A high-compaction lithium iron manganese phosphate material and a preparation method thereof

Abstract

The application discloses a high-compaction lithium manganese iron phosphate material and a preparation method thereof, and the preparation method comprises the following steps: mixing a lithium source, an iron source, a manganese source, a phosphorus source, a carbon source and water to prepare material; performing spray drying and calcination on the material to obtain a precursor material; crushing the precursor material to obtain a large-particle-size precursor and a small-particle-size precursor; mixing the small-particle-size precursor, gelatin, flaky graphene and water, then adding a crosslinking agent to perform reaction to form a gel material; performing vacuum drying on the gel material, and crushing the gel material to obtain a coated precursor; mixing the large-particle-size precursor and the coated precursor, and sintering to obtain the high-compaction lithium manganese iron phosphate material. The high-compaction lithium manganese iron phosphate material has high-compaction density and excellent electrochemical performance, can be applied to high-energy-density and high-rate-performance batteries, and has great application prospect.

Description

Technical Field

[0001] This invention belongs to the field of cathode material technology, specifically relating to a high-pressure lithium manganese iron phosphate material and its preparation method. Background Technology

[0002] Lithium-ion batteries are devices that charge and discharge by repeatedly inserting and extracting lithium ions. Currently, the positive electrode materials used in batteries are mainly ternary materials and lithium iron phosphate. However, the working voltage of lithium iron phosphate material at about 3.4V is difficult to meet the requirements of high energy density. Therefore, lithium manganese iron phosphate material, which has the same structure as lithium iron phosphate, has attracted widespread attention due to its high voltage platform.

[0003] Lithium manganese iron phosphate combines the high safety and high cycle stability of lithium iron phosphate with the high voltage platform of lithium manganese phosphate. However, lithium manganese iron phosphate still has the disadvantage of low compaction density, which limits its application in high energy density and high rate performance batteries.

[0004] Therefore, how to prepare lithium manganese iron phosphate materials with both high density and excellent electrochemical performance is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a high-density lithium manganese iron phosphate material and its preparation method, which simultaneously possesses high density and excellent electrochemical performance.

[0006] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:

[0007] A method for preparing high-pressure lithium manganese iron phosphate material includes the following steps:

[0008] The material is prepared by mixing lithium source, iron source, manganese source, phosphorus source, carbon source and water;

[0009] The material is spray-dried and calcined to obtain the precursor material;

[0010] The precursor material is crushed to obtain large-particle-size precursors and small-particle-size precursors.

[0011] Small-particle-size precursors, gelatin, sheet graphene, and water are mixed, and then a crosslinking agent is added to react and form a gel material.

[0012] The gel material was vacuum dried and crushed to obtain the coated precursor.

[0013] Large-particle-size precursors and coated precursors are mixed and sintered to obtain high-pressure lithium manganese iron phosphate material.

[0014] In one or more embodiments of the present invention, the D50 of the large-particle-size precursor is 1.0 μm-1.5 μm, and the D50 of the small-particle-size precursor is 0.1 μm-0.5 μm.

[0015] In one or more embodiments of the present invention, the mass ratio of the small-particle-size precursor, gelatin, layered graphene, and water is (20-30):(2-3):(0.1-0.3):100; and / or,

[0016] The mass ratio of the large-particle-size precursor to the coated small-particle-size precursor is (1-3):1.

[0017] In one or more embodiments of the present invention, the sheet diameter of the graphene sheet is 100nm-300nm.

[0018] In one or more embodiments of the present invention, the gel material is vacuum dried and crushed to obtain particles to be processed;

[0019] Polyvinyl alcohol and polyvinylpyrrolidone are dissolved in water at a mass ratio of (3-5):1 to prepare a treatment solution with a total mass concentration of 10%-20%.

[0020] With a mass ratio of treatment liquid to particles to be treated of (8-10):1, the treatment liquid is sprayed onto the particles to be treated, and after drying, a coated precursor is obtained.

[0021] In one or more embodiments of the present invention, the drying conditions are as follows: first drying at 35℃-40℃ for 50min-70min, and then drying at 50℃-55℃ for 2h-3h.

[0022] In one or more embodiments of the present invention, the vacuum drying conditions for the gel material are: a vacuum degree of 0.08 MPa-0.09 MPa, a temperature of 30°C-35°C, and a time of 8-10 hours; and / or,

[0023] The gel material was vacuum dried and then crushed by ball milling at a speed of 100 r / min-200 r / min for 3-5 hours; and / or,

[0024] The calcination temperature is 400℃-500℃, and the time is 3h-5h; and / or,

[0025] The sintering temperature is 800℃-870℃, and the time is 10h-12h.

