Manganese monohydrogen phosphate trihydrate production method, Mn-containing mother liquor recycling method and positive electrode material

Abstract

The invention discloses a manganese monohydrogen phosphate trihydrate production method, a Mn-containing mother liquor recycling method and a positive electrode material, and relates to the technical field of lithium ion batteries. Manganese carbonate solid slurry is used as a base solution to synthesize manganese monohydrogen phosphate, a regular octahedron morphology feature is constructed through precipitation solid-phase conversion, the specific surface area is larger, in the follow-up lithium manganese iron phosphate synthesis process, the reactivity of Mn can be improved, a more uniform lithium manganese iron phosphate positive electrode material is formed, and the lithium manganese iron phosphate positive electrode material can be applied to the field of lithium ion battery cathode materials. The compaction capacity and the electrochemical performance of the positive electrode material are improved.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, in particular to a method for producing manganese monohydrogen phosphate trihydrate, a method for recycling a mother liquor containing Mn and a positive electrode material. Background Art

[0002] Lithium manganese iron phosphate cathode material is a new type of lithium-ion battery cathode material, which is prepared by doping a certain proportion of manganese based on lithium iron phosphate. Due to its high voltage, high energy density, good cycle stability and thermal stability, it is widely used in lithium-ion batteries, especially in electric vehicles, mobile power supplies and energy storage systems.

[0003] At present, the manganese source precursors used in the synthesis of lithium manganese iron phosphate mainly include manganese oxalate, manganese carbonate, manganese tetraoxide, manganese hydroxide, etc. Manganese oxalate and manganese carbonate have a large gas production during the roasting process, resulting in a low compaction density of the obtained lithium manganese iron phosphate, which reduces the volume energy ratio of the material. Manganese tetraoxide leads to poor product distribution uniformity and low capacity. Manganese ions are easily oxidized during the production process of manganese hydroxide, and the product cost is relatively high.

[0004] Moreover, when conventional manganese monohydrogen phosphate trihydrate is used as a manganese source, its crystal form is mostly strip-shaped, aggregated and stacked in a stamen-like manner, and the size and shape are unevenly distributed, such as Figure 1 When such manganese monohydrogen phosphate trihydrate is used as a manganese source to synthesize lithium manganese iron phosphate, the consistency of the lithium manganese iron phosphate positive electrode material is poor and the compaction capacity is low. Summary of the invention

[0005] One of the purposes of the present invention is to provide a method for producing manganese monohydrogen phosphate trihydrate to solve the problem that when manganese monohydrogen phosphate trihydrate is used as a manganese source to synthesize lithium iron manganese phosphate positive electrode material, the lithium iron manganese phosphate positive electrode material has poor consistency and low compaction capacity.

[0006] The second object of the present invention is to provide a method for recycling a Mn-containing mother liquor to solve the problem that in the process of synthesizing manganese monohydrogen phosphate trihydrate in the present application, the reaction cannot be completely completed due to the limitation of Ksp, resulting in a low yield and being unsuitable for industrial production.

[0007] The third object of the present invention is to provide a positive electrode material to solve the problem of poor consistency and low compaction capacity of using ordinary manganese monohydrogen phosphate as a manganese source.

[0008] In order to solve one of the above purposes, the present invention adopts the following technical means: A method for producing manganese monohydrogen phosphate trihydrate comprises the following steps: using manganese carbonate solution as a base liquid, pumping a phosphoric acid solution or a diammonium hydrogen phosphate solution into the solution at a temperature of 50-80°C, controlling the reaction pH to be no more than 3, carrying out the reaction under the protection of an inert gas, and drying the solid material after filter pressing and washing after the reaction is completed to obtain manganese monohydrogen phosphate trihydrate.

[0009] In the process of the reaction of the manganese carbonate solution with the phosphoric acid solution or the diammonium hydrogen phosphate solution, under the condition of a low pH value not exceeding 3 and an environment of 50 to 80° C., the specific reaction temperature is preferably 58 to 62° C., OH - The reduction in ion availability reduces the kinetic coefficients of other phases in the system, such as Mn4H(PO4)3, Mn5OH(PO4)3, etc., while the substrate reduces the nucleation potential during the heterogeneous nucleation of the hydrated manganese monohydrogen phosphate trihydrate phase. Due to its lower interfacial free energy, it has a higher nucleation rate, which makes its nucleus form preferentially; thus, the entire reaction obtains a pure phase of manganese monohydrogen phosphate trihydrate.

