Sodium-ion battery positive electrode material and preparation method therefor and use thereof

Abstract

A sodium-ion battery positive electrode material and a preparation method therefor and a use thereof. The sodium-ion battery positive electrode material comprises a sodium-based transition metal oxide, and an XRD spectrogram of the sodium-based transition metal oxide satisfies: the ratio of the diffraction peak intensity of a crystal plane (003) to the diffraction peak intensity of a crystal plane (012) being greater than or equal to 2.7, and / or the ratio of the diffraction peak intensity of the crystal plane (003) to the diffraction peak intensity of a crystal plane (110) being greater than or equal to 4.0. When the XRD spectrogram of the sodium-ion battery positive electrode material satisfies the conditions, it can be ensured that the inactive crystal plane (003) has preferred orientation, helping to fundamentally ensure the air stability and cycle stability of the material to be synchronously improved.

Description

A sodium cathode material and its preparation method and application

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on July 31, 2023, with application number 202310961628.7 and application name “A sodium battery positive electrode material, its preparation method and application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The embodiments of the present application relate to the technical field of sodium ion batteries, and specifically to a sodium battery positive electrode material and a preparation method and application thereof. Background Art

[0003] Because sodium resources are abundant and inexpensive on Earth, sodium-ion batteries (SIBs) are low-cost and free of overdischarge, making them a research hotspot in the field of secondary batteries. Layered sodium-based transition metal oxides, with their high specific capacity, are commonly used as cathode active materials in SIBs. However, poor air stability and cycling stability are two key issues for these materials.

[0004] The poor air stability of the above materials is mainly due to the fact that when they are exposed to air containing water and CO2, the Na + It is easy to escape and generate alkaline substances on the surface of the material. The presence of alkaline substances on the surface will increase the surface impedance of the material, reduce its capacity, and increase the stability and coating effect of the subsequently prepared positive electrode slurry; water / CO2 in the air will also be embedded along the active surface of the material, causing cracks and other microstructural defects, affecting capacity. The poor cyclic stability of the above materials is mainly due to the multi-level phase transition and stress accumulation during the cycle process, which lead to defects such as cracks along the active surface. The generation of cracks will lead to more interfacial side reactions, which will worsen the cyclic stability. Therefore, the air / cyclic stability of the above materials is closely related to the intrinsic structure of the material.

[0005] There are reports in the industry that acid washing or surface coating can improve its air stability. However, acid washing can only reduce the initial residual alkali on the surface of the material. Residual alkali continues to be generated after the material is left aside, which cannot form a long-term barrier protection. Acid washing inevitably causes sodium ions to dissolve in the bulk phase, resulting in a decrease in specific capacity and deterioration in cycle performance. The coating amount is limited, and the air stability and interface stability of the uncoated areas are still poor. Moreover, coating cannot fundamentally reduce the generation of cracks or improve the cycle stability of the material. Therefore, it is necessary to provide a technical solution that can effectively improve the air and cycle stability of layered sodium-based transition metal oxides at the same time.

[0006] Summary of the Invention

[0007] In view of this, the present application is based on the root cause of the air / cycle stability failure of sodium-based transition metal oxides, and provides a sodium battery positive electrode material and its preparation and application. By controlling the XRD structural characteristics of layered sodium-based transition metal oxides, the inactive crystal planes are preferentially oriented, fundamentally ensuring that the air stability and cycle stability of the material are simultaneously improved.

[0008] In a first aspect, an embodiment of the present application provides a sodium-based positive electrode material, wherein the sodium-based positive electrode material includes a sodium-based transition metal oxide, and the X-ray diffraction spectrum of the sodium-based positive electrode material satisfies: the ratio of the diffraction peak intensity of the (003) crystal plane to the (012) crystal plane is greater than or equal to 2.7, and / or the ratio of the diffraction peak intensity of the (003) crystal plane to the (110) crystal plane is greater than or equal to 4.0.

[0009] When the XRD spectrum of the sodium cathode material meets the above conditions, it can be reflected that its inactive crystal plane (003) has a preferential orientation and the crystal plane is exposed more, which helps to inhibit the H2O and CO2 in the air from being embedded in the sodium-based transition metal oxide along the (012) and / or (110) active planes, and inhibit the Na + It escapes along the active surface and reacts with H2O / CO2 in the air, thereby ensuring the good air stability of the sodium-based transition metal oxide; at the same time, it also helps to suppress the problem of more interfacial side reactions caused by cracks along the active surface, and improve its cyclic stability.

[0010] In some embodiments of the present application, the ratio of the diffraction peak intensity of the (012) crystal plane to the (110) crystal plane is in the range of 1-3. This can further improve the air stability and cycle stability of the material and help suppress the problem of excessive exposure of the (110) crystal plane to produce transition metal oxide impurity phases, which affects the electrochemical performance of the material.

[0011] In some embodiments of the present application, the ratio of the diffraction peak intensity of the (003) crystal plane to the (012) crystal plane is in the range of 2.7-6.0. In this case, the air stability and cycle stability of the above-mentioned sodium cathode material are both high, and the problem of decreased sodium ion transport kinetics of the material caused by excessive orientation of the (003) crystal plane is avoided.

[0012] In some embodiments of the present application, the ratio of the diffraction peak intensity of the (003) crystal plane to the (110) crystal plane is in the range of 4.0-8.0. In this case, the air stability and cycle stability of the above-mentioned sodium cathode material are both high, and the problem of decreased sodium ion transport kinetics of the material caused by excessive orientation of the (003) crystal plane is avoided.

[0013] In an embodiment of the present application, the sodium-based transition metal oxide includes single crystal particles and / or polycrystalline particles; wherein the single crystal particles are primary particles, and the polycrystalline particles are secondary particles composed of multiple primary particles.

[0014] In the embodiments of the present application, the primary particles are hexagonal-like flake particles, and the ratio of length to thickness of the primary particles is in the range of 1.5-8. This facilitates the exposure of the inactive (003) crystal planes of the sodium-based transition metal oxide, thereby improving its air and cyclic stability and avoiding the problem of decreased sodium ion transport kinetics caused by excessive (003) crystal plane orientation.

[0015] In the embodiment of the present application, the thickness of the primary particles is in the range of 0.04 μm to 6 μm, which is conducive to ensuring that the sodium-based transition metal oxide has both good structural stability and sodium ion transport performance.

[0016] In some embodiments of the present application, the single-crystal particles have a D50 particle size within the range of 0.5 μm to 12 μm, and a D99 particle size not exceeding 30 μm. Single-crystal sodium-based transition metal oxides with an appropriate D50 particle size facilitate ensuring that the single-crystal particles have both a short sodium ion diffusion path and a high compaction density. A D99 particle size within the above range ensures good dispersion of the single-crystal particles and prevents excessive agglomeration of primary particles.

[0017] In some embodiments of the present application, the polycrystalline particles have a D50 particle size within the range of 1 μm to 15 μm, and a D99 particle size not exceeding 30 μm. Polycrystalline sodium-based transition metal oxides with an appropriate D50 particle size can ensure high structural stability, minimal interfacial side reactions, and good rate performance. A D99 particle size within the above range also prevents the presence of overly large polycrystalline particles, which can degrade rate performance.

