Preparation method of small-particle-size ammonium manganese iron phosphate precursor, positive electrode material and battery

Abstract

A preparation method of a small-particle-size ammonium manganese iron phosphate precursor, a positive electrode material and a battery, the preparation method comprising: I. configuring a metal mixed salt solution containing metal manganese, iron and M source and a phosphorus source solution, mixing the two solutions to obtain a mixed solution; II. adding pure water to a reaction kettle as a bottom liquid, and adding an alkali solution to adjust the pH value of the bottom liquid; III. adding the mixed solution and ammonia water into the reaction kettle in parallel flow to carry out reaction, to obtain ammonium manganese iron phosphate monohydrate precipitate; IV. carrying out solid-liquid separation on the ammonium manganese iron phosphate monohydrate precipitate, and then carrying out washing and drying to obtain ammonium manganese iron phosphate precursor powder; the particle morphology of the ammonium manganese iron phosphate precursor is flaky morphology, and the precursor particle size D50 is 6-15 um. In the present application, the metal liquid is mixed with the phosphorus source, so that a large number of small crystal nuclei are generated in the initial stage of reaction, which is helpful to improve the activity of the precursor, is beneficial to the diffusion of lithium in the lithium mixing sintering process and the diffusion of lithium ions in the battery material, and greatly improves the rate performance of the lithium manganese iron phosphate positive electrode material.

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 small-particle-size iron ammonium manganese 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, fully leverages the advantages of both. LFP's high-voltage platform results in higher energy density, with cycle and safety performance comparable to LFP, and superior low-temperature performance. 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 small-particle-size iron ammonium manganese phosphate precursor, a cathode material, and a battery.

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

[0007] A method for preparing a small-particle-size manganese iron ammonium phosphate precursor includes:

[0008] Step 1: Prepare a mixed salt solution containing metallic manganese, iron and an optional M source, and a phosphorus source solution. Mix the two solutions to obtain a mixed solution.

[0009] Step 2, 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;

[0010] Step 3: Add the prepared mixed solution and ammonia water to the reaction vessel in parallel to carry out the reaction, and obtain the precipitate of manganese iron ammonium phosphate monohydrate;

[0011] Step 4: The prepared ammonium manganese phosphate ferric monohydrate precipitate is subjected to solid-liquid separation, and then washed and dried to obtain ammonium manganese ferric ammonium phosphate precursor powder;

[0012] The precursor of manganese iron ammonium phosphate has a plate-like morphology and a particle size D50 of 6~15 μm.

[0013] In a further technical solution, the precursor is expressed as 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;

[0014] The molar ratio of metal element (Mn+Fe+M) to element P in the precursor is 0.95~1.05;

[0015] The precursor satisfies 0.3 g / cm³. 3 <TD <1.0g / cm 3 2m 2 / g<SSA<6m 2 / g.

[0016] In a further technical solution, in step one, the concentration of the manganese-iron mixed salt solution is 0.5~3 mol / L;

[0017] The manganese source is at least one of manganese sulfate, manganese nitrate, manganese acetate, and manganese chloride;

[0018] The iron source is at least one of ferrous sulfate, ferric nitrate, ferric acetate, and ferric chloride.

[0019] In a further technical solution, in step one, the concentration of the phosphorus source solution is 1~4 mol / L;

[0020] The phosphorus source is at least one of phosphoric acid, monoammonium phosphate, diammonium phosphate, triammonium phosphate, monosodium phosphate, disodium phosphate, and trisodium phosphate.

[0021] In a further technical solution, in step one, the molar ratio of element P to metal (Mn+Fe) in the mixed solution is (1~3):1.

[0022] In a further technical solution, in step two, an alkaline solution is added to the pure water bottom solution to adjust the pH value to 4-7;

[0023] The alkaline solution is at least one of ammonia, sodium hydroxide, and potassium hydroxide.

[0024] In a further technical solution, in step three, an inert gas or nitrogen is continuously introduced into the reactor during the reaction process. The reaction temperature is 20~70℃, the stirring speed is 300~900rpm, and the pH value of the reaction process is adjusted by controlling the flow rate of ammonia water to maintain the pH at 4-7.

[0025] In a further technical solution, in step four, the drying temperature is 60~150℃.

[0026] This invention also relates to a lithium manganese iron phosphate cathode material, which is prepared by mixing the lithium manganese iron phosphate ammonium precursor obtained by the above preparation method with lithium source and carbon source material, and calcining at 400~1000℃ for 6~20h under nitrogen atmosphere.

[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 made using the above-mentioned lithium manganese iron phosphate cathode material.

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

[0031] This invention mixes molten metal with a phosphorus source, which generates a large number of fine crystal nuclei in the early stage of the reaction, resulting in a finished product with a smaller particle size. The small particle size product helps to improve the activity of the manganese iron ammonium phosphate precursor, facilitates the diffusion of lithium during the lithium mixing sintering process and the diffusion of lithium ions in the battery material, and greatly improves the rate performance of the lithium manganese iron ammonium phosphate cathode material.

