Sodium-ion battery composite positive electrode material, preparation method thereof and sodium-ion battery

Abstract

The invention belongs to the technical field of sodium-ion batteries, and relates to a sodium-ion battery composite positive electrode material, a preparation method thereof and a sodium-ion battery. The sodium electric composite positive electrode material sequentially comprises a polyanion sodium ion positive electrode material core, a first carbon coating layer, a sodium ion layered oxide material coating layer and a second carbon coating layer from inside to outside, wherein the polyanion sodium ion positive electrode material comprises Na3Fe2 (PO4) 3, and the sodium ion layered oxide material comprises a manganese-based sodium ion layered oxide material. According to the sodium-ion battery composite positive electrode material provided by the invention, the three problems of conductivity, capacity and stability are simultaneously solved on the microstructure level for the first time, and rapid development of a high-performance sodium-ion battery is powerfully promoted.

Description

Technical Field

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

[0002] Lithium-ion batteries are a recyclable, highly efficient, and clean new energy source, and an effective technological approach to comprehensively alleviate energy, resource, and environmental problems. They are currently widely used as power sources for various electronic products and mobile devices. However, the abundance of lithium in the Earth's crust is only 0.0006%, and resource and price issues are the biggest obstacles to the large-scale application of lithium-ion batteries. Therefore, finding and developing a new generation of energy storage battery systems with excellent comprehensive performance is urgent. Sodium, as an element in the same group as lithium, has very similar electrochemical properties, is abundant (approximately 2.64% abundance in the Earth's crust), and is also cheaper. Therefore, using sodium to replace lithium in the development of sodium-ion rechargeable batteries has a very broad application prospect, and finding and developing suitable electrode materials has become one of the main tasks of sodium-ion battery research. Existing sodium-ion battery cathode material systems face a key bottleneck: a single type of material cannot simultaneously meet the comprehensive performance requirements of high energy density, high power density, and long cycle life. Specifically, while polyanionic materials possess a stable crystal framework, a high discharge plateau (approximately 3.8V), excellent thermal safety, and long cycling characteristics, their intrinsic electronic conductivity and ion mobility are relatively low, resulting in insufficient rate performance and limited volumetric energy density, thus restricting their application in power applications. On the other hand, layered oxide materials exhibit significant energy density advantages due to their high reversible specific capacity and tap density. However, during cycling, especially under high voltage or deep charge-discharge conditions, they are prone to structural phase transitions, transition metal dissolution, and interfacial side reactions, leading to continuous capacity decay and reduced lifetime. Currently, simply physically mixing these two types of materials cannot effectively synergize their advantages; instead, it may trigger new performance degradation mechanisms due to poor interfacial compatibility and mismatched ion migration pathways.

[0003] Therefore, how to overcome the performance limitations of single material systems and construct novel composite cathode materials that can balance high capacity and long lifespan has become a key issue in promoting the competitiveness of sodium-ion batteries in long-life application scenarios such as large-scale energy storage and electric vehicles. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a sodium-ion battery composite cathode material, its preparation method, and a sodium-ion battery. The sodium-ion battery composite cathode material provided by this invention solves the three major challenges of conductivity, capacity, and stability simultaneously at the microstructural level for the first time, significantly promoting the rapid development of high-performance sodium-ion batteries.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a sodium-electric composite cathode material, wherein the sodium-electric composite cathode material comprises, from the inside out, a polyanion sodium-ion cathode material core, a first carbon coating layer, a sodium-ion layered oxide material coating layer, and a second carbon coating layer.

[0007] The polyanionic sodium ion cathode material includes Na3Fe2(PO4)3, and the sodium ion layered oxide material includes manganese-based sodium ion layered oxide material.

[0008] Preferably, the carbon material in the first carbon coating layer includes a conductive agent, which includes any one or a combination of at least two of dot-shaped conductive agents, linear conductive agents, or sheet-like conductive agents, preferably linear conductive agents and sheet-like conductive agents.

[0009] Preferably, the manganese-based sodium ion layered oxide material includes an O3 phase manganese-based sodium ion layered oxide material, wherein the chemical formula of the O3 phase manganese-based layered oxide material is NaMnO2.

[0010] Preferably, the carbon material in the second carbon coating layer includes amorphous carbon, which is in situ coated on the surface of the sodium ion layered oxide material coating layer.

[0011] In a second aspect, the present invention provides a method for preparing a sodium-electric composite cathode material as described in the first aspect, the method comprising the following steps:

[0012] S1. Provide a polyanionic sodium ion cathode material core, wherein the polyanionic sodium ion cathode material includes Na3Fe2(PO4)3;

[0013] S2. The Na3Fe2(PO4)3 core is subjected to a first carbon coating treatment to form a material with a first carbon coating layer;

[0014] S3. A sodium ion layered oxide material is coated on the surface of the first carbon coating layer to form a material with a sodium ion layered oxide material coating layer, wherein the sodium ion layered oxide material includes a manganese-based sodium ion layered oxide material.

[0015] S4. A second carbon coating treatment is performed on the surface of the sodium ion layered oxide material coating layer to obtain the sodium-electric composite cathode material.

[0016] Preferably, the preparation method of the polyanionic sodium ion cathode material in step S1 includes any one or a combination of at least two of the following: sol-gel method, solid-phase method, or spray drying method.

[0017] Preferably, the sol-gel method includes: mixing a first sodium source, a phosphorus source, an iron source, a complexing agent, and a solvent, performing a sol-gel reaction to obtain a wet gel, drying the wet gel to obtain a dry gel, and subjecting the dry gel to high-temperature crystallization treatment to obtain the polyanionic sodium ion cathode material.

[0018] Preferably, the ratio of the total molar amount of metal ions in the first sodium source, phosphorus source and iron source to the molar amount of the complexing agent is 1:(1.5~3).

[0019] Preferably, the high-temperature crystallization treatment is carried out under a protective atmosphere, the heating rate of the high-temperature crystallization treatment is 2℃ / min~5℃ / min, the holding temperature after the high-temperature crystallization treatment is 450℃~650℃, and the holding time after the high-temperature crystallization treatment is 2h~4h.

[0020] Preferably, step S2, the first carbon coating treatment, includes:

[0021] A conductive agent is formed by mixing a polyanionic sodium ion cathode material core with a carbon material to form the first carbon coating layer.

