Lithium manganese iron phosphate positive electrode material as well as preparation method and application thereof

Abstract

The invention provides a lithium manganese iron phosphate positive electrode material and a preparation method and application thereof. The method comprises the following steps: mixing manganese metal and iron metal, heating, melting and uniformly mixing in an inert gas atmosphere, and grinding into powder; adding an ammonium salt solution, continuously adding the ground manganese-iron alloy powder under heating to form a suspension, introducing compressed air and stirring, reacting, filtering, washing, drying, crushing and grinding to obtain a manganese-iron oxide precursor, feeding the manganese-iron oxide precursor, a lithium source, a phosphorus source and doped metal elements into pure water, adding a carbon source, mixing to form a suspension, and grinding and drying to obtain the lithium-phosphorus-doped manganese-iron composite material. And carrying out carbon thermal reduction in an inert gas atmosphere, and crushing to obtain the lithium manganese iron phosphate positive electrode material. The ferromanganese oxide precursor prepared by heating the metal manganese and the metal iron to a molten state and mixing the metal manganese and the metal iron realizes uniform dispersion of the manganese and the iron at an atomic level, avoids the problems of nonuniform mixing of the manganese and the iron and dissolution of the manganese, and improves the conductivity and the electrochemical performance of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery preparation, and particularly relates to a lithium iron manganese phosphate cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the rapid development of the new energy industry, the scale of the lithium battery industry has expanded rapidly, resulting in a high-speed expansion of the cathode material market, which accounts for the main cost of the battery. Under this background, lithium iron manganese phosphate is expected to play an important role in the future new energy field; compared with lithium iron phosphate, its cost is further reduced, and the high voltage platform brought about by the substitution of manganese for iron brings higher energy density and improved high-temperature performance. When the molar ratio of manganese to iron is 9:1, the energy density can theoretically be increased by nearly 20%, approaching 690 Wh kg -1 .

[0003] For example, Patent CN 116216682A discloses a preparation method and application of a lithium iron manganese phosphate precursor. First, salt solutions A and B with different manganese-to-iron ratios are prepared, and they are subjected to a coprecipitation reaction in an organic solution C containing phosphoric acid or phosphate. After the reaction is completed, solid-liquid separation and dehydration are carried out to obtain the lithium iron manganese phosphate precursor. Through this process, a lithium iron manganese phosphate precursor with a concentration gradient and a core-shell structure can be constructed, reducing the distribution of manganese on the cathode surface, thereby alleviating the problem of manganese dissolution. CN115974039 A discloses a preparation method of a lithium iron manganese phosphate composite material and the lithium iron manganese phosphate composite material. First, lithium source, a first additive, and a first carbon source are incorporated into lithium iron manganese phosphate for heat treatment to form a lithium iron manganese phosphate material, and then, a second lithium source, a second additive, a second carbon source, a phosphorus source, and an iron source are added for hydrothermal reaction, so as to form a coating layer of lithium iron phosphate on the surface of the lithium iron manganese phosphate material, and finally, carbon coating is carried out to form a composite material with lithium iron manganese phosphate as the core and lithium iron phosphate and carbon as the coating layer to improve the compaction density and reduce the manganese dissolution phenomenon. CN 115974036A discloses a spherical lithium iron manganese phosphate nanoparticle and a preparation method thereof. First, lithium, iron, manganese, and phosphorus sources are mixed in a reaction kettle, and then an alkaline solution is added to adjust the pH value to generate a first precursor. Then, a small amount of lithium and phosphorus sources are added to adjust the ratio and a carbon source is added, and it is ground into a spherical shape by a sand mill for spray drying to synthesize a second precursor with a lithium iron manganese phosphate structure. Finally, through nitrogen roasting, a nano-spherical lithium iron manganese phosphate cathode material is obtained, which is beneficial to improving the compaction density and rate performance.

[0004] However, in the process of preparing the precursor mentioned in the above methods, the uniform mixing of manganese and iron elements at the atomic level cannot be achieved, resulting in crystal form disorder and agglomeration of the generated lithium iron manganese phosphate cathode material, leading to poor electrochemical performance, and the compaction density of the phosphate-based precursor cannot be effectively improved.

