Sodium battery positive electrode material and preparation method and application thereof

Abstract

The application relates to a sodium battery positive electrode material and a preparation method and application thereof, the sodium battery positive electrode material comprising a base material and a carbon layer coated on the surface of the base material; the chemical formula of the base material is Na 2+2x Fe 2‑x M3, wherein M is a polyanion, 0<=x<2; the sodium battery positive electrode material comprises a first sodium battery positive electrode material and a second sodium battery positive electrode material, the carbon layer on the surface of the base material in the first sodium battery positive electrode material is fully coated, the carbon layer on the surface of the base material in the second sodium battery positive electrode material is partially coated, and the form of the partially coated carbon layer comprises a dot shape and / or a sheet shape. The sodium battery positive electrode material provided by the application coats a carbon layer on the surface of a base material, regulates the form and morphology of the carbon coating, improves the conductivity of the sodium battery positive electrode material, and promotes the transmission of sodium ions in the material, so that the sodium battery positive electrode material has excellent capacity performance and cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemistry, in particular to a sodium battery cathode material and a preparation method and application thereof. BACKGROUND

[0002] The development of sodium battery cathode materials is imperative, and the main routes are layered oxides, prussian white and polyanionic materials. Among them, polyanionic materials have attracted much attention due to their structural stability, high working voltage, good safety performance, high cycle stability and high specific capacity. Among the many polyanionic materials, iron-based polyanionic materials have rich resources. Due to the reversible redox couple of Fe 3+ / Fe 2+ , the strong electronegativity and induction effect of polyanion, and the advantages of low production cost and high working voltage, it is considered to be a potential sodium ion battery cathode material.

[0003] CN112510198A discloses a cathode active material, an aqueous solution sodium ion battery and an electronic device. The chemical formula of the cathode active material is Na x Fe y (PO4) m (Y) n , wherein Y is one of F - , OH - , O 2- , N 3- , P2O7 4- , SO4 2- , NO3 - , CO3 2- , C2O4 2- , 1≤x≤4, 1≤y≤3, 1≤m≤3, 1≤n≤4; the iron-based mixed polyanionic sodium intercalation compound has low cost, better capacity and cycle stability compared with existing transition metal oxides, prussian blue compounds and vanadium-based polyanionic compound cathode materials, and does not contain CN - or V harmful ions, and will not affect the environment. However, the polyanionic material itself has poor conductivity, which will cause the electrochemical performance of the sodium battery cathode material to deteriorate, and often needs to be carbon-coated to obtain a material with excellent electrochemical performance.

[0004] The solid-phase ball milling method is usually used to prepare the iron-based sodium electric positive electrode material, that is, a carbon source, an iron source and a sodium source are mixed, then the materials are uniformly mixed through ball milling, and then the iron-based sodium electric positive electrode material can be obtained by sintering. However, the mixing uniformity of the materials is not good, which leads to the fact that the sample cannot effectively play the performance. Although the wet ball milling method can improve the mixing uniformity of the materials to a certain extent, there is still a large composition segregation problem, and the performance of the sample is improved to a limited extent. In addition, the wet ball milling method greatly increases the experimental steps and leads to an increase in cost. The spray drying method can effectively solve the problem of uneven dispersion of the sodium source and the iron source, but there is still a problem of uneven dispersion of the conductive carbon. In addition, the spray drying method has high production cost and low efficiency, and is not suitable for large-scale industrial production. Therefore, although the performance of the sodium ferrosulfate prepared by the spray drying method is improved to a certain extent, the spray drying method is still not the best choice. In addition, there are preparation methods such as hot solvent method, anti-solvent method and freeze-drying method, but these methods are too complex and are not suitable for large-scale production process. In addition, the carbon coating effect of the iron-based sodium electric positive electrode material obtained by the above preparation methods is poor, which affects the conductivity of the obtained sodium electric positive electrode material and the transmission of sodium ions in the positive electrode material.

[0005] Therefore, it is an urgent problem to be solved to provide a sodium electric positive electrode material with excellent performance. SUMMARY

[0006] To solve the above technical problems, the purpose of the present application is to provide a sodium electric positive electrode material, a preparation method and application thereof. The sodium electric positive electrode material provided by the present application is coated with a carbon layer on the surface of the base material, which improves the stability and conductivity of the material. Further, by regulating the form of carbon coating, the partial coating and full coating of the carbon layer on the surface of the base material are cooperated, and the specific morphology of the partial carbon coating is combined, the conductivity of the sodium electric positive electrode material is improved, and the transmission of sodium ions in the material is improved, so that the sodium electric positive electrode material can have the advantages of excellent capacity performance and stable cycle performance.

[0007] To achieve this purpose, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a sodium electric positive electrode material, which comprises a base material and a carbon layer coated on the surface of the base material.

[0009] The chemical formula of the base material is Na 2+2x Fe 2-x M3, wherein M is a polyanion, and 0≤x<2.

[0010] The sodium electric positive electrode material includes a first sodium electric positive electrode material and a second sodium electric positive electrode material, the carbon layer on the surface of the matrix material in the first sodium electric positive electrode material is fully coated, the carbon layer on the surface of the matrix material in the second sodium electric positive electrode material is partially coated, and the partially coated carbon layer includes a dot-shaped and / or sheet-shaped form.

[0011] The sodium electric positive electrode material provided by the application is coated with a carbon layer on the surface of the matrix material, reduces the contact of the matrix material with air, can improve the stability of the sodium electric positive electrode material, and can improve the conductivity of the material, making up for the defect of poor conductivity of the polyanion positive electrode material itself, thereby improving the electrochemical performance of the sodium electric positive electrode material. The application also regulates the carbon coating on the surface of the matrix material to exist in two forms of full coating and partial coating, which synergize with each other to improve the conductivity of sodium ferrous sulfate while the matrix material in the sodium electric positive electrode material can be directly contacted with electrolyte in the subsequent application process due to the existence of the partially coated sodium electric positive electrode material, reducing the hindering effect on the diffusion of sodium ions and ensuring that the sodium electric positive electrode material can exert the corresponding capacity, thereby improving the capacity performance and cycle performance of the sodium electric positive electrode material. Secondly, the form of the partially coated carbon layer in the sodium electric positive electrode material is regulated to be dot-shaped and / or sheet-shaped, the dot-shaped carbon coating has little hindrance to the transmission of sodium ions, which is beneficial to the deintercalation of sodium ions in the sodium electric positive electrode material, thereby improving the capacity performance of the battery material, and the sheet-shaped carbon coating is beneficial to the conduction of electrons due to the face contact between the base material and carbon. Further, through the matching of the dot-shaped and sheet-shaped carbon coating morphology, the obtained sodium electric positive electrode material has good electronic conduction effect while ensuring the effective transmission of sodium ions, thereby improving the comprehensive electrochemical performance of the sodium electric positive electrode material.

[0012] The sodium electric positive electrode material provided by the application is coated with a carbon layer on the surface of the matrix material, can improve the stability of the sodium electric positive electrode material and improve the conductivity of the material itself, further regulates the form of the carbon coating, synergizes the partial carbon coating and the full carbon coating on the matrix material, further regulates the specific form of the partial coating to be sheet-shaped and / or dot-shaped, can ensure that the sodium electric positive electrode material has excellent conductivity and stability, and can also promote the effective transmission of sodium ions in the material, improve the deintercalation of sodium ions in the material, thereby enabling the sodium electric positive electrode material to have multiple advantages of excellent capacity performance and stable cycle performance.

[0013] Preferably, the M includes a sulfate anion.

[0014] Preferably, the mass percentage of the carbon layer coated on the surface of the base material is 0.1-20wt%, for example 0.1wt%, 0.5wt%, 1wt%, 2wt%, 4wt%, 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, 18wt% or 20wt%, based on 100wt% of the total mass of the sodium electrode positive material.

[0015] Preferably, in the sodium electrode positive material, the mass ratio of the first sodium electrode positive material to the second sodium electrode positive material is (5-50):(50-95), for example 5:95, 10:90, 20:80, 30:70, 40:60 or 50:50, etc.

[0016] Preferably, the thickness of the carbon layer in the first sodium electrode positive material and the carbon layer in the second sodium electrode positive material is independently selected from 1-50nm, for example 1nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm or 50nm, etc.

[0017] The sodium electrode positive material of the present application regulates the thickness of the carbon layer within a reasonable range, which can ensure effective coating of the base material to ensure the improvement effect on the conductivity of the base material, while avoiding the influence of the over-thick carbon layer on the sodium ion de-intercalation in the positive electrode material, thereby causing the performance of the sodium electrode positive material to deteriorate.

[0018] Preferably, the first sodium electrode positive material is a core-shell structure.

[0019] Preferably, the second sodium electrode positive material includes any one or a combination of at least two of the positive electrode material with a carbon layer coating morphology of a point shape, the positive electrode material with a carbon layer coating morphology of a sheet shape, or the positive electrode material with a carbon layer coating morphology of a point shape and a sheet shape.

[0020] The different kinds of second sodium electrode positive materials in the present application can be matched in any ratio.

[0021] Preferably, when the morphology of the partial coating of the carbon layer is a point shape, the diameter of the carbon layer is 1-100nm, and does not include 100nm, for example 1nm, 5nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 99nm, etc.; the gap distance between the carbon layers is 1-200nm, for example 1nm, 5nm, 10nm, 20nm, 40nm, 60nm, 80nm, 100nm, 120nm, 140nm, 160nm, 180nm or 200nm, etc.

[0022] Preferably, when the partially coated morphology of the carbon layer is in the form of a sheet, the diameter of the carbon layer is 100-500 nm, and the gap distance between the carbon layers is 1-200 nm, such as 1 nm, 5 nm, 10 nm, 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, or 200 nm, etc.

[0023] Preferably, when the partially coated morphology of the carbon layer is in the form of a sheet, the diameter of the carbon layer is 100-500 nm, and the gap distance between the carbon layers is 1-200 nm, such as 1 nm, 5 nm, 10 nm, 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, or 200 nm, etc.

[0024] Preferably, when the partially coated morphology of the carbon layer is in the form of a sheet, the diameter of the carbon layer is 100-500 nm, and the gap distance between the carbon layers is 1-200 nm, such as 1 nm, 5 nm, 10 nm, 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, or 200 nm, etc.

[0025] In the present application, the "gap distance between the carbon layers" refers to the distance between the partially coated carbon layers on the surface of the base material, which can be specifically referred to as Figure 1 , wherein d represents the gap region between the carbon layers, 1 is the surface of the base material, and 2 is the carbon layer.

[0026] Preferably, the compaction density of the sodium battery positive electrode material under 3T pressure is 1.8-2.36 g / cm 3 , such as 1.8 g / cm 3 , 1.85 g / cm 3 , 1.9 g / cm 3 , 1.95 g / cm 3 , 2.0 g / cm 3 , 2.05 g / cm 3 , 2.1 g / cm 3 , 2.15 g / cm 3 , 2.2 g / cm 3 , 2.25 g / cm 3 , 2.3 g / cm 3 , or 2.36 g / cm 3 , etc.

[0027] Preferably, the specific surface area of the sodium battery positive electrode material is 5-30 m2 / g, for example 5 m 2 / g, 6 m 2 / g, 8 m 2 / g, 10 m 2 / g, 12 m 2 / g, 14 m 2 / g, 16 m 2 / g, 18 m 2 / g, 20 m 2 / g, 22 m 2 / g, 24 m 2 / g, 26 m 2 / g, 28 m 2 / g, or 30 m 2 / g, etc.

[0028] In the present application, the tap density and the specific surface area of the sodium cathode material refer to the properties of the whole sodium cathode material.

[0029] Preferably, the sodium cathode material further comprises free carbon.

[0030] Preferably, the total content of carbon in the sodium cathode material is 100 wt%, and the content of carbon coated on the surface of the base material is 10-99 wt%, for example 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, 95 wt%, or 99 wt%, etc.

[0031] Preferably, the total content of carbon in the sodium cathode material is 100 wt%, and the content of carbon coated on the surface of the base material is 10-99 wt%, for example 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt%, 90 wt%, 95 wt%, or 99 wt%, etc.

[0032] Preferably, the sodium cathode material comprises primary particles and secondary particles.

[0033] It should be noted that, on the basis of meeting the sodium cathode material being divided into the first sodium cathode material (the carbon layer on the surface of the base material being fully coated) and the second sodium cathode material (the carbon layer on the surface of the base material being partially coated), the specific form of the sodium cathode material of the primary particles and the secondary particles is not specifically limited, including but not limited to the first sodium cathode material and / or the second sodium cathode material, and a person skilled in the art can select as needed.

