Nanocrystalline O3 phase layered sodium ion battery positive electrode material and preparation method thereof

Abstract

The invention relates to a nanocrystalline O3 phase layered sodium ion battery positive electrode material, which comprises single crystal particle NaaNibFecMnd, 0.8 < = a < = 1.05, 0 < = b < = 0.33, 0 < = c < = 0.4, 0 < = d < = 0.4, b + c + d = 1, and a, b and c are not 0 at the same time. No grain boundary exists in the nanometer single crystal O3 phase layered sodium ion battery positive electrode material, and the problem of grain boundary cracking caused by anisotropic lattice change in the charging and discharging process of a similar polycrystalline material is solved. The nano single crystal O3 phase layered sodium ion battery positive electrode material provided by the invention has the characteristics of high specific surface area and high reaction activity, and can realize higher sodium ion intercalation and deintercalation quantity, thereby improving the specific capacity of the battery. Moreover, the nano single crystal O3 phase layered sodium ion battery positive electrode material can shorten the diffusion path of sodium ions and reduce the ion diffusion resistance, so that the material has good rate capability.

Description

Technical Field

[0001] The present invention belongs to the field of ion battery materials, and relates to a nanocrystalline O3-phase layered sodium-ion battery cathode material and a preparation method thereof. Background Art

[0002] Sodium-ion batteries are regarded as an important complementary technology to lithium-ion batteries because of their high cost-effectiveness, abundant and widely distributed sodium resources (the crust abundance is 2.3%, more than 1000 times that of lithium resources), and have broad application prospects especially in the fields of large-scale energy storage, low-speed electric vehicles and backup power supplies. Compared with lithium-ion batteries, sodium-ion batteries perform outstandingly in terms of low-temperature performance (capacity retention rate > 80% at -20°C), fast charging ability (charged to 80% in 20 minutes) and safety (higher thermal runaway temperature). However, due to the larger radius of sodium ions than lithium ions, the cathode materials of sodium-ion batteries face complex multiple phase transitions during charge and discharge, resulting in their structure being more unstable than that of lithium-ion battery cathode materials, and the specific capacity is also lower than that of lithium battery cathode materials.

[0003] Among the cathode materials of sodium-ion batteries, layered transition metal oxides (Na x MO2, M includes transition metals such as Mn, Fe, Cu, Ni, Co, etc.) have become the technical route with the fastest industrialization process due to their high theoretical capacity, mature synthesis process (compatible with lithium battery cathode process) and adjustable chemical composition. According to the coordination environment of sodium ions and the oxygen atom stacking mode, layered oxides can be divided into two categories: P2 type and O3 type:

[0004] 1. P2 type (sodium occupies the trigonal prism site)

[0005] P2-type materials have wide sodium-ion transmission channels and low migration energy barriers, and excellent cycle stability, but the sodium content is low (x≈0.67), and the theoretical capacity is limited.

[0006] 2. O3 type (sodium occupies the octahedral site)

[0007] O3-type materials have a high sodium content (x≈1), and the theoretical capacity can reach 190 - 220 mAh / g, and have attracted much attention due to their high energy density. However, the O3-type cathode material will undergo complex irreversible phase transitions during the cycle, resulting in poor cycle stability of the material, short layer spacing (about ), high sodium-ion diffusion energy barrier (inconvenient for sodium-ion deintercalation and intercalation), and irreversible phase transitions (such as O3→P3→O3') are likely to occur during charge and discharge, resulting in problems such as easy collapse of the structure and capacity attenuation.

