Lithium manganese iron phosphate and preparation method thereof

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses lithium manganese iron phosphate and a preparation method thereof.The preparation method comprises the following steps that SP01, a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source, a doping additive and water are mixed and ground into slurry; sP02, the slurry is subjected to screening and grading after being subjected to atomization drying; sP03, mixing the dried undersize material with a coating additive; sP04, putting the coated material into a kiln for sintering treatment; according to the method, fine powder does not exist in the obtained finished product lithium manganese iron phosphate, the graded material is coated and then sintered, and a double coating layer of a lithium ion conductor material and conductive carbon is formed on the surface of the lithium manganese iron phosphate material, so that the conductivity of the material can be improved; the direct contact between the material and electrolyte can be better protected, and the dissolution of manganese is avoided, so that the rate capability, the cycling stability and the safety of the material are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and more specifically, to lithium manganese iron phosphate and a preparation method thereof. Background Art

[0002] Lithium iron phosphate (LFP) cathode material is widely used in the new energy vehicle market and energy storage field due to its safety, environmental protection, and low raw material prices. The low energy density of lithium iron phosphate cathode materials limits its application in power batteries. An important reason restricting the improvement of lithium iron phosphate energy density is the low voltage platform. Lithium manganese iron phosphate (LMFP) is an upgraded alternative material for lithium iron phosphate. The high voltage characteristics of manganese in lithium manganese iron phosphate make lithium manganese iron phosphate have a higher voltage platform than lithium iron phosphate, thereby breaking the current upper limit of battery energy density. In addition, compared with another ternary material, lithium manganese iron phosphate has a long cycle life, good thermal stability, high safety, and no explosion risk.

[0003] However, lithium iron manganese phosphate can only move in a one-dimensional channel, resulting in a relatively low lithium ion diffusion rate and poor rate performance. In addition, the Jahn-Teller effect promotes manganese precipitation, resulting in a decrease in cycle life and reduced cycle stability. The acid produced by the decomposition of the electrolyte further corrodes the manganese ions in the positive electrode material, accelerates the Mn3+ disproportionation reaction process, and promotes the dissolution of Mn2+ and Mn4+ in the electrolyte. These shortcomings make it impossible for lithium iron manganese phosphate to fully exert its electrochemical properties, and therefore limit its further large-scale application. In view of this, we propose a lithium iron manganese phosphate and a preparation method thereof to solve the above problems. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides a lithium manganese iron phosphate and a preparation method thereof to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides a method for preparing lithium manganese iron phosphate, comprising the following steps: SP01: lithium source, iron source, manganese source, phosphorus source, carbon source and doping additives are mixed with water and ground into slurry; SP02: Sieving and grading after atomization and drying of the slurry; SP03: Dry the undersize material and mix it with the coating additive; SP04: The coated materials are put into the kiln for sintering; SP05: The sintered materials are batch mixed, screened and iron removed to obtain the finished product of lithium iron manganese phosphate.

[0006] As a preferred technical solution of the present invention, the iron source includes one or more of the following: Ferrous oxalate, ferrous phosphate, ferromanganese oxide, ferromanganese phosphate; The manganese source includes one or more of the following: Manganese carbonate, manganese dioxide, manganese tetraoxide, ferromanganese oxide, ferromanganese phosphate, manganese oxalate; The phosphorus source includes one or more of the following: Iron phosphate, ferromanganese phosphate, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid; The lithium source includes one or more of the following: Lithium carbonate, lithium hydroxide, lithium nitrate; The carbon source includes one or more of the following: Sucrose, glucose, fructose, citric acid, phenolic resin, polyvinyl alcohol, polyethylene glycol, starch, urea, carbon black, acetylene black, graphite, graphene, conductive carbon tube; The doping additive is an oxide containing one or more elements of Mg, Zn, Ni, Co, V, Ti, Zr, W, La, Al, Y, Sr, and F; The coating additives include a carbon source, a doping additive and a lithium ion conductor.

