Carbon aerogel encapsulated composite sodium-ion cathode material, preparation method thereof, cathode sheet and sodium-ion battery

Abstract

The application discloses a carbon aerogel encapsulated composite sodium-ion positive electrode material, which comprises carbon aerogel and a composite sodium-ion positive electrode material encapsulated in the carbon aerogel, and the composite sodium-ion positive electrode material comprises a layered oxide positive electrode material and a sodium vanadium phosphate positive electrode material. x Ni i Fe j Mn k M m O2, wherein M is one or more of Li + , B 3+ , Mg 2+ , Al 3+ , K + , Ca 2+ , Ti 4+ , Co 3+ , V 3+ , V 4+ , Cr 3+ , Cu 2+ , Zn 2+ , Zr 4+ , Nb 5+ and Sn 4+ ; x, i, j, k and m satisfy: 0.8

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to a carbon aerogel-encapsulated composite sodium-ion cathode material and its preparation method, cathode sheet, and sodium-ion battery. Background Technology

[0002] The most representative layered metal oxides are P2-type and O3-type materials, where O and P represent Na. + The coordination environment is in triangular prisms and octahedrons, while 2 and 3 represent the number of transition metal layers in the repeating stacked units. P-type materials tend to have better cycling and rate performance, but their low initial charge capacity due to reduced initial sodium content makes them difficult to industrialize. O3-type materials have high specific capacity, but they are prone to irreversible phase transitions during cycling, leading to structural collapse and significantly affecting their rate performance and cycle stability.

[0003] Currently, there are two main approaches to improving the rate performance and cycle stability of O3-type materials: coating and mixed-phase methods. Chinese patent application CN114744180A (published July 12, 2022) discloses a composite-coated layered oxide material that improves cycle stability and rate performance by suppressing side reactions between the material and the electrolyte and inhibiting manganese dissolution due to phase transitions. However, this method affects the specific capacity and reduces the electronic conductivity of the material. Chinese patent application CN114920306A (published August 19, 2022) discloses a mixed-phase material with a P2-type material as the outer shell and an O3-type material as the core, which improves rate performance and cycle stability through the synergistic effect of the two phases. However, introducing a P2-type material with a low sodium content inevitably affects the reversible specific capacity of the material. Summary of the Invention

[0004] The purpose of this invention is to provide a carbon aerogel-encapsulated composite sodium-ion cathode material. Using carbon aerogel encapsulation can make the material composite more uniform. Introducing sodium vanadium phosphate composite layered oxide, which is a fast ion conductor, can improve the ionic conductivity of the layered oxide, thereby improving the overall working voltage, rate performance and cycle stability of the material.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] The first aspect of the present invention provides a carbon aerogel-encapsulated composite sodium ion cathode material, comprising carbon aerogel and a composite sodium ion cathode material encapsulated in carbon aerogel, wherein the composite sodium ion cathode material comprises a layered oxide cathode material and a sodium vanadium phosphate cathode material.

[0007] The chemical formula of the layered oxide cathode material is Na.x Ni i Fe j Mn k M m O₂, where M is Li + 、B 3+ 、Mg 2+ 、Al 3 + 、K + 、Ca 2+ 、Ti 4+ 、Co 3+ 、V 3+ 、V 4+ 、Cr 3+ 、Cu 2+ 、Zn 2+ 、Zr 4+ 、Nb 5+ and Sn 4+ One or more of; x, i, j, k, m satisfy: 0.8 < x ≤ 1, 0 < i ≤ 0.4, 0 < j ≤ 0.5, 0 < k ≤ 0.6, 0 < m ≤ 0.2, and i + j + k + m = 1.

[0008] Furthermore, in the carbon aerogel encapsulated composite sodium ion cathode material, taking X, Y, and Z to represent the mass percentages of the layered oxide cathode material, sodium vanadium phosphate cathode material, and carbon aerogel respectively, then X, Y, Z satisfy: 70% ≤ X ≤ 80%, 10% ≤ Y ≤ 20%, 5% ≤ Z ≤ 10%, X + Y + Z = 100%.

[0009] Furthermore, both the layered oxide and sodium vanadium phosphate are secondary particles, and the D50 particle sizes of the layered oxide and sodium vanadium phosphate satisfy: 7.5 μm ≤ D50 ≤ 9 μm.

[0010] The second aspect of the present invention provides a preparation method of a carbon aerogel encapsulated composite sodium ion cathode material, including the following steps:

[0011] Mix the layered oxide cathode material, sodium vanadium phosphate cathode material, and carbon aerogel evenly in an organic solvent, and obtain the carbon aerogel encapsulated composite sodium ion cathode material through filtration and freeze-drying;

[0012] Among them, the chemical formula of the layered oxide cathode material is Na x Ni i Fe j Mn k M m O₂, M is Li + 、B 3+ 、Mg 2+ 、Al 3+ 、K + 、Ca2+ , Ti 4+ , Co 3+ , V 3+ , V 4+ , Cr 3+ , Cu 2+ , Zn 2+ , Zr 4+ , Nb 5+ and Sn 4+ One or more of; x, i, j, k, m satisfy: 0.8 < x ≤ 1, 0 < i ≤ 0.4, 0 < j ≤ 0.5, 0 < k ≤ 0.6, 0 < m ≤ 0.2, and i + j + k + m = 1.

[0013] Further, expressing the mass percentages of the layered oxide cathode material, sodium vanadium phosphate cathode material, and carbon aerogel in the carbon aerogel encapsulated composite sodium ion cathode material as X, Y, and Z respectively, then X, Y, Z satisfy: 70% ≤ X ≤ 80%, 10% ≤ Y ≤ 20%, 5% ≤ Z ≤ 10%, X + Y + Z = 100%.

[0014] Further, the organic solvent includes one or more of acetone, absolute ethanol, ethyl acetate, and dimethyl sulfoxide.

[0015] Further, for the preparation method of the layered oxide cathode material Na x Ni i Fe j Mn k M m O2: Mix the Ni i Fe j Mn k M m (OH)2 precursor with a sodium source by ball milling, then place it in a sintering furnace, pre-sinter for 1 - 8 h first, and then raise the temperature for high-temperature solid-state sintering for 4 - 20 h; after cooling and grinding, obtain the layered oxide cathode material Na x Ni i Fe j Mn k M m O2;

[0016] The preparation method of the sodium vanadium phosphate cathode material is: ball mill and mix a sodium source, a vanadium source, and a phosphorus source to obtain a sodium vanadium phosphate precursor powder; sinter the obtained sodium vanadium phosphate precursor powder in a non-oxidizing atmosphere to obtain the sodium vanadium phosphate cathode material.

