Composite negative electrode material for sodium ion battery, preparation method and sodium ion battery

Abstract

This application provides a composite anode material for sodium-ion batteries, a preparation method thereof, and a sodium-ion battery, belonging to the field of energy storage battery technology. The composite anode material comprises: tin-based multi-element alloy nanoparticles; and a carbon matrix coating the surface of the tin-based multi-element alloy nanoparticles; wherein the carbon matrix is ​​a three-dimensional porous carbon network co-doped with nitrogen and sulfur. This invention, through the synergistic effect of the active core and the coating matrix, balances high capacity, long cycle life, high rate performance, and economical preparation process, providing a high-performance composite anode material for the development of sodium-ion batteries.

Description

Technical Field

[0001] This application relates to the field of energy storage battery technology, and in particular to a composite negative electrode material for sodium-ion batteries, a preparation method thereof, and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries have become a research hotspot in the field of large-scale energy storage due to the abundance and low cost of sodium resources. However, the large radius of sodium ions leads to slow insertion / extraction kinetics and significant volume changes in the negative electrode material, which severely limits the cycle life and rate performance of the battery.

[0003] Currently, mainstream anode materials suffer from the following problems: Hard carbon materials: Although structurally stable, they have low specific capacity and poor first-week coulombic efficiency due to the large formation of solid electrolyte interphase (SEI) films.

[0004] Alloy materials (such as Sn and Sb) have a high theoretical specific capacity, but their volume expands greatly during alloying / dealloying, leading to material pulverization, shedding, and a sharp decline in cycle performance.

[0005] Metal oxides / sulfides also face the problems of poor conductivity and volume effect.

[0006] Patent CN200810072038.4 discloses a tin-cobalt-phosphorus alloy anode material for lithium-ion batteries and its preparation method. The composition and its content by mass percentage are: Sn:Co:P = 72%:22%:6%. Potassium sodium tartrate and potassium citrate are dissolved in water and stirred. Sodium stannate and cobalt chloride are added respectively to obtain solution A. Sodium hypophosphite is added to solution A and electrodeposited on a foamed copper current collector or a planar copper current collector to obtain the tin-cobalt-phosphorus alloy anode material for lithium-ion batteries.

[0007] Existing improvement methods, such as carbon coating, nano-sizing, or the preparation of composite materials, have shown some effectiveness, but they are often complex processes or lack sufficient synergistic effects between components, failing to simultaneously achieve high capacity, long lifespan, and high efficiency. Therefore, it is crucial to develop an anode material with innovative structure and composition that can synergistically address the aforementioned problems. Summary of the Invention

[0008] This application is made in view of the above-mentioned problems, and its purpose is to provide a composite negative electrode material for sodium-ion batteries, a preparation method thereof, and a sodium-ion battery.

[0009] Specifically, the first aspect of this application provides a composite negative electrode material for sodium-ion batteries, the composite negative electrode material comprising: Tin-based multi-element alloy nanoparticles; A carbon matrix coating the surface of the tin-based multi-element alloy nanoparticles; The carbon matrix is ​​a three-dimensional porous carbon network co-doped with nitrogen and sulfur.

[0010] Furthermore, the tin-based multi-element alloy comprises tin, a first alloying element M1, a second alloying element P, and a third alloying element M2; The first alloying element M1 is Fe or Co; The third alloying element M2 is Mg or Zn.

[0011] Furthermore, the general formula of the tin-based multi-element alloy is Sn-M1-P-M2, wherein the atomic percentage (at%) of each element satisfies: Sn 50-65%, M1 20-30%, P 5-10%, M2 5-10%.

[0012] Furthermore, the carbon matrix has a dual-modal pore size distribution, including primary mesopores with a pore size of 2-10 nm and secondary macropores with a pore size of 50-200 nm.

[0013] Furthermore, the primary mesopores originate from the pyrolysis of the metal-organic framework sacrificial template, and the secondary macropores originate from the thermal decomposition of the soft template agent.

[0014] A second aspect of the present invention provides a method for preparing a composite anode material, the method comprising the following steps: S1: A suspension providing a sacrificial template for a metal-organic framework; S2: Mix the tin source, the first alloying element source, the phosphorus source and the third alloying element source with the metal-organic framework sacrificial template suspension to allow metal ions to be adsorbed onto the metal-organic framework sacrificial template or into its pores. S3: Add carbon source, nitrogen and sulfur doping source and soft template agent to the mixture in step S2 for adsorption treatment; S4: Spray dry the mixture obtained in step S3 to obtain precursor powder; S5: The precursor powder is subjected to pre-oxidation heat treatment in an oxygen-containing atmosphere; S6: The pre-oxidized powder is subjected to programmed temperature pyrolysis under an inert atmosphere to obtain the composite anode material.