[0026] In one or more embodiments of the present invention, the lithium source, manganese source, iron source, and phosphorus source, calculated as lithium atoms, manganese atoms, iron atoms, and phosphorus atoms, have a molar ratio of 1:x:(1-x):1, 0.6≦x≦0.9;

[0027] The amount of carbon source used is 1%-3% of the total mass of iron, lithium, manganese and phosphorus sources.

[0028] In one or more embodiments of the present invention, the iron source is at least one selected from ferric phosphate, ferric oxide, ferric nitrate, and iron powder; and / or,

[0029] The lithium source is at least one selected from lithium carbonate, lithium acetate, lithium nitrate, and lithium dihydrogen phosphate; and / or,

[0030] The manganese source is at least one of manganese carbonate and manganese oxalate; and / or,

[0031] The carbon source is at least one of sucrose, glucose, dextrin, and chitosan.

[0032] Another specific embodiment of the present invention provides the following technical solution:

[0033] A high-density lithium manganese iron phosphate material is prepared by the above-mentioned high-density lithium manganese iron phosphate material preparation method.

[0034] Compared with existing technologies, this invention uses a blend of large and small particles to reduce interparticle voids and improve the compaction density of lithium manganese iron phosphate material. Simultaneously, gelatin and sheet-like graphene are used to coat the small-diameter precursor, and vacuum drying yields a precursor with a dense surface coating structure. Sintering then significantly increases the compaction density of the lithium manganese iron phosphate material, effectively improving its electrochemical performance and demonstrating great promise for applications in high-energy-density, high-rate-performance batteries. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0036] A specific embodiment of the present invention provides a method for preparing high-pressure lithium manganese iron phosphate material, comprising the following steps:

[0037] Step 1: Mix lithium source, iron source, manganese source, phosphorus source, carbon source and water to form a material, and spray dry and calcine the material to obtain the precursor material.

[0038] Specifically, the iron source is at least one of iron phosphate, iron oxide, iron nitrate and iron powder; the lithium source is at least one of lithium carbonate, lithium acetate, lithium nitrate and lithium dihydrogen phosphate; the manganese source is at least one of manganese carbonate and manganese oxalate; and the carbon source is at least one of sucrose, glucose, dextrin and chitosan. The phosphorus source is lithium dihydrogen phosphate.

[0039] In terms of usage, the molar ratio of lithium source, manganese source, iron source, and phosphorus source is 1:x:(1-x):1, 0.6≦x≦0.9, calculated as lithium atoms, manganese atoms, iron atoms, and phosphorus atoms. The amount of carbon source used is 1%-3% of the total mass of iron source, lithium source, manganese source, and phosphorus source.

[0040] Furthermore, the spray drying process uses conventional methods, with calcination conditions of 400℃-500℃ and 3-5 hours.

[0041] Step 2: Crush the precursor material to obtain large-particle-size precursors and small-particle-size precursors.

[0042] Specifically, the D50 of the large-particle-size precursor is 1.0μm-1.5μm, and the D50 of the small-particle-size precursor is 0.1μm-0.5μm. Breaking the precursor material into particles of different sizes allows the small-particle-size precursor to fill the gaps between the large-particle-size precursor during the subsequent mixing and sintering process, increasing the mixing density. This results in a high compaction density in the sintered lithium manganese iron phosphate material, effectively improving the battery's energy density.

[0043] Step 3: Mix the small-particle-size precursor, gelatin, sheet graphene and water, then add a crosslinking agent to react and form a gel material; vacuum dry the gel material and break it to obtain the coated precursor.

[0044] Specifically, firstly, a gel formed from gelatin is used to encapsulate a small-diameter precursor, creating a gel layer on its surface. During vacuum drying, the gel layer shrinks due to water loss, resulting in a denser structure. During this process, sheet-like graphene is compressed and, together with the gelatin, forms a dense coating layer on the surface of the small-diameter precursor. In the subsequent sintering process, the gelatin and sheet-like graphene carbonize, forming a dense carbon layer on the surface of the small-diameter precursor. This further improves the compaction density and optimizes conductivity when forming lithium manganese iron phosphate materials.

