Manganese pyrophosphate flake, manganese iron lithium phosphate positive electrode material and preparation method thereof

Abstract

The application provides a preparation method of a sheet-shaped manganese pyrophosphate and a lithium manganese iron phosphate positive electrode material, wherein a surfactant is added as an inducer in the preparation process of the manganese pyrophosphate to synthesize a sheet-shaped manganese pyrophosphate material with high crystallinity and uniform particle distribution, and then the manganese pyrophosphate material is used as a manganese source to synthesize the lithium manganese iron phosphate positive electrode material; the obtained positive electrode material inherits the performance of the sheet-shaped manganese pyrophosphate material, the combination of sheet-shaped large particles and granular small particles is beneficial to the exertion of the compaction performance, and meanwhile the uniformity of the small particles ensures the excellent electrical performance of the lithium manganese iron phosphate.

Description

Technical Field

[0001] This invention relates to the field of battery cathode material technology, specifically to a sheet-like manganese pyrophosphate and its preparation method, and a lithium iron phosphate cathode material and its preparation method. Background Technology

[0002] Manganese pyrophosphate is a unique inorganic non-metallic material of transition metal phosphate, widely used in catalysis, adsorption, optics, and magnetism. Manganese pyrophosphate can be used as a manganese source to prepare lithium iron phosphate (LFP) cathode materials, similar to LFP at 3.4V (vs. Li / Li). + Compared to the voltage plateau of Li / Li, the prepared lithium manganese iron phosphate material has a voltage of 4.1V (vs. Li / Li). + With the same capacity, lithium manganese iron phosphate batteries have a 20% higher energy density than lithium iron phosphate batteries.

[0003] Currently, commonly used methods for preparing manganese pyrophosphate include thermal decomposition of ammonium salts and hydrothermal and sol-gel methods. However, these methods have many drawbacks, such as complex operation processes, environmental pollution from waste gas during production, failure to meet the requirements of modern industrial production, low yield, long production cycle, and poor product quality. Furthermore, the prepared manganese pyrophosphate cannot be used as a manganese source to prepare high-performance lithium iron phosphate cathode materials. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this application first synthesizes a manganese pyrophosphate material with a lamellar structure, high crystallinity, and uniform particle distribution. Then, using this manganese pyrophosphate material as a manganese source, a lithium manganese iron phosphate cathode material is synthesized. The resulting cathode material inherits the performance of the lamellar manganese pyrophosphate material. The combination of large lamellar particles and small granular particles is beneficial to the compaction performance, while the uniformity of the small particles ensures the excellent electrical performance of lithium manganese iron phosphate.

[0005] In a first aspect, the present invention provides a method for preparing flake-shaped manganese pyrophosphate. According to an embodiment of the present invention, the method includes the following steps:

[0006] S1: Mix manganese source, phosphorus source I, surfactant and water to obtain mixed solution I, and stir to react;

[0007] S2: After the reaction is complete, filter the mixture, dry the filter cake, and perform a solid-state sintering to obtain the flake-shaped manganese pyrophosphate.

[0008] The surfactant in step S1 is a combination of fluorinated surfactant and hydrocarbon surfactant.

[0009] According to an embodiment of the present invention, step S1 of the above method may further include at least one of the following additional technical features:

[0010] According to an embodiment of the present invention, the molar ratio of the fluorinated surfactant to the hydrocarbon surfactant is 1:(10-20), preferably 1:(15-20).

[0011] Specifically, the molar ratio of the fluorinated surfactant to the hydrocarbon surfactant is 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, etc.

[0012] According to embodiments of the present invention, when the hydrocarbon surfactant comprises at least a cationic type, the fluorinated surfactant comprises at least anionic or nonionic type; when the hydrocarbon surfactant comprises at least anionic type, the fluorinated surfactant comprises at least a cationic or nonionic type.

[0013] In this invention, when the surfactant is a combination of cationic and anionic types, the electrostatic attraction between the head groups of oppositely charged ions promotes the association of cationic and anionic surfactant molecules, forming a pseudo-single-headed, double-tailed surfactant. When the surfactant includes nonionic surfactants, the mutual repulsion between fluorocarbon and hydrocarbon chains leads to hydrogen enrichment and the formation of micelles. Both of these conditions result in surfactants with superior wetting, processability, and stability properties. Under these conditions, the generated manganese pyrophosphate is encouraged to grow into a uniform and stable lamellar structure, thus facilitating the inheritance of its performance by subsequent lithium manganese iron phosphate.

