Multifunctional site co-doped high-rate multi-element iron-based phosphate positive electrode material and preparation method thereof and sodium ion battery

Abstract

This invention belongs to the field of sodium-ion battery technology, and mainly relates to a multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material, its preparation method, and a sodium-ion battery. The chemical formula of the multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material is: Na [4‑(3+n)y] Fe 3‑x Mg x (PO4) 2‑y (A) y P₂O₇ / C, where 0.001 < x < 0.05, 0.001 < y < 0.5, and n is the valence state of the doped anion, -2 or -4; the doped anion element A is selected from SiO₄. 4‑ SO4 2‑ and CO3 2‑ One or more of the following groups are used. This cathode material uses magnesium ions to partially replace iron ions, which accelerates the transport rate of sodium ions and reduces the interfacial charge transfer resistance. The doped anions replace phosphate sites, which stabilizes the material's crystal structure, enhances lattice stability, and improves the material's high-power discharge capability.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and mainly relates to a multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material, its preparation method, and sodium-ion batteries. Background Technology

[0002] In recent years, with the rapid growth in demand for electronic devices and electric mobility tools, lithium-ion batteries, which have high energy density, long lifespan, and high safety, have been widely used in the field of energy storage and power. As a result, the problems of lithium resource shortage, high cost, and uneven distribution have become increasingly prominent. Meanwhile, sodium resources are abundant, easy to obtain, and inexpensive, which has led to the rapid development of sodium-ion battery technology and accelerated its industrialization process in the fields of energy storage and small power.

[0003] As a cathode material for sodium-ion batteries, the multi-element iron-based polyanionic compound Na4Fe3(PO4)2P2O7 possesses an open and stable structural framework and a high reversible capacity (up to 129 mAh g⁻¹). -1 ) and higher average voltage (based on Fe) 2+ / Fe 3 + Na₄Fe₃(PO₄)₂P₂O₇ is considered an ideal cathode material for developing long-life rechargeable batteries (3.2V redox). However, Na₄Fe₃(PO₄)₂P₂O₇ has low intrinsic conductivity. Generally, carbon coating or carbon composite methods are used to construct a multi-level conductive network on the material surface, enhancing the electron transport capacity between particles to improve the discharge specific capacity. However, this cannot solve the problem of poor conductivity due to sodium ion diffusion within the material, resulting in poor high-rate discharge performance.

[0004] Therefore, there is an urgent need to develop a cathode material with excellent high-rate discharge performance. Summary of the Invention

[0005] To overcome the problems in existing technologies, this invention stabilizes the crystal structure of materials and enhances lattice stability through multifunctional site doping, reducing collapse caused by structural changes under high-rate discharge conditions, thereby improving the high-power discharge capability of the materials. Specifically, it utilizes magnesium ion doping and multi-site doping techniques that regulate anionic groups to strengthen the crystal structure and enhance the high-power discharge capability of the materials.

[0006] In this embodiment of the invention, a multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material is provided. The chemical formula of the multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material is: Na [4-(3+n)y] Fe 3-x Mg x (PO4) 2-y (A) yP2O7 / C, where 0.001 < x < 0.05, 0.001 < y < 0.5, and n is the valence state of the doped anion, -2 or -4; the doped anion A is selected from SiO4. 4- SO4 2- and CO3 2- One or more of the following. The positive electrode material is spherical particles with a particle size of 2μm to 8μm.

[0007] Based on the same inventive concept, this invention proposes a method for preparing the above-mentioned multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material, comprising the following steps:

[0008] S1. Add carbon source, iron source, phosphorus source, sodium source, magnesium source and anion source to pure water according to the stoichiometric ratio, stir, and obtain slurry A;

[0009] S2. The slurry A is milled to obtain slurry B;

[0010] S3. Spray dry the slurry B to obtain a multifunctional site co-doped high-rate iron-based phosphate precursor powder.

