A Lithium Iron Manganese Phosphate and a Method for Preparing the Same and Its Use

Abstract

This text discloses a lithium iron manganese phosphate, a method for preparing the same, and its uses. The preparation method includes adding an iron source, a manganese source, a phosphorus source, a carbon source, and a first lithium source to a dispersion system containing a second lithium source, mixing uniformly, grinding to obtain a slurry, then subjecting the slurry to ultrasonic spray drying to obtain a precursor powder, and finally sintering to obtain lithium iron manganese phosphate. By controlling the ratio of the first lithium source and the second lithium source in the slurry and forming the precursor by using the method of ultrasonic atomization, a plump lithium element layer can be formed on the surface of the lithium iron manganese phosphate and the distribution of lithium elements in the inner layer can be made more uniform, which is not only beneficial to improving the uniformity of the product, but also beneficial to shortening the Li ion channel, making it easier to intercalate and deintercalate during charge and discharge. The addition of the carbon source can form an interlayer carbon network between the lithium iron manganese phosphate particles, making the dispersion between the particles better and more dense, thereby improving the electrical properties of the product.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of batteries, for example, lithium iron manganese phosphate and a method for preparing the same and uses thereof. Background Art

[0002] With the shortage of fossil energy, the development of new energy vehicles is one of the important measures for the world to address climate change and optimize the energy structure. Countries have successively introduced strategic plans to promote technological innovation and application in the field of new energy vehicles. The global new energy vehicle market has entered a rapid growth period. Therefore, the requirements for power batteries in new energy vehicles have become increasingly high.

[0003] Among many cathode materials for lithium-ion batteries, the lithium iron manganese phosphate (LiMnFePO4) cathode material has attracted much attention due to its high energy density, high safety, and high charge and discharge voltage characteristics. Although the lithium iron manganese phosphate cathode material has the above advantages, the commercially available lithium iron manganese phosphate materials generally have problems such as low product stability, poor homogeneity, and poor electrical performance, which seriously restrict the application and development of lithium iron manganese phosphate. Therefore, a large amount of research is still needed to further optimize and improve lithium iron manganese phosphate.

[0004] Currently, lithium iron manganese phosphate is mainly modified by coating and doping. For example, CN108832119A discloses a method for preparing carbon-doped lithium iron manganese phosphate. Ferrous acetate, manganese acetate, ferrous dihydrogen phosphate, manganese dihydrogen phosphate, and lithium carbonate are added to pure water, and carbon dioxide is introduced into a closed reaction kettle and stirred until the solution becomes clear; spray drying is performed by a spray dryer, and the obtained material is calcined in a sintering furnace to obtain carbon-doped high-compact lithium iron manganese phosphate. CN107834034A discloses a method for using graphene to improve the preparation of lithium iron manganese phosphate electrode materials. Lithium acetate is used as the lithium source, ferrous acetate is used as the iron source, ammonium dihydrogen phosphate is used as the phosphate source, and manganese oxalate and graphene are used as doping raw materials. A precursor is obtained by grinding in absolute ethanol, and then a lithium iron manganese phosphate cathode material coated with graphene is obtained by heat treatment in an inert atmosphere. CN106848309A discloses a metal carbon nanotube composite-doped lithium iron manganese phosphate material and a preparation method thereof. The ionic conductivity and electronic conductivity of lithium iron manganese phosphate are improved by co-doping with metals such as magnesium, titanium, cobalt, zinc, rubidium, and carbon nanotubes.

[0005] The above patents respectively use doping such as graphene, metal and carbon nanotubes to improve the tap density and conductivity of lithium iron phosphate manganese, but the improvement of the homogeneity and stability of lithium iron phosphate manganese is insufficient. Therefore, the rate performance and cycle stability during high-current charge and discharge still need to be improved. Therefore, how to improve the synthesis method of lithium iron phosphate manganese on the basis of coating or doping, so that the homogeneity, stability and electrochemical performance of the lithium iron phosphate manganese cathode material can be fully improved, is of great significance for promoting the application and development of lithium iron phosphate manganese. Summary of the Invention

[0006] The following is an overview of the subject matter described in detail in this document. This overview is not intended to limit the scope of protection of the claims.

[0007] An embodiment of the present application provides a lithium iron phosphate manganese and a method and use for preparing the same. The preparation method includes adding an iron source, a manganese source, a phosphorus source, a carbon source and a first lithium source to a dispersion system containing a second lithium source, mixing evenly and then grinding to obtain a slurry, and then subjecting the slurry to ultrasonic spray drying to obtain a precursor powder, and finally sintering to obtain lithium iron phosphate manganese. By controlling the ratio of the first lithium source and the second lithium source in the slurry and forming a precursor by using the ultrasonic atomization method, a plump lithium element layer can be formed on the surface of the lithium iron phosphate manganese and the inner-layer lithium element distribution can be made more uniform, which is not only beneficial to improving the homogeneity of the product, but also beneficial to shortening the Li ion channel, making it easier to intercalate and deintercalate during charge and discharge. The addition of the carbon source can form an interlayer carbon network between the lithium iron phosphate manganese particles, making the dispersion between the particles better and denser, thereby improving the electrical properties of the product.

