Composite carbon source coated lithium manganese iron phosphate cathode material and preparation method and use thereof

Abstract

Provided are a composite carbon source-coated lithium manganese iron phosphate cathode material and a preparation method and use thereof.SOLUTION: (1) subjecting a two metal mixed solution containing a manganese source and an iron source to a co-precipitation reaction with an oxalic acid solution, followed by filtration, washing and drying to obtain a manganese iron oxalate precursor, and (2) mixing the manganese iron oxalate precursor with a lithium source and a carbon source, followed by sand grinding, spray drying, sintering and grinding to obtain the lithium manganese iron phosphate cathode material. The method has the advantages of simple preparation process, easy industrial mass production, good economic benefit and low preparation cost, and can effectively improve the charge and discharge specific capacity of the lithium manganese iron phosphate cathode material, and the composite carbon source-coated lithium manganese iron phosphate cathode material solves the problems of poor electron conductivity, low lithium ion diffusion rate and the like.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a composite carbon source-coated lithium manganese iron phosphate positive electrode material and its preparation method and use. [Background technology]

[0002] Lithium iron phosphate cathode materials have attracted much attention as the best choice for lithium-ion battery applications. They have advantages such as long life, low cost, wide range of raw materials, environmental friendliness, and excellent safety performance, and are widely used in fields such as electric vehicles, energy storage, wind and solar power generation, and vehicle backup power sources.

[0003] However, lithium iron phosphate cathode materials suffer from problems such as low energy density and poor low-temperature performance. Lithium manganese iron phosphate, an improved version of lithium iron phosphate, has attracted widespread attention. The development of lithium manganese iron phosphate cathode materials is essential and of great strategic significance. Compared to lithium iron phosphate, lithium manganese iron phosphate cathode materials can increase battery energy density by more than 15%, enabling breakthroughs in the high specific energy, high safety, long cycle life, and low cost of lithium-ion batteries, meeting the needs of electric vehicles and of long-term significance for China's energy conservation and environmental protection. In response, the present invention proposes a composite carbon source-coated lithium manganese iron phosphate cathode material, its preparation method, and use. Summary of the Invention [Problem to be solved by the invention]

[0004] The objective of the present invention is to provide a composite carbon source-coated lithium manganese iron phosphate positive electrode material, a preparation method thereof, and use thereof, in order to solve the problem that the prior art lithium iron phosphate positive electrode materials have low energy density, poor low-temperature performance, and are unable to realize the breakthroughs of high specific energy, high safety, long cycle life, and low cost of lithium ion batteries, and therefore fail to meet the needs of electric vehicles. [Means for solving the problem]

[0005] In order to achieve the above object, the present invention provides the following technical means.

[0006] A first aspect of the present invention provides a method for preparing a composite carbon source-coated lithium iron manganese phosphate cathode material, the method comprising the steps of: A step S1 of adding a manganese salt and an iron salt weighed according to a stoichiometric ratio to an appropriate amount of deionized water and dissolving them completely to obtain a two-metal mixed solution; Step S2: Weigh a certain amount of oxalate into a reactor according to the molar ratio of manganese salt and iron salt, add deionized water, start stirring under the protection of inert gas, bubble the oxalate solution in the reactor to remove oxygen, heat the solution until the oxalate is completely dissolved, and after the temperature reaches a set value, add the prepared two-metal mixed solution dropwise to the reactor at a constant flow rate, and after the dropwise addition of the two-metal mixed solution is completed, react at a constant temperature for a certain time to obtain a manganese iron oxalate suspension. After the reaction is completed, the suspension of manganese iron oxalate is recovered, filtered, washed, and vacuum dried in this order to obtain a manganese iron oxalate precursor powder (step S3). S4: Weighing the manganese iron oxalate precursor, lithium source, and carbon source according to the stoichiometric ratio, adding a solvent, and grinding them with a sand mill; After the sand mill pulverization is completed, the pulverized slurry is spray-dried to obtain a spray-dried powder (S5). A step S6 of putting the spray-dried powder into a graphite sagger by a certain mass, carrying out a high-temperature sintering reaction under inert gas protection, and obtaining a sintered material after the reaction is completed; Step S7: adjusting the grinding parameters and grinding the sintered material to obtain lithium iron manganese phosphate positive electrode material powder.

