A sodium iron phosphate cathode material, its preparation method and application

Abstract

The application provides an iron-based phosphate sodium electric positive electrode material and a preparation method and application thereof, and belongs to the technical field of electrode materials. The preparation method of the iron-based phosphate sodium electric positive electrode material provided by the application comprises the following steps: mixing a carbon source, a sodium-iron-phosphorus source and a solvent to obtain a raw material mixed solution; the molar ratio of sodium elements, iron elements and phosphorus elements in the sodium-iron-phosphorus source is x+2:x+1:x+2, and 1.0 The iron-based phosphate sodium electric positive electrode material provided by the application has less NaFePO4 impurities or even no NaFePO4 impurities, and has high electronic conductivity.

Description

Technical Field

[0001] This invention relates to the field of electrode materials technology, and in particular to an iron-based sodium phosphate positive electrode material, its preparation method, and its application. Background Technology

[0002] Currently, lithium-ion batteries are widely used in mobile phones, cameras, and even automobiles, significantly reducing the consumption of fossil fuels. However, lithium resources are limited, unevenly distributed, and difficult to extract. Therefore, developing new energy storage battery systems that are abundant in resources and low in cost has become an important goal in the current energy storage field.

[0003] Sodium, a member of the same group as lithium, is the fourth most abundant metallic element on Earth. It possesses natural advantages such as abundant reserves, low cost, and ease of mining, making sodium-ion batteries a promising new hotspot and frontier in the field of rechargeable batteries. In recent years, iron-based polyanionic polymeric materials (NFPP materials), with their advantages of safety, non-toxicity, structural stability, and unique three-dimensional ion transport channels, are expected to be applied to large-scale energy storage systems. However, this material also has the following problems: On the one hand, the NFPP materials synthesized in previous literature generally have a sodium phosphate rock type NaFePO4 impurity phase. This electrochemically inert impurity phase leads to the low specific capacity and poor rate performance of the NFPP material (Hyungsub Kim, Inchul Park, Dong-Hwa Seo, Seongsu Lee, Sung-Wook Kim, Woo Jun Kwon, Young-Uk Park, Chul Sung Kim, Seokwoo Jeon, and Kisuk Kang, New Iron-Based Mixed-Polyanion Cathodes for Lithium and Sodium Rechargeable Batteries: Combined First Principles Calculations and Experimental Study, Journal of the American Chemical Society, 2012, 134(25), 10369-10372; Xiangjun Pu, Huiming Wang, Tianci Yuan, Shunan Cao, Shuangyu Liu, Li Xu, Hanxi Yang, Xinping Ai, Zhongxue Chen, Yuliang Cao, Na4Fe3(PO4)2P2O7 / C nanospheres as low-cost, high-performance cathode material for sodium-ion batteries, Energy Storage Materials, 2019, 11, 22, 330-336. On the other hand, NFPP materials also suffer from the electronic insulation defects of polyanionic materials, which limits their further development and application. Summary of the Invention

[0004] The purpose of this invention is to provide an iron-based sodium phosphate cathode material, its preparation method, and its applications. The iron-based sodium phosphate cathode material provided by this invention has few or no NaFePO4 impurity phases and exhibits high electronic conductivity (3.27 × 10⁻⁶).-6 S cm -1 ).

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing an iron-based sodium phosphate cathode material, comprising the following steps:

[0007] A carbon source, a sodium-iron-phosphorus source, and a solvent are mixed to obtain a raw material mixture; the molar ratio of sodium, iron, and phosphorus in the sodium-iron-phosphorus source is x+2:x+1:x+2, and 1.0 < x < 2.0;

[0008] The raw material mixture is subjected to gelation treatment to obtain a gel material;

[0009] The gel material was sequentially dried, pre-sintered, and sintered to obtain the iron-based sodium phosphate cathode material.

[0010] Preferably, the raw materials providing sodium in the sodium-iron-phosphorus source include inorganic sodium salts or organic sodium salts.

[0011] Preferably, the inorganic sodium salt includes one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, sodium carbonate, and sodium bicarbonate; the organic sodium salt includes one or more of sodium acetate, sodium oxalate, and sodium citrate.

[0012] Preferably, the raw materials providing iron in the sodium-iron-phosphorus source include inorganic iron sources or organic iron sources.

