Sodium ferrous sulfate positive electrode material and preparation method and application thereof
The core-shell structured sodium ferrous sulfate positive electrode material was prepared by the seed-induced crystallization method, which solved the problem of low powder compaction density, achieved high compaction density and high specific capacity, and improved the electrochemical performance of sodium ion batteries.
Patent Information
- Application Number
- CN202510992119.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-17
- Publication Date
- 2025-10-17
AI Technical Summary
The powder compaction density of existing sodium ferrous sulfate positive electrode materials is low, which affects their electrochemical performance and limits their application in high-performance sodium-ion batteries.
The seed-induced crystallization method is adopted, and sodium ferric pyrophosphate with higher density is used as the seed crystal, which is mixed with raw materials such as iron source and sodium source. Through drying and sintering treatment, a core-shell structure material with sodium ferric pyrophosphate as the core and sodium ferrous sulfate as the shell is formed.
The compaction density and specific capacity of the sodium ferrous sulfate positive electrode material are improved, and the electrochemical performance of the sodium ion battery is enhanced.
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Abstract
Description
TECHNICAL FIELD
[0001] The application relates to the technical field of sodium ion batteries, in particular to a sodium ferrous sulfate positive electrode material and a preparation method and application thereof. BACKGROUND
[0002] With the increasing demand for energy and increasing concern about the environmental problems caused by traditional fossil energy, the research and development of new high-performance batteries have become a hot spot in the scientific research field. Sodium ion batteries have broad application prospects in large-scale energy storage, new energy vehicles and other fields due to their abundant resources and low cost, and are the current research focus.
[0003] Sodium ferrous sulfate, as a potential positive electrode material for sodium ion batteries, has advantages such as high working voltage, good rate performance and good cycle performance, and has attracted widespread attention from researchers. At present, in the preparation process of the sodium ferrous sulfate positive electrode material, sodium sulfate, ferrous sulfate and other raw materials are usually dissolved in water and then spray dried, and then the sodium ferrous sulfate positive electrode material is obtained by sintering. However, since sodium sulfate and ferrous sulfate can both be dissolved in water, the precursor obtained by the drying method of liquid phase spraying is mostly a hollow structure, and the crystal grains are small, which leads to a low tap density of the sodium ferrous sulfate obtained after sintering, thereby affecting the electrochemical performance, and the capacity of the sodium ion battery prepared based on the sodium ferrous sulfate positive electrode material is low, which limits the wide application of the sodium ferrous sulfate positive electrode material in high-performance sodium ion batteries. SUMMARY
[0004] In view of the technical problems in the background art, the application provides a sodium ferrous sulfate positive electrode material and a preparation method and application thereof, aiming to solve the technical problem of low tap density of the sodium ferrous sulfate positive electrode material powder.
[0005] In a first aspect, the embodiments of the application provide a preparation method of a sodium ferrous sulfate positive electrode material, including the following steps: Preparation of a mixed slurry containing an antioxidant, a seed crystal, an iron source, a sodium source and a carbon source, wherein the seed crystal is sodium iron pyrophosphate phosphate; Drying treatment of the mixed slurry to obtain a precursor; Sintering treatment of the precursor to obtain a sodium ferrous sulfate positive electrode material.
[0006] In the technical scheme of the embodiment of the present application, the seed crystal induction crystallization method is adopted, sodium pyrophosphate iron phosphate is used as the seed crystal, and the seed crystal is mixed with raw materials such as an iron source and a sodium source used for preparing sodium ferrous sulfate. In the drying process, the iron source and the sodium source can be adsorbed on the surface of the sodium pyrophosphate iron phosphate to form relatively dense precursor particles. After sintering treatment, sodium ferrous sulfate can be induced to nucleate and crystallize on the surface of the sodium pyrophosphate iron phosphate, so as to form a core-shell structure sodium ferrous sulfate positive electrode material with the sodium pyrophosphate iron phosphate as the core and the sodium ferrous sulfate as the shell. The sodium ferrous sulfate positive electrode material has relatively high tap density and relatively high specific capacity, and has better application prospect.
[0007] In some embodiments, the mass of the seed crystal is 2% to 8% of the theoretical mass of the sodium ferrous sulfate.
[0008] In the embodiment, the theoretical mass of the sodium ferrous sulfate is the mass of the sodium ferrous sulfate generated by the reaction of the iron source and the sodium source calculated according to the reaction equation. By adjusting the mass of the seed crystal, the problems of low tap density and capacity caused by too little seed crystal can be avoided, and the problem of capacity decline caused by too much seed crystal can be avoided, so that the prepared sodium ferrous sulfate positive electrode material has relatively high tap density and relatively high capacity at the same time.
[0009] In some embodiments, the tap density of the seed crystal is greater than or equal to 1.95 g / cm 3 .