[0008] In a first aspect, an embodiment of the present application provides a method for preparing lithium iron phosphate manganese, and the method includes the following steps:

[0009] (1) Adding an iron source, a manganese source, a phosphorus source, a carbon source and a first lithium source to a dispersion system containing a second lithium source, mixing evenly and then grinding to obtain a slurry;

[0010] (2) Subjecting the slurry obtained in step (1) to ultrasonic spray drying to obtain a precursor powder, and then sintering to obtain lithium iron phosphate manganese.

[0011] The present application controls the ratio of the first lithium source and the second lithium source in the slurry and forms a precursor by using an ultrasonic atomization method, so that a full lithium element layer is formed on the surface of the lithium iron manganese phosphate and the inner layer lithium element is more evenly distributed, which is not only beneficial to improving the uniformity of the product, but also beneficial to shortening the Li ion diffusion channel, making it easier to deintercalate during charging and discharging. The addition of a carbon source can form an interlayer carbon network between the lithium iron manganese phosphate particles, making the dispersion between the particles better and denser. The method described in the present application can obtain a lithium iron manganese phosphate material with good crystallinity and uniform element distribution, and the conductivity, lithium ion diffusion rate, specific capacity and cycle stability of the product are all improved.

[0012] When ordinary spray drying technology is used in the preparation of lithium iron manganese phosphate, there are secondary particles with large particle size, and the precursor is not evenly dispersed, which affects the incomplete reaction of the subsequent sintering stage. The present application adopts an ultrasonic spray drying method, using an ultrasonic spray dryer to convert high-frequency sound waves into mechanical energy through an ultrasonic nozzle, and the mechanical energy is transferred to the liquid to generate standing waves. The liquid is introduced into the atomizing surface through the nozzle. When the liquid leaves the atomizing surface of the nozzle, it is broken into a fine mist of uniform micron-sized droplets, thereby achieving atomization. In the ultrasonic spraying process, the droplet size and distribution can be accurately controlled by the ultrasonic frequency, so that very small droplets and particles can evaporate quickly, thereby producing particles with a high specific surface area, which is conducive to particle growth and fusion during sintering.

[0013] In the present application, the first lithium source is a sparingly soluble lithium salt, and the second lithium salt is a soluble lithium salt. The sparingly soluble lithium salt will be evenly distributed in the secondary particles during the spray drying stage, and the soluble lithium salt will be evenly distributed on the surface of the secondary particles during the spray drying stage. By mixing more sparingly soluble lithium salts and less soluble lithium salts in a suitable ratio, small-sized secondary particles with rich surface and uniform inner layer can be formed during the ultrasonic spray drying stage. The lithium salt layer on the surface can shorten the migration path of lithium ions during the sintering stage and improve the point performance of the material. Internally uniform lithium salt is conducive to ensuring the uniformity of material synthesis and forming uniform lithium iron manganese phosphate.

[0014] The following are preferred technical solutions of the present application, but are not intended to be limitations of the technical solutions provided by the present application. Through the following technical solutions, the technical objectives and beneficial effects of the present application can be better achieved and realized.