[0013] Preferably, the inorganic iron source includes one or more of iron powder, ferric nitrate, ferrous nitrate, ferric sulfate, ferrous sulfate, ferric chloride, ferrous chloride, and ferric phosphate; the organic iron source includes one or more of ferric acetylacetone, ferrous oxalate, ferric acetate, ferric citrate, and ferrous citrate.

[0014] Preferably, the carbon source includes one or more of citric acid, oxalic acid, sucrose, glucose, and ascorbic acid; the molar ratio of the carbon source to the iron source is 1 to 2:1.

[0015] Preferably, the gelation treatment is performed at a temperature of 60–90°C for 8–24 hours.

[0016] Preferably, the drying temperature is 80–140°C;

[0017] The pre-sintering temperature is 300–400℃, the holding time is 1–6 hours, and the heating rate to the pre-sintering temperature is 0.5–5℃ / min. -1 ;

[0018] The sintering temperature is 500–600℃, the holding time is 4–24 h, and the heating rate to the sintering temperature is 0.5–5℃ / min. -1 .

[0019] This invention provides an iron-based sodium phosphate cathode material prepared by the preparation method described above, comprising an iron-based phosphate and a carbon layer coated on the surface of the iron-based phosphate, wherein the chemical formula of the iron-based sodium phosphate cathode material is Na. x+2 Fe x+1 (PO4) x P2O7 / C, and 1.0 < x < 2.0.

[0020] This invention provides the application of the iron-based sodium phosphate cathode material described above in sodium-ion batteries.

[0021] This invention provides a method for preparing an iron-based sodium phosphate cathode material, comprising the following steps: mixing a carbon source, a sodium-iron-phosphorus source, and a solvent to obtain a raw material mixture; wherein the molar ratio of sodium, iron, and phosphorus in the sodium-iron-phosphorus source is x+2:x+1:x+2, and 1.0 < x < 2.0; subjecting the raw material mixture to gelation treatment to obtain a gel material; and sequentially drying, pre-sintering, and sintering the gel material to obtain the iron-based sodium phosphate cathode material. This invention strictly controls the molar ratio of sodium, iron, and phosphorus, ensuring that the NaFePO4 impurity phase in the iron-based phosphate sodium cathode material is minimal or even absent. This eliminates the need to introduce other elements or construct iron defects to overcome the low specific capacity and low rate performance caused by a large amount of NaFePO4 impurities. Furthermore, this invention introduces a carbon source, which, after carbonization, forms a uniformly coated carbon network layer on the surface of the iron-based phosphate, significantly improving the electronic conductivity of the iron-based phosphate sodium cathode material. For example, the electronic conductivity of the iron-based phosphate sodium cathode material provided by this invention is 3.27 × 10⁻⁶. -6 Scm -1 . Attached Figure Description

[0022] Figure 1 The images show the XRD patterns of the sodium-ion battery cathode materials prepared in Examples 1-3.

[0023] Figure 2 The graph shows the charge-discharge curve test results of the 2032 coin cell prepared in Application Example 1.

[0024] Figure 3 The graph shows the rate performance test results of the 2032 coin cell prepared in Application Example 1.

[0025] Figure 4The graph shows the long-cycle performance test results of the 2032 coin cell prepared in Application Example 1;

[0026] Figure 5 The XRD pattern of the sodium-ion battery cathode material prepared in Comparative Example 1;

[0027] Figure 6 The charge-discharge curve test results of the 2032 coin cell prepared in Application Example 1 are shown in the figure for comparison.

[0028] Figure 7 For comparison, the rate performance test results of the 2032 coin cell prepared in Application Example 1 are shown in the figure.

[0029] Figure 8 The graph shows the long-cycle performance test results of the 2032 coin cell prepared in Application Example 1 for comparison. Detailed Implementation

[0030] This invention provides a method for preparing an iron-based sodium phosphate cathode material, comprising the following steps:

[0031] A carbon source, a sodium-iron-phosphorus source, and a solvent are mixed to obtain a raw material mixture; the molar ratio of sodium, iron, and phosphorus in the sodium-iron-phosphorus source is x+2:x+1:x+2, and 1.0 < x < 2.0;

[0032] The raw material mixture is subjected to gelation treatment to obtain a gel material;

[0033] The gel material was sequentially dried, pre-sintered, and sintered to obtain the iron-based sodium phosphate cathode material.