[0017] Further, in the preparation method of the layered oxide cathode material Na x Ni i Fe j Mn k M m O2:

[0018] The sodium source is one or more of sodium carbonate, sodium hydroxide, sodium acetate, sodium oxalate, and sodium nitrate;

[0019] And / or, the ball milling speed is 250-750 r / min, and the ball milling time is 1-6 h;

[0020] And / or, the pre-sintering temperature is 200–550°C;

[0021] And / or, the high-temperature solid-state sintering temperature is 750–1100°C, and the heating rate is 1–10°C / min;

[0022] In the preparation method of sodium vanadium phosphate cathode material:

[0023] The sodium source is one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, sodium nitrate, and sodium hydroxide.

[0024] And / or, the vanadium source is one or more of vanadium powder, vanadium pentoxide, vanadium trioxide, and ammonium metavanadate;

[0025] And / or, the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, phosphoric acid, and ammonium hypophosphite;

[0026] And / or, the non-oxidizing atmosphere is one or more of nitrogen, hydrogen and argon;

[0027] And / or, the sintering step is as follows: first, pre-sintering at 350-550℃ for 2-10h, then heating to 600-1000℃ at a rate of 1-10℃ / min, and sintering at high temperature for 4-20h.

[0028] Furthermore, the preparation method of the carbon aerogel is as follows: a conductive carbon aqueous solution is mixed with an accelerator and subjected to a hydrothermal reaction to obtain a conductive carbon hydrogel; the conductive carbon hydrogel is freeze-dried and then carbonized to obtain the conductive carbon aerogel.

[0029] The accelerator is one or more of phenylphosphonic acid, 3-thiopheneacetic acid, 1,4-diaminobenzene, and benzenesulfonic acid.

[0030] Furthermore, the conductive carbon is one or more of carbon nanotubes, graphene, hard carbon, and carbon nanofibers;

[0031] And / or, the concentration of the conductive carbon aqueous solution is 1–15 mg / ml;

[0032] And / or, the ratio of the accelerator to water in the conductive carbon aqueous solution is 20-80 mg: 1 ml;

[0033] And / or, the hydrothermal reaction is carried out at a temperature of 130–200°C for a time of 1–40 h;

[0034] And / or, the freeze-drying time is 5 to 15 hours;

[0035] And / or, the carbonization is carried out in an inert atmosphere, which is one or more of nitrogen, hydrogen or argon;

[0036] And / or, the carbonization temperature is 300–500°C, and the time is 0.5–3.5 h.

[0037] A third aspect of the present invention provides a positive electrode sheet, comprising the aforementioned carbon aerogel-encapsulated composite sodium ion positive electrode material or the carbon aerogel-encapsulated composite sodium ion positive electrode material prepared by the aforementioned method.

[0038] A fourth aspect of the present invention provides a sodium-ion battery, including the aforementioned positive electrode.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] 1. This invention encapsulates layered oxides and sodium vanadium phosphate with carbon aerogel, which not only makes the material composite more uniform, but also buffers the volume changes that occur during sodium ion insertion / extraction, thereby increasing the stability of the material.

[0041] 2. This invention, by using sodium vanadium phosphate, a fast ion conductor, to composite with layered oxides, not only improves the ionic conductivity of the layered oxides, but also enhances the overall operating voltage, rate performance, and cycle stability of the material.

[0042] 3. Due to the extremely high conductivity of carbon aerogel, the carbon aerogel-encapsulated composite sodium ion cathode material provided by this invention can avoid the addition of conductive carbon in the subsequent slurry preparation process, which not only simplifies the slurry preparation process, but also helps to improve the overall energy density of the battery. Attached Figure Description

[0043] Figure 1 The image shows a scanning electron microscope (SEM) image of the carbon aerogel prepared in Example 1.

[0044] Figure 2 SEM image of the carbon aerogel-encapsulated composite sodium ion cathode material prepared in Example 1;

[0045] Figure 3 The XRD diffraction pattern of the carbon aerogel-encapsulated composite sodium ion cathode material prepared in Example 1 is shown below.

[0046] Figure 4 Charge-discharge curves (0.1C) of the coin cells prepared in Example 3 and Comparative Example 3. Detailed Implementation

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0048] As described in the background section, O3-type layered oxide materials have high specific capacity, but they are prone to irreversible phase transitions during cycling, leading to structural collapse and greatly affecting their rate performance and cycling stability.

[0049] To address the aforementioned technical problems, this invention provides a carbon aerogel-encapsulated composite sodium-ion cathode material. By introducing fast-ion conductor sodium vanadium phosphate into the composite with layered oxides, the ionic conductivity of the layered oxides is improved. By using porous carbon aerogel to encapsulate the composite material, not only can the material composite be made more uniform, but the volume changes generated during sodium ion insertion / extraction can also be buffered. Ultimately, this improves the overall operating voltage, rate performance, and cycle stability of the material.

[0050] Specifically, the carbon aerogel-encapsulated composite sodium ion cathode material provided by the present invention is prepared by mixing layered oxide cathode material, sodium vanadium phosphate cathode material and carbon aerogel in an organic solvent, filtering and freeze-drying to obtain the carbon aerogel-encapsulated composite sodium ion cathode material.

[0051] In this invention, the chemical formula of the layered oxide cathode material is Na. x Ni i Fe j Mn k M m O2, M is Li + B 3+ Mg 2+ Al 3 + K + Ca 2+ Ti 4+ Co 3+ V 3+ V 4+ Cr 3+ Cu 2+ Zn 2+ Zr 4+ 、Nb 5+ and Sn 4+One or more of; x, i, j, k, m are the molar ratios of the corresponding elements, which satisfy: 0.8 < x ≤ 1, 0 < i ≤ 0.4, 0 < j ≤ 0.5, 0 < k ≤ 0.6, 0 < m ≤ 0.2, and i + j + k + m = 1.

[0052] In some embodiments, the chemical formula of the above-mentioned layered oxide cathode material may be NaNi 0.15 Fe 0.15 Mn 0.65 Mg 0.05 O2, NaNi 0.2 Fe 0.1 Mn 0.6 Ti 0.1 O2, NaNi 0.3 Fe 0.3 Mn 0.35 Cu 0.05 O2, NaNi 0.25 Fe 0.25 Mn 0.4 Al 0.1 O2, etc.

[0053] Preferably, the layered oxide cathode material is an O3-type layered oxide.

