A layered oxide precursor and its synthesis method, and a sodium-ion cathode material.

Abstract

This invention discloses a method for synthesizing a layered oxide precursor for sodium-ion cathode materials, comprising the following steps: mixing a soluble metal salt and sodium hydroxide for reaction; adding an oxidant during the reaction; adding more oxidant after the reaction is complete; separating the precipitate; and washing and drying to obtain the layered oxide precursor; wherein the soluble metal salt contains a manganese salt; adding an oxidant during the reaction ensures that manganese is oxidized to manganese oxide, and part of the manganese dioxide in the manganese oxide reacts with sodium hydroxide to form sodium manganate, and sodium manganate and manganese dioxide co-precipitate in the layered oxide precursor. This invention also provides a layered oxide precursor and a sodium-ion cathode material. By adding an oxidant during the co-precipitation process, this invention can pre-incorporate a portion of sodium, making the sodium mixture more uniform and improving the material's capacity and cycle performance. Furthermore, this method has a simple synthesis process, is environmentally friendly, uses readily available materials, and is easily scalable for mass production.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, and particularly relates to a cathode material precursor and its synthesis method, as well as the cathode material. Background Technology

[0002] With the continuous expansion of the electric vehicle market, the demand for lithium-ion batteries has surged. However, global lithium reserves are limited, and resource bottlenecks are gradually emerging. This leads to cyclical fluctuations in lithium salt supply and demand, negatively impacting the operations of battery companies and OEMs. Sodium and lithium belong to the same group and share many similar physicochemical properties, which determines the potential for sodium-ion battery development. Compared to lithium-ion batteries, sodium-ion batteries have two major advantages: first, lower raw material costs, as they do not use expensive rare metals such as lithium and cobalt. Sodium's greatest advantage is its abundance in resources like seawater, making it an inexhaustible element; second, existing production processes can be utilized. The working mechanism of sodium-ion batteries is the same as that of lithium-ion batteries, and existing production equipment of battery companies can be directly used to produce sodium-ion batteries. Because minimal equipment investment is required, companies can easily use them as an alternative battery. However, one of the main factors limiting the industrialization of sodium-ion batteries is the sodium-ion cathode material.

[0003] Sodium-ion cathode materials mainly include transition metal oxides, Prussian blue analogues, polyanionic compounds, and amorphous materials. x MA[MB(CN)6]zH2O (MA and MB are transition metal ions), with a face-centered cubic crystal structure, forms a six-coordinate system with the transition metal ions and cyanide ions, while the alkali metal ions occupy three-dimensional channels and coordination vacancies, exhibiting good electrochemical stability, low cost, and good stability. However, Prussian blue compounds are hygroscopic, making it difficult to remove the water of crystallization during manufacturing. They are also susceptible to moisture absorption during storage and use, leading to decreased chemical stability and a reduced number of charge-discharge cycles. Furthermore, Prussian blue cathode materials have a narrow operating temperature range, between -20℃ and 40℃, which restricts their industrialization. Polyanionic compounds Na... x M[(XO m ) n- ] z(M represents a metal ion with variable valence; X represents elements such as P, S, and V) They are mainly divided into olivine-structured phosphates, NASCIOM (sodium ion fast ion conductor) compounds, and phosphate compounds. They have good thermal stability and cycle life, but their low electronic conductivity leads to poor rate performance, severely restricting their commercialization. Amorphous materials, also called amorphous or glassy materials, are solids in which atoms are not arranged in a specific spatial order. This lack of atomic arrangement manifests as long-range disorder and short-range order, resulting in good cycle performance and energy density, but low conductivity, poor stability, and poor acid and alkali resistance. Transition metal oxides can be divided into layered and tunnel-like transition metal oxides, commonly represented by Na... x MO2 (M = Co, Fe, Ni, Mn, etc.) indicates that layered oxides have a high theoretical capacity and are easy to synthesize, making them one of the most promising cathode materials for sodium-ion batteries. However, the energy density of the cycle stability of layered oxide cathode materials needs to be improved.

