Preparation method of sodium electric positive electrode material

Abstract

The application discloses a preparation method of a sodium battery positive electrode material, and comprises the following steps: S1, a sodium battery positive electrode material precursor and a sodium source are weighed according to a molar ratio, and then first-stage sintering is performed; S2, copper oxide is added into the product obtained in the step S1, and then second-stage sintering is performed, so as to obtain the sodium battery positive electrode material. The sodium battery positive electrode material precursor adopts different stacking modes to form a core-shell structure with a compact core and a loose shell, so that the porosity of the sodium battery positive electrode material precursor in the prior art is improved, and on the basis of improving the tap density of the sodium battery positive electrode material precursor, the porosity of the sodium battery positive electrode material precursor is also reduced.

Description

Technical Field

[0001] This invention relates to the field of materials, and more specifically to a method for preparing a sodium-ion cathode material. Background Technology

[0002] Technology changes lives. The diversification of electronic product applications has transformed our lifestyles, making our lives more convenient. While lithium-ion batteries are commonly used in current electronic products, research on sodium-ion batteries is also increasing with advancements in battery technology. Firstly, sodium is abundant; it is one of the most abundant metallic elements on Earth, with an abundance of 2.64% in the Earth's crust, 440 times that of lithium. Sodium resources are widely distributed and easy to refine, eliminating concerns about supply shortages or price fluctuations. Secondly, sodium-ion batteries are inexpensive. The positive electrode material does not require the relatively expensive metals lithium, nickel, and cobalt, and the negative electrode can use cheaper aluminum foil (compared to copper foil in lithium batteries). The material cost of sodium-ion batteries is 30%-40% lower than that of lithium-ion batteries.

[0003] Sodium-ion battery cathode materials are the source of energy density in sodium-ion batteries. Currently, the stacking method of polycrystalline sodium-ion battery cathode material precursors with a thickness of about 10 μm is basically the same inside and out. In order to facilitate the smooth insertion of sodium source into the precursor during sintering, the precursor is relatively loose overall, resulting in high porosity and low tap density. This leads to a low tap density and a large specific surface area in the final sodium-ion battery cathode material. The low tap density affects the electrode compaction density, thus affecting the cell energy density. Furthermore, the large specific surface area makes the electrolyte and the sodium-ion battery cathode material more prone to side reactions, leading to a decrease in cycle performance, especially at high voltages. Summary of the Invention

[0004] This invention addresses the problems in the prior art by disclosing a sodium-ion battery cathode material and its preparation method. The invention first obtains a sodium-ion battery cathode material with a core-shell structure. By sintering the precursor of the sodium-ion battery cathode material with the core-shell structure obtained by this invention, a sodium-ion battery cathode material with higher tap density and lower specific surface area is obtained. Using the sodium-ion battery cathode material prepared from the precursor of the sodium-ion battery cathode material with the core-shell structure obtained by this invention in batteries is beneficial for improving the battery's electrical performance.

[0005] This invention is achieved through the following technical solution:

[0006] This invention provides a sodium-ion battery cathode material. The raw materials of the sodium-ion battery cathode material include a sodium-ion battery cathode material precursor with a dense core and a loose outer shell structure, copper oxide, and a sodium source. The sodium-ion battery cathode material precursor is a nickel-iron-manganese sodium-ion battery precursor. The amount of copper oxide added is 0.2%-1% of the total mass of the sodium source and the sodium-ion battery cathode material precursor. The average size of the shell structure of the core-shell structure is 0.5μm-1.5μm.

[0007] In the above-described design of this invention, the sodium-ion cathode material selected is a precursor with a core-shell structure. The core structure of the precursor enhances the tap density, thus improving the tap density of the final sodium-ion cathode material. The loose outer shell structure of the precursor ensures that the sodium source can enter the lattice phase through the surface structure, thereby guaranteeing the energy density of the sodium-ion cathode material. Due to the different stacking methods of the inner and outer shells, the core-shell structure of this invention improves the overall porosity of the sodium-ion cathode precursor, thereby reducing its porosity and paving the way for obtaining a sodium-ion cathode material with a lower specific surface area. Based on this, we further designed copper oxide as a sintering aid. First, copper oxide can reduce the residual alkali on the surface of the sodium battery cathode material; second, it can further reduce the specific surface area of ​​the final sodium battery cathode material; third, copper oxide can also improve the structural stability of the final sodium battery cathode material in air, thereby improving the application of the sodium battery cathode material in batteries and enhancing the electrochemical performance of sodium batteries; fourth, copper oxide can also lower the sintering temperature. The shell structure size design not only ensures the rapid migration of the final sodium-ion cathode material, but also improves the final tap density of the sodium-ion cathode material. The amount of copper oxide added is directly related to the average size of the shell structure. The amount of copper oxide added needs to reduce the overall porosity of the shell structure, while also controlling the amount embedded in the shell structure. When the amount of copper oxide added is designed to be 0.2%-1% of the total mass of the sodium source and the sodium-ion cathode material precursor, and the average size of the shell structure is 0.5μm-1.5μm, a sodium-ion cathode material with a smaller specific surface area, higher tap density, and better stability can be obtained.

[0008] As a further refinement, the core structure of the core-shell structure has an average size of 6.5 μm-8.5 μm. This is beneficial for obtaining a sodium-ion battery cathode material with a high tap density.