[0010] Moreover, in the process of solid phase conversion of manganese monohydrogen phosphate trihydrate, H + Directed attachment allows manganese monohydrogen phosphate to form a regular octahedral structure. In the reaction environment of the present application, within a specific pH range and temperature, the material is in a supersaturated state, and the protons (H + ) has a lower adsorption energy on the side of the crystal than Mn 2+ The adsorption energy on the (020, 111, 102) plane makes H + Mn preferentially adsorbs on the side surface due to charge repulsion. + Adsorption is inhibited; resulting in Mn 2 + The growth rate of (020, 111, 102) faces is high. According to the Ostwald ripening rule, larger particles grow at the expense of smaller particles, resulting in isotropic crystals with similar shapes inherited from their inherent crystal properties, thereby achieving symmetrical arrangement of molecules, so that the prepared manganese monohydrogen phosphate trihydrate can form a regular octahedral morphology.

[0011] As for the overall reaction temperature, if the reaction temperature is lowered to 50-57°C, the crystal growth rate will be slow, and the crystal growth process will be easily affected by the outside world, resulting in the formation of some strip crystals, affecting the purity of the octahedral manganese hydrogen phosphate; if the reaction temperature is too high, such as 63-80°C, some impurities will be generated, and if the reaction is carried out at a temperature higher than 80°C, impurities will be completely generated, such as the monoclinic manganese phosphate mineral Mn5(PO3(OH))2(PO4)2(H2O)4. Figure 3The XRD result diagram shown. Therefore, it is difficult to produce high-purity octahedral manganese hydrogen phosphate trihydrate at too high or too low a temperature.

[0012] Moreover, for the present application, only manganese carbonate solution can be used as the reaction base solution to avoid excessive phosphoric acid solution in the early stage of the reaction and generate impurities with Marib salt.

[0013] In another embodiment, the manganese carbonate solution is prepared with a mass ratio of manganese carbonate to pure water of 1:4.

[0014] In order to ensure that the manganese carbonate solution has a suitable viscosity, it is not only convenient to transfer materials but also ensure that the manganese carbonate solution can react evenly after contacting with acid. If the concentration of the manganese carbonate solution is too high, the viscosity will increase, and it will be difficult to react evenly after encountering acid. The surface reaction will be violent, and CO2 will be released quickly, causing the bottom material to overflow. If the concentration is too low, water will be wasted, the difficulty of water treatment will be increased, and the reaction rate will be reduced. It is easy to form a mixed phase and it is impossible to ensure the synthesis of high-purity manganese monohydrogen phosphate trihydrate.

[0015] In another embodiment, the phosphoric acid solution is prepared by using 65% phosphoric acid: pure water in a mass ratio of 1:1.

[0016] By diluting the phosphoric acid solution, the rate of CO2 generation during the reaction is reduced, overflow is prevented, the risk of pressure in the system is reduced, and the rate of container corrosion is reduced.

[0017] In another embodiment, the molar ratio of manganese carbonate in the manganese carbonate solution and the phosphoric acid in the phosphoric acid solution is 1:1.05-1.10.

[0018] In the reaction process, HPO4 is provided in excess 2- , and H + , while controlling the pH of the reaction system, it participates in the reaction. If there is too little phosphoric acid, the pH will rise, and a large number of impurities with fine and uneven crystals will be produced, and the purity of the obtained manganese monohydrogen phosphate trihydrate will be too low; if there is too much phosphoric acid, the solubility of manganese monohydrogen phosphate trihydrate in the system of this application will increase, and the yield will decrease; and in the case of too much phosphoric acid, impurities with Marib salt will also be generated, affecting the formation of manganese monohydrogen phosphate trihydrate. Therefore, this application can only react with manganese carbonate solution as the base liquid.

[0019] In another embodiment, when preparing the manganese carbonate solution, the stirring rate is 200 rpm / min, and the rate of pumping the phosphoric acid solution is 50-100 L / h.

[0020] In another embodiment, after the manganese carbonate solution and the phosphoric acid solution are mixed, they are aged for 120 min to 240 min under nitrogen protection.

