Preparation method of high-compaction lithium iron manganese phosphate positive electrode material

Abstract

The application discloses a preparation method of a high-compaction lithium manganese iron phosphate positive material, and comprises the following steps: placing a manganese source, an iron source and a phosphorus source in deionized water, stirring, once high-speed ball milling, constant-temperature water bath, adding an oxidizing agent to stir and oxidize, then drying the slurry to obtain a manganese iron phosphate precursor powder; once sintering the manganese iron phosphate precursor powder to obtain a manganese iron phosphate once-sintered material; placing the manganese iron phosphate once-sintered material in deionized water, adding a lithium source and a carbon source, stirring, twice high-speed ball milling and drying to obtain a lithium manganese iron phosphate precursor powder; twice sintering the lithium manganese iron phosphate precursor powder to obtain the high-compaction lithium manganese iron phosphate positive material. The method of twice sintering and twice ball milling can effectively reduce the porosity, realize good carbon coating, and compared with other existing technologies, can keep good capacity, improve the powder compaction density of the material, improve the conductivity and effectively reduce the specific surface area of the material.

Description

Technical Field

[0001] This invention belongs to the field of lithium manganese iron phosphate cathode materials, and particularly relates to a method for preparing high-pressure compaction lithium manganese iron phosphate cathode materials. Background Technology

[0002] Lithium manganese iron phosphate (LiMn) x Fe 1-x LiFePO4 (LiFePO4) is a novel phosphate-based lithium-ion battery cathode material formed by doping a certain proportion of manganese (Mn) onto lithium iron phosphate (LiFePO4). By doping with manganese, the advantageous characteristics of both iron and manganese can be effectively combined. Furthermore, manganese and iron are both located in the fourth period of the periodic table and are adjacent to each other, possessing similar ionic radii and some chemical properties; therefore, doping does not significantly affect the original structure. Moreover, Mn can increase the voltage plateau, thereby improving the energy density of the lithium iron phosphate system. LMFP maintains the stable olivine structure of LFP and introduces the high-voltage plateau of LMP, thus improving the energy density of the lithium iron phosphate system.

[0003] However, the introduction of manganese leads to a decrease in overall electrical conductivity and powder compaction density. Current modification methods to address this poor conductivity include material nanostructuring, bulk doping, and surface carbon coating. These techniques also contribute to the increased porosity and higher powder compaction density of lithium manganese iron phosphate materials.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] Based on the problems existing in the background technology, the present invention provides a method for synthesizing manganese phosphate cathode material by using high-speed nanoball milling assisted secondary sintering. The secondary milling and secondary sintering method effectively reduces the porosity and achieves good carbon coating.

[0006] This invention is implemented through the following technical solutions:

[0007] A method for preparing a high-pressure lithium manganese iron phosphate cathode material includes the following steps:

[0008] (1) Place manganese source, iron source and phosphorus source in deionized water to obtain slurry one. After stirring, high-speed ball milling once, constant temperature water bath, oxidant is added and stirred for oxidation. Then dry the slurry to obtain manganese iron phosphate precursor powder.

[0009] (2) The precursor powder of manganese ferrophosphate is sintered once to obtain manganese ferrophosphate sintered material.

[0010] (3) Place the manganese iron phosphate calcined material in deionized water, and add lithium source and carbon source at the same time to obtain slurry 2. After stirring, high-speed ball milling twice and drying, the precursor powder of manganese iron lithium phosphate is obtained.

[0011] (4) The lithium manganese iron phosphate precursor powder is sintered twice to obtain the high-pressure compacted lithium manganese iron phosphate cathode material.

[0012] This invention synthesizes lithium manganese iron phosphate cathode material through a two-stage grinding and sintering process with carbon coating. The two grinding and sintering processes effectively mix the manganese and ferrophosphate phases uniformly. Since the ferromanganese is oxidized to trivalent and tetravalent states before the first sintering, and no carbon source is present, a reduction reaction does not occur during the first sintering, preventing crystal growth and resulting in larger crystal volumes of lithium manganese iron phosphate, which improves the compaction of the final lithium manganese iron phosphate powder. During the second grinding and sintering, the added carbon source distributes well on the surface of the solid particles during drying, forming a good and uniform coating layer. The second grinding process eliminates voids and gaps generated during the first sintering, further increasing the powder's compaction density and reducing its specific surface area.

