Method for preparing manganese iron vanadium sodium phosphate by recovering lithium manganese iron phosphate

Abstract

The invention discloses a method for preparing manganese iron vanadium sodium phosphate by recovering manganese iron lithium phosphate, and relates to the technical field of electrode materials, the method for preparing manganese iron vanadium sodium phosphate by utilizing manganese iron lithium phosphate comprises the following steps: S1, adding a sodium source, a vanadium source, an iron source, a phosphorus source and a carbon source into manganese iron ammonium phosphate, uniformly mixing, and drying to obtain a precursor; and S2, carrying out high-temperature calcination, cooling, washing and drying on the precursor to obtain the manganese iron vanadium sodium phosphate. According to the method disclosed by the invention, the ammonium manganese ferric phosphate is prepared from the waste lithium manganese ferric phosphate positive electrode material by utilizing a coprecipitation method, and the high-purity sodium manganese ferric vanadium phosphate can be prepared by taking the ammonium manganese ferric phosphate as a raw material and is applied as the positive electrode material of the sodium-ion battery, so that the sodium-ion battery has excellent specific discharge capacity, rate capability, cycle performance and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and in particular to a method for preparing sodium manganese iron vanadium phosphate by recycling lithium manganese iron phosphate. Background Art

[0002] The field of lithium-ion battery cathode materials continues to develop, among which lithium iron phosphate occupies an important market position due to its advantages such as high safety and long cycle life. However, lithium iron phosphate has a relatively low energy density and insufficient low-temperature performance, which limits its further application expansion. In order to break through the performance bottleneck of lithium iron phosphate materials, lithium manganese iron phosphate materials developed by partially replacing iron with manganese have shown significant advantages. The core improvement lies in higher energy density, which is due to the fact that Mn 2+ / 3+ Redox couple (~4.1V vs.Li + / Li) is significantly higher than Fe 2+ / 3+ Redox couple (~3.4V vs.Li + / Li). At the same time, similar to lithium iron phosphate, the stable phosphate group (PO4 3- ) form a strong covalent bond network, giving it excellent structural and thermal stability. In view of these technical advantages, lithium manganese iron phosphate is regarded as one of the most commercially promising cathode materials in the future, especially in the electric vehicle and electric motorcycle markets. In the next few years to decades, a large amount of waste lithium manganese iron phosphate batteries will inevitably be generated. The lithium manganese iron phosphate cathode materials in these discarded batteries contain valuable metals such as lithium, manganese, and iron, and their grades are usually much higher than natural ores. Therefore, it is crucial to develop efficient recycling technology for lithium iron manganese phosphate cathode materials.

[0003] Sodium-ion batteries have attracted global attention as one of the most promising alternatives to lithium-ion batteries. Considering the wide availability and low cost of sodium, in contrast to the depletable resources and local distribution of lithium, polyanionic cathodes belonging to the NASICON type have received considerable attention due to their stable 3D skeleton structure, which promotes the migration of Na ions. Among the possible compositions, vanadium-containing cathode materials have received great attention due to their high output voltage and the largest obtained capacity. Along with the low cost and relatively simple manufacture of vanadium-based materials, there is hope for electrodes for sodium-ion batteries. In view of the toxicity and high cost of vanadium, the present invention aims to prepare Na4VMn by replacing one vanadium site with ammonium manganese iron phosphate recovered from lithium manganese iron phosphate positive electrode material. x Fe 1-x (PO4)3.

