Preparation method of sodium ion battery positive electrode material, positive electrode material, positive electrode sheet and sodium ion battery

Abstract

This application provides a method for preparing a sodium-ion battery cathode material, the cathode material, the cathode electrode sheet, and a sodium-ion battery. The method for preparing the sodium-ion battery cathode material includes: subjecting a raw material containing a first sodium source, a ferrous salt, a sulfate, and a carbon source to a first ball milling process to obtain a first ball milled material; subjecting the first ball milled material to a first calcination process to obtain a sintered material; subjecting a mixture containing the sintered material and a second sodium source to a second ball milling process to obtain a second ball milled material, wherein the molar amount of sodium in the second sodium source accounts for 5% to 50% of the total molar amount of sodium in the mixture; and subjecting the second ball milled material to a second calcination process to obtain the sodium-ion battery cathode material. The secondary ball milling and calcination process can improve the crystallinity and structural stability of the cathode material, thereby improving its cycle stability and capacity retention in sodium-ion batteries.

Description

Technical Field

[0001] This application relates to the field of sodium-ion batteries, specifically to a method for preparing a sodium-ion battery cathode material, the cathode material, the cathode electrode sheet, and the sodium-ion battery. Background Technology

[0002] Sodium-ion batteries, with their abundant resources, low cost, excellent fast charging and rate performance, and outstanding safety, have demonstrated promising development prospects in the battery industry. As a crucial functional component of sodium-ion batteries, the cathode material plays a key role in improving their performance.

[0003] Polyanionic cathode materials have seen rapid development in recent years due to their advantages such as high energy density, excellent rate capability and cycle performance, high safety, and low cost. Among them, sodium ferrous sulfate polyanionic materials have attracted much attention from academia and industry due to their unique advantages such as high voltage and low cost. However, in actual production, the poor structural stability and low crystallinity of sodium ferrous sulfate materials themselves limit further improvement in their performance. Summary of the Invention

[0004] This application provides a method for preparing a sodium-ion battery cathode material, the cathode material, the cathode sheet, and a sodium-ion battery, aiming to obtain a sodium-ion battery cathode material with good crystal structure perfection and stability, thereby improving its performance, including capacity retention and cycle stability, when applied to sodium-ion batteries.

[0005] In a first aspect, embodiments of this application provide a method for preparing a sodium-ion battery cathode material, comprising:

[0006] The first ball milling material is obtained by first ball milling of raw materials containing a first sodium source, ferrous salt, sulfate and carbon source;

[0007] The first ball milling material is subjected to a first calcination treatment to obtain a sintered material;

[0008] The mixture containing the sintered material and the second sodium source is subjected to a second ball milling process to obtain a second ball milling material, wherein the molar amount of sodium element in the second sodium source accounts for 5% to 50% of the total molar amount of sodium element in the mixture;

[0009] The second ball milling material is subjected to a second calcination treatment to obtain a sodium-ion battery cathode material.

[0010] In this embodiment, sodium is added to the sodium-ion battery cathode material in two steps, followed by at least two ball milling and at least two sintering processes. This results in a sodium-ion battery cathode material with higher sodium-ion capacity and a more complete and stable crystal structure. More specifically, by subjecting the sintered material obtained from the first calcination treatment to a second ball milling treatment together with a second sodium source, the sintered material containing numerous crystal defects can be fully broken down and granulated, and thoroughly mixed with the second sodium source. Therefore, the second ball milling treatment followed by the second calcination treatment further improves the crystal structure of the material, making it more complete and stable. Furthermore, the second calcination treatment after adding the second sodium source further promotes the growth of the cathode material crystals, reduces grain boundary defects, and increases the crystallinity and crystal size of the cathode material, thereby improving the material's electronic conductivity. The cathode material with higher structural stability obtained through the second ball milling and second calcination treatments makes it less prone to irreversible structural changes or even destruction of the crystal structure during sodium ion insertion and extraction. This helps reduce capacity decay caused by cathode material structural degradation during cycling, thereby improving the cycle stability and capacity retention of the sodium-ion battery.

[0011] In some embodiments of this application, the second sodium source includes one or more combinations of sodium sulfate, sodium carbonate, sodium bicarbonate, and sodium hydroxide.

[0012] In some embodiments of this application, the second sodium source has the same chemical composition as the first sodium source.

[0013] In some embodiments of this application, the first sodium source includes one or more combinations of sodium sulfate, sodium carbonate, sodium bicarbonate, and sodium hydroxide.

[0014] In some embodiments of this application, the sulfate includes one or a combination of sodium sulfate, ferrous sulfate, or sodium sulfate.

[0015] In some embodiments of this application, the ferrous salt includes one or more combinations of ferrous sulfate, ferrous chloride, and ferrous ammonium sulfate.

[0016] In some embodiments of this application, the carbon source includes one or more combinations of carbon nanotubes, graphene, acetylene black, and conductive carbon black.

[0017] In some embodiments of this application, the first sodium source and the ferrous salt satisfy the molar ratio of sodium to iron as (0.5 to 1.9):1.

[0018] In some embodiments of this application, the sulfate and ferrous salt satisfy the molar ratio of sulfate group to iron element as (1.5~2):1.

[0019] In some embodiments of this application, the carbon source accounts for 1 wt% to 10 wt% of the total raw material.

[0020] In some embodiments of this application, the temperature of the first calcination treatment and the second calcination treatment is 300-400°C, the calcination time is 5-6 hours, and the heating rate is 2-3°C / min.