[0010] In the embodiment, by limiting the tap density of the seed crystal, a seed crystal with high tap density can be used to provide a more dense core to improve the tap density of the finally prepared sodium ferrous sulfate positive electrode material.
[0011] In some embodiments, the median particle size of the seed crystal is 0.5 to 7 microns.
[0012] In the embodiment, by adjusting the median particle size of the seed crystal, the agglomeration and sedimentation of the seed crystal can be avoided, so that the prepared sodium ferrous sulfate positive electrode material has relatively high tap density and relatively high capacity at the same time.
[0013] In some embodiments, the molar ratio of iron elements in the iron source to sodium elements in the sodium source is 1:(1-2); and / or, the mass of the antioxidant is 3% to 5% of the mass of the iron source; and / or, the mass of the carbon source is 2% to 4% of the total mass of the iron source and the sodium source; and / or, the iron source includes at least one of ferrous sulfate heptahydrate, ferrous sulfate monohydrate, and anhydrous ferrous sulfate; and / or, the sodium source includes at least one of anhydrous sodium sulfate and sodium bisulfate; and / or, the carbon source includes at least one of graphene oxide, carbon nanotubes, and Ketjen black; and / or, the antioxidant includes at least one of vitamin C, vitamin E, tea polyphenol, and grape polyphenol.
[0014] In the embodiment, by limiting the molar ratio between the iron element and the sodium element, the iron-sodium ratio in the sodium ferrous sulfate generated in the reaction can be regulated, and the electrochemical performance of the sodium ferrous sulfate is adjusted; by regulating the amount of the antioxidant, the oxidation of the iron ions in the iron source can be avoided, so as to promote the generation of the sodium ferrous sulfate; by regulating the amount of the carbon source, the conductivity of the sodium ferrous sulfate positive electrode material can be improved while avoiding the excessive carbon affecting the transmission efficiency of sodium ions. Moreover, the raw material selection range of the iron source, the sodium source, the carbon source and the antioxidant is relatively wide, and the raw material cost is relatively low, which is beneficial to the industrialized scale production.
[0015] In some embodiments, the drying treatment is spray drying, the inlet air temperature of the spray drying is 200-260 DEG C, and the outlet air temperature is 80-100 DEG C.
[0016] In the embodiment, by using the spray drying method for drying and regulating the inlet and outlet air temperatures, the iron source, the sodium source and the carbon source in the mixed slurry can be adsorbed on the surface of the sodium pyrophosphate iron phosphate during the spray drying process, forming a relatively dense precursor particle, so as to improve the tap density and capacity of the sodium ferrous sulfate positive electrode material.
[0017] In some embodiments, the sintering process includes: heating to 350-450 DEG C, and the holding time is 4-8 h.
[0018] In the embodiment, by regulating the temperature and holding time of the sintering process, the iron source and the sodium source can be promoted to react to generate sodium ferrous sulfate, and the sodium ferrous sulfate can be heterogeneously nucleated on the surface of the sodium pyrophosphate iron phosphate, thereby forming a sodium ferrous sulfate positive electrode material with the sodium pyrophosphate iron phosphate as the core and the sodium ferrous sulfate as the shell, so that the sodium ferrous sulfate positive electrode material has a high tap density and specific capacity.
[0019] In a second aspect, the embodiments of the present application provide a sodium ferrous sulfate positive electrode material, which is prepared by the preparation method provided in the first aspect; the sodium ferrous sulfate positive electrode material has a core-shell structure, including a core and a shell layer covering the outer surface of the core; the material of the core includes sodium pyrophosphate iron phosphate, and the material of the shell layer includes sodium ferrous sulfate.
[0020] In the technical solution of the embodiments of the present application, the sodium ferrous sulfate positive electrode material has a core-shell structure, the core material is the sodium pyrophosphate iron phosphate with a relatively high density, and the shell layer is the sodium ferrous sulfate, so that the sodium ferrous sulfate positive electrode material can have a high tap density and a high specific capacity at the same time.
[0021] In a third aspect, the embodiments of the present application provide a positive electrode sheet, which includes the sodium ferrous sulfate positive electrode material prepared by the preparation method provided in the first aspect of the present application.
[0022] In the embodiment, the positive plate contains the above-mentioned sodium ferrous sulfate positive material, and thus has the advantage of high specific capacity.
[0023] In a fourth aspect, the embodiments of the present application provide a secondary battery comprising the positive plate provided in the third aspect of the present application.
[0024] In the embodiment, the secondary battery contains the above-mentioned positive plate, and thus has the advantage of high specific capacity.
[0025] The above description is only a summary of the technical solutions of the present application, in order to more clearly understand the technical means of the present application, and can be implemented according to the content of the specification, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS
[0026] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.