[0034] Preferably, the size of the primary particles is 0.001-1 μm, for example 0.001 μm, 0.005 μm, 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, or 1 μm, etc.

[0035] Preferably, the size of the secondary particles is 0.01-100 μm, such as 0.01 μm, 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm, etc.

[0036] There are mainly three forms of the secondary particles in the present application: one is the secondary particles formed by agglomeration of at least two primary particles, the mass of the secondary particles formed by agglomeration of the primary particles accounting for 5-50 wt% of the total mass of all the secondary particles; two is the secondary particles formed by carbon connection, the secondary particles formed by carbon connection accounting for 5-30 wt% of the total mass of all the secondary particles; three is the secondary particles formed by both agglomeration of particles and carbon connection of particles, the mass of the secondary particles formed by both agglomeration of particles and carbon connection of particles accounting for 10-90 wt% of all the secondary particles.

[0037] Preferably, the content of the primary particles is 5-90 wt% based on the total content of the total particles of the sodium battery cathode material, such as 5 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt%, 80 wt% or 90 wt%, etc.

[0038] Preferably, the content of the secondary particles is 1-80 wt% based on the total content of the total particles of the sodium battery cathode material, such as 1 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt% or 80 wt%, etc.

[0039] In a second aspect, the present application provides a preparation method of the sodium battery cathode material according to the first aspect, the preparation method comprising the following steps:

[0040] (1) primary solid-phase mixing of a first raw material and an organic carbon source, sintering to obtain an intermediate with in-situ carbon coating; the first raw material provides sodium ions and polyanions;

[0041] (2) secondary solid-phase mixing of the intermediate with in-situ carbon coating and a second raw material and an antioxidant to obtain a precursor material; the second raw material provides ferrous ions and polyanions;

[0042] (3) pressing and sintering of the precursor material to obtain the sodium battery cathode material.

[0043] In the present application, the first raw material is used to provide sodium ions and polyanions, wherein one raw material containing both sodium ions and polyanions can be selected, and two raw materials containing sodium ions and polyanions respectively can be selected.

[0044] In the present application, the second raw material is used to provide ferrous ions and polyanions, wherein one raw material containing both ferrous ions and polyanions can be selected, and two raw materials containing ferrous ions and polyanions respectively can be selected.

[0045] The preparation method provided in the present application combines the processes of one-time solid-phase mixing-sintering-two-time solid-phase mixing-pressing sintering, can control the form and morphology of carbon coating in the sodium battery positive electrode material, ensure the coexistence of full coating and partial coating of carbon, and control the morphology of partial carbon coating, improve the conductivity of the sodium battery positive electrode material, and is conducive to improving the deintercalation of sodium ions in the sodium battery positive electrode material, thereby improving the performance of the sodium battery positive electrode material.

[0046] Further, the preparation method designed by the present application can greatly improve the production efficiency of the positive electrode material and reduce the production cost, and is more suitable for the needs of actual production. Specifically, first, the present application adopts a solid-phase mixing process of organic carbon source and first raw material, and then combines with a sintering process to obtain an intermediate with in-situ carbon coating, which can control the carbon coating morphology, improve the tightness and uniformity of the carbon material coating, ensure sufficient graphitization of the carbon material, thereby improving the conductivity of the positive electrode material. The solid-phase mixing process replaces the wet mixing process of the prior art, further optimizes the process operation, reduces the production cost, and eliminates the drying process required after the wet mixing process. The drying process (especially spray drying) has a significant impact on the organic carbon source during the mixing process. At the same time, the solid-phase mixing process combined with the selection of low-cost organic carbon source can effectively reduce the production cost and greatly improve the production efficiency, so that the carbon layer on the surface of the intermediate with in-situ carbon coating is coated with a specific morphology, and the contact between the sodium-containing compound inside the carbon coating and the moisture in the operating environment is prevented, thereby reducing the humidity sensitivity of the raw material and improving the cycle stability of the material. Secondly, the intermediate with in-situ carbon coating and the second raw material are subjected to secondary solid-phase mixing to improve the uniformity of the intermediate with in-situ carbon coating and the second raw material, and the addition of the antioxidant can inhibit the oxidation during the mixing process of the raw material, thereby improving the stability of the material. Thirdly, the precursor material obtained by mixing is subjected to a process combining pressing and sintering, which can not only control the form and morphology of the carbon coating of the obtained sodium battery positive electrode material, but also ensure the sufficient contact and reaction between the intermediate with in-situ carbon coating and the second raw material, thereby reducing the atomic diffusion barrier in the precursor material and improving the yield and product consistency of the obtained sodium battery positive electrode material, thereby improving the performance of the sodium battery positive electrode material. In addition, the pressing and sintering process can also improve the bonding degree of the precursor particles and effectively reduce the specific surface area of the carbon-coated positive electrode material and improve the compaction density of the obtained material.

[0047] Preferably, the first raw material of step (1) comprises sodium sulfate.

[0048] Preferably, the sodium sulfate comprises any one of anhydrous sodium sulfate or monohydrate sodium sulfate.

[0049] Preferably, the first raw material of step (1) is further subjected to pretreatment before the solid-phase mixing.

[0050] Preferably, the specific process of pretreatment of the first raw material comprises: after the first drying of the first raw material, the first raw material is subjected to first crushing to obtain the pretreated first raw material.

[0051] The present application carries out a pretreatment process of drying and crushing the first raw material, reduces the water content in the first raw material through drying, thereby reducing the water content in the obtained positive electrode material, and further improving the stability of the obtained sodium battery positive electrode material; and the crushing process aims to reduce the particle size of the first raw material, thereby improving the reactivity of the first raw material and promoting the full reaction between the materials.

[0052] Preferably, the temperature of the first drying is 200-350℃, such as 200℃, 220℃, 240℃, 260℃, 280℃, 300℃, 320℃, 340℃ or 350℃, etc.

[0053] Preferably, the time of the first drying is 1-15h, such as 1h, 2h, 4h, 6h, 8h, 10h, 12h, 14h or 15h, etc.

[0054] Preferably, the particle size D50 of the first raw material after the first crushing is 1μm or less, such as 1μm, 0.9μm, 0.8μm, 0.7μm, 0.6μm or 0.5μm, etc.

[0055] In the present application, the mode of the first crushing is not specifically limited, including but not limited to mechanical ball milling or air jet milling, etc., which can be selected by those skilled in the art as needed.

[0056] Preferably, the first crushing is carried out in nitrogen and / or inert gas.

[0057] Preferably, the organic carbon source in step (1) includes any one or a combination of at least two of glucose, ascorbic acid, citric acid, tea polyphenol or starch.

[0058] Preferably, the mass ratio of the first raw material to the organic carbon source in step (1) is (50-95):(5-50), wherein the selection range of the first raw material is "50-95", such as 50, 55, 60, 65, 70, 75, 80, 85, 90 or 95, etc.; and the selection range of the organic carbon source is "5-50", such as 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50, etc.

[0059] The present application regulates the mass ratio of the first raw material and the organic carbon source in the first solid phase mixing process, which can ensure the effective coating of the first raw material, while controlling the amount of the added organic carbon source to avoid the thickness of the carbon layer coating being too thick, thereby hindering the mixing effect with the second raw material and affecting the electrochemical performance of the material.

[0060] Preferably, before the first solid phase mixing in step (1), the first raw material and the organic carbon source are further subjected to first premixing.

[0061] In the present application, the way of the first solid phase mixing is not specifically limited, including but not limited to jet mill, rolling ball mill, planetary ball mill or vibration ball mill, etc., which can be selected by those skilled in the art as needed.

[0062] Preferably, the sintering temperature in step (1) is 500-800℃, such as 500℃, 550℃, 600℃, 650℃, 700℃, 750℃ or 800℃, etc.

[0063] The present application controls the sintering temperature, in-situ coats the first raw material with carbon at high temperature, avoids the decomposition of the first raw material, and improves the graphitization degree of the organic carbon material, thereby ensuring the full graphitization of the carbon material and improving the conductivity of the obtained sodium-based positive electrode material. The present application adopts high-temperature sintering in the mixing process of the first raw material and the organic carbon source, obtains an intermediate with in-situ carbon coating, and then mixes with the second raw material. Compared with the common mixing process of sodium source, carbon source and iron source in the prior art, the present application can ensure the full graphitization of the carbon material while avoiding the decomposition of the iron-based sodium-based positive electrode material during high-temperature sintering, thereby improving the product consistency of the obtained sodium-based positive electrode material.

[0064] Preferably, the sintering time in step (1) is 4-10h, such as 4h, 5h, 6h, 7h, 8h, 9h or 10h, etc.

[0065] Preferably, the sintering atmosphere in step (1) is nitrogen atmosphere and / or inert atmosphere.

[0066] Preferably, the second raw material in step (2) includes ferrous sulfate.

[0067] Preferably, the ferrous sulfate includes anhydrous ferrous sulfate and / or a hydrate of ferrous sulfate.

[0068] Preferably, the hydrate of ferrous sulfate includes any one of ferrous sulfate heptahydrate, ferrous sulfate tetrahydrate or ferrous sulfate monohydrate.

[0069] Preferably, the second raw material in step (2) is further pretreated before the second solid phase mixing.

[0070] Preferably, the specific process of the pretreatment of the second raw material includes: after the second drying of the second raw material, the second raw material is crushed to obtain the pretreated second raw material.

[0071] The present application pretreats the second raw material by drying and crushing before the second solid phase mixing, reduces the water content of the positive electrode material through the drying process, thereby improving the stability of the obtained positive electrode material, and reduces the particle size of the second raw material through the crushing process, thereby improving the reactivity of the second raw material and promoting the full reaction between the materials.

[0072] Preferably, the temperature of the second drying is 200-350℃, such as 200℃, 220℃, 240℃, 260℃, 280℃, 300℃, 320℃, 340℃ or 350℃, etc.

[0073] Preferably, the time of the second drying is 1-15h, such as 1h, 2h, 4h, 6h, 8h, 10h, 12h, 14h or 15h, etc.

[0074] Preferably, the particle size D50 of the second raw material after the second crushing is 1μm or less, such as 1μm, 0.9μm, 0.8μm, 0.7μm, 0.6μm or 0.5μm, etc.

[0075] Preferably, the second crushing is carried out in nitrogen and / or inert gas.

[0076] In the present application, the mode of the first crushing is not specifically limited, including but not limited to mechanical ball milling or jet milling, etc., which can be selected as needed by those skilled in the art.

[0077] Preferably, the molar ratio of the intermediate with in-situ carbon coating to the second raw material in step (2) is 1:(1-2), such as 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2, etc.

[0078] The present application provides the mass ratio of the intermediate with in-situ carbon coating to the second raw material, aiming to obtain sodium ferrous sulfate with different sodium-iron ratios and screen out sodium ferrous sulfate with better capacity and stability.

[0079] Preferably, the amount of the antioxidant added is 0.01-10wt% of the mass of the second raw material, such as 0.01wt%, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%, etc.

[0080] The present application regulates the amount of antioxidant added, aiming to ensure that the material is not oxidized while reducing the carbon content, improving the compaction density of the obtained sodium cathode material and reducing its specific surface area.

[0081] Preferably, the antioxidant includes any one or a combination of at least two of ascorbic acid, citric acid or tea polyphenol.

[0082] Preferably, before the secondary solid-phase mixing in step (2), the intermediate with in-situ carbon coating, the second raw material and the antioxidant are subjected to a second premixing.

[0083] In the present application, the secondary solid-phase mixing method is not specifically limited, including but not limited to airflow milling, rolling ball milling, planetary ball milling or vibration ball milling, etc., which can be selected by those skilled in the art as needed.

[0084] Preferably, the specific process of the pressing and sintering in step (3) includes: pressing the precursor material first and then sintering, or pressing and sintering the precursor material simultaneously.

[0085] In the present application, the pressing and sintering of the precursor material simultaneously means that the hot-pressing sintering process is performed on the precursor material.

[0086] Preferably, the pressure of the pressing is 50-500 MPa, such as 50 MPa, 100 MPa, 150 MPa, 200 MPa, 250 MPa, 300 MPa, 350 MPa, 400 MPa, 450 MPa or 500 MPa, etc.

