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

Abstract

The application discloses a positive electrode material based on a sodium ion battery and a preparation method and a sodium ion battery thereof, and relates to the technical field of sodium ion batteries. + The positive electrode material has a specific core-shell structure of three-level composition of a core layer of layered oxides, an intermediate layer of Fe / Co / Ni and a shell layer of CNTs, the molar ratio of Fe, Co and Ni in the intermediate layer is (0.6-0.9):(0.05-0.3):(0.05-0.3). The core layer of layered oxides provides Na + deintercalation sites and two-dimensional ion transmission channels; the intermediate layer of Fe / Co / Ni can effectively inhibit manganese dissolution, promote stable lattices and improve the structural stability of the material; and the intermediate layer of Fe / Co / Ni can also provide in-situ catalytic sites for the growth of carbon nanotubes and enhance the interface bonding force; the shell layer of CNTs is wrapped and interpenetrated between the metal particles to form a continuous three-dimensional conductive network and improve the conductivity. The three-layer structure is complementary in function and synergistic in effect, the conductivity and structural stability of the layered oxide positive electrode material are improved in a synergistic manner, and the defects of the prior art are compensated.

Description

Technical Field

[0001] This application relates to the field of sodium-ion battery technology, specifically to a positive electrode material based on sodium-ion batteries and its preparation method, and sodium-ion batteries. Background Technology

[0002] With the rapid development of the energy storage market, sodium-ion batteries have become an important development direction for large-scale energy storage systems due to their abundant resources, low cost, and good safety. Layered oxide materials, due to their high specific capacity and simple preparation process, are cathode systems with great industrialization potential. However, the structural stability and conductivity of layered oxide materials need further improvement.

[0003] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0004] This application aims to at least partially address one of the technical problems in the related art. Therefore, the purpose of this application is to propose a positive electrode material for sodium-ion batteries, a method for preparing the same, and a sodium-ion battery.

[0005] In a first aspect of this application, this application proposes a positive electrode material based on a sodium-ion battery, the positive electrode material comprising a core layer, an intermediate layer and a shell layer arranged sequentially from the core layer to the shell layer; The core layer comprises a first layered oxide, wherein the first transition metal element in the first layered oxide comprises at least two of Mn, Fe and Ni; The intermediate layer comprises a second layered oxide, wherein the second transition element in the second layered oxide comprises Fe, Co, and Ni, and the chemical composition of the second layered oxide is shown in Chemical Formula II, wherein Chemical Formula II: Na y Co a Fe b Ni c O2, wherein b satisfies: 1 > b ≥ 0.6; the molar ratio of Fe, Co, and Ni in the second layered oxide is (0.6-0.9):(0.05-0.3):(0.05-0.3). The shell layer comprises carbon nanotubes.

[0006] The cathode material provided in this application embodiment has a specific core-shell structure of a three-level composite: a layered oxide core layer, a Fe / Co / Ni enriched intermediate layer, and a CNT (carbon nanotube) outer shell layer. The layered oxide core layer provides Na... +The material incorporates insertion / extraction sites and two-dimensional ion transport channels; the intermediate Fe / Co / Ni layer effectively inhibits manganese dissolution, promotes lattice stability, and improves material structural stability; it also provides in-situ catalytic sites for carbon nanotube growth, enhancing interfacial bonding; the CNT outer shell coats and intersperses between metal particles, forming a continuous three-dimensional conductive network, thus improving conductivity. This three-layer structure is functionally complementary and synergistically enhances the conductivity and structural stability of layered oxide cathode materials, overcoming the shortcomings of existing technologies.

[0007] In some embodiments, the chemical composition of the first layered oxide is as shown in Chemical Formula I; The chemical formula I: Na x Mn α Fe M Ni z O2; where 0.6≤x≤1.15, α+β+γ+z=1, and α, β, and z are all greater than 0, γ≥0, and M includes Co.

[0008] In some embodiments, the chemical composition of the second layered oxide is as shown in Chemical Formula II; The chemical formula II: Na y Co a Fe b Ni c O2; where 0.6≤y≤1.15, a+b+c=1, and 1>a>0, 1>b>0, 1>c>0.

[0009] In some embodiments, b satisfies: 1 > b ≥ 0.6; And / or, the molar ratio of Fe, Co, and Ni in the second layered oxide is (0.6-0.9):(0.05-0.3):(0.05-0.3).

[0010] In some embodiments, the size parameters of the carbon nanotubes include: tube length of 1μm-50μm and tube outer diameter of 5nm-30nm; And / or, the carbon nanotubes coat and interweave between the metal particles to form a continuous three-dimensional conductive network.

[0011] In some embodiments, the thickness of the intermediate layer is 20nm-1000nm; And / or, the thickness of the shell is 5nm-100nm.

[0012] In a second aspect of this application, a method for preparing the cathode material described in the first aspect is proposed, comprising the following steps: Includes the following steps: Layered oxide precursor materials were synthesized using a co-precipitation method; The layered oxide precursor material is placed in a mixed salt solution containing Fe, Co, and Ni for surface enrichment to form a precursor material with Fe, Co, and Ni enriched on the surface. The precursor material enriched with Fe, Co, and Ni on the surface is mixed with sodium salt and then subjected to solid-state sintering to obtain a layered oxide material containing a solid solution of Fe, Co, and Ni enriched layers on the surface. The layered oxide material containing Fe, Co, and Ni enriched solid solutions on its surface is activated in air, and then carbon nanotubes are grown in situ on the material surface using chemical vapor deposition to obtain the cathode material.

