CN118507707A - P2/T composite phase oxide sodium ion battery positive electrode material and preparation method thereof - Google Patents

Abstract

The present invention discloses a P2/T composite oxide sodium ion battery positive electrode material, the chemical formula of which is Na _0.6 Mn _{0.97- x} Mg _x Fe _0.03 O ₂ , wherein 0≤x≤0.06, and the positive electrode material has a P2/T dual-phase structure; the positive electrode material simultaneously presents two space groups: a P63/mmc space group and a Pbam space group. The present invention designs a P2/T intergrowth structure from a bulk phase scale to give full play to the advantages of each single-phase material, and has important research prospects. The present invention provides a new technical direction for solving the problem that single-phase positive electrode materials of sodium ion battery positive electrode materials are difficult to simultaneously achieve phase transition relief, excellent electrochemical performance and reaction kinetics. The present invention provides a sodium ion battery positive electrode material, which has the characteristics of high energy density and long cycle life due to the dual-phase synergistic effect of the P2 phase and the tunnel phase.

Description

A P2/T composite phase oxide sodium ion battery positive electrode material and preparation method thereof

Technical Field

The invention belongs to the technical field of sodium ion batteries and relates to a P2/T composite phase oxide sodium ion battery positive electrode material and a preparation method thereof.

Background Art

The rapid development of large-scale energy storage systems has effectively alleviated the increasingly serious global energy problems, but the market demand for sustainable and cost-effective energy storage systems is still increasing. At present, lithium-ion batteries have been widely used in large-scale energy storage fields such as portable electronics and electric vehicles. However, the rising cost and uneven distribution of lithium resources have limited the further development and application of lithium batteries in large-scale energy storage systems. Due to the wide distribution and low cost of sodium resources, rechargeable sodium-ion batteries have been regarded as one of the most attractive alternatives to lithium-ion batteries. However, many reasons limit the commercial development of sodium-ion batteries, such as slow Na ⁺ diffusion kinetics, low energy density and poor air stability.

Transition metal oxides stand out among many cathode candidate materials due to their advantages such as low price, easy synthesis, high specific capacity, and good ion transport performance. In manganese-based materials, the tunnel structure has abundant large zigzag tunnels, thus showing rate performance and cycle stability, but its effective Na content is low and its theoretical capacity is low. In contrast, P2-type materials have a high effective sodium content and show a higher initial capacity, but their irreversible phase change and Jahn-Teller distortion effect affect the cycle life of the material.

Among the existing technologies, the P2/O3 composite structure has made significant technological progress in the field of sodium ion battery positive electrodes. The P2/O3 and P3/P2 composite structures can obtain strong cycle stability and rate capability. However, their rate performance is still hindered by the narrow two-dimensional ion diffusion path. How to design and introduce a tunnel structure to further improve the rate performance. At the same time, there are also some technical difficulties in the design of composite phase materials, which hinder their large-scale production and application, such as how to control the cost effect by doping with cheap elements; how to regulate the bulk phase ratio to give full play to the synergistic effect of each phase.

Summary of the invention

The purpose of the present invention is to provide a Co-free and Ni-free P2/T composite phase sodium ion battery positive electrode material with long cycle life, high energy density, excellent rate performance and a preparation method thereof, so as to solve the problems in the prior art.

In order to achieve the above object, the present invention provides the following technical solutions:

The invention provides a P2/T composite oxide sodium ion battery positive electrode material, the chemical formula of which is Na _0.6 Mn _{0.97- x} Mg _x Fe _0.03 O ₂ , wherein 0≤x≤0.06, and the positive electrode material has a P2/T dual-phase structure.

Furthermore, the positive electrode material simultaneously presents two space groups: a P63/mmc space group and a Pbam space group.

