Production method of manganese monohydrogen phosphate trihydrate, method for recycling Mn-containing mother liquor, and cathode material

Abstract

The present invention discloses a method for producing manganese monohydrogen phosphate trihydrate, a method for recycling Mn-containing mother liquor, and a cathode material, relating to the technical field of lithium-ion batteries. In the present invention, a solid manganese carbonate slurry is used as a bottom liquid to synthesize manganese monohydrogen phosphate. Through precipitation solid-phase transformation, an octahedral morphology feature is constructed, which has a larger specific surface area. During the subsequent synthesis of lithium iron manganese phosphate, it helps to improve the reactivity of Mn and form a more uniform lithium iron manganese phosphate cathode material, thereby improving the compaction capacity and electrochemical performance of the cathode material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries. Specifically, it is about a production method of manganese monohydrogen phosphate trihydrate, a method for recycling Mn-containing mother liquor, and a cathode material. Background Art

[0002] Lithium iron manganese 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 the fields of electric vehicles, mobile power sources and energy storage systems.

[0003] Currently, the manganese source precursors used in the synthesis of lithium iron manganese 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 tap density of the obtained lithium iron manganese phosphate, reducing the volumetric energy ratio of the material. Manganese tetraoxide leads to poor product distribution uniformity and low capacity. Manganese ions in manganese hydroxide are extremely easy to oxidize during the production process, and the product cost is relatively high.

[0004] Moreover, when conventional manganese monohydrogen phosphate trihydrate is used as the manganese source, its crystal form is mostly strip-shaped, aggregated and stacked in a flower-like shape, with uneven size and shape distribution, as Figure 1 shown. When such manganese monohydrogen phosphate trihydrate is used as the manganese source to synthesize lithium iron manganese phosphate, the consistency of the lithium iron manganese phosphate cathode material is poor and the tap capacity is relatively low. Summary of the Invention

[0005] One of the purposes of the present invention is to provide a production method of manganese monohydrogen phosphate trihydrate to solve the problem that when the existing manganese monohydrogen phosphate trihydrate is used as the manganese source to synthesize the lithium iron manganese phosphate cathode material, the consistency of the lithium iron manganese phosphate cathode material is poor and the tap capacity is relatively low.

[0006] Another purpose of the present invention is to provide a method for recycling Mn-containing mother liquor to solve the problem that in the process of synthesizing manganese monohydrogen phosphate trihydrate in this application, due to the limitation of Ksp, the reaction cannot proceed completely, resulting in a low yield and being not suitable for industrial production.

[0007] The third purpose of the present invention is to provide a cathode material to solve the problem that when using ordinary manganese monohydrogen phosphate as the manganese source currently, the consistency is poor and the tap capacity is relatively low.

[0008] To solve the above-mentioned first purpose, the present invention adopts the following technical means:

[0009] A production method of manganese monohydrogen phosphate trihydrate uses a manganese carbonate solution as the bottom liquid. Under the condition of 50-80 °C, a phosphoric acid solution or a diammonium hydrogen phosphate solution is pumped in, and the reaction pH is controlled not to exceed 3. The reaction is carried out under the protection of an inert gas. After the reaction is completed, the solid material after pressure filtration and washing is dried to obtain manganese monohydrogen phosphate trihydrate.

[0010] During the reaction between the manganese carbonate solution and the phosphoric acid solution or the diammonium hydrogen phosphate solution, under the condition of a low pH not exceeding 3 and in an environment of 50-80 °C, the specific reaction temperature is preferably 58-62 °C, OH - The reduction of the availability of OH ions reduces the kinetic coefficients of other phases in the system, such as Mn4H(PO4)3, Mn5OH(PO4)3, etc. In the heterogeneous nucleation process of the manganese monohydrogen phosphate trihydrate hydrated phase, the substrate will reduce the nucleation potential energy, and due to its lower interfacial free energy, it has a higher nucleation rate, making its crystal nuclei form preferentially; thus enabling the entire reaction to obtain pure-phase manganese monohydrogen phosphate trihydrate.

