A lithium manganese iron phosphate positive electrode material, a preparation method and application thereof

Abstract

This invention provides a lithium manganese iron phosphate cathode material, its preparation method, and its application, relating to the field of lithium-ion battery technology. The general chemical formula of this lithium manganese iron phosphate cathode material is Mn. 1‑x‑ y Fe x Me y PO4 and Me are dopant elements, with a 0.05 ≤ x ≤ 0.5 and a 0.001 ≤ y ≤ 0.1. This method involves mixing iron, manganese, and dopant elements using a melting method and heating them to a molten state. This achieves uniform dispersion of iron, manganese, and dopant elements at the atomic level, avoiding the problems of uneven mixing of manganese and iron and manganese dissolution. The precursor prepared by this invention has a high compaction density, which can reduce the particle size of the cathode material, improve the ionic conductivity and electronic conductivity of the material, effectively enhance the rate performance of the material, and develop a lithium manganese iron phosphate preparation technology with commercial application prospects.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a lithium manganese iron phosphate cathode material, its preparation method, and its application. Background Technology

[0002] With societal development, clean energy has become a crucial direction for technological advancement. Lithium-ion batteries, in particular, have garnered widespread attention due to their advantages such as high voltage, excellent cycle performance, high energy density, and lack of memory effect. The performance and cost of lithium-ion batteries are primarily determined by the cathode material. A variety of cathode materials exist, with lithium cobalt oxide, ternary materials, and lithium iron phosphate being among the most widely used. Lithium manganese iron phosphate shares the same olivine-type structure as lithium iron phosphate, and its theoretical specific capacity can reach 170 mAh·g. -1 Lithium manganese iron phosphate (LMP) boasts advantages such as low cost, good cycle performance, and a high voltage platform, resulting in a higher energy density compared to lithium iron phosphate. Therefore, the development of high-quality LMP materials holds strong promise for commercial applications.

[0003] The main problems in the preparation of lithium manganese iron phosphate cathode materials include low conductivity, low compaction density, and uneven micro-mixing of manganese and iron. Existing technologies address these problems by employing methods such as elemental doping and coating, reducing particle size, and increasing crystallinity. For example, CN 110323434 B discloses a method for preparing lithium manganese iron phosphate-carbon composite materials and the lithium manganese iron phosphate-carbon composite material itself. First, soluble manganese-containing phosphate, organic iron salt, manganese salt, and lithium salt are dissolved in deionized water according to the elemental molar ratio to obtain a precursor solution. This solution is then dried and granulated to obtain lithium manganese iron phosphate precursor powder. The precursor powder is sintered under a protective atmosphere to obtain the sintered material, which is then pulverized, refined, and vacuum-packed to obtain the lithium manganese iron phosphate-carbon composite material. CN 106486668 B discloses a modified lithium manganese iron phosphate material, its preparation method, and its application. The material includes a magnesium-doped lithium manganese iron phosphate core layer and a boron-containing coating layer covering the surface of the magnesium-doped lithium manganese iron phosphate core layer. A manganese source, phosphorus source, iron source, lithium source, magnesium source, and water are mixed to form an intermediate reaction solution. The intermediate reaction solution is then subjected to drying and pre-calcination treatments to obtain a core layer precursor. The core layer precursor is mixed with a boron source and then calcined to obtain the modified lithium manganese iron phosphate material. CN 106486668 B also discloses a method for preparing a high-compact lithium manganese iron phosphate cathode material. A soluble iron source and phosphate are dissolved in water, and the pH is adjusted to 1.0-3.0 using one or more of ammonia, sodium hydroxide, calcium hydroxide, and calcium carbonate to obtain a particle size distribution of 10-600 nm and a compaction density of 1.96 g / cm³. 3 -2.18g / cm 3Nanoscale spherical or near-spherical iron(III) phosphate intermediates were obtained by dissolving manganese, iron, and phosphorus sources in aqueous solutions in molar ratios, followed by the addition of an oxidizing agent to induce a complete oxidation reaction, yielding a particle size distribution of 500-700 nm and a compaction density of 2.4-3.2 g / cm³. 3 Manganese iron phosphate (Mn) x Fe 1-x PO4 intermediate, finally, ferric phosphate (III) intermediate, manganese iron phosphate Mn x Fe 1-x PO4 intermediates, lithium source, and carbon source were mixed in a ratio of 1:1:1.01:0.03, dissolved in pure water, and spray-dried. After cooling, spherical or near-spherical nano-sized lithium manganese iron phosphate cathode materials were obtained. However, in the preparation of the precursor and cathode materials described above, micro-agglomeration of materials is prone to occur, leading to uneven mixing of Fe / Mn at the atomic level and poor electrochemical performance. The above method cannot effectively solve the key problems existing in lithium manganese iron phosphate materials.

