Multi-element doped lithium iron manganese phosphate positive electrode material and preparation method thereof, positive plate and battery

Abstract

The invention discloses a multi-element doped lithium manganese iron phosphate positive electrode material and a preparation method thereof, a positive plate and a battery, and the preparation method comprises the following steps: mixing a solution containing soluble manganese salt, iron salt and doped element metal salt with a solution of oxalate, and then reacting at 30-60 DEG C for 3-20 hours to obtain a manganese iron compound; a manganese iron compound, a phosphorus source, a lithium source, a metal oxide and a carbon source are subjected to ball milling to obtain a manganese iron lithium phosphate precursor, and the manganese iron lithium phosphate precursor is roasted in a protective atmosphere to obtain the multi-element doped manganese iron lithium phosphate positive electrode material. The ferromanganese compound is prepared by adopting a coprecipitation method, uniform phase splitting of ferromanganese of the final material is realized, related elements are doped in the coprecipitation process, uniform distribution of the doped elements is realized, and the electrochemical performance of the material is improved.

Description

Technical Field

[0001] The present invention relates to the field of new energy materials, and in particular to a multi-element doped lithium manganese iron phosphate positive electrode material and a preparation method, a positive electrode sheet and a battery. Background Art

[0002] At present, the positive electrode materials that have been widely used in the lithium battery energy storage market are mainly ternary lithium and lithium iron phosphate. Ternary lithium has gradually been replaced by lithium iron phosphate due to its high cost, flammability, poor cycle and other safety issues. What limits the further development and application of lithium iron phosphate itself is mainly the energy density that affects its capacity.

[0003] After years of policy support and technological breakthroughs, the current lithium iron phosphate battery still has bottlenecks in energy density, and there is little room for improvement. At the same time, the price of lithium continues to soar, and the lithium iron phosphate battery, which focuses on cost-effectiveness, cannot withstand long-term price increases. Therefore, the market has turned its attention to the upgraded version of lithium iron phosphate - lithium iron manganese phosphate. As an upgraded version of lithium iron phosphate, lithium iron manganese phosphate is a new type of positive electrode material obtained by adding manganese elements to lithium iron phosphate. However, the addition of manganese elements also brings some new problems to the material. Including reducing the electronic conductivity and ionic conductivity of the material, the Jahn-Teller effect leads to reduced cycle life and cycle stability. The current preparation methods of lithium iron phosphate mainly include solid phase method and liquid phase method. The solid phase method is simple to operate, mainly mixing manganese source, lithium source, iron source and phosphorus source and then calcining. Since the manganese source and iron source are added separately, it is easy to cause uneven distribution of manganese phase and iron phase during the mixing process, affecting the electrochemical performance. The material prepared by the solvent thermal method in the liquid phase method has better performance, but the equipment requirements are high and the cost is high. Summary of the invention

[0004] The present invention aims to solve the problem of uneven distribution of manganese iron in the preparation process of lithium manganese iron phosphate, which leads to poor cycle stability. The present invention provides a simple and easy-to-scale production multi-element doped lithium manganese iron phosphate positive electrode material and a preparation method, a positive electrode sheet and a battery. The manganese iron in the multi-element doped lithium manganese iron phosphate positive electrode material is evenly distributed, so that the battery has high cycle stability and high electronic conductivity and ionic conductivity.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

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

[0007] Mixing a solution containing soluble manganese salt, iron salt and doping element metal salt with a solution of oxalate, and then reacting at 30-60° C. for 3-20 hours to obtain a manganese-iron compound;

[0008] The manganese iron compound, phosphorus source, lithium source, metal oxide and carbon source are ball-milled to obtain a lithium manganese iron phosphate precursor.

[0009] The lithium iron manganese phosphate precursor is calcined under a protective atmosphere to obtain a multi-element doped lithium iron manganese phosphate positive electrode material.

[0010] A further improvement of the present invention is that the soluble manganese salt is one or more of manganese sulfate, manganese chloride and manganese nitrate;

[0011] The iron salt is one or more of ferrous sulfate, ferrous chloride and ferrous nitrate;

[0012] The doping element metal salt is one or more of magnesium sulfate, magnesium nitrate, magnesium chloride, nickel sulfate, nickel chloride, nickel acetate and cobalt sulfate.

[0013] A further improvement of the present invention is that the oxalate is one or more of sodium oxalate, potassium oxalate or ammonium oxalate.

[0014] A further improvement of the present invention is that the molar ratio of the soluble manganese salt, the iron salt and the oxalate is (0.1-1):(0.1-1):(0.1-1).

[0015] The amount of the doping elemental metal salt is 0.1-5% of the total amount of the manganese and iron ion substances.

[0016] A further improvement of the present invention is that the phosphorus source is one or more of diammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, lithium phosphate and lithium dihydrogen phosphate;

[0017] The lithium source is one or more of lithium phosphate, lithium dihydrogen phosphate, lithium carbonate and lithium hydroxide;

[0018] The carbon source is one or more of citric acid, glucose, sucrose and ascorbic acid;

[0019] The metal oxide is one or more of nickel oxide, vanadium pentoxide and magnesium oxide.