[0021] Secondly, embodiments of this application provide a cathode material, including a sodium-ion battery cathode material obtained by the preparation method provided in the first aspect of this application.

[0022] In some embodiments of this application, the chemical formula of the sodium-ion battery cathode material is Na. x Fe(SO4) y , where 1≤x≤2, 1.5≤y≤2.

[0023] In some embodiments of this application, the average particle size Dv50 of the sodium-ion battery cathode material satisfies 1.8μm≤Dv50≤3μm.

[0024] In some embodiments of this application, the specific surface area of ​​the sodium-ion battery cathode material is 12–20 m². 2 / g.

[0025] Thirdly, embodiments of this application provide a positive electrode sheet, including a sodium-ion battery positive electrode material obtained according to the preparation method provided in the first aspect of this application or a positive electrode material provided in the second aspect of this application.

[0026] Fourthly, this application provides a sodium-ion battery, including a positive electrode sheet provided according to the embodiments of the third aspect of this application. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a scanning electron microscope (SEM) image of the sodium-ion battery cathode material in Example 1 of this application;

[0029] Figure 2 This is a scanning electron microscope (SEM) image of the sodium-ion battery cathode material in Example 2 of this application;

[0030] Figure 3 This is a scanning electron microscope (SEM) image of the sodium-ion battery cathode material in Example 3 of this application;

[0031] Figure 4This is a scanning electron microscope (SEM) image of the sodium-ion battery cathode material in Example 4 of this application;

[0032] Figure 5 This is a scanning electron microscope (SEM) image of the sodium-ion battery cathode material in Example 5 of this application;

[0033] Figure 6 This is a scanning electron microscope (SEM) image of the sodium-ion battery cathode material in Example 6 of this application;

[0034] Figure 7 This is a scanning electron microscope (SEM) image of the sodium-ion battery cathode material in Example 7 of this application;

[0035] Figure 8 This is a scanning electron microscope (SEM) image of the sodium-ion battery cathode material in Example 8 of this application;

[0036] Figure 9 This is a scanning electron microscope (SEM) image of the sodium-ion battery cathode material in Example 9 of this application;

[0037] Figure 10 This is a scanning electron microscope (SEM) image of the sodium-ion battery cathode material in Example 10 of this application;

[0038] Figure 11 This is a scanning electron microscope (SEM) image of the sodium-ion battery cathode material in Comparative Example 1 of this application;

[0039] Figure 12 This is a scanning electron microscope (SEM) image of the sodium-ion battery cathode material in Comparative Example 2 of this application;

[0040] Figure 13 This is a scanning electron microscope (SEM) image of the sodium-ion battery cathode material in Comparative Example 3 of this application;

[0041] Figure 14 This is a scanning electron microscope (SEM) image of the sodium-ion battery cathode material in Comparative Example 4 of this application;

[0042] Figure 15 This is a scanning electron microscope (SEM) image of the sodium-ion battery cathode material in Comparative Example 5 of this application;

[0043] Figure 16 These are the first-cycle charge-discharge curves of Embodiments 1, 4, 5, 6 and Comparative Example 1 of this application;

[0044] Figure 17 These are the first charge-discharge curves of Embodiments 2, 3 and Comparative Example 2 of this application.

[0045] Figure 18 These are the first charge-discharge curves of Embodiments 7, 8 and Comparative Example 3 of this application.

[0046] Figure 19 These are the first charge-discharge curves of Embodiments 9, 10 and Comparative Example 4 of this application.

[0047] Figure 20 These are X-ray diffraction (XRD) patterns of the cathode materials of Examples 7, 8 and Comparative Example 3 of this application. Detailed Implementation

[0048] The features and exemplary embodiments of various aspects of this application will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a comprehensive understanding of this application. However, it will be apparent to those skilled in the art that this application can be implemented without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of this application by illustrating examples. In the accompanying drawings and the following description, at least some well-known structures and techniques are not shown to avoid unnecessarily obscuring the application; and, for clarity, the dimensions of some structures may be exaggerated. Furthermore, the features, structures, or characteristics described below can be combined in any suitable manner in one or more embodiments.

[0049] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0050] To address the problems in the prior art, this application provides a method for preparing a sodium-ion battery cathode material, the cathode material, the cathode sheet, and a sodium-ion battery.

[0051] Preparation method of sodium-ion battery cathode material

[0052] The first aspect of this application provides a method for preparing a sodium-ion battery cathode material, the method comprising the following steps S10 to S40.

[0053] S10. The raw material containing a first sodium source, ferrous salt, sulfate and carbon source is subjected to a first ball milling process to obtain a first ball milling material;

[0054] S20. The first ball mill material is subjected to a first calcination treatment to obtain a sintered material;

[0055] S30. The mixture containing the sintered material and the second sodium source is subjected to a second ball milling process to obtain a second ball milling material, wherein the molar amount of sodium element in the second sodium source accounts for 5% to 50% of the total molar amount of sodium element in the mixture.

[0056] S40. The second ball milling material is subjected to a second calcination treatment to obtain the sodium-ion battery cathode material.

[0057] According to the embodiments of this application, in the process of preparing sodium-ion battery cathode material, sodium element is added in two steps through a first sodium source and a second sodium source, and at least two ball milling and mixing and at least two sintering are performed. That is, the first sodium source is first ball milled and mixed with other raw materials and then calcined, and then the sintered material obtained from the first calcination treatment is subjected to a second ball milling treatment and a second calcination treatment with the second sodium source. This can obtain sodium-ion battery cathode material with higher sodium ion capacity, more complete and stable crystal structure.

