A method for preparing high-voltage positive electrode material, positive electrode material and sodium ion battery

Abstract

The present invention provides a preparation method of a high-voltage positive electrode material, a positive electrode material, and a sodium ion battery, which relate to the field of battery material technology, including: doping lanthanum into the positive electrode material, and coating the positive electrode material with tin oxide; mixing a sulfur-containing sodium source, a sulfur-containing iron source, a sulfur-containing lanthanum source, and an auxiliary additive to obtain a suspension; continuously adding ammonia water to the suspension and stirring, while heating to a first temperature to obtain a sodium ferric sulfate positive electrode material precursor; mixing the sodium ferric sulfate positive electrode material precursor with tin oxide and sintering them to obtain a tin oxide-coated sodium ferric sulfate positive electrode material. Beneficial effects: effectively inhibiting grain growth, making the crystal structure more stable, thereby greatly improving the ionic conductivity of the material; effectively isolating the positive electrode material from direct contact with the electrolyte, avoiding chemical reactions that may occur during the charge and discharge process, thereby significantly improving the cycle performance of the material and optimizing the material's rate performance.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a method for preparing a high-voltage positive electrode material, the positive electrode material, and a sodium ion battery. Background Art

[0002] Lithium-ion batteries, currently the most promising high-energy battery system, are widely used and offer superior performance. However, the high price, limited reserves, and uneven distribution of lithium have severely constrained the development of lithium-ion batteries due to resource shortages. To address this issue, sodium-ion batteries have attracted considerable attention due to their similar physical and chemical properties, abundant resources, and low cost. Sodium-ion batteries share similar operating principles and compatible manufacturing processes, making it easier for battery manufacturers to switch technology paths without incurring high replacement costs.

[0003] Currently, research on cathode materials for sodium-ion batteries focuses primarily on transition metal oxide systems, polyanionic compounds (such as phosphates, fluorophosphates, and sulfates), and Prussian blue systems. Among these, sodium ferric sulfate polyanionic cathode materials have attracted significant attention due to their high voltage platform. However, existing technologies for synthesizing sodium ferric sulfate cathode materials suffer from significant technical drawbacks: Firstly, the material is prone to the generation of impurities during synthesis, which affects its purity and performance; secondly, the poor intrinsic electronic conductivity of sodium ferric sulfate cathode materials limits their performance in high-power density applications. Furthermore, the resulting cathode material readily reacts with the electrolyte during charge and discharge, resulting in a rapid decrease in capacity and poor cycling stability, further limiting the commercial application of sodium ferric sulfate cathode materials.

[0004] In response to the above-mentioned technical defects, it is necessary to solve the problems existing in the existing technology through innovative technical means, improve the performance of sodium iron sulfate positive electrode materials, and promote the development of sodium ion battery technology. Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention provides a method for preparing a high-voltage positive electrode material, comprising: step S1, mixing a sulfur-containing sodium source, a sulfur-containing iron source, a sulfur-containing lanthanum source and an auxiliary additive to obtain a suspension; step S2, continuously adding ammonia water to the suspension and stirring until the pH value of the suspension is adjusted to 3.5-6, then stopping the addition of ammonia water, and heating to 60-90°C to obtain a sodium ferric sulfate positive electrode material precursor; step S3, mixing the sodium ferric sulfate positive electrode material precursor with tin oxide and then sintering them to obtain a tin oxide-coated sodium ferric sulfate positive electrode material.

[0006] Preferably, in step S3, the sodium ferric sulfate positive electrode material precursor and tin oxide are mixed in a mass ratio of 1:(0.0005-0.04).

[0007] Preferably, the molar ratio of the sulfur-containing sodium source, the sulfur-containing iron source and the sulfur-containing lanthanum source is (1-8): (1-5): (0-0.4), wherein the molar amount of the sulfur-containing lanthanum source is not 0.

[0008] Preferably, the auxiliary additive includes a chelating agent and a carbon source, and the ratio of the molar amount of the chelating agent to the sum of the molar amounts of the sulfur-containing iron source and the sulfur-containing lanthanum source is (0.5~2):1; and / or, the mass of the carbon source is 0.04%~8% of the sum of the masses of the sulfur-containing sodium source, the sulfur-containing iron source and the sulfur-containing lanthanum source.

[0009] Preferably, the auxiliary additives include an antioxidant, a complexing agent, a carbon source, a dispersant, a defoaming agent and deionized water; the mass of the deionized water is 10% to 50% of the sum of the mass of the sulfur-containing sodium source, the sulfur-containing iron source, the sulfur-containing lanthanum source, the antioxidant, the complexing agent, the carbon source, the dispersant and the defoaming agent.

[0010] Preferably, the sintering process in step S3 includes a first sintering stage and a second sintering stage; the temperature of the first sintering stage is 100~300℃, and the time is 0.1~15h; the temperature of the second sintering stage is 300~420℃, and the time is 0.1~24h.

