Preparation method of compact ammonium manganese iron phosphate precursor, positive electrode material and battery

Abstract

The application discloses a preparation method of a compact type ammonium manganese iron phosphate precursor, a positive electrode material and a battery. A phosphorus source is mixed with ammonia water, an alkali solution is added to adjust the pH to alkalinity, and then the mixture is mixed with manganese iron metal to obtain ammonium manganese iron phosphate monohydrate with a spherical or sea urchin shape, a primary particle size of 50-800 nm, a D50 of 10-30 um, and a tap density of the precursor of 0.6 g / cm 3 <TD<1.8g / cm 3 ,0.6m 2 / g<SSA<2.5m 2 / g. Further, the application discloses a lithium manganese iron phosphate positive electrode material prepared by using the ammonium manganese iron phosphate precursor prepared by the method, as a lithium battery material. The ammonium manganese iron phosphate precursor prepared by the application has low Na / S impurity content, high tap density and good product crystallinity.

Description

Technical Field

[0001] This invention relates to the fields of inorganic materials and lithium battery material preparation, specifically to a method for preparing a dense manganese iron ammonium phosphate precursor, a cathode material, and a battery. Background Technology

[0002] With technological breakthroughs in the new energy vehicle market, lithium iron phosphate (LFP) batteries began to rebound in 2020, and their popularity remains high. However, the energy density of LFP is nearing its limit. Lithium manganese iron phosphate (LFP), a product combining LFP and LMP, leverages the advantages of both. LFP's high-voltage platform delivers higher energy density, and its cycle life and safety performance are comparable to LFP, while its low-temperature performance is superior. Furthermore, the voltage windows of LFP and ternary cathodes are close, allowing for arbitrary mixing. Adding a small amount of LFP to ternary cathode materials can effectively improve safety. Currently, LFP cathode materials have been successfully used in two-wheeled vehicles, and their reuse in ternary batteries will open up the automotive market. In the future, they will primarily replace LFP and be used in combination with ternary batteries. Global demand for LFP cathode materials is projected to reach 410,000 tons by 2025.

[0003] Lithium manganese iron phosphate (LMP) and lithium iron phosphate (LFP) both belong to the phosphate system and have similar preparation processes. The solid-phase method is simple and suitable for industrial production, while the liquid-phase method is more complex but produces products with better performance. However, unlike the LFP industry, which has mature iron phosphate as a precursor, the LMP industry is in its early stages and lacks standard precursors. Because the solid-phase method cannot achieve uniform solid solution well, performance improvement is significantly limited. Therefore, for LMP materials, precursor synthesis should be the main direction of future synthesis. Possible precursor routes include ammonium phosphate, phosphate, carbonate, and oxalate.

[0004] This invention focuses on ammonium phosphate precursors, aiming to prepare high-performance ammonium phosphate precursors to improve the performance of lithium manganese iron phosphate cathode materials. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a dense manganese iron ammonium phosphate precursor and a battery thereof.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A dense ferric ammonium manganese phosphate precursor, the precursor having the formula NH4Mn 1-x-y Fe x M y PO4·H2O, and 0<x≤0.5, 0≤y<0.1, M is at least one of Mg, Ni, Co, Cu, Zn and Ti;

[0008] The molar ratio of the metal element (Mn+Fe+M) to element P in the precursor is 0.95 to 1.05.

[0009] A further technical solution is provided, where D50 is 10–30 μm, and the primary particle size is 100–800 nm; the precursor has a density of 0.6 g / cm³. 3 <TD <1.8g / cm 3 0.6m 2 / g<SSA<2.5m 2 / g.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing a dense manganese iron ammonium phosphate precursor includes:

[0012] Step 1: Prepare a mixed solution of phosphorus source and ammonia water, and then add an alkaline solution to adjust the pH of the mixed solution to 9-11;

[0013] Step 2: Prepare a mixed salt solution containing manganese source, iron source and M source;

[0014] Step 3: Preparation of the reaction base solution: Add pure water to the reaction vessel as the base solution, and then add alkaline solution to adjust the pH value of the base solution to 4-7;

[0015] Step 4: The mixed solution prepared in Step 1 and the mixed metal salt solution prepared in Step 2 are added to the reaction vessel in parallel to carry out the reaction, and manganese iron ammonium phosphate monohydrate precipitate is obtained.

