with ammonium iron manganese phosphate, the nano manganese iron phosphate glass precursor prepared in the present invention does not contain ammonium, and there is no need to treat the tail gas during the further sintering process to prepare lithium iron manganese phosphate, with low equipment requirements, and its water content is stable, which can increase the batch stability during the sintering process of lithium iron manganese phosphate. Moreover, the precursor prepared by this method has a uniform and controllable particle size, which is beneficial to improving the tap density.

[0017] (2) The method for synthesizing manganese iron phosphate of the present invention is easy to adjust the ratio of metal elements and the ratio of metal to phosphorus, and has significant advantages in adjusting the manganese iron ratio and the ratio of metal to phosphorus and then adjusting the product performance; this method is simple and effective in adjusting the ratio between metal and phosphorus, and can assist in controlling the particle size and compaction density during the sintering process. Moreover, it is easy to incorporate other metal elements, and is easy to control the energy band structure of the sintered lithium iron manganese phosphate, improving the conductivity of the cathode material. Description of the Drawings

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0019] Figure 1 SEM image of ammonium iron manganese phosphate monohydrate obtained in Example 1.

[0020] Figure 2 SEM image of manganese iron phosphate glass nanomaterial obtained in Example 1.

[0021] Figure 3 XRD pattern of manganese iron phosphate glass nanomaterial obtained in Example 1.

[0022] Figure 4 SEM image of ammonium iron manganese phosphate monohydrate obtained in Example 4.

[0023] Figure 5 SEM image of manganese iron phosphate glass nanomaterial obtained in Example 7. Detailed implementation manners

[0024] The applicant has found through research that by controlling a relatively high precipitation pH value during the synthesis of ammonium iron manganese phosphate using the co - precipitation method, the particle size of the synthesized flaky ammonium iron manganese phosphate can be effectively controlled, thereby effectively reducing the subsequent grinding difficulty and cost. In this application, ammonium iron manganese phosphate monohydrate is synthesized at a relatively high precipitation pH, and then after further grinding to a particle size in a certain range and drying, low - temperature calcination in air can obtain the precursor manganese iron phosphate glass nanomaterial of lithium iron manganese phosphate.

[0025] Some embodiments provide a method for preparing a precursor of lithium iron manganese phosphate, including: (1) Synthesizing ammonium iron manganese phosphate monohydrate using the co - precipitation method, and controlling the pH value of the reaction system to be 5 - 10 during the co - precipitation reaction process; (2) Grinding the obtained ammonium iron manganese phosphate monohydrate until the material particle size D50 is 100 - 1000 nm, and then drying; (3) Subjecting the dried material to low - temperature calcination in air to obtain a manganese iron phosphate glass nanomaterial.

[0026] This technical solution obtains a nano manganese iron phosphate glass material with elements uniformly mixed at the molecular level, small particle size, and uniform particle size distribution through coprecipitation, ball milling, and low-temperature calcination. It can be used to synthesize lithium iron manganese phosphate with high crystallinity and controlled particle size, and due to its amorphous phase, it has a relatively high chemical potential energy. Compared with ammonium iron manganese phosphate, since it does not contain ammonium, there is no need to treat tail gas during the further sintering process to prepare lithium iron manganese phosphate, and the equipment requirements are low; its water content is stable, which can increase the batch stability during the sintering process of lithium iron manganese phosphate.

[0027] The pH of the coprecipitation reaction is 5 - 10, such as 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, etc.

[0028] In some preferred embodiments, in step (3), the temperature of the low-temperature calcination is 400 - 500 °C, such as 400 °C, 410 °C, 420 °C, 430 °C, 440 °C, 450 °C, 460 °C, 470 °C, 480 °C, 490 °C, 500 °C, etc. The time of the low-temperature calcination is 1 - 8 h.

[0029] In some preferred embodiments, in step (2), the drying is spray drying. Adopting spray drying is beneficial to improving the uniformity of product components and can also improve the fluidity of the obtained precursor.