[0022] Preferably, the amount of conductive agent added to the carbon material is 1% to 10% of the mass of the polyanionic sodium ion cathode material core.

[0023] Preferably, in step S3, the mass ratio of the sodium ion layered oxide material to the polyanion sodium ion cathode material is (70~80):(30~20).

[0024] Preferably, the coating process in step S3 includes in-situ coating, which includes:

[0025] The material with a first carbon coating layer obtained by mixing S2, a second sodium source, a manganese source and a solvent, the sodium ion layered oxide precursor material is coated on the surface of the first carbon coating layer, and then sintered to form a sodium ion layered oxide material coating layer.

[0026] Preferably, the sintering is carried out under a protective atmosphere, the sintering temperature is 300℃~500℃, and the sintering time is 2h~5h.

[0027] Preferably, the method for the second carbon coating treatment in step S4 includes:

[0028] The material with a sodium ion layered oxide coating obtained in S3 is coated with an organic carbon source and then subjected to carbonization treatment to obtain the sodium-electric composite cathode material.

[0029] Preferably, the amount of organic carbon source added is 0.5% to 3% of the mass of the material with sodium ion layered oxide material coating obtained in S3.

[0030] Thirdly, the present invention also provides a sodium-ion battery, the sodium-ion battery comprising the sodium-ion composite cathode material as described in the first aspect or the sodium-ion composite cathode material prepared by the preparation method described in the second aspect.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The sodium-ion battery composite cathode material provided by this invention uses Na3Fe2(PO4)3 polyanionic sodium-ion cathode material as the core, providing excellent structural stability. A first carbon coating layer is composited on top of the core, constructing a three-dimensional high-speed electronic conductive network within the polyanionic framework, fundamentally improving its rate performance. Then, a high-capacity manganese-based sodium-ion layered oxide material is epitaxially composited onto the conductive and activated core. This allows the robust polyanionic core to serve as a stable structural framework, internally supporting and stabilizing the outer layered oxide, effectively suppressing phase transitions and structural collapse. In conjunction with the outermost second carbon coating layer, which acts as a dense shell, it not only further enhances the overall electronic conductivity of the material but, more importantly, acts as a physical barrier, directly reducing the contact between the layered oxide and the electrolyte, suppressing transition metal dissolution and interfacial side reactions. Through the design of the core and the three specific coating layers, working in synergy, this invention solves the three major challenges of conductivity, capacity, and stability simultaneously at the microstructural level for the first time, powerfully promoting the rapid development of high-performance sodium-ion batteries. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the sodium-electric composite cathode material in Example 1.

[0034] Figure 2 The image shows the XRD pattern of the sodium-electric composite cathode material in Example 1.

[0035] Figure 3 , Figure 4 and Figure 5 All images are SEM images of the sodium-electric composite cathode material from Example 1.

[0036] Figure 6 This is a comparison chart of the charge and discharge curves of the battery provided in Example 1. Detailed Implementation

[0037] 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.

[0038] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0039] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0040] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0041] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0042] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0043] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0044] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0045] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0046] In this invention, "optional" means that something is optional, that is, it refers to any one of the two parallel solutions of "having" or "not having". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0047] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0048] In one embodiment, the first aspect of the present invention provides a sodium-electric composite cathode material, wherein the sodium-electric composite cathode material comprises, from the inside out, a polyanion sodium-ion cathode material core, a first carbon coating layer, a sodium-ion layered oxide material coating layer, and a second carbon coating layer.

[0049] The polyanionic sodium ion cathode material includes Na3Fe2(PO4)3, and the sodium ion layered oxide material includes manganese-based sodium ion layered oxide material.

[0050] The sodium-ion battery composite cathode material provided by this invention uses Na3Fe2(PO4)3 polyanionic sodium-ion cathode material as the core, providing excellent structural stability. A first carbon coating layer is composited on top of the core, constructing a three-dimensional high-speed electronic conductive network within the polyanionic framework, fundamentally improving its rate performance. Then, a high-capacity manganese-based sodium-ion layered oxide material is epitaxially composited onto the conductive and activated core. This allows the robust polyanionic core to serve as a stable structural framework, internally supporting and stabilizing the outer layered oxide, effectively suppressing phase transitions and structural collapse. In conjunction with the outermost second carbon coating layer, which acts as a dense shell, it not only further enhances the overall electronic conductivity of the material but, more importantly, acts as a physical barrier, directly reducing the contact between the layered oxide and the electrolyte, suppressing transition metal dissolution and interfacial side reactions. Through the design of the core and the three specific coating layers, working in synergy, this invention solves the three major challenges of conductivity, capacity, and stability simultaneously at the microstructural level for the first time, powerfully promoting the rapid development of high-performance sodium-ion batteries.

[0051] In some embodiments, the carbon material in the first carbon coating layer includes a conductive agent, which includes any one or a combination of at least two of dot-shaped conductive agents, linear conductive agents, or sheet-like conductive agents, preferably linear conductive agents and sheet-like conductive agents.

[0052] It is understood that the carbon-based conductive agents of the present invention are all conventional technical methods. Without violating the overall technical concept of the present invention, any carbon material with conductivity that can be used as a conductive agent is applicable to the present invention. For example, the dot-shaped conductive agent includes, but is not limited to, conductive carbon black; the linear conductive agent includes, but is not limited to, at least one of carbon nanotubes or carbon nanofibers; and the sheet-like conductive agent includes, but is not limited to, graphene.

[0053] This invention uses a conductive agent made of carbon material with excellent conductivity to coat the core, thereby achieving conductive activation. Furthermore, by combining linear and sheet-like conductive agents, a three-dimensional electronic conduction network is constructed on the particle surface or between particles of the polyanionic sodium ion cathode material, thereby improving the rate performance of the material.

[0054] Furthermore, it should be noted that the core in this invention can be a single polyanion sodium ion cathode material particle, or it can be a core obtained by stacking multiple polyanion sodium ion cathode material particles.

[0055] In some embodiments, the manganese-based sodium ion layered oxide material includes an O3 phase manganese-based sodium ion layered oxide material, wherein the chemical formula of the O3 phase manganese layered oxide material is NaMnO2.