[0027] Figure 1 Preparation flow chart of sodium ferrous sulfate positive material in embodiment 1 of the present application; Figure 2 Charge-discharge curve of the secondary battery assembled by the sodium ferrous sulfate positive material prepared in embodiment 1 of the present application. DETAILED DESCRIPTION
[0028] The embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.
[0029] 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 the present application belongs; the terms used herein are only for the purpose of describing specific embodiments of the present application, and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of drawings are intended to cover non-exclusive inclusion.
[0030] Reference to“an embodiment” herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase“in an embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. It is expressly understood that any of the embodiments described herein can be incorporated in a combination of embodiments.
[0031] In the description of the embodiments of the application, the term“and / or” is merely an association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character“ / ” herein generally represents an“or” relationship between the associated objects.
[0032] The existing sodium ferrous sulfate positive electrode material is generally prepared by dissolving the raw materials in water and then through spray drying, sintering and other processes, but the precursor obtained in this way is mostly hollow structure, and the crystal grains are small, which leads to the low tap density of the finally prepared sodium ferrous sulfate positive electrode material powder, and further affects its electrochemical performance.
[0033] In order to solve the technical problem of low tap density of sodium ferrous sulfate positive electrode material powder, the application provides a sodium ferrous sulfate positive electrode material and a preparation method and application thereof. By using the seed-induced crystallization method, sodium iron pyrophosphate phosphate with high density is used as the crystal nucleus, and sodium ferrous sulfate is induced to nucleate and crystallize on the surface of sodium iron pyrophosphate phosphate, so as to prepare a sodium ferrous sulfate positive electrode material with sodium iron pyrophosphate phosphate as the inner core and sodium ferrous sulfate as the shell. The sodium ferrous sulfate positive electrode material has high tap density and high specific capacity, and the electrochemical performance of the positive electrode sheet and the secondary battery prepared based on the sodium ferrous sulfate positive electrode material is also improved.
[0034] In a first aspect, the embodiments of the application provide a preparation method of a sodium ferrous sulfate positive electrode material, comprising the following steps: A mixed slurry containing an antioxidant, a seed crystal, an iron source, a sodium source and a carbon source is prepared, wherein the seed crystal is sodium iron pyrophosphate phosphate; The mixed slurry is dried to obtain a precursor; The precursor is sintered to obtain a sodium ferrous sulfate positive electrode material.
[0035] In the present application, by selecting sodium pyrophosphate iron phosphate with a higher density as a seed crystal, and preparing a mixed slurry of the seed crystal with an antioxidant, an iron source, a sodium source and a carbon source, the iron source, the sodium source and other raw materials can be adsorbed on the surface of the sodium pyrophosphate iron phosphate through a drying process of the mixed slurry, effectively solving the problem that the traditional ferrous sodium precursor is mostly hollow structure and has small crystal grains, so that the precursor formed in the present application has a relatively dense structure. Through sintering treatment of the precursor, the formed ferrous sodium sulfate can be inhomogeneous nucleation on the surface of sodium pyrophosphate iron phosphate, and finally a core-shell structure ferrous sodium sulfate positive electrode material with sodium pyrophosphate iron phosphate as the core and ferrous sodium sulfate as the shell is obtained, effectively improving the tap density and specific capacity of the ferrous sodium sulfate positive electrode material.
[0036] Further, in some embodiments, the mass of the seed crystal is 2% to 8% of the theoretical mass of ferrous sodium sulfate.
[0037] In the present application, the theoretical mass of ferrous sodium sulfate is the mass of ferrous sodium sulfate generated by the reaction of the iron source and the sodium source calculated according to the reaction equation. By controlling the mass of the seed crystal to be 2% to 8% of the theoretical mass of ferrous sodium sulfate, the prepared ferrous sodium sulfate positive electrode material can have both high tap density and specific capacity. If the mass of the seed crystal is too low, part of the ferrous sodium sulfate cannot form a core-shell structure with sodium pyrophosphate iron phosphate as the core, which will further result in low capacity and tap density of the prepared ferrous sodium sulfate positive electrode material. If the mass of the seed crystal is too high, the content of sodium pyrophosphate iron phosphate in the prepared ferrous sodium sulfate positive electrode material will be too high, which will result in a decrease in the capacity of the ferrous sodium sulfate positive electrode material. Specifically, the mass of the seed crystal can be 2%, 3%, 4%, 5%, 6%, 7%, 8% or any value within the range of 2% to 8% of the theoretical mass of ferrous sodium sulfate.
[0038] Further, in some embodiments, the tap density of the seed crystal is ≥1.95 g / cm 3 .