[0054] In the present invention, the preparation method of the layered oxide cathode material Na x Ni i Fe j Mn k M m O2 is as follows: After mixing the Ni i Fe j Mn k M m (OH)2 precursor with a sodium source by ball milling and then placing it in a sintering furnace, pre-sintering for 1 - 8 h first, and then heating up for high-temperature solid-phase sintering for 4 - 20 h; after cooling and grinding, a black powder-like layered oxide cathode material Na x Ni i Fe j Mn k M m O2 is obtained.

[0055] In the above preparation method, Ni i Fe j Mn k M mThe (OH)₂ precursor and the sodium source can be ground in a ball mill jar to ensure thorough mixing. The sodium source can be a common sodium salt or other sodium-containing compound, including but not limited to one or more of sodium carbonate, sodium hydroxide, sodium acetate, sodium oxalate, and sodium nitrate. During ball milling, the milling speed is 250–750 r / min, for example, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min, 500 r / min, 550 r / min, 600 r / min, 650 r / min, 700 r / min, or 750 r / min, or any range thereof; the milling time is 1–6 h, for example, 1 h, 2 h, 3 h, 4 h, 5 h, or 6 h, or any range thereof.

[0056] In the above preparation method, the ball-milled mixture can be placed in a sintering furnace, such as a muffle furnace, for sintering. During sintering, pre-sintering is preferably performed first, followed by high-temperature sintering. The pre-sintering temperature is 200–550°C, for example, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, or 550°C, or any value range between them. The pre-sintering time is 1–8 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours, or any value range between them. After pre-sintering, the muffle furnace is heated at a rate of 1–10°C / min, for example, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, or 10°C / min, or any value range between them. Next, high-temperature solid-state sintering is performed at a temperature of 750–1100℃, for example, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, or 1100℃, or any range between them. The high-temperature solid-state sintering time is 4–20 hours, for example, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, or 20 hours, or any range between them.

[0057] In this invention, the preparation method of sodium vanadium phosphate Na3V2(PO)4 cathode material is as follows: sodium source, vanadium source and phosphorus source are ball-milled and mixed to obtain sodium vanadium phosphate precursor powder; the obtained sodium vanadium phosphate precursor powder is sintered in a non-oxidizing atmosphere to obtain sodium vanadium phosphate cathode material.

[0058] In the above preparation method, the sodium source, vanadium source, and phosphorus source can be ground in a ball mill jar to ensure thorough mixing and obtain sodium vanadium phosphate precursor powder. The sodium source can be selected from common sodium salts or other sodium-containing compounds, including but not limited to one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, sodium nitrate, and sodium hydroxide; the vanadium source can be selected from elemental vanadium, common vanadium salts, or other vanadium compounds, including but not limited to one or more of vanadium powder, vanadium pentoxide, vanadium trioxide, and ammonium metavanadate; the phosphorus source can be selected from phosphoric acid, phosphates, or other phosphorus-containing compounds, including but not limited to one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, and ammonium hypophosphite. During ball milling, the ball milling speed is 550 to 950 r / min, for example, it can be 550 r / min, 600 r / min, 650 r / min, 700 r / min, 750 r / min, 800 r / min, 850 r / min, 900 r / min or 950 r / min, or any value range between them; the ball milling time is 2 to 10 h, for example, it can be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, or any value range between them.

[0059] In the above preparation method, after obtaining the sodium vanadium phosphate precursor powder, it can be placed in a tube furnace for sintering. Sintering must be carried out in a non-oxidizing atmosphere, that is, a non-oxidizing gas is continuously introduced into the tube furnace during the sintering process. The aforementioned non-oxidizing gas includes, but is not limited to, one or more of nitrogen, hydrogen, and inert atmospheres (such as argon). During sintering, pre-sintering is preferably performed first, followed by high-temperature sintering. The pre-sintering temperature is 350–550°C, for example, 350°C, 400°C, 450°C, 500°C, or 550°C, or any value range between them; the pre-sintering time is 2–10 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours, or any value range between them. After pre-sintering, the tubular furnace is heated at a rate of 1–10 °C / min, for example, 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, or 10 °C / min, or any value between them. Next, high-temperature sintering is performed at a temperature of 600–1000 °C, for example, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, 1050 °C, or 1100 °C, or any value between them. The high-temperature sintering time is 4–20 h, for example, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, or 20 h, or any value between them.

[0060] In this invention, the carbon aerogel is prepared by mixing an aqueous solution of conductive carbon with an accelerator and carrying out a hydrothermal reaction to obtain a conductive carbon hydrogel; the conductive carbon hydrogel is then freeze-dried and carbonized to obtain the conductive carbon aerogel.

[0061] In the above preparation method, the conductive carbon includes one or more of carbon nanotubes, graphene, hard carbon, and carbon nanofibers. The conductive carbon aqueous solution can be obtained by adding conductive carbon to water and then ultrasonically dispersing it. Its concentration is preferably 1–15 mg / ml, for example, it can be 1 mg / ml, 2 mg / ml, 3 mg / ml, 4 mg / ml, 5 mg / ml, 6 mg / ml, 7 mg / ml, 8 mg / ml, 9 mg / ml, 10 mg / ml, 11 mg / ml, 12 mg / ml, 13 mg / ml, 14 mg / ml, or 15 mg / ml, or any value range between them.

[0062] In the above preparation method, after the conductive carbon aqueous solution is mixed with the accelerator, a hydrothermal reaction can occur under heating conditions to generate a conductive carbon hydrogel. The accelerator is a small organic molecule with a low molecular weight, and its function is to promote and induce the formation of the conductive carbon hydrogel. The principle is that during the hydrothermal process, the accelerator, as a small molecule organic monomer, can form a hydrogel through sol-gel condensation reaction and weak interactions of small molecule non-covalent bonds. In this invention, the accelerator can be one or more of phenylphosphonic acid, 3-thiopheneacetic acid, 1,4-diaminobenzene, and benzenesulfonic acid. The preferred ratio of the accelerator to water in the conductive carbon aqueous solution is 20–80 mg:1 ml, for example, 20 mg:1 ml, 30 mg:1 ml, 40 mg:1 ml, 50 mg:1 ml, 60 mg:1 ml, 70 mg:1 ml, or 80 mg:1 ml, or any value range between them. The preferred temperature for the hydrothermal reaction is 130–200°C, for example, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, or 200°C, or any value range therebetween; the preferred time for the hydrothermal reaction is 1–40 h, for example, 1 h, 2 h, 4 h, 5 h, 8 h, 10 h, 12 h, 15 h, 20 h, 25 h, 30 h, 35 h, or 40 h, or any value range therebetween.