[0015] As a preferred technical solution of the present application, the ultrasonic frequency of the ultrasonic spray drying in step (2) is 20 - 40 kHz, such as 20 kHz, 21 kHz, 22 kHz, 23 kHz, 24 kHz, 25 kHz, 26 kHz, 27 kHz, 28 kHz, 29 kHz, 30 kHz, 31 kHz, 32 kHz, 33 kHz, 34 kHz, 35 kHz, 36 kHz, 37 kHz, 38 kHz, 39 kHz or 40 kHz, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0016] Preferably, the inlet air temperature of the ultrasonic spray drying in step (2) is 180 - 250 °C, such as 180 °C, 185 °C, 190 °C, 195 °C, 200 °C, 205 °C, 210 °C, 215 °C, 220 °C, 225 °C, 230 °C, 235 °C, 240 °C, 245 °C or 250 °C, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0017] Preferably, the outlet air temperature of the ultrasonic spray drying in step (2) is 90 - 140 °C, such as 90 °C, 95 °C, 100 °C, 105 °C, 110 °C, 115 °C, 120 °C, 125 °C, 130 °C, 135 °C or 140 °C, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0018] Preferably, the feeding rate of the ultrasonic spray drying in step (2) is 5 - 10 L / min, such as 5 L / min, 5.5 L / min, 6 L / min, 6.5 L / min, 7 L / min, 7.5 L / min, 8 L / min, 8.5 L / min, 9 L / min, 9.5 L / min or 10 L / min, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0019] As a preferred technical solution of the present application, the molar amount of iron element in the slurry obtained in step (1) is n(Fe) and the molar amount of manganese element is n(Mn), n(Fe):n(Mn) = (0.25 - 4):1, such as 0.25:1, 0.5:1, 0.75:1, 1:1, 1.25:1, 1.5:1, 1.75:1, 2:1, 2.25:1, 2.5:1, 2.75:1, 3:1, 3.25:1, 3.5:1, 3.75:1 or 4:1, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0020] Preferably, in step (1), the total molar amount of iron element and manganese element in the slurry obtained in step (1) is n(M), and the molar amount of phosphorus element is n(P), and n(P):n(M) = (0.92 - 1.05):1, such as 0.92:1, 0.93:1, 0.94:1, 0.95:1, 0.96:1, 0.97:1, 0.98:1, 0.99:1, 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1 or 1.05:1, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0021] Preferably, in step (1), the molar amount of lithium element in the first lithium source is n(Li01), and the molar amount of lithium element in the second lithium source is n(Li02), and n(Li01):n(Li02) = (1 - 99):1, such as 1:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, 55:1, 60:1, 65:1, 70:1, 75:1, 80:1, 85:1, 90:1, 95:1 or 99:1, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0022] Preferably, in step (1), the total molar amount of iron element and manganese element in the slurry obtained in step (1) is n(M), and the total molar amount of lithium element is n(Li), and n(Li):n(M) = (0.99 - 1.1):1, such as 0.99:1, 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1 or 1.1:1, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0023] As a preferred technical solution of the present application, the dispersion system in step (1) includes an aqueous solution and / or a suspension.

[0024] Preferably, the first lithium source in step (1) includes lithium phosphate and / or lithium carbonate.

[0025] Preferably, the second lithium source in step (1) includes any one or a combination of at least two of lithium hydroxide, lithium citrate, lithium oxalate, lithium dihydrogen phosphate, or lithium nitrate. Typical but non-limiting examples of the combination include the combination of lithium hydroxide and lithium citrate, the combination of lithium hydroxide and lithium oxalate, the combination of lithium hydroxide and lithium dihydrogen phosphate, the combination of lithium hydroxide and lithium nitrate, the combination of lithium citrate and lithium oxalate, the combination of lithium citrate and lithium dihydrogen phosphate, the combination of lithium citrate and lithium nitrate, the combination of lithium oxalate and lithium dihydrogen phosphate, the combination of lithium oxalate and lithium nitrate, or the combination of lithium dihydrogen phosphate and lithium nitrate.

[0026] Preferably, the iron source in step (1) includes any one or a combination of at least two of iron phosphate, iron oxide, ferrous oxalate, iron nitrate, or iron citrate. Typical but non-limiting examples of the combination include the combination of iron phosphate and iron oxide, the combination of iron phosphate and ferrous oxalate, the combination of iron phosphate and iron nitrate, the combination of iron phosphate and iron citrate, the combination of iron oxide and ferrous oxalate, the combination of iron oxide and iron nitrate, the combination of iron oxide and iron citrate, the combination of ferrous oxalate and iron nitrate, the combination of ferrous oxalate and iron citrate, or the combination of iron nitrate and iron citrate.

[0027] Preferably, the manganese source in step (1) includes any one or a combination of at least two of manganese oxalate, manganese phosphite, manganese phosphate, manganese monoxide, manganese sesquioxide, manganese ferrite, ammonium manganese ferrite, or manganese nitrate. Typical but non-limiting examples of the combination include the combination of manganese oxalate and manganese phosphite, the combination of manganese phosphate and manganese monoxide, the combination of manganese sesquioxide and manganese ferrite, the combination of manganese ferrite and ammonium manganese ferrite, the combination of manganese nitrate and manganese oxalate, the combination of manganese phosphite and manganese phosphate, the combination of manganese monoxide and manganese sesquioxide, the combination of manganese ferrite and manganese sesquioxide, or the combination of ammonium manganese ferrite and manganese nitrate.

[0028] Preferably, the phosphorus source in step (1) includes any one or a combination of at least two of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, lithium phosphate, or phosphoric acid. Typical but non-limiting examples of the combination include the combination of ammonium dihydrogen phosphate and diammonium hydrogen phosphate, the combination of lithium monohydrogen phosphate and lithium dihydrogen phosphate, the combination of lithium phosphate and phosphoric acid, the combination of diammonium hydrogen phosphate and lithium monohydrogen phosphate, the combination of lithium dihydrogen phosphate and lithium phosphate, or the combination of phosphoric acid and ammonium dihydrogen phosphate.