[0008] In the prior art, the modification strategies of O3-type layered oxides include element doping, surface coating, and single-crystallization design. Element doping is, for example, to stabilize the crystal structure by introducing elements such as Mg, Cu, Ti, etc. (Periodic law-guided design of highly stable O3-type layered oxide cathodes for practical sodium-ion batteries, 《Chemical Science》); surface coating is, for example, to reduce side reactions of the electrolyte through a carbon layer or an oxide coating (such as Al2O3) (Insights into the capacity fading and failure mechanism of an O3-NaNi1 / 3Fe1 / 3Mn1 / 3O2 layered oxide cathode material for sodium-ion batteries, 《Journal of Materials Chemistry A》); single-crystallization design is, for example, to prepare single-crystalline particles by high-temperature re-sintering to reduce grain boundary defects (High-Energy Na-ion Batteries Using Single-Crystalline Cathod, 《ACS Energy letters》).

[0009] Although certain progress has been made on O3-type layered oxides (i.e., O3-type layered cathode materials) through the above methods, O3-type layered oxides still face the following challenges:

[0010] 1. Irreversible phase transformation and structural distortion

[0011] During the sodiation / desodiation process of sodium ions, the transition metal layer undergoes slip and Jahn-Teller distortion, resulting in the O3→P3 phase transformation and dynamic fluctuations in the layer spacing. For example, O3-NaNi 0.5 Mn 0.5 O2 undergoes multiple phase transformations at 4.2 V during charging, with a volume change >5%, leading to particle cracking and interfacial failure (Ti-Substituted NaNi 0.5 Mn 0.5 -xTixO2 Cathodes with Reversible O3-P3 Phase Transition for High-Performance Sodium-Ion Batteries, 《Adv. Mater.》).

[0012] 2. Poor air stability

[0013] When the material is exposed to air, it will absorb moisture and generate Na2CO3 / NaOH, resulting in a decrease in sodium content and particle pulverization.

[0014] 3. The preparation process of nanocrystalline single crystals is complex.

[0015] Existing single crystal synthesis mostly relies on high-temperature sintering (>1000 °C) or molten salt method, with high energy consumption and uneven particle size distribution.

[0016] 4. Bottleneck in rate performance

[0017] The intrinsic sodium ion diffusion coefficient (10 -12 ~10 -11 cm 2 / s) of O3-type materials is much lower than that of P2-type (10 -10 cm 2 / s), and the capacity retention rate at 5C rate is generally <70%.

[0018] In addition, on the one hand, there are differences in the understanding of those skilled in the art; on the other hand, although the inventor studied a large number of documents and patents when making this invention, due to space limitations, all details and contents are not listed in detail. However, this does not mean that this invention does not possess the features of these prior arts. On the contrary, this invention already possesses all the features of the prior arts, and the applicant reserves the right to add relevant prior arts in the background art. Summary of the Invention

[0019] Based on the above technical problems, one of the objectives of the present invention is to provide a cathode material for sodium ion batteries to overcome the deficiencies in the prior art.

[0020] To achieve the above objective, the present invention adopts the following technical solutions:

[0021] A nanocrystalline O3-phase layered cathode material for sodium ion batteries, comprising single crystal particles of Na a Ni b Fe c Mn d , 0.8 ≤ a ≤ 1.05, 0 ≤ b ≤ 0.33, 0 ≤ c ≤ 0.4, 0 ≤ d ≤ 0.4, where b + c + d = 1, and a, b, c are not all 0 at the same time. This cathode material for sodium ion batteries is a nanocrystalline O3-type layered material.

[0022] Another objective of the present invention is to provide a preparation method for a nanocrystalline O3-phase layered cathode material for sodium ion batteries, which comprises the following steps:

[0023] Mix the transition metals including nickel source, iron source, and manganese source evenly;

[0024] Add the sodium source and stir until the sodium salt is completely dissolved to form a suspension;

[0025] Add a weak acid to form a clear and transparent solution;

[0026] Heat and stir to evaporate the ethanol;

[0027] Ignite the mixture to make it burn fully and obtain the ash after combustion;

[0028] After grinding, place it in an oxygen atmosphere and keep it at 600 - 850 °C for 1 - 10 h.