[0058] Not intended to be limited by any theory or explanation, in the process of obtaining sintered material through the first calcination treatment of the first ball milling material, a sintered material containing sodium ferrous sulfate crystals is obtained through the molten solid-phase reaction of the raw materials. However, such sintered material contains a large number of impurities (such as unreacted raw materials) and crystal defects, and these impurities and crystal defects are encapsulated inside the sintered material, making it difficult to eliminate them by further extending the sintering time, especially for crystal defects. By subjecting the sintered material obtained from the first calcination treatment to a second ball milling treatment together with a second sodium source, the sintered material containing many crystal defects can be fully crushed and granulated, and thoroughly mixed with the second sodium source. It is understandable that the fully crushed and granulated sintered material can serve as a nucleus for the recrystallization of sodium ferrous sulfate during the second sintering process, which is beneficial to the growth of sodium ferrous sulfate crystals, thereby obtaining a sodium ferrous sulfate material with reduced impurities, improved crystallinity, and better structural stability.

[0059] Furthermore, by adding a second sodium source followed by a second calcination treatment, crystal growth in the cathode material can be further promoted, grain boundary defects reduced, and the crystallinity and crystal size of the cathode material improved, thereby enhancing the material's electronic conductivity. The cathode material obtained through the second ball milling and second calcination treatments exhibits higher structural stability, making it less prone to irreversible structural changes or even destruction of the crystal structure during sodium ion insertion and extraction. This helps reduce capacity decay caused by cathode material structural degradation during battery cycling, further improving the cycle stability and capacity retention of sodium-ion batteries.

[0060] In this embodiment, when the mixture containing the sintered material and the second sodium source is subjected to a second ball milling process, the molar amount of sodium in the second sodium source accounts for 5% to 50% of the total molar amount of sodium in the mixture. This allows the second sodium source to effectively supplement the sodium source, increasing the sodium ion content of the resulting sodium-ion battery cathode material, thereby improving the capacity density of the sodium-ion battery cathode material. Therefore, the embodiments of this application can provide a sodium-ion battery cathode material that combines high capacity density and structural stability.

[0061] In some embodiments, the molar amount of sodium from the second sodium source may be 8% to 30% of the total molar amount of sodium in the mixture, and more preferably 10% to 20%.

[0062] In some embodiments, the second sodium source includes one or more combinations of sodium sulfate, sodium carbonate, sodium bicarbonate, and sodium hydroxide.

[0063] In some embodiments, the second sodium source has the same chemical composition as the first sodium source.

[0064] In this application, the second sodium source having the same chemical composition as the first sodium source means that the second sodium source and the first sodium source are the same substance or have the same composition ratio. According to the embodiments of this application, when the second sodium source and the first sodium source have the same chemical composition, it is possible to avoid introducing other impurity ions into the cathode material, ensuring that the cathode material has high purity, thereby ensuring that it has good discharge capacity and cycle performance when applied to sodium-ion batteries.

[0065] In some embodiments, the first sodium source includes one or more combinations of sodium sulfate, sodium carbonate, sodium bicarbonate, and sodium hydroxide.

[0066] In some embodiments, the sulfate includes one or a combination of sodium sulfate, ferrous sulfate, or sodium sulfate.

[0067] In some embodiments of this application, the ferrous salt includes one or more combinations of ferrous sulfate, ferrous chloride, and ferrous ammonium sulfate.

[0068] In some embodiments, the carbon source includes one or more combinations of carbon nanotubes, graphene, acetylene black, and conductive carbon black.

[0069] In some embodiments, the first sodium source and the ferrous salt satisfy the molar ratio of sodium to iron as (0.5 to 1.9):1.

[0070] According to the embodiments of this application, controlling the molar ratio of sodium to iron in the raw materials within the aforementioned range is beneficial for preparing sodium-ion battery cathode materials with a suitable proportion of sodium and iron. During battery charging and discharging, when the molar ratio of iron atoms to sodium atoms in the cathode material is within the aforementioned range, iron atoms can participate in redox reactions, providing effective charge compensation for the insertion and extraction of sodium ions while maintaining the stability of the crystal structure. This results in sodium-ion battery cathode materials exhibiting excellent electrochemical performance, such as high capacity retention and improved charge / discharge voltage plateaus.

[0071] In some embodiments, the sulfate and ferrous salt satisfy the molar ratio of sulfate groups to iron as (1.5 to 2):1.

[0072] According to embodiments of this application, by controlling the molar ratio of sulfate groups to iron within the aforementioned range, it is beneficial to prepare a sodium-ion battery cathode material containing sulfate groups and iron in a suitable proportion, resulting in a higher iron content. Simultaneously, controlling the molar ratio of sulfate groups to iron within the aforementioned range also helps to increase the proportion of the sodium-ion battery cathode material in the reaction products, improving its purity and thus enhancing the discharge capacity of the cathode material.

[0073] In some embodiments, the carbon source accounts for 1 wt% to 10 wt% of the total raw material, optionally 2 wt% to 8 wt%, and further optionally 4 wt% to 6 wt%.

[0074] According to the embodiments of this application, controlling the content of carbon source in the raw materials within the above-mentioned range can improve the conductivity of the positive electrode material of sodium-ion batteries and enhance its dynamic performance, including fast charging performance, in sodium-ion batteries.