[0004] At present, the disclosed synthesis methods of sodium manganese iron vanadium phosphate mainly include the sol-gel method and the solid-phase method. The sol-gel method dissolves raw materials such as iron source, manganese source, vanadium source, phosphorus source, and sodium source in water or an organic solvent, and prevents local precipitation by adding a chelating agent and adjusting the pH value. This process ensures that the metal ions are evenly dispersed at the atomic level and combine with the phosphorus source to form an amorphous precursor; however, the defects of the sol-gel method are process complexity, high cost, drying shrinkage, and residual impurities, which limit its application in large-scale production and the preparation of high-performance dense materials. The solid-phase method is to mix raw materials such as iron source, manganese source, vanadium source, phosphorus source, and sodium source through mechanical ball milling to obtain a manganese iron vanadium phosphate precursor, and then sinter at high temperature; this synthetic route is simple to operate, and the elements of the prepared product are evenly distributed and the proportions are precisely adjustable. Mechanical crushing increases the specific surface area of ​​the particles, significantly improving the catalytic activity and reaction rate, making it a better choice of synthetic route for industrial applications. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing sodium manganese iron vanadium phosphate by recycling lithium manganese iron phosphate. First, ammonium manganese iron phosphate is prepared from waste lithium manganese iron phosphate positive electrode materials, and then sodium manganese iron vanadium phosphate is prepared from ammonium manganese iron phosphate, thereby realizing the efficient recycling of waste lithium manganese iron phosphate positive electrode materials.

[0006] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0007] One of the objects of the present invention is to provide a method for preparing sodium manganese iron vanadium phosphate using lithium manganese iron phosphate, comprising the following steps:

[0008] S1. Add a sodium source, a vanadium source, an iron source, a phosphorus source, and a carbon source to ammonium manganese ferrous phosphate, mix well, and dry to obtain a precursor;

[0009] S2. calcining the precursor, cooling, washing, and drying to obtain sodium manganese iron vanadium phosphate.

[0010] Furthermore, the sodium source is at least one of sodium acetate and sodium carbonate.

[0011] Furthermore, the vanadium source is vanadium pentoxide.

[0012] Furthermore, the iron source is ferrous oxalate.

[0013] Furthermore, the phosphorus source is ammonium dihydrogen phosphate.

[0014] Furthermore, the carbon source is at least one of citric acid and polyethylene glycol. In the present invention, the carbon source is added twice and ball milling is performed twice accordingly, in order to control the particle size of the precursor.

[0015] Furthermore, the molar ratio of the ammonium manganese ferrovanadium phosphate, the sodium source, the vanadium source, the iron source, and the phosphorus source is 0.67:4.4:0.5:0.33:2.45. The sodium manganese ferrovanadium phosphate synthesized according to this molar ratio only produces sodium phosphate as an impurity, which can be removed by washing with water.

[0016] Furthermore, the carbon source is used in an amount of 15-20% of the total mass of the raw materials, where the total mass of the raw materials refers to the total mass of ammonium manganese ferric phosphate, the sodium source, the vanadium source, the iron source, the phosphorus source, and the carbon source. Preferably, the carbon source is composed of citric acid and polyethylene glycol (PEG) in a mass ratio of (1-2):1.

[0017] Furthermore, the mixing method is ball milling, and the ball milling speed is 500-700 rpm. The function of ball milling is to fully mix the raw materials and reduce the particle size of the precursor.

[0018] Furthermore, the drying method is vacuum drying, the drying temperature is 85-100° C., and the drying time is 10-12 hours. The purpose of vacuum drying is to prevent the divalent iron ions and manganese ions in the raw materials from being oxidized to trivalent iron ions in the air.

[0019] Furthermore, the calcination atmosphere is an argon-hydrogen mixed gas, wherein the volume fraction of hydrogen is 5-10%.

[0020] Furthermore, the calcination temperature is 650-750° C., the heating rate is 2-5° C. / min, and the holding time is 10-12 hours. The calcination can be performed once or twice.

[0021] Furthermore, the calcination is divided into two stages. The calcination temperature of the first stage is 300-400°C, the heating rate is 2-5°C / min, and the holding time is 2-3h; the calcination temperature of the second stage is 650-750°C, the heating rate is 2-5°C / min, and the holding time is 10-12h.