[0011] S4. The multifunctional site co-doped high-rate iron-based phosphate precursor powder is sintered in segments under a protective atmosphere to obtain a multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material.

[0012] As an optional implementation, in step S1, the carbon source is one or more of glucose, sucrose, cyclodextrin, gelatin, citric acid, ascorbic acid, and starch; the iron source is ferric phosphate; the phosphorus source is one or two of diammonium hydrogen phosphate and diammonium dihydrogen phosphate; the sodium source is one or more of trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, sodium hydroxide, sodium citrate, sodium acetate, and sodium oxalate; the magnesium source is magnesium acetate, magnesium oxalate, or magnesium nitrate; and the anion source is any one of silicon acetate, silicon oxalate, magnesium sulfate, or ammonium carbonate.

[0013] As an optional implementation, in step S1, the molar ratio of magnesium, anionic groups and iron in the magnesium source, anion source and iron source is 0.001-0.05:0.001-0.5:0-3.

[0014] As an optional implementation, in step S2, the grinding parameters are 1500-2500 rpm, the grinding time is 2-5 h, and the grinding is carried out until the average particle size is 500 nm-2 μm.

[0015] As an optional implementation, in step S3, the solid content of the slurry B is 10-35%, and during the spray drying process, the peristaltic speed is 25-45 rpm, the frequency is 35-60 Hz, the inlet air temperature is 200-250°C, and the outlet air temperature is 105-120°C.

[0016] As an optional implementation, in step S4, the segmented calcination specifically includes:

[0017] First stage: Heat from room temperature to 300℃~380℃ at a heating rate of 1-5℃ / min, and hold for 3h~10h;

[0018] Second stage: Increase the temperature to 450℃~600℃ at a heating rate of 1-5℃ / min, and hold for 5h~12h.

[0019] Based on the same inventive concept, this embodiment of the invention also provides a positive electrode sheet, which includes a current collector and an active layer located on the surface of the current collector, wherein the active layer includes the above-mentioned multifunctional site co-doped high-rate multi-element iron-based phosphate positive electrode material.

[0020] This invention also provides a sodium-ion battery, which includes the above-mentioned positive electrode sheet.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material of the present invention adopts an anion-cation co-doping method. Magnesium ions with similar radii (slightly smaller than Fe) and similar Fermi levels are selected to replace part of the iron sites in the material. Because the radius of the replaced metal ion is slightly smaller than Fe, the Fe-O and PO bonds in the material structure are shortened, and the Na-O bonds are lengthened and more easily broken, which improves the diffusion coefficient of Na ions and reduces the interfacial charge transfer resistance. The anion group doping is selected from SiO4 with a configuration comparable to the PO43- group. 4- SO4 2- and CO3 2- It can effectively regulate the crystal and electronic structure, increasing lattice defects, active sites, and ionic conductivity in the material. Simultaneously, it can stabilize the crystal structure, enhance lattice stability, and reduce structural collapse caused by structural changes under high-rate discharge conditions, thereby improving the material's high-power discharge capability. Within the 2-4.0V voltage range, the material's discharge specific capacity at a 20C current rate can reach 67.01 mAh g. -1 .

[0023] (2) The cathode material of the present invention uses pure water system and is prepared by sand milling, spray drying and two-stage calcination. The process is simple, the raw materials are widely available, the environment is friendly and it is easy to carry out large-scale industrial production. Attached Figure Description

[0024] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The images shown are SEM images and EDS surface scans of the multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material prepared in Example 1 of this invention, wherein Figures (a) and (b) are SEM images, and Figure (c) is the EDS energy spectrum of the material.

[0026] Figure 2 The images show the XRD patterns of the multi-component iron-based phosphate materials prepared in Example 1 and Comparative Example 1 of the present invention, where (a) is the multi-functional site co-doped high-rate multi-component iron-based phosphate cathode material prepared in Example 1, and (b) is the multi-component iron-based phosphate material prepared in Comparative Example 1.

