Modified sodium iron phosphate pyrophosphate positive electrode material, preparation method and application thereof

Abstract

The application provides a modified sodium iron pyrophosphate phosphate positive electrode material and a preparation method and application thereof, and comprises a sodium iron pyrophosphate phosphate positive electrode material, carbon and a sodium ion conductor. x MO y The composite phase material formed by the carbon and the sodium ion conductor is used for coating primary particles and secondary particles of the positive electrode material, a three-dimensional conductive / ionic network is formed on the material crystal boundary and the surface, the charge and ion transmission rate of the material is high; and the three-dimensional coating layer can protect the material from the erosion of electrolyte, has good structural stability, and has excellent cycle performance and rate performance.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery cathode material technology, specifically relating to sodium iron pyrophosphate cathode material modified with mixed conductors, its preparation method and application. Background Technology

[0002] With the development of power storage, electric vehicles, and portable electronic devices, limited lithium resources cannot meet the rapidly expanding market demand for lithium-ion batteries. Sodium is abundant and inexpensive, and it shares similar physicochemical properties and electrode potentials with lithium. Furthermore, sodium-ion batteries have similar electrochemical reaction mechanisms to lithium-ion batteries. These factors drive market competition between sodium-ion and lithium-ion batteries, and sodium-ion batteries are expected to become a substitute for lithium-ion batteries in the field of large-scale energy storage.

[0003] The cathode material largely determines the performance of a battery. Currently, the main cathode materials for sodium-ion batteries include layered oxides, Prussian blue-based materials, and polyanionic materials. Among them, the polyanionic sodium iron pyrophosphate cathode material has attracted widespread attention and research due to its low cost, good structural stability, excellent cycle performance, and high discharge voltage. However, sodium iron pyrophosphate suffers from low electronic conductivity and poor sodium ion diffusion, resulting in large polarization during charge and discharge and relatively poor rate performance, which cannot meet the requirements for rapid charge and discharge.

[0004] Carbon coating and bulk doping can improve the electronic conductivity of sodium iron pyrophosphate cathode material and the diffusion rate of sodium ions in the crystal, thus improving the material's performance to some extent. However, the modification effect is not obvious and cannot solve the problem of low sodium ion transport rate at the primary grain boundaries of the material. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a modified sodium iron pyrophosphate cathode material, its preparation method, and its application.

[0006] To achieve the above objectives, this application proposes the following technical solution:

[0007] In a first aspect, a modified sodium iron pyrophosphate cathode material is provided, comprising the sodium iron pyrophosphate cathode material, carbon and sodium ion conductors, wherein the carbon and sodium ion conductors are enriched in a uniform composite phase on the surface and grain boundaries of the sodium iron pyrophosphate cathode material, and the sodium ion conductor is Na. x MO y M is one or more of Zr, Al, Cr, Bi, Te, Pb, Co, Sb, Se, Nb, Ta, W and Mo, x takes the value of 1 to 2, and y takes the value of 2 to 4.

[0008] Furthermore, the secondary particles of the modified sodium iron pyrophosphate cathode material have a solid spherical structure and a tap density of 1.1~2.1 g / cm³. 3 The particle size D50 is 2~10μm.

[0009] Furthermore, the mass ratio of sodium iron pyrophosphate, carbon, and sodium ion conductor is 84–98:1–8:1–8.

[0010] Secondly, a method for preparing modified sodium iron pyrophosphate cathode material is provided, including:

[0011] A dispersion was obtained by uniformly mixing a phosphorus source, a ferrous source, a sodium source, a nano-M source, and a dispersant in deionized water.

[0012] The dispersion was spray-dried to obtain the precursor;

[0013] The precursor was heat-treated under an inert or reducing atmosphere to obtain Na. x MO y The cathode material is a carbon composite coated with sodium iron pyrophosphate, wherein M is one or more of Zr, Al, Cr, Bi, Te, Pb, Co, Sb, Se, Nb, Ta, W and Mo, x is 1 to 2 and y is 2 to 4.

[0014] Thirdly, a sodium-ion battery is provided, including the aforementioned modified sodium iron pyrophosphate cathode material or the modified sodium iron pyrophosphate cathode material prepared by the aforementioned preparation method.