[0021] In another embodiment, the solid material after the reaction is completed, the filter press and the washing is dried at 60°C.

[0022] If the drying temperature is too high, the prepared octahedral manganese monohydrogen phosphate trihydrate will lose water, thereby destroying its hydrated crystal structure and causing atoms to recombine to form other compounds. Therefore, the purity of the octahedral manganese monohydrogen phosphate trihydrate is affected due to the high drying temperature.

[0023] Therefore, the present application involves a method for producing manganese monohydrogen phosphate trihydrate, which uses manganese carbonate solid slurry as a base liquid to synthesize manganese monohydrogen phosphate, and constructs a regular octahedral morphology through precipitation solid phase transformation, which has a larger specific surface area. In the subsequent synthesis of lithium manganese iron phosphate, it helps to improve the reactivity of Mn and form a more uniform lithium manganese iron phosphate, thereby improving the compaction capacity and electrochemical performance.

[0024] Furthermore, in order to achieve the second purpose of this application, this application adopts the following technical means: A method for recycling a mother liquor containing Mn, applied to the aforementioned production process of battery-grade manganese monohydrogen phosphate trihydrate, comprises the following steps: S1. The filtrate after the reaction of the manganese carbonate solution and the phosphoric acid solution is used as the bottom liquid, CO2 is blown into the filtrate, ammonia is added to control the pH at 8 to 9, the reaction temperature is controlled at 60 ° C, and the reaction is carried out under a micro-pressure environment; S2. After the reaction is completed, the reaction slurry is centrifuged using a centrifuge; S3. The centrifuged solid material is dried at 105° C. to obtain manganese carbonate, which is fed into the manganese carbonate solution preparation process as a raw material; the centrifuged mother liquor is used as the diammonium hydrogen phosphate solution to react with the manganese carbonate solution to prepare manganese monohydrogen phosphate trihydrate.

[0025] In another embodiment, the micro-pressure environment is P=100Pa.

[0026] In this way, the Mn-containing mother liquor recycling method of the present application can be used to recover a large amount of Mn contained in the mother liquor during the preparation of manganese monohydrogen phosphate trihydrate due to incomplete reaction. 2+ The filtrate of ions is collected, and then the CO2 gas released during the reaction of manganese carbonate solution and phosphoric acid solution is used to remove Mn in the filtrate. 2+ ions are recovered to form manganese carbonate solid, thus providing recycled raw materials for the preparation of manganese monohydrogen phosphate trihydrate. 2+During the recovery process, while ammonia water is used to adjust the pH, after the reaction is completed, the filtrate generated during the Mn recovery process can contain a large amount of diammonium phosphate, so the filtrate generated during the Mn recovery process can also be reused as a raw material in the preparation process of manganese monohydrogen phosphate trihydrate of the present application. Therefore, the preparation method of manganese monohydrogen phosphate trihydrate involved in the present application can greatly increase the yield of manganese monohydrogen phosphate trihydrate after being used in conjunction with the method for recycling the mother liquor containing Mn, so that it is suitable for industrial production.

[0027] Finally, in order to achieve the third purpose of this application, this application also adopts the following technical means: A positive electrode material is a lithium iron manganese phosphate positive electrode material, using the manganese monohydrogen phosphate trihydrate prepared by the above-mentioned manganese monohydrogen phosphate trihydrate production method as a manganese source precursor.

[0028] Therefore, since the crystal form of the manganese monohydrogen phosphate trihydrate prepared in the present application is uniform, all of them are regular octahedral crystal forms. Therefore, using the manganese monohydrogen phosphate trihydrate prepared in the present application as a manganese source, in the process of preparing the lithium manganese iron phosphate positive electrode material, compared with the conventional strip-shaped manganese monohydrogen phosphate trihydrate, it can have a larger specific surface area, allowing Mn to have higher reactivity. The regular octahedral structure of manganese monohydrogen phosphate trihydrate can make the formed lithium manganese iron phosphate more uniform and improve its compacted capacity and electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the SEM image of ordinary manganese monohydrogen phosphate trihydrate.

[0030] Figure 2 This is the SEM image of manganese monohydrogen phosphate trihydrate prepared in this application.

[0031] Figure 3 This is the XRD result of the product under high temperature conditions in this application.