[0030] During the research process, the applicant found that the ratio of metal to phosphorus in ammonium iron manganese phosphate prepared under higher pH conditions is often relatively high. When this ratio is too high, it is not conducive to the subsequent preparation of lithium iron manganese phosphate, and additional phosphorus needs to be supplemented during the subsequent preparation of lithium iron manganese phosphate. However, it is difficult to precisely control the subsequent phosphorus supplementation, resulting in great difficulty in subsequent process control, and it is difficult to achieve good adjustment of the ratio of metal ions to phosphorus element simply by controlling the synthesis conditions. In view of this newly discovered technical problem, in some preferred embodiments, in step (2), before grinding, it further includes the step of adding ammonium phosphate salt to ammonium iron manganese phosphate monohydrate to control the ratio of metal to phosphorus within the required range; the ammonium phosphate salt is one or more of ammonium dihydrogen phosphate, ammonium phosphate, and ammonium hydrogen phosphate; the addition amount of the ammonium phosphate salt is 0 - 8% of the mass of ammonium iron manganese phosphate monohydrate, more preferably 1 - 8%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, etc.

[0031] In some preferred embodiments, in step (2), the grinding is sand grinding. Sand grinding further adjusts the particle morphology, and further grinds the larger precursor into nanomaterials. At the same time, sand grinding can also uniformly mix ammonium iron manganese phosphate with the added phosphate salt, increase the contact area between the two, and make the element distribution of the product more uniform.

[0032] In some preferred embodiments, in step (2), the obtained ammonium iron manganese phosphate monohydrate is ground until the particle size D50 of the material is 200 - 500 nm, such as 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc.

[0033] In some preferred embodiments, in step (1), the synthesis of ammonium iron manganese phosphate monohydrate by the coprecipitation method includes: S1. Prepare a mixed salt solution A of manganese salt and iron salt; prepare a solution B of ammonium dihydrogen phosphate and ammonia water; prepare the bottom liquid of the reaction kettle. S2. Add the mixed salt solution A and the solution B to the bottom liquid of the reaction kettle in a parallel flow manner, and adjust the pH value with ammonia water to carry out a coprecipitation reaction. S3. Continue through aging and solid-liquid separation to obtain ammonium iron manganese phosphate monohydrate.

[0034] In some preferred embodiments, in the mixed salt solution A, the total concentration of metal ions is 0.5 - 2 mol / L; the ratio of manganese to iron elements is set according to the molar ratio of x:1 - x, where 0 < x < 1, that is, manganese and iron can be set in any ratio.

[0035] In some preferred embodiments, in the solution B, the concentration of ammonium dihydrogen phosphate is 0.5 - 2 mol / L, and the concentration of ammonia water is 0.5 - 2 mol / L.

[0036] In some preferred embodiments, the pH value of the bottom liquid of the reaction kettle is 5 - 8; the bottom liquid of the reaction kettle is prepared from deionized water and ammonium dihydrogen phosphate as raw materials and ammonia water as a pH regulator; the concentration of ammonium dihydrogen phosphate is 0 - 1 mol / L. By controlling the composition of the bottom liquid of the reaction kettle, it is beneficial to improve the stability of the reaction system, thereby reducing the control difficulty of process conditions and improving the consistency of the synthesized material.

[0037] In some preferred embodiments, in step S2, the temperature of the coprecipitation reaction is from room temperature to 80°C, such as 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, etc.; the feeding time is 20 min - 8 h.

[0038] In some preferred embodiments, in step S3, the aging time is 20 min - 8 h.

[0039] As a general inventive concept, the present invention also provides a lithium iron manganese phosphate precursor, which is prepared by the aforementioned preparation method.

[0040] The precursor manganese iron phosphate glass prepared by the present invention has a small size and a narrow size distribution. The ratio of metal ions to phosphorus can be adjusted simply and accurately. After dehydration and ammonia treatment and then sintering, the morphology of lithium iron phosphate prepared from manganese iron phosphate lithium is spherical-like, with uniform particles and a large specific surface area, which is beneficial to the transmission of electrons and lithium ions. The element distribution in the manganese iron phosphate glass is uniform, which is beneficial to suppressing the formation of impurity phases caused by uneven element distribution during the sintering process, thereby reducing the interfacial impedance of lithium ion transmission and improving the rate performance of the product.

[0041] As a general inventive concept, the present invention also provides a lithium iron phosphate manganese phosphate, which is prepared by mixing and sintering the aforementioned lithium iron phosphate manganese phosphate precursor with a lithium source and a carbon source.

[0042] In some embodiments, the molar ratio of lithium in the lithium source to the metal in the precursor is controlled at 1 to 1.03:1.

[0043] In some embodiments, the mass ratio of the carbon source to the precursor is controlled at 4 to 15%.

[0044] In some embodiments, the sintering temperature is controlled at 600 to 720 °C, and the sintering time is controlled at 4 to 12 h.