[0007] Preferably, the iron salt of S1 includes, but is not limited to, one or more of ferrous nitrate, ferrous sulfate, ferrous acetate, and ferrous chloride, and the ferrous sulfate may be amorphous or crystalline ferrous sulfate.

[0008] Preferably, the manganese salt of S1 includes, but is not limited to, one or more of manganese nitrate, manganese sulfate, manganese acetate, and manganese chloride. The manganese sulfate may be amorphous or crystalline manganese sulfate.

[0009] Preferably, the molar ratio of the iron salt to the manganese salt in S1 is 1:1-5, and the concentration of the two-metal mixed solution is 0.3-1.5 mol / L; and the molar ratio of the two-metal mixed solution to the oxalate in S2 is 1:1-1.5, and the concentration of the oxalate solution is 0.8-2.0 mol / L.

[0010] Preferably, examples of the oxalate salt of S2 include, but are not limited to, one or more of oxalic acid, ammonium oxalate, and sodium oxalate, and the inert gas bubbled into S2 is one of argon, nitrogen, and helium.

[0011] Preferably, the stirring speed of S2 is 100 to 1000 r / min, the heating temperature range is 20 to 100°C, the drip rate of the two-metal mixed solution is 0.1 to 10 L / min, the constant reaction temperature is 20 to 100°C, and the reaction time is 0.5 to 48 hours; and the vacuum drying temperature of S3 is 20 to 120°C, and the drying time is 0.5 to 24 hours.

[0012] Preferably, the lithium source of S4 is one or more of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate, the carbon source is one or more of glucose, sucrose, citric acid, phenolic resin, polyethylene glycol, and starch, and the solvent is one of water, methanol, ethanol, and acetone; the molar ratio of the manganese iron oxalate precursor to the lithium source of S4 is 1:1 to 1.2, the mass ratio of the sum of the masses of the manganese iron oxalate precursor and the lithium source to one of the carbon sources is 1:0.01 to 0.1, and the mass ratio of the sum of the masses of the manganese iron oxalate precursor and the lithium source to the other carbon source is 1:0.01 to 0.1, and the milling time is 30 to 180 minutes.

[0013] Preferably, in the spray drying process of S5, the hot air inlet setting temperature is 165-205°C, the outlet setting temperature is 75-85°C, and the atomizer frequency is 150-250Hz; in S6, the mass put into the graphite sagger is 1-8.5kg, the reaction temperature is 750-800°C, and the reaction time is 5-30 hours; in S7, the grinding pressure is 350-450Kpa, the classifier frequency is 150-250Hz, the feed motor frequency is 40-50Hz, and the fan frequency is 20-30Hz.

[0014] A second aspect of the present invention provides a composite carbon source coated lithium manganese iron phosphate positive electrode material prepared by the method according to the first aspect of the present invention.

[0015] A third aspect of the present invention provides a use of a composite carbon source-coated lithium manganese iron phosphate positive electrode material, which can be used as an electrode material for a lithium ion battery, and the specific usage procedure is as follows: The manganese iron lithium phosphate cathode material was fabricated into a CR2032 button cell battery and a charge-discharge test was performed. N-methyl-2-pyrrolidone (NMP) was used as the solvent, and the active material, acetylene black, and PVDF were weighed in a mass ratio of 8:1:1. The mixture was then uniformly mixed and coated onto aluminum foil. The mixture was then vacuum dried at 100°C for 2 hours to obtain a cathode plate. In a glove box under argon gas protection, a metallic lithium sheet was used as the anode, and 1.0 mol / L LiPF6 dissolved in ethylene carbonate + dimethyl carbonate + ethyl methyl carbonate (volume ratio 1:1:1) was used as the electrolyte. A polypropylene porous film was used as the separator. The battery was then assembled into a button cell, and electrochemical measurements were performed using a Land electrochemical measurement device. [Effects of the Invention]

