Lithium manganese iron phosphate material and preparation method thereof

Abstract

The present invention provides a lithium iron manganese phosphate material and a preparation method thereof. The preparation method comprises step S1, sand-milling raw materials including an iron source, a first manganese source, a second manganese source, a third manganese source, and a phosphorus source to obtain a sand-milled material; step S2, mixing the sand-milled material with a carbon source to obtain a mixture; step S3, spraying the mixture to obtain a spray material, and mixing the spray material with a lithium source to obtain a mixed lithium yellow material; step S4, heat-treating and pulverizing the mixed lithium yellow material in an inert atmosphere to obtain a lithium iron manganese phosphate material; wherein the first manganese source is an inorganic water-soluble manganese compound, the second manganese source is an organic manganese source, and the third manganese source is a manganese oxide. The preparation method of the present application not only has low requirements for a sand mill, but also does not generate high energy consumption as in a two-step process. That is, the preparation method and equipment of the lithium iron manganese phosphate material of the present application are simple, cost-effective, and more conducive to industrial large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a lithium iron manganese phosphate material and a preparation method thereof. Background Art

[0002] Lithium iron manganese phosphate LiMn x Fe y PO4 (LMFP) is an important and cost-effective cathode material in lithium-ion batteries, which has a higher operating voltage than LiFePO4 (LFP) and has higher safety compared with layered oxide cathodes. However, due to the lack of an effective synthesis process to solve the problem of Li + Their commercial applications remain challenging due to their slow diffusion kinetics and complex phase transitions.

[0003] Lithium manganese iron phosphate with olivine structure + Only one-dimensional diffusion can occur along the plane direction, and charge transfer also mainly occurs on this plane, resulting in an extremely low lithium ion diffusion coefficient. Therefore, adjusting the particle size and ensuring a short diffusion plane orientation are of great significance for improving the performance of lithium manganese iron phosphate materials. When the size of lithium manganese iron phosphate material particles is nanometer-scale, the lithium ion migration path is shortened and the migration rate is accelerated. At the same time, the lithium manganese iron phosphate material is in full contact with the electrolyte, which makes the lithium manganese iron phosphate material exhibit better discharge specific capacity and thus obtain excellent electrochemical performance.

[0004] Current nano-sizing strategies are primarily achieved through two processes: one is to control the slurry D50 to a particle size significantly lower than that of the lithium iron phosphate slurry during the slurry sand milling process; the other is to synthesize the particles through a two-step sintering process. The former requires adding more sand mills and grinding times, or replacing the sand mill with one that requires a higher particle size; the latter involves the additional sand milling, spraying, and sintering steps, making the process cumbersome and complex to control.

[0005] Although the nano-sizing strategy shortens the ion transmission particle size and improves the activity of lithium manganese iron phosphate materials, it also puts higher requirements on the equipment and process for producing lithium manganese iron phosphate, thus hindering the low-cost, large-scale industrial production of lithium manganese iron phosphate materials. Summary of the Invention

[0006] The main purpose of the present invention is to provide a lithium iron manganese phosphate material and a preparation method thereof, so as to solve the problems of the preparation method of lithium iron manganese phosphate material in the prior art, such as complex equipment and process, high production cost and difficulty in achieving industrial large-scale production.

[0007] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a preparation method of a lithium iron manganese phosphate material is provided, which comprises step S1, sand-milling a raw material comprising an iron source, a first manganese source, a second manganese source, a third manganese source and a phosphorus source to obtain a sand-milled material; step S2, mixing the sand-milled material with a carbon source to obtain a mixture; step S3, spraying the mixture to obtain a spray material, mixing the spray material with a lithium source to obtain a mixed lithium yellow material; step S4, heat-treating and pulverizing the mixed lithium yellow material in an inert atmosphere in sequence to obtain a lithium iron manganese phosphate material; wherein the first manganese source is an inorganic water-soluble manganese compound, the second manganese source is an organic manganese source, and the third manganese source is a manganese oxide.

[0008] Furthermore, in the above step S1, the first manganese source is selected from any one or more of manganese sulfate, manganese nitrate, manganese chloride and manganese dihydrogen phosphate; and / or the second manganese source is selected from any one or more of manganese oxalate, manganese acetate, manganese citrate, manganese glycinate and manganese gluconate; and / or the third manganese source is selected from any one or more of manganese oxide, manganese dioxide, manganese trioxide and manganese tetraoxide.