[0013] This application provides a method for preparing a cathode material. This method mainly involves the following steps: "co-precipitation synthesis of precursor → surface enrichment of Fe / Co / Ni → solid-phase sintering with sodium salt → air activation → in-situ growth of carbon nanotubes via chemical vapor deposition." This method achieves the controllable preparation of a three-level composite core-shell structure. Furthermore, the entire process requires no additional catalyst, is simple in flow, has controllable parameters, and is easily scalable for industrial production.

[0014] In some embodiments, the step of synthesizing layered oxide precursor materials using a co-precipitation method includes the following process: In an inert gas atmosphere, a mixed metal salt containing transition metals, a precipitant, and a complexing agent are subjected to a co-precipitation reaction at a reaction temperature of 50℃-90℃ and a reaction pH of 9.0-12.0 to obtain a layered oxide precursor material. And / or, the total loading of Fe, Co, and Ni accounts for 1%-5% of the mass of the layered oxide precursor material.

[0015] In some embodiments, the solid-state sintering includes a first sintering and a second sintering, wherein the temperature of the first sintering is 400℃-500℃ and the temperature of the second sintering is 800℃-900℃. And / or, the steps for obtaining the cathode material by in-situ growth of carbon nanotubes on the material surface using chemical vapor deposition include the following processes: The activated material is then heated to 550-650℃ after being purged with an inert gas system. Reduction and activation are achieved by introducing a mixture of hydrogen and inert gas; A mixture of inert gas, hydrogen, and acetylene is introduced to grow carbon nanotubes in situ on the material surface, thus obtaining the cathode material.

[0016] In a third aspect, this application proposes a sodium-ion battery comprising the positive electrode material described in the first aspect or a positive electrode material prepared using the method described in the second aspect. Therefore, this sodium-ion battery possesses all the features and advantages of the aforementioned positive electrode material and its preparation method, which will not be elaborated further here.

[0017] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0018] The foregoing aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a scanning electron microscope (SEM) image of the precursor material with Fe, Co, and Ni enriched on its surface obtained in step 2 of Example 1 of this application.

[0019] Figure 2 This is a scanning electron microscope image of the cathode material obtained in Example 1 of this application.

[0020] Figure 3 This is a schematic diagram of the structure of the positive electrode material obtained in Example 1 of this application. Detailed Implementation

[0021] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0022] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0023] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0024] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0025] The "range" disclosed in this application is defined by 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 a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, 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 a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" 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 "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0026] In the description of this application, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0027] In the description of this application, "multiple" means two or more.

[0028] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0029] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0030] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0031] Existing methods for improving layered oxide materials mainly include bulk doping, surface coating, and composite with carbon materials such as carbon nanotubes. Traditional carbon coating is mostly a physical mixture, resulting in weak bonding and discontinuous conductive networks; meanwhile, carbon nanotube composites usually require the introduction of additional catalysts, which is complex and prone to introducing impurities. Moreover, surface coating is mostly controlled by uniform coating, lacking structural design, and it is difficult to balance the structural stability and interfacial conductivity of the material.

[0032] Therefore, this application provides a sodium-ion battery cathode material and its preparation method that are structurally stable, allow for in-situ self-catalytic conductive network construction, and feature a simple and controllable process, which has significant practical value. The specific technical solution is as follows: In a first aspect of this application, this application proposes a positive electrode material based on a sodium-ion battery, the positive electrode material comprising a core layer, an intermediate layer and a shell layer arranged sequentially from the core layer to the shell layer; The core layer comprises a first layered oxide, wherein the first transition metal element in the first layered oxide comprises at least two of Mn, Fe and Ni; The intermediate layer comprises a second layered oxide, wherein the second transition element in the second layered oxide comprises Fe, Co, and Ni, and the chemical composition of the second layered oxide is shown in Chemical Formula II, wherein Chemical Formula II: Na y Co a Fe b Ni c O2, wherein b satisfies: 1 > b ≥ 0.6; the molar ratio of Fe, Co, and Ni in the second layered oxide is (0.6-0.9):(0.05-0.3):(0.05-0.3). The shell layer comprises carbon nanotubes.

[0033] The cathode material provided in this application embodiment has a specific core-shell structure of a three-level composite: a layered oxide core layer, a Fe / Co / Ni enriched intermediate layer, and a CNT (carbon nanotube) outer shell layer. The layered oxide core layer provides Na... + The material incorporates insertion / extraction sites and two-dimensional ion transport channels; the intermediate Fe / Co / Ni layer effectively inhibits manganese dissolution, promotes lattice stability, and improves material structural stability; it also provides in-situ catalytic sites for carbon nanotube growth, enhancing interfacial bonding; the CNT outer shell coats and intersperses between metal particles, forming a continuous three-dimensional conductive network, thus improving conductivity. This three-layer structure is functionally complementary and synergistically enhances the conductivity and structural stability of layered oxide cathode materials, overcoming the shortcomings of existing technologies.