[0027] Figure 3 Rate curves of the multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material prepared in Example 1 of the present invention and the multi-element iron-based phosphate material prepared in Comparative Example 1 in the voltage range of 2-4.0V and 0.2C-20C.

[0028] Figure 4 This is a SEM image of the multi-element iron-based phosphate cathode material prepared in Comparative Example 1 of this invention. Detailed Implementation

[0029] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0030] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0031] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0032] To improve the cycle stability and specific capacity of sodium-ion battery cathode materials, the inventors of this application modified the multi-component iron-based phosphate cathode material by doping with multiple anion and cation sites. Doping was performed on Fe sites and PO4 to obtain a high-rate multi-component iron-based phosphate cathode material with the chemical formula: Na. [4-(3+n)y] Fe 3-x Mg x (PO4) 2-y (A) y P2O7 / C, where 0.001 < x < 0.05, 0.001 < y < 0.5, and n is the valence state of the doped anion, -2 or -4; the doped anion A is selected from SiO4. 4- SO4 2- and CO3 2- One or more of the following. This multifunctional site-co-doped high-rate multi-element iron-based phosphate cathode material is a spherical particle with a particle size of 2μm to 8μm.

[0033] The above-mentioned method for preparing multi-functional site doping of multi-element iron-based phosphate cathode materials includes the following steps:

[0034] S1. Add carbon source, iron source, phosphorus source, sodium source, magnesium source, and anion source to pure water according to the stoichiometric ratio, and stir to obtain slurry A; wherein the carbon source is an organic carbon source, selected from one or more of glucose, sucrose, cyclodextrin, gelatin, citric acid, ascorbic acid, and starch; the iron source is preferably ferric phosphate; the phosphorus source is one or two of diammonium hydrogen phosphate and diammonium dihydrogen phosphate; the sodium source is one or more of trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, sodium hydroxide, sodium citrate, sodium acetate, and sodium oxalate; the magnesium source is any one of magnesium acetate, magnesium oxalate, and magnesium nitrate; and the anion is a soluble salt containing Si, S, and carbonate, such as one or more of ammonium salts, acetates, or oxalates, specifically any one of silicon acetate, silicon oxalate, magnesium sulfate, or ammonium carbonate. The molar ratio of magnesium, anion groups, and iron in the magnesium source, anion source, and iron source is 0.001–0.05:0.001–0.5:0–3.

[0035] S2. The slurry A is milled to obtain slurry B. During this process, the milling parameters are 1500-2500 rpm, the time is 2-5 hours, and the average particle size is milled to 50 nm-2 μm. In this step, some of the raw materials are solid, and solids may be generated during the reaction. Therefore, it is necessary to control the particle size. Milling improves the uniformity of mixing and provides a basis for subsequent pre-calcination and calcination.

[0036] S3. The slurry B is spray-dried to obtain a high-ratio iron-based phosphate precursor powder with multifunctional co-doped sites. In this process, the spray dryer mainly plays a role in rapid drying. The spray dryer sprays the slurry into droplets and disperses them in a hot air stream, causing the moisture in the slurry to evaporate rapidly to obtain the powder. The entire drying process can be completed within a few seconds to tens of seconds. The process parameters of the spray dryer are: peristaltic speed of 25-45 rpm, preferably 35 rpm; frequency of 35-60 Hz; inlet air temperature of 200℃-250℃, preferably 220℃; and outlet air temperature of 95-120℃, preferably 105-110℃. The specific parameters are subject to the actual operating standards of the spray dryer.

[0037] S4. The multifunctional site co-doped high-ratio iron-based phosphate precursor powder is sintered in segments under a protective atmosphere to obtain a multifunctional site co-doped high-ratio multi-element iron-based phosphate cathode material. During this process, heat treatment is performed under a protective atmosphere, wherein the protective atmosphere is one or a mixture of two or more of nitrogen, argon, and hydrogen, preferably a hydrogen-argon mixture, wherein the hydrogen volume percentage is 5%. The heat treatment consists of two steps: pre-calcination and secondary calcination. The pre-calcination process involves a heating rate of 1–5°C / min, preferably 3°C / min; a temperature of 300–400°C, preferably 350°C; and a holding time of 3–8 h, preferably 5 h. The secondary calcination process involves a heating rate of 1–5°C / min, preferably 3°C / min; a temperature of 450–600°C, preferably 500°C; and a holding time of 5–15 h, preferably 10 h. Cooling is performed with the furnace.