[0009] By optimizing the types of the above three different manganese sources within the above range, it is helpful to further exert the synergistic coordination between the crystal structures and morphologies of the three different manganese sources, thereby improving the grading between the different manganese source particles, and thus making the lithium manganese iron phosphate material have a higher compaction density, and at the same time, it is beneficial to improve the efficiency of sand grinding.

[0010] Furthermore, the molar ratio of the first manganese source, the second manganese source and the third manganese source is (1-3): (3-5): (4-6) respectively, calculated based on the molar ratio of manganese element.

[0011] By controlling the molar ratio of the three different manganese sources within the above range, the compaction degree of the material can be improved while better promoting the formation of particle gradation.

[0012] Furthermore, the D50 particle size of the material after sand grinding is 0.48 μm to 0.50 μm.

[0013] Controlling the D50 particle size of the sand-milled material within the above-mentioned range has a significant impact on improving the performance of the lithium iron manganese phosphate material. Specifically, it can effectively shorten the migration path of lithium ions, accelerate the migration rate of lithium ions, and at the same time increase the contact area between the lithium iron manganese phosphate material and the electrolyte, thereby exhibiting a better discharge specific capacity, thereby enabling the lithium iron manganese phosphate material to obtain excellent electrochemical properties. At the same time, the compaction of the lithium iron manganese phosphate material is improved.

[0014] Furthermore, in the above step S1, the raw material further includes a first solvent, and the first solvent is selected from any one or more of water, ethanol, methanol and glycerol; and / or the solid content of the raw material is 30% to 50%.

[0015] By controlling the solid content of the raw materials within the above range, it is not only helpful to uniformly disperse the iron source, the first manganese source, the second manganese source, the third manganese source, and the phosphorus source in the first solvent, but also helps to ensure that the viscosity of the material after sand grinding is within an appropriate range, thereby facilitating the improvement of the uniform dispersion and stability of the lithium manganese iron phosphate material. Preferably, the first solvent is selected from any one or more of water, ethanol, methanol, and glycerol, thereby helping to increase the solubility of the iron source, manganese source, and phosphorus source therein, and at the same time, helping to improve the stability of the material during the grinding process, prevent agglomeration, and thus obtain a lithium manganese iron phosphate material with a more uniform particle size distribution.

[0016] Furthermore, in the above step S1, the phosphorus source is selected from any one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphorus pentoxide; and / or the iron source is selected from any one or more of ferric phosphate, ferric phosphate, ferric oxalate, ferric oxide, ferrous oxide, ferric hydroxide, ferric oxide and ferric acetate.

[0017] By preferably selecting the above types of phosphorus sources, it is helpful to achieve more thorough mixing between the phosphorus source and the iron source, the first manganese source, the second manganese source, and the third manganese source, and it is also possible to effectively control the particle size and morphology of the lithium manganese iron phosphate material, thereby improving its charge and discharge performance and cycle stability.

[0018] Furthermore, in the above step S2, the carbon source includes a first carbon source and a second carbon source; the mass ratio of the first carbon source to the second carbon source is (6 to 8): (2 to 4), and / or the first carbon source is selected from any one or more of glucose, sucrose, maltose, starch and fructose; and / or the second carbon source is selected from any one or more of citric acid, tannic acid, ascorbic acid, polyacrylic acid, polyvinyl alcohol, xylitol and polyethylene glycol.

[0019] In the present application, by adding a soluble composite carbon source and controlling the mass ratio of the first carbon source to the second carbon source within the above range, it is helpful to utilize the different carbonization temperatures of the first carbon source and the second carbon source, thereby forming a more uniform carbon coating conductive network on the surface of the lithium manganese iron phosphate material, thereby significantly improving the electronic conductivity of the carbon coating layer, and also helping to achieve nano-scaling of the lithium manganese iron phosphate material.

[0020] Furthermore, in the above step S2, the mixture further comprises a second solvent, and the second solvent is selected from any one or more of water, ethanol, methanol and isopropanol; and / or the solid content of the mixture is 30% to 50%.

