Preparation method for lithium manganese iron phosphate positive electrode material, positive electrode material, and lithium-ion battery

Abstract

The present application provides a preparation method for a lithium manganese iron phosphate positive electrode material, a positive electrode material, and a lithium-ion battery. The preparation method comprises the following steps: (1) performing sand-milling treatment on first slurry to obtain second slurry; and (2) performing spray drying and three-stage sintering on the second slurry to obtain a lithium manganese iron phosphate positive electrode material, wherein the first slurry comprises a lithium source, a manganese source, an iron source, a phosphorus source, and a solvent. In the preparation method provided by the present application, the lithium manganese iron phosphate positive electrode material having a wide particle size distribution, high conductivity and high compaction density is obtained.

Description

Preparation method of lithium manganese iron phosphate cathode material, cathode material and lithium-ion battery Technical Field

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

[0002] Lithium-ion batteries have advantages such as long service life and environmental friendliness, and have been widely used in portable electronic devices and new energy vehicles. Among them, the cathode material largely determines the electrochemical performance, safety performance and manufacturing cost of lithium-ion batteries.

[0003] Lithium iron phosphate, an olivine-type cathode material, has the advantages of low price and high safety, and has become one of the cathode materials for lithium-ion batteries with large-scale commercial applications. Lithium manganese iron phosphate, another olivine-type cathode material, has a higher voltage platform and energy density than lithium iron phosphate, and is therefore considered an upgraded version of lithium iron phosphate.

[0004] The main problems in the preparation of lithium manganese iron phosphate cathode materials currently include low conductivity, low compaction density, and uneven micro-mixing of manganese and iron. To address these problems, existing technologies employ methods such as elemental doping and coating, reducing particle size, and increasing crystallinity. For example, CN110323434A discloses a method for preparing lithium manganese iron phosphate-carbon composite materials and the lithium manganese iron phosphate-carbon composite material. First, soluble manganese-containing phosphate, organic iron salt, manganese salt, and lithium salt are dissolved in deionized water according to the elemental molar ratio to obtain a precursor solution. This solution is then dried and granulated to obtain lithium manganese iron phosphate precursor powder. The precursor powder is then sintered under a protective atmosphere to obtain the sintered material, which is then pulverized, refined, and vacuum-packed to obtain the lithium manganese iron phosphate-carbon composite material. CN106486668A discloses a modified lithium manganese iron phosphate material, its preparation method, and its application. The material includes a magnesium-doped lithium manganese iron phosphate core layer and a boron-containing coating layer on the surface of the magnesium-doped lithium manganese iron phosphate core layer. A manganese source, phosphorus source, iron source, lithium source, magnesium source, and water are mixed to form an intermediate reaction solution. The intermediate reaction solution is then subjected to drying and pre-calcination treatments to obtain a core layer precursor. The core layer precursor is mixed with a boron source and then calcined to obtain the modified lithium manganese iron phosphate material. However, in the preparation process of the above-mentioned precursor material and cathode material, micro-agglomeration of the materials is prone to occur, leading to uneven mixing of Fe / Mn at the atomic level and poor electrochemical performance. The above method cannot effectively solve the key problems existing in lithium manganese iron phosphate materials.

[0005] Therefore, improving the compaction density and conductivity of lithium manganese iron phosphate cathode materials, and enhancing their electrochemical performance, is an urgent research focus. Summary of the Invention

[0006] This application provides a method for preparing lithium manganese iron phosphate cathode material, the cathode material itself, and a lithium-ion battery. The preparation method provided in this application yields lithium manganese iron phosphate cathode material with a wide particle size distribution, high conductivity, and high compaction density.

[0007] In a first aspect, this application provides a method for preparing a lithium manganese iron phosphate cathode material, the method comprising the following steps:

[0008] (1) The first slurry is subjected to sand milling to obtain the second slurry;

[0009] (2) The second slurry is spray-dried and sintered in three stages to obtain the lithium manganese iron phosphate cathode material;

[0010] The first slurry includes a lithium source, a manganese source, an iron source, a phosphorus source, and a solvent.