[0004] Therefore, this invention designs a high-rate lithium manganese iron phosphate cathode material and its preparation method. Summary of the Invention

[0005] This invention provides a lithium manganese iron phosphate cathode material, its preparation method, and its application, with the aim of solving the aforementioned problems existing in the background art.

[0006] To achieve the above objectives, embodiments of the present invention provide a lithium manganese iron phosphate cathode material, its preparation method, and its application. This method involves mixing iron, manganese, and doping elements using a melting method and heating them to a molten state, achieving uniform dispersion of iron, manganese, and doping elements at the atomic level. This avoids the problems of uneven manganese-iron mixing and manganese leaching. The precursor prepared by the present invention has a high compaction density, which can reduce the particle size of the cathode material, improve the ionic and electronic conductivity of the material, effectively enhance the rate performance of the material, and develop a lithium manganese iron phosphate preparation technology with commercial application prospects.

[0007] An embodiment of the present invention provides a method for preparing lithium manganese iron phosphate cathode material, comprising the following steps:

[0008] S1: Iron, manganese, and dopant elements are mixed in an inert gas atmosphere at a molar ratio of Mn:Fe:Me=(1-xy):x:y, heated to melt and stirred evenly, poured out and cooled to room temperature, ground and crushed to obtain a manganese-iron alloy; where 0.05≤x≤0.5, 0.001≤y≤0.1;

[0009] S2: The manganese-iron alloy is added to a reaction vessel containing H3PO4 solution, and an oxidizing agent is added. The mixture is heated to react, then dried, ground, and crushed to obtain Mn.1-x-y Fe x Me y PO4 precursor;

[0010] S3: Place the Mn 1-x-y Fe x Me y The PO4 precursor was mixed with lithium and carbon sources and then ground. The mixture underwent a carbothermic reduction reaction in an inert gas atmosphere. After the reaction was completed, the mixture was naturally cooled to room temperature and then pulverized to obtain lithium manganese iron phosphate cathode material.

[0011] Preferably, in step S1, the purity of iron and manganese is above 99.9%; the doping element is one or more of Si, Ca, Ni, Cr, V, Al, Mg, Ti, Nb, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc; and the molar ratio of iron, manganese, and doping element is 0.05-0.5:0.4-0.95:0.001-0.1.

[0012] Preferably, in step S1, the heating temperature is 1500–2000°C; the stirring is electromagnetic stirring; the particle size of the grinding and crushing is 50–1000 mesh; and the inert gas is one or more of nitrogen, helium, or argon.

[0013] Preferably, the concentration of the H3PO4 solution in step S2 is 5-85%; the molar ratio of the total content of iron, manganese and dopant elements to the H3PO4 solution is 1:0.98-1.10.

[0014] Preferably, the oxidant in step S2 is one or more of sodium peroxide, hydrogen peroxide, and nitric acid, and the amount added is 6-12% (relative to the total mass of all materials in this step).

[0015] Preferably, in step S2, the heating temperature is 40–200°C; the reaction time is 1–12 h; the drying conditions are: in an air atmosphere, first dry the free water at 100–300°C, and then dehydrate at 350–850°C for 1–20 h; the powder D50 after grinding and crushing is 0.5–30.0 μm.

[0016] Preferably, in step S3, the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium oxalate, lithium acetate, lithium phosphate, lithium nitrate, and lithium dihydrogen phosphate; the carbon source is one or more of glucose, sucrose, polyethylene glycol, citric acid, and phenolic resin; and the carbon source content is Mn. 1-x-y Fe x Me y The total mass of the PO4 precursor and lithium source is 1.5–15 wt.%.

[0017] Preferably, the temperature of the carbothermic reduction reaction in step S3 is 500–800℃, and the reaction time is 5–20 h; the finished product after grinding and crushing has a D50 of 0.5–2.5 μm and a specific surface area of ​​10–25 μm. 2 g -1 The inert gas is one or more of nitrogen, hydrogen, or argon.