[0034] This invention involves mixing a carbon source, a sodium-iron-phosphorus source, and a solvent to obtain a raw material mixture. In this invention, the sodium-iron-phosphorus source is a compound capable of providing sodium, iron, and phosphorus elements. The molar ratio of sodium, iron, and phosphorus elements in the sodium-iron-phosphorus source is x+2:x+1:x+2, and 1.0 < x < 2.0. Specifically, x = 1.1, 1.4, or 1.7. In this invention, the raw material providing sodium in the sodium-iron-phosphorus source preferably includes inorganic sodium salts or organic sodium salts; the organic sodium salt preferably includes one or more of sodium acetate, sodium oxalate, and sodium citrate; the inorganic sodium salt preferably includes one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, sodium carbonate, and sodium bicarbonate, more preferably sodium dihydrogen phosphate; when sodium dihydrogen phosphate is used to provide sodium, it can also provide phosphorus, so there is no need to add an additional phosphorus source; when other sodium salts are used, it is preferable to add an additional phosphorus source to ensure that the above elemental relationship is satisfied, and the phosphorus source preferably includes ammonium dihydrogen phosphate and / or diammonium hydrogen phosphate. In this invention, the raw material providing iron in the sodium-iron-phosphorus source preferably includes an inorganic iron source or an organic iron source; the inorganic iron source preferably includes one or more of iron powder (when iron powder is used as the iron source, this invention preferably uses an acid solution to dissolve the iron powder, or adds a citric acid chelating agent to form an iron ion solution such as ferric citrate), ferric nitrate, ferrous nitrate, ferric sulfate, ferrous sulfate, ferric chloride, ferrous chloride, and ferric phosphate; the organic iron source preferably includes one or more of ferric acetylacetone, ferrous oxalate, ferric acetate, ferric citrate, and ferrous citrate, more preferably ferric acetylacetone. In this invention, preferably, the sodium-iron-phosphorus source is a compound of sodium dihydrogen phosphate and ferric acetylacetone, and the molar ratio of sodium dihydrogen phosphate to ferric acetylacetone is preferably 5.2–5.8:3.9, more preferably 5.5:3.9.

[0035] In this invention, the carbon source preferably includes one or more of citric acid, oxalic acid, sucrose, glucose, and ascorbic acid, more preferably citric acid; the molar ratio of the carbon source to the iron source is preferably 1-2:1, more preferably 1.4-1.6:1, and even more preferably 1.5:1. In this invention, the solvent preferably includes water and an organic solvent, the organic solvent being preferably an alcohol solvent, more preferably ethanol; the volume ratio of water to the organic solvent is preferably 1-9:3, more preferably 1:3.

[0036] In this invention, taking the sodium-iron-phosphorus source as a compound of sodium dihydrogen phosphate and iron acetylacetone as an example, specifically, iron acetylacetone, a carbon source, and an organic solvent are mixed to obtain a first liquid; sodium dihydrogen phosphate is mixed with water to obtain a second liquid; and the first liquid and the second liquid are mixed to obtain the raw material mixture.

[0037] After obtaining the raw material mixture, the present invention performs a gelation treatment on the raw material mixture to obtain a gel material. In the present invention, the temperature of the gelation treatment is preferably 60-90℃, more preferably 70-80℃; the time is preferably 8-24h, more preferably 12-20h, and the specific time is based on the complete evaporation of the solvent to obtain the gel material.