[0087] The present application regulates the pressure of the pressing of the precursor material, on the one hand, to improve the bonding degree of the precursor particles, reduce the specific surface area of the obtained positive electrode material, improve the compaction density of the material, and reduce the atomic diffusion potential barrier of the precursor material, thereby improving the yield and product consistency of the positive electrode material, and on the other hand, to avoid excessive pressing pressure, thereby causing excessive hardness of the material and bringing difficulties to subsequent crushing, thereby affecting the performance of the sodium battery positive electrode material. In addition, the regulation of the pressing pressure is also beneficial to the preparation of the positive electrode material in both partial carbon-coated and full carbon-coated forms.

[0088] Preferably, the temperature of the sintering is 280-380℃, such as 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃ or 380℃, etc.

[0089] The present application regulates the temperature of the sintering of the precursor material, successfully preparing the sodium battery positive electrode material with better product consistency, while avoiding decomposition of the obtained sodium ferrous sulfate matrix material due to excessive temperature, thereby affecting the yield and purity of the sodium battery positive electrode material.

[0090] Preferably, when the precursor material is pressed first and then sintered, the pressing time is 1-10 min, such as 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min or 10 min, etc.; and the sintering time is 15-25 h, such as 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h, 24 h or 25 h, etc.

[0091] Preferably, when the pressing and sintering are simultaneously performed on the precursor material, the pressing and sintering are simultaneously performed for 10-15 h, such as 10 h, 11 h, 12 h, 13 h, 14 h, or 15 h, etc.

[0092] Preferably, the product obtained after the pressing and sintering in step (3) is further subjected to crushing and sieving.

[0093] As a preferred technical solution of the present application, the preparation method of the sodium battery cathode material comprises the following steps:

[0094] S1. The first raw material is subjected to first drying at 200-350℃ for 1-15 h, and then the product after the first drying is subjected to first crushing under the protection of nitrogen and / or inert gas, the particle size D50 of the first raw material after the first crushing is below 1 μm, to obtain pretreated first raw material;

[0095] The second raw material is subjected to second drying at 200-350℃ for 1-15 h, and then the product after the second drying is subjected to second crushing under the protection of nitrogen and / or inert gas, the particle size D50 of the second raw material after the second crushing is below 1 μm, to obtain pretreated second raw material;

[0096] S2. The pretreated first raw material and the organic carbon source are first subjected to first premixing according to the mass ratio of (50-95):(5-50), and then subjected to one-time solid-phase mixing, and then subjected to sintering at 500-800℃ for 4-10 h under the atmosphere of nitrogen and / or inert gas, to obtain an intermediate with in-situ carbon coating;

[0097] S3. The intermediate with in-situ carbon coating and the pretreated second raw material, antioxidant are first subjected to second premixing, and then subjected to two-time solid-phase mixing, the molar ratio of the intermediate with in-situ carbon coating to the pretreated second raw material is 1:(1-2), and the addition amount of the antioxidant is 0.01-10 wt% of the mass of the second raw material, to obtain a precursor material;

[0098] S4. The precursor material is subjected to pressing and sintering at a pressing pressure of 50-500 MPa and a sintering temperature of 280-380℃, the specific process of the pressing and sintering comprises: the precursor material is first subjected to pressing for 1-10 min and then subjected to sintering for 15-25 h, or the precursor material is simultaneously subjected to pressing and sintering process for 10-15 h, and then the product obtained after the pressing and sintering is subjected to crushing and sieving, to obtain the sodium battery cathode material.

[0099] In a third aspect, the present application provides a positive electrode sheet, wherein the positive electrode sheet comprises the sodium battery positive electrode material according to the first aspect, or the sodium battery positive electrode material prepared by the preparation method according to the second aspect.

[0100] In a fourth aspect, the present application provides a sodium ion battery, wherein the sodium ion battery comprises the positive electrode sheet according to the third aspect.

[0101] The sodium ion battery comprising the sodium battery positive electrode material with excellent performance has excellent cycle stability and good rate performance.

[0102] Compared with the prior art, the present application has at least the following beneficial effects:

[0103] (1) The sodium battery positive electrode material provided by the present application is coated with a carbon layer on the surface of the base material, which can improve the stability of the sodium battery positive electrode material and improve the electrical conductivity of the material itself. By further regulating the form of carbon coating, the mutual coordination of partial carbon coating and full carbon coating on the base material, and the specific morphology of partial coating in the form of flakes and / or dots, the sodium battery positive electrode material can have excellent electrical conductivity and stability, and can also promote the effective transmission of sodium ions in the material, improve the deintercalation of sodium ions in the material, thereby enabling the sodium battery positive electrode material to have multiple advantages such as excellent capacity performance and stable cycle performance.

[0104] (2) The present application designs the mixing order and mixing process of raw materials in combination with the sintering process. On the one hand, the carbon coating form and morphology of the sodium battery positive electrode material can be regulated to ensure that the obtained sodium battery positive electrode material has both full carbon coating and partial carbon coating, and the morphology of partial carbon coating is regulated to improve the electrical conductivity of the sodium battery positive electrode material and facilitate the deintercalation of sodium ions in the sodium battery positive electrode material. On the other hand, the designed preparation process first sintered the first raw material and the organic carbon source after one-time solid-phase mixing to obtain an intermediate with in-situ carbon coating, regulate the carbon coating morphology, and reduce the humidity sensitivity of the intermediate to ensure the full graphitization of carbon. Then, the intermediate with in-situ carbon coating, the second raw material and the antioxidant are subjected to two-time solid-phase mixing, pressing and sintering process to regulate the form and morphology of the carbon coating of the obtained sodium battery positive electrode material, improve the full reaction of the intermediate with in-situ carbon coating and the second raw material, reduce the specific surface area of the obtained positive electrode material and improve the compaction density of the material, thereby obtaining a sodium battery positive electrode material with excellent performance. In addition, the preparation method designed by the present application can greatly improve the production efficiency of the sodium battery positive electrode material, reduce the production cost, and be more suitable for the needs of actual production. BRIEF DESCRIPTION OF DRAWINGS

[0105] Figure 1 is a schematic diagram of the gap distance between the carbon layers in the present application.

[0106] Wherein, 1, surface of the matrix material; 2, carbon layer; d, gap distance between carbon layers.

[0107] Figure 2 is a scanning electron microscope image of the in-situ carbon-coated sodium sulfate prepared in Example 1.

[0108] Figure 3 is Figure 2 is an energy dispersive X-ray spectrum of the carbon element corresponding to the scanning electron microscope image.

[0109] Figure 4 is an X-ray diffraction pattern of the sodium battery positive electrode material prepared in Example 1.

[0110] Figure 5 is a scanning electron microscope image of the sodium battery positive electrode material prepared in Example 1 at a low magnification.

[0111] Figure 6 is Figure 5 is an energy dispersive X-ray spectrum of the carbon element corresponding to the scanning electron microscope image.

[0112] Figure 7 is a scanning electron microscope image of the sodium battery positive electrode material prepared in Example 1 at a high magnification.

[0113] Figure 8 is a charge-discharge curve of the sodium ion battery provided in Application Example 1 and Application Examples 4-7 at 0.1C.

[0114] Figure 9 is a charge-discharge curve of the sodium ion battery provided in Application Example 1 and Application Examples 8-9 at 0.1C.

[0115] Figure 10 is a charge-discharge curve of the sodium ion battery provided in Application Example 1 and Application Example 14 at 0.1C.

[0116] Figure 11 is a charge-discharge curve of the sodium ion battery provided in Application Example 1, Application Example 22 and Comparative Application Example 1 at 0.1C. DETAILED DESCRIPTION

[0117] The technical solutions of the present application will be further described below in combination with the drawings and through specific embodiments. However, the following examples are only simple examples of the present application, and do not represent or limit the protection scope of the present application, and the protection scope of the present application is subject to the claims.

[0118] The following examples relate to the gap distance between carbon layers, the schematic diagram of which is as shown in Figure 1As shown, the gap distance d between the carbon layers specifically refers to the distance between the partially coated carbon layer 2 on the surface 1 of the base material and the partially coated carbon layer 2.

[0119] The following examples relate to the morphology of sodium electric positive electrode materials and parameters related to the size of the morphology thereof are obtained by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), wherein the carbon layer thickness is obtained from the cross-sectional scanning electron microscopy image of the obtained sodium electric positive electrode material; the diameters of the point-like and sheet-like carbon layers and the gap distance are determined by SEM combined with EDS, the edges of the point-like and sheet-like carbon layers coated on the surface of the base material in the sodium electric positive electrode material are determined, and the diameters are directly measured and statistically obtained; the sizes of the primary particles and the secondary particles are directly measured and statistically obtained by SEM.

[0120] The following examples use a pressing mold which is a cylinder with a diameter of 60 cm, a wall thickness of 10 cm, and a height of 40 cm.

[0121] Example 1

[0122] The present example provides a preparation method of a carbon-coated sodium ferrous sulfate positive electrode material, comprising the following steps:

[0123] S1. Anhydrous sodium sulfate is placed at 200°C for 10h of first drying, and then the anhydrous sodium sulfate after the first drying is broken by a nitrogen gas flow with a gas flow pressure of 1.5MPa for 10min to a particle size D50 of 0.8μm of the anhydrous sodium sulfate, to obtain pretreated sodium sulfate for standby.

[0124] The ferrous sulfate heptahydrate is placed at 350°C for 10h of second drying to obtain anhydrous ferrous sulfate, and then the obtained anhydrous ferrous sulfate is broken by a nitrogen gas flow with a gas flow pressure of 1.5MPa for 10min to a particle size D50 of 0.8μm of the anhydrous ferrous sulfate, to obtain pretreated ferrous sulfate for standby.

[0125] S2. 4000g of the pretreated sodium sulfate obtained in step S1 is premixed with 1000g of glucose under a high-speed mixer, followed by stirring ball milling at a speed of 400rpm for 6h, and then the product after stirring ball milling is sintered at 600°C for 8h, the sintering being carried out under a nitrogen atmosphere, to obtain in-situ carbon-coated sodium sulfate.

[0126] S3. 2085g of the in-situ carbon-coated sodium sulfate obtained in step S2 is premixed with 3028g of the pretreated ferrous sulfate obtained in step S1 and 152g of ascorbic acid in a high-speed mixer, followed by planetary ball milling at a speed of 500rpm for 6h, to obtain a precursor material.

[0127] S4. The precursor material obtained in step S3 is loaded into a hot-pressing mold, the material is placed in a hot-pressing furnace together with the mold, the pressure is increased to 100 MPa, and the temperature is increased to 350℃, and the precursor material is hot-pressed and sintered for 12 h, and then cooled to 150℃, and the material is taken out, and then the material is crushed and sieved through a 325 mesh screen to obtain the sodium battery positive electrode material.

[0128] The sodium battery positive electrode material obtained by the preparation method provided in the embodiment includes carbon-coated sodium ferrous sulfate, and has a chemical formula of Na 2.56 Fe 1.72 (SO4)3@C, the mass of the carbon layer coated on the surface of the base material is 5wt%, the sodium battery positive electrode material includes positive electrode material with the carbon layer coated on the entire surface of sodium ferrous sulfate and positive electrode material with the carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 50nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 30nm; in the sodium battery positive electrode material, the mass ratio of the positive electrode material with the carbon layer coated on the entire surface of sodium ferrous sulfate to the positive electrode material with the carbon layer coated on part of the surface of sodium ferrous sulfate is 30:70; the positive electrode material with the carbon layer partially coated includes positive electrode material with all point-shaped carbon coating, positive electrode material with all flaky carbon coating, and positive electrode material with both point-shaped carbon coating and flaky carbon coating in any proportion, wherein the diameter of the carbon layer in the positive electrode material with only point-shaped carbon coating ranges from 1nm to 65nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 70nm, the diameter of the carbon layer in the positive electrode material with only flaky carbon coating ranges from 100nm to 300nm, the gap distance between the flaky carbon layers ranges from 1nm to 90nm, in the positive electrode material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 65nm, the diameter of the flaky carbon coating ranges from 100nm to 300nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1nm to 75nm; the sodium battery positive electrode material further includes free carbon, the total content of carbon in the sodium battery positive electrode material is 100wt%, the content of carbon for coating sodium ferrous sulfate is 95wt%, and the content of free carbon is 5wt%; the sodium battery positive electrode material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 600nm, the average size is 361nm, the size of the secondary particles ranges from 0.01μm to 50μm, the average size is 26μm, the content of the primary particles is 65wt% based on the total content of the total particles in the sodium battery positive electrode material, and the content of the secondary particles is 35wt%.