[0021] The preferred type of the second solvent helps to improve the uniformity of dispersion of the sand-milled material and the carbon source therein. By controlling the solid content of the mixture within the above range, it helps to ensure that the viscosity of the mixture is within an appropriate range, thereby facilitating improved uniform dispersion and stability of the lithium manganese iron phosphate material.

[0022] Furthermore, in the above step S4, the heat treatment includes low-temperature heat treatment, medium-temperature heat treatment and high-temperature heat treatment performed in sequence; and / or the heating rate during the heat treatment process is 60°C / h to 180°C / h; and / or the temperature of the low-temperature heat treatment is 100°C to 200°C, and the time of the low-temperature heat treatment is 1h to 2h; and / or the temperature of the medium-temperature heat treatment is 450°C to 650°C, and the time of the medium-temperature heat treatment is 3h to 5h; and / or the temperature of the high-temperature heat treatment is 700°C to 750°C, and the time of the high-temperature heat treatment is 5h to 8h.

[0023] The preferred low-temperature heat treatment conditions above help to improve the dehydration efficiency and effect of the mixed lithium yellow material; the preferred medium-temperature heat treatment conditions above help to improve the efficiency and effect of lithium iron manganese phosphate phase formation; the preferred high-temperature heat treatment conditions above help to improve the crystallinity of lithium iron manganese phosphate.

[0024] According to another aspect of the present invention, a lithium iron manganese phosphate material is provided. The lithium iron manganese phosphate material is prepared by the aforementioned preparation method.

[0025] Applying the technical solution of the present invention, the present application is based on the diffusion difference between manganese ions and iron ions in the olivine skeleton structure during heat treatment (iron ions are integrated into the manganese source). On the one hand, by adopting three manganese sources with different crystal structures and morphologies, a one-time sand milling and one-time sintering process is used to prepare a lithium manganese iron phosphate material with excellent electrical properties and high compaction density, thereby improving the performance of the lithium manganese iron phosphate material while also facilitating the formation of particle grading and improving sand milling efficiency. On the other hand, mixing the carbon source separately with the sand-milled slurry can avoid the problem of carbon source coating on the particle surface hindering the effective collision of zirconium balls and the reduction of grinding efficiency caused by slurry thickening during grinding. On the other hand, mixing the lithium source with the spray material can avoid the problem of lithium ions combining with phosphate to form precipitates and causing unstable particle size monitoring, thereby ensuring the accuracy of the particle size test of the material after sand milling. Therefore, the preparation method of the present application does not require high requirements for the sand mill, nor does it produce high energy consumption such as the two-step process. That is, the preparation method and equipment of the lithium manganese iron phosphate material in the present application are simple, lower cost, and more conducive to industrial large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 The SEM image of a lithium manganese iron phosphate material prepared according to Example 1 of the present invention is shown;

[0028] Figure 2 A comparison diagram of compaction density curves of lithium manganese iron phosphate materials prepared according to Example 1 of the present invention and Comparative Examples 1 to 3 is shown. DETAILED DESCRIPTION

[0029] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0030] As analyzed in the background technology, the preparation method of lithium manganese iron phosphate material in the prior art has the problems of complex equipment and process, high production cost and difficulty in achieving industrial large-scale production. To solve this problem, the present invention provides a lithium manganese iron phosphate material and a preparation method thereof.

[0031] In a typical embodiment of the present application, a method for preparing a lithium iron manganese phosphate material is provided, which comprises: step S1, sand-milling a raw material comprising an iron source, a first manganese source, a second manganese source, a third manganese source and a phosphorus source to obtain a sand-milled material; step S2, mixing the sand-milled material with a carbon source to obtain a mixture; step S3, spraying the mixture to obtain a spray material, mixing the spray material with a lithium source to obtain a mixed lithium yellow material; step S4, heat-treating and pulverizing the mixed lithium yellow material in an inert atmosphere in sequence to obtain a lithium iron manganese phosphate material; wherein the first manganese source is an inorganic water-soluble manganese compound, the second manganese source is an organic manganese source, and the third manganese source is a manganese oxide.