[0015] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects:

[0016] The mixed conductor modified sodium iron pyrophosphate cathode material provided by this invention utilizes a composite layer formed by conductive carbon and sodium ion conductors to coat the primary and secondary particles of the cathode material, forming a three-dimensional conductive network at the grain boundaries and surface of the cathode material, resulting in a high charge transport rate of the cathode material; moreover, the three-dimensional coating layer can protect the material from electrolyte corrosion, resulting in good structural stability and excellent cycle performance and rate performance.

[0017] This invention employs a spray drying method to prepare the precursor, enabling control over the uniform morphology of the electrode material. Nanoscale M-source oxides and a dispersant are dispersed in a spray solution. Under the action of the dispersant, the nano-M-sources are uniformly distributed at the primary grain boundaries of the precursor after spray drying. Upon calcination, the dispersant carbonizes, and simultaneously, the M-sources react with the precursor surface material and the sodium source during calcination, epitaxially growing on the material surface to obtain a sodium ion conductor. This constructs a three-dimensional electron / ion transport network from the grain boundaries to the surface, significantly improving the charge transport rate. Attached Figure Description

[0018] 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.

[0019] Figure 1 The image shows the XRD pattern of the sodium iron pyrophosphate cathode material prepared in Example 1.

[0020] Figure 2 The images show the TEM and elemental mapping of the sodium iron pyrophosphate cathode material prepared in Example 1; where (a) is a HAADF-STEM image, (b), (c), (d), and (e) are elemental mapping images of O, Fe, C, and Sb, respectively, (f) and (g) are TEM images, and (h) is an HRTEM image.

[0021] Figure 3 The image shows a SEM image of the sodium iron pyrophosphate cathode material prepared in Example 1.

[0022] Figure 4 The above are charge-discharge curves of the sodium iron pyrophosphate cathode material prepared in Example 1 at different rates.

[0023] Figure 5 The charge-discharge curves of the sodium iron pyrophosphate cathode material prepared in Comparative Example 1 at different rates are shown.

[0024] Figure 6 The image shows the XRD pattern of the sodium iron pyrophosphate cathode material prepared in Example 2. Detailed Implementation

[0025] This invention provides a sodium iron pyrophosphate cathode material modified with a mixed conductor, comprising the sodium iron pyrophosphate cathode material, carbon and sodium ion conductors, wherein the carbon and sodium ion conductors are enriched in a uniform composite phase on the surface and grain boundaries of the sodium iron pyrophosphate cathode material (i.e., the carbon and sodium ion conductors are uniformly coated on the surface of the secondary and primary particles of the sodium iron pyrophosphate cathode material in a composite state), and the sodium ion conductor is Na. x MO y M is one or more of Zr, Al, Cr, Bi, Te, Pb, Co, Sb, Se, Nb, Ta, W and Mo, x takes the value of 1 to 2, for example 1, 2, and y takes the value of 2 to 4, for example 2, 3, 4.

[0026] In some preferred embodiments, the secondary particles have a solid spherical structure and a tap density of 1.1~2.1 g / cm³.3 D50 ranges from 2 to 10 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc.

[0027] In some preferred embodiments, the mass ratio of sodium iron pyrophosphate, carbon, and sodium ion conductors is 84–98:1–8:1–8, for example, 98:1:1, 97:1:2, 97:2:1, 96:1:3, 96:3:1, 96:2:2, 95:4:1, 95:1:4, 95:3:2, 95:2:3, 94:5:1, 94:1:5, 94:4:2, 94:2:4, 94:3:3, 93:6:1, 93:1:6, 93:5:2, 93:2:5, 93:4:3, 93:3:4, 92:6:2, 92:2:6, 92:5:3, 92:3:5, 92:4:4, 91:7:2, 91:2:7, 91:6:3, 9 1:3:6, 91:5:4, 91:4:5, 90:8:2, 90:2:8, 90:7:3, 90:3:7, 90:6:4, 90:4:6, 90:5:5, 89:8:3, 89:3:8, 89:7:4, 89:4:7, 89:6:5, 89:5:6, 88:8:4, 88:4:8, 8 8:7:5, 88:5:7, 88:6:6, 88:8:4, 88:4:8, 88:7:5, 88:5:7, 88:6:6, 87:8:5, 87:5:8, 87:7:6, 87:6:7, 86:8:6, 86:6:8, 86:7:7, 85:8:7, 85:7:8, 84:8:8, etc.

