Iron-containing polyanion positive electrode material and preparation method thereof, positive electrode and sodium ion battery

Abstract

The invention discloses an iron-containing polyanion positive electrode material, a positive electrode adopting the iron-containing polyanion positive electrode material, a sodium ion battery adopting the iron-containing polyanion positive electrode material and a preparation method of the iron-containing polyanion positive electrode material. The nitrogen-containing positive electrode material disclosed by the invention has the composition as shown in a formula I: NaxFey (SO4) zFm (formula I), and x is more than or equal to 0.5 and less than or equal to 1.2; 0.05 < = y < = 0.8; 0.2 < = z < = 1.5; 0.1 < = m < = 0.6. The positive electrode material provided by the invention shows excellent phase stability at high temperature and high voltage, can effectively inhibit the structure collapse phenomenon, and can meet the requirements of high-performance sodium ion batteries on energy density and rapid charge-discharge capability. In addition, through an innovative preparation process, the stability and the specific capacity of the material can be remarkably improved, and the problem that the performance of an existing material is quickly degraded in circulation is solved.

Description

Technical Field

[0001] This invention relates to the field of new energy, particularly to the field of sodium-ion batteries, and more particularly to an iron-containing polyanion cathode material and its preparation method, as well as a cathode and sodium-ion battery using the cathode material. Background Technology

[0002] Sodium-ion batteries are rechargeable secondary batteries and are currently a promising energy storage device. However, the traditional polyanionic compound cathode materials used still face many unresolved issues. Firstly, under high temperature and high voltage conditions, existing polyanionic compounds are prone to phase transitions, which not only gradually reduce battery capacity but also severely affect cycle stability, thus limiting the lifespan and performance of sodium-ion batteries. Secondly, traditional polyanionic compound synthesis methods rely heavily on high-temperature sintering, a process that leads to continuous grain enlargement. This increased grain size directly results in a decrease in both specific capacity and rate performance, failing to meet the energy density and rapid charge / discharge capabilities required for high-performance sodium-ion batteries. Furthermore, the manufacturing process is complex, cumbersome, and suffers from low raw material utilization, significantly reducing production efficiency and increasing costs, hindering the large-scale commercial application of sodium-ion batteries.

[0003] In summary, to address the existing problems with cathode materials in sodium-ion batteries, it is necessary to improve the cathode materials to enhance the performance of sodium-ion batteries. Summary of the Invention

[0004] To address the problems of phase transitions, decreased specific capacity and rate performance, and inability to meet the energy density and rapid charge / discharge capabilities required by existing sodium-ion battery cathode materials under high-temperature and high-voltage conditions, this invention provides an iron-containing polyanion cathode material, its preparation method, and a cathode and sodium-ion battery using this cathode material. The cathode material of this invention is Na... x Fe y( SO4) z F m Exhibiting excellent phase stability at high temperatures and high voltages, this material effectively suppresses structural collapse, meeting the energy density and rapid charge / discharge capabilities required for high-performance sodium-ion batteries. Furthermore, this invention, through an innovative preparation process, significantly improves the material's stability and specific capacity, addressing the problem of rapid performance degradation in existing materials during cycling.

[0005] To achieve the above-mentioned objectives of the present invention, a first aspect of the present invention provides an iron-containing polyanionic cathode material, the cathode material having the composition shown in Formula I: Na x Fe y( SO4)z F m (Formula I), where 0.5≤x≤1.2; 0.05≤y≤0.8; 0.2≤z≤1.5; 0.1≤m≤0.6. The polyanionic compound sodium electrode cathode material of the present invention is mainly composed of sodium (Na), iron (Fe), sulfur (S) and fluorine (F). This material exhibits excellent phase stability under high temperature and high voltage, and can effectively suppress structural collapse.

[0006] According to some embodiments of the present invention, the molar ratio of Na to Fe is 1:0.3-0.7. Examples of the molar ratio of Na to Fe include, but are not limited to, 1:0.3, 1:0.4, 1:0.5, 1:0.6, and 1:0.7. In this invention, at this molar ratio, the cathode material is more stable and less prone to phase transition.