The present invention also provides a method for preparing a P2/T composite phase oxide sodium ion battery positive electrode material, comprising the following steps:

(1) weighing a sodium source, a manganese source, a magnesium source, and an iron source according to a stoichiometric ratio to prepare a metal salt solution, adding a chelating agent to react at a set temperature to obtain a gel;

(2) drying the obtained gel and grinding it to obtain a precursor powder;

(3) calcining the obtained precursor powder at 400-500° C. for 6-24 hours to decompose and remove carbonic acid and acetic acid to obtain a primary calcined product;

(4) The primary calcined product is ground and pressed into tablets, and then calcined at 850-950°C for 6-24h, and the temperature is naturally cooled to room temperature _. The product is ground and sieved to obtain _{Na0.6Mn0.97 - xMgxFe0.03O2} positive _electrode material.

In order to make up for the loss of sodium during the sintering process, the sodium source is in excess of 3% to 5%.

In a preferred embodiment, in step (1), the sodium source is selected from one or more combinations of sodium carbonate, sodium nitrate, sodium oxalate, sodium citrate, and sodium acetate;

The manganese source is selected from one or more combinations of manganese acetate, manganese nitrate, manganese oxalate and manganese sulfate;

The magnesium source is selected from one or more combinations of magnesium acetate, magnesium nitrate, magnesium oxalate and magnesium carbonate;

The iron source is selected from one or more combinations of ferric acetate, ferric nitrate, ferric oxalate and ferric sulfate.

In a preferred embodiment, in step (1), the chelating agent is selected from one of citric acid, oxalic acid, tartaric acid or ethylenediaminetetraacetic acid, and the amount of the chelating agent added is 1 to 1.5 times the total molar amount of sodium, manganese, iron and magnesium.

In a preferred embodiment, in step (1), the molar ratio of manganese source: (magnesium source + iron source) is 10 to 32:1.

In a preferred embodiment, in step (1), a solution having a metal molar concentration of 2 to 10 mol/l is prepared.

In a preferred embodiment, in step (1), a chelating agent is added and the mixture is heated and stirred at 60 to 100° C. for 2 to 12 hours at a stirring rate of 200 to 400 r/min.

In a preferred embodiment, in step (2), the drying temperature is 80 to 120° C. and the drying time is 12 to 48 hours.

In a preferred embodiment, in step (3), the heating rate of the primary calcination is 1-5°C/min, the temperature is kept for 8-10 hours, and the sintering atmosphere is air.

In a preferred embodiment, in step (4), the tableting pressure is 12 to 20 MPa.

In a preferred embodiment, in step (4), the heating rate of the secondary calcination is 1 to 5°C/min, the sintering atmosphere is air, and the temperature is kept at 10 to 12 hours to obtain a P2/T composite oxide sodium ion battery positive electrode material.

The present invention designs a P2/T intergrowth structure from the bulk scale to give full play to the advantages of each single-phase material, and has important research prospects. The present invention provides a new technical direction for solving the problem that single-phase positive electrode materials of sodium ion batteries are difficult to achieve phase change relief, excellent electrochemical performance and reaction kinetics at the same time. The present invention provides a sodium ion battery positive electrode material, which has the characteristics of high energy density and long cycle life due to the dual-phase synergistic effect of the P2 phase and the tunnel phase. The preparation method of the positive electrode material disclosed in the present invention is simple and easy to operate, the raw materials are cheap and easy to obtain, it is suitable for large-scale batch production, and has good commercial application prospects.

Compared with the prior art, the beneficial technical effects of the present invention are:

(1) The present invention provides a P2/T mixed phase positive electrode material, which does not contain Co and Ni elements and is environmentally friendly. The synergistic effect of the dual-phase structure enables it to have excellent electrochemical properties. In the range of 2.0-4.0V, it has a high specific capacity of 160.25mAh g ^-1 at 0.2C (1C=200mA g ^-1 ); it exhibits a reversible capacity of 104mAh g ^-1 at 5C, and the capacity retention rate is as high as 81.4% after 200 cycles, with a long cycle life and excellent rate performance.

