A tin-copper-carbon composite anode material for sodium-ion batteries, its preparation method and application

Abstract

This invention discloses a tin-copper-carbon composite anode material for sodium-ion batteries, its preparation method, and its application. Belonging to the field of sodium-ion battery technology, the anode material has at least one of the following characteristics: (1) the anode material is a sphere with a core-shell structure and a size of 200-800 nm; (2) the anode material contains a copper-tin alloy coating layer with a thickness of 2-20 nm; (3) the mass percentage of copper in the anode material is 0.5-50%; (4) the mass percentage of tin in the anode material is 10-95%; (5) the mass percentage of carbon in the anode material is 5-60%, forming a carbon layer with a thickness of 5-50 nm. Compared with the prior art, the anode material of this invention has low battery internal resistance and excellent cycle stability, solving the technical problems of large internal resistance variation and poor cycle stability in sodium-ion battery Sn anode materials.

Description

Technical Field

[0001] This invention relates to the field of new energy sodium-ion battery technology, specifically to a tin-copper-carbon composite anode material for sodium-ion batteries, its preparation method, and its application. Background Technology

[0002] In recent decades, the rapid depletion of fossil fuels and the continuous deterioration of the environment worldwide have spurred an urgent need to develop green and renewable energy sources. Developing high-performance energy storage devices to efficiently utilize renewable energy has become a research hotspot in recent years. The uneven distribution and insufficient reserves of lithium metal cannot meet the ever-increasing demand. Sodium, with similar chemical properties to lithium, is extremely abundant and widely distributed on Earth, and does not form alloys with aluminum. Therefore, aluminum foil can be used instead of copper foil as the current collector, which will further reduce the weight and cost of sodium-ion batteries.

[0003] The performance of sodium-ion batteries largely depends on the choice of electrode materials. Although hard carbon can store sodium, its relatively low specific capacity prevents the achievement of high energy density. Therefore, it is essential to develop high-capacity anode materials to facilitate the large-scale application of sodium-ion batteries in the future. Tin (Sn)-based materials have attracted widespread attention from researchers due to their advantages such as high capacity, abundant resources, high conductivity, and environmental friendliness. Sodium ions undergo an alloying reaction with tin to form Na+. 15 Sn4, the theoretical specific capacity of this process is as high as 847 mA hg -1 .

[0004] The inventors discovered that when sodium ions are embedded into Sn atoms, Na is eventually formed. 15 Sn4 alloy. During the sodium-ion alloying process, the Sn anode experiences a volume expansion of up to 420%. However, this dramatic 420% volume expansion during sodium-tin alloying leads to significant internal stress and a series of negative consequences, such as: active material particle fragmentation and loss of electrical contact with the current collector; the formation of a solid electrolyte interphase (SEI) on the anode surface through reaction with the electrolyte, resulting in low coulombic efficiency; and poor electrode kinetics due to tin particle aggregation. Furthermore, the Sn anode material undergoes various phase transitions during sodium-ion alloying, with a gradual decrease in electronic conductivity and a gradual increase in resistance, leading to low energy efficiency. Therefore, developing a low-internal-resistance, long-life Sn anode material for sodium-ion batteries presents a significant challenge. Summary of the Invention

[0005] To address the problems in existing technologies, such as the drastic volume changes of micron-sized tin materials during cycling leading to the fragmentation of active material particles and loss of electrical contact with the current collector, the formation of a solid electrolyte film on the negative electrode surface through reaction with the electrolyte resulting in low coulombic efficiency, and the aggregation of negative electrode particles leading to poor electrode kinetics, a tin-copper-carbon composite negative electrode material for sodium-ion batteries has been invented. Compared with existing technologies, this invention overcomes the aforementioned defects. The tin-copper-carbon composite negative electrode material alleviates the mechanical stress caused by the volume expansion and contraction of tin during charging and discharging, and has advantages such as low battery internal resistance and excellent cycle stability. It solves the technical problems of large internal resistance variation and poor cycle stability of Sn negative electrode materials in sodium-ion batteries.

[0006] A first aspect of this invention aims to provide a tin-copper-carbon composite anode material for sodium-ion batteries, the anode material having at least one of the following characteristics:

[0007] (1) The anode material has a multi-core-shell structure and spheres with a size of 200-800 nm;

[0008] (2) The negative electrode material contains a copper-tin alloy cladding layer with a thickness of 2-20 nm;

[0009] (3) The mass percentage of copper in this negative electrode material is 0.5-50%;

[0010] (4) The mass percentage of tin in this negative electrode material is 10-95%;

[0011] (5) In this negative electrode material, the mass percentage of carbon is 5-60%, and a carbon layer with a thickness of 5-50 nm is formed.

