A manganese iron phosphate precursor, a preparation method thereof, a lithium manganese iron phosphate cathode material and a preparation method thereof

Abstract

The application provides a manganese iron phosphate precursor and a preparation method and a lithium manganese iron phosphate positive electrode material and a preparation method. The manganese iron phosphate precursor is a solid solution mixture formed by manganese phosphate and iron phosphate, and has a general formula of (Mn(PO4)2 / 3)X(FePO4)1-X, wherein 0.1<=X<=0.7. The manganese iron phosphate precursor has the advantages of safety and good repeatability, and is used for solving the problems of poor carbon coating effect, high powder resistivity, manganese dissolution and poor batch stability. The lithium manganese iron phosphate positive electrode material prepared by using the manganese iron phosphate precursor can effectively improve the battery capacity and the rate performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of battery material preparation, and particularly relates to a manganese iron phosphate precursor and a preparation method thereof, and a lithium iron phosphate positive electrode material and a preparation method thereof. BACKGROUND

[0002] As a battery positive electrode material, lithium iron phosphate (LFP) has become mature, and its energy density has approached the theoretical limit. Lithium manganese iron phosphate (LMFP) is currently a hot research topic and is expected to become a new generation of lithium iron phosphate product in the future. LMFP not only has the safety and long cycle characteristics of LFP, but also has a higher voltage platform than LFP due to the higher voltage platform of manganese element than iron element in LFP, which improves the low energy density of LFP.

[0003] Patent CN106299296B effectively improves the long cycle performance, but the discharge capacity is low. Patent CN116374984A effectively improves the manganese iron distribution and improves the discharge capacity, but the rate performance is low. Patent CN115636402A effectively improves the conductivity, but has the problems of low capacity and large pressure drop.

[0004] It can be seen that although LMFP has advantages such as high voltage platform and low temperature performance over LFP, LMFP is still in the initial stage of industrialization and still faces many problems that need to be solved as described above. SUMMARY

[0005] In view of the above deficiencies and shortcomings in the prior art, the application aims to provide a manganese iron phosphate precursor and a preparation method thereof, which has the advantages of safety and good repeatability, and solves the problems of poor carbon coating effect, high powder resistivity, manganese leaching and poor batch stability.

[0006] The application also provides a lithium manganese iron phosphate positive electrode material and a preparation method thereof, which is prepared by using the above-mentioned manganese iron phosphate precursor, and can effectively improve the battery capacity and rate performance.

[0007] To achieve the above-mentioned purpose, the technical scheme provided by the application is as follows:

[0008] In a first aspect, the application provides a manganese iron phosphate precursor, which is a solid solution mixture of manganese phosphate and iron phosphate, and has a general formula of (Mn(PO4) 2 / 3 ) X (FePO4) 1-X wherein 0.1<=X<=0.7, such as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 or 0.7.

[0009] In a second aspect, the present application provides a preparation method of the manganese iron phosphate precursor, comprising the following steps:

[0010] 1) mixing a manganese source, an iron source and a phosphorus source, dry grinding for a certain time by using a ball mill to obtain a mixture powder which is uniformly mixed and has a certain particle size;

[0011] 2) embedding the mixture powder obtained in step 1) into a three-dimensional honeycomb-shaped foam, making the mixture powder completely fill and cover the three-dimensional honeycomb-shaped foam, and then introducing an inert protective atmosphere for high-temperature heat treatment to obtain the manganese iron phosphate precursor.

[0012] In the present application, the manganese source in step 1) is a manganese salt compound, preferably one or more of manganese carbonate, manganese oxalate, trimanganese tetraoxide and manganese dioxide.

[0013] In the present application, the iron source in step 1) is an iron salt compound, preferably one or more of iron phosphate, ferrous oxalate, diiron trioxide and ferrous oxide.

[0014] In the present application, the phosphorus source in step 1) is a phosphorus-containing compound, preferably one or more of phosphoric acid and monoammonium phosphate.

[0015] In the present application, the amount of the manganese source, the iron source and the phosphorus source in step 1) is calculated based on the molar ratio of manganese, iron and phosphorus contained after mixing, which is (1.0-7.0):(9.0-3.0):(9.7-7.7), for example (1, 2, 3, 4, 5, 6, 7):(9, 8, 7, 6, 5, 4, 3):(9.7, 9.5, 8, 8.3, 7, 7.7).

