Lithium manganese iron phosphate as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of battery materials, and provides lithium manganese iron phosphate and a preparation method and application thereof.The preparation method comprises the steps that an indissolvable solid iron source, a phosphorus source, a manganese source and a precipitator are mixed in a solution, a precipitation reaction is conducted to obtain a precipitate, then first calcination is conducted, and a manganese iron phosphate mixed precursor is obtained; and further mixing with a lithium source and a carbon source, and calcining to obtain the lithium manganese iron phosphate. According to the preparation method, the precipitate is synthesized in advance through the insoluble solid iron source, the phosphorus source and the manganese source, the specific ferromanganese phosphate mixed precursor can be obtained through calcination, the precursor, the lithium source and the carbon source can be used for further synthesizing the lithium ferromanganese phosphate, and the preparation method can avoid the problems that the iron source and the manganese source are difficult to grind and the target particle size is difficult to achieve; manganese and iron are promoted to be fused more uniformly, the compaction density of lithium manganese iron phosphate is effectively improved, meanwhile, consumption of a phosphorus source can be reduced, supplementing of the phosphorus source is not needed, the process problem is avoided, and the cost is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and relates to a lithium manganese iron phosphate and a preparation method and application thereof. BACKGROUND

[0002] In the field of lithium ion battery cathode materials, lithium manganese iron phosphate (LMFP) as a modified material of lithium iron phosphate (LiFePO4, LFP) has attracted widespread attention in recent years due to its high energy density and excellent safety performance. LMFP introduces manganese elements into the LFP crystal structure to replace part of the iron sites to form a solid solution structure. The discharge platform voltage of LMFP is increased from 3.4 V of LFP to 4.1 V, and the theoretical energy density can be increased by 15% to 20%, while the low cost and high stability advantages of LFP are retained. However, the industrial preparation process of LMFP still faces many technical bottlenecks, and further optimization is needed to realize the large-scale production of high-performance materials.

[0003] At present, the mainstream preparation method of LMFP follows the mature process route of LFP, mainly adopting a solid phase method. The process usually includes the following steps: mixing lithium source (such as lithium carbonate), manganese source (such as trimanganese tetraoxide or manganese carbonate), iron source (such as ferrous oxalate), phosphorus source (such as ammonium dihydrogen phosphate) and carbon source (such as graphite) according to the stoichiometric ratio, then forming a precursor powder through mechanical grinding and spray drying, and finally completing the solid phase reaction through high temperature calcination to generate LMFP material. Although this process has the advantages of simple equipment and easy scaling, it still has the following key problems in practical application:

[0004] 1) Insufficient uniformity of manganese source and iron source mixture: The manganese source (such as trimanganese tetraoxide) usually exists in the form of hard large particles, which has low brittleness and poor surface activity, and is difficult to be finely ground in the wet sanding process. Although the iron source (such as ferrous oxalate) has good dispersibility, it has significant differences with the manganese source in particle morphology, density and surface properties, which leads to easy agglomeration or stratification of the two during mixing. The above problems directly lead to uneven distribution of internal components of the precursor particles, and after calcination, there may be manganese-rich regions or iron-rich regions in the material, which further causes structural defects such as lattice distortion and grain boundary cracks, significantly reducing the cycle stability and electrochemical capacity of the material.

[0005] 2) Low utilization rate of phosphorus source and process complexity: In order to ensure complete reaction, the existing process generally uses excessive addition of phosphorus source (such as ammonium dihydrogen phosphate or phosphoric acid). However, ammonium dihydrogen phosphate is easy to decompose and produce ammonia gas at high temperature, which not only causes the loss of phosphorus elements (forming phosphorus-deficient phases or non-stoichiometric compounds), but also requires the installation of a waste gas treatment system to absorb ammonia gas, increasing equipment investment and operating costs. In addition, the corrosiveness of phosphoric acid will accelerate the aging of the reaction equipment, and higher requirements are put forward for process stability and production line maintenance.