[0012] The inventors successfully prepared a multi-core-shell structured tin-copper-carbon composite anode material by constructing an intermetallic compound copper-tin alloy coating layer on the surface of Sn nanoparticles. In this tin-copper-carbon composite anode material, the intermetallic copper-tin alloy partially transforms in situ into Cu nanoparticles during sodium intercalation, effectively mitigating volume expansion, preventing structural collapse or even pulverization, enhancing ion diffusion rate and reaction kinetics, and improving the utilization rate of the tin anode. Simultaneously, the added copper nanoparticles, as an added conductive material, provide more channels for electron conduction, which is beneficial for enhancing the electron conductivity of the anode material. Furthermore, the coated carbon layer and the constructed alloy layer help the electrode maintain its original structure during cycling, while the addition of carbon and the alloy improves overall conductivity, effectively solving the problems of volume expansion before and after charge and discharge, as well as poor cycle efficiency and rate performance. In addition, the tin-copper-carbon composite anode material exhibits low battery internal resistance and excellent cycle stability, providing strong technical support for realizing high-energy-density sodium-ion batteries. Moreover, the preparation process of this invention is simple, requires low processing costs, and is suitable for industrial production.

[0013] A second aspect of this invention aims to provide a method for preparing the aforementioned tin-copper-carbon composite anode material for sodium-ion batteries, the method comprising the following steps:

[0014] (1) Preparation of hollow SnO2 nanospheres:

[0015] Hollow tin dioxide nanospheres were prepared by dissolving a tin source and a template agent in a mixed solvent and utilizing a solvothermal reaction.

[0016] (2) Preparation of SnO2@CuO:

[0017] Hollow tin dioxide nanospheres were dispersed in a copper ion solution, stirred and dissolved, then dried and calcined to obtain copper oxide-coated hollow tin dioxide nanospheres SnO2@CuO.

[0018] (3) Preparation of SnO2@CuO@PDA:

[0019] Copper oxide-coated hollow tin dioxide nanospheres were dispersed in a solution containing a carbon source, stirred and reacted, and after separation and drying, carbon-coated nanosphere precursor SnO2@CuO@PDA was obtained.

[0020] (4) Preparation of Sn / Cu6Sn5@NC:

[0021] By thermally reducing carbon-coated nanosphere precursors under a protective atmosphere, a tin-copper-carbon composite anode material Sn / Cu6Sn5@NC for sodium-ion batteries was obtained.

[0022] Further settings include:

[0023] In step (1):

[0024] The tin source includes potassium stannate, tin tetrachloride or tin dichloride, preferably potassium stannate; the mixed solvent is ethanol and water with a volume ratio of (1:10)-(5:1), preferably 3:5.

[0025] The solvothermal reaction is carried out at a temperature of 100-300℃ for 12-24 hours, and the hollow tin dioxide nanospheres are 200-800 nm in size, preferably 200-400 nm.

[0026] The specific steps for preparing hollow SnO2 nanospheres are as follows: Weigh 1-2 parts of tin source powder by mass and dissolve it in a mixed solvent. After stirring, weigh 2-6 parts of template agent and add them to the above solution, stirring continuously to accelerate its dissolution. Pour the above white solution into a high-pressure reactor for solvothermal reaction. Finally, filter, wash, and dry to obtain white powder, which is the hollow SnO2 nanosphere.

[0027] In step (2):

[0028] The concentration of the copper ion solution is 0.01-2.0 mol / L. -1 0.06 mol L is preferred. -1 The calcination process includes an aqueous solution of copper trichloride, an aqueous solution of copper acetate, or an aqueous solution of copper nitrate; the calcination temperature is 250-550℃, and the time is 0.5-3h.

[0029] Further, the specific steps for preparing SnO2@CuO are as follows: take 5-10 parts by mass of hollow SnO2 nanospheres in deionized water, disperse them by ultrasonication, add 1-2 parts of copper ion compound, stir and dissolve, dry, and calcine to obtain SnO2@CuO material.

[0030] In step (3):

[0031] The concentration of the carbon source-containing solution is 0.001-10 g / mL. -1 0.03g mL is preferred. -1 The solutions include polydopamine solution, glucose solution, resorcinol solution, polyacrylonitrile solution, sucrose solution or polypyrrole solution, preferably polydopamine solution.

[0032] Further, the specific steps for SnO2@CuO@PDA are as follows: Take 1-2 parts by weight of SnO2@CuO material and disperse it in deionized water. After ultrasonic dispersion, add tris to adjust the pH to 8.5 and 1-4 parts of carbon source, respectively, and stir for 3-48 hours. Finally, after centrifugation, washing, and drying, the SnO2@CuO@PDA material is obtained.

[0033] In step (4):

[0034] The temperature of the thermal reduction is 500-900℃, preferably 600℃; the reaction time is 1-12h, preferably 6h; the protective atmosphere is argon, nitrogen or a 5% H2 / Ar mixture, preferably high-purity argon.