[0014] In a specific embodiment of the present invention, the fluorinated surfactant is anionic perfluoropolyether carboxylate sodium (PFPE-Na), and the hydrocarbon surfactant is cationic hexadecyltrimethylammonium bromide (CTAB), or...

[0015] The fluorinated surfactant is anionic fluorinated fatty acid, and the hydrocarbon surfactant is cationic tetradecyltrimethylammonium hydroxide (TTAOH), or...

[0016] The fluorinated surfactant is a cationic perfluoropolyether (3)amidopropyl dimethylammonium iodide (PFPE-A), and the hydrocarbon surfactant is anionic sodium dodecyl sulfate (K12), or...

[0017] The fluorinated surfactant is a nonionic Zonyl-FSN-100 (C8F). 17The hydrocarbon surfactant is at least one of the following: cationic hexadecyltrimethylammonium bromide (CTAB), cationic tetradecyltrimethylammonium hydroxide (TTAOH), and anionic sodium dodecyl sulfate (K12).

[0018] The anionic fluorinated fatty acids mentioned refer to anionic fluorinated fatty acids with different carbon-fluorine chain lengths, such as C7F. 15 COOH, C8F 17 COOH, C9F 19 COOH, etc.

[0019] According to an embodiment of the present invention, in step S1, the molar ratio of manganese to phosphorus is Mn:P = 1:(1.2-1.5), for example 1:1.2, 1:1.3, 1:1.4, 1:1.5, etc.

[0020] According to an embodiment of the present invention, in step S1, the surfactant accounts for 0.1-0.3% of the total mass of the manganese source, phosphorus source I, and surfactant, for example, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, etc.

[0021] According to an embodiment of the present invention, the pH value of the stirring reaction in step S1 is 2-9, preferably 6-7.

[0022] According to an embodiment of the present invention, the reaction temperature of the stirring reaction in step S1 is 10-90°C, preferably 60-80°C.

[0023] According to an embodiment of the present invention, the stirring speed of the stirring reaction in step S1 is 300-500 rpm / min, preferably 350-400 rpm / min.

[0024] According to an embodiment of the present invention, the manganese source is at least one of manganese carbonate, manganese oxide, manganese sulfate, manganese tetroxide, and manganese oxalate, preferably at least one of manganese carbonate and manganese oxide.

[0025] According to an embodiment of the present invention, the phosphorus source I is at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, and iron phosphate, preferably at least one of diammonium hydrogen phosphate and ammonium dihydrogen phosphate.

[0026] In this application, there is no particular limitation on the amount of water used, as long as it can dissolve the manganese source, phosphorus source I, and surfactant. According to an embodiment of the present invention, the volume ratio of the mixed volume of manganese source, phosphorus source I, and surfactant to the volume of water is (1-5):10.

[0027] According to an embodiment of the present invention, step S2 of the above method may further include at least one of the following additional technical features:

[0028] According to an embodiment of the present invention, the sintering temperature of the first solid-state sintering is 400-500℃, the heating rate is 2-5℃ / min, and the sintering cycle is 2-10h.

[0029] Specifically, the sintering temperature of the first solid-state sintering is 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, etc.

[0030] Specifically, the heating rate of the first solid-state sintering is 2℃ / min, 2.3℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min, etc.

[0031] Specifically, the sintering cycle of the first solid-state sintering is 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc.

[0032] In this application, manganese phosphate with water is generated after the reaction in step S1, and then manganese pyrophosphate is generated after calcination in step S2.

[0033] In a second aspect, the present invention provides a flake-shaped manganese pyrophosphate obtained by the above preparation method, wherein the manganese pyrophosphate has a uniform particle size distribution and high crystallinity.

[0034] In a third aspect, the present invention provides a method for preparing a lithium manganese iron phosphate cathode material, comprising the following steps:

[0035] S3: Manganese pyrophosphate, lithium source, iron source, phosphorus source II are mixed with water to obtain mixed solution II, which is then spray-dried to obtain powder material;

[0036] S4: The above powder material is subjected to secondary solid-state sintering to obtain lithium manganese iron phosphate cathode material;

[0037] The manganese pyrophosphate is prepared by the aforementioned preparation method.

[0038] According to an embodiment of the present invention, step S3 of the above method may further include at least one of the following additional technical features:

[0039] According to an embodiment of the present invention, the lithium source is at least one selected from lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, and lithium acetate.