[0004] Therefore, improving the cycle stability and increasing the energy density of layered oxide cathode materials is an urgent problem to be solved. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a method for synthesizing a layered oxide precursor of a sodium-ion cathode material with high capacity and excellent cycle performance, the layered oxide precursor of the sodium-ion cathode material, and the sodium-ion cathode material itself. To solve the above technical problem, the technical solution proposed by this invention is as follows:

[0006] A method for synthesizing a layered oxide precursor for a sodium ion cathode material includes the following steps: mixing a soluble metal salt and sodium hydroxide for reaction, adding an oxidant during the reaction, adding another oxidant after the reaction is complete, separating the precipitate, washing and drying to obtain the layered oxide precursor; wherein the soluble metal salt contains a manganese salt;

[0007] During the reaction, an oxidizing agent is added to ensure that manganese is oxidized to manganese oxide (almost all manganese is oxidized and does not exist in the form of manganese hydroxide), and some of the manganese dioxide in the manganese oxide reacts with sodium hydroxide to form sodium manganate. Sodium manganate and manganese dioxide co-precipitate in the layered oxide precursor.

[0008] In the above synthesis method, preferably, adding an oxidant during the reaction means adding the oxidant and sodium hydroxide simultaneously, or adding the oxidant before sodium hydroxide, to ensure that manganese is oxidized to manganese oxide.

[0009] In the above synthesis method, preferably, sodium manganate is present in the layered oxide precursor so that the layered oxide precursor is pre-doped with sodium ions, and the doping amount of sodium ions is controlled so that the mass percentage of sodium in the layered oxide precursor is more than 0.5%.

[0010] In the above synthesis method, preferably, the layered oxide precursor is a spherical manganese iron oxide precursor with the chemical formula (Na₂O₃). x Fe y Mn z N 1-x-y-z )2O3, where 0 < x < 0.2, 0.1 < y < 0.5, 0.1 < z < 0.5, and N is a dopant element, which is one or more of Zn, Ni, and Cu.

[0011] In the above synthesis method, preferably, the soluble metal salt is at least one of sulfate, nitrate and hydrochloride, the soluble metal salt is a divalent metal salt, and the total concentration of divalent ions is controlled at 20-300 g / L.

[0012] In the above synthesis method, preferably, a complexing agent is added during the mixing reaction. The complexing agent includes at least one of Span, OP-10, sodium dodecyl sulfate, ammonium fluoride, ammonium chloride, ammonium sulfate, ammonium nitrate, sodium fluoride, ethanol, ethylene glycol, isopropanol, n-butanol, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetic acid, carboxymethyl cellulose, sodium carboxymethyl cellulose, and polyvinyl alcohol.

[0013] In the above synthesis method, preferably, the concentration of sodium hydroxide is controlled at 50-200 g / L, and the amount of sodium hydroxide added ensures that the pH value of the reaction solution is 10.5-13.5. In this invention, sodium hydroxide is used as a pH adjuster and a sodium dopant, and its amount should not be excessive.

[0014] In the above synthesis method, preferably, the oxidant includes at least one of hydrogen peroxide, oxygen, ammonium persulfate and sodium thiosulfate. After the reaction is completed, an oxidant is added to ensure that manganese oxide exists in the form of manganese dioxide.

[0015] In the above synthesis method, preferably, the reaction temperature is controlled at 40-80℃ during the mixed reaction.

[0016] As a general technical concept, the present invention also provides a layered oxide precursor obtained by the above-described synthesis method, wherein the layered oxide precursor is spherical and has a tap density of 0.5-2 g / cm³. 3 The particle size D50 is 3-12μm.

[0017] As a general technical concept, the present invention also provides a sodium ion cathode material, which is obtained by calcining the above-mentioned layered oxide precursor with a sodium source.

[0018] The specific synthesis process described above may include the following steps:

[0019] (1) Prepare a 20-300 g / L solution of soluble divalent manganese salt and iron salt (if doping is required, prepare an aqueous mixed solution of one or more soluble salts of the target content of copper, zinc, nickel and other elements and add them in);

[0020] (2) Add a complexing agent to the solution obtained in step (1) to obtain a mixed solution; adding a complexing agent can improve the surface morphology of the precursor;

[0021] (3) Prepare an aqueous solution of sodium hydroxide;

[0022] (4) Under stirring conditions, add the mixed solution in step (2) above to the reaction vessel, add oxidant to make the reaction system oxidized, then add the sodium hydroxide solution in step (3) to the reaction vessel, control the reaction temperature to 40-80℃, control the feeding rate to make the pH value of the reaction solution 10.5-13.5, carry out co-precipitation reaction, after the reaction is completed, continue to pass oxidant into the precipitate for more than half an hour to ensure that manganese is completely oxidized to manganese dioxide;

[0023] (5) Separate the reaction products obtained in step (4), then wash the separated precipitate, and then dry it to obtain spherical manganese iron oxide.