[0011] Moreover, during the solid-phase transformation of manganese monohydrogen phosphate trihydrate, in the system of this application, the manganese monohydrogen phosphate can form an octahedral structure through H + oriented attachment. Among them, for the reaction environment of this application, within a specific pH range and temperature, the material is in a supersaturated state, and the adsorption energy of protons (H + ) on the side of the crystal is lower than the adsorption energy on the Mn 2+ (020, 111, 102) planes, so that H + is preferentially adsorbed on the side. Due to the effect of charge repulsion, the adsorption of Mn + is inhibited; resulting in a high growth rate of the Mn 2 + (020, 111, 102) planes. And according to the Ostwald ripening rule, larger particles will grow at the expense of smaller particles, resulting in isotropic crystals having a similar shape inherited from their inherent crystal properties, thus realizing the tendency of molecules to be symmetrically arranged, and enabling the prepared manganese monohydrogen phosphate trihydrate to form an octahedral morphology.

[0012] For the overall reaction temperature, if the reaction temperature is reduced, such as under the condition of 50-57 °C, it will cause the crystal growth rate to be slow, and the crystal growth process is easily affected by the outside world, resulting in the formation of some strip-shaped crystals, affecting the purity of octahedral manganese monohydrogen phosphate; if the reaction temperature is too high, such as 63-80 °C, some impurity phases will be generated, and if the reaction is carried out under the condition of higher than 80 °C, impurity phases will be completely generated, such as the monoclinic manganese phosphate mineral Mn5(PO3(OH))2(PO4)2(H2O)4. It can be seen Figure 3The XRD result diagram shown. Therefore, it is difficult to produce high-purity manganese monohydrogen phosphate octahedron trihydrate at too high or too low temperatures.

[0013] Moreover, for this application, only the manganese carbonate solution can be used as the reaction bottom liquid to avoid a large excess of phosphoric acid solution at the initial stage of the reaction, and to prevent the formation of a heterogeneous phase with manganese sulfate monohydrate.

[0014] In another embodiment, the manganese carbonate solution is prepared with a mass ratio of manganese carbonate to pure water of 1:4.

[0015] In order to ensure that the manganese carbonate solution has a suitable viscosity, it is not only convenient for material transfer but also ensures that the manganese carbonate solution can react uniformly after contacting with the acid. If the concentration of the manganese carbonate solution is too high, the viscosity increases, and it is difficult to react uniformly after encountering the acid. The surface reaction is intense, and the rapid release of CO2 causes the bottom material to overflow. If the concentration is too small, water is wasted, the difficulty of water treatment is increased, the reaction rate is reduced, and it is easy to form a heterogeneous phase, making it impossible to ensure the synthesis of high-purity manganese monohydrogen phosphate trihydrate.

[0016] In another embodiment, the phosphoric acid solution is prepared with a mass ratio of 65% phosphoric acid to pure water of 1:1.

[0017] By diluting the phosphoric acid solution, the generation rate of CO2 during the reaction is reduced, overflow is prevented, the pressure-bearing risk in the system is reduced, and at the same time, the corrosion rate of the container is reduced.

[0018] In another embodiment, the molar ratio of manganese carbonate to phosphoric acid in the manganese carbonate solution to the phosphoric acid solution is 1:1.05 - 1.10.

[0019] Among them, during the reaction process, an excessive amount of HPO4 2- , and H + participate in the reaction while controlling the pH of the reaction system. If the amount of phosphoric acid is too small, while the pH increases, a large number of heterogeneous phases with fine and uneven crystal forms will be generated, and the purity of the obtained manganese monohydrogen phosphate trihydrate will be too low; if the amount of phosphoric acid is too much, the solubility of manganese monohydrogen phosphate trihydrate in the system of this application will increase, and the yield will decrease; moreover, in the case of too much phosphoric acid, a heterogeneous phase with manganese sulfate monohydrate will also be generated, affecting the formation of manganese monohydrogen phosphate trihydrate. Therefore, in this application, only the manganese carbonate solution can be used as the bottom liquid for the reaction.

[0020] In another embodiment, when preparing the manganese carbonate solution, the stirring rate is 200 rpm / min, and the rate of pumping in the phosphoric acid solution is 50 - 100 L / h.

[0021] In another embodiment, after the manganese carbonate solution and the phosphoric acid solution are mixed, the aging reaction is carried out for 120 min - 240 min under nitrogen protection.

[0022] In another embodiment, the solid material after the reaction is completed, pressure filtered and washed is dried at 60 °C.

[0023] Among them, if the drying temperature is too high, the prepared manganese monohydrogen phosphate trihydrate in octahedron form will lose water, thus destroying its hydrated crystal structure, and the atoms recombine to form other compounds. Therefore, the purity of manganese monohydrogen phosphate trihydrate in octahedron form is affected due to too high drying temperature.