[0045] Secondly, sheet-like graphene was selected so that it could better coat the surface of small-diameter precursor particles and form a dense coating layer with gelatin. At the same time, the carbon layer formed by graphene can effectively improve the conductivity of manganese phosphate materials and obtain better cycle performance.

[0046] Furthermore, in terms of dosage, the mass ratio of small-particle-size precursor, gelatin, layered graphene, and water is (20-30): (2-3): (0.1-0.3): 100.

[0047] Furthermore, the sheet-like graphene has a sheet diameter of 100nm-300nm. By controlling the sheet diameter of the sheet-like graphene, it can better encapsulate small-diameter precursors.

[0048] Furthermore, the vacuum drying conditions are: vacuum degree of 0.08MPa-0.09MPa, temperature of 30℃-35℃, and time of 8h-10h. By controlling the temperature and time, the gel layer can gradually lose moisture and become more compact. If the temperature is too high or the time is too long, the gel layer is prone to excessive water loss and cracking, which will reduce the cycle performance of the lithium manganese iron phosphate material.

[0049] Furthermore, after vacuum drying, the gel material is crushed using ball milling at a speed of 100-200 rpm for 3-5 hours. Using appropriate speed and time to crush the gel material achieves the desired crushing effect while ensuring the integrity of the resulting coated precursor structure.

[0050] Step 4: After vacuum drying and crushing the gel material, the particles to be treated are obtained; polyvinyl alcohol and polyvinylpyrrolidone are dissolved in water at a mass ratio of (3-5):1 to prepare a treatment solution with a total mass concentration of 10%-20%.

[0051] With a mass ratio of treatment liquid to particles to be treated of (8-10):1, the treatment liquid is sprayed onto the particles to be treated, and after drying, a coated precursor is obtained.

[0052] Specifically, the combined use of polyvinyl alcohol and polyvinylpyrrolidone can, on the one hand, form a uniform coating layer on the surface of the particles to be treated, which not only ensures the formation of uniform and fine particles during sintering, but also forms a uniform and dense carbon layer. Together with the carbon layer formed by the gel material, it can effectively improve the cycle performance of lithium manganese iron phosphate.

[0053] In addition, the amino groups contained in the gel layer formed by gelatin react with polyvinyl alcohol and polyvinylpyrrolidone, improving the stability of the coating layer formed by the treatment solution on the surface of the gel layer, thereby helping to form a uniform and dense carbon layer.

[0054] In addition, by controlling the concentration of the treatment solution, the mass ratio between the treatment solution and the particles to be treated, and by drying after spraying, the gel layer is prevented from absorbing too much water, which would affect the density of the layer structure.

[0055] Furthermore, the drying conditions are as follows: first dry at 35℃-40℃ for 50min-70min, then dry at 50℃-55℃ for 2h-3h.

[0056] Step 5: Mix the large-particle-size precursor and the coated precursor, and sinter to obtain high-pressure lithium manganese iron phosphate material.

[0057] Specifically, the mass ratio of large-particle-size precursor to coated small-particle-size precursor is (1-3):1. By controlling the ratio of the two, it is helpful to obtain high-density lithium manganese iron phosphate material through sintering.

[0058] Another specific embodiment of the present invention provides a high-pressure lithium manganese iron phosphate material, which is prepared by the above-mentioned high-pressure lithium manganese iron phosphate material preparation method.

[0059] The present invention will be further described in detail below with reference to specific embodiments.

[0060] All raw materials used in this invention are commercially available, with some of them sourced from polyvinyl alcohol, Sigma-Aldrich, 360627.

[0061] Example 1

[0062] With a molar ratio of lithium, manganese, iron, and phosphorus atoms of 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate, and mix them thoroughly to prepare the raw material. Separately, prepare glucose and water, with the mass of glucose being 1% of the raw material and the mass of water being 2.5 times that of the raw material.

[0063] The above raw materials were mixed and ground with 0.5 mm zirconium balls for 2 hours, spray-dried, and then calcined at 400 °C for 5 hours under a nitrogen atmosphere. The calcined product was ground to obtain a large-particle-size precursor with a D50 of 1.0 μm and a small-particle-size precursor with a D50 of 0.3 μm.

[0064] Small-particle-size precursor, gelatin, sheet graphene and water were mixed in a mass ratio of 20:2:0.2:100, and then glutaraldehyde was added. The mass ratio of gelatin to glutaraldehyde was 100:1. The mixture was reacted at 35°C for 1 hour to obtain a gel material.

