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

Abstract

The application provides a sodium ion battery positive electrode material and a preparation method and application thereof, and the chemical general formula of the sodium ion battery positive electrode material is Na m Ni x Fe y Mn z O2, wherein 0.1<=x<=0.25, 0.5<=y<=0.8, 0.1<=z<=0.25, 0.8<=m<=1.1, 0.95<=x / z<=1.05, x+y+z=1, wherein m, x, y and z are molar percentages of corresponding elements, and each component in the chemical general formula satisfies charge conservation and stoichiometric conservation. The preparation method comprises the following steps: preparing a precursor containing a nickel source, an iron source and a manganese source with a required stoichiometry by using a coprecipitation method; mixing the precursors of the nickel source, the iron source and the manganese source with a sodium source according to a certain proportion, adding a doping element, and performing first sintering to obtain a doped sodium ion battery positive electrode material; and performing second sintering on the doped sodium ion battery positive electrode material and a coating to obtain a final sodium ion battery positive electrode material. The sodium ion battery positive electrode material provided by the application has the advantages of high capacity, low residual alkali and high stability.

Description

Technical Field

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

[0002] With the rapid development of the new energy industry, the lithium resources for producing lithium-ion batteries are far from meeting the explosive growth in demand. Sodium-ion batteries, due to their similar energy storage mechanism to lithium-ion batteries and their abundant reserves, have become a strong competitor to replace lithium-ion batteries in large-scale energy storage systems.

[0003] Layered sodium-ion batteries are considered the most promising cathode materials for sodium-ion batteries. For example, CN113258060B discloses a high-nickel layered oxide material for sodium-ion batteries, its preparation method, and its applications. The general chemical formula of the high-nickel layered oxide material for sodium-ion batteries is Na. x Ni a Fe b Mn c M d 0 2±δ Ni, Fe, and Mn are transition metal elements, and M is an element that substitutes for the transition metal sites. In the structure of the oxide material, the ions at the transition metal sites form an octahedral structure with the six adjacent oxygen atoms, and are alternately arranged with octahedral coordinated NaO6 layers, constituting an O3-type high-nickel layered oxide material for sodium-ion batteries with a space group of R-3m. M specifically includes Li. + Mg 2+ Ca 2+ Cu 2+ Zn 2+ Al 3+ B 3+ Co 3+ V 3+ Y 3+ Ti 4+ Zr 4+ Sn 4+ Mo 4+ Si 4+ Ru 4+ Nb 5+ Sb 5+ Mo 5+ Mo 6+ W 6+ One or more of the following; x, a, b, c, d and 2+δ are the molar percentages of the corresponding elements, and each component in the general chemical formula satisfies charge conservation and stoichiometry conservation, and 0.67≤x≤1, 0.5≤a<1, 0.01≤b≤0.35, 0.01≤c≤0.35, 0≤d≤0.3, 0≤δ≤0.1.

[0004] However, these nickel-containing layered transition metal oxides for sodium-ion batteries suffer from problems such as high cost, high residual alkali on the surface, and poor cycle stability, which limit their large-scale application. Summary of the Invention

[0005] In view of the above, the present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a sodium-ion battery cathode material, its preparation method, and its application. The present invention, by controlling the composition and particle morphology of the transition metal elements iron and manganese, maintains high capacity of the cathode material while keeping nickel levels low, and reduces free sodium ions on the surface, thus obtaining a low-nickel sodium-ion battery cathode material with high capacity, low residual alkali, and high stability. Furthermore, the preparation method has a simple process flow and is suitable for large-scale industrial production.

[0006] Therefore, in a first aspect, embodiments of the present invention provide a sodium-ion battery cathode material, wherein the general chemical formula of the sodium-ion battery cathode material is Na. m Ni x Fe y Mn z O2, where 0.1≤x≤0.25, 0.5≤y≤0.8, 0.1≤z≤0.25, 0.8≤m≤1.1, 0.95≤x / z≤1.05, x+y+z=1, where m, x, y, and z are the molar percentages of the corresponding elements, and the components in the general chemical formula satisfy charge conservation and stoichiometry conservation.

