Nickel iron sodium manganate positive electrode material, preparation method thereof and sodium ion battery

Abstract

The invention provides a nickel iron sodium manganate positive electrode material, a preparation method thereof and a sodium ion battery, and belongs to the technical field of sodium ion battery positive electrode material manufacturing. The nickel iron sodium manganate positive electrode material comprises a matrix and a surface layer located outside the matrix, both the matrix and the surface layer are doped with P, only the surface layer is doped with F, and the positive electrode material has relatively excellent structural stability, so that the corresponding battery has the advantage of less gas production in the cycle process.

Description

Technical Field

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

[0002] Sodium-ion layered oxide cathode materials (such as sodium nickel iron manganese oxide cathode materials) have attracted widespread attention due to their low cost and high yield. However, these materials suffer from poor structural stability, which leads to severe gas generation during battery cycling and can easily cause safety issues. Summary of the Invention

[0003] The purpose of this application is to provide a sodium nickel iron manganese oxide cathode material, its preparation method, and a sodium-ion battery. The cathode material has excellent structural stability, which gives the corresponding battery the advantage of less gas production during cycling.

[0004] The embodiments of this application are implemented as follows: In a first aspect, embodiments of this application provide a sodium nickel iron manganese oxide cathode material, the cathode material comprising a matrix and a surface layer located outside the matrix, both the matrix and the surface layer being doped with P, and only the surface layer being doped with F.

[0005] In the above technical solution, both the matrix and the surface of the cathode material are doped with P. The acid radical ions (such as phosphate ions) formed after P doping can stably support the layered structure of the material, and P doping can suppress the release of lattice oxygen. At the same time, the surface is also doped with F. F doping can further improve the surface stability of the cathode material. By doping with the two elements together and distributing them in the above positions, the cathode material as a whole can have better structural stability, thus giving the corresponding battery the advantage of less gas production during cycling.

[0006] In some alternative implementations, the F content gradually decreases and the P content gradually increases in the surface layer of the cathode material, moving inward from the surface.

[0007] In the above technical solution, the F content and P content have the above distribution rules in the direction from the surface of the cathode material inward, so that the cathode material as a whole has better structural stability, thereby giving the corresponding battery the advantage of less gas production during cycling.

[0008] In some alternative implementations, the F content at the boundary between the surface layer and the substrate is 20 ppm, and the thickness of the surface layer is 20 nm to 400 nm.

[0009] In the above technical solution, limiting the thickness of the surface layer to the aforementioned range, that is, controlling the F-doped region within a suitable range, can effectively improve the surface structure stability of the cathode material, thereby effectively reducing the gas production of the corresponding battery during cycling.

[0010] In some alternative implementations, the thickness of the surface layer is 50 nm to 180 nm.

[0011] In the above technical solution, limiting the thickness of the surface layer to a more suitable range can not only further reduce the amount of gas generated by the corresponding battery during cycling, but also enable the corresponding battery to have both superior first discharge capacity and first efficiency.

[0012] In some alternative embodiments, the thickness of the surface layer is 50 nm to 180 nm, and the F content at a distance of 40 nm from the surface of the cathode material is 120 ppm to 350 ppm; or / and, the thickness of the surface layer is 50 nm to 180 nm, and the P content at a distance of 200 nm from the surface of the cathode material is 140 ppm to 260 ppm.

[0013] In the above technical solution, when the thickness of the surface layer is within the above-mentioned suitable range, the F content at a distance of 40 nm from the surface of the positive electrode material and the P content at a distance of 200 nm from the surface of the positive electrode material are respectively limited to the above-mentioned range, so that the positive electrode material is doped with a relatively appropriate amount of P and F, which can effectively improve the overall structural stability of the positive electrode material, thereby effectively reducing the gas production of the corresponding battery during the cycle.

[0014] In some alternative embodiments, the F content at a distance of 40 nm from the surface of the cathode material is 150 ppm to 300 ppm, or / and the P content at a distance of 200 nm from the surface of the cathode material is 150 ppm to 220 ppm.

[0015] In the above technical solution, when the thickness of the surface layer is within the above-mentioned suitable range, the F content at 40 nm from the surface of the positive electrode material and the P content at 200 nm from the surface of the positive electrode material are respectively limited to a more suitable range, so that the positive electrode material is doped with a more suitable amount of P and F. In addition to further reducing the amount of gas generated by the corresponding battery during the cycle, the corresponding battery can also have a better first discharge capacity and first efficiency.

[0016] In some alternative implementations, the mass ratio of F content to P content at a distance of 40 nm from the surface of the cathode material is (2~20.33):1.

[0017] In the above technical solution, when the thickness of the surface layer is 50 nm to 180 nm, limiting the mass ratio of F content to P content at a distance of 40 nm from the surface of the cathode material to the above suitable range can effectively improve the overall structural stability of the cathode material, thereby effectively reducing the gas production of the corresponding battery during cycling.

[0018] In some alternative implementations, the mass ratio of F content to P content at a distance of 40 nm from the surface of the cathode material is (2.38~16.18):1.

[0019] In the above technical solution, when the thickness of the surface layer is within a suitable range, the mass ratio of F content to P content at a distance of 40 nm from the surface of the positive electrode material is limited to the above suitable range. In addition to more effectively reducing the gas production of the corresponding battery during the cycle, the corresponding battery can also have better first discharge capacity and first efficiency.

[0020] In some alternative implementations, the surface Ni of the cathode material 2+ The proportion is 10% to 15%.

[0021] In the above technical solution, the surface Ni of the cathode material 2+ The low proportion of NiO (i.e., less NiO on the surface of the cathode material) indicates that the surface of the cathode material contains more nickel in the active valence state (i.e., Ni). 3+ This is to ensure that the corresponding battery has a superior capacity.