[0011] Preferably, in step S3, the sintering process is carried out in nitrogen and / or inert gas.

[0012] The present invention also provides a positive electrode material, wherein the positive electrode material is doped with lanthanum and coated with tin oxide, and is prepared by the preparation method described above.

[0013] The present invention also provides a sodium ion battery comprising the positive electrode material as described above.

[0014] The above technical solution has the following advantages or beneficial effects:

[0015] 1. Lanthanum is doped into the positive electrode material. This innovative measure effectively inhibits the growth of grains, making the crystal structure more stable, thereby significantly improving the ionic conductivity of the material. At the same time, the doping of lanthanum also promotes the 3+ Na + This process significantly increases the overpotential of the surface oxygen evolution reaction and effectively inhibits the production of lattice oxygen, thereby ensuring the stability of the transition metal valence state during charging and discharging.

[0016] 2. Tin oxide is used to coat the positive electrode material. This coating acts as a barrier, effectively isolating the positive electrode material from direct contact with the electrolyte, avoiding chemical reactions that may occur during the charge and discharge process, thereby significantly improving the cycle performance of the material. At the same time, the tin oxide coating also provides a uniform and stable ion transmission interface, promoting the Na + The smooth embedding and de-embedding further optimizes the rate performance of the material.

[0017] 3. The rich oxygen vacancy characteristics of tin oxide itself can effectively inhibit the loss of lattice oxygen during the charging process, which not only improves the reversibility of the redox reaction, but also plays a positive role in improving the cycle performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The figure is a flow chart of a method for preparing a high voltage positive electrode material in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0019] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. The present invention is not limited to this embodiment, and other embodiments may also fall within the scope of the present invention as long as they conform to the gist of the present invention.

[0020] In a preferred embodiment of the present invention, based on the above problems existing in the prior art, a method for preparing a high voltage positive electrode material is provided. Figure 1 As shown, it includes: step S1, mixing a sulfur-containing sodium source, a sulfur-containing iron source, a sulfur-containing lanthanum source and an auxiliary additive to obtain a suspension; step S2, continuously adding ammonia water to the suspension and stirring, and heating it to a first temperature to obtain a sodium ferric sulfate positive electrode material precursor; step S3, mixing the sodium ferric sulfate positive electrode material precursor and tin oxide and sintering them to obtain a tin oxide-coated sodium ferric sulfate positive electrode material.

[0021] Specifically, this embodiment proposes an innovative method for preparing a cathode material (primarily composed of sodium ferric sulfate, hence referred to as a sodium ferric sulfate cathode material). This method aims to precisely control the composition and structure of the material to produce a lanthanum-doped tin oxide-coated sodium ferric sulfate cathode material with excellent performance. The detailed steps of this method are as follows:

[0022] (1) Precursor preparation: First, a sulfur-containing sodium source, a sulfur-containing iron source, a sulfur-containing lanthanum source, and auxiliary additives (e.g., an antioxidant, a chelating agent, an inorganic carbon source, a dispersant, a defoaming agent, and an appropriate amount of deionized water) are mixed to form a uniform suspension.

[0023] Subsequently, the sol-gel method is used to ensure that the components are fully mixed and evenly dispersed by controlling the stirring speed and time, effectively avoiding the problem of uneven composition of the resulting cathode material. This step is key to preparing high-performance cathode materials, as uniform component distribution can significantly improve the material's capacity and cycling performance.

[0024] (2) Precursor treatment and tin oxide coating: Then, ammonia water is continuously added to the suspension and stirred while heating it to a first temperature (usually between 60-90°C). The pH value is adjusted and the reaction time is controlled (10-24 hours).

[0025] This pH adjustment process is crucial for the formation of the precursor because it can promote the precipitation and crystallization of metal ions, thereby forming a sodium iron sulfate positive electrode material precursor with stable structure and high crystallinity.

[0026] At the same time, continuous stirring and heating help accelerate the reaction process and ensure the uniformity and purity of the precursor. By precisely controlling the amount of ammonia added, the stirring speed and the heating temperature, a precursor material with excellent performance can be obtained.

[0027] Subsequently, the precursor and tin oxide are mixed in a predetermined first ratio and sintered under the protection of nitrogen or an inert gas.

[0028] In a preferred embodiment of the present invention, in step S3, the sodium ferric sulfate positive electrode material precursor and tin oxide are mixed in a mass ratio of 1:(0.0005-0.04).

[0029] The tin oxide coating effectively isolates the cathode material from direct contact with the electrolyte, preventing reactions between the cathode material and the electrolyte during charge and discharge, a key factor in improving the material's cycling performance. It also provides a uniform and stable ion transport interface, facilitating the intercalation and deintercalation of Na+, thereby improving the material's rate performance.