[0032] The present application is based on the diffusion difference between manganese ions and iron ions in the olivine skeleton structure during heat treatment (iron ions are integrated into the manganese source). On the one hand, by adopting three manganese sources with different crystal structures and morphologies, and undergoing a one-time sand milling and one-time sintering process, a lithium iron manganese phosphate material with excellent electrical properties and high compaction density is prepared, thereby improving the performance of the lithium iron manganese phosphate material while also facilitating the formation of particle grading and improving sand milling efficiency. On the other hand, mixing the carbon source separately with the sand-milled slurry can avoid the problem of carbon source coating on the particle surface hindering the effective collision of zirconium balls and the reduction of grinding efficiency caused by slurry thickening during grinding. On the other hand, mixing the lithium source with the spray material can avoid the problem of lithium ions combining with phosphate to form precipitates, which causes unstable particle size monitoring, and can ensure the accuracy of the particle size test of the material after sand milling. Therefore, the preparation method of the present application does not require high requirements for the sand mill, nor does it produce high energy consumption such as the two-step process. That is, the preparation method and equipment of the lithium iron manganese phosphate material in the present application are simple, lower cost, and more conducive to industrial large-scale production.

[0033] In one embodiment of the present application, in the above step S1, the first manganese source is selected from any one or more of manganese sulfate, manganese nitrate, manganese chloride and manganese dihydrogen phosphate; and / or the second manganese source is selected from any one or more of manganese oxalate, manganese acetate, manganese citrate, manganese glycinate and manganese gluconate; and / or the third manganese source is selected from any one or more of manganese oxide, manganese dioxide, manganese trioxide and manganese tetraoxide.

[0034] The types of the first manganese source, the second manganese source and the third manganese source are preferably within the above range, which helps to further exert the synergistic coordination between the crystal structures and morphologies of the three different manganese sources, thereby improving the grading between different manganese source particles, and thus making the lithium manganese iron phosphate material have a higher compaction density, and at the same time, it is beneficial to improve the efficiency of sand grinding.

[0035] In one embodiment of the present application, the molar ratio of the first manganese source, the second manganese source and the third manganese source is (1-3): (3-5): (4-6) respectively, calculated based on the molar ratio of manganese element.

[0036] By controlling the molar ratio of the first manganese source, the second manganese source and the third manganese source within the above range, the compaction degree of the material can be improved while better promoting the formation of particle gradation.

[0037] In one embodiment of the present application, the D50 particle size of the material after sand grinding is 0.48 μm to 0.50 μm.

[0038] Controlling the D50 particle size of the sand-milled material within the above-mentioned range has a significant impact on improving the performance of the lithium iron manganese phosphate material. Specifically, it can effectively shorten the migration path of lithium ions, accelerate the migration rate of lithium ions, and at the same time increase the contact area between the lithium iron manganese phosphate material and the electrolyte, thereby exhibiting a better discharge specific capacity, thereby enabling the lithium iron manganese phosphate material to obtain excellent electrochemical properties. At the same time, the compaction of the lithium iron manganese phosphate material is improved.

[0039] In one embodiment of the present application, in the above step S1, the raw material further includes a first solvent, and the first solvent is selected from any one or more of water, ethanol, methanol and glycerol; and / or the solid content of the raw material is 30% to 50%.

[0040] By controlling the solid content of the raw materials within the above range, it is not only helpful to uniformly disperse the iron source, the first manganese source, the second manganese source, the third manganese source, and the phosphorus source in the first solvent, but also helps to ensure that the viscosity of the material after sand grinding is within an appropriate range, thereby facilitating the improvement of the uniform dispersion and stability of the lithium manganese iron phosphate material. Preferably, the first solvent is selected from any one or more of water, ethanol, methanol, and glycerol, thereby helping to increase the solubility of the iron source, manganese source, and phosphorus source therein, and at the same time, helping to improve the stability of the material during the grinding process, prevent agglomeration, and thus obtain a lithium manganese iron phosphate material with a more uniform particle size distribution.

[0041] In one embodiment of the present application, in the above step S1, the phosphorus source is selected from any one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphorus pentoxide; and / or the iron source is selected from any one or more of ferric phosphate, ferric oxalate, ferric oxide, ferrous oxide, ferric hydroxide, ferric oxide and ferric acetate.

[0042] The above types of phosphorus sources are all soluble. The present application prefers the above types of phosphorus sources, which not only help to achieve more thorough mixing between the phosphorus source and the iron source, the first manganese source, the second manganese source, and the third manganese source, but also can effectively control the particle size and morphology of the lithium manganese iron phosphate material, thereby improving its charge and discharge performance and cycle stability.