[0075] The sodium-ion battery cathode material prepared according to the method of the embodiments of this application can be sodium ferrous sulfate particles with a carbon layer coated on the surface.

[0076] In some embodiments, the temperatures of the first calcination treatment and the second calcination treatment are 300 to 400°C, for example, 320°C, 340°C, 350°C, 370°C, 380°C, or any range of two of the above values.

[0077] In some embodiments, the first calcination treatment and the second calcination treatment are carried out for 5 to 6 hours, and the heating rate is 2 to 3 °C / min.

[0078] cathode materials

[0079] An embodiment of the second aspect of this application provides a cathode material, including a sodium-ion battery cathode material obtained according to the preparation method of the first aspect of this application.

[0080] In some embodiments, the chemical formula of the sodium-ion battery cathode material is Na. x Fe(SO4) y , where 1≤x≤2, 1.5≤y≤2.

[0081] This embodiment provides the general chemical formula for the cathode material of sodium-ion batteries. It is understood that the subscripts in the formula only indicate the relative molar ratio between the corresponding elements or groups.

[0082] According to an embodiment of this application, the positive electrode material of the sodium-ion battery is sodium ferrous sulfate particles with a carbon coating on the surface.

[0083] In some embodiments, the average particle size Dv50 of the sodium-ion battery cathode material satisfies 1.8μm≤Dv50≤3μm, and can be optionally 2.2μm≤Dv50≤2.8μm.

[0084] The average particle size Dv50 is a well-known term in the art, representing the particle size corresponding to a cumulative volume distribution percentage of 50% for a material. It can be determined using methods and instruments known in the art, such as laser diffractometer according to GB / T 19077-2016 "Particle Size Analysis by Laser Diffraction".

[0085] In some embodiments, the particle size of the sodium-ion battery cathode material is in the range of 0.5 to 18 μm.

[0086] In some embodiments, the specific surface area of ​​the sodium-ion battery cathode material is 12–20 m². 2 / g, which can be selected as 15-18m 2 / g.

[0087] Specific surface area can be determined using methods and instruments known in the art, for example, by means of the methods and instruments specified in GB / T19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method".

[0088] Positive electrode sheet

[0089] An embodiment of the third aspect of this application provides a positive electrode sheet, including a sodium-ion battery positive electrode material obtained by the preparation method according to the first aspect of this application or a positive electrode material according to the second aspect of this application.

[0090] In some embodiments, the positive electrode includes a current collector and a positive electrode material film layer disposed on at least one surface of the current collector. The positive electrode material film layer includes a positive electrode material, a conductive agent, and a binder, wherein the positive electrode material includes a sodium-ion battery positive electrode material according to embodiments of this application.

[0091] In some embodiments, the mass ratio of conductive agent, binder and positive electrode material is 1-5:1-5:85-95.

[0092] Examples of current collectors include one of aluminum foil, nickel mesh, or aluminum-plastic composite film. Examples of conductive agents include acetylene black, carbon black, graphite, or combinations thereof. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber latex, or combinations thereof.

[0093] In some embodiments, the areal density of the positive electrode is 9.5–13.5 mg / cm³. 2 .

[0094] Sodium-ion batteries

[0095] An embodiment of the fourth aspect of this application provides a sodium-ion battery, including a positive electrode according to an embodiment of the third aspect of this application.

[0096] As will be understood by those skilled in the art, the sodium-ion battery according to embodiments of this application may further include a negative electrode, a separator, and an electrolyte. The negative electrode, separator, and electrolyte may be made of materials conventionally used in sodium-ion batteries, and will not be described in detail here.

[0097] Example

[0098] The following specific embodiments illustrate the present invention. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0099] In the following embodiments, the percentage of the molar amount of sodium provided by the first sodium source relative to the total molar amount of sodium in the mixture is expressed as a, and the percentage of the molar amount of sodium provided by the second sodium source relative to the total molar amount of sodium in the mixture is expressed as b.

[0100] Example 1

[0101] A sodium-ion battery cathode material (x = 1.5, y = 1.75, a = 50%, b = 50%) is prepared by the following method:

[0102] S10, weigh out 19.58g sodium sulfate, 55.84g ferrous sulfate and 5g carbon nanotubes (CNTs);

[0103] S20. Sodium sulfate, ferrous sulfate and CNTs are added to a ball milling jar in an argon atmosphere and ball milled to obtain the first ball milling material.

[0104] S30. The first ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350℃ at a heating rate of 2.5℃ / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sintered material. The chemical formula of the sintered material is Na. 0.75 Fe(SO4) 1.375 ;

[0105] S40. Continue to weigh 19.58g of sodium sulfate and mix it with the sintering material. Then, continue to put it into the ball mill jar under an argon atmosphere for secondary ball milling to obtain the second ball milling material.

[0106] S50. The second ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350°C at a heating rate of 2.5°C / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sodium-ion battery cathode material. The chemical formula of the sodium-ion battery cathode material is Na. 1.5 Fe(SO4) 1.75 .

[0107] Example 2

[0108] A sodium-ion battery cathode material (x = 1.2, y = 1.6, a = 50%, b = 50%) is prepared by the following method:

[0109] S10, weigh out 17.07g sodium sulfate, 60.86g ferrous sulfate and 5g carbon nanotubes (CNTs);

[0110] S20. Sodium sulfate, ferrous sulfate and CNTs are added to a ball milling jar in an argon atmosphere and ball milled to obtain the first ball milling material.

