Composite carbon source coated manganese iron lithium phosphate cathode material, method for preparing the same, and use

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 particularly to a lithium manganese iron phosphate cathode material coated with a composite carbon source, its preparation method, and its use.

Background Art

[0002] The lithium iron phosphate cathode material has attracted much attention as the best - choice material for lithium - ion battery applications. It has advantages such as long life, low cost, wide raw materials, environmental friendliness, and excellent safety performance, and is widely used in fields such as electric vehicles, energy storage, wind and solar power generation, and vehicle backup power supplies.

[0003] However, the lithium iron phosphate cathode material also has problems such as low energy density and low low - temperature performance. Lithium manganese iron phosphate has attracted wide attention as an improved version of lithium iron phosphate. The development of lithium manganese iron phosphate cathode material is essential and has great strategic significance. Compared with lithium iron phosphate, the lithium manganese iron phosphate cathode material can increase the battery energy density by more than 15%, enabling epoch - making progress in high specific energy, high safety, high cycle life, and low cost of lithium - ion batteries, meeting the needs of electric vehicles, and having long - term significance for national energy conservation and environmental protection. In response to this, the present invention proposes a lithium manganese iron phosphate cathode material coated with a composite carbon source, its preparation method, and its use.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The object of the present invention is to solve the problem that the lithium iron phosphate cathode material of the prior art has low energy density and low low - temperature performance, and cannot achieve epoch - making progress in high specific energy, high safety, high cycle life, and low cost of lithium - ion batteries, and thus cannot meet the needs of electric vehicles, by providing a lithium manganese iron phosphate cathode material coated with a composite carbon source, its preparation method, and its use. [Means for solving the problem]

[0005] To achieve the above objectives, 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 manganese iron phosphate lithium cathode material, comprising the following steps: Step S1: A mixture of two metals is obtained by adding a suitable amount of deionized water to manganese salt and iron salt, weighed according to stoichiometric ratios, and completely dissolving them. Step S2: A fixed amount of oxalate is weighed into a reaction vessel according to the molar ratio of manganese salt and iron salt, deionized water is added, stirring is started under the protection of an inert gas, oxygen is removed by bubbling the oxalate solution in the reaction vessel, the solution is heated until the oxalate is completely dissolved, after the temperature reaches the set value, the prepared mixed metal solution is added dropwise to the reaction vessel at a constant flow rate, and after the dropwise addition of the mixed metal solution is complete, the reaction is carried out at a constant temperature for a constant time to obtain a suspension of manganese iron oxalate. After the reaction is complete, the manganese iron oxalate suspension is collected and subjected to filtration, washing, and vacuum drying in sequence to obtain manganese iron oxalate precursor powder (step S3). According to the stoichiometric ratios, the manganese iron oxalate precursor, lithium source, and carbon source are weighed, and the solvent is added and ground in a sand mill (S4). After the sand mill grinding is complete, step S5 is performed to spray-dry the ground slurry to obtain spray-dried powder. Step S6 involves placing a certain mass of 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 complete. Step S7 involves adjusting the grinding parameters and grinding the sintered material to obtain manganese iron lithium cathode material powder.

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

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

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

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

[0011] Preferably, the stirring speed in S2 is 100 to 1000 r / min, the heating temperature range is 20 to 100°C, the dropping rate of the mixed metal solution is 0.1 to 10 L / min, the constant temperature reaction temperature is 20 to 100°C, and the reaction time is 0.5 to 48 hours; the vacuum drying temperature in 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, phenol resin, polyethylene glycol, and starch; 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; 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.

[0013] Preferably, the inlet temperature of the hot air in the spray drying process S5 is 165-205°C, the outlet temperature is 75-85°C, and the atomizer frequency is 150-250Hz; the mass to be placed in the graphite sagger S6 is 1-8.5kg, the reaction temperature is 750-800°C, and the reaction time is 5-30 hours; the grinding pressure S7 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 manganese iron lithium phosphate cathode material prepared by the method described in the first aspect of the present invention.