[0005] Based on this, the present invention designs a lithium iron manganese phosphate cathode material, its preparation method and application. Summary of the Invention

[0006] The present invention provides a lithium iron manganese phosphate cathode material, its preparation method and application, aiming to solve the above problems existing in the background technology.

[0007] To achieve the above object, an embodiment of the present invention provides a lithium iron manganese phosphate cathode material, its preparation method and application; the precursor of the lithium-ion battery cathode material prepared by the present invention, manganese iron oxide, has a chemical general formula of x / 3(Mn3O4)·(1-x) / 2Fe2O3, where 0.5 ≤ x ≤ 0.95. This method heats metal manganese and metal iron to a molten state for mixing, thereby achieving uniform dispersion of manganese and iron at the atomic level, avoiding the problems of uneven mixing of manganese and iron and manganese dissolution, improving the conductivity and electrochemical performance of the material, and developing a lithium iron manganese phosphate preparation process flow with commercial application prospects.

[0008] An embodiment of the present invention provides a method for preparing a lithium iron manganese phosphate cathode material, comprising the following steps:

[0009] S1: Weigh manganese metal and iron metal in proportion and grind and mix them under an inert gas atmosphere to obtain a mixture;

[0010] S2: Heat and melt the mixture under an inert gas atmosphere, stir and mix it evenly, cool it to room temperature, grind it into powder to obtain a manganese-iron alloy powder;

[0011] S3: Add an ammonium salt solution to a reaction kettle, continuously add the manganese-iron alloy powder under heating to form a suspension, introduce compressed air and stir to carry out a reaction. After the reaction, filter, wash, dry, crush and grind to obtain a manganese iron oxide precursor;

[0012] S4: Charge the manganese iron oxide precursor, a lithium source, a phosphorus source, and a doped metal element into pure water in proportion, add a carbon source and mix to form a suspension, grind, dry, and then carry out a carbothermal reduction reaction under an inert gas atmosphere, and naturally cool it to room temperature and crush to obtain the product.

[0013] Preferably, the inert gas is at least one of nitrogen, helium or argon.

[0014] Preferably, in step S1, the molar ratio of iron metal to manganese metal is 0.05 - 0.5:0.5 - 0.95; the purity of iron metal and manganese metal is above 99.9%.

[0015] Preferably, in step S2, the heating and melting temperature is 1500 - 2000 °C; the stirring method is electromagnetic stirring; the particle size after grinding into powder is 50 - 1000 mesh.

[0016] Preferably, in step S3, the ammonium salt is at least one of ammonium sulfate, ammonium chloride, and ammonium nitrate, with a concentration of 1-20 g / L; the solid-liquid ratio of the suspension is 5-30% (based on the metal mass content); the chemical general formula of the iron manganese oxide precursor is x / 3(Mn3O4)·(1-x) / 2Fe2O3, where 0.5 ≤ x ≤ 0.95.

[0017] Preferably, in step S3, the continuous addition time is 0.5-3 h; the heating temperature is 30-90 °C; the reaction time is 1-12 h; the drying temperature is 100-700 °C, and the drying time is 1-20 h; the D50 of grinding and crushing is 0.5-30.0 μm.

[0018] Preferably, in step S4, the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium oxalate, lithium acetate, lithium phosphate, lithium nitrate, and lithium dihydrogen phosphate; the phosphorus source is at least one of phosphoric acid, lithium phosphate, lithium dihydrogen phosphate, and ammonium dihydrogen phosphate; the doped metal element is at least one of Si, Ca, Ni, Cr, V, Al, Mg, Ti, Nb, and rare earth elements; among them, the rare earth elements are at least one of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc; the carbon source is at least one of glucose, sucrose, polyethylene glycol, citric acid, and phenolic resin, with a content of 6-20 wt.% (based on the total mass of the iron manganese oxide precursor, lithium source, phosphorus source, and doped metal element); the iron manganese oxide precursor, lithium source, phosphorus source, and doped metal element are fed in a molar ratio of 1:1.01-1.05:0.98-1.10:0-0.1.