[0063] In the above preparation method, the conductive carbon hydrogel is freeze-dried to obtain a conductive carbon aerogel. The freeze-drying time is preferably 5–15 h, for example, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, or 15 h, or any range thereof. Next, the conductive carbon aerogel is carbonized under an inert atmosphere, which can be one or more of nitrogen, hydrogen, or an inert gas (such as argon). The carbonization temperature is preferably 300–500 °C, for example, 300 °C, 350 °C, 400 °C, 450 °C, or 500 °C, or any range thereof; the carbonization time is preferably 0.5–3.5 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, or 3.5 h, or any range thereof.

[0064] In this invention, the organic solvent is a volatile organic solvent, including but not limited to one or more of acetone, anhydrous ethanol, ethyl acetate, and dimethyl sulfoxide. The layered oxide cathode material, sodium vanadium phosphate cathode material, and carbon aerogel can be mixed uniformly by magnetic stirring for a time ranging from 3 to 24 hours, for example, 3 hours, 4 hours, 5 hours, 6 hours, 8 hours, 10 hours, 12 hours, 15 hours, 16 hours, 18 hours, 20 hours, or any range thereof. Let X, Y, and Z represent the mass percentages of the layered oxide cathode material, sodium vanadium phosphate cathode material, and carbon aerogel in the carbon aerogel-encapsulated composite sodium-ion cathode material, respectively. Then X, Y, and Z satisfy: 70% ≤ X ≤ 80%, 10% ≤ Y ≤ 20%, 5% ≤ Z ≤ 10%, and X + Y + Z = 100%. After being mixed evenly, the mixture is filtered and freeze-dried to obtain carbon aerogel-encapsulated composite sodium ion cathode material. The freeze-drying time is preferably 10 to 15 hours, for example, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours or 15 hours, or any value range between them.

[0065] In this invention, the particle size of the layered oxide and sodium vanadium phosphate should not be too small, as this will cause particle agglomeration, leading to a decrease in the solid-phase diffusion coefficient and electronic conductivity, and an increase in the battery's internal resistance. The particle size of the layered oxide and sodium vanadium phosphate should also not be too large, as the pore size of carbon aerogel is limited, and excessively large particles will affect the encapsulation effect. Preferably, both the layered oxide and sodium vanadium phosphate are secondary particles, and the D50 particle size satisfies the following condition: 7.5 μm ≤ D50 ≤ 9 μm. When the layered oxide and sodium vanadium phosphate are within the above-mentioned particle size range, particle agglomeration can be prevented, and a better encapsulation effect can be achieved.

[0066] The carbon aerogel-encapsulated composite sodium-ion cathode material prepared in this invention comprises layered oxide cathode material and sodium vanadium phosphate cathode material encapsulated within a conductive carbon aerogel. It has the following advantages:

[0067] (1) Conductive carbon aerogel has a large specific surface area and abundant mesopores and micropores, which can uniformly encapsulate the composite positive electrode material, thereby enabling full contact between the electrode material and the electrolyte.

[0068] (2) Conductive carbon aerogel has a three-dimensional interconnected spatial framework structure that encapsulates layered oxides, which can effectively buffer the volume changes generated during sodium ion insertion / extraction, thereby improving the cycling stability of the material.

[0069] (3) Sodium vanadium phosphate has excellent structural stability and high voltage plateau. By introducing sodium vanadium phosphate into the composite with layered oxides, the excellent structural stability and high voltage plateau of sodium vanadium phosphate can be used to improve the structural stability and voltage plateau of the composite material, thereby improving the cycle stability and energy density of the material.

[0070] (4) Carbon aerogel itself has extremely strong electronic conductivity, while sodium vanadium phosphate has a fast ion conductor structure and excellent ion conductivity. Therefore, through the synergistic effect of carbon aerogel and sodium vanadium phosphate, the polarization behavior of the material during long-term cycling can be greatly suppressed, and the overall electrochemical performance of the material can be improved.

[0071] (5) By taking advantage of the strong conductivity of carbon aerogel, it is possible to avoid adding conductive carbon in the subsequent preparation of slurry, thereby improving the overall energy density of the battery.

[0072] Based on the above-mentioned carbon aerogel encapsulated composite sodium-ion positive electrode material, the present invention also provides a sodium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the separator is configured to isolate the positive electrode and the negative electrode.

[0073] In the aforementioned sodium-ion battery, the positive electrode sheet can be prepared using electrode preparation processes commonly used in the art. In particular, because carbon aerogel has strong conductivity, no conductive agent needs to be added when preparing the positive electrode slurry. An illustrative preparation method is as follows: A carbon aerogel-encapsulated composite sodium-ion positive electrode material is mixed with a binder to prepare a slurry, which is then coated onto at least one side of the positive electrode current collector. After drying and pressing, the positive electrode sheet is obtained.

[0074] The type and content of the above-mentioned adhesives are not specifically limited and can be selected according to actual needs. In some embodiments, the above-mentioned adhesives include at least one of polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethyl cellulose, polymethacrylamide, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyamide, polyimide, polyacrylate, styrene-butadiene rubber, sodium alginate, chitosan, polyethylene glycol, guar gum, etc.

[0075] The type of positive electrode current collector is not specifically limited and can be selected according to actual needs. For example, the positive electrode current collector can be aluminum foil, nickel foil or polymer conductive film. Preferably, the positive electrode current collector is aluminum foil.

[0076] In the aforementioned sodium-ion batteries, the type of separator is not specifically limited and can be any separator material used in existing batteries, such as polyethylene, polypropylene, polyvinylidene fluoride, non-woven fabric, their multilayer composite membranes, and modified separators such as ceramic modification and PVDF modification, but not limited to these.

[0077] In the aforementioned sodium-ion battery, the electrolyte can be one or more of the following: organic liquid electrolyte, organic solid electrolyte, solid ceramic electrolyte, and gel electrolyte. Preferably, the electrolyte is an organic liquid electrolyte, which is obtained by dissolving a sodium salt in a non-aqueous organic solvent; wherein the sodium salt may include one or more of sodium difluorophosphate (NaPO2F2), sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSi), and sodium difluorooxalate borate (NaDFOB). The aforementioned non-aqueous organic solvent may include one or more of cyclic carbonates, chain carbonates, and carboxylic acid esters. Cyclic carbonates may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate, and γ-butyrolactone; chain carbonates may be selected from one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), methyl acetate (MA), ethyl acetate (EA), and ethyl propionate (EP).

[0078] In some embodiments, a certain amount of additives may be added to the organic liquid electrolyte. The additives may include one or more of the following: vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), vinyl sulfite (ES), methylene disulfonate (MMDS), 1,3-propanesulfonate lactone (PS), propylene sulfonate lactone (PES), propylene sulfate (TMS), trimethylsilane phosphate (TMSP), trimethylsilane borate (TMSB), and fluoroethylene carbonate (FEC).

