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

Abstract

The application discloses a high-density manganese iron lithium phosphate positive electrode material and a preparation method thereof. The preparation method of the high-density manganese iron lithium phosphate positive electrode material comprises the following steps: step 1, adding an iron source, a lithium source, a manganese source, a phosphorus source, an additive, a dispersing agent and a carbon source into deionized water, grinding, drying and sintering to obtain a primary material; step 2, coating a polydopamine layer on the primary material, and then sintering to obtain the high-density manganese iron lithium phosphate positive electrode material; wherein the dispersing agent is polyethylene glycol tert-octyl phenyl ether; the carbon source is polyvinyl alcohol and at least one of glucose, carbon nanotubes and graphene; and the additive is at least one of magnesium oxide and silicon oxide. The high-density manganese iron lithium phosphate positive electrode material has good electrical performance and compaction density, and a battery prepared by using the high-density manganese iron lithium phosphate positive electrode material has good electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and in particular relates to a high-density lithium manganese iron phosphate positive electrode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries, due to their environmental friendliness, superior safety, and high specific energy, have been widely used in electric vehicles, digital products, and energy storage materials, and demand continues to grow. Lithium-ion batteries primarily consist of a positive electrode, negative electrode, separator, electrolyte, current collector, and battery case seal. The positive electrode material accounts for over 30% of the total battery cost, and the safety and electrochemical performance of lithium-ion batteries are also largely dependent on the positive electrode material.

[0003] Lithium iron manganese phosphate (LiMnFePO4) cathode materials, composed of manganese, iron, phosphorus, and lithium, are highly anticipated in the new energy sector due to their cost-effectiveness, long cycle life, and excellent safety. However, the material's low compaction density significantly limits the potential for increasing the volumetric energy density of LiMnFePO4 batteries. Summary of the Invention

[0004] The object of the present invention is to provide a high-density lithium iron manganese phosphate positive electrode material and a preparation method thereof, wherein the high-density lithium iron manganese phosphate positive electrode material has good electrical properties and compaction density.

[0005] In order to achieve the above object, a specific embodiment of the present invention provides the following technical solutions:

[0006] A method for preparing a high-density lithium manganese iron phosphate positive electrode material comprises the following steps:

[0007] Step 1: adding an iron source, a lithium source, a manganese source, a phosphorus source, an additive, a dispersant, and a carbon source into deionized water, grinding, drying, and sintering to obtain a primary material;

[0008] Step 2: coating the primary material with a polydopamine layer and then sintering to obtain a high-density lithium manganese iron phosphate positive electrode material;

[0009] Wherein, the dispersant is polyethylene glycol tert-octylphenyl ether;

[0010] The carbon source is polyvinyl alcohol and at least one of glucose, carbon nanotubes, and graphene;

[0011] The additive is at least one of magnesium oxide and silicon oxide.

[0012] In one or more embodiments of the present invention, the molar ratio of the lithium source, manganese source, iron source and phosphorus source is 1:x:(1-x):1, calculated as lithium atoms, manganese atoms, iron atoms and phosphorus atoms, and 0.6≦x≦0.9.

[0013] In one or more embodiments of the present invention, the amount of the dispersant is 0.5-1.0% of the total mass of the iron source, lithium source, manganese source and phosphorus source.

[0014] In one or more embodiments of the present invention, the amount of the carbon source is 5-10% of the total mass of the iron source, lithium source, manganese source and phosphorus source; among the carbon sources, the amount of polyvinyl alcohol is 30-50% of the total mass of the carbon source.

[0015] In one or more embodiments of the present invention, the amount of the additive is 0.3-0.8% of the total mass of the iron source, lithium source, manganese source, and phosphorus source.

[0016] In one or more embodiments of the present invention, in step 2, the primary material is mixed with a Tris buffer having a pH value of 8.0-9.0, and then dopamine hydrochloride is added in an amount of 2-3% of the mass of the primary material. After the reaction, the mixture is centrifuged and then sintered.