[0022] Furthermore, the washing includes deionized water washing and anhydrous ethanol washing. In the present invention, impurities such as sodium phosphate are removed by washing.

[0023] Furthermore, the molecular formula of the sodium manganese iron vanadium phosphate is Na4VMn 0.5 Fe 0.5 (PO4)3.

[0024] A second object of the present invention is to provide a method for preparing ammonium manganese iron phosphate using waste lithium manganese iron phosphate positive electrode material, comprising the following steps:

[0025] (1) acid leaching the waste lithium manganese iron phosphate cathode material and filtering to obtain a leachate;

[0026] (2) slowly introducing ammonia water into the leachate to adjust the pH value to weak acidity or weak alkalinity, introducing inert gas after the pH is stabilized, aging, filtering, washing, and drying to obtain ammonium manganese ferrous phosphate.

[0027] Furthermore, the acid used for acid leaching is sulfuric acid with a concentration of 1.3 to 2 mol / L.

[0028] Furthermore, the solid-liquid ratio of the acid leaching is 1:(5-10), the stirring speed is 300-400 rpm, the temperature is 70-85° C., and the time is 2-4 h.

[0029] Furthermore, the molar ratio of manganese, iron and phosphorus in the leachate is 3:2:5.

[0030] The purpose of acid leaching is to dissolve all valuable metal ions in the acid solution. Iron and manganese ions exist in divalent state. The molar ratio of manganese, iron and phosphorus in the leachate remains 3:2:5 of the raw materials.

[0031] Furthermore, the weak acidity is pH=5-6; the weak alkalinity is pH=5-9. The ammonia solution is introduced to provide sufficient NH4 + , so that the metal ions in the solution combine with it for precipitation, and ammonia water can balance the pH value of the solution.

[0032] Furthermore, the inert gas is nitrogen or argon. The purpose of introducing the inert gas is to avoid oxidation of divalent iron and divalent manganese.

[0033] Furthermore, the stirring speed of the aging is 300-400 rpm, the temperature is 50-60°C, and the time is 2-6 hours. During the stirring and heating process, the metal ions in the solution react with NH4 + and PO4 3- Combined to form ammonium manganese iron phosphate, iron, manganese and phosphorus can be efficiently converted into products, greatly improving atomic economy and resource reusability.

[0034] Furthermore, the drying method is vacuum drying, the drying temperature is 85-100° C., and the drying time is 10-12 hours.

[0035] Furthermore, the washing is performed with deionized water to remove ammonium sulfate generated by the reaction of sulfuric acid and ammonia water.

[0036] Furthermore, the molecular formula of the ammonium manganese ferric phosphate is NH4Mn 0.6 Fe 0.4 PO4.

[0037] The beneficial effects of the present invention are as follows: the present invention utilizes a co-precipitation method to prepare ammonium manganese iron phosphate from waste lithium manganese iron phosphate positive electrode material, wherein the ammonium manganese iron phosphate has high purity, is free of impurities, and has a columnar structure; high-purity sodium manganese iron vanadium phosphate can be prepared using ammonium manganese iron phosphate as a raw material and applied as a positive electrode material for sodium ion batteries, thereby enabling the sodium ion batteries to have excellent discharge specific capacity, rate performance, cycle performance, and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The X-ray diffraction (XRD) pattern of ammonium manganese ferrous phosphate prepared in Example 1;

[0039] Figure 2 This is a scanning electron microscope (SEM) image of the ammonium manganese ferrous phosphate prepared in Example 1;

[0040] Figure 3 This is the XRD pattern of sodium manganese iron vanadium phosphate prepared in Example 2;

[0041] Figure 4 The figure shows the capacity-voltage diagram and cycle performance diagram of a button cell assembled using the sodium manganese iron vanadium phosphate prepared in Example 2 as the positive electrode material for a sodium ion battery;

[0042] Figure 5 This is a capacity-voltage diagram of a button battery assembled using the sodium manganese iron vanadium phosphate prepared in Comparative Example 1 as the positive electrode material for a sodium ion battery. DETAILED DESCRIPTION

[0043] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below with reference to specific embodiments and illustrations.

