A sodium-ion battery positive electrode material and a preparation method and application thereof

Abstract

The application discloses a sodium ion battery positive electrode material and a preparation method and application thereof, and the preparation method comprises the following steps: (1) metal salts are weighed according to the molar ratio of each metal element in a layered oxide positive electrode material of a sodium ion battery, and first mixed powder is obtained after being uniformly mixed; MXene material is uniformly mixed with sodium hydroxide to obtain second mixed powder; (2) the first mixed powder and the second mixed powder are stacked in an alternating stacking mode, wherein the bottom layer and the top layer are both second mixed powder layers, and the sodium ion battery positive electrode material is obtained through calcination treatment. In the application, MXene is used as a modifier to perform doping and coating modification treatment on the layered oxide positive electrode material, some metal atoms in the MXene enter the positive electrode material to play a doping role after etching of the MXene by sodium hydroxide, and the MXene which is not etched is coated on the surface of the layered oxide positive electrode material, so that the sodium ion positive electrode material with high conductivity and structural stability is obtained.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a sodium-ion battery cathode material, its preparation method, and its application. Background Technology

[0002] The scarcity and rising cost of lithium resources have prompted researchers to seek alternative solutions. The electrochemical intercalation and deintercalation process of sodium ions is a "rocking chair" mechanism similar to that of lithium-ion batteries, where sodium ions reversibly shuttle between the positive and negative electrode materials. Moreover, sodium resources are abundant, inexpensive, and readily available, making sodium-ion batteries a promising next-generation energy storage system that can replace lithium-ion batteries.

[0003] The cathode material for sodium-ion batteries primarily serves as a sodium-rich substrate. Currently, layered sodium oxides have attracted significant research attention due to their relative ease of synthesis, tunable voltage range, and high specific capacity. Common layered transition metal oxides include Na... x MO2 (M = Co, Mn, Fe, Cr, Ni, etc.) includes mono-, binary, and ternary multi-component layered oxides, Na x Coating MO2 ternary materials can improve their air stability, but the coating material reduces the conductivity of the layered oxide, resulting in poor rate performance of sodium-ion batteries when used as a sodium-ion cathode material. In addition, doping ternary materials can improve their cycle stability and air stability, but introducing inactive elements will reduce the specific capacity of the material.

[0004] Therefore, without affecting the specific capacity of the layered oxide cathode material in sodium-ion batteries, how to effectively improve the conductivity and air stability of the cathode material has become one of the key issues in sodium-ion battery related technologies. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a sodium-ion battery cathode material, its preparation method and application. MXene material is used as a modifier to dope and coat the layered oxide cathode material. By etching the MXene material with sodium hydroxide, some metal atoms in the MXene material enter the cathode material to play a doping role, thereby improving the structural stability of the cathode material. At the same time, the unetched MXene is coated on the surface of the layered oxide cathode material to improve the air stability and conductivity of the cathode material, thereby obtaining a sodium-ion battery cathode material with high conductivity and structural stability.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] The first aspect of this invention provides a method for preparing a sodium-ion battery cathode material, comprising the following steps:

[0008] (1) Weigh the metal salts according to the molar ratio of each metal element in the layered oxide cathode material of sodium-ion battery, mix them evenly to obtain the first mixed powder; mix MXene material with sodium hydroxide evenly to obtain the second mixed powder;

[0009] (2) The first mixed powder and the second mixed powder are stacked in an alternating layering manner to form a multi-layer alternating structure, wherein the bottom layer and the top layer of the multi-layer alternating structure are both the second mixed powder layer, and then calcined to obtain the sodium-ion battery cathode material.

[0010] Further, in step (1), the metal salt includes sodium salt and metal salts of other metal elements in the layered oxide cathode material, or includes sodium salt and precursor metal salt, wherein the metal elements in the precursor metal salt are other metal elements in the sodium-ion battery layered oxide cathode material besides sodium.

[0011] Furthermore, the metal salts of the other metal elements include one or more of copper-containing salts, nickel-containing salts, iron-containing salts, and manganese-containing salts; the copper-containing salts are one or more of copper oxide, cuprous oxide, and copper chloride; the nickel-containing salts are one or more of nickel sulfate, nickel chloride, nickel sulfamate, nickel bromide, nickel hydroxide, nickel carbonyl, and nickel oxide; the iron-containing salts are one or more of ferric oxide, ferrous oxide, ferric sulfate, ferric chloride, ferric nitrate, and ferrous oxalate; and the manganese-containing salts are one or more of potassium permanganate, potassium manganate, and manganese oxide.

[0012] More preferably, the metal salt comprises a sodium salt and a precursor metal salt Cu. x Ni y Fe z Mn 1-x-y-z (OH)2, wherein 0≤x≤0.2, 0≤y≤0.35, 0.2≤z≤0.4, 0.1≤1-xyz≤1, and more preferably 0.3≤1-xyz≤0.4; the sodium salt is selected from one or more of sodium carbonate, sodium hydroxide, sodium nitrate, and sodium oxalate.

[0013] Further, in step (1), the MXene material is M n+1 X n T x Where n is 1, 2, 3 or 4, M is Ti, V, Nb, Mo, Sc, Zr, Cr, Hf or Ta, X is C and / or N, and T is... x It can be -OH, -O, -F, or -Cl.

[0014] Further, in step (1), the MXene material is vanadium carbide (V4C3T). x ), tantalum carbide (Ta4C3T)x ), niobium carbide (Nb4C3T) x ), Titanium carbon (Ti3C2T) x One or more of the following.

[0015] Further, in step (1), the particle size D50 of the MXene material is preferably 0.5-5μm, such as 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, etc., including but not limited to the values ​​listed above.

[0016] Further, in step (1), the mass percentage of sodium hydroxide in the second mixed powder is preferably 10%-50%, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc., including but not limited to the mass percentages listed above.

[0017] Furthermore, in step (2), the mass ratio of each first powder mixing layer to each second powder mixing layer is preferably 1:0.05-0.3, for example 1:0.05-0.1, 1:0.1-0.2, 1:0.2-0.3, etc.

