Lithium manganese iron phosphate material and preparation method thereof, and lithium ion battery

Abstract

The present invention belongs to the technical field of lithium ion battery positive electrode materials, and in particular to a kind of lithium iron manganese phosphate material and preparation method thereof, lithium ion battery, the lithium iron manganese phosphate material includes lithium iron manganese phosphate and a metal-second complexing agent-carbon composite layer coated on the surface of the lithium iron manganese phosphate, wherein the metal includes at least one of zirconium, aluminum, magnesium, cobalt, nickel, and zinc, and the second complexing agent includes at least one of ethylenediaminetetraacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, N-(2-hydroxy)ethylenediamine-N,N',N'-triacetic acid, and sulfosalicylic acid. The battery made of the lithium iron manganese phosphate material provided by the present invention can significantly suppress the dissolution of manganese ions during charge and discharge, thereby significantly improving the cycle performance of the lithium iron manganese phosphate battery.

Description

Technical Field

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

[0002] The development of new energy vehicles is increasingly trending towards pure electric vehicles. The rapid development of electric vehicles has driven the development of power batteries. Currently, new energy vehicle power batteries are still mainly lithium-ion batteries. The performance of the positive electrode material directly affects the performance of the battery. The positive electrode material is the core of the lithium-ion battery.

[0003] The theoretical capacity of lithium iron phosphate (LFP) is similar to that of lithium iron phosphate, both at 170 mAh / g, but the former has a higher voltage platform (4.3V vs 3.2V). Therefore, the theoretical energy density of LFP is close to 700 Wh / kg, which is 15-20% higher than that of LFP. It has the potential advantage of high energy density, providing the possibility of breaking through the current upper limit of battery range. At the same time, the raw material cost of LFP is about 28% lower than that of LFP. In summary, LFP has the advantages of high energy density, low cost, and high safety. It is currently a widely used type of lithium-ion battery positive electrode material. For example, the patent with publication number CN113948673A discloses a lithium-ion battery positive electrode sheet, its preparation method, and a lithium-ion battery, wherein the positive electrode active material includes LFP.

[0004] However, due to the easy dissolution of manganese ions in lithium iron manganese phosphate (LIMFP), the battery's cycling performance is poor. To address this issue, existing technologies typically use coating methods to modify LIMFP, for example, by coating the material surface with a carbon material layer and a chelating agent layer. However, this method has limited ability to inhibit the dissolution of manganese ions in LIMFP, and the cycling performance of LIMFP batteries remains poor. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a lithium iron manganese phosphate material and a preparation method thereof, and a lithium-ion battery. The battery made of the lithium iron manganese phosphate material provided by the present invention can significantly inhibit the dissolution of manganese ions during the charge and discharge process, thereby significantly improving the cycle performance of the lithium iron manganese phosphate battery.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a lithium iron manganese phosphate material, comprising lithium iron manganese phosphate and a metal-second chelating agent-carbon composite layer coated on the surface of the lithium iron manganese phosphate, wherein the metal comprises at least one of zirconium, aluminum, magnesium, cobalt, nickel, and zinc, and the second chelating agent comprises at least one of ethylenediaminetetraacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, N-(2-hydroxy)ethylenediamine-N,N',N'-triacetic acid, and sulfosalicylic acid.

[0008] The battery made of the lithium manganese iron phosphate material provided by the present invention can significantly inhibit the dissolution of manganese ions during the charge and discharge process, thereby significantly improving the cycle performance of the lithium manganese iron phosphate battery.

[0009] In the above-mentioned lithium manganese iron phosphate material, as a preferred embodiment, the metal includes zirconium, and the second complexing agent includes ethylenediaminetetraacetic acid or trans-1,2-cyclohexanediaminetetraacetic acid.

[0010] In the above-mentioned lithium iron manganese phosphate material, as a preferred embodiment, the metal-second complexing agent-carbon composite layer is formed by first forming a metal-carbon composite layer on the surface of the lithium iron manganese phosphate with a metal inorganic salt and a first complexing agent, which is then reacted with trimesic acid and complexed with a second complexing agent. The second complexing agent is capable of complexing with manganese ions and metal ions corresponding to the metal in the metal-carbon composite layer. In the embodiment of the present invention, by first forming a metal-carbon composite layer on the surface of the lithium iron manganese phosphate, and then reacting with trimesic acid and complexing with a second complexing agent to form a metal-second complexing agent-carbon composite layer, the battery made of the prepared lithium iron manganese phosphate material can significantly inhibit the dissolution of manganese ions during the charge and discharge process, thereby significantly improving the cycle performance of the lithium iron manganese phosphate battery.

[0011] In the above-mentioned lithium manganese iron phosphate material, as a preferred embodiment, the metal-carbon composite layer is formed by coating a metal inorganic salt and a first complexing agent with pyrolytic carbon.

[0012] In the aforementioned lithium iron manganese phosphate material, as a preferred embodiment, the metal-second complexing agent-carbon composite layer is formed by first forming a metal-carbon composite layer on the surface of the lithium iron manganese phosphate with a metal inorganic salt and a first complexing agent, followed by a metal-organic vapor phase deposition method, which reacts with trimesic acid and complexes the second complexing agent. Compared to solid-phase mixing (conventional mechanical stirring), the metal-organic vapor phase deposition method used in the present embodiment allows the second complexing agent to be more uniformly and densely coated on the surface of the lithium iron manganese phosphate and is less likely to fall off.

[0013] In the above-mentioned lithium manganese iron phosphate material, as a preferred embodiment, the molar ratio of the metal inorganic salt to the first complexing agent is (1-3):1, for example, it can be 1:1, 2:1 or 3:1.

[0014] In the above-mentioned lithium manganese iron phosphate material, as a preferred embodiment, the mass ratio of the total mass of the metal inorganic salt and the first complexing agent to the lithium manganese iron phosphate is (2-10):100, for example, it can be 2:100, 4:100, 6:100, 8:100 or 10:100, etc.

[0015] In the above-mentioned lithium manganese iron phosphate material, as a preferred embodiment, the molar ratio of the metal inorganic salt to the trimesic acid is (1-3):1, for example, it can be 1:1, 2:1 or 3:1.

[0016] In the above-mentioned lithium manganese iron phosphate material, as a preferred embodiment, the molar ratio of the metal inorganic salt to the second complexing agent is (0.2-1):(1-3), for example, it can be 0.3:1, 0.5:1 or 0.8:3.

[0017] In the above-mentioned lithium manganese iron phosphate material, as a preferred embodiment, the metal inorganic salt includes at least one of zirconium oxychloride, aluminum chloride, magnesium nitrate, cobalt nitrate, nickel nitrate, and zinc acetate.

[0018] In the above-mentioned lithium manganese iron phosphate material, as a preferred embodiment, the first complexing agent includes at least one of ethylenediaminetetraacetic acid, aminotriacetic acid, diethylenetriaminepentaacetic acid, citric acid, tartaric acid, gluconic acid, hydroxyethylethylenediaminetriacetic acid, and dihydroxyethylglycine, and the first complexing agent here also serves as a carbon source.

