Modified polyanion positive electrode material as well as preparation method and application thereof

Abstract

The invention discloses a modified polyanion positive electrode material as well as a preparation method and application thereof. The chemical formula of the modified polyanion positive electrode material is Na (4-x) MnxFe3-yFy (PO4) zP2O7, x is greater than or equal to 0.05 and less than or equal to 0.5, y is greater than or equal to 0.01 and less than or equal to 0.3, and z is greater than or equal to 2 and less than or equal to 6. According to the invention, co-doping of cations Mn and anions F is carried out on NFPP, so that an electron conduction path is optimized, generation of impure phases is slowed down by making iron-deficiency defects, and sodium ion transmission and charge migration are also improved. The synergistic effect of Mn and F synchronously adjusts the electronic structure and the ion channel of the material, and improves the internal electron energy level structure of the material to improve the conductivity and the structural stability of the material. The modified polyanion positive electrode material disclosed by the invention has the advantages of relatively high activity, safety, environmental protection and low cost; and a battery assembled by adopting the positive electrode material has high capacity and long service life.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and specifically to a modified polyanionic cathode material, its preparation method, and its applications. Background Technology

[0002] NFPP [Na4Fe3(PO4)2P2O7], as a cathode material for sodium-ion batteries, has shown promising development prospects and advantages due to its high theoretical specific capacity, stable cycle performance, and good thermal stability. However, the poor internal conductivity and stability of NFPP limit its commercial application. Moreover, since the atomic radius of sodium ions is larger than that of lithium ions, cathode materials need to have a more superior and robust structure. Therefore, to achieve the commercialization goal of NFPP, improvement measures need to be taken to enhance the electronic conductivity and stability of the material, while ensuring its activity and low cost-effectiveness.

[0003] Material nanostructuring and elemental doping are two different modification methods, both of which can effectively solve related problems. Nanostructuring improves the reaction kinetics and electrochemical performance of materials by reducing particle size, shortening ion transport paths, and significantly increasing specific surface area. In contrast, elemental doping exhibits greater advantages because it can alter the electronic and structural properties of electrode materials at the atomic level, fundamentally affecting their conductivity and electrochemical performance. Elemental doping is divided into cation doping and anion doping: cation doping can enhance the electronic conductivity and structural stability of electrode materials because metal cations can replace existing metal ions, forming new valence states and promoting charge transport; anion doping utilizes its electronegativity to enhance the structural stability of materials and may reduce the operating voltage of electrode materials, thereby increasing energy density. However, the methods disclosed in the prior art can only solve one aspect of the problems of NFPP materials and enhance one aspect of performance, while simultaneously exposing other problems.

[0004] CN117936755A discloses a high-energy-density polyanionic cathode material, the structural formula of which is: Na4Fe 3-x-y Mn x A y(PO4)2(P2O7) / C, where: 0 < x < 3, 0.01 < y < 0.05; A is a transition metal, including any one or a combination of at least two of V, Ti, Co, and Ni; C is a carbon coating layer covering the outer layer of the cathode material. Studies have shown that replacing part of the Fe element with Mn in the preparation of NFPP cathode materials can effectively improve the battery's capacity and energy density; simultaneously, doping with a small amount of transition metal elements can improve cycle stability, thereby alleviating the problems of low operating voltage and poor capacity and energy density performance of sodium iron phosphate pyrophosphate cathode materials.

[0005] CN114057175A discloses a fluorine-doped modified sodium iron pyrophosphate for use as a cathode material in sodium-ion batteries, wherein the chemical formula of the fluorine-doped modified sodium iron pyrophosphate is Na. 4-α Fe 2+α / 2 (P2O7) 2-x F 4x Or Na2Fe(P2O7) 1-y F 4y In the above formula, 2 / 3 ≤ α ≤ 7 / 8, 0 ≤ x ≤ 0.4, and 0 ≤ y ≤ 0.2. By doping sodium iron pyrophosphate with fluorine ions, a fluorine-doped modified sodium iron pyrophosphate cathode material was prepared. Because fluorine ions have stronger electronegativity, they can affect the outer electronic structure of the material and enhance its kinetic properties, resulting in excellent electrochemical performance of the fluorine-doped modified sodium iron pyrophosphate cathode material. When the fluorine-doped modified sodium iron pyrophosphate cathode material prepared in this invention is applied to sodium-ion batteries, it improves the charge-discharge specific capacity, rate performance, cycle stability, and low-temperature charge-discharge capability of sodium-ion batteries.