[0034] In some embodiments, the chemical composition of the first layered oxide is as shown in Chemical Formula I; The chemical formula I: Na xMn α Fe M Ni z O2; where 0.6≤x≤1.15 (e.g., 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, etc.), α+β+γ+z=1, and α, β, and z are all greater than 0, γ≥0, and M includes Co. Therefore, the cathode material provided in this application contains multiple metallic elements such as Mn, Fe, and Ni in its core layer, which can enhance Na... + The reversible intercalation and deintercalation capability between layers further enhances conductivity; at the same time, the synergistic effect of multiple transition metals suppresses high-voltage phase transitions and Mn dissolution, thereby improving the structural stability of the material.

[0035] In some embodiments, 0.6 ≤ y ≤ 1.15 (e.g., 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, etc.), a + b + c = 1, and 1 > a > 0, 1 > b > 0, 1 > c > 0. Thus, forming a Fe / Mn / Ni-doped layered oxide solid solution surface layer on the layered oxide surface can effectively suppress manganese dissolution, promote stable lattice, and improve the structural stability of the material; it also provides in-situ catalytic sites for carbon nanotube growth, enhancing interfacial bonding.

[0036] In some embodiments, b satisfies: 1 > b ≥ 0.6, for example, it can be 0.6, 0.7, 0.8, 0.9, etc., preferably 0.8; And / or, the molar ratio of Fe, Co, and Ni in the second layered oxide is (0.6-0.9):(0.05-0.3):(0.05-0.3), for example, 0.6:0.2:0.2, 0.8:0.1:0.1, 0.9:0.05:0.05, 0.7:0.2:0.1, 0.6:0.3:0.1, etc. Thus, the intermediate layer exhibits iron-rich characteristics, which can further effectively reduce lattice strain and microcrack formation. While Fe dominates catalysis, Co and Ni synergistically optimize catalytic activity and structural stability, thereby synergistically improving the growth density and lattice stability of carbon nanotubes.

[0037] In some embodiments, the size parameters of the carbon nanotubes include: a tube length of 1μm-50μm, for example, 5μm, 10μm, 15μm, 35μm, 50μm or any of the aforementioned values; and an outer diameter of 5nm-30nm, for example, 5nm, 10nm, 20nm, 30nm or any of the aforementioned values. Thus, the carbon nanotubes have a suitable aspect ratio, enabling them to be coated on the surface of metal particles in a mesh-like manner and to bridge adjacent particles across the gaps between particles, forming a continuous three-dimensional conductive network.

[0038] And / or, the carbon nanotubes coat and interweave between the metal particles to form a continuous three-dimensional conductive network. This results in a highly conductive and tightly bound three-dimensional conductive network.

[0039] In some embodiments, the thickness of the intermediate layer is 20 nm to 1000 nm, for example, it can be 20 nm, 50 nm, 80 nm, 150 nm, 200 nm, 500 nm, 800 nm, 1000 nm or any range between the aforementioned values; thus, the intermediate layer has a suitable thickness, which provides sufficient Fe / Co / Ni reserves to catalyze the in-situ growth of carbon nanotubes and inhibit manganese dissolution, while avoiding excessive Na+ dissolution due to an overly thick intermediate layer. + The transport path is too long, and the ionic conductivity decreases.

[0040] And / or, the thickness of the shell layer is 5nm-100nm, for example, it can be 5nm, 10nm, 20nm, 40nm, 50nm, 70nm, 85nm, 100nm or any range between the aforementioned values. Thus, the shell layer has a suitable thickness, enabling the carbon nanotube conductive network to have appropriate coverage density and effective thickness, further improving the conductivity of the material.

[0041] In a second aspect of this application, a method for preparing the cathode material described in the first aspect is proposed, comprising the following steps: Includes the following steps: Layered oxide precursor materials were synthesized using a co-precipitation method; The layered oxide precursor material is placed in a mixed salt solution containing Fe, Co, and Ni for surface enrichment to form a precursor material with Fe, Co, and Ni enriched on the surface. The precursor material enriched with Fe, Co, and Ni on the surface is mixed with sodium salt and then subjected to solid-state sintering to obtain a layered oxide material containing a solid solution of Fe, Co, and Ni enriched layers on the surface. The layered oxide material containing Fe, Co, and Ni enriched solid solutions on its surface is activated in air, and then carbon nanotubes are grown in situ on the material surface using chemical vapor deposition to obtain the cathode material.

[0042] This application provides a method for preparing a cathode material. This method mainly involves the following steps: "co-precipitation synthesis of precursor → surface enrichment of Fe / Co / Ni → solid-phase sintering with sodium salt → air activation → in-situ growth of carbon nanotubes via chemical vapor deposition." This method achieves the controllable preparation of a three-level composite core-shell structure. Furthermore, the entire process requires no additional catalyst, is simple in flow, has controllable parameters, and is easily scalable for industrial production.

[0043] In some embodiments, the step of synthesizing layered oxide precursor materials using a co-precipitation method includes the following process: In an inert gas atmosphere, a mixed metal salt containing a transition metal, a precipitant, and a complexing agent are subjected to a co-precipitation reaction at a temperature of 50℃-90℃, for example, 50℃, 60℃, 70℃, 90℃, or any range between the aforementioned values; the reaction pH is 9.0-12.0, for example, 9.0, 9.5, 10.0, 11.0, 12.0, or any range between the aforementioned values; a layered oxide precursor material is obtained. And / or, the total loading of Fe, Co, and Ni accounts for 1%-5% of the mass of the layered oxide precursor material, for example, it can be 1%, 2%, 3%, 4%, 5% or any of the aforementioned values.

