A monolithic sagger for sintering lithium manganese iron phosphate and its preparation method

Abstract

The present invention discloses a monolithic sagger for sintering lithium manganese iron phosphate and a preparation method thereof. The specific steps of the preparation method are as follows: S1. preparing a mixture; the mixture is prepared by mixing calcium hexaaluminate particles, silicon carbide particles, calcium hexaaluminate fine powder, silicon oxynitride fine powder, silicon carbide fine powder and pure calcium aluminate cement fine powder; S2. adding potassium tripolyphosphate and potassium fluorozirconate solution to the mixture in sequence and stirring to obtain a castable; S3. placing the castable in a mold, casting and vibrating the mold, curing, and demolding to obtain a sagger green body; S4. drying the sagger green body, heat-treating it, and cooling it to room temperature to obtain a monolithic sagger for sintering lithium manganese iron phosphate. The method of the present invention has a simple process, and the prepared sagger has high density, high strength, strong corrosion resistance and permeability resistance, and high thermal shock stability.

Description

Technical Field

[0001] The present invention relates to the technical field of saggers, and in particular to an integral sagger for sintering lithium manganese iron phosphate and a preparation method thereof. Background Art

[0002] Lithium manganese iron phosphate is one of the important lithium-ion battery cathode materials developed on the basis of lithium iron phosphate. It has the advantages of low cost and high specific capacity, and its operating voltage is higher than that of lithium iron phosphate, but its cycle stability is insufficient ( Rao Yuan Yuan, Wang Kangping, Zeng Hui. Research progress of lithium manganese iron phosphate materials in lithium batteries[J]. Power Supply Technology, 2016, 40(2): 455- 457 At present, the preparation process of lithium iron phosphate is still based on that of lithium iron phosphate, and the synthesis is also carried out by high-temperature solid-phase method, that is, the raw material components are ground and mixed, spray granulated and other processes, and then added into a sagger under a protective atmosphere or a reducing atmosphere (protection of Fe 2+ Therefore, in general, due to the low alkalinity of the cathode material components and compared to the oxidizing atmosphere (air atmosphere) calcination of lithium cobalt oxide and LNCM ternary cathodes, the lithium manganese iron phosphate cathode material has a lower degree of corrosion damage to the sagger, and the service life of the sagger is also longer.

[0003] The sagger used for sintering lithium manganese iron phosphate positive electrode materials mainly refers to the process of lithium iron phosphate. The saggers used by the two are almost the same, mainly including two categories:

[0004] (1) Non-oxide crucibles with graphite as the main component. Such as the patented technology "A graphite crucible for lithium iron phosphate battery positive electrode, CN202320382050.5"; "A new type of graphite crucible for lithium iron phosphate sintering, CN202220588998.1". This type of crucible has good corrosion resistance, and due to the high thermal conductivity of the graphite component itself, the thermal shock stability of the crucible is guaranteed. In addition, service under reducing or protective atmosphere will not cause oxidation of the graphite crucible. Its main disadvantages are that, first, the cost of graphite raw materials is relatively high, and the preparation process of the crucible is relatively complicated, resulting in high development cost and expensive price of the crucible, and the advantage of single service cost is not obvious; second, the strength of the graphite crucible is relatively low, and it is easy to be damaged during service (such as turning the crucible or roller conveyor collision).

[0005] (2) Oxide saggers. Oxide components such as alumina, mullite and cordierite are used as raw materials, and rare earth oxides are introduced as additives. After mixing and molding, they are sintered. For example, "A method for preparing a high-temperature resistant sagger for producing positive electrode materials for lithium-ion batteries, CN201010269844.8" and so on, the development cost of oxide saggers is significantly lower, and most of them are machine-pressed, with good product quality stability and easy large-scale continuous industrial production. The main problem of this type of sagger is that the porosity of the machine-pressed sagger products is high, and the corrosion resistance of the oxide components is weak, which reduces the corrosion resistance and penetration resistance of the sagger.