[0009] As a further embodiment, the molar ratio of the sodium source to the sodium-ion cathode material precursor is 0.99-1.03. This ensures that sufficient sodium source can be embedded into the porous structure on the surface of the sodium-ion cathode material.

[0010] As a further embodiment, the specific surface area of ​​the shell structure material of the sodium-ion cathode precursor is 9m². 2 / g-21m 2 The tap density of the sodium-ion battery cathode material precursor is 1.4 g / cm³. 3 -2.1g / cm 3 The core-shell structure of sodium-ion cathode precursors not only improves the tap density but also reduces the porosity of traditional sodium-ion cathode precursors, thus helping to reduce the porosity of the precursors. Furthermore, the specific surface area of ​​the shell structure within this range facilitates the smooth embedding of the sodium source into the crystal lattice of the sodium-ion cathode precursor.

[0011] As a further embodiment, the specific surface area of ​​the sodium-ion battery cathode material is 0.2 m². 2 / g-0.6m 2 The tap density of the sodium-ion battery cathode material is 1.8 g / cm³. 3 -2.4g / cm 3 .

[0012] As a further option, the sodium-ion battery cathode material precursor is Ni. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2, where Ni represents nickel, Fe represents iron, and Mn represents manganese.

[0013] As a further embodiment, the D50 of the sodium-ion cathode material precursor is 7 μm-10 μm.

[0014] As a further embodiment, the sodium source includes sodium carbonate and sodium chloride. The sodium source in this invention is not limited to the listed sources; any substance that can provide sodium can be used as a sodium source, and those skilled in the art can select and design it according to the actual situation.

[0015] As a further improvement, the copper oxide is nanoscale. This is more conducive to maximizing the sintering aid's capabilities and further reducing the specific surface area of ​​the sodium-ion battery cathode material.

[0016] As a further option, the sodium-ion battery cathode material is NaCu. y Ni (1 / 3-y / 3) Fe (1 / 3-y / 3) Mn (1 / 3-y / 3) O2 (0.0025≤y≤0.01), the shell structure of the sodium-ion battery cathode material is NaCu. x Ni (1 / 3-x / 3) Fe (1 / 3-x / 3) Mn (1 / 3-x / 3) O2, where 0.006 ≤ x ≤ 0.06, and the core structure of the sodium-ion battery cathode material is NaNi. 1 / 3 Fe1 / 3 Mn 1 / 3 O2, where Na represents sodium, Cu represents copper, Ni represents nickel, Fe represents iron, Mn represents manganese, and O represents oxygen. Cu, as a dopant element embedded in the coating layer, firstly improves the stability of the final sodium-ion battery cathode material in air; secondly, it reduces the residual alkali in the sodium-ion battery cathode material, which is beneficial for improving its cycle performance; and thirdly, it further synergistically reduces the porosity of the coating layer during the sintering process of preparing the sodium-ion battery cathode material, thus contributing to obtaining a sodium-ion battery cathode material with a lower specific surface area.

[0017] The present invention also provides a preparation method for the sodium-ion cathode material, the preparation method comprising:

[0018] S1: Weigh the sodium-ion cathode material precursor and sodium source according to the molar ratio, and then carry out the first stage of sintering.

[0019] S2: Add copper oxide to the product from the first stage sintering in S1, and then perform a second stage sintering. The method of this invention employs staged sintering. In the first stage sintering, the sodium source enters the core structure through the shell structure of the sodium-ion cathode material precursor, thereby ensuring the energy density of the final sodium-ion cathode material. In the second stage sintering, copper oxide reduces the porosity of the shell structure of the sodium-ion cathode material precursor, stabilizing sodium in the core structure and ensuring the capacity of the sodium-ion cathode material. Furthermore, it helps reduce the specific surface area of ​​the sodium-ion cathode material, thereby reducing side reactions between the sodium-ion cathode material and the electrolyte. In addition, the second stage sintering can also dope copper ions into the shell structure, further improving the structural stability of the sodium-ion cathode material.

[0020] As a further embodiment, the sintering temperature of the first stage is 550℃-750℃, and the sintering time of the first stage is 4h-8h; the sintering temperature of the second stage is 800℃-900℃, and the sintering time of the second stage is 12h-16h. The design of the first-stage sintering temperature, on the one hand, facilitates sufficient sodium source energy embedding into the core structure, and on the other hand, reduces the shrinkage of the pore structure in the shell structure, which is beneficial for sodium source energy to enter the core structure through the shell structure; the design of the second-stage sintering temperature, while reducing the porosity of the shell structure, is also beneficial for copper-doped sodium cathode materials.

[0021] As a further option, processes S1 and S2 are performed in an air atmosphere.

[0022] As a further step, after adding copper oxide in step S2, it needs to be mixed evenly. The mixing conditions are 450 r / min-600 r / min, and the mixing time is 20 min-40 min. This facilitates the uniform adhesion of copper oxide to the surface of the sodium-ion battery cathode material precursor and promotes the uniform embedding of copper into the sodium-ion battery cathode material during the second-stage sintering process.

[0023] The present invention also provides a method for preparing the sodium-ion cathode material precursor, the method comprising:

[0024] A mixed aqueous solution of nickel-iron-manganese ternary salt, sodium hydroxide, and ammonia were added to the mother liquor of system 1 to deposit a sodium-ion cathode material precursor with a core structure. Then, a sodium-ion cathode material precursor with a dense core structure, sodium hydroxide, and ammonia were added to the mother liquor of system 2 to deposit a sodium-ion cathode material precursor with a core-shell structure. The pH value of the mother liquor of system 2 was higher than that of the mother liquor of system 1.