[0007] According to some embodiments of the present invention, the molar ratio of Na to S is 1:1-2. Examples of the molar ratio of Na to S include, but are not limited to, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, and 1:2. In the present invention, adjusting the molar ratio of Na to S within the above range can result in the cathode material exhibiting superior performance.

[0008] According to some embodiments of the present invention, the molar ratio of Na to F is 1:0.1-0.5. The molar ratio of Na to F is, for example, but not limited to, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, etc.

[0009] According to some embodiments of the present invention, the average particle size of the cathode material is 100-500 nm.

[0010] According to some embodiments of the present invention, the specific surface area of ​​the positive electrode material is 15-50 m². 2 / g.

[0011] According to some embodiments of the present invention, the conductivity of the positive electrode material is 10. -5 -10 -4 S / m.

[0012] According to some embodiments of the present invention, the XRD pattern of the cathode material shows diffraction peaks at 18-22°, 23-27°, and 29-33°.

[0013] A second aspect of the present invention provides a method for preparing the above-mentioned iron-containing polyanion cathode material, comprising:

[0014] Step 1: Mix the sodium source, iron source, sulfur source and fluorine source to obtain a mixed solution;

[0015] Step 2: Sonicate the mixture and add a solution to obtain a gel;

[0016] Step 3: The gel is shaped, dried and sintered.

[0017] According to some embodiments of the present invention, preferably, the sodium source is mixed with the iron source, and then the sulfur source and fluorine source are slowly added.

[0018] According to some embodiments of the present invention, the sodium source is selected from at least one of sodium oxide, sodium hydroxide, sodium chloride, sodium sulfate, sodium nitrate, sodium oxide, sodium oxalate, and sodium carbonate.

[0019] According to some embodiments of the present invention, the iron source is selected from at least one of ferric hydroxide, ferric chloride, ferric oxide, ferric sulfate, ferric chloride (III), and ferric amino(III).

[0020] According to some embodiments of the present invention, the sulfur source is selected from at least one of sulfuric acid, sodium sulfide, and sulfur tetrafluoride.

[0021] According to some embodiments of the present invention, the fluorine source is selected from at least one of sodium fluoride, sodium hydrogen fluoride, and ammonium fluoride.

[0022] According to some embodiments of the present invention, the amounts of sodium source, iron source, sulfur source, and fluorine source satisfy n(Na):n(Fe):n[(SO4)]:n(F)=x:y:z:m. In the present invention, the amounts of sodium source, iron source, sulfur source, and fluorine source satisfy that the prepared iron-containing polyanionic cathode material has the composition shown in Formula I: Na x Fe y( SO4) z F m (Equation I), where 0.5≤x≤1.2; 0.05≤y≤0.8; 0.2≤z≤1.5; 0.1≤m≤0.6.

[0023] According to some embodiments of the present invention, the concentrations of the sodium source, iron source, sulfur source, and fluorine source can be 0.1-2, 0.05-1, 0.1-2, and 0.01-0.5 mol / L, respectively. Using high-purity raw materials can effectively reduce interference from impurities, improve the purity and consistency of the material, thereby enhancing the electrochemical performance and stability of the cathode material.

[0024] According to some embodiments of the present invention, a sodium source and an iron source are first mixed, and then a sulfur source and a fluorine source are added at a rate of 1-5 mL / s. For example, but not limited to, sodium hydroxide and ferric hydroxide are fully dissolved in deionized water to form a homogeneous solution. Then, disodium hydrogen phosphate and sodium fluoride are slowly added and stirred until homogeneous. This method further improves the stability of the cathode material.

[0025] According to some embodiments of the present invention, the conditions for the ultrasonic treatment include: a frequency of 20-40 kHz and a treatment time of 30-60 min. In this invention, the ultrasonic waves can promote uniform mixing between reactants, and promote nucleation and crystal growth.

[0026] According to some embodiments of the present invention, the conformability preservation conditions include: standing at 20-30°C for 20-30 hours to ensure structural uniformity.

[0027] According to some embodiments of the present invention, the drying conditions include a temperature of 50-70°C and a time of 12-18 hours.

