High-density lithium manganese iron phosphate positive electrode material and preparation method thereof

Abstract

The invention discloses a high-density lithium manganese iron phosphate positive electrode material and a preparation method thereof.The preparation method of the high-density lithium manganese iron phosphate positive electrode material comprises the following steps that 1, an iron source, a lithium source, a manganese source, a phosphorus source, an additive, a dispersing agent and a carbon source are added into deionized water, grinding, drying and sintering are conducted, and a primary material is obtained; and 2, coating the primary material with a polydopamine layer, and sintering to obtain the high-density lithium iron manganese 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; the additive is at least one of magnesium oxide and silicon oxide. The high-density lithium manganese iron phosphate positive electrode material disclosed by the invention has relatively good electrical performance and compaction density, and a battery prepared from the high-density lithium manganese iron phosphate positive electrode material has good electrochemical performance.

Description

Technical Field

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

[0002] Lithium-ion batteries have been widely used in the fields of electric vehicles, digital products, and energy storage materials due to their good environmental protection, excellent safety, and high specific energy, and their demand is still increasing. A lithium-ion battery mainly consists of a cathode, an anode, a separator, an electrolyte, a current collector, and a battery case seal. Among them, the cathode material accounts for more than 30% of the total cost of the entire battery, and the safety and electrochemical performance of the lithium-ion battery also largely depend on the cathode material.

[0003] The lithium iron manganese phosphate cathode material is composed of manganese, iron, phosphorus, and lithium. Its high cost performance, long cycle life, and excellent safety make it one of the most anticipated cathode materials in the new energy field. However, the disadvantage of the low tap density of the lithium iron manganese phosphate material greatly limits the improvement of the volumetric energy density of lithium iron manganese phosphate batteries. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-density lithium iron manganese phosphate cathode material and a preparation method thereof, and the high-density lithium iron manganese phosphate cathode material has good electrical properties and tap density.

[0005] In order to achieve the above purpose, the technical solution provided by a specific embodiment of the present invention is as follows: A preparation method of a high-density lithium iron manganese phosphate cathode material, comprising the following steps: 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 iron manganese phosphate cathode material; Wherein, the dispersant is polyoxyethylene tert-octyl phenyl ether; The carbon source is polyvinyl alcohol and at least one of glucose, carbon nanotubes, and graphene; The additive is at least one of magnesium oxide and silicon oxide.

[0006] In one or more embodiments of the present invention, the lithium source, the manganese source, the iron source, and the phosphorus source are in a molar ratio of 1:x:(1 - x):1 in terms of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms, where 0.6 ≤ x ≤ 0.9.

[0007] In one or more embodiments of the present invention, the dosage of the dispersant is 0.5 - 1.0% of the total mass of the iron source, the lithium source, the manganese source, and the phosphorus source.

[0008] In one or more embodiments of the present invention, the dosage 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 dosage of polyvinyl alcohol is 30-50% of the total mass of the carbon source.

[0009] In one or more embodiments of the present invention, 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 In one or more embodiments of the present invention, in step 2, the primary material is mixed with a Tris buffer solution 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, and after the reaction, centrifugation is carried out, and then sintering is carried out.

[0010] In one or more embodiments of the present invention, the iron source is at least one of iron phosphate, iron oxide, iron 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.

[0011] In one or more embodiments of the present invention, in step 1, the drying temperature is 120-160 °C and the drying time is 2-3 h; the sintering operation is: first sinter at 300-400 °C for 1.5-2.5 h, and then sinter at 500-750 °C for 4-5 h.

[0012] In one or more embodiments of the present invention, in step 2, the sintering temperature is 500-750 °C and the sintering time is 4-5 h.

[0013] The technical solution provided by another specific embodiment of the present invention is as follows: A high-density lithium iron manganese phosphate cathode material is prepared by the preparation method of the above high-density lithium iron manganese phosphate cathode material.

[0014] Compared with the prior art, the high-density lithium iron manganese phosphate cathode material of the present invention not only has a high tap density, but also has excellent cycling performance, and can effectively improve the electrochemical performance of the battery. Detailed Description

[0015] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0016] A specific embodiment of the present invention provides a method for preparing a high-density lithium iron manganese phosphate cathode material, including steps 1-2.

[0017] 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.