[0007] Preferably, the sodium-ion battery cathode material contains dopant element A, and the general chemical formula of the sodium-ion battery cathode material is Na. m Ni x Fe y Mn z A p O2, wherein 0.001≤p≤0.05, 0.1≤x≤0.25, 0.5≤y≤0.8, 0.1≤z≤0.25, 0.8≤m≤1.1, 0.95≤x / z≤1.05, x+y+z=1, where m, x, y, z, and p are the molar percentages of the corresponding elements, and the components in the general chemical formula satisfy charge conservation and stoichiometry conservation. The dopant element A is one or more of the following elements: lithium, magnesium, calcium, copper, zinc, aluminum, boron, cobalt, vanadium, yttrium, titanium, zirconium, tin, molybdenum, silicon, ruthenium, niobium, antimony, and tungsten.

[0008] Secondly, embodiments of the present invention provide a method for preparing the sodium-ion battery cathode material provided in the first aspect above. The preparation method includes: preparing a precursor containing a required stoichiometric amount of nickel, iron, and manganese sources using a co-precipitation method; mixing the precursor containing nickel, iron, and manganese sources with a sodium source in a certain proportion and then adding doping elements for a first sintering to obtain a doped sodium-ion battery cathode material; and performing a second sintering of the doped sodium-ion battery cathode material with a coating to obtain the final sodium-ion battery cathode material.

[0009] Preferably, the iron source is one or more of ferrous sulfate, hydrated ferrous sulfate, ferrous nitrate, and ferrous chloride; the manganese source is one or more of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate; and the nickel source is one or more of nickel chloride, nickel oxide, nickel nitrate, nickel sulfate, and nickel aminosulfonate.

[0010] Preferably, the step of preparing precursors containing the required stoichiometric amounts of nickel, iron, and manganese sources using a co-precipitation method includes: preparing aqueous solutions of nickel, iron, and manganese sources according to stoichiometric ratios; preparing ammonia solution and sodium hydroxide solution of a certain concentration; adding the aqueous solution, ammonia solution, and sodium hydroxide solution to a reaction vessel at a certain flow rate, controlling the pH of the reaction system to 10-10.5, and carrying out a co-precipitation reaction to obtain the reaction product; washing, filtering, and drying the above reaction product to obtain the precursors of nickel, iron, and manganese sources.

[0011] Preferably, the molar ratio of the added nickel source, iron source, and manganese source satisfies n(Ni):n(Fe):n(Mn) = x:y:z; the concentration of the ammonia solution is 25%, and the concentration of the sodium hydroxide solution is 15%; the rotation speed is 300-500 rpm, and the temperature is 40-80℃; the flow rate of the aqueous solution is 1.0 L / h, the flow rate of the ammonia solution is 0.8 L / h, and the flow rate of the sodium hydroxide solution is 2.0 L / h.

[0012] Preferably, the precursors of the nickel source, iron source, and manganese source are in a molar ratio of 1:(0.8-1.1) to the sodium source, wherein the sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium sulfate, sodium chloride, sodium perchlorate, sodium nitrate, sodium phosphate, and sodium hydrogen phosphate.

[0013] Preferably, the doping element can be one or more of the following elements: lithium, magnesium, calcium, copper, zinc, aluminum, boron, cobalt, vanadium, yttrium, titanium, zirconium, tin, molybdenum, silicon, ruthenium, niobium, antimony, and tungsten; the one-time sintering process is: heating to 480°C at a heating rate of 3°C / min and holding for 4 hours.

[0014] Preferably, the coating is one or more of calcium oxide, cobalt hydroxyoxide, aluminum oxide, sodium molybdate, lanthanum oxide, aluminum metaphosphate, titanium oxide, magnesium oxide, zirconium oxide, sodium titanate, cobalt oxide, aluminum fluoride, chromium oxide, zinc oxide, strontium oxide, copper oxide, and tungsten oxide. The secondary sintering process is as follows: heating to 850°C at a heating rate of 4°C / min and holding at that temperature for 10 hours.

[0015] Thirdly, embodiments of the present invention provide a sodium-ion battery, including the sodium-ion battery cathode material provided in the first aspect above.

[0016] The sodium-ion battery cathode material, its preparation method, and its application provided in this invention employ a low-nickel layered oxide. By controlling the composition and particle morphology of the transition metal elements iron and manganese, the high capacity of the cathode material is maintained while keeping the nickel content low, and the free sodium ions on the surface are reduced, resulting in a sodium-ion battery cathode material with high capacity, low residual alkali, and high stability. Furthermore, the preparation method has a simple process flow and is suitable for large-scale industrial production. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the preparation method of sodium-ion battery cathode material provided in an embodiment of the present invention.