[0056] In this invention, O3 phase manganese-based morphological oxide material is selected as the coating layer material, which has high capacity characteristics. It works synergistically with the iron-based polyanionic core to improve ionic conductivity. As the main interface of electrochemical reaction, it has a perfect combination of core stability and shell capacity, breaking through the performance bottleneck of single materials to achieve the unity of high energy density and long life, forming the best combination of low cost, high safety, long life and excellent rate performance.

[0057] In some embodiments, the carbon material in the second carbon coating layer includes amorphous carbon, which is in situ coated on the surface of the sodium ion layered oxide material coating layer.

[0058] In some implementations, the structure of dense in-situ coating of amorphous carbon on the outermost layer not only enhances conductivity but also acts as a physical barrier to isolate the electrolyte.

[0059] In one embodiment, a second aspect of the present invention provides a method for preparing a sodium-electric composite cathode material as described in the first aspect, the method comprising the following steps:

[0060] S1. Provide a polyanionic sodium ion cathode material core, wherein the polyanionic sodium ion cathode material includes Na3Fe2(PO4)3;

[0061] S2. The Na3Fe2(PO4)3 core is subjected to a first carbon coating treatment to form a material with a first carbon coating layer;

[0062] S3. A sodium ion layered oxide material is coated on the surface of the first carbon coating layer to form a material with a sodium ion layered oxide material coating layer, wherein the sodium ion layered oxide material includes a manganese-based sodium ion layered oxide material.

[0063] S4. A second carbon coating treatment is performed on the surface of the sodium ion layered oxide material coating layer to obtain the sodium-electric composite cathode material.

[0064] The preparation method provided by this invention can obtain high-performance sodium-electric composite cathode materials through simple coating and composite means.

[0065] In some embodiments, the preparation method of the polyanionic sodium ion cathode material in step S1 includes any one or a combination of at least two of the following: sol-gel method, solid-phase method, or spray drying method.

[0066] It is understood that the preparation method of the polyanionic cathode material of the present invention is not unique. Any preparation method that can be reasonably known by those skilled in the art is applicable to the present invention. The sol-gel method can achieve atomic-level uniform mixing, improve the material uniformity, and can precisely control the stoichiometric ratio of elements during the preparation process to avoid the generation of impurity phases and obtain a single NASICON structure. Furthermore, the preparation temperature is low, the energy consumption is low, and the production cost is reduced.

[0067] In some embodiments, the sol-gel method includes: mixing a first sodium source, a phosphorus source, an iron source, a complexing agent, and a solvent, performing a sol-gel reaction to obtain a wet gel, drying the wet gel to obtain a dry gel, and subjecting the dry gel to high-temperature crystallization treatment to obtain the polyanionic sodium ion cathode material.

[0068] In some embodiments, the ratio of the total molar amount of metal ions in the first sodium source, phosphorus source and iron source to the molar amount of the complexing agent is 1:(1.5~3), for example 1:1.5, 1:1.8, 1:2, 1:2.3, 1:2.5, 1:2.8 or 1:3, etc.

[0069] In this invention, the amount of complexing agent added can be adjusted according to the raw materials. The specific choice of complexing agent is not limited in this invention. Conventional complexing agent materials that can be used for preparation by sol-gel method are all applicable to this invention.

[0070] As an example, but not a limitation, the complexing agent in this invention may be selected from citric acid, which has a good complexing effect to form a wet gel, and can also serve as a carbon source to carbonize during subsequent high-temperature crystallization, thereby improving the conductivity of the material.

[0071] In some embodiments, the reaction temperature of the sol-gel reaction is 60℃~100℃, such as 60℃, 70℃, 80℃, 90℃ or 100℃, and the reaction time of the sol-gel reaction is 8h~12h, such as 8h, 9h, 10h, 11h or 12h.

[0072] In some embodiments, the high-temperature crystallization process is performed under a protective atmosphere.

[0073] It is understood that all protective atmospheres described in this invention are gaseous atmospheres that do not participate in the reaction and only serve a protective function, such as nitrogen atmospheres or inert gas atmospheres. The inert gas is a gas type specified in the periodic table, such as argon or helium.

[0074] In some embodiments, the heating rate of the high-temperature crystallization treatment is 2℃ / min to 5℃ / min, for example, 2℃ / min, 3℃ / min, 4℃ / min or 5℃ / min.

[0075] In some embodiments, the holding temperature after the high-temperature crystallization treatment is 450℃~650℃, such as 450℃, 475℃, 500℃, 525℃, 550℃, 575℃, 600℃, 625℃ or 650℃, etc.; the holding time after the high-temperature crystallization treatment is 2h~4h, such as 2h, 3h or 4h, etc.

[0076] In some embodiments, step S2, the first carbon coating process, includes:

[0077] A conductive agent is formed by mixing a polyanionic sodium ion cathode material core with a carbon material to form the first carbon coating layer.

[0078] In some embodiments, the amount of conductive agent added to the carbon material is 1% to 10% of the mass of the polyanionic sodium ion cathode material core, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0079] In some embodiments, the amount of conductive agent added to the carbon material is controlled to be 1% to 10% of the mass of the polyanionic sodium ion cathode material core, further improving the material's performance. The carbon material is sufficient to form a continuous and stable three-dimensional electronic conduction pathway between and on the surface of the polyanionic particles, significantly reducing the charge transfer impedance (Rct) of the electrode, thereby improving the intrinsic electronic conductivity of the material. Secondly, the optimized conductive network ensures that even with small volume changes in the active material during long cycling, electronic contact can be maintained, effectively suppressing capacity decay caused by contact failure.

[0080] In some embodiments, in step S3, the mass ratio of the sodium ion layered oxide material to the polyanion sodium ion cathode material is (70~80):(30~20), for example, 70:30, 71:29, 72:28, 73:27, 74:26, 75:25, 76:24, 77:23, 78:22, 79:21 or 80:20, etc.

[0081] In step S3, the mass ratio of sodium-ion layered oxide material to polyanion sodium-ion cathode material affects the synergistic effect of the two, and is preferably (70~80):(30~20). This ratio allows the prepared material to better achieve the goal of simultaneously possessing high capacity, long cycle life, and excellent rate performance. At this ratio, the layered oxide provides a sufficient capacity base, while the polyanion material supplements it, maintaining the overall capacity at a high level. The specific capacity of the composite material mainly depends on the high-capacity active component. If the proportion of layered oxide is too low, the low capacity of the polyanion will result in a low overall capacity, leading to the loss of the composite material's capacity advantage and contradicting the original intention of the composite. If the proportion of layered oxide is too high, the stable phase is insufficient to form an effective support network, and the material performance is closer to that of pure layered oxide, but its inherent problems still exist.

