Sodium-intercalated precursors and cathode materials and their preparation methods, cathodes and sodium-ion batteries

Abstract

This invention discloses a sodium-intercalated precursor and a cathode material, their preparation methods, a cathode, and a sodium-ion battery. The disclosed method for preparing the nickel-iron-manganese sodium-intercalated precursor includes: introducing a metal salt solution, a sodium hydroxide solution, and ammonia into a reaction vessel, while simultaneously introducing oxygen and an inert gas below the liquid surface to conduct a co-precipitation reaction; the metal salt solution is a salt solution containing nickel, iron, and manganese; stopping the introduction of oxygen when the particle D50 in the reaction vessel reaches 2–5 μm; stopping the introduction of the metal salt solution and ammonia when the particle D50 in the reaction vessel increases to 2–13 μm; raising the temperature of the reaction vessel to 70–90°C, continuing to introduce sodium hydroxide solution until the pH reaches 12–13, and then introducing an oxidant solution into the reaction vessel to react fully for a period of time to obtain a slurry; and extracting the solid matter from the slurry to obtain the precursor. The precursor prepared by this method has uniform sodium intercalation and exhibits excellent electrochemical performance when used as a cathode material.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to sodium-intercalated precursors and cathode materials, their preparation methods, cathodes, and sodium-ion batteries. Background Technology

[0002] With the widespread use of portable electronic products and the rapid development of electric vehicles and grid energy storage, the demand for batteries is increasing. Lithium-ion batteries are widely used in energy storage due to their advantages such as high capacity, high energy density, and long lifespan. However, with the shortage and soaring price of lithium resources, sodium-ion batteries have become a substitute for lithium-ion batteries due to their low cost and more sustainable development, attracting widespread attention from researchers.

[0003] The performance of the cathode material is the most important factor affecting the performance of sodium-ion batteries. There are three technical routes for sodium-ion battery cathode materials: layered oxides, Prussian blue compounds, and polyanionic compounds. Layered oxides: They possess high specific capacity and high compatibility with ternary lithium-ion battery cathode process equipment, and are currently the fastest-growing technical route for industrialization, but their cycle performance still needs improvement. Prussian blue compounds: They have advantages such as high specific capacity, lower cost, high rate performance, and excellent electrochemical stability, but their cycle performance is a weakness, and the crystal water generated during production can cause structural collapse during charge and discharge. Polyanionic compounds: They have advantages such as good stability, good cycle performance, and good safety, but they suffer from low specific capacity and poor conductivity.

[0004] The morphology, structural characteristics, and manufacturing cost of sodium-ion battery cathode materials are closely related to the physicochemical properties and manufacturing costs of the precursor. Patent CN115676917A provides a method for preparing a lithium-containing metal oxide precursor, which enables more uniform lithium embedding under liquid phase conditions. However, this method lacks pretreatment during the initial particle growth stage, resulting in a low lithium intercalation rate. Excess lithium requires further recovery, complicating the process. Patent CN116443951A provides a method for preparing a sodium-intercalated lithium-ion battery cathode material. This method involves a physicochemical reaction between a sodium-containing metal compound and a hydroxide or carbonate precursor, followed by solid-liquid separation of the reaction products to obtain a sodium-intercalated metal oxide precursor. The precursor is then mixed with a lithium source and calcined to obtain the sodium-intercalated lithium-ion battery cathode material. However, this method involves a high-temperature, high-pressure physicochemical reaction between the sodium-containing metal compound and the precursor, resulting in complex procedures and equipment, and high energy consumption.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide sodium-intercalated precursors and cathode materials, methods for their preparation, cathodes, and sodium-ion batteries, aiming to improve at least one of the problems mentioned in the background art.

[0007] This invention is implemented as follows:

[0008] In a first aspect, the present invention provides a method for preparing a nickel-iron-manganese sodium-intercalated precursor, comprising:

[0009] The temperature of the reactor is controlled at 50-60℃, the pH of the bottom liquid is 10.5-11.5, and the ammonia value is 1-5g / L. Metal salt solution, sodium hydroxide solution and ammonia water are introduced into the reactor, and oxygen and inert gas are introduced below the liquid surface at the same time to carry out co-precipitation reaction. The metal salt solution is a salt solution containing nickel, iron and manganese.