[0016] The present invention has at least the following advantageous effects: The present invention provides a composite carbon source-coated lithium manganese iron phosphate positive electrode material, and its preparation and use, which comprises first co-precipitation of a two-metal mixed solution containing a manganese source and an iron source with an oxalic acid solution, followed by filtration, washing, drying, and further processing to obtain a manganese iron oxalate precursor, which is then mixed with a lithium source and a carbon source, followed by sand-milling, spray-drying, sintering, and grinding, to obtain the lithium manganese iron phosphate positive electrode material. This method has the advantages of a simple production process, easy industrial mass production, good economic benefits, and low production costs, and can effectively improve the charge-discharge specific capacity of the lithium manganese iron phosphate positive electrode material, thereby solving problems such as poor electronic conductivity and low lithium ion diffusion rate. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is an X-ray diffraction (XRD) pattern of Mn0.6Fe0.4C2O4·2H2O obtained in Example 1. [Figure 2] 1 is an X-ray diffraction (XRD) pattern of LiMn0.6Fe0.4PO4 obtained in Example 1. [Figure 3] 1 is a scanning electron microscope (SEM) image of LiMn0.6Fe0.4PO4 obtained in Example 1. [Figure 4] 1 is a diagram showing charge-discharge curves of LiMn0.6Fe0.4PO4 obtained in Example 1 and the lithium manganese iron phosphate obtained in Comparative Example 1. In the diagram, the solid line represents LiMn0.6Fe0.4PO4 obtained in Example 1, and the dashed line represents the lithium manganese iron phosphate obtained in Comparative Example 1. [Figure 5] 1 is a scanning electron microscope (SEM) image of LiMn0.7Fe0.3PO4 obtained in Example 2. [Figure 6] 1 is a scanning electron microscope (SEM) image of LiMn0.8Fe0.2PO4 obtained in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0018] Although the technical means in the embodiments of the present invention will be described in detail below, it goes without saying that the described embodiments are only some of the embodiments of the present invention and do not cover all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without any creative activity are also within the scope of protection of the present invention.

[0019] The technical means of the present invention include: 1. A method for preparing a composite carbon source-coated lithium iron manganese phosphate positive electrode material, comprising the steps of: A step S1 of adding a manganese salt and an iron salt weighed according to a stoichiometric ratio to an appropriate amount of deionized water and dissolving them completely to obtain a two-metal mixed solution; Step S2: Weigh a certain amount of oxalate into a reactor according to the molar ratio of manganese salt and iron salt, add deionized water, start stirring under the protection of inert gas, bubble the oxalate solution in the reactor to remove oxygen, heat the solution until the oxalate is completely dissolved, and after the temperature reaches a set value, add the prepared two-metal mixed solution dropwise to the reactor at a constant flow rate, and after the dropwise addition of the two-metal mixed solution is completed, react at a constant temperature for a certain time to obtain a manganese iron oxalate suspension. After the reaction is completed, the suspension of manganese iron oxalate is recovered, filtered, washed, and vacuum dried in this order to obtain a manganese iron oxalate precursor powder (step S3). S4: Weighing the manganese iron oxalate precursor, lithium source, and carbon source according to the stoichiometric ratio, adding a solvent, and grinding them with a sand mill; After the sand mill pulverization is completed, the pulverized slurry is spray-dried to obtain a spray-dried powder (S5). A step S6 of putting the spray-dried powder into a graphite sagger by a certain mass, carrying out a high-temperature sintering reaction under inert gas protection, and obtaining a sintered material after the reaction is completed; Step S7: adjusting the grinding parameters and grinding the sintered material to obtain lithium iron manganese phosphate positive electrode material powder.

