A sodium-intercalating metal compound and a sodium-ion battery cathode material

Abstract

The present application relates to a kind of sodium-embedded metal compounds and sodium-ion battery positive electrode materials, the sodium-embedded metal compound has Na2O·Me2O3 solid solution structure, wherein, Me is at least one metal element in nickel, cobalt, manganese, aluminum, iron, Na ion enters Me2O3 Crystal and occupies the site of Me.The sodium-embedded metal compound provided by the present application realizes sodium-embedding by wet liquid phase reaction system, after further calcination, the sodium-ion positive electrode material made has more outstanding advantages in specific capacity, rate performance, first discharge efficiency, compared with conventional ball milling mixing process, very suitable for industrial application and promotion.

Description

Technical Field

[0001] This invention relates to sodium battery technology, and more particularly to a sodium-intercalated metal compound and a positive electrode material for sodium-ion batteries. Background Technology

[0002] Lithium-ion batteries have advantages such as being environmentally friendly, having high energy density, and being able to charge and discharge quickly. They are currently a key product in the energy storage industry. With the depletion of lithium resources, the price of upstream raw materials for lithium batteries is rising, and the demand for developing new energy sources is constantly growing.

[0003] Sodium batteries offer high safety, which can compensate for the shortcomings of lithium batteries. At the same time, sodium resources are abundant and sodium batteries are low in cost. Therefore, the development of sodium batteries is in line with the concept of sustainable development and market demand. The main research focus is on the research of sodium-ion battery cathode materials.

[0004] Current research on sodium-ion battery cathode materials falls into two categories: one is pure sodium-ion battery cathode materials, such as transition metal oxides, polyanionic compounds, and Prussian blue; the other is sodium-lithium doping to form composite materials. Typically, before sintering the composite material, the sodium source is mechanically mixed with other materials, and then subjected to a high-temperature environment to allow sodium to form as a dopant element along with the other materials.

[0005] For example, patent application CN 114678501 A discloses a sodium manganate composite modified layered transition metal oxide cathode material, the preparation process of which includes the following steps:

[0006] (1) Place a certain proportion of sodium oxide or sodium salt and other metal oxides in a ball mill jar, and ball mill them thoroughly. After they are mixed evenly, calcine them at high temperature to obtain layered transition metal oxides.

[0007] (2) Disperse the oxide in (1) in deionized water, add soluble manganese salt and organic complexing agent, mix thoroughly, and place it in polytetrafluoroethylene for hydrothermal reaction. After the reaction is completed, MOF-coated layered transition metal oxide precursor is obtained.

[0008] (3) The precursor obtained in (2) is ball-milled and mixed with sodium oxide. After the mixture is homogeneous, it is calcined at high temperature to obtain the product.

[0009] In step (1) of this method, sodium oxide or sodium salt is added and mixed with metal oxide by ball milling. Mixing can only be achieved at the particle level. This mixture is then calcined at high temperature to obtain a crystalline mixture with impurities, that is, sodium and other metal elements exist in their own crystals and have different metallographic structures. This material has low initial charge and discharge efficiency during charging and discharging, which limits the use of the battery. Summary of the Invention

[0010] The purpose of this invention is to overcome the problem of low initial discharge efficiency in existing sodium-ion battery materials by providing a sodium-intercalated metal compound. This compound employs a wet sodium intercalation reaction, controlling appropriate reaction conditions, including a sodium ion concentration of 5–12 mol / L, a pH value of 10–13, and a reaction temperature of 50–280°C. This allows sodium elements to be intercalated into the hydroxide lattice through a chemical reaction, resulting in more uniform sodium distribution within the material, reaching the atomic level. In contrast, conventional sodium-ion battery cathode materials are mixed using mechanical and physical methods, achieving only a particle-level mixing effect, and sodium elements cannot be dispersed at the atomic level.

[0011] Furthermore, this invention employs a wet sodium intercalation process, which involves a wet reaction in a reactor, resulting in lower energy consumption and better uniformity of sodium elements in the product. This allows for a reduction in the sintering temperature during subsequent sintering, ensuring that the sodium-ion battery cathode material exhibits better material activity under sufficient crystal strength conditions. This results in excellent first-time efficiency (first discharge efficiency) during the initial charge and discharge cycle, while also demonstrating superior advantages over conventional processes in terms of specific capacity and rate performance.