[0038] Embodiments of this application also provide a positive electrode sheet, which includes a current collector and an active layer located on the surface of the current collector. The active layer includes the aforementioned high-rate multi-element iron-based phosphate positive electrode material co-doped with multifunctional sites. Furthermore, the above-mentioned electrode sheet can be assembled to obtain a sodium battery with excellent performance.

[0039] The specific implementation methods of this application have been described above. In order to objectively illustrate the technical effects produced by this application, the following examples and comparative examples will be used to describe them.

[0040] Example 1

[0041] A multifunctional site-co-doped high-rate multi-element iron-based phosphate cathode material and its preparation method include the following steps:

[0042] (1) Add ferric phosphate, ammonium dihydrogen phosphate, Na2C2O4, C4H6MgO4·4H2O, and C8H 12O8Si and glucose were dissolved in deionized water at a molar ratio of 2.995:1.0025:2.00125:0.0005:0.0025, with a carbon source added at a ratio of 2-3 wt% and a solid-liquid ratio of 3:10. The mixture was stirred continuously at room temperature for 30 minutes to obtain the first slurry.

[0043] (2) Pour the first slurry into the feed hopper of the sand mill, set the sand mill program to 1500 rpm for 1 hour, 2000 rpm for 1 hour, and 2500 rpm for 1 hour, and measure the D of the product obtained after grinding. 50 The particle size is approximately 500 nm.

[0044] (3) The slurry obtained in step 2 is sprayed and granulated to obtain a yellow-green powder; wherein the inlet temperature of the spray granulation is 220°C, the outlet temperature is 110°C, and the peristalsis speed is 35 rpm.

[0045] (4) The obtained precursor was added to an inert atmosphere and pre-calcined at 350°C for 5 hours, then heated to 500°C and held for 10 hours to obtain the product with the chemical formula Na. 4.0025 Fe 2.995 Mg 0.005 (PO4) 1.9975 (SiO4) 0.0025 P2O7 / C magnesium-silicon co-doped multi-component iron-based phosphate cathode active material.

[0046] Example 2

[0047] A multifunctional site-co-doped high-rate multi-element iron-based phosphate cathode material and its preparation method include the following steps:

[0048] (1) Add ferric phosphate, ammonium dihydrogen phosphate, Na2C2O4, C4H6MgO4·4H2O, and C8H 12 O8Si and glucose were dissolved in deionized water at a molar ratio of 2.995:1.0025:2.00125:0.0005:0.0025, with a carbon source added at a ratio of 2-3 wt% and a solid-liquid ratio of 3:10. The mixture was stirred continuously at room temperature for 30 minutes to obtain the first slurry.

[0049] (2) Take the first slurry and pour it into the feed hopper of the sand mill. Set the sand mill program to 1500rpm1h, 2000rpm1h, 2500rpm1h. The D50 particle size of the product obtained after grinding is about 600nm.

[0050] (3) The slurry obtained in step 2 is sprayed and granulated to obtain a yellow-green powder; wherein the inlet temperature of the spray granulation is 220°C, the outlet temperature is 110°C, and the peristalsis speed is 35 rpm.

[0051] (4) The obtained precursor was added to an inert atmosphere and pre-calcined at 350°C for 5 hours, then heated to 550°C and held for 10 hours to obtain the product with the chemical formula Na. 4.0025 Fe 2.995 Mg 0.005 (PO4) 1.9975 (SiO4) 0.0025 A magnesium-silicon co-doped multi-component iron-based phosphate cathode active material of P2O7 / C(550).