[0024] To address the issue that the energy density of the layered oxide precursor for sodium-ion cathode materials needs improvement in terms of cycle stability, this invention provides a method for synthesizing a layered oxide precursor for sodium-ion cathode materials. The precursor synthesized by this method has the chemical formula (Na... x Fe y Mn z N 1-x-y-z The formula is 2O3, where 0 < x < 0.2, 0.1 < y < 0.5, 0.1 < z < 0.5, and N is a dopant element, which is one or more of Zn, Ni, and Cu. This method involves adding an oxidant during the synthesis of the precursor material and controlling the oxidant addition conditions and pH value to oxidize manganese into manganese oxide (mainly manganese tetroxide, containing manganese dioxide and manganese trioxide) precipitate. Some of the manganese dioxide then reacts with sodium hydroxide to form sodium manganate. The co-precipitation of manganese dioxide and sodium manganate allows for the pre-incorporation of some sodium, resulting in more uniform sodium mixing. Subsequent oxidant introduction ensures that almost all manganese oxide is converted to manganese dioxide. After subsequent sodium-mixed calcination, the sodium distribution in the cathode material is more uniform, improving the material's capacity and cycle performance. This method has a simple synthesis process, is environmentally friendly, uses readily available materials, and is easily scalable for large-scale production.

[0025] Compared with the prior art, the advantages of the present invention are as follows:

[0026] The method for synthesizing the layered oxide precursor of the sodium-ion cathode material of the present invention allows for the pre-doping of a portion of sodium element by adding an oxidant during the co-precipitation process, resulting in more uniform sodium mixing and improved material capacity and cycle performance. Furthermore, this method features a simple synthesis process, is environmentally friendly, uses readily available materials, and is easily scalable for mass production. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The image shows the SEM images of the manganese iron oxide obtained in Example 1 (a) and (b) represent different magnifications).

[0029] Figure 2 SEM images of the manganese iron copper oxide obtained in Example 2 (in the figure (a) and (b) represent different magnifications).

[0030] Figure 3 SEM images of the manganese iron nickel oxide obtained in Example 3 (in the figure, (a) and (b) represent different magnifications).

[0031] Figure 4 SEM images of the manganese iron nickel copper oxide obtained in Example 4 (in the figure, (a) and (b) represent different magnifications).

[0032] Figure 5 SEM images of the manganese iron nickel copper oxide obtained in Example 5 (in the figure, (a) and (b) represent different magnifications).

[0033] Figure 6 SEM images of the manganese iron nickel hydroxide obtained in Comparative Example 1 (in the figure, (a) and (b) represent different magnifications).

[0034] Figure 7 The image shows the SEM images of the manganese iron oxide obtained in Comparative Example 2 (a) and (b) represent different magnifications).

[0035] Figure 8 This is a SEM image of the metal layered oxide cathode material obtained in Example 1.

[0036] Figure 9 This is a SEM image of the metal layered oxide cathode material obtained in Example 2.

[0037] Figure 10 This is a SEM image of the metal layered oxide cathode material obtained in Example 3.

[0038] Figure 11 This is a SEM image of the metal layered oxide cathode material obtained in Example 4.

[0039] Figure 12 This is a SEM image of the metal layered oxide cathode material obtained in Example 5. Detailed Implementation

[0040] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0041] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0042] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0043] Example 1:

[0044] A method for synthesizing a layered oxide precursor for a sodium-ion cathode material includes the following steps:

[0045] (1) Prepare 30L of 80g / L metal sulfate solution (Mn 2+ 50g / L, Fe 2+ Add 3g of ammonium sulfate (30g / L) and mix well;

[0046] (2) Prepare a 60 g / L sodium hydroxide solution;

[0047] (3) The obtained mixed solution of metal sulfate was added to a 20L stirred reactor using a peristaltic pump. Sufficient oxygen was added to provide an oxidation environment. Sodium hydroxide was added, and the reaction temperature was controlled at 45℃. The pH of the reaction solution was 11.0. The product was discharged from the overflow port at the top of the reactor. After the solution was added, oxygen was continued to be introduced for oxidation for half an hour. The product at the bottom of the reactor was taken, and after sedimentation and separation, it was washed with pure water until the pH value was about 7.2. Then the precipitate was dried in an oven at 120℃ to obtain manganese iron oxide.

[0048] The analytical results of the manganese iron oxides obtained in this embodiment are shown in Table 1 below, and the electron micrographs are as follows. Figure 1 As shown in the figure, this embodiment yielded a smooth, spherical manganese iron oxide.