[0018] In the embodiment of the present application, the chemical formula of the sodium-based transition metal oxide includes Na x A y M z O w , wherein A is a variable valence transition metal element, and M is selected from one or more of Li, Al, Mg, Ca, Sr, K, Sn, Ti, Zn, Zr, Nb, Mo, and B; <x≤12,0<y≤12,0≤z≤12,0<w≤12。

[0019] In some embodiments of the present application, the sodium-based cathode material further includes a coating layer coated on the surface of the sodium-based transition metal oxide; wherein the coating layer comprises one or more of an oxide, a fluoride, and a phosphate. The presence of the coating layer can further improve the air stability and cycling stability of the sodium-based cathode material.

[0020] In the embodiment of the present application, the thickness of the coating layer is 0.1 nm to 100 nm. A coating layer of appropriate thickness can effectively improve the air stability and cycle stability of the sodium cathode material while not affecting the specific capacity of the material due to excessive thickness of the coating layer.

[0021] In the embodiment of the present application, the compaction density of the sodium cathode material at 200 MPa is 2.6-3.5 g / cm 3 , with a specific surface area of ​​0.2-1.5m 2 The sodium battery cathode material has the above-mentioned XRD characteristics and primary particle morphology and size characteristics, which can make the compaction density and specific surface area of ​​the sodium battery cathode material meet the above conditions, thereby facilitating the sodium battery made from the material to have both good cycle stability and high energy density.

[0022] A second aspect of an embodiment of the present application provides a positive electrode plate, which includes a positive electrode collector and a positive electrode active material layer arranged on at least one side of the positive electrode collector, and the positive electrode active material layer includes the sodium battery composite positive electrode material described in the first aspect of the embodiment of the present application.

[0023] The sodium secondary battery made with the positive electrode sheet has good cycle stability. In addition, due to the high compaction density of the sodium positive electrode material, the compaction density of the positive electrode sheet can also be high, and the specific capacity of the sodium secondary battery can be high.

[0024] A third aspect of the present invention provides a sodium secondary battery comprising the positive electrode sheet and the negative electrode sheet as described in the second aspect of the present invention. The sodium secondary battery has good cycle performance and high specific capacity.

[0025] A fourth aspect of the present application provides an electrical device, which includes the sodium secondary battery described in the third aspect of the present application, wherein the electrical device includes one or more of an electronic device and a mobile device.

[0026] By using the sodium secondary battery provided in the embodiment of the present application to power the electrical device, the user experience and market competitiveness of the product can be improved.

[0027] A fifth aspect of the present application provides an energy storage system, comprising a plurality of sodium secondary batteries as described in the third aspect of the present application. The sodium secondary batteries used in the energy storage system have good cycle stability.

[0028] The present invention also provides a method for preparing the above-mentioned sodium cathode material, comprising the following steps:

[0029] (1) mixing a sodium source with other element sources in the sodium-based transition metal oxide to be prepared to obtain a mixed dry material;

[0030] (2) sintering the mixed dry material multiple times to obtain a sodium-based transition metal oxide-containing sodium cathode material; wherein, in the multiple sintering, the holding temperature of each sintering is within the range of 800-1200°C, and the sintered material obtained by each sintering is crushed before the next sintering, so that the X-ray diffraction spectrum of the sodium cathode material satisfies: the ratio of the diffraction peak intensity of the (003) crystal plane to the (012) crystal plane is greater than or equal to 2.7, and / or the ratio of the diffraction peak intensity of the (003) crystal plane to the (110) crystal plane is greater than or equal to 4.0.

[0031] The preparation method is simple in process and easy to operate, and can produce a sodium cathode material having the XRD spectrum characteristics described above in the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] 1A , 1B and 1C are schematic diagrams of several structures of a sodium cathode material 100 provided in an embodiment of the present application.

[0033] FIG2 is a schematic diagram of the structure of the positive electrode sheet provided in an embodiment of the present application.

[0034] FIG3 is a schematic structural diagram of a sodium secondary battery provided in an embodiment of the present application.

[0035] FIG4 is a schematic structural diagram of an electronic device provided in an embodiment of the present application.

[0036] FIG5 is a schematic structural diagram of an energy storage system provided in an embodiment of the present application.

[0037] FIG6 summarizes the X-ray diffraction (XRD) spectra of the sodium cathode materials prepared in Example 1 and Comparative Example 1.

[0038] FIG7 is an electron microscope photograph of the sodium cathode material of Example 1.

[0039] FIG8 is an XRD spectrum of the sodium cathode material prepared in Example 2.

[0040] FIG9 is a scanning electron microscope photograph of the sodium cathode material prepared in Example 2. DETAILED DESCRIPTION

[0041] The embodiments of the present application will be described below with reference to the accompanying drawings.

[0042] In order to address the problem that existing sodium-based transition metal oxides are prone to air / cycle stability failure and cannot be effectively solved, the embodiments of the present application provide a sodium battery positive electrode material.

[0043] Specifically, as shown in FIG1A , the sodium cathode material 100 provided in an embodiment of the present application includes a sodium-based transition metal oxide 10, and the XRD spectrum of the sodium cathode material 100 satisfies the following conditions: the ratio of the diffraction peak intensity of the (003) crystal plane to the (012) crystal plane is greater than or equal to 2.7, and / or the ratio of the diffraction peak intensity of the (003) crystal plane to the (110) crystal plane is greater than or equal to 4.0. The ratio of the diffraction peak intensity of the (003) crystal plane to the (012) crystal plane specifically refers to the ratio of the peak intensity (i.e., peak height) of the diffraction peak corresponding to the (003) crystal plane to the peak intensity (i.e., peak height) of the diffraction peak corresponding to the (012) crystal plane. The ratio of the diffraction peak intensities of the (003) crystal plane and the (110) crystal plane specifically refers to the ratio of the peak intensity (i.e., peak height) of the diffraction peak corresponding to the (003) crystal plane to the peak intensity (i.e., peak height) of the diffraction peak corresponding to the (110) crystal plane.

[0044] When the XRD spectrum of the sodium-based cathode material 100 meets the above conditions, it can be reflected that the sodium-based cathode material 100 has a (003) crystal plane preferential orientation, and the (003) crystal plane is correspondingly more exposed; and the (003) crystal plane is a low-activity surface (or called "inactive surface") of the sodium-based transition metal oxide, and the (012) crystal plane and the (110) crystal plane are high-activity surfaces of the sodium-based transition metal oxide, and the (003) inactive crystal plane has good air stability, and its preferential orientation / sufficient exposure helps to inhibit H2O and CO2 in the air from being embedded into the sodium-based transition metal oxide along the active surface - (012) crystal plane and / or (110) crystal plane, thereby inhibiting Na + The sodium-ion cathode material 100 is freed from the active surface and reacts with H2O / CO2 in the air to generate alkaline substances such as sodium carbonate on the surface of the material. This reduces the possibility that the presence of alkaline substances will increase the surface impedance of the material and reduce the capacity, thereby improving the stability and coating effect of the positive electrode slurry prepared using the sodium-ion cathode material. Therefore, the sodium-ion cathode material 100 has good air stability. In addition, during the cycle of the cathode material, cracks are mostly generated along the active surface, and the preferred orientation of the (003) inactive crystal plane is also conducive to inhibiting the generation of cracks, improving the structural stability of the material, inhibiting the occurrence of more interfacial side reactions caused by crack generation, improving cycle stability, and facilitating capacity development. Therefore, the sodium-ion cathode material that meets the above XRD spectrum conditions can achieve both good air stability and cycle stability.