[0006] 3) Insufficient control of ordered-disordered structure: The performance of LMFP is related to manganese (Mn) 2+ ) and iron (Fe 2+ The site ordering of Mn in the olivine structure is closely related. An ideal, highly ordered structure helps improve voltage plateau stability and cycle reversibility. However, the inhomogeneity of the manganese and iron sources in existing processes leads to... 2+ with Fe 2+ Increased randomness in occupancy within the crystal lattice leads to a broadening trend in the voltage curve, which in turn reduces the material's energy efficiency and power output capability.

[0007] In summary, the existing solid-state preparation process for LMFP has significant shortcomings in terms of raw material mixing uniformity, phosphorus source utilization, and control of structural order. There is an urgent need to develop a new preparation method that can achieve efficient mixing of manganese and iron sources, optimize phosphorus source utilization, and improve lattice order, so as to break through the current technical bottleneck and promote the industrial application of LMFP materials. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention provides lithium manganese iron phosphate, its preparation method and uses. The preparation method includes mixing a sparingly soluble solid iron source, phosphorus source, manganese source and precipitant in solution, carrying out a precipitation reaction to obtain a precipitate, and then performing a first calcination to obtain a mixed precursor of manganese iron phosphate; further mixing and calcining with a lithium source and a carbon source can obtain lithium manganese iron phosphate. The present invention pre-synthesizes a precipitate by using a sparingly soluble solid iron source, phosphorus source and manganese source, and calcining it can obtain a specific mixed precursor of manganese iron phosphate. Using this precursor, lithium manganese iron phosphate can be further synthesized with a lithium source and a carbon source. The preparation method can avoid the problem of difficult grinding of iron and manganese sources and difficulty in achieving the target particle size, promote more uniform fusion of manganese and iron, effectively improve the compaction density of lithium manganese iron phosphate, and at the same time reduce the consumption of phosphorus source, eliminating the need to replenish phosphorus source, avoiding process problems and reducing costs.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing lithium manganese iron phosphate, the method comprising:

[0011] A sparingly soluble solid iron source, phosphorus source, and manganese source are mixed with a precipitant in solution to carry out a precipitation reaction and obtain a precipitate.

[0012] The precipitate was subjected to a first calcination to obtain a mixed precursor of manganese iron phosphate.

[0013] The manganese iron phosphate mixed precursor is mixed with a lithium source and a carbon source, and spray-dried to obtain a powder. The powder is then subjected to a second calcination to obtain lithium manganese iron phosphate.

[0014] The present application can avoid the problem of difficult grinding of iron source and manganese source and difficult to reach the target particle size, promote the fusion of manganese and iron to be more uniform, effectively improve the compaction density of manganese iron phosphate lithium, and at the same time, the consumption of phosphorus source can be reduced, and the process problem can be avoided and the cost can be reduced without supplementing phosphorus source in the secondary calcination.

[0015] The following is a preferred technical solution of the present application, but not as a limitation of the technical solution provided by the present application, through the following technical solution, the technical purpose and beneficial effect of the present application can be better achieved and realized.

[0016] As a preferred technical solution of the present application, the insoluble solid iron source includes at least one of iron phosphate, dihydrogen phosphate iron, dihydrogen phosphate iron, dihydrogen phosphate iron, ferric oxide, ferric oxide, ferric oxide, ferric oxide or ferrous oxalate. Preferably, iron phosphate, other insoluble solid iron source can also be generated in the reaction process of the preparation method.

[0017] Preferably, the phosphorus source includes at least one of sodium dihydrogen phosphate, lithium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate or phosphoric acid.

[0018] Preferably, the manganese source includes at least one of manganese sulfate, manganese acetate, manganese nitrate or manganese chloride.

[0019] Preferably, the molar ratio of iron element to manganese element is (0.1-9.9):1, such as 0.1:1, 0.3:1, 0.5:1, 0.85:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 9.9:1, etc. The amount of the insoluble solid iron source and the manganese source is controlled.

[0020] The obtained manganese iron phosphate mixed precursor mainly includes a mixture of iron phosphate and manganese pyrophosphate, and the proportion can be adjusted according to the iron-manganese ratio. In the manganese iron phosphate mixed precursor, an exemplary structure can be that the iron material is the core, the manganese material is coated outside, and the iron material is coated outside again, so that the iron and manganese are mixed and coated.