[0049] Example 2:

[0050] A method for synthesizing a layered oxide precursor for a sodium-ion cathode material includes the following steps:

[0051] (1) Prepare 30L of a 120g / L metal sulfate solution (Mn 2+ 75g / L, Fe 2+ 30g / L, Cu 2+ Add 2g / L of EDTA to 15g / L of the solution and mix well.

[0052] (2) Prepare a 100 g / L sodium hydroxide solution;

[0053] (3) The obtained mixed solution of metal sulfate was added to a 20L stirred reactor using a peristaltic pump. Sufficient oxygen was added to provide an oxidation environment. Sodium hydroxide was added, and the reaction temperature was controlled at 45℃. The pH of the reaction solution was 10.5. The product was discharged from the overflow port at the top of the reactor. After the solution was added, oxygen was continued to be introduced for half an hour. The product at the bottom of the reactor was taken, and after sedimentation and separation, it was washed with pure water until the pH value was about 7.2. Then the precipitate was dried in an oven at 120℃ to obtain manganese iron copper oxide.

[0054] The analytical results of the manganese-iron-copper oxides obtained in this embodiment are shown in Table 1 below, and the electron micrographs are as follows. Figure 2 As shown in the figure, this embodiment yielded spherical manganese-iron-copper oxide with a single-layer ion-layered upward movement.

[0055] Example 3:

[0056] A method for synthesizing a layered oxide precursor for a sodium-ion cathode material includes the following steps:

[0057] (1) Prepare 30L of a 240g / L metal sulfate solution (Mn 2+ 120g / L, Fe 2+ 60g / L, Ni 2+ Add 2g / L of ethanol to 60g / L of water and mix well.

[0058] (2) Prepare a 200 g / L sodium hydroxide solution;

[0059] (3) The obtained mixed solution of metal sulfate was added to a 20L stirred reactor using a peristaltic pump. Sufficient oxygen was added to provide an oxidation environment. Sodium hydroxide was added, and the reaction temperature was controlled at 55℃. The pH of the reaction solution was 11.5. The product was discharged from the overflow port at the top of the reactor. After the solution was added, oxygen was continued to be introduced for oxidation for half an hour. The product at the bottom of the reactor was taken, and after sedimentation and separation, it was washed with pure water until the pH value was about 7.2. Then the precipitate was dried in an oven at 120℃ to obtain manganese iron nickel oxide.

[0060] The analytical results of the manganese iron-nickel oxide obtained in this embodiment are shown in Table 1 below, and the electron micrographs are as follows. Figure 3 As shown in the figure, this embodiment yielded spherical manganese-iron-nickel oxide with a single-layer ion-layered upward movement.

[0061] Example 4:

[0062] A method for synthesizing a layered oxide precursor for a sodium-ion cathode material includes the following steps:

[0063] (1) Prepare 30L of a 120g / L metal sulfate solution (Mn 2+ 60g / L, Fe 2+ 25g / L, Ni 2+ 30g / L, Cu 2+ Add 4 g / L of disodium EDTA (5 g / L) and mix well;

[0064] (2) Prepare a 100 g / L sodium hydroxide solution;

[0065] (3) The obtained mixed solution of metal sulfate was added to a 20L stirred reactor using a peristaltic pump. At the same time, sufficient hydrogen peroxide was added to provide an oxidation environment. Sodium hydroxide was then added. The reaction temperature was controlled at 50℃ and the pH of the reaction solution was 10.5. The product was discharged from the overflow port at the top of the reactor. After the solution was completely added, hydrogen peroxide was added for oxidation for another half hour. The product at the bottom of the reactor was taken, and after sedimentation and separation, it was washed with pure water until the pH value was about 7.2. Then the precipitate was dried in an oven at 120℃ to obtain manganese iron nickel copper oxide.

[0066] The analytical results of the manganese-iron-nickel-copper oxides obtained in this embodiment are shown in Table 1 below, and the electron microscope images are as follows. Figure 4 As shown in the figure, this embodiment yielded spherical manganese-iron-nickel-copper oxides with a single-layer ion-layered upward movement.

[0067] Example 5:

[0068] A method for synthesizing a layered oxide precursor for a sodium-ion cathode material includes the following steps:

[0069] (1) Prepare 30L of a 150g / L metal sulfate solution (Mn 2+ 75g / L, Fe 2+ 30g / L, Ni 2+ 35g / L, Zn 2+ Add 3g / L of EDTA to 10g / L of the solution and mix well.