[0019] In the above-mentioned lithium manganese iron phosphate material, as a preferred embodiment, the chemical composition of the lithium manganese iron phosphate is LiMn x Fe 1-x PO4, wherein 0.1≤x≤0.8, the molar ratio of Mn to Fe is x:(1-x), for example, x can be 0.1, 0.3, 0.6 or 0.8, etc.

[0020] In a second aspect, the present invention provides a method for preparing the lithium manganese iron phosphate material according to the first aspect, comprising the following steps:

[0021] S1, adding a metal inorganic salt and a first complexing agent to a first solvent, allowing the metal inorganic salt and the first complexing agent to react completely, adding a surfactant, and stirring to obtain a mixed solution B;

[0022] S2, adding the lithium manganese iron phosphate to the mixed solution B, stirring, drying, and then coating with pyrolytic carbon to obtain a metal-carbon composite-coated lithium manganese iron phosphate material;

[0023] S3, placing the metal-carbon composite-coated lithium manganese iron phosphate material in a metal organic vapor deposition system (chemical vapor deposition system) as a substrate, and reacting it with the vaporized mixture containing formic acid and trimesic acid to obtain a precursor;

[0024] S4. Placing the precursor in a metal organic vapor deposition system (chemical vapor deposition system) as a substrate, and reacting with the vaporized second complexing agent to obtain a lithium manganese iron phosphate material having a metal-second complexing agent-carbon composite coating layer.

[0025] The present invention utilizes a complexation method to react a metal inorganic salt with a first complexing agent to form a metal complex, which is then coated on the surface of lithium iron manganese phosphate particles. This metal complex is then coated with carbon through pyrolysis to obtain a metal-carbon composite-coated lithium iron manganese phosphate material. This metal complex is then reacted with a second complexing agent using a metal organic vapor deposition method to obtain a lithium iron manganese phosphate material having a metal-second complexing agent-carbon composite coating layer. The metal-second complexing agent-carbon composite-coated lithium iron manganese phosphate material prepared by the present invention, when subsequently applied to batteries, can effectively capture dissolved manganese ions or significantly inhibit manganese ion dissolution, thereby significantly improving the cycle performance of the lithium iron manganese phosphate battery.

[0026] In the above-mentioned method for preparing lithium manganese iron phosphate material, as a preferred embodiment, the first solvent is water, preferably deionized water.

[0027] In the above-mentioned method for preparing lithium manganese iron phosphate material, as a preferred embodiment, the surfactant includes at least one of sodium octadecyl sulfate, sodium stearate, sodium dodecylbenzenesulfonate, and sodium hepatocholate.

[0028] In the above-mentioned preparation method of lithium manganese iron phosphate material, as a preferred embodiment, the mass of the surfactant is 5% to 10% of the total weight of the metal inorganic salt and the first complexing agent, for example, it can be 5%, 7% or 10%.

[0029] In the preparation method of the above-mentioned lithium manganese iron phosphate material, as a preferred embodiment, the pyrolytic carbon coating includes: under the protection of an inert gas atmosphere, heat treatment at 400-650°C (for example, 400°C, 450°C, 500°C, 550°C, 600°C or 650°C, etc.) for 12-24h (for example, 12h, 15h, 18h, 20h, 22h or 24h, etc.) to perform pyrolytic carbon coating.

[0030] In the above-mentioned method for preparing lithium manganese iron phosphate material, as a preferred embodiment, the inert gas includes one of nitrogen, helium and argon.

[0031] In the above-mentioned preparation method of lithium manganese iron phosphate material, as a preferred embodiment, in step S2, the drying is constant temperature drying, and the drying temperature is 50-80°C, for example, 50°C, 60°C, 70°C or 80°C.

[0032] In the above-mentioned preparation method of lithium manganese iron phosphate material, as a preferred embodiment, in step S2, the stirring temperature is 25-50°C (for example, it can be 25°C, 35°C, 45°C or 50°C, etc.), the stirring rate is 2000-3500r / s (for example, it can be 2000r / s, 2500r / s, 3000r / s or 3500r / s, etc.), and the stirring time is 2-4h.

[0033] In the above-mentioned preparation method of lithium manganese iron phosphate material, as a preferred embodiment, in step S1, the stirring temperature is 25-60°C (for example, it can be 25°C, 40°C, 50°C or 60°C, etc.), the stirring rate is 1000-2500r / s (for example, it can be 1000r / s, 1500r / s, 2000r / s or 2500r / s, etc.), and the stirring time is 1-3h.

[0034] In the above-mentioned method for preparing the lithium manganese iron phosphate material, as a preferred embodiment, the metal-carbon composite-coated lithium manganese iron phosphate material is placed in a metal organic vapor deposition system as a substrate and reacted with the vaporized mixture containing formic acid and trimesic acid, comprising:

[0035] adding formic acid and trimesic acid to the second solvent, mixing and stirring uniformly to obtain a mixed solution C;

[0036] The metal-carbon composite-coated lithium manganese iron phosphate material is placed in a metal organic vapor deposition system as a substrate, and then the mixed solution C is vaporized and reacted with the metal-carbon composite-coated lithium manganese iron phosphate material under a nitrogen atmosphere.

[0037] In the above-mentioned method for preparing lithium manganese iron phosphate material, as a preferred embodiment, the second solvent is anhydrous ethanol.

[0038] In the above-mentioned method for preparing lithium manganese iron phosphate material, as a preferred embodiment, the precursor is placed in a metal organic vapor deposition system as a substrate to react with the vaporized second complexing agent, comprising:

[0039] adding the second complexing agent to the third solvent, mixing and stirring uniformly to obtain a mixed solution D;

[0040] The precursor is placed in a metal organic vapor deposition system as a substrate, and then the mixed solution D is vaporized and reacts with the precursor.

[0041] In the above-mentioned method for preparing lithium manganese iron phosphate material, as a preferred embodiment, the third solvent is water, preferably deionized water.

[0042] In the above-mentioned method for preparing lithium manganese iron phosphate material, as a preferred embodiment, in the step of obtaining the mixed solution C, the stirring temperature is 25-30°C, the stirring rate is 300-2000 r / s (for example, 300 r / s, 600 r / s, 1000 r / s, 1400 r / s or 2000 r / s, etc.), and the stirring time is 0.5-1.5 h.

[0043] In the above-mentioned method for preparing lithium manganese iron phosphate material, as a preferred embodiment, in the step of obtaining the mixed solution D, the stirring temperature is 25-30°C, the stirring rate is 300-2000 r / s (for example, 300 r / s, 600 r / s, 1000 r / s, 1400 r / s or 2000 r / s, etc.), and the stirring time is 0.5-1.5 h.

[0044] In the above-mentioned preparation method of lithium manganese iron phosphate material, as a preferred embodiment, in step S3, the reaction temperature is 80-150°C (for example, it can be 80°C, 100°C, 130°C or 150°C, etc.), and the reaction time is 24-48h (for example, it can be 24h, 28h, 32h, 36h, 40h or 48h, etc.).

[0045] In the above-mentioned method for preparing lithium manganese iron phosphate material, as a preferred embodiment, in step S4, the reaction temperature is 50-100°C (for example, 50°C, 70°C or 100°C, etc.), and the reaction time is 6-10h (for example, 6h, 8h or 10h, etc.).