[0052] Example 3

[0053] A multifunctional site-co-doped high-rate multi-element iron-based phosphate cathode material and its preparation method include the following steps:

[0054] (1) Add ferric phosphate, ammonium dihydrogen phosphate, Na2C2O4, C4H6MgO4·4H2O, and C8H 12 O8Si and glucose were dissolved in deionized water at a molar ratio of 2.95:1.025:2.0125:0.05:0.025, with a carbon source added at a ratio of 2-3 wt% and a solid-liquid ratio of 3:10. The mixture was stirred continuously at room temperature for 30 minutes to obtain the first slurry.

[0055] (2) Take the first slurry and pour it into the feed hopper of the sand mill. Set the sand mill program to 1500rpm1h, 2000rpm1h, 2500rpm1h. The D50 particle size of the product obtained after grinding is about 500nm.

[0056] (3) The slurry obtained in step 2 is sprayed and granulated to obtain a yellow-green powder; wherein the inlet temperature of the spray granulation is 220°C, the outlet temperature is 110°C, and the peristalsis speed is 35 rpm.

[0057] (4) The obtained precursor was added to an inert atmosphere and pre-calcined at 350°C for 5 hours, then heated to 500°C and held for 10 hours to obtain the product with the chemical formula Na. 4.025 Fe 2.95 Mg 0.05 (PO4) 1.975 (SiO4) 0.025 P2O7 / C magnesium-silicon co-doped multi-component iron-based phosphate cathode active material.

[0058] Example 4

[0059] A multifunctional site-co-doped high-rate multi-element iron-based phosphate cathode material and its preparation method include the following steps:

[0060] (1) Add ferric phosphate, ammonium dihydrogen phosphate, Na2C2O4, C4H6MgO4·4H2O, and C8H 12O8Si and glucose were dissolved in deionized water at a molar ratio of 3:4:2:0.005:0.0025, with a carbon source added at a ratio of 2-3 wt% and a solid-liquid ratio of 3:10. The mixture was stirred continuously at room temperature for 30 minutes to obtain the first slurry.

[0061] (2) Take the first slurry and pour it into the feed hopper of the sand mill. Set the sand mill program to 1500rpm1h, 2000rpm1h, 2500rpm1h. The D50 particle size of the product obtained after grinding is about 500nm.

[0062] (3) The slurry obtained in step 2 is sprayed and granulated to obtain a yellow-green powder; wherein the inlet temperature of the spray granulation is 220°C, the outlet temperature is 110°C, and the peristalsis speed is 35 rpm.

[0063] (4) The obtained precursor was added to an inert atmosphere and pre-calcined at 350°C for 5 hours, then heated to 550°C and held for 10 hours to obtain the product with the chemical formula Na. 4.01 Mg 0.01 Fe 2.99 (PO4) 1.99 (SiO4) 0.01 P2O7 / C magnesium-silicon co-doped multi-component iron-based phosphate cathode active material.

[0064] Example 5

[0065] A multifunctional site-co-doped high-rate multi-element iron-based phosphate cathode material and its preparation method include the following steps:

[0066] 1) Mix ferric phosphate, ammonium dihydrogen phosphate, Na₂C₂O₄, MgSO₄, and glucose in a molar ratio of 2.99:1:1.995:

[0067] 0.01 was dissolved in deionized water, with a carbon source ratio of 2-3 wt% and a solid-liquid ratio of 3:10. The mixture was stirred continuously at room temperature for 30 minutes to obtain the first slurry.

[0068] (2) Take the first slurry and pour it into the feed hopper of the sand mill. Set the sand mill program to 1500rpm1h, 2000rpm1h, 2500rpm1h. The D50 particle size of the product obtained after grinding is about 600nm.

[0069] (3) The slurry obtained in step 2 is sprayed and granulated to obtain a yellow powder; wherein the inlet temperature of the spray granulation is 220°C, the outlet temperature is 110°C, and the peristalsis speed is 35 rpm.