[0016] In the present application, the dry grinding in step 1) is performed for 24-48h, for example 24, 30, 35, 40, 45 or 48h; and the powder particle size D50 after dry grinding is 0.3-0.6um, for example 0.3, 0.4, 0.5 or 0.6um.

[0017] In the present application, the three-dimensional honeycomb-shaped foam in step 2) is made of one or more of polyether and polyurethane foam;

[0018] Preferably, the pore size of the three-dimensional honeycomb-shaped foam is 0.12-10mm, for example 0.12, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10mm, preferably 0.5-5mm;

[0019] Preferably, the density of the three-dimensional honeycomb-shaped foam is 0.1-1.0g / cm 3 , for example 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0g / cm 3 , preferably 0.1-0.6g / cm3 ;

[0020] Preferably, the three-dimensional honeycomb foam is one or more of 20PPI type, 60PPI type polyether, polyurethane foam. In the present application, the mass ratio of the three-dimensional honeycomb foam to the mixture powder in step 2) is 1:(3-50), for example 1:3, 1:10, 1:20, 1:30, 1:40, 1:50, preferably 1:(10-40).

[0021] In the present application, the inert protective atmosphere in step 2) is one or more of nitrogen, helium, neon, argon, krypton, xenon, radon.

[0022] In the present application, the high-temperature heat treatment in step 2) is at a temperature of 300-800℃, for example 300, 400, 500, 600, 700, 800℃, preferably 550-750℃.

[0023] Preferably, the heating process of the heat treatment is carried out in stages, specifically: first, at a heating rate of 1-5℃ / min, for example 1, 2, 3, 4, 5℃ / min, from room temperature to 300-500℃, for example 300, 350, 400, 450, 500℃, and holding for 30-180min, for example 30, 60, 90, 120, 150, 180min, then at a heating rate of 1-5℃ / min, for example 1, 2, 3, 4, 5℃ / min, continue to heat to 500-800℃, for example 500, 550, 600, 650, 700, 750, 800℃, and holding for 2-6h, for example 2, 3, 4, 5, 6h.

[0024] In the present application, the manganese iron phosphate precursor in step 2) has an average particle size of ≤1.0 microns, for example 1, 0.9, 0.8, 0.7, 0.6, 0.5 microns, preferably ≤0.8 microns.

[0025] In a third aspect, the present application provides a lithium manganese iron phosphate positive electrode material, which is prepared from the manganese iron phosphate precursor having the general formula described above or the manganese iron phosphate precursor prepared by the method described above.

[0026] In a fourth aspect, the present application provides a method for preparing the lithium manganese iron phosphate positive electrode material, which comprises the following steps:

[0027] (1) mixing the manganese iron phosphate precursor, lithium source, phosphorus source, carbon source, titanium dioxide, and adding pure water to form a slurry;

[0028] (2) after the slurry obtained in step (1) is refined to a certain particle size by a sand mill, drying to obtain a lithium manganese iron phosphate precursor powder;

[0029] (3) The lithium manganese iron phosphate precursor powder obtained in step (2) is sintered in an inert protective gas to obtain coarse powder of lithium manganese iron phosphate cathode material.

[0030] (4) The coarse powder of lithium manganese iron phosphate cathode material obtained in step (3) is subjected to air jet pulverization to a certain particle size to obtain lithium manganese iron phosphate cathode material.

[0031] In this invention, the lithium source in step (1) is a lithium salt or a lithium hydroxide, preferably one or more of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate.

[0032] In this invention, the carbon source in step (1) is an organic carbon source, preferably one or more of the following: polyethylene glycol (PEG), polyether, sucrose, glucose, etc.

[0033] In this invention, the phosphorus source in step (1) is a phosphorus-containing compound, preferably one or more of phosphoric acid and monoammonium phosphate.

[0034] In this invention, the molar ratio of the manganese iron phosphate precursor in step (1) to the lithium element in the lithium source and the phosphorus element in the phosphorus source, based on the sum of manganese and iron elements, is 1:(1.01-1.03):(0.03-0.35), for example 1:(1.01, 1.02, 1.03):(0.03, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35).

[0035] In this invention, the amount of carbon source added in step (1) is 8-15 wt% of the mass of the manganese iron phosphate precursor, for example, 8, 9, 10, 11, 12, 13, 14, or 15 wt%.