[0012] The specific plan is as follows:

[0013] A sodium-intercalated metal compound having a Na2O·Me2O3 solid solution structure, wherein Me is at least one metallic element selected from nickel, cobalt, manganese, aluminum, iron, and copper, and sodium ions are located in the crystal lattice of the metal oxide Me2O3 without altering its original structure.

[0014] Furthermore, Me is at least one metallic element selected from nickel, cobalt, manganese, iron, and copper; preferably, Me represents nickel, iron, and manganese.

[0015] Furthermore, the molar ratio of sodium to Me is (0.001-0.05):1, preferably (0.005-0.04):1, and more preferably (0.01-0.03):1.

[0016] This invention also protects a method for preparing the sodium-intercalated metal compound, comprising the following steps:

[0017] S1, add metal oxides or hydroxides, sodium-containing metal compounds, oxidants, and water to the reactor;

[0018] S2, controlling the reaction conditions of the reactor, the reaction conditions including: the concentration of sodium ions in the reactor is 5-12 mol / L, the pH value is 10-13, and the reaction temperature is 50-280℃, so that sodium ions are inserted into the metal hydroxide structure;

[0019] S3, the reactants in S2 are separated into solid and liquid components, and then dried to obtain a composite hydroxide;

[0020] S4, the composite hydroxide described in S3 is subjected to heat treatment at a temperature of 200–900°C to obtain a sodium-intercalated metal compound.

[0021] Furthermore, in S1, the metal oxide or hydroxide is an oxide or hydroxide of nickel, cobalt, manganese, aluminum, iron, or copper, or a mixed metal oxide or hydroxide of nickel, cobalt, manganese, aluminum, iron, and copper; preferably, the metal oxide or hydroxide is an oxide or hydroxide of nickel, iron, and manganese.

[0022] Optionally, the sodium-containing metal compound is at least one of sodium hydroxide, sodium acetate, sodium nitrate, sodium sulfate, and sodium bicarbonate;

[0023] Optionally, the amount of each substance added in S1 is such that the molar ratio of metal in metal oxide or hydroxide to sodium in sodium-containing metal compound to oxidant is (0.4-1.3):1:(0.5-4), preferably (0.8-1.2):1:(1.0-3.0), and more preferably 1:1:2.

[0024] The oxidant is at least one of oxygen, air, and hydrogen peroxide, preferably hydrogen peroxide, and the initial concentration of hydrogen peroxide in the reaction system is 5-20 wt%.

[0025] Furthermore, the reaction conditions described in S2 include: the concentration of sodium ions in the reactor is 7-10 mol / L, the pH value is 10-13, and the reaction temperature is 100-250℃;

[0026] Preferably, the reaction conditions further include: a reaction pressure of 0.1–50 MPa, a reaction temperature of 100–250 °C, and a reaction time of 0.5–60 h; more preferably, a reaction pressure of 2–30 MPa, a reaction temperature of 120–200 °C, and a reaction time of 10–48 h.

[0027] This invention also protects a sodium-ion battery cathode material, which is obtained by calcining a sodium-intercalated metal compound with a sodium-containing compound.

[0028] Furthermore, the sodium-containing compound is selected from at least one of sodium hydroxide, sodium acetate, sodium nitrate, sodium sulfate, and sodium bicarbonate; the calcination temperature is 500-900℃, preferably 600-900℃; the calcination time is 12-30h, preferably 15-30h; and the sintering atmosphere is air or oxygen.

[0029] Preferably, when the sodium-intercalated metal compound is mixed with the sodium-containing compound, the Na:Me molar ratio is 1.01-1.1:1, more preferably 1.05-1.1:1.

[0030] Furthermore, the sodium-ion battery cathode material has any one or more of the following items (1) to (3):

[0031] (1) The sodium-ion battery cathode material is a spherical polycrystalline material composed of primary particles, wherein the primary particles are sheet-like particles with a thickness of 300-500 nm, and the sodium-ion battery cathode material has a porous structure.

[0032] (2) The initial discharge capacity of the sodium-ion battery cathode material at 2.0-4.0V and 0.1C rate is 3-5 mAh / g higher than that of the sodium-ion battery cathode material corresponding to the non-sodium intercalation method;

[0033] (3) The sodium-ion battery cathode material has an initial discharge efficiency of greater than or equal to 98% at 2.0–4.0V and 0.1C rate.