[0029] Preferably, the carbon source in step (1) includes any one or a combination of at least two of glucose, citric acid, sucrose, phenolic resin, starch, polyaniline, lauric acid or β-cyclodextrin. Typical but non-limiting examples of the combination include the combination of glucose and citric acid, the combination of sucrose and phenolic resin, the combination of starch and polyaniline, the combination of lauric acid and β-cyclodextrin, the combination of phenolic resin and glucose, the combination of citric acid and sucrose, the combination of phenolic resin and starch, the combination of polyaniline and lauric acid, or the combination of β-cyclodextrin and polyaniline.

[0030] Preferably, the carbon source in step (1) further includes a surfactant.

[0031] Preferably, the surfactant includes any one or a combination of at least two of polyethylene glycol, dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB), Tween-80, ethylenediaminetetraacetic acid (EDTA), polyvinylpyrrolidone (PVP) or dodecyl maltoside (DDM). Typical but non-limiting examples of the combination include the combination of polyethylene glycol and dodecyltrimethylammonium bromide, the combination of cetyltrimethylammonium bromide and Tween-80, the combination of ethylenediaminetetraacetic acid and polyvinylpyrrolidone, the combination of dodecyl maltoside and polyethylene glycol, the combination of dodecyltrimethylammonium bromide and cetyltrimethylammonium bromide, the combination of Tween-80 and ethylenediaminetetraacetic acid, or the combination of polyvinylpyrrolidone and dodecyl maltoside.

[0032] As a preferred technical solution of the present application, the particle size of the slurry in step (1) is 300 - 600 nm, such as 300 nm, 320 nm, 340 nm, 360 nm, 380 nm, 400 nm, 420 nm, 440 nm, 460 nm, 480 nm, 500 nm, 520 nm, 540 nm, 560 nm, 580 nm or 600 nm, etc., but is not limited to the listed values, and other unlisted values within the above numerical range are equally applicable.

[0033] The grinding particle size of the slurry affects the particle size of the primary particles of the material. If the particle size is too large, it will increase the migration distance of lithium ions and have a negative impact on the electrical properties of the material. If the particle size is too small, it will lead to a high specific surface area of the material and increase the difficulty of subsequent battery processing.

[0034] Preferably, the equipment for grinding in step (1) includes a sand mill.

[0035] Preferably, the mixing method in step (1) includes stirring at room temperature for 10 to 60 minutes, such as 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes or 60 minutes, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0036] As a preferred technical solution of the present application, the sintering in step (2) includes first performing pre-sintering and then raising the temperature for secondary sintering.

[0037] In the present application, pre-sintering is first performed during sintering. At this time, the carbon source can be effectively decomposed and an interlayer carbon network is formed between the lithium iron manganese phosphate particles.

[0038] Preferably, the temperature of the pre-sintering is 300 to 500 °C, such as 500 °C, 320 °C, 340 °C, 360 °C, 380 °C, 400 °C, 420 °C, 440 °C, 460 °C, 480 °C or 500 °C, etc., and the time is 1 to 3 hours, such as 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours or 3 hours, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0039] Preferably, the temperature of the secondary sintering is 650 to 830 °C, such as 650 °C, 670 °C, 690 °C, 710 °C, 730 °C, 750 °C, 750 °C, 770 °C, 790 °C, 810 °C or 830 °C, etc., and the time is 6 to 12 hours, such as 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours or 12 hours, etc., but not limited to the listed values, and other unlisted values within the above value range are equally applicable.

[0040] Preferably, the sintering in step (2) is carried out in an inert atmosphere.

[0041] Preferably, the inert atmosphere includes any one or a combination of at least two of nitrogen, argon or helium. Typical but non-limiting examples of the combination include a combination of nitrogen and argon, a combination of nitrogen and helium, or a combination of argon and helium.

[0042] In a second aspect, an embodiment of the present application provides a lithium iron manganese phosphate obtained by the method according to the first aspect.

[0043] In a third aspect, an embodiment of the present application provides a positive electrode plate, and the positive electrode plate contains the lithium iron manganese phosphate described in the second aspect.

[0044] Fourthly, an embodiment of the present application provides a lithium-ion battery, and the lithium-ion battery includes the positive electrode sheet described in the third aspect.

[0045] Fifthly, an embodiment of the present application provides an electrical device, and the electrical device includes the lithium-ion battery described in the fourth aspect.

[0046] Compared with the related technical solutions, the embodiments of the present application have at least the following beneficial effects:

[0047] In the embodiments of the present application, by controlling the ratio of the first lithium source and the second lithium source in the slurry and forming a precursor by using the ultrasonic atomization method, the soluble second lithium source can form a plump lithium element layer on the surface of lithium iron phosphate manganese, and the insoluble first lithium source can make the distribution of the inner-layer lithium elements more uniform. Ultrasonic atomization can ensure that the particles are fine and evenly distributed after spraying in this system. This is not only beneficial to improving the uniformity of the product, but also beneficial to shortening the Li ion channels, making it easier for Li ions to be inserted and extracted during charge and discharge. The addition of the carbon source can form an interlayer carbon network between the lithium iron phosphate manganese particles, making the dispersion between the particles better and denser. Using the method described in the present application can obtain a lithium iron phosphate manganese material with good crystallinity and uniform element distribution, and the conductivity, lithium ion diffusion rate, specific capacity and cycle stability of the product are all improved.