[0022] In some alternative implementations, the thermal decomposition temperature of the cathode material is not less than 350°C.

[0023] In the above technical solution, the thermal decomposition temperature of the cathode material is relatively high, that is, the thermal stability of the cathode material is good, which also helps to reduce the amount of gas generated by the corresponding battery during the cycle.

[0024] In some alternative embodiments, the pH value of the cathode material is 12 to 12.43; or / and, the carbonate concentration of the cathode material in water is 9000 ppm to 16000 ppm; or / and, the carbonate concentration of the cathode material in ethanol is 400 ppm to 1000 ppm.

[0025] In the above technical solution, the pH value, carbonate concentration in water, and carbonate concentration in ethanol of the cathode material are all at low levels, indicating that the cathode material has the advantage of less residual alkali on the surface, which makes the corresponding battery have the advantage of low gas production during cycling. At the same time, it also enables the corresponding battery to have better first discharge capacity and first efficiency.

[0026] In some alternative implementations, the chemical formula of the cathode material is: Na a Nib Fe c Mn d X e F f P g O2, wherein: 0.9≤a≤1.1, 0.10≤b≤0.35, 0.20≤c≤0.40, 0.20≤d≤0.40, 0≤e≤0.02, 0.001≤f≤0.02, 0.001≤g≤0.02, and X includes at least one of Mg, K, Zr, Cu, Zn, Ce, Al, Ca, and Sr.

[0027] In the above technical solutions, the chemical formula of the cathode material can satisfy the above general formula, which can provide a variety of feasible solutions, thereby facilitating the promotion and application of the technical solutions provided in the embodiments of this application.

[0028] In some alternative implementations, 0.001 ≤ e ≤ 0.02.

[0029] In the above technical solution, when e meets the above conditions, it indicates that the cathode material also contains at least one doping element selected from Mg, Zr, Cu, Zn, Ce, Al, Ca and Sr. The doping of these elements helps to further improve the overall structural stability of the cathode material, thereby more effectively reducing the gas production of the corresponding battery during the cycle.

[0030] In some alternative implementations, 0.002 ≤ f ≤ 0.01 or / and 0.002 ≤ g ≤ 0.004.

[0031] In the above technical solution, f and g are within the more suitable range, that is, the doping amounts of F and P are both within the more suitable range. In addition to further reducing the gas production of the corresponding battery during the cycle, it can also enable the corresponding battery to have both excellent first discharge capacity and first efficiency.

[0032] Secondly, embodiments of this application provide a method for preparing a sodium nickel iron manganese oxide cathode material, comprising the following steps: S1. Sodium source, nickel source, iron source, manganese source and phosphorus source are mixed to obtain a first mixture; S2. The first mixture is sintered for the first time to obtain a P-doped cathode material precursor; S3. The cathode material precursor and fluorine source are mixed to obtain a second mixture; S4. The second mixture is sintered for the second time to obtain sodium nickel iron manganate cathode material.

[0033] In the above technical solution, the preparation is carried out according to the above process. In particular, a phosphorus source is added first for P doping, and then a fluorine source is added for F doping. Through the competition between F and P, a cathode material with P doping in both the matrix and the surface layer and F doping only in the surface layer can be prepared. This cathode material has excellent structural stability, which makes the corresponding battery have the advantage of less gas production during cycling.

[0034] In some alternative implementations, the second sintering includes a heating stage and a holding stage, wherein the heating rate during the heating stage is no higher than 3°C / min.

[0035] In the above technical solution, limiting the heating rate during the heating stage to the aforementioned range enables the prepared cathode material to have a suitable surface thickness, less residual alkali on the surface, a higher thermal decomposition temperature, and a higher surface Ni content. 2+ The lower proportion of the battery's capacity results in the battery having advantages such as low gas production during cycling, high initial discharge capacity, and high initial efficiency.

[0036] In some optional implementations, during the heat preservation stage, the sintering temperature is 700℃~900℃ and the sintering time is not less than 6 hours.

[0037] In the above technical solution, limiting the sintering temperature and sintering time during the heating stage to the aforementioned ranges enables the prepared cathode material to have a suitable surface thickness, less residual alkali on the surface, a higher thermal decomposition temperature, and a higher surface Ni content. 2+ The lower proportion of the battery's capacity results in the battery having advantages such as low gas production during cycling, high initial discharge capacity, and high initial efficiency.

[0038] Thirdly, embodiments of this application provide a sodium-ion battery, including sodium nickel iron manganese oxide cathode material prepared by the method of preparing sodium nickel iron manganese oxide cathode material as provided in the first aspect embodiment or as provided in the second aspect embodiment.

[0039] In the above technical solution, the sodium-ion battery includes sodium nickel iron manganese oxide cathode material prepared by the preparation method of sodium nickel iron manganese oxide cathode material provided in the first aspect embodiment or the preparation method of sodium nickel iron manganese oxide cathode material provided in the second aspect embodiment. Since the cathode material has the advantage of relatively stable overall structure, the battery has the advantage of low gas production during the cycle. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 A process flow diagram of a method for preparing sodium nickel iron manganese oxide cathode material provided in this application embodiment; Figure 2 This is an EDS line scan of the cathode material in Example 1; Figure 3 This is a graph showing the content distribution curves of F and P elements in the cathode material of Example 1; Figure 4 This is a graph showing the content distribution curves of F and P elements in the cathode material of Example 2; Figure 5 The graph shows the content distribution curves of F and P elements in the cathode material of Comparative Example 2. Figure 6 The graph shows the content distribution curves of F and P elements in the cathode material of Comparative Example 4. Figure 7 The graph shows the content distribution curves of F and P elements in the cathode material of Comparative Example 6. Figure 8 This is a graph showing the peak fitting results of Ni element in the XPS spectrum of the cathode material in Example 1. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0043] It should be noted that the terms "and / or" in this application, such as "feature 1 and / or feature 2", all refer to the three cases of "feature 1" alone, "feature 2" alone, and "feature 1" plus "feature 2".

