Sodium-ion positive electrode material, preparation method and sodium-ion positive electrode plate

Abstract

The application relates to the technical field of sodium ion batteries, in particular to a sodium ion positive electrode material, a preparation method thereof and a sodium ion positive electrode sheet, wherein the sodium ion positive electrode material comprises a sodium nickel-iron-manganese acid base and an organic conductive coating, the organic conductive coating is coated on the sodium nickel-iron-manganese acid base, and the organic conductive coating comprises polyacrylonitrile and a conductive agent. The sodium ion positive electrode material of the application is coated with an organic conductive coating on the surface of the sodium nickel-iron-manganese acid material, the organic conductive coating comprises polyacrylonitrile and a conductive agent, the polyacrylonitrile can effectively prevent chemical reaction between the positive electrode material and an aluminum foil, the conductive agent connects the positive electrode material and the aluminum foil, and the resistance of the positive electrode sheet is reduced. Compared with the positive electrode material coated with aluminum oxide, the compaction density of the sodium ion positive electrode sheet prepared from the sodium ion positive electrode material of the application is increased by 0.1 g / cm 3 -0.2 g / cm 3 , the capacity of the prepared sodium ion battery is increased by 14%-25%, and the cycle life is increased by 40%-80%.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a sodium-ion cathode material, its preparation method, and a sodium-ion cathode sheet. Background Technology

[0002] Sodium is widely available and abundant, and its price is far lower than that of lithium. In recent years, with the soaring price of lithium, sodium-ion batteries have attracted widespread attention due to their potential cost reduction of 30%-50% compared to lithium-ion batteries. Sodium-ion batteries have particularly attractive application prospects in energy storage, hybrid power, and lead-acid battery replacement.

[0003] Currently, sodium nickel iron manganese oxide (NaFeMnO) is the most practically valuable sodium-ion cathode material. During its preparation, an excess of sodium (Na) is added to achieve good crystallinity. Therefore, a small amount of Na remains (existing as Na2O at high temperatures). When the temperature drops to room temperature, Na2O adsorbs CO2 and H2O from the air to form NaOH and Na2CO3, making the cathode material alkaline. Furthermore, Na is more alkaline than Li, thus the alkalinity of sodium nickel iron manganese oxide (NaFeMnO) cathode material is significantly higher than that of the corresponding lithium-ion nickel-cobalt-manganese ternary cathode material.

[0004] Lithium-ion nickel-cobalt-manganese ternary cathode materials typically have a nano-alumina coating on their surface to isolate them from aluminum foil and electrolyte. Because of the relatively weak alkalinity, this significantly improves the cycle life of lithium batteries. However, for sodium-ion nickel-iron-manganese oxide cathode materials, the residual alkali on the surface is highly alkaline. The alumina coating readily reacts with the cathode material, and it's highly likely that the cathode material will continue to react with the aluminum foil after reacting with the alumina. Therefore, the traditional alumina coating on sodium nickel-iron-manganese oxide materials does not significantly improve the compaction density of the cathode sheet, and the corresponding battery cycle life is not significantly improved. Summary of the Invention

[0005] This invention provides a sodium ion positive electrode material, a preparation method thereof, and a sodium ion positive electrode sheet, in order to solve the aforementioned technical problems existing in the prior art.

[0006] In a first aspect, the present invention provides a sodium ion cathode material comprising a sodium nickel iron manganese oxide matrix and an organic conductive coating, wherein the organic conductive coating is coated on the sodium nickel iron manganese oxide matrix; the organic conductive coating comprises polyacrylonitrile and a conductive agent.

[0007] In the above-mentioned solution, addressing the issue that existing sodium-ion nickel-iron-manganese oxide (NiFeMn) cathode materials have strong residual alkalinity on their surface, and that traditional alumina coatings do not significantly improve the compaction density of the cathode sheet, resulting in no noticeable improvement in battery cycle life, the present invention coats the NiFeMn material with an organic conductive coating. This organic conductive coating comprises polyacrylonitrile and a conductive agent. The polyacrylonitrile effectively prevents contact between the cathode material and the aluminum foil, thus preventing chemical reactions between them. Simultaneously, the conductive agent in the organic conductive coating connects the cathode material and the aluminum foil, reducing the resistance of the cathode sheet. The compaction density of the sodium-ion secondary battery cathode sheet prepared using the sodium-ion cathode material of the present invention is 0.1 g / cm³ higher than that of the sodium-ion secondary battery electrode sheet coated with alumina. 3 -0.2g / cm 3 The resulting sodium-ion batteries have a 14%-25% increase in capacity and a 40%-80% increase in cycle life.