[0018] Specifically, the iron source, lithium source, and phosphorus source can be composite materials, such as iron phosphate and lithium dihydrogen phosphate. The iron source can also be ferrous oxalate dihydrate, iron oxide, iron nitrate, and iron powder. The lithium source can also be lithium carbonate, lithium acetate, and lithium nitrate. The manganese source can be manganese carbonate and manganese oxalate. The phosphorus source can also be ammonium dihydrogen phosphate. In terms of dosage, based on lithium atoms, manganese atoms, iron atoms, and phosphorus atoms, the molar ratio of the lithium source, manganese source, iron source, and phosphorus source is 1:x:(1 - x):1, where 0.6 ≤ x ≤ 0.9.

[0019] Furthermore, the additive is at least one of magnesium oxide and silicon oxide, and 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. Magnesium oxide has excellent chemical stability and high-temperature performance, can enhance the mechanical strength and stability of the cathode material, and can improve the tap density of the cathode material. Silicon oxide has high hardness and excellent stability, can fill the gaps between the cathode material particles, thereby improving the tap density of the cathode material. In addition, magnesium oxide and silicon oxide can also improve the structural stability of the cathode material, reduce the volume change of the cathode material during charge and discharge, and thus improve the cycle stability of the battery.

[0020] Furthermore, the dispersant is poly(ethylene glycol) tert-octylphenyl ether, and the dosage of the dispersant is 0.5-1.0% of the total mass of the iron source, lithium source, manganese source, and phosphorus source. After poly(ethylene 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. Thus, when the iron source, lithium source, manganese source, phosphorus source, additive, and carbon source are added to deionized water, combined with grinding, it can reduce particle agglomeration, enabling the raw materials to be uniformly mixed. Therefore, during the subsequent sintering process, it can enhance the tap density of the cathode material.

[0021] Furthermore, the carbon source is polyvinyl alcohol and at least one of glucose, carbon nanotubes, and graphene, and the dosage of the carbon source is 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 improve the tap density of the cathode material. At the same time, in combination with glucose, carbon nanotubes, or graphene, it can improve the conductivity of the cathode material, thereby improving the electrochemical performance of the battery.

[0022] Further, in the carbon source, the dosage of polyvinyl alcohol is 30-50% of the total mass of the carbon source. By controlling the dosage of polyvinyl alcohol, while ensuring that the cathode material has a high tap density, the electrochemical performance of the battery can be improved.

[0023] Further, in Step 1, the drying temperature is 120-160°C and the drying time is 2-3 h; during sintering, first sinter at 300-400°C for 1.5-2.5 h, and then sinter at 500-750°C for 4-5 h.

[0024] Step 2: Coating the primary material with a polydopamine layer and then sintering to obtain a high-density lithium iron manganese phosphate cathode material.

[0025] Specifically, mix the primary material with a Tris buffer solution having a pH value of 8.0-9.0, then add dopamine hydrochloride in an amount of 2-3% of the mass of the primary material, centrifuge after the reaction, and then sinter. The sintering temperature is 500-750°C and the sintering time is 4-5 h.

[0026] Coating the surface of the primary material with polydopamine and then sintering to form a uniform carbon layer. This carbon layer can not only further improve the conductivity of the cathode material, reduce the internal resistance of the battery, but also cooperate with the carbon layer formed in Step 1 to further improve the tap density and structural stability of the cathode material, and improve the cycling performance of the cathode material.

[0027] Another specific embodiment of the present invention provides a high-density lithium iron manganese phosphate cathode material prepared by the preparation method of the above high-density lithium iron manganese phosphate cathode material.

[0028] The following further details the present invention with specific examples. Unless otherwise specified, the reagents used in the present invention can be obtained commercially.

[0029] Example 1 With the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate. Additionally, accurately weigh magnesium oxide, polyethylene glycol tert-octyl phenyl ether, polyvinyl alcohol, and carbon nanotubes. Denote the total mass of ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate as M. The mass of magnesium oxide is 0.8% of M, the mass of polyethylene glycol tert-octyl phenyl ether is 1% of M, the total mass of polyvinyl alcohol and carbon nanotubes is 5% of M, and the mass ratio of polyvinyl alcohol to carbon nanotubes is 3:7.

[0030] Add the weighed raw materials above to a certain amount of deionized water to make the solid content 50%, and grind for 2 h using 0.5-mm zirconium balls. After grinding, dry at 120 °C for 2 h, and then under a nitrogen atmosphere, first sinter at 300 °C for 2 h, and then sinter at 600 °C for 5 h to obtain the primary material.