[0044] In addition, in the description of this application, unless otherwise stated, "one or more" means two or more; the range of "numerical value a to numerical value b" includes the two endpoints "a" and "b"; and "unit of measurement" in "numerical value a to numerical value b + unit of measurement" represents the "unit of measurement" of both "numerical value a" and "numerical value b".

[0045] The following is a detailed description of a sodium nickel iron manganese oxide cathode material, its preparation method, and a sodium-ion battery according to embodiments of this application.

[0046] In a first aspect, embodiments of this application provide a sodium nickel iron manganese oxide cathode material, the cathode material comprising a matrix and a surface layer located outside the matrix, both the matrix and the surface layer being doped with P, and only the surface layer being doped with F.

[0047] In this application, both the matrix and the surface of the cathode material are doped with P. The acid radical ions (such as phosphate ions) formed after P doping can stably support the layered structure of the material, and P doping can suppress the release of lattice oxygen. At the same time, the surface is also doped with F. F doping can further improve the surface stability of the cathode material. By doping with the two elements together and distributing them in the above positions, the cathode material as a whole can have better structural stability, thereby giving the corresponding battery the advantage of less gas production during cycling.

[0048] As an example, from the surface of the cathode material inwards, the F content gradually decreases in the surface layer, while the P content gradually increases in the surface layer.

[0049] In this embodiment, the F content and P content have the above-mentioned distribution patterns in the direction from the surface of the cathode material inward, so that the cathode material as a whole has better structural stability, thereby giving the corresponding battery the advantage of producing less gas during cycling.

[0050] As an example, the F content at the boundary between the surface layer and the substrate is 20 ppm (i.e., when the F content is detected at 20 nm, the location is considered to be the boundary between the surface layer and the substrate), and the thickness of the surface layer is 20 nm to 400 nm, for example, but not limited to, any point value or any range between 20 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm and 400 nm.

[0051] In this embodiment, limiting the thickness of the surface layer to the above-mentioned range, that is, controlling the F-doped region within a suitable range, can effectively improve the surface structure stability of the cathode material, thereby effectively reducing the amount of gas generated by the corresponding battery during cycling.

[0052] As an example, the thickness of the surface layer is 50 nm to 180 nm, for example, but not limited to any point value or a range of any two of the following thicknesses: 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm and 180 nm.

[0053] In this embodiment, limiting the thickness of the surface layer to a more suitable range not only further reduces the amount of gas generated by the corresponding battery during cycling, but also enables the corresponding battery to have both superior first discharge capacity and first efficiency.

[0054] As an example, the thickness of the surface layer is 50 nm to 180 nm, and the F content at a distance of 40 nm from the surface of the cathode material is 120 ppm to 350 ppm, for example, but not limited to any one of 120 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm and 350 ppm or any range between two of them.

[0055] In this embodiment, when the thickness of the surface layer is within the above-mentioned suitable range, the F content at a distance of 40 nm from the surface of the cathode material is limited to the above-mentioned range, so that the cathode material is doped with a relatively appropriate amount of F, which can effectively improve the overall structural stability of the cathode material, thereby effectively reducing the gas production of the corresponding battery during the cycle.

[0056] As an example, the thickness of the surface layer is 50 nm to 180 nm, and the F content at a distance of 40 nm from the surface of the cathode material is 150 ppm to 300 ppm, for example, but not limited to any one of 150 ppm, 180 ppm, 200 ppm, 220 ppm, 250 ppm, 280 ppm and 300 ppm or any range between two of them.

[0057] In this embodiment, when the thickness of the surface layer is within the above-mentioned suitable range, the F content at a distance of 40 nm from the surface of the positive electrode material is limited to a more suitable range, so that the positive electrode material is doped with a more suitable amount of F. In addition to further reducing the amount of gas generated by the corresponding battery during cycling, the corresponding battery can also have better first discharge capacity and first efficiency.

[0058] As an example, the thickness of the surface layer is 50 nm to 180 nm, and the P content at a distance of 200 nm from the surface of the cathode material is 140 ppm to 260 ppm, for example, but not limited to any one of 140 ppm, 160 ppm, 180 ppm, 200 ppm, 220 ppm, 240 ppm and 260 ppm or any range between two of them.

[0059] In this embodiment, when the thickness of the surface layer is within the above-mentioned suitable range, the P content at a distance of 200 nm from the surface of the cathode material is limited to the above-mentioned range, so that the cathode material is doped with a relatively appropriate amount of P, which can effectively improve the overall structural stability of the cathode material, thereby effectively reducing the gas production of the corresponding battery during the cycle.

[0060] As an example, the thickness of the surface layer is 50 nm to 180 nm, and the P content at 200 nm from the surface of the cathode material is 150 ppm to 220 ppm, for example, but not limited to any one of 150 ppm, 160 ppm, 170 ppm, 180 ppm, 200 ppm, 210 ppm and 220 ppm or any range between two of them.

[0061] In this embodiment, when the thickness of the surface layer is within the above-mentioned suitable range, the P content at a distance of 200 nm from the surface of the positive electrode material is limited to a more suitable range, so that the positive electrode material is doped with a more appropriate amount of P. In addition to further reducing the amount of gas generated by the corresponding battery during cycling, the corresponding battery can also have better first discharge capacity and first efficiency.

