A sodium-ion battery positive electrode material and a preparation method and application thereof

Abstract

The application provides a sodium ion battery positive electrode material and a preparation method and application thereof, the sodium ion battery positive electrode material comprises an active material and a hydrophobic coating layer, and a coating source of the hydrophobic coating layer comprises a siloxane-based compound; the siloxane-based compound is used as the coating source of the hydrophobic coating layer, a compound containing -Si-O-Na is generated on the surface of the active material, the hydrophobic property and the environmental stability can be ensured at the same time, and the sodium ion battery obtained has high ion conduction capacity, so that the sodium ion battery has good cycle performance; meanwhile, the application is coated by using a molecular self-assembly method, the thickness does not change due to the change of the morphology of the material, the process requirement is low, and the cost is low.

Description

Technical Field

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

[0002] Rechargeable batteries, including lithium-ion and sodium-ion batteries, are high-energy-density batteries with great development potential and application prospects. Currently, due to the scarcity of lithium resources, sodium-ion batteries, with their abundant raw materials and lower cost, have attracted widespread attention from researchers. Although the cost of sodium-ion battery cathode materials is relatively low, the poor environmental stability during storage and processing leads to high processing costs. Therefore, it is urgent to solve the environmental stability problem of sodium-ion battery cathode materials and reduce the production cost of sodium-ion batteries.

[0003] CN 108987708A discloses a sodium-ion battery cathode material, its preparation method, and a sodium-ion battery. The provided sodium-ion battery cathode material includes a matrix and a coating layer covering the surface of the matrix. The chemical formula of the matrix is ​​Na. 0.67 Ni 0.167 Co 0.167 Mn 0.67 O2, wherein the coating layer is a ZrO layer, and in the sodium-ion battery cathode material, the mass of the coating layer is 1-10% of the mass of the substrate, and the preparation method includes: mixing a salt solution and an alkaline solution, reacting them, and separating the solid and liquid phases to obtain nickel-cobalt-manganese carbonate; pre-calcining the nickel-cobalt-manganese carbonate to obtain ternary nickel-cobalt-manganese oxide; mixing the ternary nickel-cobalt-manganese oxide with a sodium source and calcining it to obtain a substrate; mixing the substrate with a zirconium source and calcining it to obtain the sodium-ion battery cathode material; that is, the disclosed sodium-ion cathode material uses a high-temperature sintering solid-state coating method, which results in uneven coating, an excessively thick coating layer, low ionic conductivity, high process cost, and low environmental stability.

[0004] CN 108923042A discloses a layered manganese-based cathode material for sodium-ion batteries and its preparation method, wherein the general formula of the cathode material is Na. y Mn 3-x M xO7, where M is Cu, and 0.1≤x≤2, 0≤y≤4; the cathode material has a triclinic crystal structure and a sodium acetylation oxide protective layer on the surface; the disclosed sodium-ion battery layered manganese-based material has a triclinic crystal structure and a phase-transition-free structural characteristic over a wide voltage range, which can effectively improve the structural stability of the manganese-based layered cathode material during charging and discharging as well as its stability when exposed to air. However, the preparation method of the sodium-ion battery cathode material prepared by this method is complex and not conducive to long-term storage. After storage under environmental conditions, the material is still prone to react with water and carbon dioxide, resulting in capacity loss, increased polarization, and failure.

[0005] Based on the above research, how to provide a sodium-ion battery cathode material with a uniform and thinner coating layer, high stability in the environment, hydrophobicity and high sodium-ion conductivity, and simple preparation method, which can improve the cycle performance and capacity of sodium-ion batteries, has become an urgent problem to be solved. Summary of the Invention

[0006] The purpose of this invention is to provide a sodium-ion battery cathode material, its preparation method, and its application. The sodium-ion battery cathode material has a hydrophobic coating layer, which exhibits high ionic conductivity, strong hydrophobicity, and good environmental stability. Furthermore, the coated cathode material demonstrates excellent electrochemical performance in sodium-ion battery applications.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a sodium-ion battery cathode material, the sodium-ion battery cathode material comprising an active material and a hydrophobic coating layer, wherein the coating source of the hydrophobic coating layer comprises a siloxane compound.