[0017] In one or more embodiments of the present invention, the iron source is at least one of ferric phosphate, ferric oxide, ferric nitrate and iron powder; and / or,

[0018] The lithium source is at least one of lithium carbonate, lithium acetate, lithium nitrate and lithium dihydrogen phosphate; and / or,

[0019] The manganese source is at least one of manganese carbonate and manganese oxalate.

[0020] In one or more embodiments of the present invention, the drying temperature in step 1 is 120-160°C, and the drying time is 2-3 hours; the sintering operation is: first sintering at 300-400°C for 1.5-2.5 hours, and then sintering at 500-750°C for 4-5 hours.

[0021] In one or more embodiments of the present invention, the sintering temperature in step 2 is 500-750° C., and the sintering time is 4-5 hours.

[0022] Another specific embodiment of the present invention provides a technical solution as follows:

[0023] A high-density lithium iron manganese phosphate positive electrode material is prepared by the above-mentioned preparation method of the high-density lithium iron manganese phosphate positive electrode material.

[0024] Compared with the prior art, the high-density lithium manganese iron phosphate positive electrode material of the present invention not only has a high compaction density but also has excellent cycle performance, and can effectively improve the electrochemical performance of the battery. DETAILED DESCRIPTION

[0025] To help those skilled in the art better understand the technical solutions of the present invention, the following clearly and completely describes 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 them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present invention.

[0026] A specific embodiment of the present invention provides a method for preparing a high-density lithium manganese iron phosphate positive electrode material, comprising steps 1-2.

[0027] Step 1: Add iron source, lithium source, manganese source, phosphorus source, additives, dispersant and carbon source into deionized water, grind, dry and sinter to obtain primary material.

[0028] Specifically, the iron, lithium, and phosphorus sources can be composite materials, such as iron phosphate and lithium dihydrogen phosphate. Other iron sources include ferrous oxalate dihydrate, iron oxide, ferric nitrate, and iron powder. Other lithium sources include lithium carbonate, lithium acetate, and lithium nitrate. Other manganese sources include manganese carbonate and manganese oxalate. And another phosphorus source is ammonium dihydrogen phosphate. The molar ratio of the lithium, manganese, iron, and phosphorus sources, calculated as lithium atoms, manganese atoms, iron atoms, and phosphorus atoms, is 1:x:(1-x):1, with 0.6 ≤ x ≤ 0.9.

[0029] Furthermore, the additive is at least one of magnesium oxide and silicon oxide, and the amount of the additive is 0.3-0.8% of the total mass of the iron source, lithium source, manganese source, and phosphorus source. Magnesium oxide has excellent chemical stability and high-temperature performance, can enhance the mechanical strength and stability of the positive electrode material, and can improve the compaction density of the positive electrode material. Silicon oxide has high hardness and excellent stability, can fill the gaps between the positive electrode material particles, thereby improving the compaction density of the positive electrode material. In addition, magnesium oxide and silicon oxide can also improve the structural stability of the positive electrode material, reduce the volume change of the positive electrode material during the charge and discharge process, thereby improving the cycle stability of the battery.

[0030] Furthermore, the dispersant is polyethylene glycol tert-octylphenyl ether, and the amount of the dispersant is 0.5-1.0% of the total mass of the iron source, lithium source, manganese source, and phosphorus source. When the polyethylene glycol tert-octylphenyl ether is dissolved in water, the benzene ring structure it contains can exert a steric hindrance effect, which can reduce intermolecular contact. Therefore, when the iron source, lithium source, manganese source, phosphorus source, additives, and carbon source are added to deionized water, in conjunction with grinding, particle agglomeration can be reduced, allowing the raw materials to be evenly mixed, thereby increasing the compaction density of the positive electrode material during the subsequent sintering process.

[0031] Furthermore, the carbon source is polyvinyl alcohol and at least one of glucose, carbon nanotubes, and graphene, with the carbon source used being 5-10% of the total mass of the iron source, lithium source, manganese source, and phosphorus source. Using polyvinyl alcohol as the carbon source for coating can increase the compaction density of the positive electrode material, while combining it with glucose, carbon nanotubes, or graphene can enhance the conductivity of the positive electrode material, thereby improving the electrochemical performance of the battery.