[0062] As an example, the mass ratio of F content to P content at a distance of 40 nm from the surface of the cathode material is (2~20.33):1, for example, but not limited to any point value or any range between the ratios of 2:1, 5:1, 10:1, 15:1, 20:1 and 20.33:1.

[0063] In this embodiment, when the thickness of the surface layer is 50 nm to 180 nm, limiting the mass ratio of F content to P content at a distance of 40 nm from the surface of the cathode material to the above-mentioned suitable range can effectively improve the overall structural stability of the cathode material, thereby effectively reducing the amount of gas generated by the corresponding battery during cycling.

[0064] As an example, the mass ratio of F content to P content at a distance of 40 nm from the surface of the cathode material is (2.38~16.18):1, for example, but not limited to any one of the ratios of 2.38:1, 4:1, 6:1, 8:1, 10:1, 12:1, 14:1, 16:1 and 16.18:1 or any range between the two.

[0065] In this embodiment, when the thickness of the surface layer is 50 nm to 180 nm, limiting the mass ratio of F content to P content at a distance of 40 nm from the surface of the positive electrode material within the aforementioned suitable range not only more effectively reduces the gas generation of the corresponding battery during cycling, but also enables the corresponding battery to possess both superior initial discharge capacity and initial efficiency. As an example, the surface Ni of the positive electrode material... 2+ The percentage is 10% to 15%, for example, but not limited to any one of the percentages of 10%, 11%, 12%, 13%, 14% and 15%, or any range between two of them.

[0066] It should be noted that Ni 2+ The percentage refers to Ni 2+ The percentage of Ni elements in all valence states.

[0067] In this embodiment, the surface Ni of the positive electrode material 2+ The low proportion of active nickel (i.e., less inactive NiO on the surface of the cathode material) indicates that the surface of the cathode material contains more active nickel (i.e., NiO). 3+ This is to ensure that the corresponding battery has a superior capacity.

[0068] As an example, the thermal decomposition temperature of the cathode material is not less than 350℃.

[0069] In this embodiment, the positive electrode material has a high thermal decomposition temperature, which means that the positive electrode material has good thermal stability and also helps to reduce the amount of gas generated by the corresponding battery during cycling.

[0070] As an example, the pH value of the positive electrode material is 12 to 12.43, for example, but not limited to any one of pH values ​​of 12, 12.1, 12.2, 12.3, 12.4, and 12.43, or a range between any two; or / and, the carbonate concentration of the positive electrode material in water is 9000 ppm to 16000 ppm, for example, but not limited to any one of concentrations of 9000 ppm, 10000 ppm, 11000 ppm, 12000 ppm, 13000 ppm, 14000 ppm, 15000 ppm, and 16000 ppm, or a range between any two; or / and, the carbonate concentration of the positive electrode material in ethanol is 400 ppm to 1000 ppm, for example, but not limited to concentrations of 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, and 1000 ppm. Any point value in ppm or a range of values ​​between any two.

[0071] In this embodiment, the pH value, carbonate concentration in water, and carbonate concentration in ethanol of the positive electrode material are all at low levels, indicating that the positive electrode material has the advantage of less residual alkali on the surface (the less residual alkali, the less likely it is to undergo side reactions with the electrolyte and produce gas), so that the corresponding battery has the advantage of lower gas production during cycling. At the same time, it also enables the corresponding battery to have better first discharge capacity and first efficiency.

[0072] As an example, the chemical formula of the cathode material is: Na a Ni b Fe c Mn d X e F f P g O2, wherein: 0.9≤a≤1.1, 0.10≤b≤0.35, 0.20≤c≤0.40, 0.20≤d≤0.40, 0≤e≤0.02, 0.001≤f≤0.02, 0.001≤g≤0.02, and X includes at least one of Mg, K, Zr, Cu, Zn, Ce, Al, Ca, and Sr.

[0073] In this embodiment, the chemical formula of the cathode material can satisfy the above general formula, which can provide a variety of possible implementation schemes, thereby facilitating the promotion and application of the technical solutions provided in the embodiments of this application.

[0074] As an example, 0.001 ≤ e ≤ 0.02, for example, but not limited to, e being any point value or a range value between any two of 0.001, 0.002, 0.004, 0.006, 0.008, 0.01, 0.012, 0.014, 0.016, 0.018, and 0.02.

[0075] In this embodiment, when e satisfies the above conditions, it indicates that the cathode material also contains at least one doping element selected from Mg, Zr, Cu, Zn, Ce, Al, Ca and Sr. The doping of these elements helps to further improve the overall structural stability of the cathode material, thereby more effectively reducing the amount of gas generated by the corresponding battery during cycling.

[0076] As an example, 0.002 ≤ f ≤ 0.01, for example, but not limited to f being any point value of 0.002, 0.004, 0.006, 0.008, and 0.01 or a range of values ​​between any two; or / and, 0.002 ≤ g ≤ 0.004, for example, but not limited to g being any point value of 0.002, 0.0025, 0.003, 0.0035, and 0.004 or a range of values ​​between any two.

[0077] In this embodiment, f and g are within the more suitable range mentioned above, that is, the doping amounts of F and P are both within the more suitable range. In addition to further reducing the amount of gas generated by the corresponding battery during cycling, it also enables the corresponding battery to have both superior first discharge capacity and first efficiency.

[0078] Secondly, embodiments of this application provide a method for preparing a sodium nickel iron manganese oxide cathode material, comprising the following steps: S1. Sodium source, nickel source, iron source, manganese source and phosphorus source are mixed to obtain a first mixture; S2. The first mixture is sintered for the first time to obtain a P-doped cathode material precursor; S3. The cathode material precursor and fluorine source are mixed to obtain a second mixture; S4. The second mixture is sintered for the second time to obtain sodium nickel iron manganate cathode material.