[0018] Furthermore, in step (2), the first mixed powder and the second mixed powder are stacked in an alternating layering manner to form a multi-layered alternating structure from top to bottom: second mixed powder layer - first mixed powder layer - second mixed powder layer - first mixed powder layer - second mixed powder layer.

[0019] Further, in step (2), pressure is applied to the multilayer alternating structure, the pressure being 0.1-5 MPa, preferably 1-3 MPa.

[0020] Further, in step (2), the calcination treatment step is: the heating rate is 2-10℃ / min, the calcination temperature is 700-1100℃, and the holding time is 10-24h, more preferably 10-15h.

[0021] Further, in step (2), the atmosphere of the calcination treatment includes one or more gases selected from air, CO2, N2, ammonia, oxygen, and CO.

[0022] A second aspect of this invention provides a sodium-ion battery cathode material, prepared by the method described in the first aspect, wherein the sodium-ion battery cathode material is Na... a [Ni b Fe c Mn d Cu e M' fO2@MXene, the sodium-ion battery cathode material has a core-shell structure, with MXene material coating the layered oxide cathode material of the sodium-ion battery, wherein 0.6≤a≤1.2, 0≤b≤0.4, 0<c≤0.33, 0<d≤0.4, 0<e≤0.1, b+c+d+e+f=1, M' is one or more of Zn, Mo, Co, Cr, Al, Ti, V, Nb, Sc, Zr, Hf, and Ta, and M' originates from the metal element etched out from the MXene material.

[0023] A third aspect of the present invention provides a sodium-ion battery comprising the sodium-ion battery cathode material described in the second aspect.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. This invention provides a method for preparing a sodium-ion battery cathode material. The method involves mixing and stacking metal salts, MXene materials, and an etchant in a specific manner, followed by calcination, to obtain a doped and modified cathode material. Specifically, a first mixed powder prepared by mixing the various metal salts is stacked with a second mixed powder prepared by mixing MXene materials and an etchant in an alternating layered manner to form a multi-layered alternating structure. The preparation of the second mixed powder facilitates the etching of the MXene material by the etchant, allowing some non-sodium-ion cathode material main element atoms from the MXene material to enter the cathode material, acting as dopants to improve the structural stability of the layered oxide cathode material. Furthermore, each layer of the first mixed powder is coated both above and below by the second mixed powder layer, improving the uniformity of doping and ensuring that unetched MXene materials are uniformly coated on the surface of the formed layered oxide cathode material, thereby improving the air stability and conductivity of the cathode material and ultimately enhancing the rate performance and cycle stability of the sodium-ion battery containing this cathode material.

[0026] 2. The present invention prepares sodium-ion battery cathode materials using the above-described preparation method. Compared with unmodified layered oxide cathode materials, the sodium-ion batteries constructed from these materials exhibit similar or higher specific capacity, and better rate performance and cycle stability. The specific capacity retention rate at 2C relative to the specific capacity at 0.2C is as high as 98.5%, and the capacity retention rate after 200 cycles at 1C is as high as 98.4%. Furthermore, the cathode material obtained by the above-described modification method, compared with the unmodified layered oxide cathode material, shows a smaller decrease in specific capacity when stored for the same period under the same air humidity conditions, demonstrating superior air stability. Attached Figure Description

[0027] Figure 1The image shows the XRD pattern of the sodium-ion battery cathode material prepared in Example 1.

[0028] Figure 2 The first charge-discharge curve of a sodium-ion battery constructed using the sodium-ion battery cathode material prepared in Example 1 as the cathode active material is shown.

[0029] Figure 3 The first charge-discharge curve of a sodium-ion battery constructed using the sodium-ion battery cathode material prepared in Example 4 as the cathode active material is shown.

[0030] Figure 4 The first charge-discharge curve of a sodium-ion battery constructed using the sodium-ion battery cathode material prepared in Comparative Example 1 as the cathode active material is shown. Detailed Implementation

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] As described in the background section, layered oxide cathode materials for sodium-ion batteries have attracted significant attention from researchers due to their relative ease of synthesis, tunable voltage range, and high specific capacity. However, these materials suffer from poor air stability, which affects their capacity and cycle performance in practical applications. Common Na... x MO2 ternary materials can improve their air stability through coating, but the coating material reduces the conductivity of the layered oxide, resulting in poor rate performance of sodium-ion batteries when used as a sodium-ion cathode material. While doping ternary materials can improve their cycle stability and air stability, the introduction of inactive elements will reduce the material's specific capacity.

[0033] To address the aforementioned technical problems, this invention provides a method for preparing a sodium-ion battery cathode material, comprising the following steps:

[0034] (1) Weigh the metal salts according to the molar ratio of each metal element in the layered oxide cathode material of sodium-ion battery, mix them evenly to obtain the first mixed powder; mix MXene material with sodium hydroxide evenly to obtain the second mixed powder;

[0035] (2) The first mixed powder and the second mixed powder are stacked in an alternating layering manner to form a multi-layer alternating structure, wherein the bottom layer and the top layer of the multi-layer alternating structure are both the second mixed powder layer, and the sodium-ion battery cathode material is obtained by calcination treatment.

[0036] To effectively improve the conductivity and air stability of the layered oxide cathode material without affecting its specific capacity, this invention prepares a cathode material that is simultaneously doped and modified by mixing and stacking the metal salt, MXene material, and etchant used to prepare the layered oxide cathode material in a specific manner, followed by calcination. The sodium-ion battery constructed from this cathode material has a specific capacity similar to or higher than that of the unmodified layered oxide cathode material, and also effectively improves the air stability of the cathode material, as well as the rate performance and cycle stability of the constructed sodium-ion battery.