[0082] In some embodiments, the coating process in step S3 includes in-situ coating, which includes:

[0083] The material with a first carbon coating layer obtained by mixing S2, a second sodium source, a manganese source and a solvent, and the sodium ion layered oxide precursor material are coated on the surface of the first carbon coating layer, and then sintered to form a sodium ion layered oxide material coating layer.

[0084] In some embodiments, sodium ion layered oxide material is coated on the surface of the first carbon coating layer in an in-situ coating form, resulting in a more uniform and dense coating that is less prone to falling off and thus better fulfills its function.

[0085] In some embodiments, the sintering is carried out under a protective atmosphere, the sintering temperature is 300℃~500℃, such as 300℃, 325℃, 350℃, 375℃, 400℃, 425℃, 450℃, 475℃ or 500℃, etc., and the sintering time is 2h~5h, such as 2h, 3h, 4h or 5h.

[0086] In some embodiments, the method for the second carbon coating treatment in step S4 includes:

[0087] The material with a sodium ion layered oxide coating obtained in S3 is coated with an organic carbon source and then subjected to carbonization treatment to obtain the sodium-electric composite cathode material.

[0088] In some embodiments, the amount of organic carbon source added is 0.5% to 3% of the mass of the material with sodium ion layered oxide material coating obtained in S3, for example, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8% or 3%.

[0089] In step S4 of this invention, a dense amorphous carbon coating layer can be obtained by adding a small amount of organic carbon source. The coating layer has a moderate thickness, which can effectively act as a physical barrier without affecting the effective performance of the sodium ion cathode material.

[0090] In some embodiments, the organic carbon source includes, but is not limited to, at least one of glucose, starch, or sucrose.

[0091] In some embodiments, the carbonization process includes a pre-carbonization process followed by a high-temperature carbonization process.

[0092] Specifically:

[0093] The temperature of the pre-carbonization treatment is 200℃~300℃, for example, 200℃, 250℃ or 300℃, and the time of the pre-carbonization treatment is 1h~2h, for example, 1h or 2h.

[0094] The high-temperature carbonization treatment is carried out at a temperature of 500℃~700℃, such as 500℃, 550℃, 600℃, 650℃ or 700℃, and the high-temperature carbonization treatment is carried out for a time of 2h~3h, such as 2h or 3h.

[0095] It should also be noted that:

[0096] Optionally, the first sodium source and the second sodium source are each independently selected from any one or a combination of at least two of disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium carbonate, sodium bicarbonate, sodium acetate, and sodium pyrophosphate.

[0097] Optionally, the phosphorus source is selected from any one or a combination of at least two of disodium hydrogen phosphate, sodium dihydrogen phosphate, ferrous phosphate, ferric phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, or sodium pyrophosphate.

[0098] Optionally, the iron source is selected from any one or a combination of at least two of ferric nitrate, ferrous nitrate, ferrous oxalate, ferric sulfate, ferrous sulfate, ferric oxide, ferric citrate, ferrous citrate, or ferric pyrophosphate.

[0099] Optionally, the manganese source is selected from any one or a combination of at least two of manganese sulfate, manganese acetate, or manganese nitrate.

[0100] Optionally, the solvent in the solution system of the present invention can be water and / or anhydrous ethanol.

[0101] In one embodiment, the present invention also provides a sodium-ion battery, the sodium-ion battery comprising a sodium-ion composite cathode material as described in the first aspect or a sodium-ion composite cathode material prepared by the preparation method described in the second aspect.

[0102] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0103] Raw material source provided by:

[0104] Sodium acetate, CH3COONa (Innochem, purity >99.0%).

[0105] Ammonium dihydrogen phosphate, NH4H2PO4 (Innochem, purity >99.9%).

[0106] Ferric nitrate nonahydrate, Fe(NO3)3·9H2O (Innochem, purity >99.0%).

[0107] Manganese acetate (Maclean) (purity >99.0%).

[0108] Sodium acetate (Maclean) (purity >99.0%).

[0109] Citric acid (Maclean) (purity >99.0%).

[0110] Glucose (Maclean's) (purity >99.0%).

[0111] Carbon nanotubes (Tiannai Technology).

[0112] Graphene (Tiannai Technology).

[0113] The following examples and comparative examples all use raw materials from the above sources.

[0114] Example 1

[0115] This embodiment provides a sodium-electric composite cathode material, such as... Figure 1 As shown, the sodium-ion composite cathode material comprises, from the inside out, a polyanionic sodium-ion cathode material Na3Fe2(PO4)3 core, a first carbon coating layer, a sodium-ion layered oxide material NaMnO2 coating layer, and a second carbon coating layer.

[0116] The carbon materials of the first carbon coating layer are carbon nanotubes and graphene, and the carbon materials of the second carbon coating layer are amorphous carbon.

[0117] The preparation method of the sodium-electric composite cathode material includes:

[0118] Synthesis of S1: Na3Fe2(PO4)3 (NFP) polyanionic material core:

[0119] According to the stoichiometric ratio of Na3Fe2(PO4)3, ferric nitrate nonahydrate, ammonium dihydrogen phosphate, and sodium acetate were weighed and dissolved in 25 mL of deionized water to obtain precursor solutions. Citric acid, equivalent to twice the total molar amount of metal ions in the precursor solutions, was weighed and dissolved in deionized water as a complexing agent and carbon source. All the above solutions were mixed in a glass beaker and placed in a water bath at 80°C with continuous stirring for 10 hours until a uniform and stable sol was formed, which was further converted into a wet gel. The resulting gel was dried in a circulating ventilation oven at 100°C for more than 12 hours to obtain a fluffy dry gel precursor. The dry gel precursor was ground thoroughly in an agate mortar and then transferred to a tube furnace. Under nitrogen protection, it was heated to 550°C at a heating rate of 5°C / min for high-temperature crystallization for 3 hours. After cooling with the furnace, a well-crystallized Na3Fe2(PO4)3 (NFP) polyanionic core material was obtained.