[0028] Some embodiments of the present invention provide a method for preparing a sodium iron pyrophosphate cathode material modified with mixed conductors, comprising:

[0029] A dispersion was obtained by mixing phosphorus source, ferrous source, sodium source, nano M source, dispersant and deionized water;

[0030] The dispersion was spray-dried to obtain the precursor;

[0031] The precursor was heat-treated under an inert or reducing atmosphere to obtain Na. x MO y The cathode material is a carbon composite coated with sodium iron pyrophosphate, wherein M is one or more of Zr, Al, Cr, Bi, Te, Pb, Co, Sb, Se, Nb, Ta, W and Mo, x takes the value of 1 to 2, for example 1, 2, and y takes the value of 2 to 4, for example 2, 3, 4.

[0032] In some preferred embodiments, the phosphorus source includes one or more of sodium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate.

[0033] In some preferred embodiments, the ferrous source includes one or more of ferrous acetate, ferric nitrate, ferrous oxalate, and ferrous sulfate.

[0034] In some preferred embodiments, the sodium source includes one or more of sodium dihydrogen phosphate, sodium carbonate, sodium bicarbonate, sodium acetate, sodium oxalate, and sodium citrate.

[0035] In some preferred embodiments, the dispersant includes one or more of polyvinylpyrrolidone, polyacrylamide, and sodium carboxymethyl cellulose.

[0036] The inert atmosphere can be an inert gas atmosphere, such as an atmosphere produced by inert gases like argon or neon, or a nitrogen atmosphere.

[0037] In some preferred embodiments, the nano M source includes one or more of ZrO2, Al2O3, CrO3, Bi2O3, TeO2, Pb2O3, Co2O3, Sb2O3, SeO2, Nb2O5, Ta2O5, WO3, and MoO3.

[0038] In some preferred embodiments, the particle size of the nano M source is 5~50nm, such as 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, etc.

[0039] In some preferred embodiments, the molar ratio of the nano-M source to the ferrous source is 0.1~0.6:2.1~3, for example, 0.1:2.1, 0.1:2.3, 0.1:2.5, 0.1:2.8, 0.1:3, 0.2:2.1, 0.2:2.5, 0.2:2.8, 0.2:3, 0.3:2.1, 0.3:2.5, 0.3:2.8, 0.3:3, 0.4:2.1, 0.4:2.5, 0.4:2.8, 0.4:3, 0.5:2.1, 0.5:2.5, 0.5:2.8, 0.5:3, 0.6:2.1, 0.6:2.5, 0.6:2.8, 0.6:3, etc.

[0040] In some preferred embodiments, the amount of the dispersant is 1 to 10% of the total mass of the phosphorus source, ferrous source, sodium source, carbon source and nano M source, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0041] In some preferred embodiments, the sodium source, phosphorus source, and ferrous source are prepared according to a molar ratio of Na to P and Fe of 3~4:4:2~3.

[0042] In some preferred embodiments, the heat treatment includes pre-firing and calcination; the pre-firing temperature is 250~350℃, for example 250℃, 280℃, 300℃, 320℃, 350℃, etc.; the pre-firing time is 2~10h, for example 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc.; the calcination temperature is 450~650℃, for example 450℃, 480℃, 500℃, 520℃, 550℃, 580℃, 600℃, 620℃, 650℃, etc.; the calcination time is 3~15h, for example 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, etc.

[0043] In some preferred embodiments, the inlet air temperature of the spray dryer is 120~240℃, the outlet air temperature is 90~120℃, and the spray feed flow rate is 50~2000mL / h.

[0044] Some embodiments of the present invention provide a sodium-ion battery, including the aforementioned mixed conductor modified sodium iron pyrophosphate cathode material or the mixed conductor modified sodium iron pyrophosphate cathode material prepared by the aforementioned preparation method.

