Negative active material and preparation method thereof, negative plate and battery

Abstract

The invention relates to the technical field of batteries, in particular to a negative active material, a preparation method thereof, a negative plate and a battery. The negative electrode active material is of a fiber tubular structure, a framework of the fiber tubular structure is of a shell-core structure, and the shell-core structure comprises (a) an inner core which comprises a TaSe2 / Ta heterojunction; (b) a first shell layer disposed on the surface of the inner core; the first shell layer comprises a C element and an N element; the second shell layer is arranged on the surface, far away from the inner core, of the first shell layer; and the second shell layer comprises a C element, an N element and a Se element. The negative electrode active material can solve the problems of short cycle life and capacity fading of a TaSe2 negative electrode and the problem of stress release of the material in the reaction process.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to negative electrode active materials and preparation methods thereof, negative electrode sheets and batteries. Background Art

[0002] Due to the urgent need for energy storage and conversion, lithium-ion batteries and sodium-ion batteries, as representatives of rechargeable batteries, have gradually been integrated into daily life in the past few decades. The negative electrode materials of these two batteries largely determine the electrochemical performance of the batteries. It is crucial to develop negative electrode materials with low cost and high performance.

[0003] Transition metal selenides are considered to be very promising anode materials for sodium-ion batteries and lithium-ion batteries due to their high theoretical specific capacity and wide availability. 2 ) stands out due to its high theoretical specific capacity and good electrochemical reaction activity, but it shows severe capacity decay, especially in the initial stage of the cycle, which is usually caused by its severe volume effect and slow kinetics. To solve these problems, special nanoparticles are usually designed to shorten ion transport and increase the availability of active materials, a coated carbon composite layer is constructed to suppress the volume effect and enhance conductivity, and an internal electric field is constructed through vacancy defect engineering to improve ionic conductivity. Although the above strategies have some effect, TaSe 2 There are still major challenges in achieving long cycle life of negative electrodes. It is necessary to choose a faster and more sustainable method to solve the problem of TaSe 2 The negative electrode has short cycle life and capacity attenuation problems, as well as stress release problems of the material during the reaction process. Summary of the invention

[0004] In view of this, the present invention provides a negative electrode active material and a preparation method thereof, a negative electrode sheet and a battery. The negative electrode active material can solve the problem of TaSe 2 The negative electrode has short cycle life and capacity attenuation problems, as well as stress release problems of the material during the reaction process.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides a negative electrode active material, wherein the negative electrode active material is in a fiber tubular structure, the skeleton of the fiber tubular structure has a shell-core structure, and the shell-core structure comprises:

[0007] (a) Core, the core includes TaSe 2 / Ta heterojunction;

[0008] (b) a first shell layer, the first shell layer is disposed on the surface of the inner core; the first shell layer includes C elements and N elements;

[0009] (c) a second shell layer, wherein the second shell layer is disposed on a surface of the first shell layer away from the inner core; the second shell layer comprises C element, N element and Se element.

[0010] Preferably, the length of the fiber tubular structure is 50 to 1000 μm.

[0011] Preferably, the cross-sectional radius of the fiber tubular structure is 200-800 nm.

[0012] Preferably, the aspect ratio of the fiber tubular structure is 50:1 to 500:1.

[0013] Preferably, the tube wall of the fiber tubular structure has a plurality of hole structures.

[0014] Preferably, the average pore diameter of the pore structure is 2 to 100 nm.

[0015] Preferably, the mass ratio of the inner core to the first shell is 100:(3-8).

[0016] Preferably, the mass ratio of the inner core to the second shell is 100:(5-10).

[0017] Preferably, the diameter of the inner core is 100-700 nm.

[0018] Preferably, the thickness of the first shell layer is 50-200 nm.

[0019] Preferably, the thickness of the second shell layer is 10-50 nm.

[0020] As a preferred embodiment, in the core, TaSe 2 The mass ratio of Ta is (75~90):(10~25).

[0021] Preferably, in the first shell layer, the mass ratio of C element to N element is (70-90):(10-30).

[0022] Preferably, in the second shell layer, the mass ratio of C element, N element and Se element is (60-80):(10-20):(10-20).

[0023] Preferably, the ratio of the mass proportion of the C element in the first shell layer to the mass proportion of the C element in the second shell layer is (1.2-1.5):1.

[0024] Preferably, the ratio of the mass proportion of the N element in the first shell layer to the mass proportion of the N element in the second shell layer is (1.5-3):1.

[0025] In a second aspect, the present invention provides a method for preparing the above-mentioned negative electrode active material, comprising the following steps:

[0026] S1, mixing a template, a morphology control agent, a selenium source, a tantalum source and a first solvent to obtain a precursor solution, electrospinning the precursor solution, and obtaining a first nanofiber after drying;

[0027] S2, subjecting the first nanofiber to a first calcination treatment in an oxygen atmosphere, and then subjecting the first nanofiber to a carbonization treatment in an inert gas atmosphere to obtain a second nanofiber;

[0028] S3, washing the second nanofibers with a second solvent to remove the template in the second nanofibers, and obtaining third nanofibers after drying;

[0029] S4, mixing the nitrogen-containing carbon source and the third solvent to obtain a nitrogen-containing carbon source solution; immersing the third nanofiber in the nitrogen-containing carbon source solution, stirring under vacuum, centrifuging, and drying to obtain a fourth nanofiber;

[0030] S5, in an inert gas atmosphere, subjecting the fourth nanofiber and the selenium powder to a second calcination treatment to obtain a negative electrode active material.

[0031] In step S1 of the above preparation method:

[0032] In an embodiment of the present invention, the template includes at least one of potassium chloride, potassium nitrate, potassium sulfate and potassium chromium sulfate.

[0033] In an embodiment of the present invention, the morphology control agent includes at least one of polyvinyl pyrrolidone, hexadecyltrimethylammonium bromide, urea, amino acid, polyamide, and polyurea.

[0034] In an embodiment of the present invention, the selenium source includes selenol, sodium selenate, sodium selenite, selenoester, selenourea, preferably at least one of selenol.

[0035] In an embodiment of the present invention, the tantalum source includes at least one of tantalum acetate, tantalum chloride, tantalum oxide, and tantalum fluoride.

[0036] In an embodiment of the present invention, the first solvent includes an aqueous solvent.

[0037] Preferably, the molar ratio of the template, morphology control agent, selenium source and tantalum source is (0.5-1.5):(1-2):(2.5-3.5):(4-6).

[0038] Preferably, the flow rate of electrospinning is 0.1-0.2 mm / min, the distance between the nozzle tip and the collector is 12 cm, and the voltage is 18-22 kV.

[0039] In step S2 of the above preparation method:

[0040] Preferably, the temperature of the first calcination treatment is 200-400°C, the time of the first calcination treatment is 2-6 hours, and the heating rate of the first calcination treatment is 1-5°C min -1 .

[0041] Preferably, the temperature of the carbonization treatment is 400-600° C., and the time of the carbonization treatment is 2-6 hours.

[0042] In step S3 of the above preparation method:

[0043] In an embodiment of the present invention, the second solvent includes water and / or anhydrous ethanol.

[0044] Preferably, the washing is performed 2 to 5 times.

[0045] In step S4 of the above preparation method:

[0046] In an embodiment of the present invention, the nitrogen-containing carbon source includes at least one of polyacrylonitrile, urea, melamine and acrylonitrile.

[0047] In an embodiment of the present invention, the third solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and acetone.

[0048] Preferably, in g / mL, the mass volume ratio of the nitrogen-containing carbon source to the third solvent is (0.1-1):10.

[0049] Preferably, the stirring treatment time is 5 to 8 hours.

[0050] In step S5 of the above preparation method:

[0051] Preferably, the mass ratio of the fourth nanofiber to the selenium powder is 1:(2-6).

[0052] Preferably, the temperature of the second calcination treatment is 450-650°C, the time of the second calcination treatment is 2-6 hours, and the heating rate of the second calcination treatment is 1-5°C min -1 .

[0053] In a third aspect, the present invention provides a negative electrode sheet, which includes the negative electrode active material mentioned above, and / or the negative electrode active material prepared by the above preparation method.