[0120] S2: The Na3Fe2(PO4)3(NFP) polyanionic material core synthesized in step S1 is uniformly mixed with highly conductive carbon material (carbon nanotubes and graphene in a mass ratio of 1:1) at a mass ratio of 100:5 by ball milling at a low speed of 100 rpm to form a first carbon coating layer (first intermediate material) on the surface of the Na3Fe2(PO4)3(NFP) polyanionic material core.

[0121] S3: Weigh sodium acetate and manganese acetate according to the stoichiometric ratio of NaMnO2, dissolve them in a mixed solvent of deionized water and anhydrous ethanol to obtain the coating layer solution.

[0122] The first intermediate material in step S2 is uniformly dispersed in the coating solution, wherein the mass ratio of Na3Fe2(PO4)3 material to NaMnO2 is 75:25. The dispersed solution is stirred at 60°C to slowly evaporate the solvent, so that the precursor sol of the layered oxide is uniformly coated on the surface of the intermediate material. Then, under a nitrogen atmosphere, it is sintered at 400°C for 3 hours to form a NaMnO2 coating layer (second intermediate material) on the surface of the first intermediate material.

[0123] S4: The second intermediate material in S3 is uniformly mixed with a glucose aqueous solution, wherein the amount of glucose added is 1.5% of the mass of the second intermediate material. Then, in an argon atmosphere, a pre-carbonization treatment is first performed at 300°C for 1 hour, followed by a high-temperature carbonization treatment at 700°C for 2 hours to form an amorphous carbon second carbon coating layer, thus obtaining the sodium-electric composite cathode material.

[0124] Figure 1 A schematic diagram of the sodium-electric composite cathode material in Example 1 is shown. Figure 1 It can be seen that the colored part refers to the crystal structure of the Na3Fe2(PO4)3 polyanionic material core, indicating that it is coated inside; from the inside to the outside, it includes the Na3Fe2(PO4)3 polyanionic sodium ion cathode material core, the first carbon coating layer, the NaMnO2 sodium ion layered oxide material coating layer and the second carbon coating layer.

[0125] Figure 2 The image shows the XRD pattern of the sodium-electric composite cathode material in Example 1.

[0126] Figure 3 , Figure 4 and Figure 5 All images are SEM images of the sodium-electric composite cathode material from Example 1.

[0127] from Figure 2 As can be seen from the two-phase composite XRD pattern, the core-shell structure was successfully synthesized, constructing a core-shell composite cathode material with a polyanionic material as the core and a layered oxide as the shell. In the XRD pattern of the composite material, typical diffraction peaks from the core Na3Fe2(PO4)3 and the outer layer layered oxide (such as NaMnO2) can be clearly observed simultaneously. Both phase diffraction peaks remain sharp, indicating good crystallinity. This also proves that the entire multi-step coating process, including "low-speed ball milling to introduce carbon material (CNT / graphene)" and "mixing the outer layer with glucose solution," did not damage the inherent crystal structure of the core and shell materials. Figures 3 to 5 It can be observed whether the composite material consists of regular core-shell spherical particles or irregular aggregates. The layered oxides, polyanionic materials, and their coatings form an ideal core-shell structure. This structure increases the reaction interface, improves conductivity, and protects the core, providing a solid morphological and structural foundation for ultimately achieving high capacity, long lifetime, and superior rate performance in electrochemical processes.

[0128] Example 2

[0129] This embodiment provides a sodium-electric composite cathode material, which comprises, from the inside out, a polyanionic sodium-ion cathode material Na3Fe2(PO4)3 core, a first carbon coating layer, a sodium-ion layered oxide material NaMnO2 coating layer, and a second carbon coating layer.

[0130] The carbon materials of the first carbon coating layer are carbon nanotubes and graphene, and the carbon materials of the second carbon coating layer are amorphous carbon.

[0131] The preparation method of the sodium-electric composite cathode material includes:

[0132] Synthesis of S1: Na3Fe2(PO4)3 (NFP) polyanionic material core:

[0133] According to the stoichiometric ratio of Na3Fe2(PO4)3, ferric nitrate nonahydrate, ammonium dihydrogen phosphate, and sodium acetate were weighed and dissolved in 25 mL of deionized water to obtain precursor solutions. Citric acid, equivalent to three times the total molar amount of metal ions in the precursor solutions, was weighed and dissolved in deionized water as a complexing agent and carbon source. All the above solutions were mixed in a glass beaker and placed in a water bath at 60°C with continuous stirring for 12 hours until a uniform and stable sol was formed, which was further converted into a wet gel. The resulting gel was dried in a circulating ventilation oven at 80°C for more than 13 hours to obtain a fluffy dry gel precursor. The dry gel precursor was ground thoroughly in an agate mortar and then transferred to a tube furnace. Under nitrogen protection, it was heated to 650°C at a heating rate of 2°C / min for high-temperature crystallization for 2 hours. After cooling with the furnace, a well-crystallized Na3Fe2(PO4)3 (NFP) polyanionic core material was obtained.

[0134] S2: The Na3Fe2(PO4)3(NFP) polyanionic material core synthesized in step S1 is uniformly mixed with highly conductive carbon material (carbon nanotubes and graphene in a mass ratio of 1:1) at a mass ratio of 100:10 by ball milling at a low speed of 100 rpm to form a first carbon coating layer (first intermediate material) on the surface of the Na3Fe2(PO4)3(NFP) polyanionic material core.

[0135] S3: Weigh sodium acetate and manganese acetate according to the stoichiometric ratio of NaMnO2, dissolve them in a mixed solvent of deionized water and anhydrous ethanol to obtain the coating layer solution.

[0136] The first intermediate material in step S2 is uniformly dispersed in the coating solution, wherein the mass ratio of Na3Fe2(PO4)3 material to NaMnO2 is maintained at 75:25. The dispersed solution is stirred at 80°C to slowly evaporate the solvent, so that the precursor sol of the layered oxide is uniformly coated on the surface of the intermediate material. Then, under a nitrogen atmosphere, it is sintered at 500°C for 2 hours to form a NaMnO2 coating layer (second intermediate material) on the surface of the first intermediate material.