[0034] The present invention also protects a sodium-ion battery comprising the sodium-ion battery positive electrode material.

[0035] Beneficial effects:

[0036] In this invention, by constructing suitable chemical reaction conditions, the enthalpy of the metal elements in the reaction system is changed, thereby allowing sodium to enter the sites of other metal elements. Then, with the help of thermal conditions, a sodium solid solution structure is finally formed. In the Na2O·Me2O3 solid solution structure, the metallographic structure of the material is uniform, and sodium replaces the sites of Me. In the XRD pattern, there are no crystal diffraction peaks of sodium oxide, but rather crystal diffraction peaks of Me2O3, that is, atomic-level mixing is achieved.

[0037] Furthermore, the present invention uses a wet sodium intercalation method to carry out the sodium reaction in a wet reaction vessel, which results in lower energy consumption, better uniformity of sodium elements in the product, lower sintering temperature during sintering, and lower production costs.

[0038] Furthermore, since the sodium-intercalated metal compound is calcined at a low temperature in this invention, the resulting sodium-ion cathode material has high crystal strength. Higher crystal strength of the cathode material indicates better development of the material's crystal structure, which is conducive to the diffusion of sodium ions in the crystal structure, resulting in better specific capacity, rate performance, and first discharge efficiency of the battery material.

[0039] In summary, the sodium-intercalated metal compound provided by this invention achieves sodium intercalation through a wet liquid-phase reaction system. After further calcination, the resulting sodium-ion cathode material exhibits superior advantages in specific capacity, rate performance, and initial discharge efficiency compared to conventional ball milling mixing processes, making it highly suitable for industrial application and promotion. Attached Figure Description

[0040] To more clearly illustrate the technical solution of the present invention, the accompanying drawings will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0041] Figure 1 This is a SEM image of the sodium ion cathode material provided in Embodiment 1 of the present invention;

[0042] Figure 2 This is a battery first charge and discharge curve provided in Embodiment 1 of the present invention. Detailed Implementation

[0043] Preferred embodiments of the present invention will now be described in more detail. While preferred embodiments of the present invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products. In the following embodiments, unless otherwise specified, "%" refers to weight percentage.

[0044] The battery manufacturing conditions are as follows:

[0045] Sodium-ion cathode material, conductive carbon black, and polyvinylidene fluoride (PVDF) were weighed separately at a mass ratio of 8:1:1. Under an inert atmosphere, an appropriate amount of NMP solvent was added, and the mixture was thoroughly ground to prepare a cathode slurry. The slurry was then uniformly coated onto a 16μm thick aluminum foil current collector. After drying under vacuum at 120℃ for 12 hours, the slurry was cut into sheets to obtain cathode sheets with a diameter of 19mm. Finally, in an argon-filled glove box, a metallic sodium sheet was used as the anode, and the cathode sheet, Celgard 2700 separator, and electrolyte (1mol / L NaPF6 + EC:DEC (1:1) + 5% FEC) were assembled into a CR2025 coin cell sodium-ion battery.

[0046] The following testing methods are included:

[0047] First charge / discharge test: The charge / discharge test voltage range is 2.0–4.0V, and the charge / discharge current is 0.1C (1C = 120mAh / g).

[0048] Example 1

[0049] Nickel hydroxide, iron hydroxide, and manganese hydroxide were prepared separately according to a molar ratio of nickel:iron:manganese = 1:1:1, forming a mixed metal hydroxide. The mixed metal hydroxide, sodium hydroxide, aluminum sulfate, and hydrogen peroxide were weighed according to a molar ratio of 1:1:0.05:2 and added to a reactor for reaction. During the reaction, the sodium ion concentration was controlled at 5 mol / L, the reaction pressure at 3.5 MPa, the pH at ≥12.0, and the reaction temperature at 240℃, with the reaction lasting for 3 hours. Aluminum sulfate was used as a dopant in the precursor.

[0050] After the reaction is complete, the reactants are separated into solid and liquid components and dried to obtain a composite hydroxide. Sodium exists in the composite hydroxide as sodium ions in the molecular structure of the metal hydroxide.