[0024] Therefore, a production method of manganese monohydrogen phosphate trihydrate involved in the present application uses a manganese carbonate solid slurry as the bottom liquid to synthesize manganese monohydrogen phosphate. Through precipitation solid-phase transformation, an octahedral morphology feature is constructed, which has a larger specific surface area. In the subsequent synthesis process of lithium iron manganese phosphate, it helps to improve the reactivity of Mn, and form a more uniform lithium iron manganese phosphate, improving the compaction capacity and electrochemical performance.

[0025] Furthermore, in order to achieve the second object of the present application, the following technical means are adopted in the present application:

[0026] A method for recycling the Mn-containing mother liquor is applied to the production process method of the battery-grade manganese monohydrogen phosphate trihydrate described above, and includes the following steps:

[0027] S1. Using the pressure filtrate after the reaction of the manganese carbonate solution and the phosphoric acid solution as the bottom liquid, introducing CO2, adding ammonia water to control the pH at 8-9, controlling the reaction temperature at 60 °C, and carrying out the reaction in a slightly pressurized environment;

[0028] S2. After the reaction is completed, centrifuging the reaction slurry using a centrifuge;

[0029] S3. Drying the centrifuged solid material at 105 °C to obtain manganese carbonate, which is sent as a raw material for use in the preparation process of the manganese carbonate solution; the centrifuged mother liquor is used for the reaction of the diammonium hydrogen phosphate solution and the manganese carbonate solution to prepare manganese monohydrogen phosphate trihydrate.

[0030] In another embodiment, the slightly pressurized environment is P = 100 Pa.

[0031] In this way, through the method for recycling the Mn-containing mother liquor involved in the present application, the filtrate containing a large amount of Mn ions due to incomplete reaction during the preparation of manganese monohydrogen phosphate trihydrate can be collected, and then the CO2 gas released during the reaction of the manganese carbonate solution and the phosphoric acid solution is used to recover the Mn ions in the filtrate to generate manganese carbonate solid, thereby providing recycled raw materials for the preparation of manganese monohydrogen phosphate trihydrate. Moreover, during the Mn 2+ ion collection, then using the CO2 gas released during the reaction of the manganese carbonate solution and the phosphoric acid solution, the Mn 2+ ions in the filtrate are recovered to generate manganese carbonate solid, thus providing recycled raw materials for the preparation of manganese monohydrogen phosphate trihydrate. And during the Mn 2+During the recycling process, while adjusting the pH with ammonia water, it is also possible to make the filtrate generated during the Mn recycling process contain a large amount of diammonium hydrogen phosphate after the reaction. Therefore, the filtrate generated during the Mn recycling process can also be used as a raw material and recycled to the preparation process of manganese dihydrogen phosphate trihydrate in this application. Therefore, after the method for preparing manganese dihydrogen phosphate trihydrate involved in this application is used in conjunction with the method for recycling the Mn-containing mother liquor, the yield of manganese dihydrogen phosphate trihydrate can be significantly increased, making it suitable for industrial production.

[0032] Finally, to achieve the third object of this application, the following technical means are also adopted in this application:

[0033] A cathode material is a lithium iron manganese phosphate cathode material, and manganese dihydrogen phosphate trihydrate prepared by the aforementioned method for producing manganese dihydrogen phosphate trihydrate is used as a manganese source precursor.

[0034] Therefore, due to the uniform crystal form of the manganese dihydrogen phosphate trihydrate prepared in this application, all of which are crystal forms with a regular octahedron structure. Therefore, when using the manganese dihydrogen phosphate trihydrate prepared in this application as a manganese source, during the process of preparing the lithium iron manganese phosphate cathode material, compared with the conventional strip-shaped crystal form of manganese dihydrogen phosphate trihydrate, it can have a larger specific surface area, enabling Mn to have higher reactivity. The manganese dihydrogen phosphate trihydrate with a regular octahedron structure can make the formed lithium iron manganese phosphate more uniform, improving its tap density and electrochemical performance. Description of the Drawings

[0035] Figure 1 It is the SEM image of ordinary manganese dihydrogen phosphate trihydrate.

[0036] Figure 2 It is the SEM image of the manganese dihydrogen phosphate trihydrate prepared in this application.

[0037] Figure 3 It is the XRD result of the product under high temperature conditions in this application.

[0038] Figure 4 It is the SEM image of the product in an embodiment of this application.

[0039] Figure 5 It is the XRD result of the manganese dihydrogen phosphate trihydrate prepared in this application.