[0045] To facilitate understanding of the present invention, the 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.

[0046] Example 1

[0047] (1) Sodium dihydrogen phosphate, ferrous acetate and Sb2O3 in a mass ratio of 4.79:5.21:0.29 were mixed with 6% of the total mass of deionized water and 4% of the total mass of the raw materials were added as dispersant polyvinylpyrrolidone. The mixture was stirred evenly. The mixture was stirred at room temperature for 2 h to ensure that the raw materials were fully dissolved and dispersed to obtain a dispersion.

[0048] (2) The dispersion was dried by spray dryer with the inlet air temperature set to 180℃, the outlet air temperature set to 105℃, and the spray feed flow rate set to 1000mL / h to obtain precursor powder.

[0049] (3) The precursor powder was sintered in a high-purity nitrogen atmosphere, heated to 350°C at a temperature of 2°C / min, held for 4 hours, then heated to 550°C and held for 10 hours, and then cooled naturally to obtain the cathode material.

[0050] The XRD pattern of the obtained cathode material is as follows Figure 1 As shown, from Figure 1As can be seen, the XRD pattern shows that the obtained product is pure-phase sodium iron pyrophosphate; the TEM and elemental mapping diagrams of the obtained cathode material are as follows. Figure 2 As shown in the TEM image, a coating is visible on the surface of the primary particles (i.e., enriched at the grain boundaries). Combined with elemental mapping, it can be seen that C and Sb are uniformly distributed in the coating. Furthermore, high-resolution TEM analysis of the coating reveals that Sb exists as NaSbO3 at the grain boundaries. This indicates that C and NaSbO3 are uniformly distributed in a composite state at the grain boundaries of the sodium iron pyrophosphate material, and the coating exhibits a dense state. Based on this preparation method, it can be seen that C and NaSbO3 also exist in a composite state to coat the secondary particle surface of the sodium iron pyrophosphate material. That is, C and NaSbO3 are enriched in a composite state on the surface and grain boundaries of the sodium iron pyrophosphate cathode material. In other words, C and NaSbO3 (NaSbO3 is a sodium ion conductor) are uniformly distributed in the coating layer. The two are uniformly coated in a dense composite state on the surface and grain boundaries of the sodium iron pyrophosphate cathode material. Therefore, the chemical formula of the product can be determined as Na4Fe3(PO4)2P2O7 / C&NaSbO3. Carbon and NaSbO3 are uniformly coated in a dense composite state on the surface of the primary and secondary particles of the sodium iron pyrophosphate cathode material, and NaSbO3 acts as a sodium ion conductor. Based on the density of the coating layer, it can be inferred that the cathode material with this dense coating layer has an excellent effect of inhibiting the corrosion of the material by the electrolyte.

[0051] SEM images of the obtained cathode material are as follows Figure 3 As shown, from Figure 3 It can be seen that the cathode material consists of secondary particles composed of primary particles, and the secondary particles have a solid spherical structure. The tap density of the obtained cathode material is 1.4 g / cm³, and the particle size D50 is 4.2 μm.

[0052] Sodium iron pyrophosphate positive electrode material prepared above is used to assemble sodium-ion batteries. Other components of the battery include a sodium metal negative electrode, electrolyte, and separator. The specific process for preparing the positive electrode and assembling the battery is as follows: The sodium iron pyrophosphate positive electrode material is thoroughly ground and mixed with a conductive agent (SuperP) and a binder (PVDF) at a mass ratio of 8:1:1 in NMP, and then coated onto the surface of aluminum foil. After drying in a vacuum drying oven, it is formed into a disc with a diameter of 12 mm, thus obtaining the positive electrode. The prepared positive electrode, sodium negative electrode, glass fiber separator, and electrolyte (1 mol L) are then combined. -1 NaClO4 was dissolved in a 1:1 mixture of diethyl carbonate and ethylene carbonate (by volume) and assembled into 2025 button cells in a glove box filled with argon gas and with water and oxygen concentrations both less than 0.01 ppm.

[0053] The assembled sodium-ion batteries were subjected to charge-discharge tests to evaluate their capacity, cycle stability, and rate performance.