[0011] In the preparation method provided in this application, sand milling, spray drying, and three-stage sintering are used in combination. The precursor D50 is ground to an ultra-small particle size by sand milling. After subsequent spray drying and three-stage sintering, the internal resistance of the material is greatly reduced and the electrical conductivity of the material is improved. At the same time, the uniform distribution of elements in the precursor material is achieved, and the compaction density of the lithium manganese iron phosphate cathode material is improved. A lithium manganese iron phosphate cathode material with a wide distribution of particle size, high electrical conductivity, and high compaction density is obtained.

[0012] In this application, sand milling, spray drying and three-stage sintering must be coordinated to achieve a simultaneous increase in compaction density and electrical conductivity. Without any one of these conditions, it is impossible to achieve a simultaneous increase in compaction density and electrical conductivity.

[0013] The following are optional implementation methods of this application, but are not intended to limit the implementation methods provided in this application. Through the following optional implementation methods, the technical objectives and beneficial effects of this application can be better achieved and realized.

[0014] In one embodiment, the solid content of the first slurry is 20-45%, such as 20%, 25%, 30%, 35%, 40%, or 45%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0015] In one embodiment, the first slurry further includes a carbon source.

[0016] In this application, a carbon source is added to the first slurry. After sand milling and spray drying, the carbon source is uniformly distributed inside and on the surface of the precursor. Then, a uniformly distributed conductive carbon network is obtained through three-stage sintering, which further improves the conductivity of the lithium manganese iron phosphate cathode material. In addition, this application does not limit the specific type of carbon source. All types of carbon sources that can be used for liquid phase carbon coating are applicable to this application. For example, the carbon source includes organic carbon sources or inorganic carbon sources. The organic carbon source includes, but is not limited to, at least one of sucrose, glucose, fructose, lactose, starch, citric acid, tannic acid, polyvinyl chloride (PVC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN), or phenolic resin. The inorganic carbon source includes, but is not limited to, acetylene black, graphite, conductive carbon black (Super-P), or carbon nanotubes.

[0017] In one embodiment, the amount of carbon source added is 1 to 4 wt%, based on a total mass of 100 wt% of lithium, manganese, iron and phosphorus sources, such as 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt% or 4 wt%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] In one embodiment, the grinding speed in step (1) is 1500 to 3000 rpm, such as 1500 rpm, 1800 rpm, 2000 rpm, 2300 rpm, 2500 rpm, 2800 rpm or 3000 rpm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] In one embodiment, the D50 of the solid particles in the second slurry is 120-300 nm, such as 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, 270 nm, 280 nm, 290 nm or 300 nm, etc., and can be selected as 120-150 nm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] In this application, the D50 of the solid particles (i.e., precursor materials) in the second slurry was adjusted to 120-300 nm through sand milling. This adjustment is beneficial for reducing the internal resistance of the material during the three-stage sintering process, thereby improving the electrical conductivity of the material. It is also beneficial for improving the compaction density. Further adjustment to 120-150 nm can better improve the compaction density and electrical conductivity of the lithium manganese iron phosphate cathode material.

[0021] In one embodiment, the temperature of the feed inlet of the spray dryer in step (2) is 160 to 240°C, for example, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C or 240°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] In one embodiment, the temperature of the outlet of the spray dryer in step (2) is 80 to 140°C, such as 80°C, 90°C, 100°C, 110°C, 120°C, 130°C or 140°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] In one embodiment, the three-stage sintering includes sequentially performing a first-stage sintering, a second-stage sintering, and a third-stage sintering.