[0032] Furthermore, in the carbon source, the amount of polyvinyl alcohol used is 30-50% of the total mass of the carbon source. By controlling the amount of polyvinyl alcohol used, the electrochemical performance of the battery can be improved while ensuring that the positive electrode material has a high compaction density.

[0033] Furthermore, in step 1, the drying temperature is 120-160° C., and the drying time is 2-3 hours; during sintering, the sintering is first performed at 300-400° C. for 1.5-2.5 hours, and then at 500-750° C. for 4-5 hours.

[0034] Step 2: The primary material is coated with a polydopamine layer and then sintered to obtain a high-density lithium manganese iron phosphate positive electrode material.

[0035] Specifically, the primary material is mixed with a Tris buffer solution with a pH value of 8.0-9.0, and then dopamine hydrochloride is added at an amount of 2-3% of the mass of the primary material. After the reaction, the mixture is centrifuged and then sintered at a sintering temperature of 500-750°C for 4-5 hours.

[0036] Polydopamine is coated on the surface of the primary material and then sintered to form a uniform carbon layer. This carbon layer can not only further improve the conductivity of the positive electrode material and reduce the internal resistance of the battery, but also cooperate with the carbon layer formed in step 1 to further improve the compaction density and structural stability of the positive electrode material, thereby improving the cycle performance of the positive electrode material.

[0037] Another specific embodiment of the present invention provides a high-density lithium iron manganese phosphate positive electrode material, which is prepared by the above-mentioned preparation method of the high-density lithium iron manganese phosphate positive electrode material.

[0038] The present invention is further described in detail below with reference to specific examples. Unless otherwise specified, the reagents used in the present invention can be obtained from commercial sources.

[0039] Example 1

[0040] Ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate were accurately weighed, with the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1. Magnesium oxide, polyethylene glycol tert-octylphenyl ether, polyvinyl alcohol, and carbon nanotubes were also accurately weighed, with the total mass of the ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate being denoted as M, the mass of the magnesium oxide being 0.8% of M, the mass of the polyethylene glycol tert-octylphenyl ether being 1% of M, and the total mass of the polyvinyl alcohol and the carbon nanotubes being 5% of M, wherein the mass ratio of the polyvinyl alcohol to the carbon nanotubes was 3:7.

[0041] The weighed raw materials were added to a certain amount of deionized water to a solids content of 50%. The mixture was then ground using 0.5 mm zirconium balls for 2 hours. After grinding, the mixture was dried at 120°C for 2 hours and then sintered under a nitrogen atmosphere at 300°C for 2 hours and then at 600°C for 5 hours to obtain the primary material.

[0042] The primary material was added to a Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride at a concentration of 2% of the primary material's mass. The mixture was stirred for 2 hours and centrifuged to collect the precipitate. The mixture was then sintered at 500°C for 4 hours to obtain a high-density lithium manganese iron phosphate cathode material.

[0043] Example 2

[0044] Ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate were accurately weighed, with the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.7:0.3:1. Magnesium oxide, polyethylene glycol tert-octylphenyl ether, polyvinyl alcohol, and carbon nanotubes were also accurately weighed, with the total mass of the ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate being denoted as M, the mass of the magnesium oxide being 0.5% of M, the mass of the polyethylene glycol tert-octylphenyl ether being 0.5% of M, and the total mass of the polyvinyl alcohol and the carbon nanotubes being 10% of M, wherein the mass ratio of the polyvinyl alcohol to the carbon nanotubes was 3:7.

[0045] The weighed raw materials were added to a certain amount of deionized water to a solids content of 50%. The mixture was then ground using 0.5 mm zirconium balls for 2 hours. After grinding, the mixture was dried at 150°C for 3 hours and then sintered at 350°C for 2.5 hours and then at 750°C for 4 hours under a nitrogen atmosphere to obtain the primary material.

[0046] The primary material was added to a Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride at a concentration of 3% of the primary material's mass. The mixture was stirred for 2 hours and centrifuged to collect the precipitate. The mixture was then sintered at 600°C for 4 hours to obtain a high-density lithium manganese iron phosphate cathode material.