[0009] This invention uses siloxane compounds as the coating source for a hydrophobic coating layer, providing a hydrophobic film on the surface of the active material. This prevents capacity loss caused by the reaction of the sodium-ion battery cathode material with water and carbon dioxide in the environment, resulting in excellent electrochemical performance of the coated active material in sodium-ion battery applications and significantly improving the cycle performance of the sodium-ion battery. The siloxane compounds are physically adsorbed on the surface of the active material and can also react with the active material to generate compounds containing -Si-O-Na. The -Si-O-Na is obtained by the reaction of the siloxane group -Si-OR in the siloxane compound with sodium hydroxide and / or sodium carbonate on the surface of the cathode material, thereby improving the ionic conductivity of the hydrophobic coating layer. While performing hydrophobic coating, it also ensures the sodium ion conduction capacity, resulting in a higher ionic conductivity than ordinary hydrophobic coating layers.

[0010] Preferably, the thickness of the hydrophobic coating layer is 1 to 20 nm, for example, it can be 1 nm, 2.5 nm, 5 nm, 7.5 nm, 10 nm, 12.5 nm, 15 nm, 17.5 nm or 20 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0011] The siloxane compound of the present invention has its siloxane group facing the active material and reacting with the active material to generate a compound containing -Si-O-Na. The hydrophobic end faces the outside air at the other end, thus achieving a hydrophobic effect. This ensures both the ion conductivity of the coating layer and the purpose of hydrophobicity.

[0012] The length of the hydrophobic end facing the outside air is 2 to 8 μm, for example, it can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm or 8 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0013] Preferably, the siloxane compound comprises any one or a combination of at least two of heptadecafluorodecyltrimethoxysilane, heptadecafluorodecyltriethoxysilane, pentadecylfluorononyltrimethoxysilane, pentadecylfluorononyltriethoxysilane, tridecafluorooctyltrimethoxysilane, or tridecafluorooctyltriethoxysilane. Typical but non-limiting combinations include combinations of heptadecafluorodecyltrimethoxysilane and heptadecafluorodecyltriethoxysilane, combinations of pentadecylfluorononyltrimethoxysilane and pentadecylfluorononyltriethoxysilane, or combinations of tridecafluorooctyltrimethoxysilane and tridecafluorooctyltriethoxysilane.

[0014] Preferably, the average particle size of the active material is 1 to 3 μm, for example, it can be 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] Preferably, the active material includes NaNi 0.33 Fe 0.33 Mn 0.33 O2 and / or NaCo 0.7 Mn 0.3 O2.

[0016] In a second aspect, the present invention provides a method for preparing a sodium-ion battery cathode material as described in the first aspect, the method comprising the following steps:

[0017] The active material is coated with siloxane compounds using a liquid-phase method and / or a gas-phase method to obtain the sodium-ion battery cathode material.

[0018] The liquid-phase or gas-phase method used in this invention to coat the sodium-ion battery cathode material is a molecular self-assembly coating. Compared with the traditional solid-phase sintering coating, the hydrophobic coating layer obtained by the preparation method of this invention is thinner, thus having higher ionic conductivity. Moreover, the thickness does not change due to changes in the morphology of the material, and the coating layer is more uniform. Furthermore, the coating steps are simple, have low process requirements, low cost, and low energy consumption.

[0019] The gas-phase method described in this invention produces a more uniform coating layer than the liquid-phase method, and the resulting hydrophobic coating layer is more dense, thus exhibiting stronger ion conductivity and relatively higher performance in the obtained sodium-ion battery.

[0020] Preferably, the mass ratio of the active material to the siloxane compound is 1:(0.02 to 0.08), for example, it can be 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07 or 1:0.08, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the liquid phase method includes mixing an active material with a siloxane compound in a solution, followed by filtration and drying.

[0022] Preferably, the mixing speed is 400-600 r / min, for example, 400 r / min, 500 r / min or 600 r / min, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the mixing time is 8 to 12 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the drying temperature is 70-90°C, for example, 70°C, 75°C, 80°C, 85°C or 90°C, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the drying time is 0.8 to 1.2 hours, for example, 0.8 hours, 0.9 hours, 1 hour, 1.1 hours or 1.2 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] Preferably, the solution of the siloxane compound comprises a siloxane compound and a solvent in a mass ratio of 1:(90-110), such as 1:90, 1:100 or 1:110, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the solvent comprises any one or a combination of at least two of N-methylpyrrolidone, ethanol, N,N-dimethylformamide, tetrahydrofuran, or acetone. Typical but non-limiting combinations include a combination of N-methylpyrrolidone and ethanol, a combination of N,N-dimethylformamide and tetrahydrofuran, or a combination of tetrahydrofuran and acetone.