[0024] In one embodiment, the heating rates of the first sintering stage, the second sintering stage, and the third sintering stage are each independently 1 to 10 °C / min, for example, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, or 10 °C / min, but are not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0025] In one embodiment, the sintering temperature of the first sintering stage is 120 to 350°C, such as 120°C, 125°C, 150°C, 175°C, 200°C, 225°C, 250°C, 275°C, 300°C, 325°C, or 350°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] In one embodiment, the sintering time of the first sintering stage is 1 to 6 hours, such as 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] In one embodiment, the sintering temperature of the second sintering stage is 550 to 650°C, such as 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C, or 650°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] In one embodiment, the sintering time of the second sintering stage is 1 to 10 hours, such as 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] In one embodiment, the sintering temperature of the third sintering stage is 780 to 830°C, such as 780°C, 790°C, 800°C, 810°C, 820°C, or 830°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] In one embodiment, the sintering time of the third sintering stage is 0.5 to 3 hours, such as 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0031] The three-stage sintering method provided in this application uses a three-stage heating sintering method, which is more conducive to improving the compaction density and conductivity of lithium manganese iron phosphate cathode material.

[0032] In one embodiment, the product after the three-stage sintering is pulverized.

[0033] In this application, the pulverization process is a conventional implementation method. Those skilled in the art can make adaptive adjustments according to actual needs. Specifically, this application provides a pulverization method:

[0034] In an environment with humidity <50%, the grinding process is carried out at a grinding pressure of 600-800 kPa, such as 600 kPa, 650 kPa, 700 kPa, 750 kPa or 800 kPa, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] As an optional implementation, the preparation method includes the following steps:

[0036] (1) The first slurry is milled at a speed of 1500-3000 rpm to obtain the second slurry, wherein the D50 of the solid particles in the second slurry is 120-150 nm;

[0037] (2) The second slurry is spray-dried, and the spray-dried product is sintered in the first stage at 120-350°C for 1-6 hours, then heated to 550-650°C for the second stage of sintering for 1-10 hours, and then heated to 780-830°C for the third stage of sintering for 0.5-3 hours to obtain the lithium manganese iron phosphate cathode material.

[0038] The first slurry includes a lithium source, a manganese source, an iron source, a phosphorus source, a carbon source, and a solvent.

[0039] It should be noted that in the preparation method provided in the present application, the specific types of substances of the raw materials for preparation and the specific addition ratios of the raw materials for preparation are conventional implementation manners, and those skilled in the art can adaptively select and adjust according to actual needs.

[0040] Specifically, in the present application, the addition amounts of the lithium source, manganese source, iron source, and phosphorus source are adjusted according to the chemical general formula of LiMn 1-x Fe x PO4, where 0 < x ≤ 1, such as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable, and it can be optionally 0 < x ≤ 0.5;

[0041] Optionally, the lithium source includes but is not limited to at least one of lithium carbonate, lithium hydroxide, lithium oxalate, or lithium nitrate;

[0042] Optionally, the valence of manganese in the manganese source can be +2 or +3, as long as it does not affect the progress of the reaction. For example, it includes but is not limited to at least one of manganese sulfate, manganese(III) oxide, manganese(II) chloride, manganese(II) bromide, manganese(II) nitrate, manganese(II) perchlorate, manganese(II) sulfate, or manganese(II) acetate;

[0043] Optionally, the valence of iron in the iron source can be +2 or +3, as long as it does not affect the progress of the reaction. For example, it includes but is not limited to at least one of iron(III) oxide, iron(II) chloride, iron(II) bromide, iron(II) fluorosilicate, iron(II) nitrate, iron(II) perchlorate, iron(II) sulfate, or iron(II) acetate;

[0044] In the present application, here it can be changed to that when the manganese source and iron source are in a high valence state, a reducing agent can be additionally added during the reaction process to prevent substances from being oxidized, such as adding ascorbic acid, etc.;

[0045] Optionally, the phosphorus source includes but is not limited to at least one of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate;

[0046] Optionally, the solvent includes water.

[0047] In the second aspect, the present application provides a lithium manganese iron phosphate cathode material, and the lithium manganese iron phosphate cathode material is prepared by the preparation method as described in the first aspect.

