A high-capacity sodium ferric sulfate cathode material, its preparation method and application

Abstract

This invention relates to a high-capacity sodium ferric sulfate cathode material, its preparation method, and its application, belonging to the field of sodium-ion battery technology. The high-capacity sodium ferric sulfate cathode material of this invention comprises at least one component of the formula Na. x Fe y Al z (SO4)3(PO4) m The compound is defined as / C, wherein 2≤x≤3, 1.5≤y≤2, 0<z≤0.02, and 0<m≤0.02; the values ​​of x, y, z, and m satisfy the charge balance of the chemical formula. The preparation method of this invention adds a certain amount of flux to the raw materials, improving the problem of low yield and specific capacity of active materials due to agglomeration in the mixing process in the prior art; the flux melts before the calcination temperature, promoting better contact and reaction between the raw materials, improving the problem of incomplete reaction due to agglomeration of solid-phase mixing; the added flux promotes complete reaction of the main raw materials and, to a certain extent, also promotes more uniform coating of the carbon-coated material; the added flux will ultimately generate modified cathode materials through doping and other methods, exhibiting higher discharge specific capacity.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, and particularly relates to a high-capacity sodium iron sulfate cathode material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries are widely recognized as ideal rechargeable batteries for future low-speed power and large-scale energy storage systems due to the abundance of sodium salts, low cost, high thermal stability, and wide operating temperature range. Among the various types of sodium-ion battery cathode materials, polyanionic compounds have attracted widespread attention due to their high electrode potential, robust structural framework, good thermal stability, and rapid sodium-ion insertion / extraction kinetics. Sodium iron sulfate cathode material, in particular, possesses advantages such as low raw material cost, high operating voltage, and good cycle stability, making it a highly promising cathode material.

[0003] In existing processes for preparing sodium ferric sulfate cathode materials, a high-energy planetary ball mill is generally used to crush and mix the raw materials, followed by high-temperature sintering under an inert gas atmosphere to obtain the final product. However, due to significant differences in the physicochemical properties of the various raw material components, such as material composition, hardness, and particle size, uneven crushing or agglomeration occurs during the high-energy ball milling process. Furthermore, since the sintering temperature for preparing sodium ferric sulfate generally does not exceed 400℃, while the melting point of the raw materials is generally higher than this temperature, the resulting mixed raw materials exhibit poor material consistency after sintering, easily generating inactive impurity phases or even incomplete reaction of the raw materials. Therefore, providing a novel cathode material and its preparation method to promote complete reaction of the raw materials and improve the yield of active cathode materials is of great significance. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the problem of low yield and capacity of target product caused by uneven agglomeration of solid-phase ball milling in the prior art.

[0005] To address the aforementioned technical problems, this invention provides a high-capacity sodium ferric sulfate cathode material, its preparation method, and its application. A certain amount of flux is added to the mixing formulation. Utilizing the flux's low-temperature melting and ability to lower the melting temperature of substances, a molten liquid phase is generated during the heating process, promoting complete reaction of the raw materials and improving the yield and specific capacity of the sodium ferric sulfate cathode material.

[0006] The first objective of this invention is to provide a high-capacity sodium ferric sulfate cathode material, wherein the high-capacity sodium ferric sulfate cathode material comprises at least one substance of the formula Na. x Fe y Al z (SO4)3(PO4) mCompounds of type / C, wherein 2≤x≤3, 1.5≤y≤2, 0<z≤0.02, 0<m≤0.02; the values ​​of x, y, z, and m satisfy the charge balance of the chemical formula.

[0007] A second objective of this invention is to provide a method for preparing the high-capacity sodium ferric sulfate cathode material, comprising the following steps:

[0008] S1. Under a protective atmosphere, sodium source, iron source, carbon coating material and flux are ball-milled to obtain a mixed powder;

[0009] S2. The mixed powder described in S1 is calcined to obtain the high-capacity sodium ferric sulfate cathode material.