[0045] In some embodiments of the present application, the XRD spectrum of the sodium-based cathode material 100 simultaneously satisfies the following conditions: the diffraction peak intensity ratio of the (003) crystal plane to the (012) crystal plane is greater than or equal to 2.7, and the diffraction peak intensity ratio of the (003) crystal plane to the (110) crystal plane is greater than or equal to 4.0. In this case, it indicates that the active planes (012) and (110) in the sodium-based transition metal oxide are simultaneously suppressed by the preferentially oriented (003) crystal plane, and its air stability and cycle stability are highly improved.

[0046] In the embodiment of the present application, the ratio of the diffraction peak intensity of the (012) crystal plane to the (110) crystal plane of the sodium cathode material 100 (i.e., I (012) / I (110) ) is in the range of greater than or equal to 1.0 to less than or equal to 3.0 (i.e., in the range of 1.0-3.0). (012) / I (110) A value less than 3 indicates that the highly active (012) crystal plane is further suppressed, which is more conducive to improving the air stability and cycle stability of the material. In addition, compared with the (012) crystal plane, the (110) crystal plane is prone to the aggregation of transition metal elements such as Ni, producing transition metal oxide impurity phases (such as NiO impurity phases), thereby weakening the electrochemical performance of the material. Therefore, I (012) >I (110) This can reduce the problem of NiO impurity phase caused by excessive exposure of the (110) crystal plane. In some embodiments, the ratio of the diffraction peak intensity of the (012) crystal plane to the (110) crystal plane is 1.0-2.67, for example, specifically 1.1, 1.2, 1.3, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, or 2.6. Furthermore, the ratio of the diffraction peak intensity of the (012) crystal plane to the (110) crystal plane is in the range of 1.4-2.3.

[0047] In some embodiments of the present application, the ratio of the diffraction peak intensity of the (003) crystal plane to the (012) crystal plane of the sodium cathode material 100 (i.e., I (003) / I (012)) is in the range of 2.7-6.0; for example, specifically 2.71, 2.75, 2.8, 2.9, 2.95, 3.0, 3.01, 3.02, 3.05, 3.10, 3.15, 3.20, 3.3, 3.4, 3.5, 4.0, 4.2, 4.5, 5.0, 5.5, 5.8, 5.9, 6.0, etc. In some embodiments, the ratio of the diffraction peak intensity of the (003) crystal plane to the (012) crystal plane is 2.71-5.0. In some embodiments, when the ratio of the diffraction peak intensity of the (003) crystal plane to the (012) crystal plane is 3.0-5.0, the air stability and cycle stability of the sodium cathode material 100 are both high, and the problem of decreased sodium ion transport kinetics of the material caused by excessive orientation of the (003) crystal plane is avoided. Furthermore, the ratio of the diffraction peak intensity of the (003) crystal plane to the (012) crystal plane may be 3.01-4.0.

[0048] In some embodiments of the present application, the ratio of the diffraction peak intensity of the (003) crystal plane to the (110) crystal plane of the sodium cathode material 100 (i.e., I (003) / I (110) ) is in the range of 4.0-8.0; for example, 4.01, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.05, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.2, 7.5, 7.8, 7.9, 8.0, etc. In some embodiments, the ratio of the diffraction peak intensity of the (003) crystal plane to the (110) crystal plane is in the range of 4.1-7.0. When this ratio is between 4.1 and 7.0, the sodium-ion cathode material 100 exhibits high air stability and cycle stability, while avoiding the problem of decreased sodium ion transport kinetics in the material due to excessive orientation of the (003) crystal plane. In other embodiments, the ratio of the diffraction peak intensity of the (003) crystal plane to the (110) crystal plane is in the range of 4.2 to 6.5.

[0049] It should be noted that, when the sodium-based cathode material 100 only includes a sodium-based transition metal oxide, the XRD spectrum characteristics of the sodium-based transition metal oxide are the XRD spectrum characteristics of the sodium-based transition metal oxide.

[0050] In the embodiment of the present application, the primary particles of the sodium-based transition metal oxide are hexagonal-like flaky particles, and the ratio of the length to the thickness of the primary particles is in the range of 1.5-8.0. Among them, the morphology of the primary particles is hexagonal-like flaky, which is more conducive to exposing the inactive (003) crystal plane, so that the XRD spectrum of the above-mentioned sodium positive electrode material can better meet the above requirements. The crystal planes corresponding to the upper and lower planes of the hexagonal-like flaky particles are inactive (003) crystal planes, and the crystal planes corresponding to the side surfaces of the hexagonal-like particles include at least one of the (012) crystal plane and the (110) crystal plane. In addition, the ratio of the length to the thickness of the primary particles is controlled in the range of 1.5-8.0, which not only helps to ensure that the sodium-based transition metal oxide is a crystalline material with a preferential orientation of the (003) crystal plane, ensuring that its air and cyclic stability are improved, but also avoids the problem of decreased sodium ion transport kinetics of the material caused by excessive orientation of the (003) crystal plane. Specifically, the ratio of the length to the thickness of the primary particles can be 2.0, 2.2, 2.5, 2.8, 3.0, 3.5, 4.0, 4.2, 4.5, 4.8, 5.0, 6.0, 7.0, 7.5, etc. In some embodiments, the ratio of the length to the thickness of the primary particles is in the range of 2.5-5.

[0051] In an embodiment of the present application, the length of the primary particles is in the range of 0.5 μm to 12 μm. The thickness of the primary particles is in the range of 0.04 μm to 6 μm. The length and thickness of the primary particles are in an appropriate range, which is conducive to ensuring that the sodium-based transition metal oxide has good structural stability and sodium ion transport performance. Specifically, the length of the primary particles is, for example, 0.8 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 11.5 μm, etc. The thickness of the primary particles is, for example, 0.05 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.8 μm, 1 μm, 1.5 μm, 2 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6.0 μm, etc. In some embodiments, the thickness of the primary particles is in the range of 0.05 μm to 3 μm.

[0052] In an embodiment of the present application, the sodium-based transition metal oxide may include single crystal particles and / or polycrystalline particles. The single crystal particles are the primary particles described above. The polycrystalline particles are secondary particles composed of a plurality of the primary particles, i.e., polycrystalline particles are a collection of a plurality of single crystal particles. In an embodiment of the present application, the morphology of the polycrystalline particles includes one or more of spherical, ellipsoidal, and flower-like shapes, but is not limited thereto.

[0053] In the embodiment of the present application, the D50 particle size of the single crystal particles is in the range of 0.5 μm-12 μm, and the D99 particle size does not exceed 30 μm.

