Positive electrode material and preparation method thereof, and battery

Abstract

This application relates to the field of sodium ion battery technology, in particular to a positive electrode material and its preparation method, and a battery. It is used to solve the problem that the capacity of the positive electrode material of sodium ion battery in the related art is seriously attenuated and cannot be effectively utilized. A positive electrode material, the general formula of the positive electrode material is A x BO2; wherein the A-site element includes Na and a doping element X, wherein the doping element X is selected from one or more of K, Ca, Fe, Mg, and Li; and the B-site element includes Mn; wherein 0.5≤x≤1. This application is used to prepare a sodium-ion battery.

Description

Technical Field

[0001] The present application relates to the technical field of sodium ion batteries, and in particular to a positive electrode material, a preparation method thereof, and a battery. Background Art

[0002] Sodium-ion batteries first appeared in the early 1980s, but research on them stagnated due to the superior performance of lithium-ion batteries. However, with the growing demand for power batteries, the limited and expensive reserves of lithium-ion battery materials have made the search for alternative materials urgent.

[0003] Sodium, with its abundant resources, widespread distribution, and low price, has shown great potential in applications such as low-cost vehicles and large-scale energy storage power plants. Current sodium-ion battery cathode materials primarily include transition metal layered oxides, such as sodium manganate, sodium cobaltate, sodium nickelate, and their derivatives, as well as olivine, sodium ferric phosphate, and its derivatives.

[0004] These layered oxides can generally be divided into two types: O3 and P2 structures. However, current layered oxides undergo a series of phase transitions during electrochemical cycling due to the sliding of the layers. In particular, the oxidation of oxide ions in the oxide leads to partial oxygen loss, resulting in irreversible phase transitions in the material structure (such as the O3 to P2 phase transition), which ultimately leads to capacity decay. How to inhibit irreversible phase transitions during electrochemical cycling has become an urgent problem for sodium-ion battery cathode materials. Summary of the Invention

[0005] Based on this, the present application provides a positive electrode material and a preparation method thereof, and a battery to solve the problem in the related art that the capacity of the positive electrode material of the sodium ion battery is severely attenuated and cannot be effectively utilized.

[0006] In the first aspect of the present application, a positive electrode material is provided. The general formula of the positive electrode material is A x BO2;

[0007] Wherein, the A-site element includes Na and a doping element X, and the doping element X is selected from one or more of K, Ca, Fe, Mg and Li;

[0008] B-site elements include Mn;

[0009] Among them, 0.5≤x≤1.

[0010] In a possible implementation manner of the first aspect, in the A-site elements, the molar ratio of the Na element to the doping element X is 0.67:(0.005-0.05).

[0011] In a possible implementation of the first aspect, the B-site element further includes a doping element Y, and the doping element Y is selected from one or more of Ni, Cu, Mg, Al, and V.

[0012] In a possible implementation of the first aspect, in the B-site elements, the molar ratio of the doping element Y is less than or equal to 0.6.

[0013] In a possible embodiment of the first aspect, the chemical formula of the positive electrode material is Na 0.67 Ca z Fe a Co b Mn (1-a-b) O2, z is 0.005~0.05, a is 0~0.2, and b is 0~0.2.

[0014] In a second aspect, the present application provides a method for preparing a positive electrode material, comprising:

[0015] Take the raw materials containing A site element, B site element and O element, and use the sol-gel method to prepare the positive electrode material; the general formula of the positive electrode material is A x BO2; wherein the A site element includes Na and a doping element X, and the doping element X is selected from one or more of K, Ca, Fe, Mg and Li; the B site element includes Mn; wherein 0.5≤x≤1.

[0016] In a possible embodiment of the second aspect, the preparation raw materials comprising A-site elements, B-site elements and O elements include: one or more of the acetates, nitrates, sulfates and chlorides of each element in the A-site elements, and one or more of the acetates, nitrates, sulfates and chlorides of each element in the B-site elements.

[0017] In a possible implementation of the second aspect, the preparation material is prepared by a sol-gel method, including:

[0018] preparing a mixed solution from raw materials containing the A-site element, the B-site element, and the O element;

[0019] heating and stirring the mixed solution to prepare a gel;

[0020] drying and grinding the gel to obtain a precursor;

[0021] Pre-firing the precursor;

[0022] The pre-burned precursor is calcined and ground to obtain a positive electrode material.