[0079] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0080] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0081] Example 1

[0082] 1. Ni 0.15 Fe 0.15 Mn 0.65 Mg 0.05 The (OH)₂ precursor and sodium acetate were ball-milled at a molar ratio of 1:1.05 in a ball mill jar at 300 r / min for 3 h to ensure thorough mixing. The mixed powder was then placed in a muffle furnace and pre-sintered at 200 °C for 3 h at a heating rate of 5 °C / min, followed by high-temperature solid-state sintering at 800 °C for 10 h. After natural cooling and grinding, the layered oxide material NaNi was obtained. 0.15 Fe 0.15 Mn 0.65 Mg 0.05 Black powder of O2.

[0083] 2. Sodium carbonate (5% excess), vanadium pentoxide and ammonium dihydrogen phosphate were placed in a ball mill jar and ball milled at 700 r / min for 3 h to fully mix them and obtain sodium vanadium phosphate precursor powder. The precursor powder was placed in a tube furnace with a heating rate of 3 °C / min and pre-sintered at 350 °C for 5 h in a hydrogen-argon mixed atmosphere, and then sintered at 800 °C for 15 h to obtain Na3V2(PO)4 material.

[0084] 3. Add 50 wt% carbon nanotubes and 50 wt% graphene to deionized water and mix them uniformly by ultrasonic dispersion to obtain a 10 mg / ml conductive carbon aqueous solution. Mix the conductive carbon aqueous solution with 40 mg / ml phenylphosphonic acid and perform a hydrothermal reaction at 150℃ for 20 h to obtain a conductive carbon hydrogel. Freeze-dry the obtained conductive carbon hydrogel for 15 h, and then carbonize it at 300℃ for 2 h under an argon atmosphere to obtain a conductive carbon aerogel.

[0085] 4. The NaNi prepared above 0.15 Fe 0.15 Mn 0.65 Mg 0.05 O2 material, Na3V2(PO)4, and carbon aerogel were added to anhydrous ethanol at a mass ratio of 7.5:2:0.5, and stirred on a magnetic stirrer for 18 hours to ensure thorough mixing. The mixture was then filtered and freeze-dried for 10 hours to obtain carbon aerogel-encapsulated NaNi. 0.15 Fe 0.15 Mn 0.65 Mg 0.05 O2 / Na3V2(PO)4 composite material.

[0086] 5. Encapsulating NaNi with carbon aerogel 0.15 Fe 0.15 Mn 0.65 Mg 0.05The O2 / Na3V2(PO)4 composite material and PVDF binder were ground uniformly at a mass ratio of 9.5:0.5. An appropriate amount of NMP was then added to form a slurry, which was uniformly coated onto pretreated aluminum foil. The slurry was dried at 80℃ for 1 hour in a forced-air drying oven, followed by drying at 120℃ for 12 hours in a vacuum drying oven. The resulting material was then cut into 14mm circular positive electrode sheets using a cutting machine. A CR2032 coin cell was assembled in a high-purity argon-filled glove box using a 14mm diameter, 0.2mm thick sodium metal sheet as the negative electrode, a 0.1mol / L sodium perchlorate / ethylene carbonate / dimethyl carbonate solution as the electrolyte, and a 16mm diameter Whatman GF / F glass fiber as the separator.

[0087] Figure 1 This is a scanning electron microscope (SEM) image of the carbon aerogel in Example 1. The image shows that the carbon aerogel possesses abundant micro / nanopore structures.

[0088] Figure 2 NaNi encapsulated in carbon aerogel in Example 1 0.15 Fe 0.15 Mn 0.65 Mg 0.05 Scanning electron microscope (SEM) image of the O2 / Na3V2(PO)4 composite material. The sheet-like structures in the image are layered oxides, NaNi. 0.15 Fe 0.15 Mn 0.65 Mg 0.05 O2, the spherical form is Na3V2(PO)4, and NaNi 0.15 Fe 0.15 Mn 0.65 Mg 0.05 O2 and Na3V2(PO)4 are encapsulated relatively uniformly in the carbon aerogel.

[0089] Figure 3 Encapsulation of NaNi with carbon aerogel 0.15 Fe 0.15 Mn 0.65 Mg 0.05 The XRD diffraction pattern of the O2 / Na3V2(PO)4 composite material. As can be seen from the figure, the characteristic peaks of Na3V2(PO)4 and C appear in the XRD pattern, indicating that the material contains Na3V2(PO)4 and carbon aerogel.

[0090] Example 2

[0091] 1. Ni 0.2 Fe 0.1 Mn 0.6 Ti 0.1The (OH)₂ precursor and sodium acetate were ball-milled in a ball mill at a molar ratio of 1:1.05 for 1 hour at a speed of 750 r / min to ensure thorough mixing. The mixed powder was then placed in a muffle furnace and pre-sintered at 550°C for 2 hours at a heating rate of 7°C / min, followed by high-temperature solid-state sintering at 700°C for 15 hours. After natural cooling and grinding, the layered oxide material NaNi was obtained. 0.2 Fe 0.1 Mn 0.6 Ti 0.1 Black powder of O2.

[0092] 2. Sodium carbonate (5% excess), vanadium pentoxide and ammonium dihydrogen phosphate were placed in a ball mill jar and ball milled at 500 r / min for 10 h to fully mix them and obtain sodium vanadium phosphate precursor powder. The precursor powder was placed in a tube furnace with a heating rate of 5 °C / min and pre-sintered at 550 °C for 2 h in a hydrogen-argon mixed atmosphere, and then sintered at 1000 °C for 10 h to obtain Na3V2(PO)4 material.

[0093] 3. 35 wt% carbon nanotubes, 15 wt% hard carbon, and 50% carbon nanofibers were added to deionized water and mixed uniformly by ultrasonic dispersion to obtain a 10 mg / ml conductive carbon aqueous solution. The conductive carbon aqueous solution was mixed with 40 mg / ml phenylphosphonic acid and subjected to hydrothermal reaction at 150 °C for 20 h to obtain a conductive carbon hydrogel. The obtained conductive carbon hydrogel was freeze-dried for 15 h and then carbonized at 300 °C for 2 h under an argon atmosphere to obtain a conductive carbon aerogel.

[0094] 4. The NaNi prepared above 0.2 Fe 0.1 Mn 0.6 Ti 0.1 O2 material, Na3V2(PO)4, and carbon aerogel were added to anhydrous ethanol at a mass ratio of 7.5:2:0.5, and stirred on a magnetic stirrer for 18 hours to ensure thorough mixing. The mixture was then filtered and freeze-dried for 10 hours to obtain carbon aerogel-encapsulated NaNi. 0.2 Fe 0.1 Mn 0.6 Ti 0.1 O2 / Na3V2(PO)4 composite material.

