Hollow structure precursor, preparation method thereof, positive electrode material, positive electrode and battery

Abstract

This invention discloses a hollow precursor, its preparation method, a cathode material, a cathode, and a battery. The precursor preparation method includes: under a protective atmosphere, simultaneously introducing a nickel-iron-manganese mixed salt solution, a zinc-containing solution, a complexing agent solution, and a precipitant solution into a reactor containing a base liquid; when the particle D50 in the reactor grows to 2–5 μm, stopping the introduction of the zinc-containing solution, while continuing to introduce the nickel-iron-manganese mixed salt solution, the complexing agent solution, and the precipitant solution; after the particle D50 in the reactor grows to the target size, stopping the introduction of all solutions, and then introducing sodium hydroxide solution into the reactor until the pH reaches 12.5–13.8 to dissolve the zinc, until the particle D50 in the reactor reaches the final target particle size. This preparation method can produce a hollow precursor, and the cathode material made from it exhibits good cycle performance.

Description

Technical Field

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

[0002] Sodium-ion batteries are a novel rechargeable battery technology with high energy density, low cost, and good environmental friendliness. Compared to lithium-ion batteries, sodium-ion batteries are more difficult to research because the larger radius of sodium ions leads to different reaction kinetics in the battery electrolyte and electrodes, which is the main challenge facing sodium-ion batteries. However, with the increasing demand for renewable and clean energy, and concerns about lithium resource scarcity, sodium-ion batteries are becoming a promising new rechargeable battery technology.

[0003] Maintaining excellent rate performance and cycle stability while ensuring the specific capacity of ternary cathode materials is a research hotspot. Especially with the rapid development of fast charging technology, higher demands are placed on the structural stability of ternary cathode materials. The volume changes and side reactions between the material and the electrolyte during long-term high-current charge-discharge cycles can damage the material structure, leading to rapid capacity decay. Forming a loose, porous, hollow structure within the ternary cathode material can effectively mitigate the structural damage caused by volume changes and side reactions. Simultaneously, the hollow internal structure can shorten the lithium-ion transport path during charge-discharge processes, accelerating ion migration and effectively reducing electrochemical polarization. Therefore, it is essential to prepare a porous, hollow ternary precursor.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a hollow precursor and its preparation method, a cathode material, a cathode, and a battery.

[0006] This invention is implemented as follows:

[0007] In a first aspect, the present invention provides a method for preparing a hollow precursor, comprising:

[0008] Under a protective atmosphere, a mixed salt solution of nickel, iron and manganese, a zinc-containing solution, a complexing agent solution and a precipitant solution are introduced in parallel into a reactor containing a bottom liquid.

[0009] First particle growth stage: When the particles D50 in the reactor grow to 2-5 μm, the flow of the zinc-containing solution is stopped, while the nickel-iron-manganese mixed salt solution, the complexing agent solution, and the precipitant solution continue to be flowed.

[0010] Second particle growth stage: After the particles D50 in the reactor grow to the target size, stop all solution flow. Then, introduce sodium hydroxide solution into the reactor until the pH is 12.5-13.8 to dissolve zinc until the particles D50 in the reactor reach the final target particle size.

[0011] In an optional embodiment, the temperature of the reactor is 50–75°C.

[0012] In an optional embodiment, the complexing agent solution is ammonia water, and the precipitant solution is sodium hydroxide solution; the mass concentration of the ammonia water is 10-20%, and the mass concentration of the sodium hydroxide solution is 28-35%.

[0013] In an optional embodiment, the base solution consists of ammonia water and sodium hydroxide solution introduced into the reaction vessel, wherein the ammonia value of the base solution is 2-10 g / L and the pH is 11.2-12.5;

[0014] During the first particle growth stage, the ammonia value in the reactor is kept within the range of 2 to 10 g / L and the pH value is kept within the range of 11.2 to 11.7 by dynamically adjusting the inflow rate of the complexing agent solution and the precipitant solution.

[0015] In the second particle growth stage, the ammonia value in the reactor is kept within the range of 2 to 10 g / L and the pH value is kept within the range of 10.8 to 11.5 by dynamically adjusting the inflow rate of the complexing agent solution and the precipitant solution.