[0010] During the coprecipitation reaction, the pH of the bottom solution was maintained in the range of 10.5 to 11.5, and the ammonia value was maintained in the range of 1 to 5 g / L. When the particle D50 in the reactor reached 2 to 5 μm, the oxygen supply was stopped. When the particle D50 in the reactor increased by 1 to 13 μm from 2 to 5 μm, the metal salt solution and ammonia water supply were stopped.

[0011] Raise the temperature of the reactor to 70-90°C, continue to pass sodium hydroxide solution through until the pH reaches 12-13, and then pass an oxidant solution through the reactor to fully react and obtain a slurry.

[0012] The precursor is obtained by extracting the solids from the slurry.

[0013] In an optional embodiment, the metal salt solution further contains a dopant element selected from at least one of Al, Cu, Zn, Mg, Ti, Zr, Nb, and Sr.

[0014] In an optional embodiment, the metal salt solution is prepared according to the following chemical formula: the precursor has the chemical formula Na. n Ni x Mn y Fe z M m O2, where 0.20≤x≤0.40, 0.3≤y≤0.4, 0.3≤z≤0.4, 0.05≤m≤0.1, n+x+y+z=2, and M is a dopant element.

[0015] In an optional embodiment, the oxidant solution is a hydrogen peroxide solution, and the mass fraction of hydrogen peroxide in the hydrogen peroxide solution is 10-30%.

[0016] Optionally, the reaction time after introducing the oxidant solution is 10 to 50 hours.

[0017] In optional embodiments, at least one of the following features (1) to (6) is also included;

[0018] (1) During the oxygen introduction process, the concentration of dissolved oxygen in the water is controlled to be 0.2-0.6 mg / L;

[0019] (2) Methods for extracting solid substances from the slurry to obtain precursors include:

[0020] The slurry is subjected to solid-liquid separation, the resulting solid is washed, and after another solid-liquid separation, it is dried.

[0021] (3) The inert gas is selected from at least one of nitrogen and argon;

[0022] (4) The molar concentration of ammonia solution is 1-3 mol / L; the molar concentration of sodium hydroxide solution is 5-10 mol / L; the total molar concentration of metal ions in metal salt solution is 1-2 mol / L;

[0023] (5) The flow rate of nitrogen is 15-50 L / min, and the flow rate of oxygen is 1-5 L / min;

[0024] (6) The bottom liquid accounts for 50% to 80% of the volume of the reactor.

[0025] Secondly, the present invention provides a precursor prepared by any of the preparation methods described in the foregoing embodiments.

[0026] Thirdly, the present invention provides a method for preparing a positive electrode material, comprising: mixing a sodium source with a precursor as described in the foregoing embodiments and then sintering at 800°C to 1100°C for 8 to 12 hours.

[0027] Optionally, the sodium source is sodium hydroxide.

[0028] Fourthly, the present invention provides a positive electrode material, which is prepared by the preparation method described in the foregoing embodiments.

[0029] Fifthly, the present invention provides a positive electrode, which is made of the positive electrode material as described in the foregoing embodiments.

[0030] In a sixth aspect, the present invention provides a sodium-ion battery, including a positive electrode as described in the foregoing embodiments.

[0031] The present invention has the following beneficial effects:

[0032] The precursor preparation method provided by this invention has good sodium intercalation uniformity, and the precursor prepared into a cathode material has better electrochemical performance. Compared with the common co-precipitation method for preparing hydroxide precursors and then preparing sodium-ion cathode materials by high-temperature sintering, the precursor prepared by this method has better performance when made into a cathode material, and subsequent sintering can be carried out at a lower sintering temperature, which effectively reduces sintering energy consumption and thus reduces production costs. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 SEM image of the sodium-intercalated precursor prepared in Example 1;

[0035] Figure 2 SEM image of the sodium-intercalated precursor prepared in Example 2;

[0036] Figure 3 SEM image of the sodium-intercalated precursor prepared in Example 3;

[0037] Figure 4 This is a SEM image of the sodium-intercalated precursor prepared in Example 4. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0039] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0040] The present invention provides a method for preparing a nickel-iron-manganese sodium-intercalated precursor, comprising:

[0041] The temperature of the reactor is controlled at 50-60℃, the pH of the bottom liquid is 10.5-11.5, and the ammonia value is 1-5g / L. Metal salt solution, sodium hydroxide solution and ammonia water are introduced into the reactor, and oxygen and inert gas are introduced below the liquid surface at the same time to carry out co-precipitation reaction. The metal salt solution is a salt solution containing nickel, iron and manganese.