[0015] Further, in step S3, the nitrogen-sulfur doping source is L-cysteine, and the soft template agent is block copolymer F127; and / or The molar ratio of the carbon source, nitrogen and sulfur dopant sources to the total metal ions is 2.0-3.0:0.8-1.2:1.

[0016] Further, in step S5, the conditions for the pre-oxidation heat treatment are: heating to 200-300°C at a rate of 1-3°C / min in an air atmosphere, and holding at that temperature for 1-3 hours.

[0017] Furthermore, the programmed temperature pyrolysis process described in step S6 includes: First stage: Increase the temperature to 450-550℃ at a rate of 1-3℃ / min and hold for 1-3 hours; Second stage: Increase the temperature to 600-650℃ at a rate of 3-5℃ / min and hold for 2-4 hours.

[0018] A third aspect of this application provides a sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode comprises a current collector and an active material layer coated on the current collector, and the active material layer comprises the composite negative electrode material.

[0019] The present invention has the following beneficial effects: The tin-based quaternary alloy nanoparticles of this invention serve as the main active component, with sulfur (S) providing high capacity and laying the foundation for high energy storage in sodium-ion batteries. The inert buffer phase formed by the first alloying element M1 buffers volume changes during charge and discharge, improving the battery's cycle stability. The second alloying element P acts as an interface stabilizer and amorphizer, helping to maintain the stability of the alloy structure. The third alloying element M2 brings multiple advantages: its interface welding function enhances the interfacial bonding between the alloy particles and the carbon layer, preventing particle detachment during cycling and further improving the battery's cycle life; its SEI regulation function reduces irreversible capacity loss in the first cycle and improves rate performance, resulting in better battery performance during rapid charge and discharge; and its melting point reduction function saves energy, making the manufacturing process more economical and environmentally friendly.

[0020] From the perspective of the coating matrix, the nitrogen-sulfur gradient-doped dual-mode porous carbon network structure features a nitrogen-rich inner layer that accelerates charge transfer at the alloy-carbon interface, while a sulfur-rich outer layer provides a rapid channel for sodium ions to enter and exit. These two elements work synergistically to achieve the optimal effect of "conducting electrons internally and facilitating ions externally," significantly improving electrochemical kinetics and resulting in a substantial increase in the battery's charge-discharge efficiency. In the "dual-mode porosity" structure, mesopores provide channels for electrolyte wetting and short-range rapid ion transport, while macropores provide channels for long-range sodium ion diffusion and reserve space for alloy particle volume expansion. This efficient ion transport across the entire range ensures stable battery operation under various operating conditions.

[0021] This invention, through the synergistic effect of the active core and the coating matrix, takes into account the high capacity, long cycle life, high rate performance of the battery, and the economy of the preparation process, providing a high-performance composite anode material for the development of sodium-ion batteries. Detailed Implementation To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0022] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0023] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0024] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0025] An embodiment of the first aspect of this application provides a composite negative electrode material for sodium-ion batteries, the composite negative electrode material comprising: Tin-based multi-element alloy nanoparticles; A carbon matrix coating the surface of the tin-based multi-element alloy nanoparticles; The carbon matrix is ​​a three-dimensional porous carbon network co-doped with nitrogen and sulfur.

[0026] The unique structure of this composite anode material endows it with numerous superior properties. During charge and discharge, tin-based multi-element alloy nanoparticles, as the main active material, can undergo reversible alloying / dealloying reactions with sodium ions, thereby enabling the battery's charge and discharge functions. The nitrogen-sulfur gradient-doped dual-mode porous carbon network coating its surface plays a protective and synergistic role. During battery charge and discharge, the nitrogen-rich regions of the inner layer can rapidly conduct electrons from the external circuitry to the surface of the alloy particles, allowing charge to transfer rapidly at the alloy-carbon interface, accelerating the reaction rate. Simultaneously, the sulfur-rich regions of the outer layer provide numerous channels for sodium ions to rapidly enter and exit, enabling sodium ions to efficiently embed and extract from the alloy particles, significantly improving the battery's charge and discharge efficiency.