[0006] In order to overcome the drawbacks of related technologies, it has been reported that a casting molding process is used to prepare saggers, such as "lightweight mullite-alumina hollow sphere-aluminum titanate sagger casting molding process, CN202110314143.X" and "lightweight mullite-spinel hollow sphere sagger casting molding process, CN202110311784.X". This type of technology mainly uses spherical materials to improve the fluidity and dispersibility of the castable to obtain a sagger with higher density. However, on the one hand, the price of the spherical material is too high, which significantly increases the development cost of the sagger. On the other hand, the stacking pores of the spherical material are large. Although it can be filled and complemented with other oxide components, the sintering of the spherical material is still difficult to be dense, resulting in low strength of the sagger. In addition, the oxide component has weak corrosion resistance, or the use of composite layers to form multiple structures and other technical means also makes it difficult to significantly improve the service life of the sagger. Summary of the Invention

[0007] The present invention aims to address the above-mentioned deficiencies in the prior art and to provide a monolithic sagger for sintering lithium manganese iron phosphate and a method for preparing the same. The method is simple in process, and the sagger prepared thereby has high density, high strength, strong corrosion and permeability resistance, and high thermal shock resistance.

[0008] The method for preparing a monolithic sagger for sintering lithium manganese iron phosphate of the present invention comprises the following specific steps:

[0009] S1. Prepare a mixture; the mixture is a mixture of calcium hexaaluminate particles, silicon carbide particles, calcium hexaaluminate powder, silicon oxynitride powder, silicon carbide powder and pure calcium aluminate cement powder;

[0010] S2. Potassium tripolyphosphate and potassium fluorozirconate solution were sequentially added to the mixture and stirred to obtain a castable;

[0011] S3. The castable is placed in a mold, cast and vibrated, cured, and demoulded to obtain a green sagger;

[0012] S4. The sagger green body is dried and then heat-treated, and cooled to room temperature to obtain a monolithic sagger for sintering lithium manganese iron phosphate.

[0013] Furthermore, in step S1,

[0014] The calcium hexaaluminate particles and silicon carbide particles are mixed to obtain a premixed particle material;

[0015] The calcium hexaaluminate fine powder, silicon oxynitride fine powder, silicon carbide fine powder and pure calcium aluminate cement fine powder are mixed to obtain a premixed fine powder material;

[0016] The premixed granular material and the premixed fine powder material are mixed to obtain a mixed material.

[0017] Furthermore, the mass ratio of calcium hexaaluminate particles to silicon carbide particles is 100:(13-26); and\or,

[0018] The mass ratio of calcium hexaaluminate fine powder: silicon oxynitride fine powder: silicon carbide fine powder: pure calcium aluminate cement fine powder is 100: (18-24): (12-18): (4.8-5.6); and\or,

[0019] The mass ratio of premixed granular material: premixed fine powder is 100: (62~70).

[0020] Furthermore, the potassium tripolyphosphate accounts for 0.08 to 0.16 wt % of the mixture.

[0021] Furthermore, the potassium fluorozirconate solution accounts for 5 to 9 wt% of the mixture; the concentration of the potassium fluorozirconate solution is 6 to 7 wt%.

[0022] Furthermore, in step S3, the castable is placed in a mold and cast and vibrated to form, cured at 25-30° C. for 2-3 hours, and demoulded to obtain a sagger green body.

[0023] Furthermore, in step S4, the sagger green body is placed at 100-110° C. and dried for 4-6 hours.

[0024] Furthermore, in step S4, the heat treatment is carried out at 1260-1380° C. in a nitrogen atmosphere for 3-6 hours.

[0025] Furthermore, the calcium hexaaluminate particles have a particle size of 0.5 to 3 mm, and the particle size is continuously distributed, wherein the mass ratio of [0.5 mm to 1 mm] particles: (1 mm to 2 mm] particles: (2 mm to 3 mm] particles is (25 to 35): (30 to 35): (25 to 30); and\or,

[0026] The silicon carbide particles have a particle size of 1 to 2 mm; and\or,

[0027] The particle size of the calcium hexaaluminate fine powder is 65 to 85 μm; and\or,

[0028] The particle size of the silicon oxynitride fine powder is 44 to 60 μm; and\or,

[0029] The particle size of the silicon carbide fine powder is 60 to 70 μm; and\or,

[0030] The particle size of the pure calcium aluminate cement fine powder is 20 to 30 μm; and\or,

[0031] The concentration of the potassium fluorozirconate solution is 6-7 wt %.

[0032] A monolithic sagger for sintering lithium manganese iron phosphate prepared by the above-mentioned preparation method.

[0033] The beneficial effects of the present invention are:

[0034] (1) The present invention only requires premixing the granular material and the fine powder material and then mixing them, and utilizes the chemical bonding of pure calcium aluminate cement and the ionization bonding of potassium salt to effectively improve the green strength of the sagger and reduce the scrap rate of the sagger.