[0029] According to a preferred embodiment, the sodium source is a strong base weak acid salt containing sodium salt. Preferably, the sodium source includes one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, and sodium oxalate. More preferably, the sodium source is sodium acetate.

[0030] According to a preferred embodiment, the manganese source includes one or more of manganese acetate, manganese carbonate, and manganese nitrate. Preferably, the manganese source is manganese nitrate.

[0031] According to a preferred embodiment, the nickel source includes one or more of nickel acetate, nickel carbonate, and nickel nitrate. Preferably, the nickel source is nickel nitrate.

[0032] According to a preferred embodiment, the iron source includes one or more of iron acetate, iron carbonate, and iron nitrate. Preferably, the iron source is iron nitrate.

[0033] According to a preferred embodiment, the weak acid is one or more of citric acid, oxalic acid, acetic acid, and dilute nitric acid. Preferably, the weak acid is citric acid.

[0034] According to a preferred embodiment, the nickel source, iron source, and manganese source are prepared according to the stoichiometric ratio of nickel source: iron source: manganese source = (0 - 0.33):(0 - 0.4):(0 - 0.4).

[0035] According to a preferred embodiment, the transition metal and the sodium source are prepared according to the stoichiometric ratio of sodium source: transition metal = 0.85:1.

[0036] Specifically, a preparation method of a nanocrystalline O3-phase layered sodium ion battery cathode material comprises the following steps:

[0037] Weigh sodium acetate, nickel nitrate, iron acetate, and manganese nitrate according to the stoichiometric ratio of 0.85:0.33:0.33:0.34;

[0038] First add nickel nitrate, iron acetate, and manganese nitrate salts to a beaker, add a small amount of ethanol so that it can just cover the sodium salt, and place it on a heated magnetic stirrer and stir until nickel nitrate, iron acetate, and manganese nitrate are completely dissolved to form a first solution;

[0039] Take another beaker, dissolve sodium acetate in water to form a second solution, and citric acid as a third solution;

[0040] Add the second solution to the first solution to make the solution turbid;

[0041] Add the third solution to the beaker until the solution becomes clear and transparent;

[0042] Stir well to allow the ethanol in the beaker to evaporate until the transparent colloidal solution becomes clear;

[0043] Ignite the colloidal solution to allow it to burn thoroughly;

[0044] Grind the ashes after combustion thoroughly;

[0045] Keep the ground powder at 700 °C for 3 h in an oxygen atmosphere with a heating rate of 3 °C / min;

[0046] After the sintering is completed, let it cool naturally to room temperature in air to obtain the corresponding cathode material for sodium-ion batteries.

[0047] Preferably, sodium acetate, nickel nitrate, iron acetate, and manganese nitrate are set according to the stoichiometric ratio of 0.85:0.33:0.33:0.34.

[0048] According to a preferred embodiment, based on the total mass of 100%, the mass ratio of the cathode active material is 70 - 90%; the mass ratio of the conductive carbon black is 5 - 20%; the mass ratio of polyvinylidene fluoride is 5 - 10%.

[0049] According to a preferred embodiment, based on the total mass of 100%, the mass ratio of the cathode active material is 70 - 90%; the mass ratio of the conductive carbon black is 5 - 20%; the mass ratio of polyvinylidene fluoride is 5 - 10%. N-methylpyrrolidone is 1 - 1.6 times the weight of the cathode active material.

[0050] According to a preferred embodiment, the cathode material for sodium-ion batteries further comprises conductive carbon black (Super P) and polyvinylidene fluoride (PVDF).

[0051] Preferably, the ratio of the cathode active material, conductive carbon black, and polyvinylidene fluoride is 9:0.5:0.5 by mass.

[0052] One of the objects of the present invention is also to provide the application of the above-mentioned nanocrystalline O3-phase layered cathode material for sodium-ion batteries in sodium-ion batteries.