[0020] A further improvement of the present invention is that the amount of carbon source added is 2-10% of the total mass of the phosphorus source, lithium source, metal oxide and ferromanganese compound;

[0021] The sum of the amount of ferromanganese in the ferromanganese compound, the amount of phosphorus in the phosphorus source, the amount of lithium in the lithium source and the amount of metal in the metal oxide is 0.98-1.02:0.99-1.02:0.98-1.1:0-0.02.

[0022] A further improvement of the present invention is that the ferromanganese compound, the phosphorus source, the lithium source, the metal oxide and the carbon source are uniformly mixed by ball milling; the solvent used in the ball milling is one or more of water, ethanol and isopropanol, the ball-to-material ratio is 3:1-10:1, and the solid content is 10-80%;

[0023] The calcination temperature is 600-800°C and the calcination time is 1-8h.

[0024] A multi-element doped lithium manganese iron phosphate positive electrode material.

[0025] A positive electrode sheet comprises a multi-element doped lithium manganese iron phosphate positive electrode material.

[0026] A battery comprises a negative electrode, an electrolyte and the positive electrode sheet.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention adopts a coprecipitation method to prepare a manganese iron compound, realizes uniform phase separation of manganese iron in the final material, and dopes related elements in the coprecipitation process to realize uniform distribution of doped elements and improve the electrochemical performance of the material. The present invention has a simple process, a wide source of raw materials, low price, and is easy to realize large-scale production and preparation; in the ball milling process, the second step element is doped to realize the two-step element doping effect, improve the electrochemical performance of the material, reduce the cycle life and cycle stability problems caused by the Jahn-Teller effect, and reduce the voltage drop problem during charging and discharging; the lithium ion battery prepared using this material as a positive electrode material has a high reversible specific capacity and capacity retention rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of XRD of Example 1 of the present invention;

[0030] Figure 2 This is a SEM schematic diagram of Example 1 of the present invention;

[0031] Figure 3 This is a SEM schematic diagram of Example 10 of the present invention;

[0032] Figure 4 This is a cycle diagram of the LMFP of Example 1 of the present invention at 1C. DETAILED DESCRIPTION

[0033] In order to further illustrate the above scheme, several specific embodiments are given below. Any simple modification, equivalent changes and modifications made to the following examples based on the technical essence of the present invention still fall within the scope of the technical scheme of the present invention.

[0034] A method for preparing a multi-element doped lithium manganese iron phosphate positive electrode material in the present invention comprises the following steps:

[0035] Step 1: continuously introduce nitrogen to remove oxygen from deionized water and the reaction container, add soluble manganese salt, iron salt and doping element metal salt in a certain proportion, control the solution temperature to 30-60° C., and continuously stir to prepare solution A;

[0036] Step 2, adding a certain amount of oxalate to the reaction container, controlling the solution temperature to 30-60° C., and continuously stirring to prepare solution B;

[0037] Step 3, adding one of the solutions prepared in step 1 and step 2 to the other solution by a peristaltic pump, controlling the reaction temperature to 30-60°C, stirring continuously, and after the addition is completed, stirring is continued for 3-20 hours under a nitrogen atmosphere to complete the reaction;

[0038] Step 4, centrifugally washing and drying the reactant obtained in step 3 to obtain a manganese iron compound;

[0039] Step 5, placing the ferromanganese compound obtained in step 4, the phosphorus source, the lithium source, the metal oxide and the carbon source into a ball milling jar containing a certain solvent and ball milling beads for 4-10 hours;

[0040] Step 6: Dry and crush the obtained slurry to obtain a lithium iron manganese phosphate precursor, heat it to 600-800° C. under a protective atmosphere, and keep it at 600-800° C. for 1-8 hours, then cool it down, crush it and sieve it to obtain the desired lithium iron manganese phosphate positive electrode material.

[0041] In step 1, the manganese salt is one or more of manganese sulfate, manganese chloride and manganese nitrate, and the concentration of divalent manganese ions in solution A is 0.1-1 mol / L; the iron salt is one or more of ferrous sulfate, ferrous chloride and ferrous nitrate, and the concentration of divalent iron ions in solution A is 0.1-1 mol / L; the doping element metal is one or more of magnesium sulfate, magnesium nitrate, magnesium chloride, nickel sulfate, nickel chloride, nickel acetate and cobalt sulfate, and the doping element concentration is 0.1-5% of the sum of the manganese and iron ion concentrations.

[0042] In step 1, the stirring method is magnetic stirring or mechanical stirring.

[0043] In step 2, the oxalate is one or more of sodium oxalate, potassium oxalate or ammonium oxalate, and the oxalate concentration is 0.1-1 mol / L.

[0044] In step 2, the stirring method is magnetic stirring or mechanical stirring.

[0045] In step 3, the dropping direction includes solution A dropping into solution B and solution B dropping into solution A, the dropping speed is 1-80 mL / min, and the stirring speed is 100-500 r / min.

[0046] In step 5, the phosphorus source is one or more of diammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, lithium phosphate and lithium dihydrogen phosphate, the lithium source is one or more of lithium phosphate, lithium dihydrogen phosphate, lithium carbonate and lithium hydroxide, the carbon source is one or more of citric acid, glucose, sucrose and ascorbic acid, the metal oxide is one or more of nickel oxide, vanadium pentoxide and magnesium oxide, the solvent is one or more of water, ethanol and isopropanol, the ball-to-material ratio is 3:1-10:1, and the solid content is 10-80%.