[0037] Specifically, this invention involves stacking a first mixed powder, prepared by mixing various metal salts used to prepare layered oxide cathode materials for sodium-ion batteries, and a second mixed powder, prepared by mixing MXene material and an etchant, in an alternating layering manner to form a multilayered alternating structure. On the one hand, the preparation of the second mixed powder facilitates the etching of MXene material by the etchant, thereby allowing some non-sodium ion cathode material main element atoms in the MXene material to enter the cathode material, acting as dopants to improve the structural stability of the layered oxide cathode material. Furthermore, each layer of the first mixed powder is covered by the second mixed powder layer on both the top and bottom, which can improve the uniformity of doping and allow unetched MXene material to be uniformly coated on the surface of the formed layered oxide cathode material, thereby improving the air stability and conductivity of the cathode material, and thus enhancing the rate performance and cycle stability of the sodium-ion battery containing this cathode material.

[0038] In some preferred embodiments, the metal salt comprises sodium salt and metal salts of other metal elements in the layered oxide cathode material. The metal salts of other metal elements include one or more of copper-containing salts, nickel-containing salts, iron-containing salts, and manganese-containing salts. The copper-containing salts are one or more of copper oxide and copper chloride. The nickel-containing salts are one or more of nickel sulfate, nickel chloride, nickel sulfamate, nickel bromide, nickel hydroxide, nickel carbonyl, and nickel oxide. The iron-containing salts are one or more of iron oxide, ferrous oxide, ferric sulfate, ferric chloride, ferric nitrate, and ferrous oxalate. The manganese-containing salts are one or more of potassium permanganate, potassium manganate, and manganese oxide.

[0039] In some preferred embodiments, when the metal salt includes sodium salt and metal salts of other metal elements in the layered oxide cathode material, the first mixed powder is first pressed into a thin strip, and then stacked with the second mixed powder in an alternating layering manner to form a multi-layered alternating structure.

[0040] More preferably, the metal salt includes a sodium salt and a precursor metal salt Cu. x Ni y Fe z Mn 1-x-y-z(OH)2, wherein 0≤x≤0.2, 0≤y≤0.35, 0.2≤z≤0.4, 0.3≤1-xyz≤0.4; the sodium salt is selected from one or more of sodium carbonate, sodium hydroxide, sodium nitrate, and sodium oxalate.

[0041] In some preferred embodiments, the metal salt is mixed evenly in a solvent and dried to obtain a first mixed powder.

[0042] In some preferred embodiments, the MXene material is M n+1 X n T x (MXene is a layered transition metal carbonitride), where n represents the number of atomic layers, which can be 1, 2, 3, or 4; M represents a transition metal element, which can be Ti, V, Nb, Mo, Sc, Zr, Cr, Hf, or Ta; X represents C and N elements or one of them; T x It represents a functional group, which can be -OH, -O, -F or -Cl.

[0043] In some preferred embodiments, the MXene material is vanadium carbide (V4C3T). x ), tantalum carbide (Ta4C3T) x ), niobium carbide (Nb4C3T) x ), Titanium carbon (Ti3C2T) x One or more of the following, wherein T is -OH, -O, -F and -Cl.

[0044] In some preferred embodiments, the particle size D50 of the MXene material is preferably 0.5-5 μm, such as 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc., including but not limited to the values ​​listed above. The particle size of the MXene material affects the coating effect and the material's specific capacity. To achieve a good coating effect while avoiding a significant impact on the material's specific capacity, this invention preferably uses MXene materials with a particle size D50 of 0.5-5 μm.

[0045] In addition, in the above preparation method, sodium hydroxide is used as an etchant in order to achieve the etching effect on MXene material without introducing other alkali metal ions, and to avoid other alkali metal ions remaining in the bulk phase to form impurity phases.

[0046] In some preferred embodiments, the mass percentage of sodium hydroxide in the second mixed powder is preferably 10%-50%, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc., including but not limited to the mass percentages listed above. The second mixed powder is composed of MXene material and etchant sodium hydroxide. If the content of sodium hydroxide in the second mixed powder is too small, it will not have an etching effect and will not achieve an effective doping effect; however, the content of sodium hydroxide should not be too large either. Although excessive sodium hydroxide can effectively etch MXene and obtain more doped atoms, excessive etching will cause great damage to the structure of MXene material, forming more pores, and will lead to the sacrifice of metal in MXene material, reducing the metal content doping, thereby affecting the conductivity and structural stability of the MXene material coated on the surface of the cathode material. In some preferred embodiments, the mass ratio of each first mixing layer to each second mixing layer is preferably 1:0.05-0.3, such as 1:0.05-0.1, 1:0.1-0.2, 1:0.2-0.3, etc.; for example, the mass ratio of each first mixing layer to each second mixing layer may be 8.5:1.5, 8:2, or 9.5:0.5.

[0047] In some preferred embodiments, the first mixed powder and the second mixed powder are stacked in an alternating layering manner to form a multi-layered alternating structure from top to bottom: second mixed powder layer - first mixed powder layer - second mixed powder layer - first mixed powder layer - second mixed powder layer.

[0048] In some preferred embodiments, pressure is applied to the multilayer alternating structure to bring the powders into close contact; wherein the applied pressure is 0.1-5 MPa, preferably 1-3 MPa, and more preferably 1.5 MPa.

[0049] In some preferred embodiments, in the calcination step: the heating rate is 2-10℃ / min, preferably 5℃ / min, the calcination temperature is 700-1100℃, and the holding time is 10-24h, preferably 10-15h, and even more preferably 12h.

[0050] In some preferred embodiments, the atmosphere for the calcination treatment includes one or more gases selected from air, CO2, N2, ammonia, oxygen, and CO.

[0051] This invention also provides a sodium-ion battery cathode material, prepared by the above-described method; the sodium-ion battery cathode material is Na... a [Ni b Fe c Mn d Cu e M' fO2@MXene, the sodium-ion battery cathode material has a core-shell structure, with MXene material coated on the layered oxide cathode material of the sodium-ion battery, wherein 0.6≤a≤1.2, 0≤b≤0.4, 0<c≤0.33, 0<d≤0.4, 0<e≤0.1, b+c+d+e+f=1, M' is one or more of Zn, Mo, Co, Cr, Al, Ti, V, Nb, Sc, Zr, Hf, and Ta, and M' originates from the metal element etched out of the MXene material.

[0052] The present invention also provides a sodium-ion battery, comprising the above-mentioned sodium-ion battery cathode material.