[0051] The obtained composite hydroxide was heat-treated at 760℃ for 12 hours to prepare a sodium-intercalated metal compound. The sodium-intercalated metal compound has a Na2O·Me2O3 solid solution structure, where Me represents a mixed metal of nickel, iron, and manganese, and the average valence state of Me is +3. Na ions enter the Me2O3 crystal and occupy the Me sites. The sodium-intercalated metal compound shows only three crystal structures in the XRD pattern: Ni2O3, Fe2O3, and Mn2O3.

[0052] The prepared sodium-intercalated metal compound was mixed with sodium carbonate to achieve a Na / Me ratio of 1.08 in the sodium-intercalated oxide mixture. The mixture was then heat-treated at 870 degrees Celsius for 8 hours to obtain a sodium metal composite oxide powder material, i.e., a sodium-ion cathode material. Figure 1 As shown, from Figure 1 It can be seen that the prepared sodium ion cathode material is a spherical polycrystalline material composed of sheet-like particles with a thickness of 300-500 nm, and has a distinct porous structure.

[0053] The prepared sodium-ion cathode material was used to fabricate a battery, and charge-discharge tests were conducted. The battery was charged and discharged at 0.1C. Figure 2 As shown, the material has an initial discharge capacity of 135.5 mAh / g and an initial discharge efficiency of 98.6%.

[0054] Example 2

[0055] A nickel-iron-manganese hydroxide (nickel:iron:manganese = 0.3:0.20:0.50), sodium hydroxide, aluminum sulfate, and hydrogen peroxide were weighed according to a molar ratio of 1.11:1:0.08:2 and added to a reactor for reaction. During the reaction, the sodium ion concentration was controlled at 8 mol / L, the reaction pressure at 4.0 MPa, the pH at ≥12.0, and the reaction temperature at 260℃ for 5 hours to ensure complete reaction of the Na ion metal compound. After the reaction was completed, the reactants were subjected to solid-liquid separation to obtain a sodium-intercalated metal compound with a Na / Me ratio of 0.9. The compound has a Na₂O·Me₂O₃ solid solution structure, with Na ions entering the hydroxyl hydroxide crystal structure without altering its physicochemical properties. The prepared sodium-intercalated metal compound was heat-treated at 780°C for 12 hours. Sodium carbonate was then added according to the formulation design requirements, ultimately achieving a Na / Me ratio of 1.06 in the sodium-intercalated oxide mixture. This mixture was then heat-treated at 860°C for 4 hours to obtain a sodium metal composite oxide powder material, i.e., a sodium-ion cathode material. This sodium-ion cathode material exhibits a discharge capacity of 133.2 mAh / g at 0.1C and an initial discharge efficiency of 98.1%.

[0056] Example 3

[0057] A nickel-iron-manganese hydroxide (nickel:iron:manganese = 0.25:0.15:0.60), sodium hydroxide, aluminum sulfate, and hydrogen peroxide were weighed according to a molar ratio of 1.25:1:0.065:2 and added to a reactor for reaction. During the reaction, the sodium ion concentration was controlled at 5 mol / L, the reaction pressure was atmospheric pressure, the pH was ≥12.0, the reaction temperature was 90℃, and the reaction was continued for 24 hours to allow the Na ion metal compound to fully react. After the reaction was completed, the reactants were subjected to solid-liquid separation to obtain a sodium-intercalated metal compound with a Na / Me ratio of 0.8. The compound has a Na₂O·Me₂O₃ solid solution structure, with Na ions entering the hydroxyl hydroxide crystal structure without altering its physicochemical properties. The prepared sodium-intercalated metal compound was heat-treated at 760°C for 12 hours. Sodium carbonate was then added according to the formulation design requirements, ultimately resulting in a Na / Me ratio of 1.08 in the sodium-intercalated oxide mixture. This mixture was then heat-treated at 870°C for 8 hours to obtain a sodium metal composite oxide powder material, i.e., a sodium-ion cathode material. This sodium-ion cathode material exhibits a discharge capacity of 131.6 mAh / g at 0.1C and an initial discharge efficiency of 98.7%.