(2) The method for regulating the ratio of P2 phase and tunnel phase in the positive electrode material of a sodium ion battery provided by the present invention does not need to regulate the sodium content, and the ratio of P2 and tunnel phase is regulated by the method of iron-magnesium doping to obtain a preferred ratio. Among them, doping with Fe ³⁺ can inhibit the harmful P ₂ -O ₂ phase transition in the P ₂ type structure, smooth the charge and discharge curve, and promote the sodium ion dynamics. Doping with Mg ²⁺ plays a role of a nail pillar, which can stabilize the crystal structure during the sodium removal/sodium insertion process and effectively prolong the cycle life.

(3) The preparation process provided by the present invention is simple, has a short synthesis cycle, and the raw materials are readily available, which is suitable for large-scale batch production. It has bright application prospects and good practical value in the field of sodium ion batteries.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a SEM image of the Na _0.6 Mn _0.94 Mg _0.03 Fe _0.03 O ₂ positive electrode material obtained in Example 1 of the present invention.

FIG2 is an XRD refined spectrum of the Na _0.6 Mn _0.94 Mg _0.03 Fe _0.03 O ₂ positive electrode material obtained in Example 1 of the present invention.

Figure 3 is the XRD spectra of Example 1, Example 2, and Example 3 of the present invention. All diffraction peaks of the three samples can be attributed to a composite phase composed of a _P2 -type layered structure (P63/mmc space group, JCPDS27-0751) and a tunnel structure (Pbam space group, JCPDS27-0750).

FIG. 4 is a cyclic stability curve of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention at 1C.

FIG. 5 is a graph showing rate performance in the range of 0.2C to 15C for Example 1, Example 2, and Example 3 of the present invention.

DETAILED DESCRIPTION

The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

The present invention provides a P2/T composite oxide sodium ion battery cathode material, the chemical formula of which is Na _0.6 Mn _{0.97- x} Mg _x Fe _0.03 O ₂ , wherein 0≤x≤0.06, and the cathode material has a P2 and Tunnel two-phase mixed structure; the cathode material simultaneously presents two space groups: a P63/mmc space group and a Pbam space group.

The present invention also provides a method for preparing a P2/T composite phase oxide sodium ion battery positive electrode material, comprising the following steps:

(1) weighing a sodium source, a manganese source, a magnesium source, and an iron source according to a stoichiometric ratio to prepare a metal salt solution, adding a chelating agent to react at a set temperature to obtain a gel;

(2) drying the obtained gel and grinding it to obtain a precursor powder;

(3) calcining the obtained precursor powder at 400-500° C. for 6-24 hours to decompose and remove carbonic acid and acetic acid to obtain a primary calcined product;

(4) The primary calcined product is ground and pressed into tablets, and then calcined at 850-950°C for 6-24h, and the temperature is naturally cooled to room temperature _. The product is ground and sieved to obtain _{Na0.6Mn0.97 - xMgxFe0.03O2} positive _electrode material.

The prepared positive electrode material was ground and mixed with acetylene black and polyvinylidene fluoride in a ratio of 8:1:1, and a proper amount of N-methylpyrrolidone was added to uniformly mix the slurry. The slurry was coated on aluminum foil and finally dried and rolled to obtain a positive electrode sheet. The active material loading was 2-3.5 mg·cm ^-2 .

The prepared positive electrode sheet, separator, organic electrolyte and metallic sodium are assembled into a sodium ion battery in an inert argon atmosphere with a water oxygen value lower than 0.1ppm. The prepared positive electrode sheet and metallic sodium sheet are used as the positive electrode and negative electrode respectively. The separator is a porous glass carbon fiber membrane, and the organic electrolyte is a 1M _NaClO4 solution of ethyl carbonate (EC): diethyl carbonate (DEC) (1:1) + fluoroethylene carbonate (FEC 5%).

Unless otherwise specified, the reagents used in this embodiment are all common commercial products or prepared by conventional means, and the equipment used are all conventional equipment in the art. The following are some embodiments of the inventor's experiments:

Example 1

A method for preparing a P2/T composite phase oxide sodium ion battery positive electrode material comprises the following steps:

Step (1), according to the atomic percentage of Na _0.6 Mn _0.94 Mg _0.03 Fe _0.03 O ₂ to prepare the positive electrode material, weigh sodium carbonate, manganese acetate tetrahydrate, magnesium acetate tetrahydrate, ferric nitrate nonahydrate, and anhydrous citric acid, dissolve in deionized water to prepare a solution with a concentration of 2.5 mol/L, place on a magnetic stirrer and mix thoroughly for 1 hour to make the raw materials mixed evenly.