[0015] A third aspect of the present invention provides the use of a composite carbon source coated manganese iron lithium phosphate cathode material, which can be used as an electrode material for a lithium-ion battery, and the specific usage procedure is as follows: Lithium iron manganese phosphate positive electrode material was manufactured into a CR2032 type button cell and subjected to charge-discharge tests. Using N-methyl-2-pyrrolidone (NMP) as the solvent, the active material, acetylene black, and PVDF were weighed in a mass ratio of 8:1:1, uniformly mixed, coated onto aluminum foil, and vacuum-dried at 100°C for 2 hours to obtain a positive electrode plate. A metallic lithium sheet was used as the negative electrode in a glove box protected by argon gas, 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 porous polypropylene film was used as the separator, and the cell was assembled into a button cell. Electrochemical measurements were performed using a Land electrochemical analyzer. [Effects of the Invention]

[0016] The present invention has at least the following advantageous effects: The lithium iron manganese phosphate cathode material with composite carbon source coating provided by the present invention, its preparation method, and its use are as follows: First, a mixed solution of two metals containing a manganese source and an iron source is subjected to a coprecipitation reaction with an oxalic acid solution. After filtration, washing, and drying, a post-treatment is carried out to obtain a manganese iron oxalate precursor. Then, after mixing the manganese iron oxalate precursor with a lithium source and a carbon source, sand grinding, spray drying, sintering, and grinding are sequentially carried out to obtain the lithium iron manganese phosphate cathode material. This method has the advantages that the manufacturing process is simple, it can be easily mass-produced industrially, the economic benefits are good, and the manufacturing cost is low. It can effectively improve the charge-discharge specific capacity of the lithium iron manganese phosphate cathode material. The lithium iron manganese phosphate cathode material with composite carbon source coating solves problems such as poor electronic conductivity and low lithium ion diffusion rate.

Brief Description of the Drawings

[0017] [Figure 1] XRD pattern of Mn0.6Fe0.4C2O4·2H2O obtained in Example 1. [Figure 2] XRD pattern of LiMn0.6Fe0.4PO4 obtained in Example 1. [Figure 3] SEM image of LiMn0.6Fe0.4PO4 obtained in Example 1. [Figure 4] Charge-discharge curve diagram of lithium iron manganese phosphate obtained in Example 1 and lithium iron manganese phosphate obtained in Comparative Example 1. The solid line in the figure indicates LiMn0.6Fe0.4PO4 obtained in Example 1, and the dashed line indicates lithium iron manganese phosphate obtained in Comparative Example 1. [Figure 5] SEM image of LiMn0.7Fe0.3PO4 obtained in Example 2. [Figure 6] SEM image of LiMn0.8Fe0.2PO4 obtained in Example 3.

Modes for Carrying Out the Invention

[0018] The technical means in the embodiments of the present invention will be described in detail below. However, it is needless to say that the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without creative activities belong to the protection scope of the present invention.

[0019] As the technical means of the present invention, A method for preparing a lithium iron manganese phosphate cathode material with a composite carbon source coating, comprising the following steps: Step S1 of adding the manganese salt and iron salt weighed according to the stoichiometric ratio to an appropriate amount of deionized water and completely dissolving them to obtain a two-metal mixed solution; Weigh a certain amount of oxalate according to the molar ratio of the manganese salt and iron salt, add deionized water, start stirring under the protection of an inert gas, bubble the oxalate solution in the reaction kettle to remove oxygen, heat the solution until the oxalate is completely dissolved, and after the temperature reaches the set value, drop the prepared two-metal mixed solution into the reaction kettle at a certain flow rate. After the dropping of the two-metal mixed solution is completed, react at a certain temperature for a certain period of time to obtain a suspension of manganese iron oxalate. Step S3 of recovering the suspension of manganese iron oxalate after the reaction, and successively performing filtration, washing, and vacuum drying to obtain manganese iron oxalate precursor powder; Weigh the manganese iron oxalate precursor, lithium source, and carbon source according to the stoichiometric ratio, add a solvent, and grind with a sand mill in S4; Step S5 of spray-drying the slurry after sand mill grinding to obtain a spray-dried powder; Put the spray-dried powder into a graphite crucible according to a certain mass, perform a high-temperature sintering reaction under the protection of an inert gas, and obtain a sintered material after the reaction. Step S7 of adjusting the grinding parameters and grinding the sintered material to obtain lithium iron manganese phosphate cathode material powder.