[0054] In a fourth aspect, the present invention provides a battery comprising the above-mentioned negative electrode sheet.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] 1. The negative electrode active material of the present invention (TaSe 2 / Ta@NC@NSePCNFs) can effectively improve the conductivity of the material.

[0057] 2. The negative electrode active material of the present invention (TaSe 2 The fibrous structure of / Ta@NC@NSePCNFs) presents a porous structure on the surface, which provides abundant electrochemical active sites, is conducive to achieving higher sodium and lithium ion storage capacity, and is beneficial to the penetration of electrolyte and shortening the diffusion path of ions.

[0058] 3. In the present invention, TaSe in the core 2 While providing capacity, Ta and Ni can also form a heterojunction structure and a built-in electric field, thereby improving conductivity and ion diffusion rate.

[0059] 4. The first shell (NC layer) is rich in Na + / Li + Chemical anchoring sites accelerate electron / ion transport, and the NC layer can cover TaSe 2 / Ta core, providing sufficient stress release space and improving the battery's cycle performance.

[0060] 5. The second shell layer (NSePCNFs layer) covers the NC layer to form a double-layer coating structure, further providing TaSe 2 / Ta core stress release space improves the cycle, and the C and N elements in the NSePCNFs layer improve the conductivity, and the Se element provides more capacity.

[0061] 6. Both the first shell (NC layer) and the second shell (NSePCNFs layer) contain C and N elements, which can + / Li + It has a strong physical restraint effect, promoting Na + / Li + The C and N elements in the two layers form a gradient relationship, which can form a unique channel structure that is conducive to the transmission of Na + / Li + High-speed transmission between layers. In addition, this unique gradient distribution structure can make the internal electric field more uniform, reduce local overvoltage or discharge, and improve battery safety.

[0062] 7. The first shell (NC layer) is located in the core (TaSe 2 / Ta) and the second shell (NSePCNFs layer), which can optimize the ion transmission channel and reduce Na + / Li +It can penetrate the resistance of electrode materials during the charge and discharge process; change the surface chemical environment of electrode materials to increase the electrochemical reaction rate and efficiency; and enhance the bonding between layers, which is beneficial to improving the stability of the overall electrode material.

[0063] Therefore, the negative electrode active material of the present invention can solve the problem of TaSe 2 The negative electrode has short cycle life and capacity attenuation problems, as well as stress release problems of the material during the reaction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 : TaSe prepared in Example 1 2 / Ta@NC@NSePCNFs material SEM image (500nm).

[0065] Figure 2 : TaSe prepared in Example 1 2 SEM image of / Ta@NC@NSePCNFs material (2μm).

[0066] Figure 3 : TaSe prepared in Example 1 2 TEM image of the core-shell structure of / Ta@NC@NSePCNFs material (500nm). DETAILED DESCRIPTION

[0067] The present invention discloses a negative electrode active material and a preparation method thereof, a negative electrode sheet and a battery. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve the same. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are deemed to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0068] In the description of the present invention, it should be noted that the terms "first", "second", etc. are only used for descriptive purposes, and do not indicate or imply relative importance.

[0069] In the description of the present invention, a list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A, B are listed, the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, C are listed, the phrase "at least one of A, B, C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0070] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0071] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0072] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0073] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0074] Specifically, the present invention adopts the following technical solutions:

[0075] In a first aspect, the present invention provides a negative electrode active material, wherein the negative electrode active material is in a fiber tubular structure, the skeleton of the fiber tubular structure has a shell-core structure, and the shell-core structure comprises:

[0076] (a) Core, the core includes TaSe 2 / Ta heterojunction;

[0077] (b) a first shell layer, the first shell layer is disposed on the surface of the inner core; the first shell layer includes C elements and N elements;

[0078] (c) a second shell layer, wherein the second shell layer is disposed on a surface of the first shell layer away from the inner core; the second shell layer comprises C element, N element and Se element.

[0079] The negative electrode active material (TaSe 2 The fibrous structure of / Ta@NC@NSePCNFs) can effectively improve the conductivity of the material, facilitate the penetration of the electrolyte, and shorten the diffusion path of ions. The advantages of the core-shell structure are: ① TaSe in the core 2 / Ta can form a heterojunction structure while providing capacity, forming a built-in electric field, thereby improving conductivity and ion diffusion rate. ② The first shell (NC layer) is rich in Na + / Li + Chemical anchoring sites accelerate electron / ion transport, and the NC layer can cover TaSe 2 / Ta core, providing sufficient stress release space and improving the cycle performance of the battery. ③ The second shell layer (NSePCNFs layer) covers the first shell layer (NC layer) to form a double-layer coating structure, further providing TaSe 2 / Ta core stress release space, improve the cycle, and the C and N elements in the second shell (NSePCNFs layer) improve the conductivity, and Se elements provide more capacity. ④ Both the first shell (NC layer) and the second shell (NSePCNFs layer) contain C and N elements, which can + / Li + It has a strong physical restraint effect, promoting Na + / Li + ⑤The first shell (NC layer) is located in the core (TaSe 2 / Ta) and the second shell (NSePCNFs layer), which can optimize the ion transmission channel and reduce Na + / Li + It can penetrate the resistance of electrode materials during the charge and discharge process; change the surface chemical environment of electrode materials to increase the electrochemical reaction rate and efficiency; and enhance the bonding between layers, which is beneficial to improving the stability of the overall electrode material.

[0080] Preferably, the length of the fiber tubular structure is 50 to 1000 μm. Exemplarily, the length of the fiber tubular structure is any value among 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, or any value within the range of any two of the above values. Within the above length range, the fiber tubular structure can effectively improve the conductivity of the material, facilitate the penetration of the electrolyte, and shorten the diffusion path of the ions.

[0081] Preferably, the cross-sectional radius of the fiber tubular structure is 200-800 nm. Exemplarily, the cross-sectional radius of the fiber tubular structure is any value among 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm or any value within the range of any two of the above values. Within the above cross-sectional radius range, the fiber tubular structure can effectively improve the conductivity of the material, facilitate the penetration of the electrolyte, and shorten the diffusion path of the ions.

[0082] Preferably, the aspect ratio of the fiber tubular structure is 50:1 to 500:1. Exemplarily, the aspect ratio of the fiber tubular structure is any one of 50:1, 100:1, 200:1, 300:1, 400:1, 500:1 or any value within the range of any two of the above values. The aspect ratio is the ratio of the length of a single hollow fiber tubular structure to the radius of the cross section. If the aspect ratio is too large, the fibers are prone to entanglement, breakage or uneven distribution in the matrix; in addition, a too large aspect ratio may cause the material to be easily buckled when subjected to external force, thereby reducing the cyclic stability of the overall material. If the aspect ratio is too small, the specific surface area of ​​the material is reduced, which may affect the Na + / Li + adsorption or capacity storage properties.

[0083] Preferably, the tube wall of the fiber tubular structure has a plurality of pore structures and presents a porous network structure. The pore structure provides abundant electrochemical active sites, which is conducive to achieving higher sodium ion and lithium ion storage capacity.

[0084] Preferably, the average pore size of the pore structure is 2 to 100 nm. Exemplarily, the average pore size of the pore structure is any value among 2 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or any value within the range of any two of the above values. If the average pore size is too large, the organic solvent molecules in the electrolyte may enter the pores more easily and react with the active materials in an unnecessary manner, thereby affecting the cycle stability and life of the battery; if the average pore size is too small, the diffusion resistance of ions in a small space will increase significantly, which will seriously limit the Na + / Li + The transmission speed decreases, resulting in a decrease in battery performance during high-rate charge and discharge.

[0085] Preferably, the mass ratio of the core to the first shell is 100:(3-8). Exemplarily, the mass ratio of the core to the first shell is any value in 100:3, 100:4, 100:5, 100:6, 100:7, 100:8 or any value in the range of any two of the above values. The mass ratio of the first shell is too large, resulting in the core TaSe used for energy storage. 2 The mass proportion of the Ta / Ta active material is relatively reduced, which will reduce the overall energy density of the negative electrode active material; the mass proportion of the first shell layer is too small to provide sufficient conductivity and structural support for the negative electrode active material, thus affecting the battery's rate performance and cycle stability.