[0045] For the convenience of understanding the present invention, the following will describe the present invention more comprehensively and in detail with reference to the accompanying drawings of the specification and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0046] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0047] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through the market or can be prepared by existing methods.

[0048] Example 1 (1) Dissolve 1.2 mol of manganese sulfate and 0.8 mol of ferrous sulfate heptahydrate in 1 L of water to obtain solution A.

[0049] (2) Dissolve 2 mol of ammonium dihydrogen phosphate and 320 g of 25% ammonia water in 1 L of water to obtain solution B.

[0050] (3) Dissolve 0.1 mol of ammonium dihydrogen phosphate in 1 L of water, adjust the pH to 8 with ammonia water, and add this solution to the reaction kettle as the bottom liquid.

[0051] (4) Solutions A and B were uniformly added to the base solution using a peristaltic pump. During the dropping process, the pH was adjusted with ammonia water to control the pH of the reaction system at 8, the temperature at 60 °C, and the co-precipitation reaction time with feeding at 2 h. After the feeding was completed, the aging time with continuous stirring was 2 h. After the reaction, ammonium iron manganese phosphate monohydrate (NH 4 Mn 0.6 Fe 0.4 PO 4 ·H 2 O) was obtained. The SEM image is as shown in Figure 1 . The average particle size (the distance between the two farthest ends of the particles) was about 10 μm.

[0052] (5) The prepared ammonium iron manganese phosphate was ground using a sand mill, and ammonium dihydrogen phosphate accounting for 3% of the mass of ammonium iron manganese phosphate was added during the grinding process. After grinding the D50 of the material to 500 nm, the slurry was spray-dried.

[0053] (6) The spray-dried particles were calcined at 450 °C under air conditions for 5 h to obtain a manganese iron phosphate glass nanomaterial with the chemical formula 5 - 7% H 2 O·28 - 29% MnO·18.5 - 19.5% FeO·46 - 48% P 2 O 5 .

[0054] The obtained manganese iron phosphate glass nanomaterial was characterized and tested. The SEM image is as shown in Figure 2 . It can be seen from Figure 2 that the finally synthesized material is dense spherical secondary particles, the primary particle size is small and uniform, and the diameter of most primary particles is below 100 nm; the XRD pattern is as shown in Figure 3 . It can be seen from Figure 3 that the peak envelope at 20 - 30° indicates that the material is an amorphous glass. The composition of the obtained manganese iron phosphate glass nanomaterial was characterized, and the element content of its finished product is shown in Table 1. According to Table 1, it can be calculated that the molar ratio of metal to phosphorus is 0.981.

[0055] Table 1 Element content of the finished product Example 2 The difference between this example and Example 1 is only that in step (5), ammonium dihydrogen phosphate was not added during the sand milling process.

[0056] The composition of the obtained manganese iron phosphate glass nanomaterial was characterized. After calculation, the molar ratio of metal to phosphorus was 1.02. The molar ratio of iron to phosphorus in conventional iron phosphate in the art is 0.97 - 0.98. It can be seen that the ratio of metal to phosphorus in the synthesized precursor is relatively high.

[0057] Example 3 The difference between this example and Example 2 is only that in step (1), the pH value is 10.

[0058] The composition of the obtained manganese-iron phosphate glass nanomaterial was characterized, and the calculated molar ratio of metal to phosphorus was 1.04. The average size of the ammonium manganese-iron phosphate monohydrate obtained in step (4) was about 6 μm.

[0059] Example 4 The difference between this example and Example 2 is only that in step (1), the pH value is 6.

[0060] The SEM image of the ammonium manganese-iron phosphate monohydrate (NH 4 Mn 0.6 Fe 0.4 PO 4 ·H 2 O) obtained in step (4) is as shown in Figure 4 Figure, and the average size of the obtained ammonium manganese-iron phosphate monohydrate is about 20 μm.

[0061] Comparison Figure 1 and Figure 4 It can be found that as the pH increases, the size of the synthesized ammonium manganese-iron phosphate monohydrate decreases.

[0062] The composition of the obtained manganese-iron phosphate glass nanomaterial was characterized, and the calculated molar ratio of metal to phosphorus was 1.01. By comparing the products obtained in Examples 2-4, it can be found that when the pH increases, the molar ratio of metal to phosphorus also increases.

[0063] Example 5 The difference between this example and Example 1 is only that in step (5), the addition amount of ammonium dihydrogen phosphate is 1% of the mass of ammonium manganese-iron phosphate.

[0064] The composition of the obtained manganese-iron phosphate glass nanomaterial was characterized, and the calculated molar ratio of metal to phosphorus was 1.