[0047] In step 5, the amount of carbon source added is 2-10% of the total mass of the phosphorus source, lithium source, metal oxide and ferromanganese compound.

[0048] Manganese iron compounds (Mn x Fe 1-x The ratio of the sum of the amount of manganese and iron elements in C204·2H20, the amount of phosphorus element in the phosphorus source, the amount of lithium element in the lithium source and the amount of metal element in the metal oxide is 0.98-1.02:0.99-1.02:0.98-1.1:0.005-0.02.

[0049] In step 6, the drying method is one of vacuum drying, forced air drying and spray drying, and the protective atmosphere is one of nitrogen or argon. In the present invention, drying under vacuum conditions or protective gas conditions is used to avoid problems such as oxidation and pyrolysis during the drying process of the precursor, thereby improving the electrochemical properties of the material.

[0050] The following are specific embodiments.

[0051] Example 1

[0052] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.22275 mol of manganese sulfate monohydrate, 0.1485 mol of ferrous sulfate heptahydrate, and 0.00375 mol of anhydrous magnesium sulfate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0053] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0054] Step 3, add solution B to solution A by peristaltic pump, the drop speed is 2mL / min, the reaction temperature is 30°C, mechanical stirring is continued, the stirring speed is 500r / min, after the drop addition is completed, stirring is continued under nitrogen atmosphere, and the reaction is completed in 12h;

[0055] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0056] Step 5, weighing 0.15*0.995mol dihydrate, 0.15*1.01mol diammonium dihydrogen phosphate, 0.075*1.06mol lithium carbonate, 0.15*0.005mol nickel oxide and citric acid, the mass of citric acid is 5% of the total mass of manganese iron oxalate dihydrate, diammonium dihydrogen phosphate, lithium carbonate and nickel oxide, put it in a 1000mL ball milling jar with water as solvent for ball milling, solid content 0.6, ball-to-material ratio of 10:1, ball milling time 10h, ball milling speed 400r / min;

[0057] Step 6: Dry the obtained slurry under vacuum at 60°C for 72h, take it out and crush it to obtain a lithium iron manganese phosphate precursor, heat it to 750°C under nitrogen protection, with a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the required lithium iron manganese phosphate positive electrode material.

[0058] See also Figure 1 It can be seen that the material synthesized by the present invention corresponds well to the peak of the colorimetric card PDF#13-0336.

[0059] See also Figure 2 It can be seen that the lithium manganese iron phosphate synthesized under the present invention is a uniform substance with good morphology.

[0060] Performance test: The prepared lithium manganese iron phosphate positive electrode material was mixed with conductive carbon black and polyvinylidene fluoride in a mass ratio of 8:1:1 in NMP solvent, coated on carbon-coated aluminum foil, and vacuum dried in a vacuum oven at 110°C for 12 hours to obtain a positive electrode plate. The positive electrode plate and the lithium sheet negative electrode were assembled into a 2035 button battery. At room temperature, the voltage range was 2.5-4.5V and the charge and discharge test was carried out at a current density of 0.1C. The first discharge specific capacity of the positive electrode material was measured to be 156.32mAh / g.

[0061] See also Figure 4 It can be seen that the material has basically no attenuation after 100 cycles at 1C, and the cycle stability is good.

[0062] Example 2

[0063] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.22275 mol of manganese sulfate monohydrate, 0.1485 mol of ferrous sulfate heptahydrate, and 0.00375 mol of anhydrous magnesium sulfate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0064] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0065] Step 3, add solution B to solution A by peristaltic pump, the drop speed is 2mL / min, the reaction temperature is 30°C, mechanical stirring is continued, the stirring speed is 500r / min, after the drop addition is completed, stirring is continued under nitrogen atmosphere, and the reaction is completed in 12h;

[0066] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0067] Step 5, weighing 0.15*1mol manganese ferrooxalate dihydrate, 0.15*1.01mol diammonium phosphate, 0.075*1.06mol lithium carbonate and lemonade, the mass of citric acid is 5% of the total mass of manganese ferrooxalate dihydrate, diammonium phosphate and lithium carbonate, put them in a 1000mL ball milling jar with water as solvent for ball milling, solid content 0.6, ball-to-material ratio of 10:1, ball milling time 10h, ball milling speed 400r / min;

[0068] Step 6: Dry the obtained slurry under vacuum at 60°C for 72h, take it out and crush it to obtain a lithium iron manganese phosphate precursor, heat it to 750°C under nitrogen protection, with a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the required lithium iron manganese phosphate positive electrode material.

[0069] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 154.3 mAh / g.

[0070] Example 3

[0071] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.22275 mol of manganese sulfate monohydrate, 0.1485 mol of ferrous sulfate heptahydrate, and 0.00375 mol of anhydrous magnesium sulfate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0072] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0073] Step 3, add solution B to solution A by peristaltic pump, the drop speed is 2mL / min, the reaction temperature is 30°C, mechanical stirring is continued, the stirring speed is 500r / min, after the drop addition is completed, stirring is continued under nitrogen atmosphere, and the reaction is completed in 12h;

[0074] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0075] Step 5, weighing 0.15*0.995mol of manganese ferrooxalate dihydrate, 0.15*1.01mol of ammonium dihydrogen phosphate, 0.075*1.06mol of lithium carbonate, 0.15*0.005mol of nickel oxide and lemonade, the mass of citric acid is 5% of the total mass of manganese ferrooxalate dihydrate, ammonium dihydrogen phosphate, lithium carbonate and nickel oxide, put them in a 1000mL ball milling jar with water as solvent for ball milling, solid content 0.6, ball-to-material ratio 10:1, ball milling time 10h, ball milling speed 400r / min;

[0076] Step 6: dilute the obtained slurry with ultrapure water to a solid content of 10%, spray dry it using a spray dryer to obtain a lithium iron manganese phosphate precursor, heat it to 750°C under nitrogen protection, with a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the desired lithium iron manganese phosphate positive electrode material.