[0048] After reading and understanding the drawings and the detailed description, other aspects can be understood. Description of the Drawings

[0049] The drawings are used to provide a further understanding of the technical solutions herein, and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solutions herein, and do not constitute a limitation to the technical solutions herein.

[0050] Figure 1 、 Figure 2 and Figure 3 are all scanning electron microscope images of the lithium iron phosphate manganese obtained in Example 1;

[0051] Figure 4 is the scanning electron microscope image of the precursor powder obtained in step (2) of Example 1. Specific Embodiments

[0052] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present application and should not be regarded as a specific limitation to the present application.

[0053] Example 1

[0054] This example provides a lithium iron phosphate manganese and a method for preparing the same. The method includes:

[0055] (1) Mix 470 g of manganese phosphite, 400 g of iron phosphate, 202 g of lithium carbonate, 175 g of ammonium dihydrogen phosphate, 72 g of glucose, and 20 g of CTAB and add them to 5.6 L of an aqueous solution containing 1.24 wt% of lithium oxalate, such that the molar ratio of lithium element in lithium carbonate to lithium element in lithium oxalate is 4.01:1. Then stir evenly at room temperature for 30 min, and then use a sand mill for sanding until the average particle size reaches 380 nm to obtain a slurry;

[0056] (2) Perform ultrasonic spray drying on the slurry obtained in step (1), with an ultrasonic frequency of 25 kHz, and the drying conditions are an inlet temperature of 220 °C, an outlet temperature of 110 °C, and a feeding rate of 6 L / min to obtain a precursor powder; place the obtained precursor powder in a tube furnace and perform pre-sintering in a nitrogen atmosphere. The sintering conditions are a heating rate of 3 °C / min, holding at 400 °C for 2 h, and then increasing the temperature to 725 °C at a heating rate of 5 °C / min and holding for 6 h to obtain carbon-coated spherical lithium manganese 0.6 Fe 0.4 iron phosphate lithium of PO4.

[0057] Example 2

[0058] This example provides a lithium manganese iron phosphate and a method for preparing the same, and the method includes:

[0059] (1) Mix 1194 g of manganese oxalate dihydrate, 800 g of ferrous oxalate dihydrate, 398 g of lithium phosphate, 1014 g of ammonium dihydrogen phosphate, 140 g of glucose, and 40 g of PVP and add them to 14 L of an aqueous solution containing 0.56 wt% of lithium nitrate, such that the molar ratio of lithium element in lithium carbonate to lithium element in lithium nitrate is 9.47:1. Then stir evenly at room temperature for 60 min, and then use a sand mill for sanding until the average particle size reaches 400 nm to obtain a slurry;

[0060] (2) Perform ultrasonic spray drying on the slurry obtained in step (1), with an ultrasonic frequency of 25 kHz, and the drying conditions are an inlet temperature of 220 °C, an outlet temperature of 115 °C, and a feeding rate of 10 L / min to obtain a precursor powder; place the obtained precursor powder in a tube furnace and perform pre-sintering in a nitrogen atmosphere. The sintering conditions are a heating rate of 5 °C / min, holding at 380 °C for 2 h, and then increasing the temperature to 720 °C at a heating rate of 5 °C / min and holding for 6 h to obtain carbon-coated spherical lithium manganese iron phosphate.

[0061] Example 3

[0062] This example provides a lithium manganese iron phosphate and a method for preparing the same, and the method includes:

[0063] (1) Add 1000 g of manganese iron oxalate with a manganese to iron ratio of 8:2, 213 g of lithium carbonate, 548 g of phosphoric acid, 150 g of glucose, and 50 g of CTAB to 8 L of an aqueous solution containing 1.8 wt% lithium dihydrogen phosphate, such that the molar ratio of lithium in lithium carbonate to lithium in lithium dihydrogen phosphate is 4.16:1. Then stir at room temperature for 50 min to mix evenly, and then use a sand mill for sanding until the average particle size reaches 400 nm to obtain a slurry;

[0064] (2) Perform ultrasonic spray drying on the slurry obtained in step (1). The ultrasonic frequency is 25 kHz, and the drying conditions are an inlet temperature of 220 °C, an outlet temperature of 115 °C, and a feeding rate of 7 L / min to obtain a precursor powder. Place the obtained precursor powder in a tube furnace and perform pre-sintering under a nitrogen atmosphere. The sintering conditions are a heating rate of 5 °C / min and holding at 440 °C for 2 h, and then raising the temperature to 725 °C at a heating rate of 5 °C / min and holding for 6 h to obtain spherical lithium iron manganese phosphate coated with carbon.