[0016] In an optional embodiment, the concentration of metal ions in the nickel-iron-manganese mixed salt solution is 80-120 g / L, and the inlet rate is 150-700 L / h.

[0017] The zinc ion concentration in the zinc-containing solution is 30–90 g / L, and the influent rate is 50–300 L / h.

[0018] In an optional embodiment, the molar ratio of nickel, iron, and manganese in the nickel-iron-manganese salt mixed solution is a:b:c, where a is 0.25–0.95, b is 0.25–0.95, c is 0.25–0.95, and a+b+c=1.

[0019] In an optional embodiment, the zinc-containing solution is prepared from a zinc salt solution and a sodium hydroxide solution, and the pH of the zinc-containing solution is 12.5 to 13.5.

[0020] Secondly, the present invention provides a hollow precursor, which is prepared by the preparation method described in any of the foregoing embodiments.

[0021] Thirdly, the present invention provides a sodium-ion cathode material obtained from a hollow precursor as described in the foregoing embodiments.

[0022] Fourthly, the present invention provides a positive electrode made from the sodium-ion electrode material as described in the foregoing embodiments.

[0023] Fifthly, the present invention provides a sodium-ion battery, comprising a positive electrode as described in the foregoing embodiments.

[0024] The present invention has the following beneficial effects:

[0025] A precursor core with a specific particle size was prepared using zinc, nickel, iron, and manganese ions. The zinc feed was then stopped, and the reaction continued until the target particle size was reached. After the reaction was stopped, sodium hydroxide solution was added to the reaction system to adjust the pH to a suitable range, allowing the zinc hydroxide to dissolve and creating voids in the spaces previously occupied by the zinc hydroxide. This resulted in a hollow-structured precursor for sodium-ion battery cathode materials. Furthermore, due to the small radius and low lattice distortion of zinc ions, a precursor with better performance can be obtained compared to aluminum. Attached Figure Description

[0026] 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.

[0027] Figure 1 This is an electron microscope image of the precursor particles at the first magnification in Example 1;

[0028] Figure 2 This is an electron microscope image of the precursor particles in Example 1 at the second magnification.

[0029] Figure 3 This is an electron microscope image of the precursor particles at the first magnification in Example 2;

[0030] Figure 4 This is a cross-sectional electron microscope image of the precursor particles at the second magnification in Example 2;

[0031] Figure 5 This is a cross-sectional electron microscope image of the precursor particles at the first magnification, for Comparative Example 1.

[0032] Figure 6 This is a cross-sectional electron microscope image of the precursor particles at the second magnification, which is a comparative example 1. Detailed Implementation

[0033] 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.

[0034] The hollow precursor, its preparation method, cathode material, cathode, and battery provided in the embodiments of the present invention will be described in detail below.

[0035] This invention provides a method for preparing a hollow precursor, comprising:

[0036] Under a protective atmosphere, a mixed salt solution of nickel, iron and manganese, a zinc-containing solution, a complexing agent solution and a precipitant solution are introduced in parallel into a reactor containing a bottom liquid.

[0037] First particle growth stage: When the particles D50 in the reactor grow to 2-5 μm, the flow of the zinc-containing solution is stopped, while the nickel-iron-manganese mixed salt solution, the complexing agent solution, and the precipitant solution continue to be flowed.

[0038] Second particle growth stage: After the particles D50 in the reactor have grown to the target size, stop all solution flow, and then introduce sodium hydroxide solution into the reactor until the pH is 12.5-13.8 to dissolve zinc.

[0039] A precursor core with a certain particle size was prepared using zinc, nickel, iron, and manganese ions. The zinc was then stopped, and the reaction continued until the target particle size was reached. After the reaction was stopped, sodium hydroxide solution was added to the reaction system to adjust the pH to a suitable range so that zinc hydroxide could dissolve and the space originally occupied by zinc hydroxide could be filled with voids, thus preparing a hollow sodium-ion battery cathode material precursor.

[0040] Aluminum hydroxide, like zinc hydroxide, is amphoteric. In this application, zinc, instead of aluminum, is used to prepare the hollow sodium-ion battery precursor because aluminum has a larger ionic radius, leading to lattice distortion and changes in interface properties; while zinc replaces the metal ions in the original material, forming a solid solution structure with less lattice distortion. Therefore, compared to aluminum, using zinc to prepare the hollow precursor results in a cathode material with better cycle performance.