[0013] Furthermore, the molar ratio of lithium, manganese, iron and phosphorus in the lithium manganese iron phosphate cathode material is x:y:(1-y):z, where 1≤x≤1.1, 0.1≤y≤0.9, and 1≤z≤1.05.

[0014] Furthermore, the manganese source is one or more of manganese tetroxide, manganese dioxide, manganese carbonate, manganese monoxide, and manganese iron oxide;

[0015] The iron source is one or more of the following: iron phosphate, iron(II) oxide, iron(III) oxide, ferrous oxalate, ferrous phosphate, and iron manganese oxide.

[0016] The phosphorus source is one or more of iron phosphate, phosphoric acid, lithium dihydrogen phosphate, lithium phosphate or monoammonium phosphate;

[0017] The lithium source is one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium sulfate, or lithium oxalate;

[0018] The oxidant is hydrogen peroxide.

[0019] Furthermore, in steps (1) and (3), the solid content of slurry one and slurry two is 25-45 wt%.

[0020] The stirring speed is 420-540 rpm;

[0021] The drying process employs spray drying, with an inlet air temperature of no less than 220℃ and an outlet air temperature of no less than 90℃.

[0022] Furthermore, in step (1), the temperature of the constant temperature water bath is 60-80℃, and the time is 6-10h.

[0023] Furthermore, in step (1), the rotation speed of the high-speed ball mill is 2100-3000 rpm, and the average particle size of the mixed slurry obtained after the high-speed ball mill is 100-500 nm.

[0024] Furthermore, in step (2), the temperature of the first sintering is 420-620℃, and the sintering is carried out in an air atmosphere for 3-20 hours.

[0025] Furthermore, in step (3), the rotation speed of the secondary high-speed ball mill is 2100-3000 rpm, and the average particle size of the mixed slurry obtained after the secondary high-speed ball mill is 100-600 nm.

[0026] Furthermore, in step (4), the secondary sintering temperature is 600-850℃, and sintering is carried out in a nitrogen atmosphere for 5-20 hours.

[0027] Furthermore, in step (3), the amount of carbon source added is 6-18% of the theoretical mass of lithium manganese iron phosphate;

[0028] The carbon source is one or more of glucose, lactose, sucrose, polyvinyl alcohol, phenolic resin, epoxy resin, and ascorbic acid.

[0029] The beneficial effects of this invention are:

[0030] This invention provides a method for synthesizing manganese phosphate cathode materials using high-speed nanoball milling-assisted secondary sintering. The secondary milling and sintering process effectively reduces porosity and achieves excellent carbon coating. Compared to other existing technologies, this method can improve powder compaction density, increase electrical conductivity, and effectively reduce the specific surface area of ​​the material while maintaining good capacity. Attached Figure Description

[0031] The accompanying drawings are provided to further explain the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0032] Figure 1 This is a SEM image of the lithium manganese iron phosphate cathode material prepared in Example 1 of the present invention;

[0033] Figure 2 This is a SEM image of the lithium manganese iron phosphate cathode material prepared in Example 2 of the present invention;

[0034] Figure 3 The image shows the particle size distribution of the lithium manganese iron phosphate cathode material prepared in Example 1 of this invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described more completely and in detail below with reference to the accompanying drawings and embodiments. It should be noted that the described embodiments are only a part of the embodiments of this invention, not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0036] Example 1

[0037] This embodiment provides a preparation process for lithium manganese iron phosphate cathode material, and the specific steps are as follows:

[0038] (1) Manganese tetroxide, iron tetroxide and phosphoric acid were mixed in deionized water according to the molar ratio of main elements Mn:Fe:P = 0.4:0.6:1.03 to form a solid-liquid mixture with a solid content of 40%. After stirring at 480 rpm and ball milling at 2700 rpm for 1 hour, the particle size D50 was measured to be 400 nm on average. Then, it was heated in a constant temperature water bath at 70℃ for 6 hours. Subsequently, a certain amount of oxidant was added for oxidation and the temperature was maintained at 70℃ for another hour to completely oxidize. Then, the slurry was dried in a spray dryer at 240℃ to finally obtain manganese iron phosphate precursor powder.

[0039] (2) The manganese ferrophosphate precursor powder obtained in step (1) is calcined in a tube furnace at 500°C and in air atmosphere for 10 hours to obtain manganese ferrophosphate calcined material.