[0111] S30. The first ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350℃ at a heating rate of 2.5℃ / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sintered material. The chemical formula of the sintered material is Na. 0.6 Fe(SO4) 1.3 ;

[0112] S40. Continue to weigh 17.07g of sodium sulfate and mix it with the sintering material. Then, continue to put it into the ball mill jar under an argon atmosphere for secondary ball milling to obtain the second ball milling material.

[0113] S50. The second ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350°C at a heating rate of 2.5°C / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sodium-ion battery cathode material. The chemical formula of the sodium-ion battery cathode material is Na. 1.2 Fe(SO4) 1.6 .

[0114] Example 3

[0115] A sodium-ion battery cathode material (x = 1.2, y = 1.6, a = 90%, b = 10%) is prepared by the following method:

[0116] S10, weigh out 30.73g sodium sulfate, 60.86g ferrous sulfate and 5g carbon nanotubes (CNTs);

[0117] S20. Sodium sulfate, ferrous sulfate and CNTs are added to a ball milling jar in an argon atmosphere and ball milled to obtain the first ball milling material.

[0118] S30. The first ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350℃ at a heating rate of 2.5℃ / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sintered material. The chemical formula of the sintered material is Na. 1.08 Fe(SO4) 1.54 ;

[0119] S40. Continue to weigh 3.41g of sodium sulfate and mix it with the sintering material. Then, continue to put it into the ball mill jar under an argon atmosphere for secondary ball milling to obtain the second ball milling material.

[0120] S50. The second ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350°C at a heating rate of 2.5°C / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sodium-ion battery cathode material. The chemical formula of the sodium-ion battery cathode material is Na. 1.2 Fe(SO4) 1.6 .

[0121] Example 4

[0122] A sodium-ion battery cathode material (x = 1.5, y = 1.75, a = 70%, b = 30%) is prepared by the following method:

[0123] S10, weigh out 27.41g sodium sulfate, 55.84g ferrous sulfate and 5g carbon nanotubes (CNTs);

[0124] S20. Sodium sulfate, ferrous sulfate and CNTs are added to a ball milling jar in an argon atmosphere and ball milled to obtain the first ball milling material.

[0125] S30. The first ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350℃ at a heating rate of 2.5℃ / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sintered material. The chemical formula of the sintered material is Na. 1.05 Fe(SO4) 1.525 ;

[0126] S40. Continue to weigh 11.75g ​​of sodium sulfate and mix it with the sintering material. Then, continue to put it into the ball mill jar under an argon atmosphere for secondary ball milling to obtain the second ball milling material.

[0127] S50. The second ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350°C at a heating rate of 2.5°C / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sodium-ion battery cathode material. The chemical formula of the sodium-ion battery cathode material is Na. 1.5 Fe(SO4) 1.75 .

[0128] Example 5

[0129] A sodium-ion battery cathode material (x = 1.5, y = 1.75, a = 80%, b = 20%) is prepared by the following method:

[0130] S10, weigh out 31.33g sodium sulfate, 55.84g ferrous sulfate and 5g carbon nanotubes (CNTs);

[0131] S20. Sodium sulfate, ferrous sulfate and CNTs are added to a ball milling jar in an argon atmosphere and ball milled to obtain the first ball milling material.

[0132] S30. The first ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350℃ at a heating rate of 2.5℃ / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sintered material. The chemical formula of the sintered material is Na. 1.2 Fe(SO4) 1.6 ;

[0133] S40. Continue to weigh 7.83g of sodium sulfate and mix it with the sintering material. Then, continue to put it into a ball mill jar under an argon atmosphere for ball milling to obtain the second ball milling material.

[0134] S50. The second ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350°C at a heating rate of 2.5°C / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sodium-ion battery cathode material. The chemical formula of the sodium-ion battery cathode material is Na. 1.5 Fe(SO4) 1.75 .

[0135] Example 6

[0136] A sodium-ion battery cathode material (x = 1.5, y = 1.75, a = 90%, b = 10%) is prepared by the following method:

[0137] S10, weigh out 35.24g sodium sulfate, 55.84g ferrous sulfate and 5g carbon nanotubes (CNTs);

[0138] S20. Sodium sulfate, ferrous sulfate and CNTs are added to a ball milling jar in an argon atmosphere and ball milled to obtain the first ball milling material.

[0139] S30. The first ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350℃ at a heating rate of 2.5℃ / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sintered material. The chemical formula of the sintered material is Na. 1.35 Fe(SO4) 1.675 ;

[0140] S40. Continue to weigh 3.92g of sodium sulfate and mix it with the sintering material. Then, continue to put it into the ball mill jar under an argon atmosphere for secondary ball milling to obtain the second ball milling material.

[0141] S50. The second ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350°C at a heating rate of 2.5°C / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sodium-ion battery cathode material. The chemical formula of the sodium-ion battery cathode material is Na. 1.5 Fe(SO4) 1.75 .

[0142] Example 7

[0143] A sodium-ion battery cathode material (x = 1.8, y = 1.9, a = 50%, b = 50%) is prepared by the following method:

[0144] S10, weigh out 21.71g sodium sulfate, 51.59g ferrous sulfate and 5g carbon nanotubes (CNTs);

[0145] S20. Sodium sulfate, ferrous sulfate and CNTs are added to a ball milling jar in an argon atmosphere and ball milled to obtain the first ball milling material.