[0077] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 142.01 mAh / g.

[0078] Example 4

[0079] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.225 mol of manganese sulfate monohydrate and 0.15 mol of ferrous sulfate heptahydrate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0080] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0081] Step 3, add solution B to solution A by peristaltic pump, the drop speed is 2mL / min, the reaction temperature is 30°C, mechanical stirring is continued, the stirring speed is 500r / min, after the drop addition is completed, stirring is continued under nitrogen atmosphere, and the reaction is completed in 12h;

[0082] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0083] Step 5, weighing 0.15*0.995mol manganese ferrooxalate dihydrate, 0.15*1.01mol diammonium phosphate, 0.075*1.06mol lithium carbonate, 0.15*0.0025mol magnesium oxide, 0.15*0.0025mol nickel oxide and citric acid, the mass of citric acid is 5% of the total mass of manganese ferrooxalate dihydrate, diammonium phosphate, lithium carbonate, nickel oxide and magnesium oxide, put it in a 1000mL ball milling jar with water as solvent for ball milling, solid content 0.6, ball-to-material ratio of 10:1, ball milling time 10h, ball milling speed 400r / min;

[0084] Step 6: Dry the obtained slurry under vacuum at 60°C for 72h, take it out and crush it to obtain a lithium iron manganese phosphate precursor, heat it to 750°C under nitrogen protection, with a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the required lithium iron manganese phosphate positive electrode material.

[0085] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 147.05 mAh / g.

[0086] Example 5

[0087] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.225 mol of manganese sulfate monohydrate and 0.15 mol of ferrous sulfate heptahydrate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0088] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0089] Step 3, add solution B to solution A by peristaltic pump, the drop speed is 2mL / min, the reaction temperature is 30°C, mechanical stirring is continued, the stirring speed is 500r / min, after the drop addition is completed, stirring is continued under nitrogen atmosphere, and the reaction is completed in 12h;

[0090] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0091] Step 5, weighing 0.15*0.99mol manganese ferrooxalate dihydrate, 0.15*1.01mol diammonium dihydrogen phosphate, 0.075*1.06mol lithium carbonate, 0.15*0.005mol vanadium pentoxide and lemonade, the mass of citric acid is 5% of the total mass of manganese ferrooxalate dihydrate, diammonium dihydrogen phosphate, lithium carbonate and vanadium pentoxide, put it in a 1000mL ball milling jar with water as solvent for ball milling, solid content 0.6, ball-to-material ratio of 10:1, ball milling time 10h, ball milling speed 400r / min;

[0092] Step 6: Dry the obtained slurry under vacuum at 60°C for 72h, take it out and crush it to obtain a lithium iron manganese phosphate precursor, heat it to 750°C under nitrogen protection, with a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the required lithium iron manganese phosphate positive electrode material.

[0093] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 149.23 mAh / g.

[0094] Example 6

[0095] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.225 mol of manganese sulfate monohydrate and 0.15 mol of ferrous sulfate heptahydrate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0096] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0097] Step 3, add solution B to solution A by peristaltic pump, the drop speed is 2mL / min, the reaction temperature is 30°C, mechanical stirring is continued, the stirring speed is 500r / min, after the drop addition is completed, stirring is continued under nitrogen atmosphere, and the reaction is completed in 12h;

[0098] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0099] Step 5, weighing 0.15*0.985mol of manganese ferrooxalate dihydrate, 0.15*1.01mol of ammonium dihydrogen phosphate, 0.15*1.06mol of lithium hydroxide, 0.15*0.015mol of magnesium oxide and glucose, the mass of glucose being 5% of the total mass of manganese ferrooxalate dihydrate, ammonium dihydrogen phosphate, lithium carbonate and magnesium oxide, and putting them in a 1000mL ball milling jar with water as solvent for ball milling, with a solid content of 0.6, a ball-to-material ratio of 10:1, a ball milling time of 10h, and a ball milling speed of 400r / min;

[0100] Step 6: Dry the obtained slurry under vacuum at 60°C for 72h, take it out and crush it to obtain a lithium iron manganese phosphate precursor, heat it to 750°C under nitrogen protection, with a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the required lithium iron manganese phosphate positive electrode material.

[0101] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 149.64 mAh / g.