[0030] The mass ratio of the precursor to tin oxide directly determines the thickness of the tin oxide coating. By adjusting this ratio, the thickness of the coating can be precisely controlled, thereby optimizing the performance of the material.

[0031] The appropriate coating thickness can ensure material performance while controlling costs. A coating that is too thick may increase the material preparation cost, while a coating that is too thin may not effectively isolate the electrolyte, affecting the material's cycle performance.

[0032] Through this innovative preparation method, a sodium iron sulfate cathode material with excellent performance was successfully prepared. This material not only has an extremely high discharge capacity, but also exhibits excellent cycle stability. The doping of lanthanum effectively inhibits grain growth, stabilizes the crystal structure, and improves the ionic conductivity of the material; at the same time, La3+ with Na + The ion exchange reaction significantly increases the overpotential of the surface oxygen evolution reaction, inhibits the production of lattice oxygen, and ensures the stability of the transition metal valence state during charge and discharge. In addition, the tin oxide coating layer acts as an effective barrier to isolate the direct contact between the positive electrode material and the electrolyte, avoiding side reactions during charge and discharge, and further improving the cycle performance of the material. The tin oxide coating layer also provides a uniform and stable ion transmission interface, promoting the Na + The smooth intercalation and deintercalation of the cathode material optimizes the rate performance of the material. In summary, the preparation method proposed in the present invention is not only simple and easy to implement, but also can produce a cathode material with excellent performance, providing strong support for the development of sodium ion battery technology.

[0033] In a preferred embodiment of the present invention, the auxiliary additives include an antioxidant, a complexing agent, a carbon source, a dispersant, a defoaming agent and deionized water.

[0034] Specifically, the functions of adding various materials in step S1 are as follows: Sulfur-containing sodium source: provides sodium ions, which is one of the key elements for synthesizing sodium iron sulfate positive electrode materials.

[0035] Sulfur-containing iron source: provides iron ions, which combine with sodium ions to form the main structure of sodium iron sulfate.

[0036] Sulfur-containing lanthanum source: doped into the sodium iron sulfate structure to inhibit grain growth, stabilize the crystal structure, and improve ionic conductivity.

[0037] If a sodium source, an iron source, or a lanthanum source that does not contain sulfur is used, an additional sulfur source needs to be added.

[0038] Antioxidant: Prevents the material from being oxidized during the synthesis process and protects the chemical properties of the material.

[0039] Complexing agent: By complexing with metal ions, it promotes the uniform dispersion of various components in the solution, avoids uneven precipitation, and helps to improve the uniformity and performance of the material.

[0040] Carbon source: acts as a conductive agent to improve the electronic conductivity of the material and the rate performance of the battery.

[0041] Dispersant: helps the components to be evenly dispersed in the solution, prevents agglomeration, and ensures the uniformity of the precursor.

[0042] Defoaming agent: removes bubbles generated during the mixing process to prevent bubbles from affecting the structure and performance of the material.

[0043] Deionized water: As a solvent, it helps the components to mix thoroughly and form a uniform suspension.

[0044] These materials play an auxiliary and optimizing role in the chemical synthesis process.

[0045] In a preferred embodiment of the present invention, the step S2 is stopped when the pH value of the suspension is adjusted to 3.5-6 by adding ammonia water.

[0046] Specifically, in this example, adjusting the pH of the suspension to 3.5-6 is a crucial step in the preparation of the sodium ferric sulfate cathode material. The reasons for this are detailed as follows: In chemical synthesis reactions, pH is a key factor influencing the reaction process and product properties. For the preparation of sodium ferric sulfate cathode materials, an appropriate pH range (3.5-6) ​​significantly influences the formation and properties of the precursor.

[0047] First, adjusting the pH value to an appropriate range can promote the precipitation and crystallization of metal ions. During the synthesis of sodium ferric sulfate cathode materials, metal ions such as sodium ions, iron ions, and lanthanum ions need to undergo precipitation reactions under specific chemical conditions to form a stable precursor structure. Precise control of the pH value ensures that these metal ions gradually precipitate under appropriate conditions, avoiding uneven particles or impurity formation caused by excessively fast or slow precipitation rates.

[0048] Secondly, an appropriate pH value helps stabilize the structure and performance of the precursor. When the pH value is too high or too low, the precursor may not be able to form a stable structure, resulting in a decrease in the crystallinity and purity of the material, which in turn affects the electrochemical performance of the final cathode material. By adjusting the pH value to 3.5-6, a stable chemical environment can be ensured during the formation of the precursor, resulting in a precursor material with a complete structure and excellent performance.

[0049] Furthermore, an appropriate pH value helps reduce side reactions. During chemical synthesis, these reactions often lead to impurity formation and reduced yields. Precise pH control effectively inhibits these side reactions, improving reaction selectivity and yield, thereby yielding a cathode material with higher purity and more stable performance.

