Iron-manganese-based composite phosphate material, preparation method and application thereof

Abstract

The application discloses a preparation method of an iron-manganese-based composite phosphate material, and the chemical formula of the iron-manganese-based composite phosphate material is Na4Fe 3‑x Mn x (PO4)2(P2O7), wherein 1.2<=x<=2.4, and the preparation method comprises the following steps: (1) respectively taking sodium source, iron source, manganese source, phosphorus source and carbon source according to the stoichiometric ratio, adding an organic solvent to form a dispersion liquid; (2) placing the dispersion liquid in a ball milling device, adding ball milling medium, and wet ball milling; (3) drying the reaction liquid after ball milling to obtain a precursor; and (4) placing the precursor in an inert atmosphere to perform step-by-step sintering to obtain the iron-manganese-based composite phosphate material. The application realizes the uniform dispersion of Mn and Fe in the precursor on an atomic scale through wet ball milling, reduces the influence of the Jahn-Teller effect of Mn on the stability of an electrode while increasing the proportion of Mn, and utilizes a step-by-step solid-phase sintering process to make the solid solution reaction of manganese and iron fully proceed, thereby exciting the electrochemical activity of manganese.

Description

Technical Field

[0001] This invention belongs to the field of battery electrode material powder preparation technology, specifically relating to an iron-manganese based composite phosphate material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have played a crucial role in bridging the gap between the intermittent and unstable nature of renewable energy generation, but their effectiveness is limited by the uneven distribution and high price of lithium resources. Therefore, developing alternative sodium-ion batteries for renewable energy storage and conversion, as well as for peak shaving and valley filling in smart grids, has become an urgent strategic issue.

[0003] Among the candidates for sodium-ion battery cathode materials, the iron-based polyanionic cathode material Na4Fe3(PO4)2(P2O7) has attracted widespread attention due to its abundant raw materials, open framework structure, good thermal stability, and environmental friendliness. However, the operating voltage of Na4Fe3(PO4)2(P2O7) cathode is only 3.0V, resulting in its low energy density and limited application.

[0004] Mn and Fe have adjacent atomic numbers and similar atomic radii, but Mn 2+ / Mn 3+ Redox potential ratio of Fe 2+ / Fe 3+ Furthermore, partially replacing Fe with Mn has become one of the main strategies for modifying LiFePO4. Therefore, theoretically, replacing some Fe with Mn in the Na4Fe3(PO4)2(P2O7) cathode should increase its operating voltage. However, recently reported cathode materials with lower Mn incorporation ratios, such as Na4Fe... 2.7 Mn 0.3 (PO4)2(P2O7), Na4Fe 2.4 Mn 0.6 The operating voltage of compounds such as (PO4)2(P2O7) did not show a significant increase compared to Na4Fe3(PO4)2(P2O7). This suggests that the Mn substitution ratio should be further increased. However, there are currently no reports on iron-manganese-based composite phosphate cathode materials with high Mn substitution ratios for sodium storage. The main reason is that when the Mn content in the electrode is high, the Jamette effect of Mn becomes more pronounced, easily leading to structural distortion of the cathode material during sodium storage and causing deterioration in cycle performance. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide an iron-manganese-based composite phosphate material, its preparation method and application, which realizes the uniform dispersion of Mn and Fe in the precursor at the atomic scale, reduces the influence of the Ginger Taylor effect of Mn on the electrode stability, and promotes the industrialization and application of iron-manganese-based composite phosphate sodium storage cathode material.

[0006] This invention provides the following technical solution:

[0007] This invention provides a method for preparing an iron-manganese-based composite phosphate material, wherein the chemical formula of the iron-manganese-based composite phosphate material is Na₄Fe₂O₃. 3-x Mn x (PO4)2(P2O7), wherein 1.2≤x≤2.4, the preparation method includes the following steps:

[0008] (1) Weigh out sodium source, iron source, manganese source, phosphorus source and carbon source according to stoichiometric ratio, add organic solvent to disperse and form dispersion liquid;

[0009] (2) Place the dispersion in a ball mill, add the ball milling media, and wet ball mill for 2 to 8 hours;

[0010] (3) The ball-milled reaction solution was dried at 50-100℃ for 3-10h to obtain the precursor;

[0011] (4) The precursor is placed in an inert atmosphere for segmented sintering. The first stage sintering temperature is 250-400℃ and the time is 3-6h. The second stage sintering temperature is 500-700℃ and the time is 5-12h to obtain the iron-manganese-based composite phosphate material.