[0146] S30. The first ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350℃ at a heating rate of 2.5℃ / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sintered material. The chemical formula of the sintered material is Na. 0.9 Fe(SO4) 1.45 ;

[0147] S40. Continue to weigh 21.7g of sodium sulfate and mix it with the sintering material. Then, continue to put it into the ball mill jar under an argon atmosphere for secondary ball milling to obtain the second ball milling material.

[0148] S50. The second ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350°C at a heating rate of 2.5°C / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sodium-ion battery cathode material. The chemical formula of the sodium-ion battery cathode material is Na. 1.8 Fe(SO4) 1.9 .

[0149] Example 8

[0150] A sodium-ion battery cathode material (x = 1.8, y = 1.9, a = 90%, b = 10%) is prepared by the following method:

[0151] S10, weigh out 39.07g sodium sulfate, 51.59g ferrous sulfate and 5g carbon nanotubes (CNTs);

[0152] S20. Sodium sulfate, ferrous sulfate and CNTs are added to a ball milling jar in an argon atmosphere and ball milled to obtain the first ball milling material.

[0153] S30. The first ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350℃ at a heating rate of 2.5℃ / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sintered material. The chemical formula of the sintered material is Na. 1.62 Fe(SO4) 1.81 ;

[0154] S40. Continue to weigh 4.34g of sodium sulfate and mix it with the sintering material. Then, continue to put it into the ball mill jar under an argon atmosphere for secondary ball milling to obtain the second ball milling material.

[0155] S50. The second ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350°C at a heating rate of 2.5°C / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sodium-ion battery cathode material. The chemical formula of the sodium-ion battery cathode material is Na. 1.8 Fe(SO4) 1.9 .

[0156] Example 9

[0157] A sodium-ion battery cathode material (x = 2, y = 2, a = 50%, b = 50%) is prepared by the following method:

[0158] S10, weigh out 22.96g sodium sulfate, 49.09g ferrous sulfate and 5g carbon nanotubes (CNTs);

[0159] S20. Sodium sulfate, ferrous sulfate and CNTs are added to a ball milling jar in an argon atmosphere and ball milled to obtain the first ball milling material.

[0160] S30. The first ball milling material is put into a tube furnace in a nitrogen atmosphere and heated to 350°C at a heating rate of 2.5°C / min for calcination treatment. After holding at this temperature for 6 hours, it is cooled to obtain sintered material. The chemical formula of the sintered material is NaFe(SO4). 1.5 ;

[0161] S40. Continue to weigh 22.95g of sodium sulfate and mix it with the sintering material. Then, continue to put it into the ball mill jar under an argon atmosphere for secondary ball milling to obtain the second ball milling material.

[0162] S50. The second ball milling material is put into a tube furnace under a nitrogen atmosphere and heated to 350°C at a heating rate of 2.5°C / min for calcination treatment. After holding at the temperature for 6 hours, it is cooled to obtain the sodium-ion battery cathode material. The chemical formula of the sodium-ion battery cathode material is Na2Fe(SO4)2.

[0163] Example 10

[0164] A sodium-ion battery cathode material (x = 2, y = 2, a = 90%, b = 10%) is prepared by the following method:

[0165] S10, weigh out 41.32g of sodium sulfate, 49.09g of ferrous sulfate and 5g of carbon nanotubes (CNTs);

[0166] S20. Sodium sulfate, ferrous sulfate and CNTs are added to a ball milling jar in an argon atmosphere and ball milled to obtain the first ball milling material.

[0167] S30. The first ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350℃ at a heating rate of 2.5℃ / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sintered material. The chemical formula of the sintered material is Na. 1.8 Fe(SO4) 1.9 ;

[0168] S40. Continue to weigh 4.59g of sodium sulfate and mix it with the sintering material. Then, continue to put it into the ball mill jar under an argon atmosphere for secondary ball milling to obtain the second ball milling material.

[0169] S50. The second ball milling material is put into a tube furnace under a nitrogen atmosphere and heated to 350°C at a heating rate of 2.5°C / min for calcination treatment. After holding at the temperature for 6 hours, it is cooled to obtain the sodium-ion battery cathode material. The chemical formula of the sodium-ion battery cathode material is Na2Fe(SO4)2.

[0170] Comparative Example 1

[0171] A sodium-ion battery cathode material (x = 1.5, y = 1.75, a = 100%, b = 0) is prepared by the following method:

[0172] S10, weigh out 39.16g sodium sulfate, 55.84g ferrous sulfate and 5g carbon nanotubes (CNTs);

[0173] S20. Sodium sulfate, ferrous sulfate and CNTs are added to a ball milling jar in an argon atmosphere and ball milled to obtain ball milling material;

[0174] S30. The ball-milled material is placed in a tube furnace under a nitrogen atmosphere and heated to 350℃ at a heating rate of 2.5℃ / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sintered material. The chemical formula of the sintered material is Na. 1.5 Fe(SO4) 1.75 .

[0175] Comparative Example 2

[0176] A sodium-ion battery cathode material (x = 1.2, y = 1.6, a = 100%, b = 0) is prepared by the following method:

[0177] S10, weigh out 34.14g sodium sulfate, 60.86g ferrous sulfate and 5g carbon nanotubes (CNTs);

[0178] S20. Sodium sulfate, ferrous sulfate and CNTs are added to a ball milling jar in an argon atmosphere and ball milled to obtain ball milling material;

[0179] S30. The ball-milled material is placed in a tube furnace under a nitrogen atmosphere and heated to 350℃ at a heating rate of 2.5℃ / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sintered material. The chemical formula of the sintered material is Na. 1.2 Fe(SO4) 1.6 .