[0035] A third aspect of the present invention provides a sodium-ion battery negative electrode, wherein the negative electrode is prepared using the above-mentioned sodium-ion battery tin-copper-carbon composite electrode material, or the negative electrode contains the above-mentioned tin-copper-carbon composite electrode material.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] (1) This invention innovatively designs an intermetallic compound copper-tin alloy protective layer coated on tin nanospheres. The copper-tin alloy layer effectively protects the inner metallic tin from being corroded by the electrolyte, thereby reducing the formation of more solid electrolyte interfaces and reducing electrolyte consumption. At the same time, the protective layer can prevent the aggregation of tin particles, enhance ion diffusion kinetics, improve ionic conductivity and electronic conductivity, and obtain more stable cycling performance;

[0038] (2) In the tin-copper-carbon composite anode material, the intermetallic compound copper-tin alloy is partially converted into Cu nanoparticles in situ during sodium intercalation, which helps to alleviate volume expansion, avoid structural collapse or even pulverization, and enhance ion diffusion rate and reaction kinetics, thereby improving the utilization rate of the tin anode. At the same time, the nano-copper particles, as an added conductive material, can provide more channels for electron conduction, which is beneficial to enhancing the electron conduction rate of the anode material. In addition, the coated carbon layer and the constructed alloy layer help the electrode maintain its original structure during cycling, while the addition of carbon and alloy improves the overall conductivity, effectively solving the problems of volume expansion before and after charging and discharging, poor cycle efficiency and rate performance.

[0039] (3) The tin-copper-carbon composite anode material prepared in this invention is used in 0.1A g... -1 After 250 cycles at the current density, the discharge capacity of the negative electrode material is 581.0 mAh·g. -1 It exhibits excellent cycling stability with a decay of 0.084% per cycle and a CE of 100%.

[0040] (4) The reversible specific capacities of the prepared tin-copper-carbon composite anode material at current densities of 0.2, 1, 2, 4, and 10 C were 535.9, 507.3, 509.8, 503.5, and 486.6 mAh g, respectively. -1 When the current density returns to 0.2C, the specific capacity is 522.8 mAh g. -1 Compared to the specific capacity at 0.2C, the material retains 90.8% of its capacity at 10C. (In 1A g) -1 After 1000 cycles, the specific capacity of the tin-copper-carbon composite anode is 440.1 mAh g. -1 It exhibits excellent cycling stability with a decay of only 0.024% per cycle.

[0041] (5) The process of this invention is simple, has good repeatability, low production cost, low energy consumption, and is very suitable for industrial production. It also has significant application value in sodium-ion battery applications. Attached Figure Description

[0042] Figure 1The images shown are (a) scanning electron microscope (SEM) images, (b)-(c) low-resolution transmission electron microscope (TEM) images, (d) high-resolution transmission electron microscope (TEM) images, and (ef) selected area electron diffraction (SEED) patterns of the material in Example 1.

[0043] Figure 2 The images show transmission electron microscopy (TEM) images of the material from Example 1, as well as elemental mapping diagrams for Cu, Sn, C, and N.

[0044] Figure 3 (a) X-ray diffraction pattern, (b) Raman scattering pattern, (c) thermogravimetric curve, and (d)-(h) X-ray photoelectron spectra of the materials of Example 1 and / or Comparative Example 1.

[0045] Figure 4 The material (a) of Example 1 and / or Comparative Example 1 was used at 0.1 A g. -1 (b) Electrochemical impedance spectroscopy at current density; (c) Rate performance plot; (d) At 1 A g -1 Long-cycle plot at current density.

[0046] Figure 5 The following are examples of the material from Example 1: (a) cycling curves at different scan rates, (b) log(i)-log(v) curves at different redox peaks, and (c) curves at 1.0 mV / s. -1 (d) Pseudocapacitive contribution at different scan rates. Detailed Implementation

[0047] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0048] In the following examples: Field emission electron microscopy (SEM) was performed using a NOVANanoSEM230, and transmission electron microscopy (TEM) was performed using a JEM-2100 transmission electron microscope (JEOL). X-ray diffraction (XRD) characterization was performed using an XRD-6000 instrument manufactured by Shimadzu Corporation, Japan, under CuKα, 40kV, and 30mA conditions. Raman spectroscopy was performed using a SuperLabRam-II Raman spectrometer. Thermogravimetric analysis (TGA) was performed using an SDT-Q600 thermogravimetric analyzer to quantitatively analyze the carbon content of the samples. X-ray photoelectron spectroscopy was performed using a VersaProbePHI-5000 multi-functional electron spectrometer to analyze the elemental composition of the sample surface. Cyclic voltammetry curves of the electrodes were measured at room temperature using a CHI660C electrochemical workstation (Shanghai Chenhua).

[0049] The battery was assembled and tested using the method described below.

[0050] Battery Assembly: The electrochemical sodium storage performance of the materials was tested using a CR2016 coin cell. 80% electrode active material, 10% acetylene black, and 10% carboxymethyl cellulose (CMC) binder (0.05 g / mL) were weighed according to the following mass ratio. -1 Aqueous solution was mixed and stirred in a small beaker for 8 hours to obtain a uniformly mixed electrode slurry. The slurry was evenly coated onto copper foil and dried in a vacuum oven at 60-80℃. The dried electrode sheets were pressed and punched to form round sheets with a diameter of 12mm. The electrode sheets were vacuum dried at 80℃ for 12 hours and then weighed using a precision balance. Blank copper foil sheets from the same location were pressed and weighed, and 70% of the difference was taken as the mass of active material on each electrode sheet. The dried and weighed electrode sheets were immediately transferred to a glove box filled with an argon protective atmosphere (Super1220 / 750, Microna (China) Co., Ltd., oxygen <5ppm, water <1ppm) for battery assembly. A sodium metal sheet was used as the counter electrode, 1mol / L NaPF6 dimethyl ethylene glycol (DME) was used as the electrolyte, Whatman GF / A was used as the separator, and stainless steel was used as the filler to form a CR2016 coin cell.