[0040] According to an embodiment of the present invention, the iron source is at least one selected from ferric phosphate, ferrous phosphate, ferric nitrate, ferric oxide, ferrous oxalate, and ferric oxide.

[0041] According to an embodiment of the present invention, the phosphorus source II is at least one selected from diammonium hydrogen phosphate, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, iron phosphate, and manganese phosphate.

[0042] According to an embodiment of the present invention, in step S3, the molar ratio of manganese to iron is Mn:(Fe+Mn)=(0.4-0.9):1; for example: 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, etc.

[0043] The molar ratio of lithium to iron and manganese is Li:(Fe+Mn)=(0.95-1.1):1; for example: 0.95:1, 1:1, 1.05:1, 1.1:1, etc.

[0044] The molar ratio of iron, manganese and phosphorus is (Fe+Mn):P = (0.95-1.06):1, for example: 0.95:1, 0.96:1, 1:1, 1.05:1, 1.06:1, etc.

[0045] In this invention, the molar ratio of elements includes the element in all raw materials, for example, the phosphorus source includes phosphorus in manganese pyrophosphate, phosphorus in phosphorus source II, phosphorus in lithium source (if any), and phosphorus in iron source (if any).

[0046] According to an embodiment of the present invention, step S3 includes: mixing manganese pyrophosphate, lithium source, iron source, phosphorus source II, carbon source and water to obtain mixed solution II.

[0047] According to an embodiment of the present invention, step S3 includes: mixing manganese pyrophosphate, lithium source, iron source, phosphorus source II, dopant and water to obtain mixed solution II.

[0048] According to an embodiment of the present invention, step S3 includes: mixing manganese pyrophosphate, lithium source, iron source, phosphorus source II, carbon source, dopant and water to obtain mixed solution II.

[0049] According to an embodiment of the present invention, the carbon source is at least one selected from toluene, xylene, cyclohexane, citric acid, polyethylene glycol, sucrose, carbon nanotubes, and glucose, and the mass of the carbon source accounts for 1-20% of the total mass of the raw materials, preferably 6-14%.

[0050] According to an embodiment of the present invention, the dopant element in the dopant is at least one selected from fluorine, vanadium, magnesium, niobium, titanium, and zirconium.

[0051] According to an embodiment of the present invention, the mass of the dopant element accounts for 800-8000 ppm of the total mass of the raw material, preferably 3000-5000 ppm.

[0052] According to an embodiment of the present invention, the dopant is at least one selected from ammonium fluoride, ammonium metavanadate, magnesium oxide, niobium pentoxide, titanate coupling agent, and zirconium oxide.

[0053] The term "raw materials" in the total mass of the above-mentioned raw materials refers to all raw materials excluding water, namely manganese pyrophosphate, lithium source, iron source, phosphorus source II and / or carbon source and / or dopants.

[0054] According to an embodiment of the present invention, step S4 of the above method may further include at least one of the following additional technical features:

[0055] According to an embodiment of the present invention, the secondary solid-state sintering includes: secondary sintering at 500-800℃, with a heating rate of 2-5℃ / min and a sintering cycle of 6-20h;

[0056] Preferably, the sintering is first performed at 300-500℃ with a heating rate of 2-5℃ / min and a sintering cycle of 2-6h, followed by a second sintering.

[0057] Preferably, the pre-sintering temperature is 400-450℃, and the secondary sintering temperature is 700-750℃.

[0058] Specifically, the pre-sintering temperature is 300℃, 350℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, etc.; the pre-sintering heating rate is 2℃ / min, 2.3℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min, 5℃ / min; and the pre-sintering sintering cycle is 2h, 3h, 4h, 5h, 6h, etc.

[0059] Specifically, the secondary sintering temperature is 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, etc.; the secondary sintering heating rate is 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, etc.; and the secondary sintering cycle is 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, etc.

[0060] In a fourth aspect, the present invention provides a lithium manganese iron phosphate cathode material obtained by the above-described preparation method, wherein the lithium manganese iron phosphate particles have a mixed block and granular structure, and the compaction density of the lithium manganese iron phosphate is 2.10–2.45 g / cm³. 3 Specific surface area is 8-20 m² 2 / g.