[0036] In this invention, the amount of titanium dioxide added in step (1) is 0.01-0.10 wt% of the mass of the manganese iron phosphate precursor, for example, 0.01, 0.03, 0.05, 0.07, 0.09, or 0.10 wt%.

[0037] In this invention, the slurry formed in step (1) has a solid content of 30-45 wt%, for example, 30, 35, 40, or 45 wt%.

[0038] In this invention, the slurry in step (2) is sand-milled to an average particle size ≤1.0 micrometer, for example 1, 0.9, 0.8, 0.7, 0.6, or 0.5 micrometers.

[0039] In this invention, the inert protective gas in step (3) is one or more of nitrogen, helium, neon, argon, krypton, xenon, and radon.

[0040] Preferably, the inert protective gas is continuously introduced during the sintering process, and the inert protective gas flow is controlled at 2-5 L / min, for example 2, 3, 4, 5 L / min.

[0041] In the present application, the sintering in step (3) is carried out at a temperature of 600-900℃, for example 600, 700, 800, 900℃, and for a time of 2-8h, for example 2, 3, 4, 5, 6, 7, 8h.

[0042] Preferably, the sintering process is carried out at a heating rate of 2-5℃ / min, for example 2, 3, 4, 5℃ / min.

[0043] Preferably, the sintering is carried out in a tube furnace.

[0044] In the present application, the lithium manganese iron phosphate positive electrode material obtained by crushing in step (4) has a particle size of 0.8-1.5um, for example 0.8, 0.9, 1, 1.2, 1.3, 1.4, 1.5um.

[0045] The lithium manganese iron phosphate positive electrode material according to the present application can be used as a positive electrode of a lithium ion battery.

[0046] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0047] In the sintering process of the precursor preparation, the three-dimensional honeycomb-shaped foam is embedded, and under the condition of inert gas, the honeycomb-shaped foam is decomposed into carbon and water, on the one hand, the honeycomb-shaped pores are formed to make the powder heating more uniform, on the other hand, the carbon can promote the reduction decomposition of the manganese source and accelerate the reaction with the phosphate, and through the continuous inert protective atmosphere, the manganese phosphate and the iron phosphate are fully solid-solution mixed to form the precursor, while avoiding the decomposition of the manganese phosphate and the iron phosphate. Through the solid solution of the manganese phosphate and the iron phosphate, the manganese and iron are more uniformly distributed, and the problem of poor carbon coating effect caused by the decomposition of the manganese iron phosphate precursor can be avoided, and the capacity and the cycle rate performance can be effectively improved. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 XRD comparison of the manganese iron phosphate precursors of Example 1 and Comparative Example 1;

[0049] Figure 2 SEM image of the manganese iron phosphate precursor of Example 1;

[0050] Figure 3 SEM image of the manganese iron phosphate precursor of the comparative example. DETAILED DESCRIPTION

[0051] The technical solutions of the present application are further described below in combination with specific examples. The examples provide specific implementation methods and specific operation processes, but the protection scope of the present application is not limited to the following examples.

[0052] The main raw materials in the embodiments and comparative examples of the present application are as follows, and other raw materials and reagents are commercially available unless otherwise specified:

[0053] Anhydrous iron phosphate: J1 type, purchased from Jiujiang Tianci High-tech Materials Co., Ltd.;

[0054] Trimanganese tetroxide: DCSM-5 type battery grade, purchased from Sichuan Hui'Neng Hui'Neng Zhixing New Material Co., Ltd.;

[0055] Monammonium phosphate: purity ≥ 99%, purchased from Israel Chemical Group;

[0056] Phosphoric acid: 25L barrel 85%, purchased from Wengfu Wengfu Dazhou Chemical Co., Ltd.;

[0057] Three-dimensional honeycomb polyurethane, polyether foam: 20PPI type, 60PPI type, purchased from Henan Haoyuanlai Environmental Protection Technology Co., Ltd.;

[0058] Lithium carbonate: purchased from Tianqi Lithium Industries Co., Ltd.;

[0059] Sucrose, glucose, polyethylene glycol: purchased from Beian Xiangyu Jin Gu Biochemical Technology Co., Ltd.;

[0060] Titanium dioxide: VK-30D type, purchased from Xuancheng Jingui New Materials Co., Ltd.;

[0061] Manganese carbonate: RY20230511005-7M-X1 type battery grade, purchased from Dalian Ruishang Power Co., Ltd.