[0032] Figure 4 This is a SEM image of the product in one embodiment of the present application.

[0033] Figure 5 This is the XRD result of manganese monohydrogen phosphate trihydrate prepared in this application.

[0034] Figure 6 These are electrochemical performance test diagrams of different embodiments of the present application. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0036] Example 1 S1. Manganese monohydrogen phosphate trihydrate is synthesized using manganese carbonate and phosphoric acid (or ammonium monohydrogen phosphate).

[0037] S2. Prepare manganese carbonate base material in kettle 1: mass ratio of manganese carbonate: pure water = 1:4, stir into slurry for later use.

[0038] S3. Prepare the phosphoric acid solution in kettle 2: mass ratio of 65% phosphoric acid: pure water = 1:1. Molar ratio of manganese carbonate: phosphoric acid = 1:1.05~1.10.

[0039] S4. Place the manganese carbonate slurry in the preparation kettle 1 in the reactor 1 as the bottom liquid, set the stirring rate to 200rpm / min, and set the reaction temperature to 58~62℃; use a peristaltic pump to pump the prepared phosphoric acid solution into the reactor at a rate of 50~100L / h. During the reaction, the pH is ≤3, and nitrogen protection is turned on during the reaction. Aging reaction is 120min~240min. The CO2 gas generated in the reaction is passed into the gas storage tank.

[0040] S5. The slurry after the reaction is washed by a filter press, and the washing water solid-liquid ratio is 1:1. The mother liquor obtained by the filter press is sent to the mother liquor tank 1 as the filtrate A; the washing liquid after washing is sent to the washing liquid tank 1.

[0041] After washing, the filtered material was sent to a vacuum dryer at 60°C for 12 hours to obtain monomanganese hydrogen phosphate trihydrate.

[0042] Example 2 On the basis of Example 1, the temperature for reacting the manganese carbonate solution with the phosphoric acid solution was adjusted to 55° C., and the other processes and procedures were the same as those in Example 1.

[0043] Example 3 On the basis of Example 1, the temperature for reacting the manganese carbonate solution with the phosphoric acid solution was adjusted to 65° C., and the other processes and procedures were the same as those in Example 1.

[0044] Example 4 On the basis of Example 1, the temperature for reacting the manganese carbonate solution with the phosphoric acid solution was adjusted to 85° C., and the other processes and procedures were the same as those in Example 1.

[0045] After comparing the manganese monohydrogen phosphate trihydrate produced in Example 1, Example 2, and Example 3, it was found that due to the relatively low reaction temperature in Example 2, the growth rate of the manganese monohydrogen phosphate crystals would be reduced, causing the manganese monohydrogen phosphate crystals to grow slowly, thereby generating a regular octahedral crystal form while also intermixing some strip crystals. From the SEM image of the manganese monohydrogen phosphate prepared in Example 2, it can be found that a small amount of strip crystals are intermixed in the regular octahedral crystals. In Example 3, the reaction temperature is relatively high. When the manganese monohydrogen phosphate prepared in Example 3 is subjected to XRD testing, it is found that some other impurities such as Mn5(PO3(OH))2(PO4)2(H2O)4 are generated. When the temperature is relatively high, it will greatly affect the normal generation of the manganese monohydrogen phosphate trihydrate of the present application. Among them, as for the product prepared in Example 4, after the product is tested by XRD, it is found that the product is completely converted into the Mn5(PO3(OH))2(PO4)2(H2O)4 impurity phase, such as Figure 3 As shown in the figure, Example 1 is the best example, which can produce high-purity manganese monohydrogen phosphate trihydrate with a regular octahedral crystal structure. Figure 5 shown.

[0046] Example 5 On the basis of Example 1, the reaction pH of the manganese carbonate solution and the phosphoric acid solution was adjusted to 5, and the other processes and procedures were the same as those in Example 1.

[0047] Comparing the SEM images and XRD images of the manganese monohydrogen phosphate produced in Example 1 with that in Example 5, it is found that due to the relatively high pH value in Example 4, it not only affects the synthesis of the pure phase of manganese monohydrogen phosphate, but also during the process of self-assembly of the crystals, the manganese monohydrogen phosphate prepared in Example 5 cannot synthesize a large number of regular octahedral crystals. In Example 5, the manganese monohydrogen phosphate is still mainly in the form of strip crystals.