[0028] The solvent is used for rinsing during the filtration process described in this invention.

[0029] Preferably, the gas-phase method includes heating a siloxane compound, placing the active material in the vapor of the siloxane compound, cooling and stirring the active material to complete one coating, and repeating the coating 2 to 4 times.

[0030] The coating is repeated 2 to 4 times, for example, 2, 3 or 4 times.

[0031] Preferably, the temperature for heating the siloxane compound is 80 to 100°C, for example, 80°C, 90°C or 100°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the active material is placed in the vapor of the siloxane compound for 5 to 7 hours, for example, 5 hours, 6 hours or 7 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0034] The active material is coated using a liquid-phase method or a gas-phase method. The liquid-phase method involves mixing the active material and a solution of a siloxane compound at a stirring speed of 400–600 r / min for 8–12 h, filtering, and drying at 70–90 °C for 0.8–1.2 h to obtain the sodium-ion battery cathode material.

[0035] The gas-phase method involves heating a siloxane compound at 80–100°C, placing the active material in the vapor of the siloxane compound for 5–7 hours, cooling, and then stirring the active material to complete one coating. This coating process is repeated 2–4 times to obtain the sodium-ion battery cathode material.

[0036] Thirdly, the present invention provides a sodium-ion battery, the sodium-ion battery comprising the sodium-ion battery positive electrode material as described in the first aspect.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The sodium-ion battery cathode material of this invention has a thin and uniform hydrophobic coating layer, which can ensure hydrophobic properties and thus ensure the stability of sodium-ion batteries in the environment. It also has high ion conductivity, resulting in sodium-ion batteries with good cycle performance. At the same time, this application uses a molecular self-assembly method for coating, which does not cause changes in thickness due to changes in the morphology of the material, and has low process requirements and low cost. Attached Figure Description

[0039] Figure 1 This is a scanning electron microscope image of the sodium-ion battery cathode material described in Example 1.

[0040] Figure 2 This is a schematic diagram of the contact between the sodium-ion battery cathode material and the solvent described in Example 1.

[0041] Figure 3 This is a schematic diagram of the contact between the sodium-ion battery cathode material and the solvent described in Comparative Example 1. Detailed Implementation

[0042] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0043] Example 1

[0044] This embodiment provides a sodium-ion battery cathode material, which includes NaCo. 0.7 Mn 0.3 O2 and a hydrophobic coating layer, wherein the coating source of the hydrophobic coating layer is heptadecafluorodecyltrimethoxysilane;

[0045] The hydrophobic coating layer has a thickness of 10 nm, and the NaCo 0.7 Mn 0.3 The average particle size of O2 is 2 μm;

[0046] The siloxane of the heptadecyltrimethoxysilane faces the active material and reacts with the active material to obtain a product containing a -Si-O-Na group. The only difference between the product and the coating source is that the -Si-O-Na of the product replaces the -Si-O-CH3 in the coating source, and the hydrophobic end faces the outside air at the other end.

[0047] The method for preparing the sodium-ion battery cathode material includes the following steps:

[0048] Heaping heptadecyltrimethoxysilane at 90℃, NaCo 0.7 Mn 0.3 O2 was placed in the vapor of heptadecafluorodecyltrimethoxysilane for 6 hours, and then stirred after cooling. 0.7Mn 0.3 O2 is used to complete one coating, and the coating is repeated 3 times to obtain the sodium-ion battery cathode material.

[0049] The NaCo 0.7 Mn 0.3 The mass ratio of O2 to heptadecafluorodecyltrimethoxysilane is 1:0.05;

[0050] The scanning electron microscope image of the sodium-ion battery cathode material described in this embodiment is as follows: Figure 1 As shown in the diagram, the contact diagram with the solvent is as follows: Figure 2 As shown.