[0035] (2) The present invention utilizes oxide-non-oxide composite means, utilizes the thermal conductivity and high corrosion resistance of the non-oxide itself and the lamellar structure of calcium hexaaluminate to resist the penetration of the positive electrode material and the simultaneous corrosion of lithium-manganese, thereby improving the service performance of the sagger.

[0036] (3) The present invention utilizes the liquid medium environment of pure calcium aluminate cement and potassium salt during high-temperature firing to promote the sintering of the material. At the same time, combined with the decomposition catalysis of potassium fluorozirconate, the growth of silicon carbide crystals is regulated to form silicon carbide whiskers in the calcium hexaaluminate lamellar structure, thereby improving the mechanical strength and thermal shock resistance of the sagger.

[0037] (4) The present invention utilizes a casting molding process and the ionization and coating effects of potassium tripolyphosphate to achieve the purpose of reducing water and promoting the dispersion of raw material components, thereby enhancing the uniformity of the mixing of the raw material components, which is beneficial to improving the structure of the sagger components; at the same time, the casting process does not require large-scale machine pressing equipment, the process is simple, and the equipment requirements are lower. There is no split or multi-layer composite structure design during the molding process, which avoids cracking or peeling of the composite layer structure and ensures the integrity of the sagger; in addition, casting molding reduces the resistance of the lean raw material components to external stress, and combined with the particle grading control of calcium hexaaluminate, it avoids the elastic aftereffect caused by the plastic bonding of the sagger components in processes such as machine pressing molding, and significantly improves the density of the sagger.

[0038] (5) The raw materials used in the present invention do not contain free acidic components, which reduces the degree of reaction with the lithium manganese iron phosphate positive electrode. At the same time, alkaline refractory raw materials such as calcium hexaaluminate and pure calcium aluminate cement are used to increase the alkalinity of the sagger components, further improving the sagger's resistance to alkali corrosion.

[0039] Therefore, the process of the present invention is simple, and the prepared integral sagger for sintering lithium manganese iron phosphate has high density, high strength, strong corrosion resistance and permeability resistance, and high thermal shock stability.

[0040] The integral sagger for sintering lithium manganese iron phosphate prepared by the present invention is tested:

[0041] The scrap rate of sagger is 0.8-1.1%;

[0042] Apparent porosity 15-17%;

[0043] Flexural strength 27~33MPa;

[0044] The residual flexural strength retention rate of the thermal shock stability test after three cycles of water cooling at 1100℃ is 93-96%, and the corrosion index of the static crucible method slag resistance test after 1100℃×10h is 0.6-0.8%. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a SEM image of the microstructure of the integral sagger aggregate for sintering lithium manganese iron phosphate prepared in Example 1;

[0046] Figure 2 This is an SEM image of the microstructure of the integral sagger matrix for sintering lithium manganese iron phosphate prepared in Example 1. DETAILED DESCRIPTION

[0047] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0048] Example 1

[0049] A method for preparing a monolithic sagger for sintering lithium manganese iron phosphate, the specific steps are as follows:

[0050] 1) Calcium hexaaluminate particles and silicon carbide particles were prepared in a mass ratio of 100:18 and added to a blender and mixed for 10-15 minutes to obtain a premixed granular material;

[0051] 2) adding calcium hexaaluminate fine powder: silicon oxynitride fine powder: silicon carbide fine powder: pure calcium aluminate cement fine powder in a mass ratio of 100:20:15:5.1, adding the mixture to a roller mixer and mixing for 1-2 hours to obtain a premixed fine powder;

[0052] 3) Add the premixed granules to the premixed fine powder at a mass ratio of 100:65, add the mixture into a blender and mix for 10-15 minutes to obtain a mixture;

[0053] 4) adding 0.11 wt% potassium tripolyphosphate and 8 wt% potassium fluorozirconate solution to the mixture in sequence, stirring for 6 to 10 minutes, placing the mixture in a mold, casting and vibrating the mixture, curing the mixture at 25 to 30° C. for 2 to 3 hours, and demolding the mixture to obtain a sagger green body; the concentration of the potassium fluorozirconate solution is 6 wt%.

[0054] 5) Dry the sagger green body at 100-110° C. for 4-6 hours, place it in a tunnel kiln and sinter it at 1340° C. in a nitrogen atmosphere for 5 hours, and cool it to room temperature to obtain a monolithic sagger for sintering lithium manganese iron phosphate.