[0016] Step 5: The manganese iron ammonium phosphate monohydrate precipitate prepared in Step 4 is subjected to solid-liquid separation, washing and drying to obtain manganese iron ammonium phosphate precursor powder, whose particle morphology is spherical or sea urchin-like.

[0017] A further technical solution involves controlling the molar ratio of P element to NH3·H2O to be 1:(2-5) in step one.

[0018] In a further technical solution, in step one, the alkaline solution is at least one of ammonia, sodium hydroxide, and potassium hydroxide.

[0019] In a further technical solution, in step one, the concentration of the phosphorus source solution is 1-4 mol / L; the phosphorus source is at least one of phosphoric acid, monoammonium phosphate, diammonium phosphate, triammonium phosphate, monosodium phosphate, disodium phosphate, and trisodium phosphate.

[0020] In a further technical solution, in step two, the concentration of the metal mixed salt solution is 0.5–3 mol / L; the manganese source is at least one of manganese sulfate, manganese nitrate, manganese acetate, and manganese chloride; and the iron source is at least one of ferrous sulfate, ferric nitrate, ferric acetate, and ferric chloride.

[0021] In a further technical solution, in step three, the alkaline solution is at least one of ammonia, sodium hydroxide, and potassium hydroxide.

[0022] In a further technical solution, in step four, the molar ratio of element P to metal (Mn+Fe) is maintained at (1~3):1 during the liquid injection process.

[0023] In a further technical solution, in step four, nitrogen or inert gas is continuously introduced into the reaction vessel, the reaction temperature is 20–70°C, and the stirring speed is 300–900 rpm.

[0024] In a further technical solution, the drying temperature in step five is 60–150°C.

[0025] Furthermore, the present invention also relates to a high-capacity lithium manganese iron phosphate cathode material, which is prepared by mixing the iron ammonium manganese phosphate precursor powder obtained in step five with lithium source and carbon source materials, and calcining it in a nitrogen or inert gas atmosphere for 6 to 20 hours at a calcination temperature of 400 to 1000°C to obtain the carbon-coated cathode material.

[0026] In the above scheme, the general formula of the cathode material is LiFe. x Mn 1-x PO4.

[0027] In a further technical solution, the lithium source is at least one of lithium hydroxide and lithium carbonate. The coated carbon source is one or more of sucrose, glucose, polyethylene glycol, carbon black, graphene, polyvinyl alcohol, polyacryl alcohol, citric acid, cellulose, starch, dextrin, fructose, lactose, maltose, oxalic acid, and ascorbic acid.

[0028] A further technical solution is proposed, where the cathode material is expressed as Li. y Mn x-z Fe 1-x M z PO4 / C; where 0.5≤x<1, 0.99≤y≤1.10, 0.1≤z≤1, and M is a dopant element, which is at least one of Mg, Ni, Co, Cu, Zn, and Ti.

[0029] The present invention further protects a battery that uses the aforementioned carbon-coated lithium manganese iron phosphate as the positive electrode material.

[0030] The working principle and advantages of this invention are as follows:

[0031] This invention prepares a mixture of phosphorus source and ammonia, and adds alkali to adjust the pH to alkaline, allowing for complete dissociation of phosphate ions. After the reaction begins and the solution is introduced, PO42-... 3- After complete dissociation, it combines with metal ions, promoting the forward reaction. The synthesized manganese iron ammonium phosphate product has high crystallinity and dense particle packing, thus the lithium manganese iron lithium phosphate cathode material after mixed lithium sintering has high capacity.

[0032] Meanwhile, this invention has advantages such as strong operability in production and high production capacity, making it suitable for large-scale industrial production. Attached Figure Description

[0033] Appendix Figure 1A The NH4Mn prepared in Example 1 of this invention 0.75 Fe 0.25 SEM image of PO4·H2O (Figure 1);

[0034] Appendix Figure 1B The NH4Mn prepared in Example 1 of this invention 0.75 Fe 0.25 SEM of PO4·H2O Figure 2 ;

[0035] Appendix Figure 2 The NH4Mn prepared in Example 1 of this invention 0.75 Fe 0.25 XRD pattern of PO4·H2O;

[0036] Appendix Figure 3A The NH4Mn prepared in Example 2 of this invention 0.75 Fe 0.25 SEM image of PO4·H2O (Figure 1);