[0040] Figure 6 It is the electrochemical performance test chart of different embodiments in this application. Detailed Embodiments

[0041] To make the objectives, 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 accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention.

[0042] Example 1

[0043] S1. Synthesize manganese monohydrogen phosphate trihydrate using manganese carbonate and phosphoric acid (or ammonium monohydrogen phosphate).

[0044] S2. Prepare the manganese carbonate base material in kettle 1: The mass ratio of manganese carbonate to pure water is 1:4, and stir it into a slurry for standby.

[0045] S3. Prepare the phosphoric acid solution in kettle 2: The mass ratio of 65% phosphoric acid to pure water is 1:1. The molar ratio of manganese carbonate to phosphoric acid is 1:1.05 - 1.10.

[0046] S4. Place the manganese carbonate slurry from kettle 1 into reactor 1 as the bottom liquid, set the stirring rate at 200 rpm / min, and set the reaction temperature at 58 - 62 °C; use a peristaltic pump to pump the prepared phosphoric acid solution into the reactor at a rate of 50 - 100 L / h. During the reaction, pH ≤ 3, and nitrogen protection is turned on during the reaction. Age the reaction for 120 min - 240 min. The CO2 gas generated during the reaction is introduced into the gas storage tank.

[0047] S5. Wash the reacted slurry using a filter press, and the solid-liquid ratio of the washing water is 1:1. The mother liquor filtered out is sent to mother liquor tank 1 as filtrate A; the washing liquid after washing is sent to washing liquid tank 1.

[0048] S6. Feed the material after washing and filtration into vacuum drying, and dry it under vacuum at 60 °C for 12 h. Obtain manganese monohydrogen phosphate trihydrate.

[0049] Example 2

[0050] On the basis of Example 1, adjust the reaction temperature of the manganese carbonate solution and the phosphoric acid solution to 55 °C, and other processes and procedures are the same as those in Example 1.

[0051] Example 3

[0052] On the basis of Example 1, adjust the reaction temperature of the manganese carbonate solution and the phosphoric acid solution to 65 °C, and other processes and procedures are the same as those in Example 1.

[0053] Example 4

[0054] On the basis of Example 1, adjust the reaction temperature of the manganese carbonate solution and the phosphoric acid solution to 85 °C, and other processes and procedures are the same as those in Example 1.

[0055] 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.

[0056] Example 5

[0057] 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.

[0058] 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.

[0059] Example 6

[0060] 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.

[0061] Example 7

[0062] 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.

[0063] 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 agglomeration because there are a large number of fine grains on the crystal surface, and the finished manganese monohydrogen phosphate trihydrate is prone to caking. Even if it is broken by mechanical means later, this will also affect the crystal structure integrity of manganese monohydrogen phosphate trihydrate, which is not conducive to improving the electrical properties and compaction capacity of the cathode material during the later preparation of lithium iron manganese phosphate cathode material. For Example 7, due to the decrease in the concentration of manganese carbonate, the reaction between the manganese carbonate solution and the phosphoric acid solution is relatively slow during the reaction process. During the reaction, it is easily affected by other ions in the reaction environment and is prone to form other impurity phases. 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 also other impurity phase substances. Therefore, under the conditions of Example 1, high-purity regular octahedron manganese monohydrogen phosphate trihydrate crystals can be obtained, such as Figure 2 and Figure 5 shown.

[0064] Example 8

[0065] In this example, the filtrate A obtained in Example 1 was collected and used as the bottom liquid. CO2 was bubbled in, ammonia water was added to control the pH at 8 - 9, the reaction temperature was controlled at 60 °C, and the reaction was carried out under a slightly pressurized environment;

[0066] After the reaction was completed, the reaction slurry was centrifuged using a centrifuge;

[0067] Then the centrifuged solid material was dried at 105 °C to obtain manganese carbonate, which was sent as a raw material for use in the preparation process of the manganese carbonate solution; the centrifuged mother liquor was used as the reaction between the diammonium hydrogen phosphate solution and the manganese carbonate solution to prepare manganese monohydrogen phosphate trihydrate.

[0068] Among them, the slightly pressurized environment in this example was under the condition of P = 100 Pa.

[0069] In this example, the recycled manganese carbonate and diammonium hydrogen phosphate were used as raw materials and produced under the conditions of Example 1. Similar to Example 1, high-purity manganese monohydrogen phosphate trihydrate with a regular octahedron crystal structure could also be obtained. Thus, the yield of industrial production could be significantly increased.