[0086] Preferably, the mass ratio of the core to the second shell is 100:(5-10). Exemplarily, the mass ratio of the core to the second shell is any value among 100:5, 100:6, 100:7, 100:8, 100:9, 100:10 or any value within the range of any two of the above values. If the mass proportion of the second shell is too large, the manufacturing cost of the second shell is high, and excessive use will increase the total cost of the negative electrode active material; if the mass proportion of the second shell is too small, it is impossible to form a sufficient conductive network to ensure the rapid transmission of electrons in the negative electrode active material. At the same time, the morphology control will be insufficient, resulting in the structure of the negative electrode active material being not uniform or stable enough.

[0087] Preferably, the diameter of the core is 100 to 700 nm. Exemplarily, the diameter of the core is any value among 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, or any value within the range of any two of the above values. Within the above diameter range, TaSe 2 / Ta not only provides sufficient capacity, but also can form a good built-in electric field, thereby improving conductivity and ion diffusion rate.

[0088] Preferably, the thickness of the first shell layer is 50 to 200 nm. Exemplarily, the thickness of the first shell layer is any value among 50 nm, 100 nm, 150 nm, 200 nm, or any value within the range of values ​​formed by any two of the above values. If the first shell layer is too thick, the internal resistance of the negative electrode active material will increase and the transmission efficiency of electrons and ions will be reduced; if the first shell layer is too thin, it will not effectively provide sufficient conductivity and volume change control capability.

[0089] Preferably, the thickness of the second shell layer is 10 to 50 nm. Exemplarily, the thickness of the second shell layer is any value among 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, or any value within the range of any two of the above values. If the second shell layer is too thick, it will occupy too much volume of the negative electrode active material, reducing the core TaSe2 / Ta and the effective contact area of ​​the first shell, and thicker fibers or denser networks may increase the Na + / Li + The transmission resistance reduces the power output of the battery; if the second shell is too thin, the negative electrode active material is prone to breakage or agglomeration, affecting the overall structural stability of the negative electrode active material.

[0090] As a preferred embodiment, in the core, TaSe 2 The mass ratio of Ta to Se is (75-90): (10-25). 2 The mass ratio of TaSe to Ta is any value among 75:25, 80:20, 85:15, 90:10 or any value within the range of any two of the above values. 2 While providing capacity, Ta and Ni can also form a heterojunction structure and a built-in electric field, thereby improving conductivity and ion diffusion rate.

[0091] Preferably, in the first shell layer, the mass ratio of C element to N element is (70-90):(10-30). Exemplarily, the mass ratio of C element to N element is any value among 70:30, 75:25, 80:20, 85:15, 90:10 or any value within the range consisting of any two of the above values.

[0092] Preferably, in the second shell layer, the mass ratio of C element, N element and Se element is (60-80): (10-20): (10-20). Exemplarily, the mass ratio of C element, N element and Se element is any value in 60:20:20, 65:20:15, 70:15:15, 75:10:15, 80:10:10 or any value in the range of any two of the above values. If the mass proportion of Se element is too large, the structure of the second shell layer will become loose, affecting the mechanical strength and stability of the fiber, and too much Se may also cause adverse side reactions in the electrochemical process, such as forming unstable selenides or affecting Na + / Li + If the mass proportion of Se element is too small, the high capacity advantage of Se element cannot be fully utilized, and too little Se content may also lead to insufficient active sites formed in the second shell, thus limiting the further improvement of capacity.

[0093] In the present invention, both the first shell (NC layer) and the second shell (NSePCNFs layer) contain C and N elements at the same time. The concentrations of C and N elements in the two layers gradually decrease from the first shell to the second shell, forming a concentration gradient relationship. This concentration gradient relationship helps to reduce stress concentration at the interface and improve the overall stability of the material. At the same time, this concentration gradient relationship makes the first shell and the second shell form a unique ion channel structure, which is beneficial to Na + / Li + High-speed transmission between layers. In addition, this unique gradient distribution structure can make the internal electric field more uniform, reduce local overvoltage or discharge, and improve battery safety.

[0094] Preferably, the ratio of the mass proportion of C elements in the first shell to the mass proportion of C elements in the second shell is (1.2-1.5):1. Exemplarily, the ratio of the mass proportion of C elements in the first shell to the mass proportion of C elements in the second shell is any value in 1.2:1, 1.3:1, 1.4:1, 1.5:1 or any value in the range of any two of the above values. If the ratio is too large, the proportion of non-C elements in the second shell is high, and the C element as the conductive network skeleton is relatively insufficient, resulting in a decrease in the conductivity of the second shell, affecting the transmission efficiency of electrons in the negative electrode active material; if the ratio is too small, the overall conductivity and structural stability of the negative electrode active material will be reduced.

[0095] Preferably, the ratio of the mass proportion of the N element in the first shell to the mass proportion of the N element in the second shell is (1.5-3):1. Exemplarily, the ratio of the mass proportion of the N element in the first shell to the mass proportion of the N element in the second shell is any value of 1.5:1, 2:1, 2.5:1, 3:1 or any value within the range of any two of the above values. If the ratio is too large, it will lead to instability of the material structure, especially under high temperature or electrochemical conditions; if the ratio is too small, the performance improvement brought by N doping cannot be fully utilized, and the conductivity and surface activity are insufficient.

[0096] In a second aspect, the present invention provides a method for preparing the above-mentioned negative electrode active material, comprising the following steps:

[0097] S1, mixing a template, a morphology control agent, a selenium source, a tantalum source and a first solvent to obtain a precursor solution, electrospinning the precursor solution, and obtaining a first nanofiber after drying;

[0098] S2, subjecting the first nanofiber to a first calcination treatment in an oxygen atmosphere, and then subjecting the first nanofiber to a carbonization treatment in an inert gas atmosphere to obtain a second nanofiber;

[0099] S3, washing the second nanofibers with a second solvent to remove the template in the second nanofibers, and obtaining third nanofibers after drying;

[0100] S4, mixing the nitrogen-containing carbon source and the third solvent to obtain a nitrogen-containing carbon source solution; immersing the third nanofiber in the nitrogen-containing carbon source solution, stirring under vacuum, centrifuging, and drying to obtain a fourth nanofiber;

[0101] S5, in an inert gas atmosphere, subjecting the fourth nanofiber and the selenium powder to a second calcination treatment to obtain a negative electrode active material.

[0102] In the above preparation method, step S1 is used to form the carbon skeleton (Ta-based precursor nanofiber) of the negative electrode active material of the present invention; step S2 is used to form the hollow structure of the carbon skeleton and the pore structure of the tube wall, as well as the growth and graphitization of the carbon skeleton; step S3 is used to remove the template and form the second shell; step S4 is used to add the carbon source and nitrogen source for preparing the first shell; step S5 is used to react the tantalum source and selenium powder to generate TaSe 2 / Ta heterojunction, and carbonization of the carbon source and the nitrogen source in the first shell layer to form the first shell layer.

[0103] In step S1 of the above preparation method:

[0104] In an embodiment of the present invention, the template comprises at least one of potassium chloride, potassium nitrate, potassium sulfate, and potassium red alum. The template provides a temporary, ordered structure or framework for the reaction system to control and guide the morphology, structure, and pore distribution of the final product. Potassium chloride is preferred, as potassium chloride is not prone to decomposition or harmful side reactions with other components, has good diffusivity and reactivity, and is conducive to generating a more uniform and ordered structure.

[0105] In an embodiment of the present invention, the morphology control agent includes at least one of polyvinyl pyrrolidone, hexadecyl trimethyl ammonium bromide, urea, amino acid, polyamide, and polyurea. The morphology control agent adjusts the reaction conditions, changes the interaction between the reactants, and affects the nucleation and growth process of the crystal, thereby achieving precise control of the morphology of the target material. Moreover, the morphology control agent is a nitrogen-containing organic matter. During calcination and carbonization, the morphology control agent decomposes and releases nitrogen atoms, which are then incorporated into the carbonaceous skeleton to form nitrogen-containing carbon nanofibers. Polyvinyl pyrrolidone is preferred, and the multiple functional groups on the polyvinyl pyrrolidone molecular chain can interact with the surface of the nanomaterial by dipole-dipole interaction to form a stable interaction, thereby effectively controlling the growth and morphology of the nanomaterial.