[0048] Example 6 On the basis of Example 1, the mass ratio of manganese carbonate to pure water was changed to 1:3, and the other processes and procedures were the same as those in Example 1.

[0049] Example 7 On the basis of Example 1, the mass ratio of manganese carbonate to pure water was changed to 1:5, and the other processes and procedures were the same as those in Example 1.

[0050] After comparing the manganese monohydrogen phosphate trihydrate produced in Example 1, Example 6 and Example 7, it was found that in Example 6, due to the increase in the concentration of manganese carbonate, the concentration of manganese carbonate increased, and the surface of the generated manganese monohydrogen phosphate trihydrate crystals had a large number of fine grains, which was shown in the SEM image, as shown in FIG. Figure 4As shown, the manganese monohydrogen phosphate trihydrate prepared in Example 6 is prone to mutual adhesion due to the presence of a large number of fine grains on the crystal surface, and the finished product manganese monohydrogen phosphate trihydrate is prone to caking. Even if it is damaged by mechanical crushing in the later stage, this will affect the integrity of the crystal structure of the manganese monohydrogen phosphate trihydrate, which is not conducive to the improvement of the electrical properties and compacted capacity of the positive electrode material when preparing the lithium iron manganese phosphate positive electrode material in the later stage. In Example 7, due to the reduction in the concentration of manganese carbonate, the reaction between the manganese carbonate solution and the phosphoric acid solution is relatively slow. During the reaction, it is easily affected by other ions in the reaction environment and is easy to form other impurities. In the XRD image of the manganese monohydrogen phosphate trihydrate produced in Example 7, it can be found that in addition to manganese monohydrogen phosphate trihydrate, there are other impurities. Therefore, under the conditions of Example 1, high-purity regular octahedral manganese monohydrogen phosphate trihydrate crystals can be obtained, such as Figure 2 and Figure 5 shown.

[0051] Example 8 In this example, the filtrate A obtained in Example 1 was collected and then used as the bottom liquid, CO2 was bubbled into it, ammonia water was added to control the pH to 8-9, the reaction temperature was controlled at 60°C, and the reaction was carried out under a micro-pressure environment; After the reaction is completed, the reaction slurry is centrifuged using a centrifuge; Then the centrifuged solid material is dried at 105° C. to obtain manganese carbonate, which is fed into the manganese carbonate solution preparation process as a raw material; the centrifuged mother liquor is used as the diammonium hydrogen phosphate solution to react with the manganese carbonate solution to prepare manganese monohydrogen phosphate trihydrate.

[0052] The micro-pressure environment in this embodiment is a condition of P=100Pa.

[0053] In this embodiment, the recovered manganese carbonate and diammonium hydrogen phosphate are used as raw materials and the production is carried out under the conditions of Example 1. As in Example 1, high-purity manganese monohydrogen phosphate trihydrate with a regular octahedral crystal structure can also be obtained. Thus, the yield of industrial production can be greatly improved.

[0054] Example 9 In this embodiment, the manganese monohydrogen phosphate trihydrate prepared in Example 1 is used as a manganese source to prepare a lithium manganese iron phosphate positive electrode material.

[0055] Example 10 In this embodiment, the same positive electrode material preparation process as that of Embodiment 9 is adopted, but the manganese source is replaced with manganese monohydrogen phosphate trihydrate prepared in Embodiment 2.

[0056] Embodiment 11 In this embodiment, the same positive electrode material preparation process as that of Embodiment 9 is adopted, but the manganese source is replaced with the manganese source prepared in Embodiment 3.

[0057] Example 12 In this embodiment, the same positive electrode material preparation process as that of Embodiment 9 is adopted, but the manganese source is replaced with manganese monohydrogen phosphate trihydrate prepared in Embodiment 4.

[0058] Embodiment 13 In this embodiment, the same positive electrode material preparation process as that of Embodiment 9 is adopted, but the manganese source is replaced with manganese monohydrogen phosphate trihydrate prepared in Embodiment 5.

[0059] Embodiment 14 In this embodiment, the same positive electrode material preparation process as that of Embodiment 9 is adopted, but the manganese source is replaced with the manganese source prepared in Embodiment 6.