[0021] Preferably, the molar ratio of phosphorus element to manganese element is (1-1.5):1, such as 1:1, 1.05:1, 1.1:1, 1.2:1, 1.25:1, 1.3:1, 1.35:1, 1.4:1, 1.45:1 or 1.5:1, etc.

[0022] As a preferred technical solution of the present application, the process of mixing the insoluble solid iron source, the phosphorus source and the manganese source with the precipitant in the solution comprises: preparing a bottom solution containing the insoluble solid iron source, adding the mixture of the phosphorus source and the manganese source to the bottom solution, and then adding the precipitant.

[0023] Preferably, the precipitant comprises at least one of ammonia, sodium hydroxide or sodium carbonate.

[0024] Preferably, after the insoluble solid iron source, the phosphorus source and the manganese source are added to the bottom solution, the solid content concentration is 5wt%-30wt%, such as 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, 24wt%, 26wt%, 28wt% or 30wt%, etc.

[0025] As a preferred technical solution of the present application, the process of the precipitation reaction comprises: at a first temperature, adjusting the pH to a first pH value by adding the precipitant to perform a first precipitation reaction, then increasing the temperature to a second temperature to perform aging, and then adjusting the pH to a second pH value by adding the precipitant to perform a second precipitation reaction, to obtain the precipitate.

[0026] In the present application, the first precipitation reaction in the precipitation reaction mainly obtains amorphous substances, and the second precipitation reaction can make the crystal form of the precipitate more optimal.

[0027] Preferably, the first temperature is 30-80℃, such as 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃ or 80℃, etc.

[0028] Preferably, the first pH value is 3-6, such as 3, 3.3, 3.5, 3.8, 4, 4.3, 4.5, 4.8, 5, 5.2, 5.4, 5.6, 5.8 or 6, etc.

[0029] Preferably, the time of the first precipitation reaction is 1-10h, such as 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h, etc.

[0030] Preferably, the second temperature is 80-110℃, such as 80℃, 85℃, 90℃, 95℃, 100℃, 105℃ or 110℃, etc.

[0031] Preferably, the second pH value is 6-11, such as 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5 or 11, etc.

[0032] Preferably, the second precipitation reaction is performed for 1-5 hours, such as 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, or 5 hours, etc.

[0033] As a preferred technical solution of the present application, the precipitate is dried and then subjected to the first calcination.

[0034] Preferably, the drying temperature is 70-110°C, such as 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, or 110°C, etc.

[0035] Preferably, the iron source includes at least one of ferric phosphate, iron oxide, or ferrous oxalate.

[0036] As a preferred technical solution of the present application, the first calcination is performed at a temperature of 300-800°C, such as 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, or 800°C, etc., for a time of 4-15 hours, such as 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, or 15 hours, etc.

[0037] Preferably, the first calcination is performed in at least one of air, oxygen, or nitrogen.

[0038] As a preferred technical solution of the present application, after the manganese iron phosphate precursor is mixed with the lithium source and the carbon source, the mixture is first ground to obtain a ground material, and then the ground material is subjected to the spray drying.

[0039] Preferably, the spray drying is performed at an inlet temperature of 160-240°C, such as 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, or 240°C, etc., at an outlet temperature of 60-110°C, such as 60°C, 70°C, 80°C, 90°C, 100°C, or 110°C, etc., and with a moisture content of ≤1%, such as 1%, 0.8%, 0.6%, 0.4%, 0.2%, or 0.1%, etc.

[0040] Preferably, the ground material has a D 50 The particle size is 0.2-0.8 μm, such as 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, or 0.8 μm, etc.

[0041] Preferably, the lithium source includes at least one of lithium carbonate (Li2CO3), lithium hydroxide (LiOH·H2O), or lithium nitrate (LiNO3).

[0042] Preferably, the carbon source comprises at least one of glucose, sucrose, citric acid or polyvinyl alcohol (PVA).

[0043] Preferably, the amount of the lithium source is controlled according to the ratio of the molar amount of lithium element in the lithium source to the total molar amount of manganese element and iron element in the manganese iron phosphate mixed precursor, which is (1.02~1.09):1, such as 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1 or 1.09:1, etc.

[0044] Preferably, the amount of the carbon source is controlled according to the mass percentage of the carbon source in the manganese iron phosphate mixed precursor, which is 1.5%~2%, such as 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2%, etc.