[0054] Because single crystal particles are primary particles, the D50 particle size of the single crystal particles is similar to the length range of the primary particles mentioned above. Controlling the D50 of the single crystal particles within the above range can avoid the D50 particle size of the single crystal material being too large, which will lengthen the diffusion path of the sodium ions and deteriorate the rate performance of the battery, and avoid the D50 particle size being too small, which will cause the compaction density of the single crystal material to be low. Specifically, the D50 particle size of the single crystal particles can be 0.8μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, etc.; in some embodiments, the D50 particle size of the single crystal material is in the range of 0.5μm-5μm. Among them, controlling the D99 of the single crystal particles within the above range can ensure that the single crystal particles have good dispersibility and avoid excessive agglomeration of primary particles. In some embodiments, the D99 particle size of the single crystal material may be less than or equal to 25 μm, less than or equal to 20 μm, or even less than or equal to 15 μm.

[0055] It should be noted that the D50 and D99 diameters of the single-crystal particles can be measured and statistically obtained based on electron micrographs of multiple single-crystal particles. Furthermore, the length of the single-crystal particle is measured, i.e., its maximum lateral dimension, specifically the distance between the two largest points on its cross-section. For flake particles with a hexagonal morphology, the maximum lateral dimension refers to the diameter of the circumscribed circle of the hexagon.

[0056] In the embodiment of the present application, the D50 particle size of the polycrystalline particles is in the range of 1μm-15μm, and the D99 particle size does not exceed 30μm. Among them, controlling the D50 of the polycrystalline particles within the above range can avoid the primary particles constituting the polycrystalline material from being too small, thereby increasing the specific area of ​​the secondary particles, reducing the structural stability, and increasing the probability of interfacial side reactions of the sodium-based transition metal oxide; and avoid excessively increasing the diffusion path of sodium ions in the polycrystalline particles, thereby deteriorating the rate performance of the polycrystalline material. Among them, controlling the D99 of the polycrystalline particles within the above range can avoid the presence of polycrystalline particles with too large a particle size, thereby significantly deteriorating the rate performance of the sodium-based transition metal oxide. Specifically, the D50 particle size of the polycrystalline particles may be 1.2 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 14.5 μm, etc. The D99 particle size of the polycrystalline particles may be less than or equal to 25 μm, less than or equal to 20 μm, or even less than or equal to 15 μm, etc.

[0057] In the embodiment of the present application, the compaction density of the sodium cathode material at 200 MPa is 2.6-3.5 g / cm 3 , with a specific surface area of ​​0.2-1.5m 2 / g. Based on the control of the XRD characteristics, morphology and size of the primary particles of the aforementioned sodium-based transition metal oxides in the embodiments of the present application, the compaction density and specific surface area of ​​the sodium-based positive electrode material can reach this condition, which is conducive to ensuring that the sodium battery prepared by the material has both good cycle stability and high energy density. Specifically, the compaction density of the sodium-based positive electrode material at 200MPa can be 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, or 3.45 g / cm 3 The specific surface area of ​​the sodium cathode material can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1.0, 1.1, 1.2, 1.3 or 1.4 m 2 / g, etc. In some embodiments, the specific surface area is 0.3-1.0m 2 / g.

[0058] The above compacted density can be measured by a powder compaction density meter on a powdered sodium cathode material under a pressure of 200 MPa, and the compacted density is read from the device. The above specific surface area can be obtained by testing the powdered sodium cathode material based on the BET specific surface area test method. In addition, it should be noted that when the sodium cathode material also has a coating layer as described below in this application, its compacted density and specific surface area can also meet the above ranges.

[0059] In this application, sodium-based transition metal oxide refers to an oxide containing sodium and transition metal elements. The chemical formula of the sodium-based transition metal oxide may include Na x A y M z O w , wherein A represents a variable valence transition metal element, M represents an element that can be doped / substituted for element A, and M can be selected from one or more of Li (lithium), Al (aluminum), Mg (magnesium), Ca (calcium), Sr (strontium), K (potassium), Sn (tin), Ti (titanium), Zn (zinc), Zr (zirconium), Nb (niobium), Mo (molybdenum), B (boron), etc.; <x≤12,0<y≤12,0≤z≤12,0<w≤12。

[0060] In the embodiment of the present application, the A includes one or more of V (vanadium), Fe (iron), Cr (chromium), Mn (manganese), Co (cobalt), Ni (nickel), and Cu (copper), but is not limited thereto.

[0061] In some embodiments of the present application, the sodium-based cathode material 100 may further include a coating layer 20 coated on the surface of the sodium-based transition metal oxide 10. As shown in Figures 1B and 1C, the sodium-based cathode material 100 at this time can be said to include a sodium-based transition metal oxide 10 and a coating layer 20 coated on the sodium-based transition metal oxide 10. When the XRD characteristics of the sodium-based transition metal oxide meet the above conditions, the presence of the coating layer 20 can further improve the air stability and cycle stability of the overall sodium-based cathode material 100.

[0062] In the embodiment of the present application, the coating layer 20 can completely cover the surface of the sodium-based transition metal oxide 10, that is, cover the entire surface of the sodium-based transition metal oxide 10 (as shown in FIG1B ); or it can only cover a portion of the surface of the sodium-based transition metal oxide 10 (as shown in FIG1C ). When the outer surface of the sodium-based transition metal oxide is completely covered by the coating layer 20, it can more effectively prevent the uncoated area of ​​the layered sodium-based transition metal oxide from becoming an intrusion site for water, CO2, etc., thereby better improving the air stability of the core and the stability of the slurry during the slurrying process; during the cycle of the sodium battery, the coating layer with a high degree of coverage can also effectively suppress the side reactions between the core and the electrolyte, ensuring the cycle stability and capacity of the core.

[0063] In the embodiment of the present application, the material of the coating layer 20 may include one or more of oxides, fluorides, and phosphates, but is not limited thereto. For example, the coating layer material as an oxide may be copper oxide (CuO), aluminum oxide (Al2O3), magnesium oxide (MgO), titanium oxide (TiO2), manganese-rich sodium oxide (general formula: Na j MnO2, 0<j≤0.6) etc.; the coating layer material as fluoride can specifically be one or more of sodium fluoride (NaF), aluminum fluoride (AlF3), magnesium fluoride (MgF2), copper fluoride (CuF2) etc.; the coating layer material as phosphate can be a polyanionic sodium-containing compound containing phosphate, for example, specifically one or more of NaTi2(PO4)3, NaV2(PO4)2F3, Na3V2(PO4)2F3, Na2CoPO4F, Na2NiPO4F etc.

[0064] In the embodiment of the present application, the thickness of the coating layer 20 is 0.1nm-100nm. The coating layer 20 of suitable thickness can effectively inhibit the reaction of the core layered sodium-based transition metal oxide with water and CO2 in humid air, improve the stability of the core material in the air, and help to inhibit its interface side reactions, improve the cycle stability, and will not affect the specific capacity of the core material or reduce the energy density of the sodium battery due to the excessive thickness of the coating layer 20. Specifically, the thickness of the coating layer 20 can be 0.2nm, 0.5nm, 1nm, 2nm, 5nm, 10nm, 15nm, 20nm, 30nm, 40nm, 50nm, 60nm, 80nm, 90nm, 95nm, etc. In some embodiments, the thickness of the coating layer 20 can be 1nm-50nm, and further can be 5nm-20nm.