[0070] Example 9

[0071] In this example, the manganese monohydrogen phosphate trihydrate prepared in Example 1 was used as the manganese source to prepare the lithium iron manganese phosphate cathode material.

[0072] Example 10

[0073] In this example, the same cathode material preparation process as in Example 9 was used, but the manganese source was replaced with the manganese monohydrogen phosphate trihydrate prepared in Example 2.

[0074] Example 11

[0075] In this example, the same preparation process of the positive electrode material as in Example 9 is adopted, but the manganese source is replaced with the manganese source prepared in Example 3.

[0076] Example 12

[0077] In this example, the same preparation process of the positive electrode material as in Example 9 is adopted, but the manganese source is replaced with manganese monohydrogen phosphate trihydrate prepared in Example 4.

[0078] Example 13

[0079] In this example, the same preparation process of the positive electrode material as in Example 9 is adopted, but the manganese source is replaced with manganese monohydrogen phosphate trihydrate prepared in Example 5.

[0080] Example 14

[0081] In this example, the same preparation process of the positive electrode material as in Example 9 is adopted, but the manganese source is replaced with the manganese source prepared in Example 6.

[0082] Example 15

[0083] In this example, the same preparation process of the positive electrode material as in Example 9 is adopted, but the manganese source is replaced with the manganese source prepared in Example 7.

[0084] When testing the positive electrode materials prepared in the aforementioned Examples 9 to 15, when the purity, crystal form, and homogeneity of the manganese source are affected, it will have a greater impact on the electrical properties and compaction capacity of the lithium iron phosphate manganese positive electrode material prepared by the same process. Among them, Example 9 is the lithium iron phosphate manganese positive electrode material prepared with high-purity and good-homogeneity octahedral manganese monohydrogen phosphate as the manganese source, and its electrical properties and compaction capacity have been greatly improved, significantly superior to the positive electrode materials prepared in other examples. The compaction density and discharge specific capacity under the condition of 0.1C of the samples prepared in Examples 9 to 15 are tested, and the specific results are shown in Table 1 below. Table 1 is the compaction density and discharge specific capacity of different positive electrode materials, and the electrochemical properties of different examples can be seen Figure 6 as shown.

[0085] Table 1 Compaction density and discharge specific capacity of different positive electrode materials

[0086]

[0087] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for producing manganese monohydrogen phosphate trihydrate, characterized in that, Using manganese carbonate solution as the bottom liquid, pump in phosphoric acid solution or diammonium hydrogen phosphate solution under the condition of 50-80 °C, control the reaction pH not exceeding 3, and carry out the reaction under the protection of inert gas. After the reaction is completed, filter and wash the solid material, and then dry it to obtain manganese monohydrogen phosphate trihydrate. The manganese carbonate solution is prepared with a mass ratio of manganese carbonate to pure water of 1:

4.

2. A 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 phosphoric acid solution is prepared with a mass ratio of 65% phosphoric acid to pure water of 1:

1.

4. The method for producing manganese monohydrogen phosphate trihydrate according to any one of claims 1 to 3, 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.

5. 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 pumping rate of the phosphoric acid solution is 50-100 L / h.

6. 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, age the reaction for 120 min-240 min under nitrogen protection.

7. The production method of manganese monohydrogen phosphate trihydrate according to claim 1, characterized in that, The solid material after the reaction is completed, filtered and washed is dried at 60 °C.

8. A method for recycling the Mn-containing mother liquor, characterized in that, Applied to the production method of manganese monohydrogen phosphate trihydrate described in any one of claims 1 to 6, including the following steps: S1. Use the filtrate after the reaction of the manganese carbonate solution and the phosphoric acid solution as the bottom liquid, introduce CO2, add ammonia water to control the pH at 8-9, control the reaction temperature at 60 °C, and carry out the reaction under a micro-pressure environment, P = 100 Pa; S2. After the reaction is completed, centrifuge the reaction slurry with a centrifuge; S3. Dry the centrifuged solid material at 105 °C to obtain manganese carbonate, and send it to be used as a raw material in the preparation process of the manganese carbonate solution; 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.

9. A cathode material, characterized in that it is The lithium iron phosphate manganese cathode material is prepared by using manganese monohydrogen phosphate trihydrate prepared by the production method of manganese monohydrogen phosphate trihydrate described in any one of claims 1 to 7 as a manganese source precursor.

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