[0044] Example 1

[0045] 10g of waste lithium manganese iron phosphate cathode material powder was dissolved in 100mL of dilute sulfuric acid (concentration: 1.5mol / L). The mixture was acid-leached at 85°C for 4h at a stirring speed of 300rpm. The leachate was filtered to obtain a leachate with a molar ratio of manganese, iron, and phosphorus of 3:2:5.

[0046] Slowly add 25% ammonia water to the above leachate to adjust the solution pH to 5-6, and stir at room temperature. After the pH stabilizes, introduce nitrogen gas, and age the solution at 300 rpm and 60°C for 2 hours. Ammonia water is added to maintain the pH at 5-6, and aging is continued at 300 rpm and 60°C for 2 hours. The product is washed with deionized water, filtered, and vacuum dried at 85°C for 12 hours to obtain ammonium manganese ferric phosphate.

[0047] The ammonium manganese iron phosphate prepared in Example 1 was subjected to XRD analysis and SEM scanning, and the results were as follows: Figure 1 and Figure 2 shown.

[0048] according to Figure 1 The XRD analysis results show that the diffraction peak angle of the product prepared in Example 1 is between the characteristic peaks of ammonium ferric phosphate and ammonium manganese phosphate, which can prove that NH4Mn 0.6 Fe 0.4 Successful synthesis of PO4.

[0049] according to Figure 2 The SEM scanning results show that the ammonium manganese ferric phosphate prepared in Example 1 has a columnar structure with a diameter of 10 to 20 μm.

[0050] Example 2

[0051] Take 0.2248 g of ammonium manganese iron phosphate prepared in Example 1, and add 0.7218 g of sodium acetate, 0.1818 g of vanadium pentoxide, 0.5634 g of ammonium dihydrogen phosphate, 0.1198 g of ferrous oxalate and 0.2209 g of citric acid to make the element molar ratio of sodium, vanadium, manganese, iron and phosphorus be 4.4:1:0.4:0.6:3.015. All the raw materials are crushed and mixed in a mortar, then placed in a ball mill, moistened with deionized water, ball milled at a speed of 500 rpm for 6 h, and vacuum dried at 100 ° C for 12 h. Then, 0.2209 g of PEG400 is added, ball milled at a speed of 500 rpm for 6 h, and vacuum dried at 100 ° C for 12 h to obtain a precursor.

[0052] The above-mentioned precursor was placed in a tubular furnace and introduced into an argon-hydrogen mixed gas, in which the volume fraction of hydrogen was 5%. The calcination was divided into two stages. The calcination temperature of the first stage was 350°C, the heating rate was 5°C / min, and the holding time was 2h; the calcination temperature of the second stage was 750°C, the heating rate was 5°C / min, and the holding time was 10h. The product was naturally cooled to room temperature. The product was washed several times with deionized water and anhydrous ethanol, filtered, and vacuum dried at 85°C for 12h to obtain sodium manganese iron vanadium phosphate.

[0053] The sodium manganese iron vanadium phosphate prepared in Example 2 was subjected to XRD analysis. The XRD analysis results are as follows: Figure 3 shown.

[0054] according to Figure 3 The XRD analysis results show that the diffraction peak angle of the product prepared in Example 2 is consistent with that of the standard card, and Figure 4 The charge-discharge curves show the charge-discharge platform of V, Mn, and Fe, which can prove that Na4VMn 0.5 Fe 0.5 Successful synthesis of (PO4)3.

[0055] Example 3

[0056] Ammonium manganese ferric phosphate was prepared according to the method of Example 1, except that the amount of dilute sulfuric acid was adjusted to 100 mL and the concentration was adjusted to 1.5 mol / L.