[0102] Example 7

[0103] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.225 mol of manganese sulfate monohydrate and 0.15 mol of ferrous sulfate heptahydrate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0104] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0105] Step 3, add solution B to solution A by peristaltic pump, the drop speed is 2mL / min, the reaction temperature is 30°C, mechanical stirring is continued, the stirring speed is 500r / min, after the drop addition is completed, stirring is continued under nitrogen atmosphere, and the reaction is completed in 12h;

[0106] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0107] Step 5, weighing 0.15*0.99mol manganese ferrooxalate dihydrate, 0.15*1.01mol diammonium dihydrogen phosphate, 0.075*1.06mol lithium carbonate, 0.15*0.01mol nickel oxide, and a mixture of glucose, sucrose and ascorbic acid in a mass ratio of 1:1:1, the mass of the mixture of glucose, sucrose and ascorbic acid is 5% of the total mass of manganese ferrooxalate dihydrate, phosphoric acid, lithium carbonate and nickel oxide, put it in a 1000mL ball milling jar with water as the solvent for ball milling, solid content 0.6, ball-to-material ratio of 10:1, ball milling time 10h, ball milling speed 400r / min;

[0108] Step 6: Dry the obtained slurry under vacuum at 60°C for 72h, take it out and crush it to obtain a lithium iron manganese phosphate precursor, heat it to 750°C under nitrogen protection, with a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the required lithium iron manganese phosphate positive electrode material.

[0109] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 149.73 mAh / g.

[0110] Example 8

[0111] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.225 mol of manganese sulfate monohydrate and 0.15 mol of ferrous sulfate heptahydrate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0112] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0113] Step 3, add solution B to solution A by peristaltic pump, the drop speed is 2mL / min, the reaction temperature is 30°C, mechanical stirring is continued, the stirring speed is 500r / min, after the drop addition is completed, stirring is continued under nitrogen atmosphere, and the reaction is completed in 12h;

[0114] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0115] Step 5, weighing 0.15*1mol manganese ferrooxalate dihydrate, 0.15*1.01mol diammonium phosphate, 0.075*1.06mol lithium carbonate and citric acid, the mass of citric acid is 5% of the total mass of manganese ferrooxalate dihydrate, diammonium phosphate and lithium carbonate, put them in a 1000mL ball milling jar with water as solvent for ball milling, solid content 0.6, ball-to-material ratio of 10:1, ball milling time 10h, ball milling speed 400r / min;

[0116] Step 6: Dry the obtained slurry under vacuum at 60°C for 72h, take it out and crush it to obtain a lithium iron manganese phosphate precursor, heat it to 750°C under nitrogen protection, with a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the required lithium iron manganese phosphate positive electrode material.

[0117] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 143.8 mAh / g.

[0118] Example 9

[0119] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.225 mol of manganese sulfate monohydrate and 0.15 mol of ferrous sulfate heptahydrate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0120] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0121] Step 3, add solution B to solution A by peristaltic pump, the drop speed is 2mL / min, the reaction temperature is 30°C, mechanical stirring is continued, the stirring speed is 500r / min, after the drop addition is completed, stirring is continued under nitrogen atmosphere, and the reaction is completed in 12h;

[0122] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0123] Step 5, weighing 0.15*1mol manganese ferrooxalate dihydrate, 0.15*1mol ammonium dihydrogen phosphate, 0.075*1.06mol lithium carbonate, and citric acid, the mass of citric acid is 10% of the total mass of manganese ferrooxalate dihydrate, ammonium dihydrogen phosphate and lithium carbonate, put them in a 1000mL ball milling jar with ethanol as the solvent for ball milling, solid content 0.2, ball to material ratio of 10:1, ball milling time 10h, ball milling speed 400r / min;

[0124] Step 6: Dry the obtained slurry under vacuum at 60°C for 72h, take it out and crush it to obtain a lithium iron manganese phosphate precursor, heat it to 750°C under nitrogen protection, with a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the required lithium iron manganese phosphate positive electrode material.

[0125] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 136.02 mAh / g.

[0126] Example 10

[0127] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.225 mol of manganese sulfate monohydrate and 0.15 mol of ferrous sulfate heptahydrate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0128] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0129] Step 3, add solution B to solution A by peristaltic pump, the drop speed is 2mL / min, the reaction temperature is 30°C, mechanical stirring is continued, the stirring speed is 500r / min, after the drop addition is completed, stirring is continued under nitrogen atmosphere, and the reaction is completed in 12h;

[0130] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0131] Step 5, weighing 0.15*1mol manganese ferrooxalate dihydrate, 0.15*1mol ammonium dihydrogen phosphate, 0.075*1.06mol lithium carbonate and citric acid, the mass of citric acid is 5% of the total mass of manganese ferrooxalate dihydrate, ammonium dihydrogen phosphate and lithium carbonate, put them in a 1000mL ball milling jar with water as solvent for ball milling, solid content 0.6, ball-to-material ratio of 10:1, ball milling time 10h, ball milling speed 400r / min;

[0132] Step 6: Dry the obtained slurry under vacuum at 60°C for 72h, take it out and crush it to obtain a lithium iron manganese phosphate precursor, heat it to 750°C under nitrogen protection, with a heating rate of 5°C / min, and keep it at 700°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the required lithium iron manganese phosphate positive electrode material.

[0133] See also Figure 3 It can be seen that the lithium manganese iron phosphate synthesized in this embodiment is porous spherical and has poor uniformity.

[0134] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 142.29 mAh / g.