[0051] Example 2

[0052] This embodiment provides a sodium-ion battery cathode material, which includes NaNi. 0.33 Fe 0.33 Mn 0.33 O2 and a hydrophobic coating layer, wherein the coating source of the hydrophobic coating layer is heptadecafluorodecyltrimethoxysilane;

[0053] The thickness of the hydrophobic coating layer is 1 nm, and the NaCo 0.7 Mn 0.3 The average particle size of O2 is 1 μm;

[0054] The siloxane of the heptadecyltrimethoxysilane faces the active material and reacts with the active material to obtain a product containing a -Si-O-Na group. The only difference between the product and the coating source is that the -Si-O-Na of the product replaces the -Si-O-CH3 in the coating source, and the hydrophobic end faces the outside air at the other end.

[0055] The method for preparing the sodium-ion battery cathode material includes the following steps:

[0056] Heptadecafluorodecyltrimethoxysilane, NaNi 0.33 Fe 0.33 Mn 0.33 O2 was placed in the vapor of heptadecafluorodecyltrimethoxysilane for 5 hours, cooled, and the active material was stirred to complete one coating. The coating was repeated twice to obtain the sodium-ion battery cathode material.

[0057] The NaNi 0.33 Fe 0.33 Mn 0.33 The mass ratio of O2 to heptadecafluorodecyltrimethoxysilane is 1:0.02.

[0058] Example 3

[0059] This embodiment provides a sodium-ion battery cathode material, which includes NaCo. 0.7 Mn 0.3 O2 and a hydrophobic coating layer, wherein the coating source of the hydrophobic coating layer is heptadecafluorodecyltrimethoxysilane;

[0060] The hydrophobic coating layer has a thickness of 20 nm, and the NaCo 0.7 Mn 0.3 The average particle size of O2 is 3 μm;

[0061] The siloxane of the heptadecyltrimethoxysilane faces the active material and reacts with the active material to obtain a product containing a -Si-O-Na group. The only difference between the product and the coating source is that the -Si-O-Na of the product replaces the -Si-O-CH3 in the coating source, and the hydrophobic end faces the outside air at the other end.

[0062] The method for preparing the sodium-ion battery cathode material includes the following steps:

[0063] Heptadecafluorodecyltrimethoxysilane at 80℃, NaCo 0.7 Mn 0.3 O2 was placed in the vapor of heptadecafluorodecyltrimethoxysilane for 7 hours, cooled, and the active material was stirred to complete one coating. The coating was repeated 4 times to obtain the sodium-ion battery cathode material.

[0064] The NaCo 0.7 Mn 0.3 The mass ratio of O2 to heptadecafluorodecyltrimethoxysilane is 1:0.08.

[0065] Example 4

[0066] This embodiment provides a sodium-ion battery cathode material, which includes NaCo. 0.7 Mn 0.3 O2 and a hydrophobic coating layer, wherein the coating source of the hydrophobic coating layer is heptadecafluorodecyltrimethoxysilane;

[0067] The hydrophobic coating layer has a thickness of 10 nm, and the NaCo 0.7 Mn 0.3 The average particle size of O2 is 2 μm;

[0068] The siloxane of the heptadecyltrimethoxysilane faces the active material and reacts with the active material to obtain a product containing a -Si-O-Na group. The only difference between the product and the coating source is that the -Si-O-Na of the product replaces the -Si-O-CH3 in the coating source, and the hydrophobic end faces the outside air at the other end.

[0069] The method for preparing the sodium-ion battery cathode material includes the following steps:

[0070] NaCo was mixed at a stirring speed of 500 r / min. 0.7 Mn 0.3 The sodium-ion battery cathode material was obtained by reacting O2 with a tetrahydrofuran solution of heptadecafluorodecyltrimethoxysilane for 10 hours, filtering, and drying at 80°C for 1 hour.

[0071] The NaCo 0.7 Mn 0.3 The mass ratio of O2 to heptadecafluorodecyltrimethoxysilane is 1:0.05, and the mass ratio of heptadecafluorodecyltrimethoxysilane to tetrahydrofuran is 1:100.

[0072] Example 5

[0073] This embodiment provides a sodium-ion battery cathode material, which includes NaNi. 0.33 Fe 0.33 Mn 0.33 O2 and a hydrophobic coating layer, wherein the coating source of the hydrophobic coating layer is heptadecafluorodecyltrimethoxysilane;

[0074] The thickness of the hydrophobic coating layer is 1 nm, and the NaCo 0.7 Mn 0.3 The average particle size of O2 is 1 μm;

[0075] The siloxane of the heptadecafluorodecyltrimethoxysilane faces the active material and reacts with the active material to obtain a product containing a -Si-O-Na group. The only difference between the product and the coating source is that the -Si-O-Na of the product replaces the -Si-O-CH3 in the coating source, and the hydrophobic end faces the outside air at the other end.