[0062] Example 1

[0063] The preparation of the manganese iron phosphate precursor is as follows:

[0064] 1) Take 2.3 kg of iron phosphate, 2.71 kg of trimanganese tetroxide and 2.73 kg of monammonium phosphate and mix them thoroughly, the molar ratio of manganese, iron and phosphorus in the mixture is 7:3:7.7, use a ball mill to mill for 24 h, and obtain a mixture powder with a particle size D50 of 0.6 um.

[0065] 2) embedding the mixture powder formed in step 1) into 20PPI three-dimensional honeycomb polyurethane foam (pore size 0.5mm, density 0.6g / cm3) at a mass ratio of 1:10, so that the mixture powder fills the pores of the three-dimensional honeycomb polyurethane foam and completely embeds the three-dimensional honeycomb polyurethane foam, then introducing a protective atmosphere of nitrogen, sintering in a tube furnace, the temperature rising curve: 3℃ / min from room temperature to 300℃, 300℃ for 180min, 3℃ / min from 300℃ to 600℃, 600℃ for 4h, natural cooling to room temperature to obtain a manganese iron phosphate precursor, the average particle size of the particles is 0.8 microns, and the structural formula is (Mn(PO4) 2 / 3 ) 0.7 (FePO4) 0.3 SEM analysis is as shown in Figure 2 .

[0066] The lithium manganese iron phosphate positive electrode material is prepared by the following steps:

[0067] (1) weighing 5kg of manganese iron phosphate precursor (Mn element 27.35mol, Fe element 11.72mol, PO4 3- 29.93mol), weighing 2.97kg of lithium carbonate (40.24mol), weighing 0.2kg of PEG and 0.2kg of glucose, 5g of titanium dioxide, 1122g of phosphoric acid (9.73mol), and adding 11.6kg of pure water to form a slurry with a solid content of 45wt%.

[0068] (2) the slurry obtained in step (1) is ground to a fine powder with an average particle size of 0.6 microns, and then dried to obtain a lithium manganese iron phosphate precursor powder.

[0069] (3) the lithium manganese iron phosphate precursor powder prepared in step (2) is sintered in a tube furnace at a temperature rising rate of 5℃ / min, the sintering temperature is 700℃, and the sintering is performed for 6h, a nitrogen protective atmosphere is introduced during the whole sintering process, and the gas flow is controlled at 2L / min, and a lithium manganese iron phosphate coarse powder is obtained by sintering.

[0070] (4) the lithium manganese iron phosphate coarse powder obtained in step (3) is ground by air flow to an average particle size of 1.0 microns to obtain a lithium manganese iron phosphate positive electrode material.

[0071] Example 2

[0072] The lithium manganese iron phosphate precursor is prepared by the following steps:

[0073] 1) weighing 2.8kg of iron phosphate, 2.12kg of trimanganese tetraoxide and 2.15kg of monoammonium phosphate, mixing them thoroughly, the molar ratio of manganese, iron and phosphorus in the mixture is 6:4:8.0, using a ball mill to mill for 36h to obtain a mixture powder with a particle size D50 of 0.45um.

[0074] 2) To the mixture powder formed in step 1), embed 60PPI three-dimensional honeycomb polyether foam (pore size 3mm, density 0.3g / cm3) at a mass ratio of 1:25, so that the mixture powder fills the pores of the three-dimensional honeycomb polyether foam and completely embeds the three-dimensional honeycomb polyether foam, then introduce nitrogen protective atmosphere, sinter in a tube furnace, temperature rising curve: 3℃ / min from room temperature to 400℃, 400℃ for 100min, 2℃ / min from 400℃ to 600℃, 600℃ for 3h, naturally cool to room temperature to obtain manganese iron phosphate precursor, average particle size 0.7 microns, structural formula (Mn(PO4) 2 / 3 ) 0.6 (FePO4) 0.4 .

[0075] Preparation of lithium manganese iron phosphate positive electrode material, the steps are:

[0076] (1) Take 5kg of manganese iron phosphate precursor (Mn element 22.85mol, Fe element 15.23mol, PO4 3- 30.46mol), take 2.87kg of lithium carbonate (38.84mol), take 0.2kg of PEG and 0.2kg of glucose, 1.0g of titanium dioxide, 945g of phosphoric acid (8.20mol), add 15kg of pure water to form a slurry, the solid content is 37wt%.