[0008] In a second aspect, the present invention provides a method for preparing the above-mentioned sodium-ion cathode material, comprising the following steps:

[0009] (1) NaNi was prepared by solid-state synthesis. x Fe y Mn z O2 material; where 0 < x ≤ 0.9, 0 < y ≤ 0.5, 0 < z ≤ 0.3;

[0010] (2) In a high-speed disperser, the polyacrylonitrile is dissolved in an organic solvent; then the conductive agent is added for the first dispersion to prepare a conductive organic slurry;

[0011] (3) Take the NaNi obtained in step (1) x Fe y Mn z O2 material is added to the conductive organic slurry obtained in step (2) for a second dispersion to prepare a positive electrode slurry;

[0012] (4) The positive electrode slurry obtained in step (3) is subjected to a first drying treatment to obtain the sodium ion positive electrode material.

[0013] In the above scheme, the method for preparing the sodium-ion cathode material of the present invention uses a high-speed dispersion method to effectively dissolve polyacrylonitrile in an organic solvent, and then adds a conductive agent to perform a first dispersion to obtain a uniformly dispersed conductive organic slurry. Then, the conductive organic slurry is reacted with NaNi... x Fe y Mn zThe O2 material was dispersed a second time to obtain a uniformly dispersed positive electrode slurry. Finally, the positive electrode slurry underwent a first drying treatment to remove organic solvents and allow the NaNi to precipitate. x Fe y Mn z The O2 material surface forms a uniform and dense organic conductive coating containing polyacrylonitrile and conductive agent, which can effectively prevent contact between the positive electrode material and the aluminum foil, thus preventing the chemical reaction between the two; at the same time, it can effectively reduce the resistance of the positive electrode sheet.

[0014] In one possible design, the polyacrylonitrile and the NaNi x Fe y Mn z The mass ratio of O2 material is (0.1-3):100.

[0015] Optionally, the polyacrylonitrile and the NaNi x Fe y Mn z The mass ratio of O2 material can be 0.1:100, 0.5:100, 1:100, 1.5:100, 2:100, 2.5:100 or 3:100, etc., or other values ​​within the above range, which are not limited here.

[0016] Understandably, by reacting the polyacrylonitrile with the NaNi x Fe y Mn z By limiting the mass ratio of O2 material to a reasonable range, it is possible to more effectively prevent contact between the positive electrode material and the aluminum foil, and more effectively prevent the chemical reaction between the two.

[0017] In one possible design, the conductive agent reacts with the NaNi x Fe y Mn z The mass ratio of O2 material is (0.1-2):100.

[0018] Optionally, the conductive agent reacts with the NaNi x Fe y Mn z The mass ratio of O2 material can be 0.1:100, 0.2:100, 0.3:100, 0.4:100, 0.5:100, 0.6:100, 0.7:100, 0.8:100, 0.9:100, 1:100, 1.2:100, 1.4:100, 1.5:100, 1.6:100, 1.8:100, or 2:100, etc., or other values ​​within the above range, which are not limited here.

[0019] Understandably, by combining the conductive agent with the NaNi x Fe y Mn z By limiting the mass ratio of O2 material within a reasonable range, the positive electrode material and aluminum foil can be connected more effectively, and the resistance of the positive electrode sheet can be reduced more effectively.

[0020] In one possible design, the organic solvent reacts with the NaNi x Fe y Mn z The mass ratio of O2 material is (25-80):100.

[0021] Optionally, the organic solvent reacts with the NaNi x Fe y Mn z The mass ratio of O2 materials can be 25:100, 30:100, 35:100, 40:100, 45:100, 50:100, 55:100, 60:100, 65:100, 70:100, 75:100, or 80:100, etc., or other values ​​within the above range, which are not limited here.

[0022] Understandably, by reacting the organic solvent with the NaNi x Fe y Mn z The mass ratio of O2 material is limited to a reasonable range, allowing the organic solvent to dissolve polyacrylonitrile more effectively during the preparation process, thereby enabling NaNi... x Fe y Mn z The surface of O2 material can form a more uniform and dense organic conductive coating containing polyacrylonitrile and conductive agent, which can more effectively prevent the contact between the positive electrode material and the aluminum foil and prevent the chemical reaction between the two; at the same time, it can more effectively reduce the resistance of the positive electrode sheet.

