High-stability sodium-ion battery cathode material and preparation method thereof

Abstract

This application discloses a high-stability sodium-ion battery cathode material and its preparation method, specifically including the following steps: S1, a precursor with a core-shell composition gradient distribution is synthesized through a layered reaction, and a continuous transition microstructure is formed by controlling the Cu / Fe ratio in the core / shell; S2, a metal oxide coating is applied to the surface of the precursor; S3, the coated precursor is subjected to a multi-stage gradient calcination process to obtain the gradient-doped cathode material Na. 0.67 Mn 0.77 Cu x Fe( 0.23‑x )O2@M y O2. The preparation process of this application is simple, and the product can be used as a core component of a highly stable sodium-ion battery.

Description

Technical Field

[0001] This application relates to the field of battery materials technology, specifically to a high-stability sodium-ion battery cathode material and its preparation method. Background Technology

[0002] With the global energy structure transitioning towards green and low-carbon development, the demand for large-scale energy storage systems and low-cost electric vehicles is becoming increasingly urgent. Sodium-ion batteries, due to the abundance, wide distribution, and low cost of sodium resources, are widely regarded as a strategic alternative to lithium-ion batteries in specific application scenarios. Among the many cathode material systems for sodium-ion batteries, layered transition metal oxides (especially P2-type structures) have become a research focus due to their high theoretical specific capacity and relatively simple synthesis process.

[0003] Existing technologies for preparing such materials still suffer from the following problems: traditional uniform doping cannot effectively buffer the accumulation of lattice stress during cycling, easily leading to structural degradation and capacity decay. Simultaneously, the cathode material surface is prone to side reactions with the electrolyte, causing loss of active material and increased interfacial impedance. Furthermore, existing solutions are mostly limited to single aspects such as material modification or process optimization, failing to systematically integrate the compatibility optimization of material design and interface strengthening. Therefore, there is an urgent need for a comprehensive solution that integrates material microstructure control with synergistic optimization of interface strengthening. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a solution from material microstructure control to battery system integration.

[0005] This application discloses a sodium-ion battery cathode material, specifically, the molecular formula of the sodium-ion battery cathode material is Na. 0.67 Mn 0.77 Cu x Fe( 0.23-x )O2@M y O2, which has a core-shell structure; the molar ratio of Cu to Fe in the core layer is 1:0.8 to 1.3, and the molar ratio of Cu to Fe in the shell layer is 0.8 to 1.3:1. The molar ratio is obtained by controlling the mass ratio of Cu to Fe in the core / shell during the preparation process and converting it according to the atomic weight, where 0 < x < 0.23.

[0006] Preferably, the M y The O2 is one or more of Al2O3, ZrO2, and TiO2, and its coating thickness is 5-12 nm.

[0007] This application also provides a method for preparing the above-mentioned cathode material, including the following steps:

[0008] S1 Precursor Preparation: Glycerol, urea, and manganese chloride tetrahydrate were dissolved in pure water according to stoichiometric ratio and evenly divided into solution A and solution B. Copper chloride dihydrate and ferric chloride hexahydrate were weighed and added respectively according to the proportion. Solution A was heated to 120-180℃ to form hydrothermal nucleation. Solution B was slowly added dropwise to solution A at a rate of 0.5-2 mL / min, while stirring at a speed of 400-600 r / min. The reaction was carried out at a constant temperature for 8-14 h to obtain a precursor with a core-shell gradient distribution.

[0009] S2 purification and coating: After washing and drying the precursor obtained in S1, a metal source is added for ultrasonic dispersion, and then dried to obtain precursor powder.

[0010] S3 Calcination: After calcining the precursor powder obtained in S2 in air for a period of time, the required sodium source is calculated based on the product mass. After dissolving, it is dried using a freeze dryer to obtain the matrix. The obtained matrix is ​​then subjected to segmented calcination to obtain the cathode material.

[0011] Preferably, in step S1, the mass ratio of Cu to Fe in solution A is 1:0.7 to 1.1; the mass ratio of Cu to Fe in solution B is 0.7 to 1.1:1. After conversion based on the atomic weight of Cu (63.5) and Fe (55.85), the corresponding molar ratio of Cu / Fe in the core layer is 1:0.8 to 1.3, and the molar ratio of Cu / Fe in the shell layer is 0.8 to 1.3:1, which is consistent with the molar ratio definition in the product molecular formula.