[0065] Example 4

[0066] This example provides a lithium iron manganese phosphate and a method for preparing the same. The method includes:

[0067] (1) Add 800 g of ammonium manganese iron phosphate with a manganese to iron ratio of 1:1 (molecular formula: (NH4) 0.5 Mn 0.5 Fe 0.5 PO4), 153 g of lithium carbonate, 130 g of glucose, and 40 g of PVP to 5 L of an aqueous solution containing 0.48 wt% lithium hydroxide, stir to mix evenly, such that the molar ratio of lithium in lithium carbonate to lithium in lithium hydroxide is 4.13:1. Then stir at room temperature for 50 min to mix evenly, and then use a sand mill for sanding until the average particle size reaches 400 nm to obtain a slurry;

[0068] (2) Perform ultrasonic spray drying on the slurry obtained in step (1). The ultrasonic frequency is 25 kHz, and the drying conditions are an inlet temperature of 220 °C, an outlet temperature of 120 °C, and a feeding rate of 5 L / min to obtain a precursor powder. Place the obtained precursor powder in a tube furnace and perform pre-sintering under a nitrogen atmosphere. The sintering conditions are a heating rate of 5 °C / min and holding at 450 °C for 2 h, and then raising the temperature to 735 °C at a heating rate of 5 °C / min and holding for 6 h to obtain spherical lithium iron manganese phosphate coated with carbon.

[0069] Example 5

[0070] This embodiment provides a lithium iron manganese phosphate and a method for preparing the same. Except that the mass of lithium carbonate is adjusted from 202 g to 85.36 g, and the concentration of lithium oxalate solution is adjusted from 1.24 wt% to 3.9 wt%, such that the molar ratio of lithium element in lithium carbonate to lithium element in lithium oxalate is 0.54:1, other conditions are exactly the same as those in Example 1.

[0071] Example 6

[0072] This embodiment provides a lithium iron manganese phosphate and a method for preparing the same. Except that the mass of lithium carbonate is adjusted from 202 g to 128 g, and the concentration of lithium oxalate solution is adjusted from 1.24 wt% to 2.92 wt%, such that the molar ratio of lithium element in lithium carbonate to lithium element in lithium oxalate is 1.08:1, other conditions are exactly the same as those in Example 1.

[0073] Example 7

[0074] This embodiment provides a lithium iron manganese phosphate and a method for preparing the same. Except that the mass of lithium carbonate is adjusted from 202 g to 251.06 g, and the concentration of lithium oxalate solution is adjusted from 1.24 wt% to 0.115 wt%, such that the molar ratio of lithium element in lithium carbonate to lithium element in lithium oxalate is 53.76:1, other conditions are exactly the same as those in Example 1.

[0075] Example 8

[0076] This embodiment provides a lithium iron manganese phosphate and a method for preparing the same. Except that the mass of lithium carbonate is adjusted from 202 g to 253.53 g, and the concentration of lithium oxalate solution is adjusted from 1.24 wt% to 0.063 wt%, such that the molar ratio of lithium element in lithium carbonate to lithium element in lithium oxalate is 99.1:1, other conditions are exactly the same as those in Example 1.

[0077] Example 9

[0078] This embodiment provides a lithium iron manganese phosphate and a method for preparing the same. Except that the mass of lithium carbonate is adjusted from 202 g to 253.55 g, and the concentration of lithium oxalate solution is adjusted from 1.24 wt% to 0.058 wt%, such that the molar ratio of lithium element in lithium carbonate to lithium element in lithium oxalate is 107.65:1, other conditions are exactly the same as those in Example 1.

[0079] Example 10

[0080] This embodiment provides a lithium iron manganese phosphate and a method for preparing the same. Except that the ultrasonic frequency is adjusted from 25 kHz to 15 kHz, other conditions are exactly the same as those in Example 1.

[0081] Example 11

[0082] This example provides a lithium iron manganese phosphate and a method for preparing the same. Except that the ultrasonic frequency is adjusted from 25 kHz to 20 kHz, other conditions are exactly the same as those in Example 1.

[0083] Example 12

[0084] This example provides a lithium iron manganese phosphate and a method for preparing the same. Except that the ultrasonic frequency is adjusted from 25 kHz to 30 kHz, other conditions are exactly the same as those in Example 1.

[0085] Example 13

[0086] This example provides a lithium iron manganese phosphate and a method for preparing the same. Except that the ultrasonic frequency is adjusted from 25 kHz to 40 kHz, other conditions are exactly the same as those in Example 1.

[0087] Example 14

[0088] This example provides a lithium iron manganese phosphate and a method for preparing the same. Except that the ultrasonic frequency is adjusted from 25 kHz to 45 kHz, other conditions are exactly the same as those in Example 1.