[0106] In an embodiment of the present invention, the selenium source includes selenol, sodium selenate, sodium selenite, selenoester, selenourea, preferably at least one of selenol. The selenium source is used to form the Se element in the second shell. Selenol is preferred, which has the advantages of high reactivity, easy control, and the ability to directly introduce selenium.

[0107] In an embodiment of the present invention, the tantalum source includes at least one of tantalum acetate, tantalum chloride, tantalum oxide, and tantalum fluoride. The tantalum source is used to form the TaSe in the core. 2 / Ta heterojunction. Tantalum acetate is preferred, as it is beneficial to optimizing the structure of the product, improving the performance of the product and enhancing the stability of the product.

[0108] In an embodiment of the present invention, the first solvent includes an aqueous solvent, such as water, deionized water, etc.

[0109] Preferably, the molar ratio of the template, the morphology control agent, the selenium source, and the tantalum source is (0.5-1.5): (1-2): (2.5-3.5): (4-6). Exemplarily, the molar ratio of the template, the morphology control agent, the selenium source, and the tantalum source is any value in 0.5:2:2.5:6, 1:1.5:3:5, 0.5:1:2.5:5, 1.5:1:3.5:5, 1:2:3:5, 1.5:1:3.5:4, or any value in the range of any two of the above values.

[0110] Preferably, the flow rate of electrospinning is 0.1-0.2 mm / min, the distance between the nozzle tip and the collector is 12 cm, and the voltage is 18-22 kV. Exemplarily, the flow rate of electrospinning is any value in 0.1 mm / min, 0.12 mm / min, 0.14 mm / min, 0.16 mm / min, 0.18 mm / min, 0.2 mm / min, or any value in the range of any two of the above values, and the voltage is any value in 18 kV, 19 kV, 20 kV, 21 kV, 22 kV, or any value in the range of any two of the above values.

[0111] In step S2 of the above preparation method:

[0112] Preferably, the temperature of the first calcination treatment is 200-400° C. Exemplarily, the temperature of the first calcination treatment is any value among 200° C., 250° C., 300° C., 350° C., 400° C., or any value within the range consisting of any two of the above values.

[0113] Preferably, the first calcination treatment time is 2 to 6 hours. Exemplarily, the first calcination treatment time is any value among 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours, or any value within the range of any two of the above values.

[0114] Preferably, the heating rate of the first calcination treatment is 1-5°C min -1 For example, the heating rate of the first calcination treatment is 1°C min -1 、2℃min -1 、3℃min -1 、4℃min -1 、5℃min -1 Any value in or any value in the range consisting of any two of the above values.

[0115] In the first calcination treatment stage, the first nanofibers mainly undergo the following changes:

[0116] (1) Oxidative decomposition of organic matter: Organic matter such as morphology control agents and selenium sources will undergo oxidation reactions in the presence of oxygen and gradually decompose into small molecular gases such as carbon dioxide and water vapor. The release of these gases helps to form pores in the material.

[0117] (2) Stabilization of inorganic substances: The template may undergo partial thermal decomposition at this stage to remove the crystal water or other volatile impurities therein, thereby improving its purity. At the same time, the crystal structure of the template may change to form a more stable crystal form.

[0118] (3) Ta and possible Ta compounds (such as Ta oxides or sulfides) may also undergo certain transformations in an oxygen atmosphere, but the decomposition of their outer organic matter may protect them from severe oxidation to a certain extent.

[0119] Preferably, the temperature of the carbonization treatment is 400-600° C. Exemplarily, the temperature of the carbonization treatment is any value among 400° C., 450° C., 500° C., 550° C., 600° C., or any value within the range consisting of any two of the above values.

[0120] Preferably, the carbonization treatment time is 2 to 6 hours. Exemplarily, the carbonization treatment time is any value among 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours, or any value within the range of any two of the above values.

[0121] During the carbonization process, the first nanofibers undergo the following changes:

[0122] (1) Carbonization of organic residues: Organic residues that are not completely decomposed by the morphology control agent during the calcination process (partial carbonization products of the morphology control agent) will be further carbonized during the carbonization process to form a carbonaceous skeleton, which is the basis for the subsequent formation of carbon nanofibers.

[0123] (2) Catalytic effect of inorganic substances: Templates may play a catalytic role in the carbonization process and promote the graphitization of the carbonaceous skeleton. The presence of templates can reduce the graphitization temperature of carbonaceous materials and accelerate the graphitization process. In addition, templates may also accelerate the growth of carbon nanofibers by providing catalytic active sites or promoting the diffusion of carbon atoms.

[0124] (3) Growth and graphitization of carbon nanofibers: During the carbonization process, as the temperature increases and the time increases, the carbonaceous skeleton will further grow and graphitize. In particular, under the catalytic effect of the template, the growth rate of carbon nanofibers may be accelerated and it is easier to form a graphitized structure. These graphitized carbon nanofibers have high conductivity and mechanical strength.

[0125] In step S3 of the above preparation method:

[0126] In an embodiment of the present invention, the second solvent includes water and / or anhydrous ethanol.

[0127] Preferably, the number of washings is 2 to 5. Exemplarily, the number of washings is any value among 2, 3, 4, 5, or any value within a range consisting of any two of the above values.

[0128] In step S4 of the above preparation method:

[0129] In an embodiment of the present invention, the nitrogen-containing carbon source includes polyacrylonitrile (PAN), urea (CO(NH 2 ) 2 ), melamine (C 3 H 6 N 6 ), acrylonitrile (C 3 H 3 N). PAN is preferred, as PAN contains a large amount of C and N elements in its molecular chain, and is the most direct and efficient C and N source; and PAN is relatively stable under normal conditions and is not easy to decompose or deteriorate.

[0130] In an embodiment of the present invention, the third solvent includes at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), and acetone. DMF is preferred, as DMF has excellent solubility for PAN and is not prone to side reactions with PAN or other reactants.

[0131] Preferably, in g / mL, the mass volume ratio of the nitrogen-containing carbon source to the third solvent is (0.1-1): 10. Exemplarily, the mass volume ratio of the nitrogen-containing carbon source to the third solvent is any value in 0.1:10, 0.2:10, 0.3:10, 0.4:10, 0.5:10, 0.6:10, 0.7:10, 0.8:10, 0.9:10, 1:10, or any value in the range of any two of the above values.

[0132] Preferably, the stirring time is 5 to 8 hours. Exemplarily, the stirring time is any value among 5 hours, 6 hours, 7 hours, and 8 hours, or any value within the range formed by any two of the above values.

[0133] In the preparation method of the present invention, the fiber skeleton of the third nanofiber has a fiber-like Ta as the core, and the core is coated with a second shell. During the stirring treatment under vacuum in step S4, the nitrogen-containing carbon source solution can penetrate between the core and the second shell of the third nanofiber, and in the subsequent high-temperature treatment process, the nitrogen-containing carbon source will be carbonized to generate a first shell containing C elements and N elements.

[0134] In step S5 of the above preparation method:

[0135] Preferably, the mass ratio of the fourth nanofiber to the selenium powder is 1:(2-6). Exemplarily, the mass ratio of the fourth nanofiber to the selenium powder is any value among 1:2, 1:3, 1:4, 1:5, 1:6 or any value within the range consisting of any two of the above values.

[0136] Preferably, the temperature of the second calcination treatment is 450-650° C. Exemplarily, the temperature of the second calcination treatment is any value among 450° C., 500° C., 550° C., 600° C., 650° C., or any value within the range consisting of any two of the above values.

[0137] Preferably, the second calcination treatment time is 2 to 6 hours. Exemplarily, the second calcination treatment time is any value among 2 hours, 3 hours, 4 hours, 5 hours, and 6 hours, or any value within the range of any two of the above values.

[0138] Preferably, the heating rate of the second calcination treatment is 1-5°C min -1 For example, the heating rate of the second calcination treatment is 1°C min -1 、2℃min -1 、3℃min -1 、4℃min -1 、5℃min -1Any value in the range of any two of the above values ​​or any value in the range of any two of the above values. Within this heating rate range, the reaction is complete, and the volatility of selenium is used to sublimate the selenium powder into selenium vapor, which then diffuses into the area containing the tantalum source of the Ta precursor @NSePCNFs, so that selenium and the tantalum source react to generate TaSe 2 and TaSe 2 / Ta heterojunction, and then carbonized to form a coating layer.