[0039] In the present application, by selecting a seed crystal with a tap density ≥1.95 g / cm 3 , the problem of large internal porosity caused by seed crystals with low tap density can be avoided, so that the core of the prepared ferrous sodium sulfate positive electrode material has a high degree of compactness, thereby improving the tap density of the ferrous sodium sulfate positive electrode material. Moreover, the higher the tap density of the seed crystal, the more conducive to improving the tap density of the ferrous sodium sulfate positive electrode material. At present, the highest tap density of sodium pyrophosphate iron phosphate is 2.1 g / cm 3 , under the condition of considering the tap density and raw material cost, the tap density of the seed crystal is more preferably ≥2.0 g / cm 3 , so as to obtain a ferrous sodium sulfate positive electrode material with high tap density at a lower cost.
[0040] Further, in some embodiments, the median particle size of the crystal seeds is 0.5-7 pm.
[0041] In the present application, by controlling the median particle size of the crystal seeds to be 0.5-7 pm, the prepared sodium ferrous sulfate positive electrode material can have both high tap density and capacity. If the median particle size of the crystal seeds is too small, the crystal seeds themselves will agglomerate, and there are more pores in the agglomerated crystal seeds, which will further result in low capacity and tap density of the prepared sodium ferrous sulfate positive electrode material; if the median particle size of the crystal seeds is too large, the crystal seeds are easy to settle, which will result in uneven distribution of sodium ferrous sulfate on the surface of the crystal seeds, and further affect the capacity of the sodium ferrous sulfate positive electrode material. Specifically, the median particle size of the crystal seeds can be 0.5 pm, 1 pm, 2 pm, 3 pm, 4 pm, 5 pm, 6 pm, 7 pm, or any value within the range of 0.5-7 pm.
[0042] Further, in some embodiments, the molar ratio of iron elements in the iron source to sodium elements in the sodium source is 1:(1-2); and / or, the iron source comprises at least one of ferrous sulfate heptahydrate, ferrous sulfate monohydrate, and anhydrous ferrous sulfate; and / or, the sodium source comprises at least one of anhydrous sodium sulfate and sodium bisulfate.
[0043] In the present application, by limiting the molar ratio between iron elements and sodium elements, the iron-to-sodium ratio in the sodium ferrous sulfate generated by the reaction can be controlled, and thus the electrochemical performance of the sodium ferrous sulfate can be adjusted. The raw materials of the iron source and the sodium source are widely available and low in price, and the required raw materials can be selected according to actual conditions, which can meet the needs of industrial-scale production.
[0044] Specifically, the molar ratio of iron elements in the iron source to sodium elements in the sodium source can be 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2.0, or any value within the range of 1:(1-2); preferably, the molar ratio of iron elements in the iron source to sodium elements in the sodium source is 1:(1.5-1.55), more preferably 1.7:2.6, so as to synthesize sodium ferrous sulfate of formula Na 2.6 Fe 1.7 (SO4)3, and further improve its electrochemical performance.
[0045] Further, in some embodiments, the mass of the antioxidant accounts for 3%-5% of the mass of the iron source; and / or, the antioxidant comprises at least one of vitamin C, vitamin E, tea polyphenol, and grape polyphenol.
[0046] In the present application, by controlling the amount of antioxidant, the oxidation of iron ions in the iron source can be avoided, so as to promote the generation of sodium ferrous sulfate. And the raw material selection range of antioxidant is relatively wide, which can be selected according to the needs in actual application. More preferably, in order to improve the use effect of antioxidant, the antioxidant can be added before the iron source in the process of preparing the mixed slurry, so as to avoid the oxidation of iron source. The adding sequence of other raw materials in the mixed slurry can be adjusted according to the actual needs, and the present application is not limited thereto. Specifically, the mass of antioxidant can account for 3%, 3.5%, 4%, 4.5%, 5% or any value in the range of 3% to 5% of the mass of iron source.
[0047] Further, in some embodiments, the mass of the carbon source accounts for 2% to 4% of the total mass of the iron source and the sodium source; and / or, the carbon source includes at least one of graphene oxide, carbon nanotube, and Ketjen black.
[0048] In the present application, by controlling the amount of carbon source, not only the conductivity of sodium ferrous sulfate positive electrode material can be improved by using carbon source, but also the transmission efficiency of sodium ions can be avoided by excessive carbon source. More preferably, in the process of preparing the mixed slurry, in order to improve the dispersion effect of carbon source, the carbon source can be dispersed in the slurry containing dispersant first to prepare carbon source slurry, and then the carbon source slurry is used as one of the raw materials to prepare the mixed slurry. The mass fraction of dispersant in the carbon source slurry is preferably within 0.2%. Specifically, the mass of carbon source can account for 2%, 2.5%, 3%, 3.5%, 4% or any value in the range of 2% to 4% of the total mass of iron source and sodium source.
[0049] Further, in some embodiments, the step of preparing the mixed slurry containing antioxidant, seed crystal, iron source, sodium source and carbon source includes: adding antioxidant, seed crystal, iron source, sodium source and carbon source into solvent respectively, and obtaining the mixed slurry after sufficient dispersion.