[0077] (2) The slurry obtained in step (1) is ground to an average particle size of 0.5 microns, and then spray dried to obtain lithium manganese iron phosphate precursor powder.

[0078] (3) The lithium manganese iron phosphate precursor powder prepared in step (2) is sintered in a tube furnace, the temperature rising rate is 3℃ / min, the sintering temperature is 750℃, and the holding time is 5h, the nitrogen protective atmosphere is introduced during the whole sintering process, and the gas flow is controlled at 5L / min. Sintering to obtain lithium manganese iron phosphate coarse powder.

[0079] (4) The lithium manganese iron phosphate coarse powder obtained in step (3) is subjected to air flow crushing to an average particle size of 1.5 microns to obtain lithium manganese iron phosphate positive electrode material, and the performance test data are shown in Table 1.

[0080] Example 3

[0081] Preparation of manganese iron phosphate precursor, the steps are:

[0082] 1) Take 4.0 kg of iron phosphate, 2.02 kg of trimanganese tetraoxide and 2.03 kg of monoammonium phosphate, mix thoroughly, the molar ratio of manganese, iron and phosphorus in the mixture is 5:5:8.3, use a ball mill to ball mill for 48 h, obtain a mixture powder with a particle size D50 of 0.30 um.

[0083] 2) Embed 60PPI three-dimensional honeycomb polyurethane foam (pore size 5 mm, density 0.1 g / cm3) into the mixture powder formed in step 1), the mass ratio of the mixture powder to the three-dimensional honeycomb polyurethane foam is 1:35, so that the mixture powder fills the pores of the three-dimensional honeycomb polyurethane foam and completely embeds the three-dimensional honeycomb polyurethane foam, then introduce a protective atmosphere of nitrogen, sinter in a tube furnace, the temperature rising curve is: 3℃ / min from room temperature to 450℃, 450℃ for 30 min, 2℃ / min from 450℃ to 600℃, 600℃ for 3 h, naturally cool to room temperature to obtain a manganese iron phosphate precursor, the average particle size is 0.7 microns, the structural formula is (Mn(PO4) 2 / 3 ) 0.5 (FePO4) 0.5 .

[0084] Preparation of a lithium manganese iron phosphate positive electrode material, the steps are:

[0085] (1) Take 5 kg of manganese iron phosphate precursor (Mn element 18.58 mol, Fe element 18.58 mol, PO4 3- 30.97 mol), take 2.83 kg of lithium carbonate (38.27 mol), take 0.2 kg of PEG and 0.2 kg of glucose, 5.0 g of titanium dioxide, 778.9 g of phosphoric acid (6.76 mol), add 16.7 kg of pure water to form a slurry, the solid content is 35wt%.

[0086] (2) The slurry obtained in step (1) is ground to an average particle size of 0.5 microns, then spray dried to obtain a lithium manganese iron phosphate precursor powder.

[0087] (3) Sinter the lithium manganese iron phosphate precursor powder prepared in step (2) in a tube furnace, the temperature rising rate is 3℃ / min, the sintering temperature is 800℃, the holding time is 2h, a nitrogen protective atmosphere is introduced during the whole sintering process, the gas flow is controlled at 2L / min, sintering to obtain a lithium manganese iron phosphate coarse powder.

[0088] (4) The lithium manganese iron phosphate coarse powder obtained in step (3) is subjected to jet milling to an average particle size of 0.8 microns to obtain a lithium manganese iron phosphate positive electrode material, the performance test data are shown in Table 1.

[0089] Example 4

[0090] Preparation of a lithium manganese iron phosphate precursor, the steps are:

[0091] 1) Weigh 5.0 kg of iron phosphate, 0.42 kg of manganese carbonate and 0.28 kg of phosphoric acid and mix them thoroughly, the molar ratio of manganese, iron and phosphorus in the mixture is 1:9:9.7, use a ball mill to grind for 36 h, obtain a mixture powder with a particle size D50 of 0.45 um.