[0020] The iron salts of S1 include, but are not limited to, one or more of ferrous nitrate, ferrous sulfate, ferrous acetate, and ferrous chloride. The ferrous sulfate may be amorphous ferrous sulfate or crystalline ferrous sulfate, and may specifically be one or more of anhydrous ferrous sulfate, ferrous sulfate monohydrate, and ferrous sulfate heptahydrate.

[0021] Furthermore, the iron salt of S1 is ferrous sulfate heptahydrate.

[0022] The manganese salts of S1 include, but are not limited to, one or more of manganese nitrate, manganese sulfate, manganese acetate, and manganese chloride. The manganese sulfate may be amorphous or crystalline manganese sulfate, specifically, one or more of anhydrous manganese sulfate, manganese sulfate monohydrate, and manganese sulfate tetrahydrate.

[0023] Furthermore, the manganese salt of S1 is manganese sulfate monohydrate.

[0024] The molar ratio of the iron salt to the manganese salt in S1 is 1:1 to 5, and the concentration of the two-metal mixed solution is 0.3 to 1.5 mol / L.

[0025] Examples of the oxalate salt of S2 include, but are not limited to, one or more of oxalic acid, ammonium oxalate, and sodium oxalate.

[0026] Furthermore, the oxalate salt of S2 is oxalic acid dihydrate.

[0027] The molar ratio of the two-metal mixed solution S2 to the oxalate is 1:1 to 1.5, and the concentration of the oxalate solution is 0.8 to 2.0 mol / L.

[0028] The inert gas bubbled in S2 is one of argon, nitrogen, and helium.

[0029] The stirring speed of S2 is 100 to 1000 r / min.

[0030] The heating temperature range of S2 is 20 to 100° C., and the drip rate of the two-metal mixed solution is 0.1 to 10 L / min.

[0031] The constant reaction temperature in S2 is 20 to 100° C., and the reaction time is 0.5 to 48 hours.

[0032] The vacuum drying temperature of the S3 is 20 to 120° C., and the drying time is 0.5 to 24 hours.

[0033] The lithium source of S4 is at least one of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate.

[0034] Furthermore, the lithium source of S4 is lithium dihydrogen phosphate.

[0035] The carbon source of the S4 is one or more of glucose, sucrose, citric acid, phenolic resin, polyethylene glycol, and starch.

[0036] Furthermore, the carbon sources of the S4 are glucose and polyethylene glycol.

[0037] The solvent S4 is one of water, methanol, ethanol, and acetone.

[0038] Furthermore, the solvent of S4 is methanol.

[0039] The molar ratio of the manganese iron oxalate precursor and the lithium source in S4 is 1:1 to 1.2, the mass ratio of the sum of the mass of the manganese iron oxalate precursor and the lithium source to one of the carbon sources is 1:0.01 to 0.1, and the mass ratio of the sum of the mass of the manganese iron oxalate precursor and the lithium source to the other carbon source is 1:0.01 to 0.1.

[0040] The pulverization time in step S4 is 30 to 180 minutes.

[0041] In addition, the inlet temperature of the hot air in the spray drying process of S5 is set to 165 to 205°C, the outlet temperature is set to 75 to 85°C, and the atomizer frequency is 150 to 250Hz.

[0042] The mass of the material to be put into the graphite sagger of S6 is 1 to 8.5 kg, the reaction temperature is 750 to 800° C., and the reaction time is 5 to 30 hours.

[0043] The inert gas used in S6 is one of argon, nitrogen, and helium.

[0044] Furthermore, the inert gas used in S6 is nitrogen.

[0045] The crushing pressure of S7 is 350 to 450 Kpa, the frequency of the classifier is 150 to 250 Hz, the frequency of the feed motor is 40 to 50 Hz, and the frequency of the fan is 20 to 30 Hz.