[0065] The present application also provides a method for preparing the above-mentioned sodium cathode material. Specifically, the method for preparing the sodium cathode material comprises the following steps:

[0066] (1) mixing a sodium source with other element sources in the sodium-based transition metal oxide to be prepared to obtain a mixed dry material;

[0067] (2) sintering the mixed dry material multiple times to obtain a sodium-based transition metal oxide-containing sodium cathode material; wherein, in the multiple sintering, the holding temperature of each sintering is within the range of 800-1200°C, and the sintered material obtained by each sintering is crushed before the next sintering, so that the X-ray diffraction spectrum of the sodium cathode material satisfies: the ratio of the diffraction peak intensity of the (003) crystal plane to the (012) crystal plane is greater than or equal to 2.7, and / or the ratio of the diffraction peak intensity of the (003) crystal plane to the (110) crystal plane is greater than or equal to 4.0.

[0068] In step (1), the sodium source can be one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium oxide, and sodium peroxide.

[0069] In step (1), the other element sources in the sodium-based transition metal oxide to be prepared can be provided according to the chemical formula of the sodium-based transition metal oxide to be prepared. In the embodiment of the present application, the other element sources include a variable valence transition metal element source (i.e., A source, A represents a variable valence transition metal element). Wherein, the A source can be a hydroxide, oxide, salt (such as carbonate, oxalate, acetate, nitrate, sulfate, etc.) of the A element. The A element is selected from one or more of V (vanadium), Fe (iron), Cr (chromium), Mn (manganese), Co (cobalt), Ni (nickel), and Cu (copper).

[0070] In some embodiments of the present application, the other element sources may further include an M source. Similarly, the M source may be a hydroxide, oxide, or salt (such as a carbonate, nitrate, oxalate, acetate, or sulfate) of the M element. The A element is selected from one or more of V (vanadium), Fe (iron), Cr (chromium), Mn (manganese), Co (cobalt), Ni (nickel), and Cu (copper).

[0071] In step (1), the mixing method may be one or more of ball milling, sand milling, mechanical stirring, mechanical fusion, etc.

[0072] The above step (2) can be said to be: the mixed dry material is sintered N times (N≥2), wherein the holding temperature of the i-th sintering is in the range of 800-1200°C, and the sintered material obtained by the i-th sintering is crushed and then sintered for the i+1th time, where i is any value from 1 to N-1.

[0073] Compared to calcining a mixed dry material of various element sources used to prepare the sodium-based transition metal oxide once, the present application adopts the above-mentioned multiple (greater than or equal to two) sintering process, which can better promote the preferred orientation of the (003) crystal plane of the sodium-based transition metal oxide. In addition, keeping the holding temperature of each sintering within the range of 800-1200°C helps to ensure that the sodium-based transition metal oxide has a high degree of crystallinity. The sintered material obtained after each sintering is crushed to avoid particle aggregation, ensuring that the next sintering can further improve the crystallinity and the preferred orientation of the (003) crystal plane, and ensuring that the primary particle morphology is hexagonal and flake-like.

[0074] In the embodiment of the present application, the crushing process can be specifically carried out in a wall-breaking machine or a jet mill, etc. The crushing process can be carried out after the sintered material obtained from each sintering is cooled to room temperature.

[0075] Specifically, the holding temperature of each sintering can be 800°C, 820°C, 850°C, 870°C, 900°C, 920°C, 950°C, 980°C, 1000°C, 1050°C, 1100°C, 1200°C, etc. Each holding temperature can be the same or different. Among them, the heating rate during each sintering process can be 1-10°C / min, and further can be 1-5°C / min, for example, 2°C / min, 3°C / min, 4°C / min, etc. A lower heating rate can avoid the heating rate being too fast and causing greater stress on the interface between the phases. The holding time of each sintering can be 6h-48h, and further can be 6h-20h, for example, specifically 7h, 8h, 10h, 12h, 15h, 18h, etc. In addition, the atmosphere of each sintering can be an oxygen-containing atmosphere, such as an air atmosphere or an oxygen atmosphere. An oxygen-containing atmosphere is more conducive to the decomposition of various element sources in the form of hydroxides and carbonates, the recombination of various elements, etc.

[0076] In some embodiments of the present application, the multiple sintering steps are specifically two sintering steps (i.e., N = 2), and the holding temperature of the second sintering step is higher than the holding temperature of the first sintering step. The two sintering steps, performed at increasing sintering temperatures, can more effectively repair crystal defects in the sodium-based transition metal oxide, better promote the preferred orientation of the (003) crystal plane, and enhance crystallization integrity.

[0077] In some embodiments of the present application, the mixed dry material in step (1) may further contain additives; the additives may include nano-scale oxides, hydroxides or carbonates containing at least one of Mg, B, Mo, Y, Te, In, Ga, W and Ba. The positive-valent elements contained in these additives are different from the positive-valent elements of the other element sources in step (1). The introduction of these additives and the combination of the above-mentioned multiple sintering can reduce the surface energy of the (003) crystal plane of the final sodium cathode material, promote the preferential orientation of the (003) crystal plane, suppress the intensity of the diffraction peaks of the (012) and (110) crystal planes from being too strong, and increase the ratio of the diffraction peak intensity of the (003) crystal plane to the (110) crystal plane / (012) crystal plane.

[0078] In the embodiment of the present application, the mass proportion of the additive in the mixed dry material is 0.1wt%-5.0wt%. This ensures that the (003) crystal plane of the sodium cathode material is appropriately oriented, thereby avoiding the situation where too little additive is used and the (003) crystal plane cannot be effectively promoted for preferential orientation, and avoiding the situation where too much additive is used and the resulting sodium cathode material has excessive impurities, thereby reducing the specific capacity of the resulting battery.

[0079] The preparation method of the above-mentioned sodium cathode material provided in the embodiment of the present application has a simple process, is easy to operate, is suitable for large-scale production, and can produce a sodium cathode material having the above-mentioned XRD spectrum characteristics of the present application.

[0080] It should be noted that the above steps (1) and (2) are mainly used to prepare a sodium-based transition metal oxide that meets the XRD spectrum characteristics required by this application. When the desired sodium cathode material also includes a coating layer, the coating layer can be constructed after the above step (2), and / or the coating layer raw material can be introduced into step (1) to form the coating layer through sintering.

[0081] In some embodiments of the present application, a coating layer is constructed after the above-mentioned step (2). The coating layer can be constructed by mixing a sodium-based transition metal oxide with a coating layer material or a raw material for a synthetic coating layer material. Among them, the coating layer is constructed in a manner including, but not limited to, one or more of a solid phase method, a liquid phase method, and other methods. The solid phase method can be a mechanical stirring method, a solid phase high-energy ball milling method, a mechanical fusion method, etc., and the liquid phase method can be a sol-gel method, a coprecipitation coating method, a hydrothermal / solvothermal coating method, a liquid phase high-energy ball milling method, a coating method, and a spray drying coating method. Generally, when a liquid phase method is adopted, after the mixing, a heat treatment is required to promote the formation of the coating layer material, enhance the bonding force between it and the sodium-based transition metal oxide, etc. Other methods can be one or more of a chemical vapor deposition method, a physical vapor deposition method (such as a magnetron sputtering method, a plasma sputtering method, an evaporation method), etc.

[0082] The embodiment of the present application also provides a positive electrode plate for a sodium battery, which includes the sodium battery positive electrode material described above in the embodiment of the present application.