[0050] In the present application, the adding sequence of antioxidant is preferably before the iron source, and the remaining raw materials can be added in any sequence; the carbon source is preferably added in the form of carbon source slurry, which contains dispersant to improve its dispersion effect; the solvent is preferably water; and the stirring speed in the dispersion process is preferably 400 to 500 r / s to promote the sufficient dissolution or dispersion of each raw material.
[0051] Further, in some embodiments, the drying method is spray drying; the inlet air temperature of spray drying is 200 to 260℃, and the outlet air temperature is 80 to 100℃.
[0052] In the present application, by adopting the spray drying method for drying and regulating its inlet and outlet air temperatures, the raw materials such as the iron source and the sodium source in the mixed slurry can be adsorbed on the surface of the sodium ferric pyrophosphate as a seed during the spray drying process, and relatively dense precursor particles are formed after spray drying to improve the compaction density and capacity of the sodium ferrous sulfate positive electrode material. Specifically, the inlet air temperature of the spray drying can be 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C or any value in the range of 200~260°C, and the outlet air temperature of the spray drying can be 80°C, 85°C, 88°C, 90°C, 92°C, 95°C, 100°C or any value in the range of 80~100°C.
[0053] Furthermore, in some embodiments, the sintering process includes: heating to 350-450° C. and keeping the temperature for 4-8 hours.
[0054] In the present application, by regulating the temperature and holding time of the sintering treatment, the reaction of the iron source and the sodium source to form sodium ferrous sulfate can be promoted, and the sodium ferrous sulfate can be heterogeneously nucleated on the surface of the sodium ferric pyrophosphate, thereby forming a sodium ferrous sulfate positive electrode material with sodium ferric pyrophosphate as the core and sodium ferrous sulfate as the shell, so that it has a higher compaction density and specific capacity. Among them, the atmosphere during the sintering treatment is preferably an inert atmosphere to prevent the sodium ferrous sulfate from being oxidized during the sintering process; the heating rate during the sintering treatment is preferably 2~8℃ / min. Specifically, the temperature during the sintering treatment can be raised to 350℃, 370℃, 390℃, 410℃, 430℃, 450℃ or any value in the range of 350~450℃, and after heating to the target temperature, it can be kept warm for 4h, 5h, 6h, 7h, 8h or any value in the range of 4~8h.
[0055] In a second aspect, an embodiment of the present application provides a sodium ferrous sulfate positive electrode material, which is prepared by the preparation method provided in the first aspect; the sodium ferrous sulfate positive electrode material has a core-shell structure, including a core and a shell layer coated on the outer surface of the core; the material of the core includes sodium ferrous pyrophosphate, and the material of the shell layer includes sodium ferrous sulfate.
[0056] In this application, the prepared sodium ferrous sulfate positive electrode material has high-density sodium ferric pyrophosphate as the core and sodium ferrous sulfate as the shell, achieving a simultaneous increase in compaction density and specific capacity.
[0057] In a third aspect, an embodiment of the present application provides a positive electrode plate, comprising a sodium ferrous sulfate positive electrode material prepared by the preparation method provided by the first aspect of the present application.
[0058] In the present application, the positive electrode plate contains the above-mentioned sodium ferrous sulfate positive electrode material, and thus has the advantage of high specific capacity.
[0059] In a fourth aspect, the embodiments of the present application provide a secondary battery comprising the positive electrode sheet provided in the third aspect of the present application.
[0060] In this embodiment, the secondary battery contains the positive electrode sheet described above, and thus has the advantage of high specific capacity. The specific charge capacity of the secondary battery is not less than 95 mAh / g, the specific discharge capacity is not less than 86 mAh / g, and the first coulombic efficiency is not less than 89% at 0.1C.
[0061] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If a specific technology or condition is not specified in the embodiments, the technology or condition described in the literature in the art or according to the product manual is used. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.