[0046] The positive electrode material prepared by the above method was manufactured into a lithium ion battery and tested. The test procedure was as follows: The manganese iron lithium phosphate cathode material was fabricated into a CR2032 button cell and subjected to charge-discharge tests. N-methyl-2-pyrrolidone (NMP) was used as the solvent. The active material, acetylene black, and PVDF were weighed in a mass ratio of 8:1:1 and mixed uniformly. The mixture was then applied to aluminum foil and vacuum dried at 100°C for 2 hours to obtain a cathode plate. In a glove box under argon gas protection, a metallic lithium sheet was used as the anode, 1.0 mol / L LiPF6 dissolved in ethylene carbonate + dimethyl carbonate + ethyl methyl carbonate (volume ratio 1:1:1) was used as the electrolyte, and a polypropylene porous film was used as the separator. This battery was then assembled into a button cell, and electrochemical measurements were performed using a Land electrochemical measurement apparatus.

[0047] Based on the above method, the present invention provides the following some embodiments.

[0048] Example 1 A composite carbon source-coated lithium manganese iron phosphate cathode material, with the molecular formula LiMn 0.6 Fe 0.4 PO4, the preparation method includes the following steps:

[0049] Step 1: According to the molar ratio of 4:6, 8.9 kg of ferrous sulfate heptahydrate and 8.11 kg of manganese sulfate monohydrate were weighed into a stirring tank, deionized water was added, and the mixture was stirred to dissolve, obtaining a 1.0 mol / L solution of two metals, which was then set aside for later use.

[0050] Step 2: Weigh 10.89 kg of oxalic acid into a reactor, add deionized water, and stir at 400 r / min under nitrogen gas protection. Bubble the oxalic acid solution in the reactor to remove oxygen, and heat the solution to 60°C until the oxalic acid is completely dissolved, obtaining an oxalic acid solution with a concentration of 1.08 mol / L. Once the temperature stabilizes at 60°C, add the prepared two-metal mixed solution dropwise to the reactor at a flow rate of 1.6 L / min. After the two-metal mixed solution has been added dropwise, continue the reaction at 60°C for 8 hours to obtain a manganese iron oxalate suspension.

[0051] Step 3: After the reaction is completed, the manganese iron oxalate suspension is recovered from the reaction vessel, filtered under pressure, washed repeatedly with deionized water, and dried under vacuum at 80°C for 12 hours to obtain a manganese iron oxalate precursor powder.

[0052] Step 4: Weigh out 10.5 kg of manganese iron oxalate precursor powder, 6.26 kg of lithium dihydrogen phosphate, 0.73 kg of glucose, and 0.26 kg of polyethylene glycol, add 20 L of methanol, and grind for 120 minutes to obtain a sand mill-ground slurry.

[0053] Step 5: The sand milled slurry is spray-dried under the conditions of a hot air inlet set temperature of 180°C, an outlet set temperature of 80°C, and an atomizer frequency of 220 Hz to obtain a spray-dried powder.

[0054] Step 6: 8.0 kg of the spray-dried powder is placed in a graphite sagger and kept at a constant temperature of 780°C for 10 hours under nitrogen gas protection to obtain a sintered material.

[0055] Step 7: The sintered material is pulverized under the conditions of a pulverization pressure of 430 Kpa, a classifier frequency of 190 Hz, a feed motor frequency of 45 Hz, and a fan frequency of 25 Hz. The pulverized powder is the manganese iron lithium phosphate positive electrode material.

[0056] Example 2 A composite carbon source-coated lithium manganese iron phosphate cathode material, with the molecular formula LiMn 0.7 Fe 0.3 PO4, the preparation method includes the following steps:

[0057] Step 1: According to the molar ratio of 3:7, 6.67 kg of ferrous sulfate heptahydrate and 9.47 kg of manganese sulfate monohydrate were weighed into a stirring tank, deionized water was added, and the mixture was stirred to dissolve, obtaining a 1.0 mol / L solution of two metals, which was then set aside for later use.