Step (2), placing the uniform solution in an oil bath at 80° C. and stirring and heating at a stirring speed of 400 rpm/min for 8 h until the water is completely evaporated, thereby obtaining a gel.

Step (3), drying the obtained gel in a vacuum oven at 120° C. for 24 h to further remove moisture.

Step (4), grinding the solid obtained above into powder, heating it to 400°C at a heating rate of 5°C/min in an air atmosphere in a muffle furnace and keeping it warm for 10 hours, slowly cooling it to room temperature, grinding the obtained precursor into powder and pressing it into tablets at 15MPa, and then keeping it warm at 900°C in an air atmosphere for 10 hours to obtain the final sample, and then grinding and sieving to obtain

Na _0.6 Mn _0.94 Mg _0.03 Fe _0.03 O ₂ positive electrode material.

Example 2

A method for preparing a P2/T composite phase oxide sodium ion battery positive electrode material comprises the following steps:

Step (1), according to the atomic percentage of Na _0.6 Mn _0.94 Mg _0.03 Fe _0.03 O ₂ to prepare the positive electrode material, weigh sodium carbonate, manganese acetate tetrahydrate, magnesium acetate tetrahydrate, ferric nitrate nonahydrate, and anhydrous citric acid, dissolve in deionized water to prepare a solution with a concentration of 2.5 mol/L, place on a magnetic stirrer and mix thoroughly for 1 hour to make the raw materials mixed evenly.

Step (2), placing the uniform solution in an oil bath at 80° C. and stirring and heating at a stirring speed of 400 rpm/min for 8 h until the water is completely evaporated, thereby obtaining a gel.

Step (3), drying the obtained gel in a vacuum oven at 120° C. for 24 h to further remove moisture.

Step (4), grinding the solid obtained above into powder, heating it to 400°C at a heating rate of 5°C/min in an air atmosphere in a muffle furnace and keeping it warm for 10 hours, slowly cooling it to room temperature, grinding the obtained precursor into powder and pressing it into tablets at 15 MPa, and then keeping it warm at 850°C in an air atmosphere for 10 hours to obtain the final sample, and after grinding and sieving, obtaining Na _0.6 Mn _0.96 Mg _0.03 Fe _0.03 O ₂ positive electrode material.

Example 3

A method for preparing a P2/T composite phase oxide sodium ion battery positive electrode material comprises the following steps:

Step (1), according to the atomic percentage of Na _0.6 Mn _0.94 Mg _0.03 Fe _0.03 O ₂ to prepare the positive electrode material, weigh sodium carbonate, manganese acetate tetrahydrate, magnesium acetate tetrahydrate, ferric nitrate nonahydrate, and anhydrous citric acid, dissolve in deionized water to prepare a solution with a concentration of 2.5 mol/L, place on a magnetic stirrer and mix thoroughly for 1 hour to make the raw materials mixed evenly.

Step (2), placing the uniform solution in an oil bath at 80° C. and stirring and heating at a stirring speed of 400 rpm/min for 8 h until the water is completely evaporated, thereby obtaining a gel.

Step (3), drying the obtained gel in a vacuum oven at 120° C. for 24 h to further remove moisture.

Step (4), grinding the solid obtained above into powder, heating it to 400°C at a heating rate of 5°C/min in an air atmosphere in a muffle furnace and keeping it warm for 10 hours, slowly cooling it to room temperature, grinding the obtained precursor into powder and pressing it into tablets at 15 MPa, and then keeping it warm at 950°C in an air atmosphere for 10 hours to obtain the final sample, and after grinding and sieving, obtaining Na _0.6 Mn _0.93 Mg _0.03 Fe _0.03 O ₂ positive electrode material.