[0070] (2) Prepare a 100 g / L sodium hydroxide solution;

[0071] (3) The obtained mixed solution of metal sulfate was added to a 20L stirred reactor using a peristaltic pump. Sodium hydroxide and sufficient hydrogen peroxide were added in parallel to provide an oxidizing environment. The reaction temperature was controlled at 50℃ and the pH of the reaction solution was 10.5. The product was discharged from the overflow port at the top of the reactor. After the solution was completely added, hydrogen peroxide was added for oxidation for half an hour. The product at the bottom of the reactor was taken, and after sedimentation and separation, it was washed with pure water until the pH value was about 7.2. Then the precipitate was dried in an oven at 120℃ to obtain manganese iron nickel zinc oxide.

[0072] The analytical results of the manganese-iron-nickel-zinc oxides obtained in this embodiment are shown in Table 1 below, and the electron micrographs are as follows. Figure 5 As shown in the figure, this embodiment yielded spherical manganese-iron-nickel-zinc oxide with a single-layer ion-layered upward movement.

[0073] Comparative Example 1:

[0074] A method for synthesizing a hydroxide precursor for a sodium ion cathode material includes the following steps:

[0075] (1) Prepare 30L of a 240g / L metal sulfate solution (Mn 2+ 120g / L, Fe 2+ 60g / L, Ni 2+ Add 2g / L of ethanol to 60g / L of water and mix well.

[0076] (2) Prepare a 200 g / L sodium hydroxide solution;

[0077] (3) The obtained mixed solution of metal sulfate was added to a 20L stirred reactor using a peristaltic pump, and sodium hydroxide was added. The reaction temperature was controlled at 55℃ and the pH of the reaction solution was 11.5. Sufficient oxygen was added to provide an oxidation environment. The product was discharged from the overflow port at the top of the reactor. After the solution was added, the product at the bottom of the reactor was taken, and after sedimentation and separation, it was washed with pure water until the pH value was about 7.2. Then the precipitate was dried in an oven at 120℃ to obtain manganese iron nickel hydroxide.

[0078] The analytical results of the manganese iron nickel hydroxide obtained in this comparative example are shown in Table 1 below, and the electron micrographs are as follows. Figure 6As shown in the figure, this comparative example yielded spherical manganese-iron-nickel hydroxide with elongated primary ions.

[0079] Comparative Example 2:

[0080] A method for synthesizing a layered oxide precursor for a sodium-ion cathode material includes the following steps:

[0081] (1) Prepare 30L of 80g / L metal sulfate solution (Mn 2+ 50g / L, Fe 2+ Add 3g of ammonium sulfate (30g / L) and mix well;

[0082] (2) Prepare a 60 g / L sodium hydroxide solution;

[0083] (3) The obtained mixed solution of metal sulfate was added to a 20L stirred reactor using a peristaltic pump. A small amount of oxygen was added at the same time to provide a weak oxidizing environment (to prevent all manganese from being oxidized to manganese dioxide). Sodium hydroxide was then added, and the reaction temperature was controlled at 45℃. The pH of the reaction solution was 11.0. The product was discharged from the overflow port at the top of the reactor. After the solution was added, the product at the bottom of the reactor was taken, and after sedimentation and separation, it was washed with pure water until the pH value was about 7.2. Then the precipitate was dried in an oven at 120℃ to obtain partially oxidized manganese iron oxide.

[0084] The analytical results of the manganese iron-nickel oxides obtained in this comparative example are shown in Table 1 below, and the electron micrographs are as follows. Figure 7 As shown in the figure, this comparative example yielded an irregular, diffuse, and amorphous oxide precursor.

[0085] Table 1: Performance and compositional analysis results of the precursors prepared in Examples 1-5 and Comparative Examples 1-2

[0086] μm <![CDATA[g / cm 3 ]]> <![CDATA[m 2 / g]]> ％ ％ ％ ％ ％ ％ ppm ppm ％ Example 1 5.87 0.82 0.49 33.79 19.58 / / / 4.05 90 116 0.01 Example 2 6.76 0.56 200 35.09 15.99 / 6.3 / 3.1 115 13 0.031 Example 3 4.0 0.74 105.3 29.33 15.29 17.11 / / 0.62 130 98 0.07 Example 4 5.2 1.07 112.3 28.5 12.08 15.6 2.6 / 0.53 180 42 0.052 Example 5 3.93 1.13 123 29.12 111.4 16.15 / 3.84 0.51 85 64 0.23 Comparative Example 1 4.6 1.33 14.84 20.16 20.23 21.5 / / 0.004 32 34 0.32 Comparative Example 2 4.3 0.42 155.59 37.74 25.19 / / / 0.02 75 12 0.69