[0043] In one embodiment of the present application, in the above step S2, the carbon source includes a first carbon source and a second carbon source; the mass ratio of the first carbon source to the second carbon source is (6-8): (2-4), and / or the first carbon source is selected from one of glucose, sucrose, maltose, starch and fructose, and the second carbon source is selected from any one or more of citric acid, tannic acid, ascorbic acid, polyacrylic acid, polyvinyl alcohol, xylitol and polyethylene glycol.

[0044] In this application, by adding a soluble composite carbon source and controlling the mass ratio of the first carbon source to the second carbon source within the above range, it is helpful to utilize the different carbonization temperatures of the first carbon source and the second carbon source, thereby forming a more uniform carbon coating conductive network on the surface of the lithium manganese iron phosphate material, thereby significantly improving the electronic conductivity of the carbon coating layer and further facilitating the nano-scaling of the lithium manganese iron phosphate material. The nano-scale lithium manganese iron phosphate material has a shorter ion diffusion path and a larger specific surface area, thereby improving the overall electrochemical performance of the lithium manganese iron phosphate material.

[0045] In one embodiment of the present application, in the above step S2, the mixture further includes a second solvent, and the second solvent is selected from any one or more of water, ethanol, methanol and isopropanol; and / or the solid content of the mixture is 30% to 50%.

[0046] The preferred type of the second solvent helps to improve the uniformity of dispersion of the sand-milled material and the carbon source therein. By controlling the solid content of the mixture within the above range, it helps to ensure that the viscosity of the mixture is within an appropriate range, thereby facilitating improved uniform dispersion and stability of the lithium manganese iron phosphate material.

[0047] In one embodiment of the present application, in the above-mentioned step S4, the heat treatment includes low-temperature heat treatment, medium-temperature heat treatment and high-temperature heat treatment performed in sequence; and / or the heating rate during the heat treatment process is 60℃ / h~180℃ / h; and / or the temperature of the low-temperature heat treatment is 100℃~200℃, and the time of the low-temperature heat treatment is 1h~2h; and / or the temperature of the medium-temperature heat treatment is 450℃~650℃, and the time of the medium-temperature heat treatment is 3h~5h; and / or the temperature of the high-temperature heat treatment is 700℃~750℃, and the time of the high-temperature heat treatment is 5h~8h.

[0048] The preferred low-temperature heat treatment conditions above help to improve the dehydration efficiency and effect of the mixed lithium yellow material; the preferred medium-temperature heat treatment conditions above help to improve the efficiency and effect of lithium iron manganese phosphate phase formation; the preferred high-temperature heat treatment conditions above help to improve the crystallinity of lithium iron manganese phosphate.

[0049] In another typical embodiment of the present application, a lithium iron manganese phosphate material is provided. The lithium iron manganese phosphate material is prepared by the aforementioned preparation method.

[0050] The lithium manganese iron phosphate material prepared by the above preparation method in this application has excellent electrical properties and high compaction performance.

[0051] The beneficial technical effects of the present application will be illustrated below with reference to specific embodiments and comparative examples.

[0052] Example 1

[0053] 4 mol of ferric phosphate, 1.2 mol of manganese sulfate, 2.4 mol of manganese acetate and 0.8 mol of manganese tetraoxide were dissolved in deionized water to prepare a 35% solid content liquid (I); 15% of the carbon source (glucose: polyethylene glycol 6000: citric acid = 7.2:1.8:1) of the above raw materials was weighed and dissolved in deionized water to form a 35% liquid (II); the liquid (I) was sand-milled to obtain a sand-milled material, and the particle size D50 of the sand-milled material was controlled to be 0.48-0.50 μm; the sand-milled material and the liquid (II) were mixed in a high-speed disperser for 1 hour and then spray-dried to obtain spray material; mixing the spray material with 10.15 mol of lithium hydroxide in a high mixer for 2 hours to obtain a mixed lithium yellow material; transferring the mixed lithium yellow material into a box furnace for sintering to obtain a sintered powder, specifically, the average oxygen content during the sintering process is less than 10 ppm, the heating rate is 180°C / h, during the low-temperature heat treatment, the temperature is raised to 150°C and kept warm for 2 hours, during the medium-temperature heat treatment, the temperature is continuously raised to 600°C and kept warm for 5 hours, and during the high-temperature heat treatment, the temperature is continuously raised to 720°C and kept warm for 5 hours; after the material is cooled to 50°C, it is crushed by air flow and the particle size D50 is controlled to be 0.8-1 μm to obtain a lithium manganese iron phosphate material.