[0129] Embodiment 2

[0130] The embodiment provides a preparation method of a carbon-coated sodium ferrous sulfate positive electrode material, including the following steps:

[0131] S1. The sodium sulfate decahydrate was subjected to a first drying at 350℃ for 2h to obtain anhydrous sodium sulfite, and then the obtained anhydrous sodium sulfite was broken to a particle size D50 of 1μm under the protection of argon gas flow with an argon gas flow pressure of 1MPa for 10min to obtain pretreated sodium sulfate for standby.

[0132] The anhydrous ferrous sulfate was subjected to a second drying at 200℃ for 5h, and then the anhydrous ferrous sulfate after the second drying was broken to a particle size D50 of 1μm under the protection of argon gas flow with an argon gas flow pressure of 1MPa for 10min to obtain pretreated ferrous sulfate for standby.

[0133] S2. 4000g of the pretreated sodium sulfate obtained in step S1 was premixed with 1000g of starch under a high-speed mixer, followed by vibration ball milling at a rotation speed of 400rpm for 3h, and then the product after vibration ball milling was sintered at 500℃ for 10h under an argon atmosphere to obtain in-situ carbon-coated sodium sulfate.

[0134] S3. 2085g of the in-situ carbon-coated sodium sulfate obtained in step S2 was premixed with 2500g of the pretreated ferrous sulfate obtained in step S1 and 84g of citric acid under a high-speed mixer, followed by planetary ball milling at a rotation speed of 500rpm for 10h to obtain a precursor material.

[0135] S4. The precursor material obtained in step S3 was loaded into a hot-pressing mold, and the material was subjected to hot-pressing sintering at a pressure of 150MPa and a temperature of 300℃ for 15h in a hot-pressing furnace, and then the material was cooled to 120℃ and taken out, followed by breaking and sieving with a 325-mesh screen to obtain a sodium battery positive electrode material.

[0136] The sodium battery positive electrode material obtained by the preparation method described above in this embodiment comprises carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.6 Fe 1.7(SO4)3@C, the mass of the carbon layer coated on the surface of the base material is 6wt%, the sodium battery positive electrode material includes a positive electrode material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive electrode material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 48nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 35nm; in the sodium battery positive electrode material, the mass ratio of the positive electrode material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive electrode material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 29:71; the carbon layer partially coated positive electrode material includes a positive electrode material with all point-shaped carbon coating, a sodium battery positive electrode material with all sheet-shaped carbon coating, and a positive electrode material with both point-shaped carbon coating and sheet-shaped carbon coating in any proportion, wherein the diameter of the carbon layer in the positive electrode material with only point-shaped carbon coating ranges from 1nm to 70nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 65nm, the diameter of the carbon layer in the positive electrode material with only sheet-shaped carbon coating ranges from 100nm to 400nm, the gap distance between the sheet-shaped carbon layers ranges from 1nm to 80nm, in the positive electrode material with both point-shaped carbon coating and sheet-shaped carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 70nm, the diameter of the sheet-shaped carbon coating ranges from 100nm to 350nm, and the gap distance between the point-shaped carbon layer and the sheet-shaped carbon layer ranges from 1nm to 70nm; the sodium battery positive electrode material also includes free carbon, with the total content of carbon in the sodium battery positive electrode material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 94wt%, and the content of free carbon being 6wt%; the sodium battery positive electrode material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 550nm, the average size is 352nm, the size of the secondary particles ranges from 0.01μm to 70μm, the average size is 29μm, and with the total content of the total particles in the sodium battery positive electrode material being 100%, the content of the primary particles is 62wt%, and the content of the secondary particles is 38wt%.

[0137] Example 3

[0138] The present embodiment provides a preparation method of a carbon-coated sodium ferrous sulfate positive electrode material, including the following steps:

[0139] S1. Dry anhydrous sodium sulfate at 300℃ for 5h for first drying, then crush the first dried anhydrous sodium sulfate under nitrogen protection for 5min at a nitrogen gas flow pressure of 2MPa to obtain a particle size D50 of 0.6μm of the anhydrous sodium sulfate for standby after pretreatment.

[0140] The second drying of the ferrous sulfate tetrahydrate at 300℃ for 15h obtained anhydrous ferrous sulfate, then the obtained anhydrous ferrous sulfate was broken by nitrogen gas flow with a pressure of 2MPa for 5min to obtain a particle size D50 of 0.6μm, and the pretreated ferrous sulfate was obtained for standby.

[0141] S2. 4000g of the pretreated sodium sulfate obtained in step S1 was premixed with 1000g of tea polyphenol under a high-speed mixer, then the product after rolling ball milling was sintered at 800℃ for 5h, and the sintering was carried out under a nitrogen atmosphere to obtain in-situ carbon-coated sodium sulfate.

[0142] S3. 2085g of the in-situ carbon-coated sodium sulfate obtained in step S2 was premixed with 3800g of the pretreated ferrous sulfate obtained in step S1 and 308g of citric acid under a high-speed mixer, then the product was ball milled in a planetary ball mill at a speed of 600rpm for 5h to obtain a precursor material.

[0143] S4. The precursor material obtained in step S3 was loaded into a hot-pressing mold, and the material was placed in a hot-pressing furnace together with the mold, and the precursor material was hot-pressed and sintered at a pressure of 120MPa and a temperature of 360℃ for 10h, then the material was cooled to 100℃ and taken out, then the taken-out material was broken and sieved by a mesh size of 325 to obtain a sodium battery positive electrode material.

[0144] The sodium battery positive electrode material obtained by the preparation method in the embodiment includes carbon-coated ferrous sodium sulfate, and the chemical formula is Na 2.5 Fe 1.75(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 4wt% based on the total mass of the sodium battery cathode material being 100wt%, the sodium battery cathode material includes a cathode material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a cathode material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 40nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 25nm; in the sodium battery cathode material, the mass ratio of the cathode material with the carbon layer completely coated on sodium ferrous sulfate to the cathode material with the carbon layer partially coated on sodium ferrous sulfate is 20:80; the cathode material with the carbon layer partially coated includes a cathode material with all point-shaped carbon coating, a sodium battery cathode material with all flaky carbon coating, and a cathode material with both point-shaped carbon coating and flaky carbon coating in any proportion, wherein the diameter of the carbon layer in the cathode material with only point-shaped carbon coating ranges from 1nm to 60nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 80nm, the diameter of the carbon layer in the cathode material with only flaky carbon coating ranges from 100nm to 280nm, the gap distance between the flaky carbon layers ranges from 1nm to 110nm, in the cathode material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 55nm, the diameter of the flaky carbon coating ranges from 100nm to 250nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1nm to 100nm; the sodium battery cathode material further includes free carbon, the content of the carbon used for coating sodium ferrous sulfate is 97wt% based on the total content of carbon in the sodium battery cathode material being 100wt%, and the content of the free carbon is 3wt%; the sodium battery cathode material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 700nm with an average size of 462nm, and the size of the secondary particles ranges from 0.01μm to 60μm with an average size of 38μm, the content of the primary particles is 63wt% based on the total content of the total particles in the sodium battery cathode material being 100%, and the content of the secondary particles is 37wt%.

[0145] Example 4

[0146] The difference between this example and Example 1 is that in step S2 of the preparation method provided in this example, the mass of the pretreated sodium sulfate added is 4750g, the mass of the glucose added is 250g, and the mass of the in-situ carbon-coated sodium sulfate added in step S3 is 2022g. The remaining process parameters are the same as those of Example 1.

[0147] The sodium battery cathode material obtained by the above preparation method in this example includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 1wt% based on the total mass of the sodium battery cathode material being 100wt%, the sodium battery cathode material includes a cathode material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a cathode material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 2nm to 20nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 15nm; in the sodium battery cathode material, the mass ratio of the cathode material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the cathode material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 7:93; the carbon layer partially coated cathode material includes a cathode material with all point-shaped carbon coating, a sodium battery cathode material with all flaky carbon coating, and a cathode material with both point-shaped carbon coating and flaky carbon coating in any proportion, wherein the diameter of the carbon layer in the cathode material with only point-shaped carbon coating ranges from 1nm to 25nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 75nm, the diameter of the carbon layer in the cathode material with only flaky carbon coating ranges from 100nm to 200nm, the gap distance between the flaky carbon layers ranges from 1nm to 200nm, in the cathode material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 25nm, the diameter of the flaky carbon coating ranges from 100nm to 200nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1nm to 180nm; the sodium battery cathode material also includes free carbon, the content of the carbon used for coating sodium ferrous sulfate is 97wt% based on the total content of carbon in the sodium battery cathode material being 100wt%, and the content of the free carbon is 3wt%; the sodium battery cathode material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 700nm with an average size of 537nm, and the size of the secondary particles ranges from 0.01μm to 70μm with an average size of 45μm; the content of the primary particles is 60wt% based on the total content of the total particles in the sodium battery cathode material being 100%, and the content of the secondary particles is 40wt%.

[0148] Example 5

[0149] The difference between this example and Example 1 is that in step S2 of the preparation method provided in this example, the mass of the pretreated sodium sulfate added is 4500g, the mass of the glucose added is 500g, and the mass of the in-situ carbon-coated sodium sulfate added in step S3 is 2043g. The remaining process parameters are the same as those of Example 1.

[0150] The sodium battery cathode material obtained by the preparation method described above in this example includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 2.5wt%, based on the total mass of the sodium battery cathode material being 100wt%, the sodium battery cathode material includes a cathode material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a cathode material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 2nm to 30nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 20nm; in the sodium battery cathode material, the mass ratio of the cathode material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the cathode material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 15:85; the carbon layer partially coated cathode material includes a cathode material with all point-shaped carbon coating, a sodium battery cathode material with all flaky carbon coating, and a cathode material with both point-shaped carbon coating and flaky carbon coating, wherein the diameter of the carbon layer in the cathode material with only point-shaped carbon coating ranges from 1nm to 32nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 71nm, the diameter of the carbon layer in the cathode material with only flaky carbon coating ranges from 100nm to 260nm, the gap distance between the flaky carbon layers ranges from 1nm to 200nm, in the cathode material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 32nm, the diameter of the flaky carbon coating ranges from 100nm to 260nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1nm to 120nm; the sodium battery cathode material also includes free carbon, based on the total content of carbon in the sodium battery cathode material being 100wt%, the content of carbon for coating sodium ferrous sulfate is 96wt%, and the content of free carbon is 4wt%; the sodium battery cathode material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 600nm, the average size is 486nm, the size of the secondary particles ranges from 0.01μm to 67μm, the average size is 43μm, based on the total content of the total particles in the sodium battery cathode material being 100%, the content of the primary particles is 67wt%, and the content of the secondary particles is 33wt%.

[0151] Example 6

[0152] The difference between this example and Example 1 is that in step S2 of the preparation method provided in this example, the mass of the pretreated sodium sulfate added is 3500g, the mass of the glucose added is 1500g, and the mass of the in-situ carbon-coated sodium sulfate added in step S3 is 2130g. The remaining process parameters are the same as those of Example 1.

[0153] The sodium battery cathode material obtained by the above preparation method in this example includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 7wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 1nm to 40nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 38nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 41:59; the carbon layer partially coated positive material includes a positive material with all point-shaped carbon coating, a sodium electrode positive material with all sheet-shaped carbon coating, and a positive material with both point-shaped carbon coating and sheet-shaped carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 1nm to 75nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 55nm, the diameter of the carbon layer in the positive material with only sheet-shaped carbon coating ranges from 100nm to 400nm, the gap distance between the sheet-shaped carbon layers ranges from 1nm to 70nm, in the positive material with both point-shaped carbon coating and sheet-shaped carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 75nm, the diameter of the sheet-shaped carbon coating ranges from 100nm to 400nm, and the gap distance between the point-shaped carbon layer and the sheet-shaped carbon layer ranges from 1nm to 65nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 92wt%, and the content of free carbon being 8wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 450nm, the average size is 310nm, the size of the secondary particles ranges from 0.01μm to 40μm, the average size is 21μm, and with the total content of the total particles of the sodium electrode positive material being 100%, the content of the primary particles is 70wt%, and the content of the secondary particles is 30wt%.