Comparative Example 1

Step (1) According to the atomic percentage of Na _0.6 Mn _0.97 Fe _0.03 O ₂ of the positive electrode material to be prepared, sodium carbonate, manganese acetate tetrahydrate, magnesium acetate tetrahydrate, ferric nitrate nonahydrate, and anhydrous citric acid were weighed and dissolved in deionized water to prepare a solution with a concentration of 2 mol/L. The solution was placed on a magnetic stirrer and fully mixed for 1 hour to ensure that the raw materials were mixed evenly.

Step (2) placing the uniform solution in an oil bath at 80° C. and stirring and heating at a stirring speed of 400 rpm/min for 8 h until the water is completely evaporated to obtain a gel.

Step (3) Dry the obtained gel in a vacuum oven at 120° C. for 24 h to further remove moisture.

Step (4) The solid obtained above is ground into powder, heated to 400°C at a heating rate of 5°C/min in an air atmosphere in a muffle furnace and kept warm for 10 hours. After slowly cooling to room temperature, the obtained precursor is ground into powder and pressed into tablets at 12 MPa, and then placed in an air atmosphere at 900°C for 10 hours to obtain the final sample. After grinding and sieving, Na _0.6 Mn _0.97 Fe _0.03 O ₂ positive electrode material is obtained.

Comparative Example 2

Step (1) According to the atomic percentage of Na _0.6 Mn _0.96 Mg _0.01 Fe _0.03 O ₂ of the positive electrode material to be prepared, sodium carbonate, manganese acetate tetrahydrate, magnesium acetate tetrahydrate, ferric nitrate nonahydrate, and anhydrous citric acid are weighed and dissolved in deionized water to prepare a solution with a concentration of 2 mol/L, and the solution is placed on a magnetic stirrer and fully mixed for 1 hour to ensure that the raw materials are evenly mixed.

Step (2) placing the uniform solution in an oil bath at 80° C. and stirring and heating at a stirring speed of 400 rpm/min for 8 h until the water is completely evaporated to obtain a gel.

Step (3) Dry the obtained gel in a vacuum oven at 120° C. for 24 h to further remove moisture.

Step (4) The solid obtained above was ground into powder, heated to 400°C at a heating rate of 5°C/min in an air atmosphere in a muffle furnace and kept warm for 10 hours. After slowly cooling to room temperature, the obtained precursor was ground into powder and pressed into tablets at 17 MPa, and then placed in an air atmosphere at 900°C for 10 hours to obtain the final sample. After grinding and sieving, Na _0.6 Mn _0.96 Mg _0.01 Fe _0.03 O ₂ positive electrode material was obtained.

Comparative Example 3

Step (1) According to the atomic percentage of Na _0.6 Mn _0.91 Mg _0.06 Fe _0.03 O ₂ of the positive electrode material to be prepared, sodium carbonate, manganese acetate tetrahydrate, magnesium acetate tetrahydrate, ferric nitrate nonahydrate, and anhydrous citric acid are weighed and dissolved in deionized water to prepare a solution with a concentration of 2 mol/L, and the solution is placed on a magnetic stirrer and fully mixed for 1 hour to ensure that the raw materials are evenly mixed.

Step (2) placing the uniform solution in an oil bath at 80° C. and stirring and heating at a stirring speed of 400 rpm/min for 8 h until the water is completely evaporated to obtain a gel.

Step (3) Dry the obtained gel in a vacuum oven at 120° C. for 24 h to further remove moisture.

Step (4) The solid obtained above is ground into powder, heated to 400°C at a heating rate of 5°C/min in an air atmosphere in a muffle furnace and kept warm for 10 hours. After slowly cooling to room temperature, the obtained precursor is ground into powder and pressed into tablets at 17 MPa, and then placed in an air atmosphere at 900°C for 10 hours to obtain the final sample. After grinding and sieving, Na _0.6 Mn _0.91 Mg _0.06 Fe _0.03 O ₂ positive electrode material is obtained.