[0010] In one embodiment of the present invention, in S1, the sodium source is selected from anhydrous sodium sulfate and / or sodium sulfate decahydrate; the iron source is selected from one or more of anhydrous ferrous sulfate, ferrous sulfate monohydrate and ferrous sulfate heptahydrate; and the carbon coating material is selected from one or more of conductive carbon black, graphene and carbon nanotubes.

[0011] In one embodiment of the present invention, in S1, the carbon coating material accounts for 1wt%-6wt% of the total material.

[0012] In one embodiment of the present invention, in S1, the flux includes aluminum salt flux and phosphate flux. The flux is selected from compounds with low melting points or those that can produce molten material during heating. In addition to its fluxing function, aluminum salt flux can also increase the material's volume to some extent.

[0013] In one embodiment of the present invention, the aluminum salt flux is selected from one or more of aluminum hydroxide (Al(OH)3), aluminum sulfate (Al2(SO4)3), and aluminum phosphate (AlPO4); the phosphate flux is selected from one or more of sodium dihydrogen phosphate (NaH2PO4), disodium hydrogen phosphate (Na2HPO4), sodium phosphate (Na3PO4), ammonium dihydrogen phosphate (NH4H2PO4), and diammonium hydrogen phosphate ((NH4)2HPO4).

[0014] In one embodiment of the present invention, in S1, the ball mill rotates at a speed of 200 rpm to 500 rpm for a time of 5 h to 12 h.

[0015] Furthermore, in S1, the ball milling involves placing the raw material in a vacuum ball milling jar and filling it with nitrogen for protection, to prevent the oxidation of ferrous iron due to heat generated during the ball milling process.

[0016] In one embodiment of the present invention, in S2, the calcination temperature is 300℃-400℃, the heating rate is 1℃ / min-5℃ / min, and the time is 6h-18h.

[0017] In one embodiment of the present invention, the protective atmosphere is selected from nitrogen and / or argon to prevent ferrous iron from being oxidized during calcination.

[0018] A third objective of this invention is to provide a sodium-ion battery cathode, wherein the sodium-ion battery cathode is prepared from the aforementioned high-capacity sodium ferric sulfate cathode material.

[0019] In one embodiment of the present invention, the sodium-ion battery cathode comprises the high-capacity sodium iron sulfate cathode material, a conductive agent, and a binder.

[0020] Furthermore, the conductive agent is one or more of carbon nanotubes, acetylene black, conductive carbon black, conductive graphite, carbon fiber, and graphene.

[0021] Preferably, the amount of the conductive agent is ≤10wt%. It can be 0.01wt%-10wt%, 1wt%-10wt%, 2wt%-10wt%, 3wt%-10wt%, 4wt%-10wt%, 5wt%-10wt%, 6wt%-10wt%, 7wt%-10wt%, 8wt%-10wt%, 9wt%-10wt%; 0.01wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, 10wt%; or any concentration value between any two values.

[0022] Furthermore, the adhesive is one or more of polyolefins, fluorinated resins, polypropylene resins, and rubber.

[0023] Preferably, the adhesive is selected from one or more of polyvinylidene fluoride, styrene rubber, nitrile rubber, styrene-butadiene rubber (SBR), polyacrylamide (PAA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide (PI), butadiene rubber, modified butadiene rubber, carboxyl-modified styrene-butadiene rubber, and modified polyorganosiloxane polymers.

[0024] Preferably, the amount of the adhesive is ≤10wt%. It can be 0.01wt%-10wt%, 1wt%-10wt%, 2wt%-10wt%, 3wt%-10wt%, 4wt%-10wt%, 5wt%-10wt%, 6wt%-10wt%, 7wt%-10wt%, 8wt%-10wt%, 9wt%-10wt%; 0.01wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, 10wt%; or any concentration value between any two values.

[0025] A fourth objective of this invention is to provide a sodium-ion battery, wherein the positive electrode is prepared from the aforementioned sodium-ion battery positive electrode.