[0012] This invention achieves uniform dispersion of Mn and Fe at the atomic scale in the precursor through wet ball milling. While increasing the proportion of Mn added, it reduces the influence of the Jan Taylor effect of Mn on electrode stability. Furthermore, by utilizing a segmented solid-state sintering process, the solid solution reaction of manganese and iron is fully carried out. The resulting iron-manganese-based composite phosphate material exhibits a significant voltage plateau at 4V, thereby improving the operating voltage.

[0013] Furthermore, the sodium source in step (1) includes one or more of inorganic sodium salts, organic sodium salts, and sodium oxides.

[0014] As a further preferred embodiment, the inorganic sodium salt includes at least one of trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, trisodium monohydrogen pyrophosphate, disodium dihydrogen pyrophosphate, monosodium trihydrogen pyrophosphate, sodium carbonate, and sodium bicarbonate; the organic sodium salt includes at least one of sodium acetate, sodium oxalate, and sodium citrate; and the sodium oxide includes at least one of sodium oxide and sodium peroxide.

[0015] Furthermore, the iron source in step (1) includes one or more of the following: ferric nitrate, ferric oxide, ferric tetroxide, ferric phosphate, ferrous oxalate, ferrous acetate, and ferrous carbonate.

[0016] Furthermore, the manganese source in step (1) includes one or more of manganese carbonate, manganese nitrate, manganese oxalate, manganese acetate, manganese sulfate, manganese phosphate, manganese dioxide, and manganese dihydrogen phosphate.

[0017] Furthermore, the phosphorus source in step (1) includes one or more of phosphoric acid, phosphate, and pyrophosphate.

[0018] As a further preferred embodiment, the phosphate includes one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; the pyrophosphate includes one or more of sodium pyrophosphate, trisodium monohydrogen pyrophosphate, disodium dihydrogen pyrophosphate, and monosodium trihydrogen pyrophosphate.

[0019] Furthermore, the carbon source in step (1) includes one or more of graphite, activated carbon, carbon nanotubes, and graphene, as well as one or more of common organic carbon-containing materials such as citric acid, glucose, and sucrose.

[0020] Further, the organic solvent in step (1) includes one or more of methanol, ethanol, propanol, isopropanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, diethyl ether, and ethylene glycol dimethyl ether.

[0021] Furthermore, the grinding media in step (2) includes one or more of the following: natural sand, glass beads, steel beads, zirconium oxide beads, zirconium silicate beads, and agate beads.

[0022] Furthermore, the inert atmosphere in step (4) includes one of argon, nitrogen, argon-hydrogen mixture, and nitrogen-hydrogen mixture.

[0023] Furthermore, in step (4), the two sintering temperature zones are: the first stage includes all temperatures from 250 to 400°C and various heating and cooling gradients; the second stage includes all temperatures from 500 to 700°C and various heating and cooling gradients.

[0024] The present invention also provides an iron-manganese-based composite phosphate material prepared by the above method.

[0025] This invention also provides the application of the above-mentioned iron-manganese-based composite phosphate material as a positive electrode material in sodium-ion batteries. The Na4Fe prepared by this invention... 3-x Mn x(PO4)2(P2O7) has advantages over existing transition metal oxides and Prussian blue cathode materials as a cathode material for sodium-ion batteries, such as low price and stable cycle performance, and can provide an ideal cathode for commercial sodium-ion batteries.

[0026] The present invention has the following beneficial effects:

[0027] 1. This invention employs wet ball milling to allow manganese and iron to be fully mixed and undergo preliminary solid solution reaction in a suitable chemical environment; combined with a segmented solid-phase sintering process, the solid solution reaction is fully carried out, stimulating the electrochemical activity of manganese and exhibiting a significant voltage plateau at 4V.

[0028] 2. The Na₄Fe synthesized in this invention 3-x Mn x The (PO4)2(P2O7) (1.2≤x≤2.4) cathode material, compared to Na4Fe3(PO4)2(P2O7), can increase the operating voltage from 3.0V to approximately 3.3V, thereby improving the energy density while maintaining excellent cycle and rate performance.

[0029] 3. This invention employs a low-cost and simple ball milling process, which is easy to promote industrially and enables large-scale production of cathode materials. The raw materials used include sodium, iron, manganese, phosphorus, and carbon sources, which are inexpensive, readily available, and widely distributed. These factors provide favorable conditions for the pilot-scale amplification of this material, giving it good commercial prospects. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 The positive electrode active material Na4Fe obtained in Example 1 of this invention 1.8 Mn 1.2 Comparison of charge-discharge curves of (PO4)2(P2O7) and Na4Fe3(PO4)2(P2O7) material without manganese substitution;

[0032] Figure 2 The positive electrode active material Na4Fe prepared in Example 1 of this invention 1.8 Mn 1.2 XRD pattern of (PO4)2(P2O7);

[0033] Figure 3This is a cycle performance diagram of the sodium-ion battery prepared in Example 1 of the present invention;

[0034] Figure 4 The rate performance diagram of the sodium-ion battery prepared in Example 1 of this invention is shown.