[0019] Preferably, in step S4, the solid content ratio of the suspension is 25-40%; the temperature of the carbothermal reduction reaction is 500-800 °C, and the time of the carbothermal reduction reaction is 5-20 h; the particle size D50 after pulverization is 0.5-2.5 μm, and the specific surface area is 10-25 m 2 g -1 。

[0020] Based on the general concept of an invention, an embodiment of the present invention provides a lithium iron manganese phosphate cathode material prepared by the above preparation method.

[0021] An embodiment of the present invention also provides an application of a lithium iron manganese phosphate cathode material prepared by the above preparation method or the above lithium iron manganese phosphate cathode material in a lithium ion battery.

[0022] The above solution of the present invention has the following beneficial effects:

[0023] (1) The manganese iron oxide precursor prepared by the present invention has the advantages of uniform distribution, high tap density, and large specific surface area; this method uses heating and melting mixing to uniformly mix iron and manganese at the atomic level, avoiding large differences in the local Fe / Mn molar ratio, and the addition of rare earth elements can effectively reduce the particle size, improve the tap density, and further enhance the structural stability and electrochemical performance of the lithium iron manganese phosphate material.

[0024] (2) The method for preparing the manganese iron oxide precursor proposed by the present invention does not require additives in the reaction, has simple equipment and production processes, and strong controllability; it ensures uniform mixing of raw materials and uniform growth of crystal nuclei, and can stably prepare a precursor with high tap density and large specific surface area, which is applicable to large-scale industrial production.

[0025] (3) The present invention can obtain manganese iron oxide precursor products with different Mn / Fe molar ratios and lithium iron manganese phosphate cathode materials with different properties by adjusting the molar ratio of raw material addition of manganese and iron and the addition amount of different rare earth element compounds according to the requirements of the material, which can adapt to various different application scenarios and has a wide range of material applications. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0027] Figure 1 It is the SEM diagram of the lithium iron manganese phosphate cathode material prepared in Example 1 of the present invention;

[0028] Figure 2 It is the XRD diagram of the lithium iron manganese phosphate cathode material prepared in Example 1 of the present invention. Detailed Embodiments

[0029] To make the technical problems, technical solutions, and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the drawings and specific embodiments.

[0030] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0031] Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments, and equipment used in the present invention can be obtained through the market or can be prepared by existing methods.

[0032] The present invention addresses existing problems and provides a lithium manganese iron phosphate cathode material, a preparation method thereof, and an application thereof.

[0033] Example 1

[0034] A preparation method of a lithium manganese iron phosphate cathode material includes the following steps:

[0035] S1: Weigh 1396.39 g of iron metal powder with a purity of 99.99% and 4120.5 g of manganese metal powder with a purity of 99.99% respectively. Grind and mix the weighed iron metal powder and manganese metal powder under a nitrogen atmosphere to 100 mesh.

[0036] S2: Heat the ground mixed metal powder to 1700 °C under an N2 atmosphere, stir and mix the mixed metal powder evenly, react for 10 h, then naturally cool to room temperature, and crush and grind to 100 mesh.

[0037] S3: First add ammonium sulfate with a concentration of 5 g / L to the reaction kettle, heat to 50 °C, and then continuously add the ground manganese-iron metal powder. Finally, form a suspension with a solid-liquid ratio (by metal mass content) of 10%. Continuously add compressed air and stir simultaneously, react for 6 h, then filter and wash, and perform dehydration drying at 500 °C for 3 h. After drying, crush and grind to form a 1 / 4(Mn3O4)·1 / 8Fe2O3 precursor.