[0083] Referring to Figure 2, the positive electrode sheet 200 provided in an embodiment of the present application includes a positive electrode current collector 201 and a positive electrode material layer 202 disposed on the positive electrode current collector 201. The positive electrode material layer 202 includes the sodium-ion positive electrode material 100 described above in the embodiment of the present application. The positive electrode material layer 202 may further include a binder, a conductive agent, etc. In some embodiments, the positive electrode material layer 202 may further include other positive electrode active materials different from the sodium-ion positive electrode material. The positive electrode material layer 202 is disposed on one surface or on two opposite surfaces of the positive electrode current collector 201.

[0084] Among them, positive electrode current collector, conductive agent, binder are conventional choices in the field of sodium batteries. For example, the positive electrode current collector can be aluminum foil, carbon-coated aluminum foil, aluminized polymer film, etc. The binder can specifically include but is not limited to polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyacrylamide (PAM), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) and sodium alginate, etc. One or more. The conductive agent can specifically include but is not limited to one or more of acetylene black, Ketjen black, Super P conductive carbon black, graphite, graphene, carbon nanotubes, carbon fiber, amorphous carbon, etc.

[0085] An embodiment of the present application also provides a sodium secondary battery, which includes the above-mentioned positive electrode plate.

[0086] Referring to Figure 3 , a sodium secondary battery 300 provided in one embodiment of the present application includes a positive electrode 301, a negative electrode 302, a separator 303, an electrolyte 304, and corresponding connecting components and circuits. Separator 303 is disposed between positive electrode 301 and negative electrode 302, and positive electrode 301, negative electrode 302, and separator 303 are immersed in electrolyte 304. Positive electrode 301 includes the positive electrode sheet 200 described above in the embodiment of the present application, which also includes the sodium positive electrode material 100 described above in the embodiment of the present application.

[0087] During the charging process of the sodium secondary battery 300, under the action of the external circuit, sodium ions (Na + ) escape from the positive electrode 301, pass through the electrolyte 304 and separator 303, and migrate to the negative electrode 302. Simultaneously, electrons flow from the positive electrode to the negative electrode via an external circuit, storing electrical energy. The discharge process is the opposite of charging. Sodium ions escape from the negative electrode 302 and return to the positive electrode 301 via the electrolyte 304 and separator 303. Simultaneously, electrons migrate from the negative electrode to the positive electrode via an external circuit, releasing electrical energy. Because the positive electrode of this sodium secondary battery 300 uses the aforementioned sodium cathode material 100, the battery exhibits excellent cycle stability and rate performance.

[0088] The present invention also provides an electrical device, which includes the sodium secondary battery provided in the embodiment of the present invention. The electrical device may include electronic equipment, mobile devices, etc.

[0089] The electronic devices may include various consumer electronic products, such as mobile phones, tablet computers, laptop computers, personal digital assistants (PDAs), portable computers, mobile power supplies, wearable devices (such as smart bracelets, smart watches, smart helmets, smart glasses, etc.), home entertainment devices (such as televisions, DVD players, video recorders, camcorders, radios, tape recorders, stereo systems, record players, CD players, etc.), home office equipment (such as scanners, microphones, etc.), home electronic health care equipment, vehicle-mounted equipment, etc. The electronic devices may also be wireless local loop (WLL) stations, devices with wireless or wired communication functions (such as communication conversion equipment, lightning arresters, antennas, gateways, remote controls, radars, intercoms, switches, routers, etc.), other processing devices connected to wireless modems, etc., and the embodiments of the present application are not limited to this.

[0090] In some embodiments, referring to FIG4 , the electronic device 400 provided in the embodiment of the present application includes a housing 401 and a battery 402 housed in the housing 401, the battery 402 supplies power to the electronic device 400, and the battery 402 includes the sodium secondary battery 300 described above in the embodiment of the present application. The housing 401 may include a front cover assembled on the front side of the terminal and a rear shell assembled on the rear side, and the battery 402 may be fixed on the inside of the rear shell. In some embodiments, the housing 401 may include a front cover assembled on the front side of the terminal and a rear shell assembled on the rear side, and the battery 402 may be fixed on the inside of the rear shell. In addition, a circuit board (not shown in FIG4 ) may also be housed in the housing 401. The electronic device 400 shown in FIG4 may specifically be a mobile phone, etc.

[0091] The mobile device may be any movable device used for loading, transportation, assembly, disassembly, security, etc., such as various types of vehicles, including but not limited to electric cars, electric trucks, electric motorcycles, electric bicycles, etc. Sodium secondary batteries can provide electrical energy to drive the mobile device to enable it to move.

[0092] Referring to Figure 5 , another embodiment of the present application provides an energy storage system 500. The energy storage system 500 includes a battery pack 501 and a battery management system 502 electrically connected to the battery pack 501. The battery pack 501 includes multiple sodium secondary batteries 300 provided in the embodiments of the present application described above. The battery pack 501 can be a module formed by connecting multiple sodium secondary batteries 300 in series, in parallel, or in a combination thereof. The battery management system 502 can be used to monitor the status of each sodium secondary battery 300 in the battery pack 501 and control its charge / discharge status.

[0093] The embodiments of the present application are further described below with reference to a number of embodiments.

[0094] Example 1

[0095] A preparation method of a sodium cathode material, comprising:

[0096] (1) According to the layered oxide material NaNi to be prepared 0.33 Fe 0.33 Mn 0.33 The chemical formula of O2, accurately weigh the sodium source Na2CO3, Ni 0.33 Fe 0.33 Mn 0.33 (OH)2, and add them into a wall breaking machine for mixing to obtain a mixed dry material;

[0097] (2) The mixed dry material is taken out and transferred to a sagger, and then placed in a muffle furnace for a sintering. The parameters of the first sintering include: heating to a sintering holding temperature of 800°C at a heating rate of 3°C / min, keeping warm for 10 hours, and naturally cooling to room temperature. The obtained first-fired material is crushed in a wall breaker and then sintered for a second time. The process setting is: heating to a sintering holding temperature of 1000°C at a heating rate of 5°C / min, keeping warm for 15 hours, and then naturally cooling to room temperature. The obtained second-fired material is placed in a grinder for crushing and refining, and passed through a 200-mesh sieve to obtain a sodium positive electrode material, namely NaNi 0.33 Fe 0.33 Mn 0.33 O2.

[0098] Preparation of sodium secondary batteries:

[0099] a) Preparation of positive electrode sheet: The sodium battery positive electrode material prepared in Example 1 was mixed with the conductive agent Super P and the binder PVDF in a mass ratio of 80:10:10, dissolved in a solvent N-methylpyrrolidone (NMP), and stirred evenly to obtain a positive electrode slurry; the positive electrode slurry was evenly coated on a carbon-coated aluminum foil with a doctor blade, and after drying, rolling, and slicing, a positive electrode sheet was obtained.

[0100] b) Battery Assembly: Using the aforementioned cathode sheet as the positive electrode and the sodium metal sheet as the counter electrode, a 1M solution of NaClO₄ dissolved in a mixture of propylene carbonate (PC) and fluoroethylene carbonate (FEC) (5% by volume) was used as the electrolyte. Coin-type cells were assembled in a nitrogen-filled glove box. Electrochemical performance testing of these cells was subsequently performed.