[0087] By subjecting the precursors prepared in Examples 1-5 and Comparative Examples 1-2 to sodium-mixed calcination, metal layered oxide cathode materials with good capacity and high cycle life were obtained. The coin cell detection data are shown in Table 2 below. The scanning electron microscope (SEM) images of the products obtained from the oxide precursors in Examples 1-5 are shown below. Figures 7-12 As shown in the figure, after sintering, the primary particles of the precursor become compact and have a uniform morphology, which improves the capacity and cycle life of the synthesized cathode material accordingly.

[0088] During sodium-mixed calcination, the normal sodium-mixing ratio is sodium:M(Mn+Fe+Ni) = 1.02-1.05. Considering that the examples have already undergone partial sodium pre-doping in the oxide precursor, the sodium-mixing ratio of the example samples was adjusted to sodium:M(Mn+Fe+Ni) = 1.0, which reduces the amount of sodium source input during the mixing process and also reduces the residual sodium on the surface of the cathode material after sintering, i.e., reduces the residual alkali on the surface of the cathode material. The sodium-mixing ratio of the comparative sample is M(Mn+Fe+Ni) = 1.02, the sintering temperature during sodium-mixed calcination is 950℃, the holding time is 15h, and the heating rate is 3℃ / min.

[0089] During the deduction test, the following charging and discharging system is adopted: the initial charging and discharging current is 0.33C, and the subsequent charging and discharging current is 1C; the charging and discharging voltage is 2.0-4.3V.

[0090] Table 2: Performance data of the metal layered oxide cathode materials prepared in Examples 1-5 and Comparative Examples 1-2

[0091]

Claims

1. A method for synthesizing a layered oxide precursor for a sodium-ion cathode material, characterized in that, The process includes the following steps: mixing a soluble metal salt and sodium hydroxide and reacting them; adding an oxidizing agent during the reaction; adding more oxidizing agent after the reaction is complete; separating the precipitate; and washing and drying it to obtain a layered oxide precursor; wherein the soluble metal salt contains a manganese salt. During the reaction, an oxidant is added to ensure that manganese is oxidized to manganese oxide. Almost all manganese is oxidized and does not exist in the form of manganese hydroxide. Furthermore, some of the manganese dioxide in the manganese oxide reacts with sodium hydroxide to form sodium manganate. Sodium manganate and manganese dioxide co-precipitate in the layered oxide precursor. Adding an oxidizing agent during the reaction means that the oxidizing agent and sodium hydroxide are added simultaneously, or the oxidizing agent is added before sodium hydroxide, to ensure that manganese is oxidized to manganese oxide; Sodium manganate is present in the layered oxide precursor, which pre-dops the layered oxide precursor with sodium ions, and the doping amount of sodium ions is controlled so that the mass percentage of sodium in the layered oxide precursor is more than 0.5%. After the reaction is complete, continue to add oxidant to ensure that manganese oxide exists in the form of manganese dioxide; The layered oxide precursor is a spherical manganese-iron oxide precursor with a chemical formula of (Na x Fe y Mn z N 1-x-y-z )2O3, wherein 0 0.1 0.1 0.1 N is a doping element, which is one or more of Zn, Ni, and Cu. The soluble metal salt is at least one of sulfate, nitrate and hydrochloride, and the soluble metal salt is a divalent metal salt, with the total concentration of divalent ions controlled at 20-300 g / L.

2. The synthesis method according to claim 1, characterized in that, A complexing agent is added during the mixing reaction, wherein the complexing agent includes at least one of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, and tetrasodium ethylenediaminetetraacetic acid.

3. The synthesis method according to claim 1, characterized in that, The concentration of sodium hydroxide is controlled at 50-200 g / L, and the amount of sodium hydroxide added ensures that the pH value of the reaction solution is 10.5-13.

5.

4. The synthesis method according to claim 1, characterized in that, The oxidant includes at least one of hydrogen peroxide and oxygen.

5. A layered oxide precursor obtained by the synthesis method according to any one of claims 1-4, characterized in that, The layered oxide precursor is spherical in shape and has a tap density of 0.5-2 g / cm³. 3 The particle size D50 is 3-12μm.

6. A sodium-ion cathode material, characterized in that, It is obtained by calcining a mixture of the layered oxide precursor described in claim 5 and a sodium source.

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