[0041] Specifically, the preparation method is as follows:

[0042] S1. Preparation of each solution

[0043] A complexing agent is dissolved in pure water to obtain a complexing agent solution; a precipitant is dissolved in pure water to obtain a precipitant solution; nickel salts, iron salts, and manganese salts are dissolved in water to obtain a nickel-iron-manganese mixed salt solution; a soluble zinc salt (e.g., sulfate or hydrochloride) is dissolved in pure water to obtain a zinc salt solution; and the zinc salt solution is mixed with a sodium hydroxide solution to obtain a zinc-containing solution.

[0044] Specifically, ammonia is generally chosen as the complexing agent, and the mass concentration of the prepared complexing agent solution is 10-20% (e.g., 10%, 15%, or 20%); sodium hydroxide is generally chosen as the precipitant, and the mass concentration of the prepared precipitant solution is generally 28-35% (e.g., 28%, 30%, 33%, or 35%); soluble salts such as nickel, iron, and manganese salts can be used, and sulfates are generally preferred. The concentration of metal ions in the prepared nickel-iron-manganese mixed salt solution can be 80-130 g / L (e.g., 80 g / L, 100 g / L, 110 g / L, or 130 g / L); the concentration of zinc ions in the prepared zinc-containing solution can be 30-90 mol / L (e.g., 30 mol / L, 50 mol / L, 70 mol / L, or 90 mol / L), and its pH value is 12.5-13.5 (e.g., 12.5, 12.8, 13, 13.2, or 13.5).

[0045] Furthermore, in the nickel-iron-manganese mixed salt solution, the molar ratio of nickel, iron, and manganese is a:b:c, where a is 0.25–0.95, b is 0.25–0.95, c is 0.25–0.95, and a+b+c=1.

[0046] S2, Prepare the base liquid

[0047] The stirring speed of the reactor is controlled at 150–300 rpm (e.g., 150 rpm, 200 rpm, 250 rpm or 300 rpm), and the temperature inside the reactor is controlled at 50–75℃ (50℃, 60℃, 70℃ or 75℃). Complexing agent solution and precipitant solution are introduced into the reactor to make the ammonia value inside the reactor 2–10 g / L (2 g / L, 5 g / L, 8 g / L or 10 g / L) and the pH 11.2–12.5 (e.g. 11.2, 11.5, 11.8, 12, 12.3 or 12.5).

[0048] S3, First Particle Growth Stage

[0049] An inert gas (e.g., nitrogen or argon) is introduced into the reactor. The complexing agent solution, precipitant solution, nickel-iron-manganese mixed salt solution, and zinc-containing solution are continuously and concurrently introduced into the reactor. The flow rate of the nickel-iron-manganese mixed salt solution is controlled at 150–700 L / h (150 L / h, 200 L / h, 300 L / h, 400 L / h, 500 L / h, 600 L / h, or 700 L / h), and the flow rate of the zinc-containing solution is controlled at 50–300 L / h (e.g., 50 L / h, 100 L / h, 150 L / h, 200 L / h, 250 L / h, or 300 L / h).

[0050] During this process, the pH value in the reactor is controlled at 11.2 to 11.7 (e.g., 11.2, 11.5 or 11.7) and the ammonia value is controlled at 2 to 10 g / L (e.g., 2 g / L, 5 g / L, 8 g / L or 10 g / L) by dynamically adjusting the flow rate of the precipitant solution and complexing agent solution.

[0051] When the D50 particles in the reactor are detected to have grown to 2–5 μm (2 μm, 3 μm, 4 μm or 5 μm), the flow of zinc-containing solution is stopped.

[0052] In this step, controlling the flow rate of the nickel-iron-manganese mixed solution and the zinc-containing solution within a suitable range ensures uniform co-precipitation of zinc with nickel-iron-manganese, and guarantees uniform porosity in the core during the subsequent zinc dissolution process, thereby producing a precursor with better electrochemical performance.