[0051] Charge and discharge test: The charge and discharge test was performed on the LAND battery test system (CT2001A), set to constant current charge and discharge mode, with the current density set to the set value and the charge and discharge voltage range set to 0.01-1.0V.

[0052] Example 1: Preparation of Tin-Copper-Carbon Composite Anode Material Sn / Cu6Sn5@NC Material

[0053] A method for preparing a tin-copper-carbon composite negative electrode material for sodium-ion batteries, the method comprising the following steps:

[0054] (1) Preparation of hollow SnO2 nanospheres:

[0055] 1.91 g of K₂SnO₃·3H₂O powder was weighed and dissolved in a mixed solution of 150 mL anhydrous ethanol and 250 mL deionized water. The solution was stirred manually for 3 min to ensure complete dissolution. Then, 2.40 g of urea was weighed and added to the solution, and the mixture was stirred continuously to accelerate dissolution. The resulting white solution was poured into a 500 mL high-pressure reactor lined with polytetrafluoroethylene (PTFE) and subjected to a solvothermal reaction at 200 °C for 24 h. Finally, the solution was filtered, washed, and dried to obtain a white powder, which is the hollow SnO₂ nanosphere.

[0056] (2) Preparation of SnO2@CuO:

[0057] 0.4 g of hollow SnO2 nanospheres and 0.06 g of Cu(CH3COO)2·H2O were dissolved in 5 mL of deionized water and ultrasonically dispersed for 30 min. Then, the mixture was placed in a vacuum drying oven and dried at 100 °C for 10 h. The dried sample was then placed in a muffle furnace and calcined at 350 °C for 1 h to obtain SnO2@CuO material.

[0058] (3) Preparation of SnO2@CuO@PDA:

[0059] 0.212 g of SnO2@CuO material was dispersed in 120 mL of deionized water and ultrasonically dispersed for 30 min. Tris was added to adjust the pH to 8.5, and 0.4 g of dopamine hydrochloride was added. The mixture was stirred and reacted at room temperature (25℃) for 24 h. Finally, the sample was centrifuged, washed, and dried to obtain SnO2@CuO@PDA material.

[0060] (4) Preparation of Sn / Cu6Sn5@NC:

[0061] Take 0.2g of SnO2@CuO@PDA material and disperse it evenly in a ceramic boat. Then, place the ceramic boat in a tube furnace and introduce a hydrogen-argon mixture (H2 / Ar: 5% / 95%), and heat at 2℃ for 1 minute. -1 The heating rate was adjusted to 700℃, calcined for 6 hours, and then naturally cooled to room temperature to obtain Sn / Cu6Sn5@NC material.

[0062] Comparative Example 1: Preparation of the anode material Sn@NC

[0063] The preparation method is the same as in Example 1, except that Cu(CH3COO)2·H2O is not added in step 2. The other methods are the same, and the prepared negative electrode material is labeled Sn@NC.

[0064] Product confirmation:

[0065] Figure 1 The following images show the tin-copper-carbon composite anode material Sn / Cu6Sn5@NC: (a) is a scanning electron microscope (SEM) image of the tin-copper-carbon composite anode material; (b)-(c) are low-resolution transmission electron microscope (TEM) images; (d) is a high-resolution TEM image; and (e)-(f) are selected area electron diffraction (SED) patterns. From the SEM image (1a) and the low-resolution TEM images (1b, c), it can be seen that the material has a diameter of approximately 400 nm, is uniform in size, and consists of nanospheres with a very distinct multi-yolk-shell structure. Figure 1 c clearly shows that the nanoparticles in the multi-yolk-shell structure are approximately 100-200 nm in size, and the outer amorphous carbon layer is approximately 20 nm thick. This is evident from the high-resolution TEM image ( Figure 1In d), it can be clearly observed that the two lattice fringes correspond to the interplanar spacings of Sn and η-Cu6Sn5, respectively, with the interplanar spacing of the (321) plane being approximately 0.347 nm and the interplanar spacing of the (311) plane being approximately 0.168 nm. Furthermore, from... Figure 1 The selected area electron diffraction pattern of metallic Sn in e shows characteristic single-crystal diffraction signals from the Sn(200), (101), and (112) planes, indicating that metallic Sn in the material exhibits a single-crystal structure. Figure 1 The selected area electron diffraction pattern in f shows Sn(200),(101),(211),(220) and η-Cu6Sn5(311),(132),(510) planar diffraction rings, which means that the material exhibits a polycrystalline structure.