[0027] In this embodiment, the tin-based multi-element alloy comprises tin, a first alloying element M1, a second alloying element P, and a third alloying element M2; the first alloying element M1 is Fe or Co; and the third alloying element M2 is Mg or Zn.

[0028] Furthermore, the general formula of the tin-based multi-element alloy is Sn-M1-P-M2, wherein the atomic percentage (at%) of each element satisfies: Sn 50-65%, M1 20-30%, P 5-10%, M2 5-10%.

[0029] The tin-based multi-element alloy is (Sn 60 Fe 25 P 10 ) 95 Mg5 or (Sn 60 Fe 25 P 10 ) 90 Zn 10 .

[0030] The active core of this invention is tin-based quaternary alloy nanoparticles (55-70 wt%), with Sn as the main active element, providing high capacity, accounting for 50-65% of the molar percentage. The first alloying element M1 (inert buffer phase forming element): selected from Fe or Co; molar percentage 20-30%. The second alloying element P (interface stabilization and amorphization element): selected from P, molar percentage 5-10%. The third alloying element M2: selected from Mg or Zn, molar percentage 5-10%. The third alloying element M2 has the following functions: Function 1: Mg or Zn has good affinity with the carbon matrix and can react with oxygen to form MgO or ZnO. These oxides can "anchor" at the interface between the alloy particles and the carbon layer, acting as "nano-welds," greatly enhancing interfacial bonding and preventing detachment. Function 2 (SEI regulation): Mg or Zn oxides / hydroxides tend to form thinner, more stable, and more ionicly conductive SEI films, thereby reducing irreversible capacity loss in the first cycle and improving rate performance. Function 3 (Lowering the melting point): The addition of Mg or Zn can lower the eutectic temperature of the alloy system, which helps to form a more uniform alloy phase at a lower heat treatment temperature and saves energy.

[0031] The carbon matrix is ​​a nitrogen and sulfur co-doped three-dimensional porous carbon network, and the coating matrix is ​​a nitrogen-sulfur gradient doped dual-mode porous carbon network of 30-45 wt%.

[0032] Nitrogen (N): Total doping concentration is 6-7 at% (based on carbon matrix), with an inner layer (near alloy side) concentration of approximately 8-9 at% and an outer layer concentration of approximately 4-5 at%. Sulfur (S): Total doping concentration is 3-4 at% (based on carbon matrix), with an inner layer concentration of approximately 2-3 at% and an outer layer concentration of approximately 5-6 at%.

[0033] The concentration of doped elements in the carbon layers exhibits a gradient distribution from the inside out. The inner layer (closer to the alloy particles) is nitrogen-rich (N-doped), with nitrogen providing more electron conduction channels and accelerating charge transfer at the alloy-carbon interface. The outer layer is sulfur-rich (S-doped), with sulfur significantly increasing the interlayer spacing and providing rapid entry and exit channels for sodium ions. This gradient design achieves optimal synergy between "inner electron conduction and outer ion conduction," greatly enhancing electrochemical kinetics.

[0034] In this embodiment, the carbon matrix has a dual-modal pore size distribution, including primary mesopores with a pore size of 2-10 nm, accounting for ~60% of the total pore volume; and secondary macropores with a pore size of 50-200 nm, accounting for ~40% of the total pore volume. The carbon layer coating the alloy particles has a uniform thickness of approximately 8-12 nm. Further, the primary mesopores originate from the pyrolysis of the metal-organic framework sacrificial template, and the secondary macropores originate from the thermal decomposition of the soft template agent.

[0035] Specifically, primary pores are mainly generated by the pyrolysis of metal-organic frameworks (MOFs). Their main function is to provide channels for electrolyte wetting and short-range rapid ion transport. Secondary pores are formed by soft template methods (such as surfactants). Their main function is to provide long-range diffusion channels for sodium ions and to reserve space for the volume expansion of alloy particles. The synergistic effect of the two modes of pores enables highly efficient ion transport across the entire range from nanometer to submicron scales.