[0046] In the above-mentioned method for preparing lithium manganese iron phosphate material, as a preferred embodiment, in the step of obtaining the mixed solution C, the volume ratio of the formic acid to the second solvent is (2-10):100, for example, it can be 2:100, 4:100, 6:100, 8:100 or 10:100, etc.

[0047] In a third aspect, the present invention provides a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The active material of the positive electrode sheet comprises the lithium iron manganese phosphate material provided in the first aspect or the lithium iron manganese phosphate material prepared by the preparation method of the lithium iron manganese phosphate material provided in the second aspect. The preparation method of the positive electrode sheet is as follows:

[0048] A binder (such as polyvinylidene fluoride (PVDF)), a conductive agent (such as conductive carbon black SP) and an organic solvent (N-methylpyrrolidone) are mixed together and stirred to obtain a mixed slurry. Subsequently, a lithium manganese iron phosphate material having a metal-second complexing agent-carbon composite coating layer is added to the mixed slurry, stirred and dispersed to obtain a positive electrode slurry. The positive electrode slurry is coated on the surface of an aluminum foil current collector and rolled to obtain a positive electrode sheet.

[0049] The lithium ion battery provided by the present invention has low manganese dissolution during the charge and discharge process and has high cycle performance.

[0050] Compared with the prior art, the present invention has at least one of the following advantages:

[0051] (1) The battery made of the lithium manganese iron phosphate material provided by the present invention can significantly inhibit the dissolution of manganese ions during the charge and discharge process, thereby significantly improving the cycle performance of the lithium manganese iron phosphate battery.

[0052] (2) The present invention forms a metal-carbon composite layer on the surface of the lithium manganese iron phosphate by first forming a metal-carbon composite layer, and then reacting with trimesic acid and formic acid in sequence and complexing with a second complexing agent to form a metal-second complexing agent-carbon composite layer. The present invention uses a liquid phase method and an organic metal vapor deposition method to form a metal-second complexing agent-carbon composite coating layer on the surface of the lithium manganese iron phosphate material, thereby improving the stability of the lithium manganese iron phosphate material during the cycle process from the two aspects of structural stability and manganese ion capture, thereby effectively improving the cycle life of the battery.

[0053] (3) The present invention utilizes coordination bonds to graft the complexing agent (manganese ion chelating agent) onto the surface of the lithium manganese iron phosphate material, thereby achieving coating uniformity and improving the stability of the complexing agent coating layer, thereby ensuring the capture effect of dissolved manganese ions, significantly inhibiting the dissolution of manganese ions, and effectively improving the cycle performance of the battery. DETAILED DESCRIPTION

[0054] In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples. The scope of protection of this application includes but is not limited to the following examples. The following examples are only used to illustrate the advantages and effects of the technical solutions of this application and do not constitute a limitation on the scope of protection of this application. Equivalent substitutions made by those skilled in the art based on this application are all within the scope of protection of this application.

[0055] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which this invention belongs. The experimental reagents used in the following examples, unless otherwise specified, are conventional biochemical reagents; the experimental reagent amounts, unless otherwise specified, are those used in routine experimental procedures; and the experimental methods, unless otherwise specified, are conventional methods.

[0056] In a first aspect, the present invention provides a lithium iron manganese phosphate material, which includes lithium iron manganese phosphate and a metal-second complexing agent-carbon composite layer coated on the surface of the lithium iron manganese phosphate, wherein the metal includes at least one of zirconium, aluminum, magnesium, cobalt, nickel, and zinc. The metal-second complexing agent-carbon composite layer is formed by first coating the surface of the lithium iron manganese phosphate with a metal inorganic salt and a first complexing agent through pyrolysis carbon to form a metal-carbon composite layer, and then reacting with trimesic acid and complexing with a second complexing agent using a metal organic vapor phase deposition method. The second complexing agent can complex with manganese ions and metal ions corresponding to the metal in the metal-carbon composite layer. The molar ratio of the metal inorganic salt to the first complexing agent is (1 to 3): 1, and the mass ratio of the total mass of the metal inorganic salt and the first complexing agent to the mass of the lithium iron manganese phosphate is (2 to 10): 1. 00, the molar ratio of the metal inorganic salt to the trimesic acid is (1-3):1, the molar ratio of the metal inorganic salt to the second complexing agent is (0.2-1):(1-3), the metal inorganic salt includes at least one of zirconium oxychloride, aluminum chloride, magnesium nitrate, cobalt nitrate, nickel nitrate, and zinc acetate, the first complexing agent includes at least one of ethylenediaminetetraacetic acid, aminotriacetic acid, diethylenetriaminepentaacetic acid, citric acid, tartaric acid, gluconic acid, hydroxyethylethylenediaminetriacetic acid, and dihydroxyethylglycine, the second complexing agent includes at least one of ethylenediaminetetraacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, N-(2-hydroxy)ethylenediamine-N,N',N'-triacetic acid, and sulfosalicylic acid, and the chemical composition of the lithium manganese iron phosphate is LiMn x Fe 1-x PO4, wherein 0.1≤x≤0.8, and the molar ratio of Mn to Fe is x:(1-x).

[0057] In response to the problem of manganese ion dissolution in lithium manganese iron phosphate materials, the present invention prepares a metal-second complexing agent-carbon composite coating layer by metal organic vapor deposition. First, the metal and the first complexing agent (carbon source) are uniformly coated on the surface of the lithium manganese iron phosphate material particles by a liquid phase method, and carbonized at high temperature to form a metal-carbon composite coating layer; then the second complexing agent (manganese ion chelating agent) is coordinated with the metal on the surface of the particles by metal organic vapor deposition, and finally a uniform metal-second complexing agent-carbon composite coating layer is formed on the surface of the lithium manganese iron phosphate material. On the one hand, the composite coating layer can effectively maintain the structural stability of the material, thereby improving the cycle performance of the battery; on the other hand, the second complexing agent is grafted on the surface of the material in the form of a coordination bond, which ensures the uniformity and stability of the coating layer, can effectively and quickly capture and complex the dissolved manganese ions, and at the same time increases the possibility of manganese ions re-migrating into the crystal structure, thereby improving the cycle performance of the battery.

[0058] In a second aspect, the present invention provides a method for preparing the lithium manganese iron phosphate material according to the first aspect, comprising the following steps:

[0059] S1. Adding a metal inorganic salt and a first complexing agent to water, allowing the metal inorganic salt and the first complexing agent to react completely, adding a surfactant, and stirring uniformly to obtain a mixed solution B, wherein the surfactant includes at least one of sodium octadecyl sulfate, sodium stearate, sodium dodecylbenzenesulfonate, and sodium bileate, and the mass of the surfactant is 5% to 10% of the total weight of the metal inorganic salt and the first complexing agent, the stirring temperature is 25 to 60° C., the stirring rate is 1000 to 2500 r / s, and the stirring time is 1 to 3 h.