[0065] The gel material was vacuum dried at a vacuum level of 0.08 MPa and a temperature of 30°C for 8 hours. The vacuum-dried gel material was then ball-milled at 100 r / min for 4 hours to obtain the coated precursor.

[0066] Large-particle-size precursor and coated precursor were mixed at a mass ratio of 1:1 and sintered at 800℃ for 10 h under a nitrogen atmosphere to obtain high-pressure lithium manganese iron phosphate material.

[0067] Example 2

[0068] With a molar ratio of lithium, manganese, iron, and phosphorus atoms of 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate, and mix them thoroughly to prepare the raw material. Separately, prepare glucose and water, with the mass of glucose being 2% of the raw material and the mass of water being 2.5 times that of the raw material.

[0069] The above raw materials were mixed and ground with 0.5 mm zirconium balls for 2 hours, spray-dried, and then calcined at 500 °C for 3 hours under a nitrogen atmosphere. The calcined product was ground to obtain a large-particle-size precursor with a D50 of 1.3 μm and a small-particle-size precursor with a D50 of 0.1 μm.

[0070] Small-particle-size precursor, gelatin, sheet graphene and water were mixed in a mass ratio of 25:2:0.1:100, and then glutaraldehyde was added. The mass ratio of gelatin to glutaraldehyde was 100:1. The mixture was reacted at 35°C for 1 hour to obtain a gel material.

[0071] The gel material was vacuum dried at a vacuum level of 0.09 MPa and a temperature of 35°C for 10 hours. The vacuum-dried gel material was then ball-milled at 150 r / min for 5 hours to obtain the coated precursor.

[0072] Large-particle-size precursor and coated precursor were mixed at a mass ratio of 2:1 and sintered at 850°C for 12 hours under a nitrogen atmosphere to obtain high-pressure lithium manganese iron phosphate material.

[0073] Example 3

[0074] With a molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms of 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate, and mix them thoroughly to prepare the raw material. Separately, prepare glucose and water, with the mass of glucose being 3% of the raw material and the mass of water being 2.5 times that of the raw material.

[0075] The above raw materials were mixed and ground with 0.5 mm zirconium balls for 2 hours, spray-dried, and then calcined at 450 °C for 5 hours under a nitrogen atmosphere. The calcined product was ground to obtain a large-particle-size precursor with a D50 of 1.5 μm and a small-particle-size precursor with a D50 of 0.5 μm.

[0076] Small-particle-size precursor, gelatin, sheet graphene and water were mixed in a mass ratio of 30:3:0.3:100, and then glutaraldehyde was added. The mass ratio of gelatin to glutaraldehyde was 100:1. The mixture was reacted at 35°C for 1 hour to obtain a gel material.

[0077] The gel material was vacuum dried at a vacuum level of 0.08 MPa and a temperature of 30°C for 8 hours. The vacuum-dried gel material was then ball-milled at 200 r / min for 4 hours to obtain the coated precursor.

[0078] Large-particle-size precursor and coated precursor were mixed at a mass ratio of 1:1 and sintered at 870°C for 10 hours under a nitrogen atmosphere to obtain high-pressure lithium manganese iron phosphate material.

[0079] Example 4

[0080] With a molar ratio of lithium, manganese, iron, and phosphorus atoms of 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate, and mix them thoroughly to prepare the raw material. Separately, prepare glucose and water, with the mass of glucose being 1% of the raw material and the mass of water being 2.5 times that of the raw material.

[0081] The above raw materials were mixed and ground with 0.5 mm zirconium balls for 2 hours, spray-dried, and then calcined at 400 °C for 5 hours under a nitrogen atmosphere. The calcined product was ground to obtain a large-particle-size precursor with a D50 of 1.0 μm and a small-particle-size precursor with a D50 of 0.3 μm.

[0082] Small-particle-size precursor, gelatin, sheet graphene and water were mixed in a mass ratio of 20:2:0.2:100, and then glutaraldehyde was added. The mass ratio of gelatin to glutaraldehyde was 100:1. The mixture was reacted at 35°C for 1 hour to obtain a gel material.

[0083] The gel material was vacuum dried at a vacuum level of 0.08 MPa and a temperature of 30°C for 8 hours. The vacuum-dried gel material was then ball-milled at 100 r / min for 4 hours to obtain the particles to be processed.

