Preparation method and application of sodium-ion battery cathode material

Abstract

This invention provides a method for preparing a sodium-ion battery cathode material. The method includes: dispersing a sodium source compound, ferric hydrogen phosphate hydrate, and a carbon source compound in water at a certain ratio and stirring to obtain a dispersion; milling the dispersion in a sand mill for a certain time to obtain a slurry; drying the milled slurry to obtain a powdered precursor; and sintering and pulverizing the powdered precursor to obtain the sodium-ion battery cathode material. The sodium-ion battery cathode material prepared by this invention has high crystal phase purity and higher compaction density and energy density. Sodium-ion batteries prepared based on the sodium-ion battery cathode material of this invention exhibit good battery cycle performance and stability. Furthermore, the preparation method has a simple process flow and is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and more specifically, to a method for preparing and applying a sodium-ion battery cathode material. Background Technology

[0002] As the most advanced rechargeable battery in terms of overall performance, lithium-ion batteries were first commercialized in the 1990s. After years of research, lithium-ion batteries have developed into a mature battery technology. However, limited by the abundance of lithium in the Earth's crust, lithium-ion batteries cannot support the growing energy storage market. Sodium-ion batteries operate on a similar principle to lithium-ion batteries, and sodium salts are abundant and easy to mine, giving them a greater advantage for large-scale applications in the energy storage field.

[0003] Sodium-ion batteries mainly consist of a positive electrode, a negative electrode, an electrolyte, a separator, and auxiliary components. Among these, the positive and negative electrode materials are crucial to the performance of the sodium-ion battery system, with the positive electrode material being particularly important. Sodium-ion battery positive electrode materials are classified into three main categories: transition metal oxides, Prussian white / blue, and polyanionic types. Polyanionic sodium-ion battery positive electrode materials have the advantages of structural stability and small volume change during charge and discharge. Among polyanionic sodium-ion battery positive electrode materials, iron-based sodium batteries have the advantages of lowest cost and non-toxicity. Sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7) is the most promising positive electrode material among iron-based sodium batteries, possessing advantages such as low cost, environmental friendliness, high theoretical capacity (129mAh / g), excellent cycle performance, and low volume expansion (approximately 4%).

[0004] Currently, the high-temperature solid-state method using the grinding-spraying-sintering process is the most efficient production method for preparing cathode materials for secondary batteries. However, due to the influence of the processing, the raw materials used in the preparation of sodium iron pyrophosphate using this process are not uniformly mixed at the microscopic level, resulting in the generation of impurities such as sodium iron phosphate and sodium iron pyrophosphate. This leads to low crystalline phase purity in the prepared cathode material, and these drawbacks severely limit the subsequent applications of this sodium iron pyrophosphate cathode material. Summary of the Invention

[0005] In view of the above, the present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a method for preparing a sodium-ion battery cathode material and its application. The sodium-ion battery cathode material prepared by the method of the present invention has high crystal phase purity and higher compaction density and energy density. Furthermore, the preparation method has a simple process flow and is suitable for large-scale industrial production.

[0006] Therefore, in a first aspect, embodiments of the present invention provide a method for preparing a sodium-ion battery cathode material, the method comprising: dispersing a sodium source compound, ferric hydrogen phosphate hydrate and a carbon source compound in water in a certain proportion and stirring to obtain a dispersion; placing the dispersion in a sand mill and milling for a certain time to obtain a slurry; drying the milled slurry to obtain a powdered precursor; and sintering and pulverizing the powdered precursor to obtain the sodium-ion battery cathode material.

[0007] Preferably, the sodium source compound and the iron hydrogen phosphate hydrate are added in a molar ratio of n(Na):n(Fe) = 4:3.

[0008] Preferably, the sodium source compound is one or more of sodium formate, sodium acetate, sodium citrate, sodium oxalate, sodium chloride, sodium nitrate, and sodium sulfate.

[0009] Preferably, the amount of carbon source added is 10%-55 wt% of the amount of ferric hydrogen phosphate hydrate added.

