Composite negative electrode material, preparation method thereof and battery

Abstract

This invention relates to a composite anode material, its preparation method, and a battery. The composite anode material has a hollow core-shell structure. From its center to its outer surface, the composite anode material sequentially includes a cobalt selenide sulfide layer and a hard carbon coating layer, with the cobalt selenide sulfide layer enclosing a cavity. The thickness of the cobalt selenide sulfide layer is 30%–65% of the total thickness from the center to the outer surface of the composite anode material (assuming 100% thickness). The cobalt selenide sulfide layer includes an outer shell layer and a core layer. The outer shell layer is in contact with the hard carbon coating layer, and the core layer is in contact with the cavity. The thickness of the outer shell layer and the core layer are both 10%–25% of the total thickness (assuming 100% thickness). The chemical formula of the cobalt selenide sulfide is CoS. x Se 2‑x The values ​​of x are 0.3 ≤ x ≤ 1.7, and the x value decreases from the core layer to the outer shell layer. This composite anode material exhibits excellent structural stability, low expansion, high conductivity, and good cycle stability and rate performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a composite negative electrode material, its preparation method, and a battery. Background Technology

[0002] Currently, global demand for renewable and clean energy continues to grow, and sodium-ion batteries (SIBs) have become a promising energy storage solution due to the abundance of sodium resources, low cost, and environmental friendliness. However, the radius of sodium ions (0.102 nm) is significantly larger than that of lithium ions (0.076 nm), which hinders their migration and diffusion in anode materials, thus limiting the reversible capacity and rate performance of sodium-ion batteries. Therefore, developing suitable anode materials is crucial.

[0003] Transition metal selenium sulfide compounds (such as cobalt selenide sulfide) combine the advantages of high specific capacity of sulfides and high electronic conductivity of selenides, making them a research hotspot for anode materials in sodium-ion batteries. However, cobalt selenide sulfide still faces key bottlenecks as an anode material: first, the drastic volume deformation during sodium ion insertion / extraction leads to electrode pulverization and detachment, resulting in rapid capacity decay; second, although its intrinsic conductivity is better than that of pure sulfides, it still cannot meet the requirements of high-power applications.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] This application provides a composite negative electrode material, its preparation method, and a battery to address at least one problem existing in the prior art.

[0006] The first aspect of this invention provides a composite anode material, wherein the composite anode material has a hollow core-shell structure; from the center to the outer surface of the composite anode material, the composite anode material sequentially includes a cobalt selenide sulfide layer and a hard carbon coating layer, wherein the cobalt selenide sulfide layer encloses a cavity; wherein... With the thickness of the composite negative electrode material from the center to the outer surface being 100%, the thickness of the cobalt selenide sulfide layer accounts for 30% to 65%; The cobalt selenide sulfide layer includes an outer shell layer and a core layer. The outer shell layer is in contact with the hard carbon coating layer, and the core layer is in contact with the cavity. Assuming the thickness of the cobalt selenide sulfide layer is 100%, the outer shell layer accounts for 10% to 25% of the total thickness, and the core layer accounts for 10% to 25% of the total thickness. The chemical formula of the cobalt selenide sulfide is CoS. x Se 2-x , where 0.3≤x≤1.7; the value of x decreases from the kernel layer to the outer shell layer.

[0007] Preferably, with the thickness of the composite negative electrode material from the center to the outer surface as 100%, the thickness of the cobalt selenide sulfide layer accounts for 40% to 55%; the thickness of the cavity accounts for 35% to 50%; and the thickness of the hard carbon coating layer accounts for 8% to 15%. Preferably, the nitrogen content in the hard carbon coating is 2.0 wt% to 6.0 wt%.

[0008] A second aspect of the present invention provides a method for preparing the composite negative electrode material described in the first aspect of the present invention, comprising: S1: Dissolve cobalt nitrate hexahydrate in the first solvent to obtain solution A; dissolve 2-methylimidazole in the second solvent to obtain solution B; mix solution A and solution B and heat to obtain cobalt carbon precursor; S2: Selenize the cobalt carbon precursor obtained in step S1 by introducing a selenium source, cool it down, and then sulfide it by introducing a sulfur source to obtain hollow cobalt selenide sulfide. S3: Disperse the hollow cobalt selenide obtained in step S2 in the prepolymer liquid for polymerization reaction, and then heat and carbonize it to obtain the final product.

[0009] Preferably, step S1 satisfies at least one of the following features: (1) The first solvent is selected from one or more of water, methanol, ethanol and ethylene glycol; (2) The molar concentration of cobalt nitrate hexahydrate in solution A is 50 mmol / L to 200 mmol / L; (3) The second solvent is selected from one or more of water, methanol, ethanol and ethylene glycol; (4) The molar concentration of the 2-methylimidazole in solution B is 500 mmol / L to 1000 mmol / L; (5) The volume ratio of solution A to solution B is (1~3):1; (6) The heating is carried out in an inert gas atmosphere, wherein the inert gas is selected from at least one of argon, helium, krypton and nitrogen; (7) The heating rate is 2℃ / min to 5℃ / min, the peak temperature is 500℃ to 700℃, and the duration of the peak temperature is 1h to 3h.

[0010] Preferably, step S2 satisfies at least one of the following features: (1) The selenium source is selected from one or more of selenium powder, sodium selenosulfate, and potassium selenosulfate; (2) The mass ratio of the selenium source to the cobalt-carbon precursor is (1.5~2.5):1; (3) The selenization is carried out in an inert gas atmosphere, wherein the inert gas is selected from at least one of argon, helium, krypton and nitrogen; (4) The selenization is carried out under heating conditions, the heating rate is 3℃ / min~7℃ / min, the peak temperature is 300℃~400℃, and the duration of the peak temperature is 1h~2h; (5) During the selenization process, the selenium source is located at the upper air inlet of the tubular furnace, and the cobalt-carbon precursor is located at the lower air inlet of the tubular furnace. (6) The cooling refers to cooling down to room temperature; (7) The sulfur source is selected from one or more of sulfur powder, thiourea, ammonium sulfide, and thioacetamide; (8) The mass ratio of the sulfur source to the cobalt-carbon precursor is (1.5~2.5):1; (9) The sulfidation is carried out in an inert gas atmosphere containing hydrogen, wherein the inert gas is selected from at least one of argon, helium, krypton and nitrogen, and the hydrogen accounts for 8% to 12% of the total gas volume; (10) The vulcanization is carried out under heating conditions, the heating rate is 2℃ / min~5℃ / min, the peak temperature is 400℃~600℃, and the duration of the peak temperature is 1h~3h. (11) During the sulfidation, the sulfur source is located at the upper tuyer of the tubular furnace, and the cobalt carbon precursor after selenization is located at the lower tuyer of the tubular furnace.

[0011] Preferably, step S3 satisfies at least one of the following features: (1) The steps for preparing the prepolymer solution are as follows: dissolve resorcinol, formaldehyde and zinc salt in a third solvent, and adjust the pH with dilute ammonia water to obtain the solution; (2) The polymerization reaction is carried out at a temperature of 55℃~75℃ for 7h~9h; (3) The heating carbonization is carried out in an inert gas atmosphere, wherein the inert gas is selected from at least one of argon, helium, krypton and nitrogen; (4) The heating rate of the carbonization process is 3℃ / min to 7℃ / min, the peak temperature is 750℃ to 950℃, and the duration of the peak temperature is 1h to 3h. (5) The heating carbonization process also includes a preheating step.