[0079] In this application, the cathode material is prepared according to the above process. In particular, a phosphorus source is added first for P doping, and then a fluorine source is added for F doping. Through the competition between F and P, a cathode material with P doping in both the matrix and the surface layer and F doping only in the surface layer can be prepared. This cathode material has excellent structural stability, which makes the corresponding battery have the advantage of less gas production during cycling.

[0080] As an example, before mixing the cathode material precursor and the fluorine source, the cathode material precursor is crushed and sieved; and after the second sintering, the sintered product is sieved, iron removed, and packaged.

[0081] It should be noted that the specific amounts of various raw materials added in the preparation method of the cathode material can be set with reference to the chemical formula of the cathode material in the first aspect embodiment.

[0082] As an example, in the first mixture, the molar ratio of Na, Ni, Fe, Mn and P is (0.9~1.1):(0.1~0.35):(0.2~0.4):(0.2~0.4):(0.001~0.02), for example, but not limited to any one of the following values ​​or any range between any two: 0.9:0.1:0.2:0.2:0.001, 1.0:0.3:0.3:0.4:0.002 and 1.1:0.35:0.4:0.4:0.02.

[0083] As an example, in the second mixture, the molar ratio of Na to F is (0.9~1.1):(0.001~0.02), for example, but not limited to, any one of 0.9:0.001, 1.0:0.002, and 1.1:0.02, or any range between the two.

[0084] It should be noted that the doping amounts of F and P are closely related to the structural stability of the prepared cathode material. Considering the material properties, the amount of F and P added can be further limited.

[0085] As an example, in the first mixture, the molar ratio of Na to P is (0.9~1.1):(0.002~0.004), for example, but not limited to, any one of 0.9:0.002, 1.0:0.002, 1.0:0.003, 1.0:0.004, and 1.1:0.004, or any range between the two; or / and, in the second mixture, the molar ratio of Na to F is (0.9~1.1):(0.002~0.01), for example, but not limited to, any one of 0.9:0.002, 1.0:0.004, 1.0:0.008, and 1.1:0.01, or any range between the two.

[0086] In this embodiment, the amount of P and F added is limited to the above-mentioned more suitable range, so that the prepared cathode material has a more suitable amount of P and F. In addition to further reducing the amount of gas generated by the corresponding battery during cycling, the corresponding battery can also have better first discharge capacity and first efficiency.

[0087] As an example, the second mixture also includes a compound containing element X, wherein element X includes at least one of Mg, K, Zr, Cu, Zn, Ce, Al, Ca and Sr.

[0088] In this embodiment, when the second mixture includes a compound containing element X, the prepared cathode material contains element X. The doping of element X helps to further improve the overall structural stability of the cathode material, thereby more effectively reducing the gas production of the corresponding battery during cycling.

[0089] As an example, in the second mixture, the molar ratio of Na to X is (0.9~1.1):(0.001~0.02), for example, but not limited to any one of the ratios 0.9:0.001, 1.0:0.002, 1.0:0.003, 1.0:0.004, and 1.1:0.02, or any range between the two.

[0090] In this embodiment, the amount of element X added is limited to the above range so that the prepared cathode material contains a relatively appropriate amount of element X, which can effectively improve the overall structural stability of the cathode material and thus effectively reduce the amount of gas generated by the corresponding battery during the cycle.

[0091] It should be noted that there is no limitation on the timing of the addition of element X. For example, it can be added together with source P, or together with source F, or simultaneously with both sources P and F.

[0092] It should be noted that there are no restrictions on the types of raw materials, and they can be selected and set in accordance with the conventional methods in this field. The following is an auxiliary explanation in conjunction with the preparation method of the compound containing element X in the second mixture.

[0093] As an example, step S1 includes: adding a nickel-iron-manganese hydroxide precursor (e.g., Ni...) 0.3 Fe 0.3 Mn 0.4 (OH)2), sodium carbonate, and a compound containing P and X (e.g., at least one of CaHPO4·2H2O, MgHPO4·H2O, and K2HPO4·3H2O) are mixed to obtain a first mixture.

[0094] In this embodiment, the above-mentioned types of raw materials are mixed, which has the advantage of using fewer types of raw materials.

[0095] As an example, step S3 includes: mixing the cathode material precursor with a compound containing F and X (e.g., at least one of MgF2, CaF2 and ZrF4) to obtain a second mixture.

[0096] In this embodiment, the use of the above-mentioned raw materials for mixing also has the advantage of having fewer types of raw materials.

[0097] As an example, the first sintering includes a heating stage and a holding stage, wherein the heating rate in the heating stage is 1~5℃ / min, for example, but not limited to any one of 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min and 5℃ / min or any range between two of the heating rates.

[0098] As an example, during the holding stage of the first sintering, the sintering temperature is 800~1000℃, for example, but not limited to any one of 800℃, 850℃, 900℃, 950℃ and 1000℃ or any range between two; the sintering time is 8~12 h, for example, but not limited to any one of 8 h, 9 h, 10 h, 11 h and 12 h or any range between two.

[0099] In this embodiment, by limiting the heating rate, sintering temperature and sintering time to the above ranges in the first sintering step, a cathode material precursor in which P is uniformly doped throughout the material can be prepared.

[0100] As an example, the second sintering includes a heating stage and a holding stage. In the heating stage, the heating rate is no higher than 3°C / min, for example, but not limited to any one of 0.5°C / min, 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min and 3°C / min or any range between two of them.

[0101] In this embodiment, limiting the heating rate in the second sintering step to the above range enables the prepared cathode material to have a suitable surface thickness, less residual alkali on the surface, a higher thermal decomposition temperature, and a surface Ni... 2+ The lower proportion of the battery's capacity results in the battery having advantages such as low gas production during cycling, high initial discharge capacity, and high initial efficiency.