[0006] However, the above doping methods have limited effect on improving NFPP materials. Therefore, providing a modified NFPP material to obtain better electrochemical performance is a technical problem that urgently needs to be solved. Summary of the Invention

[0007] In view of the above-mentioned technical problems existing in the prior art, the purpose of this invention is to propose a modified polyanionic cathode material, its preparation method and application.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a modified polyanionic cathode material, characterized in that the chemical formula of the modified polyanionic cathode material is Na. 4-x Mn x Fe 3-y F y (PO4) zP2O7, where 0.05≤x≤0.5, 0.01≤y≤0.3, 2≤z≤6.

[0010] In the polyanionic cathode material of the present invention, x can be, for example, 0.05, 0.07, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or 0.5; y can be, for example, 0.01, 0.03, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, 0.23, 0.26, or 0.3; and z can be, for example, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, or 6.

[0011] This invention utilizes co-doping of non-nuclear polypropylene (NFPP) with cations Mn and anions F. Mn doping at Na sites optimizes the electronic conduction pathway and mitigates impurity phase formation by creating iron-deficient defects. F doping at Fe sites, with its high electronegativity, improves sodium ion transport and charge migration. The synergistic effect of Mn and F simultaneously modulates the material's electronic structure and ion channels, improving the internal electronic energy level structure to enhance conductivity and structural stability, while reducing the amount of Fe in the material. The modified polyanionic cathode material of this invention possesses advantages such as high activity, safety, environmental friendliness, and low cost. Batteries assembled using this cathode material exhibit high capacity and long lifespan.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0013] Preferably, 0.1≤x≤0.3, 0.05≤y≤0.2.

[0014] Preferably, the median particle size of the modified polyanionic cathode material is D50, where 0.5 μm < D50 < 10 μm. Exemplarily, D50 can be, for example, 0.6 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, or 9.5 μm.

[0015] In a second aspect, the present invention provides a method for preparing the modified polyanionic cathode material as described in the first aspect, the method comprising the following steps:

[0016] (1) According to the stoichiometric ratio of the precursor, sodium source, phosphorus source, iron source and manganese source are mixed into a solution, spray dried to obtain the precursor, the chemical formula of which is Na 4-x Mn x Fe3(PO4)z P2O7;

[0017] (2) The precursor is calcined under a protective atmosphere to obtain the initial product of the cathode material;

[0018] (3) The primary cathode material is introduced with NF3 gas at a certain temperature to obtain the modified polyanionic cathode material;

[0019] Where 0.05≤x≤0.5, 2≤z≤6.

[0020] In the preparation method of the present invention, x can be, for example, 0.05, 0.07, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5; z can be, for example, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5 or 6.

[0021] This invention successfully prepared a modified polyanionic cathode material by spray drying. The modification strategy of co-doping with Mn and F anions and cations not only further improved the conductivity of the material, but also suppressed the formation of impurity phases by creating iron-deficient defects, and improved the electronic structure by utilizing the high electronegativity of fluorine, thereby improving the discharge specific capacity and cycle stability of the material.

[0022] The method of this invention is easy to prepare, low in cost, simple to operate, non-toxic and harmless, and suitable for large-scale industrial production.

[0023] As a preferred technical solution of the preparation method of the present invention, the sodium source in step (1) includes at least one of sodium dihydrogen phosphate, sodium monohydrogen phosphate, sodium phosphate, sodium acetate and sodium oxalate.

[0024] Preferably, the phosphorus source in step (1) includes at least one of sodium dihydrogen phosphate, sodium monohydrogen phosphate, and sodium phosphate.

[0025] Preferably, the iron source in step (1) includes at least one of ferric chloride, ferric sulfate, ferric nitrate and ferric dihydrogen phosphate.

[0026] Preferably, the manganese source in step (1) includes at least one of manganese sulfate, manganese nitrate, manganese oxalate and manganese dihydrogen phosphate.