[0025] Precipitating nickel-iron-manganese ternary salts under different pH environments facilitates the formation of sodium-ion battery cathode material precursors with completely different stacking patterns, thereby promoting the formation of sodium-ion battery cathode materials with a dense core and a loose outer shell. Based on this, in order to control the metal deposition rate and thus form a uniform and stable core and a uniformly porous outer shell, we designed a mother liquor system containing sodium hydroxide and ammonia. The ammonia in the mother liquor system can form a complex with the metal, balancing the rate at which sodium hydroxide promotes metal deposition. This promotes a uniform and stable stacking process of the sodium-ion battery cathode material precursor, which is beneficial for forming the core-shell structure of the sodium-ion battery cathode material precursor of this invention.

[0026] As a further embodiment, the pH1 of the mother liquor in System 1 is 10.8-11.2, and the pH2 of the mother liquor in System 2 is 11.4-12.2, with the pH2 value of the mother liquor in System 2 being higher than the pH1 value of the mother liquor in System 1. Under these conditions, it is beneficial for the growth of the nickel-iron-manganese ternary salt to form a sodium-ion cathode material precursor with a suitable dense core structure and a loose shell structure. This facilitates the entry of sodium ions into the core structure through the loose shell structure, thereby ensuring the capacity of the sodium-ion cathode material.

[0027] As a further refinement, the pH1 of the mother liquor in System 1 is 10.8-11.2, and the pH2 of the mother liquor in System 2 is 11.4-12.2. The pH2 value of the mother liquor in System 2 is 0.4-0.6 higher than the pH1 value of the mother liquor in System 1. This is beneficial for ensuring that sodium ions can enter the core structure through the loose shell structure, and can further improve the density of the core structure of the sodium-ion cathode material precursor.

[0028] As a further embodiment, the preparation method further includes stirring and reacting in the mother liquor of system 1 and stirring and reacting in the mother liquor of system 2, and the entire process of preparing the sodium-ion cathode material precursor is carried out in an inert atmosphere.

[0029] To achieve a high-density core structure in the sodium-ion cathode material precursor, a shell structure size matching the core structure was designed. The shell structure requires a certain porosity to provide channels for sodium ion insertion. During the sintering of the sodium-ion cathode material precursor with copper oxide, the shell structure size is related to both the amount of copper oxide added (appropriate copper ion doping is necessary to ensure the stability and energy density of the sodium-ion cathode material) and the overall tap density of the final sodium-ion cathode material. Therefore, to obtain sodium-ion cathode materials with higher tap density and lower specific surface area, we further designed the following: at the end of the stirring reaction in System 1, the D50 of the sodium-ion cathode material precursor with a core structure is 6.5 μm-8.5 μm; at the end of the stirring reaction in System 2, the D50 of the sodium-ion cathode material precursor with a core-shell structure is 7 μm-10 μm.

[0030] As a further embodiment, the stirring speed in the mother liquor of System 1 is 500 r / min-800 r / min, the reaction temperature is 30℃-60℃, and the reaction time is 48h-72h; the stirring speed in the mother liquor of System 2 is 300 r / min-500 r / min, the reaction temperature is 30℃-60℃, and the reaction time is 24h-48h. To further promote a more uniform and stable stacking process of the sodium-ion cathode material precursor, we further designed the stirring speed and reaction temperature during the stacking process. Stirring speeds and temperatures within this range are more conducive to the sodium-ion cathode material having higher tap density and smaller specific surface area.

[0031] As a further embodiment, the concentration of the nickel-iron-manganese ternary salt mixed aqueous solution is 1.5 mol / L-3 mol / L, the concentration of ammonia in the mother liquor of System 1 and System 2 is 6 mol / L-10 mol / L, and the concentration of sodium hydroxide added to the mother liquor of System 1 and System 2 is 4 mol / L-6 mol / L. The nickel-iron-manganese ternary salt can exhibit a suitable deposition rate in the mother liquor, thus, in conjunction with other conditions during the preparation process (stirring speed, reaction temperature, etc.), it can jointly regulate the reaction rate while also reducing the oxidation of the precursor in the preparation of sodium-ion battery cathode materials.

[0032] The preparation method further includes adding an aqueous sodium hydroxide solution during the preparation process to adjust the pH1 value of the mother liquor in System 1 and the pH2 value of the mother liquor in System 2, reducing the difference between the pH1 value of the mother liquor in System 1 and its initial pH value during the preparation of the core-structured sodium-ion cathode material precursor, and reducing the difference between the pH2 value of the mother liquor in System 2 and its initial pH value during the preparation of the core-shell structured sodium-ion cathode material precursor. Ammonia is added during the preparation process to adjust the ammonia concentration in the mother liquors of System 1 and System 2, reducing the difference between the ammonia concentration in the mother liquor in System 1 and its initial ammonia concentration during the preparation of the core-structured sodium-ion cathode material precursor, and reducing the difference between the ammonia concentration in the mother liquor in System 2 and its initial ammonia concentration during the preparation of the core-shell structured sodium-ion cathode material precursor. This helps maintain a stable precipitation environment, thereby facilitating the control of the stable stacking speed of the core and shell structures, and resulting in sodium-ion cathode material precursor materials with higher tap density and smaller specific surface area.