[0036] In this embodiment, the composite anode material exhibits superior overall performance in sodium-ion batteries due to its structure. On one hand, the synergistic effect of the elements in the tin-based quaternary alloy nanoparticles of the active core ensures high capacity and long cycle life. The high capacity of Sn provides ample energy storage, while the first alloying element M1, the second alloying element P, and the third alloying element M2 optimize battery performance from different aspects, jointly maintaining the stability of the alloy structure and the battery's performance stability during charge and discharge. On the other hand, the nitrogen-sulfur gradient-doped dual-mode porous carbon network coating the matrix, through its unique "internal electron conduction, external ion conduction" structure and "dual-mode pore" design, greatly enhances electrochemical kinetics, ensuring high charge-discharge efficiency and good rate performance. In practical applications, this composite anode material can meet the performance requirements of sodium-ion batteries in different scenarios. For example, in the field of electric vehicles, high capacity ensures vehicle range, long cycle life reduces battery replacement costs, and high charge-discharge efficiency and good rate performance enable fast charging and adaptability to different driving conditions. In the field of energy storage, high capacity and long cycle life enable batteries to store more energy and operate stably for a long time, ensuring a stable power supply to the power grid.

[0037] A second aspect of the present invention provides a method for preparing a composite anode material, the method comprising the following steps: S1: A suspension providing a sacrificial template for a metal-organic framework; S2: Mix the tin source, the first alloying element source, the phosphorus source and the third alloying element source with the metal-organic framework sacrificial template suspension to allow metal ions to be adsorbed onto the metal-organic framework sacrificial template or into its pores. S3: Add carbon source, nitrogen and sulfur doping source and soft template agent to the mixture in step S2 for adsorption treatment; S4: Spray dry the mixture obtained in step S3 to obtain precursor powder; S5: The precursor powder is subjected to pre-oxidation heat treatment in an oxygen-containing atmosphere; S6: The pre-oxidized powder is subjected to programmed temperature pyrolysis under an inert atmosphere to obtain the composite anode material.

[0038] In this embodiment, step S1 further includes the preparation of a MOF-derived carbon-coated precursor: Metal source: Zinc nitrate hexahydrate (Zn(NO3)2·6H2O, 98%) Organic ligand: 2-Methylimidazole (99%) Solution A: Dissolve 5.0 g Zn(NO3)2·6H2O in 150 mL methanol.

[0039] Solution B: Dissolve 11.0 g of 2-methylimidazole in 150 mL of methanol.

[0040] Solution B was rapidly poured into solution A under vigorous stirring (500 rpm), and the reaction was carried out at room temperature (25°C) for 1 hour, followed by static aging for 12 hours. A methanol suspension of ZIF-8 nanoparticles was obtained. Here, ZIF-8 is not used as a component of the final material, but rather as a sacrificial template to construct the primary mesoporous structure. This step ensures uniform mixing of the metal elements at the atomic level and provides the final material with a highly ordered primary mesoporous structure derived from MOF.

[0041] In step S2, the active metal sources are: stannous chloride dihydrate (SnCl2·2H2O, 98%), ferric chloride hexahydrate (FeCl3·6H2O, 99%), magnesium nitrate hexahydrate (Mg(NO3)2·6H2O, 99%), and sodium hypophosphite (NaH2PO2·H2O, 99%).

[0042] Carbon source and dopant source: D-glucose, L-cysteine; Soft template: F-127 Operating instructions: 1. Take 200 mL of the ZIF-8 suspension obtained in step one, centrifuge (8000 rpm, 10 min), discard the supernatant, and obtain the wet ZIF-8 template; 2. Redisperse the wet template in 100 mL of an ethanol / water (v / v = 1:1) mixed solvent; 3. Add the above-mentioned active metal source (according to Sn). 60 Fe 25 P 10 (Accurately weigh the atomic ratio of Mg5) and 0.5 g of NaH2PO2, and sonicate (300W power) for 30 minutes to adsorb metal ions onto the surface and pores of ZIF-8.

[0043] In this embodiment, in step S3, the nitrogen-sulfur doping source is L-cysteine, and the soft template agent is block copolymer F127; the molar ratio of the carbon source, nitrogen-sulfur doping source and total metal ion content is 2.0-3.0:0.8-1.2:1.

[0044] Specifically, add 1.2 g glucose, 0.6 g L-cysteine ​​and 0.36 g F-127 to step S2, transfer the mixture to a flask, and stir in a 40°C water bath (300 rpm) for 6 hours to ensure full adsorption.

[0045] The high specific surface area of ​​ZIF-8 ensures the high dispersion of metal ions. F-127 and carbon source are adsorbed on the outside of ZIF-8 through self-assembly, thus initially constructing the structural basis of gradient doping and dual-mode pores.