[0012] Preferably, in step S3, the step of preparing the prepolymer solution satisfies at least one of the following characteristics: (1) The zinc salt is selected from one or more of zinc acetate, zinc chloride, and zinc nitrate; (2) The mass ratio of resorcinol to zinc salt is 1:(0.4~0.6); (3) The mass-to-volume ratio (g / mL) of resorcinol and formaldehyde is 1:(1.5~1.8); (4) The third solvent is selected from one or more of water, methanol, ethanol and ethylene glycol; (5) The mass-to-volume ratio (g / mL) of the resorcinol and the third solvent is 1:(150~250); (6) Adjust the pH value to 5.5~6.5.

[0013] Preferably, in step S3, the mass ratio of resorcinol to hollow cobalt selenide sulfide is 1:(4~6).

[0014] Preferably, in step S3, the preheating is carried out in an inert gas atmosphere, wherein the inert gas is selected from at least one of argon, helium, krypton and nitrogen; Preferably, in step S3, the preheating rate is 1℃ / min to 3℃ / min, the peak temperature is 250℃ to 450℃, and the duration of the peak temperature is 0.5h to 1.5h. A third aspect of the present invention provides a battery comprising a negative electrode sheet, wherein the negative electrode sheet comprises the composite negative electrode material described in the first aspect of the present invention or comprises a composite negative electrode material prepared by the preparation method described in the second aspect of the present invention.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a composite anode material, its preparation method, and a battery. The composite anode material has a hollow core-shell structure and a continuous gradient of selenium / sulfur content from the inside to the outside. This effectively buffers the volume expansion during charge and discharge, alleviates internal stress concentration, and inhibits material pulverization and capacity decay. At the same time, it constructs a high-speed electron-ion transport channel and reduces electrode impedance. As a result, the battery using this composite anode material as the anode active material exhibits excellent rate performance, cycle stability, and high specific capacity, and its electrochemical performance is significantly improved.

[0016] In this invention, the composite anode material is prepared by a stepwise gas-phase process of selenization followed by sulfidation and zinc salt catalytic carbonization. This allows the cobalt selenide sulfide layer to form a selenium / sulfur concentration gradient and a hollow cavity structure. At the same time, the zinc salt has both catalytic graphitization and in-situ pore-forming effects, which can significantly improve the conductivity, ion permeability and mechanical strength of the carbon coating layer, strengthen the material structure stability and interfacial bonding, and significantly improve the cycle life and fast charge / discharge capability of the battery using this composite anode material as the anode active material. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1This is a schematic diagram of the structure of a composite negative electrode material provided in an embodiment of this application.

[0018] Explanation of reference numerals in the attached figures 100. Cavity; 200. Cobalt selenide sulfide layer; 210. Core layer; 220. Outer layer 300, hard carbon coating. Detailed Implementation

[0019] To make the technical solution and beneficial effects of the present invention more apparent and understandable, a detailed description is provided below by listing specific embodiments. The accompanying drawings are not necessarily drawn to scale, and local features may be enlarged or reduced to more clearly show the details of the local features. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional experimental conditions. Unless otherwise specified, all reagents and raw materials used in this invention are commercially available.

[0020] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this application. However, it will be apparent to those skilled in the art that this application can be practiced without one or more of these details. In other instances, to avoid confusion with this application, some technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and steps described in detail.

[0021] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0022] To fully understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. Preferred embodiments of this application are described in detail below; however, in addition to these detailed descriptions, this application may have other implementation methods.

[0023] Unless otherwise defined, the technical and scientific terms used in this application have the same meanings as those in the technical and scientific field to which this application pertains.

[0024] Unless otherwise specified, the techniques or conditions described in the following embodiments are generally performed in accordance with conventional techniques or conditions described in the literature in this field, or in accordance with the product manual and the manufacturer's recommendations. All numerical ranges in the following embodiments include endpoint values.

[0025] Currently, the main approach in this field is to address the problems of large volume changes, easy pulverization and shedding, capacity decay, and insufficient intrinsic conductivity to meet the requirements of high-power applications in cobalt selenide sulfide anode materials during sodium ion insertion / extraction, through carbon material coating and nanostructure design. For example, after synthesizing cobalt selenide sulfide nanoparticles using a hydrothermal method, surface coating and carbonization are carried out using carbon sources such as glucose.

[0026] However, in such methods, the carbon layer and the active material are mostly physically attached, resulting in weak interfacial bonding. Under long-term cyclic stress, the carbon layer is prone to peeling and failure. The material has a uniform internal composition, and the volume expansion of different regions is inconsistent during charging and discharging, which can easily lead to internal stress concentration and structural failure from the inside.

[0027] In view of the above, the present invention provides the following technical solution:

[0028] [Composite Anode Material]

[0029] The first aspect of this invention provides a composite anode material, wherein the composite anode material has a hollow core-shell structure; from the center to the outer surface of the composite anode material, the composite anode material sequentially includes a cobalt selenide sulfide layer 200 and a hard carbon coating layer 300, the cobalt selenide sulfide layer 200 enclosing a cavity 100; wherein, based on the thickness of the composite anode material from the center to the outer surface being 100%, the thickness percentage of the cobalt selenide sulfide layer 200 is 30%~65%; the cobalt selenide sulfide layer 200 includes an outer shell layer 220 and a core layer 210, the outer shell layer 220 being in contact with the hard carbon coating layer 300, and the core layer 210 being in contact with the cavity 100; based on the thickness of the cobalt selenide sulfide layer 200 being 100%, the thickness percentage of the outer shell layer 220 is 10%~25%, and the thickness percentage of the core layer 210 is 10%~25%; the chemical formula of the cobalt selenide sulfide is CoS. x Se 2-x , where 0.3≤x≤1.7; the value of x decreases from the kernel layer 210 to the outer shell layer 220.

[0030] In this invention, through the aforementioned hollow core-shell structure and selenium / sulfur element gradient design, the outer shell layer 220 can possess both high electronic conductivity and low volume expansion characteristics, while the core layer 210 maintains a high specific capacity advantage. The gradient transition region between the outer shell layer 220 and the core layer 210 effectively alleviates the volume effect and internal stress concentration during charging and discharging, preventing material pulverization, structural collapse, and rapid capacity decay. At the same time, the hard carbon coating layer can further enhance structural stability, improve electron transport rate and ion diffusion efficiency, enabling the composite anode material to possess both high specific capacity, excellent rate performance, and long cycle life, thus better meeting the practical application requirements of sodium-ion batteries.

[0031] In some embodiments, with the thickness of the composite negative electrode material from the center to the outer surface as 100%, the thickness of the cobalt selenide sulfide layer 200 accounts for 40% to 55%, for example, any integer or decimal value within the range of 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, or 40% to 55%.

[0032] In some embodiments, with the thickness of the composite negative electrode material from the center to the outer surface as 100%, the thickness of the cavity 100 accounts for 35% to 50%, for example, any integer or decimal value within the range of 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or 35% to 50%.