[0033] As a further embodiment, the sodium hydroxide concentration used to adjust the pH1 value of the mother liquor in System 1 and the pH2 value of the mother liquor in System 2 is 4 mol / L-6 mol / L. The ammonia concentration used to reduce the difference between the ammonia concentration of the mother liquor in System 1 and its initial concentration during the preparation of the core-structured sodium-ion cathode material precursor is 2.0 g / L-4.0 g / L. The ammonia concentration used to reduce the difference between the ammonia concentration of the mother liquor in System 2 and its initial concentration during the preparation of the core-shell structured sodium-ion cathode material precursor is 1.5 g / L-3.5 g / L. This is to ensure a more stable deposition rate of the core-shell structured sodium-ion cathode material precursor in the mother liquor, reducing the deposition rate variation caused by the concentration difference of the nickel-iron-manganese ternary salt, thus promoting more stable stacking.

[0034] As a further improvement, the ammonia concentration used to reduce the difference between the ammonia concentration in the mother liquor of system 2 and its initial concentration during the preparation of the core-shell structured sodium-ion cathode material precursor is 0.4 g / L to 0.6 g / L lower than the ammonia concentration used to reduce the difference between the ammonia concentration in the mother liquor of system 1 and its initial concentration during the preparation of the core-shell structured sodium-ion cathode material precursor. Adjusting the ammonia concentration in the mother liquors of system 1 and system 2 with ammonia is more conducive to forming a stable stacking process; and when the difference in ammonia concentration between the mother liquors of system 1 and system 2 is within this range, it is more conducive to forming a uniformly and stably stacked core-shell structured sodium-ion cathode material precursor.

[0035] As a further embodiment, the nickel-iron-manganese ternary salt is obtained by mixing a nickel source, an iron source, and a manganese source, and the molar ratio of Ni:Fe:Mn is 1:1:1 based on the elements of nickel, iron, and manganese.

[0036] As a further option, the nickel source includes one or more of nickel sulfate, nickel nitrate, and nickel chloride.

[0037] As a further embodiment, the iron source includes one or more of ferrous sulfate, ferrous nitrate, and ferrous chloride.

[0038] As a further embodiment, the manganese source includes one or more of manganese sulfate, manganese nitrate, and manganese chloride.

[0039] As a further embodiment, the inert atmosphere includes one of nitrogen, helium, neon, argon, krypton, and xenon.

[0040] As a further embodiment, the inert gas flow rate is 0.5 L / min to 1.5 L / min.

[0041] As a further embodiment, the preparation method also includes dehydrating the core-shell structured sodium cathode material precursor.

[0042] As a further embodiment, the dehydration temperature is 70℃-120℃, and the water content of the sodium-ion cathode material precursor with a core-shell structure is ≤1.5%.

[0043] The present invention also provides a battery or electrochemical device having the aforementioned sodium electrode material.

[0044] The features and beneficial effects of this invention are as follows:

[0045] The sodium-ion cathode material precursor of this invention adopts different stacking methods to form a core-shell structure with a dense core and a loose outer shell, thereby improving the porosity of sodium-ion cathode material precursors in the prior art. While increasing the tap density of sodium-ion cathode material precursors, it also reduces the porosity of sodium-ion cathode material precursors.

[0046] The sodium-ion cathode material obtained by sintering the sodium-ion cathode material precursor of the present invention has high tap density and low specific surface area, and thus better electrochemical performance.

[0047] The sodium-ion cathode material of the present invention has better stability in air and better cycle performance. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 This is a SEM image of the sodium-ion cathode material precursor of the present invention. Detailed Implementation

[0050] To facilitate understanding of the preparation method of the sodium-ion cathode material precursor of the present invention, a more comprehensive description of the preparation method of the sodium-ion cathode material precursor of the present invention will be given below, and embodiments of the present invention will be provided, but this does not limit the scope of the present invention.

[0051] The preparation methods of Examples 1-13 of this invention are as follows, wherein the parameters changed in Examples 1 and 13 are shown in Table 1, and other parameters remain unchanged:

[0052] 1. Preparation of precursors:

[0053] (1) Prepare a mixed aqueous solution of nickel-iron-manganese ternary salt with a concentration of 2.0 mol / L according to the molar ratio of Ni:Fe:Mn 1:1:1, prepare an aqueous solution of sodium hydroxide with a concentration of 5 mol / L, and prepare an aqueous solution of ammonia with a concentration of 8 mol / L.

[0054] (2) Add a mother liquor with an ammonia concentration of 2.0-4.0 g / L and a pH value of 10.3-11.8 to the reactor, and make the mother liquor account for 60% of the reactor volume;

[0055] (3) Pour nitrogen gas into the sealed reactor at a rate of 1 L / min, turn on the stirrer at a speed of 600 r / min, and continuously pump the sodium hydroxide aqueous solution and ammonia aqueous solution prepared in step (1) into the reactor for 20 min. During this period, the metal mixture pump is turned off and the ammonia-alkali pump is turned off. Turn on the metal mixture pump, pump the metal salt solution prepared in step (1) into the reactor, and test the pH value in the reactor. The pH value of the system is between 10.3 and 11.8. This process takes about 15 min.