[0135] Embodiment 11

[0136] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.22275 mol of manganese sulfate monohydrate, 0.1485 mol of ferrous sulfate heptahydrate, and 0.00375 mol of anhydrous magnesium sulfate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0137] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0138] Step 3, add solution B to solution A by peristaltic pump, the drop speed is 2mL / min, the reaction temperature is 30°C, mechanical stirring is continued, the stirring speed is 500r / min, after the drop addition is completed, stirring is continued under nitrogen atmosphere, and the reaction is completed in 12h;

[0139] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0140] Step 5, weighing 0.15*0.99mol manganese ferrooxalate dihydrate, 0.15*1.01mol lithium dihydrogen phosphate, 0.075*0.05mol lithium carbonate, 0.15*0.01mol nickel oxide, and glucose, the mass of glucose being 5% of the total mass of manganese ferrooxalate dihydrate, lithium dihydrogen phosphate, lithium carbonate and nickel oxide, and putting them into a 1000mL ball milling jar with water as solvent for ball milling, with a solid content of 0.6, a ball-to-material ratio of 10:1, a ball milling time of 10h, and a ball milling speed of 300r / min;

[0141] Step 6: Dry the obtained slurry under vacuum at 60°C for 72h, take it out and crush it to obtain a lithium iron manganese phosphate precursor, heat it to 600°C under nitrogen protection, with a heating rate of 10°C / min, and keep it at 600°C for 8h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the required lithium iron manganese phosphate positive electrode material.

[0142] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 147.8 mAh / g.

[0143] Example 12

[0144] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.22275 mol of manganese sulfate monohydrate, 0.1485 mol of ferrous sulfate heptahydrate, and 0.00375 mol of cobalt sulfate heptahydrate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0145] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0146] Step 3, add solution B to solution A by peristaltic pump, the drop speed is 2mL / min, the reaction temperature is 30°C, mechanical stirring is continued, the stirring speed is 500r / min, after the drop addition is completed, stirring is continued under nitrogen atmosphere, and the reaction is completed in 12h;

[0147] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0148] Step 5, weighing 0.15*0.99mol manganese ferrooxalate dihydrate, 0.1*1mol phosphoric acid, 0.05*1.06mol lithium phosphate, 0.15*0.01mol nickel oxide, and citric acid, the mass of citric acid is 5% of the total mass of manganese ferrooxalate dihydrate, phosphoric acid, lithium phosphate and nickel oxide, put it in a 1000mL ball milling jar with water as solvent for ball milling, solid content 0.6, ball to material ratio 8:1, ball milling time 6h, ball milling speed 400r / min;

[0149] Step 6: Dry the obtained slurry under vacuum at 60°C for 72h, take it out and crush it to obtain a lithium iron manganese phosphate precursor, heat it to 750°C under nitrogen protection, with a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the required lithium iron manganese phosphate positive electrode material.

[0150] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 144.76 mAh / g.

[0151] Embodiment 13

[0152] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.1 mol of manganese chloride, 0.12275 mol of manganese nitrate, 0.1485 mol of ferrous sulfate heptahydrate, and 0.00375 mol of anhydrous magnesium sulfate, control the solution temperature to 30° C., and continuously stir mechanically to prepare solution A;

[0153] Step 2, measure 1350 mL of deionized water, add 0.225 mol of ammonium oxalate monohydrate and 0.225 mol of sodium oxalate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0154] Step 3, add solution B to solution A by peristaltic pump, the drop speed is 2mL / min, the reaction temperature is 30°C, mechanical stirring is continued, the stirring speed is 500r / min, after the drop addition is completed, stirring is continued under nitrogen atmosphere, and the reaction is completed in 12h;

[0155] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0156] Step 5, weighing 0.15*0.99mol manganese ferrooxalate dihydrate, 0.1*1mol phosphoric acid, 0.05*1.06mol lithium phosphate, 0.15*0.01mol nickel oxide, and citric acid, the mass of citric acid is 10% of the total mass of manganese ferrooxalate dihydrate, phosphoric acid, lithium phosphate and nickel oxide, and putting them in a 1000mL ball milling jar with water as solvent for ball milling, with a solid content of 0.6, a ball-to-material ratio of 8:1, a ball milling time of 6h, and a ball milling speed of 400r / min;

[0157] Step 6: Dry the obtained slurry under vacuum at 60°C for 72h, take it out and crush it to obtain a lithium iron manganese phosphate precursor, heat it to 750°C under nitrogen protection, with a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the required lithium iron manganese phosphate positive electrode material.

[0158] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 133.93 mAh / g.

[0159] Embodiment 14

[0160] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.22275 mol of manganese sulfate monohydrate, 0.1 mol of ferrous nitrate, 0.0485 mol of ferrous chloride, and 0.00375 mol of anhydrous magnesium sulfate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0161] Step 2, measure 1350 mL of deionized water, add 0.225 mol of ammonium oxalate monohydrate and 0.225 mol of potassium oxalate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0162] Step 3, add solution B to solution A by peristaltic pump, the drop speed is 2mL / min, the reaction temperature is 30°C, mechanical stirring is continued, the stirring speed is 500r / min, after the drop addition is completed, stirring is continued under nitrogen atmosphere, and the reaction is completed in 12h;

[0163] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0164] Step 5, weighing 0.15*0.99mol manganese ferrooxalate dihydrate, 0.1*1mol phosphoric acid, 0.05*1.06mol lithium phosphate, 0.15*0.01mol nickel oxide, and citric acid, the mass of citric acid is 10% of the total mass of manganese ferrooxalate dihydrate, phosphoric acid, lithium phosphate and nickel oxide, and putting them in a 1000mL ball milling jar with water as solvent for ball milling, with a solid content of 0.6, a ball-to-material ratio of 8:1, a ball milling time of 6h, and a ball milling speed of 400r / min;

[0165] Step 6: Dry the obtained slurry under vacuum at 60°C for 72h, take it out and crush it to obtain a lithium iron manganese phosphate precursor, heat it to 750°C under nitrogen protection, with a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the required lithium iron manganese phosphate positive electrode material.