[0031] Add the primary material to a Tris buffer solution with a pH of 8.5, and then add dopamine hydrochloride at a dosage of 2% of the mass of the primary material. Stir continuously for 2 h, and centrifuge to obtain the precipitate. Then sinter at 500 °C for 4 h to obtain the high-density lithium iron manganese phosphate cathode material.

[0032] Example 2 With the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.7:0.3:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate. Additionally, accurately weigh magnesium oxide, polyethylene glycol tert-octyl phenyl ether, polyvinyl alcohol, and carbon nanotubes. Denote the total mass of ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate as M, the mass of magnesium oxide as 0.5% of M, the mass of polyethylene glycol tert-octyl phenyl ether as 0.5% of M, and the total mass of polyvinyl alcohol and carbon nanotubes as 10% of M, where the mass ratio of polyvinyl alcohol to carbon nanotubes is 3:7.

[0033] Add the weighed raw materials above to a certain amount of deionized water to make the solid content 50%, and grind for 2 h using 0.5-mm zirconium balls. After grinding, dry at 150 °C for 3 h, and then under a nitrogen atmosphere, first sinter at 350 °C for 2.5 h, and then sinter at 750 °C for 4 h to obtain the primary material.

[0034] Add the primary material to a Tris buffer solution with a pH of 8.5, and then add dopamine hydrochloride at a dosage of 3% of the mass of the primary material. Stir continuously for 2 h, and centrifuge to obtain the precipitate. Then sinter at 600 °C for 4 h to obtain the high-density lithium iron manganese phosphate cathode material.

[0035] Example 3 With the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate. Additionally, accurately weigh magnesium oxide, polyethylene glycol tert-octyl phenyl ether, polyvinyl alcohol, and carbon nanotubes. Denote the total mass of ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate as M, the mass of magnesium oxide as 0.3% of M, the mass of polyethylene glycol tert-octyl phenyl ether as 0.7% of M, and the total mass of polyvinyl alcohol and carbon nanotubes as 8% of M, where the mass ratio of polyvinyl alcohol to carbon nanotubes is 3:7.

[0036] Add the weighed raw materials above to a certain amount of deionized water to make the solid content 50%, and grind them for 2 h using 0.5-mm zirconium balls. After grinding, dry them at 160 °C for 2 h, and then, under a nitrogen atmosphere, first sinter them at 400 °C for 2 h and then at 500 °C for 5 h to obtain the primary material.

[0037] Add the primary material to a Tris buffer solution with a pH of 8.5, and then add dopamine hydrochloride in an amount of 2.5% of the mass of the primary material. Stir continuously for 2 h, and centrifuge to obtain the precipitate. Then sinter it at 750 °C for 4 h to obtain the high-density lithium iron manganese phosphate cathode material.

[0038] Example 4 With the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate. Additionally, accurately weigh magnesium oxide, poly(ethylene glycol) tert-octyl phenyl ether, polyvinyl alcohol, and carbon nanotubes. Denote the total mass of ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate as M, the mass of magnesium oxide as 0.8% of M, the mass of poly(ethylene glycol) tert-octyl phenyl ether as 0.2% of M, and the total mass of polyvinyl alcohol and carbon nanotubes as 5% of M, where the mass ratio of polyvinyl alcohol to carbon nanotubes is 3:7.

[0039] Add the weighed raw materials above to a certain amount of deionized water to make the solid content 50%, and grind them for 2 h using 0.5-mm zirconium balls. After grinding, dry them at 120 °C for 2 h, and then, under a nitrogen atmosphere, first sinter them at 300 °C for 2 h and then at 600 °C for 5 h to obtain the primary material.

[0040] Add the primary material to a Tris buffer solution with a pH of 8.5, and then add dopamine hydrochloride in an amount of 2% of the mass of the primary material. Stir continuously for 2 h, and centrifuge to obtain the precipitate. Then sinter it at 500 °C for 4 h to obtain the high-density lithium iron manganese phosphate cathode material.

[0041] Example 5 With the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate. Additionally, accurately weigh magnesium oxide, poly(ethylene glycol) tert-octyl phenyl ether, polyvinyl alcohol, and carbon nanotubes. Denote the total mass of ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate as M, the mass of magnesium oxide as 0.8% of M, the mass of poly(ethylene glycol) tert-octyl phenyl ether as 1% of M, and the total mass of polyvinyl alcohol and carbon nanotubes as 5% of M, where the mass ratio of polyvinyl alcohol to carbon nanotubes is 4:6.