[0056] (4) The three pumps are turned on at the same time, and the metal salt solution prepared in step (1) and the sodium hydroxide aqueous solution and ammonia aqueous solution prepared in step (1) are added to the reaction vessel in parallel flow. The reaction temperature is controlled at 50℃, the rotation speed is 600r / min, the NH3 concentration is 2.0-4.0g / L, and the flow rate of sodium hydroxide aqueous solution is adjusted to control the pH of the reaction solution to 10.3-11.8.

[0057] (5) As the metal salt solution continues to enter the reactor, the particle size in the system gradually increases. The particle size in the reactor is measured every hour. When the reactor is full, the overflow valve is opened to allow the material to flow into the buffer tank, and the particle size in the reactor at the time of overflow is recorded. The reaction is stopped when the average particle size of the material in the reactor and the overflow material is D50 = 7-8.5 μm. Under the parameters of the method of this invention, the time is between 48h and 72h.

[0058] (6) After the reaction is complete, the mother liquor is removed by centrifugation to obtain a high tap density nickel-iron-manganese hydroxide solid material.

[0059] (7) Add a mother liquor with an ammonia concentration of 1.5-3.5 g / L and a pH value of 11.4-12.2 to the reactor, ensuring that the mother liquor accounts for 60% of the reactor volume.

[0060] (8) Start stirring at 500 r / min. Pour the material prepared in step (6) into the reactor. Pour nitrogen gas into the sealed reactor at 1 L / min. At the same time, continuously pump sodium hydroxide aqueous solution and ammonia aqueous solution into the reactor for 20 min. During this period, turn off the metal mixture pump and the ammonia-alkali pump. Turn on the metal mixture pump and pump the metal salt solution prepared in step (6) into the reactor. Test the pH value in the reactor. The pH value of the system is between 11.4 and 12.2. This process takes about 15 min.

[0061] (9) The three pumps are turned on at the same time, and the metal salt solution prepared in step (1) and the sodium hydroxide aqueous solution and ammonia aqueous solution prepared in step (1) are added to the reaction vessel in parallel flow. The reaction temperature is controlled at 50℃, the rotation speed is 400r / min, the NH3 concentration is 1.5-3.5g / L, and the flow rate of sodium hydroxide aqueous solution is adjusted to control the pH of the reaction solution to 11.4-12.2.

[0062] (10) As the metal salt solution continues to enter the reactor, the particle size in the system gradually increases. The particle size value in the reactor is measured every 0.5 hours. When the reactor is full, the overflow valve is opened to allow the material to flow into the buffer tank, and the particle size in the reactor at the time of overflow is recorded. When the average particle size D50 of the material in the reactor and the overflow material is 1 μm-2 μm larger than that in step (5), the reaction is stopped. Under the parameters of the method of the present invention, the time is between 24h and 48h.

[0063] (11) After the reaction is complete, the mother liquor is removed by centrifugation to obtain a solid material of nickel-iron-manganese hydroxide with a loose exterior and a dense interior.

[0064] (12) The dehydrated solid material is dried at 100°C until the moisture content is ≤1.5%.

[0065] (13) The dried material is sieved through a 200-350 mesh screen. The sieved material is the precursor of sodium-ion cathode material.

[0066] 2. Material synthesis

[0067] (14) The material described in (13) is mixed with a sodium source and sintered. The molar ratio of sodium source to sodium-ion cathode material precursor is 0.98-1.02. Sodium carbonate is selected as the sodium source. The mixture is sintered in air at 550-750℃ for 4-8 hours. After removing the material, 0.2%-1% of flux nano-copper oxide is added and mixed at 500r / min for 30 minutes. The mixture is then sintered in air at 800℃-900℃ for 12-16 hours to synthesize NaCu. x Ni (1 / 3-x / 3) Fe (1 / 3-x / 3) Mn (1 / 3-x / 3) The shell structure of O2, where 0.006 ≤ x ≤ 0.06, is coated with NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 High-tape, low-specific-surface-area sodium-ion battery cathode material was obtained by sintering in an atmosphere furnace at a flow rate of 15 mL / min, followed by crushing with a jaw crusher (4 mm gap) and roller crushing (1.25 mm), and sieving through a 325 mesh sieve. 1.01 Cu 0.008 Ni 0.33 Fe 0.331 Mn 0.331 O2.

[0068] The preparation methods of Comparative Examples 1-8 are the same as those of the present invention, wherein the parameters changed in Comparative Examples 1 and 8 are shown in Table 1, and other parameters remain unchanged:

[0069] Methods for manufacturing button batteries:

[0070] A cathode material slurry was prepared using a degassing machine at a mass ratio of 90:5:5, consisting of positive electrode material, conductive agent Super P, and binder PVDF. The solid content of the slurry was adjusted to 39% using N-methylpyrrolidone (NMP). The adjusted slurry was then coated onto aluminum foil using an automatic coating machine, dried in a vacuum drying oven at 120°C, rolled by a roller press, and punched by a slicing machine. Afterward, button cell 2032 batteries were assembled in a glove box. The electrolyte was 1.2 mol / L NaPF6, with a solvent ratio of EC:PC:EMC = 1:1:1 (volume ratio), plus 2 wt% FEC. The separator was a glass fiber separator, and a sodium metal sheet was used as the counter electrode.