[0038] After obtaining the gel material, the present invention sequentially dries, pre-sintersects, and sintersects the gel material to obtain the iron-based sodium phosphate cathode material. In the present invention, the drying temperature is preferably 80–140°C, more preferably 110–120°C; the present invention does not have a specific limitation on the drying time, as long as sufficient drying is ensured. The present invention preferably grinds the dried material before performing the subsequent pre-sintering. In the present invention, the pre-sintering temperature is preferably 300–400°C, more preferably 350°C; the holding time is preferably 1–6 hours, more preferably 5–6 hours; the heating rate to the pre-sintering temperature is preferably 0.5–5°C / min. -1 More preferably 2℃min -1 In this invention, the pre-sintering is preferably carried out in a protective atmosphere, more preferably in an Ar atmosphere. Preferably, the material obtained after pre-sintering is ground and pressed into sheets before subsequent sintering, wherein pressing helps improve the crystallinity of the iron-based sodium phosphate cathode material. Preferably, the material obtained after pre-sintering is ground and poured into a pressing mold, and the pressing mold is placed in a jack and pressed into sheets for 2-3 minutes under a pressure of 20 MPa. In this invention, the sintering temperature is preferably 500-600℃, more preferably 550℃; the holding time is preferably 4-24 hours, more preferably 10-12 hours; and the heating rate to the sintering temperature is preferably 0.5-5℃ / min. -1 More preferably 2℃min -1 In this invention, the sintering is preferably carried out in a protective atmosphere, more preferably in an Ar atmosphere. The sintered material is preferably cooled to room temperature to obtain the iron-based sodium phosphate cathode material. The pre-sintering and sintering are preferably carried out in a tube furnace.

[0039] This invention provides an iron-based sodium phosphate cathode material prepared by the above-described technical solution, comprising an iron-based phosphate and a carbon layer coating the surface of the iron-based phosphate, wherein the chemical formula of the iron-based sodium phosphate cathode material is Na. x+2 Fe x+1 (PO4) x P2O7 / C, and 1.0 < x < 2.0, specifically, x = 1.1, 1.4, or 1.7. In this invention, the chemical formula of the iron-based sodium phosphate cathode material is specifically Na. 3.1 Fe2.1 (PO4) 1.1 P2O7 / C, Na 3.4 Fe 2.4 (PO4) 1.4 P2O7 / C or Na 3.7 Fe 2.7 (PO4) 1.7 P2O7 / C. In this invention, the carbon content in the iron-based sodium phosphate cathode material is preferably 5-20 wt%, more preferably 10 wt%. The iron-based sodium phosphate cathode material provided by this invention belongs to the orthorhombic crystal system with space group Pn21a.

[0040] The iron-based sodium phosphate cathode material in this invention belongs to the polyanionic material category. Through crystal structure design combined with molecular configuration concepts, its molecular configuration is decomposed into xNaFePO4·1.0Na2FeP2O7, that is, the polyanionic group includes [PO4]. 3- ] and [P2O7 2- This invention reduces the NaFePO4 impurity phase in the material by adjusting the amounts of sodium, iron, and phosphorus added during the preparation process. The preparation method provided by this invention is simple and controllable, eliminating the need to introduce other elements or construct iron defects to overcome the low specific capacity and low rate performance caused by the large amount of NaFePO4 impurities. Therefore, no other complex processes or preparation conditions are required. The resulting iron-based sodium phosphate cathode material has less or no NaFePO4 impurities, high purity, and good crystallinity. The reduction of the inert NaFePO4 impurity enhances the electron-ion transport rate of the iron-based sodium phosphate cathode material, significantly improving its specific capacity and rate performance. Furthermore, the introduction of a carbon source in this invention forms a uniformly coated carbon network layer on the surface of the iron-based phosphate after carbonization, which greatly improves the electronic conductivity of the iron-based sodium phosphate cathode material.

[0041] This invention provides the application of the iron-based sodium phosphate cathode material described above in sodium-ion batteries. Preferably, this invention utilizes the iron-based sodium phosphate cathode material to prepare a cathode sheet, which is then used in the sodium-ion battery. In this invention, the preparation method of the cathode sheet preferably includes the following steps: mixing the iron-based sodium phosphate cathode material, conductive carbon black, and sodium carboxymethyl cellulose (CMC-Na); mixing the resulting mixture with water and grinding it to form a slurry; coating the slurry onto the surface of aluminum foil and drying it; then cutting it to a preset size to obtain the cathode sheet. In this invention, the preferred mass ratio of the iron-based sodium phosphate cathode material, conductive carbon black, and sodium carboxymethyl cellulose is 7:2:1; the preferred water is deionized water. This invention does not have a specific limitation on the amount of water used; any amount known to those skilled in the art can be used. In this invention, the drying is preferably vacuum drying; the preferred drying temperature is 40–80°C, more preferably 70–80°C; the preferred drying time is 5–24 hours, more preferably 10–12 hours. In this invention, the diameter of the positive electrode is preferably 10 mm.