[0026] The technical solution of the present invention has the following advantages compared with the prior art:

[0027] (1) The preparation method of the present invention adds a certain amount of flux to the raw materials, which improves the problem of low yield and specific capacity of active materials due to mixing and agglomeration in the prior art; the flux melts before the calcination temperature to promote better contact and reaction between the raw materials, which improves the problem of incomplete reaction due to solid mixing and agglomeration; the added flux promotes the complete reaction of the main raw materials and can also promote more uniform coating of carbon coating materials to a certain extent; the added flux will eventually generate modified cathode materials by doping and other means and exhibit higher discharge specific capacity.

[0028] (2) The preparation method described in this invention is simple, low in cost, and has good economic benefits. Attached Figure Description

[0029] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0030] Figure 1 The images shown are SEM images of the cathode material of Test Example 1 of the present invention; wherein, the left image is Example 1 and the right image is Comparative Example 1.

[0031] Figure 2 This is a comparison XRD pattern of the cathode material in Test Example 2 of the present invention;

[0032] Figure 3 This is a comparison chart of the discharge performance of coin cells prepared with the cathode materials of Example 1 and Comparative Example 1 of the present invention.

[0033] Figure 4 This is a comparison chart showing the discharge performance of coin cells prepared from the cathode materials of Comparative Examples 2 and 3 of this invention. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. It should be understood that the specific embodiments are only used to explain the present invention, but the embodiments are not intended to limit the present invention.

[0035] In this invention, unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0036] In this invention, unless otherwise stated, the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0037] In this invention, unless otherwise specified, the experimental methods used in the embodiments of this invention are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0038] In this invention, unless otherwise stated, when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of the said feature, integral, step, operation, raw material, or component, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, raw materials, components, or combinations thereof.

[0039] Example 1

[0040] The high-capacity sodium ferric sulfate cathode material and its preparation method of the present invention specifically include the following steps:

[0041] S1. Mix 8.52g anhydrous sodium sulfate, 15.29g ferrous sulfate monohydrate, 1.08g carbon nanotubes, 0.039g aluminum hydroxide and 0.058g ammonium dihydrogen phosphate, add 10mm zirconium balls with a mass ratio of 10:1, fill the container with nitrogen for protection, and ball mill at 300rpm for 6h to obtain mixed powder;

[0042] S2. The mixed powder from S1 is transferred to a tube furnace and calcined under argon protection. The temperature is increased to 350℃ at a rate of 1℃ / min and held for 15 hours. After natural cooling, high-capacity sodium ferric sulfate cathode material Na is obtained. 2.4 Fe 1.8 Al 0.01 (SO4)3(PO4) 0.01 / C.

[0043] Example 2

[0044] The high-capacity sodium ferric sulfate cathode material and its preparation method of the present invention specifically include the following steps:

[0045] S1. Mix 8.52g anhydrous sodium sulfate, 15.29g ferrous sulfate monohydrate, 1.08g conductive carbon black, 0.039g aluminum hydroxide and 0.058g ammonium dihydrogen phosphate, add 10mm zirconium balls with a mass ratio of 10:1, fill the container with nitrogen for protection, and ball mill at 300rpm for 6h to obtain mixed powder;

[0046] S2. The mixed powder from S1 is transferred to a tube furnace and calcined under argon protection. The temperature is increased to 350℃ at a rate of 1℃ / min and held for 15 hours. After natural cooling, high-capacity sodium ferric sulfate cathode material Na is obtained. 2.4 Fe 1.8 Al 0.01 (SO4)3(PO4) 0.01 / C.

[0047] Example 3

[0048] The high-capacity sodium ferric sulfate cathode material and its preparation method of the present invention specifically include the following steps:

[0049] S1. Mix 8.52g anhydrous sodium sulfate, 15.29g ferrous sulfate monohydrate, 1.08g graphene, 0.039g aluminum hydroxide and 0.058g ammonium dihydrogen phosphate, add 10mm zirconium balls with a mass ratio of 10:1, fill the container with nitrogen for protection, and ball mill at 400rpm for 8h to obtain mixed powder;

[0050] S2. The mixed powder from S1 is transferred to a tube furnace and calcined under argon protection. The temperature is increased to 400℃ at a rate of 3℃ / min and held for 6 hours. After natural cooling, high-capacity sodium ferric sulfate cathode material Na is obtained. 2.4 Fe 1.8 Al 0.01 (SO4)3(PO4) 0.01 / C.

