Composite positive electrode material, preparation method thereof, sodium ion battery and electric device

Abstract

The application relates to the field of sodium ion batteries, in particular to a composite positive electrode material, a preparation method thereof, a sodium ion battery and an electric equipment. The application provides a preparation method of a composite positive electrode material, which comprises the following steps: S1, mixing a sodium source, an iron source and a phosphorus source to obtain a mixture; S2, adding a carbon source, a molybdenum source and water into the mixture to mix, so as to obtain a precursor; the molar ratio of Mo / (Fe+Mo) in the precursor is (0.01-0.1):3; the water accounts for 1%-10% of the total mass of the sodium source, the iron source, the phosphorus source, the carbon source and the molybdenum source; and S3, sintering the precursor to obtain the composite positive electrode material. The application realizes the effective improvement of the intrinsic electronic conductivity of NFPP, the improvement of the electronic conductivity of the material, the first circle charge-discharge capacity, the first circle coulomb efficiency, the rate capacity and other electrochemical performances through a simple process with low energy consumption and environmental protection.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, specifically to a composite cathode material and its preparation method, a sodium-ion battery, and electrical equipment. Background Technology

[0002] Sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7, NFPP), as a cathode material for sodium-ion batteries, possesses significant advantages such as high theoretical specific capacity, suitable operating voltage platform, good cycle stability, abundant iron and phosphorus resources, and low cost, making it considered one of the most commercially promising sodium battery cathode materials. However, the low intrinsic electronic conductivity of NFPP severely limits its rate performance and specific capacity. Currently, carbon coating is a common strategy to improve the electronic conductivity of NFPP, but simple carbon coating only improves surface conductivity and has limited effect on improving the material's intrinsic electronic conductivity. Therefore, elemental doping can effectively control the band structure of the material and improve its intrinsic electronic conductivity, which is an important way to further enhance the electrochemical performance of NFPP.

[0003] Existing technologies often employ nickel doping to modify NFPP, which can improve the electrochemical performance of the material to some extent. However, the preparation process generally uses spray drying. This process has significant drawbacks: during spray drying, slurry droplets easily adhere to the inner wall of the drying tower, causing material adhesion and resulting in significant material loss, which is detrimental to large-scale, efficient production. Furthermore, the water content of the liquid slurry used in spray drying is typically over 60%, requiring a large amount of heat energy to evaporate the moisture, leading to high drying energy consumption, increased production costs, and carbon emissions. In addition, some studies have attempted to modify other sodium electrode cathode materials with molybdenum doping, but this material system contains expensive vanadium and has potential biotoxicity, failing to meet the requirements of green and environmentally friendly development. Its preparation process often uses the sol-gel method, requiring large amounts of solvent, resulting in high drying energy consumption and long process cycles, also facing industrialization bottlenecks.

[0004] Therefore, there is an urgent need to develop a modification technology that is simple to process, low in energy consumption, environmentally friendly, and can effectively improve the intrinsic electronic conductivity of NFPP, as well as enhance the material's electronic conductivity and electrochemical performance. Summary of the Invention

[0005] This invention provides a composite cathode material and its preparation method, a sodium-ion battery, and an electrical device to solve the above-mentioned problems.

[0006] In a first aspect, the present invention provides a method for preparing a composite cathode material, comprising the following steps: S1, mix sodium source, iron source and phosphorus source to obtain a mixture; S2, add carbon source, molybdenum source and water to the mixture and mix to obtain the precursor; The molar ratio of Mo / (Fe+Mo) in the precursor is (0.01-0.1):3; The amount of water used accounts for 1%-10% of the total mass of the sodium, iron, phosphorus, carbon, and molybdenum sources. S3, the precursor is sintered to obtain the composite cathode material.

[0007] In one optional embodiment, the molar ratio of Na, Fe, and P in the sodium source, iron source, and phosphorus source is (3.9-4.1):(2.9-3.1):(3.9-4.1).

[0008] In one optional embodiment, the carbon source accounts for 8%-10% of the total mass of the sodium source, iron source, phosphorus source, carbon source, and molybdenum source.

[0009] In one alternative implementation, the mixing speed in S1 and S2 is independently 450-550 rpm, and the mixing time is independently 0.3-1 h.