[0023] In one possible design, the molecular weight of the polyacrylonitrile is 20,000-200,000, preferably 50,000-150,000.

[0024] In the above scheme, selecting a suitable molecular weight of polyacrylonitrile is beneficial to the formation of conductive organic slurry, thereby enabling NaNi x Fe y Mn z O2 materials can form a more uniform and dense organic conductive coating on their surface.

[0025] In one possible design, in step (2), the linear velocity of the first dispersion is 10 m / min-200 m / min; the dispersion time of the first dispersion is 120 min-240 min.

[0026] Optionally, in step (2), the linear velocity of the first dispersion can be 10 m / min, 20 m / min, 30 m / min, 40 m / min, 50 m / min, 60 m / min, 70 m / min, 80 m / min, 90 m / min, 100 m / min, 120 m / min, 140 m / min, 160 m / min, 180 m / min, or 200 m / min, etc., or other values ​​within the above range, which are not limited here, but preferably 30 m / min-70 m / min. The dispersion time of the first dispersion can be 120 min, 140 min, 160 min, 180 min, 200 min, 220 min, or 240 min, etc., or other values ​​within the above range, which are not limited here.

[0027] In the above scheme, by limiting the linear velocity and dispersion time of the first dispersion within a reasonable range, the polyacrylonitrile and conductive agent are fully dispersed in the organic solvent, while ensuring that the conductive agent is not damaged. If the linear velocity of the first dispersion is too low, it is difficult to achieve sufficient dispersion; if the linear velocity of the first dispersion is too high, the conductive agent is easily broken.

[0028] In one possible design, in step (3), the linear velocity of the second dispersion is 10 m / min-100 m / min; and the dispersion time of the second dispersion is 60 min-180 min.

[0029] Optionally, in step (3), the linear velocity of the second dispersion can be 10 m / min, 20 m / min, 30 m / min, 40 m / min, 50 m / min, 60 m / min, 70 m / min, 80 m / min, 90 m / min, or 100 m / min, etc., or other values ​​within the above range, which are not limited here, but preferably 20 m / min-40 m / min. The dispersion time of the second dispersion can be 60 min, 80 min, 100 min, 120 min, 140 min, 160 min, or 180 min, etc., or other values ​​within the above range, which are not limited here.

[0030] By limiting the linear velocity and dispersion time of the second dispersion to a reasonable range, NaNi can be made x Fe y Mn zThe O2 material makes full contact with the conductive organic paste, which in turn facilitates the contact between NaNi and the conductive organic paste. x Fe y Mn z Formation of an organic conductive coating on the surface of O2 material.

[0031] In one possible design, in step (4), the first drying process is vacuum drying; the temperature of the first drying process is 60℃-80℃, and the time is 1h-2h.

[0032] Optionally, the temperature of the first drying process can be 60℃, 65℃, 70℃, 75℃ or 80℃, etc., and the time can be 1h, 1.2h, 1.4h, 1.5h, 1.8h or 2h, etc., or other values ​​within the above range, which are not limited here.

[0033] By limiting the temperature and time of the first drying process within a reasonable range, it is beneficial to remove organic solvents and simultaneously facilitate the formation of the organic conductive coating on NaNi. x Fe y Mn z Uniform and effective formation of O2 material surface.

[0034] In one possible design, the organic solvent is one or two of dimethyl sulfoxide, sulfolane, and ethyl nitrate.

[0035] Choosing a suitable type of organic solvent is beneficial for the dispersion of polyacrylonitrile and conductive agents, which in turn facilitates the formation of organic conductive coatings on NaNi. x Fe y Mn z Uniform and effective formation of O2 material surface.

[0036] In one possible design, the conductive agent is selected from one or more of carbon black, acetylene black, carbon nanotubes, Ketjen black, and carbon fiber, with acetylene black and carbon nanotubes being preferred.

[0037] By selecting a suitable type of conductive agent, it is possible to effectively connect the positive electrode material and the aluminum foil, thereby effectively reducing the resistance of the positive electrode sheet.

[0038] In one possible design, in step (1), the NaNi x Fe y Mn z The preparation method of O2 materials includes the following steps:

[0039] NiO, Fe2O3, MnO2, and Na2CO3 are added to a ball mill jar in the required stoichiometric ratio, followed by the addition of ethanol solvent and then ball milling media. The milled material is then subjected to a second drying treatment to obtain a precursor. The obtained precursor is then sintered in an air atmosphere to obtain the NaNi. x Fe y Mn z O2 materials.