[0053] 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. However, the embodiments described are not intended to limit the present invention.

[0054] Example 1

[0055] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0056] (1) Ni 0.25 Fe 0.34 Mn 0.33 Cu 0.08 (OH)2 and Na2CO3 were mixed evenly in ethanol at a molar ratio of 1:0.525 and dried to obtain the first mixed powder.

[0057] MXene material (Ti3C2OH) with a D50 of 2.5±0.5μm was mixed with NaOH at a mass ratio of 7:3 to obtain a second mixed powder.

[0058] (2) Spread the second mixed powder prepared in step (1) in the crucible, then spread the first mixed powder on the second mixed powder layer, and then spread the second mixed powder on the first mixed powder layer. Repeat the above operation to prepare a multi-layer alternating structure from top to bottom: second mixed powder layer-first mixed powder layer-second mixed powder layer-first mixed powder layer-second mixed powder layer; each first mixed powder layer contains the same mass of first mixed powder, and each second mixed powder layer contains the same mass of second mixed powder, wherein the mass ratio of each first mixed powder layer to the second mixed powder layer is 8.5:1.5; calcined at high temperature in air under a pressure of 1.5 MPa, with a heating rate of 5 °C / min to 950 °C, and held for 12 h to obtain sodium-ion battery cathode material.

[0059] The sodium-ion battery cathode material prepared in this embodiment was subjected to ICP analysis, and the results are as follows: Na: 1.01, Ni: 0.22, Fe: 0.33, Mn: 0.32, Cu: 0.07, Ti: 0.06; that is, the sodium-ion battery cathode material prepared in this embodiment is Na 0.88 [Ni 0.22 Fe 0.33 Mn 0.32 Cu 0.07 Ti 0.06 O2.

[0060] The Na prepared in this embodiment 1.01 [Ni 0.22 Fe 0.33 Mn 0.32 Cu 0.07 Ti 0.06 The O2 material was characterized by X-ray diffraction (XRD), and the characterization results are shown in Table 1 below. Figure 1 As shown:

[0061] Table 1. Location of characteristic peaks of materials

[0062]

[0063]

[0064] Table 1 shows the positions of characteristic peaks and the measured Na. 1.01 [Ni 0.22 Fe 0.33 Mn 0.32 Cu 0.07 Ti 0.06 The situation was compared with the XRD peak values ​​of O2; by Figure 1 The XRD pattern shows the characteristic peaks of the layered oxide material for sodium-ion batteries and the characteristic peaks of MXene, indicating that MXene is coated on the layered oxide material for sodium-ion batteries. In addition, due to the doping of a small number of elements, the (003) diffraction peak shifts slightly and is not significant.

[0065] Example 2

[0066] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0067] (1) Ni 0.25 Fe 0.34 Mn 0.33 Cu 0.08 (OH)2 and Na2CO3 were mixed evenly in ethanol at a molar ratio of 1:0.525 and dried to obtain the first mixed powder.

[0068] MXene material (Ti3C2OH) with a D50 of 2.5±0.5μm was mixed with NaOH at a mass ratio of 7:3 to obtain a second mixed powder.

[0069] (2) Spread the second mixed powder prepared in step (1) in the crucible, then spread the first mixed powder on the second mixed powder layer, and then spread the second mixed powder on the first mixed powder layer. Repeat the above operation to prepare a multi-layer alternating structure from top to bottom: second mixed powder layer-first mixed powder layer-second mixed powder layer-first mixed powder layer-second mixed powder layer; each first mixed powder layer contains the same mass of first mixed powder, and each second mixed powder layer contains the same mass of second mixed powder, wherein the mass ratio of each first mixed powder layer to the second mixed powder layer is 8.5:1.5; calcined at high temperature in air under a pressure of 1.5 MPa, with a heating rate of 5 °C / min to 850 °C, and held for 12 h to obtain sodium-ion battery cathode material.

[0070] The sodium-ion battery cathode material prepared in this embodiment was subjected to ICP analysis, and the results are as follows: Na: 1.00, Ni: 0.22, Fe: 0.33, Mn: 0.31, Cu: 0.07, Ti: 0.07; that is, the sodium-ion battery cathode material prepared in this embodiment is Na[Ni 0.22 Fe 0.33 Mn 0.31 Cu 0.07 Ti 0.07 O2.

[0071] Example 3

[0072] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0073] (1) Ni 0.25 Fe 0.34 Mn 0.33 Cu 0.08 (OH)2 and Na2CO3 were mixed evenly in ethanol at a molar ratio of 1:0.525 and dried to obtain the first mixed powder.

[0074] MXene material (Ti3C2OH) with a D50 of 2.5±0.5μm was mixed with NaOH at a mass ratio of 7:3 to obtain a second mixed powder.

[0075] (2) Spread the second mixed powder prepared in step (1) in the crucible, then spread the first mixed powder on the second mixed powder layer, and then spread the second mixed powder on the first mixed powder layer. Repeat the above operation to prepare a multi-layer alternating structure from top to bottom: second mixed powder layer-first mixed powder layer-second mixed powder layer-first mixed powder layer-second mixed powder layer; each first mixed powder layer contains the same mass of first mixed powder, and each second mixed powder layer contains the same mass of second mixed powder, wherein the mass ratio of each first mixed powder layer to the second mixed powder layer is 8.5:1.5; calcined at high temperature in air under a pressure of 1.5 MPa, with a heating rate of 5 °C / min to 1100 °C, and held for 12 h to obtain sodium-ion battery cathode material.

[0076] The sodium-ion battery cathode material prepared in this embodiment was subjected to ICP analysis, and the results are as follows: Na: 0.98, Ni: 0.22, Fe: 0.33, Mn: 0.32, Cu: 0.08, Ti: 0.05; that is, the sodium-ion battery cathode material prepared in this embodiment is Na 0.98 [Ni 0.22 Fe 0.33 Mn 0.32 Cu 0.08 Ti 0.05 O2.