[0010] In one optional implementation, in step S3, sintering includes a first-stage sintering and a second-stage sintering; Optionally, the sintering temperature of the first stage is 250-350℃; Optionally, the holding time for the first sintering stage is 4-8 hours; Optionally, the heating rate of the first sintering stage is 4.5-5.5℃ / min; Optionally, the temperature of the two-stage sintering is 450-550℃; Optionally, the holding time for the two-stage sintering is 10-14 hours; Optionally, the heating rate of the two-stage sintering is 4.5-5.5℃ / min.

[0011] In one optional embodiment, the temperature of the first-stage sintering is 250-350℃, the holding time is 4-8h, and the heating rate is 4.5-5.5℃ / min; and / or, the temperature of the second-stage sintering is 450-550℃, the holding time is 10-14h, and the heating rate is 4.5-5.5℃ / min.

[0012] In one alternative embodiment, the sintering includes sintering in a non-reactive gas atmosphere; Optionally, the inert gas includes at least one of argon and nitrogen; Optionally, the flow rate of the inert gas is 150-250 mL / min.

[0013] In one alternative embodiment, the molybdenum source comprises a soluble salt of molybdenum; Optionally, the soluble salts of molybdenum include molybdates; Further optionally, the molybdate includes at least one of sodium molybdate and ammonium molybdate; In one alternative embodiment, the sodium source comprises a soluble salt of sodium; Optionally, the soluble salt of sodium includes at least one of sodium carbonate, sodium oxalate, sodium formate, sodium pyrophosphate, and sodium dihydrogen phosphate. In one optional embodiment, the phosphorus source includes at least one of phosphoric acid and phosphate. Optionally, the phosphate includes at least one of sodium dihydrogen phosphate and disodium hydrogen phosphate; In one optional embodiment, the iron source includes at least one of inorganic iron salts, organic iron salts, and iron oxides; Optionally, the inorganic iron salt includes at least one of ferric phosphate, ferrous sulfate, ferric chloride, and ferric nitrate; Optionally, the organic iron salt includes at least one of ferrous oxalate, ferric citrate, ferric oxalate, and ferrous acetate; Optionally, the iron oxide includes at least one of iron oxide, iron(II,III) oxide, and ferrous oxide; In one alternative embodiment, the carbon source includes an organic carbon source; Optionally, the organic carbon source includes at least one selected from glucose, citric acid, sucrose, and starch. In a second aspect, the present invention also provides a composite cathode material prepared by the above-described method.

[0014] Thirdly, the present invention also provides a sodium-ion battery comprising the aforementioned composite cathode material.

[0015] Those skilled in the art will understand that the sodium-ion battery provided by this invention, in addition to including a positive electrode sheet containing the aforementioned composite positive electrode material, also includes structural components such as a negative electrode sheet, electrolyte, separator, and casing. During the battery charging and discharging process, sodium ions (Na... + The electrolyte moves back and forth between the positive and negative electrodes, inserting and removing itself. The electrolyte acts as a conductor for sodium ions between the positive and negative electrodes. The diaphragm is placed between the positive and negative electrodes, mainly to prevent short circuits between the positive and negative electrodes, while allowing sodium ions to pass through.

[0016] As an example, the positive electrode sheet includes a positive current collector (such as aluminum foil) and a positive active material layer. The positive current collector has two opposing surfaces in its own thickness direction, and the positive active material layer is disposed on either or both of the opposing surfaces of the positive current collector. Other materials, compositions, and manufacturing methods of the positive electrode sheet used in the sodium-ion battery of the present invention may include any techniques disclosed in the prior art suitable for sodium-ion batteries. For example, the positive active material may also include, but is not limited to, layered transition metal oxides, polyanionic compounds, Prussian blue analogues, etc.

[0017] As an example, the negative electrode sheet includes a negative electrode current collector (such as copper foil or aluminum foil) and a negative electrode active material layer. The negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the opposing surfaces of the negative electrode current collector. The materials, composition, and manufacturing methods of the negative electrode sheet used in the sodium-ion battery of the present invention may include any techniques disclosed in the prior art suitable for sodium-ion batteries (e.g., the negative electrode active material may include, but is not limited to, hard carbon, soft carbon, alloy-based materials, titanium-based materials, etc.).