[0027] Preferably, the spray temperature of the spray drying in step (1) is 150℃-450℃, for example, it can be 150℃, 175℃, 200℃, 225℃, 250℃, 275℃, 300℃, 325℃, 350℃, 375℃, 400℃, 425℃ or 450℃, etc.

[0028] Preferably, the feed rate of the spray drying in step (1) is 100 mL / h-2 L / h, for example, it can be 100 mL / h, 200 mL / h, 300 mL / h, 500 mL / h, 700 mL / h, 800 mL / h, 900 mL / h, 1 L / h, 1.2 L / h, 1.3 L / h, 1.4 L / h, 1.5 L / h, 1.6 L / h, 1.8 L / h or 2 L / h, etc.

[0029] As a preferred technical solution of the preparation method of the present invention, the gas in the protective atmosphere in step (2) includes any one of nitrogen, helium, argon and hydrogen or a mixture of at least two of them.

[0030] Preferably, the calcination in step (2) includes a first-stage calcination and a second-stage calcination performed sequentially. The temperature of the first-stage calcination is 200℃-600℃ (for example, it can be 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃ or 600℃, etc.), and the holding temperature of the second-stage calcination is 300℃-800℃, for example, it can be 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃ or 800℃, etc.

[0031] Preferably, the holding temperature of the second-stage calcination is higher than the temperature of the first-stage calcination.

[0032] Preferably, the calcination time in step (2) is 4h-48h, for example, it can be 4h, 6h, 8h, 10h, 12h, 15h, 16h, 18h, 20h, 23h, 25h, 27h, 30h, 32h, 35h, 38h, 40h, 45h or 48h, etc.

[0033] Preferably, the heat preservation time for the two-stage calcination in step (2) is 3h-24h, for example, it can be 3h, 4h, 6h, 8h, 10h, 12h, 15h, 16h, 18h, 20h, 23h or 24h.

[0034] Preferably, the heating rate of calcination in step (2) is 0.5℃ / min-5℃ / min, for example, it can be 0.5℃ / min, 1℃ / min, 1.5℃ / min, 2℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min or 5℃ / min, etc.

[0035] As a preferred technical solution of the preparation method described in this invention, the certain temperature in step (3) is 25℃-350℃, for example, it can be 25℃, 45℃, 55℃, 70℃, 80℃, 100℃, 120℃, 140℃, 150℃, 170℃, 180℃, 200℃, 220℃, 240℃, 260℃, 280℃, 300℃, 325℃ or 350℃, etc.

[0036] Thirdly, the present invention provides a positive electrode comprising the modified polyanionic positive electrode material described in the first aspect.

[0037] Fourthly, the present invention provides a sodium-ion battery, wherein the sodium-ion battery includes the positive electrode described in the third aspect.

[0038] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0039] Compared with existing technologies, the present invention has the following beneficial effects:

[0040] (1) This invention co-dops NFPP with cation Mn and anion F. Mn is doped at Na sites, optimizing the electronic conduction path and mitigating the formation of impurity phases by creating iron-deficient defects. F is doped at Fe sites, and its high electronegativity improves sodium ion transport and charge migration. The synergistic effect of Mn and F simultaneously regulates the electronic structure and ion channels of the material, improves the internal electronic energy level structure of the material to enhance its conductivity and structural stability, and reduces the amount of Fe in the material. The modified polyanionic cathode material of this invention has the advantages of high activity, safety and environmental friendliness, and low cost. Batteries assembled using this cathode material have high capacity and long lifespan.

[0041] (2) The method of the present invention is easy to prepare, low in cost, simple to operate, non-toxic and harmless, and suitable for large-scale industrial production. Detailed Implementation

[0042] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0043] Example 1

[0044] This embodiment provides a modified polyanionic cathode material, the chemical formula of which is Na. 3.8 Mn 0.2 Fe 2.9 F 0.1 (PO4)4P2O7.

[0045] This embodiment also provides a method for preparing the above-mentioned modified polyanionic cathode material, including the following steps:

[0046] (1) Sodium dihydrogen phosphate, sodium phosphate, ferric chloride and manganese sulfate were mixed into a solution according to the stoichiometric ratio of the precursor, and spray-dried. The spray temperature of the spray drying was 200℃ and the feed rate of the spray drying was 300mL / h to obtain the precursor.