[0010] Preferably, the carbon source compound is one or more of the following: petrolatum, stearic acid, sucrose, oxalic acid, ascorbic acid, formaldehyde, acetaldehyde, n-butyraldehyde, lactic acid, citric acid, malic acid, oxalic acid, adipic acid, soluble starch, glucose, polyethylene glycol, maltose, cyclodextrin, carbon nanotubes, acetylene black, and graphene.

[0011] Preferably, the sand mill employs one of the following sand milling methods: disc type, pin type, or turbine type; the particle size of the slurry after sand milling is controlled to be 0.1 μm. <DN50<5μm。

[0012] Preferably, the drying method can be one or more of the following: forced air drying, vacuum drying, freeze drying, and spray drying.

[0013] Preferably, the sintering conditions include a sintering atmosphere, a sintering temperature, and a sintering time. The sintering atmosphere includes one or a mixture of nitrogen, argon, and helium. The sintering temperature is 450-700℃, and the heating rate is 1-3℃ / min. The sintering time is 6-24h.

[0014] Preferably, the pulverization method can be one or both of mechanical pulverization and air jet pulverization.

[0015] Secondly, embodiments of the present invention provide a sodium-ion battery, including the sodium-ion battery cathode material provided in the first aspect above.

[0016] The method for preparing sodium-ion battery cathode materials provided in this invention uses iron-hydrogen phosphate hydrate (Fe3(HPO4)4·H2O) with a fixed iron-phosphorus ratio as a precursor, eliminating the influence of the processing on the designed raw material ratio at the microscopic level, ensuring the uniformity of the raw materials, and resulting in sodium-ion battery cathode materials with high crystal phase purity, better crystallinity, superior electrochemical performance, and higher compaction density and energy density. Furthermore, this preparation method has a simple process flow and is suitable for large-scale industrial production. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the preparation method of the sodium-ion battery cathode material provided in an embodiment of the present invention.

[0018] Figure 2 This is a SEM image of the sodium-ion battery cathode material prepared in Example 1 of the present invention.

[0019] Figure 3 The image shows the XRD pattern of the sodium-ion battery cathode material prepared in Example 1 of this invention.

[0020] Figure 4 The first charge-discharge curve of the coin cell assembled from the sodium-ion battery cathode material prepared in Example 1 of the present invention at 0.1C.

[0021] Figure 5 The image shows the XRD pattern of the sodium-ion battery cathode material prepared in Example 2 of this invention.

[0022] Figure 6 The first charge-discharge curve of the coin cell assembled with the sodium-ion battery cathode material prepared in Example 2 of the present invention at 0.1C.

[0023] Figure 7 The image shows the XRD pattern of the sodium-ion battery cathode material prepared in Example 3 of this invention.

[0024] Figure 8 The first charge-discharge curve of the coin cell assembled with the sodium-ion battery cathode material prepared in Example 3 of the present invention at 0.1C. Detailed Implementation

[0025] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0026] The following disclosure provides numerous different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. Additionally, examples of various specific processes and materials are provided in this invention; however, those skilled in the art will recognize the applicability of other processes and / or the use of other materials.

[0027] This invention provides a method for preparing and applying a sodium-ion battery cathode material, which is used to prepare a sodium-ion battery cathode material with high crystalline phase purity, high compaction density, and high energy density. The sodium-ion battery cathode material of this invention is sodium iron pyrophosphate cathode material, with the chemical formula Na4Fe3(PO4)2P2O7. Sodium-ion batteries prepared based on the sodium-ion battery cathode material of this invention exhibit good battery cycle performance and stability.

[0028] like Figure 1 As shown, a first aspect of the present invention provides a method for preparing a sodium-ion battery cathode material, comprising the following steps:

[0029] Step S1: Disperse the sodium source compound, ferric hydrogen phosphate hydrate, and carbon source compound in water in a certain proportion and stir to obtain a dispersion;

[0030] In this embodiment of the invention, the chemical formula of the ferric hydrogen phosphate hydrate is Fe3(HPO4)4·H2O, and the amount of sodium source compound and the ferric hydrogen phosphate hydrate added in the dispersion is in a molar ratio of n(Na):n(Fe) = 4:3.