[0045] As a preferred technical solution of the present application, the temperature of the second calcination is 600~800℃, such as 600℃, 630℃, 650℃, 680℃, 700℃, 720℃, 750℃, 780℃ or 800℃, etc., and the time is 5~12h, such as 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h, etc.

[0046] Preferably, the second calcination is all carried out in an inert atmosphere.

[0047] In the second aspect, the present application provides a lithium manganese iron phosphate, which is obtained according to the preparation method of the first aspect.

[0048] In the third aspect, the present application provides a battery containing the lithium manganese iron phosphate of the second aspect.

[0049] It should be noted that, due to the limitation of the length and in order to avoid redundancy, the present application does not exhaustively list all point values in the above numerical range, but also is not limited to the listed values, and other unlisted values in the above numerical range are also applicable.

[0050] Compared with the prior art, the present application has at least the following beneficial effects:

[0051] The present application can obtain a specific manganese iron phosphate mixed precursor by pre-synthesizing precipitates from the insoluble solid iron source, phosphorus source and manganese source, and then calcining. The precursor can be further synthesized with a lithium source and a carbon source to obtain a lithium manganese iron phosphate. The preparation method can avoid the problem of difficult grinding of the iron source and manganese source and difficult achievement of the target particle size, promote the fusion of manganese and iron to be more uniform, effectively improve the compaction density of the lithium manganese iron phosphate, and reduce the consumption of the phosphorus source without the need for supplementing the phosphorus source, thereby effectively avoiding the process problems and reducing the cost. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 is the SEM test diagram of the manganese iron phosphate mixed precursor obtained in Example 1.

[0053] Figure 2 is the SEM test diagram of the lithium manganese iron phosphate obtained in Example 1.

[0054] Figure 3 is the XRD test diagram of the manganese iron phosphate mixed precursor obtained in Example 1.

[0055] Figure 4 is the XRD test diagram of the lithium manganese iron phosphate obtained in Example 1.

[0056] Figure 5 is the charge-discharge curve diagram of the battery of the lithium manganese iron phosphate obtained in Example 1. DETAILED DESCRIPTION

[0057] The technical solutions of the present application are further illustrated below through specific embodiments.

[0058] It should be understood by those skilled in the art that the embodiments are only to help understand the present application and should not be regarded as specific limitations of the present application.

[0059] Example 1

[0060] The present embodiment provides a preparation method of lithium manganese iron phosphate, which comprises:

[0061] S1. A bottom solution containing a poorly soluble solid iron source of iron phosphate is prepared, a small amount of water is first added for dilution, and then a phosphorus source of sodium dihydrogen phosphate and a manganese source of manganese sulfate are mixed into the bottom solution; the amount of the poorly soluble solid iron source and the manganese source is controlled according to the molar ratio of iron element to manganese element being 0.8:1; the amount of the phosphorus source and the manganese source is controlled according to the molar ratio of phosphorus element to manganese element being 1.2:1; after the mixing of the poorly soluble solid iron source, the phosphorus source and the manganese source in the bottom solution, the solid content solubility is 22wt%; the temperature for preparing the bottom solution and adding materials is controlled at 64℃;

[0062] The temperature is maintained at the first temperature 64℃, then a precipitant of ammonia water is added, the pH is adjusted to the first pH value 5.2 for a first precipitation reaction, the pH value of the first precipitation reaction is controlled to be not more than 3-6, stirring is maintained for 6h, then the temperature is increased to the second temperature 103℃, aging is performed, then the second temperature is maintained, the precipitant is added again to adjust the pH to increase to the second pH value 9 for a second precipitation reaction, the pH value of the first precipitation reaction is controlled to be not more than 8-11, stirring is maintained for 3h, after the reaction is completed, the material is filtered and washed, then dried at 90℃ to obtain a precipitate;

[0063] S2. The precipitate is subjected to first calcination at 660℃ for 7h under nitrogen and oxygen atmosphere to obtain a manganese iron phosphate mixed precursor;

[0064] S3. The manganese iron phosphate mixed precursor is mixed with a lithium source lithium hydroxide and a carbon source citric acid, and is subjected to grinding to obtain a D 50 grinding material with a particle size of 0.43μm, and the grinding material is subjected to spray drying to obtain a powder, and the powder is subjected to second calcination at 620℃ for 10h under an inert atmosphere of nitrogen to obtain a lithium manganese iron phosphate.