[0048] In the third aspect, the present application further provides a lithium-ion battery, and the lithium-ion battery includes the lithium manganese iron phosphate cathode material as described in the second aspect.

[0049] Compared with the prior art, the present application has the following beneficial effects:

[0050] In the preparation method provided in this application, sand milling, spray drying, and three-stage sintering are used in combination. The precursor D50 is ground to an ultra-small particle size by sand milling. After subsequent spray drying and three-stage sintering, the internal resistance of the material is greatly reduced and the electrical conductivity of the material is improved. At the same time, the uniform distribution of elements in the precursor material is achieved, and the compaction density of the lithium manganese iron phosphate cathode material is improved. A lithium manganese iron phosphate cathode material with a wide distribution of particle size, high electrical conductivity, and high compaction density is obtained. Attached Figure Description

[0051] Figure 1 shows the test results of the electronic conductivity of the lithium manganese iron phosphate cathode material provided in Example 1. Detailed Implementation

[0052] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms “comprising” and “having” and any variations thereof in this application are intended to cover non-exclusive inclusion.

[0054] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order, or primary and secondary relationship of the indicated technical features.

[0055] Example 1

[0056] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material, the method comprising the following steps:

[0057] (1) Lithium carbonate, manganese trioxide, ferric oxide, ammonium phosphate and tannic acid are dispersed in water to obtain a first slurry, wherein Li:Mn:Fe:P=1.02:0.6:0.4:1, and the total mass of lithium carbonate, manganese trioxide, ferric oxide and ammonium phosphate is 100wt%, and the amount of tannic acid added is 1.5wt%, to obtain a first slurry with a solid content of 35%;

[0058] (2) The first slurry obtained in step (1) is ground to D50 = 150nm by a sand mill with a speed of 2300rpm to obtain a uniformly dispersed second slurry;

[0059] (3) The second slurry obtained in step (2) is spray-dried and granulated to obtain a solid mixture, wherein the inlet temperature is 230°C and the outlet temperature is 95°C.

[0060] (4) The solid mixture obtained in step (3) is packed into a graphite sagger and compacted. Then the sagger containing the solid mixture is placed in an atmosphere furnace for calcination. The first stage of sintering is carried out at room temperature of 25°C, and the temperature is increased to 320°C at 5°C / min and held for 2 hours. The second stage of sintering is carried out at 2°C / min and the temperature is increased to 610°C / min and held for 5 hours. The third stage of sintering is carried out at 10°C / min and the temperature is increased to 800°C and held for 1 hour to obtain the sintered material.

[0061] (5) The sintered material obtained in step (4) is pulverized by airflow to a density of D50 = 1.2 μm and Span ≥ 1.8 (Span = (D90 - D10) / D50), wherein the airflow pulverization pressure is 700 kPa. This yields the lithium manganese iron phosphate cathode material, with carbon material coated on the surface and distributed inside the material. The resulting cathode material has the chemical formula LiMn. 0.6 Fe 0.4 PO4 / C.

[0062] Example 2

[0063] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material, the method comprising the following steps:

[0064] (1) Lithium carbonate, manganese trioxide, ferric oxide, ammonium phosphate and tannic acid are dispersed in water to obtain a first slurry, wherein Li:Mn:Fe:P=1.02:0.6:0.4:1, and the total mass of lithium carbonate, manganese trioxide, ferric oxide and ammonium phosphate is 100wt%, and the amount of tannic acid added is 2wt%, to obtain a first slurry with a solid content of 20%;

[0065] (2) The first slurry obtained in step (1) is ground to D50 = 120 nm by a sand mill at a speed of 1500 rpm to obtain a uniformly dispersed second slurry;

[0066] (3) The second slurry obtained in step (2) is spray-dried and granulated to obtain a solid mixture, wherein the inlet temperature is 160°C and the outlet temperature is 80°C.