[0023] In a possible implementation manner of the second aspect, the gel is dried at a temperature of 100 to 160° C. for 10 to 20 hours.

[0024] In a possible implementation manner of the second aspect, the pre-firing atmosphere is air or oxygen, the pre-firing temperature is 350-600° C., and the pre-firing time is 4-6 hours.

[0025] In a possible implementation manner of the second aspect, the calcination temperature is 800-980° C., and the calcination time is 15-18 hours.

[0026] In a third aspect, the present application provides a sodium ion battery, comprising:

[0027] The positive electrode sheet comprises the positive electrode material as described in the first aspect.

[0028] In the positive electrode material provided in the present application, since the doping element X is selected from one or more of K, Ca, Fe, Mg and Li, and the ions of these doping elements have similar ionic radii to sodium ions, the ions of these doping elements can be doped into the sodium ion site. The resulting positive electrode material can effectively inhibit the irreversible phase change of the sodium ion battery during the electric energy cycle. Moreover, through testing, it was found that the resulting positive electrode material, when applied to a sodium ion battery, can effectively inhibit the capacity decay of the sodium ion battery and improve the cycle stability and rate performance of the sodium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 XRD pattern of the positive electrode material provided in Example 1;

[0030] Figure 2 A scanning electron microscope image of the positive electrode material provided in Example 1;

[0031] Figure 3 This is a diagram of the first charge and discharge test of a battery prepared with the positive electrode material provided in Example 1;

[0032] Figure 4 This is a rate performance test diagram of a battery prepared with the positive electrode material provided in Example 1;

[0033] Figure 5 This is a test diagram of the cycle performance of a battery prepared with the positive electrode material provided in Example 1. DETAILED DESCRIPTION

[0034] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0036] The present application will be further described in detail below with reference to specific embodiments. The present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the present application's disclosure.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0038] In this application, "one or several" refers to any one, any two, or any two or more of the listed items. Among them, "several" refers to any two or any two or more.

[0039] In this application, the terms "combination thereof", "any combination thereof", "any combination thereof" and the like include all suitable combinations of any two or more of the listed items.

[0040] In this application, "preferred" is only used to describe an implementation method or example with better effects. It should be understood that it does not constitute a limitation on the scope of protection of this application.

[0041] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0042] In this application, when a numerical range is involved, unless otherwise specified, both endpoints of the numerical range are included.

[0043] In this application, when referring to percentage content, unless otherwise specified, for solid-liquid mixing and solid-solid mixing, it refers to mass percentage, and for liquid-liquid mixing, it refers to volume percentage.

[0044] In this application, references to percentage concentrations, unless otherwise specified, refer to final concentrations, which are the percentage of an added component in the system after the addition of that component.

[0045] In this application, when it comes to temperature parameters, unless otherwise specified, both constant temperature treatment and treatment within a certain temperature range are permitted. The constant temperature treatment allows the temperature to fluctuate within the precision range controlled by the instrument.

[0046] In view of the capacity decay problem caused by the irreversible phase transition of sodium ion battery cathode materials in the related art, the inventors of this application have sought a cathode material that is doped with an element at the Na element site. This element doping can effectively inhibit the structural phase transition of sodium ion batteries during the electrochemical cycle, thereby effectively suppressing the capacity decay problem of sodium ion batteries. The specific implementation method is described as follows:

[0047] Some embodiments of the present application provide a sodium ion battery cathode material, the general formula of which is A x BO2; wherein the A site element includes Na and a doping element X, and the doping element X is selected from one or more of K, Ca, Fe, Mg and Li; the B site element includes Mn; wherein 0.5≤x≤1.

[0048] Among them, since the doping element X is selected from one or more of K, Ca, Fe, Mg and Li, and these doping element ions have similar ionic radii to sodium ions, these ions can be doped into the sodium ion site, and the resulting positive electrode material can effectively inhibit the irreversible phase change of the sodium ion battery during the electric energy cycle. Moreover, through testing, it is found that when the resulting positive electrode material is applied to a sodium ion battery, it can effectively inhibit the capacity decay of the sodium ion battery and improve the cycle stability and rate performance of the sodium ion battery.