[0166] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 135.25 mAh / g.

[0167] Comparative Example 1

[0168] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.225 mol of manganese sulfate monohydrate and 0.15 mol of ferrous sulfate heptahydrate, control the solution temperature to 60° C., and continue mechanical stirring to prepare solution A;

[0169] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 60° C., and continue mechanical stirring to prepare solution B;

[0170] Step 3, add solution B to solution A by peristaltic pump at a dropping speed of 4 mL / min, reaction temperature of 60°C, continuous mechanical stirring at a stirring speed of 300 r / min, and continue stirring under nitrogen atmosphere after the dropping is completed, and complete the reaction for 12 h;

[0171] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0172] Step 5, weighing 0.15*1mol manganese ferrooxalate dihydrate, 0.15*1mol ammonium dihydrogen phosphate, 0.075*1.06mol lithium carbonate, and citric acid, the mass of citric acid is 10% of the total mass of manganese ferrooxalate dihydrate, ammonium dihydrogen phosphate and lithium carbonate, put them in a 1000mL ball milling jar with ethanol as the solvent for ball milling, solid content 0.2, ball to material ratio of 3:1, ball milling time 10h, ball milling speed 400r / min;

[0173] Step 6: Centrifuge the obtained slurry and vacuum dry it at 60°C for 72h. Take it out and crush it to obtain a lithium iron manganese phosphate precursor. Heat it to 750°C under nitrogen protection at a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the desired lithium iron manganese phosphate positive electrode material.

[0174] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 112.41 mAh / g.

[0175] Comparative Example 2

[0176] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.225 mol of manganese sulfate monohydrate and 0.15 mol of ferrous sulfate heptahydrate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0177] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0178] Step 3, add solution B to solution A by peristaltic pump at a dropping speed of 4 mL / min, reaction temperature of 30°C, continuous mechanical stirring at a stirring speed of 500 r / min, and continue stirring under nitrogen atmosphere after the dropping is completed, and complete the reaction for 12 h;

[0179] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0180] Step 5, weighing 0.15*1mol manganese ferrooxalate dihydrate, 0.15*1mol ammonium dihydrogen phosphate, 0.075*1.06mol lithium carbonate, and citric acid, the mass of citric acid is 10% of the total mass of manganese ferrooxalate dihydrate, ammonium dihydrogen phosphate and lithium carbonate, and putting them in a 1000mL ball milling jar with ethanol as the solvent for ball milling, with a solid content of 0.2, a ball-to-material ratio of 5:1, a ball milling time of 10h, and a ball milling speed of 400r / min;

[0181] Step 6: Centrifuge the obtained slurry and vacuum dry it at 60°C for 72h. Take it out and crush it to obtain a lithium iron manganese phosphate precursor. Heat it to 750°C under nitrogen protection at a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the desired lithium iron manganese phosphate positive electrode material.

[0182] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 119.77 mAh / g.

[0183] Comparative Example 3

[0184] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.225 mol of manganese sulfate monohydrate and 0.15 mol of ferrous sulfate heptahydrate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0185] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0186] Step 3, add solution B to solution A by peristaltic pump at a dropping speed of 4 mL / min, reaction temperature of 30°C, continuous mechanical stirring at a stirring speed of 300 r / min, and continue stirring under nitrogen atmosphere after the dropping is completed, and complete the reaction for 12 h;

[0187] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0188] Step 5, weighing 0.15*1mol manganese ferrooxalate dihydrate, 0.15*1mol ammonium dihydrogen phosphate, 0.075*1.06mol lithium carbonate, and citric acid, the mass of citric acid is 10% of the total mass of manganese ferrooxalate dihydrate, ammonium dihydrogen phosphate and lithium carbonate, put them in a 1000mL ball milling jar with ethanol as the solvent for ball milling, solid content 0.2, ball to material ratio of 10:1, ball milling time 10h, ball milling speed 400r / min;

[0189] Step 6: Centrifuge the obtained slurry and vacuum dry it at 60°C for 72h. Take it out and crush it to obtain a lithium iron manganese phosphate precursor. Heat it to 750°C under nitrogen protection at a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the desired lithium iron manganese phosphate positive electrode material.

[0190] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 123.23 mAh / g.

[0191] Comparative Example 4

[0192] Step 1, measure 375 mL of deionized water, continuously introduce nitrogen to remove oxygen in the deionized water and the reaction container, add 0.225 mol of manganese sulfate monohydrate and 0.15 mol of ferrous sulfate heptahydrate, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution A;

[0193] Step 2, measure 1350 mL of deionized water, add 0.45 mol of ammonium oxalate monohydrate thereto, control the solution temperature to 30° C., and continue mechanical stirring to prepare solution B;

[0194] Step 3, add solution B to solution A by peristaltic pump at a dropping speed of 4 mL / min, reaction temperature of 30°C, continuous mechanical stirring at a stirring speed of 300 r / min, and continue stirring under nitrogen atmosphere after the dropping is completed, and complete the reaction for 12 h;