[0055] The particle size of calcium hexaaluminate is 0.5-3 mm, and the particle size is continuously distributed, wherein the mass ratio of [0.5 mm-1 mm] particles: (1 mm-2 mm] particles: (2 mm-3 mm] particles is 30:33:28.

[0056] The particle size of silicon carbide particles is 1 to 2 mm.

[0057] The particle size of the calcium hexaaluminate fine powder is 65 to 85 μm.

[0058] The particle size of the silicon oxynitride fine powder is 44 to 60 μm.

[0059] The particle size of the silicon carbide fine powder is 60 to 70 μm.

[0060] The particle size of pure calcium aluminate cement fine powder is 20 to 30 μm.

[0061] Figure 1 This is an SEM image of the microstructure of the integral sagger aggregate for sintering lithium manganese iron phosphate prepared in Example 1; it can be seen that the lamellar calcium hexaaluminate in the sagger aggregate area is well developed and grows in a directional vertical structure. The lamellar layers are "superimposed" on each other to form a staggered structure, which is more conducive to improving the erosion resistance and permeability resistance of the sagger.

[0062] Figure 2 This is an SEM image of the microstructure of the monolithic sagger matrix for lithium manganese iron phosphate sintering, prepared in Example 1. It can be seen that in addition to the lamellar calcium hexaaluminate, the sagger matrix region also contains distinct silicon carbide whiskers. These whiskers "build" together to maintain a well-connected structure between the calcium hexaaluminate platelets. This improves the sagger's stress resistance, toughness, and thermal shock resistance. It also increases the fracture energy of the sagger, effectively enhancing its mechanical strength.

[0063] The integral sagger for sintering lithium manganese iron phosphate prepared in this embodiment was tested:

[0064] The scrap rate of the sagger is 0.9%; the apparent porosity is 17%; the flexural strength is 27MPa; the residual flexural strength retention rate after three thermal shock stability tests at 1100℃ circulating water cooling is 94%, and the erosion index of the static crucible method slag resistance test at 1100℃×10h is 0.6%.

[0065] Example 2

[0066] A method for preparing a monolithic sagger for sintering lithium manganese iron phosphate, the specific steps are as follows:

[0067] 1) Calcium hexaaluminate particles and silicon carbide particles were prepared in a mass ratio of 100:26 and added to a blender and mixed for 10-15 minutes to obtain a premixed granular material;

[0068] 2) adding calcium hexaaluminate fine powder: silicon oxynitride fine powder: silicon carbide fine powder: pure calcium aluminate cement fine powder in a mass ratio of 100:18:12:4.8, adding the mixture to a roller mixer and mixing for 1-2 hours to obtain a premixed fine powder;

[0069] 3) Add the premixed granules to the premixed fine powder at a mass ratio of 100:70, add the mixture into a blender and mix for 10-15 minutes to obtain a mixture;

[0070] 4) adding 0.16 wt % potassium tripolyphosphate and 5 wt % potassium fluorozirconate solution to the mixture in sequence, stirring for 6 to 10 minutes, placing the mixture in a mold, casting and vibrating the mixture, curing the mixture at 25 to 30° C. for 2 to 3 hours, and demolding the mixture to obtain a sagger green body; the concentration of the potassium fluorozirconate solution is 7 wt %.

[0071] 5) Dry the sagger green body at 100-110° C. for 4-6 hours, place it in a tunnel kiln and sinter it at 1380° C. in a nitrogen atmosphere for 3 hours, and cool it to room temperature to obtain a monolithic sagger for sintering lithium manganese iron phosphate.

[0072] The particle size of calcium hexaaluminate is 0.5-3 mm, and the particle size is continuously distributed, wherein the mass ratio of [0.5 mm-1 mm] particles: (1 mm-2 mm] particles: (2 mm-3 mm] particles is 25:30:30.

[0073] Other raw material parameters are the same as in Example 1.

[0074] The integral sagger for sintering lithium manganese iron phosphate prepared in this embodiment was tested:

[0075] The scrap rate of the sagger is 0.8%; the apparent porosity is 16%; the flexural strength is 32MPa; the residual flexural strength retention rate after three thermal shock stability tests at 1100℃ circulating water cooling is 93%, and the erosion index of the static crucible method slag resistance test at 1100℃×10h is 0.7%.