[0020] Furthermore, the iron salt of S1 includes, but is not limited to, one or more of ferrous nitrate, ferrous sulfate, ferrous acetate, and ferrous chloride. The ferrous sulfate may be amorphous aqueous ferrous sulfate or crystalline aqueous ferrous sulfate, and specifically, one or more of anhydrous ferrous sulfate, ferrous sulfate monohydrate, and ferrous sulfate heptahydrate.

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

[0022] The manganese salt S1 may include, but is not limited to, one or more of manganese nitrate, manganese sulfate, manganese acetate, and manganese chloride. The manganese sulfate may be amorphous aqueous manganese sulfate or crystalline aqueous manganese sulfate, and may specifically be 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] Furthermore, the molar ratio of the iron salt to the manganese salt in S1 is 1:1 to 5, and the concentration of the mixed metal solution is 0.3 to 1.5 mol / L.

[0025] Furthermore, 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 of S2 is oxalic acid dihydrate.

[0027] Furthermore, the molar ratio of the two metal mixture 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] Furthermore, the inert gas being bubbled in S2 is one of argon, nitrogen, or helium.

[0029] Furthermore, the stirring speed of S2 is 100 to 1000 r / min.

[0030] Furthermore, the heating temperature range for S2 is 20 to 100°C, and the dropping rate of the mixed metal solution is 0.1 to 10 L / min.

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

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

[0033] Furthermore, the lithium source of S4 is one or more of lithium carbonate, lithium hydroxide, and lithium dihydrogen phosphate.

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

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

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

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

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

[0039] Furthermore, the molar ratio of the manganese iron oxalate precursor to the lithium source in 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.

[0040] Furthermore, the grinding time for S4 is 30 to 180 minutes.

[0041] Furthermore, the hot air inlet temperature setting for the spray drying process in S5 is 165-205°C, the outlet temperature setting is 75-85°C, and the atomizer frequency is 150-250Hz.

[0042] Furthermore, the mass to be placed in 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] Furthermore, the inert gas used in S6 is one of argon, nitrogen, or helium.

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

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

[0046] The positive electrode material prepared by the above method was manufactured into a lithium-ion battery and tested, and the test procedure was as follows: A lithium iron manganese phosphate cathode material was manufactured into a CR2032 type button cell and subjected to charge-discharge tests. Using N-methyl-2-pyrrolidone (NMP) as the solvent, the active material, acetylene black, and PVDF were weighed in a mass ratio of 8:1:1, uniformly mixed, coated onto aluminum foil, and vacuum-dried at 100°C for 2 hours to obtain a cathode plate. A metallic lithium sheet was used as the anode in a glove box under argon gas protection, 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 porous polypropylene film was used as the separator, and the cell was assembled into a button cell. Electrochemical measurements were performed using a Land electrochemical analyzer.

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

[0048] (Example 1) A composite carbon source coated manganese iron lithium cathode material, with the molecular formula LiMn 0.6 Fe 0.4 The preparation method for PO4 includes the following steps.

[0049] Step 1: Following a molar ratio of 4:6, weigh 8.9 kg of ferrous sulfate heptahydrate and 8.11 kg of manganese sulfate monohydrate into a stirring tank, add deionized water, and stir to dissolve, obtaining a 1.0 mol / L mixed metal solution, which is set aside for later use.