[0040] In one possible design, the total mass of the ethanol solvent is 60%-80% of the total mass of NiO, Fe2O3, MnO2, and Na2CO3.

[0041] Optionally, the total mass of the ethanol solvent can be 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, or 80% of the total mass of NiO, Fe2O3, MnO2, and Na2CO3, or other values ​​within the above range, which are not limited here.

[0042] By limiting the total mass of ethanol solvent to 60%-80% of the total mass of NiO, Fe2O3, MnO2, and Na2CO3, the goal of effectively ball milling NiO, Fe2O3, MnO2, and Na2CO3 can be achieved.

[0043] In one possible design, the mass of the milling media is half the total mass of NiO, Fe2O3, MnO2, and Na2CO3.

[0044] By limiting the mass of the ball milling media to half the total mass of NiO, Fe2O3, MnO2, and Na2CO3, the goal of effectively ball milling NiO, Fe2O3, MnO2, and Na2CO3 can be achieved.

[0045] In one possible design, the ball mill rotates at a speed of 100 rpm to 200 rpm for 8 hours to 16 hours.

[0046] Optionally, the rotational speed of the ball mill can be 100 rpm, 120 rpm, 140 rpm, 150 rpm, 180 rpm or 200 rpm, etc., and the time can be 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h or 16h, etc., or other values ​​within the above range, which are not limited here.

[0047] By limiting the rotation speed and time of the ball mill within a reasonable range, it is possible to effectively ball mill NiO, Fe2O3, MnO2, and Na2CO3.

[0048] In one possible design, the second drying process is vacuum drying.

[0049] In one possible design, the temperature of the second drying process is 80℃-120℃, and the time is 1h-2h.

[0050] Optionally, the temperature of the second drying process can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃ or 120℃, etc., and the time can be 1h, 1.2h, 1.5h, 1.8h or 2h, etc., or other values ​​within the above range, which are not limited here.

[0051] By limiting the temperature and time of the second drying process to a reasonable range, the ethanol solvent can be effectively removed, resulting in a high-quality precursor.

[0052] In one possible design, the sintering process is as follows: sinter at a heating rate of 5℃ / min-15℃ / min to 350℃-500℃ for 0.5h-1h, then sinter at 700℃-900℃ for 5h-10h. Preferably, the heating rate is 10℃ / min.

[0053] By limiting the heating rate, temperature, and time during the sintering process, the sintering effect can be improved, thus enhancing the performance of NaNi. x Fe y Mn z The properties of O2 materials.

[0054] In a third aspect, the present invention provides a sodium-ion positive electrode sheet, comprising the sodium-ion positive electrode material described above or a sodium-ion positive electrode material prepared by the above-described preparation method; the maximum compaction density of the sodium-ion positive electrode sheet is 2.7 g / cm³. 3 -2.9g / cm 3 The impedance of the sodium ion positive electrode is 1Ω-2Ω.

[0055] This invention provides a sodium-ion cathode material with an organic conductive coating on the surface of sodium nickel iron manganese oxide material. The organic conductive coating includes polyacrylonitrile and a conductive agent. The polyacrylonitrile effectively prevents contact between the cathode material and the aluminum foil, thus preventing chemical reactions between them. Simultaneously, the conductive agent in the organic conductive coating connects the cathode material and the aluminum foil, reducing the resistance of the cathode electrode. The compaction density of the sodium-ion secondary battery cathode prepared using the sodium-ion cathode material of this invention is 0.1 g / cm³ higher than that of the sodium-ion secondary battery electrode corresponding to the alumina-coated cathode material. 3 -0.2g / cm 3 The resulting sodium-ion batteries have a 14%-25% increase in capacity and a 40%-80% increase in cycle life. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0057] Example 1

[0058] A method for preparing a sodium-ion cathode material is as follows:

[0059] (1) Add 20 mol NiO, 10 mol Fe2O3, 20 mol MnO2 and 30 mol Na2CO3 into the ball mill jar according to the required stoichiometric ratio, and then add ethanol solvent. The total mass of ethanol solvent is 70% of the total mass of the materials.

[0060] Then, milling media are added to the milling jar for milling; wherein the mass of the milling media is half the weight of the solid material, the milling speed is 150 rpm, and the milling time is 10 hours.

[0061] The ball-milled material was placed in a vacuum oven to dry at 90°C for 2 hours to obtain the precursor.