[0028] According to some embodiments of the present invention, the temperature is 500-800°C, the heating rate is 30-60°C / h, and the holding time after reaching the temperature is 2-6h. In the present invention, the sintering step helps to remove organic solvents and promotes the formation of the corresponding compounds.

[0029] According to some embodiments of the present invention, the solvent is selected from at least one of deionized water, ethanol, isopropanol, and dimethyl sulfoxide. Preferably, the amount of solvent added is 50-150 mL relative to 100 g of the ultrasonicated product. In the present invention, after ultrasonic treatment, an appropriate amount of water is slowly added to adjust the concentration, and the mixture is allowed to stand to react and form a gel.

[0030] According to some embodiments of the present invention, the method further includes ball milling and sieving after sintering. In this invention, after sintering, the powder can be naturally cooled to room temperature and then pulverized to a suitable particle size (100-300 nm) using a ball mill. The powder is then washed with deionized water to remove unreacted raw materials, and finally sieved to obtain a final product with uniform particle size.

[0031] A third aspect of the present invention provides a positive electrode comprising the aforementioned iron-containing polyanion positive electrode material. In the present invention, the method for preparing the aforementioned positive electrode may include, but is not limited to, coating the aforementioned iron-containing polyanion positive electrode material onto a current collector to obtain the positive electrode.

[0032] The fourth aspect of the present invention provides a method for preparing the above-mentioned positive electrode, comprising: coating the above-mentioned iron-containing polyanionic positive electrode material onto a current collector to obtain a positive electrode.

[0033] The fifth aspect of the present invention provides a sodium-ion battery, comprising the above-described positive electrode, separator, electrolyte and negative electrode.

[0034] Beneficial effects of the present invention

[0035] (1) The Na of the present invention x Fe y( SO4) z Fm The material exhibits excellent phase stability under high temperature and high voltage conditions, effectively suppressing structural collapse, which is of great significance in current research on sodium-ion battery materials.

[0036] (2) Compared with traditional materials, this material exhibits an excellent capacity retention rate during cycling. After 100 cycles, under preferred conditions, its capacity retention rate can still exceed 95%. This performance index is far superior to that of traditional materials, providing a strong guarantee for the long-life application of sodium-ion batteries.

[0037] (3) The present invention also employs an innovative preparation process, which not only increases the specific surface area of ​​the material but also enhances the ionic conductivity, thereby further improving the energy density of the battery and making it more advantageous in energy storage. Detailed Implementation

[0038] In the following technical description, for ease of explanation, numerous details are used to provide a full understanding of the disclosed embodiments. However, one or more embodiments may still be practiced without these details.

[0039] The terms "first," "second," etc., used in the specification and claims of this disclosure are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate for the embodiments of this disclosure described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0040] The present invention will be further illustrated below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0041] In this invention, the elemental composition of the polyanion cathode material is determined using an inductively coupled plasma method.

[0042] In this invention, the average particle size of the polyanion cathode material is measured using a laser particle size analyzer.

[0043] In this invention, the specific surface area of ​​the polyanionic cathode material is measured using the BET method.

[0044] In this invention, the conductivity of the polyanionic cathode material is measured by electrochemical impedance spectroscopy.

[0045] Example 1

[0046] Sodium hydroxide aqueous solution (1 mol / L) and ferric hydroxide aqueous solution (1 mol / L) were mixed separately. Then, sulfuric acid solution (1 mol / L) and sodium fluoride aqueous solution (0.1 mol / L) were added at a rate of 2 mL / s. The sodium hydroxide, ferric hydroxide, sulfuric acid, and sodium fluoride were mixed in a ratio of n(Na):n(Fe):n[(SO4)]:n(F) of 1:0.5:1:0.2 and stirred for 30 minutes. The mixture was placed in an ultrasonic cleaner, with the ultrasonic frequency set to 20 kHz and the treatment time set to 30 minutes. After ultrasonic treatment, 100 mL of deionized water was added at a rate of 1 mL / s to adjust the solution concentration relative to 100 g of the ultrasonicated liquid, and the mixture was allowed to stand for 12 hours to form a gel. The gel was maintained at room temperature for 24 hours. Then, the sample was placed in an oven and dried at 60 °C for 24 hours until constant weight was achieved, ensuring complete removal of moisture. The dried samples were transferred to a high-temperature furnace, set at 600℃ with a heating rate of 50℃ / h, and held for 3 hours for sintering. After sintering, the samples were allowed to cool naturally to room temperature. The cooled samples were then pulverized using a ball mill at 400 rpm for 2 hours to achieve a particle size of approximately 200 nm.