[0061] The beneficial effects of this invention are as follows:

[0062] 1. The manganese pyrophosphate material prepared in this invention involves the compounding of fluorinated surfactants and hydrocarbon surfactants during the preparation process. The pseudo-single-headed, double-tailed surfactant formed by the cationic and anionic surfactants, or the hydrogen-rich micelles formed by the mutual repulsion between fluorinated and hydrocarbon chains, gives the surfactants superior wetting, processability, and stability. Under this effect, on the one hand, it facilitates the growth of the generated manganese pyrophosphate into a uniform and stable lamellar structure, thus improving the performance inheritance of subsequent lithium manganese iron phosphate. On the other hand, the fluorinated surfactants can act as dopants, which helps to improve the ionic and electronic conductivity of the lithium manganese iron phosphate material.

[0063] 2. Since the reaction between manganese ions and phosphate is intense and the co-precipitation reaction is rapid, resulting in poor crystallinity, this invention adds an excess of phosphate ions and controls the pH of the solution to suppress the release rate of phosphate ions, so that phosphate ions can fully react with manganese ions, improve the crystallinity of manganese pyrophosphate, and thus improve the electrochemical performance of lithium manganese iron phosphate materials.

[0064] 3. The lithium manganese iron phosphate material prepared by the present invention has a more uniform particle distribution. Some of the particles inherit the properties of the flake-shaped manganese pyrophosphate precursor material and grow into large block particles. The combination of large block particles and small granular particles is conducive to the performance of compaction. At the same time, the presence of small particles ensures the excellent electrical properties of lithium manganese iron phosphate.

[0065] 4. The preparation process of this invention is simple, the process parameters are easy to control, and the final product has excellent properties, making it suitable for industrial mass production.

[0066] Terminology Definition

[0067] Unless explicitly stated otherwise, all scopes referenced in this invention include end values.

[0068] The term "at least one" is used in this invention to describe the elements and components described herein. This is done merely for convenience and to provide a general meaning regarding the scope of the invention. This description should be understood to include one or at least one, and the singular includes the plural, unless clearly otherwise indicated.

[0069] All figures in this invention are approximate values, regardless of whether words such as "approximately" or "about" are used. The numerical values ​​may vary by 1%, 2%, 5%, 7%, 8%, 10%, etc. Whenever a number with a value of N is disclosed, any number having a value of N+ / -1%, N+ / -2%, N+ / -3%, N+ / -5%, N+ / -7%, N+ / -8%, or N+ / -10% will be explicitly disclosed, where "+ / -" indicates addition or subtraction, and the range between N-10% and N+10% is also disclosed.

[0070] Unless otherwise stated, the following definitions as used in this invention shall apply. For the purposes of this invention, chemical elements are consistent with the CAS version of the periodic table and the 75th edition of the *Handbook of Chemistry and Physics*, 1994. Furthermore, general principles of organic chemistry can be found in *Organic Chemistry*, Thomas Sorrell, University Science Books, Sausalito: 1999, and *March's Advanced Organic Chemistry* by Michael B. Smith and Jerry March, John Wiley & Sons, New York: 2007, the entire contents of which are incorporated herein by reference.

[0071] Unless otherwise defined, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although similar or equivalent methods and materials may be used in the implementation or testing of embodiments of this invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned in this invention are incorporated herein by reference in their entirety, except where specific paragraphs are cited. In case of any conflict, this specification and its included definitions shall prevail. Furthermore, materials, methods, and examples are illustrative only and are not intended to be limiting.

[0072] In this application, "water" refers to "pure water" or "deionized water". Attached Figure Description

[0073] Figure 1 The image shows the XRD pattern of the manganese pyrophosphate material prepared in Example 1 of this invention.

[0074] Figure 2 This is a SEM image of the manganese pyrophosphate material prepared in Example 1 of the present invention;

[0075] Figure 3 This is a SEM image of the lithium manganese iron phosphate material prepared in Example 1 of the present invention;

[0076] Figure 4 This is a 0.2C charge-discharge curve of the lithium manganese iron phosphate material prepared in Example 1 of the present invention. Detailed Implementation

[0077] The preparation methods of manganese pyrophosphate and lithium manganese iron phosphate proposed in this invention will be described in detail below:

[0078] S1: Mix manganese source, phosphorus source I, fluorine-containing surfactant, hydrocarbon surfactant and water to obtain mixed solution I. Add ammonium monohydrate to adjust the pH of mixed solution I to 2-9, preferably 6-7. Stir the reaction under water bath heating conditions. The water bath temperature is 10-90℃, preferably 60-80℃. The stirring speed is 300-500 rpm / min, preferably 350-400 rpm / min.

[0079] The molar ratio of manganese to phosphorus is Mn:P = 1:(1.2-1.5).