[0062] I. Preparation method Embodiment 1 This embodiment provides a preparation method of a sodium ferrous sulfate positive electrode material, and a schematic diagram of the process flow is shown as Figure 1 The specific steps include the following steps: S1. A mixed slurry containing an antioxidant, a seed crystal, an iron source, a sodium source and a carbon source is prepared, and the specific steps include: (1) Add graphene oxide and a dispersing agent to water, and fully disperse to obtain a carbon source slurry; in the carbon source slurry, the mass fraction of graphene oxide is 5%, and the mass fraction of the dispersing agent is 0.15%; (2) Take 130.43 g of the carbon source slurry, take 7.39 g of ascorbic acid as an antioxidant, take 152.52 g of ferrous sulfate heptahydrate as an iron source, and take 58.9 g of anhydrous sodium sulfate as a sodium source. According to the mass of the iron source and the sodium source, the theoretical mass of sodium ferrous sulfate is about 142 g, and 7.1 g of sodium iron pyrophosphate phosphate is taken as a seed crystal (the compacted density is 2.1 g / cm 3 , D50=4.5 μm) according to 5% of the theoretical mass; (3) The weighed ascorbic acid is added to 1 kg of deionized water, and stirred thoroughly until the ascorbic acid is completely dissolved to obtain solution 1; the weighed sodium iron pyrophosphate phosphate is added to solution 1, and stirred at a speed of 450 r / s to disperse the crystal seeds sufficiently to obtain solution 2; the weighed ferrous sulfate heptahydrate is added to solution 2, and stirred thoroughly until it is completely dissolved to obtain solution 3; the weighed anhydrous sodium sulfate is added to solution 3, and stirred thoroughly until it is completely dissolved to obtain solution 4; the weighed carbon source slurry is added to solution 4, and stirred at a speed of 450 r / s to disperse the carbon source sufficiently to obtain solution 5, which is the mixed slurry. In the mixed slurry, the molar ratio of iron element to sodium element is 1:1.51, the mass of the antioxidant accounts for 4.8% of the mass of the iron source, and the mass of the carbon source accounts for 3% of the total mass of the iron source and the sodium source.
[0063] S2. The mixed slurry is subjected to spray drying treatment, the inlet air temperature of the spray drying is 220℃, the outlet air temperature is 93℃, and the feeding frequency is 25 Hz to obtain a precursor; the precursor is black gray powder.
[0064] S3. The precursor is placed in an inert atmosphere furnace for sintering treatment, the heating rate is set to 5℃ / min, and the temperature is raised to 400℃ and kept for 6 h to obtain a sodium ferrous sulfate positive electrode material with a core-shell structure.
[0065] Examples 2-3 and Comparative Examples 1-3 Examples 2-3 and Comparative Examples 1-3 each provide a preparation method of a sodium ferrous sulfate positive electrode material, which differs from Example 1 only in that the mass of the sodium iron pyrophosphate phosphate used in step S1 is changed. The percentage of the sodium iron pyrophosphate phosphate used in each of the examples and comparative examples to the theoretical mass of the sodium ferrous sulfate is shown in Table 1, and the amounts of the other raw materials and the preparation steps are consistent with those of Example 1, which will not be described here again.
[0066] Table 1 Percentage of the mass of the crystal seeds to the theoretical mass of the sodium ferrous sulfate in Examples 2-3 and Comparative Examples 1-3 In Comparative Example 1, the mass of the crystal seeds accounts for 0%, indicating that no crystal seeds are added, and the final sodium ferrous sulfate positive electrode material does not contain the sodium iron pyrophosphate phosphate core.
[0067] Example 4 and Comparative Example 4 Example 4 and Comparative Example 4 each provide a preparation method of a sodium ferrous sulfate positive electrode material, which differs from Example 1 only in that the tap density of the sodium iron pyrophosphate phosphate used in step S1 is changed. The tap density of the sodium iron pyrophosphate phosphate used in each of the examples and comparative examples is shown in Table 2, and the other raw materials and the preparation steps are consistent with those of Example 1, which will not be described here again.
[0068] Table 2 Compaction density of sodium pyrophosphate iron phosphate used in Example 4 and Comparative Example 4 Example 5~6 and Comparative Example 5~6 Example 5~6 and Comparative Example 5~6 respectively provide a preparation method of a sodium ferrous sulfate positive electrode material, which is different from Example 1 only in that the median particle size of sodium pyrophosphate iron phosphate used in step S1 is changed. The median particle size of sodium pyrophosphate iron phosphate used in each example and comparative example is shown in Table 3. The remaining raw materials and preparation steps are consistent with Example 1, and will not be repeated here.
[0069] Table 3 Median particle size of sodium pyrophosphate iron phosphate used in Example 5~6 and Comparative Example 5~6 Example 7~8 Example 7~8 respectively provide a preparation method of a sodium ferrous sulfate positive electrode material, which is different from Example 1 only in that the mass of the sodium source used in step S1 is changed, i.e. the molar ratio of iron elements in the iron source to sodium elements in the sodium source is changed. The remaining proportions of raw materials and preparation steps are consistent with Example 1, and will not be repeated here.
[0070] Specifically, in Example 7, the molar ratio of iron elements in the iron source to sodium elements in the sodium source is 1:1; in Example 8, the molar ratio of iron elements in the iron source to sodium elements in the sodium source is 1:2.
[0071] Example 9~10 Example 9~10 respectively provide a preparation method of a sodium ferrous sulfate positive electrode material, which is different from Example 1 only in that the heating temperature and holding time during sintering treatment in step S3 are changed. The remaining steps are consistent with Example 1, and will not be repeated here.