[0018] Figure 2 This is a flowchart of step S1 in the method for preparing sodium-ion battery cathode material provided in the embodiments of the present invention;

[0019] Figure 3 This is a SEM image of the sodium-ion battery cathode material prepared in Example 1 of the present invention;

[0020] Figure 4 This is a SEM image of the sodium-ion battery cathode material prepared in Example 1 of the present invention. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0022] The following disclosure provides numerous different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. Additionally, examples of various specific processes and materials are provided, but those skilled in the art will recognize the applicability of other processes and / or the use of other materials.

[0023] The purpose of this invention is to provide a sodium-ion battery cathode material, its preparation method, and its application. This invention employs a low-nickel layered oxide and, by controlling the composition and particle morphology of the transition metal elements iron and manganese, maintains high capacity of the cathode material while keeping the nickel content low, and reduces free sodium ions on the surface, resulting in a sodium-ion battery cathode material with high capacity, low residual alkali, and high stability. Furthermore, the preparation method has a simple process flow and is suitable for large-scale industrial production.

[0024] A first aspect of this invention provides a sodium-ion battery cathode material, wherein the general chemical formula of the sodium-ion battery cathode material is Na. m Ni x Fe y Mn z O2, wherein 0.1≤x≤0.25, 0.5≤y≤0.8, 0.1≤z≤0.25, 0.8≤m≤1.1, 0.95≤x / z≤1.05, x+y+z=1, where m, x, y, and z are the molar percentages of the corresponding elements, and the components in the general chemical formula satisfy charge conservation and stoichiometry conservation. In the structure of the sodium-ion battery cathode material described in this invention, the ions at the transition metal sites form an octahedral structure with six adjacent oxygen ions, constituting an O3-type low-nickel layered oxide sodium-ion battery cathode material with space group R-3m.

[0025] Furthermore, the sodium-ion battery cathode material contains dopant element A, and the general chemical formula of the sodium-ion battery cathode material is Na. m Ni x Fe y Mn z A p O2, where 0.001≤p≤0.05, 0.1≤x≤0.25, 0.5≤y≤0.8, 0.1≤z≤0.25, 0.8≤m≤1.1, 0.95≤x / z≤1.05, x+y+z=1, where m, x, y, z, and p are the molar percentages of the corresponding elements, and the components in the general chemical formula satisfy charge conservation and stoichiometry conservation. Element A can be lithium (Li).+ ), magnesium (Mg) 2 + ), calcium (Ca 2+ ), copper (Cu) 2+ ), Zinc (Zn) 2+ ), aluminum (Al) 3+ ), boron (B) 3+ ), cobalt (Co) 3+ ), Vanadium (V) 3+ ), Yttrium 3+ ), titanium (Ti 4+ Zirconium (Zr) 4+ ), Tin (Sn) 4+ ), molybdenum (Mo 4+ Mo 5+ Mo 6+ ), silicon (Si) 4+ ), Ruthenium (Ru) 4+ ), niobium (Nb) 5+ ), antimony (Sb) 5 ), tungsten (W) 6+ One or more of the following.

[0026] A second aspect of this invention provides a method for preparing a sodium-ion battery cathode material, such as... Figure 1 As shown, the preparation method includes the following steps:

[0027] Step S1: Prepare a precursor containing the required stoichiometric amounts of nickel, iron, and manganese sources using a co-precipitation method;

[0028] The iron source can be one or more of ferrous sulfate, hydrated ferrous sulfate, ferrous nitrate, and ferrous chloride; the manganese source can be one or more of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate; and the nickel source can be one or more of nickel chloride, nickel oxide, nickel nitrate, nickel sulfate, and nickel aminosulfonate.

[0029] Specifically, in the first embodiment of the present invention, as Figure 2 As shown, step S1 includes:

[0030] Step S11: Prepare an aqueous solution by mixing the nickel source, iron source, and manganese source according to their stoichiometric ratio;

[0031] The molar ratio of the added nickel source, iron source, and manganese source satisfies n(Ni):n(Fe):n(Mn)=x:y:z.

[0032] Step S12: Prepare an ammonia solution and a sodium hydroxide solution of a certain concentration.

[0033] The concentration of the ammonia solution was 25%, and the concentration of the sodium hydroxide solution was 15%.