[0058] Example 4

[0059] Nickel-iron-manganese hydroxide (nickel:iron:manganese = 0.3:0.20:0.50), sodium hydroxide, and hydrogen peroxide were weighed and added to the reactor in a molar ratio of 1.25:1:3.0. During the reaction, the sodium ion concentration in the solution was controlled at 8 mol / L, the reaction pressure at 4.0 MPa, the pH at ≥12.0, and the reaction temperature at 200℃. The reaction was continued for 5 hours to allow the Na ion metal compound to react completely. After the reaction was completed, the reactants were subjected to solid-liquid separation to obtain a sodium-intercalated metal compound with a Na / Me ratio of 0.8. This sodium-intercalated metal compound has a Na₂O·Me₂O₃ solid solution structure, in which Na ions enter the hydroxyl hydroxide crystal structure without changing its physicochemical properties. The obtained sodium-intercalated metal compound was heat-treated at 700 degrees Celsius for 12 hours. Sodium acetate was then added according to the formulation design requirements, ultimately making the Na / Me ratio in the sodium-intercalated oxide mixture 1.04. This mixture was then heat-treated at 750 degrees Celsius for 4 hours to obtain a sodium metal composite oxide powder material, i.e., a sodium ion cathode material. This sodium-ion cathode material has a discharge capacity of 132.7 mAh / g at 0.1C and an initial discharge efficiency of 98.0%.

[0060] Example 5

[0061] Nickel-copper-manganese hydroxide (nickel:copper:manganese = 0.3:0.20:0.50), sodium hydroxide, and hydrogen peroxide were weighed and added to the reactor in a molar ratio of 1.3:1:2.0. During the reaction, the sodium ion concentration in the solution was controlled at 10 mol / L, the reaction pressure at 2.0 MPa, the pH at ≥12.0, and the reaction temperature at 150℃. The reaction was continued for 5 hours to allow the Na ion metal compound to react completely. After the reaction was completed, the reactants were subjected to solid-liquid separation to obtain a sodium-intercalated metal compound with a Na / Me ratio of 0.77. This sodium-intercalated metal compound has a Na₂O·Me₂O₃ solid solution structure, in which Na ions enter the hydroxyl hydroxide crystal structure without altering its physicochemical properties. The obtained sodium-intercalated metal compound was heat-treated at 600°C for 12 hours. Sodium bicarbonate was then added according to the formulation design requirements, ultimately bringing the Na / Me ratio in the sodium-intercalated oxide mixture to 1.05. This mixture was then heat-treated at 650°C for 5 hours to obtain a sodium metal composite oxide powder material, i.e., a sodium-ion cathode material. This sodium-ion cathode material has a discharge capacity of 134.3 mAh / g at 0.1C and an initial discharge efficiency of 98.6%.

[0062] Comparative Example 1

[0063] Nickel-iron-manganese hydroxide (nickel:iron:manganese = 0.3:0.20:0.50), sodium hydroxide, aluminum sulfate, and hydrogen peroxide were weighed according to a molar ratio of 1.11:1:0.08:2 and added to a reactor for reaction. During the reaction, the sodium ion concentration in the solution was controlled at 3 mol / L, the reaction pressure at 4.0 MPa, the pH at ≥12.0, and the reaction temperature at 260℃. The reaction was continued for 5 hours. After the reaction was completed, the reactants were separated into solid and liquid components. It was found that although the product had a Na2O·Me2O3 solid solution structure, the Na / Me ratio of the sodium-intercalated metal compound was only 0.5.

[0064] The obtained product was heat-treated at 780 degrees Celsius for 12 hours; then, according to the formula design requirements, sodium carbonate was added, and the product was heat-treated at 860 degrees Celsius for 4 hours at a molar ratio of Na / Me = 1.06, finally yielding sodium metal composite oxide powder material, i.e. sodium ion cathode material. This sodium ion cathode material has a discharge capacity of 130.3 mAh / g under 0.1C conditions and an initial discharge efficiency of 96.5%.

[0065] Comparative Example 2

[0066] Nickel-iron-manganese hydroxide (nickel:iron:manganese = 0.3:0.20:0.50), sodium hydroxide, aluminum sulfate, and hydrogen peroxide were weighed according to a molar ratio of 1.11:1:0.08:2 and added to a reactor for reaction. During the reaction, the sodium ion concentration in the solution was controlled at 8 mol / L, the reaction pressure at 4.0 MPa, the pH at ≥12.0, and the reaction temperature at room temperature. The reaction was continued for 5 hours. After the reaction was completed, the reactants were separated into solid and liquid components. It was found that although the product had a Na2O·Me2O3 solid solution structure, the Na / Me ratio of the sodium-intercalated metal compound was only 0.4. The obtained product was heat-treated at 780 degrees Celsius for 12 hours; then, according to the formula design requirements, sodium carbonate was added, and the product was heat-treated at 860 degrees Celsius for 4 hours at a molar ratio of Na / Me = 1.06, finally yielding sodium metal composite oxide powder material, i.e. sodium ion cathode material. This sodium ion cathode material has a discharge capacity of 129.5 mAh / g under 0.1C conditions and an initial discharge efficiency of 96.2%.