[0076] The method for preparing the sodium-ion battery cathode material includes the following steps:

[0077] NaCo was mixed at a stirring speed of 400 r / min. 0.7 Mn 0.3 The sodium-ion battery cathode material was obtained by reacting O2 with an N-methylpyrrolidone solution of heptadecafluorodecyltrimethoxysilane for 12 hours, filtering, and drying at 70°C for 1.2 hours.

[0078] The NaCo 0.7 Mn 0.3 The mass ratio of O2 to heptadecafluorodecyltrimethoxysilane is 1:0.02, and the mass ratio of heptadecafluorodecyltrimethoxysilane to N-methylpyrrolidone is 1:90.

[0079] Example 6

[0080] This embodiment provides a sodium-ion battery cathode material, which includes NaCo. 0.7 Mn 0.3 O2 and a hydrophobic coating layer, wherein the coating source of the hydrophobic coating layer is heptadecafluorodecyltrimethoxysilane;

[0081] The hydrophobic coating layer has a thickness of 20 nm, and the NaCo 0.7 Mn 0.3 The average particle size of O2 is 3 μm;

[0082] The siloxane of the heptadecyltrimethoxysilane faces the active material and reacts with the active material to obtain a product containing a -Si-O-Na group. The only difference between the product and the coating source is that the -Si-O-Na of the product replaces the -Si-O-CH3 in the coating source, and the hydrophobic end faces the outside air at the other end.

[0083] The method for preparing the sodium-ion battery cathode material includes the following steps:

[0084] NaCo was mixed at a stirring speed of 600 r / min. 0.7 Mn 0.3 The sodium-ion battery cathode material was obtained by reacting O2 with an ethanol solution of heptadecafluorodecyltrimethoxysilane for 5 hours, filtering, and drying at 90°C for 0.8 hours.

[0085] The NaCo 0.7 Mn 0.3 The mass ratio of O2 to heptadecafluorodecyltrimethoxysilane is 1:0.08, and the mass ratio of heptadecafluorodecyltrimethoxysilane to ethanol is 1:110.

[0086] Example 7

[0087] This embodiment provides a sodium-ion battery cathode material, which is the same as that in Embodiment 1 except that the thickness of the hydrophobic coating layer is 0.05 nm.

[0088] The method for preparing the sodium-ion battery cathode material, excluding NaCo 0.7 Mn 0.3 Except for adjusting the mass ratio of O2 to heptadecafluorodecyltrimethoxysilane to 1:0.01, everything else is the same as in Example 1.

[0089] Example 8

[0090] This embodiment provides a sodium-ion battery cathode material, which is the same as that in Embodiment 1 except that the thickness of the hydrophobic coating layer is 22 nm.

[0091] The method for preparing the sodium-ion battery cathode material, excluding NaCo 0.7 Mn 0.3 Except for adjusting the mass ratio of O2 to heptadecafluorodecyltrimethoxysilane to 1:0.1, everything else is the same as in Example 1.

[0092] Example 9

[0093] This embodiment provides a sodium-ion battery cathode material, which is the same as in Example 1 except that the coating source heptadecafluorodecyltrimethoxysilane is replaced with pentadecylfluorononyltrimethoxysilane;

[0094] The preparation method of the sodium-ion battery cathode material is the same as that in Example 1, except for the change in the coating source.

[0095] Example 10

[0096] This embodiment provides a sodium-ion battery cathode material, which is the same as in Example 1 except that the coating source heptadecafluorodecyltrimethoxysilane is replaced with tridecafluorooctyltrimethoxysilane;

[0097] The preparation method of the sodium-ion battery cathode material is the same as that in Example 1, except for the change in the coating source.

[0098] Comparative Example 1

[0099] This comparative example provides a sodium-ion battery cathode material, wherein the sodium-ion battery cathode material is NaCo. 0.7 Mn 0.3 O2;

[0100] The contact diagram of the sodium-ion battery cathode material described in this comparative example with the solvent is shown in the figure below. Figure 3 As shown.