[0054] The charge-discharge curves of the battery assembled with the positive electrode material obtained in Example 1 at different rates are shown in the figure below. Figure 4 As shown in the figure, the battery assembled with the obtained cathode material has excellent discharge specific capacity and rate performance.

[0055] Comparative Example 1

[0056] (1) Sodium dihydrogen phosphate and ferrous acetate in a mass ratio of 4.79:5.21 were mixed with 6% of the total mass of deionized water, and 4% of the total mass of polyvinylpyrrolidone dispersant was added. The mixture was stirred evenly. The mixture was stirred at room temperature for 2 hours to ensure that the raw materials were fully dissolved and dispersed to obtain a dispersion.

[0057] (2) The dispersion was dried by spray dryer with the inlet air temperature set to 180℃, the outlet air temperature set to 105℃, and the spray feed flow rate set to 1000mL / h to obtain precursor powder.

[0058] (3) The precursor powder was sintered in a high-purity nitrogen atmosphere, heated to 350°C at a temperature of 2°C / min, held for 4 hours, then heated to 550°C and held for 10 hours, and then cooled naturally to obtain the cathode material.

[0059] The positive electrode material obtained in Comparative Example 1 was assembled into a battery using the same battery assembly method as in Example 1. The charge-discharge curves of the battery at different rates are shown below. Figure 5 As shown. Comparing the batteries assembled with the cathode materials obtained in Example 1 and Comparative Example 1, it was found that the discharge specific capacity of the battery assembled with the cathode material obtained in Example 1 was significantly higher than that of the battery assembled in Comparative Example 1 at different rates. Moreover, compared with the battery assembled in Comparative Example 1, the rate performance of the battery assembled in Example 1 was also significantly improved. After analysis, it was found that this was because C and NaSbO3 in Example 1 were uniformly coated on the surface and grain boundaries of the cathode material in a composite state, thereby improving the ion and electron transport performance of the cathode material.

[0060] Comparative Example 2

[0061] (1) Sodium dihydrogen phosphate and ferrous acetate in a mass ratio of 4.79:5.21 were mixed with 6% of the total mass of deionized water, and 4% of the total mass of polyvinylpyrrolidone dispersant was added. The mixture was stirred evenly. The mixture was stirred at room temperature for 2 hours to ensure that the raw materials were fully dissolved and dispersed to obtain a dispersion.

[0062] (2) The dispersion was dried by spray dryer with the inlet air temperature set to 180℃, the outlet air temperature set to 105℃, and the spray feed flow rate set to 1000mL / h to obtain precursor powder.

[0063] (3) The precursor powder and Sb2O3 were ball-milled and mixed, and sintered in a high-purity nitrogen atmosphere. The temperature was increased to 350°C at a rate of 2°C / min, and held for 4 hours. Then the temperature was increased to 550°C and held for 10 hours. The mixture was then cooled naturally to obtain the composite modified sodium iron pyrophosphate cathode material.

[0064] Example 2

[0065] A mixture of diammonium hydrogen phosphate, ferric nitrate nonahydrate, sodium bicarbonate, and Al₂O₃ in a mass ratio of 5.28:12.12:3.36:0.2 was mixed with 5% deionized water (by mass of the total raw materials), and 7% polyacrylamide (by mass of the total raw materials) was added as a dispersant. The mixture was stirred until homogeneous. The solution was stirred at room temperature for 3 hours to ensure complete dissolution and dispersion of the raw materials, resulting in a dispersion.

[0066] The dispersion was dried using a spray dryer with an inlet air temperature of 220℃, an outlet air temperature of 115℃, and a spray feed flow rate of 1500mL / h to obtain precursor powder.

[0067] The precursor powder was sintered in a high-purity nitrogen atmosphere, heated to 300℃ at a rate of 3℃ / min, held at that temperature for 6 hours, then heated to 600℃ and held at that temperature for 12 hours, followed by natural cooling to obtain sodium iron pyrophosphate cathode material. The XRD pattern of the obtained product is shown below. Figure 6 As shown, from Figure 6 As can be seen from the XRD pattern, the obtained product is pure-phase sodium iron pyrophosphate. Based on the raw materials, their properties, and the product obtained in Example 1, the chemical formula of the obtained product is Na4Fe3(PO4)2P2O7 / C&NaAlO2, where C and NaAlO2 form a dense composite state coating on the surface of the primary particles, and NaAlO2 acts as a sodium ion conductor.

