A doped modified sodium ion layered metal oxide positive electrode material and a preparation method and application thereof

Abstract

This invention relates to a doped and modified sodium ion layered metal oxide cathode material, its preparation method, and its applications. The material obtained by cation doping is Na... 0.9 Ni 0.3 Fe 0.3 Mn 0.3 A x B y O2, x+y=0.1, 0≤x≤0.1, 0≤y≤0.1, 0.8≤z≤0.9; the purpose of doping is to improve structural stability, reduce residual alkali, and improve rate capability and cycle life. The prepared metal oxide is a blocky (plate-like) monocrystalline layered material with a smooth and rounded surface; it can also improve the battery's cycle performance and safety performance. A binder composed of polyvinylidene fluoride and polyacrylonitrile was selected when preparing the electrode, which can further improve the stability of the battery's positive electrode.

Description

Technical Field

[0001] This invention belongs to the field of sodium ion technology, and in particular relates to a doped and modified sodium ion layered metal oxide cathode material, its preparation method, and its application. Background Technology

[0002] With the rapid development of the new energy industry, especially the booming new energy vehicle sector, the price of lithium resources has risen sharply. Coupled with the uneven global distribution of lithium resources, prices have remained high. Therefore, resource and cost issues have become bottlenecks restricting the healthy development of new energy. Thus, there is an urgent need to develop alternatives to lithium resources. Sodium-ion batteries, due to the abundance of sodium resources, have become another technological hotspot in new energy development. Sodium is the sixth most abundant element in the Earth's crust, widely distributed, and has low development costs; therefore, sodium-ion batteries are an effective alternative to lithium-ion batteries.

[0003] The key to sodium-ion batteries lies in the sodium-ion cathode material. Sodium-ion cathode materials include polyanion cathode materials and layered metal oxide cathodes (Na₂O₃). x Materials such as MO2 (where M = one or more metallic elements selected from Fe, Mn, Co, Cr, Ni, Ti, V, Al, Mg, Zr, Zn, Cu, W, Ca, Sn, B, Mo, Nb, Tc, etc.) and Prussian blue are among the most promising. Layered metal oxide cathode materials are the most likely to be widely adopted and rapidly industrialized. Layered metal oxide cathodes are classified into P2 and O3 types. P2 type cathode materials have better kinetic performance due to their larger interlayer spacing, while O3 type cathode materials have higher capacity due to their higher sodium content. Currently, layered metal oxide cathode materials exhibit structural instability during charge and discharge, high residual alkali content, and their preparation process requires strict control over environmental temperature and humidity, hindering industrial production and widespread application. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a doped and modified sodium ion layered metal oxide cathode material, its preparation method, and its application.

[0005] The technical solution adopted in this invention is: a doped and modified sodium ion layered metal oxide cathode material, wherein the active material is Na. z Ni 0.3 Fe 0.3 Mn 0.3 A x B y O2, x+y=0.1, 0≤x≤0.1, 0≤y≤0.1, 0.8≤z≤0.9; where A and B are one of Al, Cu, Mg, Zn, Co, Ca, B, Ti, Zr, Sn, Mo, W, Tc, Nb, Ag, V, Ba and Sr.

[0006] Preferably, after mixing the raw materials for the active material, the mixture is calcined at 900°C in an air or oxygen atmosphere, and the active material of the positive electrode material is adjusted by regulating the flow rate of the air or oxygen atmosphere.

[0007] Preferably, the flow rate adjustment parameter is that the flow rate of the upper atmosphere valve is set to 3-5 m / s. 3 / h, the flow rate of the lower atmosphere valve is set to 4-7m / h. 3 / h.

[0008] A sodium-ion battery cathode comprising a cathode material.

[0009] Preferably, the slurry for preparing the positive electrode also includes superconducting carbon black, a composite conductive agent of carbon nanotubes and graphene, a binder, and a solvent; wherein the mass ratio of the active material, the conductive agent, and the binder is 92-96:1-3:3-5.

[0010] Preferably, the adhesive is a mixture of polyvinylidene fluoride and polyacrylonitrile, with a mixing ratio of 1:0.25-4.

[0011] Preferably, the mixing ratio of polyvinylidene fluoride and polyacrylonitrile in the adhesive is 4:6.