[0034] Step S13: Under certain rotation speed and temperature conditions, add aqueous solution, ammonia solution and sodium hydroxide solution into the reaction vessel at a certain flow rate, control the pH value of the reaction system to 10-10.5, carry out co-precipitation reaction, and obtain reaction products;

[0035] The rotation speed can be 300-500 rpm, and the temperature can be 40-80℃. The flow rate of the aqueous solution is 1.0 L / h, the flow rate of the ammonia solution is 0.8 L / h, and the flow rate of the sodium hydroxide solution is 2.0 L / h.

[0036] Step S14: Wash, filter, and dry the above reaction products to obtain precursors for nickel, iron, and manganese sources.

[0037] Step S2: Mix the precursors of nickel source, iron source, and manganese source with sodium source in a certain proportion, add doping elements and sinter once to obtain doped sodium-ion battery cathode material.

[0038] In this process, the precursors for nickel, iron, and manganese sources are present in a molar ratio of 1:(0.8-1.1) to sodium source. The sodium source can be one or more of sodium carbonate, sodium bicarbonate, sodium sulfate, sodium chloride, sodium perchlorate, sodium nitrate, sodium phosphate, and sodium hydrogen phosphate. The doping element can be one or more of lithium, magnesium, calcium, copper, zinc, aluminum, boron, cobalt, vanadium, yttrium, titanium, zirconium, tin, molybdenum, silicon, ruthenium, niobium, antimony, and tungsten. The single-stage sintering process involves heating to 480°C at a heating rate of 3°C / min and holding at that temperature for 4 hours.

[0039] Step S3: The above-mentioned doped sodium-ion battery cathode material and the coating are sintered a second time to obtain the final sodium-ion battery cathode material.

[0040] The coating material can be one or more of calcium oxide, cobalt hydroxyoxide, aluminum oxide, sodium molybdate, lanthanum oxide, aluminum metaphosphate, titanium oxide, magnesium oxide, zirconium oxide, sodium titanate, cobalt oxide, aluminum fluoride, chromium oxide, zinc oxide, strontium oxide, copper oxide, and tungsten oxide. The secondary sintering process is as follows: heating to 850°C at a heating rate of 4°C / min and holding at that temperature for 10 hours.

[0041] The sodium-ion battery cathode material prepared by the method described in this invention is a low-nickel layered oxide material. In this material, iron exhibits electrochemical activity, enhancing the capacity of the low-nickel layered oxide. Simultaneously, the oxidation of divalent nickel on the surface leads to the precipitation of bulk sodium, resulting in a lower content of free sodium ions and greater surface stability. Furthermore, this preparation method is simple and suitable for large-scale industrial production.

[0042] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0043] Example 1

[0044] This embodiment provides a method for preparing a sodium-ion battery cathode material. The chemical formula of the sodium-ion battery cathode material prepared in this embodiment is NaNi. 0.25 Fe 0.5 Mn 0.25 O2 (where x = 0.25, y = 0.5, z = 0.25) includes the following steps:

[0045] Based on the chemical formula NaNi 0.25 Fe 0.5 Mn 0.25 O2 was used to prepare an aqueous solution of nickel sulfate, manganese sulfate, and ferrous sulfate heptahydrate in a molar ratio of nickel, iron, and manganese of 0.25:0.5:1 / 3. A 25% ammonia solution and a 15% sodium hydroxide solution were prepared at 350 rpm and 50°C. The aqueous solution, ammonia solution, and sodium hydroxide solution were added concurrently to the reactor at flow rates of 1.0 L / h, 0.8 L / h, and 2.0 L / h, respectively, maintaining the pH of the reaction system at 10-10.5 for co-precipitation. The mixture was then washed, filtered, and dried to obtain precursors for nickel, iron, and manganese sources. These precursors were then mixed with sodium carbonate at a molar ratio of 1:1.1 and heated to 480°C at a heating rate of 3°C / min for 4 hours, followed by heating to 850°C at a heating rate of 4°C / min for 10 hours to obtain NaNi. 0.25 Fe 0.5 Mn 0.25 O2 sodium-ion battery cathode material.

[0046] The SEM image of the sodium-ion battery cathode material prepared according to Example 1 is shown below. Figure 3 As shown;

[0047] The XRD pattern of the sodium-ion battery cathode material prepared according to Example 1 is shown below. Figure 4 As shown.