[0050] In summary, adjusting the pH of the suspension to 3.5-6 is an essential step in the preparation of sodium ferric sulfate cathode materials. It not only promotes the precipitation and crystallization of metal ions and stabilizes the structure and properties of the precursor, but also effectively reduces the occurrence of side reactions, providing a strong guarantee for the preparation of high-performance cathode materials.

[0051] In a preferred embodiment of the present invention, the molar ratio of the sulfur-containing sodium source, the sulfur-containing iron source and the sulfur-containing lanthanum source is (1-8): (1-5): (0-0.4), wherein the molar amount of the sulfur-containing lanthanum source is not 0.

[0052] In a preferred embodiment of the present invention, the ratio of the molar amount of the complexing agent to the sum of the molar amounts of the sulfur-containing iron source and the sulfur-containing lanthanum source is (0.5~2):1; and / or, the mass of the carbon source is 0.04%~8% of the sum of the mass of the sulfur-containing sodium source, the sulfur-containing iron source and the sulfur-containing lanthanum source.

[0053] Specifically, in this embodiment, the setting of these ratios has a significant effect on the preparation of lanthanum-doped tin oxide-coated sodium ferric sulfate positive electrode material, and is based on the consideration of optimizing material properties and preparation process.

[0054] 1. The effect and reason of the molar ratio of sulfur-containing sodium source, sulfur-containing iron source and sulfur-containing lanthanum source (1~8): (1~5): (0~0.4).

[0055] Effect:

[0056] Optimizing the crystal structure: By adjusting the molar ratio of the sodium source, iron source, and lanthanum source, the crystal structure of the sodium ferric sulfate positive electrode material can be controlled to make it more stable, which is beneficial to improving the electrochemical performance of the material.

[0057] Improve conductivity: The doping amount of lanthanum (0~0.4 molar ratio) within a certain range can significantly improve the ionic conductivity of the material and promote the deintercalation of Na+.

[0058] Inhibiting the formation of impurity phases: A reasonable molar ratio helps reduce the formation of impurity phases during the synthesis process and improve the purity of the material.

[0059] reason:

[0060] Stoichiometric ratio: The molar ratio of the sodium source, iron source, and lanthanum source needs to meet the stoichiometric ratio requirements to ensure the basic composition and structure of the material.

[0061] Doping effect of lanthanum: Appropriate amount of lanthanum doping can bring about significant improvement in electrochemical performance, but too much or too little doping may have an adverse effect on material performance.

[0062] 2. The effect and reason of the ratio of the molar amount of the complexing agent to the sum of the molar amounts of the sulfur-containing iron source and the sulfur-containing lanthanum source (0.5~2):1.

[0063] Effect:

[0064] Promote uniform dispersion: Complexing agents can promote the uniform dispersion of various components in the solution by complexing with metal ions, avoid uneven precipitation, and help improve the uniformity and performance of the material.

[0065] Stabilize suspension: An appropriate amount of complexing agent can stabilize the suspension and prevent the components from agglomerating or precipitating during the mixing process.

[0066] reason:

[0067] Complexation: Complexing agents can form complexes with metal ions, reduce the activity of metal ions, and thus promote their uniform dispersion in the solution.

[0068] Preventing agglomeration: Too much complexing agent may cause the solution to be too viscous, affecting the mixing effect; while too little complexing agent may not be able to effectively prevent the agglomeration of components.

[0069] 3. The effect and reason why the mass of the carbon source is 0.04%~8% of the sum of the mass of the sulfur-containing sodium source, the sulfur-containing iron source and the sulfur-containing lanthanum source.

[0070] Effect:

[0071] Improve conductivity: Carbon source, as a conductive agent, can improve the electronic conductivity of the material and improve the rate performance of the battery.

[0072] Promote sintering: An appropriate amount of carbon source can promote material transport and reaction during the sintering process and help form a dense coating layer.

[0073] reason:

[0074] Conductivity requirements: The positive electrode material must have a certain level of electronic conductivity to ensure the normal operation of the battery. Carbon source, as a conductive agent, can effectively improve the conductive properties of the material.

[0075] Sintering aid: Carbon source can act as an aid in the sintering process, promoting the transfer and reaction of substances, thereby helping to form a cathode material with a dense structure and excellent performance.

[0076] Summarize

[0077] These ratios are based on a deep understanding and optimization of the material's properties and preparation process. By precisely controlling these ratios, it is possible to produce a lanthanum-doped tin oxide-coated sodium ferric sulfate cathode material with excellent performance and stable structure, providing strong support for the development of sodium-ion batteries.