[0012] Preferably, the solvent is N-methylpyrrolidone.

[0013] A sodium-ion battery, including a sodium-ion battery positive electrode.

[0014] The advantages and positive effects of this invention are: by improving the sodium ion content in the sodium ion layered metal oxide material to reduce the alkalinity of the material surface, and by doping with new elements to improve the structural stability of the material, the prepared cathode material can improve cycle life, rate capability and safety performance when used in sodium batteries.

[0015] Furthermore, the performance of the positive electrode sheet can be further optimized by improving the composition and ratio of the binder in the positive electrode material, thereby further improving the stability of the sodium battery; thus improving the cycle life of the sodium-ion battery and enabling its large-scale application. Attached Figure Description

[0016] Figure 1 This is a SEM image of the O3 sodium ion layered metal oxide cathode material prepared in Comparative Example 1 of this invention;

[0017] Figure 2 This is a SEM image of the O3 sodium ion layered metal oxide cathode material prepared in Example 1 of this invention;

[0018] Figure 3 This is a SEM image of the O3 sodium ion layered metal oxide cathode material prepared in Example 2 of this invention. Detailed Implementation

[0019] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0020] This invention relates to a doped and modified sodium-ion layered metal oxide cathode material, its preparation method, and its application. The cation-doped and modified O3-type sodium-ion battery cathode material is Na. z Ni 0.3 Fe 0.3 Mn 0.3 A x B y O2, x+y=0.1, 0≤x≤0.1, 0≤y≤0.1, 0.8≤z≤0.9. The sodium content is reduced from the common 1 to 0.8-0.9. After doping modification, the capacity does not decrease significantly, residual alkali is significantly reduced, and structural stability is improved. A and B are one or more elements selected from Al, Cu, Mg, Zn, Co, Ca, B, Ti, Zr, Sn, Mo, W, Tc, Nb, Ag, V, Ba, and Sr. The main role of elements A and B is to improve the structural and air stability of the material, and to improve cycling and rate performance.

[0021] In some embodiments of the present invention, air or O2 is introduced during the sintering process, and the moisture, residual alkali, specific surface area and morphology of the finished material are precisely controlled by adjusting the gas flow rate. When the sintering atmosphere is O2, a mixed gas doped with O2 can be used with an oxygen content of not less than 50%.

[0022] The O3-type sodium-ion battery cathode material prepared by the above method can be used to make sodium battery cathodes, which can then be assembled into sodium batteries. In some embodiments of the present invention, battery performance can be further improved by adjusting the composition of the binder during the preparation of the cathode sheet. Using a mixture of PVDF (polyvinylidene fluoride) and PAN (polyacrylonitrile) in different proportions as a binder for the cathode sheet improves the adhesion between the cathode sheet and the current collector. The PVDF to PAN ratio ranges from 20% to 80%. This improves the poor processing performance and poor adhesion caused by the high alkalinity of the sodium-ion layered metal oxide cathode material. Preferably, when PVDF:PAN = 40%:60%, the adhesion of the cathode sheet ensures both processing performance and cell cycle performance, thereby improving battery safety.

[0023] Compared to prior art, this solution reduces the sodium content from 1% to 0.9%, ensuring reduced residual alkali without affecting battery capacity. Furthermore, the reduction in sodium content introduces ion vacancies, potentially leading to impurities in the material's structure and impacting structural stability, rate capability, and cycle performance. This solution addresses these issues by doping with bimetallic materials to improve structural stability, rate capability, and cycle performance. However, sodium-ion layered oxide materials are inherently unstable in air and prone to gelation during electrode fabrication. Therefore, improving the binder in the positive electrode slurry by using polyvinylidene fluoride (PVDF) and polypropylene enhances the slurry's air resistance.

[0024] After doping with specific metal elements, different calcination gas flow parameters will affect the purity of the material and the change in residual alkali on the surface. In this scheme, the gas flow adjustment parameters are limited, that is, calcination is carried out in a tunnel furnace, and the gas flow parameter of the upper valve in the tunnel furnace is set to a flow rate of 3-5 m / s. 3 / h, the flow rate of the lower atmosphere valve is set to 4-7m / h. 3 The calcination process was controlled at / h. The improved method yielded materials that, upon testing, showed improvements in surface residual alkali, structural stability, rate capability, and cycle performance.