[0066] Figure 2 This image shows a transmission electron microscope (TEM) image of the tin-copper-carbon composite anode material Sn / Cu6Sn5@NC, along with elemental mapping diagrams for Cu, Sn, N, and C. To further understand the distribution of various elements, elemental mapping analysis was performed on the Sn / Cu6Sn5@NC material. Figure 2 As can be seen, Cu and Sn form the internal core, with magenta Sn and blue Cu composing the beautiful nanospheres. The red C and green N elements on the outside perfectly outline the carbon layer, indicating uniform carbon coating. All of this fully demonstrates that Cu, Sn, N, and C elements are uniformly distributed in the Sn / Cu6Sn5@NC material, successfully constructing a Sn / η-Cu6Sn5 heterointerface.

[0067] Figure 3 The following are the X-ray diffraction patterns, (b) Raman scattering patterns, (c) thermogravimetric maps, and (d)-(h) X-ray photoelectron spectroscopy (XRD) patterns of the tin-copper-carbon composite anode materials Sn / Cu6Sn5@NC and Sn@NC: (a) X-ray diffraction pattern, (b) Raman scattering pattern, (c) thermogravimetric map, and (d)-(h) X-ray photoelectron spectroscopy (XRD). To further determine the structural phases of Sn@NC and Sn / Cu6Sn5@NC materials, X-ray diffraction (XRD) was performed on both materials, as shown below. Figure 3a. As can be seen from the figure, the Sn@NC material exhibits four distinct and sharp diffraction peaks at 2θ = 30.6°, 32.4°, 43.8°, and 44.9°, corresponding to the Sn(200), Sn(101), Sn(220), and Sn(211) crystal planes, respectively, consistent with the standard Sn card (PDF 86-2264). This indicates that the Sn@NC material possesses excellent crystallinity. Furthermore, no diffraction peaks of the precursor SnO2 were found in the XRD pattern, indicating that SnO2 was completely reduced to elemental Sn. The Sn / Cu6Sn5@NC material exhibits distinct diffraction peaks at 2θ = 30.1°, 42.9°, and 43.2°, corresponding to the (311), (132), and (510) crystal planes of η-Cu6Sn5, respectively, which are consistent with the standard card (PDF 97-015-0124) for η-Cu6Sn5. However, carbon diffraction peaks were not detected. This is because the good crystallinity of Sn and η-Cu6Sn5 makes the diffraction peaks too strong, resulting in less noticeable carbon diffraction peaks. Raman spectroscopy was used to further confirm the presence of carbon in the Sn@NC and Sn / Cu6Sn5@NC materials. Figure 3 As shown in b, two distinct vibrational peaks are located at 1327.4 cm⁻¹ and 1583.1 cm⁻¹. -1 The corresponding D and G peaks in the Sn@NC and Sn / Cu6Sn5@NC materials indicate the presence of carbon. Furthermore, calculations revealed that the intensity ratio of the D peak to the G peak in the Sn@NC and Sn / Cu6Sn5@NC samples (I0.05) was significantly higher. D / I G The values ​​are 1.21 and 1.18 respectively, indicating that the I of Sn / Cu6Sn5@NC is... D / I G The decrease in value may be due to the high-temperature catalytic effect of copper, which may have increased the degree of graphitization. Figure 3 c is the thermogravimetric analysis (TGA) plot of the Sn / Cu6Sn5@NC material. The sample was placed in air, and the programmed temperature was gradually increased from 50℃ to 800℃. Based on the mass change of the sample before and after testing, the mass fraction of carbon in the material can be determined. As can be seen from the plot, when the temperature reaches approximately 370℃, the sample begins to experience rapid weight loss, which stops at 470℃. This is mainly because carbon is consumed in the air, leading to a rapid decrease in mass. From 470℃ to 800℃, the sample begins to slowly increase in weight, primarily due to the oxidation of the internal metallic Sn and η-Cu6Sn5 to SnO2 and CuO. After calculating the mass loss, the carbon content in the Sn / Cu6Sn5@NC material is approximately 16.1%. From the XPS full spectrum (… Figure 3d) The figure clearly shows the signal peaks of the four elements Sn, Cu, C and N in the Sn / Cu6Sn5@NC material. Among them, C1s shows the highest peak intensity, indicating that the outer layer is mainly carbon, which further proves the uniformity of carbon coating. Figure 3 e is the fine energy spectrum of Sn 3d element. As shown in the figure, there are two distinct signal peaks in Sn 3d. 5 / 2 and Sn3d 3 / 2 Their binding energies are 487.1 and 495.5 eV, respectively, and the surface Sn exhibits a tetravalent morphology, possibly due to partial oxidation of the surface Sn by air. Furthermore, through peak fitting, we found that the binding energies of 493.5 and 485.1 eV correspond to the zero-valent Sn, and the detected Sn is likely metallic Sn in the Sn / Cu6Sn5 heterointerface. Figure 3 f is the fine energy spectrum of Cu 2p. According to the fitting results, two obvious signal peaks can be observed in the fine energy spectrum of Cu 2p at binding energies of 933.4 eV and 934.5 eV. The binding energy at 933.4 eV corresponds to the Cu exhibiting on the surface. + The morphology is likely due to partial oxidation of the surface Cu by air. The binding energy at 934.5 eV is attributed to Cu. 0 . Figure 3 g represents the C1s spectrum of the Sn / Cu6Sn5@NC material, which shows peaks at 284.8, 284.7, 285.7, 287, and 289.2 eV, corresponding to sp... 2 C, sp 3 C, N-sp 2 C, N-sp 3 C and C=O bonds. It is worth noting that N-sp... 2 C and N-sp 3 C corresponds to the formation of C=N and CN, respectively. N doping provides additional electrons to the large π bonds in the carbon shell, which helps to improve the electronic conductivity of Sn / Cu6Sn5@NC. Figure 3 h is the N element N1s fine energy spectrum of the C1s spectrum of Sn@η-Cu6Sn5@NC material. The three peaks at 398.3, 400.1, and 402.8 eV represent pyridine nitrogen, graphitic nitrogen, and pyrrole nitrogen, respectively, with peak area ratios of 22.1%, 44.3%, and 33.6%. Pyridine nitrogen (replacing carbon atoms with nitrogen atoms at the edges of the graphite plane) introduces numerous defects, producing Na + The active sites are beneficial for improving reversible capacity.