[0038] S4: Mix the 1 / 4(Mn3O4)·1 / 8Fe2O3 precursor with lanthanum metal powder, lithium carbonate, and ammonium dihydrogen phosphate according to a molar ratio of 0.95:0.05:1.01:1, and add glucose accounting for 7 wt.% of the total mass of the 1 / 4(Mn3O4)·1 / 8Fe2O3 precursor, lanthanum metal powder, lithium carbonate, and ammonium dihydrogen phosphate. Add the above 1 / 4(Mn3O4)·1 / 8Fe2O3 precursor, lanthanum metal powder, lithium carbonate, ammonium dihydrogen phosphate, and glucose to deionized water to form a suspension with a solid content of 30%. Then, after grinding and drying, form a mixed material. Perform carbothermal reduction on the mixed material under an N2 atmosphere at a temperature of 700 °C for 10 h, naturally cool to room temperature, and finally pulverize to obtain LiMn 0.71 Fe 0.24 La 0.05 PO4 finished product, with the particle size controlled at about 1.0 μm and the specific surface area of 18.4 m 2 g -1 . The SEM diagram of this LiMn 0.71 Fe 0.24 La 0.05 PO4 is as shown in Figure 1 shown, and the XRD diagram is as shown in Figure 2 .

[0039] Example 2

[0040] A preparation method of lithium iron manganese phosphate cathode material, comprising the following steps:

[0041] S1: First, weigh 558.5 g of iron metal powder with a purity of 99.99% and 2197.6 g of manganese metal powder with a purity of 99.99% respectively; grind and mix the weighed iron metal powder and manganese metal powder under a nitrogen atmosphere to 150 mesh;

[0042] S2: Heat the ground mixed metal powder to 1750 °C under an N2 atmosphere, stir and mix the mixed metal powder evenly, fully react for 10 h, then naturally cool to room temperature, and crush and grind to 200 mesh;

[0043] S3: First add ammonium chloride containing 10 g / L to the reaction kettle, heat to 60 °C, then continuously add the ground manganese-iron metal powder, and finally form a suspension with a solid-liquid ratio (by metal mass content) of 20%. Synchronously and continuously add compressed air and stir, react for 8 h, then filter and wash, and perform dehydration drying at 600 °C for 2 h. After drying, crush and grind to form a 4 / 15(Mn3O4)·1 / 10Fe2O3 precursor;

[0044] S4: Mix the 4 / 15(Mn3O4)·1 / 10Fe2O3 precursor with magnesium metal powder, titanium metal powder, lithium carbonate, and ammonium dihydrogen phosphate according to a molar ratio of 0.98:0.01:0.01:1.01:1 and add sucrose accounting for 10 wt.% of the total mass of the 4 / 15(Mn3O4)·1 / 10Fe2O3 precursor, magnesium metal powder, titanium metal powder, lithium carbonate, and ammonium phosphate. Add the above 4 / 15(Mn3O4)·1 / 10Fe2O3 precursor, magnesium metal powder, titanium metal powder, lithium carbonate, ammonium dihydrogen phosphate, and sucrose to deionized water to form a suspension with a solid content of 40%. Then, after grinding and drying, form a mixed material. Perform carbothermal reduction on the mixed material under an N2 atmosphere at a temperature of 800 °C for 8 h, naturally cool to room temperature, and finally pulverize to obtain LiMn 0.78 Fe 0.20 Mg 0.01 Ti 0.01 PO4 finished product, with the particle size controlled at about 1.5 μm and the specific surface area of 16.5 m 2 g -1 .

[0045] Example 3

[0046] A preparation method of lithium iron manganese phosphate cathode material, comprising the following steps:

[0047] S1: Weigh 6702 g of iron metal powder with a purity of 99.99% and 9889.2 g of manganese metal powder with a purity of 99.99% respectively; grind and mix the weighed iron metal powder and manganese metal powder under a nitrogen atmosphere to 200 mesh;

[0048] S2: Heat the ground mixed metal powder to 1650 °C under a N2 atmosphere, stir and mix the mixed metal powder evenly, fully react for 10 h, then naturally cool to room temperature, and crush and grind to 200 mesh;