[0080] The total mass of fluorinated surfactants and hydrocarbon surfactants accounts for 0.1-0.3% of the total mass of manganese source I, phosphorus source I, fluorinated surfactants, and hydrocarbon surfactants.

[0081] S2: After the reaction is complete, the product is filtered, the filter cake is washed with water at least 3 times, dried at 70-110℃, and then solid-state sintered once under an inert atmosphere to obtain flake manganese pyrophosphate.

[0082] The first solid-state sintering temperature is 400-500℃, the heating rate is 2-5℃ / min, and the sintering cycle is 2-10h.

[0083] S3: The flake-shaped manganese pyrophosphate (manganese source), lithium source, iron source, phosphorus source II, carbon source, and dopant obtained in S2 are mixed with water to obtain mixed solution II. After coarse grinding, sand grinding, and spray drying, powder material is obtained.

[0084] Among them, based on the molar amounts of manganese, iron, lithium and phosphorus in manganese pyrophosphate, lithium source, iron source and phosphorus source II, Mn:(Fe+Mn)=(0.4-0.9):1, Li:(Fe+Mn)=(0.95-1.1):1, (Fe+Mn):P=(0.95-1.06):1.

[0085] The carbon source accounts for 1-20% of the total mass of the raw material (excluding water), and the dopant element accounts for 800-8000 ppm of the total mass of the raw material (excluding water).

[0086] S4: The above powder material is subjected to secondary solid-state sintering under an inert atmosphere, and after natural cooling, it is crushed, sieved, and demagnetized to obtain lithium manganese iron phosphate cathode material.

[0087] The secondary solid-state sintering involves first pre-sintering, controlling the sintering temperature at 300-500℃, preferably 400-450℃, with a heating rate of 2-5℃ / min and a sintering cycle of 2-6h, followed by a second sintering, controlling the sintering temperature at 500-800℃, preferably 700-750℃, with a heating rate of 2-5℃ / min and a sintering cycle of 6-20h.

[0088] The following description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0089] Example 1

[0090] A method for preparing flake-shaped manganese pyrophosphate, the specific process of which is as follows:

[0091] S1: PFPE-Na and CTAB were mixed at a molar ratio of 1:20 to obtain a surfactant complex. Manganese carbonate, ammonium dihydrogen phosphate, and the above surfactant complex were mixed, with a Mn:P molar ratio of 1:1.5. The mass of the surfactant complex accounted for 0.3% of the total mass (mass of manganese carbonate, ammonium dihydrogen phosphate, and surfactant complex). Three times the volume of pure water was added and mixed to obtain a mixed solution. Ammonium monohydrate was added to adjust the pH to 6. The mixed solution was then heated to 80°C in a low-temperature constant-temperature reaction bath while stirring at 400 rpm / min for 6 hours.

[0092] S2: After the reaction is complete, the slurry is filtered, the filter cake is washed three times with water, and then transferred to a forced-air drying oven for drying at 80℃ for 12 hours. The dried powder is then transferred to a muffle furnace for solid-state sintering at 500℃ under a nitrogen atmosphere at a heating rate of 2.3℃ / min for 6 hours. After natural cooling to room temperature, a light pink powder of manganese pyrophosphate material is obtained. Figure 1 The XRD pattern of the material confirms that the light pink powder is manganese pyrophosphate. Figure 2 The image shows the SEM image of the material, which reveals that it has a sheet-like structure.

[0093] A method for preparing lithium manganese iron phosphate cathode material, the specific process of which is as follows:

[0094] S3: The manganese pyrophosphate, ferrous phosphate, lithium dihydrogen phosphate, lithium carbonate, glucose, polyethylene glycol, and ammonium metavanadate obtained in S2 are mixed and dissolved in water, and mixed evenly to obtain a mixed solution. The solid content of the slurry is controlled at 30%. The molar ratio of manganese to ferromanganese is 0.6:1, the molar ratio of lithium to ferromanganese is 1.05:1, the molar ratio of ferromanganese to phosphorus is 0.96:1, the mass of glucose and polyethylene glycol accounts for 10% of the total mass of the raw materials (excluding water), and the mass of vanadium in ammonium metavanadate accounts for 4500 ppm of the total mass of the raw materials (excluding water). The above mixed solution is subjected to coarse grinding, sand milling, and spray drying to obtain precursor powder.