[0053] One of the objects of the present invention is also to provide a method for preparing a sodium-ion battery, which comprises the following steps:

[0054] Pulverize the above-mentioned cathode active material with conductive carbon black and polyvinylidene fluoride at a mass ratio of 9:0.5:0.5 in an N-methylpyrrolidone (NMP) solution under an inert atmosphere and coat it on an aluminum foil;

[0055] After vacuum drying, it is cut into electrode sheets with a diameter of 10 - 15 mm.

[0056] Preferably, the loading of the electrode sheet is 5 - 10 mg / cm 2 .

[0057] Preferably, the diameter of the electrode sheet is 12 mm. The diameter of the electrode sheet is 10 mm. The diameter of the electrode sheet is 15 mm.

[0058] One of the purposes of the present invention is also to provide a preparation method of a sodium - ion battery, which comprises the following steps:

[0059] Mix the above - mentioned positive - electrode active material with conductive carbon black and polyvinylidene fluoride in an inert atmosphere according to the mass ratio of positive - electrode active material: conductive carbon black: polyvinylidene fluoride = 9:0.5:0.5, and make a slurry in an N - methylpyrrolidone solution which is 1.6 times the weight of the positive - electrode active material, and coat it on an aluminum foil;

[0060] After vacuum drying, it is cut into electrode sheets with a diameter of 10 - 15 mm;

[0061] Using a sodium metal sheet as the negative electrode, a 1mol / L NaClO4 / polycarbonate (PC): ethylene carbonate (EC): dimethyl carbonate (DMC) (volume ratio 1:1:1) solution as the electrolyte, and glass fiber as the separator, assemble it into a battery in an argon glove box. Preferably, the battery is a CR2025 coin - type half - cell.

[0062] The technical solution of the present invention realizes a significant improvement in discharge efficiency and cycle efficiency through the promotion of sodium - ion diffusion kinetics and capacity by the nano - single - crystal structure, the enhancement of cycle stability by the single - crystal structure, and the synergistic effect of interlayer regulation and high specific surface area.

[0063] The single - crystal structure of the material involved in the present invention constructs a continuous Na + diffusion channel by eliminating the grain - boundary effect of polycrystalline materials, significantly reducing the ion - transport resistance, and the size effect of the nano - single - crystal further shortens the diffusion path of sodium ions. Due to the absence of grain - boundary hindrance, the material with this structure exhibits a faster Na + diffusion rate and higher electronic conductivity, suppressing the accumulation of anisotropic stress, so that the high specific capacity is significantly improved at 0.5C, 2C, and 5C (160.7 mAh g -1 , 140.6 mAh g -1 , 111.4 mAh g -1 ).

[0064] Meanwhile, compared with polycrystalline materials that are prone to crack formation due to anisotropic expansion / contraction at grain boundaries during charge and discharge, the single-crystal materials involved in the present invention not only avoid crack propagation by eliminating grain boundaries but also block the penetration of the electrolyte along grain boundaries by improving the structural compactness, thereby reducing interfacial side reactions. The single-crystal structure formed by improving the synthesis method significantly enhances the capacity retention rate (85.6%) after 500 cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 XRD pattern of the O3-type nanocrystalline layered sodium-ion battery cathode material prepared in Example 1 of the present invention;

[0066] Figure 2 SEM image of the O3-type nanocrystalline layered sodium-ion battery cathode material prepared in Example 1 of the present invention;

[0067] Figure 3 XRD pattern of the O3-type polycrystalline layered sodium-ion battery cathode material prepared in Comparative Example 1 of the present invention;

[0068] Figure 4 SEM image of the O3-type polycrystalline layered sodium-ion battery cathode material prepared in Comparative Example 1 of the present invention;

[0069] Figure 5 XRD pattern of the O3-type single-crystal sodium-ion battery cathode material prepared in Comparative Example 2 of the present invention;

[0070] Figure 6 SEM image of the O3-type single-crystal sodium-ion battery cathode material prepared in Comparative Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0071] In the description of the present invention, the terms are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. In the description of the present invention, "a plurality of" means two or more unless otherwise specifically defined.