[0042] During the coprecipitation reaction, the pH of the bottom solution was maintained in the range of 10.5 to 11.5, and the ammonia value was maintained in the range of 1 to 5 g / L. When the particle D50 in the reactor reached 2 to 5 μm, the oxygen supply was stopped. When the particle D50 in the reactor increased by 1 to 13 μm from 2 to 5 μm, the metal salt solution and ammonia water supply were stopped.

[0043] Raise the temperature of the reactor to 70-90°C, continue to pass sodium hydroxide solution through until the pH reaches 12-13, and then pass an oxidant solution through the reactor to fully react and obtain a slurry.

[0044] The precursor is obtained by extracting the solids from the slurry.

[0045] In the initial stage of the precursor co-precipitation reaction, oxygen is introduced for pre-oxidation to initiate nucleation, resulting in the formation of the intermediate MeOOH (Me being a metal ion) within the particles. This facilitates a more thorough subsequent oxidation reaction. Simultaneously, the loosely structured precursor obtained through pre-oxidation increases the specific surface area of ​​the particles, promoting the subsequent intercalation of sodium. After stopping the introduction of the metal salt solution and ammonia solution, precursor particles with a MeOOH core and an outer Me(OH)2 layer are obtained. Subsequent addition of an oxidant causes the Me(OH)2 to be oxidized to MeOOH, yielding the intermediate MeOOH. With increasing temperature and pH, the reaction MeOOH + NaOH = NaMeO2 + H2O further occurs, yielding a sodium-intercalated transition metal layered oxide precursor material.

[0046] It should be noted that if the temperature of the reactor does not rise after the flow of metal salt solution and ammonia is stopped, for example, if it remains at 50-60°C, or if sodium hydroxide solution is not introduced to increase the pH value, the sodium content of the obtained sample will be significantly low.

[0047] Compared with the common co-precipitation method for preparing hydroxide precursors and then high-temperature sintering for sodium-ion cathode materials, the precursor preparation method provided by this invention enables more uniform sodium intercalation, resulting in better electrochemical performance of the precursor after it is made into cathode material. Furthermore, the subsequent sintering temperature is lower, effectively reducing sintering energy consumption and thus lowering production costs.

[0048] The specific preparation method is as follows:

[0049] S1. Prepare various raw material solutions

[0050] Prepare metal salt solutions, sodium hydroxide solutions, ammonia solutions, and oxidizing agent solutions.

[0051] The molar concentration of ammonia solution is 1–3 mol / L; the molar concentration of sodium hydroxide solution is 5–10 mol / L; and the total molar concentration of metal ions in metal salt solution is 1–2 mol / L.

[0052] Preferably, the oxidant solution is a hydrogen peroxide solution with a mass fraction of 10-30%.

[0053] When hydrogen peroxide is chosen as the oxidant, the reaction that occurs in the reactor is: 2Me(OH)2 + H2O2 = 2MeOOH + 2H2O.

[0054] Furthermore, the molar ratio of each metal element in the metal salt solution is determined according to the following chemical formula: Na n Ni x Mn y Fe z M m O2, where 0.20≤x≤0.40, 0.3≤y≤0.4, 0.3≤y≤0.4, 0.05≤m≤0.1, n+x+y+z=2, and M is a dopant element selected from at least one of Al, Cu, Zn, Mg, Ti, Zr, Nb and Sr.

[0055] Choosing different doping elements can provide different properties to cathode materials.

[0056] Alternatively, the metal salt solution can be a sulfate solution, a chloride solution, or a nitrate solution.

[0057] S2, Preparation of base liquid

[0058] The reaction vessel is heated in a water bath to a temperature of 50-60°C. Sodium hydroxide solution and ammonia water are then introduced into the reaction vessel to make the liquid in the reaction vessel reach 50-80% of the solvent content, and to make the pH value of the solution in the reaction vessel reach 10.5-11.5 and the ammonia value reach 1-5 g / L.