[0084] Polyvinyl alcohol was dissolved in water at 80°C to prepare a 10% (w / w) treatment solution. The treatment solution was sprayed onto the particles to be treated at a mass ratio of 8:1. The particles were then dried at 35°C for 60 min and then at 50°C for 2 h to obtain the coated precursor.

[0085] Large-particle-size precursor and coated precursor were mixed at a mass ratio of 1:1 and sintered at 800℃ for 10 h under a nitrogen atmosphere to obtain high-pressure lithium manganese iron phosphate material.

[0086] Example 5

[0087] With a molar ratio of lithium, manganese, iron, and phosphorus atoms of 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate, and mix them thoroughly to prepare the raw material. Separately, prepare glucose and water, with the mass of glucose being 1% of the raw material and the mass of water being 2.5 times that of the raw material.

[0088] The above raw materials were mixed and ground with 0.5 mm zirconium balls for 2 hours, spray-dried, and then calcined at 400 °C for 5 hours under a nitrogen atmosphere. The calcined product was ground to obtain a large-particle-size precursor with a D50 of 1.0 μm and a small-particle-size precursor with a D50 of 0.3 μm.

[0089] Small-particle-size precursor, gelatin, sheet graphene and water were mixed in a mass ratio of 20:2:0.2:100, and then glutaraldehyde was added. The mass ratio of gelatin to glutaraldehyde was 100:1. The mixture was reacted at 35°C for 1 hour to obtain a gel material.

[0090] The gel material was vacuum dried at a vacuum level of 0.08 MPa and a temperature of 30°C for 8 hours. The vacuum-dried gel material was then ball-milled at 100 r / min for 4 hours to obtain the particles to be processed.

[0091] Polyvinylpyrrolidone K30 was dissolved in water to prepare a 10% (w / w) treatment solution. The treatment solution was sprayed onto the particles to be treated at a mass ratio of 8:1. The particles were then dried at 35°C for 60 min and then at 50°C for 2 h to obtain the coated precursor.

[0092] Large-particle-size precursor and coated precursor were mixed at a mass ratio of 1:1 and sintered at 800℃ for 10 h under a nitrogen atmosphere to obtain high-pressure lithium manganese iron phosphate material.

[0093] Example 6

[0094] With a molar ratio of lithium, manganese, iron, and phosphorus atoms of 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate, and mix them thoroughly to prepare the raw material. Separately, prepare glucose and water, with the mass of glucose being 1% of the raw material and the mass of water being 2.5 times that of the raw material.

[0095] The above raw materials were mixed and ground with 0.5 mm zirconium balls for 2 hours, spray-dried, and then calcined at 400 °C for 5 hours under a nitrogen atmosphere. The calcined product was ground to obtain a large-particle-size precursor with a D50 of 1.0 μm and a small-particle-size precursor with a D50 of 0.3 μm.

[0096] Small-particle-size precursor, gelatin, sheet graphene and water were mixed in a mass ratio of 20:2:0.2:100, and then glutaraldehyde was added. The mass ratio of gelatin to glutaraldehyde was 100:1. The mixture was reacted at 35°C for 1 hour to obtain a gel material.

[0097] The gel material was vacuum dried at a vacuum level of 0.08 MPa and a temperature of 30°C for 8 hours. The vacuum-dried gel material was then ball-milled at 100 r / min for 4 hours to obtain the particles to be processed.

[0098] Polyvinyl alcohol and polyvinylpyrrolidone K30 were mixed in a mass ratio of 3:1. Polyvinyl alcohol was first dissolved in water at 80℃, and after cooling to room temperature, polyvinylpyrrolidone K30 was added and mixed thoroughly to prepare a treatment solution with a total mass concentration of 10%. The treatment solution was sprayed onto the particles to be treated at a mass ratio of 8:1. The particles were then dried at 35℃ for 60 min, followed by drying at 50℃ for 2 h to obtain the coated precursor.

[0099] Large-particle-size precursor and coated precursor were mixed at a mass ratio of 1:1 and sintered at 800℃ for 10 h under a nitrogen atmosphere to obtain high-pressure lithium manganese iron phosphate material.

[0100] Example 7

[0101] With a molar ratio of lithium, manganese, iron, and phosphorus atoms of 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate, and mix them thoroughly to prepare the raw material. Separately, prepare glucose and water, with the mass of glucose being 1% of the raw material and the mass of water being 2.5 times that of the raw material.