[0089] Comparative Example 1

[0090] This comparative example provides a lithium iron manganese phosphate and a method for preparing the same. The method uses 252.5 g of lithium carbonate and uses 5.6 L of pure water to replace 5.6 L of an aqueous solution containing 1.24 wt% of lithium oxalate. Except for this, other conditions are exactly the same as those in Example 1.

[0091] Comparative Example 2

[0092] This comparative example provides a lithium iron manganese phosphate and a method for preparing the same. The method uses 497.5 g of lithium phosphate and uses 14 L of pure water to replace 14 L of an aqueous solution containing 0.56 wt% of lithium nitrate. Except for this, other conditions are exactly the same as those in Example 2.

[0093] Comparative Example 3

[0094] This comparative example provides a lithium iron manganese phosphate and a method for preparing the same. The method uses 266.25 g of lithium carbonate and uses 8 L of pure water to replace 8 L of an aqueous solution containing 1.8 wt% of lithium dihydrogen phosphate. Except for this, other conditions are exactly the same as those in Example 3.

[0095] Comparative Example 4

[0096] This comparative example provides a lithium iron manganese phosphate and a method for preparing the same. In this method, 191.25 g of lithium carbonate is used, and 5 L of pure water is used instead of 5 L of an aqueous solution containing 0.48 wt% lithium hydroxide. Except for this, other conditions are exactly the same as those in Example 4.

[0097] Comparative Example 5

[0098] This comparative example provides a lithium iron manganese phosphate and a method for preparing the same. In this method, centrifugal spray drying is used instead of ultrasonic spray drying in step (2), and there are no ultrasonic parameters. Except for this, other conditions are exactly the same as those in Example 1.

[0099] Comparative Example 6

[0100] This comparative example provides a lithium iron manganese phosphate and a method for preparing the same. In this method, spray drying is not used. Instead, the slurry obtained in step (1) is directly dried to obtain a precursor powder, and then the obtained precursor powder is placed in a tube furnace and pre-sintered under a nitrogen atmosphere. The sintering conditions are a heating rate of 3 °C / min, holding at 400 °C for 2 h, and then increasing the temperature to 725 °C at a heating rate of 5 °C / min and holding for 6 h to obtain carbon-coated spherical lithium iron manganese phosphate.

[0101] The lithium iron manganese phosphate obtained in the examples and comparative examples was made into a positive electrode sheet and assembled into a battery for discharge testing. The test results are shown in Table 1.

[0102] Table 1

[0103]

[0104]

[0105] It can be seen from Table 1 that:

[0106] (1) Comparing Examples 1-4 with Comparative Examples 1-4 respectively, the capacity of Comparative Examples 1-4 is worse than that of Examples 1-4;

[0107] The lithium iron manganese phosphate obtained in Examples 1-4 are all carbon-coated spherical particles with a particle size less than 5 μm. Among them, Figures 1-3 are field emission scanning electron microscope images of the lithium iron manganese phosphate obtained in Example 1 at different magnifications. It can be seen that the particle size is between 2 and 5 μm, and carbon is evenly coated on the surface of the particles, enhancing the electrochemical performance. In addition, carbon plays a role in inhibiting the growth of particles, making the particle size more concentrated. At the same time, carbon coating can also improve the conductivity of the composite material, helping to further enhance the performance;

[0108] (2) Comparing Example 1 with Comparative Example 5 and Comparative Example 6, the lithium iron manganese phosphate prepared by ultrasonic spray drying has better sphericity and better capacity performance;

[0109] Among them, the scanning electron microscope image of the precursor powder obtained after ultrasonic spray drying in Step (2) of Example 1 is as Figure 4 shown. It can be seen that the precursor powder particles are spherical, evenly distributed, and have good particle dispersibility. In contrast, the spray-dried particles of Comparative Example 5 are larger in particle size, and the precursor powder obtained in Comparative Example 6 has no spherical particles, which ultimately affects the performance of the lithium iron manganese phosphate obtained in Comparative Example 5 and Comparative Example 6;

[0110] (3) Comparing Example 1 with Examples 5-9, the lithium iron manganese phosphate with n(Li01):n(Li02)=(1-99):1 has better capacity performance and complete particle sphericity;

[0111] (4) Comparing Example 1 with Examples 10-14, within the ultrasonic parameter range of 20-40 kHz, the ultrasonic dispersion effect is better, and the electrical properties of the obtained lithium iron manganese phosphate are better.

[0112] The present application uses the above examples to illustrate the detailed structural features of the present application. However, the present application is not limited to the above detailed structural features, that is, it does not mean that the present application must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement to the present application, the equivalent replacement of the components selected in the present application, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present application.

[0113] The preferred embodiments of the present application have been described in detail above. However, the present application is not limited to the specific details in the above embodiments. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, and these simple modifications all belong to the protection scope of the present application.

[0114] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any suitable manner. To avoid unnecessary repetition, the present application will not separately describe various possible combination methods.