[0025] The present invention will now be described with reference to the accompanying drawings. Experimental methods not specifically described in terms of operation steps are performed in accordance with the corresponding product manuals. Unless otherwise specified, the instruments, reagents, and consumables used in the embodiments can be purchased from commercial companies.

[0026] Comparative Example 1: Cathode material Na 0.9 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2

[0027] Weigh out the sample that meets the Na standard. 0.9 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 Manganese tetroxide, ferric oxide, nickel oxide, and sodium carbonate, in an O2 stoichiometric ratio, were mixed thoroughly and then sintered at 900°C for 18 hours in air. The resulting cathode material was examined by scanning electron microscopy, and the results are as follows: Figure 1 As shown, the material has a blocky (sheet-like) single-crystal layered structure with a smooth surface.

[0028] When it is prepared as a positive electrode active material, the positive electrode active material is Na. 0.9 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3O2, the conductive agent is a composite of superconducting carbon black (super P), carbon nanotubes (CNTs) and graphene, wherein superconducting carbon black accounts for 75%, carbon nanotubes 20%, and graphene 5%; the composite conductive agent contains 80% carbon nanotubes and 20% graphene; the binder is polyvinylidene fluoride (PVDF), and the solvent is N-methylpyrrolidone (NMP). The preset mass ratio of active material, conductive agent, and binder is (94±2):(2±1.0):(4±1.0).

[0029] Example 1: Doped and modified O3-type sodium ion cathode material Na 0.9 Ni 0.3 Fe 0.3 Mn 0.3 Zn 0.1 O2

[0030] Weigh out the sample that meets the Na standard. 0.9 Ni 0.3 Fe 0.3 Mn 0.3 Zn 0.1 Manganese tetroxide, ferric oxide, nickel oxide, sodium carbonate, and zinc oxide, in an O2 stoichiometric ratio, were mixed uniformly and then sintered at 900°C for 18 hours in an oxygen atmosphere (oxygen content not less than 50%). The residual alkali, BET, oxygen defects, and morphology of the material were controlled by adjusting the gas flow rate. The resulting cathode material was examined by electron microscopy, and its structure was as follows: Figure 2 As shown, the material has a blocky (plate-like) single-crystal layered structure with a smooth surface, indicating that the doping elements have entered the crystal lattice.

[0031] When it is prepared as a positive electrode active material, the positive electrode active material is Na. 0.9 Ni 0.3 Fe 0.3 Mn 0.3 Zn 0.1 The active material (O2) and conductive agent are a composite of superconducting carbon black (super P), carbon nanotubes (CNTs), and graphene, comprising 75% superconducting carbon black, 20% carbon nanotubes, and 5% graphene. The binder is polyvinylidene fluoride (PVDF), and the solvent is N-methylpyrrolidone (NMP). The preset mass ratio of the active material, conductive agent, and binder is (94±2):(2±1.0):(4±1.0).

[0032] Example 2: Doped and modified O3-type sodium ion cathode material Na 0.9 Ni 0.3 Fe 0.3 Mn 0.3 Zn 0.05 Mg 0.05 O2

[0033] Weigh out the sample that meets the Na standard. 0.9 Ni 0.3 Fe 0.3 Mn 0.3 Zn 0.05 Mg 0.05 Manganese tetroxide, ferric oxide, nickel oxide, sodium carbonate, zinc oxide, and magnesium oxide, in an O2 stoichiometric ratio, were mixed uniformly and sintered at 900℃ for 18 hours in an oxygen atmosphere (oxygen content not less than 50%). The residual alkali, BET, oxygen defects, and morphology of the material were controlled by adjusting the gas flow rate. The resulting cathode material was examined by electron microscopy, and its structure was as follows: Figure 3 As shown, the material has a blocky (plate-like) single-crystal layered structure with a smooth surface, indicating that the co-doped elements have entered the crystal lattice.