[0007] As a preferred technical solution of the present invention, the lithium ion conductor includes Li2ZrO3, LiNbO3, Li4Ti5O12, Li2TiO3, Li3VO4, LiSnO3, Li2SiO3, LiAlO2, Li3PO4, LLZO, LLTO, and LATP.

[0008] As a preferred technical solution of the present invention, the particle size of the material slurry after grinding is 0.05um-0.5um.

[0009] As a preferred technical solution of the present invention, the screening and grading equipment is an ultrasonic vibrating screen or a swinging screen. Single-layer or multi-layer screens can be used for screening and grading as needed. The mesh number of the screening and grading equipment is 325-1250 mesh.

[0010] As a preferred technical solution of the present invention, the coating method is dry coating using a high-speed mixer, a plowshare mixer, a cone mixer or an oblique mixer.

[0011] As a preferred technical solution of the present invention, the kiln sintering system is to heat the temperature to 500°C-800°C at a heating rate of 0.5°C / min-5°C / min and keep the temperature for 6h-12h in an inert atmosphere.

[0012] As a preferred technical solution of the present invention, the carbon content of the lithium iron manganese phosphate finished product is 0.5%-5%, the doping additive content is 0.05%-0.5%, and the coating additive content is 0.1%-1%.

[0013] To achieve the above and other related purposes, the present invention provides a lithium manganese iron phosphate prepared by the above preparation method.

[0014] To achieve the above and other related purposes, the present invention provides a battery positive electrode plate, which is made of the above-mentioned lithium manganese iron phosphate as a material.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention can obtain an ideal particle size and particle size distribution by screening and grading the dry material and matching sieves of different mesh sizes, so that the obtained finished product lithium iron manganese phosphate contains no fine powder. The graded material is first coated and then sintered to form a double coating layer of lithium ion conductor material and conductive carbon on the surface of the lithium iron manganese phosphate material, which can not only improve the conductive performance of the material, but also better protect the material from direct contact with the electrolyte, avoid the dissolution of manganese, thereby improving the rate performance, cycle stability and safety of the material.

[0016] Compared with the process of secondary grinding, drying and then sintering, the present invention does not require an additional secondary sintering process. Compared with using air flow milling to obtain a corresponding particle size, there is no problem of excessive crushing during the air flow milling process leading to an increase in the amount of fine powder or shedding of the surface carbon coating layer.

[0017] The present invention obtains lithium manganese iron phosphate materials of different sizes by matching sieves with different mesh sizes. In the process of preparing the positive electrode sheet of the battery, the ratio of large and small particles can be adjusted as needed to improve the compaction density of the positive electrode sheet of the battery, so that the positive electrode sheet of the battery has excellent charge and discharge capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a scanning electron microscope schematic diagram of the finished product lithium iron manganese phosphate obtained in Example 1 of the present invention; Figure 2 This is a scanning electron microscope schematic diagram of the finished product lithium iron manganese phosphate obtained in Example 2 of the present invention; Figure 3 This is a schematic diagram of a scanning electron microscope of the finished product lithium iron manganese phosphate obtained in Comparative Example 1 of the present invention; Figure 4 This is a schematic diagram of a 0.1C charge-discharge curve when the finished product lithium iron manganese phosphate obtained in Example 1 of the present invention is subjected to a performance test; Figure 5 The present invention is a schematic block diagram of the steps of a method for preparing lithium manganese iron phosphate. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] like Figure 5 As shown, the present invention provides a method for preparing lithium manganese iron phosphate, comprising the following steps: SP01: lithium source, iron source, manganese source, phosphorus source, carbon source and doping additives are mixed with water and ground into slurry; SP02: Sieving and grading after atomization and drying of the slurry; SP03: Dry the undersize material and mix it with the coating additive; SP04: The coated materials are put into the kiln for sintering; SP05: The sintered materials are batch mixed, screened and iron removed to obtain the finished product of lithium iron manganese phosphate.