[0115] In addition, any combination can be made between various different embodiments of the present application, as long as it does not violate the idea of the present application, it should also be regarded as the content disclosed in the present application.

Claims

1. A method for preparing lithium iron manganese phosphate, which comprises the following steps: (1) Adding an iron source, a manganese source, a phosphorus source, a carbon source and a first lithium source to a dispersion system containing a second lithium source, and after mixing evenly, grinding to obtain a slurry; the first lithium source includes lithium phosphate and / or lithium carbonate; the second lithium source includes any one or a combination of at least two of lithium hydroxide, lithium citrate, lithium oxalate, lithium dihydrogen phosphate or lithium nitrate; the molar amount of lithium element in the first lithium source is n(Li01), and the molar amount of lithium element in the second lithium source is n(Li02), n(Li01):n(Li02)=(1-99):1; (2) Subjecting the slurry obtained in step (1) to ultrasonic spray drying to obtain a precursor powder, and then sintering to obtain lithium iron manganese phosphate.

2. The method according to claim 1, wherein The ultrasonic frequency of the ultrasonic spray drying in step (2) is 20-40 kHz.

3. The method according to claim 1, wherein The inlet air temperature of the ultrasonic spray drying in step (2) is 180-250 °C.

4. The method according to claim 1, wherein The outlet air temperature of the ultrasonic spray drying in step (2) is 90-140 °C.

5. The method according to claim 1, wherein The feeding speed of the ultrasonic spray drying in step (2) is 5-10 L / min.

6. The method according to claim 1, wherein The molar amount of iron element in the slurry obtained in step (1) is n(Fe) and the molar amount of manganese element is n(Mn), n(Fe):n(Mn)=(0.25-4):

1.

7. The method according to claim 1, wherein The sum of the molar amounts of iron element and manganese element in the slurry obtained in step (1) is n(M) and the molar amount of phosphorus element is n(P), n(P):n(M)=(0.92-1.05):

1.

8. The method according to claim 1, wherein The sum of the molar amounts of iron element and manganese element in the slurry obtained in step (1) is n(M) and the sum of the molar amounts of lithium element is n(Li), n(Li):n(M)=(0.99-1.1):

1.

9. The method according to claim 1, wherein The dispersion system in step (1) includes an aqueous solution and / or a suspension.

10. The method according to claim 1, wherein, The iron source in step (1) includes any one or a combination of at least two of iron phosphate, iron oxide, ferrous oxalate, iron nitrate or iron citrate.

11. The method according to claim 1, wherein, The manganese source in step (1) includes any one or a combination of at least two of manganese oxalate, manganous phosphate, manganese phosphate, manganese monoxide, manganese sesquioxide, manganese tetroxide, lithium iron manganese phosphate, ammonium lithium iron manganese phosphate or manganese nitrate.

12. The method according to claim 1, wherein, The phosphorus source in step (1) includes any one or a combination of at least two of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, lithium phosphate or phosphoric acid.

13. The method according to claim 1, wherein The carbon source in step (1) includes any one or a combination of at least two of glucose, citric acid, sucrose, phenolic resin, starch, polyaniline, lauric acid, β-cyclodextrin.

14. The method according to claim 1, wherein The carbon source in step (1) further includes a surfactant.

15. The method according to claim 14, wherein The surfactant includes any one or a combination of at least two of polyethylene glycol, dodecyl trimethyl ammonium bromide, cetyl trimethyl ammonium bromide, Tween-80, ethylenediaminetetraacetic acid, polyvinylpyrrolidone or dodecyl maltoside.

16. The method according to claim 1, wherein, The particle size of the slurry in step (1) is 300-600 nm.

17. The method according to claim 1, wherein, The grinding equipment in step (1) includes a sand mill.

18. The method according to claim 1, wherein, The mixing method in step (1) includes stirring at room temperature for 10-60 min.

19. The method according to claim 1, wherein, The sintering described in step (2) includes first performing pre-sintering and then raising the temperature for secondary sintering.

20. The method according to claim 19, wherein The temperature of the pre-sintering is 300-500 °C, and the time is 1-3 h.

21. The method according to claim 19, wherein The temperature of the secondary sintering is 650-830 °C, and the time is 6-12 h.

22. The method according to claim 1, wherein, The sintering described in step (2) is carried out in an inert atmosphere.

23. The method according to claim 22, wherein, The inert atmosphere includes any one or a combination of at least two of nitrogen, argon or helium.

24. Lithium iron manganese phosphate obtained by the method according to any one of claims 1-23.

25. A positive electrode sheet, wherein, The positive electrode sheet contains the lithium iron manganese phosphate described in claim 24.

26. A lithium-ion battery, wherein, The lithium ion battery contains the positive electrode sheet described in claim 25.

27. An electrical device, wherein, The electrical device contains the lithium ion battery described in claim 26.

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