[0033] In some embodiments, the thickness of the hard carbon coating layer 300 is 8% to 15%, with the thickness from the center to the outer surface of the composite negative electrode material being 100%, for example, any integer or decimal value within the range of 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or 8% to 15%.

[0034] In some embodiments, the nitrogen content in the hard carbon coating 300 is 2.0 wt% to 6.0 wt%, for example, any integer or decimal value within the range of 2.0 wt%, 3.0 wt%, 4.0 wt%, 5.0 wt%, 6.0 wt%, or 2.0 wt% to 6.0 wt%.

[0035] [Preparation Method of Composite Anode Materials]

[0036] A second aspect of the present invention provides a method for preparing the composite negative electrode material described in the first aspect of the present invention, comprising: S1: Dissolve cobalt nitrate hexahydrate in the first solvent to obtain solution A; dissolve 2-methylimidazole in the second solvent to obtain solution B; mix solution A and solution B and heat to obtain cobalt carbon precursor; S2: Selenize the cobalt carbon precursor obtained in step S1 by introducing a selenium source, cool it down, and then sulfide it by introducing a sulfur source to obtain hollow cobalt selenide sulfide. S3: Disperse the hollow cobalt selenide obtained in step S2 in the prepolymer liquid for polymerization reaction, and then heat and carbonize it to obtain the final product.

[0037] In some embodiments, in step S1, the first solvent is selected from one or more of water, methanol, ethanol, and ethylene glycol.

[0038] In some embodiments, in step S1, the first solvent is selected from water and methanol.

[0039] In some embodiments, in step S1, the molar concentration of cobalt nitrate hexahydrate in solution A is 50 mmol / L to 200 mmol / L, for example, any integer or decimal value within the range of 50 mmol / L, 60 mmol / L, 70 mmol / L, 80 mmol / L, 90 mmol / L, 100 mmol / L, 110 mmol / L, 120 mmol / L, 130 mmol / L, 140 mmol / L, 150 mmol / L, 160 mmol / L, 170 mmol / L, 180 mmol / L, 190 mmol / L, 200 mmol / L, or 50 mmol / L to 200 mmol / L.

[0040] In some embodiments, in step S1, the second solvent is selected from one or more of water, methanol, ethanol, and ethylene glycol.

[0041] In some embodiments, in step S1, the second solvent is selected from methanol.

[0042] In some embodiments, in step S1, the molar concentration of 2-methylimidazole in solution B is 500 mmol / L to 1000 mmol / L, for example, any integer or decimal value within the range of 500 mmol / L, 550 mmol / L, 600 mmol / L, 650 mmol / L, 700 mmol / L, 750 mmol / L, 800 mmol / L, 850 mmol / L, 900 mmol / L, 950 mmol / L, 1000 mmol / L, or 500 mmol / L to 1000 mmol / L.

[0043] In some embodiments, in step S1, the mixing volume ratio of solution A and solution B is (1~3):1, for example, any integer or decimal ratio within the range of 1:1, 2:1, 3:1 or (1~3):1.

[0044] In some embodiments, in step S1, the heating is carried out in an inert gas atmosphere, wherein the inert gas is selected from at least one of argon, helium, krypton and nitrogen.

[0045] In some embodiments, in step S1, the inert gas is selected from argon.

[0046] In some embodiments, in step S1, the heating rate is 2℃ / min to 5℃ / min, for example, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min or any integer or decimal value within the range of 2℃ / min to 5℃ / min.

[0047] In some embodiments, in step S1, the peak heating temperature is 500℃~700℃, for example, 550℃, 600℃, 650℃, 700℃, or any integer or decimal value within the range of 500℃~700℃. Preferably, the peak heating temperature is 700℃. Compared with temperatures below 500℃, 700℃ allows the precursor to be completely carbonized, forming a nitrogen-doped carbon framework with a stable structure and better conductivity, while avoiding excessive aggregation of cobalt nanoparticles. This is beneficial for the subsequent selenization and sulfidation steps to form a uniform gradient structure and a complete hollow morphology, thereby improving the electrochemical performance of the composite material.

[0048] In some implementations, in step S1, the duration of the peak temperature is 1h to 3h, for example, any integer or decimal value within the range of 1h, 2h, 3h, or 1h to 3h.

[0049] In some embodiments, step S1, after mixing solution A and solution B, may further include steps of settling, filtering, washing, and drying.

[0050] In some embodiments, in step S2, the selenium source is selected from one or more of selenium powder, sodium selenosulfate, and potassium selenosulfate.

[0051] In some embodiments, in step S2, the selenium source is selected from selenium powder.

[0052] In some embodiments, in step S2, the mass ratio of the selenium source to the cobalt-carbon precursor is (1.5~2.5):1, for example, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1 or any integer or decimal ratio within the range of (1.5~2.5):1.

[0053] In some embodiments, in step S2, the selenization is carried out in an inert gas atmosphere, wherein the inert gas is selected from at least one of argon, helium, krypton and nitrogen.

[0054] In some embodiments, in step S2, the selenization is carried out in an inert gas atmosphere, wherein the inert gas is selected from argon.

[0055] In some embodiments, in step S2, the selenization is carried out under heating conditions, and the heating rate is 3℃ / min to 7℃ / min, for example, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min or any integer or decimal value within the range of 3℃ / min to 7℃ / min.

[0056] In some embodiments, in step S2, the selenization is carried out under heating conditions, and the peak temperature of the heating is 300℃~400℃, for example, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃ or any integer or decimal value within the range of 300℃~400℃.

[0057] In some embodiments, in step S2, the selenization is carried out under heating conditions, and the duration of the peak heating temperature is 1h to 2h, for example, 1h, 1.5h, 2h or any integer or decimal value within the range of 1h to 2h.

[0058] In some embodiments, during step S2, the selenium source is located at the upper tuyer of the tubular furnace and the cobalt-carbon precursor is located at the lower tuyer of the tubular furnace during selenization.

[0059] Therefore, the above selenization steps allow Se vapor to react with the Co / NC surface to form a selenium-rich shell.

[0060] In some embodiments, in step S2, the cooling is to cool to room temperature. Cooling to room temperature before proceeding to the next reaction prevents the formation of the highly toxic substance H2Se.

[0061] In some embodiments, in step S2, the sulfur source is selected from one or more of sulfur powder, thiourea, ammonium sulfide, and thioacetamide.

[0062] In some embodiments, in step S2, the sulfur source is selected from sulfur powder.

[0063] In some embodiments, in step S2, the mass ratio of the sulfur source to the cobalt-carbon precursor is (1.5~2.5):1, for example, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1 or any integer or decimal ratio within the range of (1.5~2.5):1.

[0064] In some embodiments, in step S2, the sulfidation is carried out in an inert gas atmosphere containing hydrogen, wherein the inert gas is selected from at least one of argon, helium, krypton and nitrogen.

[0065] In some embodiments, in step S2, the sulfidation is carried out in an inert gas atmosphere containing hydrogen, wherein the inert gas is selected from argon.

[0066] In some embodiments, the hydrogen gas accounts for 8% to 12% of the total gas volume, for example, any integer or decimal value within the range of 8%, 9%, 10%, 11%, 12%, or 8% to 12%.