[0047] Example 3

[0048] Ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate were accurately weighed, with the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1. Magnesium oxide, polyethylene glycol tert-octylphenyl ether, polyvinyl alcohol, and carbon nanotubes were also accurately weighed, with the total mass of the ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate being M, with the mass of the magnesium oxide being 0.3% of M, the mass of the polyethylene glycol tert-octylphenyl ether being 0.7% of M, and the total mass of the polyvinyl alcohol and the carbon nanotubes being 8% of M, wherein the mass ratio of the polyvinyl alcohol to the carbon nanotubes was 3:7.

[0049] The weighed raw materials were added to a certain amount of deionized water to a solids content of 50%. The mixture was then ground using 0.5 mm zirconium balls for 2 hours. After grinding, the mixture was dried at 160°C for 2 hours and then sintered at 400°C for 2 hours and then at 500°C for 5 hours under a nitrogen atmosphere to obtain the primary material.

[0050] The primary material was added to a Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride at a concentration of 2.5% of the primary material's mass. Stirring was continued for 2 hours, and the precipitate was collected by centrifugation. The product was then sintered at 750°C for 4 hours to obtain a high-density lithium manganese iron phosphate cathode material.

[0051] Example 4

[0052] Ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate were accurately weighed, with the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1. Magnesium oxide, polyethylene glycol tert-octylphenyl ether, polyvinyl alcohol, and carbon nanotubes were also accurately weighed, with the total mass of the ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate being denoted as M, the mass of the magnesium oxide being 0.8% of M, the mass of the polyethylene glycol tert-octylphenyl ether being 0.2% of M, and the total mass of the polyvinyl alcohol and the carbon nanotubes being 5% of M, wherein the mass ratio of the polyvinyl alcohol to the carbon nanotubes was 3:7.

[0053] The weighed raw materials were added to a certain amount of deionized water to a solids content of 50%. The mixture was then ground using 0.5 mm zirconium balls for 2 hours. After grinding, the mixture was dried at 120°C for 2 hours and then sintered under a nitrogen atmosphere at 300°C for 2 hours and then at 600°C for 5 hours to obtain the primary material.

[0054] The primary material was added to a Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride at a concentration of 2% of the primary material's mass. The mixture was stirred for 2 hours and centrifuged to collect the precipitate. The mixture was then sintered at 500°C for 4 hours to obtain a high-density lithium manganese iron phosphate cathode material.

[0055] Example 5

[0056] Ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate were accurately weighed, with the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1. Magnesium oxide, polyethylene glycol tert-octylphenyl ether, polyvinyl alcohol, and carbon nanotubes were also accurately weighed, with the total mass of the ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate being denoted as M, the mass of the magnesium oxide being 0.8% of M, the mass of the polyethylene glycol tert-octylphenyl ether being 1% of M, and the total mass of the polyvinyl alcohol and the carbon nanotubes being 5% of M, wherein the mass ratio of the polyvinyl alcohol to the carbon nanotubes was 4:6.

[0057] The weighed raw materials were added to a certain amount of deionized water to a solids content of 50%. The mixture was then ground using 0.5 mm zirconium balls for 2 hours. After grinding, the mixture was dried at 120°C for 2 hours and then sintered under a nitrogen atmosphere at 300°C for 2 hours and then at 600°C for 5 hours to obtain the primary material.

[0058] The primary material was added to a Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride at a concentration of 2% of the primary material's mass. The mixture was stirred for 2 hours and centrifuged to collect the precipitate. The mixture was then sintered at 500°C for 4 hours to obtain a high-density lithium manganese iron phosphate cathode material.

[0059] Example 6

[0060] Ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate were accurately weighed, with the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1. Magnesium oxide, polyethylene glycol tert-octylphenyl ether, polyvinyl alcohol, and carbon nanotubes were also accurately weighed, with the total mass of the ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate being denoted as M, the mass of the magnesium oxide being 0.8% of M, the mass of the polyethylene glycol tert-octylphenyl ether being 1% of M, and the total mass of the polyvinyl alcohol and the carbon nanotubes being 5% of M, wherein the mass ratio of the polyvinyl alcohol to the carbon nanotubes was 1:1.