[0065] Example 2

[0066] The embodiment provides a preparation method of a lithium manganese iron phosphate. In step S1, a precipitant ammonia water is added, a first pH value 3.4 is adjusted for a first precipitation reaction, the pH value of the first precipitation reaction is controlled to be not more than 3-5.6, stirring is maintained for 6h, the temperature is then increased to a second temperature 103℃ for aging, the second temperature is then maintained, the precipitant is added again to adjust the pH value to a second pH value 5.6 for a second precipitation reaction, the pH value of the second precipitation reaction is controlled to be not more than 5.6-6, stirring is maintained for 3h, after the reaction is completed, the material is filtered and washed, and then dried at 90℃ to obtain a precipitate; and other conditions are completely same as those in example 1.

[0067] Example 3

[0068] The embodiment provides a preparation method of a lithium manganese iron phosphate. In step S1, a precipitant ammonia water is added, a first pH value 3.4 is adjusted for a first precipitation reaction, the pH value of the first precipitation reaction is controlled to be not more than 3-5.6, stirring is maintained for 6h, the temperature is then increased to a second temperature 103℃ for aging, the second temperature is then maintained, the precipitant is added again to adjust the pH value to a second pH value 5.6 for a second precipitation reaction, the pH value of the second precipitation reaction is controlled to be not more than 5.6-6, stirring is maintained for 3h, after the reaction is completed, the material is filtered and washed, and then dried at 90℃ to obtain a precipitate; and other conditions are completely same as those in example 1.

[0069] Example 4

[0070] The embodiment provides a preparation method of a lithium manganese iron phosphate. In step S1, the molar ratio of iron elements to manganese elements is 0.1:1, and the amount of the insoluble solid iron source and the manganese source is controlled; and other conditions are completely same as those in example 1.

[0071] Example 5

[0072] The embodiment provides a preparation method of lithium iron manganese phosphate, wherein in step S2, the preparation method controls the amount of the insoluble solid iron source and the manganese source according to the molar ratio of iron elements to manganese elements being 1:1, and other conditions are completely same with those in example 1.

[0073] Example 6

[0074] The embodiment provides a preparation method of lithium iron manganese phosphate, wherein in step S2, the preparation method controls the amount of the insoluble solid iron source and the manganese source according to the molar ratio of iron elements to manganese elements being 10:1, and other conditions are completely same with those in example 1.

[0075] Example 7

[0076] The embodiment provides a preparation method of lithium iron manganese phosphate, wherein in step S2, the preparation method controls the amount of the insoluble solid iron source and the manganese source according to the molar ratio of iron elements to manganese elements being 13:1, and other conditions are completely same with those in example 1.

[0077] Example 8

[0078] The embodiment provides a preparation method of lithium iron manganese phosphate, wherein in step S2, the preparation method controls the amount of the insoluble solid iron source and the manganese source according to the molar ratio of iron elements to manganese elements being 13:1, and other conditions are completely same with those in example 1.

[0079] Example 9

[0080] The embodiment provides a preparation method of lithium iron manganese phosphate, wherein in step S2, the preparation method controls the amount of the insoluble solid iron source and the manganese source according to the molar ratio of iron elements to manganese elements being 13:1, and other conditions are completely same with those in example 1.

[0081] Example 10

[0082] The embodiment provides a preparation method of lithium iron manganese phosphate, wherein in step S2, the preparation method controls the amount of the insoluble solid iron source and the manganese source according to the molar ratio of iron elements to manganese elements being 13:1, and other conditions are completely same with those in example 1.

[0083] Comparative Example 1

[0084] The comparative example provides a preparation method of lithium iron manganese phosphate, wherein the preparation method comprises:

[0085] The lithium source, the manganese source, the iron source, the phosphorus source and the carbon source are mixed and sand-milled to obtain D 50The abrasive with a particle size of 0.43 μm is spray dried to obtain a powder, and the powder is calcined at 620°C for 10 h under an inert atmosphere of nitrogen to obtain lithium manganese iron phosphate.