[0059] S3, First Stage Reaction

[0060] A metal salt solution, sodium hydroxide solution, and ammonia water are introduced into the reactor, while oxygen and inert gas are simultaneously introduced below the liquid surface to carry out a co-precipitation reaction. When the particle D50 in the reactor reaches 2-5 μm, the oxygen is stopped, and the inert gas is continued.

[0061] The flow rates of the metal salt solution are 2–6 L / h, the sodium hydroxide solution is 1–3 L / h, the ammonia solution is 0.1–3 L / h, the oxygen solution is 1–5 L / min, and the inert gas solution is 15–50 L / min.

[0062] Optionally, the inert gas is selected from at least one of nitrogen and argon.

[0063] The reason why oxygen and inert gas are introduced together in the method provided by the present invention is that if only oxygen is introduced without nitrogen, the dissolved oxygen content in the solution is difficult to control and may easily cause the dissolved oxygen content to be too high. If the dissolved oxygen content is too high, the excess oxygen will produce other impurity phases. The introduction of nitrogen throughout the process is also to prevent the production of other impurity phases.

[0064] S4, Second Stage Reaction

[0065] When the particle size D50 in the reactor increases by 1 to 13 μm from 2 to 5 μm, the flow of metal salt solution and ammonia water is stopped.

[0066] Throughout the entire coprecipitation reaction (first stage reaction and second stage reaction), the pH of the substrate was maintained in the range of 10.5 to 11.5, and the ammonia value was maintained in the range of 1 to 5 g / L.

[0067] In a preferred embodiment, the pH of the base solution can be controlled to be greater than 10.5, while the pH value is gradually decreased throughout the co-precipitation process (including the first stage reaction and the second stage reaction).

[0068] S5, re-oxidation

[0069] Raise the temperature of the reactor to 70-90°C and continue to pass sodium hydroxide solution through until the pH reaches 12-13.

[0070] After the pH reaches 12-13, an oxidant solution is introduced into the reactor. The amount of oxidant solution introduced is based on a mass ratio of 2-5:1 (e.g., 2:1, 3:1, 4:1 or 5:1) between the oxidant and the metal elements in the reactor.

[0071] To ensure a complete reaction, an oxidant is introduced and the reaction is carried out for 10–50 hours to obtain a slurry.

[0072] Since this step involves oxidizing Me(OH)2 to MeOOH, it requires a relatively high temperature and a relatively alkaline environment. Therefore, after co-precipitation, the temperature of the reactor needs to be increased to 70-90°C and the pH increased to 12-13.

[0073] S6. Extract precursor

[0074] The slurry is subjected to solid-liquid separation, the resulting solid is washed, and after solid-liquid separation again, it is dried to obtain the precursor.

[0075] Preferably, filtration is a common method for solid-liquid separation.

[0076] The precursor provided in this embodiment of the invention is prepared using the preparation method provided in this embodiment of the invention.

[0077] The method for preparing the cathode material provided in this embodiment of the invention includes: mixing a sodium source with the precursor provided in this embodiment of the invention and sintering at 800℃~1100℃ for 8~12h.

[0078] Optionally, the sodium source is sodium hydroxide.

[0079] This invention provides a cathode material prepared using the method provided in this invention.

[0080] This invention provides a positive electrode, which is made using the positive electrode material provided in this invention.

[0081] This invention provides a sodium-ion battery, including a positive electrode provided in this invention.

[0082] Example 1

[0083] Preparation of raw material solutions: Prepare ammonia solution with a concentration of 3 mol / L, sodium hydroxide solution with a concentration of 10 mol / L, and metal sulfate solution with a concentration of 2 mol / L containing nickel, iron, manganese and copper in a molar ratio of 2:3:4:1; prepare hydrogen peroxide solution with a mass concentration of 30%.

[0084] Preparation of the base solution: Control the temperature of the reactor at 55℃, and introduce ammonia water and sodium hydroxide solution into the reactor so that the base solution occupies 50% of the reactor volume. The pH of the base solution is 11.0 and the ammonia value is 1g / L.