[0062] The obtained precursor was sintered at 450°C for 1 hour in air at a heating rate of 10°C / min, and then sintered at 850°C for 8 hours. The resulting powder was NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 materials.

[0063] (2) In a high-speed disperser, a certain amount of polyacrylonitrile is dissolved in an organic solvent, and then a conductive agent is added for the first dispersion to prepare a conductive organic slurry. The linear velocity of the first dispersion is 45 m / min, and the dispersion time is 180 min.

[0064] Polyacrylonitrile and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The O2 mass ratio is 1.5:100, and the polyacrylonitrile molecular weight is 80,000; the conductive agent and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The O2 mass ratio is 1.2:100; the conductive agent is a mixture of acetylene black and carbon nanotubes in a 1:1 ratio. Organic solvents and NaNi... 1 / 3 Fe 1 / 3 Mn 1 / 3 The mass ratio of O2 is 65:100, and the organic solvent is dimethyl sulfoxide.

[0065] (3) NaNi obtained in step (1) 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 material is added to the conductive organic slurry obtained in step (2) for a second dispersion to prepare the positive electrode slurry. The linear velocity of the second dispersion is 35 m / min, and the dispersion time is 120 min.

[0066] (4) The positive electrode slurry obtained in step (3) is subjected to vacuum drying to obtain the sodium ion positive electrode material. The vacuum drying temperature is 75°C and the drying time is 2 hours.

[0067] Example 2

[0068] A method for preparing a sodium-ion cathode material is as follows:

[0069] (1) Add 10 mol NiO, 1 mol Fe2O3, 2 mol MnO2 and 16 mol Na2CO3 into the ball mill jar according to the required stoichiometric ratio, and then add ethanol solvent. The total mass of ethanol solvent is 75% of the total mass of the materials.

[0070] Then, milling media are added to the milling jar for milling; the mass of the milling media is half the weight of the solid material; the milling speed is 150 rpm, and the milling time is 10 hours.

[0071] The ball-milled material was placed in a vacuum oven for drying at 88°C for 2 hours to obtain the precursor.

[0072] The obtained precursor was sintered at 420℃ for 1.5 h in air at a heating rate of 10℃ / min, and then sintered at 880℃ for 10 h. The resulting powder was NaNi. 0.8 Fe 0.1 Mn 0.1 O2 materials.

[0073] (2) In a high-speed disperser, a certain amount of polyacrylonitrile is dissolved in an organic solvent, and then a conductive agent is added for the first dispersion to prepare a conductive organic slurry. The linear velocity of the first dispersion is 40 m / min, and the dispersion time is 180 min.

[0074] The above describes the relationship between polyacrylonitrile and NaNi. 0.8 Fe 0.1 Mn 0.1 The O2 mass ratio is 1.8:100, and the polyacrylonitrile molecular weight is 120,000; the conductive agent and NaNi 0.8 Fe 0.1 Mn 0.1The O2 mass ratio is 1.9:100; the conductive agent is a mixture of carbon nanotubes; the organic solvent is NaNi 0.8 Fe 0.1 Mn 0.1 The O2 mass ratio is 65:100; the organic solvent is sulfolane.

[0075] (3) NaNi obtained in step (1) 0.8 Fe 0.1 Mn 0.1 O2 material is added to the conductive organic slurry obtained in step (2) for a second dispersion to prepare the positive electrode slurry. The linear velocity of the second dispersion is 35 m / min, and the dispersion time is 120 min.

[0076] (4) The positive electrode slurry obtained in step (3) is subjected to vacuum drying to obtain the sodium ion positive electrode material. The vacuum drying temperature is 75°C and the drying time is 2 hours.

[0077] Example 3

[0078] A method for preparing a sodium-ion cathode material is as follows:

[0079] (1) Add 10 mol NiO, 2 mol Fe2O3, 6 mol MnO2 and 10 mol Na2CO3 into the ball mill jar according to the required stoichiometric ratio, and then add ethanol solvent. The total mass of ethanol solvent is 80% of the total mass of the materials.

[0080] Then, milling media are added to the milling jar for milling; the mass of the milling media is half the weight of the solid material; the milling speed is 150 rpm and the milling time is 10 hours.

[0081] The ball-milled material was placed in a vacuum oven for drying at 88°C for 2 hours to obtain the precursor.

[0082] The obtained precursor was sintered at 410℃ for 1.5 h in air at a heating rate of 10℃ / min, and then sintered at 880℃ for 10 h. The resulting powder was NaNi. 0.5 Fe 0.2 Mn 0.3 O2 materials.