[0046] In step S4, spray drying and pre-oxidation: inlet temperature: 210℃, outlet temperature: 100℃, feed rate: 4 mL / min; atomizing air pressure: 0.35 MPa.

[0047] Step S5 Pre-oxidation: Spread the collected powder evenly in a crucible, place it in a muffle furnace, and heat it to 200-300℃ at 1-3℃ / min under air atmosphere, and hold it at this temperature for 1-3 hours. This step causes L-cysteine ​​and glucose to undergo oxidative polymerization and cross-linking, solidifying the gradient structure and decomposing some F-127 to initially form macropores.

[0048] In this embodiment, the programmed temperature rise pyrolysis process described in step S6 is carried out in a tube furnace, including: Step 1: Template decomposition and carbonization: Place the pre-oxidized powder in a ceramic boat, put it into a tube furnace, and purge the air by introducing Ar gas at a flow rate of 200 sccm for 30 min; raise the temperature to 450-550℃ at a rate of 1-3℃ / min and hold for 1-3 hours. During this stage, the ZIF-8 template decomposes and volatilizes, leaving behind its inherent mesoporous structure; glucose and L-cysteine ​​are carbonized to form a nitrogen-sulfur-doped carbon framework; F-127 is completely decomposed to form macropores; and metal salts are reduced to elemental metals.

[0049] Step 2: Alloying and interface welding: Heat to 600-650℃ at a rate of 3-5℃ / min and hold for 2-4 hours.

[0050] Sn, Fe, P, and Mg interdiffusion form uniform quaternary alloy nanoparticles. Mg diffuses to the particle surface and reacts with oxygen-containing functional groups (-COOH, -OH) in the carbon layer to generate a 2-5 nm thick MgO interfacial layer, achieving strong chemical bonding. After the reaction is complete, the particles are naturally cooled to room temperature.

[0051] Endpoint control: The final alloy grain size is 25-40 nm.

[0052] The obtained material is lightly ground in a mortar and passed through a 400-mesh sieve to obtain the final product.

[0053] This preparation method first achieves atomic-level uniform mixing of metal elements by adsorbing metal ions onto a metal-organic framework sacrificial template, laying the foundation for the subsequent formation of a uniform alloy phase. Next, carbon source, nitrogen-sulfur dopant source, and soft template agent are added for adsorption treatment, utilizing the self-assembly of these substances to initially construct the structural basis of gradient doping and dual-modal pores. Spray drying and pre-oxidation steps further solidify the structure and preliminarily form macropores. The final temperature-programmed pyrolysis treatment completes key processes such as template decomposition, carbonization, alloying, and interface welding, ultimately resulting in the unique structure of the composite anode material.

[0054] In this invention, the principle of gradient doping is as follows: In step S3, the MOF template already loaded with metal ions is dispersed in a solution containing glucose (carbon source), L-cysteine ​​(N / S source), and F127 (soft template), and adsorbed by stirring at 40°C for a long time (6 hours). Because glucose molecules are relatively large, their diffusion and migration rates are slow; while L-cysteine ​​molecules are smaller, their diffusion rates are faster. During the stirring adsorption process, the small L-cysteine ​​molecules penetrate and adsorb more quickly into the internal pores and near-surface region of the MOF template; while the large glucose molecules are more likely to be wrapped around the outer layer of the particles. The -SH (thiol group) and -NH2 (amino group) in L-cysteine ​​interact with the metal nodes (Zn) in the MOF framework. 2+ It has stronger coordination ability and interaction forces, which makes it more inclined to enrich internally. After this step, a "core-shell" structure precursor with "core enriched with L-cysteine ​​(N / S source) and outer layer enriched with glucose (pure carbon source)" can be obtained. This is the physical basis and prerequisite for forming the final gradient doped structure.

[0055] In addition, in step S5, the spray-dried precursor powder is kept at 250°C in air for 2 hours. Under air and heating conditions, the organic matter undergoes an oxidation reaction. L-cysteine ​​contains highly reactive -SH and -NH2, making it more easily oxidized than glucose. It will undergo cross-linking, polymerization, and cyclization reactions first, forming a stable, N- and S-rich heterocyclic polymer structure, "fixing" itself in the inner layer where it is adsorbed. The glucose in the outer layer undergoes partial caramelization and oxidation simultaneously, covalently connecting with the already cross-linked L-cysteine ​​polymer in the inner layer, forming an integral, structurally fixed network. This step permanently "locks in" and "solidifies" the "concentration gradient" of physical adsorption formed in step S3 through a chemical reaction. Without this step, in the subsequent high-temperature pyrolysis, the physically adsorbed molecules would migrate, volatilize, and homogenize, and the gradient would not be maintained. Pre-oxidation ensures that after high-temperature pyrolysis, the N and S elements remain in the originally designed region, forming a stable gradient distribution of high concentration inside and low concentration outside (N) and low concentration inside and high concentration outside (S).