[0061] The weighed raw materials were added to a certain amount of deionized water to a solids content of 50%. The mixture was then ground using 0.5 mm zirconium balls for 2 hours. After grinding, the mixture was dried at 120°C for 2 hours and then sintered under a nitrogen atmosphere at 300°C for 2 hours and then at 600°C for 5 hours to obtain the primary material.

[0062] The primary material was added to a Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride at a concentration of 2% of the primary material's mass. The mixture was stirred for 2 hours and centrifuged to collect the precipitate. The mixture was then sintered at 500°C for 4 hours to obtain a high-density lithium manganese iron phosphate cathode material.

[0063] Example 7

[0064] Ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate were accurately weighed, with the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1. Magnesium oxide, polyethylene glycol tert-octylphenyl ether, polyvinyl alcohol, and carbon nanotubes were also accurately weighed, with the total mass of the ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate being denoted as M, the mass of the magnesium oxide being 0.8% of M, the mass of the polyethylene glycol tert-octylphenyl ether being 1% of M, and the total mass of the polyvinyl alcohol and the carbon nanotubes being 5% of M, wherein the mass ratio of the polyvinyl alcohol to the carbon nanotubes was 7:3.

[0065] The weighed raw materials were added to a certain amount of deionized water to a solids content of 50%. The mixture was then ground using 0.5 mm zirconium balls for 2 hours. After grinding, the mixture was dried at 120°C for 2 hours and then sintered under a nitrogen atmosphere at 300°C for 2 hours and then at 600°C for 5 hours to obtain the primary material.

[0066] The primary material was added to a Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride at a concentration of 2% of the primary material's mass. The mixture was stirred for 2 hours and centrifuged to collect the precipitate. The mixture was then sintered at 500°C for 4 hours to obtain a high-density lithium manganese iron phosphate cathode material.

[0067] Example 8

[0068] Ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate were accurately weighed, with the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1. Magnesium oxide, polyethylene glycol tert-octylphenyl ether, polyvinyl alcohol, and carbon nanotubes were also accurately weighed, with the total mass of the ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate being denoted as M, the mass of the magnesium oxide being 0.8% of M, the mass of the polyethylene glycol tert-octylphenyl ether being 1% of M, and the total mass of the polyvinyl alcohol and the carbon nanotubes being 5% of M, wherein the mass ratio of the polyvinyl alcohol to the carbon nanotubes was 3:7.

[0069] The weighed raw materials were added to a certain amount of deionized water to a solids content of 50%. The mixture was then ground using 0.5 mm zirconium balls for 2 hours. After grinding, the mixture was dried at 120°C for 2 hours and then sintered under a nitrogen atmosphere at 300°C for 2 hours and then at 600°C for 5 hours to obtain the primary material.

[0070] The primary material was added to a Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride at a concentration of 1% of the primary material's mass. Stirring was continued for 2 hours, and the precipitate was collected by centrifugation. The product was then sintered at 500°C for 4 hours to obtain a high-density lithium manganese iron phosphate cathode material.

[0071] Example 9

[0072] Ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate were accurately weighed, with the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1. Magnesium oxide, polyethylene glycol tert-octylphenyl ether, polyvinyl alcohol, and carbon nanotubes were also accurately weighed, with the total mass of the ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate being denoted as M, the mass of the magnesium oxide being 0.8% of M, the mass of the polyethylene glycol tert-octylphenyl ether being 1% of M, and the total mass of the polyvinyl alcohol and the carbon nanotubes being 5% of M, wherein the mass ratio of the polyvinyl alcohol to the carbon nanotubes was 3:7.

[0073] The weighed raw materials were added to a certain amount of deionized water to a solids content of 50%. The mixture was then ground using 0.5 mm zirconium balls for 2 hours. After grinding, the mixture was dried at 120°C for 2 hours and then sintered under a nitrogen atmosphere at 300°C for 2 hours and then at 600°C for 5 hours to obtain the primary material.