[0085] The first stage of the reaction involves introducing a metal salt solution, a sodium hydroxide solution, and an ammonia solution while maintaining a stirring speed of 700 rpm. During this process, protective gases nitrogen and oxygen are introduced, with the oxygen flow rate controlled at 1–5 L / min and the nitrogen flow rate at 15–50 L / min. The ratio of nitrogen to oxygen flow rates is adjusted within these ranges to maintain the dissolved oxygen concentration in the solution at approximately 0.6 mg / L. Once the particle D50 reaches 2 μm, oxygen is stopped, and only nitrogen is introduced.

[0086] The second stage of the reaction involves continuing to pass through a metal salt solution, a sodium hydroxide solution, and an ammonia solution to carry out a co-precipitation reaction. The reaction is stopped when the particle size (D50) reaches 5 μm.

[0087] In the first and second stage reactions, the metal salt solution was introduced at a rate of 5 L / h. The ammonia solution was introduced at a rate of 0.1–3 L / h, and the sodium hydroxide solution was introduced at a rate of 1–3 L / h. This was to gradually decrease the pH in the reactor and ensure that the pH was above 10.5, while keeping the ammonia value around 1 g / L.

[0088] The total coprecipitation reaction time, including the first and second reaction stages, is approximately 60 hours.

[0089] Secondary oxidation: The reactor temperature was raised to 80℃, and only sodium hydroxide solution was introduced until the pH of the solution reached 12.5. Then, the introduction of sodium hydroxide solution was stopped, and hydrogen peroxide solution was introduced into the reactor. The mass ratio of hydrogen peroxide to the mass of the metal element in the reactor was 2:1. The stirring rate was 500 rpm, and the reaction was carried out for 10 hours. After washing, filtering, and drying, the slurry from the reactor yielded the sodium-intercalated oxide precursor.

[0090] ICP testing revealed that the sodium-intercalated oxide precursor Na... n Ni x Mn y Fe z In MmO2, the Na:Me ratio (referring to all metal elements except sodium) is 0.4:1. Take SEM images of the precursor, such as... Figure 1 As shown.

[0091] The sodium-intercalated precursor and sodium source were mixed at a ratio of Na:Me = 1.05:1 and sintered at 850°C for 10 hours to obtain the sodium-ion battery cathode material.

[0092] Example 2

[0093] This embodiment is basically the same as Embodiment 1, except that:

[0094] The metal sulfate solution contains nickel, iron, manganese, and magnesium in a molar ratio of 2:4:3:1.

[0095] The pH of the base solution was 10.8, and the ammonia value was 1.5 g / L.

[0096] In the first stage of the reaction, oxygen was stopped and only nitrogen was introduced after the D50 reached 2.5 μm. In the second stage of the reaction, the introduction of metal salt solution and ammonia was stopped after the D50 reached 7 μm. The total co-precipitation time was approximately 80 h.

[0097] Raise the temperature of the reactor to 70°C, continue to introduce sodium hydroxide until the pH in the reactor reaches 13, then introduce hydrogen peroxide solution and react for 12 hours.

[0098] ICP testing revealed that the sodium-intercalated oxide precursor Na... n Ni x Mn y Fe z The Na:Me ratio in MmO2 is 0.43:1. SEM images of the precursor are taken, such as... Figure 2 As shown.

[0099] The sodium-intercalated precursor and sodium source were mixed at a ratio of Na:Me = 1.04:1 and sintered at 850°C for 8 hours. This yielded the final sodium-ion battery cathode material.

[0100] Example 3

[0101] This embodiment is basically the same as Embodiment 1, except that:

[0102] The metal sulfate solution contains nickel, iron, manganese, and zinc in a molar ratio of 3:4:2:1.

[0103] The pH of the base solution was 11.2, and the ammonia value was 2 g / L.

[0104] In the first stage of the reaction, oxygen was stopped and only nitrogen was introduced after the D50 reached 3 μm; in the second stage of the reaction, the introduction of metal salt solution and ammonia was stopped after the D50 reached 6 μm. The total co-precipitation time was approximately 70 h.

[0105] Raise the temperature of the reactor to 90°C, continue to introduce sodium hydroxide until the pH in the reactor reaches 12.7, then introduce hydrogen peroxide solution and react for 12 hours.