[0095] 5. CR2032 coin cells were prepared using the same method as in Example 1.

[0096] Example 3

[0097] 1. Ni 0.3 Fe 0.3 Mn 0.35 Cu 0.05The (OH)₂ precursor and sodium acetate were ball-milled at a molar ratio of 1:1.05 in a ball mill jar at a speed of 400 r / min for 4.5 h to ensure thorough mixing. The mixed powder was then placed in a muffle furnace and pre-sintered at 200 °C for 3 h at a heating rate of 5 °C / min, followed by high-temperature solid-state sintering at 600 °C for 18 h. After natural cooling and grinding, the layered oxide material NaNi was obtained. 0.3 Fe 0.3 Mn 0.35 Cu 0.05 Black powder of O2.

[0098] 2. Sodium hydroxide (5% excess), vanadium pentoxide and ammonium dihydrogen phosphate were placed in a ball mill jar and ball milled at 500 r / min for 10 h to fully mix them and obtain sodium vanadium phosphate precursor powder. The precursor powder was placed in a tube furnace with a heating rate of 3 °C / min and pre-sintered at 350 °C for 5 h in a hydrogen-argon mixed atmosphere, and then sintered at 800 °C for 15 h to obtain Na3V2(PO)4 material.

[0099] 3. Add 40 wt% carbon nanotubes and 60 wt% carbon nanofibers to deionized water and mix them uniformly by ultrasonic dispersion to obtain a 10 mg / ml conductive carbon aqueous solution. Mix the conductive carbon aqueous solution with 40 mg / ml phenylphosphonic acid and perform a hydrothermal reaction at 150℃ for 20 h to obtain a conductive carbon hydrogel. Freeze-dry the obtained conductive carbon hydrogel for 15 h, and then carbonize it at 300℃ for 2 h under an argon atmosphere to obtain a conductive carbon aerogel.

[0100] 4. The NaNi prepared above 0.3 Fe 0.3 Mn 0.35 Cu 0.05 O2 material, Na3V2(PO)4, and carbon aerogel were added to anhydrous ethanol at a mass ratio of 7.5:2:0.5, and stirred on a magnetic stirrer for 18 hours to ensure thorough mixing. The mixture was then filtered and freeze-dried for 10 hours to obtain carbon aerogel-encapsulated NaNi. 0.3 Fe 0.3 Mn 0.35 Cu 0.05 O2 / Na3V2(PO)4 composite material.

[0101] 5. CR2032 coin cells were prepared using the same method as in Example 1.

[0102] Example 4

[0103] 1. Ni 0.25 Fe 0.25 Mn 0.4 Al 0.1The (OH)₂ precursor and sodium acetate were ball-milled in a ball mill at a molar ratio of 1:1.05 for 1 hour at a speed of 750 r / min to ensure thorough mixing. The mixed powder was then placed in a muffle furnace and pre-sintered at 550°C for 2 hours at a heating rate of 7°C / min, followed by high-temperature solid-state sintering at 700°C for 15 hours. After natural cooling and grinding, the layered oxide material NaNi was obtained. 0.25 Fe 0.25 Mn 0.4 Al 0.1 Black powder of O2.

[0104] 2. Sodium carbonate (5% excess), vanadium pentoxide and ammonium dihydrogen phosphate were placed in a ball mill jar and ball milled at 500 r / min for 10 h to fully mix them and obtain sodium vanadium phosphate precursor powder. The precursor powder was placed in a tube furnace with a heating rate of 5 °C / min and pre-sintered at 550 °C for 2 h in a hydrogen-argon mixed atmosphere, and then sintered at 1000 °C for 10 h to obtain Na3V2(PO)4 material.

[0105] 3. 35 wt% carbon nanotubes, 15 wt% hard carbon, and 50% carbon nanofibers were added to deionized water and mixed uniformly by ultrasonic dispersion to obtain a 10 mg / ml conductive carbon aqueous solution. The conductive carbon aqueous solution was mixed with 40 mg / ml phenylphosphonic acid and subjected to hydrothermal reaction at 150 °C for 20 h to obtain a conductive carbon hydrogel. The obtained conductive carbon hydrogel was freeze-dried for 15 h and then carbonized at 300 °C for 2 h under an argon atmosphere to obtain a conductive carbon aerogel.

[0106] 4. The NaNi prepared above 0.25 Fe 0.25 Mn 0.4 Al 0.1 O2 material, Na3V2(PO)4, and carbon aerogel were added to anhydrous ethanol at a mass ratio of 7.5:2:0.5, and stirred on a magnetic stirrer for 18 hours to ensure thorough mixing. The mixture was then filtered and freeze-dried for 10 hours to obtain carbon aerogel-encapsulated NaNi. 0.25 Fe 0.25 Mn 0.4 Al 0.1 O2 / Na3V2(PO)4 composite material.

[0107] 5. CR2032 coin cells were prepared using the same method as in Example 1.

[0108] Comparative Example 1

[0109] 1. Ni 0.15 Fe 0.15 Mn 0.65 Mg 0.05The (OH)₂ precursor and sodium acetate were ball-milled at a molar ratio of 1:1.05 in a ball mill jar at 300 r / min for 3 h to ensure thorough mixing. The mixed powder was then placed in a muffle furnace and pre-sintered at 200 °C for 3 h at a heating rate of 5 °C / min, followed by high-temperature solid-state sintering at 800 °C for 10 h. After natural cooling and grinding, the layered oxide material NaNi was obtained. 0.15 Fe 0.15 Mn 0.65 Mg 0.05 Black powder of O2.

[0110] 2. NaNi 0.15 Fe 0.15 Mn 0.65 Mg 0.05 Materials, Super P, and PVDF binder were ground uniformly at a mass ratio of 7:2:1. An appropriate amount of NMP was added to form a slurry, which was then evenly coated onto pretreated aluminum foil. The slurry was dried in a forced-air drying oven at 80℃ for 1 hour, followed by drying in a vacuum drying oven at 120℃ for 12 hours. Afterward, it was cut into 14mm circular positive electrode sheets using a cutting machine. A CR2032 coin cell was assembled in a high-purity argon-filled glove box using a 14mm diameter, 0.2mm thick sodium metal sheet as the negative electrode, a 0.1mol / L sodium perchlorate / ethylene carbonate / dimethyl carbonate solution as the electrolyte, and a 16mm diameter Whatman GF / F glass fiber as the separator.