[0077] Example 4

[0078] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0079] (1) Ni 0.25 Fe 0.34 Mn 0.33 Cu 0.08 (OH)2 and Na2CO3 were mixed evenly in ethanol at a molar ratio of 1:0.525 and dried to obtain the first mixed powder.

[0080] MXene material (Ti3C2OH) with a D50 of 1.0±0.5μm was mixed with NaOH at a mass ratio of 7:3 to obtain a second mixed powder.

[0081] (2) Spread the second mixed powder prepared in step (1) in the crucible, then spread the first mixed powder on the second mixed powder layer, and then spread the second mixed powder on the first mixed powder layer. Repeat the above operation to prepare a multi-layer alternating structure from top to bottom: second mixed powder layer-first mixed powder layer-second mixed powder layer-first mixed powder layer-second mixed powder layer; each first mixed powder layer contains the same mass of first mixed powder, and each second mixed powder layer contains the same mass of second mixed powder, wherein the mass ratio of each first mixed powder layer to the second mixed powder layer is 8.5:1.5; calcined at high temperature in air under a pressure of 1.5 MPa, with a heating rate of 5 °C / min to 950 °C, and held for 12 h to obtain sodium-ion battery cathode material.

[0082] The sodium-ion battery cathode material prepared in this embodiment was subjected to ICP analysis, and the results are as follows: Na: 1.01, Ni: 0.22, Fe: 0.33, Mn: 0.32, Cu: 0.07, Ti: 0.06; that is, the sodium-ion battery cathode material prepared in this embodiment is Na 1.01 [Ni 0.22 Fe 0.33 Mn 0.32 Cu 0.07 Ti 0.06 O2.

[0083] Example 5

[0084] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0085] (1) Ni 0.25 Fe 0.34 Mn 0.33 Cu 0.08 (OH)2 and Na2CO3 were mixed evenly in ethanol at a molar ratio of 1:0.525 and dried to obtain the first mixed powder.

[0086] MXene material (Ti3C2OH) with a D50 of 4.5±0.5μm was mixed with NaOH at a mass ratio of 7:3 to obtain a second mixed powder.

[0087] (2) Spread the second mixed powder prepared in step (1) in the crucible, then spread the first mixed powder on the second mixed powder layer, and then spread the second mixed powder on the first mixed powder layer. Repeat the above operation to prepare a multi-layer alternating structure from top to bottom: second mixed powder layer-first mixed powder layer-second mixed powder layer-first mixed powder layer-second mixed powder layer; each first mixed powder layer contains the same mass of first mixed powder, and each second mixed powder layer contains the same mass of second mixed powder, wherein the mass ratio of each first mixed powder layer to the second mixed powder layer is 8.5:1.5; calcined at high temperature in air under a pressure of 1.5 MPa, with a heating rate of 5 °C / min to 950 °C, and held for 12 h to obtain sodium-ion battery cathode material.

[0088] The sodium-ion battery cathode material prepared in this embodiment was subjected to ICP analysis, and the results are as follows: Na: 1.01, Ni: 0.22, Fe: 0.33, Mn: 0.32, Cu: 0.07, Ti: 0.06; that is, the sodium-ion battery cathode material prepared in this embodiment is Na 1.01 [Ni 0.22 Fe 0.33 Mn 0.32 Cu 0.07 Ti 0.06 O2.

[0089] Example 6

[0090] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0091] (1) Ni 0.25 Fe 0.34 Mn 0.33 Cu 0.08 (OH)2 and Na2CO3 were mixed evenly in ethanol at a molar ratio of 1:0.525 and dried to obtain the first mixed powder.

[0092] MXene material Ti3C2OH with a D50 of 2.5±0.5μm was mixed with NaOH at a mass ratio of 5:5 to obtain a second mixed powder.

[0093] (2) Spread the second mixed powder prepared in step (1) in the crucible, then spread the first mixed powder on the second mixed powder layer, and then spread the second mixed powder on the first mixed powder layer. Repeat the above operation to prepare a multi-layer alternating structure from top to bottom: second mixed powder layer-first mixed powder layer-second mixed powder layer-first mixed powder layer-second mixed powder layer; each first mixed powder layer contains the same mass of first mixed powder, and each second mixed powder layer contains the same mass of second mixed powder, wherein the mass ratio of each first mixed powder layer to the second mixed powder layer is 8.5:1.5; calcined at high temperature in air under a pressure of 1.5 MPa, with a heating rate of 5 °C / min to 950 °C, and held for 12 h to obtain sodium-ion battery cathode material.

[0094] The sodium-ion battery cathode material prepared in this embodiment was subjected to ICP analysis, and the results are as follows: Na: 1.04, Ni: 0.22, Fe: 0.33, Mn: 0.32, Cu: 0.07, Ti: 0.06; that is, the sodium-ion battery cathode material prepared in this embodiment is Na 1.04 [Ni 0.22 Fe 0.33 Mn 0.32 Cu 0.07 Ti 0.06 O2.

[0095] Example 7

[0096] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0097] (1) Ni 0.25 Fe 0.34 Mn 0.33 Cu 0.08 (OH)2 and Na2CO3 were mixed evenly in ethanol at a molar ratio of 1:0.525 and dried to obtain the first mixed powder.

[0098] MXene material (Ti3C2OH) with a D50 of 2.5±0.5μm was mixed with NaOH at a mass ratio of 9:1 to obtain a second mixed powder.

[0099] (2) Spread the second mixed powder prepared in step (1) in the crucible, then spread the first mixed powder on the second mixed powder layer, and then spread the second mixed powder on the first mixed powder layer. Repeat the above operation to prepare a multi-layer alternating structure from top to bottom: second mixed powder layer-first mixed powder layer-second mixed powder layer-first mixed powder layer-second mixed powder layer; each first mixed powder layer contains the same mass of first mixed powder, and each second mixed powder layer contains the same mass of second mixed powder, wherein the mass ratio of each first mixed powder layer to the second mixed powder layer is 8.5:1.5; calcined at high temperature in air under a pressure of 1.5 MPa, with a heating rate of 5 °C / min to 950 °C, and held for 12 h to obtain sodium-ion battery cathode material.