[0049] There is no specific limitation on the doping amount of the doping element X, as long as the introduction of the doping element X can effectively dope some sodium ion sites.

[0050] In some embodiments, the molar ratio of Na element to doping element X in the A-site elements is 0.67:(0.005-0.05).

[0051] In these embodiments, by controlling the molar ratio of the Na element to the doping element X within the above range, the occurrence of irreversible phase change of the sodium ion battery can be effectively suppressed while ensuring the sodium ion content in the sodium ion battery.

[0052] In some embodiments, the B-site element further includes a doping element Y, and the doping element Y is selected from one or more of Co, Fe, Ni, Cu, Mg, Al, and V.

[0053] In these embodiments, by doping the doping elements Y at the B site, the positive electrode material can be further prevented from undergoing irreversible phase change.

[0054] In some embodiments, the molar ratio of the doping element Y in the B-site elements is less than or equal to 0.6.

[0055] In these embodiments, by controlling the molar ratio of the doping element Y within the above range, the irreversible phase transition of the sodium ion battery can be effectively suppressed.

[0056] In some embodiments, the chemical formula of the positive electrode material is Na 0.67 Ca z Fe a Co b Mn (1-a-b) O2, z is 0.005-0.05, a is 0-0.2, and b is 0-0.2.

[0057] In some embodiments, the chemical formula of the positive electrode material is Na 0.67 Co 0.1 Fe 0.1 Mn 0.8 O2.

[0058] The present invention also provides a method for preparing a positive electrode material, comprising:

[0059] Take the raw materials containing A site element, B site element and O element, and use the sol-gel method to prepare the positive electrode material; the general formula of the positive electrode material is A x BO2; wherein the A site element includes Na and a doping element X, and the doping element X is selected from one or more of K, Ca, Fe, Mg and Li; the B site element includes Mn; wherein 0.5≤x≤1.

[0060] The sol-gel method involves dispersing raw materials in a solvent, generating reactive monomers through hydrolysis, which then polymerize to form a sol. The sol then ages to form a gel with a defined spatial structure. The desired material is then produced through drying and heat treatment.

[0061] In some embodiments, the preparation raw materials comprising A-site elements, B-site elements and O elements include: one or more of the acetates, nitrates, sulfates and chlorides of each element in the A-site elements, and one or more of the acetates, nitrates, sulfates and chlorides of each element in the B-site elements.

[0062] For example, taking the A-site elements including Na and doping element Ca, and the B-site elements including Mn and doping element Co as an example, the preparation raw materials containing the A-site elements, B-site elements and O elements can include: sodium acetate, calcium nitrate, manganese chloride and cobalt sulfate.

[0063] In some embodiments, the positive electrode material is prepared by a sol-gel method, comprising:

[0064] preparing a mixed solution from raw materials containing an A-site element, a B-site element, and an O element;

[0065] heating and stirring the mixed solution to prepare a gel;

[0066] drying and grinding the gel to obtain a precursor;

[0067] Pre-firing the precursor;

[0068] The pre-burned precursor is calcined and ground to obtain a positive electrode material.

[0069] In these embodiments, the mixed solution may be an aqueous solution. By pre-calcining the obtained precursor, the decomposition reaction in the precursor can be fully carried out, thereby reducing impurity ions in the positive electrode material and improving the purity of the oxide.

[0070] In some embodiments, the gel is dried at a temperature of 100 to 160° C. for 10 to 20 hours.

[0071] In some embodiments, the pre-firing atmosphere is air or oxygen, the pre-firing temperature is 350-600° C., and the pre-firing time is 4-6 hours.

[0072] In these embodiments, the positive electrode material can be fully oxidized, and the oxygen loss after sodium ion deintercalation can be suppressed, thereby reducing capacity fading.

[0073] In some embodiments, the heating rate of the pre-firing is 4-6° C. / min.

[0074] In some embodiments, the calcination temperature is 800-980° C., and the calcination time is 15-18 hours.

[0075] An embodiment of the present application further provides a sodium ion battery, comprising:

[0076] A positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the positive electrode sheet includes the positive electrode material as described above.

[0077] The positive electrode material can be prepared into a slurry and coated on an aluminum electrode or an aluminum alloy electrode, and then compacted to obtain the positive electrode sheet.