[0154] Example 7

[0155] The difference between this example and example 1 is that in step S2 of the preparation method provided in this example, the mass of the pretreated sodium sulfate added is 3000g, the mass of glucose is 2000g, and the mass of the in-situ carbon-coated sodium sulfate added in step S3 is 2229g. The remaining process parameters are the same as those of example 1.

[0156] The sodium electrode positive material obtained by the above preparation method in this example includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 10wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 1nm to 45nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 41nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 45:55; the carbon layer partially coated positive material includes a positive material with all point-shaped carbon coating, a sodium electrode positive material with all flaky carbon coating, and a positive material with both point-shaped carbon coating and flaky carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 1nm to 80nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 60nm, the diameter of the carbon layer in the positive material with only flaky carbon coating ranges from 100nm to 450nm, the gap distance between the flaky carbon layers ranges from 1nm to 60nm, in the positive material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 55nm, the diameter of the flaky carbon coating ranges from 100nm to 450nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1nm to 60nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 90wt%, and the content of free carbon being 10wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 400nm, the average size is 300nm, the size of the secondary particles ranges from 0.01μm to 35μm, the average size is 18μm, and with the total content of the total particles of the sodium electrode positive material being 100%, the content of the primary particles is 75wt%, and the content of the secondary particles is 25wt%.

[0157] Example 8

[0158] The difference between this embodiment and example 1 is that in the preparation method provided in this embodiment, the temperature of the hot-press sintering in step S4 is 330℃, and the time of the hot-press sintering is 15h. The remaining process parameters are the same as those in example 1.

[0159] The sodium electrode positive material obtained by the above preparation method in this embodiment includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 5wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 50nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 30nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 30:70; the carbon layer partially coated positive material includes a positive material with all point-shaped carbon coating, a sodium electrode positive material with all sheet-shaped carbon coating, and a positive material with both point-shaped carbon coating and sheet-shaped carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 1nm to 65nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 70nm, the diameter of the carbon layer in the positive material with only sheet-shaped carbon coating ranges from 100nm to 300nm, the gap distance between the sheet-shaped carbon layers ranges from 1nm to 90nm, in the positive material with both point-shaped carbon coating and sheet-shaped carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 65nm, the diameter of the sheet-shaped carbon coating ranges from 100nm to 300nm, and the gap distance between the point-shaped carbon layer and the sheet-shaped carbon layer ranges from 1nm to 75nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 95wt%, and the content of free carbon being 5wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 500nm, the average size is 280nm, the size of the secondary particles ranges from 0.01μm to 35μm, the average size is 15μm, and with the total content of the total particles of the sodium electrode positive material being 100%, the content of the primary particles is 75wt%, and the content of the secondary particles is 25wt%.

[0160] Example 9

[0161] The difference between this example and example 1 is that in the preparation method provided in this example, the mold containing the material is pressed at 300MPa for 3min and then sintered at 350℃ for 20h in step S4. The remaining process parameters are the same as those in example 1.

[0162] The sodium electrode positive material obtained by the above preparation method in this example includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 5wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 50nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 30nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 30:70; the carbon layer partially coated positive material includes a positive material with all point-shaped carbon coating, a sodium electrode positive material with all flaky carbon coating, and a positive material with both point-shaped carbon coating and flaky carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 1nm to 65nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 70nm, the diameter of the carbon layer in the positive material with only flaky carbon coating ranges from 100nm to 300nm, the gap distance between the flaky carbon layers ranges from 1nm to 90nm, in the positive material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 65nm, the diameter of the flaky carbon coating ranges from 100nm to 300nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1nm to 75nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 95wt%, and the content of free carbon being 5wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 400nm, the average size is 220nm, the size of the secondary particles ranges from 0.01μm to 35μm, the average size is 12μm, and with the total content of the total particles in the sodium electrode positive material being 100%, the content of the primary particles is 78wt%, and the content of the secondary particles is 22wt%.

[0163] Example 10

[0164] The difference between this embodiment and Example 1 is that the preparation method provided in this embodiment omits the pretreatment process of anhydrous sodium sulfate in step S1. The remaining process parameters are the same as those in Example 1.

[0165] The sodium electrode positive material obtained by the above preparation method in this embodiment includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 5wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 55nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 40nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 35:65; the carbon layer partially coated positive material includes a positive material with all point-shaped carbon coating, a sodium electrode positive material with all flaky carbon coating, and a positive material with both point-shaped carbon coating and flaky carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 1nm to 80nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 70nm, the diameter of the carbon layer in the positive material with only flaky carbon coating ranges from 100nm to 310nm, the gap distance between the flaky carbon layers ranges from 1nm to 90nm, in the positive material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 80nm, the diameter of the flaky carbon coating ranges from 100nm to 310nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1nm to 75nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 94wt%, and the content of free carbon being 6wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 1100nm, the average size is 530nm, the size of the secondary particles ranges from 0.01μm to 60μm, the average size is 45μm, and with the total content of the total particles of the sodium electrode positive material being 100%, the content of the primary particles is 68wt%, and the content of the secondary particles is 32wt%.

[0166] Example 11

[0167] The difference between this embodiment and Example 1 is that the preparation method provided in this embodiment omits the pretreatment process of ferrous sulfate heptahydrate in step S1. The remaining process parameters are the same as those in Example 1.

[0168] The sodium electrode positive material obtained by the preparation method described above in this embodiment includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 5wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 50nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 30nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 30:70; the carbon layer partially coated positive material includes a positive material with all point-shaped carbon coating, a sodium electrode positive material with all sheet-shaped carbon coating, and a positive material with both point-shaped carbon coating and sheet-shaped carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 1nm to 65nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 70nm, the diameter of the carbon layer in the positive material with only sheet-shaped carbon coating ranges from 100nm to 300nm, the gap distance between the sheet-shaped carbon layers ranges from 1nm to 90nm, and in the positive material with both point-shaped carbon coating and sheet-shaped carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 65nm, the diameter of the sheet-shaped carbon coating ranges from 100nm to 300nm, and the gap distance between the point-shaped carbon layer and the sheet-shaped carbon layer ranges from 1nm to 75nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 95wt%, and the content of free carbon being 5wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 1080nm, the average size is 480nm, the size of the secondary particles ranges from 0.01μm to 60μm, the average size is 34μm, and with the total content of the total particles of the sodium electrode positive material being 100%, the content of the primary particles is 62wt%, and the content of the secondary particles is 38wt%.

[0169] Example 12

[0170] The difference between this example and example 1 is that in the preparation method provided in this example, the mass of the pretreated sodium sulfate in step S2 is 4000g, and the mass of glucose is 100g. The remaining process parameters are the same as those in example 1.

[0171] The sodium electrode positive material obtained by the above preparation method in this example includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 0.4wt% based on the total mass of the sodium battery cathode material being 100wt%, the sodium battery cathode material includes a cathode material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a cathode material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 0.5nm to 10nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 0.5nm to 8nm; in the sodium battery cathode material, the mass ratio of the cathode material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the cathode material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 3:97; the carbon layer partially coated cathode material includes a cathode material with all point-shaped carbon coating, a sodium battery cathode material with all flaky carbon coating, and a cathode material with both point-shaped carbon coating and flaky carbon coating in any proportion, wherein the diameter of the carbon layer in the cathode material with only point-shaped carbon coating ranges from 0.5nm to 15nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 112nm, the diameter of the carbon layer in the cathode material with only flaky carbon coating ranges from 100nm to 150nm, the gap distance between the flaky carbon layers ranges from 1nm to 230nm, in the cathode material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 0.5nm to 15nm, the diameter of the flaky carbon coating ranges from 100nm to 150nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1nm to 210nm; the sodium battery cathode material further includes free carbon, the content of the carbon used for coating sodium ferrous sulfate is 99wt% based on the total content of carbon in the sodium battery cathode material being 100wt%, and the content of the free carbon is 1wt%; the sodium battery cathode material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 850nm with an average size of 653nm, and the size of the secondary particles ranges from 0.01μm to 85μm with an average size of 53μm; the content of the primary particles is 65wt% based on the total content of the total particles in the sodium battery cathode material being 100%.

[0172] Example 13

[0173] The difference between this example and Example 1 is that in the preparation method provided in this example, the mass of the pretreated sodium sulfate in step S2 is 2000g, and the mass of the glucose is 2500g. The remaining process parameters are the same as those in Example 1.

[0174] The sodium battery cathode material obtained by the above preparation method in this example includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 10wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 58nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 5nm to 55nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 52:48; the carbon layer partially coated positive material includes a positive material with all point-shaped carbon coating, a sodium electrode positive material with all flaky carbon coating, and a positive material with both point-shaped carbon coating and flaky carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 10nm to 80nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 58nm, the diameter of the carbon layer in the positive material with only flaky carbon coating ranges from 100nm to 480nm, the gap distance between the flaky carbon layers ranges from 1nm to 48nm, in the positive material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 10nm to 80nm, the diameter of the flaky carbon coating ranges from 100nm to 480nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1nm to 46nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 84wt%, and the content of free carbon being 16wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 300nm, the average size is 246nm, the size of the secondary particles ranges from 0.01μm to 30μm, the average size is 15μm, and with the total content of the total particles of the sodium electrode positive material being 100%, the content of the primary particles is 80wt%, and the content of the secondary particles is 20wt%.

[0175] Example 14

[0176] The difference between this embodiment and Example 1 is that in the preparation method provided in this embodiment, the sintering temperature in step S2 is 400°C. The remaining process parameters are the same as those in Example 1.

[0177] The sodium electrode positive material obtained by the preparation method described above in this embodiment includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 5wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 10nm to 65nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 10nm to 55nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 40:60; the carbon layer partially coated positive material includes a positive material with all point-shaped carbon coating, a sodium electrode positive material with all flaky carbon coating, and a positive material with both point-shaped carbon coating and flaky carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 5nm to 80nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 45nm, the diameter of the carbon layer in the positive material with only flaky carbon coating ranges from 100nm to 450nm, the gap distance between the flaky carbon layers ranges from 1nm to 60nm, and in the positive material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 5nm to 80nm, the diameter of the flaky carbon coating ranges from 100nm to 450nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1nm to 60nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 95wt%, and the content of free carbon being 5wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 1200nm, the average size is 523nm, the size of the secondary particles ranges from 0.01μm to 863μm, the average size is 107μm, and with the total content of the total particles of the sodium electrode positive material being 100%, the content of the primary particles is 56wt%, and the content of the secondary particles is 44wt%.

[0178] Example 15

[0179] The difference between this embodiment and Example 1 is that in the preparation method provided in this embodiment, the sintering temperature in step S2 is 900°C. The remaining process parameters are the same as those in Example 1.

[0180] The sodium electrode positive material obtained by the above preparation method in this embodiment includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 5wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 45nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 28nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 40:60; the carbon layer partially coated positive material includes a positive material with all point-shaped carbon coating, a sodium electrode positive material with all flaky carbon coating, and a positive material with both point-shaped carbon coating and flaky carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 1nm to 70nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 60nm, the diameter of the carbon layer in the positive material with only flaky carbon coating ranges from 100nm to 400nm, the gap distance between the flaky carbon layers ranges from 1nm to 73nm, and in the positive material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 70nm, the diameter of the flaky carbon coating ranges from 100nm to 400nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1nm to 73nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 85wt%, and the content of free carbon being 15wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 550nm, the average size is 345nm, the size of the secondary particles ranges from 0.01μm to 46μm, the average size is 22μm, and with the total content of the total particles of the sodium electrode positive material being 100%, the content of the primary particles is 70wt%, and the content of the secondary particles is 30wt%.

[0181] Example 16

[0182] The difference between this embodiment and Example 1 is that in the preparation method provided in this embodiment, the amount of ascorbic acid added in step S3 is 0.5g. The remaining process parameters are the same as those in Example 1.

[0183] The sodium electrode positive material obtained by the preparation method described above in this embodiment includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 5wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 48nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 28nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 25:75; the carbon layer partially coated positive material includes a positive material with all point-shaped carbon coating, a sodium electrode positive material with all sheet-shaped carbon coating, and a positive material with both point-shaped carbon coating and sheet-shaped carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 1nm to 60nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 80nm, the diameter of the carbon layer in the positive material with only sheet-shaped carbon coating ranges from 100nm to 280nm, the gap distance between the sheet-shaped carbon layers ranges from 1nm to 92nm, in the positive material with both point-shaped carbon coating and sheet-shaped carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 60nm, the diameter of the sheet-shaped carbon coating ranges from 100nm to 280nm, and the gap distance between the point-shaped carbon layer and the sheet-shaped carbon layer ranges from 1nm to 80nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 96wt%, and the content of free carbon being 4wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 620nm, the average size is 372nm, the size of the secondary particles ranges from 0.01μm to 56μm, the average size is 30μm, and with the total content of the total particles of the sodium electrode positive material being 100%, the content of the primary particles is 65wt%, and the content of the secondary particles is 35wt%.