[0070] (4) The obtained precursor was added to an inert atmosphere and pre-calcined at 350°C for 5 hours, then heated to 500°C and held for 10 hours to obtain the product with the chemical formula Na. 3.99 Fe 2.99 Mg0.01 (PO4) 1.99 (SO4) 0.01 Magnesium-sulfur co-doped multi-component iron-based phosphate cathode active material of P2O7 / C.

[0071] Comparative Example 1

[0072] A method for preparing a multi-component iron-based phosphate cathode material includes the following steps:

[0073] (1) Dissolve ferric phosphate, ammonium dihydrogen phosphate, and Na2C2O4 in deionized water at a molar ratio of 3:1:2, add glucose as a carbon source at a ratio of 2-3 wt%, and the solid-liquid ratio is 3:10. Stir continuously at room temperature for 30 minutes to obtain the first slurry.

[0074] (2) Take the first slurry and pour it into the feed hopper of the sand mill. Set the sand mill program to 1500rpm1h, 2000rpm1h, 2500rpm1h. The D50 particle size of the product obtained after grinding is about 500nm.

[0075] (3) The slurry obtained in step 2 is sprayed and granulated to obtain a yellow-green powder; wherein the inlet temperature of the spray granulation is 220°C, the outlet temperature is 110°C, and the peristalsis speed is 35 rpm.

[0076] (4) The obtained precursor was added to an inert atmosphere and pre-calcined at 350°C for 5 hours, and then heated to 500°C and kept at that temperature for 10 hours to obtain a multi-element iron-based phosphate positive electrode active material with the chemical formula Na4Fe3(PO4)2P2O7 / C.

[0077] Comparative Example 2

[0078] A method for preparing a magnesium-doped multi-element iron-based phosphate cathode material includes the following steps:

[0079] (1) Dissolve ferric phosphate, ammonium dihydrogen phosphate, Na2C2O4, and C4H6MgO4·4H2O in deionized water at a molar ratio of 2.99:1.01:2:0.01, add 2-3 wt% glucose as a carbon source, and the solid-liquid ratio is 3:10. Stir continuously at room temperature for 30 minutes to obtain the first slurry.

[0080] (2) Take the first slurry and pour it into the feed hopper of the sand mill. Set the sand mill program to 1500rpm1h, 2000rpm1h, 2500rpm1h. The D50 particle size of the product obtained after grinding is about 500nm.

[0081] (3) The slurry obtained in step 2 is sprayed and granulated to obtain a yellow-green powder; wherein the inlet temperature of the spray granulation is 220°C, the outlet temperature is 110°C, and the peristalsis speed is 35 rpm.

[0082] (4) The obtained precursor was added to an inert atmosphere and pre-calcined at 350°C for 5 hours, then heated to 500°C and held for 10 hours to obtain the chemical formula Na4Fe. 2.99 Mg 0.01 (PO4)2P2O7 is a multi-element iron-based phosphate positive electrode active material.

[0083] Comparative Example 3

[0084] A method for preparing a silicon-doped nickel-iron-manganese oxide-based cathode material includes the following steps:

[0085] (1) Add ferric phosphate, ammonium dihydrogen phosphate, Na2C2O4, and C8H 12 O8Si was dissolved in deionized water at a molar ratio of 3:4:2:0.01, and glucose, a carbon source, was added at a ratio of 2-3 wt%. The solid-liquid ratio was 3:10. The mixture was stirred continuously at room temperature for 30 minutes to obtain the first slurry.

[0086] (2) Take the first slurry and pour it into the feed hopper of the sand mill. Set the sand mill program to 1500rpm1h, 2000rpm1h, 2500rpm1h. The D50 particle size of the product obtained after grinding is about 600nm.

[0087] (3) The slurry obtained in step 2 is sprayed and granulated to obtain a yellow-green powder; wherein the inlet temperature of the spray granulation is 220°C, the outlet temperature is 110°C, and the peristalsis speed is 35 rpm.