[0076] Example 3

[0077] A method for preparing a monolithic sagger for sintering lithium manganese iron phosphate, the specific steps are as follows:

[0078] 1) Calcium hexaaluminate particles and silicon carbide particles were prepared in a mass ratio of 100:13 and added to a blender and mixed for 10-15 minutes to obtain a premixed granular material;

[0079] 2) adding calcium hexaaluminate fine powder: silicon oxynitride fine powder: silicon carbide fine powder: pure calcium aluminate cement fine powder in a mass ratio of 100:24:18:5.6, adding the mixture to a roller mixer and mixing for 1-2 hours to obtain a premixed fine powder;

[0080] 3) Add the premixed granules to the premixed fine powder at a mass ratio of 100:62, add the mixture into a blender and mix for 10-15 minutes to obtain a mixture;

[0081] 4) adding 0.08 wt % of potassium tripolyphosphate and 9 wt % of potassium fluorozirconate solution to the mixture in sequence, stirring for 6 to 10 minutes, placing the mixture in a mold, casting and vibrating the mixture, curing the mixture at 25 to 30° C. for 2 to 3 hours, and demolding the mixture to obtain a sagger green body; the concentration of the potassium fluorozirconate solution is 7 wt %.

[0082] 5) Dry the sagger green body at 100-110° C. for 4-6 hours, sinter it in a tunnel kiln at 1260° C. in a nitrogen atmosphere for 6 hours, and cool it to room temperature to obtain a monolithic sagger for sintering lithium manganese iron phosphate.

[0083] The particle size of calcium hexaaluminate is 0.5-3 mm, and the particle size is continuously distributed, wherein the mass ratio of [0.5 mm-1 mm] particles: (1 mm-2 mm] particles: (2 mm-3 mm] particles is 35:35:25.

[0084] Other raw material parameters are the same as in Example 1.

[0085] The integral sagger for sintering lithium manganese iron phosphate prepared in this embodiment was tested:

[0086] The scrap rate of the sagger is 1.1%; the apparent porosity is 15%; the flexural strength is 33MPa; the residual flexural strength retention rate after three thermal shock stability tests at 1100℃ circulating water cooling is 96%, and the erosion index of the static crucible method slag resistance test at 1100℃×10h is 0.8%.

[0087] Comparative Example 1

[0088] A method for preparing a monolithic sagger for sintering lithium manganese iron phosphate, the specific steps are as follows:

[0089] 1) Calcium hexaaluminate particles and silicon carbide particles were prepared in a mass ratio of 100:13 and added to a blender and mixed for 10-15 minutes to obtain a premixed granular material;

[0090] 2) adding calcium hexaaluminate fine powder: silicon oxynitride fine powder: silicon carbide fine powder: pure calcium aluminate cement fine powder in a mass ratio of 100:24:18:5.6, adding the mixture to a roller mixer and mixing for 1-2 hours to obtain a premixed fine powder;

[0091] 3) Prepare the mixture in a mass ratio of 100:50 of premixed granules and premixed fine powder, add the mixture into a blender and mix for 10-15 minutes to obtain a mixture;

[0092] 4) adding 0.08 wt% of potassium tripolyphosphate and 3 wt% of potassium fluorozirconate solution to the mixture in sequence, stirring for 6 to 10 minutes, placing the mixture in a mold, casting and vibrating the mixture, curing the mixture at 25 to 30° C. for 2 to 3 hours, and demolding the mixture to obtain a sagger green body; the concentration of the potassium fluorozirconate solution is 7 wt%.

[0093] 5) Dry the sagger green body at 100-110° C. for 4-6 hours, sinter it in a tunnel kiln at 1260° C. in a nitrogen atmosphere for 6 hours, and cool it to room temperature to obtain a monolithic sagger for sintering lithium manganese iron phosphate.

[0094] The particle size of calcium hexaaluminate is 0.5-3 mm, and the particle size is continuously distributed, wherein the mass ratio of [0.5 mm-1 mm] particles: (1 mm-2 mm] particles: (2 mm-3 mm] particles is 10:80:10.

[0095] Other raw material parameters are the same as in Example 1.

[0096] The integral sagger for sintering lithium manganese iron phosphate prepared in this comparative example was tested:

[0097] The scrap rate of the sagger is 2.5%; the apparent porosity is 22%; the flexural strength is 10.6MPa; the residual flexural strength retention rate after three thermal shock stability tests at 1100℃ circulating water cooling is 77%, and the erosion index of the static crucible method slag resistance test at 1100℃×10h is 3.2%.