[0051] Example 4

[0052] The high-capacity sodium ferric sulfate cathode material and its preparation method of the present invention specifically include the following steps:

[0053] S1. After mixing sodium source, iron source, carbon coating material, aluminum salt flux and phosphate flux, add 10mm zirconium balls with a mass ratio of 10:1, fill the tank with nitrogen for protection, and ball mill at 200rpm for 12h to obtain mixed powder.

[0054] S2. The mixed powder from S1 is transferred to a tube furnace and calcined under nitrogen and / or argon protection. The temperature is increased to 300℃ at a rate of 5℃ / min and held for 18 hours. After natural cooling, high-capacity sodium ferric sulfate cathode material Na is obtained. 2.4 Fe 1.8 Al 0.01 (SO4)3(PO4) 0.01 / C.

[0055] Comparative Example 1 is basically the same as Example 1, except that aluminum hydroxide and ammonium dihydrogen phosphate are not added.

[0056] S1. Mix 8.52g of anhydrous sodium sulfate, 15.29g of ferrous sulfate monohydrate and 1.08g of carbon nanotubes, add 10mm zirconium balls with a mass ratio of 10:1, fill the container with nitrogen for protection, and ball mill at 300rpm for 6h to obtain mixed powder.

[0057] S2. The mixed powder from S1 is transferred to a tube furnace and calcined under argon protection. The temperature is increased to 350℃ at a rate of 1℃ / min and held for 15 hours. After natural cooling, high-capacity sodium ferric sulfate cathode material Na is obtained. 2.4 Fe 1.8 (SO4)3 / C.

[0058] Comparative Example 2 is basically the same as Example 1, except that aluminum hydroxide is not added.

[0059] S1. Mix 8.52g anhydrous sodium sulfate, 15.29g ferrous sulfate monohydrate, 1.08g carbon nanotubes, 0.039g aluminum hydroxide and 0.058g ammonium dihydrogen phosphate, add 10mm zirconium balls with a mass ratio of 10:1, fill the container with nitrogen for protection, and ball mill at 300rpm for 6h to obtain mixed powder;

[0060] S2. The mixed powder from S1 is transferred to a tube furnace and calcined under argon protection. The temperature is increased to 350℃ at a rate of 1℃ / min and held for 15 hours. After natural cooling, high-capacity sodium ferric sulfate cathode material Na is obtained. 2.4 Fe 1.8 (SO4)3(PO4) 0.01 / C.

[0061] Comparative Example 3 is basically the same as Example 1, except that ammonium dihydrogen phosphate is not added.

[0062] S1. Mix 8.52g anhydrous sodium sulfate, 15.29g ferrous sulfate monohydrate, 1.08g carbon nanotubes, 0.039g aluminum hydroxide and 0.058g ammonium dihydrogen phosphate, add 10mm zirconium balls with a mass ratio of 10:1, fill the container with nitrogen for protection, and ball mill at 300rpm for 6h to obtain mixed powder;

[0063] S2. The mixed powder from S1 is transferred to a tube furnace and calcined under argon protection. The temperature is increased to 350℃ at a rate of 1℃ / min and held for 15 hours. After natural cooling, high-capacity sodium ferric sulfate cathode material Na is obtained. 2.4 Fe 1.8 Al 0.01 (SO4)3 / C.

[0064] Test Example 1

[0065] SEM tests were performed on the sodium-ion battery cathode materials of Example 1 and Comparative Example 1, and the results are as follows: Figure 1 As shown. From Figure 1 It can be seen that in the product of Example 1 with added flux, the carbon nanotubes are more uniformly combined with the particles, and there is no agglomeration or entanglement. However, in Comparative Example 1, it can be seen that the carbon nanotubes are not well coated on the particle surface, which will hinder the migration of sodium ions and thus affect the discharge performance.