[0049] S3: First add ammonium nitrate containing 20 g / L to the reaction kettle, heat to 80 °C, and then continuously add the ground manganese-iron metal powder to finally form a suspension with a solid-liquid ratio (by metal mass content) of 30%. Synchronously, continuously add compressed air and stir, react for 10 h, then filter and wash, and perform dehydration drying at 700 °C for 2 h. After drying, crush and grind to form a 1 / 5(Mn3O4)·1 / 5Fe2O3 precursor;

[0050] S4: Mix the 1 / 5(Mn3O4)·1 / 5Fe2O3 precursor with cerium metal powder, lithium carbonate, and ammonium phosphate in a molar ratio of 0.9:0.1:1.01:1 and add sucrose accounting for 8 wt.% of the total mass of the 1 / 5(Mn3O4)·1 / 5Fe2O3 precursor, cerium metal powder, lithium carbonate, and ammonium phosphate. Add the above 1 / 5(Mn3O4)·1 / 5Fe2O3 precursor, cerium metal powder, lithium carbonate, ammonium phosphate, and sucrose to deionized water to form a suspension with a solid content of 35%. Then, after grinding and drying, form a mixed material. Carry out carbothermal reduction of the mixed material under a N2 atmosphere at a temperature of 800 °C for 10 h, naturally cool to room temperature, and finally crush to obtain LiMn 0.54 Fe 0.36 Ce 0.1 PO4 finished product, with the particle size controlled at about 2.0 μm and the specific surface area of 14.2 m 2 g -1 。

[0051] Comparative Example 1

[0052] A preparation method of a lithium iron manganese phosphate cathode material includes the following steps:

[0053] Weigh 319.38 g of Fe2O3 with a purity of 99.99% and 457.62 g of 99.99% pure Mn3O 4, Add to deionized water to form a suspension to obtain Fe2O3 / Mn3O4;

[0054] Mix the above-mentioned Fe2O3 / Mn3O4 with cerium metal powder, lithium carbonate, and ammonium phosphate according to a molar ratio of 0.9:0.1:1.01:1, and add sucrose accounting for 8 wt.% of the total mass of Fe2O3 / Mn3O4, cerium metal powder, lithium carbonate, and ammonium phosphate. Then add the above-mentioned Fe2O3 / Mn3O4, cerium metal powder, lithium carbonate, ammonium phosphate, and sucrose to deionized water to form a suspension with a solid content of 35%. After grinding and drying, a mixed material is formed. The mixed material is subjected to carbothermal reduction in an N2 atmosphere at a temperature of 800 °C for 10 h, and then naturally cooled to room temperature. Finally, it is pulverized to obtain LiMn 0.54 Fe 0.36 Ce 0.1 PO4 finished product, with the particle size controlled at about 2.0 μm and the specific surface area of 15.4 m 2 g -1 。

[0055] Application and Performance Testing

[0056] The electrochemical properties of the lithium iron manganese phosphate electrode materials prepared in Examples 1 to 3 and Comparative Example 1 of the present invention were measured, and the test performance is shown in Table 1 below; button cells were used for characterization. The positive active materials were the lithium iron manganese phosphate positive electrode materials prepared in Examples 1 to 3 and the comparative example, the negative electrode was a lithium sheet, the conductive agent was Super P, the binder was polyvinylidene fluoride, the separator was a Celgard 2500 composite membrane, and the electrolyte used 1 mol / L lithium hexafluorophosphate as the lithium salt and a solution of dimethyl carbonate (DMC) and ethylene carbonate (EC) with a volume ratio of 1:1 as the solvent. The mass ratio of the positive active material, conductive agent, and binder was 8:1:1. The assembly of the button cells was completed in a glove box with an argon protection atmosphere. The electrochemical properties of the button cells were tested using a Blue-Electrochemical Test Cabinet, and the test voltage range was set at 2 V to 4.5 V.