[0047] The specific surface area of ​​this cathode material is 30.0 m². 2 / g; conductivity is 9.6×10 -5 S / m. The XRD pattern of the cathode material shows diffraction peaks at 20°, 25°, and 30°.

[0048] Example 2

[0049] The method is the same as in Example 1, except that sodium hydroxide, iron hydroxide, sulfuric acid and sodium fluoride are mixed in a ratio of n(Na):n(Fe):n[(SO4)]:n(F) of 1:0.4:1:0.25.

[0050] The specific surface area of ​​this cathode material is 28.0 m². 2 / g; conductivity 1.8×10 -5 S / m. The XRD pattern of the cathode material shows diffraction peaks at 18°, 23°, and 29°.

[0051] Example 3

[0052] The method is the same as in Example 1, except that sodium hydroxide, iron hydroxide, sulfuric acid and sodium fluoride are mixed in a ratio of n(Na):n(Fe):n[(SO4]:n(F) of 1:0.6:1:0.15.

[0053] The specific surface area of ​​this cathode material is 29.0 m². 2 / g; conductivity is 5.5×10 -5S / m. The XRD pattern of the cathode material shows diffraction peaks at 19°, 24°, and 31°.

[0054] Example 4

[0055] The method is the same as in Example 1, except that sodium hydroxide, iron hydroxide, sulfuric acid and sodium fluoride are mixed in a ratio of n(Na):n(Fe):n[(SO4]:n(F) of 1:0.0.05:0.2:0.1.

[0056] The specific surface area of ​​this cathode material is 28.8 m². 2 / g; conductivity is 5.3×10 -5 S / m. The XRD pattern of the cathode material shows diffraction peaks at 19.2°, 23°, and 30°.

[0057] Example 5

[0058] The method is the same as in Example 1, except that sodium hydroxide, iron hydroxide, sulfuric acid and sodium fluoride are mixed in a ratio of n(Na):n(Fe):n[(SO4]:n(F) of 1:0.8:1.5:0.6.

[0059] The specific surface area of ​​this cathode material is 29.0 m². 2 / g; conductivity is 5.5×10 -5 S / m. The XRD pattern of the cathode material shows diffraction peaks at 19°, 24°, and 31°.

[0060] Example 6

[0061] The method is the same as in Example 1, except that sodium hydroxide, ferric hydroxide, disodium hydrogen phosphate and sodium fluoride are replaced with sodium chloride, ferric chloride, sodium sulfate and sodium hydrogen fluoride, respectively.

[0062] The specific surface area of ​​this cathode material is 27.0 m². 2 / g; conductivity is 2.2×10 -5 S / m. The XRD pattern of the cathode material shows diffraction peaks at 19°, 24°, and 31°.

[0063] Example 7

[0064] The method is the same as in Example 1, except that the ultrasonic frequency is set to 25 kHz and the processing time is 40 minutes.

[0065] The specific surface area of ​​this cathode material is 24.0 m². 2 / g; conductivity is 2.5×10 -5 S / m. The XRD pattern of the cathode material shows diffraction peaks at 19°, 25°, and 30°.

[0066] Example 8

[0067] The method was followed as in Example 1, except that after gel formation, the sample was kept at room temperature for 20 hours. It was then placed in an oven and dried at 60°C for 24 hours until the sample reached constant weight, ensuring complete removal of moisture.

[0068] The specific surface area of ​​this cathode material is 21.0 m². 2 / g; conductivity is 2.1×10 -5 S / m. The XRD pattern of the cathode material shows diffraction peaks at 22°, 27°, and 33°.

[0069] Example 9

[0070] The method is the same as in Example 1, except that the dried sample is transferred to a high-temperature furnace, the temperature is set at 700°C, the heating rate is 30°C / h, and it is held for 2 hours for sintering.