[0032] Compared with existing technologies, this invention has advantages such as strong operability in production and high production capacity, and is suitable for large-scale industrial production. Attached Figure Description

[0033] Appendix Figure 1A The NH4Mn prepared in Example 1 of this invention 0.60 Fe 0.40SEM image of PO4·H2O (Figure 1);

[0034] Appendix Figure 1B The NH4Mn prepared in Example 1 of this invention 0.60 Fe 0.40 SEM of PO4·H2O Figure 2 ;

[0035] Appendix Figure 2 The NH4Mn prepared in Example 1 of this invention 0.60 Fe 0.40 XRD pattern of PO4·H2O;

[0036] Appendix Figure 3 The NH4Mn prepared in Example 1 of this invention 0.60 Fe 0.40 PSD image of PO4·H2O;

[0037] Appendix Figure 4 This is a SEM image of the precursor prepared in the comparative example of this invention;

[0038] Appendix Figure 5 The image shows the XRD pattern of the precursor prepared in the comparative example of this invention. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0040] 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.

[0041] 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.

[0042] 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 the case.

[0043] Example 1: 4.47 kg of 99% pure ferrous sulfate heptahydrate solid was dissolved in 13.29 L of pure water to prepare a ferrous divalent aqueous solution. 15.12 kg of battery-grade manganese sulfate solid was dissolved in 12 L of pure water to obtain a manganese divalent aqueous solution. The prepared iron and manganese aqueous solutions were mixed to obtain a 1 mol / L manganese-iron metal aqueous solution with a Mn / Fe molar ratio of 60:40. 14.4 L of a 1 mol / L monoammonium phosphate solution was prepared. The 12 L of the 60:40 manganese-iron metal solution and the 14.4 L of monoammonium phosphate were mixed evenly.

[0044] Pure water was added to the reactor, and the pH was adjusted to 4.5-5.0 with ammonia. The above-mentioned mixed solution of metal and phosphorus and a 10% ammonia solution were continuously added to the reactor to continuously produce manganese iron ammonium phosphate precipitate. Nitrogen gas was continuously introduced during the reaction process, the reaction temperature was 50℃, the stirring speed was 600 rpm, and the pH was maintained at 4.5-5.0.

[0045] 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.

[0046] Lithium iron manganese phosphate cathode material was prepared by calcining the prepared lithium iron manganese phosphate precursor with lithium source and carbon source.

[0047] Example 2: 4.47 kg of 99% pure ferrous sulfate heptahydrate solid was dissolved in 13.29 L of pure water to prepare a ferrous divalent aqueous solution. 15.12 kg of battery-grade manganese sulfate solid was dissolved in 12 L of pure water to obtain a manganese divalent aqueous solution. The prepared iron and manganese aqueous solutions were mixed to obtain a 1 mol / L manganese-iron metal aqueous solution with a Mn / Fe molar ratio of 60:40. 14.4 L of a 1 mol / L monoammonium phosphate solution was prepared. The 12 L of the 60:40 manganese-iron metal solution and the 14.4 L of monoammonium phosphate were mixed evenly.

[0048] Pure water was added to the reactor, and the pH was adjusted to 5.0-5.5 with ammonia. The above-mentioned mixed solution of metal and phosphorus and a 10% concentration of ammonia solution were continuously added to the reactor to continuously produce manganese iron ammonium phosphate precipitate. Nitrogen gas was continuously introduced during the reaction process, the reaction temperature was 50℃, the stirring speed was 600 rpm, and the pH was maintained at 5.0-5.5.

[0049] 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.

[0050] Lithium iron manganese phosphate cathode material was prepared by calcining the prepared lithium iron manganese phosphate precursor with lithium source and carbon source.

[0051] Example 3: 4.47 kg of 99% pure ferrous sulfate heptahydrate solid was dissolved in 13.29 L of pure water to prepare a ferrous aqueous solution. 15.12 kg of battery-grade manganese sulfate solid was dissolved in 12 L of pure water to obtain a manganese aqueous solution. The prepared iron and manganese aqueous solutions were mixed to obtain a 1 mol / L manganese-iron metal aqueous solution with a Mn / Fe molar ratio of 60:40. 14.4 L of a 1 mol / L monoammonium phosphate solution was prepared. The 12 L of the 60:40 manganese-iron metal solution and the 14.4 L of monoammonium phosphate were mixed evenly.

[0052] Pure water was added to the reactor, and the pH was adjusted to 6.0-6.5 with ammonia. The above-mentioned mixed solution of metal and phosphorus and a 10% ammonia solution were continuously added to the reactor to continuously produce manganese iron ammonium phosphate precipitate. Nitrogen gas was continuously introduced during the reaction process, the reaction temperature was 50℃, the stirring speed was 600 rpm, and the pH was maintained at 6.0-6.5.