[0021] Wherein, the iron source includes one or more of ferrous oxalate, ferric phosphate, ferromanganese oxide, and ferromanganese phosphate; the manganese source includes one or more of manganese carbonate, manganese dioxide, manganese tetraoxide, ferromanganese oxide, ferromanganese phosphate, and manganese oxalate; the phosphorus source includes one or more of ferric phosphate, ferromanganese phosphate, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid; the lithium source includes one or more of lithium carbonate, lithium hydroxide, and lithium nitrate; the carbon source includes one or more of sucrose, glucose, fructose, citric acid, phenolic resin, polyvinyl alcohol, polyethylene glycol, starch, urea, carbon black, acetylene black, graphite, graphene, and conductive carbon tubes; Among them, the doping additive is an oxide containing one or more elements of Mg, Zn, Ni, Co, V, Ti, Zr, W, La, Al, Y, Sr, and F; the coating additive includes a carbon source, a doping additive, and a lithium ion conductor.

[0022] Among them, lithium ion conductors include Li2ZrO3, LiNbO3, Li4Ti5O12, Li2TiO3, Li3VO4, LiSnO3, Li2SiO3, LiAlO2, Li3PO4, LLZO, LLTO, and LATP.

[0023] Among them, the particle size of the material slurry after grinding is 0.05um-0.5um.

[0024] Among them, the screening and grading equipment is an ultrasonic vibration screen or a swing screen. According to the needs, a single-layer or multi-layer screen can be used for screening and grading. The mesh number of the screening and grading equipment is 325 mesh-1250 mesh.

[0025] Among them, the coating method is dry coating using a high-speed mixer, a plowshare mixer, a cone mixer or an inclined mixer.

[0026] Among them, the kiln sintering system is to heat up to 500℃-800℃ at a heating rate of 0.5℃ / min-5℃ / min and keep warm for 6h-12h in an inert atmosphere.

[0027] Among them, the carbon content in the finished lithium manganese iron phosphate product is 0.5%-5%, the doping additive content is 0.05%-0.5%, and the coating additive content is 0.1%-1%. Example

[0028] This example is used to illustrate the preparation method of lithium manganese iron phosphate of the present invention and the lithium manganese iron phosphate obtained thereby.

[0029] (1) 603.28 g of iron phosphate, 457.62 g of manganese tetraoxide, 162.56 g of lithium carbonate, 633.97 g of lithium dihydrogen phosphate, 90 g of glucose, and 15 g of magnesium oxide were wet-grinded and mixed into a slurry of 0.3 μm using a sand mill; (2) The slurry is granulated by a centrifugal spray dryer to obtain a lithium iron manganese phosphate precursor, and then sieved and graded by an ultrasonic 400-mesh ultrasonic vibrating screen to obtain a dry material; (3) The dried material is mixed with 0.8% polyethylene glycol, 1.5% conductive carbon tubes, 0.2% tungsten trioxide and 0.5% LLTO by a high-speed mixer to form a coating material; (4) heating the coated material to 700°C in a nitrogen atmosphere at a heating rate of 0.8°C / min and maintaining the temperature for 8 hours, and obtaining lithium manganese iron phosphate material after sintering; (5) The sintered materials are batch mixed, screened and iron removed to obtain finished lithium iron manganese phosphate. Example

[0030] This example is used to illustrate the preparation method of lithium manganese iron phosphate of the present invention and the lithium manganese iron phosphate obtained thereby.

[0031] (1) 1500 g of ferromanganese phosphate, 412.62 g of lithium hydroxide monohydrate, 110 g of glucose, and 8 g of vanadium pentoxide were wet-ground and mixed in a sand mill to a particle size of 0.2 μm; (2) The slurry is granulated by a centrifugal spray dryer to obtain a lithium iron manganese phosphate precursor, and a three-layer ultrasonic vibration screen with 400 mesh, 600 mesh and 800 mesh is used to screen and grade the dried material; (3) The dried materials of each mesh size were mixed with 1.5% conductive carbon tubes, 0.5% tungsten trioxide and 0.8% LiAlO2 by a high-speed mixer to form a coating material; (4) heating the coated material to 750°C in a nitrogen atmosphere at a heating rate of 1.5°C / min and maintaining the temperature for 8 hours, and obtaining lithium manganese iron phosphate material after sintering; (5) The sintered materials are weighed in a ratio of 5:3:2, and the 400-mesh, 600-mesh and 800-mesh sieved materials are batch mixed, sieved and iron removed to obtain finished lithium iron manganese phosphate. Example