[0106] ICP testing revealed that the sodium-intercalated oxide precursor Na... n Ni x Mn y Fe z The Na:Me ratio in MmO2 is 0.45:1. SEM images of the precursor are taken, such as... Figure 3 As shown.

[0107] The sodium-intercalated precursor and sodium source were mixed at a ratio of Na:Me = 1.02:1 and sintered at 900℃ for 10 h. The final sodium-ion battery cathode material was obtained.

[0108] Example 4

[0109] This embodiment is basically the same as Embodiment 1, except that:

[0110] The metal sulfate solution contains nickel, iron, manganese, and aluminum in a molar ratio of 3:4:2:1.

[0111] The pH of the base solution was 11.5, and the ammonia value was 1 g / L.

[0112] In the first stage of the reaction, oxygen was stopped and only nitrogen was introduced after the D50 reached 3 μm; in the second stage of the reaction, the introduction of metal salt solution and ammonia was stopped after the D50 reached 10 μm. The total co-precipitation time was approximately 100 h.

[0113] Raise the temperature of the reactor to 80°C, continue to introduce sodium hydroxide until the pH in the reactor reaches 12.8, then introduce hydrogen peroxide solution and react for 20 hours.

[0114] ICP testing revealed that the sodium-intercalated oxide precursor Na... n Ni x Mn y Fe z The Na:Me ratio in MmO2 is 0.35:1. SEM images of the precursor are taken, such as... Figure 4 As shown.

[0115] The sodium-intercalated precursor and sodium source were mixed at a ratio of Na:Me = 1.03:1 and sintered at 950°C for 9 hours to obtain the sodium-ion battery cathode material.

[0116] Comparative Example 1

[0117] This comparative example is basically the same as Example 1, except that oxygen is not introduced.

[0118] ICP testing revealed that the prepared sodium-intercalated oxide precursor Na... n Ni x Mn y Fe z M m In O2, Na:Me = 0.1:1.

[0119] The sodium-intercalated precursor and sodium source were mixed at a ratio of Na:Me = 1.05:1 and sintered at 850°C for 10 hours to obtain the sodium-ion battery cathode material.

[0120] Comparative Example 2

[0121] This comparative example represents a typical coprecipitation-sintering process.

[0122] This comparative example is basically the same as Example 1, except that oxygen is not introduced, and hydrogen peroxide solution is not introduced after the first and second stage reactions are completed. The resulting slurry is directly washed, filtered, and dried.

[0123] The precursor obtained is a hydroxide precursor.

[0124] The hydroxide precursor and sodium source were mixed at a ratio of Na:Me = 1.05:1, pre-sintered at 500℃ for 5 h, and then sintered at 1000℃ for 12 h. The final sodium-ion battery cathode material was obtained.

[0125] The precursor obtained is a hydroxide precursor.

[0126] The hydroxide precursor and sodium source were mixed at a ratio of Na:Me = 1.05:1, pre-sintered at 500℃ for 5 h, and then sintered at 900℃ for 10 h. The final sodium-ion battery cathode material was obtained.

[0127] Experimental Example

[0128] The sintered cathode material was slurry-coated to prepare coin cell cathode sheets, which were then assembled with sodium sheets to form coin cell sodium-ion batteries. The coin cell sodium-ion batteries were subjected to charge-discharge cycle tests at a 0.1C rate, and the battery capacity and capacity retention are shown in the table below.

[0129] Table 1. Electrochemical performance test results of each embodiment and comparative example.

[0130]

[0131]

[0132] As can be seen from the table above, the cathode materials prepared by the preparation methods provided in the various embodiments of the present invention exhibit excellent electrochemical performance after being made into batteries.

[0133] Comparing Comparative Example 1 with Example 1, the precursor prepared in Comparative Example 1 had a lower sodium intercalation content, indicating that pre-oxidation with oxygen during the preparation process is necessary to increase the sodium intercalation content of the precursor. Furthermore, the capacity and cycling performance of Comparative Example 1 were lower than those of Example 1.