[0018] Based on a general inventive concept, embodiments of the present invention provide a lithium manganese iron phosphate cathode material prepared by the above-described preparation method.

[0019] Embodiments of the present invention also provide a lithium battery comprising a lithium manganese iron phosphate cathode material prepared by the above-described preparation method, wherein the general chemical formula of the lithium manganese iron phosphate cathode material is Mn 1-x-y Fe x Me y PO4 and Me are dopant elements, with 0.05 ≤ x ≤ 0.5 and 0.001 ≤ y ≤ 0.1.

[0020] The above-described solution of the present invention has the following beneficial effects:

[0021] 1. The manganese iron phosphate precursor prepared by this invention has the advantages of uniform distribution, large specific surface area, and high reactivity. Iron, manganese, and dopant elements are uniformly mixed at the atomic level, avoiding large differences in the local Fe / Mn molar ratio in the manganese iron phosphate precursor. The addition of dopant elements can effectively reduce the particle size, improve the material conductivity, reduce the structural distortion caused by the Jahn-Teller effect, and enhance the stability of the lithium manganese iron phosphate material structure, resulting in a lithium manganese iron phosphate cathode material with high rate performance.

[0022] 2. The preparation method of the manganese iron phosphate precursor of the present invention does not require additives in the reaction, has low impurity content, high purity, simple equipment and production process, and strong controllability; it does not produce by-products that have an impact on the environment, is green and environmentally friendly, has low water and energy consumption, requires no environmental treatment facilities, and is suitable for large-scale industrial production.

[0023] 3. Depending on the material requirements, manganese iron phosphate (MnFe) with different Mn / Fe molar ratios and dopant element contents can be obtained by adjusting the molar ratio of manganese salt and iron salt as well as the amount of different dopant elements added. 1-x-y Fe x Me y PO4 products are used to prepare lithium iron phosphate cathode materials with different properties, which can be adapted to various application scenarios and have a wide range of applications. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a SEM image of the lithium manganese iron phosphate material prepared in Example 1 of the present invention;

[0026] Figure 2 This is the XRD pattern of the lithium manganese iron phosphate material prepared in Example 1 of the present invention. Detailed Implementation

[0027] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0028] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0029] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0030] In the preparation process of existing precursor materials and cathode materials, micro-agglomeration of materials is prone to occur, resulting in uneven mixing of Fe / Mn at the atomic level and poor electrochemical performance of the materials. Existing technologies cannot effectively solve the key problems of lithium manganese iron phosphate materials. This invention provides a lithium manganese iron phosphate cathode material, its preparation method and application.

[0031] The present invention has the following advantages over the prior art:

[0032] 1. The manganese iron phosphate precursor prepared by this invention has the advantages of uniform distribution, large specific surface area, and high reactivity. Iron, manganese, and dopant elements are uniformly mixed at the atomic level, avoiding large differences in the local Fe / Mn molar ratio in the manganese iron phosphate precursor. The addition of dopant elements can effectively reduce the particle size, improve the material conductivity, reduce the structural distortion caused by the Jahn-Teller effect, and enhance the stability of the lithium manganese iron phosphate material structure, resulting in a lithium manganese iron phosphate cathode material with high rate performance.

[0033] 2. The preparation method of the manganese iron phosphate precursor of the present invention does not require additives in the reaction, has low impurity content, high purity, simple equipment and production process, and strong controllability; it does not produce by-products that have an impact on the environment, is green and environmentally friendly, has low water and energy consumption, requires no environmental treatment facilities, and is suitable for large-scale industrial production.

[0034] 3. Depending on the material requirements, manganese iron phosphate (MnFe) with different Mn / Fe molar ratios and dopant element contents can be obtained by adjusting the molar ratio of manganese salt and iron salt as well as the amount of different dopant elements added. 1-x-y Fe x Me y PO4 products are used to prepare lithium iron phosphate cathode materials with different properties, which can be adapted to various application scenarios and have a wide range of applications.

[0035] The following will be explained through specific embodiments.

[0036] Example 1

[0037] S1: Weigh out 721.30g of 99.99% pure iron metal powder and 3153.85g of 99.99% pure manganese metal powder; then weigh out 199.35g of 99.99% pure lanthanum metal powder. Grind the iron, manganese, and lanthanum metal powders to 100 mesh under a nitrogen atmosphere; heat the ground mixed metal powder to 1600℃ in a smelting furnace, melt and stir the mixed metal powder until uniform, then allow it to cool naturally to room temperature, and finally crush and grind it to 100 mesh.