[0072] Specifically, in Example 9, the heating temperature during sintering treatment is 350°C, and the holding time is 4h; in Example 10, the heating temperature during sintering treatment is 450°C, and the holding time is 8h.
[0073] Comparative Example 7 This comparative example provides a preparation method of a sodium ferrous sulfate positive electrode material, which is different from Example 1 only in that the type of seed crystal used in step S1 is changed. The compaction density and median particle size of the seed crystal and other steps are consistent with Example 1, and will not be repeated here.
[0074] Specifically, the seed crystal used in this comparative example is Na3V2(PO4)3.
[0075] II. Test method 1. Property test of sodium ferrous sulfate positive electrode material Compaction density test: The compaction density of the sodium ferrous sulfate positive electrode materials prepared in the examples and comparative examples was tested according to GB / T 24533-2019 using a compaction density tester.
[0076] 2. Property test of secondary battery The sodium ferrous sulfate positive electrode materials prepared in each example and comparative example were prepared into positive electrode sheets and applied in secondary batteries, and the battery assembly process was as follows: The positive electrode materials prepared in the above examples and comparative examples were mixed with conductive carbon powder and PVDF binder in a ratio of 90:5:5, and then uniformly coated on the surface of an aluminum foil current collector. After drying, cold pressing and slitting, the positive electrode sheets were obtained. In an inert gas glove box, the sodium sheet, electrolyte, separator, electrolyte, positive electrode sheet, gasket, spring, and positive electrode shell were sequentially assembled into a button-type half battery.
[0077] Then, the electrochemical performance of each assembled button-type half battery was tested: under the conditions of 20-30°C and normal pressure, the button-type battery was charged at a constant rate of 0.1C to 4.5V, and then discharged at a constant rate of 0.1C to 2.0V. The initial charge specific capacity and initial discharge specific capacity were measured, and the initial coulombic efficiency was calculated.
[0078] III. Analysis of test results of examples and comparative examples Figure 2 The charge-discharge curve of the battery assembled from the sodium ferrous sulfate positive electrode material prepared in Example 1 is shown in FIG. 1. Figure 2 It can be seen that the battery has good charge-discharge performance.
[0079] The compaction densities of the sodium ferrous sulfate positive electrode materials prepared in Examples 1-10 and Comparative Examples 1-7 and the electrical performance data of the batteries assembled from the corresponding positive electrode materials are shown in Table 4.
[0080] Table 4 Performance data in examples and comparative examples As can be seen from Table 4, by using the seed-induced crystallization method, the sodium iron pyrophosphate with appropriate particle size was selected as the seed crystal, the seed crystal was mixed with iron source, sodium source and other raw materials, and the amount of the seed crystal was controlled. After drying treatment and sintering treatment, the sodium ferrous sulfate positive electrode material with high compaction density was prepared. The compaction density of the sodium ferrous sulfate positive electrode material prepared in each example is ≥2.05 g / cm 3 The secondary batteries prepared from the sodium ferrous sulfate positive electrode materials provided by each example all have high charge-discharge specific capacity and coulombic efficiency.
[0081] Specifically, it can be seen from the comparison of Examples 1-3 and Comparative Examples 1-3 that the tap density of the prepared sodium ferrous sulfate positive electrode material gradually increases with the increase of the amount of the seed crystal. When no seed crystal is added or only 1% of the seed crystal is added, part of the generated sodium ferrous sulfate will not form a core-shell structure with the seed crystal sodium pyrophosphate ferric phosphate as the core, thereby resulting in lower tap density and capacity of the prepared sodium ferrous sulfate positive electrode material; when the amount of the seed crystal reaches 8%, if the amount of the seed crystal is further increased to 10%, not only the tap density of the sodium ferrous sulfate positive electrode material cannot be further improved, but also the capacity of the sodium ferrous sulfate positive electrode material will decrease due to the excessive content of sodium pyrophosphate ferric phosphate.
[0082] It can be seen from the comparison of Example 1, Example 4 and Comparative Example 4 that with the increase of the tap density of the seed crystal, the tap density and capacity of the prepared sodium ferrous sulfate positive electrode material also increase. If the tap density of the seed crystal is too low, there will be more pores in the core of the formed sodium ferrous sulfate positive electrode material, thereby affecting the tap density and capacity thereof.
[0083] It can be seen from the comparison of Example 1, Examples 5-6 and Comparative Examples 5-6 that within a certain range, appropriately increasing the median particle size of the seed crystal is beneficial to improve the tap density and capacity of the prepared sodium ferrous sulfate positive electrode material. If the median particle size of the seed crystal is too small, the seed crystal itself is prone to agglomeration, and after agglomeration, more pores will be generated, thereby resulting in lower capacity and tap density of the prepared sodium ferrous sulfate positive electrode material; when the median particle size of the seed crystal reaches 7 μm, if it is further increased to 10 μm, the too large median particle size makes the seed crystal more prone to sedimentation, thereby affecting the uniform distribution of sodium ferrous sulfate on the surface of the seed crystal, which in turn will result in the decrease of the tap density and capacity of the finally prepared sodium ferrous sulfate positive electrode material.