[0195] Step 4, centrifugally washing the reactant obtained in step 3, and drying it in a vacuum oven at 60° C. for 24 hours to obtain manganese iron oxalate dihydrate;

[0196] Step 5, weigh 0.15*1mol manganese ferrooxalate dihydrate, 0.15*1mol ammonium dihydrogen phosphate, 0.075*1.06mol lithium carbonate, and citric acid, the mass of citric acid is 5% of the total mass of manganese ferrooxalate dihydrate, ammonium dihydrogen phosphate and lithium carbonate, put them in a 1000mL ball milling jar with ethanol as the solvent for ball milling, the solid content is 0.4, the ball-to-material ratio is 10:1, the ball milling time is 10h, and the ball milling speed is 400r / min;

[0197] Step 6: dilute the obtained slurry with ultrapure water to a solid content of 10%, spray dry it using a spray dryer to obtain a lithium iron manganese phosphate precursor, heat it to 750°C under nitrogen protection, with a heating rate of 10°C / min, and keep it at 750°C for 2h, then cool it naturally to room temperature, crush it and sieve it through 325 mesh to obtain the desired lithium iron manganese phosphate positive electrode material.

[0198] Performance test: The test method is consistent with that in Example 1, and the first discharge specific capacity of the positive electrode material is measured to be 133.93 mAh / g.

[0199] By comparing Examples 1-14 with Comparative Examples 1-4, it can be seen that the first discharge specific capacity of the positive electrode material prepared in the embodiments of the present invention is higher than the first discharge specific capacity in the comparative example, indicating that the mixing effect of the material can be improved when water is used as a solvent, thereby improving the electrochemical performance of the material. In the process of preparing manganese ferrooxalate dihydrate, increasing the stirring speed and reducing the synthesis temperature are conducive to reducing the particle size of manganese ferrooxalate dihydrate, which is conducive to the subsequent preparation of lithium manganese iron phosphate, thereby improving the electrochemical performance of the material; a certain amount of element doping is conducive to improving the electrochemical performance of the material.

[0200] The above description is only for the best embodiment of the present invention, but it should not be understood as limiting the claims. The present invention is not limited to the above embodiments, and its specific structure is allowed to be changed. However, all changes made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

[0201] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

Claims

1. A method for preparing a multi-element doped lithium manganese iron phosphate positive electrode material, characterized in that: The following steps are involved: Mixing a solution containing soluble manganese salt, iron salt and doping element metal salt with a solution of oxalate, and then reacting at 30-60° C. for 3-20 hours to obtain a manganese-iron compound; The manganese iron compound, phosphorus source, lithium source, metal oxide and carbon source are ball-milled to obtain a lithium manganese iron phosphate precursor. The lithium iron manganese phosphate precursor is calcined under a protective atmosphere to obtain a multi-element doped lithium iron manganese phosphate positive electrode material.

2. The method for preparing the multi-element doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The soluble manganese salt is one or more of manganese sulfate, manganese chloride and manganese nitrate; The iron salt is one or more of ferrous sulfate, ferrous chloride and ferrous nitrate; The doping element metal salt is one or more of magnesium sulfate, magnesium nitrate, magnesium chloride, nickel sulfate, nickel chloride, nickel acetate and cobalt sulfate.

3. The method for preparing the multi-element doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The oxalate is one or more of sodium oxalate, potassium oxalate or ammonium oxalate.

4. The method for preparing a multi-element doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The ratio of the amount of soluble manganese salt, iron salt and oxalate is (0.1-1): (0.1-1): (0.1-1); The amount of the doping elemental metal salt is 0.1-5% of the total amount of the manganese and iron ion substances.

5. The method for preparing the multi-element doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The phosphorus source is one or more of diammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, lithium phosphate and lithium dihydrogen phosphate; The lithium source is one or more of lithium phosphate, lithium dihydrogen phosphate, lithium carbonate and lithium hydroxide; The carbon source is one or more of citric acid, glucose, sucrose, and ascorbic acid; The metal oxide is one or more of nickel oxide, vanadium pentoxide and magnesium oxide.

6. The method for preparing a multi-element doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The amount of carbon source added is 2-10% of the total mass of the phosphorus source, lithium source, metal oxide and manganese iron compound; The sum of the amount of ferromanganese element in the ferromanganese compound, the amount of phosphorus element in the phosphorus source, the amount of lithium element in the lithium source and the amount of metal element in the metal oxide is 0.98-1.02:0.99-1.02:0.98-1.1:0-0.

02.

7. The method for preparing a multi-element doped lithium manganese iron phosphate positive electrode material according to claim 1, characterized in that: The ferromanganese compound, phosphorus source, lithium source, metal oxide and carbon source are uniformly mixed by ball milling; the solvent used in the ball milling is one or more of water, ethanol and isopropanol, the ball-to-material ratio is 3:1-10:1, and the solid content is 10-80%; The calcination temperature is 600-800°C and the calcination time is 1-8h.

8. A multi-element doped lithium manganese iron phosphate positive electrode material prepared according to the method according to any one of claims 1 to 7.

9. A positive electrode sheet, characterized in that: A multi-element doped lithium manganese iron phosphate positive electrode material prepared by the method according to any one of claims 1 to 8.

10. A battery, characterized in that: The invention comprises a negative electrode, an electrolyte and the positive electrode sheet as claimed in claim 9.

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