[0042] Add the weighed raw materials above to a certain amount of deionized water to make the solid content 50%, and grind them for 2 h using 0.5-mm zirconium balls. After grinding, dry them at 120 °C for 2 h, and then, under a nitrogen atmosphere, first sinter them at 300 °C for 2 h and then at 600 °C for 5 h to obtain the primary material.

[0043] Add the primary material to a Tris buffer solution with a pH of 8.5, and then add dopamine hydrochloride at a dosage of 2% of the mass of the primary material. Stir continuously for 2 h, and centrifuge to obtain the precipitate. Then sinter it at 500 °C for 4 h to obtain the high-density lithium iron manganese phosphate cathode material.

[0044] Example 6 With the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate. Additionally, accurately weigh magnesium oxide, poly(ethylene glycol) tert-octylphenyl ether, polyvinyl alcohol, and carbon nanotubes. Denote the total mass of ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate as M. The mass of magnesium oxide is 0.8% of M, the mass of poly(ethylene glycol) tert-octylphenyl ether is 1% of M, and the total mass of polyvinyl alcohol and carbon nanotubes is 5% of M, where the mass ratio of polyvinyl alcohol to carbon nanotubes is 1:1.

[0045] Add the weighed raw materials above to a certain amount of deionized water to make the solid content 50%, and grind them for 2 h using 0.5-mm zirconium balls. After grinding, dry them at 120 °C for 2 h, and then, under a nitrogen atmosphere, first sinter them at 300 °C for 2 h and then at 600 °C for 5 h to obtain the primary material.

[0046] Add the primary material to a Tris buffer solution with a pH of 8.5, and then add dopamine hydrochloride at a dosage of 2% of the mass of the primary material. Stir continuously for 2 h, and centrifuge to obtain the precipitate. Then sinter it at 500 °C for 4 h to obtain the high-density lithium iron manganese phosphate cathode material.

[0047] Example 7 With the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate. Additionally, accurately weigh magnesium oxide, poly(ethylene glycol) tert-octylphenyl ether, polyvinyl alcohol, and carbon nanotubes. Denote the total mass of ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate as M. The mass of magnesium oxide is 0.8% of M, the mass of poly(ethylene glycol) tert-octylphenyl ether is 1% of M, and the total mass of polyvinyl alcohol and carbon nanotubes is 5% of M, where the mass ratio of polyvinyl alcohol to carbon nanotubes is 7:3.

[0048] Add the weighed raw materials above to a certain amount of deionized water to make the solid content 50%, and grind for 2 h using 0.5 mm zirconium balls. After grinding, dry at 120 °C for 2 h, and then under a nitrogen atmosphere, first sinter at 300 °C for 2 h, and then sinter at 600 °C for 5 h to obtain the primary material.

[0049] Add the primary material to a Tris buffer solution with a pH of 8.5, and then add dopamine hydrochloride according to the amount of 2% of the mass of the primary material, continuously stir for 2 h, and centrifuge to obtain the precipitate. Then sinter at 500 °C for 4 h to obtain the high-density lithium iron manganese phosphate cathode material.

[0050] Example 8 With the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate. Additionally, accurately weigh magnesium oxide, polyethylene glycol tert-octyl phenyl ether, polyvinyl alcohol, and carbon nanotubes. Denote the total mass of ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate as M, the mass of magnesium oxide as 0.8% of M, the mass of polyethylene glycol tert-octyl phenyl ether as 1% of M, and the total mass of polyvinyl alcohol and carbon nanotubes as 5% of M, where the mass ratio of polyvinyl alcohol to carbon nanotubes is 3:7.

[0051] Add the weighed raw materials above to a certain amount of deionized water to make the solid content 50%, and grind for 2 h using 0.5 mm zirconium balls. After grinding, dry at 120 °C for 2 h, and then under a nitrogen atmosphere, first sinter at 300 °C for 2 h, and then sinter at 600 °C for 5 h to obtain the primary material.

[0052] Add the primary material to a Tris buffer solution with a pH of 8.5, and then add dopamine hydrochloride according to the amount of 1% of the mass of the primary material, continuously stir for 2 h, and centrifuge to obtain the precipitate. Then sinter at 500 °C for 4 h to obtain the high-density lithium iron manganese phosphate cathode material.