[0137] S4: The second intermediate material in S3 is uniformly mixed with a glucose aqueous solution, wherein the amount of glucose added is 3% of the mass of the second intermediate material. Then, in an argon atmosphere, a pre-carbonization treatment at 200°C is performed for 1 hour, followed by a high-temperature carbonization treatment at 500°C for 2 hours to form an amorphous carbon second carbon coating layer, thereby obtaining the sodium-electric composite cathode material.

[0138] Example 3

[0139] This embodiment provides a sodium-electric composite cathode material, which comprises, from the inside out, a polyanionic sodium-ion cathode material Na3Fe2(PO4)3 core, a first carbon coating layer, a sodium-ion layered oxide material NaMnO2 coating layer, and a second carbon coating layer.

[0140] The carbon materials of the first carbon coating layer are carbon nanotubes and graphene, and the carbon materials of the second carbon coating layer are amorphous carbon.

[0141] The preparation method of the sodium-electric composite cathode material includes:

[0142] Synthesis of S1: Na3Fe2(PO4)3 (NFP) polyanionic material core:

[0143] According to the stoichiometric ratio of Na3Fe2(PO4)3, ferric nitrate nonahydrate, ammonium dihydrogen phosphate, and sodium acetate were weighed and dissolved in 25 mL of deionized water to obtain precursor solutions. Citric acid, equivalent to 1.5 times the total molar amount of metal ions in the precursor solutions, was weighed and dissolved in deionized water as a complexing agent and carbon source. All the above solutions were mixed in a glass beaker and placed in a water bath at 80°C with continuous stirring for 10 hours until a uniform and stable sol was formed, which was further converted into a wet gel. The resulting gel was dried in a circulating ventilation oven at 100°C for more than 12 hours to obtain a fluffy dry gel precursor. The dry gel precursor was ground thoroughly in an agate mortar and then transferred to a tube furnace. Under nitrogen protection, it was heated to 450°C at a heating rate of 5°C / min for high-temperature crystallization for 4 hours. After cooling with the furnace, a well-crystallized Na3Fe2(PO4)3 (NFP) polyanionic core material was obtained.

[0144] S2: The Na3Fe2(PO4)3(NFP) polyanionic material core synthesized in step S1 is uniformly mixed with highly conductive carbon material (carbon nanotubes and graphene in a mass ratio of 1:1) at a mass ratio of 100:1 by ball milling at a low speed of 100 rpm to form a first carbon coating layer (first intermediate material) on the surface of the Na3Fe2(PO4)3(NFP) polyanionic material core.

[0145] S3: Weigh sodium acetate and manganese acetate according to the stoichiometric ratio of NaMnO2, dissolve them in a mixed solvent of deionized water and anhydrous ethanol to obtain the coating layer solution.

[0146] The first intermediate material in step S2 is uniformly dispersed in the coating solution, wherein the mass ratio of Na3Fe2(PO4)3 material to NaMnO2 is 75:25. The dispersed solution is stirred at 60°C to slowly evaporate the solvent, so that the precursor sol of the layered oxide is uniformly coated on the surface of the intermediate material. Then, under a nitrogen atmosphere, it is sintered at 300°C for 5 hours to form a NaMnO2 coating layer (second intermediate material) on the surface of the first intermediate material.

[0147] S4: The second intermediate material in S3 is uniformly mixed with a glucose aqueous solution, wherein the amount of glucose added is 0.5% of the mass of the second intermediate material. Then, in an argon atmosphere, a pre-carbonization treatment is first performed at 300°C for 1 hour, followed by a high-temperature carbonization treatment at 700°C for 2 hours to form an amorphous carbon second carbon coating layer, thus obtaining the sodium-electric composite cathode material.

[0148] Example 4

[0149] The difference between this embodiment and embodiment 1 is that in step S3 of this embodiment, the mass ratio of Na3Fe2(PO4)3 material to NaMnO2 is 80:20.

[0150] All other conditions remain the same as in Example 1.

[0151] Example 5

[0152] The difference between this embodiment and embodiment 1 is that in step S3 of this embodiment, the mass ratio of Na3Fe2(PO4)3 material to NaMnO2 is 70:30.

[0153] All other conditions remain the same as in Example 1.

[0154] Example 6

[0155] The difference between this embodiment and Embodiment 1 is that the highly conductive material in step S2 of this embodiment is conductive carbon black.

[0156] All other conditions remain the same as in Example 1.

[0157] Example 7

[0158] The difference between this embodiment and embodiment 1 is that the coating material in step S2 of this embodiment is exactly the same as the coating material in step S4, and the mass ratio of the Na3Fe2(PO4)3(NFP) polyanionic material core to the coating material is still 100:5.

[0159] All other conditions remain the same as in Example 1.

[0160] Example 8

[0161] The difference between this embodiment and embodiment 1 is that in step S2 of this embodiment, the mass ratio of the Na3Fe2(PO4)3(NFP) polyanionic material core to the highly conductive carbon material (carbon nanotubes and graphene with a mass ratio of 1:1) is 100:15 (that is, the amount of highly conductive material added is 15% of the mass of the polyanionic material).

[0162] All other conditions remain the same as in Example 1.

[0163] Example 9

[0164] The difference between this embodiment and Embodiment 1 is that in step S3 of this embodiment, the mass ratio of Na3Fe2(PO4)3 material to NaMnO2 is 65:35.

[0165] All other conditions remain the same as in Example 1.

[0166] Example 10

[0167] The difference between this embodiment and embodiment 1 is that in step S3 of this embodiment, the mass ratio of Na3Fe2(PO4)3 material to NaMnO2 is 85:15.

[0168] All other conditions remain the same as in Example 1.

[0169] Example 11

[0170] The difference between this embodiment and embodiment 1 is that the coating material in step S4 of this embodiment is the same as the coating material in step S2, that is, the second coating layer is carbon nanotubes and graphene, rather than amorphous carbon.

[0171] All other conditions remain the same as in Example 1.

[0172] Example 12

[0173] The difference between this embodiment and embodiment 1 is that in step S4 of this embodiment, the amount of glucose added is 5% of the mass of the second intermediate material.

[0174] All other conditions remain the same as in Example 1.

[0175] Comparative Example 1

[0176] The difference between this comparative example and Example 1 is that the sodium-electric composite cathode material in this example is the Na3Fe2(PO4)3 core.