[0034] When it is prepared as a positive electrode active material, the positive electrode active material is Na. 0.9 Ni 0.3 Fe 0.3 Mn 0.3 Zn 0.05 Mg 0.0 The active material (5O2) is a composite of superconducting carbon black (super P), carbon nanotubes (CNTs), and graphene, comprising 75% superconducting carbon black, 20% carbon nanotubes, and 5% graphene. The binder is polyvinylidene fluoride (PVDF), and the solvent is N-methylpyrrolidone (NMP). The predetermined mass ratio of the active material, conductive agent, and binder is (94±2):(2±1.0):(4±1.0).

[0035] Example 3: Doped and modified O3-type sodium ion cathode material Na 0.85 Ni 0.3 Fe 0.3 Mn 0.3 Zn 0.1 O2

[0036] Weigh out the sample that meets the Na standard. 0.85 Ni 0.3 Fe 0.3 Mn 0.3 Zn 0.1 Manganese tetroxide, ferric oxide, nickel oxide, sodium carbonate, and zinc oxide in an O2 stoichiometric ratio are mixed evenly and then sintered at 900°C for 18 hours in an oxygen atmosphere (oxygen content not less than 50%). The residual alkali, BET, oxygen defects, and morphology of the material are controlled by adjusting the gas flow rate.

[0037] The positive electrode active material was prepared according to the method in Example 1.

[0038] Example 4: Doped and modified O3-type sodium ion cathode material Na 0.8 Ni0.3 Fe 0.3 Mn 0.3 Zn 0.1 O2

[0039] Weigh out the sample that meets the Na standard. 0.8 Ni 0.3 Fe 0.3 Mn 0.3 Zn 0.1 Manganese tetroxide, ferric oxide, nickel oxide, sodium carbonate, and zinc oxide in an O2 stoichiometric ratio are mixed evenly and then sintered at 900°C for 18 hours in an oxygen atmosphere (oxygen content not less than 50%). The residual alkali, BET, oxygen defects, and morphology of the material are controlled by adjusting the gas flow rate.

[0040] The positive electrode active material was prepared according to the method in Example 1.

[0041] Example 5: Preparation of a sodium battery

[0042] The positive electrode active materials prepared in Comparative Example 1 and Examples 1-5 were used to prepare sodium batteries according to the following method:

[0043] The first step is homogenization: the positive electrode active material, conductive agent, binder and dispersant are mixed according to the preset mass ratio and stirred evenly. Then, they are dissolved in a solvent for dispersion. By adjusting the amount of solvent added, the solid content of the positive electrode slurry is adjusted to 60±5% or the slurry viscosity is adjusted to 4000±1000cp.

[0044] The second step is coating: the slurry is evenly coated on the positive current collector and thoroughly dried in an oven to remove the solvent from the electrode sheet, thus obtaining a positive electrode sheet with a positive electrode film on its surface.

[0045] The third step is rolling: the dried positive electrode sheet with the positive electrode film on the surface is rolled until the compaction density of the positive electrode film meets the preset compaction density value range.

[0046] The fourth step is cutting: the rolled positive electrode sheet is cut to the specified size to obtain the finished positive electrode sheet;

[0047] Step 5, Assembly: The corresponding positive electrode, negative electrode, and separator are stacked, welded, and installed in the shell according to the following procedures.

[0048] Step 6, Formation: The above-mentioned batteries are processed through drying, liquid injection, and formation to obtain the finished battery.

[0049] Steps or raw materials not mentioned in the above method may be adopted using methods or raw materials used in the prior art.

[0050] The prepared sodium batteries were tested, and the performance of each group of batteries was compared. The specific data are shown in the table below. The data comparison in Table 1 shows that, compared with Comparative Example 1, Example 1, after Zn doping, has a comparable capacity, but significantly improved rate and cycle performance, and a lower pH value; Example 2, after co-doping with Zn and Mg, has a comparable capacity, further improved rate and cycle performance, and a further decreased pH value.

[0051] Table 1 Comparison of O3-type sodium ion cathode materials before and after cation doping modification.