[0032] (1) 603.28g of iron phosphate, 457.62g of manganese tetraoxide, 162.56g of lithium carbonate, 633.97g of lithium dihydrogen phosphate, 90g of glucose, and 10g of tungsten trioxide were wet-grinded and mixed into a slurry of 0.3 um using a sand mill; (2) The slurry is granulated by a centrifugal spray dryer to obtain a lithium iron manganese phosphate precursor, and then sieved and graded by an ultrasonic 400-mesh ultrasonic vibrating screen to obtain a dry material; (3) The dried material is mixed with 0.8% polyethylene glycol, 1.5% conductive carbon tubes, 0.2% tungsten trioxide and 0.5% LLTO by a high-speed mixer to form a coating material; (4) heating the coated material to 800°C in a nitrogen atmosphere at a heating rate of 0.8°C / min and maintaining the temperature for 12 hours, and obtaining lithium manganese iron phosphate material after sintering; (5) The sintered materials are batch mixed, screened and iron removed to obtain finished lithium iron manganese phosphate.

[0033] Comparative Example 1: Compared with the first embodiment, the difference is that there is no screening, grading and coating process, and a process of crushing materials is added after sintering.

[0034] Comparative Example 2: Compared with Example 1, the difference is that there is no screening, grading and coating process, but after the first drying, the temperature is increased to 550°C in a nitrogen atmosphere at a heating rate of 0.8°C / min and kept warm for 4 hours, the sintered material is mixed with 0.8% polyethylene glycol, 1.5% conductive carbon tubes, 0.2% tungsten trioxide and 0.5% LLTO into a slurry and then dried for a second time, and the temperature is increased to 700°C in a nitrogen atmosphere at a heating rate of 0.8°C / min and kept warm for 8 hours, and then the finished product of lithium iron manganese phosphate is obtained after secondary sintering and crushing.

[0035] like Figure 1 , Figure 2 as well as Figure 3 As shown, it can be seen that the ideal particle size and particle size distribution can be obtained by screening and grading the dry material and matching the sieves with different mesh sizes, so that there is no fine powder in the finished product lithium manganese iron phosphate.

[0036] In order to verify the advancement of the embodiments of the present invention, the following performance tests were conducted on the above-mentioned embodiments 1, 2, and 3: The above materials were mixed with SP, PVDF and carbon nanotubes in a ratio of 96:0.5:3:0.5 to prepare the positive electrode sheet. Metal lithium was used as the negative electrode sheet. The half-cell was assembled in a conventional manner. The half-cell was then tested with a half-cell test system. The charge and discharge test voltage was 2.0V-4.5V. The test results are shown in the following table: Table 1 Serial number 0.1C discharge capacity (mAh / g) 0.5C discharge capacity (mAh / g) 1.0C discharge capacity (mAh / g) 0.5C / 0.1C(%) 1.0C / 0.1C(%) 1.0C 200 cycles retention rate (%) Resistivity (Ω·cm) Example 1 153.3 147.1 141.6 96.0% 92.4% 98.9% 24 Example 2 153.0 145.1 136.9 94.8% 89.5% 98.1% 35 Example 3 151.4 143.5 137.1 94.8% 90.6% 97.9% 26 Comparative Example 1 137.6 124.6 108.8 90.6% 79.1% 88.9% 134 Comparative Example 2 149.7 140.5 130.0 93.9% 86.8% 93.4% 49 From Table 1 and Figure 4 It can be seen that the discharge capacity, cycle retention rate and conductivity of the finished lithium iron manganese phosphate obtained in Example 1, Example 2 and Example 3 are higher than those in Comparative Example 1 and Comparative Example 2. The classified materials are first coated and then sintered to form a double coating layer of lithium ion conductor material and conductive carbon on the surface of the lithium iron manganese phosphate material, which not only improves the conductivity of the material, but also better protects the material from direct contact with the electrolyte, avoids the dissolution of manganese, and improves the rate performance, cycle stability and safety of the material.