[0100] The sodium-ion battery cathode material prepared in this embodiment was subjected to ICP analysis, and the results are as follows: Na: 1.01, Ni: 0.21, Fe: 0.32, Mn: 0.31, Cu: 0.06, Ti: 0.1; that is, the sodium-ion battery cathode material prepared in this embodiment is Na 1.01 [Ni 0.21 Fe 0.32 Mn 0.31 Cu 0.06 Ti 0.1 O2.

[0101] Example 8

[0102] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0103] (1) Ni 0.25 Fe 0.34 Mn 0.33 Cu 0.08 (OH)₂ and Na₂CO₃ were added to ethanol in a molar ratio of 1:0.525, along with a small amount of TiO₂ (NiO₂). 0.25 Fe 0.34 Mn 0.33 Cu 0.08 The molar ratio of (OH)2 to TiO2 is 1:0.03. After stirring and mixing evenly, the mixture is dried to obtain the first powder mixture.

[0104] MXene material (Ti3C2OH) with a D50 of 2.5±0.5μm was mixed with NaOH at a mass ratio of 7:3 to obtain a second mixed powder.

[0105] (2) Spread the second mixed powder prepared in step (1) in the crucible, then spread the first mixed powder on the second mixed powder layer, and then spread the second mixed powder on the first mixed powder layer. Repeat the above operation to prepare a multi-layer alternating structure from top to bottom: second mixed powder layer-first mixed powder layer-second mixed powder layer-first mixed powder layer-second mixed powder layer; each first mixed powder layer contains the same mass of first mixed powder, and each second mixed powder layer contains the same mass of second mixed powder, wherein the mass ratio of each first mixed powder layer to the second mixed powder layer is 8.5:1.5; calcined at high temperature in air under a pressure of 1.5 MPa, with a heating rate of 5 °C / min to 950 °C, and held for 12 h to obtain sodium-ion battery cathode material.

[0106] The sodium-ion battery cathode material prepared in this embodiment was subjected to ICP analysis, and the results are as follows: Na: 1.01, Ni: 0.21, Fe: 0.32, Mn: 0.31, Cu: 0.06, Ti: 0.1; that is, the sodium-ion battery cathode material prepared in this embodiment is Na 1.01 [Ni 0.21 Fe 0.32 Mn 0.31 Cu 0.06 Ti 0.1 O2.

[0107] Example 9

[0108] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0109] (1) Ni 0.25 Fe 0.34 Mn 0.33 Cu 0.08 (OH)2 and Na2CO3 were mixed evenly in ethanol at a molar ratio of 1:0.525 and dried to obtain the first mixed powder.

[0110] MXene material (Ti3C2OH) with a D50 of 2.5±0.5μm was mixed with NaOH at a mass ratio of 7:3 to obtain a second mixed powder.

[0111] (2) Spread the second mixed powder prepared in step (1) in the crucible, then spread the first mixed powder on the second mixed powder layer, and then spread the second mixed powder on the first mixed powder layer. Repeat the above operation to prepare a multi-layer alternating structure from top to bottom: second mixed powder layer-first mixed powder layer-second mixed powder layer-first mixed powder layer-second mixed powder layer; each first mixed powder layer contains the same mass of first mixed powder, and each second mixed powder layer contains the same mass of second mixed powder, wherein the mass ratio of each first mixed powder layer to the second mixed powder layer is 8:2; calcined at high temperature under 1.5 MPa pressure and air, with a heating rate of 5℃ / min to 950℃, and held for 12h to obtain sodium-ion battery cathode material.

[0112] The sodium-ion battery cathode material prepared in this embodiment was subjected to ICP analysis, and the results are as follows: Na: 1.02, Ni: 0.22, Fe: 0.33, Mn: 0.32, Cu: 0.07, Ti: 0.06; that is, the sodium-ion battery cathode material prepared in this embodiment is Na 1.02 [Ni 0.22 Fe 0.33 Mn 0.32 Cu 0.07 Ti 0.06 O2.

[0113] Example 10

[0114] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0115] (1) Ni 0.25 Fe 0.34 Mn 0.33 Cu 0.08 (OH)2 and Na2CO3 were mixed evenly in ethanol at a molar ratio of 1:0.525 and dried to obtain the first mixed powder.

[0116] MXene material (Ti3C2OH) with a D50 of 2.5±0.5μm was mixed with NaOH at a mass ratio of 7:3 to obtain a second mixed powder.

[0117] (2) Spread the second mixed powder prepared in step (1) in the crucible, then spread the first mixed powder on the second mixed powder layer, and then spread the second mixed powder on the first mixed powder layer. Repeat the above operation to prepare a multi-layer alternating structure from top to bottom: second mixed powder layer-first mixed powder layer-second mixed powder layer-first mixed powder layer-second mixed powder layer; each first mixed powder layer contains the same mass of first mixed powder, and each second mixed powder layer contains the same mass of second mixed powder, wherein the mass ratio of each first mixed powder layer to the second mixed powder layer is 9.5:0.5; calcined at high temperature in air under a pressure of 1.5 MPa, with a heating rate of 5 °C / min to 950 °C, and held for 12 h to obtain sodium-ion battery cathode material.

[0118] The sodium-ion battery cathode material prepared in this embodiment was subjected to ICP analysis, and the results are as follows: Na: 1.02, Ni: 0.23, Fe: 0.33, Mn: 0.32, Cu: 0.08, Ti: 0.04; that is, the sodium-ion battery cathode material prepared in this embodiment is Na 1.02 [Ni 0.23 Fe 0.33 Mn 0.32 Cu 0.08 Ti 0.04 O2.

[0119] Example 11

[0120] This embodiment relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0121] (1) Na2CO3, NiO, Fe2O3, MnO and CuO are mixed evenly in ethanol in a molar ratio of 0.525:0.23:0.34:0.16:0.08. After drying, the first mixed powder is obtained. The first mixed powder is compacted into thin strips and marked as D1 and D2 for later use.