[0071] The button cell was charged and discharged on a Newway tester within the voltage range of 2.5~4.0V. Two charge-discharge cycles at 0.1C were performed, and the capacity of the first charge-discharge cycle and the capacity retention after 50 cycles at 1C were tested.

[0072] BET test method: The test was conducted using a Bestar dynamic adsorption-desorption surface instrument. The sample mass was 1g. The pretreatment conditions were 150℃ for 60min.

[0073] pH meter test method: Add 2g of positive electrode material to 40mL of water and stir for 10min. Let it stand for 5min and take the supernatant for pH meter test.

[0074] Tap density test: 50g of sodium electrode material is added to a 50mL graduated cylinder. After vibrating the material 3000 times at a vibration frequency of 80 using a tap density tester, the volume of the material in the graduated cylinder is read, and the tap density of the material is calculated.

[0075] Validation Result Analysis

[0076] Table 1. Parameter variations in the embodiments and comparative examples of the present invention.

[0077]

[0078] Table 2. Test results of sodium-ion cathode materials in the embodiments and comparative examples of the present invention.

[0079]

[0080] We successfully prepared a sodium-ion cathode material precursor using the preparation method of this invention, such as... Figure 1 As shown, Figure 1 To obtain the sodium-ion cathode material precursor in Example 1 of this invention, we can start from... Figure 1As can be seen from Table 1, the sodium-ion cathode material precursor of the present invention has a core-shell structure with a dense core and a porous outer shell. Table 1 shows that, comparing Examples 1-13 with Comparative Example 1, the sodium-ion cathode material precursor obtained by the present invention has a core-shell structure, and the sodium-ion cathode precursor obtained by the method of the present invention has a higher tap density and a smaller specific surface area. We believe this is because precipitation occurs in different mother liquor systems in the method of the present invention. We further designed the pH difference between the two mother liquor systems and the concentration difference of ammonia used to adjust the ammonia concentration in the mother liquor, thereby controlling the deposition rate of the nickel-iron-manganese ternary salt in the mother liquor, thus forming a sodium-ion cathode material precursor with a uniform and stable core and a uniformly porous outer shell. Furthermore, the design of the pH difference and ammonia concentration difference in the mother liquor systems is more conducive to forming a uniform and stable stacked core-shell structure, and also to forming a sodium-ion cathode material precursor with a more suitable specific surface area. This can be verified by comparing Examples 1-13 with Comparative Examples 2-3. The obtained sodium-ion cathode material precursor breaks away from the traditional precursor stacking method, thereby improving the overall porosity of the sodium-ion cathode material precursor. This reduction in porosity paves the way for obtaining sodium-ion cathode materials with lower specific surface areas. The specific surface area of ​​the sodium-ion cathode material precursor obtained in this invention is 9m². 2 / g-21m 2 The tap density of the sodium-ion battery cathode material precursor is 1.4 g / cm³. 3 -2.1g / cm 3 .

[0081] By preparing a core-shell structured sodium-ion cathode material precursor, a sodium source, and copper oxide, a sodium-ion cathode material with a lower specific surface area and a higher tap density can be obtained at a specific sintering temperature. A comparison of Examples 1-13 in Table 2 with Comparative Examples 1-8 reveals that the sodium-ion cathode material of this invention has a high tap density and a smaller specific surface area. This not only improves the energy density of the sodium-ion cathode material but also reduces side reactions between the sodium-ion cathode material and the electrolyte, thereby improving the cycle performance of the battery. We believe this is because, in this invention, the sodium source enters the core structure through the shell structure, thereby improving the energy density of the sodium-ion battery cathode material. During the second-stage sintering process, copper oxide, an auxiliary sintering agent, is used. Firstly, copper oxide can reduce residual alkali on the surface of the sodium-ion battery cathode material, thus improving its stability in the environment. Table 1 verifies that the sodium-ion battery cathode material of this invention has a lower pH value. Secondly, it can further reduce the specific surface area of ​​the final sodium-ion battery cathode material, reducing side reactions between the sodium-ion battery cathode material and the electrolyte, and improving the battery's electrical performance. Thirdly, copper oxide can also improve the structural stability of the final sodium-ion battery cathode material in air, thereby enhancing its electrochemical performance in battery applications. Fourthly, copper oxide can lower the sintering temperature, which helps reduce energy waste and cost. Therefore, the sodium-ion battery cathode material of this invention can improve the battery's electrical performance when used in batteries.

[0082] First, by comparing Examples 1-5 with Comparative Example 1, we can see that, through the combination of a core-shell structured sodium-ion cathode material precursor and copper oxide, a sodium-ion cathode material with low specific surface area and high tap density can be obtained using the method of the present invention. Based on this, we further investigated how the method of the present invention can further improve the electrical performance of the sodium-ion cathode material. Therefore, we designed different examples and comparative examples, as shown in Tables 1-2.