[0074] The primary material was added to a Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride at a concentration equal to 5% of the primary material's mass. Stirring was continued for 2 hours, and the precipitate was collected by centrifugation. The product was then sintered at 500°C for 4 hours to obtain a high-density lithium manganese iron phosphate cathode material.

[0075] Comparative Example 1

[0076] Ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate were accurately weighed, with the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1. Magnesium oxide, polyvinyl alcohol, and carbon nanotubes were also accurately weighed. The total mass of the ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate was calculated as M, with the mass of magnesium oxide being 0.8% of M and the total mass of polyvinyl alcohol and carbon nanotubes being 5% of M. The mass ratio of polyvinyl alcohol to carbon nanotubes was 3:7.

[0077] The weighed raw materials were added to a certain amount of deionized water to a solids content of 50%. The mixture was then ground using 0.5 mm zirconium balls for 2 hours. After grinding, the mixture was dried at 120°C for 2 hours and then sintered under a nitrogen atmosphere at 300°C for 2 hours and then at 600°C for 5 hours to obtain the primary material.

[0078] The primary material was added to a Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride at a concentration of 2% of the primary material's mass. The mixture was stirred for 2 hours and centrifuged to collect the precipitate. The mixture was then sintered at 500°C for 4 hours to obtain a high-density lithium manganese iron phosphate cathode material.

[0079] Comparative Example 2

[0080] Ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate were accurately weighed, with the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1. Magnesium oxide, polyethylene glycol tert-octylphenyl ether, and polyvinyl alcohol were also accurately weighed, with the total mass of the ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate being denoted as M, where the mass of the magnesium oxide was 0.8% of M, the mass of the polyethylene glycol tert-octylphenyl ether was 1% of M, and the mass of the polyvinyl alcohol was 5% of M.

[0081] The weighed raw materials were added to a certain amount of deionized water to a solids content of 50%. The mixture was then ground using 0.5 mm zirconium balls for 2 hours. After grinding, the mixture was dried at 120°C for 2 hours and then sintered under a nitrogen atmosphere at 300°C for 2 hours and then at 600°C for 5 hours to obtain the primary material.

[0082] The primary material was added to a Tris buffer solution at pH 8.5, followed by the addition of dopamine hydrochloride at a concentration of 2% of the primary material's mass. The mixture was stirred for 2 hours and centrifuged to collect the precipitate. The mixture was then sintered at 500°C for 4 hours to obtain a high-density lithium manganese iron phosphate cathode material.

[0083] Comparative Example 3

[0084] Ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate were accurately weighed, with the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1. Magnesium oxide, polyethylene glycol tert-octylphenyl ether, polyvinyl alcohol, and carbon nanotubes were also accurately weighed, with the total mass of the ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate being denoted as M, the mass of the magnesium oxide being 0.8% of M, the mass of the polyethylene glycol tert-octylphenyl ether being 1% of M, and the total mass of the polyvinyl alcohol and the carbon nanotubes being 5% of M, wherein the mass ratio of the polyvinyl alcohol to the carbon nanotubes was 3:7.

[0085] The weighed raw materials were added to a certain amount of deionized water to a solid content of 50%, and ground using 0.5 mm zirconium balls for 2 hours. After grinding, the mixture was dried at 120°C for 2 hours and then sintered at 300°C for 2 hours and then at 600°C for 5 hours under a nitrogen atmosphere to obtain a high-density lithium manganese iron phosphate cathode material.

[0086] Performance Testing

[0087] The lithium manganese iron phosphate positive electrode materials in each embodiment and each comparative example were assembled into button-type batteries and the compaction density and discharge performance were tested.

[0088] Lithium manganese iron phosphate cathode material, 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 then coated onto 20μm-thick aluminum foil, dried, rolled, and die-cut to produce positive electrode sheets. A button cell was assembled using a lithium sheet as the negative electrode, a polypropylene separator, and an electrolyte of 1 mol / L LiPF6 (EC:DMC = 1:1).