[0111] Comparative Example 2

[0112] 1. Ni 0.20 Fe 0.10 Mn 0.60 Ti 0.1 The (OH)₂ precursor and sodium acetate were ball-milled at a molar ratio of 1:1.05 in a ball mill jar at 300 r / min for 3 h to ensure thorough mixing. The mixed powder was then placed in a muffle furnace and pre-sintered at 200 °C for 3 h at a heating rate of 5 °C / min, followed by high-temperature solid-state sintering at 800 °C for 10 h. After natural cooling and grinding, the layered oxide material NaNi was obtained. 0.20 Fe 0.10 Mn 0.60 Ti 0.1 Black powder of O2.

[0113] 2. Prepare CR2032 coin cells using the same method as Comparative Example 1.

[0114] Comparative Example 3

[0115] 1. Ni 0.3 Fe 0.3 Mn 0.35 Cu 0.05The (OH)₂ precursor and sodium acetate were ball-milled at a molar ratio of 1:1.05 in a ball mill jar at a speed of 400 r / min for 4.5 h to ensure thorough mixing. The mixed powder was then placed in a muffle furnace and pre-sintered at 200 °C for 3 h at a heating rate of 5 °C / min, followed by high-temperature solid-state sintering at 600 °C for 18 h. After natural cooling and grinding, the layered oxide material NaNi was obtained. 0.3 Fe 0.3 Mn 0.35 Cu 0.05 Black powder of O2.

[0116] 2. Prepare CR2032 coin cells using the same method as Comparative Example 1.

[0117] Comparative Example 4

[0118] 1. Ni 0.25 Fe 0.25 Mn 0.4 Al 0.1 The (OH)₂ precursor and sodium acetate were ball-milled in a ball mill at a molar ratio of 1:1.05 for 1 hour at a speed of 750 r / min to ensure thorough mixing. The mixed powder was then placed in a muffle furnace and pre-sintered at 550°C for 2 hours at a heating rate of 7°C / min, followed by high-temperature solid-state sintering at 700°C for 15 hours. After natural cooling and grinding, the layered oxide material NaNi was obtained. 0.25 Fe 0.25 Mn 0.4 Al 0.1 Black powder of O2.

[0119] 2. Prepare CR2032 coin cells using the same method as Comparative Example 1.

[0120] Comparative Example 5

[0121] 1. Ni 0.25 Fe 0.25 Mn 0.4 Al 0.1 The (OH)₂ precursor and sodium acetate were ball-milled in a ball mill at a molar ratio of 1:1.05 for 1 hour at a speed of 750 r / min to ensure thorough mixing. The mixed powder was then placed in a muffle furnace and pre-sintered at 550°C for 2 hours at a heating rate of 7°C / min, followed by high-temperature solid-state sintering at 700°C for 15 hours. After natural cooling and grinding, the layered oxide material NaNi was obtained. 0.25 Fe 0.25 Mn 0.4 Al 0.1 Black powder of O2.

[0122] 2. Sodium carbonate (5% excess), vanadium pentoxide and ammonium dihydrogen phosphate were placed in a ball mill jar and ball milled at 500 r / min for 10 h to fully mix them and obtain sodium vanadium phosphate precursor powder. The precursor powder was placed in a tube furnace with a heating rate of 5 °C / min and pre-sintered at 550 °C for 2 h in a hydrogen-argon mixed atmosphere, and then sintered at 1000 °C for 10 h to obtain Na3V2(PO)4 material.

[0123] 3. NaNi 0.25 Fe 0.25 Mn 0.4 Al 0.1 O2 material, Na3V2(PO)4, super P, and PVDF binder were ground evenly at a mass ratio of 6.5:0.5:2:1. An appropriate amount of NMP was then added to form a slurry, which was evenly coated onto pretreated aluminum foil. The slurry was dried in a forced-air drying oven at 80℃ for 1 hour, followed by drying in a vacuum drying oven at 120℃ for 12 hours. The slurry was then cut into 14mm circular positive electrode sheets. Using a 14mm diameter, 0.2mm thick sodium metal sheet as the negative electrode, a 0.1mol / L sodium perchlorate / ethylene carbonate / dimethyl carbonate solution as the electrolyte, and a 16mm diameter Whatman GF / F glass fiber separator, a CR2032 coin cell was assembled in a high-purity argon-filled glove box.

[0124] Battery performance test

[0125] The CR2032 coin cells prepared in the examples and comparative examples were charged and discharged using a constant current charge-discharge mode at a current density of 0.1C. The test items included: the first charge-discharge cycle of the material in a sodium-ion battery, 100 cycles of 1C charge-discharge, and capacity retention after 200 cycles. Under the conditions of a discharge cutoff voltage of 2.0V and a charge cutoff voltage of 4.0V, the test results are shown in Table 1 and... Figure 4 As shown.

[0126] Table 1

[0127]

[0128] As can be seen from Table 1, under the same main material type and preparation method, Examples 1-4 and Comparative Examples 1-4 use carbon aerogel to encapsulate Na. x Ni i Fe j Mn k M m The O2 / Na3V2(PO)4 composite material method slightly improved the reversible capacity of the material, and the rate discharge, capacity retention after 100 cycles, and 200 cycles were all superior to those of Comparative Examples 1-4. Comparative Example 5 is a simple NaNi composite material. 0.25 Fe0.25 Mn 0.4 Al 0.1 O2 / Na3V2(PO)4 composite, compared to the single NaNi in Comparative Example 4 0.25 Fe 0.25 Mn 0.4 Al 0.1 The O2 material showed some improvement in rate performance and cycle retention, but the improvement was not significant. This indicates that the carbon aerogel and sodium vanadium phosphate have a synergistic effect, jointly improving the rate performance and cycle retention of the material.

[0129] In summary, this invention uses carbon aerogel to encapsulate Na x Ni i Fe j Mn k M m The method of O2 / Na3V2(PO)4 composite material effectively improves the structural stability and ionic conductivity of the material, resulting in excellent cycle stability and rate performance.

[0130] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A carbon aerogel-encapsulated composite sodium-ion cathode material, characterized in that, The invention includes carbon aerogel and a composite sodium-ion cathode material encapsulated in carbon aerogel, wherein the composite sodium-ion cathode material includes layered oxide cathode material and sodium vanadium phosphate cathode material. The chemical formula of the layered oxide cathode material is Na x Ni i Fe j Mn k M m O2, where M is Li + 、B 3+ 、Mg 2+ 、Al 3+ 、K + 、Ca 2+ 、Ti 4+ 、Co 3+ 、V 3+ 、V 4+ 、Cr 3+ 、Cu 2+ 、Zn 2+ 、Zr 4+ 、Nb 5+ and Sn 4+ or more than one of them; x, i, j, k, m satisfy: 0.8 < x ≤ 1, 0 < i ≤ 0.4, 0 < j ≤ 0.5, 0 < k ≤ 0.6, 0 < m ≤ 0.2, and i + j + k + m = 1; both the layered oxide and sodium vanadium phosphate are secondary particles, and the D50 particle sizes of both the layered oxide and sodium vanadium phosphate satisfy: 7.5 μm ≤ D50 ≤ 9 μm.