[0083] The amount of copper oxide added is directly related to the size of the shell structure in the core-shell structure. In this invention, the amount of copper oxide added needs to be based on the size of the shell structure. This can be verified by comparing Examples 6-7 and Examples 10-11. When the shell structure is larger, more copper oxide needs to be added to sufficiently reduce the porosity of the shell structure. If the amount added is small, on the one hand, the porosity of the shell structure cannot be reduced, the specific surface area of ​​the sodium battery cathode material is larger, and the capacity retention rate of the battery will decrease. On the other hand, the added copper oxide will also be doped into the sodium battery cathode material, improving the stability of the sodium battery cathode material. However, if the amount added is insufficient, the stability of the sodium battery cathode material will decrease. This can be verified by Comparative Example 6. Conversely, when the shell structure is smaller, relatively less copper oxide needs to be added. If more copper oxide is added, although adding more copper oxide can reduce the porosity of the shell structure, thereby significantly reducing the specific surface area of ​​the sodium battery cathode material, the amount of copper oxide added will also lead to excessive copper doping, thereby affecting the proportion of transition elements in the sodium battery cathode material, which is detrimental to the energy density of the sodium battery cathode material. This can be verified by Comparative Example 7. In this invention, when the amount of copper oxide added is 0.2%-1% of the total mass of the sodium source and the sodium-ion cathode material precursor, and the average size of the core-shell structure is 0.5μm-1.5μm, although there are some differences in the specific surface area and tap density of the sodium-ion cathode materials obtained in Examples 1-13, they are all significantly better than those in Comparative Examples 6-7. It can be seen that when the average size of the core-shell structure is 0.5μm-1.5μm, those skilled in the art can add 0.2%-1% of copper oxide of the total mass of the sodium source and the sodium-ion cathode material precursor, which can not only improve the specific surface area of ​​the sodium-ion cathode material but also enhance its stability.

[0084] Based on this, we also discovered that the selection of staged sintering time can optimize sodium-ion cathode materials. In the first stage of sintering, the sodium source energy is facilitated to enter the core structure through the sodium-ion cathode material precursor, thereby increasing the energy density of the sodium-ion cathode material and minimizing the shrinkage of the specific surface area of ​​the shell structure, laying the foundation for further reducing the porosity of the shell structure. In the second stage of sintering, the porosity of the shell structure of the sodium-ion cathode material precursor is reduced, and sodium energy is ensured to exist stably in the sodium-ion cathode material. Therefore, we designed the staged sintering temperatures. The design of the first stage sintering temperature is conducive to sufficient sodium source energy entering the core structure. Furthermore, the first stage sintering temperature also needs to reduce severe shrinkage of the pore structure in the shell structure to prevent the sodium source from failing to enter the core structure. The design of the second sintering temperature is beneficial for reducing the porosity of the shell structure while simultaneously promoting copper doping. We can verify this by comparing Examples 12-13 with Comparative Example 8. When sintering at the same temperature, the sodium source cannot be successfully embedded into the core structure, leading to a decrease in the capacity, a decrease in tap density, and an increase in the specific surface area of ​​the sodium-ion cathode material. Therefore, we designed the first stage sintering temperature to be 550℃-750℃ and the first stage sintering time to be 4h-8h, the second stage sintering temperature to be 800℃-900℃ and the second stage sintering time to be 12h-16h.

[0085] In this invention, the ratio of sodium source to sodium-ion cathode material precursor has a direct relationship with the energy density of the final sodium-ion cathode material. As shown in the comparison between Examples 8-9 and Comparative Examples 4-5, when more sodium source is added, the obtained sodium-ion cathode material has a higher energy density, and conversely, when less sodium source is added, the energy density of the sodium-ion cathode material is lower.

[0086] In summary, the sodium-ion battery cathode material obtained by this invention has a smaller specific surface area and a higher tap density, which is beneficial to improving the cycle performance and energy density of the battery.

[0087] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a sodium-ion battery cathode material, characterized in that, The preparation method includes: S1: Weigh the sodium-ion cathode material precursor and sodium source according to the molar ratio, and then carry out the first stage of sintering. S2: Add copper oxide to the product sintered in the first stage of S1, and then perform the second stage of sintering to obtain sodium-ion cathode material. The sintering temperature of the first stage is 550℃-750℃, and the sintering temperature of the second stage is 800℃-900℃; The sodium-ion cathode material precursor is a nickel-iron-manganese sodium-ion cathode precursor, which has a core-shell structure with a dense core and a loose outer shell. The average size of the shell structure of the sodium-ion cathode material precursor is 0.5 μm-1.5 μm; The amount of copper oxide added is 0.2%-1% of the total mass of the sodium source and the sodium-ion cathode material precursor; The sodium electrode material is NaCu. y Ni (1 / 3-y / 3) Fe (1 / 3-y / 3) Mn (1 / 3-y / 3) O 2， 0.0025≤y≤0.01, where Na represents sodium, Cu represents copper, Ni represents nickel, Fe represents iron, Mn represents manganese, and O represents oxygen.

2. The preparation method according to claim 1, characterized in that, The sintering time for the first stage is 4-8 hours, and the sintering time for the second stage is 12-16 hours.

3. The preparation method according to claim 1, characterized in that, The entire process of S1 and S2 takes place in an air atmosphere.

4. The preparation method according to claim 1, characterized in that, After adding copper oxide to S2, it needs to be mixed evenly. The mixing conditions are 450 r / min-600 r / min and the mixing time is 20 min-40 min.

5. The preparation method according to claim 1, characterized in that, The specific surface area of ​​the shell structure material of the sodium-ion cathode precursor is 9 m². 2 / g-21m 2 / g.

6. The preparation method according to claim 1, characterized in that, The tap density of the sodium-ion battery cathode material precursor is 1.4 g / cm³. 3 -2.1g / cm 3 .