[0068] The cathode material consists of secondary particles composed of primary particles, forming a solid spherical structure. The tap density of the secondary particles is 1.5 g / cm³, and the D50 is 5.1 μm.

[0069] Example 3

[0070] A mixture of ammonium dihydrogen phosphate, ferrous oxalate, sodium acetate, and Nb₂O₅ in a mass ratio of 5.28:4.31:3.28:0.25 was mixed with 7% (by mass) of deionized water, and 5% (by mass) of sodium carboxymethyl cellulose dispersant was added. The mixture was stirred until homogeneous. The mixture was stirred at room temperature for 2.5 hours to ensure complete dissolution and dispersion of the raw materials, resulting in a dispersion.

[0071] The dispersion was dried using a spray dryer with an inlet air temperature of 200℃, an outlet air temperature of 110℃, and a spray feed flow rate of 1200mL / h to obtain precursor powder.

[0072] The precursor powder was sintered in a high-purity nitrogen atmosphere, heated to 320°C at a rate of 2.5°C / min, held at that temperature for 5 hours, then heated to 580°C and held at that temperature for 13 hours, followed by natural cooling to obtain sodium iron pyrophosphate cathode material. Based on the raw materials, their properties, and the product obtained in Example 1, the chemical formula of the obtained product is Na4Fe3(PO4)2P2O7 / C&NaNbO3, where C and NaNbO3 form a dense composite coating on the surface of the primary particles, and NaNbO3 acts as a sodium ion conductor.

[0073] The cathode material consists of secondary particles composed of primary particles, forming a solid spherical structure. The tap density of the secondary particles is 1.6 g / cm³, and the D50 is 6.6 μm.

[0074] Example 4

[0075] Sodium dihydrogen phosphate, ferric nitrate nonahydrate, and MoO3 in a mass ratio of 4.78:12.12:0.29 were mixed with 5.5% deionized water (by mass of the total raw materials). Then, 4.5% polyacrylamide (by mass of the total raw materials) was added as a dispersant, and the mixture was stirred until homogeneous. The mixture was stirred at room temperature for 2 hours to ensure complete dissolution and dispersion of the raw materials, resulting in a dispersion.

[0076] The dispersion was dried using a spray dryer with an inlet air temperature of 210℃, an outlet air temperature of 118℃, and a spray feed flow rate of 1800 mL / h to obtain precursor powder.

[0077] The precursor powder was sintered in a high-purity nitrogen atmosphere, heated to 340°C at a rate of 2°C / min, held at that temperature for 8 hours, then heated to 650°C and held at that temperature for 9 hours, followed by natural cooling to obtain sodium iron pyrophosphate cathode material. Based on the raw materials, their properties, and the product obtained in Example 1, the chemical formula of the obtained product is Na4Fe3(PO4)2P2O7 / C&Na2MoO4, where C and Na2MoO4 form a dense composite coating on the surface of the primary particles, and Na2MoO4 acts as a sodium ion conductor.

[0078] The cathode material consists of secondary particles composed of primary particles, forming a solid spherical structure. The tap density of the secondary particles is 1.3 g / cm³, and the D50 is 3.8 μm.

[0079] The cathode materials obtained in Examples 2-4, Comparative Examples 1 and 2 were assembled into batteries using the same battery assembly method as in Example 1. The batteries assembled in Examples 1-4 and Comparative Examples 1-2 were subjected to cycle performance tests at 0.5C, and the results are shown in Table 1.

[0080] As can be seen from Table 1, the batteries assembled in each embodiment all exhibit high discharge specific capacity and superior cycle performance. Compared to the battery assembled in Comparative Example 1, the battery assembled in Example 1 shows not only a significant improvement in specific capacity but also a significant improvement in cycle performance. Analysis suggests that this may be because the individual carbon coating in Comparative Example 1 generally has porosity, while the composite coating layer in Example 1 is denser and has a better effect on inhibiting electrolyte erosion of the material.