[0053] Example 9 With the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate. Additionally, accurately weigh magnesium oxide, polyethylene glycol tert-octyl phenyl ether, polyvinyl alcohol, and carbon nanotubes. Denote the total mass of ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate as M, the mass of magnesium oxide as 0.8% of M, the mass of polyethylene glycol tert-octyl phenyl ether as 1% of M, and the total mass of polyvinyl alcohol and carbon nanotubes as 5% of M, where the mass ratio of polyvinyl alcohol to carbon nanotubes is 3:7.

[0054] Add the weighed raw materials above to a certain amount of deionized water to make the solid content 50%, and grind for 2 h using 0.5 mm zirconia beads. After grinding, dry at 120 °C for 2 h, and then under a nitrogen atmosphere, first sinter at 300 °C for 2 h, and then sinter at 600 °C for 5 h to obtain the primary material.

[0055] Add the primary material to a Tris buffer solution with a pH of 8.5, and then add dopamine hydrochloride at a dosage of 5% of the mass of the primary material. Stir continuously for 2 h, and centrifuge to obtain the precipitate. Then sinter at 500 °C for 4 h to obtain the high-density lithium iron manganese phosphate cathode material.

[0056] Comparative Example 1 With the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate. Additionally, accurately weigh magnesium oxide, polyvinyl alcohol, and carbon nanotubes. Let the total mass of ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate be M, the mass of magnesium oxide be 0.8% of M, and the total mass of polyvinyl alcohol and carbon nanotubes be 5% of M, where the mass ratio of polyvinyl alcohol to carbon nanotubes is 3:7.

[0057] Add the weighed raw materials above to a certain amount of deionized water to make the solid content 50%, and grind for 2 h using 0.5 mm zirconia beads. After grinding, dry at 120 °C for 2 h, and then under a nitrogen atmosphere, first sinter at 300 °C for 2 h, and then sinter at 600 °C for 5 h to obtain the primary material.

[0058] Add the primary material to a Tris buffer solution with a pH of 8.5, and then add dopamine hydrochloride at a dosage of 2% of the mass of the primary material. Stir continuously for 2 h, and centrifuge to obtain the precipitate. Then sinter at 500 °C for 4 h to obtain the high-density lithium iron manganese phosphate cathode material.

[0059] Comparative Example 2 With the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1, accurately weigh ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate. Additionally, accurately weigh magnesium oxide, polyethylene glycol tert-octylphenyl ether, and polyvinyl alcohol. Let the total mass of ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate be M, the mass of magnesium oxide be 0.8% of M, the mass of polyethylene glycol tert-octylphenyl ether be 1% of M, and the mass of polyvinyl alcohol be 5% of M.

[0060] Add the weighed raw materials above to a certain amount of deionized water to make the solid content 50%, and grind for 2 h using 0.5 mm zirconia beads. After grinding, dry at 120 °C for 2 h, and then under a nitrogen atmosphere, first sinter at 300 °C for 2 h, and then sinter at 600 °C for 5 h to obtain the primary material.

[0061] The primary materials were added to Tris buffer solution with a pH of 8.5, and then dopamine hydrochloride was added at a dosage of 2% of the mass of the primary materials. Stir continuously for 2 h, and centrifuge to obtain the precipitate. Then sinter at 500 °C for 4 h to obtain the high-density lithium iron manganese phosphate cathode material.

[0062] Comparative Example 3 With the molar ratio of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms being 1:0.6:0.4:1, ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate were accurately weighed. Additionally, magnesium oxide, polyethylene glycol tert-octyl phenyl ether, polyvinyl alcohol, and carbon nanotubes were accurately weighed. The total mass of ferrous oxalate dihydrate, lithium carbonate, manganese carbonate, and ammonium dihydrogen phosphate was designated as M, the mass of magnesium oxide was 0.8% of M, the mass of polyethylene glycol tert-octyl phenyl ether was 1% of M, and the total mass of polyvinyl alcohol and carbon nanotubes was 5% of M, where the mass ratio of polyvinyl alcohol to carbon nanotubes was 3:7.

[0063] The above-mentioned weighed raw materials were added to a certain amount of deionized water to make the solid content 50%, and ground with 0.5 mm zirconia balls for 2 h. After grinding, dry at 120 °C for 2 h, and then sinter in a nitrogen atmosphere, first at 300 °C for 2 h, and then at 600 °C for 5 h to obtain the high-density lithium iron manganese phosphate cathode material.