[0180] Comparative Example 3

[0181] A sodium-ion battery cathode material (x = 1.8, y = 1.9, a = 100%, b = 0) is prepared by the following method:

[0182] S10, weigh out 43.41g sodium sulfate, 51.59g ferrous sulfate and 5g carbon nanotubes (CNTs);

[0183] S20. Sodium sulfate, ferrous sulfate and CNTs are added to a ball milling jar in an argon atmosphere and ball milled to obtain ball milling material;

[0184] S30. The ball-milled material is placed in a tube furnace under a nitrogen atmosphere and heated to 350℃ at a heating rate of 2.5℃ / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sintered material. The chemical formula of the sintered material is Na. 1.8 Fe(SO4) 1.9 .

[0185] Comparative Example 4

[0186] A sodium-ion battery cathode material (x = 2, y = 2, a = 100%, b = 0) is prepared by the following method:

[0187] S10, weigh out 45.91g of sodium sulfate, 49.09g of ferrous sulfate and 5g of carbon nanotubes (CNTs);

[0188] S20. Sodium sulfate, ferrous sulfate and CNTs are added to a ball milling jar in an argon atmosphere and ball milled to obtain ball milling material;

[0189] S30. The ball milled material is put into a tube furnace under a nitrogen atmosphere and heated to 350°C at a heating rate of 2.5°C / min for calcination treatment. After holding at the temperature for 6 hours, it is cooled to obtain sintered material. The chemical formula of the sintered material is Na2Fe(SO4)2.

[0190] Comparative Example 5

[0191] A sodium-ion battery cathode material (x = 1.5, y = 1.75, a = 100%, b = 0) is prepared by the following method:

[0192] S10, weigh out 39.16g sodium sulfate, 55.84g ferrous sulfate and 5g carbon nanotubes (CNTs);

[0193] S20. Sodium sulfate, ferrous sulfate and CNTs are added to a ball milling jar in an argon atmosphere and ball milled to obtain ball milling material;

[0194] S30. The ball-milled material is placed in a tube furnace under a nitrogen atmosphere and heated to 350℃ at a heating rate of 2.5℃ / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sintered material. The chemical formula of the sintered material is Na. 1.5 Fe(SO4) 1.75 ;

[0195] S40. The sintered material is further fed into a ball mill jar under an argon atmosphere for secondary ball milling to obtain the second ball milling material.

[0196] S50. The second ball milling material is placed in a tube furnace under a nitrogen atmosphere and heated to 350°C at a heating rate of 2.5°C / min for calcination. After holding at this temperature for 6 hours, it is cooled to obtain the sodium-ion battery cathode material. The chemical formula of the sodium-ion battery cathode material is Na. 1.5 Fe(SO4) 1.75 .

[0197] Test section

[0198] 1) Average particle size Dv50 of sodium-ion battery cathode material

[0199] The sodium-ion battery cathode materials prepared in the examples and comparative examples were analyzed using a laser particle size analyzer according to GB / T 19077-2016. The test results are shown in Table 1.

[0200] 2) Specific surface area of ​​sodium-ion battery cathode material

[0201] Five grams of the obtained sodium-ion battery cathode material powder were placed in a sample tube and heated to degas. After degassing, the sample was weighed and placed on a testing instrument. Under constant temperature and low temperature (-296.7℃), the amount of gas adsorbed on the solid surface at different relative pressures was measured. Based on the Brown-Etter-Taylor (BET) multilayer adsorption theory and its formula, the monolayer adsorption amount of the sample was calculated, and the specific surface area of ​​the cathode material was determined. The test results are shown in Table 1.

[0202] 3) Preparation of sodium-ion batteries

[0203] Preparation of positive electrode sheet: Sodium-ion battery positive electrode materials prepared in each example and Comparative Example 1 were taken respectively. The conductive agent was conductive carbon black and the binder was polyvinylidene fluoride. The sodium-ion battery positive electrode material, conductive agent and binder were mixed in a mass ratio of 90:5:5. After mixing, the mixture was dissolved in N-methylpyrrolidone solvent, ground into a slurry and coated onto aluminum foil. The mixture was dried at 120°C for 12 hours to obtain the positive electrode sheet.

[0204] Preparation of coin cells: Sodium metal sheet is used as negative electrode, glass fiber is used as separator, the electrolyte consists of 1 mol / L sodium perchlorate and 5 wt% vinylene carbonate as solute, and ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1 as solvent. The positive electrode, separator, negative electrode, gasket and spring are installed in the CR2023 coin cell in the following order. 100 μL of electrolyte is injected and the coin cell is then sealed to obtain the coin cell.

[0205] The prepared button cells were subjected to charge and discharge tests, and the test results are shown in Tables 1 to 4 below.

[0206] Table 1:

[0207]

[0208] Combining the data in Table 1 and Figure 1 , Figure 4 , Figure 5 , Figure 6 , Figure 11 A comparison shows that the chemical formula of the product is Na. 1.5 Fe(SO4) 1.75When (x=1.5,y=1.75), the sodium source is ball-milled and calcined in two steps. Compared with the addition of the sodium source in Comparative Example 1, the primary particle growth of the obtained cathode material is more ordered, the crystallinity of the cathode material is significantly improved, and the crystal structure is more stable. Figure 15 SEM images of the cathode material in Comparative Example 5 are shown. It can be seen that without the addition of a second sodium source, the second ball milling and second calcination treatments alone did not significantly improve the morphology of the cathode material. This indicates that the second sodium source is one of the key factors in eliminating grain boundary defects, promoting further growth of sodium ferrous sulfate crystals, and improving crystallinity during the second ball milling and second calcination processes. Further combined with... Figure 16 The first-cycle charge-discharge curves show that the first-cycle discharge specific capacity of the cathode material obtained by adding sodium source in two steps is significantly higher than that of the cathode material obtained by adding sodium source in one step in Comparative Example 1. Furthermore, the discharge specific capacity of the cathode material is the highest when a = 80% and b = 20%, reaching 95.63 mAh / g.