[0177] In the preparation method, steps S2, S3 and S4 are not performed; only step S1 is performed.

[0178] All other conditions remain the same as in Example 1.

[0179] Comparative Example 2

[0180] The difference between this comparative example and Example 1 is that the sodium-electric composite cathode material in this example is NaMnO2 material, which does not contain a core, a first carbon coating layer, or a second carbon coating layer.

[0181] In the preparation method, steps S1, S2 and S4 are omitted, and the NaMnO2 material is directly prepared using the preparation method provided in step S3.

[0182] All other conditions remain the same as in Example 1.

[0183] Comparative Example 3

[0184] The difference between this comparative example and Example 1 is that the sodium-electric composite cathode material in this comparative example does not contain a first carbon coating layer.

[0185] In the preparation method, step S2 is not performed.

[0186] All other conditions remain the same as in Example 1.

[0187] Comparative Example 4

[0188] The difference between this comparative example and Example 1 is that the sodium-electric composite cathode material in this comparative example does not contain a sodium ion layered oxide material NaMnO2 coating layer.

[0189] In the preparation method, step S3 is not performed.

[0190] All other conditions remain the same as in Example 1.

[0191] Comparative Example 5

[0192] The difference between this comparative example and Example 1 is that the sodium-electric composite cathode material in this comparative example does not contain a second carbon coating layer.

[0193] In the preparation method, step S4 is not performed.

[0194] All other conditions remain the same as in Example 1.

[0195] Comparative Example 6

[0196] The difference between this comparative example and Example 1 is that the order of the sodium-electric composite cathode material core and the NaMnO2 coating layer is reversed, that is, NaMnO2 material is used as the core and Na3Fe2(PO4)3 material is used as the coating layer.

[0197] In the preparation method, the preparation processes of steps S1 and S3 are interchanged, and the precursor solution is mixed with the first intermediate material, and then a complexing agent is added.

[0198] All other conditions remain the same as in Example 1.

[0199] Battery fabrication and performance testing

[0200] 1) Battery manufacturing

[0201] The sodium-ion positive electrode materials provided in the examples and comparative examples were mixed uniformly with conductive agent acetylene black and binder polyvinylidene fluoride at a mass ratio of 8:1:1 to form an electrode sheet with a diameter of 14 mm, and then dried in a vacuum at 100°C for 12 h. This electrode sheet was transferred to a glove box as the positive electrode, with a metallic sodium sheet as the counter electrode and glass fiber as the separator. The electrolyte was a 1 mol / L NaPF6 solution, wherein the solvent was a mixture of EC:DMC = 1:1 vol% and 5% FEC (vol%). A 2032 coin cell was assembled by combining the positive electrode shell, electrode sheet, separator, electrolyte, sodium sheet, gasket, spring, and negative electrode shell.

[0202] 2) Performance Testing

[0203] The batteries prepared in the examples and comparative examples were subjected to performance testing on the Blue Electric System under the following conditions:

[0204] Capacity and cycle performance: At room temperature of 25℃ and a voltage range of 2V~4V, the battery was activated at 0.1C for the first three cycles, followed by 100 charge-discharge cycles at 1C. The specific capacity of the first discharge cycle at 0.1C and the capacity retention rate after 100 cycles at 1C were obtained.

[0205] Rate performance: At room temperature of 25℃, the battery was tested at a voltage range of 2V~4V. The battery was charged and discharged at 0.1C, 0.2C, 0.5C, 1C, 2C and 5C in sequence, and then the battery was tested again at a rate of 0.1C to obtain the capacity retention rate of 5C / 0.1C.

[0206] The test results are shown in Table 1.

[0207] Figure 6 The first three charge-discharge curves of Example 1 are shown. Figure 6 It can be seen that the discharge capacity of the material in the first cycle reached 146 mAh / g. Starting from the second cycle, the charge-discharge curve almost overlapped with that of the third cycle, showing good electrochemical reversibility and structural stability, which provides a foundation for long cycle life.

[0208] Table 1

[0209]

[0210] From the data in Table 1, we can obtain:

[0211] The sodium-ion composite cathode material provided by this invention, through the synergistic cooperation of Na3Fe2(PO4)3 polyanionic sodium-ion cathode material, a first carbon coating layer, a sodium-ion layered oxide coating layer, and a second carbon coating layer, solves the three major problems of conductivity, capacity, and stability at the microstructure level for the first time, thereby improving the capacity, cycle life, and rate performance of the material.

[0212] Data analysis of Examples 1, 6, 7, and 11 reveals that the first and second carbon coating layers utilize different carbon materials. The first carbon coating layer is a highly conductive carbon conductive agent, while the second carbon coating layer is an amorphous carbon material. This approach better addresses the issues of charge transport kinetic mismatch and interfacial resistance. The first carbon coating layer (highly conductive carbon) is directly coated on the surface of the polyanionic polymer (NFP), its primary task being to overcome the critical weakness of low intrinsic electronic conductivity in NFPs. It constructs an efficient electron transport channel, ensuring the rapid extraction of electrons from the active material core and significantly reducing electrochemical polarization. The second carbon coating layer (amorphous carbon) is coated on the outermost layer of layered oxide. While layered oxides exhibit acceptable electronic conductivity, their interfacial stability with the electrolyte is poor. The amorphous carbon layer primarily serves as a physical and chemical buffer layer, reducing the direct contact area between the electrode and the electrolyte, suppressing side reactions, and its porous structure allows sodium ions to pass through rapidly without significantly increasing ion transport resistance.