[0139] In a third aspect, the present invention provides a negative electrode sheet, which includes the negative electrode active material mentioned above, and / or the negative electrode active material prepared by the above preparation method.

[0140] In an embodiment of the present invention, the negative electrode sheet further includes a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and the binder, and those skilled in the art can select them according to actual needs, as long as the purpose of the present application can be achieved. The amounts of the conductive agent and the binder are conventional amounts in the art, and the present invention will not be repeated here.

[0141] In a fourth aspect, the present invention provides a battery comprising the above-mentioned negative electrode sheet.

[0142] In the embodiment of the present invention, the battery structure includes but is not limited to button batteries, soft-pack batteries, cylindrical batteries, etc.

[0143] The present application has no particular restrictions on the positive electrode sheet, separator, and electrolyte in the battery, and those skilled in the art can select them according to actual needs as long as the purpose of the present application can be achieved.

[0144] The reagents, instruments or materials used in the present invention can be obtained through commercial channels.

[0145] The present invention will be further described below in conjunction with embodiments:

[0146] Embodiment 1:

[0147] S1: Potassium chloride (KCl), polyvinyl pyrrolidone (PVP), selenol (SH) and tantalum acetate (Ta(Ac) 2 ) was added into 200 mL of deionized water at a molar ratio of 1:1.5:3:5, and a precursor solution was prepared by electrospinning. During the electrospinning process, the precursor solution was injected into a plastic syringe at a flow rate of 0.1 mm / min, the distance between the nozzle tip and the collector was 12 cm, and a voltage of 18 kV was applied. Finally, the collected nanofibers KCl-PVP-SH-Ta NFs were vacuum dried at 80 °C for 12 h.

[0148] S2: The obtained KCl-PVP-SH-Ta NFs were calcined at 200 °C for 2 h in an oxygen atmosphere with a heating rate of 2 °C min -1 , and then carbonized at 400 °C for 2 h in an argon atmosphere to obtain the product KCl-Ta precursor@NSePCNFs.

[0149] S3: Wash three times with deionized water and anhydrous ethanol by centrifugation to remove the KCl template. The washed sample is placed in a centrifuge tube and vacuum dried at 80°C for 12 h. The product is recorded as Ta precursor@NSePCNFs.

[0150] S4: The Ta precursor@NSePCNFs was immersed in polyacrylonitrile (PAN) solution (0.8 g PAN dissolved in 10 mL DMF), stirred under vacuum for 8 h, and the product was collected by centrifugation and dried under vacuum at 80 °C for 12 h.

[0151] S5: The above product and Se powder were placed on both sides of a quartz boat at a mass ratio of 1:2, placed upstream of a tube furnace, and heated at 2 °C min-1 under an argon-hydrogen atmosphere. -1 The product was heated to 450°C at a heating rate of 1.5°C and calcined at this temperature for 2 h. The annealed product was recorded as TaSe 2 / Ta@NC@NSePCNFs, the structure of the negative electrode active material is as follows Figure 1-Figure 3 shown.

[0152] Figure 1-Figure 3 The negative electrode active material is in a fiber tubular structure, and its tube wall is a porous network structure. The skeleton of the porous network structure has a shell-core structure, which includes TaSe 2 / Ta heterojunction core, a first shell containing C and N elements, and a second shell containing C, N, and Se elements; the length of the fiber tubular structure is 50 to 1000 μm, the cross-sectional radius is 200 to 800 μm, the aspect ratio is 50:1 to 500:1, and the average pore size of the pore structure is 50 nm;

[0153] The mass ratio of the inner core, the first shell layer and the second shell layer is 100:(3-8):(5-10); the diameter of the inner core is 100-700 nm, the thickness of the first shell layer is 50-200 nm, and the thickness of the second shell layer is 10-50 nm;

[0154] In the kernel, TaSe 2 The mass proportion of Al2O3 element is 75% to 90%, and the mass proportion of Ta element is 10% to 25%; in the first shell, the mass proportion of C element is 70% to 90%, and the mass proportion of N element is 10% to 30%; in the second shell, the mass proportion of C element is 60% to 80%, the mass proportion of N element is 5% to 20%, and the mass proportion of Se element is 5% to 20%.

[0155] S6: Prepared TaSe 2 / Ta@NC@NSePCNFs powder material, binder, and conductive agent are poured into an agate mortar in a mass ratio of 7:2:1, and mixed and ground for 30 minutes until the powder is evenly mixed and fine. Then add a certain amount of deionized water until the powder is evenly infiltrated and then stop dripping. The mixed slurry is evenly coated and flattened on the current collector copper foil with a coater, and then placed in a vacuum drying oven, set to a constant temperature of 80°C, and taken out after drying for 12 hours. Then use a cutter to cut the electrode into a negative electrode with a radius of 8mm.

[0156] S7: Preparation of sodium ion button half-cell (lithium ion button half-cell): the prepared negative electrode sheet is used as the working electrode, the metal sodium sheet (lithium sheet) is used as the reference electrode, Whatman GF / D glass fiber is used as the separator, and 1 mol L -1 NeA 6 Diethylene glycol methyl ether (diglyme) solution as sodium ion battery electrolyte (1 mol L -1 LiPF 6 Solution as lithium-ion battery electrolyte) and add a few drops. Assemble the half-cell in the order of positive electrode shell, negative electrode sheet, diaphragm, sodium sheet (lithium sheet), gasket, shrapnel and negative electrode shell. Clamp the assembled half-cell with insulating tweezers and place it on the packaging machine for sealing. Finally, take the packaged battery out of the glove box and let it stand for 24 hours to allow the electrolyte to fully infiltrate before conducting relevant electrochemical tests.

[0157] Embodiment 2:

[0158] The difference between this embodiment and embodiment 1 is that some preparation parameters in steps S1, S2, and S5 are different. The specific preparation method is as follows:

[0159] S1: Potassium chloride, polyvinyl pyrrolidone, selenol and Ta(Ac) 2 The precursor solution was prepared by electrospinning process by adding 200 mL of deionized water at a molar ratio of 1:1.5:3:5. During the electrospinning process, the precursor solution was injected into a plastic syringe at a flow rate of 0.12 mm / min, the distance between the nozzle tip and the collector was 12 cm, and a voltage of 19 kV was applied. Finally, the collected nanofibers KCl-PVP-SH-Ta NFs were vacuum dried at 80 °C for 12 h.

[0160] S2: The obtained KCl-PVP-SH-Ta NFs were calcined at 250 °C for 3 h in an oxygen atmosphere with a heating rate of 2 °C min -1 , and then carbonized at 450 °C for 3 h under argon atmosphere to obtain the product KCl-Ta precursor@NSePCNFs.

[0161] S3: Wash three times with deionized water and anhydrous ethanol by centrifugation to remove the KCl template. The washed sample is placed in a centrifuge tube and vacuum dried at 80°C for 12 h. The product is recorded as Ta precursor@NSePCNFs.

[0162] S4: Ta precursor@NSePCNFs were immersed in PAN solution (0.8 g PAN dissolved in 10 mL DMF), stirred under vacuum for 8 h, and the product was collected by centrifugation and dried under vacuum at 80 °C for 12 h.

[0163] S5: The above product and Se powder were placed on both sides of a quartz boat at a mass ratio of 1:3, and placed upstream of a tube furnace. In an argon-hydrogen atmosphere, the mixture was heated at 1 °C min -1 The annealed product was heated to 500 °C at a heating rate of 1.5 ℃ and calcined at this temperature for 3 h. The annealed product was recorded as TaSe 2 / Ta@NC@NSePCNFs.

[0164] S6: Prepared TaSe 2 / Ta@NC@NSePCNFs powder material, binder, and conductive agent are poured into an agate mortar in a mass ratio of 7:2:1, and mixed and ground for 30 minutes until the powder is evenly mixed and fine. Then add a certain amount of deionized water until the powder is evenly soaked and then stop dripping. The mixed slurry is evenly coated and flattened on the current collector copper foil with a coater, and then placed in a vacuum drying oven, set to a constant temperature of 80°C, and taken out after drying for 12 hours. Then use a cutter to cut the electrode into a negative electrode with a radius of 8mm.