[0056] Meanwhile, by controlling parameters such as the inlet temperature, outlet temperature, and feed rate of the spray dryer, the morphology and particle size distribution of the precursor powder can be affected; by adjusting the temperature, time, and heating rate of the pre-oxidation and programmed pyrolysis treatments, the size of the alloy grains, the structure and properties of the carbon layer can be controlled. This controllability makes the preparation method highly flexible, enabling the preparation of composite anode materials with specific properties according to different application requirements.

[0057] A third aspect of this application provides a sodium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode comprises a current collector and an active material layer coated on the current collector, and the active material layer comprises the composite negative electrode material.

[0058] The composite anode material of this invention brings significant performance improvements to sodium-ion batteries. During battery charging and discharging, the composite anode material in the active material layer of the anode can efficiently participate in electrochemical reactions. When the battery is charging, sodium ions are deintercalated from the positive electrode, rapidly pass through the separator via the electrolyte, and then intercalate at the composite anode material. Due to the unique structure of the composite anode material, the tin-based quaternary alloy nanoparticles can effectively store sodium ions, while the nitrogen-sulfur gradient-doped dual-mode porous carbon network ensures the rapid transport of sodium ions, making the charging process more efficient. During discharging, the sodium ions intercalated in the composite anode material can be rapidly deintercalated, return to the positive electrode via the electrolyte, and complete the discharge process. This efficient charging and discharging process gives sodium-ion batteries high charge / discharge efficiency and energy conversion efficiency. In addition, the structure of the composite anode material can effectively alleviate the volume expansion problem of alloy particles during charging and discharging. The secondary macropores in the dual-mode pores reserve space for the volume expansion of alloy particles, avoiding electrode structure damage caused by excessive volume expansion, thereby ensuring a long cycle life of the battery. Meanwhile, the gradient design of the composite anode material, which allows for internal electron conduction and external ion conduction, facilitates smoother charge transfer during charging and discharging, further improving the battery's rate performance. Even under high-rate charging and discharging conditions, the battery maintains good performance, meeting the needs of applications requiring high charging and discharging speeds.

[0059] Example The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.

[0060] Example 1 A composite anode material for sodium-ion batteries comprises: 60% tin-based multi-element alloy nanoparticles; wherein the tin-based multi-element alloy is Sn. 60 Fe 25 P 10 ) 95 Mg5; The carbon matrix covering the surface of the tin-based multi-element alloy nanoparticles is 40%; wherein the carbon matrix is ​​a three-dimensional porous carbon network co-doped with nitrogen and sulfur, wherein the nitrogen doping amount is 6 at% (based on the carbon matrix); and the total sulfur doping amount is 4 at% (based on the carbon matrix).

[0061] The preparation method of the composite anode material includes the following steps: S1: A suspension that provides a metal-organic framework (MOF) sacrificial template; S2: Mix the tin source, the first alloying element source, the phosphorus source and the third alloying element source with the MOF suspension to allow metal ions to be adsorbed onto the MOF template or into the pores. S3: Add glucose, L-cysteine ​​and block copolymer F127 to the mixture from step S2 for adsorption treatment; S4: Spray dry the mixture obtained in step S3 to obtain precursor powder; S5: The precursor powder is subjected to pre-oxidation heat treatment in an oxygen-containing atmosphere, with the temperature increased to 250°C at a rate of 2°C / min and held at that temperature for 2 hours. S6: The pre-oxidized powder is subjected to programmed temperature pyrolysis treatment under an inert atmosphere. First stage: the temperature is increased to 500℃ at a rate of 2℃ / min and held for 2 hours; Second stage: the temperature is increased to 630℃ at a rate of 4℃ / min and held for 3 hours to obtain the composite anode material.

[0062] Example 2 This embodiment is basically the same as Embodiment 1, except that the tin-based multi-element alloy nanoparticles are Sn. 60 Fe 25 P 10 ) 90 Zn 10 The source of M2 was changed from magnesium nitrate to zinc nitrate.