[0054] Example 2

[0055] The difference from Example 1 is that the manganese source uses 1.2 mol of manganese chloride, 2.4 mol of manganese oxalate, and 0.8 mol of manganese tetraoxide, and finally obtains lithium manganese iron phosphate material.

[0056] Example 3

[0057] The difference from Example 1 is that the total molar amount of manganese element is the same as that in Example 1, and the molar ratio of manganese sulfate, manganese acetate and manganese trimanganese tetraoxide is 0.6:1.8:1.2, and lithium manganese iron phosphate material is finally obtained.

[0058] Example 4

[0059] The difference from Example 1 is that the total molar amount of manganese element is the same as that in Example 1, and the molar ratio of manganese sulfate, manganese acetate and manganese trimanganese tetraoxide is 1.2:1.8:1, and lithium manganese iron phosphate material is finally obtained.

[0060] Example 5

[0061] The difference from Example 1 is that the total molar amount of manganese element is the same as that in Example 1, and the molar ratio of manganese sulfate, manganese acetate and manganese trimanganese tetraoxide is 0.6:0.6:1.6, and lithium manganese iron phosphate material is finally obtained.

[0062] Example 6

[0063] The difference from Example 1 is that the ratio of glucose: polyethylene glycol 6000: citric acid is 6:2:2, and lithium manganese iron phosphate material is finally obtained.

[0064] Example 7

[0065] The difference from Example 1 is that the ratio of glucose: polyethylene glycol 6000: citric acid is 8:1:1, and lithium manganese iron phosphate material is finally obtained.

[0066] Example 8

[0067] The difference from Example 1 is that the carbon source is all glucose, and lithium manganese iron phosphate material is finally obtained.

[0068] Example 9

[0069] The difference from Example 1 is that the solid content of the liquid (I) is 40%, and lithium manganese iron phosphate material is finally obtained.

[0070] Example 10

[0071] The difference from Example 1 is that the solid content of the liquid (II) is 40%, and lithium manganese iron phosphate material is finally obtained.

[0072] Example 11

[0073] The difference from Example 1 is that during the low-temperature heat treatment, the temperature is raised to 200°C and kept warm for 2 hours, during the medium-temperature heat treatment, the temperature is continued to be raised to 450°C and kept warm for 5 hours, and during the high-temperature heat treatment, the temperature is continued to be raised to 750°C and kept warm for 5 hours; after the material is cooled to 50°C, it is air flow crushed and the particle size D50 is controlled to be 0.8~1μm, and finally lithium manganese iron phosphate material is obtained.

[0074] Example 12

[0075] The difference from Example 1 is that the heat treatment is carried out at 650° C. for 8 hours from the beginning to the end, and finally the lithium manganese iron phosphate material is obtained.

[0076] Example 13

[0077] The difference from Example 1 is that the carbon source is replaced with (glucose: polyethylene glycol 6000=8:2), and finally a lithium manganese iron phosphate material is obtained.

[0078] Example 14

[0079] The difference from Example 1 is that the carbon source is replaced with (glucose: polyethylene glycol 6000=7:3), and finally lithium manganese iron phosphate material is obtained.

[0080] Example 15

[0081] The difference from Example 1 is that the temperature of the third stage is changed from 720° C. to 750° C., and finally lithium manganese iron phosphate material is obtained.

[0082] Example 16

[0083] The difference from Example 1 is that during the sintering process, the temperature is directly raised to 720° C. and kept warm for 5 hours to finally obtain the lithium manganese iron phosphate material.

[0084] Comparative Example 1

[0085] The difference from Example 1 is that manganese source 1, manganese source 2, and manganese source 3 are all manganese tetraoxide, and lithium manganese iron phosphate material is finally obtained.