[0102] As an example, during the heat preservation stage, the sintering temperature is 700℃~900℃, for example, but not limited to any one of 700℃, 750℃, 800℃, 850℃ and 900℃ or any range between two; the sintering time is not less than 6 h, for example, but not limited to any one of 6 h, 7 h, 8 h, 9 h and 10 h or any range between two.

[0103] In this embodiment, limiting the sintering temperature and sintering time in the second sintering step to the aforementioned ranges enables the prepared cathode material to have a suitable surface thickness, low surface residual alkali, high thermal decomposition temperature, and a surface Ni... 2+ The lower proportion of the battery's capacity results in the battery having advantages such as low gas production during cycling, high initial discharge capacity, and high initial efficiency.

[0104] It should be noted that, for the preparation of cathode materials, any processes or steps not specifically described or limited can be set in accordance with the conventions of the art.

[0105] As an example, a process flow diagram of the preparation method of sodium nickel iron manganese oxide cathode material is exemplarily provided. Figure 1 .

[0106] Thirdly, embodiments of this application provide a sodium-ion battery, including sodium nickel iron manganese oxide cathode material prepared by the method of preparing sodium nickel iron manganese oxide cathode material as provided in the first aspect embodiment or as provided in the second aspect embodiment.

[0107] In this application, the sodium-ion battery includes sodium nickel iron manganese oxide cathode material prepared by the method of preparing sodium nickel iron manganese oxide cathode material as provided in the first aspect embodiment or as provided in the second aspect embodiment. Since the cathode material has the advantage of relatively stable overall structure, the corresponding battery has the advantage of low gas production during cycling.

[0108] It should be noted that, apart from the cathode material, the other functional components in a sodium-ion battery can be selected and configured in accordance with conventional methods in the field.

[0109] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0110] Example 1 This application provides a method for preparing sodium nickel iron manganese oxide cathode material, including the following steps: S1 Add 10 kg Ni to a 50 L high-speed mixer 0.30 Fe 0.30 Mn 0.40 (OH)2, 6.04 Kg Na2CO3 and 86.13g CaHPO4·2H2O (first dopant source) were mixed and stirred at 900 rpm for 10 min to obtain the first mixture.

[0111] S2 The first mixture is placed in a sagger, air atmosphere is introduced, the temperature is raised to 900℃ at 3℃ / min and held for sintering for 10 h, and then cooled with the furnace. The material after being taken out of the furnace is crushed and sieved by an air jet mill to obtain the P-doped cathode material precursor.

[0112] S3 The above-mentioned cathode material precursor and 51.43 g of MgF2 (second doping source) were stirred and mixed in a 30 L high-speed mixer at 900 rpm for 10 min to obtain a second mixture.

[0113] S4 The second mixture is placed in a sagger, air is introduced, and the temperature is raised to 800℃ at 2℃ / min and sintered for 8 hours. Then it is cooled with the furnace. The material after being taken out of the furnace is crushed, sieved, iron removed and packaged to obtain sodium nickel iron manganese oxide cathode material.

[0114] All subsequent embodiments and comparative examples follow the same procedure as in Embodiment 1. To better understand the process differences between the embodiments and comparative examples, the process parameters that have changed are summarized in a table here. Please refer to Table 1 for details.

[0115] Table 1

[0116] It should be noted that “—” in Table 1 indicates no addition, and 1 and 2 in the addition sequence refer to the first doping source and the second doping source, respectively. In particular, in Comparative Example 6, both doping sources are added in step S1, and accordingly, S3 is not performed subsequently, but S4 is performed directly.

[0117] Test case (1) Characterization of the physical and chemical properties of the material The cathode materials prepared in Examples 1-14 and Comparative Examples 1-6 were used as samples. The chemical formulas of each sample were then determined, and the surface thickness, F content at 40 nm from the surface of the cathode material, the ratio of F to P content at 40 nm from the surface of the cathode material, the P content at 200 nm from the surface of the cathode material, the pH value of the cathode material, the carbonate concentration in water, the hydroxide concentration in ethanol, the thermal decomposition temperature, and the surface Ni content were all measured for each sample. 2+ The percentages were then tallied, and the results of each test were statistically analyzed in Tables 2 and 3.

[0118] The method for testing surface thickness is as follows: First, the F content of 20 ppm was set as the boundary between the surface and the substrate. Then, the cathode material was polished in cross-section using a GATAN 697 argon ion polisher. Next, images were taken using a Hitachi SU 8010 scanning electron microscope. F element was selected for EDS line scanning. The software automatically generated the line scan spectrum, and the F surface thickness was determined based on the F content in the spectrum.

[0119] The method for testing the F content at a distance of 40 nm from the surface of the cathode material is as follows: The cathode material was cross-sectionally polished using a GATAN 697 argon ion polisher, and then images were taken using a Hitachi SU 8010 scanning electron microscope. The element F was selected for EDS line scanning, and the F content at 40 nm inward from the surface of the cathode material was selected.

[0120] The method for testing the ratio of F content to P content at a distance of 40 nm from the surface of the cathode material is as follows: The cathode material was cross-sectionally polished using a GATAN 697 argon ion polisher, and then images were taken using a Hitachi SU 8010 scanning electron microscope. EDS line scans were performed on F and P elements respectively. The F and P contents at 40 nm inside the cathode material surface were selected, and the mass ratio of the two was calculated based on the test results.

[0121] The method for testing the P content at a distance of 200 nm from the surface of the cathode material is as follows: The cathode material was cross-sectionally polished using a GATAN 697 argon ion polisher, and then images were taken using a Hitachi SU 8010 scanning electron microscope. P element was selected for EDS line scanning, and the P content at 200 nm inward from the cathode material surface was selected.