[0060] S2. Add the lithium iron manganese phosphate to the mixed solution B, stir, dry at a constant temperature, and then heat treat at 400-650° C. for 12-24 hours under the protection of an inert gas atmosphere to perform pyrolysis carbon coating to obtain a metal-carbon composite-coated lithium iron manganese phosphate material, wherein the inert gas includes one of nitrogen, helium, and argon, the drying temperature is 50-80° C., the stirring temperature is 25-50° C., the stirring rate is 2000-3500 r / s, and the stirring time is 2-4 hours.

[0061] S3. Add formic acid and trimesic acid to anhydrous ethanol, mix and stir evenly to obtain a mixed solution C; place the metal-carbon composite-coated lithium manganese iron phosphate material in a metal organic vapor deposition system as a substrate, and then vaporize the mixed solution C and react with the metal-carbon composite-coated lithium manganese iron phosphate material under a nitrogen atmosphere to obtain a precursor, wherein, in the step of obtaining the mixed solution C, the stirring temperature is 25-30°C, the stirring rate is 300-2000 r / s, the stirring time is 0.5-1.5h, and the volume ratio of formic acid to the second solvent is (2-10):100; the reaction temperature is 80-150°C, and the reaction time is 24-48h.

[0062] S4. Add the second complexing agent to water, mix and stir evenly to obtain a mixed solution D; place the precursor in a metal organic vapor deposition system as a substrate, then vaporize the mixed solution D and react with the precursor to obtain a lithium manganese iron phosphate material having a metal-second complexing agent-carbon composite coating layer, wherein, in the step of obtaining the mixed solution D, the stirring temperature is 25-30°C, the stirring rate is 300-2000 r / s, and the stirring time is 0.5-1.5h; the reaction temperature is 50-100°C, and the reaction time is 6-10h.

[0063] In a third aspect, the present invention provides a lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The active material of the positive electrode sheet comprises the lithium iron manganese phosphate material provided in the first aspect or the lithium iron manganese phosphate material prepared by the preparation method of the lithium iron manganese phosphate material provided in the second aspect. The preparation method of the positive electrode sheet is as follows:

[0064] A binder (such as polyvinylidene fluoride (PVDF)), a conductive agent (such as conductive carbon black SP) and an organic solvent (N-methylpyrrolidone) are mixed together and stirred to obtain a mixed slurry. Subsequently, a lithium manganese iron phosphate material having a metal-second complexing agent-carbon composite coating layer is added to the mixed slurry, stirred and dispersed to obtain a positive electrode slurry. The positive electrode slurry is coated on the surface of an aluminum foil current collector and rolled to obtain a positive electrode sheet.

[0065] In order to further understand the present invention, the lithium manganese iron phosphate material and its preparation method and lithium ion battery provided by the present invention are described in detail below with reference to the embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0066] Example 1

[0067] The lithium iron manganese phosphate material provided in this embodiment includes lithium iron manganese phosphate and a Zr-EDTA (ethylenediaminetetraacetic acid)-carbon composite layer coated on the surface of the lithium iron manganese phosphate.

[0068] The method for preparing the lithium manganese iron phosphate material provided in this embodiment includes the following steps:

[0069] S1. Weigh 0.644 g of zirconium oxychloride and 0.584 g of ethylenediaminetetraacetic acid, add 100 mL of deionized water to dissolve, stir at 30°C for 1 h at a stirring rate of 1500 r / s to allow the zirconium oxychloride and ethylenediaminetetraacetic acid to fully react, then add 0.0745 g of sodium stearate, and continue stirring for 1 h to obtain a mixed solution B.

[0070] S2, then weigh 20.45g of unmodified lithium manganese iron phosphate (LiMn 0.7 Fe 0.3 PO4), added to the mixed solution B, stirred at 25 ° C for 3 h, and the stirring rate was 3000 r / s. The resulting solution was then placed in an 80 ° C drying oven to obtain a mixture, which was then placed in a tube furnace at a temperature of 500 ° C. and heat treated at 500 ° C for 18 h under the protection of a nitrogen atmosphere to perform pyrolytic carbon coating to obtain a zirconium-carbon composite-coated lithium manganese iron phosphate material.

[0071] S3. Weigh 0.5 mL of formic acid and 0.420 g of trimesic acid (H3BTC), add 10 mL of anhydrous ethanol, stir at 25 ° C for 1 h, and the stirring rate is 1000 r / s to obtain a mixed solution C; place the zirconium-carbon composite-coated lithium manganese iron phosphate material in a chemical vapor deposition system (metal organic vapor deposition system) as a substrate, vaporize the mixed solution C, and react the zirconium in the zirconium-carbon composite-coated lithium manganese iron phosphate material with trimesic acid under a nitrogen atmosphere. The reaction temperature is 120 ° C and the reaction time is 36 h to obtain a precursor.

[0072] S4. Weigh 3.36 g of ethylenediaminetetraacetic acid, add 10 mL of deionized water, stir at 25 ° C for 1 hour, and the stirring rate is 1000 r / s to obtain a mixed solution D; place the precursor in a chemical vapor deposition system as a substrate, vaporize the mixed solution D, and react with the precursor at a reaction temperature of 80 ° C and a reaction time of 8 hours, so that the ethylenediaminetetraacetic acid replaces the carboxyl group on the surface of the precursor to obtain a Zr-EDTA-carbon composite-coated lithium manganese iron phosphate material.

[0073] The Zr-EDTA-carbon composite-coated lithium manganese iron phosphate material prepared in this example was used as the active material for the positive electrode. A button-type battery was assembled according to the following method: the positive electrode active material, polyvinylidene fluoride (PVDF), and superconducting carbon black (SP) were mixed in a 90:5:5 mass ratio and stirred in NMP. The slurry was evenly coated on aluminum foil and dried in a vacuum oven at 80°C for 2 hours. A circular electrode piece with a diameter of 14 mm was cut using a punch to serve as the positive working electrode. The R2032 button-type battery was assembled in a glove box according to a specific assembly process, using a lithium metal sheet as the counter electrode, a Celgard 2400 porous polypropylene (PP) film as the separator, and a 1M lithium hexafluorophosphate (LiPF6) solution as the electrolyte. The electrolyte solvent was a 1:1 (volume ratio) mixture of EC and DMC. After assembly, the battery was allowed to stand for 3 hours to allow the electrolyte to fully penetrate the electrode materials.

[0074] Example 2

[0075] The lithium iron manganese phosphate material provided in this embodiment includes lithium iron manganese phosphate and a Zr-EDTA-carbon composite layer coated on the surface of the lithium iron manganese phosphate.

[0076] The method for preparing the lithium manganese iron phosphate material provided in this embodiment includes the following steps:

[0077] S1. Weigh 0.644 g of zirconium oxychloride and 0.384 g of citric acid, add 100 mL of deionized water to dissolve, and stir at 40°C for 1 h at a stirring rate of 2000 r / s to allow the zirconium oxychloride and citric acid to fully react. Then, add 0.0745 g of sodium stearate and continue stirring for 1 h to obtain a mixed solution B.