[0067] Comparative Example 3

[0068] Nickel-iron-manganese hydroxide (nickel:iron:manganese = 0.3:0.20:0.50), sodium hydroxide, aluminum sulfate, and hydrogen peroxide were weighed according to a molar ratio of 1.11:1:0.08:2 and added to a reactor for reaction. During the reaction, the sodium ion concentration was controlled at 8 mol / L, the reaction pressure at 4.0 MPa, the pH at ≥12.0, and the reaction temperature at 260℃, and the reaction was continued for 5 hours to allow the Na ion metal compound to react completely. After the reaction was completed, the reactants were separated into solid and liquid components to obtain... A sodium-intercalated metal compound with a Na / Me ratio of 0.9 was obtained. This compound has a Na₂O·Me₂O₃ solid solution structure, in which Na ions are incorporated into the hydroxyl hydroxide crystal structure without altering its physicochemical properties. The prepared sodium-intercalated metal compound was heat-treated at 780°C for 12 hours to obtain a sodium metal composite oxide powder material, i.e., a sodium ion cathode material. This sodium-ion cathode material has a discharge specific capacity of 113 mAh / g at 0.1C and an initial discharge efficiency of 95.8%.

[0069] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0070] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0071] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A sodium-intercalated metal compound, characterized in that: The sodium-intercalated metal compound has a Na2O·Me2O3 solid solution structure, wherein Me is at least one metallic element selected from nickel, cobalt, manganese, aluminum, iron, and copper, and sodium ions are located in the crystal lattice of the metal oxide Me2O3 without changing its original structure. The method for preparing the sodium-intercalated metal compound includes the following steps: S1, adding a metal oxide or hydroxide, a sodium-containing metal compound, an oxidant, and water to the reactor; the oxidant is at least one of oxygen, air, and hydrogen peroxide; S2, controlling the reaction conditions of the reactor, the reaction conditions including: the concentration of sodium ions in the reactor is 5~12 mol / L, the pH value is 10~13, and the reaction temperature is 50~280℃, so that sodium ions are inserted into the metal hydroxide structure; S3, the reactants in S2 are separated into solid and liquid components, and then dried to obtain a composite hydroxide; S4, the composite hydroxide described in S3 is subjected to heat treatment at a temperature of 200~900℃ to obtain a sodium-intercalated metal compound.

2. The sodium-intercalating metal compound of claim 1, wherein: Me is at least one metallic element selected from nickel, cobalt, manganese, iron, and copper.

3. The sodium-intercalating metal compound of claim 2, wherein: Me represents nickel, iron, and manganese.

4. The sodium-intercalating metal compound of any one of claims 1-3, wherein: The molar ratio of sodium to Me is (0.001 to 0.05):

1.

5. The sodium-intercalating metal compound of claim 4, wherein: The molar ratio of sodium to Me is (0.005~0.04):

1.

6. The sodium-intercalating metal compound of claim 5, wherein: The molar ratio of sodium to Me is (0.01 to 0.03):

1.

7. A method for preparing the sodium-intercalated metal compound according to any one of claims 1-6, characterized in that: Includes the following steps: S1, adding a metal oxide or hydroxide, a sodium-containing metal compound, an oxidant, and water to the reactor; the oxidant is at least one of oxygen, air, and hydrogen peroxide; S2, controlling the reaction conditions of the reactor, the reaction conditions including: the concentration of sodium ions in the reactor is 5~12 mol / L, the pH value is 10~13, and the reaction temperature is 50~280℃, so that sodium ions are inserted into the metal hydroxide structure; S3, the reactants in S2 are separated into solid and liquid components, and then dried to obtain a composite hydroxide; S4, the composite hydroxide described in S3 is subjected to heat treatment at a temperature of 200~900℃ to obtain a sodium-intercalated metal compound.