[0165] S7: Preparation of sodium ion button half-cell (lithium ion button half-cell): the prepared negative electrode sheet is used as the working electrode, the metal sodium sheet (metal lithium sheet) is used as the reference electrode, Whatman GF / D glass fiber is used as the separator, and 1 mol L - 1 NeA 6 Diethylene glycol methyl ether (DIGLYME) solution as sodium ion battery electrolyte (1 mol L -1 LiPF 6 Solution as lithium-ion battery electrolyte) and add a few drops. Assemble the half-cell in the order of positive electrode shell, negative electrode sheet, diaphragm, sodium sheet (lithium sheet), gasket, shrapnel and negative electrode shell. Clamp the assembled half-cell with insulating tweezers and place it on the packaging machine for sealing. Finally, take the packaged battery out of the glove box and let it stand for 24 hours to allow the electrolyte to fully infiltrate before conducting relevant electrochemical tests.

[0166] Embodiment 3:

[0167] The difference between this embodiment and embodiment 1 is that some preparation parameters in steps S1, S2, and S5 are different. The specific preparation method is as follows:

[0168] S1: Potassium chloride, polyvinyl pyrrolidone, selenol and Ta(Ac) 2 The precursor solution was prepared by electrospinning process by adding 200 mL of deionized water at a molar ratio of 1:1.5:3:5. During the electrospinning process, the precursor solution was injected into a plastic syringe at a flow rate of 0.15 mm / min, the distance between the nozzle tip and the collector was 12 cm, and a voltage of 20 kV was applied. Finally, the collected nanofibers KCl-PVP-SH-Ta NFs were vacuum dried at 80 °C for 12 h.

[0169] S2: The obtained KCl-PVP-SH-Ta NFs were calcined at 300 °C for 4 h in an oxygen atmosphere with a heating rate of 2 °C min -1 , and then carbonized at 500 °C for 4 h under argon atmosphere to obtain the product KCl-Ta precursor@NSePCNFs.

[0170] S3: Wash three times with deionized water and anhydrous ethanol by centrifugation to remove the KCl template. The washed sample is placed in a centrifuge tube and vacuum dried at 80°C for 12 h. The product is recorded as Ta precursor@NSePCNFs.

[0171] S4: Ta precursor@NSePCNFs were immersed in PAN solution (0.8 g PAN dissolved in 10 mL DMF), stirred under vacuum for 8 h, and the product was collected by centrifugation and dried under vacuum at 80 °C for 12 h.

[0172] S5: The above product and Se powder were placed on both sides of a quartz boat at a mass ratio of 1:4, placed upstream of a tube furnace, and heated at 3 °C min-1 under an argon-hydrogen atmosphere. -1 The product was heated to 550°C at a heating rate of 1.5°C and calcined at this temperature for 4 h. The annealed product was recorded as TaSe 2 / Ta@NC@NSePCNFs.

[0173] S6: Prepared TaSe 2 / Ta@NC@NSePCNFs powder material, binder, and conductive agent are poured into an agate mortar in a mass ratio of 7:2:1, and mixed and ground for 30 minutes until the powder is evenly mixed and fine. Then add a certain amount of deionized water until the powder is evenly infiltrated and then stop dripping. The mixed slurry is evenly coated and flattened on the current collector copper foil with a coater, and then placed in a vacuum drying oven, set to a constant temperature of 80°C, and taken out after drying for 12 hours. Then use a cutter to cut the electrode into a negative electrode with a radius of 8mm.

[0174] S7: Preparation of sodium ion button half-cell (lithium ion button half-cell): the prepared negative electrode sheet is used as the working electrode, the metal sodium sheet (lithium sheet) is used as the reference electrode, Whatman GF / D glass fiber is used as the separator, and 1 mol L -1 NeA 6 Diethylene glycol methyl ether (DIGLYME) solution as sodium ion battery electrolyte (1 mol L -1 LiPF 6 Solution as lithium-ion battery electrolyte) and add a few drops. Assemble the half-cell in the order of positive electrode shell, negative electrode sheet, diaphragm, sodium sheet (lithium sheet), gasket, shrapnel and negative electrode shell. Clamp the assembled half-cell with insulating tweezers and place it on the packaging machine for sealing. Finally, take the packaged battery out of the glove box and let it stand for 24 hours to allow the electrolyte to fully infiltrate before conducting relevant electrochemical tests.

[0175] Embodiment 4:

[0176] The difference between this embodiment and embodiment 1 is that some preparation parameters in steps S1, S2, and S5 are different. The specific preparation method is as follows:

[0177] S1: Potassium chloride, polyvinyl pyrrolidone, selenol and Ta(Ac) 2 The precursor solution was prepared by electrospinning process by adding 200 mL of deionized water at a molar ratio of 1:1.5:3:5. During the electrospinning process, the precursor solution was injected into a plastic syringe at a flow rate of 0.18 mm / min, the distance between the nozzle tip and the collector was 12 cm, and a voltage of 21 kV was applied. Finally, the collected nanofibers KCl-PVP-SH-Ta NFs were vacuum dried at 80 °C for 12 h.

[0178] S2: The obtained KCl-PVP-SH-Ta NFs were calcined at 350 °C for 5 h in an oxygen atmosphere with a heating rate of 2 °C min -1 , and then carbonized at 550 °C for 5 h under argon atmosphere to obtain the product KCl-Ta precursor@NSePCNFs.

[0179] S3: Wash three times with deionized water and anhydrous ethanol by centrifugation to remove the KCl template. The washed sample is placed in a centrifuge tube and vacuum dried at 80°C for 12 h. The product is recorded as Ta precursor@NSePCNFs.

[0180] S4: Ta precursor@NSePCNFs were immersed in PAN solution (0.8 g PAN dissolved in 10 mL DMF), stirred under vacuum for 8 h, and the product was collected by centrifugation and dried under vacuum at 80 °C for 12 h.

[0181] S5: The above product and Se powder were placed on both sides of a quartz boat at a mass ratio of 1:5, placed upstream of a tube furnace, and heated at 4 °C min-1 under an argon-hydrogen atmosphere. -1 The annealed product was heated to 600 °C at a heating rate of 1.5 ℃ and calcined at this temperature for 5 h. The annealed product was recorded as TaSe 2 / Ta@NC@NSePCNFs.

[0182] S6: Prepared TaSe 2 / Ta@NC@NSePCNFs powder material, binder, and conductive agent are poured into an agate mortar in a mass ratio of 7:2:1, and mixed and ground for 30 minutes until the powder is evenly mixed and fine. Then add a certain amount of deionized water until the powder is evenly infiltrated and then stop dripping. The mixed slurry is evenly coated and flattened on the current collector copper foil with a coater, and then placed in a vacuum drying oven, set to a constant temperature of 80°C, and taken out after drying for 12 hours. Then use a cutter to cut the electrode into a negative electrode with a radius of 8mm.

[0183] S7: Preparation of sodium ion button half-cell (lithium ion button half-cell): the prepared negative electrode sheet is used as the working electrode, the metal sodium sheet (lithium sheet) is used as the reference electrode, Whatman GF / D glass fiber is used as the separator, and 1 mol L -1 NeA 6 Diethylene glycol methyl ether (DIGLYME) solution as sodium ion battery electrolyte (1 mol L -1 LiPF 6 Solution as lithium-ion battery electrolyte) and add a few drops. Assemble the half-cell in the order of positive electrode shell, negative electrode sheet, diaphragm, sodium sheet (lithium sheet), gasket, shrapnel and negative electrode shell. Clamp the assembled half-cell with insulating tweezers and place it on the packaging machine for sealing. Finally, take the packaged battery out of the glove box and let it stand for 24 hours to allow the electrolyte to fully infiltrate before conducting relevant electrochemical tests.