[0060] Embodiment 15 In this embodiment, the same positive electrode material preparation process as that of Embodiment 9 is adopted, but the manganese source is replaced with the manganese source prepared in Embodiment 7.

[0061] When the positive electrode materials prepared in the above-mentioned Examples 9 to 15 are tested, when the purity, crystal form and uniformity of the manganese source are affected, it will have a greater impact on the electrical properties and compacted capacity of the lithium iron manganese phosphate positive electrode material prepared by the same process. Among them, Example 9, as a lithium iron manganese phosphate positive electrode material prepared by using high-purity and good uniformity regular octahedral manganese monohydrogen phosphate as a manganese source, has significantly improved electrical properties and compacted capacity, which is significantly better than the positive electrode materials prepared in other examples. The samples prepared in Examples 9 to 15 were tested for compacted density and discharge specific capacity under 0.1C conditions. The specific results are shown in Table 1 below. Table 1 shows the compacted density of different positive electrode materials and the discharge specific capacity under 0.1C conditions, and the electrochemical properties of different examples can be seen. Figure 6 shown.

[0062] Table 1 Compacted density and discharge specific capacity of different cathode materials Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for producing manganese monohydrogen phosphate trihydrate, characterized in that: Manganese carbonate solution is used as the base liquid, phosphoric acid solution or diammonium hydrogen phosphate solution is pumped in at 50-80°C, the reaction pH is controlled not to exceed 3, the reaction is carried out under the protection of inert gas, and the solid material after pressure filtration and washing is dried to obtain manganese monohydrogen phosphate trihydrate.

2. The method for producing manganese monohydrogen phosphate trihydrate according to claim 1, characterized in that: The reaction temperature of the manganese carbonate solution and the phosphoric acid solution or the diammonium hydrogen phosphate solution is 58-62°C.

3. The method for producing manganese monohydrogen phosphate trihydrate according to claim 1, characterized in that: The manganese carbonate solution is prepared by adopting a mass ratio of manganese carbonate to pure water of 1:

4.

4. The method for producing manganese monohydrogen phosphate trihydrate according to claim 1, characterized in that: The phosphoric acid solution is prepared by using 65% phosphoric acid: pure water in a mass ratio of 1:

1.

5. The method for producing manganese monohydrogen phosphate trihydrate according to any one of claims 1 to 4, characterized in that: The molar ratio of manganese carbonate to phosphoric acid in the manganese carbonate solution and the phosphoric acid solution is 1:1.05-1.

10.

6. The method for producing manganese monohydrogen phosphate trihydrate according to claim 1, characterized in that: When preparing the manganese carbonate solution, the stirring rate is 200 rpm / min, and the rate of pumping the phosphoric acid solution is 50-100 L / h.

7. The method for producing manganese monohydrogen phosphate trihydrate according to claim 1, characterized in that: After the manganese carbonate solution and the phosphoric acid solution are mixed, they are aged for 120 min to 240 min under nitrogen protection.

8. The method for producing manganese monohydrogen phosphate trihydrate according to claim 1, characterized in that: After the reaction is completed, the solid material after filter pressing and washing is dried at 60°C.

9. A method for recycling a Mn-containing mother liquor, characterized in that: The method for producing manganese monohydrogen phosphate trihydrate as claimed in any one of claims 1 to 7 comprises the following steps: S1. The filtrate after the reaction of the manganese carbonate solution and the phosphoric acid solution is used as the bottom liquid, CO2 is blown in, ammonia is added to control the pH at 8 to 9, the reaction temperature is controlled at 60 ° C, and the reaction is carried out under a micro-pressure environment, P = 100Pa; S2. After the reaction is completed, the reaction slurry is centrifuged using a centrifuge; S3. The centrifuged solid material is dried at 105° C. to obtain manganese carbonate, which is fed into the manganese carbonate solution preparation process as a raw material; the centrifuged mother liquor is used as the diammonium hydrogen phosphate solution to react with the manganese carbonate solution to prepare manganese monohydrogen phosphate trihydrate.

10. A positive electrode material, characterized in that The lithium manganese iron phosphate positive electrode material is prepared by using the manganese monohydrogen phosphate trihydrate obtained by the production method of manganese monohydrogen phosphate trihydrate described in any one of claims 1 to 8 as a manganese source precursor.

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