[0048] Example 2

[0049] The preparation process of the sodium-ion battery cathode material in Example 2 is the same as in Example 1, except that: x = 0.23, y = 0.54, z = 0.23, and the chemical formula of the sodium-ion battery cathode material is NaNi. 0.23 Fe 0.54 Mn 0.23 O2.

[0050] Example 3

[0051] The preparation process of the sodium-ion battery cathode material in Example 3 is the same as in Example 1, except that: x = 0.2, y = 0.6, z = 0.2, and the chemical formula of the sodium-ion battery cathode material is NaNi. 0.2 Fe 0.6 Mn 0.2 O2.

[0052] Example 4

[0053] The preparation process of the sodium-ion battery cathode material in Example 4 is the same as in Example 1, except that: x = 0.18, y = 0.64, z = 0.18, and the chemical formula of the sodium-ion battery cathode material is NaNi. 0.18 Fe 0.64 Mn 0.18 O2.

[0054] Example 5

[0055] The preparation process of the sodium-ion battery cathode material in Example 5 is the same as in Example 1, except that: x = 0.15, y = 0.7, z = 0.15, and the chemical formula of the sodium-ion battery cathode material is NaNi. 0.15 Fe 0.7 Mn 0.15 O2.

[0056] Example 6

[0057] The preparation process of the sodium-ion battery cathode material in Example 3 is the same as in Example 1, except that: x = 0.1, y = 0.8, z = 0.1, and the chemical formula of the sodium-ion battery cathode material is NaNi. 0.1 Fe 0.8 Mn 0.1 O2.

[0058] Example 7

[0059] This embodiment provides a method for preparing a sodium-ion battery cathode material. The chemical formula of the sodium-ion battery cathode material prepared in this embodiment is NaNi. 0.2 Fe 0.6 Mn 0.2 Ca 0.003O2 (where x = 0.2, y = 0.6, z = 0.2, p = 0.003) includes the following steps:

[0060] Based on the chemical formula NaNi 0.2 Fe 0.6 Mn 0.2 Ca 0.003 O2 was used to prepare an aqueous solution of nickel sulfate, manganese sulfate, and ferrous sulfate heptahydrate in a molar ratio of nickel, iron, and manganese of 0.25:0.5:1 / 3. A 25% ammonia solution and a 15% sodium hydroxide solution were prepared at 350 rpm and 50°C. The aqueous solution, ammonia solution, and sodium hydroxide solution were added concurrently to the reactor at flow rates of 1.0 L / h, 0.8 L / h, and 2.0 L / h, respectively, maintaining the pH of the reaction system at 10-10.5 for co-precipitation. The mixture was then washed, filtered, and dried to obtain precursors for nickel, iron, and manganese sources. These precursors were mixed with sodium carbonate at a molar ratio of 1:1.1. A calcium-doped compound was added, and the mixture was heated to 480°C at a heating rate of 3°C / min and held for 4 hours. Then, a cobalt hydroxyl oxide coating was added, and the mixture was heated to 850°C at a heating rate of 4°C / min and held for 10 hours to obtain NaNi. 0.2 Fe 0.6 Mn 0.2 Ca 0.003 O2 sodium-ion battery cathode material.

[0061] Example 8

[0062] The preparation process of the sodium-ion battery cathode material in Example 8 is the same as in Example 7, except that p = 0.006 and the chemical formula of the sodium-ion battery cathode material is NaNi. 0.2 Fe 0.6 Mn 0.2 Ca 0.006 O2.

[0063] Example 9

[0064] The preparation process of the sodium-ion battery cathode material in Example 9 is the same as in Example 7, except that the doping element is zinc and the chemical formula of the sodium-ion battery cathode material is NaNi. 0.2 Fe 0.6 Mn 0.2 Zn 0.003 O2.

[0065] Example 10

[0066] The preparation process of the sodium-ion battery cathode material in Example 10 is the same as in Example 7, except that the doping element is copper and the chemical formula of the sodium-ion battery cathode material is NaNi.0.2 Fe 0.6 Mn 0.2 Cu 0.003 O2.