[0057] Example 4

[0058] Ammonium manganese ferric phosphate was prepared according to the method of Example 1, except that the aging time was adjusted to 6 h.

[0059] Example 5

[0060] Ammonium manganese ferric phosphate was prepared according to the method of Example 1, except that ammonia water was added to adjust the pH to 8-9.

[0061] Example 6

[0062] Sodium manganese iron vanadium phosphate was prepared according to the method of Example 2, except that sodium acetate was replaced by sodium carbonate, and only citric acid was used as the carbon source.

[0063] Example 7

[0064] Sodium manganese iron vanadium phosphate was prepared according to the method of Example 2, except that only one calcination was performed.

[0065] The calcination temperature is 750°C, the heating rate is 5°C / min, and the holding time is 10h.

[0066] Comparative Example 1

[0067] Sodium manganese ferrovanadium phosphate was prepared according to the method of Example 2, except that no additional ferrous oxalate was added to adjust the manganese-iron ratio. All manganese-iron was derived from ammonium manganese ferrophosphate prepared in Example 1. At this time, the molar ratio of manganese and iron elements was 3:2, and the synthesized product was Na4VMn 0.6 Fe 0.4 (PO4)3.

[0068] The sodium manganese iron vanadium phosphate prepared in Example 2 and Comparative Example 1 were used as the positive electrode materials for sodium ion batteries, button cells were assembled, and the electrochemical performance was tested. The capacity-voltage diagram and the cycle performance diagram are shown in FIG. Figure 4 、 Figure 5 shown.

[0069] Assembling process of button cell: positive electrode active material (sodium manganese iron vanadium phosphate prepared in Example 2 or Comparative Example 1), conductive carbon black (Super P) and polyvinylidene fluoride were mixed with solvent N-methylpyrrolidone in a mass ratio of 7:2:1. The mixed slurry was evenly applied on aluminum carbon foil and dried in a vacuum oven at 85°C for 12 hours. The electrode was cut to a mass loading of 1 mg / cm3 of positive electrode active material on the electrode. 2CR2016 button cells were assembled in a glove box filled with argon (H2O and O2 contents below 0.1 ppm) using glass fiber (Whatman, GF / D) as the separator, a sodium metal sheet as the negative electrode, and a 1 mol / mL sodium hexafluorophosphate solution (sodium hexafluorophosphate dissolved in a mixed solvent of propylene carbonate and ethylene carbonate, with a volume ratio of 1:1).

[0070] Depend on Figure 4 、 Figure 5 It can be seen that the button cell assembled with the sodium manganese iron vanadium phosphate prepared in Example 2 as the positive electrode material of the sodium ion battery has a discharge capacity of 107.8 mAh g at a rate of 0.5C. -1 , the capacity retention rate was 60% after 1000 cycles at 5C rate; while the button cell assembled with sodium manganese iron vanadium phosphate prepared in comparative example 1 as the positive electrode material of sodium ion battery had a discharge capacity of only 88.1 mAh g at 0.5C rate. -1 .

[0071] In summary, the sodium manganese iron vanadium phosphate prepared according to the method provided by the present invention has a high specific capacity and excellent cycle performance, and at the same time achieves efficient recycling of waste manganese iron lithium phosphate positive electrode materials.

[0072] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing sodium manganese iron vanadium phosphate using lithium manganese iron phosphate, characterized in that: The following steps are involved: S1. Add a sodium source, a vanadium source, an iron source, a phosphorus source, and a carbon source to ammonium manganese ferrous phosphate, mix well, and dry to obtain a precursor; S2. calcining the precursor, cooling, washing, and drying to obtain sodium manganese iron vanadium phosphate.