[0012] Preferably, in step S2, the metal source is one or more of aluminum nitrate, zirconium oxychloride, or tetrabutyl titanate, and the amount added is 1 to 3% of the precursor mass.

[0013] Preferably, the sodium source in step S3 is one or more of anhydrous sodium carbonate, sodium bicarbonate, and disodium hydrogen phosphate.

[0014] Preferably, the calcination regime in the first stage of step S3 is: 5 hours at 400°C; the calcination regime after adding the sodium source is: first calcination at 350°C for 2 hours, then calcination at 850°C for 12 hours.

[0015] Compared with the prior art, the advantages of the present invention are as follows:

[0016] 1. This application utilizes a hydrothermal process of nucleation in liquid A and controlled growth in liquid B, combined with a gradient design of different Cu / Fe ratios in the core and shell layers, to enable the precursor particles to form a continuous gradient doped structure with Cu-rich inner layers and Fe-rich outer layers during growth. This effectively buffers the lattice stress during sodium ion insertion / extraction and suppresses harmful phase transitions and structural collapse.

[0017] 2. This application utilizes ultrasonic dispersion and in-situ drying curing to form a uniform and dense coating layer on the surface of the precursor particles, which can effectively prevent the migration and aggregation of the coating material during subsequent calcination reactions.

[0018] 3. The multi-gradient calcination process adopted in this application can effectively achieve high-quality synchronous construction of the main crystal lattice and the surface coating layer while avoiding element volatilization and impurity phase formation, thereby improving the purity and electrochemical activity of the material. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, 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 recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The figure shown is an electrochemical impedance spectroscopy diagram of the positive electrode sheet made of the positive electrode material in Example 1 and Comparative Example 1 of this application;

[0021] Figure 2 The figure shown is a cyclic voltammetry curve of the sodium-ion battery prepared in Example 1 and Comparative Example 1 of this application;

[0022] Figure 3 The diagram shows the charge-discharge curves of the sodium-ion batteries prepared in Example 1 and Comparative Example 1 of this application. Detailed Implementation

[0023] This application employs a stepwise nucleation-rate-controlled growth method to achieve a continuous gradient distribution of core and shell composition. The specific mechanism is as follows: First, Cu-rich solution A is used as the core precursor to generate Cu-rich manganese-based oxide nuclei in a hydrothermal system, forming a gradient core substrate; then, Fe-rich solution B is added slowly with strong shear stirring, combined with Cu... 2+ with Fe 3+ The precipitation rate differs in an alkaline environment; with the continuous addition of solution B, Fe... 3+ Cu is preferentially deposited on the surface of the crystal nucleus. 2 + This process exhibits a gradient-decreasing intercalation, with the Cu / Fe ratio in the reaction system continuously and gradually changing. Precursor particles are deposited layer by layer from the inside out, forming metal hydroxides / carbonates of different compositions, ultimately resulting in an atomically continuous transition structure with a Cu-rich core and a Fe-rich shell, and no abrupt interface. Simultaneously, the glycerol-urea complex stabilizes the Cu in the system. 2+ Fe 3+By adjusting the concentration of ions and matching the droplet acceleration rate with the crystal growth rate, local enrichment and phase separation of ions are avoided from the source, ensuring the uniformity and continuity of the gradient structure.

[0024] The technical solutions of the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1

[0026] Preparation of S1 precursor: 57.5 ml of glycerol, 3 g of urea, and 672.86 mg of manganese chloride tetrahydrate were dissolved in 15 ml of pure water. After stirring and dissolving, the solution was divided into two equal parts, A and B. 35.4 mg of copper chloride dihydrate and 44.6 mg of ferric chloride hexahydrate were added to solution A, with a Cu:Fe mass ratio of 1:0.7 and a corresponding molar ratio of 1:0.8. 26.9 mg of copper chloride dihydrate and 53.1 mg of ferric chloride hexahydrate were added to solution B, with a Cu:Fe mass ratio of 0.91:1 and a corresponding molar ratio of 0.8:1. The solution was stirred at room temperature until completely dissolved. Solution B was added dropwise to solution A at a rate of 1.5 mL / min. The mixture was then subjected to hydrothermal reaction at 150 °C for 10 h with continuous stirring. This allowed the ions in solution B to be deposited layer by layer on the surface of the existing particles, forming a continuous gradient structure from copper-rich inner layer to iron-rich outer layer, thus obtaining the precursor.