[0078] In a preferred embodiment of the present invention, the mass of deionized water is 10% to 50% of the sum of the mass of the sulfur-containing sodium source, the sulfur-containing iron source, the sulfur-containing lanthanum source, the antioxidant, the complexing agent, the carbon source, the dispersant, and the defoaming agent.

[0079] Specifically, in this embodiment, the effect and reason for setting the ratio of the mass of deionized water to the sum of the masses of all raw materials (sulfur-containing sodium source, sulfur-containing iron source, sulfur-containing lanthanum source, antioxidant, chelating agent, carbon source, dispersant, and defoaming agent) can be understood from the following aspects:

[0080] 1. The Effect of Proportion

[0081] Promote uniform mixing of raw materials: Deionized water is used as a solvent. Its appropriate addition can promote uniform mixing between the raw materials, ensuring that the components can fully contact and react during the preparation process, thereby obtaining a uniform precursor solution.

[0082] Controlling reaction rates and conditions: The amount of deionized water significantly impacts reaction rates and conditions. The right amount of water promotes dissolution and reaction processes, while also helping to control key parameters such as pH and temperature, ensuring the reaction proceeds under optimal conditions.

[0083] Ensure precursor quality: The right amount of deionized water ensures the quality and performance of the precursor. Too much water may result in a low precursor concentration, affecting the subsequent sintering process; too little water may lead to uneven mixing of the raw materials, or even the inability to form an effective precursor.

[0084] Optimizing material properties: By precisely controlling the amount of deionized water added, the performance of the cathode material can be optimized, such as improving the discharge capacity, cycle stability, and rate performance.

[0085] 2. Reasons for setting such a ratio

[0086] Stoichiometric ratio requirements: Raw materials must be mixed in a specific stoichiometric ratio to ensure the purity and performance of the final product. The amount of deionized water added must be determined based on the mass of the other raw materials to meet this stoichiometric ratio requirement.

[0087] Reaction kinetics and thermodynamics considerations: In chemical reactions, reaction rates and conditions are influenced by a variety of factors, including reactant concentrations, temperature, and pH. The amount of deionized water added can influence these factors, thereby impacting the reaction kinetics and thermodynamics. By precisely controlling the amount of deionized water, reaction conditions can be optimized, improving reaction efficiency and product quality.

[0088] Stability and repeatability of the preparation process: An appropriate amount of deionized water can ensure stability and repeatability of the preparation process. Too much water may cause fluctuations and instability in the preparation process; too little water may increase operational difficulty and errors during the preparation process.

[0089] Cost-effectiveness considerations: The amount of deionized water added also needs to be considered cost-effectively. Too much water increases preparation costs and handling difficulties; too little water may not meet preparation requirements, resulting in reduced product quality. Therefore, it is necessary to find an appropriate balance between adding deionized water and ensuring product quality while reducing costs.

[0090] In summary, the 10% to 50% deionized water mass ratio of all raw materials is based on a deep understanding of material properties and the optimization of the preparation process. By precisely controlling the amount of deionized water added, a lanthanum-doped tin oxide-coated sodium ferric sulfate cathode material with excellent performance and stable structure can be prepared.

[0091] In a preferred embodiment of the present invention, the sintering process in step S3 includes a first sintering stage and a second sintering stage; the temperature of the first sintering stage is 100~300℃, and the time is 0.1~15h; the temperature of the second sintering stage is 300~420℃, and the time is 0.1~24h.

[0092] Specifically, the sintering process is divided into two stages. The first stage is carried out at a lower temperature (100-300°C), which facilitates the initial bonding of the precursor and tin oxide. The second stage is carried out at a higher temperature (300-420°C) to ensure the integrity and density of the tin oxide coating. The entire sintering process temperature does not exceed 420°C. This design ensures sufficient crystallization of the material while avoiding the potential performance degradation caused by high temperatures.

[0093] In a preferred embodiment of the present invention, in step S3, the sintering process is performed in nitrogen and / or inert gas.

[0094] Specifically, the sintering process in step S3 is carried out in nitrogen or an inert gas (such as argon, helium, etc.). This measure has significant effects, which are mainly reflected in the following aspects:

[0095] 1. Effect

[0096] Preventing material oxidation: During the sintering process, high temperatures can easily cause oxidation reactions in the material, especially in the presence of oxygen. Using nitrogen or an inert gas as a shielding gas effectively isolates oxygen from the air, preventing oxidation of the sodium ferric sulfate cathode material and its precursor during the sintering process, thereby maintaining the material's chemical stability and electrochemical performance.

[0097] Reduce impurity generation: Reactive gases such as oxygen may react with certain components in the material at high temperatures to form impurities. Using nitrogen or an inert gas as a shielding gas can reduce the possibility of such impurity generation and improve the purity and performance of the material.

[0098] Promote sintering reaction: Some sintering reactions may be more likely to proceed in an oxygen-free or low-oxygen environment. A nitrogen or inert gas environment can provide such conditions, helping to promote the sintering reaction between the cathode material precursor and tin oxide, forming a dense and uniform coating layer.