[0184] Example 17

[0185] The difference between this example and Example 1 is that in the preparation method provided in this example, the amount of ascorbic acid added in step S3 is 400g. The remaining process parameters are the same as those in Example 1.

[0186] The sodium electrode positive material obtained by the above preparation method in this example includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 6wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 54nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 33nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 32:68; the carbon layer partially coated positive material includes a positive material with all point-shaped carbon coating, a sodium electrode positive material with all flaky carbon coating, and a positive material with both point-shaped carbon coating and flaky carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 1nm to 71nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 70nm, the diameter of the carbon layer in the positive material with only flaky carbon coating ranges from 100nm to 340nm, the gap distance between the flaky carbon layers ranges from 1nm to 84nm, in the positive material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 71nm, the diameter of the flaky carbon coating ranges from 100nm to 340nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1nm to 72nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 94wt%, and the content of free carbon being 6wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 570nm, the average size is 340nm, the size of the secondary particles ranges from 0.01μm to 46μm, the average size is 24μm, and with the total content of the total particles of the sodium electrode positive material being 100%, the content of the primary particles is 68wt%, and the content of the secondary particles is 32wt%.

[0187] Example 18

[0188] The difference between this embodiment and Example 1 is that in the preparation method provided in this embodiment, the pressure of the pressurization in step S4 is 10MPa. The remaining process parameters are the same as those in Example 1.

[0189] The sodium electrode positive material obtained by the preparation method described above in this embodiment includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 5wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 50nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 30nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 30:70; the carbon layer partially coated positive material includes a positive material with all point-shaped carbon coating, a sodium electrode positive material with all sheet-shaped carbon coating, and a positive material with both point-shaped carbon coating and sheet-shaped carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 1nm to 65nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 70nm, the diameter of the carbon layer in the positive material with only sheet-shaped carbon coating ranges from 100nm to 300nm, the gap distance between the sheet-shaped carbon layers ranges from 1nm to 90nm, in the positive material with both point-shaped carbon coating and sheet-shaped carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 65nm, the diameter of the sheet-shaped carbon coating ranges from 100nm to 300nm, and the gap distance between the point-shaped carbon layer and the sheet-shaped carbon layer ranges from 1nm to 75nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 95wt%, and the content of free carbon being 5wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 500nm, the average size is 30nm, the size of the secondary particles ranges from 0.01μm to 45μm, the average size is 24μm, and with the total content of the total particles of the sodium electrode positive material being 100%, the content of the primary particles is 75wt%, and the content of the secondary particles is 25wt%.

[0190] Example 19

[0191] The difference between this embodiment and example 1 is that in the preparation method provided in this embodiment, the pressure of step S4 is 600MPa. The remaining process parameters are the same as those of example 1.

[0192] The sodium electrode positive material obtained by the preparation method described above in this embodiment includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 5wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 50nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 30nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 30:70; the carbon layer partially coated positive material includes a positive material with all point-shaped carbon coating, a sodium electrode positive material with all sheet-shaped carbon coating, and a positive material with both point-shaped carbon coating and sheet-shaped carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 1nm to 65nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 70nm, the diameter of the carbon layer in the positive material with only sheet-shaped carbon coating ranges from 100nm to 300nm, the gap distance between the sheet-shaped carbon layers ranges from 1nm to 90nm, in the positive material with both point-shaped carbon coating and sheet-shaped carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 65nm, the diameter of the sheet-shaped carbon coating ranges from 100nm to 300nm, and the gap distance between the point-shaped carbon layer and the sheet-shaped carbon layer ranges from 1nm to 75nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 95wt%, and the content of free carbon being 5wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 900nm, the average size is 563nm, the size of the secondary particles ranges from 0.01μm to 105μm, the average size is 58μm, and with the total content of the total particles of the sodium electrode positive material being 100%, the content of the primary particles is 45wt%, and the content of the secondary particles is 55wt%.

[0193] Example 20

[0194] The difference between this embodiment and example 1 is that in the preparation method provided in this embodiment, the temperature of the hot-press sintering in step S4 is 200°C. The remaining process parameters are the same as those in example 1.

[0195] The sodium electrode positive material obtained by the preparation method described above in this embodiment includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 5.5wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 52nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 32nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 32:68; the carbon layer partially coated positive material includes a positive material with all point-shaped carbon coating, a sodium electrode positive material with all flaky carbon coating, and a positive material with both point-shaped carbon coating and flaky carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 1nm to 68nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 70nm, the diameter of the carbon layer in the positive material with only flaky carbon coating ranges from 100nm to 310nm, the gap distance between the flaky carbon layers ranges from 1nm to 85nm, and in the positive material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 68nm, the diameter of the flaky carbon coating ranges from 100nm to 310nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1nm to 68nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 94.5wt%, and the content of free carbon being 5.5wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 430nm, the average size is 213nm, the size of the secondary particles ranges from 0.01μm to 45μm, the average size is 23μm, and with the total content of the total particles of the sodium electrode positive material being 100%, the content of the primary particles is 72wt%, and the content of the secondary particles is 28wt%.

[0196] Example 21

[0197] The difference between this embodiment and Example 1 is that in the preparation method provided in this embodiment, the temperature of the hot-press sintering in step S4 is 400℃. The remaining process parameters are the same as those in Example 1.

[0198] The sodium electrode positive material obtained by the preparation method described above in this embodiment includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 4.9wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 48nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 29nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 29:71; the carbon layer partially coated positive material includes a positive material with all point-shaped carbon coating, a sodium electrode positive material with all sheet-shaped carbon coating, and a positive material with both point-shaped carbon coating and sheet-shaped carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 1nm to 62nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 72nm, the diameter of the carbon layer in the positive material with only sheet-shaped carbon coating ranges from 100nm to 290nm, the gap distance between the sheet-shaped carbon layers ranges from 1nm to 92nm, in the positive material with both point-shaped carbon coating and sheet-shaped carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 62nm, the diameter of the sheet-shaped carbon coating ranges from 100nm to 290nm, and the gap distance between the point-shaped carbon layer and the sheet-shaped carbon layer ranges from 1nm to 75nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 95.1wt%, and the content of free carbon being 4.9wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 650nm, the average size is 379nm, the size of the secondary particles ranges from 0.01μm to 55μm, the average size is 30μm, and with the total content of the total particles of the sodium electrode positive material being 100%, the content of the primary particles is 61wt%, and the content of the secondary particles is 39wt%.

[0199] Example 22

[0200] The difference between this embodiment and Example 1 is that in the preparation method provided in this embodiment, the pressing process of step S4 is omitted, and the precursor material is directly placed at 350℃ for 20h. The remaining process parameters are the same as those of Example 1.

[0201] The sodium electrode positive material obtained by the above preparation method in this embodiment includes carbon-coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 5wt%, based on the total mass of the sodium battery cathode material being 100wt%, the sodium battery cathode material includes a cathode material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a cathode material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 5nm to 50nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1nm to 30nm; in the sodium battery cathode material, the mass ratio of the cathode material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the cathode material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 30:70; the carbon layer partially coated cathode material includes a cathode material with all point-shaped carbon coating, a sodium battery cathode material with all flaky carbon coating, and a cathode material with both point-shaped carbon coating and flaky carbon coating in any proportion, wherein the diameter of the carbon layer in the cathode material with only point-shaped carbon coating ranges from 1nm to 65nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 70nm, the diameter of the carbon layer in the cathode material with only flaky carbon coating ranges from 100nm to 300nm, the gap distance between the flaky carbon layers ranges from 1nm to 90nm, and in the cathode material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 1nm to 65nm, the diameter of the flaky carbon coating ranges from 100nm to 300nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1nm to 75nm; the sodium battery cathode material also includes free carbon, based on the total content of carbon in the sodium battery cathode material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 92wt%, and the content of free carbon being 8wt%; the sodium battery cathode material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 300nm, the average size is 95nm, the size of the secondary particles ranges from 0.01μm to 35μm, the average size is 15μm, based on the total content of the total particles in the sodium battery cathode material being 100%, the content of the primary particles is 90wt%, and the content of the secondary particles is 10wt%.

[0202] Example 23

[0203] The difference between this example and Example 1 is that in the preparation method provided in this example, step S2 uses wet mixing and dissolution of 4000g of the pretreated sodium sulfate obtained in step S1 with 1000g of glucose and 10kg of water, then the wet mixed material is spray dried, and then the spray dried product is sintered at 600℃ for 8h, the sintering is carried out in a nitrogen atmosphere, to obtain in-situ carbon coated sodium sulfate. The remaining process parameters are the same as those of Example 1.

[0204] The sodium battery cathode material obtained by the above preparation method in this example includes carbon coated sodium ferrous sulfate, and its chemical formula is Na 2.56 Fe 1.72The sodium battery positive electrode material includes a positive electrode material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive electrode material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 2 nm to 45 nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 1 nm to 25 nm; in the sodium battery positive electrode material, the mass ratio of the positive electrode material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive electrode material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 40:60; the carbon layer partially coated positive electrode material includes a positive electrode material with all point-shaped carbon coating, a sodium battery positive electrode material with all flaky carbon coating, and a positive electrode material with both point-shaped carbon coating and flaky carbon coating in any proportion, wherein the diameter of the carbon layer in the positive electrode material with only point-shaped carbon coating ranges from 40 nm to 95 nm, the gap distance between the point-shaped carbon layers ranges from 1 nm to 35 nm, the diameter of the carbon layer in the positive electrode material with only flaky carbon coating ranges from 100 nm to 486 nm, the gap distance between the flaky carbon layers ranges from 1 nm to 46 nm, in the positive electrode material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 40 nm to 95 nm, the diameter of the flaky carbon coating ranges from 100 nm to 486 nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1 nm to 35 nm; the sodium battery positive electrode material also includes free carbon, with the total content of carbon in the sodium battery positive electrode material being 100 wt%, the content of carbon for coating sodium ferrous sulfate being 95 wt%, and the content of free carbon being 3.5 wt%; the sodium battery positive electrode material includes primary particles and secondary particles, the size of the primary particles ranges from 1 nm to 450 nm, the average size is 316 nm, the size of the secondary particles ranges from 0.01 μm to 48 μm, the average size is 24 μm, the content of the primary particles is 68 wt% based on the total content of the total particles of the sodium battery positive electrode material, and the content of the secondary particles is 32 wt%.

[0205] Example 24

[0206] The preparation method of the sodium battery positive electrode material provided in the embodiment includes the following steps:

[0207] (A) The anhydrous sodium sulfate is subjected to a first drying at 200°C for 10 h, and then the first-dried anhydrous sodium sulfate is broken by a nitrogen gas flow with a pressure of 1.5 MPa for 10 min under the protection of nitrogen to obtain a particle size D50 of 0.8 μm, thereby obtaining pretreated sodium sulfate for standby use.

[0208] The second drying of the ferrous sulfate heptahydrate at 350℃ for 10h obtained anhydrous ferrous sulfate, then the obtained anhydrous ferrous sulfate was broken by nitrogen gas flow with a pressure of 1.5MPa for 10min to obtain a particle size D50 of 0.8μm, and the pretreated ferrous sulfate was obtained for standby;

[0209] (B) The 4000g of the pretreated sodium sulfate obtained in step (A), 1000g of glucose, 3028g of the pretreated ferrous sulfate obtained in step (A) and 152g of ascorbic acid were premixed under a high-speed mixer, then stirred in a ball mill at a rotating speed of 400rpm for 6h to obtain a precursor material.

[0210] (C) The precursor material obtained in step (B) was loaded into a hot-pressing mold, and the material was placed in a hot-pressing furnace together with the mold, and the precursor material was hot-pressed and sintered at a pressure of 100MPa and a temperature of 350℃ for 12h, then cooled to 150℃ and taken out, and then the taken-out material was broken and sieved by a mesh size of 325 to obtain a sodium battery cathode material of carbon-coated sodium ferrous sulfate.