[0047] (2) The precursor is calcined under a nitrogen atmosphere. The calcination process parameters are: heating to 200°C at a heating rate of 5°C / min, holding for 12 hours, and then heating to 500°C at a heating rate of 3°C / min and holding for 12 hours to obtain the initial product of the cathode material.

[0048] (3) The initial product of the cathode material is introduced with NF3 gas at 350°C to obtain the modified polyanionic cathode material.

[0049] Example 2

[0050] This embodiment provides a modified polyanionic cathode material, the chemical formula of which is Na. 3.9 Mn 0.1 Fe 2.95 F 0.05 (PO4)2P2O7.

[0051] This embodiment also provides a method for preparing the above-mentioned modified polyanionic cathode material, including the following steps:

[0052] (1) Sodium acetate, sodium monohydrogen phosphate, ferric sulfate and manganese nitrate were mixed into a solution according to the stoichiometric ratio of the precursor, and spray-dried. The spray temperature of the spray drying was 300℃ and the feed rate of the spray drying was 1L / h to obtain the precursor.

[0053] (2) The precursor is calcined under a nitrogen atmosphere. The calcination process parameters are: heating to 400°C at a heating rate of 3°C / min, holding for 4 hours, and then heating to 600°C at a heating rate of 3°C / min and holding for 8 hours to obtain the initial product of the cathode material.

[0054] (3) The initial product of the cathode material is introduced with NF3 gas at 200°C to obtain the modified polyanionic cathode material.

[0055] Example 3

[0056] This embodiment provides a modified polyanionic cathode material, the chemical formula of which is Na. 3.6 Mn 0.4 Fe 2.9 F0.1 (PO4)6P2O7.

[0057] This embodiment also provides a method for preparing the above-mentioned modified polyanionic cathode material, including the following steps:

[0058] (1) Sodium phosphate, sodium dihydrogen phosphate, ferric nitrate and manganese oxalate were mixed into a solution according to the stoichiometric ratio of the precursor, and spray-dried. The spray temperature of the spray drying was 175℃ and the feed rate of the spray drying was 800mL / h to obtain the precursor.

[0059] (2) The precursor is calcined under a nitrogen atmosphere. The calcination process parameters are: heating to 350°C at a heating rate of 4°C / min, holding for 24 hours, and then heating to 400°C at a heating rate of 4°C / min and holding for 3 hours to obtain the initial product of the cathode material.

[0060] (3) The initial product of the cathode material is introduced with NF3 gas at 300°C to obtain the modified polyanionic cathode material.

[0061] Comparative Example 1

[0062] This comparative example provides a cathode material that is not doped with Mn. The difference between its preparation method and that of Example 1 is that manganese sulfate is not added in step (1).

[0063] Comparative Example 2

[0064] This comparative example provides a cathode material that is not doped with F element. The difference between its preparation method and that of Example 1 is that step (3) is not performed.

[0065] The positive electrode was prepared and the battery was assembled using the positive electrode materials of Examples 1-3 and Comparative Examples 1-2, including the following steps:

[0066] A positive electrode slurry was prepared by dispersing 85 wt% of positive electrode material, 10 wt% of Super P and 5 wt% of polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone (NMP) solution, coating it on an aluminum foil and drying it to obtain the positive electrode.

[0067] Lithium foil serves as the negative electrode;

[0068] The diaphragm is a PP microporous membrane (Celgard2400);

[0069] The electrolyte composition is: 1M LiPF6 (the solvent is a mixture of EC, DMC and EMC, wherein the volume ratio of EC:DMC:EMC is 1:1:1).

[0070] The above-mentioned positive electrode, separator, negative electrode and electrolyte are assembled to obtain a coin cell.

[0071] Performance testing: Cycle 1000 times at room temperature, 2.4~4.2V voltage range, and 0.5C rate, and record the initial discharge capacity and capacity retention rate after 1000 cycles.

[0072] The results are shown in Table 1.