[0086] Comparative Example 2

[0087] The difference from Example 1 is that manganese source 1, manganese source 2, and manganese source 3 are all manganese sulfate, and lithium manganese iron phosphate material is finally obtained.

[0088] Comparative Example 3

[0089] The difference from Example 1 is that the feed solution (I), the feed solution (II) and 10.15 mol of lithium hydroxide are mixed and then ground by a sand mill to finally obtain lithium manganese iron phosphate material.

[0090] Performance Testing

[0091] The lithium manganese iron phosphate materials of the above embodiment and the comparative example were taken respectively, and the lithium manganese iron phosphate material, conductive carbon black (Super P), carbon nanotubes, and binder (polyvinylidene fluoride) were mixed uniformly in a mass ratio of 90:3:2:5, ground thoroughly, added with N-methylpyrrolidone, and then placed in a vacuum ball mill and ball milled at a speed of 600 r / min for 2 h to obtain a paste-like positive electrode slurry with a viscosity of 2000 to 4000 mPa·s; then, the above-prepared positive electrode slurry was coated on the surface of an aluminum foil current collector with a thickness of 14 μm by a coating machine, and the coating thickness was set to 350 μm, and then placed at 120°C for baking to form a positive electrode active material layer, and then cold pressed to the corresponding thickness by a roller press to obtain a positive electrode sheet.

[0092] The above-mentioned positive electrode sheet and lithium sheet were used as the positive electrode and reference electrode of the lithium-ion battery, respectively. Celgard 2400 was used as the separator, and a 1 mol / L LiPF6 mixed solution of EC and EMC (v / v = 1:1) was used as the electrolyte solution. The battery was assembled into a button cell for testing, and other physical properties were tested. The specific test results are shown in Table 1.

[0093] Table 1

[0094]

[0095]

[0096] Combined with the contents of Table 1, the following conclusions can be verified: Referring to Examples 1 and 2, the comprehensive performance is better than that of Comparative Examples 1 and 2, proving that the use of three different types of manganese source solutions in this embodiment effectively improves the gram capacity and compaction density of the lithium manganese iron phosphate material.

[0097] By comparing Examples 1, 6, 7, 8, 13 and 14, it is demonstrated that the synergistic effect of different carbon sources is conducive to the performance of the material.

[0098] By comparing Examples 11, 12, and 15 with Example 16, it can be seen that appropriate temperature and sintering process are required to ensure a balance between the electrical properties and compaction of the lithium manganese iron phosphate material.

[0099] By comparing Examples 1 and 3 to 5, it can be seen that when the molar ratio of manganese sulfate, manganese acetate and manganese trimanganese tetraoxide is outside the range of (1 to 3): (3 to 5): (4 to 6), it has little effect on the compaction density of the lithium manganese iron phosphate material, but will reduce the electrical properties of the lithium manganese iron phosphate material.

[0100] Figure 2 The SEM image of the lithium manganese iron phosphate material in Example 1 is shown. Figure 2 It can be seen from the embodiment that there is a clear gradation of large and small particles. This is attributed to the use of three manganese source precursors with different morphologies. During the sintering process, iron atoms will gradually melt into the manganese source, forming a gradation based on the manganese source, thereby increasing the overall compaction density of the material. Figure 2 It can also be seen from the comparison of the compaction density curves of the lithium manganese iron phosphate materials prepared in Example 1 and Comparative Examples 1 to 3 that the compaction density is significantly improved.

[0101] It can be seen from the above table that the lithium manganese iron phosphate product prepared by the preparation method provided by the present invention is superior to the relevant products in the comparative example in terms of multiple parameters such as first charge, first effect, compaction density, specific surface area, capacity at 0.2C, and compaction density.

[0102] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0103] The present application is based on the diffusion difference between manganese ions and iron ions in the olivine skeleton structure during heat treatment (iron ions are integrated into the manganese source). On the one hand, by adopting three manganese sources with different crystal structures and morphologies, and undergoing a one-time sand milling and one-time sintering process, a lithium iron manganese phosphate material with excellent electrical properties and high compaction density is prepared, thereby improving the performance of the lithium iron manganese phosphate material while also facilitating the formation of particle grading and improving sand milling efficiency. On the other hand, mixing the carbon source separately with the sand milled slurry can avoid the problem of carbon source coating on the particle surface hindering the effective collision of zirconium balls and the reduction of grinding efficiency caused by slurry thickening during grinding, and can ensure the accuracy of the particle size test of the material after sand milling. On the other hand, mixing the lithium source with the spray material can avoid the problem of lithium ions combining with phosphate to form precipitates, which causes unstable particle size monitoring. Therefore, the preparation method of the present application does not require high requirements for the sand mill, nor does it produce high energy consumption as caused by traditional processes. That is, the preparation method and equipment of the lithium iron manganese phosphate material in the present application are simple, lower cost, and more conducive to industrial large-scale production.