[0067] Comparative Example 1

[0068] This embodiment provides a method for preparing a sodium-ion battery cathode material. The chemical formula of the sodium-ion battery cathode material prepared in this embodiment is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 (at this time x = 1 / 3, y = 1 / 3, z = 1 / 3), includes the following steps:

[0069] Based on the chemical formula NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was used to mix nickel oxide, iron oxide, and manganese oxide in a nickel:iron:manganese molar ratio of 1 / 3:1 / 3:1 / 3. Sodium carbonate (measured at m=1) was added, along with a doping compound. The mixture was heated to 480°C at a heating rate of 3°C / min and held for 5 hours. Then, it was heated to 870°C at a heating rate of 4°C / min and held for 12 hours to obtain NaNi. 1 / 3Fe 1 / 3 Mn 1 / 3 O2 sodium-ion battery cathode material.

[0070] Comparative Example 2

[0071] This embodiment provides a method for preparing a sodium-ion battery cathode material. The chemical formula of the sodium-ion battery cathode material prepared in this embodiment is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 (at this time x = 1 / 3, y = 1 / 3, z = 1 / 3), includes the following steps:

[0072] Based on the chemical formula NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3O2 was used to prepare an aqueous solution of nickel sulfate, manganese sulfate, and ferrous sulfate heptahydrate in a molar ratio of nickel, iron, and manganese of 1 / 3:1 / 3:1 / 3. A 25% ammonia solution and a 15% sodium hydroxide solution were prepared at 350 rpm and 50°C. The aqueous solution, ammonia solution, and sodium hydroxide solution were added concurrently to the reactor at flow rates of 1.0 L / h, 0.8 L / h, and 2.0 L / h, respectively, maintaining the pH of the reaction system at 10-10.5 for co-precipitation. The mixture was then washed, filtered, and dried to obtain precursors for nickel, iron, and manganese sources. These precursors were then mixed with sodium carbonate at a molar ratio of 1:1.1 and heated to 480°C at a heating rate of 3°C / min for 4 hours, followed by heating to 850°C at a heating rate of 4°C / min for 10 hours to obtain NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 sodium-ion battery cathode material.

[0073] The free sodium ion content of the sodium-ion battery cathode materials prepared in Examples 1-10 and Comparative Examples 1-2 was tested. To verify the quality of the finished sodium-ion battery cathode materials prepared using the method provided in this invention, the sodium-ion battery cathode materials prepared in Examples 1-10 and Comparative Examples 1-2 were dispersed in N-methylpyrrolidone at a mass ratio of 90:5:5 with conductive carbon black and binder polyvinylidene fluoride. After ball milling and uniform dispersion, the dispersion was coated onto aluminum foil and vacuum dried to obtain the cathode sheet. The electrolyte was 1 mol / L LiPF6 with a solvent volume ratio of EC:DMC:EMC = 1:1:1. The separator was a Celgard polypropylene membrane, and the lithium metal sheet was used as the negative electrode. All components were assembled into a coin cell. The test voltage range is 2.5V-4.5V. Charging to 4.5V is performed using a constant current / constant voltage charging method, and discharging to 2.5V using a constant current discharging method. The charging and discharging current is 0.1C for two revolutions. Specific test items and results are shown in Table 1 below.

[0074] Table 1. Test items and test results for Examples 1-10 and Comparative Examples 1-2

[0075]

[0076]

[0077] Based on the above embodiments and comparative examples, and the comparison of the test results obtained from the tests, it can be seen that the sodium-ion battery cathode material preparation method provided by the embodiments of the present invention can effectively improve the discharge specific capacity of the sodium-ion battery cathode material, reduce the content of free sodium ions on the surface of the sodium-ion battery cathode material, and improve the stability of the material.

[0078] In summary, the sodium-ion battery cathode material preparation method provided in this invention employs a low-nickel layered oxide. By controlling the composition and particle morphology of the transition metal elements iron and manganese, it maintains high capacity of the cathode material while keeping the nickel content low, and reduces free sodium ions on the surface, resulting in a sodium-ion battery cathode material with high capacity, low residual alkali, and high stability. Furthermore, this preparation method has a simple process flow and is suitable for large-scale industrial production.