[0053] 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.

[0054] Lithium iron manganese phosphate cathode material was prepared by calcining the prepared lithium iron manganese phosphate precursor with lithium source and carbon source.

[0055] Comparative example:

[0056] Prepare 14.4 L of 1 mol / L monoammonium phosphate solution;

[0057] 4.47 kg of 99% pure ferrous sulfate heptahydrate solid was dissolved in 13.29 L of pure water to prepare an aqueous solution of ferrous sulfate. 15.12 kg of battery-grade manganese sulfate solid was dissolved in 12 L of pure water to obtain an aqueous solution of manganese sulfate. The prepared iron-manganese aqueous solutions were then mixed to obtain a 1 mol / L manganese-iron metal aqueous solution with a Mn / Fe molar ratio of 60:40.

[0058] Add pure water to the reactor and adjust the pH to 4.5-5.0 with ammonia. Continuously add monoammonium phosphate aqueous solution, manganese-iron metal aqueous solution and ammonia to the reactor to continuously produce manganese-iron ammonium phosphate precipitate. Nitrogen gas is continuously introduced during the reaction process. The reaction temperature is 50℃, the stirring speed is 600 rpm, and the pH is maintained at 4.5-5.0.

[0059] 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.

[0060] Lithium iron manganese phosphate cathode material was prepared by calcining the prepared lithium iron manganese phosphate precursor with lithium source and carbon source.

[0061] The physicochemical properties of the prepared manganese iron ammonium phosphate precursor are shown in Table 1.

[0062]

[0063] The data in Table 1, comparing the comparative examples and the embodiments, show that:

[0064] When monoammonium phosphate (MAP) aqueous solution and molten metal are introduced separately, SEM reveals the formation of large, elongated aggregates, and XRD shows poor crystallinity. These large, agglomerated aggregates can lead to coarse particles after milling following lithium source mixing, thus affecting the performance of the cathode material. This invention mixes molten metal with the phosphorus source, resulting in a large number of fine crystal nuclei in the initial reaction stage, thus yielding a product with a smaller particle size. Smaller particle size helps improve the activity of the manganese iron ammonium phosphate precursor, facilitating lithium diffusion during lithium mixing and sintering, and enhancing the rate performance of the lithium iron phosphate cathode material.

[0065] The manganese iron ammonium phosphate precursor prepared by this invention has small particle size and high product activity.

[0066] 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 small particle size ammonium manganese iron phosphate precursor, characterized in that: The application relates to a preparation method of a manganese-iron-phosphorus lithium cathode material. Step one, a mixed metal salt solution containing metal manganese, iron and an optional M source is prepared; A phosphorus source solution is prepared, and the two solutions are mixed to obtain a mixed solution; A reaction bottom solution is prepared: a reaction kettle is added with pure water as a bottom solution, and then an alkali solution is added to adjust the pH value of the bottom solution to 4-7; Step two, the prepared mixed solution and ammonia water are added into the reaction kettle in parallel flow to carry out reaction, and manganese-iron-phosphorus ammonium monohydrate precipitate is obtained; Step three, the prepared manganese-iron-phosphorus ammonium monohydrate precipitate is subjected to solid-liquid separation, and then is washed and dried to obtain a manganese-iron-phosphorus ammonium precursor powder; The particle morphology of the manganese-iron-phosphorus ammonium precursor is flaky, and the particle size D50 of the precursor is 6-15 um; The precursor is expressed as 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. The molar ratio of metal elements (Mn+Fe+M) to element P in the precursor is 0.95-1.05; The precursor satisfies 0.3 g / cm 3 < TD < 1.0 g / cm 3 , 2 m 2 / g < SSA < 6 m 2 / g; In step one, the molar ratio of element P to metal (Mn+Fe) in the mixed solution is (1-3):1; In step two, inert gas is continuously introduced into the kettle during the reaction process, the reaction temperature is 20-70 DEG C, the stirring speed is 300-900 rpm, the pH value during the reaction process is adjusted by controlling the flow rate of ammonia water, and the pH value is maintained at 4-7.

2. The method of claim 1, wherein: In step one, the concentration of the mixed metal 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; The iron source is ferrous sulfate.

3. The method of claim 1, wherein: 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.

4. The method of claim 1, wherein: In step one, the alkali solution for adjusting the pH value is at least one of ammonia water, sodium hydroxide and potassium hydroxide.

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

6. A lithium iron manganese phosphate cathode material, characterized in that: The manganese-iron-phosphorus ammonium precursor prepared by the preparation method in any one of claims 1-5 is mixed with a lithium source and a carbon source material, is calcined at 400-1000 DEG C for 6-20 h under a nitrogen atmosphere, and then is obtained.

7. A battery, characterized by: The manganese-iron-phosphorus lithium cathode material in claim 6 is prepared.

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