[0072] The nanocrystalline single-crystal O3-phase layered sodium-ion battery cathode material proposed by the present invention has the characteristics of high specific surface area and high reaction activity, enabling a higher amount of sodium ion insertion and extraction, thereby improving the specific capacity of the battery. Moreover, this nanocrystalline single-crystal O3-phase layered sodium-ion battery cathode material can shorten the diffusion path of sodium ions, reduce the ion diffusion resistance, and endow the material with good rate performance.

[0073] There are no grain boundaries in the O3-phase layered sodium-ion battery cathode material of nanocrystalline single crystals, which avoids the problem of grain boundary cracking caused by anisotropic lattice changes during charge and discharge in polycrystalline materials. For example, in polycrystalline materials, the insertion and extraction of sodium ions during charging cause lattice volume changes, leading to particle cracking along grain boundaries and within grains, while this problem does not exist in single crystal materials. Since there are no grain boundaries inside single crystal materials, the electrolyte cannot penetrate along the grain boundaries, thereby reducing the side reactions between the electrolyte and the cathode material. This helps to reduce the rate of capacity decay during battery cycling and extend the battery life. The single crystal structure can effectively inhibit the generation of microcracks. Even after charging at high voltage, relatively few microcracks are formed in single crystal materials, thus maintaining a high capacity retention rate and improving the cycling stability of the battery.

[0074] Therefore, by preparing the O3-type nanocrystalline layered sodium-ion battery cathode material, a sodium-ion battery cathode material with high energy density, good cycling performance and rate performance can be obtained.

[0075] Example 1

[0076] This example provides a preparation method for a nanocrystalline O3-type layered cathode material. The preparation method includes the following steps:

[0077] After weighing sodium acetate, nickel nitrate, iron acetate, and manganese nitrate according to the stoichiometric ratio of 0.85:0.33:0.33:0.34, first add the transition metal salts containing nickel nitrate, iron acetate, and manganese nitrate to a beaker. Add a small amount of ethanol so that it just covers the transition metal salts, and place it on a heated magnetic stirrer and stir until the transition metals are completely dissolved to form a first solution;

[0078] Take another beaker, add water to dissolve sodium acetate to form a second solution;

[0079] Citric acid is the third solution;

[0080] Add the second solution to the first solution, and the solution will become turbid;

[0081] Add the third solution to the beaker until the solution becomes clear and transparent;

[0082] Place the beaker on a heating stirrer and stir to evaporate the ethanol in the beaker until only a transparent gluey liquid remains in the beaker;

[0083] Ignite the gluey liquid in the beaker and stir with a glass rod until the gluey liquid is fully burned into black ashes;

[0084] Put the ashes into a mortar and grind them thoroughly until they become gray powder;

[0085] Put the gray powder into a tube furnace, keep it at 700 °C for 3 h in an oxygen atmosphere, and the heating rate is 3 °C / min;

[0086] After the sintering is completed, naturally cool it to room temperature in air to obtain the corresponding cathode material for sodium-ion batteries.

[0087] The solution becomes turbid because the added second solution is a salt of a strong base and a weak acid, which will cause the ions to undergo hydrolysis reactions to form flocculent precipitates of hydroxides. To weaken the hydrolysis reaction of transition metal ions, a third solution is added.

[0088] The XRD and SEM of the nanocrystalline O3-type material prepared in this example are as Figure 1 and Figure 2 shown. According to the XRD diagram, this material is an O3-type material. According to the SEM diagram, the material is a single-crystalline nanomaterial.