[0044] In this application, the layered oxide precursor material synthesized by co-precipitation is a binary, ternary, or quaternary metal hydroxide containing at least two elements from manganese, iron, cobalt, and nickel. The raw materials for the co-precipitation reaction are one or more of metal sulfates, nitrates, or acetates. The precipitant is one or two of sodium hydroxide and sodium carbonate. The complexing agent is ammonia. The reaction is carried out under an inert atmosphere, at a temperature of 50-90°C, with the pH value controlled at 9.0-12.0. The reaction time is 12-120 h (e.g., 12 h, 24 h, 48 h, 50 h, 80 h, 120 h, or any range between the aforementioned values). After the reaction is completed, the addition of metal salt is stopped, and the reaction time is extended by 6-24 h (e.g., 6 h, 8 h, 10 h, 12 h, 24 h, or any range between the aforementioned values) to completely consume the metal salt in the reaction vessel, thus obtaining a sodium-ion battery cathode precursor reaction solution.

[0045] In this application, the step of placing the layered oxide precursor material in a mixed salt solution containing Fe, Co, and Ni for surface enrichment to form a precursor material with Fe, Co, and Ni surface enrichment is as follows: The enrichment of iron, cobalt, and nickel elements is achieved using salt solutions of iron, cobalt, and nickel salts. The iron salt is ferrous sulfate or ferric nitrate, the cobalt salt is cobalt sulfate or cobalt nitrate, and the nickel salt is nickel sulfate or nickel nitrate. The enrichment process involves adding a mixed solution of iron, cobalt, and nickel salts to a layered oxide precursor material solution obtained by co-precipitation synthesis of the layered oxide precursor material. The reaction is stirred for 4-36 hours (e.g., 6 hours, 8 hours, 10 hours, 12 hours, 24 hours, 36 hours, or any range thereof), and the reaction temperature is 50°C. -90℃ (e.g., 50℃, 60℃, 70℃, 90℃ or any range between the aforementioned values), pH value controlled at 9.0-12.0 (e.g., 9.0, 9.5, 10.0, 11.0, 12.0 or any range between the aforementioned values), to achieve enrichment of iron, cobalt and nickel elements on the surface of the precursor. After the reaction, the precursor material is obtained by aging, filtering, washing and drying. The total loading of iron, cobalt and nickel elements is 1-5 wt% relative to the precursor material.

[0046] In some embodiments, the solid-state sintering includes a first sintering and a second sintering. The temperature of the first sintering is 400℃-500℃, for example, it can be 400℃, 420℃, 450℃, 500℃ or any range between the aforementioned values; the temperature of the second sintering is 800℃-900℃, for example, it can be 800℃, 840℃, 870℃, 900℃ or any range between the aforementioned values. And / or, the steps for obtaining the cathode material by in-situ growth of carbon nanotubes on the material surface using chemical vapor deposition include the following processes: After activation, the material is purged with an inert gas system and then heated to 550-650°C, for example, 550°C, 580°C, 600°C, 650°C or any range between the aforementioned values; Reduction and activation are achieved by introducing a mixture of hydrogen and inert gas; A mixture of inert gas, hydrogen, and acetylene is introduced to grow carbon nanotubes in situ on the material surface, thus obtaining the cathode material.

[0047] In this application, the step of mixing the precursor material enriched with Fe, Co, and Ni on the surface with sodium salt and then performing solid-state sintering to obtain a layered oxide material containing a solid solution of Fe, Co, and Ni enriched on the surface is as follows: the sodium salt is sodium carbonate, the amount of sodium carbonate is calculated according to the stoichiometric ratio, and the excess sodium carbonate is 2-15 mol% (for example, it can be 2 mol%, 5 mol%, 10 mol%, 15 mol%, or any of the aforementioned values), to compensate for the volatilization of sodium element during the high-temperature sintering process; the high-temperature solid-state sintering adopts a segmented sintering system: first, pre-firing at 400-500℃ for 3-5 hours, then main firing at 800-900℃ for 10-15 hours, the heating rate is 2-5℃ / min, the sintering atmosphere is air or oxygen, and after sintering, the furnace is cooled to room temperature.

[0048] In this application, in the step of activating the layered oxide material containing Fe, Co, and Ni enriched solid solution on the surface by placing it in air, the temperature of the air is room temperature to 90°C. The purpose of the activation treatment is to moderately oxidize the iron, cobalt, and nickel elements enriched on the surface to form metal oxide active sites, providing catalytic centers for subsequent CVD in-situ growth of carbon nanotubes.

[0049] In this application, the activated material is subjected to in-situ growth of carbon nanotubes on the material surface using chemical vapor deposition to obtain the cathode material. The specific steps include the following: first, argon gas is introduced into a tubular furnace at a flow rate of 100-200 sccm (e.g., 100 sccm, 120 sccm, 150 sccm, 200 sccm, etc.) and purged for 25-30 minutes to remove air from the furnace; then, the tubular furnace is heated to 550-650℃ at a heating rate of 5℃ / min; a mixture of hydrogen and argon gas is introduced for reduction activation for 30-60 minutes (e.g., 30 minutes, 40 minutes, 50 minutes, 60 minutes, etc.), wherein the hydrogen gas accounts for 2-15% of the volume fraction of the mixed gas (e.g., 2%, 7%, 10%, 15%, etc.). The total flow rate is 50-100 sccm (e.g., 50 sccm, 60 sccm, 80 sccm, 100 sccm, etc.). After reduction and activation, a mixture of hydrogen, argon, and acetylene is introduced to begin in-situ growth of carbon nanotubes. The growth time is 30-360 min (e.g., 30 min, 100 min, 200 min, 360 min, etc.). The volume ratio of each component in the mixed gas is argon:argon:acetylene = (80-90):(5-10):(5-10), and the total flow rate is 50-150 sccm (e.g., 50 sccm, 100 sccm, 120 sccm, 150 sccm, etc.). After the carbon nanotubes have grown, the acetylene is stopped, and the mixture is naturally cooled to room temperature under a protective atmosphere of hydrogen and argon.