[0071] The specific surface area of ​​this cathode material is 27.0 m². 2 / g; conductivity is 1.9×10 -5 S / m. The XRD pattern of the cathode material shows diffraction peaks at 20°, 24°, and 29°.

[0072] Example 10

[0073] The method is the same as in Example 1, except that ultrasonic treatment is not performed, i.e.:

[0074] Sodium hydroxide aqueous solution (1 mol / L) and ferric hydroxide aqueous solution (1 mol / L) were mixed separately. Then, sulfuric acid solution (1 mol / L) and sodium fluoride aqueous solution (0.1 mol / L) were added at a rate of 2 mL / s, with sodium hydroxide, ferric hydroxide, sulfuric acid, and sodium fluoride mixed in a ratio of n(Na):n(Fe):n[(SO4)]:n(F) of 1:0.5:1:0.2, and stirred for 30 minutes. 100 mL of deionized water was added at a rate of 1 mL / s relative to 100 g of the sonicated liquid to adjust the solution concentration, and the mixture was allowed to stand for 12 hours to form a gel. The gel was maintained at room temperature for 24 hours. Then, the sample was placed in an oven and dried at 60 °C for 24 hours until constant weight was achieved, ensuring complete removal of moisture. The dried sample was transferred to a high-temperature furnace, set to 600 °C, with a heating rate of 50 °C / h, and held at the reached temperature for 3 hours for sintering. After sintering, the sample was allowed to cool naturally to room temperature. The cooled sample was pulverized using a ball mill at a speed of 400 rpm for 2 hours to achieve a particle size of approximately 200 nm.

[0075] The specific surface area of ​​this cathode material is 20.2 m². 2 / g; conductivity is 7.6×10 -6S / m. The XRD pattern of the cathode material shows diffraction peaks at 18°, 22°, and 28°.

[0076] Example 11

[0077] The method is the same as in Example 1, except that no gel is formed, i.e.:

[0078] Sodium hydroxide aqueous solution (1 mol / L) and ferric hydroxide aqueous solution (1 mol / L) were mixed separately. Then, sulfuric acid solution (1 mol / L) and sodium fluoride aqueous solution (0.1 mol / L) were added at a rate of 2 mL / s. The sodium hydroxide, ferric hydroxide, sulfuric acid, and sodium fluoride were mixed in a ratio of n(Na):n(Fe):n[(SO4)]:n(F) of 1:0.5:1:0.2 and stirred for 30 minutes. The mixture was then placed in an ultrasonic cleaner, with the ultrasonic frequency set to 20 kHz and the treatment time set to 30 minutes. After ultrasonic treatment, the sample was kept at room temperature for 24 hours. It was then placed in an oven and dried at 60°C for 24 hours until the sample reached constant weight, ensuring complete removal of moisture. The dried sample was transferred to a high-temperature furnace, with the temperature set to 600°C and the heating rate set to 50°C / h. After reaching the temperature, the sample was held at this temperature for 3 hours for sintering. After sintering, the sample was allowed to cool naturally to room temperature. The cooled sample was pulverized using a ball mill at a speed of 400 rpm for 2 hours to achieve a particle size of approximately 200 nm.

[0079] The specific surface area of ​​this cathode material is 20.1 m². 2 / g; conductivity is 7.2×10 -6 S / m. The XRD pattern of the cathode material shows diffraction peaks at 18.1°, 22.3°, and 28.1°.

[0080] Comparative Example 1

[0081] The method is the same as in Example 1, except that Fe is not used, that is:

[0082] Take a 1 mol / L sodium hydroxide aqueous solution and add a 1 mol / L sulfuric acid solution and a 0.1 mol / L sodium fluoride aqueous solution at a rate of 2 mL / s. The sodium hydroxide, sulfuric acid, and sodium fluoride are mixed in a ratio of n(Na):n[(SO4)]:n(F) of 1:1:0.2 and stirred for 30 minutes. Place the mixed solution in an ultrasonic cleaner, set the ultrasonic frequency to 20 kHz, and the treatment time to 30 minutes. After ultrasonic treatment, add 100 mL of deionized water at a rate of 1 mL / s to 100 g of the ultrasonicated liquid to adjust the solution concentration, and let it stand for 12 hours to form a gel. Keep it at room temperature for 24 hours. Then place it in an oven and dry it at 60 °C for 24 hours until the sample reaches constant weight, ensuring that moisture is removed. Transfer the dried sample to a high-temperature furnace, set the temperature to 600 °C, the heating rate to 50 °C / h, and hold it at the temperature for 3 hours for sintering. After sintering, allow it to cool naturally to room temperature. The cooled sample was pulverized using a ball mill at a speed of 400 rpm for 2 hours to achieve a particle size of approximately 200 nm.