[0031] The sodium source compound may be one or more of sodium formate, sodium acetate, sodium citrate, sodium oxalate, sodium chloride, sodium nitrate, and sodium sulfate.

[0032] The amount of carbon source added is 10%-55wt% of the amount of ferric phosphate hydrate added; the carbon source compound can be one or more of the following: petrolatum, stearic acid, sucrose, oxalic acid, ascorbic acid, formaldehyde, acetaldehyde, n-butyraldehyde, lactic acid, citric acid, malic acid, oxalic acid, adipic acid, soluble starch, glucose, polyethylene glycol, maltose, cyclodextrin, carbon nanotubes, acetylene black, and graphene.

[0033] Step S2: Place the dispersion in a sand mill and mill for a certain period of time to obtain a slurry;

[0034] The sand mill employs one of three milling methods: disc mill, pin mill, or turbine mill. The particle size of the milled slurry is controlled to be 0.1 μm. <DN50<5μm。

[0035] Step S3: Dry the slurry after sand milling to obtain a powdered precursor;

[0036] The drying method can be one or more of the following: forced air drying, vacuum drying, freeze drying, and spray drying.

[0037] Step S4: After sintering and pulverizing the powdered precursor, the sodium-ion battery cathode material is obtained.

[0038] The sintering conditions include the sintering atmosphere, sintering temperature, and sintering time. The sintering atmosphere includes one or a mixture of nitrogen, argon, and helium; the sintering temperature can be 450-700℃, with a heating rate of 1-3℃ / min; and the sintering time can be 6-24 hours. The pulverization method can be one or both of mechanical pulverization and air jet pulverization.

[0039] The method for preparing sodium-ion battery cathode materials provided in this invention uses ferric phosphate hydrate (Fe3(HPO4)4·H2O) with a fixed iron-phosphorus ratio as a precursor, eliminating the influence of the processing on the designed raw material ratio at the microscopic level, ensuring the uniformity of the raw materials, and resulting in sodium-ion battery cathode materials with high crystal phase purity, better crystallinity, superior electrochemical performance, and higher compaction density and energy density. Sodium-ion batteries prepared based on the sodium-ion battery cathode material of this invention exhibit good battery cycle performance and stability. Furthermore, the preparation method has a simple process flow and is suitable for large-scale industrial production applications.

[0040] The following detailed description, in conjunction with some specific embodiments, further illustrates the specific process and effects of the preparation method of the sodium-ion battery cathode material of the present invention, but does not limit the scope of protection of the present invention.

[0041] Example 1

[0042] This embodiment provides a method for preparing a sodium-ion battery cathode material. The sodium-ion battery cathode material prepared in this embodiment is Na4Fe3(PO4)2P2O7 cathode material, and includes the following steps:

[0043] 1 mol of ferric hydrogen phosphate hydrate and 4 mol of sodium nitrate were weighed and dispersed in deionized water. Glucose, at a mass equal to 20% of the ferric hydrogen phosphate hydrate mass, was added to the deionized water, and the mixture was stirred to obtain a dispersion. The dispersion was then milled until the particle size (DN50) of the solid particles in the dispersion reached 0.2 μm, at which point milling was stopped to obtain a slurry. The milled slurry was then spray-dried to obtain a powdered precursor. The obtained powdered precursor was placed in a nitrogen atmosphere and heated to 500°C at a rate of 2°C / min, held at that temperature for 18 hours, and after cooling and crushing, Na4Fe3(PO4)2P2O7 sodium-ion battery cathode material was obtained.

[0044] Figure 2 This is a SEM image of the Na4Fe3(PO4)2P2O7 cathode material prepared in this embodiment;

[0045] Figure 3 The image shows the XRD pattern of the Na4Fe3(PO4)2P2O7 cathode material prepared in this embodiment.