[0050] In a third aspect, this application proposes a sodium-ion battery comprising the positive electrode material described in the first aspect or a positive electrode material prepared using the method described in the second aspect. Therefore, this sodium-ion battery possesses all the features and advantages of the aforementioned positive electrode material and its preparation method, which will not be elaborated further here.

[0051] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0052] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0053] Example 1 This embodiment provides a cathode material (specifically a sodium-ion battery cathode material), comprising a core layer, an intermediate layer, and a shell layer arranged sequentially from the core layer to the shell layer. The core layer comprises a first layered oxide, the chemical formula of which is Na. x Mn α Fe Ni z O2, x is 1.02, α is 1 / 3, β is 1 / 3, z is 1 / 3; The intermediate layer comprises a second layered oxide containing transition metal elements iron, cobalt, and nickel, and the chemical formula of the metal particles is Na. y Co a Fe b Ni c O2, y = 1.02, a = 0.1, b = 0.8, c = 0.1; The shell layer comprises carbon nanotubes, and the size parameters of the carbon nanotubes include: a tube length of 20 μm and a tube outer diameter of 10 nm. The thickness of the intermediate layer is 100 nm, and the thickness of the shell layer is 20 nm.

[0054] The preparation method of the above-mentioned cathode material includes the following steps: Step 1, co-precipitation synthesis of precursor materials: Prepare a mixed sulfate solution of Mn:Fe:Ni = 1:1:1 with a concentration of 1.0 mol / L; prepare a 2 mol / L sodium hydroxide solution and a 1.5 mol / L ammonia solution as precipitant and complexing agent, respectively; under nitrogen protection, slowly add 1000 mL of the mixed sulfate solution to a mixture of 5000 mL of precipitant and complexing agent, control the reaction temperature at 80℃, pH = 11.5, and the stirring rate at 500 rpm, and react for 48 h; after the reaction is completed, stop adding the mixed sulfate solution and extend the reaction time by 6 hours to ensure that the metal salt in the reactor is completely consumed, and obtain a reaction solution containing layered oxide precursor materials.

[0055] Step 2, surface enrichment of iron / cobalt / nickel elements: Prepare a mixed solution of ferrous sulfate, cobalt sulfate, and nickel sulfate with a molar ratio of 8:1:1 and a concentration of 0.1 mol / L; add 100 mL of the above mixed salt solution to the reaction solution containing the layered oxide precursor material obtained in Step 1, stir and adsorb at room temperature of 80°C for 6 h to make the total loading of iron / cobalt / nickel 3 wt%; dry at low temperature of 60°C for 6 h to obtain the precursor material with Fe, Co, and Ni enriched on the surface.

[0056] Step 3, high-temperature solid-state sintering: Weigh 100g of precursor material enriched with Fe, Co, and Ni on the surface and 62g of sodium carbonate according to the stoichiometric ratio, with an excess of 10mol% sodium carbonate. Add the mixture to a high-speed mixer and mix at high speed for 6 hours. Place the mixture into a muffle furnace, pre-fire at 450℃ for 4 hours, and then fire at 850℃ for 12 hours. The heating rate is 3℃ / min, and the furnace is cooled to room temperature to obtain a layered oxide material containing a solid solution of Fe, Co, and Ni enriched layers.

[0057] Step 4, Air activation treatment: The layered oxide material containing Fe, Co, and Ni enriched solid solution obtained in Step 3 is placed in room temperature air for 3 hours to complete the activation.

[0058] Step 5, in-situ growth of carbon nanotubes by low-temperature acetylene CVD (chemical vapor deposition): The activated material obtained in Step 4 is placed in a tube furnace and purged with argon (150 sccm) for 30 min; the temperature is increased to 600℃ at 5℃ / min, and a H2 / Ar mixed gas (H2 volume fraction 10%, total flow rate 80 sccm) is introduced for reduction and activation for 40 min; then a mixed gas of Ar:H2:C2H2=85:5:10 is introduced at a total flow rate of 100 sccm, and CVD growth is carried out for 60 min; the acetylene is stopped, and the material is naturally cooled to room temperature under an H2 / Ar protective atmosphere to obtain the cathode material.

[0059] Example 2 This embodiment prepares the cathode material according to the method described in Example 1. The main difference from Example 1 is that: (1) In step 2, a mixed solution of ferrous sulfate, cobalt sulfate, and nickel sulfate is prepared, with a molar ratio of 6:1:1; correspondingly, the chemical formula of the intermediate metal particles in the obtained cathode material is Na y Co a Fe b Ni c O2, y = 1.02, a = 0.15, b = 0.7, c = 0.15.

[0060] Example 3 This embodiment prepares the cathode material according to the method described in Example 1. The main difference from Example 1 is that: (1) The total loading of iron / cobalt / nickel in step 2 is 5wt%; correspondingly, the thickness of the intermediate layer in the obtained cathode material is 200nm.