[0063] Example 3 This embodiment is basically the same as embodiment 1, except that the temperature is raised to 600°C in the second stage of step S4.

[0064] Example 4 This embodiment is basically the same as Embodiment 1, except that the atomic percentage of Mg is changed from 5% to 3%, and the tin-based multi-element alloy is Sn. 62 Fe 25 P 10 ) 97 Mg3.

[0065] Comparative Example 1 Ternary alloy Sn was prepared according to the method in Example 1. 70 Fe 25 P5@carbon, but without adding a Mg source, and adjusting the ratio of Sn, Fe, and P to approximate a conventional ternary system.

[0066] Comparative Example 2 The ternary alloy material of Comparative Example 1 was used, and then physically mixed with purchased nano MgO powder by ball milling (the MgO content was equivalent to the theoretical mass of Mg element after oxidation in E1).

[0067] Comparative Example 3 This comparative example is basically the same as Example 1, except that urea is used as the N source and thiophene is used as the S source. It is simply mixed with glucose and cannot form a gradient doping structure.

[0068] Comparative Example 4 This comparative example is basically the same as Example 1, except that F127 soft template agent is not used, and the mesoporous structure is formed solely by ZIF-8 template.

[0069] Comparative Example 5 This comparative example is basically the same as Example 1, except that the pre-oxidation heat treatment step at 250°C in an air atmosphere is omitted, and two-step pyrolysis is carried out directly after spray drying.

[0070] Comparative Example 6 Purchase commercially available hard carbon anode material for sodium batteries.

[0071] Experimental Case Electrode preparation: The active material, conductive agent (Super P), and binder (sodium alginate) were mixed in deionized water at a mass ratio of 7:2:1 and stirred for 8 hours to form a uniform slurry. The slurry was coated onto copper foil, vacuum dried at 120°C for 12 hours, and then cut into 12 mm diameter discs to serve as working electrodes.

[0072] Battery assembly: In an argon-filled glove box (H2O, O2<0.1 ppm), a CR2032 coin cell was assembled using a sodium metal sheet as the counter electrode and reference electrode, glass fiber (Whatman GF / D) as the separator, 1 M NaClO4 in EC / PC (1:1 v / v) and 5% FEC as the electrolyte.

[0073] Electrochemical testing: Constant current charge-discharge test: Using the Newway battery testing system, the first-cycle charge-discharge efficiency (ICE) was tested at a current density of 0.1 A / g, and the capacity retention rate was tested after 1500 cycles at a current density of 1 A / g.

[0074] Rate performance testing: Current density increases from 0.1, 0.2, 0.5, 1, 2, 5 to 10 A / g, with 5 cycles at each rate.

[0075] The above experiments were conducted using the negative electrode materials of Examples 1-4 and Comparative Examples 1-6, and the results are shown in Table 1.

[0076]

[0077] As shown in Table 1, the anode materials of Examples 1-4 are significantly superior to those of Comparative Examples 1-6 in terms of first-cycle coulombic efficiency, capacity retention after 1500 cycles, and capacity retention at 10 A / g. This fully demonstrates the significant performance advantages of the composite anode material prepared by this invention. Among them, the performance indicators of Example 1 are the most outstanding, with a first-cycle coulombic efficiency of 91.5%, a capacity retention of 96.2% after 1500 cycles, and a capacity retention of 75% at 10 A / g. This indicates that the preparation method of this invention achieves uniform mixing of metal elements, gradient doping, and construction of a dual-modal porous structure through a series of steps, including adsorption of metal ions onto a metal-organic framework sacrificial template, adsorption treatment with the addition of a carbon source and a soft template agent, spray drying and pre-oxidation, and programmed temperature pyrolysis treatment. Key processes such as alloying and interface welding are also achieved, resulting in a composite anode material with a unique structure and excellent performance.

[0078] Comparative Example 1 lacks an "interface welding" element, leading to easy separation of alloy particles from the carbon layer and rapid capacity decay; Comparative Example 2, with its simple physical mixture of MgO, cannot form strong chemical bonds and cannot effectively improve the interface problem; Comparative Example 3, with its uniformly doped carbon matrix, cannot achieve the synergistic effect of "internal conduction and external communication," resulting in poor high-rate performance; Comparative Example 4 lacks macroporous channels, affecting electrolyte wettability and sodium ion diffusion capacity, leading to decreased structural stability; Comparative Example 5 lacks a pre-oxidation step, resulting in the inability to effectively fix the gradient doped structure and decreased performance; Comparative Example 6, with its hard carbon material, exhibits poor rate performance, making it difficult to meet the requirements of high-energy-density and high-power-density sodium batteries.