[0083] The specific surface area of ​​this cathode material is 2.0 m². 2 / g; conductivity is 1.9×10 -6 S / m. The XRD pattern of the cathode material shows diffraction peaks at 18° and 23°.

[0084] Comparative Example 2

[0085] The method is the same as in Example 1, except that sulfur is not used, that is:

[0086] Sodium hydroxide aqueous solution (1 mol / L) and ferric hydroxide aqueous solution (1 mol / L) were mixed separately. Then, sodium fluoride aqueous solution (0.1 mol / L) was added at a rate of 2 mL / s, with sodium hydroxide, ferric hydroxide, and sodium fluoride mixed in a ratio of n(Na):n(Fe):n(F) of 1:0.5:0.2, and stirred for 30 minutes. The mixture was placed in an ultrasonic cleaner, with the ultrasonic frequency set to 20 kHz and the treatment time set to 30 minutes. After ultrasonic treatment, 100 mL of deionized water was added at a rate of 1 mL / s to adjust the solution concentration relative to 100 g of the ultrasonicated liquid, and the mixture was allowed to stand for 12 hours to form a gel. The gel was then maintained at room temperature for 24 hours. The gel was then placed in an oven and dried at 60 °C for 24 hours until the sample reached constant weight, ensuring complete removal of moisture. The dried sample was transferred to a high-temperature furnace, with the temperature set to 600 °C and the heating rate set at 50 °C / h. After reaching the temperature, the sample was held at this temperature for 3 hours for sintering. After sintering, the sample was allowed to cool naturally to room temperature. The cooled sample was pulverized using a ball mill at a speed of 400 rpm for 2 hours to achieve a particle size of approximately 200 nm.

[0087] The specific surface area of ​​this cathode material is 2.8 m². 2 / g; conductivity is 2.1×10 -6 S / m. The XRD pattern of the cathode material shows diffraction peaks at 17° and 27°.

[0088] Comparative Example 3

[0089] The method is the same as in Example 1, except that F is not used, that is:

[0090] Sodium hydroxide aqueous solution (1 mol / L) and ferric hydroxide aqueous solution (1 mol / L) were mixed separately. Then, sulfuric acid solution (1 mol / L) was added at a rate of 2 mL / s, with sodium hydroxide, ferric hydroxide, and sulfuric acid mixed in a ratio of n(Na):n(Fe):n[(SO4)] of 1:0.5:1, and stirred for 30 minutes. The mixture was placed in an ultrasonic cleaner, with the ultrasonic frequency set to 20 kHz and the treatment time set to 30 minutes. After ultrasonic treatment, 100 mL of deionized water was added at a rate of 1 mL / s to adjust the solution concentration relative to 100 g of the ultrasonically treated liquid, and the mixture was allowed to stand for 12 hours to form a gel. The gel was then maintained at room temperature for 24 hours. It was then placed in an oven and dried at 60 °C for 24 hours until the sample reached constant weight, ensuring complete removal of moisture. The dried sample was transferred to a high-temperature furnace, with the temperature set to 600 °C and the heating rate set at 50 °C / h. After reaching the temperature, the sample was held at this temperature for 3 hours for sintering. After sintering, the sample was allowed to cool naturally to room temperature. The cooled sample was pulverized using a ball mill at a speed of 400 rpm for 2 hours to achieve a particle size of approximately 200 nm.

[0091] The specific surface area of ​​this cathode material is 3.1 m². 2 / g; conductivity is 1.2×10 -6 S / m. The XRD pattern of the cathode material shows diffraction peaks at 18° and 22°.