[0101] The XRD spectrum of the sodium cathode material prepared in Example 1 is summarized in Figure 6. The (003), (012), and (110) crystal planes of the material are marked in the figure. Based on Figure 6, it can be calculated that the I (003) / I (012) =3.34>2.7, I(003) / I (110) =6.35>4.0, in addition, I (012) / I (110) =1.90, these results indicate that the material has good (003) crystal plane preferred orientation.

[0102] Figure 7 is an electron microscope photograph of the sodium cathode material of Example 1, wherein the left image in Figure 7 is a scanning electron microscope (SEM) photograph, the middle image is a transmission electron microscope (TEM) of the red dotted box area in the left image, and the right image is a high-resolution real-time Fourier map (FFT) of the red dotted box area in the middle image. It can be seen from the left image in Figure 7 that the primary particles of the sodium cathode material are hexagonal flaky particles. TEM characterization shows that the crystal plane corresponding to the most exposed plane (i.e., the upper and lower planes of the hexagonal shape) is the (003) crystal plane, which further proves that the material has a good (003) crystal plane preferred orientation. In addition, the length to thickness ratio of the above-mentioned primary particles is about 8.0, wherein the average length is 6μm and the average thickness is 0.75μm. In addition, the sodium cathode material is a single crystal particle with a D50 particle size of 7.2μm and a D99 particle size of 20.5μm.

[0103] Example 2

[0104] A sodium cathode material comprising a layered oxide material NaNi 0.33 Fe 0.33 Mn 0.33 The preparation process of O2 is basically the same as that of Example 1, except that the holding temperature of the second sintering is 900°C.

[0105] The XRD spectrum of the sodium cathode material prepared in Example 2 is shown in FIG8. Based on FIG8, it can be seen that: (003) / I (012) =3.17>2.7, I (003) / I (110) =4.7>4.0, indicating that the material has good (003) crystal plane preferred orientation. In addition, I (012) / I (110) =1.48.

[0106] Figure 9 is a scanning electron microscope (SEM) photograph of the sodium cathode material of Example 2. As can be seen from Figure 9, the length-to-thickness ratio of the primary particles of the sodium cathode material is approximately 3.88, wherein the average length of the primary particles is 3.3 μm and the average thickness is 0.85 μm. In addition, the sodium cathode material is a single crystal particle with a D50 particle size of 3.7 μm and a D99 particle size of 15.2 μm.

[0107] Example 3

[0108] A sodium cathode material comprising a layered oxide material NaNi 0.33 Fe 0.33 Mn 0.33 O2, its preparation process is basically the same as that of Example 1, except that the holding temperature of the second sintering is 900°C and the holding time is 12 hours.

[0109] Based on the XRD spectrum of the sodium cathode material obtained in Example 3, it can be seen that: (003) / I (012) =3.05>2.7, I (003) / I (110) =5.9>4.0, indicating that the material has good (003) crystal plane preferred orientation. In addition, I (012) / I (110) =1.93.

[0110] Example 4

[0111] A preparation method for a sodium positive electrode material is different from that of Example 1 in that 1000 ppm of a B2O3 additive is also added to the mixed material in step (1).

[0112] Based on the XRD spectrum of the sodium cathode material obtained in Example 4, it can be seen that: (003) / I (012) =3.9>2.7, I (003) / I (110) =6.3>4.0, indicating that the material has good (003) crystal plane preferred orientation. In addition, I (012) / I (110) =1.615.

[0113] Example 5

[0114] A preparation method of a sodium positive electrode material, which differs from Example 1 in that: after step (2), it also includes constructing a coating layer. Specifically, it includes: taking the layered oxide material NaNi obtained after secondary sintering 0.33 Fe 0.33 Mn 0.33 O2, mixed with 0.65g of magnesium oxide (MgO) powder, sintered in a tube furnace after ball milling, and naturally cooled to room temperature to obtain NaNi with MgO coated on the surface. 0.33 Fe 0.33 Mn 0.33 O2 material.

[0115] Based on the XRD spectrum of the sodium cathode material obtained in Example 5, it can be seen that (003) / I (012) =3.08>2.7, I (003) / I (110)=5.3>4.0, indicating that the material has good (003) crystal plane preferred orientation. In addition, I (012) / I (110) =1.72.

[0116] Example 6

[0117] A sodium cathode material, a layered oxide material NaNi 0.33 Fe 0.33 Mn 0.33 O2, from the XRD spectrum of the sodium positive electrode material, we can know that: (003) / I (012) =3.0>2.7, I (003) / I (110) =3.8<4.0, indicating that the material has a good (003) crystal plane preferred orientation. In addition, I (012) / I (110) =1.26.

[0118] Example 7

[0119] A sodium cathode material comprising a layered oxide material NaNi 0.33 Fe 0.33 Mn 0.33 The preparation process of O2 is basically the same as that of Example 1, except that the temperature of the second sintering is 1200°C.

[0120] Based on the XRD spectrum of the sodium cathode material obtained in Example 7, it can be seen that: (003) / I (012) =3.9>2.7, I (003) / I (110) =8.1>8.0, indicating that the material has excellent (003) crystal plane preferred orientation. In addition, I (012) / I (110) =2.07.

[0121] In order to highlight the beneficial effects of the embodiments of the present application, the following comparative examples are provided.

[0122] Comparative Example 1

[0123] A sodium cathode material comprising a layered oxide material NaNi 0.33 Fe 0.33 Mn 0.33 O2, the preparation process thereof is different from that of Example 1 in that: only one sintering is performed, and the sintering process comprises: heating the temperature to a sintering holding temperature of 800°C at a heating rate of 3°C / min, holding the temperature for 10 hours, and then naturally cooling to room temperature. The obtained fired material is crushed by a pulverizer and passed through a 200-mesh sieve to obtain a sodium positive electrode material.

[0124] The XRD spectrum of the sodium positive electrode material prepared in Comparative Example 1 is also summarized in Figure 6. Based on Figure 6, it can be calculated that the I of the sodium positive electrode material in Comparative Example 1 is (003) / I (012) =2.61<2.7, I (003) / I (110) =3.89<4.0, which indicates that the material does not have a good (003) crystal plane preferred orientation.

[0125] To measure the air stability of each sodium-ion battery cathode material in this application, the sodium-ion battery cathode materials of other examples and comparative examples were prepared into cathode slurries according to the method described in Example 1. Each cathode slurry was placed in an environment with a relative humidity of 10%, and the time required for the slurry to transition from a flowing state to a non-flowing state was measured, that is, the gelation time of the slurry was recorded. The results are summarized in Table 1 below.

[0126] To measure the cycling stability of the sodium-ion battery cathode materials used in the examples of this application, the sodium-ion battery cathode materials from the other examples and comparative examples were prepared into cathode sheets according to the method described in Example 1 and assembled into sodium button cells. The cells were tested for their initial charge capacity at 0.1C and their capacity retention after 30 cycles at 0.5C, where 1C = 150 mA / g and the voltage window is 2-4.1V.