[0037] Appendix Figure 3B The NH4Mn prepared in Example 2 of this invention 0.75 Fe 0.25 SEM of PO4·H2O Figure 2 ;

[0038] Appendix Figure 4 The NH4Mn prepared in Example 2 of this invention 0.75 Fe 0.25 XRD pattern of PO4·H2O;

[0039] Appendix Figure 5A The NH4Mn prepared in Example 3 of this invention 0.75 Fe 0.25 SEM image of PO4·H2O (Figure 1);

[0040] Appendix Figure 5B The NH4Mn prepared in Example 3 of this invention 0.75Fe 0.25 SEM of PO4·H2O Figure 2 ;

[0041] Appendix Figure 6 The NH4Mn prepared in Example 3 of this invention 0.75 Fe 0.25 XRD pattern of PO4·H2O;

[0042] Appendix Figure 7 This is a SEM image of the precursor prepared in the comparative example of this invention;

[0043] Appendix Figure 8 The image shows the XRD pattern of the precursor prepared in the comparative example of this invention. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0045] The present invention will be clearly described below with illustrations and detailed description. Any person skilled in the art who understands the embodiments of the present invention can make changes and modifications based on the technology taught in the present invention without departing from the spirit and scope of the present invention.

[0046] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the scope of this application. The terms “comprising,” “including,” “having,” etc., as used herein are open-ended, meaning they include, but are not limited to, specific embodiments.

[0047] Unless otherwise specified, the terms used herein generally have their ordinary meaning in the context of the art, the subject matter, and the specific context. Certain terms used to describe this case will be discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art in describing this case.

[0048] Example 1:

[0049] 6.8 kg of 98% pure monoammonium phosphate solid was dissolved in 24.7 L of pure water and mixed with 15 L of 20% ammonia water. The pH value was tested to be 9.22. After adding the bottom liquid to the reactor, the temperature was raised to 40 °C and nitrogen gas was introduced.

[0050] 3.85 kg of ferrous sulfate heptahydrate solid with a purity of 99% was dissolved in 4.8 L of pure water to obtain a ferrous divalent aqueous solution. 6.997 kg of battery-grade manganese sulfate solid was dissolved in 17.49 L of pure water to obtain a manganese divalent aqueous solution. The prepared iron and manganese aqueous solutions were mixed to obtain a manganese-iron metal aqueous solution with a molar ratio of Mn to Fe of 75:25.

[0051] Add pure water to the reactor and adjust the pH to 4.5-5.0 with ammonia. Add the mixed solution of phosphorus and ammonia and the prepared manganese-iron metal aqueous solution to the reactor at 55 ml / min and 50 ml / min respectively to continuously produce manganese-iron ammonium phosphate precipitate. Nitrogen gas is continuously introduced into the reaction process, the reaction temperature is 50℃, and the stirring speed is 600 rpm.

[0052] The precipitate of ferric manganese phosphate obtained from the reaction was subjected to solid-liquid separation and washing, and then dried at 90°C for 12 hours to obtain the precursor powder of ferric manganese phosphate.

[0053] Lithium iron manganese phosphate cathode material was prepared by calcining the prepared lithium iron manganese phosphate precursor with lithium source and carbon source.

[0054] Example 2:

[0055] 6.8 kg of 98% pure monoammonium phosphate solid was dissolved in 24.7 L of pure water and added to the reactor along with 20 L of 20% ammonia water to form the base solution. The pH value of the base solution was tested to be 9.86.

[0056] 3.85 kg of ferrous sulfate heptahydrate solid with a purity of 99% was dissolved in 4.8 L of pure water to obtain a ferrous divalent aqueous solution. 6.997 kg of battery-grade manganese sulfate solid was dissolved in 17.49 L of pure water to obtain a manganese divalent aqueous solution. The prepared iron and manganese aqueous solutions were mixed to obtain a manganese-iron metal aqueous solution with a molar ratio of Mn to Fe of 75:25.

[0057] Pure water was added to the reactor, and the pH was adjusted to 5.0-5.5 with ammonia. The mixed solution of phosphorus and ammonia and the prepared manganese-iron metal aqueous solution were continuously added to the reactor at 55 ml / min and 50 ml / min, respectively, to continuously produce manganese-iron ammonium phosphate precipitate. Nitrogen gas was continuously introduced during the reaction process, the reaction temperature was 50℃, and the stirring speed was 600 rpm.