[0061] Example 4 This embodiment prepares the cathode material according to the method described in Example 1. The main difference from Example 1 is that: (1) In step 5, the chemical vapor deposition temperature is adjusted from 600℃ to 550℃.

[0062] Example 5 This embodiment prepares the cathode material according to the method described in Example 1. The main difference from Example 1 is that: (1) In step 5, the chemical vapor deposition temperature is adjusted from 600℃ to 650℃.

[0063] Example 6 This embodiment prepares the cathode material according to the method described in Example 1. The main difference from Example 1 is that: (1) The transition metal elements in the layered oxide core layer of the cathode material are two of Mn, Fe and Ni, specifically Mn and Fe.

[0064] The aforementioned cathode material (specifically, a sodium-ion battery cathode material) includes a core layer, an intermediate layer, and a shell layer arranged sequentially from the core layer to the shell layer. The core layer comprises a first layered oxide, the chemical formula of which is Na. x Mn a Fe b O2, x is 1.02, a is 0.5, b is 0.5; The intermediate layer comprises a second layered oxide containing transition metal elements iron, cobalt, and nickel, and the chemical formula of the metal particles is Na. y Co aFe b Ni c O2, y = 1.02, a = 0.1, b = 0.8, c = 0.1; The shell layer comprises carbon nanotubes, and the size parameters of the carbon nanotubes include: a tube length of 20 μm and a tube outer diameter of 10 nm. The thickness of the intermediate layer is 100 nm, and the thickness of the shell layer is 20 nm.

[0065] The preparation method of the above-mentioned cathode material includes the following steps: Step 1, co-precipitation synthesis of precursor materials: Prepare a mixed sulfate solution of ferrous sulfate and manganese sulfate with a concentration of 1.0 mol / L; prepare a 2 mol / L sodium hydroxide solution and a 1.5 mol / L ammonia solution as precipitant and complexing agent, respectively; under nitrogen protection, slowly add 1000 mL of the mixed sulfate solution to a mixture of 5000 mL of precipitant and complexing agent, control the reaction temperature at 80℃, pH=11.5, and stirring rate at 500 rpm, and react for 48 h; after the reaction is completed, stop adding the mixed sulfate solution and extend the reaction time by 6 hours to ensure that the metal salt in the reactor is completely consumed, and obtain a reaction solution containing layered oxide precursor materials.

[0066] Step 2, surface enrichment of iron / cobalt / nickel elements: Prepare a mixed solution of ferrous sulfate, cobalt sulfate, and nickel sulfate with a molar ratio of 8:1:1 and a concentration of 0.1 mol / L; add 100 mL of the above mixed salt solution to the reaction solution containing the layered oxide precursor material obtained in Step 1, stir and adsorb at room temperature of 80°C for 6 h to make the total loading of iron / cobalt / nickel 3 wt%; dry at low temperature of 60°C for 6 h to obtain the precursor material with Fe, Co, and Ni enriched on the surface.

[0067] Step 3, high-temperature solid-state sintering: Weigh 100g of precursor material enriched with Fe, Co, and Ni on the surface and 68g of sodium carbonate according to the stoichiometric ratio, with an excess of 10mol% sodium carbonate. Add the mixture to a high-speed mixer and mix at high speed for 6 hours. Place the mixture into a muffle furnace, pre-fire at 450℃ for 4 hours, and then fire at 850℃ for 12 hours. The heating rate is 3℃ / min, and the furnace is cooled to room temperature to obtain a layered oxide material containing a solid solution of Fe, Co, and Ni enriched layers.

[0068] Step 4, Air activation treatment: The layered oxide material containing Fe, Co, and Ni enriched solid solution obtained in Step 3 is placed in room temperature air for 3 hours to complete the activation.

[0069] Step 5, in-situ growth of carbon nanotubes by low-temperature acetylene CVD (chemical vapor deposition): The activated material obtained in Step 4 is placed in a tube furnace and purged with argon (150 sccm) for 30 min; the temperature is increased to 600℃ at 5℃ / min, and a H2 / Ar mixed gas (H2 volume fraction 10%, total flow rate 80 sccm) is introduced for reduction and activation for 40 min; then a mixed gas of Ar:H2:C2H2=85:5:10 is introduced at a total flow rate of 100 sccm, and CVD growth is carried out for 60 min; the acetylene is stopped, and the material is naturally cooled to room temperature under an H2 / Ar protective atmosphere to obtain the cathode material.

[0070] Example 7 This embodiment prepares the cathode material according to the method described in Example 1. The main difference from Example 1 is that: (1) The transition metal elements in the layered oxide core layer of the cathode material are four of Mn, Fe, Co and Ni, specifically Mn, Fe, Co and Ni.

[0071] The aforementioned cathode material (specifically, a sodium-ion battery cathode material) includes a core layer, an intermediate layer, and a shell layer arranged sequentially from the core layer to the shell layer. The core layer comprises a first layered oxide, the chemical formula of which is Na. x Mn α Fe M Ni z O2, x is 1.02, α is 0.23, β is 0.33, γ is 0.1, z is 0.33; The intermediate layer comprises a second layered oxide containing transition metal elements iron, cobalt, and nickel, and the chemical formula of the metal particles is Na. y Co a Fe b Ni c O2, y = 1.02, a = 0.1, b = 0.8, c = 0.1; The shell layer comprises carbon nanotubes, and the size parameters of the carbon nanotubes include: a tube length of 20 μm and a tube outer diameter of 10 nm. The thickness of the intermediate layer is 100 nm, and the thickness of the shell layer is 20 nm.