[0068] Figure 4 The Sn / Cu6Sn5@NC is a tin-copper-carbon composite anode material: (a) in 0.1A g -1(a) Long-cycle plot at current density, (b) Electrochemical impedance spectroscopy, (c) Rate performance plot, (d) At 1 A g -1 Long-cycle plot at current density of 0.1 A·g. -1 After 250 cycles under current, the discharge capacity of Sn / Cu6Sn5@NC is 581.0 mAh·g. -1 The degradation rate was 0.084% per cycle, with a CE of 100%, demonstrating good cycling stability. The change in internal resistance during cycling was investigated using EIS. As can be seen from the figure, the series resistance (R) of the electrode in the high-frequency region... s The relatively small value indicates good electrical contact throughout the battery system. The charge transfer resistance (R) in the mid-frequency region... ct The internal resistance decreased from 9.42 Ω before cycling to 2.32, 2.56, and 2.67 Ω after 20, 50, and 100 cycles, respectively, indicating minimal change and high stability of the electrochemical process. EIS results showed that the multi-yolk-shell structure shortened the Na... + The transmission distance is increased, and the impedance is reduced. The Sn / η-Cu6Sn5 metal heterojunction interface in the Sn / Cu6Sn5@NC material greatly promotes charge transfer during cycling, thereby improving conductivity. Figure 4 c represents a comparison of the rate performance of Sn / Cu6Sn5@NC and Sn@NC anodes. At current densities of 0.2, 1, 2, 4, and 10C, the reversible specific capacities of the Sn / Cu6Sn5@NC anode are 535.9, 507.3, 509.8, 503.5, and 486.6 mAh g, respectively. -1 The capacity retention rate at 10C was 90.8%. When the current density recovered to 0.2C, the specific capacity remained at 522.8 mAh g⁻¹. -1 This indicates superior rate performance compared to the Sn@NC anode. The multi-yolk-shell structure of the Sn / Cu6Sn5@NC material facilitates the formation of three-dimensional transport channels, allowing the electrolyte and Na+ to pass through. + Rapid transport is achieved, while the large surface area improves electrode dynamics. Furthermore, the addition of copper and a nitrogen-containing carbon shell enhances the electronic conductivity of the tin surface, providing a surface electronic pathway from the current collector to each tin nanosphere. Finally, Figure 4 d shows the Sn / Cu6Sn5@NC and Sn@NC anodes at a current density of 1A g. -1 The long-term cycling stability performance at 0.1A g was evaluated. -1 The electrode was activated by multiple cycles. The initial discharge specific capacity of the Sn / Cu6Sn5@NC electrode was 579.0 mAh g. -1The initial coulombic efficiency (ICE) was as high as 84.9%, and the coulombic efficiency of the composite material remained above 98% after 5 cycles. The specific capacity after 1000 cycles was 440.1 mAh g. -1 The capacity decay rate per revolution is only 0.024%.