[0038] S2: Add 5 L of 85% phosphoric acid solution to the reactor, then pour in the above-ground mixed metal compound, and add 4.40 L of 30% hydrogen peroxide. React thoroughly at 150°C for 8 hours. After the reaction is complete, dry the precursor in air at 150°C for 1 hour, then dry and dehydrate at 600°C for 2 hours. The dried precursor is then ground to a particle size D50 of approximately 1 μm to obtain Mn. 0.8 Fe 0.18 La 0.02 PO4 precursor.

[0039] S3: Adjust the sucrose content according to Mn 1-x-y Fe x Me y The PO4 precursor and lithium source were mixed at 2% of their total mass and subjected to carbothermic reduction at 700℃ for 10 hours under an N2 atmosphere. After natural cooling to room temperature, the mixture was finally pulverized to obtain LiMn. 0.8 Fe 0.18 La 0.02The PO4 finished product has a particle size D50 controlled at around 1μm.

[0040] Example 2

[0041] S1: Weigh out 901.72g of 99.99% pure iron metal powder and 4139.46g of 99.99% pure manganese metal powder; then weigh out 261.55g of 99.99% pure magnesium metal powder and 257.63g of 99.99% pure titanium metal powder. Grind the iron, manganese, magnesium, and titanium metal powders to 150 mesh under a nitrogen atmosphere; heat the ground mixed metal powder to 1700℃ in a smelting furnace, melt and stir the mixed metal powder evenly, then allow it to cool naturally to room temperature, and finally crush and grind it to 150 mesh.

[0042] S2: Add 7.5 L of 85% phosphoric acid solution to the reactor, then pour in the above-ground mixed metal compound, and add 6.60 L of 30% hydrogen peroxide. React thoroughly at 200°C for 6 hours. After the reaction is complete, the precursor is dried at 100°C for 2 hours in air, then dried and dehydrated at 500°C for 3 hours. The dried precursor is then ground to a particle size D50 of approximately 1.5 μm to obtain Mn. 0.7 Fe 0.15 Mg 0.1 Ti 0.05 PO4 precursor.

[0043] S3: Adjust the sucrose content according to Mn 1-x-y Fe x Me y The PO4 precursor and lithium source were mixed at 5% of their total mass and subjected to carbothermic reduction in an N2 atmosphere at 650℃ for 12 hours. After natural cooling to room temperature, the mixture was finally pulverized to obtain LiMn. 0.7 Fe 0.15 Mg 0.1 Ti 0.05 The PO4 finished product has a particle size D50 controlled at around 1.5μm.

[0044] Example 3

[0045] S1: Weigh out 2404.34g of 99.99% pure iron metal powder and 4730.81g of 99.99% pure manganese metal powder; then weigh out 2010.92g of 99.99% pure cerium metal powder. Grind the iron, manganese, magnesium, and titanium metal powders to 200 mesh under a nitrogen atmosphere; then heat the ground mixed metal powder to 1600℃ in a smelting furnace, melt and stir the mixed metal powder evenly, then let it cool naturally to room temperature, and crush and grind it to 200 mesh.

[0046] S2: Add 10 L of 85% phosphoric acid solution to the reactor, then pour in the above-ground mixed metal compound, and add 8.79 L of 30% hydrogen peroxide. React thoroughly at 100°C for 12 h. After the reaction is complete, dry the precursor in air at 200°C for 1 h, then dry and dehydrate at 700°C for 1 h. The dried precursor is then ground to a particle size D50 of approximately 2 μm to obtain Mn. 0.6 Fe 0.3 Ce 0.1 PO4 precursor.

[0047] S3: Adjust the sucrose content according to Mn 1-x-y Fe x Me y The PO4 precursor and lithium source were mixed at 10% of their total mass and subjected to carbothermic reduction in an N2 atmosphere at 750°C for 8 hours. After natural cooling to room temperature, the mixture was finally pulverized to obtain LiMn. 0.6 Fe 0.3 Ce 0.1 The PO4 finished product has a particle size D50 controlled at around 2μm.