[0211] The sodium battery cathode material obtained by the preparation method in the embodiment comprises carbon-coated sodium ferrous sulfate, and the chemical formula is Na 2.56 Fe 1.72(SO4)3@C, the mass of the carbon layer coated on the surface of the matrix material is 8wt%, the sodium electrode positive material includes a positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate and a positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate, the thickness of the carbon layer coated on the entire surface of sodium ferrous sulfate ranges from 10nm to 75nm, and the thickness of the carbon layer coated on part of the surface of sodium ferrous sulfate ranges from 10nm to 65nm; in the sodium electrode positive material, the mass ratio of the positive material with a carbon layer coated on the entire surface of sodium ferrous sulfate to the positive material with a carbon layer coated on part of the surface of sodium ferrous sulfate is 60:40; the carbon layer partially coated positive material includes all point-shaped carbon-coated positive materials, all flaky carbon-coated sodium electrode positive materials, and positive materials with both point-shaped carbon coating and flaky carbon coating in any proportion, wherein the diameter of the carbon layer in the positive material with only point-shaped carbon coating ranges from 30nm to 99nm, the gap distance between the point-shaped carbon layers ranges from 1nm to 25nm, the diameter of the carbon layer in the positive material with only flaky carbon coating ranges from 100nm to 650nm, the gap distance between the flaky carbon layers ranges from 1nm to 35nm, in the positive material with both point-shaped carbon coating and flaky carbon coating, the diameter of the point-shaped carbon coating ranges from 30nm to 99nm, the diameter of the flaky carbon coating ranges from 100nm to 650nm, and the gap distance between the point-shaped carbon layer and the flaky carbon layer ranges from 1nm to 30nm; the sodium electrode positive material also includes free carbon, with the total content of carbon in the sodium electrode positive material being 100wt%, the content of carbon for coating sodium ferrous sulfate being 80wt%, and the content of free carbon being 20wt%; the sodium electrode positive material includes primary particles and secondary particles, the size of the primary particles ranges from 1nm to 700nm, the average size is 463nm, the size of the secondary particles ranges from 0.01μm to 78μm, the average size is 61μm, and the content of the primary particles is 45wt% and the content of the secondary particles is 55wt% based on the total content of the total particles of the sodium electrode positive material.

[0212] Comparative Example 1

[0213] The sodium electrode positive material provided by the present comparative example is different from that of Example 1 only in that the sodium electrode positive material provided by the present comparative example omits the coating of the carbon layer and is only sodium ferrous sulfate positive material, and the chemical formula is Na 2.56 Fe 1.72 (SO4)3.

[0214] The preparation method of the above-mentioned sodium electrode positive material provided by the present comparative example includes the following steps:

[0215] First step: S1. The anhydrous sodium sulfate was first dried at 200℃ for 10h, and then the first dried anhydrous sodium sulfate was broken into anhydrous sodium sulfate with a particle size D50 of 0.8μm under the protection of nitrogen gas flow with a gas flow pressure of 1.5MPa for 10min, to obtain pretreated sodium sulfate for standby use.

[0216] The ferrous sulfate heptahydrate was second dried at 350℃ for 10h to obtain anhydrous ferrous sulfate, and then the obtained anhydrous ferrous sulfate was broken into anhydrous ferrous sulfate with a particle size D50 of 0.8μm under the protection of nitrogen gas flow with a gas flow pressure of 1.5MPa for 10min, to obtain pretreated ferrous sulfate for standby use;

[0217] Second step: 2022g of pretreated sodium sulfate, 3028g of pretreated ferrous sulfate and 152g of ascorbic acid were weighed, and after premixing in a high-speed mixer, the mixture was ground in a planetary ball mill for 6h to obtain a precursor material;

[0218] Third step: The obtained precursor material was compacted and loaded into a hot-pressing mold, and the material was placed in a hot-pressing furnace together with the mold, and the pressure was increased to 100MPa while the temperature was increased to 350℃, and the precursor material was hot-pressed and sintered for 12h, and then cooled to 150℃ to take out the material, and then the material was broken and sieved through a sieve with a mesh size of 325, to obtain a sodium iron sulfate sodium battery positive electrode material.

[0219] The sodium battery positive electrode materials obtained from Examples 1-24 and Comparative Example 1 were detected for compacted density, water content and specific surface area, and the specific test process was as follows:

[0220] (1) The compacted density of the sodium battery positive electrode material was detected by using a compacted density automatic detection device;

[0221] (2) The water content of the sodium battery positive electrode material was detected by using a cassette moisture detection method;

[0222] (3) The specific surface area (BET) of the sodium battery positive electrode material was detected by using the BET method;

[0223] (4) The purity of the sodium battery positive electrode material was calculated by the formula: purity of sodium battery positive electrode material = (total product mass-impurity element content-insufficiently reacted material content-sodium-rich impurity phase content) / total product mass x 100%, through XRD to calculate the content of insufficiently reacted material and the content of sodium-rich impurity phase, through inductively coupled plasma emission spectroscopy analysis (ICP analysis) to calculate the total element content and other impurity element content.

[0224] The test results are shown in Table 1.

[0225] Table 1

[0226]

[0227]

[0228] Application Examples 1-24 and Comparative Application Example 1

[0229] The sodium electric positive electrode materials obtained from Examples 1-24 and Comparative Example 1 were assembled into sodium ion positive electrode materials, wherein the preparation process of the positive electrode was as follows: the sodium electric positive electrode materials obtained from Examples 1-24 and Comparative Example 1 were mixed with conductive carbon black (SP) and PVDF according to a weight ratio of 80wt%:10wt%:10wt%, N-methyl pyrrolidone NMP was used as a solvent, and a positive electrode slurry was obtained by dispersion, the obtained positive electrode slurry was coated on an aluminum foil current collector, and a positive electrode sheet with a surface density of 7.8 g / cm2was prepared by rolling, then the positive electrode sheet was punched into small round sheets with a diameter of 12 mm by film punching, and after drying, weighing and processing, a positive electrode was obtained; the negative electrode was metallic sodium; the electrolyte was a solvent of ethylene carbonate and propylene carbonate in a volume ratio of 1:1, and the electrolyte salt was 1 mol / L sodium hexafluorophosphate. The above-mentioned positive electrode, negative electrode and electrolyte were assembled into a 2025 button cell shell to form a sodium ion battery. 3

[0230] The sodium ion batteries assembled from Application Examples 1-24 and Comparative Application Example 1 were placed at 25°C for 4h, and then subjected to first charge-discharge capacity test, the test conditions were as follows: 0.1C charging to 4.5V, constant voltage charging to 0.025C cutoff, standing for 3min, 0.1C discharging to 2.0V, obtaining the charge-discharge specific capacity, and recording the first charge capacity C0and the first discharge capacity D0of 2-4.5V, respectively, calculating the first coulombic efficiency according to D0 / C0, and recording the capacity retention rate after 500 cycles at a rate of 5C under a voltage of 2-4.5V. The test results are shown in Table 2.

[0231] Table 2

[0232]

[0233]

[0234] From the test results in Table 1 and Table 2, it can be seen that:

[0235] ​(1) As can be seen from Examples 1 to 9 and Application Examples 1 to 9, the sodium electric positive electrode material provided by the present application is coated with a carbon layer on the surface of the base material, which improves the stability and conductivity of the material. Further, by regulating the form of carbon coating, the partial coating and full coating of the carbon layer on the surface of the base material are cooperated, and the specific form of the partial carbon coating is combined, which improves the conductivity of the sodium electric positive electrode material and improves the transmission of sodium ions in the material, so that the sodium electric positive electrode material can have the advantages of excellent capacity performance and stable cycle performance.

[0236] Figure 2 The scanning electron microscope image of the in-situ carbon-coated sodium sulfate prepared in Example 1 is given, Figure 3 For Figure 2 The energy dispersive X-ray spectrum of the corresponding carbon element is given, Figure 2 In combination Figure 3 As can be seen, a large amount of carbon layer is coated on the surface of the sodium sulfate particles in-situ.

[0237] Figure 4 The X-ray diffraction pattern of the sodium electric positive electrode material prepared in Example 1 is given, and as can be seen from the figure, the peak value in the X-ray diffraction pattern of the sodium electric positive electrode material prepared in Example 1 corresponds to standard card PDF#-01-085-6588, which confirms that the sodium electric positive electrode material obtained is coated with sodium ferrous sulfate.

[0238] Figure 5 And Figure 7 The scanning electron microscope images of the sodium electric positive electrode material prepared in Example 1 at different magnifications are given, Figure 6 For Figure 5 The energy dispersive X-ray spectrum of the corresponding carbon element is given, Figure 5 , Figure 6 And Figure 7 As can be seen, a large amount of carbon layer is coated on the surface of the sodium electric positive electrode material obtained in-situ, a part of the surface of the sodium ferrous sulfate is partially coated with a carbon layer, and a part of the surface of the sodium ferrous sulfate is fully coated with a carbon layer. Figure 5 And Figure 7 As can be seen from the scanning electron microscope images, the carbon layer coated on the surface of the sodium ferrous sulfate exists in two forms of dots and flakes.

[0239] Figure 8The charge-discharge curves of the sodium ion batteries provided in application examples 1 and 4-7 at 0.1C are shown in the figures. As can be seen from the figures, the positive electrode material used in the sodium ion battery provided in application example 4-7 controls the mass of the first raw material sodium sulfate and the organic carbon source glucose in the preparation process. As can be seen from the charge-discharge curves of application examples 1 and 4-7, controlling the amount of organic carbon source relative to the amount of first raw material controls the carbon coating amount within a reasonable range, which affects the charge-discharge performance of the obtained sodium ion battery, but still maintains excellent electrochemical performance.

[0240] Figure 9 The charge-discharge curves of the sodium ion batteries provided in application examples 1 and 8-9 at 0.1C are shown in the figures. As can be seen from the figures, the positive electrode material used in the sodium ion battery provided in application example 8 appropriately reduces the temperature of hot-press sintering and extends the holding time in the preparation process. The charge-discharge curve is close to that of application example 1, indicating that application example 8 still has excellent electrochemical performance. The positive electrode material used in the sodium ion battery provided in application example 9 uses a hot-press sintering process of first pressing and then sintering in the preparation process. Although the charge-discharge performance is lower than that of application example 1, it still has excellent performance effect.

[0241] (2) Comparing application examples 1 and 10-11, and application examples 1 and 10-11, it can be seen that if the pretreatment process of drying and crushing sodium sulfate is omitted, the material reaction will not be sufficient, and the water content of the obtained sodium battery positive electrode material will increase, thereby reducing the electrochemical performance of the positive electrode material. If the pretreatment process of drying and crushing ferrous sulfate is omitted, the material reaction will not be sufficient, and the water content of the obtained sodium battery positive electrode material will also increase, thereby reducing the electrochemical performance of the material.

[0242] (3) Comparing application examples 1 and 12-13, and application examples 1 and 12-13, it can be seen that by controlling the mass ratio of the first raw material and the organic carbon source, the coating amount of the carbon material is controlled. If the mass ratio is too large, the amount of carbon added is too small, the proportion of the positive electrode material with a carbon layer completely coated on the surface of sodium ferrous sulfate is low, the specific surface area of the sodium battery positive electrode material is reduced, the compaction density is increased, but the water content of the sample is increased, the conductivity of the material is decreased, thereby reducing the capacity rate performance and cycle stability of the sodium ion battery. If the mass ratio is too low, the carbon coating amount is increased, the proportion of the positive electrode material with a carbon layer completely coated on the surface of sodium ferrous sulfate in the sodium battery positive electrode material is increased, the specific surface area of the sodium battery positive electrode material is increased, the compaction density is decreased, the water content is decreased, the conductivity of the material is increased, but too much carbon coating will hinder the diffusion and transmission of sodium ions in the material, thereby reducing the capacity rate performance of the sodium ion battery.

[0243] (4) By comparing Example 1 and Examples 14-15, Application Example 1 and Application Examples 14-15, it can be seen that if the sintering temperature of the solid-phase mixture of the first raw material and the organic carbon source in the present application is too low, the graphitization degree of the organic carbon source will be low, thereby causing the obtained sodium battery positive electrode material to have poor electrical conductivity, and further causing the electrochemical performance of the sodium ion battery formed to be poor; if the sintering temperature is too high, sodium sulfate will be decomposed, making it difficult to synthesize high-purity carbon-coated sodium ferrous sulfate in the subsequent process.