[0069] Figure 5 The following are the CV curves of the tin-copper-carbon composite anode material Sn / Cu6Sn5@NC at different scan rates: (a) CV curves at different scan rates, (b) log(i)-log(v) curves at different redox peaks, and (c) CV curves at 0.6 mV / s. -1 The pseudocapacitive contribution is shown in Figure 1, and (d) shows the proportion of pseudocapacitive contribution at different scan rates. To explain the excellent rate performance and cycling stability of the Sn / Cu6Sn5@NC electrode material, its electrochemical reaction kinetics were systematically studied. First, the pseudocapacitive contribution of the Sn / Cu6Sn5@NC electrode material during cycling was tested. Figure 5 a represents Sn / Cu6Sn5@NC at an increasing scan rate (0.1–0.8 mV / s). -1 The CV curves were obtained at various scanning rates. The shape of the CV curves remained largely unchanged with increasing scan rate, reflecting good electrochemical reversibility; however, a slight shift in the redox peaks indicated slight polarization of the electrode material. Furthermore, the area enclosed by the CV curves gradually increased with increasing scan rate, reflecting a significant pseudocapacitive effect at high scan rates. Calculations showed that the values ​​of b corresponding to the three peaks were 0.66, 0.82, and 0.89, all within the range of 0.5 to 1 and close to 1, indicating that the pseudocapacitive effect dominates the sodium storage process of the Sn / Cu6Sn5@NC electrode material. Figure 5 The red shaded area in diagram c represents the fitted CV curve indicating the pseudocapacitive effect. Integrating the shaded area and the original CV curve, the final value of 0.6 mV / s is calculated based on the area ratio. -1 The capacitance contribution of the pseudocapacitive effect at that scan rate was approximately 84.9%. Then, the capacitance contribution of the pseudocapacitive effect at other scan rates was calculated using the same method (e.g., ...). Figure 5 d). At 0.1, 0.2, 0.4, 0.6 and 0.8 mV s -1 At the specified scan rates, the capacitance contribution ratios of the pseudocapacitive effect were 68.6%, 72.5%, 77.3%, 84.9%, and 90.1%, respectively. The calculation results clearly and strongly demonstrate that the Sn / Cu6Sn5@NC electrode material exhibits a significant pseudocapacitive effect during sodium storage, which effectively improves the material's rate performance.

[0070] Alternative Example:

[0071] By adjusting the process conditions of the embodiments, as shown in Examples 2 to 15, the purpose was to test the influence of different process conditions on the particle size of the tin-copper-carbon composite anode material. The statistics are shown in Table 1.

[0072] Example 2

[0073] The method of Example 1 differs in that, in step (1), tin salt is tin tetrachloride.

[0074] Example 3

[0075] The method of Example 1 differs in that, in step (1), the tin salt used is tin dichloride.

[0076] Example 4

[0077] The method of Example 1 differs in that the volume ratio of ethanol to water in step (1) is 1:1.

[0078] Example 5

[0079] The method of Example 1 differs in that the volume ratio of ethanol to water in step (1) is 1:2.

[0080] Example 6

[0081] The method of Example 1 differs in that: in step (1), the solvent heat treatment temperature is 150°C and the time is 12h.

[0082] Example 7

[0083] The method is the same as in Example 1, except that in step (2), the copper solution is an aqueous solution of copper nitrate with a concentration of 0.06 mol / L. -1 .

[0084] Example 8

[0085] The method is the same as in Example 1, except that in step (2), the copper solution is an aqueous solution of copper dichloride with a concentration of 0.06 mol / L. -1 .

[0086] Example 9

[0087] The method is the same as in Example 1, except that in step (3), the carbon source is a polypyrrole solution with a concentration of 0.03 g / mL. -1 The reaction temperature was 35℃, and the reaction was stirred for 12 hours.

[0088] Example 10

[0089] The method is the same as in Example 1, except that in step (3), the carbon source is a glucose solution with a concentration of 0.03 g / mL.-1 The reaction temperature was 35℃, and the reaction was stirred for 12 hours.

[0090] Example 11

[0091] The method of Example 1 differs in that the inert atmosphere for thermal reduction in step (4) is high-purity argon.

[0092] Example 12

[0093] The method of Example 1 differs in that the inert atmosphere for thermal reduction in step (4) is high-purity nitrogen.

[0094] Example 13

[0095] The method of Example 1 differs in that: in step (4), the heat reduction treatment temperature is 600°C and the time is 3h.

[0096] Example 14

[0097] The method of Example 1 differs in that: in step (4), the heat reduction treatment temperature is 800°C and the time is 3 hours.

[0098] Example 15

[0099] The method of Example 1 differs in that: in step (4), the heat reduction treatment temperature is 900°C and the time is 3 hours.

[0100] Table 1. Effects of different process conditions on product particle size

[0101]

[0102]

[0103] As shown in Table 1, different process conditions have a significant impact on the particle size of the product. Specifically:

[0104] (1) The absence of a copper source or the replacement of the copper source will result in an increase in the particle size of the material.

[0105] (2) Changing the ratio of ethanol to water affects the crystallinity of the material and causes uneven particle size. The optimal ethanol:water volume ratio is 1:1.5 to 1.8.

[0106] (3) When the carbon source is changed, different carbon layers result in differences in uniformity and particle size. The better carbon source is polypyrrole.

[0107] (4) Changing the thermal reduction temperature and changing the protective atmosphere will also have a significant impact on the crystallization and particle size of the material. The optimal thermal reduction temperature is 600 degrees and the thermal reduction atmosphere is high-purity argon.