7. The preparation method according to claim 1, characterized in that, The average size of the core structure in the core-shell structure is 6.5 μm-8.5 μm.

8. The preparation method according to claim 1, characterized in that, The molar ratio of the sodium source to the sodium-ion cathode material precursor is 0.99-1.

03.

9. The preparation method according to claim 1, characterized in that, The sodium source includes one or more of sodium carbonate and sodium chloride.

10. The preparation method according to claim 1, characterized in that, The precursor for the sodium-ion battery cathode material is Ni. 1 / 3Fe 1 / 3 Mn 1 / 3 (OH)2, where Ni represents nickel, Fe represents iron, and Mn represents manganese.

11. The preparation method according to claim 1, characterized in that, The shell structure of the sodium-ion cathode material is NaCu. x Ni (1 / 3-x / 3) Fe (1 / 3-x / 3) Mn (1 / 3-x / 3) O2, where 0.006 ≤ x ≤ 0.06, and the core structure of the sodium-ion battery cathode material is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2; where Na represents sodium, Cu represents copper, Ni represents nickel, Fe represents iron, Mn represents manganese, and O represents oxygen.

12. The preparation method according to claim 1, characterized in that, The specific surface area of ​​the sodium-ion battery cathode material is 0.2 m². 2 / g-0.6m 2 The tap density of the sodium-ion battery cathode material is 1.8 g / cm³. 3 -2.4g / cm 3 .

13. The preparation method according to claim 1, characterized in that, The method for preparing the sodium-ion battery cathode material precursor includes: adding a mixed aqueous solution of nickel-iron-manganese ternary salt, sodium hydroxide, and ammonia to the mother liquor of system 1, and depositing to obtain a sodium-ion battery cathode material precursor with a core structure; then adding the sodium-ion battery cathode material precursor with a dense core structure, sodium hydroxide, and ammonia to the mother liquor of system 2, and depositing to obtain a sodium-ion battery cathode material precursor with a core-shell structure, wherein the pH2 value of the mother liquor of system 2 is higher than the pH1 value of the mother liquor of system 1.

14. The preparation method according to claim 13, characterized in that, The pH1 of the mother liquor in System 1 is 10.8-11.2, and the pH2 of the mother liquor in System 2 is 11.4-12.

2. The pH2 value of the mother liquor in System 2 is higher than the pH1 value of the mother liquor in System 1.

15. The preparation method according to claim 13, characterized in that, The pH2 value of the mother liquor in System 2 is 0.4-0.6 higher than the pH1 value of the mother liquor in System 1.

16. The preparation method according to claim 13, characterized in that, In System 1, the stirring speed for the deposition reaction in the mother liquor was 500 r / min-800 r / min, the reaction temperature was 30℃-60℃, and the reaction time was 48 h-72 h; in System 2, the stirring speed for the deposition reaction in the mother liquor was 300 r / min-500 r / min, the reaction temperature was 30℃-60℃, and the reaction time was 24 h-48 h.

17. The preparation method according to claim 13, characterized in that, The preparation method further includes adding an aqueous sodium hydroxide solution during the preparation process to adjust the pH1 value of the mother liquor of system 1 and the pH2 value of the mother liquor of system 2, thereby reducing the difference between the pH1 value of the mother liquor of system 1 and the initial pH1 value of the mother liquor of system 1 during the preparation of the core-structured sodium-ion cathode material precursor, and reducing the difference between the pH2 value of the mother liquor of system 2 and the initial pH2 value of the mother liquor of system 2 during the preparation of the core-shell structured sodium-ion cathode material precursor. Ammonia was added during the preparation process to adjust the ammonia concentration in the mother liquor of System 1 and System 2, thereby reducing the difference between the ammonia concentration in the mother liquor of System 1 and the initial ammonia concentration in the mother liquor of System 1 during the preparation of the core-structured sodium-ion cathode material precursor, and reducing the difference between the ammonia concentration in the mother liquor of System 2 and the initial ammonia concentration in the mother liquor of System 2 during the preparation of the core-shell structured sodium-ion cathode material precursor.

18. The preparation method according to claim 17, characterized in that, The sodium hydroxide concentration used to adjust the pH1 value of the mother liquor in system 1 and the pH2 value of the mother liquor in system 2 is 4 mol / L-6 mol / L. The ammonia concentration used to reduce the difference between the ammonia concentration of the mother liquor in system 1 and the initial ammonia concentration of the mother liquor in system 1 during the preparation of the core-structured sodium-ion cathode material precursor is 2.0 g / L-4.0 g / L. The ammonia concentration used to reduce the difference between the ammonia concentration of the mother liquor in system 2 and the initial ammonia concentration of the mother liquor in system 2 during the preparation of the core-shell structured sodium-ion cathode material precursor is 1.5 g / L-3.5 g / L.

19. The preparation method according to claim 17, characterized in that, The ammonia concentration used to reduce the difference between the ammonia concentration of the mother liquor in system 2 and the initial ammonia concentration of the mother liquor in system 2 during the preparation of the core-shell structured sodium-ion cathode material precursor is 0.4 g / L to 0.6 g / L lower than the ammonia concentration used to reduce the difference between the ammonia concentration of the mother liquor in system 1 and the initial ammonia concentration of the mother liquor in system 1 during the preparation of the core-shell structured sodium-ion cathode material precursor.

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