[0102] The above raw materials were mixed and ground with 0.5 mm zirconium balls for 2 hours, spray-dried, and then calcined at 400 °C for 5 hours under a nitrogen atmosphere. The calcined product was ground to obtain a large-particle-size precursor with a D50 of 1.0 μm and a small-particle-size precursor with a D50 of 0.3 μm.

[0103] Small-particle-size precursor, gelatin, sheet graphene and water were mixed in a mass ratio of 20:2:0.2:100, and then glutaraldehyde was added. The mass ratio of gelatin to glutaraldehyde was 100:1. The mixture was reacted at 35°C for 1 hour to obtain a gel material.

[0104] The gel material was vacuum dried at a vacuum level of 0.08 MPa and a temperature of 30°C for 8 hours. The vacuum-dried gel material was then ball-milled at 100 r / min for 4 hours to obtain the particles to be processed.

[0105] Polyvinyl alcohol and polyvinylpyrrolidone K30 were mixed in a mass ratio of 4:1. Polyvinyl alcohol was first dissolved in water at 80℃, cooled to room temperature, and then polyvinylpyrrolidone K30 was added and mixed thoroughly to prepare a treatment solution with a total mass concentration of 15%. The treatment solution was sprayed onto the particles to be treated at a mass ratio of 10:1. The particles were then dried at 40℃ for 60 min and then at 55℃ for 2 h to obtain the coated precursor.

[0106] Large-particle-size precursor and coated precursor were mixed at a mass ratio of 1:1 and sintered at 800℃ for 10 h under a nitrogen atmosphere to obtain high-pressure lithium manganese iron phosphate material.

[0107] Example 9

[0108] With a molar ratio of lithium, manganese, iron, and phosphorus atoms of 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate, and mix them thoroughly to prepare the raw material. Separately, prepare glucose and water, with the mass of glucose being 1% of the raw material and the mass of water being 2.5 times that of the raw material.

[0109] The above raw materials were mixed and ground with 0.5 mm zirconium balls for 2 hours, spray-dried, and then calcined at 400 °C for 5 hours under a nitrogen atmosphere. The calcined product was ground to obtain a large-particle-size precursor with a D50 of 1.0 μm and a small-particle-size precursor with a D50 of 0.3 μm.

[0110] Small-particle-size precursor, gelatin, sheet graphene and water were mixed in a mass ratio of 20:2:0.2:100, and then glutaraldehyde was added. The mass ratio of gelatin to glutaraldehyde was 100:1. The mixture was reacted at 35°C for 1 hour to obtain a gel material.

[0111] The gel material was vacuum dried at a vacuum level of 0.08 MPa and a temperature of 30°C for 8 hours. The vacuum-dried gel material was then ball-milled at 100 r / min for 4 hours to obtain the particles to be processed.

[0112] Polyvinyl alcohol and polyvinylpyrrolidone K30 were mixed in a mass ratio of 5:1. Polyvinyl alcohol was first dissolved in water at 80℃, cooled to room temperature, and then polyvinylpyrrolidone K30 was added and mixed thoroughly to prepare a treatment solution with a total mass concentration of 20%. The treatment solution was sprayed onto the particles to be treated at a mass ratio of 9:1. The particles were then dried at 35℃ for 70 min and then at 50℃ for 3 h to obtain the coated precursor.

[0113] Large-particle-size precursor and coated precursor were mixed at a mass ratio of 1:1 and sintered at 800℃ for 10 h under a nitrogen atmosphere to obtain high-pressure lithium manganese iron phosphate material.

[0114] Comparative Example 1

[0115] With a molar ratio of lithium, manganese, iron, and phosphorus atoms of 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate, and mix them thoroughly to prepare the raw material. Separately, prepare glucose and water, with the mass of glucose being 1% of the raw material and the mass of water being 2.5 times that of the raw material.

[0116] The above raw materials were mixed and ground with 0.5 mm zirconium balls for 2 hours, spray-dried, and then calcined at 400 °C for 5 hours under a nitrogen atmosphere. The calcined product was ground to obtain a large-particle-size precursor with a D50 of 1.0 μm and a small-particle-size precursor with a D50 of 0.3 μm.

[0117] Large-particle-size precursors and small-particle-size precursors were mixed at a mass ratio of 1:1 and sintered at 800℃ for 10 hours under a nitrogen atmosphere to obtain high-pressure lithium manganese iron phosphate material.