[0092] 2) Immerse the mixture powder formed in step 1) into 60PPI three-dimensional honeycomb polyurethane foam (pore size 5 mm, density 0.1 g / cm3), the mass ratio of the mixture powder to the three-dimensional honeycomb polyurethane foam is 1:40, so that the mixture powder fills the pores of the three-dimensional honeycomb polyurethane foam and completely buries the three-dimensional honeycomb polyurethane foam, then introduce nitrogen as a protective atmosphere, sinter in a tube furnace, the temperature rising curve is: 3℃ / min from room temperature to 400℃, 400℃ for 60 min, 2℃ / min from 400℃ to 600℃, 600℃ for 3 h, naturally cool to room temperature to obtain a manganese iron phosphate precursor, the average particle size of the particles is 0.7 microns, the structural formula is (Mn(PO4) 2 / 3 ) 0.1 (FePO4) 0.9 。

[0093] Preparation of a lithium manganese iron phosphate positive electrode material, the steps are:

[0094] (1) Weigh 5 kg of manganese iron phosphate precursor (Mn element 3.39 mol, Fe element 30.49 mol, PO4 3- 32.75 mol), weigh 2.55 kg of lithium carbonate (34.56 mol), weigh 0.2 kg of PEG and 0.2 kg of glucose, 0.5 g of titanium dioxide, 189.77 g of phosphoric acid (1.65 mol), add 19 kg of pure water to form a slurry, the solid content is 30wt%.

[0095] (2) The slurry obtained in step (1) is ground to an average particle size of 0.5 microns by sand milling, then dried to obtain a lithium manganese iron phosphate precursor powder.

[0096] (3) Sinter the lithium manganese iron phosphate precursor powder prepared in step (2) in a tube furnace, the temperature rising rate is 3℃ / min, the sintering temperature is 700℃, the holding time is 6 h, nitrogen gas is introduced as a protective atmosphere during the whole sintering process, the gas flow is controlled at 2 L / min, sintering to obtain a lithium manganese iron phosphate coarse powder.

[0097] (4) The lithium manganese iron phosphate coarse powder obtained in step (3) is subjected to jet milling to an average particle size of 1.2 microns to obtain a lithium manganese iron phosphate positive electrode material, the performance test data are shown in Table 1.

[0098] Comparative Example 1

[0099] The manganese iron phosphate precursor was prepared according to the method of Example 1, except that the sintering was performed in an air atmosphere instead of an inert protective gas atmosphere, and other operations and conditions were unchanged, to obtain the lithium manganese iron phosphate positive electrode material. Figure 3 The XRD comparison of the manganese iron phosphate precursors of Example 1 and Comparative Example 1 is shown in Figure 2. Figure 1 .

[0100] Comparative Example 2

[0101] The manganese iron phosphate precursor was prepared according to the method of Example 1, except that the three-dimensional honeycomb-shaped foam was not embedded in step 2), and the sintering was performed directly in a nitrogen atmosphere, and other operations and conditions were unchanged, to obtain the lithium manganese iron phosphate positive electrode material.

[0102] Comparative Example 3

[0103] The manganese iron phosphate precursor was prepared according to the method of Example 1, except that the three-dimensional honeycomb-shaped foam was replaced with a three-dimensional honeycomb-shaped zirconia ceramic in step 2), and the sintering was performed directly in a nitrogen atmosphere, and other operations and conditions were unchanged, to obtain the lithium manganese iron phosphate positive electrode material.

[0104] Comparative Example 4

[0105] The manganese iron phosphate precursor was prepared according to the method of Example 1, except that the three-dimensional honeycomb-shaped foam was replaced with a sponge of the same size in step 2), and the sintering was performed directly in a nitrogen atmosphere, and other operations and conditions were unchanged, to obtain the lithium manganese iron phosphate positive electrode material.

[0106] The lithium manganese iron phosphate positive electrode materials prepared in the examples and comparative examples of the present application were tested for performance according to the following method, and the results are shown in Table 1.

[0107] Lithium ion battery preparation and testing method: The above-mentioned lithium manganese iron phosphate positive electrode materials prepared in the examples and comparative examples were respectively taken, and were uniformly mixed with a conductive agent and a binder in a weight ratio of 90:5:5, and the uniform mixing parameters were 2000 rpm and 15 min; the above-mentioned prepared slurry was coated on a carbon-coated aluminum foil with a coating thickness of 200 um, and was transferred to a vacuum dryer for drying to obtain a positive electrode material sheet, and the drying conditions were 120 DEG C and 3 h; then the above-mentioned positive electrode sheet was cut into a circular sheet with a diameter of 14 mm, was weighed, and was assembled according to the assembly process of a LIR2025 button cell, and the recovery capacity was tested.