[0018] The materials (such as polyolefins) and shapes (such as porous films) of the separator used in the sodium-ion battery of the present invention are not particularly limited, and may include any techniques disclosed in the prior art, provided that they can effectively isolate the positive and negative electrodes and allow sodium ion conduction.

[0019] The electrolyte used in the sodium-ion battery of the present invention is not particularly limited and may include any technology disclosed in the prior art, provided that it can effectively conduct sodium ions between the positive and negative electrodes (e.g., sodium salts such as NaPF6 and NaClO4 dissolved in organic solvents such as carbonate solvents, and may contain additives).

[0020] This invention does not specifically limit the preparation method of sodium-ion batteries. Conventional methods applicable to sodium-ion batteries in the art can be used to prepare sodium-ion batteries. For example, a positive electrode, a separator, and a negative electrode are sequentially stacked, with the separator positioned between the positive and negative electrodes. A battery cell is obtained through stacking or winding processes. Then, the sodium-ion battery of this invention is obtained through baking (to remove moisture), injection of sodium-ion battery electrolyte, formation (to form a stable solid electrolyte interphase (SEI) film), and encapsulation.

[0021] Fourthly, the present invention also provides an electrical device including the aforementioned sodium-ion battery.

[0022] It is understood that in the electrical equipment provided by this invention, the sodium-ion battery can be used as a power source for the electrical equipment, or as an energy storage unit for the electrical equipment. The electrical equipment may be, but is not limited to, stationary energy storage systems (including grid peak shaving, renewable energy support, and industrial and commercial energy storage), light electric vehicles (including electric bicycles, electric scooters, and site work vehicles), short-to-medium range electric vehicles (pure electric vehicles / plug-in hybrid vehicles), backup power supply devices (including communication base station UPS and emergency power supplies), and energy density-insensitive equipment (stationary power tools, outdoor power supplies), etc.

[0023] The technical solution of this invention has the following advantages: 1. The present invention provides a method for preparing a composite cathode material, comprising the following steps: S1, mixing sodium source, iron source, and phosphorus source to obtain a mixture; S2, adding carbon source, molybdenum source, and water to the mixture and mixing to obtain a precursor; wherein the molar ratio of Mo / (Fe+Mo) in the precursor is (0.01-0.1):3; and the amount of water used accounts for 1%-10% of the total mass of sodium source, iron source, phosphorus source, carbon source, and molybdenum source; S3, sintering the precursor to obtain the composite cathode material. This invention provides a small amount of Mo doping to reduce the diffusion barrier of sodium ions, thereby improving the electrochemical performance of NFPP powder. The molar ratio of Mo / (Fe+Mo) in the precursor is 0.01-0.1. This doping range can effectively improve the intrinsic conductivity of the NFPP cathode material, thereby achieving a significant improvement in electrical performance. This invention uses a semi-dry molybdenum doping process to prepare NFPP by controlling the amount of water added to 1%-10%. The molybdenum source, sodium source, iron source, phosphorus source, carbon source and a small amount of water are thoroughly mixed and homogenized. Then, the wet material is sintered at high temperature to obtain NFPP. This not only avoids the easy adhesion of sprayed material to the wall and the resulting material loss in conventional spray drying technology, but also achieves an effective improvement in the intrinsic electronic conductivity of NFPP through a simple, low-energy, and environmentally friendly process, as well as improves the material's electronic conductivity, first-cycle charge-discharge capacity, first-cycle coulombic efficiency, rate capacity and other electrochemical performance.

[0024] 2. The present invention provides a method for preparing a composite cathode material, wherein the carbon source accounts for 8%-10% of the total mass of the sodium source, iron source, phosphorus source, carbon source and molybdenum source, which can form a uniform and highly conductive carbon coating layer on the surface of the cathode material, effectively improving the intrinsic conductivity of the material. At the same time, controlling the carbon content within this range can balance conductivity and energy density. Attached Figure Description

[0025] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific 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 from these drawings without creative effort.

[0026] Figure 1 This is a process flow diagram of Embodiment 1 of the present invention. Detailed Implementation The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having” and any variations thereof in the text of this application are intended to cover non-exclusive inclusion.