[0067] In some embodiments, in step S2, the vulcanization is carried out under heating conditions, and the heating rate is 2℃ / min to 5℃ / min, for example, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min or any integer or decimal value within the range of 2℃ / min to 5℃ / min.

[0068] In some embodiments, in step S2, the vulcanization is carried out under heating conditions, and the peak temperature of the heating is 400℃~600℃, for example, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, 600℃ or any integer or decimal value within the range of 400℃~600℃.

[0069] In some embodiments, in step S2, the vulcanization is carried out under heating conditions, and the duration of the peak heating temperature is 1h to 3h, for example, any integer or decimal value within the range of 1h, 1.5h, 2h, 2.5h, 3h, or 1h to 3h.

[0070] In some embodiments, during step S2, the sulfur source is located at the upper tuyer of the tubular furnace during sulfidation, and the selenized cobalt-carbon precursor is located at the lower tuyer of the tubular furnace.

[0071] In some embodiments, step S2 may further include cooling, washing, and drying steps after the vulcanization step is completed.

[0072] In some embodiments, the washing is performed using CS2 washing.

[0073] Thus, through the above-mentioned sulfidation steps, S vapor can diffuse through the selenium-rich shell with the assistance of H2 to react with the internal Co, and a continuous and gradual selenium / sulfur concentration gradient from the shell to the core can be formed by the interdiffusion of Se / S; at the same time, the Kirkendall effect is used to form an internal hollow structure during the reaction process, and finally hollow cobalt selenide with radial concentration gradient is obtained.

[0074] In step S2, the cobalt-carbon precursor obtained in step S1 undergoes stepwise gas-phase selenization and sulfidation treatments to obtain hollow cobalt selenide sulfide with a selenium / sulfur concentration gradient. This results in a composite anode material that combines high conductivity and high capacity, while achieving a smooth transition of volume expansion stress. This "selenium-first, sulfur-later" process is a key step in forming an ideal gradient structure, allowing the material to exhibit a continuous distribution of decreasing selenium content and increasing sulfur content from the outside to the inside. This effectively balances high conductivity, high capacity, and volume stress buffering, significantly improving the material's charge / discharge capacity, cycle life, and rate performance.

[0075] In some embodiments, step S3 involves preparing the prepolymer solution by dissolving resorcinol, formaldehyde, and zinc salt in a third solvent and adjusting the pH using dilute ammonia.

[0076] In some embodiments, the zinc salt is selected from one or more of zinc acetate, zinc chloride, and zinc nitrate.

[0077] In the preparation method of this invention, step S3 involves introducing zinc salt into the prepolymer solution and catalytically carbonizing it at high temperature. This allows zinc to play a dual role in catalyzing graphitization and in-situ volatilization during heat treatment: on the one hand, it catalyzes the formation of highly conductive graphite-like microcrystals in the resin carbon layer, significantly improving electronic conductivity; on the other hand, high-temperature volatilization forms multi-level channels, optimizing sodium ion diffusion and electrolyte wetting, simultaneously improving the conductivity, ion permeability, and mechanical stability of the carbon coating layer, providing structural support for the excellent rate performance and long cycle life of the composite material.

[0078] In some embodiments, the mass ratio of resorcinol to zinc salt is 1:(0.4~0.6), for example, any integer or decimal ratio within the range of 1:0.40, 1:0.45, 1:0.50, 1:0.55, 1:0.60 or 1:(0.4~0.6).

[0079] In some embodiments, the mass-to-volume ratio (g / mL) of resorcinol and formaldehyde is 1:(1.5~1.8), for example, any integer or decimal ratio within the range of 1:1.5, 1:1.6, 1:1.7, 1:1.8 or 1:(1.5~1.8).

[0080] In some embodiments, the third solvent is selected from one or more of water, methanol, ethanol, and ethylene glycol.

[0081] In some embodiments, the third solvent is selected from a mixture of water and anhydrous ethanol, wherein the volume ratio of water to anhydrous ethanol is 1:1.

[0082] In some embodiments, the mass-to-volume ratio (g / mL) of the resorcinol and the third solvent is 1:(150~250), for example, any integer or decimal ratio within the range of 1:150, 1:160, 1:170, 1:180, 1:190, 1:200, 1:210, 1:220, 1:230, 1:240, 1:250.

[0083] In some implementations, the pH value is adjusted to 5.5 to 6.5, for example, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, or any integer or decimal value within the range of 5.5 to 6.5.

[0084] In some implementations, ammonia is used to adjust the pH value.

[0085] In some embodiments, in step S3, the temperature of the polymerization reaction is 55°C to 75°C, for example, any integer or decimal value within the range of 55°C, 60°C, 65°C, 70°C, 75°C, or 55°C to 75°C.

[0086] In some implementations, in step S3, the polymerization reaction time is 7h to 9h, for example, any integer or decimal value within the range of 7h, 7.5h, 8h, 8.5h, and 9h.

[0087] In some embodiments, in step S3, the heating carbonization is carried out in an inert gas atmosphere, wherein the inert gas is selected from at least one of argon, helium, krypton and nitrogen.

[0088] In some embodiments, in step S3, the heating rate for carbonization is 3°C / min to 7°C / min, for example, any integer or decimal value within the range of 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, or 3°C / min to 7°C / min.

[0089] In some embodiments, in step S3, the peak temperature of the heating and carbonization is 750°C to 950°C, for example, any integer or decimal value within the range of 750°C, 800°C, 850°C, 900°C, 950°C, or 750°C to 950°C.

[0090] Here, carbonization temperature mainly affects the microstructure and chemical state of the carbon coating layer. Low-temperature carbonization is incomplete, and the carbon layer is mainly composed of highly disordered hard carbon with few and small graphite-like microcrystals, resulting in poor conductivity and brittle mechanical properties. Under medium-temperature conditions, the catalytic effect of zinc can be fully utilized, effectively catalyzing the rearrangement of amorphous carbon to form more and larger graphite-like microcrystals embedded in the hard carbon matrix, achieving the best balance between high conductivity and good mechanical toughness. Although high-temperature carbonization results in a higher degree of graphitization, the rapid volatilization of zinc leads to a short catalytic time and uneven distribution. At the same time, excessively high temperatures can easily cause the carbon layer to become over-graphitized and brittle, increasing the difference in thermal expansion coefficients between the carbon layer and the active core, weakening the interfacial bonding force, and making it prone to cracking during long-term cycling. Preferably, the peak temperature of the heating and carbonization is 850°C. At this temperature, the catalytic effect of zinc can be fully utilized, effectively catalyzing the rearrangement of amorphous carbon to form a large number of graphite-like microcrystals of appropriate size, achieving the best balance between high conductivity and good mechanical toughness of the carbon layer. If the temperature is too low, the degree of graphitization will be insufficient and the conductivity will be weak. If the temperature is too high, the carbon layer will easily become brittle and the interfacial bonding force will decrease. Therefore, 850°C is the optimal temperature window for forming the optimal carbon layer structure.

[0091] In some implementations, in step S3, the duration of the peak heating carbonization temperature is 1h to 3h, for example, any integer or decimal value within the range of 1h, 1.5h, 2h, 2.5h, 3h, or 1h to 3h.