[0108] In the actual evaluation process, in order to evaluate the reliability of the test results, for example, the positive electrode sheet can be cut into φ14mm small round sheets by a cutting machine, weighed, and 5 round sheets with similar mass are taken to assemble LIR2025 button cells, and test the recovery discharge specific capacity (mrecovery), the average recovery capacity of 5 batteries is required to deviate from the initial capacity by ±5mAh / g, and the Sigma of the discharge specific capacity of 5 batteries is <1, which meets the above requirements, indicating that the method for rapidly evaluating the recovery capacity of the positive electrode sheet is accurate and reliable.

[0109] A set of LIR2025 type includes positive and negative electrode shells, foam nickel, which are ultrasonically cleaned with alcohol for 20min before use, and baked at 60℃ for 3h. The assembly process is as follows: negative electrode shell 1-foam nickel 2-metal lithium negative electrode 3-separator 4-electrolyte-positive electrode sheet (after cleaning) 5-positive electrode shell 6, which is assembled in the above order.

[0110] 01C charge Amh / g is the above button cell 10h full charge capacity; 01C discharge Amh / g is the above button cell 10h discharge capacity; 1C discharge is 1h discharge capacity.

[0111] Powder resistivity Ω·mm: tested by powder resistivity meter according to GB / T 30835-2014.

[0112] Carbon content %: tested by infrared carbon and sulfur analyzer according to GB / T 20123-2006.

[0113] BET m 2 / g: tested by nitrogen adsorption specific surface area instrument according to GB / T 19587-2017.

[0114] Manganese dissolution ppm: tested according to GB / T 30835-2014.

[0115] Table 1 Test results of lithium manganese iron phosphate positive electrode materials prepared in examples and comparative examples

[0116]

[0117]

Claims

1. A manganese iron phosphate precursor, characterized in that, The manganese ferric phosphate precursor is a solid solution mixture of manganese phosphate and ferric phosphate, with the general formula (Mn(PO4)). 2 / 3 ) X (FePO4) 1-X Where 0.1≤X≤0.

7.

2. A method for preparing the manganese iron phosphate precursor according to claim 1, characterized in that the step include: 1) Mix manganese, iron and phosphorus sources and dry grind them in a ball mill for a certain time to obtain a uniformly mixed powder with a certain particle size; 2) Embed three-dimensional honeycomb foam into the mixture powder obtained in step 1), so that the mixture powder completely fills and covers the three-dimensional honeycomb foam, and then pass through an inert protective atmosphere for high-temperature heat treatment to obtain the manganese iron phosphate precursor.

3. The preparation method according to claim 2, characterized in that, Step 1) The manganese source is one or more manganese salt compounds; and / or Step 1) The iron source is one or more iron salt compounds; and / or Step 1) The phosphorus source is one or more phosphorus-containing compounds; and / or The amounts of manganese, iron, and phosphorus sources used in step 1) are, based on the manganese, iron, and phosphorus elements contained in the mixture, in a molar ratio of (1.0-7.0):(9.0-3.0):(9.7-7.7); and / or The dry grinding in step 1) takes 24-48 hours; the particle size D50 of the powder after dry grinding is 0.3-0.6 μm.

4. The preparation method according to claim 3, characterized in that, The manganese source is one or more of manganese carbonate, manganese oxalate, manganese tetroxide, and manganese dioxide.

5. The preparation method according to claim 3, characterized in that, The iron source is one or more of ferric phosphate, ferrous oxalate, ferric oxide, and ferrous oxide.

6. The preparation method according to claim 3, characterized in that, The phosphorus source is one or more of phosphoric acid and monoammonium phosphate.

7. The preparation method according to claim 2, characterized in that, Step 2) The three-dimensional honeycomb foam is made of one or more of polyether and polyurethane foams; and / or Step 2) The mass ratio of the three-dimensional honeycomb foam to the mixed powder is 1:(3-50).

8. The preparation method according to claim 7, characterized in that, The mass ratio of the three-dimensional honeycomb foam to the mixed powder is 1:(10-40).

9. The preparation method according to claim 2, characterized in that, Step 2) The pore size of the three-dimensional honeycomb foam is 0.12-10 mm.

10. The preparation method according to claim 9, characterized in that, The pore size of the three-dimensional honeycomb foam is 0.5-5 mm.