[0073]

[0074] As shown in Table 1, this invention achieves its effect by co-doping NFPP with cations Mn and anions F. Mn is doped at Na sites, optimizing the electronic conduction path and mitigating impurity phase formation by creating iron-deficient defects. F is doped at Fe sites, and its high electronegativity improves sodium ion transport and charge migration. The synergistic effect of Mn and F simultaneously regulates the electronic structure and ion channels of the material, improving the internal electronic energy level structure to enhance conductivity and structural stability, while reducing the amount of Fe in the material. The modified polyanionic cathode material of this invention has advantages such as high activity, safety, environmental friendliness, and low cost. Batteries assembled using this cathode material exhibit high capacity and long lifespan.

[0075] The comparison between Example 1 and Comparative Example 1 shows that without Mn doping, the electronic conduction path of the material is not effectively optimized, the impurity phase generation rate is accelerated, resulting in a decrease of about 24% in the first discharge capacity and a decrease of about 16 percentage points in the capacity retention rate after 1000 cycles. This proves that Mn doping can significantly improve the conductivity and structural stability of the material.

[0076] The comparison between Example 1 and Comparative Example 2 shows that without F doping, the sodium ion transport and charge migration capabilities are weakened, the electronic energy level structure of the material is not effectively regulated, the initial discharge capacity decreases by about 19%, and the capacity retention rate after 1000 cycles decreases by about 12 percentage points. This indicates that F doping can improve ion transport dynamics through high electronegativity and form a synergistic effect with Mn.

[0077] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A modified polyanionic cathode material, characterized in that, The modified polyanion cathode material has the chemical formula Na. 4-x Mn x Fe 3-y F y (PO4) z P2O7, where 0.05≤x≤0.5, 0.01≤y≤0.3, 2≤z≤6.

2. The modified polyanionic cathode material according to claim 1, characterized in that, 0.1≤x≤0.3, 0.05≤y≤0.

2.

3. The modified polyanionic cathode material according to claim 1 or 2, characterized in that, The median particle size of the modified polyanionic cathode material is D50, where 0.5 μm < D50 < 10 μm.

4. A method for preparing a modified polyanionic cathode material as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: (1) According to the stoichiometric ratio of the precursor, sodium source, phosphorus source, iron source and manganese source are mixed into a solution, spray dried to obtain the precursor, the chemical formula of which is Na 4-x Mn x Fe3(PO4) z P2O7; (2) The precursor is calcined under a protective atmosphere to obtain the initial product of the cathode material; (3) The initial product of the cathode material is introduced with NF3 gas at a certain temperature to obtain the modified polyanionic cathode material; Where 0.05≤x≤0.5, 2≤z≤6.

5. The preparation method according to claim 4, characterized in that, The sodium source in step (1) includes at least one of sodium dihydrogen phosphate, sodium monohydrogen phosphate, sodium phosphate, sodium acetate, and sodium oxalate; Preferably, the phosphorus source in step (1) includes at least one of sodium dihydrogen phosphate, sodium monohydrogen phosphate, and sodium phosphate; Preferably, the iron source in step (1) includes at least one of ferric chloride, ferric sulfate, ferric nitrate, and ferric dihydrogen phosphate; Preferably, the manganese source in step (1) includes at least one of manganese sulfate, manganese nitrate, manganese oxalate and manganese dihydrogen phosphate.

6. The preparation method according to claim 4 or 5, characterized in that, The spray temperature for spray drying in step (1) is 150℃-450℃; Preferably, the feed rate of the spray drying in step (1) is 100 mL / h-2 L / h.

7. The preparation method according to any one of claims 4-6, characterized in that, The protective atmosphere in step (2) includes any one of nitrogen, helium, argon and hydrogen, or a mixture of at least two of them; Preferably, the calcination in step (2) includes a first-stage calcination and a second-stage calcination performed sequentially, wherein the temperature of the first-stage calcination is 200℃-600℃ and the holding temperature of the second-stage calcination is 300℃-800℃; Preferably, the calcination time in step (2) is 4h-48h; Preferably, the heat preservation time for the two-stage calcination in step (2) is 3h-24h; Preferably, the heating rates of the first-stage calcination and the second-stage calcination in step (2) are independently 0.5℃ / min-5℃ / min.

8. The preparation method according to any one of claims 4-7, characterized in that, The specific temperature mentioned in step (3) is 250℃-350℃.

9. A positive electrode, characterized in that, The positive electrode includes the modified polyanionic positive electrode material as described in any one of claims 1-3.

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes the positive electrode as described in claim 9.

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