[0040] (3) The manganese iron phosphate calcined material prepared in step (2) is placed in deionized water to form a slurry with a solid content of 35%. At the same time, lithium carbonate and manganese iron phosphate calcined material are added according to the element molar ratio of Li:P = 1.03:1. The carbon source is glucose, which is 10% of the theoretical mass of manganese iron phosphate to be generated. The mixture is stirred again at a frequency of 420 rpm and ball-milled at a speed of 2700 rpm for 0.5 hours. The measured particle size D50 is distributed on average at 500 nm. The slurry is dried in a spray dryer at 240 °C to finally obtain the precursor of manganese iron phosphate.

[0041] (4) The lithium manganese iron phosphate precursor prepared in step (3) is placed in a tube furnace at 700°C and in a nitrogen atmosphere for 10 hours and then naturally cooled to obtain the lithium manganese iron phosphate cathode material.

[0042] Example 2

[0043] This embodiment provides a preparation process for lithium manganese iron phosphate cathode material, and the specific steps are as follows:

[0044] (1) Manganese tetroxide, iron tetroxide and phosphoric acid were mixed in deionized water according to the element molar ratio Mn:Fe:P = 0.6:0.4:1.04 to form a solid-liquid mixture with a solid content of 35%. After stirring at 480 rpm and ball milling at 2700 rpm for 1.5 hours, the particle size D50 was measured to be 350 nm on average. Then, it was heated in a constant temperature water bath at 80℃ for 8 hours. Subsequently, a certain amount of oxidant was added for oxidation and the temperature was maintained at 80℃ for 1 hour to continue stirring for complete oxidation. Then, the slurry was dried in a spray dryer at 240℃ to finally obtain manganese iron phosphate precursor powder.

[0045] (2) The manganese ferrophosphate precursor powder obtained in step (1) is calcined in a tube furnace at 480°C and in air atmosphere for 15 hours to obtain manganese ferrophosphate calcined material.

[0046] (3) The manganese iron phosphate calcined material prepared in step (2) is placed in deionized water to form a slurry with a solid content of 35%. At the same time, lithium carbonate and manganese iron phosphate calcined material are added according to the element molar ratio of Li:P = 1.04:1. The carbon source is glucose, which is 12% of the theoretical mass of manganese iron phosphate to be generated. The mixture is stirred again at a frequency of 420 rpm and ball-milled at a speed of 2700 rpm for 0.5 hours. The measured particle size D50 is distributed on average at 450 nm. The slurry is dried in a spray dryer at 240 °C to finally obtain the manganese iron phosphate precursor.

[0047] (4) The lithium manganese iron phosphate precursor prepared in step (3) is placed in a tube furnace at 740°C and in a nitrogen atmosphere for 12 hours and then naturally cooled to obtain the lithium manganese iron phosphate cathode material.

[0048] Example 3

[0049] This embodiment provides a preparation process for lithium manganese iron phosphate cathode material, and the specific steps are as follows:

[0050] (1) Manganese dioxide, ferrous oxalate and phosphoric acid were prepared in deionized water according to the main element molar ratio Mn:Fe:P = 0.6:0.4:1.04 to form a solid-liquid mixture with a solid content of 35%. After stirring at 480 rpm and ball milling at 2700 rpm for 1 hour, the particle size D50 was measured to be 450 nm on average. Then, it was heated in a constant temperature water bath at 70℃ for 6 hours. Subsequently, a certain amount of oxidant was added for oxidation and the temperature was maintained at 70℃ for another hour to completely oxidize. Then, the slurry was dried in a spray dryer at 240℃ to finally obtain manganese ferric phosphate precursor powder.

[0051] (2) The manganese ferrophosphate precursor powder obtained in step (1) is calcined in a tube furnace at 520°C and in air atmosphere for 10 hours to obtain manganese ferrophosphate calcined material.

[0052] (3) The manganese iron phosphate calcined material prepared in step (2) is placed in deionized water to form a slurry with a solid content of 35%. At the same time, lithium carbonate and manganese iron phosphate calcined material are added according to the elemental molar ratio of Li:P = 1.04:1. The carbon source is sucrose, which is 10% of the theoretical mass of manganese iron phosphate to be generated. The mixture is stirred again at a frequency of 420 rpm and ball-milled at a speed of 2700 rpm for 0.5 hours. The measured particle size D50 is distributed on average at 500 nm. The slurry is dried in a spray dryer at 240 °C to finally obtain the precursor of manganese iron phosphate.