[0089] Comparative Example 1

[0090] This example provides a method for preparing a nanocrystalline O3-type layered cathode material. The preparation method includes the following steps:

[0091] Weigh sodium acetate, nickel nitrate, iron acetate, and manganese nitrate according to the stoichiometric ratio of 0.85:0.33:0.33:0.34, and then put the materials into a ball mill and mix them evenly;

[0092] Then put the mixed materials into a tube furnace, keep them at 850 °C for 10 h in an oxygen atmosphere, and the heating rate is 3 °C / min;

[0093] After the sintering is completed, naturally cool it to room temperature in air to obtain the corresponding cathode material for sodium-ion batteries.

[0094] The XRD and SEM of the material prepared in this example are as Figure 3 and Figure 4 shown. According to the XRD diagram, this material is an O3-type material. According to the SEM diagram, the material is a polycrystalline material.

[0095] Comparative Example 2

[0096] This example provides a method for preparing a nanocrystalline O3-type layered cathode material. The preparation method includes the following steps:

[0097] Weigh sodium acetate, nickel nitrate, iron acetate, and manganese nitrate according to the stoichiometric ratio of 0.85:0.33:0.33:0.34, and then put the materials into a ball mill and mix them evenly;

[0098] Then put the mixed materials into a tube furnace, keep them at 950 °C for 10 h in an oxygen atmosphere, and the heating rate is 3 °C / min;

[0099] After the sintering is completed, it is naturally cooled to room temperature in air to obtain the corresponding cathode material for sodium-ion batteries.

[0100] The XRD and SEM of the materials prepared in this example are as Figure 5 and Figure 6 shown. According to the XRD pattern, this material is an O3-type material. According to the SEM image, the material is a single-crystal material.

[0101] Example 2

[0102] This example involves the test experiments on the materials prepared in the examples and comparative examples.

[0103] 1. XRD Test Analysis

[0104] XRD test analysis was carried out on all the prepared materials, and the test results are as Figure 1 , 3 , and 5 shown. The results show that both the examples and comparative examples are O3-type materials.

[0105] 2. SEM (Scanning Electron Microscope) Test Analysis

[0106] The microscopic morphological structures of the materials in the examples and comparative examples were further studied by scanning electron microscope (SEM).

[0107] 3. Electrochemical Performance Test

[0108] a. Half-cell assembly: The layered oxide cathode materials for sodium-ion batteries in each example and comparative example were separately mixed with conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) at a mass ratio of 9:0.5:0.5 in an N-methylpyrrolidone (NMP) solution that is 1.6 times the weight of the positive active material, and then slurried and coated on aluminum foil. After vacuum drying, it was cut into a pole piece with a diameter of 12 mm (loading capacity about 5 - 10 mg / cm 2 ).

[0109] Using a sodium metal sheet as the negative electrode, a 1 mol / L NaClO4 / polycarbonate (PC):ethylene carbonate (EC):dimethyl carbonate (DMC) (volume ratio 1:1:1) solution as the electrolyte, and a glass fiber as the separator, a CR2025 coin-type battery half-cell was assembled in an argon glove box.

[0110] b. Charge-discharge test: The voltage range for charge-discharge of the coin-type half-cell is 2.0 - 4.1 V. Before the cycle test, it was first activated twice with a small current density of 15 mA / g (0.1C), and then cycled at a 1C rate within the same voltage range. All electrochemical performance tests were carried out at room temperature.

[0111] As shown in Table 1, the initial capacity of the material prepared in Example 1 is 156.7; the 500-cycle retention is 85.6%; the discharge capacity at 0.5C is 160.7; the discharge capacity at 2C is 140.6; the discharge capacity at 5C is 111.4.

[0112] The initial capacity of the material prepared in Comparative Example 1 is 158.2; the 500-cycle retention is 64.4%; the discharge capacity at 0.5C is 161.4; the discharge capacity at 2C is 124.2; the discharge capacity at 5C is 98.7.

[0113] The initial capacity of the material prepared in Comparative Example 2 is 153.4; the 500-cycle retention is 72.8%; the discharge capacity at 0.5C is 148.9; the discharge capacity at 2C is 129.1; the discharge capacity at 5C is 100.5.