[0050] Step 2: Weigh 10.89 kg of oxalic acid into the reaction vessel, add deionized water, stir at 400 r / min under nitrogen gas protection, remove oxygen by bubbling the oxalic acid solution in the reaction vessel, and heat the solution to 60°C until the oxalic acid is completely dissolved to obtain 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 reaction vessel at a flow rate of 1.6 L / min, and after the addition of the two-metal mixed solution is complete, continue the reaction at 60°C for 8 hours to obtain a manganese iron oxalate suspension.

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

[0052] Step 4: Weigh 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 grinding slurry.

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

[0054] Step 6: 8.0 kg of spray-dried powder is placed in a graphite sagger and held 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 crushed under the following conditions: crushing pressure of 430 kPa, classifier frequency of 190 Hz, feed motor frequency of 45 Hz, and fan frequency of 25 Hz. The crushed powder is the lithium iron manganese phosphate cathode material.

[0056] (Example 2) A composite carbon source coated manganese iron lithium cathode material, with the molecular formula LiMn 0.7 Fe 0.3 The preparation method for PO4 includes the following steps.

[0057] Step 1: Following a molar ratio of 3:7, weigh 6.67 kg of ferrous sulfate heptahydrate and 9.47 kg of manganese sulfate monohydrate into a stirring tank, add deionized water, and stir to dissolve, obtaining a 1.0 mol / L mixed metal solution, which is set aside for later use.

[0058] Step 2: Weigh 10.89 kg of oxalic acid into the reaction vessel, add deionized water, stir at 400 r / min under nitrogen gas protection, remove oxygen by bubbling the oxalic acid solution in the reaction vessel, and heat the solution to 60°C until the oxalic acid is completely dissolved to obtain 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 reaction vessel at a flow rate of 1.6 L / min, and after the addition of the two-metal mixed solution is complete, continue the reaction at 60°C for 8 hours to obtain a manganese iron oxalate suspension.

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

[0060] Step 4: Weigh 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, add 20 L of methanol, and grind for 120 minutes to obtain a sand mill grinding slurry.

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

[0062] Step 6: 8.0 kg of spray-dried powder is placed in a graphite sagger and held 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 crushed under the following conditions: crushing pressure of 430 kPa, classifier frequency of 190 Hz, feed motor frequency of 45 Hz, and fan frequency of 25 Hz. The crushed powder is the lithium iron manganese phosphate cathode material.

[0064] (Example 3) A composite carbon source coated manganese iron lithium cathode material, with the molecular formula LiMn 0.8 Fe 0.2 The preparation method for PO4 includes the following steps.

[0065] Step 1: Following a molar ratio of 2:8, weigh 4.45 kg of ferrous sulfate heptahydrate and 10.82 kg of manganese sulfate monohydrate into a stirring tank, add deionized water, and stir to dissolve, obtaining a 1.0 mol / L mixed metal solution, which is set aside for later use.

[0066] Step 2: Weigh 10.89 kg of oxalic acid into the reaction vessel, add deionized water, stir at 400 r / min under nitrogen gas protection, remove oxygen by bubbling the oxalic acid solution in the reaction vessel, and heat the solution to 60°C until the oxalic acid is completely dissolved to obtain 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 reaction vessel at a flow rate of 1.6 L / min, and after the addition of the two-metal mixed solution is complete, continue the reaction at 60°C for 8 hours to obtain a manganese iron oxalate suspension.

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

[0068] Step 4: Weigh 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 grinding slurry.

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

[0070] Step 6: 8.0 kg of spray-dried powder is placed in a graphite sagger and held 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 crushed under the following conditions: crushing pressure of 430 kPa, classifier frequency of 190 Hz, feed motor frequency of 45 Hz, and fan frequency of 25 Hz. The crushed powder is the lithium iron manganese phosphate cathode material.

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

[0073] A series of tests were conducted on the cathode materials prepared in Examples 1 to 3 described above, and their characteristics are shown in Figures 1 to 6. From the charge-discharge curve in Figure 4, it was found that the manganese iron lithium phosphate composite carbon source coating of Example 1 of the present invention exhibits excellent electrochemical properties. Due to the high degree of high-temperature graphitization of the composite carbon, a better conductive network is constructed, improving the electronic conductivity and thereby enhancing the 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 exemplary embodiments described above, and that the present invention can be carried out in other specific forms without departing from the spirit or basic features of the invention. Therefore, the examples should be considered illustrative and non-limiting in any respect, and since the scope of the present invention is limited by the claims rather than the above description, all variations within the meaning and scope of the equivalents requirement that falls within the claims are intended to be included within the present invention.