[0067] (4) The solid mixture obtained in step (3) is packed into a graphite sagger and compacted. Then the sagger containing the solid mixture is placed in an atmosphere furnace for calcination. The first stage of sintering is carried out at room temperature of 25°C, and the temperature is increased to 130°C at 3°C / min and held for 6 hours. The second stage of sintering is carried out at 5°C / min and the temperature is increased to 550°C / min and held for 10 hours. The third stage of sintering is carried out at 5°C / min and the temperature is increased to 780°C and held for 3 hours to obtain the sintered material.

[0068] (5) The sintered material obtained in step (4) is pulverized by airflow to a density of D50 = 1.2 μm and Span ≥ 1.8 (Span = (D90 - D10) / D50), wherein the airflow pulverization pressure is 600 kPa. This yields the lithium manganese iron phosphate cathode material, with carbon material coated on the surface and distributed inside the material. The resulting cathode material has the chemical formula LiMn. 0.6 Fe 0.4 PO4 / C.

[0069] Example 3

[0070] This embodiment provides a method for preparing lithium manganese iron phosphate cathode material, the method comprising the following steps:

[0071] (1) Lithium carbonate, manganese trioxide, ferric oxide, ammonium phosphate and tannic acid are dispersed in water to obtain a first slurry, wherein Li:Mn:Fe:P=1.02:0.6:0.4:1, and the total mass of lithium carbonate, manganese trioxide, ferric oxide and ammonium phosphate is 100wt%, and the amount of tannic acid added is 3wt%, to obtain a first slurry with a solid content of 45%;

[0072] (2) The first slurry obtained in step (1) is ground to D50 = 135nm by a sand mill at a speed of 3000rpm to obtain a uniformly dispersed second slurry;

[0073] (3) The second slurry obtained in step (2) is spray-dried and granulated to obtain a solid mixture, wherein the inlet temperature is 200°C and the outlet temperature is 100°C.

[0074] (4) The solid mixture obtained in step (3) is packed into a graphite sagger and compacted. Then, the sagger containing the solid mixture is placed in an atmosphere furnace for calcination. The first stage sintering, the second stage sintering and the third stage sintering are carried out in sequence. The first stage sintering is carried out at room temperature of 25℃, and the temperature is increased to 350℃ at 5℃ / min and held for 1h. The second stage sintering is carried out at 2℃ / min and the temperature is increased to 650℃ / min and held for 1h. The third stage sintering is carried out at 10℃ / min and the temperature is increased to 830℃ and held for 0.5h to obtain the sintered material.

[0075] (5) The sintered material obtained in step (4) is pulverized by airflow to a density of D50 = 1.2 μm and Span ≥ 1.8 (Span = (D90 - D10) / D50), wherein the airflow pulverization pressure is 700 kPa. This yields the lithium manganese iron phosphate cathode material, with carbon material coated on the surface and distributed inside the material. The resulting cathode material has the chemical formula LiMn. 0.6 Fe 0.4 PO4 / C.

[0076] Example 4

[0077] The difference between this embodiment and embodiment 1 is that in step (2) of this embodiment, it is ground to D50 = 300nm by sand milling.

[0078] The remaining preparation methods and parameters are consistent with those in Example 1.

[0079] Example 5

[0080] The difference between this embodiment and embodiment 1 is that the grinding speed in step (2) of this embodiment is 1000 rpm.

[0081] The remaining preparation methods and parameters are consistent with those in Example 1.

[0082] Example 6

[0083] The difference between this embodiment and embodiment 1 is that in step (4) of this embodiment, the sintering temperature of the first sintering stage is 450℃.

[0084] The remaining preparation methods and parameters are consistent with those in Example 1.

[0085] Example 7

[0086] The difference between this embodiment and embodiment 1 is that in step (4) of this embodiment, the sintering temperature of the second sintering stage is 500℃.

[0087] The remaining preparation methods and parameters are consistent with those in Example 1.