[0052] 0.2C gram capacity mAh / g 1C / 0.2C (multiplier) 0.2C, 50 cycles pH Comparative Example 127 93.2％ 89.8％ 12.92 Example 1 126.9 95.1％ 93.7％ 12.78 Example 2 126.8 96.4％ 95.8％ 12.62

[0053] To further investigate the effects of sodium content on residual alkali and cycle life, the sodium content was further reduced to 0.85 (Example 3) and 0.8 (Example 4) based on Example 1. Table 2 shows that sodium content affects the residual alkali on the material surface. Reducing the sodium content decreases both the specific capacity and the pH value of the material surface, thereby further improving rate capability and cycle life. It is evident that adjusting the sodium content and increasing the doping of metal ions can achieve multi-faceted control of the cathode material, significantly improving cycle life, rate capability, and reducing moisture content, thus enhancing the overall performance of the sodium battery.

[0054] Table 2 Comparison of sodium content reduction in O3-type sodium ion cathode materials before and after implementation.

[0055]

[0056] Example 6: The effect of optimizing electrode composition on sodium batteries

[0057] To further improve the electrode processing performance of the modified sodium-ion cathode material, battery performance is improved by optimizing the electrode formulation. The optimization method proposed in this embodiment is to adjust the composition of the binder in the cathode slurry. The cathode active material composition includes:

[0058] The positive electrode active material is Na 0.9 Ni 0.3 Fe 0.3 Mn 0.3 Zn 0.05 Mg 0.05O2, the conductive agent is a composite of superconducting carbon black (superP), carbon nanotubes (CNTs) and graphene (75% superconducting carbon black, 20% carbon nanotubes, and 5% graphene), the binder and solvent is N-methylpyrrolidone (NMP). The preset mass ratio of active material, conductive agent, and binder is (94±2):(2±1.0):(4±1.0). In Comparative Example 2, the binder is polyvinylidene fluoride (PVDF). In optimized cathode materials 1-5, the binder is a mixture of PVDF and polyacrylonitrile (PAN), with mixing ratios of 80%:20%, 60%:40%, 50%:50%, 40%:60%, and 20%:80%, respectively.

[0059] Sodium batteries were assembled using the prepared positive electrode active material materials according to the method in Example 5. The battery performance was tested, and the results are shown in Table 3.

[0060] Table 3 Comparison of O3-type sodium ion modified cationic cathode materials before and after electrode optimization

[0061]

[0062] Table 3 shows that, compared to Comparative Example 2, the optimized cathode material significantly improved electrode adhesion after using a mixed adhesive; however, increasing the PAN content led to increased electrode brittleness. The comparison revealed that the battery's cycle performance was optimal with a 40% PVDF + 60% PAN mixed adhesive ratio.

[0063] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A sodium-ion battery positive electrode, characterized in that: This includes active material materials, specifically the cation-doped modified O3-type sodium-ion battery cathode material Na. z Ni 0.3 Fe 0.3 Mn 0.3 A x B y O2, x+y=0.1, 0≤x≤0.1, 0≤y≤0.1, 0.8≤z≤0.9; where A and B are one of Al, Cu, Mg, Zn, Co, Ca, B, Ti, Zr, Sn, Mo, W, Tc, Nb, Ag, V, Ba and Sr; After mixing the raw materials for the active material, the mixture is calcined at 900℃ in an oxygen atmosphere with an oxygen content of not less than 50%. The active material of the cathode is calcined by adjusting the oxygen atmosphere flow rate in a tunnel furnace. The airflow parameter of the upper valve in the tunnel furnace is set to a flow rate of 3-5 m / s. 3 / h, the flow rate of the lower atmosphere valve is set to 4-7m / h. 3 The material is calcined at / h; it has a sheet-like, single-crystal layered structure with a smooth surface. It also includes superconducting carbon black, carbon nanotube and graphene composite conductive agent, binder and solvent; wherein the mass ratio of active material, conductive agent and binder is 92-96:1-3:3-5; The adhesive is a mixture of polyvinylidene fluoride and polyacrylonitrile, with a mixing ratio of 1:0.25-4.

2. The sodium-ion battery positive electrode according to claim 1, characterized in that: The mixing ratio of polyvinylidene fluoride and polyacrylonitrile in the adhesive is 4:

6.

3. The sodium-ion battery positive electrode according to claim 1, characterized in that: The solvent is N-methylpyrrolidone.

4. A sodium-ion battery, characterized in that: Includes the sodium-ion battery positive electrode as described in any one of claims 1-3.

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