[0213] Data analysis of Examples 1 and 8 shows that during the first carbon coating process, the amount of conductive agent added to the coating material (i.e., the highly conductive carbon material) plays a crucial role in the construction of the conductive network and the performance of the core material. Adjusting this amount to 1%~10% further achieves the fundamental solution to the poor conductivity of the core material at the lowest cost and with the best efficiency, while ensuring high energy density and good processability of the electrode. This lays the foundation for the composite cathode material to exert its comprehensive advantages of high capacity and high stability. Data analysis of Examples 1, 9, and 10 shows that the mass ratio of the ionic layered oxide material to the polyanionic sodium ion cathode material affects the synergistic effect of the two. In particular, adjusting (70~80):(30~20) can achieve synergistic advantages. The high-capacity layered oxide provides the main energy density basis, while the highly stable and high-operating-voltage polyanionic material acts as a "stabilizer" and "voltage plateau supplement." At this formulation, the material exhibits high reversible capacity, excellent cycle stability, and good rate performance, with overall performance significantly superior to embodiments with excessively high or low formulations. Data analysis of Examples 1 and 12 shows that the second carbon coating layer does not need to be excessive; a thin and uniform amorphous carbon layer is sufficient. Therefore, controlling the amount of organic carbon source added to the second carbon coating layer to 0.5%~3% is more conducive to forming an excellent electronic conductivity network. The thin carbon layer can more effectively form continuous and rapid electron conduction paths on the surface and between secondary particles, reducing charge transfer impedance. Furthermore, it forms more effective interface protection; the uniform thin layer can effectively isolate the electrode material from direct contact with the electrolyte, suppressing side reactions and improving cycle stability, while not significantly hindering sodium ion diffusion.

[0214] Analysis of the data from Example 1 and Comparative Examples 1 to 6 reveals that the coating sequence and the selection of the corresponding core and shell materials are crucial in the sodium-electric composite cathode material of the present invention. The absence of any one of these conditions leads to a significant decrease in the electrochemical performance of the material. Changes in the sequence result in uneven inner layer coating, failing to provide effective protection for the core. Unfavorable interfacial reactions occur between the outer and inner layers. A gradient buffer layer cannot be formed, making the material prone to cracking and delamination under cyclic stress. Specifically, the combination of the specific core material (such as a high-capacity layered oxide) and the specific shell material (such as a highly stable polyanionic material) used in Example 1, along with the subsequent coating, jointly constructs the optimal microstructure and interfacial properties. This design effectively suppresses phase transitions, transition metal dissolution, and electrolyte side reactions during cycling while maintaining high capacity.

[0215] 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 composite cathode material, characterized in that, The sodium-ion composite cathode material comprises, from the inside out, a polyanion sodium-ion cathode material core, a first carbon coating layer, a sodium-ion layered oxide material coating layer, and a second carbon coating layer. The polyanionic sodium ion cathode material includes Na3Fe2(PO4)3, and the sodium ion layered oxide material includes manganese-based sodium ion layered oxide material.

2. The sodium-ion battery composite cathode material according to claim 1, characterized in that, The carbon material in the first carbon coating layer includes a conductive agent, which includes any one or a combination of at least two of dot-shaped conductive agents, linear conductive agents, or sheet-like conductive agents, preferably linear conductive agents and sheet-like conductive agents.

3. The sodium-ion battery composite cathode material according to claim 1, characterized in that, The manganese-based sodium ion layered oxide material includes an O3 phase manganese-based sodium ion layered oxide material, the chemical formula of which is NaMnO2.

4. The sodium-ion battery composite cathode material according to claim 1, characterized in that, The carbon material in the second carbon coating layer includes amorphous carbon, which is in situ coated on the surface of the sodium ion layered oxide material coating layer.

5. A method for preparing a sodium-electric composite cathode material as described in any one of claims 1-4, characterized in that, The preparation method includes the following steps: S1. Provide a polyanionic sodium ion cathode material core, wherein the polyanionic sodium ion cathode material includes Na3Fe2(PO4)3; S2. The Na3Fe2(PO4)3 core is subjected to a first carbon coating treatment to form a material with a first carbon coating layer; S3. A sodium ion layered oxide material is coated on the surface of the first carbon coating layer to form a material with a sodium ion layered oxide material coating layer, wherein the sodium ion layered oxide material includes a manganese-based sodium ion layered oxide material. S4. A second carbon coating treatment is performed on the surface of the sodium ion layered oxide material coating layer to obtain the sodium-electric composite cathode material.

6. The preparation method according to claim 5, characterized in that, The preparation method of the polyanionic sodium ion cathode material in step S1 includes any one or a combination of at least two of the following: sol-gel method, solid-phase method, or spray drying method. Preferably, the sol-gel method includes: mixing a first sodium source, a phosphorus source, an iron source, a complexing agent, and a solvent, performing a sol-gel reaction to obtain a wet gel, drying the wet gel to obtain a dry gel, and subjecting the dry gel to high-temperature crystallization treatment to obtain the polyanionic sodium ion cathode material. Preferably, the ratio of the total molar amount of metal ions in the first sodium source, phosphorus source and iron source to the molar amount of the complexing agent is 1:(1.5~3). Preferably, the high-temperature crystallization treatment is carried out under a protective atmosphere, the heating rate of the high-temperature crystallization treatment is 2℃ / min~5℃ / min, the holding temperature after the high-temperature crystallization treatment is 450℃~650℃, and the holding time after the high-temperature crystallization treatment is 2h~4h.

7. The preparation method according to claim 5, characterized in that, Step S2, the first carbon coating process, includes: A conductive agent that mixes a polyanionic sodium ion cathode material core with a carbon material forms the first carbon coating layer; Preferably, the amount of conductive agent added to the carbon material is 1% to 10% of the mass of the polyanionic sodium ion cathode material core.

8. The preparation method according to claim 5, characterized in that, In step S3, the mass ratio of the sodium ion layered oxide material to the polyanion sodium ion cathode material is (70~80):(30~20). Preferably, the coating process in step S3 includes in-situ coating, which includes: The material with a first carbon coating layer obtained by mixing S2, a second sodium source, a manganese source and a solvent, the sodium ion layered oxide precursor material is coated on the surface of the first carbon coating layer, and then sintered to form a sodium ion layered oxide material coating layer. Preferably, the sintering is carried out under a protective atmosphere, the sintering temperature is 300℃~500℃, and the sintering time is 2h~5h.

9. The preparation method according to claim 5, characterized in that, Step S4, the method for the second carbon coating treatment, includes: The material with a sodium ion layered oxide coating obtained in S3 is coated with an organic carbon source and then subjected to carbonization treatment to obtain the sodium-electric composite cathode material. Preferably, the amount of organic carbon source added is 0.5% to 3% of the mass of the material with sodium ion layered oxide material coating obtained in S3.

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes the sodium-ion composite cathode material as described in any one of claims 1-4 or the sodium-ion composite cathode material prepared by the preparation method as described in any one of claims 5-9.

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