[0079] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0080] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A sodium-ion battery cathode material, characterized in that, The general chemical formula of the sodium-ion battery cathode material is Na. m Ni x Fe y Mn z A p O2, wherein 0.001≤p≤0.006, 0.1≤x≤0.25, 0.5≤y≤0.8, 0.1≤z≤0.25, 0.8≤m≤1.1, 0.95≤x / z≤1.05, x+y+z=1, where m, x, y, z, and p are the molar percentages of the corresponding elements, and the components in the general chemical formula satisfy charge conservation and stoichiometry conservation. The dopant element A is one or more of lithium, magnesium, calcium, copper, zinc, aluminum, boron, cobalt, vanadium, yttrium, titanium, zirconium, tin, molybdenum, silicon, ruthenium, niobium, antimony, and tungsten. In the structure of the sodium-ion battery cathode material, the ions at the transition metal sites form an octahedral structure with the six adjacent oxygen ions, constituting a low-nickel layered oxide sodium-ion battery cathode material of type O3 with space group R-3m.

2. A method for preparing the sodium-ion battery cathode material as described in claim 1, characterized in that, The preparation method includes: Step S1: Prepare a precursor containing the required stoichiometric amounts of nickel, iron, and manganese sources using a co-precipitation method; Step S2: Mix the precursors of nickel source, iron source, and manganese source with sodium source in a certain proportion, add doping elements and sinter once to obtain doped sodium-ion battery cathode material. Step S3: The above-mentioned doped sodium-ion battery cathode material and the coating are sintered a second time to obtain the final sodium-ion battery cathode material.

3. The method for preparing the sodium-ion battery cathode material according to claim 2, characterized in that, In step S1, the iron source is one or more of ferrous sulfate, hydrated ferrous sulfate, ferrous nitrate, and ferrous chloride; the manganese source is one or more of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate; and the nickel source is one or more of nickel chloride, nickel oxide, nickel nitrate, nickel sulfate, and nickel aminosulfonate.

4. The method for preparing the sodium-ion battery cathode material according to claim 2, characterized in that, Step S1 includes: Step S11: Prepare an aqueous solution by mixing the nickel source, iron source, and manganese source according to their stoichiometric ratio; Step S12: Prepare an ammonia solution and a sodium hydroxide solution of a certain concentration. Step S13: Under certain rotation speed and temperature conditions, add aqueous solution, ammonia solution and sodium hydroxide solution into the reaction vessel at a certain flow rate, control the pH value of the reaction system to 10-10.5, carry out co-precipitation reaction, and obtain reaction products; Step S14: Wash, filter and dry the above reaction products to obtain precursors for nickel source, iron source and manganese source.

5. The method for preparing the sodium-ion battery cathode material according to claim 4, characterized in that, The molar ratio of the added nickel, iron, and manganese sources satisfies n(Ni):n(Fe):n(Mn) = x:y:z; the concentration of the ammonia solution is 25%, and the concentration of the sodium hydroxide solution is 15%; the rotation speed is 300-500 rpm, and the temperature is 40-80℃; the flow rate of the aqueous solution is 1.0 L / h, the flow rate of the ammonia solution is 0.8 L / h, and the flow rate of the sodium hydroxide solution is 2.0 L / h.

6. The method for preparing the sodium-ion battery cathode material according to claim 2, characterized in that, In step S2, the precursors of the nickel source, iron source, and manganese source are in a molar ratio of 1:(0.8-1.1) to the sodium source, and the sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium sulfate, sodium chloride, sodium perchlorate, sodium nitrate, sodium phosphate, and sodium hydrogen phosphate.

7. The method for preparing the sodium-ion battery cathode material according to claim 2, characterized in that, In step S2, the doping element is one or more of the following elements: lithium, magnesium, calcium, copper, zinc, aluminum, boron, cobalt, vanadium, yttrium, titanium, zirconium, tin, molybdenum, silicon, ruthenium, niobium, antimony, and tungsten; the first sintering process is: heating to 480°C at a heating rate of 3°C / min and holding for 4 hours.

8. The method for preparing the sodium-ion battery cathode material according to claim 2, characterized in that, In step S3, the coating is one or more of calcium oxide, cobalt hydroxyoxide, aluminum oxide, sodium molybdate, lanthanum oxide, aluminum metaphosphate, titanium oxide, magnesium oxide, zirconium oxide, sodium titanate, cobalt oxide, aluminum fluoride, chromium oxide, zinc oxide, strontium oxide, copper oxide, and tungsten oxide. The secondary sintering process is as follows: heating to 850°C at a heating rate of 4°C / min and holding at that temperature for 10 hours.

9. A sodium-ion battery, characterized in that, The sodium-ion battery includes the sodium-ion battery cathode material as described in claim 1.

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