[0089] (1) Compaction density: First calculate the surface density of the positive electrode sheet, surface density = (electrode sheet mass - aluminum foil mass) / electrode sheet area, then measure the thickness of the electrode sheet and aluminum foil after rolling, compaction density = surface density / (electrode sheet thickness - aluminum foil thickness).

[0090] (2) Set the test voltage to 2.0-4.5V and the test temperature to 25°C, and test the capacity retention rate of the battery after 200 cycles at a 1C rate.

[0091] Table 1 Performance test results

[0092] Group Compacted density (g / cm3) Capacity retention rate / % Example 1 2.50 96.3 Example 2 2.46 95.8 Example 3 2.55 97.1 Example 4 2.42 95.4 Example 5 2.47 96.0 Example 6 2.45 95.5 Example 7 2.41 94.8 Example 8 2.46 95.7 Example 9 2.40 94.3 Comparative Example 1 2.34 87.7 Comparative Example 2 2.37 88.5 Comparative Example 3 2.28 85.0

[0093] As can be seen from Table 1, compared with the comparative example, the high-density lithium manganese iron phosphate positive electrode material in the embodiment of the present invention exhibits a higher compaction density and a better capacity retention rate, indicating that the present invention can promote the uniform dispersion of the raw materials during mixing by using a dispersant, and the use of a composite carbon source and secondary carbon coating can further improve the electrochemical performance of the battery.

[0094] It can also be seen from Example 1 and Examples 4-9 that referring to the raw material dosage disclosed in the present invention can better ensure that the battery has excellent electrochemical performance.

[0095] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes that fall within the meaning and scope of the equivalent elements of the claims are included in the present invention. In addition, it should be understood that although this specification is described in terms of implementation methods, not each implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in the various embodiments can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing a high-density lithium manganese iron phosphate positive electrode material, characterized in that: The steps include: Step 1: adding an iron source, a lithium source, a manganese source, a phosphorus source, an additive, a dispersant, and a carbon source into deionized water, grinding, drying, and sintering to obtain a primary material; Step 2: coating the primary material with a polydopamine layer and then sintering to obtain a high-density lithium manganese iron phosphate positive electrode material; Wherein, the dispersant is polyethylene glycol tert-octylphenyl ether, and the amount of the dispersant is 0.5-1.0% of the total mass of the iron source, lithium source, manganese source and phosphorus source; The carbon source is polyvinyl alcohol and at least one of glucose, carbon nanotubes, and graphene, and the amount of the carbon source is 5-10% of the total mass of the iron source, lithium source, manganese source, and phosphorus source; among the carbon sources, the amount of polyvinyl alcohol is 30-50% of the total mass of the carbon source; The additive is at least one of magnesium oxide and silicon oxide.

2. The method for preparing a high-density lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The molar ratio of the lithium source, manganese source, iron source and phosphorus source is 1:x:(1-x):1, calculated as lithium atoms, manganese atoms, iron atoms and phosphorus atoms, and 0.6≦x≦0.

9.

3. The method for preparing a high-density lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The dosage of the additive is 0.3-0.8% of the total mass of the iron source, lithium source, manganese source and phosphorus source.

4. The method for preparing a high-density lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: In the step 2, the primary material is mixed with a Tris buffer having a pH value of 8.0-9.0, and then dopamine hydrochloride is added in an amount of 2-3% of the mass of the primary material. After the reaction, the mixture is centrifuged and then sintered.

5. The method for preparing a high-density lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The iron source is at least one of ferric phosphate, ferric oxide, ferric nitrate and iron powder; and / or, The lithium source is at least one of 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.

6. The method for preparing a high-density lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: In step 1, the drying temperature is 120-160° C. and the drying time is 2-3 hours. The sintering operation is: first sintering at 300-400° C. for 1.5-2.5 hours, and then sintering at 500-750° C. for 4-5 hours.

7. The method for preparing a high-density lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: In step 2, the sintering temperature is 500-750° C., and the sintering time is 4-5 hours.

8. A high-density lithium manganese iron phosphate positive electrode material, characterized in that: The high-density lithium manganese iron phosphate positive electrode material is prepared by the preparation method of any one of claims 1 to 7.