[0127] Table 1

[0128] From the comparison of Example 1 and Comparative Example 1 in Table 1, it can be seen that compared to Comparative Example 1, whose XRD spectrum characteristics do not meet the definition of this application, the gelation time of the sodium-ion cathode material provided in Example 1 of the present application after being placed in a humid environment is significantly longer, indicating that its air stability is significantly improved and the gelation time after being placed in a humid environment is significantly longer. At the same time, the sodium button battery made using the sodium-ion cathode material of Example 1 of the present application also has a higher capacity retention rate measured under the same conditions than that of Comparative Example 1, which can be increased to 94.1%, and the battery's first charge capacity does not decrease.

[0129] Similarly, the sodium cathode materials provided in other embodiments of the present application can also take into account good air stability and cycle stability. (003) / I (012) >2.7 and I (003) / I (110) The air stability and cycle stability of the sodium cathode material of Example 6 with a value greater than 4.0 are slightly worse than those of the other examples, but still better than those of Comparative Example 1. (003) The crystal plane orientation is higher (I (003) / I (110)>8.0) has higher air stability, but its kinetic performance (reflected by the first charge capacity) is lower than that of Examples 1-3, but the decline is not obvious, and the first charge capacity of the battery is still within the high range recognized by the industry.

[0130] The above merely represents several exemplary embodiments of the present application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art would be able to make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

[0131] It should be understood that the first, second, and various numerical references used herein are merely distinctions for ease of description and are not intended to limit the scope of this application. In this application, "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A alone, A and B simultaneously, and B alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0132] In this application, "at least one" means one or more, and "more than one" means greater than or equal to two. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

Claims

1. A sodium positive electrode material, characterized in that: The sodium-based positive electrode material comprises a sodium-based transition metal oxide, and the X-ray diffraction spectrum of the sodium-based positive electrode material satisfies: The ratio of the diffraction peak intensity of the (003) crystal plane to the (012) crystal plane is greater than or equal to 2.7, and / or The ratio of the diffraction peak intensity of the (003) crystal plane to the (110) crystal plane is greater than or equal to 4.

0.

2. The sodium positive electrode material according to claim 1, characterized in that The ratio of the diffraction peak intensity of the (012) crystal plane to the (110) crystal plane is in the range of 1.0-3.

0.

3. The sodium positive electrode material according to claim 1 or 2, characterized in that The ratio of the diffraction peak intensity of the (003) crystal plane to the (012) crystal plane is in the range of 2.7-6.

0.

4. The sodium positive electrode material according to claim 3, characterized in that The ratio of the diffraction peak intensity of the (003) crystal plane to the (012) crystal plane is in the range of 3.0-5.

0.

5. The sodium positive electrode material according to claim 4, characterized in that The ratio of the diffraction peak intensity of the (003) crystal plane to the (012) crystal plane is in the range of 3.01-4.

0.

6. The sodium positive electrode material according to any one of claims 1 to 5, characterized in that The ratio of the diffraction peak intensity of the (003) crystal plane to the (110) crystal plane is in the range of 4.0-8.

0.

7. The sodium positive electrode material according to claim 6, characterized in that The ratio of the diffraction peak intensity of the (003) crystal plane to the (110) crystal plane is in the range of 4.1-7.

0.

8. The sodium positive electrode material according to any one of claims 1 to 7, characterized in that: The sodium-based transition metal oxide includes single crystal particles and / or polycrystalline particles; wherein the single crystal particles are primary particles, and the polycrystalline particles are secondary particles composed of a plurality of the primary particles.

9. The sodium positive electrode material according to claim 8, characterized in that The primary particles are hexagonal flake particles, and the ratio of the length to the thickness of the primary particles is in the range of 1.5-8.

0.

10. The sodium positive electrode material according to claim 9, characterized in that The thickness of the primary particles is in the range of 0.04 μm to 6 μm.

11. The sodium positive electrode material according to any one of claims 8 to 10, characterized in that: The D50 particle size of the single crystal particles is in the range of 0.5 μm-12 μm, and the D99 particle size is no more than 30 μm.

12. The sodium positive electrode material according to any one of claims 8 to 10, characterized in that: The morphology of the polycrystalline particles includes one or more of spherical, ellipsoidal, and flower-like shapes.

13. The sodium positive electrode material according to claim 12, characterized in that: The D50 particle size of the polycrystalline particles is in the range of 1 μm-15 μm, and the D99 particle size is no more than 30 μm.

14. The sodium positive electrode material according to any one of claims 1 to 13, characterized in that: The chemical formula of the sodium-based transition metal oxide includes Na x A y M z O w , wherein A is a variable valence transition metal element, and M is selected from one or more of Li, Al, Mg, Ca, Sr, K, Sn, Ti, Zn, Zr, Nb, Mo, and B; <x≤12,0<y≤12,0≤z≤12,0<w≤12。 15. The sodium positive electrode material according to claim 14, characterized in that The A includes one or more of V, Fe, Cr, Mn, Co, Ni, and Cu.

16. The sodium positive electrode material according to any one of claims 1 to 14, characterized in that: The sodium positive electrode material also includes a coating layer coated on the surface of the sodium-based transition metal oxide; wherein the material of the coating layer includes one or more of oxides, fluorides, and phosphates.

17. The sodium positive electrode material according to claim 16, characterized in that The coating layer has a thickness of 0.1 nm to 100 nm.

18. The sodium positive electrode material according to claim 16 or 17, characterized in that: The coating layer completely covers the surface of the sodium-based transition metal oxide.

19. The sodium positive electrode material according to any one of claims 1 to 18, characterized in that: The compaction density of the sodium positive electrode material at 200 MPa is 2.6-3.5 g / cm 3 , with a specific surface area of ​​0.2-1.5m 2 / g.

20. A positive electrode sheet, characterized in that: The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode active material layer includes the sodium battery positive electrode material according to any one of claims 1 to 19.

21. A sodium secondary battery, characterized in that: The sodium secondary battery comprises the positive electrode sheet and the negative electrode sheet as claimed in claim 20.

22. An electrical equipment, characterized in that: The electrical equipment includes the sodium secondary battery as claimed in claim 21.

23. The electrical equipment according to claim 22, characterized in that: The power-consuming device includes one or more of an electronic device and a mobile device.

24. The electrical equipment according to claim 23, characterized in that: The electronic device includes a housing and the sodium secondary battery accommodated in the housing, and the sodium secondary battery is used to power the electronic device.

25. An energy storage system, characterized in that: The energy storage system includes a battery pack and a battery management system electrically connected to the battery pack, wherein the battery pack includes a plurality of the sodium secondary batteries as claimed in claim 21.

26. A method for preparing a sodium positive electrode material, characterized in that: The following steps are involved: mixing a sodium source with other element sources in the sodium-based transition metal oxide to be prepared to obtain a mixed dry material; The mixed dry material is sintered multiple times to obtain a sodium-based transition metal oxide-containing sodium-based positive electrode material; wherein, in the multiple sinterings, the insulation temperature of each sintering is within the range of 800-1200° C., and the sintered material obtained by each sintering is crushed before the next sintering, so that the X-ray diffraction spectrum of the sodium-based positive electrode material satisfies: the ratio of the diffraction peak intensity of the (003) crystal plane to the (012) crystal plane is greater than or equal to 2.7, and / or the ratio of the diffraction peak intensity of the (003) crystal plane to the (110) crystal plane is greater than or equal to 4.0.

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