[0092] In some embodiments, in step S3, the mass ratio of the resorcinol to the hollow cobalt selenide is 1:(4~6), for example, any integer or decimal ratio within the range of 1:4, 1:4.5, 1:5, 1:5.5, 1:6 or 1:(4~6).

[0093] In some embodiments, step S3 further includes a preheating step before the heating and carbonization.

[0094] In some embodiments, the preheating is carried out in an inert gas atmosphere, wherein the inert gas is selected from at least one of argon, helium, krypton and nitrogen.

[0095] In some embodiments, the preheating rate is 1°C / min to 3°C / min, for example, any integer or decimal value within the range of 1°C / min, 2°C / min, 3°C / min, or 1°C / min to 3°C / min.

[0096] In some embodiments, the peak temperature of the preheating is 250°C to 450°C, for example, any integer or decimal value within the range of 250°C, 300°C, 350°C, 400°C, 450°C, or 250°C to 450°C.

[0097] In some embodiments, the duration of the preheating peak temperature is 0.5h to 1.5h, for example, 0.5h, 1.0h, 1.5h or any integer or decimal value within the range of 0.5h to 1.5h.

[0098] [Negative electrode plate]

[0099] A third aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising a negative electrode active material, wherein the negative electrode active material is a composite negative electrode material provided in the first aspect of the present invention or a composite negative electrode material prepared by the preparation method provided in the second aspect of the present invention.

[0100] The negative electrode sheet includes a negative current collector and a layer of negative active material disposed on the negative current collector. The negative current collector can be aluminum foil, carbon-coated aluminum foil, copper foil, porous copper foil, foamed nickel / copper foil, zinc-plated copper foil, nickel-plated copper foil, carbon-coated copper foil, nickel foil, titanium foil, carbon-containing porous copper foil, etc. The negative active material layer includes the negative active material. In this invention, the negative active material is the negative electrode material provided in the first aspect of this invention.

[0101] The negative electrode active material layer may also include one or both selected from conductive agents and binders. Conductive agents are used to improve electrode conductivity. Examples of negative electrode conductive agents include conductive carbon black, acetylene black, Ketjen black graphite, graphene, micro / nanowire conductive materials, and micro / nanotube conductive materials. The binder for the negative electrode improves the adhesion between the negative electrode active material particles and between the negative electrode active material particles and the current collector. Examples of negative electrode binders include polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, sodium carboxymethyl cellulose, polymethacrylamide, polyacrylic acid, lithium polyacrylate, polyacrylamide, polyamide, polyimide, polyacrylate, styrene-butadiene rubber, sodium alginate, chitosan, polyethylene glycol, and guar gum. The mass ratio of the components in the negative electrode active material layer can be conventional.

[0102] This application does not impose any particular limitation on the preparation method of the negative electrode sheet; any preparation method known in the art can be used, as long as it achieves the purpose of this application. For example, the preparation method of the negative electrode sheet includes, but is not limited to, the following steps: dispersing and mixing the negative electrode active material, conductive agent, and binder in a solvent to form a uniform negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector; and obtaining the negative electrode sheet after drying, cold pressing, cutting, slitting, and re-drying. The solvent for the negative electrode slurry can be a conventional solvent in the art, such as deionized water.

[0103] It should be understood that, since the negative electrode sheet provided in this application includes a negative electrode active material, which is the composite negative electrode material provided in the first aspect of the present invention or the composite negative electrode material prepared by the preparation method provided in the second aspect of the present invention, the beneficial effects of the composite negative electrode material and its preparation method described in any of the above embodiments are applicable to the negative electrode sheet.

[0104] [Battery]

[0105] A fourth aspect of the present invention provides a battery comprising the negative electrode sheet provided in the third aspect of the present invention.

[0106] In some embodiments, the battery can be a secondary battery or a primary battery, preferably a secondary battery. For example, the battery can be a sodium-ion battery, but it is not limited to this. The battery structures of this application include, but are not limited to, pouch-type sodium-ion batteries, square hard-case batteries, or cylindrical hard-case batteries.

[0107] In some embodiments, the battery further includes a positive electrode, an electrolyte, and a separator. Typically, a battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, with the separator disposed between the positive and negative electrodes. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, disposed between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0108] The positive electrode sheet includes a positive current collector and a layer of positive active material disposed on the positive current collector. The positive current collector can be aluminum foil, copper foil, titanium foil, nickel foil, iron foil, zinc foil, etc. The positive active material layer includes the positive active material. The positive active material suitable for this invention can be any known positive active material that can be used in sodium-ion batteries, capable of reversibly inserting and de-intercalating sodium ions. The positive active material can be a sodium-ion positive active material commonly used in the art, preferably selected from sodium-iron composite oxides (such as NaFeO2), sodium-cobalt composite oxides (such as NaCoO2), sodium-chromium composite oxides (such as NaCrO2), sodium-manganese composite oxides (such as NaMnO2), sodium-nickel composite oxides (such as NaNiO2), and sodium-nickel-titanium composite oxides (such as NaNiO2). 0.5 Ti 0.5 O2), sodium-nickel-manganese composite oxides (such as NaNi) 0.5 Mn 0.5 O2), sodium iron manganese composite oxides (such as Na) 2 / 3 Fe 1 / 3 Mn 2 / 3 O2), sodium-nickel-cobalt-manganese composite oxides (such as NaNi) 1 / 3 Co 1 / 3 Mn1 / 3 One or more of the following: O2), sodium iron phosphate (such as NaFePO4), sodium manganese phosphate (such as NaMnPO4), and sodium cobalt phosphate (such as NaCoPO4).

[0109] The positive electrode active material layer may also include one or both selected from conductive agents and binders. Conductive agents are used to improve the electrode conductivity. Examples of conductive agents for the positive electrode include one or more of conductive carbon black, carbon fiber (CF), acetylene black, Ketjen black, graphene, carbon nanotubes, and carbon microspheres. The binder for the positive electrode improves the adhesion between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of binders for the positive electrode include at least one selected from fluorinated resins, polypropylene resins, fiber-type binders, rubber-type binders, and polyimide-type binders. The mass ratio of the components in the positive electrode active material layer can be conventional.

[0110] The positive electrode active material layer is obtained by coating a positive electrode slurry containing the components of the positive electrode active material layer and a solvent onto a positive electrode current collector, followed by rolling and slitting. The solvent for the positive electrode slurry can be N-methylpyrrolidone (NMP).

[0111] The separator can be a polymer porous separator, an inorganic porous separator, or a polymer-inorganic composite porous separator. Polymer porous separators include single-layer polymer porous separators and multi-layer polymer porous separators.

[0112] The electrolyte typically comprises a solvent and a sodium salt. The electrolyte suitable for this invention can be conventional; for example, the solvent can be one or more selected from dimethyl carbonate (DMC), propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), or 1,4-butylpropyl carbonate, more preferably one or more selected from PC, EC, and EMC. The sodium salt can be one or more selected from NaBF4, NaClO4, NaPF6, NaFSI, and NaTFSI.

[0113] The battery of this application also includes a packaging shell for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for sodium-ion batteries. This application does not limit the aforementioned other components. This application does not impose any particular limitation on the packaging shell; it can be a packaging shell known in the art, as long as it achieves the purpose of this application.