[0122] Please refer to the details. Figures 2-7 ,in, Figure 2 The image shows the EDS selected area line scan of F and P elements in the cathode material of Example 1 - indicated by the white arrows. Figure 3 This is a graph showing the content distribution of F and P elements in the cathode material of Example 1 (the starting point of the horizontal axis is the surface of the cathode material). Figure 4 This is a graph showing the content distribution curves of F and P elements in the cathode material of Example 2; Figure 5 The graph shows the content distribution curves of F and P elements in the cathode material of Comparative Example 2. Figure 6 The graph shows the content distribution curves of F and P elements in the cathode material of Comparative Example 4. Figure 7 The graph shows the content distribution curves of F and P elements in the cathode material of Comparative Example 6.

[0123] Depend on Figures 2-4 It is known that, according to the preparation process provided in the embodiments of this application, the prepared cathode material has P doping in both the matrix and the surface layer, but only the surface layer is doped with F; Figures 5-6 It can be seen that when only F or P elements are doped, the corresponding elements are uniformly dispersed throughout the cathode material; from Figure 7 It can be seen that when F and P elements are added at the same time, F and P are uniformly distributed throughout the material.

[0124] The method for testing the pH value of positive electrode materials is as follows: Using a pHS-3C / Ray magnetic pH meter, weigh 5g of material, add 45g of purified water, stir magnetically for 30 minutes at 25℃, let stand for 30 minutes, insert the electrode to the 30 mL position, and read the value.

[0125] The test procedure for determining the carbonate concentration in water is as follows: Weigh 2g of the material, add 100mL of pure water, stir for 30min, filter about 50mL using filter paper, transfer 10mL of the solution, and determine the endpoint of CO3 using a 0.05mol / L HCl solution via potentiometric titration. 2- content.

[0126] The test steps for determining hydroxide concentration in ethanol are as follows: Weigh 2g of the material, add 100mL of pure water, stir for 60min, filter about 50mL using filter paper, transfer 10mL of the solution, and determine the endpoint using potentiometric titration with 0.05mol / L HCl solution to obtain the OH-. -content.

[0127] The test procedure for thermal decomposition temperature is as follows: The test was conducted using a TA DSC25 instrument with an equilibrium temperature of 50℃, a heating rate of 10℃ / min, a cutoff temperature of 350℃, an electrode mass of 2~3mg, an electrolyte mass of approximately 1mg, a crucible with a high-pressure sealed plate, and a 4.0V full-charge state.

[0128] Surface Ni 2+ The testing steps for the percentage are as follows: X-ray photoelectron spectroscopy (XPS) analysis was performed on an X-ray photoelectron spectrometer purchased from Shimadzu AXIS Supra, Japan. The specific steps were as follows: sample preparation in a glove box; transfer to the XPS equipment via a vacuum transfer chamber; sequential acquisition of broadband and Ni 2p high-resolution spectra; correction for charge effects using C 1s (284.8 eV); and analysis based on Ni... 2+ and Ni 3+ The characteristics are used to perform constrained peak fitting and calculate the proportion of each valence state.

[0129] For detailed peak-splitting results of the Ni 2p high-resolution spectrum, please refer to [reference needed]. Figure 8 Through Ni 2+ and Ni 3+ The corresponding peak area is convenient for calculating the proportion of divalent nickel.

[0130] Table 2

[0131] It should be noted that in Table 2, Comparative Example 1 does not contain F and P, while Comparative Examples 2 to 5 contain only F or P, and F or P is uniformly distributed throughout the material (see details). Figure 5 and Figure 6 Comparative Example 6 contains F and P, and F and P are uniformly distributed throughout the material (see details). Figure 7 ).

[0132] Table 3

[0133] It should be noted that in Table 3, "—" indicates that the thermal decomposition temperature of the sample exceeds the test upper limit of 350℃, so there are no corresponding test results.

[0134] Combining Tables 1-3 and Figures 2-7 As can be seen from the test results of Examples 1-14 and Comparative Examples 1-6, by first adding a phosphorus source for P doping and then adding a fluorine source for F doping, through the competition between F and P, a cathode material with P doped in both the matrix and the surface layer and F doped only in the surface layer can be prepared.

[0135] The test results from Examples 1-9 and Examples 10-13 show that by limiting the heating rate, sintering temperature, and sintering time in the second sintering process to a suitable range, the prepared cathode material has a suitable surface thickness, less residual alkali on the surface, a higher thermal decomposition temperature, and a higher surface Ni content. 2+ The advantage of a relatively low percentage.

[0136] (2) Electrical performance testing The cathode materials prepared in Examples 1-14 and Comparative Examples 1-6 were assembled into lithium-ion batteries. The initial discharge capacity, initial efficiency, and cycle gas production growth rate of each sample were then tested. The test results are summarized in Table 4.

[0137] The battery assembly steps are as follows: The prepared positive electrode material, acetylene black and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 90:5:5, mixed evenly, and NMP was added and stirred for 2 hours to form a viscous slurry. The slurry was evenly coated on aluminum foil, then vacuum baked at 80℃, pressed into sheets, and cut into positive electrode sheets with a diameter of 14 mm. Pure sodium sheets with a diameter of 16 mm were used as negative electrode sheets, ENA-18 from Tianci was used as electrolyte, and PP / PE / PP composite separators were used. The cells were assembled into button cells in an argon-filled glove box.

[0138] The testing procedures for the battery's initial discharge capacity and initial efficiency are as follows: The assembled button cell battery was placed in the Blue Battery device. The test temperature was set to 25±1℃, the test voltage to 2.0~4.0V, and the charging / discharging was performed at 0.2C / 0.2C. The charging cutoff current was 0.05C (1C nominal capacity is 130mAh / g). The discharge capacity and discharge capacity of the first cycle were recorded to obtain the first discharge capacity and first efficiency (first discharge capacity / first charge capacity × 100%).