[0099] Improving material performance: Sintering in nitrogen or an inert atmosphere can produce sodium ferric sulfate cathode materials with superior performance and a more stable structure. This material may exhibit improved performance in terms of discharge capacity, cycle stability, and rate capability.

[0100] In summary, the use of nitrogen or inert gas as a protective gas during the sintering process has significant effects and important significance for the preparation of high-performance lanthanum-doped tin oxide-coated sodium ferric sulfate positive electrode materials.

[0101] In a preferred embodiment of the present invention, the complexing agent includes at least one of citric acid, ethanol, ethylene glycol, DPTA, and HEEDTA; the carbon source includes at least one of acetylene black, graphene, carbon nanotubes, carbon fiber, activated carbon, and conductive carbon black; the dispersant includes at least one of sodium lauryl sulfate, polyethylene glycol, sodium alkylbenzene sulfonate, sodium alkyl sulfonate, sodium stearate, and polyvinyl pyrrolidone; the defoaming agent includes at least one of hydroxymethyl cellulose, polysiloxane, and polyether modified silicone oil; and the antioxidant is water. Soluble antioxidant; optionally, the antioxidant includes at least one of ascorbic acid, citric acid, phytic acid, uric acid, oxalic acid, formic acid, and acetic acid; the sodium source is a soluble salt containing sodium; optionally, the sodium source includes at least one of sodium sulfate, sodium bisulfate, sodium carbonate, sodium bicarbonate, sodium nitrate, and sodium hydroxide; the iron source is a soluble salt containing iron; optionally, the iron source includes at least one of ferrous sulfate, ferrous carbonate, and ferrous oxalate; the lanthanum source includes at least one of lanthanum oxide, lanthanum sulfate, lanthanum nitrate, lanthanum chloride, and lanthanum carbonate.

[0102] The present invention also provides a sodium ion battery using the lanthanum-doped tin oxide-coated positive electrode material prepared above.

[0103] Example 1

[0104] This embodiment provides a lanthanum-doped tin oxide-coated positive electrode material and a preparation method thereof, comprising the following steps:

[0105] (1) Na2SO4, FeSO4·7H2O and La2(SO4)3 were taken in a molar ratio of 2.4:3:0.05, and the molar amount of citric acid complexing agent was taken in a ratio of 1:1 to the sum of the molar amounts of the iron source and the lanthanum source. Conductive carbon black (5% by weight of the sum of the mass of the sodium source, the iron source and the lanthanum source), ascorbic acid (3% by weight), sodium alkylbenzene sulfonate (1% by weight), and polysiloxane (100 ppm by weight) were added. Deionized water was added to the stirrer reactor, and all the above reagents were added to the stirrer reactor. The stirrer speed was set to 300 r / min and stirred for 6 h to fully dissolve all the reagents except the inorganic carbon source, and finally a suspension with a solid content of 40% was obtained.

[0106] (2) The suspension obtained in (1) was stirred continuously and ammonia water was added to adjust the pH to 4, and then heated to 80°C and stirred continuously for 24 hours. The solvent was removed to obtain a sodium iron sulfate positive electrode material precursor.

[0107] (3) The sodium ferric sulfate cathode material precursor obtained in (2) and tin oxide were ball-milled and mixed, with the mass ratio of the precursor to tin oxide being 1:0.006. The mixture was transferred to a box furnace and heated to 180°C and sintered for 8 h under a nitrogen protective atmosphere. The temperature was then continued to be raised to 350°C and sintered for 12 h to obtain the sodium ferric sulfate cathode material.

[0108] Example 2

[0109] This embodiment provides a method for preparing a lanthanum-doped tin oxide-coated positive electrode material. Compared with Example 1, the difference is that, in step (1), Na2SO4, FeSO4·7H2O and La2(SO4)3 are dissolved in the solution at a molar ratio of 2.4:3:0.01 instead of Na2SO4, FeSO4·7H2O and La2(SO4)3 being dissolved in the solution at a molar ratio of 2.4:3:0.05.

[0110] Example 3

[0111] This embodiment provides a method for preparing a lanthanum-doped tin oxide-coated positive electrode material. Compared with Example 1, the difference is that, in step (1), Na2SO4, FeSO4·7H2O and La2(SO4)3 are dissolved in the solution at a molar ratio of 2.4:3:0.2 instead of Na2SO4, FeSO4·7H2O and La2(SO4)3 being dissolved in the solution at a molar ratio of 2.4:3:0.05.