[0042] After obtaining the positive electrode, the present invention uses the positive electrode to assemble the sodium-ion battery. In an embodiment of the present invention, taking the preparation of a coin cell (preferably a 2032 type coin cell) as an example, the counter electrode is specifically metallic sodium; the separator is specifically a GF / C type separator; the electrolyte is specifically prepared from sodium perchlorate (NaClO4), fluoroethylene carbonate (FEC), and polycarbonate (PC), wherein the concentration of sodium perchlorate in the electrolyte is preferably 1M; and the volume fraction of fluoroethylene carbonate is preferably 2-10%, more preferably 5%. The present invention preferably assembles the coin cell in a glove box filled with Ar gas.

[0043] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0044] Example 1

[0045] The steps for preparing a sodium-ion battery cathode material with a NaFePO4:Na2FeP2O7 molar ratio of 1.7:1 are as follows:

[0046] 0.0039 mol of ferric acetylacetone was added to a solution of 0.006 mol citric acid and 150 mL ethanol to obtain a ferric acetylacetone-citric acid mixture. 0.0053 mol of anhydrous sodium dihydrogen phosphate was dissolved in 50 mL of deionized water, and after dissolution, it was added to the ferric acetylacetone-citric acid mixture. The mixture was stirred and heated in an oil bath at 80 °C until the solvent was completely evaporated to obtain a gel material. The gel material was dried at 120 °C for 12 h, ground, and then placed in a tube furnace and heated at 2 °C for 1 minute in an Ar atmosphere. -1 The temperature was rapidly increased to 350°C and pre-sintered at 350°C for 6 hours. The resulting pre-sintered material was ground and poured into a tableting mold, which was then placed in a jack and pressed into tablets at 20 MPa for 2 minutes. The tablets were then demolded and placed in a tube furnace and pressed at 2°C for 2 minutes in an Ar atmosphere. -1 The temperature was rapidly increased to 550°C and sintered at 550°C for 12 hours, then cooled to room temperature to obtain the sodium-ion battery cathode material, denoted as Na. 3.7 Fe 2.7 (PO4) 1.7 P2O7 / C (carbon content 10wt%) is a black powder.

[0047] Example 2

[0048] Following the method described in Example 1, the only difference being that the amount of anhydrous sodium dihydrogen phosphate used in this example was 0.0055 mol, ultimately yielding a sodium-ion battery cathode material with a NaFePO4:Na2FeP2O7 molar ratio of 1.4:1, denoted as Na... 3.4 Fe 2.4 (PO4) 1.4 P2O7 / C (carbon content is 10wt%).

[0049] The Na was obtained by CA (Chronoamperometry) testing using an electrochemical workstation. 3.4 Fe 2.4 (PO4) 1.4 The electronic conductivity of P2O7 / C is 3.27 × 10⁻⁶. -6 S cm -1 .

[0050] Example 3

[0051] The procedure was followed according to Example 1, except that the amount of anhydrous sodium dihydrogen phosphate used in this example was 0.0058 mol. The final product was a sodium-ion battery cathode material with a NaFePO4:Na2FeP2O7 molar ratio of 1.1:1, denoted as Na... 3.1 Fe 2.1 (PO4) 1.1P2O7 / C (carbon content is 10wt%).

[0052] Figure 1 The XRD patterns of the sodium-ion battery cathode materials prepared in Examples 1-3 are shown. The results show that the XRD pattern of the sodium-ion battery cathode material prepared in Example 1 is basically consistent with the standard card, but an additional diffraction peak exists at 34.8°. Analysis of the standard card indicates that this substance is NaFePO4, suggesting the presence of a small amount of NaFePO4 impurity. Compared to Example 1, the sodium-ion battery cathode material prepared in Example 2 does not exhibit a NaFePO4 diffraction peak at 34.8°, indicating that the sodium-ion battery cathode material prepared in Example 2 is a pure-phase material. The sodium-ion battery cathode material prepared in Example 3 shows an additional diffraction peak near 11°. Analysis of the standard card indicates that this substance is Na2FeP2O7, suggesting the presence of a small amount of Na2FeP2O7 impurity.