[0086] Comparative Example 2

[0087] This comparative example provides a preparation method of lithium manganese iron phosphate, wherein the insoluble solid iron source iron phosphate in step S1 is replaced by the soluble iron source iron chloride, and other conditions are the same as those in Example 1.

[0088] Characterization and testing:

[0089] I. Figure 1 is an SEM test diagram of the lithium manganese iron phosphate mixed precursor obtained in Example 1. As can be seen from the diagram, the precursor has a small particle size, and there is a case of small particles coating large particles. Figure 2 is an SEM test diagram of the lithium manganese iron phosphate obtained in Example 1. As can be seen from the diagram, the obtained lithium manganese iron phosphate has complete particles and good dispersibility.

[0090] II. Figure 3 is an XRD test diagram of the lithium manganese iron phosphate mixed precursor obtained in Example 1. As can be seen from the diagram, there are diffraction peaks corresponding to iron phosphate and manganese pyrophosphate; Figure 4 is an XRD test diagram of the lithium manganese iron phosphate obtained in Example 1. As can be seen from the diagram, the lithium manganese iron phosphate has good crystallinity.

[0091] III. The tap density test: using a tap density instrument, 1-2 g of sample is taken and placed into a measuring barrel, and the weight is recorded. The test is performed at 3T.

[0092] IV. Manganese dissolution test: two samples of about 5 g are weighed and labeled. The weighed samples are dissolved in 50 mL of pure water, sealed, and allowed to stand for 70 h (actual operation is 16 h at 45°C). The samples are filtered, and the volume is set to 100 mL. 10 mL of the test solution is taken and diluted to 100 mL with pure water. The concentration of the filtered solution is determined by inductively coupled plasma emission spectrometry, and the results are calculated.

[0093] V. Electrochemical performance test:

[0094] The lithium manganese iron phosphate obtained in the examples and the comparative examples is mixed with the conductive agent acetylene black and the binder PVDF in a mass ratio of 9:0.2:0.8, and a certain amount of organic solvent NMP is added, and after stirring, the mixture is coated on an aluminum foil to prepare a positive electrode sheet. The negative electrode sheet is a lithium metal sheet, and the separator is a Celgard 2400 polypropylene porous film; the solvent in the electrolyte is a solution composed of EC, DMC and EMC in a mass ratio of 1:1:1, and the solute is LiPF6, and the concentration of LiPF6 is 1.0 mol / L. The above prepared positive electrode sheet, negative electrode sheet, separator and electrolyte are assembled into a 2023 type button cell in a glove box.

[0095] The capacity and efficiency of each obtained battery are tested: Figure 5 is the charge-discharge curve of the battery containing the lithium manganese iron phosphate obtained in Example 1, and from the figure it can be seen that the first circle discharge capacity of the battery of Example 1 is 151.2 mAh / g, and the first circle efficiency is calculated as 98.2%.

[0096] Other test results are recorded in Table 1.

[0097] Table 1

[0098]

[0099] As can be seen from Table 1, the compaction density and capacity performance of the lithium manganese iron phosphate obtained in the examples of the present application are better than those of the comparative examples, and the manganese dissolution problem can be improved. The present application can obtain a specific manganese iron phosphate mixed precursor by pre-synthesizing a precipitate from a difficult-to-dissolve solid iron source, a phosphorus source and a manganese source, and the precursor can be used to further synthesize lithium manganese iron phosphate with a lithium source and a carbon source. The preparation method can avoid the problem of difficult grinding of the iron source and manganese source and difficult to achieve the target particle size, promote the fusion of manganese and iron more uniformly, and effectively improve the compaction density and performance of the lithium manganese iron phosphate. The preparation method of the present application can further adjust the reaction pH, the ratio of manganese to iron, and the amount of phosphorus to obtain the optimal improvement effect.

[0100] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the specific details in the above-described embodiments, and various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0101] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe various possible combinations.

[0102] Furthermore, the various embodiments of the present application can be combined with each other, as long as it does not violate the spirit of the present application, and it should be considered as disclosed in the present application.