[0058] Step 2: Weigh 10.89 kg of oxalic acid into a reactor, add deionized water, and stir at 400 r / min under nitrogen gas protection. Bubble the oxalic acid solution in the reactor to remove oxygen, and heat the solution to 60°C until the oxalic acid is completely dissolved, obtaining an oxalic acid solution with a concentration of 1.08 mol / L. Once the temperature stabilizes at 60°C, add the prepared two-metal mixed solution dropwise to the reactor at a flow rate of 1.6 L / min. After the two-metal mixed solution has been added dropwise, continue the reaction at 60°C for 8 hours to obtain a manganese iron oxalate suspension.

[0059] Step 3: After the reaction is completed, the manganese iron oxalate suspension is recovered from the reaction vessel, filtered under pressure, washed repeatedly with deionized water, and dried under vacuum at 80°C for 12 hours to obtain a manganese iron oxalate precursor powder.

[0060] Step 4: 10.4 kg of manganese iron oxalate precursor powder, 6.20 kg of lithium dihydrogen phosphate, 0.72 kg of glucose, and 0.26 kg of polyethylene glycol are weighed, and 20 L of methanol is added and milled for 120 minutes to obtain a sand mill-milled slurry.

[0061] Step 5: The sand milled slurry is spray-dried under the conditions of a hot air inlet set temperature of 180°C, an outlet set temperature of 80°C, and an atomizer frequency of 220 Hz to obtain a spray-dried powder.

[0062] Step 6: 8.0 kg of the spray-dried powder is placed in a graphite sagger and kept at a constant temperature of 780°C for 10 hours under nitrogen gas protection to obtain a sintered material.

[0063] Step 7: The sintered material is pulverized under the conditions of a pulverization pressure of 430 Kpa, a classifier frequency of 190 Hz, a feed motor frequency of 45 Hz, and a fan frequency of 25 Hz. The pulverized powder is the manganese iron lithium phosphate positive electrode material.

[0064] Example 3 A composite carbon source-coated lithium manganese iron phosphate cathode material, with the molecular formula LiMn 0.8 Fe 0.2 PO4, the preparation method includes the following steps:

[0065] Step 1: According to the molar ratio of 2:8, 4.45 kg of ferrous sulfate heptahydrate and 10.82 kg of manganese sulfate monohydrate were weighed into a stirring tank, deionized water was added, and the mixture was stirred to dissolve, obtaining a two-metal mixed solution with a concentration of 1.0 mol / L, which was then set aside for later use.

[0066] Step 2: Weigh 10.89 kg of oxalic acid into a reactor, add deionized water, and stir at 400 r / min under nitrogen gas protection. Bubble the oxalic acid solution in the reactor to remove oxygen, and heat the solution to 60°C until the oxalic acid is completely dissolved, obtaining an oxalic acid solution with a concentration of 1.08 mol / L. Once the temperature stabilizes at 60°C, add the prepared two-metal mixed solution dropwise to the reactor at a flow rate of 1.6 L / min. After the two-metal mixed solution has been added dropwise, continue the reaction at 60°C for 8 hours to obtain a manganese iron oxalate suspension.

[0067] Step 3: After the reaction is completed, the manganese iron oxalate suspension is recovered from the reaction vessel, filtered under pressure, washed repeatedly with deionized water, and dried under vacuum at 80°C for 12 hours to obtain a manganese iron oxalate precursor powder.

[0068] Step 4: Weigh out 11.44 kg of manganese iron oxalate precursor powder, 6.82 kg of lithium dihydrogen phosphate, 0.79 kg of glucose, and 0.29 kg of polyethylene glycol, add 20 L of methanol, and grind for 120 minutes to obtain a sand mill-ground slurry.

[0069] Step 5: The sand milled slurry is spray-dried under the conditions of a hot air inlet set temperature of 180°C, an outlet set temperature of 80°C, and an atomizer frequency of 220 Hz to obtain a spray-dried powder.