[0139] The test procedure for the battery's cycle gas production growth rate is as follows: First, fully charge the battery and test its volume V1. Then, cycle the fully charged battery at 45°C for 300 cycles (charging to 4V at 1C constant current, then charging at 0.05C constant voltage, and finally discharging to 2.0V at 1C constant current, which is considered as one cycle). Then test the battery volume V2. The cycle gas production growth rate can be obtained by using the formula (V2-V1) / V1×100%. The volume measurement device is an electronic solid density meter TW-120E.

[0140] Table 4

[0141] Referring to Table 4, the test results of Examples 1-14 and Comparative Examples 1-6 show that the cathode material is doped with P in both the matrix and the surface layer, and only the surface layer is doped with F. Compared with other forms of cathode materials, it has better overall structural stability, which gives its corresponding battery the advantage of less gas production during cycling.

[0142] The test results from Examples 1-9 and Examples 10-13 show that the surface thickness, residual alkali, thermal decomposition temperature, and surface Ni of the cathode material are related to the cathode material. 2+ The proportions are all within a relatively suitable range. Compared with those outside the corresponding range, the corresponding batteries have the advantage of producing less gas during cycling. At the same time, the corresponding batteries also have relatively excellent first discharge capacity and first efficiency.

[0143] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A nickel-iron sodium manganate cathode material, characterized in that, The positive electrode material comprises a substrate and a surface layer outside the substrate, both the substrate and the surface layer are doped with P, and only the surface layer is doped with F.

2. The nickel-iron sodium manganate cathode material according to claim 1, characterized in that From the surface of the positive electrode material to the inside, the F content gradually decreases in the surface layer, and the P content gradually increases in the surface layer.

3. The nickel-iron sodium manganate positive electrode material according to claim 2, characterized in that The F content at the boundary between the surface layer and the substrate is 20 ppm, and the thickness of the surface layer is 20 nm to 400 nm. Optionally, the thickness of the surface layer is 50 nm to 180 nm.

4. The nickel-iron sodium manganate cathode material according to claim 3, characterized in that The thickness of the surface layer is 50 nm to 180 nm, the F content at a distance of 40 nm from the surface of the positive electrode material is 120 ppm to 350 ppm; or / and, the thickness of the surface layer is 50 nm to 180 nm, the P content at a distance of 200 nm from the surface of the positive electrode material is 140 ppm to 260 ppm. Optionally, the F content at a distance of 40 nm from the surface of the positive electrode material is 150 ppm to 300 ppm, or / and, the P content at a distance of 200 nm from the surface of the positive electrode material is 150 ppm to 220 ppm.

5. The nickel-iron sodium manganate positive electrode material according to claim 4, characterized in that The mass ratio of the F content to the P content at a distance of 40 nm from the surface of the positive electrode material is (2-20.33):

1. Optionally, the mass ratio of the F content to the P content at a distance of 40 nm from the surface of the positive electrode material is (2.38-16.18):

1. 6.The sodium nickel iron manganese oxide cathode material of any one of claims 1-5, wherein, The surface Ni of the cathode material 2+ The proportion is 10% to 15%.

7. The sodium nickel iron manganese oxide cathode material of any one of claims 1-5, wherein, The thermal decomposition temperature of the positive electrode material is not less than 350℃. 8.The sodium nickel iron manganese oxide cathode material of any one of claims 1-5, wherein, The pH value of the positive electrode material is 12-12.43; Or / and, the water-measured carbonate concentration of the positive electrode material is 9000 ppm-16000 ppm; Or / and, the ethanol-measured carbonate concentration of the positive electrode material is 400 ppm-1000 ppm. 9.The sodium nickel iron manganese oxide cathode material of any one of claims 1-5, wherein, The chemical formula of the positive electrode material is: Na a Ni b Fe c Mn d X e F f P g O2, wherein: 0.9≤a≤1.1, 0.10≤b≤0.35, 0.20≤c≤0.40, 0.20≤d≤0.40, 0≤e≤0.02, 0.001≤f≤0.02, 0.001≤g≤0.02, X includes at least one of Mg, K, Zr, Cu, Zn, Ce, Al, Ca and Sr; Optionally, 0.001≤e≤0.

02.

10. The nickel-iron sodium manganate cathode material according to claim 9, characterized in that 0.002≤f≤0.01 or / and 0.002≤g≤0.

004.

11. A method for preparing a nickel-iron-manganese sodium cathode material, characterized in that, Comprising the following steps: S1 mixing a sodium source, a nickel source, an iron source, a manganese source and a phosphorus source to obtain a first mixture; S2 performing first sintering on the first mixture to obtain a P-doped positive electrode material precursor; S3 mixing the positive electrode material precursor and a fluorine source to obtain a second mixture; S4 performing second sintering on the second mixture to obtain a sodium nickel-iron-manganese acid positive electrode material.

12. The method for preparing the cathode material according to claim 11, characterized in that, The second sintering comprises a heating stage and a holding stage, in the heating stage, the heating rate is not higher than 3℃ / min.

13. The method for preparing the cathode material according to claim 12, characterized in that, In the holding stage, the sintering temperature is 700℃-900℃, and the sintering time is not less than 6 h.

14. A sodium-ion battery, characterized in that, The nickel-iron-manganese acid sodium positive electrode material prepared by the preparation method of the nickel-iron-manganese acid sodium positive electrode material according to any one of claims 1-10 or the nickel-iron-manganese acid sodium positive electrode material according to any one of claims 11-13.

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