[0028] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that the parameter can be, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] In the description of the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0030] In the description of the embodiments of this application, the term "at least one" refers to one or more (including two).

[0031] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0032] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0033] Example 1 This embodiment provides a composite cathode material, and the process flow diagram is shown below. Figure 1 As shown, the specific steps and operating parameters are as follows: S1, sodium source (sodium carbonate), iron source (ferric phosphate) and phosphorus source (ammonium dihydrogen phosphate) are added sequentially to a high-speed mixer. The high-speed mixer rotates at 500 rpm and is stirred for 0.5 h to obtain a mixture. S2, a precursor is obtained by adding a carbon source (glucose), a molybdenum source (sodium molybdate), and water to the mixture and stirring at 500 rpm for 0.5 h in a high-speed mixer; the molar ratio of Mo / (Fe+Mo) in the precursor is 0.02:3; the molar ratio of Na, Fe, and P in the sodium, iron, and phosphorus sources is 4:2.98:4; the amount of water used accounts for 5% of the total mass of the sodium, iron, phosphorus, carbon, and molybdenum sources; the mass of the carbon source accounts for 9% of the total mass of the sodium, iron, phosphorus, carbon, and molybdenum sources. S3. The precursor is placed in a tube furnace and heated from room temperature to 300°C at a flow rate of 200 mL / min in an argon atmosphere, and held at that temperature for 6 hours. Then, the temperature is increased to 500°C at a flow rate of 5°C / min and held for 12 hours to finally obtain the composite cathode material.

[0034] Example 2 This embodiment provides a composite cathode material, and the specific steps and operating parameters are as follows: S1, sodium source (sodium carbonate), iron source (ferric phosphate) and phosphorus source (ammonium dihydrogen phosphate) are added sequentially to a high-speed mixer. The high-speed mixer rotates at 500 rpm and is stirred for 0.5 h to obtain a mixture. S2, a precursor is obtained by adding a carbon source (glucose), a molybdenum source (sodium molybdate), and water to the mixture and stirring at 500 rpm for 0.5 h in a high-speed mixer; the molar ratio of Mo / (Fe+Mo) in the precursor is 0.05:3; the molar ratio of Na, Fe, and P in the sodium, iron, and phosphorus sources is 4:2.95:4; the amount of water used accounts for 5% of the total mass of the sodium, iron, phosphorus, carbon, and molybdenum sources; the mass of the carbon source accounts for 9.5% of the total mass of the sodium, iron, phosphorus, carbon, and molybdenum sources. S3. The precursor is placed in a tube furnace and heated from room temperature to 300°C at a flow rate of 200 mL / min in an argon atmosphere, and held at that temperature for 6 hours. Then, the temperature is increased to 500°C at a flow rate of 5°C / min and held for 12 hours to finally obtain the composite cathode material.

[0035] Example 3 This embodiment provides a composite cathode material, and the specific steps and operating parameters are as follows: S1, sodium source (sodium carbonate), iron source (ferric phosphate) and phosphorus source (ammonium dihydrogen phosphate) are added sequentially to a high-speed mixer. The high-speed mixer rotates at 500 rpm and is stirred for 0.5 h to obtain a mixture. S2, a precursor is obtained by adding a carbon source (glucose), a molybdenum source (sodium molybdate), and water to the mixture and stirring at 500 rpm for 0.5 h in a high-speed mixer; the molar ratio of Mo / (Fe+Mo) in the precursor is 0.08:3; the molar ratio of Na, Fe, and P in the sodium, iron, and phosphorus sources is 4:2.92:4; the amount of water used accounts for 5% of the total mass of the sodium, iron, phosphorus, carbon, and molybdenum sources; the mass of the carbon source accounts for 8.5% of the total mass of the sodium, iron, phosphorus, carbon, and molybdenum sources. S3. The precursor is placed in a tube furnace and heated from room temperature to 300°C at a flow rate of 200 mL / min in an argon atmosphere, and held at that temperature for 6 hours. Then, the temperature is increased to 500°C at a flow rate of 5°C / min and held for 12 hours to finally obtain the composite cathode material.