[0070] Step 6: 8.0 kg of the spray-dried powder is placed in a graphite sagger and kept at a constant temperature of 780°C for 10 hours under nitrogen gas protection to obtain a sintered material.

[0071] Step 7: The sintered material is pulverized under the conditions of a pulverization pressure of 430 Kpa, a classifier frequency of 190 Hz, a feed motor frequency of 45 Hz, and a fan frequency of 25 Hz. The pulverized powder is the manganese iron lithium phosphate positive electrode material.

[0072] (Comparative Example 1) The difference between this comparative example and Example 1 is that the carbon source used was glucose alone.

[0073] A series of tests were carried out on the positive electrode materials prepared in Examples 1 to 3 above, and the resulting property evaluations are shown in Figures 1 to 6. The charge / discharge curves in Figure 4 show that the composite carbon source-coated lithium manganese iron phosphate of Example 1 of the present application has excellent electrochemical properties, and the high degree of high-temperature graphitization of the composite carbon builds a better conductive network, improving electronic conductivity and thereby enhancing electrochemical properties.

[0074] While the basic principles, main features, and advantages of the present invention have been shown and described above, it will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the present invention. The examples, therefore, are to be considered in all respects as illustrative and not limiting, and the scope of the present invention is limited not by the above description but by the claims, and all changes that come within the meaning and range of the equivalents of the claims are intended to be embraced within the present invention.

[0075] While embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention. The scope of the present invention is limited by the appended claims and their equivalents.

Claims

1. 1. A method for preparing a composite carbon source-coated lithium iron manganese phosphate positive electrode material, comprising: A step S1 of adding manganese salt and iron salt weighed according to a stoichiometric ratio to an appropriate amount of deionized water and dissolving them completely to obtain a two-metal mixed solution; Step S2: weighing a certain amount of oxalate into a reaction vessel according to the molar ratio of the manganese salt and the iron salt, adding deionized water, starting stirring under the protection of inert gas, bubbling the oxalate solution in the reaction vessel to remove oxygen, heating the solution until the oxalate is completely dissolved, and after the temperature reaches a set value, adding the prepared two-metal mixed solution dropwise into the reaction vessel at a constant flow rate, and after the dropping of the two-metal mixed solution is completed, reacting at a constant temperature for a certain time to obtain a manganese iron oxalate suspension; After the reaction is completed, the suspension of the manganese iron oxalate is recovered, filtered, washed, and vacuum dried in this order to obtain a manganese iron oxalate precursor powder (S3). S4: weighing the iron manganese oxalate precursor, the lithium source, and the carbon source according to a stoichiometric ratio, adding a solvent, and pulverizing the mixture with a sand mill; After the sand mill pulverization is completed, the pulverized slurry is spray-dried to obtain a spray-dried powder (S5); A step S6 of placing a certain mass of the spray-dried powder into a graphite sagger, carrying out a high-temperature sintering reaction under inert gas protection, and obtaining a sintered material after the reaction is completed; Step S7: adjusting the grinding parameters and grinding the sintered material to obtain a manganese iron lithium phosphate positive electrode material powder; A method for preparing a composite carbon source-coated lithium iron manganese phosphate positive electrode material, comprising:

2. 2. The method for preparing a composite carbon source-coated lithium manganese iron phosphate positive electrode material according to claim 1, wherein the iron salt in S1 includes, but is not limited to, one or more of ferrous nitrate, ferrous sulfate, ferrous acetate, and ferrous chloride, and the ferrous sulfate may be amorphous aqueous ferrous sulfate or crystalline aqueous ferrous sulfate.

3. 2. The method for preparing a composite carbon source-coated lithium manganese iron phosphate positive electrode material according to claim 1, wherein the manganese salt in S1 includes, but is not limited to, one or more of manganese nitrate, manganese sulfate, manganese acetate, and manganese chloride, and the manganese sulfate can be amorphous or crystalline manganese sulfate.