[0046] The Na4Fe3(PO4)2P2O7 positive electrode material, acetylene black, and PVDF prepared in this embodiment were mixed with an appropriate amount of NMP at a mass ratio of 70:20:10 to form a homogenized slurry. The black slurry was then coated onto aluminum foil using a 150μm four-sided coating tool. The membrane was then vacuum-dried in a 110℃ vacuum drying oven for 6 hours. The dried electrode membrane was then punched into circular pieces of uniform radius using a punching machine to obtain the positive electrode. Using metallic sodium as the negative electrode, a glass fiber membrane as the separator, and NaPF6 / EC+DEC+DMC (EC:DEC:DMC = 1:1:1 volume ratio) as the electrolyte, a coin cell half-cell was assembled in a glove box with a water and oxygen content of less than 0.01ppm. The test results are as follows: Figure 4 As shown, its discharge capacity reaches 109.7 mAh / g when the current density is 0.1C and the voltage range is 2.0-4.0V.

[0047] Example 2

[0048] This embodiment provides a method for preparing a sodium-ion battery cathode material. The sodium-ion battery cathode material prepared in this embodiment is Na4Fe3(PO4)2P2O7 cathode material, and includes the following steps:

[0049] 1 mol of ferric hydrogen phosphate hydrate and 4 mol of sodium chloride were weighed and dispersed in deionized water. Glucose, at a mass equal to 30% of the ferric hydrogen phosphate hydrate mass, was added to the deionized water, and the mixture was stirred to obtain a dispersion. The dispersion was then milled until the particle size (DN50) of the solid particles in the dispersion reached 3.0 μm, at which point milling was stopped to obtain a slurry. The milled slurry was then spray-dried to obtain a powdered precursor. The obtained powdered precursor was placed in a nitrogen atmosphere and heated to 550°C at a rate of 2°C / min, held at that temperature for 16 h, and after cooling and crushing, Na4Fe3(PO4)2P2O7 sodium-ion battery cathode material was obtained.

[0050] Figure 5 The image shows the XRD pattern of the Na4Fe3(PO4)2P2O7 cathode material prepared in this embodiment.

[0051] The Na4Fe3(PO4)2P2O7 positive electrode material, acetylene black, and PVDF prepared in this embodiment were mixed with an appropriate amount of NMP at a mass ratio of 70:20:10 to form a homogenized slurry. The black slurry was then coated onto aluminum foil using a 150μm four-sided coating tool. The membrane was then vacuum-dried in a 110℃ vacuum drying oven for 6 hours. The dried electrode membrane was then punched into circular pieces of uniform radius using a punching machine to obtain the positive electrode. Using metallic sodium as the negative electrode, a glass fiber membrane as the separator, and NaPF6 / EC+DEC+DMC (EC:DEC:DMC = 1:1:1 volume ratio) as the electrolyte, a coin cell half-cell was assembled in a glove box with a water and oxygen content of less than 0.01ppm. The test results are as follows: Figure 6 As shown, its discharge capacity reaches 112.9 mAh / g when the current density is 0.1C and the voltage range is 2.0-4.0V.

[0052] Example 3

[0053] This embodiment provides a method for preparing a sodium-ion battery cathode material. The sodium-ion battery cathode material prepared in this embodiment is Na4Fe3(PO4)2P2O7 cathode material, and includes the following steps:

[0054] 1 mol of ferric hydrogen phosphate hydrate and 4 mol of sodium acetate were weighed and dispersed in deionized water. Glucose, at a mass equal to 25% of the ferric hydrogen phosphate hydrate mass, was added to the deionized water, and the mixture was stirred to obtain a dispersion. The dispersion was then milled until the particle size (DN50) of the solid particles in the dispersion reached 4.6 μm, at which point milling was stopped to obtain a slurry. The milled slurry was then spray-dried to obtain a powdered precursor. The obtained powdered precursor was placed in a nitrogen atmosphere and heated to 600°C at a rate of 5°C / min, held at that temperature for 12 hours, and after cooling and crushing, the Na4Fe3(PO4)2P2O7 sodium-ion battery cathode material was obtained.