The sodium ion battery positive electrode materials obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were respectively used as active materials, ground and mixed according to the mass ratio of active material: acetylene black: polyvinylidene fluoride (PVDF) of 8:1:1, and the solvent N-methylpyrrolidone was added dropwise to grind into slurry, which was evenly coated on aluminum foil. Dry in a vacuum drying oven at 80°C for 12 hours, and use a sheet punching machine to make a disc electrode with a diameter of 14 mm for standby use.

Using metallic sodium as the negative electrode, porous glass carbon fiber membrane as the separator, and 1M NaClO4 solution of ethyl carbonate (EC): diethyl carbonate (DEC) (1:1) + fluoroethylene carbonate (FEC 5%) as the electrolyte, 2016 button cells were assembled in a glove box with a water oxygen value of <0.1ppm and an argon atmosphere. The battery was tested in the voltage range of 2.0-4.0V, and the electrochemical cycle performance was tested at 1C=200mAg ^-1 , 0.2C, 0.5C, 1C, 2C, 5C, 10C, 15C, and 0.5C, as shown in Table 1.

Table 1

By comparing Examples 1 to 3, it can be seen that the change in sintering temperature will affect the ratio of the P2 phase to the tunnel phase, and thus affect the electrochemical properties of the material. When the sintering temperature is low, the P2 phase tends to be formed, and the reversible specific capacity is significantly improved. When the sintering temperature is high, it is more conducive to the formation of a tunnel type, thereby improving the structural stability and cycle life.

By comparing and analyzing Examples 1 to 3, it can be seen that the 1C capacity retention rate of the materials described in Examples 1 to 3 of the present invention remains at about 80% after 200 cycles, and the 1C first discharge capacity remains at 117.4 to 138.3 mAh/g. The discharge capacity of the 5C discharge rate performance remains at 81.6 to 97.8 mAh/g. This shows that the series of P2/T composite oxide materials described in this invention all exhibit a dual-phase synergistic effect, with high specific capacity, excellent cycle stability and good rate performance.

By comparing and analyzing Example 1 and Comparative Examples 1-3, it can be seen that the sample without magnesium doping has poor cycle stability, and the capacity retention rate after 200 cycles at 1C is only 65.1%. The reasonable introduction of magnesium elements in the layered tunnel structure can not only adjust the phase ratio composition, but also improve the structural stability. However, the amount of magnesium doping is not the more the better, such as the first charge and discharge specific capacity of Comparative Example 3 is reduced to 117.6mAh/g. This is because when too much inactive magnesium elements are doped, it will be unfavorable to the improvement of the reversible specific capacity and the phase structure of the material will completely tend to the P2 phase, and the excellent cycle stability and rate performance of the tunnel type will also be lost.

FIG1 is a SEM image of the Na _0.6 Mn _0.94 Mg _0.03 Fe _0.03 O ₂ cathode material obtained in Example 1 of the present invention, and the morphology shows hexagonal flakes and rod-like particles, which belong to the P2 layered structure and tunnel structure, respectively.

FIG2 is an XRD refinement spectrum of the Na _0.6 Mn _0.94 Mg _0.03 Fe _0.03 O ₂ cathode material obtained in Example 1 of the present invention. The refinement results show that the material has good crystallinity, and the proportions of the lamellar phase and the tunnel phase are 96% and 4%, respectively.

Figure 3 is the XRD spectra of Example 1, Example 2, and Example 3 of the present invention. All diffraction peaks of the three samples can be attributed to the P2-type layered structure (P63/mmc space group, JCPDS27-0751) and the tunnel structure (Pbam space group, JCPDS27-0750), which further proves the successful synthesis of the composite structure.

Figure 4 is the cycle stability curves of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 at 1C. In the voltage range of 2.0-4.0V, the first discharge capacity of Example 1 is 138.3mAh g ^-1 , and the capacity retention rate after 200 cycles is as high as 81.4%, showing excellent cycle stability.