[0088] (4) The obtained precursor was added to an inert atmosphere and pre-calcined at 350°C for 5 hours, then heated to 500°C and held for 10 hours to obtain the product with the chemical formula Na. 4.01 Fe3(PO4) 1.99 (SiO4) 0.01 P2O7 / C multi-element iron-based phosphate cathode active material.

[0089] Spectral Analysis

[0090] The multi-element iron-based phosphate cathode materials obtained in the examples were analyzed by SEM, EDS, and XRD patterns. Taking the cathode materials obtained in Example 1 and Comparative Example 1 as examples... Figure 1 Na obtained in Example 1 4.0025 Fe 2.995 Mg 0.005 (PO4) 1.9975 (SiO4) 0.0025 SEM and EDS spectra of P2O7 / C cathode materials Figure 4 This is a SEM image of Na4Fe3(PO4)2P2O7 / C obtained in Comparative Example 1. Figure 1 (a) The SEM image shows that the material structure consists of spherical particles with a particle size of approximately 3 μm; Figure 1The EDS spectrum in (b) shows that Mg and Si elements are uniformly distributed in the material, indicating that Mg 2+ With SiO4 4- Successfully entered the material. Figure 1 and Figure 4 Comparative analysis revealed that the undoped original sample had a smooth surface and consisted of classic hollow spherical particles obtained by spraying, with varying particle sizes ranging from 2 to 10 μm. In contrast, the doped sample with Mg and SiO4... 4- The primary particles of the material are more distinct, resulting in a more stable structure. Figure 2 The XRD pattern of Example 1 shows that all diffraction peaks are similar and match well with the standard PDF card (PDF#97-023-6316). All phases can be represented by the orthorhombic crystal system of space group Pn21a, indicating the presence of small amounts of Mg and SiO4. 4- The replacement does not change the original crystal structure of NFPP (ferric phosphate).

[0091] Electrical performance analysis

[0092] Battery Assembly: Weigh 0.1600g of the positive electrode material prepared in the above examples or comparative examples, add 0.0200g of conductive carbon black as a conductive agent and 0.0200g of PVDF (polyvinylidene fluoride) as a binder, mix evenly, and coat it onto aluminum foil to form a positive electrode sheet. In a vacuum glove box, use a sodium metal sheet as the negative electrode, a Whatman GF / D glass fiber separator, and a 1mol / L NaClO4 electrolyte (EC:DMC = 1:1 (volume ratio) + 5% FEC) to assemble a CR2025 coin cell. High-rate discharge tests were conducted in the 2-4.0V range, and the results are shown in Table 1.

[0093] Table 1. Battery electrical performance test results for the cathode materials obtained in the examples and comparative examples.

[0094]

[0095] Depend on Figure 3 As shown in Table 1, compared with the material prepared in Comparative Example 1, the material in Example 1 shows a superior rate advantage after 5C, indicating that magnesium-silicon ion co-doping can stabilize the crystal structure of the material, enhance the stability of the lattice, reduce the material structure collapse caused by structural changes under high-rate discharge conditions, and thus improve the high-power discharge capability of the material.

[0096] Because Mg and Si ions play different roles in stabilizing the cathode structure, Mg mainly improves the diffusion coefficient of Na ions and reduces the interfacial charge transfer resistance by occupying specific lattice sites and replacing some iron sites, thereby improving the structural stability of the material. Silicate ions, on the other hand, replace some phosphate ions, increasing lattice defects, active sites, and ionic conductivity. In comparison, the improvement effect of single Si ion doping on the diffusion kinetics of Na ions is not as significant as that of Mg. Therefore, the rate performance of Comparative Example 2 is worse than that of Comparative Example 3. Furthermore, due to the different doping sites of Mg and silicate ions, their combined action produces a multi-element synergistic effect, effectively improving the structural stability of the material and reducing structural collapse during charging and discharging. Therefore, the rate performance of Example 4 is significantly better than that of the single-element doping in Comparative Examples 2 and 3.