[0075] While embodiments of the present invention have been illustrated 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 present invention. The scope of the present invention is limited by the appended claims and equivalents.

Claims

1. A method for preparing a composite carbon source coated manganese iron lithium cathode material, Step S1 involves adding manganese salt and iron salt, weighed according to stoichiometric ratios, to an appropriate amount of deionized water and completely dissolving them to obtain a mixed solution of two metals. Step S2 involves 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 an inert gas, removing oxygen by bubbling the oxalate solution in the reaction vessel, heating the solution until the oxalate is completely dissolved, and after the temperature reaches a set value, dropping the prepared mixed metal solution into the reaction vessel at a constant flow rate, and after the dropping of the mixed metal solution is complete, reacting at a constant temperature for a constant time to obtain a suspension of manganese iron oxalate. After the reaction is complete, the manganese iron oxalate suspension is recovered and subjected to filtration, washing, and vacuum drying in sequence to obtain manganese iron oxalate precursor powder (step S3). S4 involves weighing the manganese iron oxalate precursor powder, lithium dihydrogen phosphate, and carbon source according to stoichiometric ratios, adding a solvent, and grinding them in a sand mill. After the sand mill grinding is complete, step S5 is performed to obtain spray-dried powder by spray-drying the grinding slurry, Step S6 involves placing the spray-dried powder into a graphite sagger in a fixed mass, carrying out a high-temperature sintering reaction under inert gas protection, and obtaining a sintered material after the reaction is complete. Step S7 involves adjusting the grinding parameters and grinding the sintered material to obtain manganese iron lithium cathode material powder, A method for preparing a composite carbon source coated manganese iron lithium phosphate cathode material, characterized by containing the above.

2. A method for preparing a composite carbon source coated manganese iron lithium cathode material according to claim 1, characterized in that the iron salt of S1 contains one or more of ferrous nitrate, ferrous sulfate, ferrous acetate, and ferrous chloride.

3. A method for preparing a composite carbon source coated lithium iron phosphate cathode material according to claim 1, characterized in that the manganese salt of S1 contains one or more of manganese nitrate, manganese sulfate, manganese acetate, and manganese chloride.

4. A method for preparing a composite carbon source coated manganese iron lithium phosphate cathode material according to claim 1, characterized in that the oxalate in S2 is one or more of oxalic acid, ammonium oxalate, and sodium oxalate, and the inert gas used to bubble S2 is one of argon, nitrogen, and helium.

5. A method for preparing a composite carbon source coated manganese iron lithium phosphate cathode material according to claim 1, characterized in that the stirring speed in S2 is 100 to 1000 r / min, the heating temperature range is 20 to 100°C, the dropping rate of the mixed metal solution is 0.1 to 10 L / min, the constant temperature reaction temperature is 20 to 100°C, and the reaction time is 0.5 to 48 hours; and the vacuum drying temperature in S3 is 20 to 120°C, and the drying time is 0.5 to 24 hours.

6. A method for preparing a composite carbon source coated manganese iron lithium phosphate cathode material according to claim 1, characterized in that the inlet temperature of the hot air in the spray drying process S5 is 165 to 205°C, the outlet temperature is 75 to 85°C, and the atomizer frequency is 150 to 250 Hz; the mass to be placed in the graphite sagger S6 is 1 to 8.5 kg, the reaction temperature is 750 to 800°C, and the reaction time is 5 to 30 hours; and the grinding pressure S7 is 350 to 450 kPa, the classifier frequency is 150 to 250 Hz, the feed motor frequency is 40 to 50 Hz, and the fan frequency is 20 to 30 Hz.

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