[0112] Example 4

[0113] This embodiment provides a lanthanum-doped tin oxide-coated positive electrode material and a preparation method thereof, comprising the following steps: This embodiment provides a lanthanum-doped tin oxide-coated positive electrode material preparation method. Compared with Example 1, the difference is that, in step (1), the sodium ferric sulfate positive electrode material precursor and tin oxide are replaced by the sodium ferric sulfate positive electrode material precursor and tin oxide in a mass ratio of 1:0.0005 instead of the sodium ferric sulfate positive electrode material precursor and tin oxide in a mass ratio of 1:0.006.

[0114] Example 5

[0115] This embodiment provides a sodium ferric sulfate positive electrode material and a preparation method thereof, comprising the following steps: This embodiment provides a preparation method of a lanthanum-doped tin oxide-coated positive electrode material. Compared with Example 1, the difference is that, in step (1), the sodium ferric sulfate positive electrode material precursor and tin oxide are replaced by a mass ratio of 1:0.04 instead of a sodium ferric sulfate positive electrode material precursor and tin oxide at a mass ratio of 1:0.006.

[0116] Comparative Example 1

[0117] This comparative example provides a method for preparing a positive electrode material. Compared with Example 1, the difference is that in step (1), La2(SO4)3 is not added; in step (3), tin oxide is not added.

[0118] Comparative Example 2

[0119] This comparative example provides a method for preparing a tin oxide-coated positive electrode material. Compared with Example 1, the difference is that in step (1), La2(SO4)3 is not added.

[0120] Comparative Example 3

[0121] This comparative example provides a method for preparing a positive electrode material. Compared with Example 1, the difference is that in step (3), tin oxide is not added.

[0122] Comparative Example 4

[0123] This comparative example provides a method for preparing a positive electrode material coated with gadolinium-doped zinc oxide. Compared with Example 1, the difference is that, in step (1), ZnSO4 is used instead of La2(SO4)3, wherein the molar amount of Zn in ZnSO4 is equal to the molar amount of La in La2(SO4)3.

[0124] Test Case

[0125] The sodium iron sulfate positive electrode material prepared in the embodiment and the comparative example was mixed with the conductive agent acetylene carbon black and the binder PVDF in a mass ratio of 80:10:10, and an appropriate amount of 1-methyl-2-pyrrolidone was added and ball-milled for 1 hour to form a slurry, which was evenly coated on an aluminum sheet, dried, and pressed into a positive electrode sheet with a compaction density of 2.0 g / cm 3 2032 button-type batteries were assembled using a 1 mol / L NaClO₄ solution in PC (propylene carbonate) as the electrolyte and a sodium metal sheet as the negative electrode. Electrical performance was tested using a Siken test system. Discharge capacity at 0.1C was measured over a charge / discharge cutoff voltage range of 2.0–4.5V.

[0126] Rate performance test: The charge and discharge cut-off voltage is 2.0~4.5V. The discharge capacity C1 under 1C conditions and the discharge capacity C2 under 0.1C conditions are tested. The rate performance is C1 / C2.

[0127] High-temperature cycling performance test: At 40°C, within a cut-off voltage range of 2.0 to 4.5V, the test charge and discharge rate was 1C, and the number of cycles was 50. The test results are shown in Table 1.

[0128] Table 1 Test results comparison table

[0129]

[0130] Table 1 mainly illustrates the following test results:

[0131] Initial discharge specific capacity: Under 0.1C charge and discharge conditions, the initial discharge specific capacity of the sodium ferric sulfate cathode materials prepared in each Example and Comparative Example is shown in the table. As can be seen from the table, Example 1 has the highest initial discharge specific capacity, reaching 98.2 mAh / g, while Comparative Example 1 has the lowest initial discharge specific capacity, at 81.2 mAh / g. The initial discharge specific capacities of the other Examples fall between the two.

[0132] Rate performance: Rate performance refers to a battery's ability to retain capacity at different charge and discharge rates. In the table, this is measured by comparing the ratio of discharge capacity (C1) at 1C to discharge capacity (C2) at 0.1C (C1 / C2). Example 1 achieved the best rate performance, reaching 96.8%, while Comparative Example 1 had the worst rate performance, at 82.3%. The rate performance of the other examples also generally outperformed the comparative examples.

[0133] High-temperature cycling performance: Capacity retention of each sample after 50 cycles at a charge-discharge rate of 1C at 40°C. Example 1 had the highest 50-cycle capacity retention, at 98.4%, while Comparative Example 1 had the lowest, at 82.5%. The capacity retention of the other examples was also higher than that of the comparative example, demonstrating improved high-temperature cycling stability.

[0134] In summary, the test results in Table 1 demonstrate that the lanthanum-doped tin oxide-coated sodium ferric sulfate cathode materials (Examples 1-5) prepared using the preparation method of the present invention outperformed cathode materials undoped with lanthanum or uncoated with tin oxide (Comparative Examples 1-4) in terms of initial discharge capacity, rate capability, and high-temperature cycling performance. This demonstrates the effectiveness and superiority of the cathode materials and preparation methods provided by the present invention in improving the performance of sodium-ion batteries.