[0078] The technical effects of the sodium ion battery provided in the embodiment of the present application are basically the same as the technical effects of the positive electrode material provided in the embodiment of the present application, and will not be repeated here.

[0079] The above describes the specific implementation methods of the present application. In order to objectively illustrate the technical effects produced by the present application, the following examples and comparative examples will be used for description.

[0080] In the following examples and comparative examples, all raw materials can be purchased commercially, and in order to maintain the reliability of the experiments, the raw materials used in the following examples and comparative examples have the same physical and chemical parameters or have undergone the same treatment.

[0081] Comparative Example 1

[0082] Preparation of Na 0.67 MnO2 layered cathode materials

[0083] Step 1) Weigh a certain amount of manganese acetate, sodium acetate and citric acid into a beaker, add a certain amount of deionized water to dissolve, and stir in a water bath at 60° C. until the solution becomes gel-like.

[0084] Step 2) Place the obtained gel in a vacuum oven and bake at 120° C. for 15 h under vacuum to obtain a dry gel.

[0085] Step 3) After drying the dry gel, pour it into a mortar and grind it into powder, put it into a sintering boat and place it in a tube furnace. In an air atmosphere, raise the temperature of the tube furnace to 400°C at a heating rate of 5°C / min, pre-sinter at 400°C for 5h, then heat it to 900°C and keep it for 15h, and cool it to room temperature; grind the calcined material into powder to obtain Na 0.67 MnO2 layered cathode material.

[0086] Comparative Example 2

[0087] Preparation of Na 0.67 Fe 0.1 Mn 0.9 O2 layered cathode materials

[0088] Step 1) Weigh a certain amount of manganese acetate, ferric acetate, sodium acetate and citric acid into a beaker, add a certain amount of deionized water to dissolve, and stir in a water bath at 60° C. until the solution becomes gel-like.

[0089] Step 2) Place the obtained gel in a vacuum oven and bake at 120° C. for 15 h under vacuum to obtain a dry gel.

[0090] Step 3) Pour the dry gel into a mortar and grind it into powder, put it into a sintering boat and place it in a tube furnace. In an air atmosphere, raise the temperature of the tube furnace to 400°C at a heating rate of 5°C / min, pre-sinter at 400°C for 5h, then heat to 900°C and keep warm for 15h, and cool to room temperature; grind the calcined material into powder to obtain Na 0.67 Fe 0.1 Mn 0.9 O2 layered cathode material.

[0091] Comparative Example 3

[0092] Preparation of Na 0.67Co 0.1 Mn 0.9 O2 layered cathode materials

[0093] Step 1) Weigh a certain amount of manganese acetate, cobalt acetate, sodium acetate and citric acid into a beaker, add a certain amount of deionized water to dissolve, and stir in a water bath at 60° C. until the solution becomes gel-like.

[0094] Step 2) Place the obtained gel in a vacuum oven and bake at 120° C. for 15 h under vacuum to obtain a dry gel.

[0095] Step 3) Pour the dry gel into a mortar and grind it into powder, put it into a sintering boat and place it in a tube furnace. In an air atmosphere, raise the temperature of the tube furnace to 400°C at a heating rate of 5°C / min, pre-sinter at 400°C for 5h, then heat to 900°C and keep warm for 15h, and cool to room temperature; grind the calcined material into powder to obtain Na 0.67 Co 0.1 Mn 0.9 O2 layered cathode material.

[0096] Comparative Example 4

[0097] Preparation of Na 0.67 Co 0.1 Fe 0.1 Mn 0.8 O2 layered cathode materials

[0098] Step 1) Weigh a certain amount of manganese acetate, ferric acetate, cobalt acetate, sodium acetate and citric acid into a beaker, add a certain amount of deionized water to dissolve, and stir in a water bath at 60° C. until the solution becomes gel-like.

[0099] Step 2) Place the obtained gel in a vacuum oven and bake at 120° C. for 15 h under vacuum to obtain a dry gel.

[0100] Step 3) Pour the dry gel into a mortar and grind it into powder, put it into a sintering boat and place it in a tube furnace. In an air atmosphere, raise the temperature of the tube furnace to 400°C at a heating rate of 5°C / min, pre-sinter at 400°C for 5h, then heat to 900°C and keep warm for 15h, and cool to room temperature; grind the calcined material into powder to obtain Na 0.67 Co 0.1 Fe 0.1 Mn 0.8 O2 layered cathode material.