[0098] Compared with Example 3, it can be seen that reducing the amount of premixed fine powder and adjusting the gradation ratio of calcium hexaaluminate particles reduce the bonding and dispersion properties between the components; when the amount of potassium fluorozirconate added is reduced, the crystal growth is delayed due to the reduction in the amount of liquid phase in the system and the weakening of the decomposition catalytic effect, which in turn reduces the strength of the sagger and deteriorates the corrosion resistance of the sagger.

[0099] Any matters not mentioned above shall be subject to the existing technology.

[0100] Although some specific embodiments of the present invention have been described in detail through examples, those skilled in the art should understand that the above examples are for illustration only and are not intended to limit the scope of the present invention. Those skilled in the art of the present invention may make various modifications or additions to the described specific embodiments or replace them in similar ways, but they will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent replacements, improvements, etc. made to the above embodiments based on the technical essence of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a monolithic sagger for sintering lithium manganese iron phosphate, characterized in that: The specific steps are as follows: S1. Prepare a mixture; the mixture is a mixture of calcium hexaaluminate particles, silicon carbide particles, calcium hexaaluminate powder, silicon oxynitride powder, silicon carbide powder and pure calcium aluminate cement powder; S2. Potassium tripolyphosphate and potassium fluorozirconate solution were sequentially added to the mixture and stirred to obtain a castable; S3. The castable is placed in a mold, cast and vibrated, cured, and demoulded to obtain a green sagger; S4. The sagger green body is dried and heat treated, and cooled to room temperature to obtain lithium iron manganese phosphate sintered with a whole sagger; In step S1, the calcium hexaaluminate particles and silicon carbide particles are mixed to obtain a premixed particle material; The calcium hexaaluminate fine powder, silicon oxynitride fine powder, silicon carbide fine powder and pure calcium aluminate cement fine powder are mixed to obtain a premixed fine powder material; The premixed granular material and the premixed fine powder material are mixed to obtain a mixed material; The mass ratio of premixed granules to premixed fine powder is 100:(62~70); The calcium hexaaluminate particles have a particle size of 0.5-3 mm and are continuously distributed, wherein the mass ratio of [0.5 mm-1 mm] particles: (1 mm-2 mm] particles: (2 mm-3 mm] particles is (25-35): (30-35): (25-30); In step S4, the heat treatment is carried out at 1260-1380° C. in a nitrogen atmosphere for 3-6 hours.

2. The method for preparing a monolithic sagger for sintering lithium manganese iron phosphate according to claim 1, characterized in that: The mass ratio of calcium hexaaluminate particles to silicon carbide particles is 100:(13-26); and\or, The mass ratio of calcium hexaaluminate fine powder: silicon oxynitride fine powder: silicon carbide fine powder: pure calcium aluminate cement fine powder is 100: (18~24): (12~18): (4.8~5.6).

3. The method for preparing a monolithic sagger for sintering lithium manganese iron phosphate according to claim 1, characterized in that: The potassium tripolyphosphate accounts for 0.08-0.16 wt % of the mixture.

4. The method for preparing a monolithic sagger for sintering lithium manganese iron phosphate according to claim 1, wherein: The potassium fluorozirconate solution accounts for 5-9wt% of the mixture; the concentration of the potassium fluorozirconate solution is 6-7wt%.

5. The method for preparing a monolithic sagger for sintering lithium manganese iron phosphate according to claim 1, characterized in that: In step S3, the castable is placed in a mold, cast and vibrated, cured at 25-30° C. for 2-3 hours, and demoulded to obtain a sagger green body.

6. The method for preparing a monolithic sagger for sintering lithium manganese iron phosphate according to any one of claims 1 to 5, characterized in that: In step S4, the sagger green body is dried at 100-110° C. for 4-6 hours.

7. The method for preparing a monolithic sagger for sintering lithium manganese iron phosphate according to any one of claims 1 to 5, characterized in that: The silicon carbide particles have a particle size of 1 to 2 mm; and\or, The particle size of the calcium hexaaluminate fine powder is 65-85 μm; and\or, The particle size of the silicon oxynitride fine powder is 44 to 60 μm; and\or, The particle size of the silicon carbide fine powder is 60-70 μm; and\or, The particle size of the pure calcium aluminate cement fine powder is 20-30 μm.

8. A monolithic sagger for sintering lithium manganese iron phosphate prepared by the preparation method according to any one of claims 1 to 7.

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