[0065] Example 6 The difference between this example and Example 1 is only that in step (5), the addition amount of ammonium dihydrogen phosphate is 5% of the mass of ammonium manganese-iron phosphate.

[0066] The composition of the obtained manganese-iron phosphate glass nanomaterial was characterized, and the calculated molar ratio of metal to phosphorus was 0.957.

[0067] Example 7 The difference between this example and Example 1 is only that in step (5), spray drying is replaced by drying.

[0068] The SEM image of the obtained manganese-iron phosphate glass nanomaterial is as shown inFigure 5 As shown. Compare Figure 2 and Figure 5 It can be seen that spray drying will affect the morphology of the synthesized manganese-iron phosphate glass nanomaterials. Compared with ordinary drying, the products obtained by spray drying show more uniform spherical secondary particles, so the fluidity of the products is better.

[0069] Example 8 (1) Dissolve 1.2 mol of manganese sulfate and 0.8 mol of ferrous sulfate heptahydrate in 1 L of water to prepare solution A.

[0070] (2) Dissolve 2 mol of ammonium dihydrogen phosphate and 320 g of 25% ammonia water in 1 L of water to prepare solution B.

[0071] (3) Dissolve 0.1 mol of ammonium dihydrogen phosphate in 1 L of water, adjust the pH to 8 with ammonia water, and add this solution to the reaction kettle as the bottom liquid.

[0072] (4) Add solutions A and B to the bottom liquid evenly with a peristaltic pump. During the dropping process, adjust the pH with ammonia water to control the pH of the reaction system to 8 and the temperature to 60 °C. The feeding time for the co-precipitation reaction is 30 min. After the feeding is completed, the aging time for continuous stirring and aging is 2 h. After the reaction, ammonium manganese iron phosphate monohydrate (NH 4 Mn 0.6 Fe 0.4 PO 4 ·H 2 O) is obtained.

[0073] (5) Grind the obtained ammonium manganese iron phosphate with a sand mill, and add ammonium dihydrogen phosphate accounting for 3% of the mass of ammonium manganese iron phosphate during the grinding process. After grinding the D50 of the material to 200 nm, spray dry the slurry.

[0074] (6) Calcinate the spray-dried particles at 450 °C under air conditions for 5 hours to obtain manganese-iron phosphate glass nanomaterials.

[0075] Example 9 (1) Dissolve 1.2 mol of manganese sulfate and 0.8 mol of ferrous sulfate heptahydrate in 1 L of water to prepare solution A.

[0076] (2) Dissolve 2 mol of ammonium dihydrogen phosphate and 320 g of 25% ammonia water in 1 L of water to prepare solution B.

[0077] (3) Dissolve 0.1 mol of ammonium dihydrogen phosphate in 1 L of water, adjust the pH to 8 with ammonia water, and add this solution to the reaction kettle as the bottom liquid.

[0078] (4) Add solutions A and B evenly into the bottom solution with a peristaltic pump. During the dropping process, adjust the pH with ammonia water, control the pH of the reaction system to be 8, the temperature to be 60 °C, and the feeding coprecipitation reaction time to be 8 h. After the feeding is completed, the aging time of continuous stirring and aging is 2 h. After the reaction, ammonium iron manganese phosphate monohydrate (NH 4 Mn 0.6 Fe 0.4 PO 4 ·H 2 O) is obtained.

[0079] (5) Grind the obtained ammonium iron manganese phosphate with a sand mill, and add ammonium dihydrogen phosphate accounting for 3% of the mass of ammonium iron manganese phosphate during the sand grinding process. After grinding the D50 of the material to 1000 nm, spray dry the slurry.

[0080] (6) Calcinate the spray-dried particles at 450 °C under air conditions for 5 hours to obtain the manganese iron phosphate glass nanomaterial.

[0081] Example 10 (1) Dissolve 0.4 mol of manganese sulfate and 1.6 mol of ferrous sulfate heptahydrate in 1 L of water to prepare solution A.

[0082] (2) Dissolve 2 mol of ammonium dihydrogen phosphate and 320 g of 25% ammonia water in 1 L of water to prepare solution B.

[0083] (3) Dissolve 0.1 mol of ammonium dihydrogen phosphate in 1 L of water, adjust the pH to 8 with ammonia water, and add this solution to the reaction kettle as the bottom solution.