[0048] Applications and Testing

[0049] This invention measured the electrochemical performance of the lithium manganese iron phosphate electrode materials prepared in Examples 1-3, using button cell characterization. The positive electrode active material was the lithium manganese iron phosphate positive electrode material prepared in Examples 1-3 and the comparative examples, respectively. The negative electrode was a lithium sheet, the conductive agent was SuperP, the binder was polyvinylidene fluoride, the separator was a Celgard 2500 composite membrane, and the electrolyte was a 1 mol / L lithium hexafluorophosphate solution as the lithium salt, with a 1:1 volume ratio of dimethyl carbonate (DMC) and ethylene carbonate (EC) solution as the solvent. The mass ratio of the positive electrode active material, conductive agent, and binder was 8:1:1. The button cell assembly was completed in a glove box with an argon protective atmosphere. The electrochemical performance of the button cell was tested using a blue electric test cabinet, with the test voltage range set from 2V to 4.5V.

[0050]

[0051] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium manganese iron phosphate cathode material, characterized in that, Includes the following steps: S1: Iron, manganese, and dopant elements are mixed in an inert gas atmosphere at a molar ratio of Mn:Fe:Me = (1-xy):x:y, heated to melt and stirred evenly, poured out and cooled to room temperature, then ground and crushed to obtain a manganese-iron alloy; where 0.05 ≤ x ≤ 0.5, 0 ≤ y ≤ 0.1; S2: The manganese-iron alloy is added to a reaction vessel containing H3PO4 solution, and an oxidizing agent is added. The mixture is heated to react, then dried, ground, and crushed to obtain Mn. 1-x-y Fe x Me y PO4 precursor; S3: The Mn 1-x-y Fe x Me y The PO4 precursor was mixed with lithium and carbon sources and then ground. The mixture underwent a carbothermic reduction reaction in an inert gas atmosphere. After the reaction was completed, the mixture was naturally cooled to room temperature and then pulverized to obtain lithium manganese iron phosphate cathode material.

2. The method for preparing a lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S1, the purity of iron and manganese is above 99.9%; the doping element is one or more of Si, Ca, Ni, Cr, V, Al, Mg, Ti, Nb, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc; the molar ratio of iron, manganese and doping element is 0.05~0.5:0.4~0.95:0.001~0.

1.

3. The method for preparing a lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S1, the heating temperature is 1500~2000 ℃; the stirring is electromagnetic stirring; the particle size of the grinding and crushing is 50~1000 mesh; and the inert gas is one or more of nitrogen, helium or argon.

4. The method for preparing a lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S2, the concentration of the H3PO4 solution is 5-85%; the molar ratio of the total content of iron, manganese and dopant elements to the H3PO4 solution is 1:0.98-1.

10.

5. The method for preparing a lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S2, the oxidant is one or more of sodium peroxide, hydrogen peroxide, and nitric acid, and the amount added is 6-12%.

6. The method for preparing a lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S2, the heating temperature is 40~200 ℃; the reaction time is 1~12 h; the drying conditions are: in an air atmosphere, first dry the free water at 100~300 ℃, and then dehydrate at 350~850 ℃ for 1~20 h; the D50 of the powder after grinding and crushing is 0.5-30.0 μm.

7. The method for preparing a lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S3, the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium oxalate, lithium acetate, lithium phosphate, lithium nitrate, and lithium dihydrogen phosphate; the carbon source is one or more of glucose, sucrose, polyethylene glycol, citric acid, and phenolic resin; and the carbon source content is Mn. 1-x- y Fe x Me y The total mass of the PO4 precursor and the lithium source is 1.5~15 wt.%.

8. The method for preparing a lithium manganese iron phosphate cathode material according to claim 1, characterized in that, In step S3, the temperature of the carbothermic reduction reaction is 500–800 °C, and the reaction time is 5–20 h; the finished product after grinding and crushing has a D50 of 0.5–2.5 μm and a specific surface area of ​​10–25 μm. 2 g -1 The inert gas is one or more of nitrogen, hydrogen, or argon.

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

10. A lithium battery, characterized in that, A lithium manganese iron phosphate cathode material prepared by the preparation method according to any one of claims 1 to 8, characterized in that the general chemical formula of the lithium manganese iron phosphate cathode material is LiMn. 1-x- y Fe x Me y PO4 and Me are dopant elements, 0.05 ≤ x ≤ 0.5, 0.001 ≤ y ≤ 0.1.

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