[0037] The present invention provides a battery positive electrode plate, which is made of the lithium manganese iron phosphate obtained in the above embodiment as a material, and in the preparation process of the battery positive electrode plate, the ratio of large and small particles can be arbitrarily adjusted as needed to improve the compaction density of the battery positive electrode plate, so that the battery positive electrode plate has excellent charge and discharge capacity.

[0038] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0039] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing lithium manganese iron phosphate, characterized in that: The following steps are involved: SP01: lithium source, iron source, manganese source, phosphorus source, carbon source and doping additives are mixed with water and ground into slurry; SP02: Sieving and grading after atomization and drying of the slurry; SP03: Dry the undersize material and mix it with the coating additive; SP04: The coated materials are put into the kiln for sintering; SP05: The sintered materials are batch mixed, screened and iron removed to obtain the finished product of lithium iron manganese phosphate.

2. The method for preparing lithium manganese iron phosphate according to claim 1, characterized in that: The iron source includes one or more of the following: Ferrous oxalate, ferrous phosphate, ferromanganese oxide, ferromanganese phosphate; The manganese source includes one or more of the following: Manganese carbonate, manganese dioxide, manganese tetraoxide, ferromanganese oxide, ferromanganese phosphate, manganese oxalate; The phosphorus source includes one or more of the following: Iron phosphate, ferromanganese phosphate, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid; The lithium source includes one or more of the following: Lithium carbonate, lithium hydroxide, lithium nitrate; The carbon source includes one or more of the following: Sucrose, glucose, fructose, citric acid, phenolic resin, polyvinyl alcohol, polyethylene glycol, starch, urea, carbon black, acetylene black, graphite, graphene, conductive carbon tube; The doping additive is an oxide containing one or more elements of Mg, Zn, Ni, Co, V, Ti, Zr, W, La, Al, Y, Sr, and F; The coating additives include the aforementioned carbon source, doping additives and lithium ion conductors.

3. A method for preparing lithium manganese iron phosphate according to claim 2, characterized in that: The lithium ion conductors include Li2ZrO3, LiNbO3, Li4Ti5O12, Li2TiO3, Li3VO4, LiSnO3, Li2SiO3, LiAlO2, Li3PO4, LLZO, LLTO, and LATP.

4. The method for preparing lithium manganese iron phosphate according to claim 1, characterized in that: The particle size of the material slurry after grinding is 0.05um-0.5um.

5. The method for preparing lithium manganese iron phosphate according to claim 1, characterized in that: The screening and grading equipment is an ultrasonic vibration screen or a swing screen, and the mesh number of the screening and grading equipment is 325 meshes-1250 meshes.

6. The method for preparing lithium manganese iron phosphate according to claim 1, characterized in that: The coating method is dry coating using a high-speed mixer, a plowshare mixer, a cone mixer or an inclined mixer.

7. The method for preparing lithium manganese iron phosphate according to claim 1, characterized in that: The kiln sintering system is to heat the temperature to 500°C-800°C at a heating rate of 0.5°C / min-5°C / min and keep the temperature for 6h-12h in an inert atmosphere.

8. The method for preparing lithium manganese iron phosphate according to claim 1, characterized in that: The carbon content of the lithium manganese iron phosphate finished product is 0.5%-5%, the doping additive content is 0.05%-0.5%, and the coating additive content is 0.1%-1%.

9. A lithium manganese iron phosphate, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. A positive electrode plate for a battery, characterized in that: The method is prepared from the lithium manganese iron phosphate as claimed in claim 9.

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