[0036] Example 4 This embodiment provides a composite cathode material, and the specific steps and operating parameters are as follows: S1, sodium source (sodium oxalate), iron source (iron oxide) and phosphorus source (disodium hydrogen phosphate) are added sequentially to a high-speed mixer. The high-speed mixer rotates at 450 rpm and is stirred for 1 hour to obtain a mixture. S2, a carbon source (citric acid), a molybdenum source (ammonium molybdate), and water are added to the mixture, and the mixture is stirred at 450 rpm for 0.3 h in a high-speed mixer to obtain a precursor; the molar ratio of Mo / (Fe+Mo) in the precursor is 0.01:3; the molar ratio of Na, Fe, and P in the sodium, iron, and phosphorus sources is 4.1:2.99:3.9; the amount of water used accounts for 10% of the total mass of the sodium, iron, phosphorus, carbon, and molybdenum sources; the mass of the carbon source accounts for 8% of the total mass of the sodium, iron, phosphorus, carbon, and molybdenum sources. S3. The precursor is placed in a tube furnace and heated from room temperature to 350°C at a flow rate of 250 mL / min in an argon atmosphere, and held at this temperature for 4 hours. Then, the temperature is increased to 450°C at a flow rate of 5.5°C / min and held for 14 hours to finally obtain the composite cathode material.

[0037] Example 5 This embodiment provides a composite cathode material, and the specific steps and operating parameters are as follows: S1, sodium source (sodium formate), iron source (ferrous oxalate) and phosphorus source (phosphoric acid) are added sequentially to a high-speed mixer. The high-speed mixer rotates at 550 rpm and is stirred for 0.3 hours to obtain a mixture. S2, a precursor is obtained by adding a carbon source (starch), a molybdenum source (sodium molybdate), and water to the mixture and stirring at 550 rpm for 1 hour in a high-speed mixer; the molar ratio of Mo / (Fe+Mo) in the precursor is 0.1:3; the molar ratio of Na, Fe, and P in the sodium, iron, and phosphorus sources is 3.9:2.9:4.1; the amount of water used accounts for 1% of the total mass of the sodium, iron, phosphorus, carbon, and molybdenum sources; the mass of the carbon source accounts for 10% of the total mass of the sodium, iron, phosphorus, carbon, and molybdenum sources. S3. The precursor is placed in a tube furnace and heated from room temperature to 250°C at a rate of 5.5°C / min in an argon atmosphere at a flow rate of 150 mL / min. The temperature is held for 8 hours, and then heated to 550°C at a rate of 4.5°C / min and held for 10 hours to finally obtain the composite cathode material.

[0038] Comparative Example 1 This comparative example provides a composite cathode material, which differs from Example 1 only in that the molybdenum source is replaced with an equimolar amount of iron source; The rest is the same as in Example 1.

[0039] Comparative Example 2 This comparative example provides a composite cathode material, which differs from Example 4 only in that: No carbon source is added; The rest is the same as in Example 4.

[0040] Comparative Example 3 This comparative example provides a composite cathode material, which differs from Example 4 only in that: The molar ratio of Mo / (Fe+Mo) in the precursor is 0.005:1; The rest is the same as in Example 4.

[0041] Comparative Example 4 This comparative example provides a composite cathode material, which differs from Example 4 only in that: The molar ratio of Mo / (Fe+Mo) in the precursor is 0.15:1; The rest is the same as in Example 4.

[0042] Comparative Example 5 This embodiment provides a composite cathode material, which differs from Embodiment 1 only in that: In S2, the amount of water used accounts for 0.5% of the total mass of the sodium source, iron source, phosphorus source, carbon source, and molybdenum source; Everything else remains the same as in Example 1.

[0043] Comparative Example 6 This embodiment provides a composite cathode material, which differs from Embodiment 1 only in that: In S2, the amount of water used accounts for 15% of the total mass of the sodium source, iron source, phosphorus source, carbon source, and molybdenum source; Everything else remains the same as in Example 1.

[0044] Comparative Example 7 This comparative example provides a composite cathode material, which differs from Example 4 only in that: In S1, the molybdenum source is replaced with an equimolar amount of nickel source; The rest is the same as in Example 4.