[0083] (2) In a high-speed disperser, a certain amount of polyacrylonitrile is dissolved in an organic solvent, and then a conductive agent is added for the first dispersion to prepare a conductive organic slurry. The first dispersion has a linear velocity of 40 m / min and a dispersion time of 180 min.

[0084] The above describes the relationship between polyacrylonitrile and NaNi. 0.5 Fe 0.2 Mn0.3 The O2 mass ratio is 1.7:100, and the polyacrylonitrile molecular weight is 100,000; the conductive agent and NaNi 0.5 Fe 0.2 Mn 0.3 The O2 mass ratio is 1.6:100; the conductive agent can be a mixture of acetylene black and carbon nanotubes in a ratio of 1:2; the organic solvent and NaNi... 0.5 Fe 0.2 Mn 0.3 The O2 mass ratio is 60:100; the organic solvent is dimethyl sulfoxide.

[0085] (3) NaNi obtained in step (1) 0.5 Fe 0.2 Mn 0.3 O2 material is added to the conductive organic slurry obtained in step (2) for a second dispersion to prepare the positive electrode slurry. The linear velocity of the second dispersion is 35 m / min, and the dispersion time is 120 min.

[0086] (4) The positive electrode slurry obtained in step (3) is subjected to vacuum drying to obtain the sodium ion positive electrode material. The vacuum drying temperature is 75°C and the drying time is 2 hours.

[0087] Example 4

[0088] A method for preparing a sodium-ion cathode material, differing from Example 1 in that polyacrylonitrile and NaNi are used. 1 / 3Fe 1 / 3 Mn 1 / 3 The O2 mass ratio is 3:100, and the conductive agent and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The O2 mass ratio is 2:100; organic solvent and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The O2 mass ratio is 80:100.

[0089] Example 5

[0090] A method for preparing a sodium-ion cathode material, differing from Example 1 in that polyacrylonitrile and NaNi are used. 1 / 3Fe 1 / 3 Mn 1 / 3 The O2 mass ratio is 0.1:100, and the conductive agent and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The O2 mass ratio is 0.1:100; organic solvent and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3The mass ratio of O2 is 20:100.

[0091] Comparative Example 1

[0092] The difference compared to Example 1 lies in steps (2) and (3):

[0093] Step (2): In a high-speed disperser, a certain amount of nano-alumina powder is placed in an organic solvent for the first dispersion to prepare an organic slurry. The linear velocity of the first dispersion is 40 m / min, and the dispersion time is 180 min.

[0094] The above-mentioned nano-alumina powder and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The O2 mass ratio is 1.8:100; organic solvent and NaNi 1 / 3Fe 1 / 3 Mn 1 / 3 The mass ratio of O2 is 65:100; the organic solvent is dimethyl sulfoxide.

[0095] Step (3): The obtained NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 material is added to the organic slurry obtained in step (2) for a second dispersion to prepare the positive electrode slurry. The linear velocity of the second dispersion is 35 m / min, and the dispersion time is 120 min.

[0096] Comparative Example 2

[0097] The difference compared to Example 2 lies in steps (2) and (3):

[0098] Step (2): In a high-speed disperser, a certain amount of nano-alumina powder is placed in an organic solvent for the first dispersion to prepare an organic slurry. The linear velocity of the first dispersion is 40 m / min, and the dispersion time is 180 min.

[0099] The above-mentioned nano-alumina powder and NaNi 0.8 Fe 0.1 Mn 0.1 The O2 mass ratio is 1.8:100;

[0100] The above describes the interaction between organic solvents and NaNi. 0.8 Fe 0.1 Mn 0.1 The O2 mass ratio is 65:100; the organic solvent is sulfolane.

[0101] Step (3): The obtained NaNi 0.8 Fe 0.1 Mn0.1 O2 material is added to the organic slurry obtained in step (2) for a second dispersion to prepare the positive electrode slurry. The linear velocity of the second dispersion is 35 m / min, and the dispersion time is 120 min.

[0102] Comparative Example 3

[0103] The difference compared to Example 3 lies in steps (2) and (3):

[0104] Step (2): A certain amount of nano-alumina powder is placed in an organic solvent in a high-speed disperser for the first dispersion to prepare an organic slurry. The linear velocity of the first dispersion is 40 m / min, and the dispersion time is 180 min.