[0114] Table 1

[0115] Example Initial capacity 500 - cycle 0.5C discharge 2C discharge 5C discharge Example 1 156.7 85.6％ 160.7 140.6 111.4 Comparative Example 1 158.2 64.4％ 161.4 124.2 98.7 Comparative Example 2 153.4 72.8％ 148.9 129.1 100.5

[0116] It should be noted that the above specific embodiments are exemplary. Those skilled in the art can come up with various solutions inspired by the disclosure of the present invention, and these solutions also fall within the scope of the disclosure of the present invention and within the protection scope of the present invention. Those skilled in the art should understand that the description and drawings of the present invention are illustrative and do not constitute a limitation on the claims. The protection scope of the present invention is defined by the claims and their equivalents.

Claims

1. A nanocrystalline O3-phase layered sodium-ion battery cathode material, characterized in that, It includes the following steps: Na including single crystal particles a Ni b Fe c Mn d , 0.8 ≤ a ≤ 1.05, 0 ≤ b ≤ 0.33, 0 ≤ c ≤ 0.4, 0 ≤ d ≤ 0.4, where b + c + d = 1, and a, b, c are not simultaneously 0.

2. A preparation method of a nanocrystalline O3-phase layered sodium-ion battery cathode material, characterized in that, It includes the following steps: Mix the transition metals including nickel source, iron source, and manganese source evenly; Add the sodium source and stir until the sodium salt is completely dissolved to form a suspension; Add a weak acid to form a clear and transparent solution; Heat and stir to volatilize the ethanol; Ignite the mixture to make it burn fully to obtain the ash after combustion; After grinding, place it in an oxygen atmosphere and keep it at 600 - 850 °C for 1 - 10 h.

3. The preparation method according to claim 2, characterized in that, The sodium source is one or more sodium salts selected from sodium carbonate, sodium bicarbonate, sodium hydroxide, and sodium oxalate.

4. The preparation method according to claim 2 or 3, characterized in that, The manganese source is selected from one or more of manganese acetate, manganese carbonate, and manganese nitrate; the iron source is selected from one or more of iron acetate, iron carbonate, and iron nitrate; the nickel source is selected from one or more of nickel acetate, nickel carbonate, and nickel nitrate.

5. The preparation method according to any one of claims 2 to 4, characterized in that The weak acid is selected from one or more of citric acid, oxalic acid, acetic acid, and dilute nitric acid.

6. The preparation method according to any one of claims 2 to 5, characterized in that, The sodium source and the transition metals are prepared according to the stoichiometric ratio of sodium source:transition metals = 0.85:

1.

7. The preparation method according to any one of claims 2 to 6, characterized in that, The nickel source, iron source, and manganese source are prepared according to the stoichiometric ratio of nickel source:iron source:manganese source = (0 - 0.33):(0 - 0.4):(0 - 0.4).

8. The preparation method according to any one of claims 2 to 7, characterized in that "Mixing the sodium source, nickel source, iron source, and manganese source" includes the following steps: Mix sodium acetate, nickel nitrate, iron acetate, and manganese nitrate according to the stoichiometric ratio of 0.85:0.33:0.33:0.

34.

9. A preparation method of a sodium-ion battery, characterized in that, It comprises the following steps: Slurry the nanocrystalline O3-phase layered sodium-ion battery cathode material described in claim 1 or the nanocrystalline O3-phase layered sodium-ion battery cathode material prepared by the preparation method described in any one of claims 2 - 8 with conductive carbon black and polyvinylidene fluoride in an N-methylpyrrolidone solution respectively and coat it on an aluminum foil; After vacuum drying, cut it into electrode sheets.

10. The preparation method of the sodium ion battery according to claim 9, wherein, The nanocrystalline O3-phase layered sodium-ion battery cathode material, conductive carbon black, and polyvinylidene fluoride are mixed in a mass ratio of 9:0.5:0.5.

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