[0064] Performance Test The lithium iron manganese phosphate cathode materials in each example and each comparative example were respectively assembled into coin cells and the tap density and discharge performance were tested.

[0065] The lithium iron manganese phosphate cathode material, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 90:5:5 in N-methylpyrrolidone to make a slurry. The slurry was coated on a 20-μm-thick aluminum foil, then dried, roll-pressed, and die-cut to punch out the positive electrode sheet. A lithium sheet was used as the negative electrode, a polypropylene diaphragm was used, and the electrolyte was 1 mol / L LiPF6 (EC:DMC = 1:1), and a coin cell was assembled.

[0066] (1) Tap density: First, calculate the areal density of the positive electrode sheet, areal density = (electrode sheet mass - aluminum foil mass) / electrode sheet area, and then measure the thickness of the roll-pressed electrode sheet and the aluminum foil. Tap density = areal density / (electrode sheet thickness - aluminum foil thickness).

[0067] (2) Set the test voltage to 2.0 - 4.5 V, the test temperature to 25 °C, and test the capacity retention rate of the test battery after cycling 200 times at a 1C rate.

[0068] Table 1 Performance Test Results Group Compaction 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 As can be seen from Table 1, compared with the comparative example, the high-density lithium iron manganese phosphate cathode material in the embodiment of the present invention exhibits a higher tap density and better capacity retention rate, indicating that the use of a dispersant in the present invention can promote the uniform dispersion of each raw material during mixing, and the use of a composite carbon source and secondary carbon coating can further improve the electrochemical performance of the battery.

[0069] It can also be seen from Examples 1 and 4-9 that by referring to the raw material dosages disclosed in the present invention, it is possible to better ensure that the battery has excellent electrochemical performance.

[0070] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard 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 preparation method of a high-density lithium iron manganese phosphate cathode material, characterized in that, It includes the following steps: Step 1: Add an iron source, a lithium source, a manganese source, a phosphorus source, an additive, a dispersant, and a carbon source into deionized water, grind, dry, and sinter to obtain a primary material; Step 2: Coat the primary material with a polydopamine layer, and then sinter to obtain a high-density lithium iron manganese phosphate cathode material; Among them, the dispersant is polyoxyethylene tert-octyl phenyl ether; The carbon source is polyvinyl alcohol and at least one of glucose, carbon nanotubes, and graphene; The additive is at least one of magnesium oxide and silicon oxide.

2. The preparation method of the high-density lithium iron manganese phosphate cathode material according to claim 1, wherein, The molar ratio of the lithium source, manganese source, iron source, and phosphorus source in terms of lithium atoms, manganese atoms, iron atoms, and phosphorus atoms is 1:x:(1 - x):1, where 0.6 ≤ x ≤ 0.

9.

3. The preparation method of the high-density lithium iron manganese phosphate cathode material according to claim 1, characterized in that, The dosage of the dispersant is 0.5 - 1.0% of the total mass of the iron source, lithium source, manganese source, and phosphorus source.

4. The preparation method of the high-density lithium iron manganese phosphate cathode material according to claim 1, wherein The dosage 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 source, the dosage of polyvinyl alcohol is 30 - 50% of the total mass of the carbon source.

5. The preparation method of the high-density lithium iron manganese phosphate cathode material according to claim 1, wherein 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.

6. The preparation method of the high-density lithium iron manganese phosphate cathode material according to claim 1, characterized in that In Step 2, mix the primary material with a Tris buffer solution having a pH value of 8.0 - 9.0, then add dopamine hydrochloride in an amount of 2 - 3% of the mass of the primary material, centrifuge after the reaction, and then sinter.

7. The preparation method of the high-density lithium iron manganese phosphate cathode material according to claim 1, wherein The iron source is at least one of iron phosphate, iron oxide, iron 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.

8. The preparation method of the high-density lithium iron manganese phosphate cathode material according to claim 1, wherein, In Step 1, the drying temperature is 120 - 160°C, and the drying time is 2 - 3 h; the sintering operation is: first sinter at 300 - 400°C for 1.5 - 2.5 h, and then sinter at 500 - 750°C for 4 - 5 h.

9. The preparation method of the high-density lithium iron manganese phosphate cathode 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 h.

10. A high-density lithium iron manganese phosphate cathode material, characterized in that, It is prepared by the preparation method of the high-density lithium iron manganese phosphate cathode material according to any one of claims 1 - 9.