[0088] Example 8

[0089] The difference between this embodiment and embodiment 1 is that in step (4) of this embodiment, the sintering temperature of the third sintering stage is 900℃.

[0090] The remaining preparation methods and parameters are consistent with those in Example 1.

[0091] Comparative Example 1

[0092] The difference between this comparative example and Example 1 is that this comparative example does not perform sand milling; instead, the first slurry is directly spray-dried.

[0093] The remaining preparation methods and parameters are consistent with those in Example 1.

[0094] Comparative Example 2

[0095] The difference between this comparative example and Example 1 is that this comparative example uses oven drying instead of spray drying, that is, the second slurry after sand milling is dried in an oven.

[0096] The remaining preparation methods and parameters are consistent with those in Example 1.

[0097] Comparative Example 3

[0098] The difference between this comparative example and Example 1 is that in step (4) of this comparative example, the temperature is directly raised to 800°C at a heating rate of 10°C / min and held for 1 hour to obtain the sintered material, that is, the first stage of sintering is not performed, nor is the second stage of sintering.

[0099] The remaining preparation methods and parameters are consistent with those in Example 1.

[0100] Comparative Example 4

[0101] The difference between this comparative example and Example 1 is that in step (4) of this comparative example, the first stage of sintering is not performed, and the second and third stages of sintering are performed directly.

[0102] The remaining preparation methods and parameters are consistent with those in Example 1.

[0103] Comparative Example 5

[0104] The difference between this comparative example and Example 1 is that in step (4) of this comparative example, the second stage of sintering is not performed, only the first stage of sintering and the third stage of sintering are performed.

[0105] The remaining preparation methods and parameters are consistent with those in Example 1.

[0106] The compaction density and conductivity of the lithium manganese iron phosphate cathode materials provided in Examples 1-8 and Comparative Examples 1-5 were tested:

[0107] Compacted density: Weigh 1g of the sample to be tested, fill it into the groove of the compaction density meter, apply a pressure of 3T, hold the pressure for 30s, and record the powder compaction density of the material at 3T.

[0108] Electrical conductivity: The powder impedance of the lithium manganese iron phosphate cathode active materials prepared in the above examples and comparative examples was tested using the four-probe method at 25°C.

[0109] Figure 1 shows the test results of the electronic conductivity of the lithium manganese iron phosphate cathode material provided in Example 1. As can be seen from Figure 1, after sand milling, spray drying, and three-stage sintering, the electronic conductivity of the modified lithium manganese iron phosphate after carbon coating with tannic acid as the carbon source increased from 10% to 10% of the pure phase. -13 The S / cm ratio increased to 81.3 mS / cm, and the compaction density also reached 2.61 g / cm³. 3 .

[0110] The test results are shown in Table 1.

[0111] Table 1

[0112] Lithium-ion batteries were prepared using the lithium manganese iron phosphate cathode materials provided in Examples 1-8 and Comparative Examples 1-5, respectively.

[0113] (1) Preparation of positive electrode sheet

[0114] 0.3000g of polyvinylidene fluoride binder (PVDF) was weighed into 10.8g of N-methylpyrrolidone (NMP), stirred, and completely dissolved. Then, 2.4000g of lithium manganese iron phosphate cathode material (from Examples 1-8 and Comparative Examples 1-5, respectively) and 0.3000g of carbon black conductive agent (SP) were added, and stirred until a paste was obtained. The mass ratio of lithium manganese iron phosphate-carbon composite material, polyvinylidene fluoride binder (PVDF), and carbon black conductive agent (SP) was 8:1:1. The paste was evenly coated onto aluminum foil using a coater, and then placed in a forced-air drying oven at 60°C for 3.0h. After drying, it was transferred to a vacuum drying oven and vacuum dried at 120°C for 6.0h. The dried cathode sheet was rolled and punched to obtain a circular sheet with a diameter of 16.0mm, which served as the cathode sample sheet. Additionally, four uncoated blank aluminum foil discs were rolled and punched for later use.