[0058] The precipitate of ferric manganese phosphate obtained from the reaction was subjected to solid-liquid separation and washing, and then dried at 90°C for 12 hours to obtain the precursor powder of ferric manganese phosphate.

[0059] Lithium iron manganese phosphate cathode material was prepared by calcining the prepared lithium iron manganese phosphate precursor with lithium source and carbon source.

[0060] Example 3:

[0061] 6.8 kg of 98% pure monoammonium phosphate solid was dissolved in 24.7 L of pure water and added to the reactor along with 25 L of 20% ammonia water to form the base solution. The pH value of the base solution was tested to be 10.27.

[0062] 3.85 kg of ferrous sulfate heptahydrate solid with a purity of 99% was dissolved in 4.8 L of pure water to obtain a ferrous divalent aqueous solution. 6.997 kg of battery-grade manganese sulfate solid was dissolved in 17.49 L of pure water to obtain a manganese divalent aqueous solution. The prepared iron and manganese aqueous solutions were mixed to obtain a manganese-iron metal aqueous solution with a molar ratio of Mn to Fe of 75:25.

[0063] Pure water was added to the reactor, and the pH was adjusted to 5.5-6.0 with ammonia. The mixed solution of phosphorus and ammonia and the prepared manganese-iron metal aqueous solution were continuously added to the reactor at 55 ml / min and 50 ml / min, respectively, to continuously produce manganese-iron ammonium phosphate precipitate. Nitrogen gas was continuously introduced during the reaction process, the reaction temperature was 50℃, and the stirring speed was 600 rpm.

[0064] The precipitate of ferric manganese phosphate obtained from the reaction was subjected to solid-liquid separation and washing, and then dried at 90°C for 12 hours to obtain the precursor powder of ferric manganese phosphate.

[0065] Lithium iron manganese phosphate cathode material was prepared by calcining the prepared lithium iron manganese phosphate precursor with lithium source and carbon source.

[0066] Comparative example:

[0067] 6.8 kg of monoammonium phosphate solid with a purity of 98% was dissolved in 24.7 L of pure water to obtain an aqueous solution of monoammonium phosphate;

[0068] 3.85 kg of ferrous sulfate heptahydrate solid with a purity of 99% was dissolved in 4.8 L of pure water to obtain a ferrous divalent aqueous solution. 6.997 kg of battery-grade manganese sulfate solid was dissolved in 17.49 L of pure water to obtain a manganese divalent aqueous solution. The prepared iron and manganese aqueous solutions were mixed to obtain a manganese-iron metal aqueous solution with a molar ratio of Mn to Fe of 75:25.

[0069] Add pure water to the reactor and adjust the pH to 4.5-5.0 with 20% ammonia. Add monoammonium phosphate aqueous solution, manganese-iron metal aqueous solution and 20% ammonia solution to the reactor continuously at 55 ml / min, 50 ml / min and 30 ml / min respectively to continuously produce manganese-iron ammonium phosphate precipitate. Nitrogen gas is continuously introduced into the reaction process, the reaction temperature is 50℃ and the stirring speed is 600 rpm.

[0070] The precipitate of ferric manganese phosphate obtained from the reaction was subjected to solid-liquid separation and washing, and then dried at 90°C for 12 hours to obtain the precursor powder of ferric manganese phosphate.

[0071] Lithium iron manganese phosphate cathode material was prepared by calcining the prepared lithium iron manganese phosphate precursor with lithium source and carbon source.

[0072] The physicochemical tests of the prepared manganese iron ammonium phosphate precursor are shown in Table 1 below.

[0073]

[0074] Table 1

[0075] As shown in Table 1, comparing the data of the comparative examples and the actual cases, when monoammonium phosphate aqueous solution and ammonia aqueous solution are introduced independently, PO4... 3- The dissociation rate is slow, resulting in severe agglomeration of the prepared manganese iron ammonium phosphate, with large particle size and low tap. SEM analysis reveals that after the phosphorus source and ammonia are introduced into the solution independently, they adhere to each other into large lumps. XRD shows poor crystallinity. These adhered lumps will cause coarse particles after milling when the lithium source is mixed, thus affecting the performance of the cathode material. This invention configures a mixture of phosphorus source and ammonia water, and adds alkaline solution to adjust the pH to alkaline, allowing for complete dissociation of phosphate ions. After the reaction begins and the solution is introduced, PO4... 3- After complete dissociation, it combines with metal ions, promoting the forward reaction. The synthesized manganese iron ammonium phosphate product has high crystallinity and dense particle packing, thus the lithium manganese iron lithium phosphate cathode material after mixed lithium sintering has high capacity.