Figure 5 is a rate performance diagram of Example 1, Example 2, and Example 3 of the present invention in the range of 0.2C to 15C. Example 1 has excellent rate performance, with high reversible capacities of 167.9, 143.9, 130.1, 115.1, 97.8, 81.0, and 68.3 mAh g ^-1 at 0.2C, 0.5C, 1C, 2C, 5C, 10C, and 15C.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims (10)

1. The P2/T composite phase oxide sodium ion battery positive electrode material is characterized in that the chemical formula is Na _0.6Mn_{0.97- x}Mg_xFe_0.03O₂, wherein x is more than or equal to 0 and less than or equal to 0.06, and the positive electrode material has a P2/T double-phase structure; the positive electrode material simultaneously presents two space groups: p63/mmc space group and Pbam space group.

2. The preparation method of the P2/T composite phase oxide sodium ion battery anode material is characterized by comprising the following steps:

(1) Weighing a sodium source, a manganese source, a magnesium source and an iron source according to stoichiometric ratio, preparing a metal salt solution, adding a chelating agent, and reacting at a set temperature to obtain gel;

(2) Drying the gel, and grinding to obtain precursor powder;

(3) Calcining the obtained precursor powder at 400-500 ℃ for 6-24 h to obtain a primary calcined product;

(4) Grinding the primary calcined product, tabletting, roasting at 850-950 ℃ for 6-24 hours, cooling, grinding and sieving the obtained product, and obtaining the Na _0.6Mn_0.97-xMg_xFe_0.03O₂ anode material.

3. The method for preparing the P2/T composite phase oxide sodium ion battery positive electrode material according to claim 2, wherein the excess of the sodium source is 3% -5%;

In the step (1), the sodium source is selected from one or more of sodium carbonate, sodium nitrate, sodium oxalate, sodium citrate and sodium acetate;

The manganese source is selected from one or a plurality of combinations of manganese acetate, manganese nitrate, manganese oxalate and manganese sulfate;

The magnesium source is selected from one or more of magnesium acetate, magnesium nitrate, magnesium oxalate and magnesium carbonate;

the iron source is selected from one or more of ferric acetate, ferric nitrate, ferric oxalate and ferric sulfate.

4. The method for preparing the positive electrode material of the P2/T composite phase oxide sodium ion battery according to claim 2, wherein in the step (1), the chelating agent is selected from one of citric acid, oxalic acid, tartaric acid and ethylenediamine tetraacetic acid, and the adding amount of the chelating agent is 1-1.5 times of the molar total amount of sodium, manganese, iron and magnesium.

5. The method for preparing a positive electrode material of a P2/T composite phase oxide sodium ion battery according to claim 2, wherein in the step (1), the manganese source: the molar ratio of the magnesium source to the iron source is 10-32: 1.

6. The method for preparing a positive electrode material of a P2/T composite phase oxide sodium ion battery according to claim 2, wherein in the step (1), a solution with a metal molar concentration of 2-10 mol/l is prepared; adding chelating agent, heating and stirring for 2-12 h at 60-100 ℃, and stirring at the speed of 200-400 r/min.

7. The method for preparing the positive electrode material of the P2/T composite phase oxide sodium ion battery according to claim 2, wherein in the step (2), the drying temperature is 80-120 ℃ and the drying time is 12-48 h.

8. The preparation method of the P2/T composite phase oxide sodium ion battery positive electrode material according to claim 2, wherein in the step (3), the temperature rising rate of primary calcination is 1-5 ℃/min, the temperature is kept for 8-10 h, and the sintering atmosphere is air.

9. The method for preparing the positive electrode material of the P2/T composite phase oxide sodium ion battery according to claim 2, wherein in the step (4), the tabletting pressure is 12-20 MPa.

10. The preparation method of the P2/T composite phase oxide sodium ion battery positive electrode material according to claim 2 is characterized in that in the step (4), the temperature rising rate of secondary calcination is 1-5 ℃/min, the sintering atmosphere is air, and the temperature is kept for 10-12 h, so that the P2/T composite phase oxide sodium ion battery positive electrode material is obtained.