[0053] Application Example 1

[0054] The sodium-ion battery positive electrode materials prepared in Examples 1-3 were mixed with conductive carbon black and sodium carboxymethyl cellulose (CMC-Na) in a mass ratio of 7:2:1. The resulting mixture was then mixed with deionized water and ground in an agate mortar for 15 minutes to form a slurry. The slurry was coated onto the surface of aluminum foil and then dried in a vacuum drying oven at 80°C for 12 hours. The resulting electrode was cut into round pieces with a diameter of 10 mm to obtain the positive electrode. NaClO4, fluoroethylene carbonate (FEC), and polycarbonate (PC) were mixed to obtain an electrolyte. The concentration of NaClO4 in the electrolyte was 1 M, and the volume fraction of FEC was 5%. Using metallic sodium as the counter electrode and a GF / C type separator, a coin cell, model 2032, was assembled in a glove box.

[0055] After standing for 8 hours, the 2032 coin cell battery was subjected to a constant current charge-discharge test. The test parameters were as follows: voltage range of 1.5–4.3V, current density of 0.1C (1C = 129 mAh g). -1 ).

[0056] Figure 2 The graph shows the charge-discharge curve test results of the 2032 coin cell prepared in Example 1. The results show that, under a current density of 0.1C, the 2032 coin cell prepared using the sodium-ion battery cathode material in Example 1 can provide 100 mAh g⁻¹. -1 The reversible discharge specific capacity; the 2032 coin cell prepared using the sodium-ion battery cathode material in Example 2 can provide 110 mAh g. -1 The reversible discharge specific capacity was increased by 10 mAh g compared to the sodium-ion battery cathode material in Example 1. -1The 2032-type coin cell prepared using the sodium-ion battery cathode material in Example 3 can provide 106 mAh g. -1 The reversible discharge specific capacity decreased by 4 mAh g compared to the sodium-ion battery cathode material in Example 2. -1 .

[0057] Figure 3 The graph shows the rate performance test results of the 2032 coin cell prepared in Example 1. The results show that, under a current density of 100C, the 2032 coin cell prepared using the sodium-ion battery cathode material in Example 1 can maintain a capacity of 37 mAh g / g. -1 The reversible discharge specific capacity; the 2032 coin cell prepared using the sodium-ion battery cathode material in Example 2 can maintain 50 mAh g. -1 The reversible discharge specific capacity is better than that of the sodium-ion battery cathode material in Example 1, indicating that the removal of the electrochemically inactive NaFePO4 impurity phase can improve its electron-ion transport kinetics; the 2032 coin cell prepared using the sodium-ion battery cathode material in Example 3 can maintain 48 mAh g⁻¹. -1 The reversible discharge specific capacity of the material is worse than that of the sodium-ion battery cathode material in Example 2, indicating that the electrochemically active Na2FeP2O7 impurity also has a negative impact on the electron-ion transport kinetics of the sodium-ion battery cathode material.

[0058] Figure 4 The graph shows the long-cycle performance test results of the 2032 coin cell prepared in Example 1. The results show that at a current density of 20C, the 2032 coin cell prepared using the sodium-ion battery cathode material in Example 1 has a capacity of 61.9 mAh g / g. -1 The reversible discharge specific capacity was [not specified], and the capacity retention rate after 10,000 cycles was 86.6%; the 2032 coin cell prepared using the sodium-ion battery cathode material in Example 2 had a capacity of 65.8 mAh g⁻¹. -1 The reversible discharge specific capacity was [not specified], and the capacity retention rate after 10,000 cycles was 90.3%; the 2032 coin cell prepared using the sodium-ion battery cathode material in Example 3 had a capacity of 61.1 mAh g / g. -1 The reversible discharge specific capacity retains 90.1% after 10,000 cycles.

[0059] Comparative Example 1

[0060] The procedure was followed according to Example 1, except that the amount of anhydrous sodium dihydrogen phosphate used in this comparative example was 0.0052 mol. Finally, a sodium-ion battery cathode material with a NaFePO4:Na2FeP2O7 molar ratio of 2.0:1 was prepared, denoted as Na4Fe3(PO4)2P2O7 / C.