[0076] The manganese iron ammonium phosphate precursor prepared by this invention has low Na / S impurity content, high tap value, and good crystallinity.

[0077] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a compacted ammonium manganese iron phosphate precursor, characterized in that: The application relates to a preparation method of a carbon-coated manganese-iron-phosphorus-lithium positive material. Step one: a mixed solution of a phosphorus source and ammonia water is prepared, and an alkali solution is added to adjust the pH value of the mixed solution to 9-11; A metal mixed salt solution containing a manganese source, an iron source and an M source is prepared, and M is at least one of Mg, Ni, Co, Cu, Zn and Ti; A reaction bottom solution is prepared: a reaction kettle is filled with pure water as a bottom solution, and an alkali solution is added to adjust the pH value of the bottom solution to 4-7; Step two: the mixed solution prepared in step one and the metal mixed salt solution are added into the reaction kettle in parallel to carry out reaction, and manganese-iron-ammonium phosphate monohydrate precipitate is obtained; Step three: the manganese-iron-ammonium phosphate monohydrate precipitate prepared in step two is subjected to solid-liquid separation, washing and drying to obtain manganese-iron-ammonium phosphate precursor powder; The particle morphology of the manganese-iron-ammonium phosphate precursor is spheroid or sea urchin.

2. The method of claim 1, wherein the method is characterized by: The expression of the precursor is NH4Mn 1-x-y Fe x M y PO4-H2O, and 0 < x < 0.5, 0 < y < 0.1; The molar ratio of metal elements (Mn+Fe+M) to element P of the precursor is 0.95-1.

05.

3. The method of claim 2, wherein the method is characterized by: The D50 of the precursor is 10-30 um, and the primary particle size is 100-800 nm. The precursor 0.6 g / cm 3 < TD < 1.8 g / cm 3 , 0.6 m 2 / g < SSA < 2.5 m 2 / g.

4. The method of claim 1, wherein the method is characterized by: In step one, the molar ratio of P element to NH3H2O is controlled to be 1:(2-5).

5. The method of claim 1, wherein the method is characterized by: In step one, the alkali solution is at least one of ammonia water, sodium hydroxide and potassium hydroxide.

6. The method of claim 1, wherein the method is characterized by: In step one, the concentration of the phosphorus source solution is 1-4 mol / L; and the phosphorus source is at least one of phosphoric acid, monoammonium phosphate, diammonium phosphate, triammonium phosphate, monosodium phosphate, disodium phosphate and trisodium phosphate.

7. The method of claim 1, wherein the method is characterized by: In step one, the concentration of the metal mixed salt solution is 0.5-3 mol / L; the manganese source is at least one of manganese sulfate, manganese nitrate, manganese acetate and manganese chloride; and the iron source is ferrous sulfate.

8. The method of claim 1, wherein the method is characterized by: In step two, the molar ratio of element P to metal (Mn+Fe) is controlled to be (1-3):1 during the liquid feeding process.

9. The method of claim 1, wherein the method is characterized by: In step two, inert gas is continuously introduced into the reaction kettle during the reaction process, the reaction temperature is 20-70 DEG C, and the stirring speed is 300-900 rpm.

10. The method of claim 1, wherein the method is characterized by: In step three, the drying temperature is 60-150 DEG C.

11. A high capacity lithium iron manganese phosphate cathode material, characterized in that: The carbon-coated manganese-iron-phosphorus-lithium positive material is prepared by using the precursor prepared in any one of claims 3-10; the manganese-iron-ammonium phosphate precursor powder prepared in step three is mixed with a lithium source and a carbon source material, and is calcined under the atmosphere of inert gas for 6-20 h, and the calcination temperature is 400-1000 DEG C.

12. A battery, characterized by: The carbon-coated manganese-iron-phosphorus-lithium positive material is prepared by using the carbon-coated manganese-iron-phosphorus-lithium positive material of claim 11.

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