[0095] S4: The precursor powder was pre-sintered under a nitrogen atmosphere at a temperature of 400℃, a heating rate of 2.3℃ / min, and a sintering cycle of 6 hours. A second sintering process was then performed at 750℃, a heating rate of 4℃ / min, and a sintering cycle of 12 hours. After automatic cooling, the sintered product was pulverized, sieved, and demagnetized to obtain the lithium manganese iron phosphate cathode material.

[0096] Figure 3 The image shows the SEM image of the lithium manganese iron phosphate cathode material. As can be seen from the image, the lithium manganese iron phosphate particles have a mixed structure of block and granular particles with uniform particle distribution. Some of the particles inherit the properties of the flake manganese pyrophosphate material and grow into large block particles, which are combined with small granular particles.

[0097] Example 2

[0098] This embodiment provides a method for preparing flake-shaped manganese pyrophosphate: anionic fluorinated fatty acid C8F... 17 COOH and TTAOH were mixed in a ratio of 1:18 to obtain a surfactant compound. The remaining steps were the same as in Example 1, resulting in a light pink powdery manganese pyrophosphate material.

[0099] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material. Using the above-mentioned manganese pyrophosphate material as the manganese source, the preparation method is the same as in Example 1, and the lithium manganese iron phosphate cathode material is obtained.

[0100] Example 3

[0101] This embodiment provides a method for preparing flake-shaped manganese pyrophosphate. The difference from Embodiment 1 is that the first solid-state sintering temperature in S2 is 400°C, while the remaining operation steps are the same as in Embodiment 1, resulting in a light pink powdery manganese pyrophosphate material.

[0102] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material. Using the above-mentioned manganese pyrophosphate material as the manganese source, the operation steps are the same as in Example 1 to obtain lithium manganese iron phosphate cathode material.

[0103] Example 4

[0104] The preparation method of flake manganese pyrophosphate in this embodiment is the same as that in Example 1.

[0105] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material. The difference from Embodiment 1 is that step S4 in this embodiment is:

[0106] The precursor powder was sintered under a nitrogen atmosphere at a temperature of 750℃, a heating rate of 4℃ / min, and a sintering cycle of 12 hours. After automatic cooling, the sintered product was then pulverized, sieved, and demagnetized to obtain lithium manganese iron phosphate cathode material.

[0107] Example 5

[0108] This embodiment provides a method for preparing flake-shaped manganese pyrophosphate: PFPE-A and K12 are mixed at a molar ratio of 1:15 to obtain a surfactant complex. Manganese carbonate, ammonium dihydrogen phosphate, and the above surfactant complex are mixed, wherein the Mn:P molar ratio is 1:1.2, and the mass of the surfactant complex accounts for 0.2% of the total mass. Three times the volume of pure water is then added and mixed to obtain a mixed solution. Ammonium monohydrate is added to adjust the pH to 7. The mixed solution is then heated to 80°C in a low-temperature constant-temperature reaction bath while stirring at a stirring speed of 400 rpm / min for 6 hours. The remaining operation steps are the same as in Example 1, resulting in a light pink powdery manganese pyrophosphate material.

[0109] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material. Using the above-mentioned manganese pyrophosphate material as the manganese source, the operation steps are the same as in Example 1 to obtain lithium manganese iron phosphate cathode material.

[0110] Comparative Example 1

[0111] This embodiment provides a method for preparing flake-shaped manganese pyrophosphate: CTAB is mixed with manganese carbonate and ammonium dihydrogen phosphate, wherein the Mn:P molar ratio is 1:1.5, and the mass of Zonyl-FSN-100 accounts for 0.3% of the total mass. The remaining steps are the same as in Example 1, resulting in manganese pyrophosphate material and lithium iron phosphate cathode material.

[0112] Comparative Example 2

[0113] This embodiment provides a method for preparing flake-shaped manganese pyrophosphate: manganese carbonate and ammonium dihydrogen phosphate are mixed, wherein the molar ratio of Mn:P is 1:1.5, and the remaining steps are the same as in Example 1, to obtain manganese pyrophosphate material and lithium iron phosphate cathode material.

[0114] Comparative Example 3

[0115] This embodiment provides a method for preparing flake-shaped manganese pyrophosphate: PFPE-Na and CTAB are mixed at a molar ratio of 1:20 to obtain a surfactant complex. Manganese carbonate, ammonium dihydrogen phosphate, and the above surfactant complex are mixed, wherein the Mn:P molar ratio is 1:1.7, and the mass of the surfactant complex accounts for 0.1% of the total mass (mass of manganese carbonate, ammonium dihydrogen phosphate, and surfactant complex). Three times the volume of pure water is then added and mixed to obtain a mixed solution. Ammonium monohydrate is added to adjust the pH to 6. The mixed solution is then heated to 80°C in a low-temperature constant-temperature reaction bath while stirring at a stirring speed of 400 rpm / min for 6 hours.