[0184] Embodiment 5:

[0185] The difference between this embodiment and embodiment 1 is that some preparation parameters in steps S1, S2, and S5 are different. The specific preparation method is as follows:

[0186] S1: Potassium chloride, polyvinyl pyrrolidone, selenol and Ta(Ac) 2 The precursor solution was prepared by electrospinning process by adding 200 mL of deionized water at a molar ratio of 1:1.5:3:5. During the electrospinning process, the precursor solution was injected into a plastic syringe at a flow rate of 0.2 mm / min, the distance between the nozzle tip and the collector was 12 cm, and a voltage of 22 kV was applied. Finally, the collected nanofibers KCl-PVP-SH-Ta NFs were vacuum dried at 80 °C for 12 h.

[0187] S2: The obtained KCl-PVP-SH-Ta NFs were calcined at 400 °C for 6 h in an oxygen atmosphere with a heating rate of 2 °C min -1 , and then carbonized at 600 °C for 6 h under argon atmosphere to obtain the product KCl-Ta precursor@NSePCNFs.

[0188] S3: Wash three times with deionized water and anhydrous ethanol by centrifugation to remove the KCl template. The washed sample is placed in a centrifuge tube and vacuum dried at 80°C for 12 h. The product is recorded as Ta precursor@NSePCNFs.

[0189] S4: Ta precursor@NSePCNFs were immersed in PAN solution (0.8 g PAN dissolved in 10 mL DMF), stirred under vacuum for 8 h, and the product was collected by centrifugation and dried under vacuum at 80 °C for 12 h.

[0190] S5: The above product and Se powder were placed on both sides of a quartz boat at a mass ratio of 1:6, placed upstream of a tube furnace, and heated at 5 °C min-1 under an argon-hydrogen atmosphere. -1 The product was heated to 650°C at a heating rate of 1.5°C and calcined at this temperature for 6 h. The annealed product was recorded as TaSe 2 / Ta@NC@NSePCNFs.

[0191] S6: Prepared TaSe 2 / Ta@NC@NSePCNFs powder material, binder, and conductive agent are poured into an agate mortar in a mass ratio of 7:2:1, and mixed and ground for 30 minutes until the powder is evenly mixed and fine. Then add a certain amount of deionized water until the powder is evenly infiltrated and then stop dripping. The mixed slurry is evenly coated and flattened on the current collector copper foil with a coater, and then placed in a vacuum drying oven, set to a constant temperature of 80°C, and taken out after drying for 12 hours. Then use a cutter to cut the electrode into a negative electrode with a radius of 8mm.

[0192] S7: Preparation of sodium ion button half-cell (lithium ion button half-cell): the prepared negative electrode sheet is used as the working electrode, the metal sodium sheet (lithium sheet) is used as the reference electrode, Whatman GF / D glass fiber is used as the separator, and 1 mol L -1 NeA 6 Diethylene glycol methyl ether (DIGLYME) solution as sodium ion battery electrolyte (1 mol L -1 LiPF 6Solution as lithium-ion battery electrolyte) and add a few drops. Assemble the half-cell in the order of positive electrode shell, negative electrode sheet, diaphragm, sodium sheet (lithium sheet), gasket, shrapnel and negative electrode shell. Clamp the assembled half-cell with insulating tweezers and place it on the packaging machine for sealing. Finally, take the packaged battery out of the glove box and let it stand for 24 hours to allow the electrolyte to fully infiltrate before conducting relevant electrochemical tests.

[0193] Comparative Example 1:

[0194] The difference between this comparative example and Example 1 is that the first shell layer (NC layer) is not included. The specific preparation method is as follows:

[0195] S1: Potassium chloride, chitosan, selenol and Ta(Ac) 2 The precursor solution was prepared by electrospinning process by adding 200 mL of deionized water at a molar ratio of 1:1.5:3:5. During the electrospinning process, the precursor solution was injected into a plastic syringe at a flow rate of 0.1-0.2 mm / min, the distance between the nozzle tip and the collector was 12 cm, and a voltage of 18-22 kV was applied. Finally, the collected nanofibers KCl-PVP-SH-Ta NFs were vacuum dried at 80 °C for 12 h.

[0196] S2: The obtained KCl-PVP-SH-Ta NFs were calcined at 200 °C for 2 h in an oxygen atmosphere with a heating rate of 2 °C min -1 , and then carbonized at 400 °C for 2 h under argon atmosphere to obtain the product KCl-Ta precursor@NSePCNFs.

[0197] S3: Wash three times with deionized water and anhydrous ethanol by centrifugation to remove the KCl template. The washed sample is placed in a centrifuge tube and vacuum dried at 80°C for 12 h. The product is recorded as Ta precursor@NSePCNFs.

[0198] S4: The above product and Se powder were placed on both sides of a quartz boat at a mass ratio of 1:2, placed upstream of a tube furnace, and heated at 2 °C min-1 under an argon-hydrogen atmosphere. -1 The product was heated to 450°C at a heating rate of 1.5°C and calcined at this temperature for 2 h. The annealed product was recorded as TaSe 2 @NSePCNFs.

[0199] S5: The prepared powder material, binder, and conductive agent are poured into an agate mortar in a mass ratio of 7:2:1, and mixed and ground for 30 minutes until the powder is evenly mixed and fine. Then add a certain amount of deionized water until the powder is evenly soaked and then stop dripping. Use a coater to evenly apply the mixed slurry and scrape it flat on the current collector copper foil, then place it in a vacuum drying oven, set the constant temperature to 80°C, and take it out after drying for 12 hours. Then use a cutter to cut the electrode into a negative electrode with a radius of 8mm.

[0200] S6: Preparation of sodium ion button half-cell (lithium ion button half-cell): the prepared negative electrode sheet was used as the working electrode, the metal sodium sheet (lithium sheet) was used as the reference electrode, Whatman GF / D glass fiber was used as the separator, and 1 mol L -1 NeA 6 Diethylene glycol methyl ether (DIGLYME) solution as sodium ion battery electrolyte (1 mol L -1 LiPF 6 Solution as lithium-ion battery electrolyte) and add a few drops. Assemble the half-cell in the order of positive electrode shell, negative electrode sheet, diaphragm, sodium sheet (lithium sheet), gasket, shrapnel and negative electrode shell. Clamp the assembled half-cell with insulating tweezers and place it on the packaging machine for sealing. Finally, take the packaged battery out of the glove box and let it stand for 24 hours to allow the electrolyte to fully infiltrate before conducting relevant electrochemical tests.

[0201] Comparative Example 2:

[0202] The negative electrode active material of this comparative example is pure TaSe 2 The specific preparation method is as follows:

[0203] S1: 0.5mmol Na 2 SeO 3 and 1.0mmol Ta(Ac) 2 Ultrasonic dispersion was carried out into a mixed solution consisting of 40 mL of diethylethylenediamine and 20 mL of deionized water, and the mixture was stirred vigorously for 1 h.

[0204] S2: The above solution was transferred to a stainless steel autoclave with a polytetrafluoroethylene liner and heated at 180°C for 18 h. The product TaSe was collected by centrifugation. 2 .

[0205] S3: Finally, the product TaSe is collected by centrifugation 2 , and dried at 80 °C under vacuum conditions for further application.

[0206] S4: The prepared powder material, binder, and conductive agent are poured into an agate mortar in a mass ratio of 7:2:1, and mixed and ground for 30 minutes until the powder is evenly mixed and fine. Then add a certain amount of deionized water until the powder is evenly soaked and then stop dripping. Use a coater to evenly apply the mixed slurry and scrape it flat on the current collector copper foil, then place it in a vacuum drying oven, set the constant temperature to 80°C, and take it out after drying for 12 hours. Then use a cutter to cut the electrode into a negative electrode with a radius of 8mm.

[0207] S5: Preparation of sodium ion button half-cell (lithium ion button half-cell): the prepared negative electrode sheet is used as the working electrode, the metal sodium sheet (lithium sheet) is used as the reference electrode, Whatman GF / D glass fiber is used as the separator, and 1 mol L -1 NeA 6 Diethylene glycol methyl ether (DIGLYME) solution as sodium ion battery electrolyte (1 mol L -1 LiPF 6 Solution as lithium-ion battery electrolyte) and add a few drops. Assemble the half-cell in the order of positive electrode shell, negative electrode sheet, diaphragm, sodium sheet (lithium sheet), gasket, shrapnel and negative electrode shell. Clamp the assembled half-cell with insulating tweezers and place it on the packaging machine for sealing. Finally, take the packaged battery out of the glove box and let it stand for 24 hours to allow the electrolyte to fully infiltrate before conducting relevant electrochemical tests.