[0101] Comparative Example 2

[0102] This comparative example provides a sodium-ion battery cathode material, which includes NaCo. 0.7 Mn 0.3 O2 and sodium silicate coating;

[0103] The sodium silicate layer has a thickness of 10 nm, and the NaCo 0.7 Mn 0.3 The average particle size of O2 is 2 μm;

[0104] The method for preparing the sodium-ion battery cathode material includes the following steps:

[0105] NaCo was mixed at a mass ratio of 1:0.05. 0.7 Mn0.3 The sodium-ion battery cathode material is obtained by sintering O2 and sodium silicate at 300°C for 5 hours.

[0106] Comparative Example 3

[0107] This comparative example provides a sodium-ion battery cathode material. The sodium-ion battery cathode material is the same as that in Example 1, except that the silicon atoms in the coating source heptadecafluorodecyltrimethoxysilane are replaced with carbon atoms so that it cannot react with the active material.

[0108] The preparation method of the sodium-ion battery cathode material is the same as that in Example 1, except that the coating source is changed.

[0109] Performance testing:

[0110] Fresh sodium-ion battery cathode materials from the above-described examples and comparative examples, stored for 7 days and 14 days respectively, were mixed with conductive carbon black and polyvinylidene fluoride in an 8:1:1 ratio using N-methylpyrrolidone as a solvent to form a slurry coating, which was then used to prepare cathode sheets. These cathode sheets and sodium metal electrodes were assembled into 2032 coin cells using glass fiber as a separator. The assembled coin cells were subjected to cycle performance testing under the following conditions: 3 cycles at 0.1C, followed by cycles at 0.5C (1C = 100 mAh·g). -1 The charge / discharge cutoff voltage is 2-4.1V.

[0111] The test results are shown in Table 1:

[0112] Table 1

[0113]

[0114]

[0115] The following points can be observed from Table 1:

[0116] (1) As can be seen from Examples 1-3 and Examples 4-6 of the present invention, Examples 1-3 use the steam method for coating, while Examples 4-6 use the solution method for coating. The sodium-ion batteries obtained in Examples 1-3 have better electrochemical performance. It can be seen that the coating layer obtained by the steam coating method is more uniform and the coating layer is more dense than that obtained by the solution coating method. Therefore, the ion conduction ability is stronger and the performance of the sodium-ion battery obtained is relatively higher.

[0117] (2) As can be seen from Examples 1 and Examples 7-8, the thickness of the hydrophobic coating layer in Examples 7-8 is not within the preferred range, and its performance is reduced compared to Example 1. Therefore, the thickness of the hydrophobic coating layer is within the preferred range, which is beneficial to ensure that the coating layer has excellent ion conduction ability.

[0118] (3) As described in Examples 1 and 9-10, the hydrophobic coating source of Examples 9-10 changes, and the length of its hydrophobic chain gradually decreases. Compared with Example 1, its performance is reduced and its stability in the environment is relatively lower. It can be seen that in the preferred coating source, the longer length of the hydrophobic chain is beneficial to improving the environmental stability and cycle performance of sodium-ion batteries.

[0119] (4) As can be seen from Example 1 and Comparative Example 1, the environmental stability of the uncoated sodium-ion battery cathode material provided in Comparative Example 1 is significantly reduced. The cycle performance of the sodium-ion batteries obtained after 7 or 14 days of storage is significantly reduced. Furthermore, Comparative Example 1 has poor hydrophobic properties. Figure 3 It can be seen that the solvent has a contact angle of 0° with the surface, meaning it spreads evenly on the surface and binds... Figure 2 It can be seen that the sodium-ion battery cathode material provided in Example 1 has a large contact angle with the solvent, which proves that the sodium-ion battery cathode material provided by the present invention has strong hydrophobicity; thus, it can be seen that the present invention uses siloxane compounds as the coating source of the hydrophobic coating layer, so that the obtained sodium-ion battery has good cycle performance.

[0120] (5) As can be seen from Example 1 and Comparative Examples 2-3, Comparative Examples 2-3 use sodium silicate alone or conventional hydrophobic materials as coating layers, neither of which can achieve the technical effect of this application, and neither can simultaneously guarantee the hydrophobic and ion conduction characteristics; thus, it can be seen that the present invention uses siloxane compounds as the coating source of the hydrophobic coating layer, which can simultaneously guarantee hydrophobic characteristics and environmental stability, while also having high ion conduction capacity, so that the obtained sodium-ion battery has good cycle performance.