[0055] Figure 7 The image shows the XRD pattern of the Na4Fe3(PO4)2P2O7 cathode material prepared in this embodiment.

[0056] The Na4Fe3(PO4)2P2O7 positive electrode material, acetylene black, and PVDF prepared in this embodiment were mixed with an appropriate amount of NMP at a mass ratio of 70:20:10 to form a homogenized slurry. The black slurry was then coated onto aluminum foil using a 150μm four-sided coating tool. The membrane was then vacuum-dried in a 110℃ vacuum drying oven for 6 hours. The dried electrode membrane was then punched into circular pieces of uniform radius using a punching machine to obtain the positive electrode. Using metallic sodium as the negative electrode, a glass fiber membrane as the separator, and NaPF6 / EC+DEC+DMC (EC:DEC:DMC = 1:1:1 volume ratio) as the electrolyte, a coin cell half-cell was assembled in a glove box with a water and oxygen content of less than 0.01ppm. The test results are as follows: Figure 8 As shown, its discharge capacity reaches 110.5 mAh / g when the current density is 0.1C and the voltage range is 2.0-4.0V.

[0057] A second aspect of the present invention provides a sodium-ion battery, the sodium-ion battery comprising the sodium-ion battery cathode material prepared by the preparation method provided in the first aspect of the present invention.

[0058] In summary, the preparation method and application of the sodium-ion battery cathode material provided in this invention utilizes iron phosphate hydrate (Fe3(HPO4)4·H2O) with a fixed iron-phosphorus ratio as a precursor during the preparation process. This eliminates the influence of the processing on the designed raw material ratio at the microscopic level, ensuring the uniformity of the raw materials. This results in a sodium-ion battery cathode material with high crystal phase purity, better crystallinity, superior electrochemical performance, and higher compaction density and energy density. Sodium-ion batteries prepared based on the sodium-ion battery cathode material of this invention exhibit excellent battery cycle performance and stability. Furthermore, the preparation method has a simple process flow and is suitable for large-scale industrial production.

[0059] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0060] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing a sodium-ion battery cathode material, characterized in that, The preparation method includes: A sodium source compound, ferric hydrogen phosphate hydrate, and a carbon source compound are dispersed in water and stirred to obtain a dispersion. The sodium source compound and the ferric hydrogen phosphate hydrate are added in a molar ratio of n(Na):n(Fe) = 4:

3. The chemical formula of the ferric hydrogen phosphate hydrate is Fe3(HPO4)4·H2O, which serves as both an iron and phosphorus source. The amount of carbon source added is 10%-55 wt% of the amount of ferric hydrogen phosphate hydrate added. The dispersion was milled in a sand mill for a certain period of time to obtain a slurry. The particle size of the milled slurry was controlled to be 0.1 mm. < DN50 <5 ; The slurry after sand milling is dried to obtain a powdered precursor; After sintering and pulverizing the powdered precursor, the sodium-ion battery cathode material obtained is sodium iron pyrophosphate Na4Fe3(PO4)2P2O7.

2. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, The sodium source compound is one or more of sodium formate, sodium acetate, sodium citrate, sodium oxalate, sodium chloride, sodium nitrate, and sodium sulfate.

3. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, The carbon source compound is one or more of the following: petrolatum, stearic acid, sucrose, oxalic acid, ascorbic acid, formaldehyde, acetaldehyde, n-butyraldehyde, lactic acid, citric acid, malic acid, oxalic acid, adipic acid, soluble starch, glucose, polyethylene glycol, maltose, cyclodextrin, carbon nanotubes, acetylene black, and graphene.

4. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, The drying method is one or more of the following: forced air drying, vacuum drying, freeze drying, and spray drying.

5. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, The sintering conditions include sintering atmosphere, sintering temperature, and sintering time. The sintering atmosphere includes one or a mixture of nitrogen, argon, and helium. The sintering temperature is 450-700℃, and the heating rate is 1-3℃ / min. The sintering time is 6-24h.

6. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, The pulverization method is one or both of mechanical pulverization and air jet pulverization.

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