11. The preparation method according to claim 2, characterized in that, Step 2) The density of the three-dimensional honeycomb foam is 0.1-1.0 g / cm³. 3 .

12. The preparation method according to claim 11, characterized in that, The density of the three-dimensional honeycomb foam is 0.1-0.6 g / cm³. 3 .

13. The preparation method according to claim 2, characterized in that, Step 2) The inert protective atmosphere is one or more of nitrogen, helium, neon, argon, krypton, xenon, and radon; and / or Step 2) describes a high-temperature heat treatment at a temperature of 300-800℃; and / or The manganese iron phosphate precursor in step 2) has an average particle size ≤ 1.0 micrometers.

14. The preparation method according to claim 13, characterized in that, The high-temperature heat treatment is performed at a temperature of 550-750℃.

15. The preparation method according to claim 13, characterized in that, The heat treatment heating process is carried out in stages, specifically: first, the temperature is raised from room temperature to 300-500℃ at a heating rate of 1-5℃ / min and held for 30-180min; then, the temperature is raised to 500-800℃ at a heating rate of 1-5℃ / min and held for 2-6h.

16. The preparation method according to claim 13, characterized in that, The manganese iron phosphate precursor has an average particle size of ≤0.8 micrometers.

17. A lithium manganese iron phosphate cathode material, prepared from the lithium manganese iron phosphate precursor of claim 1 or the lithium manganese iron phosphate precursor prepared by any one of claims 2-16.

18. A method for preparing the lithium manganese iron phosphate cathode material according to claim 17, characterized in that the step... include: (1) Mix manganese iron phosphate precursor, lithium source, phosphorus source, carbon source and titanium dioxide, and add pure water to form a slurry; (2) The slurry obtained in step (1) is refined to a certain particle size using a sand mill and then dried to obtain lithium manganese iron phosphate precursor powder; (3) The lithium manganese iron phosphate precursor powder obtained in step (2) is sintered in an inert protective gas to obtain coarse powder of lithium manganese iron phosphate cathode material. (4) The coarse powder of lithium manganese iron phosphate cathode material obtained in step (3) is subjected to air jet pulverization to a certain particle size to obtain lithium manganese iron phosphate cathode material.

19. The preparation method according to claim 18, characterized in that, The lithium source in step (1) is one or more of lithium salts and lithium hydroxides; and / or The carbon source in step (1) is one or more organic carbon sources; and / or The phosphorus source in step (1) is one or more phosphorus-containing compounds; and / or The manganese iron phosphate precursor described in step (1) has a molar ratio of manganese and iron (total) to lithium in the lithium source and phosphorus in the phosphorus source of 1:(1.01-1.03):(0.03-0.35); and / or The amount of carbon source added in step (1) is 8-15 wt% of the mass of the manganese iron phosphate precursor; and / or The amount of titanium dioxide added in step (1) is 0.01-0.10 wt% of the mass of the manganese iron phosphate precursor; and / or The slurry formed in step (1) has a solid content of 30-45 wt%.

20. The preparation method according to claim 19, characterized in that, The lithium source is one or more of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate.

21. The preparation method according to claim 19, characterized in that, The carbon source is one or more organic carbon sources selected from polyethylene glycol, polyether, sucrose, and glucose.

22. The preparation method according to claim 19, characterized in that, The phosphorus source is one or more of phosphoric acid and monoammonium phosphate.

23. The preparation method according to claim 18, characterized in that, The inert protective gas in step (3) is one or more of nitrogen, helium, neon, argon, krypton, xenon, and radon; and / or The sintering in step (3) is carried out at a temperature of 600-900℃ for 2-8 hours.

24. The preparation method according to claim 18, characterized in that, Step (3) Inert protective gas is continuously introduced during the sintering process, and the flow rate of inert protective gas is controlled at 2-5L / min.

25. The preparation method according to claim 18, characterized in that, In step (3), the sintering process has a heating rate of 2-5℃ / min.

26. The preparation method according to claim 18, characterized in that, The sintering described in step (3) is carried out in a tube furnace.

27. The preparation method according to claim 18, characterized in that, Step (2) involves grinding the slurry to an average particle size ≤ 1.0 micrometers; and / or The lithium manganese iron phosphate cathode material obtained by crushing in step (4) has a particle size of 0.8-1.5 μm.

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