[0116] The remaining steps are the same as in Example 1, to obtain manganese pyrophosphate material and lithium iron manganese phosphate cathode material.

[0117] Comparative Example 4

[0118] This embodiment provides a method for preparing flake-shaped manganese pyrophosphate: PFPE-Na and CTAB are mixed at a molar ratio of 1:20 to obtain a surfactant complex. Manganese carbonate, ammonium dihydrogen phosphate, and the above surfactant complex are mixed, wherein the Mn:P molar ratio is 1:1, and the mass of the surfactant complex accounts for 0.1% of the total mass (mass of manganese carbonate, ammonium dihydrogen phosphate, and surfactant complex). Three times the volume of pure water is then added and mixed to obtain a mixed solution. Ammonium monohydrate is added to adjust the pH to 6. The mixed solution is then heated to 80°C in a low-temperature constant-temperature reaction bath while stirring at a stirring speed of 400 rpm / min for 6 hours.

[0119] The remaining steps are the same as in Example 1, to obtain manganese pyrophosphate material and lithium iron manganese phosphate cathode material.

[0120] Performance Evaluation

[0121] The lithium manganese iron phosphate positive electrode materials prepared in Examples 1-5 and Comparative Examples 1-4, the mixture of PVDF binder and NMP, and the conductive agent Super-P were weighed in a mass ratio of 92:4:4. After being ball-milled and dispersed evenly, the mixture was coated onto aluminum foil and vacuum-dried at 110°C. After rolling and punching, the positive electrode was obtained. The electrolyte was 1 mol / L LiPF6, with a solvent volume ratio of EC:DMC:EMC = 1:1:1 (volume ratio). The separator was a Celgard polypropylene membrane, and the negative electrode was a lithium metal sheet. All components were assembled into a coin cell in a vacuum glove box. The coin cell was electrochemically tested using a Blue Dot battery testing system, with a test voltage range of 2V-4.5V.

[0122] The compaction density of the lithium manganese iron phosphate cathode materials prepared in Examples 1-5 and Comparative Examples 1-4 was tested using a constant pressure method and a compaction density testing device.

[0123] The test results are shown in Table 1.

[0124] Table 1

[0125]

[0126]

[0127] As can be seen from the table, the lithium manganese iron phosphate cathode material obtained by the method in this embodiment has significantly better performance than the comparative example.

[0128] In Comparative Example 1, a single fluorinated surfactant was used, which had little inducing effect on the formation of sheet-like structures. In Comparative Example 2, no surfactant was used, and the lack of surfactant induction resulted in fine lithium manganese iron phosphate particles. Compared with the mixed particles of different sizes in this application, the electrical properties and compaction density were both inferior.

[0129] In Comparative Examples 3 and 4, the amount of phosphorus source was too high or too low when preparing manganese pyrophosphate. Too much phosphate ions would accelerate the combination with manganese ions, resulting in an overly rapid reaction and poor crystallinity of the synthesized grains; while too little phosphate ions would prevent some manganese ions from participating in the reaction normally, resulting in low purity of the material.

[0130] Figure 4 The figure shows the 0.2C charge-discharge curve of the lithium manganese iron phosphate material prepared in Example 1 of this invention. As can be seen from the figure, the lithium manganese iron phosphate cathode material prepared by flake manganese pyrophosphate has a reversible capacity of more than 158 mAh / g at a current of 0.2C, and has good electrochemical performance.

[0131] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing flake-shaped manganese pyrophosphate, characterized in that, Includes the following steps: S1: Mix manganese source, phosphorus source I, surfactant and water to obtain mixed solution I, and stir to react; S2: After the reaction is complete, filter the mixture, dry the filter cake, and perform a solid-state sintering to obtain the flake-shaped manganese pyrophosphate. In step S1, the surfactant is a combination of a fluorinated surfactant and a hydrocarbon surfactant. When the hydrocarbon surfactant contains at least a cationic type, the fluorinated surfactant contains at least anionic or nonionic types; when the hydrocarbon surfactant contains at least anionic types, the fluorinated surfactant contains at least a cationic or nonionic type.