[0118] Comparative Example 2

[0119] With a molar ratio of lithium, manganese, iron, and phosphorus atoms of 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate, and mix them thoroughly to prepare the raw material. Separately, prepare glucose and water, with the mass of glucose being 1% of the raw material and the mass of water being 2.5 times that of the raw material.

[0120] The above raw materials were mixed and ground with 0.5 mm zirconium balls for 2 hours, spray-dried, and then calcined at 400 °C for 5 hours under a nitrogen atmosphere. The calcined product was ground to obtain a large-particle-size precursor with a D50 of 1.0 μm and a small-particle-size precursor with a D50 of 0.3 μm.

[0121] Small-particle-size precursor, gelatin and water were mixed in a mass ratio of 20:2:100, and then glutaraldehyde was added in a mass ratio of 100:1. The mixture was reacted at 35°C for 1 hour to obtain a gel material.

[0122] The gel material was vacuum dried at a vacuum level of 0.08 MPa and a temperature of 30°C for 8 hours. The vacuum-dried gel material was then ball-milled at 100 r / min for 4 hours to obtain the coated precursor.

[0123] Large-particle-size precursor and coated precursor were mixed at a mass ratio of 1:1 and sintered at 800℃ for 10 h under a nitrogen atmosphere to obtain high-pressure lithium manganese iron phosphate material.

[0124] Comparative Example 3

[0125] With a molar ratio of lithium, manganese, iron, and phosphorus atoms of 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate, and mix them thoroughly to prepare the raw material. Separately, prepare glucose and water, with the mass of glucose being 1% of the raw material and the mass of water being 2.5 times that of the raw material.

[0126] The above raw materials were mixed and ground with 0.5 mm zirconium balls for 2 hours, spray-dried, and then calcined at 400 °C for 5 hours under a nitrogen atmosphere. The calcined product was ground to obtain a large-particle-size precursor with a D50 of 1.0 μm and a small-particle-size precursor with a D50 of 0.3 μm.

[0127] Small-particle-size precursor, gelatin, sheet graphene and water were mixed in a mass ratio of 20:2:0.2:100, and then glutaraldehyde was added. The mass ratio of gelatin to glutaraldehyde was 100:1. The mixture was reacted at 35°C for 1 hour to obtain a gel material.

[0128] The gel material was vacuum dried at a vacuum level of 0.08 MPa and a temperature of 45°C for 8 hours. The vacuum-dried gel material was then ball-milled at 100 r / min for 4 hours to obtain the coated precursor.

[0129] Large-particle-size precursor and coated precursor were mixed at a mass ratio of 1:1 and sintered at 800℃ for 10 h under a nitrogen atmosphere to obtain high-pressure lithium manganese iron phosphate material.

[0130] Performance testing

[0131] The lithium manganese iron phosphate materials from each embodiment and comparative example were assembled into coin cells and their compaction density and discharge performance were tested. The test results are shown in Table 1.

[0132] Lithium manganese iron phosphate, conductive carbon black, and polyvinylidene fluoride were mixed in N-methylpyrrolidone at a mass ratio of 90:5:5 to form a slurry. The slurry was coated onto a 20μm thick aluminum foil, then dried, rolled, die-cut, and punched into positive electrode sheets. A lithium sheet was used as the negative electrode, a polypropylene separator was selected, and the electrolyte was 1mol / L LiPF6 (EC:DMC=1:1) to assemble a coin cell.

[0133] (1) Compacted density: First calculate the surface density of the positive electrode sheet, surface density = (mass of electrode sheet - mass of aluminum foil) / area of ​​electrode sheet, then measure the thickness of the electrode sheet and aluminum foil after rolling, compacted density = surface density / (thickness of electrode sheet - thickness of aluminum foil).

[0134] (2) Set the test voltage to 2.0-4.5V and the test temperature to 25℃, and test the capacity retention rate of the battery after 200 cycles at 1C rate.