[0208] Test example:

[0209] (1) First cycle capacity test: Sodium ion button half-cells and lithium ion button half-cells prepared in the embodiment and the comparative example were taken respectively and tested at 0.2A g -1 The first-cycle capacity test was carried out under the test conditions of current density, charge cut-off voltage of 3.0V, and discharge cut-off voltage of 0.01V, and the first-cycle discharge specific capacity and first-cycle coulomb efficiency test results were obtained.

[0210] (2) 5A g -1 Cycle life test: Take the sodium ion button half-cell and lithium ion button half-cell prepared in the embodiment and the comparative example respectively, and conduct 5A g -1 The current density was cyclically tested (charge cut-off voltage 3.0 V, discharge cut-off voltage 0.01 V), and 5A g -1 Number of cycles at current density and 5A g -1 Capacity retention test results under current density.

[0211] (3) Electrochemical impedance spectroscopy test: The electrochemical impedance spectroscopy test of the half-cell was performed using the Letpub electrochemical workstation with a test frequency of 0.01 Hz to 100 kHz to obtain the charge transfer resistance test results of the new battery.

[0212] (4) Constant current intermittent titration technology test: The sodium ion button half-cell and lithium ion button half-cell prepared in the embodiment and the comparative example were subjected to constant current intermittent titration technology test (charging cut-off voltage 3.0 V, discharging cut-off voltage 0.01 V) at 26°C using the Xinwei battery testing system to obtain the new battery Na + / Li + Diffusion coefficient.

[0213] Table 1 Comparison of sodium ion battery performance test results

[0214]

[0215] Table 2 Comparison of lithium-ion battery performance test results

[0216]

[0217] In Examples 1-5, due to the coating of the NC layer and the NSePCNFs layer, additional active sites are provided, which promotes the embedding and deintercalation of sodium ions or lithium ions, thereby improving the discharge specific capacity. The coating of the NC layer and the NSePCNFs layer helps to reduce the irreversible capacity loss during the first charge and discharge process and improves the coulombic efficiency. The coating of the NC layer and the NSePCNFs layer enhances the structural stability of the material and reduces the capacity attenuation during the cycle. The coating of the NC layer and the NSePCNFs layer improves the conductivity of the material and reduces the internal resistance. The coating of the NC layer and the NSePCNFs layer may promote the diffusion of lithium ions and increase the diffusion coefficient. Among Examples 1-5, Example 1 has the best performance.

[0218] Comparative Example 1 has no NC layer coating and its performance is poor.

[0219] Comparative Example 2 is not coated with the NC layer and the NSePCNFs layer, and TaSe2 / Ta is directly exposed and easily affected by the external environment, such as oxidation and corrosion, resulting in performance degradation.

[0220] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A negative electrode active material, characterized in that: The negative electrode active material has a fiber tubular structure; The skeleton of the fiber tubular structure has a shell-core structure, comprising: (a) a core, the core comprising a TaSe2 / Ta heterojunction; (b) a first shell layer, wherein the first shell layer is disposed on the surface of the inner core; the first shell layer comprises C element and N element; (c) a second shell layer, wherein the second shell layer is arranged on a surface of the first shell layer away from the core; the second shell layer comprises C element, N element and Se element.

2. The negative electrode active material according to claim 1, characterized in that The length of the fiber tubular structure is 50 to 1000 μm; And / or, the cross-sectional radius of the fiber tubular structure is 200 to 800 nm; And / or, the aspect ratio of the fiber tubular structure is 50:1 to 500:1; And / or, the tube wall of the fiber tubular structure has a plurality of hole structures, and the average pore diameter of the hole structures is 2-100 nm.

3. The negative electrode active material according to claim 1, characterized in that The mass ratio of the inner core to the first shell is 100:(3-8); And / or, the mass ratio of the inner core to the second shell is 100:(5-10).

4. The negative electrode active material according to claim 1, characterized in that The diameter of the inner core is 100 to 700 nm; and / or, the thickness of the first shell layer is 50 to 200 nm; And / or, the thickness of the second shell layer is 10-50 nm.

5. The negative electrode active material according to claim 1, characterized in that: In the core, the mass ratio of TaSe2 to Ta is (75-90): (10-25); And / or, in the first shell layer, the mass ratio of the C element to the N element is (70-90): (10-30); And / or, in the second shell layer, the mass ratio of the C element, the N element and the Se element is (60-80): (10-20): (10-20); And / or, the ratio of the mass proportion of the C element in the first shell layer to the mass proportion of the C element in the second shell layer is (1.2-1.5):1; And / or, the ratio of the mass proportion of the N element in the first shell layer to the mass proportion of the N element in the second shell layer is (1.5-3):

1.

6. The method for preparing the negative electrode active material according to any one of claims 1 to 5, characterized in that: The steps include: S1, mixing a template, a morphology control agent, a selenium source, a tantalum source and a first solvent to obtain a precursor solution, electrospinning the precursor solution, and obtaining first nanofibers after drying; S2, subjecting the first nanofiber to a first calcination treatment in an oxygen atmosphere, and then subjecting the first nanofiber to a carbonization treatment in an inert gas atmosphere to obtain a second nanofiber; S3, washing the second nanofibers with a second solvent to remove the template in the second nanofibers, and obtaining third nanofibers after drying; S4, mixing the nitrogen-containing carbon source and the third solvent to obtain a nitrogen-containing carbon source solution; immersing the third nanofiber in the nitrogen-containing carbon source solution, stirring under vacuum, centrifuging, and drying to obtain a fourth nanofiber; S5, under an inert gas atmosphere, subjecting the fourth nanofiber and selenium powder to a second calcination treatment to obtain the negative electrode active material.

7. The preparation method according to claim 6, characterized in that: In the step S1, The template comprises at least one of potassium chloride, potassium nitrate, potassium sulfate and potassium chromium; And / or, the morphology control agent includes at least one of polyvinyl pyrrolidone, hexadecyltrimethylammonium bromide, urea, amino acid, polyamide, and polyurea; And / or, the selenium source comprises at least one of selenol, sodium selenate, sodium selenite, selenoester, and selenourea, preferably selenol; And / or, the tantalum source includes at least one of tantalum acetate, tantalum chloride, tantalum oxide, and tantalum fluoride; and / or, the first solvent comprises an aqueous solvent; And / or, the molar ratio of the template, the morphology control agent, the selenium source, and the tantalum source is (0.5-1.5): (1-2): (2.5-3.5): (4-6); and / or, the electrospinning flow rate is 0.1-0.2 mm / min, the distance between the nozzle tip and the collector is 12 cm, and the voltage is 18-22 kV; And / or, in step S2, The temperature of the first calcination treatment is 200-400°C, the time of the first calcination treatment is 2-6 hours, and the heating rate of the first calcination treatment is 1-5°C min -1 ; And / or, the temperature of the carbonization treatment is 400-600° C., and the time of the carbonization treatment is 2-6 hours.

8. The preparation method according to claim 6, characterized in that: In the step S3, The second solvent includes water and / or anhydrous ethanol; And / or, the number of washing is 2 to 5 times; And / or, in step S4, The nitrogen-containing carbon source includes at least one of polyacrylonitrile, urea, melamine and acrylonitrile; and / or, the third solvent comprises at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, and acetone; and / or, in g / mL, the mass volume ratio of the nitrogen-containing carbon source to the third solvent is (0.1-1):10; And / or, the stirring treatment time is 5 to 8 hours; And / or, in step S5, The mass ratio of the fourth nanofiber to the selenium powder is 1:(2-6); and / or, the temperature of the second calcination treatment is 450-650°C, the time of the second calcination treatment is 2-6 hours, and the heating rate of the second calcination treatment is 1-5°C min -1 .

9. A negative electrode sheet, characterized in that: The negative electrode sheet comprises the negative electrode active material according to any one of claims 1 to 5, and / or the negative electrode active material prepared by the preparation method according to any one of claims 6 to 8.

10. A battery, characterized in that: The battery comprises the negative electrode sheet according to claim 9.

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