8. The method for preparing the sodium-intercalated metal compound according to claim 7, characterized in that: In S1, the metal oxide or hydroxide is an oxide or hydroxide of nickel, cobalt, manganese, aluminum, iron, or copper, or a mixed metal oxide or hydroxide of nickel, cobalt, manganese, aluminum, iron, or copper.

9. The method for preparing the sodium-intercalated metal compound according to claim 7, characterized in that: In S1, the sodium-containing metal compound is at least one of sodium hydroxide, sodium acetate, sodium nitrate, sodium sulfate, and sodium bicarbonate.

10. The method for preparing the sodium-intercalated metal compound according to claim 7, characterized in that: The amount of each substance added in S1 is such that the molar ratio of metal in metal oxides or hydroxides to sodium in sodium-containing metal compounds to oxidizing agent is (0.4~1.3):1:(0.5~4).

11. The method for preparing the sodium-intercalated metal compound according to claim 8, characterized in that: The metal oxide or hydroxide is an oxide or hydroxide of nickel, iron, or manganese.

12. The method of claim 10, wherein the sodium-intercalating metal compound is prepared by the steps of: The amount of each substance added in S1 is such that the molar ratio of metal in metal oxides or hydroxides to sodium in sodium-containing metal compounds to oxidizing agent is (0.8~1.2):1:(1.0~3.0). ​ 13. The method for preparing the sodium-intercalated metal compound according to claim 12, characterized in that: The amount of each substance added in S1 is such that the molar ratio of metal in metal oxides or hydroxides to sodium in sodium-containing metal compounds to oxidizing agent is 1:1:

2.

14. The method for preparing the sodium-intercalated metal compound according to claim 7, characterized in that: The oxidant is hydrogen peroxide, and the initial concentration of hydrogen peroxide in the reaction system is 5-20 wt%.

15. The method for preparing the sodium-intercalated metal compound according to claim 7, characterized in that: The reaction conditions described in S2 include: a sodium ion concentration of 7-10 mol / L in the reactor, a pH value of 10-13, and a reaction temperature of 100-250℃.

16. The method for preparing the sodium-intercalated metal compound according to claim 15, characterized in that: The reaction conditions also include: a reaction pressure of 0.1~50MPa, a reaction temperature of 100~250℃, and a reaction time of 0.5~60h.

17. The method for preparing the sodium-intercalated metal compound according to claim 16, characterized in that: The reaction pressure is 2~30MPa, the reaction temperature is 120~200℃, and the reaction time is 10~48h.

18. A sodium-ion battery cathode material, comprising a sodium-intercalated metal compound as described in any one of claims 1-6, or a sodium-intercalated metal compound prepared by any one of claims 7-17, which is then calcined after being mixed with a sodium-containing compound, wherein the sodium-intercalated metal compound and the sodium-containing compound are mixed at a Na:Me molar ratio of 1.01-1.1:

1.

19. The sodium-ion battery cathode material of claim 18, wherein: The sodium-containing compound is selected from at least one of sodium hydroxide, sodium acetate, sodium nitrate, sodium sulfate, and sodium bicarbonate; the calcination temperature is 500-900℃ and the time is 12-30h; the sintering atmosphere is an air atmosphere or an oxygen atmosphere.

20. The sodium-ion battery cathode material according to claim 19, characterized in that: The calcination temperature is 600–900°C.

21. The sodium-ion battery cathode material of claim 19, wherein: The calcination time is 15-30 hours.

22. The sodium-ion battery cathode material of claim 18, wherein: When the sodium-intercalated metal compound is mixed with the sodium-containing compound, the Na:Me molar ratio is 1.05-1.1:

1.

23. The sodium-ion battery cathode material of any one of claims 18-22, wherein: Any one or more of the following items (1) to (3): (1) The sodium-ion battery cathode material is a spherical polycrystalline material composed of primary particles, wherein the primary particles are sheet-like particles with a thickness of 300-500 nm, and the sodium-ion battery cathode material has a porous structure. (2) The initial discharge capacity of the sodium-ion battery cathode material at 2.0~4.0V and 0.1C rate is 3~5mAh / g higher than that of the sodium-ion battery cathode material corresponding to the non-sodium intercalation method; (3) The first discharge efficiency of the sodium-ion battery cathode material at 2.0~4.0V and 0.1C rate is greater than or equal to 98%.

24. A sodium-ion battery comprising the sodium-ion battery cathode material according to any one of claims 18-23.

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