[0053] S4, Second Particle Growth Stage

[0054] The zinc-containing solution is stopped from being introduced, but the other solutions continue to be introduced. By dynamically adjusting the introduction rates of the complexing agent solution and the precipitant solution, the ammonia value in the reactor is kept within the range of 2 to 10 g / L (e.g., 2 g / L, 5 g / L, 8 g / L or 10 g / L), and the pH value is kept within the range of 10.8 to 11.5 (e.g., 10.8, 11, 11.3 or 11.5).

[0055] Once the particles D50 in the reactor are detected to have grown to the target particle size of 3–10.5 μm (e.g., 3 μm, 5 μm, 7 μm, 9 μm, or 10.5 μm), the flow of all solutions is stopped, and the reaction is halted.

[0056] S5, Zinc Dissolved

[0057] After the reaction is stopped, a certain amount of mother liquor is removed by a concentration machine. Then, sodium hydroxide solution is introduced into the reactor to make the pH value in the reactor reach 12.5 to 13.8 (e.g., 12.5, 12.8, 13, 13.2, 13.5 or 13.8), so that the zinc hydroxide in the particles dissolves out.

[0058] S3, Post-processing

[0059] The solid-liquid mixture in the reactor is discharged into an aging tank, and after washing, drying, sieving, and iron removal (referring to the removal of magnetic foreign matter from the material using a battery iron remover), the ternary precursor is obtained.

[0060] The hollow precursor provided in this embodiment of the invention is prepared using the preparation method provided in this embodiment of the invention.

[0061] The sodium-ion cathode material provided in this embodiment of the invention is obtained from the hollow-structured precursor provided in this embodiment of the invention.

[0062] The positive electrode provided in this embodiment of the invention is made from the sodium-ion battery positive electrode material provided in this embodiment of the invention.

[0063] The sodium-ion battery provided in this embodiment of the invention includes the positive electrode provided in this embodiment of the invention.

[0064] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0065] Example 1

[0066] 1. Prepare a 32% sodium hydroxide solution and a 16% ammonia solution; prepare a nickel-iron-manganese sulfate mixed solution with a nickel, iron, and manganese molar ratio of 6:2:2 and a metal ion concentration of approximately 90 g / L; dissolve zinc sulfate in pure water to obtain a zinc salt solution, and mix the zinc salt solution with the sodium hydroxide solution to prepare a zinc-containing solution with a pH of 13.0 and a zinc ion concentration of 40 g / L.

[0067] 2. Add pure water to the top of the reactor, stirring at 20cm, and control the temperature at 60℃. Introduce nitrogen as a protective gas.

[0068] 3. Adjust the pH of the reaction vessel to 11.50 and the ammonia concentration to 6.0 g / L using the sodium hydroxide solution and ammonia water prepared in step 1;

[0069] 4. Under the conditions of reactor temperature of 60℃ and stirring speed of 300rpm, nickel-iron-manganese sulfate mixed solution is added to the reactor at a rate of 400L / h, zinc-containing solution is added at a flow rate of 200L / h, and the pH of the reaction system is reduced to 11.20 by controlling the flow rate of sodium hydroxide solution and ammonia water at a rate of 0.05 pH decrease per hour, and the ammonia concentration is maintained within the range of 6.0±0.5g / L;

[0070] 5. When the particle size D50 in the slurry reaches 4.0 μm, stop the flow of zinc-containing solution, lower the pH to 11.00, reduce the stirring speed to 200 rpm, and continue the reaction until the slurry D50 reaches 10.0 μm, then stop the flow of all solutions.

[0071] 6. The clarification process is performed using a concentration machine, discharging 2.0m³ of the solution. 3 The mother liquor is then purged with sodium hydroxide solution and pure water obtained in step 1 to replenish the original liquid level and make the pH of the system 13.5. The mixture is stirred at 200 rpm for 10 hours to dissolve the zinc hydroxide core inside and form a hollow internal structure. At this time, the particle size D50 is 10 μm.

[0072] 7. The precursor slurry obtained in step 6 was aged, centrifuged, washed, dried, sieved, and iron removed to obtain the target ternary precursor.