Claims

1. A method for preparing lithium manganese iron phosphate, characterized in that, The preparation method includes: A sparingly soluble solid iron source, phosphorus source, and manganese source are mixed with a precipitant in solution to carry out a precipitation reaction and obtain a precipitate. The precipitate was subjected to a first calcination to obtain a mixed precursor of manganese iron phosphate. The manganese iron phosphate mixed precursor is mixed with a lithium source and a carbon source, and spray-dried to obtain a powder. The powder is then subjected to a second calcination to obtain lithium manganese iron phosphate.

2. The preparation method according to claim 1, characterized in that, The sparingly soluble solid iron source includes at least one of ferric phosphate, ferric phosphate dihydrate, ferric oxide, ferric oxide, ferric carbonate, or ferrous oxalate. Preferably, the phosphorus source includes at least one of sodium dihydrogen phosphate, lithium dihydrogen phosphate, potassium dihydrogen phosphate, ammonium dihydrogen phosphate, or phosphoric acid. Preferably, the manganese source includes at least one of manganese sulfate, manganese acetate, manganese nitrate, or manganese chloride; Preferably, the amount of the sparingly soluble solid iron source and the manganese source is controlled according to the molar ratio of iron to manganese of (0.1~9.9):1; Preferably, the amounts of phosphorus source and manganese source are controlled according to a molar ratio of phosphorus to manganese of (1~2.2):

1.

3. The preparation method according to claim 1 or 2, characterized in that, The process of mixing a sparingly soluble solid iron source, a phosphorus source, a manganese source, and a precipitant in a solution includes: preparing a base solution containing the sparingly soluble solid iron source, adding the phosphorus source and manganese source to the base solution and mixing them, and then adding the precipitant. Preferably, the precipitant includes at least one of ammonia, sodium hydroxide, or sodium carbonate; Preferably, after adding the sparingly soluble solid iron source, phosphorus source and manganese source to the bottom liquid, the solid content solubility is 5wt%~30wt%.

4. The preparation method according to any one of claims 1-3, characterized in that, The precipitation reaction process includes: at a first temperature, adding the precipitant to adjust the pH to a first pH value to carry out a first precipitation reaction; then raising the temperature to a second temperature for aging; and then adding the precipitant again to adjust the pH to a second pH value to carry out a second precipitation reaction to obtain a precipitate. Preferably, the first temperature is 30~80℃; Preferably, the first pH value is 3 to 6; Preferably, the first precipitation reaction takes 1 to 10 hours; Preferably, the second temperature is 80~110℃; Preferably, the second pH value is 6-11; Preferably, the second precipitation reaction takes 1 to 5 hours.

5. The preparation method according to any one of claims 1-4, characterized in that, The precipitate is dried before the first calcination is performed. Preferably, the drying temperature is 70~110℃.

6. The preparation method according to any one of claims 1-5, characterized in that, The first calcination temperature is 300~800℃, and the time is 4~15h; Preferably, the first calcination is carried out in at least one of air, oxygen, or nitrogen.

7. The preparation method according to any one of claims 1-6, characterized in that, The manganese iron phosphate mixed precursor is mixed with lithium source and carbon source, and then ground to obtain abrasive material, and then the abrasive material is spray dried. Preferably, the inlet temperature of the spray dryer is 160~240℃, the outlet temperature is 60~110℃, and the moisture content is ≤1%. Preferably, the D of the abrasive... 50 The particle size is 0.2~0.8μm; Preferably, the lithium source includes at least one of lithium carbonate, lithium hydroxide, or lithium nitrate; Preferably, the carbon source includes at least one of glucose, sucrose, citric acid, or polyvinyl alcohol; Preferably, the dosage is controlled according to the ratio of the molar amount of lithium in the lithium source to the total molar amount of manganese and iron in the manganese iron phosphate mixed precursor as (1.02~1.09):1; Preferably, the amount of carbon source is controlled at 1.5% to 2% of the mass percentage of the manganese iron phosphate mixed precursor.

8. The preparation method according to any one of claims 1-7, characterized in that, The second calcination temperature is 600~800℃, and the time is 5~12h; Preferably, the second calcination is carried out under an inert atmosphere.

9. A lithium manganese iron phosphate, characterized in that, The preparation method according to any one of claims 1-8 is obtained.

10. A battery, characterized in that, The battery contains lithium manganese iron phosphate as described in claim 9.

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