[0135] Table 1 Performance test results of lithium manganese iron phosphate materials

[0136] Group <![CDATA[Compaction density (g / cm 3 )]]> Capacity retention rate / % Example 1 2.43 96.1 Example 2 2.39 95.5 Example 3 2.41 95.9 Example 4 2.46 96.4 Example 5 2.48 96.6 Example 6 2.57 97.5 Example 7 2.53 97.0 Example 8 2.51 96.8 Comparative Example 1 2.25 85.2 Comparative Example 2 2.32 87.5 Comparative Example 3 2.34 87.8

[0137] As shown in Table 1, compared with the comparative example, the high-compact lithium manganese iron phosphate material in the embodiments of the present invention has a higher compaction density and a higher capacity retention rate. This indicates that the present invention uses a gel material formed by gelatin and sheet graphene as a coating layer, and improves the compactness of the coating layer by vacuum drying, so that the compaction density of the sintered lithium manganese iron phosphate material is effectively improved, thus exhibiting excellent capacity retention rate.

[0138] As can be seen from Examples 1 and 4-8, using only polyvinyl alcohol or only polyvinylpyrrolidone for secondary coating can further improve the compaction density of lithium manganese iron phosphate material. In particular, using the two in a certain mass ratio can have a synergistic effect, which can significantly improve the compaction density and capacity retention of lithium manganese iron phosphate material.

[0139] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from the spirit or essential characteristics of this disclosure. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this disclosure.

[0140] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing high-pressure lithium manganese iron phosphate material, characterized in that, Includes the following steps: The material is prepared by mixing lithium source, iron source, manganese source, phosphorus source, carbon source and water; The material is spray-dried and calcined to obtain the precursor material; The precursor material is crushed to obtain large-particle-size precursors and small-particle-size precursors. Small-particle-size precursors, gelatin, sheet graphene, and water are mixed, and then a crosslinking agent is added to react and form a gel material. The gel material was vacuum dried and crushed to obtain the coated precursor. Large-particle-size precursors and coated precursors are mixed and sintered to obtain high-pressure lithium manganese iron phosphate material. The mass ratio of the small-particle-size precursor, gelatin, layered graphene, and water is (20-30):(2-3):(0.1-0.3):100; The sheet-like graphene has a sheet diameter of 100nm-300nm; The vacuum drying conditions for the gel material are: vacuum degree of 0.08MPa-0.09MPa, temperature of 30℃-35℃, and time of 8h-10h. The D50 of the large-particle-size precursor is 1.0 μm-1.5 μm, and the D50 of the small-particle-size precursor is 0.1 μm-0.5 μm; The mass ratio of the large-particle-size precursor to the coated small-particle-size precursor is (1-3):1; The gel material was vacuum dried and crushed to obtain particles to be processed; Polyvinyl alcohol and polyvinylpyrrolidone are dissolved in water at a mass ratio of (3-5):1 to prepare a treatment solution with a total mass concentration of 10%-20%. With a mass ratio of treatment liquid to particles to be treated of (8-10):1, the treatment liquid is sprayed onto the particles to be treated, and after drying, a coated precursor is obtained.

2. The method for preparing high-pressure lithium manganese iron phosphate material according to claim 1, characterized in that, The drying conditions are as follows: first dry at 35℃-40℃ for 50min-70min, then dry at 50℃-55℃ for 2h-3h.

3. The method for preparing high-pressure lithium manganese iron phosphate material according to claim 1, characterized in that, The gel material was vacuum dried and then crushed by ball milling at a speed of 100 r / min-200 r / min for 3-5 hours; and / or, The calcination temperature is 400℃-500℃, and the time is 3h-5h; and / or, The sintering temperature is 800℃-870℃, and the time is 10h-12h.

4. The method for preparing high-pressure lithium manganese iron phosphate material according to claim 1, characterized in that, The lithium source, manganese source, iron source, and phosphorus source are calculated in terms of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms, with a molar ratio of 1:x:(1-x):1, where 0.6≦x≦0.

9. The amount of carbon source used is 1%-3% of the total mass of iron, lithium, manganese and phosphorus sources.

5. The method for preparing high-pressure lithium manganese iron phosphate material according to claim 1, characterized in that, The iron source is at least one selected from ferric phosphate, ferric oxide, ferric nitrate, and iron powder; and / or, The lithium source is at least one selected from lithium carbonate, lithium acetate, lithium nitrate, and lithium dihydrogen phosphate; and / or, The manganese source is at least one of manganese carbonate and manganese oxalate; and / or, The carbon source is at least one of sucrose, glucose, dextrin, and chitosan.

6. A high-pressure lithium manganese iron phosphate material, characterized in that, It is prepared by the method for preparing high-pressure lithium manganese iron phosphate material according to any one of claims 1-5.