[0073] Example 2

[0074] 1. Prepare a 32% sodium hydroxide solution and a 16% ammonia solution; prepare a nickel-iron-manganese sulfate mixed solution with a nickel, iron, and manganese molar ratio of 2:3:5 and a metal ion concentration of approximately 110 g / L; dissolve zinc sulfate in pure water to obtain a zinc salt solution; mix the zinc salt solution with the sodium hydroxide solution to prepare a zinc-containing solution with a pH of 13.1 and a zinc ion concentration of 45 g / L.

[0075] 2. Add pure water to the top 20cm of the upper agitator in the reactor (the reactor has two agitators; this means adding pure water to submerge the upper agitator by 20cm), control the temperature at 55℃, and introduce nitrogen as a protective gas.

[0076] 3. Adjust the pH of the reactor to 11.75 and the ammonia concentration to 4.5 g / L using the sodium hydroxide solution and ammonia water prepared in step 1;

[0077] 4. Under the conditions of reactor temperature of 55℃ and stirring speed of 280rpm, a nickel-iron-manganese sulfate mixed solution is added to the reactor at a rate of 500L / h, and a zinc-containing solution is added at a flow rate of 300L / h. The pH of the reaction system is reduced to 11.30 by controlling the flow rates of sodium hydroxide solution and ammonia water at a rate of 0.02 pH decrease per hour, and the ammonia concentration is maintained within the range of 6.0±0.5g / L.

[0078] 5. When the particle size D50 in the slurry reaches 2.5μm, stop the flow of zinc-containing solution, lower the pH to 11.00, reduce the stirring speed to 200rpm, and continue the reaction until the slurry D50 reaches 5.5μm, then stop the flow of all solutions.

[0079] 6. The clarification process is performed using a concentration machine, discharging 1.8m³ of the solution. 3 The mother liquor was then purged with sodium hydroxide solution and pure water obtained in step 1 to replenish the original liquid level and make the pH of the system 13.6. The mixture was stirred at 200 rpm for 10 hours to dissolve the zinc hydroxide core inside and form a hollow internal structure. At this time, the particle size D50 was 5.5 μm.

[0080] 7. The precursor slurry obtained in step 6 was aged, centrifuged, washed, dried, sieved, and iron removed to obtain the target ternary precursor.

[0081] Example 3

[0082] 1. Prepare a 32% sodium hydroxide solution and a 16% ammonia solution; prepare a nickel-iron-manganese sulfate mixed solution with a nickel, iron, and manganese molar ratio of 2:2:6 and a metal ion concentration of approximately 100 g / L; dissolve zinc sulfate in pure water to obtain a zinc salt solution, and mix the zinc salt solution with the sodium hydroxide solution to prepare a zinc-containing solution with a pH of 13.2 and a zinc ion concentration of 55 g / L.

[0083] 2. Stir the liquid at the bottom of the reactor to a depth of 20cm with pure water, control the temperature at 55℃, and introduce nitrogen as a protective gas;

[0084] 3. Adjust the pH of the reaction vessel to 11.65 and the ammonia concentration to 5.5 g / L using the sodium hydroxide solution and ammonia water prepared in step 1;

[0085] 4. Under the conditions of reactor temperature of 55℃ and stirring speed of 280rpm, nickel-iron-manganese sulfate mixed solution is added to the reactor at a rate of 300L / h, zinc-containing solution is added at a flow rate of 100L / h, and the pH of the reaction system is reduced to 11.40 by controlling the flow rate of sodium hydroxide solution and ammonia water at a rate of 0.03 pH decrease per hour, and the ammonia concentration is maintained within the range of 5.5±0.5g / L;

[0086] 5. When the particle size D50 in the slurry reaches 3.5μm, stop the flow of zinc-containing solution, lower the pH to 11.00, reduce the stirring speed to 200rpm, and continue the reaction until the slurry D50 reaches 6.0μm, then stop the flow of all solutions.

[0087] 6. The clarification process is performed using a concentration machine, discharging 1.9m³ of the solution. 3 The mother liquor was then purged with sodium hydroxide solution and pure water obtained in step 1 to replenish the original liquid level and make the pH of the system 13.7. The mixture was stirred at 200 rpm for 10 hours to dissolve the zinc hydroxide core inside and form a hollow internal structure. At this time, the particle size D50 was 6 μm.