[0092] Test case

[0093] The positive electrode materials prepared in the examples and comparative examples were mixed with conductive carbon black and polyvinylidene fluoride (PVDF) in a ratio of 8:1:1 and coated onto an aluminum foil current collector to form a positive electrode sheet. After drying and compaction, a positive electrode sheet for battery assembly was obtained. A sodium-ion half-cell was assembled using a glass fiber membrane as the separator, sodium metal as the counter electrode, and a 1M NaPF6 solution as the electrolyte.

[0094] Constant current charge-discharge tests were conducted: the test conditions were 25℃, and the discharge specific capacity was measured after 100 charge-discharge cycles at different rates of 1C, 5C, and 10C. The test results are shown in Table 1.

[0095] Table 1

[0096]

[0097]

[0098] As shown in Table 1, the battery's initial discharge capacity is significantly improved, and its capacity retention rate remains high after 100 charge-discharge cycles at a 1C current density, demonstrating excellent cycle stability and reliability.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An iron-containing polyanionic cathode material, characterized in that, The cathode material has the composition shown in Formula I: Na x Fe y( SO4) z F m (Formula I) Wherein, 0.5≤x≤1.2; 0.05≤y≤0.8; 0.2≤z≤1.5; 0.1≤m≤0.

6.

2. The iron-containing polyanion cathode material according to claim 1, characterized in that, The molar ratio of Na to Fe is 1:0.3-0.7; and / or, the molar ratio of Na to S is 1:1-2; and / or, the molar ratio of Na to F is 1:0.1-0.

5.

3. The iron-containing polyanionic cathode material according to claim 1 or 2, characterized in that, The average particle size of the positive electrode material is 100-500 nm; and / or, The specific surface area of ​​the cathode material is 15-50 m². 2 / g; and / or, The conductivity of the positive electrode material is 10. -5 -10 -4 S / m.

4. The iron-containing polyanionic cathode material according to any one of claims 1-3, characterized in that, The XRD pattern of the cathode material shows diffraction peaks at 18-22°, 23-27°, and 29-33°.

5. A method for preparing the iron-containing polyanionic cathode material according to any one of claims 1-4, comprising: Step 1: Mix the sodium source, iron source, sulfur source and fluorine source to obtain a mixed solution; Step 2: Sonicate the mixture and add a solution to obtain a gel; Step 3: The gel is shaped, dried and sintered.

6. The preparation method according to claim 5, characterized in that, The sodium source is selected from at least one of sodium oxide, sodium hydroxide, sodium chloride, sodium sulfate, sodium nitrate, sodium oxide, sodium oxalate, and sodium carbonate; and / or, The iron source is selected from at least one of ferric hydroxide, ferric chloride, ferric oxide, ferric sulfate, ferric chloride (III), and ferric amino(III); and / or, The sulfur source is selected from at least one of sulfuric acid, sodium sulfide, and sulfur tetrafluoride; and / or, The fluorine source is selected from at least one of sodium fluoride, sodium bifluoride, and ammonium fluoride; and / or, The amounts of sodium, iron, sulfur, and fluorine sources satisfy n(Na):n(Fe):n[(SO4)]:n(F)=x:y:z:m.

7. The preparation method according to claim 5 or 6, characterized in that, The conditions for the ultrasonic treatment include: a frequency of 20-40 kHz and a treatment time of 30-60 min; and / or The conditions for maintaining the shape include: standing at 20-30℃ for 20-30 hours; and / or The drying conditions include: a temperature of 50-70°C and a time of 12-18 hours; and / or The sintering conditions include: heating at a rate of 30-60℃ / h to 500-800℃, and holding at that temperature for 2-6 hours; and / or The solvent is selected from at least one of deionized water, ethanol, isopropanol and dimethyl sulfoxide; preferably, the amount of solvent added is 50-150 mL relative to 100 g of the ultrasonicated product.

8. A positive electrode comprising the iron-containing polyanionic positive electrode material according to any one of claims 1-4.

9. The method for preparing the positive electrode according to claim 8, comprising: The iron-containing polyanion cathode material according to any one of claims 1-4 is coated on the current collector to obtain the cathode.

10. A sodium-ion battery comprising the positive electrode, separator, electrolyte, and negative electrode as described in claim 9.

Images