[0105] The above-mentioned nano-alumina powder and NaNi 0.5 Fe 0.2 Mn 0.3 The O2 mass ratio is 1.8:100;

[0106] The above describes the interaction between organic solvents and NaNi. 0.5 Fe 0.2 Mn 0.3 The O2 mass ratio is 60:100; the organic solvent is dimethyl sulfoxide.

[0107] Step (3): The obtained NaNi 0.5 Fe 0.2 Mn 0.3 O2 material is added to the organic slurry obtained in step (2) for a second dispersion to prepare the positive electrode slurry. The linear velocity of the second dispersion is 35 m / min, and the dispersion time is 120 min.

[0108] Comparative Example 4

[0109] Compared with Comparative Example 1, the difference is that a conductive agent was added in step (2) of this comparative example. The conductive agent is a mixture of acetylene black and carbon nanotubes in a 1:1 ratio. The conductive agent and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The O2 mass ratio is 1.2:100.

[0110] Comparative Example 5

[0111] Compared with Example 1, the difference is that steps (2), (3) and (4) are omitted in this comparative example.

[0112] The cathode materials prepared in Examples 1-3 and Comparative Examples 1-5 were mixed with Super P, PVDF, and NMP to form a slurry, which was then coated onto a 15 μm thick aluminum foil (1060 aluminum foil from Guangzhou Nano New Material Technology Co., Ltd.). The slurry was dried at 95°C, rolled, and then the cathode sheet was obtained. Further slitting and winding yielded a 26650 cylindrical sodium-ion secondary battery. The cathode slurry composition, by mass percentage, was: cathode material 94%, Super P 3%, PVDF 3%, and NMP 60%.

[0113] The method for testing the maximum compaction density of the electrode sheet is as follows: after coating, the electrode sheet is cut into 200*200mm sizes, the pressure of the roller press is set to 30-60 tons, and the electrode sheet is rolled. After rolling, the electrode sheet is folded in half. The electrode sheet with a gap but no breakage after folding is compacted, which is the maximum compaction of the electrode sheet.

[0114] Electrode impedance test method: Cut the rolled electrode into a square size of 4cm*8cm, place the cut electrode between the probes of the BER2200 tester, apply a pressure of 5MPa, and read the value.

[0115] Battery internal resistance test method: The battery internal resistance is tested using an RJ3563 internal resistance meter at 1000Hz.

[0116] The prepared battery was subjected to a cyclic test at 25°C for N cycles. The discharge capacity of the battery in the Nth cycle and the first cycle was recorded, and the discharge retention rate was calculated. Discharge retention rate = (Nth discharge capacity / First discharge capacity) * 100%. The cyclic test was terminated when the cyclic discharge retention rate reached 80%, and the number of cycles was recorded.

[0117] Table 1 Performance Comparison of Examples and Comparative Examples

[0118]

[0119]

[0120] As can be seen from Table 1 above, the sodium-ion cathode material of the present invention, used to prepare the cathode sheet for a sodium-ion secondary battery, exhibits high compaction density, low impedance, large battery capacity, and excellent cycle life. The comparison results between Example 1 and Comparative Example 5 show that, compared to the sodium-ion cathode material without an organic conductive coating, the sodium-ion cathode material of the present invention, with its specific organic conductive coating, significantly improves the compaction density of the sodium-ion cathode sheet, reduces its impedance, and enhances the battery capacity and cycle performance of the sodium-ion battery. Furthermore, the sodium-ion cathode materials of Examples 1-4 are preferred in Examples 1-5. The compaction density of the sodium-ion secondary battery cathode sheet prepared from the sodium-ion cathode material obtained in these examples is 0.1 g / cm³ higher than that of the sodium-ion secondary battery electrode sheet corresponding to the alumina-coated cathode material of Comparative Examples 1-4. 3 -0.2g / cm 3 The resulting sodium-ion batteries have a 14%-25% increase in capacity and a 40%-80% increase in cycle life.