[0057] Table 1 Electrochemical Performance Test Table of Lithium Iron Manganese Phosphate Positive Electrode Materials in Examples 1 to 3 and Comparative Example 1

[0058]

[0059] The above is the preferred implementation manner of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a lithium iron manganese phosphate cathode material, characterized in that, It includes the following steps: S1: Weigh manganese metal and iron metal in proportion and grind and mix them under an inert gas atmosphere to obtain a mixture; S2: Heat and melt the mixture under an inert gas atmosphere, stir and mix it evenly, cool it to room temperature, and grind it into powder to obtain manganese ferrite alloy powder; S3: Add an ammonium salt solution to a reaction kettle, continuously add the manganese ferrite alloy powder under heating to form a suspension, introduce compressed air and stir, carry out a reaction, and after the reaction, filter, wash, dry, crush and grind to obtain a manganese ferrite oxide precursor; S4: Charge the manganese ferrite oxide precursor, a lithium source, a phosphorus source, and a doped metal element into pure water in proportion, add a carbon source and mix to form a suspension, grind and dry it, and then carry out a carbothermal reduction reaction under an inert gas atmosphere, and naturally cool it to room temperature and crush it to obtain the product.

2. The preparation method of the lithium iron manganese phosphate cathode material according to claim 1, wherein, The inert gas is at least one of nitrogen, helium or argon.

3. The preparation method of a lithium iron manganese phosphate cathode material according to claim 1, characterized in that, In step S1, the molar ratio of iron metal to manganese metal is 0.05 - 0.5:0.5 - 0.95; the purity of iron metal and manganese metal is above 99.9%.

4. The preparation method of a lithium iron manganese phosphate cathode material according to claim 1, characterized in that, In step S2, the heating and melting temperature is 1500 - 2000 °C; the stirring method is electromagnetic stirring; the particle size after grinding into powder is 50 - 1000 mesh.

5. The preparation method of a lithium iron manganese phosphate cathode material according to claim 1, characterized in that, In step S3, the ammonium salt is at least one of ammonium sulfate, ammonium chloride, and ammonium nitrate, with a concentration of 1 - 20 g / L; the solid-liquid ratio of the suspension is 5 - 30%; the chemical general formula of the manganese ferrite oxide precursor is x / 3(Mn3O4)·(1 - x) / 2Fe2O3, where 0.5 ≤ x ≤ 0.

95.

6. The preparation method of a lithium iron manganese phosphate cathode material according to claim 1, wherein In step S3, the continuous addition time is 0.5 - 3 h; the heating temperature is 30 - 90 °C; the reaction time is 1 - 12 h; the drying temperature is 100 - 700 °C, and the drying time is 1 - 20 h; the D50 of grinding and crushing is 0.5 - 30.0 μm.

7. The preparation method of a lithium iron manganese phosphate cathode material according to claim 1, characterized in that, In step S4, the lithium source is at least one of lithium carbonate, lithium hydroxide, lithium oxalate, lithium acetate, lithium phosphate, lithium nitrate, and lithium dihydrogen phosphate; the phosphorus source is at least one of phosphoric acid, lithium phosphate, lithium dihydrogen phosphate, and ammonium dihydrogen phosphate; the doped metal element is at least one of Si, Ca, Ni, Cr, V, Al, Mg, Ti, Nb, and rare earth elements; among them, the rare earth elements are at least one of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc; the carbon source is at least one of glucose, sucrose, polyethylene glycol, citric acid, and phenolic resin, with a content of 6 - 20 wt.%; the manganese ferrite oxide precursor, the lithium source, the phosphorus source, and the doped metal element are fed in a molar ratio of 1:1.01 - 1.05:0.98 - 1.10:0 - 0.

1.

8. The preparation method of a lithium iron manganese phosphate cathode material according to claim 1, characterized in that, In step S4, the solid content ratio of the suspension is 25 to 40%; the temperature of the carbothermal reduction reaction is 500 to 800 °C, and the time of the carbothermal reduction reaction is 5 to 20 h; after pulverization, the particle size D50 is 0.5 to 2.5 μm, and the specific surface area is 10 - 25 m 2 g -1 .

9. A lithium iron manganese phosphate cathode material prepared by the preparation method according to any one of claims 1 - 8.

10. Application of a lithium iron manganese phosphate cathode material prepared by the preparation method according to any one of claims 1 - 8 or a lithium iron manganese phosphate cathode material according to claim 9 in a lithium ion battery.

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