[0088] 7. The precursor slurry obtained in step 6 was aged, centrifuged, washed, dried, sieved, and iron removed to obtain the target ternary precursor.

[0089] Comparative Example 1

[0090] 1. Prepare a 32% sodium hydroxide solution and a 16% ammonia solution; prepare a nickel-iron-manganese sulfate mixed solution with a nickel-iron-manganese molar ratio of 6:2:2 and a metal ion concentration of approximately 90 g / L.

[0091] 2. Add pure water to the top of the reactor, stirring at 20cm, and control the temperature at 60℃. Introduce nitrogen as a protective gas.

[0092] 3. Adjust the pH of the reaction vessel to 11.50 and the ammonia concentration to 6.0 g / L using the sodium hydroxide solution and ammonia water prepared in step 1;

[0093] 4. Under the conditions of reactor temperature of 60℃ and stirring speed of 300rpm, nickel-iron-manganese sulfate mixed solution is added to reactor at a rate of 400L / h, and the pH of the reaction system is reduced to 11.20 by controlling the flow rate of sodium hydroxide solution and ammonia water at a rate of 0.05 pH decrease per hour, while maintaining the ammonia concentration within the range of 6.0±0.5g / L.

[0094] 5. When the particle size D50 in the slurry is 4.0 μm, lower the pH to 11.00, reduce the stirring speed to 200 rpm, and continue the reaction until the slurry D50 is 10.0 μm, then stop the introduction of all solutions.

[0095] 6. The clarification process is performed using a concentration machine, discharging 2.0m³ of the solution. 3 The mother liquor was then purged with sodium hydroxide solution and pure water obtained in step 1 to replenish the original liquid level and make the pH of the system 13.5. The mixture was stirred at a stirring speed of 200 rpm for 10 h, at which point the particle size D50 was 10 μm.

[0096] 7. The precursor slurry obtained in step 6 was aged, centrifuged, washed, dried, sieved, and iron removed to obtain the target ternary precursor.

[0097] The only difference between this comparative example and Example 1 is that no zinc-containing solution was introduced.

[0098] Comparative Example 2

[0099] 1. Prepare a 32% sodium hydroxide solution and a 16% ammonia solution; prepare a nickel-iron-manganese sulfate mixed solution with a nickel, iron, and manganese molar ratio of 6:2:2 and a metal ion concentration of 90 g / L; dissolve aluminum sulfate in pure water to obtain a zinc salt solution, and mix the zinc salt solution with the sodium hydroxide solution to prepare an aluminum-containing solution with a pH of 13.0 and an aluminum ion concentration of approximately 16.6 g / L.

[0100] 2. Add pure water to the top of the reactor, stirring at 20cm, and control the temperature at 60℃. Introduce nitrogen as a protective gas.

[0101] 3. Adjust the pH of the reaction vessel to 11.50 and the ammonia concentration to 6.0 g / L using the sodium hydroxide solution and ammonia water prepared in step 1;

[0102] 4. Under the conditions of reactor temperature of 60℃ and stirring speed of 300rpm, nickel-iron-manganese sulfate mixed solution is added to reactor at a rate of 400L / h, aluminum-containing solution is added at a flow rate of 200L / h, and the pH of the reaction system is reduced to 11.20 by controlling the flow rate of sodium hydroxide solution and ammonia water at a rate of 0.05 pH decrease per hour, and the ammonia concentration is maintained within the range of 6.0±0.5g / L;

[0103] 5. When the particle size D50 in the slurry reaches 4.0 μm, stop the flow of aluminum-containing solution, lower the pH to 11.00, reduce the stirring speed to 200 rpm, and continue the reaction until the slurry D50 reaches 10.0 μm, then stop the flow of all solutions.

[0104] 6. The clarification process is performed using a concentration machine, discharging 2.0m³ of the solution. 3 The mother liquor is then purged with sodium hydroxide solution and pure water obtained in step 1 to replenish the original liquid level and make the pH of the system 13.5. The mixture is stirred at a stirring speed of 200 rpm for 10 hours to dissolve the aluminum hydroxide core inside and form a hollow internal structure. At this time, the particle size D50 is 10 μm.