[0115] (2) Assembly of CR2032 button cells

[0116] Using the prepared positive electrode sheet as the positive electrode, the lithium metal sheet as the negative electrode, the PE-PP composite film as the battery separator, and 1.0 mol / L LiPF6 / (DMC+DMC) as the electrolyte, with the EC to DMC volume ratio of 1:1, a CR2032 coin cell was assembled.

[0117] (3) Performance testing:

[0118] The charging and discharging voltage was 2.0V to 4.3V. The coin cells were subjected to cyclic charging and discharging tests at charging and discharging rates of 0.1C, 0.5C and 1.0C in sequence. The test results are shown in Table 2.

[0119] Table 2

[0120] In summary, the preparation method provided in this application, through the synergistic combination of sand milling, spray drying, and three-stage sintering, grinds the precursor D50 to an ultra-small particle size through sand milling, and then sprays and sinters, significantly reduces the internal resistance of the material and improves its electrical conductivity. At the same time, it also achieves a uniform distribution of elements in the precursor material, increases the compaction density of the lithium manganese iron phosphate cathode material, and obtains a lithium manganese iron phosphate cathode material with a wide particle size distribution, high electrical conductivity, and high compaction density.

[0121] The applicant declares that the above description is only a specific implementation of this application, but the protection scope of this application is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application fall within the protection and disclosure scope of this application.

Claims

1. A method for preparing a lithium manganese iron phosphate cathode material, comprising the following steps: (1) The first slurry is subjected to sand milling to obtain the second slurry; (2) The second slurry is spray-dried and sintered in three stages to obtain the lithium manganese iron phosphate cathode material; The first slurry includes a lithium source, a manganese source, an iron source, a phosphorus source, and a solvent.

2. The production method according to claim 1, wherein The solid content of the first slurry is 20-45%; Optionally, the first slurry may further include a carbon source.

3. The production method according to claim 1 or 2, wherein The grinding speed in step (1) is 1500-3000 rpm; Optionally, the D50 of the solid particles in the second slurry is 120-300 nm, or optionally 120-150 nm.

4. The production process according to any one of claims 1 to 3, wherein The temperature of the feed inlet of the spray dryer in step (2) is 160-240℃; Optionally, the temperature of the outlet of the spray dryer in step (2) is 80 to 140°C.

5. The production process according to any one of claims 1 to 4, wherein The three-stage sintering process includes sequentially performing a first-stage sintering, a second-stage sintering, and a third-stage sintering.

6. The production method according to claim 5, wherein The heating rates of the first sintering stage, the second sintering stage, and the third sintering stage are each independently 1 to 10 °C / min; Optionally, the sintering temperature of the first sintering stage is 120–350°C, and the sintering time of the first sintering stage is 1–6 hours. Optionally, the sintering temperature of the second stage sintering is 550-650℃, and the sintering time of the second stage sintering is 1-10h; Optionally, the sintering temperature of the third sintering stage is 780–830°C, and the sintering time of the third sintering stage is 0.5–3 hours.

7. The method of making according to any one of claims 1-6, wherein, The product after the three-stage sintering is then pulverized.

8. The production method according to claim 1, wherein The preparation method includes the following steps: (1) The first slurry is milled at a speed of 1500-3000 rpm to obtain the second slurry, wherein the D50 of the solid particles in the second slurry is 120-150 nm; (2) The second slurry is spray-dried, and the spray-dried product is sintered in the first stage at 120-350°C for 1-6 hours, then heated to 550-650°C for the second stage of sintering for 1-10 hours, and then heated to 780-830°C for the third stage of sintering for 0.5-3 hours to obtain the lithium iron manganese phosphate cathode material. The first slurry includes a lithium source, a manganese source, an iron source, a phosphorus source, a carbon source, and a solvent.

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

10. A lithium-ion battery comprising the lithium manganese iron phosphate cathode material as described in claim 9.

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