[0053] (4) The lithium manganese iron phosphate precursor prepared in step (3) is placed in a tube furnace at 700°C and in a nitrogen atmosphere for 14 hours and then naturally cooled to obtain the lithium manganese iron phosphate cathode material.

[0054] The lithium iron phosphate cathode materials prepared in Examples 1 and 2 were analyzed to obtain... Figures 1 to 3 The content shown. According to... Figures 1 to 3 The following conclusions can be drawn: The lithium manganese iron phosphate cathode materials prepared in Examples 1 and 2 have clear particle boundaries and good crystallinity. Furthermore, the absence of fibrous carbon and fine particles on the surface indicates a good carbon coating effect, which is strong evidence of the material's small specific surface area and its ability to improve conductivity, resulting in excellent electrochemical performance. The ability to obtain this particle size distribution through secondary grinding is also a factor contributing to the increased powder compaction density of the material.

[0055] Comparative Example 1

[0056] Comparative Example 1 is basically the same as Example 1, except that the manganese iron phosphate precursor was not completely oxidized during preparation. The specific steps are as follows:

[0057] (1) Manganese tetroxide, iron tetroxide and phosphoric acid were placed in deionized water according to the molar ratio of main elements Mn:Fe:P = 0.4:0.6:1.03 to form a solid-liquid mixture with a solid content of 40%. After stirring at 480 rpm and ball milling at 2700 rpm for 1 hour, the particle size D50 was measured to be 400 nm on average. Then, the mixture was heated in a constant temperature water bath at 70℃ for 6 hours. Finally, the slurry was dried in a spray dryer at 240℃ to obtain manganese iron phosphate precursor powder.

[0058] (2) The manganese ferrophosphate precursor powder obtained in step (1) is calcined in a tube furnace at 500°C and in air atmosphere for 10 hours to obtain manganese ferrophosphate calcined material.

[0059] (3) The manganese iron phosphate calcined material prepared in step (2) is placed in deionized water to form a slurry with a solid content of 35%. At the same time, lithium carbonate and manganese iron phosphate calcined material are added according to the element molar ratio of Li:P = 1.03:1. The carbon source is glucose, which is 10% of the theoretical mass of manganese iron phosphate to be generated. The mixture is stirred again at a frequency of 420 rpm and ball-milled at a frequency of 2700 rpm for 0.5 hours. The measured particle size D50 is distributed on average at 500 nm. The slurry is dried in a spray dryer at 240 °C to finally obtain the manganese iron phosphate precursor.

[0060] (4) The lithium manganese iron phosphate precursor prepared in step (3) is placed in a tube furnace at 700°C and in a nitrogen atmosphere for 10 hours and then naturally cooled to obtain the lithium manganese iron phosphate cathode material.

[0061] Comparative Example 2

[0062] Comparative Example 2 is basically the same as Example 1, except that a lithium source is added in step (1). The specific steps are as follows:

[0063] (1) Lithium carbonate, manganese tetroxide, iron tetroxide and phosphoric acid were mixed in deionized water according to the molar ratio of main elements Li:Mn:Fe:P=1.06:0.4:0.6:1.03 to form a solid-liquid mixture with a solid content of 40%. After stirring at 480rpm and ball milling at 2700rpm for 1 hour, the particle size D50 was measured to be 400nm on average. Then, the mixture was heated in a constant temperature water bath at 70℃ for 6 hours. Finally, the slurry was dried in a spray dryer at 240℃ to obtain manganese iron phosphate precursor powder.

[0064] (2) The manganese iron phosphate precursor powder obtained in step (1) is calcined in a tube furnace at 500°C and in air atmosphere for 10 hours to obtain lithium manganese iron phosphate calcined material.

[0065] (3) The lithium manganese iron phosphate slag prepared in step (2) is placed in deionized water to form a slurry with a solid content of 35%. The carbon source added is glucose, which is 10% of the theoretical mass of lithium manganese iron phosphate to be generated. The mixture is stirred again at a frequency of 420 rpm and ball-milled at a frequency of 2700 rpm for 0.5 hours. The measured particle size D50 is distributed on average at 500 nm. The slurry is dried completely in a spray dryer at 240 °C to finally obtain the lithium manganese iron phosphate precursor.