4. 2. The method for preparing a composite carbon source-coated lithium manganese iron phosphate positive electrode material according to claim 1, wherein the molar ratio of the iron salt to the manganese salt in S1 is 1:1-5, and the concentration of the two-metal mixed solution is 0.3-1.5 mol / L; and the molar ratio of the two-metal mixed solution to the oxalate in S2 is 1:1-1.5, and the concentration of the oxalate solution is 0.8-2.0 mol / L.

5. 2. The method for preparing a composite carbon source-coated lithium manganese iron phosphate positive electrode material according to claim 1, wherein examples of the oxalate salt of S2 include, but are not limited to, one or more of oxalic acid, ammonium oxalate, and sodium oxalate, and the inert gas bubbled into S2 is one of argon, nitrogen, and helium.

6. 2. The method for preparing a composite carbon source-coated lithium manganese iron phosphate positive electrode material according to claim 1, wherein in step S2, the stirring speed is 100 to 1000 r / min, the heating temperature is 20 to 100°C, the drip rate of the two-metal mixed solution is 0.1 to 10 L / min, the isothermal reaction temperature is 20 to 100°C, and the reaction time is 0.5 to 48 hours; and in step S3, the vacuum drying temperature is 20 to 120°C, and the drying time is 0.5 to 24 hours.

7. 2. The method for preparing a composite carbon source-coated lithium manganese iron phosphate positive electrode material according to claim 1, wherein the lithium source of S4 is one or more of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate; the carbon source is one or more of glucose, sucrose, citric acid, phenolic resin, polyethylene glycol, and starch; and the solvent is one of water, methanol, ethanol, and acetone; the molar ratio of the manganese iron oxalate precursor of S4 to the lithium source is 1:1 to 1.2; the mass ratio of the sum of the masses of the manganese iron oxalate precursor and the lithium source to one of the carbon sources is 1:0.01 to 0.1; and the mass ratio of the sum of the masses of the manganese iron oxalate precursor and the lithium source to the other carbon source is 1:0.01 to 0.1; and the grinding time is 30 to 180 minutes.

8. 2. The method for preparing a composite carbon source-coated lithium manganese iron phosphate positive electrode material according to claim 1, wherein in step S5, the hot air inlet temperature is set to 165-205°C, the outlet temperature is set to 75-85°C, and the atomizer frequency is 150-250Hz; in step S6, the mass put into the graphite sagger is 1-8.5kg, the reaction temperature is 750-800°C, and the reaction time is 5-30 hours; and in step S7, the grinding pressure is 350-450Kpa, the classifier frequency is 150-250Hz, the feed motor frequency is 40-50Hz, and the fan frequency is 20-30Hz.

9. A composite carbon source-coated lithium manganese iron phosphate positive electrode material, characterized in that the composite carbon source-coated lithium manganese iron phosphate positive electrode material is prepared by the method according to any one of claims 1 to 8.

10. The use of the composite carbon source-coated lithium manganese iron phosphate positive electrode material according to claim 9, wherein the composite carbon source-coated lithium manganese iron phosphate positive electrode material can be used as an electrode material for a lithium ion battery, and the specific usage procedure is as follows: The manganese iron lithium phosphate cathode material was fabricated into a CR2032 button battery and subjected to a charge-discharge test. N-methyl-2-pyrrolidone (NMP) was used as the solvent. The active material, acetylene black, and PVDF were weighed and mixed uniformly in a mass ratio of 8:1:

1. The mixture was then applied to aluminum foil and vacuum dried at 100°C for 2 hours to obtain a cathode plate. In a glove box under argon gas protection, a metallic lithium sheet was used as the anode, and 1.0 mol / L LiPF6 dissolved in ethylene carbonate + dimethyl carbonate + ethyl methyl carbonate (volume ratio 1:1:1) was used as the electrolyte. A polypropylene porous film was used as the separator. The battery was then assembled into a button battery, and electrochemical measurements were performed using a Land electrochemical measurement device.

1. Use of a composite carbon source-coated lithium iron manganese phosphate positive electrode material.

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