[0072] The preparation method of the above-mentioned cathode material includes the following steps: Step 1, co-precipitation synthesis of precursor materials: Prepare a mixed sulfate solution of ferrous sulfate, cobalt sulfate, nickel sulfate, and ferrous sulfate with a concentration of 1.0 mol / L; prepare a 2 mol / L sodium hydroxide solution and a 1.5 mol / L ammonia solution as precipitant and complexing agent, respectively; under nitrogen protection, slowly add 1000 mL of the mixed sulfate solution to a mixture of 5000 mL of precipitant and complexing agent, control the reaction temperature at 80℃, pH=11.5, and stirring rate at 500 rpm, and react for 48 h; after the reaction is completed, stop adding the mixed sulfate solution and extend the reaction time by 6 hours to ensure that the metal salts in the reactor are completely consumed, obtaining a reaction solution containing layered oxide precursor materials.

[0073] Step 2, surface enrichment of iron / cobalt / nickel elements: Prepare a mixed solution of ferrous sulfate, cobalt sulfate, and nickel sulfate with a molar ratio of 8:1:1 and a concentration of 0.1 mol / L; add 100 mL of the above mixed salt solution to the reaction solution containing the layered oxide precursor material obtained in Step 1, stir and adsorb at room temperature of 80°C for 6 h to make the total loading of iron / cobalt / nickel 3 wt%; dry at low temperature of 60°C for 6 h to obtain the precursor material with Fe, Co, and Ni enriched on the surface.

[0074] Step 3, high-temperature solid-state sintering: Weigh 100g of precursor material enriched with Fe, Co, and Ni on the surface and 62g of sodium carbonate according to the stoichiometric ratio, with an excess of 10mol% sodium carbonate. Add the mixture to a high-speed mixer and mix at high speed for 6 hours. Place the mixture into a muffle furnace, pre-fire at 450℃ for 4 hours, and then fire at 850℃ for 12 hours. The heating rate is 3℃ / min, and the furnace is cooled to room temperature to obtain a layered oxide material containing a solid solution of Fe, Co, and Ni enriched layers.

[0075] Step 4, Air activation treatment: The layered oxide material containing Fe, Co, and Ni enriched solid solution obtained in Step 3 is placed in room temperature air for 3 hours to complete the activation.

[0076] Step 5, in-situ growth of carbon nanotubes by low-temperature acetylene CVD (chemical vapor deposition): The activated material obtained in Step 4 is placed in a tube furnace and purged with argon (150 sccm) for 30 min; the temperature is increased to 600℃ at 5℃ / min, and a H2 / Ar mixed gas (H2 volume fraction 10%, total flow rate 80 sccm) is introduced for reduction and activation for 40 min; then a mixed gas of Ar:H2:C2H2=85:5:10 is introduced at a total flow rate of 100 sccm, and CVD growth is carried out for 60 min; the acetylene is stopped, and the material is naturally cooled to room temperature under an H2 / Ar protective atmosphere to obtain the cathode material.

[0077] Comparative Example 1 The difference between this comparative example and Example 1 is that: (1) The cathode material consists only of the layered oxide core layer in Example 1; correspondingly, its preparation method mainly includes drying the reaction solution containing the layered oxide precursor material obtained in step 1 of Example 1 at low temperature for 6 hours at 60°C and then performing high-temperature solid-state sintering in step 3.

[0078] Comparative Example 2 The difference between this comparative example and Example 1 is that: (1) The cathode material consists only of the layered oxide core layer in Example 1 and the intermediate layer in Example 1; correspondingly, its preparation method mainly includes steps 1, 2 and 3 in Example 1.

[0079] Comparative Example 3 The difference between this comparative example and Example 1 is that: (1) The cathode material consists only of the layered oxide core layer in Example 1 and the shell layer in Example 1; correspondingly, its preparation method mainly includes drying the reaction solution containing the layered oxide precursor material obtained in step 1 of Example 1 at low temperature of 60°C for 6 hours, followed by high temperature solid-state sintering in step 3, air activation treatment in step 4, and low temperature acetylene CVD (chemical vapor deposition) in-situ growth of carbon nanotubes in step 5.

[0080] Comparative Example 4 The difference between this comparative example and Example 1 is that: (1) Step 2, surface enrichment of iron: prepare a ferrous sulfate solution with a concentration of 0.1 mol / L; add 100 mL of the above salt solution to the reaction solution of the layered oxide precursor material obtained in step 1, stir and adsorb at room temperature of 80°C for 6 h to make the iron loading 3 wt%; dry at low temperature of 60°C for 6 h to obtain the precursor material with Fe enrichment on the surface.

[0081] Comparative Example 5 The main difference between this comparative example and Example 1 is: (1) In step 2, a mixed solution of ferrous sulfate, cobalt sulfate, and nickel sulfate is prepared, with a molar ratio of 1:1:1; correspondingly, the chemical formula of the intermediate metal particles in the obtained cathode material is Na y Co a Fe b Ni c O2, y is 1.02, a is 0.33, b is 0.33, c is 0.33.