[0108] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a tin-copper-carbon composite negative electrode material for sodium-ion batteries, characterized in that, Includes the following steps: (1) Preparation of hollow SnO2 nanospheres: Hollow tin dioxide nanospheres were prepared by dissolving tin source and urea in a mixed solvent and using a solvothermal reaction. The mixed solvent was ethanol and water in a volume ratio of 3:

5. (2) Preparation of SnO2@CuO: Hollow tin dioxide nanospheres were dispersed in a copper ion solution, stirred and dissolved, then dried and calcined to obtain copper oxide-coated hollow tin dioxide nanospheres SnO2@CuO. (3) Preparation of SnO2@CuO@PDA: Copper oxide-coated hollow tin dioxide nanospheres were dispersed in a solution containing a carbon source, stirred and reacted, and after separation and drying, carbon-coated nanosphere precursor SnO2@CuO@PDA was obtained. The carbon source is selected from a polydopamine solution, a glucose solution, a resorcinol solution, a polyacrylonitrile solution, a sucrose solution, or a polypyrrole solution, and the concentration of the solution containing the carbon source is 0.001-10 g / mL -1 ; (4) Preparation of Sn / Cu6Sn5@NC: A carbon-coated nanosphere precursor was thermally reduced under a protective atmosphere to obtain a sodium-ion battery tin-copper-carbon composite anode material Sn / Cu6Sn5@NC. The thermal reduction temperature was 500-900℃, the reaction time was 1-12h, and the protective atmosphere was argon, nitrogen, or a 5% H2 / Ar mixture. The negative electrode material has at least one of the following characteristics: (1) The anode material has a multi-core-shell structure and spheres with a size of 200-800 nm; (2) The negative electrode material contains a copper-tin alloy cladding layer with a thickness of 2-20 nm; (3) The mass percentage of copper in this negative electrode material is 0.5-50%; (4) The mass percentage of tin in this negative electrode material is 10-95%; (5) In this negative electrode material, the mass percentage of carbon is 5-60%, and a carbon layer with a thickness of 5-50 nm is formed.

2. The method for preparing a tin-copper-carbon composite negative electrode material for sodium-ion batteries according to claim 1, characterized in that, In step (1): the specific steps for preparing hollow SnO2 nanospheres are as follows: weigh 1-2 parts of tin source powder according to the mass ratio and dissolve it in a mixed solvent. After stirring, weigh 2-6 parts of template agent and add them to the above solution, and stir continuously to accelerate its dissolution. Pour the resulting white solution into a high-pressure reactor for solvothermal reaction. Finally, filter, wash and dry to obtain white powder, which is the hollow SnO2 nanosphere. The tin source is potassium stannate, tin tetrachloride, or tin dichloride, and the mixed solvent has a volume ratio of 1:10 to 5:

1. The solvothermal reaction is carried out at a temperature of 100-300℃ for 12-24 hours, and the size of the prepared hollow tin dioxide nanospheres is 200-800 nm.

3. The method for preparing a tin-copper-carbon composite negative electrode material for a sodium-ion battery according to claim 2, characterized in that, In step (1): the temperature of the solvothermal reaction is 200℃ and the time is 24h, and the size of the hollow tin dioxide nanospheres prepared is 200-400nm.

4. The method for preparing a tin-copper-carbon composite negative electrode material for sodium-ion batteries according to claim 1, characterized in that, In step (2): the specific steps for preparing SnO2@CuO are as follows: take 5-10 parts of hollow SnO2 nanospheres in deionized water by mass, disperse them by ultrasonication, add 1-2 parts of copper ion compound, stir and dissolve, dry, and calcine to obtain SnO2@CuO material; The copper ion solution is selected from the group consisting of an aqueous solution of copper trichloride, an aqueous solution of copper acetate or an aqueous solution of copper nitrate; the concentration of the copper ion solution is 0.01-2.0 mol / L -1 The calcination temperature is 250-550℃ and the time is 0.5-3h.

5. The method for preparing a tin-copper-carbon composite negative electrode material for a sodium-ion battery according to claim 4, characterized in that, In step (2): the copper ion solution is an aqueous solution of copper acetate, and the concentration of the copper ion solution is 0.06 mol / L. -1 The calcination temperature is 350℃ and the time is 1 hour.

6. The method for preparing a tin-copper-carbon composite negative electrode material for a sodium-ion battery according to claim 1, characterized in that, In step (3): the specific steps of SnO2@CuO@PDA are as follows: take 1-2 parts of SnO2@CuO material by mass and disperse it in deionized water. After ultrasonic dispersion, add tris to adjust the pH to 8.5 and 1-4 parts of carbon source respectively. Stir for 3-48 hours. Finally, after centrifugation, washing and drying, SnO2@CuO@PDA material is obtained.

7. The method for preparing a tin-copper-carbon composite negative electrode material for a sodium-ion battery according to claim 1, characterized in that, In step (4): the temperature of the thermal reduction is 600℃; the reaction time is 6h; and the protective atmosphere is high-purity argon.

8. The application of the sodium-ion battery tin-copper-carbon composite anode material prepared by the method of claim 1 in the preparation of sodium-ion battery anodes.

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