[0097] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A multifunctional site-co-doped high-rate multi-element iron-based phosphate cathode material, characterized in that, The chemical formula of the multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material is: Na [4-(3+n)y] Fe 3-x Mg x (PO4) 2-y (A) y P2O7 / C, where 0.001 < x < 0.05, 0.001 < y < 0.5, and n is the valence state of the doped anion, -2 or -4; the doped anion A is selected from SiO4. 4- SO4 2- and CO3 2- One or more of the following; The preparation method of the multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material includes the following steps: S1. Add carbon source, iron source, phosphorus source, sodium source, magnesium source and anion source to pure water according to the stoichiometric ratio, stir, and obtain slurry A; S2. The slurry A is milled to obtain slurry B; S3. Spray dry the slurry B to obtain a multifunctional site co-doped high-rate iron-based phosphate precursor powder. S4. The multifunctional site co-doped high-rate iron-based phosphate precursor powder is sintered in segments under a protective atmosphere to obtain a multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material.

2. The multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material according to claim 1, characterized in that, The multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material is composed of spherical particles with a particle size of 2μm~8μm.

3. The method for preparing the multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material as described in any one of claims 1 and 2, characterized in that, Includes the following steps: S1. Add carbon source, iron source, phosphorus source, sodium source, magnesium source and anion source to pure water according to the stoichiometric ratio, stir to obtain slurry A; the molar ratio of magnesium, anion groups and iron in magnesium source, anion source and iron source is 0.001~0.05:0.001~0.5:0~3; S2. The slurry A is milled to obtain slurry B; S3. Spray dry the slurry B to obtain a multifunctional site co-doped high-rate iron-based phosphate precursor powder. S4. The multifunctional site co-doped high-rate iron-based phosphate precursor powder is sintered in segments under a protective atmosphere to obtain a multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material.

4. The method for preparing the multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material according to claim 3, characterized in that, In step S1, the carbon source is one or more of glucose, sucrose, cyclodextrin, gelatin, citric acid, ascorbic acid, and starch; the iron source is ferric phosphate; the phosphorus source is one or two of diammonium hydrogen phosphate and diammonium dihydrogen phosphate; the sodium source is one or more of trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, sodium hydroxide, sodium citrate, sodium acetate, and sodium oxalate; the magnesium source is magnesium acetate, magnesium oxalate, and magnesium nitrate; and the anion source is any one of silicon acetate, silicon oxalate, magnesium sulfate, or ammonium carbonate.

5. The method for preparing the multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material according to claim 3, characterized in that, In step S2, the grinding parameters are 1500~2500 rpm, the grinding time is 2~5 h, and the grinding is carried out until the average particle size is 500 nm~2 μm.

6. The method for preparing the multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material according to claim 3, characterized in that, In step S3, the solid content of the slurry B is 10-35%, and during the spray drying process, the peristalsis speed is 25-45 rpm, the frequency is 35-60 Hz, the inlet air temperature is 200-250℃, and the outlet air temperature is 105-120℃.

7. The method for preparing the multifunctional site co-doped high-rate multi-element iron-based phosphate cathode material according to claim 3, characterized in that, In step S4, the segmented calcination specifically includes: Pre-calcination: Heat from room temperature to 300℃~380℃ at a heating rate of 1-5℃ / min, and hold for 3h~10h; Secondary calcination: Heat to 450℃~600℃ at a heating rate of 1-5℃ / min, and hold for 5h~12h.

8. A positive electrode sheet, characterized in that, The positive electrode includes a current collector and an active layer located on the surface of the current collector, wherein the active layer includes the multifunctional site co-doped high-rate multi-element iron-based phosphate positive electrode material as described in any one of claims 1 and 2.

9. A sodium-ion battery, characterized in that, The sodium-ion battery includes the positive electrode sheet as described in claim 8.

Images