[0114] This invention does not impose any special restrictions on the battery preparation method; any technical solution known to those skilled in the art for preparing a battery, such as a secondary battery, from a negative electrode material can be used.

[0115] It should be understood that, since the battery provided in this application includes the negative electrode sheet described in the third aspect of the present invention, the beneficial effects of the negative electrode material and its preparation method described in any of the above embodiments are applicable to the battery.

[0116] [Electrical appliances]

[0117] The fifth aspect of the present invention provides an electrical device, the electrical device comprising the battery provided in the fourth aspect of the present invention.

[0118] The application of the battery in this application is not particularly limited, and it can be used in any electrical device known in the prior art. In some embodiments, the battery of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, drones, and sodium-ion capacitors, etc.

[0119] It should be understood that, since the electrical device provided in this application includes the battery described in the fourth aspect of the present invention, the beneficial effects of the negative electrode material and its preparation method described in any of the above embodiments are applicable to the electrical device.

[0120] The method of the present invention will be described below through specific embodiments. It should be understood that these embodiments are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited to the scope of the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions in conventional experiments.

[0121] Example 1 Step S101: Dissolve 12 mmol of cobalt nitrate hexahydrate in 100 mL of methanol to obtain solution A; dissolve 40 mmol of 2-methylimidazole in 50 mL of methanol to obtain solution B; slowly add solution B to solution A, stir for 15 min, let stand for 12 h, filter, wash three times with methanol, and dry at 65 °C. Heat to 700 °C at 2 °C / min under Ar atmosphere and hold for 2 h to obtain the cobalt-carbon precursor (Co / NC).

[0122] Step S102: Take 200 mg of the cobalt carbon precursor obtained in Step S101 and spread it evenly on a ceramic boat, placing it in the constant temperature zone of a tube furnace. Separately, take 400 mg of selenium powder and place it upstream. Heat to 350℃ at 5℃ / min under Ar, and hold for 1 h. After cooling to room temperature, switch to a 10% H2 / Ar mixed gas, and replace the upstream ceramic boat with one containing 400 mg of sulfur powder. Continue heating to 500℃ at 3℃ / min, and hold for 2 h. After cooling, wash with CS2 and dry at 60℃ to obtain hollow cobalt selenide sulfide (H-CoS). x Se 2-x ).

[0123] Step S103: Dissolve 0.2 g resorcinol, 0.3 mL formaldehyde, and 0.1 g zinc acetate in a mixed solvent of 40 mL deionized water / anhydrous ethanol (1:1 v / v), and adjust the pH to 6.5 by adding dilute ammonia dropwise to obtain a prepolymer solution; disperse 1 g of hollow cobalt selenide obtained in step S102 in the prepolymer solution, and carry out in-situ polymerization by stirring in a water bath at 65°C for 8 h to obtain a resin-coated precursor; heat the precursor to 350°C at 2°C / min under an Ar atmosphere, hold for 1 h, then heat to 850°C at 5°C / min, and hold for 2 h to obtain a hollow cobalt selenide carbon composite material; that is, the composite negative electrode material (H-CoS). x Se 2-x @GC-850, 0.3≤x≤1.7 and the value of x decreases from the kernel layer to the outer shell layer), where: the outer shell layer is in contact with the coating layer, and the chemical formula is CoS. 0.3 Se 1.7 The thickness is approximately 10 nm; the core layer is in contact with the cavity, and its chemical formula is CoS. 1.7 Se 0.3 The thickness is approximately 10 nm.

[0124] Example 2 The only difference between Example 2 and Example 1 is that the carbonization final temperature in step S103 is adjusted from 850°C to 750°C.

[0125] Example 3 The only difference between Example 3 and Example 1 is that the carbonization final temperature in step S103 is adjusted from 850°C to 950°C.

[0126] Example 4 The only difference between Example 4 and Example 1 is that the selenization temperature in step S102 is adjusted from 350°C to 300°C.

[0127] Example 5 The only difference between Example 5 and Example 1 is that the selenization temperature in step S102 is adjusted from 350°C to 600°C.

[0128] The structural parameters of the materials in Examples 1 to 5 are shown in Table 1.

[0129] Table 1

[0130] Comparative Example 1 Steps S101 and S103 of Comparative Example 1 are exactly the same as those of Example 1.

[0131] Step S102 is replaced with step S102': 200 mg of the cobalt-carbon precursor obtained in step S101 is spread evenly on a ceramic boat and placed in the constant temperature zone of a tube furnace. 400 mg of sulfur powder is placed upstream. The temperature is increased to 500°C at 3°C / min under a 10% H2 / Ar mixed gas and held for 2 h. After cooling to room temperature, the Ar atmosphere is switched, and the upstream ceramic boat is replaced with a ceramic boat containing 400 mg of selenium powder. The temperature is increased to 350°C at 5°C / min and held for 1 h. After cooling, it is washed with CS2 and dried at 60°C.

[0132] The final composite anode material obtained is RH-CoS 1.5 Se 0.5 @GC.

[0133] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that zinc acetate is not added in step S103.

[0134] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that step S103 is not included, and hollow cobalt selenide is used as the final product.

[0135] Comparative Example 4 Comparative Example 4 compared to Example 1: In step S101, the carbonization temperature is adjusted from 700℃ to 500℃ (step S101''). Step S102 is replaced with S102'': Take 200 mg of the product obtained in step S101'', and physically mix it with 400 mg of sulfur powder and 400 mg of selenium powder, placing them in the same ceramic boat. Under an argon atmosphere, heat the mixture to 500 °C at a rate of 2 °C / min and hold for 3 hours.

[0136] Step S103 is completely consistent with Example 1. The difference between the final negative electrode material and the composite negative electrode material obtained in Example 1 is that the material obtained in Comparative Example 4 is a cobalt selenide carbon composite material, which does not contain cavities.

[0137] Material characterization The carbon layers of the negative electrode materials prepared in Examples 1-5 and Comparative Examples 1-4 were characterized by Raman spectroscopy, and the ID / IG ratio of the carbon layers was tested and analyzed. The results are shown in Table 2.

[0138] Table 2

[0139] Electrochemical performance testing

[0140] Preparation of sodium-ion batteries: (1) Preparation of negative electrode sheet: The negative electrode materials prepared in Examples 1-5 and Comparative Examples 1-4 above are used as negative electrode active materials. Acetylene black is used as a conductive agent and carboxymethyl cellulose is used as a binder. They are mixed in a ratio of negative electrode active material: conductive agent: binder = 80: 12: 8. Deionized water is added as a solvent. The mixture is stirred under vacuum until the system is homogeneous. It is then coated on the surface of the negative electrode current collector aluminum foil and dried under vacuum at 80°C for 12 hours. The plates are then cut into circular electrode sheets using a punching machine. (2) Preparation of positive electrode: Sodium metal sheet is used as positive electrode; (3) Separator: Glass fiber diaphragm is selected as the diaphragm; (4) Electrolyte: The electrolyte is a 1 mol / L NaClO4 electrolyte in which ethane carbonate and diethyl carbonate are dissolved in a volume ratio of 1:1 (EC:DEC, volume ratio 1:1).