[0066] (4) The lithium manganese iron phosphate precursor prepared in step (3) is placed in a tube furnace at 700°C and in a nitrogen atmosphere for 10 hours and then naturally cooled to obtain the lithium manganese iron phosphate cathode material.

[0067] Table 1 shows a comparison of the electrochemical performance, powder compaction, specific surface area, and other data of five groups of samples from Examples 1-3 and Comparative Examples 1-2. As can be seen from Table 1, the lithium manganese iron phosphate cathode material prepared by the invention has good electrochemical performance, high powder compaction density, and low surface area.

[0068] Table 1

[0069]

[0070] Finally, it should be noted that the above embodiments are merely illustrative of several implementations of the present invention and are not intended to limit the scope of the invention. For those skilled in the art, any modifications, equivalent substitutions, or improvements made without departing from the concept of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a high-pressure lithium manganese iron phosphate cathode material, characterized in that, Includes the following steps: (1) Place manganese source, iron source and phosphorus source in deionized water to obtain slurry one. After stirring, high-speed ball milling once and constant temperature water bath, add oxidant and stir to oxidize manganese iron to positive trivalent and positive tetravalent. Then dry the slurry to obtain manganese iron phosphate precursor powder. (2) The precursor powder of manganese ferrophosphate is sintered once in air atmosphere to obtain manganese ferrophosphate sintered material; (3) Place the manganese iron phosphate calcined material in deionized water, and add lithium source and carbon source at the same time to obtain slurry 2. After stirring, high-speed ball milling twice and drying, the lithium manganese iron phosphate precursor powder is obtained. (4) The lithium manganese iron phosphate precursor powder is sintered twice in a nitrogen atmosphere to obtain the high-pressure compacted lithium manganese iron phosphate cathode material. In step (1), the rotation speed of the high-speed ball mill is 2100-3000 rpm; In step (3), the rotation speed of the secondary high-speed ball mill is 2100-3000 rpm.

2. The method for preparing high-pressure lithium manganese iron phosphate cathode material according to claim 1, characterized in that, The molar ratio of lithium, manganese, iron and phosphorus in the lithium manganese iron phosphate cathode material is x:y:(1-y):z, where 1≤x≤1.1, 0.1≤y≤0.9, and 1≤z≤1.

05.

3. The method for preparing high-pressure lithium manganese iron phosphate cathode material according to claim 1, characterized in that, The manganese source is one or more of manganese tetroxide, manganese dioxide, manganese carbonate, manganese monoxide, and manganese iron oxide; The iron source is one or more of the following: iron phosphate, ferric oxide, iron tetroxide, ferrous oxalate, ferrous phosphate, and iron manganese oxide. The phosphorus source is one or more of iron phosphate, phosphoric acid, lithium dihydrogen phosphate, lithium phosphate or monoammonium phosphate; The lithium source is one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, lithium sulfate, or lithium oxalate; The oxidant is hydrogen peroxide.

4. The method for preparing high-pressure lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In steps (1) and (3), the solid content of slurry one and slurry two is 25-45 wt%; The stirring speed is 420-540 rpm; The drying process employs spray drying, with an inlet air temperature of no less than 220℃ and an outlet air temperature of no less than 90℃.

5. The method for preparing high-pressure lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step (1), the temperature of the constant temperature water bath is 60-80℃ and the time is 6-10h.

6. The method for preparing high-pressure lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step (1), the average D50 particle size of the mixed slurry obtained after one high-speed ball milling is 100-500 nm.

7. The method for preparing high-pressure lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step (2), the temperature of the first sintering is 420-620℃, and the sintering is carried out in an air atmosphere for 3-20 hours.

8. The method for preparing high-pressure lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step (3), the average D50 particle size of the mixed slurry obtained after the second high-speed ball milling is 100-600 nm.

9. The method for preparing high-pressure lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step (4), the secondary sintering temperature is 600-850℃, and sintering is carried out in a nitrogen atmosphere for 5-20 hours.

10. The method for preparing high-pressure lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step (3), the amount of carbon source added is 6-18% of the theoretical mass of lithium manganese iron phosphate produced; The carbon source is one or more of glucose, lactose, sucrose, polyvinyl alcohol, phenolic resin, epoxy resin, and ascorbic acid.

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