[0066] Test Example 2

[0067] XRD tests were performed on the sodium-ion battery cathode materials of Example 1 and Comparative Example 1, and the results are as follows: Figure 2 As shown. From Figure 2 It can be seen that the characteristic peaks of Example 1 and Comparative Example 1 are not significantly different. However, the relative intensity of the characteristic peak of sodium ferric sulfate in Example 1 is higher than that in Comparative Example 1, indicating that the proportion of active product is higher, the yield is higher, and therefore the discharge specific capacity will also be higher.

[0068] Test Example 3

[0069] The positive electrode materials of Example 1 and Comparative Examples 1-3 were respectively fabricated into coin cells, wherein the weight ratio of electrode components was positive electrode material: conductive agent (acetylene black): binder (PVDF) = 90:5:5; the negative electrode was a sodium sheet, and the coin cell was tested at 25°C. The discharge performance at 0.2C was as follows: Figure 3-4 As shown. From Figure 3-4As can be seen, Example 1 exhibits a higher discharge specific capacity of 90.7 mAh / g, while Comparative Example 1 only reaches 52.1 mAh / g, indicating that the addition of flux does indeed promote the formation of active products and demonstrates better electrical performance. Compared to the performance of Comparative Example 1, Comparative Example 2 and Comparative Example 3 both show a certain degree of improvement in discharge specific capacity, reaching 72.1 mAh / g and 75.0 mAh / g, respectively. This indicates that aluminum salt flux or phosphate flux alone can play a role in fluxing and improving the yield of active products. However, compared with the results of Example 1, it shows that the effect of using both types of fluxes simultaneously is better. This may be because the two fluxes have a certain synergistic effect while fluxing, thus exhibiting better electrical performance.

[0070] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A high-capacity sodium iron sulfate positive electrode material, characterized by, The high-capacity sodium iron sulfate positive electrode material comprises at least one compound of formula Na x Fe y Al z (SO4)3(PO4) m / C, Wherein, 2≤x≤3, 1.5≤y≤2, 0<z≤0.02, 0<m≤0.02; the values of x, y, z, m satisfy the charge balance of the chemical formula; The preparation method of the high-capacity sodium iron sulfate positive electrode material comprises the following steps, S1, under a protective atmosphere, ball milling a sodium source, an iron source, a carbon-coated material, and a fluxing agent to obtain a mixed powder; the fluxing agent comprises an aluminum salt fluxing agent and a phosphate fluxing agent; the aluminum salt fluxing agent is selected from one or more of aluminum hydroxide, aluminum sulfate, and aluminum phosphate; the phosphate fluxing agent is selected from one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, ammonium dihydrogen phosphate, and ammonium hydrogen phosphate; S2, calcining the mixed powder of S1 to obtain the high-capacity sodium iron sulfate positive electrode material.

2. The high-capacity sodium iron(III) sulfate positive electrode material according to claim 1, characterized in that, In S1, the sodium source is selected from anhydrous sodium sulfate and / or sodium sulfate heptahydrate; the iron source is selected from one or more of anhydrous ferrous sulfate, ferrous sulfate monohydrate, and ferrous sulfate heptahydrate; and the carbon-coated material is selected from one or more of conductive carbon black, graphene, and carbon nanotubes.

3. The high-capacity sodium iron(III) sulfate positive electrode material according to claim 1, characterized in that, In S1, the mass fraction of the carbon-coated material is 1wt%-6wt% of the total material.

4. The high-capacity sodium iron(III) sulfate positive electrode material of claim 1, characterized in that, In S1, the rotation speed of the ball milling is 200rpm-500rpm, and the time is 5h-12h.

5. The high-capacity sodium iron (III) sulfate positive electrode material of claim 1, wherein, In S2, the calcination temperature is 300℃-400℃, the heating rate is 1℃ / min-5℃ / min, and the time is 6h-18h.

6. A sodium-ion battery cathode, characterized in that, The sodium ion battery positive electrode is prepared from the high-capacity sodium iron sulfate positive electrode material of any one of claims 1-5.

7. A sodium-ion battery, characterized in that, The positive electrode of the sodium ion battery is prepared from the sodium ion battery positive electrode of claim 6.

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