[0104] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing lithium manganese iron phosphate material, characterized in that: The preparation method comprises: Step S1, sand-milling a raw material including an iron source, a first manganese source, a second manganese source, a third manganese source, and a phosphorus source to obtain a sand-milled material; Step S2, mixing the sand-milled material with a carbon source to obtain a mixture; Step S3, spraying the mixture to obtain a spray material, and mixing the spray material with a lithium source to obtain a mixed lithium yellow material; Step S4, heat-treating and crushing the mixed lithium yellow material in an inert atmosphere to obtain a lithium iron manganese phosphate material; Wherein, the first manganese source is an inorganic water-soluble manganese compound, the second manganese source is an organic manganese source, and the third manganese source is a manganese oxide.

2. The preparation method according to claim 1, characterized in that In step S1, the first manganese source is selected from any one or more of manganese sulfate, manganese nitrate, manganese chloride and manganese dihydrogen phosphate; and / or the second manganese source is selected from any one or more of manganese oxalate, manganese acetate, manganese citrate, manganese glycinate and manganese gluconate; and / or the third manganese source is selected from any one or more of manganese oxide, manganese dioxide, manganese trioxide and manganese tetraoxide.

3. The preparation method according to claim 1 or 2, characterized in that The molar ratio of manganese element among the first manganese source, the second manganese source and the third manganese source is (1-3): (3-5): (4-6).

4. The preparation method according to claim 1 or 2, characterized in that The D50 particle size of the sand-milled material is 0.48 μm to 0.50 μm.

5. The preparation method according to claim 1 or 2, characterized in that In step S1, the raw material further includes a first solvent, which is selected from any one or more of water, ethanol, methanol and glycerol; and / or the solid content of the raw material is 30% to 50%.

6. The preparation method according to claim 1 or 2, characterized in that In step S1, the phosphorus source is selected from any one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate and phosphorus pentoxide; and / or the iron source is selected from any one or more of ferric phosphate, ferric oxalate, ferric oxide, ferrous oxide, ferric hydroxide, ferrosoferric oxide and ferric acetate.

7. The preparation method according to claim 1 or 2, characterized in that In step S2, the carbon source includes a first carbon source and a second carbon source; the mass ratio of the first carbon source to the second carbon source is (6-8): (2-4), and / or the first carbon source is selected from any one or more of glucose, sucrose, maltose, starch and fructose; and / or the second carbon source is selected from any one or more of citric acid, tannic acid, ascorbic acid, polyacrylic acid, polyvinyl alcohol, xylitol and polyethylene glycol.

8. The preparation method according to claim 1 or 2, characterized in that In step S2, the mixture further comprises a second solvent, wherein the second solvent is selected from any one or more of water, ethanol, methanol and isopropanol; and / or the solid content of the mixture is 30% to 50%.

9. The preparation method according to claim 1 or 2, characterized in that: In step S4, the heat treatment includes low-temperature heat treatment, medium-temperature heat treatment and high-temperature heat treatment performed sequentially; and / or the heating rate during the heat treatment is 60° C. / h to 180° C. / h; and / or the temperature of the low-temperature heat treatment is 100° C. to 200° C., and the time of the low-temperature heat treatment is 1 hour to 2 hours; and / or the temperature of the medium-temperature heat treatment is 450° C. to 650° C., and the time of the medium-temperature heat treatment is 3 h to 5 h; And / or the temperature of the high-temperature heat treatment is 700° C. to 750° C., and the time of the high-temperature heat treatment is 5 h to 8 h.

10. A lithium manganese iron phosphate material, characterized in that: The lithium manganese iron phosphate material is prepared by the preparation method according to any one of claims 1 to 9.

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