[0078] S2, then weigh 20.45g of unmodified lithium manganese iron phosphate (LiMn 0.7 Fe 0.3 PO4) was added to the mixed solution B, stirred at 35 ° C for 3 h at a stirring rate of 3000 r / s, and then the resulting solution was placed in an 80 ° C drying oven to obtain a mixture, which was then placed in a tube furnace at a temperature of 600 ° C and heat treated at 600 ° C for 16 h under the protection of a nitrogen atmosphere to perform pyrolytic carbon coating to obtain a zirconium-carbon composite-coated lithium manganese iron phosphate material.

[0079] S3. Weigh 0.5 mL of formic acid and 0.420 g of trimesic acid (H3BTC), add 10 mL of anhydrous ethanol, stir at 25 ° C for 1 hour, and the stirring rate is 1400 r / s to obtain a mixed solution C; place the zirconium-carbon composite-coated lithium manganese iron phosphate material in a chemical vapor deposition system (metal organic vapor deposition system) as a substrate, vaporize the mixed solution C, and react the zirconium in the zirconium-carbon composite-coated lithium manganese iron phosphate material with trimesic acid under a nitrogen atmosphere. The reaction temperature is 100 ° C and the reaction time is 38 hours to obtain a precursor.

[0080] S4. Weigh 3.36 g of ethylenediaminetetraacetic acid, add 10 mL of deionized water, stir at 25 ° C for 1 hour, and the stirring rate is 1000 r / s to obtain a mixed solution D; place the precursor in a chemical vapor deposition system as a substrate, vaporize the mixed solution D, and react with the precursor at a reaction temperature of 60 ° C and a reaction time of 10 hours, so that the ethylenediaminetetraacetic acid replaces the carboxyl group on the surface of the precursor to obtain a Zr-EDTA-carbon composite-coated lithium manganese iron phosphate material.

[0081] The Zr-EDTA-carbon composite-coated lithium manganese iron phosphate material prepared in this example was used as the active material for the positive electrode. A button-type battery was assembled according to the following method: the positive electrode active material, polyvinylidene fluoride (PVDF), and superconducting carbon black (SP) were mixed in a 90:5:5 mass ratio and stirred in NMP. The slurry was evenly coated on aluminum foil and dried in a vacuum oven at 80°C for 2 hours. A circular electrode piece with a diameter of 14 mm was cut using a punch to serve as the positive working electrode. The R2032 button-type battery was assembled in a glove box according to a specific assembly process, using a lithium metal sheet as the counter electrode, a Celgard 2400 porous polypropylene (PP) film as the separator, and a 1M lithium hexafluorophosphate (LiPF6) solution as the electrolyte. The electrolyte solvent was a 1:1 (volume ratio) mixture of EC and DMC. After assembly, the battery was allowed to stand for 3 hours to allow the electrolyte to fully penetrate the electrode materials.

[0082] Example 3

[0083] The lithium manganese iron phosphate material provided in this embodiment includes lithium manganese iron phosphate and a Zr-trans-1,2-cyclohexanediaminetetraacetic acid-carbon composite layer coated on the surface of the lithium manganese iron phosphate.

[0084] The method for preparing the lithium manganese iron phosphate material provided in this embodiment includes the following steps:

[0085] S1. Weigh 0.644 g of zirconium oxychloride and 0.584 g of ethylenediaminetetraacetic acid, add 100 mL of deionized water to dissolve, stir at 50°C for 1 h at a stirring rate of 1000 r / s to allow the zirconium oxychloride and ethylenediaminetetraacetic acid to fully react, then add 0.0745 g of sodium stearate, and continue stirring for 1 h to obtain a mixed solution B.

[0086] S2, then weigh 20.45g of unmodified lithium manganese iron phosphate (LiMn 0.7 Fe 0.3 PO4), added to the mixed solution B, stirred at 40 ° C for 3 h, and the stirring rate was 3000 r / s. The resulting solution was then placed in an 80 ° C drying oven to dry the mixture, which was then placed in a tube furnace at a temperature of 500 ° C. and heat treated at 500 ° C for 18 h under the protection of a nitrogen atmosphere to perform pyrolytic carbon coating to obtain a zirconium-carbon composite-coated lithium manganese iron phosphate material.

[0087] S3. Weigh 0.5 mL of formic acid and 0.420 g of trimesic acid (H3BTC), add 10 mL of anhydrous ethanol, stir at 25 ° C for 1 h, and the stirring rate is 1000 r / s to obtain a mixed solution C; place the zirconium-carbon composite-coated lithium manganese iron phosphate material in a chemical vapor deposition system (metal organic vapor deposition system) as a substrate, vaporize the mixed solution C, and react the zirconium in the zirconium-carbon composite-coated lithium manganese iron phosphate material with trimesic acid under a nitrogen atmosphere. The reaction temperature is 120 ° C and the reaction time is 36 h to obtain a precursor.

[0088] S4. Weigh 3.98 g of trans-1,2-cyclohexanediaminetetraacetic acid, add 10 mL of deionized water, stir at 25°C for 1 h, and the stirring rate is 1000 r / s to obtain a mixed solution D; place the precursor in a chemical vapor deposition system as a substrate, vaporize the mixed solution D, and react with the precursor at a reaction temperature of 80°C and a reaction time of 8 h, so that trans-1,2-cyclohexanediaminetetraacetic acid replaces the carboxyl group on the surface of the precursor to obtain a Zr-trans-1,2-cyclohexanediaminetetraacetic acid-carbon composite-coated lithium manganese iron phosphate material.

[0089] The Zr-trans-1,2-cyclohexanediaminetetraacetic acid-carbon composite-coated lithium manganese iron phosphate material prepared in this example served as the active material for the positive electrode. A button cell was assembled as follows: the active material, polyvinylidene fluoride (PVDF), and superconducting carbon black (SP) were mixed in a 90:5:5 mass ratio and stirred in NMP. The slurry was evenly coated on aluminum foil and dried in a vacuum oven at 80°C for 2 hours. A circular electrode piece with a diameter of 14 mm was punched out to serve as the positive working electrode. The R2032 button cell was assembled in a glove box according to a specific assembly process using a lithium metal sheet as the counter electrode, a Celgard 2400 porous polypropylene (PP) membrane as the separator, and a 1M lithium hexafluorophosphate (LiPF6) solution as the electrolyte. The electrolyte solvent was a 1:1 (volume ratio) mixture of EC and DMC. After assembly, let it stand for 3 hours to allow the electrolyte and electrode materials to fully penetrate.

[0090] Comparative Example 1

[0091] The preparation method of the lithium manganese iron phosphate material provided in this comparative example is basically the same as that of Example 1, except that zirconium oxychloride is not added in step S1, and ethylenediaminetetraacetic acid is not added in step S4, that is, no metal-second complexing agent layer is formed. Specifically, the method includes the following steps:

[0092] S1. Weigh 0.584 g of ethylenediaminetetraacetic acid, add 100 mL of deionized water to dissolve, stir at 30° C. for 1 h at a stirring rate of 1500 r / s, then add 0.0745 g of sodium stearate, and continue stirring for 1 h to obtain a mixed solution B.