[0122] MXene material (Ti3C2OH) with a D50 of 2.5±0.5μm was mixed with NaOH at a mass ratio of 7:3 to obtain a second mixed powder.

[0123] (2) Spread the second mixed powder prepared in step (1) in the crucible, then spread D1 on the second mixed powder layer, spread the second mixed powder on D1, spread D2 on the second mixed powder layer, and finally spread the second mixed powder on D2 to obtain a multi-layer alternating structure from top to bottom: second mixed powder layer-D2-second mixed powder layer-D1-second mixed powder layer; D1 and D2 contain the same mass of first mixed powder, and each layer of second mixed powder contains the same mass of second mixed powder, wherein the mass ratio of each layer of first mixed powder to second mixed powder is 8.5:1.5; calcined at high temperature in air under a pressure of 1.5 MPa, with a heating rate of 5 °C / min to 850 °C, and held for 12 h to obtain sodium-ion battery cathode material.

[0124] The sodium-ion battery cathode material prepared in this embodiment was subjected to ICP analysis, and the results are as follows: Na: 1.02, Ni: 0.22, Fe: 0.33, Mn: 0.31, Cu: 0.07, Ti: 0.07; that is, the sodium-ion battery cathode material prepared in this embodiment is Na 1.02 [Ni 0.22 Fe 0.33 Mn 0.31 Cu 0.07 Ti 0.07 O2.

[0125] Comparative Example 1

[0126] This comparative example relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0127] (1) Ni 0.25 Fe 0.34 Mn 0.33 Cu 0.08 (OH)2 and Na2CO3 were mixed evenly in ethanol at a molar ratio of 1:0.525 and then dried to obtain a mixed powder.

[0128] (2) Spread the mixed powder prepared in step (1) in a crucible and calcine it at high temperature under a pressure of 1.5 MPa and air. The temperature is increased to 950°C at a rate of 5°C / min and held for 12 hours to obtain sodium-ion battery cathode material.

[0129] The sodium-ion battery cathode material prepared in this comparative example was subjected to ICP analysis, and the results are as follows: Na: 1.00, Ni: 0.25, Fe: 0.34, Mn: 0.33, Cu: 0.08; that is, the sodium-ion battery cathode material prepared in this comparative example is Na[Ni 0.25 Fe 0.34 Mn 0.333 Cu 0.08 O2.

[0130] Comparative Example 2

[0131] This comparative example relates to the preparation of a sodium-ion battery cathode material, and the specific operations are as follows:

[0132] (1) Ni 0.25 Fe 0.34 Mn 0.33 Cu 0.08 (OH)₂ and Na₂CO₃ were added to ethanol at a molar ratio of 1:0.525, and MXene material Ti₃C₂OH and Ni were added. 0.25 Fe 0.34 Mn 0.33 Cu 0.08 The molar ratio of (OH)2 to Ti3C2OH is 1:0.012. The mixture is stirred and mixed evenly, and then dried to obtain a powder.

[0133] (2) The mixed powder prepared in step (1) is spread in a crucible and subjected to high-temperature calcination under a pressure of 1.5 MPa and air. The temperature is increased to 900°C at a rate of 5°C / min and held for 12 hours to obtain sodium-ion battery cathode material.

[0134] (3) The sodium-ion battery cathode material prepared in this comparative example was subjected to ICP detection. The detection results are as follows: Na: 1.00, Ni: 0.24, Fe: 0.34, Mn: 0.33, Cu: 0.08, Ti: 0.01; that is, the sodium-ion battery cathode material prepared in this comparative example is Na[Ni 0.24 Fe 0.34 Mn 0.33 Cu 0.08 Ti 0.01 O2.

[0135] Applications and performance characterization

[0136] 1. Assembly of button cells

[0137] The cathode materials prepared in the above embodiments and comparative examples were used as cathode active materials to assemble coin cells, as detailed below:

[0138] The positive electrode active material, conductive carbon, and PVDF are dissolved in N-methylpyrrolidone at a mass ratio of 90:5:5. After stirring evenly, the mixture is coated onto aluminum foil, dried under vacuum at 100°C, and rolled to obtain the positive electrode sheet. Then, the positive electrode sheet, the counter electrode sheet (sodium metal), the electrolyte (1 mol / L NaPF6 EC:DEC = 1:1), and the glass fiber separator are assembled into a battery.

[0139] 2. Performance Testing

[0140] The air stability of the cathode materials prepared in the above embodiments and comparative examples, as well as the rate performance and cycle stability of the assembled coin cells, were tested, as follows:

[0141] (1) Air stability test: The battery was placed in air with 20% humidity for different times, and then the specific capacity at 0.5C was tested. The specific operation is as follows: Take the material prepared above and expose it in air with 20% humidity for 0h, 2h and 4h. Then prepare it into a button cell. During the test, first place the button cell in an environment of 25±2℃ and let it stand for 8h. Then charge it with a constant current of 0.2C to 4.0V. Then let it stand for 5min. Then discharge it with a constant current of 0.2C to 2.0V. Then let it stand for 5min. Then charge it with a constant current of 0.5C to 4.0V. Then let it stand for 5min. Then discharge it with a constant current of 0.5C to 2.0V. The obtained capacity is the discharge capacity corresponding to 0.5C. Finally, stop the operation and record the second discharge capacity as the discharge capacity corresponding to 0.5C.

[0142] The test results are shown in Table 2 below:

[0143] Table 2

[0144]

[0145] As shown in Table 2, the air stability test results of different cathode materials indicate that the cathode materials prepared in Examples 1-11 and the unmodified cathode material in Comparative Example 1, when placed under the same air humidity conditions for the same period of time, exhibited a smaller decrease in specific capacity of the assembled coin cells, demonstrating better air stability. Comparative Example 2 directly used MXene mixed with metal salt and then sintered to obtain modified cathode materials, which improved air stability but significantly reduced the specific capacity of the cathode material.