[0061] Figure 5 The XRD pattern of the sodium-ion battery cathode material prepared in Comparative Example 1 is shown. The results show that the XRD pattern of the sodium-ion battery cathode material prepared in Comparative Example 1 is basically consistent with the standard card, but there are three additional NaFePO4 impurity peaks near 32.8°, 33° and 34.8°, which proves that a small amount of NaFePO4 impurity phase exists.

[0062] Comparative Application Example 1

[0063] The sodium-ion battery cathode material prepared in Comparative Example 1 was used to prepare a 2032 coin cell according to the method in Application Example 1, and constant current charge-discharge tests were performed.

[0064] Figure 6 To compare the charge-discharge curve test results of the 2032 coin cell prepared in Application Example 1, the results show that, under a current density of 0.1C, the 2032 coin cell prepared using the sodium-ion battery cathode material in Comparative Example 1 can provide 93 mAh g⁻¹. -1 The reversible discharge specific capacity decreased by 17 mAh g compared to the sodium-ion battery cathode material in Example 2. -1 .

[0065] Figure 7 To compare the rate performance test results of the 2032 coin cell prepared in Application Example 1, the results show that, under a current density of 100C, the reversible discharge specific capacity of the 2032 coin cell prepared using the sodium-ion battery cathode material in Comparative Example 1 is only 31 mAh g⁻¹. -1 This indicates that the rate performance of the sodium-ion battery cathode material prepared in Comparative Example 1 is poor.

[0066] Figure 8 To compare the long-cycle test results of the 2032 coin cell prepared in Application Example 1, the results show that at a current density of 20C, the reversible discharge specific capacity of the 2032 coin cell prepared using the sodium-ion battery cathode material in Application Example 1 is only 52.5 mAh g. -1 After 10,000 cycles, the capacity retention rate was 86.7%, which is lower than the 90.3% capacity retention rate of the sodium-ion battery cathode material in Example 2.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an iron-based phosphate sodium battery positive electrode material, comprising the following steps: mixing a carbon source, a sodium-iron-phosphorus source and a solvent to obtain a raw material mixture; the molar ratio of sodium, iron and phosphorus in the sodium-iron-phosphorus source is x+2: x+1: x+2, and 1.0 < x < 2.0; subjecting the raw material mixture to gelation treatment to obtain a gel material; and sequentially drying, pre-sintering and sintering the gel material to obtain the iron-based phosphate sodium battery positive electrode material. The sodium-iron-phosphorus source includes one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, sodium carbonate and sodium bicarbonate. The sodium-iron-phosphorus source includes one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, sodium carbonate and sodium bicarbonate. The sodium-iron-phosphorus source includes one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, sodium carbonate and sodium bicarbonate.

2. The production method according to claim 1, characterized by, The sodium-iron-phosphorus source includes one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, sodium carbonate and sodium bicarbonate.

3. The preparation method according to claim 2, characterized in that, The carbon source includes one or more of citric acid, oxalic acid, sucrose, glucose and ascorbic acid; and the molar ratio of the carbon source to the iron source is 1-2:

1.

4. The method of claim 1, wherein, The temperature of the gelation treatment is 60-90℃, and the time is 8-24 h.

5. The preparation method according to claim 4, characterized in that, The temperature of the drying is 80-140℃.

6. The method of claim 1, wherein, 10.The iron-based phosphate sodium battery positive electrode material of claim 9 is used in a sodium-ion battery.

7. The preparation method according to claim 1, characterized in that, ​ 8. The method of claim 1, wherein, ​ The pre-sintering temperature is 300-400℃, the holding time is 1-6h, and the temperature rising rate to the pre-sintering temperature is 0.5-5℃ / min -1 ; The sintering temperature is 500-600℃, the holding time is 4-24 h, and the heating rate to the sintering temperature is 0.5-5℃ / min -1 .

9. The iron-based phosphate sodium electro-positive electrode material prepared by the method of any one of claims 1-8, comprising an iron-based phosphate and a carbon layer coated on the surface of the iron-based phosphate, and the chemical formula of the iron-based phosphate sodium electro-positive electrode material is Na x+2 Fe x+1 (PO4) x P2O7 / C, and 1.0 < x < 2.

0. ​

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