[0105] 7. The precursor slurry obtained in step 6 was aged, centrifuged, washed, dried, sieved, and iron removed to obtain the target ternary precursor.

[0106] The only difference between this comparative example and Example 1 is that an aluminum-containing solution with the same molar concentration of zinc ions and the same pH value as in Example 1 is used instead of a zinc-containing solution.

[0107] Comparative Example 3

[0108] 1. Prepare a 32% sodium hydroxide solution and a 16% ammonia solution; prepare a nickel-cobalt-manganese sulfate mixed solution with a nickel, cobalt, and manganese molar ratio of 6:2:2 and a metal ion concentration of approximately 90.9 g / L; dissolve aluminum sulfate in pure water to obtain a zinc salt solution, and mix the zinc salt solution with the sodium hydroxide solution to prepare a zinc-containing solution with a pH of 13.0 and a zinc ion concentration of 40 g / L.

[0109] 2. Add pure water to the top of the reactor, stirring at 20cm, and control the temperature at 60℃. Introduce nitrogen as a protective gas.

[0110] 3. Adjust the pH of the reaction vessel to 11.50 and the ammonia concentration to 6.0 g / L using the sodium hydroxide solution and ammonia water prepared in step 1;

[0111] 4. Under the conditions of reactor temperature of 60℃ and stirring speed of 300rpm, nickel cobalt manganese sulfate mixed solution is added to reactor at a rate of 400L / h, zinc-containing solution is added at a flow rate of 200L / h, and the pH of the reaction system is reduced to 11.20 by controlling the flow rate of sodium hydroxide solution and ammonia water at a rate of 0.05 pH decrease per hour, and the ammonia concentration is maintained within the range of 6.0±0.5g / L;

[0112] 5. When the particle size D50 in the slurry reaches 4.0 μm, stop the flow of zinc-containing solution, lower the pH to 11.00, reduce the stirring speed to 200 rpm, and continue the reaction until the slurry D50 reaches 10.0 μm, then stop the flow of all solutions.

[0113] 6. The clarification process is performed using a concentration machine, discharging 2.0m³ of the solution. 3 The mother liquor is then purged with sodium hydroxide solution and pure water obtained in step 1 to replenish the original liquid level and make the pH of the system 13.5. The mixture is stirred at 200 rpm for 10 hours to dissolve the zinc hydroxide core inside and form a hollow internal structure. At this time, the particle size D50 is 10 μm.

[0114] 7. The precursor slurry obtained in step 6 was aged, centrifuged, washed, dried, sieved, and iron removed to obtain the target ternary precursor.

[0115] The only difference between this comparative example and Example 1 is that the iron ions in the nickel-iron-manganese mixed salt solution are replaced with an equimolar amount of cobalt ions.

[0116] Experimental Example 1

[0117] Electron micrographs of Examples 1, 2 and Comparative Example 1 were taken, as follows: Figures 1-6 As shown, Figure 1 , 2 These are cross-sectional electron microscope images of the precursor particles prepared in Example 1 at different magnifications. Figure 3 , 4 These are cross-sectional electron microscope images of the precursor particles prepared in Example 2 at different magnifications. Figure 5 , 6 The images are cross-sectional electron microscope images of the precursor particles prepared in Comparative Example 1 at different magnifications.

[0118] from Figure 1-4 It can be seen that the precursors obtained in Examples 1 and 2 have obvious hollow structures. The precursor obtained in Comparative Example 1 does not have a hollow structure.

[0119] Experiment Example 2

[0120] The precursors obtained in Examples 1-3 and Comparative Examples 1-3 were mixed with lithium hydroxide and sintered at a lithium ratio of 1.03 to obtain a positive electrode material. The positive electrode material was then used to make an electrode and assembled into an LIR2032 coin cell. A coin cell test was conducted under 1.0C conditions.

[0121] Record the test results in Table 1.

[0122] Table 1. Electrochemical performance of batteries prepared in each embodiment and comparative example. As can be seen from the table above, the embodiments provided by the present invention have better cycle performance. Comparing the experimental results of Comparative Example 1 with those of Example 1, Comparative Example 1 is significantly worse, indicating that the hollow structure of the precursor is beneficial to improving the cycle performance of the battery.

[0123] Comparing the experimental results of Comparative Example 2 with those of Example 1, Comparative Example 2 was significantly worse, indicating that the hollow precursor prepared with zinc has better cycle performance than aluminum when used to make cathode materials.

[0124] For cathode materials with ordinary structures, the performance of nickel-cobalt-manganese ternary materials is usually better than that of nickel-iron-manganese ternary materials. However, when comparing the experimental results of Comparative Example 3 with those of Example 1, Comparative Example 3 is significantly worse, indicating that nickel-iron-manganese precursors are more suitable for preparing hollow structures with zinc than nickel-cobalt-manganese precursors.

[0125] The present invention provides a method for preparing a hollow precursor. A precursor core with a specific particle size is prepared using zinc, nickel, iron, and manganese ions. The zinc infusion is then stopped, and the reaction continues until the target particle size is reached. After the reaction is stopped, sodium hydroxide solution is added to the reaction system to adjust the pH to a suitable range that allows zinc hydroxide to dissolve, creating voids in the spaces previously occupied by zinc hydroxide. This process produces a hollow precursor for sodium-ion battery cathode materials. Furthermore, due to the small radius and low lattice distortion of zinc ions, a precursor with better performance can be obtained compared to aluminum.

[0126] The above description is merely a preferred embodiment of the present invention and is not intended to limit the 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 hollow precursor, characterized in that, include: Under a protective atmosphere, a mixed salt solution of nickel, iron and manganese, a zinc-containing solution, a complexing agent solution and a precipitant solution are introduced in parallel into a reactor containing a bottom liquid. First particle growth stage: When the particles D50 in the reactor grow to 2-5 μm, the flow of the zinc-containing solution is stopped, while the nickel-iron-manganese mixed salt solution, the complexing agent solution, and the precipitant solution continue to be flowed. Second particle growth stage: After the particles D50 in the reactor grow to the target size, stop all solution flow. Then, introduce sodium hydroxide solution into the reactor until the pH is 12.5-13.8 to dissolve zinc until the particles D50 in the reactor reach the final target particle size.

2. The preparation method according to claim 1, characterized in that, The temperature of the reactor is 50–75°C.

3. The preparation method according to claim 1, characterized in that, The complexing agent solution is ammonia water, and the precipitant solution is sodium hydroxide solution; the mass concentration of the ammonia water is 10-20%, and the mass concentration of the sodium hydroxide solution is 28-35%.

4. The preparation method according to claim 1, characterized in that, The ammonia value of the substrate solution is 2-10 g / L, and the pH is 11.2-12.

5. During the first particle growth stage, the ammonia value in the reactor is kept within the range of 2 to 10 g / L and the pH value is kept within the range of 11.2 to 11.7 by dynamically adjusting the inflow rate of the complexing agent solution and the precipitant solution. In the second particle growth stage, the ammonia value in the reactor is kept within the range of 2 to 10 g / L and the pH value is kept within the range of 10.8 to 11.5 by dynamically adjusting the inflow rate of the complexing agent solution and the precipitant solution.

5. The preparation method according to claim 1, characterized in that, It also includes at least one of the following technical features (1) and (2); (1) The concentration of metal ions in the nickel-iron-manganese mixed salt solution is 80-130 g / L, and the inlet rate is 150-700 L / h; The concentration of zinc ions in the zinc-containing solution is 30–90 g / L, and the infusion rate is 50–300 L / h. (2) In the nickel-iron-manganese salt mixed solution, the molar ratio of nickel, iron and manganese is a:b:c, where a is 0.25 to 0.95, b is 0.25 to 0.95, c is 0.25 to 0.95, and a+b+c=1.

6. The preparation method according to claim 5, characterized in that, The zinc-containing solution is prepared from a zinc salt solution and a sodium hydroxide solution, and the pH of the zinc-containing solution is 12.5 to 13.

5.

7. A hollow precursor, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 6.

8. A sodium-ion cathode material, characterized in that, It is obtained from the precursor of the hollow structure as described in claim 7.

9. A positive electrode, characterized in that, It is prepared from the sodium-ion cathode material as described in claim 8.

10. A sodium-ion battery, characterized in that, Includes the positive electrode as described in claim 9.

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