[0045] Comparative Example 8 This comparative example provides a composite cathode material, which differs from Example 4 only in that: S2, carbon source, molybdenum source, and water are added to the mixture, and the mixture is stirred in a high-speed mixer for 0.3 hours to obtain a precursor slurry. The precursor slurry is then dried into a precursor using a spray dryer at an inlet air temperature of 250°C, an outlet air temperature of 90°C, and a feed rate of 20 ml / min. The amount of water used accounts for 70% of the total mass of the sodium source, iron source, phosphorus source, carbon source, molybdenum source, and water. The rest is the same as in Example 4.

[0046] Experimental Example 1 (1) Intrinsic electron conductivity The intrinsic electronic conductivity of the composite cathode materials provided in Examples 1-5 and Comparative Examples 1-8 was tested using the following specific testing methods: The composite cathode materials prepared in Examples 1-5 and Comparative Examples 1-8 were loaded into an insulating mold and compacted under a hydraulic press with a pressure of 15 MPa to obtain a pressed sheet. The resistance of the pressed sheet was then tested using a powder resistivity tester (model: ST2722-SZ). The intrinsic electronic conductivity of the prepared composite cathode material was calculated using the following formula: .

[0047] (2) Electrical performance test The composite cathode materials provided in Examples 1-5 and Comparative Examples 1-8 were applied to sodium-ion batteries, and then their electrical performance was tested.

[0048] The method for preparing the sodium-ion battery includes the following steps: A positive electrode sheet was prepared by uniformly mixing N-methylpyrrolidone (solvent) in a ratio of 90 (positive electrode material): 5 (PVDF): 5 (SP), followed by homogenization, coating, drying, and cutting. A metallic Na sheet was used as the counter electrode, and glass fiber was used as the separator. A 1 mol / L solution of NaPF6 was mixed in an ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) solution (volume ratio 1:1:0.5) as the electrolyte. During testing, a CR2032 coin cell was assembled from the positive electrode sheet, glass fiber separator, Na sheet, spacer, and spring contacts.

[0049] ① First-cycle charge / discharge efficiency test The assembled coin cells were subjected to their first charge and discharge at a rate of 0.1C within a voltage range of 2.0V to 4.0V. The first charge capacity and the first discharge capacity were recorded, and the first coulombic efficiency (first efficiency) was calculated.

[0050] The Coulomb efficiency for the first lap is calculated as follows: ; Where: ICE is the initial Coulomb efficiency; D1 is the initial discharge capacity at a specified rate (e.g., 0.1C); C1 represents the initial charging capacity at the same rate.

[0051] ②Rate performance test The assembled button cells were charged and discharged at constant currents of 0.1 C and 5 C within a voltage range of 2.0V to 4.0V, with a cutoff condition of 2.0V.

[0052] (3) Receiving rate This section mainly focuses on the yield of materials before sintering using semi-dry and spray-drying methods. Since the sintering processes are the same for both methods, the loss on ignition is also the same. The precursors from Example 4 and Comparative Example 8 before sintering in step S3 were dried at 150°C, and the yield (%) was calculated using the following formula: .

[0053] (4) Energy consumption test Example 4 uses a semi-dry process, the semi-dry process flow is material mixing → precursor → sintering. The spray drying process used in Comparative Example 8 is material mixing → spray drying → precursor (spray material) → sintering. The semi-dry process reduces the spray drying step compared to the spray drying process. Since the parameters of the mixing and sintering steps in Example 4 and Comparative Example 8 are the same, that is, the energy consumption is the same. Therefore, only an independent electricity meter is used here to measure the electricity consumption data of the spray drying equipment.

[0054] The specific test results are shown in Tables 1 and 2: Table 1 Electrical performance test data of Examples 1-5 and Comparative Examples 1-7

[0055] The data above show that the composite cathode materials prepared by using appropriate amounts of water content and molybdenum doping in Examples 1-5 of this invention have advantages such as high performance, high conductivity, high yield, and low energy consumption. In Comparative Examples 1-2, the absence of molybdenum doping or carbon coating significantly deteriorates the intrinsic conductivity and electrochemical performance of the prepared composite cathode materials. Comparative Examples 3-4 show that excessively low or high molybdenum doping levels reduce the conductivity of NFPP, leading to decreased electrochemical performance. Comparative Examples 5-6 show that excessively low water content affects the uniformity of material mixing, resulting in decreased electrical performance, while excessively high water content causes material agglomeration and affects sintering, also leading to decreased electrical performance. In Comparative Example 7, replacing the molybdenum source in Example 4 with a nickel source significantly reduces the intrinsic conductivity and electrochemical performance of the prepared composite cathode material, highlighting the importance of using molybdenum doping in this invention.