2. The preparation method according to claim 1, characterized in that, The molar ratio of the fluorinated surfactant to the hydrocarbon surfactant is 1:(10) 20).

3. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of manganese to phosphorus is Mn:P = 1:(1.2). 1.5); The surfactant accounts for 0.1% of the total mass of the manganese source, phosphorus source I, and surfactant. 0.3%.

4. The preparation method according to claim 1, characterized in that, The conditions for the stirring reaction in step S1 include: The reaction pH value is 2 9; and / or The reaction temperature is 10 90℃; and / or The stirring speed is 300. 500 rpm / min.

5. The preparation method according to claim 1, characterized in that, The conditions for the stirring reaction in step S1 include: The reaction pH is 6 7.

6. The preparation method according to claim 1, characterized in that, The conditions for the stirring reaction in step S1 include: The reaction temperature is 60°C. 80℃.

7. The preparation method according to claim 1, characterized in that, The conditions for the stirring reaction in step S1 include: The stirring speed is 350. 400 rpm / min.

8. The preparation method according to claim 1, characterized in that, The conditions for the first solid-state sintering in step S2 include: a sintering temperature of 400°C. 500℃, heating rate is 2 5℃ / min, sintering cycle is 2 10h.

9. The preparation method according to claim 1, characterized in that, The manganese source is at least one of manganese carbonate, manganese oxide, manganese sulfate, manganese tetroxide, and manganese oxalate, and the phosphorus source I is at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, and iron phosphate.

10. A method for preparing a lithium manganese iron phosphate cathode material, characterized in that, Includes the following steps: S3: Manganese pyrophosphate, lithium source, iron source, phosphorus source II are mixed with water to obtain mixed solution II, which is then spray-dried to obtain powder material; S4: The above powder material is subjected to secondary solid-state sintering to obtain lithium manganese iron phosphate cathode material; The manganese pyrophosphate is obtained by the preparation method according to any one of claims 1 to 9.

11. The preparation method according to claim 10, characterized in that, The lithium source is at least one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, and lithium acetate; The iron source is at least one of ferric phosphate, ferrous phosphate, ferric nitrate, ferric oxide, ferrous oxalate, and ferric oxide; the phosphorus source II is at least one of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, lithium dihydrogen phosphate, ferric phosphate, and manganese phosphate.

12. The preparation method according to claim 10, characterized in that, In step S3, the molar ratio of manganese to iron is Mn:(Fe+Mn)=(0.4) 0.9): 1; The molar ratio of lithium to iron and manganese is Li:(Fe+Mn)=(0.95) 1.1): 1; The molar ratio of iron, manganese, and phosphorus is (Fe + Mn): P = (0.95) / (0.95) 1.06):

1.

13. The preparation method according to claim 10, characterized in that, The mixing process in step S3 also includes a carbon source and / or a dopant.

14. The preparation method according to claim 13, characterized in that, The carbon source is at least one selected from toluene, xylene, cyclohexane, citric acid, polyethylene glycol, sucrose, carbon nanotubes, and glucose, and the mass of the carbon source accounts for 1 / 3 of the total mass of the raw materials. 20%.

15. The preparation method according to claim 13, characterized in that, The dopant is at least one selected from ammonium fluoride, ammonium metavanadate, magnesium oxide, niobium pentoxide, titanate coupling agent, and zirconium oxide, wherein the mass of the dopant element in the dopant accounts for 800% of the total mass of the raw material. 8000ppm.

16. The preparation method according to claim 10, characterized in that, The secondary solid-state sintering in step S4 includes: In 500 Secondary sintering at 800℃, with a heating rate of 2 5℃ / min, sintering cycle is 6 20h.

17. The preparation method according to claim 10, characterized in that, The secondary solid-state sintering in step S4 includes: first at 300... Pre-sintering at 500℃ with a heating rate of 2 5℃ / min, sintering cycle is 2 After 6 hours, a second sintering process is carried out.

18. The preparation method according to claim 17, characterized in that, The sintering temperature of the pre-sintering is 400°C. 450℃, the sintering temperature of the secondary sintering is 700℃. 750℃.

19. A lithium manganese iron phosphate cathode material obtained by the preparation method according to any one of claims 10 to 18, characterized in that, The lithium manganese iron phosphate particles have a mixed block and granular structure, and the compacted density of the lithium manganese iron phosphate is 2.10–2.45 g / cm³. 3 Specific surface area is 8-20 m² 2 / g.

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