[0084] It can be seen from the comparison of Example 1 and Examples 7-8 that with the increase of the proportion of sodium element, the tap density and capacity of the prepared sodium ferrous sulfate positive electrode material both show a trend of first increasing and then decreasing, indicating that a suitable iron-sodium ratio is beneficial to improve the performance of the sodium ferrous sulfate positive electrode material.
[0085] It can be seen from the comparison of Example 1 and Examples 9-10 that with the increase of the sintering temperature and the extension of the holding time, the tap density and capacity of the prepared sodium ferrous sulfate positive electrode material also show a trend of first increasing and then decreasing, wherein the higher sintering temperature and longer holding time have a greater impact on the capacity of the sodium ferrous sulfate positive electrode material.
[0086] It can be seen by comparing Example 1 and Comparative Example 7 that not any substance with high compaction density and suitable median particle size can be used as a seed crystal to improve the performance of the sodium ferrous sulfate positive electrode material, and the type of the seed crystal has an important influence on the performance of the sodium ferrous sulfate positive electrode material. By limiting the type of the seed crystal to sodium iron pyrophosphate, the present application can effectively improve the compaction density and capacity of the sodium ferrous sulfate positive electrode material compared to other existing seed crystals (such as Na3V2(PO4)3 in Comparative Example 7).
[0087] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration and exerting the same effects as the technical idea within the scope of the technical solutions of the present application are all included in the technical scope of the present application. Furthermore, within the scope of the gist of the present application, various modifications that can be thought of by those skilled in the art, other modes constructed by combining part of the configuration elements of the embodiments are also included in the scope of the present application.
Claims
1. A method for preparing a sodium ferrous sulfate positive electrode material, characterized in that: The steps include: preparing a mixed slurry containing an antioxidant, seed crystals, an iron source, a sodium source, and a carbon source, wherein the seed crystals are sodium ferric pyrophosphate; Drying the mixed slurry to obtain a precursor; The precursor is sintered to obtain a sodium ferrous sulfate positive electrode material.
2. The method for preparing the sodium ferrous sulfate cathode material according to claim 1, wherein: The mass of the seed crystal is 2% to 8% of the theoretical mass of sodium ferrous sulfate.
3. The method for preparing the sodium ferrous sulfate positive electrode material according to claim 1, wherein: The compacted density of the seed crystal is ≥1.95 g / cm 3 .
4. The method for preparing the sodium ferrous sulfate positive electrode material according to claim 1, wherein: The median particle size of the seed crystal is 0.5-7 μm.
5. The method for preparing the sodium ferrous sulfate positive electrode material according to claim 1, wherein: The molar ratio of the iron element in the iron source to the sodium element in the sodium source is 1:(1-2); and / or, The weight of the antioxidant accounts for 3% to 5% of the weight of the iron source; and / or, The mass of the carbon source accounts for 2% to 4% of the total mass of the iron source and the sodium source; and / or, The iron source includes at least one of ferrous sulfate heptahydrate, ferrous sulfate monohydrate, and anhydrous ferrous sulfate; and / or, The sodium source includes at least one of anhydrous sodium sulfate and sodium bisulfate; and / or, The carbon source includes at least one of graphene oxide, carbon nanotubes, and Ketjen black; and / or, The antioxidant includes at least one of vitamin C, vitamin E, tea polyphenols and grape polyphenols.
6. The method for preparing the sodium ferrous sulfate positive electrode material according to claim 1, wherein: The drying method is spray drying; the inlet air temperature of the spray drying is 200-260°C, and the outlet air temperature is 80-100°C.
7. The method for preparing the sodium ferrous sulfate positive electrode material according to claim 1, wherein: The sintering process includes: heating to 350-450° C. and keeping the temperature for 4-8 hours.
8. A sodium ferrous sulfate positive electrode material, characterized in that Prepared by the preparation method according to any one of claims 1-7; the sodium ferrous sulfate positive electrode material has a core-shell structure, including a core and a shell layer coated on the outer surface of the core; the material of the core includes sodium ferrous pyrophosphate, and the material of the shell includes sodium ferrous sulfate.
9. A positive electrode plate, characterized in that: The invention comprises a sodium ferrous sulfate positive electrode material prepared by the preparation method according to any one of claims 1 to 7 or a sodium ferrous sulfate positive electrode material according to claim 8.
10. A secondary battery, characterized in that: Including the positive electrode sheet according to claim 9.