2. The method for preparing sodium manganese iron vanadium phosphate using lithium manganese iron phosphate according to claim 1, characterized in that: The sodium source is at least one of sodium acetate and sodium carbonate; Preferably, the vanadium source is vanadium pentoxide; Preferably, the iron source is ferrous oxalate; Preferably, the phosphorus source is ammonium dihydrogen phosphate; Preferably, the carbon source is at least one of citric acid and polyethylene glycol.

3. The method for preparing sodium manganese ferrovanadium phosphate using lithium manganese ferrophosphate according to claim 1, characterized in that: The molar ratio of the ammonium manganese ferric phosphate, the sodium source, the vanadium source, the iron source and the phosphorus source is 0.67:4.4:0.5:0.33:2.45; Preferably, the amount of the carbon source is 15-20% of the total mass of the raw material; Preferably, the carbon source consists of citric acid and polyethylene glycol in a mass ratio of (1-2):

1.

4. The method for preparing sodium manganese iron vanadium phosphate using lithium manganese iron phosphate according to claim 1, characterized in that: The mixing method is ball milling, and the ball milling speed is 500-700 rpm; Preferably, the drying method is vacuum drying, the drying temperature is 85-100°C, and the drying time is 10-12 hours; Preferably, the washing includes washing with deionized water and washing with anhydrous ethanol.

5. The method for preparing sodium manganese iron vanadium phosphate using lithium manganese iron phosphate according to claim 1, characterized in that: The calcining atmosphere is an argon-hydrogen mixed gas, wherein the volume fraction of hydrogen is 5-10%; Preferably, the calcination temperature is 650-750°C, the heating rate is 2-5°C / min, and the holding time is 10-12h; Preferably, the calcination is divided into two stages, the calcination temperature of the first stage is 300-400°C, the heating rate is 2-5°C / min, and the holding time is 2-3h; the calcination temperature of the second stage is 650-750°C, the heating rate is 2-5°C / min, and the holding time is 10-12h.

6. The method for preparing sodium manganese iron vanadium phosphate using lithium manganese iron phosphate according to claim 1, characterized in that: The molecular formula of the sodium manganese iron vanadium phosphate is Na4VMn 0.5 Fe 0.5 (PO4)3.

7. A method for preparing the ammonium manganese ferric phosphate according to claim 1 using waste lithium manganese ferric phosphate positive electrode material, characterized in that: The following steps are involved: (1) acid leaching the waste lithium manganese iron phosphate cathode material and filtering to obtain a leachate; (2) slowly introducing ammonia water into the leachate to adjust the pH value to weak acidity or weak alkalinity, introducing inert gas after the pH is stabilized, aging, filtering, washing, and drying to obtain ammonium manganese ferrous phosphate.

8. The method for preparing ammonium ferric manganese phosphate using waste lithium ferric manganese phosphate positive electrode material according to claim 7, characterized in that: The acid used for acid leaching is sulfuric acid with a concentration of 1.3 to 2 mol / L; Preferably, the solid-liquid ratio of the acid leaching is 1:(5-10), the stirring speed is 300-400 rpm, the temperature is 70-85°C, and the time is 2-4 hours; Preferably, the molar ratio of manganese, iron and phosphorus in the leachate is 3:2:

5.

9. The method for preparing ammonium ferric manganese phosphate using waste lithium ferric manganese phosphate positive electrode material according to claim 7, characterized in that: The weak acidity is pH=5-6; the weak alkalinity is pH=5-9; Preferably, the inert gas is nitrogen or argon; Preferably, the stirring speed of the aging is 300-400 rpm, the temperature is 50-60°C, and the time is 2-6 hours; Preferably, the drying method is vacuum drying, the drying temperature is 85-100°C, and the drying time is 10-12 hours; Preferably, the washing is washing with deionized water.

10. The method for preparing ammonium ferric manganese phosphate using waste lithium ferric manganese phosphate positive electrode material according to claim 7, characterized in that: The molecular formula of the ammonium manganese ferrous phosphate is NH4Mn 0.6 Fe 0.4 PO4.

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