[0141] (5) Battery assembly: Assemble the negative electrode, separator and positive electrode in the order of negative electrode, separator and positive electrode, and immerse them in electrolyte. Assemble the CR2032 button cell in an argon glove box.

[0142] The performance of CR2032 button batteries using the negative electrode materials prepared in Examples 1-5 and Comparative Examples 1-4 as negative electrode active materials was tested.

[0143] 1. Initial discharge capacity, initial coulombic efficiency, and electrochemical impedance spectroscopy (EIS) tests: Using the LAND CT3001A battery testing system, charge-discharge tests were conducted at 25°C at 0.1 A / g, with a voltage range of 0.01~3.0 V. Specifically: The battery was discharged at a constant current of 0.1 A / g to 0.01 V, and the discharge capacity at this point was recorded as the initial discharge capacity; then, it was charged at a constant current of 0.1 A / g to 3 V, and the charge capacity at this point was recorded as the initial charge capacity; the initial coulombic efficiency = initial charge capacity / initial discharge capacity * 100%.

[0144] Electrochemical impedance spectroscopy (EIS) was performed using a CHI760E electrochemical workstation with a test amplitude of 5 mV and a frequency range of 0.01 Hz to 100 kHz.

[0145] The test results are shown in Table 3.

[0146] Table 3

[0147] 2. Capacity Retention Test: Using the Blue Battery Testing System, at 25℃, a current density of 0.1 A / g was first applied to the battery to measure capacity retention between 0.01 and 3.0 V vs. Na. + Five charge-discharge cycles were performed under the / Na voltage window for activation. From the sixth cycle onwards, constant current charge-discharge cycles were performed for 1000 cycles at a current density of 1 A / g under the same voltage window, and for 1500 cycles at a current density of 5 A / g under the same voltage window. The charging capacity of the first cycle and the charging capacity of the corresponding cycle number were recorded. The capacity retention rate was calculated as: (Charging capacity of the corresponding cycle number / Charging capacity of the first cycle) × 100%. The test results are shown in Table 4.

[0148] Table 4

[0149] 3. Rate Performance Testing: Using the LAND CT3001A battery testing system, under constant temperature conditions of 25℃, the voltage window was set to 0.01~3.0 V vs. Na. + / Na; constant current discharge was performed at current densities of 0.1 A / g, 0.2 A / g, 0.3 A / g, 1 A / g, 2 A / g, and 5 A / g to 0.01 V, and then constant current charging was performed at the same current density to 3.0 V to complete a single charge-discharge cycle; five cycles were continuously tested at each current density, and the average discharge capacity of the last three cycles at each current density was taken as the stable reversible capacity at that rate. The test results are shown in Table 5.

[0150] Table 5

[0151] From the contents recorded in Tables 1 to 5, we can see that: The sodium-ion battery prepared using the composite anode material obtained in Example 1 of this invention as the anode active material exhibits optimal electrochemical performance. Its initial discharge capacity at 0.1 A / g is 660 mAh / g, and its initial coulombic efficiency is 83.3%. After 1000 cycles at a current density of 1 A / g, the capacity retention rate is as high as 96.7%. Under high-rate conditions of 5 A / g, it still maintains a reversible capacity of 490 mAh / g, with a rate capacity retention rate of 74.1%, and a charge transfer impedance Rct as low as 21 Ω. This is attributed to the complete elemental gradient structure of the composite anode material in Example 1, which is composed of a selenium-rich outer shell and a sulfur-rich core. This structure fully leverages the high capacity characteristics of the sulfur-rich core and the high conductivity and low expansion interface advantages of the selenium-rich outer shell. Simultaneously, the graphitized carbon shell formed by zinc salt catalysis effectively suppresses irreversible side reactions. The gradient structure and the carbon coating layer synergistically alleviate volumetric stress during charging and discharging, maintaining the integrity of the electrode structure, thus achieving a balance between high capacity, long cycle life, and excellent rate performance.

[0152] In Example 4, the selenization temperature was 300°C. Compared with Example 1, its overall performance was slightly lower, but still significantly better than Comparative Example 1 with no gradient structure. This indicates that a selenization temperature of 300°C is sufficient to initiate an effective surface selenization reaction and form a stable selenium-rich shell.

[0153] In Example 5, the sulfidation temperature was 600℃. Compared with Example 1, its capacity retention rate after 1000 cycles at 1 A / g was 95.5%, and its reversible capacity at 5 A / g was 479 mAh / g, still outperforming all comparative examples. This indicates that under sulfidation conditions at 600℃, the elemental content gradient structure of "selenium-rich outer shell and sulfur-rich inner core" can still be stably formed and function effectively. It also shows that excessively high sulfidation temperatures only lead to a slight decrease in performance and do not affect the basic function of the gradient structure.

[0154] In Examples 2 and 3, the final carbonization temperatures were 750℃ and 950℃, respectively. The electrochemical performance of both examples was significantly lower than that of Example 1, where the final carbonization temperature was 850℃. This indicates that 850℃ is the optimal temperature window for zinc salt catalysis to form the optimal carbon layer structure. At this temperature, the catalytic graphitization effect of zinc can be fully utilized, achieving the best balance between high conductivity and good mechanical toughness of the carbon layer. Too low a temperature leads to insufficient graphitization and weak conductivity, while too high a temperature easily causes carbon layer embrittlement and a decrease in interfacial bonding, both of which are detrimental to performance improvement.

[0155] In Comparative Example 1, the process of first sulfurizing and then seleniumizing failed to form a continuous and effective elemental gradient structure of "selenium-rich outer shell and sulfur-rich inner core," and its cycle stability and high-rate capacity were significantly lower than those of Example 1. This demonstrates that the stepwise gas-phase process of first selenization and then sulfurization as described in Example 1 of this invention is a key and irreplaceable step in constructing an ideal functional gradient structure.

[0156] In Comparative Example 2, no zinc salt was added for catalytic carbonization. The resulting carbon layer exhibited low graphitization, a high ID / IG ratio of 1.22, and a charge transfer impedance (Rct) of 71 Ω. Its rate performance and cycle stability were significantly inferior to those of Example 1. This indicates that the catalytic graphitization and in-situ pore-forming effects of zinc salt can significantly improve the conductivity and ion transport capacity of the carbon coating layer, which is crucial for achieving high rate performance.

[0157] In Comparative Example 3, without a hard carbon coating layer, the active material is directly exposed to the electrolyte, failing to form effective external constraints and interface protection. During cycling, the structure is prone to pulverization and collapse, resulting in significantly lower cycling stability than Example 1. Simultaneously, the ID / IG value of Comparative Example 3 is significantly higher than that of Example 1, indicating that without an additional hard carbon coating layer, the graphitization degree is limited by the carbon framework derived solely from the precursor. In contrast, the hard carbon coating layer formed by the carbonization of zinc salt catalytic resin can significantly reduce the ID / IG value and improve the degree of graphitization and electronic conductivity. This demonstrates that the hard carbon coating layer is beneficial for reducing material defect density and improving conductivity and structural stability.