[0056] Table 2 Data for semi-dry and spray drying methods

[0057] The data above shows that, compared with the semi-dry process in Example 4, the spray drying method in Comparative Example 8 not only causes material wall-sticking loss and power consumption during the spray drying process, resulting in low yield and high energy consumption, but also significantly reduces the intrinsic conductivity and electrochemical performance of the composite cathode material.

[0058] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a composite cathode material, characterized in that, Includes the following steps: S1, mix sodium source, iron source and phosphorus source to obtain a mixture; S2, add carbon source, molybdenum source and water to the mixture and mix to obtain the precursor; The molar ratio of Mo / (Fe+Mo) in the precursor is (0.01-0.1):3; The amount of water used accounts for 1%-10% of the total mass of the sodium, iron, phosphorus, carbon, and molybdenum sources. S3, the precursor is sintered to obtain the composite cathode material.

2. The preparation method according to claim 1, characterized in that, The molar ratio of Na, Fe, and P in the sodium, iron, and phosphorus sources is (3.9-4.1):(2.9-3.1):(3.9-4.1).

3. The preparation method according to claim 1 or 2, characterized in that, The carbon source accounts for 8%-10% of the total mass of the sodium source, iron source, phosphorus source, carbon source, and molybdenum source.

4. The preparation method according to any one of claims 1-3, characterized in that, In S3, sintering includes one-stage sintering and two-stage sintering; And / or, the sintering includes sintering in a non-reactive gas atmosphere; Optionally, the inert gas includes at least one of argon and nitrogen; Optionally, the flow rate of the inert gas is 150-250 mL / min.

5. The preparation method according to claim 4, characterized in that, The sintering temperature of the first section is 250-350℃; And / or, the holding time for the sintering section is 4-8 hours; And / or, the heating rate of the sintering section is 4.5-5.5℃ / min; And / or, the sintering temperature of the two stages is 450-550℃; And / or, the holding time for the two-stage sintering is 10-14 hours; And / or, the heating rate of the sintering section is 4.5-5.5℃ / min.

6. The preparation method according to any one of claims 1-5, characterized in that, The mixing speeds in S1 and S2 are independently 450-550 rpm, and the mixing times are independently 0.3-1 h.

7. The preparation method according to any one of claims 1-6, characterized in that, The molybdenum source includes a soluble salt of molybdenum; Optionally, the soluble salts of molybdenum include molybdates; And / or, the sodium source includes a soluble salt of sodium; Optionally, the soluble salt of sodium includes at least one of sodium carbonate, sodium oxalate, sodium formate, sodium pyrophosphate, and sodium dihydrogen phosphate. And / or, the phosphorus source includes at least one of phosphoric acid and phosphate; Optionally, the phosphate includes at least one of sodium dihydrogen phosphate and disodium hydrogen phosphate; And / or, the iron source includes at least one of inorganic iron salts, organic iron salts, and iron oxides; Optionally, the inorganic iron salt includes at least one of ferric phosphate, ferrous sulfate, ferric chloride, and ferric nitrate; Optionally, the organic iron salt includes at least one of ferrous oxalate, ferric citrate, ferric oxalate, and ferrous acetate; Optionally, the iron oxide includes at least one of iron oxide, iron(II,III) oxide, and ferrous oxide; And / or, the carbon source includes an organic carbon source; Optionally, the organic carbon source includes at least one of glucose, citric acid, sucrose, and starch.

8. A composite cathode material prepared by the preparation method according to any one of claims 1-7.

9. A sodium-ion battery, characterized in that, Including the composite cathode material as described in claim 8.

10. An electrical appliance, characterized in that, Including the sodium-ion battery as described in claim 9.

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