[0093] S2, then weigh 20.45g of unmodified lithium manganese iron phosphate (LiMn 0.7 Fe 0.3 PO4), added to the mixed solution B, stirred at 25 ° C for 3 h, and the stirring rate was 3000 r / s. The resulting solution was then placed in an 80 ° C drying oven to dry the mixture, which was then placed in a tube furnace at a temperature of 500 ° C. and heat treated at 500 ° C for 18 h under the protection of a nitrogen atmosphere to perform pyrolysis carbon coating to obtain a carbon-coated lithium manganese iron phosphate material.

[0094] S3. Weigh 0.5 mL of formic acid and 0.420 g of trimesic acid (H3BTC), add 10 mL of anhydrous ethanol, stir at 25 ° C for 1 h, and the stirring rate is 1000 r / s to obtain a mixed solution C; place the carbon-coated lithium manganese iron phosphate material in a chemical vapor deposition system (metal organic vapor deposition system) as a substrate, vaporize the mixed solution C, and react the carbon-coated lithium manganese iron phosphate material with trimesic acid under a nitrogen atmosphere at a reaction temperature of 120 ° C and a reaction time of 36 h to obtain a precursor.

[0095] S4. Weigh 10 mL of deionized water to obtain solution D; place the precursor in a chemical vapor deposition system as a substrate, vaporize solution D, and react with the precursor at a reaction temperature of 80° C. for 8 hours to obtain a carbon-coated lithium manganese iron phosphate material.

[0096] Referring to the assembly method of the button battery in Example 1, the carbon-coated lithium manganese iron phosphate material prepared in this comparative example was used as the active material of the positive electrode material to assemble a button battery.

[0097] Comparative Example 2

[0098] The preparation method of the lithium manganese iron phosphate material provided in this comparative example is basically the same as that of Example 1, except that zirconium oxychloride is not added in step S1, that is, a metal coating layer is not formed, and the ethylenediaminetetraacetic acid in step S4 cannot be grafted onto the surface of the material particles through coordination bonds. Specifically, the method includes the following steps:

[0099] S1. Weigh 0.584 g of ethylenediaminetetraacetic acid, add 100 mL of deionized water to dissolve, stir at 30° C. for 1 h at a stirring rate of 1500 r / s, then add 0.0745 g of sodium stearate, and continue stirring for 1 h to obtain a mixed solution B.

[0100] S2, then weigh 20.45g of unmodified lithium manganese iron phosphate (LiMn 0.7 Fe 0.3 PO4), added to the mixed solution B, stirred at 25 ° C for 3 h, and the stirring rate was 3000 r / s. The resulting solution was then placed in an 80 ° C drying oven to dry the mixture, which was then placed in a tube furnace at a temperature of 500 ° C. and heat treated at 500 ° C for 18 h under the protection of a nitrogen atmosphere to perform pyrolysis carbon coating to obtain a carbon-coated lithium manganese iron phosphate material.

[0101] S3. Weigh 0.5 mL of formic acid and 0.420 g of trimesic acid (H3BTC), add 10 mL of anhydrous ethanol, stir at 25 ° C for 1 h, and the stirring rate is 1000 r / s to obtain a mixed solution C; place the carbon-coated lithium manganese iron phosphate material in a chemical vapor deposition system (metal organic vapor deposition system) as a substrate, vaporize the mixed solution C, and react the carbon composite-coated lithium manganese iron phosphate material with trimesic acid under a nitrogen atmosphere. The reaction temperature is 120 ° C and the reaction time is 36 h to obtain a precursor.

[0102] S4. Weigh 3.36 g of ethylenediaminetetraacetic acid, add 10 mL of deionized water, stir at 25°C for 1 h, and a stirring rate of 1000 r / s to obtain a mixed solution D; place the precursor in a chemical vapor deposition system as a substrate, vaporize the mixed solution D, and react with the precursor at a reaction temperature of 80°C and a reaction time of 8 h to obtain an EDTA-carbon composite-coated lithium manganese iron phosphate material.

[0103] Referring to the assembly method of the button battery in Example 1, the EDTA-carbon composite-coated lithium manganese iron phosphate material prepared in this comparative example was used as the active material of the positive electrode material to assemble a button battery.

[0104] Comparative Example 3

[0105] The preparation method of the lithium manganese iron phosphate material provided in this comparative example is basically the same as that in Example 1, except that ethylenediaminetetraacetic acid is not added in step S4, that is, the second complexing agent layer is not formed. Specifically, the method includes the following steps:

[0106] S1. Weigh 0.644 g of zirconium oxychloride and 0.584 g of ethylenediaminetetraacetic acid, add 100 mL of deionized water to dissolve, stir at 30°C for 1 h at a stirring rate of 1500 r / s to allow the zirconium oxychloride and ethylenediaminetetraacetic acid to fully react, then add 0.0745 g of sodium stearate, and continue stirring for 1 h to obtain a mixed solution B.

[0107] S2, then weigh 20.45g of unmodified lithium manganese iron phosphate (LiMn 0.7 Fe 0.3 PO4), added to the mixed solution B, stirred at 25 ° C for 3 h, and the stirring rate was 3000 r / s. The resulting solution was then placed in an 80 ° C drying oven to obtain a mixture, which was then placed in a tube furnace at a temperature of 500 ° C. and heat treated at 500 ° C for 18 h under the protection of a nitrogen atmosphere to perform pyrolytic carbon coating to obtain a zirconium-carbon composite-coated lithium manganese iron phosphate material.

[0108] S3. Weigh 0.5 mL of formic acid and 0.420 g of trimesic acid (H3BTC), add 10 mL of anhydrous ethanol, stir at 25 ° C for 1 h, and the stirring rate is 1000 r / s to obtain a mixed solution C; place the zirconium-carbon composite-coated lithium manganese iron phosphate material in a chemical vapor deposition system (metal organic vapor deposition system) as a substrate, vaporize the mixed solution C, and react the zirconium in the zirconium-carbon composite-coated lithium manganese iron phosphate material with trimesic acid under a nitrogen atmosphere. The reaction temperature is 120 ° C and the reaction time is 36 h to obtain a Zr-carbon composite-coated lithium manganese iron phosphate material.

[0109] S4. Weigh 10 mL of deionized water to obtain solution D; place the precursor in a chemical vapor deposition system as a substrate, vaporize solution D, and react with the precursor at a reaction temperature of 80°C for 8 hours to obtain a Zr-carbon composite-coated lithium manganese iron phosphate material.

[0110] Referring to the assembly method of the button battery in Example 1, the Zr-carbon composite-coated lithium manganese iron phosphate material prepared in this comparative example was used as the active material of the positive electrode material to assemble a button battery.

[0111] Comparative Example 4

[0112] The preparation method of the lithium manganese iron phosphate material provided in this comparative example is basically the same as that in Example 1, except that the zirconium-carbon composite-coated lithium manganese iron phosphate material does not react with trimesic acid, and specifically comprises the following steps:

[0113] S1. Weigh 0.644 g of zirconium oxychloride and 0.584 g of ethylenediaminetetraacetic acid, add 100 mL of deionized water to dissolve, stir at 30°C for 1 h at a stirring rate of 1500 r / s to allow the zirconium oxychloride and ethylenediaminetetraacetic acid to fully react, then add 0.0745 g of sodium stearate, and continue stirring for 1 h to obtain a mixed solution B.