[0101] Example 1

[0102] Preparation of Na 0.67 Ca 0.005 Co 0.1 Fe 0.1 Mn 0.8O2 layered cathode materials

[0103] Step 1) Weigh a certain amount of manganese acetate, ferric acetate, cobalt acetate, sodium acetate, calcium acetate and citric acid into a beaker, add a certain amount of deionized water to dissolve, and stir in a water bath at 60° C. until the solution becomes gel-like.

[0104] Step 2) Place the obtained gel in a vacuum oven and bake at 120° C. for 15 h under vacuum to obtain a dry gel.

[0105] Step 3) Pour the dry gel into a mortar and grind it into powder, put it into a sintering boat and place it in a tube furnace. In an air atmosphere, raise the temperature of the tube furnace to 400°C at a heating rate of 5°C / min, pre-sinter at 400°C for 5h, then heat to 900°C and keep warm for 15h, and cool to room temperature; grind the calcined material into powder to obtain Na 0.67 Ca 0.005 Co 0.1 Fe 0.1 Mn 0.8 O2 layered cathode material.

[0106] Experimental example

[0107] 1. XRD analysis: The Na 0.67 Ca 0.005 Co 0.1 Fe 0.1 Mn 0.8 X-ray diffraction analysis of O2 layered cathode materials revealed Na 0.67 Ca 0.005 Co 0.1 Fe 0.1 Mn 0.8 The diffraction pattern of O2 layered cathode material is as follows Figure 1 shown.

[0108] 2. Morphology test: The Na 0.67 Ca 0.005 Co 0.1 Fe 0.1 Mn 0.8 The micromorphology of the O2 layered cathode material was characterized and the following results were obtained: Figure 2 The Na 0.67 Ca 0.005 Co 0.1 Fe 0.1 Mn 0.8 O2 microscopic morphology.

[0109] 3. Electrochemical performance test:

[0110] In the above embodiments and comparative examples, the electrochemical performance test of the button batteries was performed using a battery testing system.

[0111] The preparation process of button batteries is as follows:

[0112] Pole sheet preparation: The positive electrode material, the active material in the battery, is mixed with a binder and a conductive agent to form a slurry. The slurry is coated on aluminum foil and dried at 120°C for 12 hours. It is then stamped and formed using a pressure of 100 MPa to form the positive electrode sheet. The binder can be PVDF, and the conductive agent can be SP or KS-6. The solvent used in preparing the slurry can be NMP. The mass ratio of NMP, active material, binder, and conductive agent can be 85:5:5:5.

[0113] Battery Assembly: In an argon-filled glove box with a water and oxygen content of less than 5 ppm, assemble the positive electrode sheet, separator, negative electrode sheet, and electrolyte into a button-type battery and let it rest for 6 hours. The negative electrode sheet is a metal sodium sheet.

[0114] The charge and discharge voltage range was controlled at 1.5 to 4.3 V. At room temperature, the button battery was charged and discharged at a current density of 0.1 C to evaluate the first discharge specific capacity of the multi-electrode material.

[0115] Cycling performance test: Control the charge and discharge voltage range to 1.5-4.3V. At room temperature, the button battery is charged and discharged 100 times at 1C to evaluate the capacity retention rate of the positive electrode material.

[0116] Rate performance test: The charge and discharge voltage range is controlled at 1.5 to 4.3 V. At room temperature, the charge and discharge cycle is performed 20 times at a rate of 5C. The rate performance of the positive electrode material is evaluated with reference to the initial discharge specific capacity.

[0117] Test results:

[0118] 1. If Figure 1 As shown, the XRD analysis pattern of the positive electrode material provided in Example 1 is Figure 1 It can be seen that the positive electrode material has good crystallinity.

[0119] 2. If Figure 2 The figure shows a scanning electron microscope image of the positive electrode material provided in Example 1. Figure 2 It can be seen that the positive electrode material has relatively uniform particles, a high tap density, and the secondary particle size of the product is about 2 microns.