[0081] Compared to the battery assembled in Comparative Example 2, the battery assembled in Example 1 not only showed a significant improvement in specific capacity but also a significant improvement in cycle performance. This indicates that the coating method in Example 1 has a superior modification effect.

[0082] Table 1 Cycle data of batteries assembled in each embodiment and comparative example at 0.5 C

[0083]

[0084] 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 modified sodium iron pyrophosphate cathode material, characterized in that, The modified sodium iron pyrophosphate cathode material comprises sodium iron pyrophosphate cathode material, carbon, and sodium ion conductors. The carbon and sodium ion conductors are enriched in a uniform composite phase on the surface and grain boundaries of the sodium iron pyrophosphate cathode material. The sodium ion conductor is Na. x MO y Where M is one or more of Zr, Al, Cr, Bi, Te, Pb, Co, Sb, Se, Nb, Ta, W, and Mo, x takes the value of 1 to 2, and y takes the value of 2 to 4. The secondary particles of the modified sodium iron pyrophosphate cathode material have a solid spherical structure. The preparation method includes: A dispersion is obtained by mixing a phosphorus source, a ferrous source, a sodium source, a nano-M source, a dispersant, and deionized water; the dispersant includes one or more of polyvinylpyrrolidone, polyacrylamide, and sodium carboxymethyl cellulose; the ferrous source includes one or more of ferrous acetate, ferric nitrate, ferrous oxalate, and ferrous sulfate; the nano-M source has a particle size of 5-20 nm; and the amount of the dispersant is 1-10% of the total mass of the phosphorus source, ferrous source, sodium source, carbon source, and nano-M source. The dispersion was spray-dried to obtain the precursor; The precursor was heat-treated under an inert or reducing atmosphere to obtain Na. x MO y Carbon composite coated sodium iron pyrophosphate cathode material.

2. The preparation method of the modified sodium iron pyrophosphate cathode material as described in claim 1, characterized in that, The phosphorus source includes one or more of sodium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate. The sodium source includes one or more of sodium dihydrogen phosphate, sodium carbonate, sodium bicarbonate, sodium acetate, sodium oxalate, and sodium citrate.

3. The preparation method of the modified sodium iron pyrophosphate cathode material as described in claim 1, characterized in that, The nano-M source includes at least one of ZrO2, Al2O3, CrO3, Bi2O3, TeO2, Pb2O3, Co2O3, Sb2O3, SeO2, Nb2O5, Ta2O5, WO3, and MoO3.

4. The preparation method of the modified sodium iron pyrophosphate cathode material as described in claim 1, characterized in that, The molar ratio of the nano-M source to the ferrous source is 0.1~0.6:2.1~3; The sodium source, phosphorus source, and ferrous source are prepared according to a molar ratio of Na to P and Fe of 3~4:4:2~3.

5. The method for preparing the modified sodium iron pyrophosphate cathode material as described in claim 1, characterized in that, The heat treatment includes pre-firing and calcination; The pre-firing temperature is 250~350℃; the pre-firing time is 2~10h; The calcination temperature is 450~650℃; the calcination time is 3~15h.

6. The method for preparing the modified sodium iron pyrophosphate cathode material as described in claim 1, characterized in that, The inlet air temperature of the spray dryer is 120~240℃, the outlet air temperature is 90~120℃, and the spray feed flow rate is 50~2000mL / h.

7. A modified sodium iron pyrophosphate cathode material, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 6.

8. The modified sodium iron pyrophosphate cathode material as described in claim 7, characterized in that, The tap density is 1.1~2.1 g / cm³. 3 The particle size D50 is 2~10μm.

9. The modified sodium iron pyrophosphate cathode material as described in claim 7 or 8, characterized in that, The mass ratio of sodium iron pyrophosphate, carbon, and sodium ion conductors is 84–98:1–8:1–8.

10. A sodium-ion battery, characterized in that, Including the modified sodium iron pyrophosphate cathode material as described in any one of claims 7 to 9.

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