[0084] (4) Add solutions A and B evenly into the bottom solution with a peristaltic pump. During the dropping process, adjust the pH with ammonia water, control the pH of the reaction system to be 8, the temperature to be 60 °C, and the feeding coprecipitation reaction time to be 2 h. After the feeding is completed, the aging time of continuous stirring and aging is 2 h. After the reaction, ammonium iron manganese phosphate monohydrate (NH 4 Mn 0.2 Fe 0.8 PO 4 ·H 2 O) is obtained.

[0085] (5) Grind the obtained ammonium iron manganese phosphate with a sand mill, and add ammonium dihydrogen phosphate accounting for 3% of the mass of ammonium iron manganese phosphate during the sand grinding process. After grinding the D50 of the material to 300 nm, spray dry the slurry.

[0086] (6) Calcinate the spray-dried particles at 450 °C under air conditions for 5 hours to obtain the manganese iron phosphate glass nanomaterial.

[0087] Example 11 The difference between this embodiment and Embodiment 1 is only that in step (6), the calcination temperature is 400 °C and the calcination time is 8 h.

[0088] Embodiment 12 The difference between this embodiment and Embodiment 1 is only that in step (6), the calcination temperature is 500 °C and the calcination time is 2 h.

[0089] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of lithium iron manganese phosphate precursor, characterized in that, it includes: (1) Synthesize ammonium manganese iron phosphate monohydrate by the co-precipitation method. During the co-precipitation reaction process, control the pH value of the reaction system to be 5-10; (2) Grind the ammonium manganese iron phosphate monohydrate until the material particle size D50 is 100-1000 nm, and then dry it; (3) Calcinate the dried material at low temperature in air to obtain a lithium iron manganese phosphate precursor manganese iron phosphate glass nanomaterial.

2. The preparation method of lithium iron manganese phosphate precursor according to claim 1, characterized in that, in step (3), the temperature of the low-temperature calcination is 400-500 °C; the time of the low-temperature calcination is 1-8 h.

3. The preparation method of lithium iron manganese phosphate precursor according to claim 1, characterized in that, in step (2), the drying is spray drying.

4. The preparation method of lithium iron manganese phosphate precursor according to claim 1, characterized in that, in step (2), the grinding is sand grinding; before grinding, it also includes the step of adding ammonium phosphate salt to ammonium manganese iron phosphate monohydrate; and / or, the ammonium phosphate salt is one or more of ammonium dihydrogen phosphate, ammonium phosphate, and ammonium hydrogen phosphate; and / or, the addition amount of the ammonium phosphate salt is 0-8% of the mass of ammonium manganese iron phosphate monohydrate.

5. The preparation method of lithium iron manganese phosphate precursor according to claim 1, characterized in that, in step (1), the synthesis of ammonium manganese iron phosphate monohydrate by the co-precipitation method includes: S1. Prepare a mixed salt solution A of manganese salt and iron salt; prepare a solution B of ammonium dihydrogen phosphate and ammonia water; prepare a reaction kettle bottom liquid; S2. Add the mixed salt solution A and the solution B to the reaction kettle bottom liquid in parallel flow, and use ammonia water to adjust the pH value of the reaction system to 5-10 to carry out the co-precipitation reaction; S3. After the co-precipitation reaction is completed, through aging and solid-liquid separation, ammonium manganese iron phosphate monohydrate is obtained.

6. The preparation method of lithium iron manganese phosphate precursor according to claim 5, characterized in that, in the mixed salt solution A, the total concentration of metal ions is 0.5-2 mol / L; and / or, in the solution B, the concentration of ammonium dihydrogen phosphate is 0.5-2 mol / L, and the ammonia water concentration is 0.5-2 mol / L.

7. The preparation method of lithium iron manganese phosphate precursor according to claim 5, characterized in that, the pH value of the reaction kettle bottom liquid is 5-8; and / or, the reaction kettle bottom liquid is prepared with deionized water and ammonium dihydrogen phosphate as raw materials and ammonia water as a pH regulator; the concentration of ammonium dihydrogen phosphate is 0.5-2 mol / L.

8. The preparation method of lithium iron manganese phosphate precursor according to claim 5, characterized in that, in step S2, the temperature of the co-precipitation reaction is room temperature-80 °C.

9. Lithium iron manganese phosphate precursor, characterized in that, it is prepared by using the preparation method according to any one of claims 1-8.

10. Lithium iron manganese phosphate, characterized in that, it is obtained by mixing and sintering the lithium iron manganese phosphate precursor according to claim 9 with a lithium source and a carbon source.

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