[0082] Test case The sodium-ion battery positive electrode material from the above examples and comparative examples was mixed with conductive carbon black and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. After mixing, the mixture was dissolved in N-methylpyrrolidone (NMP) to form a slurry, which was then coated onto aluminum foil. After drying and cutting, a positive electrode sheet was obtained. The obtained positive electrode sheet was assembled with sodium metal and a separator (Celgard 2400) into a battery case, and an electrolyte was injected. After standing for 24 hours and the voltage was stabilized, a sodium-ion battery was obtained. The electrolyte solvent was a mixture of EC and PC in a volume ratio of 1:1, and the solute was 1M NaClO4.

[0083] This test example tests the conductivity of the cathode materials obtained from the above embodiments and comparative examples. The test results are shown in Table 1.

[0084] Table 1

[0085] This test example demonstrates the conductivity of the cathode materials obtained from the above embodiments and comparative examples. The test results are shown in Table 2.

[0086] Table 2

[0087] As can be seen from Tables 1 and 2, the conductivity of the cathode material provided in the embodiments of this application is significantly improved compared with comparative examples 1-5.

[0088] Furthermore, the scanning electron microscope (SEM) image of the precursor material with Fe, Co, and Ni enriched on its surface obtained in step 2 of Example 1 of this application is shown below. Figure 1 As shown, and the scanning electron microscope (SEM) image of the cathode material obtained in Example 1, are as follows. Figure 2 As shown. Meanwhile, Figure 3 The diagram shows the structure of the cathode material obtained in Example 1, indicating that it has a core layer, an intermediate layer, and a shell layer in sequence from the core layer to the shell layer, which gives it better structural stability.

[0089] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A cathode material based on sodium-ion batteries, characterized in that, It includes a core, an intermediate layer, and a shell arranged sequentially from the core to the shell. The core layer comprises a first layered oxide, wherein the first transition metal element in the first layered oxide comprises at least two of Mn, Fe and Ni; The intermediate layer comprises a second layered oxide, wherein the second transition element in the second layered oxide comprises Fe, Co, and Ni, and the chemical composition of the second layered oxide is shown in Chemical Formula II, wherein Chemical Formula II: Na y Co a Fe b Ni c O2, wherein b satisfies: 1 > b ≥ 0.6; the molar ratio of Fe, Co, and Ni in the second layered oxide is (0.6-0.9):(0.05-0.3):(0.05-0.3). The shell layer comprises carbon nanotubes.

2. The cathode material according to claim 1, characterized in that, The chemical composition of the first layered oxide is shown in chemical formula I; The chemical formula I: Na x Mn α Fe M Ni z O2; where 0.6≤x≤1.15, α+β+γ+z=1, and α, β, and z are all greater than 0, γ≥0, and M includes Co.

3. The cathode material according to claim 1, characterized in that, 0.6≤y≤1.15, a+b+c=1, and 1>a>0, 1>b>0, 1>c>0.

4. The cathode material according to any one of claims 1-3, characterized in that, The dimensional parameters of the carbon nanotubes include: tube length of 1μm-50μm and tube outer diameter of 5nm-30nm.

5. The cathode material according to any one of claims 1-3, characterized in that, The carbon nanotubes are coated and interspersed between the metal particles to form a continuous three-dimensional conductive network.

6. The cathode material according to claim 1, characterized in that, The thickness of the intermediate layer is 20nm-1000nm; And / or, the thickness of the shell layer is 5nm-100nm.

7. A method for preparing the cathode material according to any one of claims 1-6, characterized in that, Includes the following steps: Layered oxide precursor materials were synthesized using a co-precipitation method; The layered oxide precursor material is placed in a mixed salt solution containing Fe, Co, and Ni for surface enrichment to form a precursor material with Fe, Co, and Ni enriched on the surface. The precursor material enriched with Fe, Co, and Ni on the surface is mixed with sodium salt and then subjected to solid-state sintering to obtain a layered oxide material containing a solid solution of Fe, Co, and Ni enriched layers on the surface. The layered oxide material containing Fe, Co, and Ni enriched solid solutions on its surface is activated in air, and then carbon nanotubes are grown in situ on the material surface using chemical vapor deposition to obtain the cathode material.

8. The method for preparing the cathode material according to claim 7, characterized in that, The steps for synthesizing layered oxide precursor materials using the co-precipitation method include the following: In an inert gas atmosphere, a mixed metal salt containing transition metals, a precipitant, and a complexing agent are subjected to a co-precipitation reaction at a reaction temperature of 50℃-90℃ and a reaction pH of 9.0-12.0 to obtain a layered oxide precursor material. And / or, the total loading of Fe, Co, and Ni accounts for 1%-5% of the mass of the layered oxide precursor material.

9. The method for preparing the cathode material according to claim 7, characterized in that, The solid-state sintering includes a first sintering and a second sintering, wherein the temperature of the first sintering is 400℃-500℃ and the temperature of the second sintering is 800℃-900℃. And / or, the steps for obtaining the cathode material by in-situ growth of carbon nanotubes on the material surface using chemical vapor deposition include the following processes: The activated material is then heated to 550-650℃ after being purged with an inert gas system. Reduction and activation are achieved by introducing a mixture of hydrogen and inert gas; A mixture of inert gas, hydrogen, and acetylene is introduced to grow carbon nanotubes in situ on the material surface, thus obtaining the cathode material.

10. A sodium-ion battery, characterized in that, This includes the cathode material as described in any one of claims 1-6 or the cathode material prepared by the method described in any one of claims 7-9.

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