[0114] S2, then weigh 20.45g of unmodified lithium manganese iron phosphate (LiMn 0.7 Fe 0.3 PO4), added to the mixed solution B, stirred at 25 ° C for 3 h, and the stirring rate was 3000 r / s. The resulting solution was then placed in an 80 ° C drying oven to obtain a mixture, which was then placed in a tube furnace at a temperature of 500 ° C. and heat treated at 500 ° C for 18 h under the protection of a nitrogen atmosphere to perform pyrolytic carbon coating to obtain a zirconium-carbon composite-coated lithium manganese iron phosphate material.

[0115] S3. Weigh 0.5 mL of formic acid, add 10 mL of anhydrous ethanol, stir at 25 ° C for 1 h, and the stirring rate is 1000 r / s to obtain a mixed solution C; place the zirconium-carbon composite-coated lithium manganese iron phosphate material in a chemical vapor deposition system (metal organic vapor deposition system) as a substrate, vaporize the mixed solution C, and react the zirconium-carbon composite-coated lithium manganese iron phosphate material with the vaporized mixed solution C under a nitrogen atmosphere. The reaction temperature is 120 ° C and the reaction time is 36 h to obtain a precursor.

[0116] S4. Weigh 3.36 g of ethylenediaminetetraacetic acid, add 10 mL of deionized water, stir at 25 ° C for 1 hour, and the stirring rate is 1000 r / s to obtain a mixed solution D; place the precursor in a chemical vapor deposition system as a substrate, vaporize the mixed solution D, and react with the precursor at a reaction temperature of 80 ° C and a reaction time of 8 hours, so that the ethylenediaminetetraacetic acid replaces the carboxyl group on the surface of the precursor to obtain a Zr-EDTA-carbon composite-coated lithium manganese iron phosphate material.

[0117] Referring to the assembly method of the button battery in Example 1, the Zr-EDTA-carbon composite-coated lithium manganese iron phosphate material prepared in this comparative example was used as the active material of the positive electrode material to assemble a button battery.

[0118] Comparative Example 5

[0119] The preparation method of the lithium manganese iron phosphate material provided in this comparative example is basically the same as that of Example 1, except that zirconium oxychloride is not added in step S1, that is, a metal coating layer is not formed, and the ethylenediaminetetraacetic acid in step S4 cannot be grafted onto the surface of the material particles through coordination bonds, and step S3 is not included. Specifically, the following steps are included:

[0120] S1. Weigh 0.584 g of ethylenediaminetetraacetic acid, add 100 mL of deionized water to dissolve, stir at 30° C. for 1 h at a stirring rate of 1500 r / s, then add 0.0745 g of sodium stearate, and continue stirring for 1 h to obtain a mixed solution B.

[0121] S2, then weigh 20.45g of unmodified lithium manganese iron phosphate (LiMn 0.7 Fe 0.3 PO4), added to the mixed solution B, stirred at 25 ° C for 3 h, and the stirring rate was 3000 r / s. The resulting solution was then placed in an 80 ° C drying oven to dry the mixture, which was then placed in a tube furnace at a temperature of 500 ° C. and heat treated at 500 ° C for 18 h under the protection of a nitrogen atmosphere to perform pyrolysis carbon coating to obtain a carbon-coated lithium manganese iron phosphate material.

[0122] S4. Weigh 3.36 g of ethylenediaminetetraacetic acid, add 10 mL of deionized water, stir at 25 ° C for 1 h, and the stirring rate is 1000 r / s to obtain a mixed solution D; place the carbon-coated lithium manganese iron phosphate material in a chemical vapor deposition system as a substrate, vaporize the mixed solution D, and react with the carbon-coated lithium manganese iron phosphate material at a reaction temperature of 80 ° C and a reaction time of 8 h to obtain EDTA-carbon composite-coated lithium manganese iron phosphate material.

[0123] Referring to the assembly method of the button battery in Example 1, the EDTA-carbon composite-coated lithium manganese iron phosphate material prepared in this comparative example was used as the active material of the positive electrode material to assemble a button battery.

[0124] Performance Testing

[0125] The performance of the batteries prepared in the examples and comparative examples was tested, and the test results are shown in Table 1.

[0126] Capacity test: The batteries prepared in each embodiment and comparative example were subjected to charge and discharge tests at 25±0.5°C using a lithium-ion battery charge and discharge test system. The charge and discharge conditions were: charge termination voltage 4.3V; discharge termination voltage 2V; and charge and discharge current density: 0.1C.

[0127] Cycling Performance Testing: Batteries prepared in each example and comparative example were subjected to charge-discharge cycling testing at 25±0.5°C using a lithium-ion battery charge-discharge testing system until the capacity retention rate of the lithium-ion battery decreased to 70% (testing was terminated when the capacity retention rate was less than or equal to 70%). The number of cycles was recorded. Charge and discharge conditions were: charge cut-off voltage 4.3V; discharge cut-off voltage 2V; charge and discharge current density: 1C. Results are shown in Table 1.

[0128] Manganese dissolution test of the positive electrode material after 100 cycles: After the battery has undergone 100 cycles of testing, the metal lithium sheet negative electrode of the battery is disassembled and dissolved in a 0.1 mol / L HCl aqueous solution. The amount of manganese ions in the HCl solution is tested by AAS to compare the cyclic manganese dissolution of the batteries in each embodiment / comparative example.

[0129] Table 1

[0130]

[0131]

[0132] From Table 1, we can see at least the following points:

[0133] The manganese dissolution of the batteries prepared in Examples 1 to 3 is less than that in Comparative Examples 1-5, and the cycle performance is better than that in Comparative Examples 1-5. The number of cycles with a capacity retention rate of not less than 70% can reach more than 2500 cycles. For example, in Example 1, it is 2540 cycles, that is, when the number of cycles is less than or equal to 2540 cycles, the capacity retention rate is not less than 70%, indicating that the battery made of the lithium manganese iron phosphate material prepared by the present invention can significantly inhibit the dissolution of manganese ions during the charge and discharge process, thereby significantly improving the cycle performance of the lithium manganese iron phosphate battery.

[0134] It can be seen from Example 1 and Comparative Example 1 that by replacing the carbon coating layer with a Zr-EDTA (ethylenediaminetetraacetic acid)-carbon composite layer, the manganese dissolution can be reduced from 87.3 mg / L to 0.13 mg / L, and the number of cycles can be increased from 1120 to 2540, which significantly inhibits the dissolution of manganese ions and improves the cycle performance of the lithium manganese iron phosphate battery.

[0135] It can be seen from Example 1, Comparative Example 2 and Comparative Example 5 that when the Zr-EDTA (ethylenediaminetetraacetic acid)-carbon composite layer is replaced by an EDTA-carbon composite layer, manganese dissolution is significantly increased and the cycle performance is significantly reduced. The applicant speculates that the reason may be that the EDTA layer (second complexing agent layer) in Comparative Example 2 and Comparative Example 5 is easy to fall off, resulting in the dissolved manganese ions being unable to be successfully captured. In Example 1, EDTA (second complexing agent) is grafted to the surface of the lithium manganese iron phosphate material by means of a coordination bond. While achieving coating uniformity, the stability of the EDTA coating layer (second complexing agent layer) is improved, thereby ensuring the capture effect of the dissolved manganese ions, significantly inhibiting the dissolution of manganese ions, and effectively improving the cycle performance of the battery.