[0146] (2) Discharge capacity test corresponding to a current density of 0.2C: First, the coin cell was placed in an environment of 25±2℃ and left to stand for 8 hours. Then, it was charged with a constant current of 0.2C to 4.0V, left to stand for 5 minutes, and then discharged with a constant current of 0.2C to 2.0V. This process was repeated, and the capacity obtained was the discharge capacity corresponding to 0.2C. Finally, the operation was stopped, and the discharge capacity corresponding to 0.2C was recorded. The test results are shown in Table 3 below.

[0147] (3) Discharge capacity test corresponding to a current density of 2C: First, the coin cell was placed in an environment of 25±2℃ and left to stand for 8 hours. Then, it was charged with a constant current of 0.2C to 4.0V, left to stand for 5 minutes, then charged with a constant voltage of 4.0V to a current of 0.05C, left to stand for 5 minutes, then discharged with a constant current of 2C to a voltage of 2.0V. Then, it was charged with a constant current of 2C to 4.0V, left to stand for 5 minutes, then discharged with a constant current of 2C to a voltage above 2.0V. Finally, the operation was stopped, and the capacity of the second 2C discharge was recorded as the capacity corresponding to 2C. The test results are shown in Table 3 below.

[0148] (4) Capacitance retention rate after 200 cycles at a current density of 0.5C: First, the coin cell was placed in an environment of 25±2℃ and left to stand for 8 hours. Then, it was charged at a constant current of 0.5C to 4.0V, left to stand for 5 minutes, then charged at a constant voltage of 4.0V to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.5C to a voltage of 2.0V. This cycle was repeated 50 times. Finally, the operation was stopped, and the capacitance of the first and 200th discharge cycles was recorded. The capacitance retention rate was the capacitance of the 200th discharge cycle / the capacitance of the first discharge cycle. The test results are shown in Table 3 below.

[0149] Table 3

[0150]

[0151]

[0152] As shown in Table 3, the coin cells assembled with the cathode materials prepared in Examples 1-11 have a capacity comparable to or even higher than that of the coin cells assembled with the cathode materials prepared in Comparative Example 1, while exhibiting better rate performance and cycle performance.

[0153] As can be seen from Examples 1 to 3, within a certain calcination temperature range, the specific capacity of the cathode material decreases with the increase of calcination temperature, but the cathode material prepared by high calcination temperature exhibits better rate performance and cycle stability.

[0154] As shown in Examples 1, 4, and 5, the particle size of MXene material has a certain impact on the specific capacity, conductivity, and structural stability of the cathode material. Compared with Example 1, the cathode material modified with smaller MXene particle size (Example 4) exhibits better rate performance and cycle stability in assembled coin cells, while the cathode material modified with larger MXene particle size (Example 5) not only has a lower specific capacity, but also exhibits inferior rate performance and cycle stability compared to Example 1.

[0155] As shown in Examples 1, 6, and 7, the mass ratio of MXene material to sodium hydroxide in the second powder mixture affects the specific capacity, rate performance, and cycle stability of the battery. Compared to Example 1, the second powder mixture prepared in Example 6 has a lower MXene content, resulting in a cathode material. Although the coin cell assembled from this cathode material exhibits a higher specific capacity, the conductivity and structural stability of the cathode material coated with MXene are reduced due to excessive etching, thus affecting the rate performance and cycle stability of the battery. In contrast, the second powder mixture prepared in Example 7 has an MXene material to sodium hydroxide ratio of 9:1, reducing the sodium hydroxide content. The specific capacity of the prepared cathode material is lower than that of Examples 1 and 6, but it exhibits better rate performance.

[0156] As can be seen from Examples 1, 9, and 10, the performance of the second mixed powder layer is better as the mass of the second mixed powder layer decreases. This is because the doping and coating are more complete. The mass ratio of the first mixed powder layer to the second mixed powder layer affects the specific capacity, conductivity, and structural stability of the cathode material.

[0157] Furthermore, as can be seen from Example 8, by introducing titanium dioxide into the first powder mixture, the doping amount of Ti in the prepared cathode material can be increased, which is beneficial to further improve the cycle stability of the battery.

[0158] The embodiments described above are merely preferred examples to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing a sodium-ion battery cathode material, characterized in that, Includes the following steps: (1) Weigh the sodium salt and precursor Cu according to the molar ratio of each metal element in the layered oxide cathode material of sodium-ion battery. x Ni y Fe z Mn 1-x-y-z (OH)₂, wherein 0 < x ≤ 0.2, 0 < y ≤ 0.35, 0.2 ≤ z ≤ 0.4, 0 < 1 - xyz < 1, is mixed evenly to obtain a first mixed powder; MXene material is mixed evenly with sodium hydroxide to obtain a second mixed powder; the particle size D50 of the MXene material is 0.5-5 μm; the mass percentage of sodium hydroxide in the second mixed powder is 10%-50%; (2) The first mixed powder and the second mixed powder are stacked in an alternating manner to form a multi-layer alternating structure, wherein the bottom layer and the top layer of the multi-layer alternating structure are both the second mixed powder layer, and the sodium-ion battery cathode material is obtained by calcination treatment.

2. The preparation method according to claim 1, characterized in that, In step (1), the sodium salt is selected from one or more of sodium carbonate, sodium nitrate, and sodium oxalate.

3. The preparation method according to claim 1, characterized in that, In step (1), the MXene material is M n+1 X n T x Where n is 1, 2, 3 or 4, M is Ti, V, Nb, Mo, Sc, Zr, Cr, Hf or Ta, X is C and / or N, and T is... x The functional group is represented by -OH, -O, -F, or -Cl.

4. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of each first mixing layer to each second mixing layer is 1:0.05-0.

3.

5. The preparation method according to claim 1, characterized in that, In step (2), the first mixed powder and the second mixed powder are stacked in an alternating layering manner to form a multi-layered alternating structure from top to bottom: second mixed powder layer - first mixed powder layer - second mixed powder layer - first mixed powder layer - second mixed powder layer.

6. The preparation method according to claim 1, characterized in that, In step (2), pressure is applied to the multilayer alternating structure, and the pressure is 0.1-5 MPa; In the calcination process, the heating rate is 2-10℃ / min, the calcination temperature is 700-1100℃, and the holding time is 10-24 h.

Images