[0134] Comparing Comparative Example 2 with Example 1, the capacity and capacity retention of Comparative Example 2 and Example 1 are similar, indicating that the sodium-ion battery cathode material prepared by first preparing a sodium-intercalated layered nickel-iron-manganese sodium-intercalated precursor and then sintering it is comparable in performance to the sodium-ion battery cathode material prepared by the ordinary co-precipitation-sintering process, but Comparative Example 2 requires a longer sintering temperature and sintering time.

[0135] Compared with the common co-precipitation method for preparing hydroxide precursors and then high-temperature sintering for sodium-ion cathode materials, the precursor preparation method provided by this invention enables more uniform sodium intercalation, resulting in a precursor with better electrochemical performance after being made into a cathode material. Furthermore, subsequent sintering can be carried out at a lower sintering temperature, effectively reducing sintering energy consumption and thus lowering production costs.

[0136] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a nickel-iron-manganese sodium intercalation precursor, characterized in that, Comprise: The temperature of the reactor is controlled to be 50-60℃, the pH value of the bottom liquid is 10.5-11.5, the ammonia value is 1-5 g / L, metal salt solution, sodium hydroxide solution and ammonia water are introduced into the reactor, and oxygen and inert gas are introduced below the liquid surface to carry out co-precipitation reaction, and the metal salt solution is a salt solution containing nickel, iron and manganese elements; During the co-precipitation reaction, the pH value of the bottom liquid is maintained in the range of 10.5-11.5, and the ammonia value is in the range of 1-5 g / L; when the particle D50 in the reactor reaches 2-5 μm, the oxygen is stopped; when the particle D50 in the reactor increases by 1-13 μm on the basis of 2-5 μm, the metal salt solution and ammonia water are stopped; The temperature of the reactor is increased to 70-90℃, sodium hydroxide solution is continuously introduced until the pH is 12-13, and then an oxidizing agent solution is introduced into the reactor to fully react to obtain a slurry; The solid material in the slurry is extracted to obtain a precursor.

2. The production method according to claim 1, characterized by, The metal salt solution further contains a doping element, and the doping element is selected from at least one of Al, Cu, Zn, Mg, Ti, Zr, Nb and Sr.

3. The preparation method according to claim 2, characterized in that, The metal salt solution is formulated according to the following chemical formula: the chemical formula of the precursor is Na n Ni x Mn y Fe z M m O2, wherein 0.20≤x≤0.40, 0.3≤y≤0.4, 0.3≤z≤0.4, 0.05≤m≤0.1, n+x+y+z=2, and M is the doping element.

4. The method of claim 1, wherein, The oxidizing agent solution is a hydrogen peroxide solution, and the mass fraction of hydrogen peroxide in the hydrogen peroxide solution is 10-30%.

5. The preparation method according to claim 1, characterized in that, The reaction time after the introduction of the oxidizing agent solution is 10-50 h.

6. The method of claim 1, wherein, Further comprising at least one of the following features (1)-(6); (1) During the introduction of oxygen, the concentration of dissolved oxygen in water is controlled to be 0.2-0.6 mg / L; (2) The way of extracting the solid material in the slurry to obtain a precursor comprises: The slurry is subjected to solid-liquid separation, the obtained solid is washed, and then subjected to solid-liquid separation again and dried; (3) The inert gas is selected from at least one of nitrogen and argon; (4) The molar concentration of the ammonia water is 1-3 mol / L; the molar concentration of the sodium hydroxide solution is 5-10 mol / L; and the total molar concentration of metal ions in the metal salt solution is 1-2 mol / L; (5) The flow rate of nitrogen is 15-50 L / min, and the flow rate of oxygen is 1-5 L / min; (6) The bottom liquid accounts for 50%-80% of the volume of the reactor.

7. A precursor, characterized in that, Prepared by the preparation method according to any one of claims 1-6.

8. A method for producing a positive electrode material, characterized by, Comprise: The sodium source is mixed with the precursor according to claim 7 uniformly, and then sintered at 800-1100℃ for 8-12 h.

9. The production method according to claim 8, characterized by, The sodium source is sodium hydroxide.

10. A positive electrode material, characterized in that, Prepared by the preparation method according to claim 8.

11. A positive electrode, characterized by comprising: Prepared by the preparation method according to claim 10.

12. A sodium-ion battery, characterized in that, The positive electrode material according to claim 11 is used.

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