2. The carbon aerogel-encapsulated composite sodium-ion cathode material according to claim 1, characterized in that, In the carbon aerogel-encapsulated composite sodium ion cathode material, X, Y, and Z represent the mass percentages of the layered oxide cathode material, sodium vanadium phosphate cathode material, and carbon aerogel, respectively. Then X, Y, and Z satisfy the following conditions: 70%≤X≤80%, 10%≤Y≤20%, 5%≤Z≤10%, and X+Y+Z=100%.

3. A method for preparing a carbon aerogel-encapsulated composite sodium-ion cathode material, characterized in that, Includes the following steps: Layered oxide cathode material, sodium vanadium phosphate cathode material and carbon aerogel are mixed evenly in an organic solvent, filtered and freeze-dried to obtain the carbon aerogel-encapsulated composite sodium ion cathode material. Among them, the chemical formula of the layered oxide cathode material is Na x Ni i Fe j Mn k M m O2, where M is Li + 、B 3+ 、Mg 2+ 、Al 3+ 、K + 、Ca 2+ 、Ti 4+ 、Co 3+ 、V 3+ 、V 4+ 、Cr 3+ 、Cu 2+ 、Zn 2+ 、Zr 4+ 、Nb 5+ and Sn 4+ One or more of them; x, i, j, k, m satisfy: 0.8 < x ≤ 1, 0 < i ≤ 0.4, 0 < j ≤ 0.5, 0 < k ≤ 0.6, 0 < m ≤ 0.2, and i + j + k + m = 1; both the layered oxide and sodium vanadium phosphate are secondary particles, and the D50 particle sizes of both the layered oxide and sodium vanadium phosphate satisfy: 7.5 μm ≤ D50 ≤ 9 μm.

4. The method for preparing a carbon aerogel-encapsulated composite sodium-ion cathode material according to claim 3, characterized in that, Let X, Y, and Z represent the mass percentages of layered oxide cathode material, sodium vanadium phosphate cathode material, and carbon aerogel in the carbon aerogel-encapsulated composite sodium-ion cathode material, respectively. Then X, Y, and Z satisfy: 70%≤X≤80%, 10%≤Y≤20%, 5%≤Z≤10%, X+Y+Z=100%; And / or, the organic solvent includes one or more of acetone, anhydrous ethanol, ethyl acetate, and dimethyl sulfoxide.

5. The method for preparing a carbon aerogel-encapsulated composite sodium-ion cathode material according to claim 3, characterized in that, The layered oxide cathode material Na x Ni i Fe j Mn k M m The method for preparing O2 is as follows: Ni i Fe j Mn k M m The (OH)2 precursor and sodium source were ball-milled and mixed, then placed in a sintering furnace for pre-sintering for 1-8 hours, followed by high-temperature solid-state sintering for 4-20 hours. After cooling and grinding, the layered oxide cathode material Na was obtained. x Ni i Fe j Mn k M m O2; The method for preparing the sodium vanadium phosphate cathode material is as follows: a sodium source, a vanadium source, and a phosphorus source are ball-milled and mixed to obtain sodium vanadium phosphate precursor powder; the obtained sodium vanadium phosphate precursor powder is sintered in a non-oxidizing atmosphere to obtain the sodium vanadium phosphate cathode material.

6. The method for preparing a carbon aerogel-encapsulated composite sodium-ion cathode material according to claim 5, characterized in that, In the layered oxide cathode material Na x Ni i Fe j Mn k M m In the preparation method of O2: The sodium source is one or more of sodium carbonate, sodium hydroxide, sodium acetate, sodium oxalate, and sodium nitrate; And / or, the ball milling speed is 250~750 r / min, and the ball milling time is 1~6 h; And / or, the pre-sintering temperature is 200~550℃; And / or, the high-temperature solid-state sintering temperature is 750~1100℃, and the heating rate is 1~10℃ / min; In the preparation method of sodium vanadium phosphate cathode material: The sodium source is one or more of sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium carbonate, sodium nitrate, and sodium hydroxide. And / or, the vanadium source is one or more of vanadium powder, vanadium pentoxide, vanadium trioxide, and ammonium metavanadate; And / or, the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, phosphoric acid, and ammonium hypophosphite; And / or, the non-oxidizing atmosphere is one or more of nitrogen, hydrogen and argon; And / or, the sintering step is as follows: first, pre-sinter at 350~550℃ for 2~10h, then heat up to 600~1000℃ at a rate of 1~10℃ / min, and sinter at high temperature for 4~20h.

7. The method for preparing a carbon aerogel-encapsulated composite sodium-ion cathode material according to claim 3, characterized in that, The carbon aerogel is prepared by mixing an aqueous solution of conductive carbon with an accelerator and carrying out a hydrothermal reaction to obtain a conductive carbon hydrogel; the conductive carbon hydrogel is then freeze-dried and carbonized to obtain a conductive carbon aerogel. The accelerator is one or more of phenylphosphonic acid, 3-thiopheneacetic acid, 1,4-diaminobenzene, and benzenesulfonic acid.

8. The method for preparing a carbon aerogel-encapsulated composite sodium-ion cathode material according to claim 7, characterized in that, The conductive carbon is one or more of carbon nanotubes, graphene, hard carbon, and carbon nanofibers. And / or, the concentration of the conductive carbon aqueous solution is 1~15 mg / mL; And / or, the ratio of the accelerator to water in the conductive carbon aqueous solution is 20~80 mg: 1 mL; And / or, the hydrothermal reaction is carried out at a temperature of 130~200℃ for a time of 1~40h; And / or, the freeze-drying time is 5-15 hours; And / or, the carbonization is carried out in an inert atmosphere, which is one or more of nitrogen, hydrogen or argon; And / or, the carbonization temperature is 300~500℃ and the time is 0.5~3.5h.

9. A positive electrode plate, characterized in that, The carbon aerogel-encapsulated composite sodium ion cathode material as described in claim 1 or 2, or the carbon aerogel-encapsulated composite sodium ion cathode material prepared by the method described in any one of claims 3 to 8.

10. A sodium-ion battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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