[0209] Table 2:

[0210]

[0211] Combining the data in Table 2 and 2, Figure 3 , Figure 12 A comparison shows that when the chemical formula of the product is Na... 1.2 Fe(SO4) 1.6 When x = 1.2, y = 1.6, the cathode material obtained by ball milling and calcining the sodium source in two steps also exhibits better morphology and higher crystallinity, and combines with... Figure 17 As can be seen from the first-cycle charge-discharge curve, the first-cycle discharge specific capacity of the cathode material obtained by ball milling, mixing and calcining the sodium source in two steps is also significantly improved.

[0212] Table 3:

[0213]

[0214] Combining the data in Table 3 and Figure 7 , Figure 8 , Figure 13 A comparison shows that when the chemical formula of the product is Na... 1.8 Fe(SO4) 1.9 When x = 1.8, y = 1.9, the cathode material obtained by ball milling, mixing, and calcining the sodium source in two steps also exhibits better morphology and higher crystallinity. Figure 20The X-ray diffraction patterns show that the impurity phase peaks in the cathode material obtained by ball milling and calcining the sodium source in two steps have a lower influence on the material, indicating that the secondary ball milling of ferrous sulfate is more thorough and the material has higher stability. Further combined with... Figure 18 It can be seen that the first-cycle discharge specific capacity of the cathode material obtained by ball milling, mixing and calcining the sodium source in two steps is also significantly improved.

[0215] Table 4:

[0216]

[0217] Combining the data in Table 4 and Figure 9 , Figure 10 , Figure 14 The comparison shows that when the chemical formula of the product is Na2Fe(SO4)2 (x=2, y=2), the cathode material obtained by ball milling, mixing, and calcining the sodium source in two steps exhibits better morphology and higher crystallinity. Further combined with... Figure 19 It can be seen that the first-cycle discharge specific capacity of the cathode material obtained by ball milling, mixing and calcining the sodium source in two steps is also significantly improved.

[0218] In summary, the sodium-ion battery cathode material provided in this application significantly improves the crystallinity of the cathode material by ball milling, mixing, and calcining the sodium source in two steps. The cathode material has a better crystal structure and structural stability, which, when applied to the battery, can effectively improve its performance in sodium-ion batteries, including first-cycle discharge capacity and cycle stability.

[0219] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a sodium-ion battery cathode material, characterized in that, include: The first ball milling material is obtained by first ball milling of raw materials containing a first sodium source, ferrous salt, sulfate and carbon source; The first ball milling material is subjected to a first calcination treatment to obtain a sintered material; The mixture containing the sintered material and the second sodium source is subjected to a second ball milling process to obtain a second ball milling material, wherein the molar amount of sodium in the second sodium source accounts for 5% to 50% of the total molar amount of sodium in the mixture; The second ball milling material is subjected to a second calcination treatment to obtain a sodium-ion battery cathode material. The second sodium source has the same chemical composition as the first sodium source.

2. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, The second sodium source includes one or more combinations of sodium sulfate, sodium hydroxide, sodium carbonate, and sodium bicarbonate.

3. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, The first sodium source includes one or more combinations of sodium sulfate, sodium carbonate, sodium bicarbonate, and sodium hydroxide, and / or The sulfate includes one or a combination of sodium sulfate, ferrous sulfate, and / or sodium sulfate. The ferrous salt includes one or more combinations of ferrous sulfate, ferrous ammonium sulfate, and / or The carbon source includes one or more combinations of carbon nanotubes, graphene, acetylene black, and conductive carbon black.

4. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, The first sodium source and the ferrous salt satisfy the molar ratio of sodium to iron as (0.5~1.9):1, and / or The sulfate and ferrous salt satisfy a molar ratio of sulfate groups to iron of (1.5~2):1, and / or The carbon source accounts for 1 wt% to 10 wt% of the total raw materials.

5. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, The temperature of the first calcination treatment and the second calcination treatment is 300~400℃, the calcination time is 5~6h, and the heating rate is 2~3℃ / min.

6. A positive electrode material, characterized in that, The cathode material includes a sodium-ion battery cathode material obtained by the preparation method according to any one of claims 1-5, wherein the chemical formula of the sodium-ion battery cathode material is Na. x Fe(SO4) y , where 1≤x≤2, 1.5≤y≤2.

7. The cathode material according to claim 6, characterized in that, The average particle size Dv50 of the sodium-ion battery cathode material satisfies 1.8 μm ≤ Dv50 ≤ 3 μm, and / or The specific surface area of ​​the sodium-ion battery cathode material is 12~20m². 2 / g.

8. A positive electrode sheet, characterized in that, The positive electrode sheet includes the sodium-ion battery positive electrode material obtained by the preparation method according to any one of claims 1-5 or the positive electrode material according to any one of claims 6-7.

9. A sodium-ion battery, characterized in that, The sodium-ion battery includes the positive electrode sheet as described in claim 8.

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