[0121] In summary, this invention provides a sodium-ion battery cathode material, its preparation method, and its application. It uses siloxane compounds as the coating source for the hydrophobic coating layer, generating compounds containing -Si-O-Na groups on the surface of the active material, resulting in a sodium-ion battery with good cycle performance. Furthermore, this application employs a molecular self-assembly method for coating, which avoids thickness changes due to variations in material morphology, thus requiring less sophisticated processes and incurring lower costs.

[0122] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A sodium-ion battery cathode material, characterized in that, The sodium-ion battery cathode material includes an active material and a hydrophobic coating layer formed by molecular self-assembly, wherein the coating source of the hydrophobic coating layer includes siloxane compounds. The siloxane alkyl group of the siloxane compound is oriented toward the active material and reacts with the active material to generate a compound containing -Si-O-Na; The hydrophobic end of the siloxane compound faces the outside air at the other end; The siloxane compound includes any one or a combination of at least two of the following: heptadecafluorodecyltrimethoxysilane, heptadecafluorodecyltriethoxysilane, pentadecylfluorononyltrimethoxysilane, pentadecylfluorononyltriethoxysilane, tridecafluorooctyltrimethoxysilane, or tridecafluorooctyltriethoxysilane.

2. The sodium-ion battery cathode material according to claim 1, characterized in that, The thickness of the hydrophobic coating is 1~20nm.

3. The sodium-ion battery cathode material according to claim 1, characterized in that, The average particle size of the active material is 1~3μm.

4. The sodium-ion battery cathode material according to claim 1, characterized in that, The active material includes NaNi 0.33 Fe 0.33 Mn 0.33 O2 and / or NaCo 0.7 Mn 0.3 O2.

5. A method for preparing a sodium-ion battery cathode material as described in any one of claims 1 to 4, characterized in that, The preparation method includes the following steps: The active material is coated with a siloxane compound using a liquid-phase method or a gas-phase method to obtain the sodium-ion battery cathode material.

6. The preparation method according to claim 5, characterized in that, The mass ratio of the active material to the siloxane compound is 1:(0.02~0.08).

7. The preparation method according to claim 5, characterized in that, The liquid-phase method includes mixing an active material with a solution of a siloxane compound, followed by filtration and drying.

8. The preparation method according to claim 7, characterized in that, The mixing speed is 400~600 r / min.

9. The preparation method according to claim 7, characterized in that, The mixing time is 8-12 hours.

10. The preparation method according to claim 7, characterized in that, The drying temperature is 70~90℃ and the time is 0.8~1.2h.

11. The preparation method according to claim 7, characterized in that, The solution of the siloxane compound comprises a siloxane compound and a solvent in a mass ratio of 1:(90~110).

12. The preparation method according to claim 11, characterized in that, The solvent includes any one or a combination of at least two of N-methylpyrrolidone, ethanol, N,N-dimethylformamide, tetrahydrofuran, or acetone.

13. The preparation method according to claim 5, characterized in that, The gas-phase method involves heating a siloxane compound, placing the active material in the vapor of the siloxane compound, cooling and stirring the active material to complete one coating, and repeating the coating 2 to 4 times.

14. The preparation method according to claim 13, characterized in that, The temperature at which the siloxane compound is heated is 80~100℃.

15. The preparation method according to claim 13, characterized in that, The active material is placed in the vapor of a siloxane compound for 5 to 7 hours.

16. The preparation method according to claim 5, characterized in that, The preparation method includes the following steps: The active material is coated using either a liquid-phase or gas-phase method; The liquid phase method includes mixing an active material and a siloxane compound solution at a stirring speed of 400-600 r / min for 8-12 h, filtering, and drying at 70-90℃ for 0.8-1.2 h to obtain the sodium-ion battery cathode material. The gas-phase method involves heating a siloxane compound at 80-100°C, placing the active material in the vapor of the siloxane compound for 5-7 hours, cooling, stirring the active material, completing one coating, and repeating the coating 2-4 times to obtain the sodium-ion battery cathode material.

17. A sodium-ion battery, characterized in that, The sodium-ion battery includes the sodium-ion battery cathode material as described in any one of claims 1 to 4.

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