[0158] In Comparative Example 4, the prepared material lacks a hollow structure and cannot effectively buffer the volume expansion of the active material during charge and discharge. Its cycle stability and rate performance are significantly lower than those of Example 1. Furthermore, Comparative Example 4 has an ID / IG ratio of 0.95, indicating a coating layer but a low degree of graphitization of the core carbon skeleton. This demonstrates the synergistic effect of a hollow structure, gradient, and high carbonization temperature in reducing ID / IG and improving overall performance.

[0159] It should be understood that the above embodiments are exemplary and are not intended to encompass all possible implementations included in the claims. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only illustrate several implementations of the present invention and do not limit the scope of protection of this patent.

Claims

1. A composite negative electrode material, characterized in that, The composite anode material has a hollow core-shell structure; from the center to the outer surface of the composite anode material, it sequentially includes a cobalt selenide sulfide layer and a hard carbon coating layer, with the cobalt selenide sulfide layer enclosing a cavity; wherein... With the thickness of the composite negative electrode material from the center to the outer surface being 100%, the thickness of the cobalt selenide sulfide layer accounts for 30% to 65%; The cobalt selenide sulfide layer includes an outer shell layer and a core layer. The outer shell layer is in contact with the hard carbon coating layer, and the core layer is in contact with the cavity. Assuming the thickness of the cobalt selenide sulfide layer is 100%, the outer shell layer accounts for 10% to 25% of the total thickness, and the core layer accounts for 10% to 25% of the total thickness. The chemical formula of the cobalt selenide sulfide is CoS. x Se 2-x , where 0.3≤x≤1.7; the value of x decreases from the kernel layer to the outer shell layer.

2. The composite negative electrode material according to claim 1, characterized in that, With the thickness of the composite anode material from its center to its outer surface as 100%, the thickness of the cobalt selenide sulfide layer accounts for 40% to 55%; the thickness of the cavity accounts for 35% to 50%; and the thickness of the hard carbon coating layer accounts for 8% to 15%. And / or, the nitrogen content in the hard carbon coating is 2.0 wt% to 6.0 wt%.

3. A method for preparing the composite negative electrode material according to claim 1 or 2, characterized in that, include: S1: Dissolve cobalt nitrate hexahydrate in the first solvent to obtain solution A; Dissolve 2-methylimidazole in a second solvent to obtain solution B; Solution A and solution B were mixed and heated to obtain a cobalt-carbon precursor. S2: Selenize the cobalt carbon precursor obtained in step S1 by introducing a selenium source, cool it down, and then sulfide it by introducing a sulfur source to obtain hollow cobalt selenide sulfide. S3: Disperse the hollow cobalt selenide obtained in step S2 in the prepolymer liquid for polymerization reaction, and then heat and carbonize it to obtain the final product.

4. The preparation method according to claim 3, characterized in that, Step S1 satisfies at least one of the following characteristics: (1) The first solvent is selected from one or more of water, methanol, ethanol and ethylene glycol; (2) The molar concentration of cobalt nitrate hexahydrate in solution A is 50 mmol / L to 200 mmol / L; (3) The second solvent is selected from one or more of water, methanol, ethanol and ethylene glycol; (4) The molar concentration of the 2-methylimidazole in solution B is 500 mmol / L to 1000 mmol / L; (5) The volume ratio of solution A to solution B is (1~3):1; (6) The heating is carried out in an inert gas atmosphere, wherein the inert gas is selected from at least one of argon, helium, krypton and nitrogen; (7) The heating rate is 2℃ / min to 5℃ / min, the peak temperature is 500℃ to 700℃, and the duration of the peak temperature is 1h to 3h.

5. The preparation method according to claim 3, characterized in that, Step S2 satisfies at least one of the following characteristics: (1) The selenium source is selected from one or more of selenium powder, sodium selenosulfate, and potassium selenosulfate; (2) The mass ratio of the selenium source to the cobalt-carbon precursor is (1.5~2.5):1; (3) The selenization is carried out in an inert gas atmosphere, wherein the inert gas is selected from at least one of argon, helium, krypton and nitrogen; (4) The selenization is carried out under heating conditions, the heating rate is 3℃ / min~7℃ / min, the peak temperature is 300℃~400℃, and the duration of the peak temperature is 1h~2h; (5) During the selenization process, the selenium source is located at the upper air inlet of the tubular furnace, and the cobalt-carbon precursor is located at the lower air inlet of the tubular furnace. (6) The cooling refers to cooling down to room temperature; (7) The sulfur source is selected from one or more of sulfur powder, thiourea, ammonium sulfide, and thioacetamide; (8) The mass ratio of the sulfur source to the cobalt-carbon precursor is (1.5~2.5):1; (9) The sulfidation is carried out in an inert gas atmosphere containing hydrogen, wherein the inert gas is selected from at least one of argon, helium, krypton and nitrogen, and the hydrogen accounts for 8% to 12% of the total gas volume; (10) The vulcanization is carried out under heating conditions, the heating rate is 2℃ / min~5℃ / min, the peak temperature is 400℃~600℃, and the duration of the peak temperature is 1h~3h. (11) During the sulfidation, the sulfur source is located at the upper tuyer of the tubular furnace, and the cobalt carbon precursor after selenization is located at the lower tuyer of the tubular furnace.

6. The preparation method according to claim 3, characterized in that, Step S3 satisfies at least one of the following characteristics: (1) The steps for preparing the prepolymer solution are as follows: dissolve resorcinol, formaldehyde and zinc salt in a third solvent, and adjust the pH with dilute ammonia water to obtain the solution; (2) The polymerization reaction is carried out at a temperature of 55℃~75℃ for 7h~9h; (3) The heating carbonization is carried out in an inert gas atmosphere, wherein the inert gas is selected from at least one of argon, helium, krypton and nitrogen; (4) The heating rate of the carbonization process is 3℃ / min to 7℃ / min, the peak temperature is 750℃ to 950℃, and the duration of the peak temperature is 1h to 3h. (5) The heating carbonization process also includes a preheating step.

7. The preparation method according to claim 6, characterized in that, In step S3, the step of preparing the prepolymer solution satisfies at least one of the following characteristics: (1) The zinc salt is selected from one or more of zinc acetate, zinc chloride, and zinc nitrate; (2) The mass ratio of resorcinol to zinc salt is 1:(0.4~0.6); (3) The mass-to-volume ratio (g / mL) of resorcinol and formaldehyde is 1:(1.5~1.8); (4) The third solvent is selected from one or more of water, methanol, ethanol and ethylene glycol; (5) The mass-to-volume ratio (g / mL) of the resorcinol and the third solvent is 1:(150~250); (6) Adjust the pH value to 5.5~6.

5.

8. The preparation method according to claim 7, characterized in that, In step S3, The mass ratio of resorcinol to hollow cobalt selenide sulfide is 1:(4~6).

9. The preparation method according to claim 6, characterized in that, In step S3, The preheating is carried out in an inert gas atmosphere, wherein the inert gas is selected from at least one of argon, helium, krypton and nitrogen; And / or, the preheating rate is 1℃ / min to 3℃ / min, the peak temperature is 250℃ to 450℃, and the duration of the peak temperature is 0.5h to 1.5h.

10. A battery, comprising a negative electrode, characterized in that, The negative electrode sheet includes the composite negative electrode material according to claim 1 or 2, or the composite negative electrode material prepared by the preparation method according to any one of claims 3-8.

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