[0027] S2 Purification and Coating: The precursor obtained in S1 was centrifuged and washed six times with a mixture of deionized water and anhydrous ethanol, then vacuum-dried at 60°C for 12 hours. 2% (by weight) of aluminum nitrate was added, followed by ultrasonic dispersion and spray drying to obtain precursor powder. Based on the specific surface area of ​​the precursor particles and the amount of metal oxide added, combined with the theoretical density of the metal oxide, the theoretical thickness of the coating layer can be estimated to be approximately 5–12 nm.

[0028] S3 Calcination: The precursor powder obtained in S2 was calcined at 400℃ for 5h, and anhydrous sodium carbonate was added at a molar ratio of Na to transition metal of 1.05:1. After dissolution, it was dried using a freeze dryer to avoid local aggregation of sodium source caused by heating, and the matrix was obtained. The obtained matrix was then calcined at 350℃ for 2h, and then the temperature was raised to 850℃ for 12h to obtain the cathode material.

[0029] The specific surface area of ​​the obtained cathode material is 4.5 m². 2 / g, with a particle size of 2.5μm.

[0030] Example 2

[0031] The step of "adding 2% aluminum nitrate by mass of the precursor" in step S2 of Example 1 was removed, and no coating treatment was performed. The remaining steps were the same as in Example 1. The resulting cathode material was a pure-phase layered oxide with a specific surface area of ​​5.0 m². 2 / g, with a particle size of 2.3 μm.

[0032] Example 3

[0033] In Example 1, step S1, which states that "35.4 mg of copper chloride dihydrate and 44.6 mg of ferric chloride hexahydrate were added to solution A, with a Cu:Fe mass ratio of 1:0.7 and a corresponding molar ratio of 1:0.8; 26.9 mg of copper chloride dihydrate and 53.1 mg of ferric chloride hexahydrate were added to solution B, with a Cu:Fe mass ratio of 0.91:1 and a corresponding molar ratio of 0.8:1," is adjusted to "32.8 mg of copper chloride dihydrate and 47.2 mg of ferric chloride hexahydrate were added to solution A, with a Cu:Fe mass ratio of 1:0.8 and a corresponding molar ratio of 1:0.91; 29 mg of copper chloride dihydrate and 51 mg of ferric chloride hexahydrate were added to solution B, with a Cu:Fe mass ratio of 1.02:1 and a corresponding molar ratio of 0.9:1." The remaining steps are consistent with Example 1. The specific surface area of ​​the obtained cathode material is 4.4 m². 2 / g, with a particle size of 2.4 μm.

[0034] Example 4

[0035] In Example 1, step S2, "adding 2% aluminum nitrate by mass of the precursor" was changed to "adding 3% tetrabutyl titanate by mass of the precursor," while the remaining steps remained the same as in Example 1. The resulting cathode material had a specific surface area of ​​4.1 m². 2 / g, with a particle size of 2.6 μm.

[0036] Comparative Example 1

[0037] Steps S1 and S2 of Example 1 were modified as follows: "S1 Precursor Preparation: Dissolve 57.5 ml of glycerol, 3 g of urea, and 672.86 mg of manganese chloride tetrahydrate in 15 ml of pure water. Add 62.3 mg of copper chloride dihydrate and 97.7 mg of ferric chloride hexahydrate, where the mass ratio of Cu to Fe is 1.01:1, corresponding to a molar ratio of approximately 1.15:1. Stir at room temperature until completely dissolved. Dry the resulting mixture to obtain the precursor. S2 Purification and Coating: Wash the precursor obtained in S1 six times with a mixture of deionized water and anhydrous ethanol by centrifugation, and then vacuum dry at 60°C for 12 h to obtain precursor powder." The total Cu+Fe molar ratio remained the same as in Example 1, and the remaining steps were consistent with Example 1. The resulting cathode material was a uniformly doped layered oxide with a specific surface area of ​​5.1 m² / g and a particle size of approximately 2.8 μm.