[0135] The present invention also provides a positive electrode material, in which lanthanum is doped, and the sodium ferric sulfate positive electrode material is coated with tin oxide.

[0136] The present invention also provides a sodium ion battery comprising the above-mentioned positive electrode material.

[0137] Specifically, in this embodiment, an innovative lanthanum-doped tin oxide-coated sodium ferric sulfate cathode material is proposed. This material achieves significant performance improvements through carefully designed composition and structure.

[0138] First, the present invention cleverly doped lanthanum into the sodium iron sulfate positive electrode material. This innovative measure effectively inhibited the growth of grains, making the crystal structure more stable, and thus greatly improved the ionic conductivity of the material. At the same time, the doping of lanthanum also promoted the 3+ Na + This process significantly increases the overpotential of the surface oxygen evolution reaction and effectively suppresses the production of lattice oxygen, thereby ensuring the stability of the transition metal valence state during charge and discharge. In addition, the material's intrinsic oxygen vacancies can accurately capture the oxygen released by the positive electrode material during the sodium insertion and deintercalation process, a feature that further enhances the battery's conductivity and safety.

[0139] Secondly, the present invention uses tin oxide to coat the sodium iron sulfate positive electrode material. This coating acts as a barrier, effectively isolating the direct contact between the positive electrode material and the electrolyte, avoiding chemical reactions that may occur during the charge and discharge process, thereby significantly improving the cycle performance of the material. At the same time, the tin oxide coating also provides a uniform and stable ion transmission interface, promoting the Na + The smooth intercalation and deintercalation of tin oxide further optimizes the material's rate performance. It is worth mentioning that the rich oxygen vacancies of tin oxide can effectively inhibit the loss of lattice oxygen during the charging process, which not only improves the reversibility of the redox reaction but also plays a positive role in improving the material's cycle performance.

[0140] In summary, the present invention successfully achieves both high capacity and high cycle performance of the positive electrode material by doping lanthanum into the polyanionic compound positive electrode material and introducing a tin oxide coating layer, opening up a new path for the development of sodium ion battery technology.

[0141] The above are only preferred embodiments of the present invention and do not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of this specification and illustrations should be included in the protection scope of the present invention.

Claims

1. A method for preparing a high voltage positive electrode material, characterized in that: include: Step S1, mixing a sulfur-containing sodium source, a sulfur-containing iron source, a sulfur-containing lanthanum source and an auxiliary additive to obtain a suspension; Step S2, continuously adding ammonia water to the suspension while stirring until the pH value of the suspension is adjusted to 3.5-6, then stopping the addition of ammonia water, and heating the suspension to 60-90° C. to obtain a sodium ferric sulfate cathode material precursor; Step S3, mixing the sodium ferric sulfate positive electrode material precursor and tin oxide and sintering them to obtain a tin oxide-coated sodium ferric sulfate positive electrode material, wherein in step S3, the sodium ferric sulfate positive electrode material precursor and tin oxide are mixed in a mass ratio of 1:(0.0005-0.04); The sintering process in step S3 includes a first sintering stage and a second sintering stage; The temperature of the first sintering stage is 100-300°C and the time is 8-15h; The second stage sintering temperature is 350 ~ 420 ° C, and the time is 12 ~ 24 hours; The molar ratio of the sulfur-containing sodium source, the sulfur-containing iron source and the sulfur-containing lanthanum source is (1-8): (1-5): (0-0.4), wherein the molar amount of the sulfur-containing lanthanum source is not 0.

2. The preparation method according to claim 1, characterized in that The auxiliary additive includes a complexing agent and a carbon source, and the ratio of the molar amount of the complexing agent to the sum of the molar amounts of the sulfur-containing iron source and the sulfur-containing lanthanum source is (0.5-2):1; And / or, the mass of the carbon source is 0.04% to 8% of the sum of the masses of the sulfur-containing sodium source, the sulfur-containing iron source and the sulfur-containing lanthanum source.

3. The preparation method according to claim 1, characterized in that The auxiliary additives include antioxidants, complexing agents, carbon sources, dispersants, defoaming agents and deionized water; The mass of the deionized water is 10% to 50% of the sum of the mass of the sulfur-containing sodium source, the sulfur-containing iron source, the sulfur-containing lanthanum source, the antioxidant, the complexing agent, the carbon source, the dispersant, and the defoaming agent.

4. The preparation method according to claim 1, characterized in that In step S3, the sintering process is performed in an inert gas.

5. A positive electrode material, characterized in that The positive electrode material is doped with lanthanum and coated with tin oxide, and is prepared by the preparation method according to any one of claims 1 to 4.

6. A sodium ion battery, characterized in that: Comprising the positive electrode material as claimed in claim 5.

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