[0120] 3. The electrochemical performance test results of the batteries prepared with the positive electrode materials provided in the comparative examples and the examples are shown in Table 1 below. Figure 3 As shown in FIG. 1 , the first discharge specific capacity test result of the battery prepared with the positive electrode material provided in Example 1 is shown. Figure 4As shown, this is a rate performance diagram of a battery prepared with the positive electrode material provided in Example 1, as shown in FIG. Figure 5 As shown, this is a cycle performance diagram of a battery prepared using the positive electrode material provided in Example 1.

[0121] Table 1: Electrochemical performance of Example 1 and Comparative Examples 1-4

[0122]

[0123] Combined with Table 1 and Figure 3 As shown, the first discharge specific capacity of the positive electrode material provided in Example 1 is as high as 188 mAh / g.

[0124] Combined with Table 1 and Figure 4 As shown in Table 1, compared with Comparative Examples 1 to 4, the positive electrode material provided in Example 1 has better rate performance. Rate performance is directly related to the migration ability of sodium ions. Therefore, it can be concluded that the migration ability of sodium ions in the positive electrode material provided in Example 1 is better. In addition, since the larger the capacity released at high rate, the better the battery performance, and the larger the reversible capacity, the more conducive to maintaining battery performance and reducing capacity attenuation, the reversible specific capacity of the positive electrode materials provided in the comparative examples and examples at a rate of 5C is obtained from Tables 1 and Figure 4 It can be seen that compared with Comparative Examples 1 to 4, the reversible specific capacity of the positive electrode material provided in Example 1 can reach 55 mAh / g at a rate of 5C, indicating that the capacity attenuation of the positive electrode material provided in Example 1 is small and the cycle stability is good.

[0125] Combined with Table 1 and Figure 5 As shown, compared with Comparative Examples 1 to 4, the positive electrode material provided in Example 1 is charged and discharged at a current density of 1C, and when the number of cycles is 100, the specific capacity retention rate can reach 70%, and the coulombic efficiency can reach 100%, indicating that the positive electrode material provided in Example 1 has a high capacity retention rate, good cycle performance, small capacity attenuation, and good electrochemical performance.

[0126] In summary, by doping the sodium element sites, the cycle stability and rate performance of the positive electrode material can be effectively improved, the capacity attenuation can be reduced, and good conditions are provided for the application of sodium-ion batteries.

[0127] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0128] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may 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 patent application shall be determined by the appended claims.

Claims

1. A positive electrode material, characterized in that The general formula of the positive electrode material is Na 0.67 Ca z Fe a Co b Mn (1-a-b) O2, z is 0.005~0.05, a is 0~0.2, b is 0~0.2; Among them, the A-site elements include Na and doping element Ca; The B-site element includes Mn; the B-site element further includes a doping element Y, and the doping element Y is selected from Co and Fe.

2. A method for preparing a positive electrode material, characterized in that: include: Taking a preparation raw material containing an A-site element, a B-site element and an O element, and preparing the positive electrode material by a sol-gel method; The general formula of the positive electrode material is Na 0.67 Ca z Fe a Co b Mn (1-a-b) O2, z is 0.005~0.05, a is 0~0.2, b is 0~0.2; Among them, the A-site elements include Na and doping element Ca; The B-site element includes Mn; the B-site element further includes a doping element Y, and the doping element Y is selected from Co and Fe.

3. The method according to claim 2, characterized in that The preparation raw materials containing A-site elements, B-site elements and O elements include: one or more of the acetates, nitrates, sulfates and chlorides of each element in the A-site elements, and one or more of the acetates, nitrates, sulfates and chlorides of each element in the B-site elements.

4. The method according to claim 2, characterized in that The positive electrode material is prepared by a sol-gel method, comprising: preparing a mixed solution from raw materials containing the A-site element, the B-site element, and the O element; heating and stirring the mixed solution to prepare a gel; drying and grinding the gel to obtain a precursor; pre-firing the precursor; The pre-fired precursor is calcined and ground to obtain the positive electrode material.

5. The method according to claim 4, characterized in that The gel is dried at a temperature of 100-160° C. for 10-20 hours.

6. The method according to claim 4, characterized in that The pre-firing atmosphere is air or oxygen, the pre-firing temperature is 350-600° C., and the pre-firing time is 4-6 hours.

7. The method according to claim 4, characterized in that The calcination temperature is 800-980° C. and the calcination time is 15-18 hours.

8. A sodium ion battery, characterized in that: include: A positive electrode plate, comprising the positive electrode material according to claim 1.

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