[0035] Figure 5 The positive electrode active material Na4Fe prepared in Example 2 of this invention 1.5 Mn 1.5 Charge-discharge curves of (PO4)2(P2O7) for the first two weeks;

[0036] Figure 6 The sodium positive electrode active material Na4Fe prepared in Example 3 of this invention. 0.6 Mn 2.4 Charge-discharge curves of (PO4)2(P2O7) for the first two weeks. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Example 1

[0039] The chemical formula of the iron-manganese-based composite phosphate material prepared in this embodiment is Na₄Fe₂O₃. 1.8 Mn 1.2 (PO4)2(P2O7), the specific preparation method is as follows:

[0040] Sodium dihydrogen phosphate (NaH₂PO₄·2H₂O), ferric nitrate (Fe(NO₃)₃·9H₂O), manganese oxalate (MnC₂O₄), and citric acid were used as raw materials, and ethanol was used as the solvent. Sodium dihydrogen phosphate (Na₄P₂O₇) served as both a sodium and phosphorus source, Fe(NO₃)₃ as an iron source, manganese oxalate (MnC₂O₄) as a manganese source, and citric acid as a carbon source.

[0041] 6.2404g NaH2PO4·2H2O, 7.272g Fe(NO3)3·9H2O, 1.7154g MnC2O4, and 2.1014g citric acid monohydrate were added to 100mL of 95% ethanol and ball-milled at 300rpm for 2h. The mixture was then dried at 50℃ for 10h to obtain the precursor.

[0042] The precursor was then placed in an argon atmosphere and calcined at 250°C for 6 hours in the first stage, followed by calcination at 500°C for 12 hours in the second stage to obtain Na4Fe.1.8 Mn 1.2 (PO4)2(P2O7).

[0043] Preparation of comparative sample Na4Fe3(PO4)2(P2O7): 6.2404 g NaH2PO4·2H2O, 12.12 g Fe(NO3)3·9H2O, and 2.1014 g citric acid monohydrate were added to 100 mL of 95% ethanol and ball-milled at 300 rpm for 2 h. Then, the mixture was dried at 50 °C for 10 h to obtain the precursor. The precursor was then placed in an argon atmosphere and calcined at 550 °C for 12 h to obtain Na4Fe3(PO4)2(P2O7).

[0044] The two materials were assembled into button cells in a glove box with water and oxygen levels below 0.01 ppm for experimental analysis. Figure 1 It can be seen that after manganese substitution, a new plateau at ~4V appears during the charge and discharge process, which is attributed to Mn. 2+ / Mn 3+ The redox pair exhibits a voltage plateau, based on which the average discharge voltage of the material increases from ~3V to ~3.3V. Additionally, Na₄Fe 1.8 Mn 1.2 A coin cell assembled with (PO4)2(P2O7) as the cathode material achieved a reversible capacity of 109.1 mAh / g at 0.2C. Figure 2 The positive electrode active material Na4Fe prepared in this embodiment 1.8 Mn 1.2 XRD pattern of (PO4)2(P2O7); from Figure 3 It can be seen that the assembled coin cell retains 93.4% of its capacity after 150 cycles at 0.2C. Figure 4 It can be seen that the assembled button cell has a reversible capacity of 72.9 mAh / g at 10C and 57.8 mAh / g at 20C. The capacity retention rate at 20C is about 65.5% (compared to its reversible capacity at 0.2C), showing good rate performance.

[0045] Example 2

[0046] The chemical formula of the iron-manganese-based composite phosphate material prepared in this embodiment is Na₄Fe₂O₃. 1.5 Mn 1.5 (PO4)2(P2O7), the specific preparation method is as follows:

[0047] The raw materials are NaH2PO4·2H2O, FeCO3, Mn(NO3)3·4H2O, and sucrose, with diethyl ether as the solvent. NaH2PO4 serves as both a sodium and phosphorus source, FeCO3 as an iron source, Mn(NO3)3·4H2O as a manganese source, and sucrose as a carbon source.

[0048] 6.2404 g NaH2PO4·2H2O, 1.7376 g FeCO3, 3.7652 g Mn(NO3)3·4H2O, and 3.423 g sucrose were dispersed in 100 mL of 95% diethyl ether, ball-milled at 200 rpm for 5 h, and then dried at 80 °C for 6 h to obtain the precursor.