[0121] 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 of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sodium-ion cathode material, characterized in that, It includes a sodium nickel iron manganese oxide substrate and an organic conductive coating, wherein the organic conductive coating coats the sodium nickel iron manganese oxide substrate; the organic conductive coating includes polyacrylonitrile and a conductive agent; The method for preparing the sodium ion cathode material includes the following steps: (1) NaNi was prepared by solid-state synthesis. x Fe y Mn z O2 materials; Where 0 < x ≤ 0.9, 0 < y ≤ 0.5, and 0 < z ≤ 0.3; (2) In a high-speed disperser, the polyacrylonitrile is dissolved in an organic solvent; then the conductive agent is added for the first dispersion to prepare a conductive organic slurry; the conductive agent is a mixture of acetylene black and carbon nanotubes; (3) Take the NaNi obtained in step (1) x Fe y Mn z O2 material is added to the conductive organic slurry obtained in step (2) for a second dispersion to prepare a positive electrode slurry; (4) The positive electrode slurry obtained in step (3) is subjected to a first drying treatment to obtain the sodium ion positive electrode material; The polyacrylonitrile and the NaNi x Fe y Mn z The mass ratio of O2 material is (0.1-3):100; The conductive agent and the NaNi x Fe y Mn z The mass ratio of O2 material is (0.1-2):100; The organic solvent and the NaNi x Fe y Mn z The mass ratio of O2 material is (25-80):

100.

2. The method for preparing the sodium-ion cathode material according to claim 1, characterized in that, Includes the following steps: (1) NaNi was prepared by solid-state synthesis. x Fe y Mn z O2 materials; Where 0 < x ≤ 0.9, 0 < y ≤ 0.5, and 0 < z ≤ 0.3; (2) In a high-speed disperser, the polyacrylonitrile is dissolved in an organic solvent; then the conductive agent is added for the first dispersion to prepare a conductive organic slurry; (3) Take the NaNi obtained in step (1) x Fe y Mn z O2 material is added to the conductive organic slurry obtained in step (2) for a second dispersion to prepare a positive electrode slurry; (4) The positive electrode slurry obtained in step (3) is subjected to a first drying treatment to obtain the sodium ion positive electrode material.

3. The preparation method according to claim 2, characterized in that, The polyacrylonitrile and the NaNi x Fe y Mn z The mass ratio of O2 material is (0.1-3):100; the conductive agent and the NaNi x Fe y Mn z The mass ratio of O2 material is (0.1-2):100; the organic solvent and the NaNi x Fe y Mn z The mass ratio of O2 material is (25-80):

100.

4. The preparation method according to claim 2, characterized in that, The molecular weight of the polyacrylonitrile is 20,000-200,000.

5. The preparation method according to claim 4, characterized in that, The molecular weight of the polyacrylonitrile is 50,000-150,000.

6. The preparation method according to claim 2, characterized in that, In step (2), the dispersion time for the first dispersion is 120 min to 240 min.

7. The preparation method according to claim 2, characterized in that, In step (3), the dispersion time for the second dispersion is 60 min to 180 min.

8. The preparation method according to claim 2, characterized in that, In step (4), the first drying process is vacuum drying; the temperature of the first drying process is 60℃-80℃, and the time is 1h-2h.

9. The preparation method according to claim 2, characterized in that, The organic solvent is one or two of dimethyl sulfoxide, sulfolane, and ethyl nitrate.

10. The preparation method according to claim 2, characterized in that, In step (1), the NaNi x Fe y Mn z The preparation method of O2 materials includes the following steps: NiO, Fe2O3, MnO2, and Na2CO3 are added to a ball mill jar in the required stoichiometric ratio, followed by the addition of ethanol solvent and then ball milling media. The milled material is then subjected to a second drying treatment to obtain a precursor. The obtained precursor is then sintered in an air atmosphere to obtain the NaNi. x Fe y Mn z O2 materials.

11. The preparation method according to claim 10, characterized in that, The total mass of the ethanol solvent is 60%-80% of the total mass of NiO, Fe2O3, MnO2, and Na2CO3; And / or, the mass of the ball milling media is half the total mass of NiO, Fe2O3, MnO2, and Na2CO3; And / or, the ball mill rotates at a speed of 100 rpm to 200 rpm for a time of 8 h to 16 h; And / or, the second drying process is vacuum drying; And / or, the temperature of the second drying treatment is 80℃-120℃, and the time is 1h-2h; And / or, the specific sintering process is as follows: sinter at a heating rate of 5℃ / min-15℃ / min to 350℃-500℃ for 0.5h-1h, and then sinter at 700℃-900℃ for 5h-10h.

12. A sodium ion positive electrode, characterized in that, The sodium-ion cathode material includes the sodium-ion cathode material as described in claim 1 or the sodium-ion cathode material prepared by the preparation method described in any one of claims 2-11; the maximum compaction density of the sodium-ion cathode sheet is 2.7 g / cm³. 3 -2.9g / cm 3 The impedance of the sodium ion positive electrode is 1Ω-2Ω.

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