[0079] In summary, the composite anode material and its preparation method of this invention provide an effective solution for improving the performance of sodium-ion batteries. By precisely controlling various parameters in the preparation process, composite anode materials with specific properties can be prepared according to different application requirements, thereby promoting the widespread application of sodium-ion batteries in more fields. In the future, we can further optimize the preparation process and explore more material combinations and structural designs to further improve the performance of sodium-ion batteries and meet the ever-growing energy storage demands. It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A composite negative electrode material for sodium-ion batteries, characterized in that, The composite anode material includes: Tin-based multi-element alloy nanoparticles; the tin-based multi-element alloy comprises tin, a first alloying element M1, a second alloying element P, and a third alloying element M2; the first alloying element M1 is Fe or Co; the third alloying element M2 is Mg or Zn; A carbon matrix coating the surface of the tin-based multi-element alloy nanoparticles; The carbon matrix is ​​a three-dimensional porous carbon network with nitrogen and sulfur gradient doping. The inner layer near the alloy nanoparticles is nitrogen-rich and the outer layer is sulfur-rich. Mg or Zn reacts with oxygen-containing functional groups in the carbon matrix to generate MgO or ZnO, which is anchored at the interface between the alloy nanoparticles and the carbon matrix.

2. The composite negative electrode material for sodium-ion batteries according to claim 1, characterized in that, The general formula of the tin-based multi-element alloy is Sn-M1-P-M2, wherein the atomic percentage (at%) of each element satisfies: Sn 50-65%, M1 20-30%, P 5-10%, M2 5-10%.

3. The composite negative electrode material for sodium-ion batteries according to claim 1, characterized in that, The carbon matrix has a dual-modal pore size distribution, including primary mesopores with a pore size of 2-10 nm and secondary macropores with a pore size of 50-200 nm. 4.The composite anode material for sodium-ion batteries according to claim 3, characterized in that, The primary mesopores originate from the pyrolysis of the metal-organic framework sacrificial template, and the secondary macropores originate from the thermal decomposition of the soft template agent.

5. A method for preparing a composite negative electrode material, characterized by, The method for preparing the composite anode material according to any one of claims 1-4 comprises the following steps: S1: A suspension providing a sacrificial template for a metal-organic framework; S2: Mix the tin source, the first alloying element source, the phosphorus source and the third alloying element source with the metal-organic framework sacrificial template suspension to allow metal ions to be adsorbed onto the metal-organic framework sacrificial template or into its pores. S3: Add carbon source, nitrogen and sulfur doping source and soft template agent to the mixture in step S2 for adsorption treatment; S4: Spray dry the mixture obtained in step S3 to obtain precursor powder; S5: The precursor powder is subjected to pre-oxidation heat treatment in an oxygen-containing atmosphere; S6: The pre-oxidized powder is subjected to programmed temperature pyrolysis under an inert atmosphere to obtain the composite anode material.

6. The method of claim 5, wherein the method further comprises the step of mixing the carbon material and the metal oxide material. In step S3, the nitrogen-sulfur doping source is L-cysteine, and the soft template agent is block copolymer F127; and / or The molar ratio of the carbon source, nitrogen and sulfur dopant sources to the total metal ions is 2.0-3.0:0.8-1.2:

1.

7. The method of claim 5, wherein the method further comprises a step of mixing the carbon material and the metal oxide material. In step S5, the pre-oxidation heat treatment conditions are as follows: under an air atmosphere, the temperature is increased to 200-300℃ at a rate of 1-3℃ / min, and held at that temperature for 1-3 hours.

8. The method of claim 5, wherein the method further comprises the step of mixing the carbon material and the metal oxide material. Step S6, the programmed temperature rise pyrolysis process, includes: First stage: Increase the temperature to 450-550℃ at a rate of 1-3℃ / min and hold for 1-3 hours; Second stage: Increase the temperature to 600-650℃ at a rate of 3-5℃ / min and hold for 2-4 hours.

9. A sodium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode includes a current collector and an active material layer coated on the current collector. The active material layer contains a composite negative electrode material as described in any one of claims 1-4.

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