[0049] The precursor was then placed in an argon atmosphere and calcined at 350°C for 4 hours in the first stage, followed by calcination at 600°C for 8 hours in the second stage to obtain Na4Fe. 1.5 Mn 1.5 (PO4)2(P2O7).

[0050] The obtained Na4Fe 1.5 Mn 1.5 (PO4)2(P2O7) material was assembled into coin cells in a glove box with water and oxygen levels below 0.01 ppm. From Figure 5 It can be seen that the Na4Fe prepared in this embodiment... 1.5 Mn 1.5 A coin cell assembled with (PO4)2(P2O7) as the positive electrode active material achieved a reversible capacity of 79 mAh / g at 0.2C.

[0051] Example 3

[0052] The chemical formula of the iron-manganese-based composite phosphate material prepared in this embodiment is Na₄Fe₂O₃. 0.6 Mn 2.4 (PO4)2(P2O7), the specific preparation method is as follows:

[0053] Sodium dihydrogen phosphate (NaH2PO4·2H2O), ferric nitrate (Fe(NO3)3·9H2O), manganese oxalate (MnC2O4), and citric acid were used as raw materials, and ethanol was used as a solvent. Sodium dihydrogen phosphate (Na4P2O7) served as both a sodium and phosphorus source, Fe(NO3)3 as an iron source, manganese oxalate (MnC2O4) as a manganese source, and citric acid as a carbon source.

[0054] 6.2404g NaH2PO4·2H2O, 2.424g Fe(NO3)3·9H2O, 3.4308g MnC2O4, and 2.1014g citric acid monohydrate were added to 100mL of 95% acetone and ball-milled at 200rpm for 8h. The mixture was then dried at 100℃ for 3h to obtain the precursor.

[0055] The precursor was then placed in an argon atmosphere and calcined at 400°C for 3 hours in the first stage, followed by calcination at 700°C for 5 hours in the second stage to obtain Na4Fe. 0.6 Mn 2.4 (PO4)2(P2O7).

[0056] The obtained Na4Fe 0.6 Mn 2.4 (PO4)2(P2O7) material was assembled into coin cells in a glove box with water and oxygen levels below 0.01 ppm. From Figure 6 It can be seen that the Na4Fe prepared in this embodiment 0.6 Mn 2.4 A coin cell assembled with (PO4)2(P2O7) as the positive electrode active material achieved a reversible capacity of 71 mAh / g at 0.2C.

[0057] This invention achieves uniform dispersion of Mn and Fe at the atomic scale in the precursor through wet ball milling. While increasing the proportion of Mn added, it reduces the impact of the Jameer-Taylor effect of Mn on electrode stability. Furthermore, by utilizing a segmented solid-state sintering process, the solid solution reaction of manganese and iron is fully carried out, thereby stimulating the electrochemical activity of manganese. The resulting iron-manganese-based composite phosphate material, when used as a cathode material for sodium-ion batteries, exhibits improved operating voltage and excellent cycle and rate performance.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An application of an iron-manganese-based composite phosphate material, characterized in that, The iron-manganese-based composite phosphate material is used as a positive electrode material in sodium-ion batteries. The chemical formula of the iron-manganese based composite phosphate material is Na₄Fe₂O₃. 3-x Mn x (PO4)2(P2O7), where x=1.2, the preparation method of the iron-manganese-based composite phosphate material includes the following steps: (1) Weigh out sodium source, iron source, manganese source, phosphorus source and carbon source according to stoichiometric ratio, add organic solvent to disperse and form dispersion liquid; (2) Place the dispersion in a ball mill, add the ball milling media, and wet ball mill for 2-8 hours; (3) The ball-milled reaction solution was dried at 50~100℃ for 3-10h to obtain the precursor; (4) The precursor is placed in an inert atmosphere for segmented sintering. The first stage sintering temperature is 250°C and the time is 6h. The second stage sintering temperature is 500°C and the time is 12h to obtain the iron-manganese-based composite phosphate material. In step (1), the sodium source is sodium dihydrogen phosphate; In step (1), the iron source is ferric nitrate; In step (1), the manganese source is manganese oxalate; In step (1), the phosphorus source is disodium hydrogen phosphate; The carbon source in step (1) is citric acid.

2. The application of the iron-manganese-based composite phosphate material as described in claim 1, characterized in that: The organic solvent in step (1) includes one or more of methanol, ethanol, propanol, isopropanol, acetone, methyl butyl ketone, methyl isobutyl ketone, diethyl ether, and ethylene glycol dimethyl ether.

3. The application of the iron-manganese-based composite phosphate material as described in claim 1, characterized in that: The grinding media in step (2) include one or more of the following: natural sand, glass beads, steel beads, zirconium oxide beads, zirconium silicate beads, and agate beads.

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