[0038] To verify the practical application performance of the present invention, the positive electrode materials prepared in Examples 1-4 and Comparative Example 1 were respectively made into slurries and coated onto aluminum foil pretreated with plasma. After drying, positive electrode sheets were obtained, which were then assembled into coin cells and subjected to corresponding tests. The results are as follows:

[0039] sample 0.5C initial discharge specific capacity (mAh / g) Capacity retention rate after 200 cycles (%) 2C rate specific capacity (mAh / g) Electrochemical impedance (Ω) Example 1 118.4 89.4 42.6 84 Example 2 116.6 77.6 35.3 125 Example 3 117.1 87.1 40.7 91 Example 4 116 87.5 40.2 95 Comparative Example 1 102.2 65.7 28.4 158

[0040] Combination Figure 1-3 visible, Figure 1 The electrochemical impedance of Example 1 is approximately 84 Ω, which is significantly lower than that of Comparative Example 1 (158 Ω). This indicates that the gradient core-shell structure and surface coating can effectively reduce the interfacial impedance. Figure 2 This indicates that the redox peak shape of Example 1 is sharper and more symmetrical, and its electrochemical reversibility is better than that of Comparative Example 1; Figure 3 The initial discharge specific capacity of Example 1 was 118.4 mAh / g, which was higher than that of Comparative Example 1 (102.2 mAh / g) and smoother.

[0041] Based on the above test results, the following conclusions can be drawn: The materials prepared in all embodiments, regardless of surface coating, outperform the conventionally uniformly doped material in Comparative Example 1 in terms of ion diffusion coefficient and cycle stability. This demonstrates that gradient design of the material can effectively optimize ion transport paths and buffer structural stress.

[0042] Introducing a nano-coating layer based on gradient structure design can significantly improve the cycle life and high-rate performance of the material. This demonstrates the role of the coating layer in suppressing interfacial side reactions and stabilizing the electrode / electrolyte interface. In summary, the cathode material prepared by this method can effectively solve the inherent problems of structural instability, severe interfacial side reactions, and insufficient battery system safety in layered oxide cathode materials.

[0043] This embodiment is merely an illustrative description of the present patent and does not limit its scope of protection. Those skilled in the art may make partial modifications to it. As long as they do not exceed the spirit and essence of the present patent, they shall be regarded as equivalent substitutions to the present patent and shall be within the scope of protection of the present patent.

Claims

1. A sodium-ion battery cathode material, characterized in that, The molecular formula of the sodium-ion battery cathode material is Na. 0.67 Mn 0.77 Cu x Fe( 0.23-x )O2@M y O2 has a core-shell structure; the molar ratio of Cu to Fe in the core layer is 1:0.8 to 1.3, and the molar ratio of Cu to Fe in the shell layer is 0.8 to 1.3:1, where 0 < x < 0.

23.

2. The cathode material according to claim 1, characterized in that, The M y O2 is one or more of Al2O3, ZrO2, and TiO2, and M is... y The O2 coating thickness is 5–12 nm.

3. The method for preparing the cathode material according to any one of claims 1-2, characterized in that, Includes the following steps: S1 Precursor Preparation: Glycerol, urea, and manganese chloride tetrahydrate were dissolved in pure water according to stoichiometric ratio and evenly divided into solution A and solution B. Copper chloride dihydrate and ferric chloride hexahydrate were weighed and added respectively according to the proportion. Solution A was heated to 120-180℃ to form hydrothermal nucleation. Solution B was slowly added dropwise to solution A at a rate of 0.5-2 mL / min, while stirring at a speed of 400-600 r / min. The reaction was carried out at a constant temperature for 8-14 h to obtain a precursor with a core-shell gradient distribution. S2 purification and coating: After washing and drying the precursor obtained in S1, a metal source is added for ultrasonic dispersion, and then dried to obtain precursor powder. S3 Calcination: After calcining the precursor powder obtained in S2 in air for a period of time, the required sodium source is calculated based on the product mass. After dissolving, it is dried using a freeze dryer to obtain the matrix. The obtained matrix is ​​then subjected to segmented calcination to obtain the cathode material.

4. The method for preparing the cathode material according to claim 3, characterized in that, In step S1, the molar ratio of Cu to Fe in solution A is 1:0.8 to 1.3; the molar ratio of Cu to Fe in solution B is 0.8 to 1.3:

1.

5. The method for preparing the cathode material according to claim 3, characterized in that, In step S2, the metal source is one or more of aluminum nitrate, zirconium oxychloride, or tetrabutyl titanate, and the amount added is 1 to 3% of the precursor mass.

6. The method for preparing the cathode material according to claim 3, characterized in that, In step S3, the sodium source is one or more of anhydrous sodium carbonate, sodium bicarbonate, and disodium hydrogen phosphate.

7. The method for preparing the cathode material according to claim 3, characterized in that, The calcination regime in the first stage of step S3 is: 5 hours at 400℃; the calcination regime after adding sodium source is: first calcination at 350℃ for 2 hours, then calcination at 850℃ for 12 hours.

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