[0244] Figure 10 The charge-discharge curve of the sodium ion battery provided by Application Example 1 and Application Example 14 at 0.1C is shown in the figure, and from the figure, it can be seen that compared with Application Example 1, the positive electrode material used in the sodium ion battery provided by Application Example 14 reduces the sintering temperature of the solid-phase mixture of the first raw material and the organic carbon source in the preparation process, which will cause the charge-discharge performance of the sodium ion battery to be poor.

[0245] (5) By comparing Example 1 and Examples 16-17, Application Example 1 and Application Examples 16-17, it can be seen that by controlling the amount of antioxidant added in the present application, if the amount of antioxidant added is too low, the raw materials will be oxidized during the preparation process, affecting the performance and electrochemical performance of the material; if the amount of antioxidant added is too high, the content of amorphous carbon with poor electrical conductivity will be too high, which will reduce the compaction of the material, increase the specific surface area, and be not conducive to electron transport, resulting in a decrease in the electrochemical performance of the sodium battery positive electrode material.

[0246] (6) By comparing Example 1 and Examples 18-19, Application Example 1 and Application Examples 18-19, it can be seen that if the pressure for pressing the precursor material in the present application is too low, the raw materials will not react sufficiently, the consistency of the product will be poor, and the purity will be reduced; if the pressure for pressing the precursor material is too high, the hardness of the sample will be too high, making it difficult to break in the subsequent process, resulting in large particles and the sample being unable to perform its performance.

[0247] (7) By comparing Example 1 and Examples 20-21, Application Example 1 and Application Examples 20-21, it can be seen that if the sintering temperature of the precursor material in the present application is too low, sodium ferrous sulfate cannot be synthesized, and the performance of the finished product is extremely poor; if the sintering temperature of the precursor material is too high, sodium ferrous sulfate will be decomposed, the purity of the sodium battery positive electrode material will decrease significantly, and the electrochemical performance will be poor.

[0248] (8) By comparing Example 1 and Example 22, Application Example 1 and Application Example 22, it can be seen that if the pressing and sintering process on the precursor material is replaced by a sintering process and the pressing process is omitted in the preparation of the sodium electrode material provided by the application, due to the obstruction of the in-situ carbon coating layer of the first raw material, atomic diffusion is difficult, and the first raw material and the second raw material cannot fully react, resulting in a decrease in the purity of the sodium electrode material in the obtained product, and further resulting in poor electrochemical performance of the sodium ion battery.

[0249] Figure 11 The charge-discharge curve of the sodium ion battery provided by Application Example 1 and Application Example 22 at 0.1C is given in the above table, and from the figure, it can be seen that compared with Application Example 1, the positive electrode material used in the sodium ion battery provided by Application Example 22 replaces the pressing and sintering process on the precursor material with a sintering process during preparation, and omits the pressing process, which will result in poor electrochemical performance of the sodium ion battery and reduced cycle capacity.

[0250] (9) By comparing Example 1 and Example 23, Application Example 1 and Application Example 23, it can be seen that if the solid-phase mixing of the first raw material and the organic carbon source is replaced by a wet mixing process combined with a spray drying process in the application, it will result in too large specific surface area and too low compaction density of the sodium electrode material, thereby making the electrochemical performance of the sodium ion battery worse.

[0251] (10) By comparing Example 11 and Example 24, Application Example 1 and Application Example 24, it can be seen that if the first raw material, the second raw material, the organic carbon source and the antioxidant are directly mixed to prepare the carbon-coated sodium ferrous sulfate positive electrode material combined with a hot-pressing sintering process at 350℃ in the application, it will result in a decrease in the graphitization degree of the organic carbon source, and the form and morphology of the carbon layer coating in the sodium electrode material will be affected, thereby affecting the performance of the obtained positive electrode material and the performance of the sodium ion battery composed of it.

[0252] (11) By comparing Example 1 with Comparative Example 1, and Application Example 1 with Comparative Application Example 1, it can be seen that if the first raw material and the second raw material are directly mixed to form a pure sodium ferric sulfate positive electrode material in the application, and the in-situ carbon coating is omitted, it will result in a significant increase in the water content of the obtained sodium electrode material and poor conductivity of the material, thereby making the capacity of the sodium ion battery in which it is applied low.

[0253] Figure 11 The charge-discharge curve of the sodium ion battery provided by Application Example 1 and Comparative Application Example 1 at 0.1C is given in the above table, and from the figure, it can be seen that compared with Application Example 1, the positive electrode material used in the sodium ion battery provided by Comparative Application Example 1 directly mixes the first raw material and the second raw material during preparation, and omits the in-situ carbon coating, which will result in poor charge-discharge performance of the sodium ion battery and low capacity.

[0254] In summary, the sodium battery positive electrode material provided by the present application is coated with a carbon layer on the surface of the base material, which can improve the stability of the sodium battery positive electrode material and improve the conductivity of the material itself, further regulate the form of carbon coating, through the mutual coordination of partial carbon coating and full carbon coating on the base material, and further regulate the specific morphology of partial coating in the form of sheet and / or point, which can ensure that the sodium battery positive electrode material has excellent conductivity and stability, and can also promote the effective transmission of sodium ions in the material, improve the deintercalation of sodium ions in the material, so that the sodium battery positive electrode material can have multiple advantages such as excellent capacity performance and stable cycle performance.

[0255] The applicant declares that the above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and those skilled in the art should understand that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by any person skilled in the art in the technical field, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. A sodium electro-positive cathode material, characterized in that, The sodium battery cathode material comprises a base material and a carbon layer coated on the surface of the base material; The chemical formula of the base material is Na 2+2x Fe 2-x M3, wherein M is a polyanion, 0≤x<2; The sodium battery cathode material comprises a first sodium battery cathode material and a second sodium battery cathode material, the carbon layer on the surface of the base material in the first sodium battery cathode material is fully coated, and the carbon layer on the surface of the base material in the second sodium battery cathode material is partially coated, and the partially coated carbon layer has a coating mode comprising a dot shape and a sheet shape; The M comprises a sulfate anion; The mass percentage of the carbon layer coated on the surface of the base material is 0.1-20wt% based on the total mass of the sodium battery cathode material being 100wt%; In the sodium battery cathode material, the mass ratio of the first sodium battery cathode material to the second sodium battery cathode material is (5-50):(50-95); The thickness of the carbon layer in the first sodium battery cathode material and the carbon layer in the second sodium battery cathode material is independently selected from 1-50nm; The diameter of the dot-shaped carbon layer is 1-100nm, and the diameter of the sheet-shaped carbon layer is 100-500nm; The gap distance between the dot-shaped carbon layer and the sheet-shaped carbon layer is 1-200nm; The sodium battery cathode material is prepared by a method comprising the following steps: (1) performing one solid-phase mixing of a first raw material and an organic carbon source, and performing sintering to obtain an intermediate with in-situ carbon coating; the first raw material provides sodium ions and polyanions; (2) performing secondary solid-phase mixing of the intermediate with in-situ carbon coating and a second raw material and an antioxidant to obtain a precursor material; the second raw material provides ferrous ions and polyanions; (3) performing pressing and sintering on the precursor material to obtain the sodium battery cathode material; The sintering temperature in step (1) is 500-800℃; The sintering temperature in step (3) is 280-380℃.

2. The sodium electric cathode material of claim 1, wherein, The compaction density of the sodium electric positive electrode material is 1.8-2.36 g / cm under 3T pressure 3 .

3. The sodium electric cathode material of claim 1, wherein, The specific surface area of the sodium electric positive electrode material is 5-30 m 2 / g.

4. The sodium electric cathode material of claim 1, wherein, The sodium battery cathode material further comprises free carbon.

5. The sodium electric cathode material of claim 1, wherein, The carbon content coated on the surface of the base material is 10-99wt% based on the total carbon content in the sodium battery cathode material being 100wt%.

6. The sodium electric cathode material of claim 4, wherein, The carbon content of the free carbon is 1-50wt% based on the total carbon content in the sodium battery cathode material being 100wt%.

7. The sodium electric cathode material of claim 1, wherein, The sodium battery cathode material comprises primary particles and secondary particles.

8. The sodium electric cathode material of claim 7, wherein, The size of the primary particles is 0.001-1μm.

9. The sodium electric cathode material of claim 7, wherein, The size of the secondary particles is 0.01-100μm.

10. The sodium electric cathode material of claim 7, wherein, The content of the primary particles is 5-90wt% based on the total content of the total particles of the sodium battery cathode material being 100%.

11. The sodium electric cathode material of claim 7, wherein, The content of the secondary particles is 1-80wt% based on the total content of the total particles of the sodium battery cathode material being 100wt%.

12. A method of producing the sodium electro-positive cathode material according to any one of claims 1-11, characterized in that, The preparation method comprises the following steps: (1) performing one solid-phase mixing of a first raw material and an organic carbon source, and performing sintering to obtain an intermediate with in-situ carbon coating; the first raw material provides sodium ions and polyanions; (2) performing secondary solid-phase mixing of the intermediate with in-situ carbon coating and a second raw material and an antioxidant to obtain a precursor material; the second raw material provides ferrous ions and polyanions; (3) performing pressing and sintering on the precursor material to obtain the sodium battery positive electrode material; In step (1), the sintering temperature is 500-800°C. In step (3), the sintering temperature is 280-380°C.

13. The method of claim 12, wherein, In step (1), the first raw material comprises sodium sulfate.

14. The method of claim 12, wherein, In step (1), the first raw material is pretreated before the first solid-phase mixing.

15. The preparation method according to claim 14, characterized in that, The specific process of the pretreatment of the first raw material comprises: after first drying the first raw material, the first raw material is first crushed to obtain the pretreated first raw material.

16. The method of claim 15, wherein, The first drying temperature is 200-350°C.

17. The preparation method according to claim 15, characterized in that, The first drying time is 1-15h.

18. The method of claim 15, wherein, The particle size D50 of the first raw material after the first crushing is less than 1μm.

19. The method of claim 15, wherein, The first crushing is performed in nitrogen and / or inert gas.

20. The method of claim 12, wherein, In step (1), the organic carbon source comprises any one or a combination of at least two of glucose, ascorbic acid, citric acid, tea polyphenol or starch.

21. The method of claim 12, wherein, In step (1), the mass ratio of the first raw material to the organic carbon source is (50-95):(5-50).

22. The method of claim 12, wherein, In step (1), the first raw material and the organic carbon source are first premixed before the first solid-phase mixing.

23. The method of claim 12, wherein, In step (1), the sintering time is 4-10h.

24. The method of claim 12, wherein, In step (1), the sintering atmosphere is nitrogen and / or inert atmosphere.

25. The method of claim 12, wherein, In step (2), the second raw material comprises ferrous sulfate.

26. The method of claim 12, wherein, In step (2), the second raw material is pretreated before the second solid-phase mixing.

27. The method of claim 26, wherein, The specific process of the pretreatment of the second raw material comprises: after second drying the second raw material, the second raw material is second crushed to obtain the pretreated second raw material.

28. The preparation method according to claim 27, characterized in that, The second drying temperature is 200-350°C.

29. The preparation method according to claim 27, characterized in that, The second drying time is 1-15h.

30. The method of claim 27, wherein, The particle size D50 of the second raw material after the second crushing is less than 1μm.

31. The method of claim 27, wherein, The second crushing is performed in nitrogen and / or inert gas.

32. The method of claim 12, wherein, In step (2), the molar ratio of the intermediate with in-situ carbon coating to the second raw material is 1:(1-2).

33. The method of claim 12, wherein, The antioxidant is added in an amount of 0.01-10wt% of the mass of the second raw material.

34. The method of claim 12, wherein, The antioxidant comprises any one or a combination of at least two of ascorbic acid, citric acid or tea polyphenol.

35. The method of claim 12, wherein, In step (2), the intermediate with in-situ carbon coating, the second raw material and the antioxidant are second premixed before the second solid-phase mixing.

36. The method of claim 12, wherein, In step (3), the specific process of the pressing and sintering comprises: the precursor material is first pressed and then sintered, or the precursor material is simultaneously pressed and sintered.

37. The method of claim 12, wherein, The pressing pressure is 50-500MPa.

38. The method of claim 12, wherein, The product obtained after the pressing and sintering in step (3) is further crushed and sieved.

39. A positive electrode sheet characterized by comprising: The positive electrode tab comprises the sodium battery positive electrode material according to any one of claims 1-11, or the sodium battery positive electrode material prepared by the preparation method according to any one of claims 12-38.

40. A sodium-ion battery, comprising: The sodium ion battery comprises the positive electrode tab according to claim 39.

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