[0136] It can be seen from Example 1 and Comparative Example 4 that when the zirconium-carbon composite-coated lithium manganese iron phosphate material does not react with trimesic acid, manganese dissolution significantly increases and the cycle performance significantly decreases.

[0137] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A lithium manganese iron phosphate material, characterized in that: The lithium manganese iron phosphate material includes lithium manganese iron phosphate and a metal-second complexing agent-carbon composite layer coated on the surface of the lithium manganese iron phosphate, wherein the metal includes at least one of zirconium, aluminum, magnesium, cobalt, nickel, and zinc, and the second complexing agent includes at least one of ethylenediaminetetraacetic acid, trans-1,2-cyclohexanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, N-(2-hydroxy)ethylenediamine-N,N',N'-triacetic acid, and sulfosalicylic acid; The metal-second complexing agent-carbon composite layer is formed by first forming a metal-carbon composite layer on the surface of the lithium manganese iron phosphate with a metal inorganic salt and a first complexing agent, and then reacting with pyromellitic acid to obtain a precursor. Finally, the precursor is complexed with the second complexing agent so that the second complexing agent replaces the carboxyl group on the surface of the precursor. The second complexing agent can complex with manganese ions and metal ions corresponding to the metal in the metal-carbon composite layer.

2. The lithium manganese iron phosphate material according to claim 1, characterized in that The metal includes zirconium, and the second complexing agent includes ethylenediaminetetraacetic acid or trans-1,2-cyclohexanediaminetetraacetic acid.

3. The lithium manganese iron phosphate material according to claim 1, characterized in that The metal-carbon composite layer is formed by coating the metal inorganic salt and the first complexing agent with pyrolytic carbon; And / or, the metal-second complexing agent-carbon composite layer is obtained by first forming a metal-carbon composite layer on the surface of lithium manganese iron phosphate with the metal inorganic salt and the first complexing agent, and then reacting with trimesic acid and complexing with the second complexing agent by metal organic vapor phase deposition; and / or, the molar ratio of the metal inorganic salt to the first complexing agent is (1-3):1; and / or, the mass ratio of the total mass of the metal inorganic salt and the first complexing agent to the lithium manganese iron phosphate is (2-10):100; and / or, the molar ratio of the metal inorganic salt to the trimesic acid is (1-3):1; and / or, the molar ratio of the metal inorganic salt to the second complexing agent is (0.2-1):(1-3); And / or, the metal inorganic salt includes at least one of zirconium oxychloride, aluminum chloride, magnesium nitrate, cobalt nitrate, nickel nitrate, and zinc acetate; and / or, the first complexing agent comprises at least one of ethylenediaminetetraacetic acid, aminotriacetic acid, diethylenetriaminepentaacetic acid, citric acid, tartaric acid, gluconic acid, hydroxyethylethylenediaminetriacetic acid, and dihydroxyethylglycine; And / or, the chemical composition of the lithium manganese iron phosphate is LiMn x Fe 1-x PO4, where 0.1≤x≤0.

8.

4. A method for preparing the lithium manganese iron phosphate material according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1, adding a metal inorganic salt and a first complexing agent to a first solvent, allowing the metal inorganic salt and the first complexing agent to react completely, adding a surfactant, and stirring to obtain a mixed solution B; S2, adding the lithium manganese iron phosphate to the mixed solution B, stirring, drying, and then coating with pyrolytic carbon to obtain a metal-carbon composite-coated lithium manganese iron phosphate material; S3, placing the metal-carbon composite-coated lithium manganese iron phosphate material in a metal organic vapor deposition system as a substrate, and reacting it with the vaporized mixture containing formic acid and trimesic acid to obtain a precursor; S4. Placing the precursor in a metal organic vapor deposition system as a substrate, reacting with the vaporized second complexing agent to obtain a lithium manganese iron phosphate material having a metal-second complexing agent-carbon composite coating layer.

5. The method for preparing lithium manganese iron phosphate material according to claim 4, characterized in that: The first solvent is water; And / or, the surfactant includes at least one of sodium octadecyl sulfate, sodium stearate, sodium dodecylbenzenesulfonate, and sodium bile acid salt; and / or, the mass of the surfactant is 5% to 10% of the total weight of the metal inorganic salt and the first complexing agent; And / or, the pyrolytic carbon coating comprises: heat treatment at 400-650° C. for 12-24 hours under the protection of an inert gas atmosphere to perform pyrolytic carbon coating, wherein the inert gas comprises one of nitrogen, helium, and argon; And / or, in step S2, the drying is constant temperature drying, and the drying temperature is 50-80°C; And / or, in step S2, the stirring temperature is 25-50° C., the stirring rate is 2000-3500 r / s, and the stirring time is 2-4 h; And / or, in step S1, the stirring temperature is 25-60°C, the stirring rate is 1000-2500 r / s, and the stirring time is 1-3 hours; And / or, in step S3, the reaction temperature is 80-150° C., and the reaction time is 24-48 hours; And / or, in step S4, the reaction temperature is 50-100° C., and the reaction time is 6-10 h.

6. The method for preparing lithium manganese iron phosphate material according to claim 4, characterized in that: The metal-carbon composite-coated lithium manganese iron phosphate material is placed in a metal organic vapor deposition system as a substrate to react with the vaporized mixture containing formic acid and trimesic acid, comprising: adding formic acid and trimesic acid to the second solvent, mixing and stirring uniformly to obtain a mixed solution C; The metal-carbon composite-coated lithium manganese iron phosphate material is placed in a metal organic vapor deposition system as a substrate, and then the mixed solution C is vaporized and reacted with the metal-carbon composite-coated lithium manganese iron phosphate material under a nitrogen atmosphere.

7. The method for preparing lithium manganese iron phosphate material according to claim 6, characterized in that: The second solvent is anhydrous ethanol; And / or, in the step of obtaining a mixed solution C, the stirring temperature is 25-30° C., the stirring rate is 300-2000 r / s, the stirring time is 0.5-1.5 h, and the volume ratio of formic acid to the second solvent is (2-10):

100.

8. The method for preparing lithium manganese iron phosphate material according to claim 4, characterized in that: Placing the precursor in a metal organic vapor deposition system as a substrate to react with the vaporized second complexing agent comprises: Adding the second complexing agent to the third solvent, mixing and stirring uniformly to obtain a mixed solution D, wherein the third solvent is water, the stirring temperature is 25 to 30° C., the stirring rate is 300 to 2000 r / s, and the stirring time is 0.5 to 1.5 h; The precursor is placed in a metal organic vapor deposition system as a substrate, and then the mixed solution D is vaporized and reacts with the precursor.

9. A lithium-ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, characterized in that: The active material of the positive electrode sheet includes the lithium iron manganese phosphate material according to any one of claims 1 to 3 or the lithium iron manganese phosphate material prepared by the method for preparing the lithium iron manganese phosphate material according to any one of claims 4 to 8.

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