Method for preparing sodium electric precursor by redox control potential method

Abstract

The invention discloses a method for preparing a sodium electric precursor by a redox control potential method. According to the invention, the oxidation-reduction electrode is arranged on the reaction kettle to monitor the oxidation-reduction potential of the reaction system in real time, and different potential control is realized by controlling the purity of nitrogen and other mixed gases in the reaction kettle or the dosage of an oxidation-reduction agent added into the reaction kettle; the primary and secondary particle morphology, the specific surface area and the product compaction of the product can be effectively controlled, and precursors with different physical and chemical indexes can be prepared according to different potentials. According to different characteristics of the precursor, the sintered positive electrode material has different electrochemical properties, such as higher electrochemical rate capability, gram volume and cycle performance, so as to meet application requirements of different products.

Description

Technical Field

[0001] This invention relates to the field of battery precursors, and specifically to a method for preparing sodium battery precursors using a redox controlled potential method. Background Technology

[0002] As a major lithium consumer, China faces a shortage of lithium resources, particularly those of low grade, which may constrain its development in the long term. Therefore, finding alternatives to lithium batteries is particularly urgent. Sodium batteries offer advantages such as high safety, high rate performance, excellent wide-temperature performance, and low cost. Furthermore, sodium resources are abundant in the Earth's crust. Sodium-ion batteries operate on the same principle as lithium-ion batteries, with similar production processes and equipment. Compared to lithium batteries, sodium batteries have lower energy density, making them suitable for applications with lower energy density requirements and greater sensitivity to cost and safety. With lithium prices remaining high and sodium batteries demonstrating significant advantages, the development of sodium batteries is poised for significant growth due to a confluence of internal and external factors. Against the backdrop of high global lithium battery costs and lithium resource shortages, sodium batteries are expected to find widespread application in low-speed electric vehicles, distributed energy storage, and large-scale energy storage due to their abundant resources, low cost, and high cost-effectiveness.

[0003] Sodium-ionized precursors, especially those containing iron and manganese, are highly susceptible to oxidation during synthesis. The degree of oxidation results in significant differences in the primary particle arrangement, secondary particle morphology, specific surface area, and tap value of the sodium-ionized precursors. The inventors have discovered that the morphology is closely related to the redox potential. By controlling the redox potential of the reaction system, the primary particle arrangement and secondary particle morphology of the precursors can be well controlled, thereby achieving controllability of product indicators.

[0004] Existing liquid-phase synthesis methods for sodium-electric precursors have poor controllability in the microstructure and specific surface area of ​​the primary and secondary particles of the sodium-electric precursors, and lack effective means to control the valence state of metal elements in the precursors. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing sodium-ion precursors using a redox controlled potential method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing sodium-ion precursors using a redox controlled potential method, comprising the following steps: Step 1: Add a base liquid to the reactor, ensuring it covers the stirring blades and the redox potential probe. The base liquid is pure water or a mixture of pure water and a complexing agent. The complexing agent content in the mixture of pure water and the complexing agent does not exceed one-third of the target amount for the synthesis process. The target amount for the synthesis process refers to the total amount of complexing agent used in the synthesis process (for example, if ammonia is used as the complexing agent, the target amount for the synthesis process is 6 g / L, and the ammonia content in the base liquid is controlled to be 0~2 g / L). Step 2: Replace the air in the reactor with one or a mixture of nitrogen, argon, and ammonia. Step 3: After the redox potential of the system stabilizes, based on the difference between the required redox potential and the real-time measurement, add an oxidant or a reducing agent to the bottom solution to control the redox potential value to be maintained between -600 and 300 mV. Step four involves adding a salt solution containing nickel, iron, and manganese, along with a precipitant, complexing agent, oxidant, or reductant, in a co-current flow to the reactor for reaction. The pH is controlled between 9.0 and 13.0, and the complexing agent content is 0.1–0.9 mol / L. Oxidant / reductant is continuously introduced to maintain the required redox potential. The redox potential is controlled within a range of -600 to 300 mV. Different potentials are used to prepare precursors with different morphologies, compactions, and specific surface areas. When the redox potential is higher, the primary particles are relatively finer and more porous, resulting in lower compaction. When the redox potential is lower, the primary particles become thicker and denser, increasing compaction.

[0007] The above plan is explained as follows: 1. In the above scheme, the preparation method is to control the redox state of the system. The redox potential control is achieved by introducing a displacement gas into the reaction vessel during the reaction preparation state, the initial stage of the reaction, and the reaction process, and by adding redox reagents to the bottom liquid and during the synthesis process.

[0008] 2. In the above scheme, the salt solution containing nickel, iron, manganese, copper, and zinc is a solution containing nickel, iron, manganese, copper, and zinc sulfate, chloride, nitrate, or acetate. It must contain easily oxidized elements such as iron and manganese. The total metal ion concentration of the mixed salt solution is 0.5–2.2 mol / L, and the pH value is controlled at 2–3.

[0009] 3. In the above scheme, the precipitant is sodium hydroxide solution or potassium hydroxide, and the concentration is controlled at 4-10 mol / L.

[0010] 4. In the above scheme, the complexing agent is ammonia, oxalic acid, citric acid or at least one of them, and the concentration is controlled within the range of 0.6-3 mol / L.

[0011] 5. In the above scheme, the temperature of the reactor is 40-75℃.

[0012] 6. In the above scheme, a mixed salt solution containing nickel, iron and manganese is used, wherein the hourly flow rate of the mixed salt solution is related to the effective volume of the reactor by 0.04 to 0.07, the flow rate of the alkali solution is controlled by the pH value, and the flow rate of the complexing agent is used to ensure that the complexing dosage of the system is 0.1 to 0.9 mol / L.

[0013] 7. In the above scheme, the oxidant is hydrogen peroxide, and the reducing agent includes ascorbic acid, sodium isoascorbate, and acetaldehyde.

[0014] 8. In the above scheme, the physical properties of the precursor products for sodium ion exchange, such as primary particle arrangement, secondary particle morphology, tap, and specific surface area, can be controlled by controlling different redox potentials.

[0015] 9. In the above scheme, redox electrodes are installed on the reactor to monitor the redox potential of the reaction system in real time.

[0016] 10. In the above scheme, the oxidation-reduction potential can be monitored in real time for the atmosphere of the reactor, the bottom liquid of the reactor, and the slurry during the reaction process.

[0017] 11. In the above scheme, the redox potential of the reaction system can determine the initial atmosphere state of the reactor and the state of the bottom liquid system, providing data support for the initial nitrogen replacement time and the addition of the bottom liquid redox agent.

[0018] 12. In the above scheme, an oxidation-reduction electrode is used to detect the oxidation-reduction potential of the system and the amount of oxidizing agent added is adjusted according to the detection value.

[0019] By applying the above technical solution, the present invention has the following advantages and effects compared with the prior art: The precursor synthesis process can be monitored based on the redox potential. Precursors with different microstructures and specific surface areas can be prepared according to different redox potentials. For example, for cathode materials requiring high rate performance, a precursor with a loose microstructure, relatively fine primary particles (80-120 nm), and a large specific surface area (≥25 m² / g) is required. For polycrystalline or single-crystal cathode materials with high volumetric capacity requirements, a precursor with dense primary particles, thicker primary particles (140-200 nm), and a relatively small specific surface area (10-25 m² / g) is required. Attached Figure Description

[0020] Appendix Figure 1 These are morphological images of the precursor synthesized at different potentials in Example 1-1 of the present invention.

[0021] Appendix Figure 2 These are morphological images of the precursors synthesized at different potentials in Examples 1-2 of the present invention.

[0022] Appendix Figure 3 These are morphological images of the precursor synthesized at different potentials in Example 2-1 of the present invention.

[0023] Appendix Figure 4 These are morphological images of the precursor synthesized at different potentials in Example 2-2 of the present invention.

[0024] Appendix Figure 5 These are morphological images of the precursor synthesized at different potentials in Example 3-1 of the present invention.

[0025] Appendix Figure 6 These are morphological images of the precursor synthesized at different potentials in Example 3-2 of the present invention.

[0026] Appendix Figure 7 The image shows the morphology of the precursor synthesized under uncontrolled redox potential conditions in Comparative Example 1 of the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments: Example: Application of a redox controlled potential method in sodium-ion precursors, the method comprising the following steps: Examples (1-1, 1-2): A mixed salt solution containing nickel, iron, and manganese in a 1:1:1 ratio (total concentration 2.0 ± 0.1 mol / L) and a 25% sodium hydroxide solution, 2% sodium isoascorbate, and 5 mol / L ammonia solution were added concurrently to a reactor to synthesize a precursor for sodium-ion cathode materials. The flow rate of the mixed salt solution was 0.04–0.07 times the effective volume of the reactor. The sodium isoascorbate was controlled based on the redox potential. The process was controlled by maintaining the pH value in the reactor at 9.0–13.0 with a control accuracy of ±0.05, the reactor temperature at 40–60℃ with a control accuracy of ±2℃, and the ammonia content in the system at 0.36 mol / L. Under conditions of 99.9% nitrogen purity and a flow rate of 5 L / H, a hydroxide precipitate was generated in the reactor. The redox potential was monitored and controlled during the synthesis process to be -320 ± 20 mV and -400 ± 20 mV, respectively (see [link to product morphology]). Figure 1 , Figure 2 ). Figure 1 (BET =15.3㎡ / g, TD=1.69 g / cc); Figure 2 (BET= 18.5㎡ / g, TD=1.5g / cc).

[0028] Examples (2-1, 2-2): A mixed salt solution containing 2.0±0.1 mol / L total concentration and a nickel, iron, and manganese ratio of 1:1:1 was added concurrently to a reactor with a 25% sodium hydroxide solution and 5 mol / L ammonia solution to synthesize a precursor for sodium ion cathode material. The hourly inflow rate of the mixed salt solution was 0.04–0.07 times the effective volume of the reactor. During the process, the pH value in the reactor was controlled at 9.0–13.0 with a control accuracy of ±0.05, the reactor temperature was controlled at 40–60℃ with a control accuracy of ±2℃, and the ammonia content in the system was 0.36 mol / L. Under conditions of 99.99% nitrogen purity and a flow rate of 5 L / H, 95% carbon dioxide gas was simultaneously introduced, with the flow rate controlled according to the redox potential. Hydroxide precipitate was produced in the reactor. The redox potential was monitored during the synthesis process at 68±20 mV and 90±20 mV (see the product description). Figure 3 , Figure 4 ). Figure 3 (BET =30.5㎡ / g, TD=1.35 g / cc); Figure 4 (BET==35.5㎡ / g, TD=1.25 g / cc).

[0029] Examples (3-1, 3-2): A mixed salt solution containing 2.0 ± 0.1 mol / L of nickel, iron, and manganese in a 1:1:1 ratio was added concurrently to a reactor with a 25% sodium hydroxide solution and 5 mol / L ammonia water to synthesize a precursor for sodium ion cathode material. During the process, the pH value in the reactor was controlled between 9.0 and 13.0 with an accuracy of ±0.05, the reactor temperature was controlled between 40 and 60°C with an accuracy of ±2°C, and the ammonia content was 0.36 mol / L. Hydrogen peroxide was added dropwise using a metering pump, and the amount of hydrogen peroxide added was controlled by the redox potential. The redox potentials during the synthesis process were controlled at 120 mV and 140 mV. Under conditions of 99.9% nitrogen purity and a gas flow rate of 5 L / H, a hydroxide precipitate was generated in the reactor (see synthesis product). Figure 5 , Figure 6 ). Figure 5 (BET =45.5㎡ / g, TD=1.05 g / cc); Figure 6 (BET =50.5㎡ / g, TD=0.95g / cc).

[0030] Comparative Example 1: A mixed salt solution containing 2.0±0.1 mol / L nickel, iron, and manganese in a 1:1:1 ratio, along with a 25% sodium hydroxide solution and 5 mol / L ammonia, was added concurrently to a reactor to synthesize a precursor for sodium-ion cathode materials. The hourly inflow rate of the mixed salt solution was 0.04–0.07 times the effective volume of the reactor. During the process, the pH value in the reactor was controlled between 9.0 and 13.0 with a control accuracy of ±0.05, and the reactor temperature was controlled between 40 and 60℃ with a control accuracy of ±2℃. The ammonia content in the system was 0.36 mol / L. Under conditions of 99.9% nitrogen purity and a flow rate of 5 L / H, a hydroxide precipitate was generated in the reactor. The redox potential was monitored during the synthesis process, changing between -300 and 400 millivolts. No other gases or reagents were added to control the redox potential. Figure 7 ). Figure 7 (BET 28.5㎡ / g, TD=1.3 g / cc).

[0031] The precursors prepared in Examples 1-3 were characterized in morphology, as shown below. Figure 1-6 As shown in the figure, it can be seen that precursors with different crystal structures can be obtained. The primary particles are thin and controllable, and the pore size and distribution are uniform and controllable. The secondary particles are spherical or near-spherical structures with a particle size D50 of 3-6 μm. The precursor particles have good uniformity.

[0032] The preparation of the positive electrode material includes: reacting sodium carbonate with Ni prepared in Examples 1-3 x Fe y Mn (1-x-y ) The (OH)₂ precursor was solid-state sintered at a Na / Me molar ratio of 0.8-1.2 at a sintering temperature of 800-1000℃ for 8-24 hours under an oxygen or air atmosphere, ultimately producing Na. z Ni x Fe y Mn (1-x-y) O2 sodium electrode material, 0.8≤z≤1.2.

[0033] Button cell preparation: The prepared sodium-ion cathode material, conductive carbon black, and PVDF binder are mixed at a mass ratio of 90:5:5. An appropriate amount of NMP solvent is added and thoroughly mixed to form a slurry. This slurry is then evenly coated onto aluminum foil and dried at 120 degrees Celsius to form the cathode sheet. The button cells are assembled in the following order: cathode shell, cathode sheet, glass fiber separator, sodium metal sheet, gasket, spring, and cathode shell. An appropriate amount of electrolyte is added, and the cells are pressed and sealed to form a button cell.

[0034] The assembled button cells were subjected to electrochemical testing on the Blue Electric testing system. Charge-discharge tests were conducted at 0.1C, with a test voltage range of 2-4V and a test temperature of 25℃.

[0035] The data from Examples 1 and 3 show that the redox control potential can effectively control the aspect ratio of primary particles (see Appendix). Figure 1-6 ), product TD and electrochemical performance.

[0036] The above description is merely an embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention to promote the application of secondary battery precursors. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this invention are within the protection and disclosure scope of this invention.

[0037] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing sodium-ionized precursors using a redox-controlled potential method, characterized in that: Includes the following steps: Step 1: Add a base liquid to the reactor, ensuring that the base liquid covers the stirring blades and the redox potential probe. The base liquid is pure water or a mixture of pure water and a complexing agent. The content of the complexing agent in the mixture of pure water and the complexing agent does not exceed one-third of the target amount for the synthesis process. The target amount for the synthesis process refers to the total amount of complexing agent used in the synthesis process. Step 2: Replace the air in the reactor with one or a mixture of nitrogen, argon, and ammonia. Step 3: After the redox potential of the system stabilizes, add an oxidant or a reducing agent to the bottom solution according to the difference between the required redox potential and the real-time measurement, and control the redox potential value to be maintained between -600 and 300 mV. Step four: A salt solution containing nickel, iron, and manganese, a precipitant, a complexing agent, an oxidizing agent, or a reducing agent are added in parallel to the reaction vessel to carry out the reaction. The pH value is controlled between 9.0 and 13.0, and the complexing agent content in the system is 0.1 to 0.9 mol / L. The redox potential of the system is controlled by adding an oxidizing agent / reducing agent, and the redox potential is controlled between -600 and 300 mV to prepare the precursor.

2. The method for preparing sodium-ion precursors using the redox controlled potential method according to claim 1, characterized in that: The salt solution containing nickel, iron, and manganese is a solution containing nickel, iron, manganese, copper, and zinc sulfate, chloride, nitrate, or acetate. The total metal ion concentration of the salt solution is 0.5–2.2 mol / L, and the pH value is 2–3.

3. The method for preparing sodium-ion precursors using the redox controlled potential method according to claim 1, characterized in that: The precipitant is a sodium hydroxide solution or potassium hydroxide solution with a concentration of 4–10 mol / L.

4. The method for preparing sodium-ion precursors using the redox controlled potential method according to claim 1, characterized in that: The complexing agent is one of ammonia, oxalic acid, and citric acid, with a concentration of 0.6-3 mol / L.

5. The method for preparing sodium-ion precursors using the redox controlled potential method according to claim 1, characterized in that: The temperature of the system is 40–75℃.

6. The method for preparing sodium-ion precursors using the redox controlled potential method according to claim 1, characterized in that: A mixed salt solution containing nickel, iron, and manganese is used, wherein the hourly flow rate of the mixed salt solution is related to the effective volume of the reactor by 0.04 to 0.07, the flow rate of the alkali solution is controlled based on the stable pH value, and the flow rate of the complexing agent is 0.1 to 0.9 mol / L.

7. The method for preparing sodium-ion precursors using the redox controlled potential method according to claim 1, characterized in that: The oxidizing agent is hydrogen peroxide, and the reducing agent is one or a mixture of several of the following: ascorbic acid, sodium isoascorbate, acetaldehyde, oxalic acid, and citric acid.

8. The method for preparing sodium-ion precursors by redox controlled